MRO Magazine

Linking Chain To The Application

The overall requirements of an application are important when selecting the correct type of roller or conveyor chain. The factors that most often define what chain combination should be used are: resi...


September 1, 2008
By MRO Magazine

The overall requirements of an application are important when selecting the correct type of roller or conveyor chain. The factors that most often define what chain combination should be used are: resistance to the environment, wear life and total cost.

Here are some brief characteristics to consider when selecting the chain that best suits the application.

Environment resistance

The chain selected should be capable of resisting the majority of the chemical and/or temperature requirements. If the environment is ambient in temperature, then only chemical presence need be addressed. Stainless, nickel-plated or zinc-aluminum coated chains can be considered, depending upon the severity of the chemical environment.

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Nickel-plated chain, for example, is designed to resist incidental contact or exposure to water or water-based washdown operations. Zinc-aluminum types are produced with a coating that is combined with a polymer-based resin that tightly adheres to the components during a high-temperature baking process. The combination of carbon steel components with an environment-resistant coating provides the best alternative to stainless steel in applications where stainless has historically been the only option.

If the environment is one in which the temperature is elevated or sub-zero, stainless steel chains will most often provide the best overall operation.

Wear life

If satisfactory chain life is defined as extended wear, then carbon steel based products are best suited. Nickel-plated or zinc-aluminum coated chains are typically constructed from carbon steel components having the highest level of wear resistance and strength.

Chain strength is normally defined by its allowable working load. This value is one at which the chain can be expected to operate at or below a designated load for an indefinite period of time.

It is very important to remember that allowable working load is a function of ultimate tensile strength but not actually measured using the same criteria. Chains can have very different allowable working loads but have very similar ultimate tensile strengths.

Cost

Cost is normally dependent upon the material used to produce the chain. Stainless steel chains are considerably more costly to produce than carbon-based chains. However, if the environment requires a chain with exceptional corrosion resistance, the use of carbon steel based chains may provide the user with a lower-priced product, but which ultimately has a higher cost of operation.

Case histories

A forest products company had a pin failure in its kiln dryer chain after the chain was in service for seven years. The chain was analyzed and it was determined that elongation exceeded 3% — the point at which chain is considered worn out. It was also determined that the pin failure was due to worn chain and a high shock load resulting from a jam in the conveyor system.

The chain supplier, Drives Inc., recommended the use of chain with a through-hardened pin. At the facility’s elevated operating temperatures of 340C (650F), the surface hardness between a case-hardened and through-hardened pin is comparable.

The fatigue resistance with a through-hardened pin will be about 10% higher and the shock load capabilities will be 20% higher compared to casehardened pins. The through-hardened pins help prevent chains from failing due to shock load without sacrificing measurable wear life in this application.

At a paper products company, a critical log-pusher conveyor operating in a harsh and dirty environment was a problem. The company was considering sealed-joint chains but the cost and lead time were considerably higher than chains having standard construction.

Drives Inc. suggested using its standard chains assembled with hard chrome pins. Wear life was expected to be two times or more than that of the standard chain.

The lead time was three to four weeks and the cost was slightly more than the standard chain. The results included documented savings and lower cost of operation.

For more information on chain for harsh environments, visit www.drivesinc.com.

Reader Service Card No. 403


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