U.S. patent number RE36,082 [Application Number 08/655,935] was granted by the patent office on 1999-02-09 for vacuum degassing method and its apparatus.
This patent grant is currently assigned to Asahi Glass Company Ltd.. Invention is credited to Kazuhiko Ishimura, Shinsuke Nakajima, Misao Okada, Fumiaki Saito, Masaaki Yoshikawa.
United States Patent |
RE36,082 |
Ishimura , et al. |
February 9, 1999 |
Vacuum degassing method and its apparatus
Abstract
A vacuum degassing method wherein a molten substance at an
elevated temperature in a storage tank is sucked to a vacuum
degassing vessel through an uprising pipe connecting the storage
tank and the vacuum degassing vessel by maintaining the vacuum
degassing vessel at a negative pressure, the molten substance is
degassed and the degassed molten substance falls to a guiding duct
through a downfalling pipe connecting the vacuum degassing vessel
and the guiding duct characterized by that a first flow quantity of
the molten substance rising in the uprising pipe is restrained and
a second flow quantity thereof falling in the downfalling pipe is
controlled thereby maintaining a quantity of the molten substance
in the vacuum degassing vessel at a pertinent level.
Inventors: |
Ishimura; Kazuhiko (Yokohama,
JP), Saito; Fumiaki (Yokohama, JP),
Yoshikawa; Masaaki (Yokohama, JP), Okada; Misao
(Yokohama, JP), Nakajima; Shinsuke (Kawasaki,
JP) |
Assignee: |
Asahi Glass Company Ltd.
(Tokyo, JP)
|
Family
ID: |
11672882 |
Appl.
No.: |
08/655,935 |
Filed: |
May 31, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
005798 |
Jan 19, 1993 |
05316563 |
May 31, 1994 |
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Foreign Application Priority Data
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Jan 20, 1992 [JP] |
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4-007694 |
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Current U.S.
Class: |
65/32.5;
65/134.9; 65/134.2; 266/209; 95/248; 95/266 |
Current CPC
Class: |
C22B
9/04 (20130101); C03B 5/2252 (20130101); C21C
7/10 (20130101); C03B 5/28 (20130101); C03B
5/1875 (20130101); Y10S 261/19 (20130101) |
Current International
Class: |
C03B
5/225 (20060101); C03B 5/00 (20060101); C03B
5/28 (20060101); C22B 9/04 (20060101); C03B
5/187 (20060101); C22B 9/00 (20060101); G03B
005/173 () |
Field of
Search: |
;65/134.9,134.2,32.5
;266/209 ;75/508,510 ;95/175,248,260 ;261/DIG.19 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1 485 634 |
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May 1967 |
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FR |
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2 115 176 |
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Jul 1972 |
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FR |
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2 302 345 |
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Sep 1976 |
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FR |
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333020 |
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Feb 1991 |
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JP |
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1 023 413 |
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Mar 1966 |
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GB |
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Primary Examiner: Hoffmann; John
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
We claim:
1. A vacuum degassing method for degassing molten glass, the method
comprising the steps of:
sucking a heated molten substance in a storage tank into a vacuum
degassing vessel through an uprising pipe which connects the
storage tank and the vacuum degassing vessel by maintaining the
vacuum degassing vessel at a negative pressure;
degassing the molten substance wherein the degassed molten
substance flows down to a guiding duct through a downfalling pipe
which connects the vacuum degassing vessel and the guiding
duct;
restraining a first flow quantity of the molten substance rising in
the uprising pipe by rotation of a first screw means positioned in
said uprising pipe; and
controlling a second flow quantity of the degassed molten substance
flowing in the downfalling pipe by rotation of a second screw means
positioned in said downfalling pipe;
wherein a quantity of the molten substance in the vacuum degassing
vessel is maintained at an amount which prevents an overflow of
molten substance in the vacuum degassing vessel.
2. The vacuum degassing method according to claim 1, comprising the
further step of:
maintaining a height of a first surface of material of the molten
substance in the vacuum degassing vessel the same as a height of a
second surface of material of the molten substance in the storage
tank.
