Sequential mold filling

Method and apparatus for casting molten metal or alloy into a plurality of molds that are connected by mold ingate passages in melt flow communication to a melt supply passage which is configured in a manner to completely or partially fill the molds with the molten metal or alloy sequentially one after another. Filling of the molds in this manner provides uniform mold filling, reduces foreign matter in molds filled after the first-filled mold, and improves quality of the cast articles.

FIELD OF THE INVENTION

The present invention relates to casting of molten metal or alloy and, more particularly, to method and apparatus for casting molten metal or alloy into a plurality of molds that are connected to a molten metal or alloy supply passage in a manner that the molds are partially or completely filled with molten metal or alloy sequentially one after another.

BACKGROUND OF THE INVENTION

In the investment casting of molten metal or alloy (melt), a ceramic gang mold has been employed where the gang mold comprises a melt pour cup connected to a plurality of individual article-forming molds. In one conventional casting set-up for casting gas turbine engine blades, the pour cup includes multiple main melt supply gating spokes extending therefrom. The main gating spokes each in turn branch into multiple individual melt supply gating spokes each of which extends to a respective individual mold. For example, three or more melt supply branch gating spokes may branch from each main spoke. Each article-forming mold includes at least one mold cavity having the shape of the article to be cast.

In a conventional casting set-up, the initial stream of melt poured from a crucible into the pour cup of the mold is usually narrow to insure that the melt is received in the pour cup and that there is minimum splashing of the melt inside the casting furnace. The main gating spokes are communicated to the pour cup and typically serve the dual purpose of delivery of melt to a respective individual mold via a respective branch gating spoke and of providing an adequate reservoir of melt to compensate for the liquid-to-solid shrinkage in the mold. For example, in casting equiaxed grain articles, the cross-sectional area of the spokes therefore typically has to be larger than the cross-section of the mold cavity that is filled from the spoke. For example, in a conventional equiaxed casting set-up, the collective cross-sections of the spokes can be at least ten times larger than the initial pour stream. Such a large ratio of spoke-to-initial pour stream cross-sectional areas results in inconsistent and uneven delivery of melt among the molds. The spokes that are oriented in the direction of the pour stream receive more metal flow than those spokes which are located away from the direction of pour stream, resulting in uneven initial fill of the molds.

In the above conventional casting set-up, the need for a large number of spokes to provide both initial melt delivery and melt feeding to accommodate solidification shrinkage of individual molds is disadvantageous from the standpoint that metal or alloy usage is inefficient. That is, the metal or alloy solidified in the main and branch spokes is not cast into a usable article but remains as individual gating of the molds.

The gang mold has been formed by the well known lost wax process where a wax or other fugitive pattern assembly corresponding to the gang mold features is repeatedly dipped in ceramic slurry, drained of excess slurry, and stuccoed with coarse ceramic stucco particulates to build up a desired thickness of ceramic shell thickness on the pattern assembly. The pattern assembly then is selectively removed, and the remaining ceramic gang shell mold is heated at elevated temperature to impart strength properties to the shell mold needed for subsequent casting. During casting, molten metal or alloy is poured into the pour cup and flows via the gating to fill the article-forming molds substantially concurrently. The molten metal or alloy is solidified in the molds to form an investment cast article in the molds.

In the investment casting of critical aerospace components, such as gas turbine engine blades, vanes and the like, the gang molds oftentimes include a molten metal or alloy filter placed in each melt feed runner supplying molten metal or alloy from the pour cup to the spokes in order to remove non-metallic inclusions from the molten metal or alloy before it enters the individual molds.

SUMMARY OF THE INVENTION

The present invention provides method and mold assembly for casting molten metal or alloy (melt) that involve providing a metal or alloy melt in a melt-receiving mold cup of a mold assembly and supplying the melt from the mold cup to a melt supply passage of the mold assembly for flow to a plurality of molds that are connected in melt flow communication to the melt supply passage in series arrangement one after another. The melt supply passage is configured in a manner that each of the molds of the series is at least partially filled before the next mold in the series is at least partially filled.

