What is powder coating? Powder coating is by far the youngest of the surface finishing techniques in common use today. It was first used in Australia about 1967. Powder coating is the technique of applying dry paint to a part. The final cured coating is the same as a 2-pack wet paint. In normal wet painting such as house paints, the solids are in suspension in a liquid carrier, which must evaporate before the solid paint coating is produced. In powder coating, the powdered paint may be applied by either of two techniques. The item is lowered into a fluidized bed of the powder, which may or may not be electro statically charged, or The powdered paint is electro statically charged and sprayed onto the part. The part is then placed in an oven and the powder particles melt and coalesce to form a continuous film. There are two main types of powder available to the surface finisher: Thermoplastic powders that will remelt when heated, and Thermosetting powders that will not remelt upon reheating. During the curing process (in the oven) a chemical cross-linking reaction is triggered at the curing temperature and it is this chemical reaction which gives the powder coating many of its desirable properties. Preparation The basis of any good coating is preparation. The vast majority of powder coating failures can be traced to a lack of a suitable preparation.
Transcript
What is powder coating?
Powder coating is by far the youngest of the surface finishing techniques in common use today. It was first used in Australia about 1967.
Powder coating is the technique of applying dry paint to a part. The final cured coating is the same as a 2-pack wet paint. In normal wet painting such as house paints, the solids are in suspension in a liquid carrier, which must evaporate before the solid paint coating is produced.
In powder coating, the powdered paint may be applied by either of two techniques.
The item is lowered into a fluidized bed of the powder, which may or may not be electro statically charged, or
The powdered paint is electro statically charged and sprayed onto the part.
The part is then placed in an oven and the powder particles melt and coalesce to form a continuous film.
There are two main types of powder available to the surface finisher:
Thermoplastic powders that will remelt when heated, and Thermosetting powders that will not remelt upon reheating. During the curing
process (in the oven) a chemical cross-linking reaction is triggered at the curing temperature and it is this chemical reaction which gives the powder coating many of its desirable properties.
Preparation
The basis of any good coating is preparation. The vast majority of powder coating failures can be traced to a lack of a suitable preparation.
The preparation treatment is different for different materials.
In general, for all applications the preparation treatment for aluminium is as follows:
Clean Or
Clean
Rinse Rinse
Etch Etch
Rinse Rinse
Chromate Phosphate
Rinse Rinse
Demin Rinse Demin Rinse
Oils and greases are removed in weak alkali or neutral detergent solutions and the surface is etched to remove heavy oxides. After rinsing, the aluminium is dipped into a chromate or phosphate solution to form a conversion coating on the aluminium. This film is chemically attached to the aluminium. After rinsing the aluminium is finally rinsed in demineralised water. Some non-chrome, dried in place pretreatment is beginning to come onto the market; currently, these are not recommended for exterior applications.
The conversion coating has two functions:
It presents a surface to the powder which favours adhesion more than the oxides that form very readily on aluminium surfaces, and
It reduces the incidence of under film corrosion, which may occur at holidays in the coating.
The use of demineralised water reduces the presence of chemical salts on the aluminium surface. These salts have been found to cause filiform corrosion in humid conditions.
For steel the preparation for interior applications may be:
Clean
Rinse
Derust
Rinse
Iron Phosphate
Rinse
Acidulated Rinse
For exterior applications:
Clean
Rinse
Etch
Rinse
Grain Refine
Zinc Phosphate
Rinse
Acidulated Rinse
The grain refiner is used after acid cleaning of steel surfaces and before zinc phosphating, otherwise the zinc phosphate coatings produced will be very coarse with low adhesion. The powder coating applied to a coarse phosphate will produce rough coatings (a little like "sandpaper") and possess low adhesion.
For hot dipped galvanized coatings, which have been stored for more than about 4 hours before powder coating, the following process is necessary for exterior applications.
Clean
Rinse
Etch
Rinse
Grain Refiner
Rinse
Zinc Phosphate
Acidulated Rinse
The etch is required to remove the zinc corrosion products which begin to form almost immediately the zinc is removed from the galvanizing kettle. The grain refiner ensures a fine phosphate is produced.
How is it done -- electrostatic spray?
The powder is applied with an electrostatic spray gun to a part that is at earth (or ground) potential.
Before the powder is sent to the gun it is fluidised:
to separate the individual grains of powder and so improve the electrostatic charge that can be applied to the powder and
so that the powder flows more easily to the gun.
Because the powder particles are electrostatically charged, the powder wraps around to the back of the part as it passes by towards the air offtake system. By collecting the powder, which passes by the job, and filtering it, the efficiency of the process can be increased to 95% material usage.
The powder will remain attached to the part as long as some of the electrostatic charge remains on the powder. To obtain the final solid, tough, abrasion resistant coating the powder coated items are placed in an oven and heated to temperatures that range from 160 to 210 degrees C (depending on the powder).
