GB2052152A - Electric lamp cap contacts - Google Patents

Abstract

In a bayonet-type lamp cap each contact comprises a metal plate 6 having a depression 7 in its outer surface, the depth of the depression being greater than the plate thickness, with an opening 5 for a respective lamp lead-in wire 8 being formed at the bottom of the depression. By this means the lengths of the lead-in wires can be shortened thus avoiding the possibility of an end of a wire being bent over to make contact with the lamp cap, whilst at the same time ensuring that the wires project into the depressions by an amount which permits them to be soldered to the respective contacts. <IMAGE>

Description

SPECIFICATION Electric lamp caps This invention relates to electric lamp caps of the kind (hereinafter referred to as the kind specified) designed for use in the manufacture of electric incandescent or discharge lamps and comprising a shell, usually of metal, shaped at one end to fit over an end of a lamp envelope, and closed at the other end by a body of electrically insulating material secured to the shell and carrying exposed on its outer surface a pair of metal contacts seated over apertures in the body and to which lead-in wires from the end of the lamp envelope can pass for connection to the contacts, the shell having two or more bayonet pins projecting outwards from its wall adjacent said other end to enable the cap to be coupled in known manner to a bayonet-type lampholder in use of the lamp.

It is usual in well known forms of bayonet-type electric incandescent or discharge lamps for each lead-in wire to be threaded through an opening formed in an associated metal contact of the lamp cap to which it is secured by soldiering, the solder crown or blabs thus formed on the metal contacts, which are usually in the form of flat metal plates, being arranged, in use, to engage spring-loaded current supply pins of a bayonet-type lampholder.

The lead-in wires of the lamps need to be of adequate length to ensure that satisfactory electrical connection is made between the wires and the contacts, and one difficulty which has sometimes been experienced with lamps utilising known forms of lamp caps is that, during assembly, the lead-in wires project for an appreciable distance beyond the contact surfaces, and although the ends of the wires can subsequently trimmed prior to the application of the solder, this involves an additional manufacturing step, and moreover if, for some reason, the trimming mechanism fails to operate satisfactorily it may be possible for the protruding end of a wire to be bent over so as to bridge the gap between the respective contact and the metal cap shell, or metal holder in which a lamp having a shell of insulating material might be inserted, thereby creating a hazard by rendering the metal cap shell and/or metal holder live in use.

According to the present invention, in a bayonet type lamp cap of the kind specified, each contact comprises a metal plate having a depression formed in its outwardly facing surface, the depth of which depression is greater than the plate thickness, and each plate has an opening for the passage of a lead-in wire formed in the bottom of the depression.

With this construction of lamp cap it is possible to employ shorter lamp iead-in wires, as the depth of the depression can be fixed to accommodate the tolerances in the lengths by which the lead-in wires project from the lamp envelopes in the manufacture of the lamps, so that the longest lead does not project beyond or significantly beyond the end face of the cap whilst the shortest iead still reaches the part of the contact within the depression so as to be electrically connectable to the contact by soldering in the usual way.

The depressions can have any convenient form and where the lead-in wires of a lamp fitted with a lamp cap in accordance with the invention are connected to the respective cap contacts with solder, the solder may lie wholly within the depressions or may extend above the contact surface to form solder crowns as in conventional forms of bayonet-type lamp caps. Preferably the apertured base of each depression is formed with a narrow, substantially flat, annular ledge surrounding the aperture within the depression to assist in the retention of the solder.

Now when a lamp cap of the kind specified, having solder crowns on the contacts, has been fitted into a bayonet-type lampholder for some length of time it is sometimes found that the ends of the current supply pins of the lampholder become embedded in the relatively soft solder and make it difficult to remove the lamp from the holder.

In a lamp cap in accordance with the invention the mouth of each depression is conveniently of such a shape and/or size that the entry of a current supply pin of a conventional bayonet-type lampholder into the depression is substantially prevented.

Thus the depression may be of circular shape with a mouth diameter smaller than that of conventional bayonet-type lampholder current supply pins; for example less than 3.5 mm, and preferably of the order of 2.5 mm or even smaller.

Alternatively the mouth of the depression may be of elongate shape for example approximately elliptical, with a maximum width which is less than 2.5 mm, for example 2.0 mm.

A number of embodiments of the invention will now be described by way of example with reference to Figures 1 to 6 of the accompanying schematic drawing in which: Figure 1 represents a perspective view of one lamp cap in accordance with the invention, Figure 2 represents a plan view and Figure 3 a sectional elevation of the lamp cap shown in Figure 1, Figure 4 represents a plan view of a second embodiment of the invention, and Figure 5 represents a plan view and Figure 6 a sectionai view of part of the third embodiment of the invention.

The lamp cap shown in Figures 1 to 3 comprises a stepped cylindrical metal shell 1, for example of brass or aluminium, carrying a pair of bayonet pins 2 projecting outwards from the wa!l thereof near the narrower end to enable the cap to be coupled to a bayonet-type lampholder of known kind. The shell 1 has moulded within it an electrically insulating body 3 of vitreous or other insulating material having two through passages 4 (Fig. 3) each communicating with an opening 5 in a respective one of a pair of contacts 6, in the form of metal plates, of roughly elliptical shape, which are carried by the body 3 with their outer surfaces generally flush with its end surface.

