EP2127502B1

EP2127502B1 - Plasma cutting torch

Info

Publication number: EP2127502B1
Application number: EP08702238.0A
Authority: EP
Inventors: Mauro Vancini; Silvano Dallavalle; Vittorio Colombo; Emanuele Ghedini
Original assignee: Cebora SpA
Current assignee: Cebora SpA
Priority date: 2007-01-15
Filing date: 2008-01-15
Publication date: 2015-10-28
Anticipated expiration: 2028-01-15
Also published as: WO2008087522A2; EP2127502A2; ITBO20070019A1; WO2008087522A3; PL2127502T3

Description

Technical Field

This invention relates to a plasma cutting torch, in particular a plasma torch with long-life operating elements.

Background Art

Prior art plasma torches (e.g. the one of DE4030541A1 ) basically comprise:

a torch body which extends mainly in length and which houses:
a cylindrical electrode mounted centrally on the torch body and connected by a lead to the negative pole of the power generator (cathode);
a nozzle mounted on the end of the torch body and surrounding the tip of the electrode; this nozzle is electrically isolated from the electrode and can be connected by a second lead to the positive pole of the power generator (anode);
a nozzle holder or nozzle support joined directly to the torch body, the latter's inside wall facing the outside wall of the nozzle in such a way as to form a cooling chamber through which a cooling fluid passes;
a nozzle and nozzle holder bottom covering unit adapted to separate the interior of the torch from the exterior and thus protecting it, for example, from splashes of hot molten material (especially when the torch pierces the metal).

The covering unit forms with the nozzle holder a feed channel for the flow of a secondary fluid or gas.
The nozzle and the protective element enable the plasma to be discharged through respective coaxial holes in their distal portions.
The covering unit is normally divided into two separate parts which are fitted together when the torch is assembled:

the first part is a supporting member, substantially cylindrical in shape, which, close to its distal end, can be screwed to the torch body where it is suitably isolated electrically;
the second part, the covering element proper, consists of a second, cup-shaped member which can be coupled with the proximal end of the supporting member so as to totally cover the proximal area of the torch.

This second member is provided with the above mentioned central hole for the passage of the plasma arc and with a circular internal area shaped to accommodate a secondary gas ring or diffuser interposed between the second member itself and the outside surface of the nozzle holder.
Further, this ring is provided with a plurality of openings distributed according to a well known pattern to enable the secondary gas to flow towards the plasma channel.
The flow of secondary fluid is used to prevent molten metal from entering the holes, to improve directional accuracy of the plasma arc generated and to protect the arc discharged by the torch from the atmosphere.
The widespread use of this type of torch has over time made it possible to test the torch in terms of its operating reliability and the working life of its components.
In particular, on high-amp torches where the plasma arc causes very high temperatures to be reached, it has been noticed that the covering unit and, more specifically, the second, cup-shaped member is subjected to wear and damage at a higher rate than the first member, not only on account of the high temperatures present in the working area but also because molten material from the part being worked tends to adhere to its surface especially when the part itself is pierced.
These two factors tend to reduce significantly the working life of this part of the covering unit, thus necessitating periodic replacements and machine shutdowns: this in turn reduces productivity and creates the need for a large stock of spares, with all the costs that this involves.

Aim of the Invention

After much research and testing, the Applicant has designed and produced a plasma cutting torch whose technical and structural characteristics are such as to minimize wear on the second member of the covering unit and to reduce damage to it during work. This is done by diversifying the cooling fluids flowing towards and in the vicinity of the covering unit.
According to the invention, this aim is achieved by a plasma torch according to claim 1.

Brief Description of the Drawings

The technical characteristics of the invention, with reference to the above aims, are clearly described in the claims below and its advantages are apparent from the detailed description which follows, with reference to the accompanying drawings which illustrate a preferred embodiment of the invention provided merely by way of example without restricting the scope of the inventive concept, and in which:

