Note: Descriptions are shown in the official language in which they were submitted.
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BENDING GLASS SHEETS BETWEEN A BOTTOM OUTLINE MOLD
AN~ AN UPPER VACUUM PRESS FACE
Back~round of the Invention
1. Field of the Invention
This invention relates to shaping softened glass sheets to
non-uniform curved configurations by a combination of preliminary gravity sag
bending on a ring-type outline mold and final press bendinB between the
ring-type outline mold and a vertically aligned vacuum mold disposed above the
ring-type outline mold.
2a. Technical Considerations
One or a pair of glass sheets is commonly shaped by supporting the
sheet or pair on an outline bending mold having a shaping rail with an upper
surface whose elevational contours correspond to the final desired shape of
the glass sheet slightly within its perimeter. The glass sheet or pair is
heated to its heat softened temperature and sags by gravity to enable the
perimeter portion of the sheet or pair to assume the desired configuration.
This technique is particularly well suited for simultaneously shaping two
sheets of glass used subsequently as the inner and outer plies of a
conventional laminated automobile windshield.
As glass sheet configurations become more complex and include deeper
bend sections, the shaping rails may be segmented and made to pivot from an
open position for supporting a flat glass sheet to a closed position for
supporting a continuous perimeter portion of a heat softened shaped glass
sheet. In the closed position, the s~haping rails assume the desired
elevational contours of the glass sheet to be shaped slightly inboard of its
perimeter. However, outllne bending molds by themselves cannot control the
sag cf the glass sheet within the supported outline.
Another technigue involves bending molds used to shape heat softened
glass sheets or doublets to complex configurations by pressing the glass
sheets between a pair of aligned full surface press faces. Simultaneous
pressurized engagement of a heat softened glass sheet between full-faced press
faces may mar the optical properties of the press bent glass sheet.
Upper and lower full surface pressing molds have been used in
conjunction with an outline mold wherein a lower mold moves upwardly through
the opening within the rail of the outline mold to lift the glass sheet off
the outline mold and press the lifted glass sheet against a complementary
upper mold. Once the glas~ sheet is removed from the outline mold, it is
difficult to realign the shaped glass onto the outline mold for further
movement beyond the pressing stations. Also, when the shaping surface of the
lower mold must move through the outline mold, only those portions of the
glass within the boundary of the outline mold are pressed. The
circumferential area of the glass sheet contacts only the upper press face of
the lower mold. As a result, the glass sheets are not pressed to shape out to
their peripheral edge.
In order to enlarge the area of the glass that is engaged by the
lower pressing mold, outline molds have been modified so that end portions
thereof are separated from the central portion of the Mold to permit a lower
press bending mold with portions of larger size than the outline of the
outline mold to lift the glass throughout a greater extent, i.e. the portion
that extends beyond the end portion that is normally engaged by an outline
mold. Such a feature complicates the fabrication of an outline mold
structure. In addition, it may be difficult to precisely reposition the
pressed glasq shee~ as the lower mold retracts and deposits the glass sheet
onto the outline mold.
It is also known to convey heat softened glass sheets on a roller
conveyor into a press bending station where the glass sheet is lifted by a
lower mold either of a discontinuous ring-type arrangement or a series of
shaped slats and shaped either by inertia gravity sagging or by press bending
the glass against an upper complementary shaping mold. The upper mold in some
of these cases may also be apertured to provide a vacuum for holding the glass
after the glass has been shaped, and before the vacuum is terminated, to
reposition the bent glass sheet on a glass sheet conveying apparatus which may
be additional conveyor rolls or the outline shaping ring. If the bent glass
is lowered onto additional conveyor rolls, the shape imparted by press bending
may be modified. If the bent glass sheet is lowered onto a shaping ring for
further conveyance, it must be aligned perfectly with the outline shaping ring
to insure that the glass sheet remains shaped within required tolerances.
It would be advantageous to provide a system of bending glass sheets
wherein glass sheets are continuously supported on an outline bending mold for
their preliminary shaping by sag bending into contact with the outline bending
mold and further supported continuously on the outline bending mold while
pressed between the outline bending mold and a full surface vacuum bending
mold to impart a final configuration by a combination of full surface suction
from above with continuous outline mold support from below so as to minimize
the potential problem of marking the ma~or surfaces of the glass sheets when
the glass is fully engaged between a pair of full surface pressing molds.
