CA1176820A - Apparatus for making thixotropic metal slurries - Google Patents
Apparatus for making thixotropic metal slurriesInfo
- Publication number
- CA1176820A CA1176820A CA000346480A CA346480A CA1176820A CA 1176820 A CA1176820 A CA 1176820A CA 000346480 A CA000346480 A CA 000346480A CA 346480 A CA346480 A CA 346480A CA 1176820 A CA1176820 A CA 1176820A
- Authority
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- Canada
- Prior art keywords
- mold
- molten metal
- slurry
- magnetic field
- containing means
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
- B22D11/114—Treating the molten metal by using agitating or vibrating means
- B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/12—Making non-ferrous alloys by processing in a semi-solid state, e.g. holding the alloy in the solid-liquid phase
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Continuous Casting (AREA)
- Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)
- Manufacture Of Alloys Or Alloy Compounds (AREA)
- Manufacture And Refinement Of Metals (AREA)
- Dental Prosthetics (AREA)
- Molds, Cores, And Manufacturing Methods Thereof (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An apparatus for forming a semi-solid thixotropic slurry. The apparatus includes a duplex mold arrangement for postponing solidification within the mold until the molten metal is within a magnetic field for providing magnetohydrodynamic stirring. The duplex mold includes a first portion of low thermal conductivity and a second portion of high conductivity.
An apparatus for forming a semi-solid thixotropic slurry. The apparatus includes a duplex mold arrangement for postponing solidification within the mold until the molten metal is within a magnetic field for providing magnetohydrodynamic stirring. The duplex mold includes a first portion of low thermal conductivity and a second portion of high conductivity.
Description
:1~76~3Z~ g o 6 3 -MB
J. Winter et al 2-2-2 BACKGROUND OF THE INVENTION
Thi~ invention relates to an apparatus for forming semi-601id thixotropic alloy slurries for use in application~
such as rheocasting, thixocasting, or thixoforging.
PRIOR ART STATEMENT
The known methods for producing semi-solid thixotropic alloy 61urries include mechanical stirring and inductive electromagnetic stirring. The processes for producing such a slurry with a proper structure require a balance between the ~hear rate imposed by the ~tirring and the solidification rate of the material being cast.
The mechanical stirring approach is be6t exemplified by reference to U.S. Patent Nos. 3,902,544, 3,954,455, 3,94~,650, all to Flemings et al. and 3,936,298 to Mehrabian et al. The mechanical stirring approach i~ al80 described in articles appearing in AFS International Cast Metals Journal, Sept., 1976, pages 11-22, by Flemings et al. and AFS Cast Metals Research Journal, Dec., 1973, pages 167-171, by Fascetta et al. In German OLS 2,707,774 published September 1, 1977 to Feurer et al. the mechanical stirring approach is shown in a ~omewhat different arrangement.
In the mechanical stirring proce6s, the molten metal flows downwardly into an annular space in a cooling and mixing chamber. Here the metal is partially solidified while it is agitated by the rotation of a central mixing rotor to form the desired thixotropic metal slurry for rheocasting. The mechanical stirring approache~ 6uffer from several inherent problems. The annulus formed between the rotor and the mixing chamber walls provides a low volumetric flow rate of thixotropic ,,, ^ .--~l76s~a J. Winter et al 2-2-2 slurry. There are material problems due to the erosion of the rotor. It is difficult to couple mechanical agitation to a continuous casting system.
In the continuous rheocasting processes described in the art the mixing chamber is arranged above a direct chill casting mold. The transfer of the metal from the mixing chamber to the mold can result in oxide entrainment. This is a particularly acute problem when dealing with reactive alloys such as aluminum, which are susceptible to oxidation.
The volumetric flow rates achievable by this approach are inadequate for commercial application.
The slurry is thixotropic, thus requiring high shear rates to effect flow into the continuous casting mold. Using the mechanical approach, one is likely to get flow lines due to interrupted flow and/or discontinuous solidification. The mechanical approach is also limited to producing semi-solid slurries, containing from about 30 to 60~ solids. Lower fractions of solids improve fluidity but enhance undesired coarsening and dentritic growth during completion of solidifi-cation. It is not possible to get significantly higher fractions of solids because the agitator is immersed in the slurry.
In order to overcome the aforenoted problems inductive electromagnetic stirring has been proposed in U.S. Patent 4,229,210 ; to Winter et al entitled "Method for the Preparation of Thix-otropic Slurries". In that patent two electromagnetic stirring techniques are suggested to overcome the limitations of mechanical stirring. Winter et al. use either AC induction or pulsed DC magnetic fields to produce indirect stirring of ~ ' .
~7~2~ 9063-MB
J. Winter et al 2-2-2 the solidifying alloy melt. While the indirect nature of this electromagnetic stirring is an improvement over the mechanical process, there are still limitations imposed by the nature of the stirring technique.
With AC inductive 6tirring, the maximum electromagnetic forces and associated shear are limited to the penetration depth of the induced currents. Accordingly, the section ~ize that can be effectively stirred is limited due to the decay of the induced forces from the periphery to the interior of the melt.
This is particularly aggravated when a solidifying shell i6 present. The inductive electromagnetic stirring process also requires high power consumption and the resistance heating of the stirred metal is significant. The resistance heating in turn increases the required amount of heat extraction for 601idification.
The pulsed DC magnetic field technique is also effective, however, it i6 not as effective as desired because the force field rapidly diverges as the distance from the DC
electrode increases. Accordingly, a complex geometry is required to produce the required high shear rates and fluid flow patterns to insure production of slurry with a proper structure. Large magnetic fields are required for this proce6s and, therefore, the equipment i~ co~tly and very bulky.
The abovenoted Flemings et al. patents make brief mention of the use of electromagnetic stirring as one of many alternative stirring techniques which could be u~ed to produce thixotropic slurrie~. They fail, however, to ~uggest any indication of how to actually carry out such an electromagnetic stirring approach to produce such a slurry. The German patent publication to Feurer et al. 6uggest6 that \ ;~.
~ 2~ 9063-~3 J. Winter et al 2-2-2 it is also po6sible to arrange induction coils on the periphery of the mixing chamber to produce an electromagnetic field 80 a6 to agitate the melt with the aid of the field. However, Feurer et al. doe6 not make it clear whether or not the electromagnetic agitation i6 intended to be in addition to the mechanical agitation or to be a 6ubstitute therefore. In any event, it is clear that Feurer et al. is 6uggesting merely an inductive type elec~romagnetic 6tirring approach.
There i6 a wide body of prior art dealing with electromagnetic stirring techniques applied during the ca6ting of molten metals and alloy6. U.S. Patent No6. 3,268,963 to Mann; 3,995,678 to Zavara6 et al.: 4,030,534 to Ito et al.;
4,040,467 to Alherny et al.: 4,042,007 to Zavaras et al.; and 4,042,008 to Alherny et al., a6 well as an article by Szekely et al. entitled Electromaqneticallv Driven Flows in Metals Processinq, Sept. 1976, Journal of Metal6, are illustrative of the art with respect to casting metals using inductive electromagnetic stirring provided by 6urrounding induction coils.
In order to overcome the disadvantage6 of inductive electromagnetic 6tirring it ha6 been found in accordance with the present invention that electromagnetic 6tirring can be made more effective, with a substantially increased productivity and with a le66 complex application to continuou6 type ca6ting technique6, if a magnetic field which move6 tran6ver6ely of the mold or casting axis such a6 a rotating field i6 utilized.
The use of rotating magnetic fields for 6tirring molten metal during ca6ting i6 know a6 exemplified in U.S. Patent No6.
J. Winter et al 2-2-2 BACKGROUND OF THE INVENTION
Thi~ invention relates to an apparatus for forming semi-601id thixotropic alloy slurries for use in application~
such as rheocasting, thixocasting, or thixoforging.
PRIOR ART STATEMENT
The known methods for producing semi-solid thixotropic alloy 61urries include mechanical stirring and inductive electromagnetic stirring. The processes for producing such a slurry with a proper structure require a balance between the ~hear rate imposed by the ~tirring and the solidification rate of the material being cast.
The mechanical stirring approach is be6t exemplified by reference to U.S. Patent Nos. 3,902,544, 3,954,455, 3,94~,650, all to Flemings et al. and 3,936,298 to Mehrabian et al. The mechanical stirring approach i~ al80 described in articles appearing in AFS International Cast Metals Journal, Sept., 1976, pages 11-22, by Flemings et al. and AFS Cast Metals Research Journal, Dec., 1973, pages 167-171, by Fascetta et al. In German OLS 2,707,774 published September 1, 1977 to Feurer et al. the mechanical stirring approach is shown in a ~omewhat different arrangement.
In the mechanical stirring proce6s, the molten metal flows downwardly into an annular space in a cooling and mixing chamber. Here the metal is partially solidified while it is agitated by the rotation of a central mixing rotor to form the desired thixotropic metal slurry for rheocasting. The mechanical stirring approache~ 6uffer from several inherent problems. The annulus formed between the rotor and the mixing chamber walls provides a low volumetric flow rate of thixotropic ,,, ^ .--~l76s~a J. Winter et al 2-2-2 slurry. There are material problems due to the erosion of the rotor. It is difficult to couple mechanical agitation to a continuous casting system.
In the continuous rheocasting processes described in the art the mixing chamber is arranged above a direct chill casting mold. The transfer of the metal from the mixing chamber to the mold can result in oxide entrainment. This is a particularly acute problem when dealing with reactive alloys such as aluminum, which are susceptible to oxidation.
The volumetric flow rates achievable by this approach are inadequate for commercial application.
The slurry is thixotropic, thus requiring high shear rates to effect flow into the continuous casting mold. Using the mechanical approach, one is likely to get flow lines due to interrupted flow and/or discontinuous solidification. The mechanical approach is also limited to producing semi-solid slurries, containing from about 30 to 60~ solids. Lower fractions of solids improve fluidity but enhance undesired coarsening and dentritic growth during completion of solidifi-cation. It is not possible to get significantly higher fractions of solids because the agitator is immersed in the slurry.
In order to overcome the aforenoted problems inductive electromagnetic stirring has been proposed in U.S. Patent 4,229,210 ; to Winter et al entitled "Method for the Preparation of Thix-otropic Slurries". In that patent two electromagnetic stirring techniques are suggested to overcome the limitations of mechanical stirring. Winter et al. use either AC induction or pulsed DC magnetic fields to produce indirect stirring of ~ ' .
