U.S. patent number 3,620,289 [Application Number 05/031,458] was granted by the patent office on 1971-11-16 for method for casting directionally solified articles.
This patent grant is currently assigned to United Aircraft Corporation, East Hartford, CT. Invention is credited to Charles M. Phipps, Jr..
United States Patent |
3,620,289 |
|
November 16, 1971 |
METHOD FOR CASTING DIRECTIONALLY SOLIFIED ARTICLES
Abstract
Articles in which the crystalline structure is directionally
controlled as, for example, in directionally solidified or single
crystal articles are cast in individual molds with a mechanism to
control the cooling rate and direction such that orientation of the
crystalline structure is precisely controlled. A graphite susceptor
surrounds the individual molds and in cooperation with a chill
plate provides the necessary control of the cooling rate and
direction.
Inventors: |
Charles M. Phipps, Jr.
(Wapping, CT) |
Assignee: |
United Aircraft Corporation, East
Hartford, CT (N/A)
|
Family
ID: |
26707275 |
Appl.
No.: |
05/031,458 |
Filed: |
April 1, 1970 |
Current U.S.
Class: |
164/122.1;
164/122.2; 219/632; 164/127 |
Current CPC
Class: |
B22D
27/045 (20130101); C30B 11/003 (20130101); C30B
11/002 (20130101) |
Current International
Class: |
C30B
11/00 (20060101); B22D 27/04 (20060101); B22d
025/06 (); B22d 027/20 () |
Field of
Search: |
;164/60,122,125,127,338,353,361 ;219/10.49 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: J. Spencer Overholser
Assistant Examiner: John E. Roethel
Attorney, Agent or Firm: Charles A. Warren
Parent Case Text
This is a division of Ser. No. 750,335 filed Aug. 5, 1968, now Pat.
No. 3,538,981 for Method and Apparatus for Casting.
Claims
I claim:
1. In the process of producing directionally oriented castings the
steps of providing a susceptor having a plurality of parallel
openings therein, placing a mold in each of said openings, each
mold having an article forming portion heating the susceptor and
mold to a temperature above the melting point of the alloy, filling
the article forming portion with molten alloy and then bringing a
chill plate into contact with the end of the susceptor and with the
ends of the molds in the susceptor.
2. The process of claim 1 in which the mold has a slug receiving
cavity above the article forming portion to be melted during the
heating of the mold and susceptor.
3. The process of claim 1 in which the heating is accomplished in
part by a plurality of vertically spaced induction coils around the
susceptor.
4. The process of claim 3 in which the induction coils are turned
off successively from the chill plate to the top of the mold as
solidification of alloy takes place.
5. The process of making, from high temperature alloys, castings in
which the crystal structure is directionally oriented as in single
crystal or directionally solidified castings, the steps of heating
a plurality of molds in a susceptor having a plurality of openings
to receive the individual molds therein, each mold having an
article forming portion at the bottom heating the molds and
susceptor to a temperature above the melting point of the alloy,
filling at least the article forming portions of the molds with
melted alloy, and contacting the bottom of the molds and the
susceptor with a chill plate for solidifying the alloy in the
molds.
6. The process as in claim 5 in which each mold has a circuitous
passage formed in the mold at the extreme lower end for forming
single crystal solidification, and contacting the extreme lower end
of the mold with the chill plate to start solidification at this
point.
7. The process as in claim 6 with the additional step of providing
spaced induction coils around the susceptor for heating the
susceptor and molds therein.
8. The process as in claim 7 with the additional step of placing
the molds and susceptor in a vacuum furnace for additional
heating.
9. The process as in claim 6 with the additional step of making
each mold long enough above the article forming portion to receive
a slug of alloy thereon, and placing such a slug in the mold prior
to heating the mold and susceptor.
Description
The VerSnyder U.S. Pat. No. 3,260,505 describes the casting of
directionally solidified articles such as turbine blades and vanes
and the Piearcey application Ser. No. 540,114 filed Feb. 17, 1966,
now U.S. Pat. No. 3,494,709 describes the casting of single crystal
articles. In either case newly conceived techniques have been
required to produce these articles as described in the patent and
application. Further experience in casting such articles has led to
alternative techniques by which such articles may be produced.
SUMMARY OF INVENTION
A feature of this invention is a casting process by which these
articles may be produced singly or in multiples. Another feature is
the more precise control of the cooling process in the
solidification of the alloys or metals being cast thereby to obtain
the desired structure within the cast article.
One particular feature is a casting process for the production of a
plurality of cast articles simultaneously in which the alloy in the
several cast articles need not be all the same chemical composition
and in which both directionally solidified and single crystal
articles may be produced in different molds in a single casting
process.
One feature is a new form of susceptor for use in performing the
casting process.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a sectional view through a vacuum chamber.
FIG. 2 is a plan view of the susceptor.
FIG. 3 is a vertical sectional view through the susceptor along the
line 3--3 of FIG. 2 with the heating coils around it.
FIG. 4 is an enlarged view of a mold for directionally solidified
casting positioned in the susceptor.
FIG. 5 is a fragmentary enlarged view of a mold for casting single
crystal articles.
FIG. 6 is an enlarged view similar to FIG. 4 of a modified form of
mold.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A vacuum chamber 2 has attached thereto, not shown, suitable
well-known devices for producing a vacuum therein. The chamber has
a base portion 4 and a cover 6 with cooperating flanges 8 and 10
for securing the cover in position. A lifting eye 12 may be used
for removal and positioning of the cover.
