Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/02—Use of electric or magnetic effects
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
  • B22D17/007—Semi-solid pressure die casting

Definitions

• 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.
• MMC metal- matrix composite
• 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 WOO 1/21343 (Fan) and U.S. Patents 5,501,266 (Wang et al) and 6,065,526 (Kono).
• U.S. Patent 4,321,958 discloses an electromagnetic inductor that directly provides a helically moving field within a mold.
• U.S. Patent 4,434,837 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. Patent 4,877,079 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. Patent 5,219,018 discloses the use of multiple annular coils arrayed along the length of and coaxially with a mold.
• AC polyphase alternating current
• a moving field is produced that tends to move molten and/or semi-molten metal in the mold linearly along its length.
• a toroidal circulation is set up, centered on the mold's longitudinal axis.
• U.S. Patent 5, 135,564 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. Patent 6,637,927 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.
• a rotating field as in a polyphase induction motor
• 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.
• U.S. Patent 2,786,416 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. Patent 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. Patent 4,212,592 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. Patent 4,988,267 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.
• an apparatus for mixing, agitating and transporting a slurry of molten or semi-solid metal-containing material or a metal-matrix composite material including:
• 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;
• 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.
• 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.
• 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.
• the material may be a titanium matrix composite such as CermeTi ® developed by Dynamet Technology Inc. of Burlington, Massachusetts, 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 thixo forging 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
• 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).
• MMC metal-matrix composite
• 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.
• a slurry may also be known as a semi-solid metal (SSM). This term is here to be understood as including an MMC.
• FIGURE 1 is a flow chart comparing rheocasting and thixocasting processes
• FIGURE 2 is a flow chart showing alternative steps in practicing these processes
• FIGURE 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;
• FIGURE 4 is a cross-sectional view of the duct shown in Figure 3 taken at the station "4-4" in Figure 3;
• FIGURE 5 is a developed view of a portion of an inner surface of a wall of the duct shown in Figures 3 and 4;
• FIGURE 6 is a view of the same type as Figure 5, showing a possible modification
• FIGURE 7 is a longitudinal cross sectional view of a duct comprising an alternate embodiment of an apparatus constructed according to the invention
• FIGURE 8 is a longitudinal cross section of a closed cylindrical vessel comprising a further alternate embodiment of an apparatus constructed according to the invention
• FIGURE 9 is a schematic diagram of an application of a device made according to the invention.
• FIGURE 10 is a schematic diagram of a further application of a device made according to the invention.
• FIGURE 11 is a schematic diagram of an alternate application of a device made according to the invention.
• FIGURE 12 is a schematic diagram of a further alternate application of a device made according to the invention.
• FIGURE 13 is a schematic diagram of a still further alternate application of a device made according to the invention.
• Figures 1 and 2 are process flow charts illustrating potential applications for the invention disclosed herein.
• Figure 1 shows steps in the processes known as “thixocasting” and “rheocasting”, as described and distinguished from each other in, for example, U.S. Patent 6,432,160, which is incorporated here by reference.
• a metal alloy is first melted in known manner (Stepl), often under a controlled atmosphere. At this point, the alloy liquid is at a temperature above its liquidus temperature.
• step 2 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 semisolid slurry is produced.
• Such non-dendritic forms of metal alloys, and their practical application to casting, are described in U.S. Patent 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.
• step 3 (“transfer"), the slurry is ejected from the container in which it has been so conditioned.
• 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.
• the slurry ejected at step 3 is cast almost immediately.
• the casting process can take two forms, distinguished in Figure 1.
• 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.
• 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.
• FIG 2 is similar to Figure 1 , save for the inclusion of a mixing step (shown as step Ia) in which an additive material (such as fly ash) is mixed with the molten alloy to produce an MMC.
• step Ia a mixing step
• an additive material such as fly ash
• the remaining steps are numbered the same as corresponding steps of Figure 1.
• 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).
• 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.
• the term also includes products that are identified as pozzolan, fly ash, Class F fly ash, and Class C fly ash.
• 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.
