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1 Journal of Achievements in Materials and Manufacturing Engineering

1 2006

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Friction materials operating under high stress, cryogenic temperature, and in vacuum

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Piec Z. , Nowacki J.

tom Vol. 18, nr 1-2

15--24

Purpose: of this paper was to select interfacial materials to provide friction coefficients less than μ= 0.3 which remain at this level during the machine lifetime. This material must withstand cycling motion under pressures up to 80 MPa, at 77 K, and in vacuum of 10-4 Pa. Design/methodology/approach: In the described work, experiments were conducted to determine the friction coefficient and the wear of several low friction materials. The test rig consists of a cryogenic sample holder enclosed in vacuum chamber installed into a servo-hydraulic test machine (M.T.S.). The friction coefficients have been measured cycling the samples (1,960 mm2) for about 38,000 cycles at normal pressure up to 80 MPa, sliding speed of 0.1 m/min, at 77 K, and under vacuum of 10-4 Pa. Findings: The Fiberslip B40 (woven multifilament of PTFE and glass) was selected as the best candidate material. It exhibited a friction coefficient of approximately μ = 0.22, and low wear rate was obtained. The maximum value of the friction coefficient is reached after few thousand cycles and then remains fairly constant. Research limitations/implications: Further studies on relative sliding/sticking at magnets interfaces as well as predicting the heating due to frictional forces are required. Practical implications: application of the selected material is possible in large friction interfaces operating under high compression stress, cryogenic temperature, and in vacuum one can meet in nuclear power stations. Originality/value: The experimental program verified the testing methodology, and techniques selected for measurement of coefficient of friction and wear for the friction pairs with large contact area, which are operated at temperature of 77 K, under high contact pressure and in vacuum.