US2440153A - Method of making spark gaps and products thereof - Google Patents

Description

April 20, 1948;` E QLES y 2,440,153y METHOD OF MAKING SPARK GAPS AND PRODUCTS THEREOF Filed'July 4, 1945 INVENTOR ATTORNEY Patented Apr. 20," 1948 METHOD F MAKING SPARK GAPS AND vPRODUCTS THEREOF Herbert E. Oles, Indianapolis, Ind., assigner to P. R. Mallory & Co., Inc., Indianapolis, Ind., a

corporation of Delaware Application July 4, 1945, Serial No. 603,203

Claims. l

The present invention relates to spark gaps or impulse gaps and to a novel method of making such gaps.

Spark gaps or impulse gaps are used at present for various applications, of which the principal one is their use in high frequency ignition systems. In general, such gaps comprise two spaced electrodes which are connected in an electric circuit capable of building up a high voltage between the electrodes so as to produce a spark discharge between the same. The spark di..- charge may be used to produce high frequency oscillations in a work circuit and for othery purposes. Spark gaps of the described character are disclosed, for example, in Patent Number 2,354,- 786 grantedtofAlexander C. Wall on August 1, 1944, and also in a co-pending application of Alexander C. Wall and Herbert E. Gles, Serial No. 582,136, led on March l0, 1945.

It is an object of the present invention to improve the characteristics of spark gaps or impulse gaps of the described type.

It is another object of the invention to provide a method of producing spark gaps having eX- tremely stable characteristics and particularly having a very stable break-down voltage.

(ciers-a5) I the ends of which are inserted into the annular' Other and further objects and advantages ofthe invention will become apparent from the following description, taken in conjunction with the accompanying drawing; in which Figure l is a longitudinal sectional view of a spark gap embodying the invention during the process of its manufacture;

Figure 2 is a circuit diagram of a typical impulse circuit employed in carrying the principles of the invention into practice; and

Figure 3 is a sectional View of the finished spark gap embodying the invention.

Referring now to Figure 1 of the drawing, reierence numeral I0 denotes a gap electrode of a generally circular shape constituted of a suitable refractory metal, such as, for example, tungsten. This electrode is brazed or otherwise mounted on a cup-shaped electrode holder plate I i. A n end plate I2 is welded to flange I3 of holder plate II and is provided with a U-shaped annular channel It.

Electrode l0, holder plate II and-end plate I2 constitute an electrode assembly. This assembly is mounted together with another assembly oi identical character so that the two electrodes of the respective assemblies are held in parallelspaced cooperating position. This is accomplished by means of a spacer tube I5 of glass or some other material of an insulating character,

channel I4 of the end plates. Preferably, end plates I 2 are constituted of a suitable ironchromium alloy which may be directly sealed to glass thereby providing a stable and hermetically sealed construction. The inner space surroundingthe electrodes and dened by end plates I2 and spacer tube I5 is initially in communication with the external atmosphere through openingsv or ports i6 provided in the electrode holder plates II and through openings I'I in the center portion of the end plates I2. One of the openings I'I may be sealed by means of a glass bead I 8 while the corresponding opening Il of the other endplate has a glass tube I9 sealed thereto and provides a channel or duct through 'which the inner space of the gap may communicate with the external atmosphere. As spark gaps of the described character and the method of making the same are fully disclosed in the said co-pending application Serial No. 582,136, no detailed description of the construction of the gap will be necessary.

I have discovered that the operating characteristics of a gap of the described character may be greatly improved by means of a special conditioning treatment after the structural completion of the gap and prior to applying the nal seal thereto. This treatment comprises connecting the gap in a typical impulse circuit which periodically applies high voltages to the electrodes of the gap. The impulse generating circuit may comprise a suitable source of electrornotive force, such as a conventional ignition magneto. The wave form generated may be such that it has approximately a 1000 cycle rate of rise and the output may be approximately 2000 volts peak when connected across a .015 microfarad condenser without the gap. The Work circuit may comprise a typical lead and spark plugv operating in a bomb containing nitrogen, or some other suitable inert gas, with fifty pounds pressure on the nose of the plug. The application of these periodically acting impulses may be carried on for an extended period such as for twenty hours, or more. It has been found that if thegap is filled with a suitable gas after this treatment and sealed, a spark gap of superior operating characteristics and of greatly increased stability is obtained.

The invention will now be more fully described in connection with Figure 2 in which a typical impulse circuit is diagrammatically shown. Thecircuit comprises a magneto, generally denoted by reference numeral 20. The magneto includes a primary winding 2| and a secondary winding 22, which are inductively coupled to each other. One end of both windings is grounded and a condenser` 23 is connected across primary winding 2l. The magneto also includes a pair of interrupter contacts 24 operated by means of a rotary cam 25.

Another condenser 25 yof suitable capacity is connected across secondary winding 22 of the magneto. The spark gap to be treated, includ'- ing electrodes Il) and diagrammatically shown as element 21, is connected between the .common terminal of secondary winding 22 and condenser 26, and one end of primary winding 28 of a step-up transformer. The `other end `of said winding 28 is grounded. Primary winding Z5 is inductively coupled with secondary Winding 23 of the step-up transformer one end oi which is connected to the center terminal Se of a spark plug 3l. This spark plug is inserted into a pressure-resistant container or bomb 32. The bomb may be iilled with a suitable gas, such as nitrogen, under a pressure of fifty Vpounds per square inch, in order to simulate the operating conditions within the cylinders of fan internal com-- bustion engine.

