US3317264A

US3317264A - Method of gettering impurities in electrical devices such as incandescent lamps

Info

Publication number: US3317264A
Application number: US307146A
Authority: US
Inventors: Martin Jack; Hugh C Hiner
Original assignee: Westinghouse Electric Corp
Current assignee: Philips North America LLC
Priority date: 1963-09-06
Filing date: 1963-09-06
Publication date: 1967-05-02
Anticipated expiration: 1984-05-02

Description

May 2, 1967 J. MARTIN ETAL 3,317,264 METHOD OF GETTERING IMPURITIES IN ELECTRICAL DEVICES SUCH AS INCANDESCENT LAMPS Filed Sept. 6, 1965 FIG.4.

PRELIMINARY LIGHT-UP OF FINISHED LAMP AT LOW VOLTAGE TO GETTER IMPURITIES WITHOUT RECRYSTALLIZING FILAMENT.

: FLASH FINISHED LAMP AT HIGH VOLTAGE TO RECRYSTALLIZE AND SET FTLAMENT United States Patent METHOD OF GETTERING IMPURITIES IN ELECTRICAL DEVICES SUCH AS INCAN- DESCENT LAMPS Jack Martin, Paramus, and Hugh C. Hiner, Bloomfield, NJ., assiguors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 6, 1963, Ser. No. 307,146

8 Claims. (Cl. 316-25) This invention relates to a method of processing electrical devices and has particular reference to a method of cleaning up residual impurities in tubular lamps after they have been sealed'and are ready for flashing.

During the manufacture of incandescent lamps it is very important that the lamp be kept free from material which would contaminate it and impair its performance or life. This is particularly true in the case of so called T3 quartz lamps now being marketed and used in heating and lighting applications. Such lamps are well known and consist of a tubular quartz envelope that contains a coiled tungsten filament which initially has a fibrous unrecrystallized structure and is centrally supported within the envelope. Since these lamps are very compact, they are especially sensitive to impurities that remain on the filament or residual gaseous impurities such as air that have not been removed before the envelope is sealed.

Despite all precautions, it frequently happens that small amounts of impurities are trapped in the sealed lamp. When the lamp is subsequently flashed to recrystallize and set the filament the impurities react with the hot filament and form vapors which condense on the cool ends of the lamp envelope when they form a black deposit which is not only unsightly but reduces the lamp efiiciency.

With the foregoing in mind, it is the general object of the present invention to provide a simple and economical method for cleaning up residual impurities in a finished electrical device such as an electric lamp that contains an incandescible element.

Another and more specific object is the provision of a method for gettering impurities in completed electric incandescent lamps that can be easily incorporated into high-speed manufacturing equipment and that will prevent blackening of the cooler portions of the lamp during the filament-flashing operation.

The foregoing and other objects are achieved in accordance with the present invention by placing a suitable gettering material in heat-receptive proximity to the filament and then prelighting the lamp at a predetermined voltage that is sutficient to heat the getter without recrystallizing the filament or causing it to sag. The

impurities are thus liberated by the filament at a slower rate than heretofore and the heated gettering material is able to absorb the impurities before they condense on the envelope ends. The lamp remains lighted at this loW voltage for a short time, such as 20 seconds or so, and is then lighted at the usual high voltage to flash and recrystallize the filament.

A better understanding of the invention will be obtained by referring to the accompanying drawing, wherein:

FIGURE 1 is an elevational view of a tubular T3 heat lamp which is representative of the type of device which can be processed by the method of the present invention;

FIG. 2 is an enlarged cross-sectional view of the lamp along the reference line II-II of FIG. 1;

FIG. 3 is a fragmentary sectional view through the axis of the lamp along the reference line III-III of FIG. 2; and,

FIG. 4 is a block diagram illustrating the basic steps of the process according to a preferred embodiment of the present invention.

While the invention can be used with advantage in the manufacture of various types of electrical devices having incandescible elements, it is especially adapted for use in conjunction with tubular lamps designed for heating or general lighting applications and it has, accordingly, been so illustrated and will be so described.

With particular reference to the drawing, in FIG. 1 there is illustrated a tubular T3 heat lamp 10 comprising a quartz envelope 12 that has a diameter of approximately and is closed at each end by a press seal 17 and contains a linear filament 14 of coiled tungsten wire. The filament is centrally disposed within the envelope and is held in this position by means of attached lead-in con ductors 16 that are embedded in the press seals and by a plurality of auxiliary support discs 18 that are attached to the filament at various points along its length. The lamp contains the usual inert gas filling such as argon at about 680 mm. pressure.

