Note: Descriptions are shown in the official language in which they were submitted.
CA 02617365 2008-01-07
METHOD OF COMPACTING SUPPORT PARTICULATES
FIELD OF THE INVENTION
The present invention relates to method and apparatus for compacting support
particulates about a casting mold or fugitive pattern in a container.
BACKGROUND OF THE INVENTION
Metal casting methods are known wherein a ceramic shell mold is externally
surrounded and supported by compacted support particuates, such as loose sand,
in a
container during casting. US Patent 5,069,271 and others describe such a
casting method.
Other casting methods are known wherein a foam pattern of the article to be
cast is
coated with a refractory coating and is externally surrounded and supported by
compacted support particuates, such as sand, in a container during so-called
lost foam
casting. US Patents 4,085,790; 4,616,689; and 4,874,029 describe such a lost
foam
casting method.
Compaction of support particulates around the exterior of a ceramic shell mold
or
foam pattern in a casting flask (container) is a demanding process. First,
support
particulates such as loose sand must be fluidized and transported into deeply
recessed
voids about the exterior of the shell mold or foam pattern. To promote free
flow, bridging
of particulates must be eliminated. Next the particulates must be consolidated
to provide
structural support for the ceramic shell mold or foam pattern, which can be
very fragile
depending on shell mold wall thickness and surface characteristics of the
refractory
coated foam pattern. These two requirements are contradictory.
Simple vibration of the casting flask has been employed in the past to
consolidate
support particulates over all exterior sections of a mold or pattern.Vibration
of the casting
flask must be sufficiently rigorous to cause displacement and then
consolidation of the
support particles, but not so severe as to distort or damage the fragile mold
or pattern;
another contradictory demand.
To facilitate filling long, narrow channel-shaped voids at the exterior of the
shell
CA 02617365 2014-02-28
mold or refractory coated foam pattern, the shell mold or foam pattern has
been oriented
so that those channel-shaped voids are vertical or near vertical. When this is
not possible,
most compaction processes deal with the problem by controlling the fill rate
of the
casting flask. Since only the top fraction of an inch of a free surface of
support
particulates readily flows, this approach calls for filling the particulates
media up to the
level of the difficult-to-fill horizontal channel-shaped void and pausing the
filling process
until the fluidized particulates have a chance to travel to the end of the
channel-shaped
void. Filling of the casting flask is then resumed until the next hard-to-fill
void is reached.
Relying on this technique calls for precise vibration and particulates
addition, recipes,
and accurate fill level control.
Another problem with this approach is that for part of the compaction process
the
top of the shell mold or foam pattern is supported from above, while the
bottom section is
partially buried in the vibrating support particulate media and moves with the
casting
flask. The resulting flexing of the mold or pattern can cause mold or pattern
distortion
and mold wall cracking or pattern coating cracking.
An attempt to overcome the above problems is described in US patent 6,457,510
and involves synchronizing four vibrators and altering their direction of
rotation and
eccentric phase angle relative to each other such that shaking of the casting
flask can be
altered to induce the support particulates to travel sideways. However, this
process needs
specific, vibration-vector altering recipes tailored to passage-shaped void
geometry.
Furthermore, controlled shaking is limited to one plane, perpendicular to the
axes of the
four vibrators. Finally, this patented compaction process, as well as all
other compaction
processes, are constantly fighting gravity when attempting to fluidize support
media.
SUMMARY OF THE INVENTON
The present invention provides method and apparatus for compacting support
particulates media about a casting mold or fugitive pattern in a container
wherein a
combination of systematic steps of container vibrating, container rotating,
and container
tilting relative to the gravity vector are used to vary mold or pattern
orientation in a
manner that the support particulates media are induced to fill simple and
complex voids
at a mold or pattern wall. Support particulates media are induced to flow into
the voids
where the particulates are trapped and consolidated by gravity and vibration
vectors
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variable relative to the mold or pattern during the method.
One embodiment of the invention involves continuously vibrating, continously
rotating, and continuously tilting the container to vary mold or pattern
oreintation relative
to the gravity vector. Another embodiment of the invention involves tilting
the container
in angular increments of inclination during compaction of the particulates
media
thereabout. The container can be subjected to rotation and vibration
continuously, or
intermittently at each of the angular increments of inclination. Still another
embodiment
of the invention involves subjecting the container to rotation and vibration
while the
container is tilted at a fixed angle of inclination relative to the gravity
vector.
The present invention can be practiced to compact support particulates media
about a gravity casting mold or pattern as well as a countergravity casting
mold or
pattern.
In an illustrative method embodiment of the invention, the mold or fugitive
pattern is placed in a flask, and the flask is filled with support
particulates media. The
flask is set to continuously vibrating and rotating about a first axis while
the container is
continuously or fixedly tilted about a second axis relative to the gravity
vector. The
combination of container vibration, rotation, and tilting relative to the
gravity vector
causes channels, chambers, crevices, and other voids formed by the particular
configuration of the mold or pattern wall to be repeatedly and methodically
reoriented so
that the free surface of the support particulates media in the voids is moved
past its
dynamic angle of repose and is caused to flow into those voids by the combined
action of
the vibration and the continuously changing orientation of the voids.
Systematic
repetition of such flask actions will eventually fill the voids formed by the
mold or
pattern wall with compacted support particulates media. When the orientation
of the
voids cycles during rotation such that openings of the voids are facing
downward, the
support particulates are prevented from exiting the voids by consolidated
particulates
media blocking the void opening. A lid optionally can be placed on the
upwardly facing
surface of the particulates media in the container to increase the angle to
which the
container can be tilted during practice of the compaction method.
In an illustrative apparatus embodiment of the invention, the container is
disposed
on a rotatable fixture and a first motor is provided for rotating the fixture
to impart
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rotation to the container about a first axis thereof. The fixture, in turn, is
disposed on a
tiltable frame and a second motor is providing for tilting the frame to tilt
the container
about a second axis relative to the gravity vector. One or more vibrators are
disposed on a
table supporting the frame, on the frame itself, on the fixture itself, and/or
on the
container itself. A source of support particulates is provided to fill the
container with the
particulates after the mold or pattern is received in the container.
According to an aspect of the present invention there is provided a method of
compacting particulates media about a mold or pattern, comprising disposing a
mold or
pattern in a particulates media in a container and subjecting the container to
a
combination of vibrating, rotating, and tilting in a manner that the
particulates media are
induced to fill voids at a mold or pattern wall, wherein the combination of
rotation and
tilting causes voids formed by an outside wall of the mold or pattern to be
continuously
or repeatedly reoriented so that a free surface of the particulates media in
the voids is
moved past its dynamic angle of repose, whereby the particulates media is
caused to flow
into those voids by the combined action of the vibration and a constantly
changing
orientation of the voids relative to a gravity vector.
The compaction method and apparatus of the invention are advantageous in that
they are minimally part-specific and need no complex particulates feeding
recipe.
Moreover, the compaction method and apparatus of the invention can be
practiced to
compact support particulates media about gravity casting molds or fugitive
patterns as
well as about countergravity casting molds or fugitive patterns.
