MXPA97009628A - Apparatus and method for folding vine leaves - Google Patents

Abstract

The present invention relates to an apparatus for bending glass sheets and more particularly to bending glass sheets wherein there is a step of initial bending by gravity and a step of bending by subsequent pressure. The apparatus and the automotive for subsequent lamination, for example in the manufacture of vehicle windshields

Description

APPARATUS AND METHOD FOR BENDING GLASS SHEETS The present invention relates to an apparatus for bending glass sheets and more particularly to bending glass sheets wherein there is an initial bending step by gravity and a subsequent bending step by pressing. The apparatus and method are particularly useful for bending automotive glasses for subsequent lamination, for example in the manufacture of vehicle windshields. Normally, the glass or glass for vehicle windows is curved, the curvature is imparted to planar glass by a bending process. In a bending process, the planar glass sheets are placed on female ring molds and heated to the softening point of the glass. Each sheet is bent ("pandea") under its own weight, until the periphery of the glass sheet is in contact with the ring mold. This bending technique is known as "buckling" or bending by gravity, and has been developed over the years, in order to bend glass sheets that meet the demands of vehicle manufacturers. For example, as more deeply folded glass has been required, the ring mold is modified by connecting the ends of the mold to the hinged center portion, the hinged mold ends or portions of fins progressively closing as the glass softens and progresses. bent. This avoids the tendency for the glass sheet to slide relative to the mold during bending, thus avoiding scratching. This mold is commonly called an articulated mold. The process of bending by gravity has been found particularly suitable for the production of glass to be subsequently laminated, by combining two sheets of glass with a sheet of interlayer material. The process of bending by gravity is able to produce glass with a high optical quality and it is also possible to fold two sheets of glass simultaneously, thus producing a coupled pair of glasses that give an excellent fit to the sheet. In recent years, developments in vehicle designs have required glass with complex curvature, ie glass that bends in two directions generally at right angles to each other. It is not possible to impart more than a very limited degree of complex curvature to a glass sheet by bending by gravity only. In addition, the increased use of automotive assembly by vehicle manufacturers demands that more strict dimensional tolerances be met by glass. The shape of the periphery of the folded panel must be precise, not only in terms of its bi-dimensional projection but also in three dimensions, ie the angle of the glass adjacent to the periphery must be correct. If this "entry angle" as it is known to those skilled in the art is not correct, the bent panel will not fit and seal satisfactorily on the receiving flange of the vehicle body. Furthermore, the optical properties of the window depend on the shape of the central region of the glass, which must therefore be precisely controlled in order to comply with the required optical standards. These requirements, together with the tendency to deeper and more complex bends, can no longer be fulfilled by the glass that is bent by the bending by gravity technique alone. Now it is considered necessary to complete the folding of these forms by a subsequent bending step by pressure. This stage can only involve a limited part of the area of the folded panel, for example the areas that after installation in the body of the vehicle, will be adjacent to the pillars of the windshield of the body. In many current vehicle designs, these areas of the panel are required to be bent more deeply, and in this specification, any area of a panel that is required to bend more deeply by a layer of bending by subsequent pressure will be referred to as the deep bending portion. In the step of bending by pressure, an upper mold or matrix is bent over the upper surface of the glass sheets, in such a way that the glass sheets are further bent by the action of the upper mold pressing the sheets with its lower mold. When the step of bending by pressure is carried out after bending by initial gravity, the lower mold may comprise the mold bent by gravity. Pressure bending is also employed in the art for bending planar glass sheets, without bending by initial gravity. However, this can lead to disadvantages since, since the bending profile is achieved by a pressure force applied when compressing individual sheets between two molds, the optical and physical properties of the glass sheets can be reduced compared to folding by gravity. Tension stresses can also be induced in the glass sheets, which can cause rupture or require an additional annealing step to remove them. Accordingly, the apparatus and methods employed in bending by pressure alone, that is by not following a step of bending by gravity, may be different from those employed in bending by subsequent pressure following the bending by initial gravity. EP-A-0338216 describes an example of said subsequent pressure folding step, wherein a pair of auxiliary upper molds press the deep end portions of a panel against the hinged ends of an articulated mold in which it will be carried out. the bent by initial gravity. The hinged ends lock securely in position in the pressure bending stage. The locking of the hinged ends of the articulated mold is provided by fastening means comprising a plurality of rotatable operating rods, each rod conveying at its upper end, a clamping pawl which is rotated between a clamping position and a clamp. a clamping release position by clamp. In the clamping portion, the stop arms at the hinged ends of the mold are clamped between the clamping pawls and the stop wall. The clamping means comprise a relatively complicated structure that requires an independent actuator system. The clamping means are required to extend through the bottom of the furnace, so that they can be coupled one after the other the articulated molds are transported successively through the furnace * Each mold is moved by a carriage and the means of Fastening by clamp must pass through the bottom wall of the carriage in order to attach the mold above. This structure, as it is complicated, has the disadvantage that it pulls air that can pass through holes in the bottom of the car that can lead to non-predictable temperature profiles in the vicinity of the glass in the mold. Accordingly, the described