U.S. patent application number 11/712826 was filed with the patent office on 2007-09-20 for method and apparatus for removing a fugitive pattern from a mold.
This patent application is currently assigned to Metal Casting Technology, Incorporated. Invention is credited to Mark W. Oles, John A. Redemske, Terence D. Rose.
Application Number | 20070215315 11/712826 |
Document ID | / |
Family ID | 39563572 |
Filed Date | 2007-09-20 |
United States Patent
Application |
20070215315 |
Kind Code |
A1 |
Redemske; John A. ; et
al. |
September 20, 2007 |
Method and apparatus for removing a fugitive pattern from a
mold
Abstract
A fugitive pattern, such as wax or other meltable pattern
material, residing inside of a refractory mold, which can be
unsupported or supported in a particulates bed, is removed by
discharging steam or other condensable vapor that may include a
surfactant inside the mold to contact and melt the pattern while an
exterior of the mold is subjected to a non-condensing gas
atmosphere such as air outside of the mold. Regardless of whether
the condensable vapor includes surfactant or not, the mold can be
tilted relative to gravity and rotated while it is tilted to
improve the pattern removal. Condensable vapor is condensed inside
the mold where the vapor has contacted the pattern while the
exterior of the mold remains free of condenate. The condensed vapor
and melted pattern material are drained out of the mold with the
surfactant, if present, improving drainage.
Inventors: |
Redemske; John A.; (Milford,
NH) ; Oles; Mark W.; (Francestown, NH) ; Rose;
Terence D.; (Amherst, NH) |
Correspondence
Address: |
Mr. Edward J. Timmer
P.O. Box 770
Richland
MI
49083-0770
US
|
Assignee: |
Metal Casting Technology,
Incorporated
|
Family ID: |
39563572 |
Appl. No.: |
11/712826 |
Filed: |
March 1, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10899381 |
Jul 26, 2004 |
7204296 |
|
|
11712826 |
Mar 1, 2007 |
|
|
|
Current U.S.
Class: |
164/516 ; 164/35;
164/44 |
Current CPC
Class: |
B22C 9/043 20130101 |
Class at
Publication: |
164/516 ;
164/035; 164/044 |
International
Class: |
B22C 9/04 20060101
B22C009/04 |
Claims
1. A method of removing a fugitive pattern from inside a refractory
mold, comprising introducing a condensable vapor and a surfactant
inside the mold to contact and melt the pattern material,
condensing said condensable vapor inside the mold where it contacts
and melts the pattern, and draining the melted pattern material and
condensed vapor out of the mold wherein the surfactant improves
said draining.
2. A method of removing a fugitive pattern from inside a refractory
mold, comprising introducing a condensable vapor and a surfactant
inside the mold to contact and melt the pattern material while an
exterior of the mold is subjected to a non-condensing gas
atmosphere outside of the mold, condensing said condensable vapor
inside the mold where it contacts and melts the pattern while the
exterior of the mold remains free of condensed vapor, and draining
the melted pattern material and condensed vapor out of the mold
wherein the surfactant improves said draining.
3. The method of claim 2 where the type and amount of surfactant is
selected to reduce the surface tension between the condensed vapor
and the pattern material.
4. The method of claim 2 where the condensable vapor is steam.
5. The method of claim 2 where the pattern material is wax, either
with or without a non-wax filler
6. The method of claim 2 where the surfactant is added to the
condensable vapor before the condensable vapor exits a discharge
tube and enters inside the mold.
7. The method of claim 2 where the surfactant is added to the
condensable vapor after the condensable vapor exits a discharge
tube and enters inside the mold.
8. The method of claim 7 where the surfactant is carried into the
condensable vapor stream in a diluted form using a vehicle
compatible with the condensable vapor being used.
9. The method of claim 2 wherein a pressure differential between
the condensable vapor inside the mold and the non-condensing gas
atmosphere outside of the mold is small enough as to prevent the
condensable gas from exiting outside the mold exterior and the
non-condensing gas from entering a mold cavity in the mold.
10. The method of claim 2 wherein the condensable gas and the
noncondensing gas atmosphere are at substantially the same
pressure.
11. The method of claim 2 wherein the condensable vapor comprises
steam.
12. The method of claim 2 wherein the non-condensing gas is
air.
13. The method of claim 2 wherein the condensable vapor is supplied
from a source to a discharge tube from which it is discharged
inside the mold.
14. The method of claim 2 wherein the condensable vapor is
discharged inside the mold at atmospheric pressure.
15. The method of claim 2 wherein the condensable vapor is
discharged inside the mold at superatmospheric or subatmospheric
pressure and a non-condensing gas at substantially the same
superatmospheric or subatmospheric pressure is provided exterior of
the mold in a vessel containing the mold.
16. The method of claim 15 including preventing the condensable
vapor from entering the vessel exterior of the mold using a seal
between the mold and the vessel.
17. The method of claim 2 wherein the fugitive pattern comprises
wax.
18. The method of claim 2 wherein an axis of the mold containing
the fugitive pattern is tilted with respect to the direction of
gravity during the melting of the fugitive pattern or after the
fugitive pattern has been melted and the mold is rotated about a
second axis.
19. The method of claim 2 including initially discharging the
condensable vapor inside a hollow sprue of the pattern.
20. The method of claim 19 wherein the hollow sprue is preformed in
the fugitive pattern prior to the discharging of the condensable
vapor.
21. The method of claim 20 wherein the hollow sprue is formed by
condensable vapor discharged against an exposed end of the solid
sprue.
22. The method of claim 2 wherein the exterior of the mold is
surrounded by a support particulate media in a container.
23. The method of claim 2 wherein the exterior of the mold is not
surrounded by a support particulate media.
24. Apparatus for removing a fugitive pattern from inside of a
refractory mold, comprising means for introducing a condensable
vapor at atmospheric, superatmospheric or subatmospheric pressure
inside the mold to contact and melt the pattern material and means
for providing a surfactant in the condensable vapor.
25. The apparatus of claim 24 wherein the means for introducing a
condensable vapor comprises a discharge tube communicated to the
inside of the mold.
26. The apparatus of claim 24 including a surfactant supply conduit
for supplying the surfactant to the discharge tube.
27. The apparatus of claim 24 including a surfactant discharge tube
for introducing surfactant to the condensable vapor after it is
discharged from the discharge tube.