In an illustrative method embodiment of the invention, the first mold in the series is completely or partially filled before a second mold of the series is filled. Then, the second mold is completely or partially filled before a third mold of the series is filled, and so on until remaining molds of the series are filled.

In another illustrative method embodiment of the invention, the first mold of the series is filled in dead-end manner without flow through a mold cavity thereof to the next mold in the series to help reduce the amount of foreign matter, such as non-metallic inclusions, in the melt filling subsequently filled molds of the series.

One illustrative embodiment for achieving dead-end filling involves completely filling a first mold of the series from a top thereof with melt from the melt supply passage, then filling a second mold of the series from a top thereof using a second melt supply passage extending from the top of the first mold to the top of the second mold, and so on until the molds are filled. Alternately, another dead-end filling method can involve filling the first mold using a single inlet passage at one end of the first mold that is remote from a closed opposite end thereof. The first mold can be an article-forming or non-article-forming mold configured to provide dead-end flow.

In practicing the method of the invention, the molds can be connected to a melt supply passage that is inclined at an acute angle along a length. Alternately, the molds can be connected to a melt supply passage that is constricted along a length to have variable cross-sections that decrease in cross-sectional area. Still further, the molds can be connected to a melt supply passage that is upstanding along its length. In a preferred embodiment of the invention, the adjacent molds of the series are connected by respective melt supply passages in a manner to provide sequential top-to-top filling of the molds.

In practicing particular embodiments of the invention, the molds can be disposed along a length of a linear or arcuate melt supply passage of a gang mold. The molds can be configured to cast equiaxed articles therein, directionally solidified articles therein having a plurality of columnar grains along an axis of the mold, or single crystal articles therein having a single oriented grain.

The invention also envisions a method and mold assembly for casting molten metal or alloy that involve providing metal or alloy melt in a melt-receiving mold cup of a mold assembly and supplying the melt from the mold cup to a first melt supply passage of the mold assembly to which a first plurality of molds are connected in melt flow relation in series arrangement one after another and supplying the melt from the first melt supply passage via a connector melt supply passage to a second supply passage to which a second plurality of molds are connected in melt flow relation in series arrangement one after another such that the first plurality of molds are at least partially filled before the second plurality of molds.

The invention also provides in still another embodiment method and mold assembly for casting molten metal or alloy involving supplying a metal or alloy melt to a plurality of molds which are connected in series arrangement one after another by respective melt supply members each connected between a top of a preceding mold to a top of the next mold in the series and completely filling each mold in the series before the next mold is filled.

The invention provides in another embodiment a metal or alloy casting comprising a plurality of solidified metal or alloy articles that are connected to linear or arcuate solidified gating wherein a first one of the metal or alloy articles connected to the gating includes more foreign matter than the remaining other solidified metal or alloy articles connected to the solidified gating. The casting can include solidified articles which are connected in series along a length of the solidified gating, which is inclined, which includes variable cross-sections, or which is upstanding. In another embodiment of the invention, the casting can include adjacent solidified articles that are connected top-to-top or top-to-bottom to one another by a respective solidified gating. The solidified articles can comprise equiaxed polycrystalline grain articles, directionally solidified columnar grain articles, single crystal articles, or composite articles.

The present invention is advantageous to provide more uniform and consistent filling of the molds in the series without major interruptions in filling thereof, more efficient usage of expensive metal and alloys being cast to reduce cost of manufacture, and in certain embodiments of the invention can reduce foreign matter, such as non-metallic inclusions and dross, in subsequently-filled articles of the sequence and resultant reduction in scrapped cast articles. Moreover, when the articles are cast by directional solidification to produce directionally solidified columnar grain or single crystal article, practice of the invention provides improved retained melt heat in the mold grain nucleation chamber to initiate directional solidification. Other advantages of the present invention will become more readily apparent from the following detailed description of the invention taken with the following drawings.

