Roller chains are called upon to carry heavy loads, withstand shock, and survive even the harshest environments. However, chains achieve their best longevity when properly selected and maintained. Why? Despite high hardness due to heat treatment, roller chain consists of several moving components that eventually wear, especially in demanding applications.

Let's explore the mechanics of wear and the options to maximize chain life.

Explanation of wear and elongation

Wear occurs on chain in three primary ways: Articulation of the pin against the bushing when the chain enters and exits a sprocket, rotation of the rollers against the bushing when engaging a sprocket, and on the side plates if there is rubbing or sliding on a guide. The area between the pin and bushing is both the most critical and the most difficult area to lubricate because it is internal to the chain; this is the area responsible for wear elongation.

Chain elongation should not exceed certain limits; as we'll explore, lubrication reduces the wear tha causes elongation.

Through normal operation, chain eventually elongates due to wear between the pin and bushing. Some refer to the increase in length as stretch. However, when properly loaded, it is due to wear, not actual deformation of components.

For drive applications with fewer than 60 teeth on the sprocket, replacement of the chain is suggested when it reaches 1.5% elongation, measured over at least six pitches; however, a longer length of chain allows an even better assessment. (For conveyor applications, chains can be used up to 2% elongation.) Chains can operate with up to 3% elongation, but this may result in sprocket damage, chain jumping sprocket teeth, unexpected loading, or increased vibration and noise.

Among other things, lubrication helps cushion sprocket-roller engagement for smoother operation and reduced noise.

Chains used beyond the suggested amount of wear lose fatigue strength due to material being worn from the pin.

Note: Regardless of average chain elongation, if any single pin-bushing joint experiences excessive wear, it may be necessary to replace the chain.

Fundamentals of lubrication

Lubrication acts to form a slippery film on the chain components, helping to minimize direct metal-to-metal contact, thereby reducing wear and friction. The covering of lubrication also acts to create a barrier against moisture that helps the metal components resist corrosion. An additional benefit is a reduction of noise, as the lube buffers the impact when the roller engages the sprocket.

Some manufacturers prelubricate standard drive chains using a hot soak process. Chains are submerged in a heated lubricant bath to ensure that all components are coated, even deep into the pin-bushing joint. This gives the chains maximum possible life for applications in which chains are not relubricated. For those situations in which chains are lubricated, prelubrication ensures maximum protection during the run-in period.

Lube-free chains

Where lubrication is not feasible or desirable in slow to medium-speed applications, self-lubricating chains exist. Certain chains incorporate a hardened, oil-impregnated, self lubricating bushing that provides lubrication where it is needed most — at the critical pin-bushing joint and between the bushing and roller. The pins are nickel-plated and the plates are black-oxide coated for extra protection.

Roller chains consist of links that alternate between two geometries. Self-lubricating LAMBDA chain, designed for power transmission and conveyors, carries its own oil in impregnated bushings. Nickel-plated versions offer higher corrosion resistance; LAMBDA II lasts twice as long as the original in temperatures to 150°C.

Self-lubricating chains stay cleaner because the exterior is free of excess lube, and attracts less dust and particulates than regular chain. This is essential in areas where oil contamination may be a concern, such as the paper products or wood processing industries.

These chains are available in both conveyor and drive series. Drive series has heavy, extra thick roller link plates to provide extra strength and bearing area, and has the same load capacity as standard drive chain. The conveyor series has standard ASME (ANSI) B29.1 dimensions.

Sealed roller chains

Sealed chains are useful in applications with especially high levels of abrasives or particulates that could otherwise accumulate inside the chain. Dimensionally, this class of chains is wider than standard to accommodate the seal between the plates.