APPARATUS AND METHOD FOR MIXING, AGITATING AND TRANSPORTING MOLTEN OR SEMI-SOLID METAL-MATRIX COMPOSITE MATERIALS

Abstract

An apparatus 2 and method for mixing, agitating and transporting a slurry of molten or semi-solid metal or metal-matrix composite material including a casing 1 for containment of the slurry. An electrical conductor means 10 applies to the slurry a moving magnetic field to induce flow thereof. A component 7,8 is secured and located within the casing to modify the flow pattern of the slurry induced by the moving magnetic field.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention described herein relates to a method and apparatus for processing and pumping a slurry of molten or semi-solid metals or alloys or metal-matrix composite (MMC) materials, and to the blending of additives for the preparation of MMCs, all with particular reference to die casting and like processes.

2. Background Art

Many consumer items and much industrial equipment contain components manufactured by some form of casting, such as sand casting, die casting, so-called thixocasting and the like. Such processes involve the solidification in a mold or die of a molten or semi-molten pure metal, metal alloy or metal-containing composite material.

Various approaches have been taken to providing the agitation required to form and maintain thixotropic slurries. In the “Thixomat” process described in U.S. Pat. No. 5,040,589 (Bradley et al), shearing and agitation of a slurry is by way of rotation of a rotating screw auger that fits closely in a cylindrical casing or barrel. The auger also transports the slurry to a nozzle end of the barrel and finally forces slurry accumulated there into the die or mold. Both the achievement of adequately high shear rates to break down dendritic particle formations and the use of the auger to eject the slurry into the die dictate close fitting of the auger in the barrel. Thixomat machines are therefore subject to substantial wear of the auger. Attack by the slurry (e.g. where it contains aluminum) can exacerbate the wear problem. See also the similar machines disclosed in PCT publication WO01/21343 (Fan) and U.S. Pat. No. 5,501,266 (Wang et al) and U.S. Pat. No. 6,065,526 (Kono).

Although mechanical stirring as a means of shearing the slurry continued to be developed (see for example U.S. Pat. No. 4,771,818 (Kenney) U.S. Pat. No. 5,186,236 (Gabathuler), and U.S. Pat. No. 6,470,955 (Richard et al)), stirring by moving electromagnetic fields has also been introduced.

U.S. Pat. No. 4,321,958 (Delassus) discloses an electromagnetic inductor that directly provides a helically moving field within a mold.

U.S. Pat. No. 4,434,837 (Winter et al) discloses the use of a stator similar to that of an induction motor to generate a rotating field which is used to stir the slurry in a mold about the axis around which the field rotates.

U.S. Pat. No. 4,877,079 (Long et al) discloses a “counterflow” electromagnetic stirring arrangement for continuous casting molds, using two groups of coils arranged and excited to produce two separate field patterns. The net result is patterns of induced metal movement within the mold that are more complex than for example those produced by simple rotating fields. Improved shearing and mixing movements are claimed.

U.S. Pat. No. 5,219,018 (Meyer) discloses the use of multiple annular coils arrayed along the length of and coaxially with a mold. When suitably connected to polyphase alternating current (AC), a moving field is produced that tends to move molten and/or semi-molten metal in the mold linearly along its length. In practice, a toroidal circulation is set up, centered on the mold's longitudinal axis.

U.S. Pat. No. 5,135,564 (Fujikawa et al) discloses a cylindrical tank in which molten metal is cooled and agitated to produce a non-dendritic slurry. The agitation is provided by rotation under the influence of a rotating magnetic field (as in a polyphase induction motor stator). A smooth, generally cylindrical core member is introduced into the container and is preferably coaxial with it. The slurry is contained in the annular space between the inner container wall and the core. The core eliminates a “dead zone” of limited agitation at the center of the container, and enhances the uniformity of agitation.

U.S. Pat. No. 6,637,927 (Lu, Norville et al) discloses a stirring arrangement in which a container is surrounded by a stack of coils that generate both a rotating field (as in a polyphase induction motor) and a lengthwise-moving field. The net result of these influences is that metal in the container and adjacent to its wall moves in a helical path and is recirculated along an approximately linear path inside the helix.

The use of electromagnetic induction is also known in pumps for molten metals. But such pumps are intended to provide smooth flow, not turbulent or mixing flow.

