WO2009039574A1 - Apparatus and method for manual metal arc welding - Google Patents

Apparatus and method for manual metal arc welding Download PDF

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Publication number
WO2009039574A1
WO2009039574A1 PCT/AU2008/001424 AU2008001424W WO2009039574A1 WO 2009039574 A1 WO2009039574 A1 WO 2009039574A1 AU 2008001424 W AU2008001424 W AU 2008001424W WO 2009039574 A1 WO2009039574 A1 WO 2009039574A1
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WO
WIPO (PCT)
Prior art keywords
electrode
welding
shroud gas
gas port
shroud
Prior art date
Application number
PCT/AU2008/001424
Other languages
French (fr)
Inventor
John Norrish
Paul Cooper
Ajit Godbole
Derrick Ernest Hilton
John Duffy
Original Assignee
Boc Limited
University Of Wollongong
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2007905277A external-priority patent/AU2007905277A0/en
Application filed by Boc Limited, University Of Wollongong filed Critical Boc Limited
Publication of WO2009039574A1 publication Critical patent/WO2009039574A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K9/00—Arc welding or cutting
    • B23K9/16—Arc welding or cutting making use of shielding gas
    • B23K9/173—Arc welding or cutting making use of shielding gas and of a consumable electrode
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
    • B23K35/0255—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in welding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
    • B23K35/0255—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in welding
    • B23K35/0261—Rods, electrodes, wires
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/38—Selection of media, e.g. special atmospheres for surrounding the working area

Definitions

  • the present invention relates to welding, and in particular to a welding method and apparatus providing additional shielding of a weld site.
  • the present invention also relates to a welding method and apparatus providing fume extraction in a manual metal arc welding process.
  • the invention is not limited to this particular field of use.
  • GMAW Gas Metal Arc Welding
  • MIG Metal Inert Gas
  • MAG Metal Active Gas
  • Shielded metal arc welding also known as manual metal arc (MMA) welding, or informally as "stick” welding
  • SMAW Shielded metal arc welding
  • MMA manual metal arc
  • stick welding
  • the quality of the weld produced in a MMA welding operation may be affected by a number of factors, including for example the degree to which ambient air is allowed to ingress into the weld zone. Since air consists of a number of gases (oxygen, carbon dioxide, nitrogen, hydrogen, etc), these gases can affect the weld quality in different weld metals and in different ways. For example, nitrogen absorption can significantly affect the porosity of ferritic steel welds, and therefore affect the mechanical strength of the weld resulting in, for example, an increased propensity for cracking and embrittlement. Surface oxidation of the weld can also cause deleterious effects on the weld strength, not to mention unacceptance surface appearance. As mentioned previously, the flux coating is designed to combat the ingress of ambient contaminants to the weld zone. However, ingress of ambient air is still a problem for MMA welding.
  • molten metal may evaporate during MMA welding, and the vapour may undergo oxidation forming a fume plume containing a mixture of vapour, metal oxides, gases and other more complex compounds.
  • Recent international activity has highlighted some potential risks of exposure to this welding fume (McMillan, G., International Activity in Health and Safety in Welding - International Institute of Welding, International Conference on Health and Safety in Welding and Allied Processes, Copenhagen, 9 - 11 May 2005) and it is generally acknowledged that breathing zone exposure should be minimised. Accordingly, there still remains a need for improved MMA welding methods and apparatus providing improved shielding of the weld and improved weld quality.
  • the present invention provides a method for welding with a consumable self-shielding welding electrode, said method comprising the steps of: producing a shroud gas curtain spaced radially outward from said electrode and substantially controlling the axial position of said shroud gas curtain relative to the distal end of said welding electrode during consumption of said electrode during use, said shroud gas curtain comprising a radially outward component of velocity. It will be appreciated that the axial position of said shroud gas curtain relative to the distal end of said welding electrode is controlled within a predetermined range, as discussed further below. In a related aspect for extracting fume gas from a welding site, fume gas is extracted preferably from a position radially intermediate the electrode and the shroud gas curtain.
  • the present invention provides apparatus for welding with a consumable self-shielding welding electrode, said apparatus comprising: at least one shroud gas port spaced radially outward from said welding electrode, said shroud gas port being mountable relative to said electrode and adapted to allow relative movement therebetween for allowing substantial control of the axial position of said shroud gas port relative to the distal end of said welding electrode during consumption of said electrode during use, said shroud gas port being adapted to impart to an exiting shroud gas a radially outward component of velocity.
  • a fume gas extraction port is preferably positioned radially intermediate the electrode and the shroud gas port.
  • the present invention provides apparatus for welding with a consumable self-shielding welding electrode, said apparatus comprising: at least one shroud gas port spaced radially outward from said welding electrode, and a drive assembly responsive to a user input for axially moving either said shroud gas port or said electrode such that the axial position of said shroud gas port relative to the distal end of said welding electrode is substantially controllable during consumption of said electrode during use, said shroud gas port being adapted to impart to an exiting shroud gas a radially outward component of velocity.
  • a fume gas extraction port is preferably positioned radially intermediate the electrode and the shroud gas port.
  • the present invention provides apparatus for welding with a consumable self-shielding welding electrode, said apparatus comprising: a shroud gas port axially slidably mountable with said welding electrode, such that, the axial position of said shroud gas port relative to the distal end of said welding electrode is substantially controllable during consumption of said electrode during use, said shroud gas port being spaced radially outward from said welding electrode and adapted to impart to an exiting shroud gas a radially outward component of velocity.
  • a fume gas extraction port is preferably positioned radially intermediate the electrode and the shroud gas port.
  • the welding electrode is adapted to generate an arc-protecting gas curtain around the arc and weld during use/deposition.
  • Typical electrodes for MMA welding are elongate and circular in cross section and for the purposes herein the electrode defines said axis.
  • the welding electrode holder is adapted to receive the welding electrode at the welding electrode's proximal end.
  • conventional MMA welding apparatus comprises a welding stick electrode fitted into a hand held electrode holder, which is in electrical communication with the power supply.
  • the conventional MMA welding process is manual in the respect that as the welding process proceeds the electrode is "burned off and becomes shorter, meaning that the welding operator must manually adjust for the change in the length of electrode by changing the position in which the electrode holder is held with respect to the workpiece so as to keep the arc length substantially constant.
  • the welding operator actuates the drive assembly as required to retract the shroud gas port as the welding electrode is consumed during use such that the relative axial position of the shroud gas port and the distal end of the electrode are substantially controlled, and preferably maintained during burn off of the electrode.
  • the welding operator actuates the drive assembly as required to feed or introduce the welding electrode to the welding site during its consumption such that the relative axial position of the shroud gas port and the distal end of the electrode are substantially controlled, and preferably maintained during burn off of the electrode.
  • the present invention is "manual" in the respect that the welding operator must manually retract or feed the shroud gas port or electrode respectively as required such that the shroud gas port and the distal end of the electrode are maintained in a substantially adjacent axial relationship, and of course to also maintain an appropriate stand off distance between the shroud gas port and/or the distal end of the electrode and the workpiece.
  • the welding electrode is mounted in the electrode holder and a separate hand-held shroud gas port is sleevingly slidably engaged with the electrode.
  • the shroud gas port includes a handle.
  • the hand-held shroud gas port apparatus is manually drawn back towards the proximal end of the electrode thereby to substantially control, and preferably maintain the relative axial position of the shroud gas port with respect to the distal end of the welding electrode. It will be appreciated that this particular embodiment is particularly suited for welds which are physically difficult to access.
  • the welding operator may actually bend the electrode in order to improve access to where the weld is to be deposited; the welder often supporting the free electrode with a gloved hand.
