Fixture for making glass-to-metal seals and method of making the same

Nov. 24, 1970 a. τ. Johnson 3,542,576

FIXTURE FOR MAKING GLASS-TO-METAL SEALS AND METHOD OF MAKING THE SAME

Filed Oct. 4, 1967

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INVENTOR

Arthur T. Johnson

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United States Patent Office ₄^{3 542 576} vvwvvu * Patented Nov. 24, 1970

3,542,576

FIXTURE FOR MAKING GLASS-TO-METAL SEALS AND METHOD OF MAKING THE SAME Arthur T. Johnson, Providence, R.I., assignor to GTI Corporation, a corporation of Rhode Island Filed Oct. 4,1967, Ser. No. 672,846 Int. Cl. B44d 1/14; C04b 41/06; C03c 27/02

U.S. CI. 117—2 9 Claims

ABSTRACT OF THE DISCLOSURE

A high temperature ceramic fixture is disclosed for employment in holding metal and glass components in proper position for fusing of glass-to-metal seals therebetween. The life of the fixture and the quality of the glassto-metal seals are improved by a unique method of depositing a uniformly adherent coating of carbon on the fixture at relatively low temperatures. The carbon-coated ceramic fixture is more durable and its coating can be periodically replenished during usage without the necessity of refiring or replacing the fixtures.

The present invention relates to an improved fixture for holding metal and glass components or the like in proper position during fusing to produce metal-to-glass seals therebetween, and more particularly to a ceramic fixture, having a protective coating wherein the coating is longer lived and is replenishable.

In the past, a number of such fixtures have been proposed. In one instance the fixture has been fabricated from solid carbon or graphite. Although such fixtures are useful in some applications, at elevated temperatures they tend to crack and require frequent replacement. The solid carbon or graphite fixtures moreover are fragile and difficult to handle in use.

Similar fixtures fabricated entirely from ceramic materials also have been utilized. These fixtures suffer from the disadvantages that the fused glass or the like tends to adhere thereto.

Attempts have been made to remedy this disadvantage of ceramic fixtures by depositing a coating of carbon on the ceramic fixtures. In general, a more satisfactory ceramic fixture has been produced. The carbon coating, however, according to previous applicative methods has been deposited as a relatively thin coating and has been baked on the ceramic fixtures at elevated temperatures in special atmospheres to prevent oxidation of the coating. In practice, it has been found that the life of prior carbon-coated ceramic fixtures has been relatively short and that the quality of the fused components has been impaired. The application of coating to prior carboncoated fixtures requires special equipment and the coating cannot be replenished by users of the fixtures.

Usage of previously proposed fixtures for the indicated purposes has also resulted in excessive numbers of rejects among the fused components as a result of breakage or leakage.

In my copending application Ser. No. 672,919 filed Oct. 4, 1967, I disclose an improved fixture for making glassto-metal seals which generally overcomes these problems of the prior art. The present invention is a further improvement.

I overcome the disadvantages of the prior art described above by providing a ceramic fixture having a protective coating therein which exhibits an extended life under customary conditions of usage of many times that of known ceramic fixtures and superior to that of fixtures made according to my copending application mentioned above. The character of the protective coating which my invention enables one to apply to ceramic fixtures improves considerably the quality of the finished fused components or devices. My invention permits the production of fused devices with a smaller number of rejects resulting from breakage or of imperfect seals.

Briefly, my invention provides improved coated ceramic fixtures for the purposes described and also improved methods for coating the fixtures, for example with a carbonaceous material. Thus, a preferred form of my novel method involves a cleaning and preparing the surface of the ceramic fixtures, coating the ceramic fixture with a carbonaceous drying oil such as linseed oil, baking the coated fixtures at a relatively low temperature until dry, applying to the baked fixtures a graphitic suspension or the like, followed by a coating of carbonaceous drying oil, baking the fixture a second time at low temperature and spraying the fixture while still hot with a final coating of graphite. My novel method not only produces more durable ceramic fixtures, but also the carbon coating thereof can be applied in a simple manner. The use of high temperature furnaces and special firing atmospheres is avoided. Moreover, the life of the coating applied to the fixture in accordance with my invention can be prolonged by periodic application of the graphitic coating material throughout the useful life of the fixtures.

I accomplish these desirable results by providing a coated ceramic fixture for holding components in proper position during fusing of said components to join said components, said fixture comprising a ceramic base member, a first coating of polymerized drying oil uniformly adhered to the surface of said base member, a second protective coating of graphitic material uniformly covering said first coating, a third coating of polymerized drying oil and a fired coating of graphitic material to protect the surfaces of said components when engaged by the fixture.

I also desirably provide a coated ceramic fixture wherein each of said coatings contain a carbonaceous material.

I also desirably provide a method for coating a ceramic fixture, said method comprising the steps of coating said fixture with a drying oil, baking said fixture to dry said oil, applying a suspension of carbonaceous material, and thereafter a coating of drying oil, baking said fixture to dry the same, removing said fixture from said baking step and applying a suspension of carbonaceous material to the fixture while hot.

I also desirably provide a method for coating a ceramic fixture wherein said fixture is immersed in an aqueous solution of sulphuric acid and rinsed prior to coating with a drying oil.