~7~2~ 9063-MB
J. Winter et al 2-2-2 the solidifying alloy melt. While the indirect nature of this electromagnetic stirring is an improvement over the mechanical process, there are still limitations imposed by the nature of the stirring technique.
With AC inductive 6tirring, the maximum electromagnetic forces and associated shear are limited to the penetration depth of the induced currents. Accordingly, the section ~ize that can be effectively stirred is limited due to the decay of the induced forces from the periphery to the interior of the melt.
This is particularly aggravated when a solidifying shell i6 present. The inductive electromagnetic stirring process also requires high power consumption and the resistance heating of the stirred metal is significant. The resistance heating in turn increases the required amount of heat extraction for 601idification.
The pulsed DC magnetic field technique is also effective, however, it i6 not as effective as desired because the force field rapidly diverges as the distance from the DC
electrode increases. Accordingly, a complex geometry is required to produce the required high shear rates and fluid flow patterns to insure production of slurry with a proper structure. Large magnetic fields are required for this proce6s and, therefore, the equipment i~ co~tly and very bulky.
The abovenoted Flemings et al. patents make brief mention of the use of electromagnetic stirring as one of many alternative stirring techniques which could be u~ed to produce thixotropic slurrie~. They fail, however, to ~uggest any indication of how to actually carry out such an electromagnetic stirring approach to produce such a slurry. The German patent publication to Feurer et al. 6uggest6 that \ ;~.
~ 2~ 9063-~3 J. Winter et al 2-2-2 it is also po6sible to arrange induction coils on the periphery of the mixing chamber to produce an electromagnetic field 80 a6 to agitate the melt with the aid of the field. However, Feurer et al. doe6 not make it clear whether or not the electromagnetic agitation i6 intended to be in addition to the mechanical agitation or to be a 6ubstitute therefore. In any event, it is clear that Feurer et al. is 6uggesting merely an inductive type elec~romagnetic 6tirring approach.
There i6 a wide body of prior art dealing with electromagnetic stirring techniques applied during the ca6ting of molten metals and alloy6. U.S. Patent No6. 3,268,963 to Mann; 3,995,678 to Zavara6 et al.: 4,030,534 to Ito et al.;
4,040,467 to Alherny et al.: 4,042,007 to Zavaras et al.; and 4,042,008 to Alherny et al., a6 well as an article by Szekely et al. entitled Electromaqneticallv Driven Flows in Metals Processinq, Sept. 1976, Journal of Metal6, are illustrative of the art with respect to casting metals using inductive electromagnetic stirring provided by 6urrounding induction coils.
In order to overcome the disadvantage6 of inductive electromagnetic 6tirring it ha6 been found in accordance with the present invention that electromagnetic 6tirring can be made more effective, with a substantially increased productivity and with a le66 complex application to continuou6 type ca6ting technique6, if a magnetic field which move6 tran6ver6ely of the mold or casting axis such a6 a rotating field i6 utilized.
The use of rotating magnetic fields for 6tirring molten metal during ca6ting i6 know a6 exemplified in U.S. Patent No6.
2,963,758 to Pe~tel et al. and 2,861,302 1~7t~82~ J. Winter et al 2-2-2 to Manl'L et al. and in U.K. Pantents 1,525,036 and 1,525,545.
Pestal et al. disclose both static casting and continuous casting wherein the molten metal is electromagnetically stirred by means of a rotating ield. One or more multipoled motor stators are arranged about the mold or solidifying casting in order to stir the molten metal to provide a fine grained m~3tal casting. In the continuous casting embodiment disclosed in the patent to Pestal et al. a 6 pole stator is arranged about the mold and two two pole stators are arranged sequentially there-after about the solidifying casting.
Hot-tops are known for use in direct chill casting as exemplified by U.S. Patent Nos. 3,477,494 to Burkart et al.:
Pestal et al. disclose both static casting and continuous casting wherein the molten metal is electromagnetically stirred by means of a rotating ield. One or more multipoled motor stators are arranged about the mold or solidifying casting in order to stir the molten metal to provide a fine grained m~3tal casting. In the continuous casting embodiment disclosed in the patent to Pestal et al. a 6 pole stator is arranged about the mold and two two pole stators are arranged sequentially there-after about the solidifying casting.
Hot-tops are known for use in direct chill casting as exemplified by U.S. Patent Nos. 3,477,494 to Burkart et al.:
3,612,151 to Harrington et al.; and 4,071,072 to McCubbin.
SUMMARY OF l'HE INVENTION
The disadvantages associated with the prior art approaches for making thixotropic slurries utilizing either mechanical agitation or inductive electromagnetic stirring have been overcome in accordance with the invention disclosed in our companion Canadian application no. 346,381, filed Feb.
25, 1980. In our companion application magnetohydromagnetic motion associated with a rotating magnetic field generated by a single two pole multiphase motor stator i9 used to achieve the required high shear rates of at least 500 sec.~l for producing thixotropic semi-solid alloy slurries. The mag-netohydromagnetic process therein disclosed provides high volumetric flow rates which make the process particularly adaptable to continuous or semi-continuous rheocasting.
The present invention is concerned with the design of the rheocasting mold which is used in the process and apparatus of our companion application. In constructing a l~ Z~
J. Winter et al 2-2-2 suitable casting system for use in rheocasting it is difficult to a6sociate the various elements which make up the system in such a way that the stirring force field generated by the two pole induction motor stator extends over the entire ~olidification zone. It i~ preferred to have the manifold which applies the coolant to the mold wall arranged above the stator.
This can result in a portion of the mold cavity which extends out of the region wherein an effective magnetic stirring force is provided. That in turn can cause undesired structural variations in the rheocasting which is formed.
To overcome this problem in accordance with the present invention a means is provided for postponing solidification within the mold cavity until the molten metal is within the effective magnetic field which provides the desired magnetohydrodynamic stirring force. This is accomplished in accordance with the invention by providing the mold with a first region of low thermal conductivity and a second region of high thermal conductivity. The region of low thermal conductivity postpones solidification during the mixing step until the molten metal is within the magnetic field thereby promoting the formation of a degenerate dendritic structure throughout the slurry. Preferably, a partial insulating mold liner is inserted in the upper portion of the mold to provide the region of lo~
thermal conductivity. The mold liner extends down into the mold cavity for a distance sufficient so that the magnetic stirring force field is intercepted at lea~t in part by the partial mold liner.
More specifically, the invention is directed to an improvement in an apparatus for continuously or semi-continuously forming a semi-solid thixotropic alloy slurry.
said slurry comprising throughout its cross section degenerate dendrite primary solid particles in a surrounding il~ Ei~2~
J. Winter et al 2-2-2 matrix of molten metal, said apparatus comprising means for containing moltèn metal, said containing means having a de~ired cro66 section; means for controllable cooling said molten metal in said containing means: and means for mixing said molten metal for shearing dendrites formed in a solidification zone as said molten metal i6 cooled for forming said slurry: said mixing means comprising a single two pole stator for generating a non-zero rotating magnetic field which moves transversly of a longitudinal axis of said containing means across the entirety of said cro~s 6ection of said containing means and over ~aid entire solidification zone, said moving magnetic field providing a magnetomotive stirring force directed tangetially of said containing means for causing said molten metal and slurry to rotate in 6aid containing means, said magnetic force being of 6ufficient magnitude to provide said fihearing of said dendrites, said magnetomotive force providing a shear rate of at lea~t 500 sec. 1 the improvement being wherein said containing mean~
includes a first portion of low thermal conductivity and a second portion of high thermal conductivity, said portion of low thermal conductivity extending into said magnetic field for postponing solidification within said containing means until said molten metal is within said magnetic field, thereby promoting the formation of a degenerate dendritic structure throughout the slurry.
The use of a duplex mold in accordance with thi6 invention having an upper portion of low thermal conductivity and a lower portion of higher thermal conductivity insures that the molten metal can ~olidify under the influence of the rotating magnetic field. This helps the resultant rheocast casting to have a degenerate dendritic structure throughout its cro6s section even up to its outer 6urface.
-7a-il76~2~ J. Winter et al 2-2-2 Accordingly, it is an object of thi6 invention to provide a rheocasting mold apparatus which is capable of forming a casting having a rheoca6t structure throughout its entire cro~s section.
It i6 further object of this invention to provide an apparatu6 as above wherein the mold cavity includes regions of differing thermal conductivity for preventing premature solidification.
The~e and other objects will become more apparent from the following descrietion and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 i6 a 6chematic representation in partial cross ~ection of an apparatu6 in accordance with thi~ invention for continuou61y or 6emi-continuou61y casting a thixotropic semi-solid metal slurry.
Figure 2 i6 a 6chematic repre6entation in partial cro66 6ection of the apparatu6 of Figure 1 during a casting operation.
Figure 3 i6 a partial cro66-6ectional view along the line 3-3 in Figure 1.
Figure 4 is a schematic bottom view of a non-circular mold and linear induction motor 6tator arrangement in accordance with another embodiment of thi6 invention.
Figure 5 i6 a 6chematic repre6entation of the line6 of force at a given in~tant generated by a four pole induction motor stator.
Figure 6 i6 a 6chematic repre6entation of the line6 of force at a given instant generated by a two pole motor 6tator.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMæNTS
In the background of thi6 application there have been described a number of techniques for forming semi-solid 1~7~Z~ J. Winter et al 2-2-2 thixotropic metal slurrie6 for u6e in rheocasting, thixoca6ting, thixoforging, etc. Rheoca~ting as the term i~ u~ed herein refer6 to the formation of a semi-601id thixotropic metal 61urry, directly into a desired ~tructure, 6uch a6 a billet for later proces6ing, or a die ca6ting formed from the 61urry.
Thixoca6ting or thixoforging re6pectively a6 the terms are u6ed herein refer to proce66ing which begins with a rheoca~t material which i6 then reheated for further proces6ing 6uch as die ca6ting or forging.
This invention i6 principally intended to provide rheoca6t material for immediate proces6ir.g or for later u6e in various aeplication of ~uch material, such a6 thixoca6ting and thixoforging. The advantageæ of rheocasting, etc., have been amply described in the prior art. Tho6e advantages include improved ca6ting soundness as compared to conventional die casting. This re6ult6 becau6e the metal i6 partially 601id a6 it enters the mold and, hence, le66 shrinkage poro6ity occurs.
Machine component life i6 al60 improved due to reduced ero6ion of die6 and molds and reduced thermal 6hock a660ciated with rheoca6ting.
