Patent Application
20130168035
Railway car couplers are used to couple railway cars together. A typical coupler used throughout North America is the Type-E or Type-F coupler. These couplers incorporate a lock that interacts with a knuckle of the coupler to lock the knuckle into a closed position. Generally, the lock fits within a lock chamber of the knuckle body and over a knuckle tail. The width of the lock is sized to slide within the lock chamber.
Locks used in such couplers are typically formed via a casting process. The most common technique for producing a lock is through sand casting. Sand casting offers a low cost, high production method for forming complex shapes. In a typical sand casting operation, a mold is formed by packing bonded sand around a pattern, which generally defines a gating system through which molten metal flows. The pattern is then removed from the mold forming the cavity in the shape of the part being cast, which corresponds to the final cast part. Cores for defining internal cavities and slots are placed into the mold. The mold is then closed and filled with hot liquid metal through a down sprue and the metal is allowed to cool in the mold. The solidified metal or raw casting is removed by breaking away the mold. The casting is then separated from the gating, finished, and cleaned via grinding, welding, 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 portions referred to as a cope portion (i.e., top half) and drag portion (i.e., bottom half), which are separated along a straight parting line. Draft angles of up to 3 degrees or more are machined into the pattern to ensure the pattern releases from the mold during extraction. In some sand casting operations, an exterior flask is used to support the sand during the molding process through the pouring process.
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 areas of high contraction, risers are formed in the mold to provide a secondary reservoir, available during filling. These risers are the last areas to solidify, and thereby allow the contents to remain in the liquid state longer than the cavity of 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, with clay and water as a binder; and (2) chemical or resin binder material consisting of silica sand and fast curing chemical binding systems such as phenolic urethane. Traditionally, locks have been created using the green sand process, due to the lower cost associated with the molding materials.
While the green sand has been effective at producing locks for many years, there are disadvantages to this process. For example, the surface finish of the locks tends to be rough and the thickness over the locking surfaces from lock to lock may vary. These rough surface defects and variations must be removed via grinding and other finishing operations to ensure that the final lock meets required dimensional requirements. Other problems with these casting operations will become apparent upon reading the description below.
An object of the invention is to provide a method of manufacturing a lock of a railcar coupler that substantially eliminates surface defects and dimensional variations. The method includes forming a pattern of a lock in drag and cope portions of a first mold that comprises a first molding material to thereby form a cavity that defines exterior surfaces of the lock. A cavity is formed in a second mold that comprises a second molding material. The cavity defines an interior surface that substantially complements an exterior surface of the first mold. A down sprue, gating system in fluid communicating with the down sprue, riser in fluid communicating with the gating system, and an in-gate in fluid communication with the gating system and the first mold, are formed in the second mold. The first mold and the second mold are cured. The first mold is assembled and inserted into the into the cope portion of the second mold. The second mold is assembled, and molten material is poured into the down sprue of the second mold. The molten material subsequently flows into the first mold to thereby form the lock.
A second object of the invention is to provide a method of manufacturing a lock of a railcar coupler that includes forming a pattern of a lock in drag and cope portions of a first mold that comprises a first molding material to thereby form a cavity that defines exterior surfaces of the lock. The cope portion defines a first opening configured to vent gases. A cavity with an interior surface that substantially complements an exterior surface of the first mold is formed in a second mold that comprises a second molding material. A first opening configured to vent the gases vented from the first opening in the cope portion of the first mold is formed in the cope portion of the second mold. A down sprue, gating system in fluid communication with the down sprue, and an in-gate in fluid communication with the gating system and the first mold are formed in the second molding material. The first mold and the second mold are cured. The first mold is assembled and inserted into the into the cope portion of the second mold. The second mold is assembled, and molten material is poured into the down sprue of the second mold. The molten material subsequently flows into the first mold to thereby form the lock. Gases in the first mold are forced out by the molten material through the first opening in the cope portion of the first mold and subsequently through the first opening in the cope portion of the second mold.
A third object of the invention is to provide a method of manufacturing a lock of a railcar coupler that includes forming patterns for at least two locks in drag and cope portions of a mold that comprises an air-set molding material to thereby form cavities that define exterior surfaces of the at least two locks. A down sprue, gating system in fluid communication with the down sprue, and at least two in-gates, each in fluid communication with the gating system and one of the at least two cavities, are formed in the air-set molding material. The air-set molding material is cured. The drag and cope portions of the mold are assembled. Molten material is poured into the down sprue of the cured air-set molding material, wherein the molten material subsequently flows through the gating system and into the cavities to thereby form the at least two locks.
A fourth object of the invention is to provide a casting assembly for manufacturing a lock of a railcar coupler. The casting assembly includes drag and cope portions of a first mold that defines exterior surfaces of the lock. The first mold comprises a first molding material. The casting assembly also includes a second mold formed of a second molding material. The second mold defines a cavity with an interior surface that substantially complements an exterior surface of the first mold. A down sprue is formed in the second mold. A gating system is formed in the second mold and is in fluid communication with the down sprue. An in-gate is formed in the second mold and is in fluid communication with the gating system and the first mold.