Under the influence of heat a thermosetting powder goes through 4 stages to full cure.
MELT, FLOW, GEL, CURE
The final coating is continuous and will vary from high gloss to flat matt depending on the design of the powder by the supplier.
Powder coating guns
There are at east three types of electrostatic guns in use:
Corona charging guns where electric power is used to generate the electrostatic charge. Corona guns are either internal or external charging.
Tribo charging guns where the electrostatic charge is generated by friction between the powder and the gun barrel.
"Bell" charging guns where the powder is charged by being "flung" from the perimeter of the "bell"
Not all powder is applied using guns. One system makes use of electrostatic tunnels.
How is colour introduced?
Colour is added to powder coatings during the manufacturing process, ie before the powder reaches the powder coater. There is little that can be done to change the colour consistently, once the powder leaves the manufacturing plant.
Why powder coat?
Powder coating produces a high specification coating which is relatively hard, abrasion resistant (depending on the specification) and tough. Thin powder coatings can be bent but this is not recommended for exterior applications.
The choice of colours and finishes is almost limitless, if you have the time and money to have the powder produced by the powder manufacturer.
Powder coatings can be applied over a wide range of thickness. The new Australian Standard, "AS/NZS 4506 - Thermoset powder coatings", will recommend 25 micron minimum for mild interior applications and up to 60 micron minimum for exterior applications. Care must be exercised when quoting minimum thickness because some powder will not give "coverage" below 60 or even 80 micron. "Coverage" is the ability to cover the colour of the metal with the powder. Some of the white colours require about 75 micron to give full "coverage". One of the orange colours must be applied at 80 micron.
Colour matching is quite acceptable batch to batch.
Installations and maintenance
During installations, the powder coating should be protected from damage due to abrasion and materials of construction such as mortar and brick cleaning chemicals.
Once installed, maintaining the initial appearance of a powder coating is a simple matter. The soot and grime which builds up on surfaces from time to time contains moisture and salts which will adversely affect the powder coating and must be removed. Powder coatings should be washed down regularly (at least once each 6 months in less severe applications and more often in marine and industrial environments). The coating should be washed down with soapy water -- use a neutral detergent -- and rinsed off with clean water.
When powder coated items are installed without damage to the powder coating and they are maintained regularly, they should be relatively permanent. The correctly applied coating, although not metallurgically bonded to the metal will not crack, chip or peel as with conventional paint films.
Powder coating
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Powder coating is a type of coating that is applied as a free-flowing, dry powder. The main difference between a conventional liquid paint and a powder coating is that the powder coating does not require a solvent to keep the binder and filler parts in a liquid suspension form. The coating is typically applied electrostatically and is then cured under heat to allow it to flow and form a "skin." The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals, such as "whiteware", aluminium extrusions, and automobile and bicycle parts. Newer technologies allow other materials, such as MDF (medium-density fibreboard), to be powder coated using different methods.
Contents
[hide] 1 Advantages and disadvantages of powder coating 2 Types of powder coatings 3 The powder coating process 4 Removing Powder Coating 5 See also
6 External links
[edit] Advantages and disadvantages of powder coating
There are several advantages of powder coating over conventional liquid coatings:
1. Powder coatings emit zero or near zero volatile organic compounds (VOC). 2. Powder coatings can produce much thicker coatings than conventional liquid
3. Powder coating overspray can be recycled and thus it is possible to achieve nearly 100% use of the coating.
4. Powder coating production lines produce less hazardous waste than conventional liquid coatings.
5. Capital equipment and operating costs for a powder line are generally less than for conventional liquid lines.
6. Powder coated items generally have fewer appearance differences between horizontally coated surfaces and vertically coated surfaces than liquid coated items.
7. A wide range of specialty effects is easily accomplished which would be impossible to achieve with other coating processes.
While powder coatings have many advantages over other coating processes, there are limitations to the technology. While it is relatively easy to apply thick coatings which have smooth, texture-free surfaces, it is not as easy to apply smooth thin films. As the film thickness is reduced, the film becomes more and more orange peeled in texture due to the particle size and TG (glass transition temperature) of the powder. Also powder coatings will break down when exposed to uv rays between 5 to 10 years.
For optimum material handling and ease of application, most powder coatings have a particle size in the range of 30 to 50 μm and a TG > 40°C. For such powder coatings, film build-ups of greater than 50 μm may be required to obtain an acceptably smooth film. The surface texture which is considered desirable or acceptable depends on the end product. Many manufacturers actually prefer to have a certain degree of orange peel since it helps to hide metal defects that have occurred during manufacture, and the resulting coating is less prone to show fingerprints.
There are very specialized operations where powder coatings of less than 30 micrometres or with a TG < 40°C are used in order to produce smooth thin films. One variation of the dry powder coating process, the Powder Slurry process, combines the advantages of powder coatings and liquid coatings by dispersing very fine powders of 1–5 micrometre particle size into water, which then allows very smooth, low film thickness coatings to be produced.
