RU2467845C2 - Method of igniting arc in manual arc welding with combined soft and hot starting - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: method is intended for igniting arc in manual arc welding with combined soft and hot starting. Soft start is performed at short-circuiting the electrode to part. Hit start is performed in parting the electrode from the part and setting arc discharge. Soft start current is set subject to electrode diameter or preset welding current. Changing to hot start is performed in response to signal of voltage transducer that detects arc ignition at the end of soft start. Hot start current is set subject to electrode coating type and set welding current. Microprocessor-controlled power supplies are used including thyristor rectifier, inverter-based source or transistor station controller incorporated with multi-station rectifier system. Note here that in soft start auxiliary low-power HV infeed source.

EFFECT: higher reliability.

3 cl, 3 dwg, 3 ex

Description

The invention relates to the field of welding production, in particular to the technology of manual welding with a coated electrode, mainly to a method of ignition of a welding arc by closing the electrode to the welded part.

The prior art mechanism for ignition of an arc by a short circuit, which consists in the fact that at the moment the electrode touches the part, a short circuit current exceeds the value of the adjusted welding current, due to which the temperature of the metal in microcontacts on the electrode surface and the part reaches high values, including melting or boiling points. In the interelectrode space that occurs when the electrode is removed from the part or the jumpers burn out in the microcontacts between them, the processes of electron emission from the cathode and thermal ionization of the gas in the arc column begin to develop. With the formation of a sufficient number of current carriers, electrons and ions, an independent arc discharge is established in the interelectrode space.

The implementation of the method of arc ignition during manual welding using a welding current source of known traditional design does not guarantee reliable initial ignition, which depends, inter alia, on the type of electrode coating and the qualifications of the welder. The most likely violations of the described ignition process are: sticking of the electrode to the part at the stage of short circuit and arc break at the stage of establishing the arc discharge. In addition, with repeated ignitions, it is difficult to initially establish an electrode-component contact, since after previous acts of welding with this electrode, a durable layer of non-conductive slag forms on its end.

Known improved method of ignition of the arc with the stage of the so-called "hot start". This method is most often carried out using thyristor rectifiers, invertor sources and transistor gate controllers (see, for example, the Catalog of Uraltermosvar CJSC for 2010 or the Catalog of ITS-Ural LLC for 2010). Details of this process, its purpose, modes and parameters are described in the book “Metallurgy of arc welding. Processes in an arc and melting of electrodes ”, authors Pokhodnya IK, Gorpenyuk VN et al. - Kiev: Naukova Dumka, 1990. - 224 p. To carry out the hot start stage, within 0.5-3 seconds, an initial current increase of 1.4-2 times is provided, due to which the reliability of the arc discharge is increased and, therefore, the quality of the initial section of the weld is improved. The probability of sticking of the electrode in this method is not eliminated, however, the intensity of burnout of the jumpers in the contact "electrode-part" during hot start increases. If, after burning the jumpers, the electrode continues to be pressed against the part, then, despite the hot start, sticking of the electrode to the part is still possible.

There is a known method of ignition of a welding arc, involving the stage of "soft start", carried out at a current, the value of which is in the range from 0.2 to 0.3 from the welding, while the duration of the operation is not significant, and therefore, welding can be performed by a welder of any skill. This technical solution at the first stage of a short circuit provides reliable contact between the electrode and the part without the danger of sticking, and at the second stage, following the termination of the circuit, the establishment of an arc discharge (see T. Dahlstrom. TIG logic function, "Pronews Kemppi", 2003, No. 1).

This method can be successfully used when welding with a nonconsumable electrode in an inert gas (see Lincoln Electric 2007 Product Catalog, Microstart ^ТМ function; ESAB Standard Equipment product catalog 2008, LiftArc ^ТМ function; Kemppi product catalog, 2008-2009 d., Soft Start or Contact functions).

However, when trying to use the known method for welding with a coated electrode, significant shortcomings were revealed, in particular, insufficient reliability of the transition to the second stage — the establishment of an arc discharge with the current set for welding, since when performing a soft start at the first stage — short circuit — the heating of the electrode and the part is insufficient to develop an intense process of electron emission and thermal ionization of the gas. On the other hand, it is during welding with a consumable electrode that a soft start in the first stage of a short circuit could be especially useful, in particular, with repeated ignitions performed by a cooling electrode after a long break. This is due to the peculiarities of soft start, due to which it is possible to perform additional actions to destroy the slag layer formed at the end of the electrode without the danger of the electrode sticking to the part.

