Covering for the tempering of glass

A device for air-tempering, optionally associated with bending of glass plates includes a covering made of a metal fabric and exhibiting a thermal conductivity less than 3 and preferably less than 0.2 W.M.sup.-1.K.sup.-1. It has utility for coverings of frames intended to carry glass plates during their tempering and/or their bending and/or their transport.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates essentially to air-tempering, optionally associated 
with bending of glass plates and more particularly to a covering for a 
frame intended to carry glass plates during their tempering, their bending 
and optionally their transport. 
2. Background of the Related Art 
One of the known techniques of bending and air-tempering of glass plates 
uses a frame, with a curved profile, open in its center, on which the 
glass plates rest so as to be bent, tempered, transported, etc. Such 
frames are described, for example, in French patent FR 2 572 388. 
A glass plate heated to its bending and tempering temperature is placed on 
such a frame and there can undergo bending by the simple effect of gravity 
and/or pressing, it can then be transported while still resting on this 
frame, particularly to the tempering station where it is subjected to an 
intense blowing. It is possible to use a single frame when going from one 
work station to the next, but it is also possible to use a plurality of 
frames, each coming in at a well-defined station, the glass plates 
therefore changing support means when they go from one station to the 
next. This plurality of frames in certain cases can be required only by a 
particular organization of the tasks to be performed, but rather often it 
is also made necessary by the inability of a single frame to perform all 
the roles of: bending frame, tempering frame, transport frame, etc. 
Actually, to perform all these roles the frame should perform multiple 
qualities that are not easily compatible: it should resist high 
temperatures, have a good mechanical strength to be able to withstand the 
bending operations; particularly by pressing; it should also have a poor 
thermal conductivity so as not to mark the glass thermally or even make it 
break when the glass and frame are at temperatures that are too different 
from one another. Further it should have a high porosity to air, so as not 
to constitute a screen, with regard to the glass, to the air which is 
blown during tempering. 
Various types of frames have been tried to obtain this but none has been 
completely satisfactory or able to be used in a field slightly broader 
than that for which it was strictly designed (limited curvature forms, 
limited glass/frame contact times not allowing long bending times for deep 
or complex shapes to be given to the glass, or not allowing pressing, 
etc.). 
Thus, it is standard practice to cover a frame with a metal netting with 
fine meshes, for example, of bronze; the desired porosity and mechanical 
strength are obtained but the deformability of the netting is not 
sufficient for a perfect fit of some complicated shapes of frames, and the 
thermal insulation that the netting provides is not sufficient to allow 
very long glass/frame contact times. 
In an effort to improve heat insulation, the metal netting was replaced by 
glass or ceramic fabric, but a problem of durability, i.e., of crumbling, 
of the fabric then arises. 
There were then proposed metal frames, perforated or equipped with 
small-sized projecting pins, on which the glass rests, or grooves made in 
the thickness of the metal of the frame, thus reserving passages under the 
glass for the tempering air. Generally, such frames with pins or grooves 
or perforations can function if the glass/frame contact time is short; but 
if the time is extended, in particular because of pressing or because the 
shapes it is desired to give the glass are complex and require a little 
longer shaping time, breaking of the glass is observed. 
Along the same line, French patent FR 2 597 089 proposes, instead of metal 
nettings, a perforated metal strip having a porosity to air of at least 
about 40%. Such a perforated metal strip is difficult to put in place, 
difficult to fit perfectly on frames with a complex shape, its porosity is 
too slight if it is desired that it maintain a sufficient mechanical 
strength and the thermal insulation that it provides is not sufficient. 
This invention has an object the providing of a covering exhibiting 
qualities of mechanical strength, thermal insulation, porosity to air, 
resistance to high temperature and deformability that allow its use as 
covering and means for support, contact, transport of glass and 
particularly during its bending and/or its air-tempering. 
For this, it proposes a covering and support intended to be inserted 
between objects of hot glass, particularly glass plates brought to their 
bending and tempering temperature. The covering comprises an essentially 
metal fabric exhibiting a thermal conductivity less than 3 and preferably 
less than 0.2.WM..sup.-1.K.sup.-1. 
In a first embodiment, this covering is an essentially metal fabric formed 
by rovings of a plurality of elementary threads, the rovings placed in 
different directions together to form meshes, and crisscrossing to form 
knots at the tops of the meshes, thanks to which said meshes are 
dimensionally stable. 
In a second embodiment, this covering consists of the metal fabric itself 
and an intermediate ceramic layer of the zirconium oxide type deposited 
under the metal fabric.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows an example of a fabric 1 exhibiting the characteristics 
necessary for a frame or a covering of a glass support frame, entering 
into bending, air-tempering and/or transport, namely: 
resistance to high temperatures, 
mechanical strength, 
insulation, 
porosity to air, 
deformability to fit all the profiles of the frames. 
So far, the expression support frame or support means of the glass has been 
used, which implies that this frame or this support means is placed under 
the glass. Actually, the invention is applicable to any frame or means 
coming in contact with the glass, whether it is above or below, and the 
word support is to be taken in this more general sense. 
