plating, anodizing, & finishing Q&As since 1989
Polishing of stainless steel
I am looking for a way to get a surface finish around 4 Ra or better on Stainless Steel without using EP. And of course, I'm looking for the cheapest means possible. However, the parts will be used in an Ultra High Purity setting in the semiconductor industry, so surface chemistry is a must. The parts will go through a citric passivation process after whatever polishing we end up on. I was looking into using felt bob's with some time of diamond compound; is this a good low cost solution? -KBKevin Bennett
- Santa Clara, California
Any abrasive polish can leave embedded particulates in the surface, and can disturb the material grain structure at the surface. Both are lethal to semiconductor processes as they can release microparticles into entrained gas streams. These are two of the many reasons why CMP was developed. I'm curious, though. Why the prohibition on electropolish? It leaves an excellent surface and passivates far better than Citric. Its used quite commonly for Stainless semiconductor vacuum equipment and internal surfaces of gas manifold valves & piping. It can also be done on the most complicated gizmos...internal bores and out. But EP is a bit sensitive to selection of raw materials.
CMP (Chemical Mechanical Polished) stainless steel surface can be polished to Ra of less than 1 microinch. If we can be of service, please let me know.
Michael Liu Taylor
specialty stainless steel distributor - Dallas, Texas
A couple of things. Any fine surface profile is not normally cheap. Then again, it depends upon where you are starting from, then comes volume of parts to be process and configuration. You already told us the metal. The fastest way to improve a surface finish is by using an abrasive mechanical process and that is also normally the cheapest. That usually means mass finishing systems, but it can involve buffing. The surface profile of 4Ra is a good finish but is commonly achieved using maybe a 2 step mass finishing process.
P.S.: A diamond dust compound and wheel bob is an expensive proposition and not worth the effort for that Ra. If you want to use a wheel, use a non-woven abrasive wheel. That should accomplish 4 Ra surface finish.
retired business owner - Hatboro, Pennsylvania
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