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Do you know the production process of low smoke halogen free flame retardant cable?

17-08-2017Edit: Guangdong Dengfeng
The conductor of fire-resistant cable adopts copper conductor, the conductor geometry is round, and a plurality of stranded conductors should be tightly pressed. The conductor is lapped with two or more layers of mica tape, and the wrapping angle is controlled at 40-50 degrees.
Low smoke halogen-free flame retardant cable production process
1. conductor of cable
The conductor of fire-resistant cable adopts copper conductor, the conductor geometry is round, and a plurality of stranded conductors should be tightly pressed. Compared with the circular pressing copper conductor and sector conductors have many advantages: wrapping mica tape the mica tape and the conductor tightly, is conducive to the uniform electric field distribution, enhance the cable electrical insulation properties, and can save the amount of mica tape, reduce the cost.
2. the refractory layer of cable
Two or more layers of mica tape are used to overlap the package outside the conductor. Generally, the overlap rate is not less than 30%, and sometimes the overlap rate is up to 50%, so as to meet the requirements of fire test, so as to achieve the fire resistance test as the benchmark. Wrapping angle is controlled at 40-50 degrees.
3. insulation and sheath of cables
According to the different levels of flame retardant cable insulation allows the use of cross-linked polyethylene or low smoke halogen-free flame retardant polyolefin insulation material, because the conductor overlap of two or more layers of fireproof mica tape, the conductor cross section of 25mm2 and above the cable insulation thickness allows 20% thinning, but to be able to test for reference by fire-resistant cable. The cable sheath is made of halogen free low smoke flame retardant polyolefin sheath material, and its structure size is carried out according to relevant standards.
(1) extrusion die;
In general, halogen-free, low smoke, flame retardant polyolefin insulation is extruded and extruded, and the sheath is extruded or partly extruded. The extrusion die because of the low smoke halogen-free flame retardant polyolefin melt viscosity, the die pressure increase, dense extrusion pressure, leading to die when inflated, the choice of die diameter than the finished nominal diameter 5%. The use of tube extruding or semi tube extruding production must be considered when the draw ratio, low smoke halogen-free flame retardant polyolefin stretching ratio of 2.5 - 3.2, the theory is smaller than the surface tension, more smooth, practice model: sheath core diameter = winding layer diameter + (0.6 ~ 1.5) mm, die diameter cable + = nominal diameter (2 ~ 7) mm.
(2) extrusion process
The initial temperature is generally about 5~10 degrees lower than the normal extrusion temperature, so that when the extrusion is stable, the temperature is within the range of the extrusion temperature of the material. Generally speaking, halogen free low smoke flame retardant polyolefin cable material has higher friction temperature than low smoke low halogen and ordinary flame retardant polyolefin cable material, and the process temperature range is narrow.
When the screw speed is fast and the shearing action increases, the mechanical thermal decomposition of the flame retardant is easy to be caused; the speed increases, and the heat generated by friction is also large, and it also causes the decomposition of the flame retardant, thus affecting the quality of the extruded surface. At the same time, when the screw speed is large, it will lead to overload operation of the motor.
(3) extrusion equipment;
An ideal extrusion surface can be obtained by using screw with slenderness ratio L/D of 20 or 25, and the screw compression ratio is 1:1 to 2.5:1. Extrusion equipment should have a good cooling device.
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