Patent Application
20170232503
The present disclosure relates generally to the field of railcar components, and more specifically, to the manufacturing of railcar components through the use of no-bake or air-set casting or the like.
Sand casting is one of the earliest forms of casting. Its popular use is due to its low cost and the simplicity of materials involved. A sand casting or a sand molded casting is a cast part produced through the following process: (1) placing a pattern in sand to create a mold, which incorporates a gating system; (2) removing the pattern; (3) filling the mold cavity with molten metal; (4) allowing the metal to cool; (5) breaking away the sand mold and removing the casting; and (6) finishing the casting, which may include weld repair, grinding, machining, and/or heat treatment operations. This process is now explained in more detail.
In sand casting, the primary piece of equipment is the mold, which contains several components. The mold is divided into two halves—the cope (upper half) and the drag (bottom half), which meet along a parting line. The sand mixture is packed around a master “pattern” forming a mold cavity, which is an impression of the shape being cast. The sand is usually housed in what casters refer to as flasks, which are boxes without a bottom or lid, used to contain the sand. The sand mixture can be tamped down as it is added and/or the final mold assembly is sometimes vibrated to compact the sand and fill any unwanted voids in the mold. The sand can be packed by hand, but machines that use pressure or impact ensure even packing of the sand and require far less time, thus increasing the production rate. The pattern is removed, leaving the mold cavity. Cores are added as required, and the cope is placed on top of the drag.
Cores are additional pieces that form the internal openings, recesses, and passages of the casting. Cores are typically comprised of sand so that they can be shaken out of the casting, rather than requiring the necessary geometry to slide out. As a result, sand cores allow for the creation of many complex internal features. Each core is positioned in the mold before the molten metal is poured. Recesses in the pattern called core prints anchor each core in place. The core may still shift, however, due to poor fit up between core and core prints, the flow of the metal around the core, or due to buoyancy in the molten metal.
Small metal pieces called chaplets are fastened between the cores and the cavity surface to provide further support for the cores. Chaplets are small metal pieces that are fastened between the core and the cavity surface. Chaplets consist of a metal with a higher melting temperature than that of the metal being cast in order to maintain their structure to support the core. After solidification, the chaplets are cast inside the casting and the excess material of the chaplets that protrudes is cut off.
In addition to the external and internal features of the casting, other features must be incorporated into the mold to accommodate the flow of molten metal. The molten metal is poured into a pouring basin, which is a large depression in the top of the sand mold. The molten metal funnels out of the bottom of this basin and down the main channel, called the sprue. The sprue connects to a series of channels, called runners that carry the molten metal into the cavity. At the end of each runner, the molten metal enters the cavity through a gate that controls the flow rate and minimizes turbulence.
Chambers called risers that fill with molten metal are often connected to the runner system. Risers provide an additional source of metal during solidification. When the casting cools, the molten metal shrinks and the additional material in the gate and risers acts to back fill into the cavities as needed. Open risers also aid in reducing shrinkage. When open risers are utilized, the first material to enter the cavity is allowed to pass completely through the cavity and enter the open riser. This strategy prevents early solidification of the molten metal and provides a source of material to compensate for shrinkage. Lastly, small channels are included running from the cavity to the exterior of the mold. These channels act as venting holes to allow gases to escape the cavity. The porosity of the sand also allows some air to escape, but additional vents are sometimes needed. The molten metal that flows through all of the channels (sprue, runners, and risers) will solidify attached to the casting and must be separated from the part after it is removed. Molten metal is poured into the mold cavity, and after it cools and solidifies, the casting is separated from the sand mold.
The accuracy of the casting is limited by the type of sand and the molding process. Sand castings made from coarse green sand impart a rough texture on the surface of the casting, making them easy to distinguish from castings made by other processes. Air-set, or no-bake, molds can produce castings with much smoother surfaces. The benefit to providing a smoother surface is discussed in more detail below but is not insignificant in improving the performance of castings made utilizing the air-set casting process. After molding, the casting is covered in a residue of oxides, silicates, and other compounds. This residue can be removed by various means, such as grinding or shot blasting. Several other surface condition benefits result from the use of the air-set process compared to the green sand process. These include benefits with regards to surface inclusions, surface porosity, laps, and scabs. Details of a comparison between required surface conditions and what can be obtained using the air-set process are provided below.
During casting, some of the components of the sand mixture are lost in the thermal casting process. Green sand can be reused after adjusting its composition to replenish the lost moisture and additives. The pattern itself can be reused indefinitely to produce new sand molds. The sand molding process has been used for many centuries to produce castings manually. Since 1950, partially-automated casting processes have been developed for production lines, some including hydraulics to compact the sand.
Green sand is an aggregate of sand (about 90%), bentonite clay or binder (about 7%), which includes pulverized coal, and water (about 3%). It is termed “green” because like a green tree branch, it contains water. The largest portion of the aggregate is always sand, which can be either silica or olivine. There are many recipes for the proportion of clay, but they all strike different balances between moldability, surface finish, and ability of the hot molten metal to degas. The coal, typically referred to in foundries as sea-coal, is present at a ratio of less than 5% and partially combusts in the presence of the molten metal leading to off-gassing of organic vapors. Also, the presence of 2-3% water results in increased occurrence of gas defects in the casting after reacting with the molten steel. Rough surface discontinuities can form as a result of the off gassing or vapors and can result in lower fatigue life for couplers and coupler parts. Given the cyclic loading which coupler assemblies are subjected, it is important to provide as long a fatigue life as possible.
