Low-oxygen Copper Rod VS Oxygen-free Copper Rod
Low-oxygen copper rod: The copper rod produced by continuous casting and rolling method is hot-rolled under protective conditions. The oxygen content is in the range of 200-500ppm, but sometimes it is as high as 700ppm. Generally, the copper produced by this method has a bright surface, which is called low-oxygen copper rod, sometimes it is also called polished rod.
Copper rod produced by oxygen-free copper up-casting method is called oxygen-free copper rod when the oxygen content is below 10ppm.
About the inhalation and removal of oxygen and its state of existence
The oxygen content of cathode copper for producing copper rod is generally 10-50ppm, and the solid solubility of oxygen in copper is about 2ppm at room temperature. The oxygen content of low-oxygen copper rod is generally 200 (175) - 400 (450) ppm, so the oxygen is inhaled in the liquid state of copper. From the perspective of microstructure, oxygen in low-oxygen copper exists near the grain boundary in the form of copper oxide, which is common for low-oxygen copper rods, but rare for oxygen-free copper rods. The appearance of copper oxide in the form of inclusion at the grain boundary has a negative impact on the toughness of the material. However, the oxygen in oxygen-free copper is very low, so the microstructure of this copper is uniform and single-phase, which is beneficial to toughness.
Difference between hot-rolled structure and cast structure
Low-oxygen copper rod is hot-rolled, so its structure belongs to hot-working structure. The original casting structure has been broken, and the form of recrystallization has appeared when the rod is 8mm, while oxygen-free copper rod belongs to casting structure, with coarse grains. The requirement for successful annealing of oxygen-free copper is that the annealing power of the first annealing of the wire drawn from the rod without casting structure should be 10-15% higher than that of the low-oxygen copper in the same situation. After continuous drawing, sufficient margin shall be reserved for annealing power at the later stage and different annealing processes shall be implemented for low-oxygen copper and oxygen-free copper to ensure the flexibility of products in process and finished wires.
Difference between oxygen content fluctuation and possible hot rolling defects
The stretchability of oxygen-free copper rod is superior to that of low-oxygen copper rod in all wire diameters. In addition to the above structural reasons, oxygen-free copper rod has less inclusions, stable oxygen content and no defects that may occur during hot rolling. In the process of continuous casting and rolling, if the process is unstable and the oxygen monitoring is not strict, the unstable oxygen content will directly affect the performance of the rod.
Toughness difference between low-oxygen copper rod and oxygen-free copper rod
Both can be pulled to 0.015mm, but the distance between the fine wires of low-temperature grade oxygen-free copper in the low-temperature superconducting wire is only 0.001mm.
Economic difference between raw materials and production lines
The manufacturing of oxygen-free copper rods requires high-quality raw materials. Generally, when drawing copper wire with diameter>1mm, the advantages of low-oxygen copper rod are obvious, while the advantages of oxygen-free copper rod are more obvious when drawing copper wire with diameter<0.5mm.
Difference of wire making process
The wire manufacturing process of low oxygen copper rod cannot be transferred to the wire manufacturing process of oxygen free copper rod, at least the annealing process of the two is different. Because the flexibility of the wire is deeply affected by the material composition and the rod making, wire making and annealing process, it can not be simply said that low oxygen copper or oxygen-free copper is soft and hard.
