Field of The Invention
[0001] This invention relates to an improved apparatus and method for the differential pressure,
countergravity casting of a melt in such a manner as to selectively introduce one
or more alloyants into the melt as it is cast into the mold to tailor the metallurgical
characteristics of the resultant casting, or local regions thereof.
Background Of The Invention
[0002] A vacuum countergravity casting process using a gas permeable mold sealingly received
in a vacuum housing is described in such patents as the Chandley et al U.S. Patents
3,900,064; 4,340,108 and 4,606,396. That countergravity process involves providing
a mold having a porous, gas permeable upper mold member (cope) and a lower mold member
(drag) sealingly engaged at a parting plane, sealing the mouth of a vacuum housing
to a surface of the mold such that a vacuum chamber formed in the housing confronts
the gas permeable upper mold member, submerging the under side of the lower mold member
in an underlying melt and evacuating the vacuum chamber to draw the melt through one
or more narrow ingates (pin gates) in the lower mold member and into one or more mold
cavities formed between the upper and lower mold members.
[0003] In practicing the vacuum countergravity process to produce nodular iron castings,
the melt is typically prepared in a melting vessel (e.g., a cupola) using a charge
of pig iron to which additions of alloyants are made to provide the desired base melt
chemistry. For example, in casting nodular iron, ferromanganese (Fe-Mn), ferrosilicon
(Fe-Si) and other additions are made to the base pig iron charge to provide a desired
base melt chemistry.
[0004] Once the desired base melt composition is achieved, the melt is transferred from
the melting vessel to a ladle where a nodularizing treating agent (e.g., Fe-Si-Mg)
is added to spherodize the carbon. The treated base melt is then transferred from
the ladle to a casting vessel to provide a melt pool from which a plurality of molds
are successively vacuum countergravity cast. The nodular iron castings produced in
this manner exhibit an as-cast ferritic/pearlitic microstructure depending upon the
melt composition and solidification rate. The composition of the castings corresponds
to that of the melt in the casting vessel.
[0005] In order to produce nodular iron castings having different compositions and microstructures
(e.g., corresponding to the known ferritic grade 4010 or pearlitic grade 5203), the
practice has been to prepare separate base melts of the desired different compositions
using pig iron charges to which appropriate alloy additions are made in the melting
vessel and then ladling and casting the separate base melts as described above. This
practice amounts to producing castings of one composition/microstructure in one batch
and castings of another different composition/micro-structure in a separate batch
with preparation as well as subsequent handling, treatment and casting of different
base melts for each batch.
[0006] Moreover, since the castings are produced by countergravity filling successive molds
from a more or less homogenous underlying melt pool in the casting vessel, the vacuum
countergravity casting process as currently practiced has not had the capability of
purposefully and controllably producing castings having different metallurgical characteristics
at different locations in the casting so as to alter or enhance certain properties
(e.g., mechanical properties) at localized regions of the casting as may be desired
in certain service applications.
[0007] It is an object of the present invention to provide an improved apparatus and method
for the differential pressure, countergravity casting of a melt wherein an alloyant
is positioned at one or more ingates (e.g., pin gates) of the mold drag so as to be
introduced into the melt as the melt is drawn upwardly through the ingates into the
mold cavity to produce a casting having a composition different from that of the underlying
melt.
[0008] It is another object of the present invention to provide such an improved apparatus
and method for differential pressure, countergravity casting wherein castings having
different compositions tailored for different intended uses can be countergravity
cast from a common melt to avoid the need to prepare, handle, treat and cast separate
base melts.
[0009] It is another object of the present invention to provide such an improved apparatus
and method for differential pressure, countergravity casting wherein an alloyant is
positioned at one or more of the mold ingates so as to be introduced into the melt
as it is drawn upwardly into the mold cavity to produce a microstructure in the casting
that is not obtainable by solidification of the underlying melt composition.
[0010] It is another object of the present invention to provide such an improved apparatus
and method for differential pressure, countergravity casting wherein the melt composition
is selectively altered during casting in such a manner as to produce a casting having
different metallurgical characteristics at different locations or regions of the casting
to provide different or enhanced properties where needed in the casting.
[0011] It is another object of the present invention to provide such an improved apparatus
and method for differential pressure, countergravity casting wherein melt contamination
and slag potential are reduced by reducing alloy additions and treating agent additions
(e.g., nodularizing agent additions) heretofore made to the base melt in the melting
vessel and/or in the ladle.
[0012] It is another object of the present invention to provide a mold cavity fill analysis
method for determining molten metal flow paths from the ingates into the mold cavity
during differential pressure, countergravity casting.
Summary Of The Invention
[0013] The present invention contemplates an improved apparatus and method for the differential
pressure, countergravity casting of a melt wherein an alloyant is disposed on the
mold at (i.e., within or in close proximity to) one or more of the ingates (e.g.,
narrow pin gates) to the mold cavity so as to contact the molten metal stream drawn
upwardly through the ingate(s) into the mold cavity and selectively introduce the
alloyant therein. The composition of the melt is thereby altered as it is countergravity
cast into the mold.
[0014] In one embodiment of the invention, an expendable source of the alloyant is disposed
at each of a plurality of the ingates such that the alloyant is introduced (e.g.,
dissolved) into the molten metal stream drawn upwardly through the ingate into the
mold cavity to produce a casting having a different composition from that of the melt.
The alloyant introduced to the melt can be selected to provide a casting having different
overall mechanical properties/microstructure from that obtainable from the melt. For
example, copper can be introduced to a ferritic cast iron melt as it is drawn from
the casting vessel upwardly into the mold cavity to produce a casting having a microstructure
and substantially improved tensile and yield strength corresponding to a pearlitic
cast iron grade.
[0015] In another embodiment of the invention, a fugitive nodularizing agent (e.g., Fe-Si-Mg)
is disposed at each of a plurality of ingates so as to treat the melt as it is drawn
upwardly from the casting vessel into the mold cavity for carbon nodularizing purposes.
[0016] In still another embodiment of the invention, the alloyant is disposed at some of
the ingates to the mold cavity but not others so as to produce a casting having different
compositions and resultant different metallurgical characteristics (e.g., different
mechanical properties/microstructures) at different locations of the casting. For
example, copper can be selectively introduced to the melt stream drawn upwardly into
local regions of the mold cavity that form casting features requiring increased strength
while other regions of the mold cavity that form casting features not requiring such
strength receive untreated melt (i.e., melt devoid of copper).
