Method for manufacturing bent and tempered glass sheets and apparatus for manufacturing the same

Abstract: In a quenching apparatus for quenching a glass sheet that has been heated and bent in a heating furnace, a cooling gas blows onto the glass sheet to provide a distribution of a temperature and/or a distribution of a static pressure in at least one section in the quenching apparatus. The distribution of a temperature provides different temperatures between the both surfaces of the glass sheet, while the distribution of a static pressure is nonuniform in a part of at least one surface of the glass sheet. The distributions can modify a shape of the glass sheet given in the heating furnace so that a degree of freedom in shape for manufacturing a bent and tempered glass sheet by utilizing its self-weight can be improved.

Description: The present invention relates to a method for manufacturing a bent and tempered glass sheet and an apparatus for manufacturing the same, and, more particularly, to a method and an apparatus for manufacturing a bent and tempered glass sheet useful for architecture, automobiles or the like. A tempered glass sheet, one kind of safety glass sheets, has been used extensively as a window glass sheet for buildings, automobiles or the like. As a method for manufacturing such a tempered glass sheet, an air-cooling method has been widely used, which comprises quenching a glass sheet that has been heated to a temperature around its softening point by blowing a cooling air to form a residual compression stress layer at the surface of the glass sheet. On the other hand, the demand for a glass sheet with a predetermined curved shape has become higher, especially in the field of automobile windows to meet the requirement for automobile design and an aerodynamic property. Therefore, in the air-cooling method, the heated glass sheets are often bent before blowing a cooling air. Some methods are known as a method for bending a glass sheet while tempering. For example, in one method, a glass sheet is heated and pressed by a pair of convex and concave press dies while the glass sheet is suspended by tongs (hoisting accessories). In another method, a glass sheet that has been heated while horizontally carried in a heating furnace is pressed by a pair of upper and lower press dies. In such bending methods utilizing a pair of press dies, the step of softening a glass sheet by heating and the step of bending the glass sheet are basically separated. However, a method for conducting these steps as the same step has been proposed. In this method, a glass sheet is heated while carried by a glass sheet carrying system such as a roll or a bed having a predetermined curvature in a heating furnace so that the heated glass sheet sags gradually due to its self-weight, finally forming a curved surface having the above curvature. The bent glass sheet is usually quenched in a quenching apparatus located adjacent to the heating furnace. Such a method is excellent because it does not require the step of pressing a glass sheet. In order to reap full advantage of the method, various improvements have been conventionally provided to be put to practical use (Publication of Japanese Examined Patent Application No. 44-14832, Publication of Japanese Examined Patent Application No. 48-5242, and Publication of Japanese Unexamined Patent Application No. 7-237928). For example, Publication of Japanese Unexamined Patent Application No. 7-237928 discloses a method comprising blowing a gas on one surface of a glass sheet, while the glass sheet is carried out from a heating furnace to a quenching apparatus, to provide a difference in temperature in the temperature range of its softening point or above to intentionally provide a difference in a contraction rate for both surfaces of the glass sheet. This method aims at improving the degree of freedom for forming a glass sheet without limiting the shape of the glass carrying system. However, the method described in the Publication of Japanese Unexamined Patent Application No. 7-237928 requires further providing a gas blowing system between the heating furnace and the quenching apparatus for a glass sheet. Also, this method requires discharging a gas from the gas blowing system at a pressure basically higher than that of the cooling gas. Therefore, the manufacturing method cannot be conveniently implemented by the conventional apparatus. US-A-3,497,340 discloses a method of manufacturing a bent and tempered glass sheet, the method comprising: bending a glass sheet having a first surface and a second surface utilizing the weight of the glass sheet while heating and passing the glass sheet through a heating furnace; and quenching the glass sheet while carrying the glass sheet by blowing a cooling gas onto the first and second surfaces of the glass sheet in a quenching apparatus adjacent to the heating furnace. US-A-3,497,340 further discloses an apparatus for manufacturing a bent and tempered glass sheet comprising: a heating furnace for heating a glass sheet and comprising a glass sheet carrying outlet; a quenching apparatus comprising a glass sheet carrying inlet adjacent to the glass sheet carrying outlet of the heating