AU6551401A - Earth/ground attachment for welding and cutting equipment - Google Patents

Description

Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

.e o Name of Applicant: Actual Inventor(s): Address for Service: Invention Title: Tanjant Tool Co. Pty Ltd Anthony N. THURSTON DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, Victoria 3000.

"Earth/Ground Attachment for Welding and Cutting Equipment" Details of Associated Provisional Application(s): No(s): PR0339 filed 25 September 2000 The following statement is a full description of this invention, including the best method of performing it known to me/us: P:\OPER\RSH\PR0339-O.spc.doc-28/08/) I -2- EARTH/GROUND ATTACHMENT FOR WELDING AND CUTTING

EQUIPMENT

The present invention relates to an earth/ground attachment for welding and cutting equipment operating on the basis of an electrical arc.

Welding involving the use of an electrical arc, such as manual arc welding (MAW), tungsten inert gas (TIG), and metal inert gas (MIG) welding processes, and plasma cutting processes involve the transfer of the working current in a full circuit from the power source of the equipment, to the workpiece and back to the power source via an earth/ground cable.

Hereinafter such equipment will be collectively referred to as "arc equipment", which term •will include within its scope any other welding or cutting equipment which operates by generation of an electrical arc.

The quality of the weld or cut depends significantly on having an effective earth.

Poor earthing can result in various problems including irregular weld metal transfer, sputtering, and arc failure. All arc equipment of the type discussed uses an earth/ground :"attachment for coupling the earth/ground cable to the workpiece and a poor earthing S* 20 connection to the workpiece can cause the attachment device to heat or spark and in some cases cable burnout can occur as a result of heating resulting from electrical resistance within the attachment system.

Earth/ground attachment devices may need to handle very high currents, typically in the range of 400 to 500 amperes and a poor earthing connection can cause irreparable damage to the attachment device itself. Prior forms of attachment devices are principally in the form of spring tongs, screw clamps or magnetic. With tong-type and clamp-type attachment devices a poor earthing contact can result in the establishment of a secondary circuit to the workpiece back through the device itself resulting in heating and/or arcing effects within the device and this can easily lead to permanent damage. In the case of a clamp-type device, arcing within the screw part of the device can even result in the screw part becoming welded in place, thereby making subsequent removal of the device P:\OPER\RSH\PR0339-O0.spe.doc-28/0)8/ -3extremely difficult. Likewise, magnetic-type devices can have significant problems in presenting a good contact with the work piece due to accumulation of particles of metallic debris and the like and with these devices poor earthing contact with the working surface can result in significant heating of the device and in some instances the device can become welded to the work surface.

The present invention provides an earth/ground attachment for use with arc equipment as discussed above and which substantially prevents damage to an associated clamp should a poor earth connection be established with the workpiece.

According to the present invention, there is provided an earth/ground attachment for arc equipment, said attachment comprising a contact body for establishing electrical i contact with a workpiece, said body being adapted to be electrically coupled to an earth/ground cable, and an electrically insulating mounting for mounting the body to a clamping pad of a clamp such that the clamping pad is maintained insulated from direct electrical contact with the contact body whereby to prevent a secondary circuit being established to the workpiece via the clamp when the contact body is clamped to the workpiece.

20 Advantageously, the mounting includes means for releasably attaching the mounting to the clamping pad.

S. In one form of embodiment of the invention, the insulated mounting is adjustable for mounting to clamp pads of different shapes and/or sizes. In this form the mounting advantageously comprises opposed clamping jaws engageable with opposed parts of the clamping pad by relative movement of the jaws into clamping engagement with the pad by operation of a screw device causing relative movement between the two jaws. The screw device may comprise one or more clamping screws which may also provide securement of the contact body to the insulated mounting. The contact body may also include means for guiding the clamping jaws for relative movement.

P:\OPERSH\PR0339-O0.sp.doc-2808101 -4- In another form of embodiment the insulating mounting consists of an insulated body having a recess to receive a clamp pad of predetermined size and shape and means for retaining the pad captive within the recess.

