U.S. patent number 3,801,423 [Application Number 05/148,334] was granted by the patent office on 1974-04-02 for multiple glazing panel and manufacturing method therefor.
This patent grant is currently assigned to Glaverbel S.A.. Invention is credited to Pol Baudin, Robert Van Laethem.
United States Patent |
3,801,423 |
Van Laethem , et
al. |
April 2, 1974 |
MULTIPLE GLAZING PANEL AND MANUFACTURING METHOD THEREFOR
Abstract
A panel, and the manufacturing process therefor, having two
sheets of glass or vitrocrystalline material joined in facing
relation, that face of one sheet which constitutes an external face
of the panel being chemically tempered to induce compressive
stresses therein and being weakened to reduce its resistance to
breakage due to flexures of the type which apply tensile forces
thereacross.
Inventors: |
Van Laethem; Robert (Loverval,
BE), Baudin; Pol (Ransart, BE) |
Assignee: |
Glaverbel S.A.
(Watermael-Boitsfort, BE)
|
Family
ID: |
10074531 |
Appl.
No.: |
05/148,334 |
Filed: |
June 1, 1971 |
Foreign Application Priority Data
|
|
|
|
|
May 21, 1971 [GB] |
|
|
16283/71 |
|
Current U.S.
Class: |
428/155; 156/102;
156/106; 428/192; 428/332; 428/409; 428/437; 156/101; 428/161;
428/213; 428/333; 428/412; 428/442 |
Current CPC
Class: |
B32B
27/306 (20130101); C03C 23/00 (20130101); B32B
17/10981 (20130101); E04C 2/54 (20130101); B32B
17/10761 (20130101); C03B 23/023 (20130101); B32B
17/10018 (20130101); B32B 17/10036 (20130101); C03C
21/00 (20130101); B32B 1/00 (20130101); B32B
17/10899 (20130101); Y10T 428/24777 (20150115); B32B
2329/06 (20130101); Y10T 428/31507 (20150401); Y10T
428/31649 (20150401); Y10T 428/24521 (20150115); Y10T
428/2495 (20150115); Y10T 428/261 (20150115); Y10T
428/3163 (20150401); Y10T 428/24471 (20150115); Y10T
428/26 (20150115); Y10T 428/31 (20150115) |
Current International
Class: |
B32B
17/10 (20060101); B32B 17/06 (20060101); E04C
2/54 (20060101); C03B 23/02 (20060101); C03B
23/023 (20060101); C03C 21/00 (20060101); C03C
23/00 (20060101); B32b 003/02 (); B32b 005/14 ();
B32b 017/10 () |
Field of
Search: |
;161/116,119,120,121,123,164,193,199,82,44,45,183,203,204,117
;156/82,102,153,154,101 ;65/30,31,61,65 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Fritsch; Daniel J.
Attorney, Agent or Firm: Spencer & Kaye
Claims
We claim:
1. In a panel comprising a plurality of sheet components in facing
relationship, at least one of said sheet components being a first
main sheet of an at least substantially vitreous material which is
chemically tempered to have compressive surface stresses in
external layers at at least one face of said first sheet, which
face constitutes an exterior face of said panel, the improvement
wherein said first sheet is weakened at its said one face, whereby
the tensile strength in at least one region of said first sheet,
expressed in terms of the tensile force, imposable by flexing said
first sheet, which can be sustained by the compressively stressed
external layers at said one face of said first sheet is less than
the tensile force necessary for reducing such compressive stresses
to zero.
2. An arrangement as defined in claim 1 wherein the tensile
strength of said first sheet in at least one region thereof is
substantially uniformly lower than the tensile force necessary for
reducing said compressive stresses therein to zero.
3. An arrangement as defined in claim 1 wherein the said tensile
strength of said first sheet is substantially lower over the whole
area thereof than the tensile force necessary for reducing said
compressive stresses therein to zero.
4. An arrangement as defined in claim 1 wherein said one face of
said first sheet bears surface abrasions in at least one region of
said first sheet.
5. An arrangement as defined in claim 1 wherein said one face of
said first sheet bears surface scratches in at least one region of
said first sheet.
6. An arrangement as defined in claim 5 wherein said one face of
said first sheet is provided in at least one region thereof with
surface grooves having a depth of less than 5 microns.
7. An arrangement as defined in claim 1 wherein said first sheet is
of glass and external layers of said first sheet at said one face
thereof contain fluorine ions.
8. An arrangement as defined in claim 1 wherein said tensile
strength of at least one region of said first sheet is less than 50
kg/mm.sup.2 as measured on a disc of the material of said first
sheet 11 cm in diameter.
9. An arrangement as defined in claim 1 wherein there is a second
main sheet constituting another one of said components, said first
sheet is in facing relationship to said second sheet, and said
first and second sheets are directly connected only at the margins
of said panel.
10. An arrangement as defined in claim 1 wherein said sheet
components of said panel are secured together over their entire
surface area.
11. An arrangement as defined in claim 1 wherein there is a second
main sheet constituting another one of said components, said first
sheet is in facing relationship to said second sheet, and said
second sheet is arranged to be flexed toward said first sheet, by a
flexing force acting against the face of said second sheet which is
directed away from said first sheet, to cause said second sheet to
impose flexing forces on said first sheet sufficient to break said
first sheet before said second sheet breaks.
12. An arrangement as defined in claim 1 wherein said first sheet
is held in said panel in a state of elastic flexure such that its
outer face is in a state of tension or reduced compression.
13. An arrangement as defined in claim 1 wherein there is a second
main sheet constituting another one of said components, said first
sheet is in facing relationship to said second main sheet and said
second sheet is of plastic material.
14. An arrangement as defined in claim 1 wherein said components
include in addition to said first sheet, only one second main sheet
of an at least substantially vitreous material, and said first
sheet is in facing relationship to said second main sheet.
15. An arrangement as defined in claim 14 wherein the relative
inherent strengths of said first and second sheets are such that,
independently of each other, the resistance of said first sheet to
breakage by flexure subjecting its said one face to tensioning
forces is higher than the resistance of said second sheet to
breakage by flexure which subjects to tensioning forces the face of
said second sheet which faces said first sheet in the assembled
panel.
16. An arrangement as defined in claim 14 wherein said second sheet
is of glass and over at least one region of said second sheet its
face which faces inwardly in said panel is substantially free from
flaws liable to cause stress concentrations when tensioning forces
are applied to said inner face of said second sheet.
17. An arrangement as defined in claim 14 wherein external layers
of said second sheet at said inner face are compressively
stressed.
18. An arrangement as defined in claim 17 wherein said compressive
stressing of said external layers at said inner face of said second
sheet is due at least in part to said second sheet being chemically
tempered.
19. An arrangement as defined in claim 17 wherein said second sheet
is held in said panel in a state of elastic flexure in a direction
such that compressive stresses are present in said external layers
of said second sheet due to such flexure.
20. An arrangement as defined in claim 19 further comprising a
frame in which said sheet components are held in such a manner that
said second sheet is held in said state of elastic flexure.
21. An arrangement as defined in claim 19 wherein said second sheet
is held in said state of elastic flexure at least in part by said
first sheet.
22. An arrangement as defined in claim 14 wherein said second sheet
is chemically tempered, the tensile strength of at least one region
of said second sheet, expressed in terms of the tensile force,
imposable by flexing said second sheet, which can be sustained by
the compressively stressed external layers in the face of said
second sheet facing away from said first sheet in said panel, being
less than the tensile force necessary for reducing such compressive
stresses to zero.
23. An arrangement as defined in claim 22 wherein said second sheet
bears surface abrasions over substantially the whole of the face
thereof facing away from said first sheet in said panel.
24. An arrangement as defined in claim 22 wherein second sheet
bears surface scratches over the face thereof facing away from said
first sheet in said panel.
25. An arrangement as defined in claim 22 wherein said first and
second sheets have said lower tensile strengths at regions which
are in registry with each other in said panel.
26. An arrangement as defined in claim 14 further comprising at
least one intervening sheet of organic material securing said first
and second sheets together.
27. An arrangement as defined in claim 26 wherein said intervening
sheet is of a thermoplastic selected from the group consisting of
polyvinyl butyral, polyvinyl chloride and a polycarbonate of a
bis-phenol and having each of said first and second sheets attached
to a respective surface thereof.
28. An arrangement as defined in claim 26 wherein said intervening
organic sheet is arranged to resist penetration or tearing when at
least one of said first and second sheets breaks under the impact
of a rounded object weighing 10 kg dropped from a height of about
620 cm.
29. An arrangement as defined in claim 14 wherein said second sheet
is thinner than said first sheet.
30. An arrangement as defined in claim 29 wherein said first sheet
has a thickness in the range of 1.5 to 4.0 mm and said second sheet
has a thickness in the range of 1.0 to 2.5 mm.
31. An arrangement as defined in claim 1 further comprising a
covering sheet covering said one face of said first sheet, said
covering sheet not being a strength member.
Description
BACKGROUND OF THE INVENTION
This invention relates to processes of making a panel composed of a
plurality of sheets in facing relationship, including a sheet of
glass or vitrocrystalline, including vitroceramic, material
providing an exterior face of such panel. The invention also
relates to panels formed by such processes.
As will become clearer from the present disclosure, the sheets of
such panels can be of any material, a substantial portion of which
is constituted by a vitreous phase. The proportion of the material
constituting such phase need only be large enough to enable
modifications in the properties of the vitreous phase to
significantly influence the properties of the sheet as a whole.
It is known to increase the tensile strength of glass by thermal or
chemical tempering. The tempering treatment sets up compressive
stresses in external layers of the glass. Such compressive stresses
confer on the glass sheets mechanical properties which are
advantageous for various purposes. In particular, the compressive
surface stresses influence the tensile strength and the breakage
characteristics of the glass sheets in ways which are of value for
various practical uses of the sheets, e.g. for their use as glazing
material.
Unfortunately, while it is possible by a tempering treatment to
give the glass sheets mechanical properties which are required for
various purposes, all of the manifold effects of tempering are not
always compatible with the particular product specifications to be
complied with so that a compromise has to be made. For example, the
tempering of a sheet of glass alters its breakage characteristics
in the sense that the sheet breaks into smaller pieces than do
untempered glass sheets, and at the same time the tempering
increases the tensile strength of the sheet so that it is more
resistant to breakage by flexing forces. The tempering treatment is
therefore not wholly beneficial in cases where one but not another
of these effects is required.
The problem arising from the interdependence of different
properties is particularly marked in the case of panels
incorporating a sheet of glass in facing relationship to another
sheet of glass or other material because the mechanical properties
of the panel are then determined by a larger number of
parameters.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to overcome, or at
least substantially reduce, these drawbacks and difficulties.
Another object of the invention is to provide a greater selection
of the properties of such panels.
Still another object of the invention is to permit the properties
of such panels to be made to conform more closely to that desired
with regard to a wide variety of criteria.
A further object of the invention is to modify the effect of
tempering on the sheets of such panels in a controlled manner.
