Hitachi

Drive Chain Selection Step 5: Select the Number of Teeth for the Small Sprocket Once a chain size and number of strands is tentatively selected, we now check to see what is the minimum number of teeth required on the small sprocket in order to transmit the Design Horsepower. To do this we must consult the Horsepower Tables found on the preceding pages corresponding to the chain size tentatively selected (you may also check the Horsepower Table of the next smaller chain size). Note that the horsepower values in the tables are for single strand chains only. The horsepower rating for multiple strand chains is found by multiplying the value in the table by the appropriate "Multi-Strand Factor" shown at the bottom of the page that contains the Horsepower Table and speci cations of the chain being considered (See speci cation pages 12-38). To more easily use the Horsepower Tables we will calculate a new value (Design Horsepower Table: DHPT) from the following: Step 8: Check the Final Design Use the information given in General Roller Chain Drive Principles to check the selection. In addition be aware of potential interference due to space limitations which might exist. To reduce the diameter of sprockets it is generally necessary to increase the number of chain strands and drop down to a smaller pitch. In general, the least expensive drive is one which uses a minimum number of strands. Thus, a larger pitch single strand chain is generally more economical than a multi-strand chain of smaller pitch. This is because, as can be seen by the multi-strand factors, additional strands become less effective in transmitting power while the costs of both chains and sprockets increase with the number of strands. Step 9: Calculate Chain Length in Pitches The chain length in pitches (L) is given by the following formula: L = [(N + n) / 2] + (2C) +(K / C) DHPT = DHP / Multi-Strand Factor Thus the DHPT is the DHP divided by the Multi-Strand Factor. If single strand chains are used then the Factor = 1 and DHPT = DHP. The number of teeth on the small sprocket is then determined from the following: 1. 2. Determine the DHPT from the above formula. Locate the RPM of the small sprocket on the horsepower table and read down the column until the rst value that is equal to or greater than the DHPT. Read across to the rst column (No. Of Teeth Small Sprocket). This is the minimum number of teeth required on the small sprocket for the drive to operate successfully. Note the lubrication method speci ed in the Horsepower Table. This lubrication method should be used in order to achieve reasonable chain performance. Additional information regarding lubrication may be found in the Enginnering Information section on pages 135-137. Step 6: Determine the Number of Teeth for the Large Sprocket We use the following to calculate the number of teeth on the large sprocket: N = (r / R) x n The number of teeth on the large sprocket equals the RPM of the small sprocket (r) divided by the desired RPM of the large sprocket (this is the speed ratio) times the number of teeth of the small sprocket. If the number of sprocket teeth is too large for the space where the drive is to be located, then additional chain strands and a smaller pitch chain should be speci ed. Step 7: Determine the Minimum Shaft Center Distance The minimum shaft centers, in chain pitches, may be determined by the following formula: Cmin = (2N + n) / 6 Values for "K" may be found in Table 4 on page 42. Remember that C is the center distances in pitches of chains thus to obtain C (if the center distance in inches is known), use the following formula: C = Center distance (inches) / Chain Pitch (inches) Note that whenever possible it is best to utilize an even number of pitches without an offset link. Offsets do not possess the same load carrying capacity as the rest of the chain and their use should be avoided when possible. Slow Speed Selection: If the linear chain speed (S) of the drive is less than or equal to 160 ft/min we may use a chain one size smaller than that selected by the above method. We verify this selection by calculating the actual chain tension (T) and checking to be sure it is less than the "Rated Working Load" given in the speci cation tables found on the preceding pages. The procedure is to rst calculate linear speed and then chain tension with the following formula: S = (P x n x r) / 12 P = Chain Pitch in inches n = Number of teeth on the small sprocket r = RPM of the small sprocket T = [(DHP x 33,000) / S] x F DHP = Design Horsepower F= Speed Factor given in Table Table 3: Slow Speed Factor Chain Spe e d (ft/min) Factor 0 - 49.9 1.0 50 - 99.9 1.2 100 - 160 1.4 The above is a guide only. The nal selection should be determined after consideration of the information given in General Roller Chain Drive Principles at the beginning of this section. 41

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