JPH0891848A - Vertical glass fusing furnace - Google Patents

Abstract

PURPOSE: To obtain a vertical glass fusing furnace capable of stably producing glass having excellent quality. CONSTITUTION: The glass raw material heating section of the glass fusing furnace consists of a planar resistance heating element 6 over the nearly entire area of the horizontal cross section of the fusing furnace. The thickness of the side parts of the heating element 6 facing the furnace side walls of a furnace body 10 is set at the thick part 6c thicker than the thickness of the other heating element surface (heating plate). The thick part 6c is then heated to a temp. higher than the temp. of the heating plate 6a and the glass body near the thick part 6c is heated higher at the time of fusing the glass raw material by impression of voltage from a terminal part 6b. Ascending flow is them generated in the glass body of this part and descending flow in the clearance is decreased. Since the glass body past the clearances is heated in the higher temp. region of the thick part 6c of the heating element 6, melting or heating is sufficiently executed and the passing through of the glass body insufficient in fusing or insufficient in heating from the spacing between the heating element 6 and the furnace side walls is prevented.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a vertical glass melting furnace.

[0002]

2. Description of the Related Art As a vertical electric melting furnace for glass, as shown in FIG. 5, electricity is directly applied to the glass from an electrode 5 immersed in the molten glass in the furnace, and the glass is heated by Joule heat generated to heat the surface of the glass substrate 4. In general, the glass raw material (batch) 3 supplied from the raw material inlet 1 is melted and clarified, and then the glass is conveyed to the working portion from the glass base outlet 2 provided at the bottom of the furnace. However, in the conventional vertical electric melting furnace shown in FIG. 5, which uses the rod-shaped electrode 5 and uses the heating by the Joule heat of glass, it is difficult to make the electric power distribution in the plane of the furnace uniform, and The current density in the vicinity of the tip of the electrode 5 increases, and the temperature of the glass between the tips of the electrodes 5 tends to increase. Since the electrical resistance of glass decreases as the temperature rises, more and more electric current flows in the high temperature part, which further promotes local heating. Such non-uniform temperature distribution causes heat convection in the glass base material 4 in the furnace, and as a result, the glass base material 4 having a short thermal history, that is, the glass base material 4 containing insufficient heat and containing bubbles and unmelted materials. Will flow out from the glass base outlet 2, and this will be supplied to the working part and cause a problem in the product. Furthermore, the non-uniform temperature distribution and the resulting thermal convection of the glass body 4 causes the non-uniform melting of the batch 3 on the surface of the glass body 4, causing the glass body 4 to be locally covered by the batch layer. As a result, heat loss increases and the glass temperature decreases.
Such a problem becomes remarkable when melting glass having a large electric resistance that does not contain an alkali component. That is, since the alkali-free glass has a large electric resistance, it is necessary to reduce the distance between the electrodes 5 in order to supply the glass with electric power necessary for melting. Therefore, the above-mentioned non-uniform temperature distribution becomes remarkable. It will be.

In order to solve such a problem, the applicant of the present invention has previously shown that the raw material charging port 1 is provided at the top as shown in FIG.
In a vertical type glass melting furnace having a glass base outlet 2 at the bottom, and at a level where it is immersed in the glass base 4 in the furnace, plate resistance is maintained over almost the entire area of the horizontal cross section of the furnace at that level. A vertical glass melting furnace characterized by having a heating element 6 has been developed and a patent application has been filed (Japanese Patent Laid-Open No. Hei 1
-167237, JP-A-2-199029). Figure 6
Is a vertical cross-sectional view of a vertical glass melting furnace according to an embodiment of the applicant's earlier invention, and FIG. 7 is a cross-sectional view taken along the line AA of FIG. In the vertical glass melting furnace shown in FIGS. 6 and 7, the glass raw material (batch) 3 is uniformly supplied to the surface of the glass base material 4 in the furnace body 10. The plate-shaped resistance heating element 6 immersed in the glass substrate 4 in the furnace is provided with a plate-shaped heating element 6a having a large number of uniformly distributed openings 7 and terminal portions 6b rising from both ends thereof. The end of the plate-shaped resistance heating element 6 outside the furnace is connected to a power supply V.

