U.S. TSUBAKI RS ROLLER CHAIN
Example Step 1 Data Required 1. Type of application: Centrifugal Blower 2. Shock Load: Small load fluctuation 3. Source of Power: Motor 4. HP to be transmitted: 40 hp 5. Drive shaft: Diameter 2 inches, 750 rpm Driven shaft: Diameter 3 inches, 250 rpm 6. Center distance: Less than 9 inches 7. Space limitation: Less than 20 inches Step 2 Use Table I to determine the service factor. Service Factor SF = 1.0 Step 3 Obtain Design HP Design HP= (HP to be transmitted) • SF = 40 hp • 1.0 = 40 hp Step 4 Obtain the chain number and the number of teeth on the small sprocket from the Roller Chain Selection Table (page A-24) referring to the above 40 hp and 750 rpm. Then check it by referring to the Horse- power Rating Tables (pages A-6 to A-19). 1. According to the horsepower rating, the best choice would normally be a single strand of RS80-17 teeth. Since the speed ratio is 1/3 (250/750 rpm), the necessary number of sprocket teeth would be 17 for the small sprocket and 51 for the large sprocket. But, as the outside diameters are 5.94 inches for 17 teeth and 16.81 inches for 51 teeth (refer to sprocket dimensions on pages A-79 to A-82), it exceeds the space limitation of 20 inches (5.94 + 16.81 > 20 inches). Therefore, these sprockets are not suitable. 2. As a single strand chain is not suitable, a multiple-strand RS60-2, 22 and 66 teeth would be possible. But this combination is not suitable due to the space limitation again (5.67 + 16.18 > 20 inches). 3. For triple strand, RS60-3, 15 and 45 teeth would be possible. The sprockets’ diameters are 3.90 inches and 11.18 inches respectively, the sum of which is less than 20
5. Verify that the chain has maximum allowable load which satisfies equation (C).
inches. The horsepower rating of a 15- tooth sprocket for the RS60-3 should be confirmed by the horsepower rating for the RS60 (see page A-11). The horsepower rating of a 15 tooth sprocket is 15.1 hp at 700 rpm and 17 hp at 800 rpm. So the horsepower rating at 750 rpm is about 16 hp. Since 16 hp is for a single strand chain, the horsepower rating must be multiplied by a multiple strand factor of 2.5 for a triple strand (see page A-22). Therefore, the horsepower rating of RS60-3, 15 teeth at 750 rpm is 40 hp (16 • 2.5 = 40). Step 5 Refer to Sprocket Section (C) in this catalog to check the diameter of the bore. A 45-tooth sprocket meets the necessary requirement, but since the maximum bore diameter (1.87 inches) of a 15-tooth sprocket is smaller than the drive shaft diameter of 2 inches, it can’t be used. A 16-tooth sprocket with a maximum bore diameter of 2 inches must be used. Check again that the outside diameter, 4.21 inches for 16 teeth and 11.89 inches for 48 teeth, is less than the space limitation (4.21 + 11.89 < 20). A combination of RS60-3, 16 and 48 teeth must be used to fulfill all the necessary requirements. Selection for Slow Speed When the chain speed (S) is less than 160 ft./min., select the RS roller chain that is one size smaller than the chain chosen from the horsepower rating method mentioned above. 1. Tentatively select the chain and sprocket from Table IV (page A-24) and proceed by using a one-size- smaller chain and its sprocket with the number of teeth close to the sprocket selected above. Be sure to confirm that the sprocket meets the application requirements such as bore diameter and space limitation, etc. 2. Calculate the chain speed from the number of teeth on the driving sprocket using equation (A). Also check that the speed is less than 160 ft./min. 3. Calculate the chain tension for the above drive from equation (B). 4. Select the service factor and the chain speed coefficient from Table I (page A-22) and Table III.
P • N • n 12
S=
(ft./min.) . . . . . . . . . .(A)
33,000 • HP S
T=
(lbs.) . . . . . . . . . .(B)
T • Service Factor • Chain Speed Coefficient ≤ Maximum Allowable Load . . . . . . . . . . . . . . . . . . . . . .(C) S: chain speed (ft./min.) P: chain pitch (inch) N: number of sprocket teeth n: revolutions per minute (rpm) T: chain tension (lbs.) HP: horsepower to be transmitted (hp) There are two different ways to do the next step: to increase the number of teeth, or to use the same procedure for Super Chains of the same size (refer to Super Chains on pages A-35 to A-42). Note: Please use press fit connecting links for slow speed chain selection.
Table III: Chain Speed Coefficient
Speed Coefficient
Chain Speed
Less than 50 ft./min. 50 to 100 ft./min. 100 to 160 ft./min.
1.0 1.2 1.4
Selection for High Temperatures U.S. Tsubaki Improved Drive Chains are made of heat treated carbon steel. When exposed to high temperatures, the mechanical properties of the heat treated chain components are lost. 1. The hardness, and therefore the wear resistance of pins and bushings, is reduced. 2. At temperatures above 390°F, the rollers and plates lose their hardness and strength. Standard roller chains can be used in temperatures up to 500°F with the following adjustments:
Percentage of Catalog Capacity Rating 100%
Temperature
Up to 340°F 390°F 500°F
75% 50% For temperatures below 15°F, see the Environmental Temperatures and Points of Concern Table on page B-38.
A-23
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