[0017] Similarly, a first alloyant source can be disposed at some ingates while a second
alloyant source is disposed at other ingates to produce a casting having different
metallurgical characteristics at different locations.
[0018] In still another embodiment of the invention, molds configured to produce a particular
cast part include a source of alloyant at one or more mold ingates while other molds
configured to produce a different cast part are without such alloyant sources or perhaps
include a source of a different alloyant at one or more ingates. The molds are successively
countergravity cast from the same underlying melt to produce the different cast parts
having different compositions tailored for different end uses from the common underlying
melt. For example, molds configured to produce a particular part (e.g., an exhaust
manifold) can be countergravity cast from an underlying ferritic nodular iron grade
melt with no alloyant disposed on the molds while other molds configured to produce
a different part (e.g., a connecting rod) can be countergravity cast from the same
melt with a suitable alloyant disposed at the ingates to alter the composition of
the ferritic nodular iron melt drawn into the mold cavity to produce a microstructure
and improved mechanical properties corresponding to a pearlitic cast iron grade as
desired for connecting rods.
[0019] The present invention also contemplates a mold cavity fill analysis method for determining
molten metal flow paths from the ingates into the mold cavity during differential
pressure, countergravity casting from an underlying melt. In accordance with the mold
cavity fill analysis method, a source of alloyant that affects a metallurgical characteristic
of the casting is disposed at a particular ingate such that the alloyant is selectively
introduced into the melt drawn upwardly through the particular ingate and is not introduced
into the melt drawn upwardly through other adjacent ingates. After the molten metal
is solidified in the mold cavity, the resulting casting is examined (e.g., metallographically)
to observe the distribution of the metallurgical characteristic in the casting attributable
to introduction of the alloyant to the melt at the particular ingate. In this way
the molten metal flow path from the particular ingate into the mold cavity can be
determined. This procedure can be repeated for each ingate to determine melt flow
paths from the ingates into the mold cavity. The results of such analysis can be used
to improve mold ingating designs and eliminate casting defects resulting from inadequate
ingating, thus providing higher quality castings.
[0020] The aforementioned objects and advantages of the present invention set forth hereinabove
will become more readily apparent from the detailed description and drawings which
follow.
Brief Description Of The Drawings
[0021] Figure 1 is a sectioned, side view of a vacuum countergravity casting apparatus in
accordance with the invention.
[0022] Figure 2 is an enlarged sectional view of the ingate encircled in Fig. 1.
[0023] Figure 3 is a bottom elevation of the ingate shown in Fig. 2.
[0024] Figure 4 is a bottom elevation of the mold drag taken in the direction of arrows
4-4 of Fig. 1.
[0025] Figure 5 is a bottom elevation of the mold drag of another embodiment of the invention.
[0026] Figure 6 is a bottom elevation of a particular ingate wherein alloyant needles are
disposed in the ingate.
[0027] Figure 7 is a bottom elevation of a particular ingate wherein alloyant plates or
vanes are disposed in the ingate.
[0028] Figure 8 is a bottom elevation of a particular ingate wherein a tubular alloyant
pellet is embedded in the underside of the mold drag coaxially about the ingate.
[0029] Figure 9 is a bottom elevation of a particular ingate wherein a solid alloyant disc
is disposed in the ingate.
[0030] Figure 10 is a sectional view of a particular ingate wherein the alloyant source
is disposed adjacent the outlet of the ingate.
[0031] Figure 11 is a sectional view of a particular ingate wherein the alloyant source
is disposed in a pocket formed in the ingate of a two-part mold drag.
[0032] Figures 12, 13 and 14 are top elevational views of similar cast exhaust manifolds
shaded to illustrate the presence of primary carbides bounding localized carbide-free
regions resulting from positioning a Fe-Si inoculant pellet at ingate 1 in Fig. 12,
at ingate 4 in Fig. 13 and at ingate 6 in Fig. 14.
[0033] Figure 15 is a longitudinal sectional view along lines 15-15 of Fig. 14.
Detailed Description Of Specific Embodiments
[0034] Figure 1 depicts a pool 2 of melt 4 which is to be drawn up into a mold 6 having
a gas-permeable upper mold portion 8 (cope) and a lower mold portion 10 (drag) joined
at a parting line 12 and defining a molding cavity 14 therebetween. The melt 4 is
contained in a casting furnace or vessel 3 heated by one or more induction coils (not
shown) to maintain the melt 4 at a desired casting temperature.
[0035] The lower mold portion 10 includes a plurality of narrow ingates 16 (i.e., pin gates)
communicating the underside 10a thereof with the mold cavity 14 for admitting the
melt 4 to the mold cavity 14 when it is evacuated through the upper mold portion 8
with the underside 10a immersed in the melt 4. The ingates (pin gates) 16 preferably
have a major dimension (e.g., diameter for cylindrical ingates) not exceeding about
0.50 inch, preferably not exceeding 0.25 inch (e.g., .1875 inch) for purposes set
forth in U.S. Patent 4,340,108 and hereinafter described.
[0036] The lower mold portion 10 of the mold 6 is sealed to the mouth 18 of a vacuum box
20 defining a vacuum chamber 22 via a seal 24 (e.g., high temperature rubber, ceramic
rope, etc.). The seal 24 is affixed to the lower peripheral edge of the depending
peripheral side 25 of the vacuum box 20. The vacuum chamber 22 encompasses the upper
mold portion 8 and communicates with a vacuum source 23 (e.g., a vacuum pump) via
conduit 26.
[0037] The upper mold portion 8 comprises a gas-permeable material (e.g., resin-bonded sand)
which permits gases to be withdrawn from the casting cavity 14 therethrough when a
vacuum is drawn in the chamber 22. The lower mold portion 10 may conveniently comprise
the same material as the upper mold portion 8 or other materials, permeable or impermeable,
which are compatible with the material of the upper mold portion 8. The lower mold
portion 10 includes an upstanding levee 26 surrounding the seal 24 and isolating it
from the melt 4 as described in U.S. Patent 4,745,962 and assigned to the assignee
of the present invention.
