Coreless Vacuum Induction Furnace

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1 1/8 High tech furnaces for high tech alloys and processes Coreless Vacuum Induction Furnace

2 Coreless Vacuum Induction Furnace Blaise Pascal The vacuum treatment of molten steel was developed by the steel industry in the fifties of the last century and evolved into a standard process for the production of lowgas and low-carbon steel grades. The typically large-sized treatment units of steelworks-scale capacity are unheated and enable the vacuum treatment to be performed with acceptable temperature losses. For smaller batch sizes which, e.g., steel foundries are interested in, heating of the vacuum treatment unit is indispensable. Induction heating lends itself ideally to such applications because firstly the energy input takes place in a direct and noncontaminating manner and, secondly, the electromagnetic bath movement which is variable within wide limits provides ideal homogenization of the metal bath and effective degassing via the bath surface. Vacuum treatment ensures optimum deoxidation of the melt. Alloying elements with a high affinity for oxygen can be added and stirred down with melting losses at a minimum. The technical benefits of OTTO JUNKER Coreless Vacuum Induction Furnaces have led to their increasingly widespread use in the foundry industry. Their fundamental advantages are based on the direct input of heat into the metal, as well as Patent granted to OTTO JUNKER in the selectively controlled bath movement and the metallurgically neutral melting regime. Furthermore, the vacuum induction furnace allows reactive alloys to be melted without oxidation losses and without the introduction of non-metallic impurities. Most super alloys, for example, are produced in induction furnaces under vacuum, refined under vacuum and poured under vacuum. Another field of vacuum induction furnace application to be mentioned is the selective distillation of molten metal where the vacuum induction furnace is typically operated in conjunction with a condenser tailored to suit the specific application requirements. OTTO JUNKER GmbH, Simmerath-Lammersdorf OTTO JUNKER vacuum furnaces are designed and built to comply with all relevant safety and environmental codes and regulations. OTTO JUNKER NFT St 3000 Vac, built in /8

3 MFT Vac - coil inside vacuum Fields of use High-grade steel alloys Super alloys High-purity metals Reactive metals.... Process applications Melting, alloying, treating and pouring under vacuum Alloys required to meet maximum purity requirements and minimum gas contents High-purity metals MFT St Vac for steel Benefits The enclosed design (coil inside the vacuum) allows operation at 10-2 mbar for melting, alloying, treating the metal and pouring under vacuum Rating, capacity and frequency can be tailored to suit the specific process. Rating and dimensioning options: Furnace capacity up to 25 t (related to steel) Power ratings up to 8,000 kw Frequencies from 35 to 1,000 Hz Vacuum from 10-4 to 200 mbar Only OTTO JUNKER offers two different vacuum furnace concepts MFT St Vac - mathematical furnace model for FEM studies Coil inside vacuum Coil outside vacuum Evaporation process + Pouring under vacuum ++ + Vacuum up to 10-2 mbar + + Vacuum up to 10-4 mbar + Degassing molten metal + + Furnace > 10 t + Furnace < 10 t + + Power > 3,000 kw + MFT Vac selection table 3 / 8

4 MFT Vac - coil outside vacuum Fields of use High-grade steel alloys Copper alloys Aluminium alloys Complex alloys Evaporation processes Recycling of zinc-containing waste Process applications Patent granted to OTTO JUNKER Vacuum furnace for melting Ag Zn Pb Melting, alloying and treatment under vacuum, pouring in open atmosphere Carbon reduction in high-grade steel melts Deoxidation of high-grade steel melts Degassing of melts Zinc extraction from melts Benefits Schematic vacuum furnace The induction coils with their power and cooling water connections are outside of the vacuum, freely accessible, neatly arranged and in open atmosphere. This design ensures a maximum of safety in furnace operation. It prevents electric glow discharge and does not require complex vacuum-tight bushings for power and cooling water. An additional benefit of this special design is that it rules out any hazardous contact between cooling water and molten metal inside a hermetically sealed space. Space requirements are similar to those of a standard induction furnace. Investment is lower because the frequency converter system operates at a favourably high voltage level. Rating and dimensioning options: Air cooling system Furnace capacity up to 10 t (related to steel) Power ratings up to 3,000 kw Frequencies from 35 to 150 Hz Vacuum from 10-2 to 200 mbar 4 / 8

5 Frequency converter system The parallel oscillating circuit converters of OTTO JUNKER's proprietary design have been purpose-developed for induction melting equipment and are noted for their safe and reliable performance even in extreme load conditions. The digital converter control system ZEUS (central frequency converter control unit) ensures a constant power output over the entire heat cycle while adapting perfectly to mains voltage fluctuations and changing load conditions. Characteristic features of the parallel oscillating circuit converter: High operating reliability thanks to a robust d.c. link and smoothing reactor Low inverter loads due to exposure to active current only (i.e., not to the furnace current which is higher by a factor of 5-10) High electrical efficiency Low mains pollution 6, 12 or 24-pulse design options Easy maintenance and good accessibility Additional features of the IGBT converter: ZEUS digital converter control system Outstanding inherent protection against current, voltage and temperature peaks Consistently high power factor (cosine phi) approaching 1.0 at converter input Less exacting requirements on cooling water thanks to indirect cooling Variable bath movement Multi-Frequency technology permits changes in operating frequency in the course of the melting cycle. For example, an appropriate frequency of 250 Hz is used for melting the charge material down. For alloying work and homogenization the system automatically switches to a lower frequency (e.g., 125 Hz) so as to increase the bath movement. Single-line diagram of a six-pulse system Multi-phase stirring technology creates a bath flow that is adjustable in direction and intensity. This is accomplished with the aid of phase-shift control of and variable power input to the coil sections. IGBT converter for 3,000 kw In addition to normal melting/holding mode of operation IGBT converters can be controlled in a very special way such that the coil sections behave like a linear motor. This allows a strong stirring effect to be obtained with very low energy input (temperature rise). It is even possible to reverse the classical bath movement of an induction furnace so that the molten metal tends to flow from outside towards inside. 5 / 8

6 IGBT phase shifting Mode selection: Melting Holding Stirring (35 Hz) Phase +90 Phase -90 Presentation of flow patterns and flow velocity [ m/sec ] taking the example of an aluminium melt Melting 120 kw *, 230 Hz, phi = 0 Stirring 26 kw *, 34 Hz, phi = 0 Stirring 26 kw *, 34 Hz, phi = +90 Stirring 26 kw *, 34 Hz, phi = / 8

7 OTTO JUNKER Vacuum induction furnaces Peripheral equipment The condenser The OTTO JUNKER condenser is ideally suited for the selective distillation under vacuum. The metal yield actually obtained in practice, e.g., in the distillation of zinc, is approx. 95 to 98 % with a zinc content in the raw material of approx. 65 %. Dual pump system with angle valves Process Controller JOKS-Process The process control and visualization system JOKS P monitors, controls and automates the vacuum furnace process. Air-to-water cooling circuit monitoring Process data monitoring Electrical equipment Water recooling system 7 / 8

8 Other items of our product range Channel-type holding furnace Pouring furnace for automatic pouring on mould lines Medium-frequency coreless induction furnace MFT for customized solutions OTTO JUNKER GmbH Postfach D Simmerath Phone: Fax: / 8