SU761183A1 - Electrode assembly to heads and burners for arc welding by non-fusable electrode - Google Patents

Description

The invention relates to the field of arc welding in a protective gas environment.

A non-consumable electrode for arc welding in vacuum, made in the form of a rod 10 mm in diameter with an internal channel of 1-4 mm, through which an inert gas is fed under a small pressure, is known [1].

The disadvantages of the known non-consumable electrode are the complexity of manufacturing and low resistance of the electrode in long-term operation.

Known non-consumable electrode, made in the form of a hollow tungsten rod, on the surfaces of which, in order to change the degree of concentration of thermal energy, additives from metal oxides with different emission properties are applied [2].

The disadvantages of the known non-consumable electrode are the complexity of manufacturing and low resistance of the electrode.

The closest solution to the technical nature and the achieved result to the invention is a multi-channel hollow cathode to torches for arc welding in vacuum, which is made in the form of a set of rods installed in the cage, which acts as an electrode holder. The cathode channels are formed by the outer ^, bar surface {3].

2

However, the use of the well-known multichannel cathode in the conditions of long-term automatic arc welding of pipes on electric welded pipe mills at atmospheric pressure is not possible.

The mechanism of operation of an arc discharge with a hollow electrode in vacuum and at atmospheric pressure in a protective gas medium is sharply 10 different from each other. In an arc in vacuum (low pressure arc), the active spot is located inside a hollow cathode (in the known device, taken as a prototype, on the inner walls of channels formed by the outer surfaces of a set of bars). This type of arc, characterized by low discharge stresses and strong cathode erosion, has found application in the manufacture of special 20 surfacing operations, spraying operations, as well as for welding rare and non-ferrous metals in vacuum of seams of limited length. It uses expensive unique welding equipment.

25

The arcs burning in the environment of protective gases at atmospheric pressure (high pressure arcs) are characterized by the location of the active spot on the end of the working 30 end of the cathode and a significantly higher heating temperature.

3

Therefore, at the known hollow multichannel cathode under conditions of long-term high-speed welding in protective gas at atmospheric pressure, the ends of the bars of the set are melted and the capillary channels through which plasma-forming gas is fed are closed. The highly developed emitting surface of the end of the working end of such a cathode transforms the arc burning mode to an unstable one due to the wandering of the active arc spot.

The aim of the invention is the provision of welding at high speeds by increasing spatial stability.

This is achieved by the fact that the channel of the electrode assembly, containing an electrode holder with bar electrodes installed in it, forming a channel for supplying a protective gas, is formed by three sharpened electrodes forming a common working end with a diameter of 0.6 - 0.7 bar diameter, the length of the sharpening of the bars is equal to 2-3 diameters of the rod.

FIG. 1 shows a general view of the electrode assembly; in fig. 2–3 are photographs of macrosections of the cross-section of welds made, respectively, by the electrode unit and the nonconsumable rod electrode.

Three non-consumable bars 1 with a diameter of? Pr are clamped in a common collet 2. A common working end 3 of the electrode assembly is made with a diameter of 0.6–0.7 bar diameter and a bar sharpening length of 2-3 bar diameter 1.

The diameter of the total working end of the electrode assembly, equal to 0.6–0.7 bar diameter ί / _Π ρ, is optimal from the point of view of ensuring its durability in long-term operation, in terms of increasing values of welding speed and current, as well as increasing spatial stability arc.

An increase in the diameter of the end face of the electrode node over 0.7 s? _P p leads first to the emergence of a cathode spot wandering along the enlarged surface of the working end, and then to the burning of an arc between one of the three non-melting bars constituting the cathode and the product. In this case, the welding arc loses the form of a mono-flow, and its burning mode becomes unstable. The strength of the cathode assembly is reduced. It should be noted that there are a large number of defects (burn-throughs, non-fusion) in the weld of the joint. Along with a decrease in the cathode assembly durability and arc spatial stability with increasing diameter of the working end over 0.7 s? Pr, the current density and temperature of the arc column, as well as the melting capacity of the arc as a source of thermal and dynamic effects on the material being welded, decrease.

761183

four

Reducing the diameter of the working end below the value of 0.6 s? _P p leads to the opening of the internal channel in the area of the working end of the electrode node.

Opening of the channel breaks the outflow of protective gas, the mode of combustion of the welding arc becomes unstable.

