U.S. patent application number 16/613943 was filed with the patent office on 2021-12-30 for method and apparatus for shaping a glass sheet.
This patent application is currently assigned to Pilkington Group Limited. The applicant listed for this patent is Pilkington Group Limited. Invention is credited to Michael HURST, John George LEE, Joachim PILZ.
Application Number | 20210403363 16/613943 |
Document ID | / |
Family ID | 1000005879472 |
Filed Date | 2021-12-30 |
United States Patent
Application |
20210403363 |
Kind Code |
A1 |
HURST; Michael ; et
al. |
December 30, 2021 |
METHOD AND APPARATUS FOR SHAPING A GLASS SHEET
Abstract
Methods of shaping a glass sheet are described comprising
heating the glass sheet to a temperature for shaping; positioning
the glass sheet on a shaping support; shaping the glass sheet on
the shaping support, wherein during the shaping of the glass sheet
at least one portion of the glass sheet is deliberately cooled. In
preferred embodiments, the shaping of the glass sheet involves
press bending a heat softened glass sheet between a lower shaping
support and an upper shaping member, and wherein during the shaping
of the glass sheet on the shaping support only a portion of the
major surface of the glass sheet facing the lower shaping support
is cooled by directing one or more jet of air onto said
portion.
Inventors: |
HURST; Michael; (Lancashire,
GB) ; LEE; John George; (Merseyside, GB) ;
PILZ; Joachim; (Oer-Erkenschwick, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pilkington Group Limited |
Lancashire |
|
GB |
|
|
Assignee: |
Pilkington Group Limited
Lancashire
GB
|
Family ID: |
1000005879472 |
Appl. No.: |
16/613943 |
Filed: |
June 1, 2018 |
PCT Filed: |
June 1, 2018 |
PCT NO: |
PCT/GB2018/051501 |
371 Date: |
November 15, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03B 23/0258 20130101;
C03B 27/0413 20130101; C03B 23/0235 20130101; C03B 27/0442
20130101; C03B 23/0307 20130101; C03B 23/0357 20130101; C03B
27/0404 20130101 |
International
Class: |
C03B 23/03 20060101
C03B023/03; C03B 23/023 20060101 C03B023/023; C03B 23/025 20060101
C03B023/025; C03B 27/04 20060101 C03B027/04; C03B 27/044 20060101
C03B027/044 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 1, 2017 |
GB |
1708758.6 |
Claims
1.-38. (canceled)
39. A method of shaping a glass sheet, the glass sheet having a
first major surface and a second opposing major surface, the method
comprising: heating the glass sheet to a temperature for shaping;
positioning the glass sheet on a shaping support such that the
first major surface of the glass sheet is in contact with the
shaping support; shaping the glass sheet on the shaping support;
and deliberately cooling at least a first portion of the glass
sheet during the shaping of the glass sheet on the shaping
support.
40. The method according to claim 39, wherein the shaping support
has at least one shaping rail for contacting the first major
surface of the glass sheet and/or wherein the shaping support is
configured to contact the glass sheet at a peripheral region of the
glass sheet.
41. The method according to claim 39, wherein the shaping support
is configured as a ring mould to contact the glass sheet at a
peripheral region of the glass sheet.
42. The method according to claim 39, wherein the first portion of
the glass sheet is a portion of the first major surface of the
glass sheet and/or wherein the first portion is a peripheral
portion of the glass sheet.
43. The method according to claim 39, wherein the first portion of
the glass sheet is deliberately cooled by directing at least a
first jet of fluid towards the first portion of the glass
sheet.
44. The method according to claim 39, wherein the first portion of
the glass sheet is deliberately cooled by providing a heat exchange
device configured to extract heat from the first portion of the
glass sheet.
45. The method according to claim 39, wherein during the shaping of
the glass sheet on the shaping support, the glass sheet is shaped
by pressing the glass sheet between the shaping support and a
shaping member.
46. The method according to claim 39, wherein during the shaping of
the glass sheet on the shaping support, the glass sheet is shaped
by allowing the heat softened glass sheet to sag under the
influence of gravity.
47. The method according to claim 39, further comprising
deliberately cooling a second portion of the glass sheet during the
shaping of the glass sheet on the shaping support.
48. The method according to claim 39, wherein the deliberate
cooling of the first portion of the glass sheet begins at the same
time as the shaping of the glass sheet on the shaping support
begins or the deliberate cooling of the first portion of the glass
sheet begins after the shaping of the glass sheet on the shaping
support begins but before the shaping of the glass sheet on the
shaping support has ended.
49. The method according to claim 39, wherein the duration of the
deliberate cooling of the first portion of the glass sheet is the
same as the duration of the shaping of the glass sheet on the
shaping support and/or wherein the deliberate cooling of the first
portion of the glass sheet is continued after the glass has been
shaped.
50. The method according to claim 39, wherein there is no relative
movement between the glass sheet and the shaping support during the
shaping of the glass sheet on the shaping support.
51. The method of shaping a glass sheet, the glass sheet having a
first major surface and a second opposing major surface, the method
comprising: heating the glass sheet to a temperature suitable for
shaping; positioning the glass sheet on a shaping support such that
the first major surface of the glass sheet is in contact with the
shaping support; shaping the glass sheet on the shaping support by
making shaping contact between the shaping member and the second
major surface of the glass sheet, thereby shaping the glass sheet
between the shaping support and the shaping member, deliberately
cooling at least one portion of the first major surface of the
glass sheet during the shaping of the glass sheet on the shaping
support step by directing at least one jet of fluid onto the first
portion of the first major surface; and during the shaping of the
glass sheet on the shaping support there is no jet of fluid
directed onto the second major surface of the glass sheet when the
glass sheet is on the shaping support.
52. The method according to claim 39, wherein following the shaping
of the glass sheet on the shaping support there is a surface
compressive stress in the first portion of less than or equal to CS
MPa, where CS is 40.
53. The method according to claim 39, wherein following the shaping
of the glass sheet on the shaping support there is a surface
compressive stress in the first portion, and the surface
compressive stress in the first portion is increased by between 5
MPa and 25 MPa compared to the surface compressive stress in the
first portion when there is no deliberate cooling during the
shaping of the glass sheet on the shaping support.
54. The method according to claim 39, wherein following the shaping
of the glass sheet on the shaping support the shaped glass sheet is
laminated to at least another glass sheet using an interlayer
structure comprising at least one sheet of adhesive interlayer
material.
55. The method according to claim 54, wherein the shaped glass
sheet is an outer ply in the laminated glazing, such that the first
portion of the glass sheet that was deliberately cooled during the
shaping of the glass sheet on the shaping support is part of
surface 1 of the laminated glazing.
56. The method according to claim 54, wherein the shaped glass
sheet has a soda-lime-silica composition and the at least another
glass sheet has been chemically strengthened prior to being
laminated to the shaped glass sheet.
57. Apparatus for shaping a glass sheet, the apparatus comprising a
shaping support for supporting a glass sheet on the shaping
support, a shaping member for shaping the glass sheet by pressing
the glass sheet between the shaping member and the shaping support,
an assembly of one or more nozzles for directing a fluid against a
major surface of the glass sheet when the glass sheet is being
pressed between the shaping member and the shaping support, and
control means to actuate the flow of fluid to at least one of the
one or more nozzles to carry out the method according to claim
39.
58. The apparatus according to claim 57, wherein at least one of
the nozzles is arranged to direct the fluid towards the major
surface of the glass sheet in contact with the shaping support when
the glass sheet is pressed between the shaping support and the
shaping member.
Description
[0001] The present invention relates to a method of shaping a glass
sheet and to apparatus for shaping a glass sheet.
[0002] It is known that a laminated glazing for a vehicle
windscreen usually comprises two bent sheets of glass joined by at
least one adhesive layer, usually polyvinyl butyral (PVB). It is
conventional in the art to refer to each glass sheet as a "ply".
Often the adhesive layer is referred to as a "ply" i.e. a ply of
PVB. The glass sheet configured to face the interior of the vehicle
in which the laminated glazing is installed is often known as the
"inner ply" and the glass sheet configured to face the exterior of
the vehicle in which the laminated glazing is installed is often
known as the "outer ply".
[0003] Each of the sheets of glass used in a laminated glazing for
a vehicle is usually bent in one or two mutually perpendicular
directions such that the laminated glazing is curved and many
methods are known for bending initially flat glass sheets to a
desired curvature.
[0004] One known method is to bend a pair of glass sheets at the
same time, one sheet of glass on top of another and separated with
a suitable "parting powder" such as calcium carbonate. The inner
ply and outer ply are bent at the same time by gravity sag
bending.
[0005] Another method is to bend the inner ply and the outer ply at
different times, usually one after the other, thereby forming the
inner ply and the outer ply individually.
[0006] One such method of bending the flat glass sheets
individually involves conveying heated flat glass sheets between a
pair of complementary shaping members and press bending each glass
sheet separately. The glass sheets can then be cooled, brought
together and laminated using a suitable adhesive interlayer such as
PVB. Such methods are described in EP0398759A2 and
WO2004/085324A1.
[0007] A factor that has received much attention in the prior art
is the stress characteristics of the individual glass sheets,
either when used as a monolith or when used as a ply in a laminated
glazing, and methods are known in the prior art to vary the stress
characteristics of the final glass sheet. Given that in a laminated
window for a vehicle, one of the surfaces of the laminated window
is exposed to the outside elements, the properties of this surface
are particularly important. For example, the window should be able
to withstand sufficient impact from stones and to have sufficient
scratch resistance, which in the case of a windscreen, may be due
to wiper blades.
[0008] Prior art solutions have altered the edge stress of a bent
glass sheet after the glass sheet has been formed. WO97/05074A1
describes a cooling ring assembly and method for controlling
stresses in a bent glass sheet. The cooling ring assembly includes
a cooling ring that supports the glass sheet edge, an insulator
juxtaposed inboard of the cooling ring to reduce the cooling rate,
and a cooler for providing increased cooling to at least one
localised area of the glass sheet edge.
[0009] US2005/0268661A1 describes a method for manufacturing a
curved glass plate by pressing a heated glass sheet between an
upper mould and a lower mould, wherein the formed glass plate is
cooled on the lower mould. During the step of cooling the glass
sheet on the lower mould, the lower mould is heated whereas an
inner portion of the glass sheet placed in contact with the lower
mould is forcibly cooled.
[0010] U.S. Pat. No. 6,321,570B1 describes a method of and
apparatus for bending and tempering a sheet of glass heated to a
formable state.
[0011] EP0431895A2 relates to a sheet glass bending and tempering
apparatus for bending and tempering a glass sheet at one stage.
[0012] U.S. Pat. No. 4,749,399 describes a ring mould unit for
shaping and tempering a glass sheet. A cooling ring is used to
support the bent glass sheet while the glass sheet is being
quenched and tempered by a cooling medium.
[0013] U.S. Pat. No. 4,826,522 describes the tempering of sheets of
glass and optionally their bending by the so-called contact
process.
