Electric heating – Metal heating – By arc
Patent
1987-03-13
1989-03-07
Paschall, M. H.
Electric heating
Metal heating
By arc
21912152, 219119, B23K 900
Patent
active
048108510
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to electric welding and metallurgy and, more particularly, to a method of electric arc treatment of materials with a constantly restored electrode.
BACKGROUND OF THE INVENTION
At present, one of the essential problems faced be welding and metallurgical technologies is enhancing the stability of electrodes of electric arc apparatus operated for welding and similar processes of treatment of metals, as well as for melting and similar processes of treatment of metal and slag melts in electric-arc furnaces.
Known in the art is a method of electric arc treatment of materials (U.S. Pat. No. 3,307,011, Cl. 219-74, 1963), providing for enhancing the stability of electrodes, graphite electrodes included, of electric arc apparatus. The method includes introducing into the space between the electrodes of an electric arc apparatus plasma-forming mixtures including carbon-containing compounds chosen from the class of hydrocarbons and carbon monoxide, and gases inert with respect to the material of the electrodes. With the electric arc burning, these carbon-containing gases decompose and release free carbon which is deposited on at least one of the electrodes. Used as gases inert with respect to particular materials are argon or helium when the electrode is made of graphite, or else air or nitrogen when the electrode is made of copper.
This method makes it possible to reduce the erosion of electrodes and thus to extent their operating life with stable arcing at currents from 400 to 1000 amperes.
However, this process would not ensure an equilibrium of the respective quantities of the loss of carbon and its deposition on the working surface of the electrode. The weight of the electrode would either continuously diminish, although at a small rate, which means that the electrode erodes, or else continuously grows, which means that the dimensions of the electrode increase. In the first-mentioned case the electrode becomes ultimately destroyed. In the second-mentioned case the stability of arcing is affected on account of hindered localization of the electrode-adjoining region of the arc on the increased working surface of the electrode.
The aforementioned phenomenon can be explained by the following reasons: firstly, the use of only the gases inert with respect to the material of the electrodes in the composition of a plasma-forming mixture; secondly, the lack of quantitative relationship between the arc current value, the composition and flow rate of the plasma-forming mixture; and thirdly, the lack of relationship between the variation of the composition of the plasma-forming mixture and the time of arcing, particularly, in the initial period of ignition of the arc. The necessity of using electrodes which are either block-shaped or hollow in some cases restrains the applicability of the method, as it would not ensure the required localization of either the arc or the jet of plasma within the treatment area.
It is for these reasons that the aforementioned method has not yet found industrial applications notwithstanding the fact that it was published as many as twenty years ago.
There is further known a method of electric arc or plasma treatment of materials (U.S. Pat. No. 4,317,984, Cl. 219-75, 1982; FR, B, No. 2431240, Int. Cl..sup.3 HO5H 1/48, B23K 9/16, 1983) consisting of introducing into the space between the electrodes of an electric arc apparatus a plasma-forming mixture including carbon-containing compounds and an oxidizing agent.
The oxidizing agent is introduced within a time interval corresponding to the reduction of the flow of heat into the electrode on which carbon is deposited from the peak value to a steady value. Depending on the nature of the oxidizing agent, its content in the plasma-forming mixture is taken to be either 0.4 to 0.9 or 1.05 to 2.5 by volume of that corresponding to theoretically complete conversion of hydrocarbons in the mixture. The first-mentioned range applies to an oxidizing agent in the form of either oxygen or air, and the seco
REFERENCES:
patent: 3307011 (1967-02-01), Baird
patent: 4317984 (1982-03-01), Fridlyand
Gossudarsvenny Proektny i Nauchno-Issledovatelsky Institute
Paschall M. H.
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