U.S. patent application number 09/757303 was filed with the patent office on 2002-08-08 for investment casting with improved melt feeding.
Invention is credited to Kroes, Calvin L..
Application Number | 20020104639 09/757303 |
Document ID | / |
Family ID | 25047279 |
Filed Date | 2002-08-08 |
United States Patent
Application |
20020104639 |
Kind Code |
A1 |
Kroes, Calvin L. |
August 8, 2002 |
INVESTMENT CASTING WITH IMPROVED MELT FEEDING
Abstract
Method and apparatus for casting of molten metallic material
wherein the metallic material is introduced into a mold and a
pressure cap then is clamped on the mold by a cam/cam follower
mechanism to form a seal such that pressurizing gas can be
introduced into the mold on the molten metallic material therein.
The pressure cap includes an inlet for pressurizing gas, which is
introduced on the molten metallic material in the mold after the
pressure cap is sealed thereon. Application of gas pressure on the
molten metallic material in the mold improves filling of mold with
the molten material and reduces or eliminates non-fill voids in the
solidified casting.
Inventors: |
Kroes, Calvin L.; (Wichita
Falls, TX) |
Correspondence
Address: |
Edward J. Timmer
Walnut Woods Centre
5955 W. Main Street
Kalamazoo
MI
49009
US
|
Family ID: |
25047279 |
Appl. No.: |
09/757303 |
Filed: |
January 9, 2001 |
Current U.S.
Class: |
164/319 |
Current CPC
Class: |
B22D 27/13 20130101 |
Class at
Publication: |
164/319 |
International
Class: |
B22D 023/00 |
Claims
I claim:
1. Apparatus for casting a molten metallic material, comprising: a
mold having a mold cavity to receive the molten metallic material,
and a pressure cap having a seal-carrying member disposed on said
mold and having a cam member disposed on the seal-carrying member,
said seal-carrying member including a seal for sealing on a surface
of said mold, said cam member having a cam surface, said pressure
cap including a cam follower that engages said cam surface and said
mold in a manner that said seal is compressed against said surface
between said seal-carrying member and said mold when said cam
member is moved, said pressure cap including a gas inlet for
introducing pressurizing gas into the mold on a surface of the
molten metallic material therein.
2. The apparatus of claim 1 wherein said cam follower is disposed
for movement on said seal-carrying member.
3. The apparatus of claim 2 wherein said cam follower includes a
follower surface that engages the cam surface and a mold-gripping
surface that grips the mold in a manner to urge said seal-carrying
member toward said mold when the cam member is rotated.
4. The apparatus of claim 3 wherein the mold-gripping surface
engages a frusto-conical pour cup of the mold.
5. The apparatus of claim 3 wherein said cam member includes a pair
of said cam surfaces that are engaged by a respective said cam
follower.
6. The apparatus of claim 3 wherein said cam follower includes an
upstanding follower member having the follower surface and the
mold-gripping surface thereon, said cam follower member being
disposed for up and down movement between a pair of brackets
connected to said seal-carrying member.
7. The apparatus of claim 1 where the seal resides on a lip of a
mold pour cup so as to seal thereon when the cam member is
moved.
8. The apparatus of claim 1 wherein said cam member is circular cam
plate and said seal-carrying member is a circular plate having said
seal on a side facing the mold.
9. The apparatus of claim 8 wherein the cam member includes a
handle by which it is rotated relative to the seal-carrying
member.
10. The apparatus of claim 1 including a source of inert gas
communicated to said gas inlet.
11. The apparatus of claim 1 wherein said gas inlet extends with
clearance through an aperture in the cam member and is connected to
the seal-carrying member to communicate to a mold interior.
12. Method of casting, comprising introducing molten metallic
material into a mold, placing a pressure cap on the mold after the
melt is introduced therein with a seal of said pressure cap
disposed on a mold surface, camming the pressure cap toward the
mold to compress the seal against the mold surface, and introducing
gas through an inlet in the pressure cap on the melt residing in
the mold to provide gas pressure on said melt.