  • the present invention allows the welding operator to guide the electrode safely with the hand held shroud gas port whilst simultaneously providing improved shielding to the welding site.
  • the handheld shroud gas port includes an internal ceramic insulator which the electrode can slide through, and a port adapted for attachment to a suitable source of shroud gas.
  • the shroud gas supply conduit connecting the source of shroud gas and the shroud gas port should be flexible, light, heatproof, and of adequate size to handle the gas flow.
  • the present invention relates to the provision of a shroud gas curtain adjacent the distal end of the electrode and maintenance of the relative axial position of the shroud gas port/curtain in relationship to the distal end of the electrode during its consumption during use, wherein the shroud gas port is adapted to impart to an exiting shroud gas a radially outward component of velocity.
  • the present invention in one embodiment relates to the controllable movement of the shroud gas port in response to or, in relationship to consumption of the electrode.
  • the shroud gas port is moved in synchronous relationship relative to the distal end of the electrode.
  • a sensor can be used to automatically maintain a predetermined axial relationship between the distal end of the welding electrode and the shroud gas port/curtain during consumption of the electrode during use.
  • the sensor automatically retracts the shroud gas port as the welding electrode is consumed (for the case when the electrode is non-movable with respect to the apparatus), or, in the case when the shroud gas port is non-movable with respect to the electrode holder, deliver or feed the welding electrode to the welding site during its consumption.
  • An electronic eye mounted to the shroud gas port for monitoring the tip of the electrode may be used for these purposes.
  • other sensors could be used to similar effect. If a sensor is employed it will be appreciated that the present invention is still somewhat “manual" since the welding operator will still need to maintain an appropriate stand-off distance during welding.
  • the apparatus of the invention may also include an adjustable support formation disposed on the electrode holder.
  • the support formation is preferably positioned adjacent where the welding electrode is received and assists the welding operator in maintaining a pre-determined stand-off distance between the welding electrode and the workpiece.
  • the support formation may comprise a downwardly protruding leg and be capable of rolling or sliding over the workpiece. It will be appreciated by the skilled person that the concept of substantially maintaining the relative axial position of the shroud gas curtain with respect to the distal end of the welding electrode during consumption of the electrode during use, should be construed as the maintenance of predetermined axial spacing between the tip of the electrode and the shroud gas port/curtain.
  • the shroud gas port and the distal end of the electrode are coterminous.
  • the distal end of the electrode axially protrudes relative from the shroud gas port, and the axial distance of protrusion is substantially maintained during consumption of the electrode. It will be appreciated that the distal end of the electrode could protrude by only a small distance, e.g. 5 millimetres, or a relatively large distance, e.g. 15 cm. A distance of about 30 mm would be preferred.
  • the welding operator can axially translate the shroud gas port and the distal end of said electrode relative to one another (depending on the configuration of the apparatus as described above), the welding operator can select whether the welding electrode is maintained in a protruding configuration or a coterminous relationship in situ. It will be appreciated that in use the welding operator preferably adjusts the relative positions of the shroud gas port and the electrode so that the tip of the electrode is visible to the welder.
  • the welding operator will strive to maintain a substantially constant axial distance between the tip of the consumed electrode and the shroud gas port.
  • the shroud gas port/curtain is axially moved/translated at the same rate as the rate to which the electrode is being burned off. Whilst some variation of this distance will occur during the actual welding process, it will be appreciated that this occurrence will still be within the purview of the present invention.
  • a predetermined metered length of the welding electrode is selectively delivered to the welding site upon actuation of the drive assembly. However, in other embodiments the welding electrode may be uniformly fed to the welding site upon user-actuation of the drive assembly.
  • Preferred apparatus of the invention comprises a user-actable lever disposed on a handle of the apparatus.
  • a foot-pedal could be utilised for allowing the welding operator to selectively deliver the welding electrode to the welding site on an as-needs basis.
  • these embodiments could retract the shroud gas port instead of feeding the welding electrode. Further, combinations of these embodiments are possible, as the skilled person will readily appreciate.
  • the welding electrode could include a helicoid channel on its exterior surface and the drive assembly could include a rotatable drum having a complementary helicoid formation on its exterior surface, such that rotation of the drum causes rotation of the electrode and its simultaneous axial displacement.
  • a pair of spaced delivery wheels are provided for receiving the electrode therebetween such that counter rotation of the wheels causes axial displacement of the electrode towards the welding site. Whilst several embodiments of the delivery device have been exemplified for the welding electrode, it will be appreciated that other drive assemblies could be utilised.
  • the shroud gas port is preferably adapted to direct the exiting shroud gas in a substantially radially outward direction, i.e. generally 90° to the axis of the welding electrode.
  • the exiting shroud gas may be directed generally between about 30° to about 90° with respect to the electrode.
  • the exiting shroud gas is directed about 70° with respect to the axis of the electrode and directed downwardly towards the workpiece.
  • the electrode holder includes an inner sleeve and an outer sleeve for defining therebetween an annular passage for the shroud gas, the shroud gas port being positioned at or near the distal end of the passage.
  • both the inner sleeve and the outer sleeve circumscribe the electrode and are radially spaced from at least the proximal end of the electrode.
  • At least one inlet is provided for supplying the annular passage with shroud gas.
  • the shroud gas port is adapted such that the exiting shroud gas is produced as a relatively thin "curtain" radiating away from the torch.
  • the shroud gas port is adapted such that the exiting shroud gas is produced as an expanding "wedge" of gas radiating from the torch.
  • the present invention provides significant advantages in relation to fume generation and weld quality in comparison with prior art MMA welding apparatus.
  • the present Applicants have found that the shroud gas port of the invention providing a shroud gas curtain having a radially outward component of velocity provides improved shielding to the welding site, and in particular to the weld pool.
  • the shroud gas curtain tends to form an envelope around the welding site, thus effectively isolating the welding site from the surroundings and allowing the shielding gas generated from the electrode to be concentrated about the welding site thereby increasing is efficacy.
  • the present Applicants have found synergistic improvements to shielding by combining the effects of the shroud gas curtain and the shielding provided by the consumed electrode.
  • the aforementioned apparatus may further include at least one shield gas port adapted to direct a shield gas curtain around the welding electrode and the welding site.
  • the electrode holder may include a fume gas extraction port adapted to receive fume gas from an area surrounding the welding site.
  • the fume gas extraction port is ideally positioned radially intermediate the welding electrode and the shroud gas port.
  • the Applicants have found that by introducing a radially outward component of velocity to the shroud gas, together with the extraction port described above, the wall jet flow is substantially contained and the direction of flow along the face of the work being welded is radially inwards, hi other words, the shroud gas curtain isolates the fume generation region from the surroundings and allowing the fume gas to be extracted from within the envelope. Whereas, in the absence of the additional shroud gas port and the shrouding gas this flow (the 'wall jet') continues in a radially outward direction.
  • the exiting shroud gas may be considered as a "radial gas jet" forming an "aerodynamic flange" about the welding site.
  • the shroud gas port is preferably circular in transverse cross-section. However, this type of arrangement is not critical to the design or functionality of the port, for example a port which is annular in transverse cross-section may be possible.
  • One or more of the shield gas port (if present), shroud gas port and fume gas extraction port (if present) may optionally include a plurality of sub-ports.
  • the apparatus may also include control means to control the flow rates of the shroud gas, the shield gas (if present), and the rate of fume gas extraction (if being extracted).
  • the shroud gas is preferably chosen from the group consisting of: nitrogen, helium, argon, carbon dioxide or compounds and mixtures thereof. However, it will be appreciated that any commercially available gas may be used for the shroud gas. Since the shield gas provided by the electrode provides a degree of shielding of the weld pool from atmospheric contamination, compressed air may be used for the shroud gas in some circumstances.
