High-performance plasma torch

Technical Field

This invention relates to a plasma cutting torch.

Background Art As is known, plasma cutting torches comprise:

- a torch body which extends mainly in length and which houses a cylindrical electrode mounted centrally on the torch body; the electrode is connected by a lead to the negative pole of the power generator (cathode);

- a nozzle mounted on one end of the torch body and surrounding the tip of the electrode; the 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 and whose inside wall faces the outside wall of the nozzle in such a way as to form, together with said outside wall, a cooling chamber through which a cooling fluid passes; - a unit for covering the bottom of the nozzle and nozzle holder and 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 breaks through or pierces the metal being cut).

The covering unit forms, together 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 proximal 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 element, 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 element which can be coupled with the proximal end of the supporting element so as to totally cover the proximal area of the torch.

This second element 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 element 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 the directional accuracy of the plasma arc and to protect the arc itself from the atmosphere.

In torches whose wear components reach very high temperatures (for example torches operating at high power) it has been observed that the covering unit, in particular the second cup-shaped element, is subject to very rapid wear and to considerable damage not only on account of the high temperatures of the second, cup-shaped element but also because molten material from the part being worked, especially when the torch pierces it, tends to adhere to the surface of the second element itself. These two factors tend to reduce significantly the working life of the wear components of the torch, thus necessitating frequent replacements of the second element and machine shutdowns.

That leads to lulls in productivity and the need to keep a large stock of spares, reflecting negatively on production and logistic costs. To overcome these drawbacks, the prior art has proposed plasma torches comprising a nozzle fitted at the proximal end of the torch and surrounding the electrode in such a way as to form a channel for the passage of the plasma gas, a nozzle holder for supporting the nozzle and a shield for protecting the nozzle.

The shield is fixed to the nozzle with an interposed insulating ring and forms a single part with the nozzle.

The outside of the nozzle and shield assembly is surrounded by the above mentioned nozzle holder.

The nozzle holder is designed to support the above mentioned components in such a way that they can be separated from the torch body. The shield is supported by the nozzle holder by means of a flange that abuts a part of the nozzle holder shaped to match it.

This type of torch also comprises a cooling water passage formed by the inside wall of the nozzle holder and the outside surface of the nozzle.

The flanged portion of the shield faces this channel: in other words, the channel is delimited by the nozzle holder and nozzle and ends at the flange of the shield abutting the nozzle holder.

This type of torch is not free of disadvantages, however.

In particular, the operating components of the torch (shield, nozzle, nozzle holder), that is to say, the parts most subject to wear during torch operation, are effectively cooled only as long as the torch is used to cut materials of limited thickness, that is to say, up to limited torch operating power levels.

For operation at higher power levels (for example greater than 200 Amps) plasma cutting torches of this kind cannot guarantee effective cooling of the components, which thus wear out very quickly.

Disclosure of the Invention

This invention therefore has for an aim to provide a plasma cutting torch that can cut very thick material and at the same time can guarantee effective protection of its covering unit and a high level of cooling of the components, thereby increasing the working life of the components themselves and of the torch.

The technical features of the invention according to the aforementioned aim may be easily inferred from the content of the appended claims, especially claim 1, and preferably any of the claims that depend, either directly or indirectly, on claim 1.

Brief Description of the Drawings

The advantages of this invention are more 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 a non-limiting example, and in which:

- Figure 1 is a schematic cross section, with some parts cut away in order to better illustrate others, of a plasma cutting torch according to the invention;

- Figure 2 shows an enlarged detail from Figure 1 ;

- Figure 3 is a schematic cross section of the torch according to the invention; - Figure 4 is a cross section of the torch according to the invention through the line IV-IV of Figure 3.

Detailed Description of the Preferred Embodiments of the Invention With reference to the accompanying drawings, 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 comprises: an electrode 3; a nozzle 4; a nozzle support or holder 5, a first unit 6 for covering the nozzle 4 and the nozzle holder 5 and a second unit 7 for partly covering the first unit 6.