[0014] WO2006/110145A1 describes a furnace including a section
defined as a heating section capable of attaining a predetermined
temperature, the heating section having an entrance end and an exit
end; a section defined as a cooling section capable of having a
temperature gradient from entrance end of the cooling section to
exit end of the cooling section, the entrance end of the cooling
section mounted in a fixed relationship to the exit end of the
heating section; a section defined as an edge cooling section
between the exit end of the heating section and the entrance end of
the cooling section; and an edge cooling device positioned in the
edge cooling section relative to a predetermined area, and capable
of cooling at least selected peripheral portions of the
predetermined area at a faster rate than centre portions of the
predetermined area. Soon after the glass sheets attain their
desired curvature, the shaped glass sheets are moved into the edge
cooling section.
[0015] It is known from "Glass Processing Days, 13-15 September
'97, pages 385-389" that surface and edge stress may be introduced
into a windshield due to the lamination process itself. FIG. 5 in
this publication shows a laminated glazing with a non-uniform
lamination gap. It is said the laminating forces introduce surface
tension in the final laminated glazing.
[0016] Usually issues due to an uneven lamination gap are minimized
by ensuring each glass sheet for the inner and out ply are suitably
bent as described above, for example by using a nested pair, or by
using a suitably controlled bending process for each individual
ply.
[0017] However for certain laminated products it may not be
possible to obtain two glass plies that are sufficiently well
matched in shape such that lamination stress does not become
important. For example, when a laminated glazing is produced using
two different plies, each ply may be bent separately, often with a
different bending process. Examples of such laminated glazings are
described in WO2015/092385A1 where an outer ply is press bent and
an inner ply is sag bent.
[0018] It has been found that upon laminating plies bent by
different bending processes, the lamination gap may not be uniform
resulting in increased lamination stresses of the type mentioned
above and described in "Glass Processing Days, 13-15 September '97,
pages 385-389". The lamination stresses present in the final
laminated glazing may be undesirable resulting in a final laminated
glazing that does not have the desired properties.
[0019] Accordingly the present invention provides from a first
aspect a method of shaping a glass sheet, the glass sheet having a
first major surface and a second opposing major surface, the method
comprising the steps: [0020] (i) providing a shaping support for
supporting the glass sheet; [0021] (ii) a heating step for heating
the glass sheet to a temperature suitable for shaping; [0022] (iii)
a positioning step for positioning the glass sheet on the shaping
support such that the first major surface of the glass sheet is in
contact with the shaping support; and [0023] (iv) a shaping step
for shaping the glass sheet on the shaping support,
[0024] wherein during step (iv) at least one (a first) portion of
the glass sheet is deliberately cooled.
[0025] In prior art methods of shaping a glass sheet, when a glass
sheet is shaped on a shaping support there may be natural cooling
because of contact of the glass sheet with the shaping support. The
deliberate cooling of the present invention during the shaping step
is in addition to any inherent or natural cooling during the
shaping step (iv). The cooling step that is started during the
shaping step (iv) may finish at the same time as the shaping step,
or may continue after the shaping step (iv) has been completed.
[0026] By deliberately cooling the first portion of the glass
sheet, a cooling step is begun during step (iv) to deliberately
cool the first portion of the glass sheet. As explained above, the
cooling step that is begun during step (iv) is in addition to any
inherent or natural cooling during the shaping step (iv). The
cooling step may begin at the same time that the shaping step
begins.
[0027] It has been found that by deliberately cooling the first
portion of the glass sheet during the shaping step, instead of
after the shaping step, the compressive surface stress in the first
portion of the glass sheet may be increased above that produced by
deliberately cooling after the glass sheet has been shaped. The
compressive surface stress increase in the first portion of the
glass sheet by deliberately cooling during the shaping step is the
increase in surface compressive stress above that when there is no
deliberate cooling of the first portion of the glass sheet. For
example, if carrying out steps (i)-(iv) above produces a surface
compressive stress of C1 in the first portion of the glass sheet,
by deliberately cooling the first portion of the glass sheet during
step (iv) a surface compressive stress of C2 is produced in the
first portion of the glass sheet, wherein C2>C1. Surface
compression (or compressive) stress measurements may be made using
techniques known to a person skilled in the art, for example using
a Strainoptics Laser GASP-CS
(http://www.strainoptics.com/files/Laser %20GASP-CS
%20Quick-Start%20(English).pdf). Such equipment is available from
Strainoptics, Inc., 108 W. Montgomery Avenue, North Wales, Pa.
19454 USA.
[0028] The degree of cooling may be determined by measuring the
temperature of the deliberately cooled first portion with a
thermocouple or optical pyrometer. It is preferred however to
measure the surface compressive stress in the final cooled shaped
glass sheet to determine the cooling conditions during step (iv)
required to achieve a desired surface compressive stress in the
first portion of the final cooled shaped glass.
[0029] The shaping support has a shaping surface for contacting the
first major surface of the glass sheet.
[0030] During step (iii) a first contact portion of the first major
surface of the glass sheet is in contact with a first portion of
the shaping surface of the shaping support. It is preferred that
during step (iv) the first contact portion of the first major
surface of the glass sheet does not move relative to the first
portion of the shaping surface of the shaping support.
[0031] Preferably the shaping support has at least one (a first)
shaping rail for contacting the first major surface of the glass
sheet. The first shaping rail may be straight or curved. The first
shaping rail has a shaping surface for contacting the first major
surface of the glass sheet. The shaping surface of the first
shaping rail may be continuous or comprise a plurality of
projections that define the shaping surface of the first shaping
rail.
[0032] Preferably the shaping support is configured to contact the
glass sheet at a peripheral region of the glass sheet.
[0033] Preferably the shaping support is configured as a ring mould
to contact the glass sheet at a peripheral region of the glass
sheet. A ring mould has an upper shaping surface for supporting a
glass sheet thereon. Inboard of the shaping surface of the ring
mould the ring mould does not contact the glass sheet. A ring mould
comprises one or more shaping rail.
[0034] Preferably the first portion of the glass sheet is a portion
of the first major surface of the glass sheet.
[0035] Preferably the first portion of the glass sheet is a portion
of the first major surface of the glass sheet and not a portion of
the second major surface of the glass sheet.
[0036] Preferably the first portion of the glass sheet is a
peripheral portion of the glass sheet. Preferably the peripheral
portion extends up to a distance DP from a peripheral edge of the
glass sheet wherein the distance DP is preferably between 100 mm
and 400 mm, for example the distance may be 100 mm or 150 mm or 200
mm or 250 mm or 300 mm or 350 mm or 400 mm.
[0037] Preferably the first portion of the glass sheet extends
around the entire periphery of the glass sheet.
[0038] Preferably the first portion of the glass sheet is
deliberately cooled by directing at least one (a first) jet of
fluid towards the first portion of the glass sheet. Preferably the
first jet of fluid comprises air, more preferably compressed
air.
[0039] Preferably a plurality of jets of fluid are directed at the
first portion of the glass sheet.
[0040] Preferably the first portion of the glass sheet is a
peripheral portion of the first major surface of the glass sheet
and the first portion is deliberately cooled by directing at least
one (a first) jet of fluid towards the peripheral portion of the
first major surface of the glass sheet. In such embodiments,
preferably the first jet of fluid comprises air, more preferably
compressed air.
[0041] When the deliberate cooling is achieved by directing at
least one jet of fluid, preferably air, towards the first portion
of the glass sheet, preferably the or each jet of fluid is at a
temperature and/or pressure sufficient to achieve the desired
amount of cooling.
[0042] Suitably following step (iv) the method includes a cooling
step after step (iv) for reducing the temperature of the shaped
glass to below 100.degree. C., typically to ambient temperatures
i.e. room temperature. The cooling step may comprise a thermally
toughening step and/or an annealing step. Preferably the cooling
step does not thermally toughen the shaped glass sheet. Following
such a cooling step a surface compressive stress measurement may be
made.
[0043] In some embodiments a shaping member is provided before step
(iv), and during step (iv) the glass sheet is shaped by pressing
the glass sheet between the shaping support and the shaping member.
Suitably the shaping member is provided at the same time as the
shaping support is provided, although the shaping member may be
provided before or after step (i).
[0044] Preferably the glass sheet is shaped between the shaping
member and the shaping support by moving at least one of the
shaping support and the shaping member towards the other to press
the glass sheet between the shaping support and the shaping
member.
[0045] It will be readily apparent that when a shaping member is
provided, to allow the glass sheet to be positioned on the shaping
support during step (iii) the shaping member is sufficiently spaced
apart from the shaping support.
[0046] In embodiments where a shaping member is provided and during
step (iv) the glass sheet is shaped by pressing the glass sheet
between the shaping support and the shaping member, preferably the
shaping member is a full surface shaping member having a shaping
surface for contacting the second major surface of the glass sheets
during step (iv). A full surface shaping member comprises a shaping
surface that is fixed in relation to the shaping support such that
a full surface shaping member is not a conformable shaping member.
Often in the prior art a full surface shaping member is known as a
rigid mould or a rigid full surface shaping member because the
shaping surface of the full surface shaping member is rigid i.e.
either arranged in a convex or concave configuration but not
changeable therefrom.
[0047] When a full surface shaping member is used during step (iv),
it is preferred to deliberately cool a first portion of the first
major surface of the glass sheet. As is readily apparent, a full
surface shaping member will be in shaping contact with the second
major surface of the glass sheet so it will be difficult to
deliberately cool certain portions of the second major surface of
the glass sheet during the shaping step because such portions are
not accessible. However it is within the scope of the present
invention to provide a shaping member with at least one opening in
the shaping surface thereof, through which a cooling fluid may be
directed to deliberately cool a portion of the second major surface
of the glass sheet during the shaping step (iv) if required.
[0048] Preferably the shaping member comprises at least two (a
first and a second) movable shaping members. The first movable
shaping member is movable relative to the second movable shaping
member. Suitable shaping members having at least two movable
shaping members are described in U.S. Pat. No. 5,122,177,
W2012/166365A1 and US2015/0007612A1.
[0049] In embodiments where a shaping member is provided and during
step (iv) the glass sheet is shaped by pressing the glass sheet
between the shaping support and the shaping member, there are other
preferred features.
[0050] Suitably the glass sheet is not rolled between the shaping
support and the shaping member.
[0051] Preferably the shaping support and/or the shaping member is
not a conformable pressing element. A conformable pressing element
has at least one surface for glass contact therewith that is a
pressurised surface, for example a pressurised flexible
membrane.
[0052] Preferably the shaping member and the shaping support each
have a rigid shaping surface.
[0053] Preferably the shaping member is disposed vertically
relative to the shaping support.
[0054] Preferably the shaping member and the shaping support lie
along an axis for bending, wherein prior to step (iv) the shaping
member is spaced part from the shaping support, and upon moving at
least one of the shaping member and the shaping support along the
axis for bending towards the other such that the separation thereof
decreases, a glass sheet supported on the shaping support is press
bent to a desired curvature between the shaping support and the
shaping member. It is preferred that the shaping member moves
relative to the shaping support in a direction that is parallel to,
or substantially parallel to, the axis for bending. In particular a
glass sheet supported on the shaping support is not rolled against
the shaping member.
