WO2006100701A1

WO2006100701A1 - Plasma cutting device

Info

Publication number: WO2006100701A1
Application number: PCT/IT2005/000163
Authority: WO
Inventors: Aldo Placidi
Original assignee: I-Cap Exploitation Ireland, Ltd.
Priority date: 2005-03-24
Filing date: 2005-03-24
Publication date: 2006-09-28

Abstract

Device (1) for plasma (3) cutting comprising a torch (50), means (10) for generating steam, means (20) for generating energy for the formation of plasma (3) from the steam, means (30) for the formation of the plasma arc, which performs the cutting, on the torch (50) basing on steam, operatively connected to means (20) for generating energy and means (60) for the regulation and control of functioning of the device (1). The device (1) is characterised in that it also comprises a frame (2) containing the means (10) for generating steam, the means (20) for generating energy and the regulation and control means (60) with which the torch (50) can be associated directly or via the first flexible connection means.

Description

D E S C R I P T I O N

PLASMA CUTTING DEVICE.

The present invention relates to a plasma cutting device which uses steam. Plasma cutting devices are commonly used for cutting applications, for example in civil, aerospace or marine site engineering, mechanical machining, systems engineering and industrial maintenance, in the automotive industry, above all in relation to bodywork, and in civil defence operations. The invention will be described with reference to this type of application even if it may obviously be applied in any other field wherein the properties of plasma can be used, for example in powder welding, brazing or high definition cutting.

As is known plasma is composed of a mixture of ionised gases formed by electrons, ions and neutral atoms obtained as a result of a process of ionising of the atoms, that is to say splitting of the molecules into other more simple ones through the total or partial loss of the electrons.

Devices for plasma cutting are known which function with gases other than steam, such as argon or air.

They generally consist of a main structure which contains the devices suitable for formation of plasma basing on gas and a torch wherefrom the plasma arc is released for cutting the material.

These devices have a series of disadvantages. First of all the gases commonly used, such as air, have a low heat content (enthalpy), therefore the plasma arc cools rapidly and, consequently, the capacity and speed of cutting and the yields are reduced. In the case of the cutting of metal materials these values can be increased by making the

i metal being machined react with the oxygen, generating however a considerable quantity of dust during machining. Secondarily, some components of the gases used, such as oxygen and nitrogen for

^■ example, may cause contamination on the material to be cut, complicating the subsequent machining process. Additionally, considerable noxious emissions are developed during cutting, in terms of gas and dust, and the arc also emits a luminescence in the range of ultraviolet rays which is found to be damaging to the human eye.

To avoid most of these disadvantages steam plasma cutting devices were introduced.

Notoriously these devices incorporate in the torch all the main components of the system and, therefore, the water reservoir, the elements for obtaining steam from the water introduced and the elements for the formation of the plasma and of the plasma arc for performing cutting. More particularly these devices are known as "non- transferred arc" in that the plasma arc always develops, that is to say both in a rest and a cutting situation, between a cathode and an anode present in the torch. These "non-transferred arc" cutting systems moreover, by suitable shaping of the nozzle, are able to perform strong brazing between two materials to be joined.

Despite the fact that they offer good cutting capacities, reduce contamination on the material to be cut and the polluting emissions, given the reducing power and high solubility of the water, and emit an infrared light which is therefore less dangerous, these devices too present disadvantages. Given that all the technology is grouped together in the torch, their structure is very complex and, consequently, the number of variables of the system is considerably high. Moreover these devices appear difficult to handle given the heaviness of the structure of the torch. Finally, due to the reduced volume of the water reservoir integrated in the torch, the working range is limited. The object of the present invention therefore is that of avoiding the disadvantages stated above with a plasma cutting device which gives high performances and yields, and that is to say which has a high cutting capacity, which allows work with high cutting speeds and which allows a concentrated plasma arc to be obtained so as to perform high-definition cuts. A further object of the present invention is to make available a plasma cutting device which has a simple structure, and which is easy to use and to transport. Another object of the invention is to present a plasma cutting device which guarantees high safety for the operator during use, for example as regards light emissions or separation from the electrical supply system and which also has a reduced environmental impact in relation to the pollutants generated by the cutting. Additionally it is an object of the invention to disclose a plasma cutting device which reduces the alterations and the contamination on the material to be cut. Finally the object of the present invention is to present a plasma cutting device which is simple to produce and low in cost.

