U.S. patent application number 13/287178 was filed with the patent office on 2012-02-23 for apparatus for quenching formed glass sheets.
This patent application is currently assigned to GLASSTECH, INC.. Invention is credited to David B. Nitschke, Dean M. Nitschke, Cristin J. Reinhart, Donivan M. Shetterly.
Application Number | 20120042695 13/287178 |
Document ID | / |
Family ID | 39493317 |
Filed Date | 2012-02-23 |
United States Patent
Application |
20120042695 |
Kind Code |
A1 |
Nitschke; David B. ; et
al. |
February 23, 2012 |
APPARATUS FOR QUENCHING FORMED GLASS SHEETS
Abstract
Apparatus (42) for quenching a formed glass sheet with three
steps of gas flow pressures in a manner that reduces cycle time
without excessive temporary surface tension that can cause
excessive breakage. A control (26) provides the quenching in the
three step manner with initial pressures for .5 to 1.3 seconds,
increased pressures of at least 25% greater than the initial
pressures for .5 to 4 seconds, and final quenching with decreased
cooling power that is less than the cooling power of the initial
pressures.
Inventors: |
Nitschke; David B.;
(Perrysburg, OH) ; Nitschke; Dean M.; (Maumee,
OH) ; Reinhart; Cristin J.; (Delta, OH) ;
Shetterly; Donivan M.; (Bowling Green, OH) |
Assignee: |
GLASSTECH, INC.
Perrysburg
OH
|
Family ID: |
39493317 |
Appl. No.: |
13/287178 |
Filed: |
November 2, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11565717 |
Dec 1, 2006 |
8074473 |
|
|
13287178 |
|
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Current U.S.
Class: |
65/348 |
Current CPC
Class: |
C03B 27/0404 20130101;
C03B 27/0413 20130101; C03B 27/0442 20130101; C03B 25/025 20130101;
C03B 27/0445 20130101; C03B 27/0417 20130101 |
Class at
Publication: |
65/348 |
International
Class: |
C03B 27/044 20060101
C03B027/044 |
Claims
1. Apparatus for quenching glass sheets comprising: a quench system
including a quench having lower and upper quench heads that are
operable to supply upward and downward gas flows; a quench ring for
positioning a heated and formed glass sheet between the quench
heads for quenching; a control for operating the quench to
initially supply through the lower and upper quench heads upward
and downward gas flows at initial pressures for about 0.5 to 1.3
seconds to quench the formed glass sheet; the control then
increasing the upward and downward gas flow pressures through the
lower and upper quench heads to at least 25% greater than the
initial pressures for 0.5 to 4 seconds; and the control thereafter
operating the quench system to continue to supply upward and
downward gas flows to the formed glass sheet with decreased cooling
power that is less than the cooling power of the initial pressure
quenching to eventually provide a tempered and formed glass sheet
upon cooling throughout to ambient temperature.
2. Apparatus for quenching glass sheets as in claim 1 wherein the
quench includes quench heads that are movable between an open
position where the formed glass sheet is transferred into and out
of the quench and a closed position in which the initial pressure
and increased pressure quenching are performed.
3. Apparatus for quenching glass sheets as in claim 2 wherein the
quench ring transfers the heated and formed glass sheet into the
open quench and supports the formed glass sheet during the initial
pressure and increased pressure quenching.
4. Apparatus for quenching glass sheets as in claim 3 further
including an aftercooler to which the quench ring moves the formed
glass sheet from the open quench for at least some of the decreased
cooling power quenching.
5. Apparatus for quenching glass sheets as in claim 3 further
including an aftercooler and a transfer device that receives the
formed glass sheet from the quench ring to provide transfer thereof
from the open quench to the aftercooler for at least some of the
decreased cooling power quenching.
