Gravity bending glass sheets

A gravity bending mold for bending glass sheets is disclosed. The mold comprises a final mold having a final peripheral shaping rim and an intermediate mold having an intermediate peripheral shaping rim. The final mold has a final articulated end portion having a final movable shaping rail and is mounted at an end of the mold. The intermediate mold has an intermediate articulated end portion having an intermediate movable shaping rail and is mounted at the end of the mold adjacent to the final articulated end portion. The final articulated end portion and the intermediate articulated end portion are arranged so that at least a portion of the final movable shaping rail is alignable with at least a portion of the intermediate movable shaping rail to form part of the intermediate peripheral shaping rim. There is also provided a method of bending glass sheets using such a mold.

The present invention relates to a gravity bending mould, and to an apparatus for, and a method of, gravity bending glass sheets. In particular the present invention relates to gravity bending of glass sheets, otherwise known as sag bending, in which the glass sheets are supported on a bending mould while being conveyed through a heating lehr of a glass bending furnace.

It is well known to subject glass sheets to gravity bending to shape the glass sheets for forming vehicle windows, for example automotive windows. A single glass sheet may be bent on the gravity bending mould, or two glass sheets may be bent as a stack on the gravity bending mould when the glass sheets are subsequently to be laminated together to form a laminated windscreen. Many modern automotive windows require a high degree of bending curvature at one or more edges or corners. When such a large curvature is introduced into the glass sheet or sheets, this can cause visible imperfections to be introduced into the glass sheets, reducing the optical quality of the glass sheets. Also, it may be difficult to control the bending operation consistently. Furthermore, for some applications there is a need to have a high degree of surface control so that the curved glass surface better matches the design surface. This may also ensure compatibility of a windscreen with existing windscreen wiper systems.

Furthermore, although it is possible to achieve the high degree of curvature using additional forces other than gravity, such as by using a press bending die adapted to press downwardly on the upper surface of the glass sheets, it is desirable to achieve the desired curvature by using only the force of gravity acting on the glass sheets as they soften and are caused to sag to the desired shape defined by the moulds as the sheets pass through the furnace lehr. This is because if an additional press bending die is used then the upper surface of the glass sheet is contacted during the bending operation, which may lead to a reduction in the surface quality of the glass sheets as a result of inadvertent marking of the upper surface by the die, and also the equipment costs are increased. In addition the production rate can be increased by using solely gravity bending as compared to using an additional press bending step.

On a conventional gravity bending mould for bending one or more glass sheets to form a vehicle windscreen, a central portion of the bending mould is static, and two articulated wings are mounted at opposite ends of the central portion. The central portion and the two articulated wings define a peripheral rim which supports the glass sheet or sheets along a peripheral edge of the lower glass surface. The wings are connected to counterweights which apply a rotational force to the wings, tending to rotate the wings upwardly, each about a respective pivot axis, from a substantially horizontal open initial position to a closed bent position in which the rim forms the desired bent shape of the glass sheets.

Initially, the wings are pushed downwardly to the substantially horizontal open initial position and the glass sheet or sheets are placed on the bending mould, whereby the glass sheet or sheets are supported horizontally by the portions of the peripheral rim in the wings. The assembly of the glass sheet or sheets on the gravity bending mould is then passed through a heating lehr. As the glass heats it softens and progressively sags downwardly under gravity, permitting the articulated wings progressively to be rotated upwardly about their respective pivot axes under action of the counterweights, thereby to close the mould. In the final hilly closed position, the glass sheet or sheets are supported around their entire periphery by the both the portions of the peripheral rim in the wings and by the portions of the peripheral rim in the central portion.

Sometimes a high degree of curvature is desired to be introduced into the edges or corners of the glass sheets. It is known to employ an auxiliary rim provided adjacent to the rim in the articulated wing. The auxiliary rim is either mounted on the articulated wing, or is part of an auxiliary wing which is mounted to a support for the central portion.

For example, EP-A-0885851 discloses an articulated gravity bending mould incorporating such an auxiliary rim. The auxiliary rim is located at an end of the mould and is released during the bending operation. The auxiliary rim has a larger radius of curvature than the adjacent end rail, thereby causing a small amount of cross curvature to be introduced initially and then a greater amount of cross curvature to be introduced subsequently. These two bending steps overlap in time so as to provide a transition phase between the two bending steps in which longitudinal and cross bending are simultaneously introduced. This is at least partly because the auxiliary rails are caused to drop by an internal actuation, which requires continued dynamic motion of the wings during longitudinal bending to initiate the commencement of cross curvature by dropping of the auxiliary rails. This provides the technical problem that the bending operation can be difficult to control accurately. This in turn can cause quality control problems with regard to the curvature and optical properties of the glass sheets meeting the required specification.

U.S. Pat. No. 3,235,350 discloses a gravity bending mould incorporating a pair of adjacent wing portions at each end of the central portion a gravity bending mould. The first wing portion operates in an initial bending operation and then the second wing portion takes over to complete the bending operation. This mould is complicated and not suitable for making modern vehicle windscreens of high curvature in regions located at the ends or edges of the glass sheets.

The present invention aims at least partially to overcome these problems of these known gravity bending moulds.

