Abstract:
A device for submerging scrap metal includes: (a) a drive source, (b) a drive shaft having a first end and a second end, the first end being connected to the drive source, and (d) an impeller connected to the second end of the drive shaft, the impeller preferably having two or more outwardly-extending blades. Preferably, each of the blades has a portion that directs molten metal at least partially downward. The impeller design leads to lower operating speeds, lower vibration, longer component life and less maintenance. Additionally, the impeller preferably has a connective portion. The connective portion is used to connect the impeller to the shaft and preferably comprises a nonthreaded, tapered bore extending through the impeller.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device, called a scrap melter, for submerging scrap metal in a molten metal bath. The device preferably includes a drive source, an impeller and a drive shaft. The device preferably draws molten metal downward in order to submerge scrap placed on the surface of the bath. 
     BACKGROUND OF THE INVENTION 
     Scrap melter systems, such as the one shown schematically in FIGS. 1 and 2, generally use two devices, a circulation pump and a scrap melter. As shown in FIG. 1 the vessel V containing molten metal bath B is preferably divided into two compartments. Compartment  1  (called a pump well) houses circulation pump  2 . Compartment  3  (called a charge well) houses a scrap melter  10 . The circulating molten metal moves between compartment  1  and compartment  3  and is preferably circulated throughout vessel V. Scrap S is introduced into compartment  3  and is submerged by the downward draw created by the impeller of scrap melter  10 , which pulls the scrap downward into the molten metal bath. The molten metal bath is preferably maintained, at least partially, in a remelting furnace having a heating chamber interconnected to a melting chamber. Bath B is maintained at a temperature above the melting point of the scrap metal in order to melt the scrap metal. 
     A conventional scrap melter includes an impeller affixed to a drive shaft, and a drive source for rotating the shaft and the impeller. As stated above, the impeller draws molten metal and the scrap metal downward into the molten metal bath in order to melt the scrap. The circulation pump is preferably positioned in the pump well and circulates the molten metal between the chambers in order to maintain a relatively constant temperature within bath B. Such a system, including a circulation pump and a scrap melter, is disclosed in U.S. Pat. No. 4,598,899, issued Jul. 8, 1986 to Cooper, the disclosure of which that is not inconsistent with this disclosure is incorporated herein by reference. As defined herein, the terms auger, rotor and impeller refer to the same general structure, i.e., a device used in a scrap melter for displacing molten metal. 
     Scrap melter impellers generally move molten metal radially outward away from the impeller to create a downward draw above the impeller. However, such impellers can create turbulence or flow that may partially move into the path of the fluid entering the impeller from above, in which case some scrap may not be efficiently drawn into bath B where it can be melted and mixed, thus decreasing the fluid flow to the impeller and decreasing the efficiency of the scrap melting operation. In addition, the radial turbulence may cause some fluid that has been expelled from the impeller to be immediately recirculated through the impeller, thus decreasing the flow of virgin fluid through the impeller. That further decreases efficiency because it reduces the draw of molten metal from above the impeller. As a result, in order to maintain a desired volume of fluid flow through the impeller, the speed of the impeller may be increased to overcome these effects. Increasing the speed of the impeller, however, may cause excess vibration leading to part failure, downtime and maintenance expenses. 
     Scrap melters have been developed to restrict radial flow from the impeller to limit turbulence and produce more efficient flow. One such assembly, disclosed in U.S. Pat. No. 4,930,986, issued Jun. 5, 1990 to Cooper, the disclosure of which that is not inconsistent with this disclosure is incorporated herein by reference, includes an impeller positioned inside a drum, both of which rotate as a single unit. One disadvantage to this assembly is that pieces of scrap or dross can jam in it, which decreases its efficiency. Other prior art devices are disclosed in U.S. Patent Nos. 4,286,985, 3,984,234, 4,128,415 and 4,322,245. 
