Title:
Lamp pinch seals
United States Patent 3885149


Abstract:
In an electric lamp having a pinch which hermetically seals the lamp envelope to thin foils forming part of lead-in conductors to the lamp filament, the central part of the pinch containing the foils is offset sideways slightly during pinch sealing, to prevent the inner parts of the conductors, which connect the filament to the foils, being deflected so that these parts extend into the interior of the envelope parallel to the central axis through the lamp.



Inventors:
Wolfe, Kenneth Roy (London, EN)
Underwood, Clive Arthur Evander (London, EN)
Application Number:
05/347825
Publication Date:
05/20/1975
Filing Date:
04/04/1973
Assignee:
THORN ELECTRICAL INDUSTRIES LIMITED
Primary Class:
Other Classes:
313/318.07, 313/580, 362/263
International Classes:
H01J9/32; H01K1/38; H01K3/12; H01K3/20; (IPC1-7): F21M3/00
Field of Search:
313/220,318,315 240
View Patent Images:
US Patent References:
3681640RIBBON CONDUCTOR PRESS SEAL STRUCTURE1972-08-01Martin
3622832INTERCHANGEABLE TUNGSTEN HALOGEN LAMP1971-11-23Schlessel et al.
3548245QUARTZ-TO-METAL FOIL PINCH SEAL1970-12-15Biscoff
3536946TEMPERATURE-RESISTANT REFLECTIVE COATING FOR QUARTZ ENVELOPE1970-10-27Kopelman et al.
3510718INCANDESCENT LAMP1970-05-05Vetere
3419947Compact source discharge lamp manufacture1969-01-07Gottschalk et al.
3315216Lamp base and terminal structure1967-04-18Krupp et al.
3290134Press sealing apparatus1966-12-06Camarata
3262001Electric lamp1966-07-19Rijckeart
2749527Electric light bulb having insulation piercing contacts1956-06-05Gast
1788231Incandescent lamp and mounting therefor1931-01-06Ceader et al.



Primary Examiner:
Braun, Fred L.
Attorney, Agent or Firm:
Dike, Bronstein, Roberts, Cushman & Pfund
Claims:
We claim

1. An electric lamp comprising:

2. A lamp according to claim 1, wherein said envelope has a single pinch seal into which each of said inner and outer conductors protrude, said portion of said seal containing said embedded foils having a projection on one face and a depression in its opposite face.

3. A lamp according to claim 1, further including seal capping and lamp mounting means attached to said envelope said envelope having a shoulder providing a reference abutment for said capping and mounting means, and said shoulder being at a predetermined location relative to a given point inside said envelope.

4. A lamp according to claim 3, wherein said capping and mounting means comprises: a capping box in abutment with said shoulder, a sleeve encasing said capping box, and a focussing collar secured to said sleeve.

5. A lamp according to claim 1, having a further filament carried by said supporting means, said supporting means including at least three inner and outer conductors and interconnecting foils.

6. A lamp according to claim 5, wherein said inner conductors enter a single pinch seal and all lie in a common plane containing said central longitudinal axis.

7. A lamp according to claim 5, further including a reflector carried by the supporting means.

8. A lamp according to claim 1, further including a second filament, both said filaments being made of tungsten, said envelope being quartz and containing a halogen gas, and said support means carrying a reflector adjacent one of said filaments, one end of each of said filaments being connected to a first inner conductor, and the other ends of said filaments being respectively connected to second and third inner conductors, said first, second and third inner conductors being connected through associated molybdenum foils to associated outer conductors, said foils being embedded in a common pinch seal, and said inner conductors lying adjacent one another in a common plane containing said central longitudinal axis, said foils lying in a displaced plane parallel to said axis.

9. A lamp according to claim 8, wherein said common pinch seal has a reference shoulder on one face thereof and futher including seal capping and lamp mounting means embracing said seal, said seal capping and lamp mounting means having means abutting said shoulder and a portion of said envelope adjacent said seal.

Description:
The present invention relates to improved lamp pinch seals suitable, inter alia, for precision lamps such as pre-focus lamps.

