Abstract:
The present invention provides a casting method comprising the steps of obtaining a thermal distribution of mold sand for a casting, and determining a mold wall thickness profile based at least partially on the mold sand thermal distribution.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Many manufactured products are cast from steel or other metals, including iron and aluminum. Cast products range from automobile engines, jet engines, golf club heads, valves, and sewer covers, to railcar parts including sideframes, bolsters, couplers, knuckles, and countless other products. Castings are made in a mold. Typically, the mold has a top or cope section and a bottom or drag section. The cope and drag sections of the mold are each contained in a flask. A pattern is placed over one end of each flask and sand is rammed over the pattern, thereby compacting the sand around the pattern. Sand is rammed into the flask until the flask is filled with sand. The pattern is then removed leaving an impression of the casting&#39;s external surfaces in the compacted cope and drag section mold sand.  
           [0002]    Many castings have hollow sections. The hollow sections are formed with cores. Cores define the hollow sections&#39; internal surfaces, and may define some external surfaces of the casting. Cores are also typically made from sand. The sand may contain a binding agent to maintain the core&#39;s integrity while handling the core during the casting process. Typical binding agents include phenolic resin, polyurethane, and sodium silicate.  
           [0003]    Cores are made in core boxes. The core box includes a drag box and a cope box. Cores can be produced manually or with automated core making equipment such as a core blower. To make a core with a core blower, the cope and drag boxes are fastened together, and the core box placed on the core blower. Tooling is required to fit the core box to the core blower.  
           [0004]    The core blower produces cores by blowing sand into the core box. The core blower typically uses sand containing a binding agent. After sand fills the core box, the core blower injects curing gas into the sand to cure the core. The cope and drag boxes are then separated leaving the core.  
           [0005]    Once made, the cores are placed in the bottom or drag mold. After the cores are placed in the drag mold, the cope mold is placed on top of the drag, and the cope and drag are fastened together. Molten metal is poured into the mold and allowed to cool, thus hardening the metal. The casting is then removed from the mold and the sand is shaken out. The casting is then typically heat treated, machined, and finished.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides a casting method including the steps of analyzing the stresses in the mold sand without temperature effects, obtaining a thermal distribution of mold sand for a casting, and determining a mold wall thickness profile based at least partially on the mold sand thermal distribution.  
           [0007]    In another aspect, the present invention includes a method of fabricating a mold for making a casting having the step of fabricating a cope mold and a drag mold, the cope mold having a cope mold wall thickness profile, the drag mold having a drag mold wall thickness profile, and joining the cope mold and drag mold to form a cavity.  
           [0008]    In a further aspect, the present invention includes a method for casting a metal product including the steps of fabricating a mold from mold sand, the mold having a mold thickness profile, pouring molten metal into the mold, and cooling the molten metal. In another aspect, a mold for making a metal casting, a mold including a mold wall thickness profile is provided.  
           [0009]    The casting method of the present invention provides uniform mold density throughout the entire mold. It also provides a mold that uses a great deal less sand than conventional molds. Moreover, the mold is up to 20 times stronger than prior art methods. Casting dimensional control is also dramatically increased. Further, approximately 75-95% of the sand is naturally thermally reclaimed, thereby eliminating costly sand reclamation equipment. Mold making productivity is also increased. Molds may be made at a rate of 60 per hour as opposed to the 20 per hour rate of some prior art methods. Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the figures. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0010]    [0010]FIG. 1 is a schematic showing a prior art casting mold.  
         [0011]    [0011]FIG. 2 is a schematic showing the casting mold of an embodiment of the present invention.  
         [0012]    [0012]FIG. 3 is a schematic showing the top cope mold pattern box and the bottom cope mold pattern box of an embodiment of the present invention.  
         [0013]    [0013]FIG. 4 is a schematic showing the top cope mold pattern box and the bottom cope mold pattern box joined together in an embodiment of the present invention.  
