TL;DR
Drag conveyor chain stretch causes sagging, reduced capacity, and eventual chain jam. Measure chain sag and adjust the tail shaft take-up to the correct tension.
What you might see
- chain sagging visibly between the head and tail shafts
- chain jumping or skipping on the sprockets
- increased motor current from chain riding over sprocket teeth
- drag flight hitting the trough bottom from chain sag
Likely causes
Normal chain elongation from pin and bushing wear over service hours
Overloading the conveyor beyond the design chain pull capacity
Insufficient lubrication accelerating pin and bushing wear
Material compaction in the trough increasing drag and chain tension beyond design
Required tools
- Tape measure for sag measurement
- Calipers for chain pitch measurement
- LOTO kit
- Wrench for take-up bearing adjustment
Safety first
- Lock out before reaching into the conveyor trough or near the chain. High chain tension causes severe crush injuries.
- Grain dust in enclosed conveyors is an explosion hazard. No ignition sources during inspection or maintenance.
Procedure
- 1
Stop the conveyor and lock out. Measure the chain sag at the mid-point of the top strand by pressing down on the chain and measuring the deflection with a tape measure.[1]
- 2
Compare the measured sag to the maximum allowable sag in the conveyor specification. Sag above the maximum causes the chain to ride over sprocket teeth.
- 3
Adjust the tail shaft take-up bearing on both sides equally to reduce sag to within specification. Adjust in equal increments on each side to maintain shaft perpendicularity.[1]
- 4
Measure chain pitch at three locations using a caliper. Compare measured pitch to the nominal pitch. Elongation greater than 3% indicates the chain has stretched beyond the take-up compensation range and requires replacement.
Warning: Lock out before reaching into the conveyor trough for chain measurement. The chain runs at low speed but with high tension. - 5
Inspect the chain links and flights for broken or bent members. Replace any damaged flight or link.
- 6
Check the trough for material buildup that could increase chain drag. Clean if necessary.
- 7
After adjustment, run the conveyor empty and confirm chain tracks correctly on the sprockets before returning to production.
Sources
Universal Industries Universal Industries Tapco Bucket Elevator / Drag Conveyor general technical documentation, Universal Industries
Drag conveyor chain stretch, take-up adjustment, and chain replacement, general bulk material handling practice (general)
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