Method and apparatus for bending and tempering glass sheets

Abstract: The invention relates to a method and apparatus for bending and tempering glass sheets. The apparatus comprises an arch-bendable roll conveyor and upper and lower tempering boxes (7, 5) including tempering orifices (8, 6). The conveyor includes individual rolls (4) which consist of two or more sections (4a, 4b) or are flexible, such that the mid-section of said rolls (4) can be deflected to a lower level than the ends thereof. Upper press rollers (11) are simultaneously pressed downwards by means of pneumatic cylinders (17). The press rollers (11) can be provided with a desired zonewise pressing force for producing a desired double bending.

Description: The present invention relates to a method of the type defined in the preamble of the annexed claim 1 for bending and tempering glass sheets. The invention relates also to a glass-sheet bending and tempering apparatus capable of implementing the method, comprising a roll conveyor whose rolls have a relative vertical position which is adjustable for arching the conveyor to a curvature matching a desired degree of bending around a bending axis which is transverse to the advancing direction of glass sheets or parallel to the rolls, lower tempering boxes having top surfaces provided with tempering orifices, and upper tempering boxes having bottom surfaces provided with tempering orifices, said tempering boxes being movable for bringing said top and bottom surfaces to comply with the arching of the conveyor. This type of apparatus is prior known from the Applicant's Patent publications US-4,881,962 and US-5,057,137. This apparatus has proved highly useful in the production of bent and tempered construction glass. In this prior known apparatus, the bending of a glass sheet is based on gravitational deflection within a bending and tempering station outside a heating furnace. For this reason it is sometimes necessary to overheat the glass relative to a required tempering temperature as the glass temperature falls before the glass has completely bent to its desired configuration and the glass tempering can be commenced. Depending on the glass types and conditions, the cooling of glass is typically in the order of 10°C - 25°C. A characterizing feature for this so-called overheating in that the optical errors of glass are accentuated and are more perceivable in the end product. In addition, a limitation in this prior known method and apparatus is that a glass sheet can only be bent or deflected relative to a single axis of curvature. Furthermore, there is known from US 5443609 a bending and tempering station for glass sheets comprising an archable roll conveyor and upper and lower tempering boxes provided with tempering orifices. The upper tempering boxes are fitted with a number of press rollers having a top rest position and a bottom working position. The rollers are capable of moving against the force of a pneumatic spring from the working position towards the rest position. Said conventional glass processing station however merely allows to carry out a simple bending (single curvature). From US Patent 4,773,925 there is known an adjustable roll forming arrangement for shaping heat softened glass sheets. Said prior art reference discloses complex bending (double curvature) in a continuous press-roller bending station having i.a., lower rolls whose mid section deflect downwards and a pair of upper press rollers and furthermore having a separate subsequent station with lower rolls. An object of the invention is to improve the above known method and apparatus such that glass can be bent to produce a double curvature and, in addition, said harmful overheating can be eliminated from the process for reducing the temperature of glass coming out of a furnace and for improving the glass optics. Regarding the method, this object is achieved by the invention on the basis of the characterizing features in combination with those of the preamble set forth in the annexed claim 1 and, as for the apparatus, on the basis of those set forth in the annexed claim 5. Preferred embodiments of the invention are disclosed in dependent claims 2-4 and 6-11. When adjustable press rollers are included above the glass, the gravitational bending is converted into mechanical press bending. When the glass is also supported on the rolls of an arched roll conveyor, with the mid-section of said rolls at a lower level than the ends thereof, the bending will be achieved around two axes perpendicular to each other and, in addition, the glass sheet will have a bent shape with improved precision as the bending can be controlled and forced to a desired shape. The bending of glass with a set of upper and lower rollers in a combined bending and tempering station has already been proposed in the Patent publication US-4,822,398. According to that, however, the bending is solely effected around a bending axis parallel to the advancing direction of a glass sheet. A double curvature cannot be achieved and, in addition, the rather small radii of curvature cause optical problems due to the fact that the rolls responsive to either surface of the glass during the course of bending shift laterally relative to the glass, i.e. slide along the glass surface in the direction transverse to the advancing direction. This makes it difficult to fulfil the requirement for a high optical quality. In the present invention, the bending with a smaller radius of curvature can be selected around an axis transverse to the advancing direction. The flexible suspension of press rolls and the press force adjustable during the course of bending enable the adaptation of the invention to benders in which the bending is effected around axes both transverse and parallel to the advancing direction. One way of implementing the invention will now be described in more detail with reference made to the accompanying drawings, in which fig. 1 shows a section of a bending and tempering station in a side view; fig. 2A shows schematically the transfer of a glass sheet from a furnace into a bending and tempering station and fig. 2B shows schematically the position of rolls and rollers