Roller Chain Wear Life

Why Choosing a Quality Roller Chain will Maximize Your Drive's Service Life and Minimize Costs

Abstract

Roller chains are one of the primary systems used in industry to transmit power and convey products. Since roller chains are widely used, productivity is highly dependent on the performance of roller chain. Roller chain that suffers from premature elongation ("stretch") due to wear and needs to be replaced on a frequent basis will negatively impact productivity and increase the cost of the operation.

This white paper will provide information that will go beyond the obvious factors, such as lubrication and general maintenance that prolong roller chain wear life, to other factors such as roller chain component parts fabrication, preparation and assembly. Factors that are essential to achieving maximum wear life. GiDi's strict specifications and quality control of these other factors are key to maximizing your drive's service life and minimizing operational costs.

Lubrication and Maintenance

The importance of proper lubrication and maintenance of roller chain during operation can not be overstated. Close adherence to lubrication type and method, based on the drive's specifications will not only reduce wear, but will produce other benefits such as cushion impact loads and heat dissipation. But lubrication is only part of the process that is necessary to maximize your drive's service life. Selecting a quality chain will be just as important.

Chain Wear

Roller chain is a series of connected journal bearings that articulate as they enter and leave the sprockets. This articulation results in wear on the pins and bushings. As material is worn away from these surfaces the roller chain will gradually elongate

(Fig. 1)

Elongation due to wear is a normal phenomena during drive operation. The rate of wear is dependent on several factors; these include: proper lubrication, load, and the frequency and degree of articulation between pins and bushings. The manufacturing of the critical wear components, the pins and bushings, requires the strictest attention to detail. Starting with the proper selection of raw material, the part fabrication, and part preparation prior to and including assembly. All of these are critical elements in achieving maximum performance. If the wear components are not of the highest quality, the wear life of the roller chain will suffer regardless of other factors.

Wear Elongation Measurement

Wear measurements can be made to determine if the chain has elongated to a length where replacement is necessary. To ensure accurate results, length measurements on roller chain must be done when the chain is in tension. If the chain is measured while still on the sprockets, the system must be turned off and all safety procedures must be followed. The tight span of the chain is the section that should be measured. If the chain has been removed from the sprockets, the ANSI specified measuring load should be applied to the chain so that the slack has been removed.

Measure as closely as possible from the center of pin to the center of another. The more pitches (pins) contained within the measurement increase the accuracy. If the measured value exceeds the nominal by more than the allowable percentage the chain should be replaced. The maximum allowable wear elongation is approximately 3% for most industrial applications, based upon sprocket design. The allowable chain wear in percent for large sprockets with 68 teeth or greater can be calculated using the relationship: 200/N, where N is the number of teeth in the large sprocket. This relationship is often useful since the normal maximum allowable chain wear elongation of 3% is valid only up to 67 teeth in the large sprocket. In drives having fixed center distances, chains running in parallel or where smoother operation is required, wear should be limited to approximately 1.5%.

Example: if 12 pitches (12 pins) of a #80 chain were measured and result was 12.360" or greater (using 3% as the maximum allowable wear), the chain should be replaced. Anything less than 12.360" would still be acceptable by most industrial standards.