Patent Application
20150367679
The present invention relates railroad car freight wheels, and also to apparatus and casting methods for manufacturing the same. More particularly, the present invention relates to a novel railroad car freight wheel design, and also to a new apparatus and method/process for manufacturing the wheel using vacuum-sealed molding process casting technology. However, it is contemplated that the present innovation is not limited to only railroad wheels, nor limited to only the railroad industry.
Railroad car wheels have significant functional requirements, since they must survive and function safely in difficult environments, under substantial loads/stress, and often while being subjected to sharp impacts. Further, the product and amounts of products and freight they carry can be quite valuable, so any failure within a railcar wheel can be significant. As a result, railroad car wheels may have and be subject to many functional and durability requirements. Concurrently, railcar wheels are made from relatively large castings. Such large casting processes can make it difficult to provide defect-free castings having a quality that is sufficient for purposes of the railroad industry. As a result, despite previous improvements in design and manufacturing/casting techniques and processes, some consider that the basic technology for manufacturing railroad car wheels continues to be based primarily on conventional graphite casting techniques using fundamentally old technology.
In particular, it has been long believed in the railroad industry that an “all sand” mold cannot make railcar wheels. This is partially because most industry experts believe that casting defects, such as inclusion-type defects believed to be inherent in the sand-casting process, made the process uneconomical due to the cost of rework and due to the difficulty of casting the high carbon material used in railcar wheels. The standard “all-silica” sand molds do not promote the rapid solidification of the wheel tread and feed risers as needed. Concurrently, a “standard all sand” mold is not completely stable, making accurate placement of inserts and heat sinks unfeasible, and making highly accurate castings and “directionally cooled” castings extremely difficult.
Known railroad car wheels are cast using “graphite casting” techniques, where bound sand and/or permanent molds are used to receive molten metal for cooling. For example, see Beetle U.S. Pat. Nos. 3,302,919 and 3,480,070. However, known processes, including those using graphite casting techniques, have limitations in terms of costs, very high scrap rates, secondary steps that require considerable processing time and effort and cost, and other limitations. For example, one limitation is that, due to the complicated mechanical process of filling the graphite mold and the size requirements of graphite molds, it is very difficult and/or cost prohibitive to increase the number of cavities in a graphite mold. It is desired to improve upon these methods by providing a system that reduces costs, reduces scrap rates, reduces secondary steps and other influencers of cost, and to generally reduce the cost and time required per wheel produced. Attempts, to date, have not been commercially successful.
Vacuum-sealed molding processes (commonly called “V-processes” or “V-process casting” herein) for casting materials are known. For example, Workman U.S. Pat. No. 4,100,958 discloses basic information about V-processes, including the use of thin plastic film on unbonded sand combined with vacuum to temporarily hold the sand. However, V-processes also have limitations in terms of parameters that are required to minimize scrap, difficulty in reliably holding sand shapes in the V-molding casting process, and the need for several specialized components not usually associated with casting processes (such as the thin plastic film, the unbonded sand, and vented molds). As a result, V-process casting has never been used to manufacture railroad car wheels.
According to a first aspect of the present invention, a cast metal railroad car wheel includes a hub section having an axle bore, a tread section with an axially-extending edge flange, and an uninterrupted annular web that extends between and supports the tread section on the hub section. The web includes opposing disk-shaped surfaces, wherein at least one of the opposing disk-shaped surfaces defines a substantially concave surface that is free of a reversely curved portion.
A second aspect of the present invention is a cast metal railroad car wheel including a hub section, and a tread section with an axially-extending flange that is concentric with and laterally offset from the hub section. An annular web extends from the hub section to the tread section, where the annular web supports the tread section on the hub section. The annular web includes opposing disk-shaped surfaces, wherein at least one of the disk-shaped surfaces is shaped such that a cross section of the annular web taken perpendicular to the annular web defines a concave curve of the at least one disk-shaped surface. The concave curve of the at least one disk-shaped surface includes a radius of less than 35 millimeters. The at least one disk-shaped surface is free of a reversely-curved portion.
