Eaton Corporation Airflex Division 9919 Clinton Road Cleveland, Ohio 44144-1077 Phone (216) 281-2211 Fax: (216) 281-3890 Technical Information Y Clutches and Brakes Y-1 Clutch and Brake Functions Y-2 Friction Couples and Materials Y-3 Drum and Disc Materials Y-4 Thermal Considerations Y-5 Wear and Squeal Y-6 Mounting and Alignment Y-7 Balancing Y-9 Control Devices Y-10 Air Supply Y-11 Product Elastomers, Selection Procedures Y-12 Service Factor Tables Y-14 Table of Formulas Y-17 Units of Measure, Symbols and Conversions Y-19 Multiples of SI Units Y-20 Copyright Eaton Corporation, 1997. All Rights Reserved.
Transcript
Eaton CorporationAirflex Division9919 Clinton RoadCleveland, Ohio 44144-1077
Phone (216) 281-2211
Fax: (216) 281-3890
Technical Information Y
Clutches and Brakes Y-1
Clutch and Brake Functions Y-2
Friction Couples and Materials Y-3
Drum and Disc Materials Y-4
Thermal Considerations Y-5
Wear and Squeal Y-6
Mounting and Alignment Y-7
Balancing Y-9
Control Devices Y-10
Air Supply Y-11
Product Elastomers, Selection Procedures Y-12
Service Factor Tables Y-14
Table of Formulas Y-17
Units of Measure, Symbols and Conversions Y-19
Multiples of SI Units Y-20
Copyright Eaton Corporation, 1997.All Rights Reserved.
Y - 1 Copyright Eaton Corporation, 1995, All rights reserved.
Clutches and Brakes
Clutches and Brakes
A clutch is a device which transfers energyfrom one rotating shaft to another in orderto perform some useful work.
In the simplest terms, a clutch can bethought of as a starting device because thatis what happens when a clutch is engaged.But, more importantly, while engaged it istransferring energy. The clutch takes energyfrom a power source such as an electricmotor or engine and transfers it to where itis required. The power source is referred toas the prime mover because it is the pri-mary source of energy. A clutch is engagedfor one reason — to perform some usefulwork.
A clutch consists of two halves: a drivinghalf and a driven half. The driving half is at-tached to the power source and rotates withit. The driven half is attached to the shaftrequiring the energy and is started witheach engagement. In addition, the clutchmust have some means of engaging anddisengaging the two halves.
A brake on the other hand, is a devicewhich absorbs energy that is stored in rotat-ing and linear moving components and/orprevents an energy transfer to them.
Again, in simple terms, a brake can be thoughtof as a stopping device because that is whathappens when a brake is engaged. Like a clutch,a brake also consists of two halves: a driven halfand a stationary half. The driven half is attachedto the rotating and linear moving bodies fromwhich energy must be removed. The stationaryhalf is reacted so that it cannot move. The brakealso has a means of engaging and disengagingthe two halves.
Clutch and brake engagement is made by con-necting the two halves. Since one half is rotatingand the other is stationary, the halves will slideor slip relative to each other.
When there is no relative motion betweenclutch halves, the clutch is locked and max-imum energy is transferred to the workshaft. If a relative speed differential is al-lowed to exist between each half, only par-tial energy is transferred, and the device isreferred to as a slip clutch.
When there is no relative motion betweenbrake halves, the brake is set and maxi-mum energy has been removed from thedriven components and/or prevents an en-ergy transfer to them. The latter situation isreferred to as a holding brake. If a relativespeed differential is allowed to exist be-tween each half, only partial energy is ab-sorbed, and the device is referred to as adrag or tension brake.
The connection between clutch and brakehalves for Airflex products is dependentupon a frictional couple. The product of theresulting frictional force and the distance toits axis of rotation determines the torquecapacity of the clutch or brake. The torquemagnitude determines the amount of en-ergy that can be transferred by the clutch orabsorbed by the brake.
Heat is generated whenever torque is trans-mitted and a speed differential exists be-tween the clutch and brake halves. Theability to absorb and dissipate this heat de-termines the thermal capacity of the clutchand brake.
A clutch or barke must not only have sufficienttorque capacity to transfer the required energy,but must also have sufficient thermal capacityto handle the heat generated due to slippage.
Y - 2Copyright Eaton Corporation, 1995, All rights reserved.
Clutch and Brake Functions, Friction
Brake Functions
Brake functions closely parallel those of clutches, except they absorb anddissipate the energy of the driven shaft. These functions include:
Holding function - In this function the brake prevents an energy transferto the driven shaft by holding it stationary. Holding may be required ei-ther prior to or after shaft rotation and is usually required to maintainor hold a position or location of a driven component.
