Abstract:
The invention relates to a contact tube ( 29 ) for a welding torch ( 10 ), having a longitudinal axis ( 31 ) along which a through-opening ( 30 ) for guiding a welding wire ( 13 ) from an inlet region ( 37 ) to an outlet region ( 35 ) and from an outlet opening ( 39 ) towards a workpiece ( 16 ) is provided, wherein at least one slot ( 34 ) is provided in the outlet region ( 35 ) for making contact with the welding wire ( 13 ). A contact tube ( 29 ) with improved contacting of the welding wire ( 13 ) is obtained by providing at least one further slot ( 36 ) in the inlet region ( 37 ) of the contact tube ( 29 ), wherein the slot ( 36 ) in the inlet region ( 37 ) is arranged in line with the slot ( 34 ) in the outlet region ( 35 ), and a web ( 38 ), which serves as a pivot point, is formed between the slot ( 34 ) in the outlet region ( 35 ) and the at least one slot ( 36 ) in the inlet region ( 37 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage of PCT/AT2009/000216 filed on May 25, 2009, which claims priority under 35 U.S.C. §119 of Austrian Application No. A 1034/2008 filed on Jun. 30, 2008, the disclosure of which is incorporated by reference. The international application under PCT article 21(2) was not published in English. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a contact tube for a welding torch, having a longitudinal axis, along which a continuous opening is provided for guiding a welding wire from an inlet area to an outlet area and from an outlet opening in the direction of a workpiece, at least one slot being provided in the outlet area for contacting the welding wire. 
     All supplementary materials for greatly varying welding methods are included under the term welding wire. 
     2. Description of the Related Art 
     Manifold contact tubes for welding torches are known from the prior art, which are provided with at least one slot in the area of the outlet opening for the welding wire. In this way, the contact tube becomes flexible in the area of the at least one slot, so that the diameter of the outlet opening can be reduced. A contact force can thus be exerted for contacting the welding wire. Various methods are known for achieving this contact force. 
     For example, a contact tube for a welding torch, which is provided with two slots, is known from EP 1 266 714 A1. The opening for conveying the welding wire is constricted with the aid of a ring, which is pushed over the contact tube in the area of the slots. It is disadvantageous in this case that no readjustment of the contact force is possible, and the outlet opening is expanded again by the resulting abrasion of the welding wire in the contact tube and the set contact force thus can no longer be maintained. 
     A contact tube for a welding torch is also known from U.S. Pat. No. 6,710,300 B2, by which the contacting of a welding wire is to be improved. This is performed in particular by exerting a contact force on the welding wire, in that a part of the contact tube which is provided with two slots is pressed using a spring against a fixed body. It is disadvantageous in this case that the mobility is restricted by the resistance on the fixed body, so that the contact force on the welding wire can only be set to a limited extent and increased abrasion of the welding wire is caused. Furthermore, the replacement of the contact tube is connected with an increased time expenditure, since additional connections of elements to the contact tube must be detached. 
     JP 2004001088 A and WO 2008/018594 A1 describe contact tubes for welding torches, which have, in addition to the slot which runs in the longitudinal direction, vertically situated slots in the outlet area of the welding wire, by which an adaptation of the contact tube to the welding wire can be improved. 
     SUMMARY OF THE INVENTION 
     The object of the present invention comprises providing the most consistent and permanent contacting of the welding wire possible over the service life of a contact tube of a welding torch. Disadvantages of known contact tubes are to be prevented or at least reduced. 
     This object is achieved in that at least one further slot is provided in the inlet area, the slot in the inlet area and the slot in the outlet area being situated aligned, and a web which is used as a pivot point being formed between the slot in the outlet area and the at least one slot in the inlet area. Through the aligned configuration of the slot in the inlet area and the slot in the outlet area, mirror-inverted movement of the parts of the contact tube on both sides of the slots is made possible. It is advantageous in this case that the contact force required for the contacting is automatically readjusted, in that a fixed pre-tension is set in the inlet area of the contact tube. The welding wire can thus be permanently contacted during a welding process, whereby the welding quality is increased. The outlet area is flexible and/or movable due to the slot, whereby the contact tube can be used for various welding wire diameters, within a specific range. The contact force can thus be adapted optimally to the material and the diameter of the respective welding wire. Furthermore, this has the advantage that the conveyance force for the welding wire can be kept minimal and simultaneously an optimum current transfer to the welding wire is ensured. The abrasion of the welding wire and also the abrasion of the opening in the contact tube are thus minimal and/or are compensated for by this flexible closure part, so that permanent contacting of the welding wire is provided. Furthermore, the contact tube can be replaced rapidly and easily. 
