How to Remove Old Powder from Parts
Q. If a part is already powder coated, how is the powder coat stripped before e-coating, if not by shot blasting? Does it need to go through an oven? Dip in a tank? L.M.
A. Powder is difficult to remove. It can be burned-off using a special oven that applies a controlled amount of heat (around 850°F) to char the powder to ash. It takes around four hours and it requires a power rinse to remove the ash. The capital equipment is fairly priced compared with some options, and the process is reliable. Not all parts can tolerate the temperature in a burn-off oven, so it’s effective for racks, but sometimes less effective for parts.
Powder can also be removed by a variety of chemical methods, some that are reasonably safe and clean to use. It costs a lot for the chemistry and you need to deal with a chemical management process and all of the rules that normally apply to safe handling of chemicals. Chemicals strip materials will not dissolve the coating, they will break the bond. The coating solids will collect in the tank and they need to be removed and properly disposed of. The results from chemical strips can be very effective and are usually much faster than a burn-off oven.
It can also be removed by molten salt strip. The equipment and material to do this process is expensive, but the process is very effective and fast. Molten salt will remove the coating down to bare metal in minutes. A quick rinse will leave the part clean, and you can strip virtually any metal if you have the right product in the bath. If you can afford the initial cost, this is the most effective way to remove powder from parts and it can be very cost effective, also.
Powder can also be stripped by a fluidized sand device. The part is immersed in the sand bed where a combination of heat and abrasion remove the coating. The cycle times are shorter than an oven. It is most effective when the coating is not too thick (all methods work better on thinner films). The equipment is fairly expensive, and it may not be the right method for some substrates. To learn more about your options, you should consider attending a program or obtaining a copy of the PCI Handbook.
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Masking is employed in most any metal finishing operation where only a specifically defined area of the surface of a part must be exposed to a process. Conversely, masking may be employed on a surface where treatment is either not required or must be avoided. This article covers the many aspects of masking for metal finishing, including applications, methods and the various types of masking employed.