Title of Invention

"MOLYBDENUM FOIL SEAL IN GLASS"

Abstract

An improved seal in glass, having a molybdenum foil seal comprising: - at least one molybdenum foil (4) which has at least two mutually opposite ends (4c) and two side edges (4a) extending perpendicular to the ends, the thickness of the molybdenum foil (4) continuously decreasing towards the two side edges (4a) starting from a maximum value at the foil centre such that the molybdenum foil (4) has a convex camber, and at least one end (4c) of the molybdenum foil (4) being constructed in the shape of a wedge, a glass member (1) in which the at least one molybdenum foil (4) is sealed in a gas-tight fashion, - one or more metallic bars (6) or wires (3), which are connected to the at least one molybdenum foil (4), characterized in that the at least one wedge-shaped end (4c) is constructed as a rolled cut edge (4b).

Full Text

The invention relates to an improved seal in glass having a molybdenum foil seals and an electric lamp having such a molybdenum foil seal in accordance with the preambles of Patent Claims 1 and 4. I. Technical field Molybdenum foil seals in glass are necessary, for example, for gas-tight electrical feedthroughs in lamp vessels, consisting of silica glass, of high-pressure discharge lamps and halogen incandescent lamps. Here, silica glass denotes glasses whose silica dioxide component is at least 95 per cent by weight. Since the silica glass of the lamp vessel has a substantially smaller coefficient of thermal expansion than the supply leads, which project from the lamp vessel, are usually fabricated from molybdenum wire and are used to supply electric power to the luminescent means arranged inside the lamp vessel, it is, to be specific, impossible for the supply lead wires to be sealed directly, that is to say without auxiliary measures, in a gas-tight fashion in the silica glass of the lamp vessel. In the case of heating of the lamp vessel, for example during operation of the lamp, the supply lead wires made from molybdenum would expand approximately ten times as strongly as the silica glass surrounding them. The mechanical stresses resulting therefrom would lead to cracks in the silica glass. However, despite the different coefficients of thermal expansion of silica glass and molybdenum and the mechanical stresses resulting therefrom, a gas-tight electrical feedthrough for lamp vessels can be produced with the aid of sufficiently thin molybdenum foils of sufficient ductility. For this purpose, the mutually opposite ends of the molybdenum foil are usually welded in each case to a supply lead wire made from molybdenum, and the constructional unit produced in this way is then positioned in the lamp vessel end to be sealed in such a way that one of the supply lead wires projects into the interior of the lamp vessel, while the other supply lead wire projects out of the lamp vessel. The silica glass of the lamp vessel end is then fused and the lamp vessel end is pinched tight, for example, by means of pinching jaws, over the constructional unit comprising the molybdenum foil and the supply leads. The molybdenum foil is then completely embedded in the silica glass of the lamp vessel end. The feedthrough comprising the supply leads and the molybdenum foil is sealed in the lamp vessel end in a gas-tight fashion in the region of the molybdenum foil. The molybdenum foil seals thus fulfil two different functions here. Firstly, they serve to produce an electrically conducting connection between the luminescent means arranged inside the lamp vessel and the supply leads projecting out of the lamp vessel, and secondly ensure a gas-tight closure of the lamp vessel. The molybdenum foils are usually cut off from a supply strip. They therefore have a rectangular surface which is bounded by two side edges and two cut edges extending perpendicular to the side edges. The surfaces of the molybdenum foils are usually convexly cambered, that is to say the thickness of the molybdenum foils continuously decreases towards the side edges starting from the foil centre. II. Prior art Patent specification US 4,587,454 has disclosed molybdenum foil seals in glass which, for the purpose of avoiding crack formation in the glass, have molybdenum foils with a surface roughened by sand-blast treatment. The molybdenum foils have a lancet-shaped cross-section, that is to say starting from a maximum value at the foil centre, the thickness of the foils decreases continuously in the direction of the two side edges of the foil, which extend in the longitudinal direction, transverse to the foil cut edges. German patent specification DE 29 47 230 describes molybdenum foil seals for sealing lamp vessels, which consist of at least 95% of silica glass. In order to reduce the formation of cracks in the glass, the molybdenum foils are provided with an yttrium oxide additive of 0.25 to 1 per cent by weight. It jias emerged that the formation of cracks in the glass surrounding the molybdenum foil seal cannot always be reliably prevented by the abovementioned measures belonging to the prior