Low Smoke Zero Halogen (LSZH) cables are increasingly required in public infrastructure, EV charging, data centers, and transport applications. While LSZH compounds are prized for safety, manufacturers often struggle with extrusion consistency, scrap, and surface quality.

At DXCableTech, we’ve seen factories face recurring issues when switching from PVC to LSZH: uneven insulation, die lines, surface streaks, and excessive start-up waste.

This article dives deep into why LSZH is challenging, the physics behind extrusion, and machine- and process-level solutions for long-term stability and high-quality production.

1. Understanding LSZH Material Properties

LSZH differs from PVC in several critical ways:

1. Narrow Thermal Processing Window

   Decomposition starts at temperatures only slightly above the extrusion temperature.

   Overheating can cause discoloration, degradation, and gas evolution.

2. High Melt Viscosity

   LSZH resins are more viscous than PVC, particularly at lower temperatures.

   High shear during extrusion can generate hot spots, creating surface defects or uneven flow.

3. Low Plasticizer Content

   LSZH lacks softeners present in PVC.

   Reduced flexibility during cooling increases risk of oval cross-section and spring-back.

4. Sensitivity to Moisture and Contaminants

   Any water or debris in the feed causes bubbles or voids in insulation.

   Requires material drying and strict feed system control.

5. High Shrinkage Tendency

   LSZH shrinks more upon cooling than PVC.

   Cooling and haul-off must be precisely balanced to maintain diameter and concentricity.

Key takeaway: LSZH extrusion is fundamentally more demanding. Conventional PVC extrusion setups are often insufficient.

2. Critical Equipment Features for LSZH Extrusion

2.1 Screw and Barrel Design

• Screw Profile: Compression and metering zones must minimize shear while ensuring homogeneous melt.

• Screw L/D Ratio: Higher L/D ratios improve mixing and thermal uniformity.

• Barrier Screws: Optional for precise compounding, reducing unmelted particles.

2.2 Barrel Temperature Control

• Multi-zone PID control ensures narrow ±1–2°C temperature stability.

• Real-time melt pressure feedback avoids hot spots or flow instability.

2.3 Die and Calibration System

• Die design must match conductor size and stranding.

• Smooth die surfaces minimize friction and reduce drag marks.

• Calibration troughs and water cooling need precise flow rate and temperature control.

2.4 Take-Up, Haul-Off, and Tension Control

• Stiff LSZH tends to spring back if tension is not properly applied.

• Digital tension control synchronized with screw RPM ensures dimensional stability.

• Multi-stage haul-off may be required for high-speed or fine-strand conductors.

3. Process Challenges and Optimization Techniques

3.1 Start-Up and Purging

• LSZH takes longer to stabilize than PVC.

• Start-up scrap can be reduced with pre-heating zones and specialized purging compounds.

• Establish standard start-up SOPs to minimize operator variability.

3.2 Temperature Management

• Maintain narrow melt temperature window throughout barrel and die.

• Avoid sudden cooling that causes diameter contraction or surface lines.

• Use high-resolution sensors for real-time monitoring and adjustment.

3.3 Screw Speed and Extrusion Pressure

• LSZH viscosity is sensitive to shear; high screw speeds increase risk of hot spots.

• Optimize screw RPM to balance throughput and surface quality.

• Pressure fluctuations indicate inadequate melt homogeneity or poor die design.

3.4 Tension and Take-Up Synchronization

• Improper tension leads to ovalization, insulation thinning, and dimensional inconsistency.

• Digital tension systems or servo-controlled haul-off units are recommended for repeatable production.

• Coordinate start-up, steady-state, and shutdown procedures to avoid sudden tension surges.

3.5 Moisture Control

• Pre-dry LSZH granules using proper desiccant dryers.

• Minimize exposure during feeding; even slight moisture leads to bubbles, pinholes, or surface blemishes.

4. Troubleshooting LSZH Extrusion Issues

5. Why Auxiliary Machines Matter

LSZH extrusion success is not just about the extruder:

• Pay-Off Units: Uneven conductor tension propagates defects downstream.

• Cooling Tanks: Temperature and flow control are critical to prevent spring-back.

• Coiling & Winding Machines: Improper take-up tension can cause ovality, damaging downstream insulation quality.

Internal link opportunity: DXCableTech Auxiliary Machines / Coiling & Winding / Pay-Off Systems.

6. When to Upgrade Equipment for LSZH Production

Signs that a factory may need a new extrusion line or auxiliary system:

• Frequent surface defects despite optimized parameters

• Scrap rates higher than industry standard

• Inability to stabilize LSZH extrusion across multiple speeds or conductor types

• Introduction of new products (EV, data, LSZH sheathed cables) exceeding current machine capabilities

Upgrading to DXCableTech LSZH extrusion lines ensures:

• High-quality, repeatable production

• Reduced waste and operating costs

• Stable performance for multi-material production

7. Benefits of Optimized LSZH Extrusion

• Consistent insulation thickness and roundness

• Reduced scrap and start-up losses

• Improved surface finish for better adhesion

• Energy efficiency with optimized heating and cooling

• Reliable, repeatable production for multiple cable types

By combining modern extrusion machines with matched auxiliary equipment, factories can maximize throughput, reduce waste, and meet strict safety standards.

8. Conclusion: LSZH Extrusion Requires a Complete System Approach

Extruding LSZH successfully is equipment- and process-dependent.

Key factors for success:

• Modern extrusion lines with precise screw, barrel, die, and temperature control

• Optimized tension, take-up, and haul-off systems

• Standardized start-up and changeover procedures

• Proper material handling and moisture control

At DXCableTech, LSZH extrusion is built into the core design of our lines, ensuring consistent quality, higher efficiency, and long-term reliability for cable manufacturers.