Patent Publication Number: US-6217317-B1

Title: Combination conduction/convection furnace

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Serial No. 60/112,400, filed Dec. 15, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to the field of foundry processing, and more particularly to heat treating metal castings and reclaiming sand from sand cores and sand molds used in the manufacture of metal castings. 
     Many changes have been made in the field of heat treating of metal castings and reclaiming sand from sand cores and sand molds used in the manufacture of metal castings. Examples of some recent disclosures which address the heat treating of castings, removal of sand cores, and further reclaiming of sand are found in U.S. Pat. Nos. 5,294,094, 5,354,038, 5,423,370, and 5,829,509 (hereinafter sometimes referred to collectively as the “Reference Patents”), each of which is expressly incorporated herein by reference, in their entirety. Those patents disclose a three-in-one process/integrated system that (i) receives and heat treats a casting, (ii) removes sand corelsand mold materials from the casting, and (iii) reclaims sand from the sand corelsand mold materials removed from the casting; the &#39;094 and &#39;038 patents embodying a convection furnace species, the &#39;370 patent embodying a conduction furnace species, and the &#39;509 patent alternately embodying either a conduction furnace species or a convection furnace species (and adding an integrated cooling chamber). The sand core/sand mold materials (referred to hereafter as sand core materials) comprise sand that is held together by a binder material such as, but not limited to, a combustible organic resin binder. 
     Technology such as that disclosed in the above-mentioned patents are driven, for example, by: competition; increasing costs of raw materials, energy, labor, and waste disposal; and environmental regulations. Those factors continue to mandate improvements in the field of heat treating and sand reclamation. 
     SUMMARY OF THE INVENTION 
     Briefly described, the present invention provides a single furnace system which integrates, in combination, a plurality of distinct heating environments (which in the preferred embodiments include two heating environments comprising a conduction heating environment and a convection heating environment) integrated such that the plurality of environments define a continuous heating chamber through which a moving workpiece (such as a casting) transitions from one heating environment to the other without being exposed to the atmosphere. In accordance with the preferred methods, the transitioning of the casting from one environment to the other is accomplished with no meaningful change in temperature. 
     In accordance with a second aspect of the invention, improved species embodiments of a 3-in-1 processing system of the genus described in the above identified prior patent specifications are provided. These species embodiments of the present invention disclose a system apparatus and method for processing a casting which perform the integrated processes of core removal, sand reclaiming and heat treatment in a combination conduction and convection furnace system. 
     Other objects, features, and advantages of the present invention will become apparent upon reading and understanding this specification, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic, side cut-away view of a combination conduction/convection furnace, in accordance with the preferred embodiment of the present invention. 
     FIG. 1A is an isolated view of hoist and rail components of one embodiment of a transport system utilized in the furnace of the present invention. 
     FIG. 2 is a schematic, side cut-away view of a combination conduction/convection furnace, in accordance with an alternate embodiment of the present invention. 
     FIG. 3 is a schematic, side cut-away view of a combination conduction/convection furnace, in accordance with a second alternate embodiment of the present invention. 
     FIGS. 4-6 are schematic, side cut-away views of alternate embodiments of multiple heating environments comprising an integrated continuous heating chamber of a furnace system in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings in which like numerals represent like components throughout the several views, FIG. 1 depicts in schematic representation a combination conduction/convection furnace  10  in accordance with a preferred embodiment of the present invention. The combination furnace  10  is seen as comprising a frame structure  12  which defines an enclosed heating chamber  14  and includes insulated walls  15  surrounding the heating chamber, an entrance portal  16  outfitted with a selectively closable insulated inlet door  17  and an exit portal  18  outfitted with a selectively closable insulated outlet door  19 . The heating chamber  14  is seen as divided into two major heating chamber segments  23 ,  24  which together comprise the continuous heating chamber  14  and are interconnected by a transitional passage  25 . In accordance with the preferred embodiments of the present invention, the transitional passage  25  is of sufficient size and orientation to allow for the easy movement from the first heating chamber segment  23  to the second heating chamber segment  24  of a work piece, such as a casting, as well as the free movement of heat, gases, dust, and the like from one chamber segment to the other chamber segment. An integrated transportation system  26  transports the castings from the entrance portal  16 , through the first heating chamber  23 , into and through the second heating chamber  24 , to the exit portal  18 . 
     In accordance with the preferred embodiments of the present invention, each of the first heating chamber segment  23  and second heating chamber segment  24  is equipped to heat a casting within the respective chamber segment by a furnace heating process which is of a process distinct from the furnace heating process with which the other chamber segment is equipped. 
