Note: Descriptions are shown in the official language in which they were submitted.
-
Bac~ground of the Invention
This is a divisional of Canadian Patent Application
.Serial No. 281,797 filed June 30, 1977.
1. Field of the Invention
This invention relates to the tempering of glass sheets and,
more specifically, to the cooling of hot glass sheets involved in their
tempering while conveying the sheets through a cooling station immediately
downstream of a furnace wherein the conveyed sheets are supported on a
gaseous bed with their major surfaces out of contact with solid members.
This cooling involves a system for supplying gas in heat exchange relation- _
ship and/or supporting relationship to a sheet or ribbon of glass. The
support system is particularly adapted for handling glass in sheet or ribbon
form without marring or otherwise producing uncontrollable deformation in
the major surfaces of the sheet, even when the glass is at a deformation
temperature.
In fabricating glass through known manufacturing techniques of
bending, tempering, annealing or coating and combinations of such techniques
to form end products having characteristics and uses different from the
original product, it is necessary to heat the glass sheets to a temperature
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aboye that at which the major surfaces or the contour thereof is changed
by deforming stress on contact with solid members. Where it is desired
to strengthen the glass, it is further necessary to cool the glass sheets
rapidly from such a deformation temperature to a lower temperature below
the annealing range of the glass. The effectiveness of such strengthening
is improved by an increase in the rate at which heat is removed from the
surfaces with respect to the center of the thickness of the glass sheets.
Efficient glass sheet fabrication involving the techniques
previously mentioned requires that the glass sheets undergoing treatment
be conveyed while hot. The need to convey glass sheets at high temperature
has involved undesirable deformation or marring of the major surfaces of
glass sheets undergoing treatment due to physical contact of its major
surfaces with supporting and conveying apparatus while the glass is at
elevated temperatures. Glass sheets have been supported on gaseous beds
to overcome the defects of deformation and marring due to physical contact
of their major surfaces with solid members at elevated temperatures. Glass
sheets have been conveyed through these gaseous beds by supporting the
sheets at a small oblique angle to the horizontal and engaging the lower
edges thereof with the peripheries of rotating driving discs.
Attempts to cool the glass surfaces rapidly has involved the
development of modules for supplying cool gas in a pressure pattern that
is non-uniform across the dimension of the %lass sheets transverse to
their direction of movement through a space between opposite arrays of
modules disposed above and below the upper and lower major surfaces of
the conveyed glass sheets. Non-uniform rates of cooling have developed
non-uniform stress patterns, which are accompanied by optical non-uniformities,
sometimes called Q-lines.
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One technique for minimizing the appearance of ~-lines has been
the application of blasts of air through narrow elongated slots, preferably
narrower than one millimeter, extending continuously across the entire
width of the conveyed glass sheets. Recognizing that it is difficult to
maintain uniform width along the entire length of narrow slots, the prior
art used thin mesh screens to separate the walls of the narrow slots and
to maintain the uniformity of slot width. The presence of screens impaired
the free flow of air through the slots and, hence, limited the heat transfer
rate due to the impingement against the glass surface by gas streams flowing
through the narrow slots en route to the glass surface. It became necessary
to make the prior art modules hollow and to flow heat exchanging liquid
through the hollow passages within the hollowed modules to improve th~ heat
exchange rate by radiation. This solution introduced the problem of handling
a liquid supply system.
When glass must be tempered, a large escape area must be proyided
for the impinging blasts of cooling medium, such as air, to be released
readily from the central portion of the gaseous bed to avoid the establish-
ment of a non-uniform pressure profile across the width of glass sheets
transverse to the direction of glass movement. Such pressure profile
increases toward the center of the glass and causes the glass to develop
one of two metastable conditions, one in which the center of the glass
sheets bows upward and another in which the center of the glass sheets
bows downward.
When glass is supported on a gaseous support, the thickness of
the gas bed is maintained as thin as possible to enable the incoming gas
streams to impinge on the glass surface as efficiently as possible rather
than blending with the gas bed that is already present. Therefore, when
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the glass develops a bowed shape due to the metastable conditions described
previously, there is insufficient room for the glass to be conveyed between
the upper and lower arrays of modules that supply the gaseous cooling
medium needed to cool the glass sufficiently rapidly to develop a stress
pattern through the glass thickness that strengthens the glass sufficiently
so that the glass develops at least a partial temper.
In prior art apparatus providing thin, elongated slots for the
application of gas under pressure interspersed with elongated slots for
gas removal, it was considered advantageous to have the portion of the
area of the supporting surface occupied by elongated slots to not sub-
stantially exceed 10 percent. While elongated slots extending across
the entire width tend to overcome the conditions that cause the metastable
conditions in the glass, limiting the total slot area to not substantially
more than 10 percent limits the rate at which the gas supplied for cooling
can provide heat exchange with the moving glass sheets because the rate of
gas flow through the slots and between the glass surfaces and the modules
must necessarily be limited by the limited area provided for removal of
cooling medium.
Tempering produced by heating a glass sheet above its annealing
range and then rapidly chilling its surfaces to below the strain point
while the interior is still hot and continuing the rapid chilling until
the entire glass sheet cools to below its strain point causes the glass -
sheet to develop a skin of compression stress that surrounds the glass
interior which is stressed in tension. Such a stress distribution makes
the glass sheet much stronger than untempered glass so that tempered glass
is less likely to shatter than untempered glass when struck by an object.
Furthermore, in the less frequent times when an outside force is sufficiently
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large to caus.e te~ered glass to fracture, tempered glass breaks. up into
a large numher of relatively smoothly surfaced, relatively small particles
which are far less dangerous than the relatively large pieces with
relatively jagged edges that result from the fracture of untempered glass.
