Twin Screw Extruder Operation Guide: From Startup to Shutdown

Twin Screw Extruder Operation Guide: From Startup to Shutdown

Twin screw extruders are core equipment in polymer material processing. Standardized operation directly impacts production efficiency, product quality, and equipment lifespan. This guide systematically covers operation procedures from startup to shutdown.

1. Pre-Startup Preparation

• Check connection bolts: Ensure fastening bolts at barrel, die head, and feeder positions are tight with no looseness to prevent material leakage or backflow.
• Clean residual material: Open the die head, remove residue from the previous production in the screw and barrel, paying special attention to hard lumps or carbonized material.
• Check lubrication and cooling systems: Confirm gearbox oil level is within normal range and lubricant is not degraded; ensure cooling water circulation is unobstructed with all water valves operating normally.
• Heating system pre-check: Set zone temperatures (typically increasing from feed port to die head), check that heating rings and thermocouples are working properly, and observe temperature fluctuations during heating.
• Safety device confirmation: Test emergency stop button, overload protection, and guard interlock switches for sensitivity and effectiveness.

2. Heating and Temperature Holding

• Set zone temperatures according to process requirements, with heating rate recommended at 5-10 degrees Celsius per minute to avoid thermal stress damage from excessive speed.
• After reaching set temperature, hold for 15-30 minutes to allow uniform thermal expansion of screw and barrel. During this period, manually rotate the drive belt or hand-crank to confirm screw rotation without jamming.

3. Startup Operation

• Start lubricating oil pump: Run the oil pump for 2-3 minutes first to ensure full lubrication of all gearbox components.
• Low-speed main motor start: Set screw speed to minimum (typically 10-20 r/min), observe ammeter readings and listen for abnormal sounds.
• Gradual feeding: Once screw rotation is stable, start the feeder. Initial feed rate should be 30%-50% of normal value. Gradually increase to process setpoint after material stably extrudes from the die.
• Adjust process parameters: Fine-tune screw speed, feed rate, and zone temperatures based on melt pressure, main motor current, and material plasticization condition. Keep melt pressure below rated value (typically no more than 15 MPa).
• Discharge and pelletizing: When changing materials or restarting after shutdown, first discharge head material (which may contain decomposed or unplasticized material). Start the pelletizer only after confirming normal material color and shape.

4. In-Operation Monitoring

• Regularly record key parameters: main motor current, melt pressure, zone temperatures, feed rate.
• Listen for equipment sounds: If periodic knocking or sharp friction sounds occur, stop immediately for inspection.
• Observe material extrusion state: If material strands are uneven, contain bubbles, or have scorched particles, adjust temperature or screw configuration promptly.
• Monitor bearing temperature and vibration: Gearbox bearing temperature should not exceed 70 degrees Celsius; check for smoke or odors at barrel flange area.

5. Normal Shutdown Procedure

• Stop feeding: Turn off the feeder and let the screw continue idling for 3-5 minutes to empty remaining material from the barrel.
• Reduce screw speed: Gradually decrease to 10-20 r/min while simultaneously cooling down (reduce 10 degrees Celsius every 5 minutes).
• Stop main motor: When barrel temperature drops below 120 degrees Celsius (specific to material characteristics), stop the main motor.
• Clean die head and screw: Remove the die head and clear residue from the die orifice and screw tip. If screw cleaning is needed, use proper methods to avoid damaging the screw flights.
• Shut down auxiliary systems: Stop oil pump, water circulation, vacuum pump, and disconnect main power.

6. Emergency Shutdown Situations

• Current meter needle sharply exceeds rated value and does not decrease.
• Melt pressure instantly exceeds upper limit (e.g., 20 MPa).
• Gearbox emits severe abnormal noise or smoke.
• Material decomposition produces large amounts of irritating gas or barrel catches fire.
• Cooling water or material leakage causes electrical short circuit.

Following these operation procedures can significantly reduce unplanned downtime of twin screw extruders and ensure stable product dimensions and surface uniformity.