     The slot in the outlet area is advantageously situated running along the longitudinal axis up to in front of the outlet opening of the contact tube and subsequently diagonally to the longitudinal axis, so that two jaws which differ in their shape are formed on both sides of the slot. Through such guiding of the slot in the outlet area of the contact tube, protection from contaminants, such as welding spatters, is provided, since the slot does not represent a direct engagement surface. 
     One jaw is advantageously implemented as essentially L-shaped and encloses the outlet opening for the welding wire. 
     According to a further feature of the invention, a contact area, which is adaptable to the diameter of the welding wire, is provided for contacting a welding wire in the outlet area of the contact tube, and the opening of the contact tube is implemented up to the contact area in such a manner that the welding wire can be guided essentially free running from the inlet area up to the contact area in the outlet area. Secure or permanent contacting of the welding wire is thus achieved, since the contact area essentially does not change and a constant electric arc is thus also ensured. 
     According to a further design of the contact tube, a ring-shaped expansion, having an external diameter greater than the remaining external diameter of the contact tube, is provided in the inlet area, and a stop surface is implemented on the side of the expansion oriented toward the outlet opening. This stop surface offers a hold for a fastener, via which the contact tube can be connected to the welding torch. 
     The inner surface of the ring-shaped expansion is preferably implemented as tapering conically toward the opening of the contact tube to receive a corresponding conical adapter part for fastening on the welding torch. By receiving a corresponding conical adapter part in this conical inner surface of the ring-shaped expansion, the contact tube can be spread apart in the inlet area and moved toward one another in the outlet area as a result. This is made possible by the mobility of the contact tube by the configuration of the slots according to the invention in the inlet area and outlet area. Through the mobility of the contact tube, better regulation and transmission of the contact force to the welding wire is also caused. 
     It is also advantageous if the inner surface of the ring-shaped expansion is implemented as curved. The contact between the corresponding conical adapter part and the contact tube is thus improved, from which better current transfer and better heat dissipation also result. 
     A union nut is advantageously provided for fastening the adapter part, so that the inlet area is spread apart by the conical adapter part and the jaws are moved toward one another in the outlet area as a result. 
     The union nut can be implemented so that it is situated as a protective envelope over the outlet area of the contact tube. 
     When the outlet area of the contact tube is implemented as conically tapering toward the outlet opening, a reduction of the area for the adhesion of welding spatters can be achieved. The union nut is also optionally implemented as conical in this area. 
     According to one embodiment, the adapter part has a hole for the welding wire, a cone on the side for use on the conical inner surface, and an external thread on the side diametrically opposing the cone for connection to the welding torch. Through an adapter part implemented in this manner, the contact tube can be used for arbitrary welding torches, since the adapter part is usable as an adapter. 
     An external thread for connection to a corresponding internal thread of the union nut is preferably situated on the side of the cone of the adapter part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is explained in greater detail on the basis of the appended schematic drawings. 
       In the figures: 
         FIG. 1  shows a schematic view of a welder; 
         FIG. 2  shows a welding torch in a schematic exploded view; 
         FIG. 3  shows a sectional view of a first embodiment of a contact tube according to the invention; 
         FIG. 4  shows a perspective view of the contact tube according to  FIG. 3 ; 
         FIG. 5  shows a sectional view of a union nut for fastening the contact tube on a welding torch; 
         FIG. 6  shows a perspective view of the union nut according to  FIG. 5 ; 
         FIG. 7  shows a sectional view of an adapter part for fastening the contact tube on the welding torch; 
         FIG. 8  shows a perspective view of the adapter part according to  FIG. 7 ; 
         FIG. 9  shows a sectional view of the contact tube, which is situated using the union nut and the adapter part on a torch body of a welding torch, before it is fixed; 
         FIG. 10  shows the configuration according to  FIG. 9  after corresponding fixing on the torch body; 
         FIG. 11  shows the configuration according to  FIG. 10  having a welding wire conveyed in the contact tube; 
         FIG. 12  shows a sectional view of a variant of the contact tubes on a tandem welding torch; 
         FIG. 13  shows a sectional view of a further embodiment of a contact tube; and 
         FIG. 14  shows a perspective view of the contact tube according to  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     For introductory purposes, it is noted that identical parts of the variants and embodiments are provided with identical reference numerals. 
