Method and apparatus for tempering glass sheets

Abstract

To provide a method for tempering a glass sheet and a device for the same.SOLUTION: When a glass sheet 5 travels through a quenching section, air is blown on an upper surface and a lower surface of the glass sheet by a blower 11, through blowing apertures 6 and 7 covered by a blowing box 2 and by pressure of an air compressor 12 through pipe nozzles 10. In the quenching section, at least three successive quenching zones which can separately adjust blowing pressures are disposed above and below the glass sheet. In a first quenching zone, an average convective heat transfer coefficient jointly generated on the upper surface and the lower surface of the glass sheet 5 by a jet flow of the blown air and a jet flow of the compressed air is 750 W / m2 / K or more, in a second quenching zone, it is lower by 10% or more than the average convective heat transfer coefficient of the first quenching zone, and in a third quenching zone, it is as high as or higher than the average convective heat transfer coefficient of the first quenching zone. Zone-specific differences in the heat transfer coefficient are implemented by changing the blowing pressures of the pipe nozzles 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for tempering glass sheets, in which a glass sheet at tempering temperature is subjected to rapid cooling by blowing cooling air onto both sides of the glass sheet, and also to an apparatus for carrying out the method, comprising a conveying path and cooling air boxes arranged above and below the conveying path with cooling air outlets, the cooling effect of the blowing through the outlets being directed onto the upper and lower faces of the moving glass sheet. [Background technology]

[0002] Glass tempering is a process in which glass is first heated to a tempering temperature and then rapidly cooled. A line for tempering glass sheets consists of a loading table, a furnace, a quenching section, and an unloading table. The present invention relates to the quenching section.

[0003] The most common type of tempered glass is soda-lime silicate glass. This invention is particularly concerned with tempering soda-lime silicate glass. Glass that undergoes the tempering process has excellent straightness and optical properties. The purpose of the tempering process is to sufficiently increase the strength of the glass sheet with as little degradation of straightness and optical properties as possible. In addition to strength, another desired characteristic of tempered glass is safety in the event of breakage. Untempered glass breaks into large shards that pose a cutting hazard. Tempered glass shatters into small, mostly harmless pieces.

[0004] The compressive stress (strength or tempering) formed at the surface of glass during tempering depends on the temperature profile through the thickness of the glass as it cools through its characteristic transition temperature range (from about 600°C to about 500°C for soda-lime silicate glass). In this case, the temperature profile through the thickness of the glass has an approximately parabolic shape. For example, a 4 mm thick glass that has experienced a surface compression of 100 MPa has a temperature difference between the surface and the center of the glass with respect to the temperature profile. The residual stress profile formed in glass during tempering also has a parabolic shape, with the aforementioned 100 MPa surface compression corresponding to a tensile stress of about 46 MPa at the average thickness of the glass.

[0005] At the beginning of quenching, temporary tensile stresses are formed on the surface of the glass, and theoretically, a glass sheet can withstand an average of 30 MPa. If the tempering temperature of the glass is too low, this limit will be exceeded, increasing the risk of the glass cracking. On the other hand, too high a tempering temperature will impair the optical quality of the glass. Furthermore, the temporary tensile stress at the beginning of quenching increases with the cooling efficiency.

[0006] During glass tempering, particularly when the required surface tension level is relatively high compared to conventional tempering processes, hair cracks, which are difficult to detect, form in the glass during the early stages of the tempering process. Hair cracks form in glass for various reasons, such as the expansion of microcracks already present on the glass surface, internal temperature differences in the glass, and variations in glass thickness. However, when the tempering target for the glass surface is significantly larger than that of conventional tempering, hair cracks are primarily caused by high cooling efficiency, i.e., high levels of cooling blowing pressure. Especially during the early stages of tempering, high cooling efficiency on the glass surface causes rapid cooling of the glass surface and strong temporary tensile stress, which causes the expansion of microcracks on the glass surface. In this case, the glass sheet deeper than the surface is still at a temperature close to the original tempering temperature and has high elasticity. Therefore, hair cracks only affect the surface layer of the glass. Hair cracks often form in the center of the surface layer of the glass sheet. This phenomenon is particularly accentuated when compressed air is used to promote reinforcement, in which case the heat transfer from one jet is concentrated at any one point.

