Glass coating apparatus

An apparatus for coating flat glass by directing a reactant gas over the glass surface incorporates a gas flow restrictor which comprises a chamber which is adapted to receive a supply of reactant gas and is adapted to output a flow of the reactant gas over the flat glass being coated. A series of at least two restrictions is provided in the gas flow restrictor, each restriction comprising a plate member extending across the chamber and having a plurality of apertures therethrough.

BACKGROUND OF THE INVENTION 
The present invention relates to an apparatus for coating flat glass by 
directing a reactant gas against the glass surface, the apparatus 
incorporating a gas flow restrictor. 
DESCRIPTION OF THE PRIOR ART 
It is well known that coatings with desirable properties for architectural 
uses can be produced using gaseous reactants which decompose on the hot 
glass surface. Thus silicon coatings, useful as solar control coatings, 
have been produced by pyrolysing a silane-containing gas on a hot glass 
surface, and there have been many proposals to produce other solar control 
and low emissivity (high infra red reflection) coatings from other 
appropriate gaseous reactants. Unfortunately, it has proved difficult in 
commercial practice to achieve sufficiently uniform coatings of the 
required thickness. 
UK Patent Specification No. 1507996 discloses an apparatus for coating flat 
glass in which a gas distributor extends across the width of the glass 
surface to be coated. The gas distributor includes means for releasing gas 
from a gas supply duct to a guide channel uniformly across the width of 
the channel, the channel in use extending across the width of the glass to 
be coated. The guide channel is shaped to cause the gas to flow 
substantially parallel to the glass surface to be coated under laminar 
flow conditions. The releasing means comprises a gas flow restrictor which 
is constituted by an array of channels of small cross-sectional area 
between the supply duct and the guide channel. The array of channels is 
formed by a waffle plate which comprises a plurality of crimped metal 
strips arranged "out-of-phase", as illustrated in FIG. 3 of the 
specification. 
International Patent Specification No. WO 85/01522 discloses an apparatus 
for coating a ribbon of moving glass in which a coating gas passes through 
a box housing a series of alternating converging and diverging 
passageways. The gas exits from the box onto the glass in a uniform 
laminar flow of constant velocity across the width of the glass. 
Whilst both of these prior proposals were stated to achieve uniform 
coatings on the glass substrate, nevertheless the Applicants have found 
that these proposals in practice encounter technical problems which can 
reduce the uniformity of the flow of gas over the glass and hence the 
uniformity of the coatings. In particular, the waffle plates of UK Patent 
Specification No. 1507996 are prone to blockage resulting from 
contaminants in the system. Also, in some applications the gaseous 
reactants must pass through the waffle plate at high temperatures, such as 
300-400.degree. C., and at such temperatures the metal strips are liable 
to distort or slip out of position. These phenomena can reduce the 
uniformity of the gas flow. In the apparatus of International Patent 
Specification No. W085/01522, a plurality of wall members define the 
converging and diverging passageways. These wall members each have one end 
which is fixed to an outer wall of the apparatus and a free end which is 
spaced a small distance from an opposing outer wall and defines a narrow 
slot therebetween. At high temperatures, the wall members can distort 
thereby varying the size of the narrow slot. This can affect the 
uniformity of the gas flow. In addition, the apparatus can be difficult to 
fabricate to the required standards of accuracy. 
SUMMARY OF THE INVENTION 
The present invention aims to overcome the disadvantages of the prior 
proposals described above. 
Accordingly, the present invention provides an apparatus for coating flat 
glass by directing a reactant gas over the glass surface, the apparatus 
incorporating a gas flow restrictor which comprises a chamber which is 
adapted to receive a supply of reactant gas and is adapted to output a 
flow of the reactant gas over the flat glass being coated, and a series of 
at least two restrictions, each restriction comprising a plate member 
extending across the chamber and having a plurality of apertures 
therethrough. 
The apertures of each plate member may be uniformly distributed. 
Advantageously, the apertures of adjacent plate members are out of line 
with one another. 
Preferably, the apertures in each plate member are disposed in a row. 