Other features and advantages will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional features and advantages included within this description be within the scope of the claims, and be protected by the following claims.
The accompanying drawings are included to provide a further understanding of the claims, are incorporated in, and constitute a part of this specification. The detailed description and illustrated embodiments described serve to explain the principles defined by the claims.
The embodiments below describe a method for manufacturing a plurality of locks in a single casting operation. Generally, a group of shell molds that define the shape of the lock are formed. The shell molds are molds formed from relatively expensive fine silica sand that is mixed with a thermosetting phenolic resin. The fine silica results in a lock having a smooth surface finish and a relatively high degree of dimensional accuracy as compared to locks manufactured via other casting processes.
However, current shell mold production techniques are optimized for present size shell molding machines and result in shell molds that are relatively small. While larger shell molding machines exist, they tend to be prohibitively expensive. Increasing the size of the shell molds to withstand the required large head pressure, while technically possible, would be prohibitively expensive. Thus, the shell molds are placed into an outer mold. The outer mold is made from a lower cost air-set or pep set molding material and is configured to receive the shell molds. In the described embodiments, the outer mold is configured to receive four shell molds.
A gating system formed in the outer mold is configured to distribute molten material poured into the mold via a down sprue to each of the shell molds. Vent openings in the shell molds allow air and other gases to escape as the molten material fills the shell molds. The vent openings are generally aligned with vent openings in the outer mold to allow the gases to vent to the atmosphere.
Operation of the lock 105 requires that the lock 105 slide within the lock chamber of the knuckle body and over the knuckle tail. To facilitate smooth operation of the lock 105, the knuckle-locking surface 225 and coupler locking surface 230 must be substantially parallel to one another and smooth. In addition, the distance D 207 between the two surfaces needs to be accurate and consistent from lock to lock. The distance D 207 of locks 105 formed by the disclosed casting operations is about 3.060 inches and varies from lock-to-lock by less than about ±0.010 inches. These dimensions may be achieved via the claimed casting operations alone with minimal machining of the lock. Locks produced via known manufacturing processes must be finished to produce a smooth surface finish by sand blasting or other methods. Relatively thin vent castings may be hammered off leaving relatively small areas to be ground. Likewise, a casting connection 505 (
The molding material used in the outer mold 300 is a relatively low cost and strong molding material that is generally not capable of forming locks with the required detail of surface finish and dimensional accuracy. For example, the grain fineness number (GFN) of the molding material may be in the range of 44-55 GFN.
In some implementations, the molding material is reclaimed sand. (I.e., sand that has been previously used to make castings). The reclaimed sand may be obtained by subjecting used molds to various shaking and/or crushing operations that break down the mold classify the sand into finer and finer constituent sizes until a desired grain size is obtained. Screening operations facilitate separation of the sand by size. Finally, the sand is subjected to high temperatures to burn off any residual coating or other impurities, such as the binder material. The reclaimed sand is then mixed with new binder at a ratio of about 99:1 and placed into a mold and allowed to set. Once set, the new mold is ready to receive a molten material.
In some implementations, two or more grades of molding material may be used to form the outer mold 300. For example, an outer layer 310 of the mold (i.e., that defines the exterior of the outer mold may be formed from less refined sand. The less refined material may not be subjected to the various separation operations described above. For example, thermal operations may not be carried out to save time. Moreover, a lesser amount of binder material may be utilized to bind the less refined material. For example, the ratio of sand to binder may be greater than 99:1.
An inner layer 315 of the mold may be formed from the more refined sand reclaimed via the separation processes described above. Utilizing the different grades of reclaimed material reduces overall manufacturing costs associated with the outer mold 300 as less refined sand is required. The more-refined sand may be reserved for just those portions of the outer mold 300 that require greater dimensional accuracy, or better surface finish.
Each shell mold 400 is configured to form a single lock 105. Thus, four locks 105 may be formed in a single casting operation. It should be understood that the size of the outer mold 300 may be sized differently to accommodate a different number of shell molds 400 to facilitate casting a different number of locks 105 in a given casting operation.
In the illustrated embodiment, four sets of vent openings 325 and 330 are provided on the cope portion 305 of the mold to vent gases from the four shell molds 400. The vent openings 325 and 330 are generally positioned above respective vent openings 405 and 410 of the shell mold 400. A first group of vent openings 330 is positioned over a first group of vent openings 410 of the shell mold 400 near a position of the shell mold 400 that corresponds to a first end of the lock. (E.g., The rear guide end 205). A second vent opening 325 is positioned over a second vent opening 405 of the shell mold 400 in a position of the shell mold 400 that corresponds to a second end of the lock. (E.g., The knuckle side end 215). Side vents positioned adjacent to corresponding side vents 335 (
The vent openings 330 and 325 in the outer mold cope portion 305 extend from the outside surface of the cope portion 305 (See
Positioning of the vents 405 and 410 at either end of the lock 105 helps to ensure that any gas within the shell mold 400 has an escape path. This results in a stronger lock 105 with fewer surface defects because the gases, which could otherwise form air pockets that might weaken the lock 105, do not penetrate into the casting. The position of the vents 405 and 410 also helps ensure that the thick upper section of the lock 105 (i.e., the rear guide end 205) and thinner bottom section of the lock 105 (i.e., the knuckle side end 215) remain stable without distortion or dimensional changes given the significant difference in volumes of these two lock sections.
