Method and apparatus for tempering glass sheets

Abstract

The present invention relates to a method for tempering a glass sheet to a surface compressive stress of at least 150 MPa without hairline cracks to achieve good optical properties and save energy, wherein when the glass sheet travels through a quenching section, the glass sheet is quenched by blowing air jets on the upper and lower surfaces of the glass sheet using a blower through blowing holes (6, 7) on a blow box cover and using air compressor pressure through a nozzle (10), wherein at least three consecutive compressed air convection blowing zones with individually adjustable blowing pressures are provided above and below the glass sheet, respectively. The average convection heat transfer coefficient generated by the blowing and compressed air jets on the upper and lower surfaces of the glass sheet is at least 750 W / m in the first zone. 2 / K is at least 10% lower in the second zone than in the first zone and at least as high in the third zone as in the first zone. The zone-specific differences in the heat transfer coefficient are achieved by varying the blowing pressure of the nozzle (10).

Description

Technical Field

[0001] The present invention relates to a method for tempering a glass sheet, wherein the glass sheet at the tempering temperature is quenched by blowing cooling air to both sides of the glass sheet. The present invention also relates to an apparatus for implementing the method, the apparatus comprising a conveying track and cooling air boxes located above and below the conveying track, the cooling air boxes having cooling air blowing holes, the cooling air blowing holes being positioned so that the cooling effect formed by blowing through the blowing holes is directed to the upper surface and the lower surface of the moving glass sheet. Background Art

[0002] Glass tempering refers to the process of first heating the glass to the tempering temperature and then rapidly cooling it. A glass plate tempering production line comprises a loading platform, a heating furnace, a quenching machine and an unloading platform. The present invention relates to a quenching machine.

[0003] Soda lime silicate glass is the most common type of tempered glass and the present invention is particularly concerned with the tempering of this type of glass. Glass that enters the tempering process has excellent flatness and optical properties. During the tempering process, the goal is to fully improve the strength of the glass sheet while minimizing the impact on the flatness and optical properties of the glass sheet. In addition to strength, another desirable property of tempered glass is safety in the event of breakage. Non-tempered glass will break into large pieces with a risk of cuts, while tempered glass breaks into small pieces with little risk of injury.

[0004] The compressive stress (strengthening degree or tempering degree) formed on the glass surface during tempering depends on the vertical temperature distribution of the glass when the glass is cooled within the characteristic glass transition temperature range (about 600→500°C for soda-lime silicate glass). In this case, the vertical temperature distribution of the glass approximates the shape of a parabola. For example, in a glass with a surface compressive stress of 100 MPa and a thickness of 4 mm, the temperature difference between the glass surface and the center of the glass in the temperature distribution is about 100°C. The residual stress distribution formed on the glass during tempering also has a parabolic shape, where the surface compressive stress of the above 100 MPa corresponds to a tensile stress of about 46 MPa in a glass with an average thickness.

[0005] At the beginning of quenching, instantaneous tensile stress is formed on the glass surface. Theoretically, the glass plate bears an average tensile stress of 30Mpa. If the glass tempering temperature is too low, this limit is exceeded, which increases the risk of glass breakage. On the other hand, too high a tempering temperature will damage the optical properties of the glass. The instantaneous tensile stress at the beginning of quenching also increases with the improvement of cooling efficiency.

[0006] During the tempering of glass, especially when the magnitude of the expected surface tensile stress of the glass is relatively high compared to the normal tempering process of glass, capillary cracks that are difficult to detect will form on the glass in the early stage of the tempering process due to various reasons, such as the extension of the original microcracks on the glass surface, the temperature difference inside the glass, and the change of the glass thickness. However, in the tempering process where the tempering of the glass surface is significantly greater than the normal tempering, the capillary cracks are mainly caused by the high cooling efficiency, that is, the cooling with high blowing pressure. Especially in the early stage of tempering, the cooling efficiency of the glass surface is high, resulting in rapid cooling of the glass surface and strong instantaneous tensile stress, which leads to the extension of microcracks on the glass surface. In this case, the temperature of the glass sheet deeper from the surface is almost still at the original tempering temperature and high elasticity. Therefore, the capillary cracks only affect the surface layer of the glass. In the surface area of ​​the glass sheet, the capillary cracks are usually formed in its center. This phenomenon is particularly prominent when compressed air blowing is used to enhance the tempering, in which case the heat transfer of a single jet is concentrated at any point.

