The present invention relates generally to the field of railroad couplers, and more specifically to the cores used to produce the interior spaces of the knuckle of railroad couplers and the methods used to produce these cores, as well as the structure of the knuckle itself and its method of production.
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 engagable portions of each of these couplers are known in the railway art as knuckles. 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.
Coupler knuckles are generally manufactured from a cast steel using a mold and three cores that produce the interior spaces of the knuckles. These three cores typically make up the rear core or “kidney” section, the middle core or “C-10” or “pivot pin” section, and the front core or “finger” section. During the casting process itself the interrelationship of the mold and three cores disposed within the mold is critical to producing a satisfactory railway freight car coupler knuckle.
The most common technique for producing these components is through sand casting. Sand casting offers a low cost, high production method for forming complex hollow shapes such as coupler bodies, knuckles, side frames and bolsters. In a typical sand casting operation, (1) a mold is formed by packing sand around a pattern, which generally includes the gating system; (2) The pattern is removed from the mold; (3) cores are placed into the mold, which is closed; (4) the mold is filled with hot liquid metal through the gating; (5) the metal is allowed to cool in the mold; (6) the solidified metal, referred to as raw casting is removed by breaking away the mold; (7) and the casting is finished and cleaned which may include the use of grinders, welders, heat treatment, and machining.
In a sand casting operation, the mold is created using sand as a base material, mixed with a binder to retain the shape. The mold is created in two halves—cope (top) and drag (bottom) which are separated along the parting line. The sand is packed around the pattern and retains the shape of the pattern after it is extracted from the mold. Draft angles are machined into the pattern to ensure the pattern releases from the mold during extraction. In some sand casting operations, a flask is used to support the sand during the molding process through the pouring process. Cores are inserted into the mold and the cope is placed on the drag to close the mold.
When casting a complex or hollow part, cores are used to define the hollow interior, or complex sections that cannot otherwise be created with the pattern. These cores are typically created by mixing sand and binder together and then filling a box shaped as the feature being created with the core. These core boxes are either manually packed or created using a core blower. The cores are removed from the box, and placed into the mold. The cores are located in the mold using core prints to guide the placement, and prevent the core from shifting while the metal is poured. Additionally, chaplets may be used to support or restrain the movement of cores, and fuse into the base metal during solidification.
The mold typically contains the gating system which provides a path for the molten metal, and controls the flow of metal into the cavity. This gating consists of a down sprue, which controls metal flow velocity, and connects to the runners. The runners are channels for metal to flow through the gates into the cavity. The gates can control flow rates into the cavity, and prevent turbulence of the liquid.
After the metal has been poured into the mold, the casting cools and shrinks as it approaches a solid state. As the metal shrinks, additional liquid metal must continue to feed the areas that contract, or voids will be present in the final part. In locations with heavy thick metal sections, risers are placed in the mold to provide a secondary reservoir of liquid metal. These risers are the last areas to solidify, and thereby allow the contents to remain in the liquid state longer than the cavity or the part being cast. As the contents of the cavity cool, the risers feed the areas of contraction, ensuring a solid final casting is produced. Risers that are open on the top of the cope mold can also act as vents for gases to escape during pouring and cooling.
In the various casting techniques, different sand binders are used to allow the sand to retain the pattern shape. These binders have a large effect on the final product, as they control the dimensional stability, surface finish, and casting detail achievable in each specific process. The two most typical sand casting methods include (1) green sand, consisting of silica sand, organic binders and water; and (2) no-bake or air set consisting of silica sand and fast curing chemical adhesives. Traditionally, coupler bodies and knuckles have been created using the green sand process, due to the lower cost associated with the molding materials. While this method has been effective at producing these components for many years, there are disadvantages to this process.
Many knuckles fail from internal and/or external inconsistencies in the metal through the knuckle. These inconsistencies can be caused when one or more cores move during the casting process, creating variances in the thickness of the knuckle walls. These variances can result in offset loading and increased failure risk during use of the knuckle.
