Machinery's Handbook, 31st Edition
2538 Friction Wheels wheel should be held stationary by the load, while the driving wheel revolves under its own pressure, a flat spot may not be rapidly worn on the driven wheel. The driven wheels, therefore, are usually made of iron, while the driving wheels are made of or covered with, rubber, paper, leather, wood or fiber. The safe working force per inch of face width of contact for various materials are as follows: Straw fiber, 150; leather fiber, 240; tarred fiber, 240; leather, 150; wood, 100 to 150; paper, 150. Coefficients of friction for different combinations of materials are given in the following table. Smaller values should be used for exceptionally high speeds, or when the transmission must be started while under load. Horsepower of Friction Wheels.— Let D = diameter of friction wheel in inches; N = num- ber of revolutions per minute; W = width of face in inches; f = coefficient of friction; P = force in pounds, per inch width of face. Then: . HP D N P W f 33,000 12 31416 # # # # # # = Assume . P f C 33,000 12 31416 # # # = then,
for P = 100 and f = 0.20, C = 0.00016 for P = 150 and f = 0.20, C = 0.00024 for P = 200 and f = 0.20, C = 0.00032
Working Values of Coefficient of Friction
Materials
Coefficient of Friction
Materials
Coefficient of Friction
0.26 0.27 0.31 0.30 0.15
Tarred fiber and aluminum Leather and cast iron Leather and aluminum Leather and type metal Wood and metal
0.18 0.14 0.22 0.25 0.25
Straw fiber and cast iron Straw fiber and aluminum Leather fiber and cast iron Leather fiber and aluminum Tarred fiber and cast iron Paper and cast iron
0.20 The horsepower transmitted is then:
HP D N W C # # # = Example: Find the horsepower transmitted by a pair of friction wheels; the diameter of the driving wheel is 10 inches, and it revolves at 200 revolutions per minute. The width of the wheel is 2 inches. The force per inch width of face is 150 pounds, and the coefficient of friction 0.20. . . 10 200 2 0 00024 0 96 HP horsepower # # # = = Horsepower Which May Be Transmitted by Means of a Clean Paper Friction Wheel of One-inch Face When Run Under a Force of 150 Pounds (Rockwood Mfg. Co.) Dia. of Friction Wheel Revolutions per Minute 25 50 75 100 150 200 300 400 600 800 1000 4 0.023 0.047 0.071 0.095 0.142 0.190 0.285 0.380 0.571 0.76 0.95 6 0.035 0.071 0.107 0.142 0.214 0.285 0.428 0.571 0.856 1.14 1.42 8 0.047 0.095 0.142 0.190 0.285 0.380 0.571 0.761 1.142 1.52 1.90 10 0.059 0.119 0.178 0.238 0.357 0.476 0.714 0.952 1.428 1.90 2.38 14 0.083 0.166 0.249 0.333 0.499 0.666 0.999 1.332 1.999 2.66 3.33 16 0.095 0.190 0.285 0.380 0.571 0.761 1.142 1.523 2.284 3.04 3.80 18 0.107 0.214 0.321 0.428 0.642 0.856 1.285 1.713 2.570 3.42 4.28 24 0.142 0.285 0.428 0.571 0.856 1.142 1.713 2.284 3.427 4.56 5.71 30 0.178 0.357 0.535 0.714 1.071 1.428 2.142 2.856 4.284 5.71 7.14 36 0.214 0.428 0.642 0.856 1.285 1.713 2.570 3.427 5.140 6.85 8.56 42 0.249 0.499 0.749 0.999 1.499 1.999 2.998 3.998 5.997 7.99 9.99 48 0.285 0.571 0.856 1.142 1.713 2.284 3.427 4.569 6.854 9.13 11.42 50 0.297 0.595 0.892 1.190 1.785 2.380 3.570 4.760 7.140 9.52 11.90
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