[0007] The present invention solves the capillary cracking problem mentioned above, especially for super tempered glass. In super tempering, it is necessary to temper the glass more strongly than normal tempering. Super tempering can be achieved when the cooling efficiency of the air jet in the quenching device is significantly improved relative to tempering. The most common super tempered glass is fire-resistant glass, or FRG glass, which is used to slow down the spread of fire in buildings. According to fire safety standards, the glass on the boundary surface of the fire compartment must pass strict endurance tests. The compressive stress on the surface of soda-lime silicate glass tempered to fire-resistant glass is at least 150MPa, usually higher. For example, for 6mm thick glass, its surface compressive stress usually needs to reach about 175MPa in order for the glass to more reliably pass the E30 fire test. On the other hand, there is also a demand in the market for tempered FRG glass that has undergone a more severe tempering than the above tempering, which at least passes the E60 fire test, that is, in a fire safety test, the combustion temperature and the ambient temperature during the test exceed 900°C, and the glass can withstand for more than 60 minutes. There is also a demand in the market for tempered glass that passes the E90 fire test. Therefore, the surface tensile stress of the glass needs to reach 220MPa. As the requirements for the size of the surface tensile stress of the glass increase, the requirements for the size of the glass also increase. Therefore, super tempering equipment also needs improved performance, adjustability and reproducibility. Due to the above-mentioned problems related to capillary cracks, tempering glass to a surface tensile stress exceeding 160MPa, especially exceeding 180MPa, will be problematic. Glass containing capillary cracks will basically break and is therefore not suitable for use. The present invention is able to temper glass into FRG glass while avoiding the above-mentioned breakage problem. FRG glass is typically 6-6.5mm thick, which actually means that when the glass is measured, the glass thickness is 5.8-6.7mm. There is also a need for thinner 4mm (when the glass is measured, the glass thickness is 3.8-4.2mm) FRG glass.

[0008] At present, the most common way to avoid hairline cracks is to increase the tempering temperature to above 670°C, but this will reduce the optical properties of the glass. The present invention allows the tempering temperature to be reduced. In the method according to the present invention, the appropriate final temperature in the furnace, i.e. the tempering temperature at which the soda-lime-silicate glass is tempered to a surface tensile stress of more than 180 MPa, is preferably about 645°C-665°C and in any case below 670°C.

[0009] The cooling efficiency required for super tempering is very high, and to achieve these requirements, it is necessary to use a high-power electric motor for the turbine, which consumes a lot of electricity. The present invention can also achieve significant savings in energy consumption.

[0010] A method and a device are known from patent publications FI90046B and FI104422B, in which, during the tempering phase, the cooling air jets are generated partly with compressed air through nozzles and partly with blown air through holes in the blow box. The device comprises only one quenching zone. In reference FI104422B, this zone also serves as an aftercooling zone, but the injection of compressed air is stopped during the aftercooling phase.

[0011] In the method of patent US4445921, the glass is first tempered with dry air and then tempered with gaseous sublimable material. The heat transfer coefficient of dry air is lower than that of sublimable material. In the reference example, the heat transfer coefficient of dry air is 70 BTU / hr / ft 2 / °F(=397W / m 2 / K), the heat transfer coefficient of the sublimable material is 115 BTU / hr / ft 2 / °F(=653W / m 2 / K).

[0012] In patent application US2007122580A1, by setting the heat transfer coefficient in the first zone of the quencher to be significantly lower than that in the second zone, the instantaneous tensile stress on the glass surface during the tempering process is prevented from exceeding 4800 psi (= 33 MPa) and the glass is prevented from breaking. According to the calculation in Table 3 of the reference, for example, for 0.25 inch (= 6.35 mm) thick glass, the tempering temperature is 1266F (= 686°C), and the heat transfer coefficient can be as high as 94 BTU / hr / ft 2 / °F(=533W / m 2 / K) to ensure that the tensile stress limit of 33MPa according to the reference is not exceeded, thereby ensuring that the glass does not break. The reference calculates 0.05s as the duration of the first quenching stage, which corresponds to a quenching zone length of 17.5mm at a typical conveying rate of 350mm / s. In the second quenching zone, the heat transfer coefficient is 198BTU / hr / ft 2 / °F(=1123W / m 2 / K). According to the teaching of this reference, in the first quenching zone, when the tempering temperature is 686°C, the glass sheet cannot withstand more than 121 BTU / hr / ft 2 / °F(=686W / m 2 / K). It is proposed to adjust the heat transfer coefficient of a specific zone by adjusting the blowing distance, air temperature, flow velocity or volume flow rate. Summary of the invention

