US3701578A - Method of making ceramic electrical device - Google Patents

Abstract

A METHOD OF MAKING A CERAMIC LIGHT BULB OR OTHER ELECTRICAL DEVICE HAVING A CERAMIC ENVELOPE PORTION FORMED OF A TRANSLUCENT CERAMIC MATERIAL AND A METAL CLOSURE MEMBER. THE CERAMIC MATERIAL IS METALIZED IN DESIRED AREAS. THE METAL CLOSURE MEMBER IS ASSEMBLED WITH THE CERAMIC ENVELOPE AND A FILAMENT IS MOUNTED WITHIN THE ENVELOPE WITH OPPOSITE ENDS IN CONTACT WITH METALIZED PORTIONS OF THE ENVELOPE. BRAZING METAL IS PLACED AT ALL CONTACT AREAS BETWEEN THE ENVELOPE AND THE CLOSURE MEMBER. THE ASSEMBLY IS THEN HEATED IN A FURNACE AT A TEMPERATURE AND TIME SUFFICIENT TO BRAZE THE ASSEMBLY INTO AN HERMETICALLY SEALED DEVICE.

Description

R. A. KREY 3,701,578

METHOD OF MAKING CERAMIC ELECTRICAL DEVICE Oct. 31, 1972 Original Filed Feb. 28, 1966 United States Patent Patented Oct. 31, 1972 ABSTRACT OF THE DISCLOSURE A method of making a ceramic light bulb or other electrical device having a ceramic envelope portion formed of a translucent ceramic material and a metal closure member. The ceramic material is metalized in desired areas. The metal closure member is assembled with the ceramic envelope and a filament is mounted within the envelope with opposite ends in contact with metalized portions of the envelope. Brazing metal is placed at all contact areas between the envelope and the closure member. The assembly is then heated in a furnace at a temperature and time suificient to braze the assembly into an hermetically sealed device.

BACKGROUND OF THE INVENTION This invention is a division of application Ser. No. 530,- 716, filed Feb. 28, 1966, and now abandoned for Ceramic Light Bulb with Metal Closure Member.

This invention relates to light bulbs of the incandescent type, and, more particularly, to a ceramic light bulb.

As is well known to those skilled in the lamp art, there is a constant search for light bulbs, particularly of the incandescent type, of a strong and rugged construction which will withstand abuse in handling and shock and vibration during use. It has also become a recent desire to provide light bulbs of very small size for use in many types of modern electronic devices. Small light bulbs are necessary to provide illumination of various dials and the like as Well as provide necessary indicator lights. Recent attempts at such light bulbs have resulted in small glass light bulbs such as is shown and described in Pat. No. 3,040,204. However, one problem with the light bulb disclosed therein is the use of a glass envelope which is a fragile, low temperature material. Also, the method of making such a light bulb is time consuming and expensive. As is well understood, it is desirable that light bulbs be made as simple and as economical as possible.

It has recently been discovered that simple, economical, and very rugged light bulbs can be made from translucent, ceramic material. Such light bulbs are very strong and can be made with very few parts. Also, it has been discovered that light bulbs made of ceramic material may be made with mounting means constructed as part of the light bulb, thus eliminating the necessity of separate mounting means.

It is therefore one object of this invention to provide a ceramic light bulb of simple and rugged construction.

It is a further object of this invention to provide a ceramic light bulb which is small and compact and which may be mounted in any desired location.

A further object of this invention is to provide a method of making a ceramic light bulb.

A still further object of this invention is to provide a ceramic light bulb without separate mounting means which may be mounted on any surface such as a panel, for use as an indicator or illumination light.

SUMMARY OF THE INVENTION In carrying out this invention, in one form a ceramic light bulb is provided which comprises a ceramic envelope portion formed of any desired translucent ceramic material. A metallic closure means is provided and is brazed to metalized portions of the ceramic envelope. A filament is mounted within the ceramic envelope and has its ends electrically connected in electrically isolated brazing material. The ceramic light may be mounted by the metallic closure member. The metallic closure member and a portion of the ceramic envelope at the brazing material provide electrical connections to the opposite ends of the filament.