28. A method of removing a fugitive pattern from inside a
refractory mold, comprising melting or dissolving the fugitive
pattern and subjecting the mold to a combination of rotation and
tilting to improve draining of pattern material from the mold.
29. The method of claim 28 wherein the mold is rotated about its
longitudinal axis while the longitudinal axis is tilted with
respect to gravity.
30. The method of claim 28 wherein the refractory mold comprises a
shell mold.
31. The method of claim 30 wherein the shell mold is not surrounded
by particulates media.
32. The method of claim 30 wherein the shell mold is surrounded by
particulates media.
33. The method of claim 28 wherein the fugitive pattern is melted
by introducing steam or a condensable vapor inside the mold.
34. Apparatus for removing a fugitive pattern from inside of a
refractory mold, comprising a mold clamp and rotation mechanism and
a mold support mechnism between which the mold is disposed, a
pivotable shaft on which the mold clamp and rotation mechanism and
the mold support mechnism are disposed, means for pivoting the
shaft to tilt the mold clamp and rotation mechanism and the mold
support mechnism relative to gravity, and means for removing the
fugitive pattern.
35. The apparatus of claim 34 wherein the mold clamp and rotation
mechanism comprises a rotatable shaft having an end frictionally
enagaged to an end of the mold to impart rotation thereto.
36. The apparatus of claim 36 wherein the mold clamp and rotation
mechanism is movable up and down relative to the mold to engage the
end with the mold.
37. The apparatus of claim 35 wherein the mold support mechanism
comprises a rotatable nest that receives an opposite end of the
mold.
Description
RELATED APPLICATION
[0001] This application is a continuation-in-part of copending Ser.
No. 10/899,381 filed Jul. 26, 2004.
FIELD OF THE INVENTION
[0002] This invention relates to method and apparatus for removing
a fugitive pattern from a metal casting mold.
BACKGROUND OF THE INVENTION
[0003] The well-known "lost wax" investment casting process
typically uses a refractory mold that is constructed by the buildup
of successive layers of ceramic particles bonded with an inorganic
binder on a fugitive (expendable) pattern material such as
typically a wax, plastic and the like. The finished refractory mold
is usually formed as a shell mold around a fugitive pattern.
[0004] The refractory shell mold residing on the fugitive pattern
typically is subjected to a pattern removal operation, wherein the
pattern is melted out of the shell mold. This operation leaves an
empty "green" (unfired) refractory shell mold. The fugitive pattern
materials typically have a thermal expansion rate many times
greater than that of the refractory shell mold. If the fugitive
pattern and refractory mold are heated uniformly, the fugitive
pattern material will thermally expand more than the refractory
mold. This will place the refractory shell mold under tension and
will ultimately crack the shell mold. The avoidance of such shell
mold cracking is why the fugitive pattern material removal has been
typically conducted by methods such as a high pressure steam
autoclaving or flash firing pattern removal. The removal of the
fugitive pattern material by a high pressure steam autoclaving or
flash firing is done to expose the outside of the refractory shell
mold to high temperature. This high temperature causes heat to be
conducted through the refractory shell mold more quickly so as to
melt the surface of the pattern before the interior of the pattern
thermally expands. This surface layer of melted pattern material
extends all the way to where the pattern is exposed at the open
part of the mold and accommodates the expanding pattern material
inside the mold by forcing some of the liquid surface pattern
material out of the mold opening. Such methods can still allow
cracking of the refractory shell mold if the heat is not applied in
a continuum along the surface of the fugitive pattern inside the
mold. The connecting together of the refractory shell mold between
adjacent patterns is one of the major causes of non-uniform heating
of the pattern. That is, thicker regions of the refractory shell
mold will hinder the application of heat to the pattern material
and locally delay the melting of the surface of the pattern and
disrupting of the continuum. This prevents the passage of surface
liquid pattern material from a thinner mold region more remote from
the mold opening than the thicker mold region. Such prevention of
the passage of surface liquid pattern material causes a buildup of
pattern pressure in the remote thinner mold region due to the
thermal expansion of the pattern material and can lead to mold
cracking. These problems require the use of a mold strong enough
(e.g. thick enough) to resist the expansion pressure of the pattern
material and often require the use of supplemental holes or vents
through the mold to relieve pressure from unconnected expanding
patterns. Stronger or thicker molds as well as the venting method
are undesirable as they increase processing costs.
[0005] A plurality of the green refractory shell molds (sans
patterns) then typically are loaded into a batch or continuous oven
heated by combustion of gas or oil and heated to a temperature of
1600.degree. F. to 2000.degree. F. Alternatively, the mold may be
heated by a method of U.S. Pat. No. 6,889,745 of common assignee
herewith, which describes the heating of a mold with or without
surrounded mold support sand. The heated refractory molds are
removed from the oven and molten metal or alloy is cast into
them.
[0006] The trend in investment casting is to make the refractory
shell mold as thin as possible to reduce the cost of the mold as
described above. The use of thin shell molds has required the use
of support media to prevent mold failure as described by Chandley
et. al. U.S. Pat. No. 5,069,271. The '271 patent discloses the use
of bonded ceramic shell molds made as thin as possible such as less
than 0.12 inch in thickness. Unbonded support particulate media is
compacted around the thin hot refractory shell mold after it is
removed from the preheating oven. The unbonded support media acts
to resist the stresses applied to the shell mold during casting so
as to prevent mold failure.
[0007] Thin shell molds however, are more prone to cracking during
the pattern removal operation, such as the high pressure steam
autoclave or flash fire pattern removal operation mentioned above,
wherein the pattern is melted out of the shell mold.
[0008] Copending application Ser. No. 10/899,381 filed Jul. 26,
2004 discloses a method of removing a fugitive pattern from a
bonded refractory mold by discharging condensable vapor, such as
steam, inside the mold to contact and melt the pattern while the
exterior of the mold is subjected to a non-condensing gas
atmosphere, such as ambient air, outside of the mold. The condensed
vapor and melted pattern material are drained out of the mold in a
manner that reduces cracking of the mold.