[0013] In order to avoid the disadvantages of the prior art, the object of the present invention is to provide a method and a device that can temper glass to a surface tensile stress of up to 150 MPa, preferably 180 MPa, while avoiding the above-mentioned capillary crack problem, so that the glass has good optical properties and saves energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be described in more detail below with reference to the accompanying drawings, in which

[0015] Figure 1 A cooling air box of a preferred embodiment of an apparatus for carrying out the method is shown in detail;

[0016] Figure 2 A schematic side view of a tempering device for implementing the present invention is shown;

[0017] Figure 3 The length of the quenching zone is determined. DETAILED DESCRIPTION

[0018] Figure 2 The tempering device shown comprises a furnace 15 provided with heating elements 17, by means of which a glass load moving on a roller conveyor and comprising at least one glass sheet 5 is heated to a tempering temperature. The glass load may comprise a plurality of glass sheets 5 adjacent and consecutive to one another, but for the sake of clarity, Figure 2 Only one glass sheet 5 is shown. The glass load reciprocates in the furnace, and when the heating time according to the heating scheme is over, the heated glass load is conveyed to the quenching section 16 on the rollers. The conveying speed W of the glass load is 250-800 mm / s, at which the glass load travels through the quenching section 16. The temper formed on the glass sheet 5 depends on the cooling process of the quenching section, and the purpose of the post-cooling section 18 is to cool the glass sheet to the manual handling temperature. In the post-cooling section 18, the cooling efficiency is significantly lower than that in the quenching section 16. In the quenching section 16, the blow box 2 is located above and below the conveying plane formed by the rollers, and the compressed air box 9 is located inside the blow box. Cooling air is supplied to the blow box 2 by a blower 11. Cooling air is supplied to the compressed air box 9 from a compressed air cylinder 13, which is filled by an air compressor 12. The quenching section includes a plurality of quenching zones, in which the blowing pressure of the compressed air is set to be individually adjustable by a zone-specific pressure regulating valve 1. These zones may also be referred to as compressed air blowing zones. exist Figure 2 In the example, there are five such zones above and below the glass plate. Figure 2 Each zone contains two compressed air tanks 9. Figure 1 The blow box and compressed air box are shown in more detail in FIG.

[0019] exist Figure 1In the embodiment of the present invention, the blow boxes and compressed air boxes located above and below the glass sheet 5 supported on the rollers 3 are substantially similar. Therefore, on both sides of the glass sheet, the blow boxes and compressed air boxes and their components are indicated by the same reference numerals. The length of the blow box 2 and the compressed air box 9, i.e. the moving dimension of the glass in the transverse horizontal direction, is 1-3.5 m, depending on the width of the tempering line. The blow box 2 is provided with blow holes 6 and 7, through which the air generated by the blower 11 is discharged as jets toward the glass sheet 5. These jets can be called blow air jets. The blow holes 6, 7 form rows in the longitudinal direction of the blow box 2, wherein the distance between adjacent blow holes is preferably 30-50 mm, and the distance between the blow holes on different rows and at different points in the longitudinal direction of the blow box is preferably 15-25 mm. The diameter of the blow hole 7 is 4-10 mm, preferably about 5-8 mm. When the vertical distance from the blow hole 6 to the glass sheet is shorter than the vertical distance from the blow hole 7 to the glass sheet, the diameter of the blow hole 6 is preferably 1-3 mm smaller than the diameter of the blow hole 7, and when the distances are the same, the diameters are preferably the same. The row formed by the blow hole 6 is located between the rows formed by the blow hole 7. The number of blow holes 6 may be substantially equal to the number of blow holes 7. The volume flow rate of the air flow discharged through the blow holes 6, 7 generated by the blower 11 depends on the size of the blow pressure or overpressure used, which is at least 2 kPa and in the range of 2-20 kPa, depending on the thickness of the glass and the target of tempering. The blow pressure of the blow jet is preferably in the range of 4-10 kPa. The blow pressure can be adjusted by changing the speed of the impeller of the blower 11. The blow pressure can be adjusted separately for each side of the glass, but for example, the blow pressure in the blow box above the quenching section is preferably equal in all quenching zones.

