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Table 21-4. Shock Environment Service Factors, Csv Driven Machinery Source of Power Driven Machinery Low or Normal Torque High or Non-uniform Torque No shock 1.1 1.2 Light shock 1.2 1.3 Medium shock 1.3 1.5 Heavy shock 1.4 1.7 21.6 CHAIN DRIVES A chain is a reliable machine component, which transmits power by means of tensile forces, and is used primarily for power transmission and conveyance systems. The function and uses of a chain drive are similar to those of a belt drive. The two most common types of chain include steel chain, especially the type called roller chain, which makes up the largest share of chains being produced, and plastic chain. Metal chain drives are normally used for applications below 3000 rpm where accuracy and reliability must be greater than that provided by rubber belts. Chain drives will usually maintain a constant speed under varying load conditions because the metal chain does not slip or stretch and will need only infrequent adjustment. A chain drive is a combination of chains and sprockets and a means of shaft mounting. A chain can be defined as a series of links, connected and fitted into one another to form what is in effect a flexible rack with a series of integral journal bearings. In its simplest form a chain drive consists of two sprockets of arbitrary size and a chain loop. Sprockets are wheels with external teeth shaped so that they can fit into the links of the drive or driven chain. The center distance from one hinge or joint to the next is known as the pitch of the chain and is the primary identifying dimension. Some of the advantages of chain drives over belt drives include: No slippage between chain and sprocket teeth Negligible stretch allowing chain drives to carry heavy loads Less sensitive to dust and humidity than belts and not adversely affected by sun, oil or grease Operation at higher temperatures than belt drives Belt arid Chain Drives 21 -16 Revision B

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