Oxygen-Free Copper, abbreviated as OFC, generally refers to Copper with a 99.995% purity. Theoretically, oxygen-free copper is pure copper without oxygen or any residue of deoxidizer, but in fact, it contains trace oxygen and some impurities. The standard explains the content of oxygen is not more than 0.003%, the total content of impurities is not more than 0.05%, and the purity of copper is more than 99.95%. Oxygen-free copper is characterized by no hydrogen embrittlement, high electrical conductivity, good processing and welding properties, corrosion resistance and low-temperature performance, has been widely used in audio equipment, vacuum electronic devices, cables and other electrical and electronic applications.
The oxygen-free copper often shaped in oxygen-free copper plate, oxygen-free copper strip, oxygen-free copper wires and so on. It includes linear crystalline oxygen-free copper or crystalline oxygen-free copper (LC-OFC) with purity above 99.995% and single oxygen-free crystal copper (OCC) with purity above 99.996%, which can be further divided into PC-OCC and UP-OCC, etc. Single crystal oxygen-free Copper produced by UP-OCC technology (Ultra Pure Copper by Continuous Casting Process) has no direction, high purity, corrosion resistance and extremely low electrical impedance, making the copper wire suitable for high-speed and high-quality signal transmission.
The smelting of oxygen-free copper
Oxygen-free copper is mainly smelted in a power frequency cored induction furnace or vacuum induction furnace. In order to ensure the quality of oxygen-free copper, the raw materials of electrolytic copper-containing W (Cu) > 99.97% and W (Zn) < 0.003% are generally selected, and to reducing the source of gas and covering with calcined charcoal on the surface of the molten pool, and trace phosphorus can also be added as deoxidizer. In the semi-continuous casting process, the refining process of the melt in the smelting furnace and the holding furnace is not subject to time constraints, and the casting temperature is 1150-1180℃. Continuous casting is different, the quality of the copper liquid not only depends on the refining quality of the smelting furnace and the holding furnace but also depends on the stability of the whole system and the whole process.
The properties of oxygen-free copper
Good formability. Oxygen-free copper has an excellent performance in both cold and hot processing. It can be stretched, rolled, extruded, bent, pressed, shearing, spinning, upsetting, rotary forging, forging, thread pressing, foaming and winding. Its malleability is 65% of that of forged brass. The thermal processing temperature is 800-900℃.
Good weldability. It is easy for fusion welding, soft brazing, hard brazing, gas shielded tungsten arc welding, gas-shielded metal arc welding. The performance of oxygen fuel gas welding is good. Shielded metal arc welding and most resistance welding methods are not recommended.
Machining and grinding performance. The machinability of oxygen-free copper is 20% of that of free-cutting brass C36000.
Applications of oxygen-free copper
High purity, excellent electrical conductivity, thermal conductivity, thermal processing performance and good welding performance, no “hydrogen embrittlement” or very little “hydrogen embrittlement” make oxygen-free copper widely used in electrical vacuum instrument parts, such as bus-bars, conductive bars, waveguides, coaxial cables, vacuum seals, vacuum tubes, transistor components, etc.