Method and mould assembly for bending difficult bending shapes such as an s-shape in a glass sheet

Abstract: The invention relates to a method for bending difficult bending shapes such as an S-shape in a glass sheet. The downward bending of an outline-mould supported, heated glass sheet is assisted by means of a non-engaging lower partial surface mould (6) used for blowing to a bending line or its vicinity a gas having a temperature at least equal to that of glass, the gas serving simultaneously as a glass carrier preventing its falling or excessive downward sagging. Blasting orifices (10) in the shaping surface are adapted to concentrate heating on the most problematic areas of a bending line.

Description: The present invention relates to a method for bending difficult bending shapes such as an S-shape in a glass sheet, in which method: a glass sheet is heated to the bending temperature the heated glass sheet is supported on an outline mould having a shaping surface which is complementary to a final bending shape, and the glass sheet is bent to its final configuration by sag-bending. The invention relates also to a bending mould assembly, comprising: an outline mould having a shaping surface which is complementary to a final bending shape. US Patent specification 4 260 409 discloses a method and an assembly for bending difficult bending, shapes such as an S-shape in a glass sheet. A heated glass sheet is carried on an outline mould. For the final bending step the glass sheet is lifted from the outline mould and bent between upper and lower press shaping surfaces. The shaping surfaces are glass-engaging. Within the areas of difficult bending shapes the glass is locally elongated with a glass sheet being displaced between the shaping surfaces. This results in the abrasion of glass surface. In any case, the engaging whole surface moulds leave marks on glass surface since a difficult shape cannot be obtained unless glass is relatively soft (easily deformable). An object of the invention is to provide an improved method and mould assembly for bending difficult shapes in a glass sheet in a manner that the bending can be effected in a controllable fashion also within the areas in which a glass sheet is subjected to intense elongation without creating adverse optical errors within these areas or in the immediate vicinity thereof. The term partial surface means in the following context that the surface area of a mould only is a part, typically 10 - 30 % of the surface area of the glass sheet. Even in the case where two separate partial surface moulds are used, the combined surface area thereof is typically clearly less than 30 % of the surface area of a glass sheet. The lower partial surface mould support refers a support, wherein the combined lower shaping surface does not exceed 50 % of the surface area confined by the outer periphery of the shaping surface 15 of outline mould 5. The above objects are achieved by the method of claim 1 the bending mould assembly of claim 7. The invention will now be described in more detail with reference made to the accompanying drawings, in which: fig. 1 is a schematic view of an assembly used for carrying out the method of the invention with a sectional view of a lower partial surface mould 6. Fig. 1A is a side view of a furnace unit wherein the present invention can be applied. Fig. 2 is a perspective view in vertical section of a portion of the upper mould in a mould assembly according to one embodiment of the invention. Fig. 3 shows schematically the bending of an S-shape by means of a partial surface upper press mould and a partial surface lower press mould. Fig. 4 shows the bending of an S-shape by means of a whole surface upper press mould and a partial surface lower supporting mould. Fig. 5 is a schematical view of an arrangement, wherein the gravitational bending of an S-shape is assisted by means of a non-engaging lower partial surface mould. Fig. 6 shows examples of difficult bending shapes that can be obtained by means of the method and the assembly of the invention. The embodiment of fig. 1 is shown to include a lower partial surface mould 6 which is positioned in a bending section 4 for difficult bending shapes. A glass sheet 9 supported on an outline mould 5 is carried and heated gradually in successive heating sections 2. From the final heating section 3 said outline mould 5 along with its glass sheet 9 is carried into the bending section 4, wherein the bending of a difficult shape is effected by means of the mould assembly of the invention, as described in more detail hereinafter. The bent glass sheet is gradually cooled in cooling sections 3', 2'. If necessary, the bent glass sheet can also be carried on outline mould 5 into a tempering section, so the method of the invention can also be applied in connection with the bending of automotive backlights. However, the method is particularly suitable for bending windshields. A windshield bending furnace generally indicated by reference numeral 1 is described in more detail in US Patent apecification 4 497 645. In the present case, the lower partial surface mould 6 is provided with a convex shaping surface portion 8 on either side of a supporting rib 5' included in outline mould 5. Said mould 6 further includes a shaping surface portion 7 which is substantially flat or slightly convex or concave. The shaping surface 7, 8 is provided with orifices 10 which are connected by way of an in-mould distribution manifold 16, 161, 18 to a pressure-gas pipe 12. The shaping surface, at least in the immediate vicinity of a bending line, can also be provided with suction orifices 11 which are connected by way of a collection manifold 17, 171, 19 to a suction channel 13. The suction side of a fan 22 is connected to a three-way valve 21 for controlling the relative relationship between the amounts of air coming from suction pipe 13 and a pipe 20 connected with the interior of the hottest furnace section 3. Thus, valve 20 can be used for controlling the effect of a suction prevailing on the shaping surface in relation to the effect of blowing. An adjustment of the rotating speed of fan 22 or a valve fitted in pipe 12 can be used for controlling the effect of blowing coming in through the orifices. Temperature of the blasting or blowing gas can be regulated by means of a heater 23 which is controlled by a thermostat 24. When