Arc-plasma method for welding metals

Electric heating – Metal heating – By arc

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Details

21912145, 21912136, 21912159, 219 75, B23K 1000

Patent

active

061569941

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to methods for plasma-arc welding of metals and can find application in mechanical engineering, construction engineering, and in other industries.


BACKGROUND ART

Methods for plasma-arc Welding of metals using the direct constricted-arc welding technique are in widespread use currently, wherein metal is fused with a plasma jet (cf. U.S. Pat. No. 4,791,268, IPC B23K 9/00, 1988; SU #1,683,927, IPC B23K 10/00, 1991). Extensively used nowadays are also methods for welding metals with a direct constricted arc stricken between the plasmatron electrodes and the workpiece (cf. SU #880,6,54, IPC B23K 10/02, 1981; the textbook "Microplasma-arc welding" ed. by B. Ye. Patton, Ukraine, Kiev, "Naukova dumlka" publishers, 1979, pp.19-21 (in Russian). The methods mentioned above provide for establishing a plasma jet by constricting an arc discharge with an inert gas to obtain quality welded 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 recharging gas bottles impose substantial limitation on practical applicability of the aforementioned method of plasma-arc welding. In addition, handling easily inflammable metals involves using not only a plasma-producer gas but also a shielding gas (cf. SU #1,680,463, IPC B23J 10/02, 1991).
Known in the present-state welding practice are plasma-arc welding torches (plasmatrons), wherein used for establishing a plasma jet is vapor fed from a special vapor generator or generated in the welding torch itself by evaporating the fluid by virtue of the heat released on the electrodes (cf. PCT RU Application #93/00053 published Sep. 1, 1994 under # WO/94/19139). The latter torch is most economic and simple in operation, though its use in welding is difficult due to intense metal oxidizing caused by the presence of vapor and molecular and atomic oxygen in the plasma jet.


DISCLOSURE OF THE INVENTION

The present invention is aimed at the provision of a method for plasma-arc welding of metals using vapor as a plasma-producer medium ensuring high-quality welded joints due to reduced oxidizing properties of the plasma jet. The essence of the invention resides in that in a method for plasma-arc welding of metals with a direct or indirect constricted arc comprising constricting the arc with a plasma-producer medium to obtain a plasma jet, used as the plasma-producer medium is the vapors of a fluid containing water doped with an organic solvent appearing as oxygen-containing hydrocarbon compounds capable of preventing oxygen atoms and molecules contained in said vapors from entering into oxidation reaction with the metal being handled.
It is found experimentally that the best results is obtained when used as the additives are alcohols, their optimum percentage content in the vapor-generating fluid from the viewpoint of energetics and welded joint strength being within 30 and 50. When the percentage of alcohols in the mixture is below the lower limit, a larger proportion of scale occurs in the welded joint which in turn affects adversely its strength characteristics. In case the percentage of alcohols in the mixture exceeds 50, the miscibility of the organic solvent with water is affected with the resultant stratification of the mixture and hence its nonuniform evaporation. Moreover, vapor enthalpy is reduced in this case which in turn reduces the plasma-jet temperature. Best results were obtained when using a plasma-arc welding torch, wherein the plasma-producing vapor is obtained from a fluid most commonly used in every-day life, consisting of 60% water and 40% ethanol.
Vapor can be generated immediately in the plasma-arc torch by evaporating the fluid filling a special container, by virtue of heat energy generated by the arc burning between the torch electrodes.
The herein-proposed method for plasma-arc welding of metals can be carried out using both indirect plasma-arc torches, wherein hea

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B. Paton, 1979, "Microplasma-arc Welding", Ukraine, Kiev, "Naukova dumka" publishers pp. 19-21.

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