Molding apparatus and method

This invention teaches an improved method and apparatus to make metal alloy castings, such as railroad car connector knuckles. One embodiment of the invention comprises a plurality of core mold assembly units contained within a single molding flask, wherein the mold units are filled with molten metal by way of a common runner and riser system. The said core mold assembly elements may be further comprised of a mold and core assembly formed of the same material, such as phenolic urethane impregnated sand, which is used to accurately replicate the desired shape of a final desired product. This invention eliminates the need to carefully gauge a plurality of part patterns within a single mold flask and reduces the potential for loss of parts, for example by cold shunting, by segregating each part to its own mold isolated mold unit. Such a method and apparatus allows a plurality of parts to be cast in a more accurate way, producing less scrap, improving part dimensional stability, and in some cases, reducing the number of cores needed.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates generally to methods and apparatus for use in casting, particularly to more efficiently producing castings of such items as railroad car connector knuckles.

Casting methods currently used to produce items of metal alloys employ molding techniques that replicate the interior and exterior features of a desired part. Such methods comprise an exterior mold that replicates the external surface features of the desired part, while a core or cores are used to replicate interior cavities and surfaces if such parts embody hollow or reentrant features. The mold and cores are produced from a pattern of the part and are assembled together within containers called “flasks” to produce a cavity that replicates the volume and surface features of the desired part. The mold flask is usually split into two separate components; an upper component traditionally called the “cope” and a lower component called the “drag.” A pattern of the part is placed within the cope and drag over which green molding sand is rammed to replicate the shape of the pattern. The cope and drag are configured to mate with each other to form two halves of the mold cavity to allow the removal of the part pattern from the compacted green sand leaving the desired mold cavity. Cores are subsequently placed within the mold and the mold halves fitted together to form a mold assembly. A system of sprues, runners, gates and risers embodied within the core mold assembly provide the requisite channels to direct molten metal poured into the formed part cavity to reproduce the part. Molten metal is poured into the mold assembly and is allowed to cool and solidify. Once the casting has cooled sufficiently, the cast part is shaken from the sand mold and the cores removed leaving the desired replicated part. The mold and core sand are usually reclaimed and reused.

Of the various types of molding methods used, molds made from “green sand” are the most widely used. Green sand is made from a pliable mixture of sand, clay, and water that coheres and can be molded in such a fashion as to faithfully replicate surface features of the part pattern shape. However, significant disadvantages are associated with the green sand method, some of which are the need for careful handling of the mold assembly due to the relative fragility of the green sand, as well as undesirable dimensional variations between castings associated with mold cavity and core misalignment and pattern wear. Additionally, green sand molding techniques typically employ core sand compositions which differ from molding sand making reclamation of these components difficult in that they are mixed during the part removal process and thus can cross-contaminate each other. Furthermore, multiple parts are typically cast at one time by using a plurality of part patterns to form several mold cavities within a single flask using a system of common runners. Such an arrangement increases the possibility of a number of parts scrapped due to core mold assembly misalignments and cold-shunting. What is needed is an improved casting apparatus and method to overcome these and other drawbacks.

The present invention disclosed herein addresses traditional shortcomings of green sand molding by employing a variation on the phenolic urethane cold-box system to produce stronger molds and cores of higher dimensional accuracy. Although other core and mold making methods may be embodied within this invention, the cold-box system employs molding sand impregnated with phenolic urethane “no-bake” (hence “cold-box”) binders typically used to form molding cores. One principal advantage of using a phenolic urethane binder is that it can be rapidly catalyzed at room temperature by means of an amine vapor that is blown through the core sand to produce durable cores. Removal of the core from the cast part is made easier by carefully controlling the composition of the phenolic urethane impregnated sand and curing conditions. This invention extends the use of the cold-box system to include forming the mold as well as the core resulting in a sturdy core mold assembly that has superior dimensional stability as well as improved structural integrity that permits more aggressive handling of the mold components as compared to the need to more carefully handle molding assemblies that use a relatively fragile green sand. Furthermore, this approach reduces the likelihood of misalignments in a core mold assembly and improves the finish of the cast part, consequently reducing finishing costs and part scrap rate. Depending on the part geometry, this invention also may reduce the number of needed cores used to produce a cast part. In contrast to multiple-part green sand molding methods, this invention also may be employed to form individual or modular core mold assembly units used to form individual parts. This invention also teaches a method of embodying a plurality of such modular core mold assembly units within a single external flask assembly using a system of gates and runners to produce multiple but separate parts at one pouring, eliminating the possibility of multiple part defects associated with mold misalignment of integrated parts in one core mold assembly and thereby isolating such defects to individual core mold modules and reducing potential part scrap rates.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

The present invention is directed to casting technology. In addition, the present invention teaches a core mold assembly unit apparatus as well as a method of embodying a plurality of core mold assembly units within an external cope and external drag flask assembly to produce a plurality of independently formed parts.FIG. 1shows an example of a core mold assembly unit10, which comprises a core mold left half20, a core mold right half30, a riser vent40, a filling gate50, a handling groove or grooves60, and split line90.

