Examination of dielectric constant and dynamic surface tension of lubricoolants during the bubbling

Subject and Purpose. The maintenance of physical and chemical properties and biological stability of lubricoolants during downtimes, which are bound to happen sometimes and last long, is a hot problem in metalworking industry. The procedure of bubbling for the lubricoolant mixing, saturation with oxygen and inactivation of anaerobic microflora calls for chemical and biological techniques to monitor the lubricoolant condition during the bubbling and after it. Yet the standard methods lack responsiveness and accuracy of the analysis, implying the further refinement of the output values. In the present work, microwave super-high frequency (SHF) dielectrometry is employed for the examination of the dielectric constant and dynamic surface tension of synthetic, semi-synthetic and organic emulsions during the bubbling. 

Methods and Methodology. The dielectric constant and dynamic surface tension of 5.7 % water-soluble emulsions are measured at frequency f = 37.7 GHz. A frequency sweep in the acoustic frequency range f = 20…25000 Hz is used, for which purpose the end of the 8-mm waveguide is supplied with a piezo сell.

Results. It has been revealed that the dielectric constant and dynamic surface tension of lubricoolants depend on the physicochemical characteristics that the lubricoolants acquire during a month-long downtime and after 10-, 20-, and 30-minute bubblings. The dielectric constant and dynamic surface tension demonstrate that the bubbling improves lubricating properties of all the emulsions examined. For this, a 10-minute bubbling is enough for semi-synthetic lubricoolants, and a 20-minute bubbling is needed for synthetic and organic lubricoolants.

Conclusion. The microwave dielectrometry method with a frequency sweep in the acoustic frequency range can be used in metalworking industry as an aid to lubricoolant quality control during the downtime or storage.