Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
Field of the Invention - This invention relates to the
casting of colu~nar grained or equiaxed articles particularly from
high temperature alloys in a multi-part mold made up of a plural-
ity of mold elements. Such articles may be conventionally
cast or columnar grained or may be caqt from some of the eutectics.
SUMMARY, OF THE INVENTICN
The preformed or precast parts of a multi-part ld as
described in applicants' copending application Serial No. 210,674,
filed July 4, 1975 must be held together ~ecurely in a-~sembled
relation when the mold is poured to assure no leakage from the
mold and to assure the de~ired precision in the finished casting.
The securing means must be able to withstand the heat to which
the mold is heated which, in columnar grain ca~ting, for ex-
ample, is a temperature above the melting point of the alloy. Thus ~ ~
metallic clamp~ are not readily usable, The clamp mu~t have ther~al~ ;
characteristicA similar to those of the mold, such as the co-
efficient of thermal expansion, to avoid localized stressing of ~
either the mold or the clamp. ~ -
According to the invention, a high strength ceramic ring ` ;~
is po-~itioned around the multi-part mold at one or more locations ~-
along its length, the ring being a close fit to the outer sur-
faces o~ the ld in order to hold
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the mold part~ in proper assembled relation. The ring may be a
close slidable fit or it may be formed on the assembled mold parts
to be essentially an integral part of the mold. The ring may be
separately formed to be positioned around the mold or cast around
the assembled mold or formed by the ~hell molding process in
dipping a part of the mold in a ceramic slurry and drying the
coating of ceramic formed thereon, the dipping and drying proce-~s
being repeated until a coating of the desired ~trength i8 obtained.
According to one feature the ring may have an integral pouring cup
if the ring is positioned at the top of the mold. As an
alternative to the ring, high strength ceramic clip or holding
means may be positioned over the mating flanges of the mold parts.
In accordance with one embodiment, a holding device for
use with a multi-part mold for the casting of high temperature - -
metal alloys, said mold including: opposed precast ceramic mold
sides having projecting matting edge flanges and having recesses
therein to form an article cavity comprises; a high strength
ceramic ring tightly surrounding the opposed mold sides and en-
gaging the edge flanges to hold the opposed sides together, said
ring extending a part only of the length of the mold sides and
said ring having a compatible thermal expdnsion to that of the
mold sides.
The invention also relates to a multi-part mold includ-
ing at least opposed ceramic ~ide plates with projecting edge
flanges having cooperating surfaces to hold the side plates in
assembled casting position, and means surrounding the side plates
for a portion of the length of the mold to hold the plates to-
gether, said means being a high strength ceramic ring extending
completely around the a~sembled mold and having an inner surface
conforming to substantially the outer surfaces of the projecting
edge flanges of the side plates of the mold engaged thereby to
hold the oppo3ed side plate~ in casting position, said ring being
of a material having a thermal expansion compatible with the mold ~;
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material.
From a different aspect, in accordance with the inven-
tion, there i~ provided, in the attachment of prefonmed ceramic
~old parts together, said mold parts having mating edge flanges,
the steps of, dipping at least a part of the assembled ld
elements including
a part of the edge flanges in a ceramic slurry of the shell mold
type to form a coating in the form of a ring thereon: drying the
coating, and repeating the dipping and drying until a holding
ring of the desired thickness i8 obtained.
The foregoing and other objects, features and advantages
of the present invention will become more apparent in the light
of the following detailed description of preferred embodiments ~ -
thereof a~ illustrated in the accompanying drawing~.
BRIEF DES RIPTION OF THE DRAWINGS
Fig. 1 is an elevation of a mold with a holding ring -
of the invention in position.
Fig. 2 is a sectional view along line 2-2 of Fig. 1.
Fig. 3 is a elevation of-a ld as in Fig~ 1 with a
modified form of holding ring. ~
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Fig. 4 is a ~ectional view along line 4-4 of Fig. 3.
~ ig. 5 is an elevation of a mold with other forms of
rings thereon.
