Machinery's Handbook, 31st Edition
Synchronous Belts
2615
Table 47. Torque Rating for MXL Section (0.080 in. Pitch) Rated Torque (lbf-in.) for Small Pulley (Number of Grooves and Pitch Diameter, in.)
Belt Width, (in.)
10MXL 0.255
12MXL 0.306
14MXL 0.357
16MXL 0.407
18MXL 0.458
20MXL 0.509
22MXL 0.560
24MXL 0.611
28MXL 0.713
30MXL 0.764
0.12 0.19 0.25
0.29 0.48 0.67
0.35 0.58 0.80
0.40 0.67 0.94
0.46 0.77 1.07
0.52 0.86 1.20
0.57 0.96 1.34
0.63 1.05 1.47
0.69 1.15 1.61
0.81 1.34 1.87
0.86 1.44
2.01 Horsepower Rating Method (XL, L, H, XH, and XXH Sections): Multiply the horsepower rating for the widest standard belt of the selected section by the teeth in mesh factor to obtain the corrected horsepower rating. Divide the design horsepower by the corrected horsepower rating to obtain the required belt width factor. Compare the required belt width factor with those shown in Table 48. Select the narrowest belt width that has a width factor equal to or greater than the required belt width factor. Table 48. Belt Width Factor Belt Section Belt Width (in.) 0.12 0.19 0.25 0.38 0.50 0.75 1.00 1.50 2.00 3.00 4.00 5.00 MXL (0.080) 0.43 0.73 1.00 … … … … ………… … XL (0.200) … … 0.621.00 … … … ………… … L (0.375) … … … … 0.45 0.72 1.00………… … H (0.500) … … … … … 0.21 0.29 0.45 0.63 1.00 … … XH (0.875) … … … … … … … … 0.450.721.00 … XXH (1.250) … … … … … … … … 0.35 0.56 0.78 1.00 Drive Selection: Information on design and selection of synchronous belt drives is avail able in engineering manuals published by belt manufacturers. Manufacturers should be consulted on such matters as preferred stock sizes, desirable speeds, center distances, etc. Minimum Pulley Size: The recommended minimum pulley size depends on the rpm of the faster shaft. Minimum sheave diameters for each belt cross section are listed in Table 44. Selection of Flanged Pulleys: To determine when to use flanged pulleys, consider the following conditions: 1) On all two-pulley drives, the minimum flanging requirements are two flanges on one pulley, or one flange on each pulley on opposite sides. 2) On drives where the center distance is more than eight times the diameter of the small pulley, both pulleys should be flanged on both sides. 3) On vertical shaft drives, one pulley should be flanged on both sides and other pulleys in the system should be flanged on the bottom side only. 4) On drives with more than two pulleys, the minimum flanging requirements are two flanges on every other pulley, or one flange on every pulley, alternating sides around the system. Service Factors: Service factors for synchronous belts in Table 39. Gravity Idler.— The gravity type of idler used in conjunction with many belt drives, con sists of a weighted idler pulley, so pivoted from a long arm that the idler runs near the small pulley against the loose side of the belt, in such a way as to increase the arc of contact of the belt on this pulley. These idlers are of special value on difficult drives where there is a large difference in the diameter of the driver and driven pulleys.
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