Thermal measuring and testing – Thermal testing of a nonthermal quantity – Of susceptibility to thermally induced deteriouration – flaw,...
Reexamination Certificate
1998-10-08
2002-07-23
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Thermal testing of a nonthermal quantity
Of susceptibility to thermally induced deteriouration, flaw,...
C374S005000, C374S045000
Reexamination Certificate
active
06422744
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of testing a display device comprising an air-tight envelope and at least a glass part which forms part of said air-tight envelope during the manufacture thereof.
Display devices of the type mentioned in the opening paragraph are used, inter alia, in television receivers and computer monitors.
A display device of the type mentioned in the opening paragraph is known. The known display device comprises an air-tight envelope with a display window. In the case of a cathode ray tube (CRT), the envelope also comprises a cone portion and a neck which accommodates an electron gun for generating (one or more) electron beams. These electron beams are focused on a phosphor layer on the inner surface of the display window. In the case of a plasma display panel (PDP), the air-tight envelope comprises a faceplate, which serves as the display window, and a rear plate, said plates being connected to each other by means of connecting parts. A plasma display panel contains an ionizable gas in which a plasma discharge is generated, and electroluminescent or photo-luminescent phosphors being used to produce an image.
The known display device has a number of shortcomings, in particular the occurrence of product failure during the manufacture of the display device, which product failure is caused by fracture as a result of, for example, implosion of the display device during the evacuation of the envelope.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide a method of selecting the glass parts mentioned in the opening paragraph in an early stage of the manufacturing process of the display device, so that the risk that the above-mentioned problem occurs is reduced.
To achieve this, the method in accordance with the invention is characterized in that the glass part is warmed up at a first temperature during a first time period, whereafter the glass part is immersed in a fluid at a second temperature during a second time period, said second temperature being lower than the first temperature. The fluid may be a gas or, preferably, a liquid.
Since glass is a brittle material, it is sensitive to surface damage and stress-related phenomena. Surface damage is generally difficult to detect by people who are not skilled in the art, and adverse effects of (surface) stresses in glass may not give rise to problems until late in the manufacturing process. In addition, it is not clear how and which surface damage as well as which types of stress in the part contribute substantially to product failure during the further assembly of the air-tight envelope and the display device. Product failure is caused, in particular, by implosion of the envelope of the display device when this is evacuated (for the first time). In said evacuation process the envelope is also brought to a relatively high temperature (300-400° C.). Such implosions are often initiated by said surface damage or too high a surface stress. When the air-tight envelope of the display device is evacuated for the first time, the display device already is in an advanced stage of assembly, so that an implosion during evacuation and warm-up implies a loss of production.
By subjecting the glass part to a thermoshock test in accordance with the invention, any defects, such as surface defects and stresses at the surface and in the interior of the glass part become visible. The method in accordance with the invention enables said surface damage and stresses to be detected at an early stage, so that such parts can be excluded from the further manufacturing process of the display device. If, for example, in the case of a cathode ray tube, a display window is subjected to the method in accordance with the invention, it can be determined, before the display window is provided with a phosphor pattern and a shadow mask, and before the display window is fritted to the cone portion of the envelope of the display device, whether surface damage on or stresses in the display window will lead to product failure at a later stage of the manufacturing process (for example during evacuation of the envelope). A fluid which can particularly suitably be used for immersing the glass part is the liquid medium water.
Factors involved in the initiation of surface damage of and stresses in glass parts of display devices are, in particular, scratches made in the manufacture of the glass parts and during positioning and handling the parts on a conveyor belt. Another important factor, in particular, for display windows of CRTs having a raised edge via which the display window is connected to the cone portion, and which edge is generally provided with connecting points for connecting a selection electrode or shadow mask, is the degree of compressive stress present in the raised edge of the display window. In general, the method in accordance with the invention does not make a distinction between surface damage and (internal) stresses of the glass part. The resistance to quenching generally is a combination of surface roughness and internal stress of the glass part. The term “quenching” of the glass part is to be taken to mean, in this application, a thermal shock caused by suddenly cooling the part (“thermoshock treatment”), for example by immersing in water.
Said thermoshock treatment in accordance with the method of the invention causes cracks to grow at the outside surface of the glass part. These cracks are generally caused by surface damage or they develop in a region where the stress is relatively high. Quenching of the glass part causes the outside surface to be subject to tensile stress, while the material in the interior of the glass part is subject to compressive stress; as a result, cracks do not grow through the glass (i.e. cracks do not propagate in the interior of the glass). This has the advantage that no portions of the part become detached or severed, which would lead to contamination of the set-up for carrying out the method.
A preferred embodiment of the method in accordance with the invention is characterized in that the temperature difference between the first and the second temperature ranges between 25° and 85°, and is preferably approximately 50°.
An important criterion for a good selection test is that the method yields a reliable distinction between usable and non-usable glass parts. A “non-usable” part is to be taken to mean, in this application, that there is a relatively great risk that such a part, which forms part of the air-tight envelope of a display device, will be subject to implosion during evacuation and warm-up of the envelope; conversely, a “usable” part runs a relatively small risk of implosion during evacuation and warm-up. In addition, care must be taken that, in the long run, the method does not adversely affect the glass part, for example, because the treatment causes the quality of the part to deteriorate, which may not give rise to problems until later in the life of the display device. If the temperature difference between the first and the second temperature is too large, i.e. T
2
−T
1
>85°, the risk of crack growth as a result of the thermoshock treatment is increased, which leads to a relatively high failure percentage of the glass parts, which is undesirable. In general, the failure probability increases substantially with temperature. If the temperature difference between the first and the second temperature is too small, i.e. T
2
−T
1
<25°, crack growth occurs only exceptionally, so that the selection treatment has (almost) no power of discernment. Experiments have shown that, between said differences in temperature (25°≦T
2
−T
1
≦85°), a noticeably different response to the thermoshock treatment occurs. Experiments have further shown that the method in accordance with the invention has a great power of discernment as to the further processability of the part at a temperature difference between the first and the second temperature of approximately 50° (T
2
−T
1
≈50°).
A suitable value for the first temperatu
Galenkamp Hans
Spolders Bruno W. J.
Gutierrez Diego
Koninklijke Philips Electronics , N.V.
Verbitsky Gail
LandOfFree
Method of testing a display device during the manufacture... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of testing a display device during the manufacture..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of testing a display device during the manufacture... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2907150