Abstract:
This invention relates to a process for preparing detailed foundry shapes (e.g. molds and cores) used in casting metal articles. The process involves preparing foundry shapes from hollow ceramic microspheres bonded with organic or inorganic binders. The foundry shape is then detailed by machining, cutting, stamping, or otherwise removing material from the foundry shape to provide special shapes, letters, numbers, insignia, machine readable codes, etc. on the surface of the foundry shape. The foundry shapes are used to produce detailed metal castings. This detail can be unique to a single casting to provide a permanent traceable mark for casting identification from the time of manufacture to disposal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY  
       [0001]    This application claims the benefit of U.S. provisional application serial No. 60/375,686 filed on Apr. 26, 2002. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable.  
         REFERENCE TO A MICROFICHE APPENDIX  
         [0003]    Not Applicable.  
         BACKGROUND OF THE INVENTION  
         [0004]    (1) Field of the Invention  
           [0005]    This invention relates to a process for preparing detailed foundry shapes (e.g. molds and cores) used in casting metal articles. The process involves preparing foundry shapes from hollow ceramic microspheres bonded with organic or inorganic binders. The foundry shape is then detailed by machining, cutting, stamping, or otherwise removing material from the foundry shape to provide special shapes, letters, numbers, insignia, machine readable codes, etc. on the surface of the foundry shape. The foundry shapes are used to produce detailed metal castings. This detail can be unique to a single casting to provide a permanent traceable mark for casting identification from the time of manufacture to disposal.  
           [0006]    (2) Description of the Related Art  
           [0007]    Foundry shapes used to produce metal castings are typically made by compacting organically or inorganically bonded sand against a pattern or corebox cavity to produce a molded shape. The foundry shapes have the negative shape of the pattern or corebox used to form them.  
           [0008]    The foundry shapes are typically formed into an assembly, such that a cavity results. The cavity has the shape of the metal casting to be produced. When molten metal is poured into and around the assembly and cooled, a casting is produced having the shape of the cavity, i.e. the exterior shape of the pattern and the interior shape of the core(s). Identical foundry shapes can be produced from reusable patterns or coreboxes, which can be used to produce a number of essentially identical castings.  
           [0009]    It is often desirable to detail metal castings. The detail may relate to specific geometrical shaping, the addition of certain information like part numbers, date codes, trademarks, barcodes, numerals, letters, or other identifying character data. This allows the casting to be permanently identified and tracked during various operations.  
           [0010]    The detail may either be raised above the casting surface or imprinted below the surface. While the detail can be added after the casting is produced by stamping, welding, tagging, or machining, it is often more desirable to add the detail to the foundry shape before the casting is prepared, so that the detail is an integral part of the casting after the molten metal, used to make the casting, has cooled.  
           [0011]    In order to produce foundry shapes with details, it is necessary to appropriately modify the geometry of the pattern or corebox. Thus, to produce a casting with unique details, it may be necessary to produce unique patterns or coreboxes for each casting. Alternatively, in the case of identification numbers or codes on otherwise identical castings, it may be necessary to add a unique number or code to the pattern or corebox before making each foundry shape.  
           [0012]    A significant amount of prior art exists for shaping foundry molds and cores without the use of patterns or coreboxes. U.S. Pat. No. 4,104,347 describes a method of making a shaped foundry mold by forming a block of bonded sand and then using a cutting device guided by a profiling machine form a mold cavity in the shape of the casting to be produced. U.S. Pat. No. 6,286,581 describes a method for producing sand molds and cores from a block of bonded sand using CNC controlled cutting and machining equipment. Casting Technology International, Sheffield, UK, has also established a “Patternless ®” research program to directly machine molds and cores from blocks of sand using CNC cutting and machining equipment. However, these methods relate to forming less intricately shaped molds and cores from blocks of sand and do not address the detailed marking of molds and cores.  
           [0013]    Alternately, U.S. Pat. No. 6,220,333 describes the use of a pre-made stencil to mark a foundry shape. The stencil is formed by punching or cutting holes or patterns through a thin sheet of material. The stencil is then placed on the mold/core surface. When the mold is poured, the liquid metal fills the holes/patterns in the stencil to create raised marks on the casting surface.  
