Patent Publication Number: US-6901990-B2

Title: Method and system for processing castings

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Application Ser. No. 60/397,177, filed Jul. 18, 2002. 

   TECHNICAL FIELD 
   The present invention generally relates to the manufacturing of metal castings and more particularly to heat treating metal castings during the manufacturing process. 
   BACKGROUND 
   Traditional casting processes for forming metal castings generally include one or more heat processing steps to impart the desired performance characteristics to the castings. These heat processing steps usually are conducted in separate furnaces or stations. A casting must be transported from one station to another in order to be processed. Generally, either the various stations are disposed in an enclosed system or are arranged in proximity to each other in an open system. Enclosed systems include fixed closed passageways between processing stations and tend to take up a significant amount of space and cannot be reconfigured easily. Open systems generally do not include fixed closed passageways between process stations. Although open systems generally allow more flexibility and take up less space than open systems, unfortunately, a casting will usually lose heat and drop in temperature during transport between stations in an open system. Since many processing steps in manufacturing a metal casting require that the casting be within a specified temperature range for heat treatment, if the casting temperature drops out of the specified range during transport, then additional heat must be supplied to the casting in the next station simply to bring the casting temperature back into the appropriate range. This remedial heating takes time that lowers the efficiency and productivity of the overall system. 
   Consequently, a need exists for a casting system that can provide the advantages of an open system but also reduces or eliminates any drop in the temperature of castings that are transported between processing stations. 
   SUMMARY 
   The present invention comprises a method and a system for supplying heat to a casting as it is transported from one station to another during processing. According to one embodiment of the present invention, a method of processing a casting is provided in which a casting is transferred into a furnace; the furnace is moved; and, the casting is transferred from the furnace to a processing station. Heat is supplied to the casting within the furnace by any one or more of radiant, conductive or convective heat transfer mechanisms. The method can include molding, heat treating, quenching, and holding steps. For example, the casting can be formed by pouring a molten metal material into a mold at a casting station. Heat treatment of the casting can be carried out again by exposing the casting to radiant, conductive or convective heat. In one embodiment, heat treatment can be carried out by exposing the casting to a fluidized bed within one the processing stations. 
   In another embodiment, the method of processing a casting comprises transferring a casting into a furnace; moving the furnace to a first position; transferring the casting from the furnace to a processing station; processing the casting within the processing station; returning the casting from the processing station back to the furnace; moving the furnace to a second position; and, removing the casting from the furnace. In this manner, a casting can be formed, heat treated, quenched and otherwise processed while maintaining the temperature of the casting within a desired range by applying heat to the casting while it is in the furnace. 
   The present invention also encompasses a casting system for processing castings. The casting system includes a mobile furnace and a multi-station processing array with first and second stations between which the mobile furnace moves. The mobile furnace contains a heating element for supplying heat to one or more castings disposed within the furnace. The mobile furnace moves between the first and second stations of the multi-station processing array so as to transfer castings from one processing station to the next. A casting can be deposited in the mobile furnace and be maintained within a predetermined temperature range as it is transferred from one station to another. A transfer mechanism also is provided that transfers one or more castings between the mobile furnace and the processing stations. The multi-station processing array can include a variety of stations, such as, for example, a casting station, one or more heat treating stations, quenching stations, and holding stations. The heat treating stations can include assemblies that supply radiant, conductive or convective heat to the casting. In one embodiment, the multi-station system includes a multi-chambered fluidized bed into which a casting can be deposited from the mobile furnace for heat treatment. A casting can be moved from one chamber to another of the fluidized bed by first transferring it into the mobile furnace, moving the furnace into position adjacent the next chamber and transferring the casting into the next chamber from the mobile furnace. 
