Common challenges in plastic extrusion and how to address them

• Power issues: Unstable power or sudden surges can damage equipment. Using a stable power source and surge protectors helps prevent machinery failure.
• Humidity in materials: Moisture in plastic can cause porosity in extruded products. Proper drying before extrusion ensures better quality.
• Mould weight and hoist capacity: If a mould is too heavy for the hoist, it can break, creating a safety risk. Always check that the hoist can handle the mould’s weight
• Material impurities: Contaminated or mixed plastics can make extruded products brittle and release harmful fumes. Careful sorting and cleaning of plastic before processing is essential.
• Pre-extrusion mixing: Even with the same polymer, different colours can have different densities (e.g., black HDPE is lighter than yellow HDPE). Thorough mixing is needed to ensure consistency.
• Cooling system efficiency: If the cooling system is too shallow, runs too hot, or lacks enough water, cooling takes longer, and demoulding becomes harder. A deep cooling system with proper water circulation improves efficiency.
• Material overflow (LAMS): High temperatures or idle machinery can cause excess material build up. To reduce this:
  • Follow proper extrusion procedures.
  • Speed up mould changes to maintain consistency.
  • Use a mould stopper to keep it in place.
  • Have a small crusher or grinder to reprocess excess material into reusable flakes.
• Inconsistency: When the plastic mix is not evenly blended, the extrusion process can become unstable. This leads to fluctuations in speed and an uneven profile in the final product. Using a mixing machine ensures a more harmonious blend, improving product consistency and quality.

Advice for operators

The role of an operator is critical within the production facility, not only for production efficiency but for the safety of everyone in the area. Here are a few things an operator should know.

Temperature

If a material does not reach its set temperature, it may indicate one of the following problems:

1. Mixed polymers – Different plastics have different melting points, causing uneven heating.
2. Faulty temperature control – If the temperature goes above the set point, the control system may be malfunctioning.
3. Faulty heating element – If the temperature stays below the set point, the heating element may be damaged.
4. Power output of the heating element – Over time, the power output of heating elements can weaken, reducing efficiency.
5. Humidity in the material – If the plastic contains moisture, it may take longer to heat or cause inconsistent melting.
6. The speed is set too high – This doesn’t give enough time for the material to heat up sufficiently.

How to troubleshoot

• Check for polymer contamination – Sort plastics carefully to avoid mixed materials.
• Inspect the temperature control system – Ensure sensors and controls are working properly.
• Test heating elements – Replace any that fail to reach the correct temperature.
• Measure wattage output – If wattage has dropped, consider upgrading the heating element.
• Dry the plastic before processing – This prevents humidity-related temperature issues.

Sound

Unusual sounds from the gearbox or motor can be early warning signs of mechanical or electrical issues. Monitoring these sounds can help prevent damage and downtime.

Common sounds and their causes

1. High-pitched sounds from the gearbox
   • Possible cause: The motor is overloaded.
   • How to confirm: Check the VFD display for the current motor load (measured in amps).
2. Screeching sounds from the motor
   • Possible cause: A power surge is affecting motor performance.
   • How to confirm:
     • Check the VFD display for undercurrent (measured in voltage).
     • Cross-check with the voltmeter on the control panel to verify fluctuations.

What to do

• For motor overload:
  • Reduce the load on the motor by adjusting speed or material flow.
  • Ensure the motor is not running beyond its capacity.
• For power surges:
  • Check for voltage instability in the power supply.
  • Use voltage stabilisers or surge protectors if necessary.

Regular monitoring of machine sounds and checking VFD readings can help detect and fix issues early, improving machine efficiency and lifespan.

Safety mechanisms

If there is a problem with the barrels or heating controls, the operator must notify the technician immediately to check the circuit breakers.

Why circuit breakers trip

A tripped breaker is a warning sign that something is wrong with the electrical system. Possible causes include:

1. Power short – A sudden electrical fault in the system.
2. Heating element not grounded – This can cause leakage current, increasing the risk of electric shocks.
3. Heating element short-circuited – A faulty element may overload the system, leading to a shutdown.

What to do

• The technician must identify the cause of the short circuit before switching the breaker back on.
• Do not reset the breaker without first checking for underlying electrical faults.

Regular electrical checks and maintenance help prevent hazards and protect both workers and machinery.