U.S. patent application number 11/791677 was filed with the patent office on 2009-02-26 for vaccuum die-casting method.
This patent application is currently assigned to PFEIFFER VACUUM GMBH. Invention is credited to Hedwig Lismont.
Application Number | 20090050289 11/791677 |
Document ID | / |
Family ID | 35825345 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090050289 |
Kind Code |
A1 |
Lismont; Hedwig |
February 26, 2009 |
Vaccuum Die-Casting Method
Abstract
The invention relates to an improved vacuum die-casting, in
particular for metals and metal alloys which contain Al, Mg, Zn,
and Cu. In order to improve the quality of the components, it is
proposed to produce vacuum in the mold cavity and the casting
chamber cavity in several phases of the die-casting process. The
use of the new method is contemplated for both cold-chamber and
hot-chamber die-casting.
Inventors: |
Lismont; Hedwig; (Hirten,
DE) |
Correspondence
Address: |
ABELMAN, FRAYNE & SCHWAB
666 THIRD AVENUE, 10TH FLOOR
NEW YORK
NY
10017
US
|
Assignee: |
PFEIFFER VACUUM GMBH
Asslar
DE
|
Family ID: |
35825345 |
Appl. No.: |
11/791677 |
Filed: |
November 23, 2005 |
PCT Filed: |
November 23, 2005 |
PCT NO: |
PCT/EP05/12503 |
371 Date: |
May 7, 2008 |
Current U.S.
Class: |
164/457 ;
164/55.1; 164/61; 164/63 |
Current CPC
Class: |
B22D 17/14 20130101;
B22D 17/04 20130101 |
Class at
Publication: |
164/457 ; 164/61;
164/55.1; 164/63 |
International
Class: |
B22D 18/08 20060101
B22D018/08; B22D 18/06 20060101 B22D018/06 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 2004 |
DE |
10 2004 057 324.7 |
Claims
1. A method of die-casting of metal, metal alloys, which form a
cast mass, under application of vacuum, comprising the steps of: a:
filling the casting chamber (6) with the cast mass (8), b: sealing
a casting chamber cavity (5) against atmosphere, whereby the steps
a and b can be exchanged, characterized in that after sealing and
separating the casting chamber cavity (5) from atmosphere, a first
vacuum phase is carried out, a second or further vacuum phases are
carried out after separation of the casting chamber cavity (5) from
a first conduit to vacuum system (12).
2. A die-casting method according to claim 1, wherein sealing and
separation of the casting chamber cavity (5) from atmosphere takes
place by closing the mold (21).
3. A method according to claim 1, characterized in that sealing and
separation of the casting chamber cavity (5) from atmosphere is
carried out by connecting the casting chamber (6) with the
mold.
4. A method according to claim 1 characterized in that the sealing
and separation of the casting chamber (5) is carried out by closing
a filling opening (4) with a casting piston (3).
5. A method according to claim 1, characterized in that separation
of the casting chamber cavity (5) from atmosphere is carried out
with a cover closable from outside.
6. A method according to claim 5, characterized in that sealing of
the casting chamber cavity (5) is carried out by a linear movement
of a hood (7).
7. A method according to claim 5, characterized in that sealing of
the casting chamber cavity (5) is carried out by a linear movement
of a hood (7).
8. A method according to claim 1, characterized in that metering of
the cast mass (8) takes place before carrying out the first vacuum
phase.
9. A method according to claim 1, characterized in that metering of
the cast mass (8) takes place during or by means of a vacuum
phase.
10. A method according to claim 1, characterized in that metering
of the cast mass (8) takes place after carrying out a preceding
vacuum phase.
11. A method according to claim 1, characterized in that instead of
a vacuum phase, protective or reaction gases are fed into the
casting chamber and/or a mold cavity or such a phase is
interposed.
12. A method according to claim 1, characterized in that the
filling opening (4) is closed by displacement of the piston.
13. A method according to claim 1, characterized in that separation
of the casting chamber cavity (5) from the first conduit to the
vacuum system (12) is carried out by closing a valve (13).
