US2725498A - Disc seal for electron gaseous discharge device - Google Patents

Description

29, 1955 J. A. STORMS ETAL DISC SEAL FOR ELECTRON GASEOUS DISCHARGE DEVICE 2 Sheets-Sheet l INVENTORS IE5 PETE/250M 7T0. sroe/ ls.

BY 91 'AITORNEY Filed June 25, 1952 Nov. 29, 1955 J. A. STORMS a-rm.

DISC SEAL FOR ELECTRON GASEOUS DISCHARGE DEVICE Filed June 25, 1952 2 Sheets-Sheet 2 Z s 2 1 0 m 1. 2 N 4 a M 4 4 4 w 6 m 2.5 L-rE/eso/v J'ifi. STOP/W8.

9, 6%? ATTORNEY United States Patent DISC SEAL FOR ELECTRON GASEOUS DISCHARGE DEVICE John Allen Storms, Newark, and Robert Edwin Peterson, Cedar Grove, N. J., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 25, 1952, Serial No. 295,440

2 Claims. (Cl. 313-217) This invention relates to electric gaseous discharge devices and more specifically to a disc seal between the envelope and the electrode. for such a device.

In the manufacture of gaseous discharge devices, such for example, as a high pressure short are mercury vapor lamp, the quartz to metal seal involved therein has presented many problems of quality and control. In the past, seals have been made by either wrapping spiral molybdenum ribbon along a refractory metal electrode and shrinking the quartz glass end portion down onto the ribbon and electrode or by employing a thin molybdenum ribbon embedded by automatic techniques in the quartz end portion. While the spiral winding type of seal is satisfactory, the winding of the ribbon spiral on the electrode requires considerable skill. Further, the molybdenum ribbon type seal is limited by the amount of current which it will carry and the strength of the ribbon.

Hence, it has been found advantageous according to our invention to employ a disc seal which provides an easy but positive quartz to metal seal for a high pressure short are mercury vapor lamp.

The electrode may be conveniently composed of two rods which are threadable into each other at their respective ends and hermetically brazed together with a thin refractory disc or washer therebetween. The exterior or lower rod of the electrode is then suitably beaded with a hard glass and inserted into a short quartz end portion of the lamp envelope with the disc seated in a convenient shoulder thereat. A tubular graded seal portion is then simultaneously sealed to the end portion of the lamp envelope and the bead on the lower end of the electrode. The lamp is then evacuated and the quartz glass in the end portion and graded sealed portion is collapsed upon the electrode and about the disc to provide an hermetic seal thereat.

In its general aspect the present invention has the object of overcoming the aforementioned disadvantages of prior art seals for gaseous discharge devices.

Specifically, an object of the present invention is a facile and positive disc seal for a gaseous discharge device such as a high pressure short are mercury vapor lamp.

An additional object is an electrode for sealing into a gaseous discharge device comprising a pair of rods threadable one into the other with a refractory metal disc therebetween for sealing into a quartz end portion and a graded seal portion of a gaseous discharge device envelope.

Other objects of the invention will become apparent to those skilled in the art as the description proceeds both by direct recitation thereof and by implication from the context.

Referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout:

Fig. 1 is a front elevational view of a gaseous discharge device wherein our invention is contained.

Fig. 2 is an exploded view of one of the electrodes of our invention for sealing into the gaseous discharge device of Fig. 1. 1

Fig. 3 is a side. elevational view of the electrode of our invention partially in section.

Fig. 4 is a sectional view showingthe first step of the sealing operation, namely, sealing the disc type electrode end portions and graded seal portion of the lamp envelope.

.Fig. 5 is an enlargementof a fragmentary portion of Fig. 4 showing the sealing of the disc between the end portion and the graded seal portion. e

Fig. 6 is' a view similar to Fig. 4 showing the second step of the sealing operation,- namely, collapsing the end portion and quartz portion of the graded seal portion onto the electrode and around the disc.

Fig. 7 is a view similar to a portion of Fig. 3'and show- 12 suitably quartz or some other high silica content glass.

provided with oppositely disposed refractory metal electrodes 14 and 16 suitably molybdenum or tungsten, an inert gas, such as argon for initiating a discharge therebetween and an ionizable medium such as mercury. Each of the electrodes 14 and 16, shown in Figs. 2 and 3, have an upper or inner rod 18 comprising a threaded lower portion 20 of reduced diameter and pro-v vided with a threaded opening 22 in its upper end. A lower or outer rod 24 for each electrode 14 and 16 has an annular opening 26 for threadable engagement with the lower portion 20 of inner rod 18 and is provided with a solder ring shoulder 27 at the upper end and a bead 28 of a suitable hard glass and a threaded connection on its lower end. An electrode tip 30 is threadable into the aperture 22 in the upper rod 18. A refractory metal disc or washer 32, conveniently molybdenum, secured between the rods 18 and 24, completes the electrode. As shown in Fig. 7 the threading of the lower portion 20 of the rod 18 and of the opening 26 in the rod 24 may be dispensed with.

