In Search of a High-Temp Sealant

Question:

We manufacture cases for all types of industries. We powder coat most of our aluminum cases and sometimes use silicone caulk to seal the cases to make them watertight. We want to apply the silicone before we powder coat our parts so that it cannot be seen after painting, however, we ran into some problems. We believe the silicone reacted with the trichloroethylene at 80°C. This softened the caulk, which ran down the side of the case. This was near impossible to paint over, but eventually we managed it. Do you know of a sealant that can withstand the high temperatures involved in powder coating and not to react with the trichloroethylene cleaning process? G. S.

Answer:

There are numerous reasons for not caulking the product before powder coating your parts. Many of them you have already experienced, such as having problems with the trichloroethylene cleaning process. Some problems that can happen you have yet to experience. For instance, the caulk is very flexible and the powder coating is not. Therefore, after curing the powder coating will most likely crack and chip from the sealant exposing the caulk. Furthermore, powder coating is not formulated to adhere to the caulk and will most probably peel off anyway. If that happens, what was the point of coating the caulk in the first place? I recommend that you clean and coat your products first and then use the sealant caulk. Select a caulk that has a pleasing or matching color (possibly clear). If you insist on caulking your product first, then do it after cleaning. At least you won’t have to worry about the trichloroethylene anymore.