These and other objects, which will be made clearer during the following the description, are achieved, in accordance with the present invention, by a plasma cutting device in accordance with the annexed claims. Further features and advantages of the invention will be made clearer by the description of a preferred but not exclusive embodiment of the device presented in greater detail herein below with the aid of the drawings. - Figure 1 shows a block diagram of the characteristic parts of the device of the invention;

- Figure 2 shows a block diagram of the hydraulic part of the device of

Figure 1 ; - Figure 3 shows the general wiring diagram of the device of Figure 1 ;

- Figure 4 shows a schematic representation of the means for the formation of the plasma arc;

- Figure 5 shows a view of the end part of the torch;

- Figure 6 shows a schematic view of the main components of the torch; - Figure 7 shows a front view of the frame.

Referring to the figures mentioned, a device 1 for plasma 3 cutting which uses steam according to the invention comprises five main parts represented by the means 10 for generating steam, the means 20 for generating energy for the formation of the plasma 3 from the steam, means 30 for the formation of the plasma arc connected to the means 20 for generating energy, means 60 for regulation and control and a torch 50. The device 1 for plasma 3 cutting described is characterised in that the means 10 for generating steam, the means 20 for generating energy and the means 60 for regulation and control are housed in a frame 2. Alternatively the machine could also comprise more than one frame 2 as container of the means mentioned.

Preferably the torch 50, which is the element from which the plasma arc which performs cutting is released, can be associated with the frame 2 directly or, alternatively, via first means of connection, represented by pipes able to transport simultaneously from the frame 2 to the torch 50 both the steam and the electrical signals and the power cables. These main elements of the device 1 are suitable for producing steam and conveying it to the torch 50 where the plasma 3 is developed and the plasma arc struck and maintained stable thanks to the means 20 for generating energy and means 30 for formation of the plasma arc. It should be noted that only a part of the steam from the means 10 for generating steam is transformed into plasma 3 by the torch 50 and produces the cut, otherwise unmanageable energy, temperature and voltage conditions would be created. The steam which is not transformed into the plasma 3 follows the same plasma 3 during the cutting process, incorporating the dust generated and aiding in its disposal.

The function of the means 10 for generating steam is to produce steam in an adequate amount and with controlled physical parameters for feeding the torch 50. More particularly, during the start-up phase, the flow of steam has to be limited to avoid its condensation, during the phase of awaiting the operative phase of cutting the flow must be low to restrict the losses of energy and steam and during the cutting phase its pressure must be controlled to ensure a constant flow of adequate quantity for ensuring appropriate cutting precision. As can be seen in Figure 2, the aforementioned means 10 for generating steam comprise at least one reservoir 11 for water, which can be fed through the frame 2, advantageously provided with an anti-scale filter 18 and, preferably, of such a volume as to ensure a working range of at least two hours for the device 1. They also include a generator 12 of steam operatively connected to the reservoir 11 and to the torch 50 for feeding. This steam generator 12 comprises a volumetric boiler or, alternatively, a transition boiler.

The means 10 for generating steam can also be provided with a pump 16, placed between the reservoir 1 1 and the steam generator 12 and advantageously controlled by the regulation and control means 60 so as to take water from the reservoir 11. Preferably, on the connection pipes between the pump 16 and the reservoir 1 1 , a check valve 19, with the function of avoiding backflows of water or steam and of aiding in priming the pump 16, and means 17 for monitoring, the quantity of water, advantageously comprising a flow meter, can be associated. This flow meter is provided with a pulsed output connected to the regulation and control means 60 for monitoring the state of the reservoir 1 1 and indicating any faults, such as the lack of water. The functions of the flow meter can alternatively be performed by a level gauge placed in the reservoir 11 (an alternative not shown in Figure 2). The hydraulic system described above may also comprise temperature sensors 14, preferably associated with the steam generator 12, pressure sensors 15, positioned along the waterline, and valves or solenoid valves for interrupting or deviating the flow, for example in the event of an emergency. These latter devices are advantageously connected to the regulation and control means 60. Moreover these means 10 for generating steam may comprise a separation valve 13 placed downstream of the boiler for capturing and reconveying towards the same boiler any traces of water in the liquid phase in the steam sent to the torch 50. The means 20 for generating energy comprise a constant current generator 21 associated with the input electrical system, with the function of creating power with adequate volt-ammeter parameters for the generation of plasma 3, that is to say of making available the energy required for creating a difference in potential such as to strike and sustain the plasma arc. More particularly this energy is divided into dissociation energy which allows splitting of the steam molecules and ionisation energy, which allows the formation of plasma 3 by exciting the electrons of these split molecules. A further function of the constant current generator 21 is that of separating electrically the device 1 in relation to the input electrical system for reasons of safety of the operator.

A first embodiment of the device 1 , schematically represented in Figure 3, is characterised in that the constant current generator 21 comprises an electronic inverter circuit 22, provided with an internal electronic board which allows its regulation by the regulation and control means 60. The parameters whereby this internal electronic board is designed and operates are unique and differ from those of plasma 3 made from common gases. The inverter circuit 22 is also connected to a potentiometer 63, which can preferably be regulated from the outside, for setting the intensity of the electrical current supplied. Advantageously moreover, the electronic inverter circuit 22 comprises a transformer with extremely reduced weight and dimensions for performing the aforesaid function of separation from the input electrical system. As an alternative to the electronic inverter circuit 22, the constant current generator 21 may comprise an electrical constant current transformer with regulation of power on the secondary winding which also performs the function of separation from the input electrical system (an alternative which is not shown).

The means 20 for generating energy are connected to the means 30 for formation of the plasma arc which, basing on the power generated by the aforementioned means 20 for generating energy, make the plasma arc physically feasible.

The means 30 for the formation of the plasma arc comprise, above all, a first 31 and a second electrode 32, housed in the torch 50.

At this point the device 1 may be made in three variants.

The first variant enables cutting of any type of material, whether metal or otherwise, with a plasma arc with high potential, which is developed between the first 31 and the second electrode 32 of the torch 50 which thus assume the function of cathode and anode respectively (variant not shown). Instead in the other two variants a first arc with reduced potential is first struck, known as pilot arc, between the first 31 and the second electrode 32 of the torch 50, which is maintained stable thanks to the action of the electronic inverter circuit 22. The pilot arc enables the formation and maintaining of the plasma arc and de-actuates when the latter is struck. Thanks to the pilot arc therefore it is possible to guarantee the continuity in striking of the plasma arc, necessary for example in the case wherein there are cavities in the material to be cut. Subsequently the plasma arc is struck to initiate the cutting process.

In the second variant the plasma arc is struck between the first electrode 31 of the torch 50, which assumes the cathode function, that is to say negative pole, and between a third electrode (not visible in the drawings), made for example by a ceramic part and a tungsten ring mounted on the torch 50, which performs the anode function, that is to say positive pole. This third electrode is preferably mounted below the second electrode 32 and is insulated electrically from the latter, for example thanks to the ceramic coating. Instead in the third variant the plasma arc is formed between the first electrode 31 of the torch 50 which, as previously, has a cathode function (negative pole) and the material to be cut and which assumes the function of anode (positive pole). The plasma arc between the torch 50 and the material to be cut can be formed thanks to second connection means 33, placed between the first electrode 31 and the material to be cut, advantageously made in a conductive material and ending in a gripper 45 which improves its contact with the material to be cut (Figures 3 and 4). Due to the fact that the plasma arc is formed between the first electrode 31 of the torch 50 and the material to be cut, the third alternative is defined as "transferred arc", unlike the first and the second which are known as "non-transferred arc". Consequently, using the third embodiment, only conductive materials can be cut, that is to say metal materials, given that this is the material which during the cutting process behaves like a positive electrode. The second embodiment instead enables the cutting of any material, given that the plasma arc is formed between two components of the torch 50 yet, for this reason, supplies a smaller depth and cutting definition.

