Note: Descriptions are shown in the official language in which they were submitted.
r
1~79930
. .
This invention relates to a low pressure or counter-
pressure casting apparatus which can be used for the casting of
- workpieces of non-ferrous metals.
Apparatus for casting under low pressure are known, in
1 which the crucible with the runner tube are disposed inside a
-' hermetically sealed chamber which is arranged directly under the
plate which carries the casting mould. The drawbacks of these
devices are that they limit the capacity of the crucible; it is
.,
also impossible to provide ejectors and cores in the bottom half
:,
of the casting mould, since there is no place for disposing the
mechanism for their actuation.
~ These drawbacks are not only a result of design
.' . : .
,` considerations but also of technology. The rising of the metal
in the runner tube for filling the casting mould and its return
result in oxydation along the walls of the runner tube itself
... .
which are wetted by the molten metal, and the formed oxide
'; scale is carried into the casting mold during the next casting
;'~:,";
cycle. This can be avoided by the use of an inert gas instead of
air, but this makes the process much more e~pensive.
~-, 20 The direct feeding of the casting mould from the cru-
cible is disadvantageous because the variation of the level of
; the metal in it causes a variation of the velocity of filling the
mould, which leads to an inconstancy of the quality of the pro-
- duced castings.
The frequent recharging of the crucible with molten
; metal, because of its limited volume, causes idling of the
machine and reduces its productivity.
Machines for casting under low pressure are known, in
which the crucible for molten metal is disposed outside the
machine, which makes it possible to use crucibles of greater
volume and to free space under the mould for the arrangement of
different mechanisms. However, the ability to protect the
'
:"'
79930
,,
..
metal from oxidation and absorbtion of gases from the air is
greatly impaired.
The aforementioned drawbacks are typical also for the
` known machines for casting under counterpressure.
It is, therefore, a general object of the invention to
avoid the aforementioned drawbacks of existing machines and to
- provide conditions for reducing to a minimum the oxidation of
the metal.
, More particularly, the invention is a casting apparatus
- 10 which protects the free surfaces of the metal melt by means of
an inert gas with a minimum consumption of the latter and is
featured by a rational arrangement of the units, which permits
the disposition of different mechanisms directly under the
plate of the casting mould.
; Accordingly, the invention as herein claimed is a low-
- pressure or counterpressure casting apparatus which essentially
comprises: a mould-support structure having a plate carrying
a mould and formed with an inlet for feeding molten metal into
' the mould; a main crucible, for receiving molten metal,
~` 20 hermetically sealed and provided with a delivery conduit reaching
into the mass of molten metal so that it may be transferred from
the main crucible; an intermediate crucible which receives
molten metal from the delivery conduit, which conduit opens into
it at a location above its bottom, this intermediate crucible
being hermetically sealed and having an outlet disposed below
the level at which the delivery conduit communicates with the
intermediate crucible; a siphon conduit having an upwardly
extending stretch communicating at its lower end with the outlet
of the intermediate crucible, an elbow at the upper end of the
upwardly extending stretch substantially at the level of the
inlet into the intermediate crucible, a downwardly extending
stretch running from the elbow and a further stretch rising
; ~ - 2
..... .
, ` . ~.
,-. ~ ' '.
'` , ~ ' :` ~ '` '`
79930
i
' I~
. from this downwardly extending stretch to the inlet of the
. . .
mould,this elbow being disposed above the level of the molten
metal in the intermediate crucible; a stopper valve along the
siphon conduit between the inlet to the mould and the elbow,
~i- and a source of inert gas under pressure. First, second and
$-'~ third control means connect the gas source respectively with the
~' main crucible, the intermediate crucible and the elbow for
.
regulating the inert-gas pressure therein to displace molten
metal from the main crucible to the intermediate crucible and
.. 10 from the intermediate crucible to the mould and establish an
.~. inert-gas cushion at the elbow separating molten metal in the
stretches of the siphon conduit. A gate is provided in the
, ,;,
. intermediate crucible for selectively unblocking the end of the
~e delivery conduit opening into the intermediate crucible and for
~'
~-` the gas-tight sealing thereof.
According to a preferred embodiment, there is further
.~ provided a counterpressure chamber on the structure enclosing
i- the mold, a source of air under pressure connected to the
chamber, and control means connecting the sources for balancing
: 20 the pressures applied by the sources to the crucibles and the
chamber, respectively.
. For casting, inert gas is supplied in the intermediate
-- crucible, which is filled with the necessary quantity of molten
metal, the bell to the second metal conduit coming from the
`. basic crucible being closed. The pressure of the inert gas is
..: .,
controlled in accordance with the velocity of the filling of the
, casting mould. Simultaneously, the control member for the pres-
: sure in the upper elbow of the syphon-type metal conduit is
.~: also actuated, in order not to allow the metal to pass through
. .. .