The metal compo6ition of thixotropic 61urry compri6e6 primary 601id di6crete particle6 and a 6urround~ng matrix. The surrounding matrix is solid when the metal composition is fully solidified and i6 liquid when the metal compo6tion is partially ~olid and partially liquid 61urry. The primary solid particle6 comprise degenerate dendrites or nodules which are generally 6pheroidal in shape. The primary solid particles are made up of a 6ingle phase or a plurality of phases having an average compo6ition dieferent from the average compo6ition of the 6urrounding matrix in the fully ~76~2~ 9063-MB
J. Winter et al 2-2-2 solidified alloy. The matrix itself can compri~e one or more pha6es upon further solidification.
Conventionally 601idified alloys have branched dendrite6 which develop interconnected networks as the temperature is reduced and the weight fraction of solid increases. In contrast thixotropic metal 61urrie~ consist of discrete primary degenerate dendrite particle6 separated from each other by a liquid metal matrix, potentially even up to solid fractions of 80 weight percent. The primary 601id particles are degenerate dendrites in that they are characterized by smoother surfaces and a leæ~ branched structure which approaches a spheroidal configuration. The ~urrounding solid matrix is formed during 601idification of the liquid matrix subsequent to the formation of the primary solids and contains one or more phases of the type which would be obtained during solidification of the liguid alloy in a more conventional process. The surroundinq solid matrix comprises dendrite6, single or multiphased compound6, solid solution, or mixtures of dendrites, and/or compounds, and~or solid solutions.
Referring to Figures 1 and 2 an apparatus 10 for continuously or 6emi-continuously rheocasting thixotropic metal slurries is shown. The cylindrical mold 11 is adapted for such continuous or semi-continuous rheocasting. The mold 11 may be formed of any desired nonmagnetic material such as 6tainles6 6teel, copper, copper alloy or the like.
Referring to Figure 3 it can be seen that the mold wall 13 is cylindrical in nature. The apparatus 10 and proce66 of this invention is particularly adapted for making cylindrical ingot~ utilizing a conventional two pole polyphase induction motor stator for stirring. However, it is not limited to the , .
~, ~ 2~ 906~-MB
J. Winter et al 2-2-2 formation of a cylindrical ingot cro6s 6ection since it i~
po6~ible to achieve a transversely or circumferentially moving magnetic field with a non-cylindrical mold 11 a6 in Figure 4 In the embodiment of Figure 4 the,mold 11 has a rectangular cros~ sec~ion surrounded by a polypha6e rectangular induction motor 6tator 12. The magnetic field move6 or rotates around the mold 11 in a direction normal to the longitudinal axi6 of the ca6ting which i6 being made. At thi6 time, the preferred embodiment of the invention is in reference to the u6e of a cylindrical mold 11.
The bottom block 13 of the mold 11 iB arranged for movement away from the mold as the ca6ting form& a solidifying shell. The movable bottom block 13 compri6es a 6tandard direct chill ca~ting type bottom block. It is formed of metal and i6 arranged for movement between the position shown in Pigure 1 wherein it 6its up within the confines of the mold cavity 14 and a position away from the mold 11 a6 6hown in Figure 2. Thi6 movement i8 achieved by 6upporting the bottom block 13 on a 6uitable carriage 15. Lead screw6 16 and 17 or hydraulic mean6 are used to raise and lower the bottom block 13 at a de6ired ca6ting rate in accordance with conventional practice. The bottom block 13 is arranged to move axially along the mold axis 18. It include6 a cavity 19 into which the molten metal i~
initially poured and which provide6 a 6tabili~ing influence on the re~ulting ca~ting a6 it i6 withdrawn from the mold 11.
A cooling manifold 20 i6 arranged circumferentially around the mold wall 21. The particular manifold 6hown includes a fir6t input chamber 22, a 6econd chamber ~3 connected to the fir6t input chamber by a narrow slot 24.
~7~ 906~-MB
J. Winter et al 2-2-2 A discharge slot 25 is defined by the gap between the manifold 20 and the mold 11. A uniform curtain of water is provided ab~ut the outer surface 26 of the mold 11. A suitable valving arrangemen~ 27 i8 provided to control the flow rate of the water or other coolant discharged in order to control the rate at which the slurry S solidifies. In the apparatu~ 10 a manually operated valve 27 i6 shown, however, if de~ired this could be an electrically operated valve.
The molten metal which i~ poured into the mold 11 is cooled under controlled conditions by means of the water sprayed upon the outer 6urface 26 of the mold 11 from the encompas6ing manifold 20. By controlling the rate of water flow against the mold surface Z6 the rate of heat extraction from the molten metal within the mold 11 is controlled.
In order to provide a means for stirring the molten metal within the mold 11 to form the desired thixotropic slurry a two pole multiphase induction motor stator 28 i5 arranged surrounding the mold 11. The stator 28 is comprised of iron laminations 29 about which the desired winding6 30 are arranged in a conventio~al manner to provide a three-phase induction motor stator. The motor stator 28 i6 mounted within a motor hou~ing M. The manifold 20 and the motor stator 28 are arranqed concentrically about the axis 18 of the mold 11 and casting 31 formed within it, It i6 preferred in accordance with this invention to utilize a two pole three-phase induction motor stator 28. One advantage of the two pole motor stator 28 is that there is a non-zero field acros6 the entire cross section of the mold 11.
It is, therefore, pos6ible with this invention to solidify a casting having the desired rheoca6t 6tructure ~ 6~Z~ 9063-MB
J. Winter et al 2-2-2 over it6 full cro66 section.
Figure 5 show6 the in6tantaneou6 line6 of force for a four pole induction motor 6tator at a given in6tant in time. It i6 apparent that the center of the mold does not have a de6ired magnetic field associated with it. Therefore, the ~tirring action i6 concentrated near the wall 21 of the mold 11. In comparison thereto, a two pole induction motor stator a~ shown in Figure 6 generates instantaneous lines of force at a given in6tant which provide a non-zero field acro6s the entire cross section of the mold 11. The two pole induction motor stator 28 also provide6 a higher frequency of rotation or rate of stirring of the slurry S for a given current frequency than the four pole approach of Figure 5.
A partially enclosing cover 32 is utilized to prevent spill out of the molten metal and slurry S due to the stirring action imparted by the magnetic field of the motor stator 28.
The cover 32 compri6e6 a metal plate arranged above the manifold 20 and 6eparated therefrom by a 6uitable ceramic liner 33. The cover 32 include6 an opening 34 through which the molten metal flows into the mold cavity 14. Communicating with the opening 34 in the cover is a funnel 35 for directing the molten metal into the opening 34. A ceramic liner 36 is u6ed to protect the metal funnel 35 and the opening 34. As the thixotropic metal 61urry S rotate6 within the mold 11, cavity centrifugal forces cause the metal to try to advance up the mold wall 21. The cover 32 with its ceramic lining 33 prevents the metal slurry S
from advancing or spilling out of the mold 11 cavity and causing damage to the apparatus 10. The funnel portion 35 of the cover 32 al60 serves a6 a re6ervoir of molten metal to keep the mold 11 filled in order -.;~.
~i76~Z~ 9063-MB
J. Winter et al 2-2-2 to avoid the formation of a U-shaped cavity in the end of the casting due to centrifugal force~.
Situated directly above the funnel 35 i6 a down6pout 37 through which the molten metal flows from a 6uitable furnace 38. A valve member 39 associated in a coaxial arrangement with the downspout 37 is u6ed in accordance with conventional practice to regulate the flow of molten metal into the mold 11.
The furnace 38 may be of any conventional design, it i6 not e6sential that the furnace be located directly above the mold 11. In accordance with convention direct chill ca6ting proce66ing the furnace may be located laterally displaced therefrom and be connected to the mold 11 by a serie6 of troughs or launder6.
Referring again to Figure 3, a further ad~antage of the rotary magnetic field stirring approach in accordance with thi6 invention i6 illu6trated. In accordance with the Flemings right-hand rule for a given current J in a direction normal to the plane of the drawing the magnetic flux vector B extend~
radially inwardly of the mold 11 and the magnetic 6tirring force vector F extends generally tangentially of the mold wall 21.
Thi6 6et6 up within the mold cavity a rotation of the molten metal in the direction of arrow R which generates the de6ired 6hear for producing the thixotropic slurry S. The force vector F i6 also tangential to the heat extraction direction and i8 normal to the direction of dendrite growth. This maximize6 the shearing of the dendrite6 as they grow.
It i6 preferred in accordance with thi6 invention that the 6tirring force field generated by the 6tator 28 extend , . ~
~76~2~ J. Winter et al 2-2-2 over the full solidification zone of molten metal and thixotropic metal slurry S. Otherwise the structure of the casting will comprise regions within the field of the 6tator 28 having a rheocast structure and regions outside the sta~or field tending to have a non-rheoca6t 6tructure. In the embodiment of Figures 1 and 2 the solidification zone preferably comprises the 6ump of molten metal and slurry S within the mold 11 which extend6 from the top surface 40 to the solidification front 41 which divides the solidified casting 31 from the ~lurry S. The solidification zone extends at least from the region of the initial onset of solidification and slurry formation in the mold cavity 14 to the solidification front 41.
Under normal solidification conditions, the periphery of the ingot 31 will exhibit a columnar dendritic grain structure. Such a 6tructure is undesireable and detracts from the overall advantages of the rheocast structure which occupies most of the ingot cross section. In order to eliminate or substantially reduce the thickness of this outer dendritic layer in accordance with this invention the thermal conductivity of the upper region of the mold 11 is reduced by mean6 of a partial mold liner 42 formed from an insulator such as a ceramic. The ceramic mold liner 42 extends from the ceramic liner 33 of the mold cover 32 down into the mold cavity 14 for a distance sufficient so that the magnetic 6tirring force field of the two pole motor stator 28 is intercepted at least in part by the partial ceramic mold liner 42. The ceramic mold liner 42 i8 a shell which conform~ to the internal shape of the mold 11 and is held to the mold wall 21. The mold 11 compri6es a duplex structure including a low heat conductivity upper ~ 2~ 9063-MB
J. Winter et al 2-2-2 portion defined by the ceramic liner 42 and a high heat conductivity portion defined by the exposed portion of the mold wall 21.
The liner 4Z po6tpones solidification until the molten metal is in the region of the strong magnetic stirring force.
The low heat extraction rate associated with the liner 42 generally prevents in that portion of the mold 11. Generally solidification does not occur except towards the downstream end of the liner 42 or just thereafter. The 6hearing process resulting from the applied rotating magnetic field will further override the tendency tO form a solid shell in the region of the liner 42. This region 42 or zone of low thermal conductivity thereby he}ps the re6ultant rheocast casting 31 to have a degenerate dendritic structure throughout it6 cros6 section even up to it8 outer surface.