         [0014]    [0014]FIG. 5 is a schematic showing the top cope mold pattern box and bottom cope mold pattern box joined together with a sand chamber and blow tubes in an embodiment of the present invention.  
         [0015]    [0015]FIG. 6 is a schematic showing mold sand after it has been blown into the cavity formed by the top cope mold pattern box and bottom cope mold pattern box in an embodiment of the present invention.  
         [0016]    [0016]FIG. 7 is a schematic showing the cope mold being cured in an embodiment of the present invention.  
         [0017]    [0017]FIG. 8 is a schematic of the top cope mold, top cope mold pattern box, and bottom cope mold pattern box of an embodiment of the present invention.  
         [0018]    [0018]FIG. 9 is a schematic of the top drag mold, top drag mold pattern box, and bottom drag mold pattern box of an embodiment of the present invention.  
         [0019]    [0019]FIG. 10 is a schematic showing the cavity of the cope mold and drag mold filled with molten metal in an embodiment of the present invention.  
         [0020]    [0020]FIG. 11 is a schematic showing a metal casting made in accord with an embodiment of the present invention.  
         [0021]    [0021]FIG. 12 is a three dimensional temperature distribution of a casting.  
         [0022]    [0022]FIG. 13 is a three dimensional stress distribution of a casting.  
         [0023]    [0023]FIG. 14 is a multiplanar cross-sectional view of a mold made in accord with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    [0024]FIG. 1 is a schematic of a prior art mold  10  used to make a metal casting  11  (FIG. 11). The prior art mold  10  consists of a top flask  12  and a bottom flask  14 . The top flask  12  and bottom flask  14  contain a cope mold  16  and drag mold  18 , respectively. To make the mold  10 , the cope mold  16  is placed on top of the drag mold  18 . The cope mold  16  is fastened to the drag mold  18  by clamps, weights, or any suitable fasteners.  
         [0025]    The cope mold  16  and drag mold  18  are made of mold sand  20 . The mold sand  20  is typically made of silica sand. The silica sand is usually coated with a mixture of bentonite clay and water. To make the cope mold  16 , a pattern (not shown) is placed at one end of the top flask  12 . The pattern forms the top external surface  22  of the casting  11 . The mold sand  20  is rammed either by hand or with a suitable machine over the pattern. A sand slinger is typically used with larger patterns. The pattern has also been squeezed into the mold sand  20  in a machine such as a jolt-squeeze molding machine. The mold sand  20  is thereby compacted within the top flask  12 . The mold sand  20  fills the top flask  12 .  
         [0026]    After ramming, the pattern is removed from the top flask  12 , and an impression corresponding to the top external surface  22  of the casting  11  left in the mold sand  20  of the cope mold  16 . The drag mold  18  is made in similar fashion, leaving an impression corresponding to the bottom external surface  24  of the casting  11  in the mold sand  20  of the drag mold  18 .  
         [0027]    When the cope mold  16  is placed on the drag mold  18 , a cavity  25  is formed. The cavity  25  is filled with molten metal to form the casting  11 . There are often hollow portions (not shown) in a casting  11 . These hollow portions are formed by cores (not shown) placed in the drag mold  18 . As will be understood by those skilled in the art, cores define the hollow sections&#39; internal surfaces, and may define some external surfaces of the casting. Cores are typically made from sand. The sand may contain a binding agent to maintain the core&#39;s integrity while handling the core and during the casting process. Typical binders include phenolic resin, polyurethane, and sodium silicate. A popular core sand binder system is Ashland Inc.&#39;s Isocure® binder system.  
         [0028]    [0028]FIG. 2 shows a mold  26  made in accord with the method an embodiment of the present invention. The mold  26  includes a cope mold  28  and a drag mold  30 . The cope mold  28  has a cope mold wall  29 , and the drag mold  30  has a drag mold wall  31 . The cope mold  28  rests atop the drag mold  30 . The cope mold  28  and drag mold  30  are fastened together by clamps, adhesives, weights, or any suitable means. When fastened, the cope mold  28  and drag mold  30  form a cavity  33 . Molten metal is poured into the cavity  33  to form the casting  11 . It will be understood by those skilled in the art that the casting  11  may include hollow sections. The hollow sections may be formed with cores.  