   In another embodiment, the casting system includes at least one heat treatment station and a furnace, such as a drop bottom furnace, that is movable between the heat treatment station and at least one other station of the casting system. The furnace can be moved into position above the heat treatment station so as to transfer one or more castings between the furnace and the station. A transfer mechanism can be used to move the casting from the mobile furnace to the heat treatment station and back again after heat treatment. The transfer mechanism can be operably connected to the furnace so as to raise and lower castings between the furnace and the heat treatment station. One or more removable lids also can be included in the casting system. Each lid can include a casting support for supporting one or more castings and a catch for engagement with the transfer mechanism. The removable lid having one or more castings supported thereon can be raised by the transfer mechanism into the furnace. The furnace then can be moved, with both casting(s) and lid disposed therein, over the heat treatment station. The transfer mechanism can then be activated to lower the lid and casting(s) down to the station so to deposit the castings in the station and close the station with the lid. The castings can be heat treated and then removed, along with the lid, and transferred back into the furnace, which can then be moved to the next position. 
   These and other aspects of the present invention will become apparent to those skilled in the art upon reading the following detailed description, when taken in conjunction with the accompanying drawings, which are briefly described as follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevation view of the casting system of the present invention with portions of the system removed and other portions of the system shown in cross-section. 
       FIG. 2  is a top view of the casting system of  FIG. 1  embodying principles of the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention generally comprises a method and apparatus for processing a casting and transporting the casting in a furnace between processing stations. The casting can be transferred into the furnace containing a heated interior in which the temperature of a casting can be maintained at or above a specified temperature or within a predetermined temperature range, or the casting can be quenched. The furnace is movable between two or more positions that allow for the efficient transfer of the casting between processing chambers or stations. After processing in a particular station, the casting can be returned to the same furnace or moved into another mobile furnace for transport to the next station. A casting can be molded, heat treated, quenched or otherwise processed by the method and within the system of the present invention. The method and system of the present invention can be incorporated into either an open system with no enclosed passageway between systems or closed systems including such a passageway between at least two of the stations. The processing stations included in the method and system of the present invention may include enclosed structures separated from the remainder of the system or structures that are open to other portions of the system. U.S. Provisional Application Serial No. 60/397,177, filed Jul. 18, 2002 is hereby incorporated by reference in its entirety. 
   As used herein, the term “furnace” refers to any structure that is at least partially enclosed and has a dedicated supply of heat to an interior portion thereof. The heat supply to the interior portion of the furnace can include radiant, conductive, convective heat or a combination thereof. The dedicated heat can be generated in or at the furnace or can be supply from a remote location. However, the heat supply generally is not heat that simply enters the interior of the furnace from the atmosphere immediately surrounding the furnace. Although the embodiment set forth below is described in terms of a mobile drop bottom furnace, other types of furnaces can be used according to the method and within the system of the present invention. For example, the mobile furnace can be an atmosphere furnace, a box furnace, a bell furnace, a car bottom furnace, a cover lift car bottom furnace, a pit furnace, a tip-up furnace, a roller hearth furnace, a retort, a conveyor furnace or other types of batch-type or continuous-type furnaces. 
   As used herein, the term “processing station” encompasses any locale or combination of positions where a casting is processed to alter its characteristics. Examples of various processes that may be carried out in a processing station include, but are not limited to, aging, annealing, austempering, baking, blasting, brazing, bright annealing, carbonitriding, carbon baking, carbon restoration, carburizing, coating, cooling, core removal, curing, forming, forge relief, hardening, heating, homogenizing, molding, nitriding, painting, quenching, sand/core removal, spherodizing, solution heat treating, stress-relief, tempering, and washing. 