[0004]

FIG. 6 of the above applicant,
According to the vertical glass melting furnace shown in FIG. 7, compared with the heating method using the electrode 5 shown in FIG. 5, the temperature distribution is uniform and the thermal convection is small, and the glass base material 4 having a short thermal history is less likely to flow out. Therefore, it has become possible to efficiently manufacture high-quality glass. However, since both the plate-shaped resistance heating element 6 and the furnace wall surface of the furnace body 10 are made of platinum, when they come into contact with each other, they are fused and the plate-shaped resistance heating element 6 does not come off from the furnace body 10, or the plate-shaped resistance heating element 6 does not move. There is a disadvantage that the heating current flowing through the heating element 6 also flows through the platinum portion of the furnace body 10. Therefore,
For example, as shown in FIG. 3, the plate resistance heating element 6 and the furnace body 10 are
A gap of several cm is required between the wall and the furnace wall.

However, the glass substrate 4 insufficiently melted or insufficiently heated sometimes flows out from the gap as shown by the arrow in FIG. 3 (b). Since the glass base material 4 passes through this gap, there are many bubbles, and the striae, which are inhomogeneous or weak composition unevenness, become large. When this striae is obtained, it appears as a difference in the refractive index of the glass, and it is observed as a streak-like defect, and in some cases, the glass is poor in quality and easily reboiled. An object of the present invention is to provide a vertical glass melting furnace capable of stably producing high quality glass. Another object of the present invention is to provide a vertical glass melting furnace which prevents the glass base material from being insufficiently melted or insufficiently heated in the gap between the plate resistance heating element and the furnace wall of the furnace body.

[0006]

The above objects of the present invention can be achieved by the following constitutions. That is, in a vertical glass melting furnace provided with a glass raw material charging part, a heating part for melting the glass raw material, and a glass base outlet part, the glass raw material heating part is a plate-shaped resistance heating element over almost the entire horizontal section of the melting furnace. And a vertical glass melting furnace in which the thickness of the side portion of the resistance heating element facing the side wall of the furnace is thicker than that of the other heating element surface. As shown in FIG. 2, the thickness of the thick portion 6c of the plate-shaped resistance heating element is T, the width of the thick portion 6c is A, and the length of one side of the plate-shaped resistance heating element is a. When the thickness of the heating plate 6a is t, it is preferable that t <T ≦ 3t a / 100 <A ≦ a / 10, and more preferably 3t / 2 ≦ T ≦.
It is 3t.

[0007]

As shown in FIG. 3 (a), the thickness of the side portion of the plate resistance heating element facing the furnace side wall is made thicker than that of the other heating element surface (heating plate). The thick portion can be made to have a higher temperature than other heating element surfaces. By increasing the temperature of the thick portion of the heating element surface, the glass base material 4 near the gap between the plate resistance heating element and the furnace side wall can be heated to a higher temperature, and an upward flow A is generated in the glass base material 4, and Reduce downflow at. Further, since the glass base material 4 that has passed through the gap is also heated in the high temperature region of the thick portion of the plate-shaped resistance heating element, it is sufficiently melted or heated. In this way, it is possible to prevent the insufficiently melted or insufficiently heated glass substrate 4 from passing through the gap between the plate-shaped resistance heating element and the furnace side wall.

As shown in FIG. 2, the thickness of the thick portion 6c of the plate resistance heating element is T, the width of the thick portion 6c is A, and the length of one side of the plate resistance heating element is a. The heating plate 6a
When the thickness of the portion is t, it is preferable that t <T ≦ 3t a / 100 <A ≦ a / 10, and more preferably 3t / 2 ≦ T ≦.
It is 3t. If