Fishtailing Defect in Rubber Extrusion
Fishtailing is a common and frustrating defect in rubber extrusion that affects both product quality and production efficiency. It appears when the extruded rubber profile shows a wave-like or “fish tail” pattern at the edges instead of a clean and uniform flow. In simple words, the fishtailing defect occurs when the rubber compound does not flow evenly through the extrusion die. This defect is commonly seen in flat profiles, strips, and sometimes in hollow or complex shapes, where flow balance in the die is sensitive.
This defect is especially critical for sealing profiles, tubes, weatherstrips, and custom rubber extrusions where dimensional stability, surface finish, and consistent cross-section are essential. If this issue is not corrected in time, it can lead to out-of-tolerance profiles, poor appearance, weak sealing performance, and increased production cost. Understanding why fishtailing happens and how to control it can help manufacturers reduce scrap, avoid rework, and maintain stable production.
Main Causes of Fishtailing Defect
Fishtailing is usually caused by a combination of factors rather than a single reason. The main causes include:
1. Non-uniform Flow in the Die
If the rubber does not flow evenly across the width or thickness of the die, some areas experience higher velocity than others. This non-uniform flow leads to:
- The center is moving faster than the sides.
- One edge flows more than the other
- Uneven stress and expansion at the die exit
2. Improper Die Design or Wear
A poorly designed or worn die can cause uneven material flow during the extrusion process. Die geometry plays a huge role in fishtailing, as even minor design flaws or wear can lead to distorted and unstable extrusion profiles.
- Unequal land lengths on both sides
- Poorly balanced feed channels
- Narrow or poorly polished passages
- Worn-out areas in the die that change flow resistance
3. Incorrect Compound Viscosity
If the compound is too soft (low viscosity), it may flow too fast and react strongly to small die imbalances. If it is too stiff (high viscosity), it may not fill the die uniformly, leading to uneven flow and fishtailing. Rubber viscosity changes with:
- Temperature
- Mixing quality
- Compound formulation
4. Temperature Variations
Uneven temperature in the extruder barrel, head, or die can cause different parts of the compound to flow differently. Typical causes:
- Unequal barrel zone settings
- Poor heater band contact
- Blocked cooling channels
- Hot spots in the die
5. Screw Speed and Extrusion Pressure
Very high screw speed or fluctuating screw speed can increase shear and create instability in the flow. Similarly, sudden changes in extrusion pressure can cause the extrudate to surge or oscillate, making the profile behave like a swinging tail.
- Excessive shear stress
- Unstable material flow
- Pressure fluctuation effects
- Inconsistent profile output
6. Inconsistent Feeding or Moisture
Uneven feeding of the rubber strip into the extruder, trapped air, or moisture pockets in the compound can disrupt the continuous flow. This can cause small bursts or gaps in pressure and result in irregular flow patterns.
- Uneven material feeding
- Moisture in compound
- Trapped air pockets
- Pressure flow fluctuation
How to Diagnose Fishtailing Problems
To solve fishtailing effectively, it is important to identify the root cause. Some common diagnostic steps include:
- Visual Inspection of Extrudate: Observe profile edges for wave patterns or swinging tails.
- Check Die Symmetry and Condition: Inspect die land lengths, flow channels, surface finish, and signs of wear or damage.
- Monitor Process Parameters: Record barrel temperatures, head and die temperature, screw speed, and pressure. Look for fluctuations.
- Review Compound Batch: Check mixing records, Mooney viscosity, and any changes in formulation or raw materials.
- Trial Adjustments: Change one parameter at a time (e.g., temperature, speed) and see how the fishtailing responds.
Preventive Practices for Long-Term Control
With systematic control, fishtailing can be minimized, and production becomes more predictable and efficient. Instead of only reacting when fishtailing appears, it is better to have preventive control:
- Standard operating procedures for each profile and compound
- Regular die inspection and maintenance schedule
- Monitoring of key process parameters and keeping records
- Training operators to recognize early signs of fishtailing
- Continuous improvement by reviewing scrap data and taking corrective actions
Why Choose Custom Rubber Extrusion?
At Custom Rubber Extrusion, we are driven by core values that guide our business and define our commitment to our clients.
Expertise and Experience - With years of experience in the Extrusions industries, we have the expertise to deliver custom-designed solutions that meet the most demanding requirements.
High-Quality Products - Our ExtrusionsExtrusions are made from high-quality materials, ensuring durability, clarity, and long-lasting performance.
Custom Solutions - We specialize in providing tailored Extrusions solutions that meet the unique needs of our clients.
Exceptional Customer Service - We provide end-to-end support, from initial consultation to post-delivery assistance, ensuring our clients are delighted with the results.
Conclusion
Fishtailing defect in rubber extrusion is mainly a symptom of uneven flow through the extrusion die, influenced by die design, compound viscosity, temperature settings, screw speed, and feeding consistency. While it can be a persistent challenge for rubber extrusion manufacturers, it is also manageable through proper diagnosis, balanced die design, optimized process conditions, and consistent compound quality. By understanding the root causes and applying preventive practices, companies can significantly reduce fishtailing, improve product quality, lower scrap, and maintain smooth, reliable extrusion operations.