   One embodiment of the system for supplying heat to a casting is set forth in  FIGS. 1 and 2 . The system  100  includes a multi-station casting processing system  20  in combination with a mobile furnace  34 . Generally, a casting  10  is processed in the system  100  by disposing the casting in the furnace  34  and transferring the casting  10  and the mobile furnace  34  from one station of the multi-station casting processing system  20  to another. Exemplary castings can be used in bus transmissions as an oil transfer plats. Conventional casting processes for this type of casting require approximately a nine hour bake-out to remove the core sand from the casting. Alternatively, the method and system of the present invention can accomplish this task in some cases in about 45 minutes. An example of a casting is formed from A-356 alloy and is approximately 31 inches long 24 inches wide 5 inches deep. The casting can include approximately 80 lbs of aluminum and 42 lbs of sand after it has been formed and removed from the mold. However, castings processed according to the method and with the system of the present invention may be formed of alternative alloys and metals and may have dimensions and weights that vary from the example. 
   As shown in the figures, the multi-station casting processing system  20  may include a casting machine  22  and one or more heat treatment stations, such as, for example, fluidized bed  50 . While the multi-station casting processing system  20  is shown in the figures with the casting machine  22  and the fluidized bed  50 , other configurations are contemplated for the system of the present invention. For example, the multi-station casting processing system may not include a casting machine, or instead of a fluidized bed  50 , the multi-station casting processing system  20  may include one or more convective furnaces or heating stations, other types of conductive or radiative heating stations, cooling stations or other processing stations. 
   The casting machine  22  can include one or more tilt/pour stations  24  and  26 . In one embodiment, the tilt/pour station  24  is approximately 4 feet by 8 feet. The casting mold used to form the castings in the casting machine  22  may be a permanent mold that is used in combination with cores formed with sand and binder. The casting  10  can be formed in one of the tilt/pour stations  24  and  26  by pouring a molten metal into the mold containing the core and allowing the casting to at least partially solidify in the mold. The casting can then be removed from the mold utilizing a retractor  23 . The retractor  23  may have at least three axes (in-out, rotate at the wrist, rotate about the in/out axis). It also may have a release type gripper  25  and thermal insulation for protecting the mechanism from the heat of the casting. In one embodiment, about seven castings per hour can be formed in each of the tilt/pour stations  24  and  26 , leading to a total of about fourteen castings per hour produced with two station casting machine. The casting  10  can then be moved from one of the first and second tilt/pour stations  24  and  26  using the retractor  23  and rotated for insertion into a heat treat rack or casting support  27 . The casting support  27  can include a series of brackets, shelves, hooks or similar means for mounting one or more castings thereon. 
   The casting support  27  can then be moved to a loading station  28  using a casting loader or gantry  32 . The loading station  28  may include a thermal arrest unit  29  that can either maintain or increase the temperature of the casting  10  in order to facilitate further processing thereof. The casting  10  can be held in the thermal arrest unit  29  as additional castings are added thereto until an appropriate number of castings  10  are assembled at the loading station  28  for further processing. In one embodiment, castings  10  are accumulated with a dwell of about thirteen minutes between the first and the last castings in the group, although alternative times also are encompassed. 
   The thermal arrest unit  29  includes one or more radiating panels  32  that supply heat to the casting  10 . As indicated previously, one or more castings may be positioned on the casting support  27 . Consequently, a plurality of castings can be transferred from one station of the multi-station casting processing system  20  to another for treatment. 
   The casting  10  then can be transferred into the furnace  34  from the load station  28 . The present invention also encompasses systems in which the casting  10  is transferred directly from the casting machine  22  into the mobile furnace  34 . In the embodiment shown in  FIGS. 1 and 2 , the mobile furnace  34  is a drop-bottom furnace mounted on a furnace gantry  36  that moves from one station to another of the multi-station casting processing system  20 . The furnace gantry  36  is aligned on a furnace track  37  that runs between at least two of the stations. The furnace gantry track  37  is positioned on the floor adjacent the various stations of the multi-station casting processing system  20 . However, the present invention also encompasses mobile furnaces that are suspended from by a gantry system that is at least partially suspended above or adjacent to the stations. Furthermore, the mobile furnace  34  may be moved on a gantry or similar apparatus that itself does not change position but rather rotates in order to move the furnace  34  from one station to the next. 