Powder coatings have a major advantage in that the overspray can be recycled. However, if multiple colors are being sprayed in a single spray booth, this may limit the ability to recycle the overspray.
[edit] Types of powder coatings
There are two main categories of powder coatings: Thermosets and thermoplastics. The thermosetting variety incorporates a cross-linker into the formulation. When the powder is baked, it reacts with other chemical groups in the powder polymer and increases the molecular weight and improves the performance properties. The thermoplastic variety does not undergo any additional reactions during the baking process, but rather only flows out into the final coating.
The most common polymers used are polyester, polyester-epoxy (known as hybrid), straight epoxy (Fusion bonded epoxy) and acrylics.
Production:
1. The polymer granules are mixed with hardener, pigments and other powder ingredients in a mixer
2. The mixture is heated in an extruder 3. The extruded mixture is rolled flat, cooled and broken into small chips 4. The chips are milled to make a fine powder
[edit] The powder coating process
The powder coating process involves three basic steps:
1. Part preparation or the Pre treatment 2. The powder application 3. Curing
Part Preparation Processes & EquipmentRemoval of oil, soil, lubrication greases, metal oxides, welding scales etc. is essential prior to the powder coating process. It can be done by a variety of chemical and mechanical methods. The selection of the method depends on the size and the material of the part to be powder coated, the type of soil to be removed and the performance requirement of the finished product.
Chemical pre-treatments involve the use of phosphates or chromates in submersion or spray application. These often occur in multiple stages and consist of degreasing, etching, de-smutting, various rinses and the final phosphating or chromating of the substrate. The pre-treatment process both cleans and improves bonding of the powder to the metal. Recent additional processes have been developed that avoid the use of chromates, as these can be toxic to the environment. Titanium Zirconium and Silanes offer similar performance against corrosion and adhesion of the powder.
Another method of preparing the surface prior to coating is known as abrasive blasting or Sandblasting and shot blasting. Blast media and blasting abrasives are used to provide surface texturing and preparation, etching, finishing, and degreasing for products made of wood, plastic, or glass. The most important properties to consider are chemical composition and density; particle shape and size; and impact resistance.
Silicon carbide grit blast media is brittle, sharp, and suitable for grinding metals and low-tensile strength, non-metallic materials. Plastic media blast equipment uses plastic abrasives that are sensitive to substrates such as aluminum, but still suitable for de-coating and surface finishing. Sand blast media uses high-purity crystals that have low-metal content. Glass bead blast media contains glass beads of various sizes.
Cast steel shot or steel grit is used to clean and prepare the surface before coating. Shot blasting recycles the media and is environmentally friendly. This method of preparation is highly efficient on steel parts such as I-beams, angles, pipes, tubes and large fabricated pieces.
Different powder coating applications can require alternative methods of preparation such as abrasive blasting prior to coating. The online consumer market typically offers media blasting services coupled with their coating services at additional costs.
Powder Application ProcessesThe most common way of applying the powder coating to metal objects is to spray the powder using an electrostatic gun, or Corona gun. The gun imparts a positive electric charge on the powder, which is then sprayed towards the grounded object by mechanical or compressed air spraying and then accelerated toward the workpiece by the powerful electrostatic charge. There are a wide variety of spray nozzles available for use in electrostatic coating. the type of nozzle used will depend on the shape of the workpiece to be painted and the consistency of the paint. The object is then heated, and the powder melts into a uniform film, and is then cooled to form a hard coating. It is also common to heat the metal first and spray the powder onto the hot substrate. Preheating can help to achieve a more uniform finish but can also create other problems, such as runs caused by excess powder. See the article "Fusion Bonded Epoxy Coatings"
Another type of gun is called a Tribo gun, which charges the powder by (triboelectric) friction. In this case, the powder picks up a positive charge while rubbing along the wall of a Teflon tube inside the barrel of the gun. These charged powder particles then adhere to the grounded substrate. Using a Tribo gun requires a different formulation of powder than the more common Corona guns. Tribo guns are not subject to some of the problems associated with Corona guns, however, such as back ionization and the Faraday Cage Effect.
Powder can also be applied using specifically adapted electrostatic discs.
Another method of applying powder coating, called the Fluidized Bed method, is by heating the substrate and then dipping it into an aerated, powder-filled bed. The powder sticks and melts to the hot object. Further heating is usually required to finish curing the coating. This method is generally used when the desired thickness of coating is to exceed 300 micrometres. This is how most dishwasher racks are coated.
Electrostatic Fluidized Bed Coating: Electrostatic fluidized bed application uses the same fluidizing technique and the conventional fluidized bed dip process but with much less powder depth in the bed. An electrostatic charging media is placed inside the bed so that the powder material becomes charged as the fluidizing air lifts it up. Charged particles of powder move upward and form a cloud of charged powder above the fluid bed. When a grounded part is passed through the charged cloud the particles will be attracted to its surface. The parts are not preheated as they are for the conventional fluidized bed dip process.
