EP3264867A1

EP3264867A1 - Nozzle for a narrow bevel angle plasma torch and plasma torch comprising the same

Info

Publication number: EP3264867A1
Application number: EP16177579.6A
Authority: EP
Inventors: Martin Barak; David Beran; Martin Julis; Jaroslav Kubicek; Drahoslav Kucera; Tomas Podrabsky; Pavel Topic
Original assignee: Brno University Of Technology; Siemens AG
Current assignee: Brno University Of Technology; Siemens AG
Priority date: 2016-07-01
Filing date: 2016-07-01
Publication date: 2018-01-03

Abstract

The invention relates to a nozzle (1) for a narrow bevel angle plasma torch (2). The nozzle (1) comprises a nozzle axis (3), a mounting section (4) for mounting the nozzle (1) onto a plasma torch (2), a tip section (5) for guiding a plasma beam and a main canal (6) for housing an electrode (7) of the plasma torch (2). The main canal (6) extends through the nozzle (1) via the mounting section (4) and the tip section (5). The nozzle (1) further comprises a nozzle cooling canal (8) for guiding a cooling fluid through the nozzle (1), wherein the nozzle cooling canal (8) is separated from the main canal (6). Furthermore, the invention relates to a plasma torch system (13) for a narrow bevel angle plasma welding device, wherein the plasma torch system (13) comprises a nozzle (1) of that kind.