           [0014]    These methods tend to be limited by the properties of the materials used to produce the mold, core, or stencil. In the case of sand blocks used to produce molds and cores by machining, the material tends to be dense, brittle, and difficult to machine. The level of detail and surface finish that is produced may be less than desired because of the tendency of the machining/cutting operation to remove material by fracturing chunks from the surface. The material generally can not be mechanically punched or impacted because of the tendency to crack in thin sections.  
           [0015]    In the case of stencils, a material that can be punched or cut to form the stencil may not be compatible with mold/core material and casting process. The attachment of the stencil by gluing or pinning may also create casting difficulties. Finally, the use of a thin sheet of material with holes or patterns through the stencil limits the shape and geometry of the marks that can be produced. The marks are all the same height (i.e. the thickness of the stencil material) and certain marks can not be produced because all solid areas of the stencil must be interconnected to provide support.  
           [0016]    All citations referred to under this description of the “Related Art” and in the “Detailed Description of the Invention” are expressly incorporated by reference.  
         BRIEF SUMMARY OF THE INVENTION  
         [0017]    This invention relates to a process for preparing detailed foundry shapes (e.g. molds and cores) used in casting metal articles. The process involves preparing foundry shapes from hollow ceramic microspheres bonded with organic or inorganic binders. The foundry shape is then detailed by machining, cutting, stamping, or otherwise removing material from the foundry shape to provide special shapes, letters, numbers, insignia, machine readable codes, etc. on the surface of the foundry shape. The invention also relates to a process for preparing a metal casting having a permanent identification code and a method for tracking a casting from the time of manufacturing to disposal. This allows the user and manufacturer of the casting to keep track of inventories and casting defects, and provides for accountability.  
           [0018]    Uses for the foundry shapes include prototype castings, unique or one-of-a-kind castings such a plaques or markers, castings with special geometries that can not be easily produced using conventional molding methods, and castings requiring specials markings like sequential numbering or machine readable codes. The markings can further be used to identify the source of the shape and subsequent casting, and for quality control.  
           [0019]    The use of hollow microspheres is critical to accomplishing the beneficial results of the described process. The hollow microspheres impart special physical properties to the foundry shape. Material removal is facilitated by the low density of the material and by structure of the microspheres. The relatively small particle size and hollow structure provide processing opportunities that typically can not be used with sand molds. Consequently, the markings on the foundry shape can be made by such simple, “low-tech” methods as punching using conventional steel marking punches and a hammer. Alternately, shapes and markings can be cut into the material either by hand or using appropriate machine cutters, mills, routers, rotary tools, etc. up to and including laser cutting.  
           [0020]    The use of molded shapes produced with hollow ceramic spheres provides several advantages for further processing. Because the microspheres are hollow, the molded inserts are crushed and collapse when they are stamped to form the impression on the surface of the insert. This crushing absorbs much of the mechanical force of stamping so that the insert is not cracked or broken. This crushing also compacts any powder produced by fractured spheres to provide a smooth, dense surface for casting. Although solid ceramic materials like sand or ceramic beads can also be molded to create shapes, when they are stamped, the section stamped may fracture on impact. On the other hand, if the insert made from sand does not fracture, pieces of the surface may be fractured away, leaving a rough irregular surface that is not suitable for casting.  
           [0021]    Cutting or machining shows the same types of advantages with shapes made with the hollow microspheres. Individual microspheres are powdered by the cutting tool, leaving a relatively smooth machined surface. On the other hand, when molds or cores are made with sand and marked by similar techniques, the individual sand particles are torn away from the surface by the cutting tool, often with larger chunks. This produces a rough surface, lacking in detail.  
           [0022]    These detailed foundry shapes are typically arranged in a mold assembly. After molten metal is poured into and around the mold assembly and cooled, a metal casting is formed that contains the shape or permanent marking, which is a mirror image of the geometry corresponding to the surface of the foundry shape.  
