CHAIN DRIVE SELECTION
Horsepower Rating 2) Use Table I to obtain the “Service Factor.” Basic Formula for Chain Drive The horsepower rating in Table IV on page 3) Multiply the horsepower value by the service 1) Chain speed: S A-24 is based on the following conditions: factor to obtain the design horsepower S= P • N • n (ft./min.) 1) The chains are operated under ordinary value. 12 conditions. The ambient temperature range 4) Use Table IV on page A-24 and the P : Chain pitch (inch) must be between 15°F and 140°F. They horsepower ratings tables on pages A-6 to N : Number of teeth of sprocket should not be used in an atmosphere in A-19 to obtain the appropriate chain number n : Revolution per minute (rpm) which abrasive dust or corrosive gas is and the number of teeth for small sprockets. present or where the humidity is high. Refer to the number of revolutions of the 2) Chain tension: T 2) The two transmission shafts are in a 33,000 • HP A - DRIVE CHAINS high speed shaft (the driving shaft when the T= (lbs.) horizontal position, and the chains are speed is reduced; the driven shaft when the S properly installed. speed is increased) and the design S : Chain Speed (ft./min.) 3) The suggested lubrication system and oil are horsepower value. For smoother chain drive, HP : Horsepower to be transmitted (hp) used. a smaller pitch chain is suggested. If a 4) The load does not change significantly during single strand chain does not satisfy the 3) Number of pitches of chain: L 2 transmission. The “Service Factor” given in transmission requirements, use a multiple N 2–N 1 Table I should be taken into account when N +N ( 6.28 ) strand chain. If there are space limitations, a * L= 1 2 +2C+ the chains are used under various operating multiple strand roller chain with a smaller 2 C
conditions. The load conditions will affect the pitch may be used. N1 : Number of teeth (small sprocket)
life of the chain. 5) After determining the number of teeth N2 : Number of teeth (large sprocket) 5) The increase in the horsepower rating of necessary for the small sprocket, refer to the C : Center distance in pitches multiple strand roller chain cannot be Sprocket Dimension Table (pages A-79 to A- * Any fraction of L is counted as one pitch. calculated simply by multiplying the 82) to check if the sprocket diameter horsepower rating of one strand by the satisfies the space limitations. 4) Center distance in pitches: C number of strands, since the load on each 1 6) The number of teeth for the large sprocket is C= 2L–N –N strand is not exactly the same. In order to determined by multiplying the number of 8 { 1 2 estimate the service life of a multiple strand teeth for the small sprocket by the speed 8 chain, the “Multiple Strand Factor” given in + (2L–N –N )2 – (N –N )2 ratio. More than 15 teeth on the small 1 2 9.86 2 1 } Table II must be used. When the chain length sprocket is suggested. The number of teeth is 100 pitches and the above conditions are for the large sprocket should be less than met, a service life of approximately 15,000 120. By reducing the number of teeth for the Table II: Multiple Strand Factor hours can be expected. small sprocket, the number of teeth for the Procedures for Selecting Roller Chain Number of Multiple Strand large sprocket can be reduced. Roller Chain Strands Factor 1) The following factors must be considered 7) For temperatures below 15°F, see the when selecting roller chain. Environmental Temperatures and Points of 2 1.7 a. Source of power Concern Table on page B-38. 3 2.5 b. Driven machine c. Horsepower to be transmitted 4 3.3 d. RPM of driving and driven shafts 5 3.9 e. Diameter of driving and driven shafts 6 4.6 f. Center distance of the shafts
Table I: Service Factor
Source of Power Electric Internal Combustion Engine Type of Impact Machines Motor or With hydraulic Without hydraulic Turbine drive drive Belt conveyors with small load fluctuation, chain conveyors, Smooth centrifugal blowers, general textile machines, machines with 1.0 1.0 1.2 small load fluctuation
Centrifugal compressors, marine engines, conveyors with some load Some impact fluctuation, automatic furnaces, dryers, pulverizers, general machine 1.3 1.2 1.4 tools, compressors, general work machines, general paper mills
Press, construction or mining machines, vibration machines, oil well Large impact rigs, rubber mixers, rolls, general machines with reverse or large 1.5 1.4 1.7 impact loads
A-22