Note: Descriptions are shown in the official language in which they were submitted.
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1 ~IETI-~OD AND APPARATUS FOR T~IE ~NUFACTURE 0~ GLASS
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2 ¦ 4I) r Tr~ACT
31 This invention relates to a process and an apparatus for
¦ the manufacture of fused glass, suitable for molding, wherein the
51 total time of manufacture is reduced to about one hour. The pro-
6¦ cess accelerates the homogenization and refining of glass by eli-
71 minating unfused particles and gas bubbles which are the main
8¦ factors limiting the production rate of industrial glass. This is
9¦ accomplished by increasing the temperature of the molten glass to
lO¦ produce foaming throughout its mass.
ll ¦SU~IARY' OF THE INVE_TION
12 ¦ The vitreous material undergoing treatment is first melted
¦to form a molten mass. The molten material is then foamed through
14 ¦out its mass. This foaming results in an expansion of the molten
15 ¦vitreous material, by volume, of at least about 1.5 and prefer-
16 lably between about 2 and 3. The foamed material is permitted to
17 ¦subside.
18 ¦BRIEF DES-C'RIPTI'ON OF'THE'D:RAWINGS
l9 ¦ FIGURE l is a schematic view, partially in longitudinal
20 ¦section, of the entire installation;
21 ¦ FIGURE 2 is a cross section along line II-II of Figure l;
22 ¦ FIGURE 3 is a top view of a variation of the refining
23 ¦channel;
24 FIGURE 4 is a longitudinal section along line IV-IV.of
25 Figure 3.
26 DETAILED DESCR'IPl`ION
,,
27 The vitrifiable mixtures of raw materials which can be
28 employed in the process of the present invention are of the type -'
29' commonly used in the manufacture of glass. Examples of a number
30 of these mixtures appear in Table II.
31The present invention requires that the molten material
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1 be foamed throughout its mass. To initiate the intense and com-
2 plete foaming required a number of steps may be taken. For
3 example, foaming agents can be incorporated into the raw material .
.~ The foaming agents give rise, in the temperature range, corres
5 ponding to the desired viscosities, to the formation of gas
6¦ bubbles inside the glass.
7 It is also recommended that a refining agent be present,
at least in the final phase, for the gases produced by these
9 refining agents are soluble in glass, and their solubility in the
lo molten glass increases as its temperature decreases. Thus, after
11 the elimination of most of the gases, the refining agents aid in
12 the readsorption of the bubbles which remain on cooling.
13 The foaming agents are selected such that they do not in-
1~ duce foaming of the vitreous material until that material has
15 reached a desired temperature, which temperature is maintained in
16 the refining channel. rhe following foaming agents are useful in
17 the process according to the present invention : arsenic com-
18 pounds, such as arsenic trioxide ; antimony compounds such as anti
19 mony trioxide ; sulfur compounds, such as sodium sulfate ; and
20 halogen salts such as pottasium chloride. Other agents useful in
21 the process wi-ll be apparent to those skilled in the art.
22 Another method of ensuring the thorough foaming of the
23 molten mass is to subject the batch to rapid uniform heating
24 during the foaming operation of about 20~C per minute or more. -
25 Such heating can bè obtained in various ways, possibly combined9
26 capable of acting within the batch, for example, submerged
27 burners~ submerged resistors, direct Joule effect or high-
28 frequency inducation. If desired, this foaming can be in;tiated
29 or reinforced by mechanical action using an ultTasonic generator.
In a discontinuous melting instalIation, these heating
¦means are employed at a time when the ~itreous batch contains a
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l large number of solid or gaseous nuclei and a sufficient amount
2 of foaming agents to ensure an expansion of at least l.5, and pre-
3 ~erably above 2 times the normal volume of the mass in the un-
4 foamed molten state.
51 In a continuous melting installation similar heating means
6 can be employed. The predefined time sequence corresponds to the
7 rate of treatment of the vitreous mass.
8 To aid the foaming process, it is also recommended that
9 the vitreous mass contains a large number of nuclei, such as un-
melted particles or small gas bubbles, capable of inducing the
ll foaming. When obtaining it through direct melting o-f raw
12 materials, the nuclei should be distributed throughout the molten
13 mass at a concentration of at least lO visible nuclei per cc.
14 Furthermore, it is desirable that the raw materials be agglom~
erated or sintered. The sintering ma~es it possible to preheat
16 the materials before actual melting. This melting is accomplish-
17 ed by a brief and intense heat transfer ~less than lO minutes)
18 while simultaneously keeping the temperature of the materials
9 below the foaming temperature. This permits the maintainance of
a high number of nuclei consisting of unmelted particles and gas
21 bubbles in the vitreous mass introduced into the total foaming
22 stage. The rapid melting of the sintered raw materials can be -~
23 accomplished in various ~ays, or example, by subjecting these
24 materials to hot gases at a controlled temperature, ~hich gases
are driven at high speed and have a large exchange capacity.