U.S. Pat. No. 2,786,416 (Fenemore) discloses a pump in which multiple helical interleaved windings are provided around an annular duct containing liquid metal and connected to a polyphase AC supply to provide a helical moving field. See also U.S. Pat. No. 3,885,890 (Davidson), where coils are provided in a casing at the center of an annular duct to provide a helical field. Flow straightening vanes or baffles may be provided in each case.

U.S. Pat. No. 4,212,592 (Olich) discloses a pump in which a rotating field is applied to an annular duct coaxial with the axis of rotation of the field and induces flow of metal in the duct. Flow straightening vanes are provided in the duct.

U.S. Pat. No. 4,988,267 (Yamada) discloses a pump specifically for supplying molten metal to the injection sleeve of a casting machine. A coil is provided around a duct in which metal is to be pumped to urge the metal axially along the duct. All of these pumps have an annular duct for the molten metal with a ferromagnetic core provided in a protective enclosure concentrically with the annulus.

The as-granted published specification of each of the above patents is hereby incorporated in its entirety by reference.

SUMMARY OF THE INVENTION

According to the present invention in one aspect there is provided an apparatus for mixing, agitating and transporting a slurry of molten or semi-solid metal-containing material or a metal-matrix composite material (collectively “slurry”), including:

a casing for containing the slurry;

at least one electrical conductor means in magnetic communication with the slurry, the electrical conductor means creating a moving magnetic field to induce flow of the slurry in the casing; and

at least one shaped (preferably rigid) component secured and located within the casing that modifies the flow pattern of the slurry induced by the moving magnetic field.

The casing may be or include a duct having an inlet and an outlet, the slurry flowing from the inlet to the outlet. The casing may be or include a casing or container within which the slurry flows under the influence of the moving magnetic field.

The at least one electrical conductor means comprises a set of windings connectable to a supply of alternating current.

Optionally, the casing is at least partially surrounded by a fluid coolant jacket through which a fluid coolant can be circulated to transfer heat between the metal-matrix metal or metal-matrix composite material within the casing and the coolant in the jacket.

The component preferably is one or more helical screw flights. The casing and the helical screw flights define at least one helical conduit for the flow of the slurry. Optionally, the helical conduit includes at least one segment inclined to a direction of induced movement of the slurry contained therein.

The casing and/or the component may be formed at least in part of titanium or a material including titanium. It is believed that the use of titanium or titanium-containing materials may be particularly advantageous. For example the material may be a titanium matrix composite such as CermeTi® developed by Dynamet Technology Inc. of Burlington, Mass., USA. Ceramic or ceramic-containing materials may also be suitable for use in parts or on the surfaces of the casing and/or the component(s) that are in contact with the slurry contained in the casing.

The invention in a further aspect provides a system for casting a slurry in a die or mold. The apparatus disclosed above transports the slurry directly into the die or mold of a casting or thixoforging machine, or directly into the shot sleeve of a die casting machine.

The invention in a further aspect provides a method for transporting and controlling the state of a slurry, including the steps of

placing the slurry in a casing;

applying to the slurry a moving magnetic field by at least one electrical conductor means to induce flow of the slurry in the casing; and

providing at least one component secured to and located within the casing that modifies the flow of the slurry. For example, flow may be induced and the flow pattern modified to control, prevent or limit the growth of dendritic solid particles within the slurry. The temperature of the slurry within the casing may be controlled by passing a fluid coolant through a coolant jacket surrounding the casing.

The invention in a still further aspect provides a method for incorporating an additive material into the slurry to produce a metal-matrix composite (MMC).

The invention disclosed herein thus relates to the manufacture of components from metals (including metal alloys) and MMCs in which a die is used and the material entering the die is in the form of a thixotropic slurry. Such a slurry may also be known as a semi-solid metal (SSM). This term is here to be understood as including an MMC.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart comparing rheocasting and thixocasting processes;

FIG. 2 is a flow chart showing alternative steps in practicing these processes;

FIG. 3 is a cross-sectional view of a duct comprising apparatus according to the invention, the section being taken on a plane that includes a central longitudinal axis of the duct;

FIG. 4 is a cross-sectional view of the duct shown in FIG. 3 taken at the station “4-4” in FIG. 3;

FIG. 5 is a developed view of a portion of an inner surface of a wall of the duct shown in FIGS. 3 and 4;

FIG. 6 is a view of the same type as FIG. 5, showing a possible modification;

FIG. 7 is a longitudinal cross sectional view of a duct comprising an alternate embodiment of an apparatus constructed according to the invention;

FIG. 8 is a longitudinal cross section of a closed cylindrical vessel comprising a further alternate embodiment of an apparatus constructed according to the invention;

