US 2892665 A
Description (OCR text may contain errors)
H.v D. FRASER DISCHARGE' LAMP MANUFACTURE iled Jan. 3L 1955 Exif/9057' INVENTOR. #.P. F'iewsE/e. 5% 9* 4%@ HWEA/E'Y United States Patent 2,892,665 DISCHARGE LAMP MANUFACTURE Hugh D. Fraser, West Caldwell, NJ., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 31, 1955, Serial No. 485,218 4 Claims. (Cl. S16- 26) This invention relates to discharge lamp manufacture, and has to do more particularly with the introduction of mercury into discharge lamps especially of the highintensity or high-pressure type having quartz envelopes.
Basically, the invention proposes novel means and method of incorporating the precise amount of mercury individually into a lamp so said lamp will have predetermined exact operating characteristics.
Likewise broadly considered, the invention contemplates operational steps .and apparatus repetitiously usable on successive lamps with facility and ease.
An important object of the invention is to permit nal sealing of the lamp to be deferred with a considerable time lapse after the lamp has been charged with its proper amount of mercury.
Other objects, advantages and novel features of construction andpmethod will appear to persons skilled in the art to which the invention appertains as the description proceeds, both by direct recitation thereof and by mplication from the context.
Referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout the several views;
Figure 1 is an elevational view of the discharge lamp as it appears on the exhaust machine ready for the initial seal-olf of the tubulation;
Figure 2 is a view of the initially sealed-off lamp, inverted from position shown in Fig. 1 for introduction of the mercury into the lamp envelope, ready for second sealing of the tubulation;
Figure 3 is another elevation of the lamp located in apparatus by which precise amount of mercury is determined for retention in the lamp envelope;
Figure 4 is a graph of the are voltage during operation in the apparatus of Figure 3; and
Figure 5 is a view of a part of the showing of Figure 3 indicating the discharge as discontinued and the mercury required for the same as condensed in the envelope and the excess condensed in the tubulation.
The lamp, as herein illustrated, is an elongated tubular quartz envelope 11, closed at both ends with the closures supporting main electrodes 12, 13 respectively within end regions of the hollow of the envelope and one closure also supporting an auxiliary electrode 14 in the envelope. Intermediate of the ends of the envelope of the lamp in its embryonic stage is a laterally projecting tubulation 15, which, in the completed lamp, is tipped off proximate to the envelope wall as indicated by dotted lines 16 in Fig. 5. Tubulation 15 is used, first, to connect the envelope to an exhaust machine 17 to evacuate the envelope, after which argon or other suitable gas is introduced through said tubulation into the envelope. I employ a usual construction of exhaust machine which receives the lower end of the tubulation depending from the lamp envelope. ln the tubulation is a capsule 18, upwardly open, which contains liquid mercury 19 retained therein by gravity. The capsule 18 is retained in tubulation 15 by group consisting of thon'a and zirconia.
a spring clip (as shown inFig. 1) and a necked-down 1 2,892,665 Patented June 30, 1959 ice ` and thereafter the tubulation is initially sealed-off at 20 by gas llame 21 at a location below the capsule 18. The lamp is then inverted, as shown in Fig. 2, so that tubulation projects upwardly from the lamp envelope and permits the mercury 19 to drop to the bottom of the envelope, where it splatters, forming a lot of smaller drops on the enevelope Wall. The tubulation is then sealed olf a second time, fas at 22 by gas flame 23, between the envelope and capsule.
In order to assure full discharge or gravitation of the mercury from the capsule into the lamp envelope, the mercury drop may be coated with a lm of oxide of the The application of such oxide may be made directly on the drop of mercury prior to introducing it into the capsule or into the tubulation, or may be applied by dusting the iinely powdered refractory oxide on the interior of the capsule or on the interior of the tubulation. By any one of these expedients, the mercury is kept from adhering to the tubulation so that all of the mercury will pass into the envelope when the lamp is inverted for that purpose as above described. The amount of mercury is in excess of the quantity ultimately required for proper operation of the lamp, but the excess will be eliminated in accordance with the process described hereinbelow.
Upon again inverting the lamp as in Fig. 3, it is brought to a supported horizontal position on rack cleats 24 xed at the upper side of a heat-resisting table 25, said table having a hole 26 therein properly located to receive the tubulation therethrough. At the underside of the table coaxial with said hole 26, is a heating coil 27 through which the tubulation is inserted. The coil is shorter than said tubulation whereby the lower sealed end portion 22 of the tubulation projects from the lower end of the coil. This projection of the end of the tubulation is for purpose of enabling the same to be cooler than the main body of the tubulation so that mercury may condense gradually therein.
