Electric heating – Metal heating – By arc
Reexamination Certificate
2002-10-15
2004-03-30
Paschall, Mark H. (Department: 3742)
Electric heating
Metal heating
By arc
C219S121580, C219S121480, C219S121340, C219S124220
Reexamination Certificate
active
06713710
ABSTRACT:
TECHNICAL FIELD
This invention relates to the field of metal joining, and more particularly, to a trackless movement apparatus and full-penetration method for welding of a butt joint of large steel structures.
BACKGROUND OF THE INVENTION
Arc welding technologies are widely used in modern manufacturing and industrial processes. However, in practical applications, conventional methods of arc welding have presented following drawbacks. First, in most case, multi-pass welding and beveling of the plate edge is used to complete a butt joint of thick steel plates of large structures, which increases welding time and cost. Second, mechanized equipment for welding of large steel structures is more complicated and expensive. Third, conventional automatic arc welding equipment normally employs a track for making a long weld, hence seam tracking plays a critical role in generating sound welds in many automatic welding applications. The seam tracking technique, however, cannot be widely used in welding production currently due to its low reliability and high cost.
To perform full penetration welding, it is normal practice to make butt welds from both sides of the plates. However, in large steel construction the ideal is to complete butt welds from one side, for example, it is difficult to turn a ship over for welding the second side. This procedure has led to the development of welding technologies of full penetration weld from one side. As widely known, full penetration weld from one side for a butt joint could be typically achieved in two ways.
First, methods have been proposed to sense joint penetration, such as infrared sensing, ultrasound, and pool oscillation primarily for gas tungsten arc welding process or measuring keyhole to control weld penetration for plasma arc welding process. However, these sensing technologies for welding penetration have not being used in welding production because of their sensitivity for welding conditions. For example, when weld joint gap is not constant in an entire weld line sense and control of weld penetration will be very difficult for an automated arc welding process.
In the second method for full penetration welding, a weld backing made from copper, with its length identical to the length of the weld line to be welded and its configuration fitting to the shape of the weld line, is used to hold against the underside of the weld zone where a groove is formed. In this condition, an arc welding torch or welder is moved along the weld line to weld throughout the entire length of the weld line. After completion of welding, the weld backing and its supporting members are removed.
In another application of weld backings, a number of ceramic weld backings in adequate shapes with adhesive aluminum foil adhere to the underside of the groove face of the weld zone along the entire weld line. Then, an arc welder is moved to weld throughout the entire length of the weld line, and after completion of welding, the ceramic weld backings are removed.
There are, however, a number of flaws with these conventional weld backings. For the weld backing made from copper, the length of the weld backing should be the same as the length of the weld line and the weld backing having the same curvature as that of the weld line is required in the case of a curve of weld line. Therefore, general-purpose ability of such a weld backing is poor for straight or curve weld lines and the cost of the material, processing and application increases when the weld line becomes longer. In addition, the installation and removal of such weld backings in practical welding production is difficult.
Another attempts have been proposed to overcome these drawbacks. For example, U. S. Pat. No. 5,590,829 describes a mobile weld backing mounted on a wheeled carriage to place at the underside of the workpiece during welding and to provide a moveable weld backing system along a weld line to perform full penetration welding of a box-shaped workpiece. By mounting a backing on a wheeled carriage, the foregoing flaws can be improved to some extent. However, the prior art has still some drawbacks in practical applications. In the invention, because the welder in top side of a weld line and the wheeled carriage mounting a weld backing in the underside separately travel along an entire weld line the control of the movement of the welder and the wheeled carriage with a backing synchronously is complicated. Another disadvantage of the invention is poor in general-purpose application because the method can be only used in welding of box-shaped workpiece.
Consequently, the obvious expense and complicated equipment and operation of the conventional arc welding processes have been forcing fabricators to explore new technologies for possible cost savings, increase of productivity, and simplification of machine and operation in welding of large steel structures.
Therefore, in order to overcome the above-described flaws accompanying conventional arc welding technologies, it is the main object of the invention to provide a trackless movement and full-penetration apparatus and high-efficiency arc welding methods based on this apparatus.
SUMMARY OF THE INVENTION
Accordingly, a general object of this present invention is to provide a trackless movement and full-penetration arc welding apparatus and welding methods based on this apparatus to improve productivity of conventional arc welding technologies and simplify equipment for fabricating large steel structures. In this invention, all of the above-described difficulties accompanying conventional arc welding processes can be overcome.
The basic idea of this present invention is that an apparatus with the trackless movement and full penetration functions will be assembled with a butt joint based on a preexisting gap (3 mm-10 mm) of a weld line. In the apparatus, a movable weld backing is held against the underside of the weld line to support liquid metal and control backside bead to achieve full-penetration welding of a butt weld. The movable weld backing and a fixing plate of the welding torch are arranged the underside and the top sided of the workpiece, respectively, using a connecting member through the pre-existing gap of the weld line. Thus, the moveable weld backing moves synchronously with the movement of the welding torch along an entire weld line to continuously perform full penetration welding. Three compression springs are installed a guide wheel unit and two roller units, respectively, to hold the movable backing against the underside of the workpiece in flat position for welding. The movable backing made from copper is of water cooling type. In the weld backing, shielding gas, such as CO
2
, as backing purge gas is used to protect the backside weld region from atmosphere contamination (oxygen and nitrogen) for welding of alloy steel materials.
In order to perform trackless movement, the pre-existing gap of the weld line is used to act a “guide slot” and a guide wheel unit to track the gap is designed in this apparatus. In practical applications, the guide wheel unit is placed ahead of the welding torch and a guide metal wheel with the inclined planes contacts with the pre-existing gap to guide the welding torch and the apparatus to move along the weld line to automatically perform seam tracking. For automatic arc welding systems, the invention of through-the-pre-existing-gap “guide slot” and the guide wheel unit can save an external track and a seam-tracking device, and increase the accuracy and reliability to track a weld line. The apparatus substantially simplify conventional automated arc welding equipment and methods, and welding operation, thereby, in the practical applications an electrical or a manual winch can be used as a driver to drag the apparatus with a welding torch to travel along a weld line to perform full penetration welding, irrespective of the length and configuration of a butt joint. In the automatic or semi-automatic (for a handle winch) arc welding system, the winch may be temporarily placed to an end of the base metals to be butt-welded
Paschall Mark H.
Zhang Shaobin
LandOfFree
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