[0038] The lower mold portion 10 includes a plurality of anchoring sites 28 engaged by T-bar
keepers 30 of the type described in commonly assigned U.S. patent application Serial
No. 147,863, abandoned in favor of patent application Serial No. 286,051, providing
means for mounting the mold 6 to the vacuum box 20. As described in those patent applications,
the lower mold portion 10 includes a plurality of anchoring cavities 32 adapted to
receive the T-bar keepers 30 via slots 34 in the shelves 40 overlying the anchoring
cavities 32 and attached to the lower mold portion 10. A 90° rotation of the T-bar
carrying shafts 36 (e.g., by air motors 38) causes the T-bar keepers 30 to engage
the underside of the attached shelves 40 overhanging the cavities 32 to secure the
mold 6 to the box 20. Other known mold to vacuum box mounting means can also be employed
in practicing the invention (e.g., U.S. Patent 4,658,880).
[0039] The upper mold portion 8 is pressed into sealing engagement with the lower mold portion
10 (i.e., at the parting line 12) by means of a plurality of plungers 42 so as to
eliminate the need to glue the upper mold portion 8 and the lower mold portion 10
at the parting plane 12. Feet 44 on the ends of the plungers 42 distribute the force
of the plungers 42 more widely across the top of the upper mold portion 8 to prevent
penetration/puncture thereof by the ends of the plungers 42. Pneumatic springs 46
bias the plungers 42 downwardly to resiliently press the upper mold portion 8 against
the lower mold portion 10 as the mold 6 is being positioned in the mouth 18 of the
vacuum box 22. Schrader valves 48 on the air springs 46 permit varying the pressure
in the springs 46 as needed to apply sufficient force to press the upper mold portion
8 into sealing engagement with the lower mold portion 10, and, as needed, to prevent
destructive inward flexure of the mold 6 when the casting vacuum is drawn. The force
applied by the plungers 42, however, will not be so great as to overpower and damage
the anchoring sites 28, dislodge the mold 6 from the mouth 13 of the box 20, or break
the seal formed thereat.
[0040] Countergravity casting of each casting mold 6 is effected by relatively moving each
mold 6 and the pool 2 to immerse the underside 10a of the lower mold portion 10 in
the melt 4 and evacuating the mold cavity 14 to draw the melt 4 upwardly through the
ingates 16 into the mold cavity 14. Typically, the casting mold 6 is lowered toward
the pool 2 using a hydraulic power cylinder 60 (shown schematically) actuating a movable
support arm 62 (shown schematically) that is connected to the vacuum box 20. After
filling of each mold cavity 14 with the melt 4 and initial solidification of the melt
in the ingates 16, each casting mold 6 is raised by hydraulic power cylinder 60 to
withdraw the underside 10a of the lower mold portion 10 out of the pool 2. The number
and size of the ingates 16 to achieve metal solidification initially at the ingates
16 can be selected in accordance with the teachings of U.S. Patent 4,340,108. Alternatively,
the molten iron can be allowed to solidify in both the ingates 16 and the mold cavity
14 before raising the casting mold.
[0041] Referring to Figs. 1-4, a first embodiment of the invention is illustrated for altering
the composition of a ferritic nodular iron grade melt 4 as it is drawn upwardly through
the narrow ingates (pin gates) 16 into the mold cavity 14 during the vacuum countergravity
casting process described hereinabove. In particular, this embodiment involves altering
the melt composition to produce a casting having not only a different composition
(e.g., by inclusion of copper in the melt) but also a different microstructure (e.g.,
a pearlitic cast iron grade microstructure) from that obtainable by solidification
of the ferritic nodular iron melt 4.
[0042] The melt 4 is prepared initially as a ferritic iron base melt in a melting vessel,
such as for example a cupola (not shown), by the addition of suitable alloyants to
a pig iron charge in the melting vessel. For example, additions of 49 lbs. of 50%
Fe-Si, 50 lbs. of steel, 2.5 lbs. of Fe-Mn and 1 lb. of graphite are made to 1150
lbs. of pig iron in the melting vessel to provide a ferritic iron base melt having
a composition corresponding to the known ferritic iron grade 4010 (e.g., total carbon
= 3.60 to 4.10 w/o, Mn = .25 to .90 w/o, P = .05 w/o max, S = .02 w/o max, Si = 2.20
to 2.70 w/o, Cr = .10 w/o max, Cu less than .04 w/o and balance iron).
[0043] A portion (e.g., 300 lbs.) of the ferritic iron base melt is transferred to a ladle
(not shown) where the melt is treated with a nodularizing treating agent (e.g., Fe-Si-Mg
having a nominal composition of about 5 w/o Mg and balance Fe and Si in equal amounts)
to spherodize the carbon. A Mg content of about 0.03-0.06 w/o is typically provided
in the ferritic iron base melt for this purpose. Cut steel shavings are introduced
as a cover layer over the treated base melt in the ladle to enhance recovery of magnesium.
[0044] The resulting ferritic nodular iron grade melt 4 (i.e., 300 lbs.) is then transferred
from the ladle to the casting vessel 3 where the melt 4 is inoculated by the addition
of 2 lbs. of Fe-Si alloyant and the melt temperature is maintained at about 2600°F
during the vacuum countergravity casting of successive molds 6 therefrom.
[0045] In accordance with this embodiment of the invention, an expendable source 50 of copper
alloyant is positioned at each ingate 16 so as to selectively introduce (e.g., dissolve)
copper into the ferritic nodular iron grade melt 4 as a stream of the melt 4 is drawn
upwardly through the ingates 16 into the molding cavity 14 during the vacuum, countergravity
casting process.
[0046] In particular, the mold 6 includes the sources 50 of copper alloyant in each ingate
(pin gate) 16 adjacent the inlet thereof (i.e., adjacent the underside 10a of the
lower mold portion 10). Each source 50 of copper alloy comprises a spiral of copper
electrical wire wedged in each ingate 16 adjacent the underside 10a with the axis
of the spiral coaxial with the longitudinal axis or each ingate 16, see Figs. 2-3.
It is apparent that the configuration and orientation of the spiral wire source 50
provides a plurality of upwardly extending passages 52 through which the ferritic
nodular iron melt stream can be drawn upwardly from the pool 2 into the mold cavity
14 during the vacuum countergravity casting process.