furnace, and a cooling gas blowing system located on upper and lower sides of a glass sheet carrying path for discharging a cooling gas into the glass sheet carrying path; and a glass sheet carrying system having a curvature in a direction substantially perpendicular to a glass sheet carrying direction for carrying a glass sheet to the quenching apparatus through the heating furnace. An object of the present invention is, in the light of the situation as described above, to provide a method for manufacturing a bent and tempered glass sheet which can conveniently improve the degree of freedom for forming a glass sheet and an apparatus for manufacturing the same. From a first aspect, the present invention provides a method for manufacturing a bent and tempered glass sheet, the method comprising: bending a glass sheet having a first surface and a second surface utilizing the weight of the glass sheet while heating and passing the glass sheet through a heating furnace; and quenching the glass sheet while carrying the glass sheet by blowing a cooling gas onto the first and second surfaces of the glass sheet in a quenching apparatus adjacent to the heating furnace; characterised in that in the quenching apparatus the cooling gas is blown onto the first surface so as to lower the temperature of the first surface to the softening point of the glass sheet or less before the cooling gas begins to be blown onto the second surface. Such a method can conveniently improve the degree of freedom for forming a glass sheet in a bending and tempering method for forming a glass sheet utilizing its self-weight. From a further aspect, the present invention provides a method for manufacturing a bent and tempered glass sheet, the method comprising: bending a glass sheet having a first surface and a second surface utilizing weight of the glass sheet while heating and passing the glass sheet through a heating furnace, and quenching the glass sheet while carrying the glass sheet by blowing a cooling gas onto the first and second surfaces of the glass sheet in a quenching apparatus adjacent to the heating furnace; characterised in that the cooling gas provides a nonuniform distribution of static pressure over at least one of the first and second.surfaces in at least one section in the quenching apparatus so that the shape of the glass sheet is modified from the shape obtained by bending utilizing the weight of the glass sheet. Thus a specific part of one side of the glass surfaces where a relatively high static pressure is exerted can be partly pushed out to the other side of the surfaces where a relatively low static pressure is exerted, while the static pressures on both surfaces of the glass sheet can be balanced as a whole. The method of the present invention is different from that of JP 7-237928 as described above, because a cooling gas for tempering the glass sheet in the quenching apparatus is also used for achieving the object. From a still further aspect, the present invention provides an apparatus for manufacturing a bent and tempered glass sheet comprising: a heating furnace for heating a glass sheet and comprising a glass sheet carrying outlet; a quenching apparatus comprising a glass sheet carrying inlet adjacent to the glass sheet carrying outlet of the heating furnace, and a cooling gas blowing system located on upper and lower sides of a glass sheet carrying path for discharging a cooling gas into the glass sheet carrying path; and a glass sheet carrying system having a curvature in a direction substantially perpendicular to a glass sheet carrying direction for carrying a glass sheet to the quenching apparatus through the heating furnace; characterised in that the quenching apparatus is provided with an exhaust path restriction for providing a nonuniform distribution of static pressure over at least one surface of the glass sheet in at least one section in the quenching apparatus. A preferred embodiment of the method of the invention according to the above further aspect is that an exhaust path restriction system is placed in at least a part of the exhaust path. With such an arrangement, the nonuniform distribution can be provided to the static pressure applied to the surface of the glass sheet by partially controlling the exhausting of the cooling gas, and therefore the method also can be implemented easily and reliably. In the method for utilizing a distribution of the temperature, it is preferred that the cooling air begins to blow onto one of the surfaces of the glass sheet before the cooling air begins to blow onto the other surface of the glass sheet while the other surface of the glass sheet is supported. Such a supporting can prevent the glass sheet from changing its position greatly. More preferably, the one surface of the glass sheet is cooled to the strain point of the glass sheet or lower. Such a significant difference in timing for the start of cooling for the glass sheet can increase the degree of freedom for bending a glass sheet. In the method of utilizing a distribution of the static pressure, the glass sheet bent along the shape of a glass sheet carrying system in a heating step can be partially or totally modified to a controlled shape