Although for simplicity of construction the insulating mounting of both embodiments is formed from a suitable rigid or semi-rigid plastics material, in alternative forms the mounting may be partially formed from a metallic material but suitably coated or laminated with an insulating material on the parts thereof in contact with the pad in order to ensure electrical isolation between the contact body and the pad.

Embodiments of the invention will now be described, by way of example only, .:00with reference to the accompanying drawings, in which:- Figure 1 is a perspective view of an earth/ground attachment in accordance with a first embodiment of the invention; 15 Figure 2 is an exploded view of the attachment of Figure 1 and showing, by way of example, a form of clamp to which the attachment can be mounted; Figure 3 is a longitudinal section through the attachment, the section being on line A-A of Figure 4; Figure 4 is a transverse section through the attachment, the section being on line B- B of Figure 3; Figure 5 shows the attachment mounted to the clamp; Figure 6 is a perspective view of a second embodiment of an attachment in accordance with the invention; Figure 7 is an exploded view of the attachment of Figure 6; Figure 8 is a perspective view showing the attachment of Figure 6 mounted to one suitable form of clamp shown by way of example.

The earth/ground attachment 2 of Figures 1 to 5 is adjustable and is designed for use with a wide range of available or industrial clamps, one example of which is shown at 4 in Figures 2 and 5. These clamps are conventionally used for clamping workpieces and are widely available. Although there can be significant size P:\OPER\RSH\PR0339-OO.sp.do-28/ IO8 I and shape variation in the clamping pads of different clamps of these general types currently available, the adjustability of the attachment as will subsequently be described enables the attachment to be used with a significant proportion of currently available clamps of these types.

The attachment 2 comprises a contact body 6 of a highly conductive robust metal such as brass. The body 6 consists of a contact block 8 having an outer contact surface for engagement with a surface of the workpiece. At one end of the contact block 8 there is formed an integral terminal portion 12 having a through-passage 14 for receiving the end of the earth/ground cable 16 which is clamped therein by means of grub screws 18. The contact block 8 is configured to provide a relatively large contact area for the contact surface 10. Advantageously, the contact surface 10 is formed with a longitudinallyi extending groove 20, for example of V-section to facilitate the application of the attachment to a curved surface of a workpiece. Smaller grooves 22 extending laterally across the contact surface 10 at either side of the longitudinal groove 20 facilitate displacement of small particulate matter on the work surface upon manipulation of the attachment to thereby reduce the likelihood of poor surface contact arising from surface .:e.ei contamination. The contact body 6 is coupled to an adjustable insulated mounting 24 by which the attachment 2 can be secured to a pad 4a of the clamp 4. As a result of this 20 insulated mounting, the contact body 6 is completely electrically insulated from the clamp itself and in the event of a poor contact being established between the contact surface and the work surface a secondary circuit cannot be established back to the workpiece through the clamp itself. Under these conditions where a secondary circuit is unable to be established via the clamp to another part of the workpiece (as frequently occurs in conventional clamp-type attachment devices), in the event of a poor contact either no arc will be able to be struck by the equipment or a very weak arc will be struck. In either case, this will be immediately apparent to the operator who can then take appropriate action to remedy the poor contact.

In the embodiment shown, the adjustable insulated mounting 24 comprises opposed inner and outer jaws 26,28 each composed of an insulating material such as a rigid or semi- P:\OPER\RSH\PRO339-OX).sp.doc-28/08/)I -6rigid plastics. The mounting 24 consisting of the two jaws 26,28 is coupled to the contact body 6 to ensure firm attachment between the mounting 24 and the body 6 and the two jaws 26,28 are, as will be described subsequently, designed to grip over opposite sides of a clamping pad 4a of the clamp in order to firmly secure the attachment to the pad.

