Caring for Your Drag Conveyor Chain

Biomass Conveyor for Bulk Material Handling

 

And if you don’t love me now
You will never love me again
I can still hear you saying
You would never break the chain (Never break the chain)

The Chain, Fleetwood Mac

 

Chains are one of the most maintenance-heavy components in a drag conveyor. And when they fail, it’s not just a matter of cleaning up a mess, as it is with a corroded bottom panel. The system comes to a halt until you replace or repair the chain. It is possible, however, to prevent many chain-related interruptions and extend the life of your chain. You’ll simply have to attend your chain before it fails. Here are some things you’ll need to know.

Practice Preventative Maintenance

The best thing you can do to extend the life of your conveyor chains is to practice regular, preventative maintenance. Fleetwood Mac had it right in the song The Chain: if you don’t love your chain now, you’ll never love it again. (Who knew the song was about conveyors?) Maybe preaching preventative maintenance is an industrial trope, but too many manufacturers continue to operate on an emergency basis: Machine A ceased up. Grease it. Machine B is falling apart. Weld it. Machine C stopped running and nobody knows why. Investigate it.

Attending your conveyors in paramedic-like fashion will never allow you to get ahead of problems. If you really want to “never break the chain,” schedule inspections (and perform them), change out chains when worn to the manufacturer’s recommended stretch percentage, and properly tension the chains.

During an inspection, you’ll want to note of the following:

  • Abnormal noises
  • Vibration
  • Chain rising in sprocket
  • Chain winding around sprocket
  • Stiff bending of chain/kinks
  • Appearance of chain (corrosion, damage, contact marks, excessive material buildup, cracks in link plates, wear inside the side bars)
  • Damage on sprocket teeth
  • Rotation of rollers

Finding these may indicate a problem, such as the chain being too slack or misaligned.

Slack is bad for a number of reasons. It decreases efficiency. If there’s too much slack, the chains can pulsate, slowing down then speeding up like sections of a worm instead of running smoothly through the system. Loose chains are also prone to vibration-related damage.

To prevent these issues, you’ll need to tighten the chain before you visibly notice slack. Waiting until you can observe slack is like waiting until the Check Engine light comes on in your vehicle before changing the oil. Damage has already occurred.

We recommend checking the chain weekly to learn whether the chain needs tightened. If this is not possible, you should check it at least monthly.

To measure the chain, take the average pitch of a number of chain lengths. The maximum wear is 3 percent elongation, so when the average is more than three percent above the rated pitch, it is time to replace the chain.

Say you have an 81X chain with a normal measurement of 26.1” for ten links. The maximum allowable measurement per ten links for this chain would thus be 26.1” times 103 percent (or 1.03). This comes to 26.88”. Therefore, if the chain measures equal to or greater than 26.88”, it should be replaced.

A last note on slack: when you do tighten the chains, make sure to not overtighten them. If you do, you’ll induce premature wear on the chain and on the wear materials.

Protecting Chains from Corrosion

Besides practicing preventative maintenance, there are some things you can do to lengthen the life of your chains. First, you can protect them by keeping them out of the material path. Of course, this won’t be possible in many traditional chain conveyors. In our SMART Conveyors, we run our chains in paths between wear strips on either side of the material.

The reason you want to get the chain out of the material path is because corrosion from moisture and acids attack the chain pins and bushings. Abrasion from rust, dirt, sand, etc., work alongside the corrosion to reduce the pin diameter until the pin fails under load. Although the chain sidewall is technically the weakest part of the chain, it is actually the pin that will break in practice. It’s for this reason we designed our T-Series conveyor with oversized pins—the pins can become severely eroded and still hold together.

Protect Chains from Wear

Getting the chains outside the material path has the further benefit of getting them off the bottom panels. When chains run along the bottom panels, both they and the panels wear on each other. By placing the chains on UHMW wear strips, chain wear from internal components, sprockets and curves excluded, becomes virtually nonexistent.

You can reduce wear in the curves by ensuring your conveyor has as few curves as possible upon purchase. Curves add stress to the chain (not to mention expense to the conveyor), so, if at all possible, install a straight conveyor.

You can reduce the chain wear at the sprockets by adjusting your system to move the chains and paddles as slow as possible. Sprockets are the main source of wear on the chains outside corrosion, so reducing the number of times the chains wrap around them is pivotal to increasing their life (not to mention the life of the sprockets).

More important than the speed of your chain is its working load. You want to keep the working load as low as possible. The lower the working load, the longer the chain will last. You can calculate your system’s current working load by dividing the total weight of the chain system and material it’s moving by the chain’s rated load. This will give you the percentage of the chain’s rated capacity at which the chain is working.

Decreasing the working load may mean you have to speed up the chain somewhat.  In general, adjust the system so it runs as slow as possible while keeping the chain well under its rated workload limit.

It should go without saying that you shouldn’t overload your chains. Exceeding a chain’s rating will result in accelerated wear and possible failure. Speeding up the conveyor to deal with the excess load will keep the working load down, but, as explained, it will increase wear. If you have to substantially increase the conveyor’s speed or force it to handle a load beyond the its rated capacity, it’s time to replace it with a conveyor that can handle the larger capacity.

Load the Chains Evenly

Another way to protect your chains is to evenly load your conveyor across its width. Typically, material comes into a drag conveyor at an angle. In single-chain conveyors, this results in one paddle/one flight being loaded while the opposing flight either has less material or is empty. This uneven load twists the chain and damages it. It also makes for an inefficient system, as the chain essentially wiggles its way up the conveyor.

This isn’t as big of a problem with the twin-chain conveyors that Biomass Engineering & Equipment producers. The chains in our conveyors run in paths with UHMW wear strips above and below the chains. There is little room for the chains to move, so they can’t twist like those in conveyors that have their chains running along the bottom panels.

Conclusion

Getting the best performance from your conveyor requires forethought. Neglecting maintenance now will require unwanted maintenance in the future—and no feelings of love between you and the machine (to return to the Fleetwood Mac analogy). And forethought regarding the design of what conveyor you purchase will go a long way toward avoiding unplanned maintenance, shutdowns, and unneeded expenses. Make the SMART choice and see to it that your plant benefits from enhanced performance.

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