         [0029]    An internal surface  32  of the cope mold  28  defines the top external surface  34  of the casting  11  (FIG. 11). An external surface  36  of the cope mold  28  defines a cope mold wall thickness profile  38  as described below. An internal surface  40  of the drag mold  30  defines the bottom external surface  42  of the casting  11  (FIG. 11). An external surface  44  of the drag mold  30  defines a drag mold wall thickness profile  46  as described below. The cope mold wall thickness profile  38  and drag mold wall thickness profile  46  combined form a mold wall thickness profile  47 . The cope mold wall thickness profile  38  forms the top half, and the drag mold wall thickness profile  46  forms the bottom half of the mold wall thickness profile  47 . The cope mold  28  and drag mold  30  are preferably formed from a mold sand  49  containing a binder system. The preferred binder system is a gas cured phenolic urethane system such as Ashland Inc.&#39;s Isocure® system, but any suitable binder system may be used. The mold  26  of the present invention has wall thickness profiles  38  and  46  that require much less mold sand than the prior art mold of FIG. 1.  
         [0030]    The mold sand  49  is a heat insulating material. Thus, heat does not progress quickly through the mold sand  49 . A short time after pouring molten metal into cavity  33  of the mold  26 , generally on the order of three minutes depending on the casting  11 , an outer skin of solidified metal has formed on essentially all of the casting  11 . Once the outer solidified metal skin is formed, the outer skin holds in the molten metal to prevent molten metal from running through the mold sand  49 . A shell of bonded mold sand  49  must encase the casting  11  until the outer skin has formed.  
         [0031]    [0031]FIG. 14 shows an example mold  80  for a railcar knuckle casting made in accord with an embodiment of the present invention. The mold  80  has a mold wall thickness profile  47 . To create the cope mold wall thickness profile  38  and drag mold wall thickness profile  46 , the mold wall thickness profile  47  is parted at a determined plane depending on the geometry of the casting. The mold wall thickness profile  47 , and thus the cope and drag mold wall thickness profiles  38  and  46 , are optimized to use only enough mold sand  49  to provide sufficient mold sand thickness and strength to encase the molten metal as it cools until the outer skin of solidified metal has formed on the liquid metal. Depending on casting metal thickness and other variables, the solidified molten metal skin forms at different times throughout the casting. Thus, as shown in FIG. 14, the mold  80  is thicker in certain areas and thinner in others. The resulting varying thickness in the mold  80  forms the mold wall thickness profile  47 .  
         [0032]    The predominant variable in determining the mold wall thickness profile  47  is the rate at which the mold sand  49  binder breaks down upon exposure to the elevated temperatures experienced in casting using molten metal. For the Isocure® binder system, the binder in the mold sand  49  loses its strength after it has reached approximately 500° C. for about six minutes. 500° C. is the recognized industry temperature value at which the bonded sand loses its strength. Molten steel is typically poured into the mold  26  at approximately 1,565° C. to 1,600° C. The solidification temperature of steel is approximately 1,425° C. As the molten steel is poured into the mold  26 , heat from the molten metal is transferred into the mold sand  49 , thus reducing the molten metal temperature at surfaces which contact the mold sand  49 . This temperature reduction causes the metal to quickly form the solidified outer skin where it contacts the mold  26 . For a majority of the castings under consideration for this method, the outer skin typically begins forming within a thirty second to three minute time interval after pouring. However, in some casting hot spots, it may take 10 minutes or more for the skin to form. When the mold sand  49  containing binder closest to the casting  11  reaches its binder break down temperature, there must be sufficient mold sand  49  behind the broken down mold sand to encase the casting  11  until the outer skin forms. The mold sand  49  which has been broken down does not move due to hydrostatic pressure from metal against the remaining strong mold sand  49 .  
