1. Field of the Invention
This invention relates, in general, to railroad cars and, more specifically, to a cold formed center sill and its method of manufacture.
2. Summary of the Prior Art
The center sill is the primary structural member of the underframe of a railcar. It is subjected to the buff and draft forces created during operation of the railcar and normally extends as a continuous member along the length of the car body. In the past, center sills have possessed many different cross-sectional configurations depending on the type of railcar and other considerations. Center sills have been in the shape of hat designs, C-sections and other configurations. Regardless of its particular shape, it is well known to form a center sill by welding a plurality of hot rolled flat pieces or hot rolled sections together as a unit along its substantial length. The use of numerous welds to manufacture center sills presents several long-existing problems. Because numerous welds are needed, the reliance on this process to fabricate a finished center sill is inefficient from both a cost and productivity standpoint. The application of the welds along the lengths of the pieces being joined as a center sill is labor-intensive and cannot attain high-speed production. In addition, the application of multiple welds heats the material being joined and results in heat distortion and warpage. Warpage creates deviations in the straightness or acceptable tolerances of the center sill being formed. As a result, further physical steps are needed to finish the welded center sill unit and conform it to acceptable tolerances in camber, sweep and twist to be suitable for use in a railroad car. Existing center sills are subject to crippling of the webs which requires thicker cross sections at critical structural areas. Furthermore, hot rolled sections do not always result in the desired tolerances for the finished camber of the sill. As an additional important consideration, a welded center sill is an inherently heavy structure due to its design and fabrication technique. Accordingly, it is desirable in the prior art to provide an improved, lightweight center sill in which the necessity of a plurality of welds or other securement techniques are eliminated.
It is an objective of this invention to provide an improved center sill capable of being cold formed into a straight member having close tolerances. The various configurations of the several embodiments of the invention are cold formed at a plurality of cold rolling stations from a plate or sheet of coiled steel. The flat sheet undergoes progressive formation at each rolling station whereby drawings of the steps of shaping developed by each roll station, when superimposed, form a flower diagram to assist the roll tooling designer. The center sills herein disclosed can be formed on a continuous basis without interruption between separate center sills. One unique cold forming process of the invention allows center sills having a thickness up to ⅝ inch to be formed without the use of welds as in the prior art. Because the bent sections forming the shape of the center sill are cold worked numerous times during working, the material is strengthened to resist crippling and produce a stronger cross section without thicker sections or reinforcing material. The center sills are open at the bottom to provide desired access within the center sill body. Some of the configurations of the center sill include extra structural features that provide enhanced strength characteristics without adding a significant weight.
A complete understanding of the invention will be obtained from the following description when taken in connection with the accompanying drawing figures wherein like reference characters identify like parts throughout.
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The top wall 10 and pair of side sections 12 are joined together at right angles by upper curved sections 14 having curved outer surfaces 14a and curved inner surfaces 14b, the latter being formed about a common radius such as, for example, 15/16 inch. The bottom sections 16 of the center sill 6a are inwardly formed horizontally at right angles to the side sections 12 through curved connecting sections 18 having curved outer surfaces 18a and curved inner surfaces 18b, the latter being of constant radius such as, for example, approximately 15/16 inch. The bottom sections 16 terminate with a free end 20 to form a longitudinal opening 22 through which access within the center sill 6a is provided. By way of example, the bottom sections 16 forming the bottom portions of the center sill may each extend approximately 4 inches from the side sections 12 and create the bottom opening 22 having a width of approximately 5 to 6 inches. The center sill 6a preferably possesses an average yield strength throughout its length of at least 70,000 PSI and an average tensile strength of at least 80,000 PSI to easily meet all strength requirements for the center sill, but these values may be as low as 50,000 PSI and 65,000 PSI, respectively. The curved sections 14 and 18 are cold worked numerous times during the cold rolling process. As a result, the material is cold hardened and strengthened at sections 14 and 18 as compared to its original unformed state. The resulting cross section does not require thicker sections or added material as in the prior art and provides a lightweight, high-strength member.
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In the formation of the embodiment of
After the final station in rolling mill 74 is passed, the formed single piece center sill is delivered to a cutoff press 76 which cuts the center sill to the desired length without stopping the rolling process. The separated center sill then is conveyed to a conveyor 78 on which the profile of the center sill is inspected to determine whether its dimensions are correct and whether acceptable tolerances of camber, sweep and twist have been maintained. The cold forming process of the invention attains significantly close tolerances in the final product of the center sill by a process that is capable of high production with minimum labor. This capability provides a vastly superior product with economical manufacture and a beam structure of high quality and precise shape. The single piece center sill of the invention is lightweight, being approximately 1,000 pounds or more lighter than conventional welded sills.
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The two-piece cold formed center sill 6d maintains many of the advantages of the one-piece embodiments 6a, 6b and 6c described above. The cold forming process provides sections with significantly less variance from the specified section than the prior art hot rolled sections. Additionally, the use of a single weld minimizes the assembly time associated with prior multi-weld configurations. The center sill 6d also exhibits a significant weight savings over the known prior art center sills. The two-piece center sill 6d is advantageous where the specific rolling mill 74 cannot accommodate the complete center sill cross section. A rolling mill 74 may not contain enough stations to complete the entire cross section. In this case, the rolling mill can form two cold formed halves to form the center sill 6d of
Superior strength characteristics of the center sill of the invention are attained by using a steel such as an ASTM A607, grade 70 or an ASTM A935, grade 70 for a plate or sheet having a thickness ⅜ inch. With a thicker sheet of material, such as ½ inch, an ASTM A607, grade 50 steel may be used with coiled plate or an ASTM A572, grade 50 with a coiled sheet. One suitable ASTM A607, grade 70 steel for thicknesses of ⅜ inch is known as Type 1, sold under the trademark Stelmax 70™. Stelmax 70™ has an expected yield strength of 76 KSI and a tensile strength of 86 PSI. Other steels of the type described demonstrating similar properties may be used with the invention.
Some of the advantages of the present invention are highlighted with a comparison of the present invention with a standard center sill.
Additionally, a 3K frame Bethgon Coalporter® railcar utilizing the center sill ⅜ Inch 6d was loaded to 286K gross rail load and standard AAR loads and load factors were applied. This was compared to the same type of railcar utilizing a standard center sill. The margin of safety against yield failure of the material in the center sill was greater for center sill 6d.
The above comparison illustrates that the cold formed center sills of the present invention offer significant advantages over the prior art center sills without detrimental drawbacks. It will be apparent to those of ordinary skill in the art that various changes may be made to the present invention without departing from the spirit and scope thereof. Consequently, the present invention is intended to be defined by the appended claims.
This is a continuing application of U.S. Continuation-In-Part patent application Ser. No. 08/953,337 (U.S. Pat. No. 6,119,345) filed on Oct. 17, 1997, which is a continuation-in-part of U.S. patent application Ser. No. 08/712,369 (U.S. Pat. No. 6,769,366) filed on Sep. 11, 1996.
Number | Name | Date | Kind |
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5367958 | Weiss et al. | Nov 1994 | A |
Number | Date | Country | |
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Parent | 08953337 | Oct 1997 | US |
Child | 09664118 | US |
Number | Date | Country | |
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Parent | 08712369 | Sep 1996 | US |
Child | 08953337 | US |