RU2106944C1 - Device for excitation and stabilization of burning of welding arc - Google Patents

Abstract

FIELD: electric arc welding. SUBSTANCE: invention refers to electric arc welding of metals with consumable electrode and is meant for welding of steel structures predominantly of small thickness. Device forms voltage of shock excitation with wide frequency spectrum as a result of sequence of resonances. Device is inserted with current regulator, choke, second storage circuit and symmetric thyristor commutator. First input terminal of device is connected to first input of current regulator which second input is connected to end of primary winding of input transformer. End of secondary winding of it is connected to start of secondary winding of high-voltage transformer, finish of secondary winding is connected to second output terminal of device which second input terminal is connected to start of primary winding of pulse transformer and to first output of current regulator. Second output of current regulator is connected to other lead-out of limiting element. Finish of secondary winding of pulse transformer is connected to controlling electrode of symmetric thyristor commutator. Start of secondary winding of pulse transformer is connected to second lead-out of first storage circuit which first lead-out is connected to first input terminal of device through second storage circuit and choke connected in series. EFFECT: increased operational efficiency and reliability of device. 5 dwg

Description

 The invention relates to electric arc welding of metals with an electrode and is intended for welding structures of steel mainly of small thicknesses.

 The known device [1], selected as an analogue, is characterized by the fact that in the generator the secondary winding of the pulse transformer is connected in series to the welding circuit of the power source, in series with the primary winding of the transformer are a thyristor and a capacitor charged by a voltage converter, the input of which is connected to the input of the control unit . A shunt connected to a current source is included at the input of the control unit.

 The disadvantage of the presented analogue is that the polarities of the exciting high-voltage pulse of the initiating arc and the open circuit voltage do not coincide, which, when the power supply is reduced, the efficiency of excitation and stabilization of the combustion of the welding arc will decrease.

 The known device [2], selected as an analogue, is characterized in that it consists of a pulse generator, a protective capacitor connected in parallel with the power source, an output high-frequency transformer, the secondary winding of which is connected in series to the welding circuit, and the primary is connected to a storage capacitor, to a spark gap, and the secondary winding of a step-up transformer, the primary winding of which is connected in parallel through the capacitor through the capacitor.

 The disadvantages of the presented analogue include the presence of a spark gap, the electrodes of which are susceptible to erosion, and insufficient power of the exciting high-voltage pulse, respectively, insufficient ionization efficiency of the electric arc gap.

 The closest in technical essence and the achieved positive effect to the proposed device is selected as a prototype device for excitation and stabilization of the combustion of the welding arc [3].

 A device for exciting and stabilizing the welding arc, containing an input transformer, the beginning of the primary winding of which is connected to the first input terminal of the device, and the beginning of the secondary winding of the input transformer is connected to the first output terminal of the device, the first output of the first storage element is connected to the beginning of the primary winding of the high voltage transformer, end the primary winding of which is connected to the first output of the thyristor switch, the second output of which is connected to the beginnings of the primary and secondary th windings of a pulse transformer, the end of the primary winding of which is connected to one of the terminals of the limiting element.

 The disadvantage of the prototype should include the fact that the device generates an exciting high-voltage pulse of insufficient power, respectively, provides an insufficient degree of ionization of the electric arc gap.

 The technical result of the invention lies in the fact that a sequence of current resonance and voltage resonance is formed in it. The parameters of the oscillatory circuits determine their quality factor, respectively, the amplitude of the voltage and the power of the exciting pulse.

 The technical result is achieved in that in a device for exciting and stabilizing the combustion of a welding arc containing an input transformer, the beginning of the primary winding of which is connected to the first input terminal of the device, and the beginning of the secondary winding of the input transformer is connected to the first output terminal of the device, the first output of the first storage element is connected to the beginning of the primary winding of the high voltage transformer, the end of the primary winding of which is connected to the first output of the thyristor switch, the second output it is connected to the beginnings of the primary and secondary windings of a pulse transformer, the end of the primary winding of which is connected to one of the terminals of the limiting element, unlike the prototype, a current regulator, a choke and a second storage element are introduced into it, and the thyristor switch is symmetrical and the first input terminal of the device is connected to the first input of the current regulator, the second input of which is connected to the end of the primary winding of the input transformer, the end of the secondary winding of which is connected to the beginning of the second primary winding of a high-voltage transformer, the end of the secondary winding of which is connected to the second output terminal of the device, the second input terminal of which is connected to the beginning of the primary winding of the pulse transformer and to the first output of the current regulator, the second output of which is connected to the other output of the limiting element, and the end of the secondary winding of the pulse transformer connected to the control electrode of the symmetric thyristor switch, the beginning of the secondary winding of the pulse transformer is connected to the second output terminal of the first storage element, the first output of which is connected in series through the second storage element and the inductor to the first input terminal of the device.