Accordingly, the present invention provides a gravity bending mould for bending glass sheets comprising a final mould having a final peripheral shaping rim and an intermediate mould having an intermediate peripheral shaping rim, the final mould comprising a final articulated end portion mounted at an end of the mould, the final articulated end portion having a final movable shaping rail; the intermediate mould comprising an intermediate articulated end portion mounted at the end of the mould adjacent to the final articulated end portion, the intermediate articulated end portion having an intermediate movable shaping rail; wherein the final articulated end portion and the intermediate articulated end portion are arranged so that at least a portion of the final movable shaping rail is alignable with at least a portion of the intermediate movable shaping rail to form part of the intermediate peripheral shaping rim.

The present invention also provides a gravity bending mould for bending glass sheets, the gravity bending mould comprising a final mould and an intermediate mould, the final mould comprising a first support, a final fixed portion, having at least one fixed shaping rail, mounted on the first support, and at least one final articulated end portion mounted at a respective end of the fixed portion, the or each end portion having a respective final movable shaping rail, the intermediate mould comprising a second support, an intermediate fixed portion, having at least one fixed shaping rail, mounted on the second support, and at least one intermediate articulated end portion mounted at a respective end of the fixed portion, the or each end portion having a respective intermediate movable shaping rail, a releasable lowering mechanism, interconnecting the first and second supports, adapted selectively and temporarily to dispose the intermediate mould in an initial raised position with respect to the final mould, and when released to cause relative vertical movement between the intermediate and final moulds so that the intermediate mould is in a final lowered position with respect to the final mould, and wherein at least a portion of the final movable shaping rail of the at least one final articulated end portion is alignable with at least a portion of the intermediate movable shaping rail of the at least one intermediate articulated end portion to form part of an intermediate peripheral rim of the intermediate mould when the intermediate mould is in the raised position.

The present invention further provides a glass sheet bending apparatus, the apparatus comprising a plurality of gravity bending moulds according to the present invention, a furnace, and a conveyor system for successively conveying the plurality of gravity bending moulds through the furnace, the furnace including at least one actuator mechanism provided in the furnace at a predetermined location along the furnace length, the actuator mechanism being adapted to operate the releasable lowering mechanism as each respective gravity bending mould is conveyed past the actuator mechanism.

The present invention yet further provides a method of gravity bending glass sheets, the method comprising the steps of: (a) providing a gravity bending mould comprising a final mould and an intermediate mould, the final mould having at least one final articulated end portion having a first curvature, the final articulated end portion having a final movable shaping rail; the intermediate mould having at least one intermediate articulated end portion having a second curvature, the or each intermediate articulated end portion being adjacent to a respective final articulated end portion and the second curvature thereof being lower than the first curvature of the respective final articulated end portion, (b) disposing the intermediate mould in a raised position with respect to the final mould; (c) placing at least one flat glass sheet on the intermediate mould with the or each articulated end portion of the intermediate mould being in a substantially horizontal open position, the at least one flat glass sheet being supported by at least one portion of the final movable shaping rail of the at least one final articulated end portion which forms part of an intermediate peripheral rim of the intermediate mould when the intermediate mould is in the raised position; (d) gravity bending the at least one flat glass sheet in a furnace by heating the at least one glass sheet, the heating causing softening of the at least one glass sheet thereby to gravity bend the at least one glass sheet, the gravity bending comprising two phases, (i) a first phase in which the at least one flat glass sheet is bent to an intermediate bent shape by the intermediate peripheral rim of the intermediate mould; and (ii) a second phase, after the first phase, in which the intermediate mould is in a lower position with respect to the final mould and the at least one glass sheet is bent from the intermediate bent shape to a final bent shape by the final mould.

Further advantageous embodiments of the invention will be apparent from the dependent claims.

Referring toFIGS. 1 to 7of the drawings, there is shown a gravity bending mould2for bending glass sheets in accordance with an embodiment of the present invention. The gravity bending mould2comprises a final peripheral rim3. The final peripheral rim3comprises a central portion4and two wing portions6,8. The central portion4of the final peripheral rim3is mounted on a support10. The central portion4has two opposed side shaping or bending rails11,12that are substantially parallel, substantially horizontal and static with respect to the support10. One side bending rail11is configured to shape an upper longitudinal edge of a vehicle windscreen and the other side bending rail12is configured to shape a lower longitudinal edge of the vehicle windscreen.

The wing portions6,8are articulated and are mounted at opposite ends of the central portion4. Each wing portion6,8has a respective shaping or bending rail14,16which is substantially L-shaped, and includes an end section18and one side section22. The end section18is configured to shape a respective lateral transverse edge of the vehicle windscreen and the side section22is configured to shape longitudinal end portions of an upper longitudinal edge of the vehicle windscreen. The side section22has a high degree of longitudinal curvature.

In a modification of the illustrated embodiment, two opposed side sections are provided, each wing portion6,8having a respective shaping or bending rail14,16which is substantially U-shaped, and includes an end section18and two side sections22. The end section18is configured to shape a respective lateral transverse edge of the vehicle windscreen and the two side sections22are configured to shape longitudinal end portions of, respectively, the upper and lower longitudinal edges of the vehicle windscreen. The side sections22each have a high degree of longitudinal curvature.

