US3106632A

US3106632A - Arc torch device

Info

Publication number: US3106632A
Application number: US104575A
Authority: US
Inventors: Richard C Eschenbach; George M Skinner; Robert M Gage
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1961-04-21
Filing date: 1961-04-21
Publication date: 1963-10-08
Anticipated expiration: 1980-10-08

Description

INVENTORS C. ESCHENBACH M. SKINNER M. GAGE ATTORNEY R. C. ESCHENBACH ET AL ARC TORCH DEVICE 2 Sheets-Shea?I 1 RICHARD GEORGE ROBERT Oct. 8, 1963 Oct. 8, 1963 R. c. EscHENBAcH ETAL 3,106,632

- f ARC TORCH DEVICE Filed April 2l, 1961 2 Sheets-Sheet 2 INVENTORS RICHARD C. ESCHENBACH GEORGE M. SKINNER ROBERT M. GAGE United States Patent .O

3,106,532 ARC TORCH DEVICE Richard C. Eschenbach and George M. Skinner, Indianapoiis, Ind., and Robert M. Gage, Summit, NJ., assignors to Union Carbide Corporation, a corporation of New York Filed Apr. 21, 1961, Ser. No. 104,575 13 Claims. (Cl. 219-75) The present invention relates to an improved are torch device for heating a gaseous medium such as air. More particularly, it relates to such a device fwlierein extremely hi-gh power :may be supplied to the arc and -thence to the gaseous medium.

There is an increasing need in industry for apparatus that will produce environmental conditions for certain research and tests on a scaled ldown or laboratory basis. In certain instances, :such conditions have been virtually non-reproducible on such a laboratory basis. In the aviation, missile and space exploration fields, for example, equipment is desired 'which will produce gas velocities far exceeding the speed of sound vand/or temperatures far exceeding the melting points of most known materials. Devices capable of producing such gas velocities and temperatures on a laboratory basis are largely unobtainable. The advantages to be gained from such a device are obvious in terms of making it possible to pretest airframe shapes, material durability at elevated temperatures and fthe like. Such pretesting is, of course, necessary 'to the protection of human life and the successful operation and recovery of extremely expensive unmanned vehicles.

High velocity, high temperature air streams are desired for wind tunnels and other materials testing devices. In such devices high gas velocities and tempera tures are required.

Electric arcs are essentially high temperature devices and have been used for many years as cutting torches, for plating processes, for `cr-acking hydrocarbons in the production of acetylene, and other similar uses. Of recent years, these arc .devices have become useful in Various high temperature gas hea-ting applications. In such applications, it is of prime importance to supply a maximum amount of power to the arc and then to transfer such power to the gas effluent. It has been found that if higher power to an arc device lis achieved solely through current increases, suoli additional power is used up primarily in heating the electrodes and their cooling fluid streams. Voltage increases, on the other hand, are substantially completely transmitted as higher heat to the arc gas.

Novel method and apparatus tor providing the above hot Iair streams are described in copending U.S. Patent Application Serial No. 716,323, tiled on February 20, 1958, by R. M. Gage et al, lnow U.S. Patent 3,077,108. This prior method comprises striking an arc between a stick electrode and a nozzle anode having a divergent outlet passage. In one form of apparatus for carrying out this method the stick cathode, usually of thoriated tungsten, is protected from air oxidation by means of a surrounding protective sleeve which extends in length .at least to the tip `ot the stick cathode. A shielding gas stream passes through the annulus between the protective sleeve and the cathode while an air stream travels along the exterior of the protective sleeve.

At power input levels iabove about 40 kw., the above described apparatus unde` goes severe damage at several points. First, the protective sleeve suffers erosion which enables air to reach the hot tungsten cathode and damage it by oxidation. Second, flow relationships between the shielding gas and air streams are such as to lead at mize chemical attack by the fi, i ,tifii Fatented Oct. 8, 1963 zle due to the sleeve becoming quite hot. This double arcing also contributes to sleeve erosion. The erosion and damage of the apparatus contaminates the elfluent and disturbs proper test conditions.

