Abstract
Laboratorial two-body wear testing was carried out in order to assess effects of polypropylene modification by impregnating it with oils on friction coefficient and wear in comparison to those parameters of unmodified polypropylene, Teflon, and polyamide during operation under conditions of sliding friction without lubrication. Wear behaviour of the tested specimens was investigated using ASTM G77-98 standard wear test equipment. Recording program made it possible to visualise and record the following parameters: rotational speed and load, linear wear, friction coefficient, temperature of the specimen, and ambient temperature. In addition, wear mechanisms of the analysed materials were determined with use of scanning electron microscopy. In the case of the remaining tested polymers, the most important mechanism of wear was adhesion (PP, PTFE, PA 6.6, and PA MoS2), microcutting (PTFE, PA 6.6, and PA MoS2), fatigue wear (PTFE), forming “roll-shaped particles” combined with plastic deformation (PA 6.6 and PA MoS2), and thermal wear (PP). Impregnation of polypropylene with engine oil, gear oil, or RME results in significant reduction of friction coefficient and thus of friction torque, in relation to not only unmodified polypropylene but also the examined polyamide and Teflon.
Highlights
Being a science engaged in the phenomena occurring in friction areas of mating parts, tribology considers difficult phenomena determining friction and wear of engineering materials
The polypropylene specimens were modified by impregnation with vegetable oil, that is, rapeseed oil methyl ester (RME), and with two mineral oils, that is, gear oil Hipol GL-4 80W/90 and engine oil HD Diesel Formula 15W/40
For all values of sliding velocity, impregnated PP showed an improvement in comparison to unmodified PP, PTFE, PA 6.6, and PA MoS2
Summary
Being a science engaged in the phenomena occurring in friction areas of mating parts, tribology considers difficult phenomena determining friction and wear of engineering materials. The factors decidedly affecting tribological processes in friction nodes include friction type, intensity and resistance, nature and value of applied loads, relative velocity, working temperature, and geometry of the friction node, as well as sliding direction with respect to injection flow of the polymer [1]. The above-mentioned factors determine nature and intensity of destructive processes occurring in the cooperation areas of friction pairs composed of various materials: metal-metal, metal-nonmetal (e.g., a polymer), and polymer-polymer [2, 3]. Besides the above-mentioned factors, type of wear is affected by heat dissipation from the friction area, lubricant supply and properties, and mechanism and intensity of removing wear products, as well as shape and dimensions of the wearing surfaces
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