[0007] The present invention particularly addresses the hair crack problem associated with so-called ultra-tempered glass. Ultra-tempering requires significantly greater tempering than conventional tempering. Ultra-tempering is achieved when the cooling efficiency of the air jets in the quenching unit is significantly improved relative to tempering. The most common ultra-tempered glass is so-called fire-resistant glass, or FRG glass, which is used to slow the progression of fire within buildings. Glass panes at the boundaries of fire compartments must pass strict durability tests in accordance with fire safety standards. The surface compressive stress of soda-lime silicate glass tempered to fire-resistant glass is at least 150 MPa, and is usually higher. For example, for a 6 mm thick glass, a surface compressive stress of approximately 175 MPa is often targeted to ensure passage of the E30 fire resistance test. Meanwhile, the market is also demanding tempered FRG glass with even higher strength than the above, capable of passing at least the E60 fire resistance test, i.e., capable of withstanding a fire resistance test for at least 60 minutes, in which the firing temperature and ambient temperature during the test exceed 900°C. There is also a market demand for tempered glass that meets the E90 fire resistance test. Therefore, a glass surface tension of up to 220 MPa is being targeted. As the demand for glass surface tension increases, so does the demand for glass size. Therefore, ultra-tempering equipment is also required to have improved performance, adjustability, and reproducibility. Increasing the glass surface tension to 160 MPa or higher, particularly 180 MPa or higher, poses the aforementioned hairline cracking problem. Glass containing hairline cracks is essentially broken and therefore unsuitable for use. The present invention makes it possible to temper glass into FRG glass without the aforementioned breakage problem. The thickness of FRG glass is generally 6 mm to 6.5 mm, but the actual glass thickness is 5.8 mm to 6.7 mm. There is also demand for thinner FRG glass with a thickness of 4 mm (3.8 mm to 4.2 mm).

[0008] Currently, the most common method for avoiding hair cracks is to increase the tempering temperature above 670°C, which degrades the optical quality of the glass. The present invention makes it possible to lower the tempering temperature. In the method according to the present invention, the appropriate final temperature in the furnace, i.e., the tempering temperature for soda-lime silicate glass to be tempered to a surface tension of 180 MPa or more, is preferably above about 645°C and below about 665°C, and in any case below 670°C.

[0009] The high cooling efficiency required for super-strengthening requires high-power electric motors for turbomachines, which consume a lot of power. The present invention can also save a lot of energy consumption.

[0010] In the methods and devices known from FI Patents No. 90046 and No. 104422, the cooling air jets in the intensification stage are generated partly by compressed air through pipe nozzles and partly by blowing air through openings in a blowing box. The devices comprise only one quenching zone. With reference to FI Patent No. 104422, the same zone as the one quenching zone also serves as a post-cooling zone, but in the post-cooling stage, the jet of compressed air is stopped.

[0011] In the method of U.S. Pat. No. 4,445,921, glass is first tempered with dry air and then tempered with a gaseous sublimable material. Dry air has a lower heat transfer coefficient than the sublimable material. In the example of this reference, the heat transfer coefficient of dry air is 70 Btu / hr / ft 2 / °F (=397W / m 2 / K), and the heat transfer rate of the sublimable material is 115 Btu / hr / ft 2 / °F (=653W / m 2 / K).

[0012] In U.S. Patent Application Publication No. 2007 / 122580, the heat transfer rate of the first quench zone of the quenching section is set significantly lower than that of the second quench zone, thereby preventing temporary tensile stresses on the surface from exceeding 4800 psi (=33 MPa) and breaking the glass during tempering. For example, calculations in Table 3 of this reference show that quenching a 0.25-inch (=6.35 mm) thick glass with a tempering temperature of 1266°F (=686°C) requires a heat transfer rate of up to 94 Btu / hr / ft to avoid exceeding the tensile stress limit of 33 MPa and breaking the glass, according to this reference. 2 / °F (=533W / m 2 / K). The reference calculations suggest a time of 0.05 seconds for this first quench stage, which corresponds to a quench zone length of 17.5 mm at a typical conveying speed of 350 mm / s. In the second quench zone, the heat transfer rate is 198 Btu / hr / ft 2 / °F (=1123W / m 2 / K). According to the teachings of the reference, a glass sheet with a tempering temperature of 686°C will have a thermal conductivity of 121 Btu / hr / ft in the first quenching zone. 2 / °F (=686W / m 2 / K). It has been proposed that the heat transfer coefficient for each quenching zone can be adjusted by adjusting the blowing distance, air temperature, flow rate, or volumetric flow rate. Summary of the Invention

[0013] In order to overcome the drawbacks of the prior art, the object of the present invention is to provide a method and apparatus for strengthening the surface tension of glass up to 150 MPa, preferably up to 180 MPa, without the above-mentioned hair crack problem, with good optical quality and energy efficiency.

