Patent Publication Number: US-6342102-B1

Title: Apparatus and method for increasing the diameter of metal alloy wires within a molten metal pool

Description:
U.S. GOVERNMENT RIGHTS 
     The United States government has rights in this invention pursuant to the employer-employee relationship of the Government to the inventors as U.S. Department of Energy employees at the Albany Research Center. 
    
    
     BACKGROUND OF THE INVENTION 
     This apparatus and method are an improvement in the dip forming process for increasing the diameter of metal wire or rods. The dip forming process is sometimes referred to in the prior art as a form of coating or casting. Casting usually implies the use of a die. However, “casting” is known in the art to also mean producing a metallic object with a preferred shape by running it through a molten bath and allowing the molten metal to solidify on the initial metal wire or rod. The present apparatus includes a block of metal that will be used as the coating material (referred to as the “source block of coating material”) to add diameter to the metal wire or rods (referred to as “core material”). The source block of coating material is housed within a hollow receptacle (known in the art as a “vessel” or “crucible”) and machined to include a hole that closely fits the core material that will pass through the block of coating material. The apparatus includes heating elements positioned on the exterior of the crucible such that only the upper portion of the source block of coating material housed within it will become molten while the heating elements are active and the lower portion of the source block will remain solid. The exact position of the heating elements on the crucible will vary with the size and dimensions of both the crucible and the source block, as well as with the amount of energy supplied to the heating elements. 
     The method includes passing the core material to be coated upward through the machined hole in the source block of coating material. The source block of coating material is located within the crucible and during operation exists in three physical states: (1) solid, in the base region of the source block of coating material where a machined channel or hole closely fits the core material; (2) solid/molten metal interface, where the core material and the molten metal from the source block converge; and (3) molten metal from the source block, for coating the core material as it moves upward through the crucible. 
     The core material passes upward through the machined hole within the solid portion of the source block of coating material before it contacts the molten metal that will coat the core material. A problem with the dip forming process is that small particles become entrained on the core material and form inclusions in the coated product or contaminate the molten coating material. This problem is eliminated in the subject apparatus where the closeness of fit between the core material and the hole machined within the source block of coating material provide a guide and seal to eliminate this problem. This seal prevents the core material from entering the crucible with entrained particles that may result in inclusions in the coated product or contamination of the molten metal used in the coating process. 
     The prior art has solved the problem of small particle entrainment by use of a bushing member to seal the entrance port for the core material. Use of such a bushing member has introduced new problems with the process. The dip forming processes have required that the bushing member be of different composition than the molten metal as described in U.S. Pat. No. 3,995,587 and other U.S. Patents referenced therein. 
     The closeness of fit between the solid portion of the source block and the core material is intended to serve the purpose of the bushing used in the prior art. The fit should be close enough to remove small particles that may become entrained on the core material and close enough to prevent the molten metal from entering the hole in the source block while the core material moves through the dip form processing apparatus, but not so close as to bind the core material within the source block. 
     When the bushing has a different metal composition relative to the metal that is used to coat the core material, the integrity of the process is at risk. Reactive metals, such as titanium and zirconium, readily dissolve other metals. Reactive metals used to coat the core material may dissolve the bushing on contact and may compromise the structural integrity of the crucible. The bushing otherwise effects the structural integrity of the crucible by being subject to physical wear by the moving core material. The bushing member is embedded in the vessel or crucible bottom and thus affects the ability of the crucible to hold molten metal over time. When the bushing member breaks down in the presence of reactive metals it becomes a new source of inclusions on the core material and a new source of contamination of the coating material. 
     The present apparatus and method avoid problems with the bushing by using the closeness of fit between the core material and the source block of coating material to prevent entrainment of small particles on the core material. Closeness of fit coupled with steady movement of the core material through the apparatus prevents the molten metal coating material from leaking out of the crucible. 
     OBJECTS OF THE INVENTION 
     The primary object of this invention is to provide a method for increasing the diameter of core material that does not require a bushing member at the entrance port of the crucible in order to eliminate the break down of such members particularly when reactive metals are used and to avoid the subsequent entrainment of particles within the cast product. 