The essence of the invention lies in the fact that in series-connected circuits connected in series and parallel to an alternating voltage source, shock excitation of the circuits forms a sequence of resonances in them. Due to the formation of a sequence of resonances, a shock excitation voltage with a wide frequency spectrum is created on a high-voltage transformer. In this voltage, there are frequencies f ₁ and f ₂ close to the eigenfrequencies of both vibrational circuits, at which a sequence of resonances is realized.

 The essence of the invention lies in the fact that the device generates a voltage in the primary winding of a high voltage transformer, the value of which is K times greater than the voltage source voltage; K is determined by the quality factor of the serial circuit. This allows you to significantly increase the oscillation power in the high voltage transformer by increasing the amplitude of the oscillations. An increase in the oscillation power helps to increase the degree of ionization of the electric arc gap, excitation and stabilization of arc burning.

In FIG. 1 is a functional diagram of a device for exciting and stabilizing the combustion of a welding arc; in FIG. 2 is a timing diagram of the operation of the device of FIG. one,
Where
U (wt) is the shock excitation voltage;
V (wt) is the alternating voltage;
α is the amplitude of the voltage resonance; (the phase of the fundamental harmonic ψ is zero).

 In FIG. 3 is a fragment of a shock excitation voltage diagram of the circuits of FIG. 1 (a sequence of resonances is shown at points A and B); in FIG. 4 is a timing diagram of the operation of the device of FIG. 1 with phase shock voltage regulation; in FIG. 5 is an electrical circuit diagram of an example of a specific embodiment of the device according to FIG. one.

 Presented in FIG. 1, a functional diagram of the device contains an input 1 transformer, the primary winding of which is connected through a current regulator 2 to the input terminals of the device. The second output of the current regulator through a limiting 3 element and a pulse 4 transformer is connected to the control electrode of the symmetric 5 thyristor switch. Serially connected inductor 6, accumulator 7 element and parallel connected high-voltage 8 transformer and second accumulator 9 element form respectively serial and parallel oscillatory circuits connected through high-voltage 8 transformer to electric arc 10 gap.

 The device operates as follows.

 The input transformer 1 for supplying the welding arc generates an alternating open circuit voltage of 50–70 V. For stable arc burning at such an open circuit voltage of the input transformer, the minimum welding current must be 60–100 A [4]. In this case, the input transformer should provide power to the welding circuit 3500 - 7000 watts. When welding structures of sheet metals with a thickness of 0.5 - 1.5 mm by electric arc welding, the current should be from 30 to 40 A in order to avoid thermal burn-through of the metal. Such a welding current can be used, in particular, for welding automotive metal. But at currents of 30 - 40 A, the energy in the arc gap is not enough for stable arc burning.

 For the purpose of excitation and stable burning of an alternating current arc, a high-voltage transformer connected in series with the secondary winding of the input transformer to the welding circuit generates, at the beginning of the supply of the welding current to the arc gap, high-voltage pulses with an amplitude of 4-8 kV, polarity identical to the polarity of each half-wave of the alternating output voltage input transformer.

 An alternating voltage is applied to the input terminals of the device. This alternating voltage is supplied to input transformer 1, current regulator 2, and to series and parallel oscillatory circuits consisting of inductor 6, storage elements 7 and 9, and high-voltage transformer 8.

 The current regulator 2 represents a phase-shifting device, which, with each half-wave alternating voltage connected to the input 1 transformer to the alternating voltage, generates a triggering pulse to the control electrode of the symmetric 5 thyristor switch through a limiting 3 element and a pulse 4 transformer. In this case, the alternating voltage at the capacitive divider of the series oscillatory circuit, namely at the storage elements 7, 9, is divided in proportion to their capacities, which then participates in the formation of the voltage of the shock voltage.

