WO2008072272A2

WO2008072272A2 - Arc welding torch

Info

Publication number: WO2008072272A2
Application number: PCT/IT2007/000851
Authority: WO
Inventors: Marco Dani
Original assignee: Cte Sistemi S.R.L.
Priority date: 2006-12-15
Filing date: 2007-12-05
Publication date: 2008-06-19
Also published as: ITPD20060453A1; WO2008072272A3

Abstract

An arc welding torch comprising a rod guide, by which a welding rod is supported so as to slide, an electrifier element, with which the rod is in sliding contact and from which it receives current, a layer of electrically insulating material which surrounds the rod guide and/or the electrifier element, and a protective sheath, made of abrasion-resistant material, and fitted onto at least one section of the layer of electrically insulating material, close to a free, welding end of the torch.

Description

ARC WELDING TORCH DESCRIPTION

The subject of the present invention is an arc welding torch of the type including the characteristics mentioned in the preamble of the main claim. The invention is proposed in particular for use in arc welding to be carried out on "narrow edge" bevels, such welding bevels being characterized by a high ratio between depth and width.

Within this scope, whenever a large quantity of weld material is required, submerged arc welding is typically used. In that technical field it is known to use two types of welding torch : blade type torches, flat and elongate in shape so as to be insertable into the bevel, oriented along the welding direction, parallel to the longitudinal axis of the bevel; cylindrical torches, comprising a cylindrical body, coaxial with the welding rod which slides within.

Both types of torch comprise a rod guide member, which supports the welding rod, while allowing it to slide, an element for electrifying the welding rod, in sliding contact therewith, and a layer of electrically insulating covering. In the case of the cylindrical torch, the rod guide member and the electrifying element coincide, being constituted by a tubular member made of copper, copper alloy or another conductor. Fitted and locked onto the member by suitable securing means is a tubular insulating layer, typically made of polytetrafluoroethylene.

In the case of the blade type torch, on the other hand, the layer of insulating covering is typically obtained by means of varnishing. A first problem encountered with such solutions lies in the mechanical wear due to the sliding between the insulating layer and the lateral walls of the bevel. Moreover, in particular in applications in which a cylindrical torch is used, added to the mechanical wear is the thermal wear, produced by the fact that the insulating layer does not withstand for very long the high temperatures created by the welding process.

Wear is particularly relevant in the case where a cylindrical torch is used, because of the low resistance, both thermal and mechanical, of the insulating layer of polytetrafluoroethylene described above. A further problem encountered in both torch solutions described above is raised by the optional use of same when coupled to a welding generator operating with constant output voltage. Disregarding the other contributions, the output voltage of the generator is divided between the welding rod and the arc. Since it is necessary, for correct execution of the weld, to maintain the voltage drop at the arc almost constant, the voltage drop on the section of rod traversed by the current should also not undergo significant variation. However, through the effect of the reduced play between the rod and the conductive element of the torch, it is possible that the position of the last point at which the rod receives current may vary considerably. This determines the variation in the length of the section of welding rod traversed by current, its resistance, and the voltage drop between the ends of that section of the rod.

These problems and others which will become clearer hereinafter are confronted and solved by the invention by means of an arc welding torch according to the following claims. The characteristics and advantages of the invention will become clear from the detailed description of three preferred exemplary embodiments illustrated, by way of non-limiting example, with reference to the appended drawings, in which: Figure 1 is a longitudinal sectional view of a first example of an arc welding torch according to the present invention; - Figure 2 is a longitudinal sectional view of a second example of an arc welding torch according to the present invention; Figure 3 is a longitudinal sectional view of a third example of an arc welding torch according to the present invention; Figure 4 is a sectional view of the torch of Figure 3 along the line IV-IV.

With reference to Figure 1, an arc welding torch of the cylindrical type is indicated as a whole by 1.

The torch 1 comprises, at one of its longitudinal ends, a connector 2 provided with a screw-threaded hole 3, by means of which the torch 1 can be secured to a corresponding torch-holder (not shown).

The connector 2 is made of conductive material, typically copper or copper alloy.

For example, the connector 2 may conveniently be made of an alloy of copper and tellurium.

The torch 1 comprises a rod guide member 4 of tubular shape, provided with two opposed longitudinal ends 4a, 4b. At the longitudinal end 4a the rod guide member 4 is provided with coupling means, for example comprising a forced interference fit, in order to render it integral with the connector 2. The end 4b is free.