apparatus can not be used with certain carriage configurations. For example, there are certain types of furnaces for bending glass, in order to ensure a uniform and reproducible open temperature in the vicinity of the glass sheets in the mold As they pass through the furnace, the mold is mounted on a lid cart open that has a solid base and solid side walls. This can prevent air currents that modify the temperature profile in the vicinity of the mold. The patent of the U.S.A. No. 5045101, discloses that the hinged ends of an articulated mold are provided with a tapered ring or a mold extension in its portions where the deep bending operation is conducted. This presents a relatively large area of contact between the mold and the glass sheet that affects the heat flow from the glass sheet, and can cause excessively high edge stresses to be generated in the glass during the bending operation, which leads to potential glass breakage. The patent of the U.S.A. No. 6071461, recognizes that it is convenient for the contact area of the surface of the mold for bending by gravity, which is minimized in order to reduce loss of thermal capacity. However, this desire to minimize the contact area must be balanced with the requirement for the bending mold by gravity to be strong enough, such that when the mold is used in a subsequent bending step by pressure, where a mold upper presses against the glass sheets bent by gravity in the mold, the mold bent by gravity is not distorted under the applied pressure, leading to possible breakage of the glass or an incorrect shape. Furthermore, with said minimized contact area, care must be taken that the thin edges of the bend mold by gravity do not accidentally mark the underside of the glass sheets during the pressure bending operation. A typical apparatus for bending glass sheets comprises an oven located on a conveyor loop around which carts are transported, each carrying a respective bending mold by gravity. A typical oven has 20 or more noldes. It is convenient that the structure of each mold be relatively simple in order to minimize the cost and complexity of the apparatus. A typical gravity bending mold has an annular rim that contacts the glass with a minimum surface area in order to prevent excessively high edge stresses from accidentally forming on the glass sheet. Typically, the flange has a thickness of approximately 3 to 4 mm. However, if said known gravity bending mold is subjected to a subsequent pressure bending step in the manner described in the prior art, there is a danger that the mold, as a result of having only a thin annular bead, may be deformed. during the step of bending by pressure, causing rupture or other damage to the glass sheets, or mark the bottom side of the glass sheet.

An object of the present invention is to provide an apparatus and method for bending glass sheets, which allows substantially conventional gravity bend molds to be employed in a subsequent pressure bending step. A further object of the present invention is to allow these molds to be employed without requiring the complicated clamping fixture apparatus as required by the prior art. Accordingly, the present invention provides an apparatus for bending a sheet of glass in a step of bending by gravity and in a step of bending by subsequent pressing, the apparatus includes a mold of bending by gravity comprising a fixed mold portion. and at least one hinged fin portion adjacent to the fixed mold portion, a base on which the fixed mold portion is mounted and at least one hinged locking arm mounted between the or each respective fin portion and the base, the At least one interlock arm is movable by a cam engaging action, from an unlocked position, wherein the fin portion is capable of moving vertically relative to the base, to a locked position in which the fin portion is fixed at position with respect to the base. The present invention also provides a method for bending a sheet of glass, the method comprising placing at least one sheet of glass in a mold by bending by gravity, comprising a fixed mold portion and at the one an articulated fin portion adjacent to the portion. of fixed mold, the mold is mounted on a base in a mobile carriage; transport the mold that transports the glass sheet at least through an oven in which the glass is heated to the point of softening glass and bends by gravity until the periphery of the glass sheet is in contact and adapts to the shape of the upper surface of the bending mold by gravity, the or each fin portion is provided with a locking arm which during the step of bending by gravity, moves progressively as a result of articulation of the mold from an unlocked portion to a locked position, wherein the fin portion is fixed in a predetermined position corresponding to the desired shape of the glass sheet; pressurizing the glass sheet with an upper pressing die, while the glass sheet is supported by the bending mold by gravity, the locking arm acts to lock the respective hinged fin portion in the predetermined position; cool the folded glass sheet and remove the folded glass sheet from the mold. One embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a schematic partial section side view through a furnace for heating glass sheets, showing a mold of bent by gravity that carries a pair of flat glass blades before a gravity bending operation; Figure 2 is an enlarged schematic partial sectional side view of one of the fin locking arrangements illustrated in Figure 1; Figure 3 is a schematic partial section side view on line A-A of Figure 2; Figure 4 is a plan view of the gravity folding mold that is mounted on a base on a carriage as illustrated in Figure 1; Figure 5 is a schematic partial sectional side view similar to that of Figure 1, showing an apparatus for pressing bending of glass sheets in the oven, the apparatus is illustrated before a pressure bending operation; Figure 6 shows the apparatus of Figure 5 during a pressure bending operation; and Figure 7 is an enlarged side view of one of the spacer devices illustrated in Figure 6. With reference to Figure 1, a section through a tunnel 2 furnace for bending glass sheets is illustrated., typically a pair of glass sheets 4 which after the bending operation are intended to be laminated together in order to manufacture, for example, an automotive windshield. Said tunnel kiln 2 is well known in the art and consists of an elongated track 6 which carries a succession of rolling open lid carriages 8. Each carriage has a ring mold for bending by gravity 10, the mold 10 is mounted on a base 12 which is fixed to a solid bottom wall 14 of the carriage 8. The carriage 8 also has an