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). hi this description, the term "proximal end" denotes the end portion of each torch 1 component closest to the point O shown in Figures 1 and 2. The term "distal end" denotes the end portion of each torch 1 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. The nozzle 4 can be connected to the positive pole of the generator to define an anode. Further, the nozzle 4 surrounds the tip of the electrode 3 to form a chamber

8 where plasma is generated by feeding a first fluid or gas into it (see arrows Fl, Figure 2).

The nozzle 4 has a first central through hole 9 for the passage of the plasma.

The nozzle holder 5 is associated with the torch body 2, and its truncated cone shaped inside surface 5a faces the truncated cone shaped outside surface 4a of the nozzle 4 in such a way as to form a first chamber 10 through which a cooling fluid flows in order to cool the nozzle 4 and the nozzle holder 5.

In this specification, reference is made to water as the liquid used to cool the torch, but without thereby limiting the scope of the invention. The first chamber 10 is in fluid communication with a cooling water supply conduit 11 connected to water supply means of known type and therefore not illustrated.

The above mentioned first unit 6 for covering the nozzle 4 and nozzle holder 5 comprises: - a first supporting element 12 which is substantially cylindrical in shape. Close to its distal end, the first element 12 can be associated with the torch body 2 by screwing and is electrically isolated by a suitable isolating ring 13.

- a second, cup-shaped element 14 which at least partly matches the profile of the nozzle 4 and nozzle holder 5. The annular edge 15 of the second element 14 can be associated with the proximal end (tapered) of the first supporting element 12.

Further, the second element 14 is provided with a second central hole 16, coaxial with the first hole 9, to allow the passage of the plasma arc: thus, the second element 14 constitutes the part that actually covers and protects the front of the torch 1.

The covering unit 6 also forms a channel 17 through which a second cooling fluid F2 (indicated by the arrows F2, Figure 2) flows between the nozzle holder 5 and the covering unit 6 to reach the second hole 16: this secondary fluid

F2 (which may be air - or other fluid/gas) further cools the area close to the nozzle holder 5 and nozzle 4 and is discharged through the second hole 16.

As shown in Figures 1 and 2, inside the first unit 6 there is a second chamber 18 for the passage of the cooling liquid.

The second chamber 18 for the passage of the cooling liquid is in fluid communication with the first chamber 10 and is mounted in series with the first chamber 10 in such a way that the liquid flow rate through both chambers is the same.

Further, between the first chamber 10 and the second chamber 18, there is an interposed chamber 19 for accumulating cooling water.

As shown in Figure 4, the accumulation chamber 19 is divided into two semicircular portions, namely, a first portion 20 and a second portion 21.

More in detail, the two semicircular portions 20, 21 of the accumulation chamber 19 are separated by a pair of partitions 22 located in diametrically opposite positions inside the accumulation chamber 19.

The first portion 20 of the accumulation chamber 19 is in fluid communication, through a channel 23, with the first chamber 10 for the passage of water.

The first portion 20 of the accumulation chamber 19 is in fluid communication, through a channel 24, with the second chamber 18 for the passage of water. The second semicircular portion 21 of the accumulation chamber 19 is in fluid communication, through a respective channel 25, with the second chamber 18.

Further, the second portion 21 of the semicircular chamber 19 is in fluid communication, through a hole 26, with a cooling water outlet conduit 27 connected to the above mentioned supply means.

As shown in Figure 2, the first element 12 comprises a first member 28 and a second member 29.

Looking in more detail, the first member 28 and the second 29 are concentric and each has a first portion 28a, 29a that is cylindrical, and second portion 28b, 29b that is tapered in the direction of the proximal end of the torch.

The first member 28 and the second member 29 are associated with each other in such a way that the outside surface 30 of the first member 28 faces the inside surface 31 of the second member 29.

That way, the two surfaces 30, 31 define and delimit a first zone 32 of the above mentioned second chamber 18 for the passage of the cooling water.

Like the first element 12 the second element 14 also comprises a first member 33 and a second member 34.

Looking in more detail, the first member 33 and the second 34 are concentric and are tapered in the direction of the proximal end of the torch 1. The first member 33 and the second member 34 are associated with each other in such a way that the outside surface 35 of the first member 33 faces the inside surface 36 of the second member 34.

