U.S. patent application number 15/872330 was filed with the patent office on 2018-05-17 for method and system for forming shaped glass articles.
The applicant listed for this patent is CORNING INCORPORATED. Invention is credited to Jacob Immerman, Thomas Augustus Keebler, John Robert Saltzer, JR., Ljerka Ukrainczyk.
Application Number | 20180134602 15/872330 |
Document ID | / |
Family ID | 50185070 |
Filed Date | 2018-05-17 |
United States Patent
Application |
20180134602 |
Kind Code |
A1 |
Immerman; Jacob ; et
al. |
May 17, 2018 |
METHOD AND SYSTEM FOR FORMING SHAPED GLASS ARTICLES
Abstract
A method of forming a shaped glass article includes placing a
glass sheet on a mold such that a first glass area of the glass
sheet corresponds to a first mold surface area of the mold and a
second glass area of the glass sheet corresponds to a second mold
surface area of the mold. The first glass area and the second glass
area are heated such that the viscosity of the second glass area is
8 poise or more lower than the viscosity of the first glass area. A
force is applied to the glass sheet to conform the glass sheet to
the mold surface. During the heating of the second glass area, the
first mold surface area is locally cooled to induce a thermal
gradient on the mold.
Inventors: |
Immerman; Jacob; (Corning,
NY) ; Keebler; Thomas Augustus; (Corning, NY)
; Saltzer, JR.; John Robert; (Beaver Dams, NY) ;
Ukrainczyk; Ljerka; (Painted Post, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CORNING INCORPORATED |
Corning |
NY |
US |
|
|
Family ID: |
50185070 |
Appl. No.: |
15/872330 |
Filed: |
January 16, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15399112 |
Jan 5, 2017 |
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15872330 |
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14183938 |
Feb 19, 2014 |
9550695 |
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15399112 |
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61766878 |
Feb 20, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y10T 428/24355 20150115;
G06F 1/1626 20130101; Y02P 40/57 20151101; Y10T 428/24628 20150115;
C03B 2225/02 20130101; C03B 23/0357 20130101; C03B 23/0235
20130101 |
International
Class: |
C03B 23/035 20060101
C03B023/035; G06F 1/16 20060101 G06F001/16; C03B 23/023 20060101
C03B023/023 |
Claims
1-19. (canceled)
20. A shaped glass article having an optical quality surface area
suitable for an electronic device cover glass formed by a method
comprising: placing a glass sheet on a mold having a mold surface
with a profile of the shaped glass article, the placing being such
that a first glass area of the glass sheet corresponds to a first
mold surface area of the mold surface and a second glass area of
the glass sheet corresponds to a second mold surface area of the
mold surface; heating the first glass area and the second glass
area to a glass viscosity at or above 10.sup.10.1 poise; locally
heating the second glass area to a glass viscosity at or below
10.sup.9.9 poise; applying a force to the glass sheet to conform
the glass sheet to the mold surface when the second glass area is
at a glass viscosity at or below 10.sup.9.9 poise; and locally
cooling the first mold surface area to induce a thermal gradient on
the mold surface that results in the glass viscosity in the first
glass area remaining above 10.sup.9.9 poise during the local
heating of the second glass area.
21. A shaped glass article, comprising: a glass body having a
three-dimensional shape, at least one surface of the glass body
having a waviness height less than 30 nm over a 15 mm by 25 mm
measurement area and a roughness average less than 1 nm.
22. The shaped glass article of claim 21, wherein the glass body
has a flat area that is flat to within 100 .mu.m over a 25
mm.times.25 mm area.
23. The shaped glass article of claim 22, wherein the glass body
has at least one bend area with a bend radius of less than 10
mm.
24. The shaped glass article of claim 22, wherein the glass body
has an optical transmission greater than 85% in a wavelength range
of 400 nm to 800 nm.
25. The shaped glass article of claim 22, wherein the glass body
has a compression strength greater than 300 MPa.
26. The shaped glass article of claim 22, wherein the glass body
has a hardness of greater than 7 on the Mohs scale.
27. The shaped glass article of claim 22, which is made of an
alkali aluminosilicate glass.
28. The shaped glass article of claim 22, wherein the glass body is
adapted for covering an electronic device having a flat display.
Description
[0001] This application is a divisional application of U.S.
application Ser. No. 14/183,938 filed on Feb. 19, 2014, which
claims the benefit of priority under 35 U.S.C. .sctn. 119 of U.S.
Provisional Application Ser. No. 61/766,878 filed on Feb. 20, 2013
the content of each of which is relied upon and incorporated herein
by reference in its entirety.
FIELD
[0002] The present disclosure relates to production of shaped glass
articles usable as cover glass for electronic devices.
BACKGROUND ART
[0003] Industrial design is driving demand for shaped cover glass
for portable electronic devices such as smart phones and tablets. A
typical shaped cover glass of interest has a combination of a large
flat section for covering the front side of the electronic device
and one or more curved sections for wrapping around one or more
edges of the electronic device. The curved sections include bends
and corners where they intersect with the flat sections. A flat
electronic device will require a small bend radius, e.g., less than
20 mm, to allow the curved section to wrap around an edge of the
device while maintaining the flat appearance of the device.
[0004] Shaped glass articles with small radius bends and corners
are difficult and expensive to make using glass machining Glass
machining involves large material removal, which greatly increases
cost. Total removal of machining marks with polishing is difficult
to impossible. It is also very difficult to achieve an even polish
on curved sections without inducing optical distortions in the
glass article.
[0005] Thermal reforming with molds can avoid some of the
challenges inherent in glass machining However, there are also
challenges with precision forming of small radius bends and corners
with this approach, especially when the glass has a high softening
point and requires relatively high temperatures to form the bends
and corners. At high forming temperatures, interaction between the
glass and mold becomes a concern.
SUMMARY
[0006] When forming a shaped glass article using thermal reforming
and a mold, the flat and curved areas of the glass sheet are
normally heated and force is normally applied to both the flat and
curved areas in order to conform the flat and curved areas of the
glass sheet to the flat and curved areas of the mold. To form a
bend with a small radius, e.g., less than 20 mm, without inducing
high stress in the glass sheet, the glass viscosity needs to be at
or below 10.sup.9.9 poise when the force is applied to the glass
sheet.
[0007] Normally, the glass sheet will not fully contact the bends
and corners in the mold until near the end of applying the force.
If the mold is a female mold, the flat area of the glass sheet will
sag freely into the mold cavity during the early stages of the
heating and contact the flat area of the mold. Thus the flat area
of the glass sheet will have a much longer interaction time with
the mold than the bend area of the glass sheet. In the case of a
male mold, the flat area of the glass sheet will be in contact with
the flat area of the mold during the entire heating cycle.
