Common Rubber Extrusion Defects & Solutions

Rubber extrusion is the standard method that is typically used to manufacture various profiles, tubes, cords, seals, and gaskets. However, small changes in temperature, pressure, or material quality can cause defects in the final product. These defects might result in leakage, poor fitment, early failure, and increased scrap or rework costs. Being familiar with these frequent problems along with their prevention leads to stable operation, enhanced sealing, and longer service life. Below are the most common rubber extrusion defects and the best solutions that will help in reducing rework and production downtime.

A1. Surface Roughness and Poor Finish

Surface defects deteriorate the visual appearance as well as the quality of the extruded profile. Besides that, they can eventually lead to functional problems in sealing applications.

Possible causes:

• Low compound plasticity.
• Incorrect die temperature.
• Moisture in the compound.
• Poor mixing of raw material

Solution:

• For better flow, change the barrel temperature to a higher setting.
• Good mixing will help filler dispersion in the compound.
• Optimize die design and polishing.
• If the extrusion speed is too high, reduce it.

2. Die Swell (Expansion After Exiting the Die)

The extruded rubber will expand to a greater extent than anticipated once it leaves the die. As a result, this will lead to dimensional inaccuracies or oversized profiles.

Possible causes:

• Elastic recovery of rubber as it exits the die
• Extremely fast extrusion speed
• Highly elastic compound because of the formulation
• Inadequate die design for the chosen material

Solution:

• Lower the extrusion pressure and speed
• Adjust the viscosity of the compound
• Use proper curing agents and processing aids.
• Modify the die dimensions to compensate for the expected well.

3. Dimensional Variation and Poor Tolerances

The extruded parts have a different size than the specified tolerances. Along the length, profile thickness, width, or diameter changes. It lowers the accuracy of the product and, thus, the rejection rate increases.

Possible causes:

• Inconsistent extrusion speed or pressure
• Unstable temperature control along the barrel or die
• Uneven die wear or improper die centering
• Variations in compound batch quality (viscosity changes)
• Inconsistent cooling conditions

Solution:

• Maintain stable extrusion temperature and speed.
• Re-align, polish, and balance the die.
• Use controlled cooling systems.
• Check compound viscosity consistency.

4. Porosity (Air Bubbles or Voids)

Small air pockets or tiny holes are formed inside the rubber which is extruded. These pores make the product weak, and its sealing performance also gets lower.

Possible causes:

• Moisture in raw materials or compounds
• Volatile components in the formulation
• Trapped air during compounding
• Overheating of the compound in the extruder
• Poor venting in the extruder (for vented systems)

Solution:

• Pre-dry the rubber compound.
• Improve kneading and mixing to eliminate trapped air.
• Adjust blowing agent levels.
• Apply vacuum venting to remove gases.