In the embodiment shown, the means for attaching the adjustable mounting 24 to the contact body 6, comprises a rail 30 of undercut cross section extending longitudinally along the inner surface of the contact block 8 and formed integrally therewith. Locating grooves 32 extend longitudinally through the rail 30. The inner jaw 26, which is a fixed jaw, abuts against the terminal portion 12 of the block and includes a longitudinal extension 26a of T-shaped cross section which is seated on the rail so that it covers the oupper surface of the rail (with reference to the orientation shown in the drawings), with the downwardly-projecting stem 26b of the T-section engaging in the longitudinal grooves 32 in the rail to effect proper lateral location between these components. It is however to be 15 understood that in alternative embodiments other means for effecting appropriate lateral location between these components could be used. The outerjaw 28, which is the movable jaw, is mounted on the extension 26a for slidable movement along the extension, the jaw 28 having inwardly-directed formations 28a which engage within the opposed grooves defined at opposite sides of the rail 30 in order to secure the jaw 28 to the rail 30 while 0 20 facilitating longitudinal movement of the jaw 28. A pair of clamping screws 36 extend through aligned apertures in the outer and inner jaws 26,28 into threaded apertures 38 in the terminal portion 12 of the block, with the heads 36a of the screws engaging the outer part of the outerjaw 28. It will be understood that with a clamp pad 4a located between the two jaws 26,28 tightening of the screws 36 will cause the jaws 26,28 to be clamped into tight engagement with the pad 4a and at the same time will ensure tight engagement of the mounting 24 formed by the two jaws to the contact body 6.

In the embodiment shown, each of the jaws 26,28 is of elongate form in a direction transverse to the clamping direction, with the jaws being of undercut profile so that the jaws can engage over and hold captive the opposite edge portions of a pad of the clamp.

The primary clamping surfaces 26c,28c of the two jaws 26,28 are of substantially planar P:AOPERtSISHPR03394),spe.doC-28/08/0 I -7form whereby the jaws will firmly grip either a rectangular pad as incorporated in typical F-type clamps or circular or oval pads as commonly incorporated in G or C-type clamps.

The undersurface of the undercut section is inclined as shown at 26d and 28d and these inclined surfaces 26d,28d can also act as clamping surfaces against an adjacent surface of the pad and in some instances clamping may be effected just by these surfaces without the edge of the pad being engaged by the primary clamping surfaces 26c,28d. The face of each jaw 26,28 is provided with a central notch 26e,28e which facilitates centring of the clamp pad 4a relative to the jaws. The form of the jaws just described enables the jaws to fit onto a wide range of shapes and sizes of pad and also to pads of differing thicknesses whereby the attachment can be fitted onto a wide range of industrial clamps currently available. It will be understood that when fitted onto the clamp pad no part of the clamp pad or any other part of the clamp will be in electrical contact with the contact block.

*gee :Prior earth/ground contact devices of gripper or clamp-type have been purpose- 15 built to provide the contact arrangement and the clamping or gripping mechanism. In contrast, the contact attachment of the embodiment described can be used with a wide range of already existing industrial clamps as will be found in most workshops and in S.particular an operator can select a clamp most suited to the particular type of workpiece and then temporarily mount the attachment to the pad of that particular clamp.

The attachment of the embodiment described above can be mounted on a clamp **.pad in a number of different orientations and also the cable can be inserted into the terminal portion 12 from either direction and this does provide significant versatility in use.

The embodiment just described is suitable for mounting on a wide variety of different clamps and is capable for use in high current applications. The embodiment shown in Figures 6 to 8 is of somewhat simpler construction of lower cost and is specifically designed for use with conical-type clamp pads of a predetermined diameter and is particularly suitable for lower current applications. The attachment of this embodiment comprises a contact block 50 of a highly conductive metal such as brass. The P:\OPER\RSHPR03394.0scd-28//01 -8contact surface 51 of the block 50 is formed with a series of grooves 5 1la extending across the surface to facilitate the displacement of small particulate matter on the work surface. In the embodiment shown the block is of generally circular section although other forms may adopt a different cross section or shape. The block 50 is formed with a diametrical passage 52 for receiving the end of the cable, with the cable being clamped in the passage by means of a screw 54. The block 50 is coupled to a mounting 56 of an insulating material for mounting on a conical pad 60a of a clamp 60. As shown, the mounting 56 consists of a body having a cavity 56a which fits over the clamp pad 60a. The lower face of the clamp pad 60a engages the base 56b of the cavity 56a and the clamp pad 60a is secured within the cavity 56a by tapered grub screws 62 threadedly mounted in the body to pass into the interior of the cavity 56a to contact the upper face of the pad 60a whereby the pad 60a is held captive between the base 56b of the cavity 56a and the ends of the screws 62. The mounting 56 is formed from a rigid or semi-rigid plastics material.

