Influence of Thermal Conductivity of Steels on the Friction Limit Loads on Polyamide

The results of tribotechnical tests of friction pairs of polyamide-steels of three grades including carbon and alloy steels with considerably different thermal conductivities are presented. It is shown that the thermal conductivity of steels, which is one of their physical and mechanical characteristics, has a significant influence on the polymer temperature in the tribocontact zone. The objective of the research is to determine the maximum load value, at which the contact temperature does not exceed the polyamide melting point during the test period. It is shown that this load can be taken as a limit load for the friction unit, which corresponds to the upper limit of the working load range. In order to determine the limit load, a series of experimental studies of polyamide wear resistance was conducted starting with the high loads of 1.5 MPa m/s and then subsequently reducing the load gradually in each successive series to the level of 0.6 MPa m/s. Under frictional heating, the fact of reaching the polyamide melting point was determined by a sharp increase in the friction coefficient and torque on the motor shaft. After the test was over, an increased polymer wear was recorded, and its considerable adhesion to the steel counterbody surface was observed. The polymer frictional heating was estimated by an improved method for contact temperature calculation using a modified expression to calculate the heat flow distribution coefficient. The method was developed for friction pairs with materials having considerably different heat conductivities. The applicability of the method is confirmed by good agreement of the calculated value of the contact temperature, determined under the load corresponding to the abovementioned external manifestations of scuffing, with the reference values of the polyamide melting temperature. The results of the research are presented in tabular form and in the form of graphic dependences, which can be used for determining the values of limit loads.