CA1316225C - Brazing tongs - Google Patents

Abstract

ABSTRACT

A hand held electrically powered brazing tool comprises a fixed electrode and a moveable electrode. The carbon contacts for each electrode are conical and are received in conical sockets in the electrodes. A liner protects the sockets from heat erosion. the carbon contact holders are water cooled. The moveable electrode comprises an air actuated piston within an electrically insulating cylinder. The cylinder of the moveable electrode and the fixed electrode are joined by gear hose clamps permitting their easy separation.

Description

BRAZING TONGS

This invention relates to a tool for braze welding cupreous parts by clamping them between electrically heated contacts.
The work clamping carbon contacts of conventional hand-held brazing tongs are dovetailed to their holders. No matter how precise may be the original dovetail fit, the electrical connection between the carbon contact and its holder is not perfect. With the tongs' continued operation, the white-hot contact erodes its holder's dovetail surface to the condition where the electrical connection will not conduct sufficient electric current to adequately heat the carbon contact. Hence the brazing filler material will not fuse. At this stage the carbon contact holder must be replaced or its dovetail refurbished.
The carbon contact holders of conventional hand-held brazing tongs are not water cooled. To avoid the tongs' overheating, the brazing is restricted to an intermittent operation. Indeed, to avoid the tongs' overheating it must be externally cooled in a water bath after each ~oint is brazed. No production brazing job can tolerate this intermittent mode of operation.
The moving electrode of conventional hand-held brazing tongs is moved by a hand-operated device. Besides requiring the full employment of the operator's best hand, the hand-operated device is slow and awkward to use and depends on the operator's skill to apply and maintain the proper work clamping force throughout each joint's brazing. Such a hand operated device is , ~

of complex construction and is costly to manufacture.
In some lnstances the area to be welded is inaccessible to conventional hand-held brazing tongs since the moving and fixed electrodes are no'L designed to be separated. Furthermore, the maximum and minimum gap between the moving and fixed electrode contacts of these tongs is fixed; accordingly, any given tongs will not be usable with all work pieces, since work pieces come in a wide variety of sizes.
This invention seeks to overcome drawbacks of known brazing tongs.
According to this invention there is provided a hand held tool for brazing a work piece comprising: a fixed electrode;
an electrode ~electably moveable into contact with a work piece with air pressure in order to clamp the work piece between said moveable electrode and said fixed electrode; means to supply electrical power to said fixed and moveable electrodes; and means to water cool said electrodes.
In the figures which illustrate example embodiments of this invention, figure 1 is a side view of a brazing tongs made in accordance with this invention, figure 2 is a top view of a portion of figure 1, figure 2a is a top view of a portion of figures 2, figure 3 is a side sectional view along the lines III-III of figure 2, figure 4 is a side sectional view of a portion of figure 3, figure 5 is a top view of another portion of figure 1, figure 6 is a ~ide sectional view along the lines VI-VI of figure 1 3 t S22 ) figure 7 is a longitudinal sectional view of a portion of figure 6, figure 8 is a bottom view of a portion of figure 6, figure 9 is sectional view along the lines IX-IX of figure 8, and figure 10 is a side view of a portion of figure 1.
By way of overview, the electrode carbon contacts of this brazing tongs are conically socketed to their holders. This simple conical-socket mounting ensures a permanently tight fit between the carbon contacts and their holders. This permanent tight-fitting mounting ensures a permanent perfect electrical connection between the carbon contacts and their holders. Hence, maximum electric power is permanently delivered to the contacts to en~ure the brazing tong's maximum operating efficiency.
A conical socket liner protects the socket's wall from heat erosion through contact with the white-hot carbon contact.
Hence, the socket wall never require refurbishing and, therefore, the socket liner and the carbon contact dimensions are s~andardized.
The carbon contact holders of this invention are efficiently water cooled and hence the tongs can braze large joints continually without overheating. Also, the contact-holder parts can now be soft-solder assembled without danger of the solder melting during the tongs' operation.
The moving electrode of this brazing tongs is air operated. Since the moving electrode's outer tube serves as the operating piston rod, the air-operating mechanism is simple, compact and easily constructed. The mechanism's standard coil spring retraction also simplifies its operation and construction.
The simple thumb operated three-way air valve simplifies the control of the mechanism. The work clamping force of this mechanism i9 easily controlled by regulating the air supply pressure.
The moving and fixed electrodes of this brazing tongs are separated by simply undoing two standard gear hose clamps.
This feature permits this tongs to be used on special jobs requiring the electrodes be separated for the tongs' access to the work. This simple clamping feature is also used to adjust the work clamping gap to suit the height of the individual work-piece. Hence, the electrode moving device is more compact because it now needs to provide only a short work-clamping stroke.
This brazing tongs' simple design facilitates its manufacture from standard readily available materials requiring little or no preparation. Furthermore, all current carrying components are socketted into other such components and soft soldered in place, which requires little skill to manufacture and provides a good electrical contact.
Turning to figure 1, a brazing tong 1 comprises a moving electrode assembly 2 which is clamped to a fixed electrode assembly 3 by hose clamps 3a.
The fixed electrode assembly is detailed in figures 2 and 3. Turning to figures 2 and 3, the fixed electrode assembly comprises brass cooling water inlet tube 9, brass cooling water outlet tube 10, brass foot 4, copper conical socket liner 16a, and electrode carbon contact 21a. With reference to figure 2a, the brass foot comprises cooling water inlet 6a connected to socket 1 3 1 6 2 2 ~

