GB2049521A

GB2049521A - Improvements in or relating to cladding a metal substrate by arc welding

Info

Publication number: GB2049521A
Application number: GB7913314A
Authority: GB
Original assignee: Burdett P E
Current assignee: Burdett P E
Priority date: 1979-04-17
Filing date: 1979-04-17
Publication date: 1980-12-31

Abstract

A method of cladding a metal substrate by arc welding comprises the steps of supplying electrical energy to a metal substrate to be clad as a first electrode, moving a welding head along the substrate at a controlled rate, feeding to a weld point adjacent said head, as a second electrode, a consumable electrode strip comprising a sheath of sheet metal containing a core of metal powder, and feeding flux on top of a weld bead formed of molten metal at the welding point. The strip may be pre-formed or, as shown, formed immediately ahead of the welding point from a flat strip of metal (14) by means of rollers (16,22) to enclose powdered metal from a feed hopper (20). An additional powder-cored strip may or may not be electrically energised. <IMAGE>

Description

SPECIFICATION Improvements in or relating to cladding a metal substrate by welding The invention is concerned with improvements in or relating to cladding a metal substrate by welding. In particular, it relates to an electric arc welding technique in which a weld bead is formed comprising molten metal from a consumable electrode and from metal in particulate form.

It is known in the art to provide the particulate metal in the form of metal powder in a layer at the weld point, usually submerged in flux to ensure correct weld homogeneity and to minimise oxidation.

However, it frequently occurs, especially when the consumable electrode is in strip form, that the plasma wind, caused by the arc travelling to and fro across the width of the strip, tends to blow the metal powder away from the weld point.

Several attempts have been made to minimise this loss of powder, including the use of a magnetic field at the weld point. The present invention seeks to provide a satisfactory solution to the problem.

The invention therefore provides a method of cladding a metal substrate by welding comprising the steps of supplying electrical energy to a metal substrate to be clad as a first electrode, moving a welding head along the substrate at a controlled rate by feeding to a weld point adjacent said head a consumable electrode strip as a second electrode comprising a sheath of sheet metal containing a core of metal powder, moving the powder-cored strip towards the welding point in a controlled manner and feeding flux on top of a weld bead formed of molten metal at the welding point.

Although the consumable electrode strip may be pre-formed, it may be found convenient to form the sheath from flat metal strip and fill the formed strip with powder immediately prior to the welding operation.

In one example of the invention, a single powdercored strip may be utilised, or alternatively, as in the example to be described in detail below, a second powder-cored strip may be fed into the arc to increase the rate of deposition of the cladding metal.

If desired, this second strip may also be electrically charged.

The invention also provides apparatus for use in the cladding of a metal substrate using a so-called bulk-welding technique comprising a welding head adapted to travel at a controlled rate along a metal substrate to be clad, feed rollers adapted to feed a consumable electrode strip to a weld point, forming means comprising a first set of rollers capable of forming a flat strip of metal into a substantially U-shaped cross-sectional configuration, feed means for supplying metal powder to the partially formed strip electrode, said forming means further compris ing a second set of rollers capable of closing together edges of said partially-formed strip so the powder from the feed means is completely contained within the sleeve so formed.

The apparatus according to the invention, which is to be described below with reference to the accompanying drawing, is described by way of example only and not by way of limitation.

In the drawing is shown a diagrammatic representation of apparatus for use with the method according to the invention.

A substrate 2 is a length of steel which is to be coated with a layer of metal by the method. The substrate 2 is connected to an AC or DC power supply.

A welding head, arranged to travel along the surface of the substrate in a direction from right to left as viewed in the drawing, includes a flux reservoir 4, through which passes a first strip electrode 6 to which power is also supplied to give a welding arc at the welding point 8, to which a second strip 10 is also fed. In the present example, no power is supplied to this second strip, but it is to be understood that where circumstances dictate, the second strip may also be connected to a power source.

Both strips 6, 10 are composed of a metal sleeve containing a powdered metal core. The metal and the metal powder are selected in the relative quantities required to give the desired alloy composition of a coating 12 formed on the substrate.

The powder-cored strips 6, 10 are both formed in the same manner. Aflat strip of thin gauge metal 14 is passed between a set of forcing rollers 16 in a V-formation to force edges 18 of the strip upwardly so that the strip becomes U-shaped in cross-section.

Afeed hopper 20 provides powdered metal which is received in the U-shaped portion of the strip which then passes through a second set of forming rollers 22 which closes the edges over against each other, so that the powder is completely enclosed by the sleeve formed by the metal strip 14. The electrodes so formed are fed to the weld point 18 by two series of feed rollers 24, 26, the lower ends of the electrodes being submerged in flux 28 from the reservoir 4.

Various modifications may be made within the scope of the invention.

1. A method of cladding a metal substrate by welding comprising the steps of supplying electrical energy to a metal substrate to be clad as a first electrode, moving a welding head along the substrate at a controlled rate by feeding to a weld point adjacent said head a consumable electrode strip as a second electrode comprising a sheath of sheet metal containing a core of metal powder, moving the powder-cored strip towards the welding point in a controlled manner and feeding flux on top of a weld bead formed of molten metal at the welding point.