The bending rails11,12of the central portion4and the bending rails14,16of the two articulated wing portions6,8define the final peripheral rim3which supports the glass sheet or sheets24along a peripheral edge26of the glass sheet lower surface28. The wing portions6,8are connected to counterweights30,32which apply a rotational force on the wing portions6,8, tending to rotate the wing portions6,8upwardly, each about a respective pivot axis defined by pivot mounts34,36on the support10. In the bending operation, the wing portions6,8are rotated from a substantially horizontal open initial position, shown inFIGS. 1 and 2, to a closed bent position, shown inFIGS. 3 and 4, in which the final peripheral rim3forms the desired final bent shape of the glass sheets24. The bending rails11,12of the central portion4and the bending rails14,16of the two articulated wing portions6,8have a curved upper surface which corresponds to the desired shape of the periphery of the glass sheets24so that the curved shape of the entire final peripheral rim3defines, in the closed configuration of the mould2, the final desired shape of the windscreen peripheral edge.

In accordance with the present invention, an intermediate peripheral rim40is provided in addition to the final peripheral rim3. The intermediate peripheral rim40is located inwardly of the final peripheral rim3, adjacent and substantially parallel thereto. The intermediate peripheral rim40comprises an intermediate central portion42and two intermediate wing portions44,46. The intermediate central portion42of the intermediate rim40is mounted on an intermediate support47in a fixed position relative thereto. The intermediate central portion42has two opposed intermediate side shaping or bending rails50,52that are substantially parallel, substantially horizontal and static with respect to the intermediate support47. One side bending rail50is configured preliminarily to shape an upper longitudinal edge of a vehicle windscreen and the other side bending rail52is configured preliminarily to shape a lower longitudinal edge of the vehicle windscreen.

The intermediate wing portions44,46are articulated about axes and are mounted on the intermediate support47at opposite ends of the intermediate central portion42. Each intermediate wing portion44,46has a respective shaping or bending rail54,56which includes two side sections58,60. The two side sections58,60are configured preliminarily to shape longitudinal end portions of, respectively, the upper and lower longitudinal edges of the vehicle windscreen. The two side sections58,60are spaced to define a gap59therebetween in which the end section18of the respective wing portion6,8that define the final peripheral rim3is received when the intermediate peripheral rim40is in the raised position. The intermediate wing portions44,46are therefore not provided with an end section. Instead, the only peripheral rim portion at an end section of the gravity bending mould2is provided by the end sections18of the wing portions6,8that define the final peripheral rim3.

The two side sections58,60have a lower degree of longitudinal curvature than, respectively, the end portions of the side rail50and the side section22, and introduce a preliminary degree of longitudinal curvature to an intermediate bent glass shape defined by the intermediate peripheral rim40.

The intermediate support47is mounted on the support10so as to be vertically movable relative thereto under the action of gravity between a raised position and a lowered position. The intermediate peripheral rim40is correspondingly moved between a raised position and a lowered position relative to the final peripheral rim3.

The intermediate support47and the support10have provided therebetween a hinge assembly62along one longitudinal edge and a releasable lowering mechanism64along the other longitudinal edge which permits the above-described relative vertical motion therebetween. The hinge assembly62has an elongate horizontal axis provided by a shaft66. The releasable lowering mechanism64comprises a pair of link elements68,70pivotally linked together by a pivot72at a central part of the releasable lowering mechanism64and each respectively pivotally linked, by a respective pivot74,76, at the other end thereof to the intermediate support47and the support10. The link element70pivotally linked to the support10is provided with an outwardly extending integral release plate78.

The releasable lowering mechanism64between the intermediate support47and the support10can be moved between a raised position and a lowered position correspondingly with the raising and lowering of the intermediate support47. In the raised position, the link elements68,70are aligned substantially vertically and the pivots72,74,76are aligned substantially vertically. The link elements68,70selectively and temporarily lock the intermediate support47, and consequently the intermediate peripheral rim40, in the raised position. In this position, the release plate78is substantially horizontal.

When it is desired to release the intermediate support47and permit it to drop under the action of gravity to the lowered position, the release plate78is pushed downwardly to be rotated into a downwardly inclined position. This correspondingly causes downward rotation of the lower link element70about pivot76, which in turn rotates the upper link element70about pivot74, in the opposite rotational direction as a result of the pivotal motion about central pivot72. The resultant collapsible scissor action of the link elements68,70on such release causes the intermediate support47to drop downwardly.

The articulated intermediate wing portions44,46of the intermediate peripheral rim40are rotationally movable between an open position and a closed position. In the open position the two side sections58,60of each intermediate wing portion44,46are substantially horizontal, the two opposed ends80,82of each of the side sections58,60being configured to support an initial flat glass sheet24.

Each of the intermediate wing portions44,46has a laterally outwardly extending flange45that has an upper surface49adapted to bear against a lower surface51of the respective adjacent articulated wing portion6,8of the final peripheral rim3. In the raised position of the intermediate peripheral rim40, the flange45interlocks the movement of the articulated intermediate wing portions44,46of the intermediate peripheral rim40and the respective adjacent articulated wing portions6,8of the final peripheral rim3during an initial bending phase, described hereinafter. The upper surface55of the ends80of the two side sections58,60of each intermediate wing portion44,46coincides with the upper surface57of the adjacent portion of the final peripheral rim3, which is at the corner junction between the end section18and, respectively, the end portion of the side rail50and side section22.

