Note: Descriptions are shown in the official language in which they were submitted.
5 ~ !~
METHOD AND APP~ATUS TO REDUCE TIP CURL
BACKGROUND OF THE I~VENTION
_
1 Fleld of the Inventivn
.
This invention relates to sag bending of glass sheets in a
bending lehr and in particular to a method and apparatus to reduce tip
curl caused by sag bending complicated shapes in glass sheets.
2a. Technical Considerations
The techniques of sag bending to form shaped glass windows for
automobiles and the like, as disclosed in U.S. Patent 4,375,978 to Reese,
is well known. Glass sheets are positioned on and supported by a
skeletal bending mold. The shaping rail of the mold conforms to the
shape and final configuration of the glass sheet to be shaped, slightly
inboard of the edge of the glass. The bending molds are ~hen conveyed ln
succession through a heating lehr where the glass is heated to i~s
deformation temperature and begins to sag by gravlty until the glass
sheet conforms to the configuration of the shaping rail. After the glass
sheets have properly deformed, the molds are conveyed through an
annealing zone where the glass sheets are cooled, in a controlled manner,
from their deformation temperature through their annealin~ range to
anneal the glass sheets.
The glass sagging technique has been the method used to bend
two glass shee~s simultaneously, which sheets are subsequcn~ly laminated
together to form a laminated automobile windshield. The windshield is
curved to conform and blend into the shape of an automcbile vehicle in
which it is installed.
In recent years, automobile stylists have demanded more complex
and deeper bends in glass doublets used in windshields. When glass
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sheets are shaped to relatively deep bends, the length of the chord
between the ends of the bent glass ls shor~er than the distance between
the ends of the flat glass sheet before bending. Ln order to reduce
relative sliding between the glass ends and the shaping rail which marks
the glass, the mold rall comprises articulated rail sections including an
end rail section whose contour conforms to the outline and shape desired
for the longitudinal end portion of the glass sheet to be bent. The e~d
rail section is constructed and counterweighted to pivot downward into a
lower position to support the mass of a relatively stiff flat glass sheet
to be bent, and when the glass sheet is softened by heat, to pivot upward
into an upper position where it cooperates with additional shaping rails
to form a substantially continuous outline shaping surface conforming in
contour and elevation to the shape desired for the glass sheet. When the
desired final configuration is particularly complex such as required very
deep bends and/or reverse curvatures, the heat pattern within the lehr
can be adjusted to direct localized heat toward these critical bend
areas.
It has been found that with complex deep bends, the outermost
portions of the longi~udinal end portions, or tips, of the glass sheets
tend to curl and lift off portions of the end rail section causing the
sheets to deviate from desired tolerances. Thls tip curl is caused by
the tendency of the sheets to draw glass from its end sections whan there
is a deep sag or a reverse curve. It can also be caused by overheatin~
the tip areas to achieve proper curvature along the outer edge of the
longitudinal section, or A post, of the glass sheet. The local heat
tends to preheat the glass at the tip area causing it to rise off the end
rail section. The tip does not get a chance to relax and sag back onto
the end rail.
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It would be advantageous to develop a method of forming glass
sheets to the new complex and deep sag configurations while maintaining
the desired outline eonfiguration.
2b. Patents of Interest
U.S. Patent Nos. 4,015,969 to Brown et al. and 4,077,791 to
Oelke teach an apparatus for bending glass to a relatively sharp angle.
A contact assembly is positioned over the edge of the glass sheat and
engages a conductor element on a surface of the shee~ throughout the
bending operation. The contact assembly is held in positlve engagement
with the surface of the sheet by a spring mechanism so that contact is
maintained despite vertical translation of the conductor elements. When
the sheet is fully bent, contact assemblies must be rotated off the
surface of the glass to allow its removal.
U.S. Patent No. 4,173,461 to Ebata et al. teaches the bending
of hot glass sheets wherein thP edge of ~he sheet is positively clamped
to the top of a bending table to maintain one edge of the sheet against
the table during bending. The glass is heated to its deformation
temperature and droops on account of its own dead weight onto the table
where it assumes the contour and configuration of the top. The clamped
edge of the sheet remains in contact with the table throughout the
bending operation and the clamps must be removed in order to remo~e the
shaped glass.
