EP0193456A1 - Welding or cutting plasma torch with nozzle unit - Google Patents

Abstract

The plasma welding or cutting torch comprises a hollow torch body (1) whose interior is connected to a source of plasma-producing gas, an electrode (2) disposed inside the body (1) and electrically connected to an electrical supply conductor, and a nozzle (3) provided with a plasma outlet orifice (34). This torch is characterized in that it comprises a cartridge (60) which cannot be disassembled and comprises an annular skirt (4) assembled by screwing with the torch body (1) and having a seat (18b) for the nozzle (3) which is freely slidably mounted in the skirt (4) and applied against the seat (18b) solely by the pressure of the plasma-producing gas.

Description

The present invention relates to a plasma welding or cutting torch, comprising a torch body the interior of which is connected to a source of plasma gas, an electrode housed inside this body and electrically connected to a conductor. power supply, and a plasma outlet nozzle mounted opposite and at a distance from the electrode, and pierced with an orifice for the plasma outlet.

It is known from US Patent 3,242,305, a plasma torch in which the electrode and the nozzle are cooled by a stream of liquid such as water. In this torch, the electrode is movable relative to the nozzle and to the electrical contact thereof when the torch is at rest. When the torch is energized, this causes the coolant to be pressurized, which, by means of a hydraulic mechanism, causes the compression of the spring and the separation of the electrode and the nozzle, thus creating an electric arc which generates the arcing of the electric arc in the plasma gas. Such a hydraulic system is particularly difficult to achieve and therefore expensive.

It is known from French patent 2,385,483 to initiate priming between the electrode and the nozzle by short-circuiting the latter, said electrode being screwed and brought into contact with the nozzle then unscrewed, the difference between the electrode and the nozzle then being adjusted to the desired value. Such a screwing and unscrewing system is particularly impractical to implement and requires adjustment of the jet of the torch each time it is started up.

More recently, it has been proposed in French application 83.19.554 of December 7, 1983, entitled "Arc ignition process for welding or cutting torch and torch adapted to implement this process", filed in the name of the applicant, a method of igniting a plasma torch by short circuit between the electrode and the nozzle. According to this method, the nozzle is mounted to slide freely in the torch body so as to come into contact with the electrode when the torch is applied against a workpiece to be welded or cut. By releasing the torch, an arc ignites between the electrode and the nozzle, allowing to initiate the plasma gas and maintain an electric arc which is transferred to the part to be cut.

French application 84.05.286 filed on April 4, 1984, in the name of the applicant and entitled "Welding torch or plasma cutting", describes a plasma welding or cutting torch peddling a structure particularly well suited to the implementation of the method described in the above application referenced in the name of the applicant. This torch essentially comprises a torch body, the interior of which is connected to a source of plasma gas, an electrode housed inside this body and electrically connected to an electrical supply conductor, and a mounted plasma outlet nozzle. opposite and at a distance from the electrode, and pierced with an orifice for the exit of the plasma. It further comprises a removable annular skirt, secured to the torch body, and having at least one seat for the nozzle which is mounted to slide freely in the skirt and applied to its seat only under the effect of an elastic force. According to a preferred embodiment, the elastic force which applies the nozzle to its seat is the pressure of the plasma gas.

The plasma cutting or welding torch described in the two patent applications referenced above is entirely satisfactory. However, it was found that the torch described in French application 84.05.286 could still be improved in certain applications.

It has in fact been found that this torch with its removable electrode, nozzle and skirt structure, could sometimes cause mounting errors. Thus, it was found that it was possible to mount the skirt and the electrode while forgetting to simultaneously mount the nozzle.

Furthermore, the nozzle having to be introduced through the internal orifice of the skirt whose external diameter is that of the internal diameter of the torch body, this led to a nozzle of small dimensions, and consequently, to a reduced electrode diameter , since it must partially penetrate inside the nozzle. Under these conditions, it has been found that for certain applications, it was difficult to ensure effective cooling of the parts such as the electrode and the nozzle, having such limited dimensions.