Electrostatic magnetic Brush (EMB) Coating: an innovative coating method for flat materials that applies powder coating with roller technique, enabling relative high speeds and a very accurate layer thickness between 5 and 100 micrometre. The base for this process is conventional copier technology . Currently in use in some high- tech coating applications and very promising for commercial powder coating on flat substrates ( steel, Aluminium, MDF, paper, board) as well in sheet to sheet and/or roll to roll processes. This process can potentially be integrated in any existing coating line.
Curing
When a thermoset powder is exposed to elevated temperature, it begins to melt, flows out, and then chemically reacts to form a higher molecular weight polymer in a network-like structure. This cure process, called crosslinking, requires a certain degree of temperature for a certain length of time in order to reach full cure and establish the full film properties for which the material was designed. Normally the powders cure at 200°C (390°F) in 10 minutes. The curing schedule could vary according to the manufacturer's specifications.
The application of energy to the product to be cured can be accomplished by convection cure ovens or infrared cure ovens.
[edit] Removing Powder Coating
Methylene Chloride is generally effective at removing powder coating, however most other organic solvents (Acetone, thinners, etc.) are completely ineffective. Most recently the suspected human carcinogen Methylene Chloride is being replaced by Benzyl alcohol with great success. Powder coating can also be removed with abrasive blasting. 98% sulfuric acid commercial grade also removes powder coating film.[citation needed] Certain low grade powder coats can be removed with steel wool, though this might be a more labor- intensive process than desired.
Powder coatings are a blend of resins, curing agent and pigments which are melt-mixed and pulverized into finely divided particles. They are totally solvent free. Therefore, it is the ultimate coating for environmental friendliness. It is applied to metal products by electrostatic spray, the coated item is then heated and the powder melts into smooth, continuous film.
Powder Coatings are popular because of their high quality, the apparent ease of application and the environmental friendliness of the technology. The significant benefits and features of Powder Coating Technology are:
Ease of application – Single coat application, lower rejections more productivity.
Environmentally friendly – Virtual 100 % solids, no sludge or solvent disposal, reduced health, fire
and safety hazards.
Economical – Virtually 100 % material usage, overspray can be reclaimed, lower reject costs, lower
disposal costs, lower labour costs.
Excellence of Performance & Quality – Tougher & durable coating, Excellent corrosion and humidity
resistance
These benefits have enabled powder coatings to take a significant share of the industrial finishing market. For these reasons there has been a rapid growth in the coating industry.
These area blend of resins, curing agent and pigments which are melt-mixed and pulverized into finely divided particles. There are no liquids or solvents. Therefore, it is the ultimate coating for environmental friendliness. It is applied to metal products by electrostatic spray, the coated item is then heated and the powder melts into
smooth, continuous film.
Powder Coatings are gaining in popularity because of their high quality, the apparent ease of application and the environmental friendliness of the technology. It has been a commercial reality now for close to thirty years.
Powder ClassificationsThere are two basic classifications of powder coating materials. They are “thermoplastic” and “thermoset” powders.
Thermoplastic powders are generally applied to a surface that has been preheated to a temperature significantly higher than the melting point of the powder. It melts and flow when heat is applied but continue to have the same chemical composition when they solidify on cooling. Coatings of this type are based on thermoplastic resins of high molecular weight. These coatings are both tough and chemically resistant. Typical examples are:
Polyethylene
Polypropylene
Nylon
Polyvinyl Chloride
Thermoset powders are 100% solventless and are generally applied by means of electrostatic spray equipment that provides each powder particle with a small electric charge, which in turn stick to the earthed substrate. The coated objects are heated in an oven at specified temperature. Under the influence of heat the powder melts, flows out and reacts chemically. The result is a continuous thermoset film which can not be reversed at high temperature and having excellent physical, mechanical & chemical properties. Thermoset powder coating systems offer broad formulation flexibility. They are very durable and are widely used.The primary resins used in the formulation of thermosetting powders are:
Epoxy
Polyester
Polyurethane
Acrylic
These primary resins are used with different cross linkers to produce a variety of powder materials. Many cross linkers, or cure agents, are used in powder coatings, including amines, anhydrides, melamine’s, and blocked or non-blocked isocyanates. Some materials also use more than one resin in hybrid formulas to meet specific end uses.
EpoxyEpoxy powders were the first commercially available thermoset materials and they are the most commonly used of the thermosetting powders today. They are available in a wide range of formulations for thick film functional applications and thin film decorative applications. They provide excellent toughness, chemical resistance, corrosion resistance and flexibility and can be formulated to produce attractive coatings of varying gloss and surface textures. The primary drawback with epoxies is that they will chalk within a few months when subjected to UV radiation. For this reason they are rarely used for outdoor applications.
