1. PROCESSING METALS UNDER VACUUM IN LIQUID STATE
VACUUM CAP FURNACE
VACUUM CAP FURNACES
PROCESSING METALS UNDER VACUUM IN LIQUID STATE
P.D.Chaubal
Inductotherm (India) Pvt. Ltd.

2. WHAT IS VACUUM?
ATMOSPHERIC PRESSURE MBAR
TOP OF MOUNT EVEREST     650 MBAR
50 MILES UP                           10-3 MBAR (0.001mbar)
100 MILES UP                         10-6 MBAR
300 MILES UP                         MBAR          
500 MILES UP                         MBAR
Exposing liquid metal to a vacuum in the ranges of mbar (one millionth of an atmosphere) will create a significant removal of dissolved gasses and prevent pick up from atmosphere. The key benefit of vacuum melting.
Thankfully we don’t have to go 50miles up!! These pressure levels are easily achieved with industrial vacuum pumping systems.

3. WHY BOTHER WITH VACUUM? THE SIMPLISTIC VIEW
Atmospheric air contains Nitrogen, Oxygen and Water Vapour (a source of Hydrogen)
Unfortunately all these elements usually have an undesirable effect on metals during melting and casting
Oxygen and Nitrogen react with metallic elements in the molten metal to differing degrees and give rise to inclusions in our castings
Hydrogen can have a very negative effect on the mechanical properties of castings – embrittlement
Trapped gases cause porosity
Exposing liquid metal to a vacuum can remove dissolved gases in the molten state to lessen the effects mentioned above

4. VIM & VACUUM CAP VIM VACUUM INDUCTION MELTING VAC CAP
VACUUM INDUCTION DEGASSING

5. VIM & VACUUM CAP VIM PROCESS DEFINITION
Melting , refining and pouring in a high vacuum environment (<20 microns 0.02 mbar), using induction melting.
Pouring into static ingot molds in vacuum or a controlled “backfill” of inert gas.
COMPLETE CYCLE UNDER VACUUM
Ingots produced may be used for direct forging, as electrodes for remelting or as master alloys for investment casting / precision casting.
Melt and mix of selected raw materials / scrap in batch sizes of less than 2kg to 30 Tonnes.

6. VIM & VACUUM CAP VIM PROCESS DEFINITION
Remove oxygen to low levels by vacuum carbon de-oxidation.
Reduce levels of low vapor pressure contaminants like lead, bismuth, tin, antimony.
Reduce levels of dissolved gases like hydrogen and (limited) nitrogen.
Reduce sulphur level (limited).
Usually a slag free operation.
Suitable for melting and casting metals with high reactive alloy contents e.g Nickel based super alloys containing Ti
Ideally suited to high quality, clean alloy production

7. VIM & VACUUM CAP VACUUM CAP DEFINITIONS
Melting normally in air from solid or liquid charge (could be vacuum or controlled atmosphere if required)
Refining in a moderate vacuum environment – 100 microns (1-0.1mbar), using induction melting
Pouring in air (or controlled atmosphere if required as an option)
Reaches a product range between traditional Air melt and VIM

8. VACUUM CAP DEFENITIONS
Vacuum degassing (hydrogen and nitrogen removal) not as deep degassing as VIM procedure
Reduction of low vapour pressure tramp elements e.g.Pb, Cd, Bi, Zn
Deoxidation using combination of vacuum and C-O reaction
Decarburisation - Intensified C-O reaction at low pressure enabling excellent decarburization for extra low carbon levels.
Desulphurisation – use of reducing slags and / or powder injection in air or controlled atmosphere
Melt and mix of selected raw materials / scrap in batch sizes of typically 80kg to 20T
Several benefits of VIM are retained in VCAP plus added flexibility for desulphurisation etc

9. Port for small charger , sampling, ITC
Sight glasses
Viewing or pyro
Water cooled vacuum lid (cap)
Apron section with vacuum sealing flange
80kg - 20T Steel shell fce adapted for vacuum Connected to vacuum pumping system

10. VACUUM CAP Applications and Materials
The VCAP furnaces are available to suit a wide variety of melting application in sizes ranging from 80kg – 20Tonnes (other sizes available on request). Typical applications might include:
Low and high carbon steels
Tool and Die Steels
Stainless Steels
Nickel based alloys
Cobalt based alloys
Non Ferrous alloys