[0055] Preferably the shaping support has a concave shaping surface
and the shaping member has a convex shaping surface that is
complementary to the concave shaping surface of the shaping
support.
[0056] Preferably the shaping member has a convex shaping surface
for contacting the second major surface of the glass sheet when
supported on the shaping support.
[0057] Preferably shaping member has a shaping surface having one
or more opening therein. At least one of the one or more opening in
the shaping surface of the shaping member may be in fluid
communication with a low pressure source, such as a vacuum
source.
[0058] Preferably the shaping member is provided with a protective
cover such that the protective cover of the shaping member contacts
the glass sheet during step (iv). When the shaping member comprises
a protective cover, shaping contact of the shaping member with the
glass sheet is made via the protective cover. Preferably the
protective cover of the shaping member comprises a cloth made of,
for example, stainless steel, fibre glass,
poly-phenyleneterephthalamide fibres (e.g. Kevlar.TM.), materials
blended Kevlar.TM., polybenzoxale (PBO) fibres containing graphite
(e.g. Zylon.TM.), or various weaves of these fibres.
[0059] In other embodiments where a shaping member is provided and
during step (iv) the glass sheet is shaped by pressing the glass
sheet between the shaping support and the shaping member, it is
preferred that the shaping support is a full surface shaping
support having a shaping surface for contacting the first major
surface of the glass sheet and the shaping member comprises at
least one shaping rail having a shaping rail for contacting the
second major surface of the glass sheet.
[0060] In some embodiments during step (iv) the glass sheet is
shaped by allowing the heat softened glass sheet to sag under the
influence of gravity.
[0061] In some embodiments of the first aspect of the present
invention the deliberate cooling is provided by a heat exchange
device, configured to extract heat from the first portion of the
glass sheet.
[0062] Preferably the heat exchange device does not make direct
contact with the portion of the glass sheet.
[0063] Preferably the heat exchange device comprises a cooling
circuit comprising at least one (a first) pipe for carrying a
cooling fluid.
[0064] Preferably the heat exchange device comprises a cover.
Preferably the cover for the heat exchange device comprises a cloth
made of, for example, stainless steel, fibre glass,
poly-phenyleneterephthalamide fibres (e.g. Kevlar.TM.), materials
blended Kevlar.TM., polybenzoxale (PBO) fibres containing graphite
(e.g. Zylon.TM.), or various weaves of these fibres.
[0065] In some embodiments a second portion of the glass sheet is
deliberately cooled during step (iv).
[0066] The second portion of the glass sheet may be a portion of
the first major surface or the second major surface of the glass
sheet.
[0067] The second portion of the glass sheet may be a peripheral
portion of the first major surface of the glass sheet.
[0068] Preferably the first portion is a portion of the first major
surface of the glass sheet and the second portion is a portion of
the first major surface of the glass sheet.
[0069] Preferably the first portion of the glass sheet and the
second portion of the glass sheet are isolated regions of the glass
sheet. The regions of the glass sheet are isolated when there is at
least a portion of the glass sheet between the first and second
portions thereof that is not being deliberately cooled during step
(iv).
[0070] Preferably the second portion of the glass sheet is
deliberately cooled when the first portion of the glass sheet is
being deliberately cooled.
[0071] Preferably the second portion of the glass sheet is
deliberately cooled using the same cooling means as used for
deliberately cooling the first portion of the glass sheet. Suitably
the second portion of the glass sheet is deliberately cooled by
directing at least one (a first) jet of fluid is towards the second
portion of the glass sheet, preferably wherein the first jet of
fluid that is direction towards the second portion of the glass
sheet comprises air, in particular compressed air.
[0072] For the avoidance of doubt, in a preferred embodiment of the
first aspect of the present invention there is provided a method of
shaping a glass sheet, the glass sheet having a first major surface
and a second opposing major surface, the method comprising the
steps: (i) providing a shaping member and providing a shaping
support for supporting the glass sheet thereon; (ii) a heating step
for heating the glass sheet to a temperature suitable for shaping;
(iii) a positioning step for positioning the glass sheet on the
shaping support such that the first major surface of the glass
sheet is in contact with the shaping support; and (iv) a shaping
step for shaping the glass sheet on the shaping support by making
shaping contact between the shaping member and the second major
surface of the glass sheet, thereby shaping the glass sheet between
the shaping support and the shaping member, wherein during step
(iv) at least one portion of the first major surface of the glass
sheet is deliberately cooled by directing at least one jet of
fluid, preferably air, onto the first portion of the first major
surface, further wherein during the shaping step (iv) there is no
jet of fluid, preferably air, directed onto the second major
surface of the glass sheet when the glass sheet is on the shaping
support.
[0073] Other embodiments of the first aspect of the present
invention have other preferable features.
[0074] In embodiments where the first portion is a peripheral
portion of the glass sheet, in particular a peripheral portion of
the first major surface of the glass sheet, and wherein following
step (iv) the method includes an annealing step or a cooling step
for reducing the temperature of the shaped glass to below
100.degree. C., typically to ambient temperatures i.e. room
temperature, preferably following the annealing step or cooling
step there is a surface compressive stress in the peripheral
portion of less than or equal to CS MPa, where CS is 40, or 30, or
25, or 20, or 15 i.e. the surface compressive stress in the
peripheral portion is less than or equal to 40 MPa, or the surface
compressive stress in the peripheral portion is less than or equal
to 30 MPa or the surface compressive stress in the peripheral
portion is less than or equal to 25 MPa, or the surface compressive
stress in the peripheral portion is less than or equal to 20 MPa,
or the surface compressive stress in the peripheral portion is less
than or equal to 15 MPa.
[0075] In embodiments where the first portion is a peripheral
portion of the glass sheet, in particular a peripheral portion of
the first major surface of the glass sheet, and wherein following
step (iv) the method includes an annealing step or a cooling step
for reducing the temperature of the shaped glass to below
100.degree. C., typically to ambient temperatures i.e. room
temperature, preferably following the annealing step or the cooling
step the surface compressive stress in the peripheral portion is
increased between 5 MPa and 25 MPa, preferably between 5 MPa and 20
MPa, more preferably between 5 MPa and 15 MPa, compared to the
surface compressive stress in the peripheral portion when there is
no deliberate cooling during step (iv). For example in such
embodiments the deliberate cooling may comprise directing at least
one jet of air towards the peripheral portion of the glass sheet,
and when no air is directed towards the peripheral portion the
surface compressive stress in the peripheral portion is a baseline
level, and when air is directed towards the peripheral portion
during step (iv) the surface compressive stress in the peripheral
portion is increased by between 5 MPa and 25 MPa compared to the
baseline level.
[0076] In embodiments when the first portion is a peripheral
portion of the glass sheet, in particular a peripheral portion of
the first major surface of the glass sheet, following step (iv) the
method preferably includes a thermally toughening for reducing the
temperature of the shaped glass to below 100.degree. C., typically
to ambient temperatures i.e. room temperature, such that following
the thermally toughening step there is a surface compressive stress
(CS3) in the peripheral portion of at least 50 MPa, or at least 55
MPa, or at least 60 MPa, or at least 65 MPa, or at least 70 MPa, or
at least 75 MPa or at least 80 MPa, or at least 85 MPa, or at least
90 MPa. Preferably CS3 is less than 200 MPa.
[0077] Other embodiments of the first aspect of the present
invention have other preferable features.
[0078] Preferably the shaping support comprises heating means for
heating the shaping support. By having heating means the shaping
support is able to be set at a suitable temperature for
bending.
[0079] Preferably following step (iv), the shaped glass sheet is
suitably heat treated or cooled to reduce the temperature to
ambient temperature, typically to a temperature below 50.degree. C.
and above 0.degree. C.
[0080] Preferably following step (iv) there is a surface
compressive stress in the first portion of less than or equal to CS
MPa, where CS is 40, or 30, or 25, or 20, or 15.
[0081] Preferably following step (iv) there is a surface
compressive stress in the first portion of greater than or equal to
CS1 MPa, where CS is 0, or 0.5, or 1, or 2, or 3, or 4, or 5.
[0082] Preferably following step (iv) there is a surface
compressive stress in the first portion, and the surface
compressive stress in the first portion is increased by between 5
MPa and 25 MPa, preferably between 5 MPa and 20 MPa, more
preferably between 5 MPa and 15 MPa, compared to the surface
compressive stress in the first portion when there is no deliberate
cooling during step (iv). For the avoidance of doubt, when carrying
out a method in accordance with the first aspect of the present
invention and during step (iv) there is no deliberate cooling of a
first portion of the glass sheet i.e. there is no air directed
towards a first portion of the first major surface of the glass
sheet, the first portion of the glass sheet has a baseline surface
compressive stress. When another identical glass sheet is shaped in
accordance with the first aspect of the present invention, the
surface compressive stress in the first portion of the glass sheet
is greater than the baseline surface compressive stress and it is
preferred that the increase is between 5 MPa and 25 MPa, preferably
between 5 MPa and 20 MPa, more preferably between 5 MPa and 15
MPa.
[0083] Preferably following step (iv) the shaped glass sheet is not
thermally toughened or thermally tempered.
[0084] Preferably following step (iv) there is a surface
compressive stress (CS2) in the first portion of at least 50 MPa,
or at least 55 MPa, or at least 60 MPa, or at least 65 MPa, or at
least 70 MPa, or at least 75 MPa or at least 80 MPa, or at least 85
MPa, or at least 90 MPa, and further preferably wherein CS2 is less
than 200 MPa.
[0085] The shaping step (iv) has a duration from t1 to t2, and the
deliberate cooling of the first portion of the glass sheet has a
duration from t3 to t4.
[0086] Preferably the duration of the deliberate cooling of the
first portion of the glass sheet is the same as the duration of the
shaping step (iv). That is, it is preferred that t2-t1=t4-t3.
[0087] Preferably the deliberate cooling of the first portion of
the glass sheet begins at the same time as the shaping step (iv)
begins. That is, it is preferred that t1=t3.
[0088] Preferably the deliberate cooling begins after the shaping
step begins but before the shaping step has ended. That is, it is
preferred that t3>t1 and t3<t4.
[0089] Preferably the deliberate cooling of the first portion of
the glass sheet is continued after the glass has been shaped. That
is, it is preferred that t4>t2.
[0090] Preferably the glass sheet is a soda-lime-silica glass
composition. A typical soda-lime-silicate glass composition is (by
weight), SiO.sub.2 69-74%; Al.sub.2O.sub.3 0-3%; Na.sub.2O 10-16%;
K.sub.2O 0-5%; MgO 0-6%; CaO 5-14%; SO.sub.3 0-2% and
Fe.sub.2O.sub.3 0.005-2%. The glass composition may also contain
other additives, for example, refining aids, which would normally
be present in an amount of up to 2%. The transmitted glass colour
may be measured in terms of a recognised standard such as BS
EN410.
