Passivation is simply a chemical term where a metal becomes affected by potentially corrosive environmental factors such as air and water. The process provides a shield on the outer layer of the metal to create a protective shell. Engineers use this basic process which involves applying a light coat of a protective material, such as metal oxide, to create a shell against corrosion.
1. The Problem
When stainless steel is cut or machined, “free iron” is left behind on the surface of the metal. This prevents the natural formation of protective oxides on the surface. Without the necessary “shell” protecting the metal, corrosion will weaken the metal causing the part to fail. Unseen by the naked eye, the free iron must be removed to allow the metal to “cure” with a hard shell.
2. The Solution: Stainless Steel Passivation
Passivation utilizes a two-step approach to prepare and protect the metal from corrosion. The part is immersed into a clean plastic coated basket or tub. The cleaner is heated for 20 minutes to remove any oil, polishing compounds or other foreign materials from the surface of the part.
3. “Curing” Process
The most critical step in stainless steel passivation is determining the time, temperature, and acidic composition of the chemical solution to properly clean the part. Unfortunately, the success of preparing the part is dependent on the machining and heat treatment of the part. Failure to use proper thermal processes on a part can lead to discoloration that cannot be removed.
4. Final Rinsing
After the time is up, the part is removed for rinsing and drying.
Advantage of Passivation
* The process improves the corrosion resistance of the metal
* It reduces labor-intensive steps to “cure” the surface
* It presents a smooth and polished surface
* It improves and extends the life of the product
* Cost Effective
* The only method ensuring the metal is truly “stainless steel”
Crucial Standards to Ensure Quality
The industry created two standards: the FED: Sp0ecs AMS 2700, and the ASTM A967. You should not contract with a supplier unless they follow these strict quality control measures.
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