Cement screw conveyor slows, locks or loses output
Symptom
The screw runs at normal speed empty but slows or locks with cement, delivers less than before, knocks or scrapes inside the tube, or the motor turns but the screw does not.
Likely causes
- Worn hanger bearing bushes, or a worn hanger with shaft wear.
- Worn flights (loss of radial height), or build-up at the inlet or outlet.
- Sheared drive key or splined coupling after an overload.
- Tube sagging at a flange because a support is missing.
- Blocked vent on the cement weigh hopper, slowing the flow.
- Foreign metal or hardened cement lumps inside.
Most likely and cheapest to check first.
Checks
- Compare motor current empty and loaded.
- Lock out and turn the screw by hand. It should turn evenly with no tight spot.
- Look at the flights through the inspection hatches.
- Run a string line along the tube to find sag.
- Check the weigh hopper vent filter.
Fix
- Replace hanger bushes; replace the complete hanger if the shaft is worn.
- Replace the screw section when flights have lost about 10–15 % of their radial height.
- Replace the key or coupling, and find the overload that sheared it.
- Add tube supports; repair bent flanges.
- Clean the inlet, outlet and weigh hopper vent.
Stop the equipment if
The screw is locked or the motor turns without the screw. Do not keep restarting it.
Parts you may need
Read the plate first
Cement screws usually carry a code that gives the series, the tube outside diameter, the length and the motor power (for example 219 mm tube, 7 m, 11 kW). Each section has its own plate showing its position. Photograph all of them. You need the code and serial number to order a hanger bearing, an end bearing or a screw section.
| Typical values | |
|---|---|
| Tube outside diameters | 114, 168, 219, 273, 323 mm |
| Portland cement capacity | about 7 t/h (114 mm) to 220 t/h (323 mm) |
| Maximum installation angle | 60° (above 45°, check the maker’s limits) |
| Gear reducer oil | first change 500 h, then every 2,500 h |
CAUTIONNever put a hand into a screw inlet or inspection hatch with the motor not locked out. A screw conveyor amputates.
FIELD TIPHanger bushes are the most frequent screw repair. Keep one set per screw on site.
DANGERWorkers have been pulled into screws while clearing jams or cleaning with the screw turning. Inspection covers need an interlock or a tool to remove, cut flights must be finished smooth, and a jam is never cleared with the screw running. Misalignment is the main cause of screws breaking at the hanger bearings: check straightness with a string line.
⚠ Every check inside a machine starts with full lockout. Safety disclaimer