Another type of mold is a skin-dried mold. A skin-dried mold begins like a green sand mold, but additional bonding materials are added and the cavity surface is dried by a torch or heating lamp to increase mold strength. This improves the dimensional accuracy and surface finish, but lowers the collapsibility. Dry skin molds are more expensive and require more time, thus lowering the production rate.
Another type of sand that may be used in sand casting is dry sand. In a dry sand mold, sometimes called a cold box mold, the sand is mixed only with an organic binder. The mold is strengthened by baking it in an oven. The resulting mold has a high dimensional accuracy, but is expensive and results in a lower production rate.
The casting process for the manufacture of couplers has historically employed the green sand process. While this process has served the railroad industry well, there are disadvantages associated with the green sand process, such as poor material strength, porosity, and poor surface finish, resulting in shorter fatigue life, large tolerance variation, and secondary grinding/machining is often required after the casting process. Additionally, a large number of weld repairs may be required at finishing time to fix either surface or subsurface defects. Production rates are also low and include high finishing labor costs. For reasons that will become more apparent below, these disadvantages can require earlier replacement of railcar components, and create additional manufacturing costs that can be avoided. It would be beneficial, therefore, to use another casting process in the manufacture of railcar components to overcome, or at least ameliorate, these disadvantages.
These casting processes are used to form many railcar components including, e.g., couplers, knuckles, side frames, bolsters, and the like.
For example, railway cars typically consist of a rail car that rests upon a pair of truck assemblies. The truck assemblies include a pair of side frames and wheelsets connected together via a bolster and damping system. The car rests upon the center bowl of the bolster, which acts as a point of rotation for the truck system. The car body movements are reacted through the springs and friction wedge dampers, which connect the bolster and side frames. The side frames include pedestals that each defines a jaw into which a wheel assembly of a wheel set is positioned using a roller bearing adapter.
The side frames and bolsters may be formed via various casting techniques. The most common technique for producing these components is through sand casting, as discussed. Traditionally, side frames and bolsters 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.
Side frames and bolsters produced via the green sand operation above have several problems. First, relatively large draft angles required in the patterns result in corresponding draft angles in the cast items. In areas where flat sections are required, such as the pedestal area on the side frames, and friction shoe pockets on the bolster, cores must be used to create these features. These cores have a tendency to shift and float during pouring. This movement can result in inconsistent final product dimensions, increased finishing time, or scrapping of the component if outside specified dimensions. Other problems with these casting operations will become apparent upon reading the description below.
This Summary provides an introduction to some general concepts relating to this invention in a simplified form that is further described below in the Detailed Description.
Aspects of the invention include a method for casting a railroad component such as a component of a railway car truck. The component of the railway car truck may be, e.g., a side frame or a bolster. The method includes manufacturing the railroad component made of steel in a no-bake manufacturing process including use of a chemically-bonded sand system that results in a sand mold from which the railroad component is cast. The railroad component resulting from the no-bake manufacturing process has a surface finish less than 750 micro-inches RMS, resulting in increased fatigue life compared to a railroad component manufactured by a green sand process.
According to some aspects, the method may result in reduced draft angles for typical features of the railroad component compared to a railroad component manufactured by a green sand process. For example, the side frame or bolster resulting from the no-bake manufacturing process may include draft angles comprising 1.0 (one) degree or less for a plurality of typical features of the side frame and bolster. In some embodiments, a draft angle of a shoe pocket side wall of the bolster may be no more than about ¾ degrees. In other embodiments, a draft angle for a pedestal rood of the side frame may be no more than about ¾ degrees.
According to other aspects, a surface finish and/or margin of error in dimensions may be improved from certain aspects of the railroad component compared to a railroad component manufactured by a green sand process. For example, in some embodiments a surface finish of shoe pockets of the bolster and/or a pair of pedestals of the side frame may be less than 500 micro-inches RMS. In other embodiments, a margin of error in a spacing between respective inner and outer gibs of the bolster may be within about plus or minus 0.063 inches. In still other embodiments, a tolerance between centers of the pair of pedestals of the side frame may be within about plus or minus 0.038 inches. In still other embodiments, a margin of error of shoe pocket angles of the bolster may be about plus or minus 0.5 degrees.
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.
In the following description of various example structures according to the invention, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration various example devices, systems, and environments in which aspects of the invention may be practiced. It is to be understood that other specific arrangements of parts, example devices, systems, and environments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention. Also, while the terms “top,” “bottom,” “front,” “back,” “side,” “rear,” and the like may be used in this specification to describe various example features and elements of the invention, these terms are used herein as a matter of convenience, e.g., based on the example orientations shown in the figures or the orientation during typical use. Additionally, the term “plurality,” as used herein, indicates any number greater than one, either disjunctively or conjunctively, as necessary, up to an infinite number. Nothing in this specification should be construed as requiring a specific three dimensional orientation of structures in order to fall within the scope of this invention. Also, the reader is advised that the attached drawings are not necessarily drawn to scale.
