Method for manufacturing tempered glass sheet and apparatus for manufacturing the same

Abstract: A gas is supplied to the surface of the glass sheet transferred between a heating furnace and a cooling apparatus for tempering the glass sheet. The gas is supplied from the upstream side with respect to the direction of transfer of the glass sheet by an air curtain device. This gas runs along the glass sheet surface (upper surface) downstream with respect to the direction of transfer to obstruct the flow of cooling gas from the cooling apparatus in the upstream direction. The gas prevents cooling air from the cooling apparatus from invading the heating furnace so that the difference of the curvature of the glass sheet on the front and rear part can be eliminated.

Description: This invention relates to a method for manufacturing a tempered glass sheet and an apparatus thereof. More particularly, this invention relates to a method and an apparatus for manufacturing a tempered glass sheet useful for architecture, automobiles or the like. As the window glass sheet for architecture or automobile, a tempered glass sheet is extensively used as a safety glass sheet. As a method for manufacturing a tempered glass sheet, there is extensively practiced an air-cooling method of quickly cooling the glass sheet that has been heated to a temperature near the softening point to form a compressive stress layer in the surface of the glass sheet. In view of the design and aerodynamic characteristics of automobiles, there are great demands for curved window glass sheets. Accordingly, in the air-cooling method the heated glass sheet is often formed into a curved shape before the glass sheet is cooled to temper. The method for bending a glass sheet includes a method of pressing a glass sheet suspended by a tong (a glass-suspender) with a pair of convex and concave press molds, and a method of pressing a glass sheet that has been transferred horizontally from a heating furnace with a pair of upper and lower press molds. In the bending methods involving pressing with molds, the step of heating a glass sheet and the step of bending the glass sheet are basically taken as independent steps. However, there is proposed a method to practice the two steps as a single step. In such a method the glass sheet transferring means such as rolls or beds are provided in the heating furnace with a predetermined curvature, so that the heated glass sheet is gradually bent down by its own weight until it constitutes a curved surface having the curvature. The bent glass transferred to the cooling apparatus adjacent to the heating furnace is cooled into a tempered glass sheet. This method is excellent in the point that there is no necessity to press the glass sheet individually. In order to make use of this feature, various improvements on the method have been made for practical applications (e.g., Japanese Examined Patent Publications Nos. S44-14832/1969, S48-5242/1973, and Japanese Unexamined Patent Publication No. H7-237928/1995). However, the tempered glass sheet by the method tends to be formed into a shape different from what originally was expected. Typically, as shown in FIG. 3A, when a flat tempered glass sheet is expected, the rear end part of the glass sheet in the direction of transfer becomes convex, and as shown in FIG. 3B, when a curved glass sheet that should show a convex upward shape was expected, the rear end part shows a larger curvature than the front end part in the direction of transfer. Such a difference of curvature is caused mainly by the fact that the cooling air blown to the glass sheet in the cooling apparatus goes into the heating furnace. In other words, as shown in FIG. 4, when the glass sheet is transferred to the cooling apparatus, the cooling air blown to the upper surface of the front end part in the direction of transfer of the glass sheet runs along the surface of the glass sheet to the upstream side of transfer to go into the heating furnace. The cooling air lowers the temperature on the upper surface at the rear end part of the glass sheet before it reaches the cooling apparatus. On the other hand, the lowering of the temperature on the upper surface at the front end part of the glass sheet is not so remarkable as at the rear end part of the glass sheet, because the intrusion of the cooling air into the heating furnace becomes remarkable by the flow along the surface of the glass sheet, as shown in FIG. 4. As a result, at the rear end part of the glass sheet in the direction of transfer, the temperature variation range in cooling becomes greatly different between the upper and the lower surfaces of the glass sheet and the shrinkage amounts by cooling also show differences. Thus, there has been a phenomenon that the curvatures of the glass sheet become different between the front end part and the rear end part in the direction of transfer. In view of the above problem, in Japanese Utility Model Publication No. H4-41152/1992, there is proposed to dispose a heating device between the heating furnace and the cooling apparatus. According to the heating device, the inconvenience as referred to above can be alleviated by compensating the temperature difference on the surface of the glass sheet prior to it being transferred into the cooling apparatus. However, the method using the heating device necessitates heating a specified part of the glass sheet in the course of transferring it, so that the operation is not necessarily easy, and involves a problem to be overcome. US-A-4,886,540 discloses a method for manufacturing a tempered glass sheet, comprising the steps of: transferring a glass sheet heated in a heating furnace from the heating furnace to a cooling apparatus