Patent Application
20060108929
The invention relates to an electric lamp having an outer bulb in accordance with the precharacterizing clause of claim 1. Of concern here are, in particular, metal halide lamps, mercury high-pressure discharge lamps, but also halogen incandescent lamps having an outer bulb. The inner bulb of the lamp is sealed at two ends using sealing parts. The outer bulb is fixed to one or both of the sealing parts.
EP-A 465 083 and EP-A 588 602 have already disclosed an electric lamp having an outer bulb, this lamp having a burner, which is surrounded by an outer bulb fixed to the sealing part. For a better connection, in this case in particular a radial beading is provided on the sealing part, the end of the outer bulb resting on said radial beading and being fused with the beading there.
On the other hand, it is known, for example, from WO 95/32516 to roll an outer bulb directly onto the sealing part without any beading.
U.S. Pat. No. 6,790,115 has disclosed a generic lamp, in the case of which an extension of the seal of the discharge vessel is “scratched” on one side, and the outer bulb is fixed thereto.
One disadvantage of these connection techniques is the fact that the robustness achieved of the connection between the outer bulb and the sealing part in any case leaves something to be desired. Without the beading, a time-consuming tempering process is also needed for this purpose.
One object of the present invention is to provide a lamp in accordance with the precharacterizing clause of claim 1 which ensures a reliable connection, which can be subjected to a load, between the outer bulb and the sealing part of the inner bulb.
This object is achieved by the characterizing features of claim 1. Particularly advantageous refinements are described in the dependent claims.
The lamp according to the invention has an inner bulb, which is sealed in a vacuum-tight manner, in particular a discharge vessel, which defines a lamp axis and is sealed at mutually opposing ends by sealing parts. The sealing part is a pinch seal or else a fuse seal. The luminous means in the interior of the lamp is a discharge arc between two electrodes or a luminous element. It is electrically conductively connected to the internal power supply lines leading to it. The sealing part is in particular provided with an outwardly protruding extension, which is in the form of a hollow tube.
At least one sealing part is provided having an in particular annular beading, which protrudes radially transversely with respect to the lamp axis. The beading is essentially convex in cross section, i.e. the beading forms a maximum height H on the sealing part or its extension, having an apex with a pronounced radius of curvature, which lies predominantly in the beading. The beading either does not have a point of inflection and thus has a purely convex curvature, for example following a parabola, which is provided with a pronounced apex, or else the beading has a point of inflection, which is, however, at most at a height Hw of 0.25 H, based on the maximum height H of the apex of the beading. Such a design of the beading can be produced after local heating either by compression or blowing. An even simpler method is the application of a correspondingly shaped glass bead.
Critically, the shaping makes it easier for the outer bulb to rest essentially axially on the inner side of the beading in the vicinity of the apex. In order to ensure this, the inner diameter of the end of the outer bulb is selected to be smaller than the outer diameter of the beading. The outer diameter of the end of the outer bulb is preferably approximately the same size as the outer diameter at the apex of the beading. It may also be slightly larger, in particular by up to 30%.
The outer bulb may be a continuous tube piece having a constant diameter, but also a bulb having a central bulge and tube pieces adjoining said central bulge at the ends, in particular attached to it or formed integrally with it.
One preferred embodiment provides a tubular extension piece of the sealing part, adjoined by the beading. In particular, it is attached to it or formed integrally with it. This makes the provision of a radially symmetrical beading possible, even in the case of a pinch seal which is not radially symmetrical. In the case of a fuse seal, such an extension piece is not absolutely necessary. Both the inner bulb and the outer bulb are preferably made from silica glass or hard glass.
In particular, the beading may be designed to be relatively small, the outer diameter of the beading typically being 25 to 80% larger than the diameter, lying therebeneath, of the sealing part. A typical value for the diameter of the sealing part or its extension is 7 mm, and an associated typical value for the outer diameter of the beading is 2 to 4 mm.
In one particular embodiment, a beading is preferred which is hollow such that its maximum inner diameter is larger than the outer diameter of the surrounding sealing part. A concave design of the beading is thus created which is particularly well suited for the end of the outer bulb to nestle against axially.
In the case of the conventional design of the beading, as is previously known, the outer bulb can only be attached axially with difficulty anyway since the contact zone is only very short. Disregarding this, the outer bulb in the prior art always bears against the apex of the beading completely on the outside.
The axial attachment of the outer bulb to the beading improves the strength of the transition to a quite considerable extent, in particular by up to 50%. Stress rings no longer form.
The beading may be produced from the sealing part, for example by compression, or else attached thereto as a separate bead. The breaking strength of the connection between the outer bulb and the beading in this case increases the more intimate the contact between the two.
The invention will be explained in more detail below with reference to a plurality of exemplary embodiments. In the drawing:
The ends 5 of the luminous element, in their function as an internal power supply line, are embedded directly in the pinch seal 6 and are connected there to a pinch film 7.
The pinch seal 6 has on the outside, as an extension part, which may also act as a base part, a tubular glass sleeve 11, which is integrally formed on the pinch seal and has an outer diameter of 7 mm and an inner diameter of 5 mm. The sleeve 11 is approximately 7 mm long.
A beading 12, which is essentially convex, is attached to the sleeve 11 on the outside, transversely with respect to the lamp axis. The end of an outer bulb 14, which end is in the form of a tube piece 13, is attached to said beading 12, with the result that the outer bulb extends between the two beadings 12 on both sides of the central part 4.
In addition, a base may be fitted to one end of the sealing part, as is known per se, the base having an electrical contact element (not illustrated), which is electrically conductively connected to a power supply line leading to a luminous means, the contact element being accommodated in the tubular extension of the sealing part.
In practice, it has been shown that a contact zone, which is as large as possible, primarily as long as possible in the axial direction, in the axial direction between the beading 12 and the outer bulb 14 improves the strength of the connection enormously, up to 50%. For this reason, a convex beading, as shown in
The axial length KZ should preferably be at least from 2 to 4 mm long. The outer bulb 14 is always in the inner half of the beading pointing towards the discharge, to be precise if possible at the upper edge where there is the least the degree of curvature and therefore the contact zone is at its largest. Ideally, the tube piece is such that the end of the tube piece is attached approximately tangentially to the inside of the beading at the apex, since the axial length KZ is in this case at its longest.
In a similar manner to as is shown in principle in
| Number | Date | Country | Kind |
|---|---|---|---|
| 1020044056452.3 | Nov 2004 | DE | national |
