Powder Coating: Contamination Control to Prevent Surface Defects

Powder coating is arguably preferable to wet spray painting due to its durability, high-quality finish, and resistance to corrosion. The process can give any shade to metal, from bright colors to neutral ones, and even combined tones. Surface contaminants can deteriorate the quality of powder coating finish and cause surface defects to metal. Adopting good contamination control in your manufacturing industry can help control these contaminants and produce a defect-free finish.

Sources of surface defects and control techniques

The causes of surface defects in powder coating processes can be broadly categorized in two ways: contaminates and humidification.

•    Contaminates

Dirt on the surface of metal is one of the major concerns for powder coating and a common cause of surface defects. Ineffective pre-treatment and cleaning procedures can be blamed for dirt on the metal surface during powder coating.

Airborne contaminants are other common causes of surface defects. They are usually hard to track as they can come from various sources such as the following:

•    The clothes of workers and other personnel in the plant.

•    Mechanical operations that generate dirt, wood dust, and metal shavings.

•    Outdoor contaminants such as pollen and road dust that may find their way into the plant through the doors, windows, and vents.

•    Equipment used in the coating operations may generate dirt that can cause surface defects.

Contaminants can be controlled by applying proper pre-treatment procedures before powder coating. Pre-treatment involves cleaning the surface to remove corrosive contaminates and dirt from the surface. Using a spray washer and alkaline cleaner can help remove dirt, oil, smut, and other contaminants. Mechanical procedures such as grinding, sandblasting, and polishing are also effective in removing surface defects and enhancing the corrosion properties of the metal.

•    Humidification and high temperatures

The powder used in this process requires dry air for maximum distribution. High temperatures and high humidity levels can result in a series of problems, including uneven coats, pigment clumping, and blemishes on the surface of the final finished product. Such defects can necessitate stripping and recoating of the metal due to the apparent surface defects which can undermine the quality of the product.

The relative humidity should be controlled to an average range so as to prevent surface defects resulting from excess humidification. Note that the hot parts attract powder more readily, and this can create lumps and uneven surfaces. Ensure that the parts being powder coated are cooled before the process.

With these potential causes of contamination and surface defects, achieving a smooth and blemish-free surface during powder coating can be challenging. However, by following the proper cleaning and humidity control procedure, you can substantially reduce or eliminate surface defects to achieve a high-quality finish.