Enhancing Reliability and Life of Plastic Sliding Bearings and Mobile Seals

Abstract

The antifrictional properties and wear resistance of polymeric materials when sliding on metal surface are studied. The factors contributing to enhancement of the reliability and life of plastic sliding bearings and mobile seals are determined. Plastics are used extensively as structural materials in chemical and oil and gas engineering. In spite of the wide diversity of the available engineering-purpose plastics, the number of new polymeric materials is growing steadily. For making sliding bearing and mobile seals, use is made of polyamide, polyurethane, textolite, fluoroplastic, etc. [1, 2]. The merits of these plastics when used as structural materials of sliding bearing and mobile seals are high antifrictional properties, wear resistance, corrosion resistance, ease of adapting to shaft surface without scores and with minor wear of the shaft, low heat conductivity, low cost, and adaptability to efficient manufacture of plastic parts. A marked progress in augmenting reliability and life of plastic friction parts was achieved with appearance of fluoroplastic and fluorocarbon polymers. The antifrictional properties and wear resistance of fluoroplastic-4 (Teflon) when sliding on titanium of trademark VT1-0 (roughness of titanium surface corresponded to classes 7‐8 as per State Standard GOST 2789‐73) were studied on a 2070 SMT-1 friction machine using a shaft-bushing model [3]. The sliding rate, friction path (duration of operation), and unit load (pressure in the friction zone) were varied and various lubricants were used. The friction coefficient was determined via the moment of frictional force whose value was recorded on the potentiometer chart strip. The wear resistance of the fluoroplastic bushing was determined from the wear rate [4]: I = Δm/LS, where Δm is the weight loss of the fluoroplastic bushing, kg; S is the area of the surface adjoined with the shaft, m 2 ; and L is the friction path, m. Fluoroplastic slides on titanium surface with relative ease, and in the 10 5 ‐10 6 Pa pressure range has a friction coefficient of 0.07‐0.08 at the sliding rate of 1m/sec. The sliding rate has hardly any effect on the friction coefficient and wear rate of fluoroplastic bushing. The pressure in the friction zone depends on the wear rate of the fluoroplastic bushing. The friction coefficient and, consequently, wear rate can be reduced by using various lubricating materials. Of the known lubricating materials, distilled water (compared to dry friction, the friction coefficient diminishes to 0.04‐0.06 and the wear rate diminishes by 8‐15 %) and aqueous emulsion of powdery molybdenum disulfide produced by a special procedure were found to be highly effective (friction coefficient 0.02‐0.03 and wear rate 300‐400 times lower in comparison with dry friction).