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Typical Failure Problem of Concrete Mixing Plant

Thomas Huang posted this article in June 30, 2020

Typical failure of mixing plant
1 The main motor of the mixer will not start.
Trouble phenomenon: Press the mixer start button on the console, the mixer will not start.
 Cause Analysis:
1. The air compressor is not started or the pressure of the gas supply system has not reached 0.4MPa.
 2. The overhaul protection switch of the mixing host and the keyed stop switch on the host are not connected.
 3. The emergency stop switch on the console is not reset.
 4. The host power switch is not turned on.
 5. The host stop signal must be reset.
 Processing process:
1. Check whether the compressed air detection signal (atmospheric 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 pressure of the air compressor is greater than 0.4MPa. When the pressure reaches 0.4MPa or more, I8.0 has no signal, then check whether the adjustment of the electrical contact pressure gauge is normal or damaged until I8.0 has signal.
 2. Check whether the signal of the overhaul protection switch of the mixing host is sent to the PLC, that is, whether there is a signal in I9.7.
 3. Check whether the emergency stop switch on the console is reset and whether I0.1 has a signal.
 4. Check whether the power switch of the host is turned on and whether there is a signal in I3.4.
 5. Check whether the stop button of the host is reset and whether I5.2 is connected.
2 In the automatic production process, the aggregate at the batching station is not unloaded after weighing.
Failure phenomenon: In the automatic production process, one or more aggregates are weighed in the weighing hopper, without discharging, the system stops running.
 Cause Analysis:
1. Wait until the hopper is closed.
 2. The weighing instrument has no discharge output signal.
 3. The belt conveyor is not started.
 4. The fine weighing door of aggregate weighing is not closed in place.
 5. The aggregate must define the discharge sequence.
 Processing process:
 1. Check whether the valve of the hopper is stuck or the door is not closed properly. After the door is closed, I6.7 has a signal.
 2. Check whether the aggregate weighing instrument discharges the 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 is started.
 4. Check whether the fine weighing door of the aggregate is closed in place, the fine stone 1 is called the closed door I8.2, the fine stone 2 is called the closed door I8.3, the fine sand 1 is called the closed door I8.5, and the fine sand is called the closed door I8.4.
 5. Check the computer interface, whether the sequence of aggregate discharge is defined.
 3 The inclined belt does not move
Trouble phenomenon: After the mixer starts normally, press the start button of the inclined belt on the operation platform, the inclined belt will not start.
 Cause Analysis:
1. The mixer is not started.
 2. The inclined belt maintenance stop switch is not reset.
 3. The power switch of the inclined belt conveyor is not connected.
 4. The stop button switch of the inclined belt conveyor is not reset.
 5. The washing machine button is not reset.
 Processing process:
 1. Check whether the stop switch for inclined belt maintenance is reset and I7.7 is turned on.
 2. Check whether the power switch of the inclined belt conveyor is turned on and I7.6 is turned on.
 3. Check whether the stop button switch of the inclined belt conveyor is reset and I11.4 is turned on.
 4. Check whether the washing machine button is reset and I5.3 is disconnected.
 4 Aggregate weighing hopper does not feed
Failure phenomenon: In automatic state, press cycle start or single disk start, one or several aggregates are not weighed.
Cause Analysis:
In the automatic state, the process of weighing the aggregate is that the PLC gives a weighing signal to the meter. The weighing instrument outputs the coarse and fine weighing signals to the PLC according to the set value of the recipe. After the PLC receives the coarse and fine weighing signals, When the discharge door of the aggregate weighing hopper is closed, a signal is output to the solenoid valves of the coarse and fine feed gates. After the solenoid valve receives the signal, the fine and coarse feed gates are opened and the weighing starts. . When the weight of the aggregate scale reaches the precision weighing requirement, the coarse signal of the instrument stops outputting, the coarse solenoid valve is powered off, and the coarse weighing door is closed. When the weight of the aggregate scale reaches the drop value, the meter's precision weighing signal stops outputting, the precision weighing solenoid valve is powered off, the precision weighing door is closed, and the weighing is completed. Born
It can be seen in the production process that the factors that affect weighing are: whether the weighing instrument gives a PLC weighing signal, whether the PLC gives a solenoid valve signal, and whether the solenoid valve can be normally commuted.
