MELTING HEARTH, COLD HEARTH MELTING SYSTEM, AND PROCESS FOR PRODUCING HIGH TEMPERATURE METAL ALLOYS
A melting hearth includes high temperature walls, a melting cavity having a specific topography, and conformal fluid cooling passages configured to provide a flow path for a cooling fluid that is substantially parallel to the topography of the melting cavity. In addition, the topography of the melting cavity mirrors a heat signature of a heat source used to melt a feed material in the melting hearth into a molten metal. A cold hearth melting system includes the melting hearth, a magnetic stirring system, the heat source having the heat signature, a tilting mechanism for tilting the melting hearth to a desired tilt angle, and a fluid cooling system having a fluid source in flow communication with the conformal fluid cooling passages. A process for producing high temperature metal alloys uses the cold hearth melting system and an algorithm for controlling the pouring of the molten metal from the melting hearth.
1 . A melting hearth configured to melt a feed material into a molten metal comprising:
a body having walls constructed from a high temperature material;
a melting cavity in the body configured to melt the feed material, the melting cavity having a topography that mirrors a heat signature of a heat source used to melt the feed material; and
a conformal fluid cooling passage configured to cool the melting cavity using a cooling fluid, the conformal fluid cooling passage having a contour that matches the topography of the melting cavity and provides a flow path for the cooling fluid parallel to the topography of the melting cavity.
2 . The melting hearth of claim 1 wherein the high temperature material for the walls comprises a metal selected from the group consisting of Ti, W, Mo, Hf, Nb, Y 2 O 3 , and alloys thereof.
3 . The melting hearth of claim 1 wherein the topography of the melting cavity comprises a symmetrical 3-D shape with no corners or dead ends.
4 . The melting hearth of claim 1 wherein the body comprises a monolithic structure.
5 . The melting hearth of claim 1 wherein the body comprises a hybrid structure having a high temperature coating on the topography of the melting cavity, the high temperature coating comprising yttria-stabilized zirconia (YSZ), or boron nitride (BN).
6 . The melting hearth of claim 1 wherein the melting cavity has a deep portion that aligns with a highest level of thermal radiation emitted by the heat source and a shallow portion that aligns with a lowest level of thermal radiation emitted by the heat source aligns.
7 . The melting hearth of claim 1 wherein the body comprises a 3D printed metal having a plurality of integrated fluid cooling passages.
8 . The melting hearth of claim 1 wherein the body comprises a 3-D printed metal configured to hold the melting cavity and the melting cavity comprises a different metal.
9 . A cold hearth melting system for producing a high temperature metal alloy comprising:
a heat source having a heat signature;
a melting hearth comprising:
a body having walls constructed from a high temperature material,
a melting cavity in the body configured to melt the feed material using heat from the heat source into a molten metal, the melting cavity having a topography that mirrors the heat signature of the heat source, and
a conformal fluid cooling passage in the body configured to cool the melting cavity using a cooling fluid, the conformal fluid cooling passage having a contour that matches the topography of the melting cavity to provide a flow path for the cooling fluid parallel to the topography of the melting cavity;
a magnetic stirring system formed integrally with, or proximate to the body of the melting hearth configured to stir the molten metal in the melting cavity; and
a fluid cooling system having a fluid source for the cooling fluid in flow communication with the conformal fluid cooling passage.
10 . The cold hearth melting system of claim 9 further comprising a tilting mechanism for tilting the melting hearth to pour the molten metal from the melting cavity.
11 . The cold hearth melting system of claim 9 further comprising a central processing unit (CPU) configured to control the tilting mechanism having a program that includes an algorithm for controlling a tilt angle of the melting hearth.
12 . The cold hearth melting system of claim 9 wherein the fluid cooling system comprises a fluid cooling jacket attached to the body of the melting hearth comprising a 3-D printed plastic material having a cooling passage in a complex geometrical configuration.
13 . The cold hearth melting system of claim 9 wherein the high temperature material for the walls comprises a metal selected from the group consisting of Ti, W, Mo, Hf, Nb, Y 2 O 3 , and alloys thereof.
14 . The cold hearth melting system of claim 9 wherein the topography of the melting cavity comprises a symmetrical 3-D shape with no corners or dead ends.
15 . The cold hearth melting system of claim 9 wherein the topography of the melting cavity comprises a hemisphere, a parabolic shape or a splined curve shape.
16 . The cold hearth melting system of claim 9 wherein the heat source comprises a DC transferred plasma-arc torch having a symmetrical gas formed arc-column that has a high temperature gradient, the highest temperature being at a centerline of the arc-column and the topography of the melting cavity has a deepest part along the centerline of the arc-column and the topography shallows at distances further from the centerline.
17 . The cold hearth melting system of claim 9 wherein a highest level of thermal radiation emitted by the heat source aligns with a deepest portion of the melting cavity, and a lowest level of thermal radiation emitted by the heat source aligns with a shallowest portion of the melting cavity.
18 . The cold hearth melting system of claim 9 wherein the body comprises a 3D printed metal having a plurality of integrated fluid cooling passages.
19 . The cold hearth melting system of claim 9 wherein the body comprises a 3-D printed metal configured to hold the melting cavity and the melting cavity comprises a different metal.
20 . A process for producing a high temperature metal alloy from a feed material comprising:
providing a cold hearth melting system comprising a melting hearth having a body with high temperature walls, a melting cavity having a topography and a plurality of fluid cooling passages including one or more conformal fluid cooling passages in the body having a contour that matches the topography of the melting cavity to provide a flow path for the cooling fluid parallel to the topography of the melting cavity, a heat source having a heat signature configured to melt a feed material into a molten metal, with the topography of the melting cavity mirroring a heat signature of the heat source, a magnetic stirring system integral with or proximate to the body of the melting hearth, and a tilting mechanism for tilting the melting hearth;
melting the feed material and metal alloys into a molten metal using a heating process wherein heat from the heat source is applied to the feed material in the melting cavity to form a molten metal;
stirring the molten metal during the melting process using the magnetic stirring system; and
pouring the molten metal from the melting cavity using the tilting mechanism.
21 . The process of claim 20 further comprising correcting a composition of the molten metal during the melting step by adding one or more metal alloys to the molten metal.
22 . The process of claim 21 wherein the correcting step compensates for a low melting feed material that has been vaporized during multiple melts.
23 . The process of claim 20 wherein the melting step is initiated using an on-composition starter skull configured to contact the melting cavity, followed by adding the feed material and metal alloys to the melting cavity on top of the starter skull.
24 . The process of claim 20 wherein the pouring step comprises:
providing a central processing unit (CPU) having a program;
providing an algorithm in the program that uses the topography of the melting cavity to calculate a melt pool surface area of the molten metal at different tilt angles of the melting hearth at increments through a range of motion of the melting hearth, and to calculate hearth velocity data of the molten metal at the different tilt angles; and
controlling the tilting mechanism and the tilt angles of the melting hearth using the hearth velocity data.
25 . The process of claim 20 wherein the feed material comprises a scrap material and the metal alloy comprise an additive manufacturing (AM) grade metal powder.
26 . The process of claim 20 wherein the pouring step pours the molten metal into an atomization system.
27 . The process of claim 20 wherein a highest level of thermal radiation emitted by the heat source aligns with a deepest portion of the melting cavity, and a lowest level of thermal radiation emitted by the heat source aligns with a shallowest portion of the melting cavity.