Although the contact block 50 can be secured to the mounting 56 in a number of different ways, in the embodiment shown this is conveniently achieved by snap-fitting an annular rib 64 at the underside of the mounting 56 in a peripheral groove formed around a .ooooi recess 50a in the upper surface of the block 20 The cavity 56a within the mounting 56 is designed to suit a specific diameter of clamp pad 60a and a range of mountings to suit different diameter pads may be provided.

In particular it is envisaged that a range of just two sizes to receive pads of either millimetres or 30 millimetres in diameter will facilitate usage with a reasonable number of currently available clamps of C or G type. The form of coupling particularly described to couple the contact block to the mounting enables the same contact block to be attached to mounting bodies with cavities of different diameter.

Although the attachment just described is particularly designed for temporary attachment to the pad of a clamp, nevertheless this form of embodiment could, if desired, be permanently attached to the clamp pad whereby the clamp and attachment is supplied pre-assembled to a user.

P:\OPER\RSH\PR0339-)0.spe.doc-28R08 I -9- The embodiments have been described by way of example only and modifications are possible within the scope of the invention.

Throughout this specification and claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers.

o**o *o*

Claims (12)

1. An earth/ground attachment for arc equipment, said attachment comprising a contact body for establishing electrical contact with a workpiece, said body being adapted to be electrically coupled to an earth/ground cable, and an electrically insulating mounting for mounting the body to a clamping pad of a clamp such that the clamping pad is maintained insulated from direct electrical contact with the contact body whereby to prevent a secondary circuit being established to the workpiece via the clamp when the contact body is clamped to the workpiece.

2. An attachment according to claim 1, wherein the insulating mounting includes means for releasably attaching the mounting to the clamping pad.

3. An attachment according to claim 2, wherein the insulating mounting is adjustable :15 for mounting to clamp pads of different shapes and/or sizes.

4. An attachment according to claim 3, wherein the insulating mounting comprises opposed clamping jaws engageable with opposed parts of the clamping pad by relative movement of the jaws into clamping engagement therewith.

An attachment according to claim 4, further comprising a screw device for effecting relative movement between the two jaws into clamping engagement with the pad.

6. An attachment according to claim 5, wherein the screw device comprises one or more clamping screws extending in the direction of relative movement of the jaws.

7. An attachment according to any one of claims 4 to 6, wherein the contact body also includes means for guiding the clamping jaws for said relative movement.

8. An attachment according to claim 1 or claim 2, wherein the insulating mounting P:\OPER\RSH\PR0339-00.spe.doc-28/08/0I -11 consists of an insulated body having a recess to receive a clamp pad of predetermined size and shape, and means for retaining the pad captive within the recess.

9. An attachment according to any one of claims 1 to 8, wherein the contact body is releasably attached to the insulating mounting.

An attachment according to any one of claims 1 to 9, wherein the insulating mounting is formed from a rigid or semi-rigid plastics material.

11. An attachment according to any one of claims 1 to 9, wherein the insulating mounting comprises a metallic material coated or laminated with an insulating material on the parts thereof in contact with the pad to ensure electrical isolation between the contact body and the pad.

12. An earth/ground attachment substantially as hereinbefore described with reference to the accompanying figures. DATED this day of 2 8 th day of August 2001, 20 TANJANT TOOL CO. PTY. LTD. By its Patent Attorneys: DAVIES COLLISON CAVE S S S