FR2565141A1 - Device for the guiding and the electrical supplying of a metal filler wire for arc welding, and its method of manufacture - Google Patents

Abstract

Device for the guiding and the electrical supplying of a metal filler wire for arc welding, or contact tube, comprising an elongate metal body 1 having a longitudinal channel 2 for a metal filler wire to run through and at least one refractory end-piece 15, 17 brazed to the front end of the metal body and having a channel 16, 18 lying in the extension of that of the body. According to the invention, the latter includes a tubular outer jacket 9 and an inner sheath 10 defining the said channel which are force-fitted one into the other and are made from a wear-resistant metal whose mechanical properties are hardly affected by the temperatures reached during the use of the contact tube, the end-piece being brazed limitingly (restrictively) to the jacket.

Description

Device for guiding and powering a filler metal wire for arc welding, and its manufacturing method.

The invention relates to a device for guiding and electrically supplying a filler metal wire for arc welding, commonly referred to as a "contact tube".

Such a contact tube usually comprises an elongated metal body, preferably made of copper or copper alloy, having a longitudinal channel for guiding the filler metal wire. Electric current is transmitted to the wire by contact with the wall of the channel.

Copper and some of its alloys have a poor wear resistance and undergo, when used to make the body of the contact tube, wear due to the friction of the filler metal wire, causing a widening of the channel and this at the expense of efficient guiding and good power supply to the wire.

When using a support device exerting a transverse thrust on the wire in the channel to improve the electrical contact between the wire and the wall of the channel opposite the pressure point of the support device, this improvement is accompanied by 'even increased wear at the point of contact and the resulting deformation of the channel may lead in the long run to blockage of the wire by seizing.

It has been proposed, in order to reduce wear on the body of the tube, to produce the latter in a harder copper alloy than the copper itself, for example copper with beryllium, chromium, tellurium or zirconium. But these alloys are very expensive. In addition, it is often desirable to fix, on the front face of the contact tip, a ceramic, carbide or graphite tip for example, intended to avoid the adhesion of weld splashes and the incidents which result therefrom. This fixing takes place by brazing, which involves exposing the metallic body to a high temperature at which its constituent material undergoes annealing which considerably reduces its resistance to wear, even in the case of an alloy of high performance copper, as well as its electrical conductivity.

The object of the invention is to eliminate the drawbacks set out above, and to provide a contact tube ensuring for a long period of use regular guidance of the filler metal wire and good electrical contact between it and the metallic body.

The subject of the invention is a contact tube of the kind defined above, comprising at least one refractory tip brazed at the front end of the metal body and having a channel in the extension of that of the body. According to the invention, the metal body comprises a tubular outer casing and an inner jacket, which is made of a metal which is not very sensitive to wear and whose mechanical properties are little affected by the temperatures reached when the contact tube is used, the jacket being traversed by the longitudinal channel and force fitted into the tubular casing, the end piece being brazed to the outer casing and not to the inner casing.

In the contact tube according to the invention, the functions of supporting the end piece and guiding the wire, which were previously united by a one-piece metallic body, are dissociated. The end cap is fixed to the outer casing, for which high wear resistance is not necessary and which can be of ordinary copper or alumina nium for example, and the guide itself and the electrical contact with the Filler metal wire are secured by the inner jacket, which does not have to undergo the soldering temperature.

The jacket metal is preferably a copper alloy such as silver, beryllium, cadmium, chromium, cobalt, cobalt-berylium, tellurium or zirconium copper. The high price of these alloys has a limited impact on the cost price of the contact tube, the alloy weight required to produce the inner jacket being reduced due to the reduced diameter of the latter.

The temperatures reached by the inner jacket when using the contact tube are significantly lower than the temperature to which a one-piece metal body is subjected during the brazing of a refractory end piece, and the transformations which possibly result therefrom are very slow and do not do not compromise the life of the contact tip.

In addition to or in place of the end piece intended to avoid the adhesion of weld splashes, which constitutes the front face of the contact tube, the latter may also include an end piece made of a refractory material, which conducts electricity and d '' excellent wear resistance, attached to the front end of the body and further improving the guiding of the filler metal wire. Such a wear-resistant tip is preferably made of a carbide such as tungsten carbide.