[0020] The strong air flow entering the relatively narrow space between the blow box 2 and the glass sheet 5 creates an overpressure in this area relative to the surrounding pressure. When the overpressure on the lower surface of the glass is higher than on the upper surface, there is a risk that the glass sheet will lift off the rollers, which will cause the glass sheet to hit the blow box and then break. Figure 1 In the figure, above the glass sheet 5, opposite to the roller 3, there is a dummy roller 4, the purpose of which is to increase the pressure on the upper surface of the glass sheet 5 to prevent the glass sheet from floating. For the sake of clarity, Figure 2 and Figure 3 It is omitted in the embodiment. The blowing distance of the upper and lower parts is also controlled to ensure that the glass sheet remains in contact with the roller.

[0021] The compressed air box 9 in the blow box 2 is provided with a nozzle 10 screwed thereto, which extends towards the blow hole 7. The nozzle 10 has a compressed air opening 8 with a diameter in the range of 2-5 mm. The velocity of the air flow discharged through the nozzle 10 towards the glass sheet and as a jet depends on the size of the blow pressure or overpressure used, which pressure p iIn the range of 0-10 bar, preferably 0-6 bar, it depends on the compressed air blowing zone, the thickness of the glass sheet and the surface compressive stress required for tempered glass. The jet discharged from the nozzle 10 can be called a compressed air jet. The blowing pressure can be adjusted individually for each zone by the pressure regulating valve 1. The number of nozzles 10 in a compressed air box 9 is usually 40-80 per meter of compressed air box.

[0022] The air flow discharged from the nozzle 10 is preferably discharged from the blow box 2 toward the glass sheet via the blow hole 7, through which the air from the blower 11 is also discharged toward the glass. The outer edge of the nozzle 10 tapers conically toward the tip of the nozzle. The tip of a particular nozzle 10 is almost flush with the inner surface of the blow box 2 and may extend inside the blow hole 7 or remain slightly outside the blow hole. The tip of a particular nozzle 10 preferably does not at least substantially restrict the flow area of ​​the corresponding blow hole 7. The diameter of the blow hole 7 is preferably at least 1 mm larger than the diameter of the compressed air opening 8. Preferably, 30-80% of the blow holes of the blow box 2 are provided with nozzles 10.

[0023] The vertical blowing distance from the blowing holes 6, 7 to the glass sheet is arranged to be adjustable, for example, by a chain, a gear and a motor. It is important to be able to adjust the upper blowing distance and the lower blowing distance separately. On the same side of the quenching section 16, the blowing distances of all corresponding blowing holes are the same. The vertical blowing distance from the blowing holes 6, 7 to the glass sheet is preferably 10-25 mm, in which case the distance from the tip of the nozzle 10 to the glass is preferably about 3-12 mm.

[0024] In the quenching section 16, an enhanced cooling process is carried out by blowing two types of air jets on the same surface of the glass sheet, namely, an air jet generated by an air compressor 12 through a nozzle 10, and an air jet generated by a blower 11 through the blowing holes 6, 7. These air jets together generate a convective heat transfer coefficient h on the glass surface. During quenching, the glass is also cooled by radiation, but in super tempering, the proportion of radiation is smaller. At a typical tempering temperature of 650-670°C, the glass radiation is equal to a value of about 40kW / m2 of the glass surface. 2 , which as a radiation heat transfer coefficient corresponds to a convection heat transfer coefficient of about 60 W / m 2 / K, this value decreases as the glass temperature decreases.

[0025] From the perspective of the invention, it is essential to divide the compressed air blowing into at least three, preferably at least five quenching zones, the compressed air blowing pressure of which can be adjusted individually. The cooling efficiency Q (in W / m 2 ) can be obtained from the equation Q = h × (T 玻璃 -T 空气) calculation, where T 空气 is the temperature of the air discharged toward the glass, T 玻璃 is the temperature of the glass surface. The average convection heat transfer coefficient h depends on the diameter, number, position, blowing distance and blowing pressure of the blowing holes and compressed air holes. There are local variations in the heat transfer coefficient achieved on the glass surface by the cooling air jet system. The local heat transfer coefficient is highest at the point where the air jet hits the glass surface. The average heat transfer coefficient refers to the average heat transfer coefficient over the area covered by a part of the jet system. For example, the average heat transfer coefficient of zone 1 is the average heat transfer coefficient over the area L1×WIDTH, where L1 is the length of the quencher covered by zone 1, and WIDTH is the width of the glass, that is, the dimension of the glass moving in the lateral horizontal direction. In fact, the cooling efficiency of a specific cooling air jet system on the glass surface can only be adjusted by changing the blowing distance or the blowing pressure. There will be no significant change in the cooling efficiency by changing the blowing distance alone. Adjustment by blowing pressure is obviously more efficient, simple and accurate than adjustment by blowing distance. In addition, reducing the cooling efficiency by blowing distance will not reduce the compressed air consumption at all, while reducing the blowing pressure will reduce the consumption.

