The Whitford Engineering Design Guide
The Whitford Engineering Design Guide
High-performance fluoropolymer coatings:What they are,
how they function andhow to use them
to your best advantage
Makers of the world’s largest, most complete line of fluoropolymer coatings
Every day, one way or another, we at Whitford learn a little bit more about thesurprisingly complicated business of designing and making fluoropolymer coat-ings perform to their maximum ability.
Typically, much of what we have learned comes from our mistakes.
It occurred to us that the information we have accumulated (and indeedcontinue to accumulate as we learn) might prove as helpful to our customers asit has to us. It is for that reason that we have assembled some of our basicknowledge into this brochure.
We hope it will have been worth the effort.
The information included has many sources. Perhaps the most fruitful hasbeen the practical experience that comes from Whitford’s more than threedecades of working with and learning about these remarkable materials.
Some of the statements presented are the result of long and painstaking lab-oratory tests and analyses, even if presented with the dogmatism of brevity.
Others are based on experimental work with specific products. Still othersare the opinions of people who have broad and deep experience in the field offluoropolymer coatings and are offered as the best recommendations under thecircumstances.
We invite you to read this document with some care.
We ask you to test your imagination as to how a coating might minimize —or even eliminate — a design problem you’re facing.
Think of problems caused by friction, poor release, corrosion, wear, noise.Think of other design and engineering problems for which a fluoropolymer coat-ing may never have been tested.
You may join the growing list of designers and engineers who have openedtheir minds to the surprising versatility of high-performance coatings — andsolved some difficult problems in the process.
If so, the purpose of this brochure will have been realized.
The purpose of this publication
Activ8, Passiv8, Dykor, Eclipse, EterniTex, Excalibur, QuanTanium, Quantum, Quantum2, RainCheck, Ravlex, SoilCheck, StainCheck, Suave, Superglide, Texcel, Ultralon, Whitford, Xylan,
Xylac, and Xylar are registered trademarks of the Whitford group of companies.
What you’ll find
Chapter 1: The surprising success of high-performance coatings . . . . . . . . . . . . . 2
A. New options for designers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
B. Components of Xylan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Chapter 2: High-performance coatings at work . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
A. Friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
B. Wear. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
C. Nonstick (release) properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
D. Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
E. Noise reduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
F Temperature extremes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
G. Sealing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
H. Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Chapter 3: Solving problems with Xylan coatings . . . . . . . . . . . . . . . . . . . . . . . . . 14
Chapter 4: Whitford primers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Chapter 5: Applying Xylan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
A. Substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
B. Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
C. Application techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
D. Flashing and curing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
E. Surface considerations for maximum wear resistance . . . . . . . . . . . . . . . . . . . . . 22
F. Special cure and postcure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
G. Additional considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Chapter 6: Whitford flexible finishes and the automotive industry . . . . . . . . . . . . 25
Chapter 7: Whitford coatings and the textile industry . . . . . . . . . . . . . . . . . . . . . . 27
Chapter 8: Calculating the real cost of a coating . . . . . . . . . . . . . . . . . . . . . . . . . 29
Chapter 9: Protecting the environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Chapter 10: Whitford’s wide range of other products . . . . . . . . . . . . . . . . . . . . . . 32
Chapter 11: Polymeric Systems, Inc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Chapter 12: A word from our sponsor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Index and glossary (and more information). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1
A. New options for designers
High-performance fluoropolymer coatingsare remarkable low-friction, dry-lubricant materi-als that combine the capabilities of two types of“engineering plastics”. Fluoropolymers, with thelowest coefficient of friction of any known solid,are combined with high-temperature organicpolymers to provide a unique and highly versa-tile combination of properties.
These tough lubricating coatings can oper-ate successfully at temperature extremes which,at the low end, would render ordinary fluid lubri-cants too high in viscosity and, at the high end,would char them to ash.
Originally, low-friction solids were used forapplications where sliding parts were heavilyloaded, infrequently lubricated or operated athigh temperatures. This has been true since theinception of dry lubricants, when ancient me-chanics used graphite, talc, mica and other“slick” powders to reduce sliding friction.
But, with the development of modern lubri-cating coatings, other properties have beendesigned in — including outstanding corrosionresistance. Today, when mechanical parts oper-ate under any of the above conditions, dry filmlubricants are often the only sensible, safe andeconomical way to lubricate and protect them.
In the past, the only materials recognized asdry lubricants for such applications were gra-phite and molybdenum disulfide (MoS2 or Moly)or blends of both. While useful, these materialssolved only a limited range of problems. Molycoatings were typically used in high-pressureapplications; graphite coatings were generallyused in wet service or at elevated temperatures.
Enter the matrix
Today’s fluoropolymer coatings are the resultof design engineering done several decades ago.
The first fluoropolymer coatings were rela-tively soft films, the kind found on frying pansand a few nonstick applications in industry.
Then, in 1969, a team of polymer chemistsand engineers devised the matrix concept for
coatings, “building” a coating to protect the softfluoropolymer from wear while taking advantageof its low-friction property. On this concept,Whitford was founded and Xylan fluoropolymercoatings became a reality.
The first significant order for Xylan was for abrake adjustment mechanism for GM cars. Thiswas followed by other applications: saw blades,viscous fan drives, journal bearings, switchdetents, carburetor shafts, steam valve plugs, oilrig fasteners. The list grew quickly.
Note: The full range of Xylan coatings hasbecome so extensive that properties vary widely.The coatings referred to in this brochure areprincipally those designed for industrial applica-tions, and the bulk of the data refers to them.
Over the years, these self-lubricating materi-als have been used to solve a growing range ofengineering and design problems.
Today, Xylan is the largest, most completeline of fluoropolymer coatings in the world. Asthe materials have been tried on an ever-widen-ing spectrum of applications, we have learned afew things. For instance:
• A bonded, self-lubricating coating can lastlonger than hard chrome plating in certain high-wear applications.
• Xylan can cut the cost of some pistons,plungers and splines by eliminating polishingand lapping processes.
• Xylan can replace heavy metal platings onengine journal bearings.
• Xylan can replace plating on hydraulicpistons and extend their lives in corrosive envi-ronments.
B. Components of Xylan The Xylan coating matrix is composed of
three basic ingredients:
• A polymer binder for film strength, adhesionand protection of the softer lubricating particles.
• A solid lubricant for low friction, releaseand resistance to wear.
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1. The surprising success of high-performance coatings
• Pigments, fillers and reinforcements forcolor and additional properties such as hardness.
With the exception of Whitford’s Dykor pow-ders, all materials are suspended in solvent orwater, providing a compatible carrier so that,together, they may be applied by conventionaltechniques such as spraying, dip/spinning, rollercoating, tumble coating, coil coating, curtaincoating, etc.
The result is thin, continuous, protective filmbarriers which resist chipping, spalling, abra-sion, cold flow, temperature extremes, weather-ing and a wide range of corrosive environments.
The basic elements
1. Binders: Polymer binders hold the lubricat-ing particles and hard fillers in place and enablethem to adhere to a wide variety of substrates.The coatings derive most of their corrosion andthermal characteristics from these materials.
The first binder employed in Xylan was athermosetting alloy, which offers exceptionaltoughness and is stable to 315°C/600°F. After
more than three decades, this binder is stillwidely used for industrial applications in whichits superior properties and flexible cure sched-ule make it very adaptable. This class of binderis found in the 1000, 1600, 1700 and 8110Series of Xylan coatings. (Ask for Whitford’s“Introduction to the Xylan 1000 Series”.)
Another rugged polymer employed as abinder in Xylan is a high-temperature-stablethermoplastic. It is extremely resistant to abra-sion and chemicals, and is a good choice forcomponents that operate in the presence ofstrong acids, bases or solvents. It is the binderused in the Xylan 1300 and 8300 Series coatings.
A third class of binder is a lower-temperaturethermoset. Although not as tough as some poly-mers, it provides good corrosion protection, anexceptional array of colors, plus economy. It isa part of the Xylan 1400, 5200 and 5400 Seriescoatings (used on fasteners and other industrialhardware for corrosion protection).
2. Lubricants: Small particles of low-frictionmaterials such as polytetrafluoroethylene (PTFE),molybdenum disulfide (Moly) and graphite, sus-pended in the wear-resistant binder, reduce fric-tion at the surface. PTFE tends to be softer thanthe matrix, so when coated parts rub together,the lubricant smears along the surface of thecoating and the mating surface, reducing friction.
PTFE is most commonly used in Xylan be-cause it has the lowest coefficient of friction, isstable and effective at high and low tempera-tures, and is inert to chemical attack. Also,because of its low surface tension, it is an ex-cellent release agent.
Other fluoropolymer lubricants include FEPand PFA, which are less porous because of bet-ter melt/flow characteristics, resulting in densercoatings that provide improved release. Bothhave excellent nonstick and good low-frictionproperties, and are stable in the presence of awide range of solvents and corrosives.
Each fluoropolymer offers certain propertiesrequired in specific applications, such as FEPfor its release and PFA for its glass-like finish,chemical resistance and ability to operate to260˚C/500˚F.
Moly is preferred for high-load, low-speedapplications. It increases the load-bearing capa-bility and the wear resistance of coatings that
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A matrix coating is one in which some softingredients, such as the lubricant (PTFE), areenveloped in others (the matrix) such as harder,more wear-resistant binders.
If PTFE, for example, is used by itself (with-out the matrix), and is exposed to a wear sur-face, it quickly wears away. Combined with thematrix, however, the new structure solves theengineering problems as it protects itself.
Matrix coatings are adjustable. The specificproperties of Xylan formulations depend on thematerials used to form the total coating and theirratio to one another. By judicious selection ofcompounds, we can formulate a coating to havesuperior release, wear resistance, chemicalresistance, high conductivity, etc.
Fluoropolymer-rich surface
Fluoropolymer and binder matrix
Molecular binder layerSubstrate
are filled with other lubricants (notably PTFE).Note: Encapsulating Moly in a matrix coating
seems to eliminate its characteristic sensitivity tooxygen and moisture. That’s why Whitford usesthis lubricant in Xylan 1052 and 1425, which aredesigned for high-load applications.
Graphite is used for applications with tem-peratures in excess of 260°C/500°F, and in wetservice at lower temperatures. Its drawback: ahigher coefficient of friction than PTFE or Moly.
3. Pigments/Fillers: Coatings are modified bypigments and fillers to provide properties notinherent in the primary ingredient, making themharder, more corrosion-resistant or adding color.For example, Xylan can be made electricallyconductive by the addition of fillers such as car-bon or metal particles.
4. Carriers: Solid components of coatings aredissolved in solvent or suspended/emulsified inwater, which enables them to be applied as apaint. The solvents used as carriers for Xylanare chosen for ease of application, ease ofcleanup, economy and environmental safety.
Different application systems (conventionalair spray [siphon or gravity], electrostatic, HVLP,airless, coil coating, curtain coating, dip/spin)require different carrier combinations to achieveoptimum coating performance. For instance,conventional spray systems require relativelyslow (less volatile) carriers that enable coatingsto level more uniformly on the substrate afterspraying. Other application techniques, such asdip/spin, may require fast (more volatile) carriersto “set” the coating film rapidly while parts arebeing processed.
Because of the many formulation optionspossible with Xylan matrix coatings, they can betailored to provide a wide and varied range ofproperties — to solve different problems. If youhave unique requirements for lubricity, hardness,noise reduction, corrosion protection, environ-mental compliance — even electrical conductivi-ty or resistivity — these coatings may be modi-fied to meet your exact need.
Xylan “firsts”
Whitford has frequently created special coat-ings to solve specific problems — leading to theextensive range of Xylan coatings today. In thisprocess of solving problems, many “firsts” have
been achieved by Xylan:
• First polymer coating to survive the rigorsof internal diesel engine application on pistonskirts and journal bearings.
• First tough PTFE coating with a flexiblecure schedule (see chart, page 22). You canapply it to temperature-sensitive materials suchas forged aluminum or tempered steel withoutreannealing the parts, or to many polymericparts without thermally degrading and/or warp-ing them, even to paper.
• First coating to be used by engine manu-facturers to achieve a boost in output power.
• First coating to be used to dampen “pistonslap” and resultant wear in high-performancemotorcycle engines.
• First coating to be used as a dynamic sealon air-conditioner rotor vanes.
• First coating to achieve a wear rate equalto bronze/steel bearings impregnated with PTFE-lead.
• First coating to replace cadmium and zincas a corrosion barrier on small fasteners.
• First and only self-lubricating coating to beused by NASA on a storage vault for moon rocks.
4
PTFE (polytetrafluoroethylene): Has the low-est coefficient of friction of any known solid andis the fluoropolymer most widely used in coat-ings. It feels waxy to the touch. Also blends wellwith engineering polymer binders. Is inert tomost chemicals and is approved for use in foodapplications.
FEP (fluorinated ethylene propylene): Has thebest nonstick and non-wetting characteristics ofthe three. It feels oily to the touch and lacks thehigh-temperature stability of PTFE. It is some-what more resistant to corrosives than PTFE. Approved for use in food contact applications.Has excellent stability in waterborne coatings.
PFA (perfluoroalkoxy): Has better release andnon-wetting properties than PTFE, but not quiteas good as FEP. Its wear characteristics are notas good as PTFE. It has nearly the temperaturecapability of PTFE.
The 3 principal fluoropolymers used in Xylan coatings
From the development of the first Xylanproduct (1010), Whitford has modified thebasic formulation to solve specific problems.
This has led to new materials and combinationsof materials so that, today, there are more than3,000 different formulations of Xylan.
Few products are as beneficial in so manyways as the wide range of Xylan coatings. Thisvery diversity, however, means that propertiescan vary widely.
Xylan dry-film lubricants can solve numerousproblems, including friction/wear, corrosion, tem-perature extremes, sticking, vibration, galvanicactivity, electrical insulation and conductivity.The selection of a coating depends on determin-ing the problem of the application (wear, heat,corrosion, etc.) and matching it with the materialthat most effectively solves the problem.
A. FrictionFriction causes heat, wear and loss of ener-
gy in dynamic applications. In severe circum-stances, friction can cause overheating andseizure.
Friction also causes brinelling, galling, scor-ing, and underloading of fasteners.
Drive-line vibration and chatter result fromfriction. In these cases, stick/slip motion is usu-ally the cause. This unstable sliding motionoccurs at very slow speeds, when frictionincreases above the force causing the move-ment and motion stops, then drops below themoving force, at which point motion restarts.