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2b. Patents of Interest
U.S. Patent No. 2,131,873 to Goodwillie shapes one or a pair of
glass sheets by supporting the glass sheets on an upwardly facing concave
shaping surface of a solid lower mold, allowing the glass sheets to sa8 by
gravity to conform to the shaping surface, and pressing the sheets between the
lower mold and an upper solid mold having a complementary convex shaping
surface. The glass sheets remain on the lower mold throughout the sagging and
press bending operation and are enga8ed throughout their entire extent during
the final pressing, which mars the viewing area of the bent glass.
U.S. Patent No. 2,442,242 to Lewis heats flat glass sheets having a
straight leading edge while supported on flat strips until the leading edge
engages a straight rib. A pair of heated molds having complementary shaping
surfaces, sandwich the hot glass to impress a cylindrical shape thereon. The
patent is limited in its application to sheets having a straight edge.
U.S. Patent No. 2,570,309 to Black sag bends a glass sheet by
heating it while supporting the sheet on an outline ring-type mold to conform
to the mold by gravity sagging. The gravity sagged glass sheet is then lifted
on a lower solid preScing mold of concave election into pressing engagement
against an upper solid pressing mold of complementary shape. The lower mold
does not engage and press the outer peripheral areas of the glass sheet
against the upper mold. The bent glass sheet i returned to the outline
ring-type mold to support the bent glass sheet during cooling.
U.S. Patent Nos. 3,068,672 to Black; 3,408,173 to Leflet; 3,976,462
to Sutara; and 4,687,501 to Reese disclose outline metal molds for shaping a
glass sheet of non-rectangular outline to a nonuniform shape by gravity sag
bending. Black, Sutara and Reese each further disclose a sectionalized
outline metal mold for the gravity sag bending. No means is provided in any
patent to correct the uncontrolled sag in the unsupported regions of the
shaped glass sheet.
U.S. Patent No. 3,208,839 to Nordberg press bends as many as three
glass sheets to conforming shapes simultaneously using press b~nding
techniques exclusively for the shaping process.
U.S. Patent No. 3,476,540 to Ritter et al. shapes individual glass
sheets conveyed on rollers to a shaping station wherein each sheet in turn is
lifted sufficiently rapidly by an outline mold consisting of a plurality of
shaped bars to shape the glass by the so-called inertia gravity bending method.
U.S. Patent No. 3,554,724 to Ritter et al. combines the inertia
gravity bending method of the previous patent with peripheral engagement
against a supplemental shaping surface constructed and arranged to be
contacted by the upper surface of the glass sheet when the latter is lifted.
Neither of these last two patents contain any provision for correcting
unwanted sag within the supported margin.
U.S. Patent No. 3,573,889 to McMaster et al. discloses a method of
fabricating a shaped laminated windshield comprising press bending
horizontally deposed glass sheets individually between upper and lower
pressing molds. This process i9 limited to fabricating laminates of
relatively simple gentle curvature containing glass sheets 90 thin they must
be capable of flexing. In addition, the process is inefficient as each glass
sheet is shaped individually.
U.S. Patent ~o. 3,904,460 to Gomperatore individually press bends a
pair of glass sheets to slightly different configurations as required for the
inner and outer glass plies of a curved laminated windshield for automobiles.
The need to press bend the plies separately from each other before laminating
provides an operation where efficiency could be improved.
U.S. Patent Nos. 4,260,408, 4,260,409, 4,265,650 and 4,290,796 to
Reese et al. and 4,272,275 to Reese disclose the simultaneous shaping of a
pair of glass sheets having a non-rectangular outline of nonuniform curvature
in plan by combination of gravity sag bending and press bending using full
surface, upper and lower shaping molds.
U.S. Patent No. 4,756,735 to Cathers et al. shows a glass sheet
shaping method in which glass sheets are positioned on the shaping rail of an
outline shaping mold for movement through a heating lehr and subsequently
preliminarily sag bent. The mold with the glass sheet supported thereon is
positioned between a pair of vertically aligned full surface pressing molds.
The molds include selected press surfaces that extend beyond the perimeter of
the outline mold. As the lower mold moves upwardly through the outline mold
to lift the glass sheet off the outline mold, selected portions of the shaping
rail of the outline mold move outwardly to allow the lower mold to pass
through the position occupied by the outline mold. The glass is then pressed
between the upper and lower full surface pressing molds.
U.S. Patent No. 4,778,507 to Aruga et al. disclose~ a technique for
bending glass sheets heat sagged into their approximate longitudinal shape
about a transverse axis over an outline mold and completing the transverse
shaping about a longitudinal axis by a full surface pressing mold superimposed
over the gravity sagged glass sheet. The dimensions of the full surface mold
differs from that of the outline mold so as to minimize the amount of
simultaneous engagement of the heat softened glass sheets between the upper
full surface presslng mold and the lower bending mold during the flnal press
bending step.