[0008] If the flat area of the glass sheet is below 10.sup.9.9
poise or the flat area of the mold is at the same temperature as
the bend area of the mold during the long contact between the flat
area of the glass sheet and the flat area of the mold, the glass
surface may have undesirable pitting and staining in the flat area
due to interaction with the mold. The mold life will also be
shortened if the glass is in contact with the mold at a relatively
high temperature for a relatively long period.
[0009] According to the present disclosure, it is desirable to keep
the flat area of the mold colder than the bend area of the mold
during the bend forming process. It is also desirable to get the
glass sheet and mold locally hot in the bend area so that bends and
corners can be precisely formed in the glass sheet. It is further
desirable to keep the glass sheet and mold relatively cold in the
flat area while the glass sheet and mold are hot in the bend area
so that undesirable pitting and staining in the flat area of the
glass surface can be avoided.
[0010] In one aspect, a method of forming a shaped glass article
comprises placing a glass sheet on a mold having a mold surface
with a select shaped glass article profile. The placing is such
that a first glass area of the glass sheet corresponds to a first
mold surface area of the mold surface and a second glass area of
the glass sheet corresponds to a second mold surface area of the
mold surface. The first glass area and second glass area are heated
to a glass viscosity between 10.sup.10.1 poise and 10.sup.9 poise.
Then, the second glass area is locally heated to a glass viscosity
at or below 10.sup.9.9 poise, so that the glass viscosity in the
second glass area is 8 poise or more lower than the viscosity in
the first glass area. When the second glass area is at a glass
viscosity at or below 10.sup.9.9 poise, force is applied to the
glass sheet to conform the glass sheet to the mold surface. During
local heating of the second glass area, the first mold surface area
is locally cooled to induce a thermal gradient on the mold surface
that results in the glass viscosity in the first glass area
remaining above 10.sup.9.9 poise.
[0011] In one embodiment, the local cooling of the first mold
surface area is such that the glass viscosity in the first glass
area is maintained at or above 10.sup.10.9 poise during at least a
portion of the local heating of the second glass area.
[0012] In one embodiment, the local cooling of the first mold
surface area results in a maximum thermal gradient across the first
mold surface area of less than 20.degree. C. during the local
cooling.
[0013] In one embodiment, the local cooling of the first mold
surface area is such that a temperature of the first mold surface
area is below a temperature corresponding to a glass viscosity of
10.sup.11.3 poise.
[0014] In one embodiment, a temperature of the second mold surface
area is above a temperature corresponding to a glass viscosity of
10.sup.11.7 poise when the force is applied to the glass sheet.
[0015] In one embodiment, the first mold surface area is
substantially flat and the second mold surface area comprises a
bend having a radius less than 20 mm.
[0016] In one embodiment, the force is applied to the glass sheet
by creating vacuum at the second glass area through at least one
vacuum opening located in the bend.
[0017] In one embodiment, creating vacuum includes creating vacuum
with a first vacuum pressure for a first time period followed by
creating vacuum with a second vacuum pressure for a second time
period, wherein the second vacuum pressure is reduced compared to
the first vacuum pressure.
[0018] In one embodiment, the method further includes cooling the
conformed glass sheet to a glass viscosity above 10.sup.1.3
poise.
[0019] In another aspect, a system for forming a shaped glass
article comprises a mold having a first mold surface area and a
second mold surface area. The first mold surface area includes a
substantially flat area and the second mold surface area includes
at least one bend and at least one opening. The system further
includes a cooling device coupled to the mold and configured for
active cooling of the first mold surface area. The system also
includes a vacuum plenum coupled to the mold and in communication
with the second mold surface area through the at least one opening.
The system includes a heater assembly arranged opposite to the
second mold surface area to provide localized heat to the second
mold surface area.
[0020] In one embodiment, the system further includes a furnace,
wherein the mold, cooling device, vacuum plenum, and heater
assembly are arranged in the furnace.
[0021] In one embodiment, the at least one opening is located in
the at least one bend.
[0022] In one embodiment, the at least one bend has a radius less
than 20 mm.
[0023] In one embodiment, the heater assembly includes at least one
radiant heater having a heater temperature in a range from
1000.degree. C. to 1450.degree. C.
[0024] In one embodiment, the heater assembly includes at least one
radiant heater having a peak wavelength in a range from 2.0 .mu.m
to 2.7 .mu.m.
[0025] In one embodiment, the heater assembly includes a loop
arrangement of heaters.
[0026] In one embodiment, the heater assembly includes a parallel
arrangement of heaters.
[0027] In one embodiment, the heater assembly includes at least one
radiant heater and a reflector arranged to focus heat from the at
least one radiant heater to the second mold surface area.
[0028] In another aspect, a shaped glass article having an optical
quality surface area suitable for an electronic device cover glass
is formed by the method described above.
[0029] In another aspect, a shaped glass article comprises a glass
body having a three-dimensional shape, wherein at least one surface
of the glass body has a waviness height less than 30 nm over a 15
mm by 25 mm measurement area and a roughness average less than 1
nm.
[0030] In one embodiment, the glass body has a flat area that is
flat to within 100 .mu.m over a measurement area of 25 mm.times.25
mm.
[0031] In one embodiment, the glass body has at least one bend area
with a bend radius of less than 10 mm.
[0032] In one embodiment, the glass body has an optical
transmission greater than 85% in a wavelength range of 400 nm to
800 nm.
[0033] In one embodiment, the glass body has a compression strength
greater than 300 MPa.
[0034] In one embodiment, the glass body has a hardness of greater
than 7 on the Mohs scale.
[0035] In one embodiment, the glass body is made of an alkali
aluminosilicate glass.
[0036] In one embodiment, the glass body is adapted for covering an
electronic device having a flat display.
[0037] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and are intended to provide an overview or framework for
understanding the nature and character of the embodiments. The
accompanying drawings are included to provide a further
understanding and are incorporated in and constitute a part of this
specification. The drawings illustrate various embodiments and
together with the description serve to explain the principles
described herein.
BRIEF DESCRIPTION OF DRAWINGS
[0038] The following is a description of the figures in the
accompanying drawings. The figures are not necessarily to scale,
and certain features and certain views of the figures may be shown
exaggerated in scale or in schematic in the interest of clarity and
conciseness.
[0039] FIG. 1 shows a dish-shaped glass article.
[0040] FIG. 2 is a profile of the glass article of FIG. 1.
[0041] FIG. 3 shows a sled-shaped glass article.
[0042] FIG. 4 is a profile of the glass article of FIG. 3.
[0043] FIG. 5 shows a mold for forming the glass article of FIG.
1.
[0044] FIG. 6 is a cross-sectional view of the mold of FIG. 5.
[0045] FIG. 7 shows a mold for forming the glass article of FIG.
3.