The present invention provides a process of making a panel composed
of a plurality of sheets in facing relationship, including a sheet
of glass or vitrocrystalline material providing an exterior face of
the panel, which process enables certain properties which have
hitherto been regarded as interdependent to be independently varied
so that a wider range of performance requirements can be
satisfied.
According to the present invention, a process of making a panel
composed of a plurality of sheet components in facing relationship,
including a sheet of glass or vitrocrystalline material, is carried
out by subjecting that sheet, hereafter referred to as "the first
sheet", to an ion diffusion treatment to induce compressive
stresses in external layers of the sheet material, the sheet
components of the panel are assembled so that one side of the first
sheet provides an exterior panel face, and at a stage before,
between or after the ion diffusion treatment and the assembly
operation, the first sheet is subjected, at least locally, on at
least the one side thereof, to a treatment, hereafter referred to
as "a weakening treatment", which reduces the resistance of the
first sheet in at least one region thereof to breakage due to a
flexure of the type which applies tensile forces to the external
layers which are at the one side of the first sheet and which are,
or become, compressively stressed due to the ion diffusion
treatment.
The term "vitrocrystalline material", where used in this
specification, denotes a material produced from glass by a
treatment which causes one or more crystalline phases to appear in
the glass while leaving sufficient vitreous phase or phases at the
surfaces of the material to permit compressive surface stresses to
be induced therein by an ion diffusion treatment.
On its face, the treatment of a sheet of glass or vitrocrystalline
material to cause any lowering of its tensile strength has no
proper place in a process of fabrication in which the sheet is
subjected to chemical tempering, this latter treatment being one
which has always been regarded as a toughening treatment, i.e.,
precisely a treatment for increasing the tensile strength of the
sheet. Nevertheless, it has been discovered, as part of the present
invention, that a chemical tempering treatment and a treatment to
reduce a tensile strength factor of the sheet can be performed on
one and the same sheet with important advantageous
consequences.
The process according to the invention enables a panel to be made
which has an advantageous combination of properties. In particular,
the yield strength, or tensile load level under which the first
sheet will yield, by breaking, is less than the value necessary to
overcome the compressive stresses which are due to the tempering
treatment. At the same time, due to the production of such
compressive stresses by chemical tempering, if the sheet does
break, it divides into relatively small blunt pieces. Moreover, the
yield strength of the first sheet can be controlled independently
of the compressive stressing. Consequently, a wide range of product
specifications can be achieved.
The extent to which the resistance of the first sheet to breakage
under tensile loading is affected by the weakening treatment can be
chosen in any given process, taking into account the contrary
effect or tendency of the selected chemical tempering treatment and
the particular circumstances in which the panel is to be used.
The chemical tempering treatment can be of any known kind based on
the diffusion of ions into glass or vitrocrystalline material from
a contacting medium, preferably in molten state. Thus the tempering
may be achieved by causing ions in exterior layers of the glass or
vitrocrystalline material on at least one side of the first sheet
to be replaced by larger ions deriving from a contacting medium,
while the temperature of such layers is too low to permit complete
stress relaxation in the sheet to occur during the time. The ion
exchange may for instance involve the replacement of sodium ions in
exterior layers of the glass by potassium ions deriving from the
contacting medium. Alternatively, the tempering may be achieved by
causing ions in exterior layers of the glass or vitrocrystalline
material on at least one side of the sheet to be replaced by ions
which confer on the exterior layers a lower coefficient of thermal
expansion, such substitution occurring at a temperature
sufficiently high to permit stress relaxation to occur. The
exterior layers then become compressively stressed when the sheet
cools. The ion exchange in this type of chemical tempering
treatment may for example be an exchange of sodium ions in exterior
layers of the glass for lithium ions deriving from the contacting
medium.
The chemical tempering treatment may be one in which a diffusion of
ions into exterior layers of the glass or vitrocrystalline material
occurs only at one side of the first sheet. This will indirectly
cause compressive stressing of the external layers at the other
side of the sheet.
Needless to say, the glass or vitreous phase of the
vitrocrystalline material can be of any composition capable of
being chemically tempered. The particular ion diffusion employed
can be of any type capable of chemically tempering, i.e. inducing
compressive surface stresses in the particular material employed.
The diffusion treatment can also be of the cementation type
involving substantially a movement of ions in only one
direction.
The weakening treatment is preferably performed substantially
uniformly over at least one region of the first sheet. A
predetermined breakage characteristic is thus achieved with respect
to forces of similar magnitude acting anywhere in that region. Such
region or regions subjected to such weakening treatment may be
situated within a central and/or at a peripheral part of the
sheet.
For certain purposes it is advantageous for the weakening treatment
to be performed over substantially the whole or at least the one
side of the first sheet. The weakening treatment can then be more
easily performed as part of an industrial process, there being no
need to take measures to confine the treatment to a predetermined
region or regions of the sheet area.
The weakening treatment can in some cases advantageously be
performed only on the one side of the first sheet. The treatment
can then normally be more easily and rapidly effected.
However, such weakening treatment can be performed on both sides of
the first sheet if desired. If such weakening treatment is
performed on both sides of the first sheet before the panel
components are assembled, the treated sheet can be located in the
panel with either side thereof exposed.
If diffusion of ions into the first sheet occurs only at one side
thereof, it is preferable for that side to be employed as an
exterior panel face and for the weakening treatment to be performed
at least on that side of the sheet. If this condition is observed,
a required predetermined resistance to breakage due to flexure in
one direction can be more easily achieved.
One preferred type of weakening treatment is carried out by surface
abrasion of the first sheet. This type of treatment is inexpensive
and simple to perform. When performing a chemical tempering
treatment on successive sheets, the yield strength thereby achieved
shows a certain variation from one sheet to another. The
performance of a weakening treatment by abrasion offers the
important advantage that the resistance to breakage can be brought
to a more uniform value from one sheet to another.
Abrasion can advantageously be effected using a particulate
material having an average grain size of the order of 10 microns.
With such abrasive substance, the weakening treatment can be
performed easily without causing undesirable defects in the sheet,
such as scratches visible to the naked eye.
Advantageously, the weakening treatment involves an abrasion of the
first sheet with a powder composed substantially of iron oxide,
cerium oxide, or alumina, or of a mixture of two or more of such
substances.
According to another type of weakening treatment, the weakening is
effected by surface scratching the first sheet. Preferably the
scratches are made entirely or predominantly in one direction. The
weakening effect is then greatest with respect to flexure forces
extending along planes substantially normal to the direction of the
scratches.
Before the weakening treatment, the first sheet, if it is a glass
sheet, can have at least its one side subjected, at least locally,
to a treatment, hereafter called "a supplementary strengthening
treatment", whereby the resistance of the glass to breakage by
flexure is at least temporarily increased in at least one region of
the sheet, such treatment being performed after chemical tempering
of the sheet but before the weakening treatment thereof. The
supplementary strengthening treatment has the effect of
facilitating the attainment of a predetermined degree of weakening
by the subsequent weakening treatment.
Advantageously, the supplementary strengthening treatment involves
a chemical dissolution of a surface layer of the first sheet in at
least one region thereof. This type of supplementary strengthening
treatment permits the required strengthening effect to be obtained
by a relatively brief contact of at least a given region or regions
of the sheet with a dissolving medium which may, e.g., be in liquid
or gaseous form.
The supplementary strengthening treatment can advantageously be
performed by contacting the first sheet in the region or regions to
be treated, e.g., by spraying, with an acid medium containing
fluorine ions, for example an acid medium essentially composed of a
compound such as ammonium fluoride or an aqueous solution
containing hydrofluoric acid.
It has been found that the use of an acid medium containing
fluorine ions not only gives better results in regard to mechanical
properties as before referred to, but also increases the resistance
of the glass to iridescence. This advantageous result is
particularly marked when use is made of an aqueous solution
containing hydrofluoric acid and sulphuric acid, e.g., solution
containing 6 percent by volume of hydrofluoric acid and 6 percent
by volume of sulphuric acid. With such an acid medium, satisfactory
results can be obtained very quickly, e.g., by a treatment lasting
only a few minutes.
Preferably the supplementary strengthening treatment by means of an
acid medium is performed at a temperature of between 0.degree. and
80.degree.C. In this temperature range the speed of dissolution of
the sheet material at a surface thereof can be accurately
controlled.
In the case of a glazing panel, e.g., a vehicle windshield, it is
desirable to ensure that the resistance of the first sheet to
breakage due to flexure forces tending to stretch, or tension, the
one side thereof is such that, in the completed panel, the first
sheet will break under the impact of a person against the opposite
side of the panel at impact forces below the level at which serious
injury, e.g. to the skull, becomes probable. Such level will
normally not be higher than that which corresponds to a tensile
loading of 50 kg/mm.sup.2 at the one side of the first sheet as
measured on a disc 11 cm in diameter. That maximum value may apply
over only a given region or regions of the sheet, but it preferably
applies over the whole area of the sheet. The safeguard against
serious bodily injury is then realized irrespective of the position
at which impact against the panel may occur.
In the fabrication of a panel according to the invention, the first
sheet can be secured in spaced relation to a second main sheet
component, i.e. a second strength member in sheet form, the first
and second sheets being directly connected only at marginal
portions thereof, and the space between the central parts of the
sheets being empty or containing a gaseous medium or a filling
material. The properties of the panel are then influenced by such
inter-sheet space or filling. Moreover, in the event of flexure of
the second sheet so that its inner face becomes convexly curved or
more convexly curved than originally, the first sheet is not
influenced by that flexure until it reaches a certain value which
depends on the spacing between the sheets.
However, according to preferred embodiments of the invention, the
sheet components of the panel are secured together over their
entire area to form a laminate. Such embodiments give a product in
which the behavior of the panel under flexing forces is always
influenced by the properties of the component sheets acting in
combination.
Particular importance is attached to embodiments of the invention
in which the first sheet is assembled in facing relationship to a
second main sheet component i.e., a second strength member in sheet
form, which second sheet can, in the completed panel, be flexed by
an amount to impose flexing forces on the first sheet sufficient to
break the latter sheet. The panel then has a very advantageous
combination of properties. If the panel is held at its margins and
becomes subjected to flexing forces imposed against the second
sheet, the first sheet will break at a given load while the said
second sheet is still capable of further elastic flexure. This
particular property of the panel is of importance for avoiding
concussive injury to a person who may make impact with the panel,
e.g. in the case that it is used as a vehicle windshield. Moreover,
when the first sheet breaks it divides into rather small and blunt
fragments which are not a serious accident hazard, e.g. to other
road users in the case that the panel is used in a road
vehicle.
Another very important consequence of the weakening treatment of
the first sheet used in the above embodiment, or other embodiments,
is that the maximum loading forces, as aforesaid, which the sheet
can support without breaking, is not dependent on the magnitude of
the compressive stresses induced therein by the chemical tempering
treatment. Moreover the first sheet can be of a thickness such that
it has a high resistance to breakage due to impact by small hard
objects such as stones, without losing the advantage that the sheet
will yield to loading forces of relatively small magnitude acting
against the other side of the panel.
