US3629914A

US3629914A - Method of making an elongated singly coiled filament and mounting it in a tubular incandescent lamp

Info

Publication number: US3629914A
Application number: US18227A
Authority: US
Inventors: Erik N Giertsen
Original assignee: Westinghouse Electric Corp
Current assignee: Philips North America LLC
Priority date: 1970-03-10
Filing date: 1970-03-10
Publication date: 1971-12-28
Anticipated expiration: 1988-12-28

Abstract

The elongated filament of a lumiline- or showcase-type incandescent lamp is initially wound as a coiled coil filament and attached to the lead wires of the mount assembly. When a getter is used, the getter is applied to the primary turns of the coiled coil filament before it is stretched and remains on the primary turns of the resulting singly coiled filament that is attached to the mount assembly.

Description

United States Patent Inventor Erik N; Giertsen Verona, NJ.

Appl. No. 18,227

Filed Mar. 10, 1970 Patented Dec. 28, 1971 Assignee Westinghouse Electric Corporation Pittsburgh, Pa.

METHOD OF MAKING AN ELONGATED SINGLY COILED FILAMENT AND MOUNTING IT IN A TUBULAR INCANDESCENT LAMP 6 Claims, 3 Drawing Figs.

U.S. Cl. 29/25.!5, l40/7l.5, l40/71.6 Int. Cl 1-101] 9/18, H01] 9/36 Field 01 Search 140/7 I .6, 71.5", 29/251, 25.11, 25.13, 25.17, 25.18, 25.14, 25.15

References Cited UNITED STATES PATENTS Zabel Spaeth.... Cartun Curtis Weiss Armstrong Berlec Primary Examiner.lohn F. Campbell Assistant Examiner-Richard Bernard Lazarus AttorneysA. T. Stratton, W. D. Palmer and D. S. Buleza 29/2518 X 29/2514 X 313/285 X 29/2518 X 117/219 X ABSTRACT: The elongated filament of a lumilineor showcase-type incandescent lamp is initially wound as a coiled coil filament and attached to the lead wires of the mount assembly. When a getter is used, the getter is applied to the primary turns of the coiled coil filament before it is stretched and remains on the primary turns of the resulting singly coiled filament that is attached to the mount assembly.

METHOD OF MAKING AN ELONGATED SINGLY COILED FILAMENT AND MOUNTING IT IN A TUBULAR INCANDESCENT LAMP BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electric lamps and has particular reference to an improved method of making elongated singly coiled filaments and mounting them on the lead wires of tubular incandescent lamps of the lumiline or showcase type.

2. Description of the Prior Art So-called lumilineand showcase-type incandescent lamps are well known in the art and contain an elongated singly coiled filament of suitable refractory metal wire, such as tungsten, that is electrically connected to the lead wires of a support assembly which holds the filament in suspended position within a tubular envelope. Showcase lamps are of the singleended type and have a threaded base at one end that permits the lamp to be used in conventional threaded socket fixtures. A showcase lamp of this type is disclosed in US. Pat. No. 2,425,865 issued Aug. 19, 1947 to R0. Cartun. So-called lumiline" lamps, on the other hand, are double ended and the elongated filament is electrically connected to a metal cap that is sealed to each end of the glass envelope. A lumiline lamp constructed in this fashion is disclosed in US. Pat. No. 2,667,594 issued Jan. 26, 1954 to H.E. Hermanson et al.

Heretofore, the filaments for such lamps were wound as singly coiled helices that were stretched to the required length and clamped to the lead wires. In order to obtain a stretched filament of the required electrical characteristics, it was necessary to wind the fine tungsten wire on very large mandrels. In the case of a conventional 60-watt T8 lumiline lamp for example, the diameter of the mandrel is over 13 times as large as the diameter of the tungsten wire. The percent mandrel is accordingly over 1,300 percent which makes it very difficult to manufacture such filaments.