[0091] Preferably the glass sheet has a thickness between 1 mm and
10 mm, more preferably between 1.2 mm and 4 mm, even more
preferably between 1.2 mm and 2.4 mm.
[0092] Preferably the glass sheet has a thickness between 1.5 mm
and 2.5 mm, more preferably between 1.6 mm and 2.3 mm.
[0093] Preferably following step (iv) the shaped glass sheet is
used as part of a glazing for a vehicle, in particular an
automotive vehicle. Suitably the vehicle glazing is a windscreen,
sunroof, rear window or side window.
[0094] Preferably during step (ii) the glass is heated to a
temperature between 580.degree. C. and 680.degree. C.
[0095] Preferably during step (ii) the glass sheet is uniformly
heated.
[0096] Preferably the shaping support is provided with a protective
cover such that in step (iii) the protective cover of the shaping
support contacts the glass sheet. When the shaping support
comprises a protective cover, shaping contact of the shaping
support with the glass sheet is made via the protective cover of
the shaping support. Preferably the protective cover of the shaping
support comprises a cloth made of, for example, stainless steel,
fibre glass, poly-phenyleneterephthalamide fibres (e.g.
Kevlar.TM.), materials blended Kevlar.TM., polybenzoxale (PBO)
fibres containing graphite (e.g. Zylon.TM.), or various weaves of
these fibres.
[0097] In some embodiments, following step (iv) the shaped glass
sheet is subsequently used as a first glass ply in a laminated
glazing, the laminated glazing comprising the first glass ply
joined to a second glass ply by means of at least one sheet of
adhesive interlayer material.
[0098] Preferably the second glass ply is shaped with a different
shaping process to the shaping process used to shape the first
glass ply.
[0099] Preferably the first glass ply is an outer ply in the
laminated glazing, such that the first portion of the first glass
ply that was deliberately cooled during step (iv) is part of
surface 1 of the laminated glazing. Preferably surface 1 of the
laminated glazing has a convex surface.
[0100] Preferably the first glass ply has a soda-lime-silica
composition and the second glass ply has been chemically
strengthened prior to being joined to the first glass ply.
[0101] Preferably the second glass ply has a composition comprising
66-72 mol. % SiO.sub.2, 1-4 mol. % Al.sub.2O.sub.3, 8-15 mol. %
MgO, 1-8 mol. % CaO, 12-16 mol. % Na.sub.2O, preferably wherein
MgO+CaO is between 12 and 17 mol. % and CaO/(MgO+CaO) is in the
range 0.1 and 0.4.
[0102] Preferably the second glass ply has a composition comprising
(by weight) 58% to 70% SiO.sub.2, 5% to 15% Al.sub.2O.sub.3, 12% to
18% Na.sub.2O, 0.1% to 5% K.sub.2O, 4% to 10% MgO and 0% to 1% CaO
with the provisos that the sum of the Al.sub.2O.sub.3 and MgO
exceeds 13%, that the sum of the amounts of Al.sub.2O.sub.3 plus
MgO divided by the amount of K.sub.2O exceeds 3 and that the sum of
the Na.sub.2O plus K.sub.2O plus MgO exceeds 22%.
[0103] Preferably the second glass ply has an alkali
aluminosilicate glass composition, preferably wherein the alkali
aluminosilicate glass composition includes at least about 6 wt %
aluminium oxide.
[0104] Preferably the second glass ply is thinner than the first
glass ply.
[0105] Preferably the second glass ply has a thickness between 0.5
mm and 2.1 mm.
[0106] Preferably the first glass ply is the outer ply in the
laminated glazing, such that the first portion of the first glass
ply that was deliberately cooled is part of surface 1 of the
laminated glazing. Using conventional nomenclature, surface 1 of
the laminated glazing is the outermost surface in the laminated
glazing and is the first surface a ray of sunlight strikes when the
laminated glazing is in an installed position, for example when
installed as a windscreen in a vehicle.
[0107] Preferably the at least one ply of adhesive interlayer
material comprises polyvinyl butyral (PVB).
[0108] Preferably the at least one ply of adhesive interlayer
material comprises acoustic modified PVB.
[0109] Preferably the at least one ply of adhesive interlayer
material comprises a copolymer of ethylene, such as ethylene vinyl
acetate (EVA).
[0110] Preferably the at least one ply of adhesive interlayer
material comprises polyurethane, in particular a thermoplastic
polyurethane (TPU).
[0111] In embodiments wherein following step (iv) the shaped glass
sheet is subsequently used as a first glass ply in a laminated
glazing, the laminated glazing comprising the first glass ply
joined to a second glass ply by means of at least one sheet of
adhesive interlayer material, for the avoidance of doubt, in such
embodiments, following step (iv) the shaped glass sheet is
laminated to at least another glass sheet using an interlayer
structure comprising at least one sheet of adhesive interlayer
material
[0112] Preferably the interlayer material is polyvinyl butyral,
ethylene vinyl acetate copolymer, polyurethane, polycarbonate, poly
vinyl chloride or a copolymer of ethylene and methacrylic acid.
[0113] Preferably the at least another glass sheet is shaped with a
different shaping process to the shaping process used to shape the
shaped glass sheet.
[0114] Preferably the shaped glass sheet is an outer ply in the
laminated glazing, such that the first portion of the shaped glass
sheet that was deliberately cooled during step (iv) is part of
surface 1 of the laminated glazing.
[0115] Preferably the at least another glass sheet is an outer ply
in the laminated glazing.
[0116] Preferably the shaped glass sheet and/or the at least
another glass sheet has a soda-lime-silica composition.
[0117] Preferably the at least another glass sheet has been
chemically strengthened prior to being laminated to the shaped
glass sheet i.e. prior to being joined to the shaped glass sheet
via the interlayer structure.
[0118] Preferably the shaped glass sheet has a soda-lime-silica
composition and the at least another glass sheet has been
chemically strengthened prior to being laminated to the shaped
glass sheet. Preferably the at least another glass sheet has an
alkali aluminosilicate glass composition, more preferably wherein
the alkali aluminosilicate glass composition includes at least
about 6 wt % aluminium oxide.
[0119] Preferably the at least another glass sheet is thinner than
the shaped glass sheet.
[0120] Preferably the at least another glass sheet has a thickness
between 0.5 mm and 2.1 mm, more preferably between 0.5 mm and 1.0
mm.
[0121] From a second aspect the present invention provides an
apparatus for shaping a glass sheet, the apparatus comprising a
shaping support for supporting a glass sheet thereon, a shaping
member for shaping the glass sheet by pressing the glass sheet
between the shaping member and the shaping support, and an assembly
of one or more nozzles for directing a fluid against a major
surface of the glass sheet when the glass sheet is being pressed
between the shaping member and the shaping support.
[0122] Preferably the apparatus comprises control means to actuate
the flow of fluid to at least one of the one or more nozzles to
carry out the method according to the first aspect of the present
invention.
[0123] Preferably at least one nozzle is a slot nozzle.
[0124] Preferably at least one nozzle comprises a tubular
portion.
[0125] Preferably the assembly comprises a tubular portion having
an inlet, an outlet, and a wall, there being at least one hole in
the wall such that when a fluid passes between the inlet and the
outlet, fluid is emitted from the hole in the wall of the tubular
portion of the assembly.
[0126] Preferably at least one of the nozzles is arranged to direct
the fluid towards the major surface of the glass sheet in contact
with the shaping support when the glass sheet is pressed between
the shaping support and the shaping member.
[0127] Preferably the assembly is configured to direct the fluid
towards the major surface of the glass sheet in contact with the
shaping support when the glass sheet is pressed between the shaping
support and the shaping member and the assembly is configured not
to direct the fluid towards the major surface of the glass sheet
not in contact with the shaping support when the glass sheet is
pressed between the shaping support and the shaping member. For the
avoidance of doubt, in this preferred embodiment the glass sheet to
be shaped has a first major surface and a second opposing major
surface. When the glass sheet is pressed between the shaping
support and the shaping member, the first major surface of the
glass sheet is in contact with the shaping support and the second
major surface of the glass sheet is in contact with the shaping
member. The assembly is configured such that during said pressing,
fluid may only be directed towards the first major surface of the
glass sheet.
[0128] Other embodiments of the second aspect of the present
invention have other preferable features.
[0129] Preferably the shaping support is a ring mould.
[0130] Preferably the shaping member is a full surface mould.
[0131] Preferably the shaping member comprises at least two mould
members, each being movable relative to one another.
[0132] Preferably the shaping support has a concave shaping surface
and the shaping member has a convex shaping surface. Preferably the
concave shaping surface of the shaping support is complementary
with the convex shaping surface of the shaping member.
[0133] Preferably the shaping member and/or shaping support is
provided with a protective cover such that the respective
protective cover makes shaping contact with the glass sheet when
the glass sheet is being pressed between the shaping member and the
shaping support. Preferably the protective cover comprises a cloth
made of, for example, stainless steel, fibre glass,
poly-phenyleneterephthalamide fibres (e.g. Kevlar.TM.), materials
blended Kev polybenzoxale (PBO) fibres containing graphite (e.g.
Zylon.TM.), or various weaves of these fibres.
[0134] From a third aspect the present invention provides a method
of making a laminated glazing, the laminated glazing comprising a
first glass ply and a second glass ply with at least one (a first)
ply of adhesive interlayer material therebetween, the method
comprising shaping at least one of the first and second glass plies
using a method according to the first aspect of the present
invention.
[0135] The first glass ply is joined to the second glass ply by
means of at least the first ply of adhesive interlayer material.
Any suitable lamination process may be used to join the first glass
ply to the second glass ply by means of at least the first ply of
adhesive interlayer material.
[0136] Preferably the first glass ply is shaped according to the
first aspect of the present invention and the second glass ply is
shaped with a different shaping process.
[0137] Preferably the at least one ply of adhesive interlayer
material comprises polyvinyl butyral (PVB).
[0138] Preferably the at least one ply of adhesive interlayer
material comprises acoustic modified PVB.
[0139] Preferably the at least one ply of adhesive interlayer
material comprises a copolymer of ethylene, such as ethylene vinyl
acetate (EVA).
[0140] Preferably the at least one ply of adhesive interlayer
material comprises polyurethane, in particular a thermoplastic
polyurethane (TPU).
[0141] Preferably the first glass ply is a soda-lime-silica
glass.
[0142] Preferably the second glass ply has a composition comprising
66-72 mol. % SiO.sub.2, 1-4 mol. % Al.sub.2O.sub.3, 8-15 mol. %
MgO, 1-8 mol. % CaO, 12-16 mol. % Na.sub.2O, preferably wherein
MgO+CaO is between 12 and 17 mol. % and CaO/(MgO+CaO) is in the
range 0.1 and 0.4.
[0143] Preferably the second glass ply has a composition comprising
(by weight) 58% to 70% SiO.sub.2, 5% to 15% Al.sub.2O.sub.3, 12% to
18% Na.sub.2O, 0.1% to 5% K.sub.2O, 4% to 10% MgO and 0% to 1% CaO
with the provisos that the sum of the Al.sub.2O.sub.3 and MgO
exceeds 13%, that the sum of the amounts of Al.sub.2O.sub.3 plus
MgO divided by the amount of K.sub.2O exceeds 3 and that the sum of
the Na.sub.2O plus K.sub.2O plus MgO exceeds 22%.