[0047] As the stream of melt 4 is drawn upwardly through each ingate 16, the melt 4 passes
through the passages 52 in the spiral wire source 50 for intimate contact therewith
and introduction (e.g., dissolution) of copper selectively into the melt 4 flowing
through each respective ingate 16.
[0048] In this embodiment of the invention, the amount of copper introduced into the melt
4 is selected (e.g., about .4 w/o minimum to about .5 w/o maximum) to provide a microstructure
upon solidification of the melt 4 in the mold cavity 14 (during air cooling of the
metal-filled mold 6) and improved tensile and yield strength properties at least comparable
to the known as-cast pearlitic nodular iron grade 5203.
[0049] For example, in casting trials, eight castings (in the shape of tensile specimens
each weighing between about 1.5 lbs. to 1.6 lbs.) were vacuum countergravity cast
from the ferritic nodular iron melt 4. Each tensile specimen-shaped mold cavity 14
received the melt 4 via a pair of pin gates 16 with each pin gate having a spiral
copper source 50 weighing about three (3) grams therein. A copper concentration of
about .4 w/o was measured in the resultant castings (tensile specimens). Upon examination
and testing, the castings (tensile specimens) were found to exhibit an as-cast microstructure
corresponding to the known as-cast pearlitic nodular iron grade 5203 (e.g., 50 v/o
ferrite max., 50 v/o pearlite min., 10 v/o carbide max.) and mechanical properties
more than comparable (see Table I below) to the as-cast pearlitic nodular iron grade
5203.

[0050] As is apparent, the embodiment of the invention described hereinabove with respect
to Figs. 1-4 was effective in producing pearlitic nodular iron grade castings having
significantly enhanced mechanical properties from the ferritic nodular iron melt 4
(corresponding to ferritic nodular iron grade 4010) as a result of the selective introduction
of copper into the melt 4 as it was drawn upwardly through the narrow ingates (pin
gates) 16 of the mold 6 during the vacuum-assisted countergravity casting process.
Moreover, each source 50 of copper can be positioned in the conventionally shaped/sized
narrow ingates (pin gates) 16 without having to make substantial modifications to
the ingates 16. In particular, the ingates 16 can be configured sufficiently narrow
(e.g., .1875 inch in diameter for the cylindrical ingates 16 shown) to effect initial
freeze-off of the melt 4 in the ingates 16 in accordance with U.S. Patent 4,340,108
and yet still achieve desired introduction of the alloyant (Cu) in the melt 4 during
casting.
[0051] Referring now to Fig. 5, a somewhat different embodiment of the invention is illustrated
and involves positioning the sources 50 of copper (or other) alloyant soluble in the
melt 4 at some ingates 16 but not other ingates 16' to produce a casting having different
metallurgical characteristics (e.g., different microstructures/mechanical properties)
at different locations of the casting. In particular, the sources 50 of copper alloyant
are placed at some ingates 16 to feed a certain region R of the mold cavity 14 with
the copper-modified melt 4 described hereinabove (i.e., a melt 4 containing copper
in desired amount) to produce a pearlitic cast iron grade microstructure and improved
mechanical properties upon solidification in the region R of the mold cavity 14.
[0052] On the other hand, other region L of the mold cavity 14 receives the ferritic nodular
iron melt 4 substantially devoid of copper from the ingates 16' (where there are no
sources 50 of copper alloyant) so as to produce a microstructure (e.g., 40 v/o ferrite
min., 60 v/o pearlite max., 10 v/o carbide max.) and reduced mechanical properties
(e.g., nominal tensile strength of 60,000 psi, nominal yield strength of 40,000 psi
and nominal elongation of 10%) corresponding to the known as-cast ferritic nodular
iron grade 4010 upon solidification of the melt 4 in the region L of the mold cavity
14.
[0053] Region R of the mold cavity 14 would correspond to a location of the casting requiring
increased strength while region L would correspond to a location of the casting not
requiring the higher strength but perhaps requiring more ductility. Dual property,
vacuum-assisted countergravity castings can thereby be produced.
[0054] Referring again to Fig. 5, those skilled in the art will appreciate that an expendable
source (not shown) of a second alloyant (i.e., an alloyant other than copper that
is soluble in the melt 4) may be positioned at one or more of the ingates 16' while
the copper alloyant sources 50 are positioned at the ingates 16 such that a first
alloyant (i.e., copper) is introduced into the melt 4 drawn upwardly through one or
more of the narrow ingates (pin gates) 16 while the second alloyant is introduced
into the melt 4 drawn upwardly through one or more of the ingates 16'. A casting having
different metallurgical characteristics at different locations can also be produced
in this manner in accordance with the present invention.
[0055] Moreover, castings having different metallurgical characteristics at different locations
can also be cast in accordance with the invention by introducing a first amount of
an alloyant into the melt 4 drawn upwardly through one or more ingates 16 while a
different amount of the same alloyant is introduced into the melt 4 drawn upwardly
through one or more of the other ingates 16'. The position (i.e., proximity) of the
sources 50 relative to the ingates 16,16' as well as the size and configuration of
the alloyant sources 50 can be varied to achieve introduction of different amounts
of the same alloyant into the melt 4 drawn through different ingates 16,16' during
the vacuum-assisted countergravity casting process.
[0056] In accordance with still another embodiment of the invention, different cast parts
having different metallurgical characteristics for different intended uses can be
vacuum countergravity cast from a common melt using the apparatus shown in Fig. 1.
For example, a plurality of the molds 6 having one or more connecting rod-shaped mold
cavities 14 and copper alloyant sources 50 at each of the ingates 16 can be vacuum
countergravity cast in succession from the ferritic nodular iron melt 4 as described
hereinabove to produce cast connecting rods having an as-cast microstructure and mechanical
properties at least equivalent to as-cast pearlitic nodular iron grade 5203.
[0057] Then, a plurality of other molds 6 having one or more exhaust manifold-shaped mold
cavities 14 but without copper alloyant sources 50 at any of the ingates 16 can be
vacuum countergravity cast in succession from the same (common) ferritic nodular iron
melt 4 to produce exhaust manifolds having an as-cast microstructure and mechanical
properties corresponding to as-cast ferritic nodular iron grade 4010.
