Operation and Precautions of Twin Screw Extruder

Twin screw extruder is used to extrude molten plastic through a fixed shape extrusion mouth under the action of the screw, and cut it after being water-cooling or air-cooling. It is used in the filling, blending, modification, addition, chlorination, polypropylene and processing of super absorbent resin of rubber and plastic and engineering resin.

In daily production, operation is the most involved, but if the technical operators do not strictly follow the operation specifications, not only production will be affected, resulting in loss of economic benefits, but also the damage of the extruder. Therefore, the daily operation requirements of the extruder are very important.

1. Preparation before start-up of twin-screw extruder

  • Check whether the electrical wiring of the twin-screw extruder is accurate and loose, and whether the anchor bolts of the whole unit are tightened.
  • Check the soft water volume in the water tank of the twin-screw extruder, start the water pump, and check whether the rotation direction is correct.
  • Start the feeder and check the rotation direction of the feeding screw.
  • For the operation with vacuum exhaust requirements, start the vacuum pump and check whether the rotation direction is correct. Close the vacuum pipeline and valves of the condensate tank, and check whether the sealing ring of the exhaust chamber is in good condition.
  • Clean the storage bin and hopper. After confirming that there are no sundries, fill the storage bin with materials.
  • Start the pelletizer and check if the direction of tool rotation is correct.
Twin Screw Extruder
Twin Screw Extruder

2. Startup operation of twin-screw extruder

  • The twin-screw extruder parameters must be set for the temperature control instruments in each heating zone according to the process requirements. After the heating temperature of each section reaches the set value, continue to keep the temperature for 30min, and further confirm whether the temperature control instrument and solenoid valve (or cooling fan) of each section work normally.
  • The oil pump must be started before the motor.
  • The idling speed shall not be higher than 20r/min and the time shall not be longer than 1min without feeding.
  • Start feeding at the lowest possible speed, and match the feeder with the main engine speed.
  • The auxiliary feeding device can be started according to the process requirements only after the main machine and the main feeding system operate normally.
  • For the exhaust operation, the vacuum pump shall be started after the main engine enters the stable operation state.
  • Do not stand in front of the die before the strip comes out.
  • Regularly check whether the extruded strips of the die are stable and uniform, whether there are broken strips, blocked die eyelets, poor plasticization or overheating discoloration, and whether the die pressure indication is normal and stable.
  • Each operation shall be recorded.
Twin Screw Extruder
Twin Screw Extruder
Twin Screw Extruder
Twin Screw Extruder

3. Shutdown of twin-screw extruder

  • Stop the feeding mechanism to close the vacuum pipeline valve and open the upper cover of the vacuum chamber in the normal shutdown sequence of the twin-screw extruder.

Gradually reduce the speed of the main screw and shut down the auxiliary equipment such as the pelletizer, turn off the motor and oil pump, and connect each external water inlet pipe valve.

  • Emergency shutdown of twin-screw extruder

When the host needs to be stopped in an emergency, press the red emergency stop button of the electrical control cabinet quickly, turn the host and each feeding speed control knob back to zero, and then cut off the main power switch. After the fault is eliminated, the normal startup sequence can be calibrated again.

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