When manufacturing precision lamps, internal components including, for example, filaments, reflectors or shields, conductors and the like have to be mounted with great accuracy within their envelopes. Unless this is done, the lamps are unable to provide optimum performances when installed in their associated optical equipment. Furthermore, in lamps of the tungsten-halogen type, it is essential to locate their filaments exactly in relation to the quartz envelopes otherwise poor operating characteristics and lives result.

Nowadays, it is common to pinch-seal lamp envelopes about their conductors. The conductors frequently include molybdenum foils forming conductive paths between outer conductor wires and inner conductor wires, the latter extending into the bodies of the envelopes and supporting the internal components of the lamps. Hermetic sealing is achieved by pinching the envelope material against the foils. The foils act as barriers preventing the envelope material, e.g. quartz, from flowing around these foils so that they remain central within the ultimate seals. That is, equal thicknesses of quartz are found on either side of the foil in a finished seal.

The only practical way of affixing the conductor wires to a foil is to weld them to one of the faces of the foil.

Accordingly, the conductor wires are off-centre relative to the associated foil, and during pinch sealing, the conductor wires are subjected to bending forces. In the result, the internal components of the lamps are found to be somewhat displaced from their designed positions. This phenomenon is discussed in greater detail hereinafter. Suffice it to say, here, that it has been extremely difficult, using previous pinch sealing techniques, to produce lamps with the desired degree of precision.

According to the present invention, there is provided a lamp having an envelope containing at least one filament and support means therefor, the support means including at least two inner conductors that are electrically connected through separate conductive foils to externally accessible outer conductors, the envelope being pinch sealed to the foils such that equal thicknesses of envelope material are in contact with the opposite faces of each foil, and the seal portion within which a foil is embedded being displaced laterally relative to the remainder of the seal so that each inner conductor extends into the envelope from its associated foil in a direction parallel to a central longitudinal axis through the lamp, the foils being displaced from this axis. The invention is applicable to both single and double-ended lamps, which can incorporate one or more envelope-to-conductor pinch seals as desired. The results of laterally displacing a seal portion within which a foil is embedded is that each pinch seal has a projection on one face and a corresponding depression in its other face. A lamp capping and mounting structure can be fitted to each pinch seal, and conveniently is so constructed as to ensure that the lamp accurately focussed in a light fitting designed therefor. A preferred embodiment is an automobile headlamp bulb which is single ended and has two filaments and three conductors, the inner conductor elements, which may be in the form of wires, all lying in a common plane in which the central longitudinal axis lies.

The invention further comprises a method of making a lamp, including the steps of inserting into an envelope an assembly comprising a support means bearing a filament and including lead-in-conductors having intermediate conductive foils, and closing the envelope about the foils by pinch sealing, pinch sealing being accomplished using pinch jaws which are so shaped as to displace the foils and the adjacent envelope material laterally such that, in the finished lamp, the foils are displaced from a central longitudinal axis through the lamp whilst the conductors leading from the foils to the interior of the envelope extend parallel to the said axis. The pinch jaws may comprise a female jaw into which a male jaw can slide, the female jaw having a pinch face which includes a recess and the male jaw having a pinch face including a projection, the recess and projection cooperating during pinching to displace the foils and adjacent envelope material laterally.

Preferably, the pinch seal is formed with a ledge or shoulder in a predetermined location relative to one of the internal components of the lamp in order to provide a reference abutment facilitating accurate positioning of the lamp capping and mounting structure with respect to the internal components.

The invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 is an exploded perspective view of a tungsten halogen automobile headlamp bulb embodying the invention,

FIG. 2 is a side elevation of the bulb per se illustrating a pinch seal thereof,

FIG. 3 is another side elevation of the bulb, viewed at right angles to the illustration of FIG. 2, the pinch seal being shown sectionally in the process of being formed between a pair of pinch jaws, and

FIG. 4 is a cross-section through the finished pinch seal shown in position between the pinch jaws.

The lamp 10 shown in FIG. 1 of the drawings is a tungsten-halogen automobile headlamp bulb internationally known as the "H4" type. The lamp has main and dippedbeam filaments 12 and 13 respectively. The dippedbeam filament 13 is positioned in front of a miniature bowl reflector 14 which is located, like the filaments 12, 13 within the lamp envelope 15. The envelope 15 is made of quartz and is hermetically sealed at the points 16, 17 to contain a halogen and a gaseous filling.

