Problem 2: Pulsating Chain

Causes:

1. Slack Chain
2. Misaligned Track Joints
3. Excessive Chain Pull
4. Pinched Track
5. Excessive Chain Length
6. Defective Drive

Explanation 2a: Pulsating Chain – Slack Chain
If too much slack chain is allowed to develop in a conveyor, and especially in a long system, the chain will accelerate and coast enough to telescope. This stops it momentarily, after which it surges ahead. The action described is due, in large part, to the normal elasticity of the chain. The longer the chain, the more pronounced is the surge. Also, the greater the chain pull, the greater the surge.

Correction 2a: Pulsating Chain – Slack Chain
Adjust the take-up to remove slack. In a long or level conveyor, it is preferable to use a spring loaded, counterweighted or an air operated take-up located just downstream from the unit. The automatic take-ups may be adjusted to keep a slight tension on the chain which absorbs some of the elasticity, thus reducing the surge.

Explanation 2b: Pulsating Chain – Misaligned Track Joints
Misaligned track joints interrupt the free movement of the chain wheels. While the chain may not jam, a step at the juncture of the tracks causes the wheels to stop momentarily until chain tension increases enough to pull through. Again, elasticity allows the chain to stretch until the wheels break loose. If this is the problem, the chain will surge in 6" increments, which is the vertical chain wheel centers. Usually, the offending joint can be located by inspecting the chain movement, starting at the drive and moving downstream to where the surge stops or lessens.

Correction 2b: Pulsating Chain – Misaligned Track Joints
If one track is actually offset from the other, correction is made easiest by sawing through the joint and re-welding after alignment with a TR-155 welding jig. Care should be taken to remove any weld deposits from inside the track prior to rewelding.

Explanation 2c: Pulsating Chain – Excessive Chain Pull
Systems having excessive chain tensions will often pulsate. The condition is usually more evident just downstream from the drive. Also, it will be noted that the erratic action diminishes gradually all the way back to the drive where the movement is smooth. Again, the longer the chain the worse the pulsating will be.

Correction 2c: Pulsating Chain – Excessive Chain Pull
To locate the cause of the excessive chain pull, the conveyor chain should be inspected first to insure that it is adequately lubricated and that the lateral chain wheels are not worn sufficiently to cause the vertical chain wheel to slide around the horizontal track curves. If the latter is the case, the chain must be replaced. Should the problem be lubrication, the chain must be lubricated thoroughly. Should the pulsation persist, determine the product loads (by weighing), load centers and then calculate the draw bar pull. This will probably indicate the need for an additional drive. Also, in the process of determining the pull, the second drive unit can be located.

Explanation 2d: Pulsating Chain – Pinched Track
At start up of a new or revised conveyor, very often a damaged piece of straight or curved track finds its way into the system. This is usually discovered when the conveyor chain is installed. At other times, the track is shifted after erection and possibly re-welded. In any event, the track side walls may close in at one point to create an obstruction sufficient to produce pulsation in the chain.

Correction 2d: Pulsating Chain – Pinched Track
The pinched track may be located by following the instructions set forth in #2.2. Once located, the problem is easily corrected by hitting the center of the track on top with the spherical end of a ball peen hammer. If the track sides should be bent inward, the piece in question must be replaced.

Explanation 2e: Pulsating Chain – Excessive Chain Length
Any given conveyor with an unusual number of vertical and horizontal curves plus great length will have a tendency to pulsate, regardless of the draw bar pull. As indicated earlier, the chain is elastic to a degree and the elasticity is accentuated by length. Therefore, lubrication must be adequate, chain slack must be held to a minimum and the track joints must be smooth.

Correction 2e: Pulsating Chain – Excessive Chain Length
Corrective action may be taken as outlined in #2.1. If this fails to achieve a proper operation, an additional drive must be installed.

Explanation 2f: Pulsating Chain – Defective Drive
If a conveyor should be pulsating just back or upstream of the drive unit, it would indicate a problem in the drive.

Correction 2f: Pulsating Chain – Defective Drive
By removing the caterpillar chain and one side of the drive chain track, it may be found that the caterpillar dogs are not seating down into the lateral chain links. This can occur if the chain is elongated beyond 1/4" per foot; the caterpillar chain is damaged or out of alignment; the drive chain guide is bent or; the motor drive chain is loose and bouncing up and down. An inspection of all drive components is necessary and corrections made as indicated.