US2682009A - Seal and method of fabrication - Google Patents

Description

2 Sheets-Sheet 1 INVENTOR /-/.D. F'EHSEE ATTQRNE I H. D. FRASER SEAL AND METHOD OF FABRICATION June 22, 1954 Filed Dec. 31, 1952 Julie 1954 H D. FRASER SEAL AND METHOD OF FABRICATION 2 Sheets-Sheet 2 I Filed Dec. 31, 1952 1 z z 5&5

oumzrz AGAIN SOIJIDIFIED INVENTOR H.- D. FF/ISEE 9d Patented June 22, 1954 2,682,009 SEAL AND METHOD OF FABRICATION Hugh D. Fraser, Verona, N. J

assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 31, 1952, Serial No. 328,936

2 Claims. 1

My invention relates to seals and, more particularly, to seals for quartz short are mercury lamps or other quartz lamps which draw high currents and which require conductors of high current carrying capacity, and to the method of making the seal wherein the electrodes of these lamps are maintained in alignment during the sealing operation.

The industry has been faced with the problem of finding a satisfactory seal and in the past, the higher current quartz short are mercury lamps and other related lamps have been practically impossible to make, except by carefully controlled laboratory methods because of the great difiiculty in making a satisfactory seal and in maintaining the lamp electrodes in proper alignment during fabrication of the seal. In addition, whenever relatively higher currents were required, as in the case of short are mercury lamps of over 500 watts capacity, the thin ribbon conductors would tend to oxidize, thus shortening the useful life of the lamp.

Therefore the principal object of my invention is to provide a seal for a higher current quartz short are mercury lamp in which the jointure of the ribbon conductors to the lead-in conductors and the ribbon conductors themselves are not subject to oxidation and in which the necessary seals may be made on a production line basis, instead of a complicated, hand-made basis.

A further object of my invention is to provide a method of making the seal wherein the electrodes of the lamp are maintained in proper alignment during the sealing operation.

Still another object of my invention is to provide an electrode assembly for use in the sealing operation which electrode assembly consists of a quartz retaining body with an electrode and a lead-in conductor inserted therein, the inserted portion of the electrode being of considerable length to facilitate the maintenance of the electrode alignment during the sealing operation.

Yet another object of my invention is to provide a ribbon coil around the inserted portions of the electrode and the lead-in conductor, which ribbon serves as a cushion to prevent the quartz from cracking.

An additional object of my invention is to incorporate a graded seal into my sealing arrangement in order to prevent oxidation of the ribbon conductors, especially at their jointure with the lead-in conductors.

Yet another object of my invention is to provide a flap of thin ribbon over the ledge occurring at the jointure of the heavy and the thin ribbons.

The above objects, and other objects which will become apparent as the description prosectional view of one arm,

ceeds, are achieved by using an electrode assembly comprising a quartz retaining body carrying the electrodes and lead-in conductors in conjunction With a graded seal in fabricating my seal for higher current quartz short are mercurylamps. prevented by enclosing these conductors in an. oxygen-free atmosphere.

The description of the present invention will. be better understood by reference to the drawings which illustrate a preferred embodiment; of my invention and in which:

Fig. 1 is a front elevational view of a preferable embodiment of a quartz short are mercury vapor lamp embodying my seal showing the en-- velope and two arms with the completed seal;

Fig. 2 is a perspective view of the electrode assembly which is used as a part of my seal and in fabricating my seal, including the lead-in:

conductor, electrode, and ribbon conductors which electrically connect the lead-in conductor and electrode;

Fig. 3 is a top plan view of the electrode assembly;

Fig. 4 is a front elevational View, partly in section, of a quartz bulb and arms, prior to fabrication of the lamp;

Fig. 5 is a fragmentary longitudinal cross as shown in Fig. 1,. which shows an initial step in fabricating my seal;

Fig. 6 is a fragmentary cross-sectional View of an arm, as shown in Fig. 1, showing a latter stage of fabrication of my seal;

Fig. '7 is a fragmentary cross-sectional view of one arm as shown in Fig. 1, showing the fab ricated seal;

Fig. 8 is a cross-sectional the lines VIII-VIII of Fig. of the arrows; I

Fig. 9 is a cross-sectional view taken along the lines IXIX of Fig. 7 in the direction of the arrows;

Fig. 10 is a cross-sectional view taken along the lines XX of Fig. 7, in the direction of the arrows;

Fig. 11 is a fragmentary cross-sectional View of the jointure of the ribbons which electrically connect the electrodes and the lead-in conductors.

