Abstract:
A welding torch, in particular a tungsten inert gas (TIG) welding torch, comprises a body portion ( 2 ) in which is housed an elongate, non-consumable electrode ( 10 ) the tip of which projects from the body portion ( 2 ), clamping means ( 8 ) within the body portion ( 2 ) for releasably gripping the electrode ( 10 ), control means ( 18 ) selectively movable between a first position in which the clamping means ( 8 ) hold the electrode ( 10 ) in an operative position, and a second position in which the clamping means ( 8 ) are released from the electrode ( 10 ), and an ejector mechanism ( 16 ) which, with the control means ( 18 ) in its second position, can be actuated to move the electrode ( 10 ) axially within the body portion ( 2 ).

Description:
TECHNICAL FIELD 
     This invention relates to welding torches, and more particularly to such torches incorporating non-consumable electrodes, typically of tungsten. 
     BACKGROUND OF THE INVENTION 
     Tungsten inert gas (TIG) welding torches conventionally comprise a body portion in which is housed an elongate tungsten electrode one end of which projects from the body portion for welding purposes. 
     More particularly, the tungsten electrode is held in a split collet, itself housed within the body portion of the torch, the split tip of the collet being received within a tapering bore such that, when the collet is pushed forwards within the bore, the split tip thereof is urged into clamping engagement with the electrode to hold the electrode in its operative condition. 
     Conventionally, the split collet is pushed forwards by means of a threaded plug or backstop which is screwed into the body member to react against the rear end of the collet. 
     Ideally, the projecting tip of the tungsten electrode should not touch the parent metal during the welding process. However, in practice, and primarily because welding is a manual process, there is often contact, the electrode becomes contaminated, and it is necessary to remove the electrode from the torch, either to grind off the contamination or to replace the electrode. 
     In theory, when the threaded backstop is partially unscrewed within the body portion, the clamping effect of the split collet on the electrode should be released, whereby the electrode can be pulled out of the ceramic nozzle end of the body portion by the user&#39;s gloved forefinger and thumb. 
     However, in practice, the heat generated during the welding process is often such that the split collet becomes adhered to the tungsten electrode, whereby unscrewing of the backstop does not release the split collet from the electrode, and the electrode cannot be removed from the torch other than by completely dismantling the torch. 
     Clearly this is a tedious, time consuming and inefficient exercise, which can also be painful to the operator because the torch assembly is extremely hot. 
     Furthermore, it is difficult to ensure that the decontaminated or replacement electrode is accurately positioned in the body portion when the torch is hot. 
     U.S. Pat. No. 3,097,290 discloses a welding torch substantially in accordance with the pre-characterising clause of claim  1 . 
     SUMMARY OF THE INVENTION 
     It would be desirable to be able to provide a welding torch in which the non-consumable electrode thereof was more readily handleable than heretofore. 
     According to the present invention there is provided a welding torch comprising a body portion in which is housed, and from one end of which projects the tip of, an elongate, non-consumable electrode, clamping means within the body portion for releasably gripping the electrode, a plug member selectively movable between a first position in which the clamping means hold the electrode in an operative position, and a second position in which the clamping means are released from the electrode, and an ejector mechanism which, with the plug member in its second position, can be actuated to move the electrode axially within the body portion, characterised in that the ejector mechanism comprises a slide member mounted in the plug member to be axially slidable therein, and a push rod mounted to the slide member to extend axially therefrom and through the plug member into the body portion, the push rod being co-axial with the electrode and adapted to engage the end of the electrode remote from the tip, whereby, with the plug member in its second, release position, the slide member and push rod can be moved axially within the plug member and the body portion to move the electrode axially from its operative position. 
     In a preferred embodiment of the invention, the clamping means comprises a split collet surrounding an intermediate extent of the electrode and having a foremost operative position within the body portion clamping the electrode and a release position axially rearwards of the operative position. 
     Conveniently the plug member is screwed into the body portion and has a first, operative position in which an end face thereof engages the split collet and urges the collet into clamping engagement with the electrode, and a second, release position rotationally displaces from the first position in which the end face thereof is displaced axially rearwardly of the first position to enable release of the collet from the electrode. 
     Preferably, the mounting of the push rod to the slide member is such that, for a given axial position of the slide member within the plug member, the push rod can be moved axially relative to the slide member. 
     Conveniently axial movement of the push rod relative to the slide member is achieved by rotation of the slide member within the plug member. 
     In one embodiment of the invention, the slide member is internally threaded, the push rod extending from an externally threaded head member housed within the slide member, the push rod extending through the plug member to be axially movable but non-rotatable relative thereto whereby, on rotation of the slide member within the plug member, the head member and push rod are moved axially relative to the slide member and plug member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal section through a part of a conventional TIG welding torch; 
     FIG. 2 is an exploded view, partly in longitudinal section, of a welding torch according to the invention, and 
     FIG. 3 is a longitudinal section through the ejector mechanism of the torch of FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 there is shown a conventional TIG welding torch comprising an elongate body portion  2  containing a gas lens  4  in which is formed an axial recess the forward end  6  of which is of generally tapering conical configuration. 
     A split collet  8  is housed within the recess, the configuration of the split front end of the collet  8  conforming with that of the forward end  6  of the recess. 
     An elongate tungsten electrode  10  of circular cross-section extends through the collet  8  with the front tip thereof projecting from the body portion  2 . 