[0058] Of course, the molds for casting the connecting rods and the molds for casting the
exhaust manifolds can be cast in any sequence desired since both types of molds are
cast from the common ferritic nodular iron melt 4.
[0059] This embodiment of the invention eliminates the need to prepare and handle different
base melts in one or more melting vessels/ladles. Thus, a "universal" cupola melt
can be used to produce different cast parts having different compositions and/or microstructures
and resultant mechanical properties. The manufacture of different cast parts for different
intended uses is thus simplified. Moreover, the flexibility of the vacuum countergravity
casting process in meeting ever changing production schedule variations is tremendously
improved. Furthermore, since at least some of the alloyant additions are made as the
melt 4 is drawn upwardly through one or more ingates 16 and not to the base melt in
the melting vessel or ladle, the potential for contamination and slagging is reduced.
[0060] Although Figs. 1-5 illustrate the sources 50 as spiral wound wire disposed in the
ingates 16 adjacent the underside 10a of the lower mold portion 10, the invention
is not so limited. For example, the sources 50 may assume other configurations as
illustrated in Figs. 6, 7, 8 and 9. In Fig. 6, the alloyant source 50' comprises a
plurality of circumferentially spaced alloyant needles 51' extending toward the center
of the ingate (pin gate) 16'. Fig. 7 illustrates the alloyant source 50'' as comprising
a plurality of spaced apart alloyant plates 53'' disposed in the ingate (pin gate)
16'' for contact with the melt drawn upwardly therethrough. In Fig. 8, the source
50''' is illustrated as a solid, cylindrical, tubular alloyant pellet 54''' disposed
about the ingate (pin gate) 16''' coaxial therewith for communicating directly with
the ingate. In Fig. 9, the alloyant source 50'''' comprises a solid disc 52'''' of
the alloyant positioned across the ingate 16''''. In practicing the invention using
solid disc 52'''' in the ingate 16'''', the underside of the mold 6 is immersed in
the melt 4 (see Fig. 1) until the disc 52'''' melts and then the vacuum is drawn in
mold cavity to urge the melt upwardly through the ingate (pin gate) 16'''' past the
melted disc 52'''' in such a manner that the alloyant is introduced into the melt
as it is drawn upwardly through the ingate.
[0061] The sources 50, 50', etc. can be held in the respective ingates (pin gates) 16, 16',
etc. using sodium silicate or other suitable adhesive. Alternately, the sources 50,
50', etc. can be embedded in the lower mold portion 10 in such a position as to extend
in the desired manner into the ingate 16, 16', etc. as shown in Figs. 6-9. Typically,
the alloyant source is embedded in the lower mold portion 10 while the sand-resin
mixture thereof is compliant. Then, the sand-resin mixture of the lower mold portion
10 is cured or hardened to retain the alloyant sources in position.
[0062] Moreover, although Figs. 1-9 illustrate each alloyant source 50, 50', etc. as being
disposed adjacent the inlet of the respective ingates 16, 16', etc., the invention
is not so limited. Referring to Figs. 10, the cylindrical, tubular alloyant source
150 (in the form of the cylindrical, tubular alloyant pellet 154) can be disposed
adjacent the outlet 116a of the respective ingate 115 in the lower mold portion 110
and in the mold cavity 114 formed between the upper and lower mold portions 108,110.
Alternatively, as shown in Fig. 11, the alloyant source 250 can be disposed in a small
pocket 217 formed in the narrow pin gate 216 at a parting plane P of a two-part lower
mold portion (drag) 210. The pocket 217 is located in the upper portion 210 of the
two-part lower mold portion (drag) 210 intermediate the inlet 216a and outlet 216b
of the narrow pin gate 216. The pin gate 216 is of the type described hereinabove
sized to effect initial, rapid solidification of a plug of metal therein after the
mold cavity 214 is filled with molten metal. The pin gate 216 supplies the treated
molten metal stream drawn therethrough to the mold cavity 214 formed in the upper
mold portion (cope) 208. The outer periphery of the source alloyant 250 includes slots
250a to provide a molten metal flow path through the pin gate 216.
[0063] In general, the alloyant source 50, 50', etc. need not communicate directly with
the ingate 16, 16', etc. so long as the alloyant source is in sufficiently close proximity
to the ingate to contact the melt 4 drawn upwardly through the ingate 16 and selectively
introduce the alloyant into the melt 4 drawn upwardly therethrough. For example, the
source 50, 50', etc. can be embedded in the underside 10a of the lower mold portion
10 in the manner described in the copending application (attorney docket no. P-309
GM-Plant) spaced from the inlet of the ingate 16,16', etc. and yet sufficiently close
to the inlet of the ingate 16, 16', etc. as to introduce the alloyant into the stream
of melt 4 drawn upwardly into that particular ingate 16, 16', etc.
[0064] Although the embodiments of the invention are illustrated hereinabove with respect
to the introduction of copper into the ferritic nodular iron melt 4, those skilled
in the art will appreciate that the invention is not so limited. For example, other
alloyants such as chromium, manganese, molybdenum, magnesium, silicon as well as others
that are soluble in the melt 4 may be introduced therein in accordance with the invention.
In one specific example, each alloyant source 50, Fig. 1, may comprise an iron-silicon-magnesium
nodularizing agent (having a composition of about 5 w/o Mg and balance Fe and Si in
equal amounts) to introduce magnesium into a stream of ferritic iron melt 4 as it
is drawn upwardly through the ingates 16 to nodularize the carbon of the melt that
fills the mold cavity 14. This method of introducing the nodularizing agent into the
melt 4 as it is drawn upwardly through the ingates 16 can be used in lieu of or in
addition to the method disclosed in the aforementioned copending application (attorney
docket no. P-309 GM-Plant) of common assignee herewith for maintaining the magnesium
content of the melt 4 at the required level (e.g., about 0.03 w/o-0.06 w/o) for nodularizing
the carbon of the melt 4 filling the mold cavity 14 of successively cast molds 6.
Loss or "fade" of the magnesium content of the melt 4 over time can be thereby countered.