The short are mercury lamp, as illustrated in the drawings, is generally comprised of a substantially spherical vitreous envelope l2, preferably quartz, having two oppositely disposed arms l3 extending outwardly therefrom. Supported within the arms is and extending into the lamp envelope are electrodes I4. The arms l3 each comprise three sections, the inner section l5 fused to the quartz envelope being comprised of a glass, preferably quartz, having a low coview taken along 5 in the direction Oxidation of the ribbon conductors isz 3 efficient of thermal expansion in order to enable sealing to the quartz envelope. The outer section I6 of the arm I3 is comprised of a glass of relatively high coefficient of thermal expansion, and the intermediate section joining the inner and outer sections is comprised of a graded seal H. The graded seal II consists of a series of glasses running in succession from a low thermal coeflicient of expansion glass at its inner end, to match the inner section I of the arm I3, to

a high thermal coefficient of expansion glass to match the glass of outer section IS. The high coefiicient of expansion glass enables a lead-in conductor I8 to be sealed therethrough to provide electrical connection for the electrodes 5 I4. The electrodes I4 and the lead-in conductors I8 are electrically connected by ribbon conductors I9. Fused inside the inner section I5 of the arm. I3 is -a vitreous retaining body 20, of a low coefficient of expansion glass and readily fusible .to said arm, preferably quartz, which becomes an integral part of the inner section I5 on being fused thereby forming an hermetic seal for the lamp envelope I2 and a chamber 2| in the outer end of the arm I3.

The retaining body 20, the electrode I4, lead-in conductor I8, and ribbon conductors I9 constitute an electrode assembly 22, as shown in Fig. 2. The electrode assembly 22 is of such size as to fit snugly into arms I5.

Each electrode I4 and lead-in conductor I8 is supported by and extends into the vitreous retaining body 20. That portion of the electrode I4 which is inserted into the retaining body is of suificient length to facilitate fabrication of my seal as is hereinafter explained. The portion of each electrode I l-and lead-in conductor I3 which is inserted into the retaining body 20 is wound with a thin ribbon 23 consisting of molybdenum or other suitable material. The purpose of this ribbon 23 is to provide a cushion so that when the seal of my invention is effected, the retaining body 20 of the electrode assembly 22 will not crack. The electrode I4 is preferably comprised of tungsten and may be provided with a coil 24 at its inner end containing a small amount of thorium to facilitate the starting of the lamp, as is common in the art.

The ribbon conductors I9 are preferably comprised of two end sections 25 and an intermediate section 25. The end sections '25 of ribbon conductors I9 are of a heavy type ribbon and are comprised of molybdenum or other suitable material and are preferably of approximately .004! thickness, although this may vary. The intermediate section 26 of ribbon conductors I9 is of a thin type ribbon and is comprised of molybdenum or other suitable material and is preferably of approximately .0006" thickness. It has been found that this thickness of .0006" represents a practical, usable thickness of conductor, if a good hermetic seal is to be maintained between the retaining body 20 and the inner portion I5 of the arms I3. However, this thickness of .0006" may be increased ordecreased', if desired. The inner endsection 25 of the conductor I9 is secured to the electrode I4 within the lamp envelope I2 by Wires 21 wrapped around and welded to the electrode .I4. The'outer end section 25 of the conductor, I9 is similarly secured to the lead-in conductor .I8'

within thechamber, 2I by wires. 21 and by weldns.

