Note: Descriptions are shown in the official language in which they were submitted.
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SUPPORT RING WITH WEAR STRIP
BackRround of the Invention
1. Field of the Inventlon
This invention relates to a device for transferring hot glass
sheets, and in particular relates to th~ type of transfer device that re~urns
empty to a shaping station for shaping and/or transferring successive hot
glass sheets to a cooling station for heat strengthening or tempering.
2. TechnoloRY Problems and Patents of Interest
The prior art has provided devices for transferring hot glass sheets
which comprise an outline or ring-type mold of relatively rigid metal that
includes an outline upper surface which conforms to the shape of a glass sheet
to be transferred slightly inboard of its periphery. The glass sheet is
heated and either pressed to shape between an upper mold and the ring-type
mold or between complementary molds and subseguently transferred to the
ring-type mold or sagged by heat and gravity to the shape provlded by the
upper shaping surface of the mold. After the glass sheet is shaped, it is
transferred while supported on the ring-type mold to a quenching station where
it is quenched suddenly and rapidly by applying cold air blasts against the
supported lower surface and the upper exposed surface of the glass sheet.
Heating the glass sheet to its softening temperature followed by
sudden chilling develops a stress pattern characteristic of tempered glass
that includes a surface zone highly stressed in compression surrounding an
interior zone stressed in tension. This stress pattern reduces the tendency
of the tempered glass sheet to bre&k, particularly lf the surface zone is
highly stressed. Furthermore, if tempered glass is fractured, it forms a
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number of small particles that are less dangerous than relatively large,
~agged fragments that result from the breakage of untempered glass.
When a shaped glass sheet contacts a hot, heavy metal rail during
this rapid cooling, glass breakage can result from surface venting due to high
tension stresses established locally at the glass-metal contact areas. The
prior art has recognized ~hat the difference in heat conductivity between the
glass sheet supported on the mold and the relatively heavy metal mold ring
during rapid cooling causes these high tension stresses in the hot shaped
glass sheet in the areas contacting the glasq supporting rail. Hence, in
recent years, the art has developed a ring-like member having a glass sheet
supporting surface composed of non-metallic material having a low coefficient
of thermal conductivity to insulate the glass from the heavy metal ring mold.
One effective non-metallic material used as a glass engaging member of a
ring-type support consists essentially of a phenolic resin, preferably
polyphenyl formaldehyde, reinforced with fibers composed of an aromatic
polyamide composition. This reinforced material is popularly termed aramid
and will be so identified hereafter in this specification.
The material used to engage the glass is reinforced structurally
either by thickening its lower portion, which makes a ring-like member used as
a non-metallic tempering ring awkward to handle because of the thickness
needed for rigidity, or the glass engaging material is hugged and surrounded
by a relatively heavy metal rail slightly larger than the outline of the
supported glass sheet or otherwise reinforced to impart rigidity to the
non-metallic glass engaging material. Tempering ring structures comprising a
ring-like member of aramid reinforced with a hugging heavy metal support ring
have produced results superior to the prior art by maintaining the glass sheet
in contact with the fiber reinforced phenolic resin material in spaced
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relation over the heavy metal rail of the tempering ring. However, still
better results are desired to be consistent with an objective of manufacturing
larger glass sheets of more complicated shapes than in the prior art with even
less marking or venting than previously experienced.
U.S. Patent No. 3,586,492 to McMaster discloses a glass sheet
support for a press shaping apparatus. The support includes an endless ring
frame having teeth with extended edge portions that contact the surface of the
glass sheet along it periphery. A wire mesh is disposed over the edges for
contacting the sheet.
U.S. Patent No. 3,741,743 to Seymour discloses a glass sheet shaping
frame for engaging the peripheral portion of a glass sheet during shaping and
tempering. A pair of spaced apart rigid rail are positioned about the
periphery of the glass sheet and a screen member spans between the rails to
provide a glass sheet engaging surface. The screen member is preferably a
heavy gauge mesh overlaid by a fine wire mesh.