[0026] The cooling efficiency is zoned with respect to the quenching time, i.e. in the direction of travel of the glass sheet in the quenching section, preferably by individually adjusting the blowing pressure in the successive compressed air blowing zones. From the perspective of the present invention, the zone division for cooling efficiency is necessary in order to be able to solve the problem of capillary cracks in the glass sheet during super tempering as discussed above in the specification. The glass sheet is ensured to be in contact with the roller by adjusting the blowing distance and by varying the blowing pressure of the nozzles 10 above and below the glass sheet for specific zones respectively. When the blowing pressure is at least 1 bar, the blowing pressure of the nozzles 10 located on the upper surface of the glass sheet is preferably at least 0.2 bar higher than the blowing pressure of the nozzles 10 located on the lower surface. During tempering, the upper and lower surfaces of the glass sheet should be cooled substantially along the same temperature curve to avoid bending of the finished tempered glass sheet. The uniform cooling of the glass surface is controlled by varying the blowing pressure on both sides.

[0027] exist Figure 2 In the device example, there are five quenching zones on both sides of the glass ( Figure 3 1 to 5), i.e. compressed air zones, which can be individually adjusted by the blowing pressure of the nozzle 10. The length of the quenching zone is the part of the quencher length L which the quenching zone covers. Figure 2 and Figure 3 The length of the area in is L1-L5. Figure 2 and Figure 3In the example of the device, the compressed air blowing pressure can be adjusted individually for each zone covering two roller nips and two compressed air boxes on both sides of the glass. Zones Z1-Z5 may also have different lengths. The compressed air blowing pressure of the pressure regulating valve 1 of each zone towards the upper surface of the glass is set to p u1 -p u5 , which together with the blowing air produces a convective heat transfer coefficient h on the upper surface of the glass u1 -h u5 The blowing pressure of the compressed air openings 8 in each area toward the lower surface of the glass is p l1 -p l5 , which together with the blowing air produces an average convective heat transfer coefficient h on the lower surface of the glass l1 -h l5 . Upper blowing distance H u and the blowing pressure p to the upper blowing box set by the blowing machine 11 fan,u The lower blowing distance H is the same in all zones above the glass sheet. l and the blowing pressure p to the lower blowing box set by the blowing machine 11 fan,l This is the same in all zones below the glass plate.

[0028] When the glass sheet is transported from the tempering furnace to the quenching section at a transport speed W, the glass sheet arrives at zone Z1, in which the nozzle 10 blows air on the surface of the glass sheet at a blowing pressure p 1u The air jet is blown at a blowing pressure p on the lower surface of the glass plate. 1l The blowing air jets are blown. These blowing pressures are in the range of 1-10 bar, preferably 1-6 bar. Preferably, p 1u ≥p 1l +0.2 bar. The blowing pressure above the glass as an air jet from the blower 11 into the blow box 2 and further through the blow holes 6, 7 is p fan,u , under the glass is p fan,l The average convective heat transfer coefficient generated by the air jets in zone Z1 is h on the upper surface of the glass. 1u , on the lower surface of the glass is h 1l For glass less than 3.8mm thick, the heat transfer coefficient exceeds 800W / m 2 / K, for glass at least 3.8mm thick, the heat transfer coefficient exceeds 750W / m 2 / K, preferably more than 800W / m 2 / K. The time that the glass sheet (each point thereof) remains in zone Z1 is t1=L1 / W. The length of zone Z1 is 80-550 mm, and it includes 1-4 compressed air blowing boxes 9. The length of zone Z1 is preferably 100-400 mm, and it includes 1-3 compressed air blowing boxes 9. The residence time in zone Z1 is 0.2-2 s. Preferably, the residence time in zone Z1 is 0.3-1.5 s.