 Processing process:
 1. Check the closing and in-position status of the discharge door of the weighing hopper, 1# Shizi weighing hopper close-in-position signal I5.5, 2# Shizi weighing hopper close-in-position signal I5.6, 1# sand weighing hopper close-in-position signal I6 .0, 2# sand weighing bucket closing in place signal I5.7.
 2. Check the weighing signal output by the instrument, stone 1 coarse signal I0.5, stone 1 fine signal I0.6, stone 2 coarse signal I1.0, stone 2 fine signal I1.1, sand 1 coarse signal The signal I1.6, the sand 1 is finely called the signal I1.7, the sand 2 is coarsely called the signal I1.3, and the sand 2 is finely called the signal I1.4.
 3. Check the output signal of the PLC. Stone coarse refers to the feed signal Q0.0, stone 1 refers to the feed signal Q0.1, stone 2 refers to the feed signal Q0.2, and stone 2 refers to the feed signal Q0.3. , Sand 1 coarsely calls the feed signal Q0.6, Sand 1 finely calls the feed signal Q0.7, Sand 2 coarsely calls the feed signal Q0.4, and Sand 2 finely calls the feed signal Q0.5.
 4. When there is a signal output to the solenoid valve without feeding, check whether the solenoid valve coil is burnt out or whether the valve core is stuck.
5 Powder feeding is slow
Failure phenomenon: The feeding of the screw machine is very slow, the feeding time exceeds 2 minutes, and the normal feeding is at
 Less than 20 seconds.
Cause Analysis:
The main influencing factors are poor feeding of the powder material tank and damage to the screw conveyor. The manifestations of unsatisfactory powder discharging include powder arching, material agglomeration at the discharge port of the powder tank, and the opening of the discharge butterfly valve.
Small, insufficient material in powder tank, etc. The damage of the screw conveyor is mainly due to the deformation of the spiral blade, which cannot be conveyed normally.
 Processing process:
 Processing process:
 1. Turn on the air blowing and arch breaking device.
 2. Check the opening of the unloading disc valve of the powder tank, and make the disc valve fully open.
 3. Check whether the material at the exit of the powder tank is agglomerated.
 4. Check whether the blade of the screw machine is deformed, if it is deformed, remove it for correction or replace it.
 6 belt deviation
Failure phenomenon: During the no-load or load operation of the belt conveyor, the phenomenon of deflection to the side or for a while and for a while and on the right causes leakage, abnormal wear and damage of the equipment, reduced productivity, and Will affect the normal operation of the entire set of equipment.
Cause Analysis:
 The resultant force of the external force on the tape in the width direction of the tape is not zero or caused by uneven tensile stress in the direction perpendicular to the width of the tape. Since there are many factors that cause the tape to deviate, the design, manufacture, installation, commissioning, use and maintenance of the conveyor should be used to solve the tape deviation. For example, the tightness of the two sides of the tape is different, and the height of the two sides of the tape is not the same. Similarly, if the roller bracket and other devices are not installed on the vertical section of the tape running direction, etc., it will cause the belt to deviate.
 Processing process:
 (1) Adjusting the tensioning mechanism method
 When the tape is running, if it runs off to the same side under no-load and heavy-load conditions, it means that the tape
 If the elasticity of the two sides of the belt is different, it can be adjusted in the direction shown in Figure A; if the tape is deviated from side to side and there is no fixed direction, it means that the tape is slack and the tension mechanism should be adjusted.
 (2) Adjust the drum method
If the tape deflects at the roller, it means that the installation of the roller is not level, the roller moves axially, or one end of the roller is behind the front. At this time, the horizontality and parallelism of the drum should be corrected.