SUMMARY OF THE INVENTION
[0009] An aspect of the present invention provides method and
apparatus for removing a fugitive pattern, such as wax or other
meltable pattern material, residing in a refractory mold by
introducing a condensable vapor, such as steam, that in a
particular embodiment includes a surfactant inside the mold to
contact and melt the pattern, while the exterior of the mold is
subjected to a non-condensing gas atmosphere, such as ambient air,
outside of the mold. The condensed vapor and the melted pattern
material are drained out of the mold. The surfactant lowers the
surface tension of the condensed vapor in contact with the fugitive
pattern inside the mold and increases the ease at which the melted
pattern material flows over the freshly exposed mold interior
surface to improve draining of the melted pattern material out of
the mold, leaving less residual pattern material on the interior
mold surface.
[0010] A pressure differential between the condensable vapor inside
of the mold and the non-condensing gas atmosphere outside of the
mold is small enough as to prevent the condensable gas from exiting
outside the mold exterior and the non-condensing gas from entering
the mold cavity. The condensable vapor inside of the mold and the
gas atmosphere outside of the mold preferably are at substantially
the same pressure to this end. In this way, when steam is used as
the preferred condensable vapor, the steam is condensed inside the
mold where the steam has contacted the pattern while the exterior
of the mold remains dry. The condensable vapor including the
surfactant can be introduced inside the mold at atmospheric,
subatmospheric, or superatmospheric pressure depending upon the
melting point of the pattern material.
[0011] In an illustrative embodiment of the invention, steam or
other condensable vapor is supplied to a discharge tube that is
positionable inside the mold and/or pattern sprue to discharge
steam or condensable vapor at substantially atmospheric,
subatmospheric or superatmospheric pressure therein. The surfactant
can be introduced into the condensable vapor in the discharge tube
or outside the discharge tube after the condensable vapor is
discharged.
[0012] Another aspect of the present invention provides method and
apparatus for removing a fugitive pattern, such as wax or other
meltable pattern material, residing in a refractory mold by
subjecting the mold to a combination of rotation and inclination
(tilting) during the pattern removal process in a manner to improve
draining of melted pattern material from the mold. The mold can be
tilted at any desired angle using a mold tilt drive motor, and the
mold can be rotated about an axis using a mold rotation drive
motor. The angle of mold tilting and the mold rotational speed can
be adjusted as required to drain the melting wax from the mold
cavities. The mold can be rotated while the mold is tilted at a
fixed angle of inclination relative to gravity. Alternately, the
mold can be tilted incrementally to selected angles of inclination
while the mold is rotated at each of the angle of inclination or
continuously. Further, the mold can be continuously tilted while
being rotated continuously or intermittently. Steam or other
condensable vapor can be introduced to heat and melt the fugitive
pattern inside the mold while the mold is subjected to rotation and
tilting, although this aspect of the invention can be practiced
using any pattern removal technique where the pattern is melted or
dissolved.
[0013] The above embodiments of the present invention can be
practiced to remove a fugitive pattern, such as wax or other
meltable pattern material, from an unsupported casting mold. The
present invention also can be practiced to remove a fugitive
pattern from a casting mold which is supported in particulates
media in a container. For example, steam or other condensable vapor
is introduced inside the mold to contact and melt the pattern while
an exterior of the mold contacts the particulate media and is
subjected to a non-condensing gas (e.g. steam-free) atmosphere,
condensing vapor inside the mold where it contacts the pattern
while the exterior of the mold and the particulate media
therearound are subjected to a non-condensing gas atmosphere, and
draining the melted pattern material and condensed vapor out of the
mold.
[0014] The invention is advantageous to remove one or more fugitive
patterns residing in a metal casting refractory mold, which may
have any mold wall thickness and which may be unsupported or
supported by exterior particulate media therearound. The invention
is further advantageous to remove one or more fugitive patterns
while avoiding saturating the mold wall with steam or other
condensate, which may have adverse effects on the binder used to
fabricate the mold. The invention may be practiced to reduce mold
cracking during pattern removal and to remove pattern material from
molds where steam cannot readily access the exterior of the mold
wall such as when the mold is supported with particulate support
media.
[0015] These and other advantages of the invention will become
apparent from the following detailed description taken with the
following drawings.
DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic view of a refractory casting mold
having fugitive patterns to be removed pursuant to an illustrative
embodiment of the invention by discharging atmospheric pressure
steam including a surfactant from a discharge tube shown positioned
in a hollow sprue of a pattern assembly residing inside the
mold.
[0017] FIG. 1A is a schematic view of a refractory casting mold
having fugitive patterns to be removed pursuant to another
illustrative embodiment of the invention by discharging atmospheric
pressure steam and a surfactant from separate discharge tubes shown
positioned in a hollow sprue of a pattern assembly residing inside
the mold.
[0018] FIG. 2 is a schematic view of the refractory casting mold of
FIG. 1 with the hollow sprue of the fugitive pattern assembly
already removed by melting and with the individual gates and
patterns being melted and removed.
[0019] FIG. 3 is similar to FIG. 2 after the patterns have been
completely removed from the shell mold.
[0020] FIG. 4 is an enlarged view of an individual pattern of FIG.
2 illustrating removal of the pattern.
[0021] FIG. 5 is similar to FIG. 1 but shows a pattern assembly
having a solid sprue with a steam discharge tube being moved into
the solid sprue to form in-situ a hollow sprue therein.
[0022] FIG. 6 is a schematic view of a refractory casting mold
having fugitive patterns to be removed pursuant to still another
illustrative embodiment of the invention wherein the mold is
exteriorly supported by a particulate support media
therearound.
[0023] FIG. 7 is similar to FIG. 1 and shows a refractory casting
mold having fugitive patterns to be removed pursuant to a further
illustrative embodiment of the invention by discharging steam at
superatmospheric or subatmospheric pressure from a steam discharge
tube shown positioned in a hollow sprue of a pattern assembly
residing inside the mold.
[0024] FIG. 8 is a perspective view of apparatus for subjecting a
mold to rotation and tilting during the pattern removal process
pursuant to still another illustrative embodiment of the
invention.
[0025] FIG. 9 is an elevational view, partially in section, of the
apparatus of FIG. 8.
[0026] FIG. 10 is similar to FIG. 9 showing the mold tilted
relative to gravity.
[0027] FIG. 11 is an enlarged perspective view of the top of the
mold support by which a lower end of the mold is rotatably
supported.