     The herein depicted, preferred embodiments of FIGS. 1-3 are equipped with a conduction furnace heating process, in the form of a fluidized bed furnace, in the first heating chamber segment  23  and are equipped with a convection type heating furnace in the second heating chamber segment  24 . The heating environment provided in the first heating chamber segment  23  is, thus, an environment as is created by a conduction type furnace (such as a fluidized bed furnace) and the heating environment of the second heating chamber segment  24  is, thus, an environment as is created by a convection type furnace. As depicted in the drawings, a bed  27  of particles (the fluidizing medium) mostly fills the first heating chamber segment  23 , and conduit  28  for the introduction of fluidizing gases are provided. A heating source (not shown) provides heated fluidizing gases to the conduit  28 . In this heating chamber segment  23 , castings are immersed within the fluidized bed  27  where heat is transferred to the castings from surrounding heated bed particles by conduction, and where the castings are heated to an appropriate temperature for an appropriate period of time to accomplish one or more (full or partial) desired casting processing steps (an example of which is expressed below). The convection heating chamber segment  24  includes heating sources (not shown) which heat the air inside the heating chamber segment such that the heat transfers by convection to a casting contained within the convection heating chamber segment and such that the castings are heated to an appropriate temperature for an appropriate period of time to accomplish one or more (full or partial) desired casting processing steps (an example of which is expressed below). 
     Referring again, generally, to FIG. 1 (and FIGS.  2  and  3 ), the combination furnace  10  is seen as also including a loading station  40  outside the furnace structure  12  and, an entry zone  41  inside the furnace structure  12 . The entry zone  41 , of the herein depicted embodiments of FIGS. 1 and 2, occupies a portion of the heating chamber  14  positioned above the fluidized bed segment  23  and receives rising heat, thus exposing castings in the entry zone to initial chamber heat. The integrated transport system  26 , of the herein depicted embodiments is comprised of a combination of a charge transport mechanism (depicted by arrow  43 ) and entry transport mechanism  44  (depicted in FIG. 1, for example, as a hoist), a first chamber transport mechanism  45  (depicted in FIG. 1, for example, as a ram/push device  39  and including an elongated fixed rail assembly  42  (see FIG.  1 A)), a transitional transport mechanism  46  (depicted in FIG. 1 as, for example, another hoist mechanism), a second transitional transport mechanism  47  (depicted herein as, for example, a ram/push device), and a second chamber transport mechanism  48  (depicted as, for example, a roller conveyor). With reference to FIG. 1A, an example of a hoist type entry transport mechanism  44  is depicted, together with a representative fixed rail assembly  42  of the first chamber transport mechanism  45 . The entry transport mechanism  44  includes a movable pallet  70  (formed of two spaced apart lateral rails  71  (one shown) and two, spaced apart transverse beams  72 ) and a four cornered support frame  73  supported from above by cabling  74  connected to a drive mechanism (not shown). A hoist type first transition transport mechanism  46  is of similar construction. The construction and operation of the depicted integrated transport system  26  is deemed readily understood by those skilled in the art upon reference to this specification. Movement of the casting through the various chambers is not limited to those particular mechanisms depicted herein and alternate transporting mechanisms will be apparent to those skilled in the art. 
     In a first preferred embodiment, as depicted in FIG. 1, the convection heating chamber segment  24  is comprised of an upper open air portion through which the casting moves and is heated and a lower portion formed, for example, as a hopper (or hoppers)  33  into which falls and is collected (and, preferably, is further processed) any sand core materials which may fall from the casting in this segment of the heating chamber. In the embodiment of FIG. 1, the convection segment  24  is shown outfitted with an air re-circulating system  52  which stirs air within the convection heating chamber segment  24  to assist in acquiring temperature uniformity, throughout the convection heating chamber segment (including at the vicinity of the transitional passage  25 ), as would be understood by those skilled in the art. The herein depicted recirculating system includes a re-circulating fan  53  and related ductwork  54 , though other re-circulating systems will be readily identified by those skilled in the art. In the embodiment of FIG. 1, the convection segment  24  is provided with sand reclaiming features such as screens  55  and in-hopper fluidization  56 . The structure and operation of these reclaiming features will be understood by reference to the Reference Patents, especially U.S. Pat. No. 5,294,094 and 5,345,038. In the alternate embodiment of the combination furnace  10 ′ of FIG. 2, the convection segment  24 ′ includes a furnace chamber with a trough  58  with fluidized, migrating bed  59 , discharge weir  60 , and integrated cooling chamber  61  similar to the embodiment of FIG. 1A of Reference Pat. No. 5,829,509, and the structure and operation of the furnace chamber segment  24 ′ and related reclaiming will be understood by reference to that Patent. The embodiments of FIGS. 1 and 2 are also seen as including a weir or spillway  37  by which sand or other particles accumulating within the fluidized bed furnace is allowed to spill into the hopper  33  or trough  58 , respectively, of the convection chamber  24 ,  24 ′, thus controlling the depth of the bed  27  of the fluidized bed segment  23 , and, preferably, controlling the dwell time of any sand core particles within the fluidized bed  27 . 