[0046] FIG. 8 is a cross-sectional view of the mold of FIG. 7.
[0047] FIG. 9 is a setup for forming a shaped glass article.
[0048] FIG. 10 shows a loop auxiliary heater arrangement.
[0049] FIG. 11 shows a linear auxiliary heater arrangement.
[0050] FIG. 12 shows temperature and vacuum profiles during a
process of forming a shaped glass article without active cooling of
the mold surface flat area.
[0051] FIG. 13 shows temperature and vacuum profiles during a
process of forming a shaped glass article with active cooling of
the mold surface flat area.
[0052] FIG. 14 is a plot of corner deviation of a shaped glass
article from an ideal shape as a function of mold corner
temperature.
[0053] FIG. 15A shows various monitored points on a mold
surface.
[0054] FIG. 15B shows thermal profiles corresponding to the
monitored points in FIG. 15A.
[0055] FIG. 16A shows deviations from an ideal shape of a
dish-shaped glass article formed without active cooling of the
mold.
[0056] FIG. 16B shows deviations from an ideal shape of a
dish-shaped glass article formed with active cooling of the
mold.
[0057] FIG. 17 shows deviations from an ideal shape of a
sled-shaped glass article formed with active cooling of the
mold.
DETAILED DESCRIPTION OF EMBODIMENTS
[0058] In the following detailed description, numerous specific
details may be set forth in order to provide a thorough
understanding of embodiments. However, it will be clear to one
skilled in the art when embodiments may be practiced without some
or all of these specific details. In other instances, well-known
features or processes may not be described in detail so as not to
unnecessarily obscure the description. In addition, like or
identical reference numerals may be used to identify common or
similar elements.
[0059] FIG. 1 shows a shaped glass article 10 having a glass
article flat section 12 and a glass article curved section 14. When
used to describe the shape of a glass article or mold, the term
"flat" will cover both perfectly flat, i.e., having a radius of
curvature of infinity, and substantially flat, i.e., having a
radius of curvature greater than 300 mm. The glass article curved
section 14 runs around the periphery 13 of the glass article flat
section 12 and is contiguous with the glass article flat section
12. The glass article curved section 14 includes bends 16 and
corners 17 where it intersects with the glass article flat section
12, giving the glass article 10 a dish shape. In particular
embodiments, the wall thickness of the shaped glass article 10 is
uniform. Typically, the wall thickness will be 1.5 mm or less. The
shaped glass article 10, with the appropriate dimensions, can be
used as a cover glass for a portable electronic device, where the
glass article flat section 12 will cover a flat side of the
electronic device and the glass article curved section 14 will wrap
around the edges and corners of the electronic device.
[0060] Each bend 16 has a bend angle .alpha.1 and a bend radius r1.
As shown in FIG. 2, the bend angle .alpha.1 is the outer angle of
the bend 16 measured relative to the plane of the glass article
flat section 12, and the bend radius r1 is the local radius of
curvature measured inside the bend 16. The bend radius r1 may or
may not be constant along the bend 16, hence use of the term
"local" with "radius of curvature." In some embodiments, the bend
angle .alpha.1 is in a range from greater than 0.degree. to
90.degree.. If .alpha.1 is close to 0.degree., the glass article
curved section 14 will be nearly parallel to the glass article flat
section 12. If .alpha.1 is close to 90.degree., the glass article
curved section 14 will be nearly perpendicular to the glass article
flat section 12. In some particular embodiments, the bend angle
.alpha.1 is in a range from 30.degree. to 90.degree.. The bend
radius r1 will generally be small to allow snug fitting of the
shaped glass article around the edges and corners of the electronic
device or other object to be covered. In one embodiment, the bend
radius r1 is less than 20 mm. In another embodiment, the bend
radius r1 is less than 15 mm. In yet another embodiment, the bend
radius r1 is less than 10 mm.
[0061] FIG. 3 shows a shaped glass article 10a having a glass
article flat section 12a and glass article curved sections 14a,
14b. The term "flat" is as explained above. The glass article
curved sections 14a, 14b run along the opposite edges 13a, 13b of
the glass article flat section 12a and are contiguous with these
edges. The glass article curved sections 14a, 14b include bends
16a, 16b where they intersect the glass article flat section 12a,
giving the glass article 10a a sled shape. Typically, the glass
article flat section 12a and glass article curved sections 14a, 14b
will have the same wall thickness so that the thickness of the
shaped glass article 10a is uniform. Typically, this wall thickness
will be 1.5 mm or less. The shaped glass article 10a, with the
appropriate dimensions, can be used as a cover glass for a portable
electronic device, where the glass article flat section 12a will
cover a flat side of the electronic device and the glass article
curved sections 14a, 14b will wrap around opposite edges of the
electronic device.
[0062] The bends 16a, 16b have bend angles .alpha.1a, .alpha.1b and
bend radiuses r1a, r1b, respectively. As shown in FIG. 4, the bend
angle .alpha.1a is the outer angle of the bend 16a measured
relative to the plane of the glass article flat section 12a, and
the bend radius r1a is the local radius of curvature measured
inside the bend 16a. Similarly, the bend angle .alpha.1b is the
outer angle of the bend 16b measured relative to the plane of the
glass article flat section 12a, and the bend radius r1b is the
local radius of curvature measured inside the bend 16b. The bend
angles .alpha.1a, .alpha.1b may be the same or different.
Similarly, the bend radiuses r1a, r1b may be the same or different.
In some embodiments, each of the bend angles .alpha.1a, .alpha.1b
is in a range from greater than 0.degree. to 90.degree.. In some
particular embodiments, each of the bend angles .alpha.1a,
.alpha.1b is in a range from 30.degree. to 90.degree.. The bend
radiuses r1a, r1b will generally be small to allow snug fitting of
the shaped glass article around the edges and corners of the
electronic device or other object to be covered. In one embodiment,
each of the bend radiuses r1a, r1b is less than 20 mm. In another
embodiment, each of the bend radiuses r1a, r1b is less than 15 mm.
In yet another embodiment, each of the bend radiuses r1a, r1b is
less than 10 mm.
[0063] A shaped glass article, e.g., 10 in FIG. 1 or 10a in FIG. 3,
having an optical surface area suitable for electronic device cover
glass can be formed from a flat glass sheet using thermal reforming
and a mold having a mold surface with the necessary shape profile.
The glass sheet can be made of any suitable glass composition. In
particular embodiments, the glass sheet is an ion-exchangeable
glass, typically containing relatively small alkali metal or
alkaline-earth metal ions that can be exchanged for relatively
large alkali or alkaline-earth metal ions. Examples of
ion-exchangeable glasses can be found in the patent literature,
e.g., U.S. Pat. No. 7,666,511 (Ellison et al; 23 Feb. 2010), U.S.
