WO2001066298A1 - Double stream torch for arc welding - Google Patents

Abstract

The invention concerns an electric arc welding torch comprising a central gas dispensing nozzle (1) for delivering a first gas stream, and a peripheral part forming an outer sleeve (2) arranged around at least part of said central dispensing nozzle (1) and enabling to dispense a second gas stream peripheral to said first gas stream. The invention is characterised in that the central dispensing nozzle (1) and said peripheral part (2) are spaced apart by a distance (d) ranging between 3 mm and 6 mm. The inventive torch is particularly adapted for use in a TIG, MIG or MAG welding process.

Description

 DOUBLE-FLOW TORCH FOR ARC WELDING

The present invention relates to an electric arc welding torch, in particular of the TIG (Tungsten Inert Gas), MIG (Metal Inert Gas) or MAG (Metal Active Gas) type, with gas protection double-flux intended to protect the area. welding during the welding operation.

Arc welding processes under protective gas flow are widely used in industry.

Schematically, using a gaseous protection, during a welding operation, makes it possible to avoid contamination of the weld bead thus produced from any contamination by impurities likely to be present in the ambient atmospheric air.

Indeed, it is known that, in particular the nitrogen and oxygen contained in the ambient air are harmful to the quality of the weld beads, which undergo a deterioration of their appearance due to oxidation and nitriding phenomena, and their integrity, that is to say their mechanical strength and performance characteristics.

The installation of a gaseous protection during the arc welding operation is therefore intended to avoid or minimize any contamination of the weld bead by said atmospheric impurities. However, it is known that the gaseous protection is not neutral with respect to the welding results thus obtained and in particular influences the welding speed, the penetration, the shape of the weld bead, the quantity smoke released during welding and the greater or lesser number of splashes of molten metal.

In other words, the physicochemical properties of the gases or gas mixtures used as a shielding gas generate differences in the behavior of the electric arc, of the molten metal bath and, in the case of a MIG type welding, the fusion of the fusible wire, leading to very variable welding results depending on the type of gas used; In general, in the protective gas flow, also called protective gas atmosphere, there are two main areas, namely the arc area and the actual protection area.

More precisely, the first arc zone or zone comprises the electric arc itself, the part of the welding bath situated substantially below the electric arc and the end of the welding electrode or fuse wire located near the welding bath. In addition, the second zone or protection zone encompasses the rest of the gas flow, that is to say, a zone substantially peripheral to the arc zone, in which the action of the gas protection is substantially limited protection of the weld bead. Depending on the case, the gas or the gas mixture is identical or different in these two zones, for example, it is known to use carbon dioxide (C0 ₂ ) gas distributed indifferently in the arc zone and in the zone of protection proper. When it is desired to distribute two gases of different natures or compositions in the central arc zone and in the peripheral protection zone, it is usual to use a welding torch called "double flux".

A double-flux welding torch usually consists of a torch body provided with two concentric nozzles, namely a central gas distribution nozzle for delivering a first gas flow in the arc zone, and a peripheral part forming a sleeve external arranged around at least part of the central distribution nozzle and making it possible to distribute a second gas flow peripherally to said first gas flow, that is to say in the protection zone.

Such torches are described in particular in the following documents: GB-A-2059846 and US-A-2, 919, 341.

However, in practice, it has been observed that with this type of torch there arises the problem of controlling the gas mixture at the level of the arc zone, because indeed, if no precaution is taken, it is very difficult to have in the arc zone a mixture of which the gas content circulating in the external nozzle is low and in particular in the presence of a flow rate of gas circulating in the internal nozzle.

In fact, the only way to dose the mixture is to act on the flow rates circulating in each of the nozzles:

- If the flow rate of the external gas is too high, a gas mixture is obtained in the arc zone with a high proportion of external gas;

- if we try to reduce it, then very quickly the external gas flow is too low and the weld is then poorly protected. The object of the present invention is therefore to solve the aforementioned problem by proposing an improved double-flux welding torch compared to existing torches, that is to say which allows to have a gaseous mixture in the arc zone with low external gas content while having a low internal gas flow.

The inventors of the present invention have now shown that the above-mentioned problem can be solved or minimized by means of a double-flux welding torch.

The invention therefore relates to an electric arc welding torch comprising:

a central gas distribution nozzle for delivering a first gas flow, and

- A peripheral piece forming an external sleeve arranged around at least a portion of said central distribution nozzle and making it possible to distribute a second gas flow peripherally to said first gas flow, characterized in that the thickness (e) of the central nozzle is between 3 and 6 mm.

Indeed, as detailed below, the inventors of the present invention have demonstrated that the thickness (e) has a non-negligible influence on the effectiveness of the control of the gas mixture in the arc zone.

Depending on the case, the torch of the invention may include one or more of the following characteristics: - the downstream end of the peripheral part is set back (£) by at least 1 mm relative to the downstream end of the central distribution nozzle. the distance (d) is at least 1 mm and preferably between 2 and 10 mm. - the distance (d) is between 2 mm and 9 mm, preferably between 3 mm and 5 mm.

- the downstream end of the peripheral part is set back (£) from 2 to 15 mm from the downstream end of the central distribution nozzle, preferably from 5 mm to 10 mm.

- The peripheral part forming the sleeve has a substantially cylindrical or cylindrical-frustoconical shape. - The central gas distribution nozzle and the peripheral part forming an external sleeve arranged around said central distribution nozzle are concentric.

- It further comprises at least one electrode and / or at least one fusible wire, means for supplying electric current connected to said electrode or to said fusible wire, and means for holding said electrode or of said fusible wire.

- it is chosen from TIG, MIG or MAG torches.

The invention will now be described in more detail using the appended figures, given by way of illustration but not limitation.

