US 3083289 A
Description (OCR text may contain errors)
CRGSS REFERENCE SEARCH R9055 March 26, 1963 w, MUNRO ETAL 3,083,289
PLASMA JET CONVERTER FOR ARC WELDERS Filed Jan. 18, 1960 United States Patent 3,083,289 PLASMA JET CONVERTER FOR ARC WELDERS William D. Munro, Taunton, and James R. Barker, Rehoboth, Mass., Donald E. Ellis, Santa Monica, Calif., and Joseph Gibola, Valley Falls, R.I., assignors, by mesne assignments, to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Jan. 18, 1960, Ser. No. 3,092 2 Claims. (Cl. 21975) This invention relates to plasma jet converters, and with regard to certain more specific features to such converters for conventional tungsten inert-gas-shielded arc welders.
Among the several objects of the invention may be noted the provision of a device for converting the electrode holder of a conventional tungsten inert-gas-shielded electric welder into a high-temperature plasma jet torch for applications such as melting high-melting point substances, including refractory metals, oxides or other materials in solid, powder or other forms for fabrication, coating, spraying, cutting and the like; the provision of a device of the class described which is operable with high-density currents at comparatively low voltages and at extremely high temperature without damage to the welders to which the device may be attached; and the provision of a device of the class described which is of low cost, simple in form and adapted for convenient attachment and detachment to and from conventional welders without disabling them for use again as electric arc welders. Other objects and features will be in part apparent and in part pointed out hereinafter.
The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of which will be indicated in the following claims.
In the accompanying drawings, in which one of various possible embodiments of the invention is illustrated,
FIG. 1 is a side elevation of the device applied to a conventional type of tungsten inert-gas-shielded arc welder holder;
FIG. 2 is a plan view of FIG. 1, parts being shown in section;
FIG. 3 is a cross section taken on line 3-3 of FIG. 2; and
FIG. 4 is a fragmentary rear elevation of parts of FIG. 1.
Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.
There are various commercial forms of conventional tungsten inert-gas-shielded arc welders to which the invention is applicable. As will be apparent to those skilled in the art, all such welders have so-called electrode holders including nozzles for ejecting an annulus of arc-shielding inert gas such as helium around their electrode tips. Such holder assemblies are adapted to be manually held. The particular welder assembly chosen for purposes of describing the invention is a tungsten inert-gas welding equipment known as a Standard Airco H50A Heliweld Holder, made by the Air Reduction Company. It is in connection with such a holder as an example that the present device is described as a conversion attachment.
Referring now more particularly to the drawings, there "ice is shown at numeral 1 a round tapered body portion of a conventional electrode holder such as above referred to. The body 1 has a stepped groove at 2 and a shoulder at 4, behind which is an enlargement 6. Along its central axis XX is interiorly supported an electrode 3, composed for example of a inch diameter rod of tungsten. This electrode is held in axial position by means of a collet cap 5 and associated conventional internal collet parts not necessary to describe, being known. Threaded to the other end of the body 1 beyond the groove 2 is a conventional hollow ceramic conical nozzle 7, sealed by means of an 'O-ring 9 squeezed between the nozzle and the shoulder 4. This nozzle has a inch diameter outlet 11 forming an annular orifice 17 around the inch electrode 3 which extends there from to form a tip 13. At numeral 15 is shown a hollow handle attached to the body 1. The handle 15 carries a supply line 10 for the arc-shielding gas such as helium which is introduced into the body 1 and thence into nozzle 7 for exit around the tip 13 of the electrode. The rate of helium flow is generally about 10 c.f.h. The handle 15 also carries the usual inlet and outlet coolant lines 12 and 14 connected with a coolant circulating compartment within the body 1 for cooling the electrode 3. A connection is shown at 16 for an inlet electrical cable 8 from one side of an electric circuit to the electrode 3. Preferably, cable 8 is in one of the coolant passages, as shown, so that a smaller wire may be used without overheating it. The coolant generally used is water. The supply of water which circulates in the conventional holder is comparatively small, being on the order of 1 qt. per minute.
In conventional arc-welding operations, the work is connected to one side and the electrode 3 to the other side of a circuit and the arc struck at the tip 13 while shielding gas flows from the annulus 17 around the welding are thus formed.
