Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR ASSISTING REMOVAL OF SAND
MOLDINGS FROM CASTINGS
FIELD OF THE INVENTION
The present invention relates generally to the manufacturing of metal castings
and more particularly to manufacturing castings within sand mold packs.
BACKGROUND
A traditional casting process for forming metal castings generally employs a
mold or die, such as a permanent, metal die or a sand mold, having the
exterior
features of a desired casting, such as a cylinder head, formed on its interior
surfaces.
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A sand core comprised of sand and a suitable binder material and defining the
interior
features of the casting is typically placed within the die to further define
the features
of the casting. Sand cores generally are used to produce contours and interior
features
within the metal castings, and the removal and reclaiming of the sand
materials of the
cores from the castings after the casting process is completed is a necessity.
- Depending upon the application, the binder for the sand core and/or sand
mold
may comprise a phenolic resin binder, a phenolic urethane "cold box" binder,
or other
suitable organic binder material. The die or mold is then filled with a molten
metallic
alloy, which is allowed to cool to a certain, desired degree to cause the
alloy to
solidify. After the alloy has solidified into a casting, the casting is then
moved to a
treatment furnace or furnaces for further processing, including heat-treating,
reclamation of the sand from the sand cores, and aging. Heat treating and
aging are
processes that condition metallic alloys so that they will be provided with
different
physical characteristics suited for different applications. Heat treating may
include
processing and/or thermal processing.
Sand molds and/or cores generally are removed from the casting prior to
completion of heat treatment. The sand molds and/or cores are typically
separated
from their castings by one or a combination of ineans. For example, sand may
be
chiseled away from the casting or the casting may be physically shaken or
vibrated to
break-up the sand molds and internal saiid cores within the castings and
remove the
sand. In addition, as the sand molds and castings are passed through a heat
treatment
and/or thermai sand removal furnace, the organic or thermally degradable
binder for the
sand molds and cores, generally is broken down or combusted by exposure to the
high
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temperatures for heat treating the castings to a desired metal properties so
that the sand
from the molds and cores can be removed from the castings and reclaimed,
leaving the
finished, heat-treated castings. Such furnace systems and methods of heat
treating
castings are found in U.S. Patent Nos. 5,957,188, 5,829,509, and 5,439,045.
Once the
sand is removed from the casting, heat treating and aging of the casting
generally are
completed in subsequent steps.
Technology such as that disclosed in the above mentioned patents is driven,
for
example, by competition, increasing costs of raw material, energy, labor,
waste
disposal, and environmental regulations. These factors continue to mandate
improvements in the field of heat-treating and reclamation of sand from such
metal
castings.
SUMMARY
The present invention comprises a method and system for enhancing the
removal of sand molds from castings formed within sand molds. According to one
embodiment of the present invention, the sand molds may be removed from the
castings by scoring the molds and applying a force sufficient to cause the
mold to
fracture and break into pieces. For example, the molds may be fractured by
thermal
expansion of the castings being heated therein by the application of radiant
energy or
inductive energy to the molds, or by other applications of force and/or
energy.
Additionally, a high-pressure fluid may be directed at the exterior walls of
the mold to
further aid in breaking down the mold. Once the molds are fractured and broken
into
various pieces they generally are then dislodged from the casting. After the
molds have
been removed, the castings may be heat treated while the pieces of the sand
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molds are heated to a temperature sufficient to cause the binder materials
thereof to
combust for breakdown and reclamation of sand from the molds and cores.
In a further embodiment, the method of dislodging a mold from a casting can
include placing one or more explosive charges or organic or thermally
degradable
materials at one or more selected locations within exterior walls of the mold.
The
explosive charges are detonated at specific times in the process so as to
cause the
mold to fracture and break into pieces. The broken pieces may then be
dislodged
from the casting.
Additionally, score lines may be added to the mold containing the explosive
charges or organic or thermally degradable or reactive materials. The score
lines are
operatively placed in combination with the explosive charge(s) and/or organic
or
thermally degradable materials in predetermined locations to enhance the
breaking
down and dislodging of portions of the mold from the casting upon initiation
of the
explosive charge(s). After the mold has been dislodged, heat treatment of the
casting
may begin or continue.
An additional embodiment includes a method of dislodging a mold from a
casting formed within the casting by stimulating the mold with a high energy
pulsation. The mold typically fractures after being stimulated by the high
energy
pulse and the fractured pieces may then be dislodged from the casting. The
high
energy pulsation typically includes a shock wave, pressure wave, acoustical
wave, or
combination thereof produced from either mechanical means, cannons,
pressurized
gasses and electromechanical means. Additionally, score lines may also be
applied to
the mold to aid in breaking down and dislodging the mold from the casting.