In one form of panel according to the invention, said first sheet
is assembled in facing relationship to a second main sheet
component made of a plastic material. A plastic sheet can have a
very high flexibility, which is an advantage for shock absorption.
For forming a laminate, such sheet of plastic can be directly
bonded to the first sheet of glass or vitrocrystalline material
without an intervening bonding layer.
In preferred embodiments of the invention, the first sheet is
assembled in facing relationship to only one other strength member
in sheet form and that second sheet is also a sheet of glass or
vitrocrystalline material. The panel is then of simple
construction, and makes good utilization of the advantageous
properties of glass or vitrocrystalline material. In such
embodiments the sheets are preferably secured together to form a
laminate.
In optimum forms of such embodiments, the first sheet of glass or
vitrocrystalline material is secured in facing relationship to a
second sheet of glass or vitrocrystalline material to form a
laminated panel and the relative strengths of the first and second
glass or vitrocrystalline sheets, considered independently of each
other, are such that, notwithstanding the weakening of the first
sheet by a weakening treatment, the resistance of that first sheet
to breakage due to a flexure which subjects its one side to tension
forces is higher than the resistance to breakage of the second
sheet due to a flexure which subjects to tensioning forces the side
of the second sheet which in the completed panel faces the first
sheet. This condition is not inconsistent with the condition that,
in the completed panel, the first sheet should break under flexing
forces, imposed against said second sheet, of a magnitude
insufficient to break said second sheet, because in the completed
panel the component sheets behave as a monolithic structure up to
the moment of breakage of the first sheet, and under any given
flexing force the one side of the first sheet is subjected to
higher tensile loading than the side of said second sheet facing
the first sheet. The advantage of giving the first sheet the said
higher breakage resistance is that when the panel is used as a
glazing panel, e.g., as a windshield or in a door, the first sheet
is capable of absorbing a higher proportion of impact energies
before it breaks.
The relative strengths of the first and second sheets can be
attained by giving the first sheet an appropriately greater
thickness than the second sheet. Alternatively, if in order to keep
the weight of the panel below a certain value, or for other
reasons, the thickness of the first sheet must be less than that
which would be necessary, apart from other factors, for attaining
the higher strength, such strength can be attained by the chemical
tempering treatment or by this treatment and appropriate selection
of the thickness of the sheet.
Advantageously, the first sheet is secured to a second sheet, which
is of glass, and prior to the sheet assembly operation the second
sheet is subjected to a treatment, hereafter called a "rectifying
treatment", which reduces the incidence on at least one portion of
its inner face, i.e. the face which is to be directed toward the
first sheet, of flaws liable to cause stress concentrations when
the inner side of such sheet is subjected to tensioning forces.
Such rectifying treatment gives the second sheet greater resistance
to breakage due to flexure in the direction which places the inner
face under tension. While it is very advantageous to subject the
whole of the inner face of said second sheet to a rectifying
treatment, an improvement in the resistance of the sheet to
breakage by flexure can often be achieved by subjecting a
particular zone or zones of such sheet to such a rectifying
treatment, and notably by subjecting at least one marginal zone of
the sheet face to such rectifying treatment.
Such a rectifying treatment can advantageously be performd by
heating at least one zone of the sheet so as to cause a fire
polishing thereof. Such a treatment can be performed by pre-heating
the sheet to a temperature of between 400 and 450.degree.C and then
exposing the zone or zones to be rectified for a relatively brief
period, for example from a few seconds to a few minutes, to a
higher temperature, e.g., a temperature substantially in the range
of 600 to 850.degree.C. It has been found that this type of
rectifying treatment can be performed with little or no tendency
for the optical properties of the sheet to be impaired, which is a
very important consideration when the sheet is to be used in a
panel which is to form a windshield.
Another very satisfactory type of rectifying treatment involves
chemical dissolution of a surface portion of the sheet. This type
of treatment is easy to perform. For example, the treatment can be
carried out by a simple contact of the sheet with a solvent medium
by sprinkling, spraying or immersion, there being no need to use a
large or expensive installation. Moreover the degree of
rectification can be easily controlled by varying the concentration
of the solvent medium.
Such a dissolution treatment can advantageously be performed by
contacting the surface to be treated with an acid medium containing
fluorine ions. It has been found that acid media containing
fluorine ions act quite rapidly to give very satisfactory results
and surfaces treated by such media show an improved mechanical
strength and an improved resistance to iridescence.
When performing rectification by chemical dissolution, it is
preferable to dissolve a surface layer, in the treated zone or
zones, having a thickness at least equal to the deepest surface
flaw present in such zone or zones and liable to cause a stress
concentration. In that manner, all flaws in the treated zone or
zones become eliminated and the mechanical strength of the sheet
material is made substantially uniform over the treated zone or
zones.
Preferably when performing a rectification treatment by chemical
dissolution, at least one portion of the sheet being treated is
substantially shielded from the solvent medium by a protective
layer. Such protective layer may, e.g., be a layer of paraffin wax,
a peelable varnish or a thin fluid film, for instance a film of
water which is caused to flow along the surface portion or portions
to be protected during the rectification treatment. By taking such
a protective measure, the rectification treatment can be confined
to a given zone or zones, thus reducing the amount of solvent
used.
Moreover, it has been found that certain optical flaws in a glass
sheet may be rendered more visible if a surface of the sheet is
subjected to acid treatment, particularly to treatment with an acid
medium containing fluorine ions, unless that surface is
subsequently contacted by a layer of organic material. There is
therefore sometimes an advantage, particularly when making
windshields, for the outwardly facing side of the second sheet to
not be subjected to a rectifying treatment.
The resistance of the second sheet of glass or vitrocrystalline
material to breakage due to flexures in a direction towards the
first sheet can also be improved by compressively stressing the
external layers of glass or vitrocrystalline material of that sheet
at least at the inner face thereof.
The compressive stressing of such second sheet can be achieved by
thermal tempering. Preferably, however, such compressive stressing
of the second sheet is achieved by chemically tempering the second
sheet, using any of the chemical tempering processes hereinbefore
referred to as suitable for application to the first sheet. The use
of an ion diffusion treatment for compressively stressing the
exterior layers of the second sheet achieves the advantage that in
the event such second sheet breaks, it will break into small blunt
pieces which do not involve a high risk or personal injury, or
damage to the remainder of the panel. Moreover, when an ion
diffusion treatment is used for compressively stressing exterior
layers of both of the first and second sheets, the manufacturing
plant can be laid out and operated more conveniently.
Another manner of increasing the resistance of the second sheet to
breakage due to flexure in a direction towards the first sheet is
to incorporate the second sheet into the panel while it is in a
state of elastic flexure in one or more planes and in a direction
such that the second sheet is being compressively stressed at its
inner side. This method is extremely simple. The second sheet can
be held in an elastically flexed condition by a frame, or by the
other component sheet or sheets of the panel or by the combined
action of such other sheet or sheets and a frame.
By way of example, the second sheet of the panel may be constituted
by a naturally curved glass or vitrocrystalline sheet which is
secured at its convex side to a first sheet which is naturally flat
or which has a natural curvature less pronounced than the second
sheet, so that in the completed panel the second sheet is held,
against the elastic recovery forces therein, by the first sheet in
a flat condition or at a curvature less than its natural
curvature.
The first sheet may itself be held, by a frame component and/or by
the second sheet, in a state of elastic flexure such that its outer
face is in a state of tension or reduced compression. Such flexure
has the effect of lowering the flexing load level at which the
first sheet will break.
Any two or all three of the above-described methods of increasing
the resistance of the second sheet to breakage by flexure which
subjects its inner face to tensile stress, viz: a rectifying
treatment, a chemical tempering treatment, and elastic flexure, can
be applied to one and the same second sheet.
In certain embodiments of the invention, the first sheet is secured
in facing relationship to the second sheet of glass or
vitrocrystalline material which has itself been chemically tempered
and is itself subjected, at least locally, on the side thereof
which in the completed panel faces away from the first sheet, to a
weakening treatment which reduces the resistance of the second
sheet in at least one region thereof to breakage due to a flexure
in the direction which imposes tensile forces in the external
layers which are at that side of the second sheet. Such weakening
treatment may be performed before or after the panel sheets are
assembled. By performing a weakening treatment on the outwardly
facing surfaces of both the first and second sheets, the advantage
is achieved that the resistance of the panel to breakage by impact
forces acting at either side of the panel, and tending to flex it,
can be readily brought substantially to a predetermined value.
As in the case of the weakening treatment performed on the first
sheet, the weakening treatment of the second sheet can be performed
over its whole area, to facilitate production on an industrial
scale, and it is in any case preferable for the weakening treatment
of the second sheet to be performed substantially uniformly over at
least one region thereof, disposed in a central and/or peripheral
part of such sheet.
Advantageously, the first and second chemically tempered sheets are
subjected to weakening treatments at portions of the faces which
are directed away from each other in the completed panel and which
are in registry with one another. The resistance to breakage of one
or more portions of the panel under loading forces acting against
either side of the panel can thus be readily and accurately
determined without the necessity for subjecting the whole of the
outwardly facing sides to weakening treatments. For instance, in a
door glazing panel produced according to the invention, those
portions of the outer faces of the door where strong accidental
impact is most likely to occur may be given a lower mechanical
strength. As another example, in the case of a panel constituting a
vehicle windshield, the outwardly facing sides of the first and
second sheets can be weakened in a region or regions where the head
of the driver or of a front seat passenger is likely to strike the
screen in the event of hard braking or head-on collision.
The particulars hereinbefore given relating to the manner in which
the weakening treatment can be performed on the first sheet are
also relevant for performing a weakening treatment on the second
sheet.
Advantageously, in the case that the second sheet is of glass, this
sheet is at least locally subjected, before a weakening treatment
thereof, to a supplementary strengthening treatment, at least at
the side thereof which is to face away from the first sheet. Such
supplementary strengthening treatment may be performed in any of
the ways hereinbefore described in relation to the supplementary
strengthening of the first sheet.
In a process in which the first and the second sheets are subjected
to a weakening treatment, it is often advantageous for the
weakening treatment of both sheets to be performed before the panel
sheets are assembled. This procedure is particularly advantageous
when identical weakening treatments have to be performed on such
sheets because they can be treated successively in a continuous
processing line.
In other embodiments of a process according to the invention in
which both the first and second sheets are subjected to a weakening
treatment, the weakening treatment of the two sheets is performed
after the panel sheets have been assembled. This procedure is more
particularly advantageous when the panel is not flat, for example
when the panel has a relatively small radius of curvature, and when
aligned portions of the two sheets in the panel have to be
weakened. In such cases the required weakening of the sheets can be
effected simply by passing the panel once through a machine or
installation which treats the opposed outer panel faces
simultaneously.
In the production of a laminate by a process according to the
invention, the first sheet can be secured to a second strength
member in sheet form, by means of an intervening organic sheet or
sheets, e.g., a sheet of organic material. By means of such an
intervening sheet or sheets, first and second sheets of glass or
vitrocrystalline material can be secured together to form a
transparent or translucent laminate. Moreover, the intervening
sheet or sheets can serve to retain individual pieces of the first
or second sheet in place in the event of breakage.