[0028] FIG. 12 is an enlarged perspective view of the bottom of the
mold support by which the mold end is rotatably supported.
DESCRIPTION OF THE INVENTION
[0029] The present invention improves upon the method and apparatus
for removing one or more fugitive patterns residing inside of a
refractory mold as disclosed in copending patent application Ser.
No. 10/899,381 filed Jul. 26, 2004, the disclosure of which is
incorporated herein by reference. In particular, one embodiment of
the present invention involves method and apparatus for removing
one or more fugitive patterns residing inside of a refractory mold
by introducing a condensable vapor that includes a surfactant
inside the mold. The condensed vapor and the melted pattern
material are drained out of the mold. The surfactant lowers the
surface tension of the condensed vapor in contact with the fugitive
pattern inside the mold and increases the ease at which the melted
pattern material flows over the freshly exposed mold interior
surface to improve draining of the melted pattern material out of
the mold, leaving less residual pattern material on the mold
surface.
[0030] The method is especially useful to remove one or more
fugitive patterns from inside a gas permeable "lost wax" investment
casting ceramic shell mold, although the invention is not so
limited as it can be practiced to remove one or more fugitive
patterns from other types of refractory metal casting molds which
have one or more fugitive patterns therein, which may have any mold
wall thickness, and which may be unsupported or supported by
exterior particulate media therearound. When steam is used as a
preferred condensable vapor, the invention can be practiced to
remove one or more fugitive patterns that may comprise conventional
wax patterns or other pattern materials that are melted at a
temperature below the boiling point of water (e.g. about 212
degrees F.) under the particular ambient atmospheric pressure
conditions present during the pattern removal operation.
[0031] The invention also can be practiced to remove one or more
fugitive patterns that may comprise conventional wax patterns or
other pattern materials and that are melted at a temperature above
the boiling point of water by using superatmospheric steam to this
end during the pattern removal operation pursuant to another
embodiment of the invention described below. Furthermore, the
invention can be practiced using subatmospheric pressure steam to
remove one or more fugitive patterns that may require lower
temperatures to melt them.
[0032] Alternatively in practicing the invention, the steam can be
replaced by a condensable vapor of another suitable material, such
as for purposes of illustration and not limitation, mineral spirits
having a boiling point of about 300 degrees F. wherein the vapor
can be condensed and give up heat to the fugitive pattern when it
makes contact with the pattern for pattern melting and removal
purposes.
[0033] For purposes of illustration and not limitation, an
embodiment of the present invention will be described below in
connection with FIGS. 1-4 with respect to removing a plurality of
wax patterns 10 attached by respective gate 35 to a central hollow
sprue 30 of a pattern assembly 40 from inside of a "lost wax"
investment casting shell mold 20. In FIG. 1, the hollow sprue 30
comprises a preformed wax sprue having axially elongated interior
chamber 30a and having the patterns 10 attached by wax welding or
fastening technique to its exterior surface 30s. For purposes of
illustration and not limitation, the wax sprue 30 can be preformed
to have the interior chamber 30a by molding, extrusion, by
initially forming the sprue on a cylindrical or other shape mandrel
which is subsequently removed by heating the mandrel and thus
adjacent wax to allow mandrel to be physically withdrawn, by
drilling a solid wax sprue, or by any other suitable technique.
[0034] Although two patterns 10 are shown in FIG. 1, those skilled
in the art will appreciate that additional patterns 10 typically
are attached about the sprue 30 at the same location as patterns 10
but are out of view in FIG. 1 as a result of its being a sectional
view. Moreover, additional patterns 10 can be attached by gates
about the sprue 30 at other axial locations along its length (e.g.
above the patterns 10 shown in FIG. 1) as is well known and shown
for example in U.S. Pat. No. 5,069,271, the teachings of which are
incorporated herein by reference.
[0035] Referring to FIG. 1, a "lost wax" investment casting shell
mold 20 is shown invested on a plurality of wax patterns 10
attached by gates 35 about a central wax sprue 30 by the
conventional "lost wax" process for making shell molds as
described, for example, in U.S. Pat. No. 5,069,271, wherein the
pattern assembly 40 including the patterns 10 attached by gates 35
to hollow sprue 30 is repeatedly dipped in a refractory slurry
having a binder, stuccoed with coarse refractory stucco particles,
and dried to build up the shell mold on the pattern assembly. The
patent describes a gas permeable thin wall shell mold having a mold
wall thickness of about 1/8 inch or less. Such a thin wall mold 20
as described in the patent can be supported in a casting container
60 by a particulate support media 50 (e.g. ceramic particulates) as
shown in FIG. 6 during the pattern removal operation. The invention
is not limited to practice with such a thin wall shell mold
supported by a particulate media therearound and, instead, can be
practiced with a refractory mold of any mold wall thickness,
whether exteriorly supported by particulate support media or
whether unsupported as shown in FIG. 1.
[0036] The shell mold 20 is shown inverted (i.e. oriented upside
down) to allow the melted pattern material and condensed steam to
drain by gravity from the lower end of the sprue 30. The mold 20
can be positioned in other orientations that facilitate drainage of
the melted pattern material and condensed steam out of the mold.
Moreover, the mold 20 may be moved during the pattern removal
operation in a manner that facilitates drainage of the melted
pattern material and condensed steam out of the mold.
[0037] Referring to FIG. 1, pursuant to an illustrative embodiment
of the invention, a steam discharge pipe or tube 100 connected to a
surfactant supply conduit 101 is shown positioned in the elongated
chamber 30a of the hollow sprue 30 of the pattern assembly 40 to
introduce a stream (represented by the arrow "A") of steam that
includes a surfactant (represented by arrow "SF") therein at
substantially atmospheric pressure inside the hollow sprue 30 of
the pattern assembly 40 to contact and melt the wax pattern
assembly while the exterior surface 20s of the mold 20 is subjected
to substantially ambient atmospheric air pressure (represented by
"ambient pressure"). The ambient air forming a non-condensing gas
atmosphere about the mold 20 in FIG. 1 can be at ambient
temperature or can be refrigerated relative to ambient temperature.
A typical wax material from which the pattern assembly 40 is made
melts and becomes quite fluid at about 180 degrees F. for purpose
of illustration and not limitation.
