Note: Descriptions are shown in the official language in which they were submitted.
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SU~RY Ol~ T~IE: INV~;,MTION
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The vitreous material undergoing trea-tment is first
melted ~o form a molten mass having a viscosity below about
1000 poises. The molten material is then foamed throughout
its mass. This foaming results in an expansion of the molten
vitreous material, by volume, of at least about 1.5 and pre-
ferably between about 2 and 3. The foamed material is permit-
ted to subside while maintaining its viscosity below 1000
poises.
BRIEF DESCRIPTION OF TEIE DRAWINGS
Figure 1 is a schematic view, partially in longi-
tudinal section, of the entire installation;
Figure 2 is a cross section along line II-II of
Figure 1;
Figure 3 is a top view oE a variation oE the reEining
channel;
Figure 4 is a longitudinal section along line IV-IV
of Figure 3.
DETAILED DESCRIPTION
The vitrifiable mixtures of raw materials which can
be employed in the process of the present invention are of the
type commonly used in the manufacture of glass. Examples of
a numb~r oE these mix-tures appear in Table II.
The present invention requires that the molten
material be foamed throughout its mass. To initiate the in-
tense and complete foaming required a number of steps may be
; taken. For example, foaming agents can be incorporated in-to
the raw materials. The foaming agents give rise, in the temp-
erature range, corresponding to the desired viscosities, to
the formation of gas bubbles inside the glass.
It is also recommended that a refining agent be
present, at least in the final phase, for the gases produced
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by these refining agen~s are soluble in glass, and their sol-
ubility in the molten glass increases as its temperature
decreases. Thus, af~er the elimination of most of the gases,
the refining agents aid in the readsorption of the bubbles which
remain on cooling.
The foaming agents are selected such that they do
not induce foaming of the vitreous material until that material
has reached a desired temperature, which temperature is main-
tained in the refining channel. The following foaming agents
are useful in the process according to the present invention :
arsenic compounds, such as arsenic trioxide ; antimony compounds
such as antimony trioxide ; sulfur compounds, such as sodium
sulfate ; and halogen salts such as potassium chloride. Other
agents use~ul in the process will be apparen~ to those skilled
in the art.
Another method of ensuring the thorough foaming of
the molten mass is to subject the batch to rapid uniform heating
during the foaming operation of about 20C per minute or more.
Such heating can be obtained in various ways, possibly combined,
capable of acting within the batch, for example, submerged
burners, submerged resistors, direct Joule effect or high-
frequency induction. If desired, this foaming can be initiated
or reinforced by mechanical actionusing an ultrasonic generator.
In a discontinous melting installation, these heating
means are employed at a time when the vitreous batch contains
a large number of solid or gaseous nuclei and a sufficient amount
of foaming agents to ensure an expansion of at least 1.5, and
preferably above 2 times the normal volume of the mass in the
unfoamed molten state.
In a continuous melting installation similax heating
means can be employed. The predefined time sequence corresponds
to the rate of treatment of the vitroous massO
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To aid the foaming process, it is also recommended
that the vitreous mass con~ains a large number of nuclei, such
as unmelted particles or small gas bubbles, capable of inducing
the foaming. When obtaining it through direct melting of raw
materials, the nuclei should be distributed throughout the mol-
ten mass at a concentration of at least 10 visible nuclei per
cc. Furthermore, it is desirable that the raw materials be
agglomerated or sintered. The sintering makes it possible to
preheat the materials before actual meltin~. This melting is
accomplished by a brief and intense heat transfer (less than 10
minutes) while simultaneously keeping the temperature of the
materials below the foaming temperature. This permits the
maintenance of a high number of nuclei consisting of unrnelted
particles and gas bubbles in the vitreous mass introduced into
th¢ ~otal foaming stage. The rapid melting of the sintered
raw mat~rials can be accomplished in various ways, for example,
by subjecting these materials to hok gases at a controlled
temperature, which gases are driven at high speed and have a
large exchange capacity. The granules can be introduced dir-
ectly into the stream of the gas. The raw materials can takeany number of forms, for examp]e, granules, balls, pellets or
strips. The thickness of the layer of raw materials can also
vary and can be the size of smallest oE the sintered materials
undergoing melting.