2. Description of the Prior Art
U. S. Patent No. 3,607,198 to Meunier et al discloses a method
and apparatus for moving hot glass sheets and similar ribbons that are
supported pneumatically out of contact with solid surfaces by establishing
alternate zones of static and kinetic gas pressure along the path of sheet
movement. Each zone extends substantially across the full width of the
sheet. Cool air under pressure is applied through a first multiplicity
of slots, which are parallel and extend continuously substantially the
full width of the ribbon and a second multiplicity of exhaust slots for
the exhaustion of air applied through the first multiplicity of slots. A
pair of pressure applying slots is located between each consecutive two
exhaust slots. The distance between the pressure applying slots of a pair
is greater than the distance between each pressure applying slot and its
adjacent exhaust slot. The total area occupied by the slots is not
substantially more than 10 percent of the whole glass sheet facing surface
of the supporting bed. The pressure applying slots are preferably between
0.4 and 0.7 millimeter and need not be greater than 1 millimeter wide, and
the exhaust slots are between 1.5 and 2 millimeters wide.
The Meunier et al patent is designed for annealing glass sheets.
Hence, even if there is some backward flow of the support gas into the
furnace, it is not so extensive as to impair the annealing process or to
cause glass breakage as would be the case were the glass being tempered.
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~ hile this patent states its system can be used for tempering
as well as annealing glass, it requires hollow passages in the slotted
module housings and liquid to flow through the hollow passages to supple-
ment the air cooling with radiation cooling. The small proportion of
apertures in the Meunier et al apparatus makes it impractical for tempering
by use of gas blasts exclusively. The need for a water supply system to
supplement the gas supply system makes the Meunier et al apparatus awkward
to use. The gas exhausted in the Meunier et al apparatus is recirculated.
Such recirculation impairs the efficiency of the gas applied to cool the
glass sheets unless the gas is cooled during its recirculation.
Furthermore, in handling sheets having a width on the order of
30 centimeters or more, it is difficult to maintain continuous uninterrupted
slots of uniform width across the entire width of the glass sheets without
reinforcing the modules containing slotted walls facing the opposite major
glass sheet surfaces. The reinforcements, if in the form of wire mesh as
in the Meunier et al apparatus, disrupt the contînuity and uniformity of
the flow of gas through the slots. If the reinforcements are solid members
interconnecting the walls of the modules beneath the slotted walls, they
have to be so close to the slots in the slotted walls to insure uniform
width that they interrupt the continuity and uniformity of gas flow. hny
substantial non-uniformity of gas flow imparts non-uniform cooling in an
amount sufficient to cause Q-lines in the glass, particularly from modules
installed in close proximity to the exit of the furnace.
Without the reinforcements or wire spacers in the slots of the
module construction, the elongated slots develop non-uniform width which
causes a non-uniform application of cooling medium even where the uniformity
of flow of cooling medium is not interrupted by reinforcements. Therefore,
1C~9E~7~3
the glass sheet heat treating art required a ~ethDd of treatment different
from and representing an improvement oYer tfiat provided by the ~eunier
et al patent.
Belgium Patent No. 787,880 to PPG Industries, Inc. discloses
a method and apparatus for tempering glass sheets which contains spaced
rows of modules, the glass facing walls of which are provided ~ith a series
of parallel arcuate vanes that cause streams of gaseous cooling medium to
move in curvilinear paths that result in gas streams having a relatively
large component of motion in the direction of glass sheet movement away
from a furnace, and in a downstream direction of the path of glass movement
where the gas streams impinge on the glass. The main purpose of directing
the streams of cooling fluid downstream is to avoid flow of the cooling gas
in an upstream direction into the exit portion of the furnace. Any upstream
flow of cooling gas into the exit portion of the furnace cools the exit
portion of the furnace and prevents the glass from developing sufficient
heat for tempering and may also cause the glass sheets to leave the furnace
exit at a non-uniform temperature. As a result, glass sheets insufficiently
heated tend to break when subjected to streams of cooling gas downstream
of the furnace exit.
Means is provided to adjust the effective exhaust area of the
spaces between adjacent rows of modules. Different effective exhaust areas
are most beneficial for different glass sheet thicknesses.
The tempering apparatus of the Belgium patent is composed of
square modules, each provided with arcuate vanes that gradually change the
direction of streams of cooling gas toward the major surfaces of the glass
sheets from directions normal to the respective surfaces to directions oblique
to the respective surfaces. Arcuate curving of the paths of movement for
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the cooling medium may cause some turbulence in the flow of cooling medium.
Laminar flow is more efficient in chilling a glass surface than turbulent
flow. The modules are arranged in rows 1 inch (25.4 millimeters) wide
separated by spaces ranging from 1/4 inch (6.35 millimeters) to 3/4 inch
(19.05 millimeters) depending on the thickness of glass sheets processed.
This patent is silent as to the width of the slots formed between
adjacent vanes. However, the drawings would appear to indicate that each
slot has a substantial width. Gas streams applied at a given rate of volume
through slots of such width have less velocity than gas streams applied
through thinner slots. Therefore, cooling by passing cold fluid through
the wide arcuate slots between adjacent arcuate vanes required some improvement.
