US3611014A

US3611014A - Method and apparatus for starting a long arc between hollow electrodes

Info

Publication number: US3611014A
Application number: US34382A
Authority: US
Inventors: Harden Henry Troue; Ledford H Day Jr
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1970-05-04
Filing date: 1970-05-04
Publication date: 1971-10-05
Anticipated expiration: 1988-10-05
Also published as: DE2121757A1; NO130291B; CA928372A; BR7102643D0; DE2121757B2; DE2121757C3; FR2091131A5; GB1347091A; BE766649A; NL7106022A; SE373455B; AT307564B; CH550526A

Abstract

An arc is initiated between a pair of hollow electrodes spaced a relatively substantial distance apart and contained at opposite ends in a quartz tube by passing a rod through the bore of one electrode and into the bore of the other electrode, establishing a swirling gas vortex about the rod sufficient to cause the rod to make continuous internal rotational contact with the bore of each electrode, and impressing thereafter a relatively low voltage across the electrodes while withdrawing the rod. The rod is connected to a piston assembly externally connected at one end of the torch.

Description

United States Patent Inventors Harden Henry Troue [56] R fer Cited {:'$:":P: 'i; M h L k N Y UNITED STATES PATENTS App No 34 g; 3,218,514 11/1965 'Boldt 313/149x Filed May 4, 1970 ,501,665 3/1970 Rotger et al. 315/] l 1 XY Patented Oct. 5, 1971 Primary ExaminerRoy Lake Assignee Union Carbide Corporation Assistant Examiner-Palmer C. Demeo New York, N.Y. AnorneysPaul A. Rose, Harrie M. Humphreys, Dominic .I.

Terminello and Eugene Lieberstein ABSTRACT: An arc is initiated between a pair of hollow elec- METHOD AND APPARATUS FOR STARTING A trodes spaced a relatively substantial distance apart and con- LONG ARC BETWEEN HOLLOW ELECTRODES It I t t b b d M Claims 30mm Figs. tune a opposi e en s 1n 4 quar z u e y passmg a ro through the bore of one electrode and into the bore of the U.S. Cl 3l5/lli, other electrode. establishing a swirling gas vortex about the 3l3/l2, 313/l49, 3l3/23l, 315/33] rod sufficient to cause the rod to make continuous internal lnt.Cl H01] 7/24, rotational contact with the bore of each electrode, and im- H0] j 7/36 pressing thereafter a relatively low voltage across the elec- Field of Search 3 l5/] 1 l, trodes while withdrawing the rod. The rod is connected to a 331; 3 l3/l49, 146, I98, 12, 231 piston assembly externally connected at one end of the torch.

H O/GAS H1 H2 6A5 T0 SUPPLY 0 Starter Gas l l l C70 To or From Supply M 1 /J 76' 1g .52 54 5'5 1 H 0 H 0 12 Gas I0 I Gas To IA Supply 2' I r M 62 H O PATENTED 001 5 I97| SHEET 2 0F 2 SUPPLY SOURCE RETURN FLOW Em mw Y oRm E TT N N H R EH 0 V W T m o H mm HL B METHOD AND APPARATUS FOR STARTING A LONG ARC BETWEEN HOLLOW ELECTRODES This invention relates to electric are starting and more particularly to a method and apparatus for initiating an elongated electric arc of high intensity.

Electric arcs of high intensity have utility as sources of light and heat. One such electric are light source is shown and described in US. Pat. No. 3,364,387 wherein the arc is constricted by means of a swirling gas injected into the arc chamber. The gas spirals inwardly along the central axis of the chamber creating a low-pressure region for confining and concentrating the are thereby increasing the intensity thereof. This swirl flow phenomenon is equally effective on both short and long arcs. The length of the arc is evidenced by the spacing between the electrodes. Where the spacing between the electrodes is greater than about 1 inch in length, hereinafter defined as a long are, conventional are starting techniques such as high frequency become impractical. For example, to break down a l inch gap between a pair of hollow electrodes in an argon atmosphere requires a voltage of about 40 kilovolts which is at least several orders of magnitude greater than would otherwise be necessary once the arc is established. Moreover, using high frequency there is no assurance that ignition will occur at the predesigned electrode termination cations. Hence, an arc starter system is needed which will be compatible with the swirl flow phenomenon without giving rise to contamination of the arc chamber, operate at relatively low voltage and be completely isolated from external forces.