     Another object of this invention is to provide an apparatus to allow the elimination of a bushing member from the entrance port of the crucible by utilizing a solid portion of the coating material as a guide and seal at the entrance port for the core material. 
     Another object of this invention is to heat and melt only the top portion of the source block material creating a source block/core material interface while the bottom portion of the source block remains solid. 
     SUMMARY OF THE INVENTION 
     This apparatus and method are an improvement for increasing the diameter of core material, such as metal and alloy wire and rods, by use of a molten metal pool. The method encompasses the startup and batch, intermittent, or continuous operation of coating and casting to increase diameters of core materials, especially for applying reactive metal coatings. The core material is moved upward through a source block of coating material. The invention eliminates the need for a bushing member at the entrance port and, thus, eliminates potential contamination and molten metal sealing problems due to bushings. 
     During operation the source block of coating material serves as: (1) a solid component core material entrance guide; (2) the solid/molten interface; and (3) the molten metal coating material. The invention is especially applicable for coating and increasing the diameter of reactive metal wire and rods because the same composition reactive metal source coating block material is used as the wire entrance guide, seal, and molten metal source for wire coating. The invention is applicable for cold-wall copper crucibles (both bottomless and casting crucibles with bottoms), ceramic crucibles, or any other containment crucible appropriate for the type of metal or alloy being melted. The system can be under vacuum, partial vacuum, atmospheric pressure, or positive pressure that is appropriate for the metal or alloy being melted. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of the invention. 
     FIG. 2 is a cross-sectional view of the assembled components. 
     FIG. 3 is a cross-sectional view of the apparatus during operation. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The component configuration in FIG. 1 is an exploded view of the preferred embodiment for an apparatus to increase the diameter of metal and alloy wire or rods (“core material”) by passing the core material through molten metal. The dip forming apparatus  10  consists of a crucible  20  that is a hollow, segmented water-cooled copper crucible. This particular embodiment includes water channels (not shown) through which water circulates within the crucible to assist with temperature control. However, the apparatus and method are applicable to dip forming processes that do not utilize water-cooled crucibles or vessels. The crucible  20  shown in FIG. 1 is tapered from the bottom of the crucible  20  to the top such that the circumference at the top is smaller than the bottom circumference. An induction coil  22  is wrapped around the outer surface of the upper portion of the crucible  20 . A source block of coating material  30  is shown beneath the crucible  20  and during operation of the dip forming process, the source block  30  is contained within the crucible  20 . The slightly larger bottom circumference relative to top circumference prevents the source block material  30  from being lifted out of the crucible  20 . 
     The crucible, vessel or receptacle  20  shape may also be rectangular, spherical or another shape. The main concern should be that the source block  30  cannot be lifted up and out of the crucible  20  during operation. In addition to the crucible restraint, a groove  32  around the bottom end of the source block  30  locks into a bracket  46  on top of a plate shelf  42  at the top end of the chamber  40  and serves to hold the source block of coating material in place. In the preferred embodiment the plate shelf  42  and brackets  46  form a continuous piece. However, the brackets  46  may be separate from and moveable upon the plate shelf  42 . With such a groove  32  and bracket  46  relationship, the top circumference of the crucible  20  does not need to be smaller than the bottom circumference in order to retain the source block  30 . 
     Located beneath the source block  30  is a bottom chamber  40  that houses the core material  44  to be coated. The crucible  20  has a flange  24  at its lower end. This flange  24  mates with a bottom chamber  40  section flange  48  in line with a plate shelf  42  containing a center aperture  50 . The plate shelf  42  is a separate component from the bottom chamber  40  for ease of maintenance and assembly and is bolted to the bottom chamber  40 . The center aperture  50  allows the core material  44  to enter the crucible  20  from the chamber  40  into a machined hole  38  in the source block  30  of coating material. 
     The preferred embodiment uses induction coils  22  as a heating mechanism for the dip forming process. However, this apparatus is amenable to the use of other heating methods such as electron beam or plasma melting devices being similarly situated, but focusing down into the top of the crucible  20 . The preferred embodiment also uses a segmented water-cooled copper crucible. The apparatus may include the use of casting crucibles with bottoms or a bottomless ceramic crucible for ease of operation and to retain the source material  30 . The apparatus is also amenable to use with crucibles that do not require water-cooling such as yttrium oxide crucibles with a tungsten layer. 
