CA1160677A - Method of making electrically-activated photoflash lamp with improved sealed end portion - Google Patents

Abstract

D-23,02 TITLE: METHOD OF MAKING ELECTRICALLY-ACTIVATED PHOTOFLASH
LAMP WITH IMPROVED SEALED END PORTION
ABSTRACT
A method of making an electrically-activated photoflash lamp which includes an ignition structure consisting of a pair of metallic lead wires and primer material disposed on terminations thereof. The structure is hermet-ically sealed within the end of the lamp's glass envelope by firstly applying heat (e. g. by gas-oxygen burners) to the open end portion of the tubing member (which eventually comprises the lamp's envelope) sufficiently to cause the heated glass to flow about the conductors. The final configuration of this end is achieved by introducing a gas within the tubing member's remaining open end to cause the heated end to expand to the desired shape, whereupon the end is permitted to cool. The hermetic seal, as achieved during the initial heating stage, is retained. The desired internal components (e. g., primer, combustible material, and combustion-supporting gas) are then added to the tubing member and the member's remaining open end sealed using a tipping off technique.

Description

-'~,0~2~ _ J
1 lB0677 D~SCRT-'TIOr~ ;

TITLE: METHOD OF MA~NG l~LECTRICALLY-ACTIV~TED PHC)TOFLASH I ¦
LAMP WITH IMPROVED SEALED END PORTION

TECHNICAL FIE:LD
The present invention relates to electrically-activated photoflash lamps and particularly to methods of making such lamps.
Lamps of the above type are generally classified into two varietiesO
low-vol~age and lligh-voltage. Low-voltage photoIlash lamps typically include a glass envelope with a combustion-supporting gas (e. g., oxygen) and a quantity !
10 of f ilamentary, combustible material (e . g. 7 shredded zirconiurn) thereill. A
pair of electrically conductive lead-in wires are usually se~lsd in one end of - the envelope and extend therein. A filament is utilized and interconnects the extending ends of the wires. When the filament is heated by a firing current usually generated from a low-voltage source such as battery or charged j~
15 oapacitor (G. g., having a voltage of from about 1. 5 to 15 volts), it ignites a primer material which then ignites the combustible material to produce a Elash of li~,rht. Naturally, the oxygen gas aids in the above ignition. In high-voltags lamps, the use of a filament is usually excluded by the provision of a glass or ceramic bead in which are located the extending ends of the lamp's conductive 20 lead-in wires. Primer material serves to bridge the portions of these ends which project through the bead. High-voltage lamps also include the afore-described filamentary material and combustion-supporting ~as. Flashing is accomplished by a low encr~,y riring pulse approaching a ;Eew thousand volts and usually provided by a piezoelectric element. In another type of high-25 voltage lamp, the primer is located within an indentation in the bottom of thelamp and the conductive lead-in wires extend therein The teachings of the present invention are partioularly concerned with metllods Or making high voltage lamps, although it will be understood Erom the following that said teachings may be readily extended to lamps of the earlier 30 generation, low voltage variety .

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3, 02; J

2--E~ACKGROUND
In all of 1;he aboYe varieties of lamps, the conductive lead-in wires which rorm p~rt of the lamp's ignition structure are typically sealed withi~
one end of the lamp's envelope using a press (or "pinch") sealing operation 5 during which the glass comprising this end portion is heated and compressed by a pair of opposin~, parallel-faced metallic pr0ss members which converge to engage the heated glass and ef~ect said compression. At least one engage-ment per lamp is required and on some occasions, two or three are employed.
Examples of suchlamps are illustrated inU.S. Patents 3~290J~06 (Schilling 10 etal), 3,752,636 (Warninclc), 3,884,~15 (Sobieski), and4,059,389 (Armstrong et al). While such a technique has proven to successfully provide a hermetic seal oL the metallic lead-in wires, the requirement of using a press seal possesses several drawbacks, particularly with regard to la~ps having relatively small internal volumes (e. g., less than 1. 0 oubic centimeter).
15 Firstly, there exists a strong tendancy for the two wires to "swim" within ths molten glass during pressing, which in tùrn càn result in the two becoming misaligned. Secondly, a press-sealed end adds appreciably to the overall len~th Or the lamp's envelope, a highly undesirable feature serving to defeat today's miniaturization efforts. Thirdly, the necessity for using a press seal ~0 adds to the overall costs of producing the lamp in that such a technique under-standably requires complex lamp manuEacturin~ equipment, which itself is both costly to produce and operate.
It is believed therefore that a method of making an electrically-activated photoflash lamp without the need for a press sealing operation while still 25 assuring a sound, hermetically sealed envelope in the final product would constitute a significant advancement in the art.
DlSCLOSURE OF Tl-IE INVENTION
It is, therefore, a primary object of the instant invention to provide a method of making an electrically-activated photoflash lamp without the need 30 for a press-sealing operation.
It is another object of this invention to make such a method which readily lends itself to high spsed production.