FIG. 2further illustrates an example of a core mold assembly unit10separated into core mold assembly unit left half20and core mold assembly unit right half30along a split line90to show the internal details of core assembly70and mold cavity80, which in this example, represents the molding features of a railroad car connector knuckle. In one preferred embodiment, the core mold assembly unit10is comprised of phenolic urethane treated molding sand, which lends itself to fabrication using the cold-box system known in the art wherein sand may be blown onto replicate patterns of the desired part within individual cope and drag flasks and catalyzed with an amine vapor to enhance its mechanical properties to form relatively durable core mold components20and30and mold cavity80replicating the external features of the part. A core or cores70, used to replicate the internal features of a part, may be produced using the same method (i.e., cores are made in a core box from phenolic urethane) depending on the need for such as dictated by the part geometry. To reduce effects of pattern wear and consequent irregularity between castings, one embodiment of the invention employs the use of durable cast-iron or steel patterns to replicate the desired geometry and features of part cavity80and core or cores70within the phenolic urethane treated molding sand during the core mold assembly unit10fabrication process. Handling grooves60provide a means to easily lift and transport the core mold assembly unit10. Filling gate50provides an entryway for the introduction of molten metal into the core mold assembly unit10. The riser vent40provides for venting of the core mold assembly unit10during molten metal insertion.

FIG. 3illustrates one example of a preferred embodiment wherein an external drag flask110is used to contain a plurality of core mold assembly units10. Drag flask110may be made as an external sheet metal weldment or construction of suitable thickness and strength which further comprises a drag liner120and drag runner support130. The drag liner120is preferably comprised of a castable refractory as embodied, for example, in commercial ovens and foundry furnaces desired to be durable enough to survive a plurality of casting operations, and is formed and used to constrain and retain core mold assembly units10in a closed configuration whereby core mold assembly unit halves20and30are intimately mated to form a closed molding cavity80. The drag runner support130may be similarly cast as either an integral component of the drag liner120or installed as a separate component of the same or different materials.

FIG. 4illustrates one example of a preferred embodiment wherein a drag runner140is used to direct molten metal flow to core-mold-units10as described below. Drag runner140is preferably constructed from phenolic-urethane using the cold-box process and may be constructed either as a single piece or as a plurality of pieces fitted together depending on the capacity of the cold-box system available. A plurality of drag runner gates145are symmetrically embodied along the longitudinal axis and are respectively aligned with core mold filling gates50to allow the transport of molten metal to each core mold assembly unit from a common sprue filling port, as described in more detail below.

FIGS. 5 and 6illustrate one example of a preferred embodiment of the external drag flask assembly100showing the relative placement of the drag flask110, drag flask refractory lining120, drag runner140, and drag runner support130.

FIG. 7Aillustrates one example of a preferred loading configuration wherein pluralities of core mold assembly units10are loaded within the external drag flask assembly100. Each core mold assembly unit filling gate50on each core mold assembly unit10is aligned with its respective drag runner gate145.FIG. 7Billustrates a detailed view showing the alignment of core-unit filling gates50with drag runner gates145. As shown inFIG. 12, a plurality of core mold assembly units10are loaded within the external drag flask assembly100and are oriented such that each respective core mold assembly unit filling gate50intimately addresses the drag runner140and drag runner gates145to allow the transport of molten metal to each core mold assembly unit10.

FIG. 8depicts one example of a preferred embodiment of an external cope flask150, similarly used to contain a plurality of core mold assembly units10. The external cope flask150is preferably made from a sheet metal weldment or construction of suitable thickness and strength which further comprises a cope liner160and cope runner support170. The cope liner160is preferably comprised of a castable refractory as embodied, for example, in commercial ovens and foundry furnaces desired to be durable enough to survive a plurality of casting operations. The cope runner support170may be similarly cast as either an integral component of the cope liner160or installed as a separate component of the same or different materials. Cope riser vent ports190are embodied within the cope liner160and external cope flask150to allow venting and molten metal flow out of the core mold assembly units10via core mold riser vents40.

