Conveyor chain is used throughout the world in a wide range of applications varying from sprinkler movement in the agriculture industry to moving vehicles on a production line in an automotive assembly plant. If something requires conveyance from point \”A\” to point \”B\” continually, whether it is being assembled, painted, washed, inspected, or stored for future use, chances are good that conveyor chain is at the heart 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 weight in pounds required to break the chain on a linear plane is the measurement that determines the ultimate strength of the chain. The usual method of testing is by use of a tensile testing machine. The minimum strength values for each size of chain are dictated by ANSI. The material of which the chain is made, its manufacturing process, and hardening specifications used in making its components consisting of center link, side link, and pin are controlled by the manufacturer and determines the strength of the chain.
Although the ultimate strength of any given chain will reflect the integrity of a certain material at a certain hardness, a high ultimate value does not necessarily mean that it is impervious to failure. The ultimate strength value is used for application engineering and deciding what type or size of conveyor chain to be used for various loads.
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 options in base materials that take the above into consideration. Standard SAE 1045 steel with a hardness of 370 offers good impact and fatigue resistance, a reasonable level of durability as well as meeting minimum ANSI strength requirements. A hardness of 420 BHN of the same material improves its durability and strength but at the same time loses a bit of its impact and fatigue resistance. Microtuff-15 micro alloy steel also has good wearability, higher strength value, and top impact and fatigue resistance for the same cost as the SAE 1045.
What fatigue resistance indicates is the material\’s capacity to endure continuous bending, twisting and so forth without breaking apart. This is possibly the conveyor chain\’s preeminent asset or liability. The quality of fatigue is not readily quantifiable until the material shows signs of fracture. Modern factories have higher rates of production, heavier overall chain loads, more maze-like chain paths with tighter radius turns, and the chain is more apt to undergo more subtle bending and twisting than in years past
As the conveyor chain travels around horizontal turns, the side load between the chain and the rollers or traction wheel creates a slight bending motion in the center link of the chain. This bending motion is the catalyst for fatigue. If fatigue is not recognized and the chain is not replaced immediately, the frequency of failures is sure to increase at a geometric rate. For this reason it is not recommended to use harder, more wearable, alloy chain on heavily loaded systems with multiple turns and high chain speeds. Alloy chain may be well suited for straight line over and under conveyors or slower lighter loaded conveyors in abrasive surroundings such as foundry cooling lines or incinerator draglines.
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.
In loads with frequent stops and starts, the chain, in particular the pusher dog, is vulnerable to impact failure if not made out of impact resistant material. Loading and unloading stations are other possible sources of impact. Both impact and fatigue failures do occur without any warning. Impact failures on the other hand do not by nature increase once they begin.
When choosing a conveyor chain, it is important to consider the above criteria to achieve maximum performance. Using the correct chain for a specific application increases the life of the system, while preventing failure
For more information on Rebuilt Conveyor Chain or Chain Conveyors in general, please visit Blue Water Manufacturing.