adjacent to the heating furnace, and cooling the glass sheet in the cooling apparatus with cooling air so as to temper the glass sheet, wherein gas is supplied onto an upper surface of the glass sheet transferred from the heating furnace to the cooling apparatus so that the gas supplied runs along the upper surface of the glass sheet in the downstream direction with respect to the transfer direction of glass sheet. It is an object of the present invention, at least in its preferred embodiments and in the light of the situation as described above, to provide a method and an apparatus for manufacturing a tempered glass sheet which can suppress simply and assuredly the difference of the curvatures of the glass sheet that result between the front end part and the rear end part in the direction of transport. The present invention is characterised over US-A-4,886,540 in that the glass sheet is supported by heated air supplied to a lower surface thereof while being transferred from the heating furnace to the cooling apparatus, and that the gas supplied to the upper surface of the glass sheet is heated and is supplied from within the heating furnace. According to the above methods, it is possible to suppress effectively the difference of the shape between the front end part and the rear end part in the direction of transfer of the glass sheet. This is because the cooling air from the cooling apparatus that tends to invade the heating furnace along the surface of the glass sheet is prevented from running in the direction of the heating furnace by the gas which is supplied to the surface of the glass sheet. From a further aspect the present invention provides an apparatus for manufacturing a tempered glass sheet, the apparatus comprising: a heating furnace for heating a glass sheet, the heating furnace having a transfer outlet for the glass sheet, a cooling apparatus for cooling the glass sheet with cooling air so as to temper the glass sheet, the cooling apparatus having a transfer inlet disposed to be adjacent the transfer outlet of the heating furnace, and gas blowing means arranged so as to supply gas onto an upper surface of the glass sheet which is being transferred from the heating furnace to the cooling apparatus and in the downstream direction with respect to the transfer direction of the glass sheet, characterised in that it further comprises carrying means for transferring the glass sheet from the heating furnace to the cooling apparatus through the transfer outlet and the transfer inlet, the carrying means supplying heated air to a lower surface of the glass sheet, and in that the gas blowing means are positioned in the heating furnace and supply heated gas onto the upper surface of the glass sheet. According to the apparatus for manufacturing a tempered glass sheet, it is possible to suppress effectively the difference of the curvatures between the front end part and the rear end part in the direction of transfer of the glass sheet and produce a tempered glass having a reduced difference from the expected configuration. This is because the cooling air from the cooling apparatus that tends to invade the heating furnace along the surface of the glass sheet is prevented from running in the direction of the heating furnace by the gas supplied to the surface of the glass sheet. Furthermore, according to this production apparatus, a partial difference of curvatures of the sheet glass can be suppressed simply and assuredly without requiring a large remodeling for the conventional apparatus already in use. Further, the invention has the advantage that a high temperature gas in the heating furnace is supplied to the glass sheet surface, and, when compared, for example, with the case of supplying a gas at about room temperature, it is possible to suppress the lowering of the temperature on the upper surface of the glass sheet before being carried to the cooling apparatus, and it becomes possible to alleviate the temperature difference per se on the upper and lower surfaces of the tempered glass sheet, and to improve the precision of forming the tempered glass sheet. Furthermore, in the method for manufacturing the tempered glass sheet as described above, it is preferable to subject the glass sheet to bend forming in the heating furnace. It is because the present invention method is particularly effective for improving the precision of shape of the bend tempered glass. This bend forming is preferably that made by utilizing the deformation of the heated glass sheet by own weight. Preferred embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings in which: FIG. 1 is a sectional view showing an embodiment of the production equipment of the present invention. FIG. 2 is a view showing an embodiment of the air curtain device to be used for the production equipment of the present invention. FIG. 3A is a perspective view showing a glass sheet that has different curvatures on the front and rear part in the direction of transfer, and FIG. 3B is a perspective view showing another glass sheet that has the different curvatures. FIG. 4 is a sectional view showing an embodiment of the production apparatus for the bent and tempered glass sheet in conventional use. FIG. 1 is a sectional view showing an example of the glass sheet tempering apparatus of the present invention. In the heating furnace 1, there is provided an air table 11 as the means for transferring a glass sheet. This air table 11 has a large number of nozzle holes, so that the heated air blown out from the nozzle holes jets out to the lower surface of the glass sheet to support the glass sheet for transfer. This hot air 12 takes part in transferring the glass sheet while floating and in heating the