           [0023]    The bonded hollow microsphere material provides an additional advantage with respect to casting. Because the material has a comparably low density and low thermal conductivity when compared to sand, cooling and solidification of the molten metal, used to prepare the casting, is slowed. The additional cooling time permits the metal to flow into smaller cavities in the mold surface and produces finer, more detailed identifying characters. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0024]    [0024]FIG. 1 is a photograph of a HAAS CNC milling machine.  
         [0025]    [0025]FIG. 2 is a copy of a photograph of a plaque mold insert machined from a slab of molded bonded hollow microspheres prepared in accordance with Example 1 which shows lettering machined into the insert, as a mirror image.  
         [0026]    [0026]FIG. 3 is a copy of photograph of a finished casting poured from 319 aluminum at about 730° C., which used the molded insert of FIG. 2.  
         [0027]    [0027]FIG. 4 is a copy of a magnified (6×) photograph of the casting of FIG. 3 after it was gently sand blasted to remove surface oxidation, which shows the lettering was of very good detail.  
         [0028]    [0028]FIG. 5 is a copy of a photograph of an insert made from bonded hollow microspheres, having indented numerals approximately 12 mm in height, which were created by hand stamping the insert using steel punches and a hammer.  
         [0029]    [0029]FIG. 6 is a copy of a photograph of a casting poured from Alloy A319 aluminum at approximately 730° C., using the insert of FIG. 5, which shows the raised numerals in the mirror image of the imprinted insert.  
         [0030]    [0030]FIG. 7 is a copy of a photograph of a second insert made from the bonded hollow microspheres of Example 2 that has small semi-circular or dots or depressions in the surface of the insert.  
         [0031]    [0031]FIG. 8 a copy of a magnified (6×) photograph of the insert of FIG. 7, which shows that the depressions on the surface of the insert had a smooth internal surface and showed no signs of cracking.  
         [0032]    [0032]FIG. 9 is a copy of a photograph of a casting poured from Alloy A319 aluminum at approximately 730° C., using the insert of FIG. 8 in a mold assembly, which shows the raised dots in the casting that are the mirror image of the insert.  
         [0033]    [0033]FIG. 10 is a copy of a magnified (6×) photograph of the casting of FIG. 9 showing that the raised dots on the casting had excellent detail and surface finish.  
         [0034]    [0034]FIG. 11 is a copy of a photograph of a laser marked sand core, made for comparison purposes, having readable numerals produced according to Example 3.  
         [0035]    [0035]FIG. 12 is a copy of a photograph of a casting produced with the sand core of FIG. 12, which shows that the detail of the numerals was of poor quality.  
         [0036]    [0036]FIG. 13 is a copy of a photograph of an insert, made from hollow microspheres, marked with lettering of a size comparable to the numerals on the insert shown in FIG. 12, which shows that the detail of the letters was better and the surface finish was better on the surface of the insert made with the hollow micropsheres than the details on the core shown in FIG. 12 made with sand.  
         [0037]    [0037]FIG. 14 is a copy of a magnified (6×) copy of a photograph of a portion of the casting of FIG. 13, which further shows the detail of the letters and the quality of the surface where the letters are imprinted using the insert made from the hollow microspheres.  
         [0038]    [0038]FIG. 15 is a copy of a photograph showing an insert made from hollow microspheres marked with a machine-readable code.  
         [0039]    [0039]FIG. 16 is a copy of a photograph of a casting made with the insert of FIG. 15, which shows that the casting had a raised mark with excellent cast detail and surface.  
         [0040]    [0040]FIG. 17 is a copy of a photograph of an insert made with hollow microspheres with much of the surface removed to leave protruding “bumps”.  
         [0041]    [0041]FIG. 18 is a copy of a photograph of a casting produced with the insert of FIG. 17, which shows that indented marks on the cast surface were of excellent detail and the surface finish was excellent. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0042]    The detailed description and examples will illustrate specific embodiments of the invention and will enable one skilled in the art to practice the invention, including the best mode. It is contemplated that many equivalent embodiments of the invention will be operable besides these specifically disclosed.  
