MXPA00003558A - Method and device for curving and tempering a glass sheet - Google Patents

Abstract

The invention concerns a method for curving and tempering a glass sheet, which consists in curving the glass sheet into the desired shape by means of a forming frame (1). The same forming frame (1) is used for chilling the whole surface of both sides of the curved glass sheet in a tempering station which comes immediately after the curving station by blowing cold air by means of blow boxes equipped with blow nozzles. During the chilling of the whole surface, the glass sheet edge zones resting on the forming frame (1) are subjected to an additional cold air spray by the adequate supply of compressed air into the openings (4) passing through the forming frame (1).

Description

METHOD AND APPARATUS FOR CURVING AND TEMPERING A GLASS SHEET DESCRIPTION The present invention relates to a process for bending and tempering a glass sheet, in which the glass sheet is heated to a bending temperature and formed to the desired shape in a horizontal position using a forming frame and the entire the surface of both sides of the folded glass sheet is then quickly cooled in the forming frame, in a tempering station which is behind the bending station, by blowing cold air using blow boxes that are provided with nozzles of blown. The invention also relates to the devices that are necessary to carry out this process. Processes of this kind are known in various ways. In one such process, described by DE 2,945,776 C2, the flat glass sheet is to be folded up using a plate are suckers and placed downwards on the bending former positioned vertically below the glass sheet, the Glass sheet takes the shape of the bending former due to the effect of the kinetic energy of the fall. The folding window sheet is taken to a tempering station with this forming frame.

In the process, referred to as bending by pressing, similar to that shown for example in EP 0,005,306 Bl, the forming frame acts as a crimping former by means of which the window sheet is pressed against an upper bending former, whose Full surface is convex. Then, the folded window sheet is brought to a tempering station with this forming frame and rapidly cooled therein. The forming frames which are used as support frames for the window sheets during the tempering operation must be configured so as not to prevent the essential rapid cooling of the edge region of the window sheet. This is why they are provided, on their support surfaces, with protuberances, flow channels or recesses so that the blown air directed on the underside of the window sheet also reaches the region of the edge of the sheet of glass. window and carry out the rapid cooling necessary to produce the required tempering. The forming frames for supporting a window sheet during tempering are described, for example, in US Pat. Nos. 5,118,335 and EP-B-0, 186, 529. It has been shown that it is the case that the known processes of the mentioned types before, in which the window plates are folded by means of one, and the same forming frame and are tempered while resting on their forming frame, they do not always allow satisfactory results to be obtained. Depending on the construction of the forming frame, it can happen, for example, that the tempering of the window sheet which can be obtained in the edge region is too slow or that, when a sufficient tempering is obtained, the bending operation is the cause of optically undesirable deformations at the edges of the window sheet. The optically undesirable deformations arise mainly from the protuberances or recesses in the surfaces for supporting the forming frames, which are necessary for the blown air to circulate and due to which the edges of the window sheet are subjected to unequal tensions. These unequal tensions are particularly evident and undesirable when the window sheets have to be heated relatively strongly in order to obtain a pronounced curvature and / or when the edges of the window sheet are provided with a decorative paint frame to be cured, so that, due to the increased reflection, these deformations, which in themselves are minimal, become particularly apparent. Optically undesirable deformations of this kind are especially noticeable when window sheets without a frame are placed inside the body of a motor vehicle since the edge region of the window sheet is then visible just above the current edge, point at which the deformations mentioned above are naturally the largest.