These and other advantages will become more readily apparent from the
following detailed description taken with the following drawings.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a longitudinal cross section of a ceramic shell mold having voids
at an
exterior mold wall.
Figure lA is a cross section through a casting flask containing a
hypothetical,
cylindrical mold with intricate elongated channel-shaped annular voids in the
outside
mold wall radiating away from the riser toward the flask wall. The flask is
filled with
support particulates such as sand.
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. .
,
.,
Figure 1B is an enlarged view illustrating penetration of of the support media
into
a channel-shaped void as permitted by the static angle of repose of the
support
particulates.
Figure 2 shows the flask of Figure 1 tilted to enhance particulates media flow
into
the channel-shaped voids wherein tilting is limited by the spilling of support
particulates
media over the rim of the flask. Channel-shaped voids designated 1 and 4 are
completely
filled. The remaining channel-shaped voids are only partially filled by the
small
inclination of the flask.
Figure 3 shows the flask of Figure 1 fitted with a floating lid made of a
material
denser than the bulk density of the media. The lid confines the particulates
media by
gravity and prevents media spillage at greater angle of inclination than
possible without
4a
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. .
the lid. With sufficient vibration, the larger angle of inclination enables
the filling of
channel-shaped voids 1 through 4 and the consolidation the support grain in
those voids.
Figure 4 shows the flask of Figure 1 after it has been slowly rotated 180
about
the longitudinal axis L of the flask. Channel-shaped voids 1 through 4 have
been
completely filled. The media has worked its way deeper into channel-shaped
voids 5 and
8 with openings facing downward.
Figure 5 shows the same flask after several rotational cycles about axis L.
Channel-shaped voids 1 through 5 have been completely filled with compacted
media.
The remaining channels will not fill further at this angle of inclination no
matter how
long the compaction process is continued.
Figure 6 is a cross-sectional view through a casting flask having a lost foam
pattern of an engine block residing in support particulates media. The engine
block
pattern is shown having internal oil channel-forming passages that communicate
to an
exterior surface of the pattern. The pattern is shown being tilted to 45 .
Figure 7A is a longitudinal cross-section of a square cross-section, lost foam
casting flask fitted with circular flanges and circular reinforcing rib. The
flask contains a
lost foam pattern corresponding to a pair of engine cylinder heads attached to
a riser. The
flask is filled with support media. Before the flask was tilted, a square-
shaped lid, with an
opening for the pour cup, is shown placed on the surface of the media. The
force vector,
along the axis of the flask, from the weight of the lid is shown being larger
than opposing
vector from the wedge of media above its angle of repose.
Figure 7B is a plan view of the casting flask of Figure 7A.
Figure 8A is an elevational view, partially in section, of compaction
apparatus for
rotating a casting flask with the engine block pattern of Figure 6 while is
being tilted
between selected inclination angles.
Figure 8B is a plan view of the apparatus of Figure 8A.
Figure 9 is an elevational view of a compaction test cell with an intricate
channel-
shaped void, similar to void 5 in Figures 1 through 5, that was completely
filled with
compacted sand by practice of the invention.
Figures 10A through 10L are schematic views of the test cell showing a
theoretical compaction sequence.
CA 02617365 2014-02-28
. .
. '
Figure 11A is an elevational view of a self-contained apparatus pursuant to an
embodiment of the invention for compacting support media around a counter-
gravity
casting ceramic shell mold before the container is tilted.
Figure 11B is an enlarged sectional view of the encircled area of Figure 11A.
Figure 11C is an elevational view of the self-contained apparatus of Figure
11A,
with certain components shown in cross-section for convenience, after the
container is
tilted to a selected angle of inclination.
Figure 11D is a view taken in the direction of arrows 11D of Figure 11C.
Figure 11E is a partial elevational view of the drive motor for the ACME
screw.
Figure 12A is an elevational view of apparatus pursuant to another embodiment
of the invention for compacting support media around a counter-gravity casting
ceramic
mold after the container is tilted using a harness pulled by a hand winch.
This tilting
arrangement is unaffected by vibration greater than 1 G.
Figure 12B is a plan view of the apparatus of Figure 12A.
Figure 13 is a perpsective view of hydraulically operated compaction apparatus
pursuant to still another embodiment of the invention for compacting support
media
around a ceramic shell mold or fugitive pattern.
Figure 14 is an isometric view of another hydraulically operated compaction
apparatus pursuant to still a further embodiment of the invention for
compacting support
media around a ceramic shell mold or fugitive pattern.
Figure 15 is an enlarged cross-section of the floating multi-function lid of
Figure
14.
Figure 16 is a perspective view of the apparatus of Figure 14 showing the
flask
tilted past horizontal.
Figure 17 is a partial perspective view, partially in cross section, showing
components of the flask lid of Figures 14 and 16.
Figure 18 is a perspective view of the apparatus of Figure 14 showing
vibrators
mounted directly on the casting flask. The main structure of the apparatus is
widened to
accommodate the vibrators rotating with the flask.
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. .
,
DESCRIPTION OF THE INVENTION
The present invention provides method and apparatus for compacting support
particulates about a casting mold, such as a ceramic shell mold, or a fugitive
pattern, such
as a plastic pattern, in a container using a combination of container
vibration, container
rotation, and container tilting relative to the gravity vector to vary mold or
pattern
orientation in a manner that the support particulates are induced to fill
simple and
complex voids at a mold or pattern wall. The present invention can be
practiced to
compact support particulates in voids about any type of mold or fugitive
pattern used in
the casting of metals or alloys where support of the mold or pattern is
desireable.
Referring to Figure 1 for purposes of illustration and not limitation, a thin
wall
ceramic shell mold 10 is shown having a central riser passage 10a and a
plurality of mold
cavities 10b that communicate via respective gate passages lOg with the riser
passage to
receive molten metal or alloy therefrom during countergravity casting as
described in US
Patent 5,069,271. Such a ceramic shell mold 10 is typically formed by the well
known
lost wax process wherein a fugitive (e.g. wax or plastic) pattern assembly
(not shown) is
repeatedly dipped in ceramic slurry, drained of excess ceramic slurry,
stuccoed with
coarse ceramic stucco particles, and dried until a desired shell mold wall
thickness is built
up. The fugitive pattern then is selectively removed to leave a ceramic shell
mold, which
is fired to impart sufficient strength thereto for casting a molten metal or
alloy therein.
The shell mold 10 is provided with a ceramic collar 12 for communciation with
a fill tube
(not shown) as described in the above patent for countergravity casting of a
molten metal
or alloy upwardly through the riser passage 10a and into the mold cavities 10b
and a
ceramic closure member 12'. The invention can be practiced with ceramic shell
molds
having any shell mold wall thickness where support of the shell mold wall
during casting
is desireable.
The invention is not limited to practice with ceramic shell molds of the type
shown in Figure 1 for countergravity casting of a metal or alloy and can be
practiced with
casting molds of any type and with gravity casting of metals or alloys. For
purposes of
illustration and not limitation, a ceramic shell mold supported by a support
particulates
7
,
CA 02617365 2014-02-28
. .
media for gravity casting of a metal or alloy therein can be used in practice
of the
invention. Similarly, the invention can be practiced with a fugitive pattern
such as, for
purposes of illustration and not limitation, a plastic (e.g. polystyrene) foam
pattern in a
container wherein the pattern optionally may be coated with a thin refractory
coating on
the exterior surface of the pattern.
