HEAT TREATMENT EQUIPMENT FOR FASTENERS, METALWARE AND PARTS
VACUUM FURNACES GENERAL INFORMATION
Heat treatment under vacuum and vacuum melting techniques are widely used today for a wide range of materials, unobtainable in any other way. The most perfect vacuum metallurgical processes, such as steel degassing, furnace processing, vacuum remelting, precision casting, investment casting now allows high-quality cast, as the composition of the material, and the quality of casting. However, the ever increasing technological level of modern engineering puts forward new requirements to the vacuum processing equipment. Today, vacuum metallurgy moves to a new level of creation of technological processes, is a continuous process chain in the medium vacuum, allowing on the one hand to obtain fundamentally new products, on the other hand, greatly reduce production costs.
Particularly high efficiency of these technologies in the processing of scrap precious metals when the price of processed materials commensurate with the cost of the equipment. Examples of possible applications of vacuum technology can also obtain high-technology and high-temperature precision steels alloys, precious metals is desired to obtain a material with a high degree of purity with minimal haze. Using vacuum technology can obtain materials with fine-grained structure, focus and single-crystal structure, determine in advance the properties of the resulting materials. All of the above is extremely important in terms of the use of new materials in high-tech fields of science and technology, such as aerospace, aviation and automotive industries. Increased strength and reliability of the materials used in these industries often determines the ability to develop a fundamentally new technology.
Vacuum remelting processes is used in the secondary metallurgy refining metals for redistribution or receiving the specific chemical composition in the liquid state at a predetermined temperature. There are so many different applications of vacuum technology for a wide variety of materials. Vacuum technology is indispensable for the production of special alloys which can not be prepared in a vacuum or inert atmosphere because of their high oxidizability.
Vacuum furnace provides efficient degassing of the melt and very precise composition of the alloy as melt temperature, the pressure inside the vacuum chamber, the mixing of the melt and the introduction of additional alloying elements can be performed independently. The combination of all these methods of influence on the melt creates a unique tool for foundry researcher. Typically for precision vacuum melting process is using an induction heating furnace. Advantages of vacuum melting induction heating are as follows:
- Ability to prolonged exposure of the molten metal in a high vacuum.
- The high degree of degassing (degassing of metals).
- The ability to produce a partial content of the furnace during the melting process, the active influence on the intensification of processes of reducing and refining at any time of melting.
- Ability to effectively monitor and control the state of its melt temperature and chemical composition throughout the process.
- High purity castings produced due to the absence of any non-metallic inclusions.
- The ability to produce rapid heating (direct heating due to heat generated in the melt) and consequently high speed and high performance heats.
- The high homogeneity of the melt by mixing the active metal.
- An arbitrary form of raw materials (lump materials, briquettes, powder, etc.)
- High efficiency and environmental cleanliness.
Compared to electric arc furnaces, there are many different factors that occur with the use of induction melting and significantly affect the metallurgical processes. In vacuum induction furnace (VIF) any slag is stirred constantly in contact with the surface of the crucible due to induction melting characteristic of the movement of the metal. Therefore, some metallurgical processes as well as dephosphorization and desulphurization limited. Vacuum remelting technology mainly focus on the processes in the course of which a large degree of reduced pressure is caused by the environment, such as metallurgical reactions associated with carbon, oxygen, nitrogen and hydrogen. And the ability to remove these unwanted volatile accompanying elements such as mercury, tellurium, selenium, and bismuth in the VIF is particularly important practical significance. Accurate monitoring of pressure-dependent response communication to provide excess carbon deoxidation, one example of application of various methods using a vacuum furnace for obtaining special alloys.
But in addition, many materials of special alloys in an induction melting furnace can be exposed to a treatment to remove unwanted impurities to provide the necessary and warranted. Due to the high degree of concentration of sublimability many undesired accompanying elements can be reduced to a very low level during the sublimation process of vacuum induction remelting. Virtually all high-precision and low alloy melt overheating; in conjunction with vacuum suction can eliminate these cells and to ensure high performance of the processed material. Therefore, the method of induction melting is considered the most appropriate; method of producing ultra-pure alloys.
Depending on the type of metal and smelting process, the degree of vacuum for sublimation refining process can be in the range 10-1 ÷ 10-3 mbar.