Many of the disadvantages of using the green sand process discussed above can be overcome, or at least ameliorated, by using a no-bake, or air-set, casting process. “No bake” and “air-set” refer to the same type of process and are considered interchangeable throughout this disclosure. The Association of American Railroads (AAR) coupler 100, shown in
The coupler also transmits the longitudinal forces pulling and pushing a railcar in service operations. These forces can be of significant magnitude—often many hundreds of thousands of pounds—and require that the load path of force through the coupler assembly be precisely controlled. Design loads per the AAR Specification M-211 reach 650,000 pounds for the knuckle and 900,000 pounds for the coupler body. Uniform loading helps ensure uniform wear patterns and in turn more uniform load distribution. Finally, the strength of the coupler and its fatigue life is important in order to prevent premature failure of parts, which is directly influenced by dimensional consistency and consequently the level of uniform load distribution.
Surface finish or texture of the coupler has a definite effect in maintaining the required coupler strength and fatigue life. The no-bake casting process provides better dimensional control, improved load path for operating forces, more uniform wear patterns, castings with fewer weld repairs, and improved surface texture for improved strength and fatigue life compared to the green sand process.
In no-bake mold casting, molten metal is poured into a non-reusable mold made from a mixture of sand, quick-setting resin, and catalyst, and the mold is held together until solidification occurs. No-bake sand molding produces a sand mold of considerable strength, which can be free standing without the need for a traditional, steel flask and therefore unlimited in size and shape. The traditional flask is heavy and rigid, which limits green sand operations by the molding efficiencies that result from the limitations of metal flasks.
The no-bake casting process involves the use of chemically-bonded sand systems. The use of the chemical bonding agents typically makes the no-bake process somewhat more expensive than the green sand process. As part of the no-bake casting process, a resin and catalyst are mixed together. Examples of gas catalysts used for curing include sodium silicate (CO2), amine, SO2, and ester cured phenolic systems. Examples of a liquid catalyst can include the air-set system. Through a chemical reaction, the resin hardens into a very strong bond. Sometimes an accelerator may be added to speed the hardening process. The no-bake casting process can also be less sensitive to the air temperature and moisture as compared to green sand operations.
The no-bake process uses graded kiln dried sand, which is mechanically mixed with a resin (or binder) to bind the sand together. Most binder systems are variations on a few basic chemicals, such as furan, phenolic urethane, and sodium silicate. Usually the no-bake method of forming the mold is accomplished at room temperature. Therefore, unlike the green sand process that requires curing the sand, water, and clay mixture at elevated temperature, the no-bake process derives its name by eliminating the baking process required when using the green sand method.
A chemical hardener is then added to the sand mix, which reacts with the binder and begins to set the sand into a solid form. At this point, the fluid sand is poured into a mold around a pattern or multiple patterns. Once poured, the sand is left to set. The binder causes the sand particles to bond together forming a very stable and accurate shape for the cavity that will be used to pour the final casting. Setting time depends on the type of hardener used. The sand sets into a solid block from which the pattern equipment is drawn. Cores are then added to the mold and the mold is closed and ready for casting.
Refractory coatings can be applied to resin-bonded cores and molds. These coatings are sometimes referred to as a wash. Coatings can be used for several reasons, including: (1) to improve surface finish; (2) to control the heat transfer characteristics and microstructure in the steel casting; (3) improve venting of a core; and (4) to prevent certain types of defects in the casting.
In contrast to the green sand process, as discussed, this hardened mold does not require the use of a traditional fabricated metal flask. Flask size limitations can be a detriment for the green sand process by preventing the manufacturer from varying the number of multiple parts in a single flask or by limiting the size of a single casting that can fit in a given flask because of the pre-existing fabricated metal flask sizes. Heavy, steel flasks cannot be cost-effectively modified to accommodate new customer parts sizes, if different than presently-used flasks. Purchasing various single flasks can become costly. Typical sizes can range up to four feet wide, six feet long, and depths from 18-24 inches deep for both cope and drag. Accordingly, an air-set mold is well-suited to larger, heavier castings as the mold strength allows casting of greater weights of metal. A solid sand structure allows a mold to be formed of various sizes, producing the best yields available for each solid sand structure. Also, sand use for a mold can be kept to a minimum without compromising quality so production costs are reduced. The chemical bonding of the sand particles for the no-bake process provides for a better surface condition compared to the green sand process where water and clay are used as the bonding agents.
State-of-the-art foundry equipment on modem-day air-set lines allows up to 100% reclamation of the primary raw material, sand. This reclaimed sand is broken down, cooled and filtered, to be used repeatedly. To maintain sand quality and mold strength, the reclaimed sand is mixed with new sand at a ratio of 75%:25%. This process keeps production costs to a minimum without compromising quality. Note that the new sand to reclaim sand ratio varies depending on the typical casting geometry and weight; the ratio of 75%:25% is only a typical value. Industry values range from 95%:5% to 40%:60%.
Some characteristics and advantages that distinguish the no-bake mold process from that of other sand molding processes, such as the green sand process, include: molds are chemically cured at room temperature; the process produces precise and repeatable dimensions; and finishing labor costs and scrap are reduced while obtaining high casting yields.