Below the region of controlled thermal conductivity defined by the liner 42, the normal type of water cooled metal casting mold wall 21 is present. The high heat tran6fer rates associated with thi6 portion of the mold 11 promote ingot shell formation. However, because of the zone 42 of low heat extraction rate even the peripheral shell of the casting 31 should con6ist of degenerate dendrites in a 6urrounding matrix.
It is preferred in order to form the desired rheocast structure at the surface of the ca~ting to effectively shear any initial solidified gro~th from the mold liner 42. This can be accomplished by insuring that the field a~ociated with the motor ~tator 28 extends over at least that portion of the liner 42 at which solidification i~ first initiated.
The dendrites which initially form normal to the periphery of the casting mold 11 are readily sheared off due to the .~
7 6 ~ Z ~ 9063-MB
J. Winter et al 2-2-2 metal flow resulting from the rotating magnetic field of the induction motor ~tator 28. The dendrite~ which are sheared off continue to be ~tirred to form degenerate dendrite~ until they are trapped by the 601idifying interface 41. Degenerate dendrites can also form directly within the 61urry because the rotating ~tirring action of the melt doe~ not permit preferential growth of dendrite6. To in~ure this the stator Z8 length should ereferably extend over the full length of the solidification zone. In particular the 6tirring force field associated with the stator 28 6hould preferably extend over the full length and cross section of the 601idification zone with a sufficient magnitude to generate the desired 6hear rate6.
To form a rheocasting 31 utilizing the apparatus 10 of Figures 1 and 2 molten metal is poured into the mold cavity 14 while the motor stator 28 is energized by a suitable three-phase AC current of a desired magnitude and frequency. After the molten metal is poured into the mold cavity it is stirred continuously by the rotating maqnetic field produced by the motor stator 28. Solidification begins from the mold wall 21.
The highest 6hear rate~ are generated at the 6tationary mold wall 21 or at the advancing solidification front 41. By properly controlling the rate of 601idification by any desired mean6 as are known in the prior art the desired thixotropic 61urry S i~ formed in the mold cavity 14. As a 601idifying 6hell is formed on the casting 31, the bottom block 13 is withdrawn downwardly at a desired casting rate.
The 6hear rate6 which are obtainable with the process and apparatu6 10 of thi6 invention are much higher than tho6e 1176~2~ 9063-MB
J. Winter et al 2-2-2 reported for the mechanical stirring proces6 and can be achieved over much larger cro66-6ectional area6. The~e high 6hear rate6 can be extended to the center of the ca~ting cross section even when the 601id shell of the solidifying slurry S is already present.
The induction motor stator 28 which provide6 the 6tirring force needed to produce the degenerate dendrite rheocast structure can be readily placed either above or below the primary cooling manifold 20 as desired. Preferably.
however, in accordance with this invention, the induction motor 6tator 28 and mold 11 are located below the cooling manifold 20.
The continuous casting apparatus 10 of this invention is particularly advantageous as compared to the proces6e6 and apparatuses described in the prior art. In those processes the stirrinq chamber i8 located above a continuou6 ca~ting mold and the thixotropic slurry S is delivered to the mold. This has the disadvantage that the mold i~ hard to fill and entrainment of oxides is enhanced. In accordance with this invention the stirring chamber comprises continuous casting mold 11 itself.
Thi6 process doe6 not 6uffer from the transfer of contamination problems of the prior art continuous ca6ting process.
It is preferred in accordance with the process and apparatus of this invention that the entire casting solidify in the stator 28 field in order to produce castings with proper rheocast structure through their entire cross section.
; Therefore, the casting apparatus 10 in accordance with this invention should preferably be designed to insure that the entire 601idification zone is within the stator 28 field.
`' ' ~7~2~ 9063-MB
J. Winter et al 2-2-2 This may require extra long ~tators 28 to be provided to handle some types of casting.
In accordance with thi6 invention two competing processe6 shearing and golidification are controlling. The 6hearing produced by the electromagnetic proces6 and apparatu6 of thi6 invention can be made equivalent to or greater than that obtainable by mechanical stirring. The interaction between shear rate6 and cooling rate6 cau6e6 higher 6tator currents to be required for continuou~ type casting then are required for ~tatic casting.
It ha6 been found in accordance with this invention that the effect6 of the experimental variable6 in the proce~
can be predicted from a consideration of two dimensionless groups, namely Band N a6 follows:
B = ~/~UJ ~H~ R2 (1) N R2 B2 (2) ~0 where j = ~ -1 w = angular line frequency 6 = melt electrical conductivity H~ = magnetic permeability R = melt radius B~ = magnetic induction at the mold wall n~ = melt visco6ity.
The fir6t group,B , is a measure of the field geometry effects, while the 6econd group. N, appear6 as a coupling coefficient between the magnetomotor body forceæ and the a660ciated velocity field. The computed velocity and 6hearing fields for a single value of ~ as a function of the parameter N can be determined.
~76~Z~ 9063-MB
J. Winter et al 2-2-2 From these determinations it has been found that the shear rate increases sharply toward the outside o~ the mold where it reaches its maximum. This maximum shear rate increases with increasing N. It has been concluded that the shearing is produced in the melt because the peripheral boundary or mold wall is rigid. Therefore, even when a solidifying shell is present, there 6hould still be shear stresses in the melt and they should be maximal at the liquid solid interface 41.
Further because there are always ~hear stre~ses at the advancing interface 41 it is possible to make a full section ingot 31 with the appropriate degenerate dendritic rheocast structure.
The stator current and shear rates required to achieve the desired degenerate dendritic thixotropic slurry S are very much higher than those required to achieve fine dentritic grains in accordance with the prior art as set forth in the background of this application. The process and apparatus 10 of this invention offer several unique advantages in contrast to the processes of the prior art. For example, the loss of magnetic field strength due to the presence of solidifying metal is small due to the low frequency which is used. The equipment associated with the apparatus 10 of this invention is relatively easy to fabricate since two pole induction motor stators 28 are well-known in the art. The apparatus 10 of this invention has a relatively 1GW power consumption and because of the relatively low current as compared to the AC induction method there is little resistance heating of the melt being stirred. The rotating magnetic field stirring method of this invention i6 indirect and, therefore, has insignificant associated erosion problems. Another advantage i;j 11768ZO g o 6 3 -MB
J. Winter et al 2-Z-2 of the present process and apparatus is the high volumetric flow rates which are obtainable. This i6 particularly important if one desires to carry out the rheoca6ting proce~6 continuou61y or semi-continuously. The duplex mold arrangement comprising region6 of low and high thermal conductivity produces casting having the desired rheocast ~tructure throughout while allowing flexibility in the arrangment of various components of the ca6ting 6y~tem.
EXAMPLE I
Ingot6 2.5 inche6 in diameter of alloy 6061 were cast using an apparatus 10 similar to that shown in Figures 1 and 2.
The bottom bloc~ 13 wa6 lowered and the casting was drawn from the mold 11 at 6peeds of from about 8 to 14 inches per ~inute.
The two pole three-pha6e induction motor stator 28 current was varied between 5 and 35 amps. It wa6 found that at the low current end of thi6 range, a fine dendritic grain 6tructure wa~
produced but not the characteristic 6tructure of a rheocast thixotropic slurry. At the high current end of the range particularly in and around lS amps fully non-dendritic structures were generated having a typical rheocast structure comprising generally spheroidal primary solids surrounded by a solid matrix of different compo6ition.
The mold cover 32 by enclosing the mold cavity 14 except for the 6mall centrally located opening 34 6erves not only to prevent spillage of molten metal but also to prevent the formation of a U-shaped cavity in the end of the rheocasting.
By adding sufficient molten metal to the mold to at least partially fill the funnel 35 it i6 possible to in~ure that the mold cavity 14 is completely ~17~Z~ 9063_MB
J. Winter et al 2-2-2 filled with molten metal and slurry. The cover 32 offsets the centrifugal forces and prevents the formation of the U-~haped cavity on solidification. By completely filling the mold oxide entrainment in the re~ulting casting is 6ubstantially reduced.
While it is preferred in accordance with this invention that the ~tirring force due to the magnetic field extend over the entire solidification zone it i~ recognized that the shearing action on the dendrites results from the rotating movement of the melt. This metal 6tirring movement can cause 6hearing of dendrites outside the field if the moving molten metal pool extends outside the field.
Dendrites will initially attempt to grow from the 6ides or wall 21 of the mold 11. The solidifying metal at the bottom of the mold may not be dendritic because of the comparatively low heat extraction rate which promote6 the formation of more equiaxed grains.
Suitable stator currents for carrying out the process of this invention will vary depending on the 6tator which is used. The currents mu6t be sufficiently high to provide the de~ired magnetic field for generating the desired shear rates.
Suitable shear rates for carrying out the proces6 of this invention comprise from at lea6t about 100 sec. to about 1500 ~ec. -1, and preferably from at least about 500 sec. to about 1200 sec. . For aluminum and it6 alloys a shear rate of from about 700 sec. to about 1100 sec.
has been found desirable.
The average cooling rates through the solidification temperature range of the molten metal in the mold ~hould be 1~6~Z~ 9063-MB
J. Winter et al 2-2-2 from about 0.1 C per minute to about 1000 C per minute and preferably from about 10 C per minute to about 500 C per minute. For aluminum and its alloy6 an average cooling rate of from about 40C per minute to about 500 C per minute ha~
been found to be 6uitable. The efficiency of the magneto-hydrodynamic 6tirring allows the use of higher cooling rate6 than with prior art stirring proces6es. Higher cooling rates yield highly de6irable finer grain 6tructure~ in the re6ulting rheoca6ting. Further, for continuous rheoca6ting higher throughput follow6 from the u6e of higher cooling rate6.
The parameter ¦B ¦ (~defined by eguation (1)) for carrying out the proce66 of thi6 invention 6hould compri6e from about 1 to about 10 and preferably from about 3 to about 7.
The parameter in N ( defined by equation ~2)) for carrying out the proces6 of thi6 invention 6hould comprise from about 1 to about 1000 and preferably from about 5 to about 200.
The angular line frequency ~ for a casting having a radius of from about 1" to about 10" 6hould be from about 3 to about 3000 hertz and preferably from about 9 to about 2000 hertz.