As is apparent in Figure 1, the ceramic shell mold 10 includes an exterior
configuration that forms a plurality of elongated channel-shaped or crevice-
shaped voids
V about the exterior surface or wall of the mold. The voids V are shown
extending
laterally (generally radially) relative to the riser passage 10a. For example,
the voids V
are formed between laterally extending mold sections lOs that define therein a
respective
mold cavity 10b. However, the voids V can have any shape and/or orientation
relative to
the riser passage depending upon the particular exterior configuration of the
mold that is
employed. Figure 1 is provided simply to illustrative representative voids V
which can be
filled with compacted support particulates pursuant to the invention.
Figure 1A is provided to further show a casting flask (container) 20
containing a
hypothetical, cylindrical casting mold 10 residing in support particulates
media 30
wherein the mold 10 includes illustrative hypothetical intricate elongated
channel-shaped
annular voids V which are located at the outside mold wall lOw radiating away
from the
riser passage 10a toward the inner wall of the flask 20. The voids V are shown
with
varied configurations to illustrate different void shapes which can be filled
with
compacted support particulates (e.g. dry sand) by practice of the invention.
For example, consider the hypothetical, cylindrical mold 10 with a multitude
of
intricate voids V, such as those shown in cross-section in Figure 1A. When the
mold 10 is
placed in the flask 20 and the flask is filled with a support particulates, a
small amount of
the particulates media 30, determined by its static angle of repose, will
enter each void V
as illustrated in Figure 1B. Vibration of the flask 20 will fluidize the top
inch or so of the
particulates media 30 in the flask 20, but will not induce much more
particulates media to
flow into each void V.
If the flask 20 is tilted at a fixed angle of inclination "A" relative to the
gravity
vector "GV" as shown in Figure 2, the particulates media 30 will readily flow
into those
voids V which have upfacing openings OP and in general slope downwardly. Voids
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CA 02617365 2014-02-28
designated 1 and 4 in Figure 1A will completely fill with loose (dry)
particulates media;
whereas voids 2 and 3 will fill only partially before the particulates media
starts spilling
over the edge of the flask. Vibration will enhance the flow of the
particulates media into
the voids and will increase consolidation of the particulates media in those
voids.
However, vibration will also cause more of the media to spill from the flask
20.
As the particulates media 30 flows into voids V and is compacted, media from
above flows along the gravity vector to replace it. It is helpful to visualize
the void as a
"bubble". As the media trickles down, this "bubble" becomes rarified media and
travels
up, against the gravity vector until it encounters a surface impermeable to
the media.
When this occurs, the "bubble" will form a void under such surface. Depending
on its
shape and orientation such surface may capture the "bubble". For example,
surfaces
perpendicular to the gravity vector will capture the "bubble". Compaction in
one area
may be attained at the expense of losing compaction in another area. Practice
of this
invention permits such void "bubbles' to escape by systemically reorienting
the capturing
surfaces. When the "bubble" encounters the inclined flask wall, it will travel
along the
flask wall until it escapes through the upper, open surface of the
particulates media 30.
If a loosely fitting lid 40, which is made from a material denser than the
bulk
density of the particulates media, is placed over the upper surface of the
particulates
media 30, Figure 3, the flask 20 can be tilted to a much steeper angle without
spilling of
the particulates media over the edge of the flask.. The force from the weight
of lid 40
normal to the surface of the media is greater than the lifting force due to
the
wedge of particulates media 30 created by the angle of repose as illustrated
in Figure 7A.
Because of this, the flask 20 can be tilted to 45-50 degrees without spillage
of the
particulates media 30. As shown in Figure 3, at tilt angles made possible by
the lid 40,
more voids V are filled completely with the particulates media. Vibration of
the flask 20
speeds the filling of the voids and compacts the particulates media once the
voids are
completely filled. As the particulates media fills the voids and compacts in
the flask and
voids, the resulting rarified media "bubbles" work their way to the upper
surface of the
particulates media under the lid 40 and escape along the rim of the lid. The
upper surface
of the particulates media 30 drops as a result, and the lid 40 settles deeper
into the flask
20.
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If the tilted flask 20 is slowly rotated about its longitudinal axis L, voids
V
radiating from the riser passage 10a of the mold 10 are moved to positions
where their
openings OP face upwardly as illustrated in Figure 4. Therefore, each void
will receive
particulates media during part of the rotation cycle of the flask. Figure 4
shows the mold
after one half revolution. Voids that face down do not lose particulates media
because
compacted particulates media outside the voids blocks their openings OP. If
the rotational
speed is sufficiently slow, voids designated 1 through 4 will fill in one
revolution.
However, with respect to voids 5 and 8, during the portion of the cycle when
the
openings OP to these voids face downwardly, particulates media will move
deeper into
the voids, leaving a temporary gap in the particulates media column in those
voids. After
several rotations of the flask, the zigzagging void 5 is completely filled
with compacted
particulates media as illustrated in Figures 5 and 10L.
As the rarified media "bubble" rises straight up along the gravity vector, its
path
through the media is distorted by rotation, tracing a spiral toward the flask
inner wall. If
the "bubble" encounters any obstruction impermeable to the media, it will
accumulate
under such obstruction. If the obstruction is a mold surface, it will face up
during part of
the flask rotation cycle, releasing the "bubble". Eventually the rarified
media "bubble"
will encounter the flask inner wall and due to the inclined flask rotation,
will spiral
upward along the flask inner wall until it escapes through the exposed upper
surface of
the particulates media as discussed above.
This particulate media and rarified media "bubble" movement process will
completely fill any void V, regardless of its complexity, as long as all
segments of the
void slope downward during at least a portion of the rotation cycle of the
flask 20. The
slope must be greater than the angle of repose of the particulates media for a
given
vibration imparted to the flask 20. This angle hereafter is referred to as the
dynamic angle
of repose of the particulates media and is much less than the static angle of
repose.
In Figure 5, voids 6, 7 and 8 cannot be completely filled under the flask
vibration,
rotation and tilt conditions discussed so far. This is so because the end of
void 6 slopes up
during the entire rotation cycle of the flask and the last two segments of
voids 7 and 8 are
blocked by the always upward sloping fourth segment. These voids 6, 7, and 8
can be
filled by another embodiment of the invention discussed below.
CA 02617365 2014-02-28
Although the voids V in Figures 1 through 5 are shown residing in a plane
containing the flask longitudinal (rotational) axis L, the voids can be
oriented in any
direction and filled with particulates media 30 so long as the voids slope
downwardly
during a portion of the rotation cycle of the flask 20. Further, if voids 6
through 8 in
Figures 1 through 5 were oriented in a "plane perpendicular to the flask
longitudinal
(rotational) axis", (a plane parallel to the container bottom), they could be
readily filled
with compacted particulates media by vibration and rotation of the tilted
container as
described above.