13. The method of claim 12 wherein the pressure cap is cammed
toward the mold by movement of a cam follower that engages a cam
surface on the pressure cap and that also engages the mold.
14. The method of claim 13 wherein the cam surface is moved
relative to the cam follower while the cam follower engages the
mold.
15. The method of claim 13 wherein the cam follower engages a
frusto-conical pour cup of the mold.
16. The method of claim 12 wherein an inert gas is introduced
through the inlet into the mold.
17. The method of claim 12 wherein the molten metallic material is
introduced into the mold in a vacuum casting chamber, the mold is
removed from the vacuum casting chamber, and the pressure cap is
placed on the mold after the mold is removed from the vacuum
casting chamber.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to casting of metals and
alloys in a mold in a manner to apply localized gas pressure on the
melt in the mold after it is cast into the mold to improve filling
of mold and reduce or prevent non-fill voids in the solidified
casting.
BACKGROUND OF THE INVENTION
[0002] In the manufacture of turbine blades and vanes for modern,
high thrust gas turbine engines, there has been a continuing demand
by gas turbine manufactures for internally cooled blades and vanes
having complex, internal cooling passages including such features
as pedestals, turbulators, and turning vanes in the passages in a
manner to provide desired cooling of the blade or vane. These small
cast internal surface features typically are formed by including a
complex ceramic core in the mold cavity in which the melt is cast.
The presence of the complex core having small dimensioned surface
features to form pedestals, turbulators, and turning vanes or other
internal surface features renders filling of the mold cavity about
the core with melt more difficult and more prone to inconsistency.
wettable ceramics and increased metallostatic head on the mold and
higher temperatures have been used in an attempt to improve mold
filling and reduce localized voids in such situations, but these
are costly and may be restricted by physical size of the casting
apparatus.
[0003] U.S. Pat. No. 5,592,984 describes a method of investment
casting gas turbine engine blades and vanes and other components
wherein a ceramic investment mold is disposed in a casting furnace
in a vacuum casting chamber and filled with the melt. The vacuum
casting vacuum chamber is gas pressurized rapidly enough after
filling of the mold with melt and prior to withdrawal of the mold
from the casting furnace to reduce localized void regions present
in the melt as a result of surface tension effects between the melt
and mold components such as ceramic mold and/or core.
[0004] U.S. Pat. No. 6,019,158 and 6,070,644 of common assignee
herewith describe use of pressure cap that is pivoted and sealed on
the pour cup of an investment shell mold to apply gas pressure to
the melt residing in the pour cup to improve filling of fine
mold/core details with the melt.
[0005] It is an object of the present invention to provide a method
and apparatus for casting a molten metallic material where gas
pressure is provided on the melt in the mold in a manner to improve
filling of the mold with the molten metallic material.
SUMMARY OF THE INVENTION
[0006] The present invention provides method as well as apparatus
for casting of molten metallic material wherein the molten metallic
material is introduced into a mold and a pressure cap then is
clamped on the mold using a cam/cam follower mechanism such that
pressurizing gas can be introduced into the mold on the molten
metallic material therein. The pressure cap includes a
seal-carrying member disposed on the mold and a rotatable cam
member disposed on the seal-carrying member. The seal-carrying
member includes a compressible seal that seals against a surface of
the mold, such as a lip of a mold pour cup. One or more cam
surfaces are provided on the cam member and actuate one or more cam
followers that engage(s) a respective cam surface and also the mold
in a manner that the seal is compressed on the mold surface between
the seal-carrying member and the mold when the cam member is moved.
The pressure cap includes a gas inlet for pressurizing gas, which
is introduced on the molten metallic material in the mold after the
pressure cap is clamped thereon. Application of gas pressure on the
molten metallic material in the mold improves filling of mold with
the molten metallic material and reduces or eliminates non-fill
cavities or voids in the solidified casting.
DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is an elevational view of a pressure cap of the
invention on a pour cup of an investment shell mold for practicing
a method of the invention.
[0008] FIG. 2 is a plan view of the pressure cap.