где
A - амплитуда переменного напряжения;
w - круговая частота основной гармоники;
n - номер гармоники;
α - амплитуда резонанса напряжения;
ψ - фаза основной гармоники
Зависимость согласно уравнению (1) можно представить в виде суммы двух функций:
- первая функция - косинусоида
V(wt) = ACos(wt),
есть напряжение, поданное от источника переменного напряжения и прошедшее через емкостной делитель;
вторая - биполярная последовательность прямоугольных импульсов с периодом, равным периоду косинусоиды, и аналитически представляема рядом Фурье, как

,
где
α - амплитуда прямоугольных импульсов.Through a controlled symmetric 5 thyristor switch in a circuit of a parallel oscillatory circuit, consisting of a high-voltage transformer 8 and a storage element 9, shock excitation of the circuit is formed. As a result of this, shock excitation voltage U (wt) is formed in the oscillatory circuits according to the diagram of FIG. 2 of complex shape and wide spectral composition, the analytical expression of which corresponds to the dependence in the form of a Fourier series

Where
A is the amplitude of the alternating voltage;
w is the circular frequency of the fundamental;
n is the number of harmonics;
α is the amplitude of the voltage resonance;
ψ - phase of the fundamental harmonic
The dependence according to equation (1) can be represented as the sum of two functions:
- first function - cosine
V (wt) = ACos (wt),
there is voltage supplied from an alternating voltage source and passed through a capacitive divider;
the second is a bipolar sequence of rectangular pulses with a period equal to the period of the cosine wave, and is analytically represented by the Fourier series, as

,
Where
α is the amplitude of the rectangular pulses.

 At the newly formed harmonics, a sequence of resonances is formed as a result of shock excitation of the oscillations, and the currents resonance is first carried out, since a controlled switch is installed in the parallel circuit, respectively, there is a way for direct current to pass through. Then the voltage resonance is carried out in a series circuit consisting of a reactor 6 and storage elements 7 and 9.

 According to FIG. 2, the segment AB of the voltage U (wt) corresponds to the resonance of the currents, and the segment BC to the resonance of the voltages. Further, the curve CA '(part of the cosine wave) is proportional to the application of alternating voltage to the series-connected circuits. And the segments A'B 'and B'C' correspond similarly to the above processes.

 In FIG. 3 is a fragment of a shock excitation voltage diagram of the circuits of FIG. 1 showing a sequence of resonances.

From point A to point B, a damped cosine curve characterizes the resonance of currents in a parallel circuit, carried out with a frequency f ₁ . Moreover, the resonance of the currents is carried out at the harmonic formed as a result of shock excitation of the circuits, the frequency of which is close to the natural frequency of the parallel circuit.

,
где
L₈ - индуктивность высоковольтного трансформатора;
C₉ - емкость накопительного элемента 9.

,
Where
L ₈ - inductance of a high voltage transformer;
C ₉ - the capacity of the storage element 9.

The damping decrement is determined by the losses in the circuit, mainly the closing time of the control key τ _s . After the end of the resonance of the currents, the resonance of the voltages in the series oscillatory circuit begins. From point B to point C, the damped cosine characterizes the resonance of the stresses, carried out with a frequency f ₂ . Moreover, the shift along the ordinate axis by the value of α characterizes the amplitude of the oscillatory process and is determined by the parameters of the elements of the oscillatory circuit. The resonance of the voltages is carried out at the harmonic formed during shock excitation of the circuit, the frequency of which is close to the natural frequency of the sequential oscillatory circuit.

где
L₆ - индуктивность дросселя 6;
C₇, C₉ - емкости накопительных элементов.

Where
L ₆ - inductance of the inductor 6;
C ₇ , C ₉ - capacity storage elements.

 The damping decrement is determined by losses in the series circuit.

 By changing the parameters of the oscillatory circuits, the frequencies at which the resonance sequence is carried out change. In this case, the quality factor of the contours can be brought up to 100 units and higher.

 Thus, as a result of a sequence of resonances flowing in the circuits from the secondary winding of the high voltage transformer 8, high-voltage high-voltage pulses are supplied to the electric arc gap 10, and simultaneously with the supply voltage of the arc from the secondary winding of the input transformer. This ensures the excitation and stabilization of the burning of the arc.

 In FIG. 4 is a timing diagram of the operation of the device of FIG. 1 with the regulation of the magnitude of the voltage of the shock excitation in phase.

 According to FIG. 4, the shape of the shock excitation voltage MNEO corresponds to the analytical dependence according to equation (1) (phase ψ = 0) and ensures the formation of the maximum shock excitation voltage. When the fundamental harmonic is shifted to the left by the ψ phase, the shape of the shock excitation voltage takes the form of a curve denoted by 1 MNKO (according to Fig. 4) and corresponds to equation (1) of the general case (when the phase ψ ≠ 0). In this case, the voltage generated by the resonance of the currents and applied to the primary winding of the high-voltage transformer decreases in proportion to the phase shift and, accordingly, is equal to OK. The voltage generated during voltage resonance remains unchanged.

При этом напряжение, формируемое при резонансе токов, уменьшается до величины OL.When the fundamental harmonic is shifted by 90 ^{°, the} shape of the shock excitation voltage takes the form according to curve 2 of MNLO and is analytically expressed as

In this case, the voltage generated by the resonance of the currents decreases to the value of OL.