Figure 9 is an elevational view of a compaction test cell (simulating a
section of a
mold or pattern P) with an intricate channel-shaped void V, similar to void 5
in Figures 1
through 5, that was completely filled with compacted sand by practice of the
invention. In
particular, the compaction test cell was constructed of polystyrene bars
sandwiched
between vertical, transparent acrylic plates AP. The compaction test cell
formed a
channel-shaped void having dimensions of 1 1/2 inches by 1 1/2 inches by 36
inches long,
similar in shape to void 5 in Figures 1 through 5. In the vertical orientation
shown, the
compaction test cell was placed on the bottom of a 30-inch deep cylindrical
flask, and the
flask was filled with dry CALIMO 22 support media in 32 seconds. The flask was
not
vibrated during the filling sequence. Next, the flask was tilted to a fixed
angle of
inclination of 30 relative to the gravity vector (vertical), vibrated with
less than 1 G and
rotated at 6 rpm for two minutes on a centrifugal casting machine having
capability to tilt,
rotate, and weakly vibrate for initial testing purposes.
This combination of flask vibration and rotation while the flask was tilted at
a
fixed angle of inclination for two minutes completely filled the torturous
channel-shaped
void of the test cell with compacted foundry sand.
In contrast, a comparison test using the same casting machine, the same test
cell
and same support media, was conducted where only the above-described flask
vibration
condition was employed. That is, the flask was not tilted to the fixed 30
angle of
inclination and was not rotated. The comparison test resulted in only
partially filling the
channel-shaped void above the top polystyrene bar with loose media. That is,
the
remaining portion, more than 90%, of the channel-shaped void remained empty
and not
filled with support media.
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Figures 10A through 10L illustrate a filling sequence that occurs to fill and
compact the foundry sand in the tortuous channel-shaped void V, Figure 9, of
the test
cell. This sequence is offered merely for purposes of illustration and not
limitation of the
invention. Referring to Figure 10A, the test cell is initially positioned on
its side in the
vertically oriented flask (not shown) with open end E of the test cell facing
to the left in
Figure 10A. The flask is oriented vertically with its open end facing upwardly
(e.g. see
Fig. 1A). Foundry sand 30 is then introduced into the flask until it is filled
so as to
dispose the test cell in the foundry sand, where only a portion of the foundry
sand around
the test cell in the flask is shown in Figure 10A for convenience. In Figures
10B-10L. the
foundry sand 30 around the test cell is omitted for convenience. Figure 10A
shows sand
penetration only to the static angle of repose after filling of the vertical
flask. Figure 10B
shows the extent of particulates media (sand) penetration into the voids after
the filled
flask is tilted to the 300 angle of inclination and the systematic rotation
has brought the
open end E of the test cell to a partially upward facing position, wherein
initial
orientation of the test cell about the axis of rotation is not important. In
Figure 10C, the
tilted flask is rotated 180 degrees further about its longitudinal axis at 6
rpm while being
vibrated at less 1G with the slug of particulates media being shown to have
flowed deeper
into the channel. In Figures 10D through 10K, vibration and rotation of the
tilted flask is
continued, and the particulates media continues to flow sequentially into the
void until
the void is filled with compacted foundry sand as shown in Figure 10L. Note in
these
figures how the void "bubble" is fractionated by the intruding media and how
the
"bubble" segments work their way out of the channel in counter flow with the
media.
Actual filling and compaction of the void took 12 complete revolutions of the
flask.
As mentioned above, the invention can be practiced to compact support
particulates media about a casting mold or fugitive pattern for use in gravity
or
countergravity casting processes.
GRAVITY CASTING EMBODIMENT
Figures 7A, 7B illustrate a flask 20' for use with a gravity casting lost foam
pattern 10' disposed in the flask with the flask filled with the support
particulates media
30'. For purposes of illustration and not limitation, the flask or container
20' can be made
of steel or any other appropriate material and can have any shape such as, for
example, a
CA 02617365 2014-02-28
= .
cylindrical flask or a flask with a square or other polygonal cross-section.
The fugitive pattern 10' comprises a pour cup 10a', a riser 10s', and a pair
of
engine cylinder head patterns lOp' connected to the riser lOs' by gating lOg'.
The pattern
10' can be made of polystyrene that is coated with a thin layer (e.g. 1/2 mm)
of refractory,
usually, but not limited to, a mica or silica base material.
The flask 20' includes circular flanges 20a' and circular intermediate
reinforcing
rib 20b' for for ease of rolling in the compaction apparatus of Figures 8A,
8B.
Figures 8A, 8B illustrate apparatus for compacting the particulates media 30'
about lost foam engine block pattern 10" shown in more detail in Figure 6
disposed in
the particulates media 30' in the flask 20'. For purposes of illustration and
not limitation,
the support particulates media 30' can comprise dry foundry sand or any free-
flowing
refractory particulates, which typically are unbonded particulates devoid of
resin or other
binder as described in US Patent 5,069, 271. However, the support particulates
optionally
may be bonded to a limited extent that does not adversely affect the
capability of the
support particualtes to be fluidized and compacted about the mold or pattern
in the flask
20' pursuant to the invention.
Referring to Figure 8A, the apparatus includes a conventional vibrating
compaction table (base) T' (shown schematically). Alternately or in addition
separate
vibrators can be employed in a manner shown in Figures 11A; 12A,12B; 14, 16
and 18.
Tilting of the flask 20' to a selected angle of inclination relative to the
gravity vector is
achieved by any of the trunnion (tilting) mechanisms shown in Figures 11A,
11B, 11C;
12A, 12B; 13; 14; 16; and 18 diposed on the vibrating table T and described
herebelow.
For purposes of illustration and not limitation, trunnion support stanchions
17' are
provided on the table T' to support a tiltable frame 13' on which a rotatable
nest (fixture)
50' is disposed for receiving the flask 20'.
The flask 20' is placed into the nest 50' prior to tilting of the nest 50' on
frame
13'. The nest 50'comprises a base plate 50a' on which the flask 20' is
disposed. The nest
base plate 50a' includes a cylindrical recess to receive the bottom of the
flask 20'. Nest
base plate 50a' rests on three crowned roller bearings Bl' spaced 120 degrees
apart on
support posts 13b' on the frame 13' and is centered by four more roller
bearings B2' on
support flanges 13r engaging about the circular base plate 50a' of the flask.
A gear
13
CA 02617365 2008-01-07
motor 60' rotates the nest 50' by means of a drive belt 62' engaging belt-
receiving groove
50g' on the base plate 50a'.
While the flask 20' is vertically oriented in the nest 50', the pattern 10¨ is
placed
into the flask, and the flask is filled with support particulates media 30',
such as dry
foundry sand, from any suitable particulates source, such as an overhead
hopper (not
shown). Before the flask is tilted, a square-shaped, loosely-fitting, free-
floating lid 40'
with an opening for the pour cup 10a" is shown placed on the upper surface of
the
particulates media to prevent it from spilling when the tilt angle exceeds the
angle of
repose of the particulates media. The pour cup 10a" extends through the lid
opening so to
be exposed to receive molten metal or alloy to be cast, Figure 8B, in gravity
manner from
a crucible or other melt-holding vessel (not shown). The force vector, along
the axis of
the flask from the weight of the lid 40' is shown in Figure 8A being larger
than opposing
vector from the wedge of particulates media 30' above its static angle of
repose. This
keeps the top surface of the particulates media square with the sides of the
flask when the
flask is tilted up to 50 degrees. As the media is consolidated, the lid
settles deeper into the
flask. When the flask is returned to an upright position, the top surface of
the media is
horizontal.
