Influence of synthetic lubricant fluids on the frictional coefficient

Abstract

The use of lubricant and coolant fluids permits improved machining quality and longer life of metal� cutting machines. The primary functions of such flu� ids are to reduce the temperature in the cutting zone and to minimize the frictional coefficient. These roles are interdependent: with increase in temperature, the adhesive component increases; with increase in fric� tional coefficient, the cutting temperature rises. Metalworking enterprises use different lubricant and coolant fluids for different operation. Watersolu� ble (emulsions and synthetic fluids) and oilbased mixtures are used, with concentrations of 2-10% (1). Synthetic lubricant and coolant fluids are of most interest, since they present fewer biohazards than do emulsions. The lubricating action of the fluids is mainly seen at chip-cutter contact and also blank-cutter contact. It is associated with the fluids' ability to participate in physical, chemical, and physicochemical interactions with the activated surfaces in the contact zone and to form hydrodynamic, physical (adsorptive), and chem� ical lubricant films. Depending on the cutting condi� tions, such films may be formed individually or simul� taneously. Physical and chemical lubricant films are said to be boundary films. Their thickness varies from to tens to hundreds of Angstrom. Their shear resistance is higher than for hydrodynamic films. When hydrodynamic lubricant films are formed in metal cutting (for exam� ple, in the lowspeed cutting of copper), the frictional surfaces are separated by a few microns of fluid. The viscosity of the lubricant and coolant fluid is of most importance here and must be optimal. Sometimes, the viscosity may be compensated by additions of sulfur, chlorine, or phosphorus compounds. The lubricant and coolant fluid may be selected by determining the actual frictional coefficient of fluids in machining some material and also their cooling properties, so as to improve the quality of machining (the dimensional and shape precision, the surface roughness and microstructure, etc.). The actual frictional coefficients of synthetic lubri� cant and coolant fluids in conditions resembling their working conditions may be determined on an II 5018 frictional machine, using a frictional shoe (T15K6 hard alloy) and a roller (steel 45). In the present work, we consider Biosil S, Isogrind�130EP, AkremonD�1, KonkrepolVTs, and Ekol�3 fluids, at a concentration of 10%. The force on the shoe P = 800 N; the roller speed n = 250 rpm. The table presents the results for the machining of steel 45 using synthetic lubricant and coolant fluids.