Abstract:
A thermally efficient cover for the molten metal held in a furnace, tundish, ladle, crucible or other containment vessel. Through substantially horizontal movement, this cover allows for periodic removal, particularly by retraction, for accessing contents of that furnace from a top aperture in the containment vessel. This invention further relates to a covered furnace system and methods of use.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a molten metal containment system, either portable or stationary, for the containment of ferrous and non-ferrous metals. More particularly, this invention relates to a means for increasing the thermal efficiency of metal containment vessels with an automated cover to reduce heat losses of molten metal held in that vessel assembly. This cover allows for the automated periodic removal, particularly by retraction, for accessing the contents of that furnace assembly. Ideally, relative movement of this cover over an aperture in the vessel assembly is programmable based on preset time increments. This invention further relates to a covered vessel system and methods of using the same. 
       BACKGROUND OF THE INVENTION 
       [0002]    Molten metal containment vessels including furnaces, tundishes, ladles and/or crucibles, and other means for holding certain ferrous and non-ferrous metals are well known. The most thermally efficient of these vessels use high quality insulating refractories in the furnace walls to reduce heat losses through those walls. Lids and covers for such vessels have been designed to minimize heat loss through their intrinsic design and the use of effective insulation. Many such vessels, however, require repeated access to the molten metal bath. Access is most frequently needed to withdraw molten metal from the vessel to, for example, feed a castings system. 
         [0003]    In such systems, a ladle is often used to withdraw metal from the vessel and transfers this metal to a down sprue, shot sleeve, or some other entry point to the casting process. Such access to molten metal is most often provided through a free surface of molten metal, although other means for metal withdraw, such as a pump, have also been used. Pumps can be expensive, complicated to operate, and may not provide metal withdraw with a geometry that best suits the casting process. The most frequently encountered means for withdrawing molten metal from such vessels is simply dipping a ladle through a free surface of molten metal and filling the ladle. 
         [0004]    A free (or exposed) surface of molten metal results in a high rate of heat loss from radiation, conduction and convection heat transfer mechanisms. This is illustrated in the table below, wherein heat loss rates from a 5,000 lb capacity holding furnace for molten aluminum are provided. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
               
               
                 Dissipation Estimate, T M  = 1350° F. 
               
             
          
           
               
                   
                 Area 
                 T s   
                 n s   
                 q 
                 P 
               
               
                 Surface 
                 ft 2   
                 ° F. 
                 BTU/Ft 2 -hr-° F. 
                 BTU/hr 
                 kW 
               
               
                   
               
             
          
           
               
                 Sides 
                 40.25 
                 130 
                 3.05 
                 9,821 
                 2.9 
               
               
                 Ends 
                 24.50 
                 130 
                 3.05 
                 5,978 
                 1.8 
               
               
                 Bottom 
                 31.00 
                 130 
                 3.00 
                 7,440 
                 2.2 
               
               
                 Top 
                 56.00 
                 170 
                 3.10 
                 20,832 
                 6.1 
               
               
                 Dip out well 
                 3.00 
                 1350 
                 3.10 
                 28,504 
                 8.4 
               
               
                   
                   
                   
                 Total 
                 72,575 
                 21.3 
               
               
                   
               
               
                 T Ambient  = 50 
               
               
                 T m  = 1350 
               
               
                 ε (aluminum) = 0.3 
               
             
          
         
       
