Cable surface common defects and prevention

   For fiber optic cable and other injection molding cable products, surface defects are more common product quality problems. Defects of various types, common cable surface defects are pores, pinhole, bubbles and so on. The insulation properties of the cable, mechanical properties, thermal stability and aging properties will have a certain impact. This will cause a decline in product qualification rate, rework rate increases, production costs rise, market competitiveness decline. This paper analyzes the causes of defects such as porosity and pinhole in the sheath of cable products, and accordingly puts forward some preventive measures for your reference.

 

 

  Produced by the cause of analysis

(1) Cable extrusion process, temperature, pressure, speed and other parameters are not uniform, will lead to extrusion of air bubbles and voids, affecting the quality of the cable. For example, in the process of extruding the sheath (jacket), due to PVC or PE and other sheath materials and screws, barrels and other shear load, will produce a high friction temperature, if the extruder cooling system control effect is poor, the temperature is out of control, insulation, sheath profiles will appear air holes, pinholes. If the surface temperature is too high, the surface of the product has scorched particles, pulling phenomenon; if the surface temperature is too low, the material is not enough plasticization, the surface of the product becomes rough.

 

(2) During the transportation, storage or granulation of raw materials, it is necessary to maintain a dry, clean, dust-free and oil-free environment. If the raw materials are damp, quality problems such as air holes and pinholes will occur in the insulation and sheathing profiles during deep processing.
① If the pelletizing temperature is too high, the moisture will affect the molecular arrangement structure of the material and produce air holes, and also affect the normal extrusion process.
② Water in the extrusion process by heat into water vapor, in the profile of many bubbles, not only will affect the mechanical properties of the insulation or protective layer, the more serious is to reduce the resistance of the insulation or electrical strength, so the production of insulation should be strictly controlled when the water content.

(3) Sheath material in the pelletizing process, the extruder's vacuum exhaust system failure, exhaust effect is not good. The extruder can be replaced for the second pelletizing, using the method of vacuum to discharge the gas produced by the material under high temperature conditions.

(4) In the production process of sheathing (jacket), if the mold is not properly selected, it will also produce air holes and pinholes.
① In the extrusion of large cross-section of electric (optical) cable isolation layer or sheath, generally using extrusion tube mold, if you choose a large aperture and die bearing longer outer die, in the case of extrusion of a larger thickness, die mouth pressure is small, the product profile prone to air holes, such as pinholes and other quality problems; on the contrary, it is not easy to appear.
② If the mold selection does not meet the process requirements, improper spacing between the inner and outer die, and the use of a set of molds to open a number of specifications of the product and lead to low head pressure, there will be a convex surface of the product package, the appearance of the quality of the problem is not smooth.
③ If the mold has a small damage or wear and tear will also lead to cable surface defects such as hollow.

 

 

Measures to solve the problem

(1) In the process of pre-molding, mixing, granulating and molding of sheath material, vacuum or exhaust should be sufficient;

(2) After cooling with water during granulation, the granules should be fully dried and cooled before measuring and sealing the bags;

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

(4) Before extruding, the material should be checked whether it is damp or not, and the granules should be dried;

(5) Adopt rapid cooling method to cool down the temperature, when the products leave the mouth of the mold, then use cold water to cool down directly in sections;

(6) Regularly clean the machine head, and also carefully clean the three segments of the head and replace the screen after each shift stop

 

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