Common PVC Twin Screw Extruder Problems and Solutions

PVC twin screw extruders are widely used to produce drainage pipes, water supply pipes, conduits, and profiles. During production, problems such as high motor current, unstable extrusion, material burning, screw wear, and black streaks can reduce product quality and shorten machine life. Here are the most common issues and practical solutions.

1. Normal Motor Current

For an SJZ65 conical twin screw extruder producing standard PVC pipes, the normal motor current is 40–50 A and should generally remain below 60 A. Long-term operation above this level increases screw torque, accelerates gearbox wear, and may damage the screw. Monitoring current is a simple way to evaluate machine performance.

2. Why Does Current Increase?

A sudden current increase usually means excessive screw resistance. Common causes include:

• Gearbox bearing damage, increasing mechanical load.

• Poor material flow caused by formulation changes, insufficient lubrication, or overheating.

• Material blockage in the hopper or screw channel.

Before restarting production, inspect both the mechanical system and the feeding system.

3. Current Fluctuation with High-Calcium PVC

High-calcium PVC formulations reduce material costs but require stable feeding. If current fluctuates after several hours of operation, possible reasons include unstable feeding, poor material mixing, mismatched screw and feeder speeds, or inadequate lubrication. Besides adjusting machine settings, optimize the PVC formulation and maintain consistent feeding.

4. Material Burning at the Screw Tip

Burning is often caused by excessive screw-to-barrel clearance after wear, allowing molten PVC to remain in hot areas and degrade. A deformed flow distributor can also create dead zones where material accumulates. Check flow distributor alignment and dimensions, improve plasticizing performance, and keep barrel Zones 3–4 around 130–145°C for high-calcium formulations. If burning persists, inspect the die for material retention.

5. Importance of Screw Clearance

Proper screw-to-barrel clearance ensures stable plasticizing, consistent product dimensions, lower wear, and longer equipment life. Since wear gradually changes the clearance, regular inspection and adjustment help maintain stable production and avoid costly replacement of screws and barrels.

6. Black Streaks on PVC Pipes

Black streaks are usually caused by local overheating. During extrusion, screw deformation may create contact with the barrel, generating friction and decomposing PVC. The degraded material then appears as black streaks on the pipe surface.

To reduce this problem:

• Slightly reduce the screw front diameter (about 0.5 mm) to minimize contact.

• Use wear-resistant segmented barrels.

• Regularly inspect screw clearance, barrel cleanliness, formulation flowability, and lubrication.

Conclusion

Reliable equipment and proper process control are equally important for stable PVC extrusion. Regular maintenance of the screw, barrel, gearbox, and feeding system, together with optimized formulations and processing parameters, helps prevent abnormal current, material burning, screw wear, and surface defects. Early troubleshooting improves production efficiency, extends machine life, and ensures consistent, high-quality PVC pipe production.