EP0533478A1

EP0533478A1 - Incandescent lamps having integrally supported filaments

Info

Publication number: EP0533478A1
Application number: EP92308493A
Authority: EP
Inventors: Leonard Edward Hoegler
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1991-09-18
Filing date: 1992-09-17
Publication date: 1993-03-24
Also published as: JPH05205705A; KR930006764A; CA2076078A1

Abstract

Incandescent lamps comprising a vitreous envelope containing an elongated, continuous tungsten wire filament having a plurality of filament segments and a plurality of integral filament supports for supporting the filament within the lamp envelope. The filament segments may be straight or coiled and are connected to each other by the integral supports.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to refractory metal filaments having integral supports and their use in lamps.

Background of the Disclosure

Incandescent lamps comprising an elongated light transmissive, generally tubular shaped body enclosing a coiled filament within are well known and old to those skilled in the art, having been in use for over thirty years. Lamps of this type find use for general illumination purposes, both indoor and outdoor, as well as specialty applications such as heat lamps and reprographic lamps. The filament, invariably made of tungsten, is longitudinally disposed in the lamp with its longitudinal axis generally coincident with the longitudinal axis of the lamp envelope and is held in place by means of one, and more generally a plurality of filament supports which are not part of the filament. The center portion of each filament support is attached to the filament coil with the outer periphery of the support contacting the inner surface of the lamp envelope to hold the filament in place. Typical filament supports are disclosed, for example, in U.S. Patents 3,736,455; 3,784,865 and 3,392,299. Having a filament axially supported in a longitudinal lamp envelope by filament supports which aren't an integral part of the filament itself means the manufacture, use and assembly of additional parts which increases the cost of the filament and the lamp in which it is used. In the case of incandescent heat lamps, such supports are often spirals of niobium or tantalum which are costly and difficult to assemble onto the filament. More recently multiple diameter filaments have been disclosed in U.S. 4,959,585 in which one of the turns has a diameter sufficiently large enough to contact the inner wall of the lamp envelope to axially support the filament in the envelope so that the longitudinal axis of the filament is coincident with the longitudinal axis of the lamp envelope.

SUMMARY OF THE INVENTION

In one aspect the invention provides an elongated, continuous wire filament having a plurality of both filament segments and integral supports.
In a further aspect, the invention provides an incandescent lamp comprising a light transmissive envelope enclosing within a continuous wire filament having a plurality of filament segments and a plurality of integral supports, the filament being as aforesaid, wherein at least a portion of each support is adjacent the inner wall of said envelope to support said filament within said envelope.
Incandescent lamp filaments having integral filament supports have now been made from a single length of filament wire and comprise a generally elongated or linear, coiled or uncoiled filament having a plurality of both filament segments and integral supports formed as a part of the filament. In one embodiment the filament is an elongated coil having a plurality of both filament coil segments and integral filament supports. In another embodiment, some of the filament segments are straight wire segments and some of are elongated coil segments. In yet another embodiment all of the filament segments will be straight wire segments separated by integral filament supports. In all of these embodiments the integral filament supports will be located between adjacent filament segments (but not always necessarily between all adjacent segments) irrespective of whether the filament segments are in the form of coils, straight wire, or a mixture of coil and straight wire segments. The integral supports will generally be in the shape of a spiral or ring. However, if desired, the integral support may also have other shapes such as elliptical, a partial ring, multi-sided such as hexagonal, square, triangle, etc. Finally, it will be understood to those skilled in the art that the filament supports also emit heat and light as do the filament sections.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 schematically illustrates an embodiment of a double ended, tubular heat lamp employing an integrally supported filament according to the invention.
Figure 2 schematically illustrates a single ended lamp employing an integrally supported filament of the invention.