     
         [0005]    Combined heat loss rates for the walls, bottom, and top of the furnace are 13 kW. By comparison, the dip out well of the furnace is a free surface of aluminum that results in a heat loss of 8.4 kW. Regardless of the effectiveness of the insulation used or design of the furnace sidewalls, ends and bottom, the free surface of molten metal results in an 8.4 kW drop or roughly 40% of the total heat loss. 
         [0006]    It is known to provide such metal containment assemblies with some sort of cover to minimize heat losses from the free molten metal surface. For instance, Simko U.S. Pat. No. 5,234,660 shows a ladle cover assembly made from insulating ceramic fiber mats or “batting”. Miller et al. U.S. Pat. No. 4,524,702 shows a supposedly readily repairable, lightweight ceramic fiber cover, over a metal mesh under frame, for heated vessels such as a soaking pit. 
         [0007]    It is also known to employ mechanically retractable components in the casting of metal parts. One representative example is the pouring of molten metal through a retractable shield for pour control as taught by Tabatabaci et al. U.S. Pat. No. 6,591,895. 
       SUMMARY OF THE INVENTION 
       [0008]    In a first aspect, this invention is directed to a furnace assembly for molten metal, ferrous or non-ferrous. The assembly includes a metal containment area or reservoir with at least one aperture, and means for heating that reservoir to keep its metal contents molten. The assembly further includes a cover for the aperture of the reservoir, that cover being configured for periodic removal (or retraction) from over that reservoir aperture for allowing access to the molten metal therein for a limited time. Preferably, that aperture cover can be mechanized for periodic removal from over the reservoir aperture. More preferably, movement of that cover can be programmed for prescribed timed intervals and/or for command retractions on an “as needed” basis. When this cover has been fully, or possibly even partially, retracted, access to the reservoir allows for additives to the melt and/or withdrawals (or “tapping”) of the molten metal contents to it. 
         [0009]    In a second aspect, this invention addresses an improved, more efficient, system and method for casting metal alloys that has less radiation heat losses than current practices. The system and method achieve such improvements with a removable/retractable cover over the furnace, tundish, ladle or crucible in which molten metal is held for subsequent processing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The structure, operation, and methodology of the invention, together with other objects and advantages thereof, may be better understood by reading the detailed description in conjunction with the accompanying drawings in which: 
           [0011]      FIG. 1A  is a left corner, perspective schematic showing a hot metal furnace with one embodiment of retractable cover of insulation material according to this invention before cover deployment over the top furnace aperture; 
           [0012]      FIG. 1B  is a left corner, perspective schematic with the embodiment of retractable cover from  FIG. 1A  fully deployed over the top furnace aperture; 
           [0013]      FIG. 2A  is a left corner, perspective close up focusing on the retractable cover embodiment from  FIG. 1A  before deployment over the furnace aperture; 
           [0014]      FIG. 2B  is a left corner, perspective close up from  FIG. 2B  with the  FIG. 1A  retractable cover fully deployed; 
           [0015]      FIG. 3A  is an upper left side, perspective close up of the  FIG. 1A  retractable cover before deployment; 
           [0016]      FIG. 3B  is an upper left side, perspective close up of the  FIG. 3A  retractable cover fully deployed; 
           [0017]      FIG. 4  is a top front perspective close up of the  FIG. 1A  retractable cover partially deployed over a furnace aperture; 
           [0018]      FIG. 5  is a left corner, perspective schematic showing a first alternate embodiment of retractable cover designed to slide between affixed side rails; 
           [0019]      FIG. 6A  is a left corner, perspective schematic showing a second alternate embodiment of cover designed to retract from more than one side of the furnace aperture; 
           [0020]      FIG. 6B  is a left corner, perspective schematic showing the second alternate embodiment of  FIG. 6A  which retracts from more than one side but from a different angle relative to the furnace aperture; 
           [0021]      FIG. 7A  is a left corner, perspective schematic showing a third alternate embodiment of cover shown sectionally retracted over the furnace aperture; 
           [0022]      FIG. 7B  is a left corner, perspective schematic of the  FIG. 7B  third alternate embodiment sectionally deployed over the furnace aperture; 
           [0023]      FIG. 8A  is a left corner, perspective schematic of a fourth alternate cover embodiment with flexible, sectional retraction from only one side of the furnace aperture; 
           [0024]      FIG. 8B  is a left corner, perspective schematic of the fourth alternate cover embodiment sectionally deployed from one side of the furnace aperture; 
           [0025]      FIG. 9A  is a left corner, perspective schematic of a fifth alternate cover embodiment that rigidly retracts over the furnace aperture; and 
           [0026]      FIG. 9B  is a left corner, perspective schematic of the fifth alternate cover embodiment rigidly deployed over the furnace aperture. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0027]    The molten metal maintained in a typical holding furnace needs to be periodically accessed by ladles (and other devices) for purposes of metal withdrawal or “tapping”. When there is no cover over such furnaces, approximately 2.2 kW of power will be lost or dissipate, primarily by radiated heat, from the open surface of an aluminum melt. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                   
               
               
                 T S   
                 T L   
                   
                 kW Lid Open 
                 kW Lid Closed 
               
               
                   
               
             