     Each of the conduction heating segment  23  and the convection heating segment  24 ,  24 ′ of the depicted embodiments will have additional structure and will operate in a manner all of which will be clearly understood by those skilled in the art after review of this entire specification, aided with reference to the specifications of the “Reference Patents” cited previously herein. As such, no further description is deemed necessary to enable the functionality mentioned throughout this specification 
     In operation, and in accordance with one preferred method of the present invention, a casting (not seen), typically laden with outer molds and/or inner sand cores (collectively referred to herein as “sand cores”) is positioned at the loading station  40  (“P 1 ”). The casting is, for example, carried within a wire basket or like transport container  50  which contains the casting yet allows for access to the casting by the fluidizing medium of the bed  27  and also allows for the discharge from the container of sand core material which falls from the casting. The basket and casting are moved, for example, by being pushed by the charge transport mechanism  43  through the temporarily open inlet door  17  to the entry segment  41  (at position “P 2 ”), where the basket rests on, for example, a hoist pallet  70 . The entry transport mechanism  44  lowers the pallet  70  with the basket  50  and casting into the conduction heating chamber segment  23  until the casting is fully immersed within the fluidized bed  27  and the lateral rails  71  align with the fixed rails  42 . The fluidized bed  27  is, preferably, comprised of refinery sand similar in nature to that sand of which the sand cores of the casting are created. Preferably, the fluidized bed has been preheated to an initial temperature prior to receiving the casting. The fluidized bed  27  is heated to a temperature sufficient to perform the particular casting processing steps desired to be carried out within the fluidized bed. For example, the bed  27  is heated to a temperature sufficient enough to conduct heat to the casting of a temperature sufficient to dislodged sand core materials from cavities within castings. The core materials preferably comprise sand that is bound by a thermally degradable material such as, but not limited to, an organic resin binder. Thus, in at least the preferred embodiments, the fluidized bed is heated to above the combustion temperature of the organic resin binder. In preferred embodiments, the processing steps desired to be performed in the fluidized bed segment  23  are, at least, the process of removing sand cores from the casting and the process of reclaiming sand from the core material which exits in the castings while in the fluidized bed furnace. To that end, the techniques of heating the sand core to a sufficiently high temperature as well as the techniques of retaining the discharged sand core within the fluidized bed  27  for sufficient dwell time to substantially reclaim the sand are employed as would be understood by those skilled in the art, especially with reference to the “Reference Patents”. It is not required that all moldings and sand core be removed from the casting in the fluidized bed since a certain amount of core removal and sand reclamation is provided for and acceptable within the convection segment  24 , though in preferred embodiments a meaningful amount of core removal and sand reclamation is preferred within the conduction segment  23 . A certain amount of heat treatment of the casting within the fluidized bed heating chamber segment  23  is anticipated. 
     During the time that the casting is immersed within the fluidized bed, basket  50 , with the casting, is moved by the first chamber transport mechanism  45  longitudinally through the conduction heating chamber segment  23  from its entry position at “P 3 ” to a final bed position “PF” adjacent the convection heating chamber segment  24 . Various techniques understood in the art are acceptably used for moving the basket  50  and casting through the fluidized bed, including, for example, the ram/push device  39  and rail assembly  42  depicted. The push device  39 , in the exemplary embodiments, pushes the basket  50  laterally off the rails  71  of the movable pallet  70  onto the fixed rails  42 , through the fluidized bed chamber segment  23 , to a resting position on the rails  71   a  of the movable pallet  70   a  of the first transitional transport mechanism  46  (position PF). From position PF, the movable pallet  70   a,  with the basket  50  and casting, is raised by the transitional transport mechanism  46  (for example, by a hoist) through the transitional passage  25  to a position in the convection heating chamber segment  24  adjacent the second chamber transport mechanism  48 . From this position the basket  50  is moved longitudinally off the pallet rails  71   a  and then through the convection heating chamber segment  24 , first by the second transitional transport mechanism  47  and then by the second chamber transport mechanism  48 . Again, movement of the casting through the various chambers is not limited to those particular mechanisms depicted herein and alternate transporting mechanisms will be apparent to those skilled in the art. For example, in one embodiment (not shown) the casting is acceptably transported through the entire chamber  14  by a basket supported overhead by a cable extending from a shuttle moving longitudinally over the fire structure  12  on an overhead rail. The shuttle selectively spools and unspools the cable to raise and lower the basket at appropriate times. 