annular side wall, preferably rectangular 9. The carriages 8 are mounted in succession for cyclic movement around a loop including the furnace 2. The loop includes a glass charging zone, a heating zone where the heated glass sheets are bent by gravity in the bending mold by gravity 10, a cooling zone of a glass discharge zone. The furnace 2 can be provided with other zones, for example an annealing zone, for annealing the glass in order to reduce stresses generated during the bending step, between the heating zone and the cooling zone. It will be understood by a person skilled in the art that although the present invention is exemplified by a box furnace, the present invention may alternatively be employed in any other type of lehr. The present invention is particularly concerned with the manufacture of glass sheets having deep bending portions that can not be easily achieved by the use of gravity bending alone. According to the invention, a pressure bending zone is additionally provided in the loop, immediately downstream of the bending zone by gravity. In the pressure bending zone, the glass sheets bent by gravity are further bent to a final desired shape of an upper reciprocable mold, while the glass sheets are supported in the bending mold by gravity. Figure 1 illustrates glass sheets 4 in the mold 10 on a carriage 8 before the operation of bending by gravity. The carriage 8 is arranged to move on the furnace 2 in a direction at a right angle to the plane of the drawing. The mold 10 comprises a central fixed mold portion 16 which is mounted to the mold base 12 by a plurality of supports 18. On opposite sides of the central portion 18 of the mold 8, hinged portions of respective fins 20 are hingedly mounted. The invention is described with reference to a gravity bending mold having two opposite fin portions, it will be apparent to those skilled in the art that the invention can also use a gravity bending mold having only one articulated fin portion. . The fin portions 20 are arranged to move by rotation between a lower position, as illustrated in Figure 1, wherein the mold 10 is configured to support one or more flat glass sheets 4 in the mold 10, and a top position in which the fin portions 20 define, together with the central portion 16, a continuous curved annular rim defining a surface to be reached by the glass sheet or sheets 4, when they are finally folded. The glass sheets 4 are heated as they pass through the heating zone of the oven 2, such that the glass sheets 4 are softened and progressively panded under the effect of gravity so as to conform to the desired shape as defined. by the mold 10. On the central portion 16 of the mold, the glass sheets 4 buckle until they rest against the upper mold surface thus adapting to the desired shape. On the fin portions 20, the softening effect of the glass allows the fin portions 20 to be articulated upwardly under the action of an applied force that is provided by a pair of counterweight, such that each fin portion 20 rotates. relative to a respective pivot axis 22 in the joint enters the central portion 16 and the respective fin portion 20, such that the glass sheets 4 are pushed up and bent progressively until the bottom surface of the glass sheets 4 rests against the upper surface of the fin portions 20. As will be described later, when the Deep bending portions are present in the glass sheets, those portions tend to require to be pre mechanically against the lower mold by a lower die or mold, such that the desired shape defined by the lower mold is achieved in a reliable and repetitive manner. It will be apparent that the present invention can employ molds so-called "weightless", which do not have counterweights but rather are specially configured such that the mold is articulated under the action of the weight of the glass as it softens.

A typical mold 10 is illustrated in greater detail in Figure 4. The mold 10 is mounted on the base 12 by the supports 18 which are fixed to the underside of the central portion 16 of the mold 10. The base is sufficiently rigid to minimize deflection during the subsequent pressure bending stage. The fin portions 20 are connected to the central portion 16 on their opposite sides by respective pivot axes 22. Each fin portion 20 has mounted on its opposite sides a pair of counterweights 24, each counterweight 24 is mounted on a respective arm 26 that it is fixed to a respective end 28 of a respective pivot shaft 22. The upper surface of the flange 30 of the mold 10 formed by the central position 16 and the d edge portions 20 contact the underside of the glass sheets 4 and define a final shape desired for the glass sheets 4. The surface area of the mold 10 which contacts the glass sheets 4, is preferably minimized to reduce the area available for thermal transfer between the glass sheets 4 and the metal mold 10 which can lead to undesirable tensions present in the glass sheets finally folded 4 and / or visible defects present on the edges of the glass sheets 4. These tensions can cause rupture of the glass sheets or 4. Typically, it is desired to maintain tensions in the traction area in glass sheets of less than 7 MPa. Typically, the annular rim 30 of the mold 10 defined by the upper surfaces of the central portion 10 and the fin portions 20 have a thickness of from about 3 to 4 mm, to minimize the contact area between the glass of the mold 10. However , when according to the present invention, the gravity bending mold 10 is intended to be employed as the lower mold in a subsequent pressure bending operation, the lower mold is required to be sufficiently rigid and strong so as not to deviate in uncontrollable form or distort under the action of pressure applied from the mold for bending by superior pressure. It also requires that the thin flange does not mark the underside of the glass during the pressure bending operation. In accordance with the present invention, the glass sheet bending apparatus is especially adapted to allow a conventional buckling bending mold with relatively thin annular bead, which has been employed in a subsequent pressure bending operation while being secured high Quality control of glass sheet products finally bent. The use of this third annular rim provides low stresses in the glass, as will be described below. Modifications have been made to the mold and to the remaining parts of the apparatus to reliably ensure that the mold achieves the final shape required, the mold can withstand the pressure of bending by pressure and the glass sheets are not marked or otherwise deteriorate in quality accidentally as a result of the bending operation by additional pressure.

