We all know that cables are indispensable in our lives, and for some cables, cable sheathing is essential. Cable sheathing also plays a vital role in ensuring the proper operation of cables. Because cables come in a wide variety of specifications and types, with varying performance, the required cable sheathing must possess different properties and materials.
1. What is Cable Sheathing?
The cable sheath is the outermost layer of the cable, such as VV for polyvinyl chloride insulation and PVC sheathing. The outer tube is called a protective tube.
High-density polyethylene. Compared to MDPE (medium-density polyethylene) and LD/LLD (low-density/linear low-density polyethylene), HDPE has a more regular molecular chain structure, with fewer and shorter branches. These branches are neatly arranged, with smaller distances between the chains and stronger interchain forces. These short-range structural characteristics of HDPE contribute to its fundamental properties: higher density, better crystallinity, higher crystallinity, and stronger interlayer forces. Macroscopically, the material exhibits high density, superior mechanical properties such as tensile strength compared to LLD/LD/MD, high hardness, excellent abrasion resistance, and good chemical corrosion resistance. However, due to its slightly poor melt flowability and material flexibility, higher processing requirements are imposed.
II. Cable Sheath Materials and Properties
1. Polyvinyl Chloride (PVC)
PVC is an inexpensive, relatively flexible material. By adding various additives, it can be made heat-resistant and oil-resistant. Its most significant feature is flame retardancy, making it widely used in fire protection applications.
PVC is one of the world's most produced plastics, offering a wide range of applications with low cost. PVC resin is a white or light yellow powder. Depending on the application, various additives can be added to achieve varying physical and mechanical properties. By adding appropriate amounts of plasticizers to PVC resin, a variety of hard, soft, and transparent products can be produced. It is widely used in building materials, industrial products, daily necessities, floor coverings, floor tiles, artificial leather, pipes, wire and cable, packaging film, bottles, foam materials, sealing materials, and fibers.
2. Polyethylene (PE)
PE is a thermoplastic resin made by polymerizing ethylene. It contains no halogens and is considered an environmentally friendly material. PE is odorless, non-toxic, and has a waxy feel. It has excellent low-temperature resistance (minimum operating temperature can reach -100°C to -70°C) and good chemical stability, resisting corrosion from most acids and bases (but not oxidizing acids). It is insoluble in common solvents at room temperature, has low water absorption, and offers excellent electrical insulation. However, it is relatively rigid and more expensive than PVC. By adding other substances, it can achieve a wide range of properties, similar to PVC.
3. Rubber
Rubber is a highly elastic polymer material with reversible deformation. It is elastic at room temperature and can deform significantly under minimal external force, returning to its original shape upon removal. It possesses high strength (toughness) and flexibility. However, it is more expensive than PVC and is heavier, leading to a gradual decline in its use in the fabrication industry.
Types of rubber include natural rubber (NR), chloroprene rubber (CR) with excellent environmental properties, and ethylene propylene rubber (EPM) with excellent heat resistance.
4. Silicone Rubber (Si)
Si is a highly active adsorption material. Silicone rubber, primarily composed of silicon dioxide, is chemically stable and non-flammable. It offers high-temperature resistance, cold resistance, corrosion resistance, excellent electrical insulation, and excellent water resistance, and is generally used in high-grade insulation and waterproofing materials. However, its disadvantages include low strength and high price.
5. Polyurethane (PU)
PU is an emerging organic polymer material, known as the "fifth plastic." Its excellent performance has led to its widespread use in numerous sectors of the national economy. Applications include light industry, chemicals, electronics, textiles, healthcare, construction, building materials, automotive, defense, aerospace, and aviation. It is also widely used in flexible cables, offering superior friction properties compared to PVC, but is more expensive.
6. Fluororesins (ETFE/FEP/PTFE, etc.)
Fluororesins can be used as heat-resistant wires when used in single-core wires, and they also offer heat resistance when used in cables. Due to its high heat resistance, it maintains excellent heat-resistance even with a thin coating, allowing for a thinner outer diameter. Furthermore, its excellent sliding properties make it suitable for mobile cables, preventing friction between the insulation sheaths.
7. Polyester (PBT)
PBT is a material that has only recently gained popularity as an insulation material for flexible cables requiring excellent sliding properties. It is also cheaper than fluororesin.
The above provides an overview of cable sheathing, including materials and properties. However, it's important to note that cables are categorized as either sheathed or unsheathed. Cable sheathing must be highly abrasion-resistant and meet these requirements.