Deformation or destruction of delicate mech-anisms such as lock components can becaused by excessive friction.
Friction coefficients (measured by matingsurfaces rubbing against a coating) typicallyvary from about 0.06 for PTFE materials to about0.15 for Moly coatings, although values as lowas 0.02 have been measured for some Xylancoatings.
Xylan coatings are particularly useful whentemperatures exceed the operating limits of con-ventional mineral and synthetic oils. Because
Xylan coatings are based on resin systems witha wide range of temperature capabilities, theycan be used from cryogenic levels to260°C/500°F, with many being stable for briefperiods at 315°C/600°F.
Where galling, abrasion, and high energyloss due to friction are anticipated, considerapplying coatings of 25 microns/0.001 inch ormore to minimize friction and wear. (See page24 for this processing information.)
Potential applications include rotors for com-pressors, air-cylinder pistons, hinges, slidingbearings. The best coating choice is the onewhich provides the desired coefficient of frictionand the maximum pressure/velocity (P/V) capa-bility (see sidebar, page 7).
Using a Xylan coating in a bearing cavity inwhich a fluid lubricant is also used reduces fric-tion losses in the bearing to the lowest possiblelevel because Xylan is oleophobic (it sheds oil).During rotation, viscous shear forces within thebearing are reduced slightly. Thus, instrumentbearings or other systems in which minimumbearing friction is critical can benefit from a thincoating (7.5 microns/0.0003 inch).
Excessive friction is also detrimental to bolt-ed joints, in that much of the tightening torque isexpended overcoming thread-to-thread andbearing-face friction. In these situations, if thebolt is not properly tensioned (preloaded), thejoint can be unexpectedly weak in service.
In addition, improperly fastened parts aresubject to backout when vibration occurs.Coating the threads reduces the makeup torqueby as much as 65 percent.
Because of its toughness and corrosionresistance, a PTFE-matrix in a thermosettingbinder is preferred for these applications.
The oil embargo
The oil embargo of 1974 increased fuel costsas much as 80 percent, catching America withcars that averaged 3.5 km per liter/13.3 mpg.The situation for trucks was even worse.
5
2. High-performance coatings at work
The automotive industry responded byattacking the causes of inefficiency: weight, drag,and friction. Weight and drag were reduced bysuccessive generations of lighter and morestreamlined vehicles. Friction, however, wasanother matter, particularly on the internal com-ponents of engines. Parts moving against eachother create friction. Even parts that are welllubricated experience slight friction when sur-face asperities (peaks) rub together (especiallywhen an engine is started, or when it is cold).
Previously, bonded dry-film lubricants hadbeen used as insurance to back up fluid lubri-cants. However, the internal components of anengine operate in an environment that is hostileto most low-friction coatings. It is hot (>205°C/400°F), and many of the fluids encountered(fuel, combustion vapors, battery acid, brakefluid, glycol) attack many polymer coatings.Also, wear rates on pistons, bearings, gears,valve stems, and fan drives, are greater thanmost coatings can withstand.
Several formulations of Xylan coatingsworked well in this environment. Xylan 1010,1014 and 1052 were tried and selected for sev-eral applications because they were hard, wear-resistant, and stable at over 260°C/500°F. (Askfor Whitford’s “Introduction to the Xylan 1000Series”.)
In one early experiment, a trucking firm test-
ed Xylan 1010 in the engine of adelivery unit, coating the pistons,bearings, connecting rods and crank-shaft. Careful documentation provedthat, during 200,000 miles/322,000km, the engine used almost 15 per-cent less fuel.
Over the past fifteen years,engine manufacturers have deter-mined that friction reduction hasresulted in increases in engine outputby as much as 16 percent.
In another example, a well knownmanufacturer of diesel engines usedXylan instead of PTFE “buttons” onpiston skirts to reduce piston “slap”.Other applications followed.
For viscous fan drives, a Xylancoating proved to be the ideal way toprevent the internal drive rotor fromstriking the drive housing. This elimi-
nated the heat buildup that caused the drivefluid to gel.
Many of the parking-brake actuators foundon vehicles arecoated with Xylan— because itresists corrosionand the highthread loads(2,000 kg percm2/28,000 psi).
Today, thereare hundreds ofdifferent partscoated with Xylanin automobilesaround the world,many of them inenvironments thatwould melt ordegrade othercoatings. Fromclutch actuatorsto air-conditioningcompressors,these coatingsimprove themechanical per-formance of the
Relationship of Load to Torque
Loadincreases
Torque increases
Xylan
Cad/Wax
Black/Oil
Whitford recommends the use of direct-tension indicators (DTI) todetermine proper make-up torque for each size or lot of fastenersused on a given application.
Most low-friction coatings can-not survive the hostile environ-ment of an engine’s interior.Xylan can — with ease.
6
products by reducing friction, resisting corrosionand withstanding wear.
B. Wear
Initial contact between mating metal partsresults in momentary welding of asperities(peaks) on each surface. As each part contin-ues to move, the welded asperities are rippedoff, leaving behind minute pits.
Every bearing and wear surface, no matterhow smooth the finish, has these asperities.
The problem is common to impellers andhousings, air-cylinder pistons, machine slides,telescoping mechanisms, ball joints, plungers,gear-teeth, hinges, journal bearings, valves,power screws.
Xylan coatings provide a thin layer of lubrica-tion to prevent the asperities on mating surfacesfrom making physical contact with each other.The selection of the best dry lubricant (PTFE,Moly, or graphite) for these applications de-pends primarily on the PV value (Pressure xVelocity), atmosphere, and temperature of theapplication (see sidebar).
In many cases, a dry film provides enoughlubrication to eliminate objectionable wear. Forexample, a molded nylon detent for an automo-tive signal harness was failing prematurely dueto heavy loads on the point of the detent. Thesliding coefficient of friction between the detentand its mating cam was approximately 0.40,which resulted in severe abrasive wear.
When a 10 micron/0.0004 inch film of PTFE-loaded Xylan was applied to the detent, thecoefficient of friction dropped to 0.12, anddetent life was multiplied by over 200 percent.
Wear is often severe in bearing-type applica-tions. Rods that slide through glands, rollingelement bearings, slide assemblies, telescopingbooms, ball reversers, rocker arms, ball joints,tracks, bushings, and thousands of other appli-cations are configured so that one part rolls orslides over another part.
In most cases, friction and wear of the partsare reduced when one or both are coated with adry-film lubricant. Also, the coatings serve as athin cushion, spreading high point loads in bear-ings and reducing element fatigue.
The energy that is transmitted and dissipated
in a bearing is a function of the PV of the appli-cation. As the PV increases, so do heat andwear on the bearing surfaces.
Dry lubricants have a “limiting PV value” thatthey can withstand for a reasonable wear life.Typically, the highest limiting PV which a 25micron/0.001 inch coating of Xylan can with-
7
What “PV” means and how to use itWhen two bearing surfaces rub against each
other, wear is inevitable. The rate of wear is influ-enced by the pressure they exert against eachother (P), the velocity at which they move overeach other (V), the length of time they are in con-tact (T), and a wear factor constant (K) unique foreach combination of surfaces. K is a function ofthe surface characteristics (roughness, coefficientof friction [COF], hardness, ability to resist defor-mation under load, etc.) and remains relativelyunchanged at various PV.
The formula for calculating wear is:
W = KPVT
K: wear factor unique to surfaces in contact, given in in3•min/ft•lb•hr or mm3•minm•N•hr.
Wear: material (thickness) worn away in inches or millimeters.
Pressure: force between the surfaces in lb/in2 or N/mm2.
Velocity: rate of motion in ft/min or m/min.
Time: duration of contact or operation in hr.
If K and the thickness or wear tolerance of thebearing surfaces is known, then the service life ofthe bearing may be calculated for various combi-nations of Pressure and Velocity, or “PV factors”.
Wear life will be directly proportional to PVfactors below a certain limit. This “limiting PV fac-tor” is the point at which increasing P or V con-verts normal wear into accelerated wear, oftenleading to catastrophic failure of the bearing.
Several factors influence the limiting PV factor,including temperature. Surfaces moving in con-tact generate heat which must be dissipated if thebearing is to survive. Low COF materials (lubri-cants, coatings) reduce the rate at which heat isgenerated and help preserve the bearing. Allbearing materials, including fluoropolymer coat-ings, must be used below their limiting PV factorto avoid failure.
stand is approximately 50,000 (PV). This limitingvalue varies from coating to coating. Two fac-tors to bear in mind:
First: the ability of a coating to bear loadsincreases as thickness decreases. For instance,while a 25 micron/0.001 inch film may be able tobear PV of only 50,000, a 5 micron/0.0002 inchfilm (the practical lower limit using current appli-cation techniques) may be able to bear PV of150,000. For this reason, the PV tolerance of acoating may be modified by the film thickness.
Second: the lubricants themselves. PV limitsare not constant. They tend to increase withpressure and decrease with speed.
This is particularly true with Moly coatings,which work better under high pressure and lowspeed, where galling is the principal reason forfailure.
The wear rates of many of the Xylan 1000,1420 and 1600 Series coatings are equal to thatof bronze/steel bearings impregnated with PTFE-lead when applied in thin films (17.5 microns/0.0007 inch).
For break-in, frequent starts, and marginallubrication, remember: the period of greatest
wear to a moving mechanism is when it is new.
Boundary lubrication failure
When equipment is started and stopped fre-quently, lubricants are subjected to stress, whichcan diminish their ability to lubricate. This canbring sliding metal surfaces into virtual contact(a condition known as “boundary lubrication”). Ifmetal-to-metal contact does occur, the boundarylubrication can convert into actual failure as themetal surfaces meet and begin to wear, whichcan, in turn, lead to seizure.
A thin coating of Xylan reduces the chanceof failure and lengthens the life of such productsas sprockets, seal plates for compressors, pumppistons, cams, ball joints, conveyor trolleys,gears, journal bearings.
These coatings solved wear problems understart/stop conditions in reciprocating plungers inelectrical solenoids. Typical plungers arechrome-plated (and extremely hard). But thestarting and stopping at the end of each half-cycle put the plunger into a boundary lubricationcondition, causing the plating to wear rapidly.When a matrix coating replaced chrome plating,the boundary lubrication condition was overcomeand plunger life was extended by 90 percent.
A maker of chain saws uses Xylan 1010 as afail-safe lubricant on the cage of the saw’s mainbearing. Clearance between the cage and con-necting rod is only 100 to 150 microns/0.004 to0.006 inch. When the engine started, the bear-ing was in boundary lubrication and, without thecoating, it tended to seize. As proof of the coat-ing’s ruggedness, these engines run eight hoursper day and have a life expectancy of threeyears.
8
PV
thic
knes
sfa
ctor
4
3
2
10.2/5 0.4/10 0.6/15 0.8/20 1.0/25
Film thickness (mils/microns)
In general, a coating’s ability to bear loads increases as
film thickness decreases
Cylinder PistonShaft
Swept area
Swept area
When specifying a coating for a bearingapplication, we recommend that the coating beapplied to the larger “swept” area. This willspread the wear over a larger area and providethe greater amount of lubrication.
PTFE-type Xylan coatings are recommendedfor applications where initial wear is anticipatedto be light to moderate; Moly-type coatings arerecommended for conditions of heavy wear,especially in high-load situations.
Fail-safe
In any circumstance in which a mechanismmust function when needed, even if only once,Xylan coatings provide a good margin of securi-ty, even under the most critical circumstances.
This includes aircraft parts such as bearingsfor turbine engines, solenoids, seat ejectors,actuators, door pins, and firing mechanisms forordnance.
Another category is equipment that would bedamaged were a component to fail. For exam-ple, removing a frozen bolt from chemical pro-cessing equipment could cause damage cost-ing thousands of times more than the bolt. Inrefinery equipment, the use of a wrench is infinitely safer than the use of a cutting torch.
A good rule of thumb: apply coatings ofapproximately 25 microns/0.001 inch to the sur-faces of these parts. This ensures that the com-ponent will function when required, and provides good lubrication and excellent corro-sion protection.
C. Nonstick (release) properties Nonstick should not be confused with low
friction: the two are different.
Friction results from two surfaces slidingacross each other and is measured by a dimen-sionless number that describes the reduction ofdrag (force) between the sliding parts.
Release is the property of a surface whichresults in the inability of substances to adhere toit. It is a function of surface energy that can bemeasured by the angle of contact between thesurface and a drop of liquid (see diagram). Thegreater the contact angle, the lower the surfaceenergy, and the greater release a coating has.
Release is generally associated with cook-ware, coated to release food materials. Butrelease is equally vital to industrial processessuch as thermoforming, rubber molding, auto-motive and adhesive assemblies, copymachines.
In many applications, buildup of foreign par-ticles is a far greater problem than high bearingloads or corrosion. Examples: carburetor shafts,choke plungers, butterfly spindles, conveyorparts, instrument probes, fluid injectors, copyand printer rollers.
Buildup of dirt, ice, soot, scale, food andother foreign material can jam valve butterflies,throttle shafts, float elements, orifices, plungers,solenoids and other mechanisms.
If contamination of a surface is anticipated, itcan be minimized with a thin coating of Xylan,which enables the part to shed the contami-
9
Release and contact angleA drop of liquid on a coated surface forms a
bubble whoseshape is deter-mined by the rela-tionship betweenthe surface tensionof the liquid andthe surface energyof the surface onwhich the liquidsits.
The closer thetension and theenergy, the greaterthe tendency of theliquid to flow outand wet the sur-face.
A high-tempera-ture cure, or buffingthe Xylan coating,increases releaseby spreading the fluoropolymer into a film, whichdecreases the surface energy of the plane. Theincreased differential causes the surface tension ofthe bubble to draw itself up more into a sphere.
The contact angle is the tangent between theplane and the drop of liquid. Therefore, thegreater the contact angle, the greater the releaseof the surface.
Contact angle75˚
Contact angle85˚
Contact angle94˚
Do not confuse low frictionwith release
Low friction Release
As coated @205˚C/400˚F
@345˚C/650˚F
@205˚C/400˚F and buffed
nants. If contamination is severe, buffing thecoated surface will smear the fluoropolymer onthe surface of the coating and increase itsrelease property (see page 23, Part F).