The magnetic field strength which i6 a function of the angular line frequency and the melt radiu6 6hould comprise from about 50 to 1500 gau66 and preferably from about 100 to about 600 gaus~.
The particular parameters employed can vary from metal sy6tem to metal 6y6tem in order to achieve the desired shear rate6 for providing the thixotropic 61urry. The appropriate 1~
~176~Z~ J. Winter et al 2-2-2 parameters for alloy systems other than aluminum can be determined by routine experimentation in accordance with the principles of this invention.
Solidification zone as the term is used in this appli-cation refers to the zone of molten metal or slurry in the mold wherein solidification is aking place. Magnetohydro-dynamic as the term is used herein refers to the process of stirring molten metal or slurry using a moving or rotating magnetic field. The magnetic stirring force may be more appropriately referred to as a magnetomotive stirring force which is provided by the movinq or rotating magnetic field of this invention.
The process and apparatus of this invention is applicable to the full range of materials as set forth in the prior art including but not limited to aluminum and its alloys~ copper and its alloys and steel and its alloys.
It is apparent that there has been provided in accordance with this invention an apparatus for making thixotropic metal slurries which fully satisfies the objects, means and advantages sot forth hereinbefore. While the invention has been described in combination with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims.
B
SUMMARY OF l'HE INVENTION
The disadvantages associated with the prior art approaches for making thixotropic slurries utilizing either mechanical agitation or inductive electromagnetic stirring have been overcome in accordance with the invention disclosed in our companion Canadian application no. 346,381, filed Feb.
25, 1980. In our companion application magnetohydromagnetic motion associated with a rotating magnetic field generated by a single two pole multiphase motor stator i9 used to achieve the required high shear rates of at least 500 sec.~l for producing thixotropic semi-solid alloy slurries. The mag-netohydromagnetic process therein disclosed provides high volumetric flow rates which make the process particularly adaptable to continuous or semi-continuous rheocasting.
The present invention is concerned with the design of the rheocasting mold which is used in the process and apparatus of our companion application. In constructing a l~ Z~
J. Winter et al 2-2-2 suitable casting system for use in rheocasting it is difficult to a6sociate the various elements which make up the system in such a way that the stirring force field generated by the two pole induction motor stator extends over the entire ~olidification zone. It i~ preferred to have the manifold which applies the coolant to the mold wall arranged above the stator.
This can result in a portion of the mold cavity which extends out of the region wherein an effective magnetic stirring force is provided. That in turn can cause undesired structural variations in the rheocasting which is formed.
To overcome this problem in accordance with the present invention a means is provided for postponing solidification within the mold cavity until the molten metal is within the effective magnetic field which provides the desired magnetohydrodynamic stirring force. This is accomplished in accordance with the invention by providing the mold with a first region of low thermal conductivity and a second region of high thermal conductivity. The region of low thermal conductivity postpones solidification during the mixing step until the molten metal is within the magnetic field thereby promoting the formation of a degenerate dendritic structure throughout the slurry. Preferably, a partial insulating mold liner is inserted in the upper portion of the mold to provide the region of lo~
thermal conductivity. The mold liner extends down into the mold cavity for a distance sufficient so that the magnetic stirring force field is intercepted at lea~t in part by the partial mold liner.
More specifically, the invention is directed to an improvement in an apparatus for continuously or semi-continuously forming a semi-solid thixotropic alloy slurry.
said slurry comprising throughout its cross section degenerate dendrite primary solid particles in a surrounding il~ Ei~2~
J. Winter et al 2-2-2 matrix of molten metal, said apparatus comprising means for containing moltèn metal, said containing means having a de~ired cro66 section; means for controllable cooling said molten metal in said containing means: and means for mixing said molten metal for shearing dendrites formed in a solidification zone as said molten metal i6 cooled for forming said slurry: said mixing means comprising a single two pole stator for generating a non-zero rotating magnetic field which moves transversly of a longitudinal axis of said containing means across the entirety of said cro~s 6ection of said containing means and over ~aid entire solidification zone, said moving magnetic field providing a magnetomotive stirring force directed tangetially of said containing means for causing said molten metal and slurry to rotate in 6aid containing means, said magnetic force being of 6ufficient magnitude to provide said fihearing of said dendrites, said magnetomotive force providing a shear rate of at lea~t 500 sec. 1 the improvement being wherein said containing mean~
includes a first portion of low thermal conductivity and a second portion of high thermal conductivity, said portion of low thermal conductivity extending into said magnetic field for postponing solidification within said containing means until said molten metal is within said magnetic field, thereby promoting the formation of a degenerate dendritic structure throughout the slurry.
The use of a duplex mold in accordance with thi6 invention having an upper portion of low thermal conductivity and a lower portion of higher thermal conductivity insures that the molten metal can ~olidify under the influence of the rotating magnetic field. This helps the resultant rheocast casting to have a degenerate dendritic structure throughout its cro6s section even up to its outer 6urface.
-7a-il76~2~ J. Winter et al 2-2-2 Accordingly, it is an object of thi6 invention to provide a rheocasting mold apparatus which is capable of forming a casting having a rheoca6t structure throughout its entire cro~s section.
It i6 further object of this invention to provide an apparatu6 as above wherein the mold cavity includes regions of differing thermal conductivity for preventing premature solidification.
The~e and other objects will become more apparent from the following descrietion and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 i6 a 6chematic representation in partial cross ~ection of an apparatu6 in accordance with thi~ invention for continuou61y or 6emi-continuou61y casting a thixotropic semi-solid metal slurry.
Figure 2 i6 a 6chematic repre6entation in partial cro66 6ection of the apparatu6 of Figure 1 during a casting operation.
Figure 3 i6 a partial cro66-6ectional view along the line 3-3 in Figure 1.
Figure 4 is a schematic bottom view of a non-circular mold and linear induction motor 6tator arrangement in accordance with another embodiment of thi6 invention.
Figure 5 i6 a 6chematic repre6entation of the line6 of force at a given in~tant generated by a four pole induction motor stator.
Figure 6 i6 a 6chematic repre6entation of the line6 of force at a given instant generated by a two pole motor 6tator.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMæNTS
In the background of thi6 application there have been described a number of techniques for forming semi-solid 1~7~Z~ J. Winter et al 2-2-2 thixotropic metal slurrie6 for u6e in rheocasting, thixoca6ting, thixoforging, etc. Rheoca~ting as the term i~ u~ed herein refer6 to the formation of a semi-601id thixotropic metal 61urry, directly into a desired ~tructure, 6uch a6 a billet for later proces6ing, or a die ca6ting formed from the 61urry.
Thixoca6ting or thixoforging re6pectively a6 the terms are u6ed herein refer to proce66ing which begins with a rheoca~t material which i6 then reheated for further proces6ing 6uch as die ca6ting or forging.
This invention i6 principally intended to provide rheoca6t material for immediate proces6ir.g or for later u6e in various aeplication of ~uch material, such a6 thixoca6ting and thixoforging. The advantageæ of rheocasting, etc., have been amply described in the prior art. Tho6e advantages include improved ca6ting soundness as compared to conventional die casting. This re6ult6 becau6e the metal i6 partially 601id a6 it enters the mold and, hence, le66 shrinkage poro6ity occurs.
Machine component life i6 al60 improved due to reduced ero6ion of die6 and molds and reduced thermal 6hock a660ciated with rheoca6ting.
The metal compo6ition of thixotropic 61urry compri6e6 primary 601id di6crete particle6 and a 6urround~ng matrix. The surrounding matrix is solid when the metal composition is fully solidified and i6 liquid when the metal compo6tion is partially ~olid and partially liquid 61urry. The primary solid particle6 comprise degenerate dendrites or nodules which are generally 6pheroidal in shape. The primary solid particles are made up of a 6ingle phase or a plurality of phases having an average compo6ition dieferent from the average compo6ition of the 6urrounding matrix in the fully ~76~2~ 9063-MB
J. Winter et al 2-2-2 solidified alloy. The matrix itself can compri~e one or more pha6es upon further solidification.
Conventionally 601idified alloys have branched dendrite6 which develop interconnected networks as the temperature is reduced and the weight fraction of solid increases. In contrast thixotropic metal 61urrie~ consist of discrete primary degenerate dendrite particle6 separated from each other by a liquid metal matrix, potentially even up to solid fractions of 80 weight percent. The primary 601id particles are degenerate dendrites in that they are characterized by smoother surfaces and a leæ~ branched structure which approaches a spheroidal configuration. The ~urrounding solid matrix is formed during 601idification of the liquid matrix subsequent to the formation of the primary solids and contains one or more phases of the type which would be obtained during solidification of the liguid alloy in a more conventional process. The surroundinq solid matrix comprises dendrite6, single or multiphased compound6, solid solution, or mixtures of dendrites, and/or compounds, and~or solid solutions.
Referring to Figures 1 and 2 an apparatus 10 for continuously or 6emi-continuously rheocasting thixotropic metal slurries is shown. The cylindrical mold 11 is adapted for such continuous or semi-continuous rheocasting. The mold 11 may be formed of any desired nonmagnetic material such as 6tainles6 6teel, copper, copper alloy or the like.
Referring to Figure 3 it can be seen that the mold wall 13 is cylindrical in nature. The apparatus 10 and proce66 of this invention is particularly adapted for making cylindrical ingot~ utilizing a conventional two pole polyphase induction motor stator for stirring. However, it is not limited to the , .
~, ~ 2~ 906~-MB
J. Winter et al 2-2-2 formation of a cylindrical ingot cro6s 6ection since it i~
po6~ible to achieve a transversely or circumferentially moving magnetic field with a non-cylindrical mold 11 a6 in Figure 4 In the embodiment of Figure 4 the,mold 11 has a rectangular cros~ sec~ion surrounded by a polypha6e rectangular induction motor 6tator 12. The magnetic field move6 or rotates around the mold 11 in a direction normal to the longitudinal axi6 of the ca6ting which i6 being made. At thi6 time, the preferred embodiment of the invention is in reference to the u6e of a cylindrical mold 11.
The bottom block 13 of the mold 11 iB arranged for movement away from the mold as the ca6ting form& a solidifying shell. The movable bottom block 13 compri6es a 6tandard direct chill ca~ting type bottom block. It is formed of metal and i6 arranged for movement between the position shown in Pigure 1 wherein it 6its up within the confines of the mold cavity 14 and a position away from the mold 11 a6 6hown in Figure 2. Thi6 movement i8 achieved by 6upporting the bottom block 13 on a 6uitable carriage 15. Lead screw6 16 and 17 or hydraulic mean6 are used to raise and lower the bottom block 13 at a de6ired ca6ting rate in accordance with conventional practice. The bottom block 13 is arranged to move axially along the mold axis 18. It include6 a cavity 19 into which the molten metal i~
initially poured and which provide6 a 6tabili~ing influence on the re~ulting ca~ting a6 it i6 withdrawn from the mold 11.