   The castings  10  are moved into the mobile furnace  34  using a transfer mechanism  38 . As shown in  FIG. 1 , the transfer mechanism  38  may be a hoist that is mounted or otherwise operably connected to the furnace  34  and a portion of which extends through one of the walls  40  of the furnace  34  into the interior thereof. Alternative transfer mechanisms are encompassed by the present system. For example, the transfer mechanism may include a robotic arm, elevator or similar device, any of which can be mounted to, inside or adjacent to the furnace  34  in order to transfer one or more castings  10  into or out of the mobile furnace  34 . As shown in  FIG. 1 , the casting support  27  is raised into the furnace  34  using the hoist  38 . The casting  10  is supported on the casting support and is positioned so as to be enclosed in the furnace. 
   A door  44  is movably aligned to close an opening  43  in the furnace  34  through which the casting  10  can be transferred. Although the door  44  and opening  43  are aligned on the bottom wall of the furnace  34  in  FIG. 1 , the system can also include alternative configurations of the furnace wherein the door  44  is positioned on a side or top of the furnace  34 . The door  44  is opened and closed using a door pivot mechanism  46  with which the door  44  may be slid, rotated, swung or otherwise positioned to close the furnace  34 .  FIG. 1  shows a position of the door  44  when the furnace  34  is open. In one embodiment, the interior of the furnace  34  is approximately 3′ wide, 5′ long and 5′ high. Alternative sizes also are encompassed. Airflow into the interior of the furnace is optional, since, in some cases, heat transfer to the casting  10  is not accomplished within the furnace  34 . The temperature of the casting  10  can be controlled in the furnace by either supplying heat to the casting or preventing heat loss from the casting using a radiant, convective or conductive heating element. As shown in  FIG. 1 , the heating element  42  includes one or more electric heaters mounted on the walls  40  of the furnace that supplies heat to the interior of the furnace  34  and any castings  10  that are disposed therein. In one embodiment, the heating element  42  includes electric rod-over-bend elements located on all four walls of the furnace. Heating baffles  43  are provided to efficiently distribute the heat supplied by the heating element  42  to the casting  10 . When a heating baffle  43  is used a fan is not required. The temperature of the casting  10  can be maintained within the furnace  34  so as to avoid or reduce the extent of a drop in the temperature of the casting  10 . Once a casting  10  is positioned within the furnace  34 , the furnace  34  then is moved to the next station at which the casting  10  is to be treated. 
   The furnace  34  is moved into position adjacent to the first fluidized bed chamber  51   a  of fluidized bed  50 . The fluidized bed  50  can be a deep fluidized bed having one or more independent chambers, each with individual heaters and fluidizers. The fluidized bed  50  shown in  FIG. 1  includes first, second, third and fourth fluidized bed chambers  51   a ,  51   b ,  51   c  and  51   d , respectively. Each chamber includes a fluidized bed lid  54   a ,  54   b ,  54   c  and  54   c , respectively, to which is attached a lid casting support  56   a ,  56   b ,  56   c  and  56   d , respectively, and a lid hook  58   a ,  58   b ,  58   c  and  58   d , respectively. Each fluidized bed lid  54  may be insulated and include, instead of a hook, a loop, ring, catch or other means by which the lid may be engaged and moved. Furthermore, each lid  54  may be identical or substantially similar to the casting support  27 , so that each lid  54  and support  27  may be interchangeably utilized at the various stations of the system  100 . 
   The fluidized bed chambers  51   a ,  51   b ,  51   c  and  51   d  can be maintained with either identical or dissimilar temperatures and flow characteristics. Therefore, in the case where the fluidized bed chambers are all maintained at the same temperature, a casting  10  can be placed in only one of the chambers for heat treatment and then moved out of the fluidized bed  50  and to the next station, such as the quench tank  60 . In this case, the mobile furnace  34  alternates between chambers  51   a ,  51   b ,  51   c  and  51   d  when castings  10  are loaded in the fluidized bed  50 . In one embodiment, when the bed  50  includes four chambers  51 , one rack of castings  10  can be loaded and one quenched about every 15 minutes. In a system in which a casting  10  is subjected to multiple heat treatment or other process steps in multiple fluidized beds, or other types of stations, the temperatures of each of chambers  51   a ,  51   b ,  51   c  and  51   d  are different from the others and a casting  10  is moved sequentially from one chamber to another using the furnace  34 . 