7 by passageway 5a and cooling water outlet 6b connected to socket 7 by passageway 5b. Socket chamfers 8 provide for the soft-solder sealing of cooling water inlet tube 9 and cooling water outlet tube 10 to the cooling water inlet 6a and outlet 6b, respectively. The socket 7 provides a sliding fit for the outside diameter of brass insert 12; this insert is detailed in figure 4 and, by reference to figure 4, is seen to have outside diameter 11, an annular recess 13, and an interior conical socket 15.
Returning to figure 3, insert 12 is shown soft soldered into socket 7. With insert 12 in place, a cooling water conducting channel 14 is formed between the annular recess 13 of the insert and the wall of socket 7. The conical socket 15 (seen in figure 4) of the brass insert 12 provides a tight fitting mount for conlcal copper liner 16a. Since the liner' 8 taper matches that of the conical socket 15, their assembled interface forms an excellent electrical connection. The copper liner receives electrode carbon contact 21a. The contact 21a is conical and, again, matching of the tapers of the liner and contact provides an excellent electrical connection. The taper of the conical socket 15 is just sufficiently shallow for friction to retain the liner and electrode carbon contact after the brazing tong has been operated so as to have been subjected to the normal work clamping force (which acts to push the contact into the liner).
Cooling water injected into tube 9 through union half 24a flows in the direction of arrow 26a into passageway 5a (seen in figure 2a), around channel 14, through passageway 5b (seen in figure 2a) and out tube 10. Hose barb connector 25 of tube 10 may be connected to a drain hose. The hose barb connector is a 1 3 1 6 2 f j .

standard brass fitting which is soft-solder socketted to tube 10.
The carbon contact softens somewhat at operating temperatures; the conical shape of the socket of the brass insert resists the softened contact pushing through the socket. The copper liner is expendable and shields the wall of socket 15 from erosion by the white-hot carbon contact.
The portions of insert 12 proximate contact 21a are most susceptible to heat erosion. As seen in figure 3, the liner 16a pro~ects above the top of the foot 4; this projecting portion of the liner dissapates heat and therefore reduces the operating temperature of the portion 22 of the wall of insert 12 proximate the contact 21a which would otherwise be particularly vulnerable to heat-accelerated erosion.
Since the brass insert 12 is protected from erosion by liner 16a, the electrical connection between the socket wall 18 (seen in figure 4) and the liner 16a remains sound ensuring constant maximum power being delivered to the electrode carbon contact and maximum efficiency for the brazing tongs.
Furthermore, there is no need to remachine the brass insert 12.
To maintain good operating electrical efficiency, the copper liner must be periodically replaced because its inner wall gradually heat erodes with prolonged operation of the tongs.
The end of tube 10 which is soft soldered into the blind socket 6b (seen in figure 2a) of foot 4 is notched at 23; this end notch opens tube 10 to the passageway 5b (seen in figure 2a) in foot 4. A ~imilar end notch in tube 9 opens it to the passageway 5a in foot 4. A standard brass threaded plumbing union half 24a is soft-solder socketted to the free end of tube 9 and a brass ,~ , ,~
.