Traditionally, each of the three cores needed to be set in a separate print in the mold which helps maintain each core's position. Furthermore, additional support mechanisms, such as manually inserted nails, are necessary to avoid shifting. These techniques are labor intensive and allow for human error.
Earlier designs may also allow turbulence in the flow of molten steel during the pour due to the sharp transitions in certain areas. When metal fills the molds under high velocity, it creates turbulence. Any sharp or abrupt transition in the molds or cores also creates turbulence, and/or pressure gradients that can also cause the cores to shift. Furthermore, the turbulence and pressure gradients can cause mold erosion, inclusions and reoxidation defects. These problems can cause solidification issues such as shrinkage and porosity, which in turn can lead to knuckle failure.
The issues above can all result in casting inconsistencies in the knuckle core surfaces. The ramifications of such inconsistencies and the low fatigue strength of the resulting parts can be extremely expensive, as The Association of American Railroads (AAR) has strict standards as to when a part must be scrapped and replaced. The 2011 Field Manual of the AAR notes at Rule 16, Section A, that “knuckles found broken or with cracks in any area . . . determined by visual inspection and/or by utilizing non-destructive testing as defined in AAR Specification M-220 shall be scrapped. (emphasis added). Due to these strict standards, and the expense of replacing these parts in the field, there is an ongoing need to improve the strength and/or fatigue life in coupler knuckles as well as a need to improve the design of the cores used to form the knuckles.
In a first embodiment a core assembly for creating interior spaces in a railcar coupler knuckle is designed to be set in a cavity with cope and drag sections. The cavity is shaped to form a railcar coupler knuckle and includes a first wall that forms the substantially vertical outside wall of the tail of the knuckle. The core includes a kidney section with a rear core support section that extends at least 0.5″ outside the first wall of the cavity when the core is set in the drag.
In a second embodiment, a core assembly for creating interior spaces in a railcar coupler knuckle includes a kidney section with a rear core support section having a smaller radius on the bottom of the rear core support section than on the top of the rear core support section.
In a third embodiment a railcar coupler knuckle has a tail section with an opening defined therein having a height of between about 1-1.8″ and a width of between about 1-2.2″.
In a fourth embodiment a railcar coupler knuckle has a tail section with an opening defined therein with corner radii of greater than about 0.25″.
In a fifth embodiment a railcar coupler knuckle has a tail section with an opening defined therein having a ratio of height to width of between about 1:0.4 and 1:1.3.
In a sixth embodiment a railcar coupler knuckle has a tail section with an opening defined therein having a corner radius of between about 0.1-0.8″.
In a seventh embodiment a railcar coupler knuckle has a tail section with an opening defined therein having a ratio of height to the maximum corner radius of between about 1:1.25 to 1:18.
In an eighth embodiment a railcar coupler knuckle has a tail section with an opening defined therein having a ratio of width to the maximum corner radius of between about 1:1.75 to 1:22.
The system may be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like-referenced numerals designate corresponding parts throughout the different views. Furthermore, measurements shown in the figures are examples only, and are not meant to limit the breadth of the claims.
A first goal of the present invention is to reduce core shifting during casting and therefore improve the strength and fatigue life of a coupler knuckle by utilizing two cores that include a unique interlock feature. A completed knuckle 10 is shown in
With respect to the front portion of the knuckle 10, the present invention utilizes a uniquely shaped first core referred to as a finger core 48, shown in FIGS. 4-8.
Referring again to
The section 62 has been altered from the prior art transition section 62 shown in
The first transition section 62 between the C-10 portion 60 of the core and the finger core 48 has also been improved by increasing both the width W and the height H of the transition section 62 as shown in
The height H of this transition section 62 is preferably greater than about 2.5″ and the width W is preferably greater than about 0.925″. Alternatively, the height H can be increased at least about 75% over the corresponding prior art height and the width W can be increased at least about 50% over the corresponding prior art width. In a preferred embodiment, the height H is about 3.98″ and the width W is about 1.33″.