Fig. 6 i~ a sectional view along line 6-6 of Fig. 5.
Fig. 7 is a fragmentation elevation of the top of the
mold with a modified form of the ring of Fig. 1, with parts
broken away to show the con~truction. ,~
Fig. 8 is a view similar to Fig. 7 of a modificatlon of
the ring of Fig. 5. -
; Fig. 9 is a further modification shown in elevation.
Fig. 10 is a sectional view along line 10-10 of Fig. 9.
DESCRIPTIO~ OF THE PREFERRED EMBoDIMENT
Referring first to Figs. 1 and 2 the preformed multi-
part mold is shown by way of example for making the opposed halves
of a turbine blade as described and claimed in the copending ~-
application Serial No. 210,674 above identified. The mold
includes preformed opposed mold sides 10 and 12 of a suitable -
ceramic and center divider 14 also of a ceramic. ~he divider has ,~
edge flanges 16 and 18 received in notches in cooperating edge
flanges 20 and 22 on one edge of sides 10 and 12 and other co- ,
operating edge flanges 24 and 26 on the opposite edges of sides `,~ `
10 and 12.
The molds sides 10 and 12 may have hold down flanges 28
at one end by which the mold, when assembled is held in position
on a chill plate. Although the mold has other ;
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uses, such ~ mold construct~on is particularly useful in
casting columnar grained articles of the type claimed in
VerSnyder 3,260,505 or Piearcey 3,494,707. The latter
single crystal cast article is a particular form of columnar
grain. This type of mold is also usable in casting eutectics
such as described in Gell 3,567,526, which are also columnar
grained.
Such molds must be held in secure assembled arrangement
during the casting operation and the holding device must be
such as not to be destroyed by the step of heating the mold
to a temperature above the melting point of the alloy and
also such as not to be overstressed ar to overstress the
mold parts during the heating operation or during the sub-
sequent relatively fast cooling.
To accomplish this, the mold parts are surrounded at ~ -
the desired location lengthwise of the mold parts by a ceramic ~
ring 32 cast of high strength ceramic material. This ring ~-
~ has an inner surface 34 the contour of which closely fits
; the outer surfaces of the mold parts, at least at the
mating flanges 20 and 22 at one edge and the opposite -` -
~; mating flanges 24 and 26. There is just enough clearance "~ -
to perm~t the ring to sLide down over the assembled mold to
the desired portion on the mold. Although the inner surface
of the ring i8 shown as closely fitting over the entire area
of the mold ad~acent thereto, it is obvious that the partic-
ulsr close fit i8 at the mating flanges. For this type of
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ring to be usable the mold must be the same size or smaller
from the ring area to the top of the mold so that the ring
may slide into position. Once the ring is in place it may
be additionally secured by a suitable cement, not shown.
In the arrangement shown the mold has an enlargement
34 near the base to form the root portion of the blade,
above which is the airfoil portion 36 of the mold and the
ring 32 is shaped to fit the mold at the enlargement 34 as
shown. The cast articles are formed in the mold cavities
37 and 38.
As an alternate to the ring of Figs. 1 and 2, the
holding ring may be molded around the mold as in Figs. 3
and 4. In this arrangement the mold parts 42 and 44 have
the mating edge flanges 46 and 48 and the enlarged root
portion 50 below the airfoil portion 52. This mold con-
struction also has a shroud area 54 at the top of the
airfoil portion such that the sliding ring of Figs. 1 and
2 cannot be used. Instead, the ring 56 is formed in a
ring mold, not shown, positioned around the mold. Moldable ;-
high strength ceramic is packed in the ring mold to form ~-
the ring 56 and, after suitable hardening by heating mold
and ring, the ring mold is removed to produce the structure
shown. Here the inner surface 58 of the ring is in intimate
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and permanent engagement with the mold parts 42 and 44. -
Thus these mold parts are held in secure engagement with
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each other during the casting operation. The material of
ring 56 may obviously be any of the known high strength
moldable ceramics and not necessarily the same material
as the ceramic mold parts 42 and 44. By using different
materials, the differential thermal expansion may be used
to enhance the clamping action. The ring may be located at
any position desired lengthwise of the mold. More than one
of these rings may frequently be helpful in holding the mold
parts securely together, such as the second ring 58 at the
top of the mold.