Such an intervening sheet can, e.g., be a sheet of thermoplastic
material. Particularly satisfactory interlayer materials are
polyvinyl butyral, e.g. in the form of a sheet 0.76 mm in
thickness, and certain polycarbonates of bis-phenols which may be
used together with, for example, polyacrylate adhesives.
The invention also includes a panel composed of a plurality of
sheet components in facing relationship, including a sheet of glass
or vitrocrystalline material in external layers of which
compressive surface stresses have been produced by a chemical
tempering treatment, one side of such sheet providing an exterior
face of the panel, according to the invention, in at least one
region of the glass or vitrocrystalline sheet, which corresponds to
the first sheet referred to herein, the tensile strength of such
sheet, expressed in terms of the tensile force, imposed by flexing
the sheet, which can be supported without breakage by the
compressively stressed external layers at the one side of the
sheet, is made less than the tensile force necessary for reducing
such compressive stresses to zero.
Such a panel possesses an important combination of properties. In
particular, the tensile strength of the first sheet, expressed as
above referred to, is not only determined by the magnitude of the
compressive stresses produced by tempering, and at the same time
the existence of the stresses due to chemical tempering causes the
sheet, if it does break, to divide into relatively small blunt,
i.e. non-cutting, pieces. In the case of a glazing panel, the
tensile strength of such first sheet can, for example, be low
enough to ensure that if a person should collide against the other
side of the panel, the sheet will yield before the impact force
reaches a value at which serious internal personal injury is
probable.
Advantageously, the tensile strength of the first sheet in at least
one region thereof has a uniform lower value than the tensile force
necessary for reducing the compressive stresses therein to zero.
Such uniformity is considered to exist when the tensile strength of
various samples of the sheet within that region, tested in the same
manner, is substantially the same for all samples. Such a sheet
therefore affords the advantage that it has a predetermined
resistance to breakage due to flexure under forces acting anywhere
in a given region. Preferably, the tensile strength of the first
sheet is substantially lower over the whole area of such sheet than
the tensile force necessary for reducing the compressive stresses
to zero. The advantage of this feature, and of various other
optional features of the panel hereinafter referred to, are
implicit in the statements made earlier herein concerning the
advantages afforded by the corresponding process features.
Advantageously, the one side of the first sheet bears surface
abrasions or scratches in at least one region of the sheet. The
presence of scratches is of particular value if they are entirely
or primarily in one direction. In the case of a vehicle windshield,
it is preferable for the scratches to be wholly or predominantly in
a direction normal to the longitudinal axis of the windshield.
Advantageously, at least one region of the one side of the first
sheet has grooves or scratches having a depth of less than 5
microns. Such scratches or grooves are consistent with good
transparency or other optical properties of such sheet.
It is very advantageous, in the case that the first sheet is of
glass, for at least one region of the first sheet to contain
fluorine ions in external layers of the one side thereof.
For glazing panels, e.g. windshields, which may be subjected to
impact by a person, it is advantageous for the tensile strength of
at least one region of the first sheet, expressed in the terms
hereinbefore specified, to correspond to a value of less than 50
kg/mm.sup.2 as measured on a disc 11 cm in diameter.
The first sheet may be secured in facing spaced relationship to a
second main sheet component, the first and second sheets being
directly connected only at the margins of the panel. The space
between the central portions of the sheets can be empty or may
contain a fluid medium, e.g., dry air or other gaseous medium, or a
filling material. The panel may, e.g., incorporate a filling
material having good heat insulating properties. According to a
particular embodiment, the sheets are assembled by means of a metal
ribbon or ribbons located between the sheet margins.
In panels of the most preferred type according to the invention,
the sheet components of the panel are secured together over their
entire area and form a laminate.
According to particularly important embodiments of panels according
to the invention, the first sheet is in facing relationship to a
second main sheet component of the panel, which second sheet can be
flexed to impose flexing forces on the first sheet sufficient to
break that sheet. Such a panel has a combination of properties
which are of notable value as hereinbefore described in relation to
processes according to the invention, particularly in the case of a
glazing panel, e.g., a vehicle window or windshield.
In a very simple form of panel according to the invention, the
first sheet of glass or vitrocrystalline material is in facing
relationship to a second sheet component, such second sheet being a
sheet of plastic material. The plastic sheet can be bonded to the
first sheet with or without an intervening bonding layer to form a
laminate, or the plastic sheet and the first sheet may be in spaced
relation.
Preferably, the panel consists of the first sheet of glass or
vitrocrystalline material and only one other strength member in
sheet form, that second sheet being also a sheet of glass or
vitrocrystalline material. Particular preference is given to such
panels in the case where such sheets are secured together to form a
laminate. Such embodiments are particularly important, for reasons
hereinbefore stated, in the case where the second sheet has been
chemically tempered and is more elastically flexible than the first
sheet.
In optimum embodiments of the invention, the first sheet of glass
or vitrocrystalline material is secured in facing relationship to a
second sheet of glass or vitrocrystalline material and the sheets
constitute plies of a laminate. The relative strengths of the first
and second sheets are such that the second sheet can be flexed to
impose flexing forces on the first sheet sufficient to break the
latter sheet, but they are such that the first and second sheets
were tested independently of each other, the resistance of the
first sheet to breakage due to a flexure subjecting its one side to
tensioning forces would be higher than the resistance to breakage
of the second sheet due to a flexure subjecting to tensioning
forces the side which faces the first sheet.
The relative strengths of the first and second sheets can be
determined by individually peripherally supporting a plurality of
identical sheets in turn and dropping a rounded object weighing 10
kg onto each sheet from a height which is progressively increased
from one test to the next and noting in the case of each sheet the
dropping height at which the sheet breaks. This test is very
suitable for panels to be used as vehicle windshields.
According to a preferred feature, the panel includes, as the second
sheet, a sheet of glass, the inner face of which is, over at least
one region of the sheet, substantially free from flaws liable to
cause stress concentrations when tensioning forces are applied to
the inner face of such sheet. Advantageously, the external layers
of the second sheet at the inner side thereof contain fluorine ions
in at least one region of such sheet.
In panels with optimum properties, the second sheet of glass or
vitrocrystalline material has compressively stressed external
layers at least at its inner side. Such compressive stressing is
preferably due at least in part to chemical tempering of such
second sheet.
Compressive stressing of the external layers of glass or
vitrocrystalline material at the inner side of the second sheet may
also be achieved by sheet flexure as hereinbefore described and in
certain panels according to the invention the first sheet is in
facing relation to a second sheet of glass or vitrocrystalline
material which is held in a state of elastic flexure in a direction
such that the external layers at the inner side of the second sheet
are compressively stressed. Preferably, the second sheet is held
elastically flexed by the first sheet. However, the second sheet
can be held flexed by means of a frame, or by means of the first
sheet and a frame.
Advantageously, the first sheet is held by a frame and/or by a
second sheet, in a state of flexure such that the one side of the
first sheet is in a state of tension or reduced compression.
The first sheet of glass or vitrocrystalline material may be in
facing relationship to a second sheet of glass or vitrocrystalline
material which has itself been chemically tempered, the tensile
strength of at least one region of the second sheet, expressed in
terms of the tensile force, imposable by flexing the sheet, which
can be sustained by the compressively stressed external layers, at
the side of the second sheet facing away from the first sheet,
being less than the tensile force necessary for reducing such
compressive stresses to zero. Advantageously therefore, the second
sheet bears surface abrasion or scratches in at least one region at
the side of such sheet which faces away from the first sheet. This
type of panel is particularly advantageous when there is a risk of
each side of the panel being on some occasion subjected to an
impact force under circumstances such that a very high resistance
to such force would have undesirable effects. A glazing panel of a
glass door is a case in point.
Advantageously, in an embodiment in which the first and second
sheets have been subjected to a weakening treatment, this treatment
serves to weaken the sheets in zones which are opposite each other,
i.e. in registry, in the panel. A glazed door or a windshield can
for example have its first and second sheets weakened in at least
one region of the panel where impact by a person, such as might
cause serious personal injury, is liable to occur. Such weakened
region may have a mechanical strength which is accurately
predetermined.
A panel according to the invention can advantageously be composed
of the first sheet of glass or vitrocrystalline material secured to
a second strength member in sheet form by means of an intervening
organic sheet or sheets, e.g., a sheet of organic polymeric
material such as a sheet of polyvinyl butyral or a high molecular
weight polycarbonate of a bisphenol which may be cemented by means
of a polyvinyl acrylate adhesive to the sheets between which it is
sandwiched. Such an intervening sheet can serve to hold individual
pieces of the first and second sheets in the event of breakage, and
a stable assembly of two sheets, for example of glass, can be
readily produced. Also, the panel can, if required, have a very
good transparency and other advantageous optical properties, such
as a low optical distortion.
Preferably, the first and second sheets are secured together by
means of an intervening sheet of organic material which resists
penetration or tearing if one or each of the first and second
sheets is broken by the impact of a rounded object weighing 10 kg
and dropped from a height of about 620 cm. If a panel satisfying
that test is used as vehicle windshield, there is but small risk of
the head of a driver or passenger penetrating the windshield upon
being thrown thereagainst.
In a panel according to the invention wherein the first sheet of
glass or vitrocrystalline material is in facing relationship to a
second main sheet component which is also of glass or
vitrocrystalline material which has also been chemically tempered,
it is advantageous for the first sheet to be thicker than the
second sheet. The benefits of such a panel when used as a glazing
panel, for example a windshield, are best realized when the panel
is installed with the thicker sheet facing toward the outside,
assuming that forces tending to flex the panel are most likely to
act against the inside of the panel, whereas the outside of the
panel is most likely to be struck by small hard objects causing
indentations. Preferably, the first sheet has a thickness in the
range of 1.5 to 4 mm and the second sheet has a thickness in the
range of 1 to 2.5 mm.
A selection of properties appropriate to the locations of the
different sheets can often be realized if the compressive stressing
of the thicker sheet due to chemical tempering is substantially
equal to or less than the compressive stressing of the thinner
sheet due to chemical tempering.
In any embodiment of a process or panel according to the invention,
the first sheet may be naturally flat or naturally curved in one or
more planes.
It is to be understood that the sheet of glass or vitrocrystalline
material which constitutes the first sheet may be coated before or
after the assembly operation to produce the panel. For example,
after the assembly operation, the face of the first sheet which
constitutes an external panel face may be coated with a coating
layer, e.g. an anti-reflection layer.
In the embodiments covered in the foregoing description, one side
of the first sheet of glass or vitrocrystalline material which is
subjected to a weakening treatment constitutes an exterior panel
face. By way of modification, the panel may incorporate a sheet
which covers the one face, provided that the covering sheet has
negligible resistance to flexure, i.e., provided it is not a
strength member. For example such a covering sheet may be a thin
plastic foil which is used for protective or coloring purposes.