The contact tube according to the invention can also be equipped with a thrust device, at least partially housed in the body and exerting a transverse thrust on the wire to apply the latter against the wall of the longitudinal channel.

The subject of the invention is also a method of manufacturing a contact tube in which at least one end piece is brazed at one end of a metallic tubular casing, then a jacket made of a little metal is forced into the tubular casing sensitive to wear and the mechanical properties of which are little affected by the temperatures reached when the contact tube is used, by inserting it from the opposite end of the tubular casing.

The invention will be better understood from the detailed description given below and from the accompanying drawings, in which FIG. 1 is a longitudinal section of a first contact tube according to the invention; Figure 2 is a longitudinal section showing a step in the manufacture of the contact tube of Figure 1; Figure 3 is a longitudinal section of a second contact tube according to the invention.

The contact tube shown in FIG. 1, intended for an electric arc welding machine, comprises an elongated metal body 1, having a general shape of revolution around an axis, pierced with a longitudinal axial channel 2 for the passage of a filler metal wire. The body 1 has a middle portion 4 of larger outside diameter, limited by a rear shoulder 5 and a front shoulder 6. Here, the front side of the contact tip is directed in operation towards the weld, that is to say, by which the wire leaves the tube, and behind the side where the wire enters the contact tube. The rear shoulder 5 connects the middle part 4 to a rear part 7 provided with an external thread for fixing the contact tube in a welding torch head.

Part 3 of the body located in front of the front shoulder 6 is covered to its front end by a sheath 8 made of anodized aluminum externally and internally, the surface layer of alumina ensuring the electrical isolation of the front part 3 vis-à-vis the outside and avoids the adhesion of welding spatter. The sheath 8 can be immobilized on the body 1 by a latching device not shown
The body 1 is composed of a tubular outer casing 9 and an inner jacket 10, force fitted into the casing 9 and in which the longitudinal channel 2 is formed. The casing 9 may be made of copper or of a alloy of relatively inexpensive copper, or aluminum, or aluminum alloy, this listing not being limiting.

High qualities of wear resistance are not required of this part. On the other hand, the jacket 10 is made of a metal which is not very sensitive to wear and whose mechanical properties are little affected by the temperatures, of the order of 4000C, which can be reached when the contact tube is used, allowing the body 1 ensure good wire guidance for a long time.

 In a recess 14 of the body 1, in the shape of a cone, with transverse axis, is housed a pushing device 11 composed of a conical spring 12 and a ball 13. The conical shapes of the recess 14 and the spring 12 are narrowing from the outside of the body towards its axis. When a filler metal wire is present in the channel 2, the spring 12 is under stress between the inner surface of the sheath 8 and the ball 13 , and push it against the wire.

The contact tube also comprises an end piece 15, for example made of nickel-plated tungsten carbide, housed in an axial recess at the front of the body 1. The end piece 15 is in good electrical contact with the casing 9, thanks to its fixing thereon. this by soldering, for example of the so-called silver type. I1 is pierced with a guide channel 16 of smaller diameter than the longitudinal channel 2, and which extends the latter in the direction of advance of the wire. The entrance to the channel 16 is widened by a chamfer 24. This entrance is located a short distance in front of the device 11.

The end piece 15 is hard enough to be able to guide the filler metal wire for a very long time without any appreciable wear being manifested in their contact zone. The support device 11 ensures good electrical contact between the wire on the one hand, the end piece 15 and the jacket 10 on the other hand, which, combined with the good electrical contact between these parts and the casing 9 and with good electrical conductivity of their constituent materials makes it possible to bring the welding current from the envelope 9 to the wire without excessive ohmic resistance of contact. The length of the nozzle 15 is approximately 5 mm.

The material constituting the end piece 15 being refractory, it can be brought to the high temperatures necessary for brazing and to those developed by the welding operations without loss of its mechanical characteristics.

