TAILIEUCHUNG - Tribology in Machine Design Episode 10

Tham khảo tài liệu 'tribology in machine design episode 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 258 Tribology In machine design Figure Figure Figure but not at the outer-race contact c. If the ball has an angular velocity cưn about I he axis OA then it has a rolling component or and a spin component y o relative to the outer race as shown in Fig. . The frictional heat generated at the ball-race contact where slip takes place is Hr ojsH. where is the twisting moment required to cause slip. Integrating the frictional force over the contact ellipse gives Mf lfPaEW when ứ l a-0 and E-ĩĩ 2 but whenố a 0 a 90 and E l. For the same p Mt will be greater for the ellipse with the greater eccentricity because the increase in ứ is greater than the decrease in E. In a given ballbearing that operates under a given speed and load rolling will always take place at one race and spinning at the other. Rolling will take place al the race where is greater because of the greater gripping action. This action is referred to as ball control. Ifabearing is designed with equal race curvatures race curvature is defined as the ratio of the race groove radius in a plane normal to the rolling direction to the ball diameter and the operating speed is such that centrifugal forces are negligible spinning will usually occur at the outer race. This spinning results from the fact that the inner-race contact ellipse has a greater eccentricity than the outer-race contact ellipse. The frictional heat generated at the ball-race contact where spinning lakes place accounts for a significant portion of the total bearing friction losses. The closer the race curvatures the greater the frictional heat developed. On the other hand open race curvatures which reduce friction also increase the maximum contact stress and consequently reduce the bearing fatigue life. . High speeds At high speeds the centrifugal force developed on the balls becomes significant and the contact angles at the inner and the outer races are no longer equal. The divergence of contact angles at high .

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