DETAILED DESCRIPTION OF THE INVENTION

Illustrative embodiments of the method and apparatus for casting molten metal or alloy into a plurality of molds involve providing metal or alloy melt in a melt-receiving mold cup of a mold assembly and supplying the melt from the mold cup to a melt supply passage of the mold assembly for flow to a plurality of molds that are connected in melt flow communication to the melt supply passage in series arrangement one after another wherein the melt supply passage is configured in a manner that each of the molds of the series is at least partially filled before the next mold in the series is at least partially filled.

FIGS. 1A,1B, and1C are offered to illustrate an embodiment of the invention without limiting the scope thereof. InFIGS. 1A,1B, and1C, a gang mold10is shown having an integral melt-receiving mold cup10a, a down sprue10bhaving a sprue passage10ccommunicated to the mold cup10a, and a plurality of melt supply members10dcommunicated to the down sprue and each having a melt supply passage10e. An optional conventional molten metal or alloy filter (not shown), such as for example a reticulated ceramic foam filter or cellular flow-through ceramic filter, can be typically provided in the mold cup10ato remove foreign matter before the melt enters the molds.

Pursuant to an illustrative embodiment of the invention, a plurality of article-forming molds20are shown connected in melt flow communication to each of a plurality (four shown) melt supply members10dalong their respective lengths that incline upwardly relative to horizontal in a generally radial direction extending away from the mold cup10a. Each mold20comprises ceramic shell20athat includes and defines therein an article-forming mold cavity20cthat has the shape of the cast article to be produced and a closed end20e. For purposes of illustration and not limitation, the mold cavity20cis shown having the shape of a gas turbine engine blade, although the mold cavities can be any shape to produce a desired cast article. To this end, the mold cavity includes a blade root region20r, blade platform region20p, a blade airfoil region20fand a blade tip region20t. The mold cavity20cis connected by a mold ingate passage20gthat is communicated in flow relation to the respective melt supply passage10eto receive molten metal or alloy therefrom when the molten metal or alloy is provided in the mold cup10aand flows through the down sprue and sprue passage10e. The molten metal or alloy can be poured into the mold cup10afrom a conventional crucible CR, such as a conventional tiltable crucible or bottom feeding crucible located above the mold cup, or any other melt-containment vessel. Alternately, the metal or alloy may be placed as a solid charge in the mold cup10aand melted in-situ therein by induction melting, electron beam melting, or other melting process. The molten metal or alloy can be melted and/or held in the crucible or other melt-containment vessel under vacuum, protective atmosphere, or air depending on the particular molten metal or alloy to be cast.

The gang mold10can be formed as a ceramic shell mold assembly by the well known lost wax process where a wax or other fugitive pattern assembly having the features corresponding to those of the gang mold (e.g. wax mold cup, wax down sprue, wax melt supply members, and wax molds) is assembled. The fugitive pattern assembly is repeatedly dipped in ceramic slurry, drained of excess slurry, and stuccoed with coarse ceramic stucco particulates to build up a desired thickness of ceramic shell thickness on the pattern assembly. The pattern assembly then is selectively removed, and the remaining ceramic shell gang mold is heated at elevated temperature to impart strength properties to the shell mold needed for subsequent casting.

During casting, molten metal or alloy M,FIG. 1B, can be poured from the crucible CR or other melt-containment vessel into the mold cup10afor flow by gravity through the down sprue10band the gating passages10e. Pursuant to an embodiment of the invention, the molten metal or alloy M flows from the down sprue through the inclined melt supply passages10eto fill the article-forming mold cavities20cin sequence depending upon the position of the mold10along the length of the melt supply member10d. For example, referring toFIG. 3, the molten metal or alloy M flows into mold #1to completely fill it first, then the flows into mold #2to completely fill it second, then the flows into mold #3to completely fill it third, and finally flows into mold #4to completely fill it last. The molten metal or alloy M is solidified in the molds to form an investment cast article in each mold20. The cast articles are connected to the solidified gating and down sprue and mold cup when the mold material is removed. After the mold material is removed, the cast articles are separated from the gating by cutting, sawing, breaking off at a cast-in notch, or any other separation technique.

