RU1787722C - Method of and device for alternating current welding with consumable electrode - Google Patents

Abstract

Usage: in automatic, semi-automatic and manual arc welding and surfacing with a consumable electrode of parts of metal structures. SUMMARY OF THE INVENTION: When welding with a consumable electrode using alternating current, the ratio of the powers supplied to the electrode is established in the positive and negative half-periods, equal to the ratio of the melting rates of the electrode in the negative and positive half-periods. The ratio of the power of the stabilizing pulses is equal to the ratio of the power required for re-ignition in half-periods of the same polarities. The device comprises a welding transformer with rigid external characteristics, having one primary and three secondary windings, two thyristor switches, a control unit, a capacitor and two chokes. The use of the method and device for arc welding with a melting electrode with an alternating current made it possible to increase the stability of the process both due to reliable re-ignition of the arc, and due to the condition of self-regulation of the process in both half periods, which increased the quality of welding, while expanding the control range of welding welding. 2 s.p. f-ls, 2 ill. ate G

Description

X

--U - I

The invention relates to welding and can be used for automatic, semi-automatic and manual arc welding and surfacing with a fused electrode of metal parts, mechanisms, machines in various industries. V Mv-4.:.

A large number of factors influence the stability of the welding process in an alternating manner, But the decisive factors are reliable re-ignition of the arc after each transition of the welding current through zero and the process of self-regulation, supply of the electrode to the arc gap, i.e. the electrode feed rate and its melting rate should be equal.

Fig. 1 is a circuit diagram of an apparatus for arc welding with a floating electrode. Alternating current; on fig.2 - diagrams of the current of the device connected to the active load ..

The device (Fig. 1) contains a welding transformer 1 with an air gap 2 in its magnetic circuit, a primary winding 3 connected to the network, three sequentially connected secondary windings: the first additional winding 4, the main welding winding 5, the second additional winding 6 ; the first chain shorting all three windings and consisting of the first 7 and second 8 chokes, a capacitor 9 and a switch on thyristors 10 and 11; a second chain shorting the welding winding 5 and consisting of a switch natiristor 12 and 13, a second choke 8 of the first chain and an arc gap 14; a control unit 15 connected to the arc gap 14, through diodes 16 ... 19 and phase-shifting chains consisting of adjustable resistors 20 ... 23 and capacitors 24 ... 27, with control electrodes of thyristors 10 ... 13, and also with the winding 28. It should be noted that the inductance of the throttle 8 is much larger than the inductance of the throttle 7, so that when the thyristors 12 and 13 are turned on, when the winding 4 is shorted, the short circuit current of this winding is limited by the inductive resistance of this throttle and does not exceed 20 ... 25 A.

All secondary windings (4; 5; 6 and 28) have a hard magnetic connection with the primary winding 3, and therefore, the sloping external characteristics

Figure 2 shows the diagram of the load current of the proposed device. The following notation is accepted here: pi and /% the opening angles of power thyristors, i.e. angles at which the thyristors are kept open (as can be seen from Fig. 2, these angles increase from 180 to 0 °); rz and

pz are the angles of supply of the pulses stabilizing the combustion of the arc (as can be seen from Fig. 2, these angles increase from 0 to 180 °); Uax and Imax - current through load 14 - it is determined by the angles (f and open thyristors 12 and 13

respectively, as well as the inductance value of the throttle 8 and the value of the IDLE voltage of the WINDING 5; And imin

current 14 through closed thyristors 12-13, its value is determined by the angles p and pi of the thyristors 12-13 open, the total voltage of the windings 5 and 4, as well as the total inductance of the chokes 7 and 8; In and G are the values of the current stabilizing the combustion of the arc of pulses,

which are determined, ceteris paribus, by the charging voltage of the capacitor 9 at different half-periods: the higher the charge of the capacitor 9, the greater the current and the arc stabilizing the burning of the pulse, and the charging voltage of the capacitor 9 is determined angles rz and (rl for supplying stabilizing combustion of the arc of the pulse.