Figure 1 is a longitudinal section, with some parts cut away, illustrating a part of a plasma torch according to the invention;
Figure 2 is a perspective view showing a first detail of the torch of Figure 1;
Figure 3 is a front view showing a second detail of the torch of Figure 1;
Figure 4 is a cross section through the line IV - IV shown in Figure 3;
Figure 5 is a longitudinal section in a first plane, with some parts cut away to better illustrate others, showing a variant form of the torch according to the invention;
Figure 5a shows an enlarged detail from Figure 5;
Figure 6 is a cross section through the line VI-VI of Figure 5, with some parts cut away to better illustrate others;
Figure 7 is a bottom plan view of the torch of Figure 5;
Figure 8 is a longitudinal section in a second plane showing the torch according to the second variant form of Figure 5;
Figure 9 is a cross section through the line IX-IX of Figure 8, with some parts cut away to better illustrate others;
Figure 10 is a longitudinal section, with some parts cut away to better illustrate others, showing a third variant form of the torch according to the invention.

Detailed Description of the Preferred Embodiments of the Invention

With reference to the accompanying drawings, in particular Figure 1, the plasma torch according to the invention, labelled 1 in its entirety, is used for cutting metals.
The torch 1 consists of a torch body 2 which extends mainly in length along an axis X and basically comprises: an electrode 3; a nozzle 4; a nozzle support or holder 7; a first unit 10 for covering the nozzle 4 and the nozzle holder 7; and a second unit 13 for partly covering the first unit 10.
More specifically, the electrode 3 is mounted centrally in the torch body 2 and can be connected to the negative pole of a power generator (not illustrated).
In this description, the term "proximal end" denotes the end portion of each torch component closest to the point O shown in Figures 1 and 5.
The term "distal end" denotes the end portion of each torch component furthest from the point O, that is to say, the end opposite the proximal end.
The nozzle 4 is mounted on the proximal end of the torch body 2, connectable to the positive pole of the generator to form an anode and surrounding the tip of the electrode 3 to form a chamber 5 where plasma is generated by feeding a first fluid or gas into it (see arrows F1, Figure 1), and having a first central through hole 6 for the passage of the plasma.
The nozzle holder 7 is associated with the torch body 2 and an inside wall of it faces the outside wall of the nozzle 4 in such a way as to form a cooling chamber 8 through which is fed a second, cooling fluid F2 (which, in this nonlimiting example, is water).
The solution described here is applied to a plasma cutting torch designed for use with water as the cooling fluid: this will not be understood as excluding the possibility of applying the same solution to torches using air as second cooling fluid F2.
The above mentioned first unit 10 for covering the nozzle 4 and the nozzle holder 7 comprises:

a supporting member 10a, substantially cylindrical in shape, which, close to its distal end, can be joined, for example by screwing, to the torch body 2 from which it is electrically isolated by a suitable isolating ring 50 (illustrated in detail in Figures 3 and 4);
a second, cup-shaped member 10b which at least partly matches the shape of the profile of the nozzle 4 and nozzle holder 7, and whose annular edge 100 can be joined to the proximal end (tapered) of the first supporting member 10a. Further, the second member 10b is provided with a second central hole 11, coaxial with the first hole 6, to allow the passage of the plasma arc: thus, the second member 10b constitutes an element for covering and protecting the torch 1 (shown in detail in Figure 2).