The torch according to the invention solves the problem thus posed. The object of the invention is the production of a non-removable cartridge consisting of at least the skirt and the nozzle, adaptable to the body of the torch.

According to the invention, the torch comprises an annular skirt secured to the torch body (1) and comprising on the one hand, at least one seat (18b) and on the other hand a rear stop (118b) for the nozzle (3) which is mounted to slide freely in the skirt (4), between the seat (18b) and the rear stop (118b), and applied to its seat (18b) only under the effect of an elastic force.

Preferably, the skirt (4) of electrically insulating material, is integral in its part facing the torch body (1), with a first conductive sleeve (17) screwed into a conductive element (15) of the torch body ( 1), the lower part of which faces the nozzle (3) constitutes the rear stop (118b) thereof.

According to a preferred embodiment, the torch is characterized in that the first conductive sleeve (17) has on its inner face a shoulder (17c) constituting the seat for positioning the electrode (2).

According to another embodiment, the skirt (4) in its part facing the nozzle (3) will be secured to a second metal sleeve (18) disposed inside said skirt (4) and in which is mounted sliding the nozzle (3), the upper part of said second sleeve (18) constituting the seat (18b) of the nozzle (3).

According to a first alternative embodiment, the electrode (2) will be removable. This makes it possible to monitor the development of the wear of the electrode (2) and thus to independently replace the electrode (2) and the cartridge containing the nozzle (3).

According to a second alternative embodiment, the electrode (2) will be made integral with the skirt (4), the skirt assembly (4) nozzle (3) and electrode (2) thus forming a non-removable cartridge.

In both cases, the cartridge according to the invention makes it possible on the one hand to avoid assembly errors (it is no longer possible to forget the nozzle which is always integral with the skirt) and on the other hand for a identical diameter of the torch body, the electrode and the nozzle have substantially larger dimensions than in the case described in French application 84.05.286, where the electrode and nozzle are removable.

• - la figure 1 est une vue en coupe axiale des différents éléments constitutifs de la torche selon l'invention, le corps et la cartouche étant démontés ;
• - la figure 2 est une variante préférentielle de réalisation de la cartouche illustrée sur la figure 1.

The invention will be better understood with the aid of the following embodiments, given without limitation, together with the figures which represent:

• - Figure 1 is an axial sectional view of the various components of the torch according to the invention, the body and the cartridge being disassembled;
• - Figure 2 is a preferred embodiment of the cartridge illustrated in Figure 1.

In Figure 1 is shown a sectional view of a torch according to the invention. It essentially consists of a torch body 1 and a cartridge 60. The torch body 1 comprises a central bell-shaped part 5 and a tubular lateral extension 6 terminated by a connector 7, the central part 5 in the form bell and the tubular lateral extension 6 being of electrically insulating material. On the connector 7, with external teeth, is fitted by force a flexible and electrically insulating pipe 8 for the arrival of a plasma gas, this pipe 8 being held on the connector 7 by a coaxial sleeve. external 9. The tubular lateral extension 6 of the torch body 1 is traversed by a conduit in which is housed a tube 11 of electrically conductive material. This tube opens at its outer end into the insulating sheath 8 and it is extended longitudinally at this point inside the sheath 8, by a part of its periphery constituting a tab 12 folded transversely on itself and ensuring the maintenance by crimping the end of an electrical supply conductor 13 housed in the pipe 8.

The bell-shaped part 5 of the torch body 1 has a central cavity 14 closed at its upper part and opening downwards. In this cavity 14 is housed a metal cap 15 with a cylindrical side wall 15a in which is drilled a hole which is engaged the internal end of a conductive tube 11 passing through the lateral extension 6. This conductive tube 11 is advantageously fixed to the metal cap 15 by welding. Furthermore, the cylindrical side wall 15a of the metal sleeve 15 has a thread 15b on its lower end portion extending below the hole where the end of the conductive tube 11 is fixed. This side wall 15a provided with the thread 15b s' stops at a certain distance from the lower end 5a of the bell-shaped part 5.