         [0033]    Other factors affecting the mold wall thickness profile  47  include casting geometry, the type of metal being cast, i.e., aluminum, steel, or iron, and the temperature at which the molten metal is poured into the mold  26 , the casting wall thickness, and the volume of the casting  11 . The rate at which the sand breaks down and loses its strength also increases with increasing sand temperature. The thicker the casting in certain areas, the more heat is created in those areas, thus requiring additional mold sand  49  to ensure sufficient mold sand thickness and strength to encase the casting in the mold before break down of the mold sand binder in those areas. The higher the molten metal temperature, greater heat energy enters the sand, thus breaking the sand binder down more quickly. Thus, more mold sand  49  is needed to withstand the temperature and resultant heat transfer through the mold walls  29  and  31 .  
         [0034]    The mold wall thickness profile  47 , and cope mold and drag mold wall thickness profiles  38  and  46  are preferably determined as follows. The following description assumes the use of the preferred Isocure® binder system. A preliminary finite element stress analysis without temperature effects is performed on a casting in which a mostly uniform mold sand thickness profile such as one inch is applied. The design goal of this analysis is to determine minimum mold wall thickness required to encase the metal during filling and solidification without temperature effects. This minimum wall thickness must at least remain below the binder breakdown temparature of 500° C. and encase the liquid metal until the solidified metal skin has formed. Two stresses are typically examined: (1) the stress due to the pressure of the liquid metal on the mold sand after the mold cavity has been filled with liquid metal; and (2) the maximum pressure exerted on the mold sand when the mold cavity is being filled with liquid metal. The design goal for the analysis is determining minimal wall thickness such that there is a stress safety factor of four when comparing the actual stresses in the sand to the known maximum tensile and compressive yield strengths of the bonded sand. Bonded mold sand has a known strength available from the binder manufacturer.  
         [0035]    A typical stress distribution to determine mold wall thickness required to encase the metal during filling and solidification without temperature effects is shown in FIG. 13. FIG. 13 shows a mold wall thickness that is one inch in most areas. The stress distribution for this load case shows stresses in the mold sand at any particular point. In FIG. 13, the stress is represented by Von Mises stress. For any particular point in the mold there is an x, y, and z direction stress component. The Von Mises stress is an effective stress that combines the directional stresses into a non-directional scalar value that represents the overall stress status at any one particular point. FIG. 13 shows maximum tensile stresses in the 20 to 30 psi range. The tensile strength of the bonded sand is approximately 220 psi. For this load case, the wall thickness profile provides for stress safety of approximately seven to ten. Since the stress safety fact goal is only four, the wall thickness may be substantially reduced for this load case.  
         [0036]    Once the minimum mold wall thickness without temperature effects is determined, a preliminary mold wall thickness profile  47  considering temperature effects is developed. One skilled in the art will recognize that certain casting features raise the temperature of the mold sand  49  in areas adjacent to such features. For example, where casting surfaces meet at corners, the temperature of the casting and the sand will be greater in that area. Thus, the mold  80  will have to be thicker in such areas. Where plate-like features exist in the casting, the mold  80  will need to be less thick.  
         [0037]    After arriving upon a preliminary sand mold wall thickness, a time/temperature analysis  81  is performed on the mold sand  49  during the cavity  33  filling and solidification process. The goal for the analysis is to develop a mold wall thickness profile such that a layer of sand with sufficient strength is present throughout the entire casting solidification process to contain the liquid metal until a soldified metal skin has formed. This layer of sand is to have a thickness at least equal to the minimal mold wall thickness determined from the stress analysis. The layer of sand must also be at least below the binder break down temperature of 500° C. Time/temperature data for the mold sand  49  and the casting is compared to the mold sand strength/temperature data for the binder system used. The strength/temperature data is proprietary to the binder manufacturer. To obtain such data for the preferred Isocure® binder system, contact Ashland Inc.  
