Complete Guide to Troubleshooting Concrete Mixing Plant

　　Section 1 Mechanical Parts

　　Slow feeding of powder

　　Fault phenomenon: The screw feeder is feeding very slowly, with feeding time exceeding 2 minutes, while normal feeding is under 20 seconds.

　　Cause analysis: The main influencing factors are the poor discharge of the powder tank and damage to the screw conveyor. The manifestations of poor discharge from the powder tank include arching of the powder, material caking at the discharge port of the powder tank, too small opening of the discharge butterfly valve, and insufficient material in the powder tank. Damage to the screw conveyor is mainly due to deformation of the screw blades, which cannot transport normally.

　　Processing process:

　　1. Turn on the air blowing arch breaking device.

　　2. Check the opening of the discharge butterfly valve of the powder tank and ensure it is fully open.

　　3. Check if the material at the outlet of the powder tank is caked.

　　4. Check if the screw blades are deformed; if deformed, remove, correct, or replace.

　　Belt deviation

　　Fault phenomenon: The belt conveyor deviates to one side during empty or loaded operation, causing material leakage, abnormal wear and damage to the equipment, reducing productivity, and affecting the normal operation of the entire equipment.

　　Cause analysis: The resultant force acting on the belt in the width direction is not zero, or the tensile stress perpendicular to the width direction of the belt is uneven. Since there are many factors that cause belt deviation, it should be addressed from the aspects of conveyor design, manufacturing, installation and debugging, use, and maintenance. For example, uneven tension on both sides of the belt, different heights on both sides of the belt, and the support frame of the roller not being installed on the vertical cross-section of the belt running direction can all cause belt deviation.

　　Processing process:

　　1. Adjusting the tensioning mechanism.

　　If the belt deviates to the same side under both empty and loaded conditions, it indicates that the tension on both sides of the belt is different; if the belt deviates left and right without a fixed direction, it indicates that the belt is loose, and the tensioning mechanism should be adjusted.

　　2. Adjusting the roller.

　　If the belt deviates at the roller, it indicates that the roller is not level, the roller is moving axially, or one end of the roller is in front and the other is behind. At this time, the levelness and parallelism of the roller should be corrected.

　　3. Adjusting the roller support (or frame).

　　If the belt always deviates to one side when empty, the support frame on the deviating side should be moved forward 1-50px in the direction of the belt running, or the support frame (or frame) on the other side should be appropriately raised.

　　4. Removing adhesive materials.

　　If there are materials stuck on the roller or support roller, it will increase the diameter at that point, leading to increased tension on the belt at that point, thus causing deviation. The adhered materials should be cleaned in a timely manner.

　　5. Adjusting gravity.

　　If the belt does not deviate when empty but always deviates to one side when loaded, it indicates that the belt has an uneven load. The position of the receiving hopper or belt conveyor should be adjusted to ensure even loading of the belt to prevent deviation.

　　6. Adjusting the belt.

　　If the edges of the belt are severely worn or the seams of the belt are not parallel, it will cause inconsistent tension on both sides of the belt. The belt should be re-trimmed or replaced.

　　7. Installing a self-aligning roller.

　　If several sets of automatic self-aligning rollers (flat rollers or trough rollers) are installed on the conveyor, they can automatically correct the belt deviation. For example, when the belt deviates and rubs against a small side roller, the support on that side should be moved forward in the direction of the belt running, while the other side should be moved backward relatively. At this time, the belt will move towards the side of the roller that is moving backward until it returns to the normal position.

　　8. Installing limit rollers.

　　If the belt always deviates to one side, limit vertical rollers can be installed on the frame of the deviating side; this way, the belt can be forced to return to the correct position, and the vertical roller can reduce the tension on the deviating side of the belt, causing the belt to move to the other side.

　　Aggregate feeding door jammed.

　　Fault phenomenon: The pneumatic door for stone feeding at the batching station is jammed and cannot be opened.

　　Cause analysis: The pneumatic door at the batching station has large gap doors and small gap doors. The gap of the large gap door is greater than the general stone particle size, so it will not jam. The small gap door generally has a gap of 5-10mm; when stones smaller than 10mm get stuck in the gap, it is difficult to jam the pneumatic door. After a period of use, the discharge port of the aggregate wears out, and when the gap wears down to 20-30mm, larger stones can easily get stuck in the gap during the opening process, causing the pneumatic door to be unable to open due to wedging.

