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Vacuum Induction Melting and Casting

Vacuum Induction Melting (VIM-VIDP) Furnaces for Charge Weights from 1 kg up to 30 tons

Vacuum induction melting (VIM) is one of the most commonly used processes in secondary metallurgy applied for refining treatment in the liquid state and adjustment of chemical composition and temperature. To achieve the increasing quality demands on the resulting material and at the same time

• save raw materials such as alloying elements due to higher yield; and
• save energy,

the application of vacuum in the induction melting process is a must for many specialized materials. For example, vacuum induction melting is indispensable in the manufacture of special alloys, which must be melted under vacuum or in an inert gas atmosphere because of their reactivity with atmospheric oxygen. The process is suitable for the production of high-purity metals within an oxygen-free atmosphere. This limits the formation of non-metallic oxide inclusions.

Vacuum induction melting makes possible effective degassing of the melt and extraordinarily precise adjustment of alloy composition, since the temperature, vacuum, gas atmosphere, pressure and material transport (e.g., through stirring of the bath) can be adjusted independently of one another. Besides the exact concentration of alloying elements, the content of trace elements is also important for many alloys.


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Current processing route for products cast from VIM/VIDP furnaces





Metallurgical Advantages are:
• Melting under oxygen-free atmosphere, this limits formation of non-metallic oxide inclusions and prevents oxydation of reactive elements;
• Achievement of very close compositional tolerances and gas contents;
• Removal of undesired trace elements with high vapour pressures;
• Removal of dissolved gases e.g. oxygen, hydrogen, nitrogen;
• Adjustment of precise and homogeneous alloy-composition and melt temperature.

For this reason, metallurgical operations, such as dephosphorization and desulphurization, are limited. VIM metallurgy is primarily aimed at the pressure-dependent reactions, such as reactions of carbon, oxygen, nitrogen and hydrogen. The removal of harmful volatile trace elements, such as antimony, tellurium, selenium, and bismuth in vacuum induction furnaces is of  considerable practical importance.
 
Exact monitoring of the pressure-dependent reaction of excess carbon to complete the deoxidation is just one example of process versatility using the VIM process for production of e.g., superalloys. Materials other than superalloys are decarburized, desulfurized or selectively distilled in vacuum induction furnaces in order to meet specifications and guarantee material properties. Because of the high vapor pressure of most of the undesirable trace elements, they can be reduced to very low levels by distillation during vacuum induction melting, particularly for alloys with extremely high strengths at higher operating temperatures. For various alloys which must meet the highest quality requirements, the vacuum induction furnace is the most suitable melting system.

Depending on the product and metallurgical process, vacuum levels during the refining phase are in a range of 10-1 to 10-4 mbar.

The following methods can be easily combined with the VIM system to produce
clean melts:
• Atmosphere control with low leak and desorption rates;
• Selection of a more stable refractory material for crucible lining;
• Stirring and homogenization by electro-magnetic stirring or purging gas;
• Exact temperature control to minimize crucible reactions with the melt;
• Suitable deslagging and filtering techniques during the casting process;
• Application of a suitable launder and tundish technique for better oxide
removal.

For particular applications (i.e. rotating engine parts) the quality of the material produced by VIM is the fundamental melting step but it is not sufficient to satisfy the highest requirements with respect to cleanliness and primary structure. The VIMproduced material must undergo a remelting and resolidification step as described in the chapter on ALD’s remelting technologies. For the most advanced quality requirements, the material has to undergo several refining steps such as in a triple melt process consisting of consecutive VIM (vacuum induction melting), ESR (electroslag remelting) and VAR (vacuum arc remelting) processes.

1. Sampling, 2. Temperature measurement, 3. Effective degassing/ distillation, 4. 3-phase electro-magnetic stirring for controlled bath movement during refining

ALD’s Product Range of Vacuum Induction Melting and Casting Furnaces
The casting weight in VIM furnaces by ALD can vary from 1 kg to 30 tons or more, depending on whether the furnace is being used for precision casting or for the production of ingots or electrodes for further processing. A large number of optional items allows a VIM furnace to be tailored for special requirements.