In order to obtain pure melts, various processing methods can be easily combined with the process of vacuum induction melting; Control of the atmosphere with low leakage and desorption, selection of the most stable refractory materials for lining crucible mixing and homogenization by electromagnetic stirring, inert gas purging, precise temperature control to minimize the reaction crucible with molten metal, the possibility of slag removal and filtration of the melt during casting , providing the possibility of casting the chute or through an intermediate ladle to prevent oxidation.
For particular applications, such as, for example, the production of turbine blades, the quality of material produced during vacuum induction remelting of this initial stage, but in order to ensure the highest purity requirements of the material and its structure requires subsequent processing.
Materials melted in a vacuum induction furnace must go through an additional remelting and (or) the process of directional solidification. For this VIF supply additional casting chamber. For even more stringent requirements, the materials have to go through several stages of refining, such as refining process in triplex, consisting of successive induction vacuum remelting electroslag and arc radiation or vacuum remelting.
Vacuum induction furnaces of the new generation are fundamentally different from its existing compact, smaller volume of the melting chamber, the possibility of joining with various chambers - download, casting and removal of finished products, greater functionality and cost-effectiveness. Modern VIF constructed on a modular design and can be used for melting and casting of metals in vacuum and inert gas. Often manufacturers of furnaces offer standard modules, the combination of which allows you to quickly reconfigure process. The process of casting is usually performed using a ceramic chute through which the molten metal is transported into the filling chamber with simultaneous removal of nonmetallic inclusions.
The vacuum chamber is reduced to a minimum and as a result; time reduction is achieved by pumping or power reduction set vacuum circuit equipment, improved control of the atmosphere during the process, a quick exchange of the various elements of the furnace, with a minimum stop time for the replacement of the crucible, high flexibility in the choice of methods of casting with minimizing the risk of contamination. The concept of a new generation of VIP offers opportunities economically viable production of all known metals, alloys and precision in a controlled gaseous atmosphere typically remelted in vacuum furnaces. Further development of vacuum technology in mechanical engineering - the combined process of melt, casting and forging, thus no need to use additional heating and unnecessary conversions (some analogue of continuous casting with simultaneous rolling).
The method consists in the fact that the metal is melted in a vacuum melting chamber, directly above the die - casting mold until a refiner of penetration of the workpiece. Currently fixed light sensors, and then to melt, affect the gas pressure and ultrasonic vibrations. Further, the melt enters the die-casting mold, which is moving toward him. This crystallization occurs quickly, and under the influence of ultrasonic vibrations is provided by fine-grained, dense structure of the product.
This technology allows to obtain complex shapes directly from the melt (for example, turbine blades, shaped products such as nozzles, automotive valves, seals and other sophisticated.) From both ordinary and hard-alloy, without excessive machining. The structure corresponds to the quality of the metal structure obtained during the metal forming, that is fine-grained and non-porous. This not only significantly less metal, but also dramatically reduce the cost of machining, the accuracy of manufacture of the product is close to the accuracy obtained by machining. Considering that in the manufacture of complex shaped articles in the chip takes a significant portion of expensive material (sometimes 70-90%), the use of such technology - is a qualitative leap in the field of production of high quality castings.
The sequence of melting metal in vacuum furnaces
Molten metal is produced in a vacuum furnace in a cold water-cooled crucible using the inductor. Initially held metal skull. From the top of the chamber argon gas is supplied through the pipe. Upon reaching the melt temperature triggered equipped light sensor, a valve and through the ceramic metal enters the channel shape. Simultaneously rises to form the channel comprises a vacuum pump that creates a vacuum in the lower chamber through the nozzle. The molten metal under the influence of gravity and under pressure being created in the bottom chamber begins to quickly fill the mold. At the time of joining to form a channel includes an ultrasonic transducer. Powerful ultrasonic treatment provides an easy form filling, by improving the wettability of the mold surface, provides continuous degassing and melt due to a sharp increase in the nucleation creates a fine-grained structure of the casting. This method was cast in the literature as the volume-pulse punching.
Uniform and high-quality metal casting, high mechanical properties of the resulting products, environmental friendliness of the process, economy and compact installation allows extensive use of the proposed process in the manufacture of molded parts of complex shape of hard and difficult-reactive metals and alloys, and composite materials. In particular, this technology may be obtained from the product of composite materials with reinforcement carbons, tungsten or boron fibers. Possible areas of application of such technologies cannot be overestimated - it is aircraft, shipbuilding, automotive and nuclear power engineering, medicine and special equipment.