Thu, 25 Oct 2018 03:46:35 +0000
vacuum melting classification
According to different heating sources, vacuum smelting can be divided into vacuum induction melting, vacuum arc melting, electron beam melting and so on.
Vacuum induction melting
The metal burden is placed in a crucible in a coil. When the coil is connected to an alternating current power supply, an alternating magnetic field is generated in the middle of the coil, and the inductive potential is generated in the burden. Because the metal burden itself forms a closed loop, the induction current, i.e. eddy current, is produced simultaneously in the charge. The charge is heated and melted by eddy current. The method of smelting by this principle is called induction melting. Induction melting in vacuum is vacuum induction melting. Vacuum induction melting can strictly control the content of active elements such as aluminum and titanium, effectively remove gas and non-metallic inclusions as well as non-ferrous metal impurities in the alloy, and improve the purity of the alloy. However, the staining of refractories in crucible to molten metal exists in vacuum induction melting, and ingot mold is usually used to pour. The crystal structure of ingot is not improved compared with that of ordinary melting ingot. Vacuum induction melting is mainly used to melt superalloys, precision alloys and special steel materials. Its main products are ingots, precision castings and electrode base materials used in double melting.
Vacuum arc melting
The smelting method of heating and melting metal by arc in vacuum. The electrode used in this smelting process consists of two kinds of consumable electrode and non consumable electrode. The consumable electrode is made of the melted material (i.e. furnace charge), which is gradually consumed during the smelting process; the non-consumable electrode is made of high melting point materials such as tungsten, which is basically not consumed during the smelting process. The vacuum electric arc furnace with consumable electrode is called consumable electrode electric arc furnace for short, and the vacuum electric arc furnace with non-consumable electrode is called non-consumable electrode electric arc furnace for short. Non-consumable electrode smelting has been less used, and consumable electrode smelting has been widely used in production practice, becoming one of the main means of secondary remelting. The crucible of vacuum arc melting is usually made of copper, which is cooled by water outside, called water cooled copper crystallizer. In smelting, the consumable electrode (the smelted material) can be connected with the negative electrode, the water-cooled copper mold with the positive electrode, arc discharge between the two poles after electrification, the electric energy into thermal energy, resulting in high temperature to melt the material. In the process of smelting, liquid metal droplets fall into the molten pool after passing through the high temperature arc zone and solidify into ingots in the water-cooled copper mold. Through a series of physical and chemical reactions between the liquid metal and the gas phase and in the molten pool, the purity of the metal can be improved and the crystal structure and properties can be improved. Vacuum arc smelting is not contaminated by atmosphere, refractories and molds; it can remove gas and harmful metal impurities in steel and alloy; inclusions can also be floated to remove part of the inclusions, and can improve the distribution and morphology of inclusions in the alloy; the as-cast microstructure of ingots in water-cooled copper crystallizer is better than that of ordinary ingots. But the vacuum arc melting needs prefabricated electrode and the ingot surface is poor. Vacuum arc melting can be used to melt active metals such as titanium, zirconium, tungsten, molybdenum, refractory metals and their alloys, as well as high temperature alloys and steels and alloys for special purposes.
Electron beam melting
In high vacuum, when the cathode material (usually refractory metals such as tungsten) is heated to high temperature, electrons are emitted under the action of high voltage direct current, and the electron beams are assembled by magnetic lenses. At the acceleration of the anode, the cathode material is projected at high speed to the anode (the molten material used to make the electrode is equivalent to the anode), when the high-speed electron beam is projected at the electrode. When the surface is collided, the heat energy transformed by kinetic energy will be melted by molten material. It not only melts the electrode, but also has a part of the energy that can be used to heat the metal surface, so that the bath maintains the necessary temperature and time to facilitate metal refining. Finally, the molten metal solidifies into a spindle in a water cooled crystallizer. Electron beam melting is also known as electron bombardment furnace melting. Electron beam smelting has outstanding advantages: high working vacuum (about 10-10-Pa), very conducive to the removal of gas, non-metallic inclusions and metal impurities; high smelting temperature, metallurgical reaction is sufficient to melt any refractory metal; metal droplets convergence in water-cooled crystallizer, can effectively control the temperature of the molten pool and condensation rate. It is beneficial to obtain good metal ingot structure. The application of electron beam melting has been extended from refractory metals to superalloys, precision alloys, semiconductors and some special purpose steels. Only because of its complex equipment structure and expensive construction investment, it limits its development scale.