Material jamming in WPC granulation extruder – Comprehensive troubleshooting & resolution plan

During the WPC pelletizing production process, operational errors or other factors can frequently lead to screw jamming or locking, preventing the screw from rotating. Such incidents not only directly disrupt the production workflow but may also cause irreversible damage to critical components—such as the screw and barrel—upon forced startup of the equipment; in severe cases, this can even trigger production safety accidents. Therefore, accurately identifying the type of jamming or locking fault and following standardized procedures for troubleshooting and resolution is a crucial step in ensuring the stable operation of wood pelletizing production. Drawing on practical experience in wood-plastic extrusion and pelletizing, the engineers at Yongte have developed professional troubleshooting solutions tailored to the specific causes of screw jamming.

⚠ Safety First: disconnect the power supply! Close the power switch and post a "Do Not Turn On" sign; it is strictly prohibited to forcibly start the motor to drive the fastening screw, as this could easily twist the screw or damage the reduction gearbox.

I. Prohibited Operations

1. Avoid repeatedly and frequently jogging the main motor: excessive torque can easily cause the screw rod or sliding bolt to break, or damage the reduction gearbox gears.

2. Do not simply subject materials to prolonged high-temperature baking without cleaning them: as materials carbonize and clump, they become increasingly hard, leading to more severe jamming.

3. Do not strike screws or cylinders directly with a hammer; this may cause the screws to bend.

II. First, confirm the material jamming type.

Type 1: Cold material jamming (machine downtime without complete material discharge; wood-plastic material inside the barrel is cooling and curing)

After the PEWPC is stopped, the material remains in the barrel, where it cools and hardens, thereby clamping the screw.

Type 2: Overheated carbonization jamming

Excessive temperature causes wood powder or fiber to cokes into hard lumps, which can get stuck in threads or meshing gaps.

Type 3: Foreign object jamming

Metal blocks, screws, grinding chips, or stones fell into the feeding port and became stuck between the two screws and the barrel.

III. Step-by-Step Operational Procedure

Step 1: Confirm status – Power off

Disconnect the main unit's power supply, remove the coupling cover, and manually rotate the coupling.

· If it cannot move at all: The device has completely frozen.

· If Allow slight back-and-forth rotation by a small angle: material clamping, torque overload.

Step 2: Incremental heating baking (Core Step)

1. Set the temperature for each zone to be 1530°C higher than the normal operating temperature.

PEWPC: Normal – 170–190°C; Baking – 200–220°C

1. Do not raise the temperature to an excessively high level all at once; this prevents the carbonization and coking of wood powder.

2. Insulation heating for 40,120 minutes – the longer the insulation time for the cylinder, the longer the insulation duration;

3. Every 20 minutes, disconnect the power and attempt to manually rotate the coupling; if the coupling rotates even slightly, stop heating.

Tip: Prioritize heating and feeding sections, as well as the first and second conveying sections; approximately 90% of jamming incidents occur in Zone 13, located behind the feeding port.

Step 3: Turn the crank to loosen (after heating)

1. Power off; manually rotate the steering wheel back and forth (ensure the wheel is turned in both directions – do not apply a one-way force);

2. Once the material has gradually loosened, repeatedly rotate the drum back and forth to grind the curing compound into fine particles;

3. Once the handwheel operates smoothly without any resistance, install the protective cover and then perform a low-speed, no-load jogging for several seconds to check whether the current reading is normal;

4. Then feed a small amount of material and slowly extrude the old material.

If the device still does not operate fully after heating for more than 2 hours → cold startup is ineffective; the screw must be removed.

Step 4: Unable to rotate – Disassembly and cleaning procedure

1. Raise the temperature to the process temperature; remove the machine head, die head, and transition flange; clear the front-end outlet;

2. Try again: use a push rod from the front end to push the material outward;

3. If the device still freezes: remove two screws, clean any hardened wood-plastic residue from each threaded section, and inspect the screws for wear, chunking, or bending;

4. Remove coked or hardened deposits from the barrel inner wall;

5. Before reinstalling the screw, check the clearance between the screw and the cylinder body, and remove any carbonized material from the dead corners at the meshing interface.

IV. Handling Characteristics for Foreign Body Jamming (e.g., Iron Shavings)

Symptom: After prolonged heating, the device remains completely stationary; both the front and rear plates are stuck at the same position.

👉 The screw must be removed to locate any metal debris; otherwise, the machine may immediately experience another jamming event or even damage the screw upon startup.

V. Precautions when turning on the machine after releasing the clamp

1. The no-load current at startup must be less than 60% of the rated current; if the no-load current is too high, it indicates the presence of residual hard particles.

2. Start with low speed and small feed rates, then gradually increase the speed; avoid operating at full load immediately.

3. Observe whether the extrusion discharge is uniform and whether there are any coke particles or black spots;

4. Check the gearbox for any abnormal noise or vibration.