     SUMMARY OF THE INVENTION 
     The preferred embodiment of the present invention is a scrap melter utilizing an open impeller to reduce jamming or clogging. Thus, the invention can function efficiently in virtually any scrap melting environment, handling particles of virtually any size that are likely to be encountered in any such environment. An impeller according to the invention functions by displacing molten metal to create a downward draw. It provides the benefit of reducing the problems associated with faster operating speeds (i.e., the possible creation of a vortex and turbulence, and/or part failure, greater downtime and higher maintenance costs). The way in which it achieves these results is by (a) displacing more molten metal while operating at the same speed as conventional impellers, and/or (b) moving at least some of the molten metal in a downward or partially downward direction. 
     An impeller according to the invention displaces more molten metal by the use of (1) a larger area on the blade surfaces that push against the molten metal as the impeller rotates, and/or (2) surfaces that push against the metal at angles that displace a relatively large amount of molten metal. One impeller according to the invention preferably moves molten metal at least partially in the downward direction, while another moves molten metal only in an outward direction. 
     In one preferred embodiment the impeller is preferably a four-bladed cross wherein each blade preferably includes an angled surface that directs molten metal at least partially in the downward direction. The impeller creates a draw that draws molten metal and any solid scrap metal contained therein downward into the molten metal bath. It also preferably provides at least some radial or partially radial flow, and may include a surface or structure specifically designed to generate radial or partially radial flow, to assist in circulating molten metal within the bath. 
     In another preferred embodiment, the impeller is preferably a four-bladed cross wherein each blade preferably includes a vertical surface that directs molten metal radially outward away from the impeller. The impeller creates a draw that draws molten metal and any solid scrap metal contained therein downward into the molten metal bath. It also assists in circulating molten metal within the bath. 
     A scrap melter according to the invention can be operated at lower speeds than conventional melters but still displace the same amount of molten metal per impeller revolution. Alternatively, it can be operated at the same speeds as, and displace more molten than conventional scrap melters. A benefit of the lower speed is that the scrap melter of the invention vibrates less and requires less maintenance and fewer replacement parts. 
     A preferred melter according to the invention includes a drive source, a drive shaft having a first end and a second end and an impeller. The first end of the drive shaft is connected to the drive source. An impeller according to the invention is connected to the second end of the drive shaft. The drive source is preferably a pneumatic or electric motor, but can be any device(s) capable of rotating the impeller. 
     A scrap melter according to the invention may be used in a scrap melter system comprising a scrap melter, a vessel containing a molten metal bath and a circulation pump. Conventional pumps for pumping molten metal that may be used as circulation pumps are generally disclosed in U.S. Pat. No. 2,948,524 to Sweeney et al., U.S. Pat. No. 5,203,681 to Cooper entitled “Submersible Molten Metal Pump,” pending U.S. application Ser. No. 08/59,780, filed Dec. 13, 1996, entitled Molten Metal Pump With a Flexible Coupling and Cement-Free Metal-Transfer Conduit Connection, U.S. Pat. No. to Cooper entitled Impeller Bearing System for Molten Metal Pumps, U.S. application Ser. No. 09/152,168, filed Sep. 11, 1998, entitled Improved Gas Dispersion Device, U.S. Pat. No. 5,678,807 to Cooper and U.S Pat. No. 5,662,725 to Cooper, the disclosures of which are incorporated herein by reference. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described with reference to the drawings, wherein like designations denote like elements, and: 
     FIG. 1 is a side view of a scrap melter system according to the invention comprising a scrap melter, a vessel and an impeller according to the invention. 
     FIG. 2 is a top view of the system shown in FIG.  1 . 
     FIG. 3 is a perspective view of a preferred impeller according to the invention. 
     FIG. 4 is perspective view of an alternate preferred impeller according to the invention. 
     FIG. 5 shows an exploded, perspective view of an assembly according to the invention, including a drive shaft, the impeller of FIG. 3 and a nut. 
     FIG. 6 is a partial side view of the assembly shown in FIG. 5, showing the connected components. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the figures, where the purpose is for describing a preferred embodiment of the invention and not for limiting same, FIG. 1 shows a scrap melter  10  submerged in a molten metal bath B. All of the components of scrap melter  10  exposed to molten metal bath B are preferably formed from oxidation-resistant graphite or other material suitable for use in molten metal. 