Referring again to Figure 1, the fin portions 20 each are provided with at least one locking device to latch or vertically secure the position of the fin portion during the pressure bending operation. Optionally, each fin portion has two interlocking devices and although the illustrated embodiment is only provided with one interlock device for each fin portion. The interlocking device comprises a hinged locking arm 32 which is hingedly mounted to the respective fin portion 20, and is downwardly dependent so as to be able to slide on the upper surface of a plate 34 mounted on the base 12 which provides a surface Top Cam The interlocking arm structure 32 / plate 34 is illustrated in greater detail in Figures 2 and 3. The interlocking arm 32 comprises a pair of elongated spaced plates 36 which are hingedly mounted at their upper ends with a member of extension 38 fixed to the fin portion respectively, the extension member 38 passing between the plates 36 and the pivotal mounting therebetween comprising a bolt structure 40. The locking arm 32 is downwardly dependent from the fin position 20 and the free bottom end 42 is provided with a cylindrical spacer 44, which is fixed between the plates 36 by an additional bolt structure 46. The cylindrical spacer 44 is clamped between the elongated plates 36 to prevent rotational movement relative to them. An additional spacer 48 and pin structure 50 are provided substantially at the center of the locking arm 32. The locking arm 32 is free to pivot relative to the fin portions 20 relative to the extension member 38 and the lower surface 52 is supported on the upper surface of the plate 34 comprising an elongated cam surface 54, on which the free bottom end 42 of the locking arm 32 can slide. The fin surface 54 comprises a substantially horizontal portion 56 and an inclined adjacent ramp portion 58. The ramp portion 58 is preferably tilted at an approximate angle of 20 ° to the horizontal and if desired the substantially horizontal portion 56 can be tilted. slightly relative to the horizontal by a few degrees in the same direction as the ramp portion 58. The plate 34 is adjustably mounted in a vertical configuration to the base 12, by a mounting plate 60 to which the plate 34 is removably secured by bolt structures 62. Plate 34 can be easily adjusted in height and inclination. In Figure 1, the fin portions 20 are illustrated in their collapsed configuration and in this configuration, the locking arm 32 is inclined with respect to the horizontal in a unlocked portion, and its libjN end 42 rests on the ramp portion. 58 of the cam surface 54 of the plate 34. Said configuration is illustrated in dotted lines in Figure 2. During the step of bending by gravity, the fin portion 20 turns upwards under the action of the counterweights 24 which progressively cause that the glass sheet is increased as it softens when heated. The fin portion 20 moves from the dotted line position illustrated in Figure 2, to the position illustrated by the solid lines in Figure 2. It will be seen that as the fin portion 20 ascends during the bending stage by gravity, the free end 42 of the locking arm 32 slides upwardly on the ramp portion 58, until it reaches the substantially horizontal portion 56 defining a clamping area 64 for the locking arm 32. The locking arm 32 moves in a plane perpendicular to the pivot axis 22. As illustrated in Figure 4, the plate 34 defining the cam surface 54 is at right angles to the respective pivot axis 24, such that the fin portion 20 is turned upwards relative to the respective pivot axis 22, the free end 42 of the locking arm 32 and in particular the lower surface 52 of the spacer 44 slides uniformly upwards in the ramp position 58 until the locking arm 32 is substantially vertical, with its free end 42 placed in contact with the interlocking zone 64. As illustrated in Figure 2, in order to ensure that the locking arm 32 does not accidentally move out of the cam surface 54, a wire 66 connected at opposite ends 68 with opposite respective ends 70 of the plate 34, and passing between the spaced plate member 36 of the locking arm 32, can be provided. As illustrated in Figure 2, the locking arm 32 in its locked position is substantially vertical. Preferably, the height and inclination of the plate 34 is adjusted in such a way that in the locking position the locking arm 32 is not quite vertical but is slightly inclined a few degrees from the vertical, the inclination is in the same direction as for the unlocked position. In the locking position, the lower surface 52 of the non-rotatable spacer 44 frictionally engages the camming surface 54 in the locking area 64. Since the locking zone 64 is substantially horizontal and the locking arm 32 is substantially vertical, during the subsequent pressure bending operation, which is described in detail below, wherein a downward pressing force is applied to the fin portion in its upwardly rotated position, a corresponding force is transmitted downwardly through the arm of the latter. interlock 32 and thence to the base 12 through the plate 34 and the mounting plate 60 in which the plate 34 is placed. This force is pressed downward in the fin portion 20 is transmitted with distortion or deviation towards minimum down of the fin portion 20. The interlock arm 32 acts as a rigid and bolted support column for the fin portion 20 as a result of the frictional coupling between the locking arm 32 and the locking zone 64 of the camming surface 54. This allows an articulated mold 10 to have a relatively thin annular lip 30 which is employed in a subsequent pressure bending operation. It will be appreciated that an operator is required to configure the interlocking arm structure 32 / plate 34, when the apparatus is cold. However, it is required that the apparatus operates satisfactorily and reliably at elevated temperatures in the furnace, for example from about 600 to 650 ° C. the initial configuration must take into account the expansion of the various parts of the appliance when heating, as well as slight distortion of the mechanical parts as a result of thermal cycling and also mechanical wear over time. It is obviously preferred that the apparatus be easy to assemble by an operator. Accordingly, the interlocking arm structure 32 / plate 34 is preferably configured such that the locking arm 32 is not quite vertical in the pressure bending step. This ensures that even if distortion and wear were to occur, the locking arm 32 can not rotate beyond the vertical position and slide out of the end 70 of the plate 34, This additionally allows