As shown in work 3 and described in

this material above, the ratio of the voltages Uo + / Uo 2.5,., 9, and therefore the ratio of the charging voltages of the capacitor 9 in different half-periods can reach the same values, which is carried out by selection

angles (pz, - (p4 open the thyristors 10-11. The device (Fig. 1) works as follows. When applying the mains voltage to the winding 3, the total voltage of the windings 4 and 5 is applied to the arc gap 14. The arc ignites from this total voltage, and the arc current is limited by the total inductance of the chokes 7 and 8. It is known that the current-voltage characteristic of the arc has three sections: steeply dipping - at low currents, horizontal - in the region of the working welding current, growing - at significant welding densities current. ochih welding currents the voltage on the arc hardly varies with a change in the welding current. Therefore, the required power delivered to the arc gap 14 in both half-waves, a predetermined value of welding current. The magnitude of the welding

the current is set by the angles p- and pi (Fig. 2) of the opening of the thyristors 12 and 13. While these thyristors are closed, a minimum current Imin flows through load 14 (Fig. 2 shows the current diagrams of the device connected to the active load for clarity). This current is generated by the main welding 5 and additional 4 windings connected in series, and is limited by interros 7 and 8, moreover, their total inductance is such that with fully closed thyristors 12 and 13, a current Imin 7 ... 10 A flows through the load - the minimum current arc discharge.

Since in our device angles. open the power thyristors 12 and 13 are different, then different in duration of the flow of currents lmin + and Imin. When thyristors 12 and 13 are fully open, winding 4 and inductor 7 are short-circuited and maximum load t ok - tmax from winding 5 will flow through load 14 through thyristors 12 and 13.

Let the positive half-wave come to the beginning of winding 5 (Fig. 1 is indicated by a dot) (Fig. 2 is indicated by +).

The thyristor 12 with a certain angle m, set by the control unit 15, opens and the maximum current of the positive half-wave - lmax +, flows through the load 14. A thyristor 13 with an angle p2 set by the control unit 15 will open into the negative half-wave, and the maximum current of the negative half-wave, Imax, will flow through the load 14. In the case depicted in FIG. 2, (p pi, i.e., a larger current flows through the load into the positive half-wave than into the negative:

lmax + Imax. The angles p AND (pi are regulated by the control unit 15 separately, and therefore, the current in different half-periods is set in accordance with the melting rate Vn of the electrode in different half-periods. This correspondence is established empirically for each type of electrode or wire separately, due to the different melting rates in this half-cycle. of the fact that, as noted above, the voltage on the arc is almost constant, then, in order to change the power supplied to the arc in each half-cycle, it is necessary to change the amount of current transmitted through the arc a gap in the corresponding half period, and the arc current at every half cycle establishes a empirically angles (p and (p-opening thyristor 12 and 13. The ratio of input to the half-periods of different capacities, as noted above, must satisfy the relation:

F + / F VnVVn + G / G 0.7 ... 1.5.

At present, the adjustment (selection) of angles p v (p2 is carried out empirically (empirically): the more

given half-cycle, the melting speed of the electrode, the smaller the angle p (or) of the thyristor 12 (or 13) is set when selecting the welding mode, the smaller should be the welding current in this half-cycle. This makes it possible to equalize the melting rates of the electrode (Vn + Vn) in both half-cycles. which increases the stability of the process by ensuring self-regulation of the supply of the electrode wire.

The gap 2 in the magnetic circuit of the device transformer 1 prevents this transformer from saturation due to the asymmetry of the welding current. The control unit 15 generates the triggering pulses of the thyristors 10 ... 13 depending on the feedback on the voltage of the arc and on the voltage from the winding 28. rigidly connected to the winding 1.

0. Applying appropriate feedbacks, for example, following the change in the length of the arc using software, it is possible to develop a device in the future that automatically sets the opening angles of the thyristors 12 and 13, and therefore, the current value in each half period.

For reliable reignition

0 AC arcs when it passes through zero to the arc gap, it is necessary to apply a sufficient voltage for its electrical breakdown. Therefore, the magnitude of the power invested in the arc gap by stabilizing the burning of the arc pulses for re-ignition in different half-periods is determined by the magnitude of the voltage applied to the load 14 in these half-periods.

The voltage value of the arc-stabilizing pulse is determined by the angles rz and (Fig. 2) of the thyristors 10 and 11: the larger these angles are, the more capacitor 9 is charged, the more the magnitude of the arc-stabilizing pulse is created.