[0009] FIG. 3A is an enlarged, partial elevational view, partially
broken away, of the cam/cam follower mechanism of the pressure cap
of FIG. 1. FIG. 3B is an enlarged, partial side elevational view of
the mechanism of FIG. 3A taken 90 degrees to FIG. 3A. FIG. 3C is a
partial plan view of the mechanism.
[0010] FIG. 4 is a partial plan view of the seal plate member
showing the upstanding brackets.
[0011] FIG. 5 is a partial perspective view of the cam/cam follower
mechanism.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The present invention provides method and apparatus for
casting of metals and alloys and is especially useful in investment
casting of nickel, cobalt and iron base superalloys with equiaxed,
single crystal, or columnar grain microstructures as well as
titanium and its alloys and other commonly used metal and alloys.
The present invention can be practiced to make equiaxed, single
crystal, or columnar grain castings which may be cored or not to
produce complex internal passages in the castings.
[0013] Referring to FIGS. 1-5, apparatus in accordance with an
illustrative embodiment of the invention for casting a molten
metallic material in an investment shell mold assembly 10 is
illustrated. The shell mold assembly 10 comprises a mold cluster
having a plurality of shell molds 12 (two shown) each with a mold
cavity 12a, which is filled with melt that is solidified to form a
casting in each mold cavity. The mold cavities 12a each may have an
optional ceramic core (not shown) positioned therein to form
internal passages and other features in the casting.
[0014] The shell molds 12 are disposed about a common
frusto-conical pour cup 12b and adapted to receive the molten
metallic melt via the open bottom 120 of the pour cup and
respective sprues or runners 12c that are communicated in melt flow
relation to the pour cup and each mold cavity 12a.
[0015] The mold 10 typically comprises a ceramic investment shell
mold cluster having the features described above and formed by the
well known lost wax process wherein a wax or other fugitive pattern
of the mold assembly is dipped repeatedly in ceramic slurry,
drained, stuccoed with coarse ceramic stucco and dried to build up
the desired shell mold thickness on the pattern. The pattern then
is removed from the invested shell mold, and the shell mold is
fired at elevated temperature to develop adequate mold strength for
casting. Investment shell molds formed in this manner exhibit
porosity and substantial permeability to gas as a result. The mold
assembly 10 is cast in a vacuum casting chamber (not shown) and
then removed from the vacuum casting chamber for cooling to
solidify the molten metallic material in the shell molds 12. In
particular, a conventional tiltable induction melting crucible (not
shown) is disposed in a vacuum casting chamber for heating and
melting the charge of metal or alloy to form the melt to be cast.
The melt typically is heated to a superheat temperature selected in
dependence on the metal or alloy being cast. The melt is poured
from the crucible into the pour cup 12b of the mold 10 and flows
through runners 12c into the mold cavities 12a of the molds 12. The
mold assembly 10 is filled to provide a molten metal or alloy level
L in the pour cup 12b to provide a metallostatic head in
conventional manner.
[0016] After the mold assembly 10 is cast in the vacuum casting
chamber, the chamber vacuum is broken and the melt-filled mold 10
is removed from the casting chamber into the ambient air
atmosphere. The melt-filled mold 10 is supported and held
stationary in the ambient air atmosphere on a U-shaped collar CL of
a stationary fixture.
[0017] Pursuant to an embodiment of the invention, a pressure cap
30 is clamped on the melt-filled mold assembly 10 immediately upon
its removal from the vacuum casting chamber, and a pressurizing gas
is introduced into the mold pour cup 12b in the space S above the
upper level or surface L of the molten metallic material M therein
until the molten material in mold cavities 12a at least partially
solidifies. The mold pour cup 12b and runners 12c are wrapped with
thermal insulation (not shown) upon removal of the mold assembly 10
from the vacuum casting chamber to retard cooling of the molten
material in these regions of the mold 10.
[0018] For example, the pressure cap 30 is clamped on the
melt-filled mold assembly 10 within about 2 to about 5 seconds
after removal from the vacuum casting chamber, and an inert,
non-reactive or other pressurizing gas is introduced into the space
S on top of the upper level or surface L of the molten metallic
material M in the pour cup 12b. The gas pressure applied on the
molten material in the pour cup 12b typically is up to 15-20 psi
superambient depending on shell strength with a gas pressure of 5
to 10 psi superambient being sufficient for certain applications.
