Wires and cables, serving as the core carriers for power transmission and information communication, have performance that directly depends on the insulation and sheathing covering processes. With the diversification of modern industry requirements for cable performance, four mainstream processes—extrusion, longitudinal wrapping, helical wrapping, and dip coating—demonstrate unique advantages in different scenarios. This article delves into the material selection, process flow, and application scenarios of each process, providing a theoretical basis for cable design and selection.
1 Extrusion Process
1.1 Material Systems
The extrusion process primarily uses thermoplastic or thermosetting polymer materials:
① Polyvinyl Chloride (PVC): Low cost, easy processing, suitable for conventional low-voltage cables (e.g., UL 1061 standard cables), but with poor heat resistance (long-term use temperature ≤70°C).
② Cross-linked Polyethylene (XLPE): Through peroxide or irradiation cross-linking, the temperature rating increases to 90°C (IEC 60502 standard), used for medium and high-voltage power cables.
③ Thermoplastic Polyurethane (TPU): Abrasion resistance meets ISO 4649 Standard Grade A, used for robot drag chain cables.
④ Fluoroplastics (e.g., FEP): High-temperature resistance (200°C) and chemical corrosion resistance, meeting aerospace cable MIL-W-22759 requirements.
1.2 Process Characteristics
Uses a screw extruder to achieve continuous coating:
① Temperature Control: XLPE requires three-stage temperature control (feed zone 120°C → compression zone 150°C → homogenizing zone 180°C).
② Thickness Control: Eccentricity must be ≤5% (as specified in GB/T 2951.11).
③ Cooling Method: Gradient cooling in a water trough to prevent crystallization stress cracking.
1.3 Application Scenarios
① Power Transmission: 35 kV and below XLPE insulated cables (GB/T 12706).
② Automotive Wiring Harnesses: Thin-wall PVC insulation (ISO 6722 standard 0.13 mm thickness).
③ Special Cables: PTFE insulated coaxial cables (ASTM D3307).
2 Longitudinal Wrapping Process
2.1 Material Selection
① Metal Strips: 0.15 mm galvanized steel tape (GB/T 2952 requirements), plastic coated aluminum tape (Al/PET/Al structure).
② Water-blocking Materials: Hot-melt adhesive coated water-blocking tape (swelling rate ≥500%).
③ Welding Materials: ER5356 aluminum welding wire for argon arc welding (AWS A5.10 standard).
2.2 Key Technologies
The longitudinal wrapping process involves three core steps:
① Strip Forming: Bending flat strips into U-shape → O-shape through multi-stage rolling.
② Continuous Welding: High-frequency induction welding (frequency 400 kHz, speed 20 m/min).
③ Online Inspection: Spark tester (test voltage 9 kV/mm).
2.3 Typical Applications
① Submarine Cables: Double-layer steel strip longitudinal wrapping (IEC 60840 standard mechanical strength ≥400 N/mm²).
② Mining Cables: Corrugated aluminum sheath (MT 818.14 compressive strength ≥20 MPa).
③ Communication Cables: Aluminum-plastic composite longitudinal wrapping shield (transmission loss ≤0.1 dB/m @1GHz).
3 Helical Wrapping Process
3.1 Material Combinations
① Mica Tape: Muscovite content ≥95% (GB/T 5019.6), fire resistance temperature 1000°C/90 min.
② Semiconducting Tape: Carbon black content 30%～40% (volume resistivity 10²～10³ Ω·cm).
③ Composite Tapes: Polyester film + non-woven fabric (thickness 0.05 mm ±0.005 mm).
3.2 Process Parameters
① Wrapping Angle: 25°～55° (smaller angle provides better bending resistance).
② Overlap Ratio: 50%～70% (fire-resistant cables require 100% overlap).
③ Tension Control: 0.5～2 N/mm² (servo motor closed-loop control).
3.3 Innovative Applications
① Nuclear Power Cables: Three-layer mica tape wrapping (IEEE 383 standard LOCA test qualified).
② Superconducting Cables: Semiconducting water-blocking tape wrapping (critical current retention rate ≥98%).
③ High-frequency Cables: PTFE film wrapping (dielectric constant 2.1 @1MHz).
4 Dip Coating Process
4.1 Coating Systems
① Asphalt Coatings: Penetration 60～80 (0.1 mm) @25°C (GB/T 4507).
② Polyurethane: Two-component system (NCO∶OH = 1.1∶1), adhesion ≥3B (ASTM D3359).
③ Nano-coatings: SiO₂ modified epoxy resin (salt spray test >1000 h).
4.2 Process Improvements
① Vacuum Impregnation: Pressure 0.08 MPa maintained for 30 min (pore filling rate >95%).
② UV Curing: Wavelength 365 nm, intensity 800 mJ/cm².
③ Gradient Drying: 40°C × 2 h → 80°C × 4 h → 120°C × 1 h.
4.3 Special Applications
① Overhead Conductors: Graphene-modified anti-corrosion coating (salt deposit density reduced by 70%).
② Shipboard Cables: Self-healing polyurea coating (crack healing time <24 h).
③ Buried Cables: Semiconducting coating (grounding resistance ≤5 Ω·km).
5 Conclusion
With the development of new materials and intelligent equipment, covering processes are evolving towards compositization and digitalization. For example, extrusion-longitudinal wrapping combined technology enables integrated production of three-layer co-extrusion + aluminum sheath, and 5G communication cables use nano-coating + wrapping composite insulation. Future process innovation needs to find the optimal balance between cost control and performance enhancement, driving the high-quality development of the cable industry.
Post time: Dec-31-2025