Stopping function - This function provides a means to stop the drivenshaft or machine in a controlled manner by limiting its coasting timeand/or distance. The brake torque determines how quickly the stopoccurs.
Emergency stop function - This function rapidly stops all moving com-ponents to protect the operator and/or equipment.
Cyclic function - This function works in conjunction with a clutch andpermits frequent starting and stopping of the driven shaft while allow-ing the prime mover to run continuously.
Controlled slip function - This function provides a retarding torque to thedriven shaft. There is constant relative movement between the drivenshaft and the stationary half of the brake.
In any given application, the brake can provide one or a number of thesefunctions. It is important to identify all the functions the brake will be sub-jected to in the brake selection process.
Clutch Functions
Depending upon the operating characteristics of the prime mover and theenergy demand of the work shaft there are several ways in which theclutch can function to control the energy transfer. These include:
Coupling or disconnect function - This function permits the primemover; e.g., synchronous motor or diesel engine, to obtain operatingspeed and/or temperature before being coupled or connected to thework shaft. When energy is not required at the work shaft and it is notdesirable to stop the prime mover, the clutch provides the disconnectbetween the two. This type of application is usually associated withlong periods of clutch engagement, as opposed to one in which sev-eral engagements per minute are required.
Starting function - This function permits controlled acceleration of thework shaft with minimal torsional shock when accelerating delicate orbreakable materials. For high inertia starts, it permits the prime moverto run continuously at efficient speeds.
Direction or speed change function - Multi-speeds and directionchanges in many machines are accomplished with gear boxes or geartrains equipped with clutches. Generally, one clutch is required foreach speed and for changing the direction of rotation.
Cyclic function - This function requires that the work shaft be startedvery frequently while the prime mover runs continuously. A brake isusually required to stop the work shaft in order to obtain the cyclicrate.
Continuous slip function - This function requires that the driven side ofthe clutch rotate at a speed slower than the driver side. An applicationexample is a rewind stand where material must be wound into a rollunder constant tension. By controlling clutch torque, material tensionand speed is regulated.
Overload protection function - This function limits the maximumtorque which can be transmitted to prevent damage to drive compo-nents. If the maximum torque is exceeded, the clutch will slip. Toavoid thermal damage, the clutch should not be allowed to slip for anexcessive length of time.
In any given application, the clutch can provide one or a number of thesefunctions. It is important to identify all the functions the clutch will be sub-jected to in the clutch selection process.
Friction
Friction may be defined as the resistive force occurring between two sur-faces as they slide or tend to slide across each other. The contacting sur-faces can be thought of as consisting of peaks and valleys which meshtogether. The resistive force is developed by the effort to slide the peaks oneach surface out of the meshing valleys. When the surfaces slide acrosseach other, the peaks and valleys are not as free to mesh as when the sur-faces are stationary. This is the reason frictional resistance decreaseswhen slidingoccurs.
It is apparent that the frictional resistive force is proportional to the normalforce holding the surfaces in contact with each other. The constant ofproportionability is called the dynamic coefficient of friction when slidingoccurs, and the static coefficient of friction when sliding does not occur.
Y - 3 Copyright Eaton Corporation, 1995, All rights reserved.
Friction Couples and Materials
Friction Couples
Airflex clutches and brakes are of the frictional type, that is, they rely upona frictional force occurring between two surfaces to develop the requiredtorque. The torque is called dynamic torque when slippage occurs be-tween the surfaces and static torque when no slippage occurs. Usually thetwo surfaces are of dissimilar materials. The combination of the two mate-rials used is referred to as a friction couple and their contacting surfacesas interfaces.
When the friction couple operates within a fluid, it is referred to as wet op-eration. Dry operation does not depend upon the presence of fluid.
Depending upon application, it may be desirable to have a large or smalldifferential between the static and dynamic torques. For instance, when en-gagement is made at rest (no slippage between interfaces), as would occurfor a clutch-coupling or a holding brake, the static torque should be moredominant. If the clutch or brake is required to slip continuously, as in atensioning application, very little differential is desirable to avoid astick-slip condition.
Friction Material
Friction material is a specially formulated composition intended to provide aspecific stable coefficient of friction over a wide range of operating temper-ature. Beyond the operating range, the coefficient drops drastically, result-ing in loss of frictional force. This condition is referred to as lining fade.
Some desirable friction material properties are that they have good wearlife, be non-aggressive to the surface they interface with, and have suffi-cient strength so they can be attached to other components. The material isbasically a replaceable lining to which wear can be confined; hence, the de-scription friction lining.
