Abstract:
Apparatus and methods for limiting interaction of electron beams produced by adjacent electron bean guns mounted within a vacuum chamber of a furnace. The apparatus may include one or more barriers that are suspended within the vacuum chamber between adjacent electron beam guns. The methods may include suspending one or more vertically extending barriers with the vacuum chamber between adjacent electron beam guns.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     FEDERALLY SPONSORED RESEARCH 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The subject invention relates to electron beam furnaces for processing metallic materials and, more particularly, to apparatuses and methods for controlling and limiting the interaction of electron beams generated by adjacent electron beam guns mounted within an electron beam furnace. 
     DESCRIPTION OF THE INVENTION BACKGROUND 
     A variety of different processes and apparatuses have been developed over the years for obtaining relatively pure metals or alloys. One such apparatus that has been developed to separate the slag and burn off or evaporate volatile impurities from molten metal material is known as an electron beam furnace. Such furnaces are disclosed, for example, in U.S. Pat. No. 4,027,722 to Hunt and U.S. Pat. No. 4,932,635 to Harker. 
     In general, an electron beam furnace includes a vacuum chamber that has a hearth and crucible system therein. A number of electron beam guns are typically mounted in the vacuum chamber above the hearth to melt metals that are introduced into the chamber. As the metal is melted, it flows into the crucible to be re-solidified into an ingot. The electron beam from each gun can be deflected and scanned over the surfaces of the metal. The deflection of the electron beam is typically controlled by computers and electromagnetic coils in the base of each electron beam gun which serve to deflect the beam in accordance with changes in the magnetic fields. The use and construction of such electron beam guns are known in the art as exemplified by those electron beam guns disclosed in U.S. Pat. No. 3,857,014 to Prudkovsky et al. and U.S. Pat. No. RE 35,024 to Hanks. 
     The generation of electron beams by multiple electron beam guns in close proximity to each other can result in undesirable electromagnetic interaction between the beams. Changes in deflection or beam power of one gun can cause a change of deflection in an adjacent gun, which also influences the gun adjacent to it and so on. That interaction can make it difficult to control the beams to obtain the desired result. In addition, because the interaction of the electron beams is largely a function of the location of the electron beam guns relative to each other within the vacuum chamber, the further away from the metal that the electron guns are located, the greater the likelihood of electron beam interaction. Thus, the size of the vacuum chamber is often dictated by the number and location of electron beam guns. Small vacuum chambers require more frequent cleaning to remove the buildup of condensate material therein that could hamper and possibly lead to contamination of the material passing therein. 
     Thus, there is a need for apparatuses and methods for limiting the interaction between beams of adjacently mounted electron beam guns. 
     There is a further need for apparatuses and methods for improving the ability to control electron beam guns within an electron beam furnace. 
     There is still another need for apparatus having the above-mentioned advantages that is relatively inexpensive to manufacture and install. 
     Another need exists for an electron beam furnace that has means for limiting the interaction between the beams generated by electron beam guns mounted therein. 
     SUMMARY OF THE INVENTION 
     In accordance with a particularly preferred form of the present invention, there is provided an apparatus for limiting interaction between beams generated by at least two electron beam guns mounted within an electron beam furnace having a superstructure. The apparatus may include a planar barrier sized to extend between at least two electron beam guns and a superstructure hanger connected to the planar barrier. 
     The subject invention may also comprise an electron beam furnace that includes a vacuum chamber that has an upper portion and a lower portion. The furnace also has a hearth assembly located within the lower portion of said vacuum chamber and at least two electron beam guns mounted within the vacuum chamber above the hearth assembly. In addition, the furnace includes at least one planar barrier suspended from the upper portion of the vacuum chamber such that it extends between at least two electron beam guns. 
     The subject invention may also comprise a method for limiting interaction between electron beams generated by at least two electron beam guns within a vacuum chamber of an electron beam furnace. The method includes suspending a barrier from an upper portion of the vacuum chamber such that the barrier extends between the electron beams produced by the electron beam guns. 
     It is a feature of the present invention to provide magnetic shield barriers within an electron beam furnace to limit undesirable interaction between the beams of adjacent guns. 
     It is another feature of the present invention to provide magnetic shield barriers that are relatively inexpensive to manufacture and install. 
     Yet another feature of the present invention is to provide magnetic shield barriers that enable the electron beam guns to be positioned farther from their targets which enables larger vacuum chambers to be employed in electron beam furnaces. Larger chambers reduce the frequency of clean-outs required because the condensate collection can be placed further away from the melting process and can be provided with a larger surface area which results in a slower buildup of condensate. 