U.S. Patent No. 3,973,943 to Seymour discloses an outline ring~like
transfer device for supporting shaped glass sheets after they are shaped and
during the time they are rapidly guenched. The device includes a rigid,
outline metal rail having an outline slightly smaller than that of the shaped
glass sheet and a bar or plurality of closely spaced bar members of
non-metallic materi~l having a lower heat transfer coefficient than that of
the rigid metal rail. The bar members are mo~mted in hugging relation against
the rigid metal rail in position to conform to the outline rail. An upper
edge portion of the bar or bar members is disposed above the upper edge of the
rigid metal rail in a position to provide a glass sheet supporting surface in
spaced relation above the upper edge of the rigid metal rail. The bar or bar
members of the Seymour patent are composed of a laminated structure, such as
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fiber glass cloth or asbestos woven paper layers or the like, bonded together
with a silicone resin binder or a phenolic resin binder. The glass engaging
materials of this patent have been replaced by superior aramid materials
disclosed in the following patent.
U.S. Patent Nos. 4,282,026 and 4,361,432 to McMaster et al. disclose
the use of a helical spring wound over a solid heavy metal tempering ring
closely adjacent to the glass to space the glass from direct contact with the
heavy metal tempering ring and thus reduce the cooling rate differences
between the glass and the metal. The helical spring in these patents do not
shield the glass from direct exposure to radiation from a closely ad~acent
tempering ring.
U.S. Patent No. 4,356,018 to McMaster discloses a method and
apparatus for deep bending glass sheets. The lower bending mold is of a
ring-type construction and includes a wire mesh covering to prevent chilling
of the heated glass sheet when it is received by the ring mold for bending.
U.S. Patent Nos. 4,363,163 and 4,421,482 to McMaster disclose
non-metallic materials such as aromatic polyamid fibers wound around metal
rotating conveyor rolls. However, these patents are limited to the use of
such materials as a covering for rotating conveyor rolls for conveying hot
glass sheets during thermal treatment and do not suggest using these materials
to shield glass sheets from direct exposure to radiation from closely ad~acent
heavy metal tempering rings.
U.S. Patent No. 4,525,196 to Fecik et al. discloses a structure in
which an exterior metal rail slightly larger than the outline of the supported
sheet is used to reinforce a bar or bar portions of phenolic resin reinforced
with aramid fibers to provide a support plane inboard of the metal
reinforcement rail and above the upper edge of the metal reinforcement rail.
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The superior physical characteristics of the phenol resin ~preferably
polyphenyl formaldehyde reinforced by aramid aromatic polyamide fibers) is
discussed in this patent and its disclosure, including a detailed discussion
of these characteristics, and is incorporated within this specification by
reference. It is noted in passing that the glass engaging member spaces the
glass, particularly its edge portion, from the heavy metal reinforcement rail
but does not shield the glass from direct exposure to radiation from a closely
adjacent heavy metal reinforcing rail.
U.S. Patent Nos. 4,556,407 and 4,556,408 to Fecik et al. disclose
spaced metal rails supporting a plurality of blocks spaced above the level of
the metal rails to provide spaced support members of a non~metallic material
that support hot glass sheets for tempering. The glass engaging members are
adjustable in position relative to the spaced rails in both patents and may be
pivotal, as in U.S. Patent No. 4,556,407. The glass engaging members of these
patents do not shield the glass from direct exposure to radiation from closely
adjacent metal rails.
U. S. Patent Application Serial No. 07/590,713 of George R. Claassen
et al., filed October 1, 1990, provides a tempering ring construction that
further minimizes the thermal effect on the supported glass sheet due to a
support member. More particularly, a rigid steel ring is used to reinforce
the structural rigidity of an aramid ring-like member whose upper surface
engages the glass sheet. The aramid member is constructed and arranged above
the rigid steel ring in a position to shield the supported glass sheet's
marginal edge portion from substantial direct exposure to heat radiated from a
closely adjacent metal support ring when the metal support ring reinforces the
aramid ring-like member. The aramid ring-like member also insulates the glass
sheet from direct conduction of heat from the slower cooling support ring of
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heavy metal so as to permit the glass to avoid the establishment of steep
thermal gradients during quenching that cause high tension stresses in the
glass which may in turn cause glass breakage.
