Cleaning and Pretreatment for Powder Coating – A Complete Guide
The quality of your powder coating finish often depends on the quality of preparation of your product surface. Improper preparation can lead to issues with your finish like bubbles, fish eyes, and more. Knowing that pretreatment of your powder coating surface is so important, it is critical to know important steps to properly prepare your product for powder coating. This guide will cover how to clean and pretreat a surface for powder coating so you can ensure optimal results.
Step 1 – Does the surface have rust or previous coating on it? – If yes you need to remove the rust or coating.
If the surface has any rust or previous coating on it, then sandblasting the product will be critical. Failure to remove any rust from the surface prior to powder coating will cause the rust to break through the powder coating causing pre mature failure of the coating. Removing rust from steel is commonly done using a sandblast cabinet or for larger products a sandblast pot or sandblast media recovery room. Recovering blast media can be a great idea to consider to reduce your sandblasting costs long term. You can also learn more about sandblasting through a variety of our articles here. Common blast medias you will use to remove rust prior to powder coating include crushed glass, aluminum oxide, or steel grit.
Step 2 – Chemically clean and potentially etch the surface for the Powder Coating to be applied
The next step to preparing your product for powder coating is chemically cleaning and pretreating the surface. The specifics of preparation will depend on the specifications that your customer will require. For best results you would clean, etch, and add a protective coating like a phosphatizing rinse to your product surface. However at bare minimum the product surface must be cleaned of all residual oils and soils as well as any rust (as mentioned above). Cleaners for powder coating are typically alkaline based chemicals which can be used with a dip tank, rinse, or a washer line to remove surface contaminants. Dip tanks and wash lines will use higher quality chemicals but for low volume use cleaners like TSP can be more effective than a solvent wipe. In addition to cleaning the surface, the next step for preparing a surface for powder coating will typically involve a chemical etch or etch and conversion coating process, or sandblasting the surface. A chemical etch will create a profile for your powder to adhere to and is especially important for powder coating metal like aluminum. Conversion coatings; Conversion coatings involving etching a surface and applying a chemical coating that adds further protection as well as a coating for the powder coating to adhere to. Sandblasting can also be used to create a profile for your powder coating to adhere to. Common conversion coatings include iron phosphate and zinc phosphate. Between the two iron is easier to apply but doesn’t provide the longevity of protection that zinc does, however most often iron phosphate is what is used.
Step 3 – Rinse the surface of all chemicals used and ensure it is clean and ready for powder and potentially seal the surface
The final step is to remove any chemicals used to clean and treat the surface. In a dip tank or wash line this will typically be done with neutralized water and then a slightly acidic solution to seal the surface. If you are using a hand method to clean the parts you can use a solvent like acetone after you have sandblasted to clean the surface.
Summary of Steps to Clean and Pretreat a Part for Powder Coating by Hand
Sandblast the product to remove any contaminants like rust and etch the surface
Clean the surface with TSP
Remove cleaner with Acetone
Summary of Steps for Dip Tanks and Washers
The steps will depend if you opt for a 3 or 5 stage pre treatment process. If their is rust on the surface you will want to sandblast the part. Next will be your washer. both 3 and 5 stage washers will involve a cleaning stage, a phosphate stage, and a rinse stage, additional stages like other rinse and seal stages may be included (which is common in 5 stage systems). You can learn more about the difference between 3 and 5 stage washers here.
Ultimately, proper preparation of your product surface will determine the quality of your powder coating finish outcome. By properly understanding what is needed to pretreat your powder coated surface you can ensure better results.