GB2424992A

GB2424992A - Lamp capsule pinch seal and method of making such a seal

Info

Publication number: GB2424992A
Application number: GB0507107A
Authority: GB
Inventors: Timothy Peter Perry; Simon John Ward; Andrew Bartram; Antony John Tambini; Graham Forsdkye; Andrew Davies
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2005-04-07
Filing date: 2005-04-07
Publication date: 2006-10-11
Anticipated expiration: 2025-04-07
Also published as: GB2424992B; GB0507107D0

Abstract

A pinch seal (7) for a low wattage ceramic metal halide lamp 1 which comprises a capsule (3) containing the operating parts of the lamp 1 and a pinch seal (7) closing the capsule at one end and containing the feed wires (9) for the lamp 1 in which the cross sectional shape (43) of the pinch (7) is determined by dimensional analysis of the capsule cross section prior to carrying out the pinch operation so as to give minimum of lateral flow of the quartz material. The invention also includes a method of making such a seal.

Description

LAMP CAPSULE PINCH SEAL AND METHOD OF MAKING SUCH A SEAL

This invention relates to a lamp capsule pinch seal, and a method of making such a seal.

Low wattage lamps commonly use bi-pin bases such as that known by the designation G8.5. However, such lamp bases have a number of disadvantages They have a long vertical height which restricts the closeness which the centre of the emitted light to the bottom of the base, known as the light centre length. The base pins tend to be weak and can easily be broken.

In these lamps, a pinch seal is used to hermetically seal the light source into a capsule together with electrical contacts and supports. In particular, in order to provide the requisite electrical connections, the pinch forms a seal around these connections which are in the form of a metal foil around which the material of the lamp capsule is pinched. The shorter the lengthy of the pinch, the greater is the difficulty in achieving a full hermetic seal In the operation of forming a pinch, the open end of the capsule with the metal foils of the electrical connections located in this area, is squeezed from opposite sides so as to both close the open end of the capsule and to form an hermetic seal around the metal foils. Since the capsule is generally of either a circular or oblong cross section, this squeezing action, as well as pushing opposite portions of the capsule walls together, will cause the end of the capsule to enlarge sideways, resulting in lateral movement of the quartz material which can damage the fairly fragile metal foils. The squeezing operation is, in manufacturing conditions, carried out by means of a jaw block pinch which. is shaped to provide the eventual shape or cross section of the pinch.

The present invention seeks to provide a lamp capsule pinch seal, in which the lateral movement of the capsule material during a pinching operation is minimised so as to protect the metallic connector foils while providing a good hermetic seal and enabling the use of shorter foils so as to reduce the otherwise relatively long light centre length.

According to a first aspect of the invention, there is provided -a pinch seal for a low wattage lamp which comprises a capsule containing the operating parts of the lamp and a pinch seal closing the capsule at one end and containing the feed wires for the lamp in which the cross sectional shape -of the pinch is determined by dimensional analysis of the capsule cross section prior to carrying out the pinch operation so as to give minimum of lateral flow of the quartz material.

The cross sectional shape of the pinch may be determined by plotting a graph of the amount of material in the capsule end at points of the periphery of the capsule end above and below a diameter of the capsule extending at right angles to the direction of the compression of the capsule to form the pinch, the pinch cross sectional shape being symmetrical about its longitudinal centre line.

The shape of the cross section of the pinch may be calculated by integration of the curves of the capsule end and subtraction of one integral from the other..

The shape of the cross section of the pinch may be augmented by a relief formed in the centre of the opposite sides of the pinch.

The capsule end prior to formation of the pinch may be circular, oval or oblong According to a second aspect of the invention, there is provided a method of making a pinch seal for a low wattage lamp which comprises providing a capsule containing the operating parts of the lamp and closing the capsule at one end with a pinch seal containing feed wires for the lamp, the cross sectional shape of the pinch being determined by dimensional analysis of the capsule cross section prior to carrying out the pinch operation so as to give minimum of lateral flow of the quartz material.

The method may further comprise augmenting the shape of the cross section of the pinch by forming a relief in the centre of the opposite sides of the pinch.

