Note: Descriptions are shown in the official language in which they were submitted.
~ WO 96/10~82 1 2 ~ ~ ~ 5 0 3 PCI'/GB95/02195
IMPROVE2~3NT OF PI-ATE GI.ASS EDGE STRENGT$
F;el~ of the Invent~on
This invention relates to the cutting, chamfering
and, orientation a pair of plate glass templates, e.g.,
those used to form a laminated windshield.
R~ckgrol~n~ of th_ Invention
T.~mi n~ted glass assemblies have been prepared by
bonding two plate glass templates together with an
intermediate plastics layer such as polyvinyl butyral layer.
These laminates have been widely used as windshields for
5 automobiles. The two glass templates have been made thinner
over the years to help reduce the weight of automobiles. In
order to improve their strength, the glass is generally
subjected to ~nn~ling or tempering. This th;nn~r glass
may be chipped or broken when a shock is delivered to the
20 edges of the glass, which may take place during
transportation of the glass or when the assembly is being
embedded in the frame of an automobile.
Methods have been proposed to improve the edge
strength of plate glass (float or sheet) and hence reduce
25 its fragility. U.S. patent 3,843,472 discloses improving
the edge strength of a glass article by abrading the edge of
the glass to smoothen or polish it and subjecting it to
chemical tempering and a rectifying treatment. Abrading or
grinding the edges of glass, also commonly termed
30 " chamfering" or "seaming", is routinely used in the glass
manufacturing industry to improve the edge strength of
glass. U.S. patent 4,075,381 discloses a method to improve
the edge strength of a laminated windshield by providing the
laminated windshield with a particular compressive stress in
35 the outer surfaces.
In forming a glass windshield two plate glass
templates 12 and 14 are positioned relative one another as
~ WO96/10482 ~ ~ PCT/GBg~/02195
shown in Fig. l, and would include therebetween in the
finished product an interposed plastic layer 16 to form a
laminated windshield. Plate glass template 12 has two major
surfaces, conveniently spoken of as surfaces #l and X2 in
s the glass industry. The #l surface is the smooth major
surface and faces outside toward the environment when the
windshield is installed in a vehicle. It is considered in
the glass industry to be the "smooth" major surface because
it is the surface in direct contact with the molten tin
during the float-bath production of the plate glass. Float-
glass processing is the conventional way of producing sheet
glass, used for automotive and architectural uses,
throughout the world. Major surface #2 is considered the
rough major surface, i.e., compared to major surface #l,
15 simply beca~se it was not formed in direct contact with the
molten tin bath. Plate glass template 14 of Fig. l
likewise has a smooth major surface, surface #4, and a rough
major surface, #3. Surface #4 would face the inside of the
vehicle when installed. Therefore, major surfaces #2 and #3
20 are in facing retention in a windshield assem~ly.
In current conventional production of a laminated
windshield, a first plate glass template, e.g., 12' of
Fig. 2, is formed by scribing an indentation into the rough
major surface of a glass sheet in a desired window pattern
25 and then the glass outside the scribed pattern is removed.
This cut edge (i.e., the edge adjacent major surface #2 of
template 12' of Fig. 2) is chamfered as shown as 22 in Fig.
2. The so-called '~uncut~ or ~broken~ edge (i.e., the edge
adiacent major surface #l of template 12' of Fig. 2) is
30 likewise chamfered as shown as 20 in Fig. 2. Plate glass
~emplate 14' of Fig. 2 (the second template in the
windshield) is produced differently from template 12' in
that, in current conventional production, it is smooth major
surface #4 which is scribed. The cut edge is chamfered as
35 shown as 26 in Fig. 2 and likewise the uncut edge is
chamfered as shown as 24 in Fig. 2. As discussed above,
rough major surfaces #2 and #3 are in facing retention, with
220 ~5~
-- 3
surface #1 facing the outside of the vehicle and surface #4
facing the inside of the vehicle when installed. It was
previously theorised that this is the optimal way to
manufacture the glass template pairs having the greatest
5 edge strength because any micro-cracks which may have been
formed in cut edges #2 and #4 would be "sealed up" as the
windshield is curved back toward surface #4 during
windshield shaping.
Japanese Patent 63069728 provides a method of
lo cutting a laminated glass sheet with a film in between by
grinding a V groove on both faces by a rotating diamond
wheel and then cutting the sheet with a cutting blade. The
upper and lower edges of the cut face resemble chamfered
edges and prevent the danger of cutting the hand etc.
However the edges of the cut faces would not have the
necessary edge strength required of a laminated windshield
It would be highly desirable if the edge strength
of the plate glass template pairs and the resulting
laminated windshield could be further improved. This would
20 reduce even further the number of template pairs and
windshields which are scrapped because of breakage during
storage, shipment, or attempted installation into a vehicle.
