4. How to Select Chains
According to the catalog, the maximum allowable load of RS120 is 30.4 kN. Because this value is higher than the chain design tension determined in Step 5, RS120 may be used in this application. Select the number of teeth in the large sprocket according to the speed ratio, using the same procedure as in the general selection. Confirm the chain and the sprocket: driving sprocket is RS120-15T (maxi- mum hub bore is 80 mm, and the shaft diameter is 66 mm; therefore, this may be used), and driven sprocket is RS120-38T (maximum hub bore is not shown in catalogs). Therefore, consult with the manufacturer and determine that the
38-tooth sprocket will accommodate a 94-mm shaft. Step 7. Calculate the chain length (number of links).
1,500 38.10
C =
= 39.37 mm
( N - N' ) ( —— ) 2 6.28
(38 - 15) ( —--— ) 2
( N + N' ) 6.28 L = ——-— + 2C + ——- = ———- + 2 3 39.37 + ——— 2 C 2 39.37 = 105.58 links (38 + 15) Therefore, use 106 links. Center distance = 1,508 mm. Step 8. Check the manufacturer’s catalog to determine the necessary type of lubrication (manual or drip). As you see, this selection allows you to choose a smaller and more economical chain than the general selection. But, at the same time, consider these facts: • Do not use offset links or normal connecting links for slow speeds. Use tap fit connecting links, which have a tight interference fit. If you want to use offset links or normal connecting links, check the strength derating shown in Basics Section 2.2.3 and recalculate. • Cast-iron sprockets are not strong enough for slow speeds. Therefore, use SS400, S35C, S45C, etc. • Use a hardened-tooth sprocket for the high-speed sprocket. • The bearing pressure on the chain will be very high, so lubricate the chain well. 4.1.5 Hanging Transmission Chain Selection Calculate the chain tension on both the load side and the driving side, and select a chain with a suitable maximum allowable tension to satisfy the requirements. The points of notice are shown below. • If there are any laws or guidelines for chain selection, check and calculate accordingly. Make sure to follow the manufacturer’s selections, and select the safer one of the two selections.
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