GB2179574A - Tubular welding wire manufacturing method - Google Patents

Abstract

A longitudinal groove 48 is formed in a rod by rolls such that the faces 53, 54 of the upper portion of the groove subtend a larger angle than that between the faces of the middle portion of the groove. The groove is then filled with powdered welding ingredients, and then the upper faces of the groove are closed into abutting relationship by rolls to form a seamed tube. The tube is then reduced to size in a circular or triangular cross- section. The tube is initially formed in a triangular cross-section by rolls. <IMAGE>

Description

SPECIFICATION Tubular Welding Wire Manufacturing Method The present invention relates to methods of manufacturing cored tubular welding wires.

It is known from UK Patent No. 1280526 how to manufacture a tubular electrode for arc welding by first forming a longitudinal groove in a rod and then deepening and widening the groove into a ribbon of generally uniform thickness. The U-shaped ribbon thus formed is then filled with powdered welding ingredients, closed into a tube and finally reduced to the required diameter.

In this known method the extent of deformation of the rod due to the successive rolling operations and subsequent size reduction, all carried out cold or at a temperature less than 250C, causes sufficient work hardening to make it difficult to reduce the tube to 1.6 mm diameter or smaller size without intermediate heat treatment. With the existing state of the art the smallest diameter of cored wire that is commercially produced from rod is .068" (1.73 mm) although cored wires down to 1 mm diameter are commercially produced from strip. It is the aim of the present invention to provide a method of manufacturing a tubular welding electrode from rod which reduces the amount of work performed on the rod sufficiently to make possible the production of 1.6 mm and smaller diameters without intermediate heat treatment.

It is an additional aim of the invention to provide a method of manufacture such that it is possible to produce a welding electrode suitable for gas shielded arc welding in 1.6 mm and smaller sizes at lower cost than a solid wire of the same diameter and similar chemical composition.

According to the present invention the method of making a tubular electrode comprises the steps of taking a metal rod, forming a longitudinally extending groove in the rod such that the faces of the upper portion of the groove subtend a larger angle than that between the faces of the middle portion of the groove, filling the lower portion of the groove with powdered welding ingredients consisting of flux and/or metals, and closing the upper faces of the groove in abutting relationship to enclose the welding ingredients. The tubular wire thus formed is then reduced to the desired finished size by rolling, drawing or a combination of both methods.

An advantage of the above defined method over the prior art is that by forcing the upper portion of the faces of the groove into abutting relationship much less work has to be performed on the rod material than is required if the rod is first rolled into a ribbon of approximately uniform thickness. In consequence it is possible to produce a smaller size of tubular electrode from rod than has been otherwise known to be possible without heat treatment.

An additional advantage of the present invention over the prior art is that the powder filling operation takes place after only approximately 25% to 40% reduction in the cross-section area of the rod has been completed, substantially less than is the case if the rod is first reduced to a ribbon of uniform cross section. In consequence the speed of travel of the rod atthe powderfilling station is lower. This helps to ensure that the finishing speed obtainable when the tube is being reduced to its finished size is not restricted by the difficulty of powder filling an open tube with an accurately metered quantity of powder when it is travelling at high speed.

The present invention makes it possible to produce a continuous wire for gas shielded arc welding of mild and/or low alloy steel at a lower cost than that of a solid wire of similar size and chemical composition. This is because rod for producing a suitable solid wire must contain at least two deoxidants in sufficient quantities to prevent the formation of porosity in the weld metal. Typically the combined cost of plain mild steel rod and powdered deoxidants, typically comprising manganese, ferro-manganese, ferro-silicon, silico manganese or a combination of two or more of these ingredients, for the production of a tubular wire by the method of the present invention suitable for gas shielded arc welding mild steel is less than 93% of the cost of rod for manufacturing a solid wire of similar analysis.

Production speeds obtainable in the manufacture of tubular welding wire by the present invention are similarto those for the manufacture of the same size of solid wire so that a distinct saving is potentially achievable compared with the cost of producing solid wire of similar analysis.

Embodiments of the invention will now be described, by way of example, reference being made to the Figures of the accompanying diagrammatic drawings in which: Figure 1 is a schematic side elevation of apparatus for manufacturing a tubular electrode for electric arc welding.

Figures 2, 3 & 4 are cross-sectional views showing the various shapes assumed by the rod as it passes through the apparatus of Figure 1. These views also show the cross section of the three rolls at each roll stand that are used to shape the rod in a preferred embodiment of the invention.

Figure 5 is a transverse cross-section through a finished tubular electrode.

As shown in Figure 1 a continuous rod 1 passes from left to right through a rolling mill 2.

The continuous rod 1 is first paid off a reel 3 and passes over guide rollers 4, 5 and 6 to a descaler 7 in which scale removed from the rod by the normal method of mechanical descaling is subsequently blasted onto the rod surface by compressed air and/or water to remove the residue of scale not removed by the mechanical descaling.

From the descaling unit the rod passes directly to the first two stands of the rolling mill 2. The first stand 8 has rolls 9 as shown in cross section in Figure 2, designed to roll the rod 44 into a shape having a cross-section approximating to a triangle with the top face 45 of the triangle horizontal.