a large number of heating cycles, which a range of potential interlocking positions are defined on the interlocking zone 56 corresponding to a range of slightly varying heights (with respect to the base 12) of the fin portion 20 to which the interlock arm 32 is connected. This can compensate easily any distortion and wear that may occur as a result of successive thermal cycles. The final angular position and thus the height of the fin portion 20 is defined by stop members on the arms 26 carrying the counterweights 24 defining a final position for the mold corresponding to the final desired shape of the sheets of glass. However, it is possible that the weight of the fin portion 20 varies slightly with respect to the base 12 as a result of thermal cycling and providing an interlocking range ensures that the interlock arm operates to act as a supporting column for the fin portion 20 of the mold 10 during the pressure bending operation despite said thermal cycling which has caused a slight change in the angular position of the locking arm 32. This avoids the need for regular verification and adjustments to the interlocking devices . Preferably, the locking zone 56 is tilted slightly upwards to allow smooth sliding movement by a leveraging action of the free end 42 of the locking arm 32 on the camming surface 54. The locking arm structure 32 / plate 34 is easy to configure manually simply by adjusting the height and orientation of the plate 34 relative to the base 12, and thus with respect to the locking arm 32 in the respective fin portion 20. The final configuration of the mold 10 after the bending operation by gravity and before the pressure bending operation is illustrated in Figure 5. Although the embodiment illustrated in Figures 1 to 4 only shows an interlocking arm mounted on each fin portion 20, if desired two or more locking arms can be provided on each fin. After the pressure bending operation described below, and after the pressure-bent glass sheets have been removed from the mold in the discharge zone, the fin portion 20 can be readjusted to its initial lower configuration by a operator manually pushing the locking arm 32 inward, in order to arrange it in the configuration illustrated in dotted lines in Figure 2. If desired, this operation can be performed automatically, for example by a robot. With reference to Figure 5, the pressure bending apparatus designated generally as 72 is illustrated in the pressure bending zone in the tunnel kiln 2, the pressure bending apparatus 72 is illustrated before the bending operation by Pressure. In the pressure bending zone, the carriage 8 containing the mold 10 conveys the glass sheets bent by gravity 4 with the fin portions 10, which are placed in their upwardly facing orientation 20 arranged in their downwardly rotated orientation and with the locking arms 32 in a substantially vertical orientation and resting down against the upper surface of the respective plates 34 as described above, it is transported to a preset position in which the glass sheets 43 are placed in order to disposed below the pressure bending apparatus 72. The pressure bending operation is employed when it is desired to complete the bending of the glass sheets 4 to the required shape in such a way that the finally folded glass sheets 4 have a shape defined by the bending mold by gravity 10. The pressure bending apparatus 72 comprises a mold or upper die 74 having a surface of lower mold 76 constituting a male mold surface substantially corresponding to the female mold surface defined by the bending mold by gravity 10. The glass sheets 4 are pretended bent under pressure between the upper mold 74 and the bending mold by gravity 10, to achieve the required shape. The upper mold 74 preferably comprises a ceramic body. As illustrated in Figure 5, the upper mold 74 may comprise a unitary mold. However, in alternate configurations, the upper mold 74 may comprise a pair of spaced mold parts, which are set to press against only those portions or portions of the glass sheets 4 that are required to bend deeply, ie in the vicinity of the fin portions 20. The upper mold 74 is supported by a sub-frame 78. The sub-frame 78 is downwardly dependent from the support frame 80 by a plurality of chains 82. Preferably, there are four chains 82, each located in a respective corner of the upper mold 74. Metal cables can be used instead of chains. The support frame 80 has connected to the upper surface 84 a cable (or chain 86) extending upwards from the center of the support frame 80 through the roof 87 of the tunnel kiln 2, on a first pulley 88 to be substantially horizontally on a second pulley 90 to depend vertically downwardly with the cable end 86 connected to a first counterweight 92 which in turn is connected to a matrix movement mechanism 94. The counterweight 92 and the matrix movement mechanism 94 are located laterally adjacent the tunnel kiln 2 on a common longitudinal side. The matrix movement mechanism 94 preferably comprises a hydraulic and pneumatic cylinder / piston structure which are connected at their bottom end to the floor 96. In Figure 5, the upper mold 74 is illustrated in its raised configuration with the pin / cylinder structure 94 which is in the retracted configuration. In the raised configuration of the upper mold 74, the carriage 8 can be moved from an upstream part of the tunnel kiln 2 in a position below the upper mold 74 before the bending operation by sub-sequential pressure. The counterweight 92 is provided with a desired weight to minimize the work required to be engaged by the piston / cylinder structure 94 in raising and collapsing the upper mold 74 but with the proviso that in the case of failure of the piston structure / cylinder 94, the weight of the first counterweight 92 is sufficiently high, such that the entire apparatus surely fails to pull the upper mold structure 74 upwards, away from the carriages 8 passing underneath. A second counterweight structure is also provided to allow the upper mold 74 to rest on the glass sheets 4 during the step of bending under pressure with a predetermined net weight. A rigid metal rod 98 extends upwardly away from the center of the upper surface 100 of the eub-frame 78 for the upper mold 64. A second wire 102 connects to the upper part of the rod 98 and extends successively through orifice (not shown) in the upper bateer 80 and the roof of the furnace 88, and thence on a pair of pulleys 104, 106 to connect at its other end with a second counterweight 108 that is free to move vertically. if desired, for both the first and second