 (3) Adjust the roller bracket (or frame) method
 If the tape always deflects to one side when it is empty, the roller support on the deflecting side should be moved forward by 1-2 cm along the tape running direction (see Figure B), or the roller support on the other side (or frame) ) Increase properly.
 (4) Remove sticky matter
 If material is stuck on the drum and the idler, the diameter of the area will increase, resulting in an increase in the tensile force of the tape at this location, which will cause deviation. The adhered materials should be cleaned in time.
 (5) Adjust gravity method
 If the tape does not deflect when it is not loaded, but always deflects to one side when it is heavily loaded, it means that the tape has deflected. The position of the hopper or belt conveyor should be adjusted so that the tape is evenly loaded to prevent deviation.
 (6) Adjust tape method
 If the edges of the tape are badly worn or the tape seams are not parallel, the sides of the tape will be pulled
 Not consistent. The tape should be redressed or replaced.
 (7) Install the deviation adjusting roller method
 If several sets of self-aligning rollers (flat rollers or grooved rollers) are installed on the conveyor, the deviation of the tape can be corrected automatically. For example: when the tape runs off and rubs against the small stop roller on one side, the bracket on that side should be moved forward in the running direction of the tape, and the other side should be moved relatively backward. At this time, the tape will move backward. The side of the stop roller moves until it returns to the normal position.
 (8) Installation limit roller method
If the tape always deflects to one side, a limit vertical roller can be installed on the frame on the side of the deviation; in this way, on the one hand, the tape can be forcedly reset, on the other hand, the vertical roller can reduce the tension of the tape on the side of the deviation. The tape moves to the other side.
7 Blender trip
Trouble phenomenon: During the feeding and mixing process, the mixing machine trips due to excessive current.
Cause Analysis:
 The resultant force of the external force on the tape in the width direction of the tape is not zero or caused by uneven tensile stress in the direction perpendicular to the width of the tape. Since there are many factors that cause the tape to deviate, the design, manufacture, installation, commissioning, use and maintenance of the conveyor should be used to solve the tape deviation. For example, the tightness of the two sides of the tape is different, and the height of the two sides of the tape is not the same. Similarly, if the roller bracket and other devices are not installed on the vertical section of the tape running direction, etc., it will cause the belt to deviate.
1. Excessive feeding causes excessive load on the mixer.
 2. The gap between the blade and the lining plate of the mixing system is too large, and the resistance is increased during the mixing process.
 3. The triangle transmission belt is too loose, which makes the transmission system inefficient.
 4. The safety maintenance switch on the upper cover of the mixing machine is loosened, causing downtime.
Processing process:
 1. Check whether the batching system exceeds the standard and whether there is secondary feeding phenomenon.
 2. Check whether the gap between the blade of the mixer and the lining plate is 3~8mm.
 3. Check and adjust the tightness of the V-belt of the transmission system. Check whether the safety switch on the top cover of the main unit is loose.
 8 There is no signal when the discharge door of the mixer is closed.
Fault phenomenon: after the mixer has unloaded the material, the discharge door is closed, but the door signal is not relevant, causing the program to stop running.
Cause Analysis:
 Only when the proximity switch of the discharge door of the mixer and the pointer of the rotary handle on the discharge door are within 5mm can the signal be sensed. When the discharge door does not reach the required pressure or the discharge door is closed by the residual material in the mixer when the discharge door is closed, the proximity switch cannot reach the rotary handle pointer without signal, because the proximity switch or rotary handle pointer is loose, making the proximity When the distance exceeds 5mm, the proximity switch cannot detect the signal. There is no signal output if the proximity switch is damaged.
 Processing process:
 1. Check whether the working pressure of the discharge door hydraulic system meets the requirements (13MPa)..
 2. Switch to manual and open the discharge door of the mixer to make the stuck residue fall
 Then close again.
