Eliminating Powder Buildup on Threaded Holes

Question:

The company I work for is having problems with our system. We are plugging threaded holes and getting powder buildup on the leading edges of threads, which is unacceptable to our customers. We would like to eliminate plugs altogether as it is very labor intensive. Is there a product or method that would allow us to eliminate the person required for this operation and prevent powder from getting on the threads? We have tried a Teflon coating without success. D.J.

Answer:

Before plugs were used, people would complain about using tape to mask threaded holes. The common issues with tape are the same as with plugs but to a higher degree (more labor and more time intensive process). Plugs were commonly thought of as an improvement over tape for holes and threaded areas. This has spawned an entire "generation" of powder coaters who only have experience with plugs and don't view them as "improvements" at all. The same can be said for the automobile replacing the horse and buggy. Most people complain about the air pollution and traffic problems with cars, but don't remember the problems with the horse and buggy (longer travel time and different waste "pollution" problems). Such is the fate of all "improvements" over time and the quest to find more advanced ideas.

Enough philosophy. Let's get back to your problem. Plugs are available in all sizes and shapes (straight, tapered, shouldered, etc.). You are probably using tapered plugs since they follow the "one size fits all" premise. This presents a problem. The plug body will seat before the end of the plug can mask the intended area. This can leave intended masking areas unprotected. Review this situation with your masking supplier who should recommend a straight plug, possibly with a shoulder, to mask all the intended areas. This solution will not eliminate your labor or time problems and will require a unique plug for each size hole you want to mask.

You can also contact a "hard masking" company. These vendors manufacture "hard-tooled" masks that are custom designed to mask all your intended areas at the same time using a metal fixture. These devices can be very expensive initially but are much cheaper to use in the long run, because they require little or no additional labor, especially if they are incorporated into the hanger design. They are creatively designed to mask the intended areas and yet allow the coated areas to be unencumbered. You may think that these "hard-tooled" masks are difficult to keep clean, but often they are applied as the parts enter the spray booth. After the spray booth, they are removed and cleaned with compressed air, since the powder coating has not yet been cured in the oven. However, if you apply these masks at the load area and remove them at the unload area, you must strip them just like any hanger or fixture.

These are the only two alternatives that I can think of for your problem. However, with new technologies being developed all the time, I suspect that someone is working on a new approach that may work even better. So let's ask the readers to suggest other ways to mask holes with devices that leave a defined edge using less labor.