JP2615966B2 - Glass melting furnace - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a glass melting furnace, and more particularly to a vertical electric melting furnace capable of efficiently and stably producing high-quality glass.

[Prior Art and Prior Art] Conventionally, as a vertical electric melting furnace for glass, as shown in FIG. 3, an electrode immersed in a molten glass 4 in the furnace has a raw material inlet 1 at the top of the furnace. The glass raw material (batch) 3 supplied to the surface of the glass substrate is melted and clarified by directly supplying electricity to the glass from 5 and generating the Joule heat, and then the glass is discharged from the glass outlet 2 provided at the bottom of the furnace. In general, it is configured to be transported to a work unit. As shown in FIG. 3, the electrodes 5 may be arranged such that the rod-shaped electrodes 5 are inserted horizontally from the side wall of the furnace, other electrodes are inserted vertically from the bottom of the furnace, or through the glass material layer. A device inserted from above is known.

In such an electric melting furnace, the surface of the molten glass 4 is made of a glass raw material (batch) for effective use of heat energy.
Cover with 3 layers. (The so-called “cold top” is formed.) However, melting and fining of the glass proceeds in the depth direction of the furnace.

To obtain high quality glass with such an electric melting furnace, the glass supplied to the working section through outlet 2 at the bottom of the furnace had a sufficient thermal history. It is necessary to make the substrate free of bubbles and unmelted material. The heat history of the glass reaching the outlet 2 is determined by the temperature of the glass in the furnace and the flow of the glass substrate, but the flow of the glass substrate in the furnace is mainly governed by the thermal convection caused by the temperature distribution of the glass in the furnace. Therefore, in order to produce high quality glass, the most important point of the furnace operation is to always keep the furnace in a stable thermal equilibrium.

However, in a conventional vertical electric melting furnace that uses a rod-shaped electrode and utilizes heating by Joule heat of glass, it is difficult to make the power distribution uniform in the plane of the furnace, particularly in the vicinity of the tip of the electrode. The current density increases, and the temperature of the glass between the electrode tips tends to increase. Since the electric resistance of the glass decreases as the temperature increases, an electric current flows more and more in a high-temperature portion, and local heating is further promoted. Such non-uniform temperature distribution causes thermal convection in the glass substrate in the furnace, and as a result, a glass substrate with a short heat history, that is, a glass substrate that is insufficiently heated and contains bubbles and unmelted material, is discharged from the outlet. Will be leaked,
This causes a defect in the product supplied to the working unit.

Furthermore, the non-uniform temperature distribution and the resulting thermal convection of the glass substrate cause non-uniform melting of the batch on the surface of the glass substrate, resulting in local uncovered portions of the substrate with the batch layer, resulting in heat loss. And the temperature of the glass decreases. In the melting furnace that uses the Joule heat of glass, it is extremely difficult to control the temperature of the glass substrate for the reasons described above. It is almost impossible to do.

Such a problem becomes conspicuous when melting glass having a high electric resistance containing no alkali component. That is, since such alkali-free glass has a large electric resistance,
In order to supply the glass with the power required for melting, it is necessary to reduce the distance between the electrodes, so that the above-mentioned non-uniform temperature distribution becomes remarkable.

In order to solve such a problem, the present applicant has
In a vertical glass melting furnace having a raw material charging section at the top and a glass base outlet at the bottom, at least one level of immersion in the glass base, substantially the entire horizontal cross section of the furnace at that level A glass melting furnace characterized by providing a resistance heating element over a long period of time was developed and a patent application was filed earlier (Japanese Patent Application No. 62-327892; hereinafter referred to as "prior application").

According to the glass melting furnace of the prior application, compared with the conventional heating method using electrodes, the temperature distribution is uniform, the heat convection is small, and it is difficult for the glass material having a short heat history to flow out, so that high-quality glass is used. Can be manufactured efficiently.

[Problems to be Solved by the Invention] However, even in the glass melting furnace of the prior application,
Depending on the shape of the resistance heating element, the uniformity of the temperature distribution may not be very good, or a substrate having a relatively short heat history may easily flow out.

The present invention further improves the above-mentioned prior application, makes the temperature distribution of the glass base material more uniform, more reliably prevents thermal convection, and makes it possible to stably and efficiently produce extremely high quality glass. It is an object to provide a glass melting furnace.

