Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
1999-06-02
2001-05-22
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C313S4770HC, C313S479000
Reexamination Certificate
active
06236155
ABSTRACT:
TECHNICAL FIELD
This invention relates to glass-to-metal sealing and particularly to metallic second anode buttons sealed into the glass funnels of cathode ray tubes.
BACKGROUND ART
Cathode ray tubes require numerous electrical potentials to be applied to the electrodes of the tube. One of these, the second anode has a very high potential, in the order of 30 kV or more in the case of color picture tubes, applied thereto. This potential is conventionally applied through the funnel by a connector hermetically sealed therein. This connector is conventionally called a second anode button. It is a substantially hollow, electrically conductive button having a thermal coefficient of expansion that substantially matches that of the glass into which it is sealed. Prior to insertion the button is oxidized so that an oxide to oxide bond is formed with the glass.
Prior buttons have been made from a 42%Ni-6%Cr iron alloy (ASTM F31) and more recently from a 47%Ni-6%Cr iron alloy (known commercially as N485). Other iron-based alloys that have been used for glass-to-metal seals include chromium-free nickel alloys (ASTM F30) and 18 to 26% chromium-iron alloys; however, neither of the latter two are known to have been used for anode buttons.
The thermal expansion-contraction differences between glass and metal generate the mismatch stresses that account for much of the breakage that takes place during heat cycles at fabrication. Examination of volume-temperature diagrams for the typical lead or soda-lime glasses used for the funnels show that they exhibit a non-linear behavior that can be matched to the volume-temperature curves of nickel-iron alloys in the 40 to 50% nickel range. However, due to their nickel content, these alloys are significantly more expensive than nickel-free alloys.
DISCLOSURE OF INVENTION
It is, therefore, an object of the invention to obviate the disadvantages of the prior art.
It is another object of the invention to enhance the glass-to-metal sealing of second anode buttons.
It is another object of the invention to reduce the cost of second anode buttons.
These objects are accomplished, in one aspect of the invention, by a second anode button for a cathode ray tube comprising a ferritic stainless steel alloy having a chromium content of about 10 to about 20% by weight.
This button matches the thermal coefficients of expansion of the funnel glass and is less costly than those of the prior art. It oxidizes well to form tight, hermetic seals the funnel glass, thereby enhancing the cathode ray tubes with which it is employed.
REFERENCES:
patent: 3666343 (1972-05-01), McNeill
patent: 4155614 (1979-05-01), Hall
patent: 4406637 (1983-09-01), Hernqvist
patent: 5081393 (1992-01-01), Kinami
patent: 6048644 (2000-04-01), Tsuji et al.
patent: 6104136 (2000-08-01), Abe et al.
Berck Ken A
McNeill William H.
Osram Sylvania Inc.
Patel Vip
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