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Various objects, features and advantages of the present invention will become
apparent to those skilled in the art upon reading the following specification,
when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
Figs. lA-1B are cross sectional views of a sand mold, illustrating the
fonnation of score lines at desired locations thereon and the resultant
fracture of the
mold along the score lines;
Figs. 2A-2B are cross sectional views of a sand mold and casting, illustrating
the use of score lines and explosive charges placed within the sand mold and
fracture
and dislodging of the mold upon initiation of the explosive charges;
Fig. 3 depicts a cross sectional view of a mold passing though an energy pulse
chamber within or adjacent a treatment furnace, illustrating the mold pack and
casting
being treated with high energy pulses;
Figs. 4A-4B illustrates the application of a pressurized fluid to a mold for
breakdown of the mold; and
Figs. 5A-5B illustrates movement of the molds through aii oxygen enriched
chamber for applying a flow of oxygen to pTomote combustion of the organic or
thermally degradable binder of the molds.
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DETAILED DESCRIPTION
The present invention generally comprises a method for enhancing the
breakdown and removal of a sand mold from a casting formed within the mold to
speed
up the exposure of the casting to heat treatment temperatures and enhance the
breakdown and reclamation of sand from the sand molds. The mold may be removed
from around its casting either prior to the introduction of the sand mold and
casting into
a heat treatment furnace or unit, or within the heat treatment furnace or unit
itself for
heat treatment and sand reclamation within the unit. An example heat treatment
furnace system for heat treatment of castings and at least partial breakdown
and
removal of sand molds and sand cores and reclamation of sand is shown in U.S.
Patent
Nos. 5,294,994, 5,565,046, 5,738,162, 5,957,188 and 6,217,317. By enhancing
the
breakdown and removal of the sand molds from their castings, the castings are
more
rapidly exposed to the ambient heating environment of the heat treatment
furnace or
chamber.
Less energy and time thus are required to increase the temperature of the
casting
to achieve the desired treatment and resulting metal properties of the casting
when the
mold is removed from the casting.
The method of dislodging a mold from a casting can include scoring the sand
mold. The scored mold is typically a "precision sand mold" generally comprised
of a
foundry sand material and a phenolic resin, phenolic urethane, or other
suitable organic
binder that generally decompose and/or combust when exposed to heat treatment
temperatures for treating most castings, as is conventionally known. The
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sand molds can also include semi-permanent type molds formed from a
combination
of standard binder materials and a metal such as steel. The mold typically
fractures
and breaks along the score lines set into the mold as the binder material
combusts to
facilitate the dislodging and removal of the mod from the casting contained
therein.
The score lines generally are placed at predetermined locations along or about
the
sides and/or top and bottom of each mold, with these locations generally
selected to
be optimal for breaking down the mold. The placing of the score lines in such
predetermined locations is dependent upon the shape of the mold and the
casting
formed within the mold.
The term "scoring" can include any type of cut, line, scratch, indentation,
groove or other such markings made into the top, bottom and/or side walls of
the
mold by any mechanism including cutting blades, milling devices and other,
similar
automatically and/or manually operated cutting or grooving devices. The
scoring
generally may take place on the exterior of the mold, but is not limited only
to the
exterior surfaces of the mold, and it will be understood that the interior
surfaces of the
mold also can be scored or grooved, in addition to or alternatively of the
scoring of
the exterior surfaces. Each mold may be scored by any conventional means such
as
by molded or scratched lines placed or formed on the exterior and/or interior
surfaces
of the mold during formation of the mold, or at some point thereafter, up to
the
introduction of the mold, with a casting therein, into a heat treatment
furnace.
A force may further be applied to the mold to enhance the fracture and
breaking of the mold into various pieces, which can then be easily dislodged
or
dropped away from the casting. Such a force may be applied to the inner walls
of the
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mold, to the outer walls of the mold or a combination of the two. The force
applied to
the inner walls of the mold typically results from the thermal expansion of
the casting
within the mold, with the expansion of the casting further being enhanced or
accelerated by heating the casting using radiant energy, inductive energy or a
combination thereof. The energy sources used to heat the casting may include
electromagnetic energy, lasers, radio waves, microwaves and combinations
thereof.
