Corrosion Causes and Cures
This chapter considers various types of corrosion, discusses corrosion inhibitors, and presents corrosion-testing techniques that may be used to evaluate cutting, grinding, stamping, and drawing fluids. Corrosion of a metal is the deterioration of the material because of a reaction with its environment. Rusting is the corrosion of ferrous materials, a special case given the importance of ferrous materials. Of all the metals used for structural purposes, iron and steel far outweigh all others. The most common cause of aluminum staining with metalworking fluids is when the alkalinity (pH) of the mix is too high. High pH values will dissolve away aluminum's protective oxide layer and thus expose it to further corrosion. Very mild corrosion shows up as the alloy gaining a very pale yellow or golden appearance. A water-mix cutting fluid provides a reasonably favorable environment for culturing bacteria.