3. A vacuum degassing method for degassing molten glass, the method
comprising the steps of:
providing a vacuum degassing vessel in a vacuum housing;
sucking a molten substance into the vacuum degassing vessel through
a first uprising pipe;
controlling a first flow quantity of the molten substance rising in
the first uprising pipe by rotation of a first flow quantity
control means which is positioned in a first downfalling pipe, said
first downfalling pipe being provided upstream of said first
uprising pipe and downstream of a storage area for said molten
substance with respect to a flow direction of said molten substance
and having a bottom which is connected to a bottom of the first
uprising pipe;
degassing the molten substance in the vacuum degassing vessel such
that the degassed molten substance flows down through a second
downfalling pipe; and
controlling a second flow quantity of the degassed molten substance
flowing in the second downfalling pipe by rotation of a second flow
quantity control means positioned in a second uprising pipe, said
second uprising pipe being provided downstream of the second
downfalling pipe with respect to a flow direction of said degassed
molten substance and having a bottom which is connected to the
bottom of the second downfalling pipe;
wherein top portions of the first and second flow quantity control
means are positioned outside of the vacuum housing, and the first
and second flow quantity control means maintain a first surface of
the molten substance int he vacuum degassing vessel at a level
which is substantially the same as a level of a second surface of
the molten substance which is in said storage area before said
degassing step.
4. The vacuum degassing method according to claim 3, wherein the
first and the second flow quantity control means are screws which
are respectively rotatably positioned in the first downfalling pipe
and in the second uprising pipe. .Iadd.
5. A vacuum degassing method comprising the steps of:
sucking a heated molten substance in a storage tank into a vacuum
degassing vessel through an uprising pipe which connects the
storage tank and the vacuum degassing vessel by maintaining the
vacuum degassing vessel at a negative pressure;
degassing the molten substance wherein the degassed molten
substance flows down to a guiding duct through a downfalling pipe
which connects the vacuum degassing vessel and the guiding
duct;
restraining a first flow quantity of the molten substance rising in
the uprising pipe with a first flow quantity controlling means
positioned in said uprising pipe; and
controlling a second flow quantity of the degassed molten substance
flowing in the downfalling pipe with a second flow quantity
controlling means positioned in said downfalling pipe;
whereby a height of a first surface of the molten substance in the
vacuum degassing vessel is maintained to be the same as a height of
a second surface of the molten substance in the storage tank;
wherein a quantity of the molten substance in the vacuum degassing
vessel is maintained at an amount which prevents an overflow of the
molten substance in the vacuum degassing vessel..Iaddend..Iadd.6.
The vacuum degassing method as claimed in claim 5, wherein said
first flow quantity controlling means is a
plunger..Iaddend..Iadd.7. A vacuum degassing method for degassing
molten glass comprising the steps of:
sucking heated molten glass in a storage tank into a vacuum
degassing vessel through an uprising pipe which connects the
storage tank and the vacuum degassing vessel by maintaining the
vacuum degassing vessel at a negative pressure;
degassing the molten glass wherein the degassed molten substance
flows down to a guiding duct through a downfalling pipe which
connects the vacuum degassing vessel and the guiding duct;
restraining a first flow quantity of the molten glass rising in the
uprising pipe with a first flow quantity controlling means
positioned in said uprising pipe; and
controlling a second flow quantity of the degassed molten glass
flowing in the downfalling pipe with a second flow quantity
controlling means positioned in said downfalling pipe;
whereby a height of a first surface of the molten glass in the
vacuum degassing vessel is maintained to be less than 3.5 meters
different than a height of a second surface of the molten glass in
the storage tank;
wherein a quantity of the molten glass in the vacuum degassing
vessel is maintained at an amount which prevents an overflow of the
molten glass in the vacuum degassing vessel..Iaddend..Iadd.8. A
vacuum degassing method comprising the steps of:
sucking a heated molten substance in a storage tank into a vacuum
degassing vessel through an uprising pipe which connects the
storage tank and the vacuum degassing vessel by maintaining the
vacuum degassing vessel at a negative pressure;
degassing the molten substance wherein the degassed molten
substance flows down to a guiding duct through a downfalling pipe
which connects the vacuum degassing vessel and the guiding
duct;
restraining a first flow quantity of the molten substance rising in
the uprising pipe with a first flow quantity controlling means
positioned upstream of said vacuum degassing vessel; and
controlling a second flow quantity of the degassed molten substance
flowing in the downfalling pipe with a second flow quantity
controlling means positioned downstream of said vacuum degassing
vessel;
whereby a height of the first surface of the molten substance in
the vacuum degassing vessel is maintained to be the same as a
height of a second surface of the molten substance in the storage
tank;
wherein a quantity of the molten substance in the vacuum degassing
vessel is maintained at an amount which prevents an overflow of the
molten substance in the vacuum degassing vessel..Iaddend..Iadd.9. A
vacuum degassing method comprising the steps of:
sucking a heated molten substance in a storage tank into a vacuum
degassing vessel through an uprising pipe which connects the
storage tank and the vacuum degassing vessel by maintaining the
vacuum degassing vessel at a negative pressure;
degassing the molten substance wherein the degassed molten
substance flows down to a guiding duct through a downfalling pipe
which connects the vacuum degassing vessel and the guiding
duct;
restraining a first flow quantity of the molten substance rising in
the uprising pipe with a first flow quantity controlling means
positioned upstream of said vacuum degassing vessel; and
controlling a second flow quantity of the degassed molten substance
flowing in the downfalling pipe with a second flow quantity
controlling means positioned downstream of said vacuum degassing
vessel;
whereby a height of a first surface of the molten glass in the
vacuum degassing vessel is maintained to be less than 3.5 meters
different than a height of a second surface of the molten glass in
the storage tank;
wherein a quantity of the molten glass in the vacuum degassing
vessel is maintained at an amount which prevents an overflow of the
molten glass in the vacuum degassing vessel..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a vacuum degassing method and its
apparatus for removing bubbles in a molten substance at elevated
temperature such as molten glass or molten metal, particularly to a
vacuum degassing method and an improvement of its apparatus which
is effective in a process for continuously feeding molten substance
at elevated temperature.