[0029] In the second zone Z2, the blowing pressure is p 2u 、p 2l , which is at least 0.5 bar lower, preferably at least 1 bar lower, than the blowing pressure in the first zone Z1. 2l ≥1 bar, then p 2u ≥p 2l +0.2 bar. The blowing pressure from the blower 11 into the blow box and further toward the glass sheet is the same as in zone Z1. The average convective heat transfer coefficient generated by the air jets in zone Z2 on the upper surface of the glass is h 2u , h on the lower surface of the glass 2l . These heat transfer coefficients are lower than those in zone Z1. In the second quenching zone, the heat transfer coefficient is preferably at least 10% lower than in the first quenching zone, even more preferably at least 20% lower. The length of zone Z2 is 80-550 mm, and it comprises 1-4 compressed air blow boxes 9. The length of zone Z2 is preferably 100-400 mm, and it comprises 1-3 compressed air blow boxes 9. The residence time in zone Z2 is 0.2-2 s. Preferably, the residence time in zone Z2 is 0.3-1.5 s.

[0030] In the third zone Z3, the blowing pressure is p 3u 、p 3l , preferably at least 0.5 bar higher than the blowing pressure in zone Z1 and at least 1 bar higher than the blowing pressure in zone Z2. 3u ≥p 3l +0.2 bar. The blowing pressure from the blower 11 into the blow box and further toward the glass sheet is the same as in zone Z1. The average convective heat transfer coefficient generated by the air jets in zone Z3 on the upper surface of the glass is h 3u , h on the lower surface of the glass 3l These heat transfer coefficients are higher than in zone Z2, preferably at least 20% higher than in zone Z2 and 10% higher than in zone Z1. The average convective heat transfer coefficient in the third zone Z3 is at least as high as in the first zone Z1. The blowing pressure of the nozzle is preferably at least 1 bar in the first quenching zone, at most 0.5 bar in the second zone and at least 2 bar in the third zone.

[0031] If zone 3 is the last zone, the length of zone 3 is at least 1500 mm. The quenching section preferably also includes at least a fourth zone and a fifth zone. In this case, the lengths of zones 3-5 are at least 300 mm each and at least 1500 mm in total. The blowing pressure in zone 4 is the same as in zone 3. The blowing pressure from the blower 11 to the blow box and further toward the glass sheet is the same in zones 3-5 as in zone 1.

[0032] The magnitude of the blowing pressure of the compressed air blown in the first zone and the third zone is at least 1 bar. Preferably, the magnitude of the blowing pressure of the compressed air blown in the first zone is in the range of 1-3 bar, in the second zone in the range of 0-1 bar, and in the third zone in the range of 2-5 bar.

[0033] Preferably, when the thickness of the glass sheet to be tempered is 5.8-6.7 mm, the average convection heat transfer coefficient in the first quenching zone is at least 750 W / m 2 / K, the average convection heat transfer coefficient in the second quenching zone is at most 600 W / m 2 / K, the average convection heat transfer coefficient in the third quenching zone is at least 800 W / m 2 / K. The conveying speed of the glass is preferably 250-600 mm / s, and the glass sheet is held for 0.5-1.3 seconds per unit length in the first two zones. Preferred limit values ​​for the average convective heat transfer coefficients of zones 1-3 are shown in Table 1. In particular, the heat transfer coefficient of zone 3 depends on the required surface tensile stress of the glass, which is at least 150 MPa.

[0034] Table 1

[0035] Glass thickness <![CDATA[h u1 and h l1 ]]> <![CDATA[h u2 and h l2 ]]> <![CDATA[h u3 and h l3 ]]> Less than 3.8 800–1000 200–600 1000–1500 3.8–4.2 750–1000 200–600 900–1500 5.8–6.7 750–1000 200–600 800–1500 7.8–8.2 750–1000 200–600 750–1500 mm <![CDATA[W / m 2 / K]]> <![CDATA[W / m 2 / K]]> <![CDATA[W / m 2 / K]]>

[0036] Example 1

[0037] In Example 1 of Table 2, the quenching section comprises six individually adjustable compressed air blowing zones. The blowing means, i.e. the blow boxes and compressed air boxes and their components, are identical in all zones. The roll gap is 125 mm, i.e., for example, the first zone, which is 375 mm long, comprises three compressed air boxes. The zone lengths L are shown in Table 2. i (where i is the sequential number of the zone) and the blowing pressure used, and also shows the calculated average convective heat transfer coefficient (=ht coefficient) generated by the air jets in the different zones. The thickness of the tempered glass is 6 mm, and the conveying speed W is 375 mm / s. The blowing distance of the upper surface of the glass is 15 mm, and the blowing distance of the lower surface is 15 mm. The tempering temperature of the glass is 665°C. In Table 2, the time t i It represents the residence time of a certain point of glass in this zone, that is, t i =L i / W.