Novel apparatus has now been developed which enables power input up to at least kw. to be used without appreciable equipment damage and contamination or the effluent. The present invention is an improvement over the disclosure of the `above mentioned Serial No. 716,323.

it is laccordingly the primary object of this invention to provide an electric arc gas heating device capable of handling large amounts of power Iand of transferring a large percentage of such power to the gas.

Other objects are to provide apparatus for obtaining maximum heat transfer to the gas; and to provide appara-tus for use at power levels of at least about 100 kw.

Other objects will be pointed out or become apparent from the following detailed description and drawings wherein:

FIGURE 1 is a cross-sectional view of the present invention;

FIGURE 2 is a cross-sectional view of the apparatus of the invention together with a hypersonic wind tunnel.

The torch to be described herein preferably operates in a wall-stabilized -mode such as is described in U.S. 2,858,411, issued October 28, 1958, to R. M. Gage.

As shown in FIGURE l, the device consists mainly of a torch body 16, an inner electrode 11, the shape of which forms an angle of 60 at its tip in order to minigas flowing through the torch and which is preferably made of thoria-ted tungsten, and la replaceable non-consumable nozzle electrode 12, preferably made of metal such as copper. Other nozzle materials such as silver, tungsten, molybdenum and aluminum can also be used if desired. The stick cathode is supported by collet 13. The nozzle anode is held in position by vvater jacket 14. The jacket 14 is composed of sleeve 14a and outer jacket Mb which are silver brazed together to effectively form a single unit. The jacket 14 screws into insulator l15 which, in turn, is held in position by insulator nut 16. The stick electrode preferably has a diameter of from 1/8 to 2%4 inch in order to insure that it has sufficient current carrying capacity without having an excessive amount of material. The nozzle has a throat section the diameter of ywhich is preferably between Ms and We inch in order to insure that for a given pressure the arc will be maintained within the nozzle in a stable condition.

The nozzle 12 is kept from melting during operation by improved water cooling. The water enters the cooling jacket 14 through inlet 17, passes rapidly through cooling annulus 18, then out through outlet 19. Leakage `of cooling water is prevented by Orings 2d, 21, and 2.2. In Iorder to provide maximum cooling and prevent melting of the nozzle interior, the ratio of the OD. of the nozzle to its LD. at its point of smallest cross section should be between 2.0 and `12.0. -Optimumly, when the nozzle internal diameter is about 1A 4inch at its point of smallest cross-section, the O.D.to-I.D. ratio of the nozzle is between 2.2 and 4.2. For a nozzle internal dia-meter of 1/s inch, the O.D.tc-I.D. ratio should be about 3.0 to 8.0 while a nozzle internal diameter of inch should have an GData-ID. ratio of about 2 to 4. The water cooling passage surrounding the nozzle cuter surface is made relatively thin in order to 4increase the velocity of the cooling medium in direct Contact with the nozzle electrode.

l5-90' and preferably about 60.

In contrast to the above 0.D.-to-I.D. data, the prior Serial No. 716,323 discloses use of nozzle anodes having .an O.D.-tol.D. ratio of 20 for 1/16 inch internal diameter nozzles and 4 for 1/z inch diameter nozzles.

Shielding gas, such as argon, under pressure enters through inlet 23 passes down along cathode 1l, through annulus 2d between cathode 11 and protective sleeve 25, then passes out through orifice 26 in nozzle anode 12. The passage 126 has a divergent section 27. Annul-us 24 must be at an optimum size to insure proper shielding of the tungsten cathode l1 with a minimum amount of shielding gas to minimize dilution of the gas to be heated. Specifically, the annulus must be small enough to achieve shielding gas velocities of fnom about 20 ft./sec. to 200 ft./sec. and yet be large enough to i-nsure a uniform flow of gas. An annulus width tof 0.031 inch with a shielding gas velocity of about 90 t/ sec. is preferred. However, the annulus width may have any -value in the range of tfrom about 1/64 to about 1/16.

