Common sense of vacuum electric furnace

       Vacuum electric arc furnace is known to many vacuum furnace manufacturers, but few people can explain this vacuum electric arc furnace in detail. Today, Suzhou Jiuwei Electric Furnace Equipment Co., Ltd. will give you a detailed introduction! We mainly introduce to you from three aspects: principle, characteristics and classification!

       A kind of vacuum metallurgy smelting equipment. The furnace body is a closed container, which is evacuated or filled with inert gas. After the electrodes passed from the furnace top and the water-cooled crystallizer at the bottom of the furnace are energized to start the arc, an electric arc is generated, and the metal or alloy is melted by the arc heat and solidified in the crystallizer. Electrodes made of smelted metal are called "consumable electrode vacuum arc furnaces". For example, those that use infusible materials as electrodes are called "non-consumable electrode vacuum arc furnaces." The product has few impurities, low gas content, good ingot structure, and excellent mechanical and physical properties. It is suitable for smelting high melting point metals, active metals, special steels and metals.

       Arc is a kind of arc discharge of gas. Gas arc discharge shows that the voltage between the electrodes is very low, but the current passing through the gas is very large, there is dazzling white light, and the arc zone temperature is very high (about 5000k). The huge current density comes from the thermionic emission of the cathode and the self-emission of electrons, that is, there is a layer of positive ions near the cathode to form a strong electric field, which makes the cathode automatically emit electrons. A large number of electrons collide with gaseous molecules between the electrodes to ionize them, generating a larger number of positive ions and secondary electrons. Under the action of an electric field, they impact the cathode and anode respectively, resulting in high temperature. The cathode uses part of its energy due to electron emission, so the temperature is lower than that of the anode. The interelectrode also generates high temperature due to the recombination of some positive ions and electrons.

      Electric arc furnaces are industrial furnaces that use this principle to smelt metals. An electric arc furnace in a vacuum environment is a vacuum electric arc furnace, and vacuum arc melting uses high current and low voltage, which is a short arc operation. Generally, the arc voltage is 22 ~ 65V, and the corresponding arc length is 20 ~ 50mm (the latter is a large ingot). Since the successful experiment of smelting platinum wire in 1839, people began to study the smelting of refractory metals for more than 100 years. The vacuum electric arc furnace was officially used in industry in 1953. Until 1956, the United States and many European countries were still using non-consumable furnaces to smelt titanium, and in 1955 they began to use consumable furnaces to make steel. Around 1960, the weight of ingots produced by consumable furnaces had reached more than 30 tons, and it was beginning to take shape. The current development situation can be represented by the vacuum consumable furnace manufactured by the United States Consack Company. In order to improve productivity and equipment utilization, the two furnaces share a set of main power supply, vacuum system and automatic control system. Heat treatment of the workpiece (or material) in a vacuum state can increase the service life of the tool and mold, no oxidation, no decarburization, bright surface, small deformation, energy saving and no pollution, and changes in mechanical properties and metallurgical properties.

Compared with non-vacuum electric arc furnaces such as steelmaking electric arc furnaces and submerged arc furnaces, the characteristics of vacuum electric arc furnaces are: ①It is powered by a DC power supply (electrode connected to the negative electrode, crucible connected to the positive electrode), and the arc is relatively stable in vacuum and is not easy to extinguish. ② Electrodes and crucibles are usually made of metal materials, and there is no refractory lining in the furnace. ③The metal to be smelted during smelting can be protected from oxidation and refractory material pollution, and get a good degassing and refining effect that promotes the decomposition of metal oxides. ④Because it is smelted in a closed container, the environmental pollution is small and the working environment is good. ⑤ Special attention should be paid to safety. In the work of vacuum electric arc furnace, especially when smelting active metals such as titanium and zirconium, if cooling water enters the crucible, it will cause an explosion. There are many preventive measures, mainly: the clearance distance between the electrode and the crucible wall should be greater than the arc length, the DC arc stabilizing coil should be set outside the crucible, the power supply cable should be symmetrically arranged, and the electrode automatic regulator should be sensitive enough to prevent the electrode from contacting the wall. A side arc is generated between the walls of the crucible to break down the crucible; to ensure that the cooling water is unblocked; a protective wall is set up, and the operator observes and operates outside the wall. According to the electrode type (see electric arc furnace electrode), vacuum electric arc furnace is mainly divided into two categories: consumable furnace and non-consumable furnace. Consumption furnaces are mainly used in industry. There are also furnace types that use both consumable electrodes and non-consumable electrodes. The consumable electrodes provide the main charge and the non-consumable electrodes provide auxiliary heating. The furnaces for casting castings often use this furnace type.

The electrode of the consumable furnace is made of the smelted material itself, called the consumable electrode. During the smelting process, the electrode tip is gradually melted and dropped into a water-cooled copper crucible, and the electrode itself is continuously consumed. The vacuum consumable electric arc furnace is mainly used to remelt the billets of active and refractory metals such as titanium, zirconium, molybdenum, tantalum, and niobium to produce ingots, such as remelting sponge titanium electrodes into titanium ingots. This electric arc furnace can also be used for refining alloy steel and producing large-diameter high-quality steel ingots, such as forging billets for the manufacture of generator shafts and rolls.

The electrodes of the non-consumable furnace are made of high melting point materials such as tungsten. The electrode itself is not consumed during work, and the charge needs to be added into the furnace by other means. This electric arc furnace is mainly used for pouring special-shaped castings of the above-mentioned materials in vacuum and preparing test billets in the laboratory.