  • the composition of the preferred shroud gas depends on the composition of the flux coating on the welding electrode.
  • Conventional coatings rely on the presence of air to produce a slag which protects the weld.
  • the shroud gas would need to be air.
  • the shroud gas flow rate about 1 to 50 L/min and the shield gas flow rate (if present) may be about 5 to 50 L/min.
  • the fume is preferably extracted from a location intermediate the self-shielding welding electrode (or shield gas curtain) and the shroud gas curtain at a flow rate of between about 5 to 50 L/min.
  • the ratio of the shroud gas flow rate:fume gas extraction rate is between about 1 : 1 to about 1 :2.
  • the shroud gas is cooled sufficiently to promote fume gas condensation. Cooling may be achieved by refrigeration of the shroud gas or adiabatic expansion of the shroud gas exiting the shroud gas port. However, as will be appreciated any method of gas cooling would be suitable, hi other embodiments at least a portion of the shroud gas includes a component reactive with a welding fume and/or a UV light-absorbing component.
  • the present invention provides a method for welding, comprising the steps of: engaging a consumable self-shielding welding electrode with an electrode holder, producing a shroud gas curtain spaced radially outward from said welding electrode, consuming said electrode during use, and substantially controlling the axial position of said shroud gas curtain relative to the distal end of said welding electrode, wherein said shroud gas curtain comprises a radially outward component of velocity.
  • a consumable self-shielding welding electrode with an electrode holder, producing a shroud gas curtain spaced radially outward from said welding electrode, consuming said electrode during use, and substantially controlling the axial position of said shroud gas curtain relative to the distal end of said welding electrode, wherein said shroud gas curtain comprises a radially outward component of velocity.
  • fume gas is extracted from a position radially intermediate the welding electrode and the shroud gas curtain.
  • Figure 1 is a side view of prior art MMA welding apparatus
  • Figure 2 is a sectional side view of a welding electrode for MMA welding shown during a welding operation
  • Figure 3 is a side view of MMA welding apparatus according to one embodiment of the invention.
  • Figure 4 is a close-up view of the MMA welding apparatus shown in Figure 3;
  • Figure 5 is a view similar to Figure 4 but including a fume gas extraction port and fume gas being extracted from the welding site;
  • Figure 6 is a side view of MMA welding apparatus according to a second embodiment of the invention
  • Figure 7 is a view similar to Figure 6 but including a fume gas extraction port and fume gas being extracted from the welding site;
  • Figure 8 is a side view of MMA welding apparatus according to a third embodiment of the invention.
  • Figure 9 is a view of the MMA welding apparatus shown in Figure 8 wherein the electrode is being bent.
  • welding site and “welding zone” may be used interchangeably herein, and the terms “fume” and “fume gas” are also used interchangeably herein. Fume gas is intended to not only refer to the gaseous products emanating from the welding process but also the fine particular matter which is also produced, such as metal dust.
  • welding as discussed herein also includes “hard surfacing”, which is a process in which weld metal is deposited to repair a surface defect rather than to join two pieces of metal together.
  • FIG. 1 a prior art MMA welding apparatus is shown comprising an electrode holder 1 and a consumable welding electrode 2 attached thereto at its proximal end 3. Molten metal is transferred from the consumable welding electrode 2 to the workpiece 4 and as the electrode 2 melts the flux covering 5 disintegrates, giving off a shielding gas 6 that protects the weld area 7 from oxygen and other atmospheric gases.
  • the welding electrode 2 is connected to the power supply 8 by welding cable 9, and work clamp 10 electrically connects the workpiece 3 to the power supply 8 by ground cable 11.
  • a sectional side view of a welding electrode 2 for MMA welding is shown during a welding operation.
  • Molten metal is transferred from the core wire 12 to the weld pool 13 which solidifies to form the weld deposit 14.
  • the flux 5 provides molten slag 15 which covers the weld deposit 14 as it travels from the electrode 2 to the weld pool 13. Once part of the weld pool 13, the slag 15 floats to the surface and protects the weld from contamination as it solidifies. Once hardened, it must be chipped away to reveal the finished weld.
  • a prior art MMA electrode holder 1 has been adapted according to the present invention to provide improved shielding to a welding site 7 when welding with a consumable self-shielding welding electrode 2.
  • the electrode holder 1 comprises at least one shroud gas port 16 spaced radially outward from the welding electrode 2.
  • the shroud gas port 16 is mounted relative to the electrode 2 and adapted to allow relative movement therebetween for allowing substantial control of the axial position of the shroud gas port 16 relative to the distal end 17 of the welding electrode 2 during consumption of the electrode 2 during use.
  • the shroud gas port 16 is adapted to impart to an exiting shroud gas 20 a radially outward component of velocity.
  • the electrode 2 is axially translatable with respect to the shroud gas port 16, which is fixedly mounted to the electrode holder 1.
  • the shroud gas port 16 is axially translatable with respect to the electrode 2, which is fixedly mounted to the electrode holder 1.
  • a drive assembly 18 is provided which is responsive to a user input for axially moving either the shroud gas port 16 or the electrode 2 such that the axial position of the shroud gas port 16 relative to the distal end 17 of the welding electrode 2 is substantially controllable during consumption of the electrode 2 during use.
  • a drive assembly 18 is provided which is responsive to a user input for axially moving either the shroud gas port 16 or the electrode 2 such that the axial position of the shroud gas port 16 relative to the distal end 17 of the welding electrode 2 is substantially controllable during consumption of the electrode 2 during use.
  • the welding electrode 2 is uniformly fed to the welding site 7 upon user-actuation of the drive assembly 18, as best shown in Figures 3 to 5.
  • a lever 19 disposed on the electrode holder 1 preferably actuates the drive assembly 18.
  • a foot-pedal could be utilised for allowing the welding operator to selectively deliver the welding electrode 2 to the welding site 7 on an as-needs basis.
  • the shroud gas port 16 could be retracted instead of feeding the welding electrode 2, as best shown in Figures 6 and 7.
  • the shroud gas port 16 is preferably adapted to direct the exiting shroud gas 20 in a substantially radially outward direction, i.e. generally 90° to the axis of the welding electrode 2.
  • the electrode holder 1 includes an inner sleeve 21 and an outer sleeve 22 for defining therebetween an annular passage for the shroud gas 20, the shroud gas port 16 being positioned at or near the distal end of the passage.
  • both the inner sleeve 21 and the outer sleeve 22 circumscribe the electrode 2.
  • At least one inlet 23 is provided for supplying the annular passage with shroud gas 20 from a suitable source, such as a cylinder 24 of compressed gas.
  • the shroud gas supply conduit 25 connecting the cylinder 24 of compressed shroud gas 20 and the electrode holder 1 should be flexible, light, heatproof, and of adequate size to handle the gas flow.
  • the welding electrode 2 is mounted in the electrode holder 1 and a separate hand-held shroud gas port 26 is sleevingly slidably engaged with the electrode 2.
  • the hand-held shroud gas port 26 is manually drawn back towards the proximal end 3 of the electrode thereby to substantially control, and preferably maintain the relative axial position of the shroud gas port 16 with respect to the distal end 17 of the welding electrode 2. It will be appreciated that this particular embodiment is particularly suited for welds which are physically difficult to access.
  • the welding operator may actually bend the electrode 2 in order to improve access to where the weld is to be deposited; the welder often supporting the free electrode 2 with a gloved hand.
  • the present invention allows the welding operator to guide the electrode 2 safely with the hand held shroud gas port 26 whilst simultaneously providing improved shielding to the welding site 7.