The covering unit 10 also forms a channel 12 through which a third cooling fluid F3 (indicated by the arrows F3) flows between the nozzle holder 7 and the covering unit 10 to reach the second hole 11: this secondary fluid (which may be air - or other fluid/gas - supplied by respective second means 12m illustrated as a block) further cools the area close to the nozzle holder 7 and nozzle 4 and is discharged through the second hole 11.
The above mentioned second unit 13 for partly covering the first unit 10 may be associated with the torch body 2 or (as described in more detail below) with the first member 10a, and forms, together with the outside surface of the first unit 10 facing the second unit 13, a second channel 14 for the passage of a fourth fluid F4 (for example air or other fluid/gas) leading in the direction of the second hole 11 and designed at least to permit cooling of the outside of the first unit 10 (as indicated by the arrows F4).
More specifically, the second unit 13 has a cylindrical shape, tapering inwards at its proximal end in such a way as to substantially match a part of the first unit 10.
Still with reference to Figure 1, the second unit 13 is joined indirectly, in the embodiment illustrated by way of example, to the torch body 2 at its distal end.
More specifically, the distal end of the second unit 13 may be screwed to (or stably associated with) an outside portion of the distal end of the first supporting member 10a, and both can then be locked to the torch body 2 by means of the first supporting member 10a itself.
The second cylindrical unit 13 encompasses and covers the first member 10a and is positioned with its proximal end close to the second member 10b in such a way as to enable a fourth fluid F4 to flow in the direction of the second member 10b, thereby creating a protective area around the second member 10b to prevent molten material from adhering to the second member 10b during use.
In an embodiment illustrated in Figure 1, the second member 10b may be thicker than the first member 10a, so as to form a bottom cylindrical wall 10c that protrudes from the cylindrical outside surface of the first member 10a and facing the outlet opening of the second unit 13.
As a result of this constructional architecture, the second member 10b (see Figure 2 again) may have a plurality of radial notches 15 running uniformly along the circumferential surface of the second member 10b and designed to enable the fourth fluid F4 to flow along the bottom surface of the second member 10b in order to improve cooling by increasing the heat exchange surface area.
Looking in more detail, each notch 15 may have a partly curved shape. along the top of it 15a in such a way as to direct the flow of the fourth fluid F4 out of the notches 15 in a direction D substantially parallel to the longitudinal axis X of the torch body 2.
Looking in more detail, the fourth fluid F4 can be fed into the second channel 14 through a respective conduit 16 passing through the first unit 10, that is, at the proximal end of the first member 10a.
Another feature (see also Figures 3 and 4) is provided by spacer elements 17 located between the first member 10a and the second unit 13 which support and position the second unit 13 and which keep the second annular channel 14 at a predetermined size.
These spacer elements 17 may be formed from a plurality of openings made on a ring 18 running around the first member 10a.
The fourth fluid F4 may, in a first solution, be fed by independent means 19 (illustrated as a block).
In a second solution, the fourth fluid F4 may be of the same type as the fluid F3 but fed into the second channel 14 by respective means 19 independent of - the above mentioned means 12m for feeding the third fluid F3 (see dashed line).
In a third solution, the fourth fluid F4 is of the same type as the third fluid F3 and is fed into the second channel 14 by the same means 12m that feed the third fluid F3 into the first channel 12 (see dot-dashed line).
Figures 5, 5a, 6, 7, 8 and 9 illustrate a second variant form of the torch according to this invention.
In the second variant form, too, the second member 10b is tapered in the direction of the proximal end of the torch.
With reference to Figures 5, 5a and 8 and to the direction indicated by the arrow F in Figure 5, the member 10b comprises, from the top down, a first groove 20, a first vertical, cylindrical wall 21, a supporting surface 22, a second groove 23, a second vertical, cylindrical wall 24, and a truncated cone shaped wall 25 in whose minor base the above mentioned hole 11 is made.
Similarly, the second unit 13 is tapered in the direction of the proximal end of the torch 1.
The second unit 13 comprises, at its proximal end (and from the top down with reference to the direction indicated by the arrow F in Figure 5), a first vertical, inside cylindrical wall 26, a surface 27 for supporting the member 10b and a second vertical, inside cylindrical wall 28.
