An accelerated comparative method has been applied to the tribotechnical characteristics of sliding bearings on a universal friction machine. The coefficient of friction and friction power are dependent on the axial load for the SiC-SiC pair; accelerated comparative tests have been performed on the carbonite-niresist friction pair.A method has been proposed [1] for accelerating tests on friction pairs by raising the circumferential velocity of the supporting ring by a factor of 1.2 and the pressure by a factor of 1.5-2, i.e., with the factor pv increased by comparison with the actual value in the pump (p is pressure and v is sliding velocity).A shortcoming of that method is the increase in the sliding speed by comparison with the working speed in thrust washers, which causes a temperature rise in the contact zone. It is necessary to make model specimens of supporting washers differing from the standard ones in having increased geometrical dimensions. Making model specimens leads to unjustified consumption of materials and labor.At the Center for the Development of Oil-Extracting Equipment (TsRNO), a new method has been devised for the accelerated comparative estimation of tribotechnical characteristics of thrust bearings for electrical centrifugal pumps (ECP) by means of a universal friction machine, the UMT-1 (maker the Ivanovo Tochpribor plant).The experimental chamber for the UMT-1 (Fig. 1) has the fixed holder 4 mounted coaxially on the measurement system. It contains the holder 3 with the clamped or pressed bearing 7. When the equipment runs, the holder becomes self-centering because of the sealing ring 5 and spherical surface of the ball 1. The thermocouple 6 is mounted on the test fixed bearing 7 for recording the temperature in the friction zone.The pins 2 are pressed into the holder 4 to transmit the torque. The spindle of the UMT is attached to the holder 10 with the bearing 8 installed in it. In holders 3 and 10, there are the conical cavities 11, which are filled with a lubricating medium mixed with abrasive powder.Before operations start, the working zone is closed by the protective jacket 9. The axial forces P and spindle speed are set by means of the UMT control panel.To estimate the tribotechnical characteristics of standard or experimental bearing specimens, the friction pairs are subject to metrological monitoring, in which the geometrical parameters are measured, together with the roughness and hardness of the working surface, after which the bearings are installed in the UMT chamber.
In order to assist with the prognosis of wear processes in low profile disc heart valves, an approximate haemodynamic theory has been used for the determination of opening and closing dynamics of these valves, together with the most developed theory to date of frictional fatigue. The heart valve element wear was defined by solving the contact problem, which takes account of changes to the contact surface form as a consequence of wear. Calculated values are compared with in vivo wear data for artificial heart valves. The proposed model for estimating wear in artificial heart valves allows an optimization to be made of the wear resistance in available designs and to predict the wear resistance of artificial heart valves at the design stage.
According to the International Standard ISO 5840: 1990 the wear resistance test is a necessary step in the development and production of artificial heart valves (AHV). In developing the device, it is important that a reliable prediction is made of AHV longevity, as a number of specific problems appear that are connected with the results of tests, duration of testing, efficiency and reliability of the testing device. In this paper a procedure is outlined of service life testing of mechanical AHV and a description of the device is given. A comparative example of loads acting on AHV, operating in the accelerated wear testing device and in the pulse duplicator of the physiological mode is also described.
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