Electric heating – Metal heating – Rail bond
Reexamination Certificate
1999-07-19
2001-03-27
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
Rail bond
C219S13700R, C238S164000
Reexamination Certificate
active
06207920
ABSTRACT:
The present invention relates to a method and system for welding the spaced ends of steel rails and, more particularly, welding two spaced railroad rails in the field by an arc welding process.
While the invention will be illustrated and described in detail herein in connection with the welding of railroad rails, it will be appreciated that the invention is applicable to the welding of other types of rail, such as crane rail and other rail for supporting wheeled vehicles or apparatus.
INCORPORATION BY REFERENCE
Through the years, a tremendous amount of effort have been devoted to joining spaced railroad rails by some type of butt welding process. Such efforts have generally proven costly and unsuccessful, due to limitations of the processes used, the required time for accomplishing the welding process, the cost of performing the welding process and/or the inability to obtain successful, long-lasting joints. In Devletian U.S. Pat. No. 4,429,207, the most common electric arc welding process is illustrated wherein the electroslag welding procedure is used to fill the gaps between spaced railroad rails in the field. This process involves filling the gap between the rails with a pool of molten metal covered by an appropriate slag. To prevent the mass of molten metal from flowing from the gap between the rails, side molds and a bottom member are provided that creates a large protrusion of metal below the rails and extending from the actual gap. This prior patent illustrates a modified electroslag welding (ESW) technique which can be used in the field, where the rails cannot be turned upside down for normal welding. The advantage of electroslag welding over the normal thermite technique normally-used today are explained. In this disclosure, the thermite process is revealed to have substantial deficiencies, which are known to result in numerous failures in the field. This patent is incorporated by reference herein to describe the electroslag welding process even though the process has been abandoned as a practical process because of its obvious inefficiencies and inability to obtain uniform and successful welds in the field. Indeed, this process must deal with large masses of molten metal which presents problems in the field.
As an alleged advantage over the electroslag process, the combination of the electroslag technique and the gas shielded arc welding technique is disclosed in Karimine U.S. Pat. No. 5,175,405. This patent employs an automatic welding process for butt welding the spaced ends of railroad rails using a gas shielded arc welding process in combination with an electroslag process. The deficiencies of the normally-used thermite welding technique and the previously attempted enclosed arc welding technique are discussed in detail. As indicated, the thermite technique produces joints which have an unacceptably high failure rate; however, because of the economics, the time and inability to obtain an arc welding process of success, this thermite process is still the process of choice in the field. A disadvantage of the continuous arc welding technique discussed, as in this patent, is the inability to start the arc and the need for starting and stopping the arc as the welding process is performed. To overcome some of these disadvantages, this patent discussed the use of a submerged arc process at the bottom portion of the gap between the rails to start positively the welding process for subsequent and continuous arc welding. Karimine U.S. Pat. No. 5,175,405 is incorporated by reference herein to disclose the deficiencies of the thermite process, the enclosed arc welding technique and the submerged arc technique, all of which have been attempted and have not been successful in the field. The solution suggested by Karimine U.S. Pat. No. 5,175,405 is the use of a gas shielded arc welding technique in combination with an electroslag welding process wherein the gas shielded arc welding technique is used at the base of the gap to overcome the disadvantages of the previous attempts to use total electroslag welding. However, this process of using a gas shielded arc at the bottom of a gap could not be successful in the field due to the fact that there is no technique that will ensure accurate starting and depositing the first layer of the filler metal at the bottom of the gap.
The two patents incorporated by reference illustrate the deficiencies of the prior art to which the present invention is directed wherein a combination of various types of arc welding processes have been attempted without success. Consequently, the admittedly deficient thermite process is the only process used extensively for providing molten metal between the spaced rails for joining such rails in the field.
BACKGROUND OF THE INVENTION
Railroad rails must be installed and repaired by joining ends of the rails while they are in use or assembled for use in the field. The joining process results in a joint between the rails which has a high strength, can be adjusted metallurgically, will not crack and can be economically formed in a very short time. As a criteria for such welding process, the process must be performed in substantially less than 45 minutes or such process will cause a delay or rerouting of train traffic. Two processes are now used for joining the rails in the field. The first process is the thermite technique wherein the spaced rails are surrounded by an appropriate sand mold and steel is melted and poured into the mold to fill the gap between the spaced rails. As the molten metal solidifies, the rails are joined; however, this process, which is universally used, has a failure rate that has been reported to be as high as 75%. In addition, the rails must be melted by the molten steel poured into the gaps between the rails. This melting requirement is not consistently met and also contributes to the failure of the joints produced in the field by the thermite process. To drastically decrease the deficiencies of the universally used thermite process, wherein steel is cast into the gaps between the rails, the ends of the rails may be joined by a flash butt welding process where the ends of the rails are driven together by tremendously high forces while electricity is passed between the rails. This causes the ends of the rails to become molten and pressure welded together. This process drastically reduces the failure rate of the joint to less than 10%. However, the flash butt welding process is best performed on rails in a manufacturing facility where the rails are not fixed on ties and can be forced together by stationary hydraulic equipment. To overcome the disadvantage of the universally used thermite process, the flash butt welding process has been modified for use in the field. However, the time for the welding process is substantially higher than the thermite process, since the rails must be stretched during the hydraulic forcing step, which step requires disconnecting one or both of the rails from the ties. This manual procedure must be reversed after the welding process has occurred, which is extremely time consuming.
Flash butt welding of rails consumes a portion of the rails which causes difficulties after the welding process has been completed. Also, sections of rails may have to be spliced into the rail to provide the necessary rail material for the weld.
In addition, it is deficient to transport the hydraulic equipment needed to create the tremendous pressure between the rails to remote locations as required in the field. The butt welding process also produces a flash around the periphery of the joined rails which must be sheared off and then ground to allow a smooth operation and also to prevent stress concentrations in the joint during use. Even though the flash butt welding process drastically reduces the rate of failure of the joints made in the field, the thermite process is still used because it can be done rapidly by merely putting a mold around the gap between the spaced rails. The process does not require large hydraulic equipment and is relatively inexpensive. The failure rate is a
Lincoln Global Inc.
Shaw Clifford C.
Vickers Daniels & Young
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