It would be further desirable if this could be done by a
less costly and time consuming method than that currently
employed in manufacturing windshields. The present
invention has unexpectedly been found to provide significant
edge strength improvements over those conventionally carried
out as described above and does so by a less complex method.
Summary of the invention
A first aspect of this invention is directed to a
first plate glass template and a second plate glass template
each having a smooth major surface and a rough major
surface, each of the major smooth surfaces only being
peripherally bounded by a chamfer formed at the cut edge,
and the first and second templates are joined together with
~McN~Ev S'~_T
2 2 0 ~ 5 0 ~
the rough major surfaces in facing retention. Such
templates are ugeful, e.g., in making a laminated windshield
including a plastic interlayer.
In accordance with a second aspect, the invention
s provides a process of forming a first plate glass template
and a second plate glass template each having a smooth major
surface and a rough major surface, the process comprising
the steps of: (1) forming a first plate glass template by:
~_t;~ T
~ WO96/10482 ~ 5 ~ 3 PCT/GB95102195
scribing an indentation into the smooth major surface of a
glass sheet in a desired pattern; removing the gIass outside
said scribed pattern to obtain the ~irst plate glass
template having a peripheral edge; and machining the
s peripheral edge of the first plate glass template to define
a chamfer coextensive with and removing the indentation; (2)
forming a second plate glass template by: scribing an
indentation into the smooth major surface of a glass sheet
in a pattern substantially identical to that of the first
template; removing the glass outside the scribed pattern to
obtain the second plate glass template having a peripheral
edge; and machl ni ng the peripheral edge of said second plate
glass template to define a chamfer coextensive with and
removing the indentation; and (3) joining said ~irst and
15 second plate glass templates with the rough major surfaces
in facing relationship.
The process preferably further comprises shaping
the pair of plate glass templates using heat to soften the
glass templates and form them into a desired contour, and
20 preferably is a process for forming a window, most
preferably being a laminated window. Advantageously, the
present invention increases the edge strength of pairs of
glass templates, increasing both the compressive and tensile
strength which the pairs exhibit when subjected to
25 compressive and tension loads on the edges, which improves
the ability of such glass templates to maintain their
integrity during handling, shipping, and installation.
In accordance with a further aspect, the invention
provides a window comprising first and second plate glass
30 templates each having a smooth major surface and an inner
rough major surface and having a thickness between about l.0
and 6.0 mm, each o~ the major outer smooth sur~aces only
being peripherally bounded by a chamfer formed at the cut
edge, said first and second templates being joined together
35 with the rough surfaces in ~acing retention.
~ WO96110482 2 ~ ~ ~ 5 ~ 3 P~ 95/02195
Rrief ~~escription of the ~r~wings
The invention will now be described further, by way of
example, with reference to the accompanying drawings, in
s which :-
Fig. 1 is a schematic ~iew o~ a windshieldincluding two plate glass templates and an interposed
plastic layer.
Fig. 2 is a sectional view illustrating a pair of
o prior art plate glass templates as are conventionally used
in manufacturing a laminated windshield.
Fig. 3 is a sectional view illustrating a pair of
plate glass templates according to an embodiment o~ the
present invention.