Vibration of the table T' and rotation of the flask 20* can be started while
the
flask 20' is still vertically oriented in the nest 50', although the invention
is not limited to
this sequence. The nest 50' then is tilted to a fixed angle of inclination
relative to the
gravity vector as shown in Figure 8A on the trunion support stanchions 17'
(only one
shown). The tilted flask 20" is rotatably supported in the inclined position
by two more
roller bearings B3' disposed on upstanding side plates 13s' of frame 13' in a
manner to
engage the circular intermediate rib 20b" of the flask as shown in Figure 8B.
Vibration
and rotation of the flask while it is tilted are continued until the voids on
the pattern 10",
especially on an engine block pattern, are filled with compacted foundry sand.
For further illustration, Figure 6 shows lost foam engine block pattern 10"
that
includes internal oil passages 10p". In Figure 6, a flask having the engine
block pattern is
subjected to vibration parallel to gravity as shown, although vibration in any
direction can
be used in practice of the invention, and rotation while the flask is tilted
as shown. As the
flask rotates, the longest oil channels 101p" remain inclined at 45 . Oil
channels lOpp"
14
CA 02617365 2008-01-07
perpendicular to the longest oil passages, vary between -45 and +45
inclination in a
sinusoidal manner due to the rotation. Other short oil channels lOsp" extend
in and out of
the plane of the drawing shown. These oil channels or passageways 1 Osp" are
also varied
between -45 and +45 inclination by the rotation. During compaction tests,
the engine
block pattern 10" actually was orbited offset several inches from the axis of
rotation
(longitudial axis) l. of the flask. Since one complete rotation occurs during
each orbit of
the pattern, the effect on filling and compaction of foundry sand in the oil
channels of the
pattern 10" is the same.
The apparatus of Figures 7A, 7B; 8A, 8B can be used with any mold or pattern
that needs compacted particulates media support during gravity casting. For
the gravity
casting embodiment of the invention illustrated in Figures 7A, 7B; 8A, 8B, the
method of
inclined rotary compaction pursuant to the invention involves:
Casting flask 20' is secured to variable-tilt, rotatable nest or fixture 50'
on top of a
conventional compaction table T'. A mold or pattern 10' is loaded into the
flask by hand
typically without vibration of the flask. For example, a small amount of
foundry sand is
placed in the flask and the pattern is gently pressed into the foundry sand.
In production,
the pattern would be supported in the flask by a fixture (not shown) at the
beginning of
the flask fill cycle, which fixture would release the pattern at a later time.
The vertical
flask is filled with support particulates media, such as foundry sand, by any
conventional
means. To slightly shorten the compaction process, the flask 20' may be
vibrated during
the filling operation, but it is not necessary to do so at this time. (If
vibration is not
induced during the filling process, vibration isolators are not needed on the
mold-loading
fixture.) When sufficient particulates media has been introduced to maintain
mold or
pattern orientation, the mold or pattern is released and the remainder of the
flask is filled.
If the flask is going to be tilted past the angle where the particulates media
would
spill, loosely fitting cover 40' is placed on the upper surface of the
particulates media 30'
at this time. The cover has an opening for the pour cup 10a' of the pattern.
Vibration of compaction table T' is started simultaneously with rotation of
the
flask about its vertical longitudinal axis L, and the flask 20' is tilted to
the compaction
angle of inclination with respect to the gravity vector. For most molds or
patterns 10'
having a multitude of voids, a 30-35 tilt angle is sufficient and lid 40' is
not needed.
CA 02617365 2008-01-07
The flask 20' can be tilted to a fixed angle of inclination "A" where the
flask is
vibrated and rotated either continuously or intermittently.
Alternately, the flask 20' can be tilted continously from the vertical
position to the
30-35 angle of inclination "A" and then back to the vertical position, if
desired, in back
and forth manner, while the flask is vibrated and rotated either continuously
or
intermittently.
Still further, the flask 20' can be tilted in increments between the vertical
position
and the 30-35 angle of inclination "A", such as for purposes of illustration
and not
limitation, from vertical orientation to a 100 angle for a period of time, to
a 20 angle for
a period of time, and then to a 30 angle for a period of time while the
container is
vibrated and rotated, which can occur continuously or intermittently during
the time the
container resides at each of the angular positions (e.g. 10 , 20 , etc.) . The
sequence then
can be reversed from the 30 angle for a period of time to the 20 angle for a
period of
time, and then to the 10 angle for a period of time with container vibration
and container
rotation occurring continuously or intermittently during the time the
container resides at
each of the angular positions (e.g. 10 , 20 , etc.) .
In practicing the inclined rotary compaction method embodiment of the
invention
where the flask is continuously tilted during compaction, it is preferred to
have the
rotational cycle frequency of the flask be an even multiple of the tilting
cycle frequency
of the flask. For purposes of illustration and not limitation, if the flask is
rotated at a
steady 2 rpm, then the flask is smoothly and continuously cycled through a
tilt angle from
0 (vertical) to the angle of inclination and then back to 0 position in one
minute. This
cycle is repeated until full compaction is achieved. Such parameters will
result in equal
opportunity for all voids at the mold or pattern, symmetrically oriented about
the
rotational axis, to be filled regardless of orientation.
For any support particulates media being compacted with a combination of
rotational speed, vibration frequency and vibration amplitude, a tilt angle
can be found
where the downward flow of the particulates media 30' at the upper surface
thereof is
exactly matched by the rate of rotation of the upper surface of the
particulates media. As
long as this tilt angle is not exceeded, the upper surface of the particulates
media 30'
stays parallel to the rim of the flask 20' and will be level when the flask
20' is returned to
16
CA 02617365 2008-01-07
vertical. For lost foam patterns with long, intricate internal passages, such
as oil channels
in engine blocks, a 45 tilt angle is the best, see Figures 6 - 8. A floating
lid 40' may be
required to prevent the sand from spilling.
Flask rotational speed of between 1/2 to 2 rpm is preferred for most molds or
patterns. Slow rotational speeds orient horizontal and near horizontal voids V
so they are
inclined past the dynamic angle of repose of the particulates media for
several seconds
during each rotation. This allows ample time for the voids to fill. Very slow
rotational
speed will mandate longer compaction cycles for intricate zigzagging voids
such as void
in Figures 1 - 5 because several rotations are needed to fill such voids.
High rotational speed changes void orientation before media flow to the void
is
established. At sufficiently high speed and radius of gyration, centrifugal
effects come
into play, causing rotation to become detrimental. For example, if the flask
is rotated at
60 rpm, a void V inclined at 30 relative to container axis L with an opening
5 inches or
more from the axis of rotation of the flask, the component of the gravity
vector acting
along the void will be neutralized by the centrifugal acceleration, and
particulates media
flow into the void will be blocked.
