Patent Publication Number: US-10309725-B2

Title: Immersion heater for molten metal

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of, and claims priority to U.S. patent application Ser. No. 14,804,157 (Now U.S. Pat. No. 9,481,035) filed on Jul. 20, 2015, which is a continuation of, and claims priority to U.S. patent application Ser. No. 12/880,027 (Now U.S. Pat. No. 9,108,244), filed on Sept. 10, 2010, the disclosures of which are incorporated herein in their entity for all purposes. This application also claims priority to U.S. Provisional Application No. 61/241,349 filed on Sept. 10, 2009. The drawing figures and pages 14-16 of that application are incorporated herein by reference. This application also claims priority to and incorporates by reference U.S. application Ser. No. 12/878,984 (Now U.S. Pat. No. 8,524,146), filed on Sep. 9, 2010. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a system and device for heating molten metal. 
     BACKGROUND OF THE INVENTION 
     As used herein, the term “molten metal” means any metal or combination of metals in liquid form, such as aluminum, copper, iron, zinc, and alloys thereof. The term “gas” means any gas or combination of gases, including argon, nitrogen, chlorine, fluorine, Freon, and helium, which may be released into molten metal. 
     A reverbatory furnace is used to melt metal and retain the molten metal while the metal is in a molten state. The molten metal in the furnace is sometimes called the molten metal bath. Reverbatory furnaces usually include a chamber for retaining a molten metal pump and that chamber is sometimes referred to as the pump well. 
     Known pumps for pumping molten metal (also called “molten-metal pumps”) include a pump base (also called a “base”, “housing” or “casing”) and a pump chamber (or “chamber” or “molten metal pump chamber”), which is an open area formed within the pump base. Such pumps also include one or more inlets in the pump base, an inlet being an opening to allow molten metal to enter the pump chamber. 
     A discharge is formed in the pump base and is a channel or conduit that communicates with the molten metal pump chamber, and leads from the pump chamber to the molten metal bath. A tangential discharge is a discharge formed at a tangent to the pump chamber. The discharge may also be axial, in which case the pump is called an axial pump. In an axial pump the pump chamber and discharge may be the essentially the same structure (or different areas of the same structure) since the molten metal entering the chamber is expelled directly through (usually directly above or below) the chamber. 
     A rotor, also called an impeller, is mounted in the pump chamber and is connected to a drive shaft. The drive shaft is typically a motor shaft coupled to a rotor shaft, wherein the motor shaft has two ends, one end being connected to a motor and the other end being coupled to the rotor shaft. The rotor shaft also has two ends, wherein one end is coupled to the motor shaft and the other end is connected to the rotor. Often, the rotor shaft is comprised of graphite, the motor shaft is comprised of steel, and the two are coupled by a coupling, which is usually comprised of steel. 
     As the motor turns the drive shaft, the drive shaft turns the rotor and the rotor pushes molten metal out of the pump chamber, through the discharge, which may be an axial or tangential discharge, and into the molten metal bath. Most molten metal pumps are gravity fed, wherein gravity forces molten metal through the inlet and into the pump chamber as the rotor pushes molten metal out of the pump chamber. 
     Molten metal pump casings and rotors usually, but not necessarily, employ a bearing system comprising ceramic rings wherein there are one or more rings on the rotor that align with rings in the pump chamber such as rings at the inlet (which is usually the opening in the housing at the top of the pump chamber and/or bottom of the pump chamber) when the rotor is placed in the pump chamber. The purpose of the bearing system is to reduce damage to the soft, graphite components, particularly the rotor and pump chamber wall, during pump operation. A known bearing system is described in U.S. Pat. No. 5,203,681 to Cooper, the disclosure of which is incorporated herein by reference. U.S. Pat. Nos. 5,951,243 and 6,093,000, each to Cooper, the disclosures of which are incorporated herein by reference, disclose, respectively, bearings that may be used with molten metal pumps and rigid coupling designs and a monolithic rotor. U.S. Pat. No. 2,948,524 to Sweeney et al., U.S. Pat. No. 4,169,584 to Mangalick, and U.S. Pat. No. 6,123,523 to Cooper (the disclosure of the afore-mentioned patent to Cooper is incorporated herein by reference) also disclose molten metal pump designs. U.S. Pat. No. 6,303,074 to Cooper, which is incorporated herein by reference, discloses a dual-flow rotor, wherein the rotor has at least one surface that pushes molten metal into the pump chamber. 
