Patent Publication Number: US-7900684-B2

Title: In-place cope molding for production of cast metal components

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of provisional U.S. Application No. 60/949,984, filed Jul. 16, 2007, which is specifically incorporated herein by reference, under 35 U.S.C. §119(e). 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to metal founding, and more particularly to a method of making a sand-based mold which improves the casting process by reducing the amount of materials and time necessary to produce the mold. It also includes molds made using the process. 
     BACKGROUND 
     Traditional foundry sand molding processes typically employ a two-part mold consisting of a lower half (drag) and an upper half (cope). These two halves are normally produced using the same process: a sand/binder mixture is poured onto a pattern which forms the molding or rigging cavities. When the sand binders have set, the mold and pattern are turned over and the pattern is extracted from the mold. During the mold closing process, the cope half is turned over again and placed on top the drag, forming a complete mold. 
     A more advanced molding technique, known as patternless molding, differs from the above in that two solid blocks of sand are molded without the use of a pattern. The mold and rigging cavities are then machined into the sand blocks forming the cope and drag. Again, the cope half is turned over and placed on top the drag during mold closing. 
     There are several inefficiencies inherent in both processes. First, the cope and drag sections must be thick enough to have sufficient strength to withstand the stresses produced during the turnover processes. The amount of sand and binder used for each mold is thus usually far greater than the amount needed otherwise for strength during the pouring process or that needed for thermal insulation. Second, the turnover and mold closing processes take time. And third, inaccuracies in the molding process (including dimensional changes during the binder curing) can create gaps between the cope and drag. During pouring, metal fills these gaps creating “flash” that must be removed by grinding the resulting casting. 
     Accordingly, a need exists to improve the efficiency of the casting process by reducing the amount of materials necessary to form the cope and reducing the time required to complete the full mold and reducing the amount of flash. 
     SUMMARY 
     The process, hereinafter referred to as In-Place Cope Molding or “IPCM,” is designed to reduce or eliminate certain inefficiencies inherent in the traditional molding techniques, particularly during production of the cope half of a sand mold. 
     IPCM allows the cope half of a mold to be produced directly on top of the drag half of the mold by use of a separation barrier which supports the sand above the mold cavity in the drag. The introduction of the barrier, which supports the sand above the mold and rigging cavities in the drag, allows a thinner cope layer to be molded on top of the drag half, eliminating the need to handle the cope half separately. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectioned side view of a cutaway of the full mold; 
         FIG. 2  is top perspective view of the drag layer with a barrier partially in place; 
         FIG. 3  is a top perspective view of the mold cavity and the application of barrier glue; 
         FIG. 4  is a top perspective view of a mica barrier being glued in place; 
         FIG. 5  is a top perspective view of the drag layer with a barrier secured in place; 
         FIG. 6  is a top perspective view of a heat-shrinkable plastic film barrier taped in place; 
         FIG. 7  is a top perspective view showing sleeves forming sprue and flow-offs glued to a barrier; 
         FIG. 8  is a top perspective view of sprue and vents in place on top of a barrier; 
         FIG. 9  is a top perspective view of breaker cores glued to the top of a barrier for positioning sprue and flow-off sleeves; 
         FIG. 10  is a top perspective view showing a thin layer of bonded sand distributed over a barrier; 
         FIG. 11  is a top perspective view showing sprue and flow-off sleeves attached to breaker cores and a cope plate position on top of a cope layer; 
         FIG. 12  is a top perspective view of a finished mold; and 
         FIG. 13  is a top perspective view of a finished mold with a thicker cope. 
     
    
    
     DETAILED DESCRIPTION 
     The process known as In-Place Cope Molding (“IPCM”) is designed to reduce or eliminate certain of the inefficiencies of the traditional methods during production of the cope half  20  of a foundry sand mold  10 . IPCM allows the cope half  20  of the mold  10  to be produced directly on top of the drag half  30  of the mold  10  by use of a separation barrier  40  which supports the cope layer  20  above the mold cavity  60  of the drag  30 .  FIG. 1  shows a cross-section of such an approach. 