[0065] In another specific example of another alloyant that can be introduced into the melt
in accordance with the invention, the sources 50 may comprise a Fe-Si inoculant (comprising
1 w/o Ca, 75 w/o Si and balance Fe) for promoting nucleation of graphite in the ferritic
(or pearlitic) nodular iron grade melt 4 during solidification. In particular, in
certain casting trials, a source 50 of Fe-Si inoculant (in the form of a tubular solid
pellet as shown in Fig. 8) was positioned about each ingate 16 adjacent the underside
10a of the lower mold portion 10 prior to vacuum countergravity casting of a ferritic
nodular iron melt 4. The inoculant sources 50 were effective to introduce inoculant
into the melt 4 drawn upwardly through the ingates 16 into the mold cavity 14 in such
a quantity as to significantly increase the graphite nodule count in the casting;
e.g., to 161.3 nodules per square millimeter.
[0066] Moreover, the present invention is not limited to the vacuum countergravity casting
of cast irons and instead may be used in the vacuum countergravity casting of other
metals/alloys where selective introduction of one or more alloyants is desired for
some purpose. For illustrative purposes only, the present invention may be used to
dissolve known degassing, desulfurizing, deslagging and similar treating agents into
aluminum or steel during the vacuum countergravity casting thereof.
[0067] In addition to the improved differential pressure, countergravity casting method
and apparatus described hereinabove, the invention also envisions a mold cavity fill
analysis method for determining melt flow paths into the mold cavity 14 from the ingates
16 during the countergravity casting process. For example, referring to Fig. 1, an
alloyant source 50 is disposed in close proximity to a selected one of the ingates
16 (instead of all the ingates 16 as shown) so as to introduce the alloyant only into
the melt 4 drawn upwardly through that particular ingate. The alloyant is selected
to impart a particular metallurgical characteristic to the casting which metallurgical
characteristic will be localized to a region of the mold cavity 14 that is supplied
melt 4 by the particular ingate 16 where the source 50 is placed. Regions of the casting
receiving melt 4 from the other ingates 16 where there are no alloyant sources will
not exhibit this metallurgical characteristic. As a result, the contribution of a
particular ingate 16 (where the alloyant source is placed) to the filling of the mold
cavity 14 can be determined based on an analysis of the solidified casting; i.e.,
to determine where the particular metallurgical characteristic appears in the casting.
This procedure can be repeated for each ingate 16 (or multiple ingates 16 when they
are sufficiently remote from one another) to determine melt flow paths into the mold
cavity 14 from each ingate.
[0068] Figs. 12-15 illustrate application of this method to the vacuum countergravity casting
of automobile engine exhaust manifolds 100, 100', 100'' (schematically shown) using
an apparatus similar to that shown in Fig. 1 with the exception that a single alloyant
source 50 is disposed in proximity to one, but not others, of the ingates 16. The
locations of the ingates on the cast exhaust manifolds 100, 100', 100'' are numbered
from #1 to #15 in Figs. 12-14 for identification purposes.
[0069] In Fig. 12, the exhaust manifold 100 was vacuum countergravity cast with a solid
tubular Fe-Si inoculant pellet embedded in the underside 10a of the lower mold portion
10 about the inlet of ingate #1, e.g., as shown in Fig. 8. A nodular iron melt 4 depleted
of its graphite nucleating ability was then vacuum countergravity cast into the mold
cavity 14 and solidified.
[0070] The nodular iron melt 4 drawn upwardly through ingate #1 contacted the Fe-Si inoculant
pellet embedded in proximity to the ingate #1 such that the inoculant was introduced
therein. The quantity of inoculant introduced into the melt 16 at the ingate #1 was
sufficient to promote formation of graphite nodules and inhibit formation of primary
carbides during solidification of the melt 4 in those regions of mold cavity 14 receiving
the melt 4 from ingate #1. Those regions of the mold cavity 14 filled through the
other ingates 16 received melt which was substantially devoid of inoculant and which,
as a result, solidified as "white" cast iron with primary carbide precipitation and
little or no graphite nodule formation. Thus, a noticeable metallurgical characteristic
was associated with selective introduction of the inoculant into the melt passing
through the ingate #1. The resultant exhaust manifold 100 was then sectioned at various
locations for metallographic examination.
[0071] Fig. 12 includes shaded areas A where primary carbides of the varying percentages
shown were found upon sectioning of the casting. The shaded areas A indicate those
regions of the casting (or mold cavity 14) that are not fed by the ingate #1. These
shaded areas A bound or enclose those regions of the casting that are fed with the
melt containing inoculant from ingate #1. From Fig. 12, it is apparent that the ingate
#1 feeds only a portion of flange area F1 of the cast exhaust manifold 100.
[0072] Fig. 13 includes shaded areas A' where carbides of the varying percentages shown
were observed in the cast exhaust manifold 100' when the Fe-Si inoculant pellet was
disposed at only the ingate #4 to selectively introduce silicon into the melt drawn
upwardly through that ingate #4. It is apparent that the ingate #4 feeds the melt
primarily to the flange area F2 of the cast exhaust manifold 100'. Fig. 13 also reveals
that the ingates #3, #8 and/or #9 also supply melt to this same flange area F2. The
flow of melt to the flange area F2 from ingates #3, #8 and/or #9 was not planned or
expected during the design of the gating system for the particular mold involved.
[0073] Fig. 14 includes shaded areas A'' where primary carbides of the varying percentages
shown were observed in the cast exhaust manifold 100'' when the Fe-Si inoculant pellet
was disposed at only ingate #6 to selectively introduce the inoculant into the melt
drawn upwardly through the ingate #6.
[0074] A comparison of Figs. 12 and 14 reveals that the ingate #6 feeds a much larger area
of the cast exhaust manifold 100'' than the ingate #1. Moreover, melt flow through
the ingate #6 is effective enough to blend with melt entering the flange area F1 through
the ingate #1.
[0075] Fig. 15 is a longitudinal sectional view through the flange area F1 of the cast exhaust
manifold 100'' and reveals massive carbides at the back side of the flange area F1.
The presence of these massive carbides suggests that the ingate #1 feeds melt to the
flange area F1 prior to ingate #6 and that solidification in that local region (where
massive carbides are observed) began prior to arrival of the melt from the ingate
#6.
