Considerations on Selecting the Most Appropriate Conveyor Chain ...

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The conveyor chain is a common sight in factories around the world and is seen in all types of situations from moving parts down the line in an automobile production plant to moving sprinklers around in an agricultural field. If something has to get from point "A" to point "B" on a continuous basis, whether for assembly, washing, painting, inspection or storage, you can be sure a conveyor chain is at the core of the system.

There are four critical criteria required for maximum performance of a conveyor chain. They are ultimate strength, wearability, fatigue resistance and impact resistance.

The ultimate strength of a conveyor chain is typically measured in number of pounds required to break the chain on a linear plane. This test is typically conducted on a tensile testing machine and the minimum ultimate strength values for each size chain are dictated by ANSI. A manufacturer controls how strong their chain will be by the material, manufacturing processes, and hardening specifications used in the manufacture of the conveyor chain's components (e.g., center link, side link, and pin).

The ultimate strength of a chain is determined by the integrity of the material at a specific hardness. Although a high ultimate value will not of necessity make it fail-proof. The ultimate strength value determines what type or size of conveyor chain will be used for a variety of loads and is used mainly for application engineering.

The Wearability of conveyor chain is probably the most nebulous value to document when comparing chains. Lubrication, loads, chain speed, system design, etc., are all outside factors that impact wearability. The only value that a manufacturer controls that would impact wearability is hardness. Unfortunately hardness has a major impact on the other three chain criteria. Obviously the harder a chain is the more wearable it would be but it also becomes less fatigue resistant and less impact resistant as the hardness increases.

There are different base materials that offer some options. For example, standard SAE 1045 steel at a hardness of 370 offers worthy impact and fatigue resistance, a good degree of durability, and meets minimum ANSI strength requirements. If the same material has a hardness of 420 BHN, its strength and durability would be enhanced but some of its resistance to fatigue and impact would be lost. As an alternative, microtuff-15 micro-alloy steel has good wearability and more strength along with excellent impact and fatigue resistance. It also costs the same as SAE 1045.

Fatigue resistance means that the material used is able to hold up under continuous bending, twisting, etc without breaking. It is quite possibly the conveyor chain's most important asset or liability. Until the material shows signs of fracture, however, the fatigue level is not readily measurable. In today's manufacturing world with its higher production rates, heavier loads, more convoluted chain paths with tighter radius turns, the chain is vulnerable to more subtle bending and twisting than ever.

As the conveyor chain wends its way around horizontal turns, the side load between the chain and the rollers or traction wheel instigates somewhat of a bending motion in the center link of the chain. The catalyst for fatigue is this bending process. Should the fatigue not be identified, the chain will not be immediately replaced. The incidence of failures are certain to increase exponentially. Because of this, the harder, more durable alloy chains are not recommended for heavily loaded systems with many turns at a rapid pace. Alloy chains work fine in straight line over and under conveyors or for slower, lighter loads on such conveyors in abrasive surroundings found in foundry cooling lines or incinerator drag lines.

The term impact resistance defines the conveyor chain's capability to absorb shock without breaking. Hardness and impact resistance have an inverse relationship, although there are many materials at the same hardness which have varying degrees of ability to absorb impact without fracture. A chain's impact resistance is an important factor in many power and free operations.

With loads being stopped and started frequently, the chain, especially the pusher dog, is susceptible to impact failure if it is not manufactured from an impact resistant material. Other potential impact points on a conveyor are the loading and unloading stations. Impact failures, similar to fatigue failures, occur without warning, but unlike fatigue failures, they don't necessarily multiply.

Considering the above four criteria is very important in choosing a conveyor chain for optimum performance. Selecting the chain most appropriate to the particular application will prolong the systems longevity with fewer crashes.

Visit Wilkie Brothers Coveyors for more information on conveyors or to order Saginaw Trolleys, Webb Conveyor Parts or any other related replacement parts.