As shown more particularly in FIGS. 2 and 3 the support discs 18 are of generally square configuration and are provided with a slot 22 that extends inwardly from one of its sides to a centrally located aperture 24. The discs are slightly smaller than the inner diameter of the envelope 12 and are fabricated from a metal such as tantalum that getters gaseous impurities but does not react with or absorb the inert gas fill. The discs can be attached to the filament by inserting them between adjacent turns and spacing the latter so that they compres sively clamp the discs in place as disclosed in US. Patent No. 2,980,820, issued Apr. 18, 1961, to W. L. Brundige et al. a

The desired clean up of impurities that may inadvertently be trapped within the lamp after it has been sealed is accomplished in accordance with the present invention by first lighting the lamp at a predetermined voltage below its rated voltage to vaporize and getter the impurities, and then flashing the lamp at a much higher voltage in the usual manner to recrystallize and set the filament as outlined in the block diagram shown in FIG. 4.

In order to prevent the elongated filament 14 from developing a permanent sag when energized at either the low or high voltage, the lamp 19 is preferably positioned in a magnetic field and a filtered D.-C. voltage of sufiicient magnitude is used to levitate the filament and maintain it substantially straight while it is in a heated condition. Of course, the magnitude and orientation of the magnetic field and the direction and magnitude of the filament current must be properly correlated in order to achieve such levitation. The correct procedure and a preferred apparatus for achieving levitation of the energized filament is disclosed in copending application, Ser. No. 99,331, of Gordon B. Childs, entitled Apparatus for Flashing Lamp Filaments, filed Feb. 14, 1961, and assigned to the same assignee as the present invention, which application has now matured into US. Patent No. 3,140,906.

rious sizes without recrystallizing the filament or causing it to sag in accordance with this invention as given below J in Table I. The corresponding high-voltage flashing schedule is also listed for each lamp type.

Lamps flashed in accordance with the high-voltage flashing schedule given in Table I heat the filament to The voltage and amperage listed in Table I above for the preliminary light-up are so correlated with respect to the size and resistance of the filament that the latter reaches a temperature of about 1680 C. This temperature is preferred since it enables the tantalum supports to reach a sufficiently high temperature to become activated and quickly getter the gaseous impurities liberated by and vaporized from the filament. Experience has shown that if the lamps are simply flashed at the high voltages listed in the foregoing table without this preliminary low voltage light-up, the impurities are flashed off of the filament and onto the cool ends of the envelope with resultant blackening before the tantalum supports reach a high enough temperature to absorb the impurities. While the exact nature of the impurities are unknown, it is believed that small amounts of air may be trapped within the sealed lamps which, upon heating of the filament at the beginning of the highvoltage flashing operation, react with the tungsten to form a thin oxide coating on the filament. This oxide is then flashed off the filament and condenses on the cool ends of the lamp envelope to form the undesirable blackening effect.

As will be apparent, the temperature to which the filament 14 is heated during the preliminary likht-up can be varied within rather wide limits depending upon the length of time the lamp is burned at this voltage. Since tungsten recrystallizes at a temperature of about 2100 C., it will be seen that the preliminary light-up voltage and filament temperature can vary considerably from the aforementioned preferred values, providing the time of light-up is properly adjusted. Thus, the filament ternperatnre during the degasing and gettering operation can vary from about 1500 C. to 1850 C. and the time of light-up can vary from about to 60 seconds without fully recrystallizing the filament or causing an objectionable amount of sag. The preferred temperature range is, however, from 1600" C. to 1700 C. and the time of light-up is from about 20 to 30 seconds.

As is well known, the ability of tantalum and other such metals to getter gaseous impurities increases with temperature. It is necessary, therefore, that the discs 18 reach a sufiiciently high temperature to prevent the liberated gases from reaching and blackening the cool ends of the envelope 12. At the aforementioned filament temperature ranges the tantalum support dis-cs reach a temperature within the range of approximately 500 C. to 1400 C. with the hottest portions, of course, being those that are in direct contact with the filament. The heated tantalum discs, accordingly, constitute very efficient getters and quickly clean up and absorb the gaseous impurities liberated by the filament and other portions of the lamp structure before they can recontaminate the finished lamp.

