Description

Plasma torch

Technical Field

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

Background Art

Prior art plasma torches 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 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) and forming 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 at their distal portion.

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 in sealed fashion 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 gas is designed to: prevent molten metal from entering the holes; improve directional accuracy of the plasma arc generated; and 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 second, cup-shaped member wears out much more quickly than the first member (at a higher rate) thus necessitating periodic replacements and machine shutdowns: this obviously leads to increased stock costs for the wear material.

Disclosure of the Invention After several research studies and tests, the Applicant has designed and produced a plasma torch whose structure at the nozzle and nozzle holder cover area is such to greatly reduce wear of the second member of the covering unit through optimized use of the second fluid, without significantly altering the basic structure of the covering unit, and while maintaining the high operating quality of the torch.

According to the invention, this aim is achieved by a plasma torch, in particular a plasma torch for cutting metals comprising the technical characteristics described in one or more of the appended claims.

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 in two different planes and with some parts

cut away, illustrating a part of a plasma torch according to the invention;

Figure 2 illustrates the proximal end of the plasma torch of Figure 1 in a first embodiment and in a longitudinal section with some parts cut away to better illustrate others; Figure 3 shows a scaled-up detail from Figure 2;

Figure 4 illustrates the proximal end of the plasma torch of Figure 1 in a second embodiment and in a longitudinal section with some parts cut away to better illustrate others;

Figure 5 shows a scaled-up detail from Figure 4; Figure 6 is a top plan view showing the covering unit of the torch of Figure 1;

Figure 7 shows a single part of the covering unit of Figure 6, again in a top plan view.

Detailed Description of the Preferred Embodiments of the Invention With reference to the accompanying drawings, with particular reference to

Figure 1, the plasma torch according to the invention, labelled 1 in its entirety, is used especially but without limiting the scope of the invention for cutting metals.

The torch 1 consists of a torch body 2 which extends mainly in length along an axis X and which basically comprises: an electrode 3; a nozzle 4; a nozzle support or holder 7 and a unit 10 for covering the nozzle 4 and the nozzle holder 7.

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).

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 (usually a gas, see arrows Gl in Figure 1) into it, and having a first central through hole 6 for the passage of the plasma.

The nozzle support or holder 7 is joined directly to the torch body 2 and one of the latter's inside walls 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 Fl (for example, water) is fed by respective first means 9 (represented by a block in Figure 1 since they are of known type).

The nozzle 4 and nozzle holder 7 covering unit 10 is composed of two parts (see also Figures 2 to 5): the first part is 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; the second part is a second, cup-shaped member 10b which, in the embodiment illustrated, at least partly matches the shape of the profile of the nozzle 4 and nozzle holder 7, and whose annular edge can be joined to the proximal end (tapered) of the first holder 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 front of the torch 1.

As shown in Figure 1, the distal and proximal ends refer to an imaginary observation point OS close to the holes 6 and 11.

The covering unit 10 also forms a channel 12 through which a third secondary fluid F2 (indicated by the arrows F2) flows between the nozzle holder 7 and the covering unit 10 to reach the second hole 11: the third secondary fluid (which may be air - or other fluid/gas - fed by respective means 12m, illustrated as a block, and passing through a conduit 12c) prevents molten metal from entering the holes, improves directional accuracy of the plasma arc generated and protects the arc discharged by the torch from the atmosphere.

The flow of this third fluid F2 is discharged through the second hole 11. Still with reference to Figures 2 to 5, in the area where the proximal end of the first holder member 10a is joined to the annular edge of the second holder member 10b there is a plurality of concavities 13 designed to enable a part F2a of the third cooling fluid F2 to flow through to the outside of the second member 10b (see arrows F2a) in order to cool the outside of the second member 10b itself.

More specifically, the proximal end of the first member 10a has an annular recess 14 adapted to form a surface 14p for supporting a lower annular abutment surface 15 afforded by a respective annular protrusion 16 of the second member

10b: these two areas enable the two members 10a and 10b to be slotted together during assembly of the torch 1.

