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Cause and solution of uneven and bulging of cable insulation surface
Apr 25, 2018

 

   1 causes


1.1 Raw rubber phenomenon Cross-linked insulation core in the production process can sometimes appear raw rubber phenomenon, also become insulation stiff block or hard block. The main causes of this phenomenon are: (1) The temperature of the machine neck or nose is not enough, resulting in internal local cold gum production, (2) due to the fuselage temperature or shear force is not enough to cause local plasticizing is not good, (3) When the filter liner is not in place, the final impact on the crosslinking insulation extrusion pressure, will produce raw rubber,


To cause the insulating core surface to appear concave and convex hard block.


1.2 Old gum Phenomenon Cross-linked insulation core in the production process can sometimes appear old gum phenomenon, also become a pre-crosslinking, is due to cross-linked materials extrusion when the nose temperature is too high or the long-term stay in the flow of the dead end of the channel, the old gum is amber, the longer the stay, the darker the color, the higher the temperature of its color is deeper. General production of old gum reasons are: (1) Extrusion speed too fast, the faster the screw speed, the more intense the shear force of the cross-linked material in the screw, so that the local temperature of the fuselage increases, resulting in the old gum phenomenon; (2) The stay time of the crosslinked insulating material in the barrel is too long, some of the insulating materials produce premature cross-linking, This leads to uneven surface when the core is out of the mold. (3) The filter cushion displacement causes the pressure distribution of the rubber material at the shunt board to be uneven, forming the flow path dead end, this situation will also produce old gum, at the same time may be due to filter loss of part of the filter function, after a long period of production, will also accumulate in the screw head of the old gum in the extrusion was brought out, in the insulating layer mixed with old gum,


Causes the insulation core to appear the quality problem.


1.3 Material stability Normal two-step silane crosslinked polyethylene, first with silane and PE to produce graft reaction, the generation of cross-linked PE (a material for short), in order to accelerate its cross-linking reaction, made of the catalyst containing the Masterbatch (b material), and then A, B material in accordance with a certain proportion of uniform mixing, extrusion molding and then in warm water cross-linking. The main causes of insulation core quality caused by material stability are: (1) Cross-linked polyethylene insulation ingredients mixed uneven, as a material contains cross-linking agent and a small amount of antioxidants, if the antioxidant in the production process is not evenly stirred, will cause insulation through the extrusion machine high-temperature extrusion, more concentrated antioxidant heat gasification,


Forming a bulge in the insulating layer, (2) The Xlpe insulating material is improperly stored, silane crosslinked polyethylene material, even if not joined the catalyst, at room temperature will also be slowly cross-linking, this is because the material contains traces of water (about 50x10-4%) caused by the storage of high temperature and humidity, will cause the extruded insulating layer surface is not smooth.


1.4 Cooling Process In addition to extrusion temperature, extrusion speed, crosslinking speed and material stability factors, cross-linked polyethylene from the die extrusion cooling process also may cause insulation core surface quality problems: (1) The cable surface with air bubbles, when the cable into the water, its surface if there is bubble adhesion, the position after cooling will have "small pit bag ", This is because the bubbles cover the air on the insulating surface, and the portion of the cooling rate that the bubble covers is slower than the part that is in contact with the water. The formation of air bubbles attached to the surface of the cable is generally the cooling of circulating water into the tank when the flow speed, the water is urgent, the high speed water brings the air into the water, some air attaches to the cable surface, forming the bubble, (2) The water droplets splash on the cable surface before entering the cooling water, and the contact part of it cools and shrinks first,


And with the air contact part is still in high temperature state, because of the difference of cooling speed to form insulation core surface uneven phenomenon.


2 workaround 2.1 Insulation surface of "raw rubber " and "Old Gum" phenomenon, online core appearance almost, easy to cause confusion, so pay attention to distinguish. Solution: (1) from the boot time to judge, short time production, "raw rubber" is likely to be large, long time to produce the "old gum" possibility; (2) Judging from the change of technological conditions, combined with the reasons of "raw rubber" and "Old Gum", the comprehensive analysis (3) The speed of extrusion line should be strictly in accordance with the requirements of the process specification, after the extrusion speed change, must pay close attention to the extrusion machine temperature change; (4) Check the head parts of the temperature control is accurate enough to find out which part caused by, and then adjust according to the actual situation, (5) when necessary to adjust the temperature,


Adjust the extrusion speed, cleaning filter nets and nose, and other search reasons. 2.2 Selection of production process stability, high technical and management level, continuous monitoring of impurity content, extrusion resin Melt Index constant silane crosslinking polyethylene insulating material manufacturers to ensure the stability of material properties.


The storage period of silane crosslinking material produced by two-step process is shorter, usually not more than 6 months, so high temperature and humidity should be avoided in storage to prevent the material from cross-linking, which causes the extrusion surface to be not smooth. 2.3 Cable insulation core from extruding Machine Head extrusion, should be the overall smooth into the water to avoid splashing on the surface. In the cooling water cycle, the water to the sink to pay special attention, it is advisable to use large caliber, low flow of water, this is because the caliber of water injection is small, it is bound to improve the flow rate, high-speed water will bring a large amount of air into the water, in addition to the insulation core into the water about half a meter after the addition of fine cotton yarn, such as the device, blowing the attached bubbles,


Keep the insulating core surface smooth. To sum up, to avoid silane crosslinked polyethylene insulation surface rugged, bulging and other quality defects, we must improve the quality of staff and operational skills, strict material quality, the production of different manufacturers of crosslinked polyethylene insulation materials to have a certain adjustment, only in this way can improve product quality, improve economic efficiency.


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