The apertures may be circular holes. Preferably, the holes have a diameter 
of from 2 mm to 10 mm, especially 2mm to 5mm. For stable gas flow it is 
preferred that each plate member has a thickness which is at least twice 
the diameter of the holes in that plate member. 
The shape, dimensions and relative positions of the apertures may vary for 
different plate members. 
In one preferred arrangement, a first plate member is adjacent to an inlet 
for the restrictor and a second plate member is adjacent to an outlet for 
the restrictor. Preferably, the apertures are more closely spaced in the 
plate member closest to the outlet for the restrictor than in the plate 
member closest to the inlet for the restrictor. 
The gas restrictor may further include a gas flow deflector at the outlet 
between the second plate member closest to the outlet and the glass. The 
gas flow deflector may comprise an deflector member which is disposed 
adjacent the apertures of the second plate member. 
A third plate member may additionally be provided between the first and 
second plate members.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, a gas flow restrictor, designated generally as 2, is 
mounted over a vertical channel 4 defined between two blocks 6, 8 of 
graphite which are suspended across a ribbon of glass (not shown) moving 
from left to right. The vertical channel 4 extends transversely over the 
ribbon of glass being coated. The gas flow restrictor 2 constitutes part 
of a gas distributor which may be of a similar arrangement to that 
illustrated in UK Patent Specification No. 1507996, the disclosure of 
which is incorporated herein by reference. An outlet 10 of the gas flow 
restrictor 2 is aligned with the vertical channel 4. An inlet 12 of the 
gas flow restrictor 2 is, in the illustrated embodiment, connected to a 
fantail distributor 14. The fantail distributor 14 has a front (or 
upstream with reference to the direction of glass movement) wall 16 and a 
back (or downstream, with reference to the direction of glass movement) 
wall 18, each being in the shape of an inverted fan. The front and back 
walls 16, 18 converge towards one another as the width of the fantail 
increases in a downwards direction. 
The gas flow restrictor 2 comprises pairs of opposed elongate walls 20, 22 
and 21, 23 which define an elongate chamber 24. The elongate walls 20, 22 
and 21, 23 extend transversely across the ribbon of glass being coated, 
walls 20 and 21 being upstream walls and walls 21 and 23 being downstream 
walls. Opposed end walls 26 are provided at each end of the elongate 
chamber 24, each end wall 26 being disposed parallel with the direction of 
movement of the ribbon of glass. 
At the inlet 12 of the gas flow restrictor 2, is disposed an inlet 
restriction 27 comprising an inlet elongate plate member 28 which extends 
across the chamber 24. The inlet plate member 28 is sealingly fixed 
between opposing pairs of horizontal plates 30, 32, each pair of plates 
30, 32 being attached e.g. by welding, to a respective elongate wall 20, 
22 and to the fantail distributor 14. The plates of each pair 30, 32 are 
tightly connected together by threaded connectors 34. Gaskets (not shown) 
are disposed between each pair of plates 30, 32 and the inlet plate member 
28. 
FIG. 2 shows the inlet plate member 28 in greater detail. A row of 
apertures 36 which extends along the length of the inlet plate member 28 
is provided through the plate member 28, the apertures 36 connecting the 
inlet 12 with the remainder of the chamber 24. The apertures 36 are 
circular holes. The holes preferably have a diameter of from 2 mm to 10 
mm. In one particularly preferred embodiment, the holes 36 have a diameter 
of 4 mm and have centers spaced 20 mm apart. The row of holes 36 is 
disposed on an upstream side of the elongate chamber 24 i.e. the row of 
holes 36 is nearer to the upstream wall 20 than to the downstream wall 22 
of the chamber 24. 