14. A method according to claim 1, characterized in that separation
of the casting chamber cavity (5) from the first conduit to the
vacuum system (12) is carried out by displacement of the casting
piston (3).
15. A method according to claim 1, characterized in that vacuum,
which remains behind the casting piston (3) after the first vacuum
phase, remains in at least one further phase.
16. A method according to claim 1, characterized in that vacuum,
which is necessary for several vacuum phases, is produced with a
respective buffer vessel (17, 18).
17. A method according to claim 16, characterized in that the
buffer vessels (17, 18) are evacuated by a common arrangement of
vacuum pumps (19).
18. A hot-chamber die-casting method, wherein a vacuum system is
provided with at least two vacuum conduits, including the steps of:
1. Displacing a casting piston so that a filing opening (72) is
closed 2. Producing vacuum in a casting ladle (74), an intermediate
piece (75), a mouthpiece (76) and a mold cavity via a first vacuum
conduit (12) characterized in that 3. a first vacuum phase is
carried out after the casting piston passes past the filling
opening (3) 4. thereafter, the connection with the first vacuum
conduit (12) is broken 5. finally, a second vacuum phase is carried
out.
19. A hot-chamber die-casting method according to claim 18,
characterized in that an additional valve (77) prevents penetration
of metal in the first conduit (12).
20. A hot-chamber die-casting method according to claim 19,
characterized in that the additional valve (77) is provided on the
intermediate piece (75) located between the casting ladder (74) and
the mouthpiece (76).
21. A method according to claim 17, characterized in that cast mass
(8) contains aluminum as a major component.
Description
[0001] The invention relates to a vacuum die-casting method
according to the preambles of the first and eighteenth claims.
[0002] Die-casting under vacuum has already been used for some
times for producing workpieces from metal and metal alloys in
particular alloys of metals Al, Mg, Zn, and Cu. By die-casting
under vacuum, a high quality of material of work-pieces is achieved
as less air and gases is included in the material. For workpieces
from, e.g., aluminum, which later are subjected to heat treatment
or welding, one can hardly do without vacuum.
[0003] In addition, die-casting under vacuum not only possible with
use of liquid alloys, but can also be used with other different
particular processes. As examples, one can name here: processes in
which semi-liquid or doughy materials are used as a cast mass
(usually called thixo casting or rheocasting), processes in which
the cast mass consists of a material combination (composition) of
liquid or semi-liquid metals and non-metal inclusions (MMC), and
processes in which liquid material infiltrates a head piece.
[0004] Publication EP-OS O 051 310 discloses a process which is
known in the industry under the name Vacural.COPYRGT. (a registered
trademark of Machinenfabric Muiller-Weingarten AG). This and
similar later processes are carried out with a tightly closed
casting chamber connected with a heat maintaining furnace by a
suction pipe. Metal is aspirated into the casting chamber and is
metered out by vacuum which is produced in the mold and is
precisely controlled.
[0005] The vacuum system for such a process consists essentially of
a buffer vessel the vacuum in which is produced by a vacuum pump.
Sometimes, the vacuum pump is directly connected, sometimes a
central vacuum system is used. Further, such vacuum systems also
contain interposed valves and filters and pressure measuring
tools.
[0006] Publication DE-0S 196 45 104 describes a technology which
permits to obtain a higher vacuum in the mold cavity when the
cavity is connected in succession with two different vacuum buffer
vessels, without the need to connect the vessels with each other.
This method permits to increase the stability of the process and
monitory the process by end pressures of the vessels.
[0007] In the simplest form of the vacuum die-casting, the vacuum
is generated with a deaeration valve secured on the mold. Only
after the casting piston passes past the filing opening during the
first casting phase and, thus, breaks the connection to atmosphere,
the mold can be put under vacuum. The process time, which remains
after the passing of the piston past the deaeration opening, is
generally not sufficient to establish pressure balance between the
mold cavity and the buffer vessel or to efficiently evacuate the
mold cavity with vacuum pumps. Further, the achieved vacuum is
adversely affected by the cross-section of the deaeration valve
itself and of the connection channels which extend in the mold from
the mold cavity to the deaeration valve. Also, constriction in the
mold itself can negatively influence the vacuum still further.