26 The granules can be introduced directly into the stream of the
27 gas. The raw materials can take any number of forms, for example,
28 granules, balls, pellets or strips. The thickness of the layer
29 ¦of raw materials can also vary and can be the size of smallest
30 of the sintered materials undergoing melting.
31 To assure the presence of suf~icient nuclei, outside
32 nuclei, for example, cullet or colored cullet can be added to the
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1 raw materials. In relation to the usual glass refining processes,
2 it is important to note that the present invention, requiring the
3 presence of gas producing agents and foaming nuclei, can employ
unrefined vitreous materials. It has been discovered that 1 to
2 mm grains originating from the limestone and dolomite in the
6 material introduced in the refining tank, are totally digested at
7 the end of the total foaming phase. The process according to the
8 invention is there-fore not dependent on the use o~ a vitreous
9 batch of high quality.
In terms of the vilscosity of the vitrifiable material,
11 it is preferably to maintain the viscosity of the material at
12 below about 1,000 poises while melting to form the molten mass.
13 This viscosity of 1,000 poises is also preferably maintained
14 during the foaming of the molten mass and during the time it takes
the foamed mass to subside.
16 In continuous manufacturing installations it is important
17 to avoid upstream currents or currents which exist downstream of
18 the direction of flow of the glass through the refining vessel.
19 For example, currents of thermal origin often exist or are even
deliberately created in the usual melting furnace. The currents
21 tend, in the process according to present invention, to mix
22 glasses in different stages of production. These undesirable
23 currents may be eliminated by using baf~les, dams, bottlenecks or
24 cascades stationed along the course followed by the vitreous mass
undergoing treatment.
It is advantageous for the width of the channel in which
27 the molten stream flows to be narrow in relation to its length, -
28 the ratio between the two being about 1:5 or less. Another para-
29 meter that also affects the product is the thickness of the
stream of flowing glass. In the example given below the height
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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 heiyht of the channel walls is sufficient to ensure
total expansion and damaging curr~nts 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 ob-
tained by directing the flow of the hot gases in a direckion ap-
proximately 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 vitreous batch ready to undergo
total foaming. The surface on which the thin-layer melting is
accomplished can be the inner wall of a cyclone furnace, a rotary
drum combined with a scraper to remove the vitreous batch or the in-
clined surface on which the vitreous batch flows while being formed.
The rate of flow can be regulated by the surface's slope, by the
temperature which affects the viscosity of the batch,and, con- ~-
sequentiy, the adhesion of the granules to that surface, or by the
direction and/or concentration of the gas jets. The example below
describes both the process and the device o~ 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 refining channel
is also shown in Figure 2. Channel 1 is formed from a .7 mm -
thick sheet ~f 10% rhodium-alloyed platinum. Its lenyth i5 1.5 m.
Both the width and the depth are 15 cm. At both ends, the channel ;-
contains 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). Connec:tions 2 are rhodium-alloyed platinum plates 10 mm ,'
thick, 20 cm long and 10 cm high. They are held between two copper
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jaws 4, cooled by water circulation (not shown) and to which axe
attached current lead-ins 5. At lts lower end, the channel con-
tains 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 cock 8 contain-
ing a rhodium-alloyed platinum needle valve allows for the gradual
closing of pipe 6. Above the drawing hole, the channel is pro-
vided with rhodium-plated platinum dam 9 which is welded to
the walls of the channel and leaves a free passage 9a only 20 mm
high at the bottom of the channel. ~he molten material flows
under dam 9 before exiting through draw pipe 6. At the opposite
end of the channel pl~mging resistor 10 is provided. The re-
sistor consists of a U-shaped rhodium-alloyed platinum plate 0.7 mm
thick and 20 cm long. Resistor 10 corresponds to the shape of
the interior section of channel 1. The lower part of plunging
resistor 10 is drilled with evenly distributed holes, the dimen-
sions of which are designed to reduce by approximately 25~ the
area available for passage of 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. Plun~ing resistor 10 is supplied with electric current
by alternating current generator 11 (Figure 2) with adjustable
voltage from 2 to 3V and a power of 5 kVA~ Refining channel 1
is completely ~urrounded by heat insulating cover 12-12a consist-
:
ing of alumina bricks lined wi~h unsealed insulation bricks.
~ By the contrGlled removal of insulation, one is able to determine
- the temperature curve of the material along the channel.