13162.`5 hose-barbed connector 25 is soft-solder socketted to the free end of tube 10.
Power is supplied to the fixed electrode by electrifying tube 9 at union half 24a. To minimize electrical resistance and maximize efficiency, tubes 9 and 10 are electrically connected by way of brass rod 27 which is soft-soldered between them. Brass rod 27 also prevents tubes 9 and 10 from being squeezed together under the force of 8ear hose clamps 3a (shown in figure 1).
The moving electrode assembly is detailed in figures 5 and 6. This assembly comprises a cylinder 28, concentric tubes 44 and 50 and an electrode head 46. The concentric tubes and head act as a piston 63. The cylinder 28 is detailed in figure 10.
With reference to figure 10, the cylinder comprises a key-way 42 which provides for positive keying of the trapezoidal cross-section air valve assembly 43. As well the cylinder has grooves 40 which accommodate spring clips 41a, 41b for reasons which will become apparent hereinafter. The cylinder 28 is manufactured from standard fabric-reinforced resin tubing. Due to its composition, the tubing does not conduct electricity and hence the cylinder electrically insulates the brazing tong's two electrodes.
Furthermore, the moving electrode's high electric current cannot induce a power-robbing and heating circulating electric current around the cylinder's wall. The tubing may carry close diametral dimensional tolerances so that the cylinder requires no diametral machining. Also such tubing is dimensionally stable and remains straight.
With reference to figure 1 as well as figure 6, it is noted that the simple clamping device (gear hose clamps 3a) for the fixed and moveable electrode assemblies provide for easy ad~ustment of the electrode contact gap length 53 in the extended and retracted position of piston 63.
The air-valve assembly 43 is detailed in figure 7.
Turning to figure 7, the valve assembly has a brass housing 30 which accommodates a standard normally closed three-way poppet cartridge air valve 19 such that the stem 33 of the valve projects through one end of the housing. The housing also has a pressurised air inlet 38 and a venting port 36 which communicates between the interior of cylinder 28 (of figure 6) and chamber 35.
0-rings 34 provide an air tight seal between the valve 19 and the housing 30 in order to seal off a chamber 35. The valve has an exhaust port 32 communicating with chamber 35; the valve also has an inlet through end 29 communicating with chamber 35. A spring 39 biases the valve a8ainst one end of the housing 30 exposing exhaust 32 to atmosphere. In view of the construction of the air valve assembly, cylinder 28 i9 open to the atmosphere through exhaust port 32 unless the valve stem 33 is depressed. When the valve stem is depressed, exhaust port 32 is closed so that pressurized air input to pressurized air inlet 38 is admitted to the cylinder via port 36. The valve assembly i9 anchored in place with epoxy which also effects an air seal between the wall of the cylinder 28 and the valve assembly. The valve housing is positioned so that it just clears the moving electrode's outer tube 44, as seen in figure 6.
Returning to figures 1, 5 and 6, the moving electrode a3sembly comprises a brass cooling water inlet tube 50 concentric ln brass tube 44 so as to form an annular cooling water outlet 1 3 1 6 ? ~ ' - 9 - 05074-l RDF

between the two tubes. The side of tube 44 proximate the outboard end 200 of the tongs has an opening 58. A cast brass saddle hose fitting 61 is clamped over tube 44 with two gear hose clamps 62 such that its outlet 65 is positioned over opening 58. A gasket 60 is interposed between the saddle of fitting 61 and tube 44 such that the hole of the gasket is positioned over opening 58. The gasket 60 is made of fabric reinforced sheet rubber which forms a water seal between the saddle and tube 44. A stop 71 for the moving electrode is secured to tube 44 diametrically opposite the saddle hose fitting 61 by means of the aforementioned clamps 62.
The inboard surface 70 of stop 71 acts as a stop limiting the axial movement of the moving electrode toward the fixed electrode by contact with the outboard end of cylinder 28. Furthermore, flange 72 of the fitting restricts the rotation of tube 44 by contacting one or other of tubes 9 or lO of the fixed electrode assembly (seen in figure 1). Stop 71 is made of an electrically insulating material such as fibre reinforced resin so that it does not short the moving electrode assembly to the fixed electrode assembly. The outboard end of tube 44 is sealed to inner tube 50 by way of brass gland 68 which is dimensioned with a ma~or diameter for a sliding fit inside tube 44 and a minor diameter for a sliding fit over tube 50 and is soft soldered in place. A
standard brass union half 24b is soft-solder socketted to the outboard end of tube 44.
The details of the brass moving electrode head 46 (which have béen omitted from figure 6) are detailed in figures 8 and 9.
Referring to figures 8 and 9, head 46 comprises a core which is sheathed by a brass tubular cover 45; the cover is soft soldered .....
..