glass sheet to soften it. The glass sheet to be bend-formed is heated to a temperature range in the vicinity of the softening point (preferably at more than the stress point and lower than the softening point) to have a certain curvature along the surface configuration of the air table under dead weight. The air table typically has a curvature in a direction perpendicular to the direction of transfer of the glass sheet and is shaped to be convex upward, but it may have a shape to be convex downward, and the desired tempered glass may be a flat sheet form if the objective tempered glass is a flat sheet. Alternatively, a roll or the like may be used in place of the air table 11, as the means for transferring the glass sheet. The transfer outlet of the heating furnace is preferably slightly larger than the thickness of the glass sheet, in consideration of the heating efficiency and entry of external air into the heating furnace. In practice, it is required to secure a space to a degree that the contact of the heated glass sheet can be prevented. The space defined by the transfer outlet is divided into the upper and lower spaces by the glass sheet while it passes through the outlet. Of these spaces, what provides the problem in the entry of the cooling air is a space on the upper part of the glass sheet. The space underneath the glass sheet is narrow under the effect of the dead weight of the glass sheet, and in addition, as the air which blows out from the air table plays the role of the air curtain, the entry of the cooling air is substantially of no problem. Inside the cooling apparatus 2 installed on the downstream side of transfer adjacent to the heating furnace 1, there are disposed a plurality of quench modules 21, 22 directed towards the glass sheet transfer route from upper and lower positions. By the air (typically, cooling air) supplied from these quench modules 21, 22, the glass sheet is quenched and tempered while being transferred. The quench modules 21, 22 are not limited to be of the configurations shown in FIG. 1 but may be tubular or the like. From the viewpoint of improving the glass sheet strength, the heating furnace 1 and the cooling apparatus 2 are preferably disposed nearby each other. Above the glass sheet transfer route within the heating furnace 1, there is installed an air curtain device 3. This air curtain device 3 is, as shown in FIG. 2, preferably a hollow pipe having a plurality of nozzle holes 31 arranged in a row in the lengthwise direction (the widthwise direction with respect to the glass sheet). Of course, the gas discharge port of the air curtain device 3 need not necessarily be plural nozzle holes independent from one another but may be a slit which extends in the lengthwise direction. The air curtain device 3 may have a circular or elliptical cross section as shown in FIG. 2, but without specially limitation, and the section may be other shapes such as rectangular. Each nozzle hole 31 is disposed so that the gas can be discharged obliquely downward in a downstream direction with respect to the transfer of the glass sheet. Each nozzle hole 31 is preferably disposed to jet out a gas in the direction inclined obliquely downward in the downstream direction with an inclination in the range of 30 to 60 degrees from vertical. According to this preferred embodiment, the gas running downstream on the glass sheet surface in the direction of transfer of the glass sheet can be supplied in a stabilized state. Furthermore, as shown in FIG. 2, if the glass sheet is bend-formed in a heating furnace, it is preferable for the air curtain device 3 to have a corresponding configuration, preferably for example an upwardly curved convex shape as shown in FIG. 2. The position for setting the air curtain device 3 is preferably at a height of 10 mm - 120 mm from the upper surface of the glass sheet. According to this preferred embodiment, there is no apprehension for the air curtain device 3 to come into contact with the softened glass sheet, and yet the intrusion of the cooling air into the heating furnace from the cooling apparatus can be effectively suppressed. The hole diameter of the nozzle holes 31 of the air curtain device 3 is preferably 1.0 - 2.0 mm, and the pitch of the nozzle holes is preferably 10 mm-20 mm. According to these preferred examples, entry of the cooling air blown at high pressure can be securely prevented by the "air curtain" formed by the gas jetting out from the nozzle holes. Further, the gas blown out from the air curtain device 3 is to be supplied to the upper surface of the glass sheet while involving the high temperature gas in the heating furnace. Accordingly, when a gas is supplied from the air curtain device 3 by the apparatus shown in FIG. 1, intrusion of the cooling air into the heating furnace is suppressed, and the lowering of temperature on the upper surface of the glass sheet by the supplied gas is also suppressed and the temperature difference between the upper and the lower surfaces of the glass sheet becomes smaller than if cooler air were used. Since the temperature difference between the upper and the lower surfaces of the glass sheet to be transferred into the cooling apparatus gives differences in shrinkage rate between the upper and the lower surfaces, the use of heated gas is advantageous from the viewpoint of forming the glass sheet to a predetermined shape (shape formed in the heating furnace). Next, an example of the method for manufacturing the tempered glass sheet using this apparatus is explained. The glass sheet which is heated in the heating furnace 1 and bend-formed by utilizing the dead weight of the glass sheet is passed through the glass transfer outlet of the heating furnace 1 