after the glass sheet has progressed into the bending and tempering station; fig. 3 shows a schematic side view of a bending and tempering station during a bending operation; fig. 4 is a plan view of the arrangement of press rollers; fig. 5 shows a glass sheet included in a bending and tempering station between the press rollers and a roll conveyor prior to a bending operation; fig. 6 shows the same as fig. 5 but during or after the bending operation; and fig. 7 is a perspective view showing a glass sheet bent in two directions and the position of press rollers and deflected rolls included in an arched conveyor. Downstream of a furnace 1 lies a bending and tempering station 2 provided with a conveyor 3 consisting of rolls 4. Below a glass sheet carried by the rolls 4 are tempering boxes 5 and thereabove are tempering boxes 7. The tempering boxes 5 have top surfaces 9 provided with nozzle orifices 6 and the tempering boxes 7 have bottom surfaces 10 provided with nozzle orifices 8. Nozzles enclosed in the tempering boxes 5 and 7 are not shown and the design and configuration thereof can be varied in many ways. As disclosed in more detail in U.S. Pat. No. 4,881,962 and U.S. Pat. No. 5,057,137, the conveyor 3 can be arched to a curvature corresponding to a degree of bending desired for the glass. This can be effected by any mechanism capable of moving the rolls 4 relative to each other in vertical direction. The nozzle boxes 5 and 7 are adapted to be movable in a corresponding manner, such that the upper and lower array of boxes have a curvature matching that of the conveyor 3. Thus, the box surfaces 9 and 10 maintain essentially the same distance from the glass surface, whereby the glass sheets can be tempered effectively and uniformly irrespective of their degree of bending. The major curvature (with a minor radius of curvature) of a double curvature is produced by arching the conveyor and the minor curvature (with a major radius of curvature) is produced by deflecting or arching the rolls 4, 4', as shown in figs. 5-7, such that the mid-section of the rolls shifts to a lower level than the ends thereof. The production of such a double curvature requires a particularly adjustable mechanical pressing from above. The upper tempering boxes 7 are fitted with a number of press rollers 11, each being adapted to be individually movable by means of a pneumatic cylinder 17 between an upper rest position and a lower working position. The axially short and lightweight rollers 11 are journalled onto a stub axle 13 which is fastened to the end of the piston rod of cylinder 17. Linked to the axle 13 is also a swinging arm 12 limiting the vertical movement of said axle 13. The swinging arm 12 is fastened by means of a hinge pin 14 to a lug included in the side surface of box 7. Limiting abutments 15 and 16 define the boundaries for the swinging motion of arm 12. The bottom position limiting abutment 15 is adjustable during a bending operation. No limiting abutment 15 is not required if the rolls 4 are deflectible to a continuous arch (fig. 7) and the rollers 11 are allowed in the bottom position thereof to respond to the rolls 4 (with no glass sheet therebetween). If the bottom limiting abutment 15 is used, the bottom surface of roller 11 has typically a bottom position (if there is no glass between the rollers and rolls) which is a few millimeters below the top surface of glass, yet out of contact with the rolls 4. The roller 11 may have a fixed top position, e.g. 8-10 mm from the plane defined by the top surface of rolls 4. The adjustment of the air pressure of pneumatic cylinder 17 can be used for producing a desired pressing force for promoting the glass bending. If desired, the pressing force can also be adjusted zonewise during the course of bending. Thus, the cylinders 17 included in various zones are provided with a different pressure. The pneumatic cylinder 17 has a diameter of e.g. 8-10 mm and a length which is preferably about 5 times the diameter for providing a suitable resilience. The common control of all pneumatic cylinders 17 can be used for operating all rollers 11 simultaneously between said top and bottom end positions. As shown in fig. 2A, upon the arrival of a glass sheet in the bending and tempering station, the press wheels 11 are in their top position slightly off the glass surface or they can also be in a light contact therewith. When the glass is completely inside the bending station (fig. 2B), the bending commences. The press wheels 11 are simultaneously provided with a desired and adjustable down-force forcing the glass to conform to the rolls 4 of the flexing conveyor. However, the glass reciprocates in an oscillating fashion during the course of bending. In the illustrated case, the press rollers 11 and conveyor rolls 4 are on top of each other and, in the bottom position of rollers 11, the distance therebetween is slightly less than the thickness of a glass sheet to be bent. When the leading edge of a glass sheet arrives between roll 4 and rollers 11, the rollers 11 shift a small distance upwards against the force of the pneumatic spring 17. Fig. 3 illustrates a situation in which the glass has reached a certain degree of bending. Concurrently with the arching of a conveyor to the configuration shown in fig. 3, the mid-section of individual rolls has been deflected downwards by means of a power unit 18, as illustrated in figs. 6 and 7. In the case of fig. 6, the roll 4 is divided into two sections 4a and 4b, having therebetween a link joint whose height is adjustable by means of the power unit 18. Optionally, the roll sections 4a and 4b can be permanently deflected to a certain position, whereby the deflection is not altered during a bending operation. When another degree of bending is required, the deflection is changed e.g. by means of a manually operated set screw which replaces the power unit 18. However, the deflection during the course of bending may be preferred. End bearings 19 must allow a slight turning of the roll ends. Naturally, the axle 4 can be divided into an arbitrary number of sections. It is also possible to employ an arch-bending axle 4' (fig. 7). In order to make the axle 