Abstract:
Contoured molten metal filter cups having an interstitial flow space that is maintained between the inner-wall of a molten metal pouring cone, riser sleeve or mold and the outer wall of the filter cup are disclosed. The interstitial space provided by the contoured filter cups results in significantly increased molten metal throughput during casting operations, while simultaneously providing an increased level of filtering efficiency.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/164,150 filed Mar. 27, 2009, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to filters for molten metal, and more particularly to contoured molten metal filter cups. 
       BACKGROUND INFORMATION 
       [0003]    Investment casting foundries utilize pouring cones as a core components of an investment casting tree, while other metalcasting foundries employ a wide variety of mold designs that include green sand, no-bake, permanent mold, and other materials in both horizontal and vertically-parted configurations. In various metalcasting techniques, there are advantages to filtering out slag and dross that form in the molten metal during pouring. Metalcasting foundries currently use different kinds of molten metal filter media, including ceramic foam filters, ceramic cellular filters, extruded lattice filters, and both fiberglass and silica mesh filter cups. 
         [0004]    Molten metal filter cups produced from fiberglass, silica mesh or other materials have usually been designed to fit tightly against or conform as close as possible to the inner walls of the molten metal casting structures in which they are placed, such as investment casting ceramic pour cones, runner sections within a mold, and riser sleeves. The rationale behind this technique is to ensure that the cup remains stable during pouring of the molten metal. Examples of silica mesh filter cups are described in U.S. Application Publication No. 2008/0173591, which is incorporated herein by reference. 
         [0005]    While the primary purpose of using filter cups within metal casting structures is to filter out the slag and dross, another important performance characteristic of metalcasting operations is the molten metal flow rate through the filter cups, typically referred to as “throughput”. Conventionally, the throughput of molten metal poured through filter cups or other filter media is increased or decreased by varying the size of the fabric mesh holes of the filter cups, with a larger mesh size (larger holes) providing higher throughput, and a smaller mesh size providing lower throughput. Users of ceramic filters would increase or decrease the pore size of their filter material to manipulate the throughput rate in the same manner. Unfortunately, the tradeoff for increased throughput comes at the cost of a potential reduction in filtering efficiency. While larger meshes or pore sizes permit more metal to flow through at faster rates, they also allow additional slag and dross to pass as well. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides contoured molten metal filter cups having an interstitial flow space that is maintained between the inner-wall of a metalcasting structure such as a ceramic pouring cone, mold pattern, riser sleeve and the like, and the outer-wall of the filter cup. Examples of metal casting structures also include the contact area within or used as part of any variety of metalcasting mold patterns such as green sand, no-bake, permanent mold, horizontal and vertically parted molds, and automated pouring systems such as DISAMATIC, Hunter machines, and high and low pressure die-casting machines. The interstitial space provided by the contoured filter cups results in significantly increased molten metal throughput during casting operations, while simultaneously providing an increased level of filtering efficiency. 
         [0007]    An aspect of the present invention is to provide a molten metal filter cup comprising an upper wall section having an outer surface structured and arranged to contact an inner surface of a molten metal casting structure, a generally conical lower wall section below the upper wall section structured and arranged to be spaced an offset distance from the inner surface of the molten metal casting structure when the outer surface of the upper wall section contacts the inner surface of the molten metal casting structure, and a bottom below the lower wall section. 
         [0008]    Another aspect of the present invention is to provide a molten metal filter cup comprising a generally conical upper wall section, a lower wall section, a transition between the upper and lower wall sections that extends radially inwardly from a lowermost portion of the upper wall section toward an uppermost portion of the lower wall section, and a bottom below the lower wall section. 
         [0009]    A further aspect of the present invention is to provide a molten metal filter cup comprising a generally conical upper wall section, a generally conical lower wall section, and a transition between the upper and lower wall sections that extends radially inwardly from a lowermost portion of the upper wall section toward an uppermost portion of the lower wall section. 
         [0010]    These and other aspects of the present invention will be more apparent from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a side sectional view of a contoured molten metal filter cup installed in a pouring cone in accordance with an embodiment of the invention. 
           [0012]      FIG. 2  is a side sectional view showing dimensions of the filter cup of  FIG. 1 . 
           [0013]      FIG. 3  is a side sectional view of a contoured molten metal filter cup in accordance with another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    In accordance with the present invention, contoured molten metal filter cups with an interstitial flow space between the filter cups and pouring cones or other metalcasting structures in which they are installed mitigate the tradeoff of throughput for filter efficiency by providing a geometry that maintains a set level of filtration efficiency while at the same time increasing the molten metal throughput of the pouring cone/filter cup unit. The interstitial flow space significantly increases the filtration area of the filter cups and increases overall filtration efficiency. The filter cups may be installed in a pouring cone or placed elsewhere within a mold pattern, such as the downsprue of an automated casting machine, e.g., a DISAMATIC, or within riser sleeves. The filter cups may be made from any known material, including silica or fiberglass mesh fabrics as well as ceramic material as is common with ceramic foam, ceramic cellular, and extruded lattice filters. For example, one type of filter cup material for use in accordance with an embodiment of the present invention comprises silica mesh fabric with a refractory coating as disclosed in U.S. Application Publication No. 2008/0173591. 
         [0015]      FIG. 1  illustrates a contoured molten metal filter cup  10  installed in a ceramic pouring cone  20 . Although a ceramic pouring cone  20  is shown in  FIG. 1 , it is to be understood that the filter cups of the present invention may be installed in various other types of molten metal casting structures. The filter cup  10  includes an upper rim  11 , a conical upper wall section  12 , a conical, inwardly offset lower wall section  14 , and a bottom  16 . The filter cup  10  includes a transition  13  between the upper wall section  12  and the lower wall section  14 , and another transition  15  between the lower wall section  14  and the bottom  16 . In the embodiment shown in  FIG. 1 , the conical upper wall section  12 , conical lower wall section  14  and conical pouring cone  20  are sloped at substantially the same angle measured from a vertical axial flow direction of the filter cup  10 . 