art. In particular, it was possible to establish that cracks frequently occurred in the glass surrounding the molybdenum foils at the ends, bounded by cut edges, of the molybdenum foils. III. Summary of the invention It is the object of the invention to provide a molybdenum foil seal in glass which does not have the abovementioned disadvantages. In particular, the aim is to reduce the risk of formation of cracks in the glass in the region of the molybdenum foil ends bounded by cut edges. It is also the object of the invention to provide an electric lamp with improved sealing of the lamp vessels in the "region of the electrical feedthroughs. This object is achieved according to the invention by means of the characterizing features of Patent Claims 1 or 4. Particularly advantageous embodiments of the invention are described in the subclaims. In the inventive molybdenum foil seals in glass, the at least one end, bounded.by a cut edge, of the molybdenum foil sealed in glass is constructed in the shape of a wedge. It is possible by means of this measure for burrs which have been formed on the cut edge when cutting the molybdenum foil from the supply strip to be-eliminated again, with the result that these burrs produced by cutting cannot cause cracks or flaws in the glass surrounding the molybdenum foil. The wedge shape of the molybdenum foil end bounded by a cut edge can advantageously be produced by rolling this molybdenum foil end. Any cut burrs on the cut edge of the molybdenum foil are smoothed by this rolling. The at least one molybdenum foil of the molybdenum foil seal according to the invention is advantageously bounded by two cut edges and two side edges extending transverse to the cut edges, and has a lancet-shaped cross-section parallel to the cut edges. It thereby acquires a convexly cambered surface which reduces the mechanical stresses in the molybdenum foil seal. The molybdenum foil seal according to the invention can be used with particular advantage for . gas-tight sealing of electrical feedthroughs for lamp vessels of electric lamps. Accordingly the present invention relates to a improved seal in glass a having molybdenum foil seal comprising: - at least one molybdenum foil (4) which has at least two mutually opposite ends (4c) and two side edges (4a) extending perpendicular to the ends, the thickness of the molybdenum foil (4) continuously decreasing towards the two side edges (4a) starting from a maximum value at the foil centre such that the molybdenum foil (4) has a convex camber, and at least one end (4c) of the molybdenum foil (4) being constructed in the shape of a wedge, - a glass member (1) which the at least one molybdenum foil (4) is sealed in a gas-tight fashion, - one or more metallic bars (6) or wires (3), which are connected to the at least one molybdenum foil (4), characterized in that the at least one wedge-shaped end (4c) is constructed as a rolled cut edge (4b). The present invention also relates to a method for ^t^L methed in improved seal which consists of at least ^> 95 percent by weight of silicon dioxide, there being provided for the purpose of sealing a convexly cambered molybdenum foil (4) which has two mutually opposite ends (4c) and two side edges (4a) extending perpendicular to the ends and whose thickness continuously decreases towards the two side edges (4a) starting from a maximum value at the foil centre, and at least one end (4c) of the molybdenum foil (4) being constructed in the shape of a wedge, wherein the wedge shape of the at least one end (4c) is produced by cutting the molybdenum foil (4) from a molybdenum strip and subsequently rolling the cut edge (4b) bounding the at least one end (4c). IV. Description of the preferred exemplary embodiment The invention is explained in more detail below with the aid of a preferred exemplary embodiment. In the drawings: Figure 1 shows a top view of a feedthrough of a lamp vessel having a molybdenum foil seal according to the invention, in a diagrammatic representation Figure 2 shows a side view of the electrical feedthrough of the lamp vessel from igure 1, in a diagrammatic representation Figure 3 shows a cross-section through the feedthrough from Figure 1 along the longitudinal axis A-A and perpendicular to the foil plane, in a diagrammatic representation and Figure 4 shows a cross-section through the feedthrough from Figure 1 along the line of section B-B and perpendicular to the foil plane, in a diagrammatic representation. Figure 1 shows a pinch seal 1 for a lamp vessel 2, consisting of silica glass, of an electric lamp having an electrical feedthrough which has a molybdenum foil seal according to the invention. The electrical feedthrough comprises a supply lead wire 3 projecting out of the lamp vessel, a molybdenum foil 4 sealed in a gas-tight fashion in the silica glass of the pinch seal 1, and an electrode bar 6 projecting into the interior 5 of the lamp vessel 2. The supply lead wire 3 and electrode bar 6 also consist of molybdenum and are both welded to the molybdenum foil 4. The molybdenum foil 4 has a rectangular surface whose