Leaks, in particular between the casting piston and the casting
chamber, result in worse and fluctuating vacuum values. The leaks
vary greatly with wear of the piston and the casting chamber and
depend from the temperature.
[0008] In the process according to EP-0S 051 310, these drawbacks
are partially eliminated by applying vacuum already during filling
of metal and, thus, more time is available for achieving a lower
vacuum. Nevertheless, the metering precision is greatly influenced
by the vacuum value, temperature and viscosity of the melt, and
condition of the openings through which metal flows. Also, an
expensive control is not able to completely overcome difficulties
associated with metering.
[0009] In addition, this process requires an expensive and careful
sealing of the mold and piston because they remain longer under
vacuum then at a conventional vacuum die-casting, and leaks have a
greater influence.
[0010] Accordingly, an object of the invention is to provide an
improved die-casting method with which larger deaeration
cross-sections are possible so that a higher vacuum is achieved.
The requirements to the piston and the mold with regard to
vacuum-tightness should be reduced. The metering precision during
filling of the casting chamber with metal or metal alloy should be
increased.
[0011] This object is achieved with a method of die-casting of
metal alloys which form a cast mass under application of vacuum. It
comprises the steps of: [0012] a filling the casting chamber (6)
with the cast mass (8), [0013] b sealing a casting chamber cavity
(5) against atmosphere, whereby the steps a and b can be exchanged,
and is characterized in that after sealing and separating the
casting chamber cavity (5) from atmosphere, a first vacuum phase is
carried out, and a second or further vacuum phases are carried out
after separation of the casting chamber cavity (5) from a first
conduit to a vacuum system (12).
[0014] Further claims disclose further embodiments.
[0015] The object is also achieved with a hot-chamber die-casting
method wherein a vacuum system is provided with at least two vacuum
conduits, and which includes the steps of: [0016] 1. Displacing a
casting piston so that a filling opening (72) is closed; 2.
Producing vacuum in a casting ladle (74), an intermediate piece
(75), a mouthpiece (76) and a mold cavity via a first vacuum
conduit (12), characterized in that 3) a first vacuum phase is
carried out after the casting piston passes past the filling
opening (12); 4) thereafter, the connection with the first vacuum
conduit (12) is broken; and 5) finally, a second vacuum phase is
carried out.
[0017] The new method according to claim 1 or claim 18 has at least
two vacuum phases in the total casting cycle, in which vacuum is
produced. In the first phase, the atmosphere through the casting
chamber is exhausted. This permits to use connections which have
much larger cross-sections. Contrary to exhaust through the mold or
the mold valve, noticeably better conductance in the vacuum system
and, thereby, a better end pressure are achieved. At that, the
better conductance permits to reduce the time of the first phase.
Because the greater conductance permits to achieve a better vacuum
sooner, it is possible, in comparison with the method according to
EP-OS 0 051 310, to tolerate, at a much greater degree, the leaks
in the mold and along the piston. The casting chamber, which is
closable according to the invention, enables to carry out the metal
metering with high precision independent from vacuum.
[0018] According to the invention, in a second phase, the vacuum is
generated through the mold, whereby the achieved end pressure is
improved. This phase takes place when the cavity with the metal
melt is separated from the conduit to the vacuum system of the
first phase. This can take place as a result of displacement of the
casting piston or closing of a valve in the conduit.
[0019] With a low end pressure in the mold, the amount of gases
confined in the structure of the produced component is reduced.
High metal pressures, which were required up to now, can,
therefore, be reduced because the remaining residual gas must be
compressed to a lesser degree to achieve the same quality of the
structure. The method enables to improve the quality of the
component at die-casting of metal and metal alloys.
[0020] In further embodiments, this method can be improved. By
using a vacuum system with a buffer vessel for a vacuum phase, it
is possible to achieve such low pressures in the mold that closing
of the deaeration valve is possible before the metal reaches the
valve.
[0021] According to a further embodiment, an improved end pressure
is achieved when the space behind the casting piston is likewise
evacuated during the first and/or the second phase. In one of the
embodiments, this can be achieved when the space behind the piston
forms a whole with a hood which closes the chamber or is connected
therewith. A casting chamber, which is closed with a hood has a
further advantage consisting in that after the hood is closed,
vacuum generation can be started immediately with the first phase,
while the piston has not yet closed the filling opening. Thereby,
the process time can be reduced, while the piston can have a high
speed during the first casting phase. In addition, more time
remains for carrying out the second phase.
[0022] In yet another embodiment, no use is made of a closable
hood. The separation of the casting chamber cavity from atmosphere
takes place, while the piston closes the filling opening. The
casting chamber is connected with the conduit of the first vacuum
phase by a further big-dimensioned opening. The first vacuum phase
is produced before the piston closes the second opening. The piston
can have one or several sealing rings. This embodiment can be
incorporated in existing plants without any substantial
expenses.
[0023] Alternatively, in one of the embodiments, the sealing and
separation of the casting chamber from the atmosphere take place
while the two mold halves are assembled together, i.e., the mold is
closed. Thereby, the number of the necessary components and
openings in the casting chamber is reduced.
[0024] The sealing and separation of the casting chamber cavity
from the atmosphere can in other embodiments take place, while the
casting chamber is connected with the mold. Thereby, it is possible
then to separate the casting chamber and the mold from each other
and to fill the casting chamber in this condition of the assembly.
After filling, the mold is connected with the casting chamber. This
can e.g., take place at sides of the mold with a movable ram,
slide, or piston at the chamber end or in cast-in channel.
Alternatively, e.g., a vertical or pivotal casting chamber can be
formed, as is conventional in many "squeeze casting" plants.
[0025] Further, the sealing and separation of the casting chamber
cavity from the atmosphere takes place with a movable cover that
closes the filling opening. This embodiment can be rapidly closed
and is particularly advantageous when metal is metered through the
filling opening into the casting chamber through the pouring spout.
The pouring spout or a connection tube between the pouring spout
and the casting chamber is likewise formed movable. The combination
of a metering furnace with the pouring spout is actually a most
recommended metering system for most of foundries.
[0026] In one of the embodiments in which the metering pot is
mounted on the filling opening, the casting chamber cavity and the
atmosphere are separated from each other by a (heated) closable
metering pot. Here, the metering pot serves as a storage vessel for
a to-be-metered cast mass. Thereby, the metering process is made
independent from the remainder of the casting process. The casting
chamber can, thus, be filed with metal before, during, or after
vacuumization or feeding of protective or reaction gases. The
metering pot itself is filled through a closable opening (cover,
tube, metering piston . . . ) and can itself be vacuumized or
subjected to action of protective or reaction gases.
[0027] Independent of the used method, in order to separate the
casting chamber cavity from the atmosphere, the first conduit to
the vacuum system can be connected, otherwise as descried above, to
a casting chamber cover or directly to the casting chamber, also to
the cast-in channel or a connected therewith, big-dimensioned
channel in the mold. An additional valve must be mounted at the
admission point in the mold in order to prevent penetration of the
metal in the conduit.
[0028] According to a further embodiment, the inventive method can
be used in a hot-chamber die-casting process. With this process,
mostly, magnesium, zinc, or lead-based metal alloys are cast. Hear,
a casting ladle (gooseneck) is immersed in metal in a heat
maintaining furnace. It includes, in addition to a casting chamber,
a gooseneck-shaped channel which is connected with a mold via an
intermediate piece and a mouthpiece. This unit (gooseneck,
intermediate piece, mouthpiece) in a broad sense can be seen as
analogue of the casting chamber cavity in the cold-chamber process.
