- Issue Time
- Aug 21,2015
Important Factors to Consider While Selecting the Conveyor Chain Most Appropriate to Your Application
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 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 integrity of the material at a certain hardness determines the ultimate strength of the chain, but a high ultimate value does not by itself indicate that it is not subject to failure. This value rather is used for application engineering and in the decision as to what kind or size of conveyor chain should be used in various loads.
The durability of a chain depends on a number of outside factors and is a somewhat imprecise value to use when comparing chains. A chains durability is affected by lubrication, loads, chain speed, system design as well as many other factors. Hardness is the only value that is controlled by the manufacturer that impacts wearability, and hardness has a huge impact on the other three criteria. A harder chain is the more durable chain but this very hardness causes the chain to be less fatigue and impact resistant. The harder the chain the less the resistance to fatigue and impact.
Different base materials offer some options in this regard. For instance, standard SAE 1045 steel at a hardness of 370 has good impact and fatigue resistance, reasonable wearability, and meets minimum ANSI strength requirements. The same material at a hardness of 420 BHN would improve its wearability and strength but lose some of its impact and fatigue resistance. Microtuff-15 micro-alloy steel on the other hand, has good wearability, higher strength, and excellent impact and fatigue resistance at the same cost as SAE 1045.
Fatigue resistance is the material's ability to withstand continuous bending, twisting, etc. without fracturing. It is perhaps the conveyor chain's most important asset or liability. Fatigue is not easily measurable until the material shows signs of fracture. In today's world of higher production rates, heavier overall chain loads, more intricate chain paths, with tighter radius turns, the chain is subject to more subtle bending and twisting than ever before.
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.
Impact resistance is the conveyor chain's ability to absorb shock loads without fracturing. There is an inverse relationship between hardness and impact resistance, but different materials at the same hardness have varying abilities to absorb impact without breaking. Impact resistance with regards to chain becomes a factor in many power and free systems.
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.