FI89249C - Supplementary device for protective device, such as a TIG welding device, etc. for plasma welding - Google Patents

Description

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Accessory for shielding gas such as TIG welding machine for plasma welding

Consolidation of account management, in addition to TIG management, based on plasma exchange 5

The invention relates to an accessory for plasma welding of a shielding gas welding device, such as a TIG welding device, by means of which the power supply and possibly other components of the TIG welding device 10 can be used in connection with a plasma welding torch.

In the previously known TIG (Tungsten inert Gas) welding, a direct or alternating current source supplies an arc that burns between the tungsten electrode and the 15 workpieces. The arc is normally ignited by the so-called by means of a high-frequency device or a pulse generator. When the arc is ignited, a high voltage current is applied between the workpiece and the tungsten electrode, causing the current to spark, igniting the arc without the electrode having to touch the workpiece. Light-20 ri burns in a shielding gas using either argon or helium. In manual welding, the filler is introduced directly in the form of wire by hand, and in mechanical welding, the filler wire is guided from the ball to the arc.

25 As is well known in TIG welding, the shielding gas is introduced via a pressure relief valve and a flow meter to the solenoid valve of the control unit, which opens when the welding power supply control switch is pressed and closes automatically approx. 10 seconds after the arc is extinguished. In this way, it is ensured that no air can oxidize the weld pool 30 or the tungsten electrode when they are at a high temperature. As is known, TIG welding equipment is constructed either with a power supply and. . the control devices are arranged in the same housing or so that the power supply can be connected to a separate control device.

; 35 The prior art plasma welding is an arc welding method in which a plasma gas such as argon or a 2-7% mixture thereof and hydrogen flows through a welding torch nozzle toward a workpiece. A tungsten electrode connected to the negative terminal of the welding power source exits the nozzle therethrough. ______. τ— 2 39249 constrict the arc so-called. main arc to the workpiece. In the main arc, a part of the flowing plasma gas is excited into plasma, which, when it encounters the workpiece, transfers its high energy centrally to the place to be welded. In the atmosphere, the plasma lifetime is very short, usually less than 5 1 ms, so the plasma-maintaining effect of the main arc is a basic prerequisite for plasma welding.

As is already known, an auxiliary arc, i.e. a pilot arc, is maintained to ignite the main arc, which is maintained between a voifrome electrode connected to the negative terminal of a separate auxiliary current-source 10 and a plasma torch nozzle connected to its positive terminal. In micro and medium plasma torches, the pilot arc current is in the range 1-10 A.

There are many means known in the art for igniting a pilot arc between a nozzle and a center electrode. The most common of these is the High Voltage High Frequency Ignition Circuit (-3 kV, -2 MHz), where the high voltage generated between the electrode and the nozzle ignites the pilot arc over the air gap. The high frequency is used to keep the system safe. If the design of the plasma torch allows, the pilot arc can be ignited without high voltage by making contact between the nozzle and the electrode. Particularly in such a case, the object of the present invention is to facilitate the ignition of the arc.

The plasma generated by the pilot arc makes the gap between the tungsten electrode and the workpiece 25 electrically conductive and the main arc ignites when the main welding voltage is applied. During welding, a pilot arc is only required when using a very small welding current, usually less than 5 A.

Due to the nature of the plasma, the pilot arc is not generally used in butt welding. In microplasma welding, a pilot arc is necessary to stabilize the main arc, but its current is kept to a minimum because unnecessarily high pilot current unnecessarily heats and consumes a small nozzle or forces an otherwise too large nozzle for welding and because the weld environment heats up to too high a temperature.

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The current life of the plasma nozzle is inversely proportional to the combined current of the pilot and main arc. The durability of the sharpened tip of the tungsten electrode also depends on the current used. The severity of the pilot arc, in turn, depends on the current in the pilot arc, which, when reduced, makes the pilot-5 dagger unstable and eventually shuts off and can hardly be re-ignited.

Despite the undeniable advantages of plasma welding, plasma welding equipment is relatively rare, mainly due to the high cost of plasma welding equipment.

It is therefore an object of the present invention to provide a relatively inexpensive accessory that can be connected to a common TIG welding power source or the like so that this accessory provides a plasma welding power supply that utilizes the investment of TIG welding equipment and more advantageously enjoys the undeniable advantages of plasma welding.

In order to achieve the above and later objects, the invention is mainly characterized in that the accessory is a matching unit to be connected between a plasma torch and a TIG welding device known per se, comprising an electrical intermediate connection through which the HF ignition unit and is provided with a pilot power supply known per se suitable for plasma welding, which can be connected between the central electrode of the plasma torch and the nozzle.

The accessory according to the invention can advantageously utilize the welding power source of the shielded gas welding device, generally the TIG welding device, and the HF ignition unit in plasma welding, also in microplasma welding.