A thin coating of Xylan (17.5 microns/0.0007inch) is usually sufficient to eliminate the prob-lem.
Most foreign matter is unable to cling to thewaxy surface of the coating and falls off. Whatdoes not fall off is easily scraped off when thecomponent brushes against a mating surface.
D. Corrosion
The electrochemical process of corrosion iscomplex, and can result from single or multiplesources. Oxidizing fluids such as salt water,electrolytes, under-hood chemicals, wettingagents, by-products of combustion, acid fumes,food materials, process chemicals, fuels, carwash solutions, even high-performance syntheticlubricants, can attack metal.
Dissimilar metal unions (galvanic corrosion)and vibration between tightly joined components(fretting) can also cause corrosion. The effectsrange from catastrophic failure of studs/nuts oncompressors to seizure of door-lock components.
Xylan coatings, particularly the formulationsmade with PTFE, offer a simple solution to theproblem. Xylan is an excellent corrosion barrier,even if applied as a thin film. Most formulationsform functional films at about 25 microns/0.001inch. However, there may be microscopic pinholes in the coating.
For even better protection, the coatings canbe applied in two thin layers so that pin holes inone layer are covered by the second layer.
Use of sacrificial primers increases the cor-rosion resistance (in some cases to over 7,000hours in ASTM B-117 salt fog with less than 15%red rust). Certain Xylan coatings form excellentbarriers to both acids and bases.
Even if corrosives eventually penetrate thecoating and attack the substrate, little or nounderburrowing occurs, so the parts may still beeasily disassembled for refurbishing.
This is particularly important for processequipment in extremely corrosive atmospheres,such as chemical mixers, pumps and marineequipment. Even fasteners that normally sufferfrom heavy corrosion will remain functional if
10
Eliminating ice buildupWhen air flows through a venturi, velocity
increases and temperature decreases. Thus,when the ambient temperature is near freez-ing and moisture is in the air, the potential forice to build up is high.
When carburetors were common, iceoften formed at the throat in winter, causingthe throttle butterfly to stick open or closed.A large “doughnut” of ice was sometimes vis-ible on the outside of the carburetor.
The problem was eliminated by coatingthe throttle shaft and butterfly (shown here)with a thin (17.5 micron/0.0007 inch) film of ahigh-release coating such as Xylan 1010.
Ice continued to form, but was unable toadhere to the shaft or the butterfly and wasswept into the engine and converted to watervapor. Thus, the dangers of losing power orhaving a throttle stick were eliminated.
SubstratePin holesTopcoat/
Second coat Prime/First coat
Overlapping layers of the topcoat fill in and cover any minute pin holes in the prime coat.
they are coated prior to placing them in service.
When ferrous, aluminum, or even galvanizedparts are to be exposed to oxidizing fluids orfumes, Xylan coatings can help protect them.
If corrosion is the dominant failure mode,choose a coating that offers the best protectionfrom the specific environment. If the problem isa combination of corrosion and wear, a goodchoice would be a coating that performs well inthe presence of corrosive elements and has ahigh nominal PV value.
For example, if corrosion is compounded byfretting (as found on compressor housings orother components subject to cyclic stresses), ahard, wear-resistant coating is the best choice.
Fastener-class coatings
One of the greatest contributions made byfluoropolymer coatings is increased resistanceto corrosion. Xylan coatings designed for fas-teners and other small parts have improved corrosion resistance by a factor of five.
As the petrochemical industry developed, itbegan to demand better corrosion protection.Then came the automotive industry. But theywanted corrosion protection and low friction.
Specific formulations of Xylan were devel-oped to combat the severe corrosion that affectsthe massive studs and nuts on oil drilling rigsand petrochemical processing equipment, aswell as other items associated with the Chem-ical Processing Industry (CPI). These coatingsalso permit the use of less expensive (andstronger) metals in place of stainless steel and
other more exotic and costly materials. They areapplied by conventional spray and, when fullycured, resist both corrosion and mechanicaldamage. Note: if multicoats are to be used,oversize nuts may be required.
The problem with automotive fasteners wassomewhat different. The typical automobile usesabout 2,000 small nuts and bolts on trim, acces-sories, brake components and engine sub-assemblies. Pressured by more and more con-sumers complaining that their new cars wereshowing severe rust, automakers began asearch for a better way to protect fasteners.
Previously, small fasteners were plated withcadmium. Corrosion resistance was about 96hours as measured in a salt fog cabinet (ASTMB-117). Unfortunately, cadmium, a heavy metal,has serious environmental side effects and hasbeen severely regulated or banned in manycountries. (The EU, for example, has bannedthe disposal of cadmium and other heavy metalsin landfills.)
The common replacement for cadmium iszinc plating. This, in combination with Xylan,provides the most cost-effective coating systemon the market today.
The auto industry’s search for better fastenerprotection led to a new set of standards of coat-ing performance. One of the first was issued byGeneral Motors. It called for a coating that pro-vided at least 336 hours of salt-fog protection onself-drilling and self-tapping screws — after thescrews have been driven through and removedfrom sheet-metal panels.
The Xylan 5000 Series was introduced tomeet this standard. These coatings and theirderivatives can be applied economically via thedip/spin method. More recently, Xylan 5230 wascreated, which offers the same performancewithout the use of chrome (a heavy metal andvery unfriendly to the environment).
Testing this material, automakers and otherusers of threaded fasteners found that salt fogresistance increased to about 500 hours, morethan 5 times the previous “best”, with no dangerof hydrogen embrittlement.
Another advantage of the 5000 Series is thatthe torque required to preload coated fasteners
11
A coating on threaded fasteners retards corrosion,enables preloads to be set accurately and keeps fasteners functional even if they corrode.
is more uniform than that for other fastener fin-ishes. “Torque scatter” is narrowed, meaningthat preloads on fastened joints, made byrobots, tend to be more uniform and the jointsmore secure (see chart, page 6).
Since the coatings permit the fastenings tobe tighter, back-out, or loosening from vibration,is effectively eliminated.
Corrosion, as described above, does not in-clude the severe chemical attack seen in chemi-cal plants and refinery vessels. Ask Whitford forinformation on Dykor products for these uses.
E. Noise reduction
Vibration generates noise. Vortices trailinghigh-speed impeller blades, impacting gearteeth, bearings spinning in races, slapping pis-ton skirts, plungers sliding against the walls ofactuators, reciprocating detents, and othersources of vibration are dampened when treatedwith Xylan. Under impact, noise generation isreduced.
In most cases, noise generation is effectivelyreduced by coatings of 25 to 40 microns/0.001to 0.0015 inch. When corrosion is not a consid-eration, these films may be applied in one coat,although thicker coats may have greater energy-absorbing capacity.
If excessive noise is the primary problem,multiple coats of Xylan (up to 60 microns/0.0025inch) may be applied to achieve optimumresults. Caution should be taken to avoid exces-sive thickness, since the coating could be sub-ject to delamination or tearing.
The choice of the best Xylan formulation fornoise reduction depends on the problem. If cor-rosion is not a problem, apply a soft coatingsuch as Xylan 1006; otherwise use P-92 primerand a topcoat of Xylan 1014.
A manufacturer of domestic dryers used abearing coated with Xylan 1010 to replace anoil-impregnated bearing. The problem with theold bearing was that, after approximately oneyear of service, the oil migrated out of the bear-ing and the dryer developed an annoyingsqueak. The coating not only provided therequired lubrication, but also eliminated thesqueak.
F. Temperature extremesFew fluid lubricants are recommended for
use at cryogenic temperatures (most becomesolid) or above 205°C/400°F (they oxidize rapid-ly). The Xylan 1000 Series dry-lubricant coat-ings, however, operate comfortably at bothextremes.
They retain their hardness at high tempera-tures because most binders for these coatingsare thermosetting resins. Although pigmentsand binders in some Xylan coatings may discol-or above 260°C/500°F, the coatings continue tofunction. (For best results, coatings based onthermosetting resins should be cured at30°C/50°F above the temperature at which theywill be used.)
Xylan 1000 series coatings are also useful forpreventing damaging “hot spots” between tworubbing parts, which enables some temperature-sensitive materials to operate at conditionsunder which they would otherwise fail.
G. SealingVery thin coatings of Xylan show little tendencyto cold flow (migrate under pressure), and thusare too hard to perform as conventional sealingsurfaces. Applied in thicker films, however,
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Making cutting edges work betterHeat buildup from friction at the tips and
flanks of saw blades leads to rapid loss of sharp-ness. A 25 micron/0.001 inch coating of Xylanreduces both friction and heat, extending the lifeof blades by a factor of three or more. It alsoreduces sap buildup. Similarly, a coating onhand pruners lowers friction to add power to thecutting force, making cutting easier.
these coatings will deform sufficiently underpressure to form a tight thread-to-thread seal onpressure plugs, fittings, valve stems and otherthreaded fluid-power components. Tests ofcoated pressure plugs have shown that theyresist leaking even when surge-tested repeated-ly to 950 kg/cm2/13,500 psi.
The other characteristics of the coatings —low friction, corrosion resistance and high-tem-perature stability — are beneficial in these appli-cations, too. The low coefficient of friction re-sults in lower seating torques (as much as 60percent). Because many Xylan coatings are stable up to 315°C/ 600°F, they will not migratefrom threads when equipment is operated athigh temperatures.
The coatings can be used as a dynamicseal, too. For example: when applied to thevanes of a powder metal rotor in an air-condi-tioning compressor, Xylan seals the rotor/hous-ing interface, preventing leakage of the refriger-ant past the rotor. To qualify for this application,Xylan 1010 was tested for 150 million cycles at8,000 RPM, at a temperature of 185°C/360°F.
H. Electrical characteristicsMost of the resins and several of the lubricat-
ing materials used in Xylan dry-film lubricantsare excellent insulators, with dielectric strengthin the order of 2,000 V/mil (25 microns).
The very low dielectric constant and dissipa-tion factor, combined with the high dielectricstrength and high-temperature capability ofPTFE, FEP, PFA and the matrix resins, create formulations that are excellent insulators.
This insulating property renders a coatedsurface a good capacitor. When there is particleor air motion, or other static-charge-inducingsystems, conventional Xylan coatings should beused with caution in the presence of static-sensitive products such as integrated circuits.
A fluoropolymer coating is called for on GM6076-M as a masking coat for threads, protect-ing them from the heavy buildup of today’s electrodeposited primers (a problem not only inautomotive applications, but also in furniture,building equipment, etc.). The PTFE-basedcoating “masks” the threads and provides easyremoval of the primer by the mating nut or bolt.
In addition, the coating reduces the torquebetween the coated parts and similar but non-primed fasteners in adjacent areas.
Conductive coatings, too
When formulated with such materials as carbon black, graphite, or metallic compounds,coatings can be used as conductors. These formulations are preferred for static-sensitivesystems such as computer printers and plasticweb-handling equipment, or parts that operatein explosive atmospheres. Resistivity can rangefrom 10 to 1012 ohms/square, depending on theadditives selected to make the coating conduc-tive. Whitford also offers a line of electricallyconductive coatings specially designed for copyand printer rollers.
An example: webs in paper and textile millscan be too dry to be conductive. This preventsutilization of the outstanding release propertiesof FEP heat-shrinkable tubing, because the static charge becomes a safety hazard. A conductive coating of Xylan solves the problemby providing the release while dissipating thestatic buildup.
When coatings are used to insulate or con-duct, they should be applied in films of at least25 microns/0.001 inch for maximum effective-ness. Coatings of less than 25 microns tend tobe discontinuous, and therefore electrical prop-erties are compromised.
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Rollers live a longer, more productive lifeXylan 1781 3-layer electrically conductive coat-
ing system gives end-users a smooth, coated surface that provides excellent toner release and atoughness that extends in-service life for all aluminum and steel copier and printer rollers.
The list of applications for these high-per-formance coatings is almost without end— and is growing. Here are a few exam-
ples of how various Xylan coatings have solvedsome interesting problems.
Xylan stops tapers jamming
CCL Systems makes equipment to prestressthe steel strands that reinforce concrete struc-
tures. One end of thestrand is anchored; theother is grasped by athree-part tapered collet and collar heldin the jaws of anextremely heavy-duty
jack. Loads as high as300kN (67,440 lbf) areapplied until the concreteis set, forcing the taperedparts together.
Freeing the collet oncethe tension was removed
— without permanentlydamaging the collet — was difficult. CCLSystems discovered that coating the wedgeswith Xylan 1052 eliminated the jamming com-pletely and ensured reusability.
Xylan unsticks sticky valves
No one pays attention to ball and plugvalves — until they stick, which can causeprocess fluids to be lost, product damage,waste of energy, even dan-ger to personnel.
Sticking valves are ascommon as the method gen-erally used to “fix” them: ablow from a hammer, whichusually damages the valve inthe attempt to unstick it.
A better solution is to pre-vent the problem from occur-ring in the first place — witha thin coating of Xylan (25microns/0.001 inch). Xylan
has been used on plug and ball valves for morethan thirty-five years, to provide insurance thatthe valve will work when it must.
Xylan improves blow-out preventers (BOPs)
Hydril, amanufacturerof BOPs(shown here),was unable touse an estab-lished platingmaterial forcorrosion pro-tection andlubricity for its annularBOPs due to environmentalcontrols. As aresult, thecompany hadto find a re-placement surface-finishing technology for theinternal surfaces which would facilitate quicksealing in the event of unexpected down-holepressure spikes and have the ability to stand upto harsh, corrosive wellbore fluid conditions.
Xylan 1052, a low-speed, high-pressure,anti-galling, dry-film lubricant was tested. TheBOP bowl, piston and head were first coatedwith a corrosion-resistant primer. Then Xylan1052 was applied. The new coating system wastested through 50 actuation cycles. Not only didXylan 1052 pass the test, it also improved lubric-ity and was placed in service. The BOPs areperiodically pulled from the field for inspectionand rework (remanufacture). Then they arerecoated and returned to service to help protectoperating personnel and the environment.
Xylan lengthens lifeof sleeve bearing
A unique powder metal sleeve bearing(developed by Beemer Precision, Inc., of FortWashington, PA) uses Xylan 1052 to extend its
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3. Solving problems with Xylan coatings
service life in high-load,low-speed applicationswith rotating and oscillat-ing motions.
The tough nonstickcoating virtually elimi-nates the need for “breakin” because of its lowcoefficient of friction,ideal for startup.