 3. Check whether the proximity switch and rotary handle pointer are loose.
 4. Check whether the proximity switch is damaged.
 9 Concrete mixing is uneven.
Fault phenomenon: The concrete discharged from the mixer is uneven, and it is dry and wet at the same time.
Cause Analysis:
If the mixing time is too short, the mixing will be uneven. In addition, if the nozzle of the spray pipe of the mixer is not installed correctly, the water spray will be uneven, making it easier to dry and wet the concrete.
Processing process:
1. Check whether the stirring time is too short (usually 30 seconds). If the stirring time is too short, the stirring time can be extended.
2. Check whether the installation order of the nozzles of the water spray pipe is correct. The correct arrangement order is that the nozzle on the side of the drain pump is the smallest, the nozzle on the other side is the largest, and the installation is evenly arranged in order from small to large in the middle.
 10 Aggregate weighing is not allowed.
Failure phenomenon:
1. The aggregate weighing is always too much.
   2. The aggregate weighing is always too small.
   3. Weigh aggregates for a while and more and less.
   Cause Analysis:
   Aggregate weighing error is closely related to fine setting, drop and uniformity of discharge. The fine setting data must be greater than the drop, otherwise, the fine setting signal has not been output, the drop signal has been issued, and the discharge is stopped.
   Processing process:
   1. Aggregate is always too much, which can be solved by adjusting the large drop. After the free fall is adjusted larger, it is necessary to check whether the value is smaller than the fine set value. If the free fall is larger than the fine set value, the fine set value should be adjusted accordingly.
   2. Aggregate is always too much, which can be solved by adjusting the small drop. After the drop is reduced, the fine setting value generally does not need to be adjusted.
   3. Weigh the aggregate for a while and then for a while, first check the uniformity of the discharge, check whether there is any debris stuck in the discharge port, and then adjust the fine setting and the drop.
   11 Powder weighing is not accurate.
Failure phenomenon:
1. Weighing powder is always too much.
   2. Weighing powder is always too little.
   3. Weigh the powder for a while and then for a while.
   Cause Analysis:
   The factors related to the weighing of powder materials include the setting of the drop, the feeding uniformity of the screw machine, and the influence of the negative pressure on the dust removal of the main building.
   Processing process:
   If it is always too much or always too small, it can be corrected by adjusting the drop. When the weighing is unstable, the uniformity of the feeding of the screw machine (mainly to see whether the powder can is unloaded smoothly) should be checked and processed. In addition, check whether the dust-removing pipeline and filter element of the main building are blocked.
   12 Weighing of additives is not allowed.
Failure phenomenon:
1. Weighing admixtures is always too much.
   2. Weighing of additives is always less.
   3. Weighing admixtures for a while and more and less.
   Cause Analysis:
   Mainly due to the effect of drop and manual ball valve opening.
   Processing process:
   First adjust the drop, if there is still a problem in weighing after adjusting the drop, then close the manual ball valve in the admixture line, and then adjust the drop.
   13 After the powder scale is accurately measured, the reading of the weighing instrument gradually decreases.
Failure phenomenon: In the automatic production process, the materials in the powder weighing hopper gradually become smaller after weighing.
Cause Analysis:
The main reason is that the discharge pneumatic butterfly valve is not closed tightly. The factors that the pneumatic butterfly valve is not tightly closed include: when the pneumatic butterfly valve is assembled, the position of the limit screw is not suitable, which causes the butterfly valve itself to not close properly, and the sticky material at the outlet of the butterfly valve also causes the pneumatic butterfly valve to not close properly.
   Processing process:
   1. Disassemble the red rubber hose connected to the pneumatic butterfly valve first, and check if there is any material sticking to the butterfly valve. If there is, then use the steel brush to clean the material when the butterfly valve is open.
   2. Check whether the position of the limit jacking of the butterfly valve is proper, and the opening of the butterfly valve can be restricted by adjusting the jacking.
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