US 3173735 A
Description (OCR text may contain errors)
March 16, 1965 H. A. FENN 3,173,735
CAPPING 0F ELECTRIC LAMPS Filed Nov. 24, 1961 2 Sheets-Sheet 1 March 16, 1965 H. A. FENN 3,173,735
CAPPING OF ELECTRIC LAMPS Filed Nov. 24, 1961 2 Sheets-Sheet 2 United States Patent 3,173,735 CAPHNG 0F LEQTRIC LAMPS Henry Alfred Penn, Edmonton, London, England, assignor to Associated Electrical Industries Limited, Lomdon, England, a British company Filed Nov. 24, 1961, Ser. No. 154,638 Claims priority, application Great Britain, Dec. 5, 1969, dL'i'd/dd 3 illaims. (Cl. 339144) The present invention relates to a means for securing the cap of an electric incandescent or discharge lamp to the envelope.
It is frequently necessary to provide such a lamp with a cap which supports the lamp so that the source of light, i.e. the heated filament or are discharge-is accurately positioned with respect to a lens and/or reflector constituting or forming part of an optical system with which the source is to be employed. The cap is inserted into a holder, the latter being in a predetermined position to the optical system. Usually the light source is required to be located on the optical axis of the system, so that the light emergent is in the form of a focussed beam. Such an arrangement may be provided in connection with projectors for film and like transparencies, or for the headlamps of automobiles.
It is the usual practice to provide the lamp cap with a projecting flange which, when associated with a suitable mounting forming part of the holder, eifects the desired location of the source. Moreover, it is necessary to ensure that the filament, or electrodes, between which the arc occurs, be accurately located with respect to the cap in order to achieve the desired result. In the generally used construction of incandescent lamp, the filament is attached to lead-in conductors supported in a glass pinch forming part of a stem which is sealed into a neck portion of the envelope of the lamp; in a gas discharge lamp, at least one of the electrodes is supported by the glass pinch. The envelope is then secured to the cap by attaching it at the neck portion to the cap with a suitable cement. Since the accuracy with which the stern can be sealed into the envelope cannot be closely controlled, optical control has to be used during the cementing stage of manufacture, to obtain the desired location of the source with respect to the holder, and to the optical system. Furthermore, when the light source is such that a large amount of heat is released, e.g. in projector lamps, it is difficult to obtain a capping cement which will not be adversely affected by the heat.
It has been proposed to secure the filament terminals of an incandescent projector lamp to tubular contacts, closed at their outer ends, which are directly sealed at their inner open ends to a pressed glass base which carries the filament and is sealed to the envelope. In this way, the tubular contacts are accurately located with respect to the filament, and being employed directly to plug into a holder and then to support the lamp in the holder, no cap or capping cement being then employed.
The object of the present invention is to provide an attachment not involving a cement between the cap and envelope of an electric incandescent or are discharge lamp which provides accurate positioning of the light source to the cap.
According to the invention, the envelope of an electric lamp is provided with a glass base secured to the cap through the intermediary of a cylindrical metal member, sealed to the base at one end and having at least one slot therein in which is engaged a corresponding projection provided on the inner surface of the cap, the cap being of such dimensions that it closely surrounds the cylindrical member so that the filament or electrodes of the lamp are accurately positioned with respect to the cap.
3,l73,735 Patented Mar. 16, 1965 The compositions of the metal or alloy used for the metal cylindrical member, and the glass of the base to be sealed thereto should be so chosen that their thermal expansion characteristics are substantially matched in order to avoid resultant stresses in and cracking of the glass after sealing. Conveniently, the cylindrical member is provided with, at one end, a number of projections or lugs formed integrally therewith, which are sealed into the glass base. Preferably, the lugs and slots are equiangularly displaced thereon, and in a staggered relation.
The cylindrical member is conveniently in the form of a split sleeve, and is constructed from sheet metal bent into the cylindrical form after being punched into shape. One of the projections or lugs may be divided at the split.
The projections on the inner surface of the cap may be in the form of tongues punched out of the cap and bent inwards to engage corresponding slots provided in the surface of the metal cylinder.
During manufacture, the cylindrical member, the lead wires to the filament or electrodes, and sufficient powdered glass to form the base, are placed in a suitably shaped mould, and the assembly heated to cause the glass base to fuse and be sealed to the cylindrical member and leads. Alternatively, the glass may be initially in the form of a short length of tubing. The lead wires are arranged to pass through the base when formed and the lugs or projections on the cylindrical member are located so as to simultaneously be sealed into the base, the axis of the cylindrical member being normal to the plane of the base. A glass exhaust tube may also be located in the mould so as to be sealed to the base during the same operation. Alternatively, an aperture may be left in the base into which an exhaust tube is subsequently sealed. The lead wires passing through the base are now ready to receive the filament or electrode-supporting assembly, which is jig-mounted in the required position with reference to the glass base. After this operation, the outer envelope is sealed to the periphery of the base, and the lamp evacuated and tipped off.
The invention will now be described with reference to the accompanying drawings, in which:
FIG. 1 illustrates in elevation a projection lamp and cap assembly constructed in accordance with the invention,
FIG. 2 illustrates in perspective, the cylindrical member through which the cap is attached to the glass base,
FIG. 3 is a perspective view of the cap of the lamp before assembly, and
FIG. 4 is a part cut-away elevation of the glass base showing the manner in which the cap is attached to the glass base.
