There are four main types of water-based metalworking fluids (also known as suds, coolants, slurry or soap):
- Soluble oil (emulsifiable oil): These emulsifiable oils are combinations of highly refined petroleum oils, emulsifiers and other additives. They are diluted with water at ratios of 1 part concentrate to 5-40 parts water. They are used where cooling is important and are relatively cheap.
- Semi-synthetics: These are a hybrid of water soluble and synthetic, containing lower levels of highly refined petroleum oils with emulsifiers and other additives which are diluted at ratios of 1 part concentrate to 10-40 parts water. They often appear translucent as the oil is a microemulsion. These fluids are versatile and especially useful in metal removal applications.
- Synthetics: These contain no petroleum oil, but are made from a range of chemicals. They are diluted at ratios of 1 part concentrate to 10-40 parts water. They tend to be used where cooling is important, but their properties can be varied by formulation.
- Biostable etc - Some metalworking fluids rely on other components of the fluid, which have antibacterial activity to prevent biofouling. These products are termed “biostable”
During use they can produce mists, the extent to which this occurs will depend on the nature of the fluid and the machining operation.
Since they contain water, diluted metalworking fluids can support microbial growth, so usually biocides are added to curtail this growth.