in the quenching step. The method is different from the conventional methods in providing a nonuniform distribution to the static pressure of the cooling gas. In the above method for manufacturing a bent and tempered glass sheet, it is preferred that the distribution of the static pressure is provided by partially controlling an exhaust of the cooling gas. Thus, the degree of freedom for bending a glass sheet can be improved without controlling the supply of the cooling gas that is complicated in terms of equipment. It is preferred that the exhaust is partially controlled by an exhaust path restriction system provided in an exhaust path for the cooling gas. Thus, the exhaust of the cooling gas can be partially controlled easily and reliably. Also, in the above method, the distribution of the static pressure may be provided to either one or both of the upper and lower surfaces of the glass sheet. When providing the distribution of the static pressure to both surfaces of the glass sheet, it is preferred that a static pressure having such a distribution that facilitates the deformation of the glass sheet caused by the distribution of the static pressure on one surface of the glass sheet is applied to the other surface of the glass sheet. Thus, the glass sheet is deformed by the cooperative action of the static pressures applied to both surfaces,.and therefore the degree of freedom of bending the glass sheet can be improved further. When providing the distribution of the static pressure to one surface of the glass sheet, it is preferred that a nonuniform distribution is provided only to a static pressure applied to a lower surface of the glass sheet because the space below the glass sheet is usually narrower than the space above the glass sheet due to the effect of the self-weight of the glass sheet, and therefore a static pressure distribution effective for modifying the shape of the glass sheet is easily provided. Also, in the above method, the section is provided in the vicinity of a glass sheet carrying inlet of the quenching apparatus because the shape of the glass sheet can be modified more easily by providing the distribution of the static pressure in the section where the glass sheet has a relatively high temperature. Furthermore, in the method, a curvature can be provided to the glass sheet in a glass sheet carrying direction as well. Such a glass sheet can be manufactured by a method in which the distribution of the static pressure is changed while one glass sheet passes through the section. The static pressure distribution can be changed by remote control of the exhaust path restriction system, for example. Preferred embodiments of the invention will now be described by way of example only, and with reference to the accompanying drawings in which: Figure 1 is a cross-sectional view of an embodiment of the apparatus according to the present invention. Figure 2 is a cross-sectional view of another embodiment of the apparatus according to the present invention. Figure 3 is a cross-sectional view of an embodiment of the apparatus according to the present invention. Figure 4 is a perspective view of an embodiment of the quench module portion used in the apparatus of the present invention. Figure 5 is a plan view of an embodiment of the air table and quench module portion used in the apparatus of the present invention. Figure 6 is a plan view of another embodiment of the air table and the quench module portion. Figure 7 is a cross-sectional view of an embodiment of the glass carrying path portion in the quenching apparatus used in the manufacturing apparatus of the present invention. Figure 8 is a cross-sectional view of an embodiment of the glass carrying path portion in the quenching apparatus with division of the carrying path. Figure 9 is a cross-sectional view of another embodiment of the glass carrying path portion in the quenching apparatus. Figure 10 is a perspective view of a bent and tempered glass sheet manufactured according to Example 1. Figure 11 is a perspective view of a bent and tempered glass sheet manufactured according to Example 2. Figure 12 is a cross-sectional view of a conventionally used bending and tempering apparatus. Fig. 1 shows a cross-sectional view of an embodiment of the apparatus for implementing the method for bending and tempering a glass sheet according to the present invention. In a heating furnace 1, an air table 11 is provided for carrying a glass sheet 3. The air table 11 has a number of nozzle holes, and the heated air blown off from these nozzle holes jets on the lower surface of the glass sheet 3, supporting and carrying the glass sheet. This hot air serves to carry the glass sheet 3 while floating it and to soften the glass sheet by heating. In the heating furnace 1, the glass sheet 3 is heated to be deformed along the shape of the surface of the air table due to the self-weight of the glass sheet to have a predetermined curvature. The air table 11 has a curvature in the direction perpendicular to a glass sheet carrying direction and typically has a convex upward shape. However, the air table 11 may have a convex downward shape, and the shape may be almost flat in order to obtain a flat-like tempered