     The materials forming the molten metal pump components that contact the molten metal bath should remain relatively stable in the bath. Structural refractory materials, such as graphite or ceramics, that are resistant to disintegration by corrosive attack from the molten metal may be used. As used herein “ceramics” or “ceramic” refers to any oxidized metal (including silicon) or carbon-based material, excluding graphite, capable of being used in the environment of a molten metal bath. “Graphite” means any type of graphite, whether or not chemically treated. Graphite is particularly suitable for being formed into pump components because it is (a) soft and relatively easy to machine, (b) not as brittle as ceramics and less prone to breakage, and (c) less expensive than ceramics. 
     Three basic types of pumps for pumping molten metal, such as molten aluminum, are utilized: circulation pumps, transfer pumps and gas-release pumps. Circulation pumps are used to circulate the molten metal within a bath, thereby generally equalizing the temperature of the molten metal. Most often, circulation pumps are used in a reverbatory furnace having an external well. The well is usually an extension of a charging well where scrap metal is charged (i.e., added). 
     Transfer pumps are generally used to transfer molten metal from the external well of a reverbatory furnace to a different location such as a launder, ladle, or another furnace. Examples of transfer pumps are disclosed in U.S. Pat. No. 6,345,964 B1 to Cooper, the disclosure of which is incorporated herein by reference, and U.S. Pat. No. 5,203,681. 
     Gas-release pumps, such as gas-injection pumps, circulate molten metal while releasing a gas into the molten metal. In the purification of molten metals, particularly aluminum, it is frequently desired to remove dissolved gases such as hydrogen, or dissolved metals, such as magnesium, from the molten metal. As is known by those skilled in the art, the removing of dissolved gas is known as “degassing” while the removal of magnesium is known as “demagging.” Gas-release pumps may be used for either of these purposes or for any other application for which it is desirable to introduce gas into molten metal. Gas-release pumps generally include a gas-transfer conduit having a first end that is connected to a gas source and a second submerged in the molten metal bath. Gas is introduced into the first end of the gas-transfer conduit and is released from the second end into the molten metal. The gas may be released downstream of the pump chamber into either the pump discharge or a metal-transfer conduit extending from the discharge, or into a stream of molten metal exiting either the discharge or the metal-transfer conduit. Alternatively, gas may be released into the pump chamber or upstream of the pump chamber at a position where it enters the pump chamber. A system for releasing gas into a pump chamber is disclosed in U.S. Pat. No. 6,123,523 to Cooper. Furthermore, gas may be released into a stream of molten metal passing through a discharge or metal-transfer conduit wherein the position of a gas-release opening in the metal-transfer conduit enables pressure from the molten metal stream to assist in drawing gas into the molten metal stream. Such a structure and method is disclosed in U.S. application Ser. No. 10/773,101 entitled “System for Releasing Gas into Molten Metal”, invented by Paul V. Cooper, and filed on Feb. 4, 2004, the disclosure of which is incorporated herein by reference. 
     Generally, a degasser (also called a rotary degasser) is used to remove gaseous impurities from molten metal. A degasser typically includes (1) an impeller shaft having a first end, a second end and a passage (or conduit) therethrough for transferring gas, (2) an impeller (also called a rotor), and (3) a drive source (which is typically a motor, such as a pneumatic motor) for rotating the impeller shaft and the impeller. The degasser impeller shaft is normally part of a drive shaft that includes the impeller shaft, a motor shaft and a coupling that couples the two shafts together. Gas is introduced into the motor shaft through a rotary union. Thus, the first end of the impeller shaft is connected to the drive source and to a gas source (preferably indirectly via the coupling and motor shaft). The second end of the impeller shaft is connected to the impeller, usually by a threaded connection. The gas is released from the end of the impeller shaft submersed in the molten metal bath, where it escapes under the impeller. Examples of rotary degassers are disclosed in U.S. Pat. No. 4,898,367 entitled “Dispersing Gas Into Molten Metal,” U.S. Pat. No. 5,678,807 entitled “Rotary Degassers,” and U.S. Pat. No. 6,689,310 to Cooper entitled “Molten Metal Degassing Device and Impellers Therefore,” the respective disclosures of which are incorporated herein by reference. 
     In some applications, a heating system is desirable to heat the molten metal and maintain its temperature. Some conventional molten metal heating systems use a heating element to heat the air above the molten metal while other conventional systems heat the molten metal through induction by heating a wall of the vessel in which the molten metal is contained. But, a need exists for a system and device that provides a more efficient way to heat molten metal contained within a vessel. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to systems and devices for heating molten metal contained within a vessel. A device according to the invention is an immersion heater, which means it is immersed into the molten metal, rather than heating the air above the molten metal or heating a side of the vessel in which the molten metal is contained. 