An inert gas, such as argon, is a suitable pressurizing gas for
casting conventional nickel base superalloys. The gas pressure is
applied on the molten material in the pour cup 12b for a time of
several minutes, such as for example, for a molten nickel base
superalloy, a time of 2-3 minutes until the superalloy solidifies
completely in the mold cavities 12a. The gas pressure can be
terminated after this time (e.g. 2-3 minutes), and the pressure cap
30 removed from the mold assembly 10. The mold assembly 10 then can
be allowed to cool to ambient temperature in ambient air over a
time period which may take 10 hours or more. The mold assembly 10
then is subjected to a conventional knock-out operation to remove
the castings from the shell molds 12.
[0019] The pressure cap 30 includes a non-rotatable seal-carrying
plate member 38 disposed on the mold 10 and having an annular,
compressible refractory gasket seal 40 on its underside. The
refractory gasket seal 40 can comprise a commercially available
ceramic fiber or needled material used for high temperature
gaskets. The gasket seal 40 is disposed on the underside of the
plate member 38 by mechanical clips (not shown) located on the
underside of plate member 38, adhesive, or by any other seal
fastening technique. The gasket seal 40 is adapted to engage and
seal against the annular lip surface 121 of the pour cup 12b of the
melt-filled mold assembly 10. The seal-carrying plate member 38 has
first and second support frames 34 each welded at welds WW (one
shown) or otherwise attached on opposite diametral sides thereof.
Each support frame 34 comprises a pair of spaced apart upstanding
brackets 34a with a pair of guide rods 34b being disposed between
the brackets 34a as shown in FIGS. 3A, 3B, and 4. The guide rods
34b are spaced one above the other in a common vertical plane in
the space between the brackets 34a.
[0020] The pressure cap 30 also includes a cam mechanism 32 to
clamp the pressure cap on the melt-filled mold 10 with gasket seal
40 engaging the annular lip surface 121. The cam mechanism 32
includes a rotatable cam plate member 36 that is disposed on top of
seal plate member 38 for rotation relative thereto. The cam plate
member 36 and seal-carrying plate member 38 are shown as having a
circular profile overlying the open upper annular lip 121 of the
pour cup 12b for purposes of illustration only as other shapes are
possible. The cam plate member 36 carries a plurality (e.g. two
shown) of cam surfaces 42 on the upper side of the cam plate member
36. The cam surfaces 42 are engaged by a respective cam follower
mechanism 41 disposed on a respective one of the support frames 34.
The cam surfaces 42 are machined on cam blocks 43 attached to the
cam plate member 36 by welding or mechanical fastening such as
screwing. Each cam surface 42 includes a region 42a that inclines
in the direction of arrow A at an angle of 30 degrees for purposes
of illustration only and a flat horizontal region 42b terminating
at an upstanding stop projection 42c.
[0021] Each cam follower mechanism 41 comprises a cam follower
surface, such as follower wheel 44 comprising an outer bearing race
44a and inner bearing race 44b fixed on screw 52, FIGS. 3A, with
antifriction ball bearings 44e between the races 44a, 44b so that
the cam follower wheel outer race 44a rotates relative to screw 52.
Screw 52 includes a threaded shaft portion 52a threadably received
in upstanding follower member 45 to fasten the follower wheel 44 on
follower member 45, which can comprise an elongated, rectangular
bar-shaped member. The head 52b of screw is shown only in FIGS. 3A,
3C for convenience. The follower member 45 is received in the space
between the brackets 34a as shown best in FIG. 5 for up and down
movement therein. The follower member 45 includes an upstanding
slot 45s that receives the guide rods 34b disposed between the
brackets 34a to guide movement of the follower member 45 upwardly
and downwardly between the brackets 34a as the cam plate member 36
is rotated. Each follower member 45 includes a lower end having a
mold-gripping surface 46, such as a cylindrical rod 46a, welded or
otherwise attached to the lower end to engage opposite sides of the
outwardly diverging frusto-conical wall 12w of the pour cup 12b as
shown in FIGS. 1 and 3B. The cam plate member 36 includes a
radially extending manually-operable handle 54 by which the cam
plate member is rotated by an operator (worker) relative to the
non-rotatable seal plate member 38 in the direction of arrow CW to
clamp the pressure cap 30 on the melt-filled mold 10 with the
gasket seal 40 pressed on the lip surface 121 of the pour cup 12b.
