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Powder Coating / Powdercoating: The How, What, and Why of the powder industry.
What is powder coating? Why should I consider using it? How will it work in my operation? These are the questions that every finisher needs to be asking today.
Powder coating is a dry clean finish that gives a highly durable coating. In the long run, powder coating will save you money, time and the need to use volatile organic compounds.
WHY POWDERCOAT?
Over the past decade, powder coating has been increasingly accepted as the preferred finishing process. The reasons for this conversion from wet to dry powder can be attributed to three major forces:
ECONOMY
1) Material
utilization is much higher with powder, making your material costs
much lower. 92%-98% of the powder you buy will be applied to
the parts you are finishing versus an average of 60% with an
electrostatic liquid system (The other 40% is waste and must be
disposed of).
2) Since most of the material is used on the part, there is very
little waste to be disposed of. Powder is not considered
hazardous waste, so the cost of disposal is minimal.
3) Air used to exhaust the powder spray booth is returned directly
to the plant, eliminating heating and cooling costs for the make-up
air required when air is vented outside the plant.
EXCELLENCE
1) The cured powder finish is less
susceptible to damage than a liquid finish. There is less need for repair
work on the finished item. This results in the need for much less
elaborate packaging saving time and cost on re-working and packaging.
2) Epoxy, acrylic, and hybrid powders provide excellent adhesion and harness for
improved resistance to chipping, abrasion, corrosion, and chemicals; Ant
it is flexible enough to be formable without cracking
3) Polyester powders provide additional advantages in ultraviolet and weathering
resistance.
ECOLOGY
1) Stringent regulations are being
aggressively enforced in an effort to control air pollution and hazardous waste
disposal. Powder coating is the overwhelming preference of the EPA.
2) Powder coating eliminate solvent fumes and VOC's from spray booths and oven
exhausts that pollute the air.
3) Potentially toxic sludge and water that can contaminate the earth and must be
disposed of as hazardous waste is eliminated.
WHAT IS POWDER COATING?
Powder is a dry coating. Instead of being dissolved or suspended in a liquid medium, such as solvent or water, powder is applied in a granular form. Powder coating is created by blending the various components (binders, resins, pigments, fillers and additives) and processing them through an extruder into a continuous mass. This homogenous mass is cooled and broken into small chips, which are then ground into the powder. Each powder particle contains within it the necessary components for reforming into the finished coating. After the powder is applied to the part, typically using an electrostatic spray process, the part passes through an oven and cures, melting into a smooth film on the surface of the part.
POWDER COATING EQUIPMENT
Application Equipment: Powder is usually applied with a spray gun. Most guns are similar in their function of spraying the powder. Each gun has a control unit that regulates the voltage being generated and rate at which the powder is delivered from the hopper. Areas to review when selecting the application equipment are the efficiency of the charge, the consistency of the powder flow, and the accuracy with which both can be adjusted to provide the right level of performance. Once the optimal setting has been established, it is important that they can be repeated systematically each time they are used.
Spray Booths and Recovery: Powder booths are very similar, but use two distinct types of recovery equipment, cartridge filters or a cyclone separator. Each style is particularly suitable for a different type of application. To select the appropriate system, you should consider the production size, finish quality of the desired coating, the number of different types or colors of powder being used, and the frequency with which they are changed. The should also be considered when
Therefore, prior to starting your search for the perfect powder system, you should have a clear picture of what you need and what factors are important to your operation. If you expect to change powders frequently, then a fast color change time will be high on the list of necessary features; If however, you do long runs using the same powder throughout, then a highly efficient reclaim system will be more critical. If the parts are all the same then automatic guns may be cost effective, but if they are intricate structures that are difficult to coat, manual operators may make more sense.
HOW IS THE POWDER APPLIED?
The application process involves applying a charge to the dry powder particles and spraying them onto a grounded substrate. The substrate, or part, is typically grounded through the conveyor or hanger holding the part. The powder, once attracted to the part, is then held on the surface until it is melted and cured into a smooth coating film in the bake oven. The spray process takes place inside a booth designed to contain the oversprayed powder and makes it possible to collect and reclaim it for re-use. The powder is fed pneumatically out of the powder container, or hopper, into the powder applicator, or gun. As the powder exits the gun, a low amperage high voltage charge is applied to the powder particles, causing them to be attracted to the grounded workpiece. This attraction may even cause the powder to "wrap" around the piece coating the back side. The over-sprayed powder suspended in the air contained inside the powder booth, is then passed through a separation process that permits the powder particles to be retrieved from the air. The clean air is fed back to the work environment eliminating the need for air make-up. The reclaimed powder is mixed with a proportionate amount of fresh virgin powder for reuse, achieving consistent results and up to 98% material utilization.