Despite the differences underlined, the second and third variants are based on a very similar operating principle disclosed in the part of the description below and illustrated in Figures 3 and 4.

In a preferred embodiment of the device 1 the means 30 for the formation of the plasma arc are formed by an electronic striking circuit 34, housed in the frame 2 and designed to supply high frequency power to raise the instantaneous input voltage to allow the formation of the plasma arc, and an electronic circuit 35 for generation of the pilot arc, preferably integrated in the electronic striking circuit 34. An important feature of the electronic striking circuit 34 is the fact that it is provided with an electronic component having the function of automatically de- actuating this circuit 34 once the plasma arc has been struck so as to reduce the interference caused by the striking. The electronic striking circuit 34 is also characterised by its working parameters. In order to strike the plasma arc, energy is taken from the constant current generator 21 which supplies, in conditions of non- supply of power, a voltage higher than 350 V which is raised to between 6000 V and 18000 V at a frequency between 5 MHz and 6 MHz. Once the plasma arc has been struck, the voltage on the electronic striking circuit 34 drops below 350 V and therefore this circuit 34 is automatically de-actuated.

The electronic striking circuit 34 is preferably connected to the output of the electronic inverter circuit 22 in a positive pole 36 and in a negative pole 37 (Figure 4). An important feature of this circuit 34 is that it comprises a resistor 38, connected to the positive output 36 of the inverter circuit 22 and suitable for regulating the current input in the electronic circuit 35 for generating the pilot arc so as to allow the formation of the pilot arc when the plasma arc is inactive and for de- actuating the pilot arc when the plasma arc is active. Moreover the striking circuit comprises a switch 39, preferably a remote switch, placed between this resistor 38 and the second electrode 32 and an RC circuit

41 connected to the two outputs 36,37 of the inverter circuit 22 to accumulate the voltage necessary for generation of the pilot arc. When this voltage reaches an adequate value (approximately 350 V), it is transferred by discharge means 43, formed for example by a gas discharger, connected to the RC circuit 41 , to a high voltage transformer