As illustrated in
The shell mold 400 is formed via a so called shell (thus the term shell mold) or hot box process whereby resin bonded sand or a sand/resin mix is blown via air pressure into heated metal pattern for a period of time to form a hardened shell. The sand may correspond to fine silica sand that is mixed with a thermosetting phenolic resin. For example, the silica may have a grain fineness number in the range of 60-70 GFN. The pattern may be formed from cast iron and then heated to between 230° C. to 315° C. until the sand in the pattern hardens to a suitable depth. That is, until the shell has the desired wall thickness. The shell may then be removed from the pattern and the bulk of the unhardened sand mixture inside the shell removed. The removed sand may be used for subsequent shell casting operations after a reclamation process.
The cope portion 605 and drag portion 610 of the shell mold 400 are formed via different patterns. The shell molding technique offers high dimensional stability. Each pattern defines a part of a connection opening 607 in the respective portion through which molten material flows into the shell mold 400. The pattern that defines the cope portion 605 may correspond to a generally rectangular box with an open side into which the sand is poured. The box may have tapered sidewalls that facilitate removal of the hardened cope portion 605 from the box. The cope portion of the lock 105 may be patterned in the bottom side of the box. In addition, the pattern may be configured to form a protrusion 620 in the cope portion 605. The protrusion 620 forms the slot 220 (
The pattern that defines the drag portion 610 may correspond to a generally closed box with a relatively small opening formed in a side. In an exemplary embodiment, the opening is formed on a side of the box that defines the knuckle side end 215 of the lock 105. Sand is blown into the box via the opening and hardened as described above. Uncured sand is removed via the small opening, leaving a venting cavity 710 (
As illustrated in
Returning to
At block 905, cope and drag portions 305 and 307 of an outer mold 300 are formed. The cope and drag portions 305 and 307 are formed from relatively inexpensive materials such as an air-set or pep-set material. Reclaimed material from previous casting operations may be utilized for part of the outer mold 300. The interior of the outer mold 300 is patterned to receive the shell molds 400 and to provide a tight fit with the shell molds 400 so as to support the walls of the shell mold 400 during casting.
A gating system 420 and one or more risers 415 may be patterned in the interior of the outer mold 300. The gating system 420 connects to respective shell molds 400 via an in-gate 505. The in-gate 505 is sized to facilitate separation of the lock 105 from the casting via hammering or other form of impact.
At block 910, the shell molds 400 are inserted into the outer mold 300. At block 912, the outer mold is assembled. Then, at block 915 molten material is poured into a down sprue 320 of the outer mold 300. The molten material may be steel or other suitable material. The molten material flows down through the down sprue 320, through the gating system 420, and into the shell molds 400 via the connections 505. Air and other gases that would otherwise be trapped in the shell mold 400 escape through vent openings 405 and 410 defined in the cope portion 605 of the shell mold 400 and subsequently through vent openings 325 and 330 defined in the cope portion 305 of the outer mold 300. The vent openings 325 and 330 in the outer mold 300 are generally positioned over the vent openings 405 and 410 of the shell mold 400. Other gases escape from the shell mold 400 via the cavity formed in the drag portion 605 of the shell mold 400. These gases exit via an opening 335 in the side of the drag portion 605 of the shell mold 400 and finally vent to the atmosphere via an opening in the side of the outer mold 300.
At block 920, the hardened casting is removed from the mold 300. For example, the mold 300 may be broken apart to expose the casting. The spent mold sand may be broken down and reclaimed to form subsequent molds.
At block 925, the locks 105 are separated from the casting. For example, an impact hammer may be used to break the gating system 420 and the connection 505 off the locks 105.
At block 930, the locks 105 are finished. For example, the side 207 of the lock 105 to which the connection 505 was formed may be ground to a relatively smooth finish. Any remaining material of the gating system may be ground off. The remainder of the lock 105 may then be sand blasted to a smooth surface finish. After sand blasting, the lock 105 may be ready for operational use. That is, the lock 105 may be ready to be inserted into a coupler body 100 without the need for further finishing.
As described, the exemplary embodiment for forming the lock facilitates the manufacture of a lock 105 requiring minimal finishing. For example, a shell mold 400 made of fine silica is utilized to define the lock casting. The shell mold is supported by a relatively inexpensive outer mold formed from and air-set or pep-set material. Multiple locks are capable of being produced by accommodating multiple shell molds within the outer mold. A gating system and risers are formed in the outer mold to distribute molten material to the respective shell molds. Vents formed in the respective molds allow gases to escape thus improving the dimensional accuracy to the lock.
While various embodiments of the embodiments have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of the claims. The various dimensions described above are merely exemplary and may be changed as necessary. Accordingly, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of the claims. Therefore, the embodiments described are only provided to aid in understanding the claims and do not limit the scope of the claims.