After startup, thecoating continues to
function, helping lengthen the life of the bearing.
Xylan reduces wear onair-cylinder pistons
In more and more applications, oil/air mix-tures are either proving unsafe or are interferingwith process cleanliness.
In environments in which lubricated air is notallowed by OSHA regulations or because ofother safety considerations, air-cylinder pistonsshould be coated.
The easiest, most effective way to eliminatethe oil/air problem and provide proper lubrica-tion for moving parts is to coat air-cylinder pis-tons with 25 microns/0.001 inch of Xylan 1014 or1424, which also extends the lives of the pistons.
Xylan saves bearing cages as secondary lubricant
When compressors are shut down, the pri-mary lubricant settles below the bearings. As aresult, startup can frequently be damaging tothe bearings.
A coating of Xylan is used as a secondary
lubricant to provide low-friction movement untilthe primary lubricant begins circulating.
Xylan quiets blower
How much noise can a coating dampen?That depends on the application, but the resultsobtained in diesel engines are indicative.
By coating only the rotors of a supercharger,a drop in noise emissions of 2.5 dbA was meas-ured and the efficiency of the blower was signifi-cantly improved.
Another benefit: in the case of a bearingmalfunction, the Xylan coating would act as anemergency lubricant to keep the blower fromself-destructing before it could be shut down.
Xylan shows stability under fire
Experiments conducted to reduce lossescaused by friction in diesel and spark-ignitionengines demonstrated that this environment wasdifficult for any lubricant to endure. Matrix coat-ings, however, had proved their worth in otherhot-engine applications.
Xylan 1010 wasapplied to pistons whichwere operated for a quar-ter of a million miles. Thecoating showed somesigns of scorching — indi-cating that the pistons ranin excess of 260°C/500°F— but it was still opera-tional, and the pistonsshowed little wear.
The scorching can be seen in the photo-graph — as can the coating, still in place, readyto perform and protect the piston.
15
Xylan coating prevents leaks past threads
Pressure vessels, valves, pipe unions, stor-age tanks, reactors, pipe lines, and other fluid-containment equipment are often fitted withthreaded plugs for inspection, pressure relief,filling, or tapping.
Coatings on pipe plugs not only improvetheir performance and reliability but also makethem easier to use. A thin film of Xylan elimi-nates the PTFE tape normally wrapped aroundthe threads to seal them.
In addition, the corrosion protection and low-friction properties of the coating greatly reducebreak-out torques, enabling users to remove theplugs at a later date without destroying them.
In most instances, the pipe plugs may be reused without difficulty.
Xylan coatings are also available in manycolors, enabling users to color-code particularplug sizes and different alloys.
Xylan proves a winner on the track
Reducing weight and minimizing wear aretwo major objectives of car designers aroundthe world — especially in car racing. But thereis a problem: the lighter the material, the greaterthe tendency to wear.
Cosworth Engineering, internationally re-nowned designers of high-performance en-gines, has solved many design problems withXylan coatings on engine components:
• Aluminum cylinder liners save weight, butthey suffer from scuffing. A collar of Xylansprayed around the base of the cylinder linereliminates the problem, even in the engine's
hostile environment of heat, oil and friction.
• Cosworth replaced steel throttle plates withaluminum, which is lighter, but running betweenaluminum guides soon caused scuffing. So theycoated the throttle plate and the guides withXylan, solving the scuffing problem and provid-ing permanent dry lubrication, even in the pres-ence of gasoline vapor.
• Magnesium castings are lighter, but con-tact with harder materials (such as the sinterediron rotor in Cosworth's oil scavenger pump)caused wear, rendering the castings unservice-able. A coating of Xylan 1010 completelysolved the problem. Even after extensive racingtrials, no appreciable wear was evident.
Having proved itself on the race track, Xylanis now enabling production car designers to cutweight and wear as they improve performance— all at a lower cost.
16
Most Xylan coatings are formulated tofunction as single-coat materials. Thereare times, however, when a primer will
provide significantly improved performance, andtherefore more than justify any additional cost.
Note: There is a difference between “primers”and “basecoats”, and the two should not beconfused. Whitford defines the terms as follows:
• Primer: a coating designed to stand alone and function by itself, but that can also be used to enhance the performanceof a different topcoat.
• Basecoat: a coating designed to be part of a specific system, without which the system will not perform as specified. Base-coats generally will not function properly alone.
Primers can be organic or inorganic, metallicor non-metallic. The selection of which primer ismost suitable for an application depends largelyon the desired performance enhancement, theenvironment in which the coating system willoperate, and to a lesser degree on the topcoatto be used.
The mechanisms of corrosion control arequite complex. However, as a general principle,Xylan primers improve corrosion resistance byone of three methods. The first is inhibition. Theuse of select pigments inhibits the corrosionreaction and promotes the formation of a stable,passive oxide layer on the metal surface.
The second is sacrificial protection. Primershighly filled with anodic metallic pigments cor-
rode more readily than the base metal. The by-products of this sacrificial corrosion then fill poreswithin the coating, further reducing the corrosionprocess. The third is the use of inert fillers,which can increase the length of the diffusionpath of the necessary components of corrosion.By providing a barrier to oxygen and moisture,the corrosion reaction is greatly reduced.
Regardless of the primer selection or theenvironment to which the coating system isexposed, a primer will only offer enhanced per-formance if applied to a properly prepared sur-face. This is so important to developing the fullpotential of high-performance coatings that thenext chapter is dedicated to proper surfacepreparation and application conditions.
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4. Whitford primers
Xylan, when combined with a zinc-rich sacrificialprimer, can withstand 1,080 hours of exposure in thesalt-fog cabinet. Rust is minimal, the coating is stillfunctional and the fasteners are fully serviceable.
Left: Coated bolt but with no primer in ASTM B117 after 500 hours. Right: Same conditions but with a primer. What a difference the use of the right primer can make!
Applying coatings is more complicated thanit appears, and unfortunately space pre-vents us from covering all the finer points.
For a complete evaluation of your application,consult a Whitford Quality Approved Applicatorearly in the design process (for a list of these,please call your Whitford representative).
A. Substrates
Xylan can be applied to almost any clean,dry, oil-free surface. The only materials to whichit will not adhere are those with inherent releasecharacteristics such as polyolefins and similarfluoropolymers (although, with special surfacepreparation, Xylan will adhere to these as well).
Virtually all metals
Almost every structural metal can be coatedwith Xylan, including steel (carbon and stain-less), aluminum (wrought and cast), copper (andalloys), and titanium. Note: high nickel- andchrome-bearing alloys, and some platings ofnickel, can also be coated if abrasive blasting isused and the coatings are applied within anhour or two of blasting.
Special precautions must be taken with pow-dered-metal parts. These parts appear ideal forcoating: their surface is porous and providesgood “tooth” to which a coating can cling.However, since many of these parts have beentreated with resinous impregnants, oils aretrapped within the porosity. To coat them, bakethe parts at a temperature higher than the curetemperature. Any contaminants which bleed tothe surface during the bake must be thoroughlyremoved. Then, the parts can be coated.
Die-cast parts can be a problem. They aretypically cast using aluminum, zinc and magne-sium alloys that can be “gassy” and porous.When coated parts are cured, the gas trappedin internal cavities expands and erupts. Whencured at over 235°C/450°F, these parts mayhave numerous eruptions on the coated surface.To evaluate whether the substrate can withstandthe cure temperature, prebake a part to 10-15˚C/20-25˚F higher than the anticipated cure.
Plastics
Many plastics can be coated with Xylan.Note: vinyl products containing a high content ofplasticizer can cause adhesion problems.Nylon, PEEK, PEK, PPS, ABS, polycarbonate,epoxy, polyester, phenolic — all can be coated.
Parts made of these materials must be curedat temperatures well below the softening temper-ature of the substrate to avoid distortion andpolymer degradation.
Elastomers
Some Xylan coatings may be applied toelastomeric parts not expected to elongate morethan about 30 percent in service. Greater elon-gation may cause these coatings to crack. If adiscontinuous coating is not objectionable, elon-gation greater than 30 percent is permissible.(Note: Whitford has developed flexible finishesthat can be elongated to 150 percent or greaterwith no cracking of the coating. Ask forWhitford’s “Flexible Finishes” brochure.)
Elastomeric parts successfully coated withXylan include bushings, mounts, automotivedoor and window seals, vibration dampeners.Substrates include natural rubber, EPDM, SBR,butadiene and its derivatives, and silicones.
Glass and ceramics
Fluoropolymer coatings will adhere to cleanceramic and glass surfaces, but curing the coat-ing without cracking the substrate can be diffi-cult. (If possible, use glass or ceramic intendedfor high temperatures.) In most cases, a low-temperature cure (below 150°C/300°F), followedby a slow cool-down period, will not crack thesubstrate. For glass parts, coating adhesionmay be improved by a fluorine etch or the use ofa primer.
Fabrics and composites
Xylan coatings are increasingly being used(for low friction and release at elevated tempera-tures) on woven and nonwoven industrial textilesmade from such modern materials as carbonfiber. One of the most successful applications ofXylan involves a fabric bearing which is woven
18
5. Applying Xylan
from a nylon/glass blend, then coated andcured.
These composite bearings are used underthe compressor blades of large bypass fanjetengines. The natural porosity of fabrics formssponge-like “wells” into which the coating pene-trates. In service, this extra supply can continueto provide PTFE to a wear surface long after thecoating is worn away from a smooth substrate.
Xylan adheres well to other composites, too,provided release agents have not been appliedto the material.
Paper and wood
Xylan adheres well to uncoated or unvar-nished paper products as well as wood. Asunlikely as it may seem, the coatings performevery bit as well as they do on metal and othersubstrates. Cure temperatures should notexceed 180°C/350°F.
B. PreparationCleaning and pretreatment are important.
Every surface to be coated must be clean, sincefew coatings adhere to dirty or oily substrates.
Note: The second-best coating over the bestsurface preparation is likely to perform betterthan the best coating over the second-best surface preparation.
There are many ways to clean a part, eachwith advantages and disadvantages. Sometechniques go beyond cleaning and create sur-face “structures” that enable a coating to clingbetter. It is often desirable to use a combinationof cleaning methods to achieve optimum adhe-sion. The more common methods are:
Vapor degreasing used to be the most widelyused cleaning technique, but fell into disfavorbecause of regulatory restrictions on the use ofcleaning solvents.
Where permitted, degreasing remains anexcellent technique for removing foreign materi-als from fingerprints to machine oils. It is aneconomical technique for cleaning small batch-es. Avoid using it on parts that may be attackedby the solvent, such as plastics, compositeparts, or metal parts with organic inserts.
Alkaline washing involves cleaning parts withmoderate- or high-pH cleaners. This is pre-ferred for high volumes of parts and is generally
as effective as vapor degreasing. Parts whichshould not be alkaline-washed are those whichmay be adversely affected by the chemistryinvolved (such as aluminum and magnesium).
Grit blasting with aluminum oxide or car-borundum particles is a common cleaning tech-nique, preferred for parts whose surface con-taminants — rust, scale, corrosion, old coatings— must be attacked physically to be removed.It is not, however, the most effective techniquefor removing oily or fluid contaminants. Whenparts are particularly oily, alkaline cleaning orpre-baking them before blasting will improve theeffectiveness of the blast and reduce contamina-tion of the blast medium.
Grit blasting does more than clean; it rough-ens the surface and enhances mechanicaladhesion by increasing the surface area towhich the coating can cling. A grit medium from36 to 220 mesh/250 to 70 microns is recom-mended for blasting most metal parts. (Note:the particle size quoted above runs from largerto smaller.) Steel grit is generally avoidedbecause minute particles may be left behindand become starting points for oxidation.
Shot blasting is similar to grit blasting, butemploys metal or other “shot” as the blast medi-um. For parts which will be used in fatigue/fret-ting applications, this process can be beneficialbecause it imparts residual compressive stress-es on the surface of the parts, thus lengtheningtheir lives under cyclic loads.
Tumble blasting is another variation in whichparts — usually small parts — are placed into arotating cylinder along with an abrasive mediumwhich abrades the part surfaces. The effectvaries with the medium employed, but is muchthe same as grit blasting. This technique is lesseffective than fluid cleaners for removingmachine oils and other similar contaminants.
Acid or alkaline etching is an excellent tech-nique both for cleaning and roughening the sur-face of aluminum parts. Because the size of theequipment is considerable, it is usually reservedfor high-volume production parts.
Pickling is common for removing rust/scalefrom ferrous parts after cleaning. It should notbe used on parts that will be highly loaded,since it can cause hydrogen embrittlement.
Phosphating is a secondary surface prepa-
19
ration for steel which is generally used aftervapor degreasing, alkaline washing or grit blast-ing. Whitford normally recommends a modifiedzinc or manganese phosphate with a fine crys-talline structure. Zinc phosphate is used forstatic applications, and manganese phosphatefor dynamic and higher-temperature applications.
A thin layer (15-25 gms/m2) of zinc phosphateon the surface promotes better adhesion anddramatically increases corrosion resistance andchemical protection. A good alternative: Xylan4070 Primers, which outperform conventionalphosphating.
Iron phosphate may be less expensive, butzinc phosphate has superior corrosion resist-ance and better protection from corrosive creep.Whitford prefers zinc phosphate. Note: Manga-nese phosphate has better corrosion resistanceand thermal stability than zinc, but can be moredifficult to apply, especially to high-alloy steel.
Anodizing: An electrochemical treatment ofprimarily aluminum which can greatly increasehardness. It creates a porous, corrosion-resist-ant surface that is excellent for coating, provid-ed it has not been sealed. (Other metals, suchas manganese and titanium, although much lesscommon, may be anodized.)
Conversion coating: Normally applied in abath to create an “active” surface to promoteadhesion of the coatings. Specially formulatedphosphates are available for use on aluminum.Ask about Whitford’s Activ8/Passiv8.
Other factors
Combinations of pretreatments: These arerequired for the best overall coating adhesionand corrosion protection. For common sub-strates, industry practice has been to use thefollowing pretreatments or combinations:
• Carbon steel: vapor degrease/gritblast/phosphate or plate.
• Aluminum: alkaline wash/etch or grit blast.
• Stainless steel: heat oxidize/grit blast.
• Chrome and nickel plate: vapor degrease/pre-bake/grit blast.