 From FIG. 4 and the above, it follows that by means of a current regulator 2 providing a phase shift of the triggering pulses with respect to the alternating voltage, it is possible to control the magnitude of the shock excitation voltage, respectively, the power of the high voltage triggering pulses in the arc gap.

 In FIG. 5 is an electrical circuit diagram of an example embodiment of the device of FIG. 1, in which the pulse 4 transformer is made on a ferrite core, the inductor 6 is coreless, the storage elements 7 and 9 are capacitors, and the high-voltage transformer 8 is also coreless. The current regulator 2, representing the phase-shifting device, is made in the form of a series-connected resistor 11, a potentiometer 12 and a capacitor 13. The midpoint between the capacitor 13 and the potentiometer 12 is connected through a symmetric dinistor 14 to the control electrode of the symmetric thyristor switch 15, which connects the input transformer 1 to the network AC voltage.

 The device according to FIG. 5 works as follows.

A voltage of 220 V at a frequency of 50 Hz is supplied to the input terminals of the device, from which the series-connected oscillatory circuits and the current regulator 2 are fed. The latter through the phase-shifting circuit, consisting of resistors 11, 12, the capacitor 13 and through the symmetrical 14 dynistor, generates the triggering pulses to the control electrodes of the symmetric 5, 15 thyristor switches in each half-period of alternating voltage. The alternating voltage on the capacitive dividers C ₆ and C _{7 of the} series-connected oscillatory circuits is divided according to their capacitances and then participate in the formation of the shock excitation voltage.

 Through the thyristor 5 switch, a series of resonances is launched, which flow in a parallel circuit (high-voltage transformer 8 and capacitor 9) and in a series circuit (inductor 6 and capacitors 7 and 9) to form high-voltage trigger pulses in the arc gap. Also simultaneously supplied through the input 1 transformer is the supply voltage to the arc gap.

 In FIG. 5 shows the beginning of the transformer windings, which ensure the coincidence of the polarities of the arc supply voltage and the voltage of high voltage pulses. This coincidence of polarities ensures the stability of the excitation and combustion of the arc, especially at low currents.

 The pulse transformer is designed to coordinate the phase shift between the voltage of the current regulator 2 and the voltage of the high voltage 8 transformer.

 By adjusting the potentiometer 12 of the current regulator 2, the power of the power source in the arc gap and the voltage value of the high voltage pulses are set.

 In the manufacture and testing of a laboratory sample of the welding machine, the symmetric thyristor switch TC132-50-12 was used as the key that controls the shock excitation of the circuits. It provided voltage switching in the primary circuit of a high-voltage transformer up to 1.6 - 2.0 kV. This made it possible to increase the amplitude of the exciting pulses to 8 kV.

 The positive effect of the invention lies in the fact that the device simultaneously with the supply of power to the electric arc gap generates a voltage in the primary circuit of the high-voltage transformer, the amplitude of which is several times higher than the value of the alternating voltage of the power source. This made it possible to significantly increase the power of high voltage pulses, respectively, the degree of ionization of the electric arc gap.

 Improved conditions for the excitation and stabilization of arc burning will allow welding to be carried out at a higher level.

Claims (1)

 Excitation and stabilization device for burning a welding arc containing an input transformer, the beginning of the primary winding of which is connected to the first input terminal of the device, and the beginning of the secondary winding of the input transformer is connected to the first output terminal of the device, the first output of the first storage element is connected to the beginning of the primary winding of the high voltage transformer, end the primary winding of which is connected to the first output of the thyristor switch, the second output of which is connected to the beginnings of the primary and second the secondary windings of a pulse transformer, the end of the primary winding of which is connected to one of the terminals of the limiting element, characterized in that a current regulator, a choke and a second storage element are introduced into it, and the thyristor switch is symmetrical, and the first input terminal of the device is connected to the first input of the current regulator the second input of which is connected to the end of the primary winding of the input transformer, the end of the secondary winding of which is connected to the beginning of the secondary winding of the high voltage transformer, the end of the secondary winding of which is connected to the second output terminal of the device, the second input terminal of which is connected to the beginning of the primary winding of the pulse transformer and to the first output of the current regulator, the second output of which is connected to the other output of the limiting element, and the end of the secondary winding of the pulse transformer is connected to the control electrode of the symmetric thyristor switch, the beginning of the secondary winding of a pulse transformer is connected to the second output of the first storage element, the first whose output terminal is connected in series through a second storage element and a choke to the first input terminal of the device.

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