The majority of Airflex products utilize organic linings. Their compositionconsists of three types of ingredients - fillers, fibers and binders. Fillers, inaddition to providing bulk and assisting in material processing, are used asaugmenting agents to affect the coefficient of friction. Fibers are used forreinforcement. Binders bond all the ingredients together.
Airflex magnetic and hydraulic products utilize sintered metal lining. Thisfriction material is produced from a mixture of powdered metals andnon-metals by pressure and fusion. Its primary advantage is being able towithstand high thermal stresses and operating pressures. To assist in heatdissipation, and because of its aggressiveness on its mating surface, it isintended for wet operation.
Friction linings offered by Airflex fall into three categories which are de-scriptive of their coefficient of friction. Due to the nature of the productsand their suitability to specific applications, linings in each category are notavailable for all product lines or models. The three categories are:
Standard linings - These are linings furnished as standard material onAirflex products which permits them to operate within their publishedcapacities.
Lo-co linings - These are linings which have a coefficient of friction ap-proximately 65% of the standard linings. They are formulated forcoefficient stability and wear characteristics and are used primarily forcontinuous slip applications.
Hi-co linings - These are linings which have a static coefficient of frictionhigher than the standard lining. They are used in applications requiringlarge locked-up torques with little or no slip between interfaces.
Two common types of hi-co linings furnished by Airflex are neoprene rub-ber and cork composite. The cork material is pressure sensitive. When thismaterial is used, published torque ratings are increased by the factor ob-tained from the graph shown.
Y - 4Copyright Eaton Corporation, 1995, All rights reserved.
Drum and Disc Materials
Drum and Disc Materials
Gray iron is used as an interface in the majorityof Airflex clutch and brake applications. Othermaterials used for structural or thermal reasonsinclude ductile iron, carbon steel and copper al-loys.
For applications where little or no thermal energyis generated due to slippage, material selectionis based upon their mechanical properties andcost. Cast gray iron castings are inexpensive andpatterns are available for all standard drums anddisks. Castings of ductile iron provides additionalstrength and ductility that may be needed in highspeed applications and those that must endureshock or impact loads. Plain carbon steel fabri-cations can provide the additional strength andductility without the need for a casting pattern.Fabrications may offer a price advantage whenonly one or two parts are involved and may bemore readily obtainable than cast parts. The useof copper alloys is generally limited to applica-
tions requiring high thermal conductivity andwhere high first cost is not prohibitive.
In applications where a significant amount ofheat is generated, the thermal properties of thematerials are more significant. Their pertinentproperties are shown in the table, below.
Copper alloys have thermal properties which arebest exploited by using forced-convection - usu-ally, water cooling; however, specialnon-aggressive friction material is required toprovide an acceptable wear rate of the alloy.
The thermal conductivity of gray iron combinedwith its low modulus of elasticity results in lowertemperature and stresses at its sliding surface.
Ductile iron has a lower thermal conductivity andhigher modulus of elasticity. This results inhigher surface temperatures, lining fade and ac-celerated wear under extreme conditions. Sur-face stresses are higher and prone to heatchecking.
Carbon steel has a thermal conductivity similarto that of gray iron and a modulus of elasticitysimilar to ductile iron. Therefore, it will yield lowsurface temperature, but will be somewhatprone to heat checking.
Material
ThermalConductivityk
HeatCapacityc
Coefficient ofThermal Expansionα
Modulus ofElasticityΕ
Densityρ
English SI English SI English SI English SI English SI
Y - 5 Copyright Eaton Corporation, 1995, All rights reserved.
Thermal Considerations
Thermal Considerations
High operating temperatures are detrimental toclutch and brake performance. At elevated tem-peratures torque capacities are reduced and highthermal stresses cause heat checking and warp-ing. If the units are intended for wet operation(where sliding interfaces are exposed to a cool-ant), the fluid may oxidize and decompose. Be-cause of these temperature effects, a clutch orbrake must be carefully selected to handle therequired thermal loads without overheating.
For friction type clutches and brakes to acceler-ate or decelerate machine componentssmoothly, the friction interfaces must slip untilthey attain identical speeds. Slippage generatesheat which must be dissipated.
Typically, friction materials have insulating prop-erties which confine the heat to its sliding sur-face. Surface temperatures often exceed 1000oF(540oC). Prolonged exposure causes the frictionmaterial binder to break down at the surface, re-sulting in loss of coefficient of friction (liningfade). The clutch or brake can no longer developits rated torque. Lining wear increases rapidly.The graph illustrates characteristic temperatureeffects on lining coefficient and wear.
The friction material interface is chosen for itsability to absorb (specific heat capacity) andconduct (thermal conductivity) heat away fromthe sliding interface. Absorbed heat is a functionof the interface mass (heat sink). For a givenamount of heat, the larger the heat sink, thelower the resulting temperature rise. The abilityto absorb large quantities of heat is important inhigh inertia applications, as well as other highenergy, low cyclic rate applications.
