Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a process for the
melting and casting of metals or alloys under vacuum, and it
principally applicable to very oxidisable metals. A new integrat-
ed device is proposed for carrying out the process.
French Patent No: 1,587,187 describes a process for- -
bottom feeding a centrifugal casting mould intended for the
casting of solid metal parts.
French Patent No: 1,587,403 describes a centrifugal
casting process which allows the mould to be filled without the
appearance of eddies for components having a circular bore.
The French Patent application deposited under the
number 69~28,972 on the 25th August 1969 describes a process
which allows the heating of a central cavity of a mould during
centrifugal casting. The metal is thus maintained at a suitable
temperature to ensure progressive feeding into the shrinkage hole
which forms during solidification. The quality of the components
manufactured from oxidisable metals is improved by subjecting
the mould to a constant degasification during the entire casting
process.
There are therefore known methods of bottom "pouring"
centrifugal casting, without turbulence, by supplying the molten
metal under vacuum into a centrifuging shell. However, in all
the previousiy proposed methods the metal is brought to its
melting point outside the mould and then transferred into a feed
device of the centrifuging machine.
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lhe present in~en~io~ is irLte~ded to improve the ~nowrl
procedures for centrifugal casting with a view to pre~enting
the formation of oxide or other unwanted chemical compounds
duri~g the meltin~ a~d casting o~ the metal. This is
particularl~ useful in the case o~ metalswhich are ver~
oxidisable or which combine easily with elements other than
oxygen.
~ccording to this inve~tion in a process for meltin~
and ce~trifugal casting o~ metals or alloys~ in apparatu~ . :
which comprises a rotatable shell having an axial feed
channel in communication with the interior of an airtight
chamber containing a furnace for melting the metal or allo~
in which the chamber and the shell are kept constantly under
vacuum throughout the melting of the metal or alloy, the
furnace and the shell are moved relatively to each other
to bring the feed channel from a position outside the molteh
metal to a position immersed in the molten metal~ and a gas
neutral to the metal is admitted into the chamber to create
a pressure differe~ce between the chamber and the shell. ~hus
?0 melting takes place entirel~ under vacuum, which a~oids the
formation of oxides or other chemical compounds. I~ addition~
since the feed channel is in its raised position duri~g the
melting phase~ the shell and the bath of metal are not in
communication, so th~t the bottom pouring does not take place
2~ during the raising of the temperature of the metal~
According to ~nother pre~erred feature of the invention,
regulation is carried out o~ the speed at which the liquid
metal rises into the shell~ which is at first motionless and
then set in rotation. In order to do this, there is a
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controlled amoun~ of ~as introduced into the chamber containin~
the furnace. Since the centrifuging shell is maintained under
vacuum, and fed by a channel leading into a bath of metal it
will be understood that the speed at which the metal rises in
this channel will vary with the height between the upper shell
and the level of metal in the lower f~rnace, with the density
of the metal or the alloy being cast and with the difference in
pressure between the upper shell and the lower chamber. By
regulating the flow of gas into the fixed airtight chamber, it
is possible to control the speed at which the liquid metal flows
from the furnace into the centrifuging shell. In particular,
this control may be used to feed, progressively the centrifugal
component and particularly to feed eddies which have a tendency
to form on the component during solidification.
Preferably therefore when the molten metal reaches a
pouring temperature, the furnace is raised so that the lower
end of the feed channel is immersed in the bath of metal contained
in the furnace which is then maintained at the temperature
required for centrifugal casting. It is also preferred to
;20 regulate the gas introduced into the chamber containing the
furnace to control the fIow of the liquid metal into the then
revoIving shell. It is preferred to exercise this control so
that the speed of flow of the liquid metal from the furnace into
the shell is varied in such a way as to progressively feed
molten metal into shrinkage holes which tend to form in the
cast component during solidificat~ion.