:. 30 the conduit, driving out the gas from~ the upper elbow, where
a gas cushion had been formed, which after the filling of the
casting mould and the relief of the pressure in the intermediate
B
.
"
. .
1079930
.
crucible is reformed to interrupt the metal flow.
To effect casting, it is necessary that all spaces of
the machine be hermetically sealed. Thus, a protection of the
, molten metal from oxidation is achieved in the basic crucible
as well as in the intermediate crucible and the syphon-type
metal conduit.
- The invention has further advantages, such as:
,i .
- the influence of the varying level of the molten
metal in the main crucible on the velocity of filling the casting
-
~; 10 mould is eliminated;
-: - the space under the casting mould is made available
for the arrangement of actuating mechanisms, etc.
- idle times of the machine for recharging the main
'I crucible with metal are avoided;
- it is possible to connect several casting machines,
equipped with individual intermediate crucibles, to one main
crucible.
All this leads to an improvement of the quality of the
. .
castings and to an increase in the productivity of the machines.
For a better understanding of the invention, its
, operating advantages and specific objects attained by its use,
. . .
: ; reference is made to the following description having reference
.'7 to the accompanying drawing in which there is illustrated a
preferred embodiment of the invention.
- The intermediate crucible 1 for molten metal, having
a capacity sufficient for one or several operating cycles of
the machine, is disposed outside the machine at such a height
-i that, at the highest level of the metal inside it, it remains
- lower than the level of the upper elbow 2 in the inclined branch
,~ 30 of the syphon-type metal conduit 3, which connects the inter-
~- mediate crucible 1 with the casting mould 4. In the bottom
, elbow of the syphon-type metal conduit 3, there is provided a
B 4
.
, .
.. . . . . . . .:
9930
stopper valve 5 which, in the non-operating position of the
machine as shown in the drawing, is closed and is intended to
prevent undesired variations of the level of the metal in the
syphon-type metal conduit.
. In the upper portion of the intermediate crucible 1,
~` which cannot be attained by the level of the metal, there is
~- disposed a gas-tight bell or gate 6 which is controlled from
~ outside and covers up the inlet orifice of the second metal feed
~ eonduit 7, which connects the main crucible 8 for molten metal
.$~
~`` 10 and whose volume and disposition are arbitrary and are
~........... .
determined appropriately in accordance with the conditions in
the plant, for the feeding of one or several casting machines,
for example. The main crucible 8 is also hermetically sealed.
`:~ The upper elbow 2 of the syphon-type metal conduit 3,
as well as the spaces over the metal in the intermediate cru-
~; cible 1 and in the basic crucible 8 are connected by means of
known valves 9, 11 and respective pressure control members 12,
13, 14 in between and with a reservoir or container 15 for
pressurized inert gas. The chamber 16, inside which the casting
- 20 mould 4 is disposed, is connected by means of known valves 17
and 18 to a reservoir 19 for pressurized air while both gas
.... .
systems - for the air and for the inert gas - are interconnected
~ by a known control device 20, which is used for balancing and
; ~ controlling the pressure differential between them.
The machine in accordanee with the present invention
operates as follows:
At equalized pressure in the intermediate crucible 1
and in the main crucible 8, a command is fed in a known manner
and the gas-tight bell 6 is opened and then, by increasing the
- 30 pressure in the main crucible 8, a portion of metal is poured
over into the intermediate crucible 1 which is sufficient for
one or more castings. After equalizing the pressure in both
:~, .
-- B - 5 _
1~79930
.
crucibles, thus causing the interruption of the metal flow, a
command is fed for closing the gas-tight bell 6. For filling
the casting mould 4 with metal, the stopper valve 5 of the
syphon-type metal conduit 3 is opened by the valve 10 of the
inert gas system; the pressure in the intermediate crucible 1
is increased and the metal in it rises through the syphon-type
metal conduit 3 into the casting mould 4, driving out the gas
- from the upper elbow 2 and from the pocket 2a thereby removing
; the gas cushion that had been formed therein.
After filling the casting mould 4 and the partial
solidification of the melt, the pressure in the intermediate
crucible 1 is relieved, the valve 9 provides atmosphere pressure
in the upper elbow, and as a result the metal from the vertical
branch of the syphon-type metal conduit 3 descends gravita-
tionally below the level of the upper elbow 2, the metal flow
being interrupted. This level itself is chosen appropriately
at the smallest possible distance from the level of the inlet
of the syphon-type metal conduit 3 into the casting mould 4.
' For casting under counterpressure, the counterpressure
is produced with pressurized air from ~he reservoir 19 by means
- of the valves 17 and 18, the control device 20 having the
~ function of controlling the pressure inside the intermediate
;~ cruclble 1, controlled by inert gas so that its magnitude is
higher than that in chamber 16 of the casting mould in order to
i effect a displacement of the molten metaL.
; Timing of the action of all control members can be
- effected by known techniques used for control casting machines. " .
,' , , ' ,,
'
