US3390033A - Method of separating frit sealed parts of an electron tube - Google Patents

Description

June 25. 1968 M. K. BROWN 3,390,033

METHOD OF SEPARATING FRIT SEALED PARTS OF AN ELECTRON TUBE Filed Aug. 13, 1964 2 Sheets-Sheet 1 INVENTOR.

Mm? flew/M BY June 25. 1968 M. K. BROWN 3,390,033

METHOD OF SEPARATING FRIT SEALED PARTS OF AN ELECTRON TUBE Filed Aug. 13, 1964 2 Sheets-Sheet 2 7/1 fig/J United States Patent 3,390,033 METHOD OF SEPARATING FRIT SEALED PARTS OF AN ELECTRON TUBE Martin K. Brown, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Filed Aug. 13, 1964, Ser. No. 389,365 '7 Claims. (Cl. 156-24) ABSTRACT OF THE DISCLOSURE The frit-sealed panel and funnel parts of a cathode ray tube are thermally processed to produce a bending stress in the frit seal which causes the seal to fracture. The thermal processing is performed cyclically by alternate heating and then cooling both parts (eg by alternate applications of hot and then cold water to the exterior surfaces only of both parts) to produce successive tem perature diiferentials of opposite sense between the exterior and interior surfaces.

This invention relates to a method of separating glass bulb parts of an electron tube which are sealed together with a glass frit material.

One kind of cathode ray tube bulb includes a shallow bowllike glass faceplate panel and a glass funnel memher. The sidewall of the panel is butt sealed to the large end of the funnel with a glass frit material. Because of the relatively high cost of the panel and funnel parts, it is desirable, in the case of a defective tube, that the parts be separated so that they can be salvaged for re-use.

In one prior art salvage method, either the panel or funnel is heated so that it expands outwardly relative to the other. Such differential expansion produces a shearing stress on the seal and causes the seal to fracture. In another prior art method, the entire bulb is heated both inside and out to weaken the frit seal. The bulb is then pressurized to force the two parts apart, thereby fracturing the seal. Such prior art methods,while useful, result in an undesirable high percentage of damaged bulb parts, particularly in the case of rectangularly shaped cathode ray tubes.

It is an object of this invention to provide a novel and improved method of separating frit sealed electron tube bulb parts such as those of a cathode ray tube.

It is also an object of the invention to reduce the scrap occurring in salvaging frit-sealed cathode ray tubes.

In accordance with the invention, two parts of an electron tube bulb which are sealed together with a glass frit, are thermally processed to create a temperature differential between the interior and exterior surfaces there of. Such a temperature differential produces a bending stress in the seal which causes the seal to fracture. The thermal processing is preferably performed cyclically such as by alternately and substantially uniformly heating and then immediately cooling the exterior surfaces so as to produce a back and forth bending fatigue in the seal.

In the drawings:

FIG. 1 is a partial longitudinal section of a cathode ray tube on which the invention may be practiced;

. FIGS. 2 and 3 are enlarged sections of a portion of the tube of FIG. 1 illustrating various steps of processing in accordance with the invention;

FIG. 4 is a partial longitudinal section of the tube of FIG. 1 with parts broken away illustrating another step in the process according to the invention; and

FIG. 5 is a graph illustrating temperature differentials produced in accordance with the processing of FIG. 4.

In FIG. 1, a cathode ray tube includes a glass bulb comprising a faceplate panel 14 and a funnel member 16. The panel 14 includes a saucer-shaped faceplate 18 hav- 3,390,033 Patented June 25, 1968 ing a short peripheral sidewall 20 extending therefrom. The funnel 16 includes a frusto-conical portion 22 having a cylindrical neck portion 24 extending from the small end thereof. The open end of the panel sidewall 20 and the large end of the funnel 16 are butt sealed together with a glass frit seal 26.

The tube 10 may be of the shadow mask type and include a mosaic phosphor screen 28, a. multiapertured shadow mask electrode 30, and a plural beam electron gun apparatus 32.

Various compositions of glass frit material may be used for making the frit seal 26. For example, zinc-lead-borate devitrifiable frits such as those described in US. Patent 2,889,952, issued June 9, 1959, to S. A. Claypoole have been widely used and are preferred because of their devitrifiable properties.