Coating material preparation: It’s importantto mix or roll all ingredients according to theProduct Data Sheet which accompanies the first
shipment of each Whitford product.
Preheating: Preheating parts prior to coating isrecommended when parts are in humid atmos-pheres because condensate on cool parts cancause defects. Preheating is also useful whenparts of great mass are coated and oven dwelltimes to bring them up to temperature would beuneconomical, or when films that are thickerthan normal are required.
We recommend that preheating at the time ofcoating be limited to no more than 65°C/130°F toavoid solvent or water “boiling” on the surface ofthe parts. Thin or light-gauge parts may requiregreater temperatures because of their tendencyto lose heat rapidly during transfer from the heatsource to the coating area. Note: Preheating isnot recommended with Xylan 5000 Series coatings.
C. Application techniquesThe techniques used for applying Xylan
depend on the shape of the part, the number ofparts, the desired transfer efficiency, the appli-cation rate and the type of carrier used in theXylan formulation. Here is a brief guide:
Spraying: By far the most versatile and wide-ly used technique to apply Xylan is spraying.There are five basic types: conventional (alsoknown as siphon or gravity), HVLP, airless, pressure pot, and electrostatic.
• Conventional: The choice for small num-bers of parts, where considerable manual workis required. Almost any Xylan formulation canbe applied by this technique.
• HVLP (high volume, low pressure): A varia-tion that reduces air pressure and increases liquid volume. Its greater efficiency reduces thenumber of Volatile Organic Compounds re-leased (see Chapter 9, page 30) and canincrease transfer efficiency.
• Airless: Similar to the siphon system butuses hydraulic pressure to move and atomizethe liquid instead of air.
• Pressure pot: Similar to conventionalspraying, except the coating is under positivepressure. This technique moves more coatingthan a conventional system and is recommend-ed for larger production runs. Almost any Xylanformulation can be applied by this system.
• Electrostatic: The recommended process
20
for very high production conditions or when anelectrostatic “wrap” is needed to coat complexshapes efficiently. Rods, wires, outdoor furnitureand other parts that require a 360-degree coatingare examples. Not all formulations lend them-selves to electrostatic spraying with conventionalequipment. Some (such as water-based prod-ucts) may require special electrostatic systems.
Bulk techniques: These are the most eco-nomical methods of applying coatings to smalland intricate parts such as fasteners, clips andother irregularly shaped pieces. Transfer effi-ciency is exceptionally high: as much as 95percent of the coating is applied to parts. Bulkcoating techniques operate in two basic ways:
• Dip/spin coating: This is just what thename implies. A basket filled with parts isimmersed in a reservoir half-filled with coating,raised out of the coating but still within the reservoir and spun to carry off excess fluid bycentrifugal force. Following that, the parts arecured. Because parts are in contact with eachother, which can prevent complete coverage ofthe coating, at least two passes through thisprocess are required to ensure total coverage.
• Barrel/tumble coating: This technique in-volves tumbling parts and spraying them whilehot air passes over them. This method is pre-ferred for extremely lightweight or flat parts(such as washers or small O-rings) which tendto “nest” together.
Four other methods are:
• Coil coating: This uses high-speed rollersto apply precise film thicknesses to wide, contin-uous sheets of metal, which are subsequentlydrawn or stamped. This process is used verysuccessfully for high-volume coating of cook-ware, bakeware and small appliances.
• Curtain coating: A high-volume applicationtechnique in which parts are passed through afalling curtain of the liquid coating. It’s fast, eco-nomical and highly efficient (virtually no waste).
• Roller coating: Similar to coil coating in thatit uses rollers to apply the coating to the surface.In the case of roller coating, however, the coat-ing is applied to metal blanks rather than contin-uous rolls of metal. The process is used forhigh-volume applications like cookware andbakeware. One of its drawbacks is that it tends
to create striations in the coating which are visiblein the finished and pressed piece. These stria-tions are often referred to as “chicken tracks”.
• Pad or screen printing: Adding a patternedor decorative coating over standard coatingsusing a pad or a silk screen.
Coating fabrics
The application techniques by which fluoro-polymer finishes and coatings are applied totextiles may differ significantly from those utilizedfor applying coatings to metal, rubber or plasticsubstrates.
Application can be accomplished by pad-ding, in which the greige (pronounced "grey" andmeaning "untreated") fabric is immersed in abath of the finish and the excess is removed bypassing the wet fabric through padded rollers.Padding spreads the finish evenly over bothsides of the fabric, minimizing application timeand effort.
Textiles can also be coated or impregnatedby "knife over roller". This method uses a vis-cous coating that is metered onto a rotatingroller, which supports the entire web of the fabric. As the fabric passes over the roller, theforward motion produces a well of coating, alsoknown as a rolling bank, behind a stationaryknife. The gap between the knife and the rolleris the primary determinant of the amount of coat-ing deposited onto the fabric. Variants of theknife-over-roller method include knife-over-table,knife-over-air, and knife-over-gap. Knife coatingis used for single-side application of the coatingonto the fabric.
Similar in popularity to knife coating is rollcoating of fabrics. All variants, such as directroll, kiss coating, gravure, and reverse roll, utilizea rigid roller partially immersed in the coatingsolution. The coating is either directly applied tothe fabric or is transferred to other rollers prior todeposition onto the fabric. Each variant affordsdifferent levels of efficiency, flexibility and preci-sion of deposition weight.
Other possible application techniques forfabric coatings may include transfer coating,rotary screen printing, or simply spraying.
D. Flashing and curingAchieving a tough, continuous film requires a
21
flashing process, in which the carrier is vapor-ized by brief exposure to an elevated tempera-ture (but lower than the cure temperature), and acuring process, in which the coating resins linkinto a continuous film.
Most Xylan coatings can be cured via con-vection ovens and infrared (IR) ovens. Somespecial formulations can be cured with exposureto ultraviolet (UV) light. Only a few formulationsare suitable for cure at ambient temperature.The curing process is a time/temperature rela-tionship. In all cases, the higher the tempera-ture, the shorter the curing time (see chart).Note: altering the time/temperature relationshipwill affect performance (see F, next page).
Convection systems: These use heated air tocure the coatings. They are, by far, the mostcommon type used to cure Xylan. Sophisticatedproduction ovens, which employ conveyors tomove parts, usually have at least three heatzones within them: a warm-up zone, a bakezone, and a heat-extraction zone.
Infrared systems: A line-of-sight process thatallows fast heating of the surface of the coatedsubstrate (as opposed to other, slower systems,which must heat the total part). Efficient, butmust be controlled carefully to avoid overheat-ing. Very effective for flat or shallow parts.
UV systems: These initiate a photochemicalreaction that is far faster and uses far less ener-gy than thermal systems. UV also reduces thefootprint of the curing line significantly.
Curing schedules: These vary for differentXylan formulations. However, some Xylan coat-ings permit wide latitude in the selection of curetemperatures so that cure can be compatiblewith the part. For instance, you may want tolimit the cure temperature of a die-cast part to380°C/715°F, or for a formed aluminum part toless than 235°C/450°F.
Note: Cure time is the period that beginswhen parts reach and remain at cure tempera-ture, not oven dwell time (the entire period dur-ing which the parts are in the oven).
CAUTION: Entrapped air in such parts asrollers or insulated/jacketed vessels may becomea “bomb” and explode when heated to cure tem-peratures. An air-relief hole or pressure-reliefvalve must be a part of the assembly.
E. Surface considerations formaximum wear resistance
Should the coating be applied to both sur-faces of the mating parts?
The answer is generally no, for reasons ofcost. Only a small increase in lubricity is gainedby coating both surfaces. However, part life maybe doubled because of the greater thickness.Remember: in most cases, it is easier and moreeconomical to coat the exterior of a part ratherthan the interior (a shaft instead of a bearing).
When there is a difference in mating materi-als, it is preferable to coat the softer of the two
22
426
398
371
343
315
287
260
232
204
176
148
121
093
065
800
750
700
650
600
550
500
450
400
350
300
250
200
150
˚C ˚F
5 10 15 20 25 30 35 40 45 50 55 60
Curing temperature related to curing time: Xylan 1000 Series
Minutes
surfaces (the one which, in boundary-lubricationconditions, could suffer the greater damage).
The mating surface affects the wear rate of acoating. For instance, the wear rate on a coatedjournal that supports an aluminum shaft is asmuch as 50 times that of an identical bearingthat supports a carbon steel shaft. (See “What‘PV’ means and how to use it”, page 7.)
The roughness of a mating surface also hasan effect on coating wear. The optimum surfacehas 8-12 micro-inches/0.2-0.3 microns (RMS).Surprisingly, hyper-smooth surfaces (less than 4 micro-inches/0.1 microns (RMS) produce high-er wear rates than those with a finish between 15-30 micro-inches/0.375-.75 microns (RMS).
A smoother surface permits less transfer ofPTFE to the mating surface and friction increas-es — causing wear. Surfaces which are rougherthan 30 micro-inches/.75 microns (RMS) alsoresult in high rates of abrasive wear, increasingas the roughness increases.
Caution must be used with coatings incathodically/anodically protected assemblies(contact your Whitford representative).
F. Special cure and postcureSome Xylan coatings can be processed to
improve performance for specific applications.For instance, cure affects adhesion, release,hardness, corrosion resistance, friction proper-ties, wear rate, and flexibility. Here are somesuggestions for enhancing coating performance:
• Curing for maximum hardness and chemi-cal resistance: For applications in which coat-ings will be subjected to extreme wear, we rec-ommend that they be cured at the upper (hot)end of their cure schedule. This results in maxi-mum crosslinking of the binder.
• Curing for nonstick/release: Release canbe increased by post-curing at elevated temper-atures or by buffing the surface after it has beenthoroughly cured.
• Curing for multiple coats: If applying multi-ple coats to a part, in most cases the first andintermediate coats should be flashed but notfully cured prior to the application of subsequentcoats. This increases the bond between eachlayer and results in a stronger, denser coating.
(See PDS for more specific instructions.)
G. Additional considerations• Postforming: Some Xylan formulations may
be stamped, deep-drawn, bent, punched,drilled, machined, and otherwise manipulatedwithout damaging the coating — provided thatthe part is properly pretreated before coating.
• Controlled removal for precision sizing:Many Xylan coatings may be applied in thickfilms and then machined, buffed, centerlessground, sanded, etc., to achieve a very highgloss and an extremely close tolerance.
• Higher builds: Thicker films may beachieved by preheating the substrate as previ-ously mentioned or by using formulations withhigher solids, which are available in most, butnot all, Whitford products.
• Coating removal: Once applied and cured,fluoropolymer coatings can be removed from a part mechanically by sand/grit blasting, or thermally by degrading the coating (at 480°C/900°F). Use caution when degrading thermally.
Important: At temperatures >300°C/>575˚F,fluoropolymer coatings give off fumes which cancause “polymer fume fever”, a condition notunlike a mild, 24-hour case of flu (there are noknown long-term effects). If you take fluoropoly-mers to these high temperatures, be sure thatthe work area is well ventilated.
Substrate removal: when to make room for a coating
Coatings are generally applied to parts with-out any provision for the thickness that they add(coatings are not included in the originaldesign). This is particularly true when coatingsare used as corrosion barriers (within some lim-its, the thicker they are, the better). This is alsotrue of parts that are stamped or deep-drawn.
In many bearing applications, however, toler-ances are too tight to add another 17.5 microns/0.0007 inch of material without any provision forit. For these situations, use this guide: whereparts form an interference fit, remove an amountof substrate material that is equal to half thethickness added by the dry coating film. In allcases, parts treated in this manner should bethoroughly performance tested.
23
24
Friction/wear
Corrosion barrier
• Fasteners
• Other
Electricalapplications
Steel (ferrous)
Steel (stainless)
Aluminum (die-cast)
Aluminum (wrought- bare metal)
Aluminum (anodized)
Babbitt metal
Bronze (sintered)
Cast iron
Non-metallic
Steel (ferrous)
Steel (ferrous)
Iron (cast)
Aluminum (cast)
Aluminum (wrought)
Brass, bronze
Steel
Aluminum
Copper
Degrease, grit blast to 100 µin/2.5 µm.
Degrease, grit blast to 100 µin/2.5 µm.
Degrease or alkaline wash, grit blast to 40µin/1 µm.
Degrease or alkaline wash, grit blast to 80-120 µin/2-3 µm.
Degrease or alkaline wash.
Degrease.
Bake to 260˚C/ 500˚F, degrease or alkalinewash.
Degrease, grit blast to 60 µin/1.5 µm.
Clean nondestructively.
Degrease, grit blast to 120 µin/3 µm, phos-phate and/or plate, apply primer/topcoats.
Degrease, grit blast to 120 µin/3 µm,phosphate, apply primer & topcoats.
Degrease, grit blast to 120 µin/3 µm, applyprimer & topcoats.
Alkaline wash, grit blast to 120 µin/3 µm, apply primer and topcoats.
Degrease, grit blast to 120 µin/3 µm, ano-dize if practical, apply primer and topcoats.
Degrease, grit blast to 120 µin/3 µm, applyprimer and topcoats immediately followingblasting.
Degrease, grit blast to 60 µin/1.5 µm, applytwo 0.0007 in/17.5µm coats with intermedi-ate cure at 120˚C/250˚F.
Alkaline wash, grit blast to 60 µin/1.5 µm,apply two 0.0007 in/17.5µm coats withintermediate cure at 120˚C/250˚F.
Degrease, grit blast to 60 µin/1.5 µm, applytwo 0.0007 in/17.5µm coats with intermedi-ate cure at 120˚C/250˚F.
Can be polished
Can be polished
Can be polished
Can be polished
Can be polished
Can be polished
Can be polished
Can be polished
Can be polished
None required
None required
None required
None required
None required
None required
Spark test (if insulating), ohms per square (if conductive)
Spark test (if insulating), ohms per square (if conductive)
Spark test (if insulating), ohms per square (if conductive)
Guide to application and processing techniques
Application Substrate Pretreatment Post treatment
In 1986, Whitford identified a need for alternativeproducts to traditional methods of post-treatingelastomeric seals and moldings. These con-
ventional treatments included polyamide andpolyester flocking agents, silicone solutions, fineparticle chalks, and specialty greases.
Whitford’s R&D technicians set a high priorityon these new products, and within months hadthe first product developed and tested. Theproducts have evolved over the years, andtoday are better than ever.