D~ 0 6 7 7 In accordance with a main aspect of the invention, thers is provided a melllod Or making an electrically activated photorlash lamp comprising the steps Or: (1) retaining a grlass tubing member having opposing open ends in a fixed position; ~2) orienting a pair of spaced electrical conductors within the 5 first open end of the $ubing member; (3) heating the first end, causing it to soften and form a seal about the conductors without covering the terminations thereof; (4) introducing a pressurized fluid within the tubing member through the second end to cause the heated first end to expand to a desired conEiguration while still retaining the seal between the glass and conductor members; (5) 10 cooling the expanded first end while retaining the expanded shape; (6) applying primer material to at least one of the conductor terminationsi (7) positioning filamentary combustible within the tubing member through the second, open end; and (8) sealing the second end to deEine a hermetically sealed envelope.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a Eront elevational view, in section, of an electrically-activated photoflash lamp produced in accordance `with the teachings of the instant 'inven- j; !
tion; and FIGS. 2-5 illufitrate the various steps in carrying out the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings .
With particular reference to FIG. 1, there is shown an electrically-25 activated photoflash lamp 10 manufactured in accordance with the preferred embodiment of the invention. Lamp 10 includes an hermetically sealed, light-I;r:msm~ing glass onvelopo 11 having rirsl and socond opposing soalod end portions 13 and 15 respectively. Suitable glass materials for envelope 11 include G-1 type soft glass having a mean coefficient of thermal expansion of 30 about 85 to 95 x 10 in/in/ C between 20 C and 300 C, and the harder boro-silicate glass recognized commercially as Corning type 7073, having a maan coefficient of thermal expansion of about 53.5 x 10 in/in/ C between û C
and 300 C. Borosilicate glass of this type possesses a typical composition J
D~ ) 6 7 ~

of about 63 . 4% SiO2 ~ ? . 2% Al2O3, 17 . 8% B2O3, 0 . 6% LiO, 3. 9% Na2O, 4 . 6%
K2O, 2 23 BaO, and 0.2% Cl. Another soft glass material successfully used in llle invention is sold by the assignee Or the instant invention under the product designation SG10 aud is a potash soda lead glass haying a typical ch~mical composition, I)y weighl;, of about 61% silica dioxide, 21,5% lead oxide, 7.7%
sodium oxide, 7.45% potassium oxide 2.1% alumina oxide,0.15% arsenic trioxide and 0,1% calcium oxide. SG10 glass also has a thermal expar.sion ratillg of ~3.1, a~ annealing point of about 432 degrees Celsius, a softening point Or about 62~ de~rees Celsius, and a dielectric constant of 6.7. It is thusun(lorslood thal; the invontion is capal)le of bein~ successully accomplished utilizing both soft and hard type glasses. ~
Located within envelope 11 is a quantity of filamentary combustible material 17 for providing a high intensity flash of light upon ignition thereof,th~ preferled material bein~ shredded zirconium or hafnium. A quantity of about 2 to 40 milliglams is used although it is of course understood that the quantity of material 17 varies with the internal volume of envelope 11.
Utilization of from 8 to 18 milligrams is preferred in lamps having envelopes with int~rnal volumes equal to or less than 1.00 cubic centimeters, the preferred size for the envelopes of the present invention.
Also within envelope 11 is a combustion-supporting gas, e. g., oxygen, established at a pressure within the range of about 5 to about 15 atmo-spllores. The oxygen gas understandably serves to promote burning of shredded material 17 upon lamp ignition. Lamp 10 further includes an ignition means 19 disposed within end 13 for igniting the shredded zirconium or 25 hafnium upon application of a suitable pulse as may be provided by a power source associated with many of today's electric cameras. One example of such a source is a piezoelectric element which is capable of providing a high voltage, low energy pulse approaching 5, 000 volts. This element is typically located within the camera and provides said pulse through the camera' s 30 circuitry to a corresponding socket in `which the photoflash device ~which includes several lamps 10) is inserted. Accordingly, it is understood that the photoflash lamp produced in accordance with the teachings ol the instant invention is particularly adaptsd for use with multllamp photoflash devices and particularly those wllich depend on high voltage, low energy pulses to ,~.

