Internal chill casting process for railcar knuckle

Abstract

A process of forming a railcar knuckle that includes attaching a chill to a predetermined location of a core that defines an internal cavity of a knuckle. The knuckle is molded around the core such that the chill is positioned adjacently to a throat of the knuckle so that the chill controls directional solidification of the molten metal in that region without the leaving any external surface deposits that require extra finishing for use of the knuckle.

Description

TITLEINTERNAL CHILL CASTING PROCESS FOR RAILCAR KNUCKLE BACKGROUND1. FIELD OF THE INVENTION

[0001] The present disclosure relates to railcar knuckles and, more specifically, to an internal chill casting approach for directional solidification in a railcar knuckle.2. DESCRIPTION OF THE RELATED ART

[0002] Railcar couplers are used to join one end of a railcar to an adjacent railcar using and include a pivotal knuckle that fits into the coupler and rotates about a pin between an open position that can engage the knuckle of an adjacent railcar and a closed position that can be locked in place to join the couplers of the two railcars. A knuckle is usually manufactured in a mold that shapes the outside of the knuckle and using cores within the mold that define hollow regions within the knuckle. Due to the forces involved in carrying the buff and draft loads of railcars, there are certain exterior regions of the knuckle that are highly stressed during use. As a result, these regions are prone to stress cracking and thus failure of the knuckle. Conventional approaches to improving the strength of these regions including metal chills that are positioned against the external portion of the highly stressed regions during casting to direct solidification and limit the amount of shrinkage in those regions. Such chills often attach to the knuckle surface during the molding process and thus require removal as well as extra finishing to prepare the surface for use. Accordingly, there is a need in the art for an approach that can improve the strength of the highly stressed surfaces of the knuckle without requiring additional finishing steps.BRIEF SUMMARY OF THE INVENTION

[0003] The present invention provides an approach for forming a knuckle for a railcar coupler that avoids the need for additional steps while strengthening the high load bearing region of the coupler. In one embodiment, the present invention is a process of forming a railcar knuckle that includes attaching a chill to a predetermined location of a core that defines an internal cavity of a knuckle. The knuckle may then be molded around the core such that the chill is positioned adjacently to a throat of the knuckle so that the chill controls directional solidification of the molten metal in that region without the leaving any external surface deposits that require extra finishing for use of the knuckle. The mold may comprise a cope portion and a drag portion. The step of molding the knuckle may include closing the cope portion and the drag portion around the core and then filling the mold with a moltenmetal. The step of molding the knuckle may further include allowing the molten metal to cool with the chill controlling directional solidification of the molten metal.

[0004] In another embodiment, the present invention may be a knuckle formed by the process of attaching a chill to a predetermined location of a core that defines an internal cavity of a knuckle and then molding the knuckle around the core such that the chill is positioned adjacently to a throat of the knuckle so that the chill controls directional solidification of the molten metal in that region without the leaving any external surface deposits that require extra finishing for use of the knuckle.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0005] The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:

[0006] FIG. 1 is a top view of a conventional knuckle identifying highly stressed regions to be strengthened according to the present invention.

[0007] FIG. 2 is a perspective cross-sectional view of a knuckle having an interior cavity showing the appropriate positioning of an internal chill according to the present invention.

[0008] FIG. 3 is a cross-section of a core having a chill according to the present invention.

[0009] FIG. 4 is a flowchart of a process for forming a knuckle according to the present invention.DETAILED DESCRIPTION

[0010] Referring to the figures, wherein like numerals refer to like parts throughout, there is seen in FIG. 1, a knuckle 10 having a region 12 that experiences a high degree of stress during use with a railcar coupler. Region 12 is generally referred to as the throat of knuckle 10 and comprises the surface of knuckle 10 that is adjacent to the pulling face portion of knuckle 10 that bears the buff and draft loads during use of knuckle 10 on a railcar.

[0011] Referring to FIG. 2, region 12 may be strengthened through the use of a chill 14 positioned internally of knuckle 10 during the casting process that forms the inner cavity 16 of knuckle 10 to control directional solidification and help reduce risk of stress cracking the material that forms region 12 of knuckle 10. Chill 14 may be formed from low carbon, mild steel. Alternatively, chill 14 may be formed from a thermally conductive sand, such as zirconium or chromite sand.