U.S. Patent No. 4,193,785 to Bailey ~eaches the use of opposed
locator stops on a glass bending mold. The s~ops contact the edge of the
glass sheè~ to be~bent and exert-pressure on the ends of the shèet while
maintaining ~he sheet in proper relation to the mold throughout-the
bending operation. The loca~or stops contact only the edge of the glass
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and do not provide a means for maintaining positive contact of the glass
sheet against the bending mold.
Summary of the Invention
The present invention provides an apparatus for reducing the
movement of an edge of a glass sheet away from a shaping rall of a
bending mold while said glass sheet is conveyed through a heatin~ lehr on
the bending mold to heat. The apparatus includes an edge contacting
roller that biases the roller against the glass sheet edge against said
shaping rail as the glass sheet is conveyed through the lehr. The roller
is mounted on a pivotlng frame that pivots from a first pasition wherein
~he roller is spaced from the glass edge, to a second position wherein
the roller engages the glass edge. The frame is generally parallelogram
in shape and pivots in a plane generally perpendicular to the lehr. The
edge con~acting roller maintains a constant downward inclined orien~ation
relatlve to one of a side member of the frame while in contact with the
glass sheet edge. The apparatus further includes an air cylinder
pivotally connected to frame. The cylinder pivots the frame from the
first to the second position and maintains the biasing force on the edge
contacting roll against the edge when the frame is in the second
position. An actuator controls the air cylinder to pivot the frame to
the first position when selected portions of the glass edge are at a
selected location relative to the edge contacting roller.
The present invention also provides a method of reducing tip
curl of glass sheets supported on a shaping rail of a bending mold.
Selected edge portions of the hot glass sheet are contacted with a roller
that is biased against the selected edge portions to force the edge
portions against a shaping rail o~ the mold. The roller contacts the
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selected edge portions as mold is conveyed through a heating lehr. The
roller pivots from a first positlon wherein the roller is spaced from the
select edge portions of the hot glass sheet, to a second position wherein
the roller ~ontacts the edge. The angle of said roller is maintained
throughout its contact with the glass sheet edge.
Brief Description of the Drawings
FIGS lA and lB are longitudinal side views of a typical bend~ng
lehr showing the loading, heating, shaping, annealing, and unloading
sections.
FIG 2 is a perspective cross-sectional view taken through the
shaping station of the lehr showing hot glass sheets supported on a ring
mold and the preferred glass tip roller assembly of the present
invention, with portions removed for clarity.
FIG 3 is a elevational view of the preferred glass tip roller.
FIG 4 is a view through line 4-4 of FIG 3.
FIG 5 is an alternate embodiment of the present invention.
Description of Preferred Embodiment
A descriptlon of a preferred embodim~nt of the present
invention read in conjunction wi~h the drawings should enable the reader
to understand ~his invention more clearly.
Referring to FIGS lA and lB there is shown a hea~ing, shaping
and annealing lehr for shaping glass sheets. The lehr begins downstream
with a loading zone 10 and includes an initial heating zone 12 of tunnel
type configuration, a--gravity bending zone 14 downstream of the iniela
heating zone 12, an annealing zone 16, and a cooling zone 18 in --
end-eo-end relation in the downstream portion of the lehr.- An unloading
zone 20 is beyond the lehr.
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A conveyor comprised of a plurality of stub rolls 22 disposed
in transversely opposing longitudinally spaced relation extends the
entire langth of the l~hr and defines a path of movement along a
longitudinal reference line. As illustrated in FIG 2 each stub roll 22
is mounted on a shaft that extends through a sidewall of the lehr and is
connected to a conveyor drive means (not shown). The conveyor may be
divided lnto a number of sections, each driven from its own drive means
through conventional drive rod and gear means or chain drives or the
conveyor sections may be driven from a common drive through clutches in
any manner well known in the art.