InFIGS. 1A through 1D, the molds20are shown to produce equiaxed polycrystalline investment cast articles in the mold cavities20c, although the invention is not limited in this regard since any type of cast article such as a columnar grain article, single crystal article, or composite article can be produced by practice of the invention.

Filling of the molds20in this sequential manner has been found to be advantageous to provide more uniform and consistent filling of the molds in the series without major interruptions in filling thereof. This improves the consistency and quality of the cast articles in the molds20. Moreover, filling of the molds20in this sequential manner provides more efficient usage of expensive metal and alloys being cast to reduce cost of manufacture. Practice of the invention can achieve a reduction in cast articles scrapped for porosity defects, grain defects, and radiographic-revealed defects such as non-metallic inclusions and visual defects such as non-metallic inclusions. Practice of certain embodiments of the invention can produce a reduction of foreign matter, such as non-metallic inclusions and dross, in subsequently-filled molds (e.g. molds #2-#4) of the sequence and resultant reduction in scrapped cast articles. As is known, non-metallic inclusions can be detrimental to the mechanical properties of the articles solidified in the molds, such as for example reducing the tensile, rupture and fatigue life of the cast articles in service. In aerospace applications, reduced levels of non-metallic inclusions in the metal or alloy articles solidified in molds #2, #3, #4, and so on are highly desirable and/or oftentimes required by the end user of articles, such as turbine engine or airframe manufacturers. The cast article produced in mold #1can be discarded, reworked, or remelted to recover the metal or alloy.

Referring toFIG. 1D, another illustrative embodiment of the invention envisions disposing the article-forming molds20above the inclined melt supply member10dto communicate in flow relation with melt supply passage10e. As shown inFIG. 1D, the melt supply member10dis inclined at an acute angle relative to horizontal.

InFIGS. 1A through 1Das well as in the remainingFIGS. 2 through 14, like reference numerals are used to designate like or similar features or elements.

Referring toFIG. 2, still another illustrative embodiment of the invention involves connecting the article-forming molds20in series sequence in melt flow communication to a melt supply member10dhaving a melt supply passage10ethat includes variable cross-sections (constrictions)10fthat decrease in cross-sectional area in a direction away from the mold cup. The molds20are communicated in melt flow communication via a mold gate passage20gto respective cross-sections (constrictions)10fof the melt supply passage10esuch that the molds are filled sequentially during casting. That is, the molten metal or alloy M flows into mold #1to completely fill it first, then the flows into mold #2to completely fill it second, and finally flows into mold #3to completely fill it last. Although the melt supply member10dis shown as being horizontal inFIG. 2, it can be inclined relative to horizontal as well.

Referring toFIG. 3, a further illustrative embodiment of the invention involves connecting the article-forming molds20in melt flow communication to a gating spoke10sextending from an upstanding melt supply member10d. The melt supply member10dincludes an upstanding melt supply passage10esuch that the molds20are supplied with molten metal or alloy generally horizontally through respective mold ingate passages20g. The molds are filled in sequence by the molten metal or alloy M flowing into mold #1to completely fill it first, then flowing into mold #2to completely fill it second, then flowing into mold #3to completely fill it third, and finally flows into mold #4to completely fill it last. The molten metal or alloy is poured into mold cup10aand flows by gravity downwardly through the down sprue10band then upwardly by metallostatic pressure and gravity through the melt supply passage10einto the molds. The molds20can be oriented horizontally as shown or angled downwardly with the tip regions20tlower than the root regions20r.