In a variant of construction of the invention (not shown) a threaded connection is substituted for the forced interference fit. The rod guide member 4 is made of conductive material such as, for example, copper. As an alternative, alloys based on copper, chromium and zirconium, or copper, cobalt and beryllium, known for their mechanical properties and resistance to the erosion of the arc, may conveniently be used. Housed in the rod guide member 4 is a welding rod 5, with axis X, which is guided so as to slide, during the welding process, from the end 4a to the opposite, welding end 4b of the rod guide member 4.

The rod guide member 4 further constitutes an electrifying element for the welding rod 5. A layer 6 of insulating material surrounds the rod guide member 4 on the outside. The layer 6 comprises a first section 7, close to the connector 2, made of polytetrafluoroethylene, a second section 8, made of silicone, adjacent to the section 7, and a third section 9, constituted by a bushing of ceramic material, which extends from the section 8 as far as an end 9a, close to the free end 4b of the rod guide member 4.

According to an alternative embodiment of the invention, the section 9 may be obtained by deposition by means of a plasma jet process (also known in the art as "plasma spray" process) or flame jet process (also known in the art as "flame spray" process). In a possible variant of construction of the invention (not shown), one of the sections 7 or 8 is substituted by a corresponding prolongation of the section 8 made of silicone.

In a further variant of construction of the invention (not shown) both the sections 7 and 8 are substituted by corresponding prolongations of the section 8 made of silicone. Fitted onto the layer 6 of insulating material is a protective sheath 10, of abrasion-resistant material, on which suitable locking means are arranged.

The sheath 10 is made of stainless steel, of type AISI 304 or equivalent.

According to an alternative embodiment of the invention, the layer 6 and the sheath 10 are both made of ceramic material, and preferably obtained by deposition by means of a plasma jet process (also known in the art as "plasma spray" process) or flame jet process (also known in the art as "flame spray" process).

The sheath 10 is abutted against a shoulder 6a of the layer 6 located in proximity to the connector 2. The shoulder 6a has the function of keeping the sheath 10 insulated from the connector 2.

According to a further mode of embodiment of the present invention (not shown), the sheath 10 is fitted onto a section of the layer 6, located in proximity to the free end 4b, in which there is the possibility of contact with the walls of the bevel.

The locking means between the layer 6 and sheath 10, in the example of Figure

1, comprise a compressed region 11 located at the section of insulating layer 7.

On the sheath 10, in the example of Figure 1, a deformation lib located at the end 9a is provided for locking the layer 6 axially. In a variant of construction of the invention (not shown) said locking means comprise one or more clamping clips.

With reference to Figure 2, the reference 20 indicates as a whole a second example of an arc welding torch of cylindrical type, according to the present invention. In Figures 1 and 2, analogous or technically equivalent details will be indicated by the same reference numbers.

At its free end 4b, the torch 20 comprises an electrifying element 13 for the welding rod 5, made of copper or copper alloy, for example comprising chromium and zirconium, or cobalt and beryllium. In the non-limiting exemplary embodiment of Figure 2, the electrifying element 13 is provided in the form of a tip secured to the section of rod guide member 4 adjacent thereto, via suitable securing means, for example brazing.

The electrifying element 13 comprises a calibrated through-hole 14, with axis X, in which the welding rod 5 slides in sliding contact, An electrically insulating tubular member 12, extending from the end 4a of the rod guide member 4 to the element 13, is interposed between the rod guide member 4 and the welding rod 5. The tubular member 12 is preferably made of ceramic material.

According to an alternative embodiment (not shown) of the torch 20, the tubular member 12 comprises a metal core, electrically insulated, in which the welding rod slides, and which is provided with a covering of insulating material, for example silicone.

In the non-limiting exemplary embodiment of Figure 2, the electrifying element

13 comprises a covering 15 of ceramic material. According to a non-exclusive mode of embodiment of the invention, the covering

15 is obtained by means of the insertion of a ceramic bushing.

According to a further non-exclusive mode of embodiment of the invention, the covering 15 is obtained by deposition by means of a plasma jet process (also known in the art as "plasma spray" process) or flame jet process (also known in the art as "flame spray" process). With reference to Figures 3 and 4, a further exemplary embodiment of an arc welding torch, this time of the blade type, is indicated as a whole by 30.

In Figures 3 and 4, analogous or technically equivalent details will be indicated by the same reference numbers present in Figures 1 and 2. The blade type torch 30 is provided with a longitudinal plane of symmetry Z.

In the exemplary embodiment of Figures 3 and 4, the rod guide member 4 comprises a body 16 made of bronze, or another conductive material, and two brackets 17 spaced along the axis X of the rod 5. Each of the brackets 17 is fixed to the body 16 by means of two screws 18a, 18b screwed on opposite sides with respect to the plane Z. Along one side of the body 16 a semicylindrical seat, with axis X, is provided for housing the tubular member 12. According to a variant of construction (not shown) of the torch 30, the tubular member 12 is set against a flat surface of the body 16.

