1. Field of the Invention
The invention relates to a process for bending glass sheets and a device for supporting a glass sheet heated to the forming temperature in a horizontal position, said device consisting of an enclosure in which a partial vacuum can be established and of a contact surface provided with suction orifices directed downward and against which the glass sheet is held by a suction effect.
2. Discussion of the Background
Various processes for producing bent glass sheets are known, in particular automobile glazings, which use a support device consisting of an enclosure in which a partial vacuum is established and of a contact surface provided with suction orifices directed downward. The support device is used to lift the glass sheets, heated to the bending temperature in a tunnel furnace, above the horizontal conveyor belt and deposit them on a bending tool or on another conveying device. Various embodiments of these support devices, for example, have been proposed in the patent publication Nos. DE-2 000 271, EP-3391, EP-3392 and EP-182 638. In all known embodiments, the contact surface--against which the glass sheet is held by a suction effect--is a plate, of flat surface or slightly bent, provided with vertical bores or ducts leaving the contact surface and ending in an enclosure under a partial vacuum that can be regulated. As a general rule, the partial vacuum is obtained by means of a fan placed directly on this support device. The support device is mobile along the vertical plane and optionally in a horizontal plane.
The plate provided with suction orifices that the support devices according to the art comprise is generally of a specific ceramic. The ceramic plates are rather expensive, because all the ducts must be provided.
When these support devices are used, the entire top face of the glass sheet comes in contact with the lower face of the suction plate. The feel of the top face of the glass sheet is always unfavorable if the glass sheets are sensitive to direct contact. When the top face is provided with a sensitive overlayer, for example, with a layer of printed enamel which is then in the molten state considering the temperature of the glass, these support devices cannot be used because the layer of molten enamel sticks to the contact surface and is then destroyed or at least damaged by the mechanical contact.
It is also known how to shape a glass sheet conducted by a roller conveyor under an upper bending form and lifted by an ascending current of hot air which flattens the glass sheet against the upper bending form. The glass sheet is then retrieved by a tempering frame which transfers it between blowing boxes. This process is described in a detailed manner in French Patent No. 2 567 508. The upper bending form, in this case, does not need to be pierced and is therefore less expensive. Moreover, the current of hot air acts on the entire lower face of the glass, therefore, in a way there is a pneumatic pressing which assures a very good shaping quality. However, in this process the energy expenditures are rather great because the hot air current is established for a long period of time.