Figures 1, 2a, 2b, 3 and 5 show partial diagrams of welding torches according to the invention, that is to say showing the active end of the torch comprising the two concentric gas distribution nozzles.

As shown in FIG. 1, the torch of the double-flux type is provided with a central contact tube 3 intended to carry an electrode 10 or a fusible wire.

A central distribution nozzle 1 is arranged peripherally to the contact tube 3 and is connected to means for supplying a first gas (Gl) making it possible to distribute this first gas (Gl) in the arc zone ZA.

Another nozzle or peripheral part 2 forms an external sleeve around a part of the nozzle of distribution 1; the peripheral part 2 and the central distribution nozzle 1 being concentric.

The peripheral part 2 is also connected to means for supplying a second gas G2 intended to be distributed in at least part of the protection zone ZP.

In FIG. 5, it can be seen that the arc zone ZA which contains the electric arc AE is situated substantially between the electrode 10 and the weld S carried by the material M to be welded, while the protection zone ZP is located substantially around said arc zone ZA.

According to the invention, the thickness (e) of the central nozzle is between 2 and 10 mm, preferably between 3 and 6 mm. In addition, the distance (d) separating the surface of the internal wall of the peripheral part 2 from the surface of the external wall of the central nozzle 1 is at least 1 mm, preferably 2 to 10 mm.

Finally, it is preferable that the end 2 ′ of the peripheral part 2 is set back (£) by at least 2 mm, and preferably by 5 mm to 10 mm, relative to the end l ′ of the dispensing nozzle 1.

Indeed, the inventors of the present invention have demonstrated that the thickness (e) of the central nozzle controlled, to a very large extent, the amount of external gas in the arc zone. The greater this distance, the lower the concentration of external gas in the arc zone, in particular for rather low internal gas flow rates. Likewise, the inventors of the present invention have demonstrated that the distance (d) and / or the shrinkage of length {£} have a significant influence on the quality of the gas protection of the weld bead and even if the thickness (e) of the internal nozzle is correctly dimensioned.

Indeed, if the distance (d) is too small, which is naturally sought for reasons of flow minimization, the outside air arrives at the level of the welding bath, and thus induces protection faults such as by example of porosities. Likewise, when this distance (d) is suitably chosen, it may happen that welding splashes reduce the apparent length thereby causing the same defect in gas protection. Also, it is preferable to introduce a shrinkage of length (£) so that the welding projections, which generally come from the arc zone, cannot adhere to the interior surface of the external nozzle, and do not therefore do not cause premature blockage of the external gas pipe.

In order to assess the influence of the thickness (e) on the contents of the mixture in the arc zone, said thickness (e) is varied, all other things being equal, and then the concentration of gas G2 in the arc area, 10mm below the nozzle.

In all the tests, the gases Gl and G2 are different and are chosen from argon, helium, carbon dioxide, oxygen, hydrogen and their mixtures.

To do this, a welding nozzle similar to that of FIG. 1 is used, for which el = approximately 1.25 mm and e2 = d = approximately 3.5 mm (el and e2 being kept constant).

In addition, the gas flow rate Gl is 2.5 l.min ^{_ ±} and the gas flow rate G2 is 15 l.min ^' A The results obtained are shown in the figure

4 where we see that, the more the thickness (e) (represented on the x-axis by the distance between the 2 fluxes) increases, the more the proportion of G2 in the G1 / G2 mixture produced in situ in the zone arc decreases.

As a result, it is desirable to obtain an adequate G1 / G2 mixture, that the thickness (e) is at least

1 mm, or even at least 2 mm and, in any case, less than 10 mm. Preferably, the thickness (e) is between approximately 3 and 6 mm approximately.

The torch of the invention is particularly suitable for use in a TIG, MIG or MAG welding operation.

Claims

claims 1. Arc welding torch comprising - a central gas distribution nozzle (1) for delivering a first gas flow, and - a peripheral piece forming an external sleeve (2) arranged around at least a part of said central distribution nozzle (1) and making it possible to distribute a second gas flow peripherally to said first gas flow, characterized in that the thickness (e ) of the central nozzle is between 3 and 6 mm. 2. Torch according to claim 1, characterized in that the downstream end (2 ') of the peripheral part (2) is set back (£) by at least 1 mm relative to the downstream end (I ¹ ) of the central distribution nozzle (1). 3. Torch according to one of claims 1 or 2, characterized in that the distance (d) is at least 1mm and preferably between 2 and 10 mm. 4. Torch according to one of claims 1 to 3, characterized in that the distance (d) is between 2 mm and 9 mm, preferably between 3 mm and 5 mm. 5. Torch according to one of claims 1 to 4, characterized in that the downstream end (2 ') of the peripheral part (2) is set back {£) from 2 to 15 mm relative to the downstream end (I ¹ ) of the central distribution nozzle (1), preferably from 5 mm to 10 mm. 6. Torch according to one of claims 1 to 5, characterized in that the peripheral part forming the sleeve (2) has a substantially cylindrical or cylindro-frustoconical shape. 7. Torch according to one of claims 1 to 6, characterized in that the central gas distribution nozzle (1) and the peripheral piece forming a sleeve (2) external arranged around said central distribution nozzle (1) are concentric . 8. Torch according to one of claims 1 to 7, characterized in that it further comprises at least one electrode (10) and / or at least one fusible wire, means for supplying electric current connected to said electrode (10) or said fusible wire, and holding means (3) of said electrode (10) or said fusible wire. 9. Torch according to one of claims 1 to 8, characterized in that it is chosen from TIG, MIG or MAG torches. 10. Use of a torch according to one of claims 1 to 9 in a TIG, MIG or MAG welding operation.