Patent Publication Number: US-7213634-B1

Title: Offset mold process

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
   The present invention is directed to the field of casting molten metal. More particularly, the present invention is directed to a process for bottom-filling a mold cavity and, then, offsetting the mold relative to the bottom board to cut off flow of the pumped metal and trap the mold fill. 
   Conventional mold-filling methods involve filling a sand mold from the top through a sprue hole. Such a technique can result in creation of eddy currents which produce defects in the casting. If the defect goes beneath the surface, or if the article is a precision casting, such eddy currents can require scrapping of the entire casting. 
   At least one attempt to combat these difficulties is taught in U.S. Pat. No. 5,230,379 to Voss. In the Voss patent, clamps and seals are provided to enable the molten metal to be drawn into the mold cavity from the bottom using a vacuum assist. Once the mold is completely filled, the mold can be displaced relative to a cheek mold member which has a plurality of distribution channels, cutting off the feed lines and retaining the molten metal in the mold during curing. 
   The use of vacuum with seals and clamps limits the application of this technique. Further, such features involve added complexity and expense. Lastly, the metal in the distribution channels remains attached to the finished product as the mold cools, requiring this scrap to be cut loose from the finished product. Further, in order to remelt the detached scrap, the imbedded sand must be first removed from the detached pieces to avoid contamination of the melt. This, too, adds expense to the operation. 
   It is a object of the present invention to develop a bottom-fill mold technique with broader application than the one taught by Voss. The present invention involves a method of filing a mold assembly with molten metal as the mold assembly is conveyed along a first path, the mold assembly having a first mold component positioned above a bottom board, the bottom board having an entrance port extending horizontally and a feed system including at least one vertically extending runner, the method comprising the steps of a) moving one of the mold assembly and a nozzle laterally of the first path to position the horizontally extending feed port in contact with the nozzle which is supplied with molten metal by a pumping system; b) activating the pumping system causing molten metal to flow into and fill the horizontally extending entrance port, the vertically extending runner, and the mold with molten metal; c) interrupting the flow of molten metal at a particular point in the vertically extending runner trapping the molten metal in the mold; d) moving the mold assembly away from the nozzle; e) draining the molten metal in the vertically extending runner below the particular point and in the horizontally extending entrance port into a ladle for reuse. 
   The method may also be characterized by the said step of interrupting the flow of molten metal being accomplished by moving the first mold component relative to the bottom board to close the flow path through the vertically extending runner. Preferably, the moving step is accomplished by moving the mold assembly laterally of the path into contact with the nozzle. Alternatively, the moving step can be accomplished by moving the nozzle laterally of the path into contact with the horizontally extending feed port. 
   When the method is used with a cope and drag molding, the cutoff is preferably accomplished by moving the mold relative to its base. In a lost foam molding process, a valve gate is moved laterally across the vertically extending runner to cutoff flow there through. 
   Various other features, advantages, and characteristics of the present invention will become apparent after a reading of the following detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiment(s) of the present invention is/are described in conjunction with the associated drawings in which like features are indicated with like reference numerals and in which 
       FIG. 1  is a schematic cross-sectional side view of a first embodiment of apparatus used in the offset molding method of the present invention; 
       FIG. 2  is a schematic cross-sectional side view of a second embodiment of apparatus useful in the method of the present invention; and, 
       FIG. 3  is a is a schematic cross-sectional side view of a third embodiment of apparatus useful in the present method. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S) 
   A first embodiment of molding apparatus useful in the offset molding method of the present invention is shown in  FIG. 1  generally at  20 . In the present method, a mold assembly  22  comprised of a mold bottom board  24 , a first mold component, in this case, a drag  26  sitting atop the bottom board  24 , with a second mold component, in this case cope  28  sitting atop and pinned to drag  26 . It is noted that when drag  26  is originally placed on bottom board  24 , it, too, was pinned in place. These pins ensure proper alignment of components as the during the construction of the mold, typically from green sand. However, after the formation of the mold assembly  22  is completed, the pins between the drag  26  and bottom board  24  are removed to permit relative movement there between. 
