Patent Application
20140366771
The present invention relates generally to the construction of rail cars, more particularly tank cars for transporting liquids and gases.
Railway tank cars generally comprise a tank supported by a railway undercarriage for rolling transport along a rail line. The tank typically includes an elongated cylindrical shell closed by a pair of end caps fixed at opposite ends of cylindrical shell.
A traditional method of manufacturing the tank's cylindrical shell involves making a plurality of shorter cylinders, and combining the shorter cylinders end-to-end to provide an elongated cylindrical tank shell. Each shorter cylinder is formed by bending a rectangular piece of plate material into a cylinder, and welding the adjoining end edges of the bent plate together. Several of these shorter cylinders are combined end-to-end by circumferential weld seams between adjacent shorter cylinders. An example of this type of tank construction is disclosed in U.S. Pat. No. 8,324,527 (Hybinette et al.). This traditional method is time consuming, involves difficult circumferential welding operations requiring elaborate tooling and fixtures for same, and is plagued by quality control challenges related to out-of-round variation in the shorter cylinders.
In view of these problems, various tank constructions utilizing spiral weld seams have been proposed. For example, spiral weld seems are taught in U.S. Pat. Nos. 4,664,307 (Curry et al.) and 6,875,942 (Coughlin et al.). In such constructions, coiled steel plate is unwound into a strip that is fed into a mill that rotates the strip into an appropriate diameter cylinder and applies a spiral or helical weld seam. The mill is complex, and all fabrication steps for the cylindrical shell must be performed at the same location.
The present invention provides a new and very economical approach to manufacturing a cylindrical shell for the tank of a railway tank car utilizing roll-forming technology and straight longitudinal weld seams.
In accordance with an embodiment of the present invention, the tank of a railway tank car comprises a cylindrical shell having a longitudinal axis and a uniform cross-sectional shape in a plane normal to the longitudinal axis, wherein the cylindrical shell includes a plurality of elongated segments welded together along weld seams extending parallel to the longitudinal axis of the cylindrical shell. Each elongated segment forms a portion of the cross-sectional shape and is formed by passing a flat piece of metal plate stock material through a roll-forming machine configured to progressively bend the piece of stock material. By way of non-limiting example, the uniform cross-sectional shape may be circular, and each elongated segment may be an arc in the circular cross-section. In one embodiment, exactly three identical elongated segments, each defining an arc of 120 degrees, are welded together along adjacent longitudinal edges to form a cylindrical shell having a circular cross-section.
The invention will be described in detail below with reference to the accompanying drawing figures, in which:
Reference is made also now to
In the embodiment depicted in the figures, elongated segments 22 are identical to one another, which is advantageous for production efficiency. Cylindrical shell 16 may comprise exactly three elongated segments 22, and the arc formed by each segment 22 is 120 degrees. However, the number of elongated segments may be as few as two or greater than three.
There are competing design considerations in choosing the number of elongated segments 22. Using fewer segments 22 reduces the number of weld seams 24 needed to assemble the segments into a unitary cylindrical shell 16. However, using fewer segments 22 increases the width requirement of steel plate stock for a given shell diameter, and also imposes greater demand on roll-forming machinery to provide additional angular extent of the formed arc in the case of a circular cross-sectional shape. For example, if two identical segments are used instead of three, each segment must form an arc of 180 degrees. Advantageously, only two weld seams 24 would be required instead of three weld seams, meaning fewer welding operations and a reduction in the total length of weld seam that must undergo quality control inspection. However, this also means that the width of plate stock used to manufacture elongated segments 22 would need to be 50% greater, and further roll-forming stations with wider spacing would be needed in a roll-forming machine to obtain the increased arc angle. As a consequence, the footprint of the roll-forming machine would grow and the material handling machinery used to load plate stock into the roll-forming machine would have to be capable of handling the increased weight of each piece of plate stock material.
Keeping the above considerations in mind, the inventor has determined that using exactly three elongated segments 22, each having an arc of 120 degrees, provides an optimal design for most tank sizes used in conventional railway tank cars. Nevertheless, the invention is not confined to an embodiment comprising exactly three segments 22 each having an arc of 120 degrees.
A method of manufacturing cylindrical shell 16 of railway tank car 10 will now be described with further reference to
In step S2, each piece 30 is passed longitudinally through a roll-forming machine 100 comprising a plurality of longitudinally spaced roll-forming stations 102 configured to progressively bend the piece 30 of stock material into an elongated segment 22 having a predetermined cross-sectional configuration, in this illustrative case an arc-shaped configuration. In this manner, a plurality of the arc-shaped elongated segments 22 are formed, each elongated segment having a pair of longitudinal edges 32. The number of stations 102 and their individual configuration will depend on several factors, including the cross-sectional shape and diameter of tank 12, the number of elongated segments 22 used to form cylindrical shell 16, and the thickness of plates pieces 30. In a current embodiment using three elongated segments of ½-inch thick plate to fabricate a circular tank having a diameter of 123½ inches, approximately twenty-two roll-forming stations 102 may be provided to make up roll-forming machine 100.
Step S3 is welding the plurality of elongated segments 22 together along their respective longitudinal edges 32 to make the cylindrical shell. As shown in
Embodiments of the present invention are described in detail herein, however those skilled in the art will realize that modifications may be made. By way of non-limiting example, for certain plate thicknesses, coiled plate material may be unwound and fed into roll-forming machine 100, and the roll-formed segments 22 may be cut to length after roll-forming. Such modifications do not stray from the spirit and scope of the invention.
10 Railway tank car
12 Tank
14 Undercarriage
16 Cylindrical shell
18 End caps
20 Longitudinal axis of cylindrical shell
22 Elongated segments
24 Weld seams
30 Pieces of metal plate stock material
32 Longitudinal edge
100 Roll-forming machine
102 Stations of roll-forming machine
The present application claims benefit of U.S. Provisional Patent Application No. 61/834,174 filed Jun. 12, 2013, the entire disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61834174 | Jun 2013 | US |
