Machine Design

Metal Chains

There are three methods of transmitting power mechanically from shaft to shaft: chain drives, gears, and flexible belts. The chief advantage of chains and belts over gears is chains can be used with arbitrary shaft center distances. Also, compared with gears, chains are simpler and generally less costly.

All drives can be engineered to provide a specific capacity and service life; however, within specific size constraints, chains generally do not have capacities or service lives equal to those of gears. Compared with belts, chains offer advantages in capacity and service life at temperature extremes. Chains also provide positive drive ratios.

Chains are available in a range of accuracies extending from classifications of "precision" to "nonprecision." There is no firm boundary between the two, but nonprecision chains are those that do not provide extremely close fit between sprockets and link and are not designed to articulate with exceptional smoothness. In this class are detachable, pintle, and welded-steel chain. These types are low-cost chains intended primarily for low-speed drives below 50 hp.

Precision chains are designed for smooth, free-running operation at high speeds and high power, ranging to over 1,000 hp. The most common precision chain is the roller chain.

Horsepower ratings for chains have been established by the American National Standards Institute (ANSI) and are based on criterion where the chain supposedly wears until it jumps the sprockets before failing from fracture. For a discussion of chain drives, see Chain drives in the Mechanical Fixed-Speed Drives section.

Roller chain: The basic type of power chain used throughout industry. Rated at up to about 500 hp for single-strand chain. Multistrand types are available at significantly higher horsepowers. For example, ratings for four-strand chain exceed 2,000 hp. Precision construction provides efficient, low-loss, quiet operation. Rated values are predicated upon adequate lubrication covered by ANSI B29.1. In the smaller sizes (below -in. pitch; actually "bushing" chains) speeds can exceed 9,000 fpm. Self-lubricating types, or stud-bushing chain, have oil-impregnated sleeve bearings. They are almost capable of running at the same loads as true roller chain, but at the lower end of the speed range. They provide a service life intermediate between nonlubricated and well-lubricated roller chain.

Double pitch: Designed for service less rigorous than that handled by standard roller chain. Provides the same precision construction and efficient operation of standard roller chain, except that pitch is twice as long, providing a lighter-weight construction, and ratings go only to 92 hp. Functions well on drives with long center distances. Covered by ANSI B29.3.

Inverted silent tooth: A more expensive type of chain that operates smoothly, quietly, and dependably in rigorous applications. Often used as a power takeoff from the prime mover in heavy equipment and in some automobiles. Also used as a timing chain (camshaft drive) in engines. Power capabilities generally equivalent to those of roller chain, except silent chains reach maximum power at maximum rpm, whereas roller chains reach maximum power far below their maximum rpm.

Offset sidebar: The most costly of precision chains. More costly than detachable, pintle, or welded steel, but able to carry heavier loads up to 425 hp and able to run at speeds to 2,250 fpm. Because of its "open" construction, offset sidebar tends to be tolerant of dirt and debris that might cause binding in roller chain. Offset sidebar is also more tolerant of misalignment or twisting of the sprocket axes. This type is rugged and durable and often is used to drive construction machinery. Serves well as conveyor chain in high-temperature ovens. Generally does not provide the speed or power capability available with roller chain. Well suited to use over cast sprockets at reduced speed. Larger sizes are covered by ANSI B29.10.

Bead chain: Light-duty types of chains generally used for manual-control systems such as those in television tuners and air-conditioner controls. They are also used in low-powered systems such as paper drives for business machines and laboratory recorders. Available in four standard bead diameters of 3/32, 1/8, 3/16, and 1/4 in., rated at 15, 25, 40, and 75 lb.

Bead-belt chain, a variation of the basic type, consists of plastic beads molded onto a flexible cord. This type can run faster than all-metal chain but does not carry as much load.

Detachable: The lightest, simplest, and least costly of all chains capable of transmitting significant power up to 25 hp at up to 350 fpm, but not as smooth running as precision chains. Does not require lubrication and, thus, is well suited to operation where lubricant might wash or bake away or where dust or granular materials would stick to a lubricated chain. Commonly used on farm machinery. Detachable chain in steel and in malleable iron are covered by ANSI B29.6 and B29.7.

Pintle and welded steel: For slightly more rigorous service than detachable chain. Applications are basically similar to those of detachable and they are often designed to run on the same sprockets. Rated to operate at up to 40 hp and 450 fpm. Does not require lubrication. Not as smooth running, strong, or durable as precision chains. Welded steel chain generally can carry heavier loads and offers greater wear resistance than pintle.

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