counterweights 92, 108, rails or vertical supports (not shown) can be provided to prevent accidental lateral movement of the counterweights 92, 108. The second counterweight 108 has a specific weight that is chosen to provide a predetermined net weight specific to the combined structure of the upper mold 74 and the sub-frame 78 to which the mold 74 is mounted. The net weight of the upper matrix structure is typically 50 to 10 kilograms from the mold configuration particular and the desired size and shape of the folded glass sheets. The cable 102 between the second counterweight 108 and the upper mold 74 is always in tension. The metal rod 98 is provided between the cable 102 and the sub-frame 78, to reduce straining or accidental deformation of the cable 102 in the vicinity of the upper mold 74, where the ambient temperature in the pressure zone is high. The cable 86 between the mounting frame 80 and the first counterweight 92 is also always in tension. As described below, during the pressure bending step, the chains 82 are left with clearance such that during the pressure bending operation, it is only the selected net weight of the upper mold 74 and its associated sub-frame 78. which is applied to the upper surface of the glass sheets 4. On opposite sides of the upper mold 74 and adjacent there is provided a plurality of adjacent spacer devices 109. Each of the spacer devices 109 includes an upper stop member 110 comprising a vertical body 112 having fixed at its bottom end, a substantially horizontal plate 114. The upper stop members 110 are mounted firmly in the subframe 78. A corresponding plurality of lower stop members 116 of the spacer devices are mounted on the base 12. Each lower stop member 116 comprises an upwardly extending body 118, having mounted on its upper end a member is vertically adjustable pacer 120. As illustrated in greater detail with reference to Figure 7, each spacer member 120 comprises a bolt portion 122, having a domed head portion 124, substantially hemispherical and the upper portion of which is disposed , during the pressure bending operation, for leaning against the lower surface 126 of the plate portion 114 of the respective upper stop member 110. The bolt portion 122 is roeca in the upwardly extending body 118 to be easily adjustable in height and a threaded nut 128 is provided to allow fixing the domed head portion 124 at the required height. Preferably, the plate portion 114 and the domed head portion 124 are composed of steel. The upper and lower limit stop members 116 are provided in register in pairs, preferably, three pairs of stop members 110, 116 are provided. With such configuration, as illustrated in Figure 4, two pairs of stop members are provided on a long edge 117 of the mold 10 in spaced relation and a third pair of stop members 110, 116 are provided centrally on the opposite long edge 119. of the mold * Q.

The spacer devices 109 are provided to ensure that the upper and lower molds 74, 10 are substantially separated over their entire area by a space corresponding to the second of glass sheets 4 in their final shaped form. This ensures that any excessive pressure from the glass sheets 4, which may result in marking the glass sheets 4 by the annular rim 30, is sub-substantially avoided. As described in detail below, three spacer die 109s are preferably provided, such that it is ensured that the vertical position of the upper mold 74 relative to the lower gravity bending mold 10 is determined without accidental relative oscillation of the molds 74, 10. This increases the possibility that correct spacing is reliably achieved. As with the structure of the locking arms 32, it is necessary that the spacer devices 109 be adjusted by an operator when the apparatus is cold, but the spacing devices 109 must ensure adequate spacing of the upper mold 74 and the lower mold 10 at elevated temperatures. during the bending operation with pressure, which may involve accidental expansion or other deformation that occurs as a result of thermal cycling. Providing three pairs of stop members 110, 116 ensures that the space between the upper and lower molds 74, 10 can be reliably adjusted in no oscillation of the upper mold 74 relative to the lower core 10 in the final pressure bending configuration of the upper molds. molds 10, 74. It will be appreciated that in a typical tunnel kiln 2, a plurality of carriages 8 is provided, each containing a respective gravity bending mold 10. A typical furnace 2 includes at least 20 carriage structures 8 / bending mold by gravity 10. However, only an upper pressure bending die 74 is provided. An operation is required for each lower gravity bending mold 10, and its associated carriage is suitably configured with respect to the upper pressure bending mold 74. Accordingly, the spacing devices 109 to define the correct adjustable space between the molds 10, 74 are provided in conjunction with each respective bent mold 10, such that each gravity bending mold 10 can be individually configured to operate correctly with the single upper mold 74. Each spacer device 109 is individually adjusted before of the initial operation of the furnace such that during the press-bent pressure, when the upper mold 64 collapses on the glass sheets 4 transported in the mold bent by gravity 10, the upper and lower molds 74, 10 are spaced apart a distance corresponding to the height of the sheets of glass 4 in its final folding form. The pressure bending operation will now be described with reference to Figure 6. When the lower mold 10 carrying the glass sheets 4 is presented below the upper mold 74, the piston / cylinder structure 94 is actuated to lower the frame bottom 80 supporting the upper mold 74, until the upper edge 74 is in contact with the underlying glass sheets 4 in the bending mold by gravity 10. The stroke of the piston / cylinder structure 94 is greater than just required to cause contact of the upper mold 74 with the glass sheets 4. The support frame 80 thus overruns to continue to be folded down after contact of the upper mold 74 with the glass sheets 4 in such a way that the support frame 80 has collapsed in order to be closer to the subframe 78 than in the initial configuration illustrated in Figure 5. This excessive folding of the support frame 80 causes the chains 82 they can go with ease. In this configuration, the upper mold 74 and its associated sub-frame 78 bear downwardly on the glass sheets 4 with the desired net weight that is chosen by appropriate selection of a particular weight for the second counterweight 108. The upper mold 74 in