The base 4 has a chill plate 14 mounted therein so that it is
vertically movable. In the arrangement this is accomplished by a
cooperating cylinder 16 and piston 18, the latter having a piston
rod 20 on which the chill plate is mounted. A suitable valve 22
controls the supply of actuating fluid to the piston which, as
shown, is effectively a part of the base. Suitable flexible fluid
connections 24 provide for a circulation of cooling fluid through
the chill plate.
Above the chill plate is a fixed supporting ring 26 on which is
positioned a susceptor 28 in which the molds 40, FIG. 3, are
positioned. The ring is of such a dimension that the chill plate
may be moved upward into contact with the bottom of the susceptor.
Within the vacuum chamber is also a heating means such as the
resistance heating element 32 for use in heating the chamber. Also,
in close surrounding relation to the susceptor are a plurality of
axially aligned primary windings 34a, 34b and 34c of induction
coils used for heating the susceptor. These coils are suitable
supported as by brackets 36 resting on ring 26. These coils are
individually controlled by separate switches 27, FIG. 3, as will
become apparent, so that the coils may be sequentially turned off
from the bottom to the top coil during the solidification of the
alloy.
The susceptor 28, as shown in FIGS. 2 and 3, is preferably a
cylinder which is of a dimension to fit within the induction coils
and rest on ring 26. This cylinder has a plurality of axially
extending openings 38 therethrough which may be closely spaced
leaving only thin walls therebetween. The susceptor is preferably
graphite and acts as the secondaries for the primary induction
coils. Each opening receives a mold 40, the bottom end of which is
approximately in the same plane as the bottom of the susceptor.
Spacing above this plane may be used to control the thermal
gradients in and rate of solidification in the mold. Suitable
projecting elements 42 on the walls of the openings 38 limit the
downward movement of the mold within the opening.
The openings 38 are preferably cylindrical and the dimension is
such as to fit closely the mold positioned therein. Obviously, if a
relatively flat mold were to be used it might be desirable to shape
the openings more nearly to the mold shape. The axial dimension of
the susceptor is selected to be substantially the same as that of
the molds to be used.
Each mold is the shell-mold type and the process for making these
molds is now well known. In the present process and apparatus the
mold has an article portion 44 that has a cavity conforming to the
shape of the finished article. In the arrangement shown the article
is a turbine blade having a shroud 46, an airfoil portion 48 and a
root 50. Below this article portion and forming an extension beyond
the root 50 is a growth zone 52 in the mold. The bottom of the mold
has an end closure 54.
Above the article portion of the mold is an extension 56,
preferably cylindrical to receive a slug of the alloy to be cast.
The length of the complete mold is preferably substantially the
length of the opening in the susceptor in which it is positioned.
Obviously the volume of the extension 56 is greater than that of
the remainder of the mold so that the slug when melted will fill
the remainder of the mold.
The mold, as above described, is adapted for directionally
solidified articles. A similar mold with a bottom modification will
serve for single crystal castings. For this purpose, as shown in
FIG. 5, the root portion 50a has a different form of growth zone
which is a zigzag portion 58 which has been found to produce at its
upper end a single crystal that will continue to grow as a single
crystal throughout the casting. This zigzag construction is
described and claimed in the copending application of Piearcey,
Ser. No. 540,114, filed Feb. 17, 1966, now U.S. Pat. No. 3,494,709
and having the same assignee as this application.
When the chill plate is moved into operative position in contact
with the bottom surface of the mold grain growth starts in the base
of the cavity and becomes a single crystal in the zigzag portion
with the growth proceeding upwardly on substantially a horizontal
liquid-solid interface until the alloy is completely
solidified.
A modified form of mold is shown in FIG. 6 in which the mold has
the article portion 46a and above this, instead of a cavity for
solidified alloy, there is a pouring sprue 58 through which melted
alloy, from externally of the mold is introduced to the mold. In
this arrangement several molds are all interconnected by a spider
type of pouring sprue for filling a plurality of molds
simultaneously. This arrangement is useable, for example, where all
the cast articles are formed from the same alloy.
In use the susceptor with the molds therein is placed in the
furnace and heated therein, with the chill plate spaced from the
molds until the entire mold has a temperature above the melting
point of the alloy and the mold is then filled with melted alloy
either by pouring into the mold or molds, FIG. 6, or by the alloy
melting from the top cavity and flowing down into the part of the
mold in which the casting is formed. With the susceptor and molds
above the alloy melting temperature, the alloy will be kept in a
molten condition until solidification is started.
To accomplish this the chill plate is moved into contact with the
bottom of the susceptor and the bottoms of the mold and at about
the same time the lowermost heating coil is turned off. The chill
plate cools the bottom of the molds and begins the upward
solidification within the molds. At the same time the chill plate
also cools the bottom of the susceptor and this takes place at such
a rate that the upwardly moving liquid-solid interface between the
solidified alloy and the still-liquid alloy above it remains
substantially horizontal throughout the entire solidification
process.
As the interface moves upwardly successive heating coils from the
bottom are turned off to allow the susceptor and the molds therein
to be cooled to a lower temperature so that solidification may be
completed within the mold. With a susceptor of the type shown and
described, it is possible to obtain substantially a uniform
temperature throughout the entire susceptor and the molds therein
during heating of the molds, and to control effectively the rate of
upward cooling of the molds and susceptor during solidification of
the alloy in the molds. The rate of cooling and thus the rate of
alloy solidification is readily controlled by the heat absorption
effect of the chill plate and the rate at which the successive
heating coils are cut out during the cooling. The rate of cooling
may under certain conditions be controlled by withdrawal of the
susceptor from within the induction coils rather than by
successively cutting out the coils.
* * * * *