According to another aspect of the present invention, there is
provided a panel composed of a first sheet of glass secured by
means of an intervening organic sheet to a second sheet of glass,
each of the first and second sheets having been chemically
tempered. According to novel features of the invention, the first
sheet is thicker than the second sheet, and the inherent resistance
of the first sheet to breakage by flexure in a direction such that
the flexure imposes tensioning forces on its side which is remote
from the second sheet is higher than the inherent resistance of the
second sheet to breakage by flexure which imposes tensioning forces
on the side of that sheet which faces the first sheet, but the
second sheet of the assembly can be flexed to impose flexing forces
on the first sheet sufficient to break the first sheet. The
inherent resistance of the first or second sheet to breakage is the
resistance of that sheet to breakage when tested in isolation from
the other sheet.
Such a panel has a very important combination of properties which
make it very suitable for use as a glazing panel in a building or
vehicle, and particularly as a vehicle windshield. When used as a
windshield with the thicker glass sheet facing the outside of the
vehicle, the panel affords a high degree of safety to vehicle
occupants in the event of impact of an occupant against the inside
of the windshield and in the event of the windshield being struck
from the outside by small hard objects, e.g. pieces of gravel, or
by larger objects, e.g. large stones which may fall against the
windshield while being loaded into a truck.
The panel may be flat or may be curved in one or more planes.
According to preferred embodiments of such panel, the first sheet
of glass has a thickness at least 1.25 times that of the second
sheet of glass.
Preferably, the thicker glass sheet presents an external face of
the panel, but it may be covered by a sheet which is not a strength
member.
Preferably, the thinner glass sheet also presents an external face
of the panel.
The inherent strengths of the sheets of glass of different
thicknesses may be tested, for example by individually peripherally
supporting identical sheets and dropping a rounded object weighing
10 kg onto each sheet from a height which is progressively
increased from one test to the next until the sheet breaks.
In a panel according to the invention, composed of sheets of glass
of unequal thickness and different inherent resistances to breakage
as above referred to, any of the features hereinbefore referred to
in connection with the invention in its first aspect can be
present, for example: an all-over or localized weakening of the
first sheet or of the first and second sheets; a second sheet with
a rectified inner face or an inner face which is compressively
stressed in part by reason of such sheet being held in the panel in
a state of elastic flexure; the presence of fluorine ions in the
exposed face of the first sheet and/or in the inner face of the
second sheet; and an intervening sheet of thermoplastic material
resisting penetration by an impacting rounded object as
hereinbefore referred to in the event that the second sheet breaks
under the impact.
In a panel according to the second aspect of the invention as above
referred to, the thicker glass sheet preferably has a thickness in
the range of 1.5 to 4 mm and the thickness of the thinner glass
sheet is preferably in the range of 1 to 2.5 mm. When observing
such thickness ranges, it is easy to produce a panel which is both
strong and flexible enough to avoid excessive impact shock to a
person thrown head first against the side of the panel at which the
thinner sheet is exposed. Moreover, such a panel is of fairly low
weight, which is a feature of importance in the case of panels to
be used as windshields in competition cars.
The invention also includes processes of making a panel according
to the invention in its second aspect. Such process may have any of
the process features hereinbefore referred to.
Considering now the mechanical strength tests permitting to measure
the rupture stress to flexure and being carried out on discs having
a diameter of 11 cm as described in the present specification, it
is useful to describe briefly the way to perform the said
tests:
a. the said discs are disposed freely on a ring-shaped holder;
b. the loading of the said discs is carried out with the help of a
measuring-machine Instron (Instron is a trade mark name); the
surface of applying the said loading is circular, central in
relation to the surface of the disc and has a radius of 3mm while
the rate of applying the loading is substantially equal to 50
mm/minute;
c. after having measured the deformation of the said disc due to
the loading, the tensile stresses induced in the face or external
layers of the discs which is or are stretched, are calculated with
the help of Timonshenko's theory (see Timoshenko-theory of plates
and shells).
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view of one form of panel according to the
invention.
FIG. 2 is a cross-sectional view taken along the line 2--2 of FIG.
1.
FIG. 3 is a cross-sectional view of another embodiment of a panel
according to the invention.
FIG. 4 is a cross-sectional view of a further embodiment of a panel
according to the invention.
FIG. 5 is a perspective view of one embodiment of a windshield
according to the invention.
FIG. 6 is a cross-sectional view taken along the line 6--6 of FIG.
5.
FIG. 7 is an elevational view of another embodiment of a windshield
according to the invention.
FIG. 8 is a cross-sectional view taken along the line 8--8 of FIG.
7.
FIG. 9 is a cross-sectional view of the components of one
embodiment of a windshield according to the invention prior to
assembly.
FIG. 10 is a cross-sectional view of the embodiment of FIG. 9,
after assembly.
FIG. 11 is an elevational view of one embodiment of a window panel
according to the invention.
FIG. 12 is a cross-sectional view taken along the line 12--12 of
FIG. 11.
FIG. 13 is a cross-sectional view of another embodiment of a window
panel according to the invention.
FIG. 14 is a cross-sectional view of the components of another
window panel according to the invention, prior to assembly.
FIG. 15 is a cross-sectional view of a window panel formed of the
components illustrated in FIG. 14 and after assembly.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the detailed description of the figures to be presented below,
the reference numerals, 1, 2, 3 and 4 are utilized to designate
respective faces of the components of the various embodiments of
the invention. The illustrated embodiments will be described with
reference to a series of specific examples. All of the embodiments
of the invention are multilayer articles having a flat or curved
configuration and generally constitute door or window panels, or
vehicle windshields. Therefore, reference throughout the following
description to panels or windshields is to be construed as a
reference to such multilayer articles.
Example 1
The article illustrated in FIGS. 1 and 2 is a translucent panel
intended to be utilized as a closure panel, such as a door for a
building, having a high degree of fire resistance. For safety
reasons, such a panel should satisfy numerous requirements, and in
particular the following:
a. the panel should have a high degree of fire resistance so as to
provide a maximum impediment to the propagation of fire from one
side of the panel to the other;
b. the mechanical strength of the panel should be such that, if a
person becomes imprisoned within the area closed off by the panel,
the panel can be broken to free such person by striking the panel,
or otherwise subjecting it to shocks, either from within or without
the enclosure;
c. the mechanical strength of the panel should be such that, in
case a person should accidentally run into it, he will not be in
danger of suffering serious head injuries (cranial trauma).
To construct a panel satisfying these requirements, a group of six
panels were each formed from two identical sheets 5 and 7, each
measuring 2 m .times. 2.5 m .times. 0.003 m and formed from a
vitroceramic material having the following composition, by
weight:
SiO.sub.2 65.5% Al.sub.2 O.sub.3 26.0% Li.sub.2 O 4.0% Ti.sub.2 O
4.5%
Sheets 5 and 7 were joined together by means of a sheet 6 of
polyvinyl butyral. In the finished panel, the faces 1 and 2
constitute surfaces of the sheet 5 intended to be disposed toward
the interior of the enclosure when the panel according to the
invention is utilized as a closing panel for such enclosure, while
the faces 3 and 4 constitute surfaces of the sheet 7 intended to be
directed toward the exterior of such enclosure. It should be noted,
however, that in this specific case, the panel is composed of two
sheets having identical characteristics, so that the side of the
enclosure toward which each sheet is directed is of little
importance.
Before assembling the sheets to form the panels, six sheets 5 and
six sheets 7, as well as 12 discs having a diameter of 11 cm and of
the same material and same thickness as the sheets 5 and 7, were
treated by immersion for 24 hours in a bath of potassium nitrate
maintained at a temperature of 450.degree.C. After washing and
drying these sheets and discs, the surface rupture stress due to
flexure of six of the treated discs was measured and it was noted
that the highest rupture stress measured was 91 kg/mm.sup.2 and the
lowest measured rupture stress was 74 kg/mm.sup.2.
Then, one face of each of the six remaining treated discs and one
part of the faces 1 and 4 of the sheets 5 and 7, respectively,
intended to constitute the exterior faces of the panels, were
subjected to an abrasion treatment such that the value of the
rupture stress due to flexure of those faces was made no greater
than 50 kg/mm.sup.2. The abrasion treatment was performed by using
sand whose grains had an average diameter of 10.mu., the sand being
applied to the entirety of one face of each of the six discs and to
a rectangular part 8 and 9 of each of the faces 1 and 4 of sheets 5
and 7, respectively. The rectangular part of each face 1 and 4 had
an area of 3.6m.sup.2 and the rectangular portions 8 and 9 were
disposed in registry with one another in such a manner that the
lateral sides of each of the rectangular parts 8 and 9 were 0.1m
from 2.5m long sides of the respective sheets 5 and 7, while the
lower edge of each rectangular part was spaced 0.4m from the lower
edge of each respective sheet. The rupture stress due to flexure of
the six discs which had one face submitted to the abrasion was
measured and it was noted that the lowest strength value measured
was 41kg/mm.sup.2, while the highest value measured was 50
kg/mm.sup.2.
Then, one sheet 5 which has been abraded as described above was
assembled with one sheet 7 which had been abraded in the same
manner, and the sheets were joined together by means of a high
impact polyvinyl butyral sheet having a thickness substantially
equal to 0.76mm to form a panel having the structure illustrated in
FIGS. 1 and 2. It should be noted that, in order to facilitate an
understanding of the invention, the effect of the abrasion
treatment has been greatly exaggerated in FIG. 2.
The mechanical strength tests mentioned above revealed that the
resulting panels, after installation, perfectly satisfied the
requirements enumerated earlier.
Similar panels were also constructed from sheets 5 and 7 of the
same vitroceramic material, and having the same dimensions, as
those described above, but which differed from the above-described
panels by the fact that only one face of one of the panels, i.e.,
either the face 1 or the face 4, intended to form one of the
exterior faces of the panels, was chemically tempered by being
maintained in contact for 24 hours with potassium nitrate
maintained at 450.degree.C and the above-described abrasion
treatment of faces 1 and 4 was performed before the chemical
tempering.
Strength tests identical with those described above were performed
on a lot of six such panels and revealed that all of the panels
satisfied the requirements specified earlier.
In a variation of the above-described procedures, panels similar to
those described above were each formed from a sheet 5 composed of a
soda-lime glass having substantially the following composition, by
weight:
SiO.sub.2 71% Na.sub.2 O 13% CaO 10% Al.sub.2 O.sub.3 2% MgO 3%
the remainder of the composition being constituted by minor amounts
of compounds such as K.sub.2 0, Fe.sub.2 0.sub.3. Each of these
panels also included a sheet 7 identical in composition with the
sheet 7 described above. Both of the sheets 5 and 7 had dimensions
identical with those of the sheets described above.
Before joining the sheets 5 and 7 together by means of a high
impact polyvinyl butyral intervening sheet having a thickness of
0.76 mm, the faces 1 and 4 of sheets 5 and 7 were subjected to a
strengthening treatment by being maintained for 24 hours in contact
with molten potassium nitrate at a temperature of 450.degree.C, and
to an abrasion treatment identical with that disclosed above and
utilizing sand whose grains have an average diameter of 10.mu..
After the treatment, it was noted that the last sheet 5 was no more
flexible than the vitroceramic sheet 7.