       FIG. 1  shows a welder  1  or a welding system for greatly varying processes or methods, such as MIG/MAG welding or WIG/TIG welding or electrode welding methods, double wire/tandem welding methods, plasma or soldering methods, etc. 
     The welder  1  comprises a power source  2  having a power unit  3 , a control device  4 , and a switching element  5 , which is assigned to the power unit  3  and/or the control device  4 . The switching element  5  and/or the control device  4  is connected to a control valve  6 , which is situated in a supply line  7  for a gas  8 , in particular a protective gas such as CO 2 , helium, argon, or the like, between a gas reservoir  9  and a welding torch  10 . 
     In addition, a wire feed device  11 , which is typical for MIG/MAG welding, can be activated via the control device  4 , an auxiliary material or a welding wire  13  being supplied from a storage drum  14  or a wire roll in the area of the welding torch  10  via a supply line  12 . Of course, it is also possible that the wire feed device  11 , as is known from the prior art, is integrated in the welder  1 , in particular in the main housing, and is not implemented as an auxiliary device as shown in  FIG. 1 . 
     It is also possible that the wire feed device  11  supplies the welding wire  13  to the processing point outside the welding torch  10 , for this purpose, a non-fusing electrode preferably being situated for this purpose in the welding torch  10 , as is typical in WIG/TIG welding. 
     The current for establishing an electric arc  15 , in particular a working electric arc, between the non-fusing electrode (not shown) and a workpiece  16  is supplied via a welding line  17  from the power unit  3  of the power source  2  to the welding torch  10 , in particular the electrode, the workpiece  16  to be welded, which is also formed from multiple parts, also being connected via a further welding line  18  to the welder  1 , in particular to the power source  2 , and thus a circuit being able to be established for a process via the electric arc  15  and/or the produced plasma jet. 
     To cool the welding torch  10 , the welding torch  10  can be connected via a cooling loop  19 , with a flow monitor  20  interposed, to a liquid container, in particular a water container  21 , whereby when the welding torch  10  is put into operation, the cooling loop  19 , in particular a liquid pump which is used for liquid situated in the water container  21 , being started and thus the welding torch  10  being able to be cooled. 
     Furthermore, the welder  1  has an input and/or output device  22 , via which greatly varying welding parameters, modes of operation, or welding programs of the welder  1  may be set and/or retrieved. The welding parameters, modes of operation, or welding programs which are set via the input and/or output device  22  are relayed to the control device  4  and subsequently the individual components of the welding system or the welder  1  are activated thereby and/or corresponding target values are specified for the regulation or control. 
     Furthermore, in the illustrated exemplary embodiment, the welding torch  10  is connected via a hose package  23  to the welder  1  or the welding system. The individual lines from the welder  1  to the welding torch  10  are situated in the hose package  23 . The hose package  23  is connected via a coupling device  24  to the welding torch  10 , while in contrast the individual lines in the hose package  23  are connected to the individual contacts of the welder  1  via terminal sockets or plug connections. In order that an appropriate tension relief of the hose package  23  is ensured, the hose package  23  is connected via a tension relief device  25  to a housing  26 , in particular to the main housing of the welder  1 . Of course, it is also possible that the coupling device  24  can also be used for the connection to the welder  1 . 
     Fundamentally, it is to be noted that all of the above-mentioned components do not have to be employed or used for the various welding methods or welders  1 , such as WIG devices or MIG/MAG devices or plasma devices. For this purpose, for example, it is possible that the welding torch  10  can be implemented as an air-cooled welding torch  10 . 
     A greatly simplified construction of a welding torch  10 , which is implemented as a MIG torch, is shown in  FIG. 2 . This exploded view shows the essential components of the welding torch  10 , namely the hose package  23 , the coupling device  24 , a tube elbow  27 , a torch body  28  as the current-conducting part, on which finally a contact tube  29  and a gas nozzle  55  are fastened. The hose package  23  is connected via the coupling device  24  to the tube elbow  27  or the welding torch  10 . 