FIG. 9 is a schematic diagram of an application of a device made according to the invention;

FIG. 10 is a schematic diagram of a further application of a device made according to the invention;

FIG. 11 is a schematic diagram of an alternate application of a device made according to the invention;

FIG. 12 is a schematic diagram of a further alternate application of a device made according to the invention; and

FIG. 13 is a schematic diagram of a still further alternate application of a device made according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIGS. 1 and 2 are process flow charts illustrating potential applications for the invention disclosed herein. FIG. 1 shows steps in the processes known as “thixocasting” and “rheocasting”, as described and distinguished from each other in, for example, U.S. Pat. No. 6,432,160, which is incorporated here by reference. In each of these processes, a metal alloy is first melted in known manner (Step 1), often under a controlled atmosphere. At this point, the alloy liquid is at a temperature above its liquidus temperature.

In step 2 (“condition and hold”), the melt is cooled below its liquidus temperature and above its solidus temperature and vigorously agitated. Due to cooling, dendritic solid particles begin to nucleate and grow. In the absence of sufficient agitation of the melt, these would progressively link, with the mixture progressively increasing in viscosity and in due course solidifying. The effect of agitation is to modify the microstructure of the solidifying alloy, by causing the dendritic particles to be modified into discrete degenerate dendritic particles of approximately spheroidal form. Viscosity increases as the proportion of these particles increases. With sufficient agitation (i.e. shear) and careful control of temperature, which remains between the solidus and liquidus temperatures, a semi-solid slurry is produced. Such non-dendritic forms of metal alloys, and their practical application to casting, are described in U.S. Pat. No. 3,902,544 (Flemings et al), which is incorporated here by reference.

Step 2 typically takes place in a separate container from the container in which the initial melting occurs. The slurry may be held for some time in the container, with its condition maintained. The slurry is thixotropic in that it remains flowable so long as agitation and a suitable temperature are maintained, but loses flowability if agitation stops or the temperature drops below a solidus temperature. In step 3 (“transfer”), the slurry is ejected from the container in which it has been so conditioned.

In thixocasting, the slurry is then solidified into billets (shown as step 4a). These are later re-melted (step 5a) into a slurry form and cast (step 6a). In the rheocasting process, the slurry is not solidified, remelted and then cast, but simply used directly for casting.

In rheocasting, the slurry ejected at step 3 is cast almost immediately. The casting process can take two forms, distinguished in FIG. 1. In one form, transfer/ejection (step 3) is directly into the die, so that the casting step (step 4b) simply amounts to slurry entry into and solidification in the die. In the other form, transfer (step 3) is into an intermediate container such as the injection (shot) sleeve of a cold-chamber type die casting machine. Step 4c has two steps: injection of the slurry into the shot sleeve, and then into the die or mold before solidification.

Essentially the thixocasting and rheocasting processes as to purely metal alloys are applicable to MMCs, including those based on an aluminum alloy and fly ash. See, e.g., U.S. Pat. No. 4,888,054 (Pond Sr.), which is incorporated here by reference. The main difference is that there is a mixing step to be included.

FIG. 2 is similar to FIG. 1, save for the inclusion of a mixing step (shown as step 1a) in which an additive material (such as fly ash) is mixed with the molten alloy to produce an MMC. The remaining steps are numbered the same as corresponding steps of FIG. 1. With MMC materials as with alloys, agitation and (initial) cooling to a temperature between the liquidus and solidus are required to condition the material to a semi-solid slurry of suitable consistency for the casting step(s).

As used herein, the term “fly ash” denotes a by-product of coal combustion. The material is composed primarily of complex aluminosilicate glass, mullite, hematite, magnatite spinel and quartz. A proportion of quartz (crystalline silica) in the fly ash depends on the quartz content of the coal. As used herein, the term also includes products that are identified as pozzolan, fly ash, Class F fly ash, and Class C fly ash. Conventionally, fly ash has been used as supplementary cementitious material for concrete and concrete products. It has also been used in soil stabilization and as a fine filler in asphalt and other products.

Continuing with reference to FIG. 2, the present invention has as a first objective the provision of apparatus capable of carrying out steps 1a and 2, and in addition step 3, at least (in the case of step 3) where transfer is to billet casting equipment or to the shot sleeve of a cold chamber casting machine. Alternatively, the equipment described can be used where ejection (step 3) is directly to a die or mold (i.e. at a comparatively high pressure). An additional objective is to provide improved methods for the preparation, conditioning and use of metals, metal alloys and MMCs as thixotropic slurries.