Epoxy Polyester HybridsEpoxy-Polyester” Hybrids“, like the name implies, combine epoxy resins with polyester resins. This group of powder coatings is best considered as a part of the epoxy family. These hybrids have comparable impact and bend resistance with epoxy types but are generally, slightly softer coatings. . Although some hybrids are less resistant to chemicals and solvents, they are tough, flexible and competitively priced. Hybrids are used where the good appearance qualities of polyesters are required and good UV resistance is not essential.
Polyester PowderThe most common Polyester powder coatings are the Polyesters Triglycidyl Isocyanurate (TGIC) types. These coatings have good edge coverage and good mechanical properties. These coatings are known for their good UV resistance as compared to epoxy, epoxy – polyesters. Polyester powder coatings are used widely for industrial finishing and typical applications include office furniture and aluminium extrusions, automotive wheels, lawn furniture, and air conditioner cabinets.
Urethane PolyestersUrethane cured polyester powders have excellent resistance to outdoor environments, toughness and very good appearance characteristics at 1 to 2 mil film thickness. A smooth, thin film that resists weathering and physical abuse makes the urethane polyesters a popular finish for high quality products. It is common to block the crosslinker in urethane polyesters with ecaprolactam. To begin the crosslinking process, the material must reach a temperature above the blocking agent threshold. With e-caprolactam, unblocking occurs at approximately 360 °F (182 °C). Therefore, temperatures must be higher than 360 °F to start the melt phase of the cure cycle. Powders containing e-cap are usually sensitive to films thicker than 3 mils. Thicker films with these urethanes may lose some of their mechanical properties and they may exhibit outgassing effects due to ecaprolactam evolution.They are used for exterior applications such as patio furniture, automotive wheels and trim, lawnmowers and a wide range of other products requiring high quality, decorative finishes comparable to wet coatings.
Acrylic PowdersLike the polyesters, acrylics give excellent exterior durability. Common acrylic-based materials include urethane acrylics (hydroxyl functional resins), acrylic hybrids (acid functional resins) and glycidyl methacrylate acrylics (GMA) (epoxy functional resins).Urethane acrylics require cure temperatures of 360 °F (182 °C). Like urethane polyesters, they may exhibit problems with outgassing at thicker films (3 mils/75 m). They offer excellent thin film appearance, good chemical resistance and hard films. Flexibility and impact resistance is usually poor.
Coating ComparisonThe decision on what powder to use depends on the specific appearance and performance requirements of the end product. The end user must determine what specific properties they want in the coating and
communicate that to the formulator.When selecting a powder, several variables must be considered.
Cost of the powder (applied)
Performance characteristics
Application characteristics
Appearance
The proper coating is a balance of these variables. Coating manufacturers can help the applicator in the selection process. Given a particular specification, they can often formulate a powder to meet a specific application at a reasonable cost, particularly if the volume is high. The comparison charts below show some of the performance properties and typical uses of the various resins.
Property (Range) Epoxy Pure Polyester Epoxy PolyesterColor
All colors, clear and textures
All colors, clear and textures
All colors, clear and textures
Hardness (pencil)
H–2H
H– 2H
H –2H
Impact Resistance (Kg.cm)
100 –150
100 –150
100 –275
Gloss @60°
5 – 95
5 – 95
10 –95
Salt Spray Test
1,000 hrs.
750 hrs. min.
1,000 hrs. min.
Humidity Resistance
1,000 hrs.
1,000 hrs. min.
1,000 hrs. min.
Cure range
(Obj. Temp.)
180 - 200° C
10 – 15 Minutes
180 - 200° C
10 – 15 Minutes
180 ° C
10 – 15 Minutes
Coating SelectionThe first step in the coating selection process is to define the requirements i.e. powder film performance characteristics. With these specifications a manufacturer / user can work with a coating supplier to get just the right coating formulated for their specific need. The key selection factors are:
Demonstrated film performance
Demonstrated application characteristics
Cost performance balance
Testing of performance characteristics is important. For example, if the product is to be used outdoors, resistance to UV light and outdoor weatherability should be tested.The exposure chart below shows the results of testing for comparative gloss retention of different powder chemistries:
Nerocoat Powders
Powder ClassificationsThere are two basic classifications of powder coating materials. They are “thermoplastic” and “thermoset” powders.
Thermoplastic powders are generally applied to a surface that has been preheated to a temperature significantly higher than the melting point of the powder. It melts and flow when heat is applied but continue to have the same chemical composition when they solidify on cooling. Coatings of this type are based on thermoplastic resins of high molecular weight. These coatings are both tough and chemically resistant. Typical examples are:
Kansai Nerolac Paints Ltd is an ISO-9001 certified company and is engaged in the manufacture of Thermosetting Powder Coatings since 1984. Kansai Nerolac Paints Ltd. is India`s undisputed leader in the
manufacturing of powder coatings with brand name of NEROCOAT. Nerocoat Powders are available in variety of appearance or performance characteristics.