2. A method as claimed in claim 1, wherein the sheath is preformed to contain the metal powder.

3. A method as claimed in claim 1, wherein the sheath is formed by folding an initially flat metal strip immediately prior to its consumption as the second electrode, feed means being provided to supply powdered metal onto the strip as it is folded.

4. A method as claimed in any one of the

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to cladding a metal substrate by welding The invention is concerned with improvements in or relating to cladding a metal substrate by welding. In particular, it relates to an electric arc welding technique in which a weld bead is formed comprising molten metal from a consumable electrode and from metal in particulate form. It is known in the art to provide the particulate metal in the form of metal powder in a layer at the weld point, usually submerged in flux to ensure correct weld homogeneity and to minimise oxidation. However, it frequently occurs, especially when the consumable electrode is in strip form, that the plasma wind, caused by the arc travelling to and fro across the width of the strip, tends to blow the metal powder away from the weld point. Several attempts have been made to minimise this loss of powder, including the use of a magnetic field at the weld point. The present invention seeks to provide a satisfactory solution to the problem. The invention therefore provides a method of cladding a metal substrate by welding comprising the steps of supplying electrical energy to a metal substrate to be clad as a first electrode, moving a welding head along the substrate at a controlled rate by feeding to a weld point adjacent said head a consumable electrode strip as a second electrode comprising a sheath of sheet metal containing a core of metal powder, moving the powder-cored strip towards the welding point in a controlled manner and feeding flux on top of a weld bead formed of molten metal at the welding point. Although the consumable electrode strip may be pre-formed, it may be found convenient to form the sheath from flat metal strip and fill the formed strip with powder immediately prior to the welding operation. In one example of the invention, a single powdercored strip may be utilised, or alternatively, as in the example to be described in detail below, a second powder-cored strip may be fed into the arc to increase the rate of deposition of the cladding metal. If desired, this second strip may also be electrically charged. The invention also provides apparatus for use in the cladding of a metal substrate using a so-called bulk-welding technique comprising a welding head adapted to travel at a controlled rate along a metal substrate to be clad, feed rollers adapted to feed a consumable electrode strip to a weld point, forming means comprising a first set of rollers capable of forming a flat strip of metal into a substantially U-shaped cross-sectional configuration, feed means for supplying metal powder to the partially formed strip electrode, said forming means further compris ing a second set of rollers capable of closing together edges of said partially-formed strip so the powder from the feed means is completely contained within the sleeve so formed. The apparatus according to the invention, which is to be described below with reference to the accompanying drawing, is described by way of example only and not by way of limitation. In the drawing is shown a diagrammatic representation of apparatus for use with the method according to the invention. A substrate 2 is a length of steel which is to be coated with a layer of metal by the method. The substrate 2 is connected to an AC or DC power supply. A welding head, arranged to travel along the surface of the substrate in a direction from right to left as viewed in the drawing, includes a flux reservoir 4, through which passes a first strip electrode 6 to which power is also supplied to give a welding arc at the welding point 8, to which a second strip 10 is also fed. In the present example, no power is supplied to this second strip, but it is to be understood that where circumstances dictate, the second strip may also be connected to a power source. Both strips 6, 10 are composed of a metal sleeve containing a powdered metal core. The metal and the metal powder are selected in the relative quantities required to give the desired alloy composition of a coating 12 formed on the substrate. The powder-cored strips 6, 10 are both formed in the same manner. Aflat strip of thin gauge metal 14 is passed between a set of forcing rollers 16 in a V-formation to force edges 18 of the strip upwardly so that the strip becomes U-shaped in cross-section. Afeed hopper 20 provides powdered metal which is received in the U-shaped portion of the strip which then passes through a second set of forming rollers 22 which closes the edges over against each other, so that the powder is completely enclosed by the sleeve formed by the metal strip 14. The electrodes so formed are fed to the weld point 18 by two series of feed rollers 24, 26, the lower ends of the electrodes being submerged in flux 28 from the reservoir 4. Various modifications may be made within the scope of the invention. CLAIMS

4. A method as claimed in any one of the preceding claims, wherein more than one metal powder-cored strip is used as a second electrode.

5. A method as claimed in any one of the preceding claims wherein the strip(s) islare electrically charged.

6. A method as claimed in any one of the preceding claims, wherein the lower end portions of the strips are submerged in flux.

7. Apparatus for use in the cladding of a metal substrate using a so-called bulk-welding technique comprising a welding head adapted to travel at a controlled rate along a metal substrate to be clad, feed rollers adapted to feed a consumable electrode strip to a weld point, forming means comprising a first set of rollers capable of forming a flat strip of metal into a substantially U-shaped cross-sectional configuration, feed means for supplying metal powdex to the partially formed strip electrode, said forming means further comprising a second set of rollers capable of closing together edges of said partially-formed strip so the powder from the feed means is completely contained within the sleeve so formed.

8. Apparatus as claimed in claim 7 wherein there is provided a flux reservoir.

9. A method of cladding a metal substrate, substantially as hereinbefore described with refer ence to and as shown in the drawing.

10. Apparatus for cladding a metal substrate using a bulk-welding technique, constructed and arranged substantially as hereinbefore described with reference to and as shown in the drawing.