Referring toFIG. 4, a still further illustrative embodiment of the invention involves providing metal or alloy melt in a melt-containing mold cup10aof a mold assembly and supplying the melt from the mold cup10ato a melt supply spoke10sof the mold assembly for flow to a plurality of molds20, the first of which is connected in direct melt flow communication to the passage of the melt supply spoke10sfrom the mold cup and the subsequent of which are connected in series arrangement one after another by respective melt supply members10deach connected between a top of a preceding mold to the top of the next mold in the series. In particular, this embodiment involves connecting the article-forming molds20in sequence by respective sequential melt supply passages10eof the melt supply members10dconnected to mold ingate passages20gas shown to provide a cascading top-to-top flow of molten metal or alloy from the top of the first mold #1in the sequence to the top of the second mold #2in the sequence to the top of the third mold #3in the sequence and so on such that the molds are filled sequentially during casting. The series of sequential melt supply members10dand interconnected molds20can extend in any pattern relative to the mold cup10aor down sprue10b. For example, the series of sequential melt supply members10dand interconnected molds20can extend in a linear manner or in circular or other arcuate manner relative to the mold cup and/or down sprue.

Referring toFIG. 4, the cascading flow of the molten metal or alloy is provided from the top of the mold cavity20cof each mold20to the top of the mold cavity of the next mold20in the sequence such that there is no melt flow through the mold cavity20cof the preceding mold in the series directly to the next mold in the series and, instead, the melt flow dead-ends in each mold cavity20cof the series of the molds20. In particular, a first melt supply member10dhaving passage10eis provided to supply the molten metal or alloy to the top ingate passage20gof the mold cavity20cof the first-filled mold #1from the pour cup10a(or down sprue) and a second gating member10dis provided to supply the molten metal or alloy from the first filled mold #1to the top of the mold cavity20cof the next mold #2to be filled in the sequence and so on for the next molds.

The molds are filled in sequence by the molten metal or alloy flowing from the mold cup10a(or the down sprue) into mold #1to completely fill it first, then flowing by cascading from mold #1into mold #2to completely fill it second, then flowing by cascading into mold #3to completely fill it third, and flowing into the next mold to completely fill it, and so on until all of the molds are filled with the molten metal or alloy.

Although the sequential melt supply members are shown as arc-shaped melt supply members10d, any suitable shape and cross-sectional size of the melt passage10etherein can be used. For example, the melt supply members10dcan be made of linear and/or curved segments to provide an inverted C-shape or inverted loop shape, or any other shape that provides the cascading flow from the top of the preceding mold to the next mold in the series.

An optional conventional molten metal or alloy filter F, such as for example a reticulated ceramic foam filter or cellular flow-through ceramic filter, can be provided in the passage of the melt supply spoke10sto remove foreign matter, such as dross and non-metallic inclusions, before the melt enters the molds.

FIG. 4Ais a sectional view of an alternative gang mold assembly to that ofFIG. 4having the molds20connected by arc-shaped sequential melt supply members10dhaving passages10ewherein the first mold #1and second mold #2of the series are connected to the melt supply spoke10shaving the melt filter F therein and the subsequent molds #3and so on are connected in top-to-top manner as described forFIG. 4.

The article-forming mold #1shown inFIGS. 4 and 4Aoptionally can be replaced by a faux or false non-article-forming mold of the type described below in connection withFIGS. 5 and 6and designated as mold #0in those figures. By faux or false non-article-forming mold is meant that the mold cavity20cof the non-article-forming mold does not have the shape of the article to be cast in the article-forming molds.

