Vacuum Induction Furnace Melting for Precision Alloys
Titanium materials began to be produced in large quantities in the 1950s. In the 1970s, vacuum shell furnace had a capacity of tens of tons or even hundreds of tons of vacuum smelting equipment. Now it has developed into an important production department of special materials equipped with modern technology and equipment.
The melting and ingot casting of non-ferrous metals were carried out under the conditions of lower than normal pressure and higher vacuum (from less than 100 kPa to 1.3 *10-10 Pa). It is not only the production of refractory, rare and active metal materials, but also the important modern smelting technology to obtain high purity and high quality metal materials. In 1917, vacuum smelting began to transfer from laboratory to factory scale. At that time, only a small amount of nickel-based alloys, thermocouples and resistance heating materials could be smelted. During and after World War II, with the development of vacuum technology and the need of military industry and modern science and technology for high performance new metal materials, vacuum smelting has developed rapidly.
Vacuum smelting is characterized by high purity, volatile impurities, good degassing effect, strong deoxidizing ability, thermal decomposition of some nitrides and hydrides, and some chemical reactions that can not be carried out in the atmosphere, especially those formed by gas products, so that high purity, uniform material, low gas content can be obtained. Metal materials with less impurities, less defects and excellent processability. High purity barium, hafnium, vanadium and thorium, superalloys, thermoelectric alloys and magnetic materials, active metal titanium and zirconium, refractory metal tungsten, molybdenum, tantalum, niobium and copper and nickel alloys for electric vacuum are all produced by vacuum remelting. The main vacuum smelting equipments and methods are vacuum induction furnace smelting, true arc furnace smelting (see non-ferrous metal alloy vacuum arc furnace smelting) and electron beam furnace smelting.
Vacuum induction furnace smelting is to place inductors and crucibles in vacuum and melt them in 1.3 *10-2-1.3 *10-3a vacuum for the production of high temperature and precision alloys. Electron beam furnace (EBF) melting is a process in which electron beams are emitted by one or more electron guns in high vacuum (1.3 *10-1~1.3 *10-5Pa), and the melted object is bombarded and dripped into a water-cooled copper crystallizer to form ingots. Electron beam furnace smelting is suitable for the smelting of ultrapure metals and refractory metals.
Vacuum induction melting will be widely used in the following four aspects:
(1) Melting requires precise composition control, high purity and less inclusion. Such as nickel-based superalloy, ultra-high strength maraging steel, ultra-pure ferritic stainless steel and high-purity metals, etc.
(2) Recycling precious alloys, such as nickel-based alloys, high-alloy stainless steel, etc.
(3) Production of precision casting without allowance processing;
(4) Active metal alloys such as titanium and zirconium can be melted by using water-cooled copper plate inlaid crucible and calcium oxide crucible. Generally speaking, smelting is to melt ore or concentrate (or calcined sintered block) together with flux at high temperature, so that a series of chemical reactions occur in each component of the material. As a result, two or more kinds of insoluble liquid products, crude metal or matte and slag, are obtained, and furnace gas and dust are produced. Various liquid products, due to their different densities, are automatically stratified in the smelting furnace and released separately to separate metal or metal compounds from gangue.
According to the characteristics of chemical reaction in smelting process, smelting can be divided into reduction smelting, matte smelting, precipitation smelting, oxidation smelting and chlorination smelting. According to the different smelting equipment, it can be divided into blast furnace smelting, reverberatory furnace smelting, electric furnace smelting and so on.