in place. The head has a socket 49 which accommodates the cooling water inlet tube 50 and a socket 55 which accommodates tube 44.
l'hese tubes are soft soldered in place. A conical socket 47 of the head is for reception of conical liner 16b and a conical carbon contact 21b (both seen in figure 6). It is noted that the liner and contact are identical to liner 16a and contact 21a of the fixed electrode assembly (seen in figure 3). Socket 49 (receiving tube 50) communicates with cylindrical chamber 51.
Diametrically opposite channels 52 communicate with chamber 51 and open into annular flow reversing header 54. Socket 55 (receiving tube 44) communicates with cylindrical chamber 56. Diametrically opposite channels 57 communicate with chamber 56 and open into the annular flow reversing header 54.
Referencing figures 6, 8 and 9, cooling water in~ected into the outboard end of tube 50 flow~ in the direction of arrow 26b through chamber 51 to channels 52 and the flow reversing header 54. From header 54, the water ~lows through channels 57 to the annular space between tubes 50 and 44 via chamber 56. The cooling water discharges from the annular space to outlet 65 of saddle hose fitting 61. A drain hose may be clamped over the barbs of the outlet 65.
Returning to figures 5 and 6, union half 24b is soft solder socketted to the ouboard end of tube 50 and qupplies both electrical power and cooling water to the moving electrode just as an identical union half supplies the fixed electrode. Since the inner and outer tubes are electrically connected at both ends they both share the current delivered to the carbon contact 21b so that the power delivered to the contact is maximized as is the 1 31 6~L'__~
- ll - 05074-1 ~DF

operating electrical efficiency.
A nylatron (a tm) plastic besring 73a is retained in the c~linder 28 at its outboard end by a standard spring ring retainer 41a which i8 received within the aforereferenced groove 40 proximate the outboard end of the cylinder. Similarly, a nylatron plastic bearing 73b is retained in the inboard end of the cylinder by an identical spring ring retainer 41b received within a groove 40 proximate the inboard end of the cylinder. The bearings snugly fit the bore of the cylinder and provide a sliding fit for outer tube 44~ Bearing 73a backs up a standard rubber U-packing air seal 76a. Since this U-packing adapts to reasonably toleranced diameter~, neither the bore of cylinder 28 nor the outside dlameter of tube 44 need be machined to better the manufacturer's tolerances.
A pi~ton piece 77 has a tapped hole by way of which set screw 81a locks the piston piece to tube 44, thus the piston piece acts as an enlargement on piston 63. The piston piece may be manufactured by parting off a ~uitable length of suitably dimensioned and toleranced standard fabric reinforced resin tubing. To avoid the need to machine either diameter of the piston piece 77, the tube from which the piston piece is parted may have a nominal bore 1/32 inches greater than the nominal outside diameter of tube 44 and a nominal outside diameter 1/16 inches less than the nominal inside diameter of the cylinder 28.
The piston piece 77 ~upports a standard rubber U-packing seal 76b. The bearing 73a with its U-packing seal 76a and the piston piece 77 with its identical U-packing seal 76b air seal a section of the annular space between the cylinder and tube 44 1 3 1 6 2 2 ~) indicated at 84. It will be noted that annular space 84 communicates with the air valve assembly 43.
A bumper 82 may be parted off from the same tube as the piston piece; the bumper has a tapped hole by way of which set screw 81b locks the bumper to tube 44. The bumber allows the free axial flow of air around it. The bumper limits retraction of the piston 63 by contacting the air valve assembly 43. A standard coil spring 83 provides a retracting force on the piston 63 by acting between piston piece 77 and bearing 73b.
To operate the brazing tongs, a cooling water supply and a source of electric power is connected to the union half 24a of the fixed electrode assembly 3 and to union half 24b of the moving electrode assembly 2. Each of these connections may take the form of a flexible copper cable surrounded by a rubber water hose which i8 connected to the union half through a special adapter connected to a companion union half. Electrical power to the tongs may be controlled through the clo~ing of a power supply circuit breaker operated by a foot controlled switch. A pressure regulated air ~upply is connected to inlet 38 of air valve assembly 43. A work piece with overlapping metal parts to be brazed may be pre-flaxed and loaded with brazing material and then positioned between the contacts 21a and 21b; the stem 33 of the air valve assembly i9 then depressed to subject the sealed annular space 84 to supply air pressure. The air pressure acting on piston piece 77 pushes the pi~ton 63 toward the work piece 80 that the work piece is clamped between carbon contacts 21a and 21b. The foot controlled switch may then be operated to energise the tongs. Due to the electrical resistance of the carbon contacts, the current heats J ~ .
~, .