French Patent No. 2,024,397 discloses glass sheet tempering
apparatus comprising sheets of slotted nozzles providing oblique passage-
ways for the passage of tempering medium either in a direction oblique to
the plane defining the path of glass travel through a cooling station
through slots extending along lines normal to the path of glass sheet travel
followed by obliquely arranged slots or through module rows that direct
tempering medium toward the opposite glass surfaces. Passageways are
provided for removing tempering medium in a direction parallel to the plane
of the sheet and transVerse to the path of glass travel after the medium
impinges on the opposite major surfaces of the glass sheets as the latter
pass through the cooling station. The passageways for removing tempering
medium have restricted openings which inhibit the free removal of tempering
medium from the vicinity of the respective glass surfaces. The presence
of these restricted paths and the need to turn the blasts of tempering
medium into directions normal to the component of blast movement parallel
to the path of glass travel make the apparatus of the French patent less
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effi,cient than desired to remove the tempering medium from the glass
after the tempering medium has cooled the glass surface. The glass, sheets
are conveyed either by roller discs that engage an edge of each,glass sheet
or rollers that engage a supported major surface of the glass sheets and
also provide boundaries for exhaust passages for removing temper~g medium.
U. S. Patent No. 3,395,943 to Wilde discloses the use of gaseous
streams for maintaining a gaseous support under a glass surface and directs
additional gaseous streams against the exposed periphery capable of
developing forces transversely of the sheet. Some of these additional
gaseous streams are directed against the rear edge to propel the glass sheet
forwardly and other gaseous streams are directed transversely to maintain
the lateral position of the sheet.
British Patent No. 773,469 discloses apparatus for cooling and
quenching glass sheets that are gripped by tongs during transport through
a chilling station. Cold tempering medium is applied through oblique slots
that direct air blasts obliquely away from a furnace exit in a downstream
direction of glass sheet movement. The slots are oriented to apply a
downward component of motion to the air blasts that impinge against the
opposite glass sheet surfaces to reduce any tendency of the sheets to flutter
and strike the opposite blast heads which supply air for application to the
glass surfaces through the nozzles.
Despite all the patents enumerated, a need still existed to produce
thin glass sheets having higher temper values combined with optical properties
superior to those obtainable from the prior art. The present invention
provides a novel combination of selected prior art features to attain such
desired results.
1C~987~i3
Sum~y of the Invention
The present divisional in one aspect provides
apparatus for tempering hot glass sheets by
flowing cool streams of gaseous tempering medium against the
opposite surfaces thereof comprising an upper elongated quench
bed and a lower elongated quench bed in spaced relation to and
facing said upper quench bed, each said quench bed including a
series of modules, each provided with a flat apertured wall having
elongated slots for applying thin streams of gaseous tempering
medium against the opposite major surfaces of a succession of
glass sheets conveyed longitudinally of said elongated bed past
said modules, said modules being spaced apart to provide there-
between longitudinally spaced exhaust passages extending
transversely of said elongated bed continusously across the
entire width of said conveyed glass sheets, said elongated quench
beds extending from an upstream end adapted to be located
adjacent an exit of a furnace for heating said glass sheets to
an elevated temperature suitable for tempering and a downstream
end, and means to provide cool gaseous tempering medium at a rate
sufficient to cause said gaseous tempering medium to flow through
said slots at a rate sufficient to cool said glass sheets
sufficiently rapidly to temper said sheets and to be exhausted
through said exhaust passages, whereby said modules comprise a
first pair of opposed modules located immediately downstream of
said upstream end and having their associated elongated slots
directed diagonally through the thickness of said flat, apertured
walls of said first pair of opposed modules in a downstream
direction disposed at a relatively large oblique angle to a plane
normal to the major surface of glass sheets conveyed along the
length of said elongated bed and a second pair of opposed modules
located downstream of said first pair of opposed modules and
having flat, apertured walls provided with elongated slots
directed through ~he thickness of said last named walls at a
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lesser oblique angle to said plane than said relatively large
angle.
The present divisional in a further aspect provides
a method of tempering glass sheets to provide said sheets
with a high temper and little surface distortion comprising
heating each glass sheet in a series thereof to a temperature
sufficient for tempering while conveying said sheets through a
hot atmosphere, and cooling the opposite major surfaces of each
of said heated sheets by passing each of said heated sheets
between a pair of sets of streams of cool gaseous tempering
medium, first directed at relatively large oblique angles
relative to planes normal to the major surfaces of said sheets
when the latter pass through a first region immediately down-
stream of said hot atmosphere and then to streams of cool gaseous
tempering medium directed at relatively small oblique angles
relative to said planes when said sheets pass through a second
region downstream of said first region.
Thus, it will be seen that the modules are arranged
so that those immediately downstream of the furnace exit have
their apertured walls provided with thin slots extending through
the wall thickness at a relatively large angle of obliquity with
respect to the direction normal to the major glass sheet
surfaces and modules located further downstream have their
apertured walls provided with thin slots extending through
the wall thickness at angles of less obliquity with respect
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to the planes normal to the glass sheet surfaces. Thus, tempering medium
is directed in laminar flow with a relatively small proportion of its force
provided in a component directed normal to the heat-softened glass surfaces
near the furnace exit where the relatively hot glass is most susceptible
to distortion accompanied by a relatively large proportion of its force
provided in a component in a direction of glass sheet movement away from
the furnace exit in a downstream direction. Nevertheless, the component of
force applied normal to the major glass sheet surfaces is sufficient to
produce a significant amount of cooling of the major surfaces of the glass
sheets moving across the streams of gaseous tempering medium. Tempering
medium applied through the modules with less oblique slots located further
downstream of the furnace exit provide a lesser force component in the
direction of glass sheet movement accompanied by a greater force component
normal to the glass surfaces in the region of the cooling station where the
glass surfaces are hardened sufficiently by cooling to withstand the
impingement of stronger blasts thereagainst. The blasts having intermediate
obliquity provide less resistance to the downstream flow of the oblique
blasts applied near the furnace exit than blasts applied normal to the
glass. This arrangement helps remove the blasts from the furnace exit while
improving the rate of glass cooling.