[0144] Preferably the second glass ply has an alkali
aluminosilicate glass composition, preferably wherein the alkali
aluminosilicate glass composition includes at least about 6 wt %
aluminium oxide.
[0145] Preferably the first glass ply is bent by pressing the first
glass ply between a shaping support having a shaping surface, in
particular a ring mould, and a shaping member, in particular a die
member having a convex shaping surface complementary with the
shaping surface of the shaping support.
[0146] Preferably the second glass ply is bent using a gravity sag
bending process.
[0147] Preferably the second glass ply is shaped, following which
the second glass ply is chemically strengthened.
[0148] Preferably the second glass ply is thinner than the first
glass ply.
[0149] Preferably the second glass ply has a thickness between 0.5
mm and 2.1 mm.
[0150] Preferably the first glass ply is the outer ply in the
laminated glazing, such that the first portion of the first glass
ply that was deliberately cooled is part of surface 1 of the
laminated glazing. Using conventional nomenclature, surface 1 of
the laminated glazing is the outermost surface in the laminated
glazing and is the first surface a ray of sunlight strikes when the
laminated glazing is in an installed position, for example when
installed as a windscreen in a vehicle.
[0151] Embodiments of the present invention will now be described
by way of example only with reference to the accompanying drawings,
in which:
[0152] FIG. 1 shows a schematic cross-sectional representation of a
known press bending station;
[0153] FIG. 2 shows a schematic cross-sectional representation of a
press bending station for carrying out a method in accordance with
the present invention, the press bending station being in a first
configuration;
[0154] FIG. 3 shows a schematic plan view of a shaping ring for
supporting a glass sheet with an array of nozzles inboard and below
the shaping surface of the shaping ring;
[0155] FIG. 4 shows a schematic isometric view of a portion of an
array of nozzles;
[0156] FIG. 5 shows a schematic plan view of a shaping ring for
supporting a glass sheet with a different array of nozzles than in
FIG. 3;
[0157] FIG. 6 shows a schematic plan view of a shaping ring for
supporting a glass sheet with a different array of nozzles than in
FIG. 3;
[0158] FIGS. 7a-e show schematic isometric representations of
different nozzle arrangements;
[0159] FIG. 8 shows the press bending station of FIG. 2 in a second
configuration press bending a sheet of glass;
[0160] FIG. 9 is a graph showing a shaping sequence and different
air blowing sequences;
[0161] FIG. 10 shows a schematic cross-sectional representation of
another press bending station for carrying out a method in
accordance with the present invention;
[0162] FIG. 11 shows a schematic cross-sectional representation of
a gravity bending glass mould for carrying out a method in
accordance with the present invention;
[0163] FIG. 12 shows an isometric representation of a shaping ring
of the type shown in FIG. 3, except instead of an array of nozzles
a heat exchange device is provided inboard of and below the shaping
surface of the shaping ring; and
[0164] FIG. 13 shows a schematic cross-sectional representation of
part of a glass bending line incorporating a press bending station
of the type shown in FIG. 2.
[0165] FIG. 1 shows a schematic cross-sectional representation of a
known press bending station of the type used to press bend a glass
sheet for automotive use, such a vehicle window. Such a press
bending station may be used to press bend a single glass ply, or
two glass plies as a nested pair.
[0166] The press bending station 1 has a lower portion 3 and an
upper portion 5.
[0167] The lower portion 3 comprises a ring mould 9 having first
and second upper supports 11, 13. The first upper support 11 has an
upper shaping surface 15 and the second upper support 13 has an
upper shaping surface 17. A glass sheet (not shown in this figure)
may be supported on the upper shaping surfaces 15, 17. For the
avoidance of doubt, the glass sheet has a first major surface and
an opposing second major surface. When the glass sheet is supported
on the upper shaping surfaces 15, 17, the first (or second) major
surface contacts the shaping surfaces 15, 17.
[0168] It is preferred that the first and second upper supports 11,
13 are part of a continuous shaping rail for supporting a glass
sheet thereon. As such, the shaping surfaces 15, 17 are part of the
shaping surface of the continuous shaping rail.
[0169] The first upper support 11 is mounted on a first support
member 19 and the second upper support 13 is mounted on a second
support member 21. The first support member 19 is coupled to a
first linear actuator mechanism 23 and the second support member 21
is coupled to a second linear actuator mechanism 25. Each linear
actuator mechanism 23, 25 is mounted to the base member 27. The
first and second linear actuator mechanisms 23, 25 may be operated
to move the first and second support members 19, 21, and hence the
respective first and second upper supports 11, 13 vertically in the
direction of the arrow 29.
[0170] The position of the first and second upper supports 11, 13
is shown in phantom as elements 11' and 13'. In the position of
elements 11', 13' the first and second upper supports are in a
shaping position as will hereinafter be described.
[0171] The upper portion 5 comprises a die member 31 have a lower
shaping surface 33. The lower shaping surface 33 is convex and
configured to be complementary with the upper shaping surfaces 11,
13 of the lower ring mould 9.
[0172] The die member 31 is mounted to first and second die support
members 35, 37. The first die support member 35 is coupled to
linear actuator 39 and the second die support member 37 is coupled
to linear actuator 41. The linear actuators 39, 41 are mounted to
an upper gantry 43. The upper gantry is in a fixed spatial
relationship with the base member 27.
[0173] Upon operation of the linear actuators 39, 41 the die member
31 is movable vertically towards (or away from) the ring mould 9 in
the direction of arrow 45.
[0174] The position of the die member 31 in a shaping position is
shown in phantom with the lower shaping surface being shown in the
position of line 33'.
[0175] In FIG. 1, both the lower ring mould 9 and the die member 31
are movable towards each other by means of the respective linear
actuators 23, 25 and 39, 41.
[0176] Usually the linear actuators 23, 25 are synchronised so that
both sides of the ring mould 9 move upwards (or downwards) at the
same speed. Usually the linear actuators 39, 41 are synchronised so
that both sides of the die member 31 downwards (or upwards) at the
same speed.
[0177] In an alternative to the example shown in FIG. 1, the ring
mould 9 is static and only the die member 31 is movable relative to
the ring mould. In such an embodiment the support members 19, 21
are directly mounted to the base 27, rather than being coupled to a
respective linear actuator 23, 25.
[0178] In another alternative to the example shown in FIG. 1, the
die member 31 is static and only the ring mould 9 is movable
relative to the die member 31. In such an embodiment the die
support members 35, 37 are directly mounted to the upper gantry 42,
rather than being coupled to a respective linear actuator 39,
41.
[0179] Such alternative configurations of movement for the ring
mould and die member are well known in the art.
[0180] When the first and second upper supports are in the position
shown by elements 11' and 13' and the die member 31 has been moved
downwards towards the ring mould 9 such that the shaping surface of
the die member 31 is in the position indicated by line 33', a sheet
of glass supported on the lower supports is able to be bent to a
final desired shape between the lower ring mould 9 and the upper
die member 31.
[0181] As is known in the art, the upper die member 31 may have at
least one opening in the shaping surface thereof for applying a
vacuum therethrough, for example as described in
WO2005/033026A1.
[0182] FIG. 2 shows a schematic cross-sectional representation of a
press bending station 51 of the type used carry out the present
invention.
[0183] The press bending station 51 is similar to the press bending
station 1 (and the same labels have been used to label the same
part), with the exception of the addition of an array of nozzles 53
associated with the ring mould 9. In this example the array of
nozzles 53 is in mechanical communication with the ring mould 9, as
will be described in more detail below.
[0184] The array of nozzles 53 is mounted to the support members
19, 21 by means of respective elongate members 55, 57. Each
elongate member 55, 57 is a steel strip providing a rigid
connection between the array of nozzles 53 and the respective
support member 19, 21.
[0185] With further reference to FIGS. 2, 3 and 4, the array of
nozzles 53 comprises a tubular section 59 having a plurality of
nozzles 61 in fluid communication therewith. Two such nozzles 61
and 61' are shown in FIG. 2 and two such nozzles 61* and 61** are
shown in FIG. 4 (FIG. 4 showing the section A of FIG. 3).
[0186] Each nozzle 61, 61' comprises a respective conical portion
63, 63' and a respective cylindrical portion 65, 65' having an
outlet orifice. The nozzles 61 in this example are uniformly spaced
along the length of the tubular section 59 but may not be. Upon
directing a fluid i.e. air, in particular compressed air, through
the tubular section 59 in the direction of arrow 60, a jet of fluid
is emitted from each nozzle 61 via the respective orifice 67 in the
direction of arrow 69. In FIG. 4, two nozzles 61*, 61** are shown,
so there are two jets of fluid in direct 69 emitted from the
respective outlet orifice 67.
[0187] In relation to FIG. 3, the array of nozzles 53 follows the
internal perimeter of the lower ring mould 9 and is spaced inside
the opening of the ring mould 9 and connected thereto by the
elongate members 55, 55' on one side and by the elongate member 57,
57' on the other side.
[0188] In FIG. 3 there are a plurality of nozzles of the type
described with reference to FIG. 4. The tubular section 59 is in
the form of a continuous ring having an input section 71. The input
section 71 is connected via a flexible pipe 73 to a valve 75 and
the valve is in fluid communication with fluid source 77, such as a
fan or compressed gas (i.e. air) cylinder. The valve 75 is
controllable via control means (not shown) such as a computer, to
control the flow of fluid to the array of nozzles 53 via the inlet
section 71.
[0189] As better illustrated in FIG. 2, for nozzle 61 the outlet
end of the cylindrical portion 65 is below the upper shaping
surface 15 and for nozzle 61' the outlet end of the cylindrical
portion 65' is also below the upper shaping surface 17.
[0190] When a sheet of glass is supported on the ring mould 9, jets
of fluid may be directed against the surface of the sheet of glass
in contact with the shaping surfaces 15, 17.
[0191] FIG. 5 shows a plan view of the ring mould 9, except in this
example a different array of nozzles 153 is provided. The array of
nozzles comprises four elongate slot nozzles 154, 155, 156 and 157.
Each slot nozzle may be suitably connected to a source of fluid as
described above. The array of nozzles 159 are located inboard the
walls of the ring mould 9 and follow the shape thereof. As shown in
FIG. 5, the slot nozzles 154 and 156 are curved to match the
curvature of the ring mould 9 and the slot nozzles 155, 157 are
straight to match the perimeter of the ring mould 9 in those
regions. Linear heater elements 12, 14 are also shown adjacent an
outer perimeter of the ring mould 9 to provide a heated ring mould
9. Linear heater elements 122, 124 are shown near the outer
perimeter of the upper curved portion of the ring mould 9. Shown in
phantom is linear heater element 122' which is positioned below the
upper shaping surface of the ring mould 9, wherein such a linear
heater element 122' may be instead of, or in addition to, the
linear heater element 122. Similar positioning of the heater
elements 12, 14 and 124 may also be adopted.