[0014] This object is achieved by a method according to the invention based on the features disclosed in the accompanying claim 1. This object is also achieved by an apparatus according to the invention based on the features disclosed in claim 12. The dependent claims disclose preferred embodiments of the invention. [Brief explanation of the drawings]

[0015] The invention will be explained in more detail below with reference to the accompanying drawings. [Figure 1] 1 shows in detail a cooling air box of an apparatus for carrying out a preferred embodiment of the method according to the invention; [Figure 2] 1 is a side view of a reinforcement device used to implement the present invention; FIG. [Figure 3] FIG. 1 is a diagram defining the length of the quench zone. DETAILED DESCRIPTION OF THE INVENTION

[0016] The tempering apparatus shown in FIG. 2 includes a furnace 15 with a heating device 17. This furnace is used to heat a stack of glass bodies, including one or more glass sheets 5, moving on a roller track, to a tempering temperature. The stack of glass bodies may include multiple adjacent, consecutive glass sheets 5; however, for clarity, FIG. 2 shows only one glass sheet 5. The stack of glass bodies travels back and forth within the furnace. After the heating time according to the heating recipe has elapsed, the heated stack of glass bodies are transported to a quenching section 16 on the roller track. The conveying speed W of the stack of glass bodies is 250 mm / s or more and 800 mm / s or less, and the stack of glass bodies pass through the quenching section 16 at this speed. The tempered portion formed in the glass sheet 5 depends on the cooling process in the quenching section. The purpose of the post-cooling section 18 is to cool the glass sheets to a temperature that allows them to be handled by hand. The cooling efficiency of the post-cooling section 18 is significantly lower than that of the quenching section 16. In the quenching section 16, there are blowing boxes 2 above and below the conveying surface formed by the roller tracks, and compressed air boxes 9 are installed inside the blowing boxes 2. Cooling air is supplied to the blowing boxes 2 by a blower 11. Cooling air is also supplied to the compressed air boxes 9 from compressed air cylinders 13 filled by an air compressor 12. The quenching section has multiple quenching zones, each of which is arranged so that the blowing pressure of the compressed air is individually adjusted by a pressure regulating valve 1 for each quenching zone. These quenching zones are also called compressed air blowing zones. In Figure 2, there are five such quenching zones above the glass sheet and five below the glass sheet. In Figure 2, each quenching zone spans two compressed air boxes 9. The blowing boxes and compressed air boxes are shown in more detail in Figure 1.

[0017] In Figure 1, the air blowing boxes and compressed air boxes above and below the glass sheet 5 supported by the rollers 3 are essentially the same. Therefore, the air blowing boxes and compressed air boxes and their components are given the same reference numerals on both sides of the glass sheet. The length of the air blowing box 2 and compressed air box 9, i.e., the length of the glass moving horizontally, is between 1 m and 3.5 m, depending on the width of the tempering line. The air blowing box 2 is provided with air outlets 6 and 7, through which air generated by a blower 11 is discharged as a jet toward the glass sheet 5.

[0018] These jets may be referred to as blown air jets. The outlets 6 and 7 form rows in the longitudinal direction of the outlet box 2. The distance between adjacent outlets is preferably 30 mm or more and 50 mm or less. The distance between outlets in different rows is preferably 15 mm or more and 25 mm or less between different points in the longitudinal direction of the outlet box. The diameter of the outlet 7 is 4 mm or more and 10 mm or less, preferably about 5 mm or more and about 8 mm or less. The diameter of the outlet 6 is preferably smaller than the diameter of the outlet 7 by 1 mm or more and 3 mm or less when the vertical distance from the outlet 6 to the glass sheet is shorter than that from the outlet 7. When the vertical distance from the outlets 6 and 7 to the glass sheet is the same, the diameters of the outlets 6 and 7 are preferably the same. The rows formed by the outlets 6 are arranged between the rows formed by the outlets 7. The number of the outlets 6 may be substantially equal to the number of the outlets 7. The volumetric flow rate of the airflow generated by the blower 11 as it exits through the outlets 6, 7 depends on the magnitude of the blowing pressure or overpressure used. Depending on the glass thickness and the tempering objective, this pressure is greater than or equal to 2 kPa and is in the range of 2 kPa to 20 kPa. The blowing pressure of the blowing jet is preferably in the range of 4 kPa to 10 kPa. The blowing pressure can be adjusted by changing the rotation speed of the impeller of the blower 11. The blowing pressure can be adjusted separately for each side of the glass, but it is preferable that the blowing pressure in the blowing box above the quenching section, for example, is equal in all quenching zones.

[0019] The strong airflow that penetrates the relatively narrow space between the blowing box 2 and the glass sheet 5 generates excess pressure relative to the surrounding air pressure in that area. If this excess pressure is higher on the underside of the glass than on the top, there is a risk that the glass sheet will lift off the roller, hit the blowing box, and break. In Figure 1, there is a pseudo-roller 4 above the glass sheet 5, opposite the roller 3. Its purpose is to increase the pressure on the top surface of the glass sheet 5 and prevent it from lifting. For clarity, it is omitted from Figures 2 and 3. Furthermore, the upper and lower blowing distances of the glass sheet are controlled by adjusting them separately to ensure that the glass sheet remains in contact with the roller.

[0020] A pipe nozzle 10 is threadedly fitted to a compressed air box 9 in the blowing box 2, extending toward the blowing outlet 7. The pipe nozzle 10 is provided with a compressed air port 8 having a diameter of 2 mm or more and 5 mm or less. The speed of the air flow that passes through the pipe nozzle 10 and is discharged as a jet toward the glass sheet depends on the magnitude of the blowing pressure or excess pressure used, and the pressure p i is in the range of 0 to 10 bar, preferably 0 to 6 bar, depending on the quenching zone, the thickness of the glass sheet, and the desired surface compressive stress of the tempered glass. The jets issuing from the pipe nozzles 10 are sometimes called compressed air jets. The blowing pressure can be adjusted individually for each quenching zone by means of pressure regulating valves 1. The number of pipe nozzles 10 in the compressed air box 9 is usually in the range of 40 to 80 per meter of compressed air box.

[0021] The airflow discharged from the pipe nozzle 10 is preferably discharged from the blower box 2 toward the glass sheet through the outlet 7, and air is also discharged from the blower 11 toward the glass through this outlet 7. The outer periphery of the pipe nozzle 10 is conical, tapering toward the tip of the pipe nozzle. The tip of a particular pipe nozzle 10 is approximately flush with the inner circumferential surface of the blower box 2 and may extend inside the outlet 7 or slightly outside it. The tip of a particular pipe nozzle 10 preferably does not at least substantially limit the flow area of ​​the corresponding outlet 7. The diameter of the outlet 7 is preferably at least 1 mm larger than the diameter of the compressed air outlet 8. Preferably, pipe nozzles 10 are provided in at least 30% and not more than 80% of the outlets of the compressed air box 9.

[0022] The nozzles 6, 7 are arranged so that the vertical blowing distance from the nozzles to the glass sheet can be adjusted, for example, by chains, gears, electric motors, etc. It is important that the upper and lower blowing distances can be adjusted separately. The blowing distance is the same for all corresponding nozzles on the same side of the quenching section 16. The vertical blowing distance from the nozzles 6, 7 to the glass sheet is preferably 10 mm or more and 25 mm or less, and in this case, is longer than the distance from the tip of the pipe nozzle 10 to the glass sheet by preferably 3 mm or more and 12 mm or less.

[0023] In the quenching section 16, a cooling procedure is performed which is facilitated by blowing two air jets onto the same surface of the glass sheet: one generated by an air compressor 12 through a pipe nozzle 10, and the other generated by a blower 11 through outlets 6, 7. Both air jets produce a convective heat transfer coefficient h on the surface of the glass. In quenching, the glass is also cooled by radiation, but in ultra-tempering, the radiation contribution is small. The radiation from glass at typical tempering temperatures above 650°C and below 670°C is approximately 40 kW / m² of the glass surface. 2 The radiation heat transfer coefficient corresponding to the convection heat transfer coefficient is approximately 60W / m 2 / K, but this value decreases as the temperature of the glass decreases.