6. Apparatus for quenching glass sheets comprising: a quench system
including a quench having lower and upper quench heads that are
movable between open and closed positions and operable to supply
upward and downward gas flows; a quench ring for moving a heated
and formed glass sheet to between the open quench heads which are
then closed for quenching; a control for operating the quench to
initially supply through the closed lower and upper quench heads
upward and downward gas flows for about 0.5 to 1.3 seconds at
conventional quench pressures to quench the formed glass sheet; the
control then increasing the upward and downward gas flow pressures
through the lower and upper quench heads to least 25% greater than
the initial pressures for 0.5 to 4 seconds; the control thereafter
operating the quench system to continue to supply upward and
downward gas flows to the formed glass sheet with decreased cooling
power that is less than the cooling power provided by the quench at
minimum conventional quench pressures to eventually provide a
tempered and formed glass sheet upon cooling throughout to ambient
temperature, and the decreased cooling power quenching initially
being provided by the upper and lower quench heads which are opened
by the control; and an aftercooler to which the control moves the
formed glass sheet for further decreased cooling power quenching.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 11/565,717 filed Dec. 1, 2006, the disclosure of which is
incorporated in its entirety by reference herein.
TECHNICAL FIELD
[0002] This invention relates to a method and apparatus for
quenching formed glass sheets.
BACKGROUND
[0003] Formed glass sheets are conventionally quenched to enhance
their mechanical properties. Such formed glass sheets are
conventionally used on vehicle side and back windows as well as in
other applications such as architectural applications and food
storage and display units, etc. Usually the forming and quenching
is performed to provide tempering that provides the glass sheet
with surface compression on the order of 100 MegaPascals (14,250
psi), but the quenching can also be utilized to perform heat
strengthening wherein the surface compression is less such as on
the order of 50 MegaPascals (7,250 psi).
[0004] Conventional forming and quenching systems successively form
and quench the glass sheets in a cyclical manner one after another
initially at a forming station and then downstream at a quench
station. The formed glass sheets can be formed and delivered from
the forming station faster than quenching can be performed in the
quench station such that reduction in the cycle time of the system
is limited by the time of the quenching.
[0005] Forced convection is conventionally utilized to perform
glass sheet quenching in order to establish a temperature gradient
between the glass surfaces and its center, starting from a
tempering temperature on the order of about 645.degree. C. and
cooling to the ambient. Upon the glass sheet cooling to ambient
temperature throughout its extent, the glass surfaces are in a
state of compression and the glass center is in a state of tension.
The surface compression resists breakage so as to provide
mechanical strength to the quenched glass. The extent of the center
tension and accompanying surface compression is often measured by
the glass break pattern, specifically by counting the number of
broken pieces in a number of confined areas, usually by counting
each full broken piece as one and each partial piece as one-half
and then adding to provide a total. A greater number indicates a
greater resistance to breakage. However, the surface stress should
not be too great so that the glass breaks into pieces that are too
small.
[0006] In connection with heating of the glass sheets, see U.S.
Pat. Nos. 3,806,312 McMaster et al.; 3,947,242 McMaster et al.;
3,994,711 McMaster; 4,404,011 McMaster; and 4,512,460 McMaster. In
connection with glass sheet forming, see U.S. Pat. Nos. 4,282,026
McMaster et al.; 4,437,871 McMaster et al.; 4,575,390 McMaster;
4,661,141 Nitschke et al.; 4,662,925 Thimons et al.; 5,004,491
McMaster et al.; 5,330,550 Kuster et al.; 5,472,470 Kormanyos et
al.; 5,900,034 Mumford et al.; 5,906,668 Mumford et al.; 5,925,162
Nitschke et al.; 6,032,491 Nitschke et al.; 6,173,587 Mumford et
al.; 6,418,754 Nitschke et al.; 6,718,798 Nitschke et al.; and
6,729,160 Nitschke et al.; and see also the U.S. patent application
Ser. No. 11/255,531, of Vild et al. filed on Oct. 31, 2005. In
connection with glass sheet quenching, see U.S. Pat. Nos. 3,936,291
McMaster; 4,470,838 McMaster et al.; 4,525,193 McMaster et al.;
4,946,491 Barr; 5,385,786 Shetterly et al.; 5,917,107 Ducat et al.;
and 6,079,094 Ducat et al.
SUMMARY
[0007] An object of the present invention is to provide improved
apparatus for quenching glass sheets.