These changes result in a smoother transition from the C-10/kidney core 50 to the finger core 48 than the prior art transition. The sharp angles 64 of the prior art are removed, and this smoother transition section 62 forms a more uniform wall 102 thickness in the corresponding area 104 of the finished knuckle 10 as shown in
An additional aspect of the design of the first transition section 62 of the present invention is the addition of a positive stop. The positive stop is formed from corresponding vertical walls 74, 76 on the C-10 portion 60 of the C-10/kidney core 50 and the finger core 48, respectively. As shown in
A preferred construction of the first positive stop surface 74 of the C-10/kidney core 50 is shown in
The corresponding second positive stop surface 76 having substantially equal measurements as the first positive stop surface 74 in order to maintain a substantially exact fit is defined extending 360° around the lug 52 extending from the wall 54 of the finger core 48 and being substantially parallel to the wall 54 of the finger core 48. The second positive stop 76 preferably extends between about 0.10-0.35″ outside of the surface of the lug 52. The lug 52 includes top 110 and bottom 112 walls that taper such that the height at the end 114 of the lug 52 that enters the slot 56 is less than the height of the opposite end 116 of the lug 52. The lug 52 is preferably greater than about 1.0″ from the wall 54 of the finger core 48 to the end 114 of the lug 52. The lug 52 is preferably between about 0.60-0.90″ wide and between about 2.75-3.25″ high. The taper angle A is preferably greater than about 1°.
The larger size transition section forms a much more robust joint which reduces the chance of joint breakage during handling of the cores before assembly or while they are being placed as an assembly into the mold.
In an alternative embodiment (not shown), the kidney and C-10 cores are separate. The lug and the first positive stop surface are defined on the C-10 core on a second wall 118. In this embodiment, the slot and the second positive stop surface are defined on the kidney core. The lug and slot and their respective stop surfaces are designed to fit together in the same way as the lug and slot from the previous embodiment.
In yet another alternative embodiment (not shown), a tab is defined on the slot and a corresponding hole is defined on the lug (or vice versa) to act as a failsafe so that the cores cannot be assembled backwards.
Another aspect of the present invention is the modification of a second transition 120 section (shown generally as the shaded portion in
When feeding the casting from the front face 18, the liquid metal tends to cool quicker in thinner sections. In prior designs, the wall thickness in this area varies quite a bit, especially in the abrupt transition section 122 shown in
In the present invention, as shown in
This smoother transition and more uniform throat side wall 140 is located in the throat portion 142 of the knuckle 10 and has a first section A 144 closest to the knuckle tail 40, a third section C 148 closest to the knuckle pulling face 32, and a second section B 146 between the first 144 and third 148 sections (
In one embodiment the throat side wall 140 thickness of the first section 144 is preferably greater than the throat side wall 140 thickness of the second section 146 and the throat side wall 140 thickness of the second section 146 is preferably greater than the throat side wall 140 thickness of the third section 148. Furthermore, the difference in thickness of at least part of the throat side wall 140 in the first section 144 and at least part of the throat side wall 140 in the third section 148 is less than about 17%, the difference in thickness between at least part of the throat side wall 140 in the first section 144 and at least part of the throat side wall 140 in the second section 146 is less than about 11%, and the difference between the thickness of at least part of the throat side wall 140 in the second section 146 and at least part of the throat side wall 140 in the third section 148 is less than about 11%. In another embodiment, the difference in thickness between at least part of the throat side wall 140 in the first section 144 and at least part of the throat side wall 140 in the second section 146 is less than about 17%, and the difference between the thickness of at least part of the throat side wall 140 in the second section 146 and at least part of the throat side wall 140 in the third section 148 is less than about 30%. In yet another embodiment, the difference in thickness between at least part of the throat side wall 140 in the first section 144 and at least part of the throat side wall 140 in the second section 146 is less than about 4%, and the difference between the thickness of at least part of the throat side wall 140 in the second section 146 and at least part of the throat side wall 140 in the third section 148 is less than about 11%.