Optically undesirable deformations can of course be avoided, or can be reduced to a very large extent if the surface for supporting the window sheet in the forming frame is increased, for example by enlarging the support protuberances and / or by reducing the distance between the support protuberances. However, the problem then arises again of the amount of blown air reaching the region of the edge of the window sheet which is insufficient, so that the necessary degrees of tempering are not obtained. The object of the invention is to improve the process of the type described in the preamble so as to allow both the production of bent glass sheets whose edges are free of optically undesirable deformations and which allows an irreproachable tempering of the folded window sheets in their region of the edge. According to the invention, this objective is obtained in such a way that, while the entire surface of the window sheet cools rapidly, the regions of the edge of the window sheet that are covered by the forming frame are subjected to additional blowing of cold air by means of the suitable supply, to the openings that pass through the forming frame, of compressed air at a higher pressure than the ambient pressure which prevails between the blow boxes. The suitable supply of additional cold air, at a higher pressure, in the edge regions covered by the window sheet, through the forming frame, makes it possible to design the bearing surface of the forming frame in such a way that it no longer produces deformations of the edge of the window sheet due to the uneven action of the mechanical forces of deformation. In particular, the wide flow channels in the forming frame can be omitted and, instead of them, a forming frame with holes of relatively small diameter can be provided or they can be made of a porous material. The compressed air is then supplied to the lower face of the forming frame via a circular supply channel, taking care only to ensure that the openings in the forming frame, on the one hand, and the compressed air pressure volume flow, on the other hand, another, mutually adapt in such a way that a necessary cooling effect is obtained in the regions encompassed by the forming frame. Other features and advantages of the process according to the invention will arise from the dependent claims and from the description which is provided below an example of a preferred embodiment of a forming frame suitable for the process according to the invention, and with reference to the drawings. In the drawings, Figure 1 is a perspective view of a forming frame according to the invention; Figure 2 illustrates a portion (region II) of Figure 1 on a larger scale; Figure 3 is a sectional view of the line III-III in Figure 1; and Figure 4 shows another embodiment of a forming frame in a sectional view on the line III-III in Figure 1. As shown in Figure 1, the forming frame 1 is mounted on a carriage 2 which can be moved on rails by means of wheels 3 inside a bending and tempering plant. It can also be seen in figure 2 that the forming frame 1 is a frame perforated by holes 4 designed for the suitable supply of compressed air. The holes 4 must have a diameter D and a spacing A between them which are such that a window sheet 5 heated to the softening temperature is not deformed either by its own weight or by the forces which are exerted thereon. during the braiding operation. Depending on the thickness of the window frame to be bent and tempered, the diameter D of the holes 4 is, for example, from 1 to 10 mm and the spacing between the holes 4 is, for example, from 2 to 20 mm. In the example of the training frame mode shown, by means of which a window sheet with a thickness of 3 mm is going to be bent and tempered, the holes 4 have a diameter of 2 mm and are arranged in three rows based on one below the bending former against which it is kept the window plate in place by the flow of the hot gas that blows upwards. As soon as the forming frame is in the hot zone of the furnace, the hose 12 is connected to a vacuum pipe so that the hot ambient air is sucked out through the surface to hold the forming frame. The purpose of this operation is to heat the surface of the forming frame to a suitable temperature so that contact with the hot window sheet does not cause a harmful thermal shock. Then, while still maintaining the flow of hot gas blown upwards, the upper bending former and the window sheet are lowered onto the forming frame 1 so that the window sheet, by means of the forming frame 1, is pressed. to the desired shape. Then, the window frame is deposited on the forming frame 1 by stopping the flow of hot gas. The upper convex bending former is raised and the carriage 2 with the forming frame 1 and the window sheet resting on the latter, are then directed to the hardening station between the two blowing boxes by means of which they are cooled quickly the window sheet. While the window sheet 5 is undergoing air cooling, by means of conventional blow boxes, the surface regions of the window sheet 5 which are covered by the forming frame 1 are rapidly cooled by compressed air supplied to the supply channel 8 via the circular tube 6. The compressed air leaving the supply channel 8 is directed through the holes 4 over the covered regions of the window frame 5 and subject these regions to rapid cooling. In order to obtain correct tempering in the edge region of the window frame 5, it has been shown that a pressure of, for example, 4 bar of supplied compressed air is sufficient. As regards the rest, the forming frame 1 is covered in a known manner with a mesh of gas-permeable metallic fibers 9 which are fixed on the pointed bolts 10, as can be seen in figure 2 and in the figure 3. In order to ensure that the forming frame is thermally insulated from the supply channel 8, the latter can be placed 0.5 to 3 mm away from it. This thermal insulation then allows the forming frame to heat up more quickly and cool more quickly. This can be advantageous, for example, when the cycle time of a bending and tempering plant is relatively short. Figure 4 shows another embodiment of the forming frame 1. Although the supply channel 8 is manufactured in the same manner as in the previous example, the forming frame 1 is composed of wire gauze composite panels, and this is commercially available, for example, under the trademark "Haver Porostarffi". " Wire gauze composite panels of this kind are formed from numerous gauze thicknesses of steel wire resistant to high temperatures and solidly joined together by sintering. Since individual pieces of wire gauze are selected depending on the gauge of the wires, the separation of the wires and the shape of the interstices allows the properties of the composite panels, such as gas permeability, porosity, distribution of pores and the nature of the surface are determined with precision. That oriented surface of the window sheet 5 should be as uniform as possible, that is, it should be formed of a wire gauze in which the wires are as thin as possible and the width of the intersections is small. On the other hand, the thicknesses of the wire gauze of the underlying layers can usefully have increasingly wide gaps. The gas permeability is chosen so that the interstices form the holes in the forming frame, holes through which the surface regions of the window sheet 5 which are covered by the forming frame undergo additional cooling due to the supply of compressed air and the warm ambient air is sucked away for the purpose of heating the forming frame 1. In order to acquire a better thermal insulation, the forming frame surface which is brought into contact with the window sheet 5 may include a ceramic coating 11 of 0.2 to 1 mm thick, which is known per se. The ceramic coating 11 is preferably composed of zirconium dioxide. It may be advantageous first of all to deposit a tie layer on the surface of the forming frame. A tie layer of this kind may consist, for example, of a nickel-aluminum alloy or of a nickel-chromium-aluminum alloy. Both the mooring layer and the ceramic coating are advantageously applied using plasma spray or a flame metallization process. During the coating process, it is necessary to ensure that the gas permeability of the forming frame 1 is maintained. This can be obtained by carrying out the coating operation in the finished forming frame, and pressurized air is injected simultaneously into the supply channel and leaves, via the holes in the surface of the forming frame, so that these holes are prevented become clogged during the coating operation.