DETAILED DESCRIPTION

In one embodiment, the filaments of this invention have a longitudinal axis which is radially centered with respect to the wire turns comprising both the filament segments and the integral supports. In this embodiment, the integral supports will support the filament within the filament chamber of the lamp so that the longitudinal axis of the filament is coincident with the longitudinal axis of a tubular or other filament chamber symmetrically shaped about its longitudinal axis. In the embodiment wherein the longitudinal axis of the filament segments is not coincident with that of the supports, then the longitudinal axis of the filament segments will not be coincident with the longitudinal axis of a lamp filament chamber symmetrically shaped about its longitudinal axis.
The filaments of this invention are made of a single piece of filament wire, preferably refractory metal wire and still more preferably tungsten wire. Thus, continuous wire filament in the context of the invention means a continuous, unbroken length of refractory metal wire formed into a filament, including the filament supports. The filament supports are therefore an integral part of the filament. Further, the supports, although they may be of various shapes as set forth above, will more generally be in the form of a ring, spiral or coil and generally having a diameter (or equivalent diameter in the case of a support in a non-circular shape) substantially greater than the filament segments. By substantially greater diameter is meant that the diameter of the integral support is at least twice, and more generally at least three times greater than the diameter of the filament segments. By plurality of both filament segments and integral supports is meant that a filament according to this invention will have at least two, preferably at least three filament segments and at least two, and preferably at least three integral filament supports. Thus in one embodiment the filament will have a plurality of both coiled filament segments of a substantially uniform diameter and filament supports separating said segments, wherein the diameter of said supports is substantially greater than that of said filament segments and wherein there is an abrupt change in diameter between said filament segments and said supports, as is illustrated in the Figures.
Turning now to Figure 1, double ended, tubular quartz heat lamp 10 is schematically shown as comprising fused silica (quartz) envelope 12 having filament chamber 13 and hermetic press seal portions 14 at each end which are pressed over molybdenum foil seals 16. Foil seals 16 are connected at one end to lamp outer leads 18 and at the other end to a straight wire portion 20 of filament 22. Filament 22 is fabricated from a single, unbroken length of a suitable refractory metal wire, which in this embodiment is tungsten. Filament 22 consists of a sequential series of filament coil segments 24 connected by integral spiral supports 26 which support the filament axially within lamp envelope 12 so that the longitudinal axis of filament 22 is coincident with the longitudinal axis of lamp 10. The longitudinal axis of filament 22 is radially centered with respect to the turns comprising both filament segments 24 and supports 26. The diameter of integral supports 26 is substantially greater than the diameter of the filament segments 24, and is large enough so that the outer surface of each support is adjacent or proximate to the inside surface of filament chamber 13. Filament 22 terminates at both ends in straight wire portions 20 which are connected to one end of molybdenum foil seals 16. If desired, end coil segments (not shown) similar to coil segments 24 may be substituted for a portion of straight wire ends 20. If desired, a relatively straight wire filament segment (not shown) may replace one or more of filament coil segments 24 as is disclosed, for example, in U.S. Patents 4,272,698 and 4,959,586. Further, filament coil segments 24 do not all have to be identical to each other with respect to turn diameter, pitch and spacing between turns. An essential feature of the invention is the integral support shown as discrete segments 26 to support the filament in the lamp filament chamber 13 and preferably with the longitudinal filament axis coincident with the longitudinal axis of the filament chamber of the lamp. The distance between the turns of the support segments will depend on the filament and lamp design.
Heat lamps rated at 1600 watt, 240 volt and 2450°K have been successfully made according to the present invention and as shown in Figure 1. These heat lamps have a lamp envelope made of quartz or fused silica 497 mm long (including the press seal portions) with an outside diameter of 10 mm enclosing within a filament similar to that shown in Figure 1. The length of the filament is 405 mm. The filaments were made out of 11.53 mil diameter tungsten filament wire having seventeen filament segments 24 each 20 mm long and containing 32 turns or coils of a diameter of 69 mils with a spacing between turns of 0.61 mm. Eighteen integral spiral supports 26 each consist of 2½ turns over a 3 mm spacing with each turn having an outer diameter of 270 mils so that it is adjacent the inner surface of filament chamber 13 to support filament 22. Initially these lamps had been made with a turn-to-turn distance of zero for the filament supports, but this tight coil configuration resulted in the interior quartz wall of the lamp adjacent the supports blackening and devitrifying during lamp operation. Opening up the support coils 26 reduced the heat density applied by the supports to the interior filament chamber wall with substantial reduction in blackening and quartz devitrification. The lamp also contained krypton at a pressure of over 1500 torr and minor amounts of hydrogen and bromine. During operation the color temperature of filament segments 24 was 2478°K while that of supports 26 was 2187°K. The temperature of the wall portion of the quartz envelope between supports 26 was 405°C or 628°K while that adjacent the supports was 535°C or 808°K. These lamps have lasted for over 5000 hours of operation.
Figure 2 schematically illustrates a single ended lamp 50 which may be a typical incandescent lamp or a halogen-incandescent lamp comprising vitreous lamp envelope 52 having filament chamber 53 and hermetic press seal 54 at one end over molybdenum foil seals 56. Foil seals 56 are attached to outer leads 57 at one end and to filament support wires 58 and 60 at their other end. Filament 62 is supported by support wires 58 and 60 one of which passes through integral filament support coils 68. Filament 62 has three filament coil segments 64, 65 and 66 separated by integral supports 68 which position filament 62 within elongated filament chamber 53 so that the longitudinal axis of filament 62 is coincident with the longitudinal axis of chamber 53.
The filaments employed in lamps of this invention according to Figure 1 described above were each dynamically made of a single, unbroken length of tungsten wire without the use of mandrels which have traditionally been used and are normally required to make coiled tungsten filaments. The filaments of this invention were made employing an ITAYA MCS E Series extension spring coiler Model MCS-8E available from K.P. American Corporation of Southfield, Michigan 48034. These machines are computerized spring coilers designed for making wire springs, but which have also been found useful for making the filaments of the present invention. In using such a machine to make the filaments of the invention, straightened tungsten filament wire is fed from a spool by a pair of grooved feed rolls into and through a hard metal quill. When the wire exits the quill it strikes a forming tool attached to a tool holder or slide movable by a cam. The forming tool is a grooved metal wheel or roller mounted at an angle to the longitudinal axis of the filament wire as it exits the quill. The filament wire strikes the groove in the forming tool as it exits the quill and is continuously forced into the desired coil size. As the coil is being formed, momentarily changing the distance from the forming tool to the wire results in a change of coil size, so that a filament can be formed consisting of coil or straight wire filament segments, or both, with either a gradual or abrupt increase in diameter from the filament segments to the support segments. As set forth above, the support segments or supports, while most generally in the form of a coil or ring, may be made in various other shapes on the spring coiler. Various other tools may be simultaneously employed to vary the pitch and turn-to-turn distance. In making the filament described above for the 1600 watt heat lamp using tungsten wire having a diameter of 11.5 mils on the ITAYA spring coiler machine it was found beneficial to heat the wire in 300°C air between the quill exit and forming tool. Further, using the ITAYA machine also permits one, if desired, to form the filament so that the longitudinal axis of one or more or all of the elongated filament segments is off center or not coincident with the central axis of the support (as is shown in U.S. Patent 2,454,765). Thus the longitudinal axis of the filament segments may be parallel to, but not coincident with, the longitudinal axis of the supports.
The foregoing examples of filaments of the invention and of lamps employing filaments of the invention are meant to be merely illustrative and not limiting. Filaments of the invention may be employed with other incandescent lamp embodiments in various configurations as will be obvious to those skilled in the art. Further, such lamps containing filaments of the invention may employ a thin film light interference coating or film on at least a portion of the lamp envelope for selectively transmitting various portions of the electromagnetic spectrum. Such films or coatings are well known to those skilled in the art and are now being made of alternating layers of two different refractory metal oxides differing in their index of refraction. Such films can alter the color of visible light emitted by a lamp and/or reflect infrared radiation back to the filament wherein at least a portion is converted into visible light radiation. Heat and visible light reflecting coatings may also be applied as an integral reflector. In lamps where at least a portion of the electromagnetic radiation is reflected back to the filament the longitudinal axis of the filament must be precisely radially aligned or coincident with the longitudinal axis of the filament chamber. This is accomplished in a facile, precise and economic manner employing filaments of the invention.