         [0038]    An example time/temperature analysis  81  is shown in FIG. 12. Such an analysis is performed for every casting. FIG. 12 shows a temperature distribution for the railroad knuckle casting whose mold  80  is shown in FIG. 14 at approximately three minutes after the molten metal has been poured into the mold  80 . After three minutes the outer skin of the knuckle casting has solidified. As can be seen in FIG. 12, the temperature of the mold sand  49  at reference numeral  82  exceeds 700° C. Thus, the mold sand  49  is such areas will have surpassed the mold sand binder break down temperature. Such mold sand  49  is held in place by the hydrostatic pressure of the molten metal against the remaining mold sand  84 .  
         [0039]    At reference numeral  86  of FIG. 12, the mold sand  49  has reached or neared the recognized binder break down temperature of 500° C. The mold  80  must be thicker at this point than reference numeral  88  because the temperature of the mold sand  49  has reached the binder break down temperature further from the casting  11 . If the mold sand  49  is found by the temperature analysis to exceed the break down temperature throughout the mold sand, the thickness must be increased at such area. If the temperature distribution suggests that excess mold  80  thickness exists at any point, the thickness may be decreased. The sand thickness may be decreased to a value equal to or greater than the minimum mold wall thickness value that was determined from the stress analysis. Decreasing the mold  80  thickness to that only required to encase the casting  11  also permits thermal reclamation of the mold sand  49  as described below. This process is repeated until an optimum mold wall thickness profile  47  has been determined for the particular casting  11 . Each casting  11  will require a separate time/temperature analysis and comparison to the sand strength/time data.  
         [0040]    [0040]FIGS. 3 through 7 schematically illustrate the preferred method by which the cope mold  28  is made after the desired wall thickness is determined. A top cope mold pattern box  48  and bottom cope mold pattern box  50  are placed within a mold machine (not shown). The mold machine is a core blowing machine that is well-known in the art adapted to fit the tope cope mold pattern box  48  and bottom cope mold pattern box  50 . Such core blowing machines include those manufactured by Equipment Merchants International, Laempe, and others. The top cope mold pattern box  48  is placed on top of the bottom cope mold pattern box  50 . The top cope mold pattern box  48  and bottom cope mold pattern box  50  are preferably clamped together within the machine to form a cavity  52 . The cavity  52  will accommodate mold sand  54  (FIG. 4.) The cavity  52  is in the shape of the cope mold  28  such that the mold sand  54  will form the cope mold  28 .  
         [0041]    The top cope mold pattern box  48  has blow tube openings  56  that communicate with the cavity  52 . The mold machine includes a mold sand chamber  58  that communicates with blow tubes  60  (FIG. 5). The blow tubes  60  are attached to a blow tube plate (not shown). The blow tube plate is attached to the underside of the mold sand chamber  58 . The blow tube plate has a corresponding hole for each blow tube  60 .  
         [0042]    The mold sand chamber  58  is filled with mold sand  49 . The mold sand  49  is preferably mixed with a binder system. Any suitable binder systems will work. The preferred binder system is Ashland Inc.&#39;s Isocure® system.  
         [0043]    The blow tubes  60  are inserted into the blow tube openings  56  in the top cope mold pattern box  48 . The mold sand chamber  58  is pressurized so mold sand  49  from the mold sand chamber  58  is blown into the cavity  52  until the cavity  52  is filled with mold sand  49  (FIG. 6). The blow tube openings  56  and blow tubes  60  must be positioned such that the cavity  52  is completely filled with mold sand  49 . After the mold sand  49  has filled the cavity  52 , the blow tubes  60  are removed from the blow tube openings  56 . Some residual mold sand  49  may be left in the blow tube openings  56 .  