As a measure of the dimensional stability of the no-bake process compared to the green sand process, the Steel Founders' Society of America publishes values for dimensional tolerances in Supplement 3 of their Steel Casting Handbook. Base tolerances for castings made by the no-bake process are listed as plus or minus 0.020 inches compared to plus or minus 0.030 inches for castings made by the green sand process. While these are both small dimensions, the ability to have tolerances with a reduction in range of one third is significant when it comes to assuring proper load paths and operational characteristics of coupler assemblies as explained above. The tolerances of the coupler parts depends on casting weight and dimension as will be discussed below, so the tolerance achievable with the no-bake process when compared to the green sand process varies across different parts and dimensions of the railroad coupler. In all cases, however, the tolerances achievable with the no-bake process are smaller than the tolerances required by the AAR Specification M-211.
The no-bake process also allows for smaller draft angles than the green sand process. A draft angle refers to the small slope included for the vertical surfaces of the casting pattern, as oriented in the mold box, so that the pattern can be drawn away from the mold. The draft angle must be included both in the top of the cope and the drag portions of the patterns. Where the green sand process requires a draft angle of 1.5 degrees or more for typical shapes, the no-bake process requires only a 1.0 degree draft angle. Where the green sand (manual) process requires a draft angle of 2.0 degrees or more for deep pockets, the no-bake process requires only a 1.5 degree draft angle for deep pockets. The required draft angle of the green sand process results in a significantly greater deviation from the nominal dimension at cast points that are farther from the pointing line of the entire casting than a casting produced by the no-bake process. Smaller draft angles can promote better part loading and increase bearing area. This small difference is significant when accounting for the interfacing of the complicated shapes that make up the parts in a coupler assembly, and when combined with the reduced tolerance range.
During the locking and unlocking operations, the knuckle 208 rotates about the axis of the knuckle pin 212. The knuckle tail 228 must pass under the knuckle shelf seat 232 on the lock 220 during the locking and unlocking operations. The lock must also move downward and upward in a lock chamber 236 of the body 204 during the locking and unlocking operations. Also, during lockset, the lock 220 must move upward in the lock chamber 236 of the body such that a lockset seat 240 on a lock leg 244 sits with precision on a leg-lock seat 248 of the thrower 216.
The parts of the coupler assembly 200 should have accurate dimensional characteristics to ensure successful operation. The better the dimensional characteristics, the smoother the operation. The larger the dimensional variation, the rougher the operation, and if large enough, the parts will jam and the coupler may become inoperable. Smooth surface finishes also aid in successful operation, which will be discussed in more detail below. If the tolerances of the parts are too large, interference can occur when the knuckle 208 is rotating relative to the body 204 and the lock 220. This interference can result in sticking conditions making difficult the operations of locking and unlocking the coupler. In some cases, extremes of tolerances in relative part dimensions have resulted in coupler inoperability and/or an inability to interchange parts.
The coupler load path for draft (pull) and buff (push) forces generated during train operations is also dependent on precise control of dimensional tolerances of the coupler parts. For draft forces, the coupler is designed to receive the pulling forces at the pulling faces 252 of the knuckles 208 (shown in
Buff forces are maxed during switching operations when freight cars impact each other. The coupler assembly is designed to react to the buff forces at the buffing shoulders 260 of the coupler body 204 and at the buffing shoulders 261 of the knuckle 208. If tolerances of the coupler parts are not controlled accurately, buffing forces can be transmitted at the pin protector bosses 256, 286 (see
While the green sand casting process has been used successfully for many years to produce coupler parts, the no-bake casting process results in a better surface finish and therefore can reduce cracking and associated issues that are created when surface conditions are less than optimal. The normally higher costs associated with the no-bake process have been minimized or offset by: reducing casting finishing (gauging) time, spending less capital investment on items such as special flasks that are not required, requiring less casting defect weld repair, reducing processing time, and yielding more dimensionally-consistent and higher-quality parts with improved part life.
The creation of good surface finish or texture has been established as a priority by the American Association of Railroads (AAR) through action taken by their Coupling Systems and Truck Castings Committee. In the past, certain surface conditions, such as sand inclusions and seams, have been found in critical areas of coupler parts. In some cases, surface conditions can result in cracks which result in reduced fatigue life of the coupler or knuckle. For instance, a radius area 281 between the coupler horn 264 and the shank 268 has received the attention of the Federal Railroad Administration. See Code of Federal Regulations, Title 49, 215.123. Cracks in this area now require replacement of the coupler. Furthermore, a smoother surface achievable through use of the no-bake process adds to tighter tolerances, which will be further discussed below. A part made with tighter tolerances has better fit and functions better with their mating parts, which also increases fatigue life.
In the effort to make sure surface conditions do not result in premature coupler failure, the Coupling Systems and Truck Castings Committee has included specific surface finish criteria as a part of the AAR Specification M-211. Foundry and Product Approval Requirements for the Manufacture of Couplers, Coupler Yokes, Knuckles, Follower Blocks, and Coupler Parts, Specification M-211, Last Adopted October 2009. Section 11.2 of the AAR Specification M-211 reviews specific surface acceptance levels, which are defined utilizing Steel Castings Research and Trade Association (SCRATA) Comparators for the Definition of Surface Quality of Steel Castings. The SCRATA comparators are nine categories, each with five quality levels, decreasing from 1 to 5, in which level 1 is the highest quality and level 5 is the poorest:
A. Surface Roughness—the natural surface of the casting after shot blasting.
B. Surface Inclusions—non-metallic material trapped on the casting surface.
C. Gas Porosity—indications of gas at the casting surface.
D. Laps and Cold Shuts—surface irregularities giving a wrinkled appearance.
E. Scabs—slightly raised surface irregularities.
F. Chaplets—indications of chaplets or internal chills.
G. Surface Finish—Thermal Dressing—surface remaining after using oxy-gas or air-carbon arc processes for metal removal.
H. Surface Finish—Mechanical Dressing—surface remaining after using a mechanical means of dressing a cast surface or a previously thermally dressed surface.