this way it presses the upper surface of the glass sheets with a pre-determined net weight. Even more, since the upper mold 74 is not supported from above during the pressure bending operation, at least towards the end of the d bent operation by pressure, the weight of the upper mold 74 is distributed evenly across the confining surfaces , typically over an area of approximately 1 m2, the upper mold 84 and the underlying glass sheets 4. This ensures uniform weight distribution on the glass sheets 4 during the press bending operation. The bending operation with operation typically lasts 20 seconds. At the end of the pressure bending operation, wherein the glass sheets have been pressed in intimate contact around the entire periphery with the lower gravity bending mold 10 by the upper mold 84, for each of the spacer devices 109 , the domed head 124 bears against the plate member 114 to define through substantially the entire area of the pressure bending mold, a pre-adjusted space between the upper and lower molds 74, 10 corresponding to the thickness of the sheets of glass bent by pressure. Providing the stop member ensures that excessive pressure of the glass sheets 4 does not occur during the press bending operation. This minimizes edge marking of the inner surface of the glass sheets 4 by the annular rim 30 of the bending mold by gravity 10, which is a particular problem when using a gravity bending mold having thin ridges with a thickness of the order of approximately 3 to 4 mm. The spacer devices 109 are specially configured to allow variations in the lateral positions of the upper mold 74 and the lower mold 10, because the dome head 124 can couple the plate member 110 over a selected range of lateral positions encompassed by the area of the plate member 114. This allows precise spacing to be achieved despite possible variations in the positions of the plurality of bending molds by gravity 10 around the bending loop. This structure does not restrict the lateral freedom of the placement of the upper die 84 during bending with pressure. The upper mold 74 is supported by the support frame 70 by means of a chain 72, whereby the upper mold 74 is not restricted against translational and rotational lateral movement during the pressure bending operation. Still further, the support frame 80 is suspended from the cable 86 which in turn does not restrict the upper mold 74 against lateral movement during the press bending operation. Furthermore, supporting the upper mold 74 on the one hand with a plurality of chains 82 to a support frame 80 and on the other hand on a cable 86 between the support frame 80 and the pulley 86, allows a vertical movement without restricting, for tilt example, of upper mold parts 74 during the press-bent operation. The upper mold 74 is required precisely positioned with respect to each of the plurality of molds bent by gravity 10 throughout the loop including the tunnel kiln. In practice, the translational position, both horizontally and vertically and the rotational position, both horizontally and the inclination of each bending mold by gravity 10, will vary from one car to another, not only following the initial configuration of the furnace but also also in particular after operation of the furnace. This is due to thermal expansion, deformation as a result of thermal cycling and wear of the apparatus, eg wear of the carriage sheets on the rails. Since the upper mold 74 is allowed to lodge in the shape bent by gravity of the glass sheets 4 during the pressure bending operation without any restriction of its tilting or lateral movement, the upper mold 74 can easily find its position correct for bending with precise pressure with respect to the underlying glass sheets 4 independently of the variation in position with respect to the upper mold 74 of those glass sheets 4 from a mold bent by gravity 10 to another. This freedom of movement in the upper mold 74 during the bending operation by preemption, ensures that bending is achieved by precise pressure, regardless of any variations in positions between the plurality of lower gravity bend molds. The suspension of the upper mold 74 by bending members such as chains 82, allows this movement without restriction. In addition, the upper mold 74 is supported by the chains 82, whereby the upper edge 74 can be wound in a minor proportion slightly in contact with the underlying glass sheets 4. This allows the required shape of the underlying glass sheets 4 is achieved with a progressive thrust action as a result of the upper matrix progressively coming into contact with the underlying glass sheets 4. Preferably, the upper mold 74 is wound on the upper glass surface, such that portions of deep bent are first configured by the upper mold 74. The providing bumper member wherein the lower bumper member includes a hemispherical dome and the upper bumper member consists of a flat plate against which the dome rests, ensures vertical positioning Reliable relative of the upper mold and the lower mold, to minimize accidental marking of the glass sheets by the bending mold by gravity 10. However, this is achieved without removing or reducing the ability of the upper mold 74 to move laterally both in translation and rotation direction and to tilt vertically relative to the lower edge 10 and the glass sheets 4 in an unrestricted manner, during operation of bending with pressure. Prior to the pressure bending operation, the underlying glass sheets 4 can be heated by a ceiling heater, to provide a differential temperature profile on the surface of the glass sheets 4 to assist the glass sheets 4 which reach the form required during the bending operation with pressure. This differential ceiling heating technique is described in co-pending European patent application No. 94309435.9. The present invention can allow glass sheets with bent portions having radii as small as 150 mm to be manufactured. This can be compared with a minimum radius of 450 mm, when using bending by gravity using differential heating of the glass sheets and a minimum radius of 1000 mm when using bending by gravity without differential heating. The present invention allows glass sheets with fold portions to be fabricated with edge tensions that are compared with those that are achieved using conventional buckling bending techniques. The present invention typically allows bent glass sheets to be manufactured with tensile stresses of lower edge at 7 MPa. This allows glass sheets to be folded, without requiring a subsequent annealing to remove stresses, after the bending stage with precession.