  • the welding electrode 1 may include a fume gas extraction port 27 adapted to receive fume gas from an area surrounding the welding site 7, as best shown in Figures 5 and 7. At least one outlet 30 is provided for extracting the fume gas from the fume gas extraction port 27.
  • the fume gas extraction port 27 is ideally positioned radially intermediate the welding electrode 2 and the shroud gas port 16. Surprisingly, the Applicants have found that by introducing a radially outward component of velocity to the shroud gas 20, together with the extraction port 27, the wall jet flow is substantially contained and the direction of flow along the face of the work being welded is radially inwards.
  • the shroud gas curtain 20 isolates the fume generation region from the surroundings and allowing the fume gas to be extracted from within the envelope. Whereas, in the absence of the additional shroud gas port 16 and the shrouding gas 20 this flow (the 'wall jet') continues in a radially outward direction.
  • the exiting shroud gas 20 may be considered as a "radial gas jet” forming an "aerodynamic flange" about the welding site.
  • the shroud gas 20 is preferably chosen from the group consisting of: nitrogen, helium, argon, carbon dioxide or compounds and mixtures thereof.
  • the composition of the preferred shroud gas depends on the composition of the flux coating 5 on the welding electrode 2.
  • Conventional coatings rely on the presence of air to produce a slag 15 which protects the weld 14. In order not to interfere with the slag forming reactions, in this case the shroud gas 20 would need to be air.
  • the shroud gas flow rate should be about 1 to 50 L/min and, if the apparatus is configured for fume extraction, the fume is preferably extracted at a flow rate of between about 5 to 50 L/min.
  • a welding electrode in the form of a coated manual metal arc rod.
  • the shroud gas port By configuring the shroud gas port to deliver a flow rate of about 15 to 30 L/min of a conventional welding shielding gas, and setting the extraction flow rate to approximately equal the shroud gas flow rate, it is envisaged that an extraction efficiency of at least 70% is possible.
  • the rate of consumption of the electrode is about 10 to 50 mm/min and the apparatus of the invention could be configured to provide control of the distance of the shroud gas port to tip of electrode to about 25 to 30 mm to provide line-of-sight to the weld.
  • the present invention provides improvements in weld quality.
  • improvements relate to:
  • weld mechanical properties i.e. resistance to embrittlement, toughness/ductility, tensile strength and flexural strength, and/or • the weld surface properties, i.e. such as surface oxidation (dross), surface damage, and surface appearance.
  • weld surface properties i.e. such as surface oxidation (dross), surface damage, and surface appearance.
  • the improvements in weld quality are the result of affecting one or more of the following weld characteristics: • porosity;
  • gas pickup e.g. hydrogen and nitrogen

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Abstract

The present invention relates to a method and apparatus for providing additional shielding to a weld site when welding with a consumable self-shielding welding electrode. The method comprises the steps of producing a shroud gas curtain spaced radially outward from the electrode and substantially controlling the axial position of the shroud gas curtain relative to the distal end of the welding electrode during consumption of said electrode during use, wherein the shroud gas curtain comprises a radially outward component of velocity. The present invention also relates to a welding method and apparatus for providing fume extraction in a manual metal arc welding process.

Description

"APPARATUS AND METHOD FOR MANUAL METAL ARC WELDING"
FIELD OF THE INVENTION
The present invention relates to welding, and in particular to a welding method and apparatus providing additional shielding of a weld site. The present invention also relates to a welding method and apparatus providing fume extraction in a manual metal arc welding process. However, it will be appreciated that the invention is not limited to this particular field of use.
BACKGROUND OF THE INVENTION
The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of common general knowledge in the field. Welding is key enabling technology in many sectors of industry. For example,
Gas Metal Arc Welding (GMAW), sometimes referred to as Metal Inert Gas (MIG) or Metal Active Gas (MAG) welding accounts for some 45% of all weld metal deposited in Australia (Kuebler. R., Selection of Welding Consumables and Processes to Optimise Weld Quality and Productivity, Proceedings of the 53rd WTIA Annual Conference, Darwin, 11-13 October 2005). Since welding is of such industrial importance, improvements in welding apparatus and methods remain a highly desirable goal.
Shielded metal arc welding (SMAW), also known as manual metal arc (MMA) welding, or informally as "stick" welding, is a manual arc welding process utilising a consumable metal welding electrode coated in flux. The intense heat needed to melt the metal is provided by an electric arc struck between the electrode and the workpiece. The arc may be in the form of an alternating current or direct current from a suitable welding power supply. As the weld is laid, the flux coating of the electrode disintegrates, giving off vapours that serve as a shielding gas and providing a layer of slag, both of which protect the weld area from atmospheric contamination. Because of the versatility of the process and the simplicity of its equipment and operation, shielded metal arc welding is one of the world's most popular welding processes.
The skilled person will appreciate that the quality of the weld produced in a MMA welding operation may be affected by a number of factors, including for example the degree to which ambient air is allowed to ingress into the weld zone. Since air consists of a number of gases (oxygen, carbon dioxide, nitrogen, hydrogen, etc), these gases can affect the weld quality in different weld metals and in different ways. For example, nitrogen absorption can significantly affect the porosity of ferritic steel welds, and therefore affect the mechanical strength of the weld resulting in, for example, an increased propensity for cracking and embrittlement. Surface oxidation of the weld can also cause deleterious effects on the weld strength, not to mention unacceptance surface appearance. As mentioned previously, the flux coating is designed to combat the ingress of ambient contaminants to the weld zone. However, ingress of ambient air is still a problem for MMA welding.
The skilled person will also appreciate that some of the molten metal may evaporate during MMA welding, and the vapour may undergo oxidation forming a fume plume containing a mixture of vapour, metal oxides, gases and other more complex compounds. Recent international activity has highlighted some potential risks of exposure to this welding fume (McMillan, G., International Activity in Health and Safety in Welding - International Institute of Welding, International Conference on Health and Safety in Welding and Allied Processes, Copenhagen, 9 - 11 May 2005) and it is generally acknowledged that breathing zone exposure should be minimised. Accordingly, there still remains a need for improved MMA welding methods and apparatus providing improved shielding of the weld and improved weld quality. Further, there remains a need for improved MMA welding methods and apparatus providing extraction of the potentially harmful welding fumes. It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the abovementioned prior art, or to provide a useful alternative.
DISCLOSURE OF THE INVENTION
According to a first aspect, the present invention provides a method for welding with a consumable self-shielding welding electrode, said method comprising the steps of: producing a shroud gas curtain spaced radially outward from said electrode and substantially controlling the axial position of said shroud gas curtain relative to the distal end of said welding electrode during consumption of said electrode during use, said shroud gas curtain comprising a radially outward component of velocity. It will be appreciated that the axial position of said shroud gas curtain relative to the distal end of said welding electrode is controlled within a predetermined range, as discussed further below. In a related aspect for extracting fume gas from a welding site, fume gas is extracted preferably from a position radially intermediate the electrode and the shroud gas curtain.
According to a second aspect the present invention provides apparatus for welding with a consumable self-shielding welding electrode, said apparatus comprising: at least one shroud gas port spaced radially outward from said welding electrode, said shroud gas port being mountable relative to said electrode and adapted to allow relative movement therebetween for allowing substantial control of the axial position of said shroud gas port relative to the distal end of said welding electrode during consumption of said electrode during use, said shroud gas port being adapted to impart to an exiting shroud gas a radially outward component of velocity. In a related aspect for extracting ftime gas from a welding site, a fume gas extraction port is preferably positioned radially intermediate the electrode and the shroud gas port.