With shorter grinding length less

2 ί / _Π ρ the current density and the temperature of the arc column decrease, therefore the penetration ability and spatial stability of the arc decrease.

In addition, with a decrease in the total sharpening length, an increase in the heating temperature and erosion of the section of non-consumable rods and their protruding electrode holder are noted. An increase in temperature and erosion of the working end contribute to the loss of the initially specified geometric shape of the electrode assembly and the disruption of the normal conditions of burning the arc, i.e., reducing its spatial stability.

Increasing the length of the total sharpening over

3 ί / _Π ρ, on the one hand, increases the current density and temperature of the arc column, i.e., increases its spatial stability, but, on the other hand, during long-term operation, the common working end is observed to melt, its geometric shape is disturbed, and cathode spot on the melted surface, which leads to a loss of spatial stability of the arc.

The device works as follows.

After fixing the bars 1 in the collet 2, the electrode is set so that the plane of symmetry of the triangle formed by the centers of the bars coincides with the welding speed vector, and one of the vertices of the triangle is directed along the welding speed vector. Protective gas is supplied, the arc is ignited and welding is performed.

The presence of three bars, forming one central channel, allows for a relatively small total diameter of the electrode to choose the diameter of the rod within

3-5 mm, providing the possibility of long-term operation of the electrode on. high current densities and welding speeds at atmospheric pressure, without fusing the rods, and therefore, without losing the spatial stability of the arc. The active arc spot is located at the blunting of the working end of the electrode. The arc burns steadily, and a powerful flow of shielding gas blown through the central channel coaxially with the cathode flow of the arc increases the arc penetrating ability at high welding speeds.

FIG. 2 is a photograph of the macrosection of the cross section of the weld on a plate made of steel 12X18H10T (bar diameter in a set of 3 mm).

five

Welding mode; welding current 370 A, welding speed 2.4 m / min, arc length 1.5 mm, gas consumption 7.8 l / min (argon). The formation of the seam quality with a smooth outline of the outer and reverse sides of the seam.

As a comparison in FIG. 3 is a photograph of the macrosection of a cross section of a weld welded in the usual way (in argon with a diameter of 5 mm of a non-melting electrode).

If the values of welding current and welding speed are unchanged, the mode of incomplete penetration. The formation of the seam is of poor quality (it has the form of individual melts of portions of the metal due to the low spatial stability of the arc).

The recommended dimensions of the working end of the electrode (diameter and length of blunting) are optimal from the point of view of ensuring the durability of the electrode in long-term operation at atmospheric pressure, the spatial stability of the arc at high welding speeds (5–10 m / min for welding steel 12X18H10T pipes).

The special orientation of the three-prong electrode node with respect to the welding speed vector is mandatory and contributes to an increase in the arc melting ability, an even greater increase in its spatial stability with increasing welding speed. In this case, as studies have shown, the most favorable conditions are achieved for the action of the plasma arc flow and the flow blown through the central channel of the protective gas on the weld pool. The undercut, which is a permanently formed defect inherent in high-speed welding methods, completely disappears (Fig. 2). With more bars in the kit, this effect is completely lost. In addition, the electrode assembly, composed of three rods and oriented during welding, as indicated above, does not require the use of

761183

6

special devices for the spatial stabilization of the arc. The rods forming the electrode unit are replaced by removing the compressive force on the collet. The torch used for welding with an electrode assembly is a common one, which is used in welding plants in electric pipe welders.

The use of an electrode assembly in argon-arc welding of pipes made of 12Х18Н10Т steel on pipe electric welding mills allows an increase in the productivity of equipment by 50–70% with minimal capital expenditures. It is important that the increase in welding speed is carried out without increasing the value of the welding current. This makes it possible to obtain a welded joint of a tubular billet with high mechanical characteristics.

Claims (1)

Claim Electrode assembly to heads and torches for arc welding with a non-consumable electrode, containing an electrode holder with bar electrodes installed in it, forming a channel for supplying protective gas, characterized in that, in order to ensure welding at higher speeds by increasing the spatial stability of the arc, the channel is formed by three sharpened electrodes, forming a common working end with a diameter equal to 0.6-0.7 bar diameter, while the length of the sharpening of the bars is equal to 2-3 diameters of the rod.