The frit seal 26 is made by applying a ring of frit (provided in a suspension of paste-like consistency) to the funnel 16 and allowing it to dry. The panel 14 is then set on top of the frit ring and the assembly heated to cause a fusion of the frit to both the panel and funnel. The seal 26 normally includes an external bead 34, and an internal bead 36 as shown in FIG. 2.

It has been found that best results in separating the panel 14 from the funnel 16 are usually obtained by first removing the external bead 34 by an optional acid etch treatment. When a devitrifiable zinc-lead-borate frit is used, a nitric acid etch as described in US. Patent 2,852,- 352, issued to R. Landron, Jr. on Sept. 16, 1958, has been found satisfactory.

When an acid etch treatment is employed, it may be performed as illustrated in FIG. 2. As there shown, a spray of acid 38 is directed onto the bead 34 from a suitable nozzle 40. A plurality of nozzles 40 may be positioned around the periphery of the tube 10 to spray the entire length of the bead 34. Alternatively, the external bead 34 of the seal 26 may be submerged in an acid bath. Best results have been obtained when the acid etch is such as to substantially completely remove the bead 34, but with as little as possible undercutting of the seal 26. Such a removal is illustrated in FIG. 3 which shows that the resulting seal surface 42 is substantially a continuation of the exterior funnel surface 43. It has been found that if the seal 26 is excessively undercut, e.g. greater than 20 percent of the seal distance, chipping of the bulb parts frequently occurs when the seal is subsequently fractured.

Following the acid etch removal of the external head 34 (if such step is used) a thermal processing of the panel 14 and the funnel 16 adjacent to the seal 26 is performed, e.g., as illustrated in F268. 4 and 5.

To fracture the seal 26, both the exterior surface 43 of the funnel 16 and the exterior surface 44 of the panel 14 in the region of the seal 26 are simultaneously heated such as by application of hot water thereto. The water may be applied by sprays 46 from suitable nozzles 48 so as to flow over both the funnel surface 43 and the panel surface 44 as indicated by the numeral 49'. A plurality, e.g. six, of the nozzles 48 may be employed and positioned around the entire periphery of the cathode ray tube bulb 10. When the exterior surfaces 43 and 44 are heated as illustrated in FIG. 4, the panel and funnel expand along the exterior surfaces 43 and 44 and produce a bending stress in the seal 26. Depending upon the particular structure and composition of the seal 26, fracture thereof may occur with only this initial bending. However, it has been found that the incidence of damaged bulb parts is reduced if this initial heating of the bulb is insuflicient, by itself, to produce seal fracture. Instead, it is preferred that a cyclical type of thermal processing be employed wherein an alternate heating and then immediately cooling of the bulb parts causes a fracture of the seal 26. Such cyclical thermal processing produces a back and forth bending fatigue of the seal which causes it to fracture cleanly without damage to the bulb parts.

To cyclically process the bulb parts, the initial heating of the exterior surfaces 43 and 44 is ceased and a cooling thereof is then immediately employed. The cooling step may be performed in a manner similar to the heating step, viz., by application of water sprays 46 from the nozzles 48. Such a simuitaneous cooling of the ex terior surfaces 43 and 44 produces a bending stress in the seal 26 which is of the opposite sense from that produced by the initial heating of the surfaces. The cycles of alternate heating and cooling of the exterior surfaces 43 and 44 are continued until the seal 26 is fractured as a result of the back and forth bending fatigue induced therein.

As shown by the single solid curve of FIG. 5, the exterior temperatures of the two bulb parts 14 and 16 at points A and B are substantially equal at any given time. Thus, the exterior surfaces 43 and 44 are substantially uniformly heated and cooled by the water sprays 46.

FIG. illustrates a preferred heating and cooling schedule which has been successfully used in separating frit sealed panel and funnel parts of a rectangular inch cathode ray tube bulb. In the graph of FIG. 5, temperature readings are plotted along the ordinate and elapsed time of the cyclical thermal processing along the abscissa. The temperature readings are those as recorded by four thermocouples, A, B, C, and D positioned as shown in FIG. 4 on the exterior panel surface 44, the exterior funnel surface 43, the interior funnel surface 50, and the interior panel surface 51, respectively.

As indicated on the graph of FIG. 5, hot water at a temperature of about 52 C. is applied to both of the exterior surface 43 and 44 for a period of three minutes. During this time the temperature of the exterior surfaces 44 and 43, as indicated by thermocouples A and B, rises rapidly from room temperature to approximately 52 C. within one minute and then levels off at that temperature. At the same time, the temperature of the interior funnel surface 50, as indicated by thermocouple C, although lagging behind that of the exterior funnel surface 43, rises to slightly above 50 C. The temperature of the interior panel surface 51, as indicated by thermocouple D, lags even further behind, rising to approximately 45.