To assure the presence oE suEficient nuclei, outside
nuclei, for example, cullet or colored cullet can be added to
the raw materials. In relation to the usual glass refining
processes, it is important to note that the present invention,
requiring the presence of gas producing agents and foamlng
nuclei, can employ unrefined vitreous materials. It has been
discovered that 1 to 2 mm grains originating from the limestone
and dolomite in the material introduced in the refining tank,
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are totall~ dkJcstecl at the end of the total ~oaming phase.
The process according to the invention is thereforo not depend-
ent on the u5e of a vitreous hatch of hiyh quality.
In continous manufacturinq installations it is
important to avoid upstream currents or currents which exist
downstream of the direction of flow of the glass throuyh the
refining vesselO For example, currents of thermal origin often
exist or are even deliberately created in the usual melting
furnace. The currents tend, in the process according to pre- -~
sent invention, to mix glasses in different stages of produc-
tion~ These undesirable currents may be eliminated by usiny
baffles, dams, bottlenecks or cascades stationed alony the
course followed by the vitreous mass undergoing treatment.
It is advantagcous for the wid-th of the channel in
which the molten stream Elows to be n~rrow in relation to its
lenyth, the ratio between the two being about 1:5 or less.
Another parameter that also affects the product is the thick-
ness of the stream of flowing glass. In the example given
below the height of the glass in the channel varies from ~ to
7 cm. In larger installations a height of 10 to 20`cm or more
can be used provided the height of -the channel walls is suf-
ficient to ensure total expansion ancl damaging currents are
avoided.
In order to increase the maximum velocity of the
gases in relation to the materials being heated, the materials
should be maintained in a slow moving thin layer. In practice,
this is obtained by directing the flow of the hot gases in a
direction approximately perpendicular to the inclined surface
on which the granules fall. A layer of granules is easily
fixed on that surface and within a few minutes becomes a vit~
reous batch ready to undergo total foaming. The sur~ace on
which the thin-layer melting is accomplished can be the inner
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wall of a cyclone furnace, a rotary drum combined with a scra-
per to remove the vitreous batch or the inclined surace on
which the vitreous batch flows whilc being formed. The rate
of flow can be regulated by the surface's slope, by the temp-
erature which affects the viscosity of the batch.and, con-
sequently, the adhesion of the granules to that surface, or by
the direction and/or concentration of the gas jets. The exam-
ple below describes both the process and the device of the
present invention.
The installation represented in Figure 1 comprises
a channel 1 in which the molten vitreous material circulates
from right to left while undergoing foaming. The refi.ning
channel is also shown in Figure 2. Channel 1 is formed from
a .7 mm thick sheet of 10% rhodium-alloyed platinum. Its
leng~h is 1.5 m. Both the width and the dep~h are 15 cm. ~t
both ends, the channel con~ains connections 2 supplying it with
electric current delivered by alternating current generator 3,
the voltage of which is adjustable from 0 to 10 V for a power
of up to 25 kVA (2500 A maximum). Connections 2 are rhodium-
alloyed platinum plates 10 mm thick, 20 cm long and 10 cm
high. They are held between two copper jaws 4, cooled by water
circulation (not shown) and to which are attached current lead-
ins 5. At its lower end, the channel contains a draw pipe 6.
The draw pipe is welded to the bottom of the channel and heated
by a rhodium-alloyed platinum resistor 7 wound on an insulating
tube surrounding pipe 6. A coc~ 8 containing a rhodium-alloyed ~.
platinum needle valve allows for the gradual closing of pipe 6.
