GB1562214A - Process for the manufacture of welding wires - Google Patents

Description

(54) PROCESS FOR THE MANUFACTURE OF WELDING WIRES (71) We, ACIERIES REUNIES DE BURBACH-EICH-DUDELANGE S.A.

ARBED, of Avenue de la Liberty, Luxembourg, Acieries Reunies De Burbach- a Society Anonyme organised under the laws of Luxembourg, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a welding wire having a tubular sheath and a powder core which is particularly useful for semiautomatic and automatic arc welding of metals by means of consumable electrodes with or without a protective gas atmosphere, and to the production of such wire.

In general these filled wefding wires consist of an exterior metallic sheath of external diameter 0.5 to 4 mm and a core of powdered material. More particularly the mineral or metal powders are of slag, flux, deoxidizing and denitriding materials and alloying metals, and in general the amount employed varies between 10 and 50V of the total weight of the welding wire. Lengths of at least 100 metres of filled wire are wound on supply spools for welding units.

For rapid manufacture of such filled wires there have been employed as starting materials a metal strip and a powder mixture, whose compositions are selected in accordance with the application and performance of the welding wires to be produced. In a first shaping operation the metal strip is transformed into a continuous channel of substantially semi-circular section. The welding powder is introduced into the bottom of this channel whose sides are then folded by a second shaping operation such that the edges come to abut one another.

The tubular sheath filled with powder is further passed to at least one draw plate so as to reduce the diameter of the tube and to compact the powder within. However, the permitted reduction in diameter remains very low because the edges of the shaped strip tend to open up at the time of drawing.

The same danger of opening of the joint exists when winding on the spool and upon thermal expansion of the powder during heating of the wire prior to its fusion. It follows that on the one hand one must take special protective measures for storage, the duration of which should be reduced to a maximum, and on the other hand the amount of filling must be limited as well as the intensity of preheating at the time of welding.

Various measures have already been tried to limit these disadvantages. One measure consists in shaping the sheaths in such away that the edges partially overlap or form a simple or double fold. These mechanical closures, technically difficult to effect, give only a partial improvement.

In a related process, it has been proposed to close the joint of the outer tube enveloping the powder by welding together the two edges of the joint. However the conventional processes that are used to this end, and which comprise known processes for arc welding and induction welding already used for the manufacture of welded tubes, were not suited to this use where the tube to be welded contains a fluid powder and where the composition of the starting materials frequently varies. Also in general welded joints of only mediocre quality are obtained, of the sort which make difficult the further transformation of the filled tube by drawing leading to noticeable failure and requiring limitation to low extension coefficients.

According to the invention there is provided a process for manufacturing a welding wire having a powder core surrounded by a sheath of metal which comprises surrounding the core with a strip of the metal of tubular shape with the longitudinal edges of the strip abutting and seaiing the abutting longitudinal edges of the strip by plasma arc welding, preferably transferred plasma arc welding. It can be of advantage in some cases to use at the welding site a supplementary protective gas independent of the plasma forming gas. The invention also provides a welding wire comprising a powder core in a surrounding metal strip of tubular shape with the longitudinal edges of the strip abutting and sealed by a plasma arc weld.

The invention helps to avoid the prior disadvantages mentioned and can allow manufacture in continuous fashion and at high speed of filled tubular rods with a sealed joint and whose diameter can be high compared to the sheath thickness and which lend themselves to ready transformation and extension by cold drawing.

Thanks to the high concentration of energy and to the pronounced localisation of the fusion zone with the type of welding employed according to the invention, one can obtain a regular line of excellent quality which does not impede the subsequent drawing operation. The high speed of the welding, its applicability to stainless steel, the low sensitivity to variations in the strength of the arc, and the easy regulation of the welding parameters are some of the many advantages which allow observance of very narrow tolerances not possible with prior processes mentioned above.

In a preferred mode of operation, the edges of the shaped tube are subjected to local preheating upstream of the welding position, permitting increased welding speed. The local preheating can usefully be combined with flame treatment of the entire periphery of the tube with a view to eliminating residues of lubricant for shaping.

Usually, a trough-shaped strip of the metal has a powder deposited therein along its length and is then formed to the tubular shape.