[0038] Table 2

[0039]

[0040] By quenching according to Example 1, the surface tensile stress of 6 mm glass reaches about 220 MPa, which achieves the durability required to achieve at least E60 or even E90 fire resistance level in the fire test. The tempered glass has no capillary cracks and has acceptable optical properties. It was found that significantly reducing the compressed air blowing pressure and the heat transfer coefficient in the second quenching zone relative to those in zones 1 and 3 is important for avoiding capillary cracks. On the other hand, it was found that reducing the blowing pressure in the first blowing zone to a value significantly lower than that in Table 2 (1.6 bar) has an adverse effect on the magnitude of the surface tensile stress of the tempered glass and the optical properties of the glass. For energy saving reasons, the blowing pressure at the end (i.e. in zones Z5 and Z6) is reduced, because keeping the blowing pressure at the same level as in zones Z3 and Z4 increases the surface tensile stress of the glass by about 2 MPa at most.

[0041] By adjusting the pressure level of the pressure regulating valve in each zone on both sides of the glass, the surface tensile stress of the glass can be controlled to prevent the glass from having hairline cracks and control the straightness of the glass. If the pressure regulating valve of a certain zone is not opened, the glass in the zone is only affected by the blowing pressure used during transportation.

[0042] The division of the quenching section into at least three, and preferably into at least five, individually adjustable compressed air blowing zones, and the use of pressure regulating valves, by means of which the air supply to the compressed air blowing zones can be cut off very quickly, i.e. the blowing pressure can be reduced to zero, are both very important factors from the point of view of saving energy in the production of compressed air. Blowing of compressed air to each zone begins when the leading edge of the glass load approaches the start of the zone at margin R1, and ends when the trailing edge of the glass load leaves the end of the zone at margin R2. The margins R1 and R2 are preferably in the range of 0-150 mm. More preferably, the margin R1 is 0-50 mm and the margin R2 is 0-50 mm. In the following examples, the margins are set to zero for clarity. For example, if the length of the glass load is 1000 mm, the conveying speed is 500 mm / s, and the quencher has only one zone 3000 mm long, the compressed air blowing of the entire zone will last for (3000+1000) / 500=8 s. In the case of six 500 mm long zones, the blowing time in one zone is only (500+1000) / 500=3 s. In this example, the division into zones saves 5 / 8 of the compressed air consumption. Therefore, the conveying speed of the glass and the load length determine the operating time of each individual compressed air blowing zone.

[0043] The device according to the invention also comprises a computer and means for providing the control system with position data of the glass load, according to which the pressure regulating valves of the various zones are opened and closed. Such means are, for example, the servomotors of the conveyor of the tempering furnace or the pulse transmitters connected to the actuators of the conveyor. The device according to the invention also comprises a pressure gauge for measuring the blowing pressure.

[0044] The invention described above is not limited to the disclosed embodiments but can be modified in various ways within the scope of protection defined by the claims.

Claims

1. A method for tempering a glass sheet to a surface compressive stress of at least 150 MPa, wherein the glass sheet is quenched by blowing air jets on the upper and lower surfaces of the glass sheet as the glass sheet travels through a quenching section by: blowing air jets through blowing holes (6, 7) on a blow box by an air blower; and blowing compressed air jets through a nozzle (10) by an air compressor, characterized in that The quenching section comprises at least three successive quenching zones, and the average convective heat transfer coefficient generated by the blown air jets and the compressed air jets on the upper surface and the lower surface of the glass sheet is at least 750 W / m in the first quenching zone. 2 / K is at least 10% lower in the second quenching zone than in the first quenching zone and as high in the third quenching zone as in the first quenching zone, and the zone-specific difference in the average convective heat transfer coefficient is achieved by changing the blowing pressure of the nozzle (10).

2. The method according to claim 1, characterized in that: In the first quenching zone, the average convection heat transfer coefficient is at least 800 W / m 2 / K.

3. The method according to any one of claims 1 to 2, characterized in that The tempering temperature of the glass sheet to be tempered is below 670° C. and the target compressive stress on the surface of the glass sheet is at least 180 MPa.

4. The method according to claim 1, characterized in that The average convective heat transfer coefficient in the first quench zone and the third quench zone is at least 20% higher than the average convective heat transfer coefficient in the second quench zone.

5. The method according to claim 1, characterized in that: In the second quenching zone, the blowing pressure of the nozzle (10) is at least 0.5 bar lower than the blowing pressure in the first quenching zone and the third quenching zone, wherein the blowing pressure of the nozzle (10) is at least 1 bar.