In the downstream region of the cooling station where the glass
sheet surfaces are still harder, the glass tempering modules may be provided
with slits that extend lengthwise of the modules and that are directed
normal to the glass surfaces. Impingement of tempering medium in a direction
normal to the glass surface provides a greater heat exchange rate for a
given rate of flow of gaseous tempering medium than at an oblique direction
of impingement. However, a compromise is effected between a high rate
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of impingement normal to the glass surfaces that results in upstream flo~
of tempering medium into a furnace and an oblique direction of flow that
avoids this problem at a slight sacrifice to the magnitude of the force
component directed normal to the glass sheet surfaces.
Another feature of the present invention is the pro~ision of
thin slots that extend obliquely of apertured, glass facing walls along
the length of the modules so as to avoid the need for reinforcements
interconnecting the walls of the modules that support the apertured walls,
or for screens within the slots that help maintain a uniform width of slot.
Such reinforcements break up the flow pattern of tempering medium en route
to the major glass sheet surfaces and disrupt the uniformity of cooling
pattern that would result if the flow pattern were not interrupted locally.
In addition, the oblique slots have limited length so that the module walls
provide sufficient rigidity to maintain uniform slot width without requiring
internal reinforcements or screens that interrupt free flo~ of tempering
medium.
The use of thin slots permits a series of high velocity air jets
which promote a high heat transfer coefficient at the major glass sheet sur-
faces using a given rate of flow of tempering medium. The oblique slots
are arranged relative to the apertured walls of the modules in such a manner
that adjacent slots of each module overlap one another along the length of
the elongated bed. Thus, each glass sheet increment transverse to the path
of glass sheet movement intercepts a plurality of oblique blasts imparted
through oblique slots as it traverses the portion of said path in alignment
with each of said modules. This arrangement provides substantially uniform
cooling from transverse increment to transverse increment without requiring
devices that impair the free flow of tempering medium as the cost for insuring
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uniformity of slit width over a long slot. The overlapping of slots
along the path of glass movement causes the cooling of the glass surface
to be sufficiently uniform as to minimize the development of ~-lines.
In a specific embodiment of the present invention, each module
is provided with means for ease in attachment or removal to its associated
plenum chamber. Different module arrangements may be required for pro-
cessing glass sheets of different thicknesses and/or widths. Facility in
changing module configurations with minimum loss of time from production
is an important feature of this invention.
In a specific embodiment of this invention, the plenum chambers
are arranged in groups, each group communicating with a common plenum
chamber. Means is provided to supply gaseous tempering medium under pressure
to each common plenum chamber with means for controlling the pressure
disposed in the supply system for each common plenum chamber so that the
pressure of the gaseous tempering medium applied to each common plenum
chamber may be controlled independently of the pressure for each other common
plenum chamber. Several individual plenum chambers in the form of elongated
chambers extend across the cooling station of glass sheet tempering apparatus
from each of the common plenum chambers. All of the latter are disposed
to one side of the apparatus to`permit operating personnel access to the
other side of the apparatus when needed.
The downstream common plenum chambers located in the region of
the cooling station beyond the location where the glass sheet surfaces are
set may be provided with elongated plenum chambers having nozzle-type
openings rather than modules facing the glass sheets passing therebetween.
The nozzle-type openings may include elongated slot-type openings having
much wider openings than the slots in the modules or round openings having
diameters much larger than the width of the module slots or combinations
of wider openings of either type.
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Since tempering medium is supplied under pressure from one side
of the elongated plenum chambers in a direction transverse to the length
of the cooling station, several features are included to provide a desired
pressure pattern for the gaseous tempering medium applied through the
individual modules against the opposite glass sheet surfaces. These include
providing each elongated plenum chamber with an oblique wall opposite to
the apertured wall of its attached module such that the cross-section of the
elongated plenum chambers diminishes in the direction away from their
associated common plenum chamber and/or providing each elongated plenum
chamber with one or more curved deflectors that change the ratio of gaseous
tempering medium supplied to different portions of the length of the elongated
plenum chambers and/or providing a porous member in the path of movement of
the gaseous tempering medium toward the apertured wall of at least certain
modules, the porous member being constructed and arranged to provide a desired
pattern of flow of tempering medium along the length of the apertured wall
of the associated module.
The present invention will be better understood in the light of
a description of an illustrative embodiment thereof. Although the illustrative
embodiment refers to tempering apparatus that uses a gaseous tempering medium
such as air to cool hot glass sheets sufficiently rapidly to impart a temper,
it is understood that the term "gaseous" for the purpose of the present
invention includes vapors, mixtures of gases, mixtures of gases and vapors,
sublimable materials and mixtures of gases with sublimable materials. In
fact, the tempering media suitable for use with the present invention may
incorporate materials whose heat of evaporation or heat of sublimation may
provide at least part of the cooling effect required for the tempering medium.
Only materials that react chemically with the glass surfaces to weaken the
latter when directed thereagainst are excluded from materials suitable for
use as tempering media.
