Dirt in the Powder Coated Film

Q: We have an ongoing battle with dirt defects in our powder-coated film. The finish comes out looking good but the little specks of dirt in the coating cause us to sand and refinish too often. Is there a way to better understand what the dirt is and where it comes from so we can reduce this problem? It is cutting too deeply into our margin and reducing our productivity.

A: Over the years, I have worked on several projects to identify dirt. There are systematic ways to categorize a defect and identify the root cause and solution. Knowledge and experience play a role in this, but if you start with some basic methods and work systematically, you will learn and improve over time and be better at controlling these issues.

What you call “dirt” is too broad and you need to take a closer look at that word, separating it into several different types of particulates standing up in the film. Look for some practical things that can help identify what it is and where it came from. Start by looking for where it is in the film: on the substrate in the film or on the surface? This will help to connect it to a specific step in the process like pretreatment, application or the oven.

Next, look at characteristics such as size, shape and color. This will help you better define potential sources. With information gathered on patterns like colors, locations on the part and depth in the film, you can examine process variables, days of the week and possibly times of day. Patterns help lead to sources.

Use magnification to get a better look at the particles. A simple microscope can be one of your best tools for dirt identification. Try to find something in or around the system that matches the particle. As an example, suppose you find a white fiber near the surface. You inspect the area around the system and discover that the fiber matches white cloths that are used to wipe down surfaces in the powder application area. You compare the magnified fibers in the film to fibers from the cloth and they seem to match. You may want to eliminate the white cloths and see if that gets rid of the fibers in the film. Not all particles will show such neat connections, but you get the idea.

In addition to more formal identification of particulate, be sure that you are running a clean operation. Good maintenance practices can help limit dirt sources and reduce defects.

Assign someone in the facility to work specifically on defect analysis on a regular basis. A person that spends some of their time each day with a microscope and builds a library of defects can be very effective for reduction of defects. They can see patterns quickly and help to guide resolution. They can supervise lab testing or sampling on the line to work on defect discovery. They do not have to work full time at this but as time permits. A good defect analysis person can save a lot of lost cash and rework.