Common Problems in Parallel Twin Screw Extruders and Solutions
Parallel twin screw extruders are the workhorses of the compounding and profile extrusion industry, prized for their excellent mixing capabilities and high throughput. However, the complexity of a Parallel Twin Screw system—where two screws of constant diameter rotate within a figure-eight barrel—brings specific operational challenges. To maintain peak productivity and minimize downtime, manufacturers must understand these common hurdles and how to address them effectively.
1. Accelerated Wear and Tear: The Silent Profit Killer
One of the most frequent issues is the abrasive or corrosive wear of the screw flights and barrel walls. This is especially common when processing glass-filled polymers or highly corrosive additives.
The Problem: As the clearance between the screw and the barrel increases, the "melt seal" is lost. This leads to backflow, reduced pressure, and a significant drop in output. You may notice surging or inconsistent product dimensions.
The Solution: Regular measurement of screw-to-barrel clearance is essential. When wear exceeds a specific threshold (typically $0.1$ to $0.2\text{ mm}$), it is time for a replacement. Upgrading to bimetallic barrels or screws with specialized tungsten carbide coatings can extend the lifespan by 3 to 5 times.
2. Output Fluctuations and Surging
Maintaining a steady flow of material is critical for high-quality extrusion. When the output becomes unstable, the "main motor current" often fluctuates wildly.
The Problem: This is usually caused by inconsistent feeding or "bridging" in the hopper. In a Parallel Twin Screw setup, if the screw speed and the feeder speed are not perfectly synchronized, the screw channels may be under-filled or over-stuffed, causing pressure spikes.
The Solution: Calibrate your gravimetric or volumetric feeders weekly. Ensure the feed throat cooling is functional; if the throat gets too hot, the raw material can stick and block the flow before it even enters the barrel.
3. Parallel vs. Conical Twin Screw: Understanding the Pressure Gap
Manufacturers often debate between using a Parallel Twin Screw and a Conical Twin Screw extruder. Understanding their mechanical differences helps in troubleshooting pressure-related failures.
While the conical design handles high head pressure more easily due to its robust thrust bearing space, the parallel design offers superior residence time control and modularity. If you are experiencing frequent thrust bearing failures in a parallel machine, you may be over-pressurizing the system beyond its design limits.
4. Thermal Degradation and Overheating
In a twin-screw environment, "shear heat" can quickly spiral out of control, especially with heat-sensitive materials like PVC.
The Problem: Excessive screw speed or an aggressive screw configuration (too many kneading blocks) creates localized "hot spots." This leads to "black spots" or yellowing in the final product.
The Solution: Review your screw configuration. Sometimes, removing a single kneading element or adjusting the cooling water flow in the barrel zones can solve the issue.
The Importance of Precision Manufacturing
Solving these technical problems often starts with the quality of the components themselves. A poorly machined screw will never achieve the necessary homogenization, regardless of how you tweak the settings. This is why many global manufacturers partner with a specialized screw barrel manufacturer in Ahmedabad.
The manufacturing hub in Gujarat has become a global center for extrusion technology. A reputable screw barrel manufacturer in Ahmedabad can provide custom-designed screw profiles tailored to your specific resin, ensuring the perfect balance between shear and output. They offer high-grade materials like EN41B or bimetallic alloys that are essential for resisting the intense mechanical stresses of parallel twin extrusion.
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