Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF FORMING EVACUATED GLASS PANELS
FIELD OF THE INVENTION
This invention relates to a method of forming an evacuated glass panel
having a chamber that is defined (ie, enclosed) by a~. glass wall that
includes a port
through which evacuation is effected. The invention has been developed in the
context
of evacuated door and/or window glazing {"vacuunn glazing") and the invention
is
herein after described in that context. However, it will be understood that
the invention
does have broader application, for example in forming evacuated solar
collector panels
and panel-form display devices.
BACKGROUND OF THE INVENTION
In one form of vacuum glazing, two plane spaced-apart sheets of glass are
positioned in face-to-face confronting relationship and are hermetically
sealed around
their edges with a low melting point glass that comunonly is referred to a
solder glass.
The space (ie, chamber) between the sheets is evacuated and the face-to-face
separation
of the sheets is maintained by a network of small support pillars. In typical
situations
the glazing may comprise glass sheets that have a surface area in the order of
0.02 to
4.00 square metres, sheet thicknesses in the order of 2.0 to 5.0 millimetres
and a face-to-
face spacing in the order of 0.10 to 0.20 millimetres.
The evacuation of glazing presents special problems (relative to the
evacuation of many other glass objects), in that the; region at which
evacuation is
effected should not be obtrusive in the final product and in that the
evacuating procedure
must be appropriate to panels having large surface areas or linear dimensions.
The
evacuating procedure involves heating the glazing to a high temperature in a
so-called
bake-out oven (whilst the chamber to be evacuated is connected to an
evacuating
system) in order to remove gases from surface regions of the sheets and the
pillars.
In one method of implementing the evacuating procedure, a small pump-
out tube is connected {ie, sealed) to the external surface of one of the glass
sheets in
communication with an aperture that extends through the glass sheet. The
connection
between the tube and the glass sheet is made using solder glass, normally at
the same
3o time that the solder glass edge-seal is made between the sheets. The solder
glass sealing
is normally effected at a temperature around 450°C, that is at a
temperature that is high
enough to melt the solder glass and make a leak-free joint but below a
temperature at
which significant deformation might occur in the glass sheets.
Following completion of the solder glass sealing, the structure is
normally cooled to room temperature. Thereafter, a metal evacuating head is
positioned
over the pump-out tube and is connected to a remote vacuum pump. The
evacuating
head includes a central cavity that is dimensioned) to receive the pump-out
tube and to
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which the vacuum pump is connected.
The glazing structure and the evacuating head are loaded into the bake
out oven where evacuation is effected whilst the complete structure is
subjected to an
out-gassing temperature. Thereafter, the outer end of the pump-out tube is
closed by
heating the tube to its melting temperature.
A problem that is inherent in the above described procedure flows from
the possibility that the evacuating head may be required to have a radial
dimension that
is larger than the desired distance of the pump-out tube from an edge of the
glass sheet.
This imposes a constraint on the location of the pump-out tube and, thus, may
require
that the pump-out tube be located further from the edge than might be required
to meet
aesthetic considerations.
SUMMARY OF THE INVENTION
The present invention is directed to a method of forming an evacuated
glass panel and which facilitates the location of a pump-out tube close to an
edge of the
finished panel.
Broadly defined, the invention provides a method of forming an
evacuated glass panel and which comprises the steps of:
{a) assembling first and second glass sheets in face-to-face spaced-apart
relationship, with the first sheet having an edge portion extending beyond the
2o corresponding edge portion of the second sheet,
(b) providing a pump-out tube in the first sheea at a location adjacent the
corresponding edge portion of the second sheet,
{c) edge sealing the first and second sheets to form a chamber between the two
sheets,
(d) covering the pump-out tube and a portion of the first sheet that surrounds
the
pump-out tube with an evacuating head,
(e) evacuating the chamber by way of the evacuating head,
{f) closing the pump-out tube upon completic>n of the evacuating process, and
(g) trimming the edge portion of the first sheet that extends beyond the
3o corresponding edge portion of the second sheet.
PREFERRED FEATURES OF THE INVENTION
The evacuating head may comprise one that has a first cavity that is
arranged in use to communicate with the pump-out tube, and at least one
further cavity
that surrounds the first cavity and which is arranged in use to contact the
wall portion of
the first glass sheet that surrounds the pump-out tube. With this type of
evacuating head,
the chamber will be evacuated by way of the first cavity whilst a vacuum is
maintained
in the further cavity or, if more than one, in each of the further cavities.
However, the
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evacuating head preferably comprises one having a :first cavity that
communicates with
the pump-out tube and a second surrounding cavity that contains a polymer O-
ring that
contacts the wall portion of the first glass sheet that surrounds the pump-out
tube.
The invention will be more fully understood from the following
description of embodiments of the invention. The description is provided with
reference
to the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
In the drawings:
Figure 1 shows sequential steps A to E in a preferred method of
t o fabricating glazing,
Figure 2 shows sequential steps A to E in an alternative method of
fabricating glazing, and
Figure 3 shows a schematic representation of the glazing located within a
bake-out oven and connected to one or more external vacuum pumps by way of an
15 evacuating head.
DETAILED DESCRIPTION OF THE INVENTION
As illustrated in Figures 1 and 2, an evacuating head 10 is mounted to
glazing 11 that is to be evacuated. The glazing comprises two plane glass
sheets 12 and
13 that are maintained in spaced-apart face-to-face confronting relationship.