glass. Also, a roll or the like may be substituted for the air table 11 as the glass sheet carrying system. One feature of this apparatus is that the heating furnace 1 and the quenching apparatus 2 are located adjacent to each other because the apparatus does not require the press dies for putting a softened glass therebetween for forming. The heating furnace 1 and the quenching apparatus 2 are located as closely as possible in view of improving the strength of the glass sheet. Inside the quenching apparatus 2 located adjacent to the heating furnace 1, a plurality of quench modules 21 and 22 are provided from the upper and lower sides and oriented toward the glass sheet 3 carrying path. The glass sheet is tempered while being carried by cooling gas (typically cooling air) supplied from the quench modules 21 and 22. The shape of the quench modules 21 and 22 need not be limited to the shape as shown in Fig. 1. For example, the modules may have a tube-like shape. As shown in Fig. 1, in the first embodiment, the quench modules 22 above the glass sheet carrying path are provided at a more downstream position with respect to the glass sheet carrying direction than the quench modules 21 below the glass sheet carrying path. In other words, the most upstream module below the carrying path is positioned further upstream with respect to the carrying direction than the most upstream module above the carrying path. In order to improve the productivity, usually, a plurality of glass sheets are continuously supplied to the tempering apparatus. The glass sheets each are continuously heated in the heating furnace 1 to be bent, and carried from the heating furnace 1 to the quenching apparatus 2 to be tempered by quenching in the quenching apparatus 2. In order to treat the glass sheets continuously carried, usually, the cooling gas is continuously discharged in the quenching apparatus 2. In the apparatus shown in Fig. 1, the cooling gas from the quench modules 21 and 22 is continuously discharged as well. Therefore, the glass sheet 3 carried out from the heating furnace 1 is further carried in the quenching apparatus 2, where cooling is first started with respect to only the lower surface of the glass sheet 3 by the cooling gas discharged upward from the quench modules 21. Then cooling is started with respect to the upper surface of the glass sheet 3 by the cooling gas discharged downward from the quench modules 22, so that the upper and lower surfaces of the glass sheet are quenched. The starting points of the cooling for the upper and lower surfaces of the glass sheet are thus different from each other. Such a timelag makes the coefficients of contraction for the surfaces of the glass sheet different from each other. Therefore, the glass sheet is formed to have a shape somewhat different from that at the time the glass sheet was carried out from the heating furnace, where the glass sheet is bent by conforming to the shape of the air table 11. For example, for forming a glass sheet having a convex upward shape and when the lower surface of the glass sheet was cooled before the upper surface as shown in Fig. 1, the glass sheet is bent less than when it was carried out from the heating furnace. By such a timelag in the start of cooling for the upper and lower surfaces of the glass, the degree of freedom for bending a glass sheet can be increased. The glass sheet preferably has a temperature around its softening point when it is carried out from the heating furnace. By blowing a cooling gas only on one surface of the glass sheet, the temperature of that surface decreases preceding that of the other surface, so that the temperature of the surface decreases to the softening point of the glass sheet or lower, preferably to the strain point of the glass sheet or lower, before blowing a cooling gas on the other surface of the glass sheet. Also, the glass sheet more preferably has a temperature between its strain point and its softening point when it is carried out from the heating furnace. Furthermore, in the apparatus shown in Fig. 1, a ring roller 7 is provided above the glass carrying path. The ring roller 7 serves to prevent the glass sheet being carried from being lifted too high by the cooling gas blown from only the quench modules 21. With the ring roller 7, the glass sheet can be carried stably. The ring roller functions effectively when the quench modules on one side are positioned rearward by a certain distance or longer. This distance depends on the weight of the glass sheet to be carried, the carrying speed, and the like. For a typical automobile side glass, it is preferable to provide the ring roller 7 when the distance for cooling by only the modules on one side is longer than 40 mm. The ring roller is convenient for supporting the surface of the glass sheet. However, the supporting need not be limited to the ring roller. For example, heated gas such as hot air can be used. When using a support such as rollers, it is preferable to provide this support in a position opposing the quench module provided on the most upstream side of the glass carrying path because the position is effective for maintaining the attitude of the glass sheet well. However, the