It is therefore the principle object of the present invention to provide a method and apparatus for establishing an arc in a radiation source between a pair of hollow electrodes spaced any predetermined distance apart.

It is a further object of the present invention to provide a method and apparatus for accurately igniting a constricted are between a pair of hollow electrodes spaced any predetermined distance apart using a relatively low voltage.

It is another object of the present invention to provide a method and apparatus for igniting an arc of any desired length in a radiation source employing a swirling gas vortex wherein the swirl gas is recirculated and performs an integral function of the are starting operation.

It is yet another object of the present invention to provide a method for establishing a constricted are between a pair of spaced hollow electrodes confined within an arc chamber which is highly reliable and which will not cause any chamber contamination during the starting interval. 4

These and other objects will become apparent from the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 is a longitudinal sectional view broken along the line A-A illustrating a dual hollow electrode radiation source integrally coupled to the are starting apparatus of the present invention;

FIG. 2 is a system flow diagram partly schematic and partly diagrammatic illustrating the arc starting sequence of the present invention;

FIG. 3 is an electrical schematic block diagram illustrating a circuit arrangement for performing the desired timing sequence in accordance with the present invention.

The radiation source 10 shown in the illustrated apparatus of FIG. 1 comprises a pair of substantially similar manifold assemblies l2 and 14 supporting therebetwcen an elongated tubular envelope 16 forming a gastight chamber 18. Tubular envelope 16 is surrounded by an outer tubular envelope 19 in coaxial and radially spaced relationship. The

envelopes

16 and 19. respectively, are formed from transparent material such as quartz.

Electrode 20 is detachably connected at one end to manifold assembly 14 while projecting into the chamber 18 from its opposite end. in a similar fashion. electrode 22 is detachably connected at one end to manifold assembly 12 and projects from its opposite end into chamber l8. Each electrode is of substantially cylindrical geometry having a central bore in coaxial relationship with one another and with the longitudinal axis of the chamber 18. The spacing between the electrodes is fixed and may represent for purposes of the present invention any predetermined distance; although, the advantages of the invention become more apparent for an electrode spacing of at least 1 inch in length.

The manifold assemblies 12 and 14 include fluid passages as shown in FIG. 1 for passing and withdrawing a cooling fluid such as water. Additional passages are provided for circulating a gas through the radiation source 10 in a closed cycle. The gas provides a plurality of functions including cooling the quartz envelope, constricting the are once established and providing in a manner to be described hereafter the pneumatic energy for the starter assembly. The gas flow sequence will be discussed more thoroughly in connection with FIG. 2

The arc starter assembly 30 comprises a housing 32 including a cylindrical hollow body 34 defining therewithin a piston chamber 35. Mounted in chamber 35 is a piston 36 and starter rod 38. The housing 32 is fixedly bolted to the frame of manifold assembly 14 with its cylindrical body 34 extending outwardly from manifold assembly 14 in coaxial alignment with the longitudinal axis of chamber 18. The flanged termination 40 at the rear end of cylindrical body 34 has an inner surface 42 which functions as the outer piston stop. Stem 44 of manifold assembly 14 extends into the mouth of cylindrical body 34 and functions as the forward piston stop. The stem 44 has a central bore 45 which acts as a guide for the starter rod 38. When the piston 36 is in its fully withdrawn position the pointed tip 46 of the starter rod 38 rests within the bore 45 of the stem 44.

Piston 36 is represented by a conductive sleeve element 48 mounted about the starter rod 38 at its rearward end and threadably fastened to an outer nonconductive member 50 such as Teflon. Member 50 is sufficiently biased against the inner surface of body 34 to function as a fluid seal. The engaging surfaces of piston 36 and stem 44 are tapered in order to controllably brake piston 36.