This fabric 1 is made essentially of metal threads of the refractory 
stainless steel type to contribute, thanks to the metal, a mechanical 
strength and resistance to high temperatures. 
In this first embodiment, the insulation and porosity to air are 
contributed by the fineness of the elementary threads of the fabric and 
their mode of assembly. 
The elementary threads used are thin, of a diameter less than 50 microns, 
particularly less than 30 microns and preferably less than 15 microns, for 
example on the order of 10 microns. This thinness of the threads 
contributes to the capacity of the fabric to be deformed to fit the 
profile of the frames. 
A plurality of these threads, at least about 90, is arranged in each of the 
rovings 2 and 3. By way of nonlimiting example, rovings 2 shown 
horizontally in FIG. 1 consists of several strands, for example, two 
strands 4 and 5, each strand itself consisting of one or more groups of 
elementary threads, for example, three groups of 90 elementary threads 
each. 
The other rovings 3, placed vertically in FIG. 1, as shown by way of 
example, are made up of several strands, for example, three strands 6, 7 
and 8 themselves formed by several groups of elementary threads, for 
example, two groups of 90 elementary threads. Each roving 3 is knotted 
over its entire length and in particular crisscrosses rovings 2 arranged 
in another direction to constitute meshes 10 having, at their nodes, knots 
11 for binding rovings 2 and rovings 3. 
Thanks to these knots 11 at their nodes, meshes 10 are dimensionably 
stable. 
The example of fabric shown in FIG. 1 exhibits approximately square meshes 
of about 5 mm on each side, and it has a thickness of about 0.5 to 2 mm. 
Advantageously, to increase the mechanical strength of this fabric and in 
particular the dimensional stability of its meshes, additional strands 4, 
5, 6, 7 and 8 do not belong solely to one roving 2 or 3, but over their 
length they successively belong to one roving, then to another. They form 
a series of adjacent loops, partially coverings the loops of another 
series of adjacent loops placed opposite there to and in the opposite 
direction, all these loops being knotted by fours as well as, for example, 
an additional, for example vertical, strand placed between the adjacent 
loops of each series, with a strand, for example, horizontal. 
Thus, each loop participates over a part of its length in the formation of 
a roving, for example 3, then in the formation of another roving, for 
example 2, then in the formation of a roving of type 3 close to the 
preceding one. 
Others modes of weaving are also possible. 
The porosity to air of such a fabric is at least about 60% and preferably 
on the order of at least 80%. The meshes can be quadrilaterals, for 
example squares, with a side of from 2 to 10 mm. 
Other forms are also possible, in particular when the number of rovings is 
greater than 2; the surface area of the meshes, however, always remaining 
of the same order, i.e., between about 4 mm.sup.2 and 1 cm.sup.2. 
Such a fabric has a thermal conductivity less than 3 and preferably less 
than 0.2 W M.sup.1.K.sup.-1, which corresponds to a thermal resistance 
between 10.sup.-3 and 50.10.sup.- M.sup.2.K.W.sup.-1. 
Such a fabric is used particularly to cover a tempering and/or bending 
and/or transport frame 20 as shown in FIG. 2, this frame being metal or 
essentially metal. 
To allow the tempering air to pass through this fabric 1, it is important 
that the tempering air not be stopped by frame 20 itself. This frame 20 is 
then punched; for example the frame can consist of a flat iron 21 pierced 
with orifices such as 22 as shown in FIG. 2, or constituted in an 
equivalent manner, for example formed of a section on which are fastened 
spaced pins intended to carry the glass to form a gap in which the air can 
circulate, or a section in which striae or grooves are made to let the air 
pass, or a section with a notched edge, these different embodiments not 
being represented. 
In another embodiment, the covering consists of an essentially standard 
metal lattice or a fabric identical with that described above and there is 
included an intermediate insulating layer, for example, with a ceramic 
base of the zirconium oxide type. 
This zirconium oxide is deposited, for example, on the support intended to 
come in contact with the glass, by spraying of powder in a flame, plasma 
or equivalent. 
This support covered by the insulating intermediate layer, is then covered 
by a lattice or a fabric that is essentially metal. Advantageously to 
promote anchoring of the intermediate layer to the frame and to improve 
its mechanical strength especially at high temperature, a sublayer with a 
coefficient of expansion between that of the frame and that of the 
zirconium oxide layer is provided, for example, a sublayer with a Ni and 
Cr base. Frames for tempering, bending, transport of glass plates can also 
be covered as described in this second embodiment. This unit of standard 
metal lattice and intermediate layer has the same characteristics of 
thermal conductivity or thermal resistance as the individual essentially 
metal fabric described above. 
Thanks to such coverings, the frames can carry the glass through their 
various thermal treatments, if desired, without it being necessary to 
change the frame at each treatment. 
Such coverings can also be used as electromagnetic shields, as contact 
materials between any hot body and a support, as a sheath of rollers 
intended to transport hot glass in plates, as a conveyor belt or as 
covering of a conveyor belt intended to carry hot glass objects.