[0038] The steam at substantially atmospheric pressure is generated
in a steam source 110, which may comprise a conventional steam
generator commercially available as Model LB240 from The Electro
Steam Generator Corp. The steam flows from the steam generator or
source 110 through a supply tube 120 to the steam discharge tube
100. Flow of the steam from the source or generator 110 can be
assisted by adjusting the pressure in the steam generator so that
adequate steam will flow through the pipe into the mold to replace
the amount of steam that has condensed.
[0039] Surfactant SF is introduced into the steam discharge tube
100 through the surfactant supply conduit 101 connected to a
surfactant supply pump 111. The pump 111 pumps surfactant from a
supply tank T. The surfactant in tank T is typically in a diluted
form; i.e. the surfactant is diluted at a selected concentration in
a liquid carrier vehicle. The flow of the surfactant SF in conduit
101 is regulated by using surfactant metering pump 111 or a valve
arrangement to control the flow rate of the surfactant from an
appropriate surfactant supply pump. For example, an alternative
apparatus and method for introducing the surfactant SF into the
tube 100 can involve supplying liquid surfactant at a constant
pressure to an adjustable valve and regulating the flow of
surfactant into tube 100 by the use of the adjustable valve.
[0040] Although surfactant SF is described as being introduced into
the steam inside of the discharge tube 100, the invention is not so
limited. For example, the surfactant can be introduced outside the
steam discharge tube 100 using a second surfactant discharge tube
100' as shown in FIG. 1A. The surfactant discharge tube 100'
extends inside the mold in a way to introduce surfactant SF
downstrean of the end of the steam discharge tube 100 and into the
stream of steam after it is discharged from the end of the
discharge tube 100 inside the mold as shown in FIG. 1A.
[0041] For purposes of illustration and not limitation, an
exemplary surfactant for use in practice of this aspect of the
invention comprises Tomadol grade 1-5 nonionic alcohol ethoxylate
liquid surfactant, which is available from Tomah Products, Inc.,
Milton, Wis. and which is diluted to a 0.5% by weight solution in
water (carrier vehicle) and added at a rate of 60 ml/min to the
stream of steam in the discharge tube 100 via conduit 101. The
surfactant is added to the discharge tube 100 so that it will be
present in the steam inside the mold as the refractory mold wall is
exposed as the wax pattern is melted during the pattern removal
process.
[0042] The invention is not limited to practice with the exemplary
surfactant described above since other nonionic surfactants at
other concentrations in the steam or condensable vapor can be used.
In general, the surfactant and its concentration in the condensable
vapor are selected to lower the surface tension of the condensed
vapor that is in contact with the fugitive pattern inside the mold
to increase the ease at which the melted pattern material flows
over the freshly exposed mold interior surface, thereby improving
draining of the melted pattern material out of the mold to leave
less residual pattern material on the mold surface.
[0043] Moreover, although water is described in the preceding
paragraph as the carrier vehicle for the surfactant when the
condensable vapor comprises steam, the invention is not so limited.
The surfactant can be carried in a diluted form using any liquid
vehicle that is compatible with a particular non-aqueous
condensable vapor being used. For example, when the condensable
vapor comprises mineral spirits, the carrier vehicle can comprise
mineral spirits.
[0044] The steam at substantially atmospheric pressure and
containing the surfactant SF is discharged in the chamber 30a at a
sufficiently high flow rate to displace air from the chamber 30a
and progressively contact and melt the pattern material of the wax
sprue 30 and then the gates 35 and patterns 10. The flow rate of
the steam discharged into the chamber 30a may be varied during
removal of the sprue and patterns depending upon the rate of
condensation of the steam inside the mold. This rate will be
dependant upon the surface area of the wax exposed to the steam at
that point during de-waxing, and the size of the mold. When
multiple rows of patterns and gates are attached to the sprue along
its length, the steam progressively melts the pattern material of
each pattern uniformly from the gate and sequentially proceeding
into the pattern.
[0045] In practice of the invention, the wax sprue 30 may not be
present or may be removed by other means prior to removal of the
patterns 10 by contact with the steam. That is, if only patterns 10
are present in shell mold 20 having an empty central sprue type
passage, then the steam discharge tube 100 is positioned to
discharge the steam inside the mold 20 to contact and melt only
patterns 10 and any gates 35 associated therewith.
[0046] FIGS. 2 and 4 illustrate the pattern removal process after
the central hollow sprue 30 has been melted and removed and while a
gate 35 and pattern 10 are being melted and removed. The steam
containing the surfactant is shown being drawn toward the gate 35
and associated pattern 10 as the steam condenses where the steam
has melted the wax pattern material. In particular, as the steam
condenses at the surface of the gate and pattern, a relative lower
pressure is generated at region V proximate where the gate and/or
pattern material is melted to cause fresh downstream steam to flow
toward the region of the gate and pattern that has melted. The
liquid wax material that has melted soaks partially into the inner
mold wall surface as illustrated at surface region S and acts as a
barrier to prevent steam condensate from soaking through the
thickness of the mold wall W. Moreover, the presence of atmospheric
air pressure on the exterior surface 20s of the mold 20 provides no
driving force to cause the steam condensate to pass through the
mold wall, thereby avoiding saturation of the mold wall with steam
condensate and the adverse effects on the binder present in the
mold wall. During the pattern removal operation, the exterior
surface 20s of the mold exposed to ambient air (as a non-condensing
gas atmosphere) remains dry (devoid of liquid water) as a result. A
pressure differential between the condensable vapor inside of the
mold 20 and the non-condensing gas atmosphere outside of the mold
20 is small enough as to prevent the condensable gas from exiting
outside the mold exterior through the gas permeable mold wall W and
the non-condensing gas from entering via wall W the mold cavity
occupied by the fugitive pattern assembly being removed. The
condensable vapor inside the mold and the non-condensing gas
atmosphere outside of the mold preferably are at substantially the
same pressure to this end.
[0047] In FIG. 4, inclusion of the surfactant with the condensable
vapor (e.g. atmospheric pressure steam) results in wetting of the
steam condensate to the wax soaked refractory mold and the
formation of a surface layer of steam condensate along the surface
of the wax soaked refractory wall. Molten wax pattern material
draining from the area of the pattern that is melting therefore
flows on a layer of steam condensate which because of its low
viscosity, allows the melted wax to flow more easily along the mold
wall and out of the mold cavity. This results in faster removal of
the pattern material from the mold cavity and less residual wax
pattern material left in the mold cavity.