1 ~ 1 62 ~ ) the carbon contacts white hot which raises the work piece to its brazing temperature. When the braze is complete, the tongs may be de-energised. All the while the cooling water continues to flow. When the brazing material has solidified, the air valve assembly stem 33 may be released to allow the sealed chamber 84 to exhaust to atmosphere whereupon the coil spring 83 acting between bearing 73b and piston piece 77 causes the piston 63 to retract in the cylinder until the bumper 82 contacts the air valve assembly.
The direction of the cooling water flow may be reversed to that described. Other modifications will be apparent to those skilled in the art, accordingly, the invention is defined in the claims.

~ 3 t 622~

SUPPLEMENTARY DISCLOSURE

The gear hose clamps 3a of figure 1 could be replaced by other means permitting easy separation of the fixed and moveable electrode assemblies such as nuts, bolts and toggles.
Besides providing for easy maintenance, the ability to separate the two assemblies is required on some jobs for the tongs to gain access to the work.
The contacts 21a and 21b are usually of carbonaceous material but could be an exotic metallic alloy depending on the braze application.
The fabric reinforced resin tubing from which cylinder 28 is con~tructed is unaffected by the mild heat and flame to which the end of the cylinder proximate the work piece may be subjected during a normal brazing operation of the tongs. It may be economical to mould individual cylinders from different material having similar properties to the advantageous properties described in connection with the fabric reinforced resin tubing.
; Cooling water could be supplied to each of the fixed and moveable electrode assemblies separately. Alternatively, especially for light duty brazing, the cooling water can be connected to circulate through the elements in series. Since the tongs operate at an alternating current voltage of less than twenty volts, the cooling water conducts no current.
The conical socket of the electrode head and electrode foot can be chromium plated over nickel to ensure that the wall of the socket will not be burn-corroded through contact with the white hot brazing contact. Hence the plated socket wall .
,~

1 3t 62 :' permanently provides a perfect electrical connection for the brazing contact. Also, the consumable brazing contact can now be produced to fixed standard dimensions without danger of ever having a less than perfect fit into its holder socket.
In the figures which illustrate further example embodiments of this invention, figure 11 is a side view of another embodiment of a brazing tongs made in accordance with this invention, figure 12 is a top view of a portion of figure 11, figure 13 is a side sectional view along the lines XIII-XIII of figure 12, figure 14 is a side sectional view of a portion of figure 11, figure 15 i9 a side view of another portion of figure 11, figure 16 is a bottom view of a portion of figure 13, figure 17 is a side sectional view along the lines XVII-XVII of figure 16, and figure 18 is a side view of figure 16.
Like parts in figures 11 through 18 have been designated with like reference numerals to those of the corresponding parts of figures 1 through 10.
Considering the fixed electrode assembly, with reference to figure 14, the conical wall 118 of insert 112 is chromium plated over nickel to ensure that the white hot contact 21a does not burn-corrode the wall 118. Both insert faces 119 and 120 are also chromium plated over nickel to ensure that burn-corrosion does not undermine the plating around the edges of socket wall 118.
Considering the moveable electrode assembly, with 1 3 1 6 2 2 ~

