16 Solutions for the Failures of Injection Molding Machine Plasticizing Unit

Problems of injection molding machine plasticizing unit and solutions

1. Unable to injection

  • There is someforeign matterclogged in the nozzle . Check whether the nozzle is blocked and clean or replace it.
  • The flange of the barrel is broken. Disassemble the flange to check whether it is broken, and replace the broken one.
  • The injection directional valve is stuck. Check whether the directional valve has voltage and the coil resistance is working or not. If it is normal, then it’s very likely that the valve is blocked. Clean the valve or replace the directional valve .
  • The piston rod of the injection unit is broken. Check whether the piston rod is broken or not, and replace the broken piston rod.
  • The barrel temperature is too low. Check whether the actual temperature reaches the required melting point temperature of the material, and reset the barrel temperature.
  • The piston oil seal of the injection unit is damaged. Check whether the piston oil seal is broken and replace the broken one.

2. Loud start-up sound when injecting

  • The injection speed is too fast at the beginning. Check the start injection speed, and adjust the flow rate of injection.
  • There is air in the hydraulic oil circuit. Observe whether there is vibration in each machine’s movement.

3. The sound is loud when the injection stop.

During the injection, the movement switch speed is too fast. Check whether the injection has increased the holding pressure.

Increase the holding pressure, adjust the injection stage, and extend plasticizing time.

4. Unstable injection volume

5. Semi-automatic action without injection action

  • The advancement of the injection unit is not terminated. Check whether the injection unit and themold clamping limit switchare normal.
  • Disconnected. Check the electrical wire connection of the valve.
  • Reset the linear displacement sensor of the clamping unit. When the machine clamping toggle is straight, the position should be 0, readjust the zero position of the linear displacement sensor.

6. In semi/automatic mode of the machine, the barrel temperature gradually exceeds the set value.

  • The rotating speed of the screw is too fast. Use a monitor to test whether the screw rotate speed is too fast, and reduce the it.
  • Excessive back pressure. Observe the product, and reduce the back pressure.
  • Friction between the screw and the barrel. Disassemble the screw and barrel, check the wear condition, and replace the barrel or screw.
  • Improper temperature setting. Check whether the actual temperature is too low and reset the temperature.
  • The shear heat of the plastic is too large. Check the temperature rise in the screw feeding zone and melting zone, reduce the speed of screw, and the back pressure.

7. The screw sounds when plasticizing

  • Improper installation of the drive shaft of the screw. Separate the screw from the drive shaft and rotate to check if there is any noise. If there is any, remove the bearing and reassemble it.
  • The bearing is broken. Separate the screw from the drive shaft. If there is noise,then replace the bearing.
  • The screw is bent. Remove the screw for inspection and replace the screw.
  • There is iron filings in the barrel. Disassemble the screw to check and clean the materials.
  • Use a dial indicator to check the concentricity of the screw. The beating around 0.05mm is normal.

8. Unable to plasticizing

  • Bearings or the drive shaft broken. Separate the screw from the hydraulic motor and plasticizing again, observe the soundand replace the bearing when necessary.
  • There iron filings in the barrel. Uninstall the screw from the barrel, then check the screw for iron filings. And clear the screw.
  • The plasticizing valve is blocked. Check and clean the valve.
  • The hydraulic motor is damaged. Uninstall the hydraulic motor, replace or repair the hydraulic motor.
  • The heating band of the barrel burn out. Check whether the heating band is normal or not with a multimeter and replace them if necessary.
  • The valve plug is loose. Check whether it is in poor contact.

9. The back pressure cannot be adjusted when plasticizing.

The back pressure valve is broken. Increase the back pressure when feeding the plastic resin. Check whether the screw retreats, and clean the back pressure valve if necessary.

10. The product has black spots.

  • The screw has carbon deposits. Check the cleaning screw and barrel.
  • There is carbon deposit in the barrel and the auxiliary machine is not clean. Check whether the auto-loader  has dust, polish the barrel and clean the auxiliary machine.
  • Corrosion of screw check ring check seat and tip. Check them and check.
  • Flanges and nozzles have carbon deposits. Clean up or replace.
  • The raw materials are dirty. Check raw materials and replace them.
  • The temperature is too high and the back pressure of the melt is too large. Check the temperature setting and reduce the back pressure.

11. Poor color mixing

  • Material reason. Check the masterbatch quality and replace them if needed.
  • The temperature is too low. Check the actual temperature and the required temperature of the material, and increase the temperature.
  • The back pressure is too low. Check the back pressure and increaseit.
  • Short mixing time. Extend the mixing time or replace it with a mixing screw tip.
  • The screw rotation speed is too low. Check the screw speed and increase it.

12. No suck-back action

  • High back pressure. Check the nozzle ejection speed when plasticizing inmanualmodel, and reduce the back pressure.
  • Disconnected. The valve is disconnected.
  • The directional valve is not flexible. Clean the valve.

13. When plasticizing, the hydraulic motor vibrates abnormally

  • The bearing is broken. Check whether there is any abnormal noise when plasticizing the resin, and replace the bearing.
  • Improper adjustment of bearings. Check whether the drive shaft vibrates, and re-adjust the gap.
  • Deformation of the screw. Separate the screw from the hydraulic motor and check the rotation of the drive shaft, and replace the screw.
  • The brush of the injection unit is worn out. The 2 guide rods are deformed or itsfixing are loose. Check whether brush is ground out of powder, and the brush needs to be replaced in time.

14. Injection twice

  • The nozzle is too small, and the resistance is too large when ejecting.
  • The nozzle heating brand is broken, check the heating brand or replace it.
  • Check whether the pressure and flow output is changed or not.

15. Reasons for screw fracture

  • The injection unit forwarding’s movement do not synchronized. Then, adjust the movement synchronization at the range of ±0.05.
  • The injection cylinder is not synchronized, adjust the injection cylinder to synchronize at the range of ±0.05.
  • The raw material and the screw performance do not match.
  • Start before the temperature has not reached the melting point of the resin.
  • Turn the screw on the same moment ofthe temperature is reached.
  • If the heating brand is burned out, it will not be heated. Check for the anti-cold start function and replace the heating brand.

16. Unable to adjust the mold

  • The mechanical level and parallelism are out of tolerance. Check with a spirit level angle ruler to adjust the parallelism and level.
  • The gap between the pressure plate of the column and the mold-adjusting nut is too small. Measure with a feeler gauge, adjust the gap between the pressure plate and the nut (gap ≤ 0.05 mm).
  • Check whether the nut can be turned to generate heat or iron powder is coming out. Replace the nut.
  • Adjust the upper and lower support plates. Remove the lock nut of the expense board to check and adjust the nut.
  • The I/O board is broken. Check whether there is a signal at the output point on the controller, and repair the electronic board.
  • The mold adjustment valve is stuck. Remove the valve to check and clean it.
  • Mold adjustment motor is broken. Check the motor. Replace or repairit.

Leave a Comment

Contact Us