Referring toFIGS. 5 and 6, a mold assembly is shown having a first faux or false non-article-forming mold #0supplied with melt by gating spoke10sin a dead-end flow manner to help collect or trap foreign matter, such as non-metallic inclusions and dross, and subsequent article-forming molds #1-#3and so on connected by sequential melt supply members10din top-to-bottom manner to provide flow of molten metal or alloy from the top each mold to the bottom of the next mold with melt flow through each mold cavity20cin the horizontal or inclined sequence of molds shown inFIGS. 5 and 6, respectively. In each mold cavity20cof molds #1, #2, #3, and so on, the melt flows from bottom to top as a result of the arrangement of the melt supply members10dshown. InFIGS. 5 and 6, the melt flows from the mold cup (not shown) via a passage of the gating spoke10sto the top of the faux or false mold #0. After the faux or false mold #0is completely filled, the melt flows via passage10eof first melt supply member10dfrom the top of mold #1to the bottom of mold #2. The melt flows through the mold cavity20cof mold #2from bottom to top and then via a second melt supply member10dfrom the top of the mold #2to the bottom of the next mold #3and so on. Although faux or false mold #0is shown comprising a non-article-forming mold, the first mold can be configured as an article-forming mold for example as shown inFIG. 4.

FIG. 6differs fromFIG. 5in having the article-forming molds20disposed in series sequence at different elevations relative to one another.

FIG. 7illustrates a gang mold assembly10of another embodiment of the invention having the molds20connected by a respective mold ingate passage20gto a respective sequential horizontal melt supply member10dhaving passage10ein melt flow communication to an upstanding down sprue10bin a manner to provide complete filling of the first mold #1in the sequence before complete filling of the second mold #2in the sequence. The molds are shown connected to the top of each melt supply member10d. The down sprue10breceives melt from the mold cup10a.

FIG. 8illustrates a similar gang mold assembly toFIG. 7of another embodiment of the invention having vertically stacked molds20connected in melt flow communication to one another by a connector passage P between the molds. The molds20are connected in melt flow communication by a respective mold ingate passage20gto a passage10eof respective sequential horizontal melt supply member10dconnected to upstanding down sprue10bin a manner to provide complete filling of the first stacked mold #1in the lower sequence before complete filling of the second stacked mold #2in that sequence and so on for molds #3and #4in the upper sequence.

FIG. 9illustrates a similar gang mold assembly toFIG. 7of another embodiment of the invention wherein the molds20have a respective mold ingate passage20gconnected to the bottom of the passage10eof respective melt supply members10d, which are connected to an upstanding down sprue10bin a manner to provide complete filling of the first mold #1in the sequence before complete filling of the second mold #2in the sequence.

Furthermore, referring toFIGS. 1A-1Dand2, the molds20can be disposed along the length of a linear (straight) melt supply member10dthat extends from the down sprue10bof the gang mold10.

Alternately, referring toFIG. 11, the molds can be disposed along the length of a linear (straight), inclined melt supply members10dthat extend at an acute angle to horizontal from a cross gating spoke10sin an H-shaped pattern. The cross gating spoke10sis connected in melt flow communication to the down sprue10bof the gang mold10to receive molten metal or alloy therefrom and supply the melt to the molds. The invention can be practiced using any suitable pattern of gating members and molds and is not limited to those shown and described herein

For example, the molds alternately can be disposed along the length of an arcuate gating member of the gang mold. For example, referring toFIG. 12, the melt supply member10dmay extend from a generally radial gating spoke10sconnected in melt flow communication to the down sprue10b. The melt supply member10dis shown extending in an upwardly inclined spiral manner about the mold cup10awherein the molds20are connected in melt flow communication to the spiral gating member as shown. The inclined spiral results in filling of the molds20in sequence one after another in the direction of inclination of the spiral.

In the above illustrative embodiments of the invention, the molds20are shown configured to cast equiaxed articles therein. That is, the molten metal or alloy is introduced into the mold cavities20cand solidified in air, vacuum, or protective atmosphere depending on the metal or alloy being cast to provide an equiaxed grain microstructure in the cast article. The invention is not limited to making equiaxed cast articles and can be practiced to make other cast articles including, but not limited to, directionally solidified columnar grain articles, single crystal articles, composite articles, and others.