[0192] FIG. 6 shows a plan view of the ring mould 9 where in this
example a different nozzle array 253 is used. The nozzle array 253
comprises a tubular ring section as described above, except instead
of nozzles 61, a plurality of holes 261 are provided directly in
the wall of the tubular section. This is illustrated in further
illustrated in FIG. 7a which shows a portion of the tubular section
259. In this example both linear heating elements 12, 14 and curved
heating elements 222, 223 are used to heat the ring mould 9. As
discussed above, the heating elements may be positioned to be below
the upper shaping surface of the ring mould 9.
[0193] In one example the holes 261 in the tubular section 259 are
arranged linearly along the length of the tubular section, as shown
in FIG. 7a. FIG. 7a shows a portion of the tubular section 259. The
tubular section 259 has a circular cross section along the length
thereof. The line X-X' lies along the centre of the tubular section
259. There are seven circular holes 261a, 261b, 261c, 261d, 261e,
261f, 261g and 261h in the wall of the tubular section 259, with
the centre of each hole 261a-h being aligned with the line X-X'.
When a fluid passes through the tubular section 259 (for example in
the direction of line X.fwdarw.*X'), fluid is emitted out of the
holes 261a-h.
[0194] Alternatively the holes may be arranged in a staggered
manner along the length of the tubular section, as illustrated in
FIG. 7b. FIG. 7b shows a portion of the tubular section 259. The
tubular section 259 has a circular cross section along the length
thereof. The line X-X' lines along the centre of the tubular
section 259. There are seven circular holes 261a', 261b', 261c',
261d', 261e', 261f, 261g' and 261h' in the wall of the tubular
section 259. The centre of hole 261a' is on one side of the line
X-X' and the centre of the hole 261b' is on the other side of the
line X-X', and so on.
[0195] In another example the plurality of holes 261 in the wall of
the tubular section are arranged in a "domino five" pattern as
shown in FIG. 7c.
[0196] In another example illustrated in FIG. 7d, the tubular
section 259 has a slot 271 along the length thereof, instead of a
plurality of holes as described above. Fluid, for example
compressed air, may flow out of the slot when fluid is passed along
the length of the tubular section 259.
[0197] In yet another example the tubular section 259 has a
plurality of tubular nozzles 281 extending from the surface
thereof, a section of which is shown in FIG. 7e. In FIG. 7e there
are seven tubular nozzles 281a, 281b, 281c, 281d, 281e, 281f, 281g
and 281h extending from the surface of the tubular section 259. All
the nozzles 281 are arranged in the same direction relative to the
cylindrical axis along the length of the tubular section 259, but
each nozzle may be aligned differently, for example in a staggered
arrangement as shown in FIG. 7b. Each nozzle 281 has an outlet
orifice 282 at one end, the other end of each nozzle 281 being
connected to a hole in the wall of the tubular section 259 i.e.
essentially as shown in FIG. 7a with the tubular nozzle 281a-h
extending from the respective hole 261a-h. When a fluid passes
along the length of the tubular section 259, fluid may be emitted
from the nozzles 281. With reference to nozzle 281a, the jet of
fluid from the orifice 282 is emitted in the direction 269, which
direction may be perpendicular to the cylindrical axis of the
tubular section 259.
[0198] In these examples the tubular section has a circular
cross-section, but tubular sections having different cross sections
may be used, for example rectangular or square cross sections.
[0199] The choice of nozzle arrangement is made based on the degree
of cooling required during the shaping stage. For example, with
reference to FIG. 7a, the tubular section 259 may have an internal
diameter between 15 mm and 30 mm. Each hole 261a-h may have a
diameter between 1 mm and 10 mm, in particular between 1 mm and 5
mm. The spacing between adjacent holes 261a-h may be between 5 mm
and 20 mm and the spacing thereof may be uniform. Any of the nozzle
arrangements illustrated in FIGS. 7a-7e may be used in place of the
array of nozzles 53. A typical air pressure supplied to such a
nozzle arrangement may be less than 100 psi, for example between 10
psi and 80 psi.
[0200] Whatever type of nozzle is used in the array of nozzles, the
array of nozzles are configured to direct cooling fluid such as
air, in particular compressed air, upwards (i.e. with reference to
FIG. 2, in the direction of arrows 69, 69' towards the die member
31) to directly strike the lower surface of a heat softened glass
sheet during a press bending process, as will be discussed
hereinafter.
[0201] FIG. 8 shows the press bending station 51 in a second
configuration (a shaping configuration where the upper shaping die
member 31 and the lower ring mould 9 have been moved towards each
other and are pressing a heat softened sheet of glass 100 supported
on the upper shaping surfaces 15, 17 of the ring mould 9. In this
configuration the ring mould 9 and die member 31 are often referred
to as being in a closed position.
[0202] The sheet of glass 100 has a soda-lime-silica glass
composition. A typical soda-lime-silica glass composition is (by
weight), SiO.sub.2 69-74%; Al.sub.2O.sub.3 0-3%; Na.sub.2O 10-16%;
K.sub.2O 0-5%; MgO 0-6%; CaO 5-14%; SO.sub.3 0-2% and
Fe.sub.2O.sub.3 0.005-2%. The glass composition may also contain
other additives, for example, refining aids and other colourants,
which would normally be present in an amount of up to 2%. The
transmitted glass colour may be measured in terms of a recognised
standard such as BS EN410. In the art, soda-lime-silica glass may
also be referred to as soda-lime-silicate glass.
[0203] Preferably the glass sheet 100 has a thickness between 1 mm
and 10 mm, more preferably between 1.5 mm and 4 mm, even more
preferably between 1.5 mm and 2.5 mm, even more preferably between
1.6 mm and 2.3 mm.
[0204] The upper die member 31 is shown in a position having moved
downwards towards the ring mould 9 by actuating the linear
actuators 39, 41, the die member being mounted to the first and
second die support members 35, 37 that are coupled to the
respective linear actuator 39, 41.
[0205] Since the array of nozzles 53 are coupled to the supports
19, 21 via the respective elongate members 55, 57, actuation of the
linear actuators 23, 25 to cause the first and second support
members to move thereby causing movement of the ring mould 9, also
moves the array of nozzles 53 at the same time. In an alternative
to the embodiment shown, the array of nozzles 53 may be fixed to
the base member 27. In another alternative the array of nozzles 53
may be provided with a separate actuator mechanism to move the
array of nozzles upwards and downwards (i.e. in the direction of
arrow 29) independently of the upwards and downwards movement of
the ring mould 9.
[0206] As the glass sheet 100 is being press bent between the ring
mould 9 and the upper die member 31, the glass sheet 100 remains on
the shaping surfaces 15, 17 of the lower supports 11, 13 such that
there is no movement of the glass sheet 100 on the shaping support
other than any movement inherent to the pressing action that causes
the glass sheet 100 to acquire the desired curvature. For example,
when starting in the configuration shown in FIG. 2 with a glass
sheet on the ring mould 9 i.e. in contact with the shaping surfaces
15, 17 of the lower supports 11,13, the separation of the ring
mould 9 towards the upper die member 31 is reduced to reach the
configuration shown in FIG. 8. With reference to FIG. 8, the ring
mould is moved toward the die member 31 in the direction of arrow
29 and the die member is moved towards the ring mould 9 in the
direction of arrow 45 (the directions 29, 45 are parallel to the
vertical) to press bend the glass sheet 100.
[0207] Whilst in the second configuration shown in FIG. 8, which
may last for a few seconds i.e. up to ten seconds, the valve 75 is
actuated by control means (not shown) such that cooling air from
fluid source 77 is provided to the array of nozzles 53 via the
flexible pipe 73.
[0208] Two nozzles 61, 61' are shown in FIG. 8 and upon actuation
of the valve 75 cooling air is directed towards the lower surface
of the glass sheet 100 whilst the glass sheet is being press bent
between the ring mould 9 and the die member 31. The lower surface
of the glass sheet 100 is that major surface of the glass sheet 100
that is in contact with the shaping surface of the ring mould 9.
The glass sheet 100 has an opposing major surface that may be
referred to as the upper surface of the glass sheet. The upper
surface of the glass sheet 100 is in contact with the shaping
surface 33 of the shaping die 31 during the press bending step.
[0209] As illustrated, the nozzles are sufficiently spaced from the
lower surface of the glass sheet so that the nozzles do not contact
the lower surface of the glass sheet. The outlet end of the nozzles
61, 61' may be between 10 mm and 100 mm from the lower surface of
the glass sheet during the press bending step. If the nozzles
contact the lower surface of the heat softened glass sheet, optical
distortion may result in the shaped glass sheet.
[0210] By blowing cooling air onto only the lower surface of the
glass sheet during the press bending step, it has been found that
the compressive stress in the lower surface of the glass sheet may
be increased when the glass is cooled to room temperature, compared
to the same bending process without blowing cooling air onto the
lower surface of the glass sheet during the press bending step.
Surface compression (or compressive) stress measurements may be
made using a Strainoptics Laser GASP-CS
(http://www.strainoptics.com/files/Laser
%20GASP-CS%20Quick-Start%20(English).pdf). Such equipment is
available from Strainoptics, Inc., 108 W. Montgomery Avenue, North
Wales, Pa. 19454 USA.
[0211] For example, without blowing cooling air onto the lower
surface of the glass sheet during the press bending step, it was
found that following an annealing step to cool the glass down to
room temperature, the surface compressive stress in a peripheral
region 75 mm inboard of the edge of the bent glass sheet was less
than or equal to 10 MPa i.e. between 5 MPa and 9 MPa.
[0212] Upon using the same bending process it was found that by
directing cooling air towards only the lower surface of the glass
sheet during the press bending step it was possible to increase the
surface compressive stress in the peripheral region 75 mm inboard
of the edge of the bent glass sheet. It was found that following
the same annealing step to cool the glass down to room temperature,
the surface compressive stress in the peripheral region 75 mm
inboard of the edge of the bent glass sheet could be increased by
up to about 25 MPa, for example by between 5 MPa and 25 MPa.
[0213] It is preferred to increase the surface compressive stress
in the peripheral region 75 mm inboard of the edge of the bent
glass sheet by between 5 MPa and 25 MPa, preferably by between 5
MPa and 15 MPa, more preferably by between 7 MPa and 15 MPa.
[0214] The surface compressive stress in a peripheral region 75 mm
inboard of the edge of a bent glass sheet example may be influenced
by the type of shaping process used to shape the glass sheet. For
example, using a press bending station having a similar
configuration to that shown in FIGS. 2 and 8, the surface
compressive stress in a peripheral region 75 mm inboard of the edge
of the bent glass sheet may be up to 20 MPa, for example between 2
MPa and 20 MPa. By using the present invention on this particular
press bending station, it would be expected to increase the surface
compressive stress in the peripheral region 75 mm inboard of the
edge of the bent glass sheet, for example by up to about 25 MPa
i.e. an increase of between 5 MPa and 25 MPa.