[0024] From the viewpoint of the present invention, it is important that the compressed air jets are divided into three or more, preferably five or more, quenching zones, and that the pressures of the compressed air jets can be adjusted individually. The cooling efficiency Q (unit: W / m) achieved by the air jets on the surface of the glass sheet is 2 ) can be calculated from the equation Q = h × (Tglass - Tair), where Tair is the temperature of the air being discharged toward the glass, and Tglass is the temperature on the glass surface. The average convective heat transfer coefficient, h, depends on the diameter, number, location, discharge distance, and discharge pressure of the air jets and compressed air jets. There is local variation in the heat transfer coefficient achieved by the cooling air jet system on the glass surface. The local heat transfer coefficient is highest where the air jet impinges on the glass surface. The average heat transfer coefficient is the heat transfer coefficient averaged over the area covered by a portion of the jet system. For example, the average heat transfer coefficient of the first quench zone is the average heat transfer coefficient over an area equal to L1 × WIDTH, where L1 is the length of the quenching section covered by the first quench zone, and WIDTH is the width of the glass, i.e., the length of the glass's horizontal movement. In practice, the cooling efficiency of a particular cooling air jet system on the glass surface can only be adjusted by changing the blowing distance or blowing pressure. Changing the blowing distance alone does not achieve significant changes in cooling efficiency. Adjusting by blowing pressure is clearly more effective, simpler, and more accurate than adjusting by blowing distance. Furthermore, compressed air consumption is reduced by changing the blowing pressure, but not by changing the blowing distance to reduce cooling efficiency.

[0025] The zoning of cooling efficiency based on the quenching time, i.e., the direction of travel of the glass sheet in the quenching section, is preferably achieved by individually adjusting the blowing pressure of successive quenching zones. This zoning of cooling efficiency is necessary from the perspective of the present invention to solve the hair cracking problem of the glass sheet during ultra-tempering described above. Contact of the glass sheet with the roller is ensured by adjusting the blowing distance, and specific zoning is achieved by varying the blowing pressure of the pipe nozzles 10 above and below the glass sheet. The blowing pressure of the pipe nozzle 10 on the upper surface of the glass sheet is preferably at least 0.2 bar higher than that on the lower surface when the blowing pressure is 1 bar or more. To avoid bending of the finished tempered glass sheet during tempering, the glass sheet should essentially be cooled along the same temperature curve on both the upper and lower surfaces. This uniform cooling of the glass surface is controlled by varying the blowing pressure on both sides.

[0026] In the example of the apparatus in Figure 2, there are five quenching zones (Z1-Z5 in Figure 3) on both sides of the glass, i.e., quenching zones in which the blowing pressure of the pipe nozzle 10 can be individually adjusted. The length of a quenching zone is the portion of the length L of the quenching part that is covered by the quenching zone. The lengths of the quenching zones in Figures 2 and 3 are L1-L5, respectively. In the example of the apparatus in Figures 2 and 3, each quenching zone in which the blowing pressure of compressed air can be individually adjusted covers the gap between two rollers on both sides of the glass and two compressed air boxes. In addition, each quenching zone Z1-Z5 may have a different length from each other. The blowing pressure of compressed air set in the pressure regulating valve 1 of the quenching zone toward the top surface of the glass is p u1 -p u5 and the convective heat transfer coefficient h u1 -h u5 The blowing pressure of the compressed air port 8 in the quenching zone toward the lower surface of the glass is p l1 -p l5 and the average convective heat transfer coefficient h l1 -h l5 The upper blowing distance H of the blower 11 relative to the upper blowing box is uand blowing pressure p fan,u is the same in all quenching zones above the glass sheet. Also, the lower blowing distance H l and blowing pressure p fan,l is the same in all quenching zones below the glass plate.

[0027] When the glass sheet moves from the tempering furnace to the quenching section at a conveying speed W, it arrives at the first quenching zone Z1 and the pipe nozzle 10 blows the glass sheet onto the upper surface of the glass sheet at a pressure p u1 A jet of air is blown out at the bottom, and the blowing pressure p l1 The pressure of these blowouts is in the range of 1 bar to 10 bar, preferably 1 bar to 6 bar. u1 ≧p l1 +0.2 bar. The blowing pressure of the blower 11 as a jet of air entering the blowing box 2 and passing through the outlets 6 and 7 towards the glass is p fan,u and below the glass fan,l The average convective heat transfer coefficient jointly generated by the air jets in the first quenching zone Z1 is h u1 and the lower surface of the glass is h l1 These average convective heat transfer coefficients are 800 W / m for glass less than 3.8 mm thick. 2 / K or higher, and 750W / m for glass 3.8mm or thicker 2 / K or more, preferably 800W / m 2 / K or more. The glass sheet (each point) stays in the first quenching zone Z1 for a time t1 = L1 / W. The length of the first quenching zone Z1 is 80 mm or more and 550 mm or less, and the first quenching zone Z1 is equipped with one or more and four or less compressed air boxes 9. The length of the first quenching zone Z1 is preferably 100 mm or more and 400 mm or less, and the first quenching zone Z1 is equipped with one or more and three or less compressed air boxes 9. The residence time in the first quenching zone Z1 is 0.2 seconds or more and 2 seconds or less, and preferably 0.3 seconds or more and 1.5 seconds or less.

