Steel surface treatment
Profile surface processing
The main surface treatments used in Calvi are:
• mechanical pickling (shot blasting)
• chemical pickling
• lubrication
• passivation
Mechanical pickling (Shot blasting)
Mechanical pickling removes oxide and calamine residues, oil and lubrication products from the steel surface. It is performed before the drawing operations to clean the steel surface and prepare it for the next lubrication stages.
Chemical pickling
Chemical pickling is carried out before shot blasting when very complex shapes need to made and shot blasting alone is not able not reach all the parts of the shape. Sulphuric acid is used for treating carbon or alloy steels, while nitric acid is used for stainless steels.
Lubrication
Drawing material is lubricated by immersing it in a phosphating solution, and then in soap solutions in the case of carbon or alloy steels. When stainless steels are used, they are immersed in appropriate salt solutions and drawn using lubricating oils.
Passivation
After being drawn, stainless steels are cleaned of all lubricant residues and immersed in appropriate passivation solutions to prevent contaminants from starting undesired oxidative processes.