[0008] In carrying out the above object, the apparatus for
quenching glass sheets in accordance with the invention includes a
quench system having a quench including lower and upper quench
heads that are operable to supply upward and downward gas flows
that can be at conventional quench pressures. A quench ring of the
apparatus positions a heated and formed glass sheet between the
quench heads for quenching. A control of the apparatus operates the
quench to initially supply through the lower and upper quench heads
upward and downward gas flows for about 0.5 to 1.3 seconds to
quench the formed glass sheet. The control then operates the quench
to increase the upward and downward gas flow pressures through the
lower and upper quench heads to at least 25% greater than the
initial pressures for 0.5 to 4 seconds. The control thereafter
operates the quench system to continue to supply upward and
downward gas flows to the formed glass sheet with decreased cooling
power that is less than the cooling power of the initial pressure
quenching to eventually provide a tempered and formed glass sheet
upon cooling throughout to ambient temperature. When the initial
quenching is at conventional quench pressures, the last mentioned
cooling has cooling power that is less than the cooling power of
the quench at minimum conventional quench pressures.
[0009] The quench of the apparatus includes quench heads that are
movable between an open position where the formed glass sheet is
transferred into and out of the quench and a closed position in
which the initial pressure and increased pressure quenching are
performed. A quench ring of the apparatus transfers the heated and
formed glass sheet into the open quench and supports the formed
glass sheet during the initial pressure and increased pressure
quenching. The apparatus also includes an aftercooler and in one
embodiment the quench ring moves the formed glass sheet from the
open quench to the aftercooler for at least part of the decreased
cooling power quenching. A transfer device of another embodiment
receives the formed glass sheet from the quench ring to provide
transfer thereof from the open quench to the aftercooler.
[0010] The objects, features and advantages of the present
invention are readily apparent from the following detailed
description of the preferred embodiments when taken in connection
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic elevational view of one embodiment of
apparatus constructed in accordance with the present invention to
provide the formed glass sheet quenching.
[0012] FIG. 2 is a partial schematic view similar to FIG. 1 to
illustrate another embodiment of the apparatus for performing the
formed glass sheet quenching.
[0013] FIG. 3 is a graph that illustrates quenching pressure versus
time with intermediate increased quenching and final decreased
quenching in accordance with the present invention.
[0014] FIG. 4 is a graph that illustrates quenching pressure versus
time as performed in a conventional manner without the increased
intermediate quenching and the final decreased quenching in
accordance with the present invention.
[0015] FIG. 5 is a graph that illustrates in solid line
representation the surface tension versus time of a glass sheet
quenched in accordance with the present invention and compared to
phantom line illustrated conventional quenching.
DETAILED DESCRIPTION
[0016] With reference to FIG. 1, a glass sheet forming and
quenching system is generally indicated by 10 and includes a
partially illustrated furnace 12 for heating glass sheets to a
forming and quenching temperature, a bending station 14 that
includes bending apparatus 16 for cyclically forming glass sheets
one after another and a quench system collectively indicated by 18.
The quench system 18 includes a quench 20 constructed in accordance
with the invention to perform a quenching method of the invention
as is hereinafter more fully described, and the quench system also
includes an exit cooling station 22 having an aftercooler 24 for
continuing forced convection cooling of formed glass sheets as
described below. A central control 26 includes: control connections
28 and 30 respectively to the furnace 12 and the bending station
14; control connections 32 and 34 to the quench 20 and an actuator
36 for a quench ring 38 that moves between the bending station 14,
the quench 20 and the cooling station 22; and a control connection
40 that operates the aftercooler 24 of the cooling station 22.
Apparatus 42 of the system 10 includes the quench system 18 which
includes the quench 20 for performing quenching in a manner that
reduces the time required in the quench in order to reduce the
overall cycle time of the system in successively forming and
quenching glass sheets for delivery.