Means for Solving the Problems The glass melting furnace of the present invention has a raw material charging section at the top, a glass base outlet at the bottom, and at least one level immersed in the glass base. In a vertical glass melting furnace provided with a resistance heating element over substantially the entire horizontal cross section of the furnace, the heating element is a plate-shaped heating element provided with a plurality of openings uniformly distributed, When the diameter of the opening is D, the distance between the centers of adjacent concentric openings is P, and the length of the longest diagonal line of the plate-shaped heating element is L, D> 1 mm D / L <0.5 and D / P> 0.1 Is satisfied.

That is, the present inventors have conducted intensive studies to improve the glass melting furnace of the prior application, and as a result, used a plate-like body having a plurality of openings as a resistance heating element, and specified the diameter and interval of the openings. By doing so, it was found that excellent effects were obtained, and the present invention was completed.

[Operation] In the glass melting furnace of the present invention, since the glass substrate is heated by a plate-like resistance heating element (heating plate) having a plurality of openings uniformly distributed, the calorific value can be easily controlled.

If the power is too small in the conventional direct energization method using electrodes, the glass substrate quickly flows down between the electrodes, and the substrate that has not been sufficiently clarified easily flows out of the outlet, whereas the heat generation according to the present invention occurs. In the case of using a plate, such a short path is unlikely to occur.

Since the heating plate is installed over almost the entire horizontal cross section of the furnace in the glass substrate, the temperature distribution in the plane of the glass substrate becomes extremely uniform. In addition, since the heating plate functions as an obstacle to the flow of convection, the convection is suppressed, and the surface of the heating plate has the highest temperature. It becomes a temperature distribution and thermal convection is prevented.

By the way, if the opening of the heating plate is too large with respect to the heating plate, the uniformity of the temperature distribution deteriorates, and the heat convection is promoted.
On the other hand, if the opening is too small, the opening is clogged by the glass substrate, and it is difficult to form the opening. Also, with respect to the size of the opening, if the interval between adjacent openings is too long, the glass base near the opening is easy to fall off, and the glass base far from the opening is difficult to fall off. The heat history becomes heterogeneous.

However, the above problem is solved by setting the diameter D of the opening, the longest diagonal length L of the heating plate and the opening interval P so that D> 1 mm D / L <0.5 D / P> 0.1, Good heat melting can be performed.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a longitudinal sectional view of a glass melting furnace showing one embodiment of the present invention, and FIG. 2 is a sectional view taken along the line II-II of FIG.

In the glass melting furnace shown in FIGS. 1 and 2, a furnace main body 10 made of a seed tile has a rectangular shape in plan view, a raw material charging section 1 at an upper portion, and a glass outlet at a bottom portion (projects sideways in this example). A throat 2 is provided inside which a molten glass base 4 is held. The glass raw material (batch) 3 is uniformly supplied to the surface of the glass substrate 4. Thus, at the level immersed in the glass substrate 4 in the furnace, a plate-shaped resistance heating element 6 is installed over almost the entire area of the horizontal section of the furnace at that level. This resistance heating element 6
Is a plate-like heating plate having a large number of openings 7 distributed uniformly.
6a and a terminal portion 6b rising upward from both ends thereof. An end of the resistance heating element 6 outside the furnace is connected to a power supply V.

In the present invention, the diameter D of the opening 7 (the length of the longest diagonal line when the opening shape is a polygon), the distance P between the centers of the adjacent openings 7, 7 ', and the length of the longest diagonal line of the heating plate ( In the case of a circle, its diameter) L is D> 1 mm, D / L <0.5
And set D / P> 0.1.

If the diameter D of the opening 7 is too small, clogging is likely to occur due to unmelted material, and it is difficult to perform processing for forming the opening of the heating plate 6a. Therefore, D> 1 mm.

If the size of the opening 7 is too large with respect to the size of the heating plate 6a, the uniformity of the in-plane temperature distribution of the glass material is impaired, and heat convection is promoted. Therefore, D / L <0.5.

Furthermore, if the formation interval is too large with respect to the size of the opening 7, the heat history of the glass substrate 4 becomes uneven.
That is, the substrate near the opening falls off quickly, whereas the substrate away from the opening is hard to fall off, so the heat history of the substrate near the opening is shorter than that of the substrate away from the opening, and heating is difficult. It is easy to be enough.

 Therefore, D / P> 0.1.

 In the present invention, it is particularly preferable to set 0.2> D / L 0.7> D / P> 0.3.

In the present invention, as the material of the resistance heating element 6, platinum, platinum-rhodium alloy, molybdenum, molybdenum whose surface is coated with platinum, or the like is used, and platinum or platinum-rhodium alloy is particularly desirable. Since the temperature coefficient of electric resistance of these materials is much smaller than that of glass, there is an advantage that temperature control becomes very easy.