[0215] The increase of surface compressive stress in the peripheral
region 75 mm inboard of the edge of the bent glass sheet may also
be influenced by the air pressure supplied to the array of nozzles.
For example, supplying the cooling air to the array of nozzles 53
for a fixed time during the press bending step, it was found that
using higher air pressure supplied to the array of nozzles 53
resulted in higher surface compressive stress in the peripheral
region 75 mm inboard of the edge of the bent glass sheet.
[0216] Furthermore by incorporating apparatus comprising the array
of nozzles into the press bending station, it is possible to
actuate the cooling during press bending only when required i.e.
the same press bending station 51 may be used instead of a press
bending station 1.
[0217] In accordance with an embodiment of the present invention,
cooling air is directed towards only the lower surface of the glass
sheet when the glass sheet is being shaped.
[0218] The cooling air is directed to cool selective regions of the
glass sheet during shaping, in particular the peripheral regions
thereof. The cooling air provides additional cooling to any natural
cooling that may occur when the glass sheet is being shaped.
[0219] Once cooled, the bent glass sheet 100 may be used as a
monolith or may be laminated to another sheet of glass, for example
to make a vehicle windscreen or side window. It is preferred that
the glass sheet bent according to the present invention is the
outer ply in such a laminate. When the glass sheet bent according
to the present invention is the outer ply in a laminated glazing,
in particular a vehicle windscreen, it is preferred that, using
conventional nomenclature, the cooling air is directed onto the
glass surface that will be surface 1 in the laminated glazing.
[0220] The other (second) sheet of glass in the laminated glazing
may have a different composition and/or have been bent using a
different bending process, for example a gravity sag bending
process.
[0221] By increasing the surface compressive stress in the
peripheral region, the bent glass sheet once laminated as the outer
ply in a laminated glazing may have the surface compressive stress
modified due to lamination stresses i.e. before lamination, the
inner and outer ply do not form a nested pair. The increase in
surface compressive stress helps balance the lamination stresses to
provide a laminated glazing with suitable stress
characteristics.
[0222] FIG. 9 is a graph showing a shaping sequence and different
air blowing sequences during the shaping sequence. Axis 500
represents time in seconds with each major unit on this axis being
one second. In this example the shaping sequence is a press bending
operation as described with reference to the previous figures.
[0223] Line 502 shows the variation with time of the position of a
pair of complementary press bending members when shaping a sheet of
glass therebetween. The press bending members may be as described
with reference to FIG. 8, for example an upper die member 31 and a
lower ring mould 9.
[0224] At time t=t1, the press bending members are closed and the
shaping configuration has been reached (as shown in FIG. 8). Each
press bending member is in the shaping position such that a heat
softened glass sheet is press bent between the two press bending
members.
[0225] At time t=t4, the press bending members are moved apart
(i.e. opened) such that the glass sheet is no longer being pressed
between the press bending members. For example the ring mould 9 and
the shaping die 31 may be moved to the positions shown in FIG. 2.
When the upper die member 31 is moved away from the ring mould 9
following the press bending step, the bent glass may be supported
on the shaping surface 33 of the die member 31 by provision of a
vacuum through openings in the shaping surface 33.
[0226] The duration of the shaping step i.e. the press bending step
is therefore (t4-t1) seconds.
[0227] Line 504 shows how in one embodiment the array of nozzles
are used to direct cooling air towards the lower glass surface
during the entire duration of the shaping or pressing step. That
is, with reference to FIG. 8, the valve 75 is actuated such that
the array of nozzles directs cooling air towards the glass surface
beginning at time t=t1 to end at time t=t4 when the air supply is
switched off by suitable actuation of valve 75. In this example the
air pressure to the array of nozzles was kept constant for the
duration that cooling air was being directed onto the glass surface
i.e. between times t1 and t4.
[0228] Line 506 shows how in another embodiment the array of
nozzles are suitably switched on such that cooling air is directed
onto the glass surface beginning at time t=t2 where t2>t1. The
cooling air is then switched off at time t=t4 by suitable actuation
of the valve 75. As such, there is a delay in switching on the
cooling air after the press bending members have reached the
shaping position. Again in this example the air pressure was
constant for the duration of the air pulse i.e. between t2 and t4.
The cooling air was directed onto the glass surface for a duration
of (t4-t2) seconds.
[0229] Line 508 shows how in another embodiment the cooling air is
switched on at time t=t1 and is then switched off at time t=t3,
where t3<t4. As such, the cooling air pulse is switched off
before the end of the press bending step. The cooling air was kept
at the same pressure for the duration that the cooling air was
directed onto the glass surface i.e. between t1 and t3. The cooling
air was directed onto the glass surface for a duration of (t3-t1)
seconds.
[0230] Line 510 shows how in another embodiment the cooling air is
switched on at time t=t2 where t2>t1 and is then switched off at
time t=t3, where t3<t4. As such, there is a delay in switching
on the cooling air after the shaping members have reached the
shaping position and the cooling air is switched off before the end
of the shaping step. Again in this example the air pressure was
kept constant for the duration that the cooling air was directed
onto the glass surface i.e. between t2 and t3. The cooling air was
directed onto the glass surface for a duration of (t3-t2)
seconds.
[0231] Line 512 shows how in another embodiment the cooling air is
switched on at time t=t2 where t2>t1. The cooling air is then
switched off at time t=t5, where t5>t4. As such, the cooling air
remains being directed towards the glass surface after the
completion of the press bending step. Again the air pressure was
kept the same for the duration that the cooling air was directed
onto the glass surface i.e. between t2 and t5. The cooling air was
directed onto the glass surface for a duration of (t5-t2) seconds.
For example, using the cooling sequence represented by line 512,
the surface compressive stress may be increased from a baseline
level with no cooling by up to 15 MPa, for example between 7 MPa
and 12 MPa, in a peripheral region 75 mm inboard of the edge of the
bent glass sheet. In contrast, using the same shaping conditions
but using the cooling sequence shown by line 504, the surface
compressive stress may be increased from the baseline level with no
cooling by up to 25 MPa, for example between 10 MPa and 20 MPa.
[0232] It is also within the scope of the present invention that
the air pressure may vary between the switching on time and the
switching off time of the cooling air pulse. For example with
reference to line 504, the cooling air may have a different
pressure at time t=t1 compared to at time t=t4 (the cooling air
being provided to the array of nozzles being either higher pressure
or lower pressure at time t=t1 compared to time t=t4).
[0233] FIG. 10 shows another press bending station 151 for press
bending a sheet of glass 200.
[0234] In this example the lower shaping support 179 has a convex
shaping surface. A heat softened glass sheet 200 is allowed to sag
on the convex shaping surface, and is pressed against the convex
shaping surface by an upper pressing ring 181. The upper pressing
ring 181 is in mechanical communication with a fixed upper gantry
183 such that the upper pressing ring is movable relative to the
gantry, for example by mounting the pressing ring on suitable
supports 185, 187 coupled to respective linear actuators 189, 191
that are fixed to the gantry. In this example the lower shaping
support 179 is in a fixed position relative to the gantry but may
be movable relative thereto. The upper shaping ring 181 is movable
relative to the gantry. The upper pressing ring 181 is similar to
the lower ring mould 9 described with reference to FIG. 1.
[0235] An array of nozzles 53 is attached to the supports 185, 187
for movement with the upper shaping ring. The array of nozzles 53
is as described with reference to FIG. 2, but instead of directing
jets of cooling air upwards, the jets of cooling air are directed
downwards. In this embodiment, during the press bending step
cooling air is directed only towards the major surface of the glass
sheet 200 not in contact with the lower shaping support 179 i.e.
the major surface facing the array of nozzles 53.
[0236] Although not shown in FIG. 10, the array of nozzles is in
fluid communication with a suitable valve and fluid supply in a
manner as previously described with reference to FIG. 2.
[0237] FIG. 11 shows apparatus 351 for bending a glass sheet under
the influence of gravity, often referred to as "sag bending",
"gravity sag bending" or "gravity bending". In this embodiment of
the present invention, a flat glass sheet is positioned on a ring
mould, heated to a softening temperature and allowed to sag thereon
under the influence of gravity.
[0238] The ring mould 309 is similar to the ring mould 9 described
in relation FIG. 1 in that it has an upper shaping surface for
contacting a major surface of the glass sheet during the glass
shaping. However in this example the ring mould 309 is fixed
directly to the base 307 and not movable relative thereto. Usually
the ring mould 309 is position on a conveyor system to pass the
ring mould 309 with flat glass sheet thereon through a suitable
heating furnace to raise the glass temperature to a sufficiently
high level to allow gravity sag bending on the ring mould to
occur.
[0239] Ring mould are also known having articulated portions to
impart additional curvature to certain parts of the glass as the or
each articulated portion moves from an initial position to a final
position.
[0240] The glass sheet softens under the influence of the heat and
sags into conformity with the ring mould 309. An additional upper
die (not shown) may be used to assist the with the gravity bending.
The same array of nozzles 53, flexible pipe 73, valve 75 and fluid
supply 77 as used in FIG. 2 is also used in this embodiment. The
bent glass sheet 300 is shown in the figure.
[0241] Unlike during a press bending step when it is possible to
define the press bending process as beginning when the press
bending members are "closed" i.e. in the shaping position, for a
gravity bending process it is more difficult to define an actual
start to the shaping process. However for the purpose of the
present invention the sag bending process is defined as having
begun when for a soda-lime-silica glass composition, the glass
sheet has reached a temperature of 550.degree. C.
[0242] Although the previous examples have been described with
reference to an array of nozzles for providing cooling fluid onto a
portion of the glass surface during the bending step, a heat
exchange device may be used to extract heat from the heat softened
glass sheet during glass shaping.
[0243] As an example of such a heat exchange device FIG. 12 shows a
shaping ring 609 incorporating such a heat exchange device. The
shaping ring 609 is similar to the ring mould 9 described with
reference to FIG. 1.
[0244] The shaping ring 609 has four walls 611, 612, 613 and 614
arranged such that in plan view, the shaping ring 609 has the same
configuration as the ring mould 9 shown in FIG. 3. The shaping ring
609 has an upper shaping surface 617 for supporting a glass sheet
thereon. The shaping ring 609 may be used in a press bending
operation in which case an upper male die member would also be
provided having a complementary shaping surface.
[0245] The four walls 611, 612, 613, 614 of the shaping ring define
an opening in which is located the heat exchange device 653. The
heat exchange device 653 comprises a tube 659 in an annular
configuration having an inlet 660 and an outlet 661. The inlet 660
is in fluid communication with an inlet tube 662 and the outlet 661
is in fluid communication with an outlet tube 663. Suitable
material for the tubes includes stainless steel.
[0246] The tube 659 of the heat exchange device is mounted to the
inner surface of the walls of the shaping ring by eight mounts,
only four of which are labelled as 654, 655, 656 and 657 for
clarity. The surface of the tube 659 is below the shaping surface
617 of the shaping ring such that when a glass sheet is bent on the
shaping ring, the glass sheet does not contact the tube 659. Other
suitably configured heat exchange device may be used that does
contact the glass sheet during the shaping process.