In addition, due to the dimensions of lumilineand showcase-type lamps the prior art singly coiled filaments as wound were inherently long and difficult to handle. In the case of the aforementioned 60-watt T8 lumiline lamp for example, the finished coil length (prior to stretching) is approximately 27 millimeters. The finished coils have an uncoiled leg at each end and accordingly have a tendency to tangle and become locked with one another when handled and shipped en masse. Shrinkage is accordingly high and gettering a batch of such coils requires extreme care to insure that the coils are properly coated with getter and do not become entangled. The singly coiled filaments used in the prior art are accordingly difficult and inefficient to manufacture and ship and present serious shrinkage and quality control problems during the gettering and filament-mounting operations.

SUMMARY OF THE INVENTION The foregoing problems and disadvantages associated with the prior art singly coiled filaments used in lumilineand showcase-type incandescent lamps are avoided in accordance with this invention by initially winding the filament as a coiled coil helix and then stretching it into a singly coiled helix of the proper length that is attached to the lead wires of the support assembly. Due to their coiled coil configuration, the filaments as wound are much shorter and easier to handle and getter in bulk quantities since they no longer have a tendency to tangle. The relative size of the primary mandrel on which the fine tungsten wire is wound is also greatly reduced, thus facilitating the coil-winding operation and reducing the manufacturing cost of the filaments. Since the coiled coil filaments inherently have a larger diameter and are shorter than the conventional singly coiled filaments, they can be shipped en masse and then be readily segregated, stretched and attached to the lead wires by factory personnel.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the invention will be obtained by referring to the exemplary embodiment shown in the accompanying drawings, wherein:

FIG. 1 is an elevational view, partly in section, ofa lumiline lamp that contains the improved coiled filament of the present invention;

FIG. 2 is an enlarged fragmentary view of the embryonic filament illustrating the manner in which the refractory metal wire is wound around the primary mandrel to form a composite wire which is subsequently wound into coiled coil configuration; and,

FIG. 3 is an enlarged fragmentary view of the finished coiled coil filament after the primary and secondary mandrels have been removed and before it is stretched to its final length and mounted.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown a representative lumiline incandescent lamp 10 which embodies the present invention and consists of a sealed tubular glass envelope 12 that has metal caps 13 and I4 fused to each end and contains an elongated singly coiled filament 16 of suitable refractory metal wire such as tungsten. The filament 16 is coaxially suspended within the envelope 12 by stublike conductor members such as

lead wires

18 and 20 that are clamped around the ends of the filament and secured, as by spot welding, to a pair of terminal leads 22 and 24 that are fastened to an elongated rigid support assembly 25 that extends along the wall of the envelope 12. The support assembly 25 comprises a metal channel 26 that is spot welded to the terminal lead 22 and has its opposite end embedded in a glass insulator 27 that is fused and anchored to the end of the other terminal lead 24. The terminal leads 22 and 24 are compressively seated against and thus are in electrical contact with the

respective caps

13 and 14 which serve as the lamp terminals. The support assembly 25 is prevented from moving laterally by a U-shaped wire harness 30 that is spot welded to the channel 26 and resiliently engages the curved walls of the envelope l2.

Sagging of the elongated filament 16 is prevented by a series of intermediate support wires 28 that are loosely looped around the filament l6 and have their opposite ends embedded in glass beads 29 that are fused and anchored to the metal channel 26. One end of the envelope 12 is provided with a glass tubulation (not shown) which is tipped off in the usual manner after the envelope 12 has been evacuated. The lamp 10 is of the vacuum type and the filament 16 is coated with a suitable getter material which is vaporized during the lampflashing operation and purges the sealed envelope 12 of residual gaseous impurities in the well-known manner.

In accordance with the present invention, the filament 16 is initially formed as a coiled coil instead of a singly coiled helix. As shown in FIG. 2, this is accomplished by winding the tungsten wire around a primary mandrel 19 of the dissimilar metal such as molybdenum to form a composite wire 16 of predetermined length X that consists of the primary mandrel I9 and a plurality of uniformly spaced primary turns 17 of fine tungsten wire. This composite wire 16' is then wound on a larger secondary mandrel (not shown) to provide an embryonic coiled coil helix of predetermined diameter and length. The secondary coiling operation is performed on a coiling machine which mechanically withdraws the secondary mandrel from the coiled coil after it has been formed. Such coiling machines are well known in the art.