The prior art method of ignition of an arc with a controlled sticking of the electrode, combining in a common software algorithm the stages of soft and hot start. In this case, arc ignition is performed in three stages, the first of which is the formation of a short-term initial hot start mode at the moment the electrode touches the part. Then, after a predetermined time interval has elapsed, a short-circuit current restriction mode is created at a level sufficient for a slight heating of the electrode, but without increasing the contact area and strong adhesion, thereby achieving controlled adhesion. Then, at the moment of separation of the electrode from the part, they switch to the mode of repeated hot start, as a result of which an arc is ignited in the interelectrode gap (see RF patent for invention No. 2270080 “Method of arc ignition with controlled electrode adhesion during manual arc welding”, filing date 11.06.2004 published on 02/20/2006).

The disadvantages of this method are primarily due to the mandatory, albeit fragile, adhesion of the electrode to the part. In addition, some variants of welding technology do not require the first stage of a short circuit, for example, welding of sheet structures or welding with large diameter electrodes.

Closest to the claimed invention is a method of ignition of a welding arc, which consists in sequentially performing the stages of soft and hot starts. Ignition control is as follows. At the moment the electrode touches the part, the high-voltage feed source is turned on, providing a soft start current of 20-40 A. At the moment the electrode is detached from the part, the main power source is switched on in the hot start mode with a current of 1.5 from the welding and a fixed operating time of 0.7 seconds. Then, the source switches to the main mode with a pre-set value of the welding current (see Milyutin BC and other article “Technological kits“ source-semiautomatic device ”with microprocessor control for welding fixed joints of pipelines”, magazine “Welding production”, No. 9, 2007 .).

This method is particularly effectively implemented using microprocessor-controlled power supplies, namely a thyristor or inverter rectifier, as well as a transistor fast controller - chopper. This method was tested in a wide range of grades and diameters of the electrodes, as well as welding modes and confirmed the high reliability of the initial ignition - in 50-100% of cases, the welding arc ignites after the first electrode touches the part.

However, the known method also has several disadvantages, including a fixed (set) value of the soft start current, which is high for modes using small diameter electrodes, for example 2 and 2.6 mm, and low when using large diameter electrodes, for example 5 -6 mm. In addition, it is necessary to optimize the value of the hot start current, namely, its increase for low modes and a decrease for high ones. Despite the fact that this method can be implemented using electrodes with any type of electrode coating, there are problems with the establishment of an arc discharge when welding with cellulose-coated electrodes, in which the violation of the arc excitation process occurs in the form of arc extinction immediately after the electrode is detached from the part.

The technical result, to which the claimed invention is directed, is to increase the reliability of ignition of the welding arc, independent of the grades and diameters of the electrodes, types of electrode coating, welding modes, ignition techniques, as well as personnel qualifications.

This result is achieved by the fact that in the method of ignition of the arc in manual arc welding with a combination of the stages of soft and hot starts, including the stage of soft start at the stage of short-circuiting the electrode to the part and the stage of hot start at the stage of detaching the electrode from the part and establishing an arc discharge, according to the invention current I _cpx soft start phase determined depending on the diameter d _e of electrode used in the following ratio: I = 10d _{cpx e,} or depending on the magnitude of the welding current I is configured with the following _binding ootnoshenii: I _MP = (0,2-0,3) I _binding, current hot start in step I _r is set depending on the magnitude of the welding current with the following relationship: I _r = I 1.5 _binding, and the duration is set hot start phase in the range of 0.5-1.5 s, and the transition to the hot start stage is performed according to the voltage sensor signal about the occurrence of an arc at the end of the soft start for 0.1 s at a voltage of 15-20 V.

To implement the method, microprocessor-controlled sources are used as a power source, including a thyristor rectifier, an inverter source or a transistor fast controller (chopper), which is part of a multi-post rectifier system. Moreover, at the soft start stage, an auxiliary low-power high-voltage source of recharge can be used.

The hot start current is set in the range of 100-300 A.