     It is the intention of the present invention that heat generated in the conduction heating chamber segment  23  will pass freely through the transitional passage  25  into the convection heating chamber segment  24  and, thereby, provide preheat to the convection segment and assist in effecting a continuing casting heating process from the conduction heating environment to the convection heating environment without meaningful change in temperature. As the casting is moved through the convection heating chamber segment  24 , the chamber segment is heated to sufficient temperature to perform the casting processing steps desired for this chamber segment. For example, preferably, heat treatment of the casting is performed and completed during the casting&#39;s containment within the convection heating chamber segment  24 . Simultaneously with the heat treating, it is desired that any remaining sand core is removed from the casting and the sand is substantially reclaimed from the remaining sand core portions. Upon completion of the appropriate processing, the basket and casting are conveyed out of the exit portal  18 . 
     FIG. 3 depicts a third embodiment of the combination furnace  10 ″ which does not include a hopper or a trough for retention of fallen sand core materials but, rather, includes a sand return  62  by which sand core collected in the convection heating segment  24 ″ is conveyed back to the fluidized bed segment  23  where it is further processed for reclaiming of sand. A discharge weir  64  within the fluidized bed segment  23 ″ is provided in order to discharge reclaimed sand from the fluidized bed segment, and the depth of the bed  27  is established or regulated to provide proper dwell time for reclamation. The weir  64  acceptably discharges to a cooling chamber  61 ′ as will be understood by reference to the embodiment of FIG. 113 of the U.S. Pat. No. 5,829,509. 
     In accordance with the most preferred methods of the present invention, the combination furnace  10  is utilized to perform the three-in-one processes of casting processing known as core removal, in furnace sand reclamation, and heat treatment. However, it should be understood that the combination furnace  10  of the present invention is acceptably utilized to perform one or more of the mentioned processes or other processes associated with the processing of castings using heat. In alternate embodiments where it is planned that no core removal will take place within the combination furnace (for example, when all sand core molds are removed, perhaps by vibration techniques, prior to delivery of the casting to the furnace), then the sand reclaiming features of the furnace, such as, the spillway  37 , screens  55 , and fluidizers  56  are acceptably removed. 
     The present invention is seen as relating to the integration of a plurality of (two or more) heating environments in such a manner as to effect a continuous heating chamber, and, in accordance with the present invention, at least two adjacent heating environments within the continuous heating chamber are distinct from one another. In the herein described embodiment, the distinct environments are disclosed as one being a fluidized bed conduction furnace and the other a convection furnace. 
     It is clear and understood that the combination heating environment expressed in FIGS. 1-3 herein is acceptably two segments of a larger heating chamber comprised of other heating chamber segments, including other heating environments. Such an expanded heating chamber  14 ′,  14 ″′ is schematically represented in FIGS. 4 and 6. For example, in one alternate embodiment (see FIG.  6 ), another segment  80  comprising a fluidized bed furnace type of heating environment follows the convection segment  24  of FIG.  1 . Following the spirit of the present invention, in such embodiment, a heat channeling transitional zone  81  is provided between the convection segment  24  and the additional conduction heating chamber segment  80  of FIG.  6 . 
     By way of further example, in another embodiment (not specifically shown, but inferentially seen in FIG.  4 ), a convection type heating segment is added to the front of the fluidized bed conduction segment  23  of FIG. 1, with a heat channeling transitional zone in between. In still other embodiments (not shown), a duplicate of the combination fluidized bed and convection system of FIG. 1 is “piggy-backed” to the front or back (or both) of the system shown in FIG.  1 . In such latter embodiments, the invention again includes a heat channeling transitional zone provided between each adjacent heating environment segment. 
     Furthermore, the present invention is not limited by the order of the respective heating environments. Rather, for example (as schematically represented by FIG.  5 ), should a particular processing technique favor the placement of a convection heating environment prior to a fluidized bed conduction environment, then the order of the heating environments as shown in FIG. 1 is acceptably reversed. FIG. 5 schematically shows a convection heating environment as the first heating segment  23 ″′ and a fluidized bed conduction environment as the second heating segment  24 ″′. 
     Whereas the disclosed embodiments have been explained using the fluidized bed conduction heating environment and the convection furnace heating environment as adjacent heating environments, it is clearly within the scope of the invention to incorporate any distinct heating environments as the at least two adjacent distinct heating environments. Such heating environments might acceptably include any heating environment known and understood currently or in the future by those skilled in the art, including, without limitation, conduction, convection, and radiant heating environments. 
     While the embodiments which have been disclosed herein are the preferred forms, other embodiments will suggest themselves to persons skilled in the art in view of this disclosure and without departing from the spirit and scope of the claims.