D-2;3 ,1)2G ~ 1 61~1 6 7 7 achieve sequential ignition of the lamps contained therein.
Ignition means 19 includes a pair Or spaced-apart electrical conductors 21 and 23 which are hGrmetically sealed within end 13 of envelope 11 and project therefrom. Accordingly, the aforemelltioned high voltage pulse iæ
5 applied across conductors 21 and 23 to in turn i,~ nite means 19, which in turn almost instantaneously ignites combustible 17. Conductors 21 and 23 are metallic wires having a diameter of 0. 016 inch and are each comprised of a nickel iron alloy sold under the tradename Niron. An additional material especially preferred when using the aforementioned soft glass materials Lor 10 envelope 11 is another nickel-iron alloy referred to as 52 alloy, which possesses a mean coefEicient of thermal expansion of about 101. 0 x 10 in/in/ C between 25c and 300 C. Still another acceptable material for this type of glass is Dumet, a well known nickel-~iron alloy covered with a thin film (coatin~ of copper.
Wllen using the harder glass materials for envelops 11, conductors 21 and 23 15 were preferably formed from a metal alloy of iron, nickel, and cobalt, said mat;erial known commercially as Rodar or Kovar. This alloy has a composition which is approximately 54% Fe, 29% Ni"17% Co, ~C0.5% Mn,~0.2% Si"and ~0. 06% C and a mean coefficient of thermal expansion of about 50 x 10 7 in/in/ C between 25 C and 300 C.
Each wire conductor 21 and 23 is hermetically sealed within first end 13 in accordance with the unique teachings of the invention (to be described below) and includes an enlarged, rounded termination portion 25 ~FIGS. 2~) upon which is locatsd the remaining portion Or ignition means 19, a quantity of primer material 27 . As shown in FIG. 1, primer 27 is positioned on both 25 terminations to thus substantially cover same and be in electrical contact therewith. The circuit path between the spaced-apart conductors is provided by the sl~leddod ~irconium or haCnium, which thus bridges these mombors.
It is also within the teachings of the invention to cover only one terminatiorl 25 with primer and connect this material with the remaining, exposed wire conductor30 termillation 25. Still further, the invention permits the use of non-enlargedtermination portions which may be located iilush with the lower interior surLaceof envelope 11 (at end 13) with a single, large mass of primer 27 bridging the two terminations. Other alternative embodiments are well within the scope o~ the present teachings. Approximately two milligrams of primer 27 is used 35 in the embodiment showll in FIG. 1, a pre-ferred material comprising about !