Referring to the drawings, the lamp consists of an envelope 1 containing the plane type projection filament 2 and a cap 3 secured to the glass base 4 of the envelope. The filament 2 is in the form of a number of sections arranged parallel to one another, being supported by a framework constituted of a pair of frame members 5 to which the terminals 6 of the filament are secured. The frame members 5 are attached to leading-in conductors 7 which constitute the terminal leads of the filament, into one of which may be inserted an internal fuse 8. The filament is further supported by wires 9 which are hooked to engage in the appropriate filament loop. The filament supports 9 are insulated from one another and held rigidly in position by being embedded into oppositely positi-oned glass beads 10. The frame members 5 are also secured to the beads It! by wires 11 which are also embedded in the beads.
The glass base 4 of the envelope through which the leading-in conductors 7 are sealed, is of pressed-glass construction and is provided with an evacuating tubulation 12 (FIG. 4). The presssed base may be formed from molten glass tubing, or from a powdered glass moulded and sintered. Leading-in conductors 7, to which the terminals of the filament are connected, pass through the base, a dummy le ad 13 being also provided for the purpose of connecting to one of the frame members 5 and supporting "the frame in accurate relation to the base member 4.
Eachlead-in conductor 7 is connected to the corresponding external contact terminals 19 of the lamp cap which are insul ted-from one another and from the supporting cyl i fider 3 by'rrieans of the insulating bead 20.
The filament ,2 is mounted upon the base member 4 by way of the leads 7 and ,13 in a manner such as accurately to position the filament with respect to the base member. The envelope 1, when sealed in theusual manner to the base member ,4 provides an ev'acuable enclosure .for the filament, but its position relative to the base memiberxis comparatively unimportant provided that it is substant-iallysymmetrically connected, to the base member. Since the requirementis that the filament of the lamp, when the lamp is inserted intov a holder, be accurately positioned with respect to an optical system in turn related tow the position of the holder, it is essential for the based 7 to be accurately located with respect to the capS. This is projections or lug at one end, formed integrally with the cylindrical surface. The cylindrical member 14 is also provided-with a number of slots 16 punched into its surface, and from the surface of the cap 3 (FIG. 3), a corresponding .number of tongues 17 are inwardly pressed.
The cylindrical member 14 is of a diameter slightly smaller 'than that of the cap 3, so that whenxthei-former is inserted into the cap in theappropriate position, the tongues-17 inwardly pnoject'through theholes 16. To secure the cylindrical member and the cap't-ogether, the tongues 17 are bentaround as shown in FIG. 4. Since the cylindrical member-.14 is sealed into;-the base4, as shown at 18, the
cap is now securely attached tothe base.
The-cylindrical: member 14 is conveniently in theform of a splitsleeve, and-is constructed fromsheet metal bent into the cylindrical form after being punched into shape.
One of the'projections or 1ug's 15 maybe divided at the split, as shown at 19. 1 The invention provides a firm means of attachment of the cap to theglass base, without the use of a cement or solder.
In additiontothe leads'7 and 13, further members (not shown in the drawings) in the form of stub-s may be isealedinto-the base, the purpose of the further'members being toy-supplement the'attachrrient between the base and the filament assembly. In this way, the filamentas-sem'bly ,may be giyen increased strength against lateral displacement by cross-bracing, jand another ofthe stub leads may form-the leading-in conductor from the cap to thefuse.
of there being no necessity for the afiixing of the envelope to the cap with optically controlled accuracy.
The use of the invention does not, however, avoid the necessity for ensuring that, during manufacture, the source of light, e.g. filament or are discharge, is accurately located with relation to the base of the lamp to which the envelope is subsequentlysealed; this means that the leads supporting the filament or electrodes must be accurately positioned with respect to the cylindrical member 14.
Since this can be achieved by using an accurately-formed mould for the support of the parts While the base is being made,-no particular difliculty arisesfrom this requirement.
While the construction has been described more particularly with regard to a filament type projection lamp, it is evident that it may equally well be applied to a discharge lamp, in which the leads 7 may carry the electrodes between which the arc discharge takes place.
What I claim is:-
1. An electric lamp comprising a base-plate of vitreous material, leads for supporting energy converting means sealed through said base, a cylindrical metal member sealed end-on to said basje-plate, said member having at least one slottherein, and a cylindrical cap having integral insulated terminals attached to the energy converting means, said cap being arranged closely surrounding said member and having a projection centering said slot whereby to secure said cap to said base-plate through said member.
2. An electric lamp cornprising a vitreous envelope, a
base-plate of vitreous material sealed to and forming part of the envelope, leads for supporting energy converting means sealed through said base-plate, a cylindrical metal member sealed end-on to said base-plate in accurately positioned relation to said leads, said member having at least onewslot therein, and a cylindrical cap having moulded-in insulated .terminals attached one each to the said leads, said cap being a push fit over said cylindrical member and having a projection entering said slot whereby to lock said cap to said member, and thus to the base-plate.
.3. An electric lamp comprising a vitreous envelope, a base-plate of vitreous material sealed to and forming part of the envelope, leads for supporting energy converting means sealed through said base-plate, a cylindrical ,metal member; having lugs projecting from one edge thereof sealed into said base-plate so as accurately to locate said member with relation to said leads, said member having a plurality of uniformly spaced slots in its peripheral wall, and a cylindrical cap having moulded-in terminals. attached to the respective leads, said cap closely surrounding said cylindrical member and having a plurality of projections each entering a respective slot in-said cylindrical member whereby to secure said cap integrally to the lamp envelope.
7 References Cited. by the Examiner UNITED STATES PATENTS 1,596,492 8/26 Kulp- 313 31s 1,987,427 1/35 Watson "753395444X DAVID J GALVIN, Primary Examiner. JAMES D. KALLAM, Examiner.