By a connection to this unit, a first vacuum phase can be
introduced, so that the already described invention is usable in
hot-chamber die-casting process. With large cross-sections, it is
possible to produce vacuum so rapidly that it can take place
shortly before the charging process. Thereby, it is prevented that
metal is aspirated into the mold cavity by the produced vacuum
already before the charging process itself.
[0029] The method according to the present invention can
advantageously be used for metal alloys which primarily contain
aluminum because it is with this metal, the presence of large
shares of air in the structure makes further processing (e.g.,
welding) more difficult if not impossible.
[0030] The invention will be explained in detail based on the
following description and drawings.
[0031] FIG. 1 a cross-sectional view of a die-casting machine
suitable for carrying out the method;
[0032] FIG. 2 a cross-sectional view of the casting chamber. The
sections a through c show different phases of the process;
[0033] FIG. 3 an embodiment of a vacuum system with several buffer
vessels;
[0034] FIG. 4 an embodiment with a direct connection to the casting
chamber (separation from atmosphere with the casting piston);
[0035] FIG. 5 an embodiment with a metering spout and a closing
mechanism on the filling opening;
[0036] FIG. 6 an embodiment with a closable metering pot; and
[0037] FIG. 7 an embodiment of a hot-chamber die-casting.
[0038] FIG. 1 shows a basic embodiment of a die-casting machine
suitable for carrying out the inventive method. A mold 21 is
clamped between two plates 22. A to-be-finished workpiece is
obtained by solidification of metal or metal alloy in the mold
cavity 10. A piston 3, which presses a mass of liquid metal 8 into
the mold cavity as a result of its linear movement, is displaceable
in a casting chamber 6. The casting chamber is provided with a
filing opening 4 through which the liquid metal is fed before the
first vacuum phase. A hood 7 vacuum-tightly seals the casting
chamber from outside. The cavity within the hood is connected by a
port 11 and a first conduit 12, in which the a valve 13 is located,
with a vacuum system 20. The vacuum system can be formed by an
arrangement of vacuum pumps and/or buffer vessels. Vacuum is
introduced over the first conduit during the first vacuum phase. A
second conduit 15 is connected with a valve 16 that connects a
deaeration valve 14, which is mounted on the mold with the vacuum
system 20. Over the second conduit, the vacuum is introduced during
the second vacuum phase.
[0039] The method with two vacuum phases will be explained in
detail with reference to FIG. 2. FIG. 2a shows the first step
during which metal in form of a cast mass 8 is fed into the casting
chamber 6. In this step, the hood 7 is pulled back, releasing the
filling opening 4. In the next step in FIG. 2b, the hood 7 is
pushed forward and vacuum-tightly closes the casting chamber cavity
5 at the piston side, the sealing is effected with a
circumferential seal 2 provided on the piston rod 1. Only then, the
vacuum system generates, over the port 11, vacuum which corresponds
to the first vacuum phase. This port can have a large conductance
because practically there are no spacial limitations. Thereby, the
mold cavity and the casting chamber are effectively and rapidly
evacuated. Between the second and third steps, the piston 3 is
pushed forward so that at the end, the filling opening 4 is closed.
Thereby, the volume above the cast mass is separated from the
cavity beneath the hood 7 and, therefore, from the vacuum conduit
means 11. In the third step, the mold is evacuated via the valve 14
and the second conduit 15 in accordance with the second vacuum
phase. This phase ends when the valve 14 is closed.
[0040] The phases can be explained with reference to the positions
of valves 13, 14 and 16. During filling of the casting chamber with
the cast mass, the valves are closed. As soon as the hood 7 is
pushed forward, the casting chamber becomes sealed against the
atmosphere, and the valve 13 opens, the first vacuum phase takes
place. After the displacement of the piston, the filling opening
becomes closed, and the vales 14 and 15 open (in most cases, the
valve 14 is already open), and the second vacuum phase takes place.
When the mold is filled with metal, the valves 14 and 16 are
closed. There, most of the aeration valves are closed by the metal
itself.