Embodiments of the second aspect of the invention can include any one or a combination of the following features:
A further aspect of the present invention is a process for casting a cast metal railroad car wheel. The method includes providing a V-process casting mold with opposing halves, where each opposing half includes unbonded sand adjacent a sand-retaining plastic film having a vacuum application port, and wherein the opposing halves, when positioned together with the unbonded sand held to shape by application of a vacuumed film, define a cavity shaped to form a railroad car wheel having a hub section with an axle bore, a tread section with an axially-extending edge flange and an uninterrupted annular web extending between and supporting the tread section on the hub section. The method also includes providing a fill passage in one of the opposing halves. The method further includes infeeding molten metal through the fill passage and into the cavity. Further, the method includes cooling the molten metal to maintain a shape of the cavity and thus form a cast metal railroad car wheel. The method also includes releasing a vacuum to cause the unbonded sand to fall away from the cast metal railroad car wheel.
Embodiments of this further aspect of the invention include any one or a combination of the following features:
A further aspect of the present invention is a process for casting multiple cast metal railroad car wheels simultaneously. The process includes providing a cast mold with opposing halves, each at least partially filled with sand and that, when positioned together with the sand, define a plurality of cavities each shaped to form a railroad car wheel having a hub section with an axle bore, a tread section with an axially-extending edge flange, and an uninterrupted annular web extending between and supporting the tread section on the hub section. The method also includes providing a fill passage leading into each of the cavities for communicating in-fed molded metal. Also, the process includes infeeding molten metal through the fill passages and through a filter into the cavities. Further, the process includes cooling the molten metal to simultaneously form a plurality of cast metal railroad car wheels.
Embodiments of this further aspect of the invention can include any one or a combination of the following features:
A further aspect of the present invention is a process for casting a cast metal railroad car wheel. The process includes providing a V-process casting wheel with opposing halves, each at least partially filled with unbonded sand, and having sand-retaining-plastic film and a vacuum application port and that, when positioned together with the unbonded sand held to shape by a vacuum and the film, define a cavity shaped to form a railroad car wheel having a hub section with axial bore, a tread section with an axially-extending edge flange, and an uninterrupted annular web extending between and supporting the tread section on the hub section. The process also includes providing a fill passage in one of the opposing halves leading to the hub section, the fill passage including a ceramic tube for directing flow of in-fed molten metal being motivated into the cavity. Additionally, the process includes infeeding molten metal through the fill passage and through a filter into the cavity. The method also includes cooling the molten metal to maintain a shape of the cavity and thus forming a cast metal railroad car wheel. Further, the method includes releasing a vacuum to cause the same to fall away by gravity from the cast metal car wheel.
Embodiments of this further aspect of the invention can include any one or combination of the following features:
A further aspect of the present invention is a process for casting a cast metal railroad wheel. The process includes providing a V-process casting mold with opposing halves, each at least partially filled with unbonded silica sand and having sand-retaining-plastic film and a vacuum application port, and that, when positioned together with the unbonded sand, held to shape by vacuum and the film, define a cavity shaped to form a railroad car wheel having a hub section with axial bore, a tread section with an axial-extending edge flange, and an uninterrupted annular web extending between and supporting the tread section on the hub section. The method also includes providing a fill passage in one of the opposing halves leading to the hub section. Also, the method includes feeding molten metal through the fill passage and through the filter into the cavity, where the molten metal is fed at a temperature of less than about 2,850 degrees Fahrenheit. Additionally, the method includes cooling the molten metal to maintain a shape of the cavity and thus form a cast metal car wheel. Further, the method includes releasing a vacuum to cause the sand to fall away from the cast metal railroad car wheel.
Embodiments of this further aspect of the invention can include any one or a combination of the following features:
Another aspect of the present invention is a process for casting a metal railroad car wheel. The process includes providing a V-process casting mold with opposing halves, each at least partially filled with unbonded sand and having a sand-retaining-plastic film and a vacuum application port and that, when positioned together with the unbonded sand, held to shape by a vacuum and the sand-retaining-plastic film, define a cavity shaped to form a railroad car wheel having a hub section with an axial bore, a tread section with an axial-extending edge flange, and an uninterrupted annular web extending between and supporting the tread section on the hub section. The process also includes providing a fill passage in one of the opposing halves and providing a vent-forming material touching the tread section of the cavity, the vent-forming material being one of a tubular shape and a porous material. The process also includes infeeding molten metal through the fill passage and into the cavity while venting through the vent-forming material. Additionally, the process includes cooling the molten metal to maintain the shape of the cavity and thus forming a cast metal railroad car wheel. Further, the process includes releasing a vacuum to cause the sand to fall away by gravity from the cast metal railroad car wheel.
