HEAT TRANSFER METHOD IN A GLASS SHEET BENDING FURNACE AND BENDING FURNACE

Abstract: The invention relates to a heat transfer method in a glass sheet bending furnace as well as to a bending furnace for car­ rying out the method. The furnace in­ cludes a top array of successive heating sections (2) and a bottom array of suc­ cessive cooling sections (4). The glass sheets are placed upon bending moulds (6) supported by carrier wagons (5). Success­ ive wagons (5) are advanced on an upper conveyor track (7a) from one heating sec­ tion (2) to the next and, respectively, on a lower conveyor track (8a) from one cooling section (4) to the next. Heat is transferred from bent, hot glasses (HG) in cooling section (4) to non-bent, colder glasses (CG) in heating section (2) by means of sucking air from cooling section (4) and by blasting it into heating sec­ tion (4). Air is blasted on either side of glass sheet (CG) contained in heating section (2) and further on either side of glass sheet (HG) contained in cooling sec­ tion (4).

Description: The present invention relates to a heat transfer method in a glass sheet bending furnace, comprising a top array of successive heating sections and a bottom array of successive cooling sections, whereby the glass sheets are placed upon bending moulds supported by carrier wagons and the successive wagons are advanced on the top conveyor track from one heating section to the next and, correspondingly, on the bottom conveyor track from one cooling section to the next and heat is transferred from the bent, hot glasses and moulds in said cooling sections to the non-bent, colder glasses and moulds in said heating sections. The invention relates also to a glass sheet bending furnace for carrying out the method, said furnace comprising a top array of successive heating sections and a bottom array of successive cooling sections as well as, respectively, a top and a bottom conveyor track for the carrrier wagons of bending moulds. As for the prior art, reference is made to the Proprietor's US Patent 4 497 645 which discloses the intensification of heat transfer through the wagon floors. In this prior art method, the transfer of heat is effected by means of radiation and gravitational convection. FR-A-15 84 600 discloses a glass sheet bending furnace comprising a system of gas conduits disposed in the area of the furnace in which the bending is effected for controlling the bending temperature. Hot gas from an exterior source and a cold gas sucked from a cold area of the furnace are provided by means of the conduits. The bending temperature is controlled by mixing these two gases at different ratios. An object of the invention is to provide an improved heat transfer method for further intensifying the transfer of heat from hot glass to colder glass as well as from a hot mould to a colder mould. This object is achieved by the method of claim 1 and the bending furnace of claim 4. Thus, the invention can be used for accelerating the cooling rate of glass sheets to be cooled, for accelerating the heating rate of glass sheets to be heated, for more effective exploitation of the thermal energy of glass sheets to be cooled, for retrieving glass sheets from the furnace colder than heretofore and, in addition, the invention can accomplish a more uniform cooling rate and a more uniform heating rate for glass sheets. The invention will now be described in more detail with reference made to the accompanying drawings, in which fig. 1 shows a bending furnace schematically in a side view. Fig. 2 shows a cutaway perspective view of one section of a furnace, including a top heating section and a bottom cooling section. Fig. 3 shows a cross-section of a bending furnace and fig. 4 is a graph showing the glass sheet temperature as a function of time, the successive sections being separated by vertical lines. The rising curve represents heating on the upper track and the falling curve represents cooling on the lower track. The bending furnace shown in fig. 1 includes a top or upper array of successive heating sections 2 and a bottom or lower array of successive cooling sections 4. The arrows indicate the traveling path of glass sheets along an upper conveyor track 7 and a lower conveyor track 8. The first heating sections 2 are so-called preheating sections which are followed by actual heating sections and then by one or two bending sections 3. At least the preheating sections 2 along with cooling sections 4 therebelow consist of section units 1 as shown in fig. 2. The glass sheets are placed upon bending moulds 6 supported by carrier wagons 5 shown in fig. 3. The rails 5a of carrier wagons 5 are carried on top of upper track rollers 7a and, respectively, on top of lower track rollers 8a. The successive wagons 5 are advanced on upper conveyor track 7 from one heating section 2 to the next. Correspondingly, on lower conveyor track 8 said wagons 5 are advanced from one cooling section 4 to the next. Thus, heat is transferred from the bent, hot glasses HG in cooling sections 4 to non-bent, colder glasses CG in heating sections 2. In the solution disclosed in US Patent 4 497 645, the heat is transferred by means of radiation and gravitational convection. In this invention, the transfer of heat is intensified by means of the arrangement described hereinbelow. As shown in figs. 2 and 3, the ceiling and floors of heating section 2 as well as those of cooling section 4 are fitted with blast air supply boxes 13, 15, 16 provided with blast orifices 14, 17 which are distributed substantially over the entire surface area of the sections. Both side walls of cooling sections 4 are fitted with fans 11 whose suction inlets 10 open into the cooling section. The pressure sides of fans 11 are connected by air passages 12 to said supply boxes 13, 15, 16. The fans 11 are used for the continuous suction of air from cooling section 4, whereby a hot glass sheet HG delivers heat into said air upon cooling. From the blast orifices 14, 17 of supply boxes 13, 15, 16 the air discharges as substantially vertical blast jets to the top and bottom surfaces of glass sheet CG as well as to the top and bottom surfaces of glass sheet HG. The air coming into section 2 finds its way back into section 4 through the gaps between supply boxes 13. In order to maintain thermal equilibrieum, hot air is discharged from at least one section 2 and, respectively, at least one section 4 is supplied with cold replacement air which in the lengthwise direction of the furnace is distributed from one section 4 to another section 4. Most preferably, the cold replacement air is supplied into section 4a and some hot air is discharged from section 2a (fig. 1). The heat transfer arrangement of the invention is typically carried out e.g. in three heating sections (depending on furnace capacity) and respectively in as many of the last cooling sections 4. The temperature curve of fig. 4 illustrates a situation in which the intensified heat transfer has been effected in three successive sections, indicated with ordinal numbers I, II and III. The curve indicates that in sections I, II and III, i.e. on the rising section of the curve, the glass sheet temperature increasing rate is initially very high whereby the final temperature of the section is reached quickly or, alternatively, the glass sheet takes a longer time to reach the final temperature of the section. Accordingly, on the falling section of the curve, the cooling proceeds in cooling sections I, II and III in a manner that the temperature decreasing rate is very high at the beginning of each cooling cycle. By virtue of this, the glass coming out of the furnace has a temperature substantially lower than what it would have without the intensified heat transfer of the invention. The temperature difference is indicated in fig. 4 with ΔT. The invention serves also to increase production capacity in that the furnace will be able to operate on the maximum capacity determined on the basis of time required for bending a glass sheet in bending section 3 (fig. 1). Fig. 3 illustrates flat rails 5a which run alongside wagons 5 and which carry wagons 5 resting upon conveyor rollers 7a. The end walls 18 of wagons 5 provide partitions between successive sections 2, 2 or 4, 4 whenever said wagons 5 are stopped inside the sections. At the junctions between successive heating sections 2 there is provided a resilient sealing 19 which comes into contact with the edges of end walls 18 of the wagons and which is e.g. a brush made of artificial fibers and/or hair and which provides a barrier to the air flows between the successive sections. This makes it easier to maintain the temperature differences between successive heating sections 2. On the other hand, temperature differences between the superimposed sections should be equalized as effectively as possible according to the invention.

