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Basic knowledge of wire and cable
- Jun 23, 2018 -

Wire and cable manufacturing process overview


     The manufacture of wire and cable is totally different from that of most electromechanical products. Electromechanical products are usually used to assemble parts into parts and then assemble multiple parts into a single product. The product is measured in units or pieces. Wire and cable is based on the length of the basic unit of measurement. All electric wires and cables are started from conductor processing. The outer layer of the conductor is insulated, shielded, cabled, sheathed, etc. to form wire and cable products. The more complex the product structure, the more layers are stacked.


First, the technical characteristics of wire and cable products manufacturing:


1. Large-length continuous superposition combined production method


Large-length continuous superposition of combined production methods, the impact on the production of wire and cable is global and control, which involves and affects:


(1) Production process and equipment layout


All kinds of equipment in the production workshop must be reasonably discharged according to the process flow required by the product, so that the semi-finished products in each stage are transferred in turn. The equipment configuration must consider the production efficiency to be different and balance the production capacity. Some equipment may have to configure two or more units in order to balance the production capacity of the production line. Therefore, the rational selection and combination of equipment and the layout of production sites must be balanced based on the product and production volume.


(2) Production Organization Management


The production organization and management must be scientific, reasonable, accurate, and meticulous. The operator must be meticulously executed according to the process requirements. Any problems in any link will affect the smoothness of the technological process and affect the quality and delivery of the product. Especially for multi-core cables, if the length of a certain pair or basic unit is short, or the quality is problematic, the entire length of the cable will be insufficient, resulting in scrap. Conversely, if a unit is too long, it must be sawn for waste.


(3) Quality Management


Large-length continuous superimposed combination of production methods, so that any part of the production process, an instant problem, it will affect the quality of the entire cable. The more the quality defect occurs in the inner layer, and the failure to discover the termination of production in time, the greater the damage caused. Because the production of wires and cables is different from that of assembled products, they can be dismantled and replaced with other parts; the quality of any component or process of wires and cables is almost irretrievable and remediable for this cable. Afterwards, the treatment is very negative. It is not a matter of shortening or downgrading, or scrapping the entire cable. It cannot be opened and reinstalled.


The quality management of wire and cable must go through the entire production process. The quality management and inspection department must carry out a thorough inspection of the entire production process, operator self-inspection, and mutual inspection of the upper and lower processes. This is an important guarantee and means for ensuring product quality and improving the economic efficiency of enterprises.


2. Many types of production technology, large material flow


Wire and cable manufacturing involves a wide range of processes, from smelting and pressure processing of non-ferrous metals to chemical technologies such as plastics, rubber, and paint; textile technologies such as wrapping and weaving of fiber materials; and wrapping and metal strips for metal materials. The vertical package, welding metal forming process and so on.


The various materials used in wire and cable manufacturing are not only of different types, specifications, and specifications, but also large quantities. Therefore, the amount of various materials, reserves, batch cycle and batch must be approved. At the same time, the dismantling, recycling, recycling, and waste disposal of waste products are an important part of management, and do a good job in managing material quotas and paying attention to conservation.


In the production of wires and cables, from the entry and exit of raw materials and various auxiliary materials to the storage, the flow of semi-finished products in each process is transferred to the storage and delivery of products, and the material flow rate is large. It must be rationally distributed and dynamically managed.


3. Special equipment


The production of wire and cable uses special production equipment with the technological characteristics of the industry to meet the requirements of the structure and performance of cable products, meet the requirements for large-length continuous and high-speed production, and thus form a series of special equipment for cable manufacturing. Such as extrusion machine series, cable machine series, stranding machine series, around the charter series.


The manufacturing process of wire and cable is closely related to the development of special equipment and promote each other. The new process requirements promote the generation and development of new special equipment; in turn, the development of new special equipment has boosted the promotion and application of new processes. Such as drawing, annealing, extrusion series line; physical foam production line and other special equipment, promote the development of wire and cable manufacturing process and improve, improve the cable's product quality and production efficiency.


Second, the main process of wire and cable


Wire and cable are manufactured through three processes: drawing, stranding, and cladding. The more complex the model specifications, the higher the repeatability.


