Electric heating – Inductive heating – Metal working
Reexamination Certificate
2000-02-17
2001-07-24
Hoang, Tu Ba (Department: 3742)
Electric heating
Inductive heating
Metal working
C219S136000
Reexamination Certificate
active
06265701
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the art of welding. More specifically, it relates to welding relatively thick material, such as steel pipes or plates, which require pre-heating of the weld path.
BACKGROUND OF THE INVENTION
It is well known to weld large and relatively thick pieces of steel (or other material) together. For example, pipes are often formed by taking a flat piece of steel and rolling the steel. A longitudinal weld is then made along the ends of the rolled steel, thus forming a section of pipe. A pipe line may be formed by circumferential welding adjacent sections of pipe together. Other applications of welding relatively thick steel (or other material) include ship building, railroad yards, tanker trucks, or other higher strength alloy welding.
When welding such relatively thick steel (or other material) it is generally desirable to preheat the workpiece along the weld path. (As used herein “weld path” refers to the path along which the weld will be made, or has been made.) Pre-heating is used to raise the temperature of the workpiece along the weld path because the filler metal binds to the workpiece better when the weld path is heated, particularly when a high-alloy steel is being welded. Without preheating there is a greater likelihood that the filler metal won't properly bind with the workpiece, and a crack may form. (As used herein “preheating” a weld path means heating the workpiece along the weld path to a pre-weld temperature, or a temperature sufficient to reduce the likelihood of a crack forming along the weld path. Generally, the steel is preheated to about 300° F. prior to welding. Preheating is often used for heating steel having a thickness of more than about ½″.
Generally, in the prior art, “rose buds” (gas fired flame torches) are used to preheat the steel. The rosebuds are placed along the weld path, typically one rosebud on each side of the weld path, or one covering both sides of the weld path, every 3 to 6 feet. The rosebuds are left in place a relatively long period of time (for example up to two hours for 3″ thick steel). After the weld path has been preheated, the rose buds are removed and the weld is performed before the weld path cools. Other methods of preheating a weld path include placing the entire workpiece in an oven (which takes as long as using a rosebud), induction heating, or resistance heating wires. When preheating with these alternatives in the prior art, the heating device is placed at one location on the weld path until that location is heated. Then the weld is performed and the heating device is moved. The preheating has not been done on-the-fly because the heating took much longer than the welding.
Rose buds have also been used in the prior art to dry the weld path prior to welding. In such an application the rose bud will be passed over the weld path immediately prior to welding. However, the rose bud is not applied for a length of time sufficient to preheat the weld.
Unfortunately, the use of rose buds or the other known prior art pre-heating techniques, takes an undesirable long time to heat the weld path. This results in unnecessary down time while the welder is waiting for the weld path to be preheated. In other words a rose bud or other prior art does not heat as the weld path as the weld is being performed, i.e not on-the-fly, so that the welder must wait for the preheating to be completed before welding that portion of the weld path.
Accordingly, a system for preheating weld path is desirable. Preferably, such a system will heat the weld to a pre-weld temperature immediately prior to the weld being performed. Such a system will preferably be able to preheat as fast as the weld can be performed so that as the weld is being performed on one portion of the weld path, a nearby portion is being preheated.
SUMMARY OF THE PRESENT INVENTION
According to one aspect of the invention a system for welding a workpiece includes a welding power supply and a welding torch connected to the power supply. An induction coil is connected to an induction power supply. The induction coil is adapted to be disposed near the welding torch such that as the torch is moved, the induction coil is moved, and the weld path is preheated on-the-fly.
The induction coil is in a fixed position relative to the torch in one alternative, and mounted with the torch in another alternative. Preferably, the induction coil is mounted such that as the torch is moved along a weld path, the induction coil precedes the torch.
The induction heating power supply includes capacitors that may be changed to adjust the frequency of an induction output in one alternative, and the induction heating power has an adjustable frequency output.
A robot is included in another alternative. The robot moves the welding torch and the induction coil.
Another aspect of the invention is a method of welding a workpiece that includes providing power to a welding torch and providing power to an induction coil. Also, the induction coil is disposed near the workpiece to heat a weld path on the workpiece. The welding torch is also disposed near the weld path, and the weld is performed while the workpiece and weld path are heated by the coil.
One alternative to this aspect includes holding the induction coil in a fixed position relative to the torch. Another alternative is adjusting the frequency of the power applied to the induction coil, by, for example, changing a capacitance of a power supply that supplies the power to the induction coil. Yet another alternative is to place the torch and coil in a robot, which moves the torch and coil along the weld path.
A third aspect of the invention relates to a welding torch. An induction coil is mounted with the torch such that as the torch is moved the induction coil is moved. An alternative provides that the induction coil is in a fixed position relative to the torch. Preferably, the induction coil is mounted such that as the torch is moved along a weld path, the induction coil precedes the torch along the weld path. According to another alternative the torch is adapted to be mounted on a robotic arm.
Yet another aspect of the invention is a system for welding a workpiece that includes a welding power supply connected to a welding torch. A heating device that heats the workpiece to at least a pre-weld temperature as the workpiece is being welded is also included. The heating device is adapted to be disposed near the welding torch such that as the torch is moved the heating device is moved.
The heating device is in a fixed position relative to the torch, and preferably mounted with the torch in alternative embodiments. Also, in another alternative, the heating device is mounted such that, as the torch is moved along a weld path, the heating device precedes it.
A fifth aspect of the invention is a method of welding a workpiece that includes providing power to a welding torch and pre-heating the workpiece along a weld path as a prior portion of the weld path is being welded. The weld path is heated to at least a pre-weld temperature. The welding torch is disposed near the weld path, wherein the weld is performed while the workpiece and weld path are heated to at least the pre-weld temperature.
The step of preheating include preheating a portion of the weld path a fixed distance from the welding torch in an alternative. The torch is moved robotically in another alternative.
Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.
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Bickel David
Ulrich Mark
Wiseman Donald
Corrigan George R.
Hoang Tu Ba
Illinois Tool Works Inc.
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