Machinery's Handbook, 31st Edition
Transmission Roller Chains 2639 Shafting, bearings, and foundations should be suitable to maintain the initial alignment. Periodic maintenance should include an inspection of alignment. Example of Roller Chain Drive Design Procedure.— The selection of a roller chain and sprockets for a specific design requirement is best accomplished by a systematic step-by- step procedure such as is used in the following example. Example: Select a roller chain drive to transmit 10 horsepower from a countershaft to the main shaft of a wire drawing machine. The countershaft is 1 15 ⁄ 16 -inches diameter and operates at 1000 rpm. The main shaft is also 1 15 ⁄ 16 -inches diameter and must operate between 378 and 382 rpm. Shaft centers, once established, are fixed and by initial calculations must be approximately 22 1 ⁄ 2 inches. The load on the main shaft is uneven and presents “peaks,” which place it in the heavy shock load category. The input power is supplied by an electric motor. The driving head is fully enclosed and all parts are lubricated from a central system. Step 1. Service Factor: From Table 15 the service factor for heavy shock load and an electric motor drive is 1.5. Step 2. Design Horsepower: The horsepower upon which the chain selection is based (design horsepower) is equal to the specified horsepower multiplied by the service factor, 10 × 1.5 = 15 hp. Step 3. Chain Pitch and Small Sprocket Size for Single-Strand Drive: In Table 9 under 1000 rpm, a 5 ⁄ 8 -inch pitch chain with a 24-tooth sprocket or a 3 ⁄ 4 -inch pitch chain with a 15-tooth sprocket are possible choices. Step 4. Check of Chain Pitch and Sprocket Selection: From Table 10 it is seen that only the 24-tooth sprocket in Step 3 can be bored to fit the 1 15 ⁄ 16 -inch diameter main shaft. In Table 9 a 5 ⁄ 8 -pitch chain at a small sprocket speed of 1000 rpm is rated at 15.5 hp for a 24-tooth sprocket. Step 5. Selection of Large Sprocket: Since the driver is to operate at 1000 rpm and the driven at a minimum of 378 rpm, the speed ratio 1000 ∕ 378 = 2.646. Therefore, the large sprocket should have 24 × 2.646 = 63.5 (use 63) teeth. This combination of 24 and 63 teeth will produce a main drive shaft speed of 381 rpm which is within the limitation of 378 to 382 rpm established in the original specification. Step 6. Computation of Chain Length: Since the 24- and 63-tooth sprockets are to be placed on 22 1 ⁄ 2 -inch centers, the chain length is determined from the formula: L C N n N n C 2 2 2 2 1 2 # π = + + + − a k where L = chain length in pitches; C = shaft center distance in pitches; N = number of teeth in large sprocket; and n = number of teeth in small sprocket. . . L 2 36 2 63 24 628 63 24 36 1 116 57 pitches 2 # # = + + + − = a k Step 7. Correction of Center Distance: Since the chain is to couple at a whole number of pitches, 116 pitches will be used and the center distance recomputed based on this figure using the formula on page 2632 where c is the center distance in inches and P is the pitch. . . . . c P L N n L N n N n 8 2 2 0810 64 5 2 116 63 24 2 116 63 24 0810 63 24 64 5 145 14069 2232inches, say22 8 3 inches 2 2 2 2 # # = − − + − − − − = − − + − − − − = + = _ _ ^ ^ ^ ^ ^ h h h h i h i
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