Basics of power transmission chain

A chain is a reliable machine component that transmits power by tensile force. Chains may be classified in many ways. From one viewpoint, chain is a continuous, flexible rack engaging a pair of gears. Another viewpoint terms chain a mechanical belt, running over wheels, which can be used to transmit power. Chain is basically a set of pins, rollers, bushings, and connecting links (Fig. 1).

Power transmission chain competes with V-belts, synchronous belts, and gear drives. Each has properties that enable them to carve out a niche all their own. However, there are applications where it can be an either/or situation.

Features of chain drives:

Advantages

• Speed reduction/increase of up to 7:1 can be easily accommodated.
• Can handle long shaft center distances.
• It is possible to use chain with multiple shafts or drives and both sides of the chain.
• Standardization of chains allows ease of selection.
• It is easy to cut and connect chains.
• Chain sprockets can be smaller than belt pulleys and transmit the same torque.
• Sprockets wear less than gears because the load is distributed over many teeth.
• Chain is more suitable for long-term, continuous power transmission with limited torque fluctuation.

Disadvantages

• Chain has speed variations.
• Chain needs lubrication.
• Chain wears and elongates.
• Chain is weak when subjected to side loads.

When making drive selections, consider the load imposed on the chain by the input power and type of equipment to be driven, Service factors are used to determine design horsepower or additional chain capacity required to compensate for the load (Fig. 2).

Lubrication is an important factor in obtaining the desired life from a chain. In drives where the chain is operated at established ratings, proper lubrication is as much a part of the rating as the load and speed promised by the rating.

Power transmission chains are usually pre-lubricated with rust prevention oil before shipping. However, it is essential to lubricate roller chain. Properly lubricated chain has a longer wear life and is less likely to rust.

Obtaining effective lubrication for a chain is a matter of correct application in terms of lubricant used and how and where in the strand it is provided. Lubricate the chain where tension is minimal, applying the lubricant in the clearance between link plates.

In manual lubrication, oil is applied with an oil can or brush. Apply oil about every eight hours or as needed.

In drip lubrication, oil is metered from an oil cup at 5 to 20 drops of oil per minute. The actual quantity depends on chain speed.

Oil bath lubrication submerges part of a sprocket and chain in a pool of oil. Do not have the chain submerged more than ¼ in. to ½ in. Anymore and heat will be generated, changing the oil's properties.

The relative position of the driver and driven sprockets and the tight- and slack side strands greatly influence the drive life (Fig. 3).

Plant Engineering magazine extends its appreciation to U.S. Tsubaki, Inc. for their assistance in the preparation of this article. They supplied the illustration for Fig. 1 and the flow chart for Fig. 2.