Claims

An elongated, continuous wire filament having a plurality of both filament segments and integral supports.
The filament of claim 1 having at least two filament segments and at least two integral supports.
The filament of claim 2 having at least three filament segments and at least three integral supports.
The filament of any preceding claim wherein said support has a diameter greater than that of said filament segments.
The filament of any preceding claim wherein at least a portion of said filament segments are coils.
The filament of any preceding claim wherein the longitudinal axis of at least a portion of said filament segments is coincident with the longitudinal axis of said supports.
The filament of any preceding claim wherein at least one of said filament segments is in the form of uncoiled wire.
The filament of claim 7 wherein a plurality of said filament segments are straight wire segments.
The filament of any preceding claim wherein said filament segments are connected by said supports.
The filament of any preceding claim, wherein the plurality of filament segments comprise elongated coils made of turns of substantially the same diameter wherein said filament segments are separated by integral support rings whose diameter is substantially greater than that of said filament segments.
The filament of any preceding claim made of tungsten wire.
The filament of any preceding claim wherein said support rings are disposed along a common longitudinal axis.
The filament of any preceding claim wherein said filament segments are disposed along a common longitudinal axis.
The lamp of claim 10 wherein there is an abrupt change in diameter between said filament segments and said supports.
An incandescent lamp comprising a light transmissive envelope enclosing within a continuous wire filament having a plurality of filament segments and a plurality of integral supports, the filament being as claimed in any preceding claim, wherein at least a portion of each support is adjacent the inner wall of said envelope to support said filament within said envelope.
An incandescent lamp comprising an elongated, light transmissive envelope hermetically enclosing within an elongated, continuous tungsten wire filament longitudinally disposed within said envelope and having a plurality of both coiled filament segments and integral supports, wherein said supports are in the form of rings or coils which have a diameter substantially greater than that of said filament segments and with the outer surface of said supports adjacent the inner surface of said envelope to support said filament within said envelope.
The lamp of claim 15 or 16 wherein said filament is longitudinally disposed within said envelope.
The lamp of claim 15, 16 or 17 having a light interference coating on at least a portion of said envelope.
The lamp of any of claims 15 to 18 having a light and heat relfective coating on said envelope.