Rotation of the seal-carrying plate member 38 is prevented by the
operator's gripping and holding handle 30 welded or otherwise
attached to the side of the plate 38 while the handle 54 is rotated
relative thereto. The stops 42c on cam surfaces 42 limit the
rotational motion of the cam plate member as a result of each cam
follower wheel 44 abutting stop projection 42c.
[0022] The pressure cap 30 is clamped on the melt-filled mold
assembly 10 by placing frames 34 on opposite exterior sides of the
frustoconical pour cup 12b with the cam plate member 36 and seal
plate member 38 overlying the pour cup lip 121 and with
mold-gripping surfaces 46 engaged with the pour cup wall 12w as
shown. The mold 10 and pressure cap 30 are properly positioned
relative to one another by the mold pour cup 12b engaging a
depending stop 61 welded or otherwise attached on the underside of
the handle 30, FIG. 1. The cam plate member 36 then is rotated by
an operator manually moving handle 54 in the clockwise direction
relative to handle 30 to move cam surfaces 42 relative to cam
follower wheels 44. The follower members 45 thereby are moved
upwardly by cam surfaces 42 while the mold-gripping surfaces 46
engage or grip the mold such that the seal-carrying member 38 is
urged toward the mold 10 when the cam member 36 is so rotated,
thereby compressing the gasket seal 40 on the pour cup lip 121 to
provide a seal therebetween. The compressed gasket seal 40 is
somewhat gas permeable such that perfect gas tight seal is not
provided; yet the sealing action provided by the compressed gasket
seal 40 is effective enough to permit the supply of pressurizing
gas to overcome any gas loss as a result of permeability of the
gasket seal to thereby provide the desired gas pressure on the
upper level or surface L of the molten metallic material in the
pour cup 12b. A pressurizing gas is introduced into the space S in
pour cup 12b above the molten metallic material M therein through a
threaded gas inlet fitting 62. The inlet fitting 62 extends with
clearance through an aperture 36a in the cam plate member 36 and is
threaded in a threaded bore provided in the plate member 38 to
communicate with the space S in the pour cup 12b above the level L
of molten metallic material M therein. The fitting 62 is connected
by conduit or line 64 to a source GS of pressurizing gas at
superambient pressure. The source of pressurizing gas can comprise
a conventional argon supply cylinder having a pressure regulator 66
and pressure relief valve 68 to provide argon gas pressure on the
molten material in the pour cup 12b for 2-3 minutes or other
appropriate time until the molten material solidifies in the molds
12. After the selected time period, the gas pressure to the gas
inlet 62 is terminated by shutting off the argon supply. The handle
54 then is rotated relative to handle 30 by an operator in the
counterclockwise direction to move cam surfaces 42 in the direction
to release the camming action of the cam plate member 36 on
seal-carrying plate member 38. The frames 34, cam plate member 36,
and plate member 38 then are released from the pour cup 12b to
allow removal of the pressure cap 30 from the pour cup 12b. The
mold assembly 10 then is subjected to continued cooling in ambient
air to ambient temperature. The solidified castings in molds 12
then can be removed by a conventional knock-out operation to remove
molds 12 therefrom.
[0023] The present invention facilitates the filling of details in
the mold cavity that are defined by internal mold surface features
and/or core surface features that are otherwise difficult to fill
with the molten metallic material M. The present invention is
advantageous to reduce or eliminate non-fill voids in the castings
solidified in the molds 12. It is to be understood that the
invention has been described with respect to certain embodiments
thereof for purposes of illustration and not limitation. The
present invention envisions that modifications, changes, and the
like can be made therein without departing from the spirit and
scope of the invention as set forth in the following claims.
* * * * *