reference to figures 13 and 15, the wall 140a of each groove 140 in cylinder 128 which is directed toward the bore of the cylinder is tapered to facilitate the installation of the U-packing seals 76a and 76b. Cylinder 128 has a port 85 which may be directly connected to a standard commercial three-way normally closed air valve (not shown). This air valve may be supplied from an external regulated pressure source and is finger operated to supply air to, or exhaust air from, the sealed section 84 of the cylinder.
Referencing figures 16 through 18 as well as figure 13, the wall 147a and floor 147b of conical socket 147 of electrode head 146 are chromium plated over nickel as is flange face 86 to ensure against burning corrosion. The outside diameter 148 of the core 146a of the head 146 is a sliding fit into the bore of tube 44, The core is soft soldered into tube 44 at the flange 148 of the core. Tube 50 is soft soldered into socket 149 of the core 146a. Socket 149 connects with cylindrical chamber 151.
Diametrically opposite longitudinal channels 152 connect with chamber 151 via transverse openings 153. Channels 152 open into the annular flow reversing header 154 (illustrated in phantom in figure 18) formed when the head is assembled by insertion of the core into tube 44. Diametrically opposite channels 157 open into the annular space between tubes 44 and 50. The other end of channels 157 open into the annular flow reversing header 154.
Opening 58 in tube 44 receives a standard cupreous hose barbed elbow 186 which may be brazed in place.
Cooling water entering tube 50 of the moveable electrode assembly enters chamber 151 then flows through opening 153 and 1 3 1 6 2~ ~

channels 152 to the flow reversing header 154. From header 154, the water returns along the two channels 157 to the annulus between tubes 44 and 50, exiting the moveable electrode through elbow 86.
Referring to figures 11 through 13, a stop 171 is affixed to tube 44 by gear hose clamp 192. The inboard face of the stop limits the extent to which the moving electrode head 146 may move toward the fixed electrode foot 4 by striking the outboard end of cylinder 128. Furthermore, the flange 172 of the stop acts to limit the rotation of piston 163 by contacting one of the tubes of the fixed electrode assembly. The stop may be made of any commercially available material which is an electric insulator, durable and mouldable or machinable. The clamp 192 permits easy adjustment of the limit of the extension of the electrode head toward the electrode foot.
Gear hose clamp 194 i5 clamped to the tube 44 and limits the retraction of the piston 163 (away from the electrode foot) by striking the inboard face of cylinder 128. This clamp permits the easy adjustment of the limit of retraction.
Bearings 173a and 173b are retained in either end of the cylinder 128. Bearing 173b has an air vent hole 87.
The U-packing seals 76a and 76b seal a pressurisable space 84 in the cylinder. Hole 85 in the wall of cylinder 128 communicates with this pressurizable space.
The operation of the brazing tongs of this embodiment is similar to that described in connection with the first embodiment of figures 1 through 10, however, with this second embodiment pressure regulated air may be supplied through opening t 316?2 1 85 by a standard commercial air valve in order to ~ove the piston 163 in the direction of the electrode foot.

~' '',: . ' ~ ' ,

Claims (33)

1. A hand held tool for brazing a work piece comprising:
- a fixed electrode;
- an electrode selectably moveable into contact with a work piece with air pressure in order to clamp the work piece between said moveable electrode and said fixed electrode;
- means to supply electrical power to said fixed and moveable electrodes; and - means to water cool said electrodes.

2. The tool of claim 1 wherein said fixed electrode and said moveable electrode are releasably joined to permit ready separation and reattachment.

3. The tool of claim 1 wherein said moving electrode and said fixed electrode are releasably joined to facilitate adjustment of the length of the minimum and maximum gap between the two electrodes.

4. The tool of claim 1 wherein said fixed electrode has a foot with a conical socket carrying a fitted conical liner and wherein said conical liner carries a fitted conical electrode contact and wherein said moveable electrode has a head with a conical socket carrying a fitted conical liner and wherein said conical liner carries a fitted conical electrode contact.

5. The tool of claim 4 wherein said means to cool said electrodes comprises means to circulate water around said conical socket of said foot and said conical socket of said head.

6. The tool of claim 4 wherein said cooling means comprises a channel around said conical socket of said foot and a first tube for supplying cooling water to one end of said channel and a second tube for carrying cooling water away from the other end of said channel.

7. The tool of claim 6 wherein said first tube is made of an electrically conductive material and terminates in a connection for supplying cooling water to said first tube and electric power to the wall of said tube.

8. The tool of claim 7 wherein said second tube is made of an electrically conductive material and wherein said first and second tubes are electrically connected over at least most of their length.