2. Discussion of the Related Art
Conventionally, as such a vacuum degassing apparatus, there is one
disclosed, for instance, in Japanese Examined Patent Publication
No. 4205/1969.
As shown in FIG. 7, this apparatus is employed in a process wherein
molten glass G as a molten substance at elevated temperature in a
melting tank 106, is degassed and is continuously fed to a
successive treatment furnace. As shown in FIG. 7, a vacuum housing
100 which is sucked in vacuum, accommodates a vacuum degassing
vessel 101. This vacuum degassing vessel 101 is connected to an
uprising pipe 102 wherein the molten glass G rises as a molten
substance at elevated temperature before degassing, and is
introduced into the vacuum degassing vessel 101. The vacuum
degassing vessel 101 is connected to a downfalling pipe 103 wherein
the molten glass G after degassing falls and is led out to a
successive treatment furnace. Casings 104 and 105 are provided
around the uprising pipe 102 and the downfalling pipe 103,
respectively, for insulatively coating the uprising pipe 102 and
the downfalling pipe 103, which are connected to the vacuum housing
100.
Furthermore, the uprising pipe 102 and the downfalling pipe 103 are
made of noble metals such as platinum, since temperatures of these
pipes are elevated up to 1200.degree. to 1500.degree. C. by the
molten glass G.
In the vacuum degassing apparatus of this kind, a pressure inside
the vacuum degassing vessel 101, is reduced to 1/20 to 1/3
atmospheric pressure. Therefore, it is necessary to set a
difference of levels of the molten glass G in the melting tank 106
and the molten glass G in the vacuum degassing vessel 101, to be
approximately 3.5 m. Accordingly, since lengths of the uprising
pipe 102 and the downfalling pipe 103 are prolonged, the thermal
expansion quantities of the uprising pipe 102 and the downfalling
pipe 103, are enlarged. Accordingly, the structure of the vacuum
degassing apparatus becomes unstable and is devoid of safety.
Furthermore, since, in the vacuum degassing apparatus of this kind,
the molten glass G is led from the uprising pipe 102 to the
downfalling pipe 103 only by decompression in the vacuum degassing
vessel 101, the flow control of the molten glass G is
difficult.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a vacuum
degassing method and its apparatus wherein the safety of the vacuum
degassing apparatus is promoted and the flow quantity control of
the molten glass is facilitated.
According to a first aspect of this invention, there is provided a
vacuum degassing method wherein a molten substance at an elevated
temperature in a storage tank is sucked to a vacuum degassing
vessel through an uprising pipe connecting the storage tank and the
vacuum degassing vessel by maintaining the vacuum degassing vessel
at a negative pressure, the molten substance is degassed and the
degassed molten substance falls to a guiding duct through a
downfalling pipe connecting the vacuum degassing vessel and the
guiding duct characterized by that a first flow quantity of the
molten substance rising in the uprising pipe is restrained and a
second flow quantity thereof falling and/or flowing downward in the
downfalling pipe is controlled thereby maintaining a quantity of
the molten substance in the vacuum degassing vessel at a pertinent
amount.
According to a second aspect of this invention, there is provided a
vacuum degassing method according to the first aspect, wherein the
quantity of the molten substance is maintained at a pertinent
amount by restraining the first flow quantity of the molten
substance rising in the uprising pipe and by controlling the second
flow quantity thereof falling in the downfalling pipe, and a first
surface of material of the molten substance in the vacuum degassing
vessel is maintained at a first level being the same with a second
level of a second surface thereof in the storage tank.