[0048] As further illustrated in FIG. 4, the steam condensate and
the melted wax pattern material are drained out of the mold 20 by
gravity through the sprue void or passage P created when the hollow
wax sprue 30 has been removed. The melted wax pattern material may
be collected on or in a collection tray or container (not shown)
positioned below the mold 20 in FIG. 1. An axis of the mold 20,
such as longitudinal axis L of the mold 20 of FIG. 2, containing
the fugitive pattern can be tilted with respect to the direction of
gravity during the melting of the fugitive pattern or after the
fugitive pattern has been melted.
[0049] The steam at substantially atmospheric pressure is believed
to produce only a small heat affected zone Z in the wax pattern
such that the remaining unmelted portion of the solid wax pattern
10 is relatively unaffected by the steam, although Applicants do
not wish to be bound by any theory in this regard. This small area
of heated but not melted pattern material is free to thermally
expand toward the melted surface, therefore resulting in little or
no stress on the surrounding refractory mold. The thermal expansion
of the wax inside the mold is the cause of the mold cracking during
standard autoclave de-waxing.
[0050] The discharge of steam and surfactant SF from the steam
discharge tube 100 inside the mold is continued until the entire
pattern assembly 40 (including the hollow sprue 30 and patterns 10)
is melted and removed from the mold 20, leaving an empty shell mold
20 that includes a plurality of mold cavities MC connected to the
sprue passage P as shown in FIG. 3. The mold then is ready to be
fired at a suitable firing temperature to prepare the mold for
receiving molten metal or alloy to be cast in the mold as is well
known and forming no part of the invention.
[0051] Although the chamber 30a of the hollow sprue 30 is described
above as being preformed in connection with FIGS. 1-4, the
invention is not so limited. As shown in FIG. 5, a chamber 30a' can
be formed in-situ in a solid wax precursor sprue 30' of the pattern
assembly, FIG. 5, by relatively axially moving the discharge tube
100 such that the steam discharged at atmospheric pressure from the
tube 100 and including the surfactant from tube 101 impinges
against the exposed end 30e' of the solid sprue 30' and
progressively melts out the chamber 30a' in-situ in the solid
precursor sprue 30'. After the chamber 30a' is formed, the removal
of the now hollow sprue 30' and the patterns 10 can be carried out
as described above in connection with FIGS. 1-4. In FIG. 5, like
reference numerals are used for like features of FIGS. 1-4.
[0052] In another embodiment of the invention illustrated in FIG.
6, a fugitive pattern assembly 40 is removed from a thin wall or
other refractory mold 20 that is exteriorly supported or surrounded
by a particulate support media 50 in a casting container 60 as
described in U.S. Pat. No. 5,069,271. The particulate media 50 can
comprise ceramic particles or grog as described in the patent.
Pattern removal is effected by discharging steam at substantially
atmospheric pressure from the steam discharge tube 100 and
containing the surfactant from tube 101 inside the hollow sprue 30
of the pattern assembly 40 to contact and melt the hollow sprue 30
and then the patterns 10 as described in connection with FIGS. 1-4.
The exterior surface 20s of the mold 20 contacts the particulate
media 50 and is subjected to substantially ambient atmospheric
pressure via a vent-to-atmosphere 61 on the casting container 60
during pattern removal. The exterior mold surface 20s and the
particulates media 50 remain dry (devoid of liquid water) as a
result of the melted wax soaking partially into the mold wall W as
described above with respect to FIGS. 1-4 and preventing steam
condensate from soaking through the mold wall thickness.
[0053] For purposes of further illustration and not limitation,
another method embodiment of the present invention shown in FIG. 7
will be described below wherein superatmospheric or subatmospheric
pressure steam is discharged inside the mold to remove the pattern
assembly 240 having a plurality of wax patterns 210 attached by
respective gate 235 to central hollow sprue 230 from inside of
"lost wax" investment casting shell mold 220. Use of
superatmospheric pressure steam while the exterior of the mold is
subjected to non-condensing gas at substantially the same
superatmospheric pressure permits an increase in the heat capacity
per unit volume of the steam as well as enables the melting of
higher melt point pattern materials. Use of subatmospheric pressure
steam while the exterior of the mold is subjected to noncondensing
gas at substantially the same subatmospheric pressure enables
melting and removal of pattern materials that, for example, require
lower temperatures. The following method embodiment will be
described using superatmospheric pressure steam including the
surfactant SF, although the method embodiment may also
alternatively use subatmospheric pressure steam instead.
[0054] The mold 220 is disposed inside of a pressure vessel 250
over a collection basin 252 to collect and contain melted wax and
steam condensate exiting from the mold during the pattern removal
operation. The pressure vessel 250 may comprise a casting container
of the type that includes particulate support media about the mold
220 as illustrated in FIG. 6. Alternately, the pressure vessel 250
may be devoid of the particulate support media; i.e. empty with
only the shell mold therein. The pressure vessel 250 can be formed
by a suitable pressure resistant material such as steel and
configured as a typical conventional pressure vessel. A casting
chamber 60 and mold contained therein as shown in FIG. 6 can also
be placed inside a separate pressure vessel 250 for
superatmospheric pressure de-waxing.
[0055] A seal 254 is provided between the mold 220 and the pressure
vessel wall 250a to substantially prevent mixing of gas from the
region interior of the seal 254 to the exterior of the seal 254.
The seal 254 can comprise a steel or other tubular member 254t
having a rubber or other type seal 254a for sealing to the mold
220.
[0056] Steam at superatmospheric pressure and including the
surfactant from tube 101 is discharged inside the mold 220 from
discharge tube 300. The tube 300 is connected to a source S of the
superatmospheric pressure steam, such as the previoussly described
steam generator and extending through an opening in wall 250a and
also to surfactant input conduit 101 as shown in FIG. 6.