Protective slee-ve 25 has improved -water cooling passages which prevent it from -melting and eroding during operation. Cooling water enters through :inlet 28, passes through conduit 29, annular passage 3:0, whereby cooling is imparted to the tip of the protective sleeve, passes out through conduit 31 and youtlet 32 by way of passage 32a. This improved sleeve cooling tends to prevent double arcing from cathode to sleeve to nozzle anode and thus reduces sleeve erosion due to mel-ting.

An additional feature of the protective sleeve 25 is the plated tip 38 of the sleeve. This plated portion is approxi mately .010 inch in thickness and consists of a pure aluminum oxide. Such plated portion also tends to reduce sleeve erosion due to melting caused by double arcing.

The tip of the stick cathode is preferably made flush with the tip of the protective sleeve 25. lf it is allowed to n project beyond the tip of the sleeve it will be subjected to the erosive effects of the surrounding air stream. On the other hand, if it is set back from the tip of the sleeve, the sleeve will become too hot and melt down.

The arc is further prevented from wandering `from the stick cathode to other parts yof the device other than the nozzle anode by

insulators

15 and 39. Suitable materials for the insulators have been found to be Bakelite, Formica and nylon.

Air under pressure enters through inlet 33 and passes through annular pasage 34 between protective sleeve 25 and insulator l plus nozzle 12. This annular passage should be properly dimensioned in lorder to provide a streamlined air flow approaching the throat 35 in nozzle 12. This minimizes the turbulence in the area directly in front of the tip of cathode 11 and minimizes erosion of the cathode tip andthe nozzle throat. Generally, passage 35 should have a length of from 1/2 inch to 2 inches and preferably a length of 1% inches. Its width should be between 1/32 to 1A; inch. However, in choosing any one length-width combination, care must be taken to maintain a length-to-width ratio of the passage of at least 1'5 and preferably between 20`25 so that the desired streamlined flow can be insured. To further insure a streamlined flow, the passage should have an included angle of from The air then mixes with the shielding gas las they both pass out through passage 35 and orifice 26 in nozzle l2. This description of the apparatus impl-.ies axial gas ilo-w. Alternatively, the main gas stream could be introduced to annular passage 34 in a tangential fashion to produce a vortex gas flow through

nozzle passages

35 and 27.

Nozzle erosion has been additionally minimized by maintaining a lengthtodiameter ratio in the throat section 35 of between 0.5 and 2.0. The heat concentration :is highest in the throat section 35. lf the length of the throat is too short when the first bit of erosion occurs the high heat concentration becomes aggravated because the throat tends to become a point. On the other hand, if the throat is too long the arc will terminate in the throat. The included angle of the :divergent portion Z7 of passage 26 should be less than 20 degrees and its length six times the throat diameter and preferably between 3A and l1/z inches so that the arc from electrode lll. terminates well within the nozzle under desired operation conditions. lf the angle is too large the pressure within the nozzle will become excessive causing the arc to locate at a point. On the other hand, if the angle is small enough, the pressure will be low enough to allow the arc to spread but within the nozzle.

The tip 3o of cathode 1l and the rim 37 of protective sleeve 25 are maintained at a controlled ldista-nce or setback from the ,mouth of the nozzle throat section 35. This helps to minimize turbulence 4and erosion in this area. For a cathode having a diameter from 1/s to 2%4 inch and a nozzle having la throat diameter from Ms to s/8 v inch, this set-back distance should be lfrom W32 to l inch. With an 1%4 inch cathode and a 1/s inch diameter throat and a set-back of %2, it was found that a variation in setback distance of /l inch increased erosion of the protective sleeve and stick cathode.

In operation, an electrical power source (not shown) is connected between stick cathode l1 and nozzle anode l2, and the arc is conveniently initiated by pushing electrode 11 down into arcing relation to nozzle electrode l2, then retracting it to the desired operating position. Direct current straight polarity is the preferred type of current for this device. Alternating current could also be used. The combined air-shielding gas streams force the arc down into the nozzle passage 26, where the arc becomes wall-stabilized along the so-included portion. The gases passing through this high intensity wallstablized arc are heated to desired energy content and are discharged in a supersonic hot jet.