For example, referring toFIG. 13, an illustrative gang mold for casting single crystal articles is shown comprising a mold cup10a, down sprue10b, gating spoke10s, and sequential gating members10dof the type described above in connection withFIG. 5having passages10efor supplying the molten metal or alloy to the molds20that are configured to cast single crystal articles. The gating spoke10scan branch into two, three or more branch gating spokes wherein each branch gating spoke connects in melt flow relation to a respective series of molds.

InFIG. 13, the molds20each include a grain nucleation chamber21closed off by a chill plate CP to provide unidirectional heat removal from the molten metal or alloy in the nucleation chamber, a crystal selector passage22such as a “pigtail” passage communicated to the nucleation chamber for selecting a single crystal or grain propagating upwardly therein for further propagation in the molten metal or alloy in the mold cavity20cabove the pigtail passage. In lieu of the nucleation chamber21and/or “pigtail” passage, a single crystal seed (not shown) can be placed in the mold to nucleate a single grain or crystal for propagation through the mold cavity20c. Mold #1can be closed at the lower end rather than being communicated to the chill plate as are molds #2-#3and so on. When the articles are cast by directional solidification to produce directionally solidified columnar grain or single crystal articles, practice of the invention provides improved retained melt heat in the mold grain nucleation chamber21to initiate directional solidification.

FIG. 13differs from prior single crystal casting practice wherein molds have been stacked above a melt supply chamber of the ceramic shell mold supplied with melt from a melt supply spoke of a mold pour cup, wherein the melt supply chamber has been located above a grain selector, such as pigtail, and wherein only the lowermost mold has been connected directly in melt flow communication to the melt supply chamber by a mold ingate passage, the remaining molds above the lowermost mold being connected to the next mold by an upstanding connector passage between the molds. Multiple stacks of molds also have been provided above the melt supply chamber wherein only the lowermost mold of each stack has been connected directly in melt flow communication to the melt supply chamber by a mold ingate passage, the remaining molds above the lowermost mold in each stack being connected to the next mold by an upstanding connector passage between the molds such that the lowermost molds are filled concurrently with melt, then the next highest molds are concurrently filled and so on.

Referring toFIG. 14, an illustrative gang mold for casting columnar grain articles is shown comprising a mold cup10a, down sprue10b, gating spoke10sand sequential melt supply members10dof the type described above in connection withFIG. 4having passages10efor supplying the molten metal or alloy to the molds20that are configured to cast columnar grain articles. In particular, the molds20include a grain nucleation chamber21closed off by a chill plate CP to provide unidirectional heat removal from the molten metal or alloy in the nucleation chamber. The mold cavity20cis communicated to the nucleation chamber21so that multiple crystals or grains propagating upwardly in the nucleation chamber21can be propagated in the molten metal or alloy in the mold cavity20cto form a columnar grain article. Mold #1can be closed at the lower end rather than being communicated to the chill plate as are molds #2-#3and so on.

In the above embodiments, after the molten metal or alloy solidifies in the mold cup, down sprue, gating members, and mold cavities20cof the molds20, the mold material can be removed from the metal or alloy casting. The metal or alloy casting comprises the solidified metal or alloy articles formed in mold cavities20cand connected to the solidified gating which is connected to the down sprue and pour cup The mold material can be removed from the casting in a conventional manner by knock-out operation, vibration, abrasive blasting, chemical dissolution/blasting, or other conventional mold removal processes. The solidified metal or alloy article in the first-filled mold (e.g. faux mold #0or mold #1in the figures) can include more non-metallic inclusions present in the molten metal or alloy. The remaining solidified metal or alloy articles formed in the subsequently filled molds (e.g. #2, #3, #4, etc.) can have reduced levels of non-metallic inclusions present therein.