A cooling manifold 20 i6 arranged circumferentially around the mold wall 21. The particular manifold 6hown includes a fir6t input chamber 22, a 6econd chamber ~3 connected to the fir6t input chamber by a narrow slot 24.
~7~ 906~-MB
J. Winter et al 2-2-2 A discharge slot 25 is defined by the gap between the manifold 20 and the mold 11. A uniform curtain of water is provided ab~ut the outer surface 26 of the mold 11. A suitable valving arrangemen~ 27 i8 provided to control the flow rate of the water or other coolant discharged in order to control the rate at which the slurry S solidifies. In the apparatu~ 10 a manually operated valve 27 i6 shown, however, if de~ired this could be an electrically operated valve.
The molten metal which i~ poured into the mold 11 is cooled under controlled conditions by means of the water sprayed upon the outer 6urface 26 of the mold 11 from the encompas6ing manifold 20. By controlling the rate of water flow against the mold surface Z6 the rate of heat extraction from the molten metal within the mold 11 is controlled.
In order to provide a means for stirring the molten metal within the mold 11 to form the desired thixotropic slurry a two pole multiphase induction motor stator 28 i5 arranged surrounding the mold 11. The stator 28 is comprised of iron laminations 29 about which the desired winding6 30 are arranged in a conventio~al manner to provide a three-phase induction motor stator. The motor stator 28 i6 mounted within a motor hou~ing M. The manifold 20 and the motor stator 28 are arranqed concentrically about the axis 18 of the mold 11 and casting 31 formed within it, It i6 preferred in accordance with this invention to utilize a two pole three-phase induction motor stator 28. One advantage of the two pole motor stator 28 is that there is a non-zero field acros6 the entire cross section of the mold 11.
It is, therefore, pos6ible with this invention to solidify a casting having the desired rheoca6t 6tructure ~ 6~Z~ 9063-MB
J. Winter et al 2-2-2 over it6 full cro66 section.
Figure 5 show6 the in6tantaneou6 line6 of force for a four pole induction motor 6tator at a given in6tant in time. It i6 apparent that the center of the mold does not have a de6ired magnetic field associated with it. Therefore, the ~tirring action i6 concentrated near the wall 21 of the mold 11. In comparison thereto, a two pole induction motor stator a~ shown in Figure 6 generates instantaneous lines of force at a given in6tant which provide a non-zero field acro6s the entire cross section of the mold 11. The two pole induction motor stator 28 also provide6 a higher frequency of rotation or rate of stirring of the slurry S for a given current frequency than the four pole approach of Figure 5.
A partially enclosing cover 32 is utilized to prevent spill out of the molten metal and slurry S due to the stirring action imparted by the magnetic field of the motor stator 28.
The cover 32 compri6e6 a metal plate arranged above the manifold 20 and 6eparated therefrom by a 6uitable ceramic liner 33. The cover 32 include6 an opening 34 through which the molten metal flows into the mold cavity 14. Communicating with the opening 34 in the cover is a funnel 35 for directing the molten metal into the opening 34. A ceramic liner 36 is u6ed to protect the metal funnel 35 and the opening 34. As the thixotropic metal 61urry S rotate6 within the mold 11, cavity centrifugal forces cause the metal to try to advance up the mold wall 21. The cover 32 with its ceramic lining 33 prevents the metal slurry S
from advancing or spilling out of the mold 11 cavity and causing damage to the apparatus 10. The funnel portion 35 of the cover 32 al60 serves a6 a re6ervoir of molten metal to keep the mold 11 filled in order -.;~.
~i76~Z~ 9063-MB
J. Winter et al 2-2-2 to avoid the formation of a U-shaped cavity in the end of the casting due to centrifugal force~.
Situated directly above the funnel 35 i6 a down6pout 37 through which the molten metal flows from a 6uitable furnace 38. A valve member 39 associated in a coaxial arrangement with the downspout 37 is u6ed in accordance with conventional practice to regulate the flow of molten metal into the mold 11.
The furnace 38 may be of any conventional design, it i6 not e6sential that the furnace be located directly above the mold 11. In accordance with convention direct chill ca6ting proce66ing the furnace may be located laterally displaced therefrom and be connected to the mold 11 by a serie6 of troughs or launder6.
Referring again to Figure 3, a further ad~antage of the rotary magnetic field stirring approach in accordance with thi6 invention i6 illu6trated. In accordance with the Flemings right-hand rule for a given current J in a direction normal to the plane of the drawing the magnetic flux vector B extend~
radially inwardly of the mold 11 and the magnetic 6tirring force vector F extends generally tangentially of the mold wall 21.
Thi6 6et6 up within the mold cavity a rotation of the molten metal in the direction of arrow R which generates the de6ired 6hear for producing the thixotropic slurry S. The force vector F i6 also tangential to the heat extraction direction and i8 normal to the direction of dendrite growth. This maximize6 the shearing of the dendrite6 as they grow.
It i6 preferred in accordance with thi6 invention that the 6tirring force field generated by the 6tator 28 extend , . ~
~76~2~ J. Winter et al 2-2-2 over the full solidification zone of molten metal and thixotropic metal slurry S. Otherwise the structure of the casting will comprise regions within the field of the 6tator 28 having a rheocast structure and regions outside the sta~or field tending to have a non-rheoca6t 6tructure. In the embodiment of Figures 1 and 2 the solidification zone preferably comprises the 6ump of molten metal and slurry S within the mold 11 which extend6 from the top surface 40 to the solidification front 41 which divides the solidified casting 31 from the ~lurry S. The solidification zone extends at least from the region of the initial onset of solidification and slurry formation in the mold cavity 14 to the solidification front 41.
Under normal solidification conditions, the periphery of the ingot 31 will exhibit a columnar dendritic grain structure. Such a 6tructure is undesireable and detracts from the overall advantages of the rheocast structure which occupies most of the ingot cross section. In order to eliminate or substantially reduce the thickness of this outer dendritic layer in accordance with this invention the thermal conductivity of the upper region of the mold 11 is reduced by mean6 of a partial mold liner 42 formed from an insulator such as a ceramic. The ceramic mold liner 42 extends from the ceramic liner 33 of the mold cover 32 down into the mold cavity 14 for a distance sufficient so that the magnetic 6tirring force field of the two pole motor stator 28 is intercepted at least in part by the partial ceramic mold liner 42. The ceramic mold liner 42 i8 a shell which conform~ to the internal shape of the mold 11 and is held to the mold wall 21. The mold 11 compri6es a duplex structure including a low heat conductivity upper ~ 2~ 9063-MB
J. Winter et al 2-2-2 portion defined by the ceramic liner 42 and a high heat conductivity portion defined by the exposed portion of the mold wall 21.
The liner 4Z po6tpones solidification until the molten metal is in the region of the strong magnetic stirring force.
The low heat extraction rate associated with the liner 42 generally prevents in that portion of the mold 11. Generally solidification does not occur except towards the downstream end of the liner 42 or just thereafter. The 6hearing process resulting from the applied rotating magnetic field will further override the tendency tO form a solid shell in the region of the liner 42. This region 42 or zone of low thermal conductivity thereby he}ps the re6ultant rheocast casting 31 to have a degenerate dendritic structure throughout it6 cros6 section even up to it8 outer surface.
Below the region of controlled thermal conductivity defined by the liner 42, the normal type of water cooled metal casting mold wall 21 is present. The high heat tran6fer rates associated with thi6 portion of the mold 11 promote ingot shell formation. However, because of the zone 42 of low heat extraction rate even the peripheral shell of the casting 31 should con6ist of degenerate dendrites in a 6urrounding matrix.
It is preferred in order to form the desired rheocast structure at the surface of the ca~ting to effectively shear any initial solidified gro~th from the mold liner 42. This can be accomplished by insuring that the field a~ociated with the motor ~tator 28 extends over at least that portion of the liner 42 at which solidification i~ first initiated.
The dendrites which initially form normal to the periphery of the casting mold 11 are readily sheared off due to the .~
7 6 ~ Z ~ 9063-MB
J. Winter et al 2-2-2 metal flow resulting from the rotating magnetic field of the induction motor ~tator 28. The dendrite~ which are sheared off continue to be ~tirred to form degenerate dendrite~ until they are trapped by the 601idifying interface 41. Degenerate dendrites can also form directly within the 61urry because the rotating ~tirring action of the melt doe~ not permit preferential growth of dendrite6. To in~ure this the stator Z8 length should ereferably extend over the full length of the solidification zone. In particular the 6tirring force field associated with the stator 28 6hould preferably extend over the full length and cross section of the 601idification zone with a sufficient magnitude to generate the desired 6hear rate6.
To form a rheocasting 31 utilizing the apparatus 10 of Figures 1 and 2 molten metal is poured into the mold cavity 14 while the motor stator 28 is energized by a suitable three-phase AC current of a desired magnitude and frequency. After the molten metal is poured into the mold cavity it is stirred continuously by the rotating maqnetic field produced by the motor stator 28. Solidification begins from the mold wall 21.
The highest 6hear rate~ are generated at the 6tationary mold wall 21 or at the advancing solidification front 41. By properly controlling the rate of 601idification by any desired mean6 as are known in the prior art the desired thixotropic 61urry S i~ formed in the mold cavity 14. As a 601idifying 6hell is formed on the casting 31, the bottom block 13 is withdrawn downwardly at a desired casting rate.
The 6hear rate6 which are obtainable with the process and apparatu6 10 of thi6 invention are much higher than tho6e 1176~2~ 9063-MB
J. Winter et al 2-2-2 reported for the mechanical stirring proces6 and can be achieved over much larger cro66-6ectional area6. The~e high 6hear rate6 can be extended to the center of the ca~ting cross section even when the 601id shell of the solidifying slurry S is already present.
The induction motor stator 28 which provide6 the 6tirring force needed to produce the degenerate dendrite rheocast structure can be readily placed either above or below the primary cooling manifold 20 as desired. Preferably.
however, in accordance with this invention, the induction motor 6tator 28 and mold 11 are located below the cooling manifold 20.
The continuous casting apparatus 10 of this invention is particularly advantageous as compared to the proces6e6 and apparatuses described in the prior art. In those processes the stirrinq chamber i8 located above a continuou6 ca~ting mold and the thixotropic slurry S is delivered to the mold. This has the disadvantage that the mold i~ hard to fill and entrainment of oxides is enhanced. In accordance with this invention the stirring chamber comprises continuous casting mold 11 itself.
Thi6 process doe6 not 6uffer from the transfer of contamination problems of the prior art continuous ca6ting process.
It is preferred in accordance with the process and apparatus of this invention that the entire casting solidify in the stator 28 field in order to produce castings with proper rheocast structure through their entire cross section.
; Therefore, the casting apparatus 10 in accordance with this invention should preferably be designed to insure that the entire 601idification zone is within the stator 28 field.
`' ' ~7~2~ 9063-MB
J. Winter et al 2-2-2 This may require extra long ~tators 28 to be provided to handle some types of casting.
In accordance with thi6 invention two competing processe6 shearing and golidification are controlling. The 6hearing produced by the electromagnetic proces6 and apparatu6 of thi6 invention can be made equivalent to or greater than that obtainable by mechanical stirring. The interaction between shear rate6 and cooling rate6 cau6e6 higher 6tator currents to be required for continuou~ type casting then are required for ~tatic casting.
It ha6 been found in accordance with this invention that the effect6 of the experimental variable6 in the proce~
can be predicted from a consideration of two dimensionless groups, namely Band N a6 follows:
B = ~/~UJ ~H~ R2 (1) N R2 B2 (2) ~0 where j = ~ -1 w = angular line frequency 6 = melt electrical conductivity H~ = magnetic permeability R = melt radius B~ = magnetic induction at the mold wall n~ = melt visco6ity.
The fir6t group,B , is a measure of the field geometry effects, while the 6econd group. N, appear6 as a coupling coefficient between the magnetomotor body forceæ and the a660ciated velocity field. The computed velocity and 6hearing fields for a single value of ~ as a function of the parameter N can be determined.
~76~Z~ 9063-MB
J. Winter et al 2-2-2 From these determinations it has been found that the shear rate increases sharply toward the outside o~ the mold where it reaches its maximum. This maximum shear rate increases with increasing N. It has been concluded that the shearing is produced in the melt because the peripheral boundary or mold wall is rigid. Therefore, even when a solidifying shell is present, there 6hould still be shear stresses in the melt and they should be maximal at the liquid solid interface 41.
Further because there are always ~hear stre~ses at the advancing interface 41 it is possible to make a full section ingot 31 with the appropriate degenerate dendritic rheocast structure.
The stator current and shear rates required to achieve the desired degenerate dendritic thixotropic slurry S are very much higher than those required to achieve fine dentritic grains in accordance with the prior art as set forth in the background of this application. The process and apparatus 10 of this invention offer several unique advantages in contrast to the processes of the prior art. For example, the loss of magnetic field strength due to the presence of solidifying metal is small due to the low frequency which is used. The equipment associated with the apparatus 10 of this invention is relatively easy to fabricate since two pole induction motor stators 28 are well-known in the art. The apparatus 10 of this invention has a relatively 1GW power consumption and because of the relatively low current as compared to the AC induction method there is little resistance heating of the melt being stirred. The rotating magnetic field stirring method of this invention i6 indirect and, therefore, has insignificant associated erosion problems. Another advantage i;j 11768ZO g o 6 3 -MB
J. Winter et al 2-Z-2 of the present process and apparatus is the high volumetric flow rates which are obtainable. This i6 particularly important if one desires to carry out the rheoca6ting proce~6 continuou61y or semi-continuously. The duplex mold arrangement comprising region6 of low and high thermal conductivity produces casting having the desired rheocast ~tructure throughout while allowing flexibility in the arrangment of various components of the ca6ting 6y~tem.
EXAMPLE I
Ingot6 2.5 inche6 in diameter of alloy 6061 were cast using an apparatus 10 similar to that shown in Figures 1 and 2.
The bottom bloc~ 13 wa6 lowered and the casting was drawn from the mold 11 at 6peeds of from about 8 to 14 inches per ~inute.
The two pole three-pha6e induction motor stator 28 current was varied between 5 and 35 amps. It wa6 found that at the low current end of thi6 range, a fine dendritic grain 6tructure wa~
produced but not the characteristic 6tructure of a rheocast thixotropic slurry. At the high current end of the range particularly in and around lS amps fully non-dendritic structures were generated having a typical rheocast structure comprising generally spheroidal primary solids surrounded by a solid matrix of different compo6ition.
The mold cover 32 by enclosing the mold cavity 14 except for the 6mall centrally located opening 34 6erves not only to prevent spillage of molten metal but also to prevent the formation of a U-shaped cavity in the end of the rheocasting.
By adding sufficient molten metal to the mold to at least partially fill the funnel 35 it i6 possible to in~ure that the mold cavity 14 is completely ~17~Z~ 9063_MB
J. Winter et al 2-2-2 filled with molten metal and slurry. The cover 32 offsets the centrifugal forces and prevents the formation of the U-~haped cavity on solidification. By completely filling the mold oxide entrainment in the re~ulting casting is 6ubstantially reduced.
While it is preferred in accordance with this invention that the ~tirring force due to the magnetic field extend over the entire solidification zone it i~ recognized that the shearing action on the dendrites results from the rotating movement of the melt. This metal 6tirring movement can cause 6hearing of dendrites outside the field if the moving molten metal pool extends outside the field.
Dendrites will initially attempt to grow from the 6ides or wall 21 of the mold 11. The solidifying metal at the bottom of the mold may not be dendritic because of the comparatively low heat extraction rate which promote6 the formation of more equiaxed grains.
Suitable stator currents for carrying out the process of this invention will vary depending on the 6tator which is used. The currents mu6t be sufficiently high to provide the de~ired magnetic field for generating the desired shear rates.
Suitable shear rates for carrying out the proces6 of this invention comprise from at lea6t about 100 sec. to about 1500 ~ec. -1, and preferably from at least about 500 sec. to about 1200 sec. . For aluminum and it6 alloys a shear rate of from about 700 sec. to about 1100 sec.
has been found desirable.
The average cooling rates through the solidification temperature range of the molten metal in the mold ~hould be 1~6~Z~ 9063-MB
J. Winter et al 2-2-2 from about 0.1 C per minute to about 1000 C per minute and preferably from about 10 C per minute to about 500 C per minute. For aluminum and its alloy6 an average cooling rate of from about 40C per minute to about 500 C per minute ha~
been found to be 6uitable. The efficiency of the magneto-hydrodynamic 6tirring allows the use of higher cooling rate6 than with prior art stirring proces6es. Higher cooling rates yield highly de6irable finer grain 6tructure~ in the re6ulting rheoca6ting. Further, for continuous rheoca6ting higher throughput follow6 from the u6e of higher cooling rate6.
The parameter ¦B ¦ (~defined by eguation (1)) for carrying out the proce66 of thi6 invention 6hould compri6e from about 1 to about 10 and preferably from about 3 to about 7.
The parameter in N ( defined by equation ~2)) for carrying out the proces6 of thi6 invention 6hould comprise from about 1 to about 1000 and preferably from about 5 to about 200.
The angular line frequency ~ for a casting having a radius of from about 1" to about 10" 6hould be from about 3 to about 3000 hertz and preferably from about 9 to about 2000 hertz.
The magnetic field strength which i6 a function of the angular line frequency and the melt radiu6 6hould comprise from about 50 to 1500 gau66 and preferably from about 100 to about 600 gaus~.
The particular parameters employed can vary from metal sy6tem to metal 6y6tem in order to achieve the desired shear rate6 for providing the thixotropic 61urry. The appropriate 1~
~176~Z~ J. Winter et al 2-2-2 parameters for alloy systems other than aluminum can be determined by routine experimentation in accordance with the principles of this invention.
Solidification zone as the term is used in this appli-cation refers to the zone of molten metal or slurry in the mold wherein solidification is aking place. Magnetohydro-dynamic as the term is used herein refers to the process of stirring molten metal or slurry using a moving or rotating magnetic field. The magnetic stirring force may be more appropriately referred to as a magnetomotive stirring force which is provided by the movinq or rotating magnetic field of this invention.
The process and apparatus of this invention is applicable to the full range of materials as set forth in the prior art including but not limited to aluminum and its alloys~ copper and its alloys and steel and its alloys.
It is apparent that there has been provided in accordance with this invention an apparatus for making thixotropic metal slurries which fully satisfies the objects, means and advantages sot forth hereinbefore. While the invention has been described in combination with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims.
B
Claims (11)
1. In an apparatus for continuously or semi-continuously forming a semi-solid thixotropic alloy slurry, said slurry comprising throughout its cross section degenerate dendrite primary solid particles in a surrounding matrix of molten metal, said apparatus comprising:
means for containing molten metal, said containing means having a desired cross section;
means for controllable cooling said molten metal in said containing means; and means for mixing said molten metal for shearing dendrites formed in a solidification zone as said molten metal is cooled for forming said slurry;
said mixing means comprising a single two pole stator for generating a non-zero rotating magnetic field which moves transversly of a longitudinal axis of said containing means across the entirety of said cross section of said containing means and over said entire solidification zone, said moving magnetic field providing a magnetomotive stirring force directed tangetially of said containing means for causing said molten metal and slurry to rotate in said containing means, said magnetic force being of suffi-cient magnitude to provide said shearing of said dendrites, said magnetomotive force providing a shear rate of at least 500 sec.-1;
the improvement wherein, said containing means includes a first portion of low thermal conductivity and a second portion of high thermal conductivity, said portion of low thermal conductivity extending into said magnetic field for postponing solidification within said containing means until said molten metal is within said magnetic field, thereby promoting the formation of a degenerate dendritic structure throughout the slurry.
J. winter et al 2-2-2
means for containing molten metal, said containing means having a desired cross section;
means for controllable cooling said molten metal in said containing means; and means for mixing said molten metal for shearing dendrites formed in a solidification zone as said molten metal is cooled for forming said slurry;
said mixing means comprising a single two pole stator for generating a non-zero rotating magnetic field which moves transversly of a longitudinal axis of said containing means across the entirety of said cross section of said containing means and over said entire solidification zone, said moving magnetic field providing a magnetomotive stirring force directed tangetially of said containing means for causing said molten metal and slurry to rotate in said containing means, said magnetic force being of suffi-cient magnitude to provide said shearing of said dendrites, said magnetomotive force providing a shear rate of at least 500 sec.-1;
the improvement wherein, said containing means includes a first portion of low thermal conductivity and a second portion of high thermal conductivity, said portion of low thermal conductivity extending into said magnetic field for postponing solidification within said containing means until said molten metal is within said magnetic field, thereby promoting the formation of a degenerate dendritic structure throughout the slurry.