Simultaneously to the discharge of the superatmospheric pressure
steam inside the mold 220, air pressure at substantially the same
pressure as the steam pressure inside the mold is provided in the
pressure vessel 250 via an inlet 255. The inlet 255 for the
superatmospheric air pressure is connected to a source of
compressed air, such as an air compressor; for example, Kaeser
model SP25 compressor. This method embodiment thus involves
discharging steam including surfactant from tube 101 inside the
mold 220 to contact and melt the pattern material while the
exterior of the mold 220 is subjected to a steam-free gas
atmosphere outside of the mold wherein the steam inside the mold
and the steam-free atmosphere outside of the mold are at
substantially the same pressure. The steam and corresponding air
(or other gas) pressure may be adjusted to any pressure (and
therefore temperature) appropriate for the rapid melting of the
pattern material.
[0057] The superatmospheric pressure inside the pressure vessel can
be provided by a gas other than air such as, for example, nitrogen,
inert gas, or other gas at the desired superatmospheric pressure
substantially equal to that of the steam inside the mold.
[0058] An air bleed valve 256 is provided on the pressure vessel
wall 250 so as to reside in the region inside the seal 254 to bleed
the air that was initially inside the mold 220 from the region
inside the seal 254.
[0059] The pattern removal operation of the embodiment of FIG. 7
proceeds as described above with respect to steam discharged
atmospheric pressure together with the surfactant inside the mold
20 wherein the superatmospheric steam contacts the solid wax
material of the pattern assembly and condenses. More heat is
delivered to the wax surface in this embodiment of the invention
since the superatmospheric steam is at a higher temperature when
compressed. A slightly reduced pressure is formed at the wax
surface when the steam condenses, which draws more steam into
contact with the wax surface to facilitate the pattern removal
operation. Molten wax from the wax surface and steam condensate
flows out of the mold cavity and into the wax and condensate
collection basin 252. De-waxing action occurs only internally in
the mold 220 in an orderly manner from the sprue 230 to the gates
235 and then into the wax patterns 210. The mold-to-pressure vessel
seal 254 results in no steam being applied to the exterior of the
mold 220 in the pressure vessel 250. A steam-free atmosphere is
thereby provided in the pressure vessel 250.
[0060] Referring to FIGS. 8 through 12, a further aspect of the
invention is illustrated wherein the unsupported shell mold 500
(FIG. 10) is subjected to a combination of rotation and tilting
relative to gravity during the pattern removal process using steam
or other condensable vapor in the manner described above with or
without a surfactant being included in the steam or other
condensable vapor. This embodiment is not limited to removing the
pattern using steam or other condensable vapor and envisions that
other pattern removal techniques may be employed while the mold is
subjected to a combination of rotation and tilting. For example, a
hot air or gas stream can be introduced inside the mold in a manner
to heat and melt the pattern while the mold is subjected to
combined rotation and tilting. The mold also may be located in a
furnace for flash heating the pattern while the mold is subjected
to combined rotation and tilting. Still further, a chemsical
dissolution medium may be introduced inside the mold to contact and
dissolve the pattern while the mold is subjected combined to
rotation and tilting.
[0061] Likewise, this further aspect of the invention can be
practiced to remove one or more fugitive patterns from a mold that
is exteriorly supported or supported by a surrounding particulates
media in a casting container as described above in connection with
FIG. 6 and also in U.S. Pat. No. 5,069,271.
[0062] In FIG. 10, an unsupported shell mold 500 is shown having a
plurality of fugitive (e.g. wax) patterns 510 disposed around and
along the length of a fugitive (e.g. wax) sprue 530. Each patern is
shown connected to the sprue by a gate 535. The rotary action about
the longitudinal aixs L of the mold while the mold is tilted
relative to gravity as shown in FIG. 10 pursuant to this aspect of
the invention allows the melted pattern material to drain uniformly
from all mold cavities MC that are arranged around the central
sprue passage P when the pattern and sprue material are
removed.
[0063] FIG. 8 shows illustrative apparatus for practicing this
aspect of the invention before the mold 500 is placed in the
apparatus. FIG. 9 shows the apparatus before the mold 500 is placed
in the apparatus and before the mold is tilted with respect to
gravity. FIG. 10 shows the apparatus after the mold is placed in
position and tilted with respect to gravity such that its
longitudinal axis L is oriented at an angle of inclination.
[0064] In practicing this aspect of the invention, the mold 500
having the fugitive patterns and sprue therein is placed between an
upper mold clamp and rotation mechanism 510 and a lower mold
support mechanism 512. The shell mold 500 includes an upper annular
collar 500c that is receives an end 510e of the upper mold clamp
mechanism 510 as shown best in FIG. 10. The end 510e closes off the
mold sprue passage P. The mold includes a lower annular collar 500d
that is received on rotatable nest 512n disposed on a support plate
512p of the mold support base 512b as shown best in FIGS. 10 and
11. The mold support base 512b is affixed to lateral arms A of the
frame F of the apparatus. A cross brace plate P3 is provided
between the arms A. The mold collars 500c, 500d can be formed
integral with the mold 500 or can be formed separately and attached
to the mold.
[0065] An end of a steam delivery pipe or tube 600 extends upwardly
through an opening in the mold support base 512b and support plate
512p so as to communicate with the open lower end of the mold 500
as shown in FIG. 10 to introduce steam or other condensable vapor
inside the mold 500. The pipe or tube 600 is held in fixed position
on the mold support base 512b by clamps 513 as shown in FIG. 12.
The pipe or tube 600 is connected by suitable flexible or rigid
conduit to a steam generator like steam generator 110 described
above in connection with FIGS. 1-4.
[0066] The mold support plate 512p includes a first set (three
shown) of peripherally spaced apart rotatable wheels 512f that
rotatably support the outer circumference of the rotatable nest
512n. The mold support plate 512p also includes a second set (three
shown) of peripherally spaced apart rotatable wheels 512g on which
the closure plate 512s of the rotatable nest 512n is supported for
rotation. The rotatable nest 512n thereby is supported laterally by
wheels 512f and from beneath by wheels 512g for rotation relative
to the lower mold support base 512.
[0067] Each wheel 512f is supported by bearings (not shown) on an
upstanding stud S1 mounted on the plate 512p. Each wheel 512g is
supported by bearings (not shown) on a lateral stud S2 mounted on
the support plate 512p.
[0068] The rotatable nest 512n includes an upwardly facing,
generally cylindrical recess R configured to receive the collar
500d of the mold 500 as shown in FIG. 10.
