Abstract:
A method for manufacturing a railcar coupler knuckle includes providing a first mold section having internal walls defining at least in part perimeter boundaries of a first coupler knuckle mold cavity. The method includes providing a second mold section having internal walls defining at least in part perimeter boundaries of a second coupler knuckle mold cavity. The second coupler mold cavity of the second mold section is offset from the first coupler mold cavity of the first mold section. The method includes closing the first and second mold sections and at least partially filling the first and second coupler knuckle mold cavities with a molten alloy, the molten alloy solidifying after filling to form the coupler knuckle.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application of International Application No. PCT/US2009/057305 filed Sep. 17, 2009, which designates the United States and claims priority to U.S. Patent Application Ser. No. 61/192,659, entitled “COUPLER KNUCKLE SYSTEM AND METHOD,” which was filed on Sep. 18, 2008, which are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates in general to railcars and, more particularly, to a coupler knuckle system and method. 
     BACKGROUND 
     Railcar couplers are disposed at each end of a railway car to enable joining one end of such railway car to an adjacently disposed end of another railway car. The engageable portions of each of these couplers is known in the railway art as a knuckle. For example, railway freight car coupler knuckles are taught in U.S. Pat. Nos. 4,024,958; 4,206,849; 4,605,133; and 5,582,307. 
     Knuckle failure accounts for about 100,000 train separations a year, or about 275 separations per day. Most of these separations occur when the train is out of a maintenance area. In such cases, a replacement knuckle, which can weigh about 80 pounds, must be carried from the locomotive at least some of the length of the train, which may be up to 25, 50 or even 100 railroad cars in length. The repair of a failed coupler knuckle can be labor intensive, can sometimes take place in very inclement weather and can cause train delays. 
     Over the years it has been discovered, in the railroad industry, that relatively small point to point contact surfaces of the engaged portions of these knuckles can cause premature failure due to stress points being established within the knuckle. These coupler knuckles are generally manufactured from a cast steel and during the casting process itself the interrelationship of the mold and cores disposed within the mold are critical to producing a satisfactory railway freight car coupler knuckle. For example, if, during such casting process, the mold should happen to slip or shift along the parting line for any reason then a detrimental point to point surface contact can be established in the finished knuckle. 
     It has generally been difficult to manufacture coupler knuckle castings lacking the geometry that results in the point to point contact surface engagement with other knuckles. One reason for this is the draft angles which are generally required in order to produce a satisfactory casting. Typically, a mold cavity is made using a pattern. The pattern has slight draft angles, often between about 2° and about 3°, in order to allow the pattern to be withdrawn from the mold cavity. Without the draft angles, the withdrawal of the pattern from the mold cavity can result in the sidewalls defining a perimeter boundary of the mold cavity partially collapsing or otherwise deforming. 
     One solution used in an attempt to provide a satisfactory surface involves either grinding or machining the contact or bearing surfaces of the knuckle. However, grinding and/or machining of such surface can add substantially to the cost of producing a satisfactory coupler. Moreover, grinding the bearing surfaces can also establish point to point contact in a number of other places, and, as discussed above, this can add stress to the coupler knuckle and result in premature and unpredictable knuckle failure. 
     SUMMARY 
     Particular embodiments provide a coupler knuckle method and system that substantially eliminates or reduces at least some of the disadvantages and problems associated with previous methods and systems. 
     In accordance with a particular embodiment, a method for manufacturing a railcar coupler knuckle includes providing a first mold section having internal walls defining at least in part perimeter boundaries of a first coupler knuckle mold cavity. The method includes providing a second mold section having internal walls defining at least in part perimeter boundaries of a second coupler knuckle mold cavity. The second coupler mold cavity of the second mold section is offset from the first coupler mold cavity of the first mold section. The method includes closing the first and second mold sections and at least partially filling the first and second coupler knuckle mold cavities with a molten alloy, the molten alloy solidifying after filling to form the coupler knuckle 
     In accordance with another embodiment, a railcar coupler knuckle comprising a tail section and a hub section. The hub section has a pivot pinhole formed therein. The knuckle also includes a front face section connected to the hub section. The front face section includes a nose section and a pulling face portion formed inwardly from the nose section. At least a portion of the pulling face portion includes a parting line offset from a center line of the pulling face portion. 
