Fault analysis of twin screw extruder

Fault analysis of twin screw extruder

The preface of fault analysis of twin screw extruder

Twin screw extruder for plastic is a common plastic mechanical equipment and is used widely. In the daily operation of the extruder, the double screw extruder sometimes has some failures, affecting the normal production of plastic machinery. The following are several aspects we analyze the extruder’s possible faults and maintenance tips.

twin screw extruder
Co-rotating Twin Screw Extruder

The current instability of driving motor

Possible reason  

  • Lack of one phase
  • The feed is uneven.
  • Driving motor bearing damage or poor lubrication
  • Some section of the heater fails.
  • screw adjustment pad is inappropriate or the phase is wrong, which causes interference between segments.
  • Whether the screw elements are worn? The back pressure of the material is insufficient due to the wear of the screw elements causing the materials to flow back repeatedly in the barrel.

Solution

  • Check whether the power cable is loose or disconnected.  
  • Check the feeder and troubleshoot.
  • Overhaul the driving motor and replace bearings if necessary.
  • Check whether the heaters work normally and replace the heaters if necessary.
  • Check the adjustment pad and pull out the screw to check for interference between components.
  • Check the wear condition of the screw elements, and replace the worn screw elements. Specially reminder: the screw elements must be replaced symmetrically in pairs. The wear of the mixing section is generally serious, and it is recommended to replace them all.

Twin screw
Co-rotating Twin Screw Plastic Extruder

The Driving motor cannot be started

Possible reason 

  •  Lack of one phase
  • Wrong driving procedure
  • The interlocking device related to driving motor work has problems.
  • Burnout of motor coil

Solution

  • Check whether the power cable of the motor is loose or disconnected.  
  • Check whether the motor coil is black
  • Check the procedure and follow the correct procedure.
  • Check the electro circuit of the driving motor.
  • Ensure that the emergency button is reset.
  • Ensure that the lubricating oil pump is started and the status of the interlocking device is normal. If the oil pump won’t turn on, the motor can’t work.
  • The induction power of the frequency converter is not finished and the total power supply is needed to be turned off and wait 5 minutes before starting.

The discharge of the die head is not smooth or blocked

Possible reason 

  • Some section of the heater does not work, and plasticizing of the material is poor.
  • There may be material which dropped into machine that does not melt easily.
  • The operating temperature setting is low, or the molecular weight distribution of the plastic is wide and unstable.

Solution

  • Check the heater and replace it if necessary. 
  • Clean and check the extrusion system and die head.
  • Verify the setting temperature of each section, negotiate with the technician if necessary, and increase the temperature setting value. 

The starting current of the driving motor is too high

Possible reason 

  • There are residual materials in the barrel or die head that was not cleaned up before the shutdown
  • Insufficient heating time and large torque. 
  • The heater in some sections does not work.

Solution

  • open the die head check and clean up the residual material.
  • Extend the heating time.
  • Check whether the heater is working properly.

The Driving motor makes an abnormal sound

Possible reason 

  • The driving motor bearing is damaged. 
  • the control module of frequency inverter is damaged and out of phase.

Solution 

  • Replace the driving motor bearing. 
  • Check the frequency converter, find out the fault code, and check whether the corresponding components are damaged.

Maintenance

The co-rotating twin screw extruder should be placed in well-ventilated areas to ensure the heat emission of the motor and prolong its life, meanwhile, the machine should be well grounded.

  • Any debris is not allowed in the material. Metal, sand and other hard objects are strictly prohibited to mix with the main screw and barrel.
  • When opening the pumping chamber or the barrel cover, pay attention to prevent any foreign matter from falling into the main host barrel or screw.
  • The screw shaft is only allowed to start at a low speed when idling, and the time does not exceed two minutes. The screw speed can be gradually increased after feeding.
  • Check the lubrication parts and oil level frequently, and replace all lubrication oil with new lubrication oil after running for 500 hours. Thereafter, the lubrication oil should be replaced after every 4000 hours of operation, and the time should not exceed 1 year, also the oil filter should be cleaned frequently.
  • Check the wear of the barrel and screw shaft and screw elements frequently.
  • Regularly check the wear of the seal ring at the end of the screw shaft.
  • Regularly check the operation of the gearbox and the oil seal.
  • Regularly check whether the link bolts are loose, especially the fixing bolts of the heater. The bolts expand and elongate due to long-term heating as to the heater works. If the elongated bolts are not tightened, the heater will be separated from the cylinder and cause damage.
  • Regularly check whether the heater wires and motor wires are ageing or loose.
  • When parking the twin screw extruder for a long time, anti-rust and anti-pollution measures should be taken for the twin screw extruder machine, and re-check according to the installation and debugging procedures when restarting the twin screw extruder machine.

 For any questions/needs, please contact us– Nanjing Granuwel Machinery Co., Ltd.

About us

Nanjing Granuwel Machinery CO., LTD is specializing in R&D design and manufacture of high polymer extruders, our team of top-level extrusion professionals provides the right extruder for your exact application.

Nanjing Granuwel Machinery CO. LTD 1

Nanjing Granuwel Machinery CO., LTD

We possess the excellent capability of innovation and product development and desire to provide the best products for our customers through the improvement of equipment structure and reduction of equipment energy consumption through our practical experiences and technical innovation. 

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