The glass
2o sheets would normally be composed of soda-lime glass and be interconnected
along
their edges by a bead 14 of edge-sealing solder glass.
A chamber 1 S is defined by the two glass sheets 12 and 13 and the sheets
are maintained in spaced-apart relationship by a network or array of support
pillars 16.
The chamber 15 is evacuated to a level below 10-3 Torr, this providing for
gaseous heat
25 conduction between the sheets that is negligible relative to other heat
flow mechanisms.
The glass sheet 12 is formed with a:n aperture 17, and a glass pump-out
tube 18 is positioned to locate within and project outwardly from the aperture
17. The
pump-out tube is sealed to the glass sheet by a bead 19 of solder glass.
A metal filament 20 is shown to smxound the pump-out tube 18 and this
3o may be employed, following evacuation of the cavity 15, to melt and close
the pump-out
tube, although ather techniques may be employed for this purpose.
The evacuating head 10 as shown inn Figure 1 comprises a metal body 21
which incorporates a central, first cavity 22. The first cavity is shaped and
dimensioned
to receive the pump-out tube 18 and to provide fo:r unrestricted movement of
gas during
35 evacuation and out-gassing of the chamber 15.
The first cavity 22 is connected by way of a port 23 and a conduit 24 to a
vacuum pump 25 that is located outside a baking chamber 32, as shown
schematically in
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Figure 3.
A second, annular cavity 26 also is provided within the body 21 of the
evacuating head. The second cavity 26 is positioned to surround the first
cavity 22 and
it contains a polymer O-ring 26A which contacts arkd, in use, seals against
the surface of
the glass sheet 12 that surrounds the pump-out tube 18.
A first annular land is located between the first and second cavities 22
and 26, and a second annular land 28 surrounds the annular second cavity 26.
Each of
the two lands 27 and 28 makes contact with the surface of the glass sheet over
a small
area.
t o The evacuating head 10 as shown in Figure 2 is in some respects similar
to that shown in Figure 1 and like reference numerals are employed to identify
like
parts. As shown in Figure 2, the evacuating head 10 comprises a metal body 21
which
incorporates a central, first cavity 22. The first cavity 22 is shaped and
dimensioned to
receive the pump-out tube 18 and to provide for unrestricted movement of gas
during
15 evacuation and out-gassing of the chamber 15.
The first cavity 22 is connected by way of a port 23 and a conduit 24 to a
vacuum pump 25 that is located outside of the baking chamber 32.
A second, annular cavity 26 also is 'provided within the body 21 of the
evacuating head. The second cavity 26 is positioned to surround the first
cavity 22 and
20 is arranged in use to be closed by the surface of thc: glass sheet 12 that
surrounds the
pump-out tube 18. A first annular land 27 is located between the first and
second
cavities 22 and 26, and a second annular land 28 surrounds the annular second
cavity 26.
Each of the two lands 27 and 28 makes contact with the surface of the glass
sheet 12
over a small area and so limits gas flow into the second cavity 26 and between
the two
25 cavities 22-26.
The second cavity 26 is connected Ioy way of a port 29 and a conduit 30
to a further vacuum pump 31, as indicated in Figure 3.
The evacuating heads 10 as shown in Figures 1 and 2 will typically have
an outside diameter of 50 mm to 100 mm and the first, central cavity 22 will
typically
30 have a diameter in the order of l0 mm to 20 mm. The lands 27 and 28 will
each have a
radial width in the order of 1 mm but may be in the range 0.10 rnm to 10 mm.
The sequential steps of fabricating the evacuated glazing unit in a
situation where the pump-out tube I8 is required to be located very close to
one edge of
the unit are clearly shown in Figures 1 and 2. This is achieved by cutting the
sheet 12 to
35 provide a margin or edge portion 33 that extends 'beyond the corresponding
margin or
edge portion 34 of sheet 13, as shown in Figures .A to D, and by trimming the
margin of
sheet 12 after fabrication of the complete glazing unit, as shown in Figure E.
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The sheets 12 and I3 are first assemlbled in spaced-apart relationship (as
above described) and a bead 14 of unfused solder glass is deposited around the
edge of
sheet 13. Similarly, a bead 19 of unfused solder glass is deposited around the
pump-out
tube 18 that is located within aperture 17 in sheet 12.
The further fabrication steps may then be performed by way of a single
heating procedure or two heating procedures depending upon the levels of heat
to be
employed and/or on the type of evacuating head to be used. After assembling
the two
glass sheets and depositing the beads of solder glass, the glazing unit 11 is
heated to
around 450°C within the oven 32 and, during this process, the solder
glass melts to form
seals around the edges of the glazing and around the pump out tube. The
glazing is then
cooled to a temperature (around 380°C) at which the solder glass
solidifies, and
evacuation of the chamber 15 between the two glass sheets 12 and 13 is then
effected by
connecting the vacuum system 25 to the central cavity 22 of the evacuating
head 10.
Evacuation of the chamber is maintained as the glz~zing and evacuating head
are cooled.
The specific temperature/time schedule that is used during this cooling period
will
depend upon the time necessary to achieve adequate out-gassing of the internal
surfaces
of the glazing.
When out-gassing and evacuation has been completed, the pump--out tube
I8 is melted and fused closed, using the filament element 20. Thereafter, the
margin of
2o sheet 12 is trimmed as described above with reference to Figures lE and 2E.
