Plastic wire and cable main insulation material and protective material is plastic. Thermoplastic has superior performance and good processing performance, especially for wire and cable extrusion insulation and protective layer production process is simple. The basic way of the production of plastic insulation and protective layer of wire and cable is the continuous extrusion of a single screw extruder. Because the extruder has the characteristics of continuous extrusion, the production process of plastic insulation and sheathing is also continuous. As far as wire and cable production is concerned, differences in product specifications and different extruded parts often determine certain changes in extrusion equipment and process parameters. But in general, all kinds of products, each part of the extrusion coating process is much the same, the following is based on the general, individual as a supplement to the extrusion principle, process and mold type are introduced.

Section 1 Extrusion of plastics The basic principle of plastic extrusion

The working principle of the extruder is: the use of a specific shape of the screw, rotating in the heated barrel, the plastic sent by the hopper will be extruded forward, so that the plastic is uniformly plasticized (that is, melted), through the head and different shapes of the mold, so that the plastic is extruded into a continuous plastic layer of various shapes required, extruded on the core and cable.

1. Plastic extrusion process

The plastic insulation and sheath of the wire and cable are carried out by continuous extrusion, and the extrusion equipment is generally a single screw extruder. Before the plastic is extruded, it is necessary to check whether the plastic is wet or there is other debris in advance, and then add the screw to the hopper after preheating. In the extrusion process, the plastic loaded into the hopper enters the barrel with the help of gravity or the feeding screw. Under the thrust action of the rotating screw, it continuously pushes forward, and gradually moves towards the homogenizing section from the preheating section. At the same time, the plastic is stirred and squeezed by the screw, and under the action of the external heat of the barrel and the shear friction between the plastic and the equipment, the viscous flow is formed in the screw groove. Under the action of the temperature specified in the process, the plastic is transformed from a solid state to a plastic object in a molten state, and then pushed or stirred by the screw, the completely plasticized plastic is pushed into the head; The material flow reaching the head is extruded from the mold sleeve through the annular gap between the mold core and the mold suite, and is extruded around the conductor or wire core to form a continuous dense insulating layer or sheath layer, and then cooled and cured to make wire and cable products.

2. Three stages of the extrusion process

The main basis of plastic extrusion is the plastic has a plastic state. Plastic in the extruder to complete the plastic process molding is a complex physical process, that is, including mixing, crushing, melting, plasticizing, exhaust, compaction and finally shaping. It is important to note that this process is implemented continuously. However, traditionally, people often according to the different reactions of plastics extrusion process of this continuous process, artificial into different stages, namely: plasticizing stage (plastic mixing, melting and homogenization); Molding stage (extrusion molding of plastics); The setting stage (cooling and curing of the plastic layer).

The first stage is plasticizing. Also known as the compression phase. It is completed in the barrel of the extruder, and through the rotation of the screw, the plastic is changed from a granular solid into a plastic viscous fluid. There are two sources of heat obtained by plastics in the plasticizing stage: one is the electric heating outside the barrel; The second is the friction heat generated when the screw rotates. The initial heat is generated by the electric heating outside the barrel, and when the normal driving, the heat is obtained by the friction between the screw selection material and the inner wall of the barrel and the internal friction between the material molecules in the process of compression, shearing and stirring. The second stage is the molding stage. It is carried out in the head, due to the rotation of the screw and pressure, the viscous fluid is pushed to the head, through the die in the head, the viscous fluid is formed into the extruded material of various sizes and shapes required, and is covered with the online core or the conductor.

The third stage is the setting stage. It is carried out in a cooling tank or cooling pipe, and the plastic extruded cladding is cooled to change from an amorphous plastic state to a solid state.

3. Changes in plastic flow at the plasticizing stage

In the plasticization stage, the plastic is pushed to the head along the screw axis by the screw, and experiences changes in temperature, pressure, viscosity, and even chemical structure, which are different in different sections of the screw. The plasticizing stage is divided into three stages according to the physical state change process of the plastic flow, that is, the feeding section, the melting section, and the homogenization section, which is also the segmentation method that people are accustomed to on the extrusion screw, each segment has different effects on the plastic extrusion, and the plastic presents different forms in each segment, thus showing the extrusion characteristics of the plastic.

In the feeding section, first of all, the softening temperature is provided for the granular solid plastic, and then the shear stress generated between the rotation of the screw and the fixed barrel acts on the plastic particles to achieve the crushing of the softened plastic. The most important is to rotate the screw to generate enough continuous and stable thrust and reverse friction to form a continuous and stable extrusion pressure, so as to achieve the mixing and uniform mixing of broken plastics, and initially implement heat exchange, so as to provide the basis for continuous and stable extrusion. At this stage, whether the thrust generated is continuous, uniform and stable, the shear strain rate is high or low, and whether the crushing and stirring are uniform directly affect the extrusion quality and yield.

In the melting section, the plastic, which has been broken, softened and initially mixed, moves along the screw groove to the head due to the pushing action of the screw, and enters the melting section from the feeding section. In this section of the plastic encountered a higher temperature of heat, which is a heat source, in addition to the point heating outside the barrel, the friction heat of the screw rotation is also playing a role. The thrust from the feeding section and the reaction force from the homogenization section make the plastic form a reflux in the advance, which is generated in the screw groove and the gap between the screw and the barrel, the reflux generation not only makes the material further evenly mixed, but also increases the heat exchange effect of the plastic, to achieve the surface heat balance. Since the action temperature at this stage has exceeded the rheological temperature of the plastic, coupled with the longer action time, the plastic has a change of state, and the material in contact with the heating cylinder begins to melt, forming a layer of polymer melt film on the inner surface of the cylinder. When the thickness of the melt film exceeds the gap between the top of the thread and the cylinder, it will be scraped off by the rotating thread and gather in front of the push thread. Forming a molten pool. Due to the relative movement of the barrel and the root of the thread, the circulating flow of materials is generated in the molten pool. Behind the screw edge is a solid bed (solid plastic). In the process of material moving forward along the screw groove, the depth of the melt groove in the melt section gradually becomes shallower toward the homogenization section, and the solid bed is constantly squeezed toward the inner wall of the barrel, accelerating the heat transfer process from the barrel to the solid bed. At the same time, the rotation of the screw has a shearing effect on the melt film on the inner wall of the barrel, thus melting the material at the interface between the melt film and the solid bed. The width of the solid bed gradually decreases until it completely disappears, that is, from a solid state to a viscous flow state. At this time, the molecular structure of the plastic has undergone a fundamental change, the intermolecular tension is extremely relaxed, if it is a crystalline polymer, the crystal zone begins to reduce, amorphous increase, in addition to the large molecules, the main body completed plasticization, the so-called "preliminary plasticization", and under the action of pressure, the gas contained in the solid material is excluded to achieve preliminary compaction. In the homogenization section, there are several outstanding process characteristics: this section of the screw thread depth is the shallowest, that is, the screw groove volume is the smallest, so this is the working section where the pressure between the screw and the barrel is the largest; In addition, the thrust force from the screw and the reaction force at the screen plate and other places are the direct zones of plastic "hand-to-hand contact"; This section is the highest temperature of the extrusion process, so the radial pressure and axial pressure of the plastic at this stage are the largest, and this high pressure is enough to exclude all the gases contained in the plastic, and make the melt compacted and dense. This section has the "pressure equalization section" is thus called. Due to the effect of high temperature, the polymer that has not been plasticized through the melting section is plasticized in this section, so that the "particles" are finally eliminated, so that the plastic plasticization is fully uniform, and then the plastic that is completely plasticized and melted is quantitatively and at constant pressure uniformly extruded by the head.

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.