After fabrication, such panels were installed as enclosure panels
arranged so that the glass sheet 5 was directed toward the interior
of the enclosure with which they were associated. These panels also
satisfied the requirements enumerated earlier.
Example 2
A lot of twelve sheets of soda-lime glass measuring 1.5m .times. 2
m .times. 3 mm, and having the following composition, by
weight:
SiO.sub.2 71% Al.sub.2 O.sub.3 2% Na.sub.2 O 12% CaO 12% MgO 2%
the remainder being constituted by impurities, was subjected to an
ion exchange treatment. Sodium ions initially present in the glass
were replaced by lithium ions in a bath containing 2% LiNO.sub.3
and 98% NaCl and at a temperature of 580.degree.C. The treatment
lasted 20 minutes. The sheets were then withdrawn from the bath,
cooled and cleaned.
Twelve control discs having a diameter of 11cm and of the same
thickness and composition as the above-described 12 sheets were
subjected to the same ion diffusion treatment. The rupture stress
due to flexure applied symmetrically with respect to the center of
the discs was measured for six of the 12 discs and different values
were obtained for each of the discs. The lowest measured value was
14 kg/mm.sup.2 and the highest measured value was 19
kg/mm.sup.2.
Then, the six remaining discs simultaneously had one face of each
subjected to an abrasion treatment utilizing alumina and the
abrasion treatment was halted when the rupture stress due to
flexure of one of the discs became equal to 15 kg/mm.sup.2. The
rupture stresses due to flexure of the other discs was then
measured and it was noted that the lowest measured value was 13
kg/mm.sup.2 while the highest measured value was 16 kg/mm.sup.2.
One face of each of the sheets was abraded by a treatment identical
to that carried out on the discs.
The sheets were then joined together, two by two, by means of a
sheet of high molecular weight polyvinyl chloride and utilizing a
low molecular weight polyvinyl chloride as an element aiding the
adherence between the high molecular weight polyvinyl chloride and
the glass. This resulted in panels of the type illustrated in FIG.
3, wherein the glass sheets 10 and 11 are joined together by means
of a polyvinyl chloride sheet 12, with the abraded faces 1 and 4 of
the sheets constituting the outer surfaces of the panel. This panel
is intended to be utilized as a glass door and it has been noted
that in case the door suffers a shock due to being run into by a
person, the glass sheets do not cause any head injuries because
they break before the shock impact reaches a dangerous level.
According to one modification of the above-described procedure for
forming the panel illustrated in FIG. 3, instead of the entirety of
the faces 1 and 4 of the glass sheets being subjected to an
abrasion treatment, only one part of these faces was subjected to
such a treatment, either before or after the diffusion treatment
and assembly of the panel. According to this modification, the
abraded portions of faces 1 and 4 are in registry, i.e. they are
coextensive with one another, and are disposed at the location
having the greatest probability of being struck by a person moving
against the panel. This arrangement is particularly advantageous
when the panels are utilized as glass doors, in which case there is
a greater probability that the central region of the surface of the
faces 1 and 4 will be struck by a person moving toward the
door.
Example 3
FIG. 4 illustrates a panel according to the invention, one
component of which is constituted by a rectangular glass sheet 15.
This sheet measures 1 m .times. 0.5 m .times. 0.006 m and has the
following composition, by weight:
SiO.sub.2 73% Na.sub.2 O 13% CaO 9% Al.sub.2 O.sub.3 3% MgO 1%
the remainder of the sheet being constituted by impurities. To give
this sheet its desired mechanical properties, it was subjected to
the following treatment.
Several of these sheets were immersed, together with 24 control
discs having a diameter of 11 cm and of the same thickness and
composition as the sheets, for 24 hours in a bath of potassium
nitrate maintained at 460.degree.C and containing 0.2 percent, by
weight, potassium carbonate. Then, after having been washed and
cooled, the sheets and discs were immersed for 3 minutes in an
aqueous bath containing 7 percent, by volume, hydrofluoric acid and
7 percent, by volume, sulfuric acid at a temperature of
20.degree.C. As a result of this treatment fluorine ions have been
introduced into the external layers of the glass articles. After
having then been washed in distilled water and dried in an
isopropryl alcohol vapor, the surface rupture strength with respect
to flexure of a group of six treated discs was measured in the
manner indicated above and it was noted that the lowest measured
value was 110 kg/mm.sup.2, while the highest measured value was 130
kg/mm.sup.2.
Then, all of the sheets and the remaining discs has one face of
each simultaneously subjected to an abrasion by means of a cerium
oxide powder and the abrasion operation was halted when the rupture
stress due to flexure of one of the discs reached a value of 49
kg/mm.sup.2. Then, the value of the rupture stress due to flexure
for the remaining 17 discs was measured and it was noted that the
lowest rupture stress value was 47 kg/mm.sup.2, while the highest
rupture stress value was 50 kg/mm.sup.2. An improved resistance to
iridescence was also noted.
Each of the sheets thus treated was joined, by means of a polyvinyl
butyral sheet 14, as illustrated in FIG. 4, to a sheet 13 having a
thickness of 1.2 mm in such a manner that the abraded surface of
sheet 15 constituted the outer face 4 of the resulting panel. The
sheet 13 is more flexible than the 6 mm thick sheet 15 and is
composed of a soda-lime glass which was treated by immersion for 24
hours in a potassium nitrate bath maintained at 460.degree.C and
containing 0.2 percent, by weight, potassium carbonate. The
resulting panels were intended for use as closures for the control
cabins of cranes, the 6 mm thick sheet 13 being disposed toward the
exterior.
According to one modification of the procedure which has just been
described, panels comparable to those described were formed of a
glass sheet 15 having a thickness of 6 mm and joined, by means of a
polyvinyl butyral sheet 14, to a glass sheet 13 having a thickness
of 1.2 mm. Before joining, the sheets 15 and 13 were chemically
tempered by immersion for 24 hours in a bath of potassium nitrate
maintained at 460.degree.C and containing 0.2 percent potassium
carbonate. Besides the fact that the face 4 of sheet 15 underwent
the abrasion treatment described above in the present example in
such a manner as to cause the rupture stress of that face due to
flexure to be less than 50 kg/mm.sup.2, the face 2 of glass sheet
13 was subjected to a treatment serving to at least partially
remove surface flaws, which would be sources of stress
concentrations if forces were applied to the sheet.
The surface flaw removal treatment was carried out on six sheets 13
before assembly of the panel illustrated in FIG. 4. The treatment
was carried out before the chemical tempering with potassium
nitrate, described above, and was performed on the face 2 of the
six sheets. The flaw removal treatment was carried out at a
temperature of 20.degree.C and involved the application to the face
2 of the sheets of an aqueous solution having the following
composition:
8.8 liters of water
0.6 liter of H.sub.2 SO.sub.4
0.6 liter of 70% HF.
The solution was maintained in contact with the sheets for about 60
minutes and served to remove a 60.mu. thick layer of each face 2,
which corresponded substantially to 1.5 times the depth of the most
serious flaws noted on the face before treatment. The other face 1
of sheets 13 had been preliminarily coated with paraffin to prevent
substantially any contact with the solution. After cleaning of the
sheets 13, they were joined, as described above, to corresponding
sheets 15 and it was noted that the resulting panels presented an
improved resistance to penetration due to a shock applied against
face 1.
For another group of six sheets 13 intended to be joined to six
sheets 15, a different flaw removal treatment was carried out on
the face 2 of each sheet 13 prior to the above-described chemical
tempering treatment. This flaw removal treatment was of the type
commonly known as "fire polishing". For this purpose, the sheets 13
were preheated to 450.degree.C. Then, they were placed above a
flame formed by passing propane and compressed air through a porous
refractory piece. The sheets were maintained, with their faces 2
directed toward the flame, for 45 seconds and the temperature at
the faces 2 reached a value of 660.degree.C. The sheets were then
cooled progressively in a furnace initially maintained at
450.degree.C. Then, the resulting sheets 13 were joined to
respective ones of sheets 15 prepared and treated in the manner
described above to form the panels illustrated in FIG. 4. It was
also noted that these panels presented an improved resistance to
penetration due to a shock against face 1.
Example 4
Several laminated glazings having the form illustrated in FIGS. 5
and 6 were each formed from a sheet 16 and a sheet 18 of curved,
chemically tempered glass, the sheet 16 having a thickness of 1.2
mm and the sheet 18 having a thickness of 3.2 mm. The sheets were
constituted by soda-lime glass having an ordinary composition. The
glazings were obtained by bonding the sheets 16 and 18 to
respective opposite faces of a sheet 17 of high impact polyvinyl
butyral having a thickness of 0.76 mm. The glazings were intended
to be utilized as windshields mounted in such a manner that the 3.2
mm thick sheet 18 would be disposed toward the exterior of the
vehicle, while the sheet 16, which is more flexible than the sheet
18, is disposed toward the interior of the vehicle.
Before assembly of the glazings, the sheets 16 having a thickness
of 1.2 mm and the sheets 18 having a thickness of 3.2 mm, as well
as two groups of 12 control discs having a diameter of 11 cm, one
group of discs having a thickness of 1.2 mm and the other group of
discs having a thickness of 3.2 mm, and all of the discs being of
the same composition as the sheets 16 and 18, were subjected to an
ion diffusion treatment by immersion for 24 hours in a potassium
nitrate bath maintained at a temperature of 450.degree.C. After
this potassium nitrate treatment, the rupture stress due to flexure
was measured for six discs of each group and it was noted that the
lowest value measured was 66 kg/mm.sup.2 while the highest value
measured was 108 kg/mm.sup.2. Then, all of the sheets having
thicknesses of 1.2 mm and 3.2 mm, as well as the remaining discs,
simultaneously had one face of each subjected to an abrasion by
means of a powder composed of cerium oxide and alumina. After this
abrasion, the rupture stress due to flexure was measured for the 12
discs, six of each thickness, and it was noted that the lowest
measured value was 45 kg/mm.sup.2, while the highest measured value
was 49 kg/mm.sup.2.
In addition, a group of sheets 16 and a group of sheets 18 were
subjected, after the abrasion treatment and before assembly, to a
test of their mechanical strength with respect to flexure to verify
if the strength of sheets 18 was greater than that of sheets 16.
These tests established, as expected, that the sheets 18 had a
greater mechanical strength than the sheets 16. Then, each sheet 16
was joined to a sheet 18 to form a panel, the sheets being arranged
so that the abraded faces 1 and 4 of the sheets constituted the
outer surfaces of the resulting windshield. It was determined that
in case the windshield suffered a shock due to the impact of a
human head, or an object simulating a human head, against face 1 of
the windshield, the exterior sheet 18 broke within satisfactory
limits, from a biomechanical point of view, i.e., the rupture
stress of face 4 due to flexure did not exceed 50 kg/mm.sup.2.
Example 5
A series of sandwich-type windshields were each fabricated of two
sheets of chemically tempered glass having respective thickness of
1.4 mm and 2 mm and formed from a glass having substantially the
following composition, by weight:
SiO.sub.2 72% Na.sub.2 O 10% CaO 14% Al.sub.2 O.sub.3 3%
the remainder being constituted by minor amounts of compounds such
as MgO, Fe.sub.2 O.sub.3. These windshields were fabricated by
cementing or otherwise bonding the two sheets to opposed faces of a
sheet of high impact polyvinyl butyral having a thickness of 0.76
mm.