Referring back to FIG. 1, the invention may also be useful in carrying out steps 2 and 3 with the same comment being made in relation to step 3 as in the preceding paragraph.

FIG. 3 is a cross-sectional view of a duct 1 and apparatus 2 according to one embodiment of the invention. The section is taken on a plane that includes a central longitudinal axis 3 of the duct 1. The duct 1 preferably has a circular cross-section. FIG. 4 is a cross-sectional view of the apparatus 2 shown in FIG. 3 taken on a plane normal to the axis 3 at the station “4-4” in FIG. 3. Secured within and coaxial with the duct 1 is an elongate central body 4. The body 4 and wall 5 of the duct define therebetween a space 6 that in the preferred embodiment is annular. Arranged in the annular space 6 are multiple, preferably one or two interleaved Archimedean screw flights 7 and 8, separated angularly about axis 3 (in the case of two such flights) by 180 degrees. Flights 7 and 8 are fixed to and extend between the wall 5 and the central body 4. Thus they do not rotate within the duct 1 and therefore avoid problems of wear in certain prior art approaches referenced earlier. Yet they redirect axial flow and impart a helical component thereto together with turbulent agitation.

Surrounding the duct 1 is a fluid coolant jacket 9 whereby cooling of a molten slurry or slurry in the duct can be provided. The design of liquid coolant jackets such as jacket 9 for cooling in applications of this sort is itself a sophisticated art. Jacket 9 may contain additional components or be otherwise different from the jacket 9 shown.

Surrounding the duct and water jacket are multiple, preferably three sets of coils 10 of a solenoidal type, labeled (in the embodiment depicted) as R, Y and B. In known manner, a three-phase AC supply may be connected to coils 10, with one phase connected to each of the sets R, Y and B. When the coils are energized, the effect is to create a moving magnetic field that by induction of eddy currents and associated magnetic fields in the duct 1, urges molten metal or slurry in the duct 1 in a lengthwise direction, as represented by the arrow “X”.

Screw flights 7 and 8 prevent unimpeded lengthwise movement of slurry in the space 6, instead forcing the slurry to move in helical paths along the two passages 11 and 12 defined by the flights 7 and 8, the wall 5 and the body 4. Arrows “Y” in FIG. 3 show the general direction of this helical flow. That flow, under magnetic influence, has an axial and centrifugal (in combination, a helical) component.

Within each of the passages 11 and 12, there is a difference between the axial direction in which the impressed field tends to urge the metal or slurry in the generally helical paths it is constrained to follow. Without being limited to any particular theory of the behavior of the apparatus 2, the effect of this is thought to be to superimpose a circulatory flow generally transverse to the main flow (arrows “Y”) within each passage, thus suppressing dendritic growth while enhancing mixing and heat transfer between slurry and the walls of the duct. Arrow “Z” in FIG. 3 represents such a superimposed flow in passage 11. As a result, the slurry is displaced or pumped away from inlet end 13 of the duct 1 towards outlet end 14.

Thus, the apparatus 2 shown in FIGS. 3 and 4 can be used for pumping a slurry and for providing:

(a) the flow shearing and agitation required to limit the formation of dendritically-shaped particles in the material so that they become (or remain) spheroidal degenerated dendritic particles and so that a thixotropic slurry is formed; and

(b) where desired, mixing of the slurry with a solid phase additive (e.g., fly ash), where the requirement is a slurry of an MMC material.

Moreover, the non-rotating nature of screw flights 7, 8 is believed to limit the wear that they undergo. It is also noted for the apparatus 2 that the paths followed by the metal or slurry between inlet 13 and outlet 14 are in general longer than would be the case with a purely axial flow arrangement, so that the flow path length available for mixing and agitation is greater than in an axial flow duct of the same length, while the coils 10 and cooling jacket 9 can be comparatively short.

Alternate Embodiments and Process Steps

A number of variations are possible to enhance and/or modify these effects to suit particular conditions and applications. Some are described in paragraphs (a) to (j) below.

As disclosed in the patents mentioned above, and as known in the art, different coil arrangements have been developed that may be coupled with this invention. For example, at least alternatives (a) to (e) following can be applied individually or in suitable combinations:

(a) Instead of a set of solenoidal coils 10 as shown in FIGS. 3 and 4, a stator ring arrangement (not shown) could be provided, akin to a polyphase induction motor, the duct 1 passing through the stator ring. The rotating magnetic field thus applied to the slurry tends to urge it to rotate about the duct axis 3. However, the effect of the screw flights 7 and 8 is that such movement causes axial movement as well. Further, it is believed that superimposed flows will also be caused in the apparatus 2 shown in FIGS. 3 and 4.