     Accordingly, the present invention provides solutions to the shortcomings of prior furnaces that employ electron beam guns. Those of ordinary skill in the art will readily appreciate, however, that these and other details, features and advantages will become further apparent as the following detailed description of the preferred embodiments proceeds. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying Figures, there are shown present preferred embodiments of the invention wherein like reference numerals are employed to designate like parts and wherein: 
     FIG. 1 is a partial cross-sectional elevational view of a portion of an electron beam furnace employing shield assemblies of the present invention; 
     FIG. 2 is a partial cross-sectional end view of the furnace of FIG. 1; 
     FIG. 3 is a partial plan view of the furnace of FIGS. 1 and 2, illustrating the orientation of the shield assemblies relative to the electron beam guns; 
     FIG. 4 is a partial plan view of another electron beam furnace employing another shield assembly embodiment of the present invention; 
     FIG. 5 is a side elevational view of the shield assembly depicted in FIG. 4; 
     FIG. 6 is a top view of the shield assembly of FIG. 5; 
     FIG. 7 is an end view of the shield assembly of FIGS. 5 and 6; 
     FIG. 8 is an enlarged partial view showing the struts of the shield assembly attached to the longitudinal barrier; and 
     FIG. 9 is an end elevational view of the furnace of FIG. 4, showing a transverse endplate of the subject invention attached to the condensate assembly of the furnace. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings for the purposes of illustrating the present preferred embodiments of the invention only and not for the purposes of limiting the same, FIGS.  1 - 3  show an electron beam furnace  10  for melting metals that has a shield assembly  60  of the present invention installed therein. Those of ordinary skill in the art will appreciate that the shield assembly  60  may be successfully employed in connection with a variety of different electron beam furnace configurations. Thus, the present invention should not be limited to use only in connection with furnaces that are constructed the manner depicted in the present Figures and described herein. 
     More specifically and with reference to FIGS. 1 and 2, the furnace  10  includes a vacuum chamber  12  that has a hearth assembly  20  extending therethrough. The vacuum chamber  12  has an entry end  14  into which raw material is introduced, a melting zone  16 , and a crucible mold  18 . In practice, molten material flows along the hearth assembly  20  under the influence of gravity. Raw material is introduced into the entry end  14 . The raw material is melted by bombarding it with beams of charged particles from a series of electron beam guns ( 40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52 ,  54 ) mounted within the vacuum chamber  12  above the hearth assembly  20 . The molten material flows in one continuous path through the hearth assembly  20  into the crucible mold  18 . It will be understood that by heating the molten material flowing along the hearth assembly  20  and by maintaining a relatively high vacuum, various volatile impurities and occluded gases emitted from the molten metal are exhausted from the chamber  12  through the vacuum pumps (not shown) servicing the chamber  12 . Thus, the molten material is purified as it flows through the melting zone  16  such that it achieves the desired level of purity when it reaches the crucible mold  18 . From the crucible mold  18 , the molten material is then continuously cast into a cold mold or the like in a casting zone which facilitates the continuous egress of material from the furnace in the form of, for example, metal ingots. 
     As the molten metal is heated within the processing zone, some metal is deposited on the interior walls and structures within the vacuum chamber  12 . After a predetermined period of time, the process must be interrupted to permit cleaning of the vacuum chamber  12 . The vacuum chamber  12  is typically provided with a series of condensate frame assemblies  30  that are supported from the upper superstructure  13  of the vacuum chamber  12 . See FIGS. 1 and 2. Such condensate frame assemblies  30  may be fabricated from, for example, mild steel and have a series of screens, plates, etc. that provide surfaces upon which the molten metal may adhere. Removing the excess material from the condensate frame assembly  30  can be an arduous task. Often times the excess material must be chiseled or ground from the condensate screens. Thus, to minimize the amount of downtime associated with cleaning the vacuum chamber  12 , the condensate frame assemblies  30  are typically constructed so that they may be removed from the vacuum chamber  12  and replaced with clean frame assemblies  30  to permit the contaminated frame assemblies  30  to be cleaned off line. 
     As discussed above, a series of conventional electron beam guns are mounted above the hearth assembly  20  to direct electron particle beams onto the molten material thereon. The furnace  10  depicted in FIGS.  1 - 3  has a total of eight conventional electron beam guns ( 40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52 ,  54 ) mounted thereto. The skilled artisan will of course appreciate, however, that the shield assembly  60  of the present invention may be advantageously employed in furnaces that have at least two electron beam guns mounted in adjacent relationship to each other such that the beams from the guns may interact with each other. Therefore, the shield assembly  60  of the present invention should not be limited to use in connection with furnace arrangements that employ eight electron beam guns. 
     FIGS. 2 and 3 illustrate the layout of the electron beam guns ( 40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  52 ,  54 ) in this embodiment. FIG. 3 is a plan view of the melting zone  16  of the vacuum chamber  12 . As can be seen therein, a barrier wall  17  separates the melting zone  16  into a first zone  19  and a second zone  21  and the center of the melting zone  16  is defined byaxis A—A. Conventional electron beam guns ( 40 ,  42 ,  44 ,  46 ) are equally spaced along an axis B—B within the chamber  12 . Axis B—B is substantially parallel to axis A—A. Likewise, conventional electron beam guns ( 48 ,  50 ,  52 ,  54 ) are equally spaced along an axis C—C that is substantially parallel to axes A—A and B—B. Furthermore, in this embodiment, the centers of guns ( 40 ,  48 ) are aligned on an axis D—D that is substantially transverse to axis A—A. The centers of guns ( 52 ,  54 ) are aligned on an axis E—E that is also substantially transverse to axis A—A. The centers of guns ( 44 ,  46 ) are offset from the centers of guns ( 52 ,  54 ). 
     One embodiment of the shield assembly  60  of the present invention is depicted in FIGS. 2 and 3. As can be seen in FIG. 3, the shield assembly  60  comprises a first assembly  62  that is adapted to be mounted within the first melting zone segment  19  and a second assembly  70  that is adapted to be mounted within the second melting zone segment  21 . First assembly  62  comprises a first longitudinal planar barrier  64  that may be fabricated from mild steel. A first transverse barrier  66 , fabricated from mild steel may be attached to the first longitudinal barrier  64  by, for example, welding. As can be seen in FIG. 3, the first transverse barrier member  66  may be centrally disposed between guns ( 40 ,  42 ) (i.e., distance “G” equals distance “H”). First assembly  62  may further comprise a second transverse barrier member  68  fabricated from mild steel that may be attached to the first longitudinal barrier member  62  by, for example, welding such that it is centrally disposed between the guns ( 48 ,  50 ) when installed (i.e., distance “I” equals distance “K”). As can be seen in FIG. 2, the first and second transverse barriers ( 66 ,  68 ) are configured to substantially conform to the contour of the corresponding ceiling portion  13  of the vacuum chamber  12  and the corresponding condensate frame assembly  30 . The first shield segment  62  may be suspended from the corresponding condensate frame assembly with chain or wire. Those of ordinary skill in the art will appreciate that the first shield assembly  62  may be attached to the corresponding condensate frame assembly  30  by bolted connections or other mechanical fasteners and connections. In addition, it will be further appreciated that the first transverse barrier  66  and the second transverse barrier  68  do not have to be attached to the longitudinal barrier  62 . Instead, the first transverse barrier  66  and the second transverse barrier  68  may be separately suspended or otherwise attached to the condensate frame assembly  30 . 
     The second shield assembly  70  is adapted to be mounted within the second melting zone segment  21  and comprises a second longitudinal barrier  72  that may be fabricated from, for example, mild steel. A primary transverse barrier  74 , fabricated from, for example, mild steel may be attached to the second longitudinal barrier  72  by, for example, welding. As can be seen in FIG. 3, the primary transverse barrier  74  may be centrally disposed between guns ( 44 , 46 ) (i.e., distance “L” equals distance “M”). The second shield assembly  70  may further comprise a secondary transverse barrier member  76  fabricated from mild steel that may be attached to the second longitudinal barrier member  72  by, for example, welding such that it is centrally disposed between the guns ( 52 ,  54 ) when installed (i.e., distance “N” equals distance “O”). The primary and secondary transverse barriers ( 74 ,  76 ) are configured to substantially conform to the contour of the corresponding ceiling portion  13  of the vacuum chamber  12  and the corresponding condensate frame assembly  30 . The second shield assembly  70  may be suspended from the corresponding section of the condensate frame assembly  30  with chain, wire or other suitable material. Those of ordinary skill in the art will appreciate that the second shield assembly  70  may also be attached to the corresponding portions of condensate frame assembly  30  by bolted connections or other mechanical fasteners and connections. In addition, it will be further appreciated that the primary transverse barrier  74  and the secondary transverse barrier  76  do not have to be attached to the second longitudinal barrier  72 . Instead, the primary transverse barrier  74  and the secondary transverse barrier  76  may be separately suspended or otherwise attached to the condensate frame assembly  30 . It will be further appreciated, however, that, in those furnace applications lacking the transverse barrier  17 , the first and second longitudinal barriers ( 62 ,  72 ) may comprise a unitary member. 