     The hose package  23  can also be connected to a torch handle, which is connected via the coupling device  24  to the tube elbow  27 . Such a coupling device  24  can also be used for connecting the hose package  23  to the torch handle. The torch handle can also be implemented as an adapter part however, and thus, for example, the welding torch  10  can be fastened to a robot via the adapter part. 
     The tube elbow  27  contains, inter alia, cooling ducts, supply lines for the electrical power, supply lines for the gas  8 , and in particular the supply line  12  or feed device  12  for the welding wire  13 , the so-called core or wire core, this being supplied to the tube elbow  27  via the hose package  23 . The welding wire  13  is therefore conveyed from the storage drum  14  via the feed device  12  or via a corresponding inner hole in the feed device  12  up to the contact tube  29 . This is performed at least by the wire feed unit  11 . In the contact tube  29 , the welding wire  13  is supplied with electrical power, so that an arc welding process can be performed. Accordingly, the contact tube  29  is manufactured from an electrically conductive and essentially wear-proof material, such as copper, copper alloys (tungsten), etc. 
     As is known from the prior art, the contact tube  29  has a continuous axial opening  30  along a longitudinal axis  31  of the contact tube  29 , the opening  30  being able to be divided, for example, into a guide hole  32 , a hole  33 , and an outlet opening  39  for the welding wire  13 —as shown below in  FIG. 3 . For a stable welding process, it is significant that the contacting of the welding wire  13  always occurs as much is possible in the outlet opening  39 , the welding wire  13  being able to run freely over at least a short distance up to there, for example, the length of the hole  33 . The guide hole  32  in the contact tube  29  can also be dispensed with, of course. In these cases, the feed device or wire core  12  already essentially ends in the torch body  28 , i.e., before the welding wire  13  enters the contact tube  29 . The welding wire  13  accordingly runs freely up to the outlet opening  39 , since the hole  33  is implemented as substantially larger than the diameter of the welding wire  13 . Therefore, no contacting of the welding wire  13  with the material of the contact tube  29  typically occurs in the area of the hole  33 , and therefore also no premature current transfer. 
     According to the invention, the contact tube  29  is implemented correspondingly, to be able to achieve the contacting, which is required for a stable welding process, by a force on the welding wire. The exertion of the force can be supported by additional auxiliary means. Through the contact tube  29  according to the invention it is ensured that the welding wire  13  is always contacted at the same point and permanently. 
     The contact tube  29  according to the invention is also implemented so that it can replace a typical contact tube, which is fastened using a screw connection to the torch body  28 . 
     An embodiment of the contact tube  29  is shown schematically in a sectional view in  FIGS. 3 through 9 . The contact tube  29  according to the invention has a slot  34  in the outlet area  35  and a slot  36  in the inlet area  37 . A web  38 , which is used as a pivot point, is formed between the slot  34  in the outlet area  35  and the at least one slot  36  in the inlet area  37 . The slot  34  in the outlet area  35  runs along the longitudinal axis  31  up to shortly before the outlet opening  39  of the contact tube  29  and subsequently diagonally to this axis. Therefore, two different jaws  40 ,  41  result in the outlet area  35 , one jaw  40  being implemented as essentially L-shaped and containing the outlet opening  39 . It is important that the contact tube  29  is further implemented in one piece. 
     The slot  34  in the outlet area  35  and the slot  36  in the inlet area  37  are better visible from the perspective view of the contact tube  29  according to  FIG. 4 . It may also be seen that the slot  34  and the slot  36  are connected and/or separated by a web  38 , the web  38  representing the connection between the inlet area  37  and the outlet area  35 . The opening  30  of the contact tube  29  is formed by the guide hole  32 , the hole  33 , and the outlet opening  39 . The guide hole  32 , the hole  33 , and the outlet opening  39  are each situated concentrically having a conical taper. This is significant in particular for a low-friction and centered transition of the welding wire  13  into the outlet opening  39  of the contact tube  29 , which is implemented in one piece. It is also essential that the diameters of the hole  33  and the guide hole  32  are selected so that no contacting of the welding wire  13  occurs in the hole  33 , but rather first in the outlet opening  39 . For example, the diameter of the hole  33  is three to ten times as large as the diameter of the welding wire  13 . It is thus achieved by the welding wire  13 , which runs freely in the hole  33 , that the welding wire  13  is only contacted in the outlet opening  39 . This has a positive effect in particular on the material transfer and therefore on the entire welding process, since the welding wire  13  is always contacted at the same point. 
