RU2177188C2 - Cathode-ray tube envelope resistant to confined explosion - Google Patents

Abstract

FIELD: manufacture of glass envelopes for cathode-ray tubes. SUBSTANCE: envelope of cathode-ray tube 10 has panel whose thickness t is found from equation including resultant tension. Panel takes resultant tension stress not over 1150 psi (7929 kPa) and surface compressive stress built up in the course of its manufacture; it has bezel for confined explosion protection press-fitted while hot onto panel rim to raise surface compressive stress which makes it possible to reduce panel thickness. EFFECT: reduced panel thickness. 10 cl, 2 dwg, 2 tbl

Description

 The invention relates to a bulb for a cathode ray tube, in particular to a panel for reproducing an image or a front plate of such a tube.

BACKGROUND
The cathode ray tube usually has a glass flask, which is pumped out and hermetically sealed to ensure the operation of the tube. The flask has a panel for reproducing the image, a bell and a tubular neck. An electronic gun is installed in the neck.

 A panel for reproducing an image is often called a face plate or a display window, since it is a screen on which a picture or image is formed. Typically, the panel has a peripheral edge that is welded to the socket with fusible sealing material.

 Since the tube works in an evacuated state, a pressure of one atmosphere acts on the panel. This creates a danger of an inwardly directed explosion in the event of defects arising from the cooling of the glass or caused by cracks and scratches obtained during processing. To avoid explosion, increase the thickness of the panel. Typically, a panel has glass of a greater thickness than a bell or neck, since the latter are less susceptible to defects and are closed externally during tube operation.

 The growing demand for large image cathode ray tubes has led to the creation of panels of larger and larger area. Accordingly, the weight of the panel and the tube as a whole increased. However, heavy products are difficult to handle without damaging them. In addition, the processing of such panels requires more time and energy, which increases the cost of the product. This caused an intense search for ways to protect the panel from explosion, alternative to increasing the thickness of the panel.

 Numerous proposals have been made to use the so-called hoop for protection against an inwardly directed explosion. Such a hoop tightly covers part of the side of the panel and can be tightly soldered to it. The protective hoop can be made of metal or other durable materials.

 There is also a method of increasing the strength of glass due to its tempering. This method is commonly used for products as diverse as glass car parts and glass cookware. The tempering of the glass can be thermal, due to blowing the surface with cooling air. This accelerates the hardening of the glass surface, thereby creating a compression stress in it. An alternative method was proposed - chemical hardening, in which ion exchange is carried out to create a compression stress due to the concentration of ions on the glass surface.

 The present invention is directed to an improved bulb for a cathode ray tube. In particular, it is aimed at manufacturing large-sized tubes — more than 19 inches (48.3 cm) diagonally. In addition, the invention is aimed at reducing the thickness of the glass panel of the cathode ray tube while maintaining complete protection against an inwardly directed explosion. The aim of the invention is also to provide a method of manufacturing a panel for a cathode ray tube, which has a minimum thickness while maintaining complete protection against an inwardly directed explosion.

SUMMARY OF THE INVENTION
The subject of the invention is a glass bulb for a cathode ray tube, comprising a panel whose thickness (t) is defined by the equation
δ _P = kP (a / t) ² ,
where δ _P is the resulting tensile stress in the panel, (a) is the length of the shorter axis in inches, (t) is the thickness of the panel in inches, (P) is the atmospheric pressure in pounds per square inch, (k) is the design constant, depending on tube geometry. The panel has a resulting tensile stress of not more than 1150 psi (7929 kPa), a surface compressive stress created during the manufacture of the panel, and a hoop for protection against an inward blast, installed by means of a hot fit around the side of the panel and increasing surface compression in panel, as a result of which the thickness of the panel can be made significantly less than in an untreated bulb.

In addition, the invention relates to a method of reducing the thickness of a panel of a cathode ray tube, the thickness (t) being determined by the equation δ _P = kP (a / t) ² , where δ _P is the resulting tensile stress in the panel, and the method includes creating a compression stress on surface of the panel by the surface treatment and an increase of the compressive stress by setting, by means of shrink fitting, the hoop for protection against implosion around a skirt on the panel, while maintaining δ _P value of not more than 1,150 lbs / psi (7929 kPa) to reduce tol Inu panel as compared with the untreated panel thickness.