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U.S. Patent ~o. 4,894,080 to Ree~e et al. discloses an in-lehr press
bending operating us1ng pressurized gas. Glass sheets are preliminarily
shaped on an outline bending mold and subsequently lifted off the outline mold
by a lower full surface press face and into engagement with an upper mold
having a peripheral shaping surface. The upper mold also includes a chamber
which is subsequently pressurized to urge the glass sheets against the shaping
surface of the lower mold.
S = arv of the Invention
This invention provides a method and apparatus for shaping glass
sheets wherein glass sheets are firRt sag bent by heat sagging to conform to
an outllne shaping mold positioned to support the sheet perimeter and provided
with complicated transverse bends by subsequently simultaneously engaging the
heat softened glass sheet between an upper continuous full-faced vacuum mold
while continuously supporting the glass on the outline shaping mold. The
glass is continuously supported from below on the outline shaping mold
throughout its shaping operation which includes preheating, gravity sag
bending on the outline shaping mold to impart the general desired peripheral
contour to the gla~s sheets, press bending the sag bent glass sheet between a
full-faced upper vacuum mold and the outline sag bending mold to impart the
final desired curvature to the glass sheet without harming the optical
properties of the bent glass and cool~ng the shaped glass sheets. Maintaining
the glass sheets in continuous contact with the outline shaping mold
throughout the bending and cooling operation avoids the possibility of
misalignment caused by non-continuous support on the outline sag bending mold.
Brief Descri~tion of the Drawings
Fig. 1, comprising Fig. lA and Fig. lB, is a longitudinal side view
of a glass sheet bending lehr arrangement in accordance with the present
invention. Fig. lA shows the upstream portion and Fig. lB shows the
downstream portion of the lehr, with certaln portlons omitted for clarity.
Fig. 2 is A transYerse schematic view of a shaping station showing
the essential elements of an outline mold and an upper full surface pressing
mold with the outline mold depicted in a position vertically spaced from the
pressing mold.
Fig. 3 is a sectional view taken along line 3-3 of Fig. 2.
Fig. 4 is 8 schematic view similar to that of Fig. 2 of a second
embodiment of this invention.
Fig. 5 is a partial sectional view similar to Fig. 3 showing an
alternate embodiment of the invention.
Detailed DescriDtion of the Invention
The present invention relates to shaping heat softened glass sheets
but it is understood that the invention may be used to shape any heat
softenable sheet material where it is critical that selected edge portions of
the sheet must be precisely and accurately shaped. In addition, the invention
may be used to shape a single sheet or multiple overlaying sheets. Although
not limiting in the present invention, the following discussion will be
directed toward shaping two overlaying sheets.
In the drawings, Figs. la and lb depict a heating, shaping and
annealing lehr for shaping glass sheets according to the present invention.
The lehr extends downstream from a loading zone 20 and includes a heating
zone 22 of tunnel type configuration, a gravity bending zone 24 downstream of
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the heating zone 22, a press bending or shaping station 26 immediately beyond
the gravity bending zone 24, an annealing æone 28 which may include a door 30
beyond the shaping station 26 and a cooling zone 32 in end to end relation in
a downstream portion of the lehr. An unloading zone 34 is beyond the cooling
zone 32.
Referring to Fig. ~, a pair of stub rolls 36 is shown extending
within the side walls (not shown) of the press bending station 26. A mold
support carriage 38 comprising a pair of supporting rails 40 which rides over
the rolls 36 and supports an outline bending mold 42. Although not llmiting
in the present invention, in the particular embodiment illustrated in Fig. 3,
the mold 42 includes one or more shaping rails 44 combined to form a ring-like
member conforming in elevation and plan outline to the peripheral shape of
glass sheets G supported on the upper edge surface of shaping rails 44 for
gravity sag bending slightly within the marginal perimeter of the glass
sheets G. A plurality of vertically extending uprights 46 interconnect the
mold support carriage 38 with the outline mold 42 so that the outline mold is
spaced above the carriage 38.