[0041] In a simplified embodiment, the separation of the first
conduit is carried out only by closing the valve 13, which permits
to simplify the construction. After closing, the second vacuum
phase can be carried out, independent on the position of the
piston.
[0042] A further embodiment is associated with filing of the
casting chamber with metal. This need not necessarily take place
before the first vacuum phase. It is conceivable to use a vacuum
phase for metering of the cast mass, with the metal being aspirated
into the casting chamber by vacuum, e.g., through a riser.
[0043] The metering of the cast mass should not take place in the
first vacuum phase but takes place in subsequent vacuum phases.
Thereby, the reaction of the cast mass with gases in the casting
chamber can be reduced, as those are reduced during the vacuum
phase before filling.
[0044] In an advantageous embodiment, instead of one vacuum phase,
protective or reaction gases are fed into the casting chamber
and/or the mold cavity. As a result, reactions of the cast mass
with gases are prevented, e.g., oxidation of the cast mass surface
is prevented to a great extent. Also, gases can be fed which
purposefully react with the cast mass and improve the properties of
the material.
[0045] In an advantageous embodiment, after the first vacuum phase,
no aeration of the cavity within the hood takes place. The vacuum
during one or several further vacuum phases can remain. Therefore,
the leaks along the piston are less critical, and possible leaks do
not lead to a dramatic deterioration of vacuum.
[0046] The valve 13 can remain open. With this system, particularly
low end pressure in the mold can be achieved, so that it is
possible to close the deaeration valve 14 before metal reaches
it.
[0047] In a further embodiment, the sealing of the casting chamber
against atmosphere is effected not by linear displacement of the
hood as in FIG. 2. Rather, in this embodiment, the hood is formed
as a part rotatable about the axis of the casting chamber 6 and the
piston rod 1. The filling opening becomes closes as a result of
this rotation. Such a hood proved to be advantageous, having a
shorter length and a shorter closing time.
[0048] A suitable embodiment of a vacuum system 20 is shown in FIG.
3. The first conduit 12, which is used in the first vacuum phase,
and the second conduit 15, which is used in the second vacuum
phase, are connected, respectively, with vacuum buffer vessels 17
and 18. The vessels are evacuated by vacuum pumps. Advantageously,
there is provided a common arrangement of vacuum pumps or a common
pump 19 with which the vessels can be evacuated independently from
each other in accordance with switching of the valve 23.
[0049] Advantageously, a separate vacuum buffer vessel is provided
for each phase. FIG. 4 shows an embodiment in which the casting
chamber cavity 5 is sealed against atmosphere by the piston 3. FIG.
4a shows a process step after the liquid metal 8 has filled the
casting chamber 6. After the piston 3 passed past the filling
opening 4, the casting chamber cavity 5 becomes sealed against
atmosphere, and the first vacuum phase can be introduced through
the port 42 of the first conduit 12 into the casting chamber 6.
This step is shown in FIG. 4b. When the valve 13 in the first
conduit becomes closed or the piston passes past the port 42, the
second vacuum phase can be introduced through the deaeration valve
14 and the second conduit 15. This condition is shown in FIG. 4c.
While retaining vacuum, the metal fills the mold cavity 10 under
the action of the piston 3, a shown in FIG. 4a.
[0050] Alternatively to the port 42, a connection can be formed on
the cast channel 41 or be realized in a form of a channel
connectable herewith. The cast channel 41 has, as a rule, a large
cross-section in the direction of the casting chamber cavity 5.
This connection, naturally is, closed with additional valve
(analogous to the deaeration valve 14), so that no metal can
penetrate in the first vacuum conduit 12. After this valve or the
valve 13 is closed, the second vacuum phase can be introduced.