bending a glass sheet a greater thermal effect is required on the areas in which the deformation (flexure and/or elongation) of a glass sheet is the greatest. This object is achieved by means of a lower partial surface mould 6 used for blowing a gas having a temperature at least equal to that of the glass to a glass sheet bending line or to the vicinity thereof through orifices 10. At the same time the gas serves as a glass carrier preventing its falling or excessive downward sagging. The area in which the supporting rib 5' of outline mould 5 and the bending line of a glass sheet coincide possibly includes a hard-to-control zone, said zone being provided with extra heat. Whenever required, this particular zone must be heated more than others, so over this zone, said mould 6 can have a densified orifice pitch, larger blast orifices 10, higher blasting pressure or the air blown to the zone is hotter than that blown to the rest of the area. In the latter case, it is possible to employ either a separate blasting manifold section or heating resistances disposed in some of the distribution channels 16. It is also possible to provide a system of suction orifices 11 only in critical zones for a slightly improved transfer of heat. The distribution channels 16 inside mould 6 are connected by means of transverse connecting channels 161 for producing a ladder-like or lattice-like distribution manifold. The same applies also to collection channels 17 and their connecting channels 171. The manufacturing technique of such a mould and its internal manifold is described in the Applicants' co-pending European Patent applications No. 0 448 959 and 0 451 469. Fig. 2 illustrates an upper non-engaging partial or whole surface mould which can be used in the bending of difficult shapes together with lower mould 6, The orifice systems and chaneling of a shaping surface 7', 8' included in an upper mould 6' are designed in principle the same way as described in connection with mould 6. Thus, the corresponding components are indicated with the same reference numerals provided, however, with an inverted comma. Since the shaping surface of upper mould 6' may be considerably larger than that of lower mould 6, said upper mould 6' must also be provided with suction orifices 11' for a controlled discharge of the blasting air. The lower moulds 6 having a rather large shaping surface must also be provided with an array of suction orifices 11. The pressure-gas pipe 12' and suction pipe 13' can be linked with a similar type of gas circulation system as the one shown in fig. 1. If necessary, it is possible to provide a separate channeling and a separate hot-gas pipe 14 for blowing hotter gas to hard-to-control surface areas. The same way as in the lower mould, the upper mould can also have, over a certain effective mould area, a densified orifice pitch, larger orifices or increased blasting pressure. Thus, transfer of heat can be applied to a certain effective or active area without separate channeling. Also a heating resistance 28 fitted in distribution channel 16' can used for a concentrated thermal effect. Resistance 28 is connected with wires 29 to a power source 30. Fig. 6 illustrates an S-shaped automotive windshield that can be bent by using the method and mould assembly of the invention. Reference character A indicates a section which corresponds to a present, conventional windshield configuration. When the windshield is extended beyond this section or area, the lower glass edge curves horizontally forward and the upper edge horizontally backward, thus providing an S-shape. In addition, the lateral glass edges curve backward. This produces criss-crossing bending lines BL whose crossing points are formed as a spherical surface B or some other multi-curving surface portion C. Over the areas B and C, the glass is subjected to dramatic elongation in addition to bending. Fig. 3 illustrates application of the invention in a case which involves the use of a partial surface upper mould 6' and a partial surface lower mould 6 for bending a glass sheet 9 supported on an outline mould 5. The upper partial surface mould is further provided with a mechanical press member 25 for assisting the downward bending of the marginal edge portion of the glass. The upper mould 6' can be provided with an array of blasting and suction orifices (see fig. 2). A pressure pipe 12' and a suction pipe 13' can be linked with a gas circulation system 3; 20-24 similar to the one shown in fig. 1. The lower partial surface mould 6 can only be provided with an array of blasting orifices which is connected to pressure pipe 12, wherein a hot gas is supplied from furnace section 3 as shown in fig. 1. The difference of the embodiment of fig. 4 from fig. 3 is the use of a whole surface upper mould 6''. The embodiment of fig. 5 differs from the preceding ones in that there is only used a lower partial surface mould 6 which can be provided with blasting orifices only or with blasting and suction orifices, as shown in fig. 1. Also in this case, the essential feature is to produce a concentrated heating effect and a concentrated shaping support (bearing effect) on the predetermined areas below a glass sheet by means of a glass sheet non-engaging partial surface mould. The heating effect must be concentrated locally on a bending line and its surrounding. The blasting gas must have a temperature at least equal to that of the glass. As the bending progresses, said lower partial surface mould 6 is brought closer to a bending line and it may be necessary to increase or heat up the blasting. When the bending is finished, said lower partial surface mould 6 can also be used for cooling a bending line by blowing colder air from blasting orifices 10 to the bending line or its surroundings. It is also possible to mount the lower partial surface mould 6 fixedly relative to outline mould 5, whereby the partial surface mould cannot be displaced but it can serve at the intial stage of heating e.g. as a support for glass. Hot gas is being used when bending the glass as descibed above. Also the mould has a structure as described above. The gas applied is primarily air with various gases or vapours possibly added in. For example, SO₂ can be used for building a protective coating film, whereby a possible contact between mould and surface does not as easily leave a mark on the glass surface.