The rate at which heat is absorbed is a functionof the interface area. If heat is generated fasterthan it can be conducted into the heat sink, sur-face temperatures will rise rapidly. The ability toabsorb heat at high rates is important in high en-
ergy applications wherestarting and stoppingtimes are short.
Heat dissipation occursthrough radiation andconvection, and dependsupon the relative flow overconvecting surfaces, heatradiating surface areasand the difference be-tween ambient tempera-ture and clutch and braketemperatures. Over a longtime span, clutch or braketemperature rises until therate of heat dissipationequals the rate of heat in-put. If the heat dissipationsurface is too small
and/or the flow is too low to accommodate therate of heat input, clutch and brake operatingtemperatures will be high. Clutches and brakesshould be designed so air can circulate freely;vanes are often added to encourage flow andfins are added to increase radiating surface area.The ability to dissipate large quantities of heat isimportant in high cycle and constant tensioningapplications.
For a given application, operating temperaturesare lower with increased clutch or brake size be-cause of greater frictional area, larger heat radi-ating surfaces and more heat sink capacity.When size must remain small, but thermal loadis large, then external cooling must be applied.Water, oil and forced air cooling are common.
Forced air convection is the simplest way to im-prove heat dissipation. Blowers or fans are usedto create air flow and shrouding is usuallyneeded to direct the flow across critical sur-faces. Forced air cooling is not always practicalas large volumes of air must be circulated to re-duce the operating temperature. Shrouding, ductwork and the blower require considerable spaceand give the equipment a bulky appearance.Noise and vibration may be objectionable.
Water cooling is a more efficient means of dissi-pating heat. When a clutch or brake is watercooled, materials which could not otherwise beemployed can now be used for the friction inter-faces. Using an interface with a high thermalconductivity will rapidly conduct heat away fromthe sliding surface to its underside which is ex-posed to circulating water. Because almost allthe heat flow is into the water, friction materialswhich would be rejected because of their ten-dency to fade at elevated temperatures becomepractical.
Y - 6Copyright Eaton Corporation, 1995, All rights reserved.
Wear and Squeal
Wear
Wear can best be explained by the adhesion the-ory. According to the theory, when two nominallysmooth surfaces are pressed together, very highstresses exist over small regions or junctionswhere high spots touch each other. Thesestresses lead to local plastic deformation, which,in turn, produces the real area of contact.
A strong adhesion or bond takes place at thejunctions. Friction force then arises from theneed to break the junctions in shear. From thewear standpoint, it is desirable to have frictioninterfaces which limit the strength of the bondsformed. Wear results whenever a junction, in be-ing broken, parts along some line other than theoriginal interface. These wear particles then be-come embedded into one of the interfaces, usu-ally the friction lining, and tend to score or dig agroove into the other interface.
Since these particles have little mass, they in-stantly absorb a tremendous amount of heat dur-ing clutch or brake engagement and fusetogether. Eventually, these particles form a masslarge enough to prevent lining contact.
Wear is influenced by a combination of factorswhich include, but not limited to:
Contacting materials - It is desirable to have afriction couple which limits the strength ofthe adhesion or bond formed between theinterface.
Micro-structure constituents - Strength of themetallic interface is affected by the amountand disposition of graphite. Graphite coun-teracts thermal shock and reduces scoringby lubricating the sliding surfaces.
Surface hardness - Wear rate decreases as ma-terial hardness increases. Hardness isincreased by alloying or heat treatment.However, thermal conductivity is reducedand increased wear may occur because ofhigher resulting operating temperatures.
Pressure - Wear appears to increase almostproportionally with pressure.
Temperature - High temperatures break downfriction material binders and cause heatchecking on the metallic interface.
Surface finish - Generally, the rougher the sur-face, the higher the wear rate. However,very smooth surfaces cannot store protec-tive contaminants that may tend to lubricatethe sliding surfaces.
Contaminants - Contaminants can be beneficial,like lubricants; or harmful, like abrasives.
Slipping speed - In general, wear rate increaseswith higher speeds.
As discussed above, contributors to wear arenot only mechanical, but also metallurgical andthermal in nature. A combination of any or all ofthese factors make wear life difficult to predict.
Squeal
Squeal, like wear, is influenced by several factorswhich make it difficult to predict and/or elimi-nate. Squeal can result from thermal distortion ofthe friction interfaces. Temperature and humiditycan affect the coefficient of friction and cause asqueal condition.