~et~ile~ ~escription of the ~referre~ e~hoc -ent
While the present invention is relevant to any set
of glass templates, e.g., those used to make windows, and
20 particularly laminated windows like windshields, it will be
described for simplicity in the following paragraphs
relative a windshield assembly embodiment of the present
invention. As discussed above, Fig. 1 shows a general
windshield assembly including two plate glass templates 12
25 and 14 and interposed plastic layer 16. According to the
present invention, first and second plate glass templates,
12 and 14 are formed (in either order) as follows. A first
plate glass template 12" of Fig. 3 is formed by scribing an
indentation into the smooth major surface of a glass sheet
30 in a desired pattern, e.g., a window pattern. Then the
glass outside the scribed pattern is removed to obtain the
first plate glass template having a peripheral edge. The
scribing of the glass in the desired windcw pattern and the
removal o~ the glass outside the scribed pattern can be
35 carried out in various ways as would be appreciated by those
skilled in the art in view o~ the present disclosure,
neither being critical to this in~ention. For example, the
-
3~ WO96110482 PCT/GB95/0219
-- 6
glass may be scribed with a scribing wheel as generally
carried out in the industry. Removal of the glass outside
the scribed area is often by mechanical, pneumatic, or
thermal techniques as would be known to those skilled in the
5 art. The peripheral edge of the first plate glass template
12" (Fig. 3) is machined, e.g., as by grinding or abrading,
to define a chamfer coextensive with and removing the
indentation. This results in a plate glass template 12"
having, on the cut edge, a chamfer 30 as shown in Fig. 3. A
second plate glass template l4" in Fig. 3 is likewise formed
by scribing an indentation into the smooth major surface of
a glass sheet in a pattern substantially identical to that
of the ~irst template (12" of Fig. 3). Then the glass
outside the scribed pattern is removed to obtain the second
lS plate glass template having a peripheral edge. As with the
~irst plate glass template, the peripheral edge of the
second plate glass template is machined, as by grinding or
abrading, to define a chamfer coextensive with and remo~ing
the indentation. The resulting chamfer in this cut edge is
20 shown as 36 in Fig. 3. The angle or the particular shape of
the chamfer is not critical to the invention, as it may be
rounded or flat. Preferably, however, the chamfers are flat
and at an angle roughly 45~ relative to the major smooth
sur~ace of the template. According to this in~ention, the
25 uncut edges 32 and 34 of templates 12" and 14",
respectively, are not machined (chamfered). Hence,
manuCacturing template pairs according to the present
invention is less costly than manufacturing as described in
the above prior art (Fig. 2) because it requlres that only
30 two of the edges, i.e., only the cut edges, are machined,
rather than all four edges as is conventionally done in the
prior art (Fig. 2).
In the present invention, the first and second
plate glass templates are joined with the rough surfaces
35 (major sur~aces ~2 and ~3 ) in facing retention. This is
not meant to suggest that the glass templates are adhered to
one another, they only need be placed with the rough
~ WO96/10482 ~ 2 ~ ~ ~ 5 ~ 3 PCT/GB9S/02195
surfaces in facing retention to one another. While it is
most preferable that the peripheral edges of each of the
plate glass templates are machined prior to joining the two
plate glass templates together, it may in some situations be
s preferred to machine the peripheral edge of the plate glass
templates after the templates have been joined together.
This embodiment is also within the scope of this invention.
As pointed out above, and as shown in prior art
Fig. 2, conventionally the edges adjacent each of the major
surfaces of each of the two glass templates used in forming
a windshield are chamfered, i.e., those adjacent surfaces
#l, X2, ~3, and #4 are chamfered In contrast, in the
present invention, only the edge adjacent surfaces #l and #4
are chamfered as shown in Fig. 3. Further, in the prior
art Fig. 2 templates in con_rast to those of this invention,
one of the templates is cu_ on the smooth major surface and
the other template is cut on the rough major surface.
While the inventors do not wish to be bound by theory, they
believe that the advantages realised from their invention
20 derive from the fact that in their invention, only the major
smooth surface has been subjected to scribing to form an
indentation and then the indentation formed by the scribing
(which later results in a cut edge, sometimes termed in the
industry a scored edge) is machined to remove the
25 indentation. It is beiieved that the ma~k; n; ng, which forms
the chamfer, removes the imperfections or micro-cracks which
occur in the region of the indention in the glass durlng
scribing and hence removes potential sites for the
propagation of future cracks. Additionally, by being
30 scribed on the smooth major surface, it is believed that the
glass is less likely to develop micro-cracks during the
scribing in the region of the indention. Thus, scribing only
in the smooth major surface and then machining so to remove
the indentation formed during scribing, is believed to
35 synergistically act to strengthen the glass template pairs.
Neither of the peripheral edges aajacent the rough major
surfaces are machined.
' ~ W096/10482 2 2 ~ ~ 5 ~ 3 PCTtGB9510219~
While the above discussions have focused on one
embodiment of the present invention, that directea to making
windshields using the invention process, the invention is
not meant to be so limited. The invention process can be
5 used in forming any window comprising tWO plate glass
templates, either with or without an interlayer, such as
side automotive windows, architectural windows, etc. The
particular glass composition employed in the present
invention, and its thickness, is not critical herein.
Commonly, a form of soda-lime-silica glass is used in most
automotive and architectural glazing, but any glass
composition may be employed. Generally, the glass plate
used in automotive or architectural glazing has a thickness
of between about l.o to 6.0 mm, although the templates o~
this invention are not to be so limited. In this invention,
the first and second plate glass templates may be of the
same or different thickness. In the case of windshields and
architectural glazing, the plate glass used is often
subjected to ~nn~l ing or tempering to improve the strength
20 of the glass and control its ~racture characteristics. In
many applications, a laminate is formed wherein the plate
glass templates are interposed with a plastic layer, such as
that made of polyvinylbutyral (~VC) or other polymeric
material. Preferably, the PVC layer so employed has a
25 thic~ness between about 0.5 mm and 4.0 mm, corresponding to
between about 0.020 inches to 0.160 inches. As would be
expected, if the joined glass templates are to have a
special configuration as for a windshield, they may be
subsequently shaped, e.g., as by subjecting the templates to
30 heat and a mould. This may involve passing the pair of
templates through a gas or electric hearth on a bending
fixture and allowing the glass templates to conform to a
mould by "sagging" or by subjecting the templates to heat
and pressure in a mould. Still other methods of shaping the
35 templates will be apparent to those skilled in the art in
view of the present disclosure.