•: The accessory according to the invention must be provided with its own pilot power supply, which is preferably as described in the applicant's FI patent application 920282, so that the TIG welding device provided with the accessory is also suitable for microplasma welding.

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When modifying the TIG welding plate or the like with an accessory according to the invention to suit plasma welding, the water cooling of the plasma torch can be taken from the water cooling connection of the TIG device. Alternatively, the accessory is equipped with its own water cooling system or intermediate system, which makes the water cooling system of the TIG device suitable for a plasma torch. The accessory according to the invention includes a shielding gas and plasma gas system which utilizes the Ar shielding gas commonly used in TIG devices. In addition, the accessory can be equipped with a separate plasma gas connection. In this case, e.g.

10 gases Ar + 5% H2. This plasma gas system can be connected to the shielding gas system of the device by means of a valve device so that the hydrogen content of the plasma gas can be adjusted, for example, in the range 0 ... 7% H2.

The electrical power required by the accessory according to the invention can be taken either from an alternating current network or from an auxiliary transformer generally included in the TIG welding device. The latter arrangement is, for example, more advantageous than the former in terms of electrical safety regulations. In addition, the accessory includes various control devices, such as switches and relays, with which the shielding gas flows and the ignition and deactivation of the main arc can be controlled, as is known per se.

In the following, the invention will be described in detail with reference to the prior art of the invention shown in the figures of the accompanying drawing and to some application examples of the invention, to the details of which the invention is in no way narrowly limited.

Figure A shows the principle of connection of a previously known plasma welding torch and its power supplies.

Figure 1 shows an accessory according to the invention connected between a plasma torch known per se and a TIG welding device known per se.

Figure 2A shows a first embodiment of the electrical matching circuit 35 of the accessory according to the invention.

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Fig. 2B shows, in a manner similar to Fig. 2A, another embodiment of the adapter connection of the accessory according to the invention.

Fig. 2C shows a third embodiment of the matching circuit 5 in a manner similar to Figs. 2A and 2B.

Fig. 2D shows a fourth embodiment of the matching circuit in a manner similar to Figs. 2A, 2B and 2C.

Figure 3 schematically shows the principle of a gas system applicable in connection with an accessory according to the invention.

As shown in Fig. A, the prior art power supply 10 used in plasma welding comprises a main arc power supply 9A, the positive terminal C 15 of which is connected to the workpiece 2. The negative terminal of the current source 9A is .

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According to Figure A, the so-called welding arc used in a plasma arc torch the main arc 3 illuminates between the tungsten electrode 1 of the torch and the workpiece 2. The nozzle part of the torch consists of two nested chambers 4 and 6, of which the inner chamber 6 has a tungsten electrode 125 in the middle and a hole 8 at its tip. Plasma gas is fed to the inner chamber 6 A shielding gas surrounding the arc 3 is supplied to the outer chamber 4.

Since the arc 3 of the plasma torch burns in the gas between the workpiece 2 and the tungsten electrode 1, it must be ionized before igniting the main arc 3 in order for the gas to conduct electricity. The ionization takes place between the nozzle 5 formed by the inner chamber 6 and the tungsten electrode 1 by means of a burning pilot arc 7, which is provided by a pilot current source 10A. The pilot arc 7 ionizes the plasma gas, whereby an electrically conductive ion bridge 6 '09249 is formed between the workpiece 2 and the tungsten electrode 1, and the main arc 3 can ignite. The main arc 3 may burn only between the electrode 1 and the workpiece 2, because a high-power arc burning between the electrode 1 and the nozzle 5 would quickly destroy the nozzle 5. The cooling of the nozzle 5 and the electric and magnetic forces in the burner 5 prevent the main arc 3 from igniting between the electrode 1 and the nozzle 5.

In the following description and claims, for the sake of brevity, reference is made to a TIG welding device 30, which, however, means all 10 shielding gas welding devices known per se, which can also be utilized by means of the accessory 20 according to the invention in plasma welding.

When attempting to draw current from the main arc of the plasma torch from the TIG welding power source 30 known per se shown in Fig. 1 15, current collection is not possible without changing the internal connections of the TIG welding device. Therefore, the auxiliary device 20 according to the invention has an electrical matching circuit according to Fig. 1, in which the plasma nozzle 5 is grounded at a high frequency (HF) through a capacitor 20 dance of the capacitor 22 and the inductance L of the coil 23 loads the voltage source 33 of the TIG current source 30. In the spark generated between the HF center electrode 1 and the plasma nozzle 5. The resistance Re of the control resistor 21 acts as an additional load alongside the coil 23 so that the spark strength can be adjusted to suit different devices, because e.g. the lengths of the welding cables and the voltage, current and waveform of the HF power supply affect the spark strength. It is necessary to limit the intensity of the spark because the power of the ignition spark used in TIG welding is unnecessarily high in a plasma torch, which can cause breakthroughs and even damage inside the plasma torches.