         [0016]    In accordance with the present invention, the filter cup  10  has an interstitial flow space  18  representing the volume between the inner surface of the pouring cone  20  and the outer surface of the lower wall section  14 . While the upper wall section  12  of the filter cup  10  contacts the inner surface of the pouring cone  20 , the lower wall section  14  is located radially inwardly of the pouring cone  20  to provide the interstitial flow space  18 . 
         [0017]      FIG. 2  illustrates several dimensions of the filter cup  10 . The upper rim  11  has an outer diameter OD R  and an inner diameter ID R . The upper wall section  12  has an outer diameter OD U  measured at the lowermost portion of the upper wall section, and a height H U . The lower wall section  14  has an outer diameter OD L  measured at its uppermost portion, and a height H L . The lower wall section  14  has an offset distance D representing the distance between the outer surface of the lower wall section  14  and the inner surface of the pouring cone  20 . The conical lower wall section  14  is sloped at an angle A measured from a vertical axial flow direction of the filter cup  10 . The bottom  16  has an outer diameter OD B  measured at the transition  15  between the lower wall section  14  and the bottom  16 . The filter cup  10  has a thickness T. 
         [0018]    The dimensions of the filter cup  10  shown in  FIG. 2  may be selected depending upon the particular geometry of the pouring cone or other metal casting structure. For example, the outer diameter OD R  of the upper rim  11  may typically be from about 4 to about 7 inches, e.g., about 5.5 inches. The inner diameter ID R  of the upper rim  11  may typically be from about 2.5 to about 6 inches, e.g., about 3.25 inches. The outer diameter OD U  of the upper wall section  12  may be typically from about 2 to about 5 inches, e.g., about 3 inches. The outer diameter OD L  of the lower wall section  14  may typically be from about 2.2 to about 5.5 inches, e.g., about 3 inches. The height H U  of the upper wall section  12  may typically be from about 0.2 to 1 inch, e.g., about 0.4 inch. The height H L  of the lower wall section  14  may typically be from about 0.5 to about 4 inches, e.g., about 2 inches. The offset distance D of the lower wall section  14  may typically be from about 0.1 to about 0.5 inch, e.g., about 0.13 inch. The cone slope angle A of the lower wall section  14  may typically be from about 1 to about 30 degrees, more typically from about 5 to about 20 degrees, e.g., about 15 degrees. The slope angles of the upper wall section  12  and pouring cone  20  may be the same as, or different from, the slope angle A of the lower wall section  14 . The diameter OD B  of the bottom  16  may typically be from about 1 to about 3 inches, e.g., about 1.5 or 1.6 inches. The thickness T of the filter cup  10  may be typically from about 0.01 to about 0.1 or 0.2 inch, e.g., about 0.04 inch. Although specific dimensional ranges are given above, it is to be understood that the various dimensions may be adjusted as desired, depending upon the particular casting operation and pouring cone or other metal casting structure geometry. 
         [0019]    At the top of the pouring cone  20  and filter cup  10 , the rim  11  and the upper wall section  12  contact and remain flush against the contour and angle of the inner wall of the ceramic pouring cone  20  to provide a cup weight-bearing area. They continue down to the point where the two are separated from each other at the transition  13 . The cavity or space  18  created between the lower wall  14  of the filter cup  10  and the inner surface of the pouring cone  20  provides the interstitial flow space  18 , which starts at the end of the cup weight-bearing area (point of separation) and continues downward along the outer surface of the lower wall section  14 , following the sloping contour of the pouring cone  20  and ends at the transition  15  at the hemispherical or flat bottom  16  of the filter cup  10 . 
         [0020]      FIG. 3  illustrates a filter cup  110  in accordance with another embodiment of the present invention, with like reference numerals designating similar elements in both  FIGS. 2 and 3 . In a particular embodiment, the filter cup  110  shown in  FIG. 3  may have an outer rim diameter OD R  of about 5.5 inches, an inner rim diameter ID R  of about 4 inches, an outer diameter OD U  of the upper wall section  12  of about 3.5 to 3.7 inches, an outer diameter OD L  of the lower wall section  14  of about 3.3 to 3.5 inches, an upper wall section height H U  of about 0.4 inch, and a lower wall section height H L  of about 1.4 inches. The diameter OD B  of the bottom  16  may be about 2.7 or 2.8 inches. The filter cup thickness T and offset distance D of the interstitial flow space  18  in the embodiment shown in  FIG. 3  may be similar to those of the embodiment of  FIG. 2 . 
         [0021]    To confirm the improved throughput of the present filters, tests were conducted using standard investment casting techniques to cast a stainless steel alloy (nickel chrominum Stainless Steel Alloy 625) in multiple runs of 75 pounds each. The same testing parameters and number of iterations were run and data recorded using a conventional filter cup design with no interstitial flow space in comparison with the contoured filter cup design shown in  FIG. 2 . The average pour time for the conventional filter was 8 seconds, in comparison with an average pour time of 6 seconds for the filter cup design of the present invention. An average throughput increase of 25 percent was thus achieved with the contoured filter cup of the present invention. 
         [0022]    The casting test results confirm an average increase in measured molten metal throughput of at least 20 or 25 percent. Further, the effective filtration area in the cup may be increased by over 50 percent, typically over 75 percent, as the molten metal is able to flow through the side walls and into the interstitial flow space, instead of being force-focused at the very bottom of the filter cup as in conventional designs. 
         [0023]    Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.