(b) Another coil arrangement that may be used (not shown) is one that provides a helically traveling field. Such a coil arrangement is disclosed in U.S. Pat. No. 2,786,416 for example. If the helix angle and direction of the screw flights 7 and 8 match those of the traveling impressed magnetic field, the effect is to urge the metal or slurry along the between-flight flow passages 11 and 12 with, it is thought, a comparatively low level of superimposed circulatory flow and mixing. However, if there is a mismatch between the screw flight and field helix angles, it is believed that the relative proportions of firstly the flow along the helical flow passages 11 and 12 and secondly the superimposed flows within those paths will be different, and therefore promote turbulence. Suitable degrees of mismatch can be chosen.

(c) Different types of coils may be used in combination. For example it is possible to use a longitudinally arranged “stack” of solenoidal coils (such as the coils 10 in FIG. 3) in combination with one or more stator-ring arrangements (not shown) as discussed above at (a). In this way, one can provide a range of degrees and forms of mixing, agitation and pumping along the length of apparatus 2.

(d) The coils are excited in various ways. For example, by varying the line frequency, it is thought that both the speed of movement of the slurry and the degree of penetration of the field (rotating or solenoidal for example) into the slurry can be varied, with consequent changes in the flow patterns, and hence in pumping and mixing. Another possibility is to use not a steady AC current, but pulsed DC current.

(e) It may be possible in some arrangements to provide coils (not shown) inside the central body 4 of the apparatus shown in FIGS. 3 and 4, either instead of or in addition to external coils such as coils 7 and 8. For example, U.S. Pat. No. 3,885,890 discloses an arrangement of coils that can provide a helically traveling field and that can be mounted in a body inside an annular flow space. By combining different types of coils, e.g. helical in the central body and solenoidal outside, one can produce a wide range of shear intensities and induced flow paths and so affect the mixing process.

(f) In FIGS. 3 and 4, apparatus 2 has two screw flights 7 and 8 only, of constant pitch, and of a particular helix angle. However, variations can be made to the design of the flights. For example, the number and helix angle of the flights can be varied and the pitch can be changed along the duct length. This will affect the turbulence characteristics that can be developed, for example. It may also be desirable to deliberately mismatch the pitch of the screw flights and the longitudinal spacing of coils to promote flow variation and mixing along the duct length. (This is not shown in FIG. 3, where there is an integral number of coils per flight pitch length.)

It is also possible to provide interruptions to the screw flights. One embodiment is shown in FIGS. 5 and 6. FIG. 5, provided for reference, is a developed view of the inner surface 15 of wall 5 where it is secured to the screw flights 7 and 8. To understand FIG. 5, imagine wall 5 to be cut lengthwise at the circumferential position indicated as “Q” in FIG. 4, then rolled flat. In FIG. 5 screw flights 7 and 8 are shown where they are secured to surface 15. Leading edges 16 and 17 of screw flights 7 and 8 are marked in FIGS. 3 and 5. FIG. 6 is constructed in the same way as FIG. 5 and is intended to be directly comparable. In the flight arrangement of FIG. 6, there are four screw flights 18, 19, 20 and 21. Flights 18 and 19 are identical to flights 7 and 8 of FIGS. 3, 4 and 5 except that they are shorter, extending lengthwise only in section 22 of the duct 1. After a short lengthwise gap 23, flights 20 and 21 begin and extend along section 24 of the duct 1. Their helix angle “T” is shown as equal in magnitude to that of flights 18 and 19 but flights 20 and 21 are of opposite hand to flights 18 and 19 and their leading edges 25 and 26 are circumferentially displaced from trailing edges 27 and 28 of flights 18 and 19.

The effect of this arrangement, when used with a set of solenoidal type coils (like the set of coils 10) arranged to urge contained metal or slurry in the axial direction of the duct (shown by arrow “P” in FIG. 6) is that within flight groups 18/19 and 20/21 there is a component of force in the axial direction. The metal or slurry moves along the duct 1, but there is or should be substantially improved shearing agitation and mixing, especially in the region between firstly flights 18 and 19 and secondly flights 20 and 21.