Embodiments of this further aspect of the invention can include any one or combination of the following features:
A further aspect of the present invention is a process for casting a cast metal railroad car wheel. The process includes providing a V-process casting mold with opposing halves, each at least partially filled with unbonded sand and having sand-retaining-plastic film and a vacuum application port and that, when positioned together with the unbonded sand held to shape by a vacuum and the sand-retaining-plastic film, define a cavity shaped to form a railroad car wheel having a hub section with an axle bore, a tread section with an axially-extending edge flange, and an uninterrupted annular web extending between and supporting the tread section on the hub section. The method also includes providing a fill passage in one of the opposing halves and providing a cast-cooling-accelerator material touching the tread section of the cavity. The process also includes infeeding molten metal through the fill passage and into the cavity. Additionally, the process includes cooling the molten metal to maintain a shape of the cavity and thus form a cast metal railroad car wheel, including accelerating the cooling of the cast metal railroad car wheel via the cast-cooling accelerator material. Further, the process includes releasing the vacuum to cause the sand to fall away by gravity from the cast metal railroad car wheel.
Embodiments of this further aspect of the invention can include any one or a combination of the following features:
A further aspect of the present invention is a process for casting a railroad wheel. The process includes providing a V-process casting mold including unbonded sand defining at least one cavity shaped to form a railroad car wheel. The process also includes filling the cavity with molten metal. Further, the process includes cooling the molten metal to thus form a metal railroad car wheel casting.
Embodiments of this further aspect of the invention can include any one or a combination of the following features:
A further aspect of the present invention is a cast metal railroad wheel that includes a hub section with an axle bore, a tread section with an axially-extending edge flange, and an uninterrupted annular web extending between and supporting the tread section on the hub section. The annular web includes opposing disk-shaped surfaces. At least one of the disk-shaped surfaces, when cross-sectioned through the hub and tread sections, defines a cross-sectional shape having a radius of less than 35 millimeters.
Embodiments of this further aspect of the invention can include any one or a combination of the following features:
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.
In the drawings:
A prior art railroad car wheel 10 (
The present cast metal railroad car wheel 50 (
Referring to
Additionally, as illustrated in
Referring again to
A significant part of the present innovation is the use of a vacuum-process (“V-process”) casting to cast railroad wheels. V-process casting is known, and is described in various publically available ways, for example, Workman U.S. Pat. No. 4,100,958, the disclosure of which is incorporated herein in its entirety for its teachings.
A vacuum-sealed molding process (V-process), illustrated in
Due to a compact size and other characteristics of V-process casting, as described hereafter, it is contemplated that molds can be multi-cavity (shown in
One optional feature that may be used in the V-process casting process is the use of argon shrouding to reduce oxygenation and micro porosity. Notably, micro porosity is one of the most critical factors in a life cycle of a railroad wheel. Oxygenation (occurring due to the presence of oxygen) can be problematic when molten metal 70 is held in a melting pot, and/or when molten metal 70 is being poured. By using argon shrouding, oxygenation is reduced, leading to less micro porosity. Argon gas can be used to assist by reducing a presence of oxygen. Other shrouding gases can include, but are not limited by, nitrogen, other inert gases, combinations thereof, and others. Notably, V-process casting processes naturally reduce oxygenation due to a lower temperature of the molten metal 70. Shrouding can be used to further improve a quality of castings, which can be important in railroad wheels, due to their size and due to safety/functional regulations.
The V-process utilizes a pattern secured to a carrier box, with a number of narrow passageways leading from the hollow interior of the carrier box to the surface of the pattern. A heated plastic film 85 (about 0.01 millimeters thick) is draped over the pattern and caused to cling to the surface thereof by reducing the pressure in the interior of the carrier box to sub-atmospheric/vacuum (by connection to a suction pump). A mold box in the form of the V-process casting mold 80 is located around the periphery of the pattern and loaded with unbonded sand 83 which is compacted by vibration. A further heated plastic film 86 is placed on the exposed surface of the body of sand which is then subjected to sub-atmospheric pressure by virtue of a vacuum source 90, such as a suction pump, being connected to the mold box which has a perforated wall in contact with the body of sand. With this body of sand maintained at a sub-atmospheric pressure (of about 0.5 atmospheres) the shape of the sand mold 60 is maintained in a hard condition and can be removed from the pattern. Upper and lower mold halves 81, 82 produced in this manner can be subjected to pouring of molten metal 70 immediately after the opposing mold halves 81, 82 are brought together and the sub-atmospheric pressurizing of the two sand molds 60 is maintained until the cast molten metal 70 has cooled sufficiently to be released.