Technical solutions that coincide with the totality of the essential features of the claimed invention have not been identified, which allows us to conclude that the claimed invention meets such a patentability condition as “novelty”.

The claimed essential features that predetermine the receipt of the specified technical result, do not explicitly follow from the prior art, which allows us to conclude that the claimed invention meets such a patentability condition as "inventive step".

The patentability condition "industrial applicability" is confirmed by the example of a specific implementation.

The essence of the proposed method of arc ignition in manual arc welding with a combination of the stages of soft and hot starts is illustrated by drawings, where

Figure 1 - diagram of the welding (thyristor) source used to implement the proposed method;

Figure 2 - graph of the current control according to the claimed invention;

Figure 3 - waveforms of current and voltage obtained during the implementation of the claimed invention.

Used to implement the proposed method, for example, a thyristor rectifier with a microprocessor (MP) controller A contains (Fig. 1) a power circuit breaker QF, a power step-down transformer TM, a power thyristor rectifier unit VS and a power choke LM in the main welding circuit. In addition, the rectifier is equipped with a welding current sensor BI, voltage sensor BU, welding current generator RP1 I _st and RP2 other process parameters, in particular I _gp , t _gp , U _per depending on the diameter of the electrode, type of electrode coating, etc. . The device also contains a make-up circuit including a KV magnetic starter, a low-power TV transformer, a low-power VD diode rectifier unit, and an adjustable RV ballast. Make-up is necessary to fill the dips of the welding current when the thyristors are off, as it provides increased open-circuit voltage.

The make-up circuit is used to power the arc at the soft start stage, while the soft start current I _{MP is} adjusted using the ballast rheostat RV. In the case of arc supply at the soft start stage from the main welding circuit, an unregulated ballast rheostat (not shown) is used in the feed circuit.

Before welding, the settings RP1 and RP2 are set accordingly. Microprocessor controller A receives commands from these devices, as well as signals from the welding current sensors BI and voltage BU. In turn, the MP controller issues commands for phase control of the thyristor rectifier unit VS, for switching on the magnetic starter KV and switching the ballast resistor RV in the make-up circuit. Before starting welding, the safe voltage on the interelectrode gap, necessary for detecting the state of this gap, is 10-12 V.

In addition, an inverter source or chopper can be used as a source of welding current - a transistor fast controller, which is part of a multi-post rectifier system. In this case, the MP controller provides pulsed control of the sources, namely, amplitude, frequency or latitudinal.

The ignition of the arc begins when the electrode touches the surface of the part t ₁ (figure 2). At the command of the voltage sensor BU, MP-regulator A starts the source in soft start mode: turns on the KV magnetic starter in the make-up circuit or switches on the main power circuit. A short circuit occurs with a limited current of I _megapixel soft start, sufficient to establish reliable contact in the circuit "electrode-part" and a slight heating of the electrode, which does not lead to adhesion. The values of the soft start current I _MP are set in the range from 0.2 to 0.3 from the adjusted welding current I _st .

At the moment t _{2 of the} electrode is detached from the part, the moment t _{3 of the} transition to hot start is initiated, which is not pre-configured. In this case, a low-power arc with a current of I _megapixels arises, which is necessary for detecting the ignition moment with the help of a voltage sensor BU. Confirmation of the ignition moment, and not a random flash, is considered to be the conservation of an arc with a transition voltage U _per equal to 15-20 V for 0.1 second. When these conditions are met, the MP-controller A transfers the main power circuit to the hot start mode from the moment t ₃ .

Further, the establishment of the arc process occurs at an increased current of I _gp , which leads to the rapid heating of the electrode and the part and, as a result, to intensification of electron emission from the cathode and thermal ionization in the arc column. Due to the smooth transition from soft start to hot start, the conditions of arc burning are improved and its breaks are prevented with excessive initial elongation. In addition, hot start promotes rapid penetration of the part and high-quality formation of the initial section of the weld.

The hot start phase ends at time t ₄ , which corresponds to the end of a pre-configured time interval t _GP . After the hot start, the source switches to welding mode with a pre-set value of the welding current I _St.

The implementation of the proposed method is confirmed by examples of specific performance.

