Corrosion is a problem faced by every user—and manufacturer—of water diluted metalworking fluids. Corrosion can occur even with dry cutting and is not simply due to the use of water-based fluids. Water has a greater capacity for removing heat than oil; however, water alone in contact with freshly machined metal leads to corrosion. Heat removal is one of the most important functions of metalworking fluid. In placed with bad humidity inside the production shops especially in the eastern and midwestern areas of the united states during July, August, and September when temperatures and the relative humidity are high.
When the temperature rises, the rate of all chemical reactions also increases. Which creates corrosion. The high temperature in the presence of moisture and oxygen in the atmosphere is the reason corrosion happens more in the summertime.
Moisture condenses on a part and acts as an electrolyte to form a galvanic cell. If the concentration of the fluid, which provided rust protection during the fall and winter months, does not provide protection when the humidity climbs, an adjustment in the fluid concentration is necessary. If the concentration of 1:30 was adequate during fall and winter, then the concentration may need to be increased to 1:25 or to the point where rust is no longer seen. If a fluid user objects to increasing the concentration of his central system mix for reasons such as foam and potential skin problems, it may be necessary to increase rust protection with the use of additives. The additives used depend upon the type of metal(s) involved, the user’s chemical restrictions, additive availability and the fluid used.
The ph of a metalworking fluid is a factor in controlling corrosion. A high ph, greater than 9, will protect ferrous metals but will adversely affect the corrosion control of non-ferrous metals, such as aluminum, brass, and bronze.
When the ph is low in an individual machine, the easiest solution to the problem is to dump, clean and recharge with a new mix of the fluid product at the recommended concentration. If treating a central system mix, which is being used on ferrous metals, adjust the ph to between 8.8 and 9.2 with the proper additives. Excessively high mix phs are usually a sign of contamination, and the mix should be dumped and recharged.
If non-ferrous metals are being machined, and staining or pitting is a problem, check the product information to determine if the product was designed for use with non-ferrous metals.