GB2072416A

GB2072416A - Halogen incandescent lamp

Info

Publication number: GB2072416A
Application number: GB8108451A
Authority: GB
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1980-03-21
Filing date: 1981-03-18
Publication date: 1981-09-30
Also published as: NL179957B; IT8120408A1; BE888028A; HU186388B; JPS56145653A; CA1165800A; FR2478877B1; NL8001670A; IT1168112B; NL179957C; IT8120408A0; DE3110395A1; GB2072416B; BR8101590A; FR2478877A1

Abstract

A halogen incandescent lamp comprises a built-in fuse (11, 12). Within a pinch (2) a space (11) is formed through which a part (12) of an internal current conductor (7) to the filament (4) extends so as to be circumferentially free from the quartz glass of the pinch (2). In an embodiment of the lamp the weld (8) between the internal current conductor (7) and the metal foil (6), which as a current lead-through conductor is sealed in a vacuum-tight manner in the pinch (2), is also situated in the space (11). The space (11) is located in a boss (14) on the surface of the pinch (2). <IMAGE>

Description

SPECIFICATION Halogen incandescent lamp The invention relates to a halogen incandescent lamp having a quartz glass lamp envelope, whose cavity is filled with a halogencontaining inert gas and in which a tungsten filament is accommodated, which lamp envelope is sealed by means of a pinch in which at least one metal foil is embedded to whose respective ends an internal current conductor to the filament and an external current conductor are welded, which lamp has a fuse accommodated in an enclosed space bounded by the pinch. Such a lamp is disclosed in the United States Patent Specification 3,264,516.

In by far most of the cases, halogen incandescent lamps have a gas filling with a pressure of approximately 1 bar or more which during operation increases by a factor of 4 or 5. When at the end of the life of such a lamp the filament or an internal current conductor fuses, a discharge arc is formed in the lamp which produces a high current strength and can penetrate into the pinch. The rapid evaporation of the metal parts incorporated in the pinch then causes cracking of the pinch, the lamp exploding as a result of the high gas pressure. This process occurs so rapidly that the use of an external fuse does not prevent explosion of the lamp with certainty. In addition many luminaires do not have such a fuse.

In the lamp which is disclosed in the abovementioned United States Patent Specification, a hollow space adjoins the end of the pinch remote from the filament and is closed by a second pinch. A thin conductor extends in said space and is connected at one end via a thicker conductor to the foil in the pinch of the lamp and at its other end is connected to a contact cap situated outside the lamp envelope. This thin conductor serves as a fuse.

The construction of the known lamp suffers from a number of disadvantages. The manufacture of the lamp is considerably more laborious than that of lamps without a fuse. More components are used therein than in lamps without a fuse. The fuse wire should be very thin because otherwise a vacuum-tight second pinch cannot be made around the wire due to the large differences in coefficients of thermal expansion between quartz glass and metal.

However, a vacuum-tight seal is necessary so as to prevent corrosion of the wire. The small diameter of the wire - a vacuum-tight seal is possible on wires up to approximately 100 ,um diameter - causes loss of energy. With an extra enclosed space for the fuse of 20 mm length and an extra pinch at the relevant end of the lamp envelope the construction produces a considerably longer lamp. Furthermore measures should be taken to prevent corrosion of the fuse wire in so far as it projects beyond the extra pinch.

It is an object of the invention to provide a lamp having a built-in fuse in which said disadvantages are at least mitigated, more especially a lamp which, in spite of the presence of a built-in fuse, need not comprise more or different components than a comparable lamp without a fuse.

According to the invention this object is achieved in a lamp of the kind described in the opening paragraph in that the enclosed space is provided within the pinch such that a part of the internal current conductor extends through the space so as to be circumferentially free form the surrounding quartz glass of the pinch, which part constitutes the fuse.

Quartz glass is to be understood to mean herein glass having a silicon dioxide content of at least 95% by weight.

If as a result of the fusing of the filament or an internal current conductor, a discharge arc is formed in the cavity of the lamp envelope in which the filament is accommodated. As a result, the current through the lamp, and hence through the internal current conductor, increases considerably. Since at least one internal current conductor is circumferentially free from the glass over a part of its length in the enclosed space within the pinch, the heavy current through said internal current conductor results in a larger rise in temperature than if said current conductor were embedded in the glass of the pinch and would hence be cooled by said glass. As a result of this the conductor fuses very rapidly.However, it has been found that no discharge arc is formed in the enclosed space within the pinch, possibly because the temperature in said space, which communicates with the cavity of the lamp envelope only via a narrow capillary duct which is inevitably formed during making the pinch, is much lower than in the cavity of the lamp envelope in which the filament is accommodated.