42 connected to the first electrode 31 , via which the voltage on the first electrode 31 is raised (preferably from -500V to -15000 V). A further component of the electronic striking circuit 34 is an RC filter 44 connected to the cathode and to the anode of the plasma arc, that is to say to the first electrode 31 of the torch 50 and to the third electrode, in the second variant, and to the material to be cut in the third. The function of the RC filter 44 is that of placing in communication the cathode and the anode of the plasma arc when power is supplied at high frequency and to interrupt this communication should the voltage of the electronic striking circuit 34 be characterised by low frequency. An alternative embodiment to the preferred one can instead comprise an electronic microcircuit with very high frequency housed in the torch 50 to allow the striking of the plasma arc (alternative not shown). The torch 50 of any embodiment of the device 1 preferably consists of a body 51 in insulating material provided with a button for actuation of the plasma arc by an operator, connected to regulation and control means 60, and an element 52, again in an insulating material for regulating the distance between the first 31 and the second electrode 32. Again in accordance with the invention, the connection cables between the actuation button and the means 60 for regulation and control are physically interrupted to prevent the frequency interference generated in the torch by the plasma, both in the striking and working phases, from being conducted towards the regulation and control means 60. The continuity of the connection between the button and regulation and control means 60 is ensured by an optical connection (not shown) comprising an independent and galvanically insulated power supply unit which, by means of the button, switches on and off a light source inserted in an optical fibre and an optical fibre circuit which carries this signal to the regulation and control means 60. The torch 50 also comprises means 53 for generating a substantially rotary turbulence movement on the steam to increase the heat content of the flow. They may consist of a suitably shaped distribution ring or the first 31 or second electrode 32 after appropriate shaping. The regulation and control means 60 mainly consist of an electronic board, equipped with a microprocessor, whereon software is implemented, suitable for regulating the times of all the operations of the device 1 on the basis of the parameters detected inside the same device 1 and those set externally. The microprocessor can in fact be connected to an external computer, for example by means of an RS-232 serial port, so as to set the working parameters. Alternatively these parameters can be entered via the frame 2 of the device 1. For example the acceptable pressure and temperature ranges, the intensity of the cutting current, which must be selected according to the thickness of the material to be cut, the number of litres of water for performing the change of the filter 18 of the reservoir 1 1 or the feeding of anti-scale powder to perform a washing cycle, the time of replacement of the first 31 and of the second electrode 32, the duration of the pilot arc and the waiting time of the pilot arc before switching-off of the device 1 if the plasma arc is not struck can be set.

The objective of these regulation and control means 60 is to supply steam at constant pressure and constant temperature while the inverter 22 feeds the plasma arc at constant current. They receive in fact in input the signal detected by the temperature sensors 14 located on the steam generator 12 and by the pressure sensors 15 located on the hydraulic pipes supplying the torch 50 to regulate appropriately the components of the means 10 for generating steam also on the basis of the temperature and pressure ranges set externally by the operator. The regulation and control means 60 are also suitable for checking the status of the working parameters of the device 1 and for reporting possible faults therein by indication and emergency means 62, preferably represented by leds positioned on a panel mounted on the frame 2 (Figure 7). These faults can relate for example to the condition of the reservoir 1 1 being empty, the need to replace the filter 18 or the feeding of anti-scale power and wear of the interchangeable elements of the torch 50, the excessive overheating of the constant current generator 21 and the reaching of the emergency pressure.

Again in accordance with the invention, the device 1 described can also be applied to operations of soft brazing, strong brazing and welding of metal materials, thanks to the high heat content value of the steam which involves slow cooling of the plasma arc. To achieve this, the shaping of the first 31 and second electrode 32 has to be adjusted extending, in particular, the diameter of the second electrode 32 and, if necessary, reducing the diameter of the first electrode 31 and altering the distances between the first 31 and the second electrode 32. Simultaneously to these mechanical operations the pressure and flow rate of the steam have to be reduced markedly and simultaneously the current of the plasma 3 regulated to very low values according to the thickness of the material to be welded. In this case the actual atoms of the steam (i.e. H2 and 02) act as a shield gas. A further application is high-definition cutting, given that the device 1 , particularly in the "transferred arc" variant, ensures high cutting precision, comparable to laser technologies.

By way of an example a description is given of operation of a preferred embodiment of the present invention wherein the means 30 for the formation of the plasma arc are structured in accordance with the third variant. For proper working of the device 1 the following conditions must occur at striking: the reservoir 1 1 must contain an adequate quantity of water, the torch 50 must be connected to the frame 2 (directly or via the first connection means 4), the input electrical system whereto the device 1 is connected must supply correct power and, finally, a connection must be made with the part to be cut via the second connection means 33. At this point the regulation and control means 60 command the pump 16 to take water from the reservoir 1 1 so that the steam can be produced in the generator 12. When such a quantity of steam is accumulated so as to allow proper working of the device 1 , the regulation and control means 60, via the indication means 62 on the panel mounted on the frame 2, indicate to the operator the status of machine ready for proceeding with the cutting operation. During this working phase the regulation and control means 60 receive and check the signals detected by the pressure sensor 15 and temperature sensor 14 and by the means 17 for monitoring and, via the separation valve 13, send back to the boiler any parts of water present in the flow of steam towards the torch 50.