     Technical advantages of particular embodiments include a coupler knuckle system and method that eliminates a parting line in a load path or bearing surface of the coupler knuckle. Other technical advantages of particular embodiments include the use of cope and drag mold portions offset at a pulling face portion of the knuckle to increase the strength of the knuckle at this portion and its ability to withstand high impact operational forces thereby increasing knuckle lifespan. The pulling face portion may include a substantially flat bearing surface area to distribute the contact load between two adjoining knuckles more evenly. Particular embodiments with an offset parting line add material in the transition areas above and below the pulling face. Particular embodiments also have a clear and even transition from the pulling face to the rest of the knuckle. 
     Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some or none of the enumerated advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and its advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a top view of a coupler knuckle; 
         FIG. 2  is an isometric view of the coupler knuckle of  FIG. 1 ; 
         FIG. 3  is another isometric view of the coupler knuckle of  FIG. 1 ; 
         FIG. 4  is a schematic illustration of a coupler knuckle manufacturing assembly; 
         FIG. 5  illustrates a coupler knuckle adjacent an external manufacturing core; 
         FIG. 6  illustrates a coupler knuckle, in accordance with a particular embodiment; 
         FIG. 7  illustrates a cope mold portion used to form a coupler knuckle, in accordance with a particular embodiment; 
         FIG. 8  illustrates a drag mold portion used to form a coupler knuckle, in accordance with a particular embodiment; 
         FIG. 9  illustrates a coupler knuckle, in accordance with a particular embodiment; 
         FIG. 10  illustrates a pattern used for forming the mold cavities for forming a knuckle having the described offset, in accordance with a particular embodiment; and 
         FIG. 11  illustrates a coupler knuckle, in accordance with a particular embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a top view of an example coupler knuckle  10 . Coupler knuckle  10  includes a tail section  20 , a hub section  30 , and a front face section  18 . Hub section  30  includes a pivot pin hole  14  formed therein for receiving a pivot pin to pivotally couple the knuckle  10  to a coupler for coupling to a railcar. Pivot pin hole  14  may have generally cylindrical sidewalls and may have a middle region lacking sidewalls. Coupler knuckle  10  also includes a buffing shoulder  16 , a tail stop  21 , a pulling lug  26 , a lock wall  36 , a throat  38 , and a heel  44 . 
     Front face section  18  includes a nose section  22 , which includes a generally cylindrical flag opening  24  formed in an end region of the nose section  22 . A pulling face portion  28  is disposed inwardly from nose section  22 . At least a portion of the pulling face portion  28  includes a bearing surface area  12  which bears against a similar surface of a coupler knuckle of an adjacent railcar to couple the railcars together. 
       FIGS. 2 and 3  are isometric views of the example coupler knuckle  10  of  FIG. 1 . Evident in  FIGS. 2  and/or  3  are tail section  20 , nose section  22 , pulling lug  26 , hub section  30 , bearing surface area  12 , pivot pin hole  14 , flag opening  24 , pulling face portion  28 , lock wall  36 , throat  38 , and parting line  32 . Tail section  20  includes an opening  35 . The illustrated embodiment also includes a pin protection portion  15  to provide protection for the pivot pin during use of the knuckle. 
     Coupler knuckles include various surfaces and cavities that conform to standard specifications as set forth by the Standard Coupler Manufacturers Committee. Casting gages are designed to be applied to the coupler knuckle in a prescribed manner to verify that certain dimensions of the knuckle fall within an allowable variation or tolerance range. Gages have a primary role in guaranteeing the uniformity of all manufacturers&#39; knuckles. Railroad cars that operate in interchange traffic, switching from one train to another, are required to be equipped with couplers and other draft system components which will reliably mate with other assembly components. 
