Analysis and treatment of common fault causes of extrusion granulation unit

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The extrusion granulation unit is highly integrated with machinery, electricity and instrumentation, 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 times, which will affect the normal operation of the entire polypropylene plant and greatly reduce the economic benefits of production. Combining the theoretical knowledge of the extrusion granulation production process and more than ten years of management experience in actual production operations, our company analyzed and judged the common causes of failure of the unit during operation, and formulated corresponding solutions and processing methods to ensure Its long-term stable operation.


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In the extrusion granulation unit, the friction clutch disengagement during operation of the extrusion granulation unit and the reasons for chain shutdown of the unit can be divided into four major categories.


Ⅰ. Main motor system failure

  1. Main motor torque is too high or too low;

  2. Main motor speed is too low;

  3. Main motor bearing temperature is too high;

  4. Main motor winding temperature is too high;

  5. The temperature of the main motor water-cooled cooler inlet and outlet is too high;

  6. Main motor bearing lubricating oil pump outlet flow rate is too low;

  7. Main motor bearing lubricating oil pump outlet pressure is too low;

  8. The water leakage of the water-cooled cooler of the main motor is too high, etc.


II. Transmission system failure

  1. Gearbox shift lever position deviation;

  2. Instrument air pressure of friction clutch is too high;

  3. Friction clutch speed difference is too large;

  4. Gearbox lubricating oil pump outlet pressure is too low;

  5. Gear box lubricating oil pump outlet oil temperature is too high;

  6. Friction clutch internal failure, etc.


III. Failure in the screw process section of the extrusion

  1. Die melt pressure is too high;

  2. The melt pressure difference between the front and back of the screen changer is too large;

  3. Screw wear.


IV. Failure in the water pelletizing system

  1. Pelletizing motor temperature is too high;

  2. Cutter speed is too low;

  3. Pelletizer torque is too high;

  4. Water pressure is too high or too low;

  5. Granular water flow is too low;

  6. The blade is not clamped.


Analysis of common fault causes and solutions


I. Main motor torque is too high

Cause: Failure of the oil lubrication system, poor alignment between the output shaft of the main motor and the entry and exit shaft of the gearbox, vibration of the motor and clutch, etc. will damage the main motor bearings, resulting in excessive torque. In addition, excessive feeding load or poor material melting will also cause the main motor torque to be too high.

Solution:

  1. Regularly inspect and clean the lubricating oil system, use vibration measuring instruments and infrared thermometers to measure the main motor bearings and form a trend chart. If it exceeds the trend value, determine whether the idling current value or power value of the main motor exceeds the specified value, and determine whether the bearing should be replaced. 

  2. Regularly check the alignment between the main motor output shaft and the gearbox input shaft. The alignment must be checked after three months of first startup or bearing replacement.

  3. Conduct an electrical test to determine the cause of the rotor imbalance; perform a vibration speed test on the clutch, and readjust the dynamic balance if it exceeds the specified value. 

  4. Regularly inspect the cylinder heating and cooling systems to ensure that the materials are heated evenly and melted fully. 

  5. If the main motor power curve and melt pressure curve increase instantaneously when the extruder is started, it indicates that the feeding amount of the feeding system is too large instantaneously, and the feeding amount should be reduced.


II. Main motor torque is too low

Cause: Feeding system failure causing the screws to idle will cause the main motor torque to be too low.

Solution: Check to determine whether there is a fault in the additive system or the main material unloading system, and clear the blockage point.


III. Friction clutch failure

Cause : The instant starting voltage of the main motor is too low, the friction disc and friction disc are overheated, the air pressure of the friction disc is too low and other reasons can cause the clutch to disengage.

Solution: When the main motor is started, the peak power consumption should be avoided, the feeding load should be reduced, and the minimum restart interval should be 30 minutes; in summer, when the main motor is started more than twice, the interval should be extended or Use a fan to force cooling. Blow with instrument air and wipe the dust on the surface of the friction plate and friction plate with a rag. If the wear is heavy or "vitrification" appears on the surface, the friction plate and friction plate should be replaced. Confirm whether the air pressure value can make the friction disc and friction plate fit together.


IV. High melt pressure

Cause: high mesh number of the filter, low melting index of polypropylene and large feeding volume, low temperature of each section of the cylinder causing incomplete melting of the material, low opening rate of the template which hinders the extrusion of the material from the machine head, etc.

Solution: When producing products with low melt index, low-mesh filters should be used, and the opening of the throttle valve should be increased to reduce back pressure; the filter should be replaced in a timely manner, and the quality of various additives and the ash content in polypropylene powder should be monitored. Reduce feed load. Without affecting the quality of the extruded product, the temperature of the cylinder in each section is increased to increase the melt temperature of the polypropylene and increase the fluidity of the material. After the extruder is stopped, increase the temperature of the machine head and keep it constant for a period of time, then rinse and clean the template thoroughly.


V. Fail of pelleting system

Cause: Excessive wear of the cutter or damage to the cutting edge, too low particle water flow, excessive vibration of the pelletizer, loose fit between the cutter and the template, large fluctuations in the melting index of the material, resulting in inconsistent discharge flow rates, and excessive particle water temperature. High-level reasons can cause the underwater pelletizing system to stop.

Solution: After stop the machine, visually check whether the cutting edge is excessively worn or damaged. If so, all cutters should be replaced. Check and confirm whether the granular water is leaking internally, and whether the granular water tank filter and cooler are blocked. If clogged, they should be cleaned manually. Check whether the inlet and outlet pressure of the granular water pump is normal. If not, the granular water pump and the valves on the pump pipeline should be repaired. Check whether the alignment between the cutter shaft and the pelletizing motor is out of tolerance, whether the bearing assembly of the cutter shaft is damaged, and whether the dynamic balance of the cutter rotor is unbalanced. During operation, check whether there is any gap in the contact between the four moving wheels of the pelletizing car and the guide rail. Control the volatile matter in the polypropylene powder and eliminate the vibration of the cutter and cutter shaft when flowing through the template hole. Reduce the temperature of the hot oil at the template, check the temperature distribution of the cylinder and template, and whether the flow, pressure and temperature of the cylinder cooling water are normal; confirm the time setting for "water, knife, and material" to arrive at the template to prevent premature watering of particles Reaching the template causes the template holes to freeze and block. After closing the machine head of the pelletizer, the feeding amount should be quickly increased to the set load of the extruder.

Machine for reference: https://www.jorbinmachinery.com/product/polystere-fabric-cloth-recycling-and-pelletizing-machineagriculture-waste-pellet-machine.html.

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