Electric welding guns (e. g., MIG welding guns) are often provided with water cooling systems for cooling, among other things, the nozzle of the torch. If the nozzle is not cooled, molten splatter will adhere to the nozzle and require frequent cleaning or replacement of the nozzle. In a conventional"wet nozzle"cooling system, water (or other liquid coolant) comes into direct contact with the nozzle.

While this system has a high cooling efficiency, it is typically expensive, prone to leak, and requires turnoff of the coolant flow system before the nozzle can beremoved. In a conventional"dry nozzle"cooling system, coolant does not come into direct contact with the nozzle so there is less risk of leakage. Morever, the nozzle can be removed without stopping circulation of the coolant. However, cooling efficiency is reduced.

Figs. 1-3 illustrate a prior art electric welding torch (e. g., a MIG welding torch), generally designated 1, having a"dry nozzle"type cooling system. In this system, a tubular conductor 3 comprising concentric inner and outer tubes 5,7 surrounded by an insulating sheath 9 extends forward from a handle 11 of the gun. A nozzle 13 is held on the conductor 3 by a three-piece nozzle holder generally indicated at 15. The nozzle holder 15 includes an inner metal tube 17, an outer tube 19 of electrically insulating material, and a middle metal sleeve 21 interposed between portions of the inner and outer tubes 17,19. The outer surface of the inner conductor tube 5 is recessed to form a supply channel 23 and a return channel 25 for the flow of coolant into and out of the holder, as indicated by the arrows in Fig. 2. This system is relatively inefficient from a heat transfer standpoint (thus causing the nozzle 13 to run hot), because the insulating tube 19 of the nozzle

holder is disposed between the metal nozzle and the other metal parts of the nozzle holder, which reduces heat transfer from the nozzle to the coolant. A plurality of 0- rings 29 seal against the leakage of coolant when the nozzle 13 is removed.

Summary of the Invention Among the several objects of the present invention may be noted the provision of an electric welding gun having a "dry"nozzle cooling system which provides for more efficient transfer of heat from the nozzle to the coolant so that the nozzle runs cooler for longer life and ease of maintenance; the provision of an improved nozzle holder for use with such an electric welding gun; the provision of such a welding gun and nozzle holder which allow easy removal of the nozzle from the nozzle holder, without leakage of coolant and without the need to shut off the flow of coolant to the torch; the provision of such a nozzle holder which can be used with either manual welding guns or robotic welding guns; and the provision of such a welding gun and nozzle holder which are economical to manufacture.

Generally, a liquid cooled electric welding gun of the present invention comprises a handle, a tubular conductor extending forward from the handle, and a liquid coolant supply passage and a liquid coolant return passage in the conductor. The improvement comprises a tubular nozzle holder surrounding the conductor and secured thereto for removably holding a metal nozzle at a forward end of the conductor. The nozzle holder has an outer metal layer engageable by the nozzle and an inner layer of electrically insulating material disposed between the metal layer and the conductor for electrically insulating the conductor from the nozzle. The nozzle holder defines a liquid coolant chamber in direct fluid communication with the liquid coolant return and supply passages and with the outer metal layer of the nozzle holder to enable direct contact of the liquid coolant with the outer metal layer for efficient transfer of heat

away from the metal nozzle. Seals prevent leakage of liquid coolant from the liquid coolant chamber when the nozzle is removed from the nozzle holder.

The present invention is also directed to a nozzle holder of the type described in the preceding paragraph.

Other objects and features will be in part apparent and in part pointed out hereinafter.

Brief Description of the Drawings Fig. 1 is a partial sectional view of a prior art welding gun, including a handle, conductor tube, nozzle holder and nozzle; Fig. 2 is an enlarged portion of Fig. 1 showing details of the nozzle holder; Fig. 3 is an enlarged section on line 3--3 of Fig. 2; Fig. 4 is partial sectional view of a welding gun of the present invention, including a handle, conductor and nozzle holder for holding a nozzle; Fig. 4A is an enlarged portion of Fig. 4 showing details of the nozzle holder of this inventin; Fig. 5 is an enlarged section on line 5--5 of Fig. 4 ; Fig. 6 is an enlarged section on line 6--6 of Fig. 4 ; Fig. 7 is an enlarged section on line 7--7 of Fig. 4 ; and Fig. 8 is a partial sectional view of a second embodiment of a nozzle holder of the present invention mounted on a conductor of robotic welding gun.

Corresponding parts are designated by corresponding reference numbers throughout the drawings.

Detailed Description of the Preferred Embodiment Referring now to the drawings, and first more particularly to Figs. 4,4A and 5, an electric welding gun (e. g., a MIG welding gun) of the present invention is designated in its entirety by the reference numeral 51. The gun is liquid cooled, water being the preferred and

conventional coolant. The welding gun 59 comprises a handle 53 and a tubular conductor, generally designated 55, extending forward from the handle. The conductor 55 includes an inner conducting tube 59 having an open front end, and a concentric outer conducting tube 61 surrounding the inner conducting tube and terminating short of the forward end of the inner tube. The outer conducting tube 61 is also open at its forward end. The inner and outer conducting tubes 59,61 define supply and return passages 63,65 for liquid coolant. A sheath 67 of electrically insulating material encloses the outer conductor tube 61.

The welding gun 51 also includes a tubular nozzle holder, generally indicated at 71, surrounding the conductor 55 and secured thereto for removably holding a metal nozzle 73 in a position where the nozzle projects beyond the forward end of the outer conducting tube 59. The nozzle 73 is generally cylindric in shape and of conventional construction.