If squeal does occur, the installation should beinspected to determine if supporting structureshave sufficient rigidity and that all bolts and nuts
have been sufficiently torqued. The frictioncouple should be inspected to determine if theinterfaces are in full contact, and, if not, be al-lowed to wear in.
In most cases, squeal can be eliminated by us-ing a friction material having a lower coefficientof friction and increasing interface pressure.Changing lining flexibility by grooving or slottingmay also help. Dampening clutch and brake
components by the addition of weight orsprings, where feasible, will reduce vibration thatmay be contributing to the squealing condition.
Plastic deformation and adhesion
Wear particles
Fracture line
Y - 7 Copyright Eaton Corporation, 1995, All rights reserved.
Mounting
Mounting Arrangements
For all applications it is highly desirable to mount the smaller inertia clutchand/or brake components on the driven shaft and the larger inertia compo-nents on the driving shaft. This component arrangement minimizes thethermal load on the clutch or brake. It is essential for cyclic applications.The cyclic thermal graphs which appear in the catalog are based upon thisarrangement.
For those applications where it is not practicable to mount the componentsin the preferred manner, close attention must be given to the clutch orbrake thermal load. Oversize units may be necessary to handle the require-ment.
Some components are designed to circulate cooling air through the clutchor brake. These components should be mounted on the shaft which rotatescontinuously or has the longer period of rotation. The open end of clutch orbrake drums should be exposed to the atmosphere to avoid hot air pock-ets. Ventilating holes should be provided so cooling air can circulate freely.
Gap arrangements for clutch couplings are preferred over the closemounted arrangements. The gap between shaft ends allows clutch removalwithout disturbing the driving or driven components. When applications areclose mounted or mounted between shaft support bearings, space shouldbe provided to permit axial movement of components in order to accessthe clutch or brake for maintenance. If space does not exist, splitable unitsshould be considered. Certain sizes of clutch and brake elements are avail-able with this feature.
Bearing mounted clutch arrangements are available having provisions forattaching sheaves or sprockets. These arrangements can be mounted onshaft extensions or between shaft support bearings.
Whatever arrangement is employed, mounting shafts must be of sufficientdiameter to accommodate the torsional and bending stresses associatedwith each installation.
Component Shaft Mounting
To accommodate the shock, transient and vibratory torques associated withany power transmission drive, it is recommended that all shaft mountedcomponents be affixed with a key and an interference (shrink) fit. The inter-ference fit minimizes, if not eliminates, fretting corrosion, key and keywaydamage, which would result with a loose fit. In addition, some componentsrely on the interference fit to provide a bore to shaft seal for the actuatingmedia.
Y - 8Copyright Eaton Corporation, 1995, All rights reserved.
Alignment
Product Alignment
Good shaft and component alignment is highly desirable to minimize un-necessary mechanical stresses in couplings, clutches, brakes, shafts,bearings and their supporting structure. Perfect alignment, which for allpractical purposes is unattainable, can only occur if the dynamic axes ofrotation are concentric throughout their entire lengths.
Misalignment is completely described by measurements of parallel and an-gular misalignment. Since both types of misalignment occur in the horizon-tal and vertical planes, top-to-bottom and side-to-side measurements mustbe taken.
Parallel misalignment, also referred to as offset or run out, occurs whenthe axes of rotation are parallel to each other. It is measured by attaching adial indicator to one shaft; rotating the shaft with the indicator about theoutside diameter of the other shaft and noting indicator readings.
Angular misalignment, also referred to as gap, occurs when the axes of ro-tation intersect each other. Either a micrometer or dial indicator can beused to take gap measurements as shown in the figure.
Parallel and angular measurements are then used to determine the neces-sary adjustments. Initial shaft alignment should be done as accurately aspossible. Foundation movement, frame deflection and expansion canchange the initial alignment to the point where full misalignment capacity ofthe product is required. Although shaft speed generally dictates misalign-ment tolerances, the values shown in the table have been found acceptablefor the Airflex product lines. The angular indicator reading should not ex-ceed the product of the table value and the diameter at which the indicatorreadings were taken.
Parallel
Angular
Product
Parallel Angular
in mm in/in of dia.mm/mmof dia.
CB, CM, EB, ER 0.015 0,38 0.0007 0,0007
CS, CSA, CTF,DBA, DBB, DC,DP, E, HB3,HC3, VE, VC,WC, WCB, WCS
0.010 0,25 0.0005 0,0005
CH 0.005 0,13 0.0003 0,0003
AR, AS, SB, SC 0.003 0,08 0.0003 0,0003
Note:
Ê Diameter at which measurements are taken.
ÊÊ
Y - 9 Copyright Eaton Corporation, 1995, All rights reserved.
