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| This is U. S. Patent 4000997 |
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Method for reducing thermally induced fracture in cathode ray tube bulbs
Method for reducing the likelihood of cathode ray tube glass bulb and bulb component fracture which are caused by temperature cycling in the cathode ray tube manufacturing process and which are associated with defects in the glass. Temperature gradients between glass exterior surfaces and glass interior, arising during cooling, are locally reduced. In a preferred embodiment, a thermal insulator is applied prior to or during cooling, over a defect and its vicinity in order to locally reduce the rate of surface cooling and thus locally reduce the cooling-induced surface tensile forces. An improved component-in-process is depicted which has a reduced susceptibility to thermally induced fracture. Description BACKGROUND OF THE INVENTION This invention is concerned with reducing occurrences of breakage of television cathode ray tube glass bulbs and bulb components resulting from various temperature changes introduced in manufacturing and salvage processes. Color television cathode ray tube bulbs include two major components -- (i) a glass front panel for, among other things, supporting arrays of cathodo-luminescent phosphor deposits and (ii) a glass funnel member whose large end is eventually sealed to the face panel and whose small end houses at least one electron beam source. Black and white television cathode ray tube bulbs, although taking on the same basic final exterior appearance as color bulbs, do not comprise separate components, but rather are produced as a single integral unit. During the various processes of cathode ray tube manufacture, glass bulbs and glass bulb components undergo numerous temperature variations which cause glass breakage with the obvious consequence of decreased yield and thus increased manufacturing cost. For instance, color television front panels prior to application of the phosphor arrays, are heated in order to anneal or stress relieve the glass (commonly known as compaction). Also, following application of phosphor arrays and a lacquer film, front panels are subjected to bake-outs, i.e., the front panel is raised to a high temperature which drives out volatile materials. Black and white tubes undergo a similar bake-out process. | U. S. Patent Attorneys Dunlap, Grubb & Weaver, P.C. 1200 G Street NW, Suite 800, Washington, District of Columbia 20005 U.S.A. "Innovative Lawyers for Innovative Businesses" Cahn & Samuels, LLP 1100 17th Street, NW, Suite 401, Washington, District of Columbia 20036 U.S.A. Attorney at Law Christopher & Weisberg, P.A. 1455 Pennsylvania Avenue, N.W., Suite 100, Washington, District of Columbia 20004 U.S.A. Attorneys at Law Manelli Denison & Selter PLLC 2000 M Street, N.W. Suite 700, Washington, District of Columbia 20036-3307 U.S.A. Attorneys at Law Greenberg & Lieberman, LLC 2141 Wisconsin Avenue, N.W., Suite C-2, Washington, District of Columbia 20007 U.S.A. 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