Above the drawing hole, the channel is provided with a rhodium-
plated platinum dam 9 wllicll is welded to the walls of the chan- . .
nel and leaves a free passage 9a only 20 mm high at the ~ottom
of the channel. The molten material flows under dam 9 before
exiting through draw pipe 6. At the opposite end of the channel
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plungin~ resistor 10 is providccl. The resistor consists of a
U-shapcd rhodium-alloyed platinum pl~te 0.7 mm thic~ and 20
cm lon~. Resistor 10 corresponds to the shape of the interior
section of channel 1. The lower part of plunging resistor 10
is drillcd with evenly distributed holes, the dimensions of
which are designed to reduce by approximately 25% the area
available for passage o~ electric current. The purpose of
this is to localize the dissipation of electric power and to
improve the stirring of the vitreous mass in the course of
foaming. Plunging resistor 10 is supplied with electric current
by alternating current generator 11 (Figure 2) wi~h adjust-
able voltage from 2 to 3 V and a power of 5 kVA. Refining
channel 1 is completely surrounded by heat insu]ation cover
12-12a consisting of alumina bric~s lines with unsealed insul-
ating bricks. By the con-trolled rcmoval of insulation, one is
able to determine th~ temperature curve of th~ material along
the channel.
The refining channel is fed at its upper end with a
vitreous batch formed in melting furnace 13 by means of junc-
tion 14 containing inclined hearth 15. Hearth 16 of melting
furnace 13 is also inclined. Steel pipes 17 cross hearths
15 and 16 perpendicular to the plane of symmetry of the system.
In order to regulate the temperature of the hearths cooling
fluids are passed through these pipes. ~rches 18 and 19 of
junction 14 and furnace 13 respectively are also covered with
insulating bric~s. Furnace 13 and junction 14 are heated,
on one side, by burners ~0 which cross the arçh and are dir-
ected perpendicular to the hearths to which they correspond.
On the other side, they are heated by burners 21 crossing the
base of stack 22 of the furnace and stationed so that their
flames converge in the area of hearth 16 where the granular
material is introduced. These burners are of the type commonly
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called "intcnsive," i.e., the rate of ejection of the gases is
greater than the rate of fuel combustion. The fl~me is caught
in the combustion chamber created in the arch. These burners
can be fed with a mixture of propane, air and/or oxygen from
a mixer ~not shown) with a capacity of 600,000 calories per
hour. The flames escape through stack 22 crossing heat ex-
changer 23 in which gravity causes the pre-sintered vitrifiable
mixture to flow backward. The gases exhausted in heat exchang-
er 23 as well as those coming directly from stack 22 (through
bypass 2~) enter dust-separating cyclone 25. The circulation
and discharge of the gases are assured by fan 26. Heat
exchanger 23 is made of refractory steel and contains a double
wall in which is placed a powdery heat-insu]ating material
such as kieselguhr. The introduction into the furnace of
vitrifiable raw materials, sintered and preheated in exellanger
23, is assured by clistributing drum 27. The rate oE rotation
of drum 27 regulates the feed to the furnace.
; In the melting operation the vitrifiable raw material
used is a material sintered in an extrusion press which sup-
plies compacted bars 7 mm in diameter. ~ suitable composition
of the vitrifiable materials for producing 90 kg of glass is:
Sand (250 ~m) 60 kg
Limestone (100 ~m) 8.5 kg
Dolomite ~1 mm 1~.5 kg
Feldspar (500 ~m) 5.5 kg
Dense sodium carbonate 6.8 kg
Caustic soda with 50~ NaOH20.2 kg
Fine sodium sulfate 0.9 kg
The granules can-be dried in a ventilated electric
oven at 250C, and stored away from moisture without other
precautions.
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Exchanger 23 is fed at the top with cold granules
which are progressively heated to a temperature r~nging between
500 and 600C at distributing drum 27. Simultaneously, the
gases ~ntering the exchanger at 750C are mixed with cold air
admitted through hole 28 and are sucked toward cyclone 25 at
a temperature of about 200C. The granules deli~ered by
distributor 27 fall directly on hearth 16 in the zone of cov-
ergence of burners 21. They are rapidly converted into a vit-
reous mass which flows over hearth 16 at an average rate of 10
cm per minute. Upon arrival at llearth 15, the temperature of
the batch is 1300C. Hearth 15 -transfers the ma-terial very
rapidly, due to its steeper slope and without notable heating,
to the inlet of refining channel 1. Corrosion oE hearths 15
and 16 is rendered negligible by limiting the temperature of
their surEace to approximately 800C. This is accomplished
by the cooling fluid in pipcs 17. The temperature in the
arches of these regions, however, is about 1450C.
