Vacuum Arc Remelting (VAR)
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ALD Vacuum Technologies High Tech is our Business Vacuum Arc Remelting (VAR) Vacuum Arc Remelting Processes and Furnaces ALD / VAR / 2019.05 EN ALD / VAR Vacuum Arc Remelting (VAR) ALD is one of the leading suppliers of vacuum melting furnace technologies for engineered metals 12 ton VAR furnace from ALD VAR is widely used to improve the Fields of Application VAR Applications cleanliness and refine the structure of standard air-melted or vacuum in- O Aerospace O Superalloys for aerospace duction melted ingots (called O Power generation O High strength steels consumable electrodes). VAR steels O Chemical industry O Ball-bearing steels and superalloys as well as titanium O Medical and nuclear industries O Tool steels (cold and hot work steels) for milling cutters, drill bits, etc. and zirconium and its alloys are used O Die steels in a great number of high-integrity O Melting of reactive metals (titanium, applications where cleanliness, zirconium and their alloys) for aero- homogeneity, improved fatigue space, chemical industry, off-shore and fracture toughness of the final technique and reactor technique product are essential. 02 VAR Advantages & ALD Features ALD has numerous references in the field offering the highest levels of system automatization 10 ton VAR furnace from ALD Primary benefits of VAR Further advantages Features of VAR furnaces from ALD O Removal of dissolved gases, such O Removal of Oxides by chemical and as hydrogen, nitrogen and CO physical processes O Ingot diameters up to 1,500 mm O Reduction of undesired trace O Removal of Nitrides by thermally O Ingot weights up to 50 tons elements with high vapor pressure dissociation or reduction by carbon O Electrode is melted by means of a O Achievement of directional present in the alloy, and final removal DC arc under vacuum (electrode solidification of the ingot from via the gas phase negative, melt pool positive) bottom to top O Removal of Stable Non-metallic O Remelting currents up to 50 kA O Elimination of macro-segregation Inclusions O Vacuum range: 1 - 0.1 Pa (some and reduction of micro-segregation Some inclusions (e.g. alumina and applications up to 1,000 Pa) O Improvement of oxide cleanliness titanium-carbonitrides) are removed O Electrode weighing system by flotation during remelting. The O Stable or free-standing gantry design remaining inclusions are broken O Coaxial high current feeding system up and evenly distributed in the cross-section of the solidified ingot. 03 Process Technology and Process Characteristics ALD´s process expertise guarantees high process reproducibility and material quality 12 ton VAR furnace from ALD VAR is the continuous remelting O DC power is applied to strike an to remove impurities and prevent of a consumable electrode by arc between the electrode and the oxide formation means of an arc under vacuum. baseplate of a copper mold contained O Ingot cooling is controlled for in a water jacket directional solidification The main process stages O The intense heat generated by the ALD has improved the basic design of O A consumable VAR electrode is electric arc melts the tip of the VAR furnace in computer control and generated by VIM, ESR, EB or plasma electrode and new ingot collects in regulation continuously over the years to methods, assembled from titanium the mold achieve: sponge, scrap or bulk, or by a prior O The melt rate is precisely regulated O Fully-Automatic remelting processes VAR melt by the VAR control system O Improved Reproducibility of the O A high vacuum is maintained metallurgical properties throughout the remelting process 04 Directional Solidification of the Vacuum Arc Remelting Process Precise control of the local solidification rate of the temperature gradient at the liquid/solid interface Achieving the optimum VAR solidification, at the solidification front. Even in the case of directional solidification, ingot solidification structure The direction of the heat flow is always micro-segregation increases with dendrite requires precise control of the perpendicular to the solidification arm spacing. A solidification structure local solidification rate and the front or, in case of a curved interface, with dendrites parallel to the ingot axis temperature gradient at the perpendicular to the respective tangent. yields optimal results. liquid/solid interface. The growth direction of the dendrites is thus a function of the melt pool profile Optimal Melt Rates High Temperature Gradient during solidification. A good ingot surface requires a certain at the solidification front must be level of energy input. Optimal melt rates maintained during the entire Melt Pool Profile and energy inputs depend on ingot remelting process to achieve a As pool depth increases with the diameter and material grade, which directed dendritic primary structure. remelting rate, the growth angle of the means that the necessary low remelting dendrites, with respect to the ingot axis, rates for large diameter ingots cannot Dendrite Growth Direction also increases. Without proper VAR always be maintained to achieve axis- conforms to the direction of the melt controls, the ingot core can solidify parallel crystallization. temperature gradient, i.e., the direction non-directionally, e.g. in equiaxed grains, of the heat flow at the moment of leading to segregation and micro-shrinkage. 