The electrodes, as Well as said coil 27, are connected to an electric source and a discharge will thereby be instigated and maintained within the envelope. The discharge creates heat in addition to the heat developed by said coil, and the mercury in the envelope vaporizes. Consequential upon such vaporization of the mercury, the pressure in the envelope increases to a maximum for the amount Vof mercury present, and this maximum is intentionally greater than that desired for normal operation of the lamp. In order to conserve the heat and obtain full vaporization of the mercury, a cozy or hood 28 is applied over the lamp while being thus processed. The amount of heat developed by coil 27 may be adjusted by a rheostat 29 or other current controlling mechanism in the electrical circuit to the coil.
Mercury vapor of course lls the tubulation as well as the envelope, and since the lower end of the tubulation is relatively cool, the mercury will gradually condense thereat, thereby reducing the pressure. As the discharge voltage across the electrodes depends directly upon mercury vapor pressure in the envelope, reduction of the pressure reduces the discharge voltage to substantially the desired equilibrium value. The rate of the reduction of pressure can be controlled by adjustment of the current supply heating the tubulation by coil 27, and when the discharge voltage reaches the aforesaid equilibrium value, the current and heating are discontinued. The voltage values may be observed on a voltmeter 30 connected across the lines supplying equilibrium voltage, that is, the voltage at which the lamp is intended to function in use, is designated as volts. In practice, it
has been found that this equilibrium or operating voltage is slightly lower than the value at which the discharge voltage and heating are discontinued. The discharge or arc voltage during` fabrication of the lamp is indicated by solid line graphv 3-1 of Fig. 4, the discharge starting at A at about eighteen volts and mounting, in the exampie shown, toa maximum of about 175 volts at B, and then dropping' back to 145 volts at C where heating and discharge voltage for fabrication purposes are discontinued. The operating voltage of the finished lamp is designated by broken line graph 32 of Fig. 4 and shown as leveled oi at' D. Since heating coil 27 and hood 28 are not used with the completed lamp, the warm-up period is slightly longer than during fabrication, but as the mercury has been reduced in the finished lamp from the amount originally in the envelope during fabrication, the operating voltage levels off. at substantially l40 volts in the illustrated embodiment.
During fabrication, immediately upon discontinuance of theY arc voltage and heating-coil current, a cooling stream, preferably air, isdirected against a lower part of the envelope at a distance from the tubulation. lt is a characteristic of mercury vapor, that it will condense at a cool spot. Consequently substantially all of the vapor isV converted to liquid state at-33, Fig'. 5, in a restricted area of the envelope immediately adjacent to an air-jet tube 34 shown terminating close to the envelope near one end thereof. rlThe tiltedl downwardly away from condensed mercury 33 does not enter the tubulation and mix with the condensed portion 3S or mercury' that has collected in the bottom of said tubulation. At any convenient time thereafter, the tubulation is sealed at le proximate tothe envelope, thus removing the condensed mercury 3S of the tubulation and leaving only the condensed mercury 33 remaining in the envelope. The pressure in the completedy lamp, when the lamp is not in operation, isv usually less than one atmosphere, but with the lamp in operation, the-pressure created by the vaporization of the mercuryV may riseto several atmospheres.
Illustrative of controlling mechanism for fabrication purposes, l have indicated feed lines 56 (Fig. 3), from the usual alternating current commercial supply. These feed lines energize the primary 37 ofv a transformer the secondary 38 of which supplies energy to the electrodes through switches 40, 41. Those lines also supply energy through two other switches 42, 43, one of which, as 42, is in` serieswith a solenoid' coil 44 the core 4S of which is operatively connected to an air valve 46 for tube 34, and another one, as 43, closes the heating coil circuit. These several switches are operated in unison, for instance by a magnet 47 to simultaneously open switches 40, 41 and 43 to the electrodes and to the heating coil and to close the switch 42. to the air valve solenoid 44'; Circuit to magnet 47 is appropriately manipulated automatically or by the operato-r to thus operate the bank of switches 40, 4l, 42 and 43 when the arc voltage, as indicated by vol'tmeter 39, has dropped back to the desired or appropriate level or reading. Current to the magnet may be reduced in voltage by interposing a transformer 48 in the circuit thereto from the line, and an operator-controlled switch 49 is shown in the primary line of that transformer.