     The torch is completed by a plug  12  which screws into the rear end of the body portion  2  and has a fully inserted operative position in which an end face  14  thereof engages the end of the collet  8  and pushes the collet  8  axially forwards within the body portion  2  such that the split front end thereof is urged into the forward end  6  of the recess whereby the collet  8  securely grips the electrode  10  and retains it in an operative position. 
     In order to release the collet  8  from its grip on the electrode  10 , the plug  12  is unscrewed to disengage the end face  14  thereof from the collet  8  whereby the collet  8  can move axially rearwardly within the recess. 
     However, as detailed above, the split collet  8  often becomes adhered to the electrode  10  whereby the grip of the collet  8  on the electrode  10  is not released on unscrewing of the plug  12 . The extent of the electrode  10  projecting from the body portion  2  is usually short, making it difficult, if not impossible, to pull the electrode  10  out manually. 
     The invention provides means for overcoming these problems, and will be described with reference to FIGS. 2 and 3. 
     The plug  12  of the conventional torch is replaced by an ejector mechanism indicated generally at  16  and comprising a plug member  18  having a threaded portion  20  with an end face  22  for screwing into the rear of the body portion  2  in the manner of the plug  12 . 
     The plug member  18  is hollow and houses a generally hollow cylindrical slide member  24  therein the rear end of which projects rearwardly from the plug member  18 . The member  24  is slidable axially within the plug member  18  between a foremost position determined by abutment of the front end of the slide member  24  with a front end face of the hollow interior of the plug member  18 , and a rearmost position determined by abutment of a shoulder  26  on the slide member  24  with a rear end wall  28  of the plug member  18 . 
     As well as being slidable axially within the plug member  18 , the slide member  24  is rotatable in said member  18  for reasons which will become apparent. 
     The hollow interior of the slide member  24  is internally threaded and houses therein an externally threaded cylindrical head or piston  30  to which is secured an elongate push rod  32  of non-circular, preferably hexagonal, cross-section, the push rod  32  extending through a correspondingly shaped bore in the plug member  18  to project forwardly therefrom, whereby the push rod  32  is guided for axial movement relative to the plug member  18 , but rotational movement relative to the plug member  18  is restrained. 
     It will thus be appreciated that the construction of the ejector mechanism as described is such that, for a given position of the plug member  18 , the slide member  24  together with the piston  30  and the push rod  32  can be moved axially backwards and forwards within the plug member  18  between the foremost and rearmost positions of the slide member  24  within the plug member, and, for a given axial position of the slide member  24  within the plug member  18 , the slide member  24  can be rotated within the plug member  18  whereby the threaded piston  30  and the push rod  32  are moved axially relative to the plug member  18  in a direction determined by the direction of rotation of the slide member  24 . 
     In use, the ejector mechanism  16  is screwed into the body portion, the end face  22  of the threaded portion  20  of the plug member  18  engaging the rear end of the collet  8  whereby, with the plug member fully screwed into the body portion  2 , the split end of the collet  8  grips the electrode  10  and secures it in its operative position with the front tip thereof projecting from the body portion  2 . In this condition of the torch, the ejector mechanism  16  is inoperative. 
     When it is desired to remove or adjust the electrode  10 , the plug member  18  is unscrewed, typically about one quarter of a turn, to disengage the end face  22  of the threaded portion  20  from the collet  8  and whereby the grip of the collet  8  on the electrode  10  is released. The slide member  24 , together with the piston  30  and push rod  32 , can then be moved as a unit further into the body portion  2  whereby the free end of the push rod  32  engages the rear end of the electrode  10  and pushes the electrode forwards out of any remaining grip by the collet  8  and further out of the front end of the body portion whereby the electrode can be readily gripped and totally withdrawn from the torch. 
     Thus, it will be appreciated that the ejector mechanism  16  enables a considerable axial force to be applied to the electrode  10 , either by pushing or impacting upon the slide member  24 , whereby any remanent gripping of the electrode  10  by the collet  8  can be overcome, and removal of the electrode  10  from the body portion  2  is readily achieved for decontamination or replacement purposes. 
     On insertion of the electrode  10  into the body portion  2 , and prior to clamping of the electrode  10  by the split collet  8 , the axial position of the electrode  10  in the body portion  2  can be accurately set by means of the ejector mechanism  16 . More particularly, and with the slide member  24  in a given axial position within the plug member  18  with the free end of the push rod  32  engaging the inner end of the electrode  10 , rotation of the slide member  24  moves the push rod axially relative to the body portion  2  whereby the precise axial position of the electrode  10  can be fine tuned. Once the desired position is reached, the plug member  18  is screwed into the body portion  2  to engage the collet  8  and clamp the electrode  10  in that position. 
     Thus there is provided a welding torch which gives the operator complete control over movement of the tungsten electrode within the torch when previously there was none. Total removal is readily achieved despite potential adherence to the clamping means, while adjustment of stick-out length is greatly simplified and can be set extremely accurately. 
     Clearly the precise construction of the ejector mechanism  16  could differ from that described and illustrated without departing from the scope of the invention. In particular the means for achieving axial movement of the push rod may take a variety of different forms, for example by making the push rod itself externally threaded to be rotatable in a threaded nut carried by a slide member, the nut being restrained from rotation with the slide member but axially movable therewith. 
     Other modifications and variations will be apparent to those skilled in the art.