Note: Descriptions are shown in the official language in which they were submitted.
CA 02622106 2008-02-25
METHOD AND APPARATUS FOR REMOVING A FUGITIVE PATTERN
FROM A MOLD
Related Application
This application is a continuation-in-part of copending Serial No. 10/899,381
filed
July 26, 2004.
Field of the Invention
This invention relates to method and apparatus for removing a fugitive pattern
from a metal casting mold.
Background of the Invention
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.
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
CA 02622106 2008-02-25
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.
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 F to 2000 F. Alternatively, the mold may be heated by a
method of
US Patent 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.
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. US Patent 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
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CA 02622106 2008-02-25
applied to the shell mold during casting so as to prevent mold failure.
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.
Copending application Serial No. 10/899,381 filed July 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
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
emboiment
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 mateial out of the mold, leaving less residual pattern material
on the
interior mold surface.
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
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CA 02622106 2008-02-25
inside the mold at atmospheric, subatmospheric, or superatmospheric pressure
depending
upon the melting point of the pattern material.
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.
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.
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
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CA 02622106 2008-02-25
therearound are subjected to a non-condensing gas atmosphere, and draining the
melted
pattern material and condensed vapor out of the mold.
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 pattem 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.
These and other advantages of the invention will become apparent from the
following detailed description taken with the following drawings.
Description of the Drawings
Figure 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.
Figure lA 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.
Figure 2 is a schematic view of the refractory casting mold of Figure 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.
Figure 3 is similar to Figure 2 after the patterns have been completely
removed
from the shell mold.
Figure 4 is an enlarged view of an individual pattern of Figure 2 illustrating
removal of the pattern.
CA 02622106 2008-02-25
Figure 5 is similar to Figure 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.
Figure 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.
Figure 7 is similar to Figure 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.
Figure 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.
Figure 9 is an elevational view, partially in section, of the apparatus of
Figure 8.
Figure 10 is similar to Figure 9 showing the mold tilted relative to gravity.
Figure 11 is an enlarged perspective view of the top of the mold support by
which
a lower end of the mold is rotatably supported.
Figure 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
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 Serial No. 10/899,381 filed July 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
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CA 02622106 2008-02-25
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 mateial out of the mold, leaving less residual pattern material
on the mold
surface.
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.
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.
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.
For purposes of illustration and not limitation, an embodiment of the present
invention will be described below in connection with Figures 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
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CA 02622106 2008-02-25
mold 20. In Figure 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.
Although two patterns 10 are shown in Figure 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 Figure 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
Figure 1) as is
well known and shown for example in US Patent 5 069 271, the teachings of
which are
incorporated herein by reference.
Referring to Figure 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 US Patent 5 069 271, wherein the pattern assembly 40 including the
patterns
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 Figure 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 Figure 1.
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
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CA 02622106 2008-02-25
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.
Referring to Figure 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 Figure 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.
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.
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
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CA 02622106 2008-02-25
at a constant pressure to an adjustable valve and regulating the flow of
surfactant into
tube 100 by the use of the adjustable valve.
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 Figure lA. 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 Figure 1 A.
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,
Wisconsin 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. T'he 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.
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.
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.
CA 02622106 2008-02-25
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.
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.
Figures 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-
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CA 02622106 2008-02-25
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.
In Figure 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.
As further illustrated in Figure 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 Figure 1. An axis of the mold 20, such as
longitudinal
axis L of the mold 20 of Figure 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.
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-
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waxing.
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 Figure 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.
Although the chamber 30a of the hollow sprue 30 is described above as being
preformed in connection with Figures 1-4, the invention is not so limited. As
shown in
Figure 5, a chamber 30a' can be formed in-situ in a solid wax precursor sprue
30' of the
pattern assembly, Figure 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 Figures 1-4. In Figure 5,
like
reference numerals are used for like features of Figures 1-4.
In another embodiment of the invention illustrated in Figure 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 US Patent 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 Figures 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
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respect to Figures 1-4 and preventing steam condensate from soaking through
the mold
wall thickness.
For purposes of further illustration and not limitation, another method
embodiment of the present invention shown in Figure 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.
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 vesse1250 may comprise a
casting
container of the type that includes particulate support media about the mold
220 as
illustrated in Figure 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.
A sea1254 is provided between the mold 220 and the pressure vessel wall 250a
to
substantially prevent mixing of gas from the region interior of the sea1254 to
the exterior
of the sea1254. 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.
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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 wa11250a and also to surfactant
input
conduit 101 as shown in Figure 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.
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.
An air bleed valve 256 is provided on the pressure vessel wall 250 so as to
reside
in the region inside the sea1254 to bleed the air that was initially inside
the mold 220
from the region inside the seal 254.
The pattern removal operation of the embodiment of Figure 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
CA 02622106 2008-02-25
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.
Referring to Figures 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.
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 Figure 6 and also in US Patent 5 069 271.
In Figure 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 Figure 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.
Figure 8 shows illustrative apparatus for practicing this aspect of the
invention
before the mold 500 is placed in the apparatus. Figure 9 shows the apparatus
before the
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CA 02622106 2008-02-25
mold 500 is placed in the apparatus and before the mold is tilted with respect
to gravity.
Figure 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.
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 Figure 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 Figures 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.
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 Figure 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 Figure 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 Figures 1-4.
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.
Each wheel 512f is supported by bearings (not shown) on an upstanding stud S 1
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.
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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 Figure 10.
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.
T'he 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 P 1. 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.
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 H 1 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.
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
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512 thus are mounted on the sleeve 553 so that they rotate or pivot with the
shaft 550.
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 Figure 10 while the mold is rotated.
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.
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 Figures 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 Figure 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 unifonnly 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).
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
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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.
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.
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.
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.