After the preliminary light-up and gettering operations have been completed the lamp is flashed at a much higher voltage in the regular manner, as indicated by the block diagram in FIG. 4. However, this second step is optional as far as the cleaning-up operation is concerned since substantially all of the impurities have been gettered during the preliminary light-up. The second block in the diagram is, accordingly, shown in dotted lines to indicate that it can be omitted if desired.

a temperature in the order of 2700 C. so that recrystallization of the filament occurs very rapidly. Thus, the configuration of the filament is set and will be substantially straight if a DC flashing voltage is used and the filament is properly oriented within a magnetic field in accordance with the teachings of the aforementioned copending patent of Gordon Childs.

It will be appreciated from the foregoing that the objects of the invention have been achieved insofar as a very simple and inexpensive method of purging a completed lamp of deleterious impurities has been provided which method can be very conveniently incorporated into high-speed manufacturing apparatus, such as the flashing magnetic apparatus disclosed and claimed in the foregoing copending patent of Gordon Childs.

While one embodiment has been disclosed in detail, it will be appreciated and understood that various modifications can be made in the method without departing from the spirit and scope of the invention. For example, the filament can be flashed and recrystallized in a hydrogen atmosphere before the discs are mounted and the filament is sealed within the envelope. In this case, the low-voltage light-up would be performed merely to clean up the impurities and recrystallization and filament sag would not present any problem.

We claim as our invention:

1. In the manufacture of an electrical device having a sealed envelope that contains an elongated incandescible filament which is designed to operate at a predetermined rated voltage, the method of maintaining said filament in a predetermined position within said envelope and removing impurities from said filament after it has been sealed Within said envelope and thereafter preventing such impurities from recontaminating the completed device, which method comprises:

attaching to said filament, prior to the assembly thereof with said envelope, a support member which (1) is adapted to engage a part of said envelope when the filament is disposed in assembled relationship with said envelope and (2) is composed of gettering material that is adapted when heated to absorb gaseous impurities liberated by said filament;

placing said filament in assembled relationship with said envelope so that the attached suppoit-gettering member interiorly engages the aforesaid part of said envelope;

sealing said filament in said envelope and completing the assembly of said device;

heating said filament to a predetermined temperature below the temperature which it attains when it is operated at its rated voltage but which is sufficient to vaporize impurities associated with said filament without vaporizing the support-gettering member; and

maintaining the filament at said predetermined temperature for at least several seconds so that the support-gettering member is heated by said filament and absorbs the vaporized impurities emanating from said filament.

2. In the manufacture of an electrical device having a sealed envelope that contains an elongated filament of refractory metal wire which is designed to operate at a predetermined rated voltage and initially has an unrecrystallized fibrous structure, the method of maintaining said filament in a predetermined position within said envelope and removing impurities from said filament after it has been sealed within the envelope and before it is flashed and set and thereafter preventing such impurities from recontaminating the completed device, which method comprises:

attaching to said filament, prior to the assembly thereof with said filament, a support member which (1) laterally protrudes beyond the filament and is adapted to engage a part of said envelope when the filament is disposed in assembled relationship with said envelope and (2) is composed of gettering material that is adapted when heated to absorb gaseous impurities liberated by said filament;

placing said filament in assembled relationship with said envelope so that the attached support-gettering member interiorly engages the aforesaid part of said envelope;

sealing said filament within said envelope and completing the assembly of said device;

heating the unflashed filament to a predetermined temperature that is below its recrystallization temperature but sufficient to vaporize impurities carried by said filament and heat, but not vaporize, said support-gettering member; and

maintaining the filament at said predetermined temperature for about 20' seconds to enable the heated support-gettering member to .absonb the liberated vaporized impurities without substantially recrystallizing the fialment.

3. In the manufacture of an electric device having a sealed envelope that contains an incandescible filament of refractory metal wire that initially has an unrecrystallized fibrous structure and is subject to sag, the method of removing impurities from said filament after it has been sealed into said envelope and before it is flashed and recrystallized and preventing such impurities from subsequently recontaminating the completed device, which method comprises:

mounting on said filament, prior to its assembly with said envelope, a member fabricated from a metal which when heated will getter gaseous impurities liberated by said filament;

heating the unflashed filament to a temperature approximately 400 C. below its recrystallization temperature to activate said gettering member solely by the heat imparted to it by said filament and vaporize impurities associated with said filament; and

maintaining the filament at said temperature for a period of about 20 seconds so that said heated getter member absorbs substantially all of the liberated gaseous impurities before the filament becomes recrystallized or develops an appreciable amount of sag.