             
               
                 175 
                 265 
                 CURRENT 
                 45.5 
                 34.4 
               
               
                 120 
                 180 
                 Target 
                 33.2 
                 22.1 
               
               
                   
               
             
          
         
       
     
         [0028]    A retractable cover primarily designed for reducing radiation losses by reflection will improve furnace energy efficiencies. Such a cover need only retract when access to the molten metal in the furnace/container is needed. More importantly, the retractable cover, system and methods of this invention do NOT move air in and out of the head space above a furnace melt by any sort of fanning action or effect. A large permanent door that has to be repeatedly lifted and then lowered back into place over a furnace aperture, especially as often as 1-2 times per minute, would lower furnace efficiencies by such “fanning” back and forth. 
         [0029]    One preferred cover design would use relatively thin refractory cloth, one having a low emissivity/reflectivity rating. That cloth should be lightweight, yet somewhat flexible, perhaps even “foldable”. One representative material is a ceramic fiber, or fiber cloth, like the type made and sold by 3M as Nextel® 312. Other materials include various silica-based cloths such as well known “S Glass”, and calcium aluminate mats such as the line of Fiberfrax® products sold by Carborundum Company. 
         [0030]    Preferably, the aforementioned material is wound or otherwise situated on one or more torsion spring-loaded rolls for opening by retracting, on cue or when prompted, thereby allowing limited duration metal access. In one embodiment, material retraction on these rolls is robotically controlled using an air cylinder, solenoid or other activation means. Alternately, the material may be wound by rolls loaded by a rack and pinion-type system. 
         [0031]    A more preferred molten metal furnace cover according to this invention should possess low mechanical inertia so as to not require excessive energy for retraction. The material should also be relatively “lightweight”. As used herein, lightweight is meant to cover materials with a bulk density range between about 20-70 lb/ft 3 . Also considered lightweight herein are covers with a material density between about 50-250 lb/ft 3 . This includes many refractory products. Preferred lightweight materials should also have preferential porosity, void fraction and/or material density combinations. 
         [0032]    Ideally, relative movement of the cover to the furnace top (and its aperture there through) should be substantially planar, and more preferably horizontal to the plane of said furnace top. Retraction of a cloth cover over the furnace aperture can be accomplished by several, preferred mechanical means. These include: moving the cover mostly laterally from at least one roll situated directly over that furnace aperture. Ideally, that cover roll can be spring-loaded for movement using an air actuator, a hydraulic actuator and/or one or more electrical solenoids. On a preferred basis, the spring-loaded cover roll (or rolls) further includes at least one traction motor. 
         [0033]    For optimum efficiencies, relative movement of the cover can be programmed with movement of an automated metal withdraw device. The frequency of molten metal withdraw is determined by the cycle time of the casting process being supported by the furnace. Representative cycle times include mechanically opening and closing the cover: more than 10 times per minute for removing metals from that furnace for uses elsewhere in the metal part production process. For still other applications, the cover may be programmed to open and close roughly 5 to 10 times per minute, or 2 to 4 times per minute for (reason?). In other applications, the cover timing may be set to automatically open and close less than 2 times per minute, or possibly as infrequently as more than once per hour. Finally, for any programmable timer, there can be included a manual override for rapid cover retraction in the event of an unplanned emergency, or to otherwise allow melt access during an unscheduled cycle time. 
         [0034]    It should be noted that common features in the different views of this invention are shown with the same reference numeral(s). For alternate embodiments of the same component, there is consistent numbering though in the next hundred series. When referring to any numerical ranges herein, it should be noted that all numbers within the range, including every fraction or decimal between its stated minimum and maximum, are considered to be designated and disclosed by this description. As such, disclosing a preferred cloth thickness, or cloth width ranging from 20 to 30 inches, expressly covers widths sizes of 20.5, 21, 22 and 23.5 inches . . . and so on, up to about 27.5, 28, 29 and 29.99 inches. The same applies for every other numerical and/or quantitative range herein including those for kW&#39;s saved, temperatures observed and even varied cycle times between cover opening and closing (or retraction and deployment). 