         [0043]    For purposes of this invention, a foundry shape is any shape made by mixing an aggregate and binder and shaping the mixture (e.g. a mold, core, or an insert) for use in the casting of metal parts. The foundry shapes are typically formed into a “mold assembly”, such that a cavity results. The cavity has the shape of the metal casting to be produced. When molten metal is poured into and around the assembly and cooled, a casting is produced having the shape of the cavity, i.e. the exterior shape of the pattern and the interior shape of the core(s). The cast metal part may be, for example, an engine block, piston, water pump, etc. Typical metals used for casting include iron, steel, aluminum, copper, and brass.  
         [0044]    The shapes are prepared by mixing aluminosilicate microspheres and an effective amount of a chemically reactive binder. The shapes are typically cured by contacting the shape with an effective amount of a curing catalyst.  
         [0045]    The hollow aluminosilicate microspheres used to prepare the shapes have low densities, low thermal conductivities, and excellent insulating properties. The thermal conductivity of the hollow aluminosilicate microspheres ranges from about 0.05 W/m. K to about 0.6 W/m.K at room temperature, more typically from about 0.1 W/m.K to about 0.5 W/m.K. They typically have a diameter of about 10 microns to 350 microns, preferably with a mean diameter greater than 100 microns. It is believed that hollow microspheres made of material other than aluminosilicate, having insulating properties, can also be used to replace, or used in combination with, the hollow aluminosilicate microspheres.  
         [0046]    The weight percent of alumina to silica (as SiO 2 ) in the hollow aluminosilicate microspheres can vary over wide ranges depending on the application, for instance from 25:75 to 75:25, typically 33:67 to 50:50, where said weight percent is based upon the total weight of the hollow microspheres. It is known that hollow aluminosilicate microspheres having a higher alumina content are better for making foundry shapes used in pouring metals such as iron and steel which have casting temperatures of 1300° C. to 1700° C. because hollow aluminosilicate microspheres having more alumina have higher melting points. Thus, shapes made with these hollow aluminosilicate microspheres will not degrade as easily at higher temperatures.  
         [0047]    Minor amounts, less than 20 percent based upon the volume of the hollow aluminosilicate microspheres, of other refractories, may be used to prepare the foundry shapes. Examples of such refractories include silica, magnesia, alumina, olivine, chromite, aluminosilicate, and silicon carbide among others.  
         [0048]    The density of the composition used to make the marked shapes typically ranges from about 0.1 g/cc to about 0.9 g/cc, more typically from about 0.2 g/cc to about 0.8 g/cc.  
         [0049]    The binders that are mixed with the hollow aluminosilicate microspheres to form the aggregate mix are well known in the art. Most no-bake or cold-box binders, which will sufficiently hold the mix together in a shape and polymerize in the presence of a curing catalyst, will work. Examples of such binders are phenolic resins, phenolic urethane binders, furan binders, alkaline phenolic resole binders, epoxy-acrylic binders, epoxy-acrylic-polyisocyanate binders, and silicate binders, among others. Particularly preferred are epoxy-acrylic and phenolic urethane no-bake and cold-box binders sold by Ashland Specialty Chemical Company, a division of Ashland Inc. The phenolic urethane cold-box binders, sold under the ISOCURE® trademark, and the phenolic urethane no-bake binders, sold under the PEP SET® trademark, are described in U.S. Pat. Nos., 3,485,497 and 3,409,579, which are hereby incorporated into this disclosure by reference. These binders are based on a two-part system, one part being a phenolic resin component and the other part being a polyisocyanate component. The epoxy-acrylic binders, sold under the ISOSET® trademark, are cured with sulfur dioxide in the presence of an oxidizing agent, and are described in U.S. Pat. No. 4,526,219, which is hereby incorporated into this disclosure by reference.  
         [0050]    The amount of binder needed is an effective amount to maintain the shape and allow for effective curing, i.e. which will produce a shape, which can be handled or self-supported after curing. An effective amount of binder is greater than about 3 weight percent, based upon the weight of the microspheres. Preferably, the amount of binder ranges from about 5 weight percent to about 15 weight percent, more preferably from about 6 weight percent to about 12 weight percent.  
