Antifriction basalt-plastics based on polypropylene

Abstract

A study is made of the dependence of the mechanical and friction-engineering properties of polypropylene reinforced with basalt fibers on the viscosity of the polymer matrix. It is established that the main factors that determine the mechanical properties of the plastics are the quality of impregnation of the fibers by the binder and the residual length of the reinforcing filler in the composite after extrusion and injection molding. The material that was developed has a low friction coefficient and low rate of wear within a relatively broad range of friction conditions. The basalt-plastics can be used in the rubbing parts of machines and mechanisms subjected to dry friction.Glass and asbestos fibers are currently the materials most commonly used as reinforcing f'dlers for polypropylene [1, 2]. The introduction of these fibers into the polymer increases the strength properties and heat resistance of the plastic while reducing its shrinkage. However, fdling polypropylene with glass fibers appreciably diminishes the resistance of the material to shock loads, while asbestos is carcinogenic. It is thus important to f'md a replacement for glass and asbestos fibers. One possible substitute might be basalt fibers, which make it possible to create a composite with good service properties that is low in cost and less toxic.We used polypropylene with a melt index (MI) of 6 and.. 20 g/10 min as the polymer matrix. Basalt fibers based on ZhBTR 0-330 roving (TU U 00292729.001-96), chopped into segments with a length from 5 to 30 rnm, were used as the reinforcing fdler. The polymer matrix and fibrous Idler were mixed with a worm-disk extruder [3]. The content of basalt fibers in the polypropylene was 20% by weight. The high Idler content adversely affects the impregnation of the f'dler by the thermoplastic binder. The defect content of the composite increases and its strength characteristics decrease. We prepared standard specimens by injection molding to determine the mechanical properties of composites of the resulting granular material. The service characteristics of the specimens were determined in accordance with the GOST (All-Union State Standard) for plastics. A thermogravimetric analysis of the properties of the plastics was performed with a Paulik-Paulik-Erdei derivatograph made by the Hungarian f'nan MOM. The friction-engineering properties of the composites without lubrication were studied on friction testing machine 2070 SMT-1 by the disk-chock method. Steel 40Kh, heattreated to a hardness HRC 38-48 and having the roughness parameter R a = 0.63 ttm, was used to make the counterweight. The area of contact of the specimen and the counterweight was 2.10 -4 m 2.When thermoplastics are f'dled with individual fibers, the size of the particles of f'dler --especially their length --is of paramount importance [2]. It follows from the data shown in Fig. 1 that the dependence of the tensile strength of polypropylene-based basalt-plastics on the length of the reinforcing fibers is of an extreme nature. This is a manifestation...

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