The end sections 25 and intermediate-sections 4 26 of conductor I9 are welded together forming a ledge 23. Over the ledge 28 is welded a thin flap of molybdenum 29 or other suitable material of a thickness equivalent to the intermediate section 26 of conductor I9. This is illustrated in Fig. 11. It has been found that cracks will form in the low thermal expansion glass, if it is fused onto a ledge of greater than .001" depth. Since in the disclosed embodiment of my invention the ledge 28 formed by the jointure of the intermediate section 26 and end sections 25 of conductors I9 is-over .003, the flap 29 is used to gradually reduce the gradient and act as a cushion, as shown in Fig. 11, and thus prevent the formation of cracks in the low thermal expansion glass at the ledge 28. The thin intermediate section 26'of conductor I9 cannot be satisfactorily welded or secured to the electrode I4 or the leadin conductor I8v because the jointure would not. withstand the shocks of service due to the fragile character of this very thin ribbon. Thus. the. heavy type ribbon end sections 25 are required.

for this jointure, since they will much better withstand the shocks of service. However, the heavy type ribbon end sections 25 have too great a thickness to allow a satisfactory hermetic seal. to be effected between the inner portion I5 of the arm 13 and the retaining body 20-of the electrode assembly 22. Thus both the thin and heavy typeribbon sections 25 and 2B are necessary in the preferred embodiment of my invention. The number of ribbon type conductors I9 may vary according to the current at which the lamp is desired to operate.

To facilitate fusing the lead-in conductor I8 to the outer section I5 of the arms I3, a glass bead- 3| is slipped over the lead-in conductor I8,

as is common in the art. A flexible lead'32 may be attached to the lead-inconductor I8, if desired.

In fabricating my seal, the electrode assemblies 22 are slipped into the arms I3. In the preferable embodiment of my lamp, the two electrode assemblies 22 and the arms I3 are identical. The tips of the electrodes I4 are positioned and then aligned with respect to one another and the envelope I2 is firmly grasped in a chuck.

Heat is then applied to the outer section IE of arm I3 to fuse the outer section I6 of the glass bead M on lead-in conductor I8 to make an air-tight seal 33 at the outer end of the arm I3, as shown in Fig. 5. Fig. 8 shows a crosssectional view of Fig. 5 taken at XIIL-XIII in the direction of the arrows and illustrates the air gap which exists between the electrode assembl 22 and the inner surface of the inner section I5 of the arm I3 in this stage of fabrication. The envelope I2 and the arms I3 are then evacuated through an exhaust tubulation 35. An inert gas may be now inserted into the envelope I2 and arms I3, if desired, or the vacuum may be maintained;

The partially assembled lamp is thengrasped by a chuck 38 at the outer section I8 andgraded seal sectionI'I of the arm I3. Thisis illustrated in Fig. 6. Either both ends of the lampmay be simultaneously grasped or the assembly may be grasped atone end by a chuck 36, as shown in Fig. 6 and by another chuck, not shown, at the envelope I2;

The assembly is then rotated andheat applied to the inner portion I5 of arm I3 at a point 31 near the graded seal I8, as shown in Fig. 6.

trode assembly 22 at the point of heat. The heat may be supplied by the gas jet 38, as is common in the art.

The gas jet 38 is moved slowly toward the envelope l2 from point 31 at a rate sufiicient to allow the glass under the flame to become plastic and fuse, the inner portion of the arm I3 sinking down onto the retaining body 29 of the electrode assembly 22. It is obvious that when heat is applied at point 31 the electrodes [4 are held rigidly in alignment with respect to one another by the chucks which hold the arms firm, or in the alternative by a chuck 36 holding one arm and another chuck, not shown, holding the envelope 12. As the glass becomes plastic under the flame, this electrode alignment is always maintained by the chucks, as there is always unheated and solidified glass between one chuck and the electrodes, since only one arm at a time is fused and sealed.

As the gas jet 38 is moved upward toward the point 39 at approximately the midpoint of inner section I 5 of arm I3, as shown in Fig. 6, the glass surrounding the furthest inserted portion of electrode i4 becomes plastic. not inserted a sufiicient amount into the retaining body 29, the plastic glass would allow the electrode being heated to move with respect to the other electrode. However, the inserted portion of electrode I i is of sufficient length so that some part of the inserted portion of electrode H3 is always surrounded by solidified glass, thus restraining any movement of one electrode I 4 with respect to the other electrode.