The capsule end prior to formation of the pinch may be circular, oval or oblong The invention will now be described in greater detail, by way of example, with reference to the drawings, in which:- Figure 1 is a diagrammatic front view of a miniature lamp having a pinch in accordance with the invention; Figure 2 is a diagrammatic side view of the lamp as shown in figure 1; Figure 3 is a schematic view of the pinch area of the capsule without the base; Figures 4a, b and c show examples of known pinch shapes and the jaws used to make them; Figure 5 is a graphical illustration of the dimensional analysis of the quartz capsule cross section before heating to make the pinch, and Figures 6a and 6b are views similar to Figure 4 but showing examples of pinch shapes and the jaws used for two embodiments of the invention.

Referring to figures 1 and 2, there is shown one form of miniature lamp to which the pinch in accordance with the invention is applied, The lamp 1 comprises a capsule 3 in which the light emitting materials and structure 5 is housed, the capsule 3 being closed at one end by means of a pinch 7.

Electrical feed wires 9 connect the structure 5, by way of the pinch 7 to pins 11 located on the lower part 13 of a suitably sized base 15 The general construction of the pinch 7 is shown in Figure 3 which shows the lower part of the capsule 3 before attachment to the base. Thus it will be seen that the feed wires 9 pass into the region of the pinch 7 where they are welded to two metal foils 17, suitably of molybdenum. The two metal foils 17 being in turn welded to further outwardly extending wires 19 by means of which the capsule 3 is attached to the pins 11 on the base 15 (See figures 1 and 2). The use of the foil connectors 17 has the purpose of enabling the pinch 7 to provide an hermetic seal and also allowing some flexibility of the wires during the pinching process.

The way in which the pinch is manufactured is firstly to assemble all the parts of the lamp together with the lead wires extending through the open end of the capsule. Then the capsule is heated at its open end to enable movement of the material and this heated end is the compressed between the jaws of a compression device to push the opposite sides of the quartz tube together so as to bond theses sides together with the lead wires and foils trapped in between. Because of the heated state of the quartz, the two sides, when pressed together form a single body resulting in an hermetic seal.

A problem arises when pinching the ends of the capsules of very small lamps, say of the order of 55.5 mm long by about 12 mm wide in that, during the pinching operation, the quartz of the capsule end will flow laterally under the pinching action and this will have a deleterious effect on the positioning of the lead wires and foil and can cause damage to the foil. The result of such operations can result in the pinch being no longer hermetically sealed or to the lead wires being badly out of line with the base to which they are to be attached or even cause a break in the electrical circuitry.

This problem has been largely overcome in large lamps by providing, instead of a flat pinch, a pinch in which reliefs have been provided at the ends of the pinch and possibly additionally in the middle thereof. Such a situation is illustrated in Figures 4 a, b and c.

In Figure 4, the opposing jaws 21 and 22 of a two jaw pinch showing the shape of the pinch jaws and, between them, the shape of the pinch formed by theses jaws. Thus Figure 4a shows a standard rectangular block pinch which provides for a parallel sided pinch. Figure 4b shows a variation of the block pinch providing an "I" shaped pinch with side reliefs 25. To this end, both of the jaws 21 and 22 are rebated at their edges at 27.

Figure 4c shows the final known variation of the pinch shape in which, not only is the pinch provided with edge relief but also with an additional central relief 29 formed by the rebates 31.

While these various reliefs have reduced the problem to some extent, there is still a considerable lateral flow of the quartz when the pinch is being made which, as previously discussed, can have a deleterious effect.

The inventors have realised that to effectively minimise this lateral flow, a special shape of pinch is needed, i.e. one that produces a neutral quartz flow.

This is achieved in a situation in which the pressure distribution across the region of the pinch containing the foils is evenly distributed. It is of course necessary to have some flowing of the quartz material in order for the appropriate bonding to take place but, in order to reduce the lateral flow, the flow of the quartz needs to be concentrated basically in a direction parallel with the line of operation of the jaws.

The inventors have discovered that this can, to a large extent be achieved by designing the shape of the jaws by the use of dimensional analysis of the glass capsule prior to the pinch forming operation.

The way in which this dimensional analysis is carried out, in this case using a circular section capsule, will now be explained with reference to figure 5. In this figure there is shown a graphical representation 41 of the circular section of the unheated lower part of the capsule. It is shown with its diameter lying on the X-axis of the graph with the vertically most distant parts of the capsule section from the X-axis being the points at which the jaws of the clamp will be applied. What is then carried out is an analysis of the amount of the quartz material lying vertically above and below the centre line, represented by the X- axis at all points.

