SEED Guides Component Selection - Chain Drives < >

By far the most common type is the roller chain and this is widely used for both power transmission and conveyor applications. A less frequently used type of transmission chain is the inverted tooth or silent chain as it is called. Another type of chain is the Galle chain which comprises just side plates and pins. This chain is now little used in transmission applications and is largely limited to load carrying uses. Finally, lifting chain is specifically designed for the purpose of supporting load and simply comprises a series of welded links and is used in a range of sling and hoist lifting arrangements. The selection of lifting chain and hoist arrangements, though, is outside the scope of this Procedural Guide.

Roller Chains

A length of roller chain is made up from a number of links and each chain link comprise side plates, pins, bushes and rollers (see Figure 1). The ends of a chain are joined together when in mesh with the drive and driven sprocket. As the sprocket teeth engage with the rollers, rolling rather than sliding contact occurs - thus making this a very efficient form of transmission element.

Roller chains are available in various standard forms, including stainless steel, plastic (for their self lubricating qualities) and various bespoke forms (especially for use on agricultural and conveying applications). Because of the predominant use of roller chain this type is dealt with in detail later.

Conveyor Chain

Roller chains are specifically manufactured for use on material handling and conveyor equipment. Such chains are widely used in the textile, food processing, mining and agricultural industries, for escalators, elevators and also on modern machine tools.

Special chain is necessary because the requirement and working environment is very different from that of transmission chains. Instead of primarily transferring power between shafts, conveyor chain is required to pull one or a number of loads - usually along a straight line at relatively slow speed. Consequently, conveyor chain is rated in terms of Breaking Load rather than power and speed.

For material handling and packaging equipment in the food processing industries, hygiene is of paramount importance, consequently, stainless steel is widely used and any lubrication has to be carefully contained so as not to contaminate foodstuffs. As long spans of chain are frequently necessary, and fully enclosing the chain is impractical, the ingress of foreign matter can present serious problems.

Although, the roller chain used for conveyor applications is basically similar to that used for transmission chain, generally larger pitch sizes are used and sprocket wheels tend to have much broader teeth as illustrated in Figure 2a. Also, one or both of the outer side plates is often designed to accommodate a special attachment or incorporate an integral fixture - possibly to aid synchronised movement in some mechanical handling mechanism (see Figure 2b).

Inverted Tooth (or Silent) Chain

This type of chain has teeth formed in the links and these engage with the teeth in the sprockets. Inverted tooth chain sprockets can be likened to gears but instead of meshing with each other they connect across a greater centre distance by means of a chain (see Figure 3). This type of chain consists of alternately mounted toothed links which are designed such that the link joints articulate during engagement with the sprocket teeth. Due to the compliance of individual links, there is less impact force when a link first engages with sprocket teeth and consequently an inverted tooth chain drive can operate more quietly and at higher speed than roller chain of comparable size.

In addition, because of the articulating, rocker joint feature it means that all sprocket teeth in the arc of contact (or wrap angle as it is sometimes called) fully engage with the mating chain teeth and consequently the load is very efficiently distributed. Some inverted tooth chains are produced with an involute gear profile, this enables a higher power transmitting capability to be achieved compared to roller chains but at extra cost. With good lubrication, inverted tooth chain will typically operate with an efficiency of 95 % but may even be as high as 99%.

Figure 3 Inverted Tooth Chain