The press bending station 26 of Figs. 2 and 3 also contains an upper
vacuum press bending mold 48 having a downward facing shaping surface 50 with
a peripheral shape complementing the shape of the outline sag bending mold
42. Shaping surface 50 is curved as depicted in Fig. 3 to conform to the
final configuration to be imparted to the glass sheets G. A piston 52 is
attached to mold support carriage 38 to engage and lift a plate 54 affixed to
a cross beam on mold support carriage 38 so that the latter moves vertically
parallel to a fixed vertical axis that preferably intersects the geometric
center of the mold support carriage 38 and press bending mold 48 when the
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former is properly positioned wlthin press bending station 26. ~he details of
aligning the outline mold 42 and the mold support carriage 38 within press
bending station 26 are well known in the art and details thereof can be
obtained by reference to U.S. Patent No. 4,756,735 to Cathers et al., which is
incorporated herein by reference, and particularly at column 5, line 32 to
column 6, line 45.
In operation, a plurality of mold supporting carriages 38 each
supporting a pair of glass sheetq G positioned on shaping rails 44 of mold 42
are conveyed along the length of the shaping and anneallng lehr. One carriage
at a time comes to a stop and is positioned within shaplng station 26 so that
the mold 42 is aligned with the upper vacuum mold 48 as depicted in Figs. 2
and 3. By the time each outline mold 42 arrives at the press bending station
26, its supported glass sheets G have been sub~ected to elevated temperatures
for sufficient time to sag bend and generally conform their periphery to the
elevational contours of shaping rail 44.
Once positioned within shaping station 26, the piston 52 lifts the
mold support carriage 38 into a position wherein the upper heat softened glass
sheet, previously sag bent to conform to the upper shaping surface of the
shaping rail 44 of outline sag bending mold 42, engages the downward facing
shaping surface 50 of upper vacuum mold 48. The periphery of the heat
softened glass sheets is sealed against the shaping rail 44 of the outline sag
bending mold 42 so that when a vacuum is supplied through the upper vacuum
mold 48, the glass sheets develop the configuration of the downward facing
shaping surface 50 by differential pressure due to subatmospheric pressure
applied along shaplng surface 50. More particularly, because the upper mold
48 and shaping rails 44 seal the periphery of the heat softened glass sheets
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G, as vacuum is drawn through the upper mold 48 via outlet 561 the upper glass
sheet will be drawn into contact with its shaping surface 50. As the upper
glass sheet tries to separate from the lower glass sheet, a partial vacuum
between the sheets is formed which results in the lower glass sheet moving
along with the upper glass sheet. As a result, both sheets are shaped by the
vacuum mold 48.
Vacuum mold 48 is made of a ceramic material, as shown in Fig. 3 or
is metal, e.g. cast iron, stainless steel, or mechanite, and is provided with
a pattern of holes having a diameter of 3/16 inch on 2 inch centers (0.48 cm
on 5.08 cm centers). Vacuum has been supplied at levels ranging from 8 inches
to 30 inches (20.32 cm to 76.2 cm) of water column, for a vacuum hold time of
2 to 30 seconds with both glass sheets conforming to the transverse shape of
the downward facing shaping surface 50 of upper vacuum mold 48.
In order to further assure that the outline mold 42 is properly
aligned with the upper vacuum mold 48, an alignment device 58 may be
provided. Although not limiting in the present invention, in the particular
embodiment illustrated in Figs. 2 and 3, device 58 is a rod and cone assembly
which includes a downwardly extending rod member 60 attached to the support 62
for upper mold 48 and a cone receiving member 64 mounted on the mold support
carriage 38. Cone member 64 is positioned to receive rod member 60 as
carriage 38 is lifted to press the glass sheets G against upper mold 48. The
device 58 accurately aligns the carriage 38 relative to the upper mold 48
prior to its engagement with the glass sheets.
While the outline sag bending mold 66 is lifted by piston 52 in the
embodiment depicted in Figs. 2 and 3 and held for the time intervals at the
vacuum range described previously, it is also possible to have the sag bending
S~t~
mold 42 and its supporting mold support carriage 38 remain in a vertlcally
stationary position while lowering upper press bending mold 48 against the
upper maJor surface of the upper glass sheet supported on the outline mold 42
as depicted in Fig. 4. In either embodiment, outline mold 42 continuously
engages the glass sheet slightly inboard of the glas~ sheet edge on the
shaping rail 44 of the outline sag bending mold 42 for a sufficient time to
allow the vacuum mold 48 to provide sufficient vacuum to ensure the imposition
of its transverse shape as depicted in Fig. 3 without causing the sheets to
separate when bent as a pair.
It is understood that the time and vacuum level necessary to ensure
that the glass sheets do not separate from one another during the pressing and
vacuum shaping of glass sheets G when the pair is pressed between the upper
vacuum mold 48 and the lower outline mold 66 varies depending on the glass
sheet thickness and bending temperature.