After this initial three minute spray with 52 C. hot water, a spray 46 of 21 C. cold water from the nozzles 48 is flowed over both of exterior surfaces 43 and 44 for a period of approximately three minutes. During this time the surface temperatures of the panel and funnel drop as indicated by their respective curves. Then after this three minute spray with cold water, both of the exterior surfaces 43 and 44 are again heated with a 52 C. hot water spray 46, which causes the surface temperatures of the panel and funnel to again rise, this time as shown by their respective curves beyond the six minute mark on the graph.

In treating a 25" rectangular shadow mask bulb as described with reference to the graph of FIG. 5, a fracture of the frit seal 26 has consistently occurred after about 6 minutes of elapsed time. As shown by the graph of FIG. 5, at the 6 /2 minute mark the exterior surfaces 43 and 44 are at a substantially higher temperature than the interior surfaces 50 and 51. Such a temperature differential establishes that the fracture is occurring, not because of a lateral shear induced in the seal, but rather because of a bending fatigue as hereinbefore described.

For a given bulb-design and seal structure and composition, the temperatures and durations of application of the heating and cooling media may be adjusted to produce seal fracture after two, three, or more cycles of thermal processing. While the three cycle (heat-cool-heat) process described with reference to FIG. 5 has been found preferable for one design of rectangular 25 inch bulb, a twocyclc process may be successfully used, and may, in fact, be preferred for some other bulb designs. Generally speaking, the more extreme the temperatures of the heating and cooling, the fewer the number of cycles that are required to produce seal fracture. On the other hand, the less extreme the temperatures, the greater the number of cycles required, and the less likely the chance of injury to the bulb parts.

Various thermal processing procedures to produce the desired temperature differential between the exterior surfaces 43 and 44 and the interior surfaces 59 and 51 may be used. Instead of the preferred alternate heating and cooling of the exterior surfaccs43 and 44, a similar alternate heating and cooling may be applied to the interior surfaces 50 and 51. Alternatively, the exterior surfaces 43 and 44 may be heated and the interior surfaces 50 and 51 simultaneously cooled, this procedure being alternately reversed until seal fracture occurs.

Instead of the preferred spraying of hot and cold liquids onto only the funnel 16 and allowing it to flow over both the funnel and panel surfaces 43 and 44, the liquids may be sprayed onto only the panel 14 and allowed to flow over both the funnel and panel surfaces 43 and 44. Alternatively, the spray itself may be directed onto both the panel 14 and the funnel is.

Furthermore, thermal treatment by means other than liquid spray may be used. For example, hot and/or cold gases, e.g. air, may be directed onto the panel and funnel surfaces. Also, the desired portions of the panel and funnel, i.e., those portions adjacent to the seal 26 may be submerged in hot and/or cold liquid baths.

Any of these or other thermal processing procedures may be used provided they are such as to produce the desired temperature differential between the exterior surfaces 43 and 44 and the interior surfaces 50 and 51, whereby to produce the seal-fracturing bending stress. However, it has been found through practice that best and speediest results are obtained when the faceplate 18 is not directly heated during the thermal processing. For example, if water spray is used, the tube 10 is so positioned and the spray so controlled as to minimize the how of water over the faceplate.

The choice of means for performing the thermal processing may, to a large degree, depend upon the type of cathode ray tube involved and the already existing condition of the electrode parts therein. For example, in the case of a shadow mask cathode ray tube having a good shadow mask electrode 30 therein, it is undesirable to introduce into the tube any heating medium such as hot water which would be corrosive to the mask electrode. In such a case, it is preferable to apply the thermal processing to only the exterior surfaces 43 and 44, or to use a non-corrosive treating medium such as dry air in thermally treating the interior surfaces 59 and 51.

