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A process and apparatus for continuously and semi-continuously casting molten metals and alloys. Control of the initial stages of solidification is carried out through application of a thermal insulating layer on the coolant side of a casting mold wall. The layer modifies the heat flux characteristi

A process and apparatus for continuously and semi-continuously casting molten metals and alloys. Control of the initial stages of solidification is carried out through application of a thermal insulating layer on the coolant side of a casting mold wall. The layer modifies the heat flux characteristics of the mold along a selected length thereof.

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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 m

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 including a mold wall for containing and extracting heat from said thixotropic slurry, said containing means having a desired cross section; means for controllably 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 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 magnetic force being of sufficient magnitude to provide said shearing of said dendrites, said magnetomotive force providing a shear rate of al least 500 sec. -1 ; the improvement wherein said apparatus comprises a first insulating layer extending over at least a portion of the inside surface of said mold wall and terminating at a lower edge projection within said mold wall, means for cooling said mold wall arranged about on outside surface of said mold wall; and a second insulating layer located along a specific length of the outside surface of said mold wall, said specific length beginning approximately at said lower edge projection of said first insulating layer and extending a predetermined distance below said projection, said second layer comprising a coating serving to alter the thermal characteristics of said mold wall along said length as compared to the remainder of said liner. 2. An apparatus as in claim 1 wherein said coating comprises an insulating material selected from the group consisting of polymers, resins, enamels, plastics, oxides, metals with low thermal conductivity, metal alloys, and metal oxides. 3. An apparatus as in claim 1 wherein the thickness of said insulating layer satisfies the following relationship: ##EQU## 4. An apparatus as in claim 1 wherein said slurry comprises degenerate primary solid particles in a surrounding matrix of molten metal; and said thixotropic slurry forming means comprises means for mixing said molten metal and creating a stirring force which causes said molten metal and slurry to rotate in said mold. 5. An apparatus as in claim 4 wherein said mixing and stirring force creating means comprises electromagnetic means for generating a magnetic field which moves transversely of a longitudinal axis of said mold. 6. An apparatus as in claim 5 wherein said electromagnetic means comprises a multi-phase, two pole induction motor stator surrounding said mold. 7. 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, said means including a mold wall for containing and extracting heat from said thixotropic slurry; 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; 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 said forming process comprises placing a first thermal insulating layer on said mold wall, said first insulating layer extending over at least a portion of the inside surface of said mold wall and terminating at a lower edge projection within said mold wall; cooling said mold wall from an outside surface of said mold wall; and coating a second thermal insulating layer along a specific length of the outside surface of said mold wall, said specific length beginning approximately at said lower edge projection of said first insulating layer and extending a predetermined distance below said projection, said second coated layer serving to alter the thermal characteristics of said mold wall along said length as compared to the remainder of said mold wall. 8. A process as in claim 7 wherein said step of coating comprises spraying said insulating material onto said outside surface. 9. A process as in claim 8 wherein said coating comprises an insulating material selected from the group consisting of polymers, resins, enamels, plastics, oxides, metals having low thermal conductivity, metal alloys, or metal oxides. 10. A process as in claim 7 wherein the thickness of said insulative layer satisfies the following relationship: ##EQU## 11. A process as in claim 7 wherein said slurry comprises degenerate dendrite primary solid particles in a surrounding matrix of molten metal and said step of forming said thixotropic slurry comprises mixing said molten metal and creating a stirring force which causes said molten metal and slurry to rotate in said mold.