These windshields are intended to be mounted in automobiles in such
a manner that the 2 mm thick sheet, represented by the sheet 18 of
FIG. 6, is disposed toward the exterior of the vehicle, while the
1.4 mm thick sheet, constituted by the sheet 16 of FIG. 6, is
disposed toward the interior. Before assembly, the series of 1.4 mm
thick sheets, the series of 2 mm thick sheets, and two groups of
control discs 11 cm in diameter, one group of discs having a
thickness of 1.4 mm and the other group of discs having a thickness
of 2 mm, both groups of discs being of the same compositions as the
sheets, were subjected to an ion diffusion treatment by immersion
for 24 hours in a bath of potassium nitrate maintained at a
temperature of 450.degree.C. After this treatment, the rupture
stress due to flexure was measured for 12 discs, six discs of each
thickness, and it was determined that the highest measured value
was 125 kg/mm.sup.2 and the lowest measured value was 56
kg/mm.sup.2.
Then, one face of each of the 2 mm thick sheets, the face
constituting the face 4 of the arrangement illustrated in FIG. 6,
as well as one face of the six treated control discs having a
thickness of 2 mm, were subjected to an abrasion utilizing alumina
powder. After this abrasion, the rupture stress due to flexure was
measured for the six abraded control discs, and it was observed
that the lowest value measured was 39 kg/mm.sup.2 and the highest
value measured was 47 kg/mm.sup.2. It was also observed, by
comparative tests, that the flexure strength of the chemically
tempered 2 mm thick sheets, corresponding to the sheet 18 in the
arrangement of FIG. 6, was after the abrasion treatment still
greater than the strength of the chemically tempered 1.4 mm thick
sheets, corresponding to the sheet 16 of FIG. 6.
Windshields having the form illustrated in FIG. 6 were then formed
from one each of the 1.4 mm thick sheets and the 2 mm thick sheets,
the faces of the 1.4 mm thick sheet not having undergone any
abrasion treatment, and that face of the 2 mm thick sheet which
underwent an abrasion treatment constituting the face 4 of the
arrangement illustrated in FIG. 6. These windshields were subjected
to mechanical strength tests and it was observed that they
satisfied the biomechanical requirements for the safety of persons
within the automobile, i.e., in every case the tensile rupture
stress of the face 4 was no greater than 50 kg/mm.sup.2.
According to a modification of the above procedure, windshields
were produced in the manner described above in the present example,
with the exception that the abrasion treatment was performed after
joining together the sheets 16 and 18 and it was noted that the
resulting windshields also satisfied the biomechanical requirements
for the safety of the occupants of the automobile.
Example 6
FIGS. 7 and 8 illustrate another embodiment of an automobile
windshield according to the invention composed essentially of two
sheets 20 and 22, each formed from a soda-lime glass having the
following composition, by weight:
SiO.sub.2 71% Na.sub.2 O 12% CaO 14% Al.sub.2 O.sub.3 2%
the remainder being constituted by minor amounts of other
compounds.
The sheet 22 has a thickness of 1.5 mm and is intended to be
directed toward the interior of the automobile, while the sheet 20
has a thickness of 3.2 mm and is intended to be directed toward the
exterior of the automobile. Before being joined together to form
the windshield, these sheets were treated in the following
manner:
Firstly, the sheets corresponding to sheet 20 of FIGS. 7 and 8 were
cut by tracing around the periphery of the sheet, 1 cm from the
edge and only on the face 4, a groove 19 having a depth of 0.03 mm.
This constituted a weakening treatment. After this weakening
treatment, the sheets 20 as well as the sheets 22 which did not
undergo a weakening treatment, were subjected to a strengthening
treatment by immersion for 24 hours in a bath of potassium nitrate
maintained at a temperature of 450.degree.C. After washing and
drying, the sheets 20 and 22 were joined together by means of a
high impact polyvinyl butyral sheet 21 having a thickness of 0.76
mm.
The resulting windshields were subjected to mechanical stresses and
it was observed that this type of windshields satisfied the
biomechanical requirements for the safety of persons within the
automobile, i.e., in all cases the tensile rupture stress due to
flexure of the face 4 was no greater than 50 kg/mm.sup.2.
Further, another group of sheets 22 and a group of sheets 20, these
sheets having been treated in the manner described above, i.e., the
sheets 20 having undergone a chemical tempering with potassium
nitrate maintained at 450.degree.C and the sheets 20 having, before
the chemical tempering, been provided with grooves 19, were
subjected to tests of their mechanical strength with regard to
flexure and it was noted that the sheets 22 were more flexible than
the sheets 20 and that the sheets 20, after having been weakened by
the provision of grooves and strengthened by chemical tempering,
had a mechanical strength with regard to flexure which was still
greater than the corresponding mechanical strength of the sheets
22.
Example 6a
A batch of windscreens illustrated by FIGS. 9 and 10 was made. The
windscreen components, immediately prior to the assembly step, were
substantially the same as the components of the windscreens made as
described in Example 6, immediately prior to the assembly of those
components, with the exception however that the sheet 22 of each
windscreen had a natural curvature somewhat more pronounced than
the natural curvature of the sheet 20 of the screen. The components
of the windscreen shown in FIGS. 9 and 10 and the groove or scratch
in the thicker glass sheet thereof bear the same reference numerals
as the corresponding parts in FIGS. 7 and 8. For assembling the
sheets to form a windscreen shown in FIG. 10, the sheet 22 had to
be elastically flexed so that in the panel the inner side of the
sheet 22 was compressively stressed due to the flexure. The
laminated sheets could be held flat as shown in FIG. 10 by means of
a frame (not shown) or the sheets could remain at a curvature
intermediate the natural curvatures of the sheets 20, 22, each
sheet being sustained at that curvature by the elastic recovery
forces stored in the other sheet. In either case, due to the fact
that the inner side of sheet 22 was compressively stressed due to
flexure, the sheet 22 was able to withstand higher impact forces
acting against face 1 of the panel so that there is less risk of
the windscreen being penetrated by a body in the event of it making
high energy impact against such face. The windscreens fully met the
required biomechanical specifications for avoiding serious risks of
injury to a driver or passenger. The tensile strength of face 4 of
the windscreens was at most 50 kg/mm.sup.2. In order to prevent the
groove 19 in face 4 from causing optical faults, e.g., due to
accumulation of dust in such groove, a sheet 24 of
polymethylmethacrylate 0.5 mm in thickness and having an optical
quality at least as good as that of the glass sheet 20 was glued to
that sheet.
Example 7
A series of panels having the form illustrated in FIGS. 11 and 12
were formed by cementing a stretched acrylic plastic sheet 26
having a thickness of 12.7 mm to a sheet of glass 25 having a
thickness of 2.2 mm. The sheet 25 was made of a glass having the
following composition, by weight:
SiO.sub.2 72% Na.sub.2 O 14% CaO 9% Al.sub.2 O.sub.3 3% MgO 1%
the remainder being impurities.
Before being joined to the sheet 27, the glass sheet 25 was
strengthened by immersion for 24 hours in a potassium nitrate bath
maintained at 460.degree.C. To this end, a group of 12 sheets 25,
as well as 12 samples in the form of discs having a diameter of 11
cm, and having the same thickness and composition as the sheets 25,
were immersed for 24 hours in a bath of potassium nitrate at
460.degree.C.
After this treatment, the mechanical strength relative to flexure
was measured for a group of six discs and it was observed that the
lowest measured value was 70 kg/mm.sup.2 while the highest measured
value was 90 kg/mm.sup.2. Then, six of the sheets 25 and six of the
discs, which had been chemically tempered, each had one face
subjected to an abrasion by means of a powder composed of alumina
and cerium oxide and the abrasion treatment was halted when the
mechanical strength with regard to flexure of one of the discs
reached a value of 48 kg/mm.sup.2. Then, the five remaining discs
which had been abraded were subjected to mechanical strength tests
with respect to flexure and it was observed that the lowest rupture
stress measured was 40 kg/mm.sup.2 and the highest value measured
was of the order of 49 kg/mm.sup.2.
For a group of three sheets 25, the abrasion took place before
assembly, while for a group of three other sheets 25, the abrasion
took place after assembly. No noticeable difference was observed in
the six resulting assemblies formed from these two groups of sheets
25. In addition, for the assemblies having the form illustrated in
FIGS. 11 and 12, it was observed that, in case of shock applied
against face 1 of the assembly, the sheet 26 was more flexible than
the sheet 25 and that the biomechanical safety conditions were
satisfied if the face 4 of sheet 25 had been abraded in the manner
described above, because the face 4 of sheet 25 then had a rupture
stress with respect to tension of no greater than 50
kg/mm.sup.2.
According to one modification of the procedure just described, it
was also noted that it was possible to obtain assemblies of the
type illustrated in FIGS. 11 and 12 which were satisfactory from
the point of view of biomechanical requirements if grooves having a
depth of the order of 0.05 mm were cut in the face 4 of sheet
25.
Example 8
FIG. 13 illustrates another panel formed according to the
invention, which could be utilized as a fire resistant panel. These
panels are constituted by a sheet 28 of vitroceramic material
measuring 2.1 m .times. 1 m .times. 0.006 m and formed from a
vitro-ceramic material having the following composition, by
weight:
SiO.sub.2 74.0% Al.sub.2 O.sub.3 16.2% Li.sub.2 O 5.8% TiO.sub.2
4.0%
and a glass sheet 27 measuring 2.1 m .times. 1 m .times. 0.002 m
and formed from a window glass of ordinary composition.
The sheet 28 is intended to be disposed toward the exterior when
the panel is utilized as a closure panel of a dwelling, a door of
an enclosure or an elevator, or a window of an enclosure. The panel
is assembled in the following manner. Around the periphery of the
face 2 of sheet 27 and the face 3 of sheet 28 thin copper films 29
and 30, respectively, are disposed. The sheets 27 and 28 are then
soldered together by means of a tin solder layer 31 which becomes
bonded to the copper films 29 and 30. For purposes of illustration,
the thicknesses of films 29 and 30 and of solder layer 31 have been
greatly exaggerated. Air trapped within the space 32 between sheets
27 and 28 had been thoroughly dried before the space became
completely sealed by the solder layer 31. According to one
modification, similar panels were produced but, to improve the
insulation and acoustic property of the panels, the space 32 was
filled with glass wool.
Before assembly, the two types of sheets, i.e., the vitroceramic
sheets 28 and the glass sheets 27, were subjected to the same
chemical tempering treatment performed by immersion of the sheets
for 24 hours in a bath of potassium nitrate maintained at a
temperature of 460.degree.C. After this chemical tempering
treatment and a washing and drying, the sheets were assembled as
described above to form the panel illustrated in FIG. 13.