Description

This invention is directed to a nozzle for a narrow bevel angle plasma torch and a narrow bevel angle plasma torch comprising a nozzle of that kind.
The principle of plasma welding is based on the dissociation and ionization of process gas, also denominated as plasma gas, during its passage through a contracted, respectively constricted, electric arc. An opening angle of a contracted electric arc of a plasma welding process usually is about 6°, wherein an opening angle of a standard tungsten inert gas (TIG) electric arc normally is about 45°. Thus, power density of plasma welding is higher than power density of TIG welding. A degree of ionization of the plasma gas is dependent on the temperature of the electric arc, wherein at increased temperatures a higher degree of ionization of the plasma gas is obtained.
Plasma is also known as the fourth aggregate state, wherein plasma in a plasma welding process is obtained by a series of physical processes. In a dissociation step, plasma gas is divided into its atomic components. In a subsequent ionization step, some valence electrons are separated from their atoms by ejecting or releasing them from their outer valence orbitals. As a result, plasma is a mixture of freely moveable electrons, ions and neutral atoms. The released electrons have a negative charge and, therefore, can conduct electric current in the plasma. The ionized nucleus of the atom, i.e. ion with remaining electrons, has a positive charge. Outwardly, the plasma behaves electrically neutrally. However, due to the existence of freely moveable free charge carrier, plasma can be influenced by electric as well as magnetic fields.
For plasma welding processes, usually two different kind of gases are used, namely an active and a non-active gas. The active gas is the plasma gas, which provides the atoms to be ionized and stability of the plasma beam due to a more or less constant plasma gas flow. The non-active gas is a protective gas, e.g. an inert gas, that is transported into an environment of the weld joint for establishing a protective atmosphere around the weld joint by displacing air from that area. With the protective atmosphere, the weld joint and its close surroundings are protected from oxidation by air oxygen.
Standard plasma torches have a circular shape with a diameter between 25 and 60 mm, depending on the electric power of the plasma torch. In a number of applications, in order to reduce costs, a width of the weld joint and therefore a bevel of the weld joint are reduced. Such weld joints are called "narrow bevel" weld joints. Since narrow bevel weld joints can have a width about 18 mm, standard plasma torches cannot be used in such applications. Therefore, a special, narrow bevel angle plasma torch has been developed. With such narrow bevel angle plasma torches, weld joints with a width of 18 mm and a weldment thickness of up to 300 mm can be produced. Furthermore, such narrow bevel angle plasma torches allow manipulation and collision-free navigation within the narrow bevel due to its overall construction with a diameter that does not exceed 14 mm. A working temperature of the narrow bevel angle plasma torch can reach up to 450°C. Since its small dimensions and high working temperatures, known narrow bevel angle plasma torches are susceptible to overheat and need long cool down phases. As a consequence, live span is reduced and/or production down times are increased due to increased maintenance or cooling down time. All these drawbacks lead to an increase of manufacturing costs.
Consequently, it is an objective of the present invention to provide a nozzle for a narrow bevel angle plasma torch as well as a narrow angle plasma torch that do not have the drawbacks of the state of the art. It is especially the object of the present invention to provide a nozzle for a narrow bevel angle plasma torch as well as a narrow angle plasma torch that have an increased live span, require less maintenance and less production down times.
This objective is solved by the patent claims. In particular, this objective is solved by a nozzle for a narrow bevel angle plasma torch according to claim 1 and a narrow bevel angle plasma torch according to claim 9. The dependent claims describe preferred embodiments of the invention.
According to a first aspect of the invention, the objective is solved by a nozzle for a narrow bevel angle plasma torch. The nozzle comprises a nozzle axis, a mounting section for mounting the nozzle onto a plasma torch, a tip section for guiding a plasma beam and a main canal for housing an electrode of the plasma torch. The main canal extends through the nozzle via the mounting section and the tip section. The nozzle further comprises a nozzle cooling canal for guiding a cooling fluid through the nozzle, wherein the nozzle cooling canal is separated from the main canal.
The nozzle is a narrow bevel angle nozzle and is configured for being mounted onto a narrow bevel angle plasma torch. In the following, the term "nozzle" is to be understood as "narrow bevel angle nozzle", preferably with a very slim cylindrical shape, unless explicitly indicated otherwise. The term "plasma torch" is to be understood as "narrow bevel angle plasma torch", preferably with a width between 12 mm and 14 mm and a length of 70 mm to 90 mm, especially 80 mm, unless explicitly indicated otherwise. Such nozzle and plasma torch are configured for being used for narrow bevels, e.g. with a width about 18 mm and a depth of up to 300 mm. A narrow bevel or narrow bevel angle can also be described as a narrow gap. The outer dimensions of the nozzle and the torch - at least the parts of the torch that have to be navigated within a gap at a welding location - have to be small enough to ensure collision free navigation during the welding procedure.
The mounting section of the nozzle is configured for mounting the nozzle onto a plasma torch. Consequently, the plasma torch is a holder for the nozzle. Preferably, the mounting section comprises mounting means, e.g. a threaded portion, for fixing the mounting section onto a respective receiving portion of the plasma torch. Furthermore, the mounting section preferably comprises an assembly surface for engagement of an assembly tool, wherein the assembly surface preferably is facing away from the nozzle axis.