The contact tip also includes a graphite shield 17 located at its front end, and having an outlet channel 18 extending the guide channel 16 of the end piece 15. The diameter of the channel 18 can be equal to that of the channel 14 or slightly superior. The shield 17 has a cylindrical rear portion 19 of the same outside diameter as the end piece 15 to which it is adjacent, housed at the front end of the recess of the body 1, the bottom of which is occupied by the end piece 15. At the portion rear 19 is connected to a middle portion 20 of the same diameter as the front part of the body 1, and supported by a shoulder 25 on the front face thereof. The shield ends with a front portion 21 in the form of a spherical cap, the base diameter of which is that of the middle portion 20. The sheath 8 extends over the periphery of the middle portion 20 and is folded inwards on the peripheral zone of the front portion 21. A chamfer 22 is provided at the entrance to the channel 18.

The casing 9, the end piece 15 and the shield 17 are brazed together according to a joint 26 obtained from a ring of silver-based filler metal, the diameter of which corresponds to that of the end piece and of part 19 of the shield, and which was introduced between these two parts.

The shield 17 prevents the adhesion of metal splashes from the weld pool on the front end of the contact tip. Thanks to the continuity between the shield 17 and the sheath 8, the entire front part of the contact tip is protected against these projections.

FIG. 2 shows the positioning of the jacket 10 in the casing 9 already equipped with the end piece 15 and the shield 17.

The prior brazing of the end piece and the shield exposed the casing 9 to a temperature above 4000C, for example of the order of 600 to 8000C. At such a temperature, copper alloys, even ceFx possessing excellent mechanical properties, undergo annealing which deteriorates them and no longer allows the materials to withstand without friction rapid wear of a filler metal wire.

The sleeve 10 is forcibly fitted in, the outside diameter of which corresponds to the inside diameter of the casing 9, by introducing it through the rear end of the casing, that is to say opposite the front end where the end piece 15 and the shield 17 are arranged. To facilitate assembly, the parts 9 and 10 can be brought to different temperatures, either by heating the casing 9, or by cooling the jacket 10, or by combining these two operations. The jacket 10 is moved forward (arrow F) until its front end 26 abuts against the rear end 27 of the end piece 15. In the illustrated embodiment, the rear end 28 of the shirt 10 then place in the plane of the rear end 29 of the envelope 9, as shown in FIG. 1, the length of the jacket being equal to the distance between the rear ends of the end piece 15 and of the envelope 9. L press fitting ensures perfect immobilization of the jacket 10 and good electrical contact between it and the casing 9. Part of the electric current supplied to the filler metal wire is so, without excessive contact resistance , via the sleeve 10, the end piece 15 also participating in this supply of electric current.

The jacket 10, put in place after brazing the end piece 15 and the shield 17, does not have to undergo any rise in temperature during the manufacture of the contact tube. The temperatures reached during the use of the tube are much lower than those due to the brazing operations, and if they cause metallurgical transformations, these are very slow and the degradations of mechanical properties which result therefrom do not compromise the duration of life of the tube.

The production of the contact tube is completed by piercing the recess 14 in the thickness of the casing 9 and of the jacket 10, by introducing the elements of the support device T1 there and by threading the sheath 8 on the part front of the tube. A chamfer 23 can be produced at the entrance to the channel 2 of the jacket 10, before or after mounting of the latter. Depending on the relative values of the inside diameter and the outside diameter of the jacket 10, the chamfer, if it is produced after assembly, may extend over the cross section of the envelope 9.

The contact tube shown in FIG. 3, in which the same references are used as in FIG. 1 to designate similar elements, differs from the contact tube of FIG. 1 essentially by the absence of the support device 11, and of the recess 14 provided for receiving it, as well as the end piece 15. The jacket 10 is longer than that of Figure 1, and the diameter of the longitudinal channel 2 is slightly smaller, providing just enough play for easy sliding of the filler metal wire. The shield 17 'is made of ceramic, for example of alumina, and its channel 18 has substantially the same diameter as the longitudinal channel 2. The shield 17' is therefore electrically insulating while the shield 17 is electrically conductive, the properties non-sticking of the two shields being the same. The shield 17 'is brazed to the casing 9 according to a seal 26'.

When welding large parts, it is advantageous to heat the parts over a relatively large region around the weld zone to avoid mechanical stresses on cooling. Advantageously, a shield is then provided in an electrically conductive material, for example in graphite, and part of the electric current supplied to the contact tube flows between the shield and the parts to be welded by means of the gases ionized by the potential difference. necessary for the production of the electric arc, thus contributing to the desired heating of the parts.