The heating is then continued up to a point 49 at approximately the inner end of retaining body 20, as shown in Fig. 6, at which time one arm has been fused and sealed, the glass of the inner section 15 of the arm [3 sinking onto the retaining body 29 of the electrode assembly 22. The same procedure is then followed on the other arm. Care must be taken not to seal too closely to the point where the graded seal I! is fused to the inner section l5 of the arm l3. Likewise, care must be taken not to seal too closely to the envelope l2.

The envelope is now given a final exhaust through exhaust tubulation 35 and the necessary amount of mercury and an inert ionizable gas such as argon is inserted into the envelope, as is common in the art. The exhaust tubulation 35 is then tipped off, as shown in Fig. 1.

Fig. 7 represents an assembly of my seal after the seal has been completed and Figs. 9 and 10 illustrate how the glass of inner section l5 of arm I3 has been sunk down over the conductors l9 and the retaining body 20.

When fabrication of my seal is completed, the chamber 2| is substantially oxygen free, so that when ribbon conductors I9 are heated due to heavy currents or due to heat conducted from envelope 12, there will be no oxidation of the ribbon conductors 19. In order to maintain the oxygen-free atmosphere of the chamber 2|, graded seal I! is necessary to complete the hermetic seal 34 about the lead-in conductor I8. Thus, it is obvious from the foregoing that my seal has been fabricated with no misalignment of the electrodes and with a high cceificient of thermal expansion glass to conductor seal 34, which seal will not admit air to the oxygen-free chamber 2| when the seal 34 is heated by the conduction of heavy currents or by heat from the lamp.

While I have described a specific embodiment Were the electrode [4 of my invention, it will be understood that modifications may be made within the spirit and scope of my invention.

I claim:

1. A seal for a short are mercury lamp comprising a quartz envelope having an arm connected thereto, said arm being comprised of a quartz cylinder having an inner and an outer end, a glass tube having a higher coefficient of thermal expansion than said quartz, a tubular graded seal connecting one end of said higher coefficient of expansion glass tube to the outer end of said quartz cylinder, said quartz cylinder being connected at the inner end to said envelope, an electrode part of which is inserted into the inner end of said quartz cylinder, the end of said electrode opposite said inserted part projecting into said envelope, a lead-in conductor part of which is inserted into the outer end of said quartz cylinder, the other end of said higher coefficient of expansion glass tube being fused around said lead-in conductor to form an hermetic seal, a chamber enclosed by the outer end of said quartz cylinder, said graded seal, said higher coefficient of expansion glass tube, and said hermetically sealed lead-in conductor, said chamber having a substantially oxygen-free atmosphere, said envelope having a substantially oxygen-free atmosphere, a ribbon conductor electrically connecting said lead-in conductor and said electrode, and said ribbon conductor being totally enclosed within said chamber, said quartz cylinder and said envelope.

2. A short arc mercury lamp comprising a quartz envelope having two outwardly extending arms connected thereto, each arm being comprised of a quartz cylinder having an inner and an outer end, a glass tube having a higher coefiicient of thermal expansion than said quartz, a tubular graded seal connecting one end of said higher coefiicient of expansion glass tube to the outer end of said quartz cylinder, said quartz cylinder being connected at the inner end to said envelope, an electrode part of which is inserted into the inner end of said quartz cylinder, the end of said electrode opposite said inserted part projecting into said envelope, a lead-in conductor part of which is inserted into the outer end of said quartz cylinder, the other end of said higher coefiicient of expansion glass tube being fused around said lead-in conductor to form an hermetic seal, a chamber enclosed by the outer end of said quartz cylinder, said graded seal, said higher coeiiicient of expansion glass tube, and said hermeticaly sealed lead-in conductor, said chamber having a substantially oxygen-free atmosphere, said envelope having a substantially oxygen-free atmosphere, ribbon conductors electrically connecting said lead-in conductors and said electrodes in each arm, and said ribbon conductors being totally enclosed within said chamber, said quartz cylinder and said envelope.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,320,114 Birdsall Oct. 28, 1919 2,353,668 Hinman. July 18, 1944 2,367,595 Marden Jan. 16, 1945 2,518,944 Scott Aug. 15, 1950 FOREIGN PATENTS Number Country Date 541,980 Great Britain Dec. 19, 1941

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