Masking Machined Surfaces

Question:

My company produces industrial control valves. We are painting these control valves and are looking for some way to protect the machined surfaces between valve cover and the body. We cannot get paint on these machined surfaces. Do you have any ideas how we could protect our machined surfaces on the castings from corrosion, before painting, that will not affect the machined tolerances? We would like 400 hours salt spray or better. G.K.

Answer:

For instructional purposes, the answers to your question can be classified as easy, difficult and impossible. I offer these instructions for you and the benefit of others who may have similar problems. One easy answer is: mask the machined surfaces before painting. Another easy answer is: apply a strippable coating to the machined surfaces, which can be removed after assembly. Neither of these solutions will work for you because they will not provide corrosion protection. The difficult answer is: apply a temporary corrosion-resistant coating to the machined surfaces, which can be dissolved by a solvent before assembly. This solution may work for you if the temporary coating can provide 400 hours salt spray resistance. The impossible answer is: to get 400 hours salt spray resistance, you have to use a corrosion-resistant coating on the machined surfaces. This solution will not work for you because it will mess up the tolerances.