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1~;P987~i3
In describing the presént invention, the term "tempering" is
intended to mean establishing a stress pattern in a glass sheet having a
surface compression stress of at least lO,OOO pounds per square inch (about
340 kilograms per square meter) as measured by a DSR refractometer described
in "The Nondestructive Measurement of Surface Stresses in Glass" by
R. W. Ansevin, ISA Transactions, Volume 4, Number 4, October 1965.
Brief Description of the Drawings
In the drawings that form part of a description of an illustrative
embodiment of the present invention and wherein like reference numbers
refer to like structural elements,
FIG. l is a fragmentary longitudinal side elevation of a portion
of glass sh~et tempering apparatus incorporating an illustrative embodiment
of the present invention with special emphasis on its cooling station;
! FIG. 2 is a fragmentary, longitudinal sectional view of the
portion of the apparatus depicted in FIG. l;
FIG. 3 is an enlarged fragmentary sectional view taken along
the line 3-3 of FIG. 2 showing how a pair of opposing upper and lower
elongated plenums and their associated modules are arranged in said apparatus;
FIG. 4 is a composite of FIGS. 4A, 4B and 4C, which are fragmentary
transverse sectional views of different pairs of adjacent modules located
at different locations along the cooling station and taken along the lines
4A-4A, 4B-4B and 4C-4C of FIG. 2;
FIG. 5 is a composite of FIGS. 5A, 5B and 5C, which are fragmentary
plan views taken of apertured walls of the modules depicted in FIG. 4;
FIG. 6 is an enlarged section taken along the lines 6-6 of a
portion of a module depicted in FIG. 5A;
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FIG. 7 is an enlarged sectionalized view taken along the lines 7-7
of a portion of a module depicted in FIG. 5B; and
FIGS. 8 and 9 are plan views of two types of porous members capable
of use in conjunction with the modules and elongated plenum chambers according
to the present invention.
Description of the Illustrative Embodiment
Referring to the drawings, an illustrative embodiment of apparatus
incorporating the present invention comprises a gas hearth type furnace 10
of the type depicted in U. S. Patent No. 3,300,290 to George W. Misson. In
such a gas hearth furnace, glass sheets are introduced into a support area
at a temperature below that at which the major surfaces will mar on physical
contact with solid objects. The glass sheets are heated in turn above the
deformation temperature while being supported primarily by gas supplied
through apertures in a gas support bed 12 and the glass sheets are cooled after
they leave the furnace to a temperature below deformation temperature before
they are removed from a gas support. When glass sheets are so treated, the
heating is usually supplied by hot gas through the gas support bed supple-
mented by radiant heat supplied by heaters within the furnace 10. The latter
are usually electrical radiant heaters, alghough gas heaters may also be
employed. After the glass sheets are heated to a temperature sufficient for
tempering, they are usually cooled sufficiently rapidly to temper and, hence,
strengthen the sheets.
According to a typical gas hearth operation, the gas support bed 12
is supported on vertically adjustable jacks (not shown) which support the bed
12 so that its upper surface extends transversely to its length at a slight
oblique angle tless than 15 degrees) to the horizontal, usually approximately
5 degrees, and the glass sheets while supported on a gaseous support of the
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~L~9~7e~3
gas support bed 12 in such a tilted relatipnship to the hDrizontal have
their lower edges driven by friction in contact with a plurality of rotating
driving discs 14 of uniform diameter, each mounted on a different drive
shaft 15. The latter are aligned along a line parallel to the longitudinal
dimension of the gaseous bed 12 so that the driving discs 14 have a common
tangential line extending parallel to the direction of movement of the glass sheets.
Beyond the gas hearth type furnace 10 is a cooling station 16, at
one side of which are located additional rotating driving discs 14 aligned
with the driving discs that propel the glass sheets through the gas hearth
type furnace 10. In the cooling station, there are a plurality of longitu- -
dinally spaced, upper, elongated plenum chambers 18 directly opposing a corres-
ponding series of lower, elongated plenum chambers 20, the latter being
arranged in alignment with the bed 12 to form a continuation thereof at an
orientation depicted in FIG. 3. The plenum chambers 18 and 20 are in the form
of narrow elongated fingers having non-uniform height and extend parallel to -.
one another transversely of the length of the cooling station 16. The higher
ends are disposed to the side of the cooling station opposite the side occupied
by the rotating driving discs 14, and merge into respective upper and lower
common plenum chambers 22 and 24, respectively. Each of the upper common
plenum chambers 22 communicates through one of a series of flexible upper
supply conduits 26 to blower means (not shown). The lower common plenum
chambers 24 are connected through flexible lower supply conduits 28 to blower
means (not shown). Suitable pressure controls are provided by way of
adjustable valves (not shown) in the supply conduits 26 and 28.
The illustrated apparatus comprises five upper common plenum
chambers 22 and five opposite lower common plenum chambers 24. Each common
plenum chamber is supplied with pressurized air through two flexible supply
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conduits. There are approximately 50 upper and 50 lower elongated plenum
chambers for each common plenum chamber, except that the first upper and
lower common plenum chambers are subdivided into two zones, each individually
controlled and each communicating with about 25 elongated plenum chambers.
However, the exact number can be varied according to the design of the system.
Each of the elongated upper plenum chambers 18 and elongated
lower plenum chambers 20 is attached to a module 32 and 34, respectively,
(FIG.3). Each module is closed at its ends and has an open side facing its
attached module. Each upper module 32 has a lower apertured wall 36 and each
lower module 34 has an upper apertured wall 38 so that gas supplied under
pressure is directed through narrow slots through the thickness of the apertured
walls 36 and 38. The slots of the upstream modules are angled to provide a
component of force for cold gas in a downstream direction of movement for
glass sheets away from the exit of the furnace 10 when cold air is supplied
under pressure to the elongated plenums 18 and 20. In addition, the slots
extend obliquely across the apertured walls 36 and 38 at an angle such that
a component of force is provided to urge the glass sheets in a downward
direction transverse to the path of movement to force their lower edges into
a slightly greater frictional engagement against the inner common tangential
line of the driving discs 14 than would be provided by the mass of each glass
sheet alone. To provide this feature, the slots for the apertured walls of
each of the modules, in the first part of the cooling station 16, are angled
through the slotted wall of their respective modules facing the opposite
surfaces of glass sheets moving between the upper plenum chambers 18 and the
lower plenum chambers 20 so that the upwardly facing apertured walls 38 of
lower modules 34 are provided with narrow, elongated slots that are
disposed obliquely across their upper surfaces as depicted in FIG. 5A. The
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angle of obliquity can be 20 to 70 degrees with respect to the axis of
movement of the glass sheet. However, the view~ in FIG. 5A shDws the slots
angled at 45 degrees to the path of movement.