         [0044]    After the mold sand  49  is blown into the cavity  52 , a gas manifold  62  is attached to the top cope mold pattern box  48  (FIG. 7). The gas manifold  62  has a tamper plate  64  to which tamper pins  66  are attached. It is preferred that each tamper pin  66  be hollow and have an have an opening (not shown) and a vent (not shown) at its end  68  distal to the tamper plate  64 . The hollow tamper pins  66  are inserted into the blow tube openings  56 . The tamper pines  66  compact the residual sand that is left in the blow openings to the desired mold shape profile and dimension. The gas manifold  62  is pressurized with a curing gas  70 . The curing gas  70  acts as a catalyst to initiate curing the binder in the mold sand  49 . Different binder systems may require different curing gases. For the preferred Isocure® binder system, an amine gas is preferred.  
         [0045]    The top cope mold pattern box  48  may also have vents for curing gas  70  to pass through the gas manifold  62  into the mold sand  49 . In the preferred embodiment, the curing gas  70  passes through both the hollow tamper pins  66  and the top cope mold pattern box vents into the mold sand  49 . Curing gas  70  is passed through the mold sand  49  until the mold sand  49  is adequately bonded. The time curing gas  70  is passed through the mold sand  49  depends on the thickness, volume of sand, and porosity of the sand. The bottom cope mold pattern box  50  is vented to provide an outlet for the curing gas  70 .  
         [0046]    After curing the tamper pins  66  are removed from the top cope mold pattern box  48 . The top cope mold pattern box  48  and bottom cope mold pattern box  50  are separated, and the cope mold  28  is removed and ready to be used (FIG. 8). The external surface  36  of the cope mold  28  has a cope mold thickness profile  38  that corresponds to the determined optimum cope mold thickness profile by the manner previously described.  
         [0047]    The drag mold  30  is made in a similar manner to the cope mold  28  (FIG. 9). A top drag mold pattern box  72  and bottom drag mold pattern box  74  are placed within the mold machine. The drag mold  30  can be made in the same mold machine as the cope mold  28 , or on a different mold machine. It will be described here as the same mold machine. The top drag mold pattern box  72  is placed on top of the bottom drag mold pattern box  74 . The top drag mold pattern box  72  and bottom drag mold pattern box  74  are clamped together within the mold machine to form a cavity. The cavity accommodates the mold sand  49  and is in the shape of the drag mold  30  such that the mold sand  49  will form the drag mold  30 .  
         [0048]    Like the top cope mold pattern box  48 , the top drag mold pattern box  72  has blow tube openings  76  that communicate with the cavity. The mold machine cooperates with the mold sand chamber  58  that communicates with blow tubes  60 . The blow tubes  60  are attached to a blow tube plate. The blow tube plate is attached to the underside of the mold sand chamber  58 . The blow tube plate has a corresponding hole for each blow tube  60 .  
         [0049]    The mold sand chamber  58  is filled with mold sand  49 . The mold sand  49  is preferably mixed with a binder system. The blow tubes  60  are inserted into the blow tube openings  76  in the top drag mold pattern box  72 . The mold sand chamber  58  is pressurized so mold sand  49  from the mold sand chamber  58  is blown into the cavity until is filled with mold sand  49 . The blow tube openings  76  and blow tubes  60  must be positioned such that the cavity is completely filled with mold sand  49 . After the mold sand  49  has filled the cavity, the blow tubes  60  are removed from the blow tube openings  76 . Some residual mold sand  49  may be left in the blow tube openings  76 .  
         [0050]    After the mold sand  49  is blown into the cavity, a gas manifold  62  is attached to the top drag mold pattern box  72 . The gas manifold  62  has a tamper plate  64  to which tamper pins  66  are attached. It is preferred that each tamper pin  66  is hollow and has an opening (not shown) and a vent (not shown) at its end  68  distal to the tamper plate  64 . The hollow tamper pins  66  are inserted into the blow tube openings  76 . The tamper pins  66  compact the residual sand that is left in the blow tube openings  76  to the desired mold shape profile and dimension. The gas manifold  62  is pressurized with a curing gas  70 . The curing gas  70  acts as a catalyst to initiate curing the binder in the mold sand  49 .  