Pat. No. 4,483,700 (Forker, Jr. et al.; 20 Nov. 1984), and U.S.
Pat. No. 5,674,790 (Araujo; 7 Oct. 1997), all incorporated by
reference in their entireties, and are also available from Corning
Incorporated under the trade name GORILLA.RTM. glass. Typically,
these ion-exchangeable glasses are alkali-aluminosilicate glasses
or alkali-aluminoborosilicate glasses. The ion-exchangeable glass
will allow chemical strengthening of the shaped glass article by
ion-exchange after the forming process.
[0064] FIG. 5 shows a mold 20 for forming the shaped glass article
10 (in FIG. 1). The mold 20 has a mold body 22 with an upper
surface 24. A mold surface 30 extending below the upper surface 24
defines a mold cavity 26 within the mold body 22. Alignment pins 28
on the upper surface 24 are for precisely locating a glass sheet on
the mold 20, or above the mold cavity 26. The mold surface 30 has a
mold surface flat area 32 for forming the glass article flat
section 12 (in FIG. 1) and a mold surface curved area 34 for
forming the glass article curved section 14 (in FIG. 1). The mold
surface curved area 34 runs around the periphery 33 of the mold
surface flat area 32 and includes bends 36 and corners 37 where it
intersects the mold surface flat area 32. The characteristics of
the bends 36 and corners 37 will be dictated by the shaped glass
article 10 or any other article to be formed by the mold 20.
[0065] FIG. 6 shows a vacuum plenum 38 located underneath the mold
surface curved area 34. The vacuum plenum 38 could be formed in the
mold body 22 or could be provided in a separate body that is bolted
or otherwise attached to the bottom of the mold body 22. In one
embodiment, vacuum openings 40 are formed in the mold surface
curved area 34 and extend from the mold surface curved area 34,
through the mold body 22, to the vacuum plenum 38. The vacuum
openings 40 may extend straight down or may extend at an angle to
the vacuum plenum 38. For example, the vacuum openings 40 may
extend to the vacuum plenum 38 in a direction generally normal to
the mold surface curved area 34.
[0066] In particular embodiments, as shown in FIG. 5, the vacuum
openings 40 are located in the bends 36 and corners 37 and may be
very close to the periphery 33 of the mold surface flat area 32,
e.g., within 5 mm of the periphery 33 of the mold surface flat area
32. The vacuum openings 40 may be slots or holes or a combination
of slots and holes. Slots have the advantage of allowing continuous
and high vacuum flow over a wider area of the mold surface curved
area 34. Typically, the vacuum openings 40 will have a small width
or diameter, e.g., on the order of 1 mm. However, the number, size,
and arrangement of the vacuum openings 40 are not restricted to
what is shown in FIG. 5 or discussed above and may be optimized to
achieve the desired vacuum distribution across the mold surface
curved area 34.
[0067] Returning to FIG. 6, a vacuum pump can be connected to the
vacuum plenum 38, e.g., through a port 42, and operated to create
vacuum pressure at the mold surface curved area 34, or more
particularly at the bend area of the mold surface curved area 34,
where the vacuum openings 40 are located. The resulting vacuum
force can be used to pull a glass sheet that is on the mold 20 or
sagging into the mold cavity 26 against the mold surface curved
area 34 in order to conform the glass sheet to the mold.
[0068] A cooling device 44 is provided for actively cooling the
mold surface flat area 32. By active cooling, it is meant that the
parameters of the cooling device are controlled and adjusted to
maintain the mold surface flat area 32 a predetermined thermal
profile at the mold surface flat area 32. In one embodiment, the
cooling device 44 includes a cooling chamber 46 formed underneath
the mold surface flat area 32. The cooling chamber 46 may be formed
in the mold body 22 or in a separate body that is bolted or
otherwise attached to the bottom of the mold body 22. The
arrangement of the cooling chamber 46 is such that the opposite
ends 48a, 48b of the cooling chamber 46 are generally aligned with
the periphery of the mold surface flat area 32. In particular
embodiments, the cooling chamber 46 does not extend to underneath
the mold surface curved area 34 so that the active cooling is
substantially restricted to the mold surface flat area 32. The
cooling device 44 include ports 50, 52, 54 connected to the cooling
chamber 46. In one embodiment, the ports 50, 52 are inlet ports and
are located near the opposite ends 48a, 48b of the cooling chamber
46. In one embodiment, the port 54 is an outlet port and is located
generally midway between the opposite ends 48a, 48b of the cooling
chamber 46.
[0069] Cooling fluid 56 is supplied into the cooling chamber 46
through the ports 50, 52. In some embodiments, the cooling fluid is
an inert gas such as nitrogen, helium, or argon. Air can also be
used as a cooling fluid, but in some embodiments may not be used
due to its oxidizing properties at high temperature. The fluid
entering the ports 50, 52 will impinge on the wall of the cooling
chamber 46 at locations close to the periphery of the mold surface
flat area 32. The impinging fluid will then move towards the center
of the cooling chamber 46, carrying with it the heat absorbed near
the periphery of the mold surface flat area 32. Finally, the
cooling fluid will exit the cooling chamber 46 through the outlet
port 54, as shown at 58.
[0070] The cooling device 44 works to equalize temperature
distribution across the mold surface flat area 32. If the periphery
of the mold surface flat area 32 is hotter than the center of the
mold surface flat area 32, the cooling device 44 will move heat
from the periphery of the mold surface flat area 32 to the center
of the mold surface flat area 32, thereby decreasing the thermal
gradient across the mold surface flat area 32. In some embodiments,
the action of the cooling device 44 results in a maximum thermal
gradient across the mold surface flat area 32 that is less than
20.degree. C. In particular embodiments, the action of the cooling
device 44 results in a maximum thermal gradient across the mold
surface flat area 32 that is less than 15.degree. C. In addition to
working to equalize the temperature distribution across the mold
surface flat area 32, the cooling device 44 can be operated to
maintain the temperature across the mold surface flat area 32 in a
desired temperature range while the temperature in other areas of
the mold surface 30, such as at the mold surface curved area 34, is
in a different temperature range. The pressure and flow rate of the
cooling fluid entering the inlet ports 50, 52 are used to control
how much heat is removed from the mold surface flat area 32 by the
cooling device 44. The pressure and flow rate may respond to the
outputs of temperature monitoring elements, such as thermocouples,
mounted near the mold surface flat area 32.