     As can be seen in FIG. 2, the electron beam guns ( 42 ,  44 ,  46 ,  48 ,  50 ,  52 ,  54 ) emit beams of electron particles generally designated as  80 . In this embodiment, the barriers ( 64 ,  66 ,  68 ,  72 ,  74 ,  76 ) extend downward toward the hearth assembly  20  from the condensate frame assembly  30  a distance of approximately 18 inches (45.7 cm)(represented by arrow “P” in FIG.  1 ). Those of ordinary skill in the art will appreciate that the distance that the shield assembly  60  protrudes downward is a function of the orientation of the electron beam guns. It is desirable for the shield assembly  60  to extend downward from the condensate shield assembly  30  as far as possible to minimize the amount of interaction between the beams  80  of adjacent guns, but not so far such that the beams  80  begin to degrade and/or melt the barriers ( 64 ,  66 ,  68 ,  72 ,  74 ,  76 ). Such distance may be determined by installing plates of various sizes between the adjacent guns to determine the maximum distance that the barriers can extend without being degraded or melted. In the embodiment depicted in FIGS. 1 and 2, the distance “P” is approximately 18 inches (45.7 cm). Angle “R” is approximately 15° and angle “S” is approximately 15°. It is conceivable, however, that other distances and angles may be successfully employed. 
     Another embodiment of the shield assembly of the present invention is depicted in FIGS.  4 - 9 . FIG. 4 is a plan view of a portion of a condensate frame assembly  130  of an electron beam furnace  110  that corresponds to a section of the furnace that has four electron beam guns. Thus, the condensate frame assembly  130  has four gun ports ( 132 ,  134 ,  136 ,  138 ) therein. As can be seen in FIGS.  4 - 7 , this embodiment of the shield assembly  160  comprises a longitudinal barrier  162  that is fabricated from, for example, mild steel. Also in this embodiment, first and second transverse plates ( 164 ,  166 ) may be attached together by, for example, welding to opposing sides of the longitudinal barrier  162 . It will be appreciated, however, that the first and second transverse plates ( 164 ,  166 ) do not have to be attached to the longitudinal barrier, but may be separately suspended or otherwise attached to the condensate frame assembly  130 . When installed, the longitudinal barrier  162  is centrally disposed between the gun ports ( 132 ,  134 ) and the gun ports ( 136 ,  138 ). The first and second transverse plates ( 164 ,  166 ) are centrally disposed between ports ( 132 ,  136 ) and ports ( 134 ,  138 ), respectively. See FIG.  4 . The end of the first transverse plate  164  may be approximately six inches (15.24 cm) from the centerlines of gun ports ( 132 ,  134 ) (distance “T”) and the end of the second transverse barrier  166  may be approximately six inches (15.24 cm) from the centerlines of the gun ports ( 136 ,  138 ) (distance “U”). 
     To facilitate removable attachment to the condensate frame assembly  130 , superstructure hangers in the form of transverse hanger struts  180  fabricated from, for example, mild steel, are attached to the longitudinal barrier  162  by pieces of steel angle  182  welded thereto. Those of ordinary skill in the art will appreciate that the hanger struts  180  may be attached to the longitudinal barrier  162  by a variety of different methods without departing from the spirit and scope of the present invention. The struts  180  are oriented to correspond with cross members of the condensate frame assembly  130  to enable the struts  180  to be removably affixed thereto by chain or wire  182 . However, the struts  180  may be attached to the condensate frame assembly  130  or the vacuum chamber  112  by any suitable means including bolting, clamping, welding, etc. 
     As can be seen in FIG. 9, additional barrier plates  190  may be affixed to each end of the frame assembly  130 . To facilitate such attachment, a series of holes  192  may be provided through the plate  190  to enable the plate  190  to be wired or chained to the frame assembly  130  by attachment members  194 . The plate  190  may, however, be attached to the condensate frame assembly or vacuum chamber superstructure  13  by a variety of different fastening methods such as bolting or welding. As can also be seen in FIG. 9, the plates  190  may be provided with a relatively arcuate upper edge  196  to enable the plates to conform to the shape of the upper portion of the vacuum chamber  112  or the condensate frame assembly  130 . In that embodiment, the bottom of the barrier plate  190  coincides with the bottom of the condensate frame assembly  130 . 
     Thus, from the foregoing discussion, it is apparent that the present invention may be used in connection with a variety of different electron beam furnaces. The subject invention may be advantageously adapted to limit interaction of electron beams emitted from adjacent electron beam guns mounted within a furnace. In addition, because the shield assemblies are removably attached to the condensate screen assemblies, they can be easily removed therefrom for cleaning purposes. It will be understood, however, that the shield assemblies of the present invention may be non-removably affixed to the condensate screen assembly or to the vacuum chamber itself, if so desired. 
     Accordingly, the present invention represents an easy and inexpensive method of limiting interaction of electron beams in an electron beam furnace. Those of ordinary skill in the art will, of course, appreciate that various changes in the details, materials and arrangement of parts which have been herein described and illustrated in order to explain the nature of the invention may be made by the skilled artisan within the principle and scope of the invention as expressed in the appended claims.