The man behind aerospace materials: vacuum induction melting furnace

At present, many countries in the world, especially developed countries, in order to carry out space technology, occupied space category, add fast modernization of national defense, strengthen the national defense strength, do not hesitate to denounce is gigantic endowment, scrambling to development and production of advanced carrier, shipping day, sail the sea equipment, such as: the spacecraft and the international space station, artificial satellites, nuclear submarines, long-distance jet bombers, atomic energy, rockets, missiles, etc.

However, these sophisticated equipment on the production of its data performance requirements are very strict, high purity, high uniformity, high temperature resistance, high pressure resistance, impact resistance, fatigue resistance and a series of special strict requirements for the steel, alloy, blank, especially for the data performance of stability, consistency and reliability is very high.

However, satisfying these requirements has been beyond the reach of well - known general exercise equipment. For this reason, new smelting equipment and processes have long been discussed and discussed by metallurgists in order to advance and improve the quality and purity of special steels and alloys used in aerospace equipment.

Through a large number of theoretical and practical discussions of the system, as well as the discussion and discussion of the physical and chemical reaction mechanism in the metallurgical process from the aspects of thermodynamics and dynamics, the important conclusion is drawn that the process that can satisfy the above requirements is the exercise of aerospace data in a vacuum chamber.

This is because :(1) in the vacuum state, can avoid being smelted metal and alloy mixed with non-metallic materials biochemical reaction; (2) In the vacuum state, the harmful soluble gas and pollutants in the liquid molten metal can be eliminated to improve the purity of the molten metal.

According to the current domestic and foreign industrial level, there are three kinds of equipment that can complete the above information: vacuum induction melting furnace, vacuum consumable arc furnace and electroslag remelting furnace. In other words, to develop aerospace industry rapidly, we must develop these three kinds of high-grade exercise equipment and new technology.

1 Vacuum induction melting furnace (VIM)

The world's first vacuum induction furnace was created in Germany in 1917 to melt aircraft and rocket engines. Vacuum induction melting furnace is one of the widely used equipment in vacuum metallurgy.

It has been proved that the alloys and special steels required by the aerospace, missile, rocket, atomic energy equipment and electronics industries account for an appropriate proportion of the products produced by vacuum induction melting furnaces.

For example, the thermal and mechanical properties of nickel-based, cobalt-based and ferri-based superalloys are obviously improved when they are smelted by vacuum induction furnace. Like stainless steel, heat resistant steel, ultra-high strength steel, tool steel, bearing steel, as well as magnetic material, elastic alloy, expansion alloy and so on are simply selected vacuum induction melting furnace smelting, in order to ensure data performance and quality.

In addition, with the development of the secondary remelting process, another use of vacuum induction melting furnace is to supply high quality consumable electric arc furnace or electroslag remelting furnace, as well as to produce parent alloy for fine casting.

It is well known that the vacuum induction melting furnace process, the whole process of metal melting, refining and alloying, is carried out in the vacuum state, thus avoiding contamination by the same gas phase mutual effects. Secondly, in the vacuum condition, carbon has a strong ability to deoxidize, its deoxidizing product CO is constantly pumped out of the system, to overcome the choice of metal deoxidizing agent deoxidizing pollution problem.

Vacuum induction melting furnace process can be accurately manipulation of the chemical composition of alloy, live about containing oxygen, nitrogen and strong affinity sex element Al, Ti, B, Zr, etc., can be manipulated within a few of low melting point metals volatile impurities, such as Pb, Bi, Sn, Sb to evaporation, the progress of data properties have an important effect. Strong induction mixing effect can speed up the reaction speed, which is very effective in the aspects of uniform molten pool temperature and uniform chemical composition.

The vacuum induction smelting process can be developed rapidly, which is closely related to the data of the superalloys needed by aerospace industry, such as the superalloys needed by aerospace, missile, rocket and atomic energy equipment. For superalloys produced without the use of vacuum smelting method, the grand working temperature usually stands at 750~810℃; For superalloys produced by means of vacuum smelting, the grand working temperature can reach 980~1090℃. This is primarily because the selection of vacuum induction melting of nickel, iron, cobalt based superalloy, the reduction of void elements O2, N2, H2, can thoroughly eliminate the non-metallic dopant, as well as remove low melting point harmful metal impurities, such as Pb, Bi, Sb, Cu, Sn, Te and so on.

The equipment of vacuum induction melting furnace is mainly composed of furnace shell, inductor, crucible, dumping furnace mechanism, ingot mold mechanism, power supply equipment and water cooling system. The furnace shell is provided with such equipment as investigation, temperature measurement, feeding, sampling and ramming. The furnace body is equipped with vacuum system, power supply system and control system. Vacuum induction melting furnace is intermittent and half - connected type, can be made of vertical or horizontal.

The important problem to be considered in the structure design of vacuum induction melting furnace is to avoid vacuum discharge. For this reason, all charged bodies in the furnace shell need to be treated with insulation, and the structure of the inductor should be free from sharp angles, burrs and sharp edges.

To sum up, vacuum induction melting furnace has the following characteristics :(1) in the vacuum state, it can melt some precious active metals, such as titanium alloy; (2) in the vacuum state, can eliminate the smelted metal and alloy, with non-metallic doped materials biochemical repercussions. (3) In the vacuum state, can eradicate the liquid molten metal in the harmful soluble gas and pollutants.

From the application of the products, mainly used in the production of aerospace, missile, rocket, atomic energy and electronics industry needed high temperature alloy, ultra high strength steel, stainless steel, and other special use of alloys.