Articles written in Sadhana

    • Evaluation of tribomechanical behavior of Polytetrafluoroethylene materials for cryogenic refrigerators


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      In GM refrigerator and GM-type pulse tube refrigerator, a rotary valve is located in between the compressor and cold head to generate the pressure pulse. In a typical rotary valve, the rotor rotates over the stator plane of the valve stator plate to generate the pulsating pressure wave. Thus, a surface contact occursbetween the stator plane and rotor, which leads to the formation of wear between them. If the generated wear particles will flow to the cold head unit with helium, it will be stacked in the regenerator wire meshes, and hence deteriorates its thermal performance. Also, these worn out particles may be stacked within the orifice and double inlet valves and thereby changes their flow coefficient. Thus, good quality materials having better tribological and mechanical properties are essential for smooth operation of those refrigerators. In this paper, an experimental investigation is conducted by taking different grades of olytetrafluoroethylene (PTFE) materials, and the wear rates and coefficient of friction have been determined. Different materials used in this investigation areGlass-filled PTFE, Rulon- filled PTFE, Molybdenum disulfide bronze (MoS2)-filled PTFE, and Graphite-filled PTFE, and it is observed that the wear rate of Rulon-filled PTFE is smaller than the remaining materials. Furthermore, the analysis is extended to investigate the tribological behavior of materials by varying differentparameters like load, speed and sliding distance. It is evident that with an increase in load, the wear rate increases. Also, the wear rate rises with a rise in the sliding distance. The Vickers hardness number and Brinell hardness number of different materials is also tested in this investigation.

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