Low-oxygen copper rods vs. oxygen-free copper rods, dont be confused anymore

Copper rods are the main raw material in the cable industry. Due to different production processes, the oxygen content and appearance of the produced copper rods vary. Due to the difference in manufacturing methods, they are divided into low-oxygen copper rods and oxygen-free copper rods, each with its own characteristics. Today, the editor of Zhonglan Network will introduce the differences between the two

Low-oxygen copper rods vs. oxygen-free copper rods

Low-oxygen copper rods: Copper rods produced by the continuous casting and continuous rolling method are hot-rolled under protective conditions, with an oxygen content ranging from 200 to 500ppm, but sometimes it can even exceed 700ppm. Generally, the copper produced by this method has a bright surface and is called low-oxygen copper rods, sometimes also referred to as smooth rods.

Oxygen-free copper rods: Copper rods produced by the continuous casting method are called oxygen-free copper rods when the process is appropriate and the oxygen content is below 10ppm.

1. Regarding the inhalation and removal of oxygen and its state of existence

The oxygen content of the cathode copper used in the production of copper rods is generally between 10 and 50ppm. At normal temperature, the solid solubility of oxygen in copper is approximately 2ppm. The oxygen content of low-oxygen copper rods is generally between 200 (175) and 400 (450) ppm. Therefore, oxygen is inhaled in the liquid state of copper. From the perspective of structure, oxygen in low-oxygen copper exists in the form of copper oxide near the grain boundaries, which is common for low-oxygen copper rods but rare for oxygen-free copper rods. The appearance of copper oxide in the form of inclusions at grain boundaries has a negative impact on the toughness of the material. The oxygen content in oxygen-free copper is very low, so the structure of this copper is a uniform single-phase structure, which is beneficial to its toughness.

2. The differences between hot-rolled microstructure and cast microstructure

Low-oxygen copper rods, due to hot rolling, have a hot working structure. The original casting structure has been broken, and recrystallization has already appeared in the form of 8mm rods. In contrast, oxygen-free copper rods have a casting structure with coarse grains. The successful annealing requirement for oxygen-free copper is that the annealing power of the first annealing when the rod is drawn but the structure has not yet been cast should be 10-15% higher than that of low-oxygen copper in the same situation. After further drawing, sufficient margin should be left for the annealing power in the subsequent stages, and different annealing processes should be implemented for low-oxygen copper and oxygen-free copper to ensure the flexibility of the work-in-progress and finished wires.

3. The difference between oxygen content fluctuations and the possible existence of hot-rolling defects

The tensile property of oxygen-free copper rods is superior to that of low-oxygen copper rods in all wire diameters. Besides the above-mentioned organizational reasons, oxygen-free copper rods have fewer inclusions, stable oxygen content, and no defects that may be caused by hot rolling. During the continuous casting and continuous rolling production process, if the process is unstable and oxygen monitoring is not strict, the unstable oxygen content will directly affect the performance of the rods.

4. The difference in toughness between low-oxygen copper rods and oxygen-free copper rods

Both can be drawn to 0.015mm, but in the low-temperature grade oxygen-free copper of low-temperature superconducting wires, the spacing between the fine wires is only 0.001mm.

5. The economic difference from the raw materials for making rods to the production of wires

The manufacture of oxygen-free copper rods requires high-quality raw materials. Generally, when drawing copper wires with a diameter greater than 1mm, the advantages of low-oxygen copper rods are more obvious, while oxygen-free copper rods are more superior when drawing copper wires with a diameter less than 0.5mm.

6. Differences in wire-making processes

The wire-making process of low-oxygen copper rods cannot be directly applied to that of oxygen-free copper rods. At least, the annealing processes of the two are different. Because the flexibility of the wire is deeply influenced by the material composition and the processes of rod making, wire making and annealing, it cannot be simply said which is softer, low-oxygen copper or oxygen-free copper.