According to a third aspect of this invention, there is provided a
vacuum degassing apparatus comprising:
a vacuum housing being sucked in vacuum;
a vacuum degassing vessel accommodated in the vacuum housing for
degassing a molten substance at an elevated temperature;
an uprising pipe connected to the vacuum degassing vessel for
rising and introducing the molten substance before degassing into
the vacuum degassing vessel;
a downfalling pipe connected to the vacuum degassing vessel for
falling and leading out the molten substance degassed by the vacuum
degassing vessel;
a first flow quantity controlling means provided in the uprising
pipe for restraining a first flow quantity of the molten substance
rising in the uprising pipe; and
a second flow quantity controlling means provided in the
downfalling pipe for controlling a second flow quantity of the
molten substance falling in the downfalling pipe.
According to a fourth aspect of this invention, there is provided a
vacuum degassing apparatus according to the third aspect, wherein
the first and the second flow quantity controlling means maintain a
first surface of the molten substance in the vacuum degassing
device at a first level the same with a second level of a second
surface thereof in storage before degassing.
According to the present invention, the flow quantity of the molten
substance at elevated temperature rising in the uprising pipe, is
restrained by the first flow quantity controlling means, and the
flow quantity of the molten substance at elevated temperature
falling in the downfalling pipe, is increased by the second flow
quantity controlling means, thereby maintaining the molten
substance at elevated temperature in the vacuum degassing vessel at
a pertinent amount.
Accordingly, it is possible to reduce the difference between the
levels of the molten substance in the vacuum degassing vessel and
that in a storage tank and the guiding duct, or to nullify the
level difference. In this way, since the lengths of the uprising
pipe and the downfalling pipe can be set to be short, the thermal
expansion quantities of the uprising pipe and the downfalling pipe
can be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional diagram showing the side of a process
integrated with a first embodiment of a vacuum degassing apparatus
according to the present invention;
FIG. 2 is a perspective view of FIG. 1;
FIG. 3 is a sectional diagram showing the first embodiment of a
vacuum degassing apparatus according to the present invention;
FIG. 4 is a sectional diagram showing the side of a process
integrated with a second embodiment of a vacuum degassing apparatus
according to the present invention;
FIG. 5 is a sectional diagram showing an apparatus employed in a
third embodiment of a method of making colored glass;
FIG. 6 is a sectional diagram taken along a line A--A of FIG.
5;
FIG. 7 is a sectional diagram of a conventional vacuum degassing
apparatus; and
FIG. 8 is a sectional diagram of a fourth embodiment of a vacuum
degassing apparatus according to the present invention.
.Iadd.FIG. 9 shows plungers according to the invention having
conical shapes at their lowest portions .Iaddend.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A detailed explanation will be given of a vacuum degassing method
and its apparatus according to the present invention in reference
to the attached drawings, as follows.
FIGS. 1 and 2 show a first embodiment of an example of a process
wherein molten glass is degassed and is continuously fed to a
successive treatment furnace.
As shown in FIGS. 1 and 2, a melting tank 1 heats molten glass G by
plate-like electrodes 1a, and a guiding duct 2 is connected to the
bottom of a side wall of the melting tank 1. The guiding duct 2
leads the molten glass G from the melting tank 1 to a storage tank
3, while heating the molten glass G by rod-like electrodes 2a. The
storage tank 3 temporarily stores the molten glass G. The molten
glass G stored in the storage tank 3 is degassed in a vacuum
degassing vessel of the vacuum degassing apparatus 4 under a
reduced pressure. The reduced pressure in the vacuum degassing
vessel in this case is set to be 1/20 to 1/3 atmospheric
pressure.
Furthermore, a difference H between levels of the molten glass G in
the melting tank and the molten glass G in the vacuum degassing
vessel, is set to be smaller than a level difference to which the
"siphon" principle is applicable. Generally speaking, when the
pressure in the vacuum degassing vessel is set to be 1/20 to 1/3
atmospheric pressure, the difference between the levels of the
molten glass G in the melting tank and the molten glass G in the
vacuum degassing vessel, is to be approximately 3.5 m to apply the
"siphon" principle to the vacuum degassing apparatus 4, which is
well known. Accordingly, in the vacuum degassing apparatus 4, the
difference H between the levels of the molten glass G in the
melting tank and the molten glass G in the vacuum degassing vessel,
is set to be smaller than 3.5 m.