number of the supports such as rollers need not be limited to one as shown in Fig. 1. A plurality of the supports may be provided as required. In order to implement the method of the present invention, in the apparatus shown in Fig. 1, the quenching apparatus above the glass sheet carrying path is positioned rearward on the glass sheet carrying downstream side. Instead of positioning the apparatus rearwardly, a padding may be stuffed into the quench module 22 located within a predetermined distance from the most upstream position to prevent a cooling gas from discharging. In the apparatus shown in Fig. 2, the quenching apparatus on the lower side of the glass sheet carrying path is positioned rearward on the carrying downstream side, contrary to the apparatus shown in Fig. 1, so that the upper surface of the glass sheet carried out from the heating furnace is cooled before the lower surface is begun to be cooled. When the upper surface of the glass sheet is cooled earlier than the lower in forming a glass sheet having a convex upward shape, the glass sheet can be further bent than when it was carried out from the heating furnace. Fig. 3 shows a cross-sectional view of an example of the apparatus of the present invention. In a heating furnace 1, an air table 11 is provided for carrying a glass sheet. The air table 11 has a number of nozzle holes, and the heated air blown off from these nozzle holes jets on the lower surface of a glass sheet, supporting and carrying the glass sheet. The hot air 12 serves to carry the glass sheet while floating it and to soften the glass sheet by heating. The bent glass sheet is heated to a temperature range around its softening point (preferably between its strain point and its softening point) to have a constant curvature along the shape of the surface of the air table due to its self-weight. The air table 11 typically has a curvature in the direction perpendicular to a glass sheet carrying direction and has a convex upward shape. However, the air table 11 may have a convex downward shape. Also, a roll or the like may be substituted for the air table 11 as the glass sheet carrying system. Inside a quenching apparatus 2 located on the carrying downstream side adjacent to the heating furnace 1, a plurality of quench modules 21 and 22 are provided from the upper and lower sides toward the glass sheet carrying path. The glass sheet is tempered by quenching while being carried by cooling gas (typically cooling air) 31 and 32 supplied from the quench modules 21 and 22. The shape of the quench modules 21 and 22 need not be limited to the shape as shown in Fig. 3. For example, the modules may have a tube-like shape. Also, the heating furnace 1 and the quenching apparatus 2 preferably are located as closely as possible in view of improving the strength of the glass sheet. The cooling gas supplied from the quench modules 21 and 22 is mainly released through cooling gas discharge paths 23 and 24. The cooling gas discharge paths 23 and 24 usually have a capacity sufficient for releasing the cooling gas. In the manufacturing apparatus shown in Fig. 3, exhaust path restriction devices 4 are located in a part of the cooling gas discharge paths, so that, in a section 5 where the restriction devices 4 are located, the discharge of the cooling gas 31 is partially restricted. In the portion where the discharge of the cooling gas 31 is restricted, the static pressure of the gas on the surface of the glass sheet increases. Fig. 4 shows a perspective view of the quench modules 21, in the section 5 where the exhaust path restriction device 4 is placed. As shown in Fig. 4, a slit-like space extending in the direction of the width of the glass carrying path (a horizontal direction perpendicular to the glass carrying direction) is provided between the quench modules 21 as the exhaust inlet to the cooling gas discharge path 23. The exhaust path restriction device 4 is located below and close to the exhaust inlet 25, restricting the release of the cooling gas 31 discharged from the quench module 21. Also, the restriction device 4 may be provided on a more downstream side of the discharge path 23. However, the restriction device 4 is preferably located near the exhaust inlet 25 to obtain a static pressure distribution that effectively affects the shape of the glass sheet. Fig. 5 shows a plan view of the area around the section 5, where the exhaust path restriction device 4 is placed. In Fig.5, the glass sheet 3 is moved further upstream than in Fig. 3 for easiness of illustration, which is common to Fig. 6. As shown in Fig. 5, the exhaust path restriction device 4 is placed in a part of the width in the direction of the width of the glass carrying path (the central portion in Fig. 5) rather than all the width, restricting the discharge of the cooling gas in that portion. Therefore, a static pressure having a nonuniform distribution in the direction of the width of the glass carrying path is provided to the lower surface of the glass sheet passing through the section 5 where the restriction device 4 is located. By thus partially restricting the discharge of the cooling gas in the quenching apparatus, the static pressure having a nonuniform