7 Common Problems in Extrusion Moulding and How to Fix Them

If you’ve ever worked with an extrusion line, you probably know that achieving a flawless product isn’t always as easy as it looks.
Even with top-tier extrusion moulds, small changes in temperature, pressure, or material flow can cause visible defects.

At Hubei Junhui Mould Co., Ltd., we’ve helped manufacturers solve these challenges every single day. Based on our years of experience in PVC, WPC, PE, and ABS extrusion moulds, here are seven common problems — and practical ways to fix them.

1. Uneven Wall Thickness

Problem: The final product has varying thickness, especially near the edges.
Cause: Uneven material flow inside the mould or poor die calibration.

Solution:

• Check if the die gap is symmetrical.

• Ensure uniform heating and pressure across the mould.

• Use Junhui’s precision-balanced mould channels, designed to deliver stable flow and avoid deformation.

When the mould flow path is optimized, the difference in thickness almost disappears.

2. Surface Roughness or Scratches

Problem: The surface of the extruded part looks dull or scratched.
Cause: Contaminated raw material, dirty die surface, or low melt temperature.

Solution:

• Clean the die regularly to remove residue buildup.

• Increase melt temperature slightly for smoother flow.

• Use high-quality PVC or WPC raw materials that match your mould’s specification.

Junhui Mould’s advanced polishing and die treatment help prevent such surface defects before they happen.

3. Bubbles or Voids in the Product

Problem: Air bubbles or hollow spots appear in the final product.
Cause: Moisture in the raw materials or trapped air inside the extrusion flow.

Solution:

• Dry the material properly before extrusion.

• Adjust venting pressure in the mould.

• Use a properly sized extrusion line with optimized cooling control.

We often say, “A stable mould flow means a flawless product.”

4. Warping or Bending

Problem: After cooling, the product curves or twists instead of staying straight.
Cause: Uneven cooling or incorrect pulling speed.

Solution:

• Balance the cooling water flow rate on both sides.

• Adjust puller speed to match extrusion rate.

• In some cases, redesigning the die outlet geometry may help.

Junhui’s co-extrusion die design minimizes internal stress, keeping your profiles straight and uniform.

5. Poor Adhesion in Co-Extruded Layers

Problem: The layers in a co-extruded product don’t bond well.
Cause: Incompatible material combination or wrong temperature ratio between layers.

Solution:

• Use compatible materials or adhesive layers.

• Maintain the right temperature gradient between layers.

• Work with a mould supplier (like Junhui) experienced in multi-layer co-extrusion systems.

6. Color Inconsistency

Problem: Color varies across the extruded profile.
Cause: Uneven mixing or unstable processing temperature.

Solution:

• Check dosing accuracy of pigments.

• Maintain stable barrel and die temperatures.

• Use Junhui’s extrusion moulds with consistent thermal control to ensure uniform color distribution.

Consistency is everything — both in your raw material and your tooling.

7. Short Mould Lifespan

Problem: The mould wears out or deforms too quickly.
Cause: Poor steel quality, incorrect cooling, or lack of maintenance.

Solution:

• Always select moulds made from high-grade steel with good wear resistance.

• Follow a regular cleaning and inspection schedule.

• Junhui Mould uses heat-treated, corrosion-resistant steel to ensure long lifespan even under heavy-duty production.

Remember, a good mould isn’t an expense — it’s an investment in long-term performance.

Connecting Back: From Selection to Perfection

If you’ve read our previous article, “how to Choose the Right Extrusion Mould,” you already know that selecting the correct mould design is step one.
This article takes it further — once you’ve chosen the right mould, understanding how to maintain and troubleshoot it ensures long-term quality and efficiency.

At Hubei Junhui Mould Co., Ltd., our goal is to help clients not only buy good moulds, but also use them effectively.
From PVC profiles to WPC decking and ABS components, our extrusion solutions are designed to reduce these common issues right from the source.