As an example, the thickness of at least part of the throat side wall 140 within section A 144 can be at least about 1.39″, the thickness of at least part of the throat side wall 140 within section B can be at least about 1.34″ and the thickness of at least part of the throat side wall 140 within section C can be at least about 1.19″. As a reference, in the prior art knuckle shown in
In an additional embodiment the throat side wall 140 thickness of the first section 144 is preferably less than the throat side wall 140 thickness of the second section 146 and the throat side wall 140 thickness of the second section 146 is preferably less than the throat side wall 140 thickness of the third section 148. In this embodiment, the thickness of the wall in the entire throat side wall 142 of the throat section comprising sections A, B and C varies by less than 10% throughout the throat section. In yet another embodiment, the entire throat side wall 140 comprising sections A, B and C varies by less than 17% throughout the tail stop side wall 141. In yet another embodiment, the entire throat side wall 140 comprising sections A, B and C varies by less than 3.5% throughout the tail stop side wall 141.
A similar change has been applied to the tail stop side 133 of the core. Material has been added to the vertical height H2 and the horizontal width W2 of this section. This smoother transition results in more uniform tail stop side wall 141 thickness as shown in
In one embodiment, the tail stop side wall 141 thickness of at least part of the first section 145 is preferably greater than the tail stop side wall 141 thickness of the second section 147 and the tail stop side wall 141 thickness of the second section 147 is preferably greater than the tail stop side wall 141 thickness of the third section 149. Furthermore, the difference in thickness between at least part of the tail stop side wall 141 in the first section 145 and at least part of the tail stop side wall 141 in the second section 147 is less than about 32%, and the difference between the thickness of at least part of the tail stop side wall 141 in the second section 147 and at least part of the tail stop side wall 141 in the third section 149 is less than about 68%. In another embodiment, the difference in thickness between at least part of the tail stop side wall 141 in the first section 145 and at least part of the tail stop side wall 141 in the second section 147 is less than about 4%, and the difference between the thickness of at least part of the tail stop side wall 141 in the second section 147 and at least part of the tail stop side wall 141 in the third section 149 is less than about 51%.
As an example, the thickness of at least part of the tail stop side wall 141 within section X 144 can be at least about 1.23″, the thickness of at least part of the tail stop side wall 141 within section Y can be at least about 1.19″ and the thickness of at least part of the tail stop side wall 141 within section Z can be at least about 0.58″. As a reference, in the prior art knuckle shown in
In yet another embodiment, the entire tail stop side wall 141 comprising sections X, Y and Z varies by less than 32% throughout the tail stop side wall 141. In yet another embodiment, the entire tail stop side wall 141 comprising sections X, Y and Z varies by less than 3.2% throughout the tail stop side wall 141.
Furthermore, in another embodiment the tail stop side wall 141 thickness of the first section 145 is preferably less than the tail stop side wall 141 thickness of the second section 147 and the tail stop side wall 141 thickness of the second section 147 is preferably less than the tail stop side wall 141 thickness of the third section 149. Again, in this alternative embodiment, it is preferred that the tail stop side wall 141 thickness throughout the entire throat section comprising sections, X, Y, and Z varies by less than 17%. In a further alternative embodiment, it is preferred that the tail stop side wall 141 thickness throughout the entire throat section comprising sections, X, Y, and Z varies by less than 3.5%. These changes result in a slightly thicker cross sectional area in one of the highest stress areas in the casting. The thicker area lowers the stress.
This newly designed second transition section 120 results in a knuckle 10 having walls 150 that are approximately 1.0″ thick or greater, as shown in
In an alternative embodiment of the invention, three cores are used as in the prior art, but with the structural changes to the transition sections as detailed above. Furthermore, with respect to utilizing separate C-10 and kidney cores, it is envisioned that a lug and slot connection mechanism with positive stops on the vertical walls of each core can be used in the same fashion as the lug and slot connection with positive stops between the C-10/kidney and finger cores, as previously described. This would form a transition section having positive stops, a lug and a slot in the area between the kidney and C-10 cores. The lug would preferably extend from the C-10 core into a corresponding slot on the kidney core.