Preferably the interior of the shell is submit~ed
to constant degasification during the entire time of melting
and then pouring, and centrifuging the metal, so that
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saturating vapour of the metal at the pouring -temperatur~
is removedO
According to .~nother preferred fea-ture, which is aimed
at even further improving the quality of the component
produced, the shell is submitted to a constant desgasification
throughout the casting process, principally in order to
remove saturating vapour from the metal or the alloy at the
casting temperatureO
~he carrying out o~ the procedure in accordance with the
invention is principally intended for the manufacture of a~nular
or tubular parts from very oxidisable metal which it is difficult
to cast in the presence of air, such as titanium, magnesium
a~d their alloys~
According to a~other preferred feature of the invention,
apparatus for carrying out the process of melting under
vacuum and centrifugal casting comprises a centrifuging shell
with a depending central feed tube and an airtight chamber
containing a furnace for the ~elting of metal, the airtight
chamber being arranged co-axially w~th and below the shell
and the central feed tube communicating with the i~-terior
o~ the chamber, an air-tight seal between the stationary
components of the apparatus a~d the moving components
being ensured b~ revolvin~ seals including a first revolving
seal effective between the feed tube and the airtight chamber,
and a second revolving seal effective between the centrifuging
shell and a valve connected to a ~acuum pump~ Further the
apparatus preferably comprises a safety system ~or the
airtightness of the chamber, this system being constituted
by a ca~ enclosing the first revolving seal a~d part
of the fced tube, there being a third re~olving seal between
the casing and the tube, a~d the casing being filled under
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pres~ure with a gas inert in relation to the liquid metal~
so that a leak in the firs-t revol~ing seal would allow the
introduction into the chamber only of the inert gas from
inside this ca~ingO
~he characteristics of the inver;tion ~ill be better
understood from the following descriptio~ of apparatus and
its method of use in accordance with the invention, which
description is given by way~of ex~mple only, with reference
to the accompanying drawings in which:-
~igure 1 is a vertical section throu~h a device for
achieving the melting and c^ntrifugal casting of metal under
vacuum~
~igure 2 is a view similar to Figure 1 showin~ the
position of the parts during the supply of molten metal to
an upper shell or mould,
~igure 3 is a veiw similar to Figure 2 illustrati~g
the pouring of a centrifuged tubular component,
~igure 4 shows in vertical cross-section a safe-ty device
: for ensuring air-tightness between a lower chamber and a
revolving shelll and
~igure 5 is a graph illustrating how the process according
to the invention allows the regulation of the speed at which
the metàl flows into the mould~
~here is shown in the drawings a vertical shell 1 which
may be rotated by known means (notlshown) about a vertical
axis 2~ ~he internal cylindrical wall 3 of this shell defines
a ~olume 7. A hollow portion 4 integral with the shell 1 ex*ends
vertically below and coaxial with the shell 1~ A hollow shaft 8
havin~ a reduced diameter lower portion 8a defines a channel 9
which is an axial extension of the portion 4 a~d puts the
~ centrifugi~g vol.ume 7 of the shell 1 into communicatio~ with a
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lower chamber 6. ~his chamber contains a furnace which in
this particular instr~nce i~ shown as GOmprising a crucible 10
made of refractory m~terial carried by a support 11 which is
mobile in a vertical directionO ~his crucible is provided with
a known type of heating system~ such for example a~ the
coils 12 of an induction heaterD Its upper part is closed
by a cover 1~ in which a central opening 14 is provided to
allow the introductio~ into the chamber 6 of the lower end
15 of the vertical shaft 80 A gas inlet pipe 16a which
includes a valve 16, co~nects the i~terior of the chamber 6
with a gas source (not shown~ containing a gas neutral to the
metal or alloy to be melted, and a~ exhaust pipe 17a which
include~ a valve 17, connects the interior o~ the chamber 6
with a vacuum pump ~not shown)0 '~his inlet and exhau~t s~stem
permits the creation o~ a vacuum inside the chr~mber 6 or the
introductio~ into it of a gas under con~rolled pressure.
me shell 1, hollow portion ~ and the tube 8 are adapted
to revolve, whils-t the chamber 6 ls fixed. hir-tightness
between the rotating parts and the stationary part of the
a~paratus is ensured by a first revolving seal 18 arranged
; between ~n ~nd wall o~ the chnmber 6 and the wall of the tube 8.
h ~cond revolving seal 19 mounted on a cover 20 o~ the ~hell 1
is connected to a vacuum pump (not shown) via a control
valve 24. ~inally one or several airtight doors in the wall
; 25 21 of the chamber 6 allow metal or alloy to be introduced
into the crucible 10 of the furnace~ ~he crucible assembly
is fitted in the chamber 6 at the time of construction, and
it is vertically movable by means of a remote control over the
support 11 (Figures 1, 2 and 3).
~or carrying out the process according to the invention
the apparatus is used as follow~:-
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~ he shell 1 and the hol.low shaft 8 are
stationary~ but they communicate -through the seal 18 with the
interior of the open chamber 60 'rhe metal or alloy to be
melted is introduced through one of the access doors into the
chamber 6 and placed in the crucible 10, after which the access
door is closed, so that the interior of the chamber 6 is then ~:
sealed from the surrounding atmosphere~ With the gas inlet
valve 16 closed~ a vacuum is created in the chamber 6 and in
the communicating centrifuging shell 1, by opening the valves
17 and~or 24 and operating the vacuum pumpO '~he remotely
controlled support 11 of the ~urnace is kept in its lower
pos1tion so ~that the end 15 of the tube 8 is ou-tside the
furnace.
When the required degree o~ vacuum is obtained, the ~-
means of heating the furnace are energised to raise the
temperature of the crucible 10 and to bring the metal contained
in it up to its melting point. During the entire operation of
melting under vacuum, the vacuum pump or pumps connccted to
- the valves 17 and/or 2'~ continue working, whilst the remotely
controlled support 11 is kept in its lower position
(~igure 1)O During this first phase, onl~ the melting under
vacuum of the metal 25 is carried out, the metal not being ir
communication with the feed channel 9 to the shell 1~
Second phase. When the me-tal 25 has reached its pouring
temperature, the crucible 10 containing the bath of metal is
raised vertically by raising the remotely co~trolled suppor.t 11
along a vertical guide, not shown~ 'rhe lower end 15 of the
feed tube 8 is then immersed in the liquid metal 25 (see
Figure 2).