[0071] FIG. 7 shows a mold 20a for forming the shaped glass article
10a (in FIG. 3). The main differences between the mold 20a and the
mold 20 (in FIG. 5) are in the particular details of the mold
surface and placement of vacuum plenums. In FIG. 5, a mold surface
30a defines a mold cavity 26a within a mold body 22a. The mold
surface 30a has a mold surface flat area 32a for forming the flat
section 12a (in FIG. 3) of the shaped glass article and curved mold
surface areas 34a, 34b for forming the curved sections 14a, 14b (in
FIG. 3) of the shaped glass article. The curved mold surface areas
34a, 34b are located on opposite edges 33a, 33b of the mold surface
flat area 32a and include bends 36a, 36b where they intersect with
the mold surface flat area 32a. The bend angles and bend radiuses
of the bends will be dictated by the bend angles and bend radiuses
of the bends of the shaped glass article.
[0072] In FIG. 8, vacuum plenums 38a, 38b are arranged underneath
the mold surface curved areas 34a, 34b. The vacuum plenums 38a, 38b
could be formed in the mold body 22a or provided as separate bodies
that are attached to the mold body 22a. Vacuum openings 40a, 40b
located in the mold surface curved areas 34a, 34b extend from the
mold surface curved areas 34a, 34b, through the mold body 22a, to
the vacuum plenums 38a, 38b. The vacuum openings 40a, 40b may
extend straight down to the vacuum plenums 38a, 38b or may be
slanted. In particular embodiments, the vacuum openings 40a, 40b
are located in the bends 36a, 36b and may be very close to the
opposite edges 33a, 33b (in FIG. 7) of the mold surface flat area
32a. The vacuum openings and plenums allow generation of vacuum
force that can be used to conform a glass sheet to the mold surface
curved areas 34a, 34b. It should be noted that conforming the glass
sheet to the mold surface curved areas 34a, 34b will also result in
conforming the glass sheet to the mold surface flat area 32a. Also
in FIG. 8, a cooling device 44a is located underneath the mold
surface flat area 32a for active cooling of the mold surface flat
area 32a. The cooling device 44a works similarly to the cooling
device 44 (in FIG. 6) described above.
[0073] FIG. 9 shows a setup for forming the shaped glass article 10
(in FIG. 1) using the mold 20 (in FIG. 5). The setup includes a
glass sheet 60 placed on the mold 20 such that the glass sheet 60
is above the mold cavity 26. The mold 20 and glass sheet 60 are
arranged inside a furnace 64. A furnace heater assembly includes
one or more primary heaters 66 provided inside the furnace 64 to
heat the glass sheet 60 and mold 20. The primary heaters 66 can be
any heaters suitable for use in process chambers where rapid
heating to high temperature with low contamination is necessary. In
particular embodiments, the primary heaters 66 are radiant heaters
and are arranged above the mold 20, e.g., near the roof of the
furnace 64. Radiation from the primary heaters 66 will be directed
towards the glass sheet 60 on the mold 20. Some of the radiation
will be absorbed by the glass sheet 60, and some of the radiation
will pass through the glass sheet 60 to the mold surface 30. In
particular embodiments, the glass sheet 60 has high absorption in
the medium infrared range and the primary heaters 66 are
medium-wave infrared heaters with peak wavelength where the glass
sheet has high absorption. For example, the medium wave infrared
heaters may have peak wavelength in a range from 2.0 to 2.7
.mu.m.
[0074] The glass sheet 60 has a glass flat area 70, which after
shaping with the mold 20 will become the glass article flat section
12 (in FIG. 1), and a glass curve area 72, which after shaping with
the mold 20 will become the glass article curved section 14 (in
FIG. 1). The glass curve area 72 includes a glass bend area 74,
which after shaping with the mold 20 will include the bends 16 (in
FIG. 1) and corners 17 (in FIG. 1) of the glass article. An
auxiliary heater assembly includes one or more auxiliary heaters
75, which are arranged above the mold 20 to locally heat the glass
curve area 72 (or more specifically the glass bend area 74) to a
glass viscosity that is different from that of the remainder of the
glass sheet 60, e.g., the glass flat area 70. The area of the mold
20 below the glass curve area 72, or glass bend area 74, will also
be locally heated as the radiation passes through the glass curve
area 72 to the mold surface 30.
[0075] The auxiliary heaters 75 can be any heaters suitable for use
in process chambers where rapid heating to high temperature with
low contamination is necessary. For all types of auxiliary heaters,
the heater temperature is in a range from 1000 to 1450.degree. C.
In particular embodiments, the auxiliary heaters 75 are radiant
heaters. In one embodiment, the auxiliary heaters 75 are
medium-wave infrared heaters with peak wavelength where the glass
sheet 60 has high absorption. The heater type can be KANTHAL.RTM.
iron-chromium-aluminum alloy wire or tungsten coils in quartz tube,
silicon carbide heating element, or other type of small form factor
resistive heating element.
[0076] The auxiliary heater assembly can further include reflectors
78, e.g., mirrors, for focusing heat from the auxiliary heaters 75
towards the mold surface curved area 34. When the glass sheet 60 is
in place on the mold 20, the reflectors 78 will be opposite the
local area of the glass sheet to be heated and will increase the
efficiency of heating the local area by focusing the radiation from
the auxiliary heaters 75 to the local area. The reflectors 78 may
also be effective in shielding the glass areas that are not to be
locally heated, such as the glass flat area 72, from the radiation
of the auxiliary heaters 75. A suitable radiant heater for any of
the auxiliary heaters 75 is QRC.RTM. infrared emitter with
nano-reflector from Heraeus Noblelight. In the case of the QRC.RTM.
infrared emitter, the reflector is part of the quartz tube
enclosing the filament.
[0077] The auxiliary heaters 75 are arranged in close proximity to
the glass area to be locally heated. In particular embodiments, the
auxiliary heaters 75 are arranged at a height of less than 10 mm
above the glass area to be locally heated. Where the auxiliary
heaters 75 are radiant heaters, the size of the auxiliary heaters
75 are selected such that the radiation they emit is substantially
confined to the glass area to be locally heated. Typically, the
diameter or width of the auxiliary heaters 75 will be less than 25
mm. In some embodiments, the auxiliary heaters 75 are arranged to
form a shape that follows the contour of the glass area to be
locally heated, which would also serve to substantially confine the
radiation from the auxiliary heaters 75 to the glass area to be
locally heated. FIG. 10 shows a loop arrangement of auxiliary
heaters 75 that tracks the contour of the glass sheet 60 and mold
20 in the curved or bend area. This arrangement can be used to make
the glass article 10 in FIG. 1 that has a curved or bend section in
a loop shape.
