GB2106312A - Shank support for high pressure discharge lamps - Google Patents

Abstract

In high pressure discharge lamps location the electrodes 19, 20 in relatively long leg parts (30, 31) attached to the bulb (12) is assisted by providing a reinforcing abutment, preferably a quartz annulus (26, 27) fused to the inside of the leg members, and resilient clips (24, 25) fitting around the shanks (21, 22) of the electrodes and bearing against the abutments to centrally locate and support the shanks. <IMAGE>

Description

SPECIFICATION Support shank for high pressure discharge This invention relates to high pressure discharge lamps. More particularly the invention is concerned with discharge lamps having a fill of rare gas such as xenon. The xenon lamps in question consist of an arc burning between solid tungsten electrodes in a pressure of between 10 to 40 atmospheres of 99% pure xenon. They may be designed to operate from AC or DC supply and be of compact or linear form. In the compact form the arc of the source is a few millimetres in length and is located at the centre of a relatively large bulb approximately spherical shape. Cold filling pressures of xenon up to 12 atmospheres are commonly used and as a result there is a potential hazard from explosive failure and hence the lamp is usually encased in some kind of safety harness.

The tungsten electrodes comprising an anode and cathode can be of pure tungsten but the cathode is of 3% thoriated tungsten to provide improved emissive properties. Both electrodes are carried by tungsten shanks within relatively long leg members attached to the lamp bulb. Because the anode is a relatively massive member and because of the relative length of the tungsten shanks there is a tendency for the anode to become missal and due to the bending load imposed by the weight of the anode. This movement is detrimental to the efficacy of the lamp which is dependent on the correct separation distance of the electrodes and also on the correct alignment of the electrodes with the longitudinal axis of the lamp.One solution to this problem is that disclosed in UK patent 1 486 389 wherein the shank members are supported in cylindrical members loosely inserted within the leg members.

This has the disadvantage that close manufacturing tolerances must be maintained in order to ensure the correct clearance fit of the tungsten shanks within the support members. This is difficult because of the problems of machining.

hard materials such as quartz and tungsten.

Moreover this arrangement does not solve the alignment problem since the tungsten shanks must be a clearance fit within their supports and consquently the anode could become misaligned at least to the extent of this clearance.

An arrangement for locating an electrode in a cold cathode discharge lamp is described in British Patent No. 670 292. However this particularly supports the electrode itself by means of a ring of thermally insulating material onto which the electrode is fitted and in the period elapsed since its publication in 1952 has not proved to provide any useful teaching for the present problem of the location of electrodes in high pressure discharge lamps.

A further problem with these lamps results from the high pressures encountered when the lamp is at its working temperature. This pressure of between 10 and 40 atmospheres exerts a considerable bursting load on the envelope wall and is probably the major factor influencing the life of the lamp.

An object of this invention is therefore to provide an improved high pressure discharge lamp having an improved support for the electrode shank within the envelope thereof.

Accordingly we provide a high pressure discharge lamp including: a lamp envelope having a lamp bulb and at least one leg member attached to the bulb; an electrode shank within the leg member, carrying an electrode; a reinforcing abutment formed on the inside surface of the wall of the leg member; and a support clip arranged to resiliently engage the shank and the reinforcing abutment to form a resilient suuport for the shank within the leg member.

Preferably, the said clip has an inner part and an outer part which respectively engage the shank member and the lamp envelope to provide a resilient support therebetween.

In a preferred embodiment the clip of the invention is made from material which maintains its resilience at the working temperature of the lamp and molybdenum is such a material.

In a further preferred embodiment the lamp envelope and quartz ring are both made of ozone inhibiting quartz with the ring being fused to the envelope wall.

In a further embodiment of the invention there is provided a clip member for use in a high pressure discharge lamp to support an electrode shank carrying an electrode within a leg member of the lamp envelope, the clip including an outer part for resiliently engaging a part of the inner surface of the leg member and an inner part for resiliently engaging a part of the shank and the clip further including extension pieces forming means to centralise the shank within the leg member.

The invention will now be described by way of example with reference to the accompanying drawings wherein: Figure 1 is a general view of a lamp incorporating the invention, Figure 2 is an elevation of the clip of the invention, Figure 3 is a sectional end elevation of the clip, Figure 4 is an elevation of a further embodiment of the invention, and Figure 5 is an elevation of another further embodiment of the invention.

In Figure 1 the lamp 10 of the invention is seen to comprise a quartz envelope 11 having a generally bulbous part 12 running into elongated tubular leg members 13 and 14 which form outer seal tubes. Inner quartz seal tubes 1 5 and 16 are hermetically joined to the outer seal tubes 13, 14 respective and include the usual foil members and leads (not shown) encased in cap members 1 7 and 1 8 all of which is well known construction. An anode 1 9 is carried by a tungsten shank member 21 while the cathode 20 is carried by a tungsten shank member 22. The shank members in turn are supported within their respective inner seal tubes 1 5 and 1 6.

As is evident from Figure 1 the anode 1 9 of pure tungsten comprises a relatively massive member in comparison to the cathode 20 which is of 3% thoriated tungsten to improve its emissive properties. This gives rise to the problem previously described as it will be evident that the weight of the anode 1 9 acting at the end of the relatively long shank member 21 will impose a considerable bending load on the shank tending to deflect it and causing a misalignment of the anode 19 with the longitudinal axis 23 of the lamp 10. In the case of the cathode 20 the problem is not as severe as with the anode 19.

According to this example of the invention, additional support for both electrodes is provided by resilient clip members 24 and 25 which grip around the respective shank members 21 and 22.