The weld of the internal current conductor to the metal foil, which generally consists of tungsten or molybdenum, may be present beyond the enclosed space which is provided within the pinch. In an embodiment of the lamp in accordance with the invention said weld, however, may be present in the enclosed space provided within the pinch. Because it is difficult to weld tungsten wire to a tungsten or molybdenum foil, it is likely that, in manufacturing lamps, besides many good welds also a few bad welds are obtained. As a result of the high contact resistance of bad welds, high temperatures may arise which lead to cracking of the pinch. In the lastmentioned embodiment of the lamp in accordance with the invention, this danger is also avoided.

The lamp in accordance with the invention not only has the advantage that no additional parts are necessary as compared with non safeguarded lamps and that the fuse is excluded from the ambient air by the vacuumtight seal of the lamp itself so that air cannot cause corrosion, it also has the advantage that a variety of constructions of internal current conductors which are in common use may be used. For example, the straight limb of a single coiled (s.c.) filament or the single coild limb of a coiled coil (c.c.) filament may be used as an internal current conductor. On the other hand it is possible to construct the internal current conductor as a straight wire wound helically at one or both ends or as an entirely helically wound wire which is screwed in or around one end of the filament.In a coiled coil filament, furthermore, a single coiled limb may be slid over a straight wire and be attached thereto by pinching or welding. In cases in which an internal current conductor is helically wound in the region where it is welded to the metal foil, a straight piece of wire is often inserted into the helix of the internal current conductor so as to facilitate the making of a weld with the metal foil. Such a piece of wire may be omitted in a construction in which a second layer of turns is provided on the helically wound internal current conductor in the region where the weld is to be made. The second layer of turns may be formed from the same wire as the first layer.

This may be the case both when the internal current conductor is the limb of the filament, and also when the internal current conductor is a separate component. An short event, when making the internal current conductor the winding wire, after having made the first layer of the turns, is wound with opposite winding sense over the first layer, after which, if desired, a third layer of turns can be provided with the original winding sense. The advantage of this latter embodiment is that several intercoupled filaments can be obtained in a continuous operation, which filaments are then separated.

In lamps having a long computed life the danger exists that the part of the internal conductor extending in the cavity of the lamp envelope is attacked by the halogen of the gas filling. This attack may result in such a local reduction in diameter of the internal current conductor that the lamp extinguishes prematurely when said current conductor fuses.

Lamps in accordance with the invention present the possibility of readily constructing the internal current conductor whilst nevertheless taking into accound requirements which, dependent on the type of the lamp, are imposed on said current conductor for the satisfactory operation of the lamp, for example a minimum wire diameter for the said current conductor. It has been found that the wire diameter of the internal current conductor may be larger than the wire diameter of the filament so that the number of hours in operation in which the internal conductor is at tacked to such an extent as to break or to fuse can be matched to the computed life of the filament. For example with internal conductors having a 20% larger wire diameter than the wire diameter of the filament, a reliable fuse in lamps in accordance with the invention was nevertheless obtained.

Since in the lamp in accordance with the invention the use of thinner than normal (i.e.

fusible) conductors, and the use of additional components can be avoided, mechanically strong lamps can be manufactured in a simple manner and nevertheless have a built-in fuse.

The fuse construction of lamps in accordance with the invention makes it possible to con struct the lamp as a mono-pinch or as a two pinch lamp. In mono-pinch lamps one or both internal current conductors to the filament may extend through the enclosed space pro vided within the pinch. In two-pinch lamps, both internal current conductors may extend through an enclosed space provided within the respective pinches.

The presence of an enclosed space within the pinch through which the internal current conductor extends so as to be circumferenti ally free from the glass of the pinch, is revealed by the presence of a local boss on the pinch surface. This is obtained by provid ing the pinching blocks with which the pinch is manufactured with a recess. The boss, and hence the resulting enclosed space, preferably extends substantially over the whole width of the pinch so that the enclosed space is a large as possible without this involving any or any noteworthy increase of the overall length of the lamp.

It is to be noted that in lamps in accordance with the invention, as is always the case in lamps having a metal foil incorporated in the pinch as a current lead-through conductor, the vacuum-tight seal of the lamp envelope is realised in that zone of the pinch which is situated between the welds on the metal foil.