In the closed position of the intermediate peripheral rim40, shown in phantom inFIG. 4, the upper surfaces of the two side sections58,60are respectively aligned with the upper surfaces of the two opposed intermediate side shaping rails50,52of the intermediate central portion42to define a continuous intermediate curved shape for the peripheral edge of the glass sheets24. A stop member53on the intermediate central portion42prevents over-rotation of the respective articulated intermediate wing portion44,46and ensures that the articulated intermediate wing portion44,46terminates in the closed position of the intermediate peripheral rim40.

In the raised position of the intermediate peripheral rim40carried on the intermediate support47, the upper shaping surface50of the intermediate peripheral rim40is higher than that of the final peripheral rim3except that at least the ends of the end section18of the wing portion6,8of the final peripheral rim3are at the same height as the ends80of the side sections58,60of the intermediate wing portions44,46. In the lowered position of the intermediate peripheral rim40, the upper shaping surface50of the intermediate peripheral rim40is lower than that of the final peripheral rim3along its entire length.

The wing portions6,8of the final peripheral rim3can each be latched by a respective latch35that cooperates between a weight arm37carrying the respective counterweight30,32and a peg39on the intermediate support47. The latching holds up the final peripheral rim3, and in particular the end sections18of the wing portions6,8thereof that define the glass edges at the A-pillar of the windscreen, after the preliminary bending step on the intermediate peripheral rim40. When the intermediate support47is in the raised position, as shown inFIG. 2, the latch35is not engaged with the peg39. The upward movement of the wing portions6,8during the preliminary shaping on the intermediate peripheral rim40is achieved by the biasing force from the counterweights30,32. However, when the intermediate support47is in the lowered position, as shown inFIG. 4, the latch35engages with the peg39to provide a locking upward force on the wing portions6,8. This latching keeps the wing portions6,8at an upper limit position corresponding to the desired position of the wing portions6,8after the final peripheral rim3has closed completely to a final curved shape defining a final curvature for the glass sheets.

During the preliminary moulding of the glass sheets24on the intermediate peripheral rim40, the end section18remains in contact with the glass sheets24because at least the ends of the end section18are at the same height as the ends of the side sections58,60as a result of operation of the flange45. After engagement of the latch35, which occurs by dropping of the intermediate support47, the counterweights30,32are urged to rotate further downwardly under a greater applied force than their own weight, thereby assisting the wing portions6,8to continue to rotate upwardly away from the intermediate position towards a final desired position of the wing portions6,8defining a final curvature for the glass sheets by the final peripheral rim3, and the wing portions6,8, have closed completely.

As is known in the art, as shown inFIG. 8, a series of bending moulds2are provided, each being mounted on a respective carriage92which is conveyed, in turn, through a heating lehr94of a glass bending furnace96by a conveyor system98.

In accordance with the invention, an actuator mechanism100is provided in the furnace96at a predetermined location along the furnace length. The actuator mechanism100is adapted to operate the release plate78of the releasable lowering mechanism64as the respective bending mould2passes thereby. Typically, the actuator mechanism100comprises an elongate member102, such as a metal bar104carrying a flange106at its end, the flange106having a downwardly directed curved cam surface108. The actuator mechanism100pushes the release plate78downwardly as the bending mould2is conveyed past the actuator mechanism100. This causes the releasable lowering mechanism64to be released at a specific point of time in the glass bending operation, which in turn causes the intermediate peripheral rim40, carried on the intermediate support47, to drop under the action of gravity from the raised position to the lowered position with respect to the final peripheral rim3.

In addition, upstream of the furnace entrance97is located a first priming actuator99, illustrated schematically inFIG. 8. Before, or after in some embodiments, the glass sheets are loaded onto the bending mould, the first priming actuator97engages the mould2to dispose the intermediate peripheral rim40in the raised position prior to passage of the bending mould2through the furnace. This priming actuator72primes the bending mould2ready for the first phase of the bending operation, whereas the first actuator mechanism100initiates the commencement of the second phase of the bending operation.

The glass bending operation will now be described.

Initially, the intermediate peripheral rim40carried on the intermediate support47is disposed in the raised position, e.g. by the first priming actuator99and supported in that position by the releasable lowering mechanism64. The wing portions6,8of the final peripheral rim3and the intermediate wing portions44,46of the intermediate rim40are pushed downwardly to the substantially horizontal open initial position as shown inFIGS. 1,2and5. The initial planar glass sheet or sheets24are placed on the bending mould2, whereby the flat glass sheet or sheets24are supported horizontally by at least the ends of the end sections18of the final peripheral rim3and by the ends80,82of the side sections58,60of the intermediate wing portions44,46of the intermediate peripheral rim40.

The assembly of the glass sheet or sheets24on the gravity bending mould2is then passed through the heating lehr94. As the glass heats it softens and progressively sags downwardly under gravity, permitting the articulated wing portions6,8progressively to be rotated upwardly about their respective pivot axis under action of the counterweights30,32, thereby progressively to bend the glass sheet or sheets24and close the mould2.

During a first phase of the glass bending operation, the ends of the glass sheet or sheets24are supported on the end sections18of the wing portions6,8of the final peripheral rim3and on the side sections58,60of the intermediate wing portions44,46of the intermediate peripheral rim40. As the wing portions6,8pivot upwardly, the wing portions44,46correspondingly pivot by the interlocking action between the flange45of the intermediate peripheral rim40and the final peripheral rim30. The lower glass surface sags into contact with the end sections18of the wing portions6,8of the final peripheral rim3, the side sections58,60of the intermediate wing portions44,46of the intermediate peripheral rim40, and the intermediate side shaping rails50,52of the intermediate central portion42. The intermediate wing portions44,46rotate to their stop position defined by the stop member53. This closes the intermediate peripheral rim40to its final configuration, and forms an intermediate curved shape for the glass sheet or sheets24. This is shown inFIG. 6.