The downwardly facing apertured walls 36 of upper modules 32
have their lower surfaces provided with slots that are also angled to
provide a mirror image of the angling of the slots through the apertured
walls 38 of the lower modules 34. This obliquity of the surface.slots in
walls 36 and 38 provides the component of motion transverse to the path of
glass sheet movement that insures sufficient frictional force between the
glass sheets against the rotating driving discs 14 as to insure uniform
movement of the glass sheets through the cooling station 16.
FIGS. 4A, 4B, 4C, 6 and 7 show how the slots are directed obliquely
through the thickness of the apertured walls of the modules in a direction
toward the glass sheet movement path at different positions along the first
zones. Near the furnace exit the slots extend at a maximum forward angle
of obliquity to minimize the chance of cold tempering medium flowing upstream
into the furnace 10. At an intermediate position, the slots extend at a
smaller angle of obliquity and in the downstream positions of the first zone
and throughout the second zones extend through the wall thickness normal to
the glass major surfaces. Such combination of obliquities permits a combination
of low chance of upstream flow of tempering medium that would cool the furnace
with most efficient glass surface cooling consistent with minimum surface distortion.
The upper surface of the apertured walls 38 of the lower modules
34 are aligned with the upper surface of the gaseous bed 12 in the furnace 10.
Thus, glass sheets are supported for movement through the furnace 10 and the
cooling station 16 in approximately the same oblique plane with their lower
major surface supported on a gaseous bed of hot gas within the hot furnace
and on a supporting bed of cool gaseous tempering medium, usually pressurized
air, within the cooling station 16.
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1~987~3
The lower plenu~ chambers 2Q and the lower co~mon plenum chambers.
24 are vertically adjustable relatiye to a support structure 4Q. Each of
the upper common plenum chambers 22 and their elongated upper plenum chambers
18 are pivoted to the support structure 40 through a piston arrangement 42.
The latter is pivotally attached to a rigid superstructure 44 of the support
structure 40 at its upper end and at its lower end to a cantilever housing
46 to which an associated upper common plenum chamber 22 is attached. Each
cantilever housing 46 is pivoted on pivot rods 48 carried by the support
structure 40. The piston arrangements 42 are useful to plvot the cantilever
housings 46 about their respective pivot rods 48, which extend longitudinally
of the cooling station 16, to separate the upper plenum chambers 18 from the
lower plenum chambers 20 whenever it is necessary to inspect or provide
_.le sort of maintenance or repair to the cooling station 16. The pivot rods
48 are located on the longitudinally extending side of the cooling station 16
that is also occupied by the tempering medium delivery system comprising
the flexibile upper supply conduits 26 and the flexible lower supply conduits
28. This leaves sufficient space for operating personnel to gain access
to the space between the upper plenum chambers 18 and the lower plenum
chambers 20 when the piston arrangement is actuated to separate the respective
associated upper common plenum chamber from its opposite lower common
plenum chamber.
Depending on the thickness of glass sheets being processed, their
speed of conveyance through the furnace and other factors that relate to
the temper desired for the glass, modules of different construction and
different arrangements of the combination of modules may be required. For
example, the length, width, distance of separation and the orientation of
the slots in the apertured walls of the modules may require changing as the
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_
~9~37~3
pattern of production parts undergoing production is changed. Therefore,
it is desirable to make it possible to change a module attached to each
elongated plenum chamber with facility when required.
Each end of each module is provided with an apertured end lug 50
adapted to mate with a corresponding lug 52 carried by the corresponding
elongated plenum chamber. The lugs are readily bolted together. When
attached properly, each module fits exactly in communication with its
corresponding elongated plenum chamber so that gaseous tempering medium
applied under pressure to the plenum chamber is directed through the
corresponding module to be discharged through the narrow slots on the
apertured wall of the module.
The apertured walls of the modules are separated from one another
to provide a clearance 150 mils (3.81 millimeters) high between the opposing
surfaces of the apertured walls of the opposing sets of modules when the
apparatus is handling glass sheets 90 mils (2.286 millimeters) thick. In
a specific embodiment of this invention, the modules are l inch (25.4
millimeters) wide with a spacing of ll2 inch (12.7 millimeters~ between
adjacent modules. The initial modules have their slots oriented at a 45
degree angle to the axis of glass sheet movement through the
cooling station 16 that is parallel to the line of alignment of the driving
shafts 15 of the rotating driving discs 14.
The first three pairs of modules are oriented through the thickness
of their respective apertured walls at a forward angle of 45 degrees as is
shown in FLG. 4A and in FIG. 6. The next five pairs of opposing modules
have their slots oriented so that they extend at a 45 degree angle with
the axis of glass travel through the cooling station 16 as depicted in FIG. 5B.
However, the slope of the slots through the thickness of the apertured walls
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.
- ~987~3
of the opposing modules is at a small angle with respect to the normal to
the opposite glass sheet surfaces. In a typical embodiment depicted in
FIGS. 4B and 7, this angle is 7.5 degrees.
