24_ch 17 Mechanical Design budynas_SM_ch17

# 24_ch 17 Mechanical Design budynas_SM_ch17 - • Function H...

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Chapter 17 443 17-26 Given: No. 40-4 chain, N 1 = 21 teeth for n = 2000 rev/min, N 2 = 84 teeth, h = 20 000 hours . (a) Chain pitch is p = 4 / 8 = 0 . 500 in and C ˙= 20 in. Eq. (17-34): L p = 2(20) 0 . 5 + 21 + 84 2 + (84 21) 2 4 π 2 (20 / 0 . 5) = 135 pitches (or links) L = 135(0 . 500) = 67 . 5in Ans . (b) Table 17-20: H tab = 7 . 72 hp (post-extreme power) Eq. (17-40): Since K 1 is required, the N 3 . 75 1 term is omitted. const = ( 7 . 72 2 . 5 ) (15 000) 135 = 18 399 H ± tab = ± 18 399(135) 20 000 ² 1 / 2 . 5 = 6 . 88 hp Ans . (c) Table 17-22: K 1 = ³ 21 17 ´ 1 . 5 = 1 . 37 Table 17-23: K 2 = 3 . 3 H a = K 1 K 2 H ± tab = 1 . 37 ( 3 . 3 )( 6 . 88 ) = 31 . 1hp Ans. (d) V = N 1 pn 12 = 21(0 . 5)(2000) 12 = 1750 ft/min F 1 = 33 000(31 . 1) 1750 = 586 lbf Ans . 17-27 This is our ﬁrst design/selection task for chain drives. A possible decision set: A priori decisions
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Unformatted text preview: • Function: H nom , n 1 , space, life, K s • Design factor: n d • Sprockets: Tooth counts N 1 and N 2 , factors K 1 and K 2 Decision variables • Chain number • Strand count • Lubrication type • Chain length in pitches Function : Motor with H nom = 25 hp at n = 700 rev/min; pump at n = 140 rev/min; m G = 700 / 140 = 5 Design Factor : n d = 1 . 1 Sprockets : Tooth count N 2 = m G N 1 = 5(17) = 85 teeth–odd and unavailable. Choose 84 teeth. Decision : N 1 = 17, N 2 = 84...
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