The material or body to be tested is located at point X in the hot air effluent that is discharged from the device. For example, in FlGURE 2, there is depicted a hypersonic wind tunnel 5@ connected to the described arc air heater 10 for testing aircraft materials at hypersonic velocities. The hot air effluent coming from the torch body 10 is expanded through expansion section 51 and then directed against the material to be tested at 52. By connecting a suitable vacuum pump to the exit of the iiow section 53, a desired pressure drop can be obtained between the flow section and the expansion section to yield the desired velocities. Testing is thereby accomplished under conditions that closely simulate conditions of actual ilight of such body or material.

In the following example of the operation of the present novel device, apparatus of the type depicted in FGURE 1 was used.

In this example an arc of 355 volts (D.C. SP.) and 400 amperes was maintained between a 3/16 diameter thoriated tungsten stick cathode and a nozzle anode having a divergent orifice section expanding from a diameter of 9&2 to a diameter of 15/32. The nozzle had an outer diameter of 1%. Argon shielding gas at 800 c.f.h. and air at 7600 c.f.h. passed separately into the apparatus and then mixed while passing out through the nozzle anode orifice. Under these conditions the total power developed was 142 kw. of which 122 kw. went to the gas to yield an enthalpy of 750 Btu/lb. The hot air eiuent discharging from a chamber pressure of 224 p.s.i.g. through the nozzle had a calculated exit velocity of 4500 ft./sec. at a calculated exit pressure of 23 p.s.i.a., which is approximately Mach 2.1 for these conditions.

While air and argon gas are given above by way of example, it will be understood that other reactive gases, such as carbon dioxide, oxygen, and iiuorine, may be used in admixture with or in place of air, and other gases inert relative to the cathode, such as helium, hydrogen, krypton, neon, nitrogen, xenon, carbon monoxide, and mixtures thereof, may be used in admixture with or in place of argon. Also, the latter may be used in admixture with or in place of air without departing from the basic concept of the invention.

As can be seen by the drawing and as is apparent from the description of the apparatus, the internal parts of the torch, such as the inner electrode, the nozzle electrode, and the protective sleeve, are easily replaceable.

in summary, the present invention consists of an improved non-transferred arc torch which is capable of operating at power levels at least as high as 100 kw. with an air stream passing through the nozzle without appreciable damage to the stick cathode, protective sleeve, or nozzle anode.

What is claimed is:

1. An electric arc gas heater device comprising the combination of a stick electrode, a replaceable protective sleeve surrounding the arc end of said electrode and electrically isolated from said electrode in spaced concentric relation, means for delivering a shielding gas to the annular space between said sleeve and stick electrode which is discharged `from said sleeve about such end of said electrode to protect such arc end, a replaceable cooled non-consumable nozzle electrode having an internal conical gas passage surrounding the end of said sleeve in spaced concentric relation, means for delivering gas under pressure to said conical passage for ilow about such end of said sleeve, said nozzle having a gas outlet comprising a throat leading to an expansion passage of increasing diameter for the expansion of such gas as it is discharged therefrom, means for striking a high-pressure arc between said nozzle and the arc end of said stick electrode for heating the gas discharged by said nozzle, insulator means surounding at least part of said sleeve and cooperatingy with the walls of said nozzle electrode defining said internal conical gas passage to form an annular passage with said sleeve, said annular passage having a length-towidth ratio of at least about 15, and means for providing a cooling medium in direct contact with said protective sleeve, whereby cooling is imparted to the end of said protective sleeve such that said arc torch may deliver up to about 100 kw. Without damage to said torch.

2. Apparatus according to claim 1 wherein said protective sleeve is provided with a plated tip, the thickness of said plating being approximately .010 inch and consists of a pure aluminum oxide.

3. Apparatus according to claim 1 wherein the lengthto-diameter ratio of said throat section is between about 0.5 and 2.0 and the included angle of said increasing diameter expansion passage is less than 20 degrees.

4. Apparatus according to claim 3 wherein said ininciuded angle is between about 5 to 10 degrees.

5. Apparatus according to claim 1 wherein said annular passage has a length-to-width ratio of between about 20 and 25.

6. Apparatus according to claim 1 wherein said stick electrode has a diameter of from s to 2%4 inch; said throat has a diameter or from 1/s to inch and said cathode is set back from said throat section from about 5)/32 inch to 1 inch.