Whitford’s new products were designed tomeet increasing performance demands of auto-motive manufacturers including:
1. Reduction of coefficient of friction.
2. Suppression of noise generated by seals due to micromovement between the car doors and the car body.
3. Elimination of sticking of seals to car doors.
4. Protection of rubber and thermoplastics against the effects of weathering.
5. Offering of novel colors, appearances, andtextures.
In addition to these attributes, the new prod-ucts (marketed under Whitford’s “Xylan” tradename) are cost-effective, easy to apply througha variety of spray and brush techniques, and areavailable in waterborne, VOC-compliant formsengineered to meet the most vigorous environ-mental regulations in the world.
Who’s using Xylan?
Xylan coatings for flexible finishes have beentested and approved and are used by more than30 automotive manufacturers around the world.
As more and better coatings for flexible fin-ishes are developed by Whitford (a never-endingproject), more manufacturers are taking advan-tage of their benefits.
A variety of substrates
EPDM (ethylene-propylene-diene monomer)rubber is one of the most common substrates onwhich Xylan flexible finishes are used. Never-theless these coatings are also being used onmany other surfaces, including NBR, PVC, TPEs,TPOs, acrylics, ABS, and polyesters.
Pretreatment
Depending on the quality of the substrateand the performance requirements of the coat-ing, substrate pretreatment may be required.Adhesion of Xylan products can be optimized bysolvent degreasing, priming, corona discharge,plasma treatment, flame treatment, or throughmechanical abrasion.
Curing
Xylan coatings are easily cured by conven-
6. Whitford flexible finishes and the automotive industry
25
Whitford’s flexible finishes are used by major auto-motive manufacturers all over the world.
Xylan flexible finishes are ideal for applications suchas EPDM weatherstripping.
tional methods, although the fastest, most effi-cient, least expensive of all is by ultraviolet light.Whitford was the first coating company to devel-op UV-curable coatings for flexible substrates.
The UV cure has these advantages:
• Uses a fraction of the energy of conven-tional ovens.
• Once powered up, the UV-cure equipmentstabilizes in minutes, saving hours of time a conventional oven takes to reach full heat.
• Saves space by replacing the many feet ofa curing oven with a cabinet not much larger than an office desk.
• Does not impart heat to the substrate, allowing temperature-sensitive materials tobe used.
Typical applicationsXylan flexible finishes have an exceptional
track record in a diverse array of automotiveapplications. In glass-run channels, Xylan’sremarkable abrasion resistance ensures long-lasting, smooth, silent window operation com-bined with consistently low levels of friction.When used on trunk (boot) seals, this versatilematerial provides excellent release even in themost adverse conditions.
Additionally, Xylan protects door seals, bodyseals, and drip rails by providing superior exteri-or durability. These products have surpassedthe most rigorous automotive specifications forresistance to accelerated weathering and waterimmersion. Further, they have been engineered
to provide outstanding release characteristics,as well as to eliminate the “stick-slip” effect,which reduces noise attributed to the micro-movement of seals against glass and paintedbody panels.
Quality standards
Whitford is one of a select group of compa-nies which have achieved and maintained thehighest quality standards in the industry.
This commitment to the most exacting stan-dards is carried out by quality assurance teamsat each of Whitford’s worldwide facilities wherethese products are manufactured.
Choosing the right coating
Whitford supplies coatings which have beenformulated to solve specific problems on a vari-ety of substrates. The coatings are classifiedinto the following categories:
1. Glass-Run Applications: These productsare designed to withstand the abrasive forcesassociated with the movement of glass windowsalong seals during operation.
2. Weatherstrip Applications: These includecoatings for primary and secondary door seals,trunk (boot) seals, and hood (bonnet) seals.These coatings ensure freeze-release, weather-ing resistance, and noise suppression.
3. Appearance Applications: These coatingsare generally recommended for decorativeeffects, and have excellent weathering resist-ance. They are used for a colored, textured(soft feel), or metallic effect.
Note: Many Xylan coatings for flexible sub-strates have found use outside the auto industry.
26
Xylan flexible finishes are designed to withstand themost demanding climatic conditions that vehiclescan encounter, from blistering heat to sub-zero freez-ing, and still perform.
Thanks to Xylan, the absence of itch and squeak letsthe beauty of nature speak in its own quiet way.
Perhaps the most revolutionary change inthe world of textiles in several thousandyears was the invention of synthetic fibers.
The next most revolutionary change was theintroduction of surface treatments to enhance theperformance of textiles in many ways, such aswater repellency, release, strength, resistance tochemicals, etc. Whitford has been a leader inthe development of special coatings and finish-es for the textile industry (such as EterniTex®).
EterniTex coatings are typically a blend ofPTFE and other fluoropolymers reinforced by amatrix, designed to provide a wide range ofbenefits. Belts coated with EterniTex, for exam-ple, last up to ten times longer than the samebelts coated with PTFE.
Superior water repellency
There are many different treatments to helpprevent the passage of water through fabric.Some repel moisture better than others. Somelast longer. EterniTex offers a treatment thatworks better than most other treatments avail-able. It offers additional benefits, too:
• Increased, longer-lasting water repellency.
• Increased fabric strength.
• Outstanding protection against ultra-violet damage.
EterniTex also offers maximum release on high-temperature textiles. Typical application: high-temperature belting. EterniTex provides releaseup to 240˚C/465˚F and dramatically extendsservice life on a woven Kevlar® laminating beltcompared to the same belt treated with silicone.
Other formulations, designed for low-temper-ature belt applications, provide outstandingresistance to abrasion and wear as belts bendaround rollers and rub against the deck.
7. Whitford coatings and the textile industry
Superb resistance to UV has been designed intoEterniTex to prolong fabric life as well as protect fabric color.
EterniTex, with its superior water repellency, showsno signs of water penetration, even at 2,000 mm ofhydrostatic head (more than 3 times as much).
Coating “A”Coating “A” EterniTexEterniTex
Coating “A” at 600 mm of hydrostatic head: themoisture penetrates from below and shows clearlyon the top of the fabric.
27
Service life is extended by at least several times.Another benefit: controlled friction, which con-tributes to longer life. And EterniTex can bemade conductive to dissipate static discharge,always a threat to the workplace.
Superior belting reinforcement
Textiles coated with EterniTex are also usedas a reinforcing component to add strength toconveyor and power-transmission belts. TheEterniTex coating creates an internal lubricatingsystem within the weave of the fabric. Thisallows the fibers to move easily against eachother as the belt is subjected to stress andstrain, rather than to abrade each other. It alsoenables far greater capacity to absorb shockunder tension — without damage to the textile.
Superior thinking
The classic uses for textile coatings and fin-
ishes are well understood, and it is generally aquestion of finding the material that provides thebest solution for a particular application.
As new versions of EterniTex are developed,pioneering minds are taking these treated fab-rics into entirely new areas, where they are hav-ing a significant impact. For example:
• Reprographic textiles
• Gasket materials
• Filtration textiles
• “Quiet” textiles
• Anti-wicking fabrics (lighter, more efficient sails for racing boats)
• Breathable waterproof fabrics (tents, tar-paulins).
Thesesuperior coat-ings of Eterni-Tex are easilyapplied by allconventionalmethods usedin the textileindustry. Andthey are virtual-ly all VOC-compliant.
Note:Please seepage 21 forapplicationmethods relatedto fabrics.
28
A laminating belt coated with EterniTex for excellentrelease properties and longer belt life.
Coefficient of friction comparison
Uncoated textile belt
Belt coated with EterniTex
1.2
1.0
0.8
0.6
0.4
0.2
0
Coe
ffici
ento
ffric
tion
Extension (mm)20 40 60 80 100 120 140 1600
Uncoated textile versus same textile coated withEterniTex. The uncoated version tolerates only limit-ed deformation, while the coated version toleratesmore, easily doubling the life of the belt.
Comparison of shock resistanceof reinforcing textiles
used in elastomeric belting
Incr
easi
ngre
sist
ance
tosh
ock
Increasing stress
EterniTex-coated textile
Uncoated textile
EterniTex prevents wicking, reduc-ing the weight of sails (and its UVresistance protects colors, too).
That may sound like a simple task, but theanswer is more complicated*. If you judgeprice by the cost of a gallon, liter or kilo,
you will not only be wrong but may wind up pay-ing far more than you think. That’s because alower price for a given quantity or weight maymean a higher price per unit area of coverage.
The only valid way to compare the cost of acoating is to compare the cost of coverage of agiven area at a specific film thickness (normally25 microns/0.001 inch).
What gives a coating its coverage? Theanswer is the amount of solids by volume** itcontains (not solids by weight). And few coat-ings contain the same amount of solids. A typical (and real) example:
• Coating “T” costs $80.00 per gallon.Coating “X” costs $88.00 per gallon, or 10 per-cent more per gallon.
• Coating “T” has 13 percent volume solids.Coating “X” has 20 percent volume solids.
• 20 divided by 13 gives 1.54, so the gallonof Coating “X” has 54 percent more volumesolids, which means that “X” covers 54 percentmore square feet or meters than “T.”
• Coating “T” gives 209 square feet of cover-age. Since Coating “X” gives 54 percent more,it covers 321 square feet.
• $80 (the cost of “T”) divided by 209 givesa theoretical cost*** of 38.3 cents per squarefoot. $88 (the cost of “X”) divided by 321 givesa theoretical cost of 27.4 cents per square foot.
• You pay 10 percent “more” per gallon forCoating “X.” Yet, in terms of coverage (actualcost), Coating “T” is really 40 percent moreexpensive than Coating “X.”
There are a few other factors worth mention-ing that are not directly related to cost/coverage:
1. Cost also depends on transfer efficiency,the percentage of coating that actually reachesand remains on the part. And transfer efficiencydepends on several factors, including the formu-lation, the method of application used, the config-
uration of the part and the skill of the applicator. 2. The pretreatment you select can have a
significant effect on cost. And it will affect per-formance of the part.
*In some industrial applications, the coating maybe only a small part of the total cost because of thecost of the labor needed to mask, rack, multicoat andpackage (as well as the cost of packaging materials).
**Volume solids: all liquid coatings contain a vari-ety of solid materials. When the coating is cured andthe liquids driven off, only the solids remain. Weightsolids are different, so don’t be confused. Somesolid ingredients weigh more than others, but don’tcover as much area. Coverage depends on thethickness of the coating and the area covered, whichis volume, not weight.
***Theoretical cost assumes 100 percent transferefficiency in application of the coating.
The volume of one U.S. gallon represents 1604square feet of liquid at a thickness of 25 microns/0.001 inch. The liter represents 1000 squaremeters at one micron (or 40 square meters at 25microns). Obviously, these coverage figureschange proportionally with coating thickness. Withcoatings that are less than 100 percent solids (allliquid coatings), these figures decrease propor-tionally. Use the following formulae to calculatecoverage:
Coverage/US gallon (in sq. ft.) = (1604 ft2/mil) x (% solids by volume)
film thickness in mils
Coverage/liter (in sq. mtrs.) = (1000 m2/micron) x (% solids by volume)
film thickness in microns
Finally, cost per unit of area =Cost/gallon or liter
coverage/gallon or liter
Calculating coverage and cost
8. Calculating the real cost of a coating
29
Ask for a copy of Whitford’s Cost Calcu-lator, which comes as an Excel spreadsheetand automatically calculates everything youmight want to know about a coating’s coveragewith the simple click of the mouse.
The so-called “Green Movement” is here tostay. And well it should be. Most of ushave ignored the environment and con-
tributed to the contamination of the world inwhich we live. One of the manifestations is theemphasis on VOCs — Volatile Organic Com-pounds* — and the need to lower and controlemission of these chemicals.
Whitford supports this and presents the fol-lowing to help you understand the restrictionsand measure the VOCs you may be emitting.
What are VOCs?
VOCs are those ingredients in a paint orcoating, defined as photochemically reactive bythe USA’s Environmental Protection Agency, thatescape into the atmosphere during the drying orcuring process. With some exceptions, organicsolvents are classified as VOCs.
In general, Whitford coatings come underthe “Extreme Performance” industry guideline.(“Extreme Performance” includes coatingsexposed to any of the following: the weather allof the time, temperature consistently above95°C/205°F, detergents, abrasive and scouringagents, solvents, corrosive atmospheres or simi-lar environmental conditions.) This guidelinecalls for the following limits on VOCs:
• Pigmented coatings: normal use . 3.0 lb/gal.• Pigmented coatings:
extreme performance. . . . . . . . . . . 3.5 lb/gal.
• Clear coatings: . . . . . . . . . . . . . . . . 4.3 lb/gal.
Note: some countries measure VOC limits inmetrics (grams per liter). To make the conver-sion, simply multiply the lb/gal by 120. For ex-ample: 3.5 lb/gal x 120 = 420 gms/ltr.
A few more things to rememberIn most of the United States, regulations per-
mit the averaging of VOCs emitted during a 24-hour period. If you use a low-VOC material, youcan also use the same amount of a high-VOCmaterial (as high as the other was low) — pro-vided the total amount of VOCs produced during
that period does not exceed the local limits.
There is little question that present VOC lim-its will be tightened as time goes by.
Southern California, with severe air qualityproblems, has led the way to more stringent reg-ulations. Recently, the state raised the transferefficiency requirement for wood-spray equip-ment from 40 percent to 65 percent. And legis-lation now limits VOCs for the “extreme perform-ance” category for coating metal parts andproducts as follows:
Air-dried Baked lbs/gal gms/ltr lbs/gal gms/ltr
3.5 420 3.0 360
The calculations for these VOCs, of course,exclude the water and other exempt compounds.
Not all the news is bad
Whitford has spent considerable time (andfunds) engineering new coatings that conformto, and surpass, the most stringent regulations inthe world. Many of our coatings are low-VOCand/or waterborne. We’re developing moreproducts of this type, which will be announcedas they come on stream.
If you’d like information on any of these prod-ucts, or have questions regarding VOCs, pleasecontact your Whitford representative.
How to measure VOCs
There is a simple formula for calculating theamount of volatile organic compounds in anysolvent-based coating:
VOCs =Density (lb/gal) x (1 - % solids by weight)
The following examples show how the formu-la works in several types of coatings. (Note:these are white coatings with the ratio of Ti02 toresin at 1 to 1; the assumed density of theorganic solvent at 7.5 lb/gal; the density of theresin solids at 9.5 lb/gal.)