The lehr includes a plurality of glass suppor~ molds 24, one of
which is shown in FIG. 2, each being supported by a mold carriage 26.
Although not limited in this invention, the mold 24 is an articulating
mold and includes 8 pair of cross bars 28 which support a number of
vertical posts 30. The vertical posts 30 support the ends of
longitudinal shaping rails 32. The su ff ace contours of the shaping rails
32 conform to the shape desired along the longitudinal edges of ~he glass
sheet G supported for bending on the mold 24. Longitudina~ members 34
interconnect the cross bars 28 to form a framelike structure adapted ~o
b~ supported on the mold support carriage 26 for movement in a directlon
transverse to the length of the glass shee~ G supported on the mold 24
through a conventional glass bending lehr. Moun~ed on members 34 are
hinge support posts 36 each of which supports a hinge 38 whlch includes a
weighted lever arm 40 adaptabla for pivo~ing in a substantially vertical
plane about an axis defined by the associated hlnge 38.
The mold 24 is also provided with two end mold section~ 42.
Each of the end mold sections 42 comprises an end rail section 44 whose
upper edge forms a surface conformlng an elevation and outline to the
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shape desired for one or the other end portion of the glass sheets G to
be shaped on the mold 24. Each end mold section 42 also includes an
outrigger 46 rigidly attached to the under surface of the end rail
sect~on 44. The outrigger 46 extends outward of the end mold section 42
toward one of the hinges 38 and is attached to the weighted lever arm
40. When the glass sheet becomes heat softened, the lever arm 40
provides a closing pressure that causes the end mold sec~ions 42 to pivot
from a spread position, in which they support the flat glass sheet G,
into a closed position, where the upper edges of the end mold sections 42
form continuations of the shaping surfaces provided along the upper edges
of the shaping rails 32 so that the shaping rails 32 and 44 form an
outline shaping surface to which the glass sheet G conforms when shaped.
Cross baxs 28 are mounted on support beams 48 of the mold
support carriage 26. The end portions of ~he cross bars 28 are rigidly
attached ~o rigid end frame 50 which includes vertiral posts 52, upper
carriage rail 54 and lower carriage rail 56. Lower car~iage rail 56
rides on the driven stub rolls 22 of the lehr, as the rolls convey the
mold 24 through the lehr as previously discussed.
FIG 2 shows glass roller assemblies 58 and 60 which are the
subjec~ of this invention as they are positioned at the lehr relative to
the support mold 24 and carriage 26. The assemblies 58 and 60 are similar
in construction. The follow~ng discussion will be directed to the
assembly 58 with the understanding that the discussion is applicable to
assembly 60 unless indicated otherwise. Referring now to FIGS. 3 and 4,
the glass roller assembly 58 includes a glass edge roller means 62 to
contact ~he edge of the glass shee~ G, a posi1Oning and biaslng means 64
to maintain the edge roller means 62 in contact with the glass sheet
edge, an actuating means 66 to activate the positioning and biasing means
64 and a support s~and 68.
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The edge roller ~eans 62 which contacts the edge of the glass
sheet G on end mold section rail 44 (see FIG 2) is inserted into the lehr
through opeuing 70 in lehr wall 72 and includes a glass contacting roller
74 mounted on one of the short sides of a parallelogram-shaped llnkage
assembly 76. The linkage assembly 76 which is comprised of an upper arm
78, a lower arm 80 and a roller bracket 82, has corresponding ends of the
upper arm 78 and lower arm 80 pivotally connected to the roller bracket
82 and the support stand 68, preferably by nut and bolt assemblies 84 and
86, respectlvely, such that the upper arm 78 is parallel to the lower arm
80. The roller bracket 82 preferably includes side plates 88, only one
of which is shown in FIG. 3, to which bolt and nut assembly 84 attach the
bracket 82 to the upper arm 78 and lower arm 80, and cross plate members
90. Roller 74 is preferably connected to the lower portion of the
bracket 82. If required, a spring 91 can be positioned between upper arm
78 and lower arm 80, and between support stand 68 and roller bracke~ 82
to remove any slack in the assembly 76. Although not limlted in thls
invention, the surface of the roller 74 which contacts ~he edge of the
glass sheet G is a ceramic material. In the preferred embodiment, a
ceramic tube 92 slips over an inner support shaf~ 94 and is held in place
by any convenient manner to allow rotation thereabout. It has been found
that the larger the diame~er of the ceramic tube 92, the more easily it
rotates about shaft 94. As an alternative, a metal tube used wleh high
temperature bearings could be used to replace ths ceramic tube 92.