BRIEF DESCRIPTION OF THE DRAWINGS
In FIG. 1 of the accompanying drawings is a side view in partial cross-section of a cathode ray tube according to the invention; in FIG. 2 is a plan view of the panel of FIG. 1.

DESCRIPTION OF THE INVENTION
The invention relates to a glass flask used for the production of cathode ray tubes. In particular, it relates to a panel of such a glass bulb designed to reproduce an image. Both the tube and the bulb are usually identified by the geometry of the panel. The present invention is not limited to any particular tube geometry. However, it was developed in connection with a common rectangular flask, and such a flask is described below.

 In FIG. 1 shows a side view of a cathode ray tube with a partial sectional view, generally indicated by 10. Tube 10 includes standard glass bulb elements: a panel 12 for reproducing an image, a bell 14 and a tubular neck 16. An electron gun 18 is installed in the neck 16. To simplify the drawings other tube elements not related to the present invention, for example a fluorescent screen and a mask, are not shown.

 The image reproduction panel 12 has a bead 20 and is connected to the bell 14 by an alloy connection 22 between the edges of the bead 20 and the bell 14.

SUMMARY OF THE INVENTION
When the tube 10 is evacuated, there is a pressure difference of approximately one atmosphere between the pressure of the external environment and the internal pressure substantially equal to zero. This pressure difference acts over the entire surface of the tube, but is particularly dangerous for the panel 12, since in the television receiver this panel is open. The specified pressure difference creates tensile stress in the panel, which must be limited in order to avoid the spread of surface defects and subsequent destruction of the tube flask.

 In FIG. 2 shows a top view of a rectangular panel 12, where the major axis 24 and minor axis 26 are shown by dashed lines. It was found that the region experiencing the greatest stress and, therefore, the weakest region of the panel is region 28 near the end of minor axis 26 .e. if the flask is destroyed, then its destruction begins with this area.

Careful examination has shown that an inwardly directed explosion can be prevented by limiting the final tensile stress in the panel to 12 to 1150 psi (82 to 7929 kPa). Tensile tests of hundreds of samples showed that even at the stresses of the indicated level and below, even the most roughly processed samples are not destroyed. However, at higher tensile stresses, for example 1400 psi (9928 kPa), at least a few fractures were observed. The tensile stress δ _P is determined in accordance with the formula
δ _P = kP (a / t) ²
Obviously, the allowable thickness (t) is determined by the resulting tensile stress. This voltage shall not exceed 1150 psi (7929 kPa). It is also obvious that the weight of the panel increases with increasing thickness.

 The aim of the present invention is to reduce the thickness and, consequently, the weight of the panel while maintaining a tensile stress of not more than 1150 psi (7929 kPa).

 It was found that the typical thickness of the tube panel can be reduced by about 10-35% depending on the production conditions. To reduce the thickness of the panel used two means of increasing surface compression on the outer surface of the panel 12.

 The rapid cooling of the panel 12 during the manufacturing process can create significant compression stress on its surface. Depending on the prevailing conditions, a surface compression stress in the range of 450-1650 psi may be provided. inch (3103-11376 kPa). Subsequently, this surface compression stress can be reduced by heat treatment in the final annealing cycle. The tube goes through such a cycle before final sealing. Assuming that a possible reduction in compression stress can be up to 30%, the residual compression stress will be at least 315-1155 psi. inch (2172-7963 kPa). This compression stress compensates for a tensile stress of 1150 psi, so that the resulting tensile stress becomes 835 psi (5757 kPa).

 In addition, it was found that a further increase in the compression stress in the panel can be achieved by hot-fitting a metal hoop 30 of a special shape around the bead 20 of the panel 12. Thus, compression stresses of 170-290 psi (1172-1999 kPa) can be obtained. This reduces the resulting tensile stress to approximately 665 psi (4585 kPa).