[0028] In the second quenching zone Z2, the blowing pressure is p u2 and p l2 and is lower than the pressure in the first quenching zone Z1 by at least 0.5 bar, preferably by at least 1 bar. l2 If ≥ 1 bar, p u2 ≧p l2 The pressure of the blower 11 into the blowing box and towards the glass is the same as that in the first quenching zone Z1. The average convective heat transfer coefficient jointly produced by the air jets in the second quenching zone Z2 is h u2 and the lower surface of the glass is h l2 These average convective heat transfer coefficients are lower than those of the quenching zone Z1. In the second quenching zone, each average convective heat transfer coefficient is preferably at least 10%, more preferably at least 20%, lower than that of the first quenching zone. The length of the second quenching zone Z2 is 80 mm to 550 mm, and the second quenching zone Z2 is equipped with one to four compressed air boxes 9. The length of the second quenching zone Z2 is preferably 100 mm to 400 mm, and the second quenching zone Z2 is equipped with one to three compressed air boxes 9. The residence time in the second quenching zone Z2 is 0.2 seconds to 2 seconds, and preferably 0.3 seconds to 1.5 seconds.

[0029] In the third quenching zone Z3, the blowing pressure is p u3 and p l3 and each blowing pressure is preferably 0.5 bar or more higher than that of the first quenching zone Z1 and 1 bar or more higher than that of the second quenching zone Z2. u3 ≧p l3 The pressure of the blower 11 into the blowing box and towards the glass is the same as that in the first quenching zone Z1. The average convective heat transfer coefficient jointly generated by the air jets in the third quenching zone Z3 is h u3 and the lower surface of the glass is h l3These average convective heat transfer coefficients are higher than those in the second quenching zone Z2, preferably at least 20% higher, and at least 10% higher than those in the first quenching zone Z1. Furthermore, in the third quenching zone Z3, the average convective heat transfer coefficient is equal to or higher than that in the first quenching zone Z1. The blowing pressure of the pipe nozzle is preferably 1 bar or more in the first quenching zone, 0.5 bar or less in the second quenching zone, and 2 bar or more in the third quenching zone.

[0030] The length of the third quenching zone is 1500 mm or more if the third quenching zone is the last quenching zone. The quenching section preferably includes at least a fourth quenching zone and a fifth quenching zone. In this case, the length of each of the third to fifth quenching zones is 300 mm or more, for a total length of 1500 mm or more. The blowing pressure of the fourth quenching zone is at the same level as that of the third quenching zone. From the third quenching zone to the fifth quenching zone, the blowing pressure of the blower 11 entering the blowing box and further toward the glass is the same as that of the first quenching zone.

[0031] The magnitude of the blowing pressure of the compressed air blown in the first quenching zone and the third quenching zone is 1 bar or more. Preferably, the magnitude of the blowing pressure of the compressed air in the first quenching zone is in the range of 1 bar or more and 3 bar or less, in the second quenching zone is in the range of 0 bar or more and 1 bar or less, and in the third quenching zone is in the range of 2 bar or more and 5 bar or less.

[0032] Preferably, when the thickness of the glass sheet to be tempered is greater than or equal to 5.8 mm and less than or equal to 6.7 mm, the average convective heat transfer coefficient in the first quenching zone is greater than or equal to 750 W / m 2 / K or more. In the second quenching zone, 600 W / m 2 / K or less, and in the third quenching zone, 800W / m 2 / K or more. The glass conveying speed is preferably 250 mm / s or more and 600 mm / s or less, and the length of the glass sheet is such that it remains in each of the first and second quenching zones for 0.5 seconds or more and 1.3 seconds or less. Table 1 shows preferred limits for the average convective heat transfer coefficient from the first quenching zone to the third quenching zone. In particular, the average convective heat transfer coefficient in the third quenching zone depends on the desired surface tension of the glass, which is 150 MPa or more.

[0033] [Table 1]

[0034] Example 1 In Example 1 of Table 2, the quenching section comprises six individually adjustable quenching zones. The blowing equipment, i.e., blowing box and compressed air box, and their characteristics were identical in all quenching zones. The length of the gap between the rollers was 125 mm, i.e., for example, the first quenching zone, 375 mm long, covered three compressed air boxes. The length L of each quenching zone was 125 mm. i The quenching zones (i is the serial number of the quenching zone) and the blowing pressures used are shown in Table 2, which also shows the calculated average convective heat transfer coefficient (= ht coefficient) jointly produced by the air jets of the different quenching zones. The tempered glass had a thickness of 6 mm and a conveying speed W of 375 mm / s. The blowing distance on the top surface of the glass was 15 mm and that on the bottom surface was 15 mm. The tempering temperature of the glass was 665°C. In Table 2, the time t i means the residence time of each point of the glass in each quenching zone, i.e., t i =L i / W.