     The immersion heater includes an outer cover formed of one or more materials resistant to the molten metal in which the heater will be used and a heating element inside of the outer cover, wherein the heating element is protected from contacting the molten metal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one embodiment of the invention. 
         FIG. 2  is a side cut away view of the embodiment depicted in  FIG. 1 , illustrating, among other things, a flow of gas in the molten metal and immersion heater  300 . 
         FIG. 3  is a side cut away view of the embodiment depicted in  FIGS. 1 and 2 , illustrating a flow of molten metal. 
         FIG. 4  is a side cut away view of the embodiment depicted in  FIGS. 1, 2, and 3  illustrating both a flow of molten and a flow of gas. 
         FIG. 5A  is a perspective view of another embodiment of the invention depicting exemplary lifting mechanisms. 
         FIG. 5B  is a side view of the embodiment depicted in  FIG. 5A  in the up, or lifted, position. 
         FIG. 6  depicts a side cut away view of an immersion heating element housed within a vessel according to one embodiment of the invention. 
         FIG. 7  is side cut away view of one embodiment of the invention depicting the heat radiating from an immersion heating element. 
         FIG. 8  is a perspective view of one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made to the present exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings.  FIGS. 1 and 2  depict a system  10  according to the invention. The system  10  includes a vessel  1  for holding molten metal, having a lower wall  2  and side walls  3 . The vessel  1  can be any suitable size, shape, and configuration. 
     The system  10  as shown includes one or more rotary degassers  50 , each of which include a shaft  100  and an impeller  200 . Shaft  100 , impeller  200 , and each of the impellers used in the practice of the invention, are preferably made of graphite impregnated with oxidation-resistant solution, although any material capable of being used in a molten metal bath, such as ceramic, could be used. Oxidation and erosion treatments for graphite parts are practiced commercially, and graphite so treated can be obtained from sources known to those skilled in the art. 
     If a rotary degasser is used with the invention, it may be any suitable type and exemplary rotary degassers are described in some of the documents already incorporated herein by reference. 
     The exemplary system  10  depicted in  FIGS. 1 and 2  includes a pair of degassers  50  separated by an immersion heater  300 . An immersion heater according to the invention has an outer cover  360  and one or more heating elements  370  (hereafter, “heating element”) positioned within the outer cover  360 . The outer cover  360  is comprised of heat-resistant material, such as refractory material (for example, ceramic or graphite) selected so that it can be placed into molten aluminum, molten zinc or other molten metals so that the material is suitable for the environment in which the invention will be used. The outer cover  360  has a cavity that retains the heating element  370 , or the outer cover  360  can be formed around the heating element  370  (in a casting process, molding process or other suitable process) so that the outer cover  360  protects the heating element  370  and prevents it from contacting the molten metal when the immersion heater  300  is positioned in the molten metal. This enables heat to be applied directly from the heating element  370  through the outer cover  360  to virtually any portion of the molten metal bath, based on the shape and position of the immersion heater  300 . Due to the heat generated by the heating element  370 , the portion of the outer cover  360  that is in contact with the molten metal (which as shown are sides  360 A and the ends of outer cover  360 ) can reach temperatures of, for example, 500° F.-1500° F., 500° F.-1200° F. or 500° F.-900° F., or any other suitable temperature depending upon the heating element, outer cover and type of molten metal. 
     The immersion heater  300  of the present invention is inserted into the molten metal and heats it directly, and is thus considerably more efficient than conventional molten metal heating systems, including those that heat the air above the molten metal. 
     The immersion heater  300  is preferably suspended and retained in place by a superstructure  380 . Superstructure  380  as shown is a steel bar with bolts  382  that connect to the outer cover  360 , but any suitable method or structure can be used to position an immersion heater  300  in a vessel. 
     As shown, the immersion heater  300  divides vessel  1  into two chambers ( 213  and  214 ). Here, each chamber defines a separate degassing zone and each chamber includes a degasser  20 . The immersion heater  300  heats the molten metal in both chambers ( 213  and  214 ) within the vessel  1 . A degassing system of the present invention may include any number of immersion heaters  300  of any suitable shape or size and any number of degassers  20 . Any or all of the functions of each degasser  20 , such as the speed of each impeller  200 , may be independently controlled. 
       FIG. 6  depicts a side view of one embodiment of an immersion heater  300 . In this embodiment, heater  300  includes three separate heating structures  311 ,  312 ,  313  that are approximately equally spaced apart. Heating structures  311 ,  312 ,  313  may be made from any suitable material and may be any suitable size, shape, and configuration, as previously described. While the heater  300  may be configured to provide any suitable amount of heat, the heater in the present exemplary embodiment can produce about 30 kW of heat. An immersion heater  300  of the present invention may include any number of individual heating elements. 
     The temperature of each heating structure  311 ,  312 ,  313 , may be independently controlled or controlled as a group in any suitable manner. In one exemplary embodiment, each element is controlled by a full-proportioning silicon controlled rectifier (SCR) power controller, which can help prevent the heating element  300  from overheating, resulting in a longer service life. While the heater  300  may be formed from any suitable materials, in the present exemplary embodiment each heating structure comprises a graphite or silicon carbide outer cover  360  in which the individual heating elements are positioned. The shaded arrows in  FIG. 7  illustrate how the heating element  300  of the present invention can provide heat to the molten metal within the vessel  1 , including both chambers  213 ,  214  simultaneously. 
     In one embodiment the heating elements  311 ,  312 ,  313  may be controlled by an optional control system. This control system may be operated and controlled by a user and/or software. The heating elements  311 ,  312 ,  313  may be individually controlled. The system  10  may also include one or more temperature sensors which directly or indirectly measure the temperature of the molten metal and/or components of the system  10 . The measured temperatures may be used with the computerized control system to achieve a desired temperature of the molten metal. Also, these measured temperatures may be used to diagnose potential problems with the components of the system  10 . 
     A degassing pattern provided by the rotor  200  according to one embodiment of the invention is depicted by the shaded arrows in  FIG. 2 . In this example, the rotor  200  of each degasser circulates the molten metal while dispersing gas (depicted in the drawings as bubbles) into the molten metal. In this manner, the molten metal in each chamber ( 213 ,  214 ) is mixed with the gas. 
     Additionally, the system  10  may include one or more dividers  235  to help redirect the flow of gas mixed with molten metal. Dividers  235  may be of any suitable size and be made out of any suitable material for use in the molten metal bath. In the preferred embodiment, the dividers  235  are made from refractory materials such as graphite and/or ceramic. The dividers  235 , vessel  1 , and immersion heater  300  may be sized, shaped, and configured in any desired manner to achieve a desired flow pattern of the molten metal and/or gas. 
     Although any suitable flow pattern may be implemented in the present invention, the shaded arrows in  FIG. 3  depict one preferred flow pattern of molten metal through vessel  1 . Molten metal is introduced to vessel  1  through inlet  280 . Inlet  280  is in fluid communication with outlet  290 . The arrows of  FIG. 3  depict one flow pattern on molten metal from the inlet  280  through the vessel  1  to the outlet  290 . This metal flow pattern helps to thoroughly disperse gas into the molten metal passing through the system  10 . The shaded arrows in  FIG. 4  depict the combined flow pattern of the molten metal and the degassing patterns of  FIGS. 2 and 3 . The darker arrows represent the degassing pattern, while the lighter arrows represent the metal flow pattern. 
       FIGS. 5A and 5B  illustrate another view of the present invention wherein each degasser  20  is coupled to a removable cover  350  that can be independently positioned onto, or removed from, the vessel  1 . A cover  350  operating in conjunction with the present invention may be any suitable size, shape, and configuration, and may be formed from any suitable material(s). In the present embodiment, each cover  350  is encased in steel and insulated to help retain heat. Also, the cover  350  at least partially maintains an inert gas environment when it is in position on the vessel  1 . 
     In this exemplary embodiment, in its first position, each cover  350  is positioned to help retain gas and heat. Weirs (not shown) at the inlet  280  and outlet  290  likewise help retain gas and heat within the vessel  1 . 
     Each cover  350  may be independently moved from a first position on the top surface of vessel  1  (i.e., the cover  350  in the background of  FIG. 5A ) to a second position removed from the vessel  1  (i.e., the cover  350  in the foreground of  FIG. 5A ). Cover  350  may be manually positioned or removed, but the present exemplary embodiment utilizes a lifting mechanism  510 . The lifting mechanism  510  may include any suitable system, structure, or device to manipulate the cover  350 . Through use of the removable cover  350  and the lifting mechanism  510 , components of the system  10 , such as the heating element  300 , shaft  100  and rotor  200  may be easily accessed, replaced and/or cleaned. In one embodiment, the lifting mechanism  510  includes a gear-driven 4-bar linkage. 
     Having thus described some embodiments of the invention, other variations and embodiments that do not depart from the spirit of the invention will become apparent to those skilled in the art. The scope of the present invention is thus not limited to any particular embodiment, but is instead set forth in the appended claims and the legal equivalents thereof. Unless expressly stated in the written description or claims, the steps of any method recited in the claims may be performed in any order capable of yielding the desired result.