Housing 32 of starter assembly 30 includes a gas passage 52 for passing a gas into the chamber 35 through openings 54 located at the far end of the cylindrical body 34. The injected gas is confined to the area behind the piston 36. When sufficient pressure is built up piston 36 will advance downstream toward chamber 18 causing the starter rod 38 to proceed through the bore 60 of electrode 20 then axially across the chamber 18 and into the bore 62 of electrode 22 until the piston 36 is stopped by stem 44. The length of the starter rod 38 is determined by the distance to be traversed between the

electrodes

20 and 22, respectively. The tip 46 of starter rod 38 should preferably extend only a short distance within bore 62 of electrode 22.

A power supply (not shown) is connected to a pair of

terminal posts

68 and 70, respectively; with the negative side of the supply connected so as to render electrode 20 the cathode. It is preferred in accordance with the present invention to have the starter rod 38 function as an extension of the cathode in establishing an are between the electrodes. With this arrangement, reliable starting has been demonstrated without emitting spatter from the starter rod 38.

The cathode electrode 20 may be composed substantially of tungsten or may comprise a conductive outer body such as copper with a tungsten or thoriated tungsten inner layer at the end adjacent the arc chamber 18. The anode electrode 22 may be fonned from any conductive material such as copper. The starter rod 38 should be composed of a relatively strong conductive material such as tungsten or 2 percent thoriated tungsten. For proper operation, the diameter of the starter rod 38 must be smaller than the bore size of each

electrode

20 and 22, respectively. To avoid possible contamination of chamber 18 during the starting period and to provide optimum starting reliability, cordance with the sequence as reference to FIGS. 1-3 inclusive.

outlined hereafter with the starting operation should be carried out in ac- As shown in FIG. 2, supply source 78 delivers gas under pressure to radiation torch 10 and the starter assembly 30. Any inert gas such as for example, argon, krypton or xenon may be used. The direction of gas flow is determined by means of a plurality of conventional, electrically actuated, control valves SVl, SV2, SV3, 8V4, 8V5, and SV6, respectively. Control valve SVll is a conventional three-way valve having two separate flow paths one of which opens supply line 84 into line 86 while the other vents line 86 into exhaust line 87. Additional gas control is provided by restricted

orifices

80 and 82, respectively. The retum path for the gas is shown in FIG. 2 in dotted linw. Although a closed return path to the supply source is shown, it should be apparent that the exhaust gas may be directly vented into the atmosphere.

At the beginning of an arc ignition cycle the starter rod 38 is at rm in its fully withdrawn position with the piston 36 up against the outer stop 42, the power across the electrodes off, and all of the control valves closed. The piston and starter rod assembly is then primed by energizing three-way control valve SVH opening supply line 84 into line 86. The exhaust to line 87 is closed. Gas now flows from supply source 78 along line 84 through restricted orifice 80 into line 86 and then into the starter assembly 30. As more clearly shown in FIG. 1, the gas enters starter assembly 30 via passageway 52 and into chamber 35 through openings 54 located at the rear end of the assembly behind piston 36. The piston 36 and the accompanying starter rod 38 advance downstream until the piston is stopped by stem 44 with the tip 46 of starter rod 38 positioned within the bore 62 of anode electrode 22. The restricted orifree 80 limits the gas flow rate to chamber 35 thereby controlling the speed of piston travel. After the piston 36 has completed its downstream stroke, control valve SV2 is opened bypassing orifice 80 and bringing on full flow and maximum supply pressure behind piston 36 to firmly hold it in place. Control valve V3 is then opened permitting gas to flow from supply source 78 into radiation torch 10. The gas enters arc chamber 18 of torch through openings positioned about the circumference of electrode 20. The gas spirals inwardly from electrode in a fashion similar to that of a tornado. The buildup of swirl flow is controlled by restricted orifice 82. A slow buildup of swirl flow is considered desirable to prevent the starter rod from being damaged. The gas exhausts through the central bore of each

electrode

20 and 22, respectively, passing through a pair of

conventional heat exchangers

90 and 92 and then into line 94. From line 94 the exhaust gas passes through a pressure relief valve 96 and returns to the supply source 78. Relief valve 96 performs the important function of constricting the exhaust flow for creating sufficient back pressure across the starter assembly and hence starter piston 36 to enable the starter rod 38 to be swiftly withdrawn as will be discussed hereinafter.

