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The impulsive friction variators are very specific transmitters. They are characterised by the periodical impulse transmission of power and motion. For research purposes, the device was made to simulate wear of the tribomechanical system: external envelope (coulisse) – roller and roller-shaft in the free motion mechanism with use of the impulsive friction variators. Monitoring of the elements of tribomechanical system was conducted by recording the changes of dimensions depending on the investigation time. Roughness parameters were measured and wear traces of the tribomechanical system were recorded. It was concluded that at the shaft (star), a dominant mechanism of wear is pitting, and that destruction of the oil film precedes the damage at the coulisse (roller). By analysing the change of the gap and influence of the change of wedging angle, it is determined that the period of intensive wear at the beginning and the period of constant wear can be differentiated. It was concluded that the change of the gap clearly represents the, Impulsni tarni varijatori su vrlo specifični prijenosnici. Karakterizira ih impulsni periodični prijenos snage i gibanja. U cilju istraživanja izrađen je ispitni uređaj za simuliranje trošenja tribosustava: vanjski prsten (kulisa) - valjčić i vratilo - valjčić u mehanizmu slobodnog hoda pri radu impulsnih tarnih varijatora. Praćenje elemenata tribosustava vršeno je snimanjem promjena dimenzija u ovisnosti o trajanju ispitivanja. Mjereni su parametri hrapavosti i snimani tragovi trošenja elemenata tribosustava. Zaključeno je da je kod vratila (zvijezde) dominantni mehanizam trošenja pitting, a da oštećenju vanjskog prstena (valjčića) prethodi razaranje uljnog filma. Analizom promjene zazora i utjecaja promjene kuta zaklinjavanja utvrđeno je da se mogu razlučiti period početnog intenzivnog trošenja i period ustaljenog trošenja. Zaključeno je da promjena zazora jasno prikazuje krivulje trošenja triboelemenata. Povećanje zazora direktno utječe na promjenu kuta zaklinjavanja, a samim time i na povećanje neravnomjernosti rotacije izlaznog vratila.

Investigation of machinability of materials is continuously faced with new demands, new principles and new achievements. The outcome of evaluation of machinability presented in this paper resulted out from observation of two tribological parameters: coefficient of friction and width of the wear area on contact between two sliding bodies, blocks and discs. Measurements are performed on tribometer in condition of wet sliding while one body is sliding over the other. A block is made of material which is usually used for cutting tool, and a disc is made of material which is used as a material of workpiece. Achieved contact condition (normal loading and sliding speed) meets real machining-cutting condition. The aim of the tests performed on tribometer “Block on Disc” is to evaluate the opportunity of investigation of materials machinability by tribological parameters (coefficient of friction and width of wear area on the block). Comparison of experimental results obtained during real cutting condition setup and tribological setup show a good correlation between wear values and cutting forces. For certain conditions, it is possible to acquire machinability indexes obtained on a tribometer with respect to friction coefficients and wear on the block as relevant and representative for real cutting condition.