When a multi-disc screw press or its accompanying screw conveyor stops rotating, the cause is usually related to the electrical control system, drive components, mechanical jamming, or material overload. The first step in troubleshooting is to determine whether the motor starts, whether the gearbox output shaft turns, and whether the screw shaft is obstructed by material or foreign objects. These conditions can produce similar symptoms but require different corrective actions.
Electrical Control System Faults
Electrical faults commonly prevent the motor from starting or cause the equipment to stop shortly after startup. When the multi-disc screw press and conveyor are connected to a shared PLC control system, the interlocks between the machines should also be checked.
Power supply or protection device faults
Circuit breaker tripping or thermal overload relay activation: The protection device may disconnect the motor circuit because of motor overload, an abnormal power supply, or a short circuit. Check the motor load, power supply, and mechanical drive before resetting the device. Repeatedly resetting the breaker without identifying the cause can lead to further damage.
Phase loss or voltage abnormalities: A missing phase, unbalanced three-phase voltage, or loose electrical terminals can prevent the motor from starting properly. These conditions may also cause abnormal current and activate the motor protection device.
Contactor or wiring faults: A damaged contactor coil, burnt main contacts, loose terminals, or a broken cable can interrupt the power supply to the motor.
Control signal or equipment interlock faults
Emergency stop or safety circuit not reset: The control system may inhibit startup when an emergency stop button, safety switch, or other safety circuit remains open.
Abnormal sensor signals: A faulty level switch, speed monitoring device, or limit switch may send an incorrect signal to the control system. Sensors covered with sludge or affected by wiring problems can also cause unexpected shutdowns or prevent startup.
Inverter or PLC alarms: An inverter overload, communication error, unsatisfied PLC interlock condition, or incorrect startup sequence may prevent the motor from running as intended. Check the control panel alarm history and equipment status rather than assuming that the PLC program itself is faulty.
Motor and Mechanical Drive Faults
If the control system has issued a start command but the motor or screw shaft still does not rotate, inspect the motor, gearbox, and connecting components.
Motor or gearbox faults
Motor winding damage: Insulation deterioration, moisture ingress, or burnt windings may prevent the motor from starting or cause abnormal operation.
Motor bearing seizure: Worn bearings, insufficient lubrication, or bearing damage can increase rotational resistance. In severe cases, the motor shaft may become unable to turn.
Internal gearbox damage: Worn or broken gear teeth, damaged bearings, or insufficient lubricating oil can reduce the gearbox output torque. Severe internal damage may also cause the output shaft to seize.
Gearbox output shaft or connection failure: Damage to the output shaft, key connection, or other drive components may interrupt power transmission. One possible symptom is that the motor runs normally while the screw shaft remains stationary.
Coupling and other transmission component failures
Coupling failure: A damaged coupling element, broken connecting pin, or loose coupling bolt may interrupt power transmission between the motor and gearbox, or between the gearbox and screw shaft.
Drive chain or sprocket damage: On equipment using chain drives, a broken or detached chain or a damaged sprocket can disconnect the drive from the screw shaft.
Bearing damage or misalignment: Worn support bearings, incorrect bearing positioning, or a deformed shaft can increase rotational resistance and eventually cause the screw shaft to seize.
Contact between the screw flight and housing: A bent screw shaft, misalignment, or deformed flight may cause the flight to rub against the trough or liner. Continuous contact can increase the load and eventually block rotation.
Blockage or Excessive Load in the Multi-Disc Screw Press
A multi-disc screw press uses the relative movement between the screw shaft and the moving and fixed rings to convey and dewater sludge. Sludge accumulation inside the dewatering section, restricted discharge, or an excessive processing load can increase the resistance against the screw shaft. The motor may then trip on overload.
Sludge feed exceeding the machine's capacity
An excessive feed rate, a significant change in sludge solids concentration, or an actual processing load above the machine's design capacity can increase the operating load on the screw shaft. Prolonged operation under these conditions may cause sludge to accumulate inside the dewatering section and overload the screw shaft drive motor.
Unsuitable flocculation performance
An incorrect flocculant dosage, improper chemical preparation, or insufficient mixing can result in poorly formed sludge flocs. This may reduce dewatering performance, cause solids to escape with the filtrate, or interfere with sludge discharge. If sludge continues to accumulate inside the dewatering section, the load on the screw shaft may increase.
Discharge outlet blockage or excessive back pressure
If dewatered sludge cannot leave the machine at the required rate, it may accumulate near the discharge end of the dewatering section. On machines equipped with an adjustable back-pressure plate, an excessively narrow opening or a jammed adjustment mechanism can also restrict cake discharge. The resulting resistance may increase the load on the screw drive.
Sludge or foreign objects trapped between the moving and fixed rings
The clearances between the moving and fixed rings are relatively small. Sludge that remains in these gaps may accumulate and harden over time. Sand, metal fragments, and other hard foreign objects in the feed can also interfere with the movement of the rings and increase the rotational resistance of the screw shaft. Foreign objects may cause localized jamming and abnormal wear.
Residual sludge left inside the machine after shutdown
If a large amount of sludge remains in the dewatering section, flocculation and mixing zone, or discharge passage after shutdown, it may settle, harden, or block the clearances between the rings. When the machine starts again, the screw shaft must overcome this additional resistance. In severe cases, it may fail to start. Follow the equipment manufacturer's instructions for sludge discharge and flushing after shutdown.
Blockage or Drive Faults in the Accompanying Screw Conveyor
The screw conveyor connected to a multi-disc screw press usually transports the dewatered sludge cake. If the conveyor develops a blockage or drive fault, the press may continue operating while the sludge cake cannot be discharged properly.
Excessive feed or material buildup in the trough
Feed rate exceeding conveyor capacity: If the press discharges sludge faster than the conveyor can handle, material may accumulate in the trough and increase the resistance to screw rotation.
Foreign objects obstructing the screw: Plastic bags, fibers, pieces of wood, metal fragments, or large hardened sludge lumps may become trapped between the screw flight and trough, preventing the screw from turning.
Discharge outlet or downstream equipment blockage: A blocked conveyor outlet, chute, or downstream receiving unit prevents material from leaving the system. The resulting buildup inside the conveyor may cause an overload or mechanical jam.
Screw shaft and support component faults
Worn or seized bearings: Damage to the drive-end bearings or intermediate supports can increase the rotational resistance of the screw shaft.
Deformed or worn screw flight: A bent or deformed flight may contact the trough abnormally. Damage to the wear liner can also lead to unwanted contact between moving components.
Shaft or connection failure: On conveyors with sectional screws, damage to a connecting shaft, coupling pin, or other transmission component may prevent the drive end from turning the downstream screw sections.
Shutdown Caused by Equipment Interlocks
Some multi-disc screw press systems connect the main dewatering unit, sludge feed pump, flocculation mixer, and sludge cake conveyor to a shared PLC control system. Interlocks are configured according to the operating conditions of the connected equipment. When one unit trips, raises an alarm, or reports an abnormal operating state, the control system may stop other units according to the programmed sequence.
For example, if the screw shaft drive motor of the press trips on overload, the system may stop sludge feeding and then shut down the accompanying conveyor according to its control logic. Conversely, if the sludge cake conveyor becomes blocked, some systems may stop the press to prevent further sludge discharge.
A simultaneous shutdown does not necessarily mean that all the motors or drive components have failed. Check the PLC alarm history, operating status of each unit, and interlock conditions to identify which equipment first triggered the shutdown.
Initial Checks When the Equipment Stops Rotating
During troubleshooting, use the equipment's operating symptoms to narrow down the possible causes.
| Equipment symptom | Areas to check first |
|---|---|
| The motor does not start or show any apparent movement | Power supply, circuit breaker, contactor, thermal overload relay, emergency stop circuit, and PLC startup conditions |
| The motor hums but cannot rotate normally | Phase loss, motor bearings, gearbox, and possible mechanical jamming of the screw mechanism |
| The motor runs but the screw shaft does not turn | Coupling, connecting pins, key connections, drive chain, and gearbox output |
| The screw shaft rotates but material is not conveyed properly | Feed conditions, screw direction of rotation, blockage inside the trough, and discharge outlet |
| The equipment stops after running for a period and triggers an overload alarm | Feed load, sludge accumulation in the dewatering section, discharge resistance, bearings, and gearbox condition |
| The multi-disc screw press and conveyor stop at the same time | PLC alarm history, equipment interlock conditions, and the unit that first developed a fault |
Before inspection, stop the material feed and isolate the power supply to the relevant equipment in accordance with the site's safety procedures. Apply lockout/tagout and verify that the machinery has completely stopped before opening guards or inspection covers. Do not clean foreign objects, inspect couplings, or work on bearings while the equipment is energized or could start unexpectedly.
If the screw shaft needs to be turned manually, drive components need to be removed, or an internal blockage in the dewatering section needs to be cleared, the work should be carried out by trained and authorized personnel in accordance with the equipment manufacturer's instructions. Do not repeatedly restart the machine, force the shaft to turn, or change the motor's direction of rotation without identifying the cause. These actions may cause further damage.
Hansheng Automation provides CNC precision machining of non-standard metal components according to customer-supplied engineering drawings. Our machining work also covers components for yacht equipment, RC racing cars, tobacco and packaging machinery, and filling machinery.