[0078] To make the shaped glass article 10, the glass sheet 60 and
mold 20 are heated inside the furnace 64 using the primary heaters
66. As the glass sheet 60 and mold 20 approach the temperatures
where the glass sheet 60 can be conformed to the mold 20, typically
after 1-3 minutes of heating with the primary heaters 66, the
auxiliary heaters 75 are turned on. Once the glass sheet 60 and
mold surface 30 have reached the desired temperatures, vacuum is
applied to conform the glass curve area 72 to the mold surface
curved area 34. Conforming the glass curve area 72 to the mold
surface curved area 34 includes conforming the glass bend area 74
to the bends and corners of the mold surface. Also, by pulling the
glass to the bends and corners of the mold, the glass flat area 70
will also be pulled against the mold surface flat area 32, thereby
fully conforming the glass to the mold surface 30. The auxiliary
heaters 75 are turned on before vacuum is applied because the
auxiliary heaters 75 need time to warm up. The warm up time will
depend on the heater type. For example, tungsten heaters have a
shorter warm up time than KANTHAL.RTM. heaters. Typically, the warm
up time will be in a range from 5 to 60 seconds.
[0079] The glass sheet 60 may sag into the mold cavity 26 and the
glass flat area 70 may contact the mold surface flat area 32 before
vacuum is applied to conform the glass curve area 72 to the mold
surface curved area 34. To prevent undesirable interaction between
the mold surface flat area 32 and the glass flat area 70, the glass
flat area 70 is kept relatively cold, e.g., at a glass viscosity
between 10.sup.10.1 poise and 10.sup.9 poise, while the glass flat
area 70 is in contact with the mold surface flat area 32. Active
cooling of the mold surface flat area 32 can be used to control the
temperature of the glass flat area 70 once the glass flat area 70
touches the mold surface flat area 32. Active cooling can start
before the auxiliary heaters 75 are turned on, i.e., in case the
glass flat area 70 touches the mold surface flat area 32 before the
glass sheet 60 and mold surface 30 have reached the desired
temperatures where vacuum can be applied. In particular
embodiments, the cooling device 44, which is used in active cooling
of the mold surface flat area 32, starts operating as soon as the
glass sheet 60 and mold 20 are loaded into the furnace 64. In some
embodiments, the cooling device 44 operates such that the thermal
gradient across the mold surface flat area 32 is below 20.degree.
C. In particular embodiments, the cooling device 44 operates such
that the thermal gradient across the mold surface flat area 32 is
below 15.degree. C.
[0080] In one or more embodiments, the local heating and cooling of
the glass sheet 60 is such that the glass viscosity in the glass
bend area 74 is 8 poise or more lower than the glass viscosity in
the glass flat area 70 at the time that vacuum is applied to
conform the glass sheet mold 60 to the mold surface 70. In
particular embodiments, at the time that vacuum is applied to
conform the glass sheet 60 to the mold surface 30, the following
conditions are true: (1) the glass viscosity of the glass flat area
70 is at or above 10.sup.10.1 poise, (2) the mold surface flat area
32 is at a temperature below T.sub.11.3, where T.sub.11.3 is the
temperature at which the glass viscosity is 10.sup.11.3 poise, (3)
the glass viscosity in the glass bend area 74 is at or below
10.sup.9.9 poise, (4) the mold surface curved area 36 or the
portion of the mold surface curved area 36 including the bends and
corners is at a temperature above T.sub.11.7, where T.sub.11.7 is
the temperature at which the glass viscosity is 10.sup.11.7 poise.
The term "glass viscosity" is based on the glass composition of the
glass sheet 60. The actual values of the temperatures recited above
will thus vary from one glass composition to another.
[0081] In particular embodiments, vacuum is applied in multiple
stages. In a first stage, the applied vacuum is sufficient to
conform the glass sheet 60 to the mold surface 30 in the bend area.
For a second stage, the applied vacuum is reduced to a level that
is just sufficient to hold the glass sheet 60 against the mold
surface 30 in the bend area. For example, the vacuum pressure may
be above 20 kPa for the first stage and may be reduced below 10 kPa
for the second stage. The first stage will have a shorter duration
than the second stage. For example, the first stage may have a
duration of less than 20 seconds, while the second stage may have a
duration of 40 or more seconds. The multi-stage vacuum allows the
glass to settle at lower vacuum level, which is less damaging to
mold life and glass cosmetics. Additional step downs in vacuum may
be added as needed to create the best balance between the force
needed to hold the glass against the mold and the mold life. Also,
multi-stage vacuum with repeated heating and cooling of the bend
area can be used to relieve stress and reduce snap back. Stress
relief and reduction in snap back can also be achieved by holding
vacuum while cooling the glass on the mold. However, in some
embodiments, this may not be done because the glass surface can
become damaged as it is being held by vacuum against the mold while
it is contracting during cooling.
[0082] After the glass sheet has been conformed to the mold, the
resulting shaped glass article is allowed to cool to a glass
viscosity above 10.sup.13 poise while still in the mold. Then, the
cooled shaped glass article is removed from the mold. Any number of
processes may be carried out after separating the shaped glass
article from the mold, such as chemical strengthening of the shaped
glass article by ion-exchange.
[0083] Above, it was discussed that the glass sheet and mold were
first heated using the primary heaters 66, followed by local
heating of the glass using the auxiliary heaters 75. Both of these
heatings took place in the same furnace 64. In alternate
embodiments, it is possible for these heatings to take place in
separate furnaces or multiple zones in a continuous furnace. The
heating by the primary heaters 66 can take place in a first furnace
or first set of heating zones in a continuous furnace, after which
the glass sheet and mold can be transported to a second furnace or
a second set of furnace zones where the local heating of the glass
will take place in order to conform the glass sheet to the mold
surface in the bend area. If the auxiliary heaters 75 are left on
in the second furnace or second set of furnace zones, there will be
no need for a heater warm up time before vacuum can be applied to
conform the glass to the mold surface. This alternate embodiment
may be used to increase throughput in a continuous manufacturing
setup. The number of furnace zones in manufacturing depends on the
desired throughput. Auxiliary heaters can also be arranged in
non-consecutive furnaces so that the bend areas of the glass and
mold can be alternately heated and cooled during a multi-stage
vacuum process as mentioned above.
[0084] The method described above can also be used to make the
shaped glass article 10a in FIG. 3, except that the setup of FIG. 9
will need to be slightly modified. To form the shaped glass article
10a, the mold 20 in the setup of FIG. 9 can be replaced with the
mold 20a of FIG. 7. Also, the arrangement and configuration of the
auxiliary heaters 75 can be replaced with the one shown in FIG. 11.
In FIG. 11, a parallel arrangement of long auxiliary heaters 75a
can be used to locally heat the bend areas of the glass sheet and
mold surface. Conditions (1)-(4) mentioned above will apply at the
time that vacuum is used to conform the glass sheet to the mold. In
the case of the shaped glass article 10a, condition (3) will apply
to both bend areas of the glass sheet and condition (4) will apply
to both bend areas of the mold.
[0085] A shaped glass article having a 3D shape is formed using the
method described above. The shaped glass article has a flat area
and at least one bend area. In one embodiment, the shaped glass
article is configured for use as a cover glass article for an
electronic device having a flat display.
