Electric heating – Metal heating – By arc
Patent
1999-01-11
2000-07-11
Paschall, Mark
Electric heating
Metal heating
By arc
21912145, 21912151, 21912159, B23K 1000
Patent
active
060876166
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to methods of plasma-arc welding of metals and is applicable in mechanical engineering, automotive industry, construction engineering, and many other industries.
BACKGROUND ART
A method of plasma-arc welding of metals using the so-called constricted arc (cf. a textbook "Microplasma-arc welding" ed. by B. Ye. Patton, Ukraine, Kiev, "Naukova dumka" publishers, 1979, pp.19-21 (in Russian). The essence of the method resides in that the arc discharge occurs in a stream of inert gas between the cathode of the plasma-arc welding torch of a plasmatron and the workpiece--anode, while the diameter of the arc discharge is restricted to the torch nozzle passage. Insofar as direct arc striking between the electrode and the workpiece across a narrow nozzle passage is difficult, first a pilot arc is initiated between the electrode and the torch nozzle--anode, whereupon an inert gas is fed thereto.
While being under pressure said gas emerges from the outlet of the nozzle--anode to establish a plasma jet due to constriction of the pilot arc. As soon as the plasma jet contacts the workpiece the main arc is started. In this case the pilot arc may persist, thus stabilizing the main arc under low-amperage conditions. While controlling the consumption rate of the plasma-producer gas, one can vary the pressure exerted on the molten weld pool and hence the depth of penetration of the workpiece--anode.
The afore-discussed known method is instrumental in obtaining quality weld joints; however, provision of an external inert-gas source involves some operational inconveniences in carrying said method into effect, while high production cost of the inert gas and considerable expenses for charging gas bottles and their delivery impose substantial limitation on practical applicability of the aforementioned method of plasma-arc welding.
DISCLOSURE OF THE INVENTION
The present invention is aimed at eliminating the aforementioned disadvantages of the known method.
The essence of the proposed method of plasma-arc welding with a direct electric arc resides in using water vapor as the plasma-producer gas, the straight (normal) polarity of the main arc being mandatory. Vapor can be generated directly in the welding torch due to heat energy released by the pilot arc. The plasma jet may be controlled to suit the required weld penetration by varying the pilot arc amperage.
It should be noted that known from prior art are plasma-arc torches, wherein used as the plasma-producing medium is water vapor generated immediately in the torch due to water evaporation under the effect of high temperatures of the electrodes (cf. PCT/RU93/00053 published on Sep. 1, 1994 under #WO94/19139). However, said torches have not so far been used for welding of metals with direct electric arc stricken between the torch cathode and the workpiece.
BRIEF DESCRIPTION OF THE INVENTION
FIG. 1 shows the plasma welding system as disclosed.
DETAILED DESCRIPTION OF THE INVENTION
A drawing appended to the present specification presents the device for carrying into effect the welding method, according to the present invention. The device comprises a plasma-arc welding torch which incorporate a cathode 1, a nozzle--anode 2 provided with passages for a plasma-producing medium, a container 3 filled with a moisture absorbent material, and a pilot arc power source 4, a direct arc power source 5, and a pilot arc current regulator 6. The torch is provided with an insulating pressure-tight cover 7. Used as a moisture absorbent material may be kaolin wool, carbon fabric, or carbon felt.
The device operates as follows.
An inlet 10 of the container is opened and water is filled therein, whereupon and the inlet 10 of the container 3 is closed. Then a voltage is applied from the pilot arc power source 4 to the cathode 1 and the nozzle--anode 2.
Next the pilot arc is initiated by, e.g., reciprocating the cathode 1 till contacting the nozzle--anode 2. The heat energy released by the pilot arc on the nozzle--anode 2 evaporates the water he
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"Microplasma-arc Welding", B. Paton, Ukraine, Kiev; Naukova dimka publishers, 1979 p. 19-21.
Apunevich Alexandr Ivanovich
Titarenko Evgeny Ivanovich
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