JPS602260B2 - Batch for alkali-free glass suitable for electric melting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a batch for alkali-free glass useful in electromelting.

When melting glass in a heavy oil-fired tank kiln, it is well known that the difficulty of melting varies greatly depending on the raw material, and in some cases it may be extremely difficult or impossible to melt glass.

For example, in Jikosho 44-5559, a highly viscous glass surface layer is formed in the early stages of melting, and bubbles generated by decomposition of batch raw materials are blocked by this viscous glass layer and are prevented from escaping into the atmosphere. This results in a thick layer of foam. This foam layer acts as a heat insulator, making it difficult for heat to transfer to the molten glass.
It is stated that glass becomes difficult to melt. In order to prevent the formation of a layer of bubbles that are harmful to the melting process and to increase the glass melting efficiency, it is effective to use an alkali metal borate (for example, colemanite), an alkali metal silicate, or an aluminate as a raw material. It states that there is. Alkali-free glass fibers are also continuously melted in heavy oil heated tank kilns, but the batches are generally made from raw materials such as kaolin talley, colemanite, calcium carbonate, aluminum hydroxide, and dolomite. (For example, the one shown in number 1 in Table 3), a high-quality product is obtained.

In recent years, electrical melting of glass has become popular due to the problem of exhaust gas from heavy oil combustion, and attempts have been made to electrically melt alkali-free glass. When No. 1) in Table 3 is used, the gas generated during the vitrification reaction becomes bubbles, and a highly viscous non-breathable layer is formed above the bubbles. Over time, these bubbles accumulate and develop into a large layer. However, when it finally breaks through the upper viscous layer and escapes into the atmosphere, both the batch and the molten glass spill over from the top of the kiln, making it impossible to obtain a stable molten state.

Such a "blowing phenomenon" is not observed in soda glass, shelf silicate glass, lead glass, etc. The mechanism of the "blowing phenomenon" is schematically shown in Figure 1.

FIG. 2 shows a stable melting state without any "blowing phenomenon." In Fig. 1 and Fig. 2, the input batch 1 is
It becomes molten glass 5 after passing through a cracked condensation layer 2, a highly viscous vitrification reaction layer 3, and a foam layer 4. In a stable molten state without the "blowing phenomenon" as shown in FIG. can escape into the atmosphere through the cracks in the

Therefore, a stable molten state is maintained without the formation of a bubble layer 4 under the vitrification reaction layer 3. In the case shown in FIG. 1, the highly viscous vitrification reaction layer 3 gradually becomes thicker and becomes unable to be easily broken by the pressure of the generated bubbles 4'.

The foam layer 4 also becomes thicker with the passage of time, and since this foam layer 4 becomes a heat insulating layer, the viscosity of the vitrification reaction layer 3 becomes higher and becomes more difficult to break. Then, the pressure of the foam layer 4 gradually increases, and finally the vitrification reaction layer 3, the dawn condensation layer 2, and the batch layer 1 are pushed up all at once, and the bubbles escape into the atmosphere. At this time, a considerable amount of molten glass and batches spill out from the top of the kiln. The vitrification reaction layer 3 in this case is a white layer so strong that it cannot be pierced with an iron rod, and contains a large amount of unmelted quartz. As a result of various studies, the inventors found that it is necessary to make the vitrification reaction layer 3 as thin as possible in order to obtain a stable molten state. It has been found that it is extremely effective to make the particle size as small as possible.

In order to minimize the amount of quartz contained in the batch, a compound of Si02 and other components may be used as the raw material.

Si02-AI203-H20 minerals and composite minerals of these minerals and quartz are examples, but from the composition of the alkali-free glass that is the object of the present invention (see Table 4),
The molar ratio of Si02/mountain 203 needs to be 2 or more. Examples of such minerals include kaolin and pyrophyllite for the former, and kaolin clay and pyrophyllite clay for the latter. Si02-N203-day 20
In addition to other minerals, wollastonite (Ca○/Si02) is also a suitable raw material for this purpose.