After a further short delay, control valves 8V4 and SV5 are opened. Control valve 5V4 pennits full swirl flow to develop in the arc chamber 18. Pressure relief valve 93 located in series with control valve SVS is used to regulate the delivery pressure at electrode 20 and hence in chamber 18 by bleeding off a controlled amount of gas from line 99. By maintaining a reduced chamber pressure, the starting voltage requirement is minimized. A voltage of the order of i000 volts has been found satisfactory to start an are 4 inches long for example.

Power across the electrodes is now turned on and an arc is immediately developed between the pointed tip of starter rod 38 and at some point within the bore 62 of anode electrode 22. The swirling gas acts to rotate the starter rod about its central axis as well as to cause the starter rod to spin or wobble, making continuous internal rotational contact within the bore of each electrode. it should be noted that the swirl gas is introduced into the radiation source prior to turning on power. If this sequence were out of order, the tip of the starter rod might possibly weld itself to the anode electrode bore 62. Moreover, the arc would not be properly confined along the longitudinal axis of the radiation torch 10. In addition, it would be difficult to prevent the are from pitting the circumference of the starter rod at the point of contact with the cathode electrode face 60.

At the same time power is turned on three-way control valve SVl is again energized closing the supply pressure to line 86 and opening the discharge port thereof for connecting line 86 to line 87. The' pressure behind the piston 36 is now vented through line 87 and returned to the main supply source 78. As stated hereinabove relief valve 96 constricts the gas exiting from the electrode bores in order to develop a back pressure across the starter assembly 30 and starter piston 36. The gas flow through starter assembly 30 is in parallel with the gas flow through relief valve 96. Once the pressure from chamber 35 of starter assembly 30 is released the starter rod is forced to withdraw back to its original at rest position with the piston 36 positioned against the end stop 42. As the starter rod moves upstream it extends the are until the are contacts the bore 60 of cathode electrode 20. Here again the swirl flow in arc chamber 18 plays an important part during the starting operation. The swirl gas not only constricts the are but prevents the are from being drawn out of the anode electrode bore 62. Without swirl flow the extended are would seek the path of least resistance which at the anode electrode end would be between the tip of the starter rod 46 and the tip of the anode electrode 22 rather than remain within the anode electrode bore 62 as desired.

After the piston 36 is returned to its original at rest position, SV6 is energized. With control valve SV6 open, relief valve 96 is bypassed reducing the pressure drop across the starter assembly 30 and starter piston 36 to that experienced across the heat exchangers and 92, which for purposes of the present invention, can be neglected. Control valve SVS is then closed bringing delivery pressure to its maximum valve to provide maximum swirl strength and pressure in the arc chamber 18.

Solenoid control valves SVl through SV6 may be actuated automatically in the above-described preferred sequence using any number of different conventional timing circuits. A simplified timing circuit for energizing the control valves in consecutive order is shown in FIG. 3. The circuit includes a number of conventional time delay relays each of which is mechanically preset to actuate its contacts, upon energization, after a predetermined time delay. As shown a source of alternating current 100 is impressed across TD (time delay relay n) which after, for example It seconds, closes normally open contact TDC,,(contaet n of time delay relay n) of relay TD, thereby energizing SV (solenoid valve n). The alternating current source 100 is concurrently impressed across a plurality of similar paired parallel branches; where one branch of each pair contains a time delay relay and a contact of the time delay relay of the preceding parallel branch in series therewith and where the other branch of the pair contains a solenoid control valve in series with a time delay relay contact of the time delay relay in that branch. This is more easily visualized with reference to FIG. 3 where the second paired parallel branch symbolically represents a string of such paired branches; one leg of each branch having a time delay relay TD in series with a time delay relay contact TDC, and the other leg having a solenoid control valve SV in series with a time delay relay contact TDC where n represents consecutive numbers and A is a integral step later. As can be noted, the action of any solenoid such as SV,,, for example, can be cancelled at a later point in the sequence by action of a normally closed contact such as TDC Aof time delay relay TD The amount of time that should elapse between each event in the starting sequence is not critical. A time period between events, where a time elapse has been indicated, is generally in the range of 4-l5 seconds.