     System setup: Referring to FIG. 2, a source block  30  of coating material has a circumference larger than the circumference of the top of the crucible  20 . The source block  30  enters the crucible  20  through the base of the crucible  20 , where the circumference is larger than that of the source block  30 . This arrangement prevents the source block  30  from being lifted out of the crucible  20  during operation. The source block  30  has a hole  38  that is machined to the size and shape of the core material  44  to produce a close tolerance fit between the source block hole  38  and the particular core material  44  to be processed. The source block hole  38  need not extend the entire length of the source block  30  because the upper portion of the source block  30  will become molten allowing the core material  44  to be easily pushed through the crucible  20 . The core material  44  is embedded within the source block hole  38 . The source block  30  is positioned within the crucible  20  such that when the induction coils  22  are activated, the upper part of the source block  30  will melt to form a molten metal region extending from the top of the source block to the upper portion of the embedded core material  44 . The upper portion of the embedded core material  44  is then surrounded by the molten metal within the source block as the molten metal fills the gap between the source block  30  and the interior of the crucible  20 . 
     Once the source block  30  is positioned inside the crucible  20 , brackets  46  attached to the plate shelf  42  are inserted into a groove  32  of the source block  30 . The crucible  20  is secured to the chamber  40  by connecting flanges  24  and  48  on the crucible  20  and bottom chamber  40 . The core material  44  is contained within the chamber  40  and an end is inserted through the plate shelf aperture  50  and into the hole  38  in the source block  30 . An appropriate upward force is maintained on the embedded core material  44  by commonly available single or variable speed drive rolls, pinch rolls, or equivalent mechanisms  60  located within or outside the bottom chamber  40 . The upward force is maintained at a level that is sufficient to drive the core material  44  up and out of the containment crucible  20  once the core material  44 /block  30  interface becomes molten. 
     Operation: FIG. 3 more clearly shows the internal configuration of metal phases while the dip form process is in operation. The induction coils  22  are positioned outside the crucible  20  so that the top portion of the source block  30  is heated. The dip form processing apparatus  10  is configured so that only the upper portion of the source block  30  becomes molten while the lower portion intentionally remains solid. As the upper portion of the source block  30  becomes molten  34  it flows down around the outside of the unmelted portion of the solid block  30 . This melting and subsequent flowing around the unmelted portion produces a solidified layer  36  that conforms to the inner surface of the crucible  20 . The solidified layer  36  widens the base of the source block  30  and further prevents the source block  30  from being lifted out of the crucible  20  should the core material  44  become stuck to the source block  30 . 
     The closeness of fit between the core material  44  and the hole  38  in the source block  30  prevents the molten metal  34  from falling through the aperture and into the chamber  40 . Molten metal is further prevented from falling through the hole  38  in the source block  30  by initially positioning the core material  44  as far into the source block  30  as the hole  38  extends. An upward force is maintained on the core material  44  by conventional means such as a pinch roller system  60  to facilitate the initial push through the molten metal  34  once the interface between the source block  30  and the core material  44  becomes molten. This upward movement will tend to keep the molten metal  34  from entering into the space occupied by the embedded core material  44 . As the molten region  34  becomes established and encompasses the core material  44  and source block  30  interface, the core material  44  proceeds through the molten metal region  34  of the melt, molten metal  34  from the melt solidifies on the surface of the core material  44  forming a coating which increases its diameter. The speed at which the core material  44  travels through the molten metal  34  is varied to attain the desired increase in diameter. 
     The system is large enough to facilitate continuous charge feeding and continuous coated core material  44  withdrawal. When rods are to be coated, the process may be batch, intermittent, or continuous limited only by the length of rod to be coated. The coated core material  44  is collected at the top end of the dip forming apparatus  10  by conventional means such as a pinch roller system or drum assembly for a coiled product  70 . The whole system can be under vacuum, partial vacuum with an inert atmosphere, or atmospheric pressure depending on the type of metal being melted, and can be run continuously, intermittently, or batchwise.