Predicting the Operating Characteristics and Play of Machine Sliding Bearings Made from Composite Materials

Abstract

Polymer sliding materials are being used more and more in combinations of machine parts. The sliding properties and other characteristics of thermoplastics (acetal resins, polyamides) are temperature dependent. The main limitation of thermoplastic sliding bearings is the temperature. Calculation of the load capacity of thermoplastic sliding bearings should therefore form the basis for the thermal calculation of the sub-assembly, the purpose of which is to determine the operating temperature of the sub-assembly or (at a given permissible operating temperature) to determine the permissible operating parameters for the thermoplastic sliding bearing in the sub-assembly in question. Because of the low heat conduction and high thermal expansion coefficients of polymers, there are certain difficulties with heat dissipation through the bearing and the permissible tolerances when using thermoplastic sliding bearings. On the basis of algorithms developed for the purpose, a program package has been developed to calculate the strength and stiffness of thermoplastic sliding bearings made from the most varied of materials. This presentation points out certain graphic dependences, determined with a plotter, of the initial dimensions on material properties and sub-assembly design. Analysis of these relationships together with others determined during these machine experiments leads to the conclusion that the greatest efficiency can be achieved by simultaneously increasing the thermal conduction of the composite material by two to two and a half times and reducing the coefficient of friction to two thirds of the original value. By adding graphite fibres, the coefficient of thermal expansion can be reduced by 35%. This parameter has a decisive effect on the magnitude of the play in the sliding combination.