The attachment forming the invention for converting the Welder into a high-temperature plasma jet torch will now be described. It consists of an auxiliary conductive hollow nozzle or double-walled jacket of cup shape generally indexed 19, having an inside sleeve-forming cylindrical wall 21 adapted to slip telescopically over a cylindrical rearward shoulder portion 23 of the ceramic nozzle 7. It is telescoped into place after an insulating fibre ring 25 has been placed against the shoulder 4 outside of the O-ring 9 and after application to the face of ring 25 of an additional sealing O-ring 27. At its forward end and around the electrode tip 13, the cylindrical wall 21 is tapered inwardly, as shown at 29. This forms an orifice or outlet 31 opposite this tip. Around the inner wall 21, 29 is formed an outer wall 33 which, with end walls 35 and 37, provides an integral coolant jacket for a circulating coolant 39, which preferably is water.
Leading at one side into the front end of the jacket is a water inlet pipe 41, and leading at the other side from its rear end is a water outlet pipe 43. These pipes are made up with threaded nipple portions 45 which slidably pass through openings in an insulating fibre plate or reaction member 47. This member 47 has a central opening 49 adapted to slip over the tapered part of body 1 and to seat thereon. Nuts 51 screwed on the nipple portions '45 and bearing against the back of plate 47, are used to pull the pipes 41 and 43 rearward, thus drawing reaiward the nozzle 19 to press against the fibre ring 25 with the sealing O-ring 2.7 therebetween. Thus the pipes 41 and 43 are used as tension members or draw screws to clamp the electrode holder assembly between the plate 47 and the auxiliary nozzle 19. Thus quickattachable and -detachable means is provided to hold the inner sleeve portion of the jacket 19 on the shoulder 23. The result is a quick-attachable and -detachable connection between the welder assembly on the one hand, and the plasma assembly on the other hand constituted by the jacket 19 and the pipes 41, 43 and 57 carried thereby. At 53 are shown couplings for attaching fiexible water tubes 55 to the pipes 41 and 43.
At numeral 57 is shown an inert-gas supply tube, coupled at 59 with a flexible gas supply line 61. As shown in FIG. 3, the tube 57 passes in a tangential direction through the walls 21 and 33 and opens into the inside of the nozzle 19. The preferred gas to be supplied through this tube is argon. In view of the tangential connection this gas will upon introduction move spirally towards the outlet 31 as shown by the dart D. The conductive nozzle 19 is preferably composed of copper, as are also the pipes 41 and '43. An electrical connection 63 on pipe 43 affords a return connection to the circuit which supplies current to the electrode 3.
Operation is as follows, assuming that the electrode tip 13 has been adjusted to about 7 inch from the tapered wall 29:
Helium is initially introduced over the conventional gas line through handle 15 to supply a flow thereof out of the opening 17 around the tip 13 at the stated normal rate of about c.f.h. Argon is supplied over tube 57 at the higher rate of 150 c.f.h., which moves spirally out of the opening 31 around the tip 13. Cooling water is supplied through the usual connection through handle 15 to the body 1 for cooling the electrode 3, for example at the stated rate of one quart per minute. Cooling water is supplied through pipes 41 and 43 to the nozzle 19 at the much higher rate of one gallon per minute. The DC. power supply should be capable of supplying the desired amperage at approximately are volts and should include a conventional high-frequency arc-starting unit. The D.C. power supply is turned on at 40 volts and 100 amperes, the high-frequency starting unit being temporarily connected. If the are fails to ignite, the argon flow through pipe 57 may temporarily be reduced until ignition occurs. The arc-starting unit is then cut off. Also, the argon flow is held at or rapidly restored to the 150 c.f.h. value. Thereafter the are current may be increased to the desired quantity for the temperature desired. The flow of helium from the orifice 17 may or may not be cut ofl. The resulting plasma jet will extend about 1%. inches beyond the orifice 31 and will be located centrally therein, without touching the orifice walls at any point. In order to shut off the device, the circuit should be opened first and the gas and water coolant circuits thereafter shut off in order to avoid burning the inside of the nozzle 19. If under starting conditions it is noted that the jet is touching the walls of the orifice 31, the flow of argon through pipe 57 should be increased. Any flow of helium from the annular orifice 17 is elective, and this flow may be cut off after the arc has been struck. The plasma jet cannot be maintained from this conventional source of gas alone from the orifice 17. The plasma jet is maintained primarily by the large volume of gas passing through the auxiliary nozzle over pipe 57.
