Process: Powder Coating
Unlike conventional liquid or wet painting, powder coating is a dry finishing process. Fine, grounded up particles containing pigments and resins are sprayed onto a metal substrate using an electrostatic spray gun. Unlike liquid paints, the powder coating process does not involve the use of any solvents, making it an almost pollution free application!! In addition, unused, excess powder can be recycled and reused making this the greenest of all paint applications!!! The powder coating process involves three basic steps, part preparation or pre-treatment, powder application, and curing. However, there are other steps involved prior to these that are essential.
Often times before a manufactured part can be powder coated; it is necessary that specified areas are masked off to be free of any coating. We use a variety of masks such as silicone caps and plugs, high temperature green tape, spot masks and even steel templates depending on the masking requirements, size of the part, tolerances allowed, and quantity of parts to be masked.
Caps and plugs are specifically used when masking threaded holes and pem nuts. Threaded areas are always masked off to prevent powder build up which interrupts the final and proper assembly of a coated part. All caps and plugs are removed before the finished product reaches the customer. This is done during the final inspection and packaging of the coated parts.
(Shown above is a large chassis that has over 100 threaded areas that must be capped and plugged)
Masking is also done on parts that require paint free areas for electrical grounding contact. Moreover, many parts even require that the entire interior surfaces be free of powder. This involves the use of specifically sized masking tape, custom diameter spot masks, plugs and caps, or a combination of all. We only use the highest quality, highest temperature masking tape so that the application and removal is easy without leaving any adhesive residues on the finished product. This also results in clean, straight lines between where the masked edges meet the coated surface. The range of masking performed at Coatings Applications is limitless. The photos below will give you an idea as to how wide this masking spectrum is. Obviously, all masking is done based on specific customer requests and requirements.
(Example of spot masking, with a specific area masked off for electrical grounding)
(This part requires all holes be masked off using custom sized spot masks)
(Finished product showing spot masked areas free of coating)
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(This project required that the entire interior surface be masked off and free of any coating)
STAGE 2: RACKING/HANGING PARTS
Once all masking requirements are completed, all parts must be hung, or racked, on our conveyor line before passing through the three stage washer. The quality and cleanliness of these racks is extremely vital to the quality of the finished product. Coatings Applications has a planned schedule to regularly strip and clean our racking systems to prevent excess powder build-up, which reduces the grounding and electrostatic attraction properties essential to the powder coating process. In addition, racks free of excess powder drastically lower the chances of dirt defects and blemishes on the final product that can result from this excess powder cracking during the curing process. Most importantly, at Coatings Applications, we have an ample supply of racks so that production is never halted, or slowed down!!
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(CLEAN, POWDER FREE RACKS)
STAGE 3: PRETREATMENT AND DRY OFF OVEN 3-STAGE IRON PHOSPHATE WASH
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The success or failure of most powder coating applications can almost always be traced back to the quality of, or lack of pretreatment of a substrate before coating. The goal of pretreatment is to create a clean, porous surface which promotes good paint adhesion while also helping to prevent under film corrosion after the coating process is complete.
Coatings Applications utilizes a three stage iron phosphate system to properly pretreat and prepare parts to be powder coated. This three-stage system is comprised of a degreaser/phosphate in one stage, followed by a water rinse and a seal rinse in the third and final stage. This phosphating process, also referred to as conversion coating, adds significantly to the overall cosmetic qualities, durability, and corrosion resistance of the finished product. This is a direct result of the uniform substrate surface that is created during the phosphate process. Once treated by the phosphate wash system, metal parts will appear blue and gray in color, signifying that an iron oxide base has been formed and that the parts are clean, degreased, and free of oils, residues or any other chemicals remaining from the fabrication process.
The next step for all parts is to pass through our dry-off oven. The main goal of the dry off oven is to expose parts to high temperature and heat to ensure that all moisture remaining from the phosphate wash is thoroughly removed. Furthermore, the elevated temperatures will force oils and residues from fabrication out of the metal. This drying stage adds significantly to the quality of the finished product by helping to prevent runs and water marks. Once they have passed through the dry off oven, parts are ready to be powder coated.
STAGE 4: POWDER APPLICATION
The powder application is done using an electrostatic spray gun. Electrostatic guns work because the powder is electrically charged utilizing compressed air and voltage. The powder is held in the hopper and fluidized. Once the trigger is pulled on the spray gun, the powder is pulled to and out of the gun using compressed air. In addition a voltage source creates an electrostatic field at the tip of the gun which imparts the powder with a positive charge. As a result, the powder adheres to the grounded part until heated in our convection oven, which initiates the curing process. Once coated, the parts are sent into our convection oven.
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The curing process, known as cross linking, occurs when the powder coating is exposed to elevated temperatures. The specific powder being used will determine what temperature the parts are cured at, and for what amount of time. The range of cure time and temperature is typically in the range 350 °F and 400 °F (177 - 204 °C) for 10-15 minutes. The heat causes the powder coating to melt, flow out and harden. Convection curing is both dependable and flexible. Depending on the specific application, the oven temperature as well as the conveyor’s line speed can be easily adjusted.
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STAGE 6: INSPECTION AND PACKAGING
After the parts have passed through the oven, the only thing left is to inspect, remove any masking, and properly package them for transit. Depending on the size, shape, weight and quantity of the parts, they are packaged using a variety of packaging materials. All parts are carefully wrapped and packaged to prevent them from moving around during transit.
to continue onto shipping methods.