     One manner in which a coupler knuckle may be manufactured to conform to standard specifications is through a casting process with steel or other alloy. The casting process typically includes the use of cope and drag mold sections and one or more cores that aid in forming appropriate cavities within the coupler and external surfaces of the coupler. The cores are typically made of resin or otherwise hardened sand. 
     The cope and drag mold sections each include internal walls, formed of sand using a pattern or otherwise, that define at least in part perimeter boundaries coupler knuckle mold cavities. Sand, such as green sand, may be used to define the interior boundary walls of the mold cavities. The mold cavities correspond to the desired shape and configuration of a coupler knuckle to be cast using the cope and drag mold sections. The cope and drag mold sections are placed together such that their respective mold cavities form one large cavity that is filled with steel or other alloy that solidifies to form the coupler knuckle. The mold cavities may include a gating system for allowing molten alloy to enter the mold cavity. As discussed above, one or more cores may be positioned within the mold cavity to form internal cavities or other surfaces of the coupler knuckle. 
     This conventional manufacturing process creates parting line  32  on the knuckle where the mold cavities of the cope and drag sections meet. This parting line runs approximately mid-way between top and bottom portions of the knuckle since a depth of the mold cavity in the cope section may be approximately equal to a depth of the mold cavity in the drag section. Thus, parting line  32  may run generally along a center line of the knuckle at the pulling face portion of the knuckle. The parting line may be further accentuated by the pattern draft angles, often between about 2° and about 3°, generally required in order to allow the pattern to be withdrawn from the mold cavity. This increases the chance of forming a bearing surface area with a raised point running through the bearing surface area at the parting line. Parting line  32  extends within bearing surface area  12  that bears the most force from a knuckle coupled to an adjacent railcar. The parting line many times results in a raised surface that increases the chance of detrimental point to point contact surfaces of the engaged portions of these knuckles which can cause premature failure due to stress points being established within the knuckle point. In some cases, bearing surface area  12  may have a height of approximately four inches and be generally centered between the illustrated top and bottom portions of the coupler knuckle. In some cases, the coupler knuckle may have a total height at the bearing surface area of approximately 11 inches. 
       FIG. 4  is a schematic illustration of a conventional coupler knuckle manufacturing assembly. Knuckle manufacturing assembly  200  includes a cope mold section  210 , an upper section  220  of a coupler knuckle, a core  230  used in the manufacturing process to create internal knuckle cavities, a lower section  240  of the coupler knuckle and a drag mold section  250 . 
     Cope mold section  210  and drag mold section  250  include mold cavities  212  and  252 , respectively. Mold cavities  212  and  252  are configured to correspond to the desired external surfaces of the coupler knuckle to be manufactured using cope and drag mold sections  210  and  250 . Core  130  includes finger, pivot pin and kidney portions to form corresponding cavities within the coupler knuckle. Once the cores are in place, the cope and drag mold portions may be brought together and closed. The cavity may be filled with molten alloy, which takes up all the space open between the cope and drag portions and the cores. After solidifying, the cope and drag mold portions are separated, and the casting is shaken out resulting in the breaking up of the cores and their exit from designed openings in the casting. As discussed above, this conventional manufacturing process creates a parting line  232  on the knuckle where the mold cavities of the cope and drag sections meet. 
     In the manufacturing of some coupler knuckles, an additional core may be used to define a bearing surface area that will bear the impact and forces of an adjacent knuckle when two railcars are coupled together, as described in U.S. Pat. No. 7,337,826 which is hereby incorporated by reference herein in its entirety. FIGURE illustrates a coupler knuckle  310  adjacent such an additional core  335  used to form the bearing surface during casting. This core may be positioned in the mold cavity of either the cope or drag sections for forming the bearing surface area. As evident, the use of core  335  may eliminate parting line  332  from extending to a bearing surface area of the coupler knuckle. However, the use of cores such as this external core in the manufacturing process presents variability issues as a result of potential movement of the core during casting. In addition, the use of such a core adds time and expense to the manufacturing process for the formation of the core and for its placement into the mold. Also evident in  FIG. 5  are tail section  320 , nose section  322 , hub section  330 , pivot pin hole  314 , flag opening  324 , and throat  338 . 