Furthermore, the degassed molten glass G is led to a guiding duct 5
which communicates with the storage tank 3. A partition plate 6 is
provided between the storage tank 3 and the guiding duct 5. The
partition plate 6 maintains the storage tank 3 and the guiding duct
5 in a closed state.
As shown in FIG. 2, the vacuum degassing apparatus 4 is provided
with a vacuum housing 11 made of stainless steel. The vacuum
housing 11 is sucked in vacuum by a vacuum pump 10. A vacuum
degassing vessel 12 is provided in the vacuum housing 11. An
uprising pipe 13 made of platinum is fixedly connected to a side of
the bottom of the vacuum degassing vessel 12, and the lower end
portion of the uprising pipe 13 is immersed in the molten glass G
stored in the storage tank 3.
On the other hand, a downcoming pipe 14 is connected to the other
side of the bottom of the vacuum degassing vessel 12, which is made
of platinum as in the uprising pipe 13. The lower end portion of
the downfalling pipe 14 is immersed in the molten glass G in the
guiding duct 5. The position of the lower end portion of the
downfalling pipe 14 is set to be a little lower than that of the
uprising pipe 13. The uprising pipe 13 and the downfalling pipe 14
are heated by electricity based on a temperature control system,
not shown, and are maintained at predetermined temperatures.
Furthermore, casings 15 and 16 made of stainless steel are provided
around the uprising pipe 13 and the downfalling pipe 14,
respectively. The casings 15 and 16 are connected to the vacuum
housing 11. The lower end portions of the uprising pipe 13 and the
downfalling pipe 14 are exposed to the outside from openings 15A
and 16A of the casings 15 and 16. An insulating material 17 is
provided in the vacuum housing 11, and the casings 15 and 16,
surrounding the uprising pipe 13 and the downfalling pipe 14.
As shown in FIG. 3, a screw 20 and a screw 21 are rotatably and
coaxially provided in the uprising pipe 13 and the downfalling pipe
14. The screws 20 and 21 are made of platinum. The screw 20
consists of a shaft 20A and a blade 20B. The blade 20B is helically
provided on the shaft 20A, so that the blade 20B pushes down the
molten glass G in the downward direction, when the shaft 20A
rotates in the clockwise direction.
Furthermore, the screw 21 consists of a shaft 21A and a blade 21B
as in the screw 20, which pushes down the molten glass G in the
downward direction, when the shaft 21A rotates in the clockwise
direction. Top end portions of the shafts 20A and 21A are connected
with motors (not shown), which rotate the screws 20 and 21 in the
clockwise direction.
An explanation will be given of the operation of the first
embodiment of the vacuum degassing device according to the present
invention, composed as above.
First, as a pre-stage for operating the vacuum degassing apparatus
4, the molten glass G is introduced into the vacuum degassing
apparatus 4. The partition plate 6 is opened, the molten glass G in
the storage tank is introduced into the side of the guiding duct 5,
and the lower end portions of the uprising pipe 13 and the
downfalling pipe 14 are immersed in the molten glass G. After the
immersing is finished, the vacuum pump 10 is operated and the
inside of the vacuum degassing vessel 12 is made into a negative
pressure state of 1/20 to 1/3 atmospheric pressure.
The molten glass G is sucked to rise through the uprising pipe 13
and the downfalling pipe 14, into the vacuum degassing vessel 12.
Accordingly, the molten glass G is introduced into the vacuum
degassing device 4. However, since the difference between the
levels of the molten glass G in the melting tank and the molten
glass G in the vacuum degassing vessel is set to be smaller than
the level difference for sufficiently operating the "siphon"
principle, the molten glass G overflows in the vacuum degassing
vessel.
To prevent the overflow, the apparatus is operated as follows. When
the screws 20 and 21 are rotated in the clockwise direction by
driving motors (not shown) connected to the screws 20 and 21, the
molten glass G rising in the uprising pipe 13 and the downfalling
pipe 14, is pushed down in the downward direction, by the blades
20B and 21B. Accordingly, the rising flow rate of the molten glass
G rising in the uprising pipe 13 and the downfalling pipe 14, is
retarded. In this case, the rising flow rate of the molten glass G
rising in the uprising pipe 13 and the downfalling pipe 14, is
controlled so that the molten glass G moves from the uprising pipe
13 to the downfalling pipe 14, as in the "siphon" principle. When
the partition plate 6 is closed at this stage, the molten glass G
which has risen through the uprising pipe 13 and has been degassed
in the vacuum degassing vessel 12, is introduced to the side of the
guiding duct 5 through the downfalling pipe 14. In this case, the
flow rate of the molten glass G rising in the uprising pipe 13 is
the same with the flow rate of the molten glass G falling in the
downfalling pipe 14. In this way, the difference H between the
levels of the molten glass G in the melting tank and the molten
glass G in the vacuum degassing vessel, which is necessitated in
the conventional vacuum degassing apparatus which is not provided
with the screws 20 and 21, can be set at a small value.