The ends126of the glass sheet or sheets24are given a relatively low preliminary longitudinal curvature in the first phase, which is significantly lower that the final longitudinal curvature in the ends126. The central portion128of the glass sheet or sheets24is given a relatively low preliminary longitudinal curvature in the first phase, which is substantially similar to the final longitudinal curvature in the central portion128. In the first phase, both the ends126of and the central portion128of the glass sheet or sheets24are given a relatively low preliminary cross curvature in the first phase, which is substantially similar to the final cross curvature. In the first phase, the lateral peripheral edges130of the glass sheet or sheets24are bent to their final curvature.

After the desired preliminary curvature has been introduced completely by full closing of the intermediate peripheral rim40, in a subsequent second phase of the glass bending operation the intermediate peripheral rim40is released by operation of the actuator mechanism100, external of and separate from the bending mould2, which is located in the furnace96at the predetermined location along the furnace length. The actuator mechanism100operates the release plate78as the respective bending mould2passes thereby, causing the releasable lowering mechanism64to be released, which in turn causes the intermediate peripheral rim40on the intermediate support47to drop under the action of gravity from the raised position to the lowered position with respect to the final peripheral rim3.

The dropping of the intermediate support47engages the latch35by the peg39so that the final peripheral rim3, and in particular the wing portions6,8thereof, is locked and supported in a final closed position.

As the intermediate peripheral rim40drops downwardly, the preliminarily bent glass sheet or sheets24are supported solely by the final peripheral rim3. Initially in the second phase, only the lateral peripheral edges130of the glass sheet or sheets24are supported, in particular by the end sections18. Thereafter in the second phase, the glass sheet or sheets24are progressively bent further to a final curvature and sag by gravity into contact with the remainder of the final peripheral rim3. In particular, the side sections22introduce a high degree of longitudinal curvature to the final bent glass shape, in particular in the end portions126. The final configuration is shown inFIGS. 3,4and7.

This enables the glazing ends to be bent to the desired high degree of longitudinal curvature defined by the shape of the side sections20,22only after the preliminary longitudinal shaping to a lower degree of longitudinal curvature has been completed by the side sections58,60of the intermediate peripheral rim40.

This completes the bending operation. The mould and bent glass thereon pass through the remainder of the furnace, undergoing a conventional annealing and cooling schedule. After the bending mould2exits the furnace, the bent glass sheets24are removed from the bending mould2and allowed to cool. The bending mould2is returned to the entrance of the furnace, primed and loaded with flat glass sheets in a subsequent glass bending cycle.

In the first embodiment, the upper shaping surface of each end section18has only a low degree of curvature, or even has no curvature and is linearly flat. Consequently, at the beginning of the bending operation, or shortly thereafter, the lower surface28of the glass sheet24contacts the upper shaping surface of each end section18. This ensures that the lower surface28of the glass sheet24is constantly and commonly in contact with a significant proportion of the final peripheral rim3throughout a significant proportion of the entire bending operation. This is because the end section18acts as a common shaping section of the peripheral rim3which is employed in both the initial shaping phase and the final shaping phase. This ensures a high degree of positional accuracy of the glass sheet24on the gravity bending mould2because the common contact of the lower surface28with a significant length of the final peripheral rim3during the bending operation tends to prevent any inadvertent shifting or sliding movement of the glass sheet24on the gravity bending mould2.

In accordance with a second embodiment of the present invention, a modified end rail structure is provided when the upper shaping surface of each end section18has a higher degree of curvature than in the first embodiment. Such a modified structure ensures, as for the first embodiment, that the lower surface28of the glass sheet24is constantly and commonly in contact with a significant proportion of the final peripheral rim3throughout a significant proportion of the entire bending operation, with the end rail acting as a common shaping section of the peripheral rim3which is employed in both the initial shaping phase and the final shaping phase. This again ensures a high degree of positional accuracy of the glass sheet24on the gravity bending mould2during the bending operation which tends to prevent any inadvertent shifting or sliding movement of the glass sheet24on the gravity bending mould2.

Referring therefore toFIGS. 9 to 13, in which for clarity the intermediate mould is not shown, in accordance with the second embodiment of the present invention an auxiliary end rail140is provided on each wing portion6,8of the final peripheral rim3. The auxiliary end rail140is mounted adjacent and substantially parallel to a respective end section18of the respective wing portion6,8. In accordance with the embodiment illustrated inFIGS. 9 to 13, the auxiliary end rail140is mounted to the end section18laterally inwardly of the end section18, by means of a series of spaced slider mounts142that are adapted to permit substantially vertical sliding movement of the entire auxiliary end rail140with respect to the respective end section18. Each auxiliary end rail140can move between a raised, supported position (FIGS. 9 to 11) and a lowered unsupported position (FIGS. 12 and 13) relative to the respective end section18. Each slider mount142comprises a substantially horizontal pin143fixed to the end section18and slidably received in a substantially vertical slot145in the respective auxiliary end rail140.