I also desirably provide a method for coating a ceramic fixture wherein the final application of carbonaceous material is accomplished by spraying while said fixture is still hot and the sprayed fixture is permitted to dry at room temperature.

I also desirably provide a method for coating a ceramic fixture wherein the final coating of said fixture is replenished periodically during use of said fixture.

During the foregoing discussion,, various objects, features and advantages of the invention have been set forth. These and other objects, features and advantages of the invention together with structural details thereof will be elaborated upon during the forthcoming description of certain presently preferred embodiments of the invention and presently preferred methods of practicing the same. In the accompanying drawings I have shown certain presently preferred embodiments of the invention and have illustrated certain presently preferred methods of practicing the same, wherein:

FIG. 1 is a longitudinally sectioned view of a typical ceramic fixture coated in accordance with my invention; and

3,542,576

FIG. 2.is an enlarged sectional view of a portion of the fixture shown in FIG. 1.

Referring now more particularly to the drawings the exemplary form of my invention shown therein includes a coated fixture 10, which is useful in supporting, for example, metal and glass components 12 and 14 during the fusing process to form a glass-to-metal seal 16 therebetween. Thus, the fixture 10 includes recess 18 shaped generally to receive the glass component 14 and recess 20 shaped to receive likewise the metal component 12.

The fixture 10 as better shown in FIG. 2 is provided with a first baked-on layer 22 of linseed or other drying oil, a second coating 23 of carbon, graphite or other carbonaceous protective material, a third coating 24 of linseed or other drying oil and a final sprayed-on layer 25 of carbon, graphite or similar carbonaceous material. The layer 24 provides a suitable base surface to which the sprayed-on coating 25 can properly adhere. On the other hand the final layer 25 protects and extends the life of the baked-on uniformly adherent coating layers 22 and 23, and the four coating layers 22-25 provide a proper surface of engagement with juxtaposed portions of the metal and glass components 12, 14.

It has been found that the use of my multiple-coating ceramic fixture 10, including the coating layers 22, 23, 24 and 25 produces a superior glass-to-metal seal 16 and does not mar the adjacent surfaces of the metal and glass components 12, 14 in contrast to previously proposed fixtures. I have also found during usage of the fixtures such as the fixture 10 that the outer carbonaceous layer 25 can be periodically renewed without the use of firing or baking or special gaseous environments or the like. I have found, on the contrary, that I can periodically replenish the outer coating 25 on the fixture 10 as by spraying or dipping or the like to renew the outer coating layer 25 followed by drying the newly applied layer 25 for a brief interval at room temperature and without a special atmosphere. Thus the outer coating 25 can be replenished periodically by the user and without the use of special equipment.

Desirably I clean the fixture prior to coating by dipping the same in a cleaning solution including desirably about 50 volume percent sulphuric acid (H2SO4), and 50 volume percent water (H₃O). The cleaning solution preferably is maintained at a temperature of about 90° F.±10° F., and the fixture is permitted to remain therein for about 15 minutes.

Following this interval, I desirably remove the fixture from the last-mentioned solution and immerse and rinse the fixture thoroughly in distilled water.

After removing the fixture from the rinse, I coat the same with raw linseed oil and then bake at 250° F. until dry (about 15 minutes). I then coat the dried coated fixture with a graphitic suspension or a suspension of other suitable carbonaceous material and then with another coating of raw linseed oil. The fixture is again baked, this time at about 300° F. for 8-10 hours. The fixture is removed from the furnace and sprayed while hot with two successive coatings of graphitic suspension. Preferably the coating is allowed to air dry for an interval of 30 minutes until dry. Preferably, I formulate the graphitic suspension in the following proportions: 25 grams of concentrated graphite (Aquadag) in 100 cc. of water. Aquadag is a trade name for a finely divided collodial dispersion of graphite available from Acheson Colloids Co.

The several steps of my method together with the preliminary surface preparational steps produces a uniformly adherent coating on the fixture of the metal from the drying oils and the graphitic suspension. This well adhered coating protects the surfaces of the fixture and more importantly those surfaces of the metal and glass components 12, 14, which are engaged by the fixture 10. Most importantly the adhered coating provides a proper base to receive the second or outer carbonaceous coating applied in the final Step of my method. This latter protective coat4 ing otherwise would not adhere to the bare ceramic surface of the fixture 10.

The several drying oil coatings as well as the carbonaceous layers can be applied by brushing or dipping a graphitic suspension on the coated fixture or by analogous methods.

In any event it will be seen that the final protective coating 25 thus applied to the fixture 10 can be periodically renewed without the use of special equipment or without the necessity of returning the fixtures to the manufacturer for reprocessing. Discarding of used fixtures is therefore frequently avoided.

During usage of the fixture, the outer coating layer of the fixture desirably is replenished periodically. This is accomplished by reapplying the outer coating layer 25 as by spraying and drying in the manner described above. Where the fixture is employed for the fusing of glass and metal components to effect a glass-to-metal seal therebetween, the fixture desirably is recoated as by spraying after every 15 passes through the furnace employed for fusing the glass and metal parts.

From the foregoing it will be apparent that novel and efficient forms of fixtures for making glass-to-metal seals have been described herein. While I have shown and described certain presently preferred embodiments of the invention and have illustrated presently preferred methods of practicing the same, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced.