US2987643A - Filament joint for electric lamps or similar devices - Google Patents

Description

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June 6, 1961 s, c, ACKERMAN 2,987,643

FILAMENT JOINT FOR ELECTRIC LAMPS OR SIMILAR DEVICES Filed May 2, 1956 United States Patent York Filed May 2, 1956, Ser. No. 582,290 Claims. (Cl. 313271) My invention relates in general to electric incandescent lamps and similar devices and more particularly to an improved joint or connection between the filament and leading-in conductors of such devices.

In the service for which certain types of incandescent lamps are intended, the lamp is normally subjected to constant or prolonged periods of severe vibration. This is particularly true, for instance, in the case of lamps employed for aircraft service such as aircraft landing lamps. Where the filaments of such lamps, as in the case of the aforementioned aircraft landing lamps, are unsupported except for their points of connection to the lead-in conductors or wires of the lamp, the resulting flexure of the filament produced by the vibration of the lamp subjects the filament connections or joints to severe stresses. Adequate filament or mount strength against such vibration and resulting stresses therefore becomes an important factor in the construction of such type lamps.

In the manufacture of incandescent lamps designed for such severe vibration service, as for example in the manufacture of aircraft landing lamps, it has been common practice to connect the filaments to the lead-in conductors of the lamp by welding the end legs of the filament to the lead-in conductors. These filaments are conventionally formed of tungsten wire. However, when a refractory type metal like tungsten is welded to the lamp lead-in conductors, a re-crystallized area with very coarse grain structure is very apt to develop in the filament wire at the region of the welded joint or connection, even though the most careful control is exercised over the welding operation. With the formation of this large crystal growth in the tungsten filament wire, the tungsten becomes brittle at the welded joint or connection. The result is a filament joint or connection of relatively low strength and inadequate resistance to Withstand the stresses such as are imposed on the joint by the vibration normally encountered in aircraft service.

It is an object of my invention, therefore, to provide an electric incandescent lamp or similar device with a filament joint of improved strength and resistance to vibrational stresses. Another object of my invention is to provide an electric incandescent lamp or similar device having a welded type filament joint of a construction such that the points of maximum stress developed in the filament on vibration are located at regions inwardly of the filament from the regions of their welded connections to the support or lamp lead-in members.

Briefly stated, in accordance with one aspect of my invention, the end legs of the filament are mechanically connected or clamped to the lead-in conductors of the lamp by thin metal strap or plate members suitably secured to the lead-in conductors as by welding, and the filament end legs are welded to the said metal strap members at points outwardly of the filament relative to their points of mechanical attachment to the lead-in conductors by the strap members.

Further objects and advantages of my invention will appear from the following detailed description of a species thereof and from the accompanying drawing.

In the drawing, FIG. 1 is an elevation, in section, of

an electric incandescent lamp comprising my invention.

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FIG. 2 is a perspective view, on an enlarged scale, of the mount structure of the lamp shown in FIG. 1.

FIG. 3 is an elevation, partly in section and on an enlarged scale, of the filament joint comprising my invention, and

FIG. 4 is a transverse section, on a greatly enlarged scale, of the mount structure and showing one of the filament joints thereof in section.

Referring to the drawing, the lamp there illustrated is of the self-contained reflector type described and claimed in U.S. Patent 2,148,314, D. K. Wright, issued February 21, 1939, and assigned to the assignee of the present invention. The lamp comprises a bulb or envelope 1 consisting of a preformed pressed glass reflector section 2 sealed around its periphery to a preformed pressed glass cover section 3. The interior surface of the reflector section 2 is of suitable light-concentrating shape such as paraboloidal, for instance, and it is covered with a metallic coating 4, preferably of aluminum, constituting a re fleeting surface. Mounted on the reflector section 2, exteriorly thereof and at the apex of said section, is a base structure 5. The base structure 5 may be of the type described and claimed in U.S. Patent 2,272,512, Cotman et al., dated February 10, 1942, and comprising a pair of metal lugs 6 suitably secured, as by soldering, to metallic cups or thimbles 7 having their edges sunk and embedded in the glass of the reflector section 2 around openings 8 therein, the cups or thimbles 7 thus hermetically closing the said openings 8. The envelope 1 is exhausted and filled with a suitable gas through an exhaust tube 9 attached to the reflector section 2 at its apex. After the gas filling is introduced into the lamp envelope, the exhaust tube 9 is tipped off, as indicated at 10, to hermetically seal the envelope.