         [0035]    Referring now to  FIGS. 1A through 4 , there is shown a first embodiment of this invention for covering a container  10  of molten metal M. As shown, the container  10  has a top planar face  12  with an aperture  14 . There is also a fixed lid section  15  over at least part of aperture  14 . In the embodiment shown, the container is substantially cylindrical in cross-section and the aperture  14  extends through the top for repeated access to the molten metal M contained therein. 
         [0036]    For better heat efficiencies by minimizing radiant heat loss, the aperture  14  is at least temporarily covered by a cloth-like material  16 . As shown, a preset length of said material  16  is stored (or wound) about a take-up roller  18 . Atop the roller stand, there is situated an actuator  20  for extending and retracting a rod  22  which causes the take-up roller to move back and forth over the top planar face  12  of container  10 . Such movement effects a gradual unwinding of material  16  from the lone roller  18  of this embodiment. More importantly, movement of the material  16  repeatedly off the roller  18  to deploy over the aperture  14  and then back onto the roller  18  for a temporary, partial retraction of the cover does not disturb or unnecessarily fan the molten metal contents of container  10 . With a nominal, substantially horizontal retraction and deployment of material  16 , this invention achieves a substantial heat savings. In the accompanying views,  FIGS. 1A ,  2 A,  3 A and  4  show from varying angles a retracted cover, with the material  16  mostly wrapped about take up roller  18 . But with the timed extension of rod  22  from actuator  20 , this same section of material  16  unwinds from roller  18  for a temporary deployment over aperture  14  of container  10 , This full deployment view for cover material  16  is better seen in accompanying  FIGS. 1B ,  2 B and  3 B. 
         [0037]    In  FIG. 5 , there is shown a first alternate embodiment of cover for that container  110 . Over the aperture  114  for this embodiment, there is positioned a roller  118  from which material  116  will deploy with rod  122  is extended from actuator  120 . To better control the horizontal movement of material  116  over top planar face  112 , this embodiment further includes a plurality of mounted tracks  124 ,  126  between which the roller  118  can wind and unwind. Such spacing of material  116  preserves the relative lifespan for same by lessening the wear and tear from frictional engagement with the top planar face  112  of container  110 . 
         [0038]      FIG. 6A  shows a second alternate embodiment of this invention wherein the material  216  is deployed between a pair of rollers  218 ,  219  for repeated positioning over the top aperture  214  for container  210 . Such positioning is achieved by extension of a first and second rod  222 ,  223  from actuator  220 . Alternately, a separate actuator (not shown) could be used to separately operate one of the roller pairs. 
         [0039]    In  FIG. 6B , there is shown a minor, angular modification to the embodiment of  FIG. 6A . Particularly, in this variation of the second alternate embodiment, the roller pairs  318 ,  319  are situated ninety degrees (or at a right angle) to the front face of fixed lid section  315 . In this manner, extensions of rod  322  from actuator  320  causes a more lateral (or side-to-side) deployment and retraction of material  316  over aperture  314  of container  310 . 
         [0040]      FIGS. 7A  and B show a third embodiment of molten metal containment covering wherein the substantially horizontal movement of lidding material  416  is effected sectionally over the aperture  414  of container  410 , appearing more as pie-shaped segments in front of fixed lid  415 . For easier viewing, the actuator components for this alternate embodiment have been left off of the accompanying schematics. In  FIG. 7A , the segments of material  416  partially overlap one another for deployment by rotation about a central axis point. Once fully deployed, as in  FIG. 7B , these segments of material  416  cover most, if not all, of top aperture  414 . 
         [0041]      FIGS. 8A  and B show another variation of the FIGS.  7 A/B embodiment. Therein, deployment of a more flexible, accordion-like material  516  is accomplished by rotation from only one side of the aperture  514  for container  510 . When retracted ( FIG. 8A ), the material  516  repeatedly folds onto itself. But once deployed, it effects coverage over the container aperture in somewhat of an umbrella-like manner. 
         [0042]      FIGS. 9A  and B show yet another alternate embodiment of this invention for effecting temporary aperture coverage by mostly horizontal placement of a more rigid material  616  (in this case, semi-circular in shape to more closely match the relative size and shape of aperture  614  in container  610 ) over said aperture  614 . Therein, relative movement of a more rigid lidding is accomplished by the relative extension of rod  622  from actuator  620 . It is to be understood that still other means exist for accomplishing a lateral movement of rigid cover material  616  back-and-forth over aperture  614 . 
         [0043]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.