J. winter et al 2-2-2
2. An apparatus as in claim 1 wherein said first portion of said mold is formed of an insulating material and wherein said second portion of said mold is formed of a non-magnetic metal or alloy.
3. An apparatus as in claim 2 wherein said cooling means is arranged about said first portion of mold.
4. An apparatus as in claim 1 wherein said mold comprises a metal wall member for surrounding said molten metal and slurry, said wall member defining a top and bottom thereof and wherein a partial mold liner is provided internally of said mold wall extending from said top of said mold wall to a position intermediate said top and bottom of said mold wall to define said first portion of said mold, said liner leaving a portion of said metal wall member exposed which defines said second protion of said mold.
5. An apparatus as in claim 4 wherein said liner is formed from an insulating material.
6. An apparatus as in claim 5 wherein said magnetic field overlaps said liner.
7. An apparatus as in claim 6 wherein said mold wall has a cylindrical shape.
8. An apparatus as in claim 6 wherein said mold wall has a non-cylindrical shape.
9. An apparatus as in claim 6 wherein said mold comprises a mold for continuously or semi-continuously forming a rheo-casting.
10. An apparatus as in claim 9 wherein said cooling means is arranged about said first protion of said mold and said magnetic field generating means is arranged below said cooling means so that said magnetic field at least in part overlaps said liner.
J. winter et al 2-2-2
J. winter et al 2-2-2
11. In a process for continuously or semi-continuously forming a semi-solid thixotropic alloy slurry, said slurry comprising throughout its cross section degenerate dendrite primary solid particles in a surrounding matrix of molten metal, said process comprising:
providing a means for containing molten metal having a desired cross section;
controllably cooling said molten metal in said containing means; and mixing said contained molten metal for shearing dendrites formed in a solidification zone as said molten metal is cooled for forming said slurry;
said mixing step comprising generating solely with a two pole stator a non-zero rotating magnetic field which moves transversely of a longitudinal axis of said containing means across the entirety of said cross section of said containing means and over said entire solidification zone, said moving magnetic field providing a magnetomotive stirring force directed tangentially of said containing means for causing said molten metal and slurry to rotate in said containing means, said magnetomotive force being of sufficient magnitude to provide said shearing of said dendrites, said magnetomotive force providing a shear rate of at least 500 sec.-1;
the improvement wherein a first region of low thermal conductivity and a second region of high thermal conductivity is provided within said containing means, said region of low thermal conductivity postponing solidi-fication during said mixing step until said molten metal is within said magnetic field, thereby promoting the formation of a degenerate dendritic structure throughout the slurry.
providing a means for containing molten metal having a desired cross section;
controllably cooling said molten metal in said containing means; and mixing said contained molten metal for shearing dendrites formed in a solidification zone as said molten metal is cooled for forming said slurry;
said mixing step comprising generating solely with a two pole stator a non-zero rotating magnetic field which moves transversely of a longitudinal axis of said containing means across the entirety of said cross section of said containing means and over said entire solidification zone, said moving magnetic field providing a magnetomotive stirring force directed tangentially of said containing means for causing said molten metal and slurry to rotate in said containing means, said magnetomotive force being of sufficient magnitude to provide said shearing of said dendrites, said magnetomotive force providing a shear rate of at least 500 sec.-1;
the improvement wherein a first region of low thermal conductivity and a second region of high thermal conductivity is provided within said containing means, said region of low thermal conductivity postponing solidi-fication during said mixing step until said molten metal is within said magnetic field, thereby promoting the formation of a degenerate dendritic structure throughout the slurry.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US1505979A | 1979-02-26 | 1979-02-26 | |
| US015059 | 1979-02-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1176820A true CA1176820A (en) | 1984-10-30 |
Family
ID=21769305
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000346480A Expired CA1176820A (en) | 1979-02-26 | 1980-02-26 | Apparatus for making thixotropic metal slurries |
Country Status (10)
| Country | Link |
|---|---|
| JP (1) | JPS55117555A (en) |
| BR (1) | BR8001089A (en) |
| CA (1) | CA1176820A (en) |
| DE (1) | DE3006618A1 (en) |
| ES (1) | ES488944A0 (en) |
| FR (1) | FR2449498A1 (en) |
| GB (1) | GB2042385B (en) |
| IT (1) | IT1141384B (en) |
| MX (1) | MX152791A (en) |
| SE (1) | SE8001285L (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4450893A (en) * | 1981-04-27 | 1984-05-29 | International Telephone And Telegraph Corporation | Method and apparatus for casting metals and alloys |
| US4465118A (en) * | 1981-07-02 | 1984-08-14 | International Telephone And Telegraph Corporation | Process and apparatus having improved efficiency for producing a semi-solid slurry |
| US4457354A (en) * | 1981-08-03 | 1984-07-03 | International Telephone And Telegraph Corporation | Mold for use in metal or metal alloy casting systems |
| US4594117A (en) * | 1982-01-06 | 1986-06-10 | Olin Corporation | Copper base alloy for forging from a semi-solid slurry condition |
| US4494461A (en) * | 1982-01-06 | 1985-01-22 | Olin Corporation | Method and apparatus for forming a thixoforged copper base alloy cartridge casing |
| US4537242A (en) * | 1982-01-06 | 1985-08-27 | Olin Corporation | Method and apparatus for forming a thixoforged copper base alloy cartridge casing |
| US4638535A (en) * | 1982-01-06 | 1987-01-27 | Olin Corporation | Apparatus for forming a thixoforged copper base alloy cartridge casing |
| US4482012A (en) * | 1982-06-01 | 1984-11-13 | International Telephone And Telegraph Corporation | Process and apparatus for continuous slurry casting |
| US4565241A (en) * | 1982-06-01 | 1986-01-21 | International Telephone And Telegraph Corporation | Process for preparing a slurry structured metal composition |
| US4569702A (en) * | 1984-04-11 | 1986-02-11 | Olin Corporation | Copper base alloy adapted to be formed as a semi-solid metal slurry |
| US4555272A (en) * | 1984-04-11 | 1985-11-26 | Olin Corporation | Beta copper base alloy adapted to be formed as a semi-solid metal slurry and a process for making same |
| US4661178A (en) * | 1984-04-11 | 1987-04-28 | Olin Corporation | Beta copper base alloy adapted to be formed as a semi-solid metal slurry and a process for making same |
| US4585494A (en) * | 1984-04-11 | 1986-04-29 | Olin Corporation | Beta copper base alloy adapted to be formed as a semi-solid metal slurry and a process for making same |
| FR2634677B1 (en) * | 1988-07-07 | 1990-09-21 | Pechiney Aluminium | PROCESS FOR THE MANUFACTURE BY CONTINUOUS CASTING OF THIXOTROPIC METAL PRODUCTS |
| CH691354A5 (en) | 1994-11-22 | 2001-07-13 | Alusuisse Tech & Man Ag | Cradle for bolts. |
| CH689446A5 (en) * | 1995-03-24 | 1999-04-30 | Alusuisse Lonza Services Ag | Continuous casting mould of modular construction |
| DE19738821A1 (en) * | 1997-09-05 | 1999-03-11 | Aeg Elotherm Gmbh | Device for electromagnetic stirring of a molten metal |
| US6397925B1 (en) * | 1998-03-05 | 2002-06-04 | Honda Giken Kogyo Kabushiki Kaisha | Agitated continuous casting apparatus |
| CN100417935C (en) * | 2001-07-30 | 2008-09-10 | 西北工业大学 | Method and equipment for observing frozen organization of metal material and researching its rheologic behavour |
| DE602004001339T2 (en) * | 2003-02-10 | 2007-05-10 | Csir, Pretoria | METHOD AND DEVICE FOR PROCESSING HALF-RESISTANT METAL ALLOYS |
| CN108655357A (en) * | 2017-03-28 | 2018-10-16 | 宝山钢铁股份有限公司 | A kind of metal melting continuous casing |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1026399A (en) * | 1963-06-12 | 1966-04-20 | Aluminium Lab Ltd | Improvements in or relating to the continuous casting of metal |
| GB1097186A (en) * | 1965-03-11 | 1967-12-29 | Reynolds Metals Co | Continuous casting system |
| US3902544A (en) * | 1974-07-10 | 1975-09-02 | Massachusetts Inst Technology | Continuous process for forming an alloy containing non-dendritic primary solids |
| NL7700977A (en) * | 1976-02-24 | 1977-08-26 | Alusuisse | METHOD AND DEVICE FOR CONTINUOUS CASTING OF METAL MELT IN CASTING MOLDS. |
| JPS5522341A (en) * | 1978-08-04 | 1980-02-18 | Mitsui Eng & Shipbuild Co Ltd | Fluidized bed reaction tank |
-
1980
- 1980-02-18 SE SE8001285A patent/SE8001285L/en not_active Application Discontinuation
- 1980-02-19 GB GB8005620A patent/GB2042385B/en not_active Expired
- 1980-02-22 DE DE19803006618 patent/DE3006618A1/en active Granted
- 1980-02-25 IT IT20141/80A patent/IT1141384B/en active
- 1980-02-25 BR BR8001089A patent/BR8001089A/en unknown
- 1980-02-26 MX MX181328A patent/MX152791A/en unknown
- 1980-02-26 CA CA000346480A patent/CA1176820A/en not_active Expired
- 1980-02-26 FR FR8004177A patent/FR2449498A1/en active Granted
- 1980-02-26 JP JP2234080A patent/JPS55117555A/en active Pending
- 1980-02-26 ES ES488944A patent/ES488944A0/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| GB2042385B (en) | 1983-01-06 |
| DE3006618A1 (en) | 1980-09-04 |
| ES8100125A1 (en) | 1980-11-01 |
| IT1141384B (en) | 1986-10-01 |
| DE3006618C2 (en) | 1987-08-27 |
| IT8020141A0 (en) | 1980-02-25 |
| BR8001089A (en) | 1980-10-29 |
| SE8001285L (en) | 1980-08-27 |
| ES488944A0 (en) | 1980-11-01 |
| MX152791A (en) | 1986-06-06 |
| FR2449498B1 (en) | 1983-12-30 |
| JPS55117555A (en) | 1980-09-09 |
| GB2042385A (en) | 1980-09-24 |
| FR2449498A1 (en) | 1980-09-19 |
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