Strictly distinguish, oxygen free copper should be divided into ordinary oxygen free copper and high-purity oxygen free copper. Ordinary oxygen free copper can be melted in power frequency iron core induction furnace, while high-purity oxygen free copper should be melted in vacuum induction furnace.

When semi continuous casting is adopted, the refining process of melt in smelting furnace and holding furnace can be free from time constraints. The quality of the whole smelting furnace and the stability of the whole smelting furnace are not only dependent on the quality of the smelting furnace, but also on the quality of the whole smelting furnace.

In order not to pollute the melt, oxygen free copper smelting generally does not use any additives for smelting and refining. The surface of the molten pool is covered with charcoal and the reducing atmosphere formed is the commonly used smelting atmosphere.

The induction furnace for smelting oxygen free copper should have good sealing.

High quality cathode copper should be used as raw material for smelting oxygen free copper. Smelting high-purity oxygen free copper should use high-purity cathode copper as raw material. Before the cathode copper enters the furnace, if it is dried and preheated first, the water or moist air that may be adsorbed on its surface can be removed.

When smelting oxygen free copper, the thickness of the charcoal layer covered on the surface of the molten pool in the furnace should be double that when smelting ordinary pure copper, and the charcoal needs to be updated in time.

Although charcoal covering has many advantages, such as heat preservation, air isolation and reduction, it also has some disadvantages. For example, charcoal is easy to absorb moist air and even directly absorb water, which makes it possible for copper liquid to absorb a large amount of hydrogen.

Charcoal or carbon monoxide can reduce cuprous oxide, but it can't do anything about hydrogen. Therefore, charcoal should be carefully selected and calcined before being added to the furnace.

Comprehensive protection of the melt is a necessary condition for oxygen free copper production in the process of smelting, transfer injection, heat preservation and the whole casting process. Many of the smelting and casting lines are fully protected by the oxygen free casting line, including the preheating and drying of the casting line.

Some modern large-scale oxygen free copper production lines use generator gas as protective gas, while most gas generators use natural gas as raw material.

A manufacturing method of protective gas commonly used abroad is: firstly, the natural gas with low sulfur content and 94% ~ 96% methane are burned with theoretical value air, and the hydrogen is removed with nickel oxide as the medium. The gas is mainly composed of nitrogen and carbonic acid gas. Then, the carbonic acid gas is changed into carbon monoxide through hot wood charcoal to obtain an oxygen free gas containing 20% ~ 30% carbon monoxide and the rest is nitrogen.

In addition to generator gas, gases such as nitrogen, carbon monoxide or argon are also used as medium materials for oxygen free copper melt protection or refining.

Vacuum smelting should be the best choice for smelting high-quality oxygen free copper.

Vacuum melting can not only greatly reduce the content of oxygen, but also greatly reduce the content of hydrogen and some other impurity elements.

When smelting in vacuum medium frequency coreless induction furnace, graphite crucible and twice refined high-purity cathode copper or remelted copper are mostly used as raw materials. The flake graphite powder used for deoxidation is also put into the furnace together with the cathode copper.

In fact, deoxidation is mainly carried out through the carbon in the graphite crucible material. The consumption of carbon can be known by calculation. For example, 1 kg of copper consumes 100 g of carbon. Experience shows that the higher the oxygen content in the molten copper at the beginning, the faster the deoxidation reaction in the initial stage of smelting.

The oxygen content of oxygen free copper obtained by vacuum melting can be less than 0.0005%, and the hydrogen content can be less than 0.0001% ~ 0.0003%. In fact, only the copper melted and cast under a certain vacuum can obtain castings completely free of oxygen and other gases. Therefore, the vacuum degree of the vacuum furnace used to produce copper materials for electronic tubes should be more than 10-6.

Source: Lvxing Metal Co., Ltd

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