On falling into refining channel 1, the material is
subjected to rapid heating by contract with the bottom and
side walls of the channel and with submerged resistor 10, the
temperature of which is maintained at about 1530C. For a
flow of 52 kg of glass per hour, the electric power dissipated
is 28 k~A in the channel proper and ~ kVA in the submeryed
resistor. Due to the intense heating of the glass, upon cros-
sing the submerged resistor 10, a swelling of the mass occurs
so that the thic~ness of the batch about 4 cm abo~e the sub-
merged resistor is 13 to 14 cm.
A probe inserted at the bottom of the channel,
immediately below submerged resistor 10, shows that the vitreous
mass has passed totally to the foam stateO At a temperature
o about 1520C downstream of resistor 10, a constant rate
of swelling by foaming is obtained over appro~imately a 1 m
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length. This corresponds to a sojourn of about 15 minutes.
Over~the ncxt 10 to 15 cm, the foam subsides very rapidly and
the vitreous mass becomes per~ectly refined glass at dam 9,
where the temperature is no more than about 1~50C. l`he
refined glass which has passed under dam 9 i5 drawn off through
pipe 6. The level of the material in the channel is kept
constant by regulating its delivery through pipe 6 using cock 8.
In the example just ~escribed, from the time a pre-
heated granule falls on hearth 16 of the melting furnace and
the time when the refined glass corresponding to that granule
is drawn off through pipe 6`only 30 minutes el~pses. The
device is capable, without changing its dimensions, of sup-
plying yreater flows of refined glass, for exampl~, 100 kg per
hour, provided the rate o~ foamirlcJ is reduced. For an iden-
t~ical vitrifiable composition, the quantity oE fine sodium
sulfate introduced in the vitrifiable mixture is reduced to
0.7 kg per 100 kg of glass produced. Under those conditions,
the initial height of the batch above resistor 10 is 7 cm, and
expands to about 1~ cm for an expansion of 2. Regardless of
the method employed (discontinuous or continuous), for a
given increase in temperature and a given vltrifi~ble mixture,
having an identical sodium sulfate content, the refining time
remains constant.
Foaming of the vitreous batch throughout its mass,
which constitutes the essential characteristic of this inven-
tion, has never been heretofore proposed as making it possible
to accelerate the process of melting, refining and homogeniza-
tion of fused glass.
The following tables give examples of the manufacture
of five glasses of common type by the process according to the
invention. Parts are by weight unless otherwise indic:ated.
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Table I furnishes an analysis of those glasses
expressed in percentages by weight of oxides. The fusion
described in the foregoing example was glass No. 1.
Table II furnislles the composition by weight of five
vitrifiable mixtures suitable for manufacture of the glass in
question.
Table III indicates the characteristics of the pro-
cess as applied to the five glasses.