In the glass melting furnace of this embodiment, the heating plate 6a
A resistance heating element 6 having a square plate shape of 0 cm and made of 90% Pt-10% Rh was installed. The opening 7 was a circle having a diameter of 10 mm, and the interval between adjacent openings was set to 20 mm.

In the glass melting furnace having such a configuration, the glass is heated by energizing the resistance heating element 6. On this occasion,
The resistance value of the resistance heating element 6 is uniquely determined according to the temperature, and a predetermined amount of heat can be generated accurately by supplying a predetermined power. In addition, since the heating plate 6a of the resistance heating element 6 is provided uniformly over the entire area of the horizontal section of the furnace, the glass substrate is uniformly heated over the entire area of the horizontal section. The temperature distribution of the glass body in the cross section becomes extremely uniform.

For this reason, convection of the glass substrate due to temperature unevenness in the horizontal plane is prevented. Further, the temperature of the glass substrate 4 in the glass melting furnace at the portion in contact with the surface of the heating plate 6a has the highest temperature, and the temperature becomes lower as the depth becomes deeper than the heating plate 6a. Therefore, heat convection hardly occurs in the glass substrate 4 below the heating plate 6a.

Above the heat generating plate 6a, the lower the temperature becomes, the higher the temperature becomes. However, since the heating plate 6a is provided so as to separate the upper side and the lower side, the heat convection of the glass substrate above the heating plate 6a is almost lower than the heating plate 6a. Not transmitted.

The heat convection above the heating plate 6a is also extremely weak because the upper portion is shallowly separated by the heating plate 6a and the temperature distribution in the horizontal direction is uniform. The situation such as uneven melting of the batch 3 and exposure of the glass substrate does not occur.

For this reason, according to this glass melting furnace, the glass batch can be uniformly melted, and a clear glass base material free of bubbles and undissolved substances can be reliably produced.

In the embodiment shown in FIGS. 1 and 2, the plate-like heating plate 6a
An example in which the opening 7 is circular is shown, but the shape of the opening 7 is not particularly limited, and the amount of heat generated is uniform over the entire surface of the heating plate 6a of the heating element and the flow of the glass substrate 4 is not hindered. Then, in the shape, number, arrangement, etc. of the openings,
Various other aspects can be taken. The heating plate is 1
Not limited to two sheets, two or more sheets can be provided in multiple stages.

The position where the resistance heating element is installed is preferably as close to the batch layer 3 as possible as high as possible in the glass substrate 4, but if it is too close to the batch layer 3, unmelted glass and / or unfinished glass may be It flows down through the opening of the heating element to the bottom of the furnace. Therefore, the position of the heating element (the position of the lowermost heating element in the case where a plurality of heating elements are provided) is such that the glass is completely melted at that position and the glass is free from unmelted matter and bubbles. It is preferred that

In a normal case, the heating element is preferably installed at a position of about 3 to 40 cm below the batch layer.

[Effects of the Invention] As described above, according to the glass melting furnace of the present invention, high-quality glass can be produced efficiently, reliably and stably.

Further, the glass melting furnace of the present invention can be applied to almost any kind of glass under almost the same conditions. That is, as described above, in a conventional electric melting furnace using Joule heat of glass, according to the electric resistance value of glass,
In other words, it is necessary to change the distance between the electrodes, the arrangement of the electrodes, the applied voltage, and the like, depending on the type of glass to be melted. Can be used.

[Brief description of the drawings]

1 is a longitudinal sectional view of a glass melting furnace showing one embodiment of the present invention, FIG. 2 is a sectional view taken along the line II-II of FIG. 1, and FIG. 3 is a longitudinal section of a conventional vertical glass melting furnace. FIG. 1. Material input port 2. Glass base outlet (throat) 3. Batch layer 4. Glass base 5. Electrode 6. Heating element 6a Heating plate.

Claims (1)

(57) [Claims] An apparatus having a raw material charging section at the top, a glass base outlet at the bottom, and at least one level of immersion in the glass base, at least one level of resistance heating over substantially the entire horizontal cross section of the furnace at that level. In a vertical glass melting furnace provided with a body, the heating element is a plate-shaped heating element provided with a plurality of openings uniformly distributed, the diameter of the openings is D, and the adjacent openings are concentric. Glass melting characterized by satisfying the following relations: D> 1 mm D / L <0.5 and D / P> 0.1, where P is the center-to-center distance and L is the longest diagonal of the plate-shaped heating element. Furnace.