Hitachi

Drive Chain Selection Introduction Roller chains are one of the most efficient and cost effective ways to transmit mechanical power between shafts. They operate over a wide range of speeds, handle large working loads, have very small energy losses, and are generally inexpensive compared with other methods of transmitting power between rotating shafts. Successful selection involves following several relatively simple steps involving algebraic calculation and the use of Horsepower and Service Factor tables. For any given set of drive conditions, a number of possible chain and sprocket combinations are possible. The designer therefore, should be aware of several roller chain drive selection principles which, when applied correctly, help to balance overall drive performance and cost. The purpose of this section is to help designers make selections that meet the requirements of the drive, and are cost efficient. IMPORTANT NOTE: The horsepower ratings and working load ratings published in this catalog are for use ONLY with Hitachi Inspire SeriesTM SBR® Roller Chains. When operating at or near the capacities shown in these tables we recommend the use of machine cut hardened tooth sprockets. General Roller Chain Drive Principles a) The recommended number of teeth for the small sprocket is 15. The minimum which should be used is 09. Smoother operation is achieved with more teeth. b) The recommended maximum number of teeth for the large sprocket is 120. c) Speed ratios should be 7:1 or less (optimum) and never more than 10:1. d) The recommended minimum wrap of the small sprocket is 120 degrees. e) The recommended center distance between shafts is 30-50 pitches of chain. There are some exceptions however as follows: 1. Center distance must be greater than ˚ the sum of the outside diameters of the driver and driven sprockets to prevent interference. 2. For speed ratios greater than 3:1 the center distance should not be less than the outside diameter of the large sprocket minus the outside diameter of the small sprocket to assure a minimum 120 degrees of wrap over the small sprocket. Required Information For Drive Chain Selection 1. Type of input power (electric motor, internal combustion engine with mechanical or hydraulic drive), and type of equipment to be driven. 2. Amount of horsepower required to provide sufficient power to the driven shaft. 3. Full load speed of the fastest running shaft (rpm). 4. Desired speed of the slow running shaft (i.e. the speed ratio). NOTE: If speeds are variable determine the horsepower to be transmitted at each speed. 5. Diameters of the driver and driven shafts. 6. Center distance of the shafts. NOTE: If this distance is adjustable determine the amount of adjustment. 7. Note the position of the drive and any space limitations that might exist. Usually these limitations are on the maximum sprocket diameter (restricts the use of single strand chains) or on the width of the chains (restricts the use of multiple strand chains). 40 8. Conditions of the drive. It is advisable to consult with Hitachi Maxco, Ltd. engineering personnel when unusual conditions such as widely fluctuating loads, temperatures, or severely abrasive or corrosive environments exist. Abbreviations Used in Equations N Number of teeth on the large sprocket. n Number of teeth on the small sprocket. R Speed in revolutions per minute (rpm) of the large sprocket. r Speed in revolutions per minute (rpm) of the small sprocket. C Shaft center distance in chain pitches. HP Horsepower of the drive motor or engine. SF Service Factor. The Drive Chain Selection Procedure The following nine steps should be used to select the chain and sprocket sizes, determine the minimum center distance, and calculate the chain length in pitches. Step 1: Determine the Class of the Driven Load Estimate which of the following best characterizes the condition of the drive: Uniform: Smooth operation. Little or no shock loading. Soft start up. Moderate: Normal or moderate shock loading. Heavy: Severe shock loading. Frequent starting and stopping. Step 2: Determine the Service Factor From Table 1 below determine the appropriate Service Factor (SF) for the application. Table 1: Service Factors Type of Input Powe r Class of Drive n Load Internal Combustion Engine with Hydraulic Drive Electric Motor or Turbine Internal Combustion Engine with Mechanical Drive Uniform 1.0 1.0 1.2 Mode rate 1.2 1.3 1.4 He avy 1.4 1.5 1.7 Step 3: Calculate Design Horsepower Design Horsepower (DHP) = HP X SF The Design Horsepower is equal to the motor horsepower times the Service Factor (SF) found in table 1. Step 4: Tentative Chain Selection Make a tentative chain selection from the Quick Selector Chart on page 42 as follows: 1. Locate the design horsepower calculated in step 3 by reading up the single, double, triple, or quad chain columns, in that order, until the design horsepower is located. Draw a horizontal line through this value. 2. Locate the RPM of the small sprocket on the horizontal axis of the chart. Draw a vertical line through this value. 3. The intersection of the two lines should indicate the tentative chain selection.

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