The filaments 12, 13 and reflector 14 are supported within the envelope 15 by a sheet metal support having a plurality of individual fingers, generally indicated by 20. The support 20 is stiffened by an insulating bridge 21, and its fingers are provided with individual conductors most clearly seen in FIG. 1. Fabrication and assembly of the internal components of the lamp 10, namely the filaments 12, 13, reflector 14, support 20 and insulating bridge 21, are disclosed in greater detail in our copending patent application Ser. No. 135,002, filed Apr. 19, 1971, now U.S. Pat. No. 3,774,064.

The individual conductors seen in FIG. 2 each include an inner conductor element 23, in the form of either the end portion of the associated finger or a wire attached thereto. This element 23 is welded to one end of a molybdenum foil 24. The other end of the molybdenum foil is welded to an outer conductor element or wire 25. The wire 25 in turn is electrically connected to one of three input terminals 26 of a capping structure 27. The molybdenum foil is of the order of 0.001-0.002 inches thickness and 2-4 m.m. wide. The function of the molybdenum foil 24 is to enable a good hermetic seal 17 to be obtained between the envelope 15 and the individual conductors, as is well known. The seal 17 is made by a pinching technique which will be described shortly.

The capping structure 27 includes a rectangular capping box 30 having two sprung ears 31. The ears 31 serve to hold the box 30 firmly to the pinch seal 17 and to assist in centering the box 30 within an aperture of a cupshaped element 32. The box 30 has two inturned tangs 33 which abut against a reference shoulder 34 of the pinch seal 27, formed during the pinch-sealing operation, and against the envelope at the point 35 where the envelope swells outwardly from the pinch seal 17. Only one tang 33 is visible in the drawings. It will be appreciated that the purpose of the two tangs 33 is to locate the box 30 correctly and positively relative to the reference shoulder 34.

The element 32 is brazed or welded to the box 30 and its rim 35 is brazed or welded to the inner wall of a cylindrical sleeve 38 forming the body of the capping structure 27. A flanged element 39, commonly called a "focussing collar", is then likewise secured to the sleeve 38. The sleeve 38 may be provided with locating lugs to fix the axial position of the flanged element 39 relative to the sleeve 38. The flanged element 39 is appropriately shaped to enable the lamp 10 to be fitted and centered accurately in the receiving aperture of a standard vehicle headlamp reflector. The lower end of the sleeve 38 is closed by an insulating disc 40 bearing the terminals 26.

It will be recognised that the automobile lamp 10 must be very accurately made because its filaments 12, 13 have to be located precisely relative to the optical axis and focal point of the associated reflector. If the lamp 10 is inaccurately made, poor lighting performance results. Furthermore, the filaments 12, 13 have to be carefully and precisely located relative to the wall of the envelope 15 for an efficient halogen cycle to take place. Accurate manufacture of the capping structure 27 has presented few problems, although in the past difficulty has arisen in locating the structure 27 axially relative to the filaments 12, 13. The principal difficulty has been to ensure that the internal components of the lamp 10 retain their desired positions in the envelope after pinch sealing.

It will be seen from the drawings that the conductor elements 23, 25 are welded to one face of the molybdenum foil 24. During pinch sealing, the foil 24 presents a barrier resisting flow of the softened quartz. Thus, the foil 24 always remains central within the pinch seal, equal thicknesses of quartz being found in contact with the opposite faces of the foil 24 in the finished pinch seal. As a result, previous pinch sealing techniques have led to the conductor elements or wires 23, 25 being subjected to bending movements such that they become off-centred. Correspondingly, the internal components carried by the element 23 tended to depart from their designed positions within the envelope 15. Considerable lamp to lamp variations of the positions of the internal components have been observed.

The pinch seal 17 according to this invention has a configuration which ensures that the conductor wires, particularly elements 23, retain their desired alignment relative to the central longitudinal axis of the lamp 10 during and after pinch sealing. As a result, the three elements 23 lie in a common plane containing the central longitudinal axis and all are parallel thereto.