Claims (12)

1. A process for bending and tempering a window sheet, in which, the window sheet is heated to the bending temperature and bent into the desired shape in a horizontal position using a forming frame, and the entire surface of both sides of the folded window sheet is then quickly cooled in this forming frame, in a tempering station which is behind the bending station, by blowing cold air using blow boxes that are provided with blowing nozzles, the process is characterized because, while the entire surface of the window sheet cools rapidly, the edge regions of the window sheet that are covered by the forming frame are subjected to additional blowing of cold air by the adequate supply to the openings passing through. of the compressed air forming frame at a pressure higher than the ambient pressure, which prevails between the blow boxes.

2. The process as described in claim 1, characterized in that the forming frame is heated by ambient hot air which is sucked out through the openings with which it is drilled before coming into contact with the window sheet heated to the temperature of folded.

3. A forming frame for carrying out the process as described in claim 1 or 2, characterized in that a supply channel, which can be connected to a pressurized gas line or to a vacuum line, is placed along the at least part of the perimeter of the forming frame and wherein the openings lead, from the supply channel, through the direct forming frame to the surface of the latter on which the window sheet rests.

4. The forming frame, as described in claim 3, characterized in that the supply channel is located below the forming frame.

5. The forming frame, as described in claim 3, characterized in that the supply channel, observed in the radial direction, lies outside the forming frame.

6 The forming frame, as described in claims 3 to 5, characterized in that the supply channel which rests directly against the forming frame is connected to the latter.

7. The forming frame, as described in claims 3 to 5, characterized in that the supply channel is located at a distance of 0.5 to 3 mm from the forming frame so that it is thermally insulated from the latter.

8. The forming frame, as described in any of claims 3 to 7, characterized in that the forming frame consists of a perforated metal plate with holes.

9. The forming frame, as described in any of claims 3 to 8, characterized in that the forming frame consists of a composite material formed from gas permeable wire gauze piece.

10. The forming frame, as described in claim 9, characterized in that the composite material that builds the forming frame is composed of several superimposed pieces of wire gauze which are bonded by sintering and have interstices of various widths, the upper layer consists of a very fine mesh gauze.

11. The forming frame, as described in any of claims 3 to 10, characterized in that the surface of the forming frame on which the window sheet rests is covered by a mesh, woven or felt texture of metallic fibers, which it is resistant to high temperatures and is permeable to gas, the individual fibers of which have a diameter of 5 to 1 micrometers.

12. The forming frame, as described in any of claims 3 to 11, characterized in that the surface of the forming frame on which the window sheet rests is covered with a ceramic coating of aluminum oxynitride, silicon aluminum oxynitride, titanate of aluminum or zirconium dioxide.