Metal idler sprockets maintain proper chain tension, and guideline the chain around obstacles and stop excessive chain put on and vibration. You don’t need any particular tightener shafts for ball bearing idler sprockets. Composite sprocket idlers need no lubrication and so are corrosion resistant and wear-resistant.
An idler sprocket is a device used to maintain the strain in a chain or chain drive program. Often consisting of only a sprocket mounted on a spring tensioned arm, the idler sprocket pulls against the chain in a constant manner to keep carefully the chain tight at all times. The size of the sprocket used in an idler sprocket assembly has no effect on the efficiency of the chain 
drive; however; a more substantial sprocket will often last longer due to the slower velocity of the sprocket, which will save use on the sprocket’s bearings. Maintenance for the idler assembly is commonly no more than an occasional greasing of the sprocket’s bearings.
When generating a machine by chain, the tension of the chain should be kept at a constant in order to avoid the chain coming off of the drive sprockets. By installing an idler sprocket in the drive system, the chain is kept taut without being over-tightened. Working a chain within an over-tight condition can lead to premature bearing and chain failing while an idler sprocket placed in the system is often a way to greatly extend the life span of the chain, sprockets and the bearings on the machine’s sprocket shafts.
The ideal installing the idler sprocket is on the contrary side of the chain between the drive sprocket and the driven sprocket. The application form should place the idler sprocket in a position that has the sprocket pressing or pulling the chain towards itself as it loops the two main sprockets in a shape like the letter B. This design allows the pulleys to draw the chain hard without hindering the idler in any way as the drive chain passes over the sprocket. If a condition presents itself which needs the drive to exert excess strain on the drive chain, the idler will flex against the chain, allowing it to expand while leftover in touch with the drive sprockets.
While the vast majority of idler sprockets are produced of steel, many materials are used to manufacture an idler sprocket. Many poly or composite sprockets have been used with great success plus some wooden sprockets have also been used on some machinery without concern. Many machines, in an attempt to reduce the use on the drive chain, use an aluminum, cast iron or steel sprocket coated in a nylon material. The metallic hub enables the idler sprocket to remain very strong while the nylon covering is definitely mild on the chain links.