D~ 26 99~/0 ~irconium powde3c and 1/~ cellulose nitrite on a dried basis. The rounded, enlarged terminations are formed by applying a flame to each OI the several ends of wires 21 and 23 to cause the ends to melt back to the rounded configu-ration depicted. Primer 27 is added to terminations 25 in the manner defined 5 below.
Ignition of lamp 10 is achieved by application of the aforedefined high voltage pulse across the externally projecting eLds of conductors 21 and 23 to cause an electrical breakdown of primer 27, resulting in a de~lagration thereof and ignition of material 17. The total light output of fillished lamp 10lO is about 2,500 to 3,500 lumen-seconds although it is of course undsrstood t;hat; I;lliS level can be either increased or decreased si~nificanMy by varyingthe quantities of zirconium (or hafnium), the internal envelope pressures, etc.
Dimensionwise, lamp 10 has an envelope external length of about 15 0.700 inch, an exl;ernal diameter of about 0.300 inch, and a wall thlckness of about 0. 032 inch. This substantially reduced size over many known oompara-tive lamps makes lamp 10 especially adaptable to today's miniaturization l~
efEorts regarding multilamp photoflash devices.
In FIGS. 2-5, there are illustrated the preferred steps in the method of 20 making lamp 10. In FIG. 2, a preformed lead wire structure 31 is illustrated as being positioned within a holder 33 located below a vertically oriented elon~ated piece of glass tubing 35 having opposing open ends 37 and 39. Tub-in~ member 35 preLerably has an external diameter of 0. 300 inch, and an internal diameter of 0. 23G inch. It is understood that tubing member 35 is to 25 eventually comprise the envelope 11 illustrated in FIG. 1. Accordingl~r, member 35 is comprised of one of the aforementioned glass materials.
Member 35 is securedly retained within a second holder 41.
As illustrated, open end 37 is vertically positioned below the upper open end 39 and the pair of projecting ends of wire structure 31 are ailigned so as to 30 project vertically upward within end 37 and therefore inside oE tubing member35 a predetermined distance. It is understood that these projecting ends eventually comprise metallic lead wires 21 and 23 of the ~inished lamp 10.
Accordingly, said projecting wires are ~iven the numerals 21 and 23 in FIGS.
2-5. Subsequent to sealing these projecting components within end 37 (to be D-~;3, 02(~ 6 0 6 7 ~