The'fabrication operations, in brief, include sealing o the tubulation three times, irst an initial seal-olf at 2i@ beyond'capsule i8, then after the envelope has been inverted, a second seal-off at 22 between the envelope and capsule, and ultimately a nal seal-off contiguous to the envelope, as at 16, after the mercury content has been vaporized and segregated with the desired condensation thereof in the envelope and the excess in the portion of the tubulation beyond thenal seal-off. This separate condensation of the needed mercury to remain in the lamp and the excess mercury to be excluded' avoids necessityj of making the final seal at the moment that the vapor the tubulation so that the envelope is kept level or I pressure is at its current value. Instead, I am enabled to delay the 'dnalseal-olf indefinitely and still have proper amount of mercury and vapor pressure for operation of the lamp after the envelope is ultimately sealed-olf. While the circuit shown is advantageous for commercial fabrication of lamps, it will be understood that the switches controlling the arc current andthe heating coil current may be hand operated and likewise the air valve is operable by hand and I have made many lar'nps utilizing such hand operations.
l. The method of introducing mercury into an arc tube in an amount corresponding to that required to produce a mercuryLvapor' pressure within said arc tube which mercury-vapor pressure corresponds` to a predetermined arc tube operating voltage, comprising exhausting said arc tube through an elongated tubulation, introducing into said arc tube through `said tubulation a predetermined pressure" of inert ionizable gas and an excess of mercury over that desired, tipping off said elongated tubulation' at a point considerably removed from' said arc tube, positioning' said tubulation soV that it is substantially below said arc' tube, operating an electric discharge within said arc tube to cause same to heatV and' vaporize the mercury therein, the operating electric discharge within said arc tube having an operating potential which is" proportional to the pressure of mercury vapor therein, maintaining the lowermost portion of said tubulation at a' tentperature substantially lower than the temperature of the operating' arc tube to cause some of thc mercury vapor formed by the heat of the operating arc tube to' condense therein, applying heat to said' tubulation intermediatev the ends thereof to limit and control the rate of mercury condensationvin the cooler lowermost portion of said tubulation, de-energiing the electric discharge within said arc tube and withdrawing said applied heat' from said tubulation" when the operating voltage of said discharge has reduced to a predetermined value, cooling a portion of thestill-hot arc tube which is lowermos't and removed from said tubulation to condense on said cooled arc tube portion the desired amount of mercury now present in" said arc tube and to rapidly` drop the mercuryvapor pressure in said arc tube to less than atmospheric', and thereafter tipping on said tubulation at a pointv con# tiguous to s'aid'arc tube.
2. The method of processing a mercury-discharge device having an envelope' charged with an excess of; mer? cury over the amount needed, said envelope having an elongated tubulation opening therein, and said tubulation having a sealed end portion considerably removed from said envelope, which method comprises vaporizing said mercury in said envelope by heat appliedrelative to said envelope, condensing the excesspart of said vaporized mercury in said tubulation proximate the sealed end portion thereof in addition to heating another portion of said tubulation by a separate controlled source'of heat to control the rate of mercury condensation in said tubulation, condensing the needed part of said mercury in a portion of said envelope away from said tubulation, and sealing-off from said envelope vsaid tubulation containing said excess condensed mercury thereby isolating the same from said envelope.
3. The method of processing a mercury-discharge device having an envelope vcharged with an excessv of mercury over the amount needed, said envelope having an elongated tubulation opening therein, and said tubulation having a sealed end portion considerably removed from said envelope, which method comprises vaporizing said mercury in said envelope by heat applied relative toV said envelope, condensing the excess part of said mercury' in said tubulation proximate the sealed end portionA thereof in addition to heating another portion of said tubulation by a separate controlled source of heat to' control the rate of mercury condensation in said tubulation, cooling a limited area 0f Said' envelope away from said tubulation to condense the needed part of said mercury thereat for retention in said envelope, and sealing-olf from said envelope said tubulation containing said excess condensed mercury thereby isolating the same from said envelope.
4. The method of processing a mercury-discharge device having an envelope charged with an excess of mercury over the amount needed, said envelope having an elongated tubulation opening therein, and said tubulation having a sealed end portion considerably removed from said envelope, which method comprises vaporizing said mercury in said envelope by heat applied relative to said envelope, in addition heating a portion of said tubulatio-n removed from the sealed end portion thereof by a separate controlled source of heat to vaporize mercury in the heated portion of said tubulation, condensing vaporized mercury proximate the sealed end portion of said tubulation, controlling the heating of said heated tubulation portion to Control mercury condensation in said tubulation proximate the sealed end portion thereof, continuing to condense vaporized mercury in said tubulation proximate the sealed end portion thereof until excess mercury over the amount needed in said envelope is condensed in said tubulation, and sealing-off from said envelope said tubulation containing excess mercury.
References Cited in the le of this patent UNITED STATES PATENTS