The invention can also be operated by transferring the electrical connection at 63 to a metallic workpiece, shown for example by dotted lines W. This allows the invention to be used for high-speed cutting of such metals as stainless steel, aluminum and other metals not capable of being properly cut by the numerous oxygen cutting processes extant.
The argon is introduced into the nozzle 19 for two purposes: first, the motion of the gas along the inside of wall 21 and cone 29 keeps the nozzle cool by confining the gas ionization to the center of the torch; and, second, the motion of the gas assumes a spiral form which has a pinch effect upon the are. This raises the current density, which in turn raises the temperature to very high values. The unit may operate, for example, at current raised to 550 amperes and 40 volts, and even to 700 amperes at 40 volts if a larger amount of cooling water is sent through the nozzle 19. A typical but not limiting temperature is 18,000" P. The device may operate at a power level of 28 kw. for short periods of time and under sustained operations at 22 kw., the latter providing a current density of 7,008 kw. per square inch. Thus it will be seen that the plasma jet is composed of gas which is highly ionized by the arc and therefore becomes a path of very high current density which is responsible for the high temperatures obtained. While the values herein given by way of example are useful, it will be understood that these may be varied.
It is to be understood that inert gases other than helium and argon may be used for the purposes above described, but that the amount of gas ordinarily employed for shielding purposes when welding, which comes out of the outlet 17, is not sufiicient to sustain the plasma jet action, although the addition of such gases to the amount flowing through tube 57 when operating as a plasma jet is admissable as an operating condition. It will also be understood that the amount of water ordinarily employed for circulation in the body 1 for cooling purposes when used as a conventional arc welder is not sufiicient for operating the plasma jet attachment, and that the substantially larger amounts entering and leaving the tubes 41 and 43 are required for such purposes.
It will be seen that the device comprises a converter in the form of a compact water-cooled inert-gas, containedarc discharge capsule for quick-detachable connection to a welder for obtaining a high-temperature plasma jet operable over relatively long periods of time. Its advantages as a quick-detachable device for rapid application to and removal from a conventional shielded arc welder are enhanced by the fact that circuit connections are completed through the nozzle 19 and connections 63, rather than conventionally through the tip 13 of electrode 3 to grounded work, as during ordinary welding operations.
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.
1. A quick-attachable and -detachable conversion unit for converting an electric arc welder into plasma jet apparatus, said welder being of the type having an areforming electrode extending from a gas-shielding sleeve therefor, said electrode adapted to be connected with one side of an electric circuit; said unit comprising in combination a shoulder-forming portion for the sleeve, a double-walled hollow liquid-coolant jacket of a form adapted at one end to telescope over said sleeve and engage said shoulder, said jacket at its other end having an orifice for plasma, said orifice adapted to be positioned adjacent the end of the electrode when the jacket is telescoped onto the sleeve and into engagement with said shoulder, an inlet pipe for a plasma-forming gas supported by said jacket and connected with its hollow interior for injection therein of plasma-forming gas and flow of the same to said orifice, coolant pipes supported by and connected to the space between the walls of the jacket for coolant circulation around said sleeve and the orifice, a reaction member having openings for the reception of a part of the welder spaced from said shoulder and also for the reception of portions of said coolant pipes, draw means on the coolant pipes adapted when the reaction member is applied to the rearward part of the welder to telescope and to hold the telescoped jacket on said sleeve and against said shoulder, said gas and coolant pipes carrying coupling portions for efiecting attachments to plasma gas and coolant lines respectively, and an elec trical terminal having a conductive connection for supplying current to said sleeve.
2. A conversion unit according to claim 1, wherein said double-walled liquid-coolant jacket is of elongate 10 References Cited in the file of this patent UNITED STATES PATENTS Rava Oct. 23, 1956 Jones, et al. Oct. 14, 1958 Oyler, et al. June 9, 1959