Spool shields for producing variable thermal gradients in an...

Details Spool shields for producing variable thermal gradients in an... Spool shields for producing variable thermal gradients in an...

1999-05-04

2001-04-03

Pyon, Harold (Department: 1722)

Metal founding

Means to shape metallic material

Including means to heat mold

C164S350000, C164S352000

Reexamination Certificate

active

06209618

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for solidifying a casting to create a directionally solidified or single crystal casting and, more particularly, to an apparatus which is capable of introducing a cooling spool into a casting mold and withdrawing the casting mold from a stationary heating chamber.
2. Related Art
Solidifying molten materials, such as molten metal, in a mold cavity to create a directionally solidified or single crystal casting is known.
FIGS. 1
a
and
1
b
illustrate a conventional apparatus
10
for producing a casting. An example of this is disclosed in U.S. Pat. No. 4,969,501. The apparatus
10
includes a heating chamber
12
defining an interior volume
16
which is heated via heating elements
14
. A plurality of casting molds
20
are disposed in an annular array on a vertically movable chill plate
22
. The molds are supported in and removable from the interior volume
16
by the movable plate
22
. The movable plate
22
is vertically displaced by column
24
. More particularly, the casting molds
20
may be removed from the interior volume
16
by displacing the plate
22
in the direction of arrow A (
FIG. 1
b
) while the heating chamber
12
remains stationary.
Unfortunately, apparatus
10
produces directionally solidified or single crystal castings having less desirable material properties due to lower thermal gradient during casting. A thermal baffle or heat sink is not introduced into an interior region of the casting mold apparatus during the withdrawal from the heating chamber
12
to selectively absorb radiant heat being supplied from the molds
20
. Indeed, there is very little if any control of thermal gradients at the molds
20
to obtain directionally solidified castings.
In order to obtain a directionally solidified or single crystal casting, a casting mold must be removed from a heating chamber using special procedures.
FIGS. 2
a
and
2
b
show another conventional apparatus
50
to produce a directionally solidified or single crystal casting. An example of this is disclosed in U.S. Pat. No. 5,778,961. The apparatus
50
includes a heating chamber
12
defining an interior volume
16
for receiving an annular array of casting molds
20
. The casting molds
20
surround and define an interior space
21
. The molds are disposed on an annular chill plate or disk
30
which includes a central aperture
31
. A thermal baffle or heat sink
34
us shaped and sized to pass through the aperture
31
in the plate
30
, and the baffle is movable vertically upward in the direction of arrow C (
FIG. 2
b
) with respect to the plate
30
by its supporting column
36
. In particular, the thermal baffle
34
may be moved into the interior space
21
by moving the column
36
upward, and vice versa. The radiation baffle
19
is disposed below the open end of the heating chamber
12
.
As illustrated, the casting molds
20
are maintained in a substantially fixed position and height with respect to a floor
32
. The casting molds
20
are removed from the interior volume
16
of the heating chamber
12
by raising the heating chamber
12
in the direction of arrow B (
FIG. 2
b
). Thermal baffle
34
may be moved into interior space
21
while the heating chamber
12
is moved. Of course, the chamber
12
can remain stationary and the molds may be moved out downwardly.
The thermal baffle
34
serves as a heat sink to absorb radiant heat from the molds
20
such that the molten material within the molds
20
is solidified directionally by a thermal gradient defined from the heating chamber
12
to the thermal baffle
34
. The thermal gradient is a function of the temperature difference and relative positions of the heating chamber
12
and the thermal baffle
34
. Therefore, the higher is the temperature of the heating chamber
12
and the greater is the magnitude of heat that the thermal baffle
34
can absorb, the higher are the thermal gradients obtained.
Since the thermal baffle
34
may be moved relative to the molds
20
, the thermal gradient may be controlled to some extent. Unfortunately, apparatus
50
only maximizes the thermal gradient and, therefore, does not satisfactorily provide the thermal gradient control needed to produce castings of different geometries and configurations or single components having substantially complex geometries and still result in desirable directionally solidified or single crystal articles.
Moreover, when a component is manufactured in a fixed thermal gradient system as shown in
FIG. 2
a
-
2
b
, the constant thermal gradient applies to the entire article and is normally not optimized over respective areas of the article. Constant, and particularly high thermal gradients may cause increases in casting scrap because hot tear prone alloys may crack as a result of thermal stresses due to the high thermal gradient.
Accordingly, there is a need in the art for a directionally solidified or single crystal casting apparatus which provides a high degree of control of thermal gradients when withdrawing casting molds from a heating chamber.
SUMMARY OF THE INVENTION
In order to overcome the disadvantages of the prior art, the casting apparatus of the present invention includes a heating chamber having a substantially open lower end. An outer cooling spool is disposed at the periphery of the open lower end of the heating chamber. A chill plate is movable through the lower end of the heating chamber from the lower end of the chamber to below that end by movement of at least one of the chill plate or the heating chamber.
A mold assembly is receivable into the lower end of the heating chamber via the movable chill plate. The assembly includes at least one, and typically includes an annular array of a plurality of mold cavities peripherally disposed around the chill plate.
A movable spool shield is disposed proximate to the outer cooling spool and operable to vary an amount of surface area of the outer cooling spool available for absorbing radiant heat from the heating chamber.
In an alternate embodiment, there is an additional inner cooling spool movable inside the area surrounded by the casting molds for receiving radiant energy. A second spool shield at the inner spool controls its available surface area.
Other objects, features, and advantages of the casting apparatus of the present invention will become apparent to those skilled in the art in view of the description below taken in conjunction with the accompanying drawings.


REFERENCES:
patent: 3810504 (1974-05-01), Piwonka
patent: 3897815 (1975-08-01), Smashey
patent: 4178986 (1979-12-01), Smashey
patent: 4969501 (1990-11-01), Brokloff et al.
patent: 5072771 (1991-12-01), Prasad
patent: 5197531 (1993-03-01), Hugo et al.
patent: 5778961 (1998-07-01), Hugo et al.

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