Simultaneously the means 20 for generating energy detect the current set externally via the potentiometer 63 associated with the panel of the frame 2 and, by means of the electronic inverter circuit 22, generate the power necessary for generation of the plasma arc and transfer it to the electronic striking circuit 34, wherein the circuit 35 for generating the pilot arc is integrated, connected to the output 36, 37 of the inverter circuit 22. The electronic striking circuit 34 then strikes the pilot arc. When the plasma arc is struck for cutting, by means of the button positioned on the torch 50, this pilot arc is de-actuated whereas if the plasma arc is not actuated within a programmed time, the regulation and control means 60 switch off the device 1 .

In practice any dimensions and materials may be used according to needs. Moreover all the parts can be replaced by other, technically equivalent elements.

The invention achieves important advantages. First of all the use of plasma obtained from steam, having a high energy content on a par with the amperes of current supplied, allows a considerable increase in the yield and performances of the device. In particular the device has a greater cutting capacity: for example, at a current of 10 A, the cutting depth reaches 7 mm, unlike the devices which function with plasma obtained from air which reach 2 mm. Secondarily the plasma arc is more concentrated and therefore creates flat and clean cutting faces and, consequently, allows performances to be achieved which are comparable to those of high definition cutting commonly performed with laser technology. Moreover the very high heat content of the steam plasma arc allows a reduction in the thermally altered area on the material to be cut, given that it is possible to transfer to the same material a higher quantity of heat yet at a lower temperature compared to the plasma arc generated with other gases. Finally the action of the steam plasma arc induces only melting of the material being cut, preventing, during the cutting process, the generation of dust. A further advantage generated by a plasma cutting device operating with steam is therefore due to the fact that the hydrogen prevents chemical reactions between the oxygen and the material to be cut and this enables the cut parts to be submitted directly to subsequent machining without the need for additional intermediate machining which has a negative effect on times and, above all, costs. In addition to this, metal oxide dust is not generated which represents the main problem of common air plasma. Moreover, given the high solubility of the steam and its subsequent ambient re-condensation, washing and agglomeration of all the dust generated by the cutting (such as for example paint or surface galvanising) are performed and therefore the dust emitted by the cutting process is further reduced. A further advantage created by the use of steam lies in the fact that the light emissions of the plasma arc come within the infrared zone which is less damaging to the human eye compared to the ultraviolet one. The device described also has a compact and rational structure which is easy to use and to transport and it can also be used in the home. In addition to this, having removed all the basic components from the torch and inserting them in the frame has, advantageously, allowed a very easy-to-haπdle device to be obtained and the number of variables to be monitored at the torch level to be reduced considerably, simplifying management of the regulation and control means. Finally an additional advantage of the device is the safety of use for the operator thanks to separation from the electrical system and the reduced pollution.

_{* * * * *}

Claims

1 ) Device (1 ) for plasma cutting comprising: a torch (50), means (10) for generating steam, means (20) for generating energy for the formation of plasma (3) from said steam, means (30) for the formation of a plasma arc from said torch (50) on said steam, operatively connected to said means (20) for generating energy, and means (60) for the regulation and control of the functioning of said device (1 ); characterised in that it also comprises, a frame (2) operatively connected to said torch (50) and containing said means (10) for generating steam, said means (20) for generating energy and said regulation and control means (60).

2) Device (1 ) according to the previous claim, characterised in that it comprises at least two frames (2) and in that said means (10) for generating steam, said means (20) for generating energy and said regulation and control means (60) are housed in said two at least frames (2).

3) Device (1 ) according to any one of the previous claims, characterised in that said torch (50) can be associated with said frame (2) by means of first flexible connection means (4).