After the second coiling operation has been completed, the primary molybdenum mandrel 19 is removed by immersing the embryonic coiled coils in a bath of sulfuric and nitric acids which dissolves and removes the molybdenum mandrel but does not dissolve the tungsten wire. The finished coiled coil filament 32 is shown in FIG. 3 and consists of a compound helix of predetermined-length Y and diameter Z which has a predetermined number of spaced secondary turns 34, a

predetermined number of spaced primary turns 17, and longitudinally extending singly coiled legs 35 at each end.

The finished coiled coil filaments 32 are spray coated with a suitable getter material and dried in masse by placing them in an oven in the customary manner.

Mounting of the gettered coiled coil filaments 32 is accomplished by clamping the end of one of the coil legs 35 within the hooked end of one of the stub leads 18, 20 of the support assembly 25 and pulling the other coil leg 35 to stretch and convert the coiled coil into a singly coiled filament 16 of the type shown in FIG. 1 that is slightly longer than the spacing between the stub leads l8 and 20. The free end of the stretched singly coiled filament 16 is then slipped through the loops of the support wires 28 and clamped to the hooked end of the other stub lead, thus completing the assembly of the filament mount. The length X of the primary coil and length Y of the coiled coil 32 are such that the latter is stretched to a length at mounting that is greater than dimension X. Hence, the coiled coil helix 32 is stretched into a singly coiled helix which, in turn, is stretched into a singly coiled filament 16 of the proper length.

Surprisingly, it has been found that very little, if any, of the coated getter material is dislodged from the primary coil turns 17 when the coiled coil filament 32 is stretched. Due to the manner in which the filament 16 is manufactured and then mounted on the stub leads 18 and 20, the segment of the filament leg 35 is located within and extends beyond one of the lead wire clamps consists of primary turns 17 that are spaced closer together than the primary turns in the main. body portion of the stretched filament 16. In a conventional lamp, the coil legs usually comprise uncoiled segments of wire and these are clamped within the lead wire hooks.

While the invention has been illustrated and described in terms of a lumuline lamp, it can be employed with the same manufacturing and cost reduction advantages in other types of lamps, such as showcase lamps, which require long singly coiled filaments of small diameter, or even in lamps which utilize uncoiled filaments.

SPECIFIC EXAMPLE As a specific example, excellent results have been obtained in the case of a 60-watt T8 lumiline lamp of the type shown in the drawing by winding a tungsten wire 0.05 millimeter in diameter around a primary molybdenum mandrel having a diameter of 0.117 millimeter to form a composite wire 91.6 millimeters long (dimension X) and 0.217 millimeter in diameter with a primary winding of 340 turns per inch. The percent mandrel (diameter of mandrel divided by diameter of wire) was accordingly 234 percent. The composite wire was wound on a retractable secondary mandrel 0.401 millimeter in diameter (185 percent secondary mandrel) at 79 t.p.i. to provide a coiled coil that had a length of 19.1 millimeters (dimension Y), a barrel diameter of 0.835 millimeter (dimension Z), and contained 44 secondary turns. The primary turns of the finished coiled coil filament were spray coated with a getter consisting of 77 percent by weight cryolite and 23 percent by weight red phosphorus suspended in a suitable liquid vehicle such a mixture of nitrocellulose and amyl acetate, which serve as a binder and a thinner, respectively. The spacing between he stub leads of the lamp mount was 436 millimeters and the gettered coils were stretched to a slightly longer length at mounting.

in contrast, the filament heretofore used in the same type lumiline lamp consisted of a singly coiled filament that was formed by winding a ODS-millimeter diameter tungsten wire around a primary mandrel 0.66 millimeter in diameter (1,320 percent mandrel) at 316 t.p.i. The resulting singly coiled filament was 26.7 millimeters long, 0.76 millimeter in diameter and was stretched to a length slightly in excess of 436 millimeters prior to mounting. Tests have shown that the shrinkage during coil winding was frequently over 20 percent in the case of the prior art singly coiled filaments and that less than 1 ercent s rlnkage occurred when the filaments were initially wound as coiled coils and subsequently stretched in accordance with the invention.