In carrying outthe method `of the-invention, the spark gap 2l to be treated is connected into the 'impulse circuit of vFig-ure 2. 1n order to olotainnthe desired resultsyit is 'essential that the gaseous products of the presparking treatment be continuously removed from the interiorof 'the spark gap. In the simplest case, this may be ac complished by maintaining the interior of the gap `communication with the atmosphere through ports Iii and I1 and glass tube I9 4(liig. l). It 4is also possible, however, to pass -a flow of a. filtered and cleaned gas, 4such as airfthrough the gap., said flow being introduced through tube ISiand withdrawn or discharged through port Vifi before it is sealed at I8.

IDuring the operation of vthe magneto, a high `voltage, as described, is periodically built up across condenser 26. .After this voltage has reached the break-down voltage of gap A2l, an oscillatory discharge will take placethrough'said gap and through primary winding 280i the :stepup transformer. An oscillatory current of similar high frequency buto'f considerably higher voltage will be built up across secondary winding 2-9 and willlproduce high frequency sparks between-center electrode 30 and electrodes 33 of spark plug 3i.

This presparking treatment is `preferably continued for an extended period `of time'such as for twenty to Vforty hours. `In general, a presparking treatment for approximately twenty hours at Aabout twenty-two sparks per second has been found to provide vsatisiactoryresults.

After the presparkingtreatment has been completed, the spark gap may be evacuated, 'filled with a suitablegaseous charge, and Yis hermetically sealed. Excellent results, however, 'have been obtained by sealingthe spark 4gap immediately after the presparkin'g treatment without'fa preliminary evacuation process. nfthat'case, the inner space of the gapwill be lled 'with a gaseous charge having a composition which is substantially identical with that of atmospheric air, that is, it will contain approximately 21 per cent of oxygen, 79 per cent of nitrogen and 'traces'of certain noble gases foundin 'small quantities in atmospheric air,'such as helium, neon, argon, krypton and' xenon. This charge will be under normal atmospheric pressure, corresponding to the pressure vat the time of Asealing thegap.

The finished gap is illustrated in Figure 3 and is in every respect identical with that shown in Figure 1, except that glass tube I9 has been sealed off close to the lower end plate, constituting a glass bead 34 similar to glass bead I8 sealing the upper end plate.

Experience has demonstrated that lasspark gap produced in accordance with the principles of the present invention provides important advantages. Thus, the spark gaps made by the method of the invention possess extremely stable physi- 'cal characteristics. For example, the voltage neofe'ssary to produce a discharge between the electrodes will vary only as little as five per cent or less. Moreover, spark gaps prepared according 4tothe invention will retain their desirable physical characteristics for a very long time and as a result, Vhave a very long useful life.

The physical principles underlying the descried presparking treatment and responsible for the lgreatly improved operating characteristics ci the gaps treated in accor-dance with the inven tion are not fully understood. It is believed that during the presparking treatment minute but critically important changes are caused in the electrode surfaces, while the gaseous and solid try-products of the treatment are removed for example by permitting them to escape into the atmosphere. Therefore, any possible initial changes in the physical characteristics of the electrodes and of the gap will already occur during the presparking period which is continued until such characteristics are permanently stabilized. While this explanation appears to be well supported by `experimental evidence, the vinvention is, of course, independent from the merits of Iany theoretical consideration.

Although the present invention has been disclosed in connection with a preferred embodiment thereof, variations and modifications may be resort-ed to by those skilled in the art without departing from the principles of the invention. I consider all of these variations and modifications to be within the true spirit and scope of the present invention, as disclosed in the foregoing description, and vdeiinedby the appended claims.

What is claimed is:

1. The method of making impulse gaps of Ystable characteristics which comprises providing a pair of spaced plane electrodes constituted of refractory metal within a gas-tight container, maintaining said container in communication with the external atmosphere, presparking lsaid electrodes for a period of several hours, and then hermetically sealing said container.

2. The method of making impulse gaps of stable characteristics which comprises providing a pair of plane parallel-spaced tungsten electrodes within a vessel adapted to be hermetically sealed, initially maintaining the interior of said vessel in communication with the external atmosphere, connecting said electrodes to an impulse circuit toproduce a plurality 'of electric sparks per second between said electrodes for a period'of several hours, a-nd hermetically -sealing said Vessel after said sparking period thereby to obtain an impulse gap of stable operating characteristics.

3. The method of making impulse gaps of stable characteristics which comprises providing a pair of parallel-spaced circular tungsten elec trodes within a vessel adapted to be hermetically sealed, maintaining the gaseous atmosphere within said vessel in communication with the external atmosphere, connecting said electrodes to an electrical impulse circuit to produce electric sparks in the order of about twenty sparks per second for a period in the order of about twenty to forty hours, and hermetically sealing said vessel after said sparking period thereby to obtain lan impulse gap of stable operating characteristics.

4. The method of making impulse gaps of the type including a pair of spaced electrodes within a sealed vvessel which comprises establishing communication between the interior of said vessel and the external atmosphere, presparking said electrodes for a predetermined period while maintaining such communication, and then hermetically sealing said vessel.

5. An impulse gap of stable characteristics comprising a hermetically sealed vessel, a. gaseous atmosphere in said vessel having a composition similar to that of the external atmosphere, and a pair of plane electrodes constituted of refrac- 6 tory metal mounted in said vessel in parallelspaced position, said electrodes having surfaces of such physical characteristics as is obtained by presparking them for an extended period.

HERBERT E. CLES.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,879,131 Dobke Sept. 27, 1932 1,933,329 Hull Oct. 31, 1933 1,965,584 Foulke July 10, 1934 2,199,866 Alterthum May 7, 1940 2,288,861 Watrous July 7, 1942 2,300,931 Kalischer Nov. 3, 1942

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