SU1145560A1 - Method of electric-arc treating of metals in carbon-containing gas with continuously renewable electrode - Google Patents

Abstract

METHOD FOR ELECTRIC ARC metalworking UGLERODSODERZHA1TSEM GAS PERMANENTLY VOZOBNOVLYAYUI | IMSYA ELECTRODE with rod graphite active insert, characterized in that, in order to increase the service life of the electrode, an electric arc treatment of metals is effected at a current density in the insert 10 and the thermal resistance of the insert in its cross section, not exceeding 2.910 m K / VTO

Description

The invention relates to the field of electric arc, in particular, plasma treatment, welding, surfacing, on-dusting in mechanical engineering. shipbuilding, and can also be used in the smelting and remelting of metals in electrometallurgy.

The known method of electric arc, in particular plasma, treatment in chemically active plasma-forming mixtures, in which an electrode (cathode) is used, made composite, in the form of an active insert made of metal with corresponding thermoelectronic and thermochemical characteristics; rigidly fixed in a copper water-cooled holder

The disadvantage of this method is the small life of the electrode (even at low currents, up to 300 A), not exceeding several hours, due to the intensified erosion of the active insert.

The closest technical solution to the proposed is spos. $

Electroarcoupling of metals in carbon dioxide by a constantly renewed electrode with a graphite core insert.

In this method, the active insert is made of the same material as the component of the plasma-forming medium, which precipitates out of it when the arc is burning on the working surface

- (sd sl insert and its constant renewing, in particular when the arc is burning in carbon-containing gases (Hydrocarbons,

O5 carbon dioxide, mixtures of them with each other or with other gases) the active insert is made of graphite. Such a solution makes it possible to exclude the appearance in the insert and the matching of the term on the surface of the true electrode (cathode) of thermomechanical stresses caused by the difference in the properties of materials and leading to the destruction of the electrode,

However, the disadvantage of this method. | It is a low life of the electrode, because the dimensions are not determined

active insert, in particular its diameter, is directly proportional to the current density associated with it during electric arc processing

The aim of the invention is to increase the operation of the electrode in the constant resumption mode.

This is achieved by the fact that in the method of arc treatment of metals in carbon-containing gas by a constantly renewing electrode with a rod graphite active insert, arc treatment of metals is carried out at a current density in the insert 10 - 10 A / cm and the thermal resistance of the insert in its cross section not exceeding 2 , 9 x MO m K / W „

The operation of the electrode in the mode of continuous resuming is provided that the losses G of the electrode material do not exceed the flow of the same material from the outside G to it from the gas phase.

in particular, when the electrode is used as a cathode, the loss of G is determined by evaporation and cathode sputtering, and the flow of G is by planting fresh material mainly in the form of positive ions neutralizing on the cathode working surface

I

Permanent electrode renewal (a cathode is possible from any gas atmosphere containing dissociating compounds at an arc temperature with release of products capable of landing on the cathode working surface and possessing corresponding thermionic and thermal physical characteristics. Prevalence is cheap, easy delivery to the consumer, simplicity and safety in handling allow to give preference to an atmosphere that provides a permanent electrode rejuvenation with a carbon-containing compound: ok 1m carbon CO and CO, Dissociation in hydrocarbons, the arc of these compounds provides obtaining, along with other components of carbon, which has both a high phase transition temperature (4000K) and a relatively low work function (S 4.7 eV) „

Fig. 1 shows a schematic diagram of a forming electrode which is constantly renewed, and Fig. 2 shows the scheme for implementing the proposed method.