         [0051]    Curing the shape by the cold-box process takes place by blowing or ramming the foundry mix into a pattern and contacting the foundry mix with a vaporous or gaseous catalyst. Various vapor or vapor/gas mixtures or gases such as tertiary amines, carbon dioxide, methyl formate, and sulfur dioxide can be used depending on the chemical binder chosen. Those skilled in the art will know which gaseous curing agent is appropriate for the binder used. For example, an amine vapor/gas mixture is used with phenolic-urethane resins. Sulfur dioxide (in conjunction with an oxidizing agent) is used with epoxy-acrylic resins.  
         [0052]    See U.S. Pat. No. 4,526,219, which is hereby incorporated, into this disclosure by reference. Carbon dioxide (see U.S. Pat. No. 4,985,489, which is hereby incorporated into this disclosure by reference) or methyl esters (see U.S. Pat. No. 4,750,716 which is hereby incorporated into this disclosure by reference) are used with alkaline phenolic resole resins. Carbon dioxide is also used with binders based on silicates. See U.S. Pat. No. 4,391,642, which is hereby incorporated into this disclosure by reference.  
         [0053]    Preferred cold-box binders are phenolic urethane cold-box binders cured by passing a tertiary amine gas, such a triethylamine, through the molded foundry mix in the manner as described in U.S. Pat. No. 3,409,579, or the epoxy-acrylic binder cured with sulfur dioxide in the presence of an oxidizing agent as described in U.S. Pat. No. 4,526,219. Typical gassing times are from 0.5 to 3.0 seconds, preferably from 0.5 to 2.0 seconds. Purge times are from 1.0 to 60 seconds, preferably from 1.0 to 10 seconds.  
         [0054]    Curing the shape by the no-bake process takes place by mixing a liquid curing catalyst with the foundry mix (alternatively by mixing the liquid curing catalyst with the foundry composition first), shaping the foundry mix containing the catalyst, and allowing the foundry shape to cure, typically at ambient temperature without the addition of heat. The preferred no-bake binder are phenolic urethane binders cured by mixing with a liquid catalyst where the liquid curing catalyst is a tertiary amine and the preferred no-bake curing process is described in U.S. Pat. No. 3,485,797, which is hereby incorporated by reference into this disclosure. Specific examples of such liquid curing catalysts include 4-alkyl pyridines wherein the alkyl group has from one to four carbon atoms, isoquinoline, arylpyridines such as phenyl pyridine, pyridine, acridine, 2-methoxypyridine, pyridazine, 3-chloro pyridine, quinoline, N-methyl imidazole, N-ethyl imidazole, 4,4′-dipyridine, 4-phenylpropylpyridine, 1-methylbenzimidazole, and 1,4-thiazine.  
       ABBREVIATIONS  
       [0055]    The following abbreviations are used:  
         [0056]    Detailing machining, cutting, stamping, embossing, or otherwise removing material from the foundry shape to provide special shapes, letters, numerals, insignia, machine readable codes, etc. on the surface of a foundry shape.  
         [0057]    Foundry mix a mixture a foundry aggregate and a foundry binder.  
         [0058]    Foundry shape a mold, core, insert, or other shape made from a foundry mix used to cast metals.  
         [0059]    Mold assembly an assembly of molds, cores, and/or inserts made from a foundry aggregate (typically sand) and a foundry binder, which is placed in a casting assembly to provide a shape for the casting.  
         [0060]    PEP SET® X1000/X2000 a three-part no-bake phenolic urethane amine cured binder having a Part I to Part II ratio of about 55/45, and about 3.0% amine catalyst based on the Part I, sold by Ashland Specialty Chemicals Division of Ashland Inc.  
         [0061]    SGT microspheres hollow aluminosilicate microspheres sold by PQ Corporation having a particle size of 10-350 microns and an alumina content between 28% to 33% by weight based upon the weight of the microspheres.  
