C11000 Soft Annealed Copper Foil for Transformer Windings
2026-07-02
With the global trend towards higher power density, miniaturization, and higher energy efficiency in power equipment, foil windings have become the mainstream structural solution for distribution transformers, new energy transformers, and high-frequency reactors due to their high space utilization, excellent heat dissipation, and strong short-circuit withstand capability. C11000 soft annealed copper foil, as the core conductive substrate for foil windings, directly determines the manufacturing efficiency and long-term operational reliability of the windings through its material purity, performance uniformity, and surface quality. Haomei Aluminum, leveraging its mature copper processing and heat treatment technology system, has launched C11000 soft annealed copper foil conforming to ASTM B152 standards, providing global transformer customers with a high-quality substrate solution suitable for high-speed foil winding processes.
C11000 copper foil belongs to the electrolytically toughened copper (ETP) grade and is a commonly used winding conductive material in the international transformer industry. Haomei Aluminum uses high-purity cathode copper as raw material, employing precise smelting and continuous casting processes to ensure a total copper-silver content of no less than 99.90% in the finished product. The proportion of harmful elements such as oxygen, sulfur, and bismuth is strictly limited, with oxygen content consistently controlled below 0.02%, avoiding the risks of grain boundary embrittlement and hydrogen embrittlement under high-temperature operation. The intrinsic conductivity of the material reaches 100%~101% IACS, allowing for a reduction in winding cross-sectional area and overall transformer size for the same current carrying capacity. Under high-frequency operating conditions, the uniform material structure reduces additional losses caused by the skin effect, comprehensively optimizing transformer load losses and temperature rise performance, and meeting the design requirements of high-efficiency and energy-saving transformers.
Soft annealing is a core process ensuring the forming performance and consistency of copper foil for transformer. Addressing industry pain points such as easy oxidation, adhesion, and uneven performance in the heat treatment of thin copper foil, Haomei Aluminum uses a continuous inert gas protected soft annealing production line. Through segmented and precise temperature control, complete recrystallization is achieved, completely eliminating lattice distortion and residual stress caused by cold rolling, allowing the copper foil to reach a stable and completely soft state. The finished copper foil exhibits a uniform Vickers hardness control within the range of HV55 to HV65, with a full-width hardness deviation not exceeding HV5. It boasts an elongation at break ≥35% and excellent bending and bonding performance. During winding, it exhibits no springback or cracking, tightly conforming to the curved surface of the winding skeleton with no gaps between turns, effectively improving the winding fill factor and preventing long-term fatigue cracking caused by residual stress.
In terms of precision machining, this series of copper foils covers a thickness range of 0.05mm to 1.0mm. Customized cutting widths can be achieved according to customer winding designs, with thickness tolerances strictly controlled within ±0.005mm and side straightness ≤1mm/m. It is compatible with high-speed foil winding machines for continuous automated production. The strip edges are finished with a specialized rounded-edge grinding process to remove burrs and sharp corners, preventing partial discharge faults caused by sharp protrusions piercing the insulation paper between winding layers. The surface is cleaned to remove residual oil, oxide spots, and scratches, exhibiting uniform roughness. This allows for direct compatibility with insulation layer lamination and vacuum impregnation processes without additional pretreatment, effectively shortening customer production cycles.
Haomei Aluminum has established a full-process quality traceability system for C11000 soft-annealed copper foil for transformer winding. From casting to finished product, each process undergoes online testing and sampling re-inspection. Complete material certificates and performance reports are included with each shipment, meeting international power equipment access standards. Products support large-roll customization, reducing the number of winding joints, lowering the risk of welding defects and joint losses, and adapting to large-scale mass production needs. Customized solutions such as tin plating for oxidation resistance and single-sided passivation are also available, widely used in dry-type distribution transformers, photovoltaic and wind power step-up transformers, high-frequency reactors, and other fields.
With the advancement of new power system construction, the performance requirements for conductive substrates in transformers continue to increase. Haomei Aluminum continuously optimizes copper foil processing and annealing processes, providing reliable winding substrate support to transformer manufacturers worldwide with stable material properties, precise dimensional control, and customized services, helping power equipment upgrade towards greater efficiency, compactness, and longer lifespan.