4. The method set forth in claim 3 wherein said filament is heated by means of an electric current.

5. In the manufacture of an electric lamp having a tubular envelope that contains an elongated coiled filament of tungsten wire which initially has a fibrous unrecrystallized structure and is susceptible to sagging before it is flashed and recrystallized, the method of removing impurities from said filament after it is sealed within said envelope and before it is flashed and set and preventing such impurities from subsequently contaminating the completed lamp, which method comprises:

attaching a tantalum member to said filament before it is sealed in said envelope, applying a voltage to the completed lamp suificient to heat the filament to a temperature of from about 1500 C. to 1850 C. and the tantalum member to a temperature of about 500 C., and

continuing the application of said voltage for a period of time within the range of about 20 to seconds and sufiicient to enable the heated tantalum member to absorb gaseous impurities liberated by the filament without substantially recrystallizing the latter and causing it to sag.

6. The method set forth in claim 5 wherein; said tantalum member comprises a disc that serves as a filament support, the applied voltage is such that the filament is heated to a temperature of from 1600 C. to 1700 C. and the disc to a temperature of from 500 C. to 1400 C., and the filament is maintained at said temperature for about 20 seconds.

7. In the manufacture of an electric lamp having a tubular envelope that contains an elongated coiled filament of tungsten wire which initially has a fibrous unrecrystallized structure and is susceptible to sagging before it is flashed and recrystallized, the method of removing impurities from said filament after it is sealed within said envelope and before it is flashed and set and preventing such impurities from subsequently recontaminating the finished lamp, which method comprises:

attaching a tantalum support member to said filament before it is sealed into said envelope,

applying a voltage to the finished lamp suflicient to heat the filament to a temperature above about 1500 C. but below the recrystallization temperature of tungsten,

continuing the application of said voltage for a period of time sufiicient to heat the tantalum support member and enable it to getter gaseous impurities liberated by the filament without substantially recrystallizing the latter, and then flashing the finished lamp at a voltage sufficient to recrystallize and set the filament.

8. The method set forth in claim 7 wherein; the filament is heated by means of direct current, said lamp is energized while the filament is in a magnetic field and disposed transverse to the lines of flux, and the magnitude and polarity of said current and magnetic field are so correlated that the filament is levitated and prevented from sagging during the gettering operation.

References Cited by the Examiner UNITED STATES PATENTS 2,489,261 11/1949 Braunsdorfi 31625 X FRANK E. BAILEY, Primary Examiner.

Claims

3. IN THE MANUFACTURE OF AN ELECTRIC DEVICE HAVING A SEALED ENVELOPE THAT CONTAINS AN INCANDESIBLE FILAMENT OF REFRACTORY METAL WIRE THAT INITIALLY HAS AN UNRECRYSTALLIZED FIBROUS STRUCTURE AND IS SUBJECT TO SAG, THE METHOD OF REMOVING IMPURITIES FROM SAID FILAMENT AFTER IT HAS BEEN SEALED INTO SAID ENVELOPE AND BEFORE IT IS FLASHED AND RECRYSTALLIZED AND PREVENTING SUCH IMPURITIES FROM SUBSEQUENTLY RECONTAMINATING THE COMPLETED DEVICE, WHICH METHOD COMPRISES: MOUNTING ON SAID FILAMENT, PRIOR TO ITS ASSEMBLY WITH SAID ENVELOPE, A MEMBER FABRICATED FROM A METAL WHICH WHEN HEATED WILL GETTER GASEOUS IMPURITIES LIBERATED BY SAID FILAMENT; HEATING THE UNFLASHED FILAMENT TO A TEMPERATURE APPROXIMATELY 400* C. BELOW ITS RECRYSTALLIZATION TEMPERATURE TO ACTIVATE SAID GETTERING MEMBER SOLELY BY THE HEAT IMPARTED TO IT BY SAID FILAMENT AND VAPORIZE IMPURITIES ASSOCIATED WITH SAID FILAMENT; AND MAINTAINING THE FILAMENT AT SAID TEMPERATURE FOR A PERIOD OF ABOUT 20 SECONDS SO THAT SAID HEATED GETTER MEMBER ABSORBS SUBSTANTIALLY ALL OF THE LIBERATED GASEOUS IMPURITIES BEFORE THE FILAMENT BECOMES RECRYSTALLIZED OR DEVELOPS AN APPRECIABLE AMOUNT OF SAG.