Balancing
Balancing
Unbalance exists when a body’s mass is notequally distributed about its axis of rotation. Theunbalance results in centrifugal forces acting onthe body’s support bearings and structure andinduces forced vibrations which affects the wearand life of all machine components.
Balancing of a body attempts to redistribute itsmass about the axis of rotation by mass removalor addition. Because all bodies are both staticallyand dynamically unbalanced, mass correctionsshould be made. If the body diameter is greaterthan twice the distance between the planes inwhich corrections can be made, single planecorrection is usually sufficient for most installa-tions.
Since the mass corrections are never perfect,some residual unbalance will always exist. Re-sidual unbalance is measured in ounce-inches,gram-inches or gram-millimeters. Its value is theproduct of an amount of weight or mass and its
distance from the axis of rotation. The value ofthe weight and mass or distance can vary aslong as the product of the two does not exceedthe required residual unbalance.
ISO1940 addresses the balance quality of rotat-ing rigid bodies. Balance quality grades havebeen established which permit a classification ofthe quality requirements; however, their recom-mendations are not intended to serve as accep-tance specifications. Permissible values ofresidual unbalance can only be determined ex-perimentally by observing how the amount ofunbalance affects the vibration, running smooth-ness and operation of the machine.
Some Airflex products are routinely balancedprior to shipment. The quality and method of bal-ance is indicated in the table. If a finer balancequality is necessary, a balancing charge is re-quired. Products not shown are only balanced
when specified and are subject to a balancingcharge.
Components balanced to an acceptable value,when combined (element and spider or drumand hub), can result in an assembly having un-acceptable residual unbalance. The unbalanceoccurs due to the fit and geometrical tolerancesand the mass addition of connecting elements(bolts and keys). If individually balanced compo-nents are unacceptable, the assembled compo-nents can be balanced as a unit. The position ofthe assembled components relative to eachother must be match marked and assembledwith shoulder bolts so that they cannot be reas-sembled in a different position.
ProductNumber ofBalancing Planes
Correction by MassISO BalanceQuality and Grade
12 thru 45 CB Single Elements Ê Single Addition 16
12 thru 45 CB Dual Elements Ê Two Addition 16
12 thru 45 CB Spiders Ë Single Removal 16
CB Sheave Clutches Ê Single Addition 16
CM Elements Ê Single Addition 16
CM Drums Single Removal 16
VC Single Narrow Elements Ê Single Addition 16
VC Dual Narrrow Elements Ê Two Addition 16
14 thru 52 VC Single Wide Elements Ê Two Addition 24
60 and 66 VC Single Wide Elements Ê Single Addition 24
14 thru 42 VC Dual Wide Elements Ê Two Addition 24
VC Spiders Ë Single Removal 16
VC Ventilated Adapters Single Removal 16
E and EB Vaned Drums Single Removal 16
DBA Solid Discs Single Removal 6.3
FSPA Combination Drums Single Removal 40
Notes:Ê Clutch elements have moving parts, which make
them non-rigid bodies. The grades indicated arenominal. Actual values can be above or belowthese grades.
Ë Components ordered with unfinished bores are notbalanced.
Y - 10Copyright Eaton Corporation, 1995, All rights reserved.
Control Devices
Pneumatic and Hydraulic Control Devices
There are numerous devices available which,when incorporated into a control system, en-ables the clutch and/or brake to perform the re-quired function. The most common devices arediscussed below:
Pressure regulator - This device is used to es-tablish the maximum pressure of theactuating media. Since torque is dependentupon media pressure, it follows that theregulator setting establishes the torque ca-pacity of the clutch or brake.
Check valve - This device allows media flow inone direction only. Its purpose is to preventreverse media flow should a pressure dropor failure occur in the pressure source.
Pressure switch - This device senses mediapressure and makes or breaks electricalcontacts once a predetermined pressure isreached. It acts as a safety device ensuringthat sufficient pressure is or is not availablefor clutch or brake actuation.
On/off/exhaust valve - This device is used topermit or prevent passage of the actuatingmedia. It can be activated by an electric so-lenoid, a pressure-activated pilot ormanually by an operator.
Flow control valve - This device is used tocontrol the flow rate of the actuating media.The rate of flow determines the rate ofpressure build-up and hence the rate ofclutch or brake engagement. The valve set-ting is done manually. Once established, itneed only be changed when changes occurin the operating conditions. These valvesusually have controlled flow in one direc-tion, and free flow in the opposite direction.
Pressure modulating valve - This device pro-vides a means to continually adjust theclutch or brake pressure within a range de-termined by the minimum and maximumoperating pressure of the valve. Adjustmentis usually done manually by movement of alever. It permits operator control of the ac-celeration or deceleration of changingloads, for instance, when starting or stop-ping a fully loaded, partially loaded orunloaded conveyor.