Thanks to this structure, the above mentioned plurality of concavities 13 is formed on the annular supporting surface 14p of the first member 10a (as clearly shown in Figures 6 and 7).

More specifically, each concavity 13 formed on the supporting surface 14p may have, preferably but without limiting the scope of the invention, a semicircular cross section. This plurality of semicircular concavities 13 are formed on the entire circular join area and are uniformly distributed on the annular supporting surface

Looking more closely at the structural details, still with reference to Figures 6 and 7, each concavity 13 formed on the first member 10a is alternated with a flat surface section 14p for supporting the second member 10b.

Figures 1, 2 and 4 show that the second member 10b has an annular recess 17 which at least partly accommodates a ring 18 interposed between the second member 10b itself and the nozzle holder 7.

The ring 18, which constitutes a diffuser for the third fluid F2, has a plurality of holes 18a through which the third cooling fluid F2 can flow out towards the second hole 11. The holes 18a are made, as known, at defined angles relative to a plane perpendicular to the axis X of the torch (or perpendicular to the axis X itself), and/or at defined angles relative to predetermined radial directions on the plane of the ring 18 so as permit generation of a suitable fluid flow towards the second hole 11.

In this type of architecture, the above mentioned join area between the first and the second member 10a and 10b, is located upstream of the ring 18 relative to a third fluid F2 feed direction D.

To allow a part of the F2a of the third fluid F2 to flow to the outside, the first and the second members 10a and 10b have respective facing annular surfaces 19 and 20 located below the join area between the first and the second member 10a and 10b (that is to say, under the concavities 13).

The surfaces 19 and 20 are spaced from each other to form a channel 21 through which the part F2a of third cooling fluid F2 flows towards the outside surface of the second member 10b: this enables the second member 10b to be cooled also on the outside. These two surfaces 19 and 20 may be made in different geometrical configurations depending on the direction to be imparted to the outflowing fluid F2a.

In a first embodiment, the two surfaces 19 and 20 (cylindrical) are parallel to each other and their generator is parallel to the longitudinal axis X along which the torch 1 extends (see Figures 2 and 3).

In a second embodiment, at least the surface 20 of the second member 10b is inclined at an angle to the longitudinal axis X along which the torch 1 extends (see Figures 4 and 5) in such a way as to form a conic surface whose generator is inclined at an angle to the axis X and lies in the plane through the axis X. In a third embodiment, the two surfaces 19 and 20 are parallel to each other and extend at an angle to form respective conic surfaces whose generator is inclined at an angle to the longitudinal axis X along which the torch 1 extends

(again see Figures 4 and 5) and lies in the plane through the axis X.

In the second and third embodiments, the surface or surfaces 19 and/or 20 may be inclined in the direction of the plasma arc discharge holes 6 and 11 at an angle α to the longitudinal axis X: thanks to this architecture of the surfaces 19 and 20, the part F2a of the third fluid flow F2 can come into contact with the outside of the second member 10b thereby cooling it and reducing the probability of molten material adhering to its walls.

A plasma torch made in this way therefore achieves the above mentioned aims thanks to a simple set of a concavities which are formed on the surface that supports the second member of the protective covering unit and through which a part of the second cooling fluid can flow to the outside.

The possibility of making the holder members with differently shaped surfaces according to the type of flow to be obtained makes the torch extremely flexible and adaptable to the type of end use, thus optimizing conditions for cooling the outside of the second member and increasing the latter's working life.

Furthermore, it should also be considered that this constructional solution is extremely versatile: thus, while it is not necessary to cool the second part 10b of the covering unit (allowing savings on third fluid) it is possible to fit a traditional second part provided with a seal ring without necessarily having to substitute the first part 10a.

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 inventive concept. Moreover, all the details of the invention may be substituted by technically equivalent elements.