At the next stand 10 the top roll 11 forms a longitudinal groove in the rod which acquires a cross section shown in Figure 3. In the preferred embodiment, in which the rod entering this stand has a triangular cross section with the top face 45 horizontal, the work performed on the rod to produce a groove 48 is minimised by allowing the lower faces 46 and 47 of the triangular cross section rod to curve outwards into the concave faces 49 and 50 of rolls 51 and 52.

The rod exiting from stand 10 passes through cleaning apparatus 12 to remove water soluble lubricant, used in the preceding rolling operations, from the inside of the groove. This cleaning operation may be performed by using jets of steam followed by a jet of compressed air.

The groove in the tube is then passed under a hopper 13 containing powdered welding ingredients that are fed into the tube at a controlled rate by one of the various methods known to those skilled in the art of tubular electrode manufacture.

The rod then passes through roll stand 14 which has rolls 15 to force the upper faces 53 and 54 of the groove in the rod into abutting relationship forming a seamed tube shown in cross section in Figure 4.

At roll stands 16 to 34 rolls reduce the overall dimensions of the tube by progressively rolling to triangular form in rolls 17,21,25,29 and 33 and then into round form in rolls 15, 19,23,27,31 and 35. The tube is finally sized in roll stand 36 by rolls 37. A cross section of the finished tube is shown in Figure 5 As the tube exits from the rolling mill 2 it passes through apparatus for cleaning to remove the water soluble lubricant used in the rolling mill. Lubricant removal is accomplished by jets of steam followed by compressed air. Fumes from the cleaning operation are removed by an extractor 39.

The tubular electrode then passes to a reeling machine 40 incorporating an accumulator 41 and large reel 42.

In order to reduce work hardening of the steel rod to a minimum and thus permit production of tubes down to 1 mm diameter or equivalent crosssectional area two steps are proposed which may be employed singly or in combination: 1. The powder fill can be limited to providing only sufficient de-oxidants, e.g. Mn, Si, Al, Ti, Mg necessary to produce porous free welds when the electrode is used for arc welding in a shield of CO2 or Argon/CO2 mixture. Thus the weight of fill in relation to the total weight of the electrode may be as low as 1.5% and typically would be in the region of 2.5% to 5%.

2. The rod can be preheated (e.g. by electrical induction) just prior to entering the forming rolls thereby reducing the yield or proof stress of the rod and consequently the work hardening effect. A preheat of 300C will reduce the 0.2% proof stress by approximately 20%.

A tubular electrode is most easily used if it has no inherent tendency to twist as it emerges from the welding torch. To achieve this result it is desireable that the neutral axis of the cross-section of the tube should lie on the geometric centre line of the tube.

This can be accomplished by designing the grooving roll 11 such that the thickness of the tube underneath the bottom of the grooving roll is a little greater than the length of the upper faces 53 and 54 of the groove to compensate for the increased thickness of the tube walls immediately adjacent to the seam. Increased thickness of the tube wall at the point opposite to the seam gives a further advantage in reducing the amount of seam opening due to hoop stress created when the upper faces of the groove are first brought into abutting relationship.

Using the production method of the present invention it is possible to produce copper coated welding wire by first coppering the rod using a chemical exchange or an electrolytic process.

Reduction to size by rolling causes less damage to the copper coat than reduction by drawing particularly if the rod has been coppered electrolytically.

In an alternative embodiment of the invention the final rolls in the rolling mill can form the finished tube into an approximately triangular cross section instead of the normal circular cross section.

Claims (12)

1.A method of manufacturing a cored tubular welding electrode comprising the steps of taking a metal rod, forming a longitudinal extending groove in the rod such that the faces of the upper portion of the groove subtend a larger angle between each other than the angle between the faces of the middle portion of the groove, depositing powdered welding ingredients in the groove and closing the upper faces of the groove in abutting relationship to enclose the welding ingredients.

2. A method as claimed in claim 1 in which the rod is first rolled into an approximately triangular crosssection.

3. A method as claimed in claims 1 or 2 in which the groove is rolled into the rod in a single operation using either two or three rolls.

4. A method as claimed in any one of claims 1 to 3 in which the depth of the groove and the length of the upper faces of the groove are such that when the tube has been formed the neutral axis of the cross-section of the tube lies on the geometric centre line of the tube.

5. A method as claimed in any one of claims 1 to 4 in which the tube is reduced in size by successively reducing the tube to a triangular cross-section and then to a round cross-section.

6. A method as claimed in any one of claims 1 to 5 in which the rod is first copper coated.

7. A method as claimed in any one of claims 1 to 6 in which the rod is preheated to a temperature of 250C or more prior to grooving.

8. A method as claimed in any one of claims 1 to 7 in which the tubular welding electrode is reduced in size to 1.6 mm or smaller diameter without intermediate heat treatment.

9. A method as claimed in any one of claims 1 to 8 in which the welding ingredients comprise 5% or less of the weight of the tubular electrode.

10. A method as claimed in any one of claims 1 to 9 in which the welding ingredients comprise 10% or less of the weight of the tubular electrode.

11. A method as claimed in any one of claims 1 to 10 in which the finished tubular electrode is rolled into an approximately triangular cross-section.

12. A method of making a cored tubular welding electrode substantially as hereinbefore described with reference to the accompanying drawings.