Nerocoat Advantages:Here are some good reasons for buying Nerocoat Powder coatings:
Quality: Nerocoat’s extensive product line has a well-deserved reputation for quality that ranks with the best in the industry.
Batch to batch Consistency: When it comes to consistency, Nerocoat products exceed the industry norm by a wide margin.
Faithful Color Matching: Give us your difficult colors. Precision color matching is our specialty.
Problem solving: Since pioneering the production of decorative powder coating in the country, Nerocoat has found effective solutions to hundreds of difficult coating problems.
Customer Service: You can depend on Nerocoat’s total package of efficient order handling, prompt delivery and attention to details. It adds up to superior customer service.
Technical Support: Our specialists will roll up their sleeves to help make your equipment run at its best and solve any on line problems.
Prompt & Flexible Response: We know that you need service, you need it now. Prompt attention is one of our priorities. This is the best down-time prevention insurance you can buy.
Nerocoat Range of ProductsNerolac manufactures Powder Coating in the following types:
Nerocoat Epoxy Powders Nerocoat Epoxies have the advantage of better chemical and solvent resistance.Application Areas: Nerocoat Epoxies can be used on Ferrous and Non Ferrous bases. These are suitable for internal usage, both in terms of decorative effect and surface protection in terms of long term corrosion and chemical resistance. Nerocoat Epoxies are not recommended for outdoor use when colour and gloss durability are required. However, if the loss of gloss and chalking is not of importance and superior salt spray and chemical resistance is required these can be used for exterior applications.Functional Qualities: Apart from the Excellent adhesion, corrosion preventive qualities, Nerocoat Epoxy coatings are well known for its supreme resistance to solvents and chemicals. There are many important products that require Epoxy coatings including kitchen cabinets and laboratory cabinets that require a certain type of chemical resistance.General characteristics of Epoxy PowderExcellent- Hardness, flexibility, corrosion, protection, chemical resistance, flow & finishFair-Over baking capabilitiesPoor- Very limited gloss & color stability from heat or UV exposureGloss @ 60 degree- 5 to 90 units PDS MSDS
Nerocoat Epoxy- Polyester ( Hybrid ) Powders Nerocoat Epoxy – Polyester powders have been developed for applications where the good appearance qualities of polyesters are required and good UV resistance is non-essential. These powders are economical, exhibit good transfer efficiency and can be sprayed by Electrostatic equipment or by friction charging.Application Areas: Nerocoat hybrid powders are mainly used for indoor coating of household appliances, furniture , light fittings ,electrical cabinets, etc.General characteristics of Epoxy Polyester PowderExcellent- Mechanical properties & colour stability on curing, corrosion resistance, flow & finish.Poor - Exterior durability and limited resistance against chalking from UV exposure.Gloss @ 60 degree 10-95 units PDS MSDS
Nerocoat Pure Polyester Powders These coatings have good edge coverage, good mechanical properties and exhibit excellent U.V. resistance. With proper surface preparation, baking and an adequate coating thickness, the corrosion resistance is good but resistance against specific solvents is limited. Application Areas: Nerocoat Polyester powders are ideal for use on components which could be subjected to outside exposure such as Air – conditioners, Garden furnitures, Agricultural equipments and external Automobile parts, etc.General characteristics of Pure Polyester PowderExcellent - Resistance to chalking from UV exposure, mechanical properties gloss & color stability from effects of heat. Excellent flow & finish.Gloss @ 60 degree 5 - 95 units PDS MSDS
Range of Nerocoat finishes High Gloss - Good Flow Finishes - Excellent decorative properties
The Powder Coating Process Powder coating processes may vary by the type of coating material being applied.However, the processes can generally be divided into four functions:
Preparation of the Surface Application of the Powder Heating of the Part Curing of the Coating
Preparation of the surface starts with a process to insure that the surface is properly cleaned and free of “soils” such as manufacturing oils. Subsequent surface treatments might include blasting, if required and iron phosphate or zinc phosphate depending on the long term corrosion performance desired Thermoplastic powders normally require a primer to promote adhesion. Thermoset powders do not need a primer because they have an adhesion promoter built-in. However, primers may be used with thermosets to enhance certain properties. The priming material used must be compatible with the curing temperatures required for powder coatings.PretreatmentThe term pretreatment refers to the mechanical or chemical surface treatment for a manufactured product. It may be as simple as a solvent wipe or it may be a multistage spray washer that cleans the part and applies a conversion coating for good paint adhesion and performance. The level of pretreatment employed is directly related to the appearance and performance requirements of the product in the field. Pretreatment provides a better bond of the coating helps to prevent the undercoat creepage of corrosion and also adds value to the product and extending its useful life.There are number of options to the type and extent of the pretreatment process used. In determining which process is required for a particular situation, one must consider the performance requirements of the final part, the coating being applied, the type of substrates being coated and the different types of pretreatment available. Knowledge of metal surfaces and the condition of their surfaces prior to coating is essential.SubstratesPretreatment chemicals and process vary from substrate to substrate. Given below are the types of pretreatment suitable for most widely used sheet metals.