With the roller 74 in a horizontal orientation, the biasing
force on the glass edge tends to buckle the glass sheet as the roller 74
approaches tip 96 of the glass shee~ G along A post edge 98 (see FIGS. 2
and 3). To help eliminate the buckling, the roller 74 is preferably
inclined downward a~ an angle X to reduce this force. FIG. 3 illus~rates
s~
the inclination of the glass sheet G as it is supported on the end rail
section 44. This angle is commonly referred to as the approach angle Y.
As can be seen, if the roller inclination angle X of the roller 74 is
greater than the approach angle Y, inboard end 100 of the roller 74 would
contact the upper surface of glass sheet G rather than the surface of the
roller 74 contacting edge 98, resulting in marking of the glass sheet G
or marking of a paint band (not shown) around the perimeter of the glass
sheet G. As a result, angle X should be less than angle Y.
Although not limited by this Invention, in the preferred
embodiment the support stand 68 includes a pair of spaced channel members
102 with upper arm 78 and lower arm 80 rotatably positioned
therebetween. Channels 102 are secured on a mounting plate 104 which is
slidably secured on base plate 106 via nut and bolt assemblies 108. Slot
pairs 110 and 112 in the base plate 106 allow support stand 68 and base
plate 104 to slide toward and away from the lehr wall 80 that the roller
74 can be properly aligned with ~he edge 98 of the glass sheet G to be
shaped, or completely removed from engage~ent with the glass sheet G.
The base plate 106 is rigidly attached to a tube support 114 which
supports the glass roller assembly 58 outside the lehr.
The linkage assembly 76 is pivoted by the positioning and
biasing means 64, which preferably is an air cylinder 116 mounted on
cylinder support plate 118 which is.the support stand 68, and linked to
the upper arm 78 through linkage arrangement 119. As show~ in FIG. 3,
the cylinder and 122 o~ air cylinder 116 rota~ably connec~ed to support
angle 124 and eye bracket 126 on cylinder support plate 118.
Reciprocating-arm end 120 is pivotally pinn~d to leg portlon 128 of
L-shaped link 130 which in turn 1s pivotally mounted through mount 132 on
plate 118. The other leg portion 134 of L-shaped link 130 is pinned ~o
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support frame llnk 136 which is pivotally connected to upper arm 78 of
assembly 76. As the reciprocatlng arm 120 of the air cylinder 116
retracts, the L-shaped link 130, which is fastened to reriprocating arm
end 120 through a clevis member 138, pivots counterclockwise about pin
140 on the mount 132. This pivoting action translates into a
counterclockwise rotation, as viewed in FIG. 3, of the linkage assembly
76 about the support stand 68 through link 136 which is pivotally
connected at one end ~o the L-shaped link 130, and the other end to the
upper arm 78. When the reciprocating arm end 120 extends ou~wardly from
the air cylinder 116, the previously described actlon is reversed: the
link 130 pivots clockwise, as viewed in FIG. 3, about pin 140, and
assembly 76 pivots clockwise about nut and bolt assemblies 86.
Although the air cylinder 116 is the preferred positioning and
biasing means, other mechanisms such as hydraulic cylinders or a cam and
spring ~rrangement can be used to move and bias the roller 74.