The refining channel is fed at its upper end with a
vitreous batch Eormed in melting furnace 13 by means of junction --
14 containing inclined hearth 15. Hearth 16 of mel~ing furnace ~-
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13 is also inc].incd. Steel pipes 17 cros~ hearths 15 and 16
perpendicular to the plane of symmetry o~ the system. In order
to regulate the temperature of the hear.ths cooling fluids are
passed through these pipes. Arches 18 and 19 of junction 1~ and
furnace 13 respectively are also covered with insula-ting bricks.
~urnace 13 and junction 14 are heatecl, on one side, by burners
20 which cross the arch and are directed 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 called "intensive," i.e., the rate of
ejection of the gases is greater than the rate of fuel combustion.
The flame 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 exchanger 23 in which gravity causes the pre-sintered vitrifi-
able mixture to flow backward. The gases exhausted in heat ex
changer 23 as well as those coming directly from stack 22 (through
bypass 24) 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-insulating material such as ~ieselguhr. The
- introduction into the furnace of vitrifiable raw materials,
sintered and preheated in exchanger 23, is assured by distribu-
ting drum 27. The rate of 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 extrusio~ press which supplies
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compacted bars 7 mm in diameter. A suitable composition o~ the
vitrifiable materials for produciny 90 kg o~ yl~s is:
Sand (250~ m) 60 kg
Limestone (100~ m) 8.5 kg
Dolomite cl mm 14.5 kg
Feldspar (500~ m) 5.5 kg
Dense sodium carbonate6.8 kg
Caustic soda with 50~ NaOH20.2 ky
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.
Exchanger 23 is fed at the top with cold granules which
are progressively heated to a temperature ranging between 500 and
600C at distributing drum 27. Simultaneously, the gases entsring
the exchanger at 750C are mixed with cold air admitted through
hole 2S and are sucked toward cyclone 25 at a temperature of about
200~C. The granules delivered by distributor 27 fall directly on
hiearth 16 in the zone of covergence of burners 21. They are
rapidly converted into a vitreous mass which ~lows over hearth
16 at an average rate of 10 cm per minute. Upon arrival at hearth
15, the temperature of the batch is 1300C. Hearth 15 transfers
the material very rapidly, due to its steeper slope and without
notable heatiny, to the inlet of refinin~ channel 1. Corrosion of
hearths 15 and 16 is rendered negligible by limiting the-tempera-
ture of their surface to approximately 800C. This is accomplished
by the cooling fluid in pipes 17. The temperature in the arches
of these regions, however, is about 1450~C.
On falling into refining channel 1, the material is
sub~ected to rapid heating by contact with the bottom and side
30 walls of the channel and with submerged resistor 10, the
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temperature of which is main~ained at abou-t 1530C. ~or a flow
of 52 kg of glass per hour, the electric power dissipated i5
28 kVA in the channel proper and ~ kVA in the submerged resistor.
Due to the intense heatin~ of the glass, upon crossiny the
submerged resistor 10, a swelling of the mass occurs so that the
thickness of the batch about 4 cm above the submerged resistor
is 13 to 14 cm.
A probe inserted at the bottom of the channel, immediate-
ly below submerged resistor 10, shows that the vitreous mass has
passed totally to the foam state. At a temperature of about lS20C
downstream of resistor 10, a constant rate of swelling by foaminy
is obtained over approximately a 1 m length. This corresponds to
a sojourn of about 15 minutes. Over the next 10 to 15 cm, the
foam subsides very rapidly and the vitreous mass becomes perfectly
refined glass at dam 9, where the temperature is no more than
about 1450C. The refined glass which has passed under dam 9
is 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 described, from the time a
preheated 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 elapses. The device
is capable, without changing its dimensions, of supplying greater
~` flows of refined glass, for example, 100 kg per hour, provided
the rate of foaming is reduced. For an identical vitrifiable
composition, the quantity of fine sodium sulfate introduced ~n
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 14 cm for
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1 ~n expansion of 2. Regardless the method employed (discontinuous
2 ~r continuous), Eor a given increase in temperature and a given
3 ~itrifiable mix~ure, having an identical sodiu~ sui~ate content,
41 the refining time remains constant.
5 ¦ Foaming of the vitr~eous batch throughout its mass, which
61 constitutes the essential characteristic of this invèntion, has
71 ever been heretofdre proposed as making it possible to accelerate
81 the process of melting, refining and homogenization of fused glass.
9¦ The ~ollowing tables give examples of the manufacture
10¦ of five glasses of common type by the process according to the
11¦ invention. Parts are by weight unless otherwise indicated.
12¦ Table I furnishes an analysis of those glasses
131 expressed in percentages by weight of oxides. The fusion
141 described in the foregoing example was glass No. 1.