Adjacent the outlet 10 of the gas flow restrictor 2 is disposed an outlet 
restriction 38. The outlet restriction 38 is of substantially the same 
construction as the inlet restriction 27 in that it comprises an outlet 
elongate plate member 40 which is sealingly fixed between two opposing 
pairs of plates 42, 44, the upper plate of each of said pairs of plates 
42, 44 being connected e.g. by welding to a respective elongate wall 21, 
23. The plates 42, 44 are separated from the outlet plate member 40 by 
gaskets (not shown). The plates 42, 44 are tightly connected together by 
threaded connectors 46 which also firmly attach the plates 42, 44, and 
thereby the gas flow restrictor 2, to a plate 48 which is fixed to the 
tops of the graphite blocks 6, 8. The outlet plate member 40 is provided 
with a row of holes 52 having a diameter of 4mm and centres spaced 10mm 
apart, the row of holes 52 being disposed on the upstream side of the 
elongate chamber 24. 
A gas flow deflector 54 is mounted at the outlet 10 of the gas flow 
restrictor 2 below the outlet plate member 40. The gas flow deflector 54 
comprises an elongate L-shaped member 56 which is integral with the lower 
of said pair of plates 42 and is disposed adjacent the holes 52. The free 
arm 58 of the L-shaped member 56 extends upwardly towards the outlet plate 
member 40 to define therebetween a gap 60 through which reactant gas from 
the holes 52 must pass after having been deflected by the horizontal arm 
62 of the L-shaped member 56. 
The purpose of the gas flow deflector 54 is to remove certain localised 
increases in gas flow which may occur. Thus there is a tendency for the 
gas flow to be more intense in the immediate vicinity of each of the holes 
52 in the outlet plate member 40 on the downstream side of the plate 
member 40. The presence of the gas flow deflector 54 evens out these 
localised increased intensities of flow. In some instances it may be 
possible to omit the gas flow deflector 54 from the gas flow restrictor of 
the invention. 
An intermediate restriction 64 is disposed between the inlet and outlet 
restrictions 27, 38. The intermediate restriction 64 has the same 
construction as the inlet restriction 27 and comprises an intermediate 
elongate plate member 66 with a row of holes 68. The intermediate plate 
member 66 is sealingly fixed between opposing pairs of horizontal plates 
70, 72 which are attached e.g. by welding to the elongate walls 20, 21 and 
22, 23 respectively. Gaskets (not shown) are disposed between the plates 
70, 72 and the intermediate plate member 66 and the flanges 70, 72 are 
tightly connected together by threaded connectors 74. The row of holes 68 
of the intermediate plate member 66 is, in contrast to the inlet and 
outlet plate members 28, 40, disposed on a downstream side of the elongate 
chamber 24 i.e. the row of holes 68 is nearer to the downstream walls 22, 
23 than to the upstream walls 20, 21 of the chamber 24. This arrangement 
results in the row of holes of adjacent elongate plate members being out 
of line with each other. In a preferred embodiment, where the holes in the 
plate members have a diameter of 4mm, the plate members each have 
thickness of 10mm. 
The operation of the gas flow restrictor 2 will now be described. 
The gas flow restrictor 2 forms part of a coating apparatus which is 
suspended across an advancing ribbon of glass. The coating apparatus may 
have one or more of the vertical channels 4 and a corresponding number of 
gas flow restrictors 2 depending on whether one or more reactant gases are 
to be introduced separately into a coating chamber over the ribbon of 
glass. The or each vertical channel exits above the ribbon of glass and 
when there is more than one vertical channel, the channels are located in 
series in a direction along the direction of movement of the ribbon of 
glass. An exhaust duct is provided downstream of the vertical channel(s). 
When the ribbon of glass is float glass, the width of the ribbon of glass 
may be about 3 meters. Each vertical channel and each gas flow restrictor 
must be the same length as the width of the glass to be coated so that 
reactant gas is directed uniformly over the glass surface. Accordingly, 
the gas flow restrictor may be about 3 meters long and it is this length 
requirement which has led to the problems in the prior art referred to 
above concerning the attainment of a uniform gas flow over the entire 
width of the glass to be coated. 
With the present invention, these problems are overcome by tightly clamping 
each restriction and providing in each restriction apertures whose 
distribution and size can be accurately controlled and are not subject to 
significant variations as a result of differential thermal expansion in 
different parts of the gas distributor. 