The resilient clips 24 and 25 are arranged to fit between their respective shank members and an abutment 26, 27 on the inner periphery 28, 29 of the wall of the leg members 13,14. The abutment 26,27 are formed by fitting a quartz annulus or ring at the appropriate place within the leg members 13, 14. Preferably the envelope wall is then softened by heating and pressed around the ring so that the ring becomes fused to the wall. In this way the quartz ring becomes an integral part of the envelope structure, forming a reinforcement and considerably strengthening the wall section against the bursting pressure exerted by the gas fill. It is preferred that both the quartz ring and the wall of the leg member are made from ozone inhibiting quartz.

The resilient clip used in the embodiment of the invention shown in Figure 1 is shown in greater detail in Figure 2, and in Figure 3 which is a sectional view on AA' of Figure 2. In Figure 2 the clip 40 comprises an inner part 41 designed to engage a major portion of the diameter of the shank member while outer parts 42 and 43 are arranged to engage the inner periphery of the abutment 26, 27 formed in the leg member. The clip is formed by taking a length of flat molybdenum strip, approximately 0.25 mm thick by 6 mm wide, bending it first into a circular shape approximating to the blank shape, then bending the strip back upon itself to form a shape approximating to the inside diameter of the abutments 26 and 27.It will be evident from Figure 2 that an outer part 44, of the outer leg 43 engages the inner periphery of the abutments 26, 27 while the inner part 45 of the inner leg member 41 will engage the outer surface of the shank members 21,22. The free ends 46,47 are turned over as shown to form extension pieces 48, 49 of approximately 1 mm in length. The extension pieces are an important part of the preferred embodiment of the invention as they prevent the outer legs from collapsing upon themselves. In effect they form means to centralise the shank member within the bore of the leg member.

Likewise the portions 50, 51 connecting the inner leg 45 and the outer legs 42, 43 prevent the legs of the clip from collapsing upon themselves to keep the clip central within the bore. The clip is preferably made from molybdenum since this material retains its resilience at the working temperature of the lamp which is between 500 and 10000C.

Figure 4 is an elevation of a further embodiment of the invention. In figure 4 two clip members 52 and 53 have turned over ends 55 and 54 which anchor in slots formed in the tungsten shank 56. The oppositely acting free ends 57 and 58 tend to centralise the shank member 56 within the bore of the leg of the discharge tube.

Figure 5 shows an elevation of another embodiment of the invention. In Figure 5 the clip members 59 and 60 are shown attached to the tungsten shank 61 by welding at 62 and 63. The oppositely acting free ends 64 and 65 tend to centralise the shank member 61 within the base of the leg of the discharge tube. It should be noted, however, that these alternative embodiments are somewhat difficult to produce in practice due to the problems associated with working the material tungsten.

Claims (18)

1. A high pressure discharge lamp including: a lamp envelope having a lamp bulb and at least one leg member attached to the bulb; an electrode shank within the leg member, carrying an electrode; a reinforcing abutment formed on the inside surface of the wall of the leg membe,r; and a support clip arranged to resiliently engage the shank and the reinforcing abutment to form a resilient support for the shank within the leg member.

2. A lamp according to claim 1 in which the support clip includes an inner part and an outer part which respectively engage the shank and the reinforcing abutment to provide resilient support therebetween.

3. A lamp according to claim 2 in which the resilient clip further includes extension pieces forming means adapted to centralise the shank within the leg member.

4. A lamp according to either claim 2 or claim 3 in which the support clip is formed of a flat metal strip bent into a substantially circular shape approximating to the circumference of the shank and bent back upon itself to form an outer part of a shape approximating to the inside surface of the abutment.

5. A lamp according to any preceding claim in which the support clip is made of a material retaining its resilience at the working temperature of the lamp.

6. A lamp according to claim 5 in which the said working temperature is between 500 and 1 0000C.

7. A lamp according to either claim 5 or claim 6 in which the material is molybdenum.

8. A lamp according to any preceding claim in which the reinforcing abutment comprises a quartz annulus having outside diameter substantially the same as the inside diameter of the leg member and fitting closely therein.

9. A lamp according to claim 8 in which the quartz annulus is fused to the wall of the leg member.

10. A lamp according to either claim 8 or claim 9 in which the quartz annulus and the wall of the leg member are both made of ozone-inhibiting quartz.

11. A lamp according to any preceding claim in which the anode is supported within its respective leg member by the said clip and abutment.

12. A lamp according to claim 11 in which the cathode is supported within another leg member by a similar cooperating support clip and reinforcing abutment.

13. A high pressure discharge lamp substantially as herein described with reference to Figure 1 together with Figures 2 and 3 or Figure 4 or Figure 5 of the accompanying drawings.

14. A lamp according to any preceding claim having a xenon fill.

1 5. A clip member for use in a high pressure discharge lamp to support an electrode shank carrying an electrode within a leg member of the lamp envelope, the clip including an outer part for resiliently engaging a part of the inner surface of the leg member and an inner part for resiliently engaging a part of the shank and the clip further including extension-pieces forming means to centralise the shank within the leg member.

16. A clip member according to claim 15 formed of a flat metal strip bent into a substantially circular shape to form the inner part and bent back upon itself in a further substantially circular shape of larger diameter to form the outer part, the free ends thereof bent bent in towards the inner part to form said extension pieces.

17.A clip member substantially as herein described with reference to Figures 2 and 3 of the accompanying drawings.

18. An electrode shank formed integrally with a supporting clip member substantially as herein described with reference to Figure 4 or Figure 5 of the accompanying drawings.