　　Processing process: Check the gap of the pneumatic door and adjust it to an appropriate value. If it cannot be adjusted to an appropriate value due to excessive wear, steel plates or round steel should be welded at the discharge port to achieve a reasonable gap.

　　Dust coming out of the top of the tank when conveying powder.

　　Fault phenomenon: During the process of pumping powder into the powder tank from a bulk cement truck, powder is seen coming out of the top of the cement tank.

　　Cause analysis: Powder is conveyed to the powder tank through compressed air. After the compressed air sends the powder to the powder tank, it is discharged into the air through the dust collector filter at the top of the tank. If the dust collector filter is blocked, the compressed air cannot be discharged in time, causing "pressure build-up". When the pressure reaches the opening pressure of the safety valve at the top of the tank, the safety valve opens, and the compressed air and powder are discharged into the atmosphere through the safety valve, causing dust to come out. Additionally, if the level gauge fails and powder continues to be fed after the tank is full, dust will also come out of the top of the tank.

　　Processing process:

　　1. Check the condition of the dust collector filter at the top of the tank and clean it.

　　2. Once the gray phenomenon occurs, it is necessary to clean the powder around the safety valve to avoid the powder being wet and blocked by rain.

　　3. If the gray phenomenon occurs due to overfilling of powder, the reliability of the feeding level gauge and the full material alarm device must be checked.

　　Belt slipping on rainy days

　　Fault phenomenon: The inclined belt slips when running under load on rainy days.

　　Cause analysis: On rainy days, the moisture in the aggregate and the exposed part of the belt are easily damp, especially the inner circle of the belt, which reduces the friction coefficient between the belt and the drive roller, resulting in a decrease in the torque transmitted to the belt by the roller. When this torque is less than the torque required for the belt to transport materials, the belt will slip.

　　Processing process:

　　1. Increase the weight of the belt tensioning device or tighten the belt adjustment screw to increase the positive pressure between the belt and the roller, thereby increasing the friction between the drive roller and the belt.

　　2. Adjust the tensioning roller near the drive roller to increase the wrap angle of the belt on the drive roller, thereby increasing the friction.

　　3. Cut straight grooves on the rubber layer of the drive roller to increase the friction coefficient.

　　4. If the first three methods cannot solve the problem, the anti-slip roller needs to be replaced.

　　Additive pump not working

　　Fault phenomenon: The additive pump does not pump the additive when it is working.

　　Cause analysis:

　　1. There are air bubbles in the additive pump.

　　2. Insufficient material in the additive tank.

　　3. Damage to the additive pump impeller.

　　Processing process:

　　1. Disassemble the additive exhaust screw to release the air bubbles in the additive.

　　2. Add additive to the additive tank.

　　3. Check the condition of the additive impeller and replace parts as needed.

　　Belt damage

　　Fault phenomenon: After using for a period of time, the surface of the belt shows signs of delamination, cracking, and scratching.

　　Cause analysis: If the metal belt cleaner is not adjusted in time, it can easily damage the belt, causing the rubber on the surface of the belt to fall off. If the cleaner is installed incorrectly, sharp stones stuck between the cleaner can damage the belt. Poor quality of the belt itself can also lead to the above defects.

　　Processing process: Once the belt shows defects such as delamination, cracking, or scratching, it should be repaired in a timely manner. When the belt is damaged, the first step is to address the factors causing the damage, such as if the cleaner is damaged, it should be adjusted or replaced immediately, and then the belt should be repaired promptly. If the damage to the belt is small, it can be repaired on-site with belt repair glue. If the damage area is large or the local damage is severe, the damaged part of the belt can be cut off and replaced with a new section, bonded using a vulcanizing machine. If the damage to the belt is not addressed in a timely manner and spreads to the entire belt, it will no longer be worth repairing and will need to be replaced entirely.

　　Uneven aggregate delivery by the belt

　　Fault phenomenon: There is accumulation of material from the aggregate scale onto the belt, causing scattered materials on the belt, or there are gaps in the aggregate being transported on the belt, causing pebbles to scatter.

　　Cause analysis: The unloading sequence and time interval of various aggregates at the batching station can be adjusted at any time. Generally, the unloading sequence requires that the last aggregate to be unloaded is sand, and the unloading time interval requires that the tail of the previous aggregate coincides with the head of the next aggregate as it falls onto the belt. If the time interval is too short, there will be overlapping piles of the previous and next aggregates, and excessive piling will cause scattered materials. If the time interval is too long, there will be gaps between the two aggregates, and if the previous material is pebbles, they will roll and fall off the belt.