[0247] At the inlet tube 662 a cooling fluid i.e. a liquid such as
water or oil, is introduced to flow in the direction of arrow 667.
The liquid flows around the heat exchange tube and then flows out
of the outlet tube 663 in the direction of arrow 669. The cooling
liquid allows heat to be extracted from the glass sheet during the
shaping step. The heat exchange device may be used instead of, or
in addition to, an array of nozzles as previously described.
[0248] FIG. 13 shows a schematic cross-sectional representation of
part of a glass bending line 701 incorporating a press bending
station 51 of the type shown in FIG. 2.
[0249] The glass bending line 701 comprises a heating furnace 702,
a press bending furnace 704 and an annealing furnace 706.
[0250] A roller conveyor bed 708 extends through the heating
furnace 702, the press bending furnace 704 and the annealing
furnace 706 to define a path of conveyance for a glass sheet 700.
The roller conveyor bed comprises a plurality of rollers 710
configured to convey a glass sheet 700 in the direction of arrow
712. In this example the glass sheet 700 is shown to be in contact
with the rollers 71, but the glass sheet 700 may be positioned on a
carriage, the carriage being in contact with the rollers 710. As an
alternative to rollers 710, or in addition to rollers 710, an air
flotation device may be used to convey the glass sheet in the
direction of arrow 712.
[0251] In the heating furnace 702 the glass sheet 700 is heated to
a temperature suitable for shaping or bending. The furnace may
incorporate electric/gas heating and convective heating as
required.
[0252] Inside the press bending furnace 704 is press bending
station 51 as previously described. When the glass sheet 700 is
conveyed to between the lower ring mould 9 and the die member 31,
the glass sheet is positioned on the ring mould 9 for subsequent
press bending. Methods are known in the prior art for transferring
the glass sheet from the conveyor rollers 710 to the ring mould 9,
for example some of the conveyor rollers may be configured as drop
rollers, or a vacuum platen may be used to lift the heat softened
glass sheet from the conveyor rollers for depositing onto a
suitably configured ring mould 9.
[0253] The upper die member 31 and/or linear actuators 39, 41
is/are in electrical communication with a control means 714, such
as a computer, for controlling the movement of the die member 31 by
suitable actuation of the linear actuators 39, 41. The control
means 714 may be in electrical communication with other parts of
the glass bending line 701, for example the conveyor roller bed 708
to control the speed of the rollers.
[0254] With the glass sheet 700 positioned on the ring mould 9, the
ring mould 9 and upper die 31 are moved towards each other (in
direction of arrow 45) for press bending the glass sheet 700.
[0255] When the die member 31 and the lower ring mould 9 are in the
shaping position (see FIG. 8), the control means 714 sends a signal
to the valve 75. The valve 75 then opens and air from fluid supply
77 passes through the coupling pipe 73' that is in fluid
communication with the valve 75 and the flexible pipe 73. Cooling
air is then able to flow through the nozzles towards only the lower
surface of the bent glass sheet during the shaping operation (the
press bending step) as previously described.
[0256] The valve 75 is in electrical communication with the control
means 714 via suitable cabling 78. The fluid source 77 may be in
electrical communication with the control means 714 via suitable
cabling 76.
[0257] When the glass sheet is on the ring mould 9 and being press
bent, it is preferred that the glass sheet does not move relative
to the ring mould, other than to conform to the shaping surfaces of
the ring mould and the die member. For example, at the beginning of
the press bending process when the press bending members are
"closed", a point p1 on the glass surface facing the ring mould 9
is coincident with a point p2 on the ring mould 9. It is preferred
that throughout the press bending step (i.e. between t1 and t2 in
FIG. 9), the points p1 and p2 are coincident and there is no
relative movement therebetween.
[0258] A carrier ring 718 is shown between the press bending
furnace 704 and annealing furnace 706 and is movable between the
position shown in FIG. 13 to a position between the die member 31
and the ring mould 9 by suitable actuators (not shown) i.e. by
moving in the direction of arrow 720. The actuators controlling the
movement of the carrier ring 718 may also be controlled by the
control means 714.
[0259] Once a glass sheet is being shaped between the die member 31
and the ring mould 9, a vacuum may be provided to openings in the
shaping surface of the die member 31 to hold the glass sheet
against the convex shaping surface of the die member 31. The ring
mould 9 may then be lowered in the direction of arrow 29 and die
member raised in the direction of arrow 45. The carrier ring 718
moves to be between the glass sheet supported on the shaping
surface 33 of the die member 31 and the ring mould 9. The vacuum
provided to the openings in the shaping surface of the die member
31 may then be removed, possibly with a subsequent jet of air
applied to the same openings in the shaping surface of the die
member to urge the bent glass sheet therefrom. The bent glass sheet
then drops onto the suitably positioned carrier ring 718 to be
supported thereon and the carrier ring moves back to the position
shown in FIG. 13 to deposit the bent glass sheet onto the conveyor
section 708' for subsequent conveyance in the direction of arrow
712 into the annealing furnace 706.
[0260] Although in the figures previous figures the ring mould 9
and the die member 31 are shown as having exposed shaping surfaces
15, 15 and 33 respectively, in preferred embodiments either or both
the ring mould 9 and die member 31 may be provided with a
protective cover to cover and protect the shaping surface of the
respective mould member(s) from damage and wear. Preferably the
cover comprises a cloth made of, for example, stainless steel,
fibre glass, poly-phenyleneterephthalamide fibres (e.g.
Kevlar.TM.), materials blended Kevlar.TM., polybenzoxale (PBO)
fibres containing graphite (e.g. Zylon.TM.), or various weaves of
these fibres.
[0261] The press bending station 51 may be used to bend an outer
ply of a laminated glazing for a vehicle, for example a vehicle
windscreen or side window. The outer ply may have a
soda-lime-silica glass composition and have a thickness between 1
mm and 10 mm, in particular 1.5 mm and 2.5 mm. As is evident from
FIGS. 8 and 13, when the outer ply of a laminated glazing for a
vehicle, for example a vehicle windscreen, is made using the glass
bending line 701, using conventional nomenclature, surface 1 of the
laminated glazing has been cooled by directing cooling air onto
said surface during the press bending step.
[0262] The inner ply of such a laminated glazing may be produced as
follows.
[0263] A sheet of chemically strengthenable glass is provided and
will be used for the inner ply of the laminated glazing i.e. a
vehicle windscreen. Suitable chemically strengthenable glass
compositions include alkali aluminosilicates compositions such as
those described in U.S. Pat. No. 7,666,511 B2. Other suitable
chemically strengthenable glass compositions are described in
WO2014/148020A1 and WO99/48824A1.
[0264] A specific composition for the inner ply is 68 mol %
SiO.sub.2, 2.5 mol % Al.sub.2O.sub.3, 11 mol % MgO, 3.7 mol % CaO,
14.2 mol % Na.sub.2O, 0.6 mol % K.sub.2O. For this composition
MgO+CaO is 14.7 mol % and Na.sub.2O+K.sub.2O is 14.8 mol %. This is
composition number 13 in table 2 on page 20 of WO2014/148020A1 as
published.
[0265] The sheet of chemically strengthenable glass is 1 mm thick
and is cut to have the same periphery as the unbent outer ply
(although may be slightly smaller in dimensions to account for this
being the inner ply). The sheet of chemically strengthenable glass
may have a thickness between 0.4 mm and 1.2 mm, or a thickness
between 0.5 mm and 1 mm.
[0266] The sheet of chemically strengthenableglass may be suitably
edge worked and washed prior to being bent.
[0267] The sheet of chemically strengthenable glass is placed on a
suitable ring mould to support the sheet of chemically
strengthenable glass close to the periphery thereof. The sheet of
chemically strengthenable glass is heated to sufficient temperature
to cause the chemically strengthenable glass sheet to soften and
sag under the influence of gravity, conventionally referred to as
sag bending. The glass sag bends to a shape close to that of the
shaped outer ply produced using the method according to the first
aspect of the present invention. However the curvature of the inner
ply may not be the same as the outer ply.
[0268] The bent inner ply of chemically strengthenable glass is
then annealed using controlled cooling to reduce the temperature to
room temperature.
[0269] The bent inner ply of chemically strengthenable glass is
chemically strengthened using an ion exchange process. Typically
sodium ions are chemically exchanged for potassium ions. A flat
sheet of chemically strengthenable glass may also be chemically
strengthened.
[0270] For the specific composition mentioned above, it is possible
to chemically strengthen the inner ply to have surface compressive
stress greater than 400 MPa, typically between 450 MPa and 675 MPa.
The depth of layer (DOL) of the chemically strengthened glass ply
may be between 10 .mu.m and 60 .mu.m.
[0271] It is also envisaged that the bent inner ply may be
thermally toughened although it is difficult to thermally toughen
plies of glass that have a thickness of 1 mm or less.
[0272] In an embodiment, to produce the laminated glazing a bent
outer ply having a soda-lime-silica glass composition and a bent
inner ply having a glass composition that has been bent and
chemically strengthened as described above are provided.
[0273] The pair of bent inner and outer plies are washed and a ply
of interlayer material having a thickness between 0.3 mm and 1.5 mm
is positioned between the inner ply and the outer ply. In this
particular example the interlayer material was a 0.76 mm thick ply
of PVB, although other suitable adhesive interlayer material may be
used, for example ethylene vinyl acetate (EVA) or acoustic modified
PVB.
[0274] The assembly of inner ply and outer ply with PVB ply
therebetween are laminated using suitable lamination conditions to
join the inner ply to the outer ply via the PVB ply.
[0275] The laminated glazing so produced has modified stress
characteristics compared to bending the outer ply without the
provision of deliberate cooling of selected regions of the outer
ply during the shaping step. Any lamination stresses introduced to
the laminated glazing following lamination are compensated for by
the modified compressive stressed produced in the outer ply when
the outer ply is shaped in accordance with the present
invention.
[0276] Methods of shaping a glass sheet are described comprising
the steps (i) providing a shaping support for supporting the glass
sheet; (ii) heating the glass sheet to a temperature for shaping;
(iii) positioning the glass sheet on the shaping support; and (iv)
shaping the glass sheet on the shaping support, wherein during step
(iv) at least one portion of the glass sheet is deliberately
cooled. In preferred embodiments the shaping step (iv) comprises
press bending a heat softened glass sheet between a lower shaping
support and an upper shaping member, wherein during step (iv) only
a portion of the major surface of the glass sheet facing the lower
shaping support is cooled by directing one or more jet of air onto
said portion. The shaped glass sheet finds particular use in a
laminated glazing. Apparatus useful in carrying out the method of
shaping is also described.
[0277] The present invention provides a particular advantage for
controlling the stress in an outer ply of a laminated glazing when
the inner glass ply has not been bent to the same precision as the
outer ply. By using the present invention the outer ply in the
resulting laminated glazing may have improved impact performance
and scratch resistance in a peripheral region extending around the
perimeter of the outer ply, compared to the same laminated glazing
produced without using the present invention.
* * * * *
References