If mounted onto a plasma torch, the tip section is facing away from the plasma torch. The tip section is configured for directing a plasma gas flow and thus for guiding a plasma beam in direction of a welding area. A welding area is an area the weld is produced. Preferable, the tip section is configured for directing the plasma gas in a straight direction for ensuring a laminar plasma gas flow. With such laminar plasma gas flow, a straight and focused plasma beam is creatable. Such plasma beam has the advantage of a very high energy density and is especially suitable for narrow bevel welding.
The main canal is preferably coaxial with the nozzle axis and the electrode. The main canal is configured for housing the electrode, wherein there is no direct contact between the electrode and an inner wall of the main canal. Moreover, the main canal is configured for enabling the plasma gas flow through the nozzle and out of the nozzle at an end of the tip section that is facing away from the mounting section of the nozzle. The electrode is preferably a tungsten electrode for narrow bevel angle plasma welding.
The nozzle cooling canal is separated from the main canal and extends at least through the mounting section of the nozzle. The nozzle cooling canal is configured for guiding a cooling fluid flow through the nozzle, thereby cooling the nozzle. The nozzle cooling canal is closed in a direction facing away from the mounting section and open in a direction facing the plasma torch in order to receive cooling fluid from the plasma torch. Preferably, the nozzle cooling canal is formed in a way that a heat exchange between the nozzle and the cooling fluid is improved, e.g. by providing a relatively big surface for heat exchange. Since the nozzle cooling canal is separated from the main canal, interexchange of cooling fluid and plasma gas is prevented.
The inventive nozzle has the advantage, that a continuous narrow bevel angle welding process is possible, wherein an overheat of the nozzle and/or the plasma torch is prevented efficiently and in a cost effective way due to the nozzle cooling canal. By these means, quality of a narrow bevel angle weld can be improved. Furthermore, since the nozzle cooling canal is separated from the main canal, the welding process is not negatively affected by the cooling fluid. As a consequence, with the inventive nozzle, costs of a narrow bevel angle welding process can be reduced and production capacity of a narrow bevel angle plasma torch system can be increased due to less necessary system down time, e.g. due to less maintenance or overheat of the plasma torch or the nozzle.
It is preferred that the nozzle cooling canal extends through a part of the tip section of the nozzle. The closer the nozzle cooling canal extends to an end of the tip section that is facing away the mounting section, the better cooling action can be provided by the nozzle cooling canal due to an increased surface of the nozzle cooling canal for temperature exchange with the material of the nozzle. Thus, especially the tip section of the nozzle can be cooled in a more efficient way.
In a preferred embodiment of the invention a surface of the mounting section that is facing away from the nozzle axis comprises a form fit section for being engaged, e.g. positively gripped, by an assembly tool. A form fit section can be a hexagon or a pair of preferably plain surfaces that are arranged parallel to each other. An assembly tool is slideable onto such form fit section. In a following step, the nozzle is e.g. screwable onto the plasma torch or unscrewable off the plasma torch by turning the nozzle around the nozzle axis in a respective direction. Such form fit section provides for easy assembly and disassembly of the nozzle with the plasma torch.
Preferably, a maximum extension of the tip section perpendicular to the nozzle axis exceeds a maximum extension of the mounting section perpendicular to the nozzle axis. Such tip section has the advantage that an increased volume for the nozzle cooling canal is provided within the tip section. By these means, a more efficient cooling can be provided to the tip section of the nozzle. Moreover, this is an advantage because especially the tip section of the nozzle is exposed to heat emitted by the plasma beam.
It is advantageous that the tip section has a conical shape or at least a substantially conical shape, wherein the tip section tapers off in a direction facing away from the mounting section. With such nozzle, a stream of protective gas that is flowing between an outer surface of the nozzle and an inner surface of a housing that is surrounding the nozzle can be guided to a welding area more efficiently. Thus, a protective atmosphere can be established at the welding area in a more efficient way.
In a preferred embodiment of the invention, the main canal comprises a main canal end section for guiding the plasma beam, wherein the main canal end section has a first diameter that is smaller than a second diameter of the main canal in the mounting section. Preferably, the first diameter is smaller than a diameter of the electrode. Such main canal has the advantage that a flow of plasma gas can be provided at relatively high speed at the end of the nozzle. Thus, shape stability of a plasma beam due to better laminar flow of the plasma gas is improved.
Preferably, at the main canal end section the nozzle cooling canal is closer to the nozzle axis than at the mounting section. The part of the nozzle that is subjected to the highest temperatures during plasma welding is the end of the main canal at the tip section. Consequently, it is advantageous to provide an efficient cooling action to that area. This objective is solved by a nozzle cooling canal that is close to the nozzle axis. Preferably, the nozzle cooling canal is directed towards the nozzle axis or at least approaching the nozzle axis with respect to an end of the tip section that is facing at the welding area. Since the main canal end section has a first diameter that is smaller than the second diameter of the main canal, the nozzle cooling canal can be arranged closer to the nozzle axis at the main canal end section than at the mounting section.