J. Welds—indications of welds fully or partially removed by thermal or mechanical dressing.
The following Tables 1 and 2 are comparison charts respectively for the coupler 204 and knuckle 208 that show the minimum surface conditions required by the AAR Specification M-211 and the improved surface conditions achievable using the no-bake process. Fig. A.11 referred to in Table 1 is a three-page figures shown in Appendix A of the AAR Specification M-211 in which the shaded areas are the critical areas and the non-shaded areas are the non-critical areas. One of ordinary skill in railroad couplers would know to refer to Fig. A.11 to determine which areas are currently considered critical as distinguished from non-critical areas by the AAR. In general, however, the critical areas are those areas that take on more load force with regards to the draft and buff forces discussed above and also those areas that interface or wear with other parts.
The data in Table 1 was obtained through visual comparison of a number of coupler bodies 204 produced by the no-bake process with SCRATA plates representing 1 through 5 in each of the above categories. With reference to categories D through J in Table 1, no laps, scabs, chaplets, or welding were observed. Also, surface conditions of Thermal Dressing and Mechanical Dressing do not depend on the casting process, but result from an individual performing surface conditioning after the casting process has been completed. The frequency with which Thermal and Mechanical Dressing operations must be performed is, however, a result of the casting process, so a comparison with the green sand process is still helpful. As indicated, the surface quality of a coupler produced by the no-bake process is superior in just about every category, and at least equal to the minimum requirements under the AAR Specification M-211.
The data in Table 2 was obtained through visual comparison of a number of knuckles 208 produced by the no-bake process with SCRATA plates representing 1 through 5 in each of the above categories. With reference to categories D through J in Table 1, no laps, scabs, chaplets, or welding were observed. As with the coupler, the surface quality of the knuckles was superior in almost every category, or at least equal to the minimum requirements under the AAR Specification M-211.
The no-bake process may be used to manufacture the coupler body 204, the knuckle 208, the lock 220, the thrower 216, and the locklift 224 in such a way that better (smaller) tolerances for various relative dimensions are achieved due to the no-bake process. As discussed above, tolerances for the no-bake process is plus or minus 0.020 inches and the draft angle is about one (1.0) degree or less for typical features. Actual tolerances, however, vary with weight and dimension of the casted parts according to the Steel Founder's Society of America (SFSA) Tolerance Tables. Table 3 below shows the T3 tolerances used for the no-bake process used by the manufacturers. For comparison, Table 4 shows the T5 tolerances that correspond to the green sand process typical of conventional railroad couplers.
By way of a simple example, suppose a casted part is made by both the no-bake and the green sand processes, both that weigh about 100 pounds. Suppose a dimension of interest is about 2.0 inches. The tolerance achievable by the no-bake process is about 0.051 inches while the tolerance of the part made by the green sand process is about 0.102, which is about twice that achievable by the no-bake process.
Because one must round the weight up to 500 pounds and the length up to 4 inches in the example of
Using the same 500 pound estimate, and rounding to 6 inches, the 5% inch dimension in Table 3 indicates a tolerance of about plus or minus 0.080 inches. Because of rounding, this tolerance is probably closer to plus or minus 0.075 inches. The corresponding tolerance from Table 4 using the green sand process is about plus or minus 0.167 inches, again about twice that which is achievable using the no-bake process.
The 5⅞ inch dimension between the knuckle pulling lug 258 and the knuckle pin hole 282 results in a tolerance of about plus or minus 0.061 inches for the no-bake process compared to about plus or minus 0.108 inches for the green sand process, not quite a two-fold improvement. The 1⅝ inch dimension between the knuckle pin hole 282 and the pin protector bosses 286 results in a tolerance of about plus or minus 0.049 inches for the no-bake process compared to about plus or minus 0.095 inches for the green sand process, again about a two-fold improvement.
According to some aspects of the disclosure, the no-bake process can be used to manufacture other railcar components such as, e.g., side frames and bolsters.
The bolster opening 1110 is defined by a pair of side frame columns 1120, a compression member 1125, and a spring seat 1127. The bolster opening 1110 is sized to receive an outboard end section 1705 (
A pair of wear plates 1135 are positioned between shoe pockets 1710 of the outboard end sections 1705 of the bolster 1700 and the side frame columns 1120. A single exemplary wear plate 1135 is illustrated in
In operation, pressure is produced against the wear plates 1135 by the movement of the bolster 1700 within the bolster opening 1110. In known side frames, the side frame columns 1120 tend to elastically deform under these wedge pressures. As a result, the fasteners securing the wear plates 1135 to the side frame columns 1120 become loose. To overcome these problems, an embodiment of the side frame 1100 of the application includes column stiffeners 1205 (
Returning to
At block 1400, a mold 1500 for manufacturing the side frame 1100 may be formed. Referring to
The respective portions may be formed by first providing first and second patterns (not shown) that define an outside perimeter of the drag side 1102 and cope side 1103, respectively, of the side frame 1100. The patterns may partially define one or more feed paths 1540 for distribution of molten material within the mold 1500. The one or more feed paths 1540 are advantageously positioned in a center region of the mold 1500, which results in an even distribution of the molten material throughout the mold 1500. For example, the feed paths 1540 may be positioned in an area of the mold 1500 that defines the bolster opening 1110 of the side frame 1100.