   As seen in  FIG. 1 , a separate replaceable sand mold  31  positioned in the bottom board  24  will typically be provided with a horizontal runner  34  with entrance port  35 . Primary sand mold  30 , also made of green sand, is formed with a plurality of ingates  32  which interconnect with runner  34 , a core  36  for a hollow casting which is hung on ears  37 , and the space  38  itself which is to be filled with molten metal. It will be understood that the mold cavity  38  is formed by compressing the green sand around a pattern (not shown) which is subsequently removed. When the molten metal fills multiple risers  39 , a clear indication is given that the mold has filled properly and the feed pump  11  can be shut off. 
   Mold assembly  22  is conveyed along a roller conveyor (not shown) until it reaches shuttle car  40  opposite pumping station  10 . Bottom board  24  sits atop rollers  42 . Hydraulic cylinder  50  translates shuttle car  40  laterally of the conveyor path along rails  44  bringing the entrance  35  of runner  34  into contact with nozzle  13  of fill pipe  15 . While in the depicted embodiments, the mold assembly  22  is translated to meet the nozzle  13  of the pumping system  11 , it will be understood that the nozzle  13  could be moved to contact the Pump  11  is operated until the molten metal can be clearly seen emerging from risers  39 , at which time, a second hydraulic cylinder  52  shifts drag  26  relative to bottom board  24 . With ingates  32  misaligned with runner  34 , the flow of molten metal is stopped, the mold fill is trapped in the mold assembly  22 , and pump  11  is shut off. Hydraulic cylinder  50  retracts shuttle car  40  allowing the molten metal in runner  34  to drain into catch ladle  17 . This considerable amount of material does not have to be cut off the completed molded article nor does the embedded sand have to be burned off prior to remelting, as is the case with conventional molding operations. Mold assembly  22  is indexed to a cooling station and another mold moved into position opposite pumping station  10 . 
   A second embodiment of equipment which can be used with the method of the present invention is depicted in  FIG. 2  generally at  20 ′. Rather than using a drag-cope mold, mold assembly  22 ′ is comprised of a lost foam apparatus. A first mold component in the form of flask  25 ′ sits atop bottom board  24 ′. A dry sand core  33 ′ forms metal entrance  35 ′ which is shifted into contact with nozzle  13 ′ of pumping station  10 ′ by translating shuttle car  40 ′ laterally. A second dry sand mold  37 ′ seals the opening  23 ′ in flask  25 ′ through which styrofoam runner  34 ′ extends into flask  25 ′. Styrofoam pattern  19 ′ is inserted in flask  25 ′ with styrofoam vents  39 ′ extending upwardly therefrom. Flask  25 ′ is then filled with dry, unbonded sand which is vibrated to compact it and fill all openings. First hydraulic cylinder  50 ′ translates shuttle car  40 ′ to bring metal entrance  35 ′ into contact with nozzle  13 ′. Pump  11 ′ is activated to fill the mold until the passageways formed by styrofoam vents  39 ′ are filled. Just as was done with the first embodiment, second hydraulic cylinder  52 ′ shifts flask  25 ′ relative to bottom board (approximately 1.5″) to misalign runner  34 ′ relative to dry sand core  33 ′ to seal the mold fill in the flask  25 ′. Pump  11 ′ is shut off and first hydraulic cylinder  50 ′ moves shuttle car  40 ′ back away from nozzle  13 ′ allowing the molten metal in dry sand mold  33 ′ to drain out of metal entrance  35 ′ and be caught in catch ladle  17 ′. 
   A third embodiment of apparatus useful with the method of the present invention is shown in  FIG. 3  generally at  20 ″. This third structural embodiment is similar to the second, also involving a lost foam casting technique. However, in this embodiment, the flow cutoff apparatus is different. The second hydraulic cylinder  52 ″ is mounted on the pumping station  10 ″. When the bottom filling of the mold assembly  22 ″ is completed, second hydraulic cylinder  22 ″ is actuated moving a knife-edge plunger  54 ″ to cutoff flow through runner  34 ″. As with the previous embodiments, when first hydraulic cylinder  50 ″ retracts shuttle car  40 ″, the molten metal remaining in the metal entrance  35 ″ below the cutoff point will drain into the catch ladle  17 ″. 
   Various changes, alternatives and modifications will become apparent to one of ordinary skill in the art following a reading of the foregoing specification. It is intended that any such changes, alternatives and modifications as fall within the scope of the appended claims be considered part of the present invention.