What are the common malfunctions of engineering plastic extrusion production lines?

Screw and Barrel Wear: The Leading Cause of Output Instability

The most common malfunction in an Engineering Plastic Extrusion Production Line is screw and barrel wear, which directly affects output, melting quality, and product consistency. In high-performance engineering plastics such as PA, PC, or PBT, glass fiber content can reach 30%–50%, significantly accelerating mechanical wear.

After approximately 8,000–12,000 operating hours, standard nitrided screws may show measurable diameter reduction, leading to unstable pressure and a drop in output of up to 10–20%. This results in dimensional fluctuation and poor surface finish.

Practical Solutions

• Use bimetallic or tungsten carbide-coated screws for abrasive materials.
• Monitor melt pressure trends weekly to detect early wear.
• Schedule preventive inspection every 6 months.

Temperature Control Failure and Melt Degradation

Engineering plastics typically require precise processing temperatures between 220°C and 320°C. A deviation of just ±5°C can cause viscosity instability, discoloration, or even polymer degradation.

Faulty thermocouples, heater band burnout, or PID controller malfunction are common root causes. In severe cases, overheating may increase scrap rates by 15% or more.

Preventive Measures

• Calibrate temperature sensors quarterly.
• Install dual-sensor redundancy in critical zones.
• Use alarm systems for abnormal temperature fluctuation.

Vacuum Calibration and Cooling System Problems

In pipe, profile, or sheet extrusion, vacuum calibration systems ensure dimensional accuracy. Insufficient vacuum pressure (below -0.08 MPa) often causes ovality, surface dents, or wall thickness deviation.

Cooling water temperature should remain between 15–25°C. Higher temperatures reduce cooling efficiency and may increase product shrinkage variance by 2–3%.

Haul-Off and Traction Synchronization Errors

Speed mismatch between the extruder and haul-off unit is another frequent malfunction in an Engineering Plastic Extrusion Production Line. Even a 1–2% speed deviation can cause stretching or compression of profiles.

Servo motor instability or encoder failure often leads to inconsistent pulling force, which affects product tolerance control.

Electrical and Control System Failures

PLC system faults, inverter trips, and wiring issues account for nearly 25% of unexpected downtime in modern extrusion workshops. Voltage fluctuations exceeding ±10% may trigger protective shutdown.

Material Feeding and Moisture-Related Issues

Engineering plastics such as PA and PET are highly hygroscopic. If moisture exceeds 0.2%, hydrolysis may occur during extrusion, reducing mechanical strength by up to 30%.

Hopper blockage, inconsistent gravimetric feeding, or dryer malfunction frequently result in unstable melt flow index (MFI).

FAQ: Common Questions About Engineering Plastic Extrusion Production Lines

What is the most frequent malfunction?

Screw and barrel wear is the most frequent issue, especially when processing glass fiber-reinforced materials.

How often should screws be inspected?

Inspection is recommended every 6 months or after 4,000–6,000 operating hours.

Why does product size fluctuate?

It is usually caused by vacuum instability, haul-off speed mismatch, or temperature drift.

How can scrap rates be reduced?

By implementing precise temperature control and stable feeding systems, scrap can often be reduced below 5%.

What moisture level is acceptable?

For most hygroscopic engineering plastics, moisture should remain below 0.2% before processing.

How to minimize unexpected downtime?

Adopt preventive maintenance schedules, install monitoring sensors, and keep critical spare parts in stock.