ALD and its predecessor, Leybold-Heraeus, has designed, manufactured and put into operation more than 2000 VIM furnaces worldwide.

VIM Application Advantages
The following advantages have a decisive influence on the high demand for ALD’s vacuum induction melting furnaces in metal production:

• Flexibility due to different batch size;
• Fast change of program for different types of steels and alloys;
• Low losses of alloying elements by oxidation;
• Achievement of very close compositional tolerances;
• Precise temperature control;
• Low level of environmental pollution from dust output;
• Removal of undesired trace elements with high vapor pressures;
• Removal of dissolved gases e.g., hydrogen and nitrogen.;       
• Choice of vacuum, controlled atmosphere, normal atmosphere or reactive atmosphere;               
• Choice of different pumping systems       
• High level of operational safety and good accessibility;              
• Broad range of standard accessories and options;                   
• High reliability and high productivity.

The installation of a programmable control system for automation provides best reproducibility of the melts.
In this way, increasing metallurgical demands for cleanliness and homogeneity can be met.
In addition, close composition tolerances can be achieved, as all of the process data are registered, stored and analyzed by a statistical process control.

VIM Chamber Furnaces Product Line
The product line is based on the chambertype VIM (Vacuum Induction Melting) or on the compact VIM-VIDP furnace design. Depending on production and economical requirements, the VIM furnace technology can be expanded by
different implements. These are:

VIM 02–4000

Vacuum Induction Melting

VIM–VIDP

in the range of 0.2 to 4,000 liters crucible volume; basic equipment

VIM–MT

with Mold Treatment

VIM–VCC

with Vertical Continuous Casting

VIM–HCC

with Horizontal Continuous Casting

VIM–DS

with Directional Solidification

VIM–FC

with Flakes Casting

VIM–HMC

with separate Horizontal or alternatively Vertical Mold Chamber

VIM–P

with Over-Pressure Operation

VIDIST

with Vacuum Induction Distillation

VID

Vacuum Induction Degassing


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1. Laboratory vacuum induction melting furnace. The basic equipment is a single-chamber system with a tiltable crucible and an integrated vertical mold chamber, a vacuum pump unit and a melt power supply. 2. Small vacuum induction melting (VIM) furnace for pilot production

ALD offers a complete product line of VIM furnaces with charge weights varying from 1 kg up to 30 tons for the making of:

• Semi-finished products, such as:
-  Wires, strips, rods
-  Ingots and electrodes
-  Targets
-  Structural parts
-  Powders

by the following procedures:
• Mold casting
• Continuous casting
• Centrifugal casting
• Powder production
• Spray forming
• Vacuum induction distillation

for use in:
• Research & development
• Electronic industry
• Dental applications
• Automotive and aerospace industry
• Ferrous applications
• Non-ferrous applications
• Precious metal industry


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1. VIM-VMC furnace with vertical mold chamber system, 2. VIM-VMC. The VIM-VMC-furnace is a two-chamber design with vertical mold chamber, 3. VIM-VCC. Vacuum induction melting with subsequent vertical continuous casting technology under inert gas prevents surface oxidation of cast wires, rods or strips, 4. VIM-VCC with vertical continuous strip or wire casting

Comparison of Larger Standard VIM Chamber Systems
ALD specializes in developing and implementing system designs tailored to customers’ specific needs. The furnaces are equipped with accessories for charging, sampling, temperature measurement, melt stirring facilities for melt treatment, turntable or mold carriage for several molds, etc. In addition to these “engineered” solutions ALD offers a variety of basic versions whose designs fundamentally differ from one another:


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1. VIM-VMC furnace with vertical mold chamber system, 2. VIM. Typical charge weights: 0.5–15 metric tons single-chamber system with vertical melting chamber, 3. VIM-HMC. Typical charge wheights: 0.5 to 20 tons; two-chamber system with horizontal mold chamber.