The removable cartridge 60 essentially consists of three elements, the electrode 2, the nozzle 3 and the skirt 4. The latter comprises a casing 16 of insulating material of annular shape, for example frustoconical, with taper directed downwards. The casing 16 is overmolded on a lower metal sleeve 18 nozzle holder and on an upper metal sleeve 17 electrode holder, this sleeve 17 forming a single part with the electrode 2. This cylindrical sleeve 18 plays the role of the seat on which the nozzle 3 comes to bear at 18b. For this, this nozzle, of substantially cylindrical shape with an outside diameter equal to the inside diameter of the sleeve 18, apart from play, has an annular flange 51 in its upper part which comes to bear on the seat 18b. The nozzle 3 ends in a cap 31 of substantially spherical shape, but thicker in its center than in its peripheral part. The nozzle 3 is delimited by an internal lateral surface 33, also cylindrical, joining the substantially spherical internal surface of the cap 31. The latter is pierced right through with an axial hole 34 for the passage of the plasma gas.

The electrode 2 secured to the upper sleeve 17, has on its upper end part, a thread 21 intended to be screwed into the internal thread 15b of the cap 15 of the torch body 1. The upper sleeve 17 of diameter e is extended by the body proper electrode 61, of substantially cylindrical shape, but of diameter much less than e. The metal electrode 2 has a blind axial bore 22 open upwards, that is to say towards the inside of the torch body 1. Significantly at mid-height, is arranged at least one opening 26, allowing passage plasma gas from inside the electrode through the blind bore 22 towards the nozzle 3. Preferably, the aperture (s) 26 are oriented tangentially with respect to the electrode 2, so as to create a vortex of plasma gas in the space 19 and up to the channel 34. In the central part of the relatively thick lower front wall 27 of the electrode 2, is housed axially an insert 28, for example made of zirconium, favoring the initiation of the arc . The electrode 2 also includes a cylindrical insert 64 mounted coaxially in the blind bore 22 leaving a passage 66 between its lower end and the bottom of the blind bore 22, on the one hand, as well as between its outer wall 65 and the wall of the blind bore 22, so as to allow the circulation of the plasma gas.

It will be noted that the diameter e of the sleeve 17 and of the internal bore of the casing 16 at the level of the sleeve 17 is greater than or equal to the clearance, to the outside diameter c of the annular flange 51 of the nozzle 3.

When mounting the cartridge 60, the sleeve 18 is first introduced into the casing 16. Next, the electrode is brought back 2 in the envelope 16, by joining the upper sleeve 17 of the electrode 2 with the upper part of the envelope 16.

When the plasma torch is assembled, the upper sleeve 17 of the removable skirt 4 is screwed by its thread 21 into the thread 15b of the cap 15 of the torch body 1. The distance between the two seats 118b and 18b is at least equal to the distance necessary for the nozzle 3 to slide in the lower sleeve 18 to come into contact with the electrode 2 and cause the initiation of an arc between the electrode 2 and the nozzle 3. The plasma gas sent into the insulating pipe 8, penetrates inside the torch and flows into the tube 11 extending through the lateral extension 6 of the torch body 1. It then passes inside the cap 15 then it flows longitudinally towards the bottom in the bore 22 of the electrode 2 in the insert 64. By the way, it cools the lower front wall 27 of the electrode 2. Then it rises between the outer wall of the insert 64 and the inner wall of the bore 22 of the electrdoe 2 and it tangentially emerges from it through the openings 26 to pass on the one hand into the space delimited by the end of the electrode 2 and the nozzle 3 then through the axial hole 34 and on the other hand into the lateral pipes 52 and 53 (FIG. 2 ) between the lower sleeve 18 and the envelope 16 of the skirt 4. The two gas streams thus created have a substantially different flow rate. The first between the electrode and the nozzle represents from 10 to 20% of the supply flow and leaves this nozzle axially through the hole 34, to form the plasma. The second current corresponds to the excess of gas (from 80 to 90% of the flow ... of supply) and flows in the various channels such as 52 and 53 (figure 2) to exit the torch in the form of 'a plurality of jets surrounding the central jet forming the plasma. In some applications, the relative proportions of the first and second streams may be significantly different. Preferably, these proportions will vary from 1/1 to 1/10.