FIG. 10illustrates a gang mold assembly10pursuant to another embodiment of the invention having a mold cup10a, a down sprue10band a generally radial gating spoke10sin melt flow communication. The gating spoke10sextends to a first arcuate melt supply member10dhaving passage10eto which a first plurality of molds20are connected in melt flow communication. The first arcuate melt supply member is connected in melt flow communication to a second arcuate melt supply member10d′ having a passage10e′ to which a second plurality of molds20′ are connected in melt flow communication. The first and second melt supply members are connected in melt flow communication by an arc-shaped melt supply connector member10gin a manner that the first plurality of molds20are completely or partially filled before the second plurality of molds20′. The melt supply members10d,10d′ can be ring shaped or partial rings as shown. Alternately, the melt supply members can be straight or any other configuration. Additional arcuate or straight melt supply members (not shown) can be connected by suitable melt supply connector members (not shown) similar to connector member10g′ to provide a third, fourth, fifth, etc. melt supply members each having respective molds connected in series in melt flow relation thereto.

In practicing the invention, the mold assembly can be cast using a variety of casting processes. For example, the mold assembly can be gravity cast by providing the melt in the mold cup10aand flowing the melt by gravity to the molds20, which can be disposed in air, a vacuum, or a protective atmosphere. Moreover, the mold assembly can be cast with gas pressure applied to the melt residing in the mold cup10ato assist flow to the molds as disclosed for example in U.S. Pat. Nos. 6,019,158 and 6,070,644. Further, the mold assembly can be provided with an exterior glaze layer or coating to reduce mold wall gas permeability, and the melt provided in the mold cup in a vacuum chamber, which is then gas pressurized to assist melt flow to the molds as described in U.S. Pat. No. 6,453,979.

The following Example is offered to further illustrate the invention without limiting the scope thereof.

Example

A ceramic investment shell mold assembly was made to directionally solidify high pressure turbine blades. The mold assembly included a central mold cup into which was poured a commercially available nickel base superalloy (RENE 142) melt under vacuum and superheat of 500 degrees F. The mold cup10aincluded six (6) radially extending melt supply spokes10seach being connected in melt flow communication to a respective one of six (6) respective mold gangs each comprising a first-filled cylindrical faux (non-article-forming) shell mold and ten (10) article-forming (turbine blade-forming) shell molds, which were connected top-to-top in series to one another by arc-shaped melt supply passages in a manner similar toFIG. 4A. The faux mold and the first article-forming mold were connected to each melt supply spoke10sin a manner similar toFIG. 4Awhere the cylindrical faux mold resided in the position shown for mold #1ofFIG. 4Aand the article-forming molds to form turbine blade castings resided in the positions shown for molds #2, #3and so on inFIG. 4A. Each faux mold included a cylindrical cross section mold cavity that communicated at its lower end to the chill plate CP. The article-forming molds and the chill plate were similar to that shown inFIG. 14with the exception that the article-forming molds were arranged in a circular pattern on the chill plate about the mold cup. A conventional melt ceramic filter having 20 ppi (pores per linear inch) was provided in each radially extending melt supply spoke at a location similar to thatFIG. 4A.

Multiple mold assemblies of the type described in the preceding paragraph were cast over time using the sequential filling method of the example to make turbine blade castings. The castings formed in the faux molds were cylindrical in shape and not turbine blade castings. The percentage of turbine blade castings scrapped for inclusion scrap was in the range of about 1.2% to 2.5% for the second through tenth turbine blade castings of each of the series of article-forming molds cast by the sequential filling method of the example. For the first turbine blade casting cast in each of the series of molds by sequential filling, the percentage of castings scrapped for inclusion scrap was about 5%. Thus, the second through tenth turbine blade castings of each of the series cast pursuant to the example exhibited a significantly reduced percentage of castings scrapped as compared to the first turbine blade cast in each series.

Although the invention has been described above with respect to certain embodiments, those skilled in the art will appreciate that the invention is not limited to these embodiments since modifications, changes, and the like can be made therein without departing form the spirit and scope of the invention as set forth in the appended claims.