[0069] The mold clamp and rotation mechanism 510 includes a shaft
510s having the end 510e that frictionally engages in the collar
500c of the mold 500. To this end, the end 510e can be made of
rubber or other mateiral to achieve friction engagement with the
mold collar 500c so that rotation can be imparted to the mold by
rotation of shaft 510s.
[0070] The shaft 510s is rotatable by having an upper end sprocket
510f thereof in driving engagement with a drive chain 510c. The
chain is driven by an output sprocket 513s of a conventional gear
reducer GR1 driven by a conventional electric or hydraulic motor M1
that is disposed on horizontal fixed plate P1 of the frame F. The
shaft 510s is supported for rotation by bearing blocks 510b affixed
on a vertical fixed frame plate P2, which is fastened to frame
plate P1. In this way, the mold 500 clamped between the mold clamp
and rotation mechanism 510 and the mold support mechanism 512 can
be rotated by shaft 510s.
[0071] The mold clamp and rotation mechanism 510 is movable up and
down relative to the mold support mechanism 512 by a sliding
vertical shaft 700s guided at a lower end in fixed housing H1 by a
pair of bearings 700b and at an upper end in fixed housing H2. An
air cyclinder (not shown) is connected between the frame 512 (e.g.
plate P3) and the mechanism 510 (e.g. shaft 700s) in a manner to
raise the mechanism 510 to permit placement of a mold in the
apparatus and to lower the mechanism 510 to clamp the mold in
place. When the air cylinder is in the raised position, an
anti-rotation shaft 800s exits the antirotation guide tube 800t to
allow the mechanism 510 to rotate sideways out of the way for ease
of loading a new mold into the apparatus.
[0072] A main shaft 550 is rotatably mounted on the frame F by
bearing blocks 552 so as to be rotatable or pivotable about its
longitudinal axis, which is perpendicular to the longitudinal axis
of the mold 500. A square cross-section support sleeve 553 is
affixed, such as by welding, on the shaft 550 for rotation
therewith. The frame arms A that carry the mold support mechanism
512 are fastened such as by welding to the sleeve 553 so that they
rotate or pivot with the shaft 550. The mold clamp and rotation
mechanism 510 is fastened to sleeve 553 by means of the shaft 550,
antirotation shaft 800s, and air cylinder. The mold clamp and
rotation mechanism 510 and the mold support mechanism 512 thus are
mounted on the sleeve 553 so that they rotate or pivot with the
shaft 550.
[0073] The shaft 550 is rotated or pivoted by a conventional
electric drive motor M2 connected to the end of the shaft 550 by a
gear reducer GR2. The gear reducer GR2 is connected to the machine
frame 512 by a reaction linkage L' that keeps the gear reducer from
rotating with the shaft. The drive motor can be of the stepping
motor type. The drive motor M2 thus can incrementally or
continuously rotate or pivot the shaft 550 about its longitudinal
axis. In this way, the mold 500 clamped between the mold clamp and
rotation mechanism 510 and the mold support mechanism 512 can be
tilted relative to gravity as shown in FIG. 10 while the mold is
rotated.
[0074] In operation of the apparatus, the mold 500 having the
fugitive pattern and sprue therein is placed on the rotatable nest
512n with its lower collar 500d received in the recess R of the
rotatable nest 512n. Then, the end 510e of the shaft 510s of the
mold clamp and rotation mechanism 510 is lowered to engage the end
510e in the upper collar 500c of the mold 500 so that rotation of
the shaft 510s will impart rotation to the mold.
[0075] Steam flow to pipe or tube 600 is initiated. The steam flow
is introduced inside the mold via pipe or tube 600. The steam may
include the surfactant FS described above in connection with FIGS.
1-4, or the surfactant may be omitted in certain pattern removal
situations. The main shaft 550 is pivoted to tilt the mold clamp
and rotation mechnsim 510 and the mold supprt mechansim 512, and
thus the mold 500, to any desired angle of inclination relative to
gravity, see FIG. 10. The angle of the mold tilt and mold
rotational speed can be adjusted as required to drain the melting
wax from the mold cavities MC. In this way, the wax can be drained
uniformly from all mold cavities MC arranged around a center sprue
P. This aspect of the invention thus allows wax to be drained out
of mold cavities even where a substantial volume of a mold cavity
is below the level of the gate G when the mold is in the vertical
position. The melted wax drains out of the bottom of the molds and
is captured in a pan (not shown).
[0076] The mold 500 can be rotated while the mold is held tilted at
a fixed angle of inclination relative to gravity. Alternately, the
mold can be tilted incrementally to selected angles of inclination
while the mold is rotated at each of the angle of inclination or
continuously. Further, the mold can be continuously tilted while
being rotated continuously or intermittently. Practice of the
method is dependent on the shape of patterns being dewaxed
(removed). It may be typical to start with vertical non-rotating
mold de-waxing and then change to tilted mold rotary de-waxing as
the de-waxing proceeds into portions of the mold that hang below
the gate opening. The angle of mold tilt, rotational speed and the
time duration depends on the sahpe of th patterns being
de-waxed.
[0077] Steam or other condensable vapor is introduced via pipe or
tube 600 inside the mold 500 to heat and melt the fugitive pattern
and sprue while the mold is subjected to a combination of rotation
and tilting, although this aspect of the invention is not limited
to use of steam or other condensable vapor to heat and melt the
pattern and sprue. For example, a hot air or gas stream can be
introduced inside the mold in a manner to heat and melt the pattern
while the mold is subjected to a combination of rotation and
tilting. The mold also may be located in a furnace for flash
heating the pattern while the mold is subjected to combined
rotation and tilting. Still further, a chemical dissolution medium
may be introduced inside the mold to contact and dissolve the
pattern while the mold is subjected to combined rotation and
tilting.
[0078] The invention is advantageous to remove one or more fugitive
patterns from a metal casting refractory mold, which may have any
mold wall thickness and which may be unsupported or supported by
exterior particulate media therearound. The invention is further
advantageous to remove one or more fugitive patterns while avoiding
saturating the mold wall with steam condensate. The invention may
be practiced to reduce mold cracking during pattern removal and to
allow the use of thinwalled molds without mold cracking.
[0079] Those skilled in the art will appreciate that the invention
is not limited to the embodiments described above and that changes
and modifications can be made therein within the spirit of the
invention as set forth in the appended claims.
* * * * *