Quick release valve - This device provides aconvenient port, close to a pressurizedchamber, for quickly releasing the actuatingmedia. It improves operation by reducingexhaust time and overlap between clutchand brake engagements.
PressureRegulator
Check Valve
PressureSwitch
Storage Tank
Pressure Gage
Relief Valve
3-Way SolenoidValve
Optional ManualModulating Valve
Optional Flow-ControlValve
OptionalQuick-Release Valve
Filter
2-Way Pilot Valve
3-Way ManualValve
Supply
To Clutchor Brake
OR
OR
OR
Y - 11 Copyright Eaton Corporation, 1995, All rights reserved.
Air Supply
Air Supply
Section Y contains information pertaining to aircompressor capacity. Refer to this section tosize a new compressor or to determine if an ex-isting compressor has ample capacity to handlenew requirements.
To ensure that sufficient pressurized air is avail-able (essential for high cyclic applications), it isrecommended that an air receiver tank be in-stalled as close as possible to the clutch and/orbrake location. For very infrequent engagements,tank volume should be approximately 10 timesthe clutch and brake engagement volume. Forhigh cyclic engagements, tank volume should beapproximately 20 times the engagement volume.
A typical air receiver tank and suggested acces-sories are shown in the diagram. The air filter re-moves compressor and air line contaminates,the pressure regulator establishes the maximumair receiver pressure, and the check valve pre-vents air flow back to the air supply source. Therelief valve ensures that the maximum allowableworking tank pressure is not accidentally ex-ceeded. The pressure switch determines if suffi-cient pressure is available and if not, preventsoperation through its electrical interlocks. Watercondensation can be removed from the tankthrough the drain valve. A pressure gauge at theout port of the receiver provides visual confirma-tion of the supply pressure to the clutch and/orbrake.
Use full size valves and piping, with a minimumnumber of bends and fittings, between the air re-ceiver tank and the clutch or brake. Do not uselong lengths of flexible hose. Pipe size should beconsistent with the recommended rotorseal sizefor a clutch application or the tube inlet valve fora brake application. Optimum sizing of the circuitfor rapid response may require experimentationon the application.
Air filter
Pressure regulator
Check valvefree-flow in
direction shown
Pressure switch
Drain valve
Safety relief valve
Pressure gage
Air supply toclutch or brake
Main air supply
Y - 12Copyright Eaton Corporation, 1995, All rights reserved.
Product Elastomers and Selection Procedure
Product Elastomers
The following specification applies to the rubberactuating tubes used in the CB, CM, E, EB, ER,VC and VE elements and the diaphragms used inDBA elements.
Elastomer: Inner & outer tube cover neoprenecompound, type SC classification as cov-ered by SAE10R4 Specifications forAutomotive Elastomer Compounds. Cordplies have natural rubber coating.
Durometer: 60 æ 5 Shore A. Tube should be re-moved from service when it reaches adurometer reading of 72 Shore A or showscracks from brittleness.
Temperature:
Heat - for continuous service 200oF (82oC to93oC); for intermittent service up to 250oF(121oC). Over 250oF (121oC) the elastomerhardens and rapidly loses resilience.
Cold - little change in performance characteris-tics down to -10oF (-23oC). Below thisrange, the elastomer stiffens and becomesbrittle at -40oF (-40oC).
Resistance to Oils and Grease: Aniline pointmust be 200oF (93oC) or higher. Limited tonon-aromatic hydrocarbons.
Resistance to Chemicals: Little change in prop-erties when exposed to alkalies, dilutemineral acids or inorganic salt solutions.Acid and salt solutions of a highly oxidizingnature will cause surface deterioration andloss of strength.
An aliphatic hydro-carbon solvent can be used toclean grease and oil from the tubes. Kerosene isa good example of this type of solvent. Aftercleaning, any residue can be removed by wipingthe tube with a clean cloth soaked in isopropylalcohol.
Compounds used in other products are:
• Polyurethane - for the diaphragm orplunger seal used in the quick releasevalves.
• Buna N - for the CS, CSA and CTEbrake pistons.
Selection Procedure
Analytical Method
The analytical procedure for determining theclutch and brake requirements is the same forany given application and consists of making thefollowing determinations:
• Required Torque
• Thermal Load
• Mounting and Space Envelope
• Operating Environment
• Industrial and Federal Regulations
Formulas for calculating the torque and thermalload are given elsewhere in this section. Regard-less of the application the operating data requiredto perform the calculations is basically the sameand includes the torque to perform the neces-sary machine work, total inertia (including clutchand brake components) which must be startedor stopped, acceleration or deceleration time,speeds of all rotating and linear moving compo-nents, clutch or brake shaft speed and frequencyof clutch or brake engagement.