Another form of holding ring for the multi-part mold
is shown in Figs. 5 and 6. Here the mold sides 62 and 64
with mating edge flanges 66 and 68 and a central mold
divider 70 are held together at top and bottom by rings 72
and 74, the latter enclosing the bottom flanges 76.
Each of these rings is formed by suitably holding the
mold parts together between the ends as by a stretchable ~ -
band, not shown, around the non-ceated portion. Each end
is then dipped in a ceramic slurry to form a coating, and
then dried, with the dipping and drying being repeated
enough times to produce the desired thickness of coating - ~
to form a ring of adequate strength around the mold. ~ - -
1 After each dipping the wet dip coat may be coated with
I a granular ceramic. This is the procedure~used to form -` -
' a shell mold and after the desired ring thickness i8
I obtained, the mold with the rings thereon is baked as ~
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in an oven to cure the material of the rings. In this
way a suitable holding ring is produced with adequate
strength to hold the mold parts in place for a casting
operation.
To prevent the inner mold cavities from being con-
taminated by the slurry in making the rings 72 and 74 the
ends of the mold assembly may be temporarily closed as by
a sheet of ¢ardboard or the like adhered thereto. Either
ring 72 or 74 may be formed independently of the other
and only one ring may be used in certain mold structures.
In any event the holding rings are securely attached to
and form a permanent connection with the molds. The ring
material is removed from the cast articles in the same
manner as the mold material.
The slidable ring of Figs. 1 and 2 may be modified,
if placed on the top end of the mold as in Fig. 7. Thus
the ring 80, slidably mounted on the top end of the multi- ~-
part mold 82, has an integral filler cup 84 cast with the
ring. The cup forms a shoulder 85 that limits the position
of the ring o* the mold. The cup receives the molten alloy -
when the mold i8 being poured.and directs it into the mold.
The ring thus serves both to hold the mold parts in assembled
relation and as a filler cup. The ring and filler cup are `-
molded into the configuration shown and baket to harden
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Instead of a ring and integral filler cup positionable
on the mold, the ring may be formed on the mold by the shell
molding process. Thus as in Fig. 8, a shell mold type of
coating 86 is formed on the upper end of the mold 88, but
in this arrangement a wax pattern 89 positioned on the top
of the mold forms a filler cup 90 that is integral with the
ring 92. Both elements 90 and 92 are simultaneously formed
by dipping and drying the end of the mold as above described
with reference to Figs. 5 and 6 until the desired thickness
of ring is produced. The ring produced in this way becomes
securely and permanently a part of the mold and performs its
holding function while the mold is poured.
In some circumstances the presence of a surrounding
ring as described may affect the cooling of the alloy after ~-~
the mold is poured. To avoid this the mold halves 92 and 94, ^
Figs. 9 and 10, may be held together by a shell mold type
of coating located only along the mat~ng side flanges 96
a~d 98. To do this, these side flanges are repeatedly dipped `~'
in a slurry for coating and then dried to build up a holding -~
clip 100 and 102 that overlies the edge flanges but does
not cover the parts of the mold directly external to the ~i
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part being cast. Again the material used i8 a high strength
ceramic which is hardened as by baking after the desired
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thickness is obtained thereby to obtain the desired strength.
Thege clip~ are essentially a permanent part of the assembled
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mold when the latter is ready to be used and serve to
hold the opposed mold halves securely in desired relation
during the casting operation,
Although the drawings show a three-part mold in-
cluding a center element, it is obvious that the invention
is equally applicable to a two-part mold.
Although the invention has been shown and described
with respect to a preferred embodiment thereof, it should
be understood by those skilled in the art that various
changes and omissions in the form and detail thereof may
be made therein without departing from the spirit and the
scope of the invention.
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