After completion of the pressing and vacuuming shaping, the vacuum
is terminated and the vacuum mold 48 and outline mold 42 are separated, either
by lowering the outline mold 42 onto the stub rolls 36 (following the method
of Figs. 2 and 3) or raising the upper vacuum mold 48 (following the method of
Fig. 4), while continuing to support the glass sheets on outline mold 42. The
shaped glass sheets remain supported on rails 44 of mold 42 while the mold
support carriage 38 ~oves into the annealing zone 28 where the glass sheets G
are cooled at a desired cycle of cooling to develop the desired anneal in the
bent glass sheets.
Although the bending mold 42 as previously discussed include rails
44 that support the glass sheets G on the rail edge inboard the sheet
periphery, other types of rail configurations may be used. Referring to
Fig. 5, rails 144 of bending mold 142 have an L-shaped configuration so that
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the marginal edge portion 100 of the glass sheets G are fully supported on the
upper extended surface 102 of rails 144 about the glass sheet periphery. This
type of rail shape has been known to reduce marking of the glass sheets that
sometimes occurs when the sheets are supported inboard of the sheet periphery
on the edge of a shaping rail as shown in Fig. 3. It should be noted that
with an L-shaped rail configuration, during the final shaping operation, the
entire periphery of the glass sheets G are pressed between the upper vacuum
mold 48 and the rail 144 to more positively shape the marginal edge portion
100 of the glass sheets G.
It is understood that the schematic illustrations of this invention
depicted in Figs. 2, 3 and 4 provide sufficient basis for understanding the
principles of this invention and that additional structural details may be
found in U.S. Patent 4,756,735 to Cathers et al. However, the present
apparatus omits a full-face lower pressing mold, the lower mold pressing
actuating means that lifts and lowers the lower pressing mold and the
expanding outline mold arrangement which allows the lower mold to pass through
the outline mold, all of which are disclosed in the Caehers et al. patent.
The downward facing shaping surface 50 of upper vacuum mold 48 is
large enough to be coextensive with the area and outline of the glass sheets G
mounted on the outline sag bending mold 42. This enables the glass sheets G
to be engaged simultaneously between the rails 44 of outline mold 42 at a
slight distance inward of the perimeter of the glass sheets G on their bottom
surface and throughout their entire extent at their upper surface by upper
vacuum mold 48. This gives the glass sheets G a shape by suction without
inducing pad marks on the lower ma~or surface of the glass that results from
simultaneous pres~uriæed engagement of the entire glass sheet surface from
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above and below. In addition~ it is believed that the pad marking on the
upper major of the glass sheet will be less when the glass is shaped by the
vacuum ~s compared to pressing the glass between a pair of full surface
bending molds. The combination of full surface engagement from above and
perimeter engagement only from below imparts better optical properties in the
bent glass than full surface engagement of the outwardly facing ma~or surfaces
of the glass sheets.
It i8 understood that the press bending mold 48 may be provided with
a cover of woven fiber glass or other material that insulates the upper
surface of the glass G from direct contact with the surface 50 of bending mold
48 and also provides means for diffusing the flow of vacuum into the apertures
arranged throughout the entire extent of the upper vacuum mold 48.
It i9 also understood that when the outline sag bending mold 42 and
upper press bending mold 48 are separated from one another, it may be desired
to reverse the flow of vacuum and pressurize the interface between the
downwardly facing shaping surface 50 and the upper surface of the glass
sheets G momentarily to help release the upper surface of the glass from
contact with the vacuum mold 48 and retain the intimate contact between the
shaped glass and the outline sag bending mold 42 so that the glass does not
become displaced relative to its outline bending rails 44 that support the
glass around its perimeter portion.
The present invention may also be used to impart reverse, or "S
shape," curvatures in the central portions of the glass sheets. More
particularly, a pan mold (not shown) as disclosed in U.S. Patent No. 4,979,977
to Frank et al. which teachings are hereby incorporated by reference, may be
positioned within the rails 44 of the bending mold 42 to preliminarily form
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the reverse curve in the glass sheets. Press mold 48, being provided with a
shaping surface 50 that includes the final desired glass sheet curv~ture,
including the reverse curvature, would then be used to shape the glass sheets
in a manner as discussed earlier.
The form of the invention shown and described in this disclosure
represents an illustrative embodiment thereof and a variation thereof. I~ is
understood that various changes may be made without departing from the
teachings of this invention defined by the claimed sub~ect matter which
follows:
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