distribution is provided to the surface of the glass sheet, and the shape of the glass sheet can be modified by this static pressure. In other words, according to the location of the restriction device 4 shown in Fig. 5, the static pressure on the lower surface of the glass sheet is higher in the central portion of the carrying path, so that this portion of the glass sheet is raised upward. Therefore, a glass sheet bent to have a convex upward shape can be controlled so that the curvature of its central portion is lowered. The location of the exhaust path restriction device 4 need not be limited to the location shown in Fig. 5. For example, the restriction device 4 may be placed near the edge portions of the glass sheet to be carried as shown in Fig. 6. In this case, the static pressure on the lower surface of the edge portions of the glass sheet is higher, and therefore the glass sheet bent to have a convex upward shape is deformed so that the curvature of the edge portions is raised. The material and the shape of the exhaust path restriction device 4 need not be limited to a specific material and shape as long as the restriction device functions as the exhaust obstacle in the cooling gas discharge paths 23 and 24. Any suitable material such as metal materials, resin materials, or inorganic materials can be used. Also, the shape of the restriction device need not be limited to the shape having a circular cross-section as shown in Figs. 1 and 2, and the shape need not be limited to a rod shape. Any shape such as sheet-like shape, lump-like shape, or pipe-like shape can be used. Also, the restriction device 4 may be located over the entire length of the carrying path of the quenching apparatus 2, or the restriction device may be located in at least one of the sections provided by dividing the carrying path in the direction of its length. However, it is preferred that the restriction device 4 is at least placed near the glass sheet carrying inlet of the quenching apparatus 2 as shown in Fig. 5 as described above. Next, a specific example of the exhaust path restriction device 4 will be described. Fig. 7 shows a cross-sectional view of the glass carrying path and its vicinity in the quenching apparatus seen from the glass carrying upstream side toward the downstream side, in which an exhaust valve 41, an example of the exhaust path restriction device 4, is placed in the central portion of the glass carrying path. The valve 41 has a structure in which two rods 42 are connected via a shaft portion 43. The rods 42 extending like a wing on both sides of the shaft portion 43 can be rotated around the shaft portion 43 by remote operation so that the restriction of the exhaust path 23 is controlled by the rotation of the rods 42. By locating the shaft portion 43 in the position being substantially in contact with the lower portion of the quench module 21 as shown in Fig. 7, the exhaust valve 41 can function so that the restriction of the exhaust path caused by the rotation of the rods 42 is at the maximum near the shaft portion 43 and is gradually released as being away from the shaft portion 43. Therefore, by locating the shaft portion 43 in the central portion of the carrying path, the restriction is gradually released as approaching the edge portions of the carrying path. Such an exhaust valve 41 is excellent because it can provide a smooth static pressure distribution to the glass sheet. Also, if the static pressure distribution is changed by adjusting the angle of the rods 42 by remote control while one glass sheet passes, the curvatures in the front end portion and the back end portion of the glass sheet in its carrying direction can be changed, and furthermore, the curvature can be provided in the carrying direction. The shape of the exhaust valve 41 need not be limited to the shape shown in Fig. 7. For example, the rods 42 may be extended over the entire width in the direction of the width of the carrying path, being curved along the quench module 21, or they may be further extended. Also, other shapes such as sheet, rather than the rods 42, may be used. Thus, an exhaust path restriction device 4 preferably comprises an arm member and a shaft member connected to one end of the arm member. The exhaust path also can be restricted by providing a padding member for inhibiting the outflow of the cooling gas in part of the exhaust path inlet 25. In other words, by providing the padding member in part of the exhaust inlet in the direction of the width of the carrying path, a nonuniform static pressure distribution can be provided to the glass sheet in a manner similar to that of the above exhaust valve 41. This method is convenient and preferred especially when the restriction of the exhaust path need not be changed. In this case, rubber tubes, roll-like glass fabrics, or the like can be preferably used for the padding member. (Forth Embodiment) Next, an embodiment in which static pressure distributions are provided to both surfaces of a glass sheet will be described. Fig. 8 shows a cross-sectional view of the glass carrying path and its vicinity in the quenching apparatus seen from the glass carrying upstream side toward the downstream side, similar to that