It is furthermore to be noted that a lamp for general lighting purposes (GLS lamp) is de scribed in British Patent Specification 460.976, (published already in 1937) which lamp also has a fuse. The lamp has a con struction which, except for the fuse, is similar to that of the current GLS lamp: the lamp envelope is sealed to a stem tube of which the end situated within the lamp envelope is sealed in a gas-tight manner with a pinch around wires which have an matched coeffici ent of expansion and serve as current lead through conductors To the respective ends of these current lead-through wires, inner and outer current conductors are welded. In this known lamp, contrary to current GLS lamps, the fuse consists of a central portion of one of said current lead-through wires, which central portion is situated in a cavity within the pinch and has a smaller diameter than the other current lead-through wire. As in said known lamp the fuse is constituted by the central portion of the wire, that is with its ends, adjacent to the central portion, embedded in the pinch in a vacuum-tight manner, said cavity within the pinch is hermetically separated from the cavity of the lamp envelope and from the ambient atmosphere.

In this connection it is to be noted that we have established experimentally, that in halogen incandescent lamps the current leadthrough conductor (the metal foil) incorporated in a corresponding manner with its central portion free from the glass in the cavity in the pinch, does not form a reliable fuse. Consequently, instead of an incentive to arrive at the lamp in accordance with the invention, the known lamp constituted an impedance thereto. Moreover the lamp of the invention has the advantage over said known GLS lamp that no other, thinner parts need to be used than are commonly used in lamps without a fuse. The presence of the fuse furthermore constitutes no inconvenience in the manufacture of the lamp and the fuse causes no or hardly any additional power consumption during normal operation of the lamp.

The lamps in accordance with the invention are particularly suitable for design as mains voltage lamps. They may be used inter alia as theater lamps, film lamps, studio lamps and photo lamps.

Embodiments of halogen incandescent lamps according to the invention are shown in the accompanying drawing. In the drawing: Figure 1 is an elevation of a first embodiment of a lamp; Figure 2 is an axial sectional view of a modified embodiment of the lamp shown in Fig. 1 rotated 90 about its axis; Figure 3 is an elevation of a further embodiment of a lamp; Figure 4 is an elevation of a mono-pinch lamp; Figure 5a is an elevation of an embodiment of a two pinch lamp; Figure 5b is a diagrammatic representation of a component of Fig. 5a, and Figure 6 is an elevation of a further embodiment of a two-pinch lamp.

In Fig. 1 a quartz glass lamp envelope 1 is sealed by means of pinches 2. In the cavity 3 of the envelope, which is filled with inert gas and hydrobromide, a tungsten filament 4 is accommodated which is centred by supporting members 5. Incorporated in each of the pinches 2 is a molybdenum foil 6 as a current lead-through conductor to which a limb 7 of filament 4 is secured by a weld 8. External current conductors 9 are secured to the foils 6 by means of respective welds 10. A space 11 is provided within the pinches 2, in which space a part 1 2 of the respective internal current conductors 7 is circumferentially free from the glass of the respective pinch 2. The pinch 2 is vacuum-tight over the zone 1 3 centrally of the foil 6.The space 11 communicates with the cavity 3 of the lamp envelope 1 through a capillary duct around the internal current condutor 7, which duct has been formed after pinching in that the (tungsten) conductor 7 has a larger coefficient of expansion than the quartz glass of the lamp envelope.

In Fig. 2 in which the same reference numerals are used for the same components as in Fig. 1, pinch 2 is identical to the pinches 2 in Fig. 1 but pinch 22 is a conventional pinch in which the internal current conductor 27, in so far as it extends within the pinch, is embedded in the glass of the pinch. 14 denotes a boss on the pinch surface of pinch 2 which surrounds the presence of the cavity 11 in the pinch 2 is expressed.

In Fig. 3 the lamp envelope 31 has a pinch 32. A filament 34 centred by a supporting member 35 is accommodated in the cavity 33. A metal foil 36 to which a wire 37 wound helically for the greater part is welded at 38 is embedded in the pinch 32. The wire 37 is screwed in the helical filament 34 as an internal current conductor. An external current conductor 39 is welded to the foil 36 at 40.

A cavity 41, in which the weld 38 between the foil 36 and the internal current conductor 37 is situated, is formed within the pinch 32.

A part 42 of said internal conductor 37 extends in said cavity 41 so as to be circumferentially free from the glass.

