Machinery's Handbook, 31st Edition
2564 Pulley Speeds and Belt Lengths is the pitch diameter of the large pulley. For serrated belt drives, the length determined by use of these equations should be divided by the serration pitch. The belt length must then be adjusted to provide a whole number of serrations. Pulley Diameters and Speeds.— If D = diameter of driving pulley, d = diameter of driven pulley, S = speed of driving pulley, and s = speed of driven pulley: , , , D S d s d s D S S D d s and s d D S # # # # = = = = Example 1: If diameter of the driving pulley D is 24 inches, its speed is 100 rpm, and the driven pulley runs at 600 rpm, diameter of the driven pulley, d = 24 × 100 ⁄ 600 = 4 inches. Example 2: If the diameter of the driving pulley D is 60 cm, its speed is 100 rpm, and the driven pulley is to run at 600 rpm, the diameter of the driven pulley, d = 60 × 100 ∕ 600 = 10 cm. Example 3: If the diameter of the driven pulley d is 36 inches, its required speed is to be 150 rpm, and the speed of the driving pulley is to be 600 rpm, the diameter of the driving pulley D = 36 × 150 ∕ 600 = 9 inches. Example 4: If diameter of driven pulley d is 4 inches, its required speed is 800 rpm, and diameter of driving pulley D is 26 inches, speed of driving pulley = 4 × 800 ∕ 26 = 123 rpm. Example 5: If diameter of driven pulley d is 10 cm, its required speed is 800 rpm, and diameter of driving pulley D is 25 cm, speed of the driving pulley = 10 × 800 ∕ 25 = 320 rpm. Example 6: If the diameter of the driving pulley D is 15 inches and its speed is 180 rpm, and the diameter of the driven pulley d is 9 inches, then the speed of the driven pulley = 15 × 180 ∕ 9 = 300 rpm. Pulley Diameters in Compound Drive.— If speeds of driving and driven pulleys, A , B , C , and D (see illustration) are known, the first step in finding their diameters is to form a fraction with the driving pulley speed as the numerator and the driven pulley speed as the, denominator, and then reduce this fraction to its lowest terms. Resolve the numerator and the denominator into two pairs of factors (a pair being one factor in the numerator and one in the denominator) and, if necessary, multiply each pair by a trial number that will give pulleys of suitable diameters. Example 7: If speed of pulley A is 260 rpm and the required speed of pulley D is 720 rpm, find the diameters of the four pulleys. Reduced to its lowest terms, the fraction 260 ∕ 720 = 13 ∕ 36, which represents the required speed ratio. Resolve this ratio 13 ∕ 36 into two factors:
36 13
2 18 1 13 #
# =
Multiply by trial numbers 12 and 1 to get:
2 12 18 1 1 12 13 1 # # # # # # ^ ^ ^ ^ h h h h
24 18 12 13 # #
=
A
B
C
D
Compound Drive with Four Pulleys
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online