At the centre of each contact the metal is deformed to provide, in the outer surface of the contact, a circular depression 7 having a depth of between 1.5 and 4.0 mm in the outer surface, for example 3.0 mm, the respective opening 5 being formed at the base of the depresssion as shown in Figure 3.

The diameter at the mouth of the depression is approximately 2.5 mm, and the diameter of the opening 5 is approximately 1.5 mm.

During manufacture of the lamp cap the insulating material of the body 3 is moulded into the end of the shell 1 by well known techniques, the contacts 6, with the depressions 7 and openings 5 already formed therein, being held in their respective positions during the moulding process so that they are secured in position when the insulating material has set, with the openings 5 in register with the passages 4 which are formed in the body.

In the manufacture of a lamp the lead-in wires (e.g. at 8 in Figure 3) are threaded through the passages 4 and openings 5, and the cap 1 is secured to the lamp neck. | The ends of the wires which lie within the depressions 7 are then conductively connected to the contacts by the use of solder (not shown) which fills the depressions and stands slightly proud of the contact surfaces.

The lengths of the lead-in wires can be adjusted to avoid the ends projecting or projecting to any significant extent beyond the contact surfaces.

The depth of the depressions 7 is such that even the shortest length of lead-in wire 8 which would normally be experienced in manufacture of a lamp using the cap will extend into a depression so that it will be conductively connected to the respective contact when the solder is subsequently applied. Moreover the diameter of the mouths of the depressions is less than the diameter of the current supply pins of a conventional bayonet-type lampholder so that the possibility of a pin of a lampholder into which the lamp is fitted penetrating the solder and entering a depression is effectively avoided.

In the second embodiment of the invention illustrated in Figure 4 the lamp cap is constructed in a similar manner to that already described, except that in this case the mouths of the depressions 7 are of elongate, elliptical shape, having a minor axis of approximately 2.0 mm, that is to say only marginally greater than the diameter of the holes 5. The depth of the depressions is the same as in the previous embodiment, to ensure a satisfactory connection between the lamp lead-in wires and the contacts without the need for making the wires of such a length that they project to any significant extent beyond the contact surfaces.

After threading the wires through the openings 5 in the manufacture of a lamp, and the securing of the cap to the lamp envelope, the ends of the wires are conductively connected to the plates by solder which fills the depressions and stands slightly proud of the contact surfaces as previously described.

With this arrangement the possibility of a current supply pin of a conventional bayonet-type lampholder into which the lamp is fitted penetrating the solder and entering a depression is again effectively avoided, as the maximum transverse width of the depressions is less than the diameters of standard supply pins.

Although the major axes of the depressions 7 of the lamp cap illustrated are shown in alignment with those of the contacts 6 it will be appreciated that they can have any other orientation. In addition the contact plates themselves may have any other convenient shape, for example circular, and their contact-making surfaces need not necessarily be flat. Thus in some cases they may be slightly dome shaped.

In the third embodiment the lamp cap is again constructed in a similar manner to those already described, although the depressions 7 in the contact plates 6 are formed somewhat differently as shown in Figures 5 and 6.

Thus in this case two opposed rectangular tongues 9, approximately 2.0 mm wide, are pressed out of the plane of each contact plate so that they are inclined thereto with their adjacent edges spaced approximately 2.0 mm apart to form an opening 5.

When the plates are secured to the vitreous material body 3 the tongues effectively form a depression 7 the length of the tongues being such that the depth of the depression is again of the order of 3.0 mm. The depressions 7 are again filled with solder (not shown) after threading the lamp lead-in wires through the openings 5 to connect the wires to the contacts 6. The width of the depressions which are formed are again narrower than the diameter of standard bayonettype lamp cap supply pins so that entry of lampholder supply pins into the depression is again prevented.

It will be understood that the invention includes within its scope the manufacture of electric lamps using caps in accordance with the invention with the lengths of the lead-in wires adjusted to avoid projecting ends as hereinbefore described, and also the electric lamps so manufactured.

Claims (8)

1. A bayonet-type lamp cap of the kind specified with each contact comprising a metal plate having a depression formed in its outwardly facing surface, the depth of said depression being greater than the plate thickness, and each plate having an aperture formed in the bottom of the depression for the passage of a lead-in wire.

2. A bayonet-type lamp cap according to Claim 1 in which a narrow, substantially flat, annular ledge is formed surrounding each said aperture to assist in the retention of solder.

3. A bayonet-type lamp cap according to any preceding claim in which the boundary of each depression in said outwardly facing surface has dimensions such that entry of a current supply pin of a conventional bayonet-type lampholder into said depression is prevented.

4. A bayonet-type lamp cap according to Claim 3 in which said boundary of said depression has a circular shape with a diameter smaller than that of conventional bayonet-type current supply pins.

5. A bayonet-type lamp cap according to Claim 4 in which said diameter is less than 3.5 mm.

6. A bayonet-type lamp cap according to Claim 3 in which said boundary of the depression has an elongate shape with a maximum width of less than 2.5 mm.

7. A bayonet-type lamp cap substantially as hereinbefore described with reference to Figures 1 to 3 or Figure 4 or Figures 5 and 6 of the accompanying drawings.

8. A lamp incorporating a bayonet-type cap according to any preceding claim.