According to a third aspect the present invention provides apparatus for welding with a consumable self-shielding welding electrode, said apparatus comprising: at least one shroud gas port spaced radially outward from said welding electrode, and a drive assembly responsive to a user input for axially moving either said shroud gas port or said electrode such that the axial position of said shroud gas port relative to the distal end of said welding electrode is substantially controllable during consumption of said electrode during use, said shroud gas port being adapted to impart to an exiting shroud gas a radially outward component of velocity. In a related aspect for extracting fume gas from a welding site, a fume gas extraction port is preferably positioned radially intermediate the electrode and the shroud gas port.
According to a fourth aspect the present invention provides apparatus for welding with a consumable self-shielding welding electrode, said apparatus comprising: a shroud gas port axially slidably mountable with said welding electrode, such that, the axial position of said shroud gas port relative to the distal end of said welding electrode is substantially controllable during consumption of said electrode during use, said shroud gas port being spaced radially outward from said welding electrode and adapted to impart to an exiting shroud gas a radially outward component of velocity. In a related aspect for extracting fume gas from a welding site, a fume gas extraction port is preferably positioned radially intermediate the electrode and the shroud gas port.
Preferably the welding electrode is adapted to generate an arc-protecting gas curtain around the arc and weld during use/deposition. Typical electrodes for MMA welding are elongate and circular in cross section and for the purposes herein the electrode defines said axis. Preferably the welding electrode holder is adapted to receive the welding electrode at the welding electrode's proximal end. It will be appreciated that conventional MMA welding apparatus comprises a welding stick electrode fitted into a hand held electrode holder, which is in electrical communication with the power supply. The conventional MMA welding process is manual in the respect that as the welding process proceeds the electrode is "burned off and becomes shorter, meaning that the welding operator must manually adjust for the change in the length of electrode by changing the position in which the electrode holder is held with respect to the workpiece so as to keep the arc length substantially constant.
In one embodiment of apparatus according to the present invention where the electrode is fixed with respect to the electrode holder, the welding operator actuates the drive assembly as required to retract the shroud gas port as the welding electrode is consumed during use such that the relative axial position of the shroud gas port and the distal end of the electrode are substantially controlled, and preferably maintained during burn off of the electrode.
In an alternative embodiment, where for instance the shroud gas port is fixed with respect to the electrode holder, the welding operator actuates the drive assembly as required to feed or introduce the welding electrode to the welding site during its consumption such that the relative axial position of the shroud gas port and the distal end of the electrode are substantially controlled, and preferably maintained during burn off of the electrode. In these embodiments the present invention is "manual" in the respect that the welding operator must manually retract or feed the shroud gas port or electrode respectively as required such that the shroud gas port and the distal end of the electrode are maintained in a substantially adjacent axial relationship, and of course to also maintain an appropriate stand off distance between the shroud gas port and/or the distal end of the electrode and the workpiece. In a further embodiment, the welding electrode is mounted in the electrode holder and a separate hand-held shroud gas port is sleevingly slidably engaged with the electrode. Preferably the shroud gas port includes a handle. As the electrode is burned off and consumed during use the hand-held shroud gas port apparatus is manually drawn back towards the proximal end of the electrode thereby to substantially control, and preferably maintain the relative axial position of the shroud gas port with respect to the distal end of the welding electrode. It will be appreciated that this particular embodiment is particularly suited for welds which are physically difficult to access. In such circumstances, the welding operator may actually bend the electrode in order to improve access to where the weld is to be deposited; the welder often supporting the free electrode with a gloved hand. However, the present invention allows the welding operator to guide the electrode safely with the hand held shroud gas port whilst simultaneously providing improved shielding to the welding site. Preferably the handheld shroud gas port includes an internal ceramic insulator which the electrode can slide through, and a port adapted for attachment to a suitable source of shroud gas. It will be appreciated by the skilled person that the shroud gas supply conduit connecting the source of shroud gas and the shroud gas port should be flexible, light, heatproof, and of adequate size to handle the gas flow.
Whilst various embodiments have been exemplified above, it will be appreciated that the present invention relates to the provision of a shroud gas curtain adjacent the distal end of the electrode and maintenance of the relative axial position of the shroud gas port/curtain in relationship to the distal end of the electrode during its consumption during use, wherein the shroud gas port is adapted to impart to an exiting shroud gas a radially outward component of velocity. In other words, the present invention, in one embodiment relates to the controllable movement of the shroud gas port in response to or, in relationship to consumption of the electrode. In other embodiments the shroud gas port is moved in synchronous relationship relative to the distal end of the electrode. It will be appreciated that either the electrode is axially translatable or positionable with respect to the shroud gas port, or vice versa. Whereas this invention is illustrated and described with reference to embodiments presently contemplated as the best modes or modes of carrying out such invention in actual practice, it is to be understood that various changes may be made in adapting the invention to different embodiments without departing from the broader inventive concepts disclosed herein.
Whilst the foregoing embodiments are manual, in a semi-automatic embodiment it will be appreciated that a sensor can be used to automatically maintain a predetermined axial relationship between the distal end of the welding electrode and the shroud gas port/curtain during consumption of the electrode during use. To explain, the sensor automatically retracts the shroud gas port as the welding electrode is consumed (for the case when the electrode is non-movable with respect to the apparatus), or, in the case when the shroud gas port is non-movable with respect to the electrode holder, deliver or feed the welding electrode to the welding site during its consumption. An electronic eye mounted to the shroud gas port for monitoring the tip of the electrode may be used for these purposes. However, it will be appreciated that other sensors could be used to similar effect. If a sensor is employed it will be appreciated that the present invention is still somewhat "manual" since the welding operator will still need to maintain an appropriate stand-off distance during welding.
In other preferred embodiments, the apparatus of the invention may also include an adjustable support formation disposed on the electrode holder. The support formation is preferably positioned adjacent where the welding electrode is received and assists the welding operator in maintaining a pre-determined stand-off distance between the welding electrode and the workpiece. In one embodiment the support formation may comprise a downwardly protruding leg and be capable of rolling or sliding over the workpiece. It will be appreciated by the skilled person that the concept of substantially maintaining the relative axial position of the shroud gas curtain with respect to the distal end of the welding electrode during consumption of the electrode during use, should be construed as the maintenance of predetermined axial spacing between the tip of the electrode and the shroud gas port/curtain. For example, in some embodiments the shroud gas port and the distal end of the electrode are coterminous. However, in other embodiments the distal end of the electrode axially protrudes relative from the shroud gas port, and the axial distance of protrusion is substantially maintained during consumption of the electrode. It will be appreciated that the distal end of the electrode could protrude by only a small distance, e.g. 5 millimetres, or a relatively large distance, e.g. 15 cm. A distance of about 30 mm would be preferred. Of course, since the welding operator can axially translate the shroud gas port and the distal end of said electrode relative to one another (depending on the configuration of the apparatus as described above), the welding operator can select whether the welding electrode is maintained in a protruding configuration or a coterminous relationship in situ. It will be appreciated that in use the welding operator preferably adjusts the relative positions of the shroud gas port and the electrode so that the tip of the electrode is visible to the welder.
In preferred embodiments, the welding operator will strive to maintain a substantially constant axial distance between the tip of the consumed electrode and the shroud gas port. In other words, the shroud gas port/curtain is axially moved/translated at the same rate as the rate to which the electrode is being burned off. Whilst some variation of this distance will occur during the actual welding process, it will be appreciated that this occurrence will still be within the purview of the present invention. In one embodiment, a predetermined metered length of the welding electrode is selectively delivered to the welding site upon actuation of the drive assembly. However, in other embodiments the welding electrode may be uniformly fed to the welding site upon user-actuation of the drive assembly. Preferred apparatus of the invention comprises a user-actable lever disposed on a handle of the apparatus. However, in alternative embodiments a foot-pedal could be utilised for allowing the welding operator to selectively deliver the welding electrode to the welding site on an as-needs basis. Alternatively, it will be appreciated that these embodiments could retract the shroud gas port instead of feeding the welding electrode. Further, combinations of these embodiments are possible, as the skilled person will readily appreciate.