4) Device (1 ) according to any one of the previous claims, characterised in that said means (10) for generating steam comprise at least one reservoir (1 1 ) for water, a generator (12) of said steam, operatively connected to said reservoir (1 1 ) and to said torch (50) for feeding said torch (50) with said steam, and devices (13, 14, 15, 19) for controlling said steam connected to said regulation and control means (60).

5) Device (1 ) according to claim 4, characterised in that said generator (12) of said steam comprises a volumetric boiler.

6) Device (1 ) according to claim 4, characterised in that said generator (12) of said steam comprises a transition boiler.

7) Device (1 ) according to any one of claims 4 to 6, characterised in that said devices (13, 14, 15, 19) for controlling said steam comprise at least one temperature sensor (14) for said steam and/or at least one pressure sensor (15) for said steam.

8) Device (1 ) according to any one of claims 4 to 7, characterised in that said means (10) for generating steam also comprise a pump (16) connected by pipes to said reservoir (1 1 ) and to said generator (12) of said steam.

9) Device (1 ) according to any one of claims 4 to 8, characterised in that said means (10) for generating steam also comprise means (17) for monitoring the quantity of water present in said boiler.

10) Device (1 ) according to claim 9 when dependent on claim 8, characterised in that said means (17) for monitoring the quantity of water present in said boiler comprise a flow meter placed between said pump

(16) and said boiler.

11 ) Device (1 ) according to claim 9, characterised in that said means

(17) for monitoring the quantity of water present in said boiler comprise a level gauge associated with said reservoir (1 1 ).

12) Device (1 ) according to any one of the previous claims, characterised in that said means (20) for generating energy comprise a constant current generator (21 ) which can be associated with an input electrical system.

13) Device (1 ) according to claim 12, characterised in that said constant current generator (21 ) comprises an electronic inverter circuit (22) provided with an internal electronic board and connected to said regulation and control means (60) by means of said internal electronic board.

14) Device (1 ) according to claim 12, characterised in that said constant current generator (21 ) comprises an electrical transformer.

15) Device (1 ) according to any one of the previous claims, characterised in that said means (30) for the formation of said plasma arc comprise a first (31 ) and a second electrode (32) housed in said torch (50). 16) Device (1 ) according to claim 15, characterised in that said first electrode (31 ) is suitable for performing a cathode function during the formation of said plasma arc and in that said second electrode (32) is suitable for performing the anode function during the formation of said plasma arc. 17) Device (1 ) according to claim 15, characterised in that said first electrode (31 ) is suitable for performing the cathode function during the formation of said plasma arc and a pilot arc and in that said second electrode (32) is suitable for performing the anode function during the formation of said pilot arc. 18) Device (1 ) according to claim 17, characterised in that said means (30) for the formation of said plasma arc also comprise a third electrode associated with said torch (50) and electrically insulated from said second electrode (32), suitable for performing the anode function during the formation of said plasma arc.

19) Device (1 ) according to claim 17, characterised in that said means (30) for the formation of said plasma arc also comprise second means

(33) of connection between said torch (50) and a material to be cut, said second connection means (33) being made in a conductive material to allow the formation of said plasma arc between said torch (50) and said material to be cut which is suitable for performing the anode function during the formation of said plasma arc.

20) Device (1 ) according to any one of claims 15 or 17 to 19, characterised in that said means (30) for the formation of said plasma arc also comprise an electronic striking circuit (34), housed in said frame (2) and suitable for supplying high frequency power for raising the instantaneous input voltage and allowing the formation of said plasma arc and an electronic circuit (35) for generation of said pilot arc between said first (31 ) and second electrode (32).

21 ) Device (1 ) according to claim 20, characterised in that said electronic circuit (35) for the generation of said pilot arc is integrated in said electronic striking circuit (34).

22) Device (1 ) according to claims 20 or 21 , characterised in that said electronic striking circuit (34) operates at a voltage above 350 V and in that said voltage raised by said electronic striking circuit (34) is between 6000 V and 18000 V and said high frequency of said power supplied by said electronic striking circuit (34) is between 5 ^'MHz and 6 MHz.