Claims: A heat transfer method in a glass sheet bending furnace, including a top array of successive heating sections (2) and a bottom array of successive cooling sections (4), whereby the glass sheets are placed upon bending molds (6) supported by carrier wagons (5) and successive wagons (5) are advanced on an upper conveyor track (7) from one heating section (2) to the next and, correspondingly, on a lower conveyor track (8) from one cooling section (4) to the next and heat is transferred from bent, hot glass (HG) in said cooling sections (4) to non-bent, cooler glasses (CG) in said heating sections (2), characterized in that in order to intensify said heat transfer, air is sucked from at least one cooling section (4) and blasted into the corresponding overlaying heating section (2) on either side of a glass sheet (CG) contained in said at least one heating section (2) and also back into the at least one cooling section on either side of a glass sheet (HG) contained in said at least one cooling section (4). A method as set forth in claim 1, characterized in that the substantially vertical blast jets are directed to the opposite surfaces of a glass sheet from the ceiling and floor of said sections (2, 4), said jets being distributed over substantially the entire surface of the sections. A method as set forth in claim 1 or 2, characterized in that the blast air is sucked from either side of said cooling sections (4). A glass sheet bending furnace for carrying out the methods set forth in any of claims 1 to 3, said furnace including a top array of successive heating sections (2) and a bottom array of successive cooling sections (4) and, respectively, an upper and a lower conveyor track (7 and 8) for carrier wagons (5) of bending molds (6), characterized in that between at least one cooling section (4) and a corresponding overlaying heating section (2) there is a system of air passages (12) provided with a fan (11) in a manner that a suction inlet (10) of the air passage system is provided in said at least one cooling section (4) for sucking air from said at least one cooling section, and air jet blast orifices (14, 17) are provided in the ceiling and floor of said corresponding heating section as well as in the ceiling and floor of said at least one cooling section (2) for blasting said air into both said at least one heating section and said at least one cooling section. A furnace as set forth in claim 4, characterized in that the ceiling and floor of each heating section (2), as well as those of each cooling section (4), are fitted with blast air supply boxes (13, 15, 16) provided with said blast orifices (14, 17) which are distributed over substantially the entire surface area of the sections. A furnace as set forth in claim 4 or 5, characterized in that said fans (11), along with said suction inlets (10) thereof, are located on both side walls of said cooling sections (4). A furnace as set forth in any of claims 4 to 6, characterized in that the end walls (18) of said wagons (5) provide partitions between successive sections (2,2 or 4,4), wherein at the junctions between successive sections there is provided a resilient sealing (19) which comes into contact with the edges of said end walls (18) of the wagons and which provides a barrier to the air flow between successive sections whenever said carrier wagons (5) are stopped inside the sections.

Inventors: PELTONEN, ESKO JUHANI
Applicants: TAMGLASS ENGINEERING OY
Application year: 1989
Main classification: C03B25
IPC codes: C03B29, C03B23, C03B35, C03B25