     In order that the contacting of the welding wire  13  always occurs at the same point, i.e., in the outlet opening  39 , the effect of the slot  36  in the inlet area  37  is significant. This essentially allows the introduction of a force onto the contact tube  29  and/or the welding wire  13  running therein. The force on the welding wire  13  can be set using a union nut  42  (described below), which is used for fastening the contact tube  29  to the welding torch  10 . 
     It is obvious from  FIG. 9  that the contact tube  29  is mounted using the union nut  42  on an adapter part  49 , which is in turn installed on the torch body  28 . In this case, forces still do not act on the contact tube  29  or on the welding wire  13  guided therein. If the contact tube  29  is fastened on the adapter part  49 , as shown in  FIG. 10 , through the force shown by the arrows  56 , which results through the complete fastening of the union nut  42 , the inlet area  37  is spread apart—as shown by the double arrow  57 , and the slot  34  in the outlet area  35  is compressed and/or the jaws  40 ,  41  are moved toward one another. For complete fastening of the contact tube  29 , the union nut  4 . 2  is rotated until it stops on the stop surface  44  of the ring-shaped expansion  52  of the contact tube  29 . The contact tube  29  has a fixed pre-tension, which allows a variable contact force via the mobile or flexible jaws  40 ,  41 . The welding wire  13  is therefore contacted using the optimum contact force essentially over its entire service life of the contact tube  29 . The contact force for permanent contacting of the welding wire  13  is shown by the arrows  58 . In particular, the jaw  40 , which is formed by the slot  34  in the outlet area  35 , and the jaw  41  in the area of the outlet opening  39  are moved toward one another, so that a diameter of the outlet opening  39  results which is smaller than the diameter of the welding wire  13 . The welding wire  13  conveyed through the outlet opening  39 , as shown in  FIG. 11 , is therefore essentially clamped or the welding wire  13  must press the jaws  40 ,  41  apart. This causes the welding wire  13  to be permanently contacted at the same point. The outlet area  35  therefore produces a defined contact area having at least two contact points formed from the jaws  40 ,  41 . These contact points are located directly adjacent to the hole  33 , i.e., in a first part of the outlet opening  39 . The second part of the outlet opening  39  is located in the L-shaped jaw  40 , which completely encloses the second part of the outlet opening  39  and is essentially used as a guide for the welding wire  13 . This guide can also be insulated correspondingly. 
     The above-described effect is independent of the direction in which the welding wire  13  is conveyed through the opening  30  of the contact tube  29 . The contact tube  29  according to the invention can thus also be used for a CMT (cold metal transfer) welding process, in which the welding wire  13  is conveyed both in the direction of the workpiece  16  and also away from the workpiece  16 . 
     The web  38  is used in such a contact tube  29  as a pivot point and allows the mirror-inverted movement of the parts of the contact tube  29  in the inlet area  37  and outlet area  35 . If the inlet area  37  is spread open, the outlet area  35  or the jaws  40 ,  41  are compressed. The jaws  40 ,  41  are accordingly movable in the defined contact area. The forces required for this purpose are thus transmitted by the web  38  from the inlet area  37  to the outlet area  35 , so that permanent contacting of the welding wire  13  is ensured. The required forces are adapted to the diameter or to a defined range of diameters of the welding wire  13 . In general, the forces result from the relationship between the width of the slot  34  and the width of the slot  36 . The wider the slot  36  in the inlet area  37 , the wider the jaws  40 ,  41  may move away from one another. In contrast, the width of the slot  34  affects how far apart the jaws  40 ,  41  may be pressed by the welding wire  13  and for which welding wire diameter the contact tube  29  is designed, or for which range of welding wire diameters it can be used. These relationships are also dependent on the width of the web  38  or the distance between the slot  34  and the slot  36 . In the case of a narrow web  38 , more force can be transmitted and vice versa. Because of these relationships, the contact tube  29  according to the invention can thus be manufactured, which is adapted to one specific welding wire diameter or to multiple welding wire diameters lying in one range. Permanent contacting can thus be ensured for these welding wires  13 . 