Mounted within the envelope 1 and supported therein from the metal thimbles 7 is a mount structure 11 comprising an electric energy translation element or filament 12 disposed between and connected to a pair of rigid lead- -in wires or conductors 13 of suitable material, such as nickel or iron. The lead-in conductors 13 are rigidly secured at their outer ends to the metal thimbles 7, as by soldering or brazing, and they extend straight through the openings 8 in the reflector section into the interior thereof in parallel relation to one another and preferably in a plane parallel to and including the axis of the reflector section 2. The lead-in conductors 13 are held in rigid spaced relation by an insulating bridge or cross bar member comprising a glass rod 14 extending between and secured to the lead-in conductors 13 by short fastening wires 15 which may be spot-welded to the lead-in conductors. The inner end of one of the lead-in conductors 13 is formed with a lateral extension 16 to which is secured a shield 17 for intercepting certain of the direct radiations from the filament which otherwise would pass out through the cover glass 3 of the lamp envelope.

The filament 12 comprises a linear coiled-coil (the filament proper) of tungsten wire disposed coaxially of the reflector axis in a position in definite optical relation to the focus of the reflecting surface 4, preferably symmetrically about the reflector focus. Each end of the filament 12 is provided with a straight or uncoiled end section or leg portion 18 extending laterally of the lead-in conductors 13 and over which is slipped a coil 19 of a suitable heat-resisting metal such as tungsten or molybdenum or an alloy thereof. The slip-over coil 19 is wound with a relatively close pitch, i.e. closely coiled, and is preferably made just large enough in diameter to fit more or less snugly around the filament end leg 18.

The coil-enclosed end legs 18 of the filament 12 are connected to the respective lead-in conductors 13 by a filament joint or connection 20 constructed in accordance with the invention. To this end, each coil-enclosed file 3 l ment end leg 18 extends across and is firmly pressed or clamped against the respective lead-in conductor 13 by a thin metal strap or plate member 21 which is securely fastened to the lead-in conductor in any suitable manner, for instance, as by welding it to the lead-in conductor at points on either side of the filament end leg 18, as indie cated at 22. The tight clamping of the coil-enclosed filament end leg 18 to the lead-in conductor 13 thus forms a rigid mechanical clamp connection therebetween which constitutes the first point of completely rigid anchorage of the filament end leg outwardly therealong from the main body of the filament or filament proper. The metal strap or plate members 21 may be made of any suitable material such as nickel or iron for example, and they are fastened to the lead-in conductors in a manner such as to extend outwardly away from the said conductors in opposite directions therefrom and substantially in the plane of the said conductors 13 whereby the plate members 21 intercept a minimum of the radiations from the filament so as not to produce undesirable shadows or dark spots in the light beam projected by the lamp.

In accordance with the invention, each filament end leg 13, instead of being welded directly to the lead-in conductor 13 as in prior constructions, is extended outwardly beyond the lead-in conductor and is welded to the metal strap or plate member 21 at a point along its length spaced some distance, for example, one-eighth inch or so outwardly thereof from its mechanical clamp connection to the lead-in conductor as indicated at 23. In the particular case illustrated, the metal strap or plate members 21 are formed of sheet metal having a thickness preferably of about .020 inch for example, and they are of rectangular shape having a length along the leadin conductors of around one-half inch to five-eighths inch and a width or" the order of one-quarter inch. As shown in FIG. 1, the strap or plate members 21 are each formed with a cross corrugation 24 extending thereacross and preferably tapered down in size (i.e. both in width and depth) in a direction outwardly from the respective leadin conductor to provide a correspondingly tapered groove or channel 25 for accommodating the coil-enclosed filament end leg 18 therein. This tapering of the channel or groove 25 in the metal strap 21 serves to raise or expose the coil-enclosed end leg 18 of the filament above the plane of the Welding faces of the metal strap, thereby assuring contacting of the welding electrode with the coilenclosed filament end leg during the welding thereof to the metal strap 21.

By shifting the welded connection 23 between the coilenclosed filament end leg 18 and the lead-in member 13, 21 to a point outwardly of the lead-in conductor 13 relative to the filament in accordance with the principle of my invention, so that the first point of completely rigid anchorage of the filament end leg outwardly therealong from the filament proper is its mechanical clamp connection to the lead-in conductor 13 by the clamping strap or plate member 21, the points of maximum fiexure stress that develop in the filament on vibration thereof then occur at the mechanical pressure or clamp connection of the coil-enclosed filament end leg to the lead-in conductor and are thus kept away from the re-crystallized section of the filament which is produced at the weld 23 thereof to the metal strap 21. As a result, a filament joint 20 is provided of greatly increased vibration strength over that which is obtained where the filament is welded directly to the lead-in conductor so that the points of maximum fiexure stress in the filament are located at the welded and re-crystallized section of the filament. The outward shifting of the welded connection between the filament end leg and the lead-in conductor in the manner disclosed also provides an added safety factor in that the filament end leg 18 is secured at two different points to the lead-in member 13, 21. The metal strap or plate members 21, in addition to serving as a means of locating the welded connection of the filament to the lead-in 4 l conductor at a point outwardly of the conductor relative to the filament, also serve as a means for dissipating the heat from the filament joint 20 so as to maintain the filament joint at a minimum operating temperature below that temperature at which distortion. of the lead-in conductors might occur. Moreover, because of the increased current-carrying cross section which theyprovide at the filament joints, the metal straps or plate members 21 further serve to diminish the rate of heating of the filament joints by the current passing therethrough during lamp operation.