In separating cathode ray tube bulb parts as described above, an additional optional step which may be used involves the application of low air pressure to the inside of the bulb. As shown in FIG. 4, the neck of the tube it) may be closed with a stopper 52 and air pressure applied to within the tube by a hose 54 connected between the stopper 52 and a source of compressed air 56. A pressure of about one lb. per sq. inch or less relative to the pressure on the exterior of the bulb is adequate. Such a pressure may be applied throughout all or any terminal part of the thermal processing of the bulb parts. For example, it may be applied only during the last thermal cycle before seal fracture. Applications of low air pressure within the bulb: (l) aids in the separation of the bulb parts, (2) serves to indicate to the operator when seal fracture has occurred, and (3) prevents water from seeping into the bulb through the seal fracture and causing possible corrosive damage to the mask electrode 3t).

What is claimed is:

l. The method of separatin two glass parts of an electron tube bulb sealed together with a glass frit seal, comprising the steps of: alternately and substantially uniformly heating and cooling the exterior surfaces only of both said parts adjacent to said seal in immediate succession to produce bending stress of alternating sense in said seal to thereby cause bending fatigue and fracture of said seal the temperatures of both of said exterior surfaces being substantially the same during said method.

2. The method of separating two glass electron tube bulb parts sealed together with a divitrified glass frit seal, comprising the steps of:

(a) acid etching a surface of said seal, and

(b) alternately and substantially uniformly heating and cooling the exterior surfaces only of both said parts adjacent to said seal in immediate succession to produce a fracture of said seal the temperatures of both of said exterior surfaces being substantially the same during the heating and cooling steps.

3. In the method of separating two glass parts of a cathode ray tube bulb which are butt sealed together with a glass frit and which have exterior and interior surfaces, said method comprising the steps of:

(a) creating a temperature differential of one sense between said exterior and interior surfaces of said parts adjacent to said seal, and then immediately (b) creating a temperature differential of the opposite sense between said exterior and interior surfaces of said parts adjacent to said seal the temperatures of both of said exterior surfaces being substantially the same during said method.

4. The method of separating a faceplate panel part from a funnel part of a cathode ray tube bulb having exterior and interior surfaces, said parts being butt sealed together by a seal of devitrified Zinc-lead-borate glass frit, said seal having an external bead portion extending around said tube, said method comprising the steps of:

(a) acid etching the exterior surface of said seal to remove said external bead therefrom, then (b) heating the exterior surfaces only of both said panel and said funnel in the region of said seal, then immediately (c) cooling the exterior surfaces only of both said panel and said funnel in the region of said seal, and then immediately ((1) heating the exterior surfaces only of both said panel and said funnel in the region of said seal while applying low air pressure to within the bulb,

(e) whereby to produce successive temperature differentials of alternating sense between said exterior and interior surfaces and thereby fracture said seal, the temperatures of both of said exterior surfaces being substantially the same during the heating and cooling steps.

5. The method of separating a faceplate panel part from a funnel part of a cathode ray tube bulb, which parts are butt sealed together by a frit seal and which have an exterior and an interior surface, said method comprising the steps of (a) flowing hot water over said exterior surfaces only of said panel and said funnel in the region of said seal, then immediately (b) flowing cold water over said exterior surfaces only of said panel and said funnel in the region of said seal, and then immediately (c) flowing hot water over said exterior surfaces only of said panel and said funnel in the region of said seal, the temperatures of both of said exterior surfaces being substantially the same during said method.

6. The method of separating two glass parts of a cathode ray tube bulb which has an exterior and an interior surface, said parts being butt sealed together with a glass frit seal, said method comprising the steps of acid etching the exterior surface of said seal, and then in immediate succession successively heating then cooling, then heating the exterior surfaces only of both of said parts adjacent to said seal by alternate hot and cold water sprays, whereby temperature differentials of alternating sense are successively created in said parts between the exterior and interior surfaces thereof which produce bending fatigue within and fracture of said seal, the temperatures of both of said exterior surfaces being substantially the same during the heating and cooling steps.

7. The method of separating two glass parts of a cathode ray tube bulb which has an exterior and an interior surface, said parts being butt sealed together with a glass frit seal, said method comprising the steps of:

(a) acid etching the exterior surface of said seal; and

then

(b) alternately and substantially uniformly heating and cooling the exterior surfaces of both of said parts adjacent to said seal to produce successive temperature differentials of alternating sense between the exterior and interior surfaces of said parts, and

(c) applying low air pressure to within said bulb during at least a portion of said heating and cooling steps and maintaining said pressure until said seal fractures, the temperatures of both of said exterior surfaces being substantially the same during the heating and cooling steps.

References Cited UNITED STATES PATENTS JACOB H. STEINBERG, Primary Examiner.

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