Table of Contents
XLPE (crosslinked polyethylene) is widely used as insulation in medium- and high-voltage cables due to its excellent performance and long-term stability. It is also commonly applied in power, telecommunications, and renewable energy sectors. Through crosslinking, polyethylene chains form a three-dimensional network, significantly enhancing thermal resistance, electrical properties, and mechanical strength, ensuring reliable long-term operation of cables.
Silane Crosslinking: Safe and Efficient Process
In the silane crosslinking method (Sioplas process), production follows a two-step procedure:
1. Grafting Reaction (A-material production)
Polyethylene is mixed with silane and peroxide in the cable material plant to produce A-material with grafted silane.
2. Extrusion Crosslinking (B-material mixing)
A material is then combined with a catalyst masterbatch (B-material), extruded, and crosslinked via hot water or steam at the cable factory.
Compared with the one-step method (Monosil), the two-step silane process offers advantages in safety, energy efficiency, and controllability, making it the industry standard.
Process Features and Safety Measures
Due to the volatility, flammability, and strong moisture sensitivity of silane liquids, the production process requires strict safety and sealing measures. The COWIN system incorporates:
- Explosion-proof design for tanks, pipelines, and dosing systems, with nitrogen protection throughout the line to prevent air and moisture intrusion;
- Vacuum drying and dehumidification of raw materials to ensure stable and reproducible grafting reactions;
- Vacuum venting sections to remove by-products and moisture, maintaining stable reaction pressure.
Twin-Stage Extrusion: Segmented Reaction and Pelletizing
To achieve uniform grafting and stable pellet quality, COWIN employs a twin-stage extrusion system:
Stage 1: Co-rotating twin-screw reaction section
Ensures uniform grafting of polyethylene with silane and peroxide. The low-speed, high-torque design prevents local overheating and premature crosslinking, while vacuum venting removes by-products and stabilizes pressure.
Stage 2: Single-screw pelletizing section
Handles melt conveying and pressure-stable pelletizing. Hydraulic screen changers and water-ring pelletizers ensure uniform particle size, and the barrel and screw are made of nitrided steel for wear and corrosion resistance.
This design guarantees stable grafting reactions and consistent pellet quality, aligning with mainstream A-material production configurations worldwide.
Post-Processing and Precise Temperature Control
To prevent moisture absorption or agglomeration and maintain material performance, the system is equipped with a complete drying and storage line:
Vibrating Sieve → Fluidized Bed Dryer → Molecular Sieve Dehumidification → Finished Material Silo → Packaging Scale
Precise temperature control is achieved through mold temperature control and a constant-temperature water bath:
- Mold temperature remains stable to prevent bubble formation and gel;
- Water bath cooling is uniform to maintain consistent pellet shape;
- Line temperature is controlled within ±1°C, ensuring material stability during storage, transport, and processing.
Reliable and Stable System Design
COWIN understands that the quality of XLPE cable material depends on precise process control and robust equipment design. The system integrates explosion-proof structures, nitrogen protection, precise dosing, and automated temperature control to ensure safe, reliable production and consistent pellet quality.
The twin-stage extrusion system has been successfully implemented in leading domestic and international companies, with positive user feedback. Across cable materials and other high-performance plastics, COWIN twin-screw extruders are recognized for their stability, reliability, and consistent performance.