     In addition, however, the exposed slot  34  is not to be contaminated, as is frequently the case by welding spatters, for example. These could also stick together the slot  34 , for example, so that the effect according to the invention would no longer be provided. This is solved according to the invention in that the slot  34  only runs along the longitudinal axis  31  essentially up to the middle of the outlet opening  39  and subsequently runs diagonally to the longitudinal axis  31 , as already noted. The slot  34  thus runs behind the L-shaped jaw  40  and protects it from contamination. 
     As already noted, the contact tube  29  is fastened using the union nut  42  on the torch body  28  or on the adapter part  49 , since the contact tube  29  according to the invention does not have a separate fastening capability, such as a screw connection or a similar feature. The union nut  42  is described in detail in  FIGS. 5 and 6 . The union nut  42  can have a hexagon for operation using a corresponding tool. 
     Fundamentally, the union nut  42  has the form of a dome nut, which on one side has an opening  43  having a diameter, which corresponds to the external diameter of the contact tube  29 , so that the union nut  42  can be pushed over the outlet area  35  of the contact tube  29  up to a stop surface  44 . The stop surface  44  is situated in the inlet area  37  or directly forms the beginning of the inlet area  37 . The contact tube  29  has, in the inlet area  37 , a ring-shaped expansion  52 , whose diameter is greater than the external diameter of the remaining contact tube  29 . The diameter of the stop surface  44  is greater than the external diameter of the contact tube  29 , the diameter of the stop surface  44  corresponding to the internal diameter of the union nut  42 . The contact tube  29  can thus be fastened by the union nut  42  on the torch body  28 . This is preferably performed by a corresponding internal thread  45  in the union nut  42  and an external thread  46  corresponding thereto on the torch body  28 . The ring-shaped expansion  52  of the contact tube  29  has an inner surface  47 , which is implemented as conical toward the opening  33  of the contact tube  29 . This conical inner surface  47  is required to achieve the desired spreading of the inlet area  37 . For this purpose, a conical adapter part  49  corresponding to the conical inner surface  47  is provided. The cone  48  of the adapter part  49  has a minimally greater diameter than the inner diameter of the ring-shaped expansion  52 . When the union nut  42  and thus the contact tube  29  is screwed onto the torch body  28 , the slot  36  is thus pressed or spread apart in the inlet area  37 . This in turn causes the jaws  40 ,  41  in the outlet area  35  to move toward one another and a permanent contact of the welding wire  13  to be achieved. The union nut  42  accordingly exerts a force via the cone  48  of the adapter part  49  on the contact tube  29 , through which a contact force results in the outlet area  35 , as was already described in detail. This contact force finally allows the permanent contacting of the welding wire  13 . 
     Of course, the stop surface  44  can also be in the area of the web  38 , the conical inner surface  47  always being maintained directly at the beginning of the inlet area  37 . The height of the ring-shaped expansion  52  is varied accordingly. Therefore, the placement of the stop surface  44  on the contact tube  29  is preferably adapted to the configuration of the contact tube  29  in the welding torch  10 , the number of the contact tubes  29  in the welding torch  10 , etc. The configuration of the stop surface  44  is dependent in particular on the type of the welding torch  10  and is adapted accordingly thereto. 
     It is also dependent on the type of the torch  10  whether the torch body  28  has a corresponding external thread  46  for receiving the union nut  42 . However, it is currently the case in commercially-available welding torches  10  that they have an internal thread in the torch body  28  instead of the required external thread  46 . 
     Accordingly, the use of the adapter part  49  is necessary, which is screwed into the commercially-available internal thread of the burner body  28  and has the external thread  46  required for receiving the union nut  42 . For such a screw connection, corresponding notches are provided on the adapter part  49 , so that it can be fastened using an open-ended wrench or the like, for example. Therefore, nearly any commercially-available welding torch  10  can be retrofitted with the contact tube  29  according to the invention using the adapter part  49  according to the invention. The adapter part  49  can also be viewed as an adapter. The adapter part  49  is shown in detail in  FIGS. 7 and 8 . The external thread  46  and a second external thread  50  as well as the cone  48  situated on the front side of the adapter part  49  are obvious therefrom. The external thread  50  is used for fastening in the internal thread of the torch body  28  and the external thread  46  is used for fastening the union nut  42 . The cone  48  on the front side of the adapter part  49  causes, during the fastening of the contact tube  29  on the threaded pin  49  using the union nut  42 , the inlet area  37  to be spread apart, so that the outlet opening  39  is adapted to the diameter of the welding wire  13 . The cone  48  on the adapter part  49  and the conical inner surface  47  are adapted to one another in such a way that the outlet opening  39  is adapted to the diameter of the welding wire  13 . Of course, the adapter part  49  also has an opening  51  along its longitudinal axis, which is used for the passage of the welding wire  13 . 
