Transcript Prakash-Chaubal-Indu..

VACUUM CAP FURNACE
VACUUM CAP
FURNACES
PROCESSING
METALS UNDER
VACUUM IN LIQUID
STATE
P.D.Chaubal
Inductotherm (India) Pvt. Ltd.
Copyright ©2003 by Consarc Corporation
WHAT IS VACUUM?
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ATMOSPHERIC PRESSURE
TOP OF MOUNT EVEREST
50 MILES UP
100 MILES UP
300 MILES UP
500 MILES UP
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Exposing liquid metal to a vacuum in the ranges of 10-1 -10-3 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.
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Thankfully we don’t have to go 50miles up!! These pressure levels are
easily achieved with industrial vacuum pumping systems.
1000 MBAR
650 MBAR
10-3 MBAR (0.001mbar)
10-6 MBAR
10-8 MBAR
10-10 MBAR
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WHY BOTHER WITH VACUUM?
THE SIMPLISTIC VIEW
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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
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VIM & VACUUM CAP
VIM
VAC CAP
VACUUM INDUCTION
VACUUM INDUCTION
DEGASSING
MELTING
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VIM & VACUUM CAP
VIM PROCESS DEFINITION
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Melting , refining and pouring in a
high vacuum environment (<20
microns 0.02 mbar), using induction
melting.
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Pouring into static ingot molds in
vacuum or a controlled “backfill” of
inert gas.
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COMPLETE CYCLE UNDER VACUUM
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Ingots produced may be used for
direct forging, as electrodes for
remelting or as master alloys for
investment casting / precision
casting.
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Melt and mix of selected raw materials
/ scrap in batch sizes of less than 2kg
to 30 Tonnes.
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VIM & VACUUM CAP
VIM PROCESS DEFINITION
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Remove oxygen to low levels by vacuum
carbon de-oxidation.
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Reduce levels of low vapor pressure
contaminants like lead, bismuth, tin,
antimony.
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Reduce levels of dissolved gases like
hydrogen and (limited) nitrogen.
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Reduce sulphur level (limited).
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Usually a slag free operation.
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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 Copyright ©2003 by Consarc Corporation
VIM & VACUUM CAP
VACUUM CAP DEFINITIONS
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Melting normally in air from solid or liquid
charge (could be vacuum or controlled
atmosphere if required)
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Refining in a moderate vacuum environment
1000 – 100 microns (1-0.1mbar), using
induction melting
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Pouring in air (or controlled atmosphere if
required as an option)
Reaches a product range between traditional
Air melt and VIM
Copyright ©2003 by Consarc Corporation
VACUUM CAP DEFENITIONS
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Vacuum degassing (hydrogen and nitrogen removal)
not as deep degassing as VIM procedure
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Reduction of low vapour pressure tramp elements
e.g.Pb, Cd, Bi, Zn
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Deoxidation using combination of vacuum and C-O
reaction
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Decarburisation - Intensified C-O reaction at low
pressure enabling excellent decarburization for extra
low carbon levels.
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Desulphurisation – use of reducing slags and / or
powder injection in air or controlled atmosphere
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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
Copyright ©2003 by Consarc Corporation
Sight glasses
Viewing or
pyro
Port for small
charger ,
sampling, ITC
Water cooled vacuum lid (cap)
Apron section with
vacuum sealing flange
80kg - 20T Steel shell fce
adapted for vacuum
Connected to vacuum
pumping system
Copyright ©2003 by Consarc Corporation
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
Copyright ©2003 by Consarc Corporation
VACUUM CAP
Copyright ©2003 by Consarc Corporation
VACUUM CAP
Copyright ©2003 by Consarc Corporation
VACUUM CAP
Induction furnace with
shell prepared and
sealed for vacuum
operation
Melt down
Lid off in air
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VACUUM CAP
Degas under vacuum
lid on
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VACUUM CAP
Pour - lid off
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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
Copyright ©2003 by Consarc Corporation
VACUUM CAP
Copyright ©2003 by Consarc Corporation
VACUUM CAP
Copyright ©2003 by Consarc Corporation
VACUUM CAP METALLURGICAL
Anticipated gas levels in Alloys … A Rough Guide!
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
50%
Group 3
High alloys steels, Stainless, Ni Alloys
Fe and Ni alloys
4 -> 1.6
60%
300 -> 170
40-45%
80 ->50
>35%
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.
Copyright ©2003 by Consarc Corporation
VACUUM CAP METALLURGICAL
Deoxidation
The application of negative pressure above the melt bath allows the CO 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.
Copyright ©2003 by Consarc Corporation
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.
Copyright ©2003 by Consarc Corporation
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.
Copyright ©2003 by Consarc Corporation
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
Copyright ©2003 by Consarc Corporation
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
Copyright ©2003 by Consarc Corporation
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?
Copyright ©2003 by Consarc Corporation
VACUUM CAP
Copyright ©2003 by Consarc Corporation
VACUUM CAP
Pour - lid off
Copyright ©2003 by Consarc Corporation
THANK YOU
Copyright ©2003 by Consarc Corporation