4' thinner and more readily bendable, it is possible to employ a flexible shaft fitted at small intervals with supporting rollers. Thus, the shaft and the rollers together provide a roll 4', above which the press rollers 11 are suspended from pneumatic cylinders 17. Upon reaching the final degree of bending, the tempering blast is commenced while the glass sheet continues oscillation between rolls 4 and rollers 11. As the tempering operation is finished, the upper press wheels 11 are lifted and returned to their top position. Thus, the bottom position of rollers 11 is a working position and the top position is a rest position. Fig. 4 illustrates the disposition of press wheels , selected so as not to form successive rows relative to the glass advancing direction. The press wheels are structurally light and well journalled for free rotation. The wheels are provided e.g. with plastic bodies and on their peripheries with a fibrous coating of a material temporarily resistant to a high temperature (about 630°C). The coating material can be any material used in roll coatings. The resilient suspension and adjustable pressing force of rollers provide an essential advantage over conventional benders in which the roller axles are fixedly connected to tempering boxes. Since bending around the longitudinal axis is lesser, the tempering boxes need not necessarily deflected in said direction. However, the tempering boxes 5, 7 can also be divided in their longitudinal direction in two or more sections which can be deflected relative to each other in a manner corresponding to the deflection between the sections (e.g. 4a, 4b) of rolls 4. The invention is not limited to the above exemplary embodiment but its structural details can be varied in many ways without departing from the scope of the invention as defined by the claims. For example, the pneumatic springs 17 can be replaced with other types of springs. Also the restriction of the movement of rollers 11 to a top and bottom position can be provided in a plurality of ways. The press rollers or wheels need not necessarily be suspended to nozzle boxes 7 but the suspension can be effected to any structures. One and the same horizontal axle 13 can also be used for journalling a plurality of press wheels 11 supported by a single pneumatic spring 17.

Claims: A method for bending and tempering glass sheets, in which method a glass sheet is heated in a furnace (1) to a bending temperature, the heated glass sheet is transferred from the furnace onto a roll conveyor (3) included in a bending and tempering station, the roll conveyor is arched by varying the relative vertical position of rolls (4), and a tempering gas is blasted to both surfaces of the heated glass sheet while the glass sheet lies on the arched roll conveyor, characterized in that the rolls (4) have their mid-section deflected downwards from the plane of the roll ends and simultaneously press rollers (11) in contact with the top surface of the glass sheet are pressed downwards with a desired pressing force for producing a desired double curvature. A method as set forth in claim 1, characterized in that each press roller (11) is pressed by means of a separate pneumatic spring (17) which simultaneously functions for operating the press rollers (11) between a top rest position and a bottom working position. A method as set forth in claim 2, characterized in that the pneumatic springs (17) are subjected to zonewise varying pressures, whereby the press rollers (11) included in different zones produce a different pressing force. A method as set forth in any of claims 1-3, characterized in that the press rollers (11) are shifted from rest position to working position as soon as the glass sheet to be bent has arrived from the furnace on the conveyor (3) below the rollers (11). An apparatus for bending and tempering glass sheets, said apparatus comprising a roll conveyor (3) consisting of rolls (4) having a relative vertical position which is variable for arching the conveyor to a curvature corresponding to a desired degree of bending, lower tempering boxes (5) having top surfaces (9) provided with tempering orifices (6), and upper tempering boxes (7) having bottom surfaces (10) provided with tempering orifices (8), said tempering boxes (5,7) being movable for bringing said top and bottom surfaces (9, 10) to conform to the arching of said conveyor (3), wherein above said rolls (4) are provided a number of press rollers (11) capable of moving in vertical direction against a spring force for applying a pressing force to the top glass surface, characterised in that the rolls (4) have their mid-section deflected or deflectable downwards from the plane of the roll ends. An apparatus as set forth in claim 5, characterized in that said spring force is produced by means of a pneumatic spring (17). An Apparatus as set forth in claim 6, characterized in that said pneumatic spring (17) is a pneumatic cylinder (17) which simultaneously functions for operating the press roller (11) between a rest position and a working position. An apparatus as set forth in any of claims 5-7, characterized in that, in the working position, the distance of the lowest point of said press roller (11) from the conveying plane defined by the highest point of said conveyor rolls (4) is less than the thickness of glass to be bent, whereby the leading edge of glass lifts the press rollers (11) against the force of said spring (17). An apparatus as set forth in any of claims 5-8, characterized in that the rolls (4) are made of two or more successive axial sections (4a, 4b), having therebetween a link joint whose vertical position is variable by means of a power unit (18). An apparatus as set forth in any of claims 5-8, characterized in that the rolls (4') consist of flexible axles which can be deflected by means of a power unit (18). An apparatus as set forth in any of claims 5-10, characterized by limiting abutments (15-16) for defining a working position and a top rest position for the press rollers (11).

Inventors: LEHTO ESKO, LEHTO, ESKO
Applicants: TAMGLASS ENG OY, TAMGLASS ENGINEERING OY
Application year: 1995
Main classification: C03B23
IPC codes: C03B23, C03B27