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T~BLE I
COMPOSITION OF T~IE GL~SSES
_
No of Glasses
Oxides 1 2 3 4 5
SiO270.7 73.7 29.5 56.0 63.0
A123 1.3 1.2 2.4 0.05 2.95
Fe23 0.25
CaQ 10.3 0.5 0.17 0.05 7.35
MgO 3.3 0.25 3.1
BaO 0.15 2.5
Na2014.0 4.8 ~.45 4.2 14.1
K20 0.3 2.55 11.0 0.8
PbO 48.9 27.4
B203 17.3 16.S5 5.9
Sb23 Q-7
A52~3 0.7
TABLE II
VITRIFIABLE MIXTURES
No. of Glasses
com~onents 1 2 3 4 5
Sand 67.0 72.2 26.65 56.3 56.1
Limestone9.47
Dolomite16.2 1.45 13.6
Feldspar6.13
Phonolite 12.4-
Kaolin 3.2 6.35
Sodium carbonate 7.58 1.5 6.65 19.65
Potassium carbonate 2.35 16.15
Barium carbonate 0.2 3.25
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Lead oxide (PbO) 49.0 28.0
Boric aci.d 12.7 30.0
Borax 15.65 '
Rasorite 5.6
Calcined colemanite 8.55
50% Caustic soda22.5
Sodium sulfate 1.0 1.3
Sodium ni~rate 0.5 1.. 5 1.0
Potassium chloride 1.5
Antimony trioxide . 1.0
Arsenic trioxide 2.0
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TABLE III
CHAR~CTE~IST:tCS OF TR~AI'MEN'l'
No. of Glasses 1 2 3 4 5
Preliminary melting
temperature (C)1350 1400 1050 1250 1300
Rate of expansion
heating (C/min) 25 25 30 35 ~ 25
Expansion starting
temperature (C)1400 1450 1100 1300 1430
Expansion 3 2-3 2-3 2-3 2-3
Time of expansion
until clarification
(in minutes) 10 15 8 5 4
Clarification temp-
erature (C) 1520 1550 1260 1480 1480
Figures 3 and 4 describe an alternate device,having a
refining crucible in which the glass is heatecl by direct Joule
effect. This device is not useful in the manufacture of the lead
glasses of Examples 3 and 4, but is more economical than the
previous method, because it uses molybdenum electrodes.
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The crucible consist~ of a channel of refractory
material 30, the interior rectangular cross section of which is
about 25 s~uare centimeters. Its length is about 2 meters. The
lower part contains a narrow funnel type portion 31 about 5 cen
timeters above hearth 32 and reducing the width to a few centi-
meters in order to conduct the glass to outlet 33 while avoiding
any blind angles likely to create stagnation.
The hearth and wall of channel 31 as well as its arch
(not shown) are of a material commonly employed in conventional
glass melting furnaces, an alumina and zircon-base electrofused
material. Cover 3~ consisting of briclcs of a light refractory
material provides heat insulation. The heating of the glass pas-
sing through the channel and the regulation of its temperature
are assured by six pairs oE electrocles El to r!6 . 'l'hese elec-
t~odes, distributed along the edcJas o the channcl, are mad~ of
3-eentime-ter plates and are arranged symmetrically in relation
to the axis of the channel. They are distributed along the edges
of this channel. Each pair of electrodes is connected to an
independent adjustable electric power source. The current lead-
ins of the electrodes horizontally cross the walls of the ehanneland make possible erosswise placement of the eleetrodes. The
lead-ins are made of molybdenum.
The glass thiekness above outlet 33 is sufEieien-t to
entirely submerge the electrodes and protect them from oxidation.
The eurrent lead-ins are protected by bathing their hot parts in
a reducing atmosphere consisting, for example, town gas.
The glass has free passage around the electrodes along
the hearth and side wallsO Passage of the eurrent from one
electrode to the other produces active thermal conveetion whieh
favors the erosswise homogeni~ation of the molten mass and eli-
minates parasitic longitudinal eurrentsO The result approaches
a uniform flow of glass called "piston" flow. ~ifferent
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temperaturc readings are tal:en at the points Tl to T7.
Table IV shows the characteristics of the electric
power supply used in a refining operation simi]ar to that of
the foreyoing example, i.e., in which the batch of glass, result-
ing from preliminary melting of composition No. 1, is introducecl
into the tank at point 1'1 at a temperature of about 1250 to
1300C and at a flow of approximately 50 kg/h.
TABL~ IV
Supply devices El E2 E3 E4 E5 E6
Rated characteristics
Power (kVA) 20 20 6 6 6 6
Voltage (V) 80 80 60 60 60 60
Intensit~ (~) 250 250 100 100 100 100
Conclitions for a cl~livery
of 50 kg/h (glass No. 1)~
Power supplied (kVA) 10 10 3 3 1 0
Temperature :
Measuring points T 11' 2 T 3 T 4 T 5 T 6 T 7
1250
1400 1550 1550 1520 1380 1250
Values (C) 1300
20This application is a division of copending
Canadian application Serial No. 233,203, filed August 14, 1975.
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