The lamp envelope 51 in Fig. 4 has only one pinch 52 in which metal foils 56 are embedded to which external current conductors 59 are secured by means of respective welds 60. Internal current conductors 57 in one end have a tungsten wire 63 inserted therein on which a weld has been made to a respective metal foil 56. The part 62 of one of the current conductors 57 is circumferentially free from the surrounding glass in a cavity 61 formed in the pinch 52. The internal current conductors 57 are each screwed into the filament 54 which is supported by means of a hooked support.

In Fig. spa a coiled coil filament 74 is accommodated in the cavity 73 of the lamp envelope 71, of which filament the limb 77 is an internal current conductor. The limb 77 consists of three layers of turns of the wire from which the filament 74 is wound. The limb 77 was obtained (see Fig. 5b) by providing on a single coiled part 77a turns of opposite winding sense as a second layer 77b and providing thereon a third layer of turns 77chasing the original winding sense.

A part 82 of the internal current conductor 77 is incorporated in a space 81 formed within the pinch 73, in which space it is circumferentially free from the glass and is welded to a molybdenum foil 76 to which an external current conductor 79 has also been welded.

In Fig. 6 corresponding reference numerals denote the same components as in Fig. 5. In the single coiled limb 83 of the filament 74 a wire 84 is inserted which is welded to the foil 76. The wire extends substantially up to the filament 74 and is welded to the limb 83 in a place situated in the space 81. The wire 84 and the limb 83 together constitute an internal current conductor which in the space 81 is circumferentially free from the glass of the pinch 72.

Example 1.

A lamp which consumed 500 W at 220-230 V was constructed with both ends as shown in Fig. 6 and had a coiled coil filament wound from tungsten wire of 121 ,um diameter. In each of the single coiled limbs 83 of the filament (internal diameter of the turns of the limbs 190 m) a tungsten wire (84) of 140 m has been inserted and secured therein by pleating a few of the turns.

The length, in the axial direction of the lamp, of the spaces 81 formed in each of the pinches was 6 mm. The largest height of said spaces (measured perpendicularly to the pinch) was 2.5 mm. The welds of the tungsten wires 64 to the foils 76 were situated in the spaces 81 recessed within the pinch. The lamp was filled with 99.7% by volume of Ar and 0.3% by volume of CH3Br to a pressure of 2.5 X 105 Pa and further comprises 5 mg of iodine.

2. A lamp which consumed 300 W at 220-230 V was constructed at each end as shown in Fig. 5a. The coiled coil filament was wound from tungsten wire of 82 ym diameter (inside diameter of the primary tuns 111,us).

The winding wire had been wound backwards and forwards on the single coiled limbs (77) of the filament (Fig. 5b), so that three layers of turns were present. The limbs 77 were each welded to a molybdenum foil as an internal current conductor. In each of the pinches 72 a cavity 81 had been formed having a length of 4 mm and a height of 2.5 mm, in which the weld to the molybdenum foil was also present. The amp was filled with 99.8% by volume of Ar and 0.2% by volume of CH2Br2 to a pressure of 2.5 x 105 Pa and further comprises 5 mg of iodine.

Both lamps were destined for use as a flood-light lamp.

A few tens of each of these types of lamps were tested for the effectiveness of the incorporated fuse. During the'test. the filament was fused by means of a laser during operation of the lamps. The fuses became operative and switched off the lamps substantially instantaneously.

A few lamps of both types were manufactured with a filament which was short-circuited for 1/4 part of its length by means of a mandrel inserted therein A voltage of 280 V was applied to the lamps. The incorporated fuses fused substantially instantaneously within a few milliseconds.

Claims

1. A halogen incandescent lamp having a quartz glass lamp envelope whose cavity is filled with a halogen containing inert gas and in which a tungsten filament is accommodated, which lamp envelope is sealed by means of a pinch in which at least one metal foil is embedded to whose respective ends an internal current conductor to the filament and an external current conductor are welded, which lamp has a fuse accommodated in a space bounded by the pinch, characterized in that the space is formed within the pinch such that a part of the said internal current conductor extends through the space so as to be circumferentially free from the surrounding quartz glass of the pinch, which part constitutes the fuse.

2. A halogen incandescent lamp as claimed in Claim t, characterized in that the weld of the internal current conductor to the metal foil is also situated in the said space.

3. A halogen incandescent lamp as claimed in Claim 1 or 2, characterized in that both internal current conductors extend through said space so as to be circumferentially free from the quartz glass of the pinch.

4. A halogen incandescent lamp substantially as herein described with reference to any of Figs. 1 to 6 of the accompanying drawings.