15¦ Table II furnishes the composition by weight of five
1~¦ vitrifiable mixtures suitable for manufacture of the glass in
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171 uestion.
181 - Table III indicates the characteristics of the
lg¦ rocess as applied to the five glasses.
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23
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28
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1 ¦ TABLE I
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2 ¦ COMPOSITION OF THE GL.~SSES
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5 1` sio2 70.7 73. 7 29.5 56.o ~3.o
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6 ¦ A123 1~3 1. 2 2n4 0~0~ 2~95
7 1 Fe23 00 25
81 CaO 10.3 00l5 0~17 O.OS 7.35
~ MgO 3.3 0.25 3.1
10 ¦ Ba O 0 . 15 2 ~
11 ¦ Na20 14 . û 4 A 8 1~ 45 ~ . 2 14 .1
121
I K20 0.3 2.55 11.0 0~8
13
14 ¦ PbO ~48.9 27.4
15 ¦ B203 1703 16055
18¦ Sb23 . - 007
li I AS23 ~ 7
18 I ~
¦ TABLE I I .
20 ¦ ~7IT~ F I AE~L~ T KTDI~
21 o. or Glasses
comPonents 1 2 3 4
22
and 67. 0 72. 2 26. 65 56 ~ 3 ~6.1
23
imestone 9. 47
2~
olomite 16 . 2 1. 45 - 13. 6
eldspar 6.13
26
Phonol i te 12 . 4
27
aslin 3.2. 6.35
28 odium ca~bonate 70 58 1. 5 6 ,, 65 lg.. 6S
29 otassium carbonate 2. 35 16.15
3ar i um c ar bona .e 0 v 2 3 . 25
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;.ld oxid~ (PbO) 49.0 28.0
~oric acid 12.7 30.0
Borax 15.65
Rasorite 5.6
Calcined coiemanite 8.55
50~ Caustic soda22.5
Sodium sulfate 1~0 1.3
Sodium nitrate 0.5 1.5 1.0
Potassium chloride 1.5
10 Antimony trioxide 1.0
: Arsenic trioxide 2.0
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TABLE I I I
CHARP~CTERISTICS OF TREATMENT
No. of Glasses 1 2 3 4 5
Preliminary melting 1350 1400 1050 1250 1300
temperature (C)
Rate of expansion 25 25 30 35 25
heating ~C/min)
Expansion starting 1400 1450 1100 1300 1430
20 temperature (C)
Expansion . 3 2-3 2-3 2-3 2-3
Time of expansion
: until clarification 10 15 8 S 4
~in minutes)
. Clarification temp-
erature (C) 1520 1550 1260 14~0 1480
`; Figures 3 and 4 describe an alternate device having a
~ refining crucible in which the glass is heated 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 eIectrodes.
`~ ~ The cruci.ble consists o~ a channel of refractory
material 30, the interior rectangular cross section of which iæ
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about 25 centimeters. Its length iB ~bout ~ 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 cen-
timeters 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 co~ventional
glass melting furnaces, an alumina and zircon-base electrofused
material, Cover 34 consisting of bricks of a liyht refractory
material provides heat lnsulation. The heating of the glass
passing through the chan~el and the regulation of its temperature
are assured by six pairs of electrodes E1 to E6. These electrodes,
distributed along the edges of the channel, are made of 3-centimeter
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 channel and make
; possible crosswise placement of the electrodes. The lead-ins are
made of molybdenum.
The glass thickness above outlet 33 is sufficient to
entirely submerge the electrodes and protect them from oxidation.
The current 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 walls. Passage of the current from
;' one electrode to the other produces active thermal convection
which favors the crosswise homogenization of the ~Olten mass
and eliminates parasitic longitudinal currents. The result approa-
ches a uniform flow of glass called "piston" flow. Di~ferent
temperature readings are taken at the points Tl to T7.
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Table IV shows the oharacteristics of the electric
power supply used ln a refining operati~ similar to that of
the foregolng example, i.e., in which the batch of glass,
resulting from preliminary me3ting of composition No. 1, is
introduced into the tank at point Tl at a temperature of about
1250 to 1300C and at a flow of approximately 50 kg/h.
TABLE IV
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Supply devices El E2 E3 E~ E5 6
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Rated characteristics:
Power (kVA) 20 20 6 6 6 6
Voltage (V) 80 80 60 60 60 60
Intensity (A) 250 250 100 100 100 100
Conditions for a delivery
~ of 50 kg/h (glass No.l):
; Power supplied (kVA) 1010 3 3 1 0
Temperature:
Measuring points Tl T2 T3 T4 T5
J 1250
Values (C) 1400 1550 1550 1520 1380 1250
1300
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