US2482178A - Composite structure for forming a seal with glass - Google Patents

Description

Sept. 20, 1949. A. HARRIS :rm. 2,432,178

COMPOSITE s'rnuc'nms FOR FORMING A SEAL WITH GLASS Filed Feb. 2 9 1944 VE/V Toes E. A f/fl/PE/S I C. C. Farm/v 8) z. AM,

77'OENEY Patented Sept. 20, 1949 UNITED STATES PATENT OFFICE COMPOSITE STRUCTURE FOR FORMING A SEAL WITH GLASS Application February 29, 1944, Serial No. 524,504

3 Claims. 1

This invention relates to the art of sealing metal to glass and particularly to a composite structure for forming a seal with glass.

The invention is particularly applicable to the sealing or uniting of copper and glass members used in some types of vacuum tubes in which the uniting of these members is a matter of material importance in order to provide for electronic efliciency and reliability of such tubes. In the practice of sealing copper to glass, the efliciency of the seal depends upon the adherence of copper oxide to the base metal. A type of oxygenfree high conductivity copper has been generally used for the tube member and no difliculty was experienced due to a lack of oxide adherence, but diiiiculties are encountered in readily machining such copper members. By adding small amounts of tellurium or other suitable ingredients, the machinability of the resultant copper alloy is greatly improved, but at the same time, due to the presence of the tellurium, the oxide scale flakes oif, thus preventing an effective seal.

Objects of the present invention are to provide a simple and practicable seal between a readily machinable metal alloy and glass, whereby the above-referred-to difficulties encountered in forming an effective seal between such an alloy and lass are overcome.

In accordance with the above object, in one embodiment of the invention, a tellurium copper alloy member to be sealed to a glass member is electroplated, or otherwise coated, upon a surface thereof to be united to the glass member, with pure copper of a suitable thickness, which provides an eifective barrier to prevent the migration of the tellurium to an oxidized surface of the copper coating on the copper alloy member which unites it to the glass member, and thus the effectiveness of the seal is maintained.

Other objects and advantages of the invention will more fully appear from the following detailed description taken in conjunction with the accompanying drawing, in which the single figure is a fragmentary longitudinal section through a seal embodying the features of this invention as applied to the uniting of a glass tube and a copper alloy memberof a certain type of vacuum tube.

Referring to the drawing, wherein there is fragmentarily illustrated a machined tellurium copper alloy member i having a hollow frusto-conical portion H, into which an open end of a glass tube I2 is entered and sealed, the effectiveness of the seal depending on the adherence of copper oxide formed on the surface of the tellurium copper al-. loy member to be united to the glass tube, the

member and tube forming a part of one type of vacuum tube. The member I0 is mainly composed of oxygen-free high conductivity copper, to which has been added a small amount, for ex- 5 ample, 25% to 2% of tellurium or some other suitable ingredient, such as selenium or lead, to render the blank from which the member is formed more readily machlnable. Such copper, without the addition of a suitable ingredient. makes it difiicult to machine a blank to the desired shape, On the other hand, the addition of tellurium, for example, to the copper has a deleterious action in that the tellurium tends to migrate to the surface of the copper alloy member ID and, if a surface l3 thereof, which is to be united or sealed to the glass tube i2, is not treated in a manner to be presently described, it results in a poor seal between the parts, since the resultant oxidized surface upon which an effective seal depends tends to disintegrate and flake oil. To

overcome this dificulty, the surface l3 of the member Hi to be united to the glass tube, I2 is first coated, by electroplating, or other suitable means, with pure copper of a suitable thickness. This coating of pure copper, indicated at H, is effective to prevent the. deleterious action of the tellurium on the oxidized surface and thus the effectiveness of the seal is maintained.

In practicing a sealing method using the composite structure of this invention as applied to the sealing or uniting of the above-described vacuum tube member In and glass tube ii, a tellurium copper alloy blank is first machined to the desired shape and then given the electroplated pure copper coating l4 upon its inner surface i3, which is to be united to the glass tube. In some cases, it may be found desirable to machine or otherwise finish the inner surface of the pure copper coating H to provide the desired fit be- 4O tween it and the surface of the glass tube l2.

After the above-described preparation, the member i0 and tube l2 may be supported in axial alignment in rotatable chucks and heated by a suitable gas torch, the copper alloy member ID 5 being heated at its end to be entered into the glass tube I! to red heat and the corresponding end of the tube heated until it is plastic and in this condition is tapered to fit the inner conical face of the member iii. Such heating of the copper alloy member is continued until a good oxide coating is formed thereon. Following this, the tapered end of the rotating plastic glass tube i2 is longitudinally moved toward the rotating member i0 and gently set into it and held under a suitable pressure and, while so held and with U the member and tube rotating, and while sub- Jected to heat of, for example, 1400' F. to 1600 F. from a gas torch for a suitable period, the sealing of the copper alloy member and glass tube is completed.

What is claimed is:

1. A composite structure for forming a seal with glass comprising a member composed of copper and teilurium for rendering the copper more readily machinable, and a barrier coating thereon of substantially pure copper having an oxidized surface.

2. A composite structure for forming a seal with glass comprising a member composed of copper and an ingredient for rendering the same more 15 Number rendering the same more readily machinable, 25

3 surface thereof, thus providing an excellent surface for the fusing of glass thereto.

ROBERT A. HARRIS. CHARLES C. PATTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 1,350,907 Yanai Aug. 24, 1920 1,649,907 Mayer Nov. 22, 1927 1,692,998 Ruben Nov. 27, 1928 1,980,840 Wright et a1. Nov. 13, 1934 2,010,145 Eitel Aug. 6, 1935 2,038,136 Smith Apr. 21, 1936 2,167,431 Bowie July 25, 1939 2,267,090 Freeman Dec. 23, 1941 2,268,939 Hensel Jan. 6, 1942

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