         [0062]    SLG microspheres hollow aluminosilicate microspheres sold by PQ Corporation having a particle size of 10-300 microns and an alumina content of at least 40% by weight based upon the weight of the microspheres.  
       EXAMPLES  
       [0063]    While the invention has been described with reference to a preferred embodiment, those skilled in the art will understand that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. In this application, all units are in the metric system and all amounts and percentages are by weight, unless otherwise expressly indicated.  
       Example 1  
     (Preparation of Casting Having Imprinted Markings from a Mold Insert Having Machined Lettering Made from Hollow Microspheres)  
       [0064]    A plaque mold insert was machined from a slab of molded material. The insert was produced by mixing eight weight percent of PEPSET® X1000/X2000 with SLG microspheres. Lettering was machined into the insert as a mirror image to create the mold, using a HAAS CNC milling machine (FIG. 1) with a half-round, 90° point, carbide tool turning at 7000 rpm and with a feed rate of 15 inches per minute. The machined insert is shown in FIG. 2.  
         [0065]    The material machined easily at a feed rate of 15 inches per minute and it was expected that the material could be machined at a feed rate up to 70 to 80 inches per minute. The tooling did not get dirty during the cutting process and the mold held together, even when it was not delicately handled. Loose material from the mold was easily removed during cutting using a small portable vacuum cleaner.  
         [0066]    The machined mold slab was then inserted into a mold assembly and molten 319 aluminum, having a temperature of about 730° C. was poured into the cavity formed by the mold assembly. When the metal cooled, the finished casting (FIG. 3) was removed from the mold.  
         [0067]    The casting was gently sand blasted to remove surface oxidation. The lettering produced by the machined slab showed very good detail (FIG. 4), equal to a plaque with the lettering produced from a lettered pattern.  
       Example 2  
     (Preparation of Castings Having Raised Markings from Mold Inserts with Stamped Marks)  
       [0068]    A small insert of molded material made from SGT microspheres bonded with ten weight percent PEPSET® X1000/X2000 was hand stamped using steel punches and a hammer to create a marked insert with indented number approximately 12 mm in height (FIG. 5). The insert was placed into a mold assembly and molten gray cast iron, having temperature of approximately 1425° C., was poured into the cavity formed by the assembly. The resulting casting contained raised numbers in the mirror image of the imprinted insert (FIG. 6.).  
         [0069]    A second insert of similar molded material was machine punched using a PINSTAMP ® marking device manufactured by Telesis Technologies Inc. The device produced small semi-circular dots or depressions in the surface of the insert (FIG. 7). These depressions had smooth internal surface and showed no signs of cracks (FIG. 8). The insert was placed in a mold assembly and the mold was poured will Alloy A319 aluminum at approximately 730° C. The resulting casting (FIG. 9) contained raised marks in the mirror image of the insert. The raised dots showed excellent detail and surface finish (FIG. 10).  
       Example 3 and Comparative Example A  
     (Preparation of Castings Having both Raised and Indented Marking from Laser Cut Mold Inserts Made from Bonded Hollow Microspheres and Bonded Sand)  
       [0070]    A series of mold inserts were molded using SGT microspheres and ten percent by weight of ISOCURE® 450/852 binder. The molded inserts were marked using a ProScript® laser marking system provided by Telesis Technologies, Inc. Several inserts were placed into a mold assembly. A sample of a laser marked sand core was also procured for comparison. The sand core and marked inserts were placed in a mold assembly and poured with alloy A319 aluminum. The resulting casting was examined for the level of detail and surface finish.  
         [0071]    The laser marked sand core (FIG. 11) produced readable letters, but the cast surface and detail were of poor quality (FIG. 12). A marked insert with lettering of comparable size (FIG. 13) produced much better surface and detail (FIG. 14). A marked insert with a machine-readable code cut into the insert (FIG. 15) produced a raised mark with excellent cast detail and surface (FIG. 16). A marked insert with much of the surface removed to leave protruding “bumps” (FIG. 17) produced indented marks on the cast surface, again with excellent cast detail and surface (FIG. 18).