In another aspect of the present invention, the rear core support 156 of the kidney section 59 of the C-10/kidney core 50 has been redesigned in order to improve core support and reduce shifting. During casting, the cores that form the interior spaces of the part are seated in the core prints of a mold 160 comprising cope and drag sections with the cores 48, 50 positioned in the drag. The redesigned rear core support section 156 also eliminates a sharp corner 162 that is typically formed in prior art cores due to an acute angle 164 at the plane 166 where the rear core support 156 exits the cope and drag. An exemplary prior art design is shown in
The term “cavity” as used below refers to the portion of the cope and drag that forms the outside walls 168 of the knuckle 10.
In a preferred embodiment the rear core support 156 comprises a flared section 172 and a straight section 170. The top 180 and bottom 182 walls of the straight section 170 of the rear core support 156 are at least about 2.12″ wide. The side walls 184, 186 of the straight section 170 of the rear core support 156 are at least about 1.76″ tall. The distance from the exit plane 166 to the end 186 of the core print is preferably at least about 0.25″. The radii of the corners 196 of the straight section 170 of the rear core support 156 are preferably about 0.3-0.6″. The width W3 of the rear core support 156 is preferably about 2.12″ and the height is preferably about 1.76″. Furthermore, it is important to note that these measurements can change to accommodate different core print sizes. The area of the rear core support 156 is between about 1.5-4.0 square inches. In an alternative embodiment, the rear core support section 156 includes a smaller radius on the bottom of said rear core support section 156 than on the top of said rear core support section 156.
The use of this core combination 48, 50 results in a knuckle 10 as shown in
In a further embodiment of the present invention, a method of forming a core for a coupler knuckle is provided. Traditionally, cores are formed in a mold that results in a part having a horizontal parting line 199, as shown in
The method of the present invention can incorporate a vertically oriented parting line 190 positioned along the approximate middle of the core running from the rear core extension 198 to the end of the C-10 portion of the core 60. This parting line 190 is illustrated in
Although loading of the C-10 pin in the current design is avoided, should some loading occur after wear of knuckle 10 loading surfaces has occurred, a uniformly loaded C-10 pin will result because of the zero draft C-10 pin hole 14. In comparison, the C-10 hole of a horizontally parted core typically has up to a 3° draft angle and results in point loading of the C-10 pin and knuckle C-10 pin hole 14. Point loading of the C-10 pin is more likely to result in bending of the pin or pin failure, either of which can make the coupler knuckle 10 difficult or impossible to operate properly. Point loading can also occur in the drafted C-10 knuckle pin hole 14, which can also lead to higher than expected loading conditions in the C-10 pin hole 14. The 90° shift of the parting line allows for extremely accurate dimensioning of the C-10 pin hole as compared to point loading of a drafted C-10 pin hole.
The above method may be used to form cores through a shell core process, an air set process, or any other core production process known in the art.
Furthermore, if the cores 48, 50 include an interlock feature such as that described above, a separate loose piece 194 can be used in the corebox 192 positioned in a recess on the outside of the C-10 portion of the corebox 192 on the side where the finger core 48 would include a corresponding lug 52. The loose piece 194 includes an extension 198 on at least one side that extends into the opening that forms the C-10 portion of the core. The extension 198 of the loose piece preferably measures at least about 3.0″ high and at least about 0.8″ wide. Furthermore, the loose piece 194 includes a flat face 200 adjacent the extension 198 that forms the first positive stop 74 on the C-10 portion of the core. This flat face measures at least about 4.0″ high and at least about 1.3″ wide and extends 360° around the extension 198.
The top knuckle pulling lug 34 was also redesigned to create a more unified wall thickness, as shown in
Because the pulling lugs 34 transmit the major portion of the longitudinal load applied to the coupler, the uniform wall thickness, particularly at the bottom radius 210 of the top pulling lug 34, results in a stronger design. The uniform section wall thickness also permits more consistent metal filling and more consistent metal cooling, which should improve the solidity or soundness of the casting in this area and reduce the likelihood of hot tears. This is important because the AAR places a high standard on these areas of the knuckle. They are required to pass a static tension test of a minimum ultimate load of 650,000 lbs. This large load that must pass through these pulling lugs 34 can result in very high stress and deflections, not to mention the repeated loading of this feature creates extreme fatigue conditions requiring near perfect surface and subsurface material conditions.
It is intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.
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