It will be appreciated that any method of delivery of the welding electrode to the welding site would be within the purview of the present invention. For example, the welding electrode could include a helicoid channel on its exterior surface and the drive assembly could include a rotatable drum having a complementary helicoid formation on its exterior surface, such that rotation of the drum causes rotation of the electrode and its simultaneous axial displacement. In other embodiments a pair of spaced delivery wheels are provided for receiving the electrode therebetween such that counter rotation of the wheels causes axial displacement of the electrode towards the welding site. Whilst several embodiments of the delivery device have been exemplified for the welding electrode, it will be appreciated that other drive assemblies could be utilised. It will also be appreciated that other drive assemblies could be used to retract the shroud gas port, depending on the particular embodiment as described above. Furthermore, the drive assembly could be pneumatically driven or electrically driven. However, since the shroud gas port requires a source of compressed gas the source of gas for the shroud gas port could conveniently be simultaneously used to actuate the drive assembly.
The shroud gas port is preferably adapted to direct the exiting shroud gas in a substantially radially outward direction, i.e. generally 90° to the axis of the welding electrode. However, it will be appreciated that the exiting shroud gas may be directed generally between about 30° to about 90° with respect to the electrode. Preferably the exiting shroud gas is directed about 70° with respect to the axis of the electrode and directed downwardly towards the workpiece. In one embodiment, the electrode holder includes an inner sleeve and an outer sleeve for defining therebetween an annular passage for the shroud gas, the shroud gas port being positioned at or near the distal end of the passage. Preferably both the inner sleeve and the outer sleeve circumscribe the electrode and are radially spaced from at least the proximal end of the electrode. At least one inlet is provided for supplying the annular passage with shroud gas.
In preferred embodiments the shroud gas port is adapted such that the exiting shroud gas is produced as a relatively thin "curtain" radiating away from the torch.
However, in alternative embodiments the shroud gas port is adapted such that the exiting shroud gas is produced as an expanding "wedge" of gas radiating from the torch. The present invention provides significant advantages in relation to fume generation and weld quality in comparison with prior art MMA welding apparatus. To explain, the present Applicants have found that the shroud gas port of the invention providing a shroud gas curtain having a radially outward component of velocity provides improved shielding to the welding site, and in particular to the weld pool. To explain, the shroud gas curtain tends to form an envelope around the welding site, thus effectively isolating the welding site from the surroundings and allowing the shielding gas generated from the electrode to be concentrated about the welding site thereby increasing is efficacy. Further, the present Applicants have found synergistic improvements to shielding by combining the effects of the shroud gas curtain and the shielding provided by the consumed electrode.
The aforementioned apparatus may further include at least one shield gas port adapted to direct a shield gas curtain around the welding electrode and the welding site. In other embodiments the electrode holder may include a fume gas extraction port adapted to receive fume gas from an area surrounding the welding site. The fume gas extraction port is ideally positioned radially intermediate the welding electrode and the shroud gas port. Surprisingly, the Applicants have found that by introducing a radially outward component of velocity to the shroud gas, together with the extraction port described above, the wall jet flow is substantially contained and the direction of flow along the face of the work being welded is radially inwards, hi other words, the shroud gas curtain isolates the fume generation region from the surroundings and allowing the fume gas to be extracted from within the envelope. Whereas, in the absence of the additional shroud gas port and the shrouding gas this flow (the 'wall jet') continues in a radially outward direction. The exiting shroud gas may be considered as a "radial gas jet" forming an "aerodynamic flange" about the welding site. As a consequence, efficient fume extraction via the fume gas extraction port may be obtained. The shroud gas port is preferably circular in transverse cross-section. However, this type of arrangement is not critical to the design or functionality of the port, for example a port which is annular in transverse cross-section may be possible. One or more of the shield gas port (if present), shroud gas port and fume gas extraction port (if present) may optionally include a plurality of sub-ports. The apparatus may also include control means to control the flow rates of the shroud gas, the shield gas (if present), and the rate of fume gas extraction (if being extracted).
The shroud gas is preferably chosen from the group consisting of: nitrogen, helium, argon, carbon dioxide or compounds and mixtures thereof. However, it will be appreciated that any commercially available gas may be used for the shroud gas. Since the shield gas provided by the electrode provides a degree of shielding of the weld pool from atmospheric contamination, compressed air may be used for the shroud gas in some circumstances.
The skilled person will appreciate that the composition of the preferred shroud gas depends on the composition of the flux coating on the welding electrode. Conventional coatings rely on the presence of air to produce a slag which protects the weld. In order not to interfere with the slag forming reactions, in this case the shroud gas would need to be air. However, it would however be possible formulate a flux coating which could tolerate the use of a different shroud gas.
The shroud gas flow rate about 1 to 50 L/min and the shield gas flow rate (if present) may be about 5 to 50 L/min. If the apparatus is configured for fume extraction, the fume is preferably extracted from a location intermediate the self-shielding welding electrode (or shield gas curtain) and the shroud gas curtain at a flow rate of between about 5 to 50 L/min. Preferably the ratio of the shroud gas flow rate:fume gas extraction rate is between about 1 : 1 to about 1 :2. Optionally the shroud gas is cooled sufficiently to promote fume gas condensation. Cooling may be achieved by refrigeration of the shroud gas or adiabatic expansion of the shroud gas exiting the shroud gas port. However, as will be appreciated any method of gas cooling would be suitable, hi other embodiments at least a portion of the shroud gas includes a component reactive with a welding fume and/or a UV light-absorbing component.
According to a fifth aspect the present invention provides a method for welding, comprising the steps of: engaging a consumable self-shielding welding electrode with an electrode holder, producing a shroud gas curtain spaced radially outward from said welding electrode, consuming said electrode during use, and substantially controlling the axial position of said shroud gas curtain relative to the distal end of said welding electrode, wherein said shroud gas curtain comprises a radially outward component of velocity. Preferably fume gas is extracted from a position radially intermediate the welding electrode and the shroud gas curtain.
Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term "about". Any examples are not intended to limit the scope of the invention. In what follows, or where otherwise indicated, "%" will mean "weight %", "ratio" will mean "weight ratio" and "parts" will mean "weight parts".
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a side view of prior art MMA welding apparatus; Figure 2 is a sectional side view of a welding electrode for MMA welding shown during a welding operation;
Figure 3 is a side view of MMA welding apparatus according to one embodiment of the invention;
Figure 4 is a close-up view of the MMA welding apparatus shown in Figure 3; Figure 5 is a view similar to Figure 4 but including a fume gas extraction port and fume gas being extracted from the welding site;
Figure 6 is a side view of MMA welding apparatus according to a second embodiment of the invention; Figure 7 is a view similar to Figure 6 but including a fume gas extraction port and fume gas being extracted from the welding site;
Figure 8 is a side view of MMA welding apparatus according to a third embodiment of the invention; and Figure 9 is a view of the MMA welding apparatus shown in Figure 8 wherein the electrode is being bent.
DEFINITIONS
In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one having ordinary skill in the art to which the invention pertains.
The terms "welding site" and "welding zone" may be used interchangeably herein, and the terms "fume" and "fume gas" are also used interchangeably herein. Fume gas is intended to not only refer to the gaseous products emanating from the welding process but also the fine particular matter which is also produced, such as metal dust. The term "welding" as discussed herein also includes "hard surfacing", which is a process in which weld metal is deposited to repair a surface defect rather than to join two pieces of metal together.