The ceramic light bulb is made in a preferred form by metalizing ceramic material used to form the light envelope. The, thin film of metal formed by metalizing is ground off of the ceramic material, as necessary, in the areas where translucency is desired and in those other areas where electrical insulation is desired. A metal closure member is assembled with the ceramic envelope and a filament is mounted within the ceramic envelope with its opposite ends in contact with metalized portions of the envelope which are electrically isolated from each other. Brazing metal is placed at all contact areas of the ceramic envelope, the filament and the metal closure member. The assembly is then heated in a furnace, in an atmosphere of hydrogen at a temperature and for a time sufficient to braze the assembly into an hermetically sealed light. The light is then heated in a vacuum at approximately 700 C. for approximately ten minutes to remove the hydrogen by diffusion through the hot metal closure member.

The invention which is sought to be protected will be clearly pointed out and distinctly claimed in the claims appended hereto. However, it is believed that this invention, and the manner in which its various objects and advantages, as well as other objects and advantages, are obtained will be more fully understood by reference to the following detailed description of preferred embodiments thereof, particularly when considered in the light of the accompanying drawing.

BRIEF DESCRIPTION OF DRAWING FIG. 1 is a perspective view of a ceramic light bulb according to a preferred embodiment of this invention;

FIG. 2 is a sectional view of the ceramic light bulb shown in FIG. 1;

FIG. 3 is a sectional view similar to FIG. 2 showing another form of the ceramic light bulb according to this invention; and

FIG. 4 is a sectional view of a ceramic light bulb, as shown in FIGS. 1 and 2, showing a preferred method of construction.

DESCRIPTION OF PREFERRED EMBODIMENTS While the following description will set forth a preferred ceramic light bulb and a preferred method of making such bulb, according to the embodiments of the invention disclosed in the drawing, it will be understood that such description is for illustrative purposes only and should not be considered as limiting the scope of the invention.

Reference will now be made to the drawing, in which like parts will be indicated by like numerals throughout the various views thereof. Referring first to FIG. 1, there is shown a ceramic light bulb 10 made according to the present preferred embodiment of this invention. As shown, ceramic light bulb 10 comprises a ceramic envelope portion formed of ceramic members 12 and 14. 14 is the base member, as clearly shown in FIG. 2. The ceramic envelope portion of bulb 10 is sealed by a metallic closure member 16. As will be apparent from FIG. 1, the ceramic light bulb will provide illumination, particularly through ceramic member 12 when filament 18 (FIG. 2) is heated by electric current.

Considering FIG. 2 of the drawing, it can be seen that the ceramic envelope portion, comprising ceramic members 12 and 14, is metalized to provide the thin metallic films or layers indicated at 20, 22 and 24. As will be understood, the ceramic members 12 and 14 may be made of any desired translucent ceramic material. Alumina and forsterite are two examples of translucent ceramic which may be used in this invention. The ceramic members. may be metalized in any known manner. One method of metalizing, which is described in Pat. No. 2,647,218 for Ceramic Electron Tubes, uses finely divided molybdenum powder, which is coated on the ceramic. The coated ceramic is then fired in hydrogen to a temperature of approximately 1500 C. This sinters the metal powder to the ceramic surface, producing a thin metallic layer which is firmly bonded to the surface of the ceramic. Another method of metalizing is shown and described in Pat. No. 3,215,555 issued in the name of the present inventor. Of course, any other method of metalizing may be used. In the preferred form of this invention the molybdenum film is plated with nickel to aid the flow of the brazing metal during the brazing operation, as will be more fully described hereafter.

Referring again to FIG. 2, ceramic member 12 may be metalized only along the rim 26, as is indicated by metal film 20. The base member 14 is provided with a dished portion 28 and a hole 30 extending through to the dished portion 28, as shown. Ceramic member 14 will be metalized on both sides to provide the metal film 24 in both the dished portion 28 and in the hole 30, as shown. The metal film 22 is also formed around the edge of base member 14. After base member 14 has been metalized, the upper and lower surface will be ground to remove the metal film from these surfaces while leaving it in the dished portion 28, the hole 30 and the edge. The grinding will isolate electrically the metal film 24 in dished portion 28 and hole 30 from the metal film 22 at the edge of ceramic base member 14. The flanged metal closure member 16 is cylindrical in shape, having an upper edge 32 and a flange 34 on its lower end. As shown, cylindrical member 16 is sized such that the upper edge 32 will mate with the rim 26 of the upper ceramic member 12. Also, lower ceramic member 14 will fit snugly within the lower portion of closure member 16, as shown. The metal closure memher is preferably made of metal which will have the same thermal expansion as the ceramic material. When the ceramic material is forsterite a 52% nickel iron metal may be used. Metal such as kovar may be used with alumina.