It should be noted that as tha assembly 76 is rotated by the
air cylinder 116 or by the roller 74 contacting and riding the edge 98 of
the glass sheet G, the angle X of the roller 74 remains constant due to
the geometric properties of the assembly 76. The assembly 74 is a
parallelogram, that is, a four sided figure wi~h opposite sides parallel
and equal. As the assembly 76 rotates, it maintains a parallelogram
shape. The nut and bolt assemblies.86 maintain corresponding poin~s on
the upper arm 78 and lower arm 80 at support stand 68 in an orientation,
one vertically disposed above the other so the orientation of the roller
bracket 82 also remains vertical as the assembly 76 rotates. Since the
roller 74 is fixed to the to the bracket 829 ~he angle X of the roller 74
rema~ns constant.
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With continuing reference to FIGS 3 and 4, the air cylinder 116
ls activated by actuator means 66 whlch includes an elongated L-shaped
pivoting trip arm 142 mounted to the underYide of base plate 106 by
pillow blocks 144. End 146 of the trip arm 142 is positioned within the
lehr and extends downward wi~h a tip portion 148 generally aligned with
and terminating adjacent to the upper surface 150 of the upper carriage
rail 54 of the rigid end frame 50. As ehe mold support carriage 26 is
conveyed through the lehr, the tip portion 148 contacts teading end 152
of a trip plate 154 mounted on the upper surface 150 of the upper rail 54
cf the carriage 26 causing the trip arm 142 to rotate clockwise, as
viewed in FIG. 4, about an axis defined by the pillow blocks 144. This
rotation of trip arm 142 rotates a tab 156 at end 158 of ~he trip arm 142
into contact with a microswitch (not shown) positioned in close proximity
to the tab 156, which activates the air cylinder 116. After this lnitial
rotation, the tip 148 rides along the top surface 160 of trip plate 154
and maintains its rotated position so that the tab 156 remains in contact
with the microswitch. As the mold support carriage 26 continues to move
through the lehr, the tip 148 slides down trailing end 162 of the trip
plate 154 &llowing the trip arm 142 to rotate counterclockwise, as viewed
in FIG. 4, thus rotating the tab 156 to its i~i~ial position9 breaklng
its contact with the microswitch and deactivating the air cylinder 116.
The length of the trip plate 154 and the conveying speed of the mold
support carriage 26 determines the amount of time that the tab 156
maintains contact with the microswitch and thus the t~me interval that
the air cylinder 116 remalns activated.
The reciprocating action of the air cylinder 116 is controlled
by the aforementioned microswltch (not shown). When end portion 146 of
the trip arm 142 is in a vertical position and tab 156 is not in contact
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with the microswitch, the air cylinder 116 is retracted and the roller 74
is in a raised position. When the microswitch is engaged by the tab 156
due to the rotation of the trip arm 142 upon contact with the trip plate
154, the air cylinder 116 is pressurized causing reciprocating arm end
120 to extend outwardly, moving the roller 74 downward into engagement
with the glass sheet G.
It is obvious that there are other ways well k~G~t in the art
to actlvate the air cylinder 116. For example, two activator tabs could
replace trip plate 154 such that the first activstor tab would ro~ate
trip arm 142 to contact a microswitch which would activate air cylinder
116. Pressure in the cylinder could be maintained after tab 156 rotates
out of contact with the microswitch until the mlcroswitch i3 contacted a
second time, due the rotation of the trip arm upon contact with the
second activator tab. Another alternatlve would include the use of
sensors and timers that would locate the exact position o the glass
sheet G and support carriage 26 within the lehr, and activate and
deactivate an air cylinder based on a timing sequence.
As stated earlier, the air cylinder 116 is used to raise and
lower roller 74 as well as maintain pressure on the edge of the glass
sheet G through contact with the roller 74 to force it against the mold
end section rails 44 in critical sections. Flow control for the air
cylinder flow lines (not shown) automatically equalizes pressure in the
air cylinder 116 as the roller 74 contacts the glass edge 98 and rotates
the assembly 76 so that the pressure applied by the roller 74 remains
constant. The flow control for the air cylinder 116 also allows the
pressure applied to the glass edge 98 to be varied if required.
