Archive: Feb 2023

What is the Powder Coating Process?

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The powder coating process is a dry painting process that is mainly used for coating metal. There are several methods for applying powder coating. The most commonly used method is spraying electrostatically charged particles of pigment and resin onto an electrically grounded piece. Heat is used to melt the powder, causing it to flow, form a thin film and eventually dry to a hard, scratch-resistant shell.

As with any painting job, the most important step in the powder coating process is preparing the surface. Before the powder coat is applied, metal surfaces are thoroughly cleaned to remove oils, dirt and grease. After the metal has been cleaned, it is generally rinsed and given an acid bath to etch the surface. An etched or slightly rough surface helps to ensure proper adhesion and an even distribution during the powder coating process.

The next step in the process is the actual powder application. The application method varies depending on the type of powder being used. The two main types of media used in the powder coating process are thermoplastic powder and thermoset polymer. Both types of powder rely on heat curing, but they do so in different ways.

Thermoplastic powder is usually applied to a heated work piece. The hot metal causes the powder to melt, flow and then harden upon cooling. Thermoplastic powder does not undergo any chemical change as it hardens. That means that the finished work can often be reheated to even out any thin or uneven spots in the finish.

Thermoset polymer is applied to the work at room temperature, then heat-cured in an oven. The part is heated and held for a set period of time at temperatures of 320-410 degrees Fahrenheit (about 160-210 degrees Celsius). During that time, the polymer undergoes a chemical change known as “cross-linking.” The curing of thermoset polymer happens in four phases, which include melting, flowing, forming a gel and, finally, curing to a hard shell.

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What Is Powder Paint?

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Powder paint is a dry, colored powder that is sprayed onto a steel structure by using a special application gun that uses air to discharge the powder. The special powder paint is positively charged while the material the powder is being applied to is negatively charged, causing the powder to stick to the steel. Once covered in powder paint, the item is placed into a large, specially-designed oven and baked for a time specific for the type and color of powder used. Once baked and cured, the result is a durable and very tough finish that resists cracking, scratching and dulling. The finish can be maintained, much like traditional paint, by washing and waxing.

Due to the method used to cure the powder paint, entire body panels are not usually finished with this type of coating. Typical candidates for the powder paint are chassis, wheels and other smaller steel components. Roll cages and motorcycle frames are also fine projects to use powder paint on. The finish is very thick and very hard to remove, making the taping of threaded holes and other areas that paint is not wanted on very important. It is also very crucial that even coverage is achieved as the blending and touching up of powder paint is very difficult.

Surface preparation is as critical with the powdered version as it is with traditional paints. Grease and oil must be removed from any surface with a quality remover to promote proper powder adhesion to the steel surface. Once the powder has been applied, it is important that the parts be placed in the oven and cured as soon as possible. This will lessen the chances that the powder will be touched and rubbed off of the steel. The powder will melt in the oven, creating a liquid that will flow out evenly and fill any small voids or cracks in the surface of the steel.

Once cooled, the powder paint becomes a hard finish that is resistant to scratching and chipping. The thick finish is often responsible for making tight-fitting components very tough to assemble. It is sometimes necessary to scrape or sand some of the finish away to enable the parts to fit together when reassembling some components. While this type of finish is favored by many race car builders, it is often a problem when an accident requires the frame or chassis to be welded. In order to weld on the cured powder paint, the finish must be ground away.

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