     The mold  10  consists of a lower mold half or “drag” layer  30 , which may be molded using traditional foundry techniques employing a pattern around which a chemically or thermally bonded sand (e.g. silica sand mixed with phenolic urethane binder and other additives) is packed. The drag  30  of the mold  10  may be formed by any traditional method. Once the sand has been cured, the pattern is removed and the resulting mold cavity forms a negative image of the part to be cast. Other molding techniques such as permanent molds or patternless molds where the mold cavity is produced by machining the cavity into a block of bonded sand, may also be employed. 
     In the prior art, using any of the existing molding techniques, a second, upper layer or “cope” layer  20  is then molded separately and must be “turned over” or “rolled over” and placed on top of the drag  30 . In order to withstand the stresses of the turnover process, the drag  30  and cope  20  must be thick enough to provide sufficient strength. The amount of sand and binder used for each mold  10  is thus usually much greater than the amount needed otherwise for strength during the pouring process or that needed for thermal insulation. Traditional molding would typically require a cope  20  thickness of 6″ to 10.″ 
     The IPCM process of the present invention provides increased advantages over the traditional methods described above by eliminating the time-consuming and costly turn-over process by allowing production of the cope  20  on top of the drag  30 , and in turn necessitating the need for only a very thin cope  20 . Copes  20  using the IPCM process may be made as thin as 1″ or less, as handling strength is no longer a consideration. This significantly thinner cope layer  20  requires a significantly smaller amount of sand and binder materials. This is important because sand and binder costs often represent a significant portion of the mold costs, particularly if expensive additives are used. 
     Important to the IPCM process is the introduction of a barrier  40  which supports the cope layer  20  above the mold cavity  60  in the drag  30 . As seen in  FIG. 1 , the barrier  40  supports the sand above the mold cavity  60  in the drag  30 , and allows a thinner cope  20  to be molded on top of the drag  30 . This avoids the need to turn over the cope half  20  onto the drag  30 , reducing labor and costs necessary to perform this step in the traditional processes.  FIG. 2  shows a barrier  40  partially in place on top of the drag layer  30 . The barrier  40  may be affixed to the drag  30  above the mold cavity  60  by use of an adhesive  42  (such as an epoxy, hot melt, or any other suitable foundry adhesive) as shown in  FIGS. 3-5 . Other means of affixing the barrier  40 , such as mechanical pinning using nails, staples, tape ( FIG. 6 ), or interlocking sand, may also be used. 
     Because the cope  20  can be relatively thin in the IPCM process, the barrier  40  can be made of relatively weak materials compared to those used in traditional molding processes. An appropriate barrier  40  is selected to suit the particulars of the mold  10  to be made. The material used for the barrier  40  is selected to have: 1) sufficient strength to support the sand in the cope  20  until the binders in the sand/binder mixture set; 2) adequate gas permeability to allow venting during pouring of the molten metal into the mold cavity  60 ; and 3) sufficient flexibility to form to the shape of the highest points of the drag  30 . Examples of materials used successfully for this barrier  40  include paper, plastic film ( FIG. 6 ), refractory felt, and mica paper ( FIG. 4 ). For example, a thin, high tensile strength paper may be used if the open areas of the mold cavity  60  are relatively narrow. Such thin paper would minimize the risks of producing flash which forms as the paper is combusted during pouring of the mold  10 . Paper has an added advantage of being extremely low cost. A compressed mica paper or board might be used for applications where a stronger barrier  40  is needed to support greater spans across larger mold cavities  60  or mold cavities  60  with wider open areas. If mica paper is used, the mica does not combust at all, so flash is kept to a minimum regardless of the thickness of the barrier  40 . On the other hand, the stiffness of the mica as compared to paper may reduce the conformance of the sand of the cope  20  to the drag  30 . Of course, a wide variety of materials could be used for the barrier  40 . 
