Tsubaki Roller Chain Drive Selection Process Horsepower Rating The horsepower rating in Table 4 on page 253 is based on the following conditions: 1. The chains are operated under ordinary conditions. The ambient temperature range must be between 15°F and 140°F. They should not be used in an atmosphere in which abrasive dust or corrosive gas is present or where high humidity is present. 2. The two transmission shafts are in a horizontal position, and the chains are properly installed. 3. The suggested lubrication system and oil are used. 4. The load does not change significantly during transmission. The service factor given in Table 1 should be taken into account when the chains are used under various operating conditions. The load conditions will affect the life of the chain. 5. The increase in horsepower rating of multiple strand roller chain cannot be calculated simply by multiplying the horsepower rating of one strand by the number of strands, since the load on each strand is not exactly the same. In order to estimate the service life of the multiple strand chain, the multiple strand service factor given in Table 2 must be used. When the chain length is 100 pitches and the above conditions are met, a service life of approximately 15,000 hours can be expected. a. Source of Power b. Driven machine c. HP to be transmitted d. RPM of drive and driven shafts e. Diameter of shafts f. Center distance of shafts 2. Use Table 1 to obtain the service factor. 3. Multiply the horsepower value by the service factor to obtain the design horsepower value. Procedures for Selecting Roller Chain 1. The following must be considered when selecting roller chain: 4. Use Table 4 on page 253 and the HP ratings tables on pages 8-21 to obtain the chain number and the number of teeth for small sprockets. Refer to the number of revolutions of the high speed shaft (the driving shaft when the speed is reduced; the driven shaft when the speed is increased) and the design horsepower value. For smoother chain drive, a smaller pitch chain is suggested. If a single strand chain does not satisfy the requirements, use a multi-strand chain. If space is limited, a smaller pitch, multi-strand roller chain can be used. 5. After determining the number of teeth for the small sprocket, refer to the sprocket dimension table on page …..to check if the sprocket diameter satisfies the space limitations. 6. The number of teeth for the large sprocket is determined by multiplying the number of teeth for the small sprocket by the speed ratio. More than 15 teeth on the small sprocket is suggested. The number of teeth for the small sprocket should be less than 120. By reducing the number of teeth for the small sprocket, the number of teeth for the large sprocket can be reduced. 7. For temperatures below 15°F, see the environmental temperatures and points of concern table on page 262. Table 1 – Service Factor
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: 40HP 5. Drive shaft: Diameter – 2”, 750 RPM Driven Shaft: Diameter – 3”, 250 RPM 6. Center distance: Less than 9 inches 7. Space limitation: Less than 20 inches
2. Calculate the chain speed from the number of teeth on the drive sprocket using the equation (A). Also, check that the speed is less than 160 ft/min. 3. Calculate the tension for the above from equation (B). 4. Select the service factor and the chain speed coefficient from Table 1 and Table 3. 5. Verify that the chain has maximum allowable load which satisfies equation (C).
Basic Formula for Chain Drives 1. Chain Speed: S
P x N x n 12
S =
= (Ft/min)
P = Chain Pitch N = Sprocket tooth count n = RPM
2. Chain tension: T
33,000 x HP S
STEP 2 – Use Table 1 to determine the service factor Service Factor SF = 1.0
T =
= (lbs)
S = Chain Speed (ft/min) HP = Horsepower transmitted
STEP 3 – Obtain Design HP Design HP = (HP to be transmitted) x SF = 40hp x 1 = 40hp
T • Service factor • chain speed coefficient ≤ Maximum allowable load …..(C)
3. Number of chain pitches: L
S: Chain speed (ft/min) P: chain pitch N: No. of sprocket teeth n: RPM T: chain tension (lbs.) HP: Transmitted horsepower
STEP 4 – Obtain the chain number and the number of teeth on the small sprocket from the roller chain selection table page 240 referring to the above 40 hp and 750 rpm. Then check it by referring to the Horsepower Rating Tables (Pages 8-21) 1. According to the horsepower rating, the best choice would be a single strand 80 – 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 outside diameters are 5.94 inches for 17T and 16.81 inches for 51T. This exceeds the limitation of 20 inches (5.67 + 16.81 > 20 inches). 2. As a single strand chain is not suitable, a multi-strand chain of 60-2 with sprockets of 22 and 66 teeth also would not fit this working envelope. 3. A triple strand, 60-3 with 15 and 45 teeth would fit the working envelope. The sprocket diameters are 3.90 and 11.18 inches respectively and the sum is less than 20 inches. The HP rating of the 15T is 15.1 at 700 rpm and 17 hp at 800 rpm. A single strand chain rates at 16 hp and thus must be multiplied by a strand factor of 2.5for a triple strand. Therefore, the horsepower rating of 60-3 15-teeth at 750 rpm is 40 hp.
6.28 )
( N 2 − N 1
2
N 1 + N 2 2
+2 C +
L =
C N 1 = Small sprocket teeth N 2 = Large sprocket teeth C = Center distance in pitches *Any fraction of L is counted as one pitch
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.
4. Center distance in Pitches: C
NOTE: Please use press-fit connecting links for slow speed chain selection.
1 8 {
2 }
2 L − N 1 − N 2 + ( 2 L − N 1 − N 2 ) 2 − 8 9.86
Table 3
( N 2 − N 1 )
" C =
Chain Speed
Speed Coefficent
Less than 50ft/min 50 to 100 ft/min 100 to 160 ft./min
1.0 1.2 1.4
Table 2 – Multi-Strand Factor
Number of Chain Strands
Multi-Strand Factor
2 3 4 5 6
1.7 2.5 3.3 3.9 4.6
Selection for High Temperatures
STEP 5 – Refer to the sprocket section to check the diameter of the bore.
Tsubaki 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 the pins and bushings is reduced. 2. At temperatures of 390°F, the rollers and plates lose their hardness and strength.
A 45-tooth sprocket meets the necessary requirement, but since the maximum bore diameter is 1.87 inches of a 15-tooth sprocket is smaller than the drive shaft, diameter of 2 inches, it cannot be used. A 16-tooth sprocket with a maximum bore of 2 inches must be used. Check again that the O.D. of 4.21 inches for 16 teeth and 11.89 inches for 48 teeth is less than the space limitation. A combination of 60-3, 16 and 48 teeth must be used to fulfill the necessary application requirements. Selection for slow speed When the chain speed (S) is less than 160 ft/min, select the roller chain that is one size smaller than the chain chose from the horsepower rating method mentioned above. 1. Tentatively select the chain and sprocket from Table 4 and proceed by using the on-size-smaller chain and its sprocket with the number of teeth close to the sprocket selected above. Be sure to confirm the sprocket meets the application requirements such as bore diameter and space limitations.
Source of Power
Type of Impact
Machines
Standard roller chains can be used in temperatures up to 500°F with the following adjustments.
Internal Combustion Engine
Electric Motor or Turbine
With Hydraulic Drive
Without Hydraulic Drive
Temperature
% of Catalog Capacity Rating
Belt conveyors with small load fluctuation, chain conveyors, centrifugal blowers, general textile machines, machines with small load fluctuation. Centrifugal compressors, marine engines, conveyors with some load fluctuation, automatic furnaces, dryers, pulverizers, general machine tools, compressors, general work machines, general paper mills. Press, contruction or mining machines, vibration machines, oil well rigs, rubber mixers, rolls, general machines with reverse or large impact loads.
Smooth
1.0
1.0
1.2
Up to 340° F
100%
390° F 500° F
75% 50%
Some Impact
1.3
1.2
1.4
Large Impact
1.5
1.4
1.7
251
252
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