One of the least understood variables in a cleaning process is the soils to be removed. The attitude often is that oil is oil. Alternatively the oil is a standard soil in industrial use. The vast variation of base oil and proprietary additives is heavily discounted. This often results in cleaning processes that were initially producing parts that were cleaned for the purpose intended: now being unsatisfactory. The coolant, rust preventive, stamping compound change is not acknowledged until well into the trouble-shooting cycle.
Oils and their ability to be removed vary greatly. Naphthenic feed stocks are generally the easiest to clean. Paraffinic feed stocks have more cleaning issues. The issue becomes more complicated when materials with a high melt temperature have been dissolved into a solvent/oil.
Each feed stock and blended oil has its own HLB number. HLB stand for Hydrophobic-lypophobic Balance. Organics known as surfactants or detergents each has a corresponding HLB. The formulating trick is to blend surfactants in such a way that the widest variety of HLB is covered. On occasion a specific cleaning compound must be developed for a specific soil.
“Water Based” coolants and stamping compound bring their own concerns to cleaning. Generally these are addressed by the correct detergent builder system.
Chlorinated metal forming materials bring the unique condition of becoming more difficult to clean with time. The longer the formed part is allowed to sit before cleaning the more “varnish” and possibly rust is formed. Often a caustic rust remover step is required before continuing with the normal wash process.