     Once the barrier  40  has been affixed to the drag  30 , sleeves forming the vents  70 , sprues  72 , flow-offs  74  or other rigging cavities are attached to or through the top of the barrier  40  as shown in  FIG. 7 . The sprue  72  is the entryway for metal to fill the mold cavity  60 . Vents  70  are passages designed to allow the air in the mold cavity  60  and gasses formed during pouring to escape. Flow-offs  74  function similar to vents, but also allow a substantial volume of the first metal that enters the mold cavity  60  to flow into them (this metal typically contains a higher volume of contaminants). In another embodiment, risers (not shown) may also be attached to or through the top of the barrier  40  along with the vents  70 , sprues  72  and flow-offs  74 . Risers are reservoirs which fill with liquid metal and are designed to be the last metal to solidify, thereby providing metal to fill the voids which form from the volumetric reduction during solidification. Vents  70  and flow-offs  74  are subsequently removed from the casting during finishing. For additional support of the sleeves forming the sprue  72 , vents  70  and flow-offs  74 , these components may be supported using forms  76  as shown in  FIG. 8 . Vents  70 , sprues  72 , flow-offs  74  and risers may be molded in the cope  20  using sleeves, plugs or patterns that may be removed from the top surface of the cope  20 . In addition, rigid foam, e.g. polystyrene foam, may be used to mold such components, and removal of the foam may be unnecessary as it is combusted by the molten metal during the pouring process. 
       FIG. 9-11  show a process where sand cores known as “breaker cores”  78  affixed to the barrier  40  are used to locate and anchor the sleeves for the sprue  72 , vents  70 , flow-offs  74 . These cores  78  may also serve to allow easy removal of the flow-offs  74  after casting by producing a small, easily broken connection. The cope  20  is then created by distributing the sand/binder mixture over the barrier  40  as shown in  FIG. 10 . 
     If a very thin cope  20  is used, sufficient weight and strength to resist the forces from the molten metal are provided by a cope plate  90 , which is a steel plate placed on the cope  20  before the binder in the sand sets. The cope plate  90  is placed on top of the cope  20  and the sprue  72  and flow-off  74  sleeves are attached to the breaker cores  78 , as shown in  FIG. 11 . The cope plate  90  serves to provide strength to the thin sand cope  20  and to add weight or to distribute clamping force to the cope  20  to counteract the forces created by the pressure of the molten metal filling the mold cavity  60  attempting to “float” the cope  20 . 
     Finally, as show in  FIG. 12 , the sprue  72  and flow-off  74  sleeves are anchored by packing their bases in bonded sand, the cope plates  90  are clamped to the mold  10  base and weights  92  are added to counteract the pressure of the molten metal, and the cope plate  90  is covered in unbonded sand to shield it from damage from spilled molten metal. 
     In some cases, it may be advantageous to use a standard thickness cope  20 . For example, a short production run may not justify the expense of creating a new configuration of cope plate  90 . In such cases, a thin layer of a sand/binder mixture is distributed over the barrier  40  and allowed to cure, forming a thin cope  20 . Once the thin cope  20  has sufficiently hardened, additional sand/binder mixture can be added to reach a traditional cope  20  thickness, obviating the need for a cope plate  90 . For purposes of comparison,  FIG. 13  shows an IPCM mold  10  for the same casting but made with a traditional cope  20  thickness. 
     As seen in the above detailed description and in the drawings, there are numerous advantages in using and in-place cope molding process. The cope  20  can be much thinner, as handling strength is no longer a consideration, resulting in much lower sand and binder costs. The labor required to mold the cope  20  is typically less than with traditional methods, and labor and equipment to turn over the cope  20  is eliminated. Additionally, because the barrier  40  may be selected to allow close conformance to the variations in height of the mold cavity  60  features, gaps between the cope  20  and drag  30  are reduced or eliminated, greatly reducing the occurrence of flash and subsequent requirements for grinding. 
     Although the invention has been herein described in what is perceived to be the most practical and preferred embodiments, it is to be understood that the invention is not intended to be limited to the specific embodiments set forth above. Rather, it is recognized that modifications may be made by one of ordinary skill in the art of the invention without departing from the spirit or intent of the invention and, therefore, the invention it so be taken as including all reasonable equivalents to the subject matter of the appended claims and the description herein.