Electric heating – Metal heating – By arc
Reexamination Certificate
1998-12-22
2001-01-09
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C313S402000, C445S030000
Reexamination Certificate
active
06172326
ABSTRACT:
The invention relates to a process and a device for joining fastening elements belonging to the mask frame subassembly of picture tubes by welding with the aid of laser beams and is applicable in the production of color picture tubes.
In the production of color picture tubes, the installation of the mask frame subassembly in the screen part requires special attention. Of decisive importance is not only the defined position of the mask in relation to the screen part's inner contour, but also the repeated reproducible installation of the subassembly.
As the mask is used for the exposure of photoresists and phosphor layers, the reproducibility of repeated installations in exactly the same position determines the color quality of the finished picture tube.
To install the mask frame subassembly in the screen part, the walls of the screen part include pins which are fused therein with high positional accuracy. To hold the mask frame subassembly, the subassembly normally features four resilient bimetallic holders, one end of each of which is firmly welded to the frame while the other end has a mating hole which fits onto the pin. To prevent the tolerances in the pin positions and in the holders from causing distortion of the installed mask frame subassembly, one holder on one of the long side walls of the subassembly does not feature a mating hole. Instead, this holder has an enlarged, aperture to permit the completely distortion-free engagement of the mask frame subassembly. The subassembly is then fixed in this position by a fixing washer which features a mating hole and is pressed by the holder onto the pin. By welding together the fixing washer and holder, the distortion-free condition of the mask frame subassembly in the screen part is maintained, thus ensuring the reproducibility of multiple re-installations.
In accordance with the known prior art, the fixing washer and holder are joined using a resistance welding process. In this process, problems occur due to weld spatters, which arise almost inevitably, causing damage to the glass part. Furthermore, distortion of the mask frame subassembly in the downstream high-temperature process steps may arise due to the different treatment of the various holders as a consequence of the welding process. This may result in a deterioration in the picture tube optical parameters.
To prevent such effects, a process is known from DE 42 08 319 A1 for the tension-free joining of the fixing washer and holder. In this process, the washer and holder are joined using laser welding technology. The laser beam is guided in this process from the inside of the frame-mask combination. It strikes the side of the holder facing the frame, the holder being provided with so-called welding ducts. Welding is performed on the edges of the welding ducts facing the fixing washer.
A drawback of this process is that, as a result of the positioning of the laser source within the mask frame, not every desired point of the fixing washer-holder combination can be welded, because shadows are cast by the frame. A special arrangement of weld spots therefore has to be selected. Moreover, the choice of welding ducts, which also have to be inclined according to the incident laser beam, places extreme demands on the positional accuracy of the washer and holder, on the adjustment of the overall device, and on the production of the welding ducts themselves.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a process and a device for joining fastening elements on the mask frame of picture tubes by means of which a permanent joint is established between the fixing washer and holder, which prevents the occurrence of all weld spatters and in which the connection process does not entail distortion of the mask frame subassembly. Furthermore, no structural modifications of the joining elements are to be undertaken and the requirements of adjustment precision in the welding process are to be kept as low as possible.
According to the invention, this object is achieved with the aid of a laser without any structural modifications of the elements being effected. In this process, the laser beam is focused on the fixing washer through the screen glass wall and welding is performed with spot welds. Surprisingly, by taking the precautions specified according to the invention, there is no damage to the glass nor are there any other effects.
A special advantage of the invention is that it rationalizes and renders effective the picture tube production process by welding the fastening elements after positioning with laser beams from at least one laser source, with the laser source positioned outside the mask frame. The laser beams are guided before welding through the glass wall of the screen trough. The use of spot welds has proven beneficial.
As the welding process can be performed directly on the assembled screen part without any separation of the frame-mask subassembly or any other manipulation of the subassembly having to be performed, the process can be executed automatically, utilizing the existing transfer systems. As no mechanical modification of the position of the fastening elements at all is undertaken during the welding process, it is possible to achieve a distortion-free condition.
REFERENCES:
patent: 4162390 (1979-07-01), Kelly
patent: 4828523 (1989-05-01), Fendley et al.
patent: 4854905 (1989-08-01), Shibuya et al.
patent: 5013275 (1991-05-01), Kautz
patent: 5576595 (1996-11-01), Inoue
patent: 3620585 (1987-12-01), None
patent: 4208319 (1993-09-01), None
Chang Jin-Kook
Heine G{umlaut over (u)}nter
Jahn Herbert
Evans Geoffrey S.
Leydig , Voit & Mayer, Ltd.
Samsung Display Devices Co. Ltd.
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