     A drive source  28  is connected to impeller  100  by any structure suitable to transfer driving force from source  28  to impeller  100 . Drive source  28  is preferably an electric, pneumatic or hydraulic motor although, as used herein, the term drive source refers to any device or devices capable of rotating impeller  100 . 
     A drive shaft  12  is preferably comprised of a motor drive shaft (not shown) connected to an impeller drive shaft  40 . The motor drive shaft has a first end and a second end, the first end being connected to motor  28  by any suitable means and which is effectively the first end of drive shaft  12  in the preferred embodiment. An impeller shaft  40  has a first end  42  (shown in FIG. 4) and a second end  44 . The preferred structure for connecting the motor drive shaft to impeller drive shaft  40  is a coupling (not shown). The coupling preferably has a first coupling member and a second coupling member. The first end  42  of impeller shaft  40  is connected to the second end of the motor shaft, preferably by the coupling, wherein the first end  42  of impeller shaft  40  is connected to the second coupling member and the second end of the motor drive shaft is connected to the first coupling member. The motor drive shaft drives the coupling, which, in turn, drives impeller drive shaft  40 . Preferably, the coupling and first end  42  of the impeller shaft  40  are connected without the use of connecting threads. 
     Impeller  100  is an open impeller. As used herein the term open refers to an impeller that allows dross and scrap to pass through it, as opposed to impellers such as the one shown in U.S. Pat. No. 4,930,986, which does not allow for the passage of much dross and scrap, because the particle size is often too great to pass through the impeller. Preferred impeller  100  is best seen in FIG.  3 . Impeller  100  provides a greater surface area to move molten metal than conventional impellers. Impeller  100  is preferably imperforate, has two or more blades, is preferably formed of solid graphite, is attached to and driven by shaft  12 , by being attached to shaft  40  in the preferred embodiment, and is preferably positioned centrally about the axis of shaft  40 . Impeller  100  may, however, have a perforate structure (such as a bird-cage impeller, the structure of which is known to those skilled in the art) or partially perforate structure, and be formed of any material suitable for use in a molten metal environment. 
     Impeller  100  most preferably has four blades  102  and is shaped like a cross when viewed from the top. Impeller  100  includes a central section, or hub,  104  that is the area defined by the intersection between blades  102 , when impeller  100  has three or more blades. In the preferred embodiment, hub  104  is an approximately 8″ square. A connective portion  106  is preferably a nonthreaded, tapered bore extending through hub  104 , but can be any structure capable of connecting impeller  100  to drive shaft  12 . The preferred embodiment of impeller  100  also has a top surface  112 , a bottom surface  114 , and a trailing face  116 . The diameter of connective portion  106  is approximately 5″ at upper surface  112  and tapers to approximately 4″ at lower surface  114  to form a tapered bore as shown in FIGS. 3 and 5. 
     The height of surface  116 , measured vertically, is preferably between 6 and 7 inches. Each blade  102  preferably extends approximately 10″ outward from hub  104 , the overall preferred length and width of impeller  100 , including hub  104 , therefore being approximately 28″. A recess (not shown) may be formed from top surface  112  to trailing surface  116 . 
     Preferably, each blade  102  has the same configuration so only one blade  102  shall be described. In the preferred embodiment, blade  102  has a leading face  108 . Face  108  is on the leading side of blade  102  as it rotates (as shown impeller  100  is designed to rotate in a clockwise direction). Face  108  includes an angled portion  108 A and a vertical lip  108 B. Portion  108 A directs molten metal at least partly in the downward direction, toward the bottom of vessel V, as shown in FIG.  1 . Surface  108 A may be substantially planar or curved, or multi-faceted, such that, as impeller  100  turns, surface  108 A directs molten metal partially in the downward direction. Any surface or structure that functions to direct molten metal downward or partially downward can be used, but it is preferred that surface  108 A is formed at a 30°-60° , and most preferably a 45° planar angle. Alternatively, leading face  108  may itself be, or include a surface that is, (1) vertical, (2) substantially vertical, or (3) angled to direct molten metal in a partially upward direction, because the radial displacement of molten metal alone will create a downward draw in the space above impeller  100 . 