The patterns (not shown) also define a pedestal jaw portion 1520 that defines the pedestal jaw 1140 of the side frame 1100. In known forming methods, the patterns do not define the details of the pedestal jaw 1140. Instead, a core having the general shape of the inner area of the pedestal jaw 1140 is inserted into the mold prior to casting. The cores tend to move during the casting process resulting in inaccurate dimensions, large core seams that have to be removed.
The pattern above and a group of risers 1535 may then be inserted into respective flasks 1525 and 1526 for holding a molding material 1527. The risers 1535 may inserted in the cope portion 1510. The risers 1535 correspond to hollow cylindrical structures into which molten material fills during casting operations. The risers 1535 are positioned at areas of the mold that correspond to thicker areas of the side frame that cool more slowly than other areas of the side frame. The risers 1535 function as reservoirs of molten material that compensate for contraction that occurs in the molten material as the molten material cools, and thus prevent shrinkage, or hot tearing of the cast side frame in the thicker areas that might otherwise occur. Exemplary risers 1550 for the side frame 1100 are illustrated in
In known casting operations, the precise locations requiring accurate feeding are not generally known. Therefore, relatively large risers (e.g., 6 inches or more) that cover larger areas are utilized. By contrast, in the disclosed embodiments, the precise locations requiring accurate feeding have been determined via various analytical techniques, as described below. As a result, risers 1435 that are considerably smaller in diameter (e.g., about 4 inches or smaller) may be utilized, which improve the yield of the casting. The riser heights may be between about 4 and 6 inches. In one embodiment, less than 10% of the gross weight of the casting material poured into the mold ends up in the risers. This leads to more efficient use of the casting material.
The flasks 1525 and 1527 are generally sized to follow the shape of the pattern, which is different than flasks utilized in known casting operations. These flasks are generally sized to accommodate the largest cast item in a casting operation. For example, in known casting operations, the flask may be sized to accommodate a bolster or an even larger item. By contrast, as illustrated in
A molding material 1527 is then packed into the flask 1525 and over and around the pattern until the flasks 1525 are filled. The molding material 1527 is then screeded or leveled off with the flask, and then cured to harden the molding material 1527. The patterns are removed once the molding material 1527 cures.
The molding material 1527 may correspond to a chemical or resin binder material such as phenolic urethane, rather than green-sand products utilized in known casting operations. The chemical binder material product enables forming molds with greater precision and finer details.
To facilitate removal of the patterns (not shown), sides of the respective cavities in the drag and cope portions of the mold 1500 are formed with a draft angle D 1515 of 1°, ¾°, or even less to prevent damage to the mold 1500 when removing the pattern. The draft angle of the mold forms a corresponding draft angle D 1305 along sides of the side frame 1100. The draft angle formed on most surfaces of the side frame 1100 may be of little consequence. However, in certain regions, such as the contact surfaces 1115 of the pedestal jaws 1140 draft angles of greater than 1° may not be tolerated. The chemical or resin binder material such as phenolic urethane facilitates forming sides with draft angles of 1° or less versus green-sand products, for which draft angles of 3° or greater are required to prevent damaging the mold. In the pedestal jaws 1140 green-sand products require additional cores to create these features to maintain flatness requirements. These cores create large seams and dimensional variation among castings.
At block 1405, a core assembly 1545 that defines the interior region of the side frame 1100 is formed. Referring to
For example, a mold that includes a cope and drag portion that defines a given core may be formed. Molding sand may be inserted into the core box and cured. The core box is then removed to reveal the cured core. The respective cores may be formed individually, integrally, or in some combination thereof. The respective cores may be-formed as two portions. For example, each core (i.e., pedestal core, bolster core, etc.) may include a cope portion and a drag portion formed separately in separate core boxes (i.e., a cope mold and drag mold). After curing, the formed portions may be attached. For example, the cope and drag portions of a given core may be glued together to form the core.
At block 1410, the core assembly 1545 is inserted in the mold and the side frame 1100 is cast. For example, the core assembly 1545 may be inserted into the drag portion 1505 of the mold 1500. The cope portion 1510 may be placed over the drag portion 1505 and secured to the drag portion 1505 via clamps, straps, and the like. In this regard, locating features may be formed in the drag portion 1505 and the cope portion 1510 to ensure precise alignment of the respective portions.
After securing the respective portions, molten material, such as molten steel, is poured into the mold 1500 via an opening in the cope portion 1510. The molten material then flows through the gating 1540 and throughout the mold 1500 in the space between the mold 1500 and the core assembly 1545.
