Glass manufacturing – Processes – Fining or homogenizing molten glass
Reexamination Certificate
1999-06-07
2002-01-01
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes
Fining or homogenizing molten glass
C065S157000, C065S347000
Reexamination Certificate
active
06334336
ABSTRACT:
The present invention relates to a vacuum degassing apparatus for molten glass, which removes bubbles from molten glass continuously supplied, and a method for building the apparatus.
In order to improve the quality of formed glass products, there has been used a vacuum degassing apparatus which removes bubbles generated in a molten glass before the molten glass that has been molten in a melting tank is formed by a forming apparatus, as shown in FIG.
4
.
The vacuum degassing apparatus
110
shown in
FIG. 4
is used in a process wherein molten glass G in a melting vessel
120
is vacuum-degassed and is continuously supplied to a subsequent treatment vessel. In the vacuum degassing apparatus are provided a vacuum housing
112
which is evacuated to be depressurized therein for vacuum-degassing the molten glass, a vacuum degassing vessel
114
which is provided in the vacuum housing
112
and is depressurized together with the vacuum housing, and an uprising pipe
116
and a downfalling pipe
118
which are connected to respective end portions of the vacuum degassing vessel in a downward and vertical direction. The uprising pipe
116
has a lower end immersed in the molten glass G in an upstream pit
122
in communication with the melting vessel
120
. Likewise, the downfalling pipe
118
has a lower end immersed in the molten glass G in a downstream pit
124
in communication with the subsequent treatment vessel (not shown).
The vacuum degassing vessel
114
is substantially horizontally provided in the vacuum housing
112
which is evacuated through a suction port
112
c
by a vacuum pump, not shown, to be depressurized therein. Since the inside of the vacuum degassing vessel
114
is depressurized, through suction ports
114
a
and
114
b
in communication with the inside of the vacuum housing
112
, to a pressure of {fraction (1/20)}-⅓ atmosphere together with the inside of the vacuum housing
112
, the molten glass G in the upstream pit
122
before degassing is sucked and drawn up by the uprising pipe
116
, and is introduced into the vacuum degassing vessel
114
. After the molten glass has been vacuum-degassed in the vacuum degassing vessel
114
, the molten glass is drawn down by the downfalling pipe
118
to be discharged into the downstream pit
124
.
The vacuum housing
112
may be a casing made of metal, such as stainless steel and heat-resisting steel. The vacuum housing is evacuated by the vacuum pump, not shown, for instance, to be depressurized therein, maintaining the inside of the vacuum degassing vessel
114
provided therein in a depressurized state, such as a pressure of {fraction (1/20)}⅓ atmosphere. In the vacuum degassing vessel
114
is formed an upper space
114
s
above the molten glass which has been filled at a certain depth in the vacuum degassing vessel.
Around the vacuum degassing vessel
114
, the uprising pipe
116
and the downfalling pipe
118
in the vacuum housing
112
is provided thermal insulation material
130
, such as refractory bricks, to cover these members for thermal insulation.
Since the conventional vacuum degassing apparatus
110
is configured to deal with the molten glass G having a high temperature, such as a temperature at 1,200-1,400° C., paths for molten glass in direct contact with the molten glass G, such as the vacuum degassing vessel
114
, the uprising pipe
116
and the downfalling pipe
118
, are constituted by circular shells, which are made of noble metal, such as platinum and platinum alloy, as shown in JP-A-2221129 in the name of the applicants.
The reason why the paths for molten glass, such as the vacuum degassing vessel
114
, the uprising pipe
116
and the downfalling pipe
118
, are made of noble metal, such as platinum and platinum alloy, is that there is no inclusion of impurities into the molten glass G and a certain strength is ensured at high temperatures since it is hardly possible due to low reactivity of the noble metal with the molten glass at a high temperature that, when the noble metal contacts the molten glass G at such a high temperature, the noble metal elutes by reaction with the molten glass G.
When the vacuum degassing vessel
114
is constituted by a circular shell made of noble metal, an increase in the wall thickness of the shell directly and significantly rises the cost since noble metal such as platinum is quite expensive. From this viewpoint, the diameter of the circular shell is limited to a certain value in terms of cost and strength, and it is difficult to significantly increase the diameter of the circular shell. This creates a problem in that the quantity of the molten glass G to be vacuum-degassed in the vacuum degassing vessel
114
is limited to a certain level, and that it is impossible to build the vacuum degassing apparatus so as to have a large throughput.
Since the molten glass G is obtained by dissolution reaction of powders raw material, it is preferable that the temperature in the melting vessel
120
is high in dissolution. Since the viscosity of the molten glass G decreases at high temperatures, it is preferable that the temperature of the molten glass is high in vacuum-degassing. Although the conventional vacuum degassing apparatus requires to use alloy with noble metal included therein in the vacuum degassing vessel
114
and the like in terms of high temperature strength, it is difficult to increase the wall thickness of the circular shells in terms of cost because noble metal is expensive. Even if noble metal, such as platinum, is used, the strength thereof inevitably lowers as the temperature becomes higher. As a result, the temperature of the molten glass at an inlet of the vacuum degassing apparatus
110
has been limited to the certain temperature (1,200-1,400° C.) as stated earlier.
When the paths for the molten glass having a high temperature are made of platinum, the formation of holes due to wearing of the thin platinum must be taken into account in designing, and the apparatus is required to be configured so as to enable to repair and replacement of platinum for a short period of time after the production of glass products has been temporarily standstill. Since the paths made of platinum (the vacuum degassing vessel, the uprising pipe and the downfalling pipe) in the conventional vacuum degassing apparatus are provided in series, repair and replacement of the paths has required to release the depressurized state and expel all the molten glass from the inside of the vacuum vessel, the uprising pipe and the downfalling pipe, to drop the temperature of the entire vacuum apparatus to an ordinary temperature, and then to carry out repair or replacement of platinum. Since it is appropriate that the molten glass is cut at the lower ends of the uprising and downfalling pipes for repair or replacement of platinum, the vacuum degassing apparatus has been required to have a structure that the entire apparatus can be lifted by at least 1 m to separate the uprising and downfalling pipes from the high temperature glass reservoirs thereunder when, in particular, the uprising pipe and the downfalling pipe are repaired. However, lifting the entire vacuum degassing apparatus
110
has required an extremely difficult operation since the apparatus is large and extremely heavy in consideration of the operation at a high temperature and in the depressurized state.
As stated earlier, it is difficult to provide the apparatus in a large size in terms of cost since platinum or platinum rhodium, which has low reactivity at high temperatures, is expensive. Even if the apparatus is build in a large size, it is impossible to provide the circular shells with a sufficient wall thickness. As a result, it is impossible to obtain strength required to resist heat. This prevents the temperature of the molten glass from being raised, making it difficult to decrease the viscosity of the molten glass so as to exhibit a vacuum-degassing effect in a sufficient way. Since the provision of an insufficient wall thickness needs repair or replacement required by wearing, accompanie
Inoue Shigekuni
Matsuwaki Masataka
Sasaki Michito
Sugimoto Mitsuo
Takei Yusuke
Asahi Glass Company Ltd.
Vincent Sean
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