The control resistor 21 can alternatively be replaced by an adjustable inductance.

Figures 2A, 2B, 2C and 2D show, as substitute connections, substantially equivalent implementations for matching connections between the TIG power supplies, the accessory pilot power supply 10A, and the plasma torch. The surrogate connection of Figure 2A corresponds to the fitting connection of Figure 1.

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In surrogate circuits, UT refers to the voltage of the power supply of the TIG welding machine, which provides the main current, which is either direct current or mains AC alternating current with a headset component. Voltage UP means the terminal voltage of pilot current source 10A, and capacitances Cc 5 refer to the capacitances of a welding current cable distributed over the entire length of the cable.

The voltage-reducing effect of the inductance L of the inductance L of the circuit 23 of Fig. 2A is based on the characteristics of the HF voltage source 33 of the TIG device 30. Because the internal resistance of the HF voltage source 33 is very high, the current it produces does not vary much from a short circuit to a situation where the load is a few kiloohms. Depending on the distance, shapes and purity or the like between the plasma nozzle 8 and the central electrode 1, there must be at least a voltage Uk min -15 of 0.5-1.0 kV between them before a spark can be generated (i.e. IK> 0). Since Ix is constant, the voltage across the coil 23 is UL * UT and UL - ZLIL - UK + cable losses. Preferably L = 5 ... 50 μΗ, which corresponds to an impedance ZL = 60 ... 600 Ω, (Z - 2 * fL), at a frequency of 2 MHz. The resistance of the control resistor 21 is preferably in the range of 60 Ω ... 10 kQ.

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Figures 2B and 2C show some alternative connections to the connections of Figures 1 and 2A. The purpose of the connections of Figures 2B and 2C is to keep the voltage between the electrode 1 and the workpiece 2 higher than in the connection of Figure 2A, so that a high frequency spark can also ignite between the workpiece 2 and the center electrode 1, which is desirable in some welding situations.

In the intermediate circuits of Figures 2A and 2B, the capacitance Cj of the capacitor 22 grounds the high frequency current, but disconnects the pilot current source 30A and the main arc current from ground. Likewise, the capacitor C2 of the capacitor passes the high-frequency pilot current source 10A. The inductance L of the coil 23 represents a considerable impedance for the high frequency current, but allows the pilot current to pass through substantially unobstructed. Some or all of the inductance L could be placed in the conductor 35 going to the center electrode, but then the cross-section of the conductor of the coil 23 would have to be considerably large because the main current would pass through the coil.

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In the coupling Cj «C2« 0.1 μΈ of Figures 1 and 2A and L - 5 ... 50 raH and R, - 60 Ω ... 10 kfl. In the circuit of Fig. 2B, the inductance L: speed Nx * N2 of the coil 23b, the latter being the speed of the coil L2. In the circuit of Figure 2B Uee> Ueg and Lx + 1¾ - L. In the circuit of Figure 2C 5 ZL1 + Ζς3 - ZL and C3 - 100 pF. . . 500 pF.

In Figure 2D, the pilot power supply acts as a spark period spark load. Resistance R2 acts as an additional load to adjust the intensity of the spark. In the circuit of Figure 2D, R2 = 60 Ω ... 10 kΩ, L »6 mH (1-10 mH), 10 Ci« 5 μι (0.2-20 a * F), C3 = C2 »0.1 / jF ( 10-100 μΈ). First, the estimated most suitable value of the component and the range in parentheses are shown.

As the pilot power supply 10A, either the power supply according to the applicant's FI application 920282 (filed January 22, 1992) or the like can be used, in which a pulsating DC voltage is preferably used as the pilot power supply 10A. low that the accessory 20 is also suitable for microplasma welding. The no-load voltage 20 of the pilot power supply 10A is preferably selected in the range of 50-90 V and the arc current is arranged to be adjustable in the range of 0.5-10 A (DC) with an arc voltage of 10-30 V, preferably 13-20 V.

For the pilot power supply 10A, it is essential that it does not produce radio interference or noise and that the current is adjustable, preferably between 1-10 A, and the idle voltage should be in the range of 50-90 V.

The auxiliary device 20 according to the invention can utilize the welding power source 31 of the TIG welding device as a power source 30 for the main arc 3 of the plasma torch and the HF ignition unit 33 for the ignition of the main arc 3. In addition, if the TIG welding device 30 is equipped with a 220 V auxiliary transformer 32, the pilot power supply 10A of the auxiliary 20 can be supplied via the electrical connection 11 from the auxiliary transformer 32, which is a preferred solution especially for electrical safety.

