Conveyor dryers have only a few moving parts. Topping the list as the most important moving component is the conveyor bed. If a conveyor bed is not operating, you are not making product. If you are not making product, you are not making money -- which always gets your supervisor’s attention. Adjustments can always be made for poorly performing fans or heat sources that will still allow some production. But if the conveyor bed crashes, you are completely out of business with a major interruption in your production schedule.
With just a little extra attention, you can prevent a major bed crash and schedule routine maintenance at a convenient time. Following are a few simple tips that will maximize the life of your conveyor bed.
Properly Tension the Belt. Dryer manufacturers typically use a spring at the takeup end of their bed assembly to properly tension the bed. It is important to compress the springs to a specified compressed length for proper operation. (Check with your dryer manufacturer for compressed spring length.) A bed that is too loose is at risk of a crash from poor tracking. Beds that are too tight increase wear on the chain and conveyor bearings.
More importantly, the compressed spring length must be the same from side to side of the bed. Unequal spring loads can cause the bed to rack, which may lead to hard rubbing against the chain guides, increased wear, metal contamination and, in extreme cases, damage to the main frame structure.
The takeup springs are not to be used as a bed-tracking device. This is only a “band-aid” to the real problem: a misaligned bed. More times than not, if the bed tracking is only kept in check by the takeup springs, the bed is at risk of a crash from improper spring tension.
Conveyor Chain Wear. Maintenance managers are sometimes caught off guard when they discover that their chain is totally worn out. The problem often is discovered only after seeing obvious damage to the bedplates. In this situation, the dryer needs not only new chains, but conveyor bedplates as well.
As a conveyor chain wears, the clearance between the pins and bushings increases, which causes the chain pitch to increase. When using a hinged type bedplate, this increase in chain pitch can cause bedplate failures at the hinge. Different types of chain have different degrees of wear. For most engineered chains, an increase of 2 percent in pitch is the maximum allowable wear. (Check with your dryer manufacturer for maximum allowable chain wear.)
Chain wear can be easily inspected and monitored by measuring a convenient length of pitches. To understand how, consider this typical example: While the conveyor bed is under proper tension, select an accessible length of chain to measure. For this example, suppose you have an 8" pitch conveyor chain. The section you will measure is 4' long and has six pitches of chain. Multiply the six pitches by 2 percent (48" x 1.02 = 48.96"). This is the maximum allowable chain wear.
The result of your measurement -- how close it is to the maximum allowable chain wear -- also indicates approximately where you are in the chain’s life span. Using this simple calculation, you can plan for replacing the chain well before a major bed crash.
Conveyor Sprockets. Though sometimes overlooked, wear on conveyor sprockets can lead to troubles, so periodically check the tooth wear on the sprocket. If the root of the tooth wears excessively, it changes the pitch diameter of the sprocket. This change in pitch diameter will stress the bedplate, which can cause damage to the hinge. If the sprocket teeth show excessive wear, it is best to replace them at the next convenient shut down.
In addition, when installing new conveyor chain, always install new sprockets. Using worn sprockets on a new bed assembly can cause the new chain to wear prematurely.
Lubrication. Some dryers are equipped with an automatic chain-lubrication system, which must be maintained to avoid several potential problems. Excessive chain wear from lack of lubrication is common, causing surging conveyor beds. Even worse is a chain that is lubricated on one side and not the other, causing the bed to rack and run hard to one side.
Lubrication nozzles should be inspected on a regular basis to ensure that the oil is being applied properly. Remember that you are trying to get oil to the chain’s pins and bushings, not just the roller. Check that the oil nozzle is applying oil where it needs to go.
Before opening the oil reservoir to refill it, clean all debris from the fill spout. Small particles will quickly clog nozzles. Determine the frequency of fill required, and be certain to keep the reservoir full.
Finally, because bedplates and chain can be a long lead-time item, keep some preassembled bed in your inventory to help minimize downtime in the event of a major crash.
With a little attention to a few details, you can dramatically increase the life of your bed assembly and minimize untimely shutdowns. It is always better to plan your maintenance and be proactive rather than reactive.