Example 1

The implementation of the proposed method of ignition of the welding arc was carried out with recording waveforms of the welding current and voltage obtained by ignition of the arc using electrodes of the brand LB-52U with a diameter of 2.6 mm, a welding current of 80 A. As a power source, a thyristor rectifier brand VDU-306 MT with MP control (figure 3). The time stamps in this figure correspond to the marks in FIG. 2. The results show that before starting welding (up to time t ₁ ), the power source is in a standby state with a safe voltage of 10 V.

From the moment the electrode touches the part t ₁ in the soft start mode, the recharge source is turned on. In a short circuit condition, a soft-start current of 20 A occurs, while the voltage across the electrode gap decreases to almost zero. At time t ₂ , the electrode detaches from the part and the arc voltage increases rapidly as its length increases. With the simultaneous fulfillment of two conditions, namely: increasing the voltage to a value exceeding 15 V, and maintaining it for more than 0.1 second, the MP controller at time t ₃ starts the main source in the hot start mode with a current of I _gp equal to 120 And those. 1.5 times the value of the specified welding current I _st equal to 80 A. In this case, the voltage continues to increase to an anomalously high value of 28 V. as the welding arc lengthens. This is due to the fact that the initial arc length is assigned to be 10 mm. After 0.5 seconds at time t _{4, the} MP regulator puts the power source in welding mode with the given parameters - current of 80 A and voltage of 18 V.

This example proves the reproducibility of the claimed invention with high accuracy.

Example 2

The method is carried out under the following conditions: welding current - from 40 to 270 A, electrodes with a diameter of 2 to 6 mm with rutile and basic coatings of grades OZS-12, OZS-4 and UONI 13/55, reverse polarity arc, the selected power source VDU-306 MT thyristor rectifier with MP control. The reliability of the initial ignition was evaluated with a combination of the stages of soft and hot starts.

In accordance with GOST 25616-83 "Power supplies for arc welding. Testing methods for welding properties ”reliability of ignition rated 4-5 points. This means that in 60-100% of cases, ignition occurs after the electrode first touches the part, and in other cases, the arc ignites after the electrode moves slightly along the part. In addition, it was found that the limiting initial arc length during ignition under specified conditions is from 12 to 16 mm.

Example 3

When used as a power source for a transistor guard controller — a chopper of the ChPR-315 brand, fed from a multi-post rectifier of the VDM-1201 brand, the maximum initial arc length from 10 to 18 mm was obtained in the modes specified in Example 2. The reliability of ignition of the arc in particularly adverse conditions was also evaluated using this power source using Fox Cel cellulose-coated electrodes of 3.2 and 4 mm diameter, with a straight polarity arc. It should be noted that the use of an arc of direct polarity creates significant difficulties in comparison with the previous examples, since the arc voltage in this case reaches an abnormally high value of 30-40 V. In addition, the mains supply voltage of the multi-post rectifier was reduced by 25%. However, the probability of ignition of the arc from the first touch was 50-80%.

Thus, the inventive method of arc ignition in manual arc welding with a combination of the stages of soft and hot starts has advantages over known technical solutions and can be used in a wide range of grades and diameters of electrodes, as well as welding modes.

Claims (3)

1. The method of ignition of the arc in manual arc welding with a combination of the stages of soft and hot starts, including the stage of soft start at the stage of short circuit with the electrode to the part and the stage of hot start at the stage of separation of the electrode from the part and the establishment of the arc discharge, characterized in that the current I _MP The soft start stage is set depending on the diameter d _{e of the} electrode used in the following ratio: I _mp = 10d _e or depending on the value of the adjusted welding current I _s with the following ratio: I _mp = (0.2-0.3) I _s , current at the mountain stage which start set depending on the magnitude of the welding current I customized _{communication} in the following ratio: I _r = I 1.5 _binding, and duration of the stage hot start is set in the range of (0.5-1.5) s, wherein the hot branches to step start-up is performed by a voltage sensor signal about the occurrence of an arc at the end of a soft start for 0.1 s at a voltage of 15-20V. 2. The method according to claim 1, characterized in that microprocessor-controlled sources are used as a power source, including a thyristor rectifier, an inverter source or a transistor fast controller, which is part of a multi-post rectifier system. 3. The method according to claim 2, characterized in that at the stage of soft start use a high-voltage source of recharge.

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