FIG. 9depicts one example of a preferred embodiment of a cope runner200, which is preferably constructed similarly to the drag runner140, from phenolic-urethane using the cold-box process and may be constructed either as a single piece or as a plurality of pieces fitted together depending on the capacity of the cold-box system available. A cope sprue filling port180, as shown inFIG. 8, is preferably provided to permit the introduction of molten metal into the cope runner200via cope runner sprue filling port210. A plurality of cope runner gates215are symmetrically embodied along the longitudinal axis of the cope runner200and are respectively aligned with core mold filling gates50and drag runner gates145to allow the transport of molten metal to each core mold assembly unit10from a common cope sprue filling port180via cope runner sprue filling port210as further illustrated inFIGS. 7,8and9.

FIGS. 10 and 11illustrate one example of a preferred embodiment of the external cope flask assembly300showing the relative placement of the external cope flask150, cope lining160, cope runner200, and cope runner support170, cope riser vents190, and cope sprue filling port180.

FIG. 12illustrates one example of a preferred embodiment of a fully loaded external drag assembly100wherein the relative position of the external cope assembly300is shown in an exploded configuration above the external drag assembly100just prior to closure further showing alignment of the cope riser vent ports190with core mold riser vents40.

FIG. 13illustrates one example of a preferred embodiment of a fully loaded external drag assembly100wherein the relative position of the external cope assembly300is shown in closed configuration conjoined with drag assembly100just prior to a casting operation.

During a casting operation, molten metal is poured into the cope sprue filling port180, as shown inFIG. 13, which subsequently flows to the core mold assembly units10via the cope runner sprue filling port210and cavity formed by the mated cope runner200and drag runner140. Molten metal exits the cavity formed by the mated cope runner200and drag runner140via mated drag runner gates145and cope runner gates215into the core mold filling gates50and finally into the core mold assembly unit cavity80. The pouring of molten metal is typically continued until molten metal is observed to approach or exit the cope riser vents190thus ensuring that core mold assembly unit cavities80are completely filled to form the desire part.

FIG. 14illustrates an exploded view of an alternative example of a preferred embodiment of the present invention wherein the cope assembly300is replaced by a modified cope runner250, at least one core mold filling sprue tube350, and at least one core mold riser vent tube400.

FIG. 15depicts one example of a preferred alternative embodiment of modified cope runner250, which is preferably constructed similarly to the drag runner140, from phenolic-urethane using the cold-box process and may be constructed either as a single piece or as a plurality of pieces fitted together depending on the capacity of the cold-box system available. A modified cope runner sprue filling port265is provided to permit the introduction of molten metal into the modified cope runner250via core mold filling sprue tube350. A plurality of modified cope runner gates275are symmetrically embodied along the longitudinal axis of the modified cope runner250and are respectively aligned with core mold filling gates50and drag runner gates145to allow the transport of molten metal to each core mold assembly unit10as similarly described above.

FIG. 16illustrates an example of a loaded external drag flask assembly100just prior to a casting operation further showing the integrated alternative molding assembly. Although not a limitation and is shown by way of example, a single core mold filling sprue tube350may be used to direct molten metal into the modified cope runner250via cope runner sprue filling port265and subsequently into core mold assembly units10to cast a part as similarly described above, wherein each core mold assembly unit10is vented by means of at least one core mold riser vent tube400placed concentrically about the core mold assembly unit riser vent40. The core mold riser vent tubes400and core mold filling sprue tube350may be fixably attached to core mold assembly units10and modified cope runner250as illustrated by means of a refractory adhesive or bonding agent known to those skilled in the art. It should be furthermore noted that the inventors have discovered that the external drag flask110and drag liner120, as shown inFIG. 3and embodied within external drag flask assembly100, may be optionally replaced using, for example, a retaining band or bands450that bind the core mold assembly units10together with the aforementioned components upon a flat metal plate500to provide the integrated alternative molding assembly, as illustrated inFIG. 17, wherein retaining bands450may be comprised of metal, plastic, composite materials or combinations thereof.

It should be noted that the description of the invention and method herein is provided as an example and should not be considered limiting or restrictive in any fashion as any number of core mold assembly units and possible casting configurations may be practiced as known to those familiar in the art. This invention thus provides the following advantages not limited to:Elimination of the need for pattern gauging;Improvement of mold component alignment and reduction of misalignment casting defects;Permittance of more aggressive handling of molding components, thereby improving part production rate;Improvement of dimensional stability from casing to casting;Reduction of finishing costs and scrap rates;Simplification of molding and core sand reclamation;Reduction of the number of cores needed in some cases; andSimplification of a core or core assemblies within the mold cavity.