Backup Bar-hand Wheel Retracted–with Threaded Rod
The backup bar holds the caterpillar chain in the correct relation to the conveyor power chain. It assures that the caterpillar pusher dogs will properly engage the center links of the rivetless power chain.
The backup bar assembly is extended or retracted by a hand wheel turning a threaded rod. There is a locking bolt that must be loosened before retracting the backup bar assembly. Retracting the back up bar disengages the caterpillar chain from the conveyor power chain. This allows the conveyor power chain to be pulled through the drive subbase without interfering with the caterpillar chain. A retractable backup bar can be used when there is more than one drive on the conveyor line but not all the drives are to be operated at the same time. All the drives on a multi-drive line may not be operational at the same time due to a breakdown. If there is a main and a standby drive on the line, both drives should not be engaged at the same time.
Adjusting the Sub-Base Assembly
The dimension between the face of the power chain back-up rolls and the center line of the power chain track should be 1″ for 678 chain, 11/16″ for 458 chain, and 17/32″ for 348 chain. Make sure that the backup rolls are turning. The distance from the top of the 4” I-beam to the centerline of the 678 overhead chain is 7 7/16”. The centerline of the backup rollers should be 7 9/16” below the top of the 4” I-beam. Look at the position of the caterpillar sub-base, the pusher dogs on the caterpillar chain should clear the backup rolls by 1/16th to 1/8th of an inch when the sub-base is pushed all the way in against the hard stops. This dimension is adjusted by moving the caterpillar chain backup bar in or out with the backup bar, jack bolts. This adjustment will assure that the caterpillar chain dogs are meshing properly with the power chain. The power chain should pass through the drive smoothly and not move sideways when looking into the drive from either end. The caterpillar chain take-up should be tight enough so that the chain does not sag away from the return backup bar. When a new caterpillar chain is installed, the tightness of the chain should be checked after two or three shifts of running. It will usually loosen up by that time, and need to be retightened.
Check for wear on the caterpillar chain, the pusher dogs, the sprockets, and the backup bars. The most likely place for wear on the caterpillar chain is on the trailing chain ferrule behind the chain dog. As the front edge of the chain dog pushes on the power chain, the dog tends to cock and so puts extra pressure on the back pin of that link of roller chain. If the caterpillar chain is not pushed in far enough it will cause extra pressure on the trailing chain ferrule behind the chain dog. Note the amount of lubrication on the caterpillar chain. It should have a moist oil appearance. Automatic caterpillar chain lubricators are recommended.