[0017] The furnace 12 and bending station 14 may be constructed in
any conventional manner but are preferably constructed in
accordance with the disclosure of U.S. Pat. No. 7,958,750 of Vild
et al. which is assigned to the assignee of the present invention,
and the entire disclosure of which is hereby incorporated by
reference. At its downstream end, the bending station 14 includes a
door 44 that is opened and closed to permit the quench ring 38 to
be moved by the actuator 36 through a connection 46 into the
bending station to receive a formed glass sheet G in preparation
for cooling of the glass sheet. The quench 20 of the quench system
18 includes lower and upper quench heads 48 and 50 that have the
general shape of the glass sheet to be quenched and that are
movable between a phantom line partially illustrated open position
and the full solid line indicated closed position. During movement
of the quench ring 38 from the bending station 14 to the quench 20,
the lower and upper quench heads 48 and 50 of the quench are in the
open position and are then closed to commence the quenching. The
lower and upper quench heads 48 and 50 respectively then provide
upward and downward gas flows 52 and 54 that perform the quenching
as is hereinafter more fully described. Thereafter, the quench 20
is moved to its open position and the actuator 36 moves the quench
ring 38 to the cooling station 22 into the aftercooler 24 between
its lower and upper cooling heads 56 and 58 that supply upward and
downward cooling gas flows 60 and 62 but at pressures that provide
lesser cooling power than prior quenching in the quench 20 as is
more fully described below. The pressure of the upward gas flows 60
is subsequently increased to lift the glass sheet from the quench
ring 38 upwardly against a transfer device 64 which is illustrated
as a conveyor having a conveying loop 66 extending around wheels 68
at least one of which is rotatively driven to move the lower reach
of the conveying loop in the direction shown by arrow 70 so the
glass sheet is moved toward the right for further cooling and
delivery. After the glass sheet is lifted upwardly from the quench
ring 38 in the aftercooler 24, the actuator 36 moves the quench
ring 38 back through the open quench 20 to the bending apparatus 16
of the bending station 14 to receive another formed glass sheet for
subsequent movement back toward the right into the quench 20 in
preparation for commencing the next cycle.
[0018] Before completing the description of the manner in which the
quenching takes place in the quench system 18, reference should be
had to FIG. 2 which illustrates another embodiment of the apparatus
42' whose quench 18 also has a quench 20 and cooling station 22
like the previously described embodiment. However, in this
embodiment, a transfer device 72 includes an extractor 74 that is
moved by an actuator 76 under the control of a connection 78 to the
central system control (not shown in this view) so as to provide
coordination with the rest of the system. After the lower and upper
quench heads 48 and 50 of the quench 20 are moved to their open
position as shown by solid lines in FIG. 2, the pressures of the
upward and downward gas flows 52 and 54 are modified to lift the
glass sheet upwardly from the quench ring 38 against the extractor
74 of the transfer device 72. Actuator 76 then moves the extractor
74 and the glass sheet toward the right to the aftercooler 24
between its lower and upper cooling heads 56 and 58 whose upward
and downward gas flows 60 and 62 are then at pressures that
initially maintain the glass sheet upwardly against the extractor
as additional cooling is provided. The pressures of the upward and
downward gas flows 60 and 62 are then modified so that the glass
sheet is released downwardly from the extractor 74 onto a lower
conveyor 80 on an upper reach of a conveying loop 82 thereof which
extends over wheels 84 at least one of which is rotatively driven
to move the glass sheet toward the right as shown by arrow 86 for
delivery. After the upward lifting of the glass sheet in the quench
20, the quench ring 38 is moved toward the left by its actuator 36
back to the bending apparatus of the bending station to receive
another formed glass sheet in preparation for subsequent movement
back to the quench 20 to commence the next cycle.
[0019] As previously mentioned, forced convection is conventionally
utilized to perform glass sheet quenching in order to establish a
temperature gradient between the glass surfaces and its center,
starting from a tempering temperature of about 645.degree. C. and
cooling to the ambient temperature. Actually, while glass at
ambient temperature acts much like a solid, it is actually a highly
viscous liquid since glass is amorphous without any crystalline
structure. The outer glass surfaces upon initial quenching are
cooled and temporarily tensioned for about one second or more. This
tension results from greater contraction of the glass outer
surfaces as they are initially cooled faster than the glass center
which is cooled slower and thus contracts less. The glass surface
tension subsequently reduces as the thermal gradient between the
cooler glass surfaces and the hotter glass center stops increasing
and the stresses partially relax due to flow within the glass.
After the glass cools down to a temperature referred to as the
"strain point", that is normally approximately 520.degree. C.
