Maintaining the original form of a metal is important in the long run for better performance of machinery. This includes subjecting them to passivate which involves removal of any free iron and other ferrous contaminants from the surface of the metal treated to passivation. The metal must be subjected to passivate to remove all the unwanted debris and oils from the metal surface that is part of any machine. Stainless steel is basically corrosion proof but when it becomes a part if certain machinery then there is contact with other materials that come in contact with the apparatus which may alter the physical properties of the metal. Thus,passivate is required in certain cases to prevent corrosion of the metal and also rusting of it.
Why Passivate?
Most often debris, dirt, oil particles, free iron, etc have certain effects on the strength of the metal causing it to deteriorate which cannot be detected by the human eyes. To protect it from such damage passivate is performed which involves removing of free iron, debris, dirt, oil, grease, etc.
Though stainless steel is naturally corrosion resistant they are prone to rusting. Most often you find small spots of rust on the surface of the stainless steel. This happens because of the grain boundaries or foreign materials like grease and dirt deposited on the metal surface as they allow the oxidation of water molecules settled on them. This process is better known as rouging than rusting in case of stainless steel. And depending on the grade of the metal passivate is recommended to prevent rouging.
Factors to Consider for Metal to be Passivated
But there are certain pointers one must consider before subjecting the metal to passivate because it might not be the right process for metals or certain kind of steel. For instance most of the popular grades of stainless steel containing low levels of chromium and nickel must not passivate. This is because in such case there is always the risk of flask attack that is known to weaken the base material causing irreparable damage.
Being passivated does not remove the discoloration on welded and brazed parts and thus is not recommended for such metal parts. A superior process this known as BritePassivate process involving mild electro polishing of the metal is recommended for making the metal corrosion resistant.
Tips for Metal Passivate
While performing passivation, by your own using the passivate chemicals you must make sure that you clean the parts thoroughly and get rid of all kinds of grease, dirt, etc from the metal surface. To prepare the solution use good grade of water and avoid water rich in chlorides as they might cause flash attack. Make sure that you replace the passivate baths regularly which ensures the passivate potential of the solution.
Only free-machining stainless steel requires to be individually treated in the passivate bath while you can attempt batch passivate for other smaller parts to save time. When you follow these above mentioned pointers you can be certain that the metal will last long and you are protecting it from damages resulting from rusting and corrosion.