A preferred heat insulating material available commercially that is
useful for the glass-engaging ring-like member of this invention is a phenolic
resin, preferably polyphenyl formaldehyde, reinforced with aramid fiber
available from Spalding Fiber Company, Inc., of Buffalo, New York under the
tradename ARR-2~. The term "aramid" is a generic name for a class of aromatic
polyamide fibers, preferably synthetic aromatic polyamids that are high
molecular weight polymers in which amide linkages (CONH) occur along the
molecular chain. Aramid is available from E.I. duPont deNemours and Company,
Delaware, under the tradename KEVLAB~. While this material has preferred low
thermal conductivity properties, its durability after repeated exposure at
elevated temperature to sliding of the bottom edge corner connecting the
bottom ma~or surface of the glass sheet to its edge surface leaves something
to be desired. It is de~qirable to improve the durability of the insulation
material without significantly reducing the heat insulation properties of a
structure that improves the durability problem.
The~e and other benefits of this invention will be better
understood in the light of a study of a description of preferred embodiment
which follows.
Brief DescriDtion of this Invention
This invention provides a support rig for shaping and~or tempering
heat softened glass sheets that uses a thin metal foil between the
previously exposed upper glass sheet engaging 3urface of the insulating
member of non-metallic low thermal conductivity material and the sliding
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edge portion of the glass sheet. It has been found that a metal foil having
a thickness of on the order of 0.010 inch (0.25mm) or le~s provides a smooth
glass contacting surface that has better durability than the non-metallic
low thermal conductivity material and does not cause the resulting structure
to have heat-insulating properties significantly inferior to that of the
non-metallic low thermal conductivity material that is not covered by said
metal foil.
This and other benefits of this invention will be better understood
in the light of a description of a preferred embodiment and structural
equivalents that follows.
Brief Descri~tion of the Drawin~s
Figure 1 is a perspective view of a glass sheet ring incorporating
novel features of this invention.
Figure 2 is an enlarged cross-sectional view of a sheet supporting
portion of the ring depicted in Figure 1.
Figure 3 is a fragmentary side view of the supporting portion
depicted in Figure 2, with the supported glass sheet omitted for clarity.
Figure 4 is a view similar to Figure 2 of an alternate embodiment
of this invention.
Description of Preferred Embodiments
Although the present invention is illustrated in combination with a
ring type structure that may be used to both shape a hot glass sheet and/or
support a hot glass sheet during a cooling operation, preferably tempering,
it should be appreciated that the invention may be used in other operations
where excessive wear of non-metallic, thermally insulating materials is a
concern.
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Figure 1 shows a perspective view o a ring 10 supported by
frame 11 that includes an insulating structure comprising a plurality of
peripherally spaced, thermally insulating fingers 12, e.g. aramid fingers,
extending laterally inward over a metal support ring or rigid outline
rail 14 having the general outline configuration corresponding to that of a
glass sheet 6 to be supported. Referring to Figures 2 and 3, each finger 12
thermally insulates a supported glass sheet G from ring 10 and has an upper
surface 16 and a lower surface 18. Rail 14 is preferably a solid member
provided with a peripherally extending continuous outer frame portion 20 and
a plurality of spaced apart, inwardly extending pro~ections 22 whose upper
surfaces support the inner portions of a corresponding finger 12 along its
lower surface 18. A series of elongated clamps 24 are arranged in
end-to-end relation over different portions of the outer frame 20 of outline
rail 14. Each clamp 24, which is probably a rigid metal bar, is provided
with an attachment means 26. Although not limiting in the present
invention, in the particular embodiment shown in Figures 1-3, the attachment
means 26 includes one or more screws extending through clamp 24 which engage
a threaded aperture located along the outer frame 20 of outline rail 14.
Each finger 12 has an outer portion that rests on the peripherally extending
frame portion of rigid outline rail 14 and is clamped in sets by clamps 24
to rail 14. The exact number of fingers 12 secured to ring 14 by a
longitudinal curvature of rigid outline rail 14 depends on the size and
peripheral curvature of the glass sheet 6 to be supported. Clamps 24 and
attachments 26 secure the fingers 12 to rigid outline ra~l 14 so that each
finger 12 extends laterally inwardly over a corresponding inwardly extending
pro~ection 22 to provide circumferentially spaced supports for the perimeter
portion of a supported glass sheet in thermally insulated relation rom ring
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structure 10. In ~he particular embodiment of the invention shown ln
Figures 1-3, the inwardly directed end 28 of each finger 12 is flush with
the generally vertlcal face 30 of pro~ection 22, but such an arrangement i9
not required.