At slow rotational speeds, slower than 10 rpm, the centrifugal effect is
negligible
and can be ignored. As described earlier, because of the tilt angle (angle of
inclination) of
the flask, horizontal voids that rotate to partially face upwardly readily
fill under the
combined influence of gravity and vibration. As the flask rotates, filled
voids partially
face downwardly during half of the rotational cycle. However, they will not
empty
because their openings are now blocked by compacted particulates media
blocking the
openings. The compacted particulates media around the mold or pattern prevents
the
mold or pattern from shifting in the flask; therefore the mold or pattern need
not be
supported during the compaction cycle.
Because the mold or pattern is not attached to a non-vibrating element, such
as
mold-loading fixture, but is free to float, mold or pattern distortion is
minimized.
Deep or contorted voids or large-volume voids with small openings OP may not
completely fill during one rotation cycle. This, however, is not a problem. As
the free
surface in such void rotates past the dynamic angle of repose, particulates
media flow is
reestablished. Compacted media that has now rotated above the void, thus left,
will
17
CA 02617365 2008-01-07
fluidize and flow down into the void again. (see Figure 10.) Conventional
particulates
compaction techniques will not do this.
Bridging of the particulates media granules or particles will randomly occur.
If
bridging occurs near the opening (e.g. opening OP-Fig. 1A) of a narrow
internal void, or
in the void, particulates media flow to the void may be temporarily blocked by
a dome-
like secondary void formed in-situ at the opening or in the void. However,
flask rotation
will turn such a secondary dome-like void on its side, causing the dome-like
void to
collapse; reestablishing media flow to the void. Once a void is completely
filled. gravity
and vibration will consolidate the particulates media in the void while the
void is sloped
past the dynamic angle of repose of the particulate media. Once there are no
free surfaces
left in voids, no more particulates media fluidization will occur, except on
the top, free
surface.
The compaction cycle is completed by returning the flask to the vertical
orientation and stopping the rotation and the vibration.
Figure 13 illustrates another apparatus embodiment of the invention for
gravity or
countergravity casting a mold or pattern. Figure 13 shows a hydraulically
operated
compaction apparatus that is attached to the support deck 100 of a
conventional
compaction table (base) T. A flask 120 is supported in a rotatable nest
(fixture) 150,
which in turn is disposed on a tiltable nest support frame 113. The nest
support frame 113
is tiltably (pivotally) supported on fixed trunnion posts or stanchions 117 by
pivot pins
135 (one shown). The trunnion support stanchions 117 reside on a base pad 141
that is
fixedly mounted on deck 100. The nest support frame 113 includes arcuate
runners 132
that slide on arcuate rails 133a of a cradle 133 formed as part of or fixedly
attached to the
base pad 141. Vibration is transmitted from the table (base) T to the flask
120 through
base pad 141 to rails 133a of a cradle 133 and then to the runners 132 of the
nest support
frame 113 on which the flask 120 is carried.
The cradle and runner arrangement also serves as a centering device about
coaxial
trunnion pivot pins 135 (one shown). The flask 120 is tilted in the manner
described
above about the pivot pins 135 by the action of hydraulic cylinders 136
connected at one
end to the cradle 133 and at the other end to the outer side of the flask 120.
The upper
half of the flask rides on a pair of roller bearings B3 while the flask is
rotated. The lower
18
CA 02617365 2014-02-28
end of the flask 120 sits in the cylindrical rotatable nest 150 disposed on
the nest support
frame 113. The nest 150 is free to rotate on a combination radial/thrust
bearing (hidden in
this view). The nest 150 is rotated by a hydraulic motor through a friction
drive by a
pneumatic tire (also hidden in this view). The flask 120 receives a mold or
pattern (not
shown) of the type discussed above and particulates media (not shown) of the
type
discussed above for compaction about the mold or pattern.
COUNTERGRAVITY CASTING
The apparatus of Figures 11A-11E can be used with any mold or pattern that
needs compacted particulates media support during countergravity casting.
Figures 11A-11E illustrate a self-contained apparatus for compacting support
particulates media 230 around a counter-gravity casting ceramic shell mold 210
in flask
220. This apparatus also can be used as well for compacting support
particulates media
about any kind of a gravity-poured mold or about any kind of lost foam
pattern. Only the
bottom of the flask 210 and the mold clamping arrangement would need to be
different.
In Figure 11C, a ceramic fill tube 211 is shown fastened to the shell mold
210,
which is of the type described in US Patent 5,069,271 and illustrated as
ceramic shell
mold 10 in Figure 1. The mold 210 is placed into the casting flask 220 so that
tube 211
protrudes from the bottom of the flask 210. The flask 210 is filled with
support
particulates media 230 and is covered with a lid 240 if the flask is to be
tilted to the point
where the particulates media 230 would spill from the flask. Flask 210 rests
in a
cylindrical nest (fixture) 250 comprising base plate 250a which is supported
by three
crowned roller bearings Blsupported on the bottom of tiltable frame 213.
Nest support frame 213 is supported by trunnions 235 resting in stanchions 217
of
the main frame (base) 218. Each stanchion includes a plate 217a attached
thereto for
mounting electric vibrators 222 in a combination of orientations. The
vibrators can be
mounted with their axes vertical, for sideward vibration, or horizontal for up
and down
vibration. They can be mounted counter rotating for essentially linear
vibration, or
rotating in the same direction for a circular vibration pattern. Frequency and
amplitude of
vibration also can be adjusted. The compaction apparatus is supported on four
pneumatic
vibration isolators 221. In this arrangement the entire apparatus vibrates.
19
CA 02617365 2014-02-28
. .
Rotation of the flask 220 is achieved by means of a gear motor 260 turning
flask
nest 250 by means of drive belt 262. Tilting of frame 213 is by means of
another gear
motor 265, drive belt 267, turning an ACME screw 269, which in turn drives an
ACME
nut 269a attached to bar 270, which tilts the frame by acting on lever 271.
Large
amplitude vibration, greater than 1 G, causes unacceptable wear in the brass
ACME nut.
The tilted flask 220 is supported in rotation by two more roller bearings B3
that are
disposed on the titlable frame 213 and support the side of the flask.
For a countergravity casting embodiment of the invention, the method of
inclined
rotary compaction pursuant to the invention is similar to that descibed above
for the
gravity casting embodiment with the following exceptions:
The ceramic shell mold 210 is permanently assembled to the ceramic tube 211
through which the melt will be drawn into the mold.
The countergravity casting embodiment involves the following steps. The
vertical
flask 220, Figure 11A, is filled with support particulates media 230, such as
foundry
sand, by any conventional means. To slightly shorten the compaction process,
the flask
220 may be vibrated during the filling operation, but it is not necessary to
do so at this
time. (If vibration is not induced during the filling process, vibration
isolators are not
needed on the mold-loading fixture.)
If the flask is to be tilted past the point where media would spill over the
rim a
floating cover 240 is placed on the exposed surface to contain the media 230.