According to the picture, the creation of a pulse stabilizing the burning of an arc is an example. Let in

0 the beginning (indicated by dots) of windings 5 and 6 comes a positive half-wave voltage. The control unit 15 instructs the thyristor 11 to open with a certain angle rz, which pushes the pulse to

5 is a relatively large distance from zero. The voltage across windings 5,6 and 4 (if thyristors 12 and 13 are closed) will have time to increase to a certain value and the capacitor 9 will charge to the value necessary for the electric breakdown of the arc gap. When the polarity changes from positive to negative half-wave with an angle RA pz at the electrode, the thyristor 10 opens and the capacitor 9 charges to a lower voltage, because in connection with a smaller angle. prl, the windings 5,6 and 4 will also have a lower voltage (with the arrival of the cathode electrode, a lower voltage is required). The magnitude of these pulses for each specific electrode or wire is again determined empirically. Thus, a pulse stabilizing the burning of the arc is generated with the arrival of the anode electrode (positive polarity) more than with the arrival of the cathode on the electrode. This makes it possible to create good conditions for reignition of the arc in both half periods and to avoid the excess energy of the pulse stabilizing the burning of the arc with the arrival of the cathode electrode, which increases the stability of the process. As a view from figure 2, the current stabilizing the burning of the arc pulses and the arc current are inverse phase. This is done on purpose, since in this case the stability of the burning of the arc is higher than with the same phasing of the pulse current and the arc current,

. The use of the method and device for arc welding with a melting electrode with an alternating current made it possible to increase the stability of the process both due to reliable re-ignition of the arc and due to the condition of self-regulation of the process in both half periods, which increased the quality of welding, while expanding the range of regulation of welding current .

AC welding using the proposed method and device is more technologically advanced than DC welding for the following reasons: when welding with alternating current, an effect of modulation with a frequency of 50 Hz is observed, and modulation improves the quality of welding; when welding with alternating current there is no magnetic blast, which when welding with constant current by a wire of a larger diameter does not allow to raise operating modes above 250 ... 300 A, especially when welding into a narrow gap.

 In the IES them. E.O. Paton Academy of Sciences of the Ukrainian SSR created a device for arc welding with a melting electrode with alternating current with separate control of pulsed energy input in both half-periods. Such types of welding with alternating current with a melting electrode were tested on it: manual arc welding with electrodes with a basic coating (type UONI-13/45 , UONI-13/55, OEL-3, etc.), mechanized welding with Sv-08G2S wire in a mixture

Ar + COa, as well as mechanized saark with flux-cored wire in a CO2 medium and self-shielding wire. As the welded metal, StZSp steel was used.

Previously, all these types of welding were carried out only with direct current. The developed device provides reliable re-ignition and process stability of the listed types of welding

on alternating current, which is more efficient (30 to 50%) than DC welding.

Claims (2)

1. The method of arc welding melting an alternating current electrode, in which stabilizing energy pulses are fed into the arc gap for reignition of the arc in each half-cycle, characterized in that, for the purpose of improving the quality of welding and expanding the ranges of the welding mode by increasing the stability of the process and choosing the optimal welding modes in both half periods, the ratio of the powers supplied to the positive and negative half periods is set equal to the ratio of the melting rates of the electrode wire in the negative and positive half periods, and the ratio of powers stabilizing pulses are set equal to the ratio of powers required for re-ignition of the arc discharge in half-periods of the same polarities. 2. A device for arc welding with a consumable electrode by alternating current, comprising a welding transformer with rigid external characteristics, having a primary winding, a secondary welding winding, first and second secondary auxiliary windings, two chokes, capacitor, two thyristor switches and a control unit for thyristors with phase-shifting chains, characterized the fact that, in order to improve the quality of welding and expand the ranges of the welding mode by increasing the stability of the process and choosing optimal welding modes in both half periods, the first secondary additional winding, the secondary welding winding, the second additional secondary winding, the first thyristor switch are connected in series with each other. , capacitor, first and second chokes, output the second throttle is connected to the terminal of the first additional secondary winding, the other terminal of which is connected through the second thyristor switch to the connection point of the first and second chokes. FIG. 2.