       FIG. 6  illustrates a coupler knuckle  350 , in accordance with a particular embodiment. Knuckle  350  includes a parting line  360  that is offset from the generally centered nature of parting lines in conventional knuckles. For example, parting line  360  is offset from a center line  362  at the pulling face portion of knuckle  350 . As a result, parting line  360  does not run through a bearing surface of the knuckle. This increases the knuckle load-bearing consistency and leads to a longer knuckle life. In some embodiments, parting line  360  may be two inches or more away from a center line between the top and bottom portions of the knuckle at the pulling face portion. 
       FIG. 7  illustrates a cope mold portion  400  used to form a coupler knuckle, in accordance with a particular embodiment. Cope mold portion  400  includes a cope mold cavity  410 . While the face of the specific mold cavity surface that forms the pulling face portion with the bearing surface area is at least partially hidden as a result of the angle of the figure, referenced height  420  of the cavity generally corresponds to a height of the cavity at the pulling face portion. In some embodiments, referenced height  420  may be approximately 3.1875 inches or approximately 3.5 inches. In some embodiments, this height may be in the range of approximately 3 to 4 inches or approximately 2.5 to 5 inches. 
       FIG. 8  illustrates a drag mold portion  440  used to form a coupler knuckle, in accordance with a particular embodiment. Drag mold portion  440  includes a drag mold cavity  450 . While the face of the specific mold cavity surface that forms the pulling face portion with the bearing surface area is at least partially hidden as a result of the angle of the figure, referenced height  460  of the cavity generally corresponds to a height of the cavity at the pulling face portion. In some embodiments, referenced height  460  may be approximately 7.8125 inches or approximately 7.5 inches. In some embodiments, this height may be in the range of approximately 7 to 8 inches or approximately 6 to 8.5 inches. 
     Since referenced heights  420  and  460  of cope and drag mold cavities  410  and  450 , respectively, generally correspond to the heights of their respective mold cavities at the knuckle pulling face portion, the combination of their heights generally corresponds to the height of the knuckle at the pulling face portion. As evident, these heights are not equal (height  460  is greater than height  420 )—this creates an offset in the cope and drag mold cavities at the pulling face portion of the knuckle. Since it is where these mold cavities meet that forms the parting line in the knuckle, the parting line in a knuckle formed by using cope mold portion  400  and drag mold portion  440  will be offset from a general center line of the knuckle at the pulling face portion. In some embodiments, this parting line may be approximately 2 inches or more from a general center line of the knuckle at the pulling face portion. This may ensure that the parting line does not extend through a bearing surface area of the pulling face portion such as bearing surface area  12  of knuckle  10  of  FIGS. 1-3 . 
     In some embodiments, the offsets illustrated in the cope and drag mold portions  400  and  440  may be reversed such that the offset in  400  may occur in the drag portion and vice versa. 
       FIG. 9  illustrates a coupler knuckle  480 , in accordance with a particular embodiment. Knuckle  480  is formed with cope and drag mold sections with offset mold cavities such that parting line  490  is offset from a general center line of the knuckle at particular locations on the knuckle. For example, while the specific pulling face portion of the knuckle is at least partially hidden in this figure, it is evident that the parting line runs below a center line of the knuckle at the pulling face portion. Referenced distance  494  may correspond to a height of a cope mold cavity at that location on the knuckle, and referenced distance  492  may correspond to a height of a drag mold cavity at that location, or vice versa. 