　　Processing process:

　　1. Adjust the unloading sequence of the aggregates to ensure that sand is the last to be unloaded.

　　2. Adjust the unloading time intervals of various aggregates based on the distribution of aggregates on the belt to ensure continuous and even distribution of materials on the belt. The time intervals generally need to be adjusted multiple times.

　　3. Troubleshooting methods for concrete mixing station

　　Pressure regulator in the air source three-piece cannot be adjusted

　　Fault phenomenon: The rotary pressure regulator adjustment handwheel is turned, but the pressure cannot be adjusted.

　　Cause analysis:

　　1. The inlet and outlet directions of the pressure regulator are installed incorrectly.

　　2. Foreign objects are embedded in the valve core or foreign objects are stuck in the sliding parts of the valve core.

　　3. The pressure regulating spring, reset spring, diaphragm, rubber pad on the valve core, etc. are damaged.

　　Processing process:

　　1. Check whether the installation direction of the pressure regulator's inlet and outlet is correct.

　　2. Disassemble and check the valve core and related parts, and clean the debris on the parts.

　　3. If parts are damaged, replace the pressure regulator.

　　Oil mist generator in the air source three-piece does not drip oil or the oil amount is too small

　　Fault phenomenon: Compressed air flows, but the oil mist generator does not drip oil or drips very little.

　　Cause analysis:

　　1. The inlet and outlet directions of the oil mist generator are installed incorrectly.

　　2. Oil passage blockage.

　　3. The oil filling plug gasket is damaged or the oil cup sealing gasket is damaged, preventing pressure from building up in the oil cup.

　　4. Air passage blockage, oil cup chamber not pressurized.

　　5. The throttle valve is not opened or the opening is insufficient.

　　6. The viscosity of the oil is too high.

　　Processing process:

　　1. Check the installation direction of the oil mist generator's inlet and outlet.

　　2. Stop the gas, disassemble, clean the oil passage; replace the gasket and seal; clean the gas passage.

　　3. Adjust the opening of the throttle valve.

　　4. Replace with a lubricant of lower viscosity.

　　The air compressor starts frequently.

　　Fault phenomenon: During operation, the air compressor starts frequently.

　　Cause analysis:

　　1. The pressure difference of the air compressor is too small. 2. The gas circuit system has serious air leaks.

　　Processing process:

　　1. Check the pressure difference of the air compressor and adjust it, generally to 0.2MPa.

　　2. Check whether the gas circuit system's airtightness meets the requirements and deal with the leaking parts.

　　The magnetic switch on the cylinder cannot close or sometimes cannot close.

　　Fault phenomenon: When the cylinder is closed or opened to position, the magnetic steel approaches the switch, but the switch does not close or sometimes cannot close.

　　Cause analysis: 1. Power failure; 2. Poor wiring; 3. The installation position of the magnetic switch has shifted; 4. There is a strong magnetic field around the cylinder; 5. The temperature inside the cylinder is too high or the temperature at the magnetic switch exceeds 70 degrees; 6. The magnetic switch is impacted, reducing sensitivity; 7. The magnetic switch momentarily passed a large current and broke the line.

　　Processing process: 1. Check if the power supply is normal; 2. Check if the wiring is loose; 3. Adjust the installation position of the magnetic switch; 4. Add a magnetic isolation plate. 5. Cool down. 6. Replace the magnetic switch.

　　Section 2 Control Part

　　The main motor of the mixer cannot start.

　　Fault phenomenon: Pressing the start button of the mixer on the control panel, the mixer does not start.

　　Cause analysis:

　　1. The air compressor has not started or the pressure of the gas supply system has not reached.

　　2. The maintenance protection switch of the mixing host and the emergency stop switch with a key on the host are not connected.

　　3. The emergency stop switch on the control panel has not been reset.

　　4. The power switch of the host is not connected.

　　5. The stop signal of the host must be reset.

　　Processing process:

　　1. Check whether the compressed air detection signal (pressure signal greater than 0.4MPa) is sent to the PLC, that is, whether I8.0 has a signal. If I8.0 has no signal, check whether the air compressor pressure is greater than 0.4MPa. When the pressure reaches above 0.4MPa, if I8.0 still has no signal, check whether the adjustment of the electric contact pressure gauge is normal or damaged, until I8.0 has a signal.

