HIGH-PRESSURE DISCHARGE LAMP

Abstract: The invention relates to a high-pressure discharge lamp comprising a discharge vessel (3) enclosing a discharge space (3b) and provided with two main electrodes (4,5). Each of the main electrodes is connected to a lead-through member (40,50), which is enclosed with a clearance space (10) by a closing part (30) and is connected thereto by means of a melting glass connection (9) in a gas-tight manner. According to the invention, the lead-through member is provided with a protuberance (51) reaching as far as the closing part in such a manner that the lead-through member (50) is passed with clamping fit through the ceramic closure member. Thus, the lead-through member is fixed, as a result of which the manufacture of the lamp is considerably simplified.

Description: The invention relates to a high-pressure discharge lamp comprising a discharge vessel enclosing a discharge space and provided with a ceramic wall and with two main electrodes, between which the discharge takes place in the operating condition of the lamp, at least one of these main electrodes being connected to a lead-through member which is passed through a closing part of the discharge vessel and is enclosed with an intermediate space by the closing part and is connected thereto by means of a melting glass connection in a gas-tight manner, this lead-through member being provided with a protuberance reaching as far as the closing part. The term "ceramic wall" is to be understood herein to mean a wall consisting of a crystalline oxide, such as, for example, monocrystalline sapphire or polycrystalline densely sintered aluminium oxide. The closing part may be constituted by the wall itself of the discharge vessel. It is alternatively possible that the discharge vessel is provided with a separate closure member, which is connected, for example by sintering, or by a melting glass connection, to the wall of the discharge vessel. The filling of the discharge vessel may contain besides one or more metals also one or more rare gases and one or more halides. The filling may further be partly present in excess quantity. European Patent Application 0 087 830 A1 (PHN 10282) discloses a lamp of the kind mentioned in the opening paragraph. The known lamp is an efficient light source. In the known lamp, the protuberance extends throughout the circumference of the lead-through member, as a result of which a limitation of the melting glass connection is formed and it is achieved that melting glass is screened from the filling of the discharge vessel. The properties of a lamp are determined to a considerable extent by the relative position of each of the main electrodes. The latter is determined by the extent to which the lead-through member is passed through the closure member. Therefore, it is necessary that the position of the lead-through member in the closure member is fixed during the step of providing a melting glass connection. For this purpose, it is usual to provide the lead-through member on the one hand with a stop which abuts against the closure member and to fix on the other hand the lead-through member in the abutment position by means of an externally exerted force, for example by means of a weight. After the melting glass connection has been provided, the externally exerted force, for example the weight, should be removed. This results in a comparatively laborious method of manufacturing. A further aspect of the usual manufacture is that the position of the lead-through member by application of the external force is generally found to vary due to deformation to which the stop is then subjected. The accuracy of the main electrode position is thus adversely affected. The invention has for its object to provide a means by which a lamp of the kind mentioned in the opening paragraph can be manufactured in a simpler and more accurate manner. For this purpose, the lamp according to the invention is characterized in that the lead-­ through member is passed through the ceramic closing part with clamping fit due to the protuberance. An advantage of the invention is that during the manufacture of the lamp the lead-through member need not be fixed by means of a temporarily externally exerted force. A further advantage is that the lead-through member need not be provided itself with an abutment stop. The invention can be used in a construction for limiting the melting glass connection, but it is not limited thereto. Thus, a melting glass limitation construction may be formed separately. The invention can also be used in a lamp vessel construction in which a melting glass limitation construction is not desired. In a preferred embodiment, the lead-through member is pin-­ shaped and the protuberance of the pin-shaped lead-through is obtained by bending. A pin can be bent with comparatively small effort. Moreover, when a pin-shaped lead-through member thus formed is provided in a ceramic part, the risk of a defect is small. This in contrast, for example, with the case in which the protuberance is formed by scraping of the pin-shaped part. The scraped protuberance can in fact break off under the influence of the friction with the ceramic part, as a result of which the clamping fit is lost entirely or in part. In a further preferred embodiment, the pin-shaped lead-­ through member is provided with two protuberances obtained by bending and located on either side of the longitudinal axis of the lead-through member. The protuberances ensure together with a third point of the lead-through member that a three-point clamping fit of the lead-through member is obtained. Thus, the clamping fit substantially does not influence the extent of the melting glass connection provided so that it does not adversely affect either the gas-tightness of the melting glass connection. Although, in case the lead-through member comprises a thin-walled tube portion which is passed with clamping fit through the ceramic closing part, all kinds of geometric forms of protuberances can be used, the outer surface of the tube portion is preferably provided with several mutually separated protuberances which are distributed along the periphery of the tube portion. The protuberances may then be located in a common plane at right angles to the longitudinal axis of the tube portion. However, viewed along the longitudinal axis, they may alternatively be distributed along the outer surface. Thus, it has proved possible to provide on the one hand a clamping fit sufficient for fixing and on the other hand an only local interruption to an only small extent of the gas-tight melting glass connection between the closing part and the lead-through member. Two protuberances arranged diametrically opposite to each other have proved to be sufficient. By a suitable choice of distribution along the periphery, with three protuberances a centering of the lead-through member in the closing part is also possible. Preferably, the protuberances of the tube portion are obtained by means of a plastic non-removing metal deformation of the thin-walled tube portion, as a result of which the clamping fit cannot be lost by the fact that one or more protuberances break off. Moreover, the possibility of occurrence of a perforation of the wall of the tube portion is a minimum with such an operation. In the case of a perforation of the tube portion, the tube portion has generally to be considered to be unsuitable as a lead-through member. A lamp according to the invention will now be described with reference to a drawing, in which : Figure 1 shows the lamp; Figure 2 shows of the first embodiment in detail a partial sectional view of the discharge vessel of the lamp shown in Figure 1, Figure 3 shows a second embodiment in detail a partial sectional view of the discharge vessel of the lamp shown in Figure 1. Figure 1 shows a lamp comprising an outer envelope 1 and an lamp cap 2. Inside the outer envelope 1 there is arranged a discharge vessel 3 enclosing a discharge space 3b and provided with two main electrodes 4 and 5. The main electrode 4 is connected to a lead-through member 40, which is electrically connected through a flexible conductor 6´ to a rigid current conductor 6. The main electrode 5 is connected to the lead-through member 50, which is electrically connected through an auxiliary conductor 7 to the rigid current conductor 8. The part of the discharge vessel 3 with a cylindrical ceramic wall 3a shown in sectional view in Figure 2 shows the main electrode 5 connected to the pin-shaped lead-through member 50. The lead-through member 50 is passed through the closing part 30 and is enclosed with an intermediate space 10 by the closing part 30. The closing part 30 consists of a separate ceramic closure member extending in part outside the cylindrical part 3a of the discharge vessel. The lead-through member 50 is provided with protuberances 51 and 52 each reaching as far as the closing part 30. An end 53 of the pin-shaped lead-through member bears on the closure member 30 and ensures together with the protuberances 51 and 52 that the lead-through member 50 is passed with a three-point clamping fit through the closure member 30. The lead-through member is connected in a gas-tight manner to the closing part 30 by means of a melting glass connection 9 extending in the intermediate space 10. In a number of practical discharge vessels of the construction shown in Figure 2 the wall of the discharge vessel consisted, like the closure member, of polycrystalline densely sintered aluminium oxide. The wall and the closure member were joined together by means of sintering a gas-tight manner. The electrodes 4 and 5 consisted of tungsten pins having a cross-section of 300 µm and a length of 3 mm. The distance between the electrodes was 13 mm. The lead-­ through members were niobium pins having a cross-section of 0.72 mm and the closure members each had an inner diameter of 0.76 mm. The cylindrical part of the discharge vessel had an inner diameter of 2.5 mm. The filling of the discharge vessel contained 10 mg of mercury sodium amalgam comprising 73 % by weight of mercury and xenon at a pressure at 300 K of 53 kPa. The use of such a discharge vessel in an outer envelope yields a lamp which, when connected in series with a stabilization ballast of about 1.4 H and operated at a supply voltage of 220 V, 50 Hz, consumes a power of about 30 W. The part of the discharge vessel 3 with the ceramic wall 3a, which is shown in sectional view in Figure 3, has a main electrode 4 consisting of electrode windings 4b on an electrode rod 4a which is connected to the lead-through member 40. The lead-through member 40 is passed through the closing part 30 and is enclosed with an intermediate space 10 by the closing part 30. The closing part 30 consists of a separate ceramic closure member, which is secured by means of sintering to the wall 3a of the discharge vessel. The lead-through member is provided with altogether three approximately spherical protuberances 41 which are located in one plane, which each reach as far as the closing part 30 and which are uniformly distributed along the periphery of this lead-through member. The lead-through member is connected in a gas-­ tight manner to the closing part 30 by means of the melting glass connection 9. The melting glass connection 9 extends in the intermediate space 10. The lead-through member 40 is constructed as a thin-walled tube portion of niobium or molybdenum, which at the area of the spherical protuberances 41 is plastically deformed by a non-removing metal operation. In a practical embodiment, the thin-walled tube portion of niobium has an outer diameter of 2 mm and an inner diameter of 1.68 mm. Each of the protuberances has a largest radial dimension with respect to the outer surface of 0.07 mm and a centre line measured along the periphery of the tube 0.5 mm. The ceramic closing part consisting of polycrystalline densely sintered aluminium oxide has an inner diameter of 2.06 mm.

