**1.1. The metods of investigations**

Tribological tests were conducted with a widely-used friction tester SMT-1. Fig. 1 shows the apparatus and the structure of the friction node.

Laboratory tests were conducted in two stages. In the first stage tribological tests were conducted according to the authors' own methododology. Next the tests were conducted according to the method applied in FŁT in Kraśnik (Poland). These tests were meant to compare the two methods and evaluate their influence on test results. It should be noted that the load is strictly radial, without a longitudinal component which has been verified experimentally, and this is due to the construction SMT1.