of Fig. 7. The carrying path is divided into three regions in the direction of its width (left portions 61a and 62a, central portions 61b and 62b, and right portions 61c and 62c). The static pressures can be controlled individually in each region or in each surface of the glass sheet by exhaust path restriction devices as described above. When providing distributions to the static pressures on both surfaces of the glass sheet, it is preferred that the static pressure distributions on both surfaces are controlled so that the deformation of a glass sheet by one distribution can be encouraged by the other distribution. More specifically, when further bending the glass sheet that is formed to have a convex upward shape, the static pressures on the portions corresponding to the lower surface of the glass central portion 61b and the upper surfaces of the glass end portions 62a and 62c are set higher so that the actions on the static pressure distributions of the upper and lower surfaces can provide a desired shape effectively. On the other hand, when reducing the curvature of a glass sheet that is formed to have a convex upward shape, to bend it less, the static pressures on the portions corresponding to the upper surface of the central portion 62b and the lower surfaces of the glass end portions 61a and 61c should be set higher. The method for providing distributions to the static pressures on both surfaces of the glass sheet provides a higher degree of freedom for formation than the method for providing a static pressure only to one surface of the glass sheet. Also, this method provides excellent stability in carrying a glass sheet when greatly modifying the shape of the glass sheet. In the embodiments of the present invention as described above, attention should be given to the fact that the quenching of the glass sheet is reduced by a partial rise in static pressure. Therefore, the static pressure is preferably controlled to satisfy the thermal conductivity for the required quenching determined by the thickness of the glass sheet, a predetermined strength, and the like. EXAMPLE Next, specific examples in which the shape of a bent and tempered glass sheet is modified by the method of utilizing a static pressure distribution will be described. (Example 1) A green glass sheet having a thickness of 3.1 mm and a rectangular shape of 500 mm by 600 mm was supplied to an apparatus for bending and tempering a glass sheet conventionally used as shown in Fig. 12 so that the short side having a length of 500 mm was in the direction of the width of the glass carrying path. As a result, a bent and tempered glass sheet of a convex upward shape having a uniform curvature of 1300 mm was obtained. This curvature was equal to that provided to the air table near the glass carrying outlet of the heating furnace and to the glass carrying path in the quenching apparatus. Next, exhaust valves 41 were provided in the lower center of the carrying path in the quenching apparatus in a manner similar to that shown in Fig. 7 to partially modify the curvature of the glass sheet. The length of the exhaust valve 41 in the direction of the width of the carrying path (41a in Fig. 7) was 100 mm, corresponding to 20% of the width of the glass sheet (3a in Fig. 7). Rods 42 were positioned so that the restriction of the exhaust was reduced as approaching the end portions from the central portion. The exhaust valves were placed in the exhaust inlets of the quenching apparatus, in the first to the fourth rows on the most upstream for carrying the glass sheet, in a manner similar to that shown in Fig. 5. The same glass sheet as the above was thus supplied to the apparatus. As a result, a bent and tempered glass sheet whose edge portions have a curvature of 1300 mm and whose central portion has a curvature of 1100 mm was obtained. The curvature of the obtained glass was smoothly changed as a whole rather than being changed only in the portion, as shown in Fig. 10. (Example 2) As shown in Fig. 9, exhaust valves 41 were placed at the edge portions of the lower portion of the carrying path so that approximately half the length of the exhaust valve (about 50 mm) overlapped the region for passage of a glass sheet 3. Also, the exhaust valves 41 were provided in the exhaust inlets of the quenching apparatus, in the first to the sixth rows on the most upstream position for carrying the glass sheet, in a manner similar to that shown in Fig. 6. A glass sheet was supplied to the apparatus in a manner similar to that of Example 1, except for the above manner. As a result, a bent and tempered glass sheet whose edge portions have a curvature of 1500 mm and whose central portion has a curvature of 1300 mm was obtained. The curvature of this glass sheet was smoothly changed as shown in Fig. 11. (Example 3) Exhaust valves 41 were located in a similar manner to that of Example 1, and the restriction of the exhaust valve 41 was changed by remote operation while one glass sheet passed. As a result, a two-dimensionally bent glass sheet, whose central portion has a lower curvature where the exhaust path was restricted and that has a substantially uniform curvature where the exhaust path was open, was obtained.