Claims: A method for bending difficult bending shapes such as an S-shape in a glass sheet (9), in which method: the glass sheet is heated to the bending temperature, the heated glass sheet is supported on an outline mould (5) having a shaping surface (15) which is complementary to the final bending shape, the glass sheet remains in contact with the outline mould and is bent to its final configuration by downward sag-bending of the glass sheet (9), which is assisted by means of a non-engaging lower partial surface mould (6), i.e. a mould covering the surface area of the glass partially, supporting the glass sheet from below either with or without pressing it from above, which lower mould is used for blowing to a bending line (BL) or its vicinity a gas having a temperature at least equal to that of the glass, which gas serves simultaneously as a glass carrier preventing its falling or excessive downward sagging. A method as set forth in claim 1, characterized in that the heating caused by said hot-gas blowing is concentrated on the most problematic areas of the bending line, particularly on crossing points (B) of several bending lines (BL). A method as set forth in claim 1 or 2, characterized in that the hot gas is blown from blasting orifices (10) of the shaping surface (7,8) of the lower mould (6) while the gas is simultaneously sucked or allowed to escape through suction or outlet orifices (11) of this shaping surface, and that the pressure ratio between blowing and suction is adjusted as the shaping surface (7,8) approaches said glass sheet (9). A method as set forth in any of claims 1 through 3, characterized in that the downward sag-bending of the glass sheet is assisted by means of a non-engaging upper partial surface mould (6', 6'') used for applying a bending force to the glass sheet simultaneously with a locally concentrated thermal effect. A method as set forth in claim 1, characterized in that the bending of the glass sheet (9) is stopped by blowing colder-than-glass air through the blasting orifices (10; 10') of the mould (6) or moulds (6; 6'). A method as set forth in any of claims 1 through 5, characterized in that the hot gas to be delivered into the moulds (6, 6', 6'') is sucked partially from a heating furnace (1,3) and partially from the mould or moulds through suction orifices (11, 11') made in its or their shaping surface (7, 8; 7', 8'). A bending mould assembly for bending difficult bending shapes such as an S-shape in a glass sheet, said assembly comprising: an outline mould (5) having a shaping surface (15) which is complementary to the final bending shape, a non-engaging lower partial surface mould (6), i.e. a mould covering the surface area of the glass sheet partially, having a shaping surface (7, 8) which is complementary to the final bending shape, and is provided with blasting orifices (10) which are connected by way of a distribution manifold (16, 161, 18) in the mould body to a pressure-gas pipe (12) which is connected to a hot-gas supply (23, 22; 3), said shaping surface blasting orifices (10) being adapted to concentrate a greater amount of air provided by the hot-gas supply and/or hotter air, i.e. hot gas provided by extra heating of the gas in the hot-gas supply or separately provided, on the regions (8) of the shaping surface that are curved more and correspond to the areas of the most dramatic deformations of the glass sheet, especially at the crossing points (B,C) of several bending lines (BL). An assembly as set forth in claim 7, characterized in that the assembly further includes a non-egaging upper partial or whole surface mould (6', 6'') having a shaping surface (7', 8') provided with blasting and suction orifices (10', 11'), and that said blasting orifices (10') are connected by way of a distribution manifold (16', 161') in the mould body to a pressure-gas pipe (12') which is connected to the hot-gas supply (23, 22; 3). An asembly as set forth in claim 7 or 8, characterized in that said lower partial surface mould (6) is also provided with suction orifices (11) which are connected by way of a distribution manifold (17, 171, 19) in the mould body to a degassing or suction pipe (13). An assembly as set forth in claim 8 or 9, characterized in that the pressure side of a hot-gas blower (22) is connected to the pressure-gas pipes (12, 12') and the suction side is connected to an adjustable three-way valve (21) which receives the degassing pipes (13, 13') of the moulds (6, 6') as well as an air pipe (20) leading to a heating furnace (1,3). An assembly as set forth in claim 7, 8 or 9, characterized in that the distribution and/or collection manifolds (16, 161; 17, 171 or 16', 161'; 17', 171') in the mould body make up a ladder-like or lattice-like channel system. An assembly as set forth in claim 7, characterized in that the surface area of the lower partial surface mould (6) is 10 to 30 % of the surface area of the glass sheet (9). An assembly as set forth in claim 7, characterized in that the surface area of the lower partial surface mould (6) or the combined surface area of two simultaneously used lower partial surface moulds is less than 50 %, preferably 10 to 30% of the surface area confined by the outer periphery of shaping surface (15) of the outline mould (5).

Inventors: LEHTO ESKO OLAVI, VEHMAS JUKKA HEIKKI, LEHTO, ESKO OLAVI, VEHMAS, JUKKA HEIKKI
Applicants: TAMGLASS ENG OY, TAMGLASS ENGINEERING OY
Application year: 1991
Main classification: C03B23
IPC codes: C03B23