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Discussion on extrusion process of low-smoke halogen-free cable
Classification:
Technical knowledge
2019/03/13 15:08
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[Abstract]:
With the development of flame retardant technology for cable materials, new types of flame-retardant cables have also been produced, from ordinary flame-retardant cables to low-smoke low-halogen flame-retardant cables and low-smoke halogen-free flame-retardant cables. This shows that the requirements for flame retardant cables are getting higher and higher in recent years. In countries such as Europe, America and Japan, environmentally-friendly wire and cable has become the mainstream product of all cable types. It is strictly forbidden to use or import non-environment-friendly cables. Ordinary flame retardant materials contain a large amount of halogen, which will generate a large amount of smoke and toxic corrosive hydrogen halide gas during combustion. The halogen-free flame retardant is mainly selected in polyolefins, so the low-smoke halogen-free cable will be The main trend of development in the future, so the following aspects of the extrusion of low-smoke halogen-free cable materials will be discussed.
First, the extrusion equipment
A. The main component of the wire and cable extrusion equipment is the screw, which is related to the application range and production efficiency of the extruder. In order to meet the needs of different plastic processing, there are many types of screw. The low-smoke halogen-free flame-retardant cable material contains high-filled magnesium hydroxide or aluminum hydroxide, so the general-purpose screw is generally selected for the selection of the screw and its compression ratio cannot be too large, generally 1:1~1 : 2.5 is more suitable.
B. There is also an important factor in the extrusion process that affects the extrusion of low-smoke halogen-free cable materials, that is, the cooling device of the extruder, because of the particularity of low-smoke halogen-free materials, during the extrusion process, due to friction Large amounts of heat are generated, which requires the extruder to have a good cooling device to control the process temperature. This is a problem that cannot be ignored. If the temperature is too high, the surface of the cable will have a large air hole. If the temperature is too low, the current of the device will increase, which will easily damage the device.
Second, the extrusion die
Due to the high filling material of the low-smoke halogen-free cable material, the strength, the draw ratio and the viscosity of the melt in the molten state are greatly different from those of other cable materials, so the matching of the molds is also different. The first is the choice of the extrusion method of the mold. For the extrusion of low-smoke and halogen-free cable materials, the extrusion-molding mold should be extruded, and the semi-extrusion should be used in the process of jacket extrusion, so as to fully ensure the tensile strength and elongation of the material. Rate and surface finish. Secondly, the choice of the mold sleeve. When using the extrusion mold, the pressure of the machine head is large due to the high viscosity of the material. When the extrusion leaves the mold, it will expand, so the mold sleeve should be smaller than the actual size. . Finally, the mechanical properties of low-smoke and halogen-free are superior to those of ordinary cable materials and low-smoke and low-halogen materials. The stretch ratio is small, only about 2.5 to 3.2, so the stretching should be fully considered when selecting the mold. Performance, which requires that the selection of the mold sleeve should not be too large, otherwise the surface of the cable is not dense, and the package is loose.
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