[0051] FIG. 5 shows an embodiment in which the filling opening 4 of
the casting chamber 6 can be closed with a lid 53, and the metal 8
is metered into the casting chamber 6 over a movable pouring spout
51. FIG. 5 shows the process during metering of the metal. After
the casting chamber 6 is filled with the metal 8, the pouring spout
51 is lifted off the filling opening 4 vertically upward, so that
the lid 53 can pivot beneath the pouring spout 51 and can be
lowered onto a lid seat 52 after a short vertical movement. This
seals the filling opening 4, and the first vacuum phase can be
introduced through the first conduit 12.
[0052] The vertical movement of the pouring spout 51 and the
rotational movement of the lid prevents the sealing surface between
the lid and the lid seat from contact with the hot metal and its
contamination. The seal 54 is preferably mounted on the underside
of the lid 53. In order to eventually collect the draining metal, a
drain metal sheet 55 is mounted above the lid 53.
[0053] Alternatively to movement of the pouring spout 51, a short
movable feed tube 58 can be provided, which is displaced downwardly
during metering to bridge the distance between the outlet of the
pouring spout 51 and the filling opening 4. Thereby, sidewise flow
of the metal or its splashing is prevented.
[0054] The cavity behind the piston is likewise connected, in the
embodiment shown in FIG. 5, by a connection 57 with the first
vacuum conduit 12.
[0055] The embodiment of FIG. 6 represent a solution that
contemplates filling of the casting chamber 6 with metal 8 using
the metering pot 61. The metering pot simultaneously provides for
separation of the casting chamber cavity 5 from atmosphere.
[0056] The metering pot is filled with metal in the first step
(FIG. 6a). After the mold 21 is closed, the first vacuum phase can
already be introduced at a very early point in time (FIG. 6b). This
takes place in this embodiment over the first vacuum phase conduit
12. Independent therefrom, alternatively, the metering pot cavity
63 can be brought to a certain underpressure. By pulling the plug
62, the metal is metered into the casting chamber 6 through the
filling opening 4. An eventually occurring (positive) pressure
difference between the metering pot cavity 63 and the casting
chamber cavity 5 would accelerate the metering process. After
filling with metal and closing the valve (13) in the first conduit,
immediately thereafter a further vacuum phase is introduced.
[0057] FIG. 6a shows a modification of the metering pot 61 with a
closable lid 64. The lid can be open after the plug 62 reliably
closes the through-opening. It makes sense to wait with opening of
the lid until the piston 3 passes past the filling opening 4 in
order not to jeopardize the tightness of the casting chamber cavity
5 by a possible leakage at the plug 62. Then, the metering pot 61
is filled again with the cast mass 8 by an arbitrary point in time.
In case, e.g., the metering pot cavity 63 is under a protective
gas, the metering pot 61 can be filled through a closable tube or a
metering piston instead through a closable lid 64.
[0058] In another embodiment, instead of a metering pot, a closable
metering tube or a metering piston can be excused.
[0059] An embodiment for a hot-chamber method is shown in FIG. 7.
As it is conventional with the use of the hot-chamber method, the
casting ladle (gooseneck) 74 is immersed in metal that fills a heat
maintaining furnace 71. The casting ladle 74 has a casting chamber
73 having a filing opening 72 that connects the casting chamber 72
with the metal bath in the heat maintaining furnace. The casting
ladle has also a gooseneck-shaped channel that connects the casting
ladle through an intermediate piece 75 and a mouthpiece (heated) 76
with the mold 21. FIG. 7a shows an initial position in which the
piston 3 is in its initial position and the metal in the casting
ladle 74 is at the same level as in the heat maintaining furnace
71. In a second step, the piston 3 closes the filling opening 72 so
that no metal can flow. At this time, the conduit 12 can introduce
a first vacuum phase (FIG. 1b). Before the metal raises up to the
intermediate piece 75, an additional valve (piston) 77 becomes
closed, so that no metal can flow in the first conduit 12 to the
vacuum system. By this time, a second vacuum phase can be
introduced over the conventional deaeration valve and the second
conduit 15. This step is shown in FIG. 7c. In the last FIG. 7d, the
piston 3 advances the metal further into the mold over the
intermediate piece 75 and the mouthpiece 76.
* * * * *