Such relative sliding motion may sometimes be inhibited by mechanical interference, for example by inadvertent catching or rubbing of insulating material on one or both of the parts, between the respective auxiliary end rail140and the respective end section18which would inhibit a free dropping action of the auxiliary end rail140relative to the respective end section18as described in detail hereinafter.

Accordingly, to avoid such mechanical interference,FIG. 14shows a schematic side elevation of an alternative third embodiment of the mounting of auxiliary end rail240on the articulated wing portion6,8of the gravity bending mould2. In this embodiment, the auxiliary end rail240is mounted to the end section18laterally inwardly of the end section18, by means of a series of spaced pivot mounts242that are adapted to permit substantially arcuate movement of the entire auxiliary end rail240with respect to the respective end section18. The mounts242are spaced along each end section18/auxiliary end rail240pair in a manner similar to the mounts142of the second embodiment. Each auxiliary end rail240can move between a raised, supported position and a lowered unsupported position relative to the respective end section18. Each pivot mount242comprises upper and lower parallel pivot arms246a,246b, each pivotally mounted at a respective first pivot248a,248bto the respective wing portion6,8and at a respective second pivot250a,250bto the respective auxiliary end rail240. The first pivots248a,248band the second pivots250a,250bhave substantially horizontal pivot axes. The provision of parallel pivot arms ensures that the auxiliary end rails138,140move smoothly in a defined arc and is maintained in a vertical configuration through the arcuate movement. This ensures that the auxiliary end rails138,140do not inadvertently engage the wing portions during their arcuate downward motion.

When moving from the raised, supported position shown in solid lines inFIG. 14to the lowered unsupported position shown in phantom inFIG. 14, each pivot arm246a, brotates downwardly in a first rotational sense (e.g. clockwise inFIG. 14) about the first pivot248a, band the respective auxiliary end rail240rotates about the second pivot250a, ba second opposite rotational sense (e.g. anticlockwise inFIG. 14). This causes the auxiliary end rail240to be moved laterally away from the respective end section18during the dropping motion. Such lateral movement reduces the possibility of any mechanical interference, for example by inadvertent catching or rubbing of insulating material on one or both of these parts, between the respective auxiliary end rail240and the respective end section18which would inhibit a free dropping action.

For the second embodiment, a similar structure being present in the third embodiment, a tripping support mechanism146selectively and temporarily supports the auxiliary end rail140in a raised position with respect to the respective end section18. The support mechanism146can be temporarily locked in the support position, and can be subsequently released by a latch mechanism148connected thereto. The latch mechanism148is adapted to release the support for the auxiliary end rail140so that the auxiliary end rail140drops under the action of gravity from the raised position to a lowered position with respect to the respective end section18.

In the illustrated embodiment, each auxiliary end rail140is automatically pushed upwardly into the raised position with respect to the respective end section18and the support mechanism146is automatically locked in the support position when the wing portions6,8are opened prior to the loading operation for the flat glass sheets24.

In the illustrated embodiment, the upper surface150of the auxiliary end rail140is flat, or at least substantially flat, so that the auxiliary end rail140introduces no, or at least substantially no, transverse curvature to the glass sheets24during the bending operation. However, some relatively minor degree of curvature may be present in the upper surface150of the auxiliary end rail140. In contrast, the upper surface151of the adjacent end section18has a higher degree of curvature that the upper surface150of the auxiliary end rail140.

In the raised position (seeFIGS. 9 to 11) the upper surface150of the auxiliary end rail140is, in a central portion thereof, higher than the upper surface151of the respective end section18, but at the opposed longitudinal ends of the auxiliary end rail140the upper surface150coincides in height with the upper surface151of the respective wing portion6,8at the opposed ends of the end section18. In contrast, in the lowered position shown inFIGS. 12 and 13, the upper surface150of the auxiliary end rail140is lower than the upper surface151of the respective end section18.

In accordance with the invention, as shown inFIG. 8, a second actuator mechanism160is provided in the furnace56at a predetermined location along the furnace length, downstream of the first actuator mechanism100. The second actuator mechanism160is adapted to operate the latch mechanism148as the respective bending mould2passes thereby. Typically, the second actuator mechanism160comprises an elongate member162, such as a metal bar164carrying a flange166at its end, the flange having an inwardly directed curved cam surface168. The second actuator mechanism160pushes the latch mechanism148as the bending mould2is conveyed past the second actuator mechanism160. This causes the support mechanism146to be released at a specific point of time in the glass bending operation, which in turn causes the respective auxiliary end rail140to drop under the action of gravity from the raised position to a lowered position with respect to the respective end section18.

In addition, upstream of the furnace entrance97is located a second priming actuator101, illustrated schematically inFIG. 8. Before, or after in some embodiments, the glass sheets are loaded onto the bending mould, the second priming actuator101engages the mould2to dispose the auxiliary end rails140in the raised position prior to passage of the bending mould2through the furnace. This second priming actuator101primes the bending mould2ready for the first and second phases of the bending operation, whereas the second actuator mechanism160initiates the commencement of the third phase of the bending operation.

The glass bending operation for the second and third embodiments will now be described.

In the first embodiment the gravity bending is carried out in two phases, a first phase in which the at least one flat glass sheet is bent to an intermediate bent shape by the intermediate peripheral rim of the intermediate mould; and a second phase, after the first phase, in which the intermediate mould is in a lower position with respect to the final mould and the at least one glass sheet is bent from the intermediate bent shape to a final bent shape by the final mould.