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4. VIM with launder system. Two-chamber system with one turntable for short ingots and another for long ingots. Replaceable heated launders. 5. VIM with bottom purging. The VIM furnace can be equipped with a tundish preheating unit and a crucible gas bottom purging device in order to treat the melt with gases. Oxygen blowing for R&D purposes is also possible. 6. 1 - 20 ton. The VIM furnace one chamber system with horizontal melt chamber and moveable sidedoor for crucible coil service.


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7. VIM with double-door arrangement. Typical charge weights: 5–30 metric tons. Two-chamber system with horizontal melting chamber and two interchangeable induction furnaces. 8. VIM-HMC. Multi-chamber system with a laterally movable door and furnace insert for easy maintenance. Hydraulic tilting device and power cables are arranged at atmosphere. 9. VIM-V 6, 4/6 t, Production of Fe-Ni based electric/magnetic materials.


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10. VIM-V 6, 25 t, Melt/cast chamber with separate mold chamber for production of superalloys. 11. VIDP Furnace for superalloy barsticks Ø 40 - 200 mm. 12. VID – vacuum induction degassing. The VID furnace has a compact design with small chamber volume, appropriate for steel melt shops and foundries. It is suitable for liquid and solid charging. It is applied for melting and degassing of special steel and non-ferrous metals, pouring at atmosphere into ladles or casting molds. The standard furnace capacity ranges from 1 up to 15 metric tons.


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13. VIDP – 8 t Furnace for continuous casting, Doncaster (Ross & Catherall) Sheffield. 14. 3 t VIM VID 300, Vacuumschmelze, Hanau, Germany. Tiltable compact furnace chamber. Casting under atmosphere or inert gas pressure.

VIDP Features
Small furnace volume
• Reduced desorption surfaces
• Smaller vacuum pumping system
• Optimum control of the furnace atmosphere
• Lower inert gas consumption

High flexibility
• Through a range of interchangeable lower furnace bodies
• Variable pouring techniques (ingot casting, horizontal continuous casting, powder production)
• Unit can be modularly expanded
• Connection to multiple casting chambers

Fast furnace change
• <1hour with hot crucible
• High operating availability
• Increased productivity by up to 25 %
• Rapid alloy change
• Separate crucible break out and relining stations
• Vacuum drying of crucible available

Easy to maintain
• Power cables and hydraulic lines are outside the melting chamber – leaks do not affect the vacuum
• Simplified maintenance of the vacuum pumps with effective filter system
• Smaller vacuum pumping system
• Tried and tested components           
• Preventive fault diagnostic
• No large vacuum chamber to clean

System Design


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Basic principle of a
VIDP furnace with
tilting vacuum furnace

In comparison to conventional VIM chamber furnaces, the VIDP design is characterized by its compact design with a small melt chamber volume, versatile connection capabilities for a variety of casting chambers and a high degree of costeffectiveness. The VIDP concept is based on a modular design that can be extended to melting and casting in a vacuum or protective gas atmosphere. The casting process is realized by using a  eramic launder which transfers the liquid metal through a pouring tunnel to the casting (mold) chamber.
The vacuum chamber size is reduced to a minimum – the result is lower pressure, shorter pumping time or smaller pump system capacity,  better control of process atmosphere, fast replacement of different furnace bodies with shorter downtimes for crucible exchange, high flexibility in the type of pouring technique, reduced risk of contamination by eliminating all flexible power cables, water hoses and hydraulic lines from inside the vacuum chamber, lower desorption and leakage rates compared to a conventional chamber-type VIM furnace.

The VIDP concept opens the way for economical production under controlled atmosphere of all high-grade metals and alloys commonly processed in chambertype VIM furnaces. In detail, the system with a capacity range from 1 ton to 30 tons is applied for the production of

• High-quality super alloys or special steels;
• Critical copper alloys and oxygen-free copper.

A video about the VIDP can be found here


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1. VIDP production unit at ThyssenKrupp VDM, 2. Total view of a VIDP production unit for ingot casting


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