Although a preferred embodiment of my invention has been disclosed, it will be understood that the invention is not to be limited to the specific construction and arrangement of parts shown, but that they may be widely modified within the spirit and scope of my invention as defined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric lamp, the combination of a lead-in conductor, a filament having an end portion extending across and beyond said conductor, and a metal plate member secured to said conductor over and tightly clamping said filament end portion to said conductor to form a rigid mechanical clamp connection therebetween, said mechanical clamp connection constituting the first point of completely rigid anchorage of the said filament. end portion outwardly therealong from the filament proper, said filament end portion being welded to said metal plate member at a point along the length of said filament end portion outwardly thereof from its said mechanical clamp connection to'said conductor and being entirely free of welded regions inwardly of its said point of welded connection to the metal plate member,

2. In an electric lamp, the combination of a lead-in conductor, a filament having an end portion extending across and beyond said conductor, and a metal plate member welded to said conductor on each side of and extending over the said filament end portion and tightly clamping it to said conductor to form a rigid mechanical clamp connection therebetween, said mechanical clamp connection constituting the first point of completely rigid anchorage of the said filament end portion outwardly therealong from the filament proper, said filament end portion being welded to said metal plate member at a point along the length of said filament end portion outwardly thereof from its said mechanical clamp connection to said conductor and being entirely free of welded regions inwardly of its said point of welded connection to the metal plate member.

3. In an electric lamp, the combination of a lead-in conductor, a filament having an end portion extending across and beyond said conductor, a slip-over coil on the said end portion of the said filament, and a metal plate member secured to said conductor over and tightly clamping the said coil-enclosed filament end portion to said conductor to form a rigid mechanical clamp connection therebetween, said mechanical clamp connection constituting the first point of completely rigid anchorage of the said coil-enclosed filament end portion outwardly therealong from the filament proper, said coil-enclosed filament end portion being welded to said metal plate member at a point along the length of said filament end portion outwardly thereof from its said mechanical clamp connection to said conductor and being entirely free of welded regions inwardly of its said point of welded connection to the metal plate member.

4. In an electric lamp, the combination of a lead-in conductor, a filament having an end portion extending across and beyond said conductor, a slip-over coil on the .said end portion of the filament, and a metal plate member extending over and tightly clamping said coil-enclosed filament end portion against said lead-in conductor to .form a rigid mechanical clamp connection therebetween, said mechanical clamp connection constituting the first point of completely rigid anchorage of the said filament end portion outwardly therealong from the filament proper, said metal plate member being welded to the lead-in conductor at points on opposite sides of the coil-enclosed filament end portion and said coil-enclosed filament end portion being welded to said metal plate member at a point along the length of said filament end portion outwardly thereof from its said mechanical clamp connection to said conductor, said coil-enclosed filament end portion being entirely free of welded regions inwardly of its said point of welded connection to the metal plate member.

5. In an electric lamp, the combination of a lead-in conductor, a filament having an end portion extending across and beyond said conductor, a slip-over coil on the said end portion of the filament, and a metal plate member secured to and extending alongside said lead-in conductor and over said coil-enclosed filament end portion and tightly clamping it against said lead-in conductor to form a rigid mechanical clamp connection therebetween, said mechanical clamp connection constituting the first point of completely rigid anchorage of the said filament end portion outwardly therealong from the filament proper, said metal plate member having a groove therein within which the said coil-enclosed filament end portion fits, said groove slightly tapering down in size in a direction outwardly of the plate member from theifil ament so as to accommodate within its smaller size end region less than the full diametrical width of the coil-enclosed filament end portion, said filament end portionbeing welded to said metal plate member at a point along the length of said filament end portion outwardly thereof from its said mechanical clamp connection to said conductor and being entirely free of welded regions inwardly of its said point of welded connection to the metal plate member.

References Cited in the file of this patent UNITED STATES PATENTS 1,829,423 Sutherlin Oct. 27, 1931 2,247,688 Kinyon July 1, 1941 2,366,292 Smith Jan. 2, 1945 2,404,992 Stone July 30, 1946 2,632,126 Curtis Mar, 17, 1953 2,716,714 Adams Aug. 30, 1955 2,738,435 Voreaux Mar. 13, 1956 2,791,713 Dean May 7, 1957 2,791,714 Beesley May 7, 1957

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