US3817296A

US3817296A - Method of making an electrode having a filament with extending legs

Info

Publication number: US3817296A
Application number: US00345564A
Authority: US
Inventors: E Lemmers
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1973-03-28
Filing date: 1973-03-28
Publication date: 1974-06-18
Anticipated expiration: 1991-06-18
Also published as: DE2414423A1; BE812983A; GB1450997A; JPS5027369A; NL7403798A

Abstract

An electrode, such as for a fluorescent lamp, is made by providing a helically wound filament, attaching the filament near the ends thereof to a pair of support wires, temporarily holding an intermediate portion of the filament, and pulling or stretching turns of the filament between the held intermediate portion and the lead wires to form legs on the filament.

Description

United States Patent I [191 Lemmers METHOD OF MAKING AN ELECTRODE HAVING A FILAMENT WITH EXTENDING LEGS M [75] Inventor: Eugene Lemmers, Cleveland Heights, 01116 [73] Assignee: General Electric Company,

Schenectady, NY.

22 Filed: Mar. 28, 1973 211 A 1.1\16.;34s,s64-

52 us. c1. l40/7l.6, 29/2515 51 1111.01 B21f 45/00 [58] Field of Search 140/7l.6; 29/2513, 25.15

[56] References Cited UNITED STATES PATENTS 3,058,497 10/1962 Buck l40/7l.6

[ 1 June 18, 1974 3,073,356 1/1963 Rowan et '61 140/71.6 3,096,795 7/1963 LCHZ l40/71.6 3,160,181 12/1964 Voyce et a1... l40/71.6 3,629,914 12/1971 Giertsen 140/716 Primary Examiner-Lowell A. Larson Art0r ney, Agent, or Firm-Norman C. Fulmer; Lawrence R. Kempton; Frank L. Neuhauser 571 ABSTRACT An electrode, such as for a fluorescent lamp, is made by providing a helically wound filament, attaching the filament near the ends thereof to a pair of support wires, temporarily holding an intermediate portion of the filament, and pulling or stretching turns of the filament between the held intermediate portion and the lead wires to form legs on the filament.

4.Claims, 5 Drawing Figures 1 METHOD OF MAKING AN ELECTRODE HAVING A FILAMENT WITH EXTENDING LEGS BACKGROUND OF THE INVENTION The invention is in the field of making filament-type electrodes for use in electric discharge lamps such as fluorescent lamps.

Fluorescent lamps generally comprise a pair of electrodes respectively sealed into the ends of an elongated glass envelope which contains a combination of gases at suitable pressure for causing an electric discharge when voltage is applied across the electrodes. Each of the lamp electrodes comprises one or more elongated filaments carried by a lead-in wire arrangement. The filaments are coated with suitable electron emission materials so as to function as cathodes, i.e., a source of electrons for current flow in the lamp. The lamp electrodes may also be provided with anode elements, or in some cases, the cathodes may also function as anodes to receive the discharge electron flow on alternate halfcycles of a-c electrical energy.

In a typical electrode construction, the filament is held -by a pair of lead-in support wires bent so as to clamp against the elongated helically'coiled filament near the two ends thereof, respectively. The lead-in wires support the filament and function to carry current to the electric discharge in the lamp, and also function to carry heating current to the filament in preheat and rapid start types of lamps. After a filament is attached to the support wires, an electron emission material is coated onto an intermediate portion of the filament between the support wires, and is heated by passing current through the filament to volatilize and drive off a binder that was in the emission material. It is important that the emission mix not be applied to the support wires nor to the filament near the support wires, as these regions will not get hot enough to volatilize the binder, and binder remaining at these regions in a lamp will give off gases that will degrade lamp performance.

One technique for making the helically coiled elongated filaments so as to facilitate applying emission mix to the desired intermediate portion is to provide each filament with a pair of legs consisting of end portions of the filament wire extending axially outwardly from the otherwise closely coiled filament. The support wires are bent around, so as to be clamped against, the two legs. When the emission mix is applied to the coiled intermediate portion of the filament, the parts of the legs between the support wires and the coiled portion of the filament prevent the emission material from creeping toward the support wire clamps. A disadvantage of this technique is that, in automatic production equipment for feeding the filaments to the support wires, the filaments tend to get tangled and jammed due to legs of some filaments engaging with the helical wound portions to other filaments. Another technique, disclosed in U.S. Pat. Nos. 2,479,192 and 2,479,l93, instead of providing legs on the filament, is to provide a widely spaced turn near each end region of the filament. When the end regions of the filament have been in automatic machinery for the filaments to get tangled and jammed together at their widely spaced turns.