• the present invention has as a first objective the provision of apparatus capable of carrying out steps Ia 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.
• 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.
• 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 thixo tropic slurries.
• Figure 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.
• Figure 4 is a cross-sectional view of the apparatus 2 shown in Figure 3 taken on a plane normal to the axis 3 at the station "4-4" in Figure 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.
• Flights 7 and 8 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.
• a fluid coolant jacket 9 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.
• a three-phase AC supply may be connected to coils 10, with one phase connected to each of the sets R, Y and B.
• 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 Figure 3 show the general direction of this helical flow. That flow, under magnetic influence, has an axial and centrifugal (in combination, a helical) component.
• the apparatus 2 shown in Figures 3 and 4 can be used for pumping a slurry and for providing:
• Another coil arrangement that may be used is one that provides a helically traveling field.
• a coil arrangement is disclosed in U.S. Patent 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.
• 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.
• apparatus 2 has two screw flights 7 and 8 only, of constant pitch, and of a particular helix angle.
• variations can be made to the design of the flights.
• 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.
• Figures 5 and 6 are developed views of the inner surface 15 of wall 5 where it is secured to the screw flights 7 and 8.
• Figure 5 is a developed view of the inner surface 15 of wall 5 where it is secured to the screw flights 7 and 8.
• wall 5 to be cut lengthwise at the circumferential position indicated as "Q" in Figure 4, then rolled flat.
• 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 Figures 3 and 5.
• Figure 6 is constructed in the same way as Figure 5 and is intended to be directly comparable.
• Flights 18 and 19 are identical to flights 7 and 8 of Figures 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.
• a duct could have a larger number of axially arrayed sets of flights than the two sets (18/19 and 20 /21) shown in Figure 6.
• flights 7 and 8 are shown that extend completely between the duct wall and central body.
• 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.
• the gap is expected to enhance shearing/agitation of the contained metal or slurry.
• openings holes, slots or the like
• shaped free edges of flights may be provided to enhance mixing and shearing/agitation of the contained slurry.
• 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.
• 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 Figure 7.
• Figure 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.
• 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 Figure 7.
• 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.
• the metal or metal-based material that forms at least a part of the slurry includes aluminum or magnesium or alloys thereof.
• Figure 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. Patent 6,637,927 ' .
• coils for impressing a magnetic field have been omitted from Figure 8.
• FIG 9 shows in simplified schematic manner an illustrative way that the apparatus of the invention can be used.
• a duct 52 formed at least in part by a device 53 according to the invention (as shown in Figures 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.
• 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 Figure 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.
• Figure 10 shows in simplified schematic manner a further possible use of a device 60 according to the invention.
• a thixotropic slurry or simply a fully molten metal
• 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.
• the pressure to be developed by device is required to be higher and this would be reflected in variations to its design.
• other components that may be required according to the details of the application are not shown in this simplified diagram.
• 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.
• 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.
• 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. Patents 5,501,266 and 6,065,526.
• Figure 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 Figure 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.
• 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).
• Figure 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 hi 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 Figure 3, possibly with a modification such as that shown in Figure 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.
• 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.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Continuous Casting (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Furnace Details (AREA)

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• 2005
  • 2005-02-10 EP EP05713206A patent/EP1846180A1/de not_active Withdrawn
  • 2005-02-10 WO PCT/US2005/004103 patent/WO2006085875A1/en active Application Filing
  • 2005-02-10 BR BRPI0519975-1A patent/BRPI0519975A2/pt not_active IP Right Cessation
  • 2005-02-10 CN CNA2005800494180A patent/CN101166594A/zh active Pending
  • 2005-02-10 US US11/815,957 patent/US20100192727A1/en not_active Abandoned
  • 2005-02-10 CA CA002597676A patent/CA2597676A1/en not_active Abandoned
  • 2005-02-10 AU AU2005327268A patent/AU2005327268A1/en not_active Abandoned
  • 2005-02-10 MX MX2007009599A patent/MX2007009599A/es not_active Application Discontinuation

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