Vibration of the main frame 218 by vibrators 222 is started simultaneously
with
rotation of the flask about its vertical axis L and the flask is tilted
continuously,
incrementally, or at a fixed angle of inclination in the manner decribed above
with respect
to the gravity vector. For most molds or patterns having a multitude of
cavities, a 30-35
maximum tilt angle is sufficient and a lid is not needed.
For any support particulates media being compacted with a combination of
rotational speed, vibration frequency and vibration amplitude, a tilt angle
can be found
where the downward flow of the particulates media on the upper surface is
exactly
matched by the rate of rotation of the upper surface. As long as this tilt
angle is not
exceeded, the particulates media upper surface stays parallel to the rim of
the flask and
will be level when the flask is returned to vertical.
CA 02617365 2008-01-07
Flask rotational speed of between 1/2 to 2 rpm works best for most molds or
patterns. Because of the tilt angle (angle of inclination) of the flask,
horizontal voids that
rotate to partially face upwardly readily fill under the combined influence of
gravity and
vibration. As the flask rotates, filled voids partially face downwardly during
half of the
cycle. However. they will not empty because their openings (e.g. OP) are now
blocked by
compacted particulates media.
The compacted particulates media around the mold or pattern prevents the mold
or pattern from shifting in the flask; therefore the mold or pattern need not
be supported
during the compaction cycle.
Because the mold or pattern is not attached to a non-vibrating element, such
as
mold-loading fixture, but is free to float, mold or pattern distortion is
minimized. Deep or
contorted voids or large-volume voids with small openings may not completely
fill
during one rotation cycle. This, however, is not a problem. As the free
surface in such
void rotates past the dynamic angle of repose, particualtes media flow is
reestablished.
Compacted media that has now rotated above the void, thus left, will fluidize
and flow
down into the void again. (see Figure 10.) Conventional particulates
compaction
techniques will not do this.
Bridging of the particulates media granules or particles will randomly occur.
If
bridging occurs near the opening of a narrow internal void, or in the void,
particulates
media flow to the void may be temporarily blocked by dome-like secondary void
formed
in-situ at the opening or in the void. However, flask rotation will turn such
a secondary
dome-like void on its side, causing the dome-like void to collapse;
reestablishing flow to
the void.
Once a void is completely filled, gravity and vibration will consolidate the
particulates media in the void while the void is sloped past the dynamic angle
of repose
of the particulate media. Since there are no free surfaces left in voids, no
more
particulates media fluidization will occur in or near the voids.
The compaction cycle is completed by returning the flask to the vertical
orientation, Figure 11A, and stopping the rotation and the vibration.
Of course, countergravity casting of molten metal or alloy upwardly through
the
riser passage and into the mold cavities of the shell mold 210 is conducted in
a manner
CA 02617365 2008-01-07
different from gravity casting and is described in detail in US Patent
5,069,271.
Figures 12A, 12B depict a similar apparatus as that shown in Figures 11A, 11B
and differing only in having a flask tilting mechanism that comprises a
harness 280
pulled by a hand winch 282. An electric winch could be used just as well to
pull the
harness 280. This tilting arrangement is advantageous in that it is unaffected
by vibration
greater than 1 G. In Figures 12A, 12B, like reference numerals are used in
connection
with like features of Figures 11A, 11B.
Owing to the compaction efficiency of variable gravity and vibration vectors
relative to the mold or pattern, vibration amplitude need not be as great as
needed for
conventional compaction techniques. For many compaction applications,
vibration
acceleration less than 1 G is sufficient. At amplitudes less than 1 G, the
flask maintains
contact with the support bearings, compaction noise is low and equipment wear
is
acceptable. The apparatus of Figures 11 through 13 will work well at these
lower
amplitudes.
Accelerometer measurements have shown that for an unrestrained flask, such as
shown in Figures 11 through 13, vibration in one plane will induce vibration
in all
directions. Therefore, location and orientation of the vibrator(s) is
relatively unimportant.
It is preferable to attach the vibrators to stationary components of the
compaction
apparatus, because its more convenient.
Typically, during the entire compaction process, the flask needs to rotate
less than
a dozen times. Alternately, the flask can be rotated as little as 360 , and
then rotated in
the reverse direction for 360 . This rotational oscillation can be repeated as
many times
as needed. Each 3600 rotational oscillation will have the same effect as two
continuous
revolutions in the same direction. Usually, 2 to 6 oscillations will achieve
complete
compaction. This technique make it easy to supply power to vibrators mounted
directly
on the flask as shown in Figure 18 where vibrators 322 are shown disposed
directly on
the flask 320. The advantage of this embodiment is that more vibration energy
is
transmitted to the particulate media (not shown) in the flask 320. The flange
320f of the
casting flask 320 is bolted, clamped or otherwise supported on a hub or nest
(fixture) 350,
which is retained on tiltable platform frame 352 with impact resistant
synthetic plates
being used as bearing surfaces between the flange, the hub or nest 350 and the
platform
22
CA 02617365 2014-02-28
. .
,
frame 352 as described below in connection with Figures 14-15. The hub or nest
350 is
rotated by drive belt 362, driven by hydraulic motor 360. Tilting of the
platform frame
352 up to 180 is accomplished via hydraulic actuator 355 disposed on
stanchions 317,
which are mounted on a table T. The table is mounted on four pneumatic
vibration
isolators 321. The flask can be sealed by a lid (not shown but described in
connection
with Figures 14-15). The spread of the stanchions 317 is widened to
accommodate the
vibrators rotating with the flask. The advantage of this variation is that
more vibration
energy is transmitted to the media in the flask.
If vibration amplitude greater than 1 G is needed and low noise level is
desired,
the casting flask needs to be secured to the rotating and vibrating components
of the
compaction apparatus. Such an embodiment is depicted in Figures 14 through 18
where
the flange 320f of casting flask 320 is bolted or clamped to a hub or nest
350, which is
retained between flange 351 and platform frame 352. The hub or nest 350
rotates on
synthetic bearing surfaces 349, Figure 15. This assembly is captured between
retaining
flange 351 and platform 352. The hub 350 is rotated through drive belt 362
driven by
hydraulic motor 360. Tilting of the platform 352 up to 180 is accomplished
via hydraulic
actuator 355 disposed on stanchions 317, which are mounted on a table T. The
table is
mounted on four pneumatic vibration isolators 321.
The flask 320 is sealed by a lid 340 that rests on top of the support media
330.
The lid includes an inflatable rim seal tube 340t and a rotary union 361
connected to a
vacuum source, such as vacuum pump (not shown). The inflatable rim seal tube
340t
provides an airtight seal against the wall of flask 320. The lid 340 includes
a screen 359
through which air can pass but not the particulates media 330, thereby
allowing for the
partial evacuation of the flask through plenum 372 disposed on the lid 340.
The plenum
372 communicates via a fitting Fl of rotary union 361 to a vacuum pump and via
fitting
F2 to an air pump to inflate seal 340t, Figure 17, which can be a commercially
available
rotary union. The plenum 372 includes radial fins 372a to provide
reinforcement for
screen 359. Atmospheric air pressure causes elastic membrane 363 of the lid
340 to bulge
and to conform to top of the particulates media in the flask. The flask can be
evacuated to
partial vacuum (e.g. 3-4 psi vacuum) through rotary union 361 and plenum 372.