Rigid outline rail 14 is machined to be contoured to conform to the
elevational and marginal edge shape desired for the glass sheet G, with the
upper surface 32 of rigid outline rail 14 and pro~ections 22 inclined
downwardly and inwardly. When the rlng 10 is used to initially bend a flat
heat softened glass sheet, the spaced fingers 12 restlng on pro~ections 22
initially support a flat glass sheet G along its sharp edge corner formed
between its peripheral edge surface and its lower ma~or surface as depicted
in solid lines in Figures 2 and 4. After bending, glass sheet G is
supported along its marginal edge portion in an inwardly and downwardly
oblique plane parallel to upper surface 32 of rigid outline rail 14 and
upper surf~ce 16 of fingers 12. A finger 12 is preferably applied with its
inner end portion resting substantially flush on the upper surface 32 of a
corresponding pro~ection 22 before a clamp 24 secures a set of ad~acent
fingers 12 to the outer frame of outline rail 14 to improve the flush
contact between fingers 12 and pro~ections 22 of outline rail 14. Clamping
forces the fingers 12 to conform into the localized orientation of the rigid
metal pro~ections 22 of outline rail 14.
With continued reference to Figures 2 and 3, a covering 34,
preferably a metal foil such as but not limited to nichrome ribbon or the
like, is applied over upper surface 16 of each finger 12 before a set of the
latter is clamped to upper surface 32 of rigid outline rail 14 to provide a
wear strip that prctects each finger 12 against premature wear. Although
not required, the inwardly directed end 36 may be folded downward over the
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end 28 of finger 12. The thickness of foil 34 is such that the combination
of foil 34 and finger 12 has a heat conductivity that does not differ
materially from that of finger 12 without its cover of thin foil 34. Thus,
breakage of glass sheets in production has not increased appreciably and the
durability of the fingers 12 has increased appreciably.
Although not limiting in the present invention in one particular
embodiment, the fingers 12 were aramid members which were 2 inches long by
0.25 inch wide by 0.25 inch high (5.08 cm by 0.64 cm by 0.64 cm). The
fingers 12 were sized to overlay a 0.75 inch (1.91 cm) high rigid outline
rail 14 having 0.25 inch (0.64 cm) wide pro~ections 22 spaced 0.25 inch
(0.64 cm) apart and extending 0.50 inch (1.27 cm) from an outer portion 1.50
inch (3.81 cm) wide. The thin foil 34 was a nichrome ribbon having a width
of 0.25 inch (0.64 cm) and a thickness on the order of 0.010 inch (0.25 mm).
Figure 4 shows an alternate embodiment of this invention wherein a
metal foil 134 covers only the outer portion of surface 16 of finger 12
where the sharp glass edge corner slides over fingers 12. The surface of
the glass about its marginal edge comes into direct contact with an
uncovered inner surface portion of fingers 12 only after glass sheet sliding
over metal foil 134 due to bending is complete. The effect of any heat
capacity of the thin metal foil 134 on the glass edge is further reduced
without unduly raising the danger of damage to fingers 12.
It is also withln the scope of this invention to construct the
fingers 12 in such a manner that the laterally outer end of each of a set of
fingers is interconnected by an outer frame portion (not shown) which
overlays the upper surface 32 of outline ring 14 along outer frame 20.
Clamps 24 force the multifingered members, including both the fingers 12 and
outer connecting portions, to conform more closely to the upper surface 32
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of a local circumferential portion of rigid outline rail 14 when they clamp
the members thereagainst. If desired, the individual foll members 34 may be
interconnected in a similar manner.
It is also contemplated that the foil members 34 may be
individually glued to each finger 12. As an alternative, the foil 34 may be
laminated to a non-metallic insulating material prior to cutting and/or
shaping the fingers 34.
While the embodiments of this invention previously described have
been limited to those having laterally inwardly extending fingers, it is
understood that the thin foil may be applied to cover the upper glass edge
supporting surface of any insulating member having any convenient shape to
space a glass sheet from direct exposure to a metal outline ring and that
any convenient manner of securlng the thin foil to the tempering ring
structure other than clamping may be used to keep the foil interposed
between a bare glass engaging member of low heat capacity non-metallic
material and the glass without departing from the gist of this invention.
Conforming to the requirements of the patent statutes, the
inventors have described and illustrated what they presently consider to be
preferred embodiments of their invention. However, it is understood that
variations may be made within the limits defined by the claimed sub~ect
matter that follows without departing from the gist of this invention.
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