[0035] [Table 2]

[0036] For the quenching according to Example 1, a surface tension level of approximately 220 MPa was achieved for 6 mm glass, and in fire tests, the durability required for a fire resistance classification of at least E60, even E90, was obtained. Furthermore, the tempered glass was free from hair cracks and had acceptable optical quality. It was found that a significant reduction in the compressed air outlet pressure and heat transfer coefficient in the second quenching zone relative to the outlet pressures in the first and third quenching zones was important to avoid hair cracks. On the other hand, a reduction in the outlet pressure in the first quenching zone significantly below the value in Table 2 (1.6 bar) was found to have a negative impact on the surface tension level and optical quality of the tempered glass. The pressure reduction in the last quenching zone, i.e., in zones Z5 and Z6, was implemented to save energy because maintaining the same pressure level as zones Z3 and Z4 would not increase the surface tension of the glass by more than approximately 2 MPa.

[0037] In the apparatus according to the present invention, the surface tension level of the glass, prevention of hair cracks, and straightness of the glass are controlled by adjusting the pressure levels of the pressure regulating valves on both sides of the glass in each quenching zone. If the pressure regulating valves in each quenching zone are not opened at all, the glass in the quenching zone is only affected by the blowing pressure used during transport.

[0038] Dividing the quenching section into three or more, preferably five or more, individually adjustable quenching zones and the ability of the pressure regulating valve to quickly shut off the air supply to the quenching zones, i.e., to zero the blowing pressure, are very important factors in terms of energy conservation in the generation of compressed air. The blowing of compressed air to each quenching zone begins when the leading edge of the loaded glass body approaches a margin distance R1 from the start of the quenching zone and ends when the trailing edge of the loaded glass body moves away from the end of the quenching zone by a margin distance R2. The margin distances R1 and R2 are preferably in the range of 0 mm or more and 150 mm or less. More preferably, the margin distance R1 is 0 mm or more and 50 mm or less, and the margin distance R2 is 0 mm or more and 50 mm or less. In the following examples, the margin distances are set to 0 mm for clarity. For example, if the length of the loaded glass body is 1000 mm, the conveying speed is 500 mm / s, and the quenching section has only one quenching zone with a length of 3000 mm, it takes (3000 + 1000) / 500 = 8 seconds to blow compressed air to the entire quenching zone. If there are six quenching zones with a length of 500 mm, it takes only (500 + 1000) / 500 = 3 seconds to blow air to each quenching zone. In this example, by dividing the system into multiple quenching zones, the amount of compressed air consumed can be reduced to 5 / 8. Thus, the operating time of each quenching zone is determined by the glass conveying speed and the length of the loaded glass body.

[0039] The apparatus according to the present invention also includes a computer and a device for providing position data of the loaded glass bodies to the control system, and the pressure regulating valves in each quenching zone are opened and closed based on the data. This device is, for example, a pulse transmitter connected to a servo motor or an actuator of the conveyor of the tempering furnace. The apparatus according to the present invention also includes a pressure gauge for measuring the blowing pressure.

[0040] The invention described above is not limited to the disclosed embodiments, but various modifications are possible within the scope of protection defined in the claims.

Claims

1. A method for tempering a glass sheet to temper the surface compressive stress of the glass sheet to 150 MPa or more, comprising: As the glass sheet moves through the quenching section, the glass sheet is quenched by blowing air onto the upper and lower surfaces of the glass sheet by means of a blower through the outlets (6, 7) of a blowing box and by means of the pressure of an air compressor through a pipe nozzle (10); the quenching section comprises three or more successive quenching zones; In the first quenching zone, the average convective heat transfer coefficient jointly generated by the blown air jets and the compressed air jets on the upper and lower surfaces of the glass sheet is 750 W / m ２ / K or more, In the second quenching zone, the average convective heat transfer coefficient is at least 10% lower than the average convective heat transfer coefficient in the first quenching zone; in the third quenching zone, the average convective heat transfer coefficient is greater than or equal to the average convective heat transfer coefficient in the first quenching zone; The difference in the average convective heat transfer coefficient between the quenching zones is achieved by varying the blowing pressure of the pipe nozzle (10).