Using extremely fine raw materials, a stable melt can be obtained even with significant quartz content in the batch. However, it is extremely difficult to pulverize the raw material into fine particles beyond a certain level, and it is economically disadvantageous. for example,
As for quartz, kaolin and pyrophyllite,
Properties (hardness, hardness) related to the crushing of these minerals are shown in Table 1. Table 1 As is clear from Table 1, quartz is very hard and difficult to grind, so it is difficult to economically grind quartz into fine particles.

Kaolin clay and pyrophyllite clay, which are composite minerals of kaolin and pyrophyllite (Si02-yama203-day20 series minerals) and quartz, are easier to crush than quartz alone, but they can be crushed into fine particles of 10 μm or less. It is economically disadvantageous to do so. Therefore, in order to improve solubility,
It is advantageous to contain as little quartz as possible in the batch. For example, the above-mentioned kaolin clay and pyrophyllite clay have an average particle size of about 15 French, and materials that are relatively easy to crush such as kaolin and pyrophyllite have an average particle size of about 5 French, but raw materials such as silica sand have an average particle size of about 5 French. The amount of quartz contained in the batch can be reduced by 10
It was confirmed that a stable molten state could be obtained by reducing the anchorage to 35 parts or less. From the viewpoint of pulverization and solubility, Si
02-N203-A composite mineral of day 20 series mineral and quartz is
It is desirable that the Si02-AI203-QO mineral is contained in an amount of 25% by weight or more. Kaolin (Mountain 20)
3. Raft i02, 2nd 20) or Pyrophyllite (Mountain 2
Kaolin clay and py are composite minerals of 03/time i021 day 20) and quartz.

The chemical composition of phyllitoclay and the amount of quartz contained in the clay are shown in Table 2. Table 2 (Weight*) Table 3 shows the melting results for various combinations of raw materials.

The numerical value indicates the number of parts per glass 10, and the value in parentheses indicates the average particle size (r) of the raw material. The amount of quartz contained in each batch is noted in parts per 100 parts of glass. Common to each combination: 8 parts dolomite and 0 parts soda*ash. ＄Orima description has been omitted. Using an electric melting kiln of 17 W, the maximum pulling amount of sufficiently melted glass in a stable molten state is expressed as k9'KW.

"Unable" indicates that the "blowing phenomenon" was severe, the molten state was unstable, and it was impossible to pull up the glass. 3. The glass obtained by melting had a composition approximately shown in Table 4.

As is clear from Table 4 and Table 3, colemanite reduced the meltability in electric melting.

In heavy oil combustion kilns, colemanite is used as a raw material to prevent the formation of a bubble layer harmful to melting and to significantly improve glass melting efficiency, as described in the aforementioned Japanese Patent Publication No. 44-5559. In the melting process, in the case of batches containing colemanite, a very hard sintered layer 2 (see Fig. 1) is formed, and the generated air bubbles 4' form the hard sintered layer 2.
could not break the vitrification reaction layer 3 lined with
A thick foam layer 4 is created, and the above-mentioned "blowing phenomenon" finally occurs. This "blowing phenomenon" is due to the fact that instead of colemanite, amorphous calcium shelfate (e.g., B2
0346.0, Ca036.3, and H2017.4). After repeated studies as described above, the inventors came to the following conclusion.