3~ 3~ he inlet valve 16 is then opened~ allowing
the neutral gas to flow into the chamber 60 Since the interior
of the shell 7 is under vacuum9 that is at a minim~m pressure
. PO~ the introduction of the neutral gas through the valve 16
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causes the pressure in the chamber 6 to rise to a value P~,
greater than P0. ~he di~ference (P1 - Po) in pressure causes
the liquid metal 25 to rise into the interior volume 7 of
the shell 10 ~hus an operation of vacuum i'pouring" from
below is carried outO At the beginning of the "pouring" the
shell 1 remains stationaryO '~he metal 25 is kept liquid both
in the crucible 10 and in the feed channel 9 which is heated by
known methodsO
When this pouring has begun, the shell is revolved around
the vertical c~xis 20 ~he rotation of this shell causes the
molten metal flowing into the shell -to flow -to the inside of
the wall 3 of the shell (as shown in Figure 3) by centrifu~al
action, and in this way a tube 30 is moulded agai~st the wall
of the revolving shell 1.
It has been shown -that when a certain quantity of gas
is introduced into the chamber 6, a pressure difference P1-Po
is established~ between the airtight interior volume 6 and the
upper airtight volume 70 It is obvious that this difference in
pressure varies with the flow of gas through the valves 16,17
and 240 I~ it is supposed that the out-flows through the valves
17 and 24 remain constant, the speed at which the metal rises
through the channel 9 into the shell 1 will be a function of
the flow of gas through the inlet valve 16. ~his flow may be
~egulated so as to control the supply -to the centrifuged
. 25 component 30. In particular, at the end of the "pouring",
it is possible to supply molten metal progressively into
the shrinkage holes which form during the solidification of
the centrifuged tube 309 particularly for non-eutectic alloys~
or those with a long solidification period.
~; 3o me pressure difference necessary between the chamber 6
and the interior of the shell for a given rising speed of the
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metal~ or ~or machi~es with diffcrent heights~ increases with
the density of the metal or alloy to be pourcd~ and with the
distance separating the bath of metal in the crucible 10
from the centrifuging shell 1.
In Figure 5, the velocity V of the molten metal flowing
upwards into the shell 1 is plotted against three possible
bases~ namely the pressure differential P = (P1 Po)i the
densit~ d of the metal being cast7 and the level di~erence H ;~
between the ~hell 1 c~d the crucible 10~ ~hc curve A shows ~`
the variation of the rising speed V with the pressure
differential P; the curves ~ and C indicate respectively thc
variation o~ this speed V with the densi-t~ d of the metal
or with the difference in lcvel Ho
Since -the closed centrifuging shell 1 is airtight, it is
sufficient in theory to create a vacuum through the exhaust
pipe 17a and the valve 170 Thus in a simplified construction,
the revolving seal 19 and the valve 24 are no-t required~ and ~ :
~ the operation remains the same as previously described.
; Centrifugal casting under vacuum is carried ou-t by ensuring
that the lower end 15 of the tube 8 remains constantl~ immersed
- in the liquid metal contained in the crucible of the furnace,
which is not completely emp-tied during the casting processO
However, the revolving seal 19 and the extraction valve
24 are advantageous~ and in particular allow -the sa-turating
; 25 vapour from the metal at the pouring temperature to be removed
from the shell 1~
~or some processes particularly ~hen casting metals or
alloys such as titanium allo~s which cannot be melted in
the presence of air i-t is desirable to use a safety device
3 against leaks through the revolving seal 18 ~ shown in
Figure 40 This device comprises c~n airtight chamber 31
attached to the top of the chamber 6 and effective between
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the seal 18 ~d a supplemen-tary ~seal 32 surrounding -the tube
80 ~his chc~mber 31 is fitted with c~n entry pipe 33 controlled
by a valve 34 and with c~n ou-tlet pipe ~5 controlled by a
valve 360 The chc~mber 31 is filled, at a pressure P~ with a
gas inert in relation to the metal or alloy being meltedO The
melting and the centrifugal casting are processes exactly
the same as those previously describedO
~he safety device opercates in the following manner:-
If the seal 18 de~elopes a leak~ only -the neutral gas
con-tained in the chamber 31 penetrates into the chamber 6,
from which it is evacuated through the valve 170 If the seals
18 and 32 leak simultaneously, the mixture of gas penetrating
into the chamber would be composed of a neutral gas carrying
only a very small percentage of airn
~he opening of the ~alve 16 may be programmed in
: relation to -the bath of metal to be "poured" in such a w~y
as to control the speed of rising of this bath by regulation
of the pressure in the chamber. It will be appreciated
that the process m~y be used for centrifugal casting of ~:~
all kinds of metals and alloys, including light alloys or
. very oxidisable metals~
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