At block 1415, the mold 1500 is removed from the side frame 1100 and the side frame 1100 is finished. For example, the contact surfaces 1115 are machined to remove portions of the residual draft angle D 1305 produced as a result of the draft angle D 1515 of the mold. Other material may be removed. For example, riser material formed in the risers 1535 is removed. In some implementations, the mold 1500 is configured so that a wedge or recess is formed in riser material just beyond the side of the side frame 1100. The wedge or recess enables hammering the riser material off, rather than more time consuming flame cutting utilized in known casting operations.
As shown by the various operations, the side frames 1100 may be produced with a minimum of wasted material and time. For example, the flask configurations minimize the amount of casting material needed to form the mold 1500. Smaller risers result in the removal of less material (i.e., solidified steel) during finishing. The precision of the mold enables, for example, producing dimensionally accurate pedestal jaws. These improvements result in removal of less than 10% of the material during finishing.
In addition to these advantages, other advantages are realized. For example, as noted above, the flasks 1525 and 1526 are not required when casting the side frame 1100. Therefore, the flasks 1525 and 1526 may be utilized to form new molds while a given side frame 1100 is being cast.
As noted above, various analytic techniques may be utilized to precisely determine various dimensions. To achieve tolerances narrower than normally achievable for green sand, or chemical or resin binder material such as phenolic urethane molding, an iterative process of casting and three-dimensional scanning to measure critical dimensions and variability is utilized. This approach may be utilized throughout the manufacturing of the core boxes, patterns, manufacturing cores, manufacturing cope and drag mold portions, and casting the final part. By accurately measuring each step of the process, the exact shrink rates are known in all three directions (i.e., vertical, longitudinal, lateral) as well as how well the cores and mold collapse during solidification.
In one implementation, the scanning may be performed with a 30 point cloud scanner, such as a Z Scanner, Faro Laser Scanner, or a similar device. 30 point cloud data may be analyzed in software such as Geomagic®, Cam2®, and Solidworks® to measure and compare the tooling, cores, and final parts. These comparisons may be utilized to calculate actual casting shrink, which is usually expressed as a percentage. For example, typical pattern maker shrink allowance for a carbon steel casting may be about 1.56%. This typical shrink allowance is not exact, and varies depending on the complexity of the shape being cast. In some cases, shrink allowance may be as much as 2%. For large castings, such as a side frame or bolster, this range of shrink allowance may create casting differences of up to 0.5″, and therefore out of tolerance. In the described embodiments, the actual shrinkage rates in vertical, longitudinal, and lateral directions were determined using this process, and is reflected in the tooling dimensions.
In addition to calculating the shrink of the casting as it cools, it is important to understand how the cores and mold collapse during solidification. Controlling the collapsibility of the cores and mold can control the range of tolerances achieved. This can be achieved through a combination of molding materials, and geometry of the core and mold. For critical side frame dimensions, such as column spacing A 1170 (
In addition to determining the range of manufacturing variance achieved of the molds and cores for calculating shrink and collapse, core print sizes may be reduced. Reducing the clearance between the interface between the core print in the mold and core protrusion reduces core movement during pouring. Less core movement creates more accurate wall thicknesses and part tolerances. In addition to the accuracy of the mold and tooling tolerances, a controlled amount of mold wash has been achieved to minimize the variance of core print dimensions. The clearance used in this process was 0.030″, wherein the mold was 0.030″ larger than the inserting protrusion created in the core, as illustrated by dimension F 1561, which illustrates a cross section taken along section 1555 (
Another advantage of these operations is that the surface finish of the cast side frame is smoother than in known casting operations. The smoother the surface, the greater the fatigue life of the part. The operations above facilitate manufacturing side frames with a surface finish less than about 750 micro-inches RMS, and with a pedestal surface finish that is less than about 500 micro-inches RMS.
Each outboard end section 1705 includes a pair of friction shoe pockets 1710. The surfaces of the respective shoe pockets 1710 are known to be a critical area of the bolster 1700 from a finishing perspective as the shoe pockets 1705 are configured to abut the wear plates 1135 and cooperate with the wear plates 1135 to function as shock absorbers, as described above. There are wedges which are assembled into the shoe pockets, and the wedges wear against the column guide wear plates.
As described above, the main body section 1715 of the bolster 1700 defines a pair of brake window openings 1725 configured to enable the use of brake rigging. These windows also act as core prints to support the main body core in the mold.
The bolster 1700 may be formed in a manner similar to that of the side frame 1100. For example, cope and drag sections of a mold may be formed from a casting material, such as a chemical or resin binder material such as phenolic urethane. Patterns that define the exterior of the respective cope and drag sections of the bolster 1700 may be utilized to form respective cavities in the cope and drag sections of the mold. The draft angles of the sides of the patterns may be 1° or less. As in the side frame, flasks for forming the mold may be sized to follow the shape of a pattern that defines the bolster. A flask configured in this manner minimizes the amount of molding material needed to cast a bolster. For example, in some embodiments, the ratio of the molding sand to the molten material poured into the mold in subsequent operations may be less than 3:1. This is an important consideration given that the mold may only be used a single time when casting.
Risers 1805 (
In known casting operations, the entire parting line forms a plane that cuts through the bolster. For example, the parting line may extend between the end • sections and may be centered within the end sections such that the parting line bisects the shoe pockets and passes through the upper portions of the brake windows. In green sand, pockets are created with cores, because the operation cannot create this shape.