 Obviously, the goal is not to reduce the tensile stress per se, but to reduce the thickness of the panel, and thus the weight of the tube. Therefore, the practical effect of the implementation of the present invention is to limit the resulting tensile stress of the tube panel to 1150 psi. inch (7929 kPa). Using the formula below, you can calculate the allowable minimum panel thickness. The calculation showed that the normal thickness of the untreated flask panel can be reduced by 25%. Thus, a panel that is cooled in the usual way and having a thickness of 1/2 inch (1.27 cm) can be made thinner - with a thickness of up to 3/8 inch (0.95 cm).

 Although various types of hoops installed by hot-seating can be used, it has been found that better results are achieved using a hoop such as a welded joint plate. This type of hoop is described in Evaluation of Fabrication and Reliability of Metal Band Joining Techniques for Long Term Safety of CRTs, Keith Guenther et al. , May 21, 1996 issue of '96 Displayworks.

 The preferred means of generating compression stress in the glass panel is air cooling. However, it is understood that chemical quenching by ion exchange would be just as effective, albeit not in such a practical way. According to another embodiment of the invention, a controlled release of the generated stresses is carried out and thereby a compression stress is created on this surface. The controlled removal of the generated stresses by heat treatment is an effective way to create a high surface compression stress in the cathode ray tube panel.

 Below are the test results, which compared several groups of evacuated and sealed cathode ray tubes. The tubes in each group had essentially identical physical characteristics, but the characteristics of the tubes of different groups differed from each other. In particular, each group had certain values of the thickness in the center of the panel (TSC) and the surface compression stress (PS).

 The thickness at the center of the panel is the thickness in inches at the center of the tube panel. Surface compression is the compression in psi. inch to resist tensile stress. Tests were conducted for 100 days, all tubes were prepared in accordance with standard commercial practice, and all panels were slightly worn to simulate expected operating conditions.

 Table 1 gives the values of the TCP and PS for each group (PS values are measured along the edges of the sealed section), the number of tubes in each group and the number of broken tubes.

 Obviously, within certain limits, the required thickness in the center of the panel varies inversely with the surface compression stress. Based on this and other tests, it was found that the thickness at the center of the panel can vary upward from approximately 0.480 inches (1.22 cm) in the 27-inch (68.6 cm) panel, while the surface compression stress varies between 600 and 1700 psi (4137-11721 kPa).

 In addition, vacuum tubes must pass impact tests. These tests are described in UL 1418, "Standard for Safety of CRTs" from Underwriters Lab, and in CAN / CSA-C22.2, No. 228-92, "Canadian Standards for CRTs".

 These tests involve striking with a ball or test shell of a given weight under specified conditions. They are needed to guarantee the safety of viewers in case the cathode ray tube explodes inward due to a strong blow by a large object. In this test, the distance over which glass fragments fly in the explosion should not exceed 0-5 feet (0-15 cm). The span of the fragments depends on two factors, namely: 1) the size of the fragment and, consequently, its mass, and 2) the energy received by it.

 The first factor is affected by the compression stress created by the hoop, since stronger compression contributes to the cohesion of several fragments, which increases the mass of the resulting fragment. The last factor is determined by three sources of energy, namely: 1) energy due to vacuum, 2) energy due to bending due to pressure difference, and 3) energy due to local deformation due to compression stress created by the hoop. The first two components of the total energy are determined by the size of the cathode ray tube and, therefore, are relatively constant, i.e. cannot be changed. However, the third component can be changed by controlling the compression stress created by the hoop, simply by changing its width, thickness, or both.

 In addition to reducing energy, local deformation caused by the hoop changes the value of the convexity of the panel in the center. The bulge value is the distance that the center point on the tube panel protrudes, i.e., tilts outward or upward due to the applied compression stress. It should be noted that the center of the panel during pumping moves inward, and the hoop contributes to its return to its original position. Thus, the convexity value can be restored. Some bulge is the inevitable result of creating a given voltage. However, tests showed that in order for the tube to pass the tests, the convexity of the panel should be limited.

 Table 2 shows the values of the TCP and PS, as well as the bulge values measured on several groups of finished cathode ray tubes, which were tested according to the Underwriters Lab standard and the Canadian standard. The table also shows the width of the hoop used to create compression stress.