7. Apparatus according to claim l wherein said nozzle anode has an O.D.to.l.D. ratio of from about 2.2 to about 4.2 when the internal diameter thereof at the point of smallest cross section is about M1, inch.

8. Apparatus according to claim 1 wherein said nozzle anode has an CLD-toil). ratio of from about 3 to about 8 when the internal diameter thereof at the point of smallest cross section is about 1%; inch.

9. Apparatus according to claim 1 wherein said nozzle anode has an O.D.to-I.D. ratio of from about 2 [to about 4 when the internal diameter thereoiT` at the point of smallest cross section is about inch.

l0. Apparatus according to claim l nuiar space has a 1/16 inch.

1l. Apparatus according to claim `1 wherein said annular space has a wid-"h of about .031 inch.

12. Apparatus according to claim 1 wherein said nozzie electrode has an O.D.-tol.D. ratio of from about 2.0 to about 12.0.

13. Apparatus according to claim 1 wherein said nozzle electrode is non-consumable and in which at least a portion of said arc is wall-stabilized.

wherein said anwidth of from about 1&4 inch to about References CCited in the tile of this patent UNITED STATES PATENTS 1,002,721 Mathers Sept. 5, 1911 2,093,821 Southgate Sept. 21, v1937 2,616,017 Anderson Oct. 28, 1952 2,890,322 Oylcr et al June 9, 1959

Claims

1. AN ELECTRIC ARC GAS HEATER DEVICE COMPRISING THE COMBINATION OF A STICK ELECTRODE, A REPLACEABLE PROTECTIVE SLEEVE SURROUNDING THE ARC END OF SAID ELECTRODE AND ELECTRICALLY ISOLATED FROM SAID ELECTRODE IN SPACED CONCENTRIC RELATION, MEANS FOR DELIVERING A SHIELDING GAS TO THE ANNULAR SPACE BETWEEN SAID SLEEVE AND STICK ELECTRODE WHICH IS DISCHARGED FROM SAID SLEEVE ABOUT SUCH END OF SAID ELECTRODE TO PROTECT SUCH ARC END, A REPLACEABLE COOLED NON-CONSUMABLE NOZZLE ELECTRODE HAVING AN INTERNAL CONICAL GAS PASSAGE SURROUNDING THE END OF SAID SLEEVE IN SPACED CONCENTRIC RELATION, MEANS FOR DELIVERING GAS UNDER PRESSURE TO SAID CONICAL PASSAGE FOR FLOW ABOUT SUCH END OF SAID SLEEVE, SAID NOZZLE HAVING A GAS OUTLET COMPRISING A THROAT LEADING TO AN EXPANSION PASSAGE OF INCREASING DIAMETER FOR THE EXPANSION OF SUCH GAS IT IS DISCHARGED THEREFROM, MEANS FOR STRIKING A HIGH-PRESSURE ARC BETWEEN SAID NOZZLE AND THE ARC END OF SAID STICK ELECTRODE FOR HEATING THE GAS DISCHARGED BY SAID NOZZLE, INSULATOR MEANS SURROUNDING AT LEAST PART OF SAID SLEEVE AND COOPERATING WITH THE WALLS OF SAID NOZZLE ELECTRODE DEFINING SAID INTERNAL CONICAL GAS PASSAGE TO FORM AN ANNULAR PASSAGE WITH SAID SLEEVE, SAID ANNULAR PASSAGE HAVING A LENGTH-TOWIDTH RATIO OF AT LEAST ABOUT 15, AND MEANS FOR PROVIDING A COOLING MEDIUM IN DIRECT CONTACT WITH SAID PROTECTIVE SLEEVE, WHEREBY COOLING IS IMPARTED TO THE END OF SAID PROTECTIVE SLEEVE SUCH THAT SAID ARC TORCH MAY DELIVER UP TO ABOUT 100 KW. WITHOUT DAMAGE TO SAID TORCH.