05 Understanding and Preventing Solidification Defects Metallurgists agree that in spite of Tree ring patterns White Spots directional solidification, defects such as “tree ring patterns”, “freckles” and O Can be identified in a macro-etched O White spots are typical defects in VAR “white spots” can occur in remelted transverse section as light-etching ingots. They are recognizable as light ingots. These defects can lead to rings etching spots on a macro-etched rejection of the ingot, particularly in O Usually represent a negative crystal surface the case of special alloys. segregation O They are lower in alloying elements, e.g. O Seem to have little effect on material titanium and niobium in Inconel 718 properties ALD mitigates these problems Freckles in the VAR with precise and stable melt rate and arc gap Freckles and white spots have a much control, and robust power greater effect on material properties supplies designed specifically as compared to tree ring patterns and for this purpose. can represent a significant cause for premature failure of turbine disks in aircraft engines. Tree Ring Patterns Freckles White Spots Intended 06 ALD VAR Furnaces Design Features 1 8 3 5 Schematic of the VAR furnace 4 9 1 Electrode feed drive 2 Furnace chamber 3 Melting power supply 2 4 Busbars/cables 7 5 Electrode ram 6 Water jacket with crucible 6 7 Vacuum suction port 8 X-Y adjustment 9 Load cell system Design Features of all ALD VAR Furnaces O Gantry design of furnace head O Power supply with space saving super-structure features design, thyristor or saturable simple platform installation reactor control designed with no flexure of the super- specifically for fast response structure under load. and tight current control. Consistent centering of the O Sophisticated weight manage- electrode. ment system including highly O Proven electro-mechanical accurate, fully temperature dual electrode drive system compensated load cell system for very precise control of and statistical based melt rate small melt speeds during algorithm. the remelting process and O Completely automatic operation fast speeds for charging of the furnace by the use of procedures. password-protected preset melt O Remotely controlled, pneu- recipes, stored locally or down- matically operated electrode/ loaded from any host system. stub clamp with maximum O Statistical Process Analysis melting current transfer to (SPA) is possible with the data the electrode. acquisition system of the Operator O The furnace is of fully coaxial Interface PC in combination design avoiding stirring action with the optional Supervisory of the melt bath due to unsym- Sytem PC. metrical magnetic stray fields. 07 VAR Process Control ALD’s automatic melt control system (AMC) is unsurpassed in the world for its accuracy, reproducible metallurgical quality and ease of operation ALD provides precise control of all VAR remelting parameters for reproducible production of homogeneous ingots, which are free of macro-segregation and show controlled solidification structure and superior cleanliness. Computer controlled process Communication via field bus or O Can be optionally equipped with an automation used by VAR specific interfaces Ethernet network interface which may furnaces fulfills today’s most be utilized for data transfer to other stringent material quality Operator interface PC (OIP) computers connected to the local specifications. area network (e.g. supervisory PC, O Acts hierarchically as master of the customer’s main frame, etc.) ALD’s VAR control systems handle: automatic melt control system (AMC) O Logic control functions O Utilized as interface between operator Melt Recipes O Continuous weighing of the and VAR process consumable electrode O Serves for process visualization, O ALD furnaces work with established O Closed loop control of process featuring parameter indications, remelting parameters, stored as parameters (e.g. remelting rate, graphic displays and soft keys for remelting recipes on hard disk, for arc gap based on arc voltage operator commands, editing and repeatable VAR production of specific or drop short pulse rate) handling of remelting recipes, data ingot sizes and material grade O Data acquisition acquisition and storage and for combinations, to assure full O Data management generation of melt records metallurgical ingot quality ALD Vacuum Technologies GmbH ALD Vacuum Technologies ALD-C&K Vacuum Technologies OOO ALD Vacuum Technologies Otto-von-Guericke Platz 1 North America, Inc. (USA) (Suzhou) Co., Ltd. (PR China) (Russia) www.ald.vt.com/ru 63457 Hanau, Germany www.ald-usa.com www.ald-cnk.com [email protected] [email protected] [email protected] Phone: +49 6181 307-0 Phone: +1 860 386 7227 Phone: +86 512 6385 8833 Phone: +7 495 78767-34/33/31 Fax: +49 6181 307-3290 E-Mail: [email protected] ALD Vacuum Technologies ALD Thermo Technologies Internet: www.ald-vt.com India Pvt.