SUMMARY OF THE INVENTION In a preferred method of the invention, an electrode, such as for a fluorescent lamp, is made by the steps of providing a helically wound filament (not provided with legs at the ends thereof), attaching the filament near the ends thereof to a pair of support wires, temporarily holding an intermediate portion of the filament, and pulling or stretching turns of the filament between the held intermediate portion and the lead wires so as to form legs on the filament. The legs can be formed by slightly spreading apart the support wires. Thus, the closely wound helical filaments are readily handled by automatic production machinery without becoming tangled together, and also the filaments are provided with legs at the ends thereof prior to applying the emission material, thereby preventing the emission material from creeping toward the support wires.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cutaway side view of the end portion of a fluorescent lamp, showing an electrode made in accordance with the invention;

FIG. 2 is a side view of an electrode structure in which a helically coiled filament has been clamped near the ends thereof by a pair of support wires;

FIG. 3 illustrates the step of holding an intermediate portion of the filament prior to pulling legs on it;

FIG. 4 illustrates the step of pulling legs on the filament by spreading apart the support wires while the interrnediate region of the filament is being held; and

FIG. 5 is a side view of the completed electrode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The lamp shown in FIG. 1 comprises an elongated tubular glass bulb 11 having a coating of phosphor mate rial 12 on the inner surface thereof. An electrode 13 is sealed at each end of the bulb, respectively, in wellknown manner. The electrode 13 comprises a filament or cathode 16 attached at the ends thereof to in-lead support wires 17a and 17b which are sealed through a glass stem 18 provided with an exhaust and fill tubulation 19. The bult 11 may contain mercury and argon or other suitable fill material for sustaining an electric discharge between the electrodes in the lamp.

The electrode 13 is made by the following method. As shown in FIG. 2, a close wound continuous helical filament 21, preferably made of tungsten wire in a coiled or coiled-coil manner, is attached near the ends thereof to the respective lead wires 17a and 17b, such as by bending the end portions of the wires around the filament in a tight manner so as to clamp and hold the filament. Then, as shown in FIG. 3, an intermediate portion 26 of the filament 21 is temporarily held by means such as a suitable clamp or clip, or by a pronged member 27 having a pair of prongs 28 and 29 inserted between turns of the filament 21 at places a few turns away from the support wire clamps 22 and 23. Next, as shown in FIG. 4, legs 31 and 32 are pulled on the filament 21, by spreading the support wires 17a and 17b relatively apart as indicated by the arrows 33 and 34, or by otherwise moving the temporarily held intermediate portion 26 of the filament with respect to the support wires 17a and 17b, such as up or down or sideways, preferably followed by spreading the support wires 17 relatively apart to make the pulled legs 31 and 32 approximately axially straight with respect to the rest of the filament 21. Preferably one, two, or three turns of the filament are pulled to form each leg, and each leg preferably is about 3 millimeters long.

The temporary holding means 27 is then removed, and a suitable electron emission mixture or material 36 (FIG. is coated onto the intermediate portion 26 of the filament, which remains in helically wound form. The legs 31 and 32 of the filament prevent the emission material 36 from creeping or spreading toward the support wire clamps 22 and 23. Current is then passed through the filament 21, by means of the support wires 17a and 17b, to heat the filament to a temperature sufficient to volatilize and drive off binders or solvents contained in the emission material 36, and this can be done either before or after sealing the electrode into a lamp. After removing the temporary holding means, and prior to applying the emission material to the filament, it is desirable to spread the support wires slightly farther apart, to make the filament taut and to slightly spread apart the individual turns of the filament, to prevent electrical shorting between adjacent filament turns. The invention provides a simple and economical manufacturing method for making an electrode structure provided with a filament having all the advantages of the leg mounted type of filament, plus all the advantages of having the filament in a tightly wound helical form when being handled by automated equipment prior to being clamped by the lead wires 17a and 17b, thereby preventing tangling and jamming of the filaments in the automatic handling machinery.

While preferred embodiments of the invention have been shown and described, various other embodiments and modifications thereof will become apparent to persons skilled in the art and will fall within the scope of the invention as defined in the following claims.

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

1. A method of making an electrode comprising the steps of providing a helically wound filament, attaching said filament near the respective ends thereof to a pair of support wires, temporarily holding an intermediate portion of said filament, and moving said support wires and said intermediate portion of the filament with respect to each other to pull out one or more filament turns between the intermediate portion and the support wires thereby forming legs on said filament between said intermediate portion and said support wires.

2. A method as claimed in claim 1 in which said step of pulling out one or more filament turns comprises spreading said support wires apart.

3. A method as claimed in claim 1 in which said step of temporarily holding an intermediate portion of the filament comprises interposing a pair of prongs between turns of the filament at the ends of said intermediate portion.

4. A method as claimed in claim 1 in which said helically wound filament has closely spaced turns along the entire length thereof prior to said step of attaching the filament to a pair of support wires.