desc~riL~ed bclow), structure 31 is released from holder 33.
Prior to the above procedure, it is preferred to cover selected portions of terminations 25 with a gLass first coating (not shown) approximately 1. 5 to 2 mils thick. The preferred f rit, oonsisting of a fine powder of , 5 glass blended with a binder of amyl acetate and nitrocelluloe, is prepared inslurry form and 1;erminations 25 dipped therein. ~ir drying is used to dry the wet slurry coating prior to orientation within tubing member 35. As described in IJ.S. patent 4,059,389, frit coatings have been found to success-fully prevent preignition short circuits across the lamp's conductors through 10 the combustible material. A second feature of this material is that utilizatio~
thsreof results in a near doubling of the primer ~)reakdown volta~ required to ignite lamp 10. This in turn assures a more reliable finished photoflash unit and a substantial reduction in production shrinkage. Other features, advan-tage, etc of using glass frit coatings in an ignition structure such as that shown in l~lG. 1 aro fully detailed in 4,059,389. It is of course understood tbat whenprimer 27 is added to the terminations 2~5 having a Erit coating thereon, selected regions of coating are removed to assure an electrical connection between the ~!
metal conductors and corresponding primer.
When using the glass tubing memljer 35 having the described internal 20 diameter and wall thickness, it is preferred that conductors 21 and 23 pro~ect al~out 0.12a inch within open end 37. Once the conductors 21 and 23 are positioned therein in the manner illustrated in ~IG. 2, heat is applied to pre-selected external areas of the open end portion 37 of tubing glass member 35 SO 3S to raise the temperature thereof sufficiently to cause this end to soften,25 that is, to assume a plastic state. While in this state, end portion 37 (to comprise the first sealed ond 13 of lamp 10) assumes a beaded form aboul;
the projecting wires 21 and 23 such that the wires are surrounded in the manner depicted in FIG. 3. It is believed that this beading action is the result of surface tension forces acting upon the glass while in the described plastic state. The surprising result is a hermetic seal of end portion 37 with tho conducl;ors 21 and 23 sealed and secured therein. As shown in FIG. 3, this unique procedure provided the defined seal without glass m~terial covering the terminations of the respective wire mer~bers 21 and 23. The terminatiolls (25) are thus free Or glass and capable of providin~ the subse-D-~,O~ BO~;7 7 ~luen~ elecl;ric~l oontact with l;he lamp's primer mal;erial 27 (to be applied later) .
The deIined application of heat to tubing member 35 is preferably accomplished by utilization of a pair of opposing gas-oxygen burners 45 located on opposing sides of the cylindrioal tubing member, each burner preferably adjacent a respective one oE the wire conductors. Use of gas-oxygen or similar pressurized burners is preferred over other forms o~
heating (e. g., resistance type3 because the forces exerted by the impinging flames against the heated external surfaceæ aE member 35 serv~ to accelerate the aforedescribed deforming and sealing operation. The preferred tempera-tures lor heating open end portion 37 are within the range of between 600 degrees Celsius and 1150 de~rees Celsius, dependin~ on the gdass material utili~ed. It is of course only essential to heat the glass of the tubing member's first end portion to a temperature sufficient to cause it to assume the defined plastio (or softened) state such that it will flow a~out conductors 21 and 23.
The resulting col~figuration (FIG. 3) assumed by the heated glass of first end 37, though forming a sound, hermetic seal with conductors 21 and 23, was not decmed totally satisïaotory îor use in lamp 10 because of its relativoly reduced volume ~caused by the indentations or depressions within the heated ~lass sides). Accordingly, it was surprisingly determined that this end portion could be expanded (while in the heated state) without sacrificing the hermetic seal attailled. rhis was achieved by introducing a pressurized fluid within lul~in" member 35 through the romaining, upp~r open end 39. The pr~rerred iluid used was air, however, inert gases (e. g., nitrogen, argon) could also be succesqfully used. The ~luid was passed through a suitable nozzle 51 (FIG. 4) which was located immediately adjacent (or even partially within) end 39. The surprising end result was an expandinv or "balloonirlg' of the heated glass sides of end portion 37 to a rounded configuration in the manner depicted in FIG ~1.
With regard to the invention, by the term pressurized is meant the introduction of a lluid within the open-ended tubular member to increase tlle internal pressure of the member and oausq the described expa~sion or allooning" of the member's heated 3nd 3~n, This increased pressure within the tubing member would inherenMy be greater than atmospheric. Noæzle 51 1..`
. . ~ . ., ~-~." O~G `~~ `J
~ ~8~1~77 g contained, in on~ example, an orifice 0.032 inch in diameter an~ was connected to a twenty-one inch steel manifold having an internal diameter of 1. 00 inch. The pressure within the manifold was established at fifty pounds.
After permitting the glass to cool to room temperature, the resulting shal~e was also surprisingly Lound to be stronger than ends formed using the aforedefined press sealing techniques, as indicated by scratch and upshoclc tests normally used to test small glass structures such as photoElash lamps.
The most significant gain, however, was in overall internal volume for lamp 10 compared to a similar length envelope having a press-seal. A typical pre~s-sealed end accounted îor about 22% o~ the tolal envelope le~g~h. IIsing a seal made possible by the teachings of the invention, a similar length and diameter envelope reali~ed a volume increase over the press-sealed envelopes of about 15 per cent. By way of example, an envelope having an overall length of 0. 700 inch, an external diameter of 0. 300 inch, and a wall thicknessof 0. 032 inch7 realized a gain in internal length Oe about 0. 06 inoh over a comparative sized (externally) press-sealed envelope. Accordin~ly, it is ,' possible to reduce internal pressure without altering the envelope's exterior dimensions. Alternatively, it is possible to procluce lamps hasring reduced external features while maintaining the desired similar internal volumes.
Still another highly advantageous feature of the invention is that it can be readily performed on existing photoflash production equipmellt without substantial modification thereto, as clearly indicated by the relatively simple components (e.g., holders 33, 41) required.
In FIG. 5, there is illustrated the final steps of ma~ufa¢turinglamp 10 in acc:ordance with the teachings of the invention. The terminations Or wires 21and 23 have been coated with primer 27 using a suitable applicator (;~ot shown) introduced through end 39. Subsequent to drying of the primer, the necessary quantity of filamentary combustible 17 is added, also through open end 39.
Any dispenser known in the art can be employed to locate material 17 and Iurtller definition is not believed necessary. This also holds true for the means of depositing primer 27. It is u~derstQod from the above that primer 27 is applied while in a liquid state and sul~sequentlydries while in position. This dryin~ can be facilitated by the introduction of heated air through second end D-23,026 1 160677 39. Additionally, the shredded ~irconium or hafnium material 17 is inserted within ~pen end 39 in order to frictionally cl~gage the ir~ternal side walls Oe tubing member 35 in the manner illustrated in FIG. 5. Glass tubing member 35 is then evacuated through open end 39, a quantity of the described combustion-5 supporting gas (oxygen) is introduced within the member 35 through end 39,and end 3~ is thereaEter sealed using a tipping-off technique. Such a technique is well known in the art of manufacturing photoflash lamps and iurther definition is not deemed necessary. It is known, oE course, l;hat such a technique requires a "necking down" of the tubing member in the region oE ' 10 end 39 prior to final closure, thus reæulting in a discarding of that portion of glass material above the constricted region and corresponding reduction from the original length to the desired 0. 700 inch length for final envelope 11.
In the above technique, the upwardly projecting wires 21 and 23 were positioned within open end 37 so as not to engage the internal surfaces of this 15 end portion Or the glass tubin~ member. This alignment (FIG. 2) was con-sidered necessary in order to accomplis,h the unique hermetic sealing de,s-cribed. It was also obs~rved during all of the aboYe techniques that direc~ ie~posure oE wires 21 and 23 to the flames emitted by the gas-oxygen burners 45 on occasion resulted in the formation of a loose oxide layer on the wires.
20 Such a layer could defeat ~ormation of a sound hermetic seal between the &lass and metal components and eventually result in gas leakags in the finished product. This potential problem was readily overcome by directing the burner flames only OlltO the designated glass surfaces (FIGS. 2, 3). Under-standably, utilization of other varieties of heaters may also prevent such an 25 occurrence. The use of the gas-oxygen burners 45 is preferred7 however, for the reason cited.
There has thus been shown and described a new and unique process for forming a hermetic seal within an end of a ~lass envelope between the glass and the photoflash lamp's metallic lead wires secured within t'he end.
30 The described 1;echnique eliminates the need for the aEorementioned press seal and thereEore provides the soveral advanta~eous fea1;ures described above .