The shape of the pinch seal 17 is most clearly seen in FIGS. 2 and 4 of the drawings. A central square or rectangular area 42 thereof, within which the foils 24 lie, is displaced laterally relative to the remainder of the seal 17 and the said central longitudinal axis. The cross-section of FIG. 4 shows this displacement most clearly. The displacement of area 42 is such that the elements 23 are moved into coincidence with a plane 43 which is to be understood to contain the said central longitudinal axis. The single element 23 shown in FIG. 4 extends along this axis and likewise lies in the plane 43. The molybdenum foils 24 are thus located to one side of the plane 43. The surfaces 44, 45 of the area 42 are equidistant from the surfaces of the foils 24 but are unequally spaced from the plane 43.

The remainder of the seal 17 consists of two longitudinally-extending ribs 47, 48 on either side of the area 42 and a transverse rib 50 at the end of the seal 17 furthest from the main body of the envelope 15. The appearance of the area 42 is that of a projection on one side of the seal 17 and a corresponding depression between the ribs 47, 48 and 50 on the other side of the seal.

The rib 50 defines the reference shoulder 34 previously mentioned. During manufacture, it is arranged that the distance between the shoulder 34 and, say, the adjacent end of the filament 13 is constant from lamp to lamp. By doing so, the axial location of the filaments relative to the capping structure 27, and particularly to the flanged element 39, can be kept substantially constant during lamp manufacture.

The pinch seal 17 is formed, after heating an end of the envelope 15 to soften the quartz, by squeezing the quartz between a pair of pinch jaws 51, 52 of interfitting male and female nature respectively.

The male pinch jaw 51 has an outstanding portion 53 having an end wall 54, the configuration of which may be regarded as the negative of the side of the ultimate pinch seal 17 containing the above-mentioned depression. Thus, the end wall 54 includes a central rectangular or square projection 55 for forming the said depression. Along either side of the projection the end wall 54 is recessed to define shoulders 56 for forming the adjacent faces of the ribs 47, 48. The lower part of the projection 55 is stepped to form a transverse surface 57 extending across the width of the male portion 53. The surface 57 is approximately equidistant from the faces of the shoulders 56 and the face of the projection 55. The surface 57 is intended to form the transverse rib 50 of the ultimate pinch seal 17.

The female pinch jaw 52 includes a cavity or groove 59 into which the portion 53 of the male jaw 51 can slide. The cavity or groove 59 is of substantially U-shaped cross-section and its mouth is slightly tapered outwardly to enable the male jaw 51 to slide into the cavity 59. The innermost wall 60 of the cavity 59 is of stepped configuration: the central part of the wall 60 being recessed to form the seal projection corresponding to the said rectangular or square depression.

In operation, the internal components of a lamp, together with the associated conductors are held in a suitable jig and are then inserted into a length of quartz tubing. The region of tubing which is to form the eventual pinch seal is heated to soften the quartz and then the pinch jaws 51, 52 are closed upon the heated quartz. The jaws are advanced until a seal as shown in FIG. 4 is produced. The jaws 51, 52 may be stopped automatically by providing them with cooperating stopping faces, not shown. Alternatively, stopping faces can be incorporated in the associated jaw carriers of a pinch sealing machine to prevent excessive pinching.

It will be recognised that the present invention is not limited to pinch sealing of automobile headlight bulbs. The invention can be applied wherever it is desired to produce a lightbulb in which internal components such as filaments have to be accurately located relative to the envelope and seal region. The invention is thus of particular value in the manufacture of precision lightbulbs for example of the pre-focus type.

The cup-shaped element 32 as described and illustrated adapts the sleeve 38 of a conventional lamp cap, used for lamps having moulded glass seals, to fit the capping box 30. As an alternative, parts 32, and 38 are made an integral construction which includes a hollow cylindrical portion and an end wall. The end wall is apertured appropriately to receive the capping box 30 and has flanges, e.g. two in number, for engagement by the surface of the capping box 30. The flanges preferably extend into the hollow interior of the cylindrical portion. The capping box 30 is welded or brazed to the said end wall. The alternative construction is applicable not only to vehicle headlamp bulbs but to any lamp, including a prefocus lamp, where it is desired to fit a base structure to a pinch seal. The use of such an alternative construction in fabricating a lamp base is advantageous on the grounds of accuracy, ease of manufacture and economy.