GLASS SUPPORT SYSTEM FOR A WINDSCREEN BENDING MOULD

Abstract: The invention relates to a glass support system for a windscreen bending mould. The breakage of long, thin glass sheets to be bent in a mould is prevented by means of glass-­ carrying brackets (4), supported on aluminium wires (7) which, on softening above a certain temperature, lose their supporting power.

Description: The present invention relates to a glass support system for a windscreen bending mould, said mould being provided with an arched shaping surface, a glass sheet softening by the action of heat bending in conformity thereto. If the glass sheets to be bent are placed on a mould so as to be supported by the mould at their ends only, the sagging central region of sheets will be subjected to major stresses. Thus, long and thin glass sheets may break off before the glass has heated sufficiently to sustain major deflections without breaking. This hazard of glass sheet breakage exists all the time from placing the glass sheets on a mould until reaching a sufficient softening temperature, at which a glass sheet sustains major deflections without breaking. It is prior known (e.g. US Patent publication 3 023 542) to prevent the shattering of long, thin glass sheets to be bent in a mould by fitting said mould with glass-carrying brackets extending above the lower sections of a shaping surface and losing their supporting ability above a certain temperature. The prior art solutions have employed two metals having different expansion coefficients at a glass bending temperature for providing support members for said glass-carrying brackets. The mechanism is structurally inconvenient and requires strict accuracy, thus increasing the costs of a mould. In addition, if a bimetallic element is used to effect triggering from full support action to complete elimination of support, the triggering temperature must be selected very carefully in a manner that an excessively rigid glass sheet does not break off or an excessively soft glass sheet does not fall heavily against the shaping surfaces to leave marks or local deformations on the edges of a glass sheet. Even the glass-carrying brackets leave their marks on a glass sheet if the full bearing power is maintained as the glass softens. An object of the invention is to provide a glass support system for a windscreen bending mould for eliminating the hazard of breaking the long, thin glass sheets to be bent in a mould by means of a simple-design apparatus without the above drawbacks. This object is achieved by the invention as set out in claim 1. One embodiment of the invention will now be described with reference made to the accompanying drawing, showing a side view of a glass support system of the invention for a windscreen bending mould. The bending mould may be a windscreen bending mould of any prior known type. The top surface of a bending mould 1 comprises an arched shaping surface 2, a glass sheet 3 softening through the application of heat and deflecting into conformity with said surface by the action of gravity. The general practice is to bend two glass sheets on top of each other. According to the invention, a mould 1 is provided with glass-carrying brackets 4 extending above the lower sections of shaping surface 2, said brackets, in the present case, comprising upright rods guided in sleeves 5 mounted on the mould body. The lower ends of brackets 4 are designed to be fork-shaped or yoke-shaped for supporting them upon aluminium wires 7. On the other hand, the aluminium wires are mounted on supports 6 which are fixed relative to mould 1. The thickness of aluminium wires 7 is selected with respect to the distance of fixed supports 6 in a manner that said aluminium wires 7 do not deflect with permanent deformation or plastically under the weight of glass sheets 3 placed on the mould. Thus, long and thin glass sheets 3 can be placed on a mould and the mould carried into a heating furnace without the hazard of shattering said glass sheets 3. As soon as glass sheets 3 together with their mould 1 are inside a heating furnace, the temperature of glass sheets 3 and aluminium wires 7 increases until the temperature is reached at which said aluminium wires 7 become soft and glass-carrying brackets 4 lose their bearing power. By this time, however, the temperature of glass sheets 3 has risen sufficiently for the glass sheets to sustain deflection without a hazard of breakage. As the temperature rises further to attain a final bending temperature, said aluminium wires 7 soften to such a degree that brackets 4 exert practically no counter-action at all against the deflection of glass sheets 3. In other words, the softening temperature of aluminium wires 7 is substantially below the temperature at which said glass sheets 3 finally bend into conformity with shaping surface 2. However, well before the attainment of the final bending temperature, the surface of glass sheets 3 has softened sufficiently for eliminating the build-up of breakage-causing major stresses in the surface. It is obvious that the above embodiment is just an example and one possible approach for working the invention. Thus, an aluminium wire 7, and the way of supporting it, can be substituted with any means which is thermoplastic and thus loses its supporting power above a certain temperature. Hence, said glass-carrying brackets 4 can be fixed to the mould body e.g. with a thermoplastic adhesive. Also the number and disposition of glass-carrying brackets can be varied. What is essential is that the disappearance of the bearing power of a support system is based on the use of a single thermoplastic element, the release of glass-carrying power being achieved at a slow but controlled rate over a certain temperature range.

Claims: A glass support system for a windscreen bending mould, said mould (1) being provided with an arched shaping surface (2) for deflecting a thermoplastic glass sheet (3) therealong, the breakage of long, thin glass sheets to be bent in the mould being prevented in that said mould (1) is provided with glass-carrying brackets (4) extending above the lower sections of said shaping surface (2) and losing their supporting power above a certain temperature, characterized in that said glass-carrying brackets (4) are supported on elements (7), which soften at said temperature and thus lose their supporting power. A glass support system as set forth in claim 1, characterized in that said thermoplastic elements comprise aluminium wires (7). A glass support system as set forth in claim 2, characterized in that said aluminium wire (7) is mounted by its ends on fixed supports (6) and said glass-carrying bracket (4) is carried by said aluminium wire (7) between said fixed supports (6). A glass support system as set forth in any of claims 1-3, characterized in that said glass-carrying brackets (4) comprise upright rods, guided in sleeves (5) mounted on the mould body.

Inventors: LINNAMAA, LASSE OTTO HEIKKI
Applicants: TAMGLASS OY
Application year: 1985
Main classification: C03B23
IPC codes: C03B23