The bulb is assembled by brazing the metal closure member 16 to the ceramic envelope portion. The upper member 12 of the envelope is brazed to edge 32, as shown using any desired brazing metal. The brazing metal will firmly adhere the metal film on rim 26 to the upper edge 32. The lower, base portion 14 of the envelope is brazed to the lower end of the cylindrical closure member 16, the brazing metal making a firm bond between the metal closure member 16 and the metal film 22 on the edge of base member 14. As will be understood, the brazing of closure member 16 to the ceramic envelope portion will form an hermetic seal between these members, providing an hermetically sealed bulb 10. The filament member 18 is mounted within bulb member 10, having one end electrically connected to the brazing metal between edge 32 and rim 26. The opposite end of filament 18 is mounted in hole and is brazed to the metal film 24 during the brazing operation. If desired, a lead wire, indicated at 19 may be attached to the inner end of filament 18, such lead wire being brazed to metal film 24. Thus, the bulb 10 is provided with contacts formed by flange 34 of metal closure member 16 and the metal film 24 in dished portion 28 of the lower member 14 of the envelope. As will be apparent from FIGS. 1 and 2, the bulb 4 10 may be mounted by means of flange 34 to any desired surface. The light from bulb 10 will diffuse through the ceramic envelope, formed by ceramic members 12 and 14.

FIG. 3 shows another embodiment of the ceramic bulb of this invention. In the embodiment of FIG. 3, a ceramic bulb 10 is shown, provided with a ceramic envelope portion composed of ceramic members 42 and 44. Ceramic member 42 is in the form of a circular cap member having a depressed rim 46, as shown. Ceramic member 44 is in the form of a cylindrical member. Depressed rim 46 and upper and lower rims or edges 48 of cylindrical member 44 are metalized to provide the metal films 50 on rim 46 and 52 on edges 48.; Also edge 54 of cap member 42 is metalized to provide the metal film 56. A metal closure member 58 is provided, brazed to the lower edge 48 of ceramic cylinder 44, as shown. As will be understood, cap member 42 is also brazed to the upper edge 48 of cylinder 44, thereby forming an hermetically sealed bulb 10'. Filament member 60 is mounted diagonally across ceramic cylinder 44, with its opposite ends electrically connected to the brazing metal in the sealed areas between ceramic cap 42 and the cylinder 44 at one end and the closure member 58 and the cylinder 44 at the other end. As will be apparent from FIG. 3 bulb 10' may be mounted by metal base member 58, with the electrical connections made between the base metal closure member 58 and the metal film 56 on the ceramic cap 42. If desired, ceramic part 42 could be of smaller diameter, leaving a ledge on the upper edge 48 of ceramic member 44, thereby providing a contact to metal film 52.

FIG. 4 shows a preferred manner of making the ceramic bulb of this invention. The embodiment shown in FIG. 4 is the same as that shown in FIGS. 1 and 2. As shown in FIG. 4, the ceramic envelope is formed of two pieces of ceramic material 12 and 14, both being approximately 50 mils thick. Metal closure member 16 is formed from a compatible metal approximately 10 mils thick. As earlier noted, when the ceramic material of parts 12 and 14 is forsterite then metal member 16 is desirably formed of 52% nickel iron. Filament member 18 is formed of approximately 0.5 mil tungsten. Ceramic parts 12 and 14 of the envelope are metalized, for example with molybdenum and then coated with nickel. The parts are then ground, as necessary, to leave metal film 20 on rim 26 of part 12, and film 22 on the edge of part 14, with film 24 in dished portion 28 and hole 30. The base member 14 is placed within the lower end of metal closure member 16 and a ring of brazing metal, for example copper, is placed on top of the base member 14 against the inner surface of metal closure member 16. The filament member 18 is then mounted with one end secured to a lead in wire 19, which is mounted within hole 30 in contact with metal film 24. The other end of filament 18 rests on the upper edge 32 of closure member 16. A brazing ring 72 is placed around the end of the lead wire 19 within the hole 30, as shown. In the preferred form of this invention, lead wire 19 is formed of molybdenum, approximately 15 mils in diameter. The hole 30 is approximately 17 mils in diameter. However, it should be understood that lead wire 19 may be omitted and the end of filament 18 brazed to metal film 24 in hole 30. Another brazing ring 74 is placed on top of flange 32. This ring 74 is preferably made from 3 mil flat stock. In place of brazing ring 74, a 3 mil coat of copper, or other brazing material may be coated on metal film 20. Then the upper ceramic member 12 is placed on top of the brazing ring 74. If desired, a molybdenum clamp 76 may be used to clamp the assembly together, as is shown. Alternatively, a clamping fixture may be provided. The clamped assembly is then placed in a furnace, preferably in an atmosphere of hydrogen, and heated to a temperature sufficient to melt the brazing metal and braze the part together. This will form an hermetically sealed light bulb 10. The assembly may then be placed in a vacuum oven and heated to a temperature of approximately 700 C. for approximately ten minutes to evacuate the sealed bulb by diffusing the hydrogen out through the heated metal, which is porous to hydrogen when heated.

