Cement Screw Conveyor Problems
This guide covers 11 common faults on the screw conveyors that carry cement from the silo to the weigh hopper, with the symptoms, possible causes and checks and fixes for each.
Safety warning: The checks and interventions in this guide must only be carried out by trained maintenance personnel. Before entering the mixer or working on the hydraulic, pneumatic or electrical system, stop the plant, isolate the power and apply the LOTO (lockout/tagout) procedure; release the pressure in the hydraulic and pneumatic lines. If in doubt, contact MEKA technical service.
Screw loses torque or locks up under load
Symptom: The screw turns at normal speed when empty, but when cement enters it loses torque and slows down sharply or locks up.
Checks and fixes:
- Check the electrical connections and cables for damage
- Inspect the gearbox, coupling and shaft connections for mechanical wear, play or damage
- Check the screw shaft, bushings and bearing points for binding or friction
- Check the screw for deformation or foreign matter that could cause material jams
- Measure the motor current empty and under load to detect overloading
- Check the cement feed rate and the screw fill level
Low cement flow rate to the weigh hopper
Symptom: Although the screw shaft turns in the right direction, the cement flow rate to the weigh hopper stays very low.
Checks and fixes:
- Check the screw speed and the motor running speed
- Inspect the screw flights for wear, deformation or breakage
- Check the clearance between the screw and the tube/housing
- Check the cement inlet and outlet for blockages or build-up
- Inspect the screw fill level and the material flow from the feed chamber
- Check the gearbox, coupling and shaft connections for slipping or power transmission problems
- Check the weigh hopper feed calibration and flow rate settings
Metallic scraping and knocking from the screw housing
Symptom: While the screw is running, continuous metallic scraping and intermittent knocking come from inside the housing.
Checks and fixes:
- Check the running clearance between the screw flights and the housing
- Inspect the screw shaft for bending, misalignment or deformation
- Check the screw bearings and bushings for wear or play
- Check the housing for foreign metal parts or hardened material build-up
- Inspect the screw flights for breakage, wear or marks from contact with the housing
- Mechanically check the motor, gearbox and coupling connections
- After adjustments, cleaning and part replacement, test-run the screw empty and under load
Butterfly valve is open but no cement reaches the screw
Symptom: Even though the butterfly valve under the silo is open, the cement feed to the screw inlet chamber stops or slows down sharply.
Checks and fixes:
- Check that the butterfly valve opens fully and works correctly
- Inspect the valve for cement build-up, jamming or foreign matter blocking the flow
- Check the silo outlet for bridging or lumps blocking the material flow
- Check the screw inlet chamber for blockages and material jams
- Check the pneumatic actuator, air pressure and valve control system
- Check the silo venting system and filters, and eliminate any vacuum that hampers material flow
- After maintenance and adjustments, test the cement feed rate
Inverter shows an "Overcurrent" fault
Symptom: The screw motor drive (inverter) keeps stopping with an "Overcurrent" fault.
Checks and fixes:
- Measure the screw motor current empty and under load
- Check the screw, shaft, bearings and gearbox for mechanical binding or overload
- Inspect the screw for material jams, foreign objects or overfilling
- Check the electrical connections, cables and terminals between the motor and the inverter
- Check the motor insulation and phase balance
- Check the inverter current limits, motor parameters and acceleration/deceleration settings
- Rectify faults in the gearbox and drive components that could cause strain
- After maintenance and adjustments, test the system under load
Sheared key: the motor turns but the screw shaft does not
Symptom: The key (keyed shaft) connection that holds the main shaft on the screw drive has sheared; the motor turns but the main shaft does not.
Checks and fixes:
- Check the key and keyway for wear, breakage or deformation
- Replace the sheared or damaged key connection
- Inspect the keyways on the drive shaft and main shaft for play or loss of dimension
- Repair or replace worn shafts, couplings or connecting parts
- Check the alignment and tightness of the motor, gearbox and coupling connections
- To prevent a recurrence, check for mechanical causes of overloading, jamming or sudden torque peaks
- After fitting, test-run the screw empty and under load
Motor protection breaker trips after 5–10 minutes
Symptom: The screw motor protection breaker (thermal overload) trips randomly 5–10 minutes after production starts.
Checks and fixes:
- Measure the motor running current and compare it with the thermal overload setting
- Check for screw jams, material density or mechanical friction that could overload the motor
- Inspect the motor bearings, gearbox and drive system for strain or wear
- Check the motor supply voltage and phase balance
- Check the electrical connections, terminals and cable connections for looseness or heating
- Verify that the thermal overload breaker is set to the correct current
- After maintenance and adjustments, test the motor under load for an extended period
Cement dust leaking from the tail bearing, noisy bearing
Symptom: Cement dust keeps leaking out of the rear (tail-end) bearing of the screw shaft and the bearing is noisy.
Checks and fixes:
- Check the bearing and sealing elements in the tail-end bearing unit
- Inspect the bearing seals, dust seals and protective elements for wear
- Seal the bearing against cement dust ingress
- Replace the damaged or worn bearing
- Check the screw shaft for misalignment, bending or excessive load at the bearing
- Check the bearing lubrication and that a suitable grease is used
- After fitting, test the bearing area for sealing and performance
Screw will not turn in cold weather or after a long stop
Symptom: In winter or after long stoppages, the screw motor does not turn at all when started and stays locked.
Checks and fixes:
- Check the screw for cement residue or material that has hardened or jammed during long stoppages
- Check the screw shaft, bearings and drive group for mechanical binding
- Check that the motor, gearbox and coupling connections move freely
- In cold weather, check the gearbox oil for viscosity changes and that a suitable oil is used
- Inspect the motor starting current and inverter parameters
- Reduce the initial breakaway load with heating, light tapping to loosen the material, or pre-run procedures
- After cleaning, lubrication and maintenance, recommission and test the system
Contactor does not pull in on the "Start Screw" command
Symptom: Although the automation gives a "Start Screw" command, the screw contactor in the panel does not pull in at all.
Checks and fixes:
- Check the PLC output signal and whether the command reaches the contactor control circuit
- Measure the contactor coil supply voltage
- Inspect the contactor coil for burn-out, an open circuit or mechanical sticking
- Check whether the thermal relay, motor protection breaker or safety circuits are open
- Check the emergency stop, cover safety switches and other interlock signals
- Check the fuses, relays, terminals and cable connections in the panel
- Replace faulty contactors, relays or control elements
- After the checks, run the screw from the automation command to test it
Screw tube sags at the flanges and the shaft rubs the housing
Symptom: The screw tube sags at the middle joint flanges and the shaft rubs against the housing.
Checks and fixes:
- Check the straightness and alignment of the screw tube and the middle joint flanges
- Inspect the flange connections for loosening, deformation or loss of load capacity
- Check the screw shaft alignment and the running clearance inside the housing
- Check the condition of the intermediate hanger bearings and supports
- Correct any insufficient support or mechanical deformation causing the sag
- Repair or replace deformed flanges, tube sections or supports
- After fitting, check that the screw shaft turns freely
- Test-run the screw empty and under load to check for rubbing and noise
Still not solved? If the fault persists after these checks, you can reach the MEKA technical service team 24/7. For the genuine parts you need, see Concrete Batching Plant Spare Parts.
Other concrete batching plant troubleshooting guides:
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