         [0051]    The top drag mold pattern box  72  may also have vents for curing gas to pass through from the gas manifold  62  into the mold sand  49 . The preferred embodiment is where the curing gas  70  passes through both the hollow tamper pins  66  and the top cope mold pattern box vents into the mold sand  49 . Curing gas  70  is passed through the mold sand  49  until the mold sand  49  is adequately bonded. The time curing gas  70  is passed through the mold sand  49  depends on the thickness, volume of sand, and porosity of the sand. The bottom drag mold pattern box  74  is vented to provide an outlet for the curing gas  70 .  
         [0052]    After curing the tamper pins  66  are removed from the top drag mold pattern box  72 . The top drag mold pattern box  72  and bottom drag mold pattern box  74  are separated, and the drag mold  30  is removed and ready to be used (FIG. 9). The external surface  44  of the drag mold  30  has a drag mold thickness profile  46  that corresponds to the determined optimum drag mold thickness profile by the manner previously described.  
         [0053]    To make a casting, the cope mold  28  is placed on top of the drag mold  30  forming a cavity  25  (FIG. 2). Molten metal  78  is poured into the cavity  25 . The molten metal  78  is allowed to cool. The sand is removed leaving the metal casting  11 . The metal casting  11  is ready for further processing such as heat treating, grinding, and finishing.  
         [0054]    After the sand is removed from the casting, there are both economical and environmental advantages to reclaiming the sand and using it again to either make molds or cores. To effectively use the sand again to make molds or cores, the foundry needs to remove a majority of the binder that is left in the sand. In the past, the reclamation process required post-processing equipment to remove a majority of the binder that is left in the sand used to make a mold. The present invention eliminates the need for post-processing equipment to remove the majority of the residual binder that was used in the mold.  
         [0055]    Preferably, either while the molten metal  78  is poured into the cavity  25 , or after immediately pouring, the mold is placed on a tray. The tray can consist of a plate having upwardly extending flanges around its ends. Instead of a plate, a screen may also be used. After the mold has cooled sufficiently, heat from the molten metal shall have transferred to the sand and binder causing the binder to break down through essentially all of the sand. The mold wall thickness profile  47 , and hence the cope mold wall thickness profile  38  and drag mold wall thickness profile  46 , is determined to permit optimum thermal reclamation. While enough sand must be initially be present to prevent premature break down of the binder before the outer skin of the casting  11  forms, it must also be optimized such that nearly all of the mold sand  49  binder has reached its break down temperature after sufficient cooling of the molten metal. At his point, the mold sand  49  should essentially be falling off of the casting and onto the plate or screen, all of the binder having reached its burnout temperature of approximately 500° C. As the mold sand heats up while the casting cools, more and more of the mold sand binder will reach its burnout temperature. This will cause the sand to essentially flake away and fall from the casting. This eliminates the need for mechanical and thermal sand reclamation. To remover remaining sand, the plate or screen is placed on a shaker or vibrator to remove the residual sand on the casting. The sand will fall or be placed on a conveyor to be re-used.  
         [0056]    The method of the present invention also facilitates approximately 75-95% of the sand is naturally reclaimed during the solidification process. The prior art method requires thermal reclamation equipment such as that sold by Gudgeon Thermfire International Inc or Castec, Inc. Thermal reclamation equipment consists essentially of an oven which heats the sand containing binder until the binder burns out leaving unbound sand. A conveyor typically brings the sand. A sand crusher was also sometimes used to crush the bound sand to more easily facilitate transport on the conveyor and heating.  
         [0057]    The method of the present invention results in improved mold cycle times. Mold cycle times are the amount of time required used to make a mold. A mold is more quickly made with bonded sand on a blowing machine than with a sand rammer.  
         [0058]    Moreover, much less and is used in the method of the present invention. The prior art method required filling the flask with mold sand. The present invention&#39;s method only requires a few inches thick wall of bound mold sand. Molds made using the method of the present invention are also up to twenty times stronger than green sand molds. Moroever, dimensional control is much improved over prior art methods.  
         [0059]    It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.