It is preferred that the main canal end section is elongated for guiding the plasma beam parallel to the nozzle axis. In this context, elongated means that a length of the main canal end section is at least double, preferably between two and four times of its diameter. By these means, a distance between the electrode and the welding area is increased. This has the advantage that an improved laminar plasma gas flow can be provided. As a result, shape stability of a plasma beam is improved.
According to a second aspect of the invention, the objective is solved by a plasma torch system for a narrow bevel angle plasma welding device. The plasma torch system comprises a narrow bevel angle plasma torch and a nozzle. The plasma torch comprises an upper torch section, a lower torch section and an electrical insulation section, wherein the upper torch section and the lower torch section are interconnected via the electrical insulation section. The plasma torch further comprises an electrode and a plasma canal that extends at least through a part of the upper torch section and the lower torch section, wherein the electrode is arranged within the plasma canal. Furthermore, the nozzle is a nozzle according to the first aspect of the invention, wherein the plasma torch further comprises a torch cooling canal extending through the lower torch section, and wherein the torch cooling canal is connected in fluid communication to the nozzle cooling canal of the nozzle.
The plasma torch of the plasma torch system preferably has a cylindrical or substantially cylindrical shape and is preferably coaxial with the electrode and the nozzle axis. A cylindrical shape has the advantage that collision free navigation of the plasma torch within a gap for a narrow bevel angle weld is improved. The upper torch section and the lower torch section are connected and electronically insulated from each other by the electrical insulation section in order to prevent ignition of an electric arc between the tip section of the nozzle and the welding area. Hence, only an electric arc between the electrode and the welding area can be ignited.
The plasma canal extends within the plasma torch parallel to the nozzle axis and is configured for housing the electrode and directing plasma gas to the tip section of the nozzle. Therefore, the plasma canal is connected in fluid communication, preferably coaxially, with the main canal of the nozzle.
The torch cooling canal and the nozzle cooling canal form a common cooling canal for cooling the nozzle, especially the tip section of the nozzle, by means of a cooling fluid, e.g. water or the like. The torch cooling canal and nozzle cooling canal are preferably designed in a way that the path of a cooling fluid is from the lower torch section to the nozzle and back to the lower torch section within the common cooling canal. Since the nozzle cooling canal extends within the nozzle, an efficient cooling of the nozzle is provided.
The plasma torch system according to the invention has the same advantages over the state of the art as the nozzle according to the invention.
Preferably, the lower torch section comprises a cooling fluid inlet for guiding cooling fluid into the torch cooling canal and a cooling fluid outlet for guiding fluid out of the torch fluid canal. By these means, relatively cold cooling fluid can be provided to the common cooling canal via the cooling fluid inlet and relatively warm cooling fluid can be drained of the common cooling canal via the cooling fluid outlet. This has the advantage that a cooling circuit for effective cooling of plasma torch and the nozzle is provided by the plasma torch system.
Further, it is preferred that the plasma torch comprises a spacer element that is located within the plasma canal of the lower torch section for keeping the electrode spaced away from an inner wall of the lower torch section. The spacer element prevents an electric current flow between the lower torch section and the electrode while enabling the plasma gas flow past the spacer along the nozzle axis. The spacer element preferably comprises a heat resistant material that is electrically insulating, like ceramics. Moreover, the spacer element has the advantage that the electrode is kept in place with respect to the plasma canal. Thus, process stability, especially stability of the plasma beam, is improved.
Preferably, the spacer element comprises a knurled surface for enabling plasma gas passing by the spacer element within the plasma canal. The knurled surface comprises e.g. a plurality of rims and walls that are extending parallel to the nozzle axis. This has the advantage that a laminar stream of plasma gas is allowed to pass the spacer element. Furthermore, such spacer element is easy to manufacture at relatively low costs and by simple production means.
In a preferred embodiment of the invention, at least the lower torch section of the plasma torch is encompassed by a housing that is spaced away the lower torch section, thus providing a protective gas canal for guiding protective gas to the tip section of the nozzle. The housing preferably has an inner shape that corresponds to an outer shape of the lower torch section and/or the nozzle. Thus, a relatively homogenous protective gas canal is formed, enabling a relatively laminar and homogenous protective gas flow. It is preferred that the housing has the shape of a hollow cylinder, wherein a part of the housing adjacent the nozzle is tapered corresponding to the nozzle. A housing has the advantage that a protective gas atmosphere can be provided at the welding area efficiently.
It is preferred that the electrical insulation section comprises a Teflon ring. A Teflon ring has the advantage that it provides an electrical insulation that is heat resistant. Thus, the electrical insulation can withstand high temperatures of the upper torch section and the lower torch section due to the welding process. According to a preferred embodiment the Teflon ring is the electrical insulation section.
Preferably, adjacent the nozzle, the plasma torch has a diameter of 14 mm or less. Such plasma torch is in particular suitable for most narrow bevel angle welding applications due to its compact dimensions.
The present invention is further described hereinafter with reference to an illustrated embodiment shown in the accompanying drawings, in which:

Figure 1: illustrates schematically in a side view a preferred embodiment of a plasma torch system with an inventive nozzle; and
Figure 2: illustrates schematically in a magnified side view the nozzle of Figure 1.

Hereinafter, a preferred embodiment for carrying out the present invention is described in detail. The preferred embodiment is described with reference to the drawings, wherein features with the same attributes are assigned to the same reference numerals. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of a preferred embodiment. These details are not meant to delimit the scope of the invention in any way.
FIG 1 illustrates schematically a preferred embodiment of a narrow bevel angle plasma torch system 13 according to the second aspect of the invention. The plasma torch system 13 comprises a nozzle 1 and a plasma torch 2. The nozzle 1 is shown in detail in FIG 2. The plasma torch 2 comprises an upper torch section 14, a lower torch section 15 and an electrical insulation section 16, that are coaxially aligned with a central nozzle axis 3, wherein the electrical insulation section 16 is interposed between the upper torch section 14 and the lower torch section 15, e.g. glued together. The nozzle 1 is mounted with its mounting section 4 onto the lower torch section 15, e.g. by screwing.
A plasma canal 17 of the plasma torch 2 extends from the upper torch section 14 through the lower torch section 15 to the nozzle 1. A electrode 7, in particular a tungsten electrode, is arranged within the plasma canal 17, spaced away from an inner wall 22 of the lower torch section 15 by a spacer element 21. The spacer element 21 can have a knurled surface 23 facing towards the inner wall 22 of the lower torch section 15, thus forming a plurality of small canals for allowing the plasma gas passing the spacer element 21 within the plasma canal 17. In the upper torch section 14, a plasma gas inlet 24 is arranged for providing a flow of plasma gas to the plasma gas canal 17.
The lower torch section 15 further comprises a torch cooling canal 18 for guiding cooling fluid to a nozzle cooling canal 8 of the nozzle 1. The lower torch section 15 further comprises a cooling fluid inlet 19 for providing cool cooling fluid to the torch cooling canal 18 and a cooling fluid outlet 20 for allowing heated cooling fluid exiting the torch cooling canal 18. Cooling fluid that enters the torch cooling canal 18 via the cooling fluid inlet 19 will flow along a first part of the torch cooling canal 18 (shown on the left side in this drawing) to the nozzle cooling canal 8, via the nozzle cooling canal 8 to a second part of the torch cooling canal 18 (shown on the right side in this drawing) and exit the torch cooling canal 18 via the cooling fluid outlet 20. A housing for forming a protective gas canal is not shown in the drawing.
In FIG 2 the nozzle 1 part of FIG 1 is illustrated in a magnified view. The mounting section 4 and the tip section 5 are shown, wherein the mounting section 4 is mounted onto the lower torch section 15 of the plasma torch 2 and the tip section 5 is facing away from the plasma torch 2. The mounting section 4 comprises a form fit section 9, e.g. a hexagon, for engagement of an assembly tool like a jaw wrench. The form fit section 9 is facing away from the nozzle axis 3. Within the mounting section 4 the nozzle 1 comprises a seal ring 25 that is contacting the inner wall 22 of the lower torch section 15. The seal ring 25 is preferably made of silicone or the like. This ensures a tight seat of the nozzle 1 at the plasma torch 2.
A main canal 6 is formed coaxial with the nozzle axis 3 and the plasma canal 17 of the plasma torch 2 (see FIG 1). In an upper part of the main canal 6 a tip part of the tungsten electrode 7 is located. In that upper part, the main canal 6 has a second diameter 12, which is bigger than an outer diameter of the electrode 7. In this preferred embodiment, the plasma canal 17 has the second diameter 12 as well. A main canal end section 10 has a first diameter 11, wherein the first diameter 11 is smaller than the second diameter 12. The main canal 6 tapers off from the upper part to the main canal end section 10 corresponding to a taper of the tip part of the electrode 7.
Within a distance to the nozzle axis 3, the nozzle 1 comprises a nozzle cooling canal 8 extending from the mounting section 4 to the tip section 5, at least 180 degrees around the tip section 5 and back to the mounting section 4. The nozzle cooling canal 8 is open towards the torch cooling canal 18 of the plasma torch 2 and preferably has the same diameter. Cooling fluid can enter the left part of the nozzle cooling canal 8 from the left part of the torch cooling canal 18, flow within the nozzle cooling canal 8 at least 180 degrees around the tip section 5 of the nozzle 1 and flow to the right part of the torch cooling canal 18 via the right part of the nozzle cooling canal 8. The massive material of the tip section 5 of the nozzle 1 provides for a high thermal and mechanical resistance of the nozzle 1.
In an alternative embodiment, the nozzle cooling canal 8 is arranged for approaching the nozzle axis 3 in the tip section while travelling away from the mounting section 4, e.g. corresponding to the taper of the main canal 6, in order to provide effective cooling action to the main canal end section 10.