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9. Protecting the environment
*Since “VOC” is an American term, the formulae areexpressed in the units of measurement used by US regula-tory authorities.
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By weight
40% solvent
60% solids
Specifications% solids by weight . . . . 60% solids by volume . . . . 43.1Density. . . . . . . . . . . . . . 10.67 lb/galCoverage. . . . . . . . . . . . 691 sqft/gal @1.0 mil
To calculate the VOCs in this coating, substi-tute the correct numbers in this formula:
VOCs = 10.67 lb/gal x (1 - 0.60)or
VOCs = 10.67 lb/gal x 0.4 = 4.28 lb/gal
By weight
25% solvent
75% solids
Specifications% solids by weight . . . . 75% solids by volume . . . . 60.3Density. . . . . . . . . . . . . . 11.93 lb/galCoverage. . . . . . . . . . . . 691 sqft/gal @1.0 mil
The formula remains the same:
VOCs = 11.93 lb/gal x (1 - 0.75)or
VOCs = 11.93 lb/gal x 0.25 = 2.98 lb/gal
Solvent-borne coatings
High-solids coatings
By weight
20% solvent
60% solids
Specifications% solids by weight . . . . 60% solids by volume . . . . 44.4Density. . . . . . . . . . . . . . 10.98 lb/galCoverage. . . . . . . . . . . . 712 sqft/gal @1.0 milWater weight @20% . . . 2.20 lb% water volume
@8.33 lb/gal . . . . . . . . .0.26 (2.20/8.33)
As before, substitute the values in the formulaas we do here:
VOCs = 10.98 lb/gal x (1 - 0.6 - 0.2)(1 - 0.26)
orVOCs = 10.98 lb/gal x 0.2 = 2.97 lb/gal
0.74
Waterborne coatings
Volatile Organic Compounds are nowcalculated in terms of pounds per gallon ofcoating less water and less exempt com-pounds (of which there are few).
After removing any water and exemptcompounds, the material remaining isexpanded to the gallon equivalent — givinga VOC reading higher than the actual VOCsfor that gallon.
In this example, the formula becomesslightly more complicated:
VOCs = Density x (1 - %solids by weight-%water by weight)
(1 - % water by volume)
20% water
If you’d like information on low-VOC products, orhave questions regarding VOCs, please contactyour Whitford representative.
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Whitford manufactures the largest, mostcomplete line of fluoropolymer coatingsin the world — as well as a group of
inorganic coatings.
Fluoropolymer coatings first became knownas cookware coatings for their release and easycleanup properties. They were not uniform andsuffered from poor adhesion and durability.
Over time, and especially within the past fewyears, cookware coatings have evolved intoincreasingly sophisticated systems.
Here is a simplified list of Whitford products.
Xylan is Whitford’s brand name for a widerange of one-, two- and three-coat conventionaland reinforced nonsticks. These coatings comein many different variations that offer a wide vari-ety of performance levels at remarkably lowprices.
Whitford uses the 7000 and 8000 designa-tions for all Xylan coatings used for food contactor food-associated applications.
In the United States, the Food & DrugAdministration (FDA) regulates coatings thatcome into contact with food. In other countries,
similar regulatory authorities serve essentiallythe same purpose. While a complicated issue, itis worthwhile mentioning that any coating soldby Whitford for use in food applications meetsthe most stringent requirements of authoritiesthroughout the world.
For answers to any questions in this compli-cated area, please contact Whitford’s RegulatoryAffairs Department.
Quantum2 is Whitford’s nonstick “doublyreinforced to outlast all conventional nonsticks”.Reinforced internally with hard ceramic particles,it has twice the durability of other reinforcednonsticks (that’s why the “2” in “Quantum2”). Itis ideal for cookware and bakeware.
QuanTanium is “reinforced with titanium tostand up to almost anything”. That’s becausecertain alloys of titanium, the lightest, toughest
10. Whitford’s wide range of other products
Xylan: one-coat products.
Xylan Plus: two-coat products.
Xylan Eterna: three-coat products.
Xylan on the inside, Xylac on the outside. Whitfordcoatings are used on cookware and bakeware incountries all around the world.
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metal known, are many times harder than thealuminum and steel used in the pots and pansthemselves. While not as resistant to wear andabrasion as Eclipse, it consistently outperformsother internally reinforced cookware coatings.
Tests show that Eclipse outlasts other inter-nally reinforced coatings by a significant factor.The reason: a unique primer reinforced with ahigh percentage of materials virtually as hard asdiamonds. The midcoat also contains the rein-forcing materials, leaving the topcoat dedicatedentirely to “release”.
Eclipse is ideal for all types of aluminumcookware and bakeware, from smooth to grit-blasted to hard-anodized.
It was Excalibur that took nonstick coatingsto the top end of the cookware market. That’sbecause Excalibur is far more than a nonstickcoating. It is a unique system. What makes itdifferent from — and superior to — all other non-sticks is that it is externally reinforced.
The substrate is blasted with an abrasive.Then, white-hot particles of stainless steel aresprayed onto the surface. Welded to it, theyform permanent “peaks and valleys” that pro-vide a tough base for the nonstick coatings.
A first coat of tough nonstick is applied, set-tling down into the valleys. Then, a second andthird coat are applied, filling in all the valleysand covering the peaks. The coatings are nowbonded to the surface for extra durability.
Excalibur combines the strength of stainlesssteel with the low friction and release character-istics of nonsticks.
The Suave line includes Whitford’s “soft-touch” and “silk-touch” coatings. Suave offersnew dimensions to the aesthetic and tactile pos-sibilities of design. The soft-to-the-touch textureprovides a firm, comfortable grip to help preventslipping. Suave comes in an unlimited range of colors (color-matching is easy) and has goodresistance to wear.
Suave is user-friendly, easily applied to phenolic, ABS, melamine, PVC, methacrylates,nylon, aluminum, iron, stainless steel, and curesat low temperatures.
Acquired from ICI, Ultralon products come inone- and two-coat systems for industrial applica-tions such as conductive multicoats for fuserand release rollers on photocopiers.
The secret of Excalibur’s durability: a patented stain-less-steel alloy that forms a hard matrix into whichthree coats of tough nonstick are sprayed.
A Suave coating on many items provides a hand-some, matte, rubber-like surface that improves gripand helps prevent things from slipping. And Suavecomes in many eye-catching colors!
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Xylac coatings are high-temperature decora-tive finishes for cookware and associated prod-ucts, bridging the gap between acrylic paintsand more expensive porcelain coatings whilemaintaining resistance to all household cleaningand dishwashing compounds.
All are based on organic polymers with out-standing high-temperature properties, unlimitedcolors, one-coat coverage, excellent gloss reten-tion at elevated temperatures, adhesion to allmetallics, flexible cure schedule(s), minimal sur-face preparation, and high impact resistance.
Dykor 200s and 600s are combinations ofresins from the polyvinylidene (PVDF) family andappropriate fillers, typically graphite and mica.When combined and applied at 0.6 mm/25 mils,the system provides outstanding chemical, cor-rosion and UV resistance.
Dykor 700s are attractive, functional powdercoatings often used for wire goods and smallelectric appliances. A range of formulations isavailable offering various colors, levels of easy-clean, and operating temperatures. Dykor 800sare high-build fluoropolymer powder coatings forchemical resistance and high release.
Xylar coatings are thin-film surface-protec-tion finishes, ideal for extending the lives ofparts where environments are extremely hot,corrosive and/or abrasive.
Based on an alloy of ceramic and metallicmaterials, Xylar forms a thin, hard, high-tempera-ture-stable, sacrificial ceramic metallic barrier.In many cases, these coatings enable parts tobe used in environments that would normallypreclude their use. In others, they enabledesigners to replace expensive super alloys withless costly metals coated with Xylar. Topcoatsmay be added to modify or improve the propertiesof the basecoats (such as increasing corrosionresistance or decreasing coefficients of friction).
Dykor protects against many hostile environments. Itcomes in both liquid and powder forms.
Xylar 2 Silver protects against high-temperature oxida-tion, provides sacrificial corrosion protection andresists atmospheric and salt-water corrosion.
Xylac decorative exterior coatings offer many optionsto add eye appeal to products, from high-gloss clearcoats to colorful hammertone finishes.
Late in 2003, Whitford reached an agreementwith the shareholders of Polymeric Systems,Inc. (PSI), to purchase the company. Poly-
meric Systems, Inc. develops and manufactureshigh-performance sealants, caulks, and epoxyadhesives. Its leading product line is a 2-partepoxy putty stick, offered in a range of formula-tions, each for specific applications.
The origins of PSI date from 1959, when TedFlint, a chemical engineer, and a partner starteda business to manufacture adhesives andsealants. That business was sold to TeledyneCorporation in 1967.
Ted Flint then formed Polymeric Systems in1969. Its first product was a line of sealants forthe insulating glass industry.
In 1972, Mr. Flint developed a 2-part epoxyputty product with an innovative core/shell (cylin-der form) for easy user application. Strongpatent protection was secured for the product
technology, with additional patents obtained forimprovements incorporated into the expandingproduct line. The company experienced steadygrowth through its sale in 2003.
The company was merged into Whitford andis now housed in Whitford’s headquarters inPennsylvania, due west of Philadelphia. Poly-meric Systems’ operations occupy 80,000square feet in Whitford’s multi-story building onsixty-three acres of property (which allows sub-stantial room for expansion).
While PSI does private-label and toll manu-facturing, it also markets its own products.
PSI-labeled products include a range of con-struction sealants and epoxy putties, pastes andgels (all of which are available for private label).PSI’s entire product line is either low in solventsor solvent-free. A new line of non-irritatingepoxy adhesives has just been introduced andpatents filed on this unique material.
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11. Polymeric Systems, Inc.
One of PSI’s leading product lines is a series of 9 patented Epoxy Putty Sticks, each custom-formulated to pro-vide fast, easy and permanent repairs to a series of materials from concrete to wood to plastic to metal.
PSI’s epoxy putty sticks consist of pre-meas-ured components (an activator and base) incylinder form, allowing the required portion to becut, then mixed and molded by hand prior touse. This line has evolved into a family of nineproducts specifically formulated to adhere to avariety of surfaces — including metals, wood,plastic, fiberglass and concrete — and for arange of temperature and moisture conditions.There is even a version that can be mixed andapplied under water for plumbing or marine use.
In recent years, the Company has developedsome PSI-branded sales of epoxy sticks throughdo-it-yourself (“DIY”) retail channels.
PSI has two other major product-line offerings:urethane- and silicone-based elastomeric seal-ants. These are reactive products of single, 2-part, and multi-part components, packaged inliquid or paste form in containers from tubes todrums. The primary markets for these elasto-meric sealants are the construction, marine,automotive, and wood construction industries.
In 1995, PSI brought to market a new pack-aging system called SUM PAK.® This is a single-use pack of a two-component reactive adhesiveor sealant. The package holds the two compo-nents in separate pouches until pressure isapplied (such as with a pencil or pen pressingover them), at which point the components arereleased into a series of chambers connectedwith mixing holes. The top is cut with scissors,and the same pencil or pen moves up the pack-age, forcing the two components through themixing holes until they reach the top, thoroughlymixed (actually achieving molecular mixing).The glue is applied as needed. The remarkablepack is easy to use, with no mess, and offers anextended shelf life.
PSI's production is geared to accommodatevarying batch sizes to increase flexibility — arequirement for most private-label manufacturers.Many of these systems have been custom-designed for the PSI products, particularly theepoxy putty sticks. Its packaging systemscapabilities include tube and cartridge fillingsystems, pail filling, labeling and capping, blisterpacks, as well as a custom-designed form, filland seal machine for their SUM PAK products.
To no small extent, the products producedby PSI overlap those produced by Whitford(especially in terms of raw materials), so thecoming together of the two companies madegood sense from every perspective — and fromthe very beginning.
Sili-Thane 801 offers all the benefits of silicone andpolyurethane-type sealants with none of the disadvan-tages. There are no solvents or isocyanates. VOCsare less than 1%. 801 adheres well to a wide rangeof substrates, resists discoloration and is paintable.
PSI’s SUM PAK®: The patented package uses up-ward pressure to burst the two pouches holding sep-arate ingredients, which are then mixed — perfectly— by the channels through which they pass on theway to the top. “Molecular” mixing in a matter of afew seconds!
QuikWood® epoxy patches wood easily and quickly.It can be sanded, stained and painted.
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Whitford Corporation was founded in WestChester, Pennsylvania, in 1969. Sixmonths later, Whitford Plastics Limited
was founded in Runcorn, England. From thestart, Whitford has taken a global approach to itsbusiness.
Since then, Whitford has grown into a world-wide organization with manufacturing facilities inseven countries, direct employees in eight more,and agents in an additional 25. We operate inmore than fifty countries.
What business are we in?Some companies develop products in the
abstract — and then bend problems to fit theproducts. At Whitford we take the oppositepoint of view.
We believe that we are in the business ofsolving problems more than the business of sell-ing products. The coatings we engineer aresimply the vehicles by which we solve problemsfor our customers.
We believe that the way to a better productis to start with a specific problem, then create aproduct specifically designed to solve it.
It is this approach to the business that hasled Whitford to have the largest, most completeline of fluoropolymer coatings in the world —despite the fact that one of our competitors islarger than we are in terms of annual turnover.
Our worldwide mission statement summa-rizes what we do:
“We provide attentive, innovative solutions to our customers’ problems via
our products and related technology.”
This philosophy, of course, demands a seri-ous commitment to research and development.
One advantage that Whitford enjoys is thatwe are a private company, so we can allocateour funds as we see fit. As a result, we commitan annual average of at least six percent of oursales to R&D, something disinterested share-holders of a public company (who expect largerdividends every quarter) would be unlikely topermit.
May we help?
You may have a design problem that a fluo-ropolymer coating could solve. If so, we’d liketo hear from you. Please tell us about the prob-lem in sufficient detail so we can determine if wehave the precise product to solve it.
If we don’t, we’ll create one.
12. A word from our sponsor
Whitford suggests that customers send samples oftheir finished products for laboratory testing to assuremaximum coating performance.
Whitford’s Rheometer measures the flow and deforma-tion of component materials in a coating formula, keyto film formation, curing and aging.
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These definitions are given primarily in theirrelation to high-performance fluoropolymercoatings and their use in this publication.