Accordingly, even when the difference H between the levels of the
molten glass G in the melting tank and the molten glass G in the
vacuum degassing vessel, is set to be small, by providing the
screws 20 and 21, the uprising quantity of the molten glass G
rising in the uprising pipe 13 is reduced by the screw 20 and the
downfalling quantity of the molten glass G falling in the
downfalling pipe 14, is increased by the screw 21. Therefore, the
rising quantity of the molten glass G rising in the uprising pipe
13 and the downfalling quantity of the molten glass G falling in
the downfalling pipe 14, can be controlled to the same one.
Accordingly, the difference H between the levels of the molten
glass G in the melting tank and the molten glass G in the vacuum
degassing vessel, can be set to be smaller than approximately 3.5 m
which is necessary for the conventional apparatus, when the
pressure in the vacuum degassing vessel is set to be 1/20 to 1/3
atmospheric pressure.
In this way, the molten glass G which has passed through the vacuum
degassing device 4, is led to the guiding duct 5.
Furthermore, by changing the rotational speeds of the screws 20 and
21, the flow rate of the molten glass G can easily be
controlled.
In the first example, the difference H between the levels of the
molten glass G in the melting tank and the molten glass G in the
vacuum degassing vessel, is set to be smaller than the level
difference to which the "siphon" principle is applicable. However,
as in a second embodiment shown in FIG. 4, it is possible to set
the respective surfaces of the molten glass G in the melting tank
and the molten glass G in the vacuum degassing vessel, to the same
level, by nullifying the level difference between the molten glass
G in the melting tank and the molten glass in the vacuum degassing
vessel.
A detailed explanation will be given of a second embodiment of a
vacuum degassing method and its apparatus according to the present
invention in reference to FIG. 4, as follows.
As shown in FIG. 4, a vacuum degassing apparatus 50 of the second
embodiment is provided with an uprising pipe 52. The lower end
portion of the uprising pipe 52 is connected to a cooling tank 56
through a connecting pipe 54. Furthermore, the upper portion of the
uprising pipe 52 is connected to the left end portion of the bottom
of a vacuum degassing vessel 60. The upper portion of a downfalling
pipe 62 is connected to the right end portion of the bottom of the
vacuum degassing vessel 60. The bottom of the downfalling pipe 52
is connected to a spout of a successive step through a connecting
pipe 64 or the like. The reduced pressure in the vacuum degassing
vessel 60 is set to be 1/20 to 1/3 atmospheric pressure as in the
first embodiment.
A screw 66 and a screw 68 are rotatably and coaxially provided in
the uprising pipes 52 and in the downfalling pipe 62, respectively.
The screws 66 and 68 are composed similar to the screws 20 and 21
in the first embodiment. A blade 66B and a blade 68B are helically
provided on a shaft 66A of the screw 66 and a shaft 68A of the
screw 68, respectively. When the shaft 66A and the shaft 68A rotate
in a constant direction, the blade 66B and the blade 68B push down
the molten glass G in the uprising pipe 52 and the downfalling pipe
62 in the downward direction.
In this case, the rotational speeds of the shaft 66A and the shaft
68A are controlled so that surfaces of the molten glass G in the
vacuum degassing vessel 60 and the molten glass G in the cooling
tank 66 are on the same level. Accordingly, since it is not
necessary to elevate the molten glass G at an elevated temperature
to a high position (by the difference H between the levels of the
molten glass G in the melting tank and the molten glass G in the
vacuum degassing vessel as in the first embodiment), the safety
thereof is promoted. Furthermore, since it is not necessary to
provide the vacuum degassing vessel 60 or the like at a high
position, magnifying of facilities and cost reduction of facilities
are enabled.
A vacuum housing 72 in the vacuum degassing apparatus 50, is sucked
in vacuum by a vacuum pump (not shown) as in the first
embodiment.
In the above first and the second embodiments, the screws are
employed as the first and the second flow quantity controlling
means. However, this invention is not restricted by these examples
and may employ other flow quantity controlling means. As the other
flow quantity controlling means, for instance, a plunger of which
lower end portion is formed in a conical form or the like, may be
considered. The conical portions of the plunger is fitted to an
upper end portion of each of the rising pipes 13 and 52, and an
opening ratio of each of the uprising pipes 13 and 52 is
controlled, thereby controlling the rising quantity of the molten
glass G.