I~ opera~ion, the shape of the glass sheet G on the glass
support mold 24 determines if and when the roller 74 must be moved via
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the air cylinder 116. Generally, glass sheets are conveyed through the
lehr with the lcadlng edge being the top edge of the sheets as
installPd. If the shape of the glass sheet G is such that the inboard
end 100 of angled roller 74 would hit glass edge 98 and/or shaping rail
44 causing chipping or marking of the glass shee~ G, movement of the
glass sheet G on the rail 44, or damage to the roller 74, the roller 74
must be raised to allow this critical area of the mold 24 and edge 98 to
pass outboard of the inboard end 100 of the roller 74. The roller 74 can
thereafter be lowered until it contacts the glass sheet G.
The same considerations are present in determining when the
roller 74 should be lifted off the glass sheet after it has ridden up the
glass edge 98 and past the glass tip 96. The roller 74 can be raiqed
after it reaches its maximum elevation at the tip 96, or can be allowed
to slide down the trailing edge of the glass sheet. As stated earlier,
the length of the trip plate 154 and the lehr conveying speed will
determine how long the roller 74 will contact the glass sheet G.
If the glass shape is such that ~here will be no destructive
interference, the roller 74 and assembly 76 can be maintained in a
constant lowered position.
In order to provide greater flexibili~y and accuracy in
positioning changes as is required in glass pattern changeover, the
positioning of the glass roller assembly 58 can be automated in any
manner well known in the art. For example, individual dr~ves can be
positioned to slide the assembly 58 in a direction perpendicular to the
lehr. Cylinders or cam assemblies can be used to raise or lower the
asseDbly 58 or to tilt it to change the angle X of the roller 74, if
required. The entire positioning arrangemen~ could be controlled by a
preprogrammed computer that would automatically reposition ~he assembly
58 when a new glass pattern is being formed.
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It has been found tha~ on occasion, the downward force exerted
by the a~r cylinder 116 on the roller 74 to press the glass edge against
the end rail section 44 is suffic~ent to overcome the closing pressure
provided by the weightad lever arms 40 of the end mold section 42 wlth
the result that the end mold sections 42 open and the force on the glass
sheet G is reduced. To prevent this, a hinge locking member 164 is
attached to the end mold section 42 to lock it in a closed position after
it has closed normally (see FIG. 2). This allows the tip 96 and glass
edge 98 to be pressed against a rigid mold band.
During testing, it was found that the assembly 58 worked best
when placed at the end of the last lehr heating zone ~uæt prior ~o the
shaped glass sheet entering ~he annealing zone 16. At this poin~, the
glass is soft enough to be formed with the roller 74, yet it hardens
quickly once it passes the roller 74 and enters the annealing zone 16,
preventing the tip curl from reforming. Under production conditions, it
may be advantageous to position several assemblies 58 in the lehr. Each
succeeding roller 74 of the assembly 58 would provide some additional
force and movement ~o the glass until the tip curl is flattened.
In addition, to further li~it the downward move~ent of the
roller 74, an adjuseable stop 166 is mounted on the assembly 76.
Although not limited by this invention, ad~ustable s~op 166 includes a
nut 168 rigidly secured to the upper arm 78 and threaded bolt 170 passing
therethrough such that ehe lower tip 172 of the bolt 170 abuts mounting
plate 104. The downward travel of the roller 74 ls adJusted by rotating
threaded bolt 170.
An alternate embodiment of the presen~ invention is shown in
FIG 5. This embodiment retains the parallelogrsm-shaped assembly 76, the
roller 74, the roller bracket 82 and a modified support stand 174, but an
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adjustable spring assembly 176 replaces the air cylinder 116 to provide
the biasing force to the ~oller 74. A spring 178 of the spring assembly
176, which is mounted to push upward on the upper arm 78, is held in
position by bolt assembly 180 and is adjusted by rotating nu~ 182 upward
to increase the spring biasing force and downward to decrease the spring
biasing force. It is obvious that a spring assembly could be mounted
between roller 74 and support stand 174 to pull lower arm 80 downward to
achieve the same biasing result.
The forms of this invention shown and described in this
disclosure represent illustrative embodi~ents, and it is understood that
various changes may be made without departing from the scope of the
invention.
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