Claims: 1. A high-pressure discharge lamp comprising a discharge vessel enclosing a discharge space and provided with a ceramic wall and with two main electrodes, between which the discharge takes place in the operating condition of the lamp, at least one of these main electrodes being connected to a lead-through member which is passed through a closing part of the discharge vessel and is enclosed with an intermediate space by the closing part and is connected thereto by means of a melting glass connection in a gas-tight manner, this lead-through member being provided with a protuberance reaching as far as the closing part, characterized in that the lead-through member is passed through the ceramic closing part with clamping fit due to the protuberance. 2. A lamp as claimed in Claim 1, characterized in that the lead-through member is pin-shaped and in that the protuberance of the pin-shaped lead-through member is obtained by bending. 3. A lamp as claimed in Claim 2, characterized in that the pin-shaped lead-through member is provided with two protuberances which are obtained by bending and are located on either side of the longitudinal axis of the lead-through member. 4. A lamp as claimed in Claim 1, characterized in that the lead-through member comprises a thin-walled tube portion which is passed through the ceramic closing part with clamping fit and in that the outer surface of the tube portion is provided with several mutually separated protuberances which are distributed along the periphery of the tube portion. 5. A lamp as claimed in Claim 4, characterized in that the protuberances of the tube portion are obtained by means of a plastic non-­ removing metal deformation of the thin-walled tube portion.

Inventors: JANSSEN, MARC FRANCOIS ROSALIA, RENARDUS, MAX LEO PIETER
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1986
Main classification: H01J61
IPC codes: H01J61