[0086] In one embodiment, the flat area of the shaped glass article
is flat to within 100 .mu.m over a 25 mm.times.25 mm area, as
measured by a Tropel.RTM. FlatMaster.RTM. surface measurement tool
available from Corning Incorporated. The flatness is measured as a
comparative height difference between a reference plane and the
flat area of the shaped glass article. "Flat to within 100 .mu.m"
means that any variations in the height difference between the
reference plane and the flat area is within 100 .mu.m.
[0087] The surface texture of the shaped glass article can be
characterized by two parameters: surface roughness and waviness.
Roughness is a measure of the finely spaced surface irregularities.
Waviness is a measure of surface irregularities with a spacing
greater than that of surface roughness.
[0088] In one embodiment, at least one of the surfaces of the
shaped glass article has a roughness average (Ra) of less than 1
nm. In another embodiment, at least one of the surfaces of the
shaped glass article has a roughness average of less than 0.7 nm.
In yet another embodiment, at least one of the surfaces of the
shaped glass article has a roughness average of less than 0.3
nm.
[0089] In one embodiment, the surfaces of the shaped glass article
each have a waviness height less than 30 nm over a 15 mm by 25 mm
3D area, as measured by a Zygo.RTM. Newview 3D optical surface
profiler. The waviness height is the peak to valley distance of the
surface profile. The spacing between the surface irregularities
measured is typically in a range from 3 to 5 mm.
[0090] In one embodiment, the bend area of the shaped glass article
has a bend radius less than 10 mm. The small bend radius is
possible using a combination of active cooling of the mold and/or
localized heating of the bend area of the glass sheet and
conforming the glass sheet by applying vacuum through slot(s) or
opening(s) in the bend area and corners of the mold, as described
in one or more embodiments above.
[0091] In one embodiment, the wall thickness of the shaped glass
article is in a range from 0.3 mm to 3 mm. In one embodiment, the
wall thickness is uniform, e.g., variation in the wall thickness of
the shaped glass article is within 100 .mu.m.
[0092] In one embodiment, the shaped glass article is transparent
and has an optical transmission greater than 85% in a wavelength
range of 400 nm to 800 nm.
[0093] In one embodiment, the shaped glass article has a
compression strength greater than 300 MPa and a hardness greater
than 7 on the Mohs scale. In one embodiment, the shaped glass
article has at least one surface compressively-stressed region and
a depth of layer of the compressively-stressed region is at least
25 .mu.m. The compression strength and/or compressively-stressed
region can be achieved by subjecting the shaped glass article to a
strengthening process, which may be chemical or thermal. In some
embodiments, the compression strength and/or compressively-stressed
region is achieved by subjecting the shaped glass article to an
ion-exchange process.
[0094] In one embodiment, the shaped glass article is made from an
alkali aluminosilicate glass composition comprising from about 60
mol % to about 70 mol % SiO.sub.2; from about 6 mol % to about 14
mol % Al.sub.2O.sub.3; from 0 mol % to about 15 mol %
B.sub.2O.sub.3; from 0 mol % to about 15 mol % Li.sub.2O; from 0
mol % to about 20 mol % Na.sub.2O; from 0 mol % to about 10 mol %
K.sub.2O; from 0 mol % to about 8 mol % MgO; from 0 mol % to about
10 mol % CaO; from 0 mol % to about 5 mol % ZrO.sub.2; from 0 mol %
to about 1 mol % SnO.sub.2; from 0 mol % to about 1 mol %
CeO.sub.2; less than about 50 ppm As.sub.2O.sub.3; and less than
about 50 ppm Sb.sub.2O.sub.3; wherein 12 mol
%.ltoreq.Li.sub.2O+Na.sub.2O+K.sub.2O.ltoreq.20 mol % and 0 mol
%.ltoreq.MgO+CaO.ltoreq.10 mol %. This glass composition and others
may be found in U.S. Pat. No. 8,158,543 (Dejneka et al., "Fining
Agents for Silicate Glasses").
[0095] In another embodiment, the shaped glass article is made from
an alkali-aluminosilicate glass composition comprising at least
about 50 mol % SiO.sub.2 and at least about 11 mol % Na.sub.2O, and
the compressive stress is at least about 900 MPa. In some
embodiments, the glass composition further comprises
Al.sub.2O.sub.3 and at least one of B.sub.2O.sub.3, K.sub.2O, MgO
and ZnO, wherein
-340+27.1Al.sub.2O.sub.3-28.7B.sub.2O.sub.3+15.6Na.sub.2O-61.4K.sub.2O+8.-
1(MgO+ZnO).gtoreq.0 mol %. In particular embodiments, the glass
composition comprises from about 7 mol % to about 26 mol %
Al.sub.2O.sub.3; from 0 mol % to about 9 mol % B.sub.2O.sub.3; from
about 11 mol % to about 25 mol % Na.sub.2O; from 0 mol % to about
2.5 mol % K.sub.2O; from 0 mol % to about 8.5 mol % MgO; and from 0
mol % to about 1.5 mol % CaO. These glass compositions and others
may be found in U.S. Publication No. 2013/0004758 (Dejneka et al.,
"Ion Exchangeable Glass with High Compressive Stress,") filed Jul.
1, 2011, the content of which is incorporated herein by reference
in its entirety.
EXAMPLE 1
[0096] A shaped glass article was formed using a mold with a
dish-shaped mold cavity. The forming process included local heating
of the bend area without active cooling of the mold surface flat
area. Various profiles characterizing the process are shown in FIG.
12. The thermal profile at the center of the mold surface flat area
is shown at 100. The thermal profile at a bend on the mold surface
curved area is shown at 102. The thermal profile at a corner on the
mold surface curved area is shown at 104. The vacuum profile is
shown at 106. The furnace power profile is shown at 108. The
furnace temperature profile is shown at 110. The time at which the
furnace was opened is indicated at 112. The temperature difference
between the mold surface flat area (represented by thermal profile
100) and the mold surface curved area (represented by thermal
profile 102 or 104) is relatively small. The temperature difference
between the mold surface flat area and the mold surface curve area
peaks at about 25.degree. C. when vacuum is applied.
EXAMPLE 2
[0097] A shaped glass article was formed using a mold with a
dish-shaped mold cavity. The forming process include local heating
of the bend area with active cooling of the mold surface flat area.
Various profiles characterizing the process are shown in FIG. 13.
The thermal profile at the center of the mold surface flat area is
shown at 114. The thermal profile at a point on the mold surface
curve area is shown at 116. The thermal profile at the center of
the glass flat section is shown at 118. The thermal profile at a
point on the glass curved section is shown at 120. The vacuum
profile is shown at 122. The furnace power profile is shown at 124.