　　2. Check whether the maintenance protection switch of the mixing host sends a connection signal to the PLC.

　　3. Check whether the emergency stop switch on the control panel has been reset.

　　4. Check whether the power switch of the host is connected.

　　5. Check whether the stop button of the host has been reset.

　　During the automatic production process, the aggregate in the batching station is weighed but not discharged.

　　Fault phenomenon: During the automatic production process, one or more aggregates are weighed in the measuring hopper and not discharged, causing the system to stop running.

　　Cause analysis:

　　1. The waiting hopper door is not closed properly.

　　2. The weighing instrument does not have a discharge output signal.

　　3. The belt conveyor has not started.

　　4. The precision door of the aggregate scale is not closed properly.

　　5. The discharge order of the aggregate must be defined.

　　Processing process:

　　1. Check whether the valve of the waiting hopper is jammed or not closed properly. After closing properly, I6.7 has a signal.

　　2. Check whether the aggregate weighing instrument has a discharge output signal: Stone 1 discharge I0.4, Stone 2 discharge I0.7, Sand 1 discharge I1.5, Sand 2 discharge I1.2.

　　3. Check whether the belt conveyor has started.

　　4. Check whether the precision door of the aggregate is closed properly: Stone 1 precision door I8.2, Stone 2 precision door I8.3, Sand 1 precision door I8.5, Sand 2 precision door I8.4.

　　5. Check the computer interface to see if the discharge order of the aggregate is defined.

　　The inclined belt cannot start.

　　Fault phenomenon: After the mixer starts normally, pressing the start button of the inclined belt on the control panel does not start the inclined belt.

　　Cause analysis:

　　1. The mixer has not started.

　　2. The maintenance stop switch of the inclined belt has not been reset.

　　3. The power switch of the inclined belt has not been connected.

　　4. The stop button switch of the inclined belt has not been reset.

　　The digital drift of the measuring instrument when static.

　　Fault phenomenon: In a natural state, the instrument displays data that continuously changes.

　　Cause analysis: The weight data displayed by the weighing instrument comes from the current signal transmitted from the sensor junction box. If the weight displayed by the instrument fluctuates greatly, it indicates that the current transmitted from the sensor junction box fluctuates. Damage to the internal bridge of the sensor or loose wiring at the sensor junction box can cause current fluctuations.

　　Processing process: Remove all wiring of a certain sensor at the junction box and see if the instrument data continues to drift. If the instrument data stops drifting, it can be determined that the wiring of that sensor is loose or the sensor is damaged. Reconnect all wiring of the removed sensor to the junction box. If the instrument data stops drifting, it indicates that the cause is due to loose wiring. If the instrument data continues to drift, the sensor is damaged, and replacing the sensor will solve the problem. If the instrument data continues to drift after removing a certain sensor, remove another sensor (do not reconnect the wiring of the removed sensor) and process it in a similar manner.

　　The mixer does not discharge after the mixing time is up.

　　Fault phenomenon: During the automatic production process, after the mixing time becomes zero, the mixer does not discharge.

　　Cause analysis: Under normal circumstances, after the mixing time becomes zero, the mixer will automatically discharge, but if the pause button on the control panel is pressed or the discharge control on the computer monitoring interface is clicked during the production process, the mixer will not discharge after the mixing time is up. Additionally, if the discharge door solenoid valve is damaged and the discharge door cannot open, the mixer will also not discharge.

　　Processing process:

　　1. Check if the pause button on the control panel is pressed; if pressed, reset it.

　　2. Check if the discharge control on the computer monitoring interface is activated; if activated, Cancel it.

　　3. Check if the discharge solenoid valve is working properly.

　　The mixer trips due to overload.

　　Fault phenomenon: During the feeding and mixing process, the mixing host trips due to excessive current.

　　Cause analysis:

　　1. Excessive feeding causes the mixer to be overloaded.

　　2. The gap between the mixing system blades and the liner is too large, increasing resistance during mixing.

　　3. The triangular drive belt is too loose, resulting in low efficiency of the drive system.

　　4. The safety maintenance switch on the cover of the mixing host is loosened, causing a shutdown.

　　Processing process:

　　1. Check if the batching system is exceeding standards and if there is a secondary feeding phenomenon.

　　2. Check if the gap between the mixer blades and the liner is between 3~8mm.

　　3. Check the tightness of the triangular belt in the drive system and adjust it.

　　4. Check if the safety switch on the cover of the host is loose.

　　The mixer discharge door closes without a signal.

　　Fault phenomenon: After the mixer discharges, the discharge door closes, but there is no door signal, causing the program to stop running.