In a mode of operation which is preferred though not necessary for good working of the process, the powder in the open trough is covered by a further strip whose longitudinal edge portions extend towards the bottom of the trough; the further strip or sheet is for example bent, e.g. in an arc of a circle, in such a way that its edges touch the trough and entirely cover over the powder which is thus isolated in the bed of the trough. The further strip or sheet serving as the cover of the powder preferably has a longitudinal groove in its dorsal part facing and extending along the joint of the tube. By this means one can avoid splitting of the cover sheet on welding or sticking thereof to the weld, with improved protection at the reverse side of the weld and without displacement of the powder.

Thanks to this measure one can increase the amount of filling in the trough while avoiding dispersal of the powder and its deposition on the edges of the trough when they approach one another and upon welding of the joint.

The further strip or sheet is advantageously a continuous metal strip which is wound off a spool at the same speed as the strip which will form the tubular sheath, being shaped with the aid of rollers prior to its introduction into the trough. There may be chosen as the material for the cover sheet an alloyed or nonalloyed steel, or other metal or available alloy, a metal making up or substituted for a constituent of the exterior metal sheath or of the filling powder, Qr a non metallic product such as plastics or paper.

According to the nature of the powder employed, one can effect levelling and compaction prior to the closing of the trough.

Finally it is equally possible to pre-sheathe the powder in an envelope of non metallic (e.g. plastics) or metallic material or to incorporate a lubricant in the powder and extrude it in the form of a continuous coherent strand into the trough.

A process according to the invention is illustrated, by way of example only, in the accompanying schematic drawing which represents a side elevation view of a manufacturing unit for filled welding wires.

A metal strip 10 of analysis and dimensions chosen in accordance with the nature and diameter of the welding wire to be produced is led after appropriate lubrication towards a profiling stage having rollers 20. Between two pairs of horizontal rollers the strip is shaped in two successive steps to a trough profile 11 with a rounded lower part.

Powder 21, whose composition and quantity relative to the weight of the metal sheath are chosen to guarantee for a given type of electrode the optimum conditions in use, flows continuously and in metered amount from a vibrating receptacle 22 through a nozzle 23 into the preformed trough 11 which passes under the said nozzle 23.

The preformed trough 11 filled with a continuous line of powder is then pulled through a draw plate 24. In this draw plate the extremities of the profile are folded into the form of a tube in which the longitudinal edges of the strip 10 abut.

The unsealed tube 12 thus obtained is freed of lubricant residues by the flames of an annular burner 25.

In order to preheat the two edges forming the open joint of the tube 12, at least one longitudinal burner 26 disposed to face the joint is advantageously provided upstream of the welding position.

The welding by plasma arc is carried out when the preformed tube 12 is between two vertical axis rollers 28 which ensure contact between the edges of the tube. The welding torch 29 is situated above the tube joint between the narrow upper edges of the rollers 28. The welding is carried out by transferred arc plasma welding.

The strand of closed tube 13 is very regular and does not require finishing. At the exit of the welding station the tube is lubricated and subjected to at least one drawing-pass through the draw plate 30 to give minimal pressure on the powder. After passage round the traction drum 31 the filled predrawn tube 14 is wound on the reel 32.

The filled tube obtained is then subjected in a separate operation to drawing to the required diameter. Thanks to the good quality of the welded joint and the very uniform filling, this diameter can be greatly less than I mm.

The filled wires obtained generally have one or more of the following advantages.

- They tolerate a high amount of drawing, so that one can commence with a thicker sheet and obtain increased productivity they offer high filling values, given that one can weld envelopes having a high diameter-wall thickness ratio and can fill the preformed trough to the maximum they ensure isolation of the powder which thus cannot be contaminated by air, humidity or the lubricants employed for profiling and drawing - they are not prone to folding upon reeling and unreeling they can be strongly preheated and thus facilitate high speed welding.

WHAT WE CLAIM IS: 1. A process for manufacturing a welding wire having a powder core surrounded by a sheath of metal which comprises surrounding the core with a strip of the metal of tubular shape with the longitudinal edges of the strip abutting and sealing the abutting longitudinal edges of the strip by plasma arc welding.

2. A process according to claim 1 wherein the welding is effected by transferred plasma arc.

3. A process according to claim 1 or 2 in which the abutting longitudinal edges of the strip are subjected to localised preheating prior to the welding.