The furnace temperature profile is shown at 126. The active cooling
profile is shown at 128. Nitrogen was used as the cooling fluid.
The time at which the furnace was opened is indicated at 130. The
temperature difference between the mold surface flat area
(represented by thermal profile 114) and the mold surface curved
area (represented by thermal profile 116) peaks at about 80.degree.
C. when vacuum is applied. This shows that active cooling is
effective in keeping the mold surface flat area relatively cold
while the mold surface curved area or bend area is being locally
heated.
EXAMPLE 3
[0098] Various dish-shaped glass articles were formed using a mold
with a dish-shaped mold cavity. Local heating of the mold surface
area and active cooling of the mold surface flat area were employed
in the process. The glass articles were made from Code 2317
GORILLA.RTM. glass available from Corning Incorporated. The glass
sheets used in making the glass articles had a thickness of 0.8 mm.
The dish shape had a bend radius of 10 mm. The effect of mold
corner temperature on corner deviation of the formed shape from the
ideal shape was investigated by varying the temperature in the mold
surface bend area. The results are shown in FIG. 14. In FIG. 14,
the diamond markers 140 represent DOE ("design of experiments")
data and the square markers 141 represent the final process data.
The data shows that increased mold bend temperature resulted in
reduced deviation from ideal shape, thus demonstrating the
importance of increasing edge and corner temperatures. For the
particular glass composition and dish shape investigated, the
corner deviations exceed 0.1 mm if the corner temperature of the
mold is below about 710.degree. C. In this case, the deviations are
high because the mold surface bend area is too cold to allow the
bend radius to be achieved. On the other hand, if the corner
temperature of the mold is too high, the corner deviation of the
formed shape worsens because the glass flat area distorts and the
distorted glass flat area causes the glass corners to have high
deviation as the glass corners are pulled away from the mold
corners by the distortion.
EXAMPLE 4
[0099] A dish-shaped glass article was made using a mold with a
dish-shaped mold cavity. Local heating of the mold surface bend
area and active cooling of the mold surface flat area were employed
in the process. FIG. 15A shows the points 150-158 monitored on the
mold during the process of forming the shaped glass article. FIG.
15B shows the thermal profiles at the points indicated in FIG. 15A.
The same reference numbers are used for the points and thermal
profiles to make it easier to map the points on the mold to the
thermal profiles. The thermal profile 164 represents the
temperature at the side of the mold, approximately 0.5 inches below
the mold surface. The furnace power profile is shown at 160. The
vacuum profile is shown at 162.
[0100] FIG. 15B shows that active cooling can flatten out the
thermal gradients in the mold surface flat area (represented by
thermal profiles 150, 152) while there are still very high
temperature differences between the mold surface flat area
(represented by thermal profiles 150, 152) and the mold surface
curved area (represented by thermal profiles 154, 156, 158). FIG.
15B also shows that active cooling can reduce the temperature near
the edges of the mold surface flat area (represented by thermal
profile 152) so that the temperature distribution across the mold
surface flat area is more uniform even as the mold surface curved
area is being locally heated. The temperature gradient in the mold
surface flat area remained below 15.degree. C. while the glass
sheet was on the mold.
EXAMPLE 5
[0101] FIGS. 16A and 16B show deviations from the ideal shape for
dish-shaped glass articles made without and with active cooling of
the flat area of the mold, respectively. Without active cooling
(FIG. 16A), the corners are not formed properly and deviations
significantly exceed the .+-.0.1 mm target. With active cooling
(FIG. 16B), the shape is well within .+-.0.1 mm target.
EXAMPLE 6
[0102] FIG. 17 shows the deviations of a sled-shaped glass article
formed using localized heating in the bend area with active cooling
in the flat area. The article has a bend radius of 6 mm and overall
dimensions of 120 mm by 70 mm by 3 mm and a glass thickness of 0.7
mm. The absolute deviation from the ideal shape is less than 100
.mu.m.
EXAMPLE 7
[0103] Table 1 below shows glass temperatures and difference
between glass and mold temperatures during two separate processes
of forming a dish-shaped glass article with a bend radius of 10 mm
from a glass sheet. In Process No. 1, the dish-shaped glass article
was formed without active cooling of the mold and without localized
heating of the glass sheet in the bend area. In Process No. 2, the
dish-shaped glass article was formed with active cooling of the
mold and/or localized heating of the glass sheet in the bend area
as described in this disclosure. Both processes involved vacuum
conforming by applying vacuum via slot(s) or opening(s) located in
the bend area and corners of the mold.
TABLE-US-00001 TABLE 1 Glass Temp. Difference Location at the start
Log glass between Process on of applying viscosity glass and mold
No. Glass vacuum (.degree. C.) (poise) temperatures (.degree. C.) 1
Flat area 790-806 8.4-8.1 160-200 Bend area 800-816 8.2-7.9 2 Flat
area 720-730 10-9.7 <100 Bend area 770-790 8.8-8.4
EXAMPLE 8
[0104] Impact of glass temperature/viscosity on "orange peel" was
investigated. The investigation involved forming a first
dish-shaped glass article from a first glass sheet without active
cooling of the flat area and with localized heating of the bend
area and forming a second dish-shaped glass article from a second
glass sheet with active cooling of the flat area and/or localized
heating of the bend area. With active cooling and/or localized
heating of the bend area, the glass viscosity at the flat area can
be above a level that may cause glass reboil, which can generate
"orange peel." With active cooling and/or localized heating of the
bend area, it was found that the glass viscosity at the flat area
can be kept 1.5 orders of magnitude higher compared to without
active cooling and localized heating. The higher glass viscosity in
the flat area allowed for approximately 10 times improvement in
peak to valley of surface roughness. In one specific example, both
surfaces of a glass article made according to Process No. 2 of
Example 7, i.e., with active cooling and/or localized heating, each
had a waviness height of less than 30 nm over a 15 mm by 25 mm
area, as measured by Zygo.RTM. Newview 3D optical surface profiler.
In comparison, both surfaces of a glass article made according to
Process No. 1 of Example 7, i.e., without active cooling and
localized heating, has a waviness height of 200 nm over the same
measurement area.
EXAMPLE 9
[0105] A dish-shaped glass article formed according to this
disclosure, i.e., with active cooling of mold and/or localized
heating of glass sheet in the bend area and vacuum conforming of
the glass sheet to the mold, was compared to a dish-shaped glass
article formed by pressing a glass sheet between two molds. It was
found that with pressing, small mold errors can create an
over-constrained condition that results in non-uniform strain
across the formed article and distortion in the flat area of the
formed article. The type of non-uniform strain and distortion
observed with pressing was not observed with the vacuum conforming
process. In the vacuum conforming process, there is only one mold.
Further, the flat glass area is stretched uniformly over the mold
by applying vacuum through the slot(s) near the bend area.
* * * * *