Extrusion International 3-2026

36 Extrusion International 3/2026 EXTRUSION TECHNOLOGY Misunderstood Technology – Why Many PVC Extruders Fail to Unlock the Full Potential of Twin-Screw Extrusion Twin-screw extrusion has long been regarded as the reference technology for rigid PVC processing. Its capability to handle heat-sensitive materials with stable fusion and low shear makes it ideal for pipe, pro le, window systems, and technical extrusions. Despite this, many PVC manufacturers continue to experience inconsistent quality, excessive scrap, and avoidable downtime – often because the technology is not fully understood or correctly applied. By: Dariusz Kozlowski Two issues repeatedly surface in audits and produc- tion reviews: limited understanding of how twin-screw extrusion actually generates melt, and the widespread misuse of freeze materials that are incorrectly treated as purge compounds. Twin-Screw Extrusion Performance: What the Data Typically Shows When twin-screw extrusion lines are properly con g - ured and operated, processors typically achieve: • Scrap rates below 2 to 3% on stable production runs • Melt temperature reductions of 10 to 25°C com- pared with equivalent single-screw processes • Torque utilisation in the 65 to 80% range, leaving a stable process window • Die pressure uctuations below ±5%, supporting consistent surface quality However, in plants where twin-screw systems are op- erated using single-screw logic—higher barrel tempera- tures, aggressive shear input, or poorly matched formu- lations—performance metrics deteriorate signi cantly. Scrap rates of 6 to 10%, unstable melt temperatures, and frequent start-up rejects are commonly observed, eroding both margins and capacity. The key issue is not the machine, but how its funda- mentals are applied. Twin-Screw Plasticisation: Compression, Not Shear Counter-rotating twin-screw extruders plastify PVC primarily through controlled compression and residence time, rather than extreme shear. This allows full fusion at relatively low melt temperatures, preserving thermal stability and surface quality. When operators compensate for poor fusion by in- creasing temperature rather than addressing mechani- cal plasticisation, the result is a narrower processing window and higher degradation risk—especially during speed changes or brief stoppages. Over time, this leads to plate-out, colour instability, and premature wear of screws and dies. Freeze Compounds: A Protective Tool, Not a Purge Material Freeze materials are not designed to clean. Their func- tion is to protect PVC remaining in the extruder during standstill. When hot PVC stops owing, degradation ac - celerates rapidly. Freeze compounds stabilise the mate-