It is very difficult to make powder coating run, drip or sag, resulting in significantly lower reject rates for appearance issues. Powder coating operations require minimal operator training and supervision when compared with some other coating technologies. Employees typically prefer to work with dry powder rather than liquid paints, and housekeeping problems and clothing contamination are kept to a minimum. Also, compliance with federal and state regulations is easier, saving both time and money.
There are two types of powder coatings: thermoplastic and thermosetting. Thermoplastic powders melt and flow when heat is applied, but they continue to have the same chemical composition once they cool and solidify. Thermosetting powder coatings also melt when exposed to heat, but they then chemically cross-link within themselves or with other reactive components. The cured coating has a different chemical structure than the basic resin.
Thermosetting coatings are heat-stable and, unlike thermoplastic powders, will not soften back to the liquid phase when reheated. Thermoset powders can also be applied by spray application to develop thinner films with better appearance than some thermoplastic powder coatings.
The main driver in the development of powder coating materials was the pursuit of an environmentally friendly alternative to solvent-laden paints. In pursuit of a spray-able, low-VOC coating, Dr. Pieter g. This made powder coating materials much more consistent and provided the opportunity for thinner-film thermoset products that could better compete with liquid coatings.
De Lange also developed the electrostatic spray application method for thermoset powder coatings in The process was introduced in the United States in the s, and rapid growth continued for the next 30 years. The first step in the powder coating process is to prepare or pretreat the parts. The product to be coated is exposed to cleaning and pretreatment operations to ensure that surfaces to be coated are clean and free of grease, dust, oils, rust and other contaminants.
Chemical pretreatment normally takes place in a series of spray chambers. Parts are first cleaned using an alkaline, acidic or neutral cleaner. In many cases the part is surface-treated with a conversion coating of iron or zinc phosphate or a transitional metal conversion coating such as a zirconium oxide product.
Each stage is typically separated by a rinse stage to remove residual chemistry. Spray systems enable pretreatment of a wide variety of part sizes and configurations; dip tanks may be used instead of spray for some applications.
The specific pretreatment process selected depends on the characteristics of the coating and substrate materials, and on the end use of the product being coated. Pretreatments most often used in powder coating are iron phosphate for steel, zinc phosphate for galvanized or steel substrates, and chromium phosphates or non-chrome treatments for aluminum substrates. In addition to traditional phosphate processes, a new group of technologies has emerged that uses transition metals and organo-metallic materials or other alternatives.
These alternative conversion coatings can be applied with little or no heat, and they are less prone to sludge buildup in the pretreatment bath than conventional iron or zinc phosphate formulations. The result is greater operating efficiencies in terms of lower energy costs, reduced floor-space requirements and decreased waste-disposal requirements.
Other advances include non-chrome seal systems, which can yield improved corrosion protection on steel, galvanized steel and aluminum alloys. Dry-in-place pretreatment products, such as a seal rinse over an alkali metal phosphate, can reduce the number of stages required before powder coating application. Chrome dried-in-place treatments are effective on multi-metal substrates and may be the sole pretreatment required for some applications. Non-chrome technologies are commonly used as well.
Non-chrome aluminum treatments have become very popular over time with excellent performance properties. After the chemical pretreatment process is complete, parts are dried in a low-temperature dry-off oven. They are then ready to be coated. For many functional applications, a mechanical pretreatment such as sand or shot blasting can be used.
With this method, high-velocity air is used to drive sand, grit or steel shot toward the substrate, developing an anchor pattern on the part that improves the adhesion of the powder coating to the substrate.
Mechanical cleaning is particularly useful for removal of inorganic contaminants such as rust, mill scale and laser oxide. Mechanical blasting can be used alone or along with a chemical treatment.
The blast operation creates an excellent surface for bond but does not add any additional corrosion protection. In many cases, the blasted surface is first coated with a suitable primer to add additional corrosion protection for blast-only surfaces.
The primer can be further enhanced by using a zinc containing material. The most common way to apply powder coating materials uses a spray device with a powder delivery system and electrostatic spray gun. A spray booth with a powder recovery system is used to enclose the application process and collect any oversprayed powder.
Powder delivery systems consist of a powder storage container or feed hopper, and a pumping device that transports a mixture of powder and air into hoses or feed tubes. Some feed hoppers vibrate to help prevent clogging or clumping of powders prior to entry into the transport lines.
New Cars. Car Culture. Type keyword s to search. Today's Top Stories. R for This type is much cheaper compared to thermoplastic. Preparation is the first step of the process and perhaps the most important one. This step determines how well the powder coating adheres to the metal surface, and there are various options for cleaning and prepping the surface. The powder is then applied using the spray gun, and curing begins right after that. Powder coating is based on polymer resin combined with pigments, curative, flow modifiers, leveling agents, and several other additives.
All ingredients are melt mixed together, then cooled and ground into a powder. Preheating achieves a uniform finish, and cooling helps form a hard coating. The powder coating process eliminates overspray wastage that may be experienced with solvent-based paints. Powder coatings are different from paint in the fact that they need an electric charge to work, while paint needs an adhesive. An electrostatic paint sprayer is used for the application process.
It imparts a positive electric charge on the powder and accelerates it towards the components through an electrostatic charge. The chemical bonding process strengthens the powder coating because once cured, the bonds solidify.
One of the most significant advantages of using powder coatings is that once solidified, more layers can be added id thickness is desired. Thicker coatings mean longevity and increased protection. Powder coatings are suitable for metal because they repel corrosive materials, such as chemicals and water.
This is hands down one of the most durable coatings you could use as a finish for a variety of surfaces, not just metal. Upon application of the coating, the next step in the powder-coating process is curing, which involves baking the workpiece in a specially designed oven.
Curing results in the formation of a protective skin and promotes coating adhesion. In general, curing is performed at F for approximately minutes, although these parameters can vary based on the type of powder coating. This normally entails the removal of grease, oil, dirt and other materials via chemical, physical or mechanical methods to clean the surface and promote coating adhesion.
The powder-coating process is extremely efficient — most jobs require only one coat, which helps to minimize project costs. Powder coating is cheaper than wet paint and results in lower energy and disposal costs.
It is also easy to adapt the coating thickness to meet the protective requirements of the project.
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