Further downstream of the first zones and through the second zones
where the glass sheets have their surfaces sufficiently hardened by cooling,
the slots in the apertured walls of the opposing modules are shown to extend
normal to the axis of glass sheet movement and to extend through the thickness
of the walls in a direction normal to the major opposing surfaces of the glass
sheets. In this location of the cooling station 16, the modules may be pro-
vided with internal reinforcements interconnecting the walls extending away
rom the apertured module walls to insure uniform slot width. The interruptions
in uniformity of gas flow around the internal reinforcements do not have a
significant deteriorating effect on the optical characteristics of the glass
because the glass surfaces are sufficiently hard by the time the glass
reaches those modules depicted in FIG. 5C.
With the arrangement thus described, glass sheets that leave the
exit of furnace 10 are cooled by blasts of relatively cool gaseous tempering
medium directed with a relatively large component in the direction of glass
movement immediately downstream of the furnace exit and the angle of orienta-
tion in the direction of glass sheet movement is diminished and eventually
eliminated completely for gaseous tempering medium expelled through the modules
disposed in the downstream portion of the first zone.
The additional common plenum chambers downstream of the second zones
provide air under individually controlled pressure to an array of nozzles of
conventional construction, such as pipe stems or slot-type nozzles having
relatively large openings. These additional common plenum chambers are pro-
vided for cooling the glass to handling temperature as the temper is established
as the glass passes through the first and second zones of the first pair of
opposing common plenum chambers.
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9~37~3
Since the tempering mediy,m, is, supplied from one s,ide of the
cooling station into the elongated plenum chambers 18 and 20, additional
features are incorporated in the elongated plenum chamber structure to
equalize the flow of tempering medium into the slots in ~he apertured module
walls 36 and 38, respectively. These structural features'include one or
more arcuate deflectors 54 fixed in position in each of the elongated upper
plenum chambers 18 and each of the elongated lower plenum chambers 20. The
arcuate deflectors 54 are concavely curved in their surface facing the
respective modules. In addition, the cross-sectional area of the opposing
elongated upper plenum chambers 18 and elongated lower plenum chambers 20
decreases from their relatively high ends that communicate with upper and
lower common plenum chambers 22 and 24, respectively, and their opposite ends
adjacent the rotating driving discs 14 by providing oblique remote walls 55
for the respective elongated plenum chambers 18 and 20. The oblique remote
walls 55 are constructed and arranged to be a maximum distance from the
respective module for the elongated plenum chamber at the ends adjacent
the associated common plenum chamber and to have the distance diminish gradually
toward the other end of the elongated plenum chamber near the driving discs 14.
Another feature used to control the flow pattern of tempering
medium across the width of the cooling station 16 involves the use of porous
members 60. The porous members 60 may be in the form of screens or apertured
plates or channel shaped members of a porous construction having relatively
large apertures 62 at one end near the common plenum chamber and relatively
small apertures 64 at their other ends (as in FIG. 8) or apertures 66 of
uniform size disposed with a greater aperture concentration at the end of the
porous member closer to the common plenum chamber and a lesser concentration
of open area at the other end of the porous member ~as in FIG. 9~ or any
other desired configuration.
~9~37g33
The porous members 60 are preferably of channel shape and are
made of spring-like material having separate flanges 68 that fit snugly
within screen receiving grooves contained in the modules 32 and 34, as is
clearly shown in FIGS. 4A, 4B and 4C. Thus, air or other tempering medium
that is applied to the upper and lower elongated plenum chambers 18 and 20
is deflected by virtue of the arcuate deflectors 54 and the oblique remote
walls 55 together with the non-uniform filtering of the incoming gaseous
tempering medium by virtue of the non-uniformity of the porosity along the
length of the porous members 60 to provide a flow of tempering medium of
any desired flow pattern against each of the surfaces of the glass sheets
passing through the cooling station.
The porous members may be used to serve an additional purpose
of independently controlling the rate of flow of gaseous tempering medium
jnto each individual module supplied from a common plenum chamber. This
erables operating personnel to adjust the rate of flow of gaseous tempering
medium along the length of the gaseous bed in the cooling station 16.
Where required, the lower modules 34 have recessed outer portion
69. These recessed outer portions 69 are constructed and arranged in such a
manner as to provide clearance spaces for the rotating driving discs 14 to
enable the latter to have access to the edge of the glass sheets as the
latter pass between opposed modules.
In a specific embodiment of the invention, the slots are of uniform
width about 20 mils (approximately .51 millimeter) wide, although slot
widths ranging from about 10 mils-~approximately -.25 millimeter)=toll/32
inch (approximately 0.8 millimeter) wide are acceptable.
The modu]es have a wall thickness of 1/8 inch (approximately 3.2
millimeters) for the side walls and approximately 3/16 inch (approximately
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1(~987~3
4.8 millimeters) for the apertured walls. In the apertured wall surface
facing the glass sheets, the slots are parallel to one another and are
spaced from one another approximately 1/4 inch ~approximately 6.35
millimeters) along the length of the modules (transverse to th axis of
glass movement). The modules near the furnace exit extend obliquely of
said axis. Further downstream in the cooling station, the apertured walls
of the modules comprise four slots, each about 15 mils (approximately .38
millimeter) wide extending continuously along the length of the apertured
module wall normal to said axis.
