Oxygen copper rod and oxygen free copper rod have their own 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 is about 2ppm at room temperature. The oxygen content of the low oxygen copper rod is generally 200 (175) - 400 (450) ppm, so the oxygen is inhaled in the liquid copper, while the oxygen free copper rod of the upward drawing method is on the contrary. After being kept in the liquid copper for a long time, the oxygen is reduced and removed. Generally, the oxygen content of this rod is below 10 ~ 50ppm, with a minimum of 1 ~ 2ppm. From the perspective of structure, the oxygen in the low oxygen copper exists near the grain boundary in the form of copper oxide, This is common for low oxygen copper rods, but rare for non oxygen copper rods.

Copper oxide appears at the grain boundary in the form of inclusions, which has a negative effect on the toughness of the material. The oxygen content in oxygen free copper is very low, so the microstructure of this copper 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

Due to hot rolling, the structure of low oxygen copper rod belongs to hot working structure. The original casting structure has been broken, and recrystallization has occurred in the form of 8mm rod, while the oxygen free copper rod belongs to casting structure, with coarse grains. 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 occurs near the grain boundary. The oxygen free copper rod has coarse grains, and the grain size can even reach several millimeters. Therefore, the grain boundary is small. Even through drawing deformation, the grain boundary is relatively small compared with the oxygen free copper rod. Therefore, higher annealing power is required.

The requirements for successful annealing of oxygen free copper are as follows: for the first annealing of the wire drawn from the rod but without casting structure, the annealing power should be 10 ~ 15% higher than that of low oxygen copper in the same case. After continuous drawing, sufficient margin shall be reserved for annealing power in the later stage and different annealing processes shall be implemented for low oxygen copper and non oxygen copper to ensure the softness of products in process and finished wires.

(3) Inclusions, oxygen content fluctuations, surface oxides and possible hot rolling defects

Compared with low oxygen copper rod in all wire diameters, oxygen free copper rod is superior to low oxygen copper rod. In addition to the above structural reasons, oxygen free copper rod has less inclusions, stable oxygen content, no defects that may occur during hot rolling, and the thickness of oxide on the rod surface can be ≤ 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 surface oxide of the rod can be made up in the continuous cleaning of the subsequent process, but it is troublesome that a considerable amount of oxide exists in the "subcutaneous", which has a more direct impact on the wire breaking. Therefore, in order to reduce the wire breaking during the drawing of micro fine wire and ultra-fine wire, sometimes the copper rod has to be peeled, or even the reason for the secondary peeling, in order to remove the subcutaneous oxide.

(4) The toughness of low oxygen copper rod is different from that of non oxygen copper rod

Both of them can be pulled to 0.015mm, but the spacing between the wires of low-temperature oxygen free copper in low-temperature superconducting wire is only 0.001mm

(5) There are differences in the economy from the raw materials for rod making to the production line.

High quality raw materials are required for manufacturing oxygen free copper rods. Generally, when drawing copper wire with diameter >1mm, low oxygen copper rod has obvious advantages, while oxygen free copper rod is more superior to drawing copper wire with diameter <0.5mm.

(6) The wire making process of low oxygen copper rod is different from that of non oxygen copper rod.

The wire making process of low oxygen copper rod cannot be changed to that of non oxygen copper rod. At least the annealing process of the two is different. Because the softness of the wire is deeply affected by the material composition, rod making, wire making and annealing process, we can not simply say that low oxygen copper or oxygen free copper is the soft and the hard.

Copper has high conductivity and thermal conductivity, good weldability, excellent plasticity and ductility, excellent cold working performance and non-magnetic, while dispersed oxygen free copper overcomes the shortcomings of low yield strength after annealing and poor creep resistance at high temperature. It has the characteristics of high temperature, high strength and high thermal conductivity, and is highly valued by electronic materials experts. Copper and its alloys have been widely used in the electronic industry. In vacuum electronic devices, oxygen free copper has ranked first among the seven structural materials in the field.

Oxygen content is one of the most important properties of oxygen free copper. Since the amount of oxygen and copper is very small, the oxygen in oxygen free copper actually exists in the form of Cu2O. At high temperature, hydrogen diffuses in copper at a great speed, meets Cu2O and reduces it, producing a large amount of water vapor.

The amount of water vapor is proportional to the oxygen content of copper. For example, for copper with 0.01% oxygen content, after annealing, 14cm3 of water vapor will be formed in 100g of copper. The water vapor cannot be diffused through dense copper. Therefore, in the place where Cu2O exists, a pressure of several thousand MPa will be generated, which will destroy the copper, produce embrittlement and lose Vacuum Densification. Therefore, the oxygen content must be strictly limited.

Source: website of Lvxing Metal Co., Ltd

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