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Unformatted text preview: MECH 325 Machine Elements
Tutorial 6 – Bushings 1. Adapted from Shigley, Problem 12‐22 (8 and 9th Eds.) th An Oiles SP 500 alloy brass bushing is 1 in long with a 1‐in bore and operates in a clean environment at 70°F. The allowable wear without loss of function is 0.005 in. The radial load is 500 lbf. The shaft speed is 200 rev/min. Part 1: To be demonstrated by the TA a. Estimate the number of revolutions for radial wear to be 0.005 in. Part 2: To be done by the class b. Estimate the wear expected for 1 million revolutions if the speed is reduced to 80 rev/min, the load is increased to 800 lbf, and the material is changed to Oiles SP 800. 2. Adapted from Shigley, Problem 12‐23 (8th and 9th Eds.) A cast bronze bushing is to give a maximum wear of 0.002 in for 1000h of use with a 125 rev/min journal and 100 lbf radial load. The maximum permissible lubricant temperature is Tmax = 300°F and ambient temperature is T∞ = 70°F. The overall coefficient of heat transfer is ћCR = 2.7 Btu/(h∙ft2∙°F). The coefficient of sliding friction is fs = 0.03. There is to be a design safety factor of nd = 2. Assume that available bushing sizes are given by the entries with “●” in the table below. The environment is clean. L ID ½” ⅝” ¾” ⅞” 1 ” 1¼” 1½” 1¾” 2 ” ½” ● ● ● ● ● ⅝” ● ● ● ● ¾” ● ● ● ● ⅞” ● ● ● 1” ● ● ● ● ● ● 1¼” ● ● ● ● ● 1½” ● ● ● ● ● 1¾” ● ● ● ● 2” ● ● Part 1: To be demonstrated by the TA a. Using starting values for f1 and f2 of unity, find the required bushing length. Part 2: To be done by the class b. Use the result from part a. to refine the computation and see if there is a better choice of bushing. (Hints: the approximations f1 = f2 = 1.0 are likely not valid; the value of D is not fixed at this point.) MECH 325 Additional Information
Tutorial 6: Bushings ...
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 Fall '10
 PeteOstafichuk

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