(964.degree. F.), the glass becomes more viscous and does not move
as fast as when it was hotter so relative flow between inner and
outer layers is arrested and stress created by thermal contraction
differences between layers can no longer be relaxed with time by
flow in the glass. The glass center is hotter than the surfaces
upon cooling through the strain point temperature. As such, upon
the entire glass sheet reaching ambient temperature, the center has
cooled through a greater temperature differential and contracted
more than the surfaces so the center goes into tension and
consequently forces the surfaces into compression. The surface
compression as previously mentioned resists breakage so as to
provide increased mechanical strength to the quenched glass.
[0020] FIG. 3 is a graph that illustrates the quench pressures
utilized to perform the quenching in accordance with the present
invention versus time and is comparable to the prior art graph
illustrated in FIG. 4 which shows that the quenching previously has
required a much longer high pressure quench time which increases
the cycle time of the entire system. It should be appreciated that
the pressures illustrated will vary depending upon the glass
thickness, quench construction and compressive surface tension
desired such that the specific values shown are for purposes of
illustration only. As shown in FIG. 4, conventional quenching uses
a constant quench pressure versus time of about 25 inches (63.5 cm)
of water column for eight seconds or so to perform quenching that
provides an acceptable break pattern for 3.8 mm thick glass. As
previously mentioned, the break pattern or, more precisely, a count
of the number of particles within a specified area of the broken
glass surface, is the standard way of determining the extent of the
center tension in the glass and the accompanying surface
compression. That entire eight seconds or so must be performed
within the quench 20 so that when added to the time of the quench
ring movements between the bending station and quench station, or
between the bending station, quench station and cooling station,
will require a cycle time on the order of about 13 seconds or more.
The present invention as described below in connection with FIG. 3
allows a reduction in the time while still providing an equivalent
break pattern.
[0021] A more complete description of glass sheet tempering will be
helpful in understanding the present invention and the manner in
which it reduces cycle time. As discussed above, the extent of
quenching is measured by the resultant break pattern. Typically,
quenching is controlled so that the break pattern satisfies
recognized standards to assure glass strength and stresses that
provide resistance to breakage. One widely recognized standard is
the European Standard identified as ECE R43, which specifies that
upon breakage square areas with 5 cm. sides located anywhere on the
surface of the broken glass shall have a minimum particle count of
no less than 40 and a maximum particle count no greater than 400.
This particle count is provided by counting each particle fully
within the square as one and each particle partially within the
square as one half and then adding to sum the total. The tempered
and formed glass sheets are normally tested by breaking in more
than one location since the location of the nucleus of the breaking
can affect the particle count.
[0022] The extent of quenching power for providing formed glass
sheets with acceptable temper levels, i.e. recognized break pattern
standards, depends on many factors including glass thickness and
temperature upon initial quenching, the number of quench nozzle
openings for a given area, the spacing of the nozzle openings with
respect to each other, the size of the nozzle openings, the
proximity of the nozzle opening outlets to the adjacent glass
surface, the angles of incidence of the quench jets upon impinging
with the glass surface, the pressure of the nozzle jets, the
velocity of the nozzle jet flows, and the time length of the
quenching, etc. For any given quench and formed glass sheet being
quenched, there is a range of pressures that will provide the
required effect to meet recognized break pattern standards. This
range will thus have minimum and maximum pressures for meeting the
standard, and usually the upward flow pressure will be slightly
less than the downward flow pressure so the formed glass sheet
being quenched will remain on a quench ring that provides its
support at the glass periphery. For purposes of this application,
"conventional quench pressure" is any pressure in the range of
pressures that when applied in the "conventional" constant pressure
method for 10 seconds from a specific quench to a specific formed
glass sheet heated to a specific quenching temperature will produce
a tempered glass sheet upon eventual cooling throughout which when
broken provides a break pattern with maximum and minimum particle
counts that meet the European Standard ECE R43. As discussed above,
the conventional quench pressures, both upward and downward, will
have both minimum pressures and maximum pressures that will provide
quenching that will produce tempered and formed glass sheets
meeting the applicable standard.