The energy sources used to heat the mold and/or casting may also include
lasers, radio waves, microwaves, or other fonns of electromagnetic energy
and/or
combinations thereof. In general, these and other energy sources are radiated
toward
the exterior or directed to specific areas of the mold or casting for the
purpose of
heating the mold and casting to cause thermal expansion leading to mold and/or
core
sand fracture or breakdown. Alternately, inductive energy involves enveloping
the
casting and mold in a field of electromagnetic energy which induces a current
within
the casting leading to the heating of the metal, and to a lesser degree, the
mold.
Typically, with the molds being insulative rather than conductive, inductive
energy
generally offers some limited heating effect directly within the mold, but not
to the
degree of the heat generated within the casting. Of course there may be other
methods of heating and expanding the casting for fracturing the molding.
Additionally, score lines can be added to the mold or by the mold itself to
aid in the
dislodging of the mold from the casting or mold in conjunction with the
applicatioin of
force thereto.
Pulsations of energy also may be applied within specially designed process
chambers such as for example a furnace. Design features may include the
capability
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of withstanding pulsations and resultant effects, provide for the
transportation of
mold/casting into and out of the chamber to provide precise control of the
pulsation.
The energy pulsations generally enhance to some degree heat transfer to the
mold
cores and castings. The pulsations also promote mass transport of decomposed
binder
gases out of the mold and cores, oxygen bearing process gas to the mold and
cores,
and loosens sand out of the casting. The pulsations may occur at both low or
high
frequencies, where low frequency pulsations would generally be utilized to
generate a
force for fracturing the mold or cores and the higher frequencies would be
employed
to enhance the transfer, mass transport and some fracturing on a smaller
scale. Higher
frequency pulsations induce vibration effects to some degree within the
casting to
promote the mechanical effects of the above process.
Furthermore, the mold and/or cores may be broken down by the application of
any or all of these energy sources to the mold and/or cores to promote the
decomposition of the organic or thermally chemical binder of the sand mold
and/or
core, which binder breaks down in the presence of heat thus facilitating the
degradation of the mold. Additionally, the mold may be broken down by the
application of a high pressure fluid(s) such as air, products of combustion,
oxygeri
enriched gases or other fluid materials to the exterior walls of the mold.
Furthermore, a direct application of force in the form of shock waves,
pressure
waves, acoustical waves, or a combination thereof can be applied to the mold,
cores,
or casting to aid in fracturing and breaking the mold into pieces. In one
embodiment,
the mold and/or core is stimulated with a high energy pulsation for direct
application
of a force, which may also penetrate the walls of the mold and cause heating
of the
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mold to further aid in the combustion of the mold binder and the resultant
breaking
down of the mold. The pulsation energy may be a constantly recurring or
intermittent
force and can be in the form of shock waves, pressure waves, acoustical waves,
or any
combination thereof produced by mechanical, electromechanical and/or other
known
means such as compression cannons or pressurized gasses. Alternatively, low
power
explosive charges or organic or thermally degradable materials can be placed
in the
mold and set off or initiated by the heating of the mold to assist in break up
and
dislodging of the mold from about its casting.
In greater detail, the present invention envisions several alternative
embodiments and/or methods for performing this function of dislodging or
breaking
up the sand molds prior to or during heat treatment of the castings. It will
also be
understood that any of the described methods can be used in conjunction with
or
separately from one another. These various methods are illustrated in Figs. 1A
through 5B.
In a first embodiment of the invention illustrated in Figs. IA and IB, a sand
mold 10 with a casting 11 therein is shown with at least one, and typically
multiple,
score lines 12 or relief lines formed in the exterior side walls 13 of the
mold 10. The
score/relief lines 12 typically will be cut or otherwise formed as grooves or
notches in
the exterior side walls of the mold and act as break lines for the exterior
walls of the
mold pack. It is also possible to cut or form the score/relief lines 12A in
the interior
walls 14 of the mold as shown in Fig. IA and/or in the top and bottom walls 16
and
17 of the mold 10.
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As further illustrated in Fig. IB, these score/relief lines weaken the mold
walls
so as to predetermine the locations and positions of the fracture or breaking
apart of the
mold 10, such that as a force F is applied to the walls of the mold, walls of
the mold are
caused to crack and break apart along these score/relief lines as illustrated
at 18 in Fig.