Claims (20)

1. CLAIMS 1. An apparatus for bending a sheet of glass in a step of bending by gravity, and in a step of bending by subsequent pressure, the apparatus includes a mold of bending by gravity, which contains a fixed mold portion and at least one portion of hinged fin adjacent to the fixed mold portion, and a base on which the fixed mold portion is assembled characterized in that at least one hinged locking arm mounted between the or each respective fin portion and the base, the arm at least one interlock is progressively movable as a result of the articulation of the mold from an unlocked position in which the fin portion is able to move vertically relative to the base to a locked position where the fin portion is fixed in position against downward movement with respect to the base. An apparatus according to claim 1, characterized in that the locking arm is arranged to interlock the respective fin portion over a range of heights of the fin portion relative to the base. An apparatus according to claim 1 or 2, characterized in that the locking arm is mounted hingedly on the respective fin portion and has a free end which is arranged to slide on a surface of the base. 4. An apparatus according to claim 3, characterized in that the base is provided with an elongated cam surface which is configured to define an interlocking zone whereby the locking arm can be locked in the locked position, when the free end is in position. the interlocking zone. An apparatus according to claim 4, characterized in that the locking area of the cam surface is substantially horizontal and the camming surface is also configured to define an unlocking zone comprising an adjacent ramp portion. 6. An apparatus according to claim 5, characterized in that the ramp portion inclines at an angle of approximately 20 ° with respect to the horizontal. 7. An apparatus according to any of claims 4 to 6, characterized in that the cam surface is formed by an upper edge of a vertical plate. 8. An apparatus according to claim 7, characterized in that the plate is mounted on the base to be vertically adjustable relative thereto. 9. An apparatus according to any of claims 1 to 8, characterized in that the free end of the locking arm has a cylindrical surface that slides on the cam surface. 10. An apparatus according to claim 9, characterized in that the locking arm comprises a pair of spaced plate members, which have a spacer fixed between them at their free end, the spacer defining the cylindrical surface. 11. An apparatus according to claim 10, characterized in that it further comprises an alignment member that passes between the plate members and is fixed to the base to prevent the spacer from moving laterally out of the cam surface. 12. An apparatus according to any preceding claim, characterized in that the locking arm moves in a plane perpendicular to the pivot axis with respect to which the fin portion ee articulates the fixed mold portion with respect to a pivot axis. 13. An apparatus according to any preceding claim, characterized in that the locking arm is substantially vertical in the locked position. 14. An apparatus in accordance with the claim 13, characterized in that in the locked position the locking arm inclines a few degrees with respect to the vertical and in the unlocked position the locking arm is substantially inclined with respect to the vertical in the same direction as in the locked position. 15. A method for bending a sheet of glass, the method comprises placing at least one sheet of glass in a bending mold by gravity, consisting of a fixed mold portion and at least one hinged fin portion adjacent to the fixed mold portion , the mold is mounted on a base in a mobile cart; transport the mold that carries the glass sheet at least through an oven where the glass is heated to the softening point of the glass and bends by gravity until the periphery of the glass sheet is in contact with and adapts to the shape of the upper surface of the bending mold by gravity; pressurizing the glass sheet with a bending die by higher pressure, while the glass sheet is supported by the bending mold by gravity; cooling the folded glass sheet and removing the folded glass sheet from the mold, characterized by the or each fin portion being provided with a locking arm, and during the step of bending by gravity, the or each locking arm moves progressively as a result of the articulation of the mold from an unlocked position to an interlocked position, wherein the fin portion is fixed at a predetermined position corresponding to the desired shape of the glass sheet; and in the step of bending by pressure, the locking arm acts to lock the respective hinged fin portion in the predetermined position. 16. A method according to claim 15, characterized in that the locking arm moves from the unlocked position to the locked position by a cam coupling action. A method according to claim 16, characterized in that the locking arm is mounted in a hinged manner on the respective fin portion and has its free end that slides on a surface of the base. 18. A method according to claim 17, characterized in that the free end slides on an elongate cam surface which is configured to define a locking zone, whereby the locking arm can be located in the locked position when the end free is in the interlocking zone. 19. A method according to claim 18, characterized in that the locking area of the cam surface is substantially horizontal and the cam surface is also configured to define an unlocked zone comprising an adjacent ramp portion. 20. A method according to any of the claims 15 to 19, characterized in that it further comprises the step of allowing the articulated fin portion to be released to its initial position after the step of removing the glass sheet when pushing the arm of locking from the locked position to the unlocked position. The present invention relates to an apparatus for bending glass sheets and more particularly to bending glass sheets wherein there is an initial bending step by gravity and a subsequent bending step by pressing. The apparatus and method are particularly useful for automotive glass bending for subsequent lamination, for example in the manufacture of vehicle windshields. RS / írp / 23 / PCT048