The electric current is brought to the electrode 2 by the electrical connection provided between the upper conductive sleeve 17 and the metal cap 15 to which the tube 11 is welded.

In operation, when the pressurized gas is supplied to the torch according to the invention, the nozzle 3 is pressed against its seat 18b only under the effect of the pressure of the gas.

2 shows a preferred embodiment of the cartridge of Figure 1, in which the same elements as those of Figure 1 have the same references. In this figure 2, the electrode 2 is removable: the nozzle 3, the casing 16 of the skirt 4, as well as the sleeve 18 are integral with each other. To make this cartridge non-removable and thus avoid losing the nozzle 3, the casing 16 has an upper internal bore of diameter e, greater than or equal to the diameter c of the nozzle 3. After introduction of the latter, one comes to l inside the envelope 16 the upper sleeve 17, comprising an internal bore 24 of diameter b less than diameter c. In this way, and in the absence of the electrode 2, the displacement of the nozzle 3 is limited by the shoulder 118b located on the lower part of the sleeve 17. The distance between the lower 18 and upper 17 sleeves is such that , during the inversion of the cartridge, the shoulder 51 abuts against the shoulder 118b. This prevents the nozzle 3 from completely coming out of its sliding and guide sleeve 18.

The upper sleeve 17 has on its upper part a bore delimiting a circular bearing 17c serving as a stop for the cylindrical shoulder 23 of the electrode 2. When the latter is in position, its lower part has substantially the same position as the part corresponding to the cartridge electrode of figure 1.

In this second variant, the electrode is removable, which makes it possible to check the condition of the electrode and possibly to change it without changing the nozzle, or vice versa.

Of course, the lateral pipes 52, 53 can take different shapes and orientations. In particular, they can be oriented radially.

Claims (6)

1. - Welding and plasma cutting torch comprising a torch body (1) the interior of which is connected to a source of plasma gas, an electrode (2) housed inside this body (1) and connected electrically to a power supply conductor, and a plasma outlet nozzle (3) mounted opposite and at a distance from the electrode (2) and pierced with an orifice (34) for the plasma outlet, characterized in that that it comprises an annular skirt (4) secured to the torch body (1) and comprising on the one hand at least one seat (18b) and on the other hand a rear stop (118b) for the nozzle (3) which is mounted to slide freely, in the skirt (4), between the seat (18b) and the rear stop (118b), and applied to its seat (18b) only under the effect of an elastic force. 2. - plasma welding or cutting torch according to claim 1, characterized in that the skirt (4) of electrically insulating material, is integral in its part facing the torch body (1) with a first conductive sleeve (17) screwed into a conductive element (15) of the torch body (1) and the lower part of which, facing the nozzle, constitutes the rear stop (118b) thereof. 3. - welding torch or plasma cutting according to one of claims 1 or 2, characterized in that the skirt (4), in its part facing the nozzle, is integral with a second metal sleeve (18) disposed inside said skirt (4), and in which the nozzle (3) is slidably mounted, the upper part of said second sleeve (18) constituting said seat (18b) of the nozzle (3). 4. - welding torch or plasma cutting according to one of claims 2 or 3, characterized in that the first conductive sleeve (17) has on its internal face a shoulder (17c) constituting the seat of the electrode (2 ). 5. - welding torch or plasma cutting according to one of claims 1 to 4, characterized in that the skirt (4) and the nozzle (3) are assembled in the form of a non-removable cartridge. 6. - welding torch or plasma cutting according to claim 5, characterized in that the skirt (4), the nozzle (3) and the electrode (2) are assembled in the form of a non-removable cartridge.

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