[0012] Referring to FIG. 3, chill 14 may be attached to a core 18 used to define the shape of internal cavity 16 of knuckle 10 during casting. Chill 14 is positioned on core 18 so that chill 14 is positioned in the appropriate location, as seen in FIG. 2, to guide solidification of the molten metal used to form region 12 of knuckle 10. As an example, when region 12 is the portion of knuckle 10 referred to as the throat, the critical portion of knuckle 10 for casting using chill 18 is the center one-third of the throat, centered on the parting line. The use of chill 18 on the parting line in this area of region 12 increases the section thickness and the use of chill 14 encourages and thus improves directional solidification. Because of the limited thickness between the standard pin hole 32 and throat area of region 12, chill 14 ensures that the material in this portion of knuckle 10 is solid with little to no porosity or micro shrinking. It should be recognized that knuckle 10 must have a particular contour to comply with AAR rules regarding interoperability between equipment produced by different manufacturers. Chill 14 may therefore be useful in any design knuckle 10 as every knuckle 10 has a contoured throat corresponding to the AAR approved design. Chill 14 is optimally positioned adjacently to the thinnest part of the cross-section of knuckle 10 along the parting line. Solidification analysis may be used to adjust the position of chill 14 to produce the best result.

[0013] Referring to FIG. 3, an exemplary process 20 for forming knuckle 10 may include the steps of attaching 22 a chill 14 to a predetermined location of core 18 that aligns with region 12 of the completed knuckle 10. Core 18 with chill 14 are then positioned 24 in the appropriate locations within the cope portion 22 and drag portion 24 of a mold 26, such as those used in sand casting processes, that have been shaped to define the outer surfaces of knuckle 14, including region 12 that is subjected to buff and draft loads during use. The cope portion 22 and drag portion 24 of mold 26 may then be closed 26 about core 18 and chill 14. The molten metal used to form knuckle 12 is then be injected 28 into mold 26. Mold 26 with the molten metal is allowed to cool 30, with chill 14 controlling directional solidification of the molten metal in mold 26, thereby helping reduce the risk of stress cracking of the portion of the solidified metal that forms region 12 of knuckle 10. Chill 14 may then be removed along with core 18. Process 20 may be implemented in a shell or thermally cured sand core, and may also be used in connection with no-bake or cold box molds.

Claims

CLAIMSWhat is claimed is:

1. A process of forming a railcar knuckle, comprising the steps of. attaching a chill to a predetermined location of a core that defines an internal cavity of a knuckle; and molding the knuckle around the core such that the chill is positioned adjacently to a throat of the knuckle during molding.

2. The process of claim 1, wherein the chill is positioned adjacently to a central position of the throat.

3. The process of claim 2, wherein the central position of the throat comprising a middle third of the throat.

4. The process of claim 3, wherein the chill is positioned along a parting line of the throat.

5. The process of claim 4, wherein the chill is positioned adjacently to a thinnest portion of the throat.

6. The process of claim 5, wherein the chill is formed from a material selected from the group consisting of steel and thermally conductive sand.

7. The process of claim 6, wherein the step of molding the knuckle around the core includes positioning the core including the chill in one of a cope portion and a drag portion of a mold and then positioning another core including another chill in the other of the cope portion and the drag portion of the mold.

8. The process of claim 7, wherein the step of molding the knuckle around the core including closing the mold and then injecting an amount of molten metal into the mold.

9. The process of claim 8, further comprising the step of allowing the molten metal to cool with the core including the chill in place to control directional solidification of the molten metal under the knuckle has solidified.

10. The process of claim 9, further comprising the step of removing the core with the chill from the knuckle after the knuckle has solidified.

11. A railcar knuckle formed by the process of claim 1.

12. The railcar knuckle of claim 11, wherein the core with the chill has been removed.

13. The railcar knuckle of claim 11, wherein the throat of the knuckle has directional solidification.

14. The railcar knuckle of claim 11, wherein the throat of the knuckle has less porosity compared to a standard knuckle formed without the chill attached to the core.

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