SteelFor iron/steel surface maximum corrosion and salt spray resistance is obtained by a zinc phosphate coating which is applied by dip or spray process. Between the two the former is preferred as it gives better coating and can coat recessed areas of the components which are otherwise unapproachable by spray process.Process Sequence Phosphating: Spray or DipSubstrate: Mild SteelStage 1: alkaline degreasingStage 2: Water rinseStage 3: ConditioningStage 4: PhosphatingStage 5: Water RinseStage 6: Rinse with Chromate or deionized water.Stage 7: Dry in oven 100 degree Celsius.
AluminumPure Aluminum (99.5% Al) has low density, high ductility and low strength. Aluminum can be alloyed to produce metals with many of the desirable characteristics of the pure metal and added properties from the alloy for strength. Aluminum is commonly alloyed with one or more of the elements of copper, manganese, magnesium, silicon, nickel, tin, and zinc as major constituents and chromium, iron, nickel, silicon, and titanium as minor constituents or normal impurities. Since some alloys may have less corrosion resistance than the pure metal, they are sometimes clad with pure aluminum or another alloy with better corrosion resistance. The various alloys may respond differently to cleaning and treating.Process SequencePhosphating: Spray or DipSubstrate: Mild finish AluminumStage 1: Alkaline degreasing
Stage 2: Water rinseStage 3: Etching/PickingStage 4: Water rinseStage 5: DesmutStage 6: Water RinseStage 7: ChromatingStage 8: Water rinseStage 9: Dry in oven.
Zinc AlloyZinc coating of steel to produce galvanized steel can be produced by hot-dipping the steel into a molten bath of zinc or by electrolytic application in an ionic zinc solution. Galvanized materials are used to provide an additional layer of corrosion protection. The performance properties of the galvanized product produced by hot-dip or electrolytic process are not much different. However, the surface chemical properties do have some significant differences.Application of the powder is a function with many variations of two basic techniques. These techniques are fluidized bed and electrostatic spray. The fluidized bed is the original powder coating technique. It is still the primary technique used for the application of thermoplastic powders. The fluidized bed is also used for the application of some thermoset powders where high film build is required or components to be coated are very small. Thermoset powders designed for electrical insulation often use the fluidized bed technique. The parts are preheated to a temperature significantly higher than the melting point of the powder. The parts are then immersed into a “fluidized bed” of the coating powder where the plastic powder is melted onto the part.Electrostatic spray is the primary and most popular technique used for thermoset powders. The fundamental principle for this method is as follows :A high negative voltage ( 40 – 100 kV) causes a large number of electrons to attach to the powder particles. These electrically charged powder particles are attracted towards the grounded part and attach themselves like little magnets to the part. This provides an even film thickness.Tribostatic or Friction charging : Powders are also applied by friction charging that gets developed when powder particles with high flow speed rubbed against the gun hose wall made up of Teflon. Thus between the spray gun and the object, no powerful electric fields and lines of force develop. This makes it possible to achieve good powder penetration into otherwise inaccessible areas. By being less dependent on spray distance and the geometry of components, the tribostatic method often secures a more uniform coating thickness, however, powders have to be specially formulated for such application.
Powder Curing :Curing of the coating is the most important operation in powder coating plant. Careful selection of oven type, oven construction and oven dimensions are therefore very important. The sequence in the curing of thermosetting powder coatings is as follows:
Heating Melting of the powder Flowing Setting Curing ( cross linking / hardening)
All done in the same unit either a box or a continuous oven.Thermosetting powders normally melt in the range of 75 - 85° C, whereas the curing takes place at somewhat higher Temperatures, from 180 to 200° C. Melting and hardening are very important phases in the curing process. While the workpiece temperature increases the powder particles melt into liquid film with falling viscosity. At the same time the cross-linking of the polymer starts causing the viscosity to increase and the flow to stop within 1 to 2 minutes. The melt is transformed into a solid film. At this stage the film is brittle and glassy, but the subsequent heat treatment changes its properties to give flexibility , adhesion and other mechanical and chemical properties.
Basic conditions for successful powder coatingGood Earthing of the objectConventional electrostatic powder application leads to large quantities of negative charges being transferred to the object. If this large surplus of electrons cannot be efficiently earthed, the coated surface rapidly develops a powerful negative charge thus repelling the negatively charged powder from the spray gun. Consequently, without sufficient earthing it becomes impossible to build up a thick layer of powder with good flow and finish, rapidly and efficiently.Inadequate earthing can be easily recognized by little or no powder accumulation around the hanging point of the object being coated.