Although each preferred step of the starting operation has been described fully it should be understood that not all of the steps are necessary to carry out the invention. For example, the gradual buildup of swirl flow as well as the gradual buildup of piston pressure, although desired, are unessential. In addition, although preferred, it is not necessary to regulate the pressure within the arc chamber during the starting interval. Furthermore, although the invention has been described in terms of a recircuiting gas system, it is obvious that the exhaust gas may, if desired, be vented into the atmosphere. Moreover, a separate gas supply may be used for the starter assembly. It is, however, desirable for proper operation, in accordance with the invention, to have the swirl gas introduced into the chamber before the power across the electrodes is turned on.

What is claimed is: g

l. A method of starting an electric are between spaced first and second electrodes contained within a chamber, each electrode having a central bore in substantially coaxial relation with each other and with the longitudinal axis of the chamber comprising the steps of:

a. pasing a rod, having a diameter smaller than the diameter of each electrode bore, through said first electrode bore and into said second electrode bore until said rod extends between said electrodes;

b. injecting a gas into said chamber in such manner as to establish a strong swirling flow pattern about the longitudinal axis of the chamber sufficient to cause said rod to spin about said axis such that continuous internal rotational contact is made with the bore of each electrode;

c. impressing a relatively low voltage across said electrodes for establishing an are between said rod and said second electrode; and

d. approximately simultaneously therewith withdrawing said rod thereby extending said arc from the second electrode to the first electrode.

2. A method as defined in claim 1 wherein the first electrode represents the cathode and wherein the second electrode represents the anode.

3. A method as defined in claim 2 wherein said rod is connected to a piston and wherein gas is introduced behind said piston for developing a gas pressure to drive said rod through the bores of said electrodes.

4. A method as defined in claim 3 wherein said gas pressure is maintained behind said piston while injecting gas into said chamber in accordance with step b.

5. A method as defined in claim 4 further comprising the steps of releasing the gas pressure from behind the piston and developing a pressure differential across the rod sufficient to cause the rod to be automatically withdrawn from the chamber after an arc has been established.

6. A method of starting an electric are between spaced first and second electrodes contained within a transparent chamber, each electrode having a central bore in substantially coaxial relation with each other and with the longitudinal axis of the chamber comprising the steps of:

a. applying a pressurized gas behind a piston and rod assembly to cause the rod to advance downstream through the bore of said first electrode along the line of axis of the chamber into the bore of said second electrode;

b. injecting a gas into the arc chamber in such manner as to establish a strong swirling flow pattern about the longitudinal axis of the chamber sufficient to spin the rod about said axis such that continuous internal rotational contact is made with the bore of each electrode;

c. impressing a relatively low voltage across said electrodes for establishing an are between said rod and second electrode;

d. discharging said gas being injected into the chamber through each electrode bore respectively;

e. recycling said discharged gas back into said chamber; and

f. withdrawing the pressurized gas applied behind the piston while restricting the flow of discharge gas from the chamber for developing a pressure differential across the piston sufficient to cause the piston to recede upstream thereby pulling the rod back out of the bore of each electrode and extending the are from said second electrode to said first electrode. 7. A method as defined in claim 6 wherein said first electrode is the cathode and wherein said second electrode is the anode.

8. Apparatus for generating a high intensity source of light radiation which comprises:

a. an elongated tubular envelope providing an arc chamber having a light transmitting portion; first and second electrodes each having a central bore axially disposed at opposite ends of the chamber;

b. a piston assembly mounted in a cylinder extending from the first electrode external of the arc chamber;

c. a rod connected to the piston in line with the longitudinal axis of the chamber, said rod having an external diameter smaller than the bore of each electrode;

d. first means for introducing a gas into the cylinder behind the piston thereby driving the piston until the rod extends longitudinally between the electrodes with the tip of the rod confined within the bore of the second electrode;

e. second means for introducing gas in said chamber to effect a strong swirling flow of gas about a straight line axis which extends between said electrodes;

f. third means for controllably draining the gas exiting from said chamber through the central bore of each electrode;

g. fourth means for impressing a voltage across the electrodes;

h. fifth means for releasing the gas from the piston cylinder;

and

i. means for actuating in a consecutive timed sequence said first, second, third, fourth and fifth means.

