A turbidimetric method for the rapid evaluation of MWF emulsion stability

The stability of metalworking emulsions is a critical characteristic impacting its usefulness as a lubricant and rust inhibitor. Loss of stability usually results in replacement of the fluid leading to both economic loss and environmental discharge. In this paper, the loss of stability caused by accumulation of hardness ions is examined by a turbidimetric method. The method is based on following the change in the wavelength exponent of the emulsions caused by changing particle size. The stability as determined by this method is compared to conventional testing based on phase separation over 24 h. The turbidimetric method is shown to be a more conservative estimate of emulsion stability. The simplicity of the method makes it useful for both product formulation and process control.