The extrusion process includes insulation and sheathing production. The insulation production methods are: coating, wrapping, extrusion, and their combination. At present, the main insulation production is coating (winding wire, no longer within the scope of production license management) and extrusion (wire and cable).

First, plastic extrusion equipment and mold

1. Plastic extrusion equipment: extruder

1.1 The working principle of the extruder: The use of a specific shape of the screw in the heated barrel rotation, the plastic sent by the hopper forward pressure, so that plastic uniformly plasticized, through the head and different shapes of the mold, so that the plastic extrusion into various shapes of products.

1.2 The basic structure of the extruder: The extruder is composed of an extrusion system, a transmission system and a heating system (cooling).

1.2.1 Extrusion system (including five parts: screw, barrel, hopper, head and mold)

① Screw: screw is an important part of the extruder, it is made of high strength, heat and corrosion resistant alloy steel, its role is to push forward the plastic, produce pressure, stirring, rotation and friction heat with the plastic, so that the plastic melt, and continuously the melt into the organ extrusion, it is directly related to the application range and productivity of the extruder.

② The barrel is a metal barrel, generally with high strength of heat and pressure resistance, strong wear-resistant, corrosion-resistant alloy steel or composite steel lined with alloy steel, it and the screw constitute the basic structure of the plastic plasticizing and conveying extrusion system, the length of the barrel is generally 15 to 30 times its diameter, so that the material can be heated and plasticized fully for the principle. The barrel should have sufficient thickness, stiffness and inner wall should be smooth. A resistance or induction heater measuring device and a cooling system are arranged on the outside of the barrel.

(3) The hopper is usually a conical container, and its volume should be able to hold the material for at least 1 hour, the bottom of the hopper is equipped with a cutting off material flow truncation device, and the side of the hopper is equipped with a visual hole for calibration and measurement.

④ The head is the forming part of the extruder, the head is mainly composed of a filter device (porous plate and screen), connecting pipes, shunt, mold core base, mold and so on.

1.2.2 Transmission system

Its function is to ensure that the screw rotates at the required torque and speed at a constant speed, and the general flexible system includes three necessary links: prime power - transmission - reducer. The speed of the screw is required to be stable and does not change with the change of its load to ensure uniform product quality. However, in different occasions, the screw is required to change speed to achieve the requirements of a device that can extrude different specifications of products. For this purpose, the transmission motor is generally used rectifier motor, DC motor and so on.

1.2.3 Heating and cooling system

Function: Heating or cooling through the barrel to ensure that the plastic is always extruded within its process temperature range.

① Heating method of the plastic machine: When the extruder screw speed remains constant, the main factor affecting the stability of the amount of glue is the body temperature of the extruder.

There are usually two heating methods for crosslinked extruders, using carrier (such as heated water) heating and resistor heating. The carrier heating is characterized by uniform heating, which is not easy to produce local overheating phenomenon, but the carrier heating temperature has high requirements for the sealing performance of the system and high cost. Therefore, it is used on extruders with higher temperature control requirements.

(2) Plastic machine cooling: during the extrusion process, the plastic temperature in the barrel is often too high and the heat is too much. If too much heat is not discharged in time, it is easy to cause the material to be "pre-crosslinked"; The extruder is generally cooled in two parts: barrel cooling and head cooling.

a. Barrel cooling (there are two kinds of barrel cooling methods: air cooling and water cooling)

From the cooling effect point of view, air cooling is relatively soft, cooling speed is slow, water cooling speed is fast, but more intense, easy to cause strong "thermal vibration", the design of water cooling system is more complex, in addition to having a good cooling effect, but also should have good sealing to prevent leakage, so that when there is no need to cool, it is best to make all the water in the cooling system escape. So as not to block the cooling system due to the scale generated by the water storage, the structure should also be conducive to maintenance, most of the current water cooling system is in the outer surface of the barrel out of the spiral groove, and then coiled cooling pipe.

b. Screw cooling

The main purpose of the cooling screw is to prevent the plastic from overheating, and the feeding section of the cooling screw is also conducive to the conveying of materials to the head. The cooling medium through the screw is usually water, and the water temperature can be maintained according to the requirements. Even the cooling length of the screw can be adjusted, sometimes the full length of the cooling, sometimes only a part of the cooling, the latest design of the extruder screw temperature can be adjusted in zones.

1.2.4 Screw parameters of extruder

The main parameters of the screw are diameter to diameter ratio, compression ratio, pitch, width of the screw groove, screw Angle, clearance between the screw and the barrel, etc.

① Screw diameter D: The size specification of the extruder is usually expressed by the diameter of the screw, the larger the diameter, the greater the amount of glue, the extrusion amount is approximately proportional to its square, so a small increase in the diameter of the screw will cause a significant increase in the amount of extrusion.

② Length-diameter ratio L/D: the ratio of the length L of the working part of the screw to the diameter D. When the screw diameter is fixed, increasing the length-diameter ratio means increasing the length of the screw, and the larger the length-diameter ratio, the larger the material is conducive to full plasticization, and the greater the pressure can be generated to ensure that the product is more dense and improve the quality. However, the length to diameter ratio is too large, too much plasticization of the cross-linked material, causing the early cross-linking of the material, for the extruder of the cross-linking unit, the length to diameter ratio is generally between 20 and 25 times.

③ The compression ratio is the ratio of the volume of the first tank in the feeding section to the volume of the last spiral tank in the homogenization section. The selection of the compression ratio should be determined according to the raw material, the nature of the plastic is not the same, the compression ratio is not the same, the particles are large and the compression ratio is small; The particle size is small, the compression ratio is large, and the compression ratio of low-density polyethylene is 2 to 3 times.

④ Screw groove depth H: that is, the difference between the outer radius of the thread and the root radius, according to the compression requirements, the groove depth of the feeding section is greater than the melting section, the melting section is greater than the homogenizing section, the depth of the feeding section is large, which is conducive to improving its conveying capacity, the melt section and the homogenizing section are shallow, the screw can produce a higher shear rate on the material, which is conducive to the heat transfer of the cylinder wall to the material and the mixing and plasticizing of the material.

2. Mould of extruder

2.1 Molds of extruder are divided into extruded, semi-extruded and extruded.

2.2 Characteristics of various molds:

2.2.1. Extrusion advantages:

1) The structure of the extruded plastic layer is tight and strong.

2) The insulation and conductor are tightly bonded without gaps, and the insulation strength of the extruded cladding is reliable.

3), the outer surface is smooth.

2.2.2. Extrusion disadvantages:

1), adjusting the core is not easy.

2), the accuracy of the mold requirements are high, product quality depends on the mold.

3) The bending of the extrusion line is not good.

2.2.3 Advantages of extruded tube

1), extrusion speed is fast.

2), simple operation, easy to adjust the core.

3), large gap, small wear, long service life.

4), the mold is convenient.

5), plastic directional stretching, plastic extrusion strength increased.

6), sheath thickness is easy to control.

2.2.4 Extrusion pipe disadvantages:

1), poor density.

2), poor combination of plastic and wire core.

2.2.5 Semi-extruded tube: Absorb the advantages of extruded and extruded tube.

Qingdao Tianxing Cable Co., Ltd. is a technology enterprise specializing in the production of wire and cable in Shandong Province, with more than 150 sets of domestic excellent cable production equipment and testing equipment, excellent production technology, modern testing equipment, to ensure stable product quality and timely supply. The company's main products are power cable, mineral cable, high life wire and cable, radiation crosslinked cable, control cable, computer cable, photovoltaic cable, communication cable, data cable, low smoke halogen free cable, flame retardant series wire and cable.