Metal founding – Means to shape metallic material – Including ladle or crucible type melt receptacle
Reexamination Certificate
1999-05-27
2003-02-04
Dunn, Tom (Department: 1725)
Metal founding
Means to shape metallic material
Including ladle or crucible type melt receptacle
C164S312000, C164S155200, C164S155400
Reexamination Certificate
active
06513571
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to low pressure casting machines and in particular to an apparatus and process for automatic refilling of a low pressure casting machine.
Many vehicle components, including wheels and full face wheel discs are cast in permanent multi-piece molds from alloys of light weight metals, such as aluminum, magnesium and titanium. Due to the large volume of parts needed, the casting processes are highly automated. Two frequently utilized casting processes are gravity-poured and low pressure casting. Gravity-poured casting involves pouring a charge of molten metal into a mold cavity. Gravity causes the molten metal to fill the mold cavity while gases within the mold cavity are forced out of mold vents. Riser cavities are formed in the upper portions of the mold cavity to assure that the mold cavity is completely filled and to feed additional molten metal into the mold to compensate for metal shrinkage as the casting cools and solidifies. After the casting is removed from the mold, the risers are removed and re-melted.
Low pressure casting involves forcing molten metal into the cavity mold under a low pressure, which, for casting wheel components, is typically within a range from approximately six psi to approximately seven psi. The pressure assures that the mold cavity is completely filled with molten metal. Typically, because the pressure force-fills the mold, the size of the riser cavities can be reduced, or the riser cavities may be eliminated entirely. Accordingly, less molten metal is needed for each casting and the need to re-melt the risers is reduced or eliminated. Additionally, low pressure casting facilitates casting of more complex shapes since the pressure forces the molten metal into all the portions of the mold cavity. Also, low pressure casting usually runs at lower mold temperatures and shorter cycle times than conventional gravity-poured casting processes. The rapid solidification rates associated with low pressure casting processes result in castings with finer grain size, smaller spacing between dendrite arms and enhanced mechanical properties.
Referring now to the drawings, there is illustrated in
FIG. 1
a typical known low pressure casting machine
10
. The machine
10
includes a thermally insulated lower chamber
11
which holds a pool of molten metal
12
. A filler tube
13
extends through a side of the lower chamber
11
from above the maximum height of the metal pool
12
. A removable filler cap
14
is mounted upon the upper end of the filler tube
13
. When closed, the filler cap
14
forms an air-tight seal for the lower chamber
11
. A pressurization port
14
A is formed through the lower chamber walls to allow pressurization of the chamber
11
. Similarly, a vent port
14
B is formed through the lower chamber walls to allow venting of the chamber
11
.
A multi-piece mold
15
is typically mounted above the lower chamber
11
; however, the chamber
11
is not necessarily positioned below the mold
15
. As illustrated in
FIG. 1
, the mold
15
includes an upper member
16
which cooperates with a lower member
17
to form a mold cavity
18
. For simplicity, a two piece mold
15
is illustrated in
FIG. 1. A
hollow fill tube, or stalk,
19
extends from the mold
15
and through the top of the casting machine's lower chamber
11
. The lower end of the stalk
19
extends into the pool of molten metal contained within the chamber
11
. The upper end of the stalk
19
extends through the lower mold member
17
and communicates with the mold cavity
18
. The upper mold member
16
is attached to a conventional mechanism
20
which raises the upper member
16
to allow removal of the casting from the mold cavity
18
. Once the casting is removed from the mold cavity
18
, the mechanism
20
is reversed to lower the upper member
16
and re-close the mold
15
.
To operate the low pressure casting machine
10
, the filler cap
14
is opened and molten metal poured into the filler tube
13
to fill the lower chamber
11
to the level of the lower end of the filler tube
13
. The filler tube
13
is then cleared of molten metal and the filler cap
14
closed and sealed. The mold
15
is closed and a pressurized gas is introduced through the pressurization port
14
A into the lower chamber
11
. The pressurized gas forces molten metal up the stalk
19
and into the mold cavity
18
, as shown by the small arrows in FIG.
1
. The pressure is maintained while the molten metal in mold cavity
18
solidifies into a casting for a component. The pressurized gas is then vented from the lower chamber
11
through the vent port
14
B and the upper mold member
16
is raised to open the mold
15
opened for removal of the casting from the mold cavity
18
. The upper mold member
16
is lowered to close the mold
15
and the lower chamber
11
re-pressurized to cast another component.
After each casting, the level of molten metal remaining in the lower chamber
11
is reduced. Accordingly, after a number of components are cast, the filler cap
14
is re-opened and the chamber
11
refilled with molten metal. The molten metal is typically manually transported to the individual casting machine from a centrally located refractory furnace in a thermally insulated covered ladle. Because the lower end of the filler tube
13
is some distance above the surface of the remaining metal when refilling occurs, the molten metal being added to the lower chamber
11
tends to cascade into the chamber
11
.
SUMMARY OF THE INVENTION
This invention relates to an apparatus and process for automatic refilling of a low pressure casting machine.
The prior art low pressure casting machine described above has a number of disadvantages. While the lower chamber is being refilled, the casting machine is out of service, which results in a loss of production and loss of mold temperature. Refilling the lower chamber of the casting machine interrupts the production process, causing process variability and corresponding product quality problems. The transport of molten metal to the casting machine for refilling the lower chamber is labor intensive. Because refilling requires pouring molten metal from a ladle and though a filler tube into the lower chamber, there is a chance that some of the molten metal could be spilled. Accordingly, the refilling process is hazardous. Manual refilling of the lower chamber is the last barrier to a fully automated low pressure casting process.
The agitation and turbulence caused by molten metal cascading from the filler tube into an almost empty lower chamber is conductive to generating oxidation byproducts and air bubbles which can be entrapped in the molten metal. When the oxidation byproducts and air bubbles are then cast into the component, the resulting product may have to be scrapped. Such raw material level variations are a source of process variability introduced by the traditional manual refilling process for the lower chamber.
Accordingly, it would be desirable to provide an apparatus for automatically refilling the lower chamber of a low pressure casting machine.
The present invention contemplates a low-pressure casting machine having a thermally insulated chamber adapted to retain a supply of molten metal and a mold having a cavity which communicates with the chamber. The machine also includes a pressurization device communicating with the chamber which is selectively operative to supply a pressurized gas to the chamber to force molten metal from the chamber into the mold cavity. The machine further includes a fill line communicating with the chamber, the fill line being operative to supply molten metal into the chamber. A normally closed fill valve is disposed in the fill line. The fill valve is selectively operative to control the flow of molten metal through the fill line and into the chamber.
In the preferred embodiment, the fill valve is actuated by a solenoid and the fill line communicates with a refractory furnace which supplies molten metal to the fill line. Gravity urges the molten metal
Dunn Tom
Hayes Lemmerz International Inc.
Lin I.-H.
MacMillan Sobanski & Todd LLC
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