Common Problems and Solutions in the Processing of Halogen-Free LSZH/HFFR Cable Materials

Common Problems and Solutions in the Processing of Halogen-Free LSZH/HFFR Cable Materials

As we all know that flame retardant Magnesium hydroxide and aluminum hydroxide are widely used in halogen-free flame retardant cable material manufacturing. So the majority of our customers belong to the cable industry. During the past decade, we helped our customers solved many problems during the production of cable compound and cable. Among these problems, most of them are similar, so today I would like to conclude some of the problems and solutions. Hope this passage will help you a little bit.

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Before we move on to the common problems and solutions, let’s first look at the differences among the LSZH cable compound, PE compound, and PVC compound.

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  1. Tensile strength ad elongation at break is lower than PVC compound, PE compound.

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  • The oxygen index is higher than the PVC compound, but the flame retardant performance is worse, halogen free compound has poor self-extinguishing ability.
  • Halogen-free compound added a lot of flame retardant, the density is higher.

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2. The extrusion process is different from that of PVC, PE compound:

1) The material has larger shearing, it is better to use a special screw with a small compression ratio (1:1.1~1.5), especially for an extruder with a large screw diameter;

2) The load is large, the current of the main machine is high, so it’s better to choose an extruder with large main motor power.

3) The output of glue is small and has a slow line extrusion speed.

4) The temperature is hard to control. Too high will cause air holes on the surface or the cut edge of the cable.

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The above differences can help us better understand problems and solutions in the processing of halogen-free LSZH/HFFR cable materials.

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Issue 1: The surface of the cable is rough, there are small holes at the cut section of the cable.

Possible causes: 

A) the material is damp. 

B) the process temperature is too high, the flame retardant decomposed.

Solutions: 

A) Pre-dry the material: using blowing device drying 2~3 hours under 70~80℃;

B) Reduce the screw speed or lower the temperature of the body and mold.

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Issue 2: The motor current is too high, the production speed is slow, and the screw cannot be rotated in severe cases.

Possible causes: 

A) the material is not plasticized and melted completely, high shearing and severe frictional heat.

B) too much back pressure.

Solutions: 

A) Increasing process temperature, especially feeding zone.

B) Use a small mesh filter screen, or remove the filter screen and manifold if necessary.

C) Select the screw speed to be at the appropriate current level.

D) Use a low compression ratio screw.

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Issue 3: The outer diameter of the cable fluctuates during extrusion

Possible causes

A) Unstable discharge of extruder.

B) Unstable traction.

C) Fluctuation of cable core outer diameter.

Solutions: 

A) When the host current and extrusion line speed allow, reduce the temperature of the extruder, or increase the filter screen and the shunt plate so that the material can obtain sufficient and stable thrust in the barrel.

B) Check the matching of molds and choose a reasonable mold core and mold sleeve.

C) Repair unstable traction system.

D) Control the outer diameter of the semi-product in the previous process.

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These are some common problems that we might encounter during our production, and the solutions are also based on our experiences, and if you have more to add or discuss, please feel free to contact author Elena kmt_elena@163.com.

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