[0076] The mold cavity fill analysis method of the invention illustrated hereinabove with
reference to Figs. 12-15 provides to the casting engineer a tool for determining melt
flow patterns from particular ingates 16 into the mold cavity 14 during vacuum-assisted
countergravity casting of molten metal. This method will help the casting engineer
to improve and optimize mold gating systems for a particular casting to be produced.
This method also will help reduce the development and lead times required to design
a particular casting mold and thus facilitate meeting scheduling demands for production
castings. The prospect of producing quality castings on a production basis should
be improved as a result.
[0077] While the invention has been described in terms of specific embodiments thereof,
it is not intended to be limited thereto but rather only to the extent set forth hereafter
in the claims which follow.
1. Apparatus for the differential pressure, countergravity casting of molten metal, comprising:
(a) a mold having a mold cavity, a lower mold portion adapted to engage an underlying
source of said molten metal and an ingate communicating the mold cavity with the lower
mold portion for supplying molten metal drawn from said source into said cavity,
(b) means for applying a sufficient differential pressure between the mold cavity
and the source while the lower mold portion is engaged with the source to urge the
molten metal upwardly through the ingate into the mold cavity, and
(c) an alloyant disposed on the mold at the ingate so as to selectively contact the
molten metal stream drawn upwardly through said ingate into the mold cavity and substantially
selectively introduce the alloyant into such stream.
2. The apparatus of claim 1 wherein said source comprises a pool of molten metal and
said lower mold portion is adapted for immersion in said pool.
3. The apparatus of claim 1 wherein the alloyant is disposed adjacent an inlet of the
ingate.
4. The apparatus of claim 3 wherein the alloyant is secured to the lower mold portion.
5. The apparatus of claim 1 wherein the alloyant is disposed adjacent an outlet of the
ingate.
6. The apparatus of claim 5 wherein the alloyant is disposed in the mold cavity.
7. The apparatus of claim 1 wherein the alloyant is disposed in the ingate.
8. The apparatus of claim 1 wherein the mold includes a plurality of ingates and alloyant
is positioned at each ingate.
9. Apparatus for the differential pressure, countergravity casting of molten metal to
form a casting having different metallurgical characteristics at different locations,
comprising:
(a) a mold having a mold cavity and a first ingate and a second ingate communicating
a respective first location and second location of the mold cavity with a lower mold
portion adapted to engage an underlying source of said molten metal,
(b) alloyant disposed on the mold at the first ingate to so contact the molten metal
drawn upwardly through said first ingate as to substantially selectively introduce
the alloyant therein remote from the second ingate, and
(c) means for applying a sufficient differential pressure between the mold cavity
and the source while the lower mold portion is engaged with the source to urge the
molten metal upwardly through the first ingate to supply the first location of the
mold cavity with the molten metal having the alloyant introduced therein and through
the second ingate to supply the second location of the mold cavity with the molten
metal substantially devoid of the alloyant.
10. Apparatus for the differential pressure, countergravity casting of molten metal to
form a casting having different metallurgical characteristics at different locations,
comprising:
(a) a mold having a mold cavity and a first ingate and a second ingate communicating
a respective first location and second location of the mold cavity with a lower mold
portion adapted to engage an underlying source of said molten metal,
(b) first alloyant disposed on the mold at the first ingate to so contact the molten
metal drawn upwardly through the first ingate as to substantially selectively introduce
the first alloyant therein,
(c) second alloyant disposed on the mold at the second ingate to so contact the molten
metal drawn upwardly through the second ingate as to substantially selectively introduce
the second alloyant therein, and
(d) means for applying a sufficient differential pressure between the mold cavity
and the source while the lower mold portion is engaged with the source to urge the
molten metal upwardly through the first ingate to supply the first location of the
mold cavity with the molten metal having the first alloyant introduced therein and
through the second ingate to supply the second location of the mold cavity with the
molten metal having the second alloyant introduced therein.
11. Apparatus for the differential pressure, countergravity casting of molten metal to
form a casting having different metallurgical characteristics at different locations,
comprising:
(a) a mold having a mold cavity and a first ingate and a second ingate communicating
a respective first location and second location of the mold cavity with a lower mold
portion adapted to engage an underlying source of said molten metal,
(b) alloyant disposed on the mold at the first ingate to so contact the molten metal
drawn upwardly through said first ingate as to introduce a first amount of the alloyant
therein,
(c) alloyant disposed on the mold at the second ingate to so contact the molten metal
drawn upwardly through said second ingate as to introduce a second amount of the alloyant
therein, and
(d) means for applying a sufficient differential pressure between the mold cavity
and the source while the lower mold portion is engaged with the source to urge the
molten metal upwardly through the first ingate to supply the first location of the
mold cavity with the molten metal having said first amount of the alloyant therein
and through the second ingate to supply the second location of the mold cavity with
the molten metal having said second amount of the alloyant therein.
12. Apparatus for the differential pressure, countergravity casting of molten metal to
form a casting having different metallurgical characteristics at different locations,
comprising:
(a) a mold having a mold cavity and a plurality of ingates communicating different
locations of the mold cavity with an underside of the mold adapted to engage an underlying
source of said molten metal,
(b) alloyant disposed on the underside at at least one of said ingates to so contact
the molten metal drawn upwardly through said one ingate as to substantially selectively
introduce said alloyant therein remote from another of said ingates, and
(c) means for applying a sufficient differential pressure between the mold cavity
and the source while the underside is engaged with the source to urge the molten metal
upwardly through said one ingate to supply one location of the mold cavity with the
molten metal having the alloyant introduced therein and through said another of the
ingates to supply another location of the mold cavity with the molten metal substantially
devoid of said alloyant.
13. A method of differential pressure, countergravity casting of molten metal, comprising:
(a) forming a mold having a mold cavity and an ingate communicating the mold cavity
with a lower mold portion adapted to engage an underlying source of the molten metal,
including disposing a source of an alloyant on the mold in such relation to the ingate
that the molten metal drawn upwardly through the ingate contacts the alloyant,
(b) relatively moving the mold and the source to engage the lower mold portion and
the source,
(c) applying a sufficient differential pressure between the mold cavity and the source
while the lower mold portion is engaged with the source to urge the molten metal upwardly
through the ingate into the mold cavity, including so contacting the molten metal
and the alloyant as to substantially selectively introduce said alloyant into the
molten metal drawn upwardly through the ingate into the mold cavity, and
(d) solidifying the molten metal in the mold cavity.