     Impeller  300 , shown in FIG. 4, is also an open impeller. Preferred impeller  300  is best seen in FIG.  4 . Impeller  300 also provides a greater surface area to move molten metal than conventional impellers. Impeller  300  is preferably imperforate, has two or more blades, is preferably formed of solid graphite, is attached to and driven by shaft  12 , by being attached to shaft  40  in the preferred embodiment, and is preferably positioned centrally about the axis of shaft  40 . Impeller  100  may, however, have a perforate structure (such as a bird-cage impeller, the structure of which is known to those skilled in the art) or partially perforate structure, and be formed of any material suitable for use in a molten metal environment. 
     Impeller  300  most preferably has four blades  302 . Impeller  300  includes a central section, or hub,  304  that is the area defined by the intersection between blades  302 , when impeller  300  has three or more blades. In the preferred embodiment, hub  304  is an approximately 8″ square. A connective portion  306  is preferably a nonthreaded, tapered bore extending through hub  304 , but can be any structure capable of connecting impeller  300  to drive shaft  12 . The preferred embodiment of impeller  300  also has a top surface  312 , a bottom surface  314 , and a trailing face  316 . The diameter of connective portion  306  is approximately 5″ at upper surface  312  and tapers to approximately 4″ at lower surface  314  to form a tapered bore as shown in FIG.  4 . 
     The height of surfaces  308 ,  316 , measured vertically, is preferably between 6 and 7 inches. Each blade  302  preferably extends approximately 10″ outward from hub  304 , the overall preferred length and width of impeller  300 , including hub  304 , therefore being approximately 28″. A recess (not shown) may be formed from top surface  312  to trailing surface  316 . 
     Preferably, each blade  302  has the same configuration so only one blade  302  shall be described. In the preferred embodiment, blade  102  has a leading face  308 . Face  308  is on the leading side of blade  302  as it rotates (as shown impeller  300  is designed to rotate in a clockwise direction). Face  308  is vertical (as used herein, the term vertical refers to any vertical or substantially vertical surface) and directs molten metal outward away from impeller  300 . Face  308  may be substantially planar or curved, or multi-faceted, such that, as impeller  300  turns, face  308  directs molten metal outward. Any surface or structure that functions to direct molten metal outward can be used, but it is preferred that surface  308  is vertical and extends the full height of blade  308  so that blade  308  has a square cross section. Alternatively, face  308  may itself be, or include a surface that is angled to direct molten metal in a partially upward direction, because the radial displacement of molten metal alone will create a downward draw in the space above impeller  300 . 
     As shown in FIGS. 5 and 6, second end  44  of impeller drive shaft  40  preferably has a tapered section  44 A that is received in the tapered bore of the preferred embodiment of connecting portion  106 . End  44  also preferably has a threaded section  44 B that extends below bottom surface  114  of impeller  100  when section  44 A is received in connecting portion  106 . In this preferred embodiment, a nut  200 , that has a threaded opening  202 , is screwed onto section  44 B to retain impeller  100  on end  44  of rotor drive shaft  40 . Nut  200  and section  44 B preferably have 4″-4½″ U.N.C. threads. Nut  200  is preferably a hex head nut having an overall diameter of approximately 7″. 
     The purpose of tapered bore  106  is easy removal of end  44  of shaft  40  from connective portion  106 . Some prior art devices utilize either a threaded bore and/or a right cylindrical bore, i.e., a bore having the same diameter at the top and bottom to connect the drive shaft to the impeller. The problem with such structures is that during operation of the scrap melter molten metal seeps between the end of the shaft and the bore in the impeller. This leads to difficulty in removing the shaft from the bore, and often the shaft must be chiseled out. The nonthreaded, tapered bore  106  of the invention alleviates this problem. Although only the preferred attachment of impeller  100  is shown, impeller  300  would preferably be attached to shaft  12  in the same manner as described for impeller  100 . 
     Preferred embodiments having now been described, variations that do not depart from the spirit of the invention will occur to others. The invention is thus not limited to the preferred embodiment but is instead set forth in the following claims and legal equivalents thereof, which are contemplated to cover any such variations. Unless specifically stated in the claims, any of the claimed inventions may include structures or devices other than those specifically set forth in the claims.