edge is formed by two mutually opposite cut edges 4b and by two side edges 4a extending in the longitudinal direction A-A, perpendicular to the cut edges 4b. The cut edges 4b are produced when the molybdenum foil 4 is cut from a supply strip. The surface of the molybdenum foil 4 is convexly cambered, that is to say starting from the foil centre its thickness decreases continuously to both side edges 4a, with the result that the molybdenum foil 4 has a lancet-shaped cross-section parallel to the cut edges 4b (Figure 4) . The ends 4c, bounded by cut edges 4b, of the molybdenum foil 4 taper in the shape of a wedge. In order to produce the wedge shape, the foil ends 4c are rolled before the molybdenum foil 4 is welded to the supply lead wire 3 and the electrode bar 6. The welding point 7 between the electrode bar 6 and the molybdenum foil 4 or between the supply lead wire 3 and molybdenum foil 4 are located outside the wedge-shaped foil ends 4c. The representations of Figures 1 to 4 are not true to scale, but only diagrammatic. The thickness of the molybdenum foil 4 is approximately 20 µm in the foil centre. The diameters of the supply lead wire 3 and electrode bar 6 are more than 20 times larger than the foil thickness. In order to produce the molybdenum foil seal, a rectangular piece of molybdenum foil 4 is cut from a molybdenum strip arranged on a supply roll. This molybdenum strip is already convexly cambered, that is to say, starting from the strip centre, its thickness decreases continuously towards its side edges. As a result, the molybdenum foil 4 also has the convex camber. In order to eliminate burrs on the cut edges 4b of the molybdenum foil 4, the foil ends 4c are tapered in the shape of a wedge by rolling. The ends of the molybdenum foil 4 are welded outside the wedge-shaped regions 4c to the supply lead wire 3 and to the electrode bar 6, which likewise both consist of molybdenum. The constructional unit 3, 4, 6 thus produced is then inserted into the lamp vessel end to be sealed gas-tight. Subsequently, the silica glass 1 is softened in the region of the lamp vessel end by heating and pressed onto the molybdenum foil 4, for example by means of pinching jaws. After the silica glass 1 has become cold, the constructional unit comprising the supply lead wire 3, the electrode bar 6 and the molybdenum foils 4 forms an electrical feedthrough for the lamp vessel 2, which is sealed in a gas-tight fashion in the lamp vessel end in the region of the molybdenum foil 4. WE CLAIM: 1. Molybdenum foil seal in glass, the molybdenum foil seal comprising: - at least one molybdenum foil (4) which has at least two mutually opposite ends (4c) and two side edges (4a) extending perpendicular to the ends, the thickness of the molybdenum foil (4) continuously decreasing towards the two side edges (4a) starting from a maximum value at the foil centre such that the molybdenum foil (4) has a convex camber, and at least one end (4c) of the molybdenum foil (4) being constructed in the shape of a wedge, - a glass member (1) whose glass consists of at least 95 percent by weight of silicon dioxide and in which the at least one molybdenum foil (4) is sealed in a gas-tight fashion, - one or more metallic bars (6) or wires (3), which are connected to the at least one molybdenum foil (4), characterized in that the at least one wedge-shaped end (4c) is constructed as a rolled cut edge (4b). 2. Method for producing a molybdenum foil seal in glass which consists of at least 95 percent by weight of silicon dioxide, there being provided for the purpose of sealing a convexly cambered molybdenum foil (4) which has two mutually opposite ends (4c) and two side edges (4a) extending perpendicular to the ends and whose thickness continuously decreases towards the two side edges (4a) starting from a maximum value at the foil centre, and at least one end (4c) of the molybdenum foil (4) being constructed in the shape of a wedge, wherein the wedge shape of the at least one end (4c) is produced by cutting the molybdenum foil (4) from a molybdenum strip and subsequently rolling the cut edge (4b) bounding the at least one end (4c). 3. Electric lamp having one or more lamp vessels made from glass, a luminous means enclosed in a lamp vessel, and electrical feedthroughs, wherein it has one or more molybdenum foil seals as claimed in claim 1. 4. Molybdenum foil seal in glass substantially as hereinbefore described with reference to the accompanying drawings. 5. Method for producing a molybdenum foil seal in glass substantially as hereinbefore described with reference to the accompanying drawings.

Documents:

1475-del-1998-abstract.pdf

1475-del-1998-claims.pdf

1475-del-1998-correspondence-others.pdf

1475-del-1998-correspondence-po.pdf

1475-del-1998-description (complete).pdf

1475-del-1998-drawings.pdf

1475-del-1998-form-1.pdf

1475-del-1998-form-13.pdf

1475-del-1998-form-19.pdf

1475-del-1998-form-2.pdf

1475-del-1998-form-3.pdf

1475-del-1998-form-4.pdf

1475-del-1998-form-6.pdf

1475-del-1998-gpa.pdf

1475-del-1998-petition-137.pdf

1475-del-1998-petition-138.pdf