Self-lubricating dry rubbing bearings-fundamentals and methods of calculation

Following a general discussion about the construction and the lubrication mechanisms of compound bearings made of a steel backing with a porous bronze layer filled with a PTFE/solid lubricant mixture, problems in conjunction with the use of pU diagrams are pointed out. Instead of pU values parameters such as the overlap ratio, the compressive strain or the shear stress ratio for example which are imporant, for a reliable design of dry rubbing bearings are represented then. As basis for the friction calculation a relationship between the shear stress ratio and the quotient of the compressive strain and the overlap ratio was experimentally found and the temperature-dependent curves of the Young's modulus and of the shear strength of PTFE are shown. After that, the contact angle influenced by deformation, wear and temperature rise is examined and an approximation equation for determining the contact angle is introduced. A method for calculating temperature, friction and working life of dry rubbing bearings that is based on theoretically and experimentally established data is offered afterwards. In addition the positive effect of a wear particle trap is demonstrated. Finally, calculation examples show the mode of operation of the calculation method.