One pile of Si02 with a molar ratio of Si02/AI2Q of 2 or more
03 is a composite mineral of 20-series mineral and quartz, and the Si02
- Raw materials containing 25% or more by weight of AI203-QO minerals (e.g. kaolin clay, pyrophyllite clay, etc.) and Si02-AI203-based minerals with a molar ratio of 2 or more of Si02/AI203 (e.g. kaolin, pyrophyllite, etc.) and amorphous calcium oxides (e.g., in weight percent, &0346.0, Ca0
A batch containing 36.3 and 2017.4) as the main raw material is most suitable for electric melting of alkali-free glass.
By making the grain size of each raw material in the batch as fine as possible and minimizing the amount of quartz contained in the batch, a good molten state can be obtained more easily. However, as mentioned above, it is not easy to make the raw material finer and it is economically disadvantageous. Therefore, from an economic point of view, the average particle size of the Si02-Yama203-Hi20 series mineral, which is relatively easy to crush, is set to about 5r or less, and the Si02-N203-H20 series mineral, which is a raw material that is somewhat difficult to crush, and quartz are combined. For practical purposes, it is sufficient to keep the average particle size of the composite minerals below about 15 mm, to minimize the amount of raw materials such as mint sand, and to limit the amount of quartz contained in the batch to about 35 parts per 10 parts of glass. It is. It goes without saying that the narrower the particle size distribution, the better the results.

However, it is technically and economically difficult to obtain a product with a narrow particle size distribution through pulverization on an industrial scale, and it is unavoidable that the particle size distribution becomes wide to some extent. but,
Even if the average particle size is 5 m or less or 15 m or less as described above, the incorporation of particles with a large particle size of, for example, 50 m is undesirable because it adversely affects the molten state. Dolomite, soda ash, wollastonite, calcium carbonate, etc. can be added to the above batch as necessary.

Generally, electrodes in the electric melting industry are provided at a position approximately 30 degrees or more deep from the glass liquid level. In such a conventional electric melting furnace, the melting efficiency of the batch according to the present invention was extremely low, and melting was sometimes difficult. As a result of various studies, the present inventors succeeded in significantly improving the melting efficiency3 by providing the electrode at a position shallower than about 20 arcs (distance to the center of the electrode) from the glass liquid level.

The materials shown in Table 3 were melted in an electric melting furnace in which the electrode was installed at a position approximately 11 skins above the gas liquid level, and an extremely stable melted state was obtained. However, even in this case, the batch used in the heavy oil combustion kiln (Table 3, number 1
), a "blowing phenomenon" occurred and it was impossible to melt. As is done in general electric melting kilns, a small amount of electric power is applied to the electrode at the bottom of the melting tank to adjust the viscosity of the glass flowing into the working tank, but if the temperature at the bottom of the melting tank becomes too high, the IJ
Boiling occurred and many bubbles were generated on the molten glass surface of the working tank, the molten glass surface of the working tank was not kept constant, and the temperature of the glass was unstable, which hindered the molding operation. An auxiliary electrode for applying a very small amount of electric power may be provided between the above-mentioned electrode provided at a position shallower than about 20 arcs from the glass liquid level and the bottom of the melting tank.

As described above, the present invention is a composite mineral of a Si02-AI203-ratio ○ series mineral with a Si02/AI203 molar ratio of 2 or more and quartz, and the Si02-AI203-20 series mineral per day is 25% by weight. % or more, and Si0
The present invention provides a batch for alkali-free glass subjected to electric melting, which contains a SiQ/AI203 day 20 mineral having a molar ratio of 2/mount 203 of 2 or more and amorphous calcium shelf oxide.

According to the present invention, high-grade alkali-free glass fines can be economically advantageously obtained. Note that the glass fiber was molded by a general method.

[Brief explanation of drawings]

FIG. 1 is a sectional view schematically showing the "blowing phenomenon", and FIG. 2 is a sectional view schematically showing a stable melting state. Figure 1 Figure 2

Claims (1)

[Claims] 1 SiO with a molar ratio of SiO_2/Al_2O_3≧2
A composite mineral of _2-Al_2O_3-H_2O mineral and quartz, which contains a raw material containing 25% by weight or more of the SiO_2-Al_2O_3-H_2O mineral and a molar ratio of Si
SiO_2-Al_2O with O_2/Al_2O_3≧2
A batch for alkali-free glass that is suitable for electric melting and whose main ingredients are _3-H_2O minerals and amorphous calcium borate.