Seamless copper tube for cable
Seamless copper cable tubes are high-precision, tubular copper materials used for cable protection, conductor shielding, and as inner sheaths for high-voltage cables. Due to copper’s high conductivity, corrosion resistance, and mechanical strength, they play a key role in high-voltage power cables, submarine cables, and specialty cables. They typically have an outer diameter of 8-150 mm and a wall thickness of 0.5-5 mm. Customizable to meet cable structural requirements, these tubes are typically made from T2 or T3 copper. In some high-voltage applications, copper alloys such as Cu-Ag and Cu-Cr-Zr are used to enhance high-temperature strength and softening resistance. The seamless structure provides excellent sealing and pressure resistance, effectively protecting the cable’s internal structure from environmental corrosion.
The production process for seamless copper tubes for cables requires precision processes including smelting and casting, hot extrusion, cold rolling, annealing, and surface treatment. First, electrolytic copper with a purity of at least 99.95% is smelted in an industrial frequency induction furnace at a controlled temperature of 1150-1200°C. A phosphorus copper deoxidizer is added to reduce the oxygen content to below 0.003%. An online degassing system removes hydrogen and impurities to ensure the purity of the molten copper. The ingots are then cast using a semi-continuous casting process into solid round ingots with a diameter of 80-200 mm. The cooling rate is controlled during the casting process to avoid pores and cracks. Hot extrusion is the core process for producing seamless tube billets. The ingots are heated to 800-900°C and extruded through an extrusion die into a rough tube in one go. The extrusion ratio is controlled between 8-15 to ensure a smooth, scale-free inner tube surface. Cold rolling gradually adjusts the outer diameter and wall thickness of the pipe through multiple cold rolling passes, with a reduction rate of 10%-20% per pass. Specialized lubricants are used for cooling and lubrication to ensure an outer diameter tolerance of ≤±0.1 mm, a wall thickness tolerance of ≤±0.05 mm, and an inner wall roughness Ra ≤1.6 μm. Annealing is performed according to performance requirements, heating to 300-500°C under nitrogen for 2-4 hours to reduce the pipe’s hardness to HV60-100 and an elongation of ≥25%, meeting bending and processing requirements. Finally, the surface is cleaned and passivated to remove oil and oxide layers and improve corrosion resistance.
The performance advantages of seamless copper tubes for cables make them irreplaceable in the field of cable protection and electrical conductivity. First, excellent electrical and thermal conductivity. The electrical conductivity of T2 copper tubes can reach more than 97% IACS , and the thermal conductivity is ≥ 380W/(m・K) . When used as the inner conductor of the cable, it can efficiently transmit current. When used as a shielding layer, it can quickly conduct interference current. At the same time, it can promptly dissipate the heat generated by the cable during operation and reduce temperature rise. Second, high strength and pressure resistance. The tensile strength of cold-rolled seamless copper tubes can reach 300-400MPa , which can withstand external pressure during cable laying and operation. For example, copper tubes for submarine cables can withstand high pressure in the deep sea to ensure that the internal insulation layer is not damaged. Third, good sealing. The seamless structure and high-precision dimensions ensure the airtightness and watertightness of the pipes, which can effectively prevent moisture, humidity and corrosive media from invading the interior of the cable and extend the service life of the cable. Fourth, excellent corrosion resistance. The oxide film formed on the copper surface can resist corrosion from the atmosphere, seawater and other environments. In complex environments such as coastal areas and underground, the service life can reach 30 years. Over 100 years, nickel-plated or chrome-plated copper tubes have better corrosion resistance; fifthly, good processing performance. The annealed copper tubes have good flexibility and can be bent, welded and other processes to adapt to the complex paths when laying cables.
In application scenarios, seamless copper tubes for cables are an important component of high-end cables. In the field of high-voltage power cables, 110kV and above cross-linked polyethylene insulated cables often use seamless copper tubes as metal shielding layers and inner sheaths, which are wrapped around the cable core by longitudinal wrapping or welding, which not only shields the electric field but also protects the insulation layer from mechanical damage. For example, 220kV cables often use T2 copper tubes with an outer diameter of 30-50 mm and a wall thickness of 1-2 mm. In the field of submarine cables, the armor layer of deep-sea cables uses thick-walled seamless copper tubes (wall thickness 2-5 mm), which have both mechanical protection and anti-corrosion functions, and can resist seawater pressure and marine organism attachment. In the field of special cables, the sheaths of high-temperature cables and flame-retardant cables use seamless copper tubes, which take advantage of their high-temperature resistance and fire resistance to adapt to high-temperature environments such as metallurgy and chemical industry. In rail transit cables, the feeder cables of subways and light rails use seamless copper tubes as outer sheaths to improve the vibration resistance and wear resistance of the cables. In the field of new energy, the collector cables of photovoltaic power stations and wind farms use seamless copper tube shielding layers to ensure stable operation in harsh outdoor environments.
Industry trends indicate that seamless copper tubes for cables are moving toward thinner walls, higher strength, and more complex functions. Continuous breakthroughs in thin-wall copper tube production technology have enabled the stable production of high-precision copper tubes with wall thicknesses under 0.3 mm, suitable for miniaturized cables and reducing material consumption. High-strength alloy copper tubes, by adding elements such as chromium and zirconium, achieve tensile strength exceeding 500 MPa while maintaining high conductivity (≥90% IACS), making them suitable for high-voltage and long-span cables. Composite copper tubes are becoming increasingly popular, such as copper-aluminum composite tubes, which combine the conductivity of copper with the lightweightness of aluminum, reducing cable weight and cost. Copper tubes with smooth inner surfaces reduce friction during cable installation and protect the insulation layer. Furthermore, the promotion of green production processes, using recycled copper raw materials and environmentally friendly lubricants, reduces energy consumption and pollution during production, and has increased the copper tube recycling rate to over 95%. With the rapid development of ultra-high voltage transmission, deep-sea development, and the new energy industry, demand for high-performance seamless copper tubes for cables will continue to grow, driving the industry to achieve greater breakthroughs in material research and development, process optimization, and performance enhancement.