It will be recognized that other flight arrangements can be conceived to enhance mixing and shearing/agitation of the contained metal or slurry. For example, a duct could have a larger number of axially arrayed sets of flights than the two sets (18/19 and 20/21) shown in FIG. 6.

(g) In FIGS. 3 and 4, flights 7 and 8 are shown that extend completely between the duct wall and central body. However, a further possibility is to provide for flights (not shown) that either are secured to the central body and extend only part way outwards to wall, leaving a gap, or are secured to the wall and extend inwards part way to the central body. In each case, the gap is expected to enhance shearing/agitation of the contained metal or slurry. More generally, openings (holes, slots or the like) or shaped free edges of flights (where the flight in question is not secured to a central body or wall) may be provided to enhance mixing and shearing/agitation of the contained slurry.

Note that because movement of the metal or slurry in the duct is driven by an externally applied moving magnetic field, gaps between the flights and the duct (or central body) boundaries do not need to be kept as small as in a case where the flights are mechanically rotated to provide such movements. Thus it is believed that wear may be reduced. It is possible also to modify the casing and/or flight shape to change the cross-sectional shape of the flow conduits.

(h) In alternate embodiments, one can secure in any of the conduits through which the contained material flows, means for turbulating, such as bodies or structures other than flights, which themselves introduce turbulence or shearing or other disturbance to the flow past them to enhance mixing and/or agitation.

(i) Optionally, the central body 4 could be made of different diameter, or its diameter could vary in a lengthwise direction. It could contain a ferromagnetic (or other) material or component suitable to modify the magnetic flux pattern in the annular space 6 between the central body 4 and the duct wall 5. Means could be provided in the central body 4 for cooling (or heating) its external surface. The central body 4 could even be omitted altogether as shown in FIG. 7. FIG. 7 shows in longitudinal cross-sectional view, a duct 30 having helical flights 31 extending inwardly from an inner surface 32 of the duct wall but leaving a central space 33. If there is no flow in the duct 30 (for example if it is a duct leading slurry to a casting machine and the machine is between shots) agitation and circulation of the slurry in the duct 30 can be maintained by movement through the flights 31 with recirculation through space 33, as shown by arrows 34. Shearing/agitation and mixing take place between the flights and on the cylindrical surface dividing space 33 from the flights' edges 35. The necessary coils for impressing a magnetic field are omitted from FIG. 7.

(j) The specific chemistry of the slurry or metal contained in the duct is not essential to the invention, provided it includes material that is susceptible to magnetic influence. Preferably, however, the metal or metal-based material that forms at least a part of the slurry includes aluminum or magnesium or alloys thereof.

FIG. 8 shows a closed vessel 40 in which screw flights 41 are provided on a wall 42 to promote a circulating flow as shown by the arrows 43, and agitation. The flow is believed to be similar to that induced by different means in U.S. Pat. No. 6,637,927. For clarity, coils for impressing a magnetic field have been omitted from FIG. 8.

Other Embodiments and Methods

FIG. 9 shows in simplified schematic manner an illustrative way that the apparatus of the invention can be used. From a reservoir 50 containing a thixotropic slurry 51 (or simply a fully molten metal or metal alloy) a duct 52 formed at least in part by a device 53 according to the invention (as shown in FIGS. 3 and 4 for example) leads to an outlet 54. The outlet 54 directs the metal or slurry into the shot sleeve 55 of a casting machine 56, from which in known manner it can be injected by a plunger 57 into a die 58. Here, the device 53 is acting as a pump, and is actuated when required, once per casting cycle, to deliver metal or slurry 51 to the casting machine 56. No flow control valves, heating jackets, or other equipment are shown in FIG. 9, but it is to be understood that these and other components would be provided as required, in known manner.

A similar application (not shown) is to use a device similar to device 53 to pump SSM to a position between the die halves of a thixoforging machine.

FIG. 10 shows in simplified schematic manner a further possible use of a device 60 according to the invention. From a reservoir 61 containing a thixotropic slurry (or simply a fully molten metal) 62 a duct 63 formed at least in part by device 60 leads to a nozzle 64. Slurry 62 passes from the nozzle 64 directly into a die 65. By contrast with the application shown in FIG. 9, in this case the pressure to be developed by device is required to be higher and this would be reflected in variations to its design. As before, other components that may be required according to the details of the application are not shown in this simplified diagram.

In a similar application (not shown) to that shown in FIG. 10, slurry could be directed to an upstream side of an extrusion die, the device providing the necessary pressure and continuous or semi-continuous volume flow for extruding the material.