D-23 ~26 ~ ~ ~0677 While tllere have bee~ shown and described what are at present c(>l~sidorcd l;he proïerred ombodiments Or the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the 5 appended claims.

Claims (10)

D-23,026 -12-WHAT IS CLAIMED IS:

1. A method of making a pressurized, electrically-activated photoflash lamp, said method comprising:
securedly retaining an elongated glass tubing member having first and second opposing open end portions in a vertical position such that said first open end portion is located below said second oper end portion;
positioning a pair of spaced-apart electrical conductors within said first open end portion such that said conductors project a predetermined distance within said glass tubing member and do not engage the internal surfaces of said tubing members, the portions of said conductors projecting within said first open end portion not being physically connected;
heating said first open end portion of said glass tubing member to a predetermined temperature to cause said first end portion to soften and assume a first position about said projecting conductors, the glass material of said heated first end portion forming a hermetic seal with said conductors without covering the terminations of said conductors;
introducing a pressurized fluid within said glass tubing member through said second open end portion when said first end portion is heated to cause the sides of said heated first end portion located about said conductors to assume a second, expanded position about said conductors while retaining said seal therewith;
permitting said heated first end portion to cool while in said second, expanded position;
applying a quantity of primer material to said terminations of said conductors through said second open end portion;
positioning a predetermined quantity of filamentary combustible material within said glass tubing member through said second open end portion;
introducing a combustion-supporting gas at an established pressure within said glass tubing member through said second open end; and thereafter sealing said second open end portion of said glass tubing member to provide a hermetically sealed envelope having said combustion-supporting gas at said established pressure therein.

D-23,026 -13-

2. The method according to Claim 1 wherein said electrical conductors are positioned below said first end portion of said tubing member and project upwardly within said first open end portion of said glass tubing member prior to said heating of said first open end portion.

3. The method according to Claim 2 wherein said electrical conductors project upwardly in a vertical direction during said heating of said first open end portion.

4. The method according to Claim 1 wherein said predetermined temperature is within the range of from about 600 degrees Celsius to about 1150 degrees Celsius.

5. The method according to Claim 1 wherein said fluid is an inert gas.

6. The method according to Claim 5 wherein said inert gas is selected from the group consisting of argon and nitrogen.

7. The method according to Claim 1 wherein said fluid is air.

8. The method according to Claim 1 further including the step of evacuating said glass tubing member through said second open end portion after said positioning of said combustible material therein and before said introducing of said combustion-supporting gas.

9. The method according to Claim 8 wherein said combustion-supporting gas is established at a pressure of from about 5 to about 15 atmospheres.

10. The method according to Claim 1 wherein said heating of said first open end of said glass tubing member is accomplished using pressurized burners which only direct heat onto the external glass surfaces of said first open end portion of said glass tubing member during said heating step.