As with all moving mechanical parts, wear occurs on the contact between parts. In conveyor chains, wear is measured by elongation over a given number of links. At a given number of pitches, this elongation/pitch extension should not exceed 2% of the original chain length. The chain should be replaced once the length increases by more than 2%. Because conveyor chain wear is measured by the increase in length, wear occurs between the chain pins and bushings whenever the chain is hinged, such as when winding the sprocket under tension.
Chain wear measurement
There are many factors that can extend the wear life of a chain. The biggest factors that increase chain wear life are:
- Properly lubricate the chain. This reduces friction between the pin and bushing.
- Replace the sprockets when installing a new chain. Worn sprockets often have an increased tooth pitch due to wear from the old chain. Putting a new chain on a worn sprocket will cause the chain to wear prematurely - the chain will stretch to accommodate the worn sprocket. This is an important but often overlooked factor in chain wear life.
Conveyor chain manufacturers can also help extend chain life and reduce chain wear;
- Grind parts after heat treatment. This ensures smooth mating surfaces and reduces surface friction. This also reduces the initial break-in elongation.
- Ensure minimal component clearance. This increases the mating surface area, reduces bearing pressure, and helps prevent contamination from the outside.
- Control component hardness. Tight tolerances in component surface hardness ensure that one part does not wear prematurely by another, which helps distribute wear evenly over an extended period of time. This is best controlled by having similar hardness levels on mating parts, such as pins + bushings and bushings + rollers.
- Machined bushings. The use of precision machined bushings over rolled or crimped bushings ensures minimal movement due to hoop stress distribution during heat treatment, but also eliminates connections that can cause premature wear of the rollers and chain pins” “Lip”. Machined bushings are more expensive, but this extra expense is often offset by increased chain wear life, which in turn reduces the total cost of ownership.
It should be noted that some chain manufacturers tend to discuss breaking load rather than wear life. Breaking loads are only relevant at the original machine design stage. By increasing the working load of the system beyond its original specification, thereby increasing the breaking load of the chain, wear life will be shortened due to increased bearing pressure.
