18_ch 12 Mechanical Design budynas_SM_ch12

18_ch 12 Mechanical Design budynas_SM_ch12 -...

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Chapter 12 321 Now we can check the performance at c min , ¯ c , and c max . Of immediate interest is the fom of the median clearance assembly, 9 . 82, as compared to any other satisfactory bearing ensemble. If a nominal 1.875 in bearing is possible, construct another table with t b = 0 and t d = 0 . cb d ¯ T f T max h o P st T max fos fom 0.0020 1.879 1.875 157.2 194.30 × ±±± 7.36 0.0030 1.881 1.875 138.6 157.10 ± 8.64 0.0035 1.882 1.875 133.5 147.10 ± 9.05 0.0040 1.883 1.875 130.0 140.10 ± 9.32 0.0050 1.885 1.875 125.7 131.45 ± 9.59 0.0055 1.886 1.875 124.4 128.80 ± 9.63 0.0060 1.887 1.875 123.4 126.80 × 9.64 The range of clearance is 0 . 0030 < c < 0 . 0055 in . That is enough room to fit in our de- sign window. d = 1 . 875 + 0 . 000 0 . 001 in, b = 1 . 881 + 0 . 003 0 . 000 in The ensemble median assembly has fom =− 9 . 31 . We just had room to fit in a design window based upon the ( h o ) min constraint. Further reduction in nominal diameter will preclude any smaller bearings. A table constructed for a d = 1 . 750 in journal will prove this. We choose the nominal 1.875-in bearing ensemble because it has the largest figure of merit. Ans. 12-19 This is the same as Prob. 12-18 but uses design variables of nominal bushing bore b and radial clearance c . The approach is similar to that of Prob. 12-18 and the tables will change slightly. In the
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