We need to understand about the level of finish needed and how it can be achieved in case of various industrial equipment and parts. In the process industry, standard surface finishes are needed which is usually set by the regulatory agencies
Also, the manufacturers specify certain finishing level on processing equipment to ensure cleanability and sanitation. They need sanitary finishes to get minimum roughness which is typically measured in unit of µ inches or µ meters.
You may know about your type of finish needed for the application, but in case you need to really understand all terms and their definitions used for say stainless steel surface finish, then you may read about them.
Surface finishes are enhanced by various means using both mechanical as well as chemical treatments that are also used for sanitary valves too. Following are few methods used in our industry.
- Mill Finish
Mill finishes will offer you matte non-uniform or dull appearance with roughness of minimum 100 µ inches. This finish may not meet requirements for sanitary processing finishing.
- 2B Mill Finish
This finish will have more reflective appearance, like any cloudy mirror. In various food, chemical applications this finish is very common and can have large range of roughness values too.
- No. 4 Finish
It will have roughness of 29 – 40 µ inches. You can also find this finish for clean rooms and also in equipment for food processing.
- No. 4A Finish
It is similar to above no. 4 finish which can be characterized by short and polished brush lines however use finer grit polish. The roughness of this finish is 18 to 31 µ inches.
- Bead blasting
It uses fine bead material, like glass, at high pressure for providing a certain finish level. Roughness values are greater than 45 based on blasting process.
This means removing all the excess iron/iron compounds from surface of metal by using acid solution.
Removing these impurities will allows formation of oxide layer which protects rest of steel from corrosion. There will be little effect of passivation roughness values.
This is electrochemical process in which the surface metal will be dissolved and all the embedded contaminants will be removed. This will create a “smooth” mirror like finish and which can result in enhanced smoothness.
Therefore, many kinds of chemical and other processes are used for achieving various level of smooth finishes.
While selecting equipment for higher-end finishes, often we can see processors select to exceed minimal standards that set by the regulatory agencies for decreasing bacteria risk.