23) Device (1 ) according to any one of claims 20 to 22, characterised in that said electronic striking circuit (34) is provided with an electronic component suitable for automatically de-actuating said electronic striking circuit (34) when said plasma arc is struck.

24) Device (1 ) according to any one of claims 20 to 23, characterised in that said electronic circuit (35) for generating said pilot arc is suitable for taking current from said means (20) for generating energy by means of a resistor (38) suitable for regulating said current inputted in said electronic circuit (35) for generating said pilot arc to allow the formation of said pilot arc between said first (31 ) and said second electrode (32) when said plasma arc is inactive or for de-actuating said pilot arc when said plasma arc is active.

25) Device (1 ) according to claim 24 when dependent on claim 13, characterised in that said electronic striking circuit (34) is connected to an output of said electronic inverter circuit (22) via a positive pole (36) and a negative pole (37) and in that it also comprises, a switch (39) placed between said resistor (38) and said second electrode (32), said resistor (38) being connected to said positive pole (36), an RC circuit (41 ) connected to said positive pole (36) and to said negative pole (37) so as to accumulate the voltage required for the formation of said pilot arc, a high voltage transformer (42) connected to said RC circuit (41 ), discharge means (43) placed between said RC circuit (41 ) and said transformer (42) so as to transfer said voltage accumulated in said RC circuit (41 ) to said transformer (42) and an RC filter (44) connected to said transformer (42) and to said anode of said plasma arc for placing in communication said first electrode (31 ) and said anode of said plasma arc once said high frequency power is supplied. 26) Device (1 ) according to any one of claims 1 to 19, characterised in that said means (30) for the formation of said plasma arc also comprise a very high frequency electronic microcircuit housed in said torch (50) to allow the striking of said plasma arc. 27) Device (1 ) according to any one of the previous claims, characterised in that said torch (50) comprises a body (51 ) in an insulating material, provided with a button for the actuation of said plasma arc by an operator, connected to said regulation and control means (60) via third connection means and an element (52) in insulating material suitable for regulating the distance between said first (31 ) and said second electrode (32).

28) Device (1 ) according to claim 27, characterised in that said third connection means comprise an optical connection system for preventing the frequency interference generated in said torch (50) by said plasma (3) from propagating in said regulation and control means (60).

29) Device (1 ) according to claim 28, characterised in that said optical connection system comprises a power supply unit, suitable for activating a light source via said actuation button, and an optical fibre, suitable for carrying a signal generated by said light source to said regulation and control means (60).

30) Device (1 ) according to any one of claims 27 to 29, characterised in that said torch (50) also comprises means (53) for generating a substantially rotary turbulence motion of said steam.

31 ) Device (1 ) according to claim 30, characterised in that said means (53) for generating a turbulence motion of said steam comprise a shaped distribution ring. 32) Device (1 ) according to claim 30, characterised in that said means (53) for generating a turbulence motion of said steam comprise one of said first (31 ) and second (32) shaped electrodes.

33) Device (1 ) according to any one of the previous claims, characterised in that said regulation and control means (60) comprise an electronic board equipped with a microprocessor provided with software and command means (61 ) for setting working parameters of said device (1 ) by said operator.

34) Device (1 ) according to claim 33, characterised in that said microprocessor of said electronic board can be connected to an external computer for the setting of said working parameters by said operator.

35) Device (1 ) according to claims 33 or 34, characterised in that said command means (61 ) comprise a potentiometer (63) which allows the current intensity of said constant current generator (21 ) to be set. 36) Device (1 ) according to any one of claims 33 to 35, characterised in that said regulation and control means (60) comprise indication and emergency means (62) suitable for ascertaining the status of said working parameters of said device (1 ) and for indicating any faults. 37) Device (1 ) for the welding and/or brazing of materials, characterised in that it is made according to any one of the previous claims.