 If, on the contrary, we are working on parts of small dimensions likely to be damaged by excessive heating, an insulating shield, for example made of ceramic, allows a concentration of the electric current in the filler wire and the limitation of the power thermal release to that required for carrying out the weld.

Furthermore, an alumina shield is not suitable when using bronze or aluminum as the filler metal, because the friction tears off metal particles which deposit on the wall of the channel and, in the event of rising of the arc, the wire is welded to the ceramic thus metallized, rendering the contact tube unusable. For these applications, it is therefore preferable to use a graphite shield.

 A high wear resistance tip, as shown at 15 in Figure 1, is particularly advantageous in combination with a graphite shield, which is itself sensitive to wear. This nozzle improves the precision of the guide of the wire at the entry of the shield and prevents flaring of the outlet channel 18.

It is also possible, when using an aluminum filler wire, to provide the contact tube with a single tip of refractory carbide playing both the role of anti-nrojection shield and anti-wear tip, projections of aluminum not adhering to refractory carbides.

The end piece 15 and the support device 11 can be used independently of one another, as well as in combination.

The support device is particularly useful in fully automatic installations where constant quality of electrical contact is essential.

 When such a support device is used, it is preferable to make the jacket 10 in a material with a low coefficient of friction, such as cobalt or cobalt-beryllium copper, to limit the friction between the wall of the channel. longitudinal and the wire applied to it by the action of the support device. In the absence of a support device, it is naturally possible to use these same materials, but also other alloys such as silver, cadmium, chromium, tellurium and zirconium copper, some of which are less expensive. than those containing cobalt.

The contact tip according to the invention can be used in particular in welding installations with gas protection (MIG: Metal Inert Gas, tlAG: Metal Active Gas), or under flux, protection of the welding zone being ensured in the latter case by a supply of powder.

Claims (11)

Claims. 1. Device for guiding and powering a filler metal wire for arc welding, or contact tube, comprising an elongated metal body (1) having a longitudinal channel (2) for passing through a filler metal wire, and at least one refractory end piece (15, 17; 17 ') brazed at the front end of the metal body and having a channel (16, 18) in line with that of the body, characterized in that the latter comprises, force-fitted into each other, a tubular outer casing (9) and an inner jacket (10) limiting said channel, made of a metal which is not very sensitive to wear and whose properties mechanical effects are little affected by the temperatures reached during the use of the contact tip, the end piece being brazed limitatively to the casing. 2. Contact tube according to claim 1, characterized in that the metal of the jacket is a copper alloy. 3. Contact tube according to claim 2, characterized in that said alloy is chosen from silver, beryllium, cadmium, chromium, cobalt, cobaltberyllium, tellurium and zirconium brass. 4. Contact tube according to one of the preceding claims, characterized in that it comprises a nozzle (17, 17 ') made of a refractory material which does not adhere to the metal projections coming from a weld pool, forming the face front end of the tube, 5. Contact tube according to claim 4, characterized in that the material does not indhérlnt to metal projections is electrically insulating. 6. Contact tube according to claim 4, characterized in that the material which does not adhere to the metal projections is electrically conductive. 7. Contact tube according to one of the preceding claims, characterized in that it comprises at the front end of the body an end piece (15) made of a refractory material, electrically conductive and of excellent resistance to wear. 8. Contact tube according to claim 7, characterized in that the channel (16) passing through the wear-resistant conductive endpiece has a diameter smaller than the diameter of the longitudinal channel of the body. 9. Contact tube according to one of the preceding claims, characterized in that it comprises a thrust device (11) at least partially housed in the body and exerting a transverse thrust on the wire to apply the latter against the wall of the longitudinal channel (2).  10. A method of manufacturing a contact tube according to one of the preceding claims, characterized in that at least one tip is brazed at one end of a metallic tubular casing and which is then force-fitted into the casing tubular jacket made of a metal which is not very sensitive to wear and whose mechanical properties are little affected by the temperatures reached when the contact tube is used, by inserting it from the opposite end of the tubular casing. 11. Method according to claim 11, characterized in that before fitting the shirt into the envelope provided with the end piece, they are brought to different temperatures, the temperature of the shirt being lower than the temperature of the envelope .