The oxygen content and appearance of the copper rods produced are different due to the different processes of the two. The copper rod produced by upward drawing is called oxygen free copper rod when the oxygen content is below 10ppm; The copper rod produced by continuous casting and continuous casting is hot rolled under protective conditions, and the oxygen content is within the range of 200-500ppm, but sometimes it is as high as 700ppm. Generally, the copper produced by this method is bright in appearance, and the low oxygen copper rod is sometimes called polished rod.
Copper rod is the main raw material of the cable industry. There are two main production methods - continuous casting and rolling method and upward continuous casting method. There are many production methods for continuous casting and rolling of low oxygen copper rod, which is characterized by that after the metal is melted in the shaft furnace, the copper liquid passes through the holding furnace, chute and tundish, enters the closed mold cavity from the pouring tube, cools with greater cooling intensity, forms the casting billet, and then carries out multi pass rolling. The produced low oxygen copper rod is a hot processing structure, and the original casting structure has been broken, The oxygen content is generally between 200~400ppm. Oxygen free copper rods are basically produced by up drawing continuous casting method in China. After the metal is melted in the induction furnace, it is continuously cast by up drawing through graphite mold, and then cold rolled or cold processed. The oxygen free copper rods produced are of casting structure, and the oxygen content is generally below 20ppm. Due to different manufacturing processes, there are great differences in the structure, oxygen content distribution, impurity form and distribution and many other aspects.
Low oxygen copper rod and oxygen free copper rod have different characteristics due to different manufacturing methods.
1、 About the inhalation and removal of oxygen and its existing state
The oxygen content of cathode copper for producing copper rod is generally 10-50ppm, and the solid solubility of oxygen in copper at room temperature is about 2ppm. The oxygen content of the low oxygen copper rod is generally 200 (175) - 400 (450) ppm, so the oxygen is inhaled in the liquid of copper, while the oxygen free copper rod of the upward drawing method is on the contrary. After the oxygen is kept under the liquid copper for a long time, it is reduced and removed. Generally, the oxygen content of this rod is below 10 - 50 ppm, and the lowest can be up to 1-2 ppm. From the organizational point of view, the oxygen in the low oxygen copper is in the state of copper oxide, It exists near the grain boundary, which can be said to be common for low oxygen copper rods but rare for oxygen free copper rods. The inclusion of copper oxide in the grain boundary has a negative impact on the toughness of the material. However, oxygen in oxygen free copper is very low, so the copper structure is homogeneous and single-phase, which is beneficial to toughness. Porosity is uncommon in oxygen free copper rods, but it is a common defect in low oxygen copper rods.
2、 Difference between hot-rolled structure and cast structure
The low oxygen copper rod has been hot-rolled, so its structure belongs to the hot processing structure. The original casting structure has been broken, and the recrystallization form has appeared when the rod is 8mm long. The oxygen free copper rod belongs to the casting structure, and the grain is coarse. This is the inherent reason why the recrystallization temperature of oxygen free copper is high, and higher annealing temperature is required. This is because recrystallization takes place near the grain boundary. The grain size of oxygen free copper rod is even several millimeters, so there are few grain boundaries. Even through drawing deformation, there are fewer grain boundaries than that of low oxygen copper rod, so higher annealing power is required. The requirement for the successful annealing of oxygen free copper is that the annealing power of the first annealing of the wire drawn from the rod but without casting structure should be 10-15% higher than that of low oxygen copper in the same situation. After continuous drawing, enough allowance shall be reserved for annealing power in the later stage and different annealing processes shall be implemented for low oxygen copper and oxygen free copper to ensure the flexibility of wires in process and finished products.
3、 Inclusion, fluctuation of oxygen content, difference between surface oxide and possible hot rolling defects
The tensile property of oxygen free copper rod is superior to that of low oxygen copper rod in all wire diameters. In addition to the above organizational reasons, oxygen free copper rod has less inclusions, stable oxygen content, no possible defects caused by hot rolling, and the oxide thickness on the rod surface can reach ≤ 15A. 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. If the oxide on the surface of the rod can be made up in the continuous cleaning of the subsequent process, but it is troublesome that there are quite a lot of oxides in the "skin", which have a more direct impact on the wire break of the stay wire. Therefore, in order to reduce the wire break during the drawing of micro fine wires and ultra fine wires, sometimes the copper rod has to be peeled or even peeled for the second time, Objective To remove subcutaneous oxide.
4、 The toughness of low oxygen copper rod is different from that of oxygen free copper rod
Both can be pulled to 0.015mm, but the distance between the low temperature oxygen free copper filaments in the low temperature superconducting wire is only 0.001 mm
5、 There are differences in the economy from the raw material of rod making to the line making.
High quality raw materials are required for manufacturing oxygen free copper rods. In general, when drawing copper wire with diameter>1mm, the advantages of low oxygen copper rod are obvious, while oxygen free copper rod is more advantageous in drawing copper wire with diameter<0.5mm.
6、 The manufacturing process of low oxygen copper rod is different from that of oxygen free copper rod.
The manufacturing process of low oxygen copper rod cannot be transferred to that 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, rod making, wire making and annealing process, it cannot be simply said that the soft and hard of low oxygen copper or oxygen free copper.
