Common Defects And Prevention Of Outer Sheath In Optical Cable Production

For injection-molded cable products such as optical cables, surface defects are a common product quality problem. There are many types of defects, and common cable surface defects include pores, pinholes, bubbles, etc. They will have a certain impact on the insulation performance, mechanical properties, thermal stability and aging performance of the cable. This will cause a decrease in product qualification rate, an increase in rework rate, an increase in production costs, and a decrease in market competitiveness. This article analyzes the causes of defects such as pores and pinholes in the sheath of cable products, and also proposes some corresponding preventive and solution measures for your reference.

?Common Problem

1.During the cable extrusion process, uneven parameters such as temperature, pressure, and speed will cause air bubbles and gaps in the extrusion, affecting the quality of the cable. For example, during the extrusion of the sheath (sleeve), due to the large shear load between the sheath materials such as PVC or PE and the screw and barrel, a high friction temperature will be generated. If the extruder cooling system has poor control effect and the temperature is out of control, pores and pinholes will appear on the insulation and sheath profiles. If the surface temperature is too high, there will be burnt particles and wire drawing on the product surface; if the surface temperature is too low, the material is not plasticized enough and the product surface becomes rough.

2. During the transportation, storage or granulation of raw materials, a dry, clean, dust-free and oil-free environment needs to be maintained. If the raw materials are damp, quality problems such as pores and pinholes will occur in the insulation and sheath profile during deep processing.

2.1 If the granulation temperature is too high, the moisture will affect the molecular arrangement structure of the material and produce pores, and will also affect the normal progress of the extrusion process.

2.2 During the extrusion process, the moisture is heated to become water vapor, and many bubbles are generated in the profile, which will not only affect the mechanical properties of the insulation or sheath, but more seriously, it will reduce the resistance or dielectric strength of the insulation, so the water content should be strictly controlled when producing insulation.

3. During the granulation process of the sheath material, the vacuum exhaust system of the extruder fails and the exhaust effect is poor. The extruder can be replaced for secondary granulation, and the gas generated by the material under high temperature conditions can be discharged by vacuuming.

4. In the production process of the sheath (sleeve), if the mold is not properly selected, pores and pinholes will also occur.

4.1 When extruding the isolation layer or sheath of large-section electric (optical) cables, a tube extrusion mold is generally used. If an outer mold with a larger aperture and a longer die bearing is selected, the cross-section of the product is prone to quality problems such as pores and pinholes when the extrusion thickness is large and the die mouth pressure is low; otherwise, it is not easy to appear.

4.2 If the selection of the mold does not meet the process requirements, the spacing between the inner and outer molds is inappropriate, and one set of molds is used to open multiple specifications of products, resulting in low head pressure, quality problems such as convex bulges on the surface of the product and rough appearance will occur.

4.3 If the mold has slight damage or wear, it will also cause defects such as holes on the cable surface.

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Solution

1. During the pre-plasticization, mixing, granulation and molding of the sheath material, the vacuum or exhaust should be fully drawn;

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2. After cooling with water during granulation, the pellets should be fully dried and cooled before metering and bagging;

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3. Pay attention to moisture and pollution prevention during transportation, and do a good job of packaging protection;

4. Before extrusion, check whether the material is damp and dry the pellets;

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5. Use the rapid cooling method to cool down. When the product leaves the die, use cold water to cool it in sections;

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6. Clean the machine head regularly, and clean the three sections of the machine head carefully after each shift, and replace the filter;

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7. For materials produced in different seasons and manufacturers, product sampling analysis and process parameter optimization should be strengthened;

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8. Be sure to prevent the material from getting damp during the rainy season. Warehouse staff should strictly distribute materials according to the principle of "first in, first out" and stack them in batches. The storage time should not be too long.

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At FCST, we manufacture top-quality microduct connectors, microduct closure, telecom manhole chambers?and fiber splice boxes?since 2003. Our products boast superior resistance to failure, corrosion, and deposits, and are designed for high performance in extreme temperatures. We prioritize sustainability with mechanical couplers and long-lasting durability.

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