That way, the two surfaces 35, 36 define and delimit a second zone 37 of the above mentioned second chamber 18 for the passage of the cooling water. As shown in Figure 3, inside the first zone 32 of the second chamber 18, there are two partitions 38 at diametrically opposite positions and designed to divide the first zone 32 of the second chamber 18 into two semicircular portions and thus to allow the water flowing in the first zone 32 to pass only through one of the two semicircular portions. Advantageously, the partitions 38 are co-planar with the partitions 22, so as to allow the cooling liquid to flow in optimum manner from the first semicircular portion 20 of the chamber 19 to the second portion 21 through the second chamber 18.

This feature allows the cooling liquid to reach and cool the element 14 in ideal manner. The partitions 38 terminate at the end of the first zone 32 of the second chamber 18.

As shown in Figures 1 and 2, the above mentioned second unit 7 for partly covering the first unit 6 may be associated with the torch body 2 or with the first element 12, and forms, together with the outside surface of the first unit 6 facing the second unit 7, a second channel 39 for the passage of a third fluid F3 (for example air or other fluid/gas) leading in the direction of the second hole 16 and designed to permit cooling at least of the outside of the first unit 6 (as indicated by the arrows F3). More specifically, the second unit 7 has a cylindrical shape, tapering inwards at its proximal end in such a way as to substantially match a part of the first unit 6.

Still with reference to Figure 1, the second unit 7 is associated indirectly, in the embodiment illustrated by way of example, with the torch body 2 at its distal end.

More specifically, the distal end of the second unit 7 may be fastened by screwing to (or permanently associated with) an outside portion of the distal end of the first element 12, and both may then be fastened to the torch body 2 through a supporting member 100, illustrated in Figure 1, screwed to the torch body. The second unit 7 has openings 40 made in it at the second element 14 of the first unit 6 in such a way as to allow the third fluid F3 to flow out in the direction of the second element 14 itself, allowing the outside of the latter to be cooled.

In use, the cooling water supply means are activated at the same time as the torch starts piercing and cutting a material.

The water flows along the conduit 11 until it reaches the first chamber 10.

Inside the first chamber 10, the cooling water comes into contact with the entire truncated-cone shaped inside surface 5a of the nozzle holder 5 and with the entire truncated-cone shaped outside surface 4a of the nozzle. From the first chamber 10, the cooling water flows along the channel 23 and enters the first semicircular portion 20 of the accumulation chamber 19.

From the first semicircular portion 20 the water proceeds through the channel 24 until it reaches the first zone 32 of the second chamber 18.

As shown in Figure 3, the first zone 32 of the second chamber 18 contains the above mentioned partitions 38: that way, the water in the first zone 32 of the second chamber 18 flows only in half of the second chamber 18.

At the end of the first zone 32, where the partitions 38 terminate, the water fills the second zone 37 of the second chamber 18, coming into full contact with the entire outside surface 35 of the first member 33 and with the entire inside surface 36 of the second member 34, allowing a high level of heat exchange.

The water flows out of the second chamber 18 through the channel 25 and enters the second semicircular portion 21 of the accumulation chamber 19.

From the second portion 21 the water flows along the conduit 27 through the hole 26 and is recycled by the above mentioned water supply means of known type and therefore not illustrated.

The flow of the water along the path described is repeated for the entire duration of the piercing and cutting operations performed by the torch.

The invention as described above brings important advantages.

In particular, the provision of two separate chambers allows efficient and complete cooling of the torch.

More in detail, the first chamber allows the water to come into contact and hence exchange heat with the entire outside surface of the nozzle and with the entire inside surface of the nozzle holder.

The second chamber, on the other hand, is dedicated exclusively to cooling the second unit.

More specifically, thanks to the shape of the second unit, the water comes into contact with the entire inside surface of the second member of the second element and with the entire outside surface of the first member of the second element. Thanks to the large heat exchange surface, the operating components of the torch receive a high degree of cooling and it is therefore possible to allow the torch to operate even at very high power levels in order to pierce materials of considerable thicknesses without reducing the efficiency and working of the torch components.