Glass manufacturing – Fusion bonding means – Glass to metal
Reexamination Certificate
1999-07-30
2001-12-04
Colaianni, Michael (Department: 1731)
Glass manufacturing
Fusion bonding means
Glass to metal
C065S059100, C065S059200, C065S059260, C065S059270, C065S059280, C065S155000
Reexamination Certificate
active
06324870
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns metal-glass bonding, particularly when these two materials possess different coefficients of expansion.
In electromagnetic radiation devices, notably X-ray tubes, such bonds are used to permit the passage of electric conductors through the glass walls of an X-ray tube, in order to connect the cathode and anode of the X-ray tube to an electric power source. In fact, the cathode and anode are placed inside a glass wall and are kept under vacuum. The junction between the electric conductors and the glass panel must therefore be tight.
In a known manner, it is possible to use a glass tube, for example, one made of glass manufactured by the SCHOTT company under Nos. 8245 and 8250, sealed with a collar made of Kovar (iron-nickel-cobalt alloy), the thermal expansion coefficients of which are similar. These materials are therefore suited to use in an X-ray tube whose temperatures varies widely, from room temperature to approximately 450° C. However, the cost of such a glass tube is very high.
A Pyrex® tube and a Kovar collar can also be used. Pyrex® and Kovar possess different coefficients of expansion, a progressive junction is produced by means of a succession of types of glass having coefficients of expansion which vary from that of Kovar to that of Pyrex®, such as SCHOTT's 8447, 8448, 8449 and 7740 types of glass.
The Pyrex® tube is therefore equipped at its end bonded to the Kovar collar with a plurality of rings of these different types of glass. It is easily understandable why manufacture of such a Pyrex® tube is very expensive.
BRIEF SUMMARY OF THE INVENTION
The present invention is intended to remedy the disadvantages of the above-mentioned devices by proposing a collar device capable of being bonded to glass part of different coefficient of expansion.
The invention is also intended to provide a collar to be fitted to a Pyrex® part.
The metal collar device is of the type used for integrating a glass part and a metal part of different expansion coefficients. The collar is cylindrical and comprises a first portion intended to be in contact with the metal part, a second portion intended to be in contact with the glass part and a bonding portion placed between said first and second portions. The second portion is not as thick as the first portion and as the bonding portion, so that it can adjust to the expansion of the glass part by exerting stresses on the latter below the limit of resistance of said glass part. An inexpensive glass part can thus be used without risk of breakage during temperature variations.
In one embodiment of the invention, the thickness of the second portion is less than one-tenth the thickness of the first portion and of the bonding portion. The second portion is thus considerably more flexible than the first portion and the bonding portion.
The second portion is advantageously beveled, the free end of the second portion being roughly
10
microns thick.
In another embodiment of the invention, the second portion is less than 200 microns thick.
The second portion advantageously possesses an angle roughly equal to 1° from the axis of the collar. The collar can be made of stainless steel, for example, of 304L type.
The invention also concerns an electromagnetic radiation device, for example, an X-ray tube, comprising a glass tube, a cathode and an anode, the anode comprising an electric conductor provided with a bond on the outside of the tube. The electromagnetic radiation apparatus includes a collar, such as previously described, placed between the glass tube and the bond. The tube is preferably made of Pyrex®. This results in a cost reduction of the tube equipped with its collar by a factor in the order of 50% to 70%.
The invention also concerns a method of manufacture of a circular collar comprising a first portion intended to be in contact with a metal part, a second portion intended to be in contact with a glass part and a bonding portion placed between the first and second portions.
The method comprises the following steps:
forming by stamping of the first and second portions and of the bonding portion of the collar,
machining of the second portion in order to give it a bevel with a 1° angle, and
electrolytic polishing of the second portion.
A further step of oxidation of the surface of the second portion of the collar is provided, which makes it possible to improve integration of the collar and glass part. This integration is carried out by steps of constant heating of the glass part, followed by axial insertion of the collar into one end of the glass part of the same diameter as the collar.
The second portion thus penetrates the thickness of the glass, which ensures tightness between the collar and the glass part. Electrolytic polishing of the second portion makes it possible to reduce its thickness, thereby reducing accordingly the stresses exerted on the glass part by the second portion upon temperature variations.
In the invention, the costs of manufacture of a glass part in tight contact with a metal part are reduced considerably, while guaranteeing satisfactory tightness and strength in a wide temperature range.
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Dalton, Robert, “How to Design Glass-to-Metal Joints”, Product Engineering, pp. 62-71, Apr. 1965.*
Patent Abstracts of Japan, vol. 012, No. 467, JP 63-185844, Dec. 7, 1988.
Chabin Eric
Gabbay Emile
Chaskin Jay L.
Colaianni Michael
GE Medical Systems S.A.
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