1. Cement Weighing System Inaccurate

Fault Description

The cement weighing system may show correct values after calibration with standard weights, but after unloading, the display does not return to zero. After resetting and loading weights again, the displayed value changes significantly.

Although the sensor resistance value is within the normal range and the weighing indicator has no problems, the weighing accuracy remains unstable.

Possible Causes

The main reasons may include:

• Transportation fixing brackets of the weighing frame have not been removed

• The pressure head or pressure plate is stuck

• The weighing system contacts surrounding structures

• Three load cells are not the same model

• Material loading is uneven, causing weighing imbalance

Solutions

• Remove transportation fixing brackets before operation

• Check and clean the pressure head and pressure plate to ensure smooth movement

• Separate the weighing system from surrounding objects to avoid interference

• Replace inconsistent load cells with the same model

• Adjust material feeding position to avoid uneven loading

Regular calibration and inspection of the weighing system are essential for maintaining concrete quality.

2. Aggregate Bin Discharge Gate Opens Slowly Without Material

Fault Description

When there is no material inside the aggregate hopper, the discharge gate opens and closes slowly with weak cylinder movement.

However, inspection shows:

• No mechanical friction or blockage

• Solenoid valve works normally

• Air cylinder has no air leakage

Possible Causes

The common reasons include:

• Poor air supply caused by a dirty filter element in the air treatment unit

• Blocked muffler reducing air pressure difference inside the cylinder

Solutions

• Clean or replace the filter element of the pneumatic system

• Clean the muffler regularly to ensure smooth airflow

Maintaining the pneumatic system can improve the response speed of discharge gates.

3. Powder Outlet Does Not Discharge Material

Fault Description

When the contactor is activated and the motor rotates clockwise, the screw conveyor outlet does not discharge powder.

After running for a short time, the circuit breaker trips.

Restarting the motor causes the same problem, while inspection shows that the powder material is not hardened.

Possible Causes

Possible reasons include:

• Screw conveyor motor running in reverse direction

• Damaged circuit breaker

• Poor contact of one phase in motor wiring

Solutions

• If the motor rotates reversely, exchange any two motor wires to change the rotation direction

• Replace the damaged circuit breaker

• Check and repair motor wiring connections

Correct motor rotation direction is critical for screw conveyor operation.

4. Mixer Shaft Stuck or Motor Overloaded

Fault Description

During concrete mixing, the mixer shaft rotates with difficulty or stops completely.

This problem is commonly called mixer shaft "stuck" or motor overload failure.

Possible Causes

The reasons may include:

• Severe overloading of the mixer

• Excessive material wrapping around the mixing shaft

• Incorrect operation causing secondary feeding

• Inaccurate weighing system

• Large gap between mixing blades and tank wall

• Foreign objects stuck between blades and lining plate

• Low power supply voltage

• Incorrect mixing parameter settings

Solutions

• Reduce mixing load and remove hardened concrete materials

• Remove excess materials caused by incorrect feeding operations

• Recalibrate the weighing system

• Adjust the gap between mixing blades and tank wall (normally not more than 5 mm)

• Remove foreign objects inside the mixer

• Check and stabilize power supply voltage

• Correct mixing parameters in the control system

Regular inspection of mixing blades and liners can effectively prevent mixer overload.

5. Main Mixer Discharge Door Cannot Open

Fault Description

During automatic operation, the main mixer discharge door fails to open after mixing is completed, and the discharge indicator light does not turn on.

Possible Causes

The causes may include:

• Foreign materials or accumulated concrete between discharge door and sealing plate

• Insufficient air pressure in the pneumatic system

• Air cylinder internal leakage

• Damaged oil mist lubricator

• Loose wiring between solenoid valve and relay

• Damaged relay

• Burned solenoid valve coil

• Solenoid valve spool stuck

• Damaged time relay causing PLC signal failure

Solutions

• Remove foreign materials and clean the discharge door

• Check air pressure, cylinder, joints, and lubricator condition

• Repair wiring connections and replace damaged relays

• Replace damaged solenoid valves

• Replace faulty time relays

Regular inspection of pneumatic and electrical systems can prevent discharge failures.

6. Conveyor Belt Misalignment

Fault Description

Conveyor belt deviation is one of the most common problems in concrete batching plants.

There are mainly three situations:

Situation 1:

The belt continuously moves toward one side during both empty and loaded operation.

Situation 2:

The belt moves left and right randomly without a fixed direction.

Situation 3:

The belt deviates only in the middle section of the conveyor.

Possible Causes

Common causes include:

• Uneven conveyor foundation

• Material accumulation on rollers

• Uneven installation of trough rollers

• Improper adjustment of driving and return rollers

• Loose conveyor belt tension