6. The method according to claim 1, characterized in that In the first quenching zone, the blowing pressure of the nozzle (10) is at least 1 bar, in the second quenching zone it is at most 0.5 bar, and in the third quenching zone it is at least 2 bar.

7. The method according to claim 1 or 5, characterized in that: In at least one quenching zone, the blowing pressure of the nozzle (10) located above the glass sheet is at least 0.2 bar higher than the blowing pressure of the nozzle (10) located below the glass sheet.

8. The method according to claim 1 or 5, characterized in that: In each of the quenching zones, when the leading edge of the glass load is 0-150 mm close to the starting point of the quenching zone, the compressed air is blown by the nozzle (10), and when the trailing edge of the glass load is 0-150 mm away from the end point of the quenching zone, the blowing is stopped.

9. A method for tempering a glass sheet to a surface compressive stress of at least 150 MPa, wherein the glass sheet is quenched by blowing air jets on the upper and lower surfaces of the glass sheet as the glass sheet travels through a quenching section by: blowing air jets through blowing holes (6, 7) on a blow box by an air blower; and blowing compressed air jets through a nozzle (10) using an air compressor, characterized in that The quenching section comprises at least three successive quenching zones, and the average convective heat transfer coefficient generated by the blown air jets and the compressed air jets on the upper surface and the lower surface of the glass sheet is at least 750 W / m in the first quenching zone. 2 / K, is at least 10% lower in the second quenching zone than in the first quenching zone, and is at least 10% higher in the third quenching zone than in the first quenching zone, and the zone-specific difference in the average convective heat transfer coefficient is achieved by changing the blowing pressure of the nozzle (10).

10. The method according to claim 9, characterized in that The tempering temperature of the glass sheet to be tempered is below 670° C. and the target compressive stress on the surface of the glass sheet is at least 180 MPa.

11. A method for tempering a glass sheet to a surface compressive stress of at least 150 MPa, wherein the glass sheet is quenched by blowing air jets on the upper and lower surfaces of the glass sheet as the glass sheet travels through a quenching section by: blowing air jets through blowing holes (6, 7) on a blow box by an air blower; and blowing compressed air jets through a nozzle (10) using an air compressor, characterized in that The quenching section comprises at least three successive quenching zones, wherein the average convective heat transfer coefficient generated by the blown air jet and the compressed air jet on the upper surface and the lower surface of the glass sheet is achieved by changing the blowing pressure of the nozzle (10), the thickness of the glass sheet to be tempered is 5.8-6.7 mm, and the average convective heat transfer coefficient in the first quenching zone is at least 750 W / m 2 / K, the average convection heat transfer coefficient in the second quenching zone is at most 600 W / m 2 / K, the average convection heat transfer coefficient in the third quenching zone is at least 800 W / m 2 / K.

12. The method according to claim 11, characterized in that The tempering temperature of the glass sheet to be tempered is below 670° C. and the target compressive stress on the surface of the glass sheet is at least 180 MPa.

13. An apparatus for tempering a glass sheet to a surface compressive stress of at least 150 MPa, wherein: When the glass sheet passes through the quenching section, the glass sheet is quenched by blowing air jets on the glass surface in the following manner: blowing air jets through the blowing holes (6, 7) on the blow box by a blower (11); and blowing compressed air jets through a nozzle (10) attached to a compressed air box in the blow box by an air compressor, characterized in that in the quenching section, there are at least three compressed air convection blowing zones of the nozzle (10) on either side of the glass sheet, the blowing pressure of the compressed air convection blowing zones is set to be individually adjustable, and the lengths of the first zone and the second zone are both 80-550 mm, and the average convection heat transfer coefficient jointly generated by the blowing air jets and the compressed air jets on the upper and lower surfaces of the glass sheet is at least 750 W / m in the first zone. 2 / K is at least 10% lower in the second zone than in the first zone and is as high in the third zone as in the first zone.

14. The device according to claim 13, characterized in that At the beginning of the quenching section, there are at least five consecutive compressed air countercurrent blowing zones above and below the glass sheet, the blowing pressure of which can be adjusted individually.

15. The device according to claim 13, characterized in that The lengths of the first zone and the second zone are both 100-400 mm.

16. The device according to claim 13, characterized in that The first zone and the second zone are each covered by 1-3 compressed air blow boxes located on either side of the glass sheet.

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