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The auxiliary device 20 according to the invention also has a gas flow arrangement according to Fig. 3. Rotameters 15, 16 and 17 or other components used to control the shielding gas flow Gj and the plasma gas flow GP are positioned so that either pure 5 argon Ar, strongly hydrogen doped argon Ar + 5% H2 or a mixture of these Ar + 0 ... can be used as the plasma gas. 5% H2.

Figure 3 shows the shielding gas tank 18 of the TIG welding device 30 and the plasma gas tank 19 of the plasma gas unit 26 of the accessory 20. By means of valves 10, 15, 16 and 17, the hydrogen content of the plasma gas can be controlled within the above-mentioned limits of 0 ... 5% H2.

According to Figure 1, the accessory 20 comprises a unit 25 for providing the water cooling flow W of the plasma torch, which includes a water pump, a cooling cell 15 and connections to the plasma torch cable. Alternatively, the TIG welding device 30's own or other torch cooling system 34 may be used. The accessory 20 preferably also has a fan to cool the cell and the pilot power supply 10A. The cable 12a of the plasma torch provides a control signal to the mechanical valve 20 for switching the shielding gas flow via the cable 12a and a signal to the main arc switching switch 13 via the polarizing relay 14.

The following claims set forth within the scope of the inventive idea as defined by the various details of the invention may vary and differ from those set forth above by way of example only.

Claims (8)

1. A supplementary device for a protective gas welding device, such as a TIG welding device for plasma welding, by means of which the scattering source 5 of the TIG welding device (30) and possibly other components can be used in connection with a plasma welding torch, characterized in that the additional device (20) is a per se known adapter (20) which can be coupled between a plasma burner (1-8) and a TIG welding device (30), the unit comprising an electrical intermediate coupling, through which the HF ignition unit (33) of the TIG the welding a-socket (30) and the welding current source (31) can be connected to the electrical poles (A, B, C) of the plasma torch (1-8) and the auxiliary device (20) is provided with a pilot power source known per se. (10A) suitable for plasma welding, which source can be coupled between the center electrode (1) of the plasma torch (1-8) and the nozzle (5). 2. Auxiliary device according to claim 1, characterized in that, in order to lower the power of the ignition spark of a current source in a TIG welding device (30), said intermediate circuit comprises a capacitor (22), whose capacitance (Cx) earns the HF voltage source ( 33) of the TIG device (30) and said intermediate coupling comprises a coil (23) whose inductance (L) loads the TIG current source (33) by both limiting its Current (Ik) and voltage (Uk) in the spark formed between the center electrode (1) and the plasma nozzle (5) (Figures 1 and 2A). 25 Auxiliary device according to claim 1 or 2, characterized in that the LC coupling comprises a capacitor (24) connected between the pole of the pilot current source (10A), whose capacitance (C2) passes past the high frequency of the HF ignition unit (33) past the pilot current source (10A). ) And the inductance (L) of said coil (23) is thus dimensioned to represent a considerable impedance of the high frequency, passing through the pilot current substantially without hindrance. 4. An additional device according to any one of claims 1-3, characterized in that a control resistor (21) is connected in parallel with said coil (23), whose resistance (Rs) is arranged to act as an additional load parallel to said coil. (23) so that the power of the ignition spark can be adjusted appropriately for different device combinations (30; 1-8). An additional device according to any one of claims 1-4, characterized in that a coil (23b) is connected in series with said capacitor (Cx), one of which is connected to said capacitance (22) and the other output to The HF ignition unit (33) of the TIG welding device (30) and said coil (23b) are provided with intermediate terminals coupled to the minus coil of the pilot power source (10A) (Figure 10 2B). An auxiliary device according to any of claims 1-5, characterized in that the inductance (L) of the coil (23) of said LC intermediate circuit is selected in the range L - 5 ... 50 mH and that the capacitance 15 ( Cx) of the capacitor (22) of said LC intermediate circuit is of class C1 = 1 and that the capacitance (C2) of the passage capacitor (24) connected to the poles by the pilot current source (10A) is of class C2 - 0.1 pF. 7. Auxiliary device according to any of claims 1-6, characterized in that the auxiliary device (20) is provided with connections with which the protective gas source (35) of the TIG welding device (30) can be connected as a protective gas stream (Gr). for the plasma burner (1-8) and / or that the additional device (20) is provided with a cooling water connection (25), with which the water cooling (34) of the burner of the TIG welding device (30) can be coupled as cooling water stream (W ) for the plasma burner (1-8) and / or that said additional device is provided with connections (26) with which the plasma gas container (19) can be joined to the plasma welding burner. 30 8. Auxiliary device according to any one of claims 1-7, characterized in that the voltage of the pilot current source (10A) is a pulsating DC voltage, the frequency of which is selected in the audio frequency range, most preferably in the range 0.8 ... 6 kHz. the gas stream produced by the pilot current source (10A) and the beak voltage are so selected that the auxiliary device (20) is also suitable for microplasras welding.