1B. Typically, this force F includes the exertion of pressure against the
interior walls
14 of the mold 10 by the castings themselves due to the thermal expansion of
the metal
of the castings as they are subjected to heating or elevated temperatures for
heat
treating the castings. As the metal of the castings expands in response to
heat in the
heat treatment furnace, it presses against and urges the walls of the mold
outwardly,
causing the mold to crack and break apart at the points of weakness therein
created by
the score/relief lines. As a result, sections or portions of the mold will be
readily and
easily dislodged from the mold and its casting generally prior to or during an
initial
phase of the heat treatment process for the castings, rather than the mold
simply
breaking down and slowly degrading as its binder material is combusted over
time in
the heat treatment furnace.
Figs. 2A-2B illustrate an alternative embodiment of the present invention for
breaking down and dislodging a mold 10 from a casting 11 formed therein. In
this
alternative method, low impact explosive charges 22 are mounted at one or more
points
within the side walls 23 of the mold pack 10. The explosive charges generally
are
strategically located within the mold pack structure, generally near critical
joints 24
within walls, such as between the side walls 23 and the top and bottom walls
26 and 27,
so as to dislodge the mold from the casting, while still retaining the casting
intact. As
additionally shown in Fig. 2B, after explosion of the low intensity explosive
charges,
gaps or channels 28 are formed in the niold pack 10, extending deeply through
the side
walls and upper and lower portions of the mold. As a result, the mold is
substantially
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weakened at or along these channels or gaps such that the mold tends to
readily break
apart in sections or pieces along these channels 28 in response to presence
from the
thermal expansion of the castings and/or as the binder materials of the mold
is
combusted for ease of removal of the mold from its casting.
Still a further embodiment of the present invention for breaking apart and
enhancing the removal of mold 10 and from the castings is illustrated in Fig.
3. In this
embodiment of the present invention, vibratory forces of nature to promote
fracture of
mold/core sand is applied to the molds in the high-energy pulses or waves 32
which are
directed at the molds 10 as they are passed through a process chamber 33,
which
typically is positioned in front of or at the input end of a heat treatment
furnace so that
the molds and castings generally pass therethrough prior to heat treatment of
the
castings. The high-energy pulses of variable frequency or wavelength are
typically
directed at the side walls 34 and/or upper portions or top walls 36 of the
molds from
one or more pulsation or wave generators 37 mounted within the chamber. Such
high
energy pulsations or waves would typically be generated in the form of shock
waves,
pressure waves, or acoustical waves propagated through the atmosphere of the
process
chamber. Alternatively, electromagnetic energy could be pulsed or radiated
onto the
walls of the molds as described to promote fracture, heat absorption, binder
degradation, or other process effect for the purpose of dislodging mold and
core sand
from the casting. Such electromagnetic radiation would be in the form of
lasers, radio
waves, microwaves, or other form that would result in the process effects
described
above.
The high energy pulses directed towards the molds stimulate the molds and
cause them to vibrate without requiring physical contact with the mold packs.
As the
pulsations pass through the molds, the stimulation and vibration of the molds
tends to
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cause fracturing and breaking apart of the molds. The pulsation may be either
a
sustained pulse or directed as discrete pulses. The discrete pulses may be
administered
at regular intervals. Pulsations administered in sustained or discrete fashion
would be
carefully controlled in terms of frequency, interval of application, and
intensity, so as to
accomplish the process effects without harming the casting. In addition, the
molds can
also be scored or pre-stressed/weakened, at selected points as discussed above
and as
indicated at 38 in Fig. 3, so as to facilitate or promote the breaking apart
of the molds
as they are vibrated or otherwise impacted by the high energy pulses. The
molds
accordingly are caused to be broken down and dislodged from their castings as
the
castings are moved into a heating chamber of the heat treatment furnace or
other
processing of the castings. In addition, as discussed in U.S. Patent No.
6,672,367, the
energy pulses further typically cause the castings within the molds to be
heated, which
further results in thermal expansion of the castings so as to apply a force
against the
interior side walls of the molds to further facilitate and enhance the
breaking apart of
the molds.
In still a further embodiment of the present invention for enhancing the
breakdown and removal of a sand mold from a casting I 1 formed therein (or,
for
example, as discussed in regard to this embodiment, removal of sand cores
located
within the casting) as illustrated in Figs. 4A-4B, a series of nozzle stations
58, 63
generally are positioned at specific locations or positions along the path of
travel of the
mold/core laden casting into or within a heat treatment furnace, either as a
part of the
heat treatment furnace, such as in an initial or prechamber, or placed in
front of or prior
to the heat treatment furnaces, to aid in the removal of the sand core from
the castings.