11. VACUUM CAP

12. VACUUM CAP

13. Induction furnace with shell prepared and sealed for vacuum operation
VACUUM CAP
Induction furnace with shell prepared and sealed for vacuum operation
Melt down
Lid off in air

14. Degas under vacuum lid on
VACUUM CAP
Degas under vacuum lid on

15. VACUUM CAP
Pour - lid off

16. In Air its just as efficient as a normal airmelt system
VACUUM CAP
Inductotherm Dual Voltage VIP power supply for optimum air and vacuum melting efficiency
In Air its just as efficient as a normal airmelt system
Lower voltage (vacuum) and frequency at holding power for improved stirring and degassing

17. VACUUM CAP

18. VACUUM CAP

19. Reductions in gas content, ppm and %
VACUUM CAP METALLURGICAL
Anticipated gas levels in Alloys … A Rough Guide!
Actual values cannot be guaranteed as they are very much dependant on the raw materials, scrap mixes used and individual melting practice. Gas levels can also be improved with additional time for holding the liquid metal in the molten state under vacuum.
Alloy type
Reductions in gas content, ppm and %
Hydrogen
Nitrogen
Oxygen
Group 1
C steels also with elevated Si, Mn contents
5 -> 1.5
70%
150 -> 80
45%
120 -> 60
50%
Group 2
Low to medium alloy steels
3 -> 1
66%
200 ->120
40%
100 ->50
Group 3
High alloys steels, Stainless, Ni Alloys
Fe and Ni alloys
4 -> 1.6
60%
300 -> 170
40-45%
80 ->50
>35%

20. VACUUM CAP METALLURGICAL
Deoxidation
The application of negative pressure above the melt bath allows the C-O boil to continue to much greater extent than is possible at atmospheric pressure.
Both Oxygen and Carbon levels are simultaneous reduced to lower levels. This effect is time related –> longer time = lower gas levels.
Deoxidation can also be enhanced by using Argon purging with porous plug.

21. VACUUM CAP METALLURGICAL
Hydrogen and Nitrogen removal
Hydrogen removal is the most rapid of degassing effects and can be reduced to very low levels 1-2ppm
Nitrogen removal is slower due to the thermodynamics and is very much influenced by alloy type, vacuum level and time for holding in vacuum state.

22. VACUUM CAP METALLURGICAL
Decarburisation
The level of decarburisation is also dependant on a number of factors including alloy type, oxygen level within melt and treatment time.
Decarburizations of 0.05 to 0.1% C can be considered in a Vac Cap furnace.  This is achieved by the intense C-O reaction at reduced pressure.
This effect can also be enhanced by adding small quantities of metallic oxide to the base charge or using dilute oxygen / inert gas mixtures with a porous plug in the base of the furnace. Caution must be taken when using oxygen containing gases in any induction furnace.

23. VACUUM CAP METALLURGICAL
Technical Benefits of Degassing
Generally significant improvement of mechanical properties, such as yield strength, ductility impact strength, fatigue and stress rupture elevated temperature properties.
Improvement of technological characteristics, like hot workability, weldability and machinability.
Better microcleanliness due to strong carbon deoxidation and smaller residual inclusions.
Significantly reduced scatter in product properties and characteristics, less rejections.
More exact chemistry control in general

24. VACUUM CAP METALLURGICAL
Foundry Benefits
What does it mean to the foundry….?
Opportunity to process a wider range of alloys (including alloys with small reactive element contents e.g. Ti up to 0.6%) – NEW MARKETS NEW OPPORTUNITIES, HIGHER ADDED VALUE
Can use lower cost scrap for expensive alloys COST
Ability to recycle large quantities scrap materials (70-100%) not possible in air melting (runners and risers) and use lower cost raw materials. COST
Fewer blow holes and rejects of castings due to gas related defects YIELD
Can use lower / quality cost (recycled) sand in the face coat of moulds COST
There is reduced loss of alloying elements COST
Less deoxidation additions required CaSi, CaMnSi, Al, etc COST
Better fluidity of melt, less casting misruns, better casting surfaces YIELD

25. VACUUM CAP
Of course investing in new Vacuum Technology is more expensive than conventional airmelt
Questions to consider
Are some of your customers already looking for improved quality?
Can improved quality and new alloy types open new doors?
Is it time to invest for the future?

26. VACUUM CAP

27. VACUUM CAP
Pour - lid off

28. THANK YOU