   When a casting  10  is to be processed in the fluidized bed  50 , the mobile furnace  34  containing the casting  10  is moved into positioned adjacent to the chamber of the bed  50  into which the casting  10  is to be inserted. The door  44  is opened and the transfer mechanism  38  transfers the casting  10  and casting support  27  or lid  54  out of the furnace  34 . The casting  10  is then deposited in the chamber  51  as the upper portion of the casting support  27  or lid  54  engages the walls  52  of the bed  50  so as to close the chamber  51 . The casting  10  is processed within the chamber  51  and then removed from the chamber in a similar fashion. In one embodiment, sand or other core material is removed from the casting  10  in the fluidized bed  50 . For example, in one particular embodiment, approximately 42 lbs of sand is removed in the bed  50  from each casting  10 . When fourteen castings  10  are processed per hour, approximately 588 lbs of sand or other core material is removed from the castings  10 . After a casting  10  has been deposited in a chamber  51 , the mobile furnace  34  may be moved to other stations to remove and deposit other castings in other stations. When a chamber  51  does not contain a casting  10 , the chamber  51  may be either open or have a temporary lid placed thereon, which is removed prior to a casting being deposited in the chamber  51 . The temperature and flow within a chamber  51  can be controlled so that it is lowered or otherwise maintained when the chamber is open. For example, the supply of heat to a chamber  51  can be stopped when the chamber is open. 
   The system  100  also may include a quench tank  60 . The quench tank  60  contains an appropriate fluid, such as air or water, to quench castings  10  therein. Once a casting  10  has been treated in one of the chambers  51  of the fluidized bed  50 , the mobile furnace  34  is positioned over the chamber and the hoist  38  is lowered to engage hook  58  the lid  54  of that particular chamber. The lid  54  is then raised into the furnace  34  and the door  44  is closed. The casting  10  is supported on the lid casting support  56 . The mobile furnace is then moved on a furnace gantry track  37  to be aligned with the quench tank  60 . The door  44  then is opened and the hoist  38  lowers the lid  54 , casting support  56  and casting  10  into the quench tank  60 , wherein the temperature of the casting is adjusted or maintained. In one embodiment, the quench tank  60  is approximately 5 feet long, 4 feet wide and 4 feet deep. The quench tank  60  includes a propeller agitator  61  and a submersible tank heater  61   a . The quench tank  60  may also include a filtration system such as a cyclone type filter that removes sand from the quenchant. 
   Once the casting  10  has been processed in the quench tank  60 , it can then be removed from the quench tank  60  using the quench tank transfer mechanism or gantry  62 . The gantry  62  can include an electric hoist  63  for raising the lid  54 , casting support  56  and casting  10  from the quench tank  60 . The gantry  62  also includes a boom  64  that can be pivoted into position over the quench tank and moved into position over the unloading station  65  that is positioned along a return track  64  and includes a basket, cart, truck or similar device  67  for moving the casting  10  along the return track  64 . The casting  10  then is moved to the unload position  66  and transfer from the unload position  66  using an unloading mechanism or gantry  68 . The casting  10  can be returned to the thermal arrest unit  30  or other area for further processing. The casting support  27  or lid  54  can then be moved to the casting machine  22  by loader  32  for further additional cycles. 
   It will be understood by those skilled in the art that while the present invention has been discussed above with reference to certain embodiments, various additions, modifications and changes can be made thereto without departing from the spirit and scope of the invention as set forth in the following claims.