Most of the wire and cable products are products with the same cross-section (cross-section) shape (ignoring manufacturing-related errors) and long strips, which are used as features in the system or equipment to form lines or coils. Determined. Therefore, research and analysis of the structural composition of cable products, only need to observe and analyze from its cross section.
The structural components of wire and cable products can be divided into four main structural components: wire, insulation, shielding and sheath, as well as filling components and tensile components. According to the product requirements and application, some products have extremely simple structure, only one structural part of the wire, such as overhead bare wire, contact wire, copper-aluminum bus (bus bar), etc.; the external electrical insulation of these products depends on installation and installation. It is ensured by insulators and space distance (ie, insulated by air).
1, the wire
The wire is the most essential and essential component of the product for current or electromagnetic wave information transmission. The wire is an abbreviation for the conductive core, and is made of non-ferrous metal with excellent electrical conductivity such as copper or aluminum. Optical cables for optical communication networks that have been rapidly developed in the past three decades have used optical fibers as wires.
It is a member that is electrically insulated around the periphery of the wire. That is, it can ensure that the transmitted current or electromagnetic wave and light wave travel only along the wire without flowing to the outside, and the potential (ie, the potential difference formed by the surrounding object, that is, the voltage) on the conductor can be isolated, that is, the normal transmission of the wire must be ensured. Function, but also to ensure the safety of external objects and people.
Wires and insulation are the two basic components that must be available to form a cable product (except for bare wires).
3, protective layer
When wire and cable products are installed and operated in a variety of different environments, they must have components that protect the entire product, especially the insulating layer. This is the sheath.
Because insulation materials are required to have excellent electrical insulation properties, the purity of the materials must be extremely high, and the impurity content is extremely small; often, the ability to protect the outside world cannot be taken into consideration, so the external environment (ie, installation, use, and use) The tolerance or resistance of various mechanical forces, the resistance to the atmosphere, the resistance to chemicals or oils, the prevention of biological damage, and the reduction of fire hazards must be borne by various sheath structures.
Many cable products used in a good external environment (such as clean, dry, no mechanical external force), or products with a certain mechanical strength and weather resistance, can be without the protective layer. .
It is a member that isolates the electromagnetic field in the cable product from the external electromagnetic field; the cable product also needs to be isolated from each other between different pairs (or groups). It can be said that the shielding layer is an "electromagnetic isolation screen".
For many years, the industry has been accustomed to using the shield as part of the sheath structure, which the author believes should be used alone as a component. The reason is that the function of the shielding layer is electromagnetic isolation—that is, the information transmitted in the cable product does not leak out, and does not interfere with external instruments or other lines; the external electromagnetic waves do not enter the cable through electromagnetic coupling. In the product, these functional requirements are different from the traditional sheath functions. Also, because the shielding layer is not disposed outside of the product, it is placed between the grouping of each pair or multiple logarithmic cables. In the past ten years, with the rapid development of wire and cable for information transmission systems and the increasing number of electromagnetic wave interference sources in the atmosphere, the variety of shielding structures has been multiplied, and the shielding layer is used as a cable product. The understanding of a basic component has become more and more recognized.
5, the filling structure
Many wire and cable products are multi-core. For example, low-voltage power cables are mostly four-core and five-core cables (for three-phase systems). The city's telephone cables are 800 pairs, 1200 pairs, 2400 pairs to 3600 pairs. After these insulated cores or pairs are cabled (or bundled multiple times), one is not rounded, and the other is that there is a large gap between the insulated cores. Therefore, it is necessary to add a filling structure when filling the cable. The structure is to make the outer diameter of the cable relatively round to facilitate the wrapping and squeezing of the sheath, and also to make the cable structure stable and internal stone, and the force is uniform during use (stretching, compressing and bending in manufacturing and laying) Does not damage the internal structure of the cable. Therefore, although the filling structure is an auxiliary structure, it is also necessary, and its material selection and shape design are also detailed.
6, tensile components
The traditional wire and cable products use the armor layer of the sheath to withstand the pulling force caused by external tension or self-weight. The typical structure is steel tape armor and steel wire armor (for example, the submarine cable should be φ8mm thick steel wire, twisted synthetic armor layer). However, in order to protect the optical fiber from small pulling force, the optical fiber cable is provided with primary and secondary coatings and special tensile force-receiving components in the optical cable structure to prevent the optical fiber from being slightly deformed and affecting the transmission performance. In addition, if the earphone cord of the mobile phone is made of a thin copper wire or a thin copper strip wound around the synthetic fiber, the synthetic fiber is a tensile element. In short, the tensile element plays a major role in products that have been developed in recent years and that are particularly small and flexible, and that require multiple bends and twists.