According to our invention the tip 30 is threaded into the hole 22 in the upper rod 18 and the lower threaded portion 20 of said rod is screwed into the opening 26 in the lower member 24 with the disc 32 therebetween and a solder ring 34 suitably cupro-nickel in the shoulder 27. The electrode 14 or 16 is then baked in a hydrogen atmosphere at a temperature sufiiciently high to cause the nickel ring 34 to melt and hermetically braze the rods 18 and 24 and the disc 32 together.

The electrode 16 for example is then inserted into an end portion 38 of the vitreous envelope 12 so that the disc 32, shown in Fig. 4 rests in a suitable shoulder therein. A graded vitreous tube 40 having its quartz end 41 adjacent the disc 32 and its relatively soft glass end 42 adjacent the head 28, is then slipped over the lower rod 24 of the positioned electrode 16 and a suitable source of heat, such as the burners 44 and 46, is employed to simultaneously fuse the end 41 of the envelope end portion 38 (as shown in Fig. 5) with the disc 32 therebetween and also the end 42 to the bead 28 of the electrode 16. V

The electrode 14 is then similarly sealed to an end portion 48 of the envelope 12 and a graded vitreous tube 49 as shown in Fig. 4. The envelope 12 is then evacuated thru a suitable exhaust tubulation 50 and heat is supplied to the quartz portion 41 of the graded seal tube 40 and the envelope end portion 38 to cause the collapse of said portions onto the electrode 16 and about the disc 32 to provide an hermetic seal thereat.

It will be understood that the relatively soft glass end 42 of the graded seal tube 40 is not collapsed onto the rod 24 of the electrodes 14 and 16 thereby preventing creation of, any strains therein. The quartz end portion 48 of the envelope 12 and the quartz end of the graded vitreous tube 49 are similarly collapsed onto the electrode 14 and the lamp 1t) isvthen ready for exhaust.

Thus it will be seen from the foregoing description that our invention has overcome the defects of the ribbon seal and the spiral wrapped electrode seal for gaseous discharge devices. We have provided a two piece electrode hermetically joined to a refractory metal disc for hermetic sealing between the quartz end portion of an envelope and a graded vitreous tube to provide an easy but positive quartz glass to metal seal for a high pressure. short arc vapor lamp.

Whereas an embodiment of our invention has been disclosed it will be understood that modifications may be made within the spirit and scope of the invention.

,We claim:

1. A gaseous discharge device comprising a sealed envelope provided with tubular end portions, an ionizable medium therein, a pair of oppositely disposed electrodes in said envelope, at least one of said electrodes having inner and outer refractory metal rods and a refractory metal disc of substantially greater diameter than said inner and outer rods hermetically joined between said rods, an inner hermetic seal comprising said disc, said end portion and a hard glass end of a graded vitreous 4 tube, said inner seal embedding said disc and said electrode in said end portion and said hard glass end of said graded tube, and an outer hermetic seal comprising the soft glass end of said graded tube and the soft glass beaded outer end of said outer metal rod.

2. A stem for a gaseous discharge device comprising a vitreous end tube, an electrode having inner and outer refractory metal rods and a refractory metal disc of substantially greater diameter than said inner and outer rods hermetically joined between said rods, an inner hermetic seal comprising saiddisc, said end tube and the hard glass end of a graded vitreous tube, said inner hermetic seal embedding said disc and said electrode in said end tube and said hard glass end of said graded tube, and an outer hermetic seal comprising the soft glass end of said graded tube and the soft glass beaded end of said outer metal rod.

References Cited in the file of this patent UNITED STATES PATENTS 1,293,441 Housekeeper Feb. 4, 1919 2,039,167 Hopkins Apr. 28, 1936 2,243,250 Dietz May 27, 1941 2,518,944 Scott Aug. 15, 1950 2,549,328 Nelson et al Apr. 17, 1951 2,630,471 Peters Mar. 3, 1953 2,664,180 Peters Dec. 29, 1953

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