The cable sheath is the outermost protective structure wrapped around the cable. As a core barrier ensuring the safety of the cable's internal structure, it can resist mechanical damage during installation and use, and also provide environmental protection such as waterproofing, chemical corrosion resistance, UV resistance, and ozone resistance. The selection of its materials must consider both compatibility with connectors and environmental adaptability (e.g., flexible sheaths are required in extremely cold environments).
Characteristics and Applications
PVC (Polyvinyl Chloride)
Made from polyvinyl chloride as a base resin, with added stabilizers, plasticizers, etc., it is low in cost, flexible, and strong, possessing fire and oil resistant properties. However, it contains harmful substances, limiting its environmental friendliness. Its performance deteriorates in special environments (such as high temperature and extreme cold), and it is gradually being replaced by more environmentally friendly materials.
PE (Polyethylene)
With its excellent electrical insulation and processing properties, it is widely used in cable insulation and sheathing layers. Low-density PE (LDPE) is flexible and moisture-proof, while high-density PE (HDPE) is hard and wear-resistant. Crosslinking technology (XLPE) enhances its high-temperature deformation resistance, making it more environmentally friendly and with superior performance than PVC.
PUR (Polyurethane)
It has outstanding oil and abrasion resistance, mechanical properties similar to rubber, and combines thermoplasticity and elasticity (TPE characteristics). Suitable for power and signal connections in harsh environments (such as oil-proof and mechanical damage-proof scenarios) in industrial equipment, sensors, and household appliances.
TPE/TPR (Thermoplastic Elastomers)
Excellent low-temperature performance, eliminating the need for the high cost of thermosetting materials. Resistant to chemical corrosion and oil stains, flexible with good surface texture, but its abrasion resistance is inferior to PUR. It is often used in applications requiring high flexibility.
TPU (Thermoplastic Polyurethane Elastomers)
Superior abrasion resistance, high tensile strength, and aging resistance. Available in polyester and polyether types, with a wide hardness range (60HA-85HD). Used in high-strength environments such as marine cables, industrial robots, and mining machinery. It is a mature and environmentally friendly material.
Thermoplastic CPE (Chlorinated Polyethylene)
Suitable for extreme and harsh environments. Lightweight, high hardness, low coefficient of friction, oil and water resistance, and UV resistance. Low cost, commonly used in chemical and outdoor applications.
Ceramicized Silicone Rubber
Excellent fire-retardant properties. After combustion, it forms a hard ceramic shell, maintaining circuit integrity for 90 minutes at 950℃-1000℃. No dripping, low smoke, and non-toxic. With a simple processing technology and higher production efficiency than traditional fire-resistant cables, it is suitable for high-fire-risk locations (such as building fire protection and rail transportation).
The selection of cable sheath materials requires comprehensive consideration of environmental adaptability, mechanical properties, environmental requirements, and cost. From general-purpose PVC/PE to high-performance PUR/TPU, and then to special ceramicized silicone rubber, continuous breakthroughs in material technology provide diversified solutions for the safe operation of cables in extreme environments. In the future, with increasingly stringent environmental regulations and growing demand in emerging fields (such as new energy and intelligent manufacturing), high-performance, environmentally friendly sheath materials will become the mainstream development direction.
How do flame-retardant cables achieve flame retardancy?
Flame-retardant cables achieve their flame-retardant effect primarily through the synergistic effect of material selection, structural design, and flame-retardant mechanisms. This inhibits flame spread, reduces heat release, and minimizes the generation of toxic gases during a fire. The specific methods are as follows:
Core Applications of Flame-Retardant Materials
1. Flame-Retardant Properties of Insulation and Sheath Materials
Adding Flame Retardants: Flame retardants are added to the cable's insulation layer (such as PVC, XLPE) and sheath material. Common types include:
Halogenated Flame Retardants: These release halogen free radicals to capture active hydrogen free radicals in the combustion reaction, inhibiting the combustion chain reaction. However, they may release toxic hydrogen halide gases during combustion.
Halogen-Free Flame Retardants: These release moisture upon thermal decomposition, absorbing heat and diluting combustible gases. They are environmentally friendly flame-retardant materials widely used in low-smoke halogen-free cables.
Phosphorus-Based Flame Retardants: These form a carbonized layer that isolates oxygen during combustion, while simultaneously inhibiting the generation of combustible gases.
1. Flame-retardant modification of the material itself: Flame-retardant polymer materials, such as silicone rubber and fluororubber, are used, as their molecular structure inherently possesses flame-retardant properties.
2. Flame-retardant effect of filling and wrapping materials
Flame-retardant mica tape, fiberglass tape, etc., are used as wrapping layers, or flame-retardant rock wool, ceramicized silicone rubber, etc., are used as filling materials. These materials can form a heat insulation layer at high temperatures, preventing the spread of flames into the cable.
Structural design enhances flame-retardant performance
1. Multi-layer protective structure
Cables typically employ a multi-layer structure of "insulation layer + flame-retardant wrapping layer + sheath layer," with each layer possessing flame-retardant properties, forming multiple fire barriers. For example:
The mica tape wrapping layer forms a hard, ceramic-like shell at high temperatures, isolating flames and heat;
The sheath layer uses flame-retardant PVC or low-smoke halogen-free materials to prevent external flame intrusion.
2. Low-Smoke Halogen-Free Design (Environmentally Friendly Flame-Retardant Cable)
Abandoning traditional halogen-containing materials, this cable utilizes halogen-free flame-retardant polyolefins and other materials. During combustion, it produces low smoke concentration and releases no toxic hydrogen halide gases, making it suitable for densely populated areas (such as subways and hospitals).
Through dual optimization of material innovation and structural design, the flame-retardant cable constructs a complete "prevention-inhibition-isolation" protection system in fire scenarios: from the synergistic effect of flame retardants at the molecular level, to multi-layered thermal insulation barriers at the physical level, and the application of environmentally friendly low-smoke halogen-free materials, it not only significantly improves the cable's fire resistance limit but also greatly reduces secondary fire hazards. As global emphasis on public safety and ecological protection continues to rise, cable products that combine high-efficiency flame retardancy with green environmental characteristics will inevitably become the core choice for rail transit, new energy, and intelligent buildings, providing a solid guarantee for the safe operation and sustainable development of modern society.