What in effect takes place is that thin vertical sections of the capsule cross section are taken and the amount of the material in these sections being plotted along the Y-axis of the graph. This produces a shape as shown at 43.

As can be seen, the maximum amount of quartz lies at the outside with the minimum amount, being only twice the thickness of the capsule at the centre.

This calculation can, of course be carried out by integrating the curves of the capsule section.

While the shape shown at 43 is the ideal shape to provide the neutral flow characteristics of the pinch, for manufacturing reasons, a slightly more rounded shape, such as that indicated by the line 45 would be used instead.

Figures 6a and b are views similar to figure 4 but showing the arrangement in accordance with the invention. Figure 6a shows the situation as designed by the method shown in Figure 5. Here, as can be seen, both the pinch shape and the shape of the jaws 21 and 22 follow the line 45 in this figure.

While such a shape is usually successful for most purposes, it is sometimes desired to promote a slight inward lateral flow of the quartz in the central region of the pinch to avoid any outward movement of the lead wires and foils.

In this situation, the outline provided in figure 6a can be supplemented by the addition of a central relief, of the sort shown in Figure 4c and this is shown in figure 6b.

It will be appreciated that the above describes only one example of the invention. For example, some of the capsules are of oval or oblong cross section and the shape of the pinch achieved in this will be different as the dimensional analysis carried out as discussed in connection with figure 5 will have a different result.

While the lamp has been discussed as having a base with downwardly extended pins, any other suitable base structure could be used. It is interesting to note that the current shape of the pinch allows a dish shape to be formed on opposite sides of the pinch and these dish shaped portions are very useful in providing a channel between the pinch and the aperture in the base in which it sits into which a suitable adhesive or cement can be located.

-. -7- The type of lamp described here would also be suitable for use in built in reflector type lamps.

Claims

CLAIMS:- 1. A lamp comprising a capsule containing the operating parts of

the lamp and a pinch seal closing the capsule at one end and containing the feed wires for the lamp in which the cross sectional shape of the pinch seal is determined by dimensional analysis of the capsule cross section prior to carrying out the pinch operation so as to give minimum of lateral flow of the quartz material.
2. A lamp as claimed in claim 1 wherein the cross sectional shape of the pinch is determined by plotting a graph of the amount of material in the capsule end at points of the periphery of the capsule end above and below a diameter of the capsule extending at right angles to the direction of the compression of the capsule to form the pinch, the pinch cross sectional shape being symmetrical about its longitudinal centre line.
3. A lamp as claimed in claim 1 or 2, wherein the shape of the cross section of the pinch is calculated by integration of the curves of the capsule end and subtraction of one integral from the other..
4. A lamp as claimed in any preceding claim wherein the shape of the cross section of the pinch is augmented by a relief formed in the centre of the opposite sides of the pinch.
5. A lamp as claimed in any preceding claim wherein the capsule end prior to formation of the pinch is circular.
6. A lamp as claimed in any one of claims 1 to 4 wherein the capsule end prior to the formation of the pinch is oval or oblong
7. A method of making a pinch seal for a lamp which comprises providing a capsule containing the operating parts of the lamp and closing the capsule at one end with a pinch seal containing feed wires for the lamp, the cross sectional shape of the pinch being determined by dimensional analysis of the capsule cross section prior to carrying out the pinch operation so as to give minimum of lateral flow of the quartz material.
8. A method as claimed in claim 7 wherein the cross sectional shape of the pinch is determined by plotting a graph of the amount of material in the capsule end at points of the periphery of the capsule end above and below a diameter of the capsule extending at right angles to the direction of the compression of the capsule to form the pinch, the pinch cross sectional shape being symmetrical about its longitudinal centre line.
9. A method as claimed in claim 7 or 8, wherein the shape of the cross section of the pinch is calculated by integration of the curves of the capsule end and subtraction of one integral from the other..
10. A method as claimed in any one of claims 7 to 9, further comprising augmenting the shape of the cross section of the pinch by forming a relief in the centre of the opposite sides of the pinch.
11. A method as claimed in any one of claims 7 to 10, wherein the capsule end prior to formation of the pinch is circular.
12. A method as claimed in any one of claims 7 to 10, wherein the capsule end prior to the formation of the pinch is oval or oblong
13. A pinch seal for a low wattage lamp substantially as described herein with reference to the drawings.
14. A method of making a pinch seal for a low wattage lamp substantially as described herein with reference to the drawings.