Configuring the parting line according to the disclosed embodiments has several advantages over known parting line configurations. For example, the upper and lower portions of the respective brake windows are known to be regions of high stress. Placement of the parting line near such locations, as is the case in known configurations, renders the bolster more susceptible to higher stresses. By contrast, in the disclosed embodiments, the parting line 1905 is positioned in the middle of the brake window openings 1720 where the stress is lower. The parting line of the mold is also in the same location as the parting line of the cores. This allows for uniform wall thicknesses of the side walls, thereby promoting even cooling of the casting.
No finishing of the shoe pockets 1710 is required because the parting line does not pass through the shoe pockets 1710. In known parting line configurations, the parting line may be a straight line that bi-sects the bolster and passes through a middle region of the shoe pockets. This may necessitate finishing of the core seams surrounding the shoe pockets. However, the disclosed parting line is configured to be above the shoe pockets 1710. That is, the shoe pockets 1710 are formed entirely in either the cope or the drag portion of the mold. As noted earlier, the shoe pockets 1710 are a more critical region of the bolster 1700. Therefore, elimination of a finishing operation is advantageous.
The cross-sectional thickness of the bolster is more symmetrical about the parting line 1905. As noted above, patterns are utilized to form cavities in the drag and cope portions of the mold. The patterns are formed with draft angles to enable removal of the patterns from the mold. Core boxes are used to create the cores defining the inside of the bolster. The two halves of the core boxes meet at a parting line, from which draft angles also extend to allow the removal of the core. Where the parting lines of a core, and parting line of a mold do not match, non-uniform wall thicknesses occur. Placing the parting line towards the top of the bolster, as is the case in known parting line configurations, results in a non-uniform thickness in the cross-section of the bolster. The non-uniform thickness results in the utilization of excess material in casting the bolster. This non-uniform thickness also prevents uniform cooling, and may allow shrinkage and voids to be present. To prevent shrinkage and voids from occurring, large risers to feed the critical sections must be used. By contrast, positioning the parting line 1905 as disclosed enables the formation of a bolster 1700 with a symmetrical side wall thickness about the parting line 1905 as illustrated by thicknesses T111005 and T211010 in
Another advantage of the disclosed parting line 1905 configuration is that it enables easy alignment of the drag and cope portions of the mold. In known molding operations, locating features, such as pins and openings, are arranged within the drag and cope flask portions to align the two portions. Any amount of misalignment in the locating features results in misalignment between the drag portion and cope portion of the bolsters. The described parting line 1405, however, is keyed by virtue of the geometry of the parting line 1405 and the drag portion and cope portion essentially interlock with one another in such a manner that the two portions self-align. As a result, pins and bushings known in art are not necessary to maintain alignment of the drag and cope portions.
After forming the drag and cope portions, one or more cores 11100 that define an interior of the bolster 1700 are formed. Referring to
The techniques described above with respect to a side frame for constraining the tolerance of various dimensions may be applied to the bolster. For critical bolster dimensions such as shoe pocket angles N 11020 (
The distance H 1950 (
Another advantage of these operations is that the surface finish of the cast bolster is smoother than in known casting operations. The smoother the surface, the greater the fatigue life of the part. The operations above facilitate manufacturing bolsters with a surface finish less than about 750 micro-inches RMS, and with shoe pockets with a surface finish less than about 500 micro-inches RMS.
The terms and descriptions used herein are set forth by way of illustration only and are not meant as limitations. Those skilled in the art will recognize that many variations can be made to the details of the above-described embodiments without departing from the underlying principles of the disclosed embodiments. For example, the steps of the methods need not be executed in a certain order, unless specified, although they may have been presented in that order in the disclosure. The scope of the invention should, therefore, be determined only by the following claims (and their equivalents) in which all terms are to be understood in their broadest reasonable sense unless otherwise indicated.
This application is a continuation-in-part of U.S. patent application Ser. No. 14/739,857, filed Jun. 15, 2015, which is a continuation of U.S. patent application Ser. No. 14/337,722, filed Jul. 22, 2014, issued as U.S. Pat. No. 9,079,590; which is a continuation of U.S. patent application Ser. No. 13/916,114, filed Jun. 12, 2013, issued as U.S. Pat. No. 8,783,481; which is a continuation of U.S. patent application Ser. No. 12/685,346, filed Jan. 11, 2010, issued as U.S. Pat. No. 8,485,371. This application is also a continuation-in-part of U.S. patent application Ser. No. 14/943,269, which is a continuation of U.S. patent application Ser. No. 13/109,843, filed May 17, 2011, issued as U.S. Pat. No. 9,216,450. This application is also a continuation-in-part of U.S. patent application Ser. No. 15/152,860, filed May 12, 2016. The disclosures of the foregoing applications are herein incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13109843 | May 2011 | US |
| Child | 14943269 | US | |
| Parent | 14337722 | Jul 2014 | US |
| Child | 14739857 | US | |
| Parent | 13916114 | Jun 2013 | US |
| Child | 14337722 | US | |
| Parent | 12685346 | Jan 2010 | US |
| Child | 13916114 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14943269 | Nov 2015 | US |
| Child | 15362381 | US | |
| Parent | 14739857 | Jun 2015 | US |
| Child | 13109843 | US | |
| Parent | 15152860 | May 2016 | US |
| Child | 12685346 | US |