A reactant gas, diluted in a carrier gas, is fed to the inlet 12 of the gas 
flow restrictor 2 through the fantail distributor 14. The gas impinges on 
the inlet restriction 27 and is forced through the apertures 36 at high 
velocity. The pressure drop across the apertures 36 through the inlet 
plate member 28 is greater than that along the inlet 12. The restriction 
27 accordingly tends to cause the gas to be evenly distributed along the 
length of the chamber 24. The flow is then forced through the apertures 68 
in the intermediate plate member 66 of the intermediate restriction 64. 
The apertures 68 are not in line with the apertures 36 of the inlet 
restriction 27. Accordingly, this prevents a "jetting" effect, i.e. a jet 
of gas cannot pass through one aperture 36 in the inlet restriction 27 and 
then directly through a corresponding aperture 68 in the intermediate 
restriction 64 without being deflected. Again, the gas is forced through 
the apertures 68 at high velocity and a pressure build up on the inlet 
side of the intermediate restriction 64 causes further equalisation of gas 
flow along the length of the intermediate restriction 64. In a similar 
manner the gas issuing from the apertures 68 is then forced through the 
apertures 52 in the outlet restriction 34. Since the apertures 68, 52 in 
the intermediate and outer restrictions are out of alignment, the jetting 
effect referred to above is prevented. The gas issues from the apertures 
52 in the outlet restriction 38 as a gas flow which is substantially 
uniform across the length of the gas flow restrictor 2 i.e. across the 
width of the ribbon of glass. The gas is deflected by the gas flow 
deflector 54 and is forced through the gap 60. The gas flow deflector 54 
prevents jets of gas from the apertures 52 impinging directly on the 
ribbon of glass which could cause localised regions of increased coating 
thickness and could result in a streaking effect on the coating. A uniform 
gas flow issues from the gap 60 and is directed downwardly along the 
channel 4 towards the ribbon of glass. 
The advantages of the gas flow restrictor described are that each 
restriction is substantially unaffected by the high temperatures of around 
300.degree.-400.degree. C. which are typically encountered. Because for 
each aperture in the restriction, the whole circumference of each aperture 
is defined by a single plate, the size of each aperture (and hence the 
distribution of the gas flow) is not affected by differences in the 
thermal expansion of two separate members. This is in contrast to the 
situation in which the gas flows through a slot defined between the edges 
of two separate members, when differences in thermal expansion between the 
two members are liable to lead to irregularities in the width of the slot. 
It is difficult enough to produce narrow slots of regular width over a 
distance of about 3 meters; when such narrow slots are subjected to the 
high temperatures encountered when coating a hot ribbon of float glass 
there is a risk that the slots will distort and lead to non-uniform flows 
of gas. The present arrangement, which relies on a series of holes in a 
plate member, is not susceptible to the same problems of distortion. 
Although the dimensions of the holes will be affected by temperature, the 
holes will all tend to expand to the same extent and provide more uniform 
gas flow across the width of the gas restrictor. 
As indicated above, although the gas flow restrictor can be 3 meters wide, 
the distortion problems of the prior art systems are overcome or at least 
alleviated by the present invention. Also, each plate member is relatively 
easy to manufacture by drilling and reaming a row of holes in the plate 
member. Each restriction is fully sealed by the adjacent plate and this 
ensures that the gas is constrained to flow only through the apertures 
which are of predetermined dimensions and spacing. This enables proper 
control over the uniformity of flow of gas across the ribbon of glass to 
be maintained. 
The number of restrictions in the gas flow restrictor may be varied as 
desired depending upon the particular coating application. Thus for 
example, in some applications, the intermediate restriction 6 may be 
omitted; in this case, it is desirable to have the row of holes 68 on the 
downstream side of the elongate chamber 24 to prevent "jetting" through 
aligned holes in the row of holes 36 and the row of holes 52. 
Furthermore, the size, spacing and positions of the holes in the 
restrictions can be varied. In addition, the shape, dimensions and 
relative positions of the holes may vary for different plate members.