WO96~10482 2 2 ~ PCT/GB95/0219
Thus, the most general embodiment of a final
product according to the present invention comprises first
and second plate glass templates each ha~ing an outer smooth
major surface and an inner rough major sur~ace and only each
s o~ the major outer smooth surfaces being peripherally
bounded by a chamfer formed at the cut edge. In this
product, the first and second templates are joined together
with the rough surfaces in facing retention. While the
invention process is directed to forming windows, as would
be appreciated by those skilled-in the art, the improvement
realised by the first and second plate glass templates could
be applied for other than windows, e.g., any automotive,
architectural, or structural pair of glass templates,
particularly laminates using first and second plate glass
15 templates.
Embodiments of the first and second plate glass
templates according to the present invention have shown
improved compression load and tension load edge strength as
compared to conventional chamfered glass as discussed above.
20 Details of such improved edge strength is discussed in
detail in the ~ollowing example and the accompanying
figures.
~x~ple
Windshield template pair embodiments of the
present invention were made ~s in the configuration shown in
Fig. 3, some heing formed into a laminated windshield by
adding a P~3 interlayer. For comparison, windshield
30 templates pairs (and also laminated windshield using such
templates) of the same glass composition and thickness were
made as in the con~iguration shown in prior art Fig. 2. The
edge strength of the template pairs and the laminated
windshield were tested 6 mms [0.24 inches] from the template
35 edge with the use of a three-point load device. As is known
in the industry, such a device is commonly used to measure
the mechanical tensile failure load required tO break glass.
~ WO96110482 ~ PCT/GBgS/0219~
- 10 -
The comparative example template pair and resulting
laminated windshield required a force of 10.6 and 14.3 kg
[24 and 32.2 lbs.], respecti~ely, to break the glass. In
contrast, the invention embodiment template pair and
s resulting windshield laminate required a force of 22.7 and
24 kg [51 and 54 lbs.], respectively, to ~reak the glass.
From these results, it is seen that present invention
embodiments of a template pair and resulting windshield
laminate displayed a 112~ and 68%, respectively, increase in
o the edge strength relative that o~ the comparative prior art
example. It was also found, that when a pair of templates
was made as described above for the invention embodiment,
but modified (to form another comparative example) by
chamfering the #2 and #3 edges (so that all four edges are
15 chamfered), the edge strength o~ this modi~ied comparative
example decreased. That is, the force required to break the
~lat template pair with four chamfered edges (#1, #2, #3,
and #4) decreased to 13.4 kg [30 lbs.] (~rom the 22.7 Kg
[51 lbs.] required for the invention embodiment with only
20 two chamfered edges, #l and #4).
~x~le II
Another common way to currently manufacture
25 windshields involves cutting the templates as described for
Fig. 2 prior art template pairs (i.e., cutting surfaces #2
and #4) but, in contrast to that shown in Fig. 2, except
that only the outer edges (near surfaces Xl and ~4) are
machined to provide chamfers 20 and 26. Thus, the edges
30 adjacent surfaces #2 and #3 are not chamfered. Comparative
example windshield templates were made in this modified way
from a soda-lime-silica glass. Using this same glass,
windshield templates were made according to embodiment of
the present invention as shown in Fig. 3. Windshield
35 template pairs as well as laminated windshields (with a PVC
interlayer) were subjected to the test described in
WO96/1048t ~ 2 ~ ~ 5 Q ~ PCT/GB95l02l95
Example I. A comparative template pair o~ this example
required 5.2 Kg [11.6 lbs.] to break the pair while the
invention embodiment pair in this example required 17.2 Kg
t38.6 lbs.] to break the pair. Thus, the invention
s embodiment pair displayed a 232 ~ increase in edge strength.
Similarly the comparative example laminated windshield and
the laminated windshield o~ this example were subjected to
the breakage test. The comparative example windshield
required 8 Kg tl8.0 lbs.] to break, while the invention
o embodiment laminated windshield required 20.9 Kg [47.0 lbs.]
Thus, the invention embodiment windshield displayed a 161
increase in edge strength over that of the prior art
comparative example.