BEST MODE FOR CARRYING OUT THE INVENTION Throughout the figures presented herein like features have been given like reference numerals. Further, it will be appreciated the arrows in the Figures that represent gas flows present simplified versions of the gas flow regimes. Referring initially to Figure 1, a prior art MMA welding apparatus is shown comprising an electrode holder 1 and a consumable welding electrode 2 attached thereto at its proximal end 3. Molten metal is transferred from the consumable welding electrode 2 to the workpiece 4 and as the electrode 2 melts the flux covering 5 disintegrates, giving off a shielding gas 6 that protects the weld area 7 from oxygen and other atmospheric gases. The welding electrode 2 is connected to the power supply 8 by welding cable 9, and work clamp 10 electrically connects the workpiece 3 to the power supply 8 by ground cable 11.
Referring to Figure 2, a sectional side view of a welding electrode 2 for MMA welding is shown during a welding operation. Molten metal is transferred from the core wire 12 to the weld pool 13 which solidifies to form the weld deposit 14. The flux 5 provides molten slag 15 which covers the weld deposit 14 as it travels from the electrode 2 to the weld pool 13. Once part of the weld pool 13, the slag 15 floats to the surface and protects the weld from contamination as it solidifies. Once hardened, it must be chipped away to reveal the finished weld.
Turning now to Figures 3 to 7, a prior art MMA electrode holder 1 has been adapted according to the present invention to provide improved shielding to a welding site 7 when welding with a consumable self-shielding welding electrode 2. The electrode holder 1 comprises at least one shroud gas port 16 spaced radially outward from the welding electrode 2. The shroud gas port 16 is mounted relative to the electrode 2 and adapted to allow relative movement therebetween for allowing substantial control of the axial position of the shroud gas port 16 relative to the distal end 17 of the welding electrode 2 during consumption of the electrode 2 during use. Preferably the shroud gas port 16 is adapted to impart to an exiting shroud gas 20 a radially outward component of velocity. In the embodiments as shown in Figures 3 to 5 the electrode 2 is axially translatable with respect to the shroud gas port 16, which is fixedly mounted to the electrode holder 1. However, in the embodiments as shown in Figures 6 and 7 the shroud gas port 16 is axially translatable with respect to the electrode 2, which is fixedly mounted to the electrode holder 1.
In preferred embodiments a drive assembly 18 is provided which is responsive to a user input for axially moving either the shroud gas port 16 or the electrode 2 such that the axial position of the shroud gas port 16 relative to the distal end 17 of the welding electrode 2 is substantially controllable during consumption of the electrode 2 during use. In addition to this movement of either shroud gas port 16 or electrode 2, it will be appreciated that as the welding process proceeds the welding operator must also manually adjust for the change in the length of electrode 2 by changing the position in which the electrode holder 1 is held with respect to the workpiece 4 so as to keep the arc length substantially constant.
Preferably the welding electrode 2 is uniformly fed to the welding site 7 upon user-actuation of the drive assembly 18, as best shown in Figures 3 to 5. A lever 19 disposed on the electrode holder 1 preferably actuates the drive assembly 18. However, a foot-pedal could be utilised for allowing the welding operator to selectively deliver the welding electrode 2 to the welding site 7 on an as-needs basis. Alternatively, the shroud gas port 16 could be retracted instead of feeding the welding electrode 2, as best shown in Figures 6 and 7.
The shroud gas port 16 is preferably adapted to direct the exiting shroud gas 20 in a substantially radially outward direction, i.e. generally 90° to the axis of the welding electrode 2. The electrode holder 1 includes an inner sleeve 21 and an outer sleeve 22 for defining therebetween an annular passage for the shroud gas 20, the shroud gas port 16 being positioned at or near the distal end of the passage. Preferably both the inner sleeve 21 and the outer sleeve 22 circumscribe the electrode 2. At least one inlet 23 is provided for supplying the annular passage with shroud gas 20 from a suitable source, such as a cylinder 24 of compressed gas. The shroud gas supply conduit 25 connecting the cylinder 24 of compressed shroud gas 20 and the electrode holder 1 should be flexible, light, heatproof, and of adequate size to handle the gas flow.
In a further embodiment, as best shown in Figures 8 and 9, the welding electrode 2 is mounted in the electrode holder 1 and a separate hand-held shroud gas port 26 is sleevingly slidably engaged with the electrode 2. As the electrode 2 is burned off and consumed during use the hand-held shroud gas port 26 is manually drawn back towards the proximal end 3 of the electrode thereby to substantially control, and preferably maintain the relative axial position of the shroud gas port 16 with respect to the distal end 17 of the welding electrode 2. It will be appreciated that this particular embodiment is particularly suited for welds which are physically difficult to access. In such circumstances, the welding operator may actually bend the electrode 2 in order to improve access to where the weld is to be deposited; the welder often supporting the free electrode 2 with a gloved hand. However, the present invention allows the welding operator to guide the electrode 2 safely with the hand held shroud gas port 26 whilst simultaneously providing improved shielding to the welding site 7.
In other embodiments the welding electrode 1 may include a fume gas extraction port 27 adapted to receive fume gas from an area surrounding the welding site 7, as best shown in Figures 5 and 7. At least one outlet 30 is provided for extracting the fume gas from the fume gas extraction port 27. The fume gas extraction port 27 is ideally positioned radially intermediate the welding electrode 2 and the shroud gas port 16. Surprisingly, the Applicants have found that by introducing a radially outward component of velocity to the shroud gas 20, together with the extraction port 27, the wall jet flow is substantially contained and the direction of flow along the face of the work being welded is radially inwards. In other words, the shroud gas curtain 20 isolates the fume generation region from the surroundings and allowing the fume gas to be extracted from within the envelope. Whereas, in the absence of the additional shroud gas port 16 and the shrouding gas 20 this flow (the 'wall jet') continues in a radially outward direction. The exiting shroud gas 20 may be considered as a "radial gas jet" forming an "aerodynamic flange" about the welding site.
The shroud gas 20 is preferably chosen from the group consisting of: nitrogen, helium, argon, carbon dioxide or compounds and mixtures thereof. However, the skilled person will appreciate that the composition of the preferred shroud gas depends on the composition of the flux coating 5 on the welding electrode 2. Conventional coatings rely on the presence of air to produce a slag 15 which protects the weld 14. In order not to interfere with the slag forming reactions, in this case the shroud gas 20 would need to be air. The shroud gas flow rate should be about 1 to 50 L/min and, if the apparatus is configured for fume extraction, the fume is preferably extracted at a flow rate of between about 5 to 50 L/min.
The Applicants envisage an MMA welding apparatus adapted according to the present invention which uses a welding electrode in the form of a coated manual metal arc rod. By configuring the shroud gas port to deliver a flow rate of about 15 to 30 L/min of a conventional welding shielding gas, and setting the extraction flow rate to approximately equal the shroud gas flow rate, it is envisaged that an extraction efficiency of at least 70% is possible. In a typical welding process the rate of consumption of the electrode is about 10 to 50 mm/min and the apparatus of the invention could be configured to provide control of the distance of the shroud gas port to tip of electrode to about 25 to 30 mm to provide line-of-sight to the weld.
As discussed in the foregoing, the present invention provides improvements in weld quality. For example such improvements relate to:
• improvement in the resultant weld mechanical properties, i.e. resistance to embrittlement, toughness/ductility, tensile strength and flexural strength, and/or • the weld surface properties, i.e. such as surface oxidation (dross), surface damage, and surface appearance.
The improvements in weld quality are the result of affecting one or more of the following weld characteristics: • porosity;
• discontinuities (fissures or cracks);
• weld consistency; and
• gas pickup (e.g. hydrogen and nitrogen).
Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

CLAIMS:
1. A method for welding with a consumable self-shielding welding electrode, said method comprising the steps of: producing a shroud gas curtain spaced radially outward from said electrode and substantially controlling the axial position of said shroud gas curtain relative to the distal end of said welding electrode during consumption of said electrode during use, said shroud gas curtain comprising a radially outward component of velocity.
2. A method according to claim 1 wherein said welding electrode is adapted to generate an arc-protecting gas curtain around the arc and weld during use/deposition, said electrode being elongate and defining said axis.
3. A method according to claim 1 or claim 2 wherein the relative axial position of said shroud gas curtain and said distal end of said electrode are substantially maintained during burn off of said electrode during use.
4. A method according to claim 3 wherein said shroud gas curtain and the distal end of said electrode are maintained in a substantially coterminous relationship.
5. A method according to claim 3 wherein the distal end of said electrode is maintained relative to said shroud gas curtain such that the distal end of the electrode protrudes from said shroud gas curtain during consumption of said electrode.
6. A method according to any one of the preceding claims including the step of directing the exiting shroud gas in a substantially radially outward direction.
7. A method according to any one of the preceding claims wherein said method provides improved shielding to a welding site.
8. A method according to any one of the preceding claims including the step of extracting fume gas from a position radially intermediate said electrode and said shroud gas curtain.
9. Apparatus for welding with a consumable self-shielding welding electrode, said apparatus comprising: at least one shroud gas port spaced radially outward from said welding electrode, said shroud gas port being mountable relative to said electrode and adapted to allow relative movement therebetween for allowing substantial control of the axial position of said shroud gas port relative to the distal end of said welding electrode during consumption of said electrode during use, said shroud gas port being adapted to impart to an exiting shroud gas a radially outward component of velocity.
10. Apparatus according to claim 9 wherein said welding electrode is adapted to generate an arc-protecting gas curtain around the arc and weld during use/deposition, said electrode being elongate and defining said axis.
11. Apparatus according to claim 9 or claim 10 wherein the relative axial position of said shroud gas port and said distal end of said electrode are substantially maintained during burn off of said electrode during use.
12. Apparatus according to claim 11 wherein said shroud gas port and the distal end of said electrode are maintained in a substantially coterminous relationship.
13. Apparatus according to claim 11 wherein the distal end of said electrode is maintained relative to said shroud gas port such that the distal end of the electrode protrudes from said shroud gas port during consumption of said electrode.
14. Apparatus according to any one of claims 9 to 13 wherein said shroud gas port is movable with respect to said electrode, and said shroud gas port is retracted during burn off of said electrode during use.
15. Apparatus according to any one of claims 9 to 13 wherein said electrode is movable with respect to said shroud gas port, and said electrode is fed or introduced to the welding site during its consumption during use.
16. Apparatus according to claim 14 or claim 15 including a drive assembly for retracting said shroud gas port or feeding or introducing said electrode to the welding site during its consumption during use.
17. Apparatus according to claim 16 wherein a predetermined metered length of said welding electrode is selectively delivered to the welding site upon actuation of the drive assembly.
18. Apparatus according to claim 17 including a lever disposed on a handle of said apparatus or a foot-pedal for allowing the welding operator to selectively deliver the welding electrode to the welding site on an as-needs basis or for retracting the shroud gas port.
19. Apparatus according to claim 17 further including a sensor for automatically maintaining a predetermined axial relationship between the distal end of the welding electrode and the shroud gas port/curtain during consumption of the electrode during use.
20. Apparatus according to any one of claims 9 to 19 wherein said shroud gas port is adapted to direct said exiting shroud gas in a substantially radially outward direction.
21. Apparatus according to any one of claims 9 to 20 including a fume gas extraction port positioned radially intermediate said electrode and said shroud gas port, said fume gas extraction port being adapted to receive fume gas from an area surrounding a welding site.
22. Apparatus according to claim 21 including an inner sleeve and an outer sleeve for defining therebetween an annular passage for said shroud gas, said shroud gas port being positioned at or near the distal end of said passage.
23. Apparatus according to claim 22 wherein said inner sleeve and said outer sleeve circumscribe said electrode.
24. Apparatus according to any one of claims 9 to 23 further including at least one shield gas port adapted to direct a shield gas curtain around said welding electrode and said welding site.
25. Apparatus according to claim 24 wherein said shroud gas or said shield gas is chosen from the group consisting of: nitrogen, helium, argon, air, carbon dioxide or compounds and mixtures thereof.
26. Apparatus according to claim 24 or claim 25 wherein the flow rate of said shroud gas about 1 to 50 L/min.
27. Apparatus according to any one of claims 24 to 26 wherein the flow rate of said shield gas is about 5 to 50 L/min.
28. Apparatus according to any one of claims 24 to 27 wherein the fume is extracted at a flow rate of between about 5 to 50 L/min.
29. Apparatus according to any one of claims 9 to 28 wherein the shroud gas is cooled sufficiently to promote fume gas condensation.
30. Apparatus according to any one of claims 9 to 29 wherein at least a portion of said shroud gas includes a component reactive with a welding fume and/or a
UV light-absorbing component.
31. Apparatus for welding with a consumable self-shielding welding electrode, said apparatus comprising: at least one shroud gas port spaced radially outward from said welding electrode, and a drive assembly responsive to a user input for axially moving either said shroud gas port or said electrode such that the axial position of said shroud gas port relative to the distal end of said welding electrode is substantially controllable during consumption of said electrode during use, said shroud gas port being adapted to impart to an exiting shroud gas a radially outward component of velocity.
32. Apparatus for welding with a consumable self-shielding welding electrode, said apparatus comprising: a shroud gas port axially slidably mountable with said welding electrode, such that, the axial position of said shroud gas port relative to the distal end of said welding electrode is substantially controllable during consumption of said electrode during use, said shroud gas port being spaced radially outward from said welding electrode and adapted to impart to an exiting shroud gas a radially outward component of velocity.
33. Apparatus according to claim 32 wherein said shroud gas port is sleevingly slidably engageable with said electrode.
34. Apparatus according to claim 32 or claim 33 wherein said shroud gas port is hand-held.
35. Apparatus according to claim 34 wherein said shroud gas port is manually drawn back towards the proximal end of the electrode during burn-off of the electrode thereby to substantially control the relative axial position of the shroud gas port with respect to the distal end of the welding electrode.
PCT/AU2008/001424 2007-09-27 2008-09-25 Apparatus and method for manual metal arc welding WO2009039574A1 (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5276242A (en) * 1975-12-23 1977-06-27 Nippon Kokan Kk High speed gas shielded arc welding process
EP0799666A1 (en) * 1996-04-03 1997-10-08 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Process and apparatus for reducing the emission of ozone produced during a gas shielded arc welding operation
JP2003334660A (en) * 2002-05-17 2003-11-25 Babcock Hitachi Kk Narrow groove tig welding method and device
US20040084420A1 (en) * 2002-10-30 2004-05-06 Milburn Richard G. Welding torch
US20040188390A1 (en) * 2003-03-19 2004-09-30 Toyoyuki Satou TIG welding equipment and TIG welding method

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5276242A (en) * 1975-12-23 1977-06-27 Nippon Kokan Kk High speed gas shielded arc welding process
EP0799666A1 (en) * 1996-04-03 1997-10-08 L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude Process and apparatus for reducing the emission of ozone produced during a gas shielded arc welding operation
JP2003334660A (en) * 2002-05-17 2003-11-25 Babcock Hitachi Kk Narrow groove tig welding method and device
US20040084420A1 (en) * 2002-10-30 2004-05-06 Milburn Richard G. Welding torch
US20040188390A1 (en) * 2003-03-19 2004-09-30 Toyoyuki Satou TIG welding equipment and TIG welding method

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