Claims: A method for manufacturing a bent and tempered glass sheet, the method comprising: bending a glass sheet (3) having a first surface and a second surface utilizing the weight of the glass sheet while heating and passing the glass sheet through a heating furnace (1); and quenching the glass sheet while carrying the glass sheet by blowing a cooling gas onto the first and second surfaces of the glass sheet in a quenching apparatus (2) adjacent to the heating furnace; characterised in that , in the quenching apparatus the cooling gas is blown onto the first surface so as to lower the temperature of the first surface to the softening point of the glass sheet or less before the cooling gas begins to be blown onto the second surface. A method as claimed in claim 1, wherein the cooling gas is blown onto the first surface while the second surface is supported before the cooling gas begins to be blown onto the second surface. A method for manufacturing a bent and tempered glass sheet, the method comprising: bending a glass sheet (3) having a first surface and a second surface utilizing weight of the glass sheet while heating and passing the glass sheet through a heating furnace (1), and quenching the glass sheet while carrying the glass sheet by blowing a cooling gas onto the first and second surfaces of the glass sheet in a quenching apparatus (2) adjacent to the heating furnace; characterised in that the cooling gas provides a nonuniform distribution of static pressure over at least one of the first and second surfaces in at least one section in the quenching apparatus so that the shape of the glass sheet is modified from the shape obtained by bending utilizing the weight of the glass sheet. A method as claimed in claim 3, wherein the distribution of the static pressure is provided by partially controlling exhausting of the cooling gas. A method as claimed in claim 4, wherein the exhausting of the cooling gas is partially controlled by an exhaust path restriction (4) provided in an exhaust path for the cooling gas. A method as claimed in any one of claims 3 to 5, wherein a static pressure having a distribution that facilitates the deformation of the glass sheet (3) caused by the distribution of the static pressure on the first surface of the glass sheet is applied to the second surface of the glass sheet. A method as claimed in any one of claims 3 to 5, wherein the distribution of the static pressure is provided only to a static pressure applied to a lower surface of the glass sheet (3). A method as claimed in any one of claims 3 to 7, wherein the said section is provided in the vicinity of a glass sheet carrying inlet of the quenching apparatus (2). A method as claimed in any one of claims 3 to 8, wherein the distribution of the static pressure is changed while one glass sheet (3) is passing through the section. An apparatus for manufacturing a bent and tempered glass sheet (3) comprising: a heating furnace (1) for heating a glass sheet and comprising a glass sheet carrying outlet; a quenching apparatus (2) comprising a glass sheet carrying inlet adjacent to the glass sheet carrying outlet of the heating furnace, and a cooling gas blowing system located on upper and lower sides of a glass sheet carrying path for discharging a cooling gas into the glass sheet carrying path; and a glass sheet carrying system having a curvature in a direction substantially perpendicular to a glass sheet carrying direction for carrying a glass sheet to the quenching apparatus through the heating furnace; characterised in that the quenching apparatus is provided with an exhaust path restriction (4) for providing a nonuniform distribution of static pressure over at least one surface of the glass sheet in at least one section in the quenching apparatus. An apparatus as claimed in claim 10, wherein the exhaust path restriction (4) has a shaft member (43) and an arm member (42) having one end connected to the shaft member and which can be adjusted in use to vary the extent to which the exhaust path is restricted.

Inventors: FUTAGAMI TORU, SHINOZAKI KAZUSHI, TAKIMURA MAMORU, YABUNO TAKESHI, YOSHIZAWA HIDEO, FUTAGAMI, TORU, SHINOZAKI, KAZUSHI, TAKIMURA, MAMORU, YABUNO, TAKESHI, YOSHIZAWA, HIDEO
Applicants: NIPPON SHEET GLASS CO LTD, NIPPON SHEET GLASS CO., LTD.
Application year: 1998
Main classification: C03B23
IPC codes: C03B23, C03B27