4. A process according to claim 1, 2 or 3 wherein a trough-shaped strip of the metal has the powder deposited therein along its length and is then formed to the tubular shape.

5. A process according to claim 4 wherein the powder in the open trough is covered by a further strip whose longitudinal edge portions extend towards the bottom of the trough.

6. A process according to claim 5 wherein the further strip has a longitudinal groove positioned to be open towards and extend along the line along which the edges of the strip of tubular shape abut.

7. A process according to claim 5 or 6 wherein the further strip is of metal.

8. A process according to any of claims 4 to 7 wherein the deposited powder is compacted prior to closure of the trough.

9. A process according to claim 4 wherein the powder is pre-sheathed with metallic or non-metallic material before introduction into the trough.

10. A process according to any of claims 4 to 7 wherein the powder kneaded with a lubricant is extruded into the metal trough.

I I. A process according to any preceding claim wherein there is used at the welding site a supplementary protective gas independent of the plasma forming gas.

12. A process of manufacturing a welding wire, the process being substantially as hereinbefore described with reference to the accompanying drawing.

13. A welding wire comprising a powder core in a surrounding metal strip of tubular shape with the longitudinal edges of the strip abutting and sealed by a plasma arc weld.

14. A powder core welding wire obtained by a process according to any of claims 1 to 12.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (14)

**WARNING** start of CLMS field may overlap end of DESC **. The welding by plasma arc is carried out when the preformed tube 12 is between two vertical axis rollers 28 which ensure contact between the edges of the tube. The welding torch 29 is situated above the tube joint between the narrow upper edges of the rollers 28. The welding is carried out by transferred arc plasma welding. The strand of closed tube 13 is very regular and does not require finishing. At the exit of the welding station the tube is lubricated and subjected to at least one drawing-pass through the draw plate 30 to give minimal pressure on the powder. After passage round the traction drum 31 the filled predrawn tube 14 is wound on the reel 32. The filled tube obtained is then subjected in a separate operation to drawing to the required diameter. Thanks to the good quality of the welded joint and the very uniform filling, this diameter can be greatly less than I mm. The filled wires obtained generally have one or more of the following advantages. - They tolerate a high amount of drawing, so that one can commence with a thicker sheet and obtain increased productivity they offer high filling values, given that one can weld envelopes having a high diameter-wall thickness ratio and can fill the preformed trough to the maximum they ensure isolation of the powder which thus cannot be contaminated by air, humidity or the lubricants employed for profiling and drawing - they are not prone to folding upon reeling and unreeling they can be strongly preheated and thus facilitate high speed welding. WHAT WE CLAIM IS:

1. A process for manufacturing a welding wire having a powder core surrounded by a sheath of metal which comprises surrounding the core with a strip of the metal of tubular shape with the longitudinal edges of the strip abutting and sealing the abutting longitudinal edges of the strip by plasma arc welding.

2. A process according to claim 1 wherein the welding is effected by transferred plasma arc.

3. A process according to claim 1 or 2 in which the abutting longitudinal edges of the strip are subjected to localised preheating prior to the welding.

4. A process according to claim 1, 2 or 3 wherein a trough-shaped strip of the metal has the powder deposited therein along its length and is then formed to the tubular shape.

5. A process according to claim 4 wherein the powder in the open trough is covered by a further strip whose longitudinal edge portions extend towards the bottom of the trough.

6. A process according to claim 5 wherein the further strip has a longitudinal groove positioned to be open towards and extend along the line along which the edges of the strip of tubular shape abut.

7. A process according to claim 5 or 6 wherein the further strip is of metal.

8. A process according to any of claims 4 to 7 wherein the deposited powder is compacted prior to closure of the trough.

9. A process according to claim 4 wherein the powder is pre-sheathed with metallic or non-metallic material before introduction into the trough.

10. A process according to any of claims 4 to 7 wherein the powder kneaded with a lubricant is extruded into the metal trough.

I I. A process according to any preceding claim wherein there is used at the welding site a supplementary protective gas independent of the plasma forming gas.

12. A process of manufacturing a welding wire, the process being substantially as hereinbefore described with reference to the accompanying drawing.

13. A welding wire comprising a powder core in a surrounding metal strip of tubular shape with the longitudinal edges of the strip abutting and sealed by a plasma arc weld.

14. A powder core welding wire obtained by a process according to any of claims 1 to 12.