The true electrode cathode 1 with a diameter of df is planted with a thin layer on the surface of the active insert 2 with a diameter d and adjacent to it a section of copper water-caged casing. . Further, the insert becomes passive, performed like a copper water-cooled holder, the lines of the function of one of the heat transfer units from the working surface of the electrode to the cooling water. This is the main and fundamental difference of the constantly renewable electrode from the traditional, to some extent, aerosating electrode, the electrode (cathodic) arc region for which occurs only and always on the surface formed by either the insertion material (W, Mo in argon), or the joints of this material with the components gas atmosphere (N.G., Zr, Ti in air) Therefore, the diameter of the active insert for traditional cathodes is always equal to or greater than the diameter of the working surface visited by the cathode arc area. The diameter of the true electrode, if it is constantly renewed, is shown diameter of the active insert. For example, on an electrode made in the form of a copper cage with an active graphite insert 0.15 cm in diameter pressed into it when the arc is burning at a current of 500 A, it is formed and constantly renewed from a gas fi There is a true graphite cathode with a diameter of about 0.3 cm. Considering that a constant electrode renewal is possible only if the insertion of material from the gas phase and the material leave as a result of evaporation on the working surface is equal, there are two basic conditions for the electrode to work The first condition determines the content of the planting material in the gas phase. The second condition determines the heat removal from the working surface of the electrode to the cooling water. It consists in that, as in the known method e electric arc treatment during arc burning at a given current, the working surface of the electrode should not exceed the melting temperature or sublimation temperature of the planting material (for graphite 4000K) o The table shows the calculated by experimentally and experimentally confirmed temperatures on the working surface of the cathode arc at a current 500A in a mixture of carbon dioxide and natural gases, depending on the diameter and current density in a graphite insert. The same table shows the thermal resistance of the insert in its cross section. This is calculated in accordance with the above formula (R -), based on the condition that the thickness of the heated layer (S) is equal to pa. d. insertion analysis The analysis of the presented data shows that at current densities in the insertion smaller than 10 A / cm, i.e., when the insertion diameter is greater than the critical value for a current of 500 A, the cathode is destroyed due to the excess temperature on its working surface 4000Ka graphite. Similar results were obtained for all other current values of current I. Thus, the current density in the insert 10 A / cm determines at this current that critical diameter of the insert, the increase of which (diameter) leads to its destruction in connection with by singing on the working surface of a true electrode the temperature of sublimation of graphite. When Tolca density is greater due to the smallness of the surface of the contact of the true electrode with the active insert, their adhesion strength decreases sharply. This leads to mechanical destruction of the electrode as a result of peeling off the true electrode from the insert, transient cuttings: switching on and off the arc, a sharp change in its current strength and t, DoI Experiments have shown that processing at a current density in an insert of 10-10 A / cm is necessary, About the insufficient condition for increasing the electrode life in the constant renewal mode. The second condition is that the thermal resistance of the insert in its cross section, defined by its diameter, must not exceed a certain value for graphite (D g 60 W / MK) the limiting thermal resistance in the cross section of the insert is d. 27i 27bO - which corresponds to the limiting diameter of the active insert 0.35 cm With a larger diameter of the insert, as a result of its increased thermal resistance, the heat sink to the cooling water decreases, the insert material overheats much higher than the sublimation temperature, and it intensively erodes From the thermal point of view thermal resistance is only positive. The proposed method is carried out as follows: A copper water-cooled casing 3 with an active insert 2 pressed into it the form of a graphite rod Q with thermal resistance in the longitudinal (axial) direction 3.3 - ((rod length 0.2 - 0.3 cm) and in cross section J not exceeding 2,) (rod diameter not more than 0.35 cm) Connect one of the poles of power supply 4, in the case of direct current - negative. An insert cage assembled in such a way is inserted into a nozzle assembly, which provides for the blowing of the working surface of the active insert with carbon-containing gas or an eiO-based mixture. The main element of the nozzle-node is the nozzle 5, the channel 6 of which is coaxial with the holder. both inside the nozzle channel and outside of it. The first case is characteristic of plasma treatment, the second case is of ordinary gas-electric. Other poles of the power supply source (put 1st 1st in

7P

In case of direct current, they are connected either to the nozzle or directly to the metal processed by the electric arc 7. Cooling water is supplied to the assembled holder with the active insert, and, if necessary, also to the nozzle unit and turn on the carbon-containing gas or the mixture to it. basis into the space surrounding the working surface of the active insert on which the true graphite non-melting electrode Io is constantly being renewed. Ignite the electric arc 8, one of the electrodes of which is the working surface of the active insert, and the other is either the nozzle or processed Mt. alLo Set the arc current, which provides for a given diameter of the graphite active insert, the current density in it is 10–10 A / cm and electric arc plasma treatment is carried out on this current. NOSTA active insert is formed continuously and is resumed from a true arc gas atmosphere graphite electrode (cathode

Example ID Plasma welding was performed on flanging steel sheets with a TOL1TSIN of 0.3 cm in carbon dioxide at a flow rate of 0.4–0.6 m / Cho. Welding is carried out on a current i 95 A with an external arc plasma torch with a composite water-cooled, consisting of a copper sleeve with pressed into it there is an active insert made of rod graphite of grade C-2 with a thermal resistance in the longitudinal direction of 3.3 (length 0.2 cm) and in the cross-sectional plane of 4.540 m K / W (diameter 0.05 cm), at current density in -avka 9, A / cm is almost equal to 10 A / cm (less by only 0.66%), which is In the range of measurement errors, welding takes place with a constant renewal of the cathode, and Toe, its constant dimensions and geometry are almost unlimited.