 As can be seen from table 2, cathode ray tubes having a thickness in the center of the panel of 0.491 inches (12.47 mm) and too large convexity of the panel (i.e. more than 0.110 mm), due to the standard hoop width of 1.496 inches (38 mm), do not pass explosion tests.

 Obviously, the hoop plays a dual role. In addition to creating compression stress in the panel, the hoop affects the convexity of the panel, and by changing the width of the hoop, you can adjust the convexity of the panel, i.e. bending strain energy. As the width of the hoop is reduced to 1.388 inches (35 mm), the compression stress and bulge decrease, which contributes to an explosion test, as can be seen from table 2. Thus, so that the tubes with thinner panels, within the tolerance of thickness, pass explosion tests, they should have a narrower hoop.

 As a result of the tests, it was found that the width of the metal hoop imposed on the side of the 27-inch (68.58 cm) cathode-ray tube panel should lie in the range from 1.378 to 1.496 inches (from 35 to 38 mm). In addition, for the tube to pass safety tests under the Underwriters Lab and Canadian standards, the bulge should be between 0.088 and 0.110 mm.

Claims (11)

1. Glass bulb for a cathode ray tube, containing a panel, the thickness (t) of which is determined by the equation:
σ _P = kP (a / t) ² ,
where σ _P is the resulting tensile stress in the panel;
a - the length of the smaller axis in inches;
t is the panel thickness in inches;
P is atmospheric pressure in pounds per square inch;
k is the structural constant, depending on the geometry of the tube,
moreover, the panel has a resulting tensile stress of not more than 1150 psi. inch (7929 kPa) and the surface compression stress created during the panel manufacturing process, and is equipped with a hoop for protection against an inwardly directed explosion, installed by hot landing around the side of the panel and increasing the surface compression stress in the panel.  2. The glass bulb according to claim 1, characterized in that the panel has a rectangular shape.  3. The glass bulb according to claim 1, characterized in that the surface compression stress created during the manufacture of the panel is in the range of 450-1650 psi (3102-11376 kPa).  4. The glass bulb according to claim 1, characterized in that the surface compression stress created by the hoop to protect against an inwardly directed explosion is in the range of 170-290 psi (1172-1999 kPa).  5. The glass bulb according to claim 1, characterized in that said hoop is a hoop in the form of a welded connecting plate. 6. A method of reducing the thickness of a glass panel in a cathode ray tube in which the thickness (t) is determined by the equation
σ _P = kP (a / t) ² ,
where σ _P is the resulting tensile stress in the panel;
a - the length of the smaller axis in inches;
t is the panel thickness in inches;
P is atmospheric pressure in pounds per square inch;
k is the structural constant, depending on the geometry of the tube,
moreover, the method includes creating a compression stress on the surface of the panel by surface treatment and increasing this compression stress by installing a hoop around the side of the panel by means of a hot landing to protect against an inwardly directed explosion while maintaining the value of σ _{P of} not more than 1150 psi (7929 kPa), which reduces the thickness of the panel.  7. The method according to p. 6, characterized in that by treating the surface create a compressive stress on the surface of the panel in the range of 450-1650 psi. inch (3102-11376 kPa).  8. The method according to p. 6, characterized in that the surface treatment is carried out by cooling at a higher speed than the cooling rate of its inner surface.  9. The method according to p. 6, characterized in that the surface treatment is carried out by heat treatment.  10. The method according to claim 6, characterized in that a hoop in the form of a welded connecting plate is installed around the side of the panel by means of a hot landing.  11. A method of manufacturing a panel for a cathode ray tube, including stamping a glass panel having a predetermined shape and such a thickness that at a pressure of one atmosphere, the resulting tensile stress in the panel does not exceed 1150 psi. inch (7929 kPa), cooling the outer surface of the panel when it is cooling or controlling the release of generated stresses to create compression stress on the surface and installing, by means of a hot fit, a hoop to protect against an inward explosion around the side of the panel to increase the compression stress in the panel, and the total the compression stress reduces the resulting tensile stress in the panel to a value of not more than 1150 psi (7929 kPa) when the cathode ray tube is under pressure in one atmosphere.

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