Good earthing of Spraying EquipmentTo ensure plant safety, it is absolutely essential to fully and effectively earth spray equipment, spray booths, and related equipment. This ultimately maximizes the avoidance of high voltage discharge and the possibility of resultant electrical sparks.Air QualityRelative humidity within the working environment is of great significance for spraying efficiency. Ideal relative humidity being 45 - 55% . A quicker build up of powder film and even coating are the advantages achieved by controlled humidity of working environment.Compressed Air QualityOnly clean, dry compressed air should be supplied to powder coating equipment. The quality of the compressed air can change the electrostatic charging and transporting properties of the powder. Impure compressed air may also cause visual defects in the coating.Other factors influencing spraying efficiencySpraying efficiency can be expressed as the percentage of sprayed powder which adheres to the object at the first application attempt. Maximum spraying efficiency provides several advantages, both technical and economic.The following are the representative of the most important factors that influence spraying efficiency.
The three criteria affecting powder coverage per kg. are: 1. The specific gravity (density) of the powder. 2. The thickness of the film
3. The percentage spraying loss Specific gravity is controlled by the type of resin and the amount and type of pigment used in the formulation.The film thickness is controlled by the method of application and for electrostatic spray application usually falls in the 50 to 100 microns range.The spraying loss for full filtration booth is usually about 2%. With a simple gravity dust collection system losses amount to no more then 10%. In the table below, no allowance has been made for spraying loss. If the actual coverage per kilo is required the spraying loss must be taken into consideration i.e. with a theoretical coverage of 10 sq. meters per kilo and a loss factor of 10% the actual coverage will be 9 sq. meters per kilos.Theoretical Coverage (square meter per kilogram) at 100% Application Efficiency
Price per kg. X Specific gravity X film Thickness in Microns Powder cost/sq. m. = -------------------------------------------------------------------------- 1000
Advice and GuidanceNormal problems which can arise in connection with powder coating with suggestions for their solution.
1. Problem/Fault: Coat too thin/impossible to increase thickness
Increase voltage, increase fluidization. Increase powder feed Check resistance between different support/objects on conveyer, ideal film reading is 0 ohm. Check earth connection from conveyer and outward. Check spraying equipment fuses, voltage, electrodes in gun mouth, all electrical connections to high
tension cable. Check powder by using another powder spray gun.
2. Problem/Fault: Thin or no coat at support hooksSuggested action
Problem is due to poor earth connection and should be investigated. 3. Problem/Fault: Poor flow /orange peel effectSuggested action
Increase fluidization from spray gun If possible reduce voltage Use fastest possible heating cycle in oven Adjust film thickness to give best possible appearance Check optimum distance between object and gun mouth.
4. Problem/Fault: Different powder outputs from gunsSuggested action
Different hose lengths between powders feed and gun. Air pressure too low. Ejector fault or partial blocking of ejector hose or gun.
5. Problem/Fault: Yellow or brown spots or stripes on the final coat.Suggested action
Poor cleaning Residues of cleaning agent Check that compressed air is free of water and oil.
6. Problem/Fault: CuringSuggested actionIf problems arise due to over or under curing from oven
Check that all thermostats are working properly. If possible check metal temperature using temperature recorder. Check air circulation. When all above points are functioning serviceably, increase or decrease the conveyer speed until
hardening is correct. 7. Problem/Fault: No powder from gunSuggested action
Check all fuses. Check compressed air. Blow through pneumatic system with air gun. Powder level in feed hoppers
8. Problem/Fault: Particles/dirt in powder coat filmSuggested action
Check that product is completely clean before coating Prevent dust from entering spray booth. Sieve powder and examine residue in sieve.
9. Problem/Fault: Craters full depthSuggested action
Indicate contamination of object prior to coating Check whether water-based paint has been used nearby. Check whether there is silicon in any materials/lubricants etc. Often used when welding.
10. Problem/Fault: Craters-fish eyesSuggested actionUsually indicate contamination of the powder, though may also indicate contamination of the object
Check that compressed air is free of water and oil. Check that powder is free of craters when using another spray gun or by melting powder on a plate. Test the powder coat on other objects.
11. Problem/Fault: Poor ChargingSuggested action When it becomes unusually difficult to get powder into the inside corners, there are three common things that should be checked.
Grounding Powder flow rate Voltage
Grounding may be lost from excess build-up of coating on the hangers. Measure the resistance from the part to the conveyor rail with an ohmmeter. If the resistance is greater than 1 mega ohm, the path to earth ground is not adequate. Check the components of the racking arrangement find the insulated component and clean it to make good contact.Excessive powder flow rates will cause a reduction in charging efficiency. Check the gauges and reduce the flow rate.The voltage at the gun tip needs to create a field of high potential. Check voltage at the gun tip to make sure that it is compatible with the gauge.
12. Problem/Fault: AdhesionSuggested actionPoor adhesion is usually related to poor pretreatment or under cure.
Undercure Run an electronic temperature recording device with a probe on the part to ensure that the metal temperature reaches the prescribed cure index
Pretreatment Perform regular titration and quality checks to avoid a pretreatment problem.
