Electric heating – Metal heating – By arc
Reexamination Certificate
2000-10-19
2002-06-18
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C219S054000, C219S124340
Reexamination Certificate
active
06407364
ABSTRACT:
INCORPORATION BY REFERENCE
Through the years a tremendous amount of effort has been devoted to joining spaced railroad rails by some type of butt welding process. Assignee of the present application has issued patents Morlock U.S. Pat. No. 5,773,779 and Morlock U.S. Pat. No. 5,877,468, which patents are incorporated by reference herein as showing the background of the invention. These patents relate to an electric arc welding method and system for joining the ends of two spaced rails utilizing a backing between the flat bases of the rails so that the root pass or first welding layer is deposited on the backing plate spanning the gap between the rail ends as the plate is consumed. These two patents disclose in detail the total welding process above the root pass for initially joining the ends of the railroad rails and closing the gap between the rail ends. The details of such welding process do not form a part of the invention need not be repeated.
BACKGROUND OF INVENTION
When depositing the first layer of molten metal onto the top of the backing plate between the bottom ends of the rails certain difficulties have been encountered, these difficulties affect the appearance of the weld which is to be made in the field in a very short time. The advancing welding wire used in the root pass has heretofore been moved by a robotic control in a normal weave pattern where the welding wire moves back and forth between the rails as the wire progresses along the backing plate in the bottom of the gap. This procedure causes the arc to blow through the backing plate resulting in irregular undersurface for the root pass and certain malformations in the root pass. Such blow through occurs more easily when the wire is moved too rapidly and pulls away from the weld puddle. As the robotic control moves the electrode in a robotic weave axially along the root of the gap, the arc is not pointed toward the intersection between the end of the rail and the lower backing plate. This further results in certain irregularities at this intersection. This problem is accentuated due to the fact that the backing plate is a relatively thin sheet whereas the two spaced rails are massive pieces of metal. The arc blow through of the backing plate and the inability to actually have a blow through at the intersection between the plate and rail ends has presented substantial inconsistencies in the root pass of the previously performed process. These problems affect the appearance of the root pass which is a disadvantage when attempting to use this new welding process as a replacement for prior butt welding and arc welding processes used in the field.
THE INVENTION
The present invention is a method and system for depositing molten metal from an advancing welding wire controlled by a robot to form a root pass of weld metal in the bottom of a gap between the railroad rails which gap is closed by a backing plate that is between the rails and it will be described with particular reference thereto; however, the invention has broader applications and may be used in welding the ends of railroad rails having various types of lower backing plates or in other welding operations where a root pass between two heavy metal members is deposited on the top of a relatively thin backing plate or bridging element. The present invention produces a root pass which overcomes the disadvantages heretofore experienced in producing the root pass of railroad rails by melting the backing plates as metal is deposited along the backing plate.
In accordance with an aspect of the present invention, the normal robotic weave pattern heretofore used in the gap between the rails is modified to a pendulum weave wherein the advancing welding wire controlled by a robotic mechanism is swung back and forth between the two rail ends. In this manner, the welding procedure followed by the welding wire is controlled to first swing the wire between an angle pointing toward one rail end to an angle pointing toward the other rail end. After this swinging action, the robotic mechanism moves the welding wire as it points toward the intersection between the backing plate and a rail end in a longitudinal direction. This move is a short distance, often in the range of 2-3 mm when the welding wire is about 1.6 mm. Thereafter, the swinging action is accomplished in the opposite direction bringing the welding wire to a position pointing toward the opposite intersection between the backing plate and the opposite rail end. When in the second angular position, the welding wire is again shifted longitudinally to complete a cycle of movement. The cycle is repeated to define a selected path extending along the backing plate to deposit the root pass as the backing plate is melted at least on its upper surface. The backing plate defines a barrier that produces a smooth undersurface for the resulting joint created by the root pass. In accordance with this aspect of the invention, the robotic mechanism maintains the spacing of the wire holding torch above the backing plate at a constant distance during the swinging action of the welding wire carried by the torch. By using the pendulum action and maintaining a constant height above the backing plate, the welding wire produces a consistent root welding pattern.
The selected path of the welding torch is a square weave. In the path, the torch or welding wire moves perpendicularly to the end walls of the rails. This movement is accomplished by an angular swinging action of the torch directing current to the welding wire for the welding process. Upon reaching the side wall oft he rail, the torch maintains its angle pointed toward the joint between the plates and rail end and then moves parallel to the side wall of the rail. After moving a short predetermined distance along the rail end, the robotic mechanism stops the torch carrying the welding wire. Thereafter, the torch and welding wire is pivoted or swung back toward the opposite rail. When the torch reaches the opposite rail, the angle of the torch carrying the welding wire is equal but opposite to the torch angle at the other side. Thereafter, a short forward movement is made by the torch and the cycle is repeated to create a selected welding pattern or path. By using this square wave, swinging or pendulum welding action, together with a maintenance of the height of the torch from the backing plate, advantages of the various aspects of the present invention are obtained.
In accordance with another aspect of the invention, the thin metal insert or consumable backing plate used to support the root pass as it is laid in place is held below the ends of the rail by protruding tabs and is supported on a ceramic tile. The backing plate spans the gap between the two objects being welded which, in the preferred embodiment, are the ends of railroad rails. By using a thin consumable backing plate, there is a possibility of arc blow through whereby the arc penetrates completely through the backing plate. Such arc blow through or blow through hole is not desirable as the wire moves transversely across the backing plate. The structural defect of a blow through is corrected by using the present invention. The disadvantage of this blow through is that it tends to create a cutting action as the torch swings transversely across the insert. To prevent such blow through, it is necessary to keep a puddle of metal under the arc as it is advancing between the rails. When the torch is moved too rapidly and is ahead of the weld puddle or the weld puddle flows away from the arc, the propensity for an unwanted arc blow through is substantially increased. Thus, it is advantageous to prevent the cutting action of a blow through by maintaining a wire movement speed along the selected path at a rate where a molten puddle is maintained between the arc and the plate being consumed. This can not always be done; therefore, the present invention provides an arrangement for detecting and compensating for unwanted arc blow through as the electrode or wire pivots between the ends of the rails. Blow through is detected by
Lincoln Global Inc.
Shaw Clifford C.
Vickers Daniels & Young
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