9. The tool of claim 5 wherein said cooling means comprises a channel around said conical socket of said head, one end of said channel opening centrally of said head and the other end of said channel opening proximate the periphery of said head, said cooling means further comprising a third tube connected to the central opening end of said channel and a fourth tube concentric with, and surrounding, said third tube wherein the annulus between said third and fourth tubes forms a connection to said channel opening proximate the periphery of said head.

10. The tool of claim 9 wherein said third tube is made of an electrically conductive material, projects from said fourth tube, and terminates in a connection for supplying cooling water to said third tube and electric power to the wall of said third tube.

11. The tool of claim 4 wherein said moveable electrode comprises a piston incorporating said head, said piston retained within an insulating cylinder by bearing means.

12. The tool of claim 11 including a first air seal at the end of said cylinder distal from said foot and an enlargement on said piston forming a second air seal between said cylinder and said piston spaced from said first air seal in order to form a pressurisable zone within said cylinder.

13. The tool of claim 12 including an air valve for connection to a source of pressurized air for selectively pressurizing said pressurisable zone in order to drive said piston to a work piece clamping position.

14. The tool of claim 13 including a stop to limit the travel of said piston in the direction of said work piece.

15. The tool of claim 14 including biasing means to bias said piston away from said work piece clamping position.

16. The tool of claim 15 including means to restrain said piston from rotation.

17. The tool of claim 4 wherein said conical liners are expendable and protect said sockets from erosion.

18. The tool of claim 1 wherein said fixed electrode comprises an electrode contact, a cupreous foot body and two cupreous tubes connected to said foot body for supplying coolant and electric power to the foot body, the sides of said cupreous tubes being connected with a cupreous joining member.

19. The tool of claim 6 wherein said moveable electrode comprises a piston incorporating said head, said piston retained within a insulating cylinder by bearing means and wherein said first tube and said second tube of said fixed electrode are arranged side-by-side to form a cradle for said insulating cylinder.

20. The tool of claim 9 wherein said fourth tube is made of an electrically conductive material and terminates, proximate said projection of said third tube from said fourth tube, in an electrically conductive gland which water seals said annulus.

21. The tool of claim 20 wherein said fourth opens to a drain fitting proximate said annulus gland.

22 CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE

22. The tool of claim 1 wherein said fixed electrode has a foot with a conical socket carrying a fitted conical electrode contact and wherein said moveable electrode has a head with a conical socket carrying a fitted conical electrode contact.

23. The tool of claim 22 wherein the taper of said fixed electrode conical socket and said moveable electrode conical socket is sufficiently shallow to allow the contact to be retained by friction.

24. The tool of claim 23 wherein the conical walls of said fixed electrode conical socket and said moveable electrode conical socket are chromium plated over nickel.

25. The tool of claim 24 wherein the faces of said electrode foot and head adjacent said conical walls are chromium plated over nickel.

26. The tool of claim 22 wherein said cooling means comprises a channel around said conical socket of said foot and a first tube for supplying cooling water to one end of said channel and a second tube for carrying cooling water away from the other end of said channel.

27. The tool of claim 26 wherein said moveable electrode comprises a piston incorporating said head, said piston retained within an insulating cylinder by bearing means and wherein said first tube and said second tube of said fixed electrode are arranged side-by-side to form a cradle for said insulating cylinder.

28. The tool of claim 27 wherein said piston comprises concentric inner and outer tubes joined at one end to said head and wherein said head has a cooling channel joined at one end to said one end of said inner tube and joined at its other end to the annulus formed between said inner tube and said outer tube.

29. The tool of claim 28 wherein said piston carries an adjustable retraction stop between said cylinder and said head for abutting said cylinder to limit the retraction of said head toward said cylinder.

30. The tool of claim 29 wherein said piston carries an adjustable extension stop for abutting said cylinder to limit the extension of said piston and wherein said extension stop includes a flange for contacting either said first tube or said second tube in order to restrict the rotation of said piston.

31. The tool of claim 30 wherein said cylinder has a pressurizable zone between an enlargement on said piston and the end of said cylinder remote from said head.

32. The tool of claim 31 including biasing means to bias said piston to a retracted position whereat said retraction stop abuts said cylinder.

33. The tool of claim 32 wherein said pressurizable zone includes a passageway whereby an air valve may selectively direct pressurized air to said pressurizable zone or exhaust said pressurizable zone to atmosphere in order to selectively extend said piston of said moveable electrode.