The
pressure differential thus established across the lid 340 is used to retain
the mold or
23
CA 02617365 2014-02-28
pattern and the particulates media in the flask when the flask is upended or
inverted past
horizontal as shown in Figure 16. The lid 340 with inflatable rim seal tube
340t is
retained by atmospheric pressure acting against the partially evacuated flask
320.
Vibration of the flask 320 during compaction is provided by two electric
vibrators
322' and/or vibrators 322 of the type shown in Figures 14 and 16, mounted on
the
stachions, or in Figure 18 mounted directly on the flask 320. The apparatus is
mounted on
four pneumatic vibration isolators 321, which support the table T.
During compaction about the mold 310, the upper surface of the particulates
media 330 drops as the particulates media is compacted into the voids V at the
mold 310
(or pattern) in the flask. The lid 340 continues to engage the upper surface
of the
particulates media as it receeds into the flask, regardless of flask
orientation, by virtue of
the pressure differential between the outside ambient air pressure and the
partial vacuum
in the flask 320. Air tight, moveable sealing between the lid 340 and adjacent
wall of the
flask 320 is maintained by inflatable rim seal tube 340t.
The apparatus of Figures 14-18 for use with vibration amplitude greater than 1
G
differs from the other apparatus emodiments by replacing ball roller bearings
with radial
and thrust bearings 349 fabricated from impact resistant, low friction plastic
as illustrated
in Figure 15. Alternately two large-diameter angular-contact, ball bearings
(not shown)
could be used, with the rotating nest captured between them. Regardless, there
are no
loose components to bounce free, so noise and impact forces are controlled in
Figures 14-
18.
As mentioned, the casting flask 320 is bolted, clamped or otherwise fastened
to
the rotating hub or nest 350 that is sandwiched between components of a
tilting platform.
Because the rotating hub or nest 350, along with the flask 320 secured to it,
are confined
to the extent that they can only rotate and tilt, the vibration transmitted to
the flask
preserves its directional nature to a greater extent and secondary vibration
out of the
plane of the vibration vector is diminished. This has the desirable effect of
simultaneously changing both the gravity and the vibration vectors relative to
the mold or
pattern in the flask in a smooth, continuous, methodic manner. A hydraulic
motor
provides rotation to the nest 350, while a hydraulic actuator tilts the
platform 352 up to
180 degrees continuously, incrementally or to a fixed angle of inclination.
24
CA 02617365 2008-01-07
The flask contains ceramic shell mold 310 having fill tube 311. The flask
includes
a lid 340 that has inflatable tube seal 340t along its periphery and that has
a rotary union
361 for seal inflation and for the partial evacuation of the flask.
Alternately, an inner
tube-type check valve (not shown) can be used on the inflatable tube seal 340t
such that
the air passage in the rotary union for the seal 340t can be eliminated. The
lid has a
flexible membrane exposed to ambient air on one side and to the flask interior
on the
other side. Once the flask 320 is fitted with the mold or pattern, filled with
loose
particulates media 330, covered by the lid 340, the seal 340t is inflated and
the flask 320
is evacuated to 3 - 4 psi vacuum.
At this point the casting flask 320 can be completely upended. Atmospheric
pressure will support the lid 340, and the contents of the flask regardless of
its
orientation.
During compaction of the particulates media 330 in the apparatus of Figures 14-
18, the particulates media flows into voids at the mold or pattern and is
compacted. A
"bubble" comprising rarified media will develop and travel toward the high
point of the
flask 320. If the flask is tilted past horizontal the high point will be at
the bottom corner
of the flask. As it floats up, the "bubble" will spread at the angle of repose
and
accumulate under any impermeable obstruction encountered during the upward
passage.
With an upended flask an air gap will form at the bottom of the flask. As the
rotating
flask is tilted back toward vertical, the air gap will spiral along the flask
wall to the top of
the flask where it is accommodated by the lid 340 settling into the flask to
take up some
of this space and the rest of the space being filled by the flexible membrane
363 as it is
bulged into the flask by atmospheric pressure. The displaced air in the flask
exits through
the screen 359 on the bottom center of the lid 340. Pressure from the lid 340
and the
flexible membrane 363 further compacts the top layer of the media. When the
flask is
upended again, the pressure maintains compaction. Through repeated cycling of
partially
evacuated flask inclination, simultaneous with methodic flask rotation and
vibration, all
voids and rarified media volumes are channeled along the flask wall and
eliminated
through the screen 359 in the lid 340.
In practicing this more complex inclined rotary compaction method embodiment
of the invention, it is preferred to have the rotational cycle frequency be an
even multiple
CA 02617365 2014-02-28
of the tilting cycle frequency. For example, if the flask is rotated at a
steady 2 rpm, then
the flask is smoothly and continuously cycled through a tilt angle from 0 to
180 and then
back to 0 in one minute. This cycle is repeated until full compaction is
achieved. Such
parameters will result in equal opportunity for all voids at the mold or
pattern to be filled
regardless of orientation. The apparatus described in Figures 14 through 18
will
completely fill all voids shown in Figures 1 through 5 with compacted
particulates media.
This embodiment of the invention can be practiced for compacting particulate
media around gravity casting molds also. Regardless of flask geometry, a lid
can be
fabricated with a seal and flexible membrane as described previously above.
The pour
cup on the casting mold is temporarily sealed and the entire casting mold,
including the
pour cup is covered in support media. The lid is fitted to the chamber, the
lid seal is
inflated and the flask is evacuted to 3-4 psi below ambient pressure. The
flask can now be
completely upended during the compaction process. The low pressure
differential across
the lid is sufficient to retain the contents of the flask. After compaction is
complete, the
flask is returned to vertical, the lid is removed, and sufficient media is
removed to expose
the pour cup for casting.
Practice of the inclined rotary compaction process has several advantages
including, but not limited to, remote void recesses and horizontal overhangs
at molds or
patterns are efficiently filled with compacted media, any free particulates
media surface
buried deep under compacted support particulates media will start filling the
voids again
during at least 1/4 of each flask rotation cycle, and bridging by the media
particles or
grains is efficiently eliminated by methodic tilting of the above-described
bridged dome-
like secondary voids that can result from bridging onto their sides and tops
so that the
dome-like secondary voids are either collapsed, or are filled. Moreover,
because the
mold or pattern does not need to be supported and the gravity vector is
continuously and
smoothly varied relative to the mold or pattern during compaction, distortion
of the mold
or pattern is minimized. The feeding rate of the particulates media to the
flask does not
have to be varied as in existing lost foam compaction systems. The flask can
be quickly
filled and compacted afterward. The vibration vector of the compaction table
does not
have to be varied. Instead the mold or pattern orientation is methodically
varied relative
to the vibration and gravity vectors. The compaction method is part
independent, and no
26
CA 02617365 2008-01-07
special compaction recipes are required for different molds or patterns.
Although the invention has been described with respect to certain embodiments,
those skilled in the art will appreciate that changes, modifications and the
like can be
made thereto without departing from the spirit and scope of the invention as
set forth in
the appended claims.
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