9. Apparatus as defined in claim 8 wherein the gas is supplied from a common inert gas supply source and returned to said supply source.

10. Apparatus as defined in claim 9 wherein said gas is selected from the class consisting of argon, krypton, and xenon,

11. Apparatus as defined in claim 10 wherein said rod is composed of 2 percent thoriated tungsten.

12. Apparatus as defined in claim 11 wherein the tip of said rod is pointed.

13. Apparatus as defined in claim 8 wherein the piston assembly comprises an insulating member mounted about the end of the rod and biased against the inner surface of said cylinder thereby acting as a fluid seal.

14. Apparatus as defined in claim 13 wherein said insulating member is composed of Teflon.

Claims

1. A method of starting an electric arc between spaced first and second electrodes contained within a chamber, each electrode having a central bore in substantially coaxial relation with each other and with the longitudinal axis of the chamber comprising the steps of: a. passing a rod, having a diameter smaller than the diameter of each electrode bore, through said first electrode bore and into said second electrode bore until said rod extends between said electrodes; b. injecting a gas into said chamber in such manner as to establish a strong swirling flow pattern about the longitudinal axis of the chamber sufficient to cause said rod to spin about said axis such that continuous internal rotational contact is made with the bore of each electrode; c. impressing a relatively low voltage across said electrodes for establishing an arc between said rod and said second electrode; and d. approximately simultaneously therewith wIthdrawing said rod thereby extending said arc from the second electrode to the first electrode.

6. A method of starting an electric arc between spaced first and second electrodes contained within a transparent chamber, each electrode having a central bore in substantially coaxial relation with each other and with the longitudinal axis of the chamber comprising the steps of: a. applying a pressurized gas behind a piston and rod assembly to cause the rod to advance downstream through the bore of said first electrode along the line of axis of the chamber into the bore of said second electrode; b. injecting a gas into the arc chamber in such manner as to establish a strong swirling flow pattern about the longitudinal axis of the chamber sufficient to spin the rod about said axis such that continuous internal rotational contact is made with the bore of each electrode; c. impressing a relatively low voltage across said electrodes for establishing an arc between said rod and second electrode; d. discharging said gas being injected into the chamber through each electrode bore respectively; e. recycling said discharged gas back into said chamber; and f. withdrawing the pressurized gas applied behind the piston while restricting the flow of discharge gas from the chamber for developing a pressure differential across the piston sufficient to cause the piston to recede upstream thereby pulling the rod back out of the bore of each electrode and extending the arc from said second electrode to said first electrode.

7. A method as defined in claim 6 wherein said first electrode is the cathode and wherein said second electrode is the anode.

8. Apparatus for generating a high intensity source of light radiation which comprises: a. an elongated tubular envelope providing an arc chamber having a light transmitting portion; first and second electrodes each having a central bore axially disposed at opposite ends of the chamber; b. a piston assembly mounted in a cylinder extending from the first electrode external of the arc chamber; c. a rod connected to the piston in line with the longitudinal axis of the chamber, said rod having an external diameter smaller than the bore of each electrode; d. first means for introducing a gas into the cylinder behind the piston thereby driving the piston until the rod extends longitudinally between the electrodes with the tip of the rod confined within the bore of the second electrode; e. second means for introducing gas in said chamber to effect a strong swirling flow of gas about a straight line axis which extends between said electrodes; f. third means for controllably draining the gas exiting from said chamber through the central bore of each electrode; g. fourth means for impressing a voltage across the electrodes; h. fifth means for releasing the gas from the piston cylinder; and i. means for actuating in a consecutive timed sequence said first, second, third, fourth and fifth means.

12. Apparatus as defined in claim 11 wherein the tip of said rod is pointed.