[0023] The cooling power during quenching is the measure of the
heat flow rate per area produced for each degree of temperature
difference between the glass and the quenching gases provided by a
set of quench factors as described above. When all other factors
remain the same, the cooling power increases as the quench pressure
increases, and the cooling power decreases as the nozzle to glass
spacing increases.
[0024] More specifically, the cooling power is the convective heat
transfer coefficient of the quenching factors governed by the
equation:
.DELTA.Q/.DELTA.t=(h)(A)(.DELTA.T),
[0025] where the rate of the heat flow, .DELTA.Q/.DELTA.t, is equal
to the heat transfer coefficient, h, times the area over which the
heat flow was measured, A, times the temperature difference between
the glass and the gas of the quench jets, .DELTA.T.
[0026] When the heat flow rate is in calories per second, with the
area in square centimeters and the temperature difference in
degrees Centigrade, the heat transfer coefficient is measured in
calories per second per square centimeter per degree
Centigrade.
[0027] As illustrated in FIG. 1, the present invention provides
quenching of a glass sheet that is immediately increased to a
conventional pressure for about 0.5 to 1.3 seconds and as shown in
FIG. 5 maintains the temporary glass sheet surface tension in the
range of about 14 to 20 MegaPascals, below which range there is
insufficient quenching and above which range glass fracture is more
likely during the quenching. Then, before the maximum temporary
glass surface tension substantially decreases, such as at location
88 shown in FIG. 5, the upward and downwardly gas flow pressures at
the quench 20 are increased at least 25% through the associated
lower and upper quench heads from the initial pressures. More
specifically, as illustrated in FIG. 3, the increased pressure
quenching is performed for 0.5 seconds to 4 seconds with pressures
greater than 50% of the initial pressures and most preferably in
the range of 50 to 100% greater than the initial pressures.
Thereafter, the upward and downward gas flows to the formed glass
sheet are continued at pressures that provide less cooling power
than the initial pressures as shown in FIG. 3. This decreased
cooling is initially provided within the quench 20 and thereafter
within the aftercooler 24 of the cooling station 22 as previously
described. More specifically, this decreased quenching is performed
with upward and downward gas flows that provide a decreased cooling
power that is no greater than 75% of the cooling power of the
initial pressure quenching, preferably no greater than 60% of the
cooling power of the initial pressure quenching, and most
preferably about 50% of the cooling power provided by the initial
pressure quenching. When initial conventional quench pressures are
used, i.e. those that will produce glass with a break pattern
having particle counts that will meet European Standard ECE R43
when continued for about 10 seconds, the decreased cooling power
quench is less than the cooling power provided by the quench at
minimum conventional quench pressures. More specifically the
decreased cooling is then no greater than 80%, preferably less than
70% and most preferably about 60% of the cooling power provided by
the quench at minimum conventional quench pressures.
[0028] In an actual practice of the present invention, 3.8 mm thick
full sized automobile backlites were processed on an actual
production furnace and quench under two conditions, specifically
under conventional processing and the three step quenching of the
present invention.
[0029] For the conventional processing, glass temperature at the
start of quenching was 643.degree. C., quench pressure was 25
inches of H.sub.2O and the quench time was 8.0 seconds, as in FIG.
4. The break pattern yielded a central particle count of 196 pieces
per 5.times.5 cm square from a break point in the driver's side
lower corner. When this conventional quench time was reduced to 4.5
seconds, the particle count was 39 pieces.
[0030] For the three step quenching of the present invention, glass
temperature at the start of quenching was 643 degrees C., quench
pressure started at 25 inches of H.sub.2O for 0.7 seconds, was then
increased to 40 inches of H.sub.2O for 3.8 seconds and was then
decreased to 6 inches of H.sub.2O for 3.5 seconds, as in FIG. 3.
The break pattern yielded a central particle count of 227 pieces in
a 5.times.5 cm square from a break point in the driver's side lower
corner. So, the time required to be in the high pressure quench was
reduced from 8.0 to 4.5 seconds.
[0031] Quenching of the glass with the three steps of quenching
described above thus prevents excessive initial temporary surface
tension and reduces the cycle time of the processing.
[0032] While preferred modes of the invention have been illustrated
and described, it is not intended that these modes illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification are words of description rather than
limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention.
* * * * *