There are practical limitations on doubling the iconic scale. We can double pulley diameters and the center-to-center distance. With the belt we could: • Use the same A-3 belt and double its width; | Chapter 17 17-1 Preliminaries to give some checkpoints 1 VR 2 Angular velocity ratio Hnom 2 hp 1750rev min C 9 12 108 in Ks nd 1 dmin 1in Fa 35 lbf in y lbf in3 f b 6 in d 2 in from Table 17-2 for F-1 Polyamide t in from Table 17-4 Cp . w 12ybt 12 6 lbf ft 6d rad exp f6 perhaps _ ndn n 2 1750 V Y2 ft min 12 w V 2 a Eq. e Fc 4 v c 60 2 lbf 60 Ans. T 63025 2 1 lbf. 2T A F d 1750 2 90 90 lbf 2 Eq. 17-12 F a bFaCpCv 6 35 1 147 lbf Ans. F2 F1a - AF 147 - 90 57 lbf Ans. Do not use Eq. 17-9 because we do not yet know f . Eq. i Fi F1a F2 - Fc 147 57 - lbf Ans. . 1 lnP F1 a - Fc 6d L F2 - Fc ln 147 - 57 - J The friction is thus undeveloped. b The transmitted horsepower is AF V 33 000 H nfs H K Hnom Ks 90 33 A 5 1 2 From Eq. 17-2 L in Ans. z _ 3C2w c From Eq. 17-13 dip 2 Fi where C is the center-to-center distance in feet. 3 108 12 2 dip ------2 101 n------- in Ans. . 432 Solutions Manual Instructor s Solution Manual to Accompany Mechanical Engineering Design Comment The friction is under-developed. Narrowing the belt width to 5 in if size is available will increase f . The limit of narrowing is bmin in whence w lbf ft Fc lbf T 90 lbf in same AF Fi a - F2 90 lbf Fi lbf Longer life can be obtained with a 6-inch wide belt by reducing Fi to attain f . Prob. 17-8 develops an equation we can use here F AF Fc exp f 6 - Fc i exp f 6 - 1 F2 F1 - A F F1 F2 Fc Fi a Ibf F2 Ibf f f dip in Fi F1 - Fc F2 Fc f ln J dd 3 CD 12 2w dip 2 Fi which in this case gives F1 Ibf F2 Ibf Fi Ibf Fc Ibf f dip in 2 So reducing Fi from lbf to lbf will bring the undeveloped friction up to with a corresponding dip of in. Having reduced F1 and F2 the endurance of the belt is improved. Power service factor and design factor .