With an increase in the welding current to 210 A, which, with a given active insert diameter of 0.05 cm, corresponds to a current density of 1.0710 A / cm, or only 6.9% above. The top allowable current density problem, every time the arc is turned off, the true cathode is disconnected from the active insert. This is not pos. 55608

It is necessary to ensure a long life of the cathode in the mode of constant renewal

EXAMPLE 2: Mechanized plasma spraying of a heat-resistant protective coating made of corundum powder (alu-Fri oxide) on the surface of carborundum (car;

Q bid silicon). For plasma formation1, a mixture of natural and carbon dioxide was used with a flow rate of 2.0 and 6.0 MV4, respectively. Sputtering was conducted on a current of 600 A with a plasma torch of the type

5 PVCs with a composite cathode made in the form of a water-cooled copper sleeve with a graphite core active insert pressed into it with thermal resistance in the longitudinal direction 5 (height 0.3 cm) in the cross-sectional plane 1 "10 m K / W (diameter 0 , 12 cm) at current density in box 5 ,, the cathode operates in the constant mode

5 renewal in a few months

Example Zo Produced plasma melting of nickel-containing slags Dp plasma-forming was used

0 a mixture of methane and carbon dioxide with a flow rate of 1.5 and 3.0, respectively. Melting was carried out on a current of 820 A by an arcing plasma torch with a water-cooled composite cathode consisting of a copper bushing and an active insert made of rod graphite pressed into it with thermal sintering in the longitudinal direction 540 (height 0.3 cm) in the transverse section 0 plane - 2 , 66 40 m -K / W (diameter 0.32 cm) at the current density in the insert, 1, A / cm, practically equal to 10 A / cm (most of it only Ij95%, which falls within the range of measurement error). With a decrease in current with the same cathode to 750 A, which corresponded to a current density in the insert of 9.3-10 A / cm, or 6.7% below the limit value JQ 10 A / cm, intense insertion erosion occurred. In a few minutes

Example 4, Plasma heating of copper billets with a wall thickness of 20 mm for welding was briefly 30–50 times each, with exposure to a plasma jet generated in a plasma torch similar to that used for spraying in Example 3

Morae samples used a mixture of methane and carbon dioxide with a flow rate of 4 and 10, m / h, respectively. Heating was conducted on current I100A with composite water-cooled cathodes with active graphite inserts having different thermal resistances in the transverse direction and the same (5 L x 10 m% / W) in the longitudinal direction. direction. In the first case, the thermal resistance of the insert in its cross section was 2.5 K / W (insert diameter 0.3 cm), in the second 3 "10 m K / W (insert diameter 0.36 cm) o In the first case, the treatment was carried out at a current density in the insert of 1.5540 A / cm, in the second - at a current density in the insert of 1.08 A / cm about

556010

Despite the fact that in ov6oHx cases, the current density in the insert exceeded, in the first case, when the thermal resistance in the transverse section of the insert was less than 2.9f X, the cathode worked in a constant resumption mode for several tens of cycles, and in the second case, when the thermal resistance in

0 cross section of the insert exceeded 2.9 K / W, was destroyed after 1 - 2 cycles

Io relation to a known method

r processing with a constantly renewing cathode, increasing the life of the cathode allows this method to be applied in continuous production: metallurgy, chemistry and top production.

0.15 2.83. 10 0.50 2.55 10 1.65 -10 2.15. ten;. 2.50. 10 4.50. 10 The cathode is operating in the constant resumption mode - the cathode is destroyed. The cathode is intensively destroyed.

Claims (1)

METHOD OF ELECTRIC ARC TREATMENT OF METALS IN A CARBON-CONTAINING GAS WITH A CONSTANTLY RENEWABLE ELECTRODE with a rod graphite active insert, characterized in that, in order to increase the service life of the electrode, the electric arc treatment of metals is carried out at current density A and cm insert in its cross section not exceeding the city of ECHO '^ m ^ K / W ”