Claims

Nozzle (1) for a narrow bevel angle plasma torch (2), the nozzle (1) comprising a nozzle axis (3), a mounting section (4) for mounting the nozzle (1) onto a plasma torch (2), a tip section (5) for guiding a plasma beam and a main canal (6) for housing an electrode (7) of the plasma torch (2), wherein the main canal (6) extends through the nozzle (1) via the mounting section (4) and the tip section (5),
c h a r a c t e r i z e d i n t h a t ,
the nozzle (1) further comprises a nozzle cooling canal (8) for guiding a cooling fluid through the nozzle (1), wherein the nozzle cooling canal (8) is separated from the main canal (6).
Nozzle (1) according to claim 1,
c h a r a c t e r i z e d in that,
the nozzle cooling canal (8) extends through a part of the tip section (5) of the nozzle (1).
Nozzle (1) according to claim 1 or 2,
characterized in that,
a surface of the mounting section (4) that is facing away from the nozzle axis (3) comprises a form fit section (9) for being engaged by an assembly tool.
Nozzle (1) according to any of the previous claims,
characterized in that,
a maximum extension of the tip section (5) perpendicular to the nozzle axis (3) exceeds a maximum extension of the mounting section (4) perpendicular to the nozzle axis (3).
Nozzle (1) according to any of the previous claims,
characterized in that,
the tip section (5) has a conical shape or at least a substantially conical shape, wherein the tip section (5) tapers off in a direction facing away from the mounting section (4).
Nozzle (1) according to any of the previous claims,
characterized in that,
the main canal (6) comprises a main canal end section (10) for guiding the plasma beam, wherein the main canal end section (10) has a first diameter (11) that is smaller than a second diameter (12) of the main canal (6) in the mounting section (4).
Nozzle (1) according to claim 6,
characterized in that,
at the main canal end section (10) the nozzle cooling canal (8) is closer to the nozzle axis (3) than at the mounting section (4).
Nozzle (1) according to claim 6 or 7,
characterized in that,
the main canal end section (10) is elongated for guiding the plasma beam parallel to the nozzle axis (3).
Plasma torch system (13) for a narrow bevel angle plasma welding device, comprising a narrow bevel angle plasma torch (2) and a nozzle (1), wherein the plasma torch (2) comprises an upper torch section (14), a lower torch section (15) and an electrical insulation section (16), wherein the upper torch section (14) and the lower torch section (15) are interconnected via the electrical insulation section (16), wherein the plasma torch (2) further comprises an electrode (7) and a plasma canal (17) that extends at least through a part of the upper torch section (14) and the lower torch section (15), wherein the electrode (7) is arranged within the plasma canal (17),
characterized in that,
the nozzle (1) is a nozzle (1) according to any of claims 1 to 8, wherein the plasma torch (2) further comprises a torch cooling canal (18) extending through the lower torch section (15), and wherein the torch cooling canal (18) is connected in fluid communication to the nozzle cooling canal (8) of the nozzle (1).
Plasma torch system (13) according to claim 9,
characterized in that,
the lower torch section (15) comprises a cooling fluid inlet (19) for guiding cooling fluid into the torch cooling canal (18) and a cooling fluid outlet (20) for guiding fluid out of the torch cooling canal (18).
Plasma torch system (13) according to claim 9 or 10,
characterized in that,
the plasma torch (2) comprises a spacer element (21) that is located within the plasma canal (17) of the lower torch section (15) for keeping the electrode (7) spaced away from an inner wall (22) of the lower torch section (15).
Plasma torch system (13) according to claim 11,
characterized in that,
the spacer element (21) comprises a knurled surface (23) for enabling plasma gas passing by the spacer element (21) within the plasma canal (17).
Plasma torch system (13) according to any of claims 9 to 12,
characterized in that,
at least the lower torch section (15) of the plasma torch (2) is encompassed by a housing that is spaced away the lower torch section (15), thus providing a protective gas canal for guiding protective gas to the tip section (5) of the nozzle (1).
Plasma torch system (13) according to any of claims 9 to 13,
characterized in that,
the electrical insulation section (16) comprises a Teflon ring.
Plasma torch system (13) according to any of claims 9 to 14,
characterized in that,
adjacent the nozzle (1), the plasma torch (2) has a diameter of 14 mm or less.