In the second and third embodiments the gravity bending is carried out in three phases, a third phase following the aforesaid first and second phases. In the first and second phases the opposed ends of the glass sheet are supported on the auxiliary ends rails, so that in these two phases the opposed ends have no, or substantially no, cross curvature introduced thereinto. The opposed ends are supported throughout the first and second phases by contact with the auxiliary end rail. In the third phase, after the second phase, the auxiliary ends rails are dropped away from the glass sheet, and the opposed ends are permitted to sag downwardly into contact with the curved upper surface of the end sections. This introduces significant cross curvature into the opposed ends of the glass sheet.

Initially, at the beginning of the first phase, shown inFIGS. 9 and 10, the auxiliary end rails140are disposed in the raised position and supported in that position by the support mechanism146, e.g. by the second priming actuator101. The initial planar glass sheet or sheets24are supported horizontally at their opposed longitudinal ends on the auxiliary end rails140.

The assembly of the glass sheet or sheets24on the gravity bending mould2is then passed through the heating lehr94. As the glass heats it softens and progressively sags downwardly under gravity, permitting the articulated wings6,8progressively to be rotated upwardly about their respective pivot axis under action of the counterweights30,32, thereby progressively to bend the glass sheet or sheets24and close the mould2.

As described above, in the first phase the glass sheet sags into contact with the intermediate peripheral rim40of the intermediate mould and in the second phase the intermediate mould has been dropped downwardly below the final mould and the glass sheet sags into contact with the final peripheral rim3of the final mould.

During the first and second phases of the glass bending operation, the ends of the glass sheet or sheets24are supported on the auxiliary end rails140of the final mould. Since the upper surfaces150of the auxiliary end rails140are linearly straight or substantially linearly straight, no, or substantially no, transverse or cross curvature is introduced into the glass sheet or sheets24during the first and second phases of the glass bending operation. During the first and second phases of the glass bending operation, the two wing portions6,8pivot upwardly fully to the closed position, as discussed above with respect to the first embodiment, to provide the necessary longitudinal curvature prior to any movement of the auxiliary end rails140relative to the respective end section18. The glass sheets24sag under gravity so as to contact, and be supported by, the final peripheral rim3around the entire periphery of the glass sheets24at the end of the second phase.

In these first and second phases of the glass bending operation, the ends of the glass sheet or sheets24are not bent to give any cross curvature because they are supported on the linearly straight horizontal auxiliary end rails140. Instead, the ends of the glass sheet or sheets24remain constantly substantially planar throughout the first and second phases.

After the desired longitudinal curvature has been introduced completely by full closing of the articulated bending mould2, as shown inFIGS. 12 and 13in the third phase of the glass bending operation the auxiliary end rails140are released by operation of the second actuator mechanism160, external of and separate from the bending mould2, which is located in the furnace56at the predetermined location along the furnace length. The second actuator mechanism160operates the latch mechanism148as the respective bending mould2passes thereby, causing the support mechanism146to be released, which in turn causes the respective auxiliary end rail140to drop under the action of gravity from the raised position to the lowered position with respect to the respective end section18. This enables the glazing ends to be bent to the desired cross curvature defined by the shape of the end sections18in a third phase only after the longitudinal shaping has been completed in the first and second phases. The glazing ends sag into contact with the end sections18. This completes the bending operation. The mould and bent glass thereon pass through the remainder of the furnace, undergoing a conventional annealing and cooling schedule.

After the bending mould2exits the furnace, the bent glass sheets24are removed from the bending mould2and allowed to cool. The bending mould2is returned to the entrance of the furnace, primed and loaded with flat glass sheets in a subsequent glass bending cycle.

Although the illustrated embodiments show a gravity bending mould for bending glass sheets to form a windscreen, having symmetric wing portions on opposite ends of a central portion, it will be apparent to those skilled in the art that other gravity bending mould configurations may be employed in accordance with the present invention. For example, only a single wing may be provided, or alternatively the opposed wings may not be symmetrical. In addition, the or each wing may have only two sides, as opposed to three sides (to form the U-shape) as shown in the illustrated embodiment. Yet further, the inclination of the various rails to the longitudinal direction of the gravity bending mould may be varied. Also, the intermediate peripheral rim may be mounted laterally outwardly of the final peripheral rim.

In the illustrated embodiment, the intermediate rim drops under the action of gravity when released so as to commence the second phase of the bending operation, the final rim being in a fixed vertical position. However, the present invention may alternatively provide that the final rim is configured to move upwardly with respect to the intermediate rim, the latter being in a fixed vertical position. In either case, there is relative vertical motion between the intermediate rim and the final rim going from the first phase to the second phase of the bending operation, and the raised final rim takes over the bending operation from the intermediate rim.

In accordance with the present invention, a minority, in particular a low proportion, of the longitudinal curvature of the highly curved parts of the final glazing is introduced into the glass sheets in a first preliminary shaping phase and a majority, in particular a high proportion, of the longitudinal curvature of the highly curved parts of the final glazing is introduced into the glass sheets in a second final shaping phase. The two bending phases are separate. This separation, and the initiation of the second phase, is readily controlled within the furnace by use of an actuator external of the mould to trip the release plate to release the intermediate preliminary rim at a precise period within the bending operation. This provides the technical advantage of greater control over the bending operation, but still using a simple bending mould structure. The provision of a common part of the intermediate and final peripheral rims, that is the end rail of the final rim in the illustrated embodiment, contacting and supporting the glass sheets throughout the entire bending operation provides a stable support for the glass sheets and a controlled transition from the preliminary peripheral rim, defining an intermediate curvature, to the final peripheral rim, defining a final curvature.

