JPS6251212B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for strengthening plate glass, and in particular to a method for strengthening plate glass in which the generation of sharp edges (elongated fragments) is extremely small when glass plates are crushed. When tempered glass is shattered, it appears to be broken into fine pieces almost uniformly, but in some cases long thin pieces called sharp edges may be generated. As automobiles become lighter, tempered glass is becoming thinner, and as tempered glass becomes thinner, sharp edges tend to occur more easily, and measures against sharp edges are becoming more important. To briefly describe the fracture phenomenon of tempered glass, the fragment density (number of fractures per 50 mm square) Fd is a function of Fd = f (σ ₀ , σ), where the stress value σ of the tempered glass and the stress value σ ₀ at the point of fracture start As shown in Figure 1, the fracture of tempered glass is represented by a radial progression from the fracture starting point A, and after a certain distance it branches to form a branching point C. It is repeatedly crushed into small pieces. Furthermore, sharp edges tend to occur more often when the strengthened glass is fractured at the center than at the edges. Conventionally, in the production of curved tempered glass, a sheet glass is bent and then strengthened using a press die that is equipped with a wave-shaped heating element to prevent cooling due to contact with the press surface of the sheet glass ( Japanese Patent Application Laid-open No. 51-97553), and a method in which sheet glass is bent and then strengthened using a press die in which a plurality of heating elements are arranged in parallel on the surface of the press die (Japanese Patent Laid-Open No. 55-95629) are known. ing. However, although it is possible to increase the degree of reinforcement of sheet glass and reduce the occurrence of sharp edges by providing a heating element in the press mold as in the above-mentioned known example, this is still not sufficient. Therefore, in a method for strengthening plate glass in which a plate glass heated above the strain point is pressed against a pair of press dies and then strengthened by spraying a cooling medium, at least one of the pair of press dies is pressed outward from the center. The present applicant previously proposed in Japanese Patent Application No. 57-226406 that the sharp edge can be effectively reduced by providing heating elements concentrically, and the unachieved drawbacks of the prior art have been overcome. The present applicant further studied the method proposed above and found that the same effects as those described above can be obtained by providing a cooling element in the press mold and performing preliminary cooling, leading to the present invention. That is, the present invention provides a method for strengthening plate glass in which a plate glass heated above the strain point is pressed against a pair of press dies, and then a cooling medium is sprayed to strengthen the plate glass. The gist of this method is to provide a method for strengthening plate glass, which is characterized in that cooling elements are provided concentrically toward the glass for preliminary cooling, and then rapid cooling is performed by spraying a cooling medium. Here, the plate glass heated above the strain point is, for example, one heated to a temperature of 600 to 700°C. A pair of press dies may include a convex press die and a concave press die for forming curved glass, or a press die with a flat press surface or frame for strengthening flat sheet glass. It's okay. Air or water mist is used as the cooling medium to strengthen the sheet glass using a normal cooling method. The cooling element facing outward from the center is made of iron, stainless steel, etc., and a glass cloth is pasted on its surface, and the glass cloth is coated with silicone oil, machine oil, etc. The temperature of the cooling element is set at room temperature to 100°C, and when used continuously, it may be cooled with water. When arranging the cooling elements concentrically,
It is best to set the center of the concentric circles at position 3 of the crushing test specified in the tempered glass section of BS, JIS standards, etc., and set two large and small circles centered on this point. It is more effective to place a concentric cooling element between them, and the optimal width of the concentric cooling element is usually about 5 to 20 mm, but the arrangement density and number should be determined depending on the shape of the glass plate to be strengthened. This varies depending on the size, sliding conditions, arrangement of cooling air nozzles, etc. Furthermore, the concentric shapes may be circular or elliptical, spiral, or polygonal. Next, the method for strengthening plate glass of the present invention will be explained based on the drawings. The drawings illustrate one embodiment of the invention. The plate glass 4 is suspended by a hanging tool and heated in a heating furnace to a temperature higher than the strain point, for example, 600 to 700°C, and then transferred to a press device 6 for bending.
The press device 6 has a convex press type 7 and a concave press type 8.
The press molds 7 and 8 are configured such that the plate glass 4 can be pressed against or separated from the cylinders 9 and 10 by means of cylinders 9 and 10. The convex press die 7 has a convex surface that contacts the glass plate 4, and a glass cloth or the like is adhered to the surface. Also, the concave press type 8 is the convex press type 7.
A press frame 11 is provided on the outer periphery so as to correspond to the press frame 11. The cooling element 13 is installed inside the concave press die 8 and/or the convex press die 7 together with the substrate 12, and the temperature of the cooling element 13 is kept constant by a pipe 14 through which water is circulated from the back side. It's starting to be preserved. In addition, the heat transfer coefficient during pre-cooling is 30~
A value of about 200 Kcal/m ² ·hr·°C is good; if it is smaller than this, the effect will be reduced, and if it is larger than this, it will be damaged during preliminary cooling or the optical properties will deteriorate. Example 1 A plate glass of 1200 x 700 mm and 3.0 mm thickness heated to a temperature of 670 to 680°C was molded using a pair of press molds as shown in Figs. 2 and 3, using an apparatus equipped only with a concave press as a cooling element. After bending, air pressure 2500mm
Aq, air cooling reinforcement treatment was carried out at an air flow rate of 560 Nm ³ /min as the present example, and a case without a cooling element as a comparative example. Table 1 shows the test results. The degree of reinforcement of sheet glass is expressed by the number of fractures when the glass is shattered at fracture starting points (impact points) 1, 2, and 3 in a crushing test of tempered glass, and the number of sharp edges is determined by the length of the fragments.
Items with a length to width ratio of 60 mm or more and a length to width ratio of 4 or more were counted as one piece.

【table】

[Table] According to the present invention, by arranging the cooling elements concentrically outward from the center of the press die, the number of sharp edges can be significantly reduced, as is clear from Table 1. It has significant effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the breaking phenomenon of tempered glass. FIG. 2 is a schematic side view showing a glass plate press apparatus used in carrying out the present invention. FIG. 3 is a schematic front view of the concave press mold of the apparatus shown in FIG. 2. 4... Plate glass, 6 ... Press device, 7... Convex press mold, 8... Concave press mold, 12... Heat resistant substrate, 13... Cooling element, 14... Piping.

Claims (1)

[Claims] 1. In a method for strengthening plate glass in which plate glass heated above the strain point is pressed against a pair of press dies and then strengthened by spraying a cooling medium, at least one of the pair of press dies is formed with concentric circles extending outward from the center. A method for strengthening plate glass, which comprises preliminary cooling by providing a cooling element in the shape of a glass, and then rapid cooling by spraying a cooling medium.