Electric heating – Metal heating – By arc
Patent
1995-01-10
1996-03-19
Paschall, Mark H.
Electric heating
Metal heating
By arc
219123, 21912152, 21912149, B23K 1000
Patent
active
055005012
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a plasma torch device equipped with an axial magnetic field in order to rotate the arc around the torch's centre axis.
BACKGROUND OF THE INVENTION
Plasma torches are mainly designed according to two principles. In one embodiment two or more tube electrodes are used located coaxially outside one another. In a second embodiment two or more tube electrodes are used wherein the electrodes are located coaxially opposite one another. The electrodes are connected to an electrical power supply and can be supplied with either alternating current or direct current. Gas is supplied to the torch, usually through or between the electrodes. A high-temperature plasma is formed by means of the gas which is heated by the electric arc which extends between the electrodes.
There are known plasma torches equipped with a magnetic field. From German patent DE 1 300 182 there is known a plasma torch with two tube electrodes located coaxially outside each other. A coil to which direct current is supplied is placed around the external electrode. It produces an axial magnetic field in the torch which causes the arc to rotate around the torch's centre axis.
The patent also describes a plasma torch with two tube electrodes located coaxially opposite each other. A coil is located in each of the hollow electrodes producing a magnetic field which causes the arc to rotate.
From U.S. Pat. No. 4 390 772 is known a plasma torch device where the magnetic field generated by a magnetic field generator is conducted to the arc's area of operation through a body formed from a magnetic material provided with cooling channels. The plasma arc is thus forced to rotate. In plasma torches not only the rotation of the plasma arc is of importance but also the ability to make adjustments to the magnetic field in the arc's area of operation to keep the arc in correct position in relation to the end faces of the electrodes. However, this feature is not disclosed in this patent.
From DE 2 913 464 is known a plasma torch device with two electrodes located coaxially opposite each other. A coil is placed around the torch body and generates an axial magnetic field in the plasma zone. By moving either the coil or the movable electrode the length of the arc can be adjusted. In the arc's area of operation a ferromagnetic body will reinforce the field and have a much greater effect on the adjustment of the arc. However, this feature is not disclosed in the patent.
The object of the magnetic field is primarily to provide an electromagnetic force to act on the arc, causing it to rotate around the torch's centre axis, thereby obtaining even wear around the torch and maintaining an even rotational symmetry in the actual electrodes. When the arc rotates sufficiently rapidly, moreover, the maximum temperature of the arc's foot points decreases, thereby reducing the speed of evaporation of the electrode material, or in other words the wear and tear. In consequence, the power load on the electrodes can be increased. Plasma torches which utilize a magnetic field are provided with one or more annular coils or with one or more annular permanent magnets. Such a coil or magnet is usually located around the electrodes and preferably in the area of the torch where the arc is formed or close to this area. The axis of the coil or permanent magnet is normally coincident with the electrodes' centre axis.
When a coil is supplied with direct current, a rotationally symmetrical magnetic field is created around it. In the coil cross section the field is axially and approximately constant. It is deflected towards the ends of the coil, and at the end surfaces the field intensity is reduced in relation to the value in the middle of the coil. Outside the coil's end surfaces the field intensity drops rapidly and is already reduced to only a small percentage of the value in the middle of the coil at a short distance from the ends.
In a coil cross section live conductors and bodies located there will affect this magnetic field. In particular bodi
REFERENCES:
patent: 4390772 (1983-06-01), Hiratake
Derwent's abstract, No. 59-D5084B/16 week 5916 Abstract of SU, A1 609217 (Korshakovskii S I), 30 May 1978.
Haugsten Kjell
Hox Ketil
Hugdahl Jan
Lynum Steinar
Myklebust Nils
Kvaerner Engineering A.S.
Paschall Mark H.
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