The cylindrical walls 21, 24, 26 and 28 which, in the embodiment illustrated, are vertical, may, in another embodiment that is not illustrated, be inclined at a predetermined angle.
The member 10b is associated with the first member 10a at the first groove 20, with an interposed sealing ring 29 inserted in the first groove 20 itself.
As illustrated in Figure 8, the supporting surface 22 of the member 10b rests on the supporting surface 27 of the second unit 13 and the first vertical cylindrical wall 21 of the member 10b is positioned side by side with the first vertical, inside cylindrical wall 26 of the second unit 13: thus, the member 10b is connected to the second unit 13 and is centred with respect to the latter thanks to the vertical wall 26 of the second unit 13.
As shown in Figures 5a and 6, the second unit 13 comprises a plurality of notches 30, uniformly distributed along the entire supporting surface 27.
Each notch 30 constitutes an extension 31 of the second channel 14 for the passage of the fluid F4 between the member 10b and the second unit 13 so that the fluid F4 is discharged at the second groove 23.
In the embodiment illustrated, there are twelve notches 30 and they are substantially semicircular in shape, without thereby limiting the scope of the invention, meaning that the torch 1 may have a different number of notches and that the notches may be otherwise shaped.
The top end 24a of the second vertical wall 24 of the member 10b and the bottom end 28a of the second vertical inside wall 28 of the unit 13 are positioned side by side and define a passage 32 through which the fluid F4 is discharged from the second groove 23 to the outside of the torch 1, in the direction of the above mentioned hole 11.
Thus, the second channel 14 also comprises the extension 31, the second groove 23 and the passage 32.
Advantageously, as shown in Figure 7, the passage 32 is a circular crown 33 whose width is equal to the distance between the bottom end 28a of the second wall 28 of the second unit 13 and the top end 24a of the second wall 24 of the member 10b.
Thus, in this second variant form, the member 10b is fixed to the torch 1 through its connection to the second unit 13.
As described above, this connection is achieved by placing the supporting surface 22 over the supporting surface 27 and placing the wall 21 side by side with the wall 22 so as to centre the member 10b with respect to the second unit 13.
The fluid F4 therefore flows through the second channel 14 and along the extension 31 of the second channel 14 formed by the notches 30 in the second unit 13, at the supporting surface 27.
The fluid F4 flows through the extension 31 and into the second groove 23 and from there out through the passage 32 in the direction of the hole 11.
Thanks to the circular crown shape of the passage 32, the fluid F4 externally surrounds all the space around the member 10b.
In a variant form that is not illustrated the member 10b does not have the second groove 23 and the fluid F4 flows through the extension 31 of the second channel 14 and out directly through the passage 32.
Figure 10 illustrates a third variant form of the torch 1 according to this invention.
As shown in Figure 10, the second unit 13 of the third variant form comprises a first part 13a and a second part 13b.
The first part 13a comprises, at its proximal end, a seat 34 designed to receive a corresponding portion 35 of the second part 13b.
Further, the second part 13b comprises a portion 36 designed to be connected to a corresponding portion 37 of the second member 10b.
Looking in more detail, the portion 36 is step-shaped and the portion 37 is a protrusion shaped to match the portion 36 and designed to fit into the portion 36 itself.
The second part 13b and the second member 10b are fixed by connecting the portion 36 and the portion 37 by interference.
In a manner similar to the other variant forms described above, the first part 13a and the second part 13b define the second outlet channel 14 for discharging the fluid F4 in the direction of the hole 11.
A plasma torch made in this way therefore achieves the above mentioned aims thanks to a second unit adapted to form the second channel for the fourth fluid allowing the second member to be cooled and consequently protecting it against splashes of molten material that would otherwise damage it: this is achieved also thanks to the special structure of the second member which includes notches for directing the flow.
This second cylindrical unit requires limited structural modifications to the torch. Moreover, the fourth fluid may be a liquid or gas of the same type as the third fluid already used in the first channel of the torch.
The invention described above is susceptible of industrial application and may be modified and adapted in several ways without thereby departing from the scope of the appended claims. Moreover, all the details of the invention may be substituted by technically equivalent elements.