1. Draw


In metal press working, the technical process of forcing the metal through a die (pinch roller) under the action of an external force, compressing the cross-sectional area of the metal, and obtaining the required cross-sectional shape and dimensions is called metal drawing.


Drawing process points: monofilament drawing and strand drawing.


2. Stranded


In order to improve the flexibility and overall degree of wire and cable, two or more single wires are intertwined in the specified direction and are called twisted.


Stranding process points: conductor stranding, cable, weaving, wire mounting and winding.


3. Coating


According to different performance requirements for wire and cable, special equipment is used to coat different materials on the outside of the conductor. Coating process:


A. Extrusion: rubber, plastic, lead, aluminum and other materials.


B. Vertical package: rubber, wrinkle aluminum strip material.


C. Wrapping: banded paper tape, mica tape, alkali-free glass fiber tape, non-woven fabric, plastic tape, linear cotton yarn, silk and other fiber materials.


D. Dipping: Insulating paint, asphalt, etc.


Third, the basic process of plastic wire and cable manufacturing


1. Copper and aluminum monofilaments


Copper and aluminum rods, commonly used in wire and cable, are stretched at one or several passes through a drawing machine at room temperature to reduce the cross section, increase the length, and increase the strength. Drawing is the first process of each wire and cable company, and the main process parameter of drawing is the matching technology.


2. Monofilament annealing


The copper and aluminum monofilaments are heated to a certain temperature to increase the toughness of the monofilaments and reduce the strength of the monofilaments in a manner of recrystallization to meet the requirements of the wire and cable for the conductive cores. The key to the annealing process is to eliminate the oxidation of the copper wire.


3. Stranding of conductors


In order to improve the flexibility of the wire and cable, in order to facilitate the laying and installation, the conductive core is formed by twisting multiple monofilaments. From the twisted form of the conductive core, it can be divided into regular twisting and irregular twisting. Irregular stranding is further divided into bundle stranding, concentric twin stranding, and special stranding.


In order to reduce the occupied area of the wire and reduce the geometric size of the cable, a tightly-pressed form is adopted while the conductor is stranded, so that the ordinary round shape is mutated into a semicircle, a fan shape, a tile shape, and a tightly-pressed round shape. This type of conductor is mainly used in power cables.


4. Insulation extrusion


Plastic wire and cable are mainly extruded solid insulation layer, the main technical requirements for plastic insulation extrusion:


4.1. Eccentricity: The deviation from the extruded insulation thickness is an important indicator of the level of extrusion technology. Most of the product's structural dimensions and their deviations are clearly defined in the standard.


4.2. Smoothness: The surface of the extruded insulating layer is required to have a smooth surface, and no undesirable quality problems such as surface roughness, burnt, and impurities are allowed.


4.3. Density: The cross-section of the extruded insulation layer should be dense and solid, with no visible pinholes, to prevent the presence of air bubbles.


5. Cable


For the multi-core cable, in order to ensure the degree of molding and reduce the appearance of the cable, it is generally required to twist it into a round shape. The mechanism of stranding is similar to that of conductor stranding. Because of the large diameter of the twisted section, most of the strands are not twisted back. The technical requirements for cabling are as follows: First, to prevent the twisting of the cable caused by the inconvenience of the insulated wire core; and secondly, to prevent the insulating layer from being scratched.


Most of the cables are completed with the completion of two other processes at the same time: one is padding to ensure roundness and stability of the cable after the cable is laid, and the other is tying to ensure that the cable core is not loose.


6. Inner sheath


In order to protect the insulated wire core from being scratched by armouring, proper protection of the insulating layer is required. The inner protective layer is divided into: the inner sheath (separator sheath) and the inner sheath (cushion). The padding layer instead of the binding band is synchronized with the cabling process.


7. Decoration


Laying in underground cables, the work may be subject to a certain positive pressure, the choice of internal steel strip armored structure. When cables are laid in places where there is both positive pressure and tensile force (such as in water, vertical shafts, or soils with large gaps), the structure with internal steel wire armor should be used.


8. Outer sheath


The outer sheath is the part of the structure that protects the insulation of the wire and cable from environmental factors. The main role of the outer sheath is to improve the mechanical strength of the wire and cable, prevent chemical corrosion, moisture, water leaching, and prevent the cable from burning. According to the different requirements of the cable, the plastic jacket is directly squeezed by the extruder.