Unformatted text preview: MECH 325 Machine Elements
Tutorial 7 – Bearings 1. Adapted from Shigley, Problem 11‐1 (8 and 9th Eds.) th A certain application requires a ball bearing with the inner ring rotating. The design life is 30,000 hours at a speed of 300 rev/min. The radial load is F = 1.898 kN. The loads are unsteady, so an application factor of af = 1.2 has been recommended. The reliability goal for this design is 0.90. (See the general bearing information on the following page.) Part 1: To be demonstrated by the TA a. Find the dimensionless life, xD, and basic load rating, C10 b. Choose a 02‐series deep‐groove ball bearing from Table 11‐2. c. Find the reliability of this bearing in use Part 2: To be done by the class Assume the radial load from Part 1 is increased to F = 6.00kN, the reliability goal is increased to 0.95, and a cylindrical roller bearing is now to be selected. d. Find the new dimensionless life, xD, and basic load rating, C10 e. Select an 02‐series cylindrical roller bearing from the Table 11‐3 f. Find the reliability of the selected bearing in use 2. Adapted from Shigley, Problem 11‐6 (8th Ed.) An 02‐series deep‐groove ball bearing is to be selected to carry a radial load of 8kN and a thrust load of 4 kN. The desired life, LD, is to be 5000 hours with an inner‐ring rotation rate of 900 rev/min. Part 1: To be demonstrated by the TA a. What is the basic load rating that should be used in selecting a bearing for a reliability goal of 0.90? Part 2: To be done by the class b. What is the basic load rating that should be used for an angular contact bearing if the outer‐ring rotates at 1000 rev/min, the axial load is increased to 5 kN, and a reliability goal of 0.95 is selected? 3. Adapted from Shigley, Problem 11‐10 (8th Ed.) (For home practice) The figure shown (next page) is a geared countershaft with an overhanging pinion at C. The force on gear A is FA = 600 lbf, and the shaft is to run at a speed of 480 rev/min. The reaction force at O is RO = ‐387j + 467k lbf, and at B is RB = 316j – 1615k lbf. Assume an application factor of 1.4, a desired life of 50,000 h, and a combined reliability goal of 0.90. Show that an 02‐60 mm angular contact bearing at O and a 03‐60 mm straight roller bearing for mounting at B will satisfy design requirements. For these problems, assume the bearing manufacturer has provided the following information: Rating life (L10) = 106 revolutions θ = 4.459 b = 1.483 Rating parameters: x0 = 0.02 ⎡ ⎛ x − x ⎞b ⎤ 0 R = exp ⎢ − ⎜ ⎟ ⎥ θ − x0 ⎠ ⎥ ⎢⎝ ⎣ ⎦
R = reliability x = dimensionless life (L/L10) x0 = guaranteed dimensionless life ...
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- basic load rating