Subsequently, the face 4 of vitroceramic sheet 28 was weakened by
cutting therein a groove 33 having a depth of the order of 0.05 mm
and extending around the periphery of the face at a distance of 1
cm from the edge. With the face 4 weakened in this manner, it was
noted that the panels presented numerous advantages, the principal
ones of which are:
a. while retaining a good resistance to fire, the panels could be
easily broken from the interior, which permitted easy evacuation of
persons trapped in the enclosure closed by the panel;
b. while retaining a good mechanical resistance to flexure in case
of a shock against sheet 27, which is much more flexible than the
sheet 28, the sheet 28 absorbs a part of the energy received by the
sheet 27 when the latter comes in contact with sheet 28, and sheet
28 breaks when subjected to a rupture stress inferior to the value
at which head injuries could occur, if the shock were due to a
person striking the panel, it being recalled that this critical
value is of the order of 50 kg/mm.sup.2.
Example 9
FIG. 15 illustrates another type of hollow panel formed according
to the invention and composed essentially of two sheets 34 and 35,
both made of glass having the following composition, by weight:
SiO.sub.2 71.0% Na.sub.2 O 16.0% CaO 11.0% MgO 0.6% Al.sub.2
O.sub.3 1.4%
The two sheets 34 and 35 had respective thicknesses of 1.5 mm and 3
mm and were joined together by means of a frame 36.
Two different types of panels comparable to that illustrated in
FIG. 15 were constructed. To produce the first type of panel, the
following procedure was employed. Firstly, the sheets 34 and 35
were initially given respectively different curvatures, as shown in
FIG. 14, where the sheet 34 is flat and the sheet 35 is curved. The
sheet 35 is intended to be directed toward the exterior of a
building or room when the resulting panel is utilized as a closing
panel and its curvature is such that its face 4 will be placed in a
state of compression when the sheet 35 is forced into a flat
configuration by the holding action of frame 36.
Before assembly, the sheets 34 and 35 were subjected to a chemical
tempering treatment by immersing them for 24 hours in a potassium
nitrate bath maintained at a temperature of 450.degree.C. Twelve
control discs, six of each thickness, each having a diameter of 11
cm and formed from the same glass as the sheets 34 and 35 were
chemically tempered together with those sheets. Subsequently, each
sheet 35 was treated by being brought into contact for 60 minutes
with an aqueous solution maintained at a temperature of 20.degree.C
and having the following composition:
8.8 liters of water
0.6 liter of H.sub.2 SO.sub.4
0.6 liter of 70% HF
It was observed that this treatment which introduced fluorine ions
into the external layers of the glass sheets not only increased the
mechanical strength of the sheets relative to flexure, but also the
sheets had a better resistance to iridescence. Before assembly, the
entirety of the face 4 of each sheet 35 and one face of each of the
control discs having the same thickness were subjected to an
abrasion treatment by means of an alumina powder whose grains had
an average diameter of 15.mu.. This abrasion treatment was halted
when the rupture stress due to traction of one of the discs was
measured to be 49 kg/mm.sup.2.
It was then noted, by mechanical strength tests, that for a group
of six sheets 35 treated as described above, the value of the
rupture stress of the sheets with respect to traction was between
45 kg/mm.sup.2 and 50 kg/mm.sup.2.
As regards sheets 34, the face 2 of each of these sheets was
subjected to a rectifying treatment such as a treatment utilizing
hydrofluoric acid or the fire polishing treatment described above
in Example 3. In both cases, the strength of face 2 was improved
and each sheet 34 withstood a shock produced by a steel ball
weighing 227 grams and falling from a height of 2.9 m onto face
1.
Then, each treated sheet 34 was assembled with a treated sheet 35
by means of a frame 36 in such a manner that the sheet 35 was
caused to assume a planar configuration and it was noted that the
resulting panels possessed numerous advantages, the principal ones
of which are:
a. the face 4 presented a good resistance to indentation and to
iridescence;
b. in case of a shock caused by a person striking face 1 of the
panel, the sheet 34, being more flexible than the sheet 35, came to
bear against the sheet 35 and the latter broke when the tensile
stresses induced in the face 4 by sheet 34 reached a value of 50
kg/mm.sup.2, so that it was possible to prevent serious head
injuries.
According to a modification of the above procedure, the second type
of panel was formed from a sheet 34 which was chemically tempered
and slightly curved before assembly in such a manner that, during
assembly, the sheet 34 was forced to assume a planar configuration
so that compressive stresses were induced in its face 2. This
permitted the mechanical strength of the sheet due to flexure to be
increased. According to the conditions imposed by the user, one can
combine this treatment for increasing the mechanical resistance of
the sheets 34 to flexure with a fire polishing treatment of the
face 2, or with a treatment by an aqueous solution of hydrofluoric
acid, or simply subject the face 2 to one of these treatments.
Example 10
Windscreens as shown in FIGS. 5 and 6 were made, each comprising
two sheets 16, 18 of soda-lime glass having the following
composition by weight:
SiO.sub.2 72.2% Na.sub.2 O 16.4% CaO 9.4% MgO 0.6% Fe.sub.2 O.sub.3
0.2% Al.sub.2 O.sub.3 0.5% Na.sub.2 SO.sub.4 0.7
secured together by an interposed sheet 17 of high impact
polyvinylbutyral, 0.76 mm in thickness. The sheets 16, 18 were 1.2
mm and 2.0 mm in thickness respectively.
Before assembly, the glass sheets were separately subjected to an
ion diffusion treatment by immersion in a bath of potassium nitrate
at a temperature of 450.degree.C. After such ion diffusion
treatment, measurements were made of the resistance of samples of
the sheets 16, 18 to breakage by flexure placing their convex faces
in tension. In other words each sample was flexed to determine the
maximum tensile loading which could be imposed on face 2 or 4, as
the case may be, by flexing the sample, before breakage of the
sample occured. It was found that sheet 18 could withstand a higher
tensile loading on its convex side than the sheet 16.
A batch of the windscreens was subjected to different mechanical
strength and biomechanical tests as hereafter specified.
In one test each of 10 of the windscreens was subjected to impact
by a body weighing 10 kg of rounded shape and having substantially
the volume of a human head by dropping the body onto face 1 of the
windscreen from a height of 620 cm while the screen was
peripherally supported. In each case the sheet 16 shattered into
small blunt fragments at the zone of impact, but in no case did the
body penetrate or even rupture the polyvinylbutyral intersheet
17.
In another test, each of another ten of the windscreens was
subjected to a similar impact by a rounded body weighing 10 kg
dropped from a height of 620 cm, the body being covered with two
chamois leathers to simulate human skin, and the intensity of the
impact force sustained by the body and the gravity of the cuts in
the leather skins were measured. This involves measuring the
so-called combined index, defined as the sum of:
i. one hundredth of the weighted safety index defined by General
Motors Corporation, viz:
.intg.a.sup.2.5 dt where a = deceleration expressed in multiples of
g = acceleration due to weight;
ii. laceration index having a value from 0 to 10 depending on the
gravity of the cuts; 0 being the value assigned in the absence of
cuts and 10 the value assigned to fatal cuts.
Thus the combined index is: .intg.(a.sup.2.5 dt/100) + laceration
index. For meeting the safety specifications in view, the value of
the combined index should be less than 20.0. In the case of the
batch of windscreens made according to the present example and
subjected to the said test, the value of the combined index was in
no case higher than 7.0.
A further batch of the windscreens made according to this Example
were also subjected to the impact of pieces of hard gravel
projected against face 4 of the screen at different speeds. It was
found that in 90 percent of the tests in which pieces of the gravel
were projected against the screens at 70 km per hour the
windscreens were apparently unaffected or at most a dent from 50 to
100 microns in depth appeared in face 4. In no case was there any
cracks radiating from the indentation so that windscreens affected
in that way during use would not have to be replaced.
A further batch of the windscreens made according to the present
Example were subjected to flexure by the application of an
increasing pressure against face 1 while the screen was
peripherally supported. In each case, notwithstanding the higher
inherent tensile strength of sheet 18 as shown by the tests on
individual sheets 16, 18 as hereinbefore referred to, the sheet 18
broke when a certain flexing load was reached but at that point the
sheet 16 was unbroken and could be subjected to some further
flexure.
Example 11
A batch of vehicle windscreens was made, each windscreen being of
the form illustrated in FIGS. 5 and 6 and comprising two sheets 16,
18 of soda-lime glass having the following composition by
weight:
SiO.sub.2 76% Na.sub.2 O 12% CaO 10% Al.sub.2 O.sub.3 2%
and a sheet 17 of high impact polyvinylbutyral 0.76 mm in
thickness. The glass sheets 16, 18 were 1.5 mm and 3 mm in
thickness respectively. The sheets 16, 18 were subjected to
identical ion diffusion treatment by immersion for 24 hours in a
potassium nitrate bath kept a temperature of 450.degree.C and each
sheet 16 was then secured to one of the sheets 18 by means of a
sheet 17 of polyvinylbutyral.
The resulting windscreens were subjected to various mechanical
strength and biomechanical tests and it was found that they
satisfactorily met the required specifications for the safety of a
vehicle driver or passenger. For instance, impact strength tests
were carried out on several of the windscreens by allowing a
rounded body weighing 10 kg and having substantially the volume of
a human head to fall onto face 1 of the windscreen from a height of
620 cm. In each case the face 1 shattered into very small blunt
fragments at the zone of impact but in none of the cases was the
intersheet of polyvinylbutyral penetrated or even torn. In similar
tests, the intensity of the shock received by the mass representing
the human head was measured and it was found that with such impacts
the weighted safety index defined by General Motors Corporation and
corresponding to the formula:
I (weighted safety index) : .intg.a.sup.2.5 dt.
where: a = deceleration expressed in multiples of g = acceleration
due to weight, never reached the critical value of 1,000. This
value of the weighted safety index is that at which head injuries
become highly dangerous if not fatal.
Moreover face 4 of each of several of the windscreens was subjected
to the impact of pieces of hard gravel projected against the screen
at different speeds. In 90 percent of the tests in which the pieces
of gravel were projected against the screens at 110 kg per hour,
the windscreens were apparently unaffected or at most a dent from
50 to 100 microns in depth was formed in face 4. In no case were
there any cracks radiating from the indentation so that windscreens
affected in that way during use would not have to be replaced.
In addition, tests were made on six chemically tempered sheets 16
and six chemically tempered sheets 18, as used in the windscreens,
to determine their respective resistances to breakage by flexure in
a direction placing their convex faces (faces 2 to 4) in tension.
It was found that the resistance of the sheet 18 was higher than
the resistance of sheet 16. In other words, face 4 was able to
withstand a higher tensile loading than face 2. The relative
strengths of the said sheets were however such that when one of the
completed windscreens was flexed in a direction such as to place
faces 2 and 4 in tension by exerting increasing flexing pressure
against the central zone of sheet 16 while the windscreen was
peripherally supported, sheet 18 broke when a certain flexing load
was reached while sheet 16 remained capable of further flexure.
It will be understood that the above description of the present
invention is susceptible to various modifications, changes and
adaptations, and the same are intended to be comprehended within
the meaning and range of equivalents of the appended claims.
* * * * *