Furthermore, in the above first and second embodiments, explanation
has been given to cases wherein transparent glass is produced.
However, the vacuum degassing method and its apparatus of this
invention can be employed in the production of colored glass. An
explanation will be given of a third embodiment of a method for
making colored glass in reference to FIGS. 5 and 6, as follows. A
member similar to or the same with the member in FIG. 4 of the
second embodiment, is attached with the same notation and the
explanation will be omitted.
A colorant feeder 74 is provided at the upstream portion of a
mixing area 56A. The lower end portion of the colorant feeder 74 is
situated above the molten glass G. A colorant 76 is charged into
the molten glass G from the lower end portion of the colorant
feeder 74. In this case, since stirrers 58 are rotated and the
molten glass G is stirred to maintain the homogeneous distribution
of the charged colorant 76, bubbles are generated in the molten
glass G.
Furthermore, the molten glass G generated with bubbles is
introduced to the lower end portion of the uprising pipe 52 through
the connecting pipe 54. The molten glass introduced to the lower
end portion of the uprising pipe 52, rises in the uprising pipe 52.
At this occasion, since the screw 66 is rotating, the molten glass
G is pushed down in the downward direction by the blade 66B of the
screw 66. Accordingly, the rising quantity of the molten glass G is
restrained.
On the other hand, since the pressure in the vacuum degassing
vessel 60 is reduced to 1/2 to 1/3 atmospheric pressure, the molten
glass G introduced into the vacuum degassing vessel 60 by rising in
the uprising pipe 52, is degassed in the vacuum degassing vessel
60. Accordingly, the bubbles are removed from the molten glass
G.
Furthermore, since the screw 68 is rotating in the downfalling pipe
62 at this state, the molten glass G in the degassed state is
pushed down in the downward direction by the blade 68B of the screw
68. Accordingly, the molten glass G falls in the downfalling pipe
62 and is discharged from the vacuum degassing vessel 60. In this
way, the bubbles can be removed from the molten glass G charged
with the colorant 76.
According to the method of making colored glass wherein the
addition of the colorant, the stirring and the vacuum degassing are
continuously performed, the stirring operates to uniformly
distribute the material in the melting tank and the colorant, and
the reduced pressure operates to rapidly enlarge the bubbles
generated in the stirring chamber and to remove them by floating
them. Accordingly, in case of the change of the material to change
the color tone of the glass, this invention has an excellent effect
in saving the raw material cost and the energy cost and an effect
in making homogeneous colored glass. Furthermore, this invention
has an effect of reducing bubbles in glass. In the above-mentioned
method of making color glass, it is possible to make homogeneous
colored glass having little bubbles, in a continuous tank furnace,
considerably saving the raw material cost, the energy cost and the
like, which are accompanied by the color changing in the continuous
tank furnace. Therefore, the industrial value is great.
In the method of making colored glass, the molten glass G added
with the colorant 76 is not restricted with respect to the
composition so far as the glass is made by the heat-melting method.
For instance, lime-silica series glass employed as ordinary window
glass and borosilicate glass employed as vessel glass are pointed
out.
As the viscosity of the molten glass in case of adding the colorant
76, a value of 10.sup.3 poise or less is preferable. When the
viscosity exceeds 10.sup.3 poise, the colorant 76 is difficult to
be mixed uniformly, which is not preferable. Such molten glass can
be provided by continuously charging the raw material which is
controlled to have a target composition, and by heating and melting
the raw material.
As the colorant added to such molten glass, a metallic ion of Ti,
V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Ce or the like, a metallic selenium
of an element-like selenium, is pointed out. The kind and the
addition quantity of the colorant is determined by a target color
tone of glass. Although such colorant may be added in an oxide form
or in a metallic form, it is particularly preferable to add the
colorant as colored frits previously mixed in frits having a low
melting point, since the homogeneous distribution of the colorant
in the molten glass, is facilitated.
As shown in FIG. 5, the stirrers 58 stirring the molten glass added
with such colorant, are immersed in the molten glass. The stirrer
58 is of a publicly known type provided with a stirring blade
attached to a rod-like rotating shaft. Furthermore, instead of the
stirrer 58, a stirrer performing a comb-like reciprocating motion,
can be employed. The stirrer or the stirrers can be provided
singularly or plurally in the direction of flow of the molten glass
(in case of FIGS. 5 and 6, two of them are provided in the
direction of flow of the molten glass). Or, the stirring may be
preformed when the colorant is added.