Abrasion: A wearing, grinding, or rubbingaway by friction. Pages 3, 5, 25, 26, 27, 33.
Additives: Materials added to coatings toenhance certain properties. Page 13.
Alkaline wash: Cleaning process thatemploys a high pH solution (caustic). A goodchoice for parts with little buildup of contami-nants. Pages 19, 20, 24.
Aluminum oxide: Hard particulate mediumused in grit blasting to clean and roughen sur-faces that are to be coated. Pages 19, 41.
Anodizing: Creating a hard oxide layer onaluminum parts via an electrolytic process.Unsealed hard anodized surfaces have a porosi-ty that makes them excellent substrates for coat-ings. Page 20.
Babbitt metal: a soft alloy of tin, copper andantimony. Page 24.
Binder: Tough polymer that acts as an adhe-sive to join elements of matrix coatings. Pages2, 3, 4, 5, 12, 23, 39, 40.
Boundary lubrication: Condition in which alubricating film between sliding surfaces has lostits hydrodynamic property due to heat, pressureor low speed. As a result, the surfaces are virtu-ally touching, separated only by a layer of lubri-cant too thin to be effective. Potential for metal-to-metal contact and damage to surfaces isgreat. Page 8.
Break in: Initial wear of mechanical compo-nents when large surface asperities (peaks) cancause high friction and wear rates. Page 15.
Brinelling: Surface fatigue of steel compo-nents that undergo cyclic stress, which causesminute flexing resulting in work-hardening of thesurface. Eventually, brinelling may cause sur-face cracking or spalling. Page 5.
Buffing/Burnishing: Process of polishing acured coating to enhance release and low fric-tion properties. Pages 9, 10, 23.
Carrier: Liquid portion of a coating in whichsolids are dissolved or suspended. Pages 3, 4,20, 22.
Cold flow: Tendency of plastic materials tomigrate slowly under heavy loads and/or overtime. Pages 3, 12.
Conductor: Material that can support flow ofelectrical current. Coatings are normally insula-tors, but can be modified with certain fillers andpigments to make them conductive. Page 13.
Corrosion: Process of metal decomposition(oxidation) in which metal ions are united withoxygen to form metal oxides. Fluoropolymercoatings provide excellent barriers against mostcorrosives. Pages 1, 2, 3, 4, 5, 6, 7, 9, 11, 12, 14,16, 17, 19, 20, 23, 24, 34.
Crosslinking: Quality of thermosetting plasticresins in which polymer chains combine duringcuring process. In general, the greater thecrosslinking, the tougher and more chemicallyresistant the coating. Page 23.
Cryogenic: Temperatures less than -130°C/ -200°F. Bonded dry-film lubricants continue toperform at these temperatures. Pages 5, 12.
Index and glossary
Whitford‘s unique Gyrograph provides a sensitivemeasure of abrasion and coating adhesion, especial-ly of intercoat adhesion (a common source of failure).
39
Curing: Process of bonding or fusing a coat-ing to a substrate. Pages 1, 4, 18, 21, 22, 2526, 30, 37.
Dielectric strength: Ability of a coating toresist the passage of direct electric current.Page 13.
Dip/spin: Coating application technique inwhich small parts are placed in a basket that islowered into a coating bath, then raised andspun to remove excess coating. An economicalsystem for coating high volumes of small parts.Pages 3, 4, 11, 20, 21.
Dry (solid) lubricants: Solid materials such asPTFE, Molybdenum Disulfide (MoS2) and graphitethat have low coefficients of friction. Pages 2, 7.
Elastomers: Any of various elastic sub-stances resembling rubber. Page 18.
Electrostatic spray: Spray applicationprocess in which the coating and part to becoated are oppositely charged; process pro-vides excellent “wrap” of coating around thepart, even on sides opposite the spray gun.Page 21.
Engineering plastics: Plastic resins that havehigh-performance properties such as high tem-perature stability, hot hardness, abrasion resist-ance, and corrosion resistance. Page 2.
EPDM: Ethylene-propylene-diene monomer,an elastomeric substitute for rubber used exten-sively in the automotive industry. Pages 18, 25.
Epoxy: A flexible resin, usually thermosetting,made by polymerization of an epoxide and used
chiefly in coatings and adhesives. Pages 18, 35.
Fabrics: Woven or nonwoven materials thatcan be impregnated with fluoropolymer coatingsto impart low friction, improve chemical resist-ance, and increase strength. Pages 18, 19, 21,28.
FEP (fluorinated ethylene propylene): A ther-moplastic member of the fluoropolymer family ofplastics. FEP has the best nonstick and nonwet-ting properties of these materials. Pages 3, 4,13.
Fillers: Pigments and other solids used toalter properties of coatings. Pages 3, 4, 17, 34.
Flashing: A brief subcure (at lower tempera-tures than the final cure) to drive off solvents/carriers prior to full cure. This helps preventbubbling. See “Partial cure.” Pages 1, 21, 22.
Fluoropolymers: Family of engineering plas-tics containing fluorine, characterized by highthermal stability, almost universal chemical resis-tance and low friction. Pages 2, 4,18, 23, 27.
Fretting: Wear phenomenon caused by vibra-tion among tightly clamped or fastened sur-faces. Pages 10, 11, 19.
Friction (dynamic): Resistance to continuedmotion between two surfaces; also known assliding friction. Pages 1, 2, 3, 4, 5, 6, 7, 9, 11,12, 13, 15, 16, 18, 23, 24, 25, 26, 28, 33, 34.
Friction (static): Resistance to initial motionbetween two surfaces. Pages 1, 2, 3, 4, 5, 6, 7,9, 11, 12, 13, 15, 16, 18, 23, 24, 25, 26, 28, 33,34.
Graphite: Carbon-based dry lubricant that ispreferred for high-temperature applications.Pages 2, 3, 4, 7, 13, 34.
Hot hardness: Ability of a coating to retainhardness and wear resistance at elevated tem-peratures. Usually a characteristic of coatingsbased on thermosetting resin binders. Page 38.
HVLP (high volume, low pressure): A type ofspray gun utilizing high pressure in combinationwith low air velocity to increase transfer efficien-cy and reduce air pollution. Pages 4, 20.
Hydrogen embrittlement: Embrittlement ofcarbon steel caused by absorption of atomichydrogen in plating, pickling or acid cleaningprocesses. Pages 11, 19.
Kesternich: German scientist who developedthe Kesternich Cabinet and test method used for
Dip/spinning is ideal for small, complicated parts.
acid-rain simulation (DIN 50018). Page 39, 40.kN: Kilo-Newton, a measure of force, also
expressed as “pounds force” (lbf). Page 14.
lbf: Pounds force, a measure of force, alsoexpressed as “kilo-Newtons” (kN). Page 14.
µ: One micron, a millionth of a meter. Alsoexpressed as µM, or micro-meter. Page 24.
µ inch: One micro-inch, a millionth of aninch. Page 24.
Matrix coating: One in which some ingredi-ents, such as the lubricant (PTFE), which is soft,are enveloped in others (the matrix, such asharder, more wear-resistant binders). Pages 3,4, 8, 15.
Moly, moly disulfide, molybdenum disulfide,MoS2: Four names for the same naturally occur-ring substance that has good low-friction andhigh load-bearing properties. Pages 2, 3, 4.
Noise dampening: The absorption of soundvibrations. Xylan coatings form good noise-reducing surfaces. Page 12.
Oleophobic: Oil-shedding. Page 5.
Partial cure: A process sometimes utilizedwhen multiple layers of fluoropolymer coatingsare to be applied. The first coat is incompletelycured. The second coat is applied and both arefully cured together. See “Flashing”. Page 39.
PFA (perfluoroalkoxy): Thermoplastic mem-ber of fluoropolymer family of engineering plas-tics, characterized by excellent release and lowfriction. Pages 3, 4, 13.
Phenolic: A resin or plastic, usually thermo-setting, made by condensation of a phenol withan aldehyde and used for molding, insulating,coatings and adhesives. Pages 18, 33.
Phosphating: Surface pretreatment used onferrous parts that provides a very thin crystallinefilm that enhances both corrosion resistance andadhesion. Pages 19, 20.
Polymer fume fever: 24-hour flu-like symp-toms (with no known long-term effects) causedby inhaling the gases released during fluo-ropolymer decomposition. Page 23.
Post cure: A second cure at high tempera-ture to enhance specific properties such asrelease and nonwetting. Page 23.
Postforming: Process of shaping parts after acoating has been applied and cured, a tech-nique commonly used with stamped, blanked, orspun parts. Page 23.
Powder metal: Material formed by compres-sing metal particles and heating (sintering) tosolidify and strengthen them. Pages 13, 14.
PPS (Polyphenylene sulfide): A thermoplasticengineering polymer second only to PTFE inchemical resistance. In fact, PPS is unaffectedby any solvent to 400˚F/205˚C. Page 18.
Preheating: Warming of parts prior to appli-cation of coating, recommended when adhesionis critical and when parts are being coated inhumid atmospheres. In some cases, this tech-nique can be used to achieve higher-than-nor-mal film builds. Pages 20, 23.
Preloads (for fasteners): The “tightness” of afastener equals the make-up energy appliedminus the energy required to overcome frictionat the fastener’s bearing surfaces and threads.Page 11.
Pressure spraying: Coating technique similarto siphon spraying, except that the coating isdelivered from a pressurized pot to the spraynozzle under positive pressure. Generally usedfor high-volume production. Page 24.
Pretreatment: Processes for cleaning andconditioning a substrate to be coated. Next tothe choice of coating, this may be the mostimportant factor in the use of high-performance
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Whitford keeps Kesternich cabinets running virtuallyall the time at several of its research laboratoriesaround the world.
coatings. Pages 19, 20, 25, 29.PTFE (polytetrafluoroethylene): A thermo-
plastic member of the fluoropolymer family ofplastics. PTFE has the lowest coefficient of fric-tion of any known solid and the highest tempera-ture resistance of the fluoropolymers. Pages 3,4, 5, 6, 7, 8, 9, 10, 13, 16, 19, 23, 27, 28.
PV, limiting PV (LPV) factor: Mathematicallimit of a coating’s load-carrying ability and wearresistance under bearing conditions. Pages 7,8, 11, 23, 25, 33, 34.
PVDF (Polyvinylidene fluoride): High-molecu-lar-weight thermoplastic of vinylidene fluoridewith greater strength, wear resistance and creepresistance than FEP, PFA or PTFE. Page 34.
Resistance (electrical): The oppositionoffered by a coating to the passage through itof an electric current. Pages 1, 2, 3, 5, 10, 11,12, 17, 20, 22, 23, 26, 27, 28, 33, 34.
Salt fog: ASTM B-117 test procedure thatsimulates the corrosive environment caused byroad salt and marine spray. Pages 10, 11.
Sand blasting (also grit blasting): Surfacecleaning and roughening process that providesa mechanical “tooth” to aid coating adhesion.Media include aluminum oxide, carborundum,even crushed walnut shells. The medium mustbe chosen to match the substrate and the for-
eign material on the substrate to be removed.Pages 19, 20, 23.
Static electricity: An imbalance of positiveand negative charges usually associated withtwo nonconductors rubbing together. Page 5.
Stick-slip (chatter): Unstable sliding conditionin which movement of one part over anotherstarts and stops, caused by temporary overcom-ing of static coefficient of friction. Page 26.
Substrate: Any surface to be coated. Thiscan include metals such as steel, cast iron,bronze, brass, aluminum, stainless steel, chro-mium, and (with special precautions) nickel.Paper, most plastics, wood, leather, fabrics, andglass can also be coated. Pages 1, 3, 4, 10, 18,19, 20, 21, 22, 23, 24, 25, 26, 27, 33, 36.
Thermoplastic: Plastic resin that softenswhen reheated. Pages 3, 25.
Thermoset: Plastic resin that crosslinks dur-ing cure so that it does not soften when reheat-ed. Pages 3, 5, 12.
Transfer efficiency: The amount (percentage)of a coating that actually reaches and stays onthe part being coated. Some coating methodsgive far higher transfer efficiency than others.Pages 20, 21, 29, 30.
Volatile organic compounds (VOCs): Theingredients in a paint or coating, defined as pho-tochemically reactive by the USA’s Environmen-tal Protection Agency, that escape into theatmosphere during the drying or curing process.Pages 20, 30, 31.
Wear: Deterioration by friction (abrasion,spalling, cutting, fretting). Pages 1, 2, 3, 4, 5, 6,7, 8, 9, 11, 15, 16, 19, 22, 23, 24, 27, 33.
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Salt-fog cabinets perform an ongoing and importantrole at Whitford in the development of fastener-classcoatings with better resistance to corrosion.
For more information...While this document may seemlengthy, it is only scratching the sur-face of the knowledge that we haveacquired over the years.Whitford offers many brochures, flyersand the like with far greater detail onspecific subjects.If you’d like more information on agiven subject, please contact us.
NON-WARRANTY: THE INFORMATION PRESENTED IN THIS PUBLICATION IS BASED UPON THE RESEARCH AND EXPERIENCE OFWHITFORD. NO REPRESENTATION OR WARRANTY IS MADE, HOWEVER, CONCERNING THE ACCURACY OR COMPLETENESS OFTHE INFORMATION PRESENTED IN THIS PUBLICATION. WHITFORD MAKES NO WARRANTY OR REPRESENTATION OF ANY KIND,EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTIC-ULAR PURPOSE, AND NO WARRANTY OR REPRESENTATION SHALL BE IMPLIED BY LAW OR OTHERWISE. ANY PRODUCTS SOLDBY WHITFORD ARE NOT WARRANTED AS SUITABLE FOR ANY PARTICULAR PURPOSE TO THE BUYER. THE SUITABILITY OF ANYPRODUCTS FOR ANY PURPOSE PARTICULAR TO THE BUYER IS FOR THE BUYER TO DETERMINE. WHITFORD ASSUMES NORESPONSIBILITY FOR THE SELECTION OF PRODUCTS SUITABLE TO THE PARTICULAR PURPOSES OF ANY PARTICULAR BUYER.WHITFORD SHALL IN NO EVENT BE LIABLE FOR ANY SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES. WC1/06
How to contact WhitfordWhitford manufactures in 7 countries, has em-ployees in 8 more and agents in an additional 25.To find the office nearest you, please visit ourwebsite: www.whitfordww.com or email us [email protected].
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