Liquid coolant for cooling the nozzle 73 is delivered from a suitable supply (not shown) via the supply passage 63 and returned to the supply by means of the return passage 65. As shown in Fig. 5, these passages 63,65 are formed by a pair of flats 77,79 milled in the otherwise circular outer surface of inner conducting tube 59. The flats 77,79 extend lengthwise of the inner tube 59 and are spaced from the inner wall of the outer conducting tube 61 to form passages 63 and 65 for the flow of coolant. (The supply and return passages 63,65 are sealed from one another due to the close fit of the circular inner surface of the outer conducting tube 61 with the curved portions of the outer surface of the inner tube 59.) The supply and return passages 63,65 could be formed in other ways, such as by grooves in the outer surface of the inner conducting tube 59, or flats or grooves in the inner surface of the outer conducting tube 61, or by spacing the inner and outer tubes 59,61 to form an annular gap therebetween with suitable barriers to divide the supply and return flows.

In accordance with the present invention, the nozzle holder 71 has an outer metal layer formed by a sleeve 81 of brass, for example, having an annular shoulder 83 connecting the rearward portion of the sleeve and a reduced diameter forward portion of the sleeve. The forward portion of the sleeve 81 has an external diameter only slightly less than the inside diameter of the nozzle 73 so that the nozzle can be slidably pushed onto the sleeve to a position abutting the shoulder 83 and retained in this position due to the friction fit between the nozzle and the sleeve. The fit is sufficiently close to provide for good heat transfer between the sleeve 81 and the nozzle 73.

The nozzle holder 71 also has an inner layer formed by a tubular insulator 87 of electrically insulating material (e. g., a glass fiber composite) disposed between the outer metal sleeve 81 and the conductor 55 for electrically insulating the conductor from the nozzle 78. The insulator 87 has a rearward portion sized for a close sliding fit on the outer conducting tube 61 and a forward portion having a close sliding fit on the inner conducting tube 59. The outer metal sleeve 81 is fixedly secured to the insulator 87, as by crimping or swaging the rearward portion of the sleeve against the insulator, the latter being of slightly reduced diameter at this location as illustrated in Fig. 4.

The insulator 87 has internal threads 91 at its forward end which mate with threads 93 on the inner conductor 59, the insulator being threadable to a point where two internal shoulders 97,99 on the insulator engage the forward end of the outer tube 61 and the forward end of the conductor sheath 67.

The inner layer (insulator 87) of the nozzle holder 71 and the inner conducting tube 59 form a liquid coolant chamber 103 which communicates with the supply and return passage 63,65 defined by the inner and outer conducting tubes 57,61. Specifically, the coolant chamber 103 is defined at least in part by an internal recess (e. g., an annular groove 105 in Figs. 4A, 6 and 7) in the insulator 87

at a location forward of internal shoulder 97. One or more (preferably several) holes 111 are provided in inner layer 87 to enable coolant in the chamber 103 to move into direct contact with the outer metal sleeve 81 of the nozzle holder to maximize the transfer of heat away from the nozzle 73.

By way of illustration, six such holes may be provided at equally spaced intervals around the nozzle holder 71. The radially outer ends of these holes 111 immediately adjacent the outer metal sleeve 81 are chamfered to increase the area of the outer layer 81 exposed to the coolant. Since there is no thermal barrier between the coolant and the nozzle 73 (only a single metal layer 81 having a high thermal conductivity), the transfer of heat away from the nozzle is maximized, resulting in more efficient cooling of the nozzle for longer life and less frequent maintenance.

The nozzle holder 71 is provided with a plurality of seals 115 (e. g., five seals) to ensure that the nozzle 73 remains"dry", meaning that there will be no leakage from the liquid coolant chamber 103 even when the nozzle is removed. These seals 115 are annular seals (e. g., O- rings), two of which are received in grooves in the inner surface of the insulator 87 for sealing engagement with the inner and outer conducting tubes 59,61, as shown in Fig.

4A, and three of which are received in grooves in the outer surface of the insulator 87 for sealing engagement with the outer sleeve 81 of the nozzle holder 71. The arrangement is such that the nozzle 73 can be removed without leakage and without shutting off the flow of coolant to the coolant chamber 103.

In use, the nozzle holder 71 is threaded onto the conductor 55 into the position shown in Figs. 4 and 4A. The nozzle 73 can be slidably positioned on the nozzle holder 71 either before or after installation of the nozzle holder on the conductor 55. Liquid coolant is then circulated through the welding gun, with coolant being delivered to the coolant chamber 103 via the supply passage 63 and removed from the coolant chamber via return passage 65. The holes 111 in the

inner layer 87 of the nozzle holder 71 allow coolant in the chamber 103 to come into direct contact with the outer metal sleeve 81 which is, in turn, in direct contact with the nozzle 73 to be cooled. As discussed above, this arrangement provides for very efficient transfer of heat away from the nozzle 73 so that it remains relatively cool.

Indeed, the cooling efficiency of this design is believed to rival that of a"wet nozzle"cooling system, but without the drawbacks (e. g., leakage).

Fig. 8 shows an alternative embodiment of the nozzle holder, generally designated 121, adapted for use with robotic welding equipment. This construction of this holder 121 is similar to that of the holder 71 described above except that the outer metal layer 123 is secured to the inner insulating layer 125 by pins 127 (instead of crimping), and the forward end portion of the outer layer 123 is threaded at 131 for a threaded connection with a nozzle 133. Also, the seal arrangement is slightly different.

When introducing elements of the present invention or the preferred embodiment (s) thereof, the articles"a","an", "the"and"said"are intended to mean that there are one or more of the elements. The terms"comprising","including" and"having"are intended to be inclusive and mean that there may be additional elements other than the listed elements.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.