     The adapter part  49  does not have to be implemented as an expendable part, but rather is to be viewed as part of the torch body  28  and not as part of the contact tube  29  or an expendable part. The adapter part  49  is thus a type of extension of the torch body  28 , which relays the welding current to the contact tube  29  and dissipates the heat of the contact tube  29 . 
     The contact tube  29  according to the invention is shown in  FIG. 9 , as it is fastened using the union nut  42  on the adapter part  49 , and the adapter part  49  is connected to the torch body  28 . It is obvious therefrom that the contact tube  29  according to the invention is only fastened using a screw connection on the torch body  28 . No additional effort or disadvantage with respect to typical contact tubes  29  and therefore arises in the case of maintenance or replacement. 
     Further embodiments of contact tubes  29  are shown in  FIGS. 12 through 14 . A so-called tandem welding torch  10  is shown in  FIG. 12 , which has two contact tubes  29  according to the invention. The contact tubes  29  essentially correspond to the above-described embodiment, which are screwed diagonally into an extension  53  of the torch body  28 . A body  54  having a thread can also be implemented, on which the contact tube  29  is in turn diagonally fastened. A union nut  42  which is situated over the outlet area  35  of the contact tube  29  can also be used. The protection from contamination can thus be improved still further. The contact tube  29  is thus essentially enveloped entirely by the union nut  42 , only one opening for the welding wire  13  being provided in the union nut  42 . 
     In addition, it is obvious from the contact tubes  29  shown herein that the slot  34  in the outlet area  35  has a club-like form in the area of the web  38 . This embodiment of the contact tube  29  is shown in detail in  FIGS. 13 and 14 . The mobility of the outlet area  35  or the jaws  40 ,  41  is made easier by the club-like form, since less material is provided in this area. The contact force on the welding wire  13  can also be adapted and/or set and/or influenced by the size of the club-like form of the web  38 . A further feature of this embodiment is the curved inner surface  47  of the ring-shaped expansion  52 . In this manner, independently of the tightening force of the union nut  42 , a contact is always produced between the inner surface  47  and the cone  48  of the adapter part  49 . The current transfer and the heat dissipation between torch body  28  and contact tube  29  is accordingly decisively improved and continuously ensured. This is essentially to be attributed to a consistent contact surface, which is also not changed by manufacturing tolerances, but rather at most displaced. The friction force during the fastening of the contact tube  29  to the union nut  42  is also reduced by the curved inner surface  47 , so that the defined pre-tension always remains consistent, even during a replacement of the contact tube  29 . This can also be provided in the above-described embodiment of the contact tube  29 . 
     In the contact tube  29  according to the invention, the union nut  42  is used as a means for introducing a force onto the contact tube  29 , by which the inlet area  37  is spread apart. Through the force, the outlet area  35  or the jaws  40 ,  41  are compressed, a contact force is exerted on the welding wire  13 , and the welding wire is permanently contacted over the entire service life of the contact tube  29 . Of course, a corresponding gas nozzle  55  which is known from the prior art is also usable in each case. 
     In general, it is also to be noted that the contact tube  29  according to the invention essentially causes a constriction of the outlet opening  39 , so that during conveyance of the welding wire  13  through the outlet opening  39 , a required contact force acts on the welding wire  13 . The contact tube  29  is also movable in a defined area, essentially in the outlet area  35 , because of the acting force. The jaws  40 ,  41  are the basic requirement for the mobility of the contact tube  29 . The contact force can be adjusted by changing the lever conditions on the contact tube  29 . This is performed, for example, by a corresponding configuration of the pivot point (web  38 ) and the force introduction. 
     Known grinding out of the outlet opening  39  is also compensated for in the case of the contact tube  29  according to the invention, since in spite of the grinding out caused by the conveyed welding wire  13 , permanent contacting of the welding wire is ensured. This is to be attributed to the contact force acting on the welding wire  13  being readjusted. For this purpose, the above-described mobility of the contact tube  29  or the fact that the jaws  40 ,  41  always attempt to move toward one another is decisive.