A service factor SF is generally applied to the re-quired torque M to determine clutch torque Mc orbrake torque Mb. This is done for two reasons: tohave sufficient torque to accommodate any un-predictable transient torques or lining fade, andto compensate for the accuracy of the data.Typically, service factors range from a minimumvalue of 1.3 to a maximum value of 2. A factor inthe low range is used when the drive and data isaccurately defined. Values in the higher range areused when there are several unknowns.
A thermal load occurs whenever clutch or brakeslippage occurs. During starting or stopping the
thermal load Wt is basically the energy W re-quired adjusted to reflect the work done Ww, ifany, by the machine during the period of accel-eration or deceleration. If slippage occurs duringmachine operation, the thermal load is deter-mined by the product of clutch or brake torqueand the angle through which slippage occurs.The total energy and the rate at which it must beabsorbed and/or dissipated must be within theclutch or brake capacity.
A clutch or brake is then selected which hasequal or larger torque and thermal capacities.The unit’s dimensional and physical propertiesare then reviewed for drive compatibility. It mustfit within a space which is free of all interferencewhen the machine is both running and stopped.Mounting components and other machine com-ponents such as shafts and bearings must beable to handle the unit’s weight and the stressesinvolved during operation. Operating speedsmust not exceed the unit’s limitation.
The clutch or brake location should have suffi-cient ventilation to dissipate the thermal load.The location must take into account the safety ofall operating personnel. All rotating equipmentmust be well guarded. Actuating means and ex-ternal cooling, when required, must be readilyaccessible, as well as an effective actuationroute and/or cooling circuits to them.
Unusual or harsh environmental conditions canaffect the success of an application. Externalprotection must be provided if the conditionscannot be avoided. These conditions includehigh or low ambient temperatures, saltwaterspray, heavy dust concentration and exposure tooil.
And, finally, all laws and regulations and indus-trial standards must be considered when makingthe final selection.
Y - 13 Copyright Eaton Corporation, 1995, All rights reserved.
Selection Procedure
Service Factor Method
While it is preferable to use the detailed analyticalmethod to evaluate applications, there is a sim-plistic alternative procedure which uses servicefactors. This procedure sizes clutches andbrakes by multiplying the power rating of theprime mover by a factor. This factor is an experi-ence based number developed for the specifictype of application and is intended to compen-sate for the thermal loads and other consider-ations normally encountered. Values range froma minimum value of 1.5 to a maximum value of5. Selection by service factor is used extensivelywhere machines and power trains are standard.It is not to be used for flywheel driven machines,which are dependent upon flywheel slowdownfor its power requirements.
The product of the power rating and the servicefactor is referred to as the design hp. Its value isused to calculate torque at the clutch or brakeshaft.
Care must be used when selection by servicefactor is employed. Problems can occur whenthe application is not typical of the standard,or when the prime mover is not properly sizedor sized on criteria other than torque.
These notes apply to the following Service Factor Tables:Ê If no service factor is shown, refer to Section X,
Power Presses, Brakes and Shears.
Ë If no service factor is shown, refer to Section X,Engines Clutches.
Ì Refer to Section X, Marine Drives.
Í Refer to Section X, Grinding Mills.
Î If no service factor is shown, refer to Section X,Well Drilling.
Ï If no service factor is shown, refer to Section X,Paper Machine Drives.
Ð Selection dependent upon thermalcapacity.
Ñ Torsional analysis required.
Ò Refer to Section X, Tensioning, Winding and Un-winding.
Y - 14Copyright Eaton Corporation, 1995, All rights reserved.
Service Factor Table
Agricultural Crop Spraying 1.5Grain Elevator 2.5Irrigation 1.8Sugar Refining 2.5
Quantity of Heat J joule J British Thermal Unit BTU 1.055 E+03 ⋅ BTU = J
Current I ampere A Ampere i —
Potential V volt V volt v —
Heat
Ele
ctr
ical
Multiples of SI Units
The prefixes given in the table are used to formnames and symbols of multiples of the SI units.
Factor Prefix Symbol
E+06 mega M
E+03 kilo k
E+02 hecto h
E+01 deca da
E-01 deci d
E-02 centi c
E-03 milli m
E-06 micro µ
Y - 21 Copyright Eaton Corporation, 1995, All rights reserved.
Engine Clutch Applications
Typical CB engine mounted clutchapplications. At left, a dual24CB500 clutch installed on a 1200HP (895 kW) @ 1200 rpm enginemud pump drive. Lower applicationuses a 20CB500 clutch in a powertake-off arrangement.