The viscosity of glass in performing the stirring, is preferably to
be 10.sup.2 to 10.sup.3 poise. When the viscosity of glass is
smaller than 10.sup.2 poise, the wear of the stirrer becomes
considerable, whereas, when the viscosity is larger than 10.sup.3
poise, the molten glass and the colorant are difficult to mix
together uniformly, which is not preferable. The molten glass
uniformly mixed with the colorant is degassed under the reduced
pressure. Furthermore, as the pressure in case of performing the
degassing, a value of 1/20 to 1/3 atmospheric pressure is
preferable. When the pressure is higher than 1/3 atmospheric
pressure, the degassing action is deteriorated, which is not
preferable. Conversely, when the pressure is lower than 1/20
atmospheric pressure, the apparatus is magnified, which is not
preferable. Furthermore, the time of holding the glass under the
reduced pressure, and the viscosity of glass depend on a quantity
of allowable residual bubbles. For instance, in case of allowing
bubbles of 0.1 particle per kg, the purpose of decreasing bubbles
can be sufficiently achieved by the viscosity of glass of 10.sup.2
to 10.sup.2.5 poise and the holding time of approximately 0.5 to 2
hours.
The glass which is removed of the bubbles as above, is controlled
of its temperature to a predetermined temperature, is transmitted
to a floating bath or the like and is formed continuously.
On the other hand, in case of changing the material for changing
the color tone of the obtained glass, the color tone of the
material can be changed by changing the colorant while the molten
glass in the melting tank remains as it is.
Next, an explanation will be given to a fourth embodiment of this
invention in reference to FIG. 8. This embodiment is a particularly
preferable embodiment in this invention.
At the end of the cooling tank 56, a first downfalling pipe 162 is
provided. The bottom thereof is connected to the bottom of a first
uprising pipe 152. The upper end portion of the first uprising pipe
152 is connected to the vacuum degassing vessel 60. The downstream
end of the vacuum degassing vessel 60 is connected to the upper end
portion of a second downfalling pipe 163. The bottom of the second
downfalling pipe 163 is connected to the bottom of a second
uprising pipe 153. The first downfalling pipe 162 is provided with
a screw 166 wherein a blade 166B is helically provided. The screw
166B rotates in the directions of the arrow mark, operates to pull
up the falling molten glass in the upward direction, and, as a
result, controls the flow quantity of the molten glass G rising in
the first uprising pipe 152. Similarly, the second uprising pipe
153 is provided with a screw 168 having a helical blade 168B. This
screw rotates in the direction of the arrow mark, and operates to
pull up the rising molten glass. As a result, the flow quantity of
the molten glass falling in the second downfalling pipe 163, is
controlled.
The glass surface in the vacuum degassing vessel 60 and the glass
surface in the cooling tank 56 are controlled to be approximately
on the same level, by these screws 166 and 168.
The lower end portion of the first downfalling pipe 162, the lower
end portion of the second uprising pipe 153, the first uprising
pipe 152, the vacuum degassing vessel 60 and the second downfalling
pipe 163 are all arranged in the vacuum housing 11. On the other
hand, the upper end portion of the first downfalling pipe 162, the
upper end portion of the second uprising pipe 153 and the upper end
portions of the screws 166 and 168 are all arranged outside the
vacuum housing 11.
The pressure inside the vacuum housing 11 is set to be 1/20 to 1/3
atmospheric pressure as in the first and the second embodiments. In
the fourth embodiment, since movable portions of the screws 166 and
168 are arranged outside the vacuum housing 11, seals are not
necessary. Therefore, this is a particularly preferable device.
As stated above, according to the vacuum degassing vessels and its
apparatus of this invention, even when the the height of the vacuum
degassing vessel is set to be low, the rising quantity of the
molten substance at elevated temperature in the uprising pipe and
the falling quantity of the molten substance in the downfalling
pipe, can be controlled to the same quantity. Accordingly, it
becomes possible to reduce the level difference between the molten
substance in the vacuum degassing vessel and that in the storage
tank and the guiding ducts, or to nullify the level difference.
Accordingly, since the lengths of the uprising pipe and the
downfalling pipe can be set to be short, the promotion of the
safety of the vacuum degassing apparatus can be achieved.
Furthermore, since it is not necessary to bring the molten
substance to a high position by nullifying the level difference
between the surfaces of the molten substance in the vacuum
degassing vessel and that in the storage tank and the guiding
ducts, the safety is promoted.
Furthermore, it is possible to easily control the flow quantities
of the molten substance flowing in the uprising pipe and that in
the downfalling pipe by the first and the second flow quantity
controlling means.
* * * * *