The number of nozzle stations can vary as needed, depending upon the core
print or
design of the casting being formed in the mold. Each of the nozzle stations or
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assemblies 63 generally includes a series of nozzles 64, 64' mounted and
oriented at
known or registered positions about the side walls, top or upper walls and/or
lower or
bottom walls of the molds 10 corresponding to known, indexed positions of the
cores
and castings 41. The number of nozzles in each nozzle station is variable,
depending
upon the core prints of the castings, such that different types of castings
having
differing core prints can utilize an optionally different arrangement or
number of
nozzles per nozzle station. The nozzles also may be automatically controlled
through a
control system for the heat treatment station or furnace that can be operated
remotely to
cause the nozzles to move to various desired positions 56 about the side walls
and top
and bottom walls of the mold as indicated by arrows 66 and 67 in Figs. 4A and
4B.
Each of the nozzles is typically supplied with a high-pressure heated media.
The high-pressure media may include air, thermal oils, water or other known
fluid
materials that are directed at the side walls, top wall and/or bottom wall of
each
mold/core under high pressure, typically in the range of 5 psig to 45 psig,
although
greater or lesser pressures also can be used as required for the particular
casting
application. These fluid pressures are converted to high fluid velocities at
the nozzle
exit which delivers the energy of the fluid to the mold/core and applies
forces sufficient
to at least partially fracture and/or otherwise degrade the mold and/or cores.
High fluid
velocities typically cause or promote higher heat transfer to the casting,
mold, and cores
which has added benefit in breaking down mold and core sands. The pressurized
fluid
flows, which are administered by the nozzles, can be applied in continuous
flows or as
intermittent blasts that impact or contact the mold walls to cause the mold
walls to
fracture or crack and can promote more rapid decomposition and/or combustion
of the
binder materials of the sand molds to help at least partially degrade or break
down the
mold.
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Figs. 5A-5B illustrate still a further alternative embodiment of the present
invention for enhancing the breakdown and removal of molds 10 from castings 11
contained therein. In this embodiment, prior to or as the molds 90 and their
castings
are moved into a heat treatment furnace or chamber 92, they are passed through
a low
velocity oxygen chamber 93. The oxygen chamber generally is an elongated
autoclave
or similar pressurized heating chamber capable of operating under higher than
ambient
pressures. The oxygen chamber 93 is provided with an enriched oxygenated
environment and includes a high pressure upstream side 94 and a low pressure
downstream side 96 that are positioned opposite each other to assist in
drawing an
oxygen flow therebetween.
As the molds are passed through the low velocity oxygen chambers of the
heating chamber 93, heated oxygen gas is directed at and is forced through the
molds,
as indicated by arrows 97 (Fig. 5A) and 97' (Fig. 5B). The oxygen gas is drawn
or
flows under pressure from the high atmospheric pressure side to the low
atmospheric
pressure side of the oxygen chamber, so that the oxygen gas is urged or forced
into and
possibly through the molds and/or cores. As a result, a percentage of the
oxygen gas is
combusted with the binder materials of the sand molds/cores, so as to enhance
the
combustion of the binder material within the heating chamber. This enhanced
combustion of the binder materials of the molds and cores are further supplied
with
energy from the enhanced combustion of the binder material thereof and the
oxygen,
which helps enhance and/or speed up the breakdown and removal of the molds
from
their castings. This breakdown of the molds can be further assisted by scoring
or
forming relief lines in the molds, as discussed in greater detail above, so as
to pre-
stress/weaken the molds so that as the binder materials are combusted, the
mold walls
will tend to crack or fracture so that the molds will break and fall away from
their
CA 02422646 2004-10-06
castings in sections or pieces.
In addition, the enhanced combustion of the binder materials further serves as
an additional, generally conductive heat source to thus increase the
temperature of the
castings in the mold packs and facilitate combustion of the binder materials
of the sand
cores for ease of removal and reclamation. As a result, the castings are
raised to their
heat treatment temperatures more rapidly, which helps reduce the residence
time of the
castings in the heat treatment furnace tiiat is required to properly and
completely heat
treat the castings, as discussed in copending U.S. Patent No. 6,672,367.
It will be understood by those skilled in the art that while the present
invention
has been disclosed above with reference to preferred embodiments, various
modifications, changes and additions can be made to the foregoing invention,
without
departing from the spirit and scope thereof.
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