Diagnosing Chain Failure in Conveyors

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While you may be tempted to blame your supplier when a chain breaks in your conveyor, it’s important you analyze what all happened leading up to the event to determine why the chain broke. It’s unlikely that the chain failed due to a flaw, so if you don’t identify the root cause, the same thing is going to happen again.

When a chain breaks, it’s a good idea to first consider how many hours it ran and under what conditions. Consider, too, the working load on the chain. It may be that the chain had simply reached the end of its useful life and should have been replaced before the failure occurred. Harsher conditions and a higher working load will decrease a chain’s life, as will running the chain at a faster speed. You’ll have to consult your records to determine whether the chain’s life was within expected parameters.

To avoid having a chain break unexpectedly due to normal wear and tear, check the chain stretch at regular intervals. When the chain has reached the manufacturer’s recommended limit, make sure to replace the chain. Chains are case hardened, which means the metal on the outside of the chain pin is harder than the metal on the inside of the pin. When the hard outside metal has worn through, the pin will deteriorate rapidly.

After considering the chain’s lifecycle, consider other failures the machine has experienced. Had something obstructed the conveyor? Had another chain recently gone out—thereby straining the remaining chain(s)? Did something get into the conveyor that shouldn’t have been there? Failures rarely affect just one component. They stress the entire system, including the chains. It could be that an incident had damaged the chain that failed.

Taking time to consider previous failures will also tell you how often chain failures occur at your operation. Are chains usually a problem? If they fail regularly and you’re not experiencing obstructions, something may be wrong with the conveyor’s design. Again, the chain is not likely the problem itself. It’s responding to conditions.

Customers with twin-chain conveyors sometimes also complain that one chain is much looser than the other. They think one chain has something wrong with it or that it’s the wrong chain. Virtually every time this occurs, it isn’t because it’s the wrong chain, however. There’s something going on with the conveyor. Usually, that something is that the paddles are not being loaded evenly, which means that one chain is pulling more of the load through the conveyor than the other chain (and wearing out faster). Sometimes, the issue is that maintenance personnel don’t tighten the chains evenly. In other words, you need to determine what is causing one chain to wear faster than the other. Don’t blame the chain.

When a chain breaks soon after a crew has installed it, customers often assume that this certainly points to a problem with the quality of the chain. But again, quality isn’t normally the issue. Chains just don’t break by themselves. Either the installation crew mounted the chain incorrectly, or they also installed new wear strips and didn’t mount the strips correctly, or they left a tool in the conveyor and it became lodged, or something else happened to be in the material stream at the time that should not have been there.

The issue could also be with the conveyor design. While we always calculate the chain load before selecting a chain and conveyor style, this practice is not normative throughout the industry. We’ve seen conveyors with loads too high on the chain—in some cases high enough that the conveyors were virtually useless.

When the cause of a failure isn’t obvious, we suggest isolating where the chain broke and going backward from there. Where are the marks? Where do you find wear? Based on these items alone, you can usually determine what caused the failure, the possibilities of which are manifold. The conveyor could have the wrong sprockets, for example. Perhaps the chains were overtightened and wore faster as a result. It could also be cyclic fatigue—wear that occurs as chains stretch around something in the conveyor, such as lodged material. The repetitive back and forth weakens the metal over time and can cause it to break. If you find grainy failure, this indicates that the chain broke suddenly, usually due to an obstruction or because the chains were overloaded.

When you’re unsure, you can also contact the conveyor’s manufacturer. While you may have some experience with a few of the manufacturer’s machines, the manufacturer has the benefit of data from all its machines that have been in service. Because of this, your vendor can often be of great service in determining what happened. They know how their machines typically respond to given stimuli, where the weak points are, and where they’re unlikely to break. Your vendor has a vested interest in determining problems with their machinery, so don’t count them out, even if they tell you the chain isn’t the problem (because it’s probably not).

 

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