2. In the first quenching zone, the average convective heat transfer coefficient is 800 W / m ２ 2. The method for tempering a glass plate according to claim 1, wherein the glass temperature is 1000°C or higher.

3. 2. The method of claim 1, wherein the average convective heat transfer coefficient in the third quenching zone is at least 10% higher than the average convective heat transfer coefficient in the first quenching zone.

4. The thickness of the glass sheet to be tempered is 5.8 mm or more and 6.7 mm or less; The average convective heat transfer coefficient in the first quench zone is 750 W / m ２ / K or more, and in the second quenching zone, 600 W / m ２ / K or less, and in the third quenching zone, ２ 2. The method for tempering a glass plate according to claim 1, wherein the glass temperature is 1000°C or higher.

5. The method for tempering a glass plate according to any one of claims 1 to 4, wherein the glass plate is tempered at a tempering temperature of 670°C or less, and the compressive stress on the surface of the glass plate is set to 180 MPa or more.

6. 2. The method of tempering a glass sheet according to claim 1, wherein the average convective heat transfer coefficient in the first quenching zone and the third quenching zone is at least 20% higher than the average convective heat transfer coefficient in the second quenching zone.

7. 2. The method for tempering a glass sheet according to claim 1, wherein in the second quenching zone, the blowing pressure of the pipe nozzle (10) is at least 0.5 bar lower than the blowing pressure of the pipe nozzle (10) in the first quenching zone and the third quenching zone, and the blowing pressure of the pipe nozzle (10) is at least 1 bar.

8. 2. The method for tempering a glass sheet according to claim 1, wherein the blowing pressure of the pipe nozzle (10) is 1 bar or more in the first quenching zone, 0.5 bar or less in the second quenching zone, and 2 bar or more in the third quenching zone.

9. 8. The method for tempering a glass sheet according to claim 1, wherein in one or more quenching zones the blowing pressure of the pipe nozzles (10) above the glass sheet is at least 0.2 bar higher than the blowing pressure of the pipe nozzles below the glass sheet.

10. 2. The method for tempering a glass sheet according to claim 1, wherein a conveying speed of the glass sheet is 250 mm / s or more and 600 mm / s or less, and the length of the glass sheet is such that the glass sheet stays in each of the first quenching zone and the second quenching zone for a time of 0.3 seconds or more and 1.5 seconds or less.

11. 8. The method for tempering a glass sheet according to claim 1, wherein in each of the quenching zones, the blowing of compressed air by the pipe nozzle (10) starts when the leading edge of the glass body to be loaded approaches a distance of 0 mm or more and 150 mm or less from the start point of the quenching zone, and ends when the trailing edge of the glass body to be loaded moves away from a distance of 0 mm or more and 150 mm or less from the end point of the quenching zone.

12. A glass plate tempering apparatus for tempering a glass plate until the surface compressive stress of the glass plate reaches 150 MPa or more, quenching of the glass sheet is carried out by blowing jets of air onto the glass surface as the glass sheet moves through the quenching section, the jets of air being generated by a blower (11) through the outlets (6, 7) of the blowing box and by the pressure of an air compressor through a pipe nozzle (10) attached to a compressed air box in the blowing box; The quenching section is provided with three or more quenching zones of the pipe nozzles (10) on both sides of the glass sheet, The blowing pressure of the pipe nozzle (10) is set so as to be individually adjustable, In the first quenching zone, the average convective heat transfer coefficient jointly generated by the blown air jets and the compressed air jets on the upper and lower surfaces of the glass sheet is 750 W / m 2 / K or more; In the second quenching zone, the average convective heat transfer coefficient is at least 10% lower than the average convective heat transfer coefficient in the first quenching zone; in the third quenching zone, the average convective heat transfer coefficient is greater than or equal to the average convective heat transfer coefficient in the first quenching zone; The apparatus for tempering a glass sheet, wherein the length of the first quenching zone and the second quenching zone is 80 mm or more and 550 mm or less.

13. 13. The apparatus for tempering a glass sheet according to claim 12, wherein an initial portion of the quenching section is provided with five or more continuous quenching zones above and below the glass sheet, each capable of individually adjusting the blowing pressure.

14. 13. The apparatus for tempering a glass sheet according to claim 12, wherein the length of the first quenching zone and the second quenching zone is not less than 100 mm and not more than 400 mm.

15. 13. The apparatus for tempering a glass sheet according to claim 12, wherein the first quenching zone and the second quenching zone cover at least one and at most three compressed air boxes on either side of the glass sheet.

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