How to Unlock Potential in PVC Compounding

How Kombiplast Technology Ensures Superior PVC Compound Quality

PVC compounds, particularly those used in cable applications, require precise processing conditions to preserve material properties and achieve consistent product quality. Excessive shear can negatively impact the compound and lead to quality variations.

Coperion's Kombiplast concept addresses this challenge through a two-stage compounding process. The first stage, the ZSK twin screw extruder, performs feeding, plastification, homogenization, and degassing. Using specially designed screw geometries with deep screw flight depths shear rates are low. This ensures gentle treatment of shear-sensitive PVC formulations and contributes to improved product quality. The second stage is a downstream single screw extruder that builds up pressure for pelletizing. 

This separation of process tasks allows PVC compounds to be processed more gently while maintaining excellent mixing performance and high throughput. 

The Benefits of Integrated Feeding Technology in the Kombiplast Process

PVC compounds often contain significant amounts of additives, fillers, stabilizers, and processing aids. Reliable and high-accuracy feeding of these ingredients is essential for consistent product performance.

The ZS-B side feeder unit can be attached to the ZSK extruder’s feed zone. It has a high screw diameter ratio Do/Di (outer-to-inner screw diameter) and allows additives to be introduced directly into the process section of the ZSK. Even dry blends and lightweight powders can be very efficiently fed into the process via the ZS-B. In many applications, the ZS-B can even replace a separate gravimetric feeder while ensuring stable material intake.

When processing powders, the integration of Coperion's Feed Enhancement Technology (FET) further improves feeding performance and process reliability. In this patented technology, the feed section of the ZSK twin screw extruder is equipped with a gas-permeable wall connected to a vacuum system. By removing entrained air directly at the feed intake, FET significantly increases material intake capacity, enabling throughput rates of up to three times higher for feed-limited formulations. As a result, processors benefit from higher output, improved process efficiency, and a more cost-effective PVC compounding operation.

Optimized Pelletizing with the EGR in new Design

After pressure is built up in the single screw extruder, the PVC melt is transferred to the pelletizing stage, where it is converted into uniform pellets. Pelletizing is a critical step in PVC compounding, particularly because PVC is sensitive to thermal degradation. Fast access and easy maintenance are important to minimize downtime and ensure safe operation.

Coperion recently launched a new generation of its EGR eccentric pelletizer, specifically designed for PVC compounding. Featuring a range of innovative enhancements, the new EGR enables particularly efficient, reliable, and safe pelletizing of PVC compounds.

The latest EGR generation offers several significant advantages:

• Divided, pivoting pelletizer hood design for substantially faster and easier die plate changes
• Improved accessibility and enhanced operator safety during maintenance
• Easy access to the EGR's knife blade for faster, more precise adjustments to the pelletizing knives which in turn improves cut quality
• Reduced conveying pressure levels, lowering blower requirements and decreasing energy consumption
• New inflatable seals for pellet removal simplifying operation and improving reliability
• Faster product changeovers, helping reduce downtime and improve productivity 

A Proven Platform for PVC Success

Whether you are producing cable compounds, rigid PVC, or flexible PVC formulations, advanced processing technology can unlock significant potential across your operation. By combining gentle compounding, efficient feeding, and next-generation pelletizing, Coperion helps PVC manufacturers achieve higher quality, lower operating costs, and greater productivity.