The dimensions and arrangements described are subject to some
modification within limits, depending on various parameters enumerated
previously. It is also understood that the number and arrangements of slots-
of the modules further downstream in the cooling station may vary from the
exact number and arrangement shown. However, it is preferred to have three
to five slots per downstream module. A typical slot arrangement comprises
five slots equally distant to one another across the width of an apertured
wall of a module having successive widths of 21 mils (approximately .53
millimeter), 21 mils (approximately .53 millimeter), 15 mils (approximately
.38 millimeter), 21 mils (approximately .53 millimeter) and 21 mils (approxi-
mately .53 millimeter), respectively. Also, the width and separation of the
obliquely extending slots in the upstream portion of the cooling station 16
may vary to some extent, depending on the thickness of glass sheet being
treated. Generally, a higher cooling rate is needed for thinner glass sheets
than for thicker glass sheets so that a larger number of thinner, more closely
spaced slots is generally required for tempering thinner glass sheets than
for thicker glass sheets.
lG9~ 3
Jacks 70 are provided to engage the lower common plenum chambers
24 to adjust the position and orientation of the latter for alignment of
the lower elongated bed of the cooling station 16 with the bed 12 in the
furnace 10. The upper common plenum chambers 22 are provided with adjust-
ment means to raise and lower said upper common plenum chambers 22 to
control the vertical distance that the upper module walls 36 are spaced
above and parallel to the lower module walls 38. This distance varies
with the thickness of glass sheet being processed.
Typical operating parameters for the illustrative embodiment
of apparatus conforming to the present invention and results obtained there-
from will now be provided. The apparatus was provided with three opposing
pairs of rows of modules set at obliquities of 45 degrees through the module
wall thickness followed by five opposing pairs of rows of modules set at
obliquities of 7.5 degrees and followed by 17 opposing pairs of modules
having four slots each 20 mils wide in the first zones and 25 opposing pairs
of moduleslin the second zones of the first pair of common plenum chambers
followed by conventional supply pipes extending from the elongated plenum
chambers communicating with the additional four opposing pairs of common
plenum chambers.
Shadowgraph tests have been developed at PPG Industries, Inc.,
the assignee of this invention,as a means of determining the optical qualities
of glass sheets. In this test, a Balopticon projector located 25 feet
(7.62 meters) from a screen is set up in a dark room to illuminate the screen.
A glass sheet to be tested is supported betw~en the projector and the screen
and is oriented and its position ad~usted until the illumination pattern
has the worst non-uniform pattern obtainable. Its position relative to
the screen is adjusted while maintaining the aforesaid orientation until a
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1~987~3
position is determined where the pattern begins to appear or disappear
depending on the direction of glass sheet movement relative to the screen.
Generally, the optical properties are considered better when said position
is at a greater distance from the screen. While no standards have been
established yet in the United States, at Canadian Pittsburgh Industries,
a Canadian subsidiary of PPG Industries, Inc., a glass to screen distance
of 3 inches (76.2 millimeters) is considered acceptable for glass sheets
having a nominal thickness of 1/8 inch (3.2 millimeters) and a glass to
screen distance of 8 inches (203.2 millimeters) is considered acceptable
for glass sheets having a nominal thickness of 3/16 inch (4.8 millimeters)
based on shadowgraph test results.
The results of the shadowgraph tests are reported in units that
correspond to the distance in inches from the screen to the sheet where
the pattern begins to disappear. Thus, a value of 3 is the acceptable
standard for glass 1/8 inch (3.2 millimeters) thick and 8 is the accept-
able standard for glass 3/16 inch (4.8 millimeters) thick on the
shadowgraph test. Higher values than those listed as acceptable indicate
acceptable test units while values below those listed indicate that the
test units providing such results are usually unacceptable.
During a recent run on production apparatus constructed in
accordance with the illustrative embodiment previously described and using
standard operating conditions in the furnace and in the cooling station
whose first pair of opposing common plenum chambers were modified by use
of the module arrangement described previously, the following results
were obtained for random sheets of clear float glass 34 inches by 76 inches
(nominally 0.9 by 2 meters) of the thicknesses indicated.
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1~987~3
NOMINAL SURFACE SHADOWGRAPH ACCEPTABLE
GLASS COMPRESSION TEST SHADOWGRAPH
THICKNESSSTRESS (PSI)* SCORE STANDARD
1/8 in. (3.2 mm) 19,650 11 3
1/8 in. (3.2 mm) 19,484 13 3
l/8 in. (3.2 mm) 18,773 11 3
1/8 in. (3.2 mm) 18,887 12 3
1/8 in. (3.2 mm) 18,559 11 3
1/8 in. (3.2 mm) 17,900 13 3
3/16 in. (4.8 mm) 22,300 6 8
3/16 in. (4.8 mm) 22,073 10 8
3/16 in. (4.8 mm) 21,760 9 8
3/16 in. (4.8 mm) 22,272 9 8
3/16 in. (4.8 mm) 21,362 11 8
3/16 in. (4.8 mm) 22,130 10 8
3/16 in. (4.8 mm) 20,964 11 8
3/16 in. (4.8 mm) 20,480 11 8
* Surface compression stresses reported are the average of readings obtained
using the Differential Stress Refractometer at 9 different regions uni-
formly distributed on each sheet.
By way of comparison, the same production line having the
elongated plenum chambers installed in the cooling station provided with
so-called rosette modules of the type depicted in U.S. Patent No. 3,223,500
to Misson, developed shadowgraph test readings averaging 5.67 units during
production of glass sheets of nominal thickness of 3/16 inch (4.8 millimeters)
in glass sfieets of the same pattern size and in a corresponding temper range.
The results obtained indicated a combination of high stress
values with acceptable optical properties for the modified tempering
apparatus, thereby demonstrating the utility of the apparatus as modified
by the inclusion of modules arranged as taught by the present invention.
- 28 -
9~733
The form of the invention shown and described in this disclosure
represents an illustrative preferred embodiment and certain modifications
thereof. It is understood that various changes may be made without
departing from the gist of the invention as defined in the claimed subject
matter that follows.
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