The chemical, physical and biological properties of a neat cutting oil during prolonged use in a large manufacturing facility.

A 5-year study was conducted to investigate changes in the chemical, physical and biological properties of a neat cutting oil during prolonged use in a large manufacturing facility. Samples of cutting oil and other materials as appropriate, were collected at regular intervals. They were analysed for individual and total 4-6 ring polycyclic aromatic hydrocarbons (PCAs), additive and wear elements, boiling range, viscosity and particulates and in addition they were tested biologically to determine irritancy, sensitization and carcinogenic potential. Records were kept of plant utilization data and all oil additions, including the headstock lubricant and hydraulic oil which entered the cutting oil as contaminants on a regular basis. The cutting oil was 'laundered' each year. This involved removal of water and particulates, the lowering of viscosity by addition of mineral seal oil and the adjustment of the additive balance. The total amount of new oil entering the system during the study period amounted to an oil renewal rate averaging 38% by volume per annum. The generation of individual PCAs during the use of the cutting oil was slow and the dilution effect of oil additions prevented their excessive build-up. An equilibrium was reached after 2-3 years. The low level of build-up of individual PCAs was sufficient to produce a measurable increase in total PCAs determined by a gravimetric method. Laundering had no effect on individual PCA content or on the presence of wear elements but was useful in maintaining the physical properties and additive content. No evidence of any increase in irritancy, sensitizing or carcinogenic potential was found in the course of the study. These findings may also be applicable to other cutting oil systems, if the manner of use, the solvent-refined quality of all oils used, rate of oil losses and additions and the volume of the systems, are comparable with those described in the study.