The brackets 17 surround the tubular member 12 and lock it with respect to the body 16.

The tubular member 12 of the torch 30 comprises a metal core 21, electrically insulated, in which the welding rod 5 slides and which is provided with a covering

22 of insulating material, for example silicone.

In the non-limiting exemplary embodiment of Figures 3 and 4, the electrifying element 13 is of the plate-like type and is secured to the body 16 by means of a plurality of screws 19, parallel to the axis X.

The layer 6 of the torch 30 is made of silicone and surrounds both the rod guide member 4 and the electrifying element 13.

The torch 30 comprises a cylinder 23, which runs along one side thereof, with axis parallel to the axis X, and is made of silicone and placed outside the layer 6, in proximity to the rod 5. The cylinder 23 spaces, and therefore electrically insulates, the sheath 10 from the parts of the torch 30 traversed by the current. In the non-limiting exemplary embodiment of Figures 3 and 4, the sheath 10 is constituted by a metal sheet which surrounds the layer 6 and the cylinder 23. According to an alternative embodiment of the torch 30, the layer 6 and the sheath 10 are both made of ceramic material and are obtained by deposition by means of a plasma jet process (also known in the art as "plasma spray" process) or flame jet process (also known in the art as "flame spray" process). The present invention makes it possible to provide an arc welding torch in which the presence of the sheath 10 allows its thermal and/or mechanical resistance to be increased. This resistance is further improved by the presence of the silicone insulating layer.

Owing to the effect of the insertion of the insulating tubular member 12, the welding rod 5 receives current from the electrifying element 13 only at the end of the torch.

This makes it possible to render almost fixed, the position of the last point at which there is a transfer of current to the welding rod.

By means of this stratagem, an arc welding torch produced according to the invention, when coupled to a welding generator operating with a constant output voltage, makes it possible to control the voltage of the arc efficiently.

The present invention therefore solves the problems mentioned above with respect to the prior art cited.

Claims

C L A I M S

1. An arc welding torch comprising a rod guide member, by which a welding rod is supported so as to slide, an electrifier element, with which said rod is in sliding contact and from which said rod receives current, and a layer of electrically insulating material which surrounds at least one of said rod guide member and electrifier element, characterized in that it comprises a protective sheath, made of abrasion-resistant material, and fitted onto at least one section of said layer of electrically insulating material, close to a free, welding end of said torch.

2. A welding torch according to claim 1, wherein said sheath is made of metallic material.

3. A welding torch according to claim 1, wherein said sheath is made of stainless steel.

4. A welding torch according to claim 1, wherein said tubular layer of insulating material and said sheath are composed of the same ceramic material.

5. A torch according to claim 1 or claim 4, wherein said tubular layer of insulating material and said sheath are obtained by means of a plasma jet or flame jet process.

6. A welding torch according to claim 1, wherein said tubular layer of insulating material comprises at least one segment based on polytetrafluoroethylene.

7. A welding torch according to claim 1 or claim 6, wherein said layer of insulating material comprises at least one silicone-based segment.

8. A welding torch according to any one of claims 1 to 7, wherein said layer of insulating material comprises a segment made of ceramic material.

9. A welding torch according to claim 1, wherein said tubular layer of insulating material comprises a first segment based on polytetrafluoroethylene, close to an opposite end of said torch from said free, welding end, a second, intermediate, silicone-based segment, and a third segment made of ceramic material, close to said free, welding end.

10. An arc welding torch comprising a rod guide member, by which a welding rod is supported so as to slide, characterized in that it comprises an electrically insulating tubular member interposed between at least one section of said rod guide member and a corresponding section of said welding rod.

11. A welding torch according to claim 1 or claim 10, wherein said rod guide member is tubular in shape.

12. A welding torch according to claim 1 or claim 10, wherein said rod guide member and said electrifier element coincide.

13. A welding torch according to claim 10, wherein said electrically insulating tubular layer comprises at least one section made of ceramic material.

14. A welding torch according to claim 10 or claim 13, wherein said electrically insulating tubular member comprises an electrically insulated metal core, in which said welding rod slides.

15. A welding torch according to claim 14, wherein a covering of insulating material is provided on said metal core.

16. A welding torch according to claim 15, wherein said insulating material is silicone.

17. A welding torch according to claim 10, or according to any one of claims 13 to 16, comprising, at the welding end of said torch, an electrifier element, with which said rod is in sliding contact and from which said rod receives current.

18. A welding torch according to claim 14, wherein a calibrated passage hole is provided for said welding rod on said electrifier element.