Analysis And Solution Of Common Failures Of Plastic Extruder

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The extruder is an essential piece of equipment for plastic molding processing and pelletizing. The extruder’s everyday use can give full play to the machine’s efficiency and maintain an excellent working condition. It must carefully keep unremittingly to extend the service life of the appliance. The extruder’s primary failure is abnormal noise and abnormal vibration caused by abnormal wear, wear or damage of transmission parts, and inadequate lubrication.

Common faults of plastic extruder:

1. The host current is unstable

Reasons for production:

  1.   Uneven feeding.
  2. The main motor bearing is damaged or poorly lubricated.
  3. A specific section of the heater fails and does not heat up.
  4. The screw adjustment pad is wrong, or the phase is terrible, and the components interfere.

Approach:

  1.  Check the feeder and troubleshoot.
  2. Overhaul the main motor and replace the bearings if necessary.
  3. Check whether each heater is usually working, and replace the heater if required.
  4. Check the adjustment pad and pull out the screw to check if there is any interference in the screw.

2. The main motor cannot start

Cause:

  1.  There is an error in the driving procedure.
  2. There is a problem with the main motor thread, whether the fuse burn.
  3. The interlocking device related to the primary motor works

Approach:

  1.  Check the procedure and drive again in the correct driving sequence.
  2. Check the primary motor circuit.
  3. Check whether the lubricating oil pump is started and check the interlocking device’s status related to the main motor. The oil pump cannot turn on, and the engine cannot turn on.
  4. The induction current of the inverter has not been discharged. Turn off the main power supply and wait for 5 minutes before starting.
  5. Check whether the emergency button is reset.

3.The machine head is not smooth or blocked

Cause:

  1.  A particular section of the heater does not work, and the material’s plasticization is poor.
  2. The operating temperature is set too low, or the plastic’s molecular weight distribution is wide and unstable.
  3. There may be foreign objects that are not easy to melt.

Approach:

  1.  Check the heater and replace it if necessary.
  2. Verify the set temperature of each section, negotiate with the technician if necessary, and increase the temperature set value
  3. Clean and check the extrusion system and the machine head.

4. The primary starting current is too high

Cause:

  1. The heating time is insufficient, and the torque is ample.
  2. A specific section of the heater does not work.

Approach:

  1. Before driving, use the handwheel. If it is not easy, extend the heating time or check whether each section of the heater everyday work.

5. The main motor makes an abnormal sound

Cause:

  1. The main motor bearing is damaged.
  2. A certain SCR in the SCR rectifier circuit of the primary motor is damaged.

Approach:

  1. Replace the main motor bearing.
  2. Check the thyristor rectifier circuit, and replace the thyristor element if necessary.

6.The main motor bearing temperature rise is too high

Cause:

  1. Poor bearing lubrication.
  2. The bearing is worn out seriously.

Approach:

  1. Check and add lubricant. Check the motor bearings and replace them if necessary.

7.The head pressure is the unstable

Cause:

  1. The rotation speed of the primary motor is uneven.
  2. The speed of the feeding motor is variable, and the feeding amount fluctuates.

Approach:

  1. Check the central motor control system and bearings.
  2. Check the feeding system motor and control system.

8. Low lubricating oil pressure

Cause:

  1. The pressure setting value of the lubricating oil system’s pressure regulating valve is too low.
  2. The oil pump is faulty, or the oil suction pipe is blocked.

Approach:

  1. Check and adjust the pressure regulating valve of the lubricating oil system.
  2. Check the oil pump and suction pipe.

To avoid failure and daily maintenance, maintenance, and overhaul in strict accordance with the requirements, it is also necessary to pay attention to the wear of the extruder screw.

The normal wear of the screw and barrel of the plastic extruder mainly occurs in the feeding area and the metering area. The leading cause of wear is the dry friction between the chip particles and the metal surface; when the chip heats up and softens, it decreases.

single screw extruder
single screw extruder

Abnormal wear of the screw and barrel will occur when the screw lock by ring knots and foreign objects. A ring knot means that the condensed material locks the screw. If the screw extruder lacks a suitable protection device, the powerful driving force may twist. If the screw is stuck, it will produce colossal resistance, causing severe damage to the surface of the screw and severe scratches on the barrel.

The scratches on the barrel are challenging to repair. The barrel is designed in principle to ensure that the service life is longer than that of the screw. For normal barrel wear, it is generally not repaired. The method of improving the screw thread is often used to restore the radial gap between the barrel’s inner hole and the outer diameter of the screw.

Solution:

The local damage of the screw thread repair by surfacing welding of special anti-wear and corrosion-resistant alloy. Generally, inert gas shielded welding, and plasma argon is welding, and metal spraying technology can also be used for repair. First, grind the outer surface of the worn screw to a depth of about 1.5mm, then overlay the alloy layer to a sufficient size to ensure adequate machining allowance, and finally grind the outer circle of the screw and the side of the screw to the original size of the screw size.

Abnormal noise

  1. If it occurs in the reducer, it may be caused by bearing damage or inadequate lubrication or caused by gear wear, improper installation, and adjustment, or poor meshing. It can solve by replacing bearings, improving lubrication, replacing gears, or adjusting gear meshing conditions.
  2. If the noise is a sharp scraping sound, consider the possibility of the shaft head and the drive shaft sleeve scraping due to the barrel position’s deflection. It can solve by adjusting the barrel.
  3. If the barrel makes noise, it may be because the screw is bent to sweep the bore or the set temperature is too low, causing excessive friction of solid particles. It can be processed by straightening the screw or increasing the set temperature.

Abnormal vibration

If this happens at the reducer, it is caused by the wear of the bearings and gears, which can be solved by replacing the bearings or gears. If it happens at the barrel, it is due to the complex foreign matter mixed in the material, and the cleanliness of the material needs to be checked. If necessary, install a solid magnetic device in the hopper to adsorb iron filings.

Annular blockage at the screw inlet

This failure mainly causes by the interruption of cooling water or insufficient flow. The cooling system needs to check, and the flow and pressure of the cooling water must adjust to the specified requirements. It may also be that a large piece of recycled material in the raw material blocks the inlet and needs to clean. Inlet.

The above is the typical failure analysis and plastic extruder solutions. See if you have learned it?

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