From the above description, it will be apparent to those skilled in the lamp art that there has been provided a novel ceramic light bulb. Obviously, the light bulb of this invention will be rugged and capable of being manufactured in very small sizes at low costs. If desired, support members may be provided for the filament as is well understood in this art. Such supports could be brazed to isolated metal films on one of the ceramic members.

While there have been shown and described the present preferred embodiments of this invention, and the preferred method of manufacture, it will be clear that many changes may be made in the various described constructions without departing from the scope of this invention, as set forth in the appended claims.

What is claimed as new and which it is desired to secure by Letters Patent of the United States is:

1. A method of making a ceramic light bulb comprising the steps of; metalizing ceramic material forming an envelope to form a metal film thereon, grinding said metalized ceramic material envelope to remove said metal film from desired translucent areas and to electrically isolate portions of said film, assembling a metal closure member with said ceramic envelope, mounting a filament member within said envelope and in electrical contact with electrically isolated portions of said metal film, placing brazing metal at all contact areas, brazing said assembly in a furnace with a hydrogen atmosphere, and then heating said brazed assembly in a vacuum oven at a temperature of approximately 700 C. for approximate- 1y ten minutes to evacuate the hydrogen from said assembly by diflfusing it through the heated metal.

2. A method of making an hermetically sealed electrical ceramic device comprising the steps of; forming a ceramic envelope; metalizing portions of said ceramic envelope forming electrically isolated areas of metal film thereon; assembling a metal closure member with said ceramic envelope; mounting an electrical member within said envelope and in electrical contact with said isolated film areas; placing brazing metal at all contact areas; and brazing said assembly to seal said assembly.

3. A method of making an hermetically sealed electrical ceramic device as claimed in claim 2 in which the brazing step is carried out in a hydrogen atmosphere and then heating said brazed assembly in a vacuum oven at a temperature of approximately 700 C. for approximately 10 minutes to evacuate the hydrogen from said assembly by diffusion through the heated metal.

References Cited UNITED STATES PATENTS 573,088 12/1896 Hawkins 313-315 X 2,245,782 6/1941 Holloway 313-315 X 2,393,711 11/1946 Schwarze 431-93 2,427,711 9/1947 Cartun 313-318 X 2,719,185 9/1955 Sorg et al. 313-317 X 3,020,437 2/1962 Horan 313-318 3,065,291 11/1962 Rexer, Jr. 313-318 X 3,243,635 3/ 1966 Louden 313-317 2,296,575 9/ 1942 Rowley et al 29-583 2,810,283 10/1957 Cohen et a1 313-318 3,149,396 9/1964 Warren 29473.1 X 3,188,512 6/1965 Moore 313-315 X 3,302,961 2/ 1967 Franklin 29-473.1 X 3,386,011 5/1968 Murray, Jr., et al. 29-583 X 3,576,066 4/1971 Steward et al. 316-18 OTHER REFERENCES R.C.A. Technical Notes, No. 610, March 1965, Detailed Description Ceramic or Ceramic Metal Lamps by Roger A. Krey.

JOHN F. CAMPBELL, Primary Examiner R. B. LAZARUS, Assistant Examiner US. Cl. X.R.

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