Claims

A plasma cutting torch comprising:
- a torch body (2);

- an electrode (3) mounted in the torch body (2);

- a nozzle (4) mounted on the proximal end of the torch body (2), surrounding the tip of the electrode (3) to form a chamber (5) where plasma is generated by feeding a first fluid (F1) into it, and having a first central through hole (6) for the passage of the plasma;

- a nozzle support or holder (7) joined to the torch body (2) and whose inside wall faces the outside wall of the nozzle (4) in such a way as to form a cooling chamber (8) through which a second, cooling fluid (F2) flows;

- a first nozzle (4) and nozzle holder (7) covering unit (10) joined to the torch body (2) having a proximal end and a distal end, the proximal end of the first unit (10) being provided with a second central hole (11) for the passage of the plasma;

- a first channel (12) formed between the nozzle holder (7) and the covering unit (10) and allowing a third fluid (F3) to flow towards the second hole (11);

- a second unit (13) for partly covering the first unit (10) and designed to form, together with the outside surface of the first unit (10) facing the second unit (13), a second channel (14) for the passage of a fourth fluid (F4) leading to the outside of the first unit (10) in the direction of the second hole (11), thereby cooling at least the outside of the first unit (10) itself,
characterized in that the first unit (10) comprises a first part composed of a first supporting member (10a) which, close to its distal end, can be joined to the torch body (2), and a second part composed of a second member (10b) which is shaped to at least partially match the profile of the nozzle (4) and of the nozzle holder (7) and which can be joined by its annular edge (100) to the proximal end of the first supporting member (10a), wherein the second unit (13), which is cylindrical in shape, encompasses and covers the first member (10a) and is positioned with its proximal end close to the second member (10b) in such a way as to enable said fourth fluid (F4) to flow in the direction of the second member (10b), thereby creating a protective area around the second member (10b) to prevent molten material from adhering to the second member (10b).
The torch according to claim 1, characterized in that the second unit (13) has a cylindrical shape, tapering inwards at its proximal end in such a way as to substantially match a part of the first unit (10).
The torch according to claim 2, characterized in that the second unit (13) is joined to the first unit (10) at its distal end.
The torch according to claim 1, characterized in that the second member (10b) is thicker than the first member (10a), so as to form a bottom cylindrical wall (10c) that protrudes from the cylindrical outside surface of the first member (10a) and facing the outlet opening of the second unit (13).
The torch according to claims 4, characterized in that the second member (10b) comprises a plurality of radial notches (15) running uniformly along the circumferential surface of the second member (10b) and designed to enable the fourth fluid (F4) to flow along the bottom surface of the second member (10b) in order to increase the heat exchange surface area.
The torch according to claim 5, characterized in that each notch (15) has a partly curved shape along the top of it (15a) in such a way as to direct the flow of the fourth fluid (F4) out of it in a direction (D) substantially parallel to the longitudinal axis (X) of the torch body (2).
The torch according to claim 1, characterized in that the fourth fluid (F4) can be fed into the second channel (14) through a respective conduit (16) passing through the first unit (10).
The torch according to claim 1, characterized in that between the first member (10a) and the second unit (13) there are spacer elements (17) which support the second unit (13) and which keep the second annular channel (14) at a predetermined size; said spacer elements (17) being formed from a plurality of openings made in a ring (18) running around the first member (10a).
The torch according to claim 7 or 8, characterized in that the fourth fluid (F4) is fed by independent means (19).
The torch according to claim 7, characterized in that the fourth fluid (F4) is the same as the third fluid (F3) and is fed into the second channel (14) by respective means (19) independent of means (12m) that feed the third fluid (F3).
The torch according to claim 7, characterized in that the fourth fluid (F4) is the same as the third fluid (F3) and is fed into the second channel (14) by the same means (12m) that feed the third fluid (F3) into the first channel (12).
The torch according to claim 1, characterized in that the fourth fluid (F4) is air.
The torch according to claim 1, characterized in that the second unit (13) is joined to the first supporting member (10a) at its distal end.
The torch according to claim 1, characterized in that the second unit (13) comprises, at its proximal end, a surface (27) for supporting the second member (10b) and a first substantially vertical, inside cylindrical wall (26) designed to placed side by side with a corresponding first vertical wall (21) of the second member (10b).
The torch according to claim 14, characterized in that the second member (10b) comprises, at the annular edge (100), a supporting surface (22) designed to be placed over the surface (27) which supports the second unit (13), so that the second member (10b) is joined to both the first member (10a) and to the second unit (13).
The torch according to claim 15, characterized in that the surface (27) which supports the second unit (13) comprises a plurality of notches (30), each of said notches constituting an extension (31) of the second channel (14) allowing the passage of the fluid (F4) between the supporting surface (27) and the supporting surface (22).
The torch according to claim 16, characterized in that the second unit (13) comprises, at its proximal end, a second vertical, inside wall (28) and in that the second member (10b) comprises a second vertical cylindrical wall (24), the second inside wall (28) and the second vertical wall (24) being positioned side by side in such a way as to form an outlet passage (32) allowing the fluid (F4) from the second channel (14) to flow out of the torch.
The torch according to claim 1, characterized in that the second unit (13) comprises a first part (13a) joined to the first unit (10) at its distal end and a second part (13b) connected to the proximal end of the first part (13a); the second part (13b) surrounding the second member (10b) in such a way as to allow the fourth fluid (F4) to flow in the direction of the second member (10b), thereby creating a protective area around the second member (10b) itself.