　　Cause analysis: The proximity switch of the mixer discharge door must be within 5mm of the pointer on the discharge door to sense the signal. When the discharge door is stuck due to insufficient oil pump pressure or when it is blocked by residual material in the mixer while closing, the proximity switch cannot get close enough to the pointer and thus does not receive a signal. If the proximity switch or the pointer is loose, causing the distance to exceed 5mm, the proximity switch will also not sense a signal. If the proximity switch is damaged, there will also be no signal output.

　　Processing process:

　　1. Check if the hydraulic system pressure of the discharge door meets the requirements.

　　2. Switch to manual mode, open the mixer discharge door to let the stuck residual material fall off, and then close it.

　　3. Check if the proximity switch and the pointer are loose.

　　4. Check if the proximity switch is damaged.

　　Concrete mixing is uneven.

　　Fault phenomenon: The concrete discharged from the mixer is uneven, with one side dry and the other side wet.

　　Cause analysis: A mixing time that is too short will result in uneven mixing; additionally, if the spray nozzle of the mixer is installed incorrectly, it will spray unevenly, making it easier for the concrete to be one side dry and the other side wet.

　　Processing process:

　　1. Check if the mixing time is too short (generally 30 seconds); if the mixing time is too short, extend the mixing time.

　　2. Check if the installation order of the spray nozzle is correct; the correct order is that the nozzle next to the drainage pump is the smallest, the nozzle on the other side is the largest, and the nozzles in the middle are arranged in an increasing order.

　　Aggregate weighing is inaccurate.

　　Fault phenomenon:

　　1. Aggregate weighing is always too much.

　　2. Aggregate weighing is always too little.

　　3. Aggregate weighing fluctuates between too much and too little.

　　Cause analysis: The weighing error of aggregates is closely related to fine setting, drop, and the uniformity of discharge. The fine setting data must be greater than the drop; otherwise, if the fine setting signal has not been output, the drop signal has been sent, stopping the discharge.

　　Processing process:

　　1. If the aggregate is always too much, it can be resolved by adjusting the drop to a larger value. After increasing the drop, check if its value is less than the fine setting value; if the drop is greater than the fine setting, the fine setting value should be adjusted accordingly.

　　2. If the aggregate is always too little, it can be resolved by adjusting the drop to a smaller value. After decreasing the drop, the fine setting value generally does not need to be adjusted.

　　3. If the aggregate weighing fluctuates, first check the uniformity of the discharge, check if there are any obstructions at the discharge port, and then adjust the fine setting and drop.

　　Powder weighing is inaccurate.

　　Fault phenomenon: 1. Powder weighing is always too much; 2. Powder weighing is always too little; 3. Powder weighing fluctuates between too much and too little.

　　Cause analysis: Factors related to powder weighing include the setting of the drop, the uniformity of the screw feeder, and the influence of the negative pressure in the main building's dust removal system.

　　Processing process: If it is always too much or too little, it can be corrected by adjusting the drop. When weighing is unstable, check the uniformity of the screw feeder (mainly check if the powder tank discharges smoothly) and address any issues. Also, check if the dust removal pipeline and filter element in the main building are blocked.

　　Admixture weighing is inaccurate.

　　Fault phenomenon:

　　1. Admixture weighing is always too much.

　　2. Admixture weighing is always too little.

　　3. Admixture weighing fluctuates between too much and too little.

　　Cause analysis: Mainly due to the impact of the drop and the manual valve opening.

　　Processing process: First adjust the drop. If there are still issues after adjusting the drop, then reduce the opening of the manual valve in the additive pipeline, and then adjust the drop.

　　After the powder scale measurement is accurate, the reading of the measuring instrument gradually decreases.

　　Fault phenomenon: During the automatic production process, the material in the powder measuring hopper gradually decreases after being weighed.

　　Cause analysis: Mainly caused by the pneumatic butterfly valve not closing tightly. The factors for the pneumatic butterfly valve not closing tightly include: the position of the limit screw during the assembly of the pneumatic butterfly valve is not suitable, causing the butterfly valve itself to not close properly, and if material sticks to the outlet of the butterfly valve, it will also cause the pneumatic butterfly valve to not close properly.

　　Processing process:

　　1. First, remove the red rubber tube connected to the pneumatic butterfly valve and check if there is any material stuck to the butterfly valve. If so, clean the material off with a steel brush while the butterfly valve is in the open position.

　　2. Check if the position of the limit screw of the butterfly valve is appropriate, and adjust the screw to limit the opening of the butterfly valve.