     In some embodiments, the total vertical distance of the coupler at the bearing surface area is approximately 11 inches. In some embodiments, referenced distance  494  at the bearing surface area may be approximately 7.5 inches or, in some cases, approximately 7 13/16 inches; and distance  492  at the bearing surface area may be approximately 3.5 inches or, in some cases, approximately 3 3/16 inches. In some embodiments, referenced distance  492  at the bearing surface area may be in the range of approximately 3 to 4 inches or in the range of approximately 2.5 to 5 inches. In some embodiments, referenced distance  494  at the bearing surface area may be in the range of approximately 7 to 8 inches or in the range of approximately 6 to 8.5 inches. 
     As discussed elsewhere, in some embodiments the location of the parting line may be reversed such that referenced distance  492  at the bearing surface area may be greater than referenced distance  494  at the bearing surface area. 
       FIG. 10  illustrates a pattern  500  used for forming the mold cavities for forming a knuckle having the described offset, in accordance with a particular embodiment. When forming the mold cavities, the pattern itself may be tilted on the pattern plate. To avoid a point caused by a draft from the offset parting line on an offset pattern as described and illustrated, the pattern may be tilted at 1° relative to the offset parting line so the “flat” portion of the knuckle pattern, between references  502  and  504 , can be pulled from the mold without drafting it. This increases the likelihood of achieving a flatter bearing surface area with an offset parting line. Thus, in some cases the pattern and/or mold cavities may be tilted (e.g., at approximately 1 degree) about the parting line to ensure a flatter surface at the bearing surface area of the knuckle. 
       FIG. 11  illustrates a coupler knuckle  610 , in accordance with a particular embodiment. Coupler knuckle  610  includes tail section  620 , nose section  622 , hub section  630 , bearing surface area  612 , pivot pin hole  614 , flag opening  624 , pulling face portion  628 , lock wall  636 , throat  638 , pin protection portion  15 , and parting line  632 . Tail section  620  includes an opening  635 . 
     As evident, parting line  632  (which is illustrated through only the nose and pulling face portions and is thus only partially illustrated) does not run through a center line of the knuckle at the pulling face portion. In some embodiments, parting line  632  may be approximately two inches or more from a center line of the knuckle at the pulling face portion. In this embodiment, parting line  632  does not run through bearing surface area  612  which leads to a flatter bearing surface area than a conventional knuckle having a bearing surface with a parting line through it. This leads to a reduced risk of point to point contact in the bearing surface, reduced chance of knuckle failure during operation, and longer life. Mold cavities of cope and drag portions used to form knuckle  610  may be offset to form a parting line away from a center line of the knuckle at the pulling face portion as described above. In various embodiments, offset parting line  632  may continue around the knuckle and return at any suitable location and still provide the benefits discussed herein. Specifically, in some embodiments, an offset parting line may extend into a nose section and further around a front face section of a coupler knuckle and return to a center line position elsewhere on the knuckle. 
     While particular knuckles are discussed herein with parting lines at various locations, it should be understood that coupler knuckles can be formed with parting lines at any suitable offset location at the pulling face portion in accordance with various embodiments. Cope and drag mold cavities may have any suitable configuration to form such offset parting line. In some cases, other manufacturing processes may be used without cope and drag mold portions to create a knuckle that does not include a parting line through its bearing surface area. 
     Coupler knuckles manufactured in accordance with particular embodiments may be provided in the combination of a railway freight car coupler (not shown) having incorporated therein the coupler knuckle casting as described. The knuckles may also be configured to be suitable for retrofitting an existing railway freight car couplers (not shown). 
     Although the present invention has been described in detail with reference to particular embodiments, it should be understood that various other changes, substitutions, and alterations may be made hereto without departing from the spirit and scope of the present invention. The present invention contemplates great flexibility in the manufacturing process of coupler knuckles and the shape, configuration and arrangement of one or more internal cores used in the manufacturing process. 
     Numerous other changes, substitutions, variations, alterations and modifications may be ascertained by those skilled in the art and it is intended that the present invention encompass all such changes, substitutions, variations, alterations and modifications as falling within the spirit and scope of the appended claims.