A further application of devices according to the invention is to mix molten metals with particulate additives and to condition the mixture to form a slurry and maintain it in a suitable condition for subsequent casting. For example, FIG. 11 shows schematically an apparatus 69 having a duct 70 including several devices according to the invention 71, 72 and 73 (in any of the suitable forms disclosed above) and an input end 74 that communicates with a container 75 of molten metal 76 and a container 77 of a particulate additive 78. The molten metal 76 and additive 78 may be (for example) an aluminum- or magnesium-based alloy and fly ash (or other additive material) respectively, being constituents of an MMC material.

In this application, devices 71-73 carry out three functions, namely: combining of the metal 76 and the additive 78; providing agitation during cooling of the mixture as required for the formation of a non-dendritic thixotropic slurry; and transportation of the mixture to an outlet end 79 of the duct 70 from which the slurry can be directed to a further processing station as required (e.g. a casting or thixoforging machine).

Three devices 71-73 are shown to emphasize the fact that different operating characteristics may be found desirable at different points along the length of duct. However, this is not intended to imply that three are required or that each carries out one defined function—each may to a different degree contribute several of the functions of transporting, mixing and agitating. The individual application will determine the number and all parameters of the devices in question.

Apparatus 69 is a “once through” apparatus, in that metal and additive pass through once and a slurry of specified properties emerges from the outlet, ready for use “on demand” or for further processing. Apparatus 69 could be a substitute for example for the augers and barrels of machines of the types shown in U.S. Pat. Nos. 5,501,266 and 6,065,526.

Although not shown, it would be possible as variation to devices such as 53, 60 and 69 to provide for electromagnetic induction-melting of the metal or alloy itself in known manner. This raises the further possibility of apparatus in which solid metal is added to one inlet, an additive for mixing with the metal is added to another inlet (if an MMC is to be produced) and a thixotropic slurry is transferred out from an outlet continuously or semi-continuously.

FIG. 12 shows schematically an apparatus 100 that includes a containment vessel 101 and an apparatus 102 for transporting and agitating a molten or semi-molten metal, metal alloy or metal matrix composite material. Apparatus 102 could for example be of the type shown in FIG. 3. Apparatus 102 and vessel 101 are connected by ducts 103 and 104, so that the contents of vessel 101 can be circulated (as shown by arrows “A”) through apparatus 102. Thus the condition of the contents of vessel 101 can be maintained over time (or if required modified) by apparatus 102. Vessel 101 could have separate outlets and inlets for its contents (not shown).

FIG. 13 shows a possible apparatus 105 for the production of a metal matrix composite material and for subsequently holding it and maintaining it in a condition suitable for use in a casting process (e.g. die casting). A containment vessel 106 is provided and apparatus 107 for mixing, transporting and agitating the material passing through it. Apparatus 107 might be for example of the type shown in FIG. 3, possibly with a modification such as that shown in FIG. 6 to enhance mixing. Apparatus 107 is connected to vessel 106 by ducts 109 and 110, so that the contents of vessel 106 can be cyclically transported through apparatus 107, as indicated by arrows “B”. Means 108 are provided for introducing an additive material (e.g. fly ash) into metal or metal alloy passing from vessel 106 through duct 110 into apparatus 107. Apparatus 107 transports, mixes and agitates the material passing through it. Vessel 106 may be fitted with its own heating and cooling means independently of apparatus 107. Over a suitable period, an MMC material can thus be produced, brought to a suitable condition for subsequent use and maintained in that condition as required.

Many possible variations of the invention disclosed herein will be apparent to persons skilled in the art, which do not extend beyond the spirit and scope of the invention. While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.

Claims

1. An apparatus for mixing, agitating and transporting a slurry of one or more molten or semi-solid metals or metal-containing alloys or metal-matrix composite materials including:

a casing for containing the slurry;

at least one electrical conductor means in magnetic communication with the casing and arranged for applying to the slurry a magnetic field to induce slurry flow in the casing; and

at least one component secured and located within the casing that modifies flow of the slurry induced by the magnetic field.

2. The apparatus of claim 1 wherein the casing includes an inlet and an outlet, the slurry flowing from the inlet to the outlet under the influence of the magnetic field.

3. The apparatus of claim 1 wherein the at least one electrical conductor means comprises one or more sets of windings that are connectable to an alternating current.

4. The apparatus of claim 1 further including:

one or more fluid coolant jackets that at least partially lie in thermal communication with the casing so that a fluid coolant can pass therewithin to transfer heat between the slurry and the fluid coolant.