In the embodiments described herein, the final mould and the intermediate mould each have a fixed portion. However it will be readily apparent to one skilled in the art that the final mould and the intermediate mould may comprise no fixed portions. For example, the gravity bending mould may have an intermediate mould having only two intermediate articulated end portions and a final mould having only two final articulated end portions. The gravity bending mould may therefore comprise a final mould having a final peripheral shaping rim and an intermediate mould having an intermediate peripheral shaping rim. The final mould comprises a final articulated end portion mounted at an end of the mould, which has a final movable shaping rail. The intermediate mould comprises an intermediate articulated end portion mounted at the end of the mould adjacent to the final articulated end portion, which has an intermediate movable shaping rail. The final articulated end portion and the intermediate articulated end portion are arranged so that at least a portion of the final movable shaping rail is alignable with at least a portion of the intermediate movable shaping rail to form part of the intermediate peripheral shaping rim.

Alternatively, the gravity bending mould may have a fixed portion that is common to the final mould and the intermediate mould, the fixed portion having a fixed shaping rail wherein the fixed shaping rail forms part of the intermediate shaping rim and the final shaping rim. The fixed portion may be a straight rail. The fixed portion may be a ‘U’ shaped rail in which case the final articulated end portion is mounted at the open end of the ‘U’, with the intermediate articulated end portion being mounted adjacent to the final articulated end portion. For a gravity bending mould having a ‘U’ shaped fixed portion, only one end of the glass sheet will be subject to the method of bending in accordance with the present invention.

As an alternative, the gravity bending mould may comprise a final mould that has a final fixed portion having a final fixed shaping rail and an intermediate mould that has an intermediate fixed portion having an intermediate fixed shaping rail, the final fixed shaping rail forming part of the final peripheral shaping rim and the intermediate fixed shaping rail forming part of the intermediate peripheral shaping rim. The final fixed portion may be in mechanical communication with the intermediate fixed portion via a releasable lowering mechanism adapted selectively and temporarily to dispose the intermediate mould in an initial raised position with respect to the final mould, and which when released causes relative vertical movement between the intermediate and final moulds, such that when the intermediate mould is in the raised position, the intermediate peripheral shaping rim comprises a portion of the final movable shaping rail. The gravity bending mould may be configured such that the final fixed portion is mounted on a first support, the intermediate fixed portion is mounted on a second support, the final articulated end portion is mounted at an end of the final fixed portion, the intermediate articulated portion is mounted at the end of the intermediate fixed portion adjacent to the final articulated end portion, and the releasable lowering mechanism interconnects the first and second supports.

The present invention has particular application in the manufacture of vehicle windscreens for which a high degree of curvature is desired to be introduced into the edges or corners of the glass sheets.

The embodiments of the present invention provide the technical advantage that a division of the glass bending in the longitudinal direction is achieved, so that high longitudinal curvature is introduced in a separate phase at the end of the glass bending operation. This can enhance the optical quality of the bent glass sheets and of vehicle glazing produced therefrom. In particular, kinks and inverse curvature, the latter resulting from reverse bending, can be substantially eliminated, in particular from regions of high curvature. Furthermore, the problem of inadvertent lift of the lower glass surface from the peripheral rim can be avoided. In summary, these benefits permit the production of glass sheets of high curvature with enhanced properties.

In accordance with the second and third embodiments of the present invention, in addition all of the longitudinal curvature is introduced into the glass sheets prior to any (or substantially any) cross curvature being introduced. The longitudinal bending and cross (transverse) bending are separate. This separation, and the initiation of the third phase, is readily controlled within the furnace by use of an actuator external of the mould to trip the latch mechanism to release the auxiliary end rails at a precise period within the bending operation. This provides the technical advantage of greater control over the bending operation, but still using a simple bending mould structure.

These embodiments of the present invention further provide the technical advantage that a separation of the glass bending in the longitudinal and cross (transverse) directions is achieved. This can further enhance the optical quality of the bent glass sheets and of vehicle glazing produced therefrom. In particular, by completing the longitudinal bending before commencing the cross bending, kinks and inverse curvature, the latter resulting from reverse bending, can be substantially eliminated, in particular from regions of high curvature. Furthermore, the problem of inadvertent lift of the lower glass surface from the peripheral rim can be avoided. In summary, these benefits permit the production of glass sheets of high curvature with enhanced properties.

Yet further, these enhanced properties can be achieved using a low cost mould in a readily controllable production, and at a high production rate.

In the illustrated second and third embodiments, the auxiliary rail drops under the action of gravity when released so as to commence the third phase of the bending operation. However, the present invention may alternatively employ an auxiliary rail having a fixed vertical position, and instead the final ring (or an articulated wing thereof) may be configured to move upwardly with respect to the auxiliary rail. In either case, there is relative vertical motion between the auxiliary rail and the adjacent peripheral rail going from the second phase to the third phase of the bending operation, and the raised adjacent peripheral rail takes over the bending operation from the lowered auxiliary rail.