The various embodiments of the V-process casting, as illustrated in
As illustrated in
It is noted that while certain specific dimensional details of the web 53 (including the hub section 51, the tread section 52 and the web 53, including thickness and details of the sweep) are included herein, such details are not necessary for an understanding of the present invention by a person skilled in the art of railroad car wheel design. The dimensions and structural strengths are important, but particular dimensions are not needed for an understanding. For example, as illustrated in
Referring now to
As illustrated in
Referring now to
It is contemplated that infeeding molten metal 70 will be fed as fast as possible and at a relatively-low molten temperature through the fill passage 97 into the cavity 91. For example, it is contemplated that the molten metal 70 (i.e., the metal necessary to form a railroad car wheel 50) will be fed at a rate of at least about 50 kilograms per second (or slightly slower depending on requirements of an overall system, such as 45 kilograms per second) and fed at a temperature of less than about 2900 degrees Fahrenheit (or more preferably less than about 2850 degrees Fahrenheit, or most preferably at about 2825 degrees Fahrenheit). There is a possibility that the temperature of the molten metal 70 could even be poured lower than about 2825 degrees Fahrenheit. Notably, a temperature of approximately 2825 degrees Fahrenheit is only about 95 degrees Fahrenheit above the solidification temperature of molten metals 70 typically used in casting railroad car wheels 50 (2730 degrees Fahrenheit). It is also contemplated that the molten metal 70 could be fed at a temperature of less than 2825 degrees Fahrenheit. In various embodiments, the molten metal 70 can be fed at a temperature of approximately 60 degrees Fahrenheit above the solidification temperature of molten metals 70, or about 2790 degrees Fahrenheit. This closeness of the temperature of the inflow molten metal 70 to solidification temperature results in a considerably shorter cooling period. Such a short cooling period reduces cooling times substantially sooner than a conventional “similar” graphite molding process. For example, V-process casting can form and release the vacuum source 90 in a time period of five minutes, which not only speeds the overall cycle time, but also allows the wheel 50 freedom to cool and shrink without restriction, thereby reducing internal stress. This fast inflow rate of the molten metal 70 and decreased temperature of the molten metal 70 is made possible using sand molding technology, such as that used in V-process molding. As discussed earlier, use of sand molds 60 is very contrary to the traditional thinking of experts in the casting industry for railroad wheels which uses only graphite moldings, where inflow temperatures must be higher, when compared to V-process casting temperatures, and cooling times can be 20 minutes or longer. However, the disclosed V-process casting works well since faster inflow speeds of the molten metal 70 cause the molten metal 70 to reach a desired location within the cavity 91 before the fill passages 94 begin to breakdown and/or distort (as in graphite molding). Also, the molten metal 70 can be moved to reach its desired destination in the mold cavity 91 before cooling starts to set in that might cause distortion near the end-filled stage of filling a casting cavity 91.
Referring now to
Referring again to
Persons skilled in the art will recognize a variety of additional modifications are possible, while still staying within a scope of the present invention. For example, as illustrated in
The present innovation using V-process technology as described herein includes novel aspects in at least the following areas: 1) a new wheel cross section with a single curve or “single-sweep” rib, 2) first railroad car wheel cast using V-process casting, 3) first process where multiple cavities can be cast in a single casting operation, 4) first V-process casting method using A) ceramic infill tile (tubes), B) emphasizing pour casting fast and with “cold” molten material, C) special venting system for V-process, E) plastic risers, F) cluster handling system, G) providing 65%+ yield (or more preferably 80% yield, or most likely 85% yield if properly controlled) on casting wheels, H) one sand type for cores and molding. The present innovation is believed to provide molding times that are faster, more efficient (such as through use of multiple cavities in a single mold), and with far greater yield (i.e. greatly reduced scrap and defective castings) such as 65% or greater yield (or more preferably 80% yield, or most likely 85% yield if properly controlled) on cast railroad wheels 50.
It is contemplated that any of the individual features of the embodiments of the railroad car wheels 50 and 50A as well as the various steps and features of the embodiments of the V-process casting can be combined with any other feature or features of the various embodiments of the railroad car wheels 50, 50A and the V-process casting steps and features.
It is to be understood that variations and modifications can be made on the aforementioned structure without departing from the concepts of the present invention, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US14/68613 | 12/4/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61912888 | Dec 2013 | US |