and transferred to the cooling apparatus. When the front end part of the transferred glass sheet approaches the cooling apparatus 2 and cooling air from the cooling modules 21, 22 comes to be blown onto the surface of the front end part, the cooling air tends to run upstream with respect to the direction of transfer along the upper surface of the glass sheet. However, as the gas from the air curtain device 3 has already been supplied to the upper surface of the glass sheet and said gas has run to the downstream side with respect to the transfer direction along the upper surface of the glass sheet, the flow of the cooling air to the upstream side is obstructed, and the intrusion of the cooling air into the inside of the heating furnace is suppressed. Ordinarily, in order to improve productivity, a plurality of glass sheets are continuously supplied to the tempering apparatus, and the respective sheet is bend-formed according to necessity, and transferred from the heating furnace 1 to the cooling apparatus 2, in which it is quenched to be tempered. In order to meet the glass sheet which comes to be continuously transferred, cooling air is continuously supplied in the cooling apparatus 2. Accordingly, it is desirable for the gas from the air curtain device 3 to be continuously supplied. Moreover, in order to suppress effectively the intrusion of the outside gas into the heating furnace, the discharge pressure of the gas supplied from the air curtain device 3 can be 0.02 kg/cm 2 -3 kg/cm 2 . This is because, when the discharge pressure is too low, it becomes difficult to obstruct intrusion of cooling air, and when it is too high, there is an apprehension that the stabilized transfer of the glass sheet could be compromised. Especially, when the discharge pressure is increased, there is a likelihood for the discharge gas from the air curtain device 3 to cause springing up of the rear end of the glass sheet after passage of the glass sheet to hamper the stabilized transfer of the glass sheet. Therefore, when importance is attached to such a point, the discharge pressure of the gas is more preferably no more than 2 kgf/cm 2 . Further, in practicing the present invention method, as described above, ordinarily, during the transfer of a sheet of glass sheet from the heating furnace to the cooling apparatus, a gas is incessantly supplied to the glass sheet surface from the air curtain device. Alternatively, the gas may be jetted only to a predetermined portion in the glass by opening or closing the solenoid valve provided on the intermediate part of the piping for supply of gas to the air curtain device. According to this method, by positively utilizing the surface temperature decrease of the glass sheet by intrusion of the cooling air into the heating furnace or by blowing of gas, it becomes possible to give the intended curvature to the glass sheet in the transfer direction.

Claims: A method for manufacturing a tempered glass sheet, comprising the steps of: transferring a glass sheet (G) heated in a heating furnace (1) from the heating furnace to a cooling apparatus (2) adjacent to the heating furnace, and cooling the glass sheet in the cooling apparatus with cooling air so as to temper the glass sheet, wherein gas is supplied onto an upper surface of the glass sheet transferred from the heating furnace to the cooling apparatus so that the gas supplied runs along the upper surface of the glass sheet in the downstream direction with respect to the transfer direction of the glass sheet, characterised in that the glass sheet is supported by heated air (12) supplied to a lower surface thereof while being transferred from the heating furnace to the cooling apparatus, and that the gas supplied to the upper surface of the glass sheet is heated and is supplied from within the heating furnace. A method as claimed in claim 1, wherein the glass sheet is formed into a curved shape in the heating furnace due to the self-weight of the glass sheet. A method as claimed in claims 1 or 2, further comprising the step of heating the glass sheet nearly to the softening point thereof in the heating furnace. An apparatus for manufacturing a tempered glass sheet, the apparatus comprising: a heating furnace (1) for heating a glass sheet (G), the heating furnace having a transfer outlet for the glass sheet, a cooling apparatus (2) for cooling the glass sheet with cooling air so as to temper the glass sheet, the cooling apparatus having a transfer inlet disposed to be adjacent the transfer outlet of the heating furnace, and gas blowing means (3) arranged so as to supply gas onto an upper surface of the glass sheet which is being transferred from the heating furnace to the cooling apparatus and in the downstream direction with respect to the transfer direction of the glass sheet, characterised in that it further comprises: carrying means (11) for transferring the glass sheet from the heating furnace to the cooling apparatus through the transfer outlet and the transfer inlet, the carrying means supplying heated air to a lower surface of the glass sheet, and in that the gas blowing means are positioned in the heating furnace and supply heated gas onto the upper surface of the glass sheet. An apparatus as claimed in claim 4, wherein the carrying means (11) has a curved surface.

Inventors: FUJIOKA NORIHIRO, FUTAGAMI TORU, YOSHIZAWA HIDEO, FUJIOKA, NORIHIRO, FUTAGAMI, TORU, YOSHIZAWA, HIDEO, Fujioka, Norihiro, c/o Nippon Sheet Glass Co. Ltd., Futagami, Toru, c/o Nippon Sheet Glass Co., Ltd., YOSHIZAWA, HIDEO, C/O NIPPON SHEET GLASS CO., LTD.
Applicants: NIPPON SHEET GLASS CO LTD, NIPPON SHEET GLASS CO., LTD.
Application year: 1998
Main classification: C03B29
IPC codes: C03B27, C03B29, C03B23