Common failure causes and treatment methods of the

2022-09-27
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Common failure causes and treatment methods of plastic extrusion granulation machine

the extrusion granulation machine is highly integrated with machine, electricity and instrument, and has a high level of automation control. Therefore, in actual operation, there will be many faults that are difficult to diagnose, resulting in long processing time, which will affect the normal operation of the whole polypropylene plant and greatly reduce the production economic benefits. Combined with the theoretical knowledge of the extrusion granulation production process and the management experience of the actual production and operation for more than ten years, the author analyzes and judges the common causes of the failure of the unit in operation, and formulates the corresponding solutions and treatment methods, so as to ensure its long-term stable operation

fault cause

in the extrusion granulation unit, the friction clutch disengages during the operation of the extrusion granulation unit, and the reasons for the interlocking shutdown of the unit can be divided into four categories:

main motor system fault

1, the torque of the main motor is too high or too low; 2. The speed of main motor is too low; 3. The bearing temperature of main motor is too high; 4. The winding temperature of the main motor is too high; 5. The inlet and outlet temperature of the water-cooled cooler of the main motor is too high; 6. The outlet flow of lubricating oil pump of main motor bearing is too low; 7. The outlet pressure of lubricating oil pump of main motor bearing is too low; 8. The water leakage of the water-cooled cooler of the main motor is too high

transmission system fault

1, gear box shift lever position deviation; 2. The instrument air pressure of friction clutch is too high; 3. The speed difference of friction clutch is too large; 4. The outlet pressure of gearbox lubricating oil pump is too low; 5. The oil temperature at the outlet of gearbox lubricating oil pump is too high; 6. Internal failure of friction clutch, etc

screw process section failure of extrusion granulator

1. Melt pressure before and after throttle valve is too high; 2. The melt pressure of the die is too high; 3. The melt pressure difference before and after the exchanger is too large; 4. Start up valve rotation failure, etc

fault of underwater pelletizing system

1. The winding temperature of pelletizing motor is too high; 2. The rotating speed of the pelletizer is too low; 3. The cutter torque is too high; 4. Automatic switching failure of granular water bypass; 5. Particle water pressure is too high or too low; 6. Particle water flow is too low; 7. The clamping bolt of the pelletizer is not tightened; 8. The bypass water valve of the pelletizing chamber is not closed; 9. The hydraulic clamping pressure of the pelletizer is too low; 10. Pelletizing motor failure; 11. The axial feed pressure of hydraulic cutter is too low

among the above fault causes, the frequent ones are: the main motor torque of the main motor system is too high or too low; Friction clutch failure of transmission system; The melt pressure of the screw process section system of the extrusion granulator is high; Underwater pelletizer system failure, etc. The causes of these common faults will be analyzed in detail below, and the corresponding solutions will be given

common fault cause analysis and solutions

main motor torque is too high

cause analysis:

oil lubrication system failure, poor alignment of main motor output shaft and gearbox inlet and outlet shaft, motor and clutch vibration and other reasons will damage the main motor bearings, resulting in excessive torque. In addition, excessive feeding load or poor material melting will also lead to excessive torque of the main motor

solutions:

regularly check and clean the lubricating oil system, measure the main motor bearings with vibration measuring instrument and infrared thermometer, and form a trend chart. If the trend value is exceeded, measure whether the idle current value or power value of the main motor exceeds the specified value, and judge whether the bearing should be replaced. Regularly check the alignment between the output shaft of the main motor and the input shaft of the gearbox. The alignment must be checked three months after the first start-up or bearing replacement. Conduct electrical test and inspection to determine the cause of rotor imbalance; Test the vibration speed of the clutch. If it exceeds the specified value, readjust the dynamic balance. Check the heating and cooling system of the cylinder regularly to ensure that the materials are heated evenly and melted fully. If the power curve of the main motor and the melt pressure curve increase instantaneously at the start of the extruder, it indicates that the feeding volume of the feeding system is too large instantaneously, and the feeding volume should be reduced

the torque of the main motor is too low

cause analysis:

the failure of the feeding system will lead to the idling of the twin-screw, which will lead to the low torque of the main motor

solutions:

check and judge whether the additive system or the main material blanking system is faulty, and clean up the blocking points

friction clutch failure

cause analysis:

the instantaneous starting voltage of the main motor is too low, the friction disc and friction plate are overheated, the friction disc and friction plate are aging, and the air pressure of the friction disc is too low, which can lead to clutch disengagement

Energy efficiency, environmental protection and product quality must be comprehensively considered

solutions:

when the main motor is started, it should avoid the peak power consumption, reduce the feeding load, and the restart interval should be at least 30 minutes; In summer, when the main motor is started repeatedly for more than two times, the interval should be extended or the fan should be used to forcibly cool down. Purge with instrument air and wipe the dust on the surface of the friction plate and friction disc with a rag. If the wear is heavy or the surface appears "vitrification", replace the friction plate and friction disc. Confirm whether the air pressure value can make the friction disc fit the friction plate

high melt pressure

cause analysis:

the number of filter meshes is high. BMW Group aims to strengthen the transparency of its cell supply chain. Low melt index of polypropylene powder and large feeding volume, low barrel temperature in each section makes the material melt incomplete, low template opening rate makes the extrusion of head materials blocked, and other reasons can lead to high melt pressure

solutions:

when producing low melt index products, low mesh filtration should be used, and the opening of throttle valve should be increased to reduce back pressure; Change the filter in time, monitor the quality of various additives and the ash content in polypropylene powder. Reduce the feeding load. Without affecting the quality of extruded products, increase the barrel temperature of each section, increase the melt temperature of polypropylene, and increase the fluidity of materials. After the extruder stops, raise the head temperature and keep it constant for a period of time, and then thoroughly wash and clean the formwork

failure of underwater pelletizing system

cause analysis:

excessive wear of the cutter or damage of the blade edge, low particle water flow, excessive vibration of the pelletizer, loose fit between the cutter and the template, fluctuation of material melt index, inconsistent discharge flow rate, high particle water temperature and other reasons can lead to shutdown of the underwater pelletizing system, resulting in interlocking shutdown of the whole unit

solutions:

after parking, visually check whether the cutting edge of the cutter is excessively worn or damaged. If so, replace all the cutters. Check and confirm whether the particulate water is leaking, and whether the filter and cooler of the particulate water tank are blocked. If blocked, manually clean it up; Check whether the inlet and outlet pressure of the particle water pump is normal. If not, overhaul the particle water pump and the valves on the pump pipeline. Although the plastic packaging material has not achieved the environmental protection goal, check whether the alignment between the cutter shaft and the upper pelletizing motor is out of tolerance, whether the bearing components of the cutter shaft are damaged, and whether the dynamic balance of the cutter rotor is unbalanced. During operation, check whether there is clearance between the four moving wheels of the pelletizing car and the guide rail. Control the volatile in polypropylene powder and eliminate the vibration of the cutter and cutter shaft when flowing through the template hole. Reduce the hot oil temperature at the formwork, check the temperature distribution of the cylinder and formwork, and check whether the flow, pressure and temperature of the cylinder cooling water are normal; Confirm the time setting of "water, knife and material" arriving at the formwork to prevent the particle water from arriving at the formwork too early and blocking the formwork hole. After the cutter closes the head, the feeding amount should be quickly raised to the set load of the extruder

if the above fault cause points can be combined with the logical relationship of interlocking to compile into fault diagnosis software, it can provide quick and intuitive reference and help for the operation, maintenance and management of the unit

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