5. The apparatus of claim 1 wherein the at least one component comprises a pair of helical screw flights that define therebetween at least one conduit for guiding the flow of the slurry.

6. The apparatus of claim 5 wherein the at least one conduit includes at least one segment inclined to a direction of movement of the slurry for promoting turbulence.

7. The apparatus of claim 1 wherein the casing is formed at least in part of titanium or a titanium-containing material.

8. The apparatus of claim 1 wherein the at least one component is formed at least in part of titanium or a titanium-containing material.

9. The apparatus of claim 1 wherein the at least one electrical conductor means comprises one or more solenoidal coils.

10. The apparatus of claim 1 wherein the at least one electrical conductor means includes a stator ring through which the casing passes so that a rotating magnetic field is applied to the slurry, thereby urging it to rotate about a longitudinal axis of the casing.

11. The apparatus of claim 1 wherein the at least one electrical conductor means provides a helically traveling field whereby the slurry is urged along one or more passages defined between the at least one component.

12. The apparatus of claim 1 wherein the at least one electrical conductor means comprises one or more solenoidal coils in combination with one or more stator-ring arrangements in order to provide a range of degrees and forms of mixing, agitation and pumping along the length of the casing.

13. The apparatus of claim 1 further including:

means for varying the manner in which the at least one electrical conductor means is excited so that by varying a line frequency, movement of the slurry within the casing and the depth of penetration of the magnetic field can be varied in order to produce changes in the flow pattern and so influence pumping and mixing characteristics.

14. The apparatus of claim 1 further including:

a source of electrical energy connected to the at least one electrical conductor means, the source being selected from the group consisting of an AC current, a pulsed DC current, and combinations thereof.

15. The apparatus of claim 1 wherein the at least one component comprises two screw flights.

16. The apparatus of claim 15 wherein each of the two screw flights has a constant pitch and a common helix angle.

17. The apparatus of claim 1 wherein the at least one component comprises two screw flights, each flight having a helix angle and pitch that can be varied.

18. The apparatus of claim 1 wherein a gap is defined between the at least one component and an inner wall of the casing.

19. The apparatus of claim 1 further including means for turbulating extending from the at least one component which introduce turbulence or shearing or other disturbance to flow past the turbulating means so that mixing and/or agitation are enhanced.

20. The apparatus of claim 1 further including means for modifying a magnetic flux pattern in an annular space between the at least one component and an internal wall of the casing.

21. The apparatus of claim 1 wherein the at least one component extends inwardly from an internal wall of the casing, thereby leaving an axially extending space through which the slurry may flow.

22. A method for casting a slurry, comprising the steps of:

providing the apparatus of claim 1; and

transporting the slurry from an outlet of the casing to a destination selected from the group consisting of a die, a mold of a casting machine, a mold of a thixoforging machine, a shot sleeve of a die casting machine, and combinations thereof.

23. A method for transporting and controlling the state of a slurry including steps of:

placing the slurry in a casing;

providing at least one electrical conductor means in magnetic communication with the slurry so that a moving magnetic field is applied to the slurry to induce flow thereof in the casing; and

providing at least one component secured to and located within the casing so as to modify the flow pattern of the slurry, thereby controlling, preventing or limiting the growth of dendritic particles.

24. The method of claim 23 further including the step of:

passing a fluid coolant through a coolant jacket in thermal communication with the casing so that the temperature of the slurry can be controlled.

25. A method for incorporating an additive material into a slurry of molten or semi-molten metal or metal alloy to produce a metal-matrix composite, including steps of:

introducing the slurry into a casing that includes an internal containment space therefor;

introducing the additive material into the internal containment space for mixture with the slurry;

energizing at least one electrical conductor means in magnetic communication with the slurry, thereby applying to the slurry within the internal containment space a magnetic field to induce flow; and

providing at least one component secured to and located within the casing so as to modify the flow of the slurry induced by the magnetic field and thereby enhancing mixing thereof with the additive material.

26. A method for controlling the growth of dendritic solid particles in a slurry of molten or semi-molten metal or metal alloy or metal-matrix composite material, including steps of:

introducing the slurry into a casing;

energizing at least one electrical conductor means in magnetic communication with the casing so that the slurry is subjected to a moving magnetic field that induces flow; and

providing at least one component secured to and located within the casing to modify the flow of the slurry and thereby retarding dendritic nucleation and growth.