14. The method of claim 13 including disposing the alloyant on the lower mold portion
in close proximity to an inlet of the ingate.
15. The method of claim 13 including disposing the alloyant in close proximity to an outlet
of the ingate.
16. The method of claim 13 including disposing the alloyant in the ingate.
17. The method of claim 13 wherein the mold includes a plurality of ingates and a source
of the alloyant is disposed in close proximity to each ingate.
18. A method of differential pressure, countergravity casting of molten metal to form
a casting having different metallurgical characteristics at different locations, comprising:
(a) forming a mold having a mold cavity and a first ingate and a second ingate communicating
a respective first location and second location of the mold cavity with a lower mold
portion adapted to engage an underlying source of said molten metal,
(b) disposing an alloyant at the first ingate to so contact the molten metal drawn
upwardly through said first ingate as to substantially selectively introduce said
alloyant therein remote from the second ingate,
(c) relatively moving the mold and the source to engage the lower mold portion and
the source,
(d) applying a sufficient differential pressure between the mold cavity and the source
while the lower mold portion is engaged with the source to urge the molten metal upwardly
through said first ingate to supply one location of the mold cavity with the molten
metal having the alloyant introduced therein and through said second ingate to supply
said second location of the mold cavity with the molten metal substantially devoid
of the alloyant, and
(e) solidifying the molten metal in the mold cavity.
19. A method of differential pressure, countergravity casting of molten metal to form
a casting having different metallurgical characteristics at different locations, comprising:
(a) forming a mold having a mold cavity and a first ingate and a second ingate communicating
a respective first location and second location of the mold cavity with a lower mold
portion adapted to engage an underlying source of said molten metal,
(b) disposing a first alloyant at the first ingate and a second alloyant at the second
ingate to so contact the molten metal drawn upwardly through said first ingate and
the second ingate as to substantially selectively introduce the respective first alloyant
and second alloyant therein,
(c) relatively moving the mold and the source to engage the lower mold portion and
the source,
(d) applying a sufficient differential pressure between the mold cavity and the source
while the lower mold portion is engaged with the source to urge the molten metal upwardly
through said first ingate to supply said first location of the mold cavity with the
molten metal having the first alloyant introduced therein and through said second
ingate to supply said second location of the mold cavity with the molten metal having
the second alloyant introduced therein, and
(e) solidifying the molten metal in the mold cavity.
20. A method of differential pressure, countergravity casting of molten metal to form
a casting having different metallurgical characteristics at different locations, comprising:
(a) forming a mold having a mold cavity and a first ingate and a second ingate communicating
a respective first location and second location of the mold cavity with a lower mold
portion adapted to engage an underlying source of said molten metal,
(b) disposing a first source of an alloyant at the first ingate and a second source
of the alloyant at the second ingate to selectively contact the molten metal drawn
upwardly through said first ingate and second ingate,
(c) relatively moving the mold and the source to engage the lower mold portion and
the source,
(d) applying a sufficient differential pressure between the mold cavity and the source
while the lower mold portion is engaged with the source to urge the molten metal upwardly
through the first ingate and the second ingate, including so contacting the first
source of said alloyant and the molten metal drawn upwardly through said first ingate
as to supply one location of the mold cavity with the molten metal having an amount
of the alloyant introduced therein and so contacting the second source of said alloyant
and the molten metal drawn upwardly through said second ingate as to supply said second
location of the mold cavity with the molten metal having a different amount of the
alloyant introduced therein, and
(e) solidifying the molten metal in the mold cavity.
21. A method of differential pressure, countergravity casting of molten metal to form
a casting having different metallurgical characteristics at different locations, comprising:
(a) forming a mold having a mold cavity and a plurality of ingates communicating different
locations of the mold cavity with an underside of said mold adapted to engage an underlying
source of said molten metal,
(b) disposing an alloyant on the underside at at least one of the ingates to so contact
the molten metal drawn upwardly through said at least one of the ingates as to introduce
said alloyant therein remote from another of the ingates,
(c) relatively moving the mold and the source to engage the underside and the source,
(d) applying a sufficient differential pressure between the mold cavity and the source
while the underside is engaged with the source to urge the molten metal upwardly through
said at least one of the ingates to supply one location of the mold cavity with the
molten metal having the alloyant introduced therein and through said other of the
ingates to supply another location of the mold cavity with the molten metal substantially
devoid of the alloyant, and
(e) solidifying the molten metal in the mold cavity.
22. A method of differential pressure, countergravity casting a first part and a second
part having different compositions, comprising:
(a) forming a first mold for casting the first part,
(b) forming a second mold for casting the second part,
(c) providing a common source of molten metal from which the first mold and the second
mold will be cast,
(d) disposing a source of an alloyant on one of said first mold or second mold in
such relation to an ingate thereof that the alloyant is introduced into the molten
metal drawn upwardly through the ingate during casting,
(e) drawing the molten metal of the common source upwardly through the ingate and
into a mold cavity of the first mold while the first mold is engaged with the common
source, and
(f) drawing the molten metal of the common source upwardly through the ingate and
into a mold cavity of the second mold while the second mold is engaged with the common
source,
whereby the molten metal drawn upwardly into the mold cavity of said one of the first
mold or second mold will contain said alloyant and the molten metal drawn upwardly
into the mold cavity of the other of the first mold or second mold will be devoid
of said alloyant.
23. A mold cavity fill analysis method, comprising:
(a) forming a mold having a mold cavity and a plurality of ingates communicating different
locations of the mold cavity with a lower mold portion adapted to engage an underlying
source of molten metal,
(b) disposing an alloyant on the mold at one of the ingates to so contact the molten
metal drawn upwardly through said one of the ingates as to introduce said alloyant
therein in a sufficient quantity to affect a metallurgical characteristic of said
molten metal upon solidification,
(c) countergravity casting the molten metal into the mold cavity by drawing the molten
metal upwardly through the ingates and into the mold cavity while the lower mold portion
is engaged with said source,
(d) solidifying the molten metal in the mold cavity to form a casting, and
(e) examining the casting to locate any region thereof exhibiting the metallurgical
characteristic attributable to the presence of the alloyant in the solidified metal.