It will be apparent from the foregoing that an improved method has been provided for manufacturing elongated filaments for electric lamps and mounting them on the support assembly which reduces the cost of the filament and lamps. The invention permits the filaments to be wound in an efficient manner and then be handled and shipped in bulk quantities without becoming tangled or distorted.

I claim:

1. In the manufacture of an electric incandescent lamp having an elongated singly coiled filament of refractory metal wire that is held in suspended position within a tubular envelope by a support structure that includes a pair of spaced conductor members, the method of making said filament and mounting it on said support structure, which method comprises;

initially winding the refractory metal wire into a coiled coil filament that is shorter than the spacing between said conductor members, stretching and thereby converting said coiled coil filament into a singly coiled filament having a plurality of spaced primary turns and a length that is slightly longer than the spacing between said conductor members, and then attaching the ends of said stretched singly coiled filament to the respective conductor members so that said filament is suspended therebetween.

2. The method of claim I wherein;

said conductor members comprise a pair of lead wires and said stretched singly coiled filament is attached to said lead wires by forming the free ends of the wires into hooks and closing said hooks around the ends of the filament.

3. The method of claim I wherein;

the primary turns of said coiled coil filament are coated with getter material before the coiled coil filament is stretched into a singly coiled filament, and

the length of said coiled coil filament and the initial spacing between the primary turns thereof are such that the coated getter material remains on the primary turns of the stretched singly coiled filament.

4. The method of claim 1 wherein;

said coiled coil filament is formed by winding the refractory metal wire on a primary mandrel to provide a composite wire,

said composite wire is wound on a secondary and larger mandrel to form an embryonic coiled coil filament having a longitudinally extending singly coiled leg at each end, and

said primary and secondary mandrels are removed from the embryonic coiled coil filament to provide a finished coiled coil filament.

5. The method of claim 4 wherein;

said refractory metal wire comprises tungsten wire,

said primary mandrel is composed of molybdenum and is chemically dissolved from the embryonic coiled coil filament and said secondary mandrel is mechanically withdrawn from the embryonic coiled coil filament.

6. The method of claim 4 wherein the length of said finished coiled coil filament compared to the spacing between said pair of conductor members is such that both the coiled coil filament and the resulting singly coiled filament are stretched before the latter is attached to said conductor members.

t t i

Claims

1. In the manufacture of an electric incandescent lamp having an elongated singly coiled filament of refractory metal wire that is held in suspended position within a tubular envelope by a support structure that includes a pair of spaced conductor members, the method of making said filament and mounting it on said support structure, which method comprises; initially winding the refractory metal wire into a coiled coil filament that is shorter than the spacing between said conductor members, stretching and thereby converting said coiled coil filament into a singly coiled filament having a plurality of spaced primary turns and a length that is slightly longer than the spacing between said conductor members, and then attaching the ends of said stretched singly coiled filament to the respective conductor members so that said filament is suspended therebetween.

2. The method of claim 1 wherein; said conductor members comprise a pair of lead wires and said stretched singly coiled filament is attached to said lead wires by forming the free ends of the wires into hooks and closing said hooks around the ends of the filament.

3. The method of claim 1 wherein; the primary turns of said coiled coil filament are coated with getter material before the coiled coil filament is stretched into a singly coiled filament, and the length of said coiled coil filament and the initial spacing between the primary turns thereof are such that the coated getter material remains on the primary turns of the stretched singly coiled filament.

4. The method of claim 1 wherein; said coiled coil filament is formed by winding the refractory metal wire on a primary mandrel to provide a composite wire, said composite wire is wound on a secondary and larger mandrel to form an embryonic coiled coil filament having a longitudinally extending singly coiled leg at each end, and said primary and secondary mandrels are removed from the embryonic coiled coil filament to provide a finished coiled coil filament.

5. The method of claim 4 wherein; said refractory metal wire comprises tungsten wire, said primary mandrel is composed of molybdenum and is chemically dissolved from the embryonic coiled coil filament and said secondary mandrel is mechanically withdrawn from the embryonic coiled coil filament.