US3629642A

US3629642A - Insulated filament supports

Info

Publication number: US3629642A
Application number: US6772A
Authority: US
Inventors: Nickolas P Demas
Original assignee: Wagner Electric Corp
Current assignee: Cooper Industries LLC
Priority date: 1970-01-29
Filing date: 1970-01-29
Publication date: 1971-12-21
Anticipated expiration: 1988-12-21

Abstract

A new type of support for filaments in incandescent lamps and vacuum tubes is disclosed. The support is nonconductive, able to resist high temperatures, rigid, malleable, and it eliminates variation in rating and stability of rating in lamps and tubes caused by filament contact with the support.

Description

United States Patent Nickolas P. Dumas (Zranlord. NJ.

Dec. 21 1 97 l Wagner Electric Corporation Inventor Appl. No. Filed Patented Assignee INSULATED FILAMENT SUPPORTS 5 Claims, 3 Drawing Figs.

US. Cl 313/277,

313/257, 313/289, 313/352 Int. Cl H0lj 1/90 Field of Search 313/276,

[56] References Cited UNITED STATES PATENTS 1,047,541 12/1912 Ledever 313/277 X 1,203,635 11/1916 Ledever 313/277 2,191,331 2/1940 Van Liempt. 313/277 2,945,978 7/1960 Hodge 313/276 X Primary Examiner-David Schonberg Assistant Examiner-Toby H. Kusmer Attorney-Eyre, Mann & Lucas ABSTRACT: A new type of support for filaments in incandescent lamps and vacuum tubes is disclosed. The support is nonconductive, able to resist high temperatures, rigid, malleable, and it eliminates variation in rating and stability of rating in lamps and tubes caused by filament contact with the sup port.

PATENIEB m2! an INVENTOR N/CKOLAS I? DEMAS IY a n... ('M

A TTOR/VEYS INSULATED FILAMENT SUPPORTS The present invention relates to a new type of support for incandescent lamps and vacuum tubes which is rigid, malleable, nonconductive and capable of withstanding high temperatures.

Incandescent lamps and vacuum tubes which contain a filament usually have some type of support at one or more places on the filament to avoid the phenomenon known as microphonism. Microphonism is an undesirable phenomenon which results from a vibration of the filament. When the microphonism is in an audio circuit, such as a radio, the vibrating filament causes an audible sound which is annoying. To counteract this, a support is used to divide the filament into sections, each of which is relatively short. This reduces the length of the filament which is free to vibrate and thereby eliminates the microphonism.

The most desirable type of support is one which is rigid, yet malleable and capable of withstanding high temperatures. As a result, metallic supports are usually employed. The disadvantage of standard metallic supports is that they conduct electricity and thus can cause a short circuiting of the filament which results in variations in rating and in the stability of rating of the lamp, especially when the lamp is subjected to vibration such as in automobile radios. A plurality of turns of the filament can come into contact with the support and, if the filament is thus touching the support at more than one point, the filament may be shorted out at two or more points of contact. This effectively changes the length of the filament by shortening it which changes the rating of the lamp or tube in which the filament is employed. The lamp or tube will thus exhibit noise," which is a variation in rating or in stability of rating.

Numerous methods of insulating the supports have been tried in order to eliminate this short circuiting, but none of these are satisfactory either because of high cost or difficulty of application. The major problem is the high temperature in an inert atmosphere which the support must withstand. The temperature is frequently in the neighborhood of 1,800" C. and the atmosphere is usually argon or a vacuum. Standard insulating materials either will not withstand this high temperature in an inert atmosphere, or, if they will, they do not have the desired properties of being strong, rigid and malleable. Aluminum oxide, for example, while it will withstand the high temperatures in air, will not withstand them in an inert atmosphere. Ceramics, n the other hand, will withstand the high temperatures in an inert atmosphere, but they are not malleable and are therefore difficult to work with. Additionally, ceramics and other similar insulating materials applied to a metallic core will usually prove unsatisfactory because of their tendency to flake off when the core is formed into its desired shape.

We have now discovered an insulated support which eliminates all of the above-mentioned disadvantages but yet retains the properties of being strong, rigid, malleable and capable of withstanding high temperatures. The support comprises a tantalum oxide coating on a core such as a metal. For best results a metallic support is employed made with a tantalum metal or tantalum alloy for high strength and durability. The tantalum oxide coating is nonconductive even at high temperatures in inert atmospheres, and it eliminates the possibility of short circuiting the filament and causing noise.

The tantalum oxide coating is preferably formed by oxidizing a tantalum or tantalum alloy strip of wire, thereby forming the tantalum oxide coating as an integral part of the support. The preferred method of forming the tantalum oxide coating is to anodize the selected tantalum wire in conventional manner as for example at about 600 volts in a citric acid bath. The anodization is continued until the flow of current approaches 0 amperes due to the formation of the tantalum oxide coating, which is nonconductive. A spool of tantalum wire may be continuously coated by anodization by passing it through a citric acid bath at a rate which will forma substantially nonconductive tantalum oxide coating thereon.

The tantalum oxide coating may completely surround the support, or it may be only at the point where the support and the filament come into contact. Additionally, it may cover the entire support or only a section or sections of it, as desired.

We have found that the tantalum oxide coated support is especially useful in anchor type supports. Anchor supports are used to break the filament up into segments. Each anchor is usually held firmly in place, as by means of a glass bead. This type of support is most frequently used in incandescent lamps and vacuum tubes.

The tantalum oxide coated support has many useful applications, and is not limited to use in incandescent bulbs or vacuum tubes. It may be used in any application where it is desired to have a nonconductive support for a relatively long filament or other current carrying member. It may also be used either as a rigid support, as in an anchor, or as a free floating support, for example, as a separator between two filaments. In this application it could be held in place only by contact with the filaments.

These and other features of the present invention may be more fully understood by reference to the drawings, in which the same number is used to identify identical parts of the structure, and in which:

FIG. 1 shows an incandescent lamp with anchor wires;

FIG. 2 shows a filament in contact with the anchor wire where they interconnect; and

FIG. 3 shows a filament in contact with the point of interconnection and another point on the anchor.

FIG. 1 is an example of a standard incandescent lamp [0 in which anchors 12 are employed. Anchors are desireable in this bulb because of the length of the filament 14. If the clamps 16 which hold the filament 14 were separated so that the filament 14 was taut, the filament would extend over quite a length. Any vibration of a filament this long would continue for quite a while due to the length of the filament and would result in the phenomenon known as microphonism. The anchors which are inserted along the length of the filament 14 divide the filament into sections, each of which is relatively short thereby eliminating a long free-standing length of filament which would tend to vibrate. Both the clamps l6 and the anchors 12 are maintained in position by a glass head 18.

FIG. 2 is an enlarged view of the interconnection of the filament 14 with the anchor 12. The anchor 12 has been cut away so that the filament 14 may be more clearly seen.

Points

22, 24, 26, 28 and 30 on filament 14 are representative of the turns of the filament. As shown,

points

24, 26 and 28 are in contact with the anchor 12 and, if the anchor is conductive, there will be a short circuit between points 24 and 28 which will result in a shortening of the effective length of the filament, thereby creating the phenomenon known as noise. If there is vibration of the lamp, as by road vibration in an automobile, the filament will tend to vibrate and as it vibrates it is possible for points 22 and 30 to also come in contact with the anchor 12, thereby causing an even shorter efiective length and therefore even greater noise. In accordance with the present invention, the anchor is made nonconductive by the forming of a tantalum oxide coating 32 on the tantalum core 34 of the anchor 12. When the turns 22, 24, 26, 28 and 30 of the filament 14 come in contact with the tantalum oxide coating 32 there is no short circuiting since the tantalum oxide coating is nonconductive. Since there is no short circuiting, there is no noise, and, hence, there is no variation in rating or in stability of rating.

FIG. 3 illustrates another type of short circuiting which can occur between the filament 14 and the anchor 12. Here, the filament 14 is in contact with the anchor 12 at point 26 and also farther down the anchor at point 36. This causes short circuiting between

points

26 and 36 and results in the creation of noise. This short circuiting can be avoided by using the anchor of the present invention, which can be insulated throughout its length if desired. The insulated anchor is not conductive and therefore there will be no short circuiting between

points

26 and 36 of the filament'l4 even'when these

points

26 and 36 are in contact with the anchor 12. Note that if there is no nonconductive coating it is also possible for the filament to be short circuited from point 36 on one anchor to point 36 on the other anchor, thereby effectively eliminating most of the useful length of the filament, and creating a substantial variation in rating of the lamp.

It will be understood that it is intended to cover all changes and modifications of the preferred embodiment of invention herein chosen for the purpose of illustration which do not constitute departure from the spirit and scope of the invention.

What is claimed is:

l. A malleable support for current-carrying members having a tantalum oxide coating on at least a portion thereof said coating being substantially nonconductive and stable at temperatures of l,800 C. in an inert atmosphere.

2. The support of claim 1 wherein the current-carrying member is a filament.

3. The structure of claim 1 in which the support is a metallic tantalum.

4. A method of producing malleable nonconductive supports for current-carrying members which comprises oxidizing at least a portion of a tantalum support thereby forming a tantalum oxide coating on at least a portion of said support, said coating being substantially nonconductive to electricity and stable at temperatures of l ,800" C. in an inert atmosphere.

5. A substantially nonconductive malleable anchor support for filaments in incandescent lamps which comprises a tantalum support at least a portion of which has a tantalum oxide coating thereon, said coating being substantially nonconduc tive to electricity and stable at temperatures of 1,800" C. in an inert atmosphere.

Claims

1. A malleable support for current-carrying members having a tantalum oxide coating on at least a portion thereof said coating being substantially nonconductive and stable at temperatures of 1,800* C. in an inert atmosphere.

2. The support of claim 1 wherein the current-carrying member is a filament.

3. The structure of claim 1 in which the support is a metallic tantalum.

4. A method of producing malleable nonconductive supports for current-carrying members which comprises oxidizing at least a portion of a tantalum support thereby forming a tantalum oxide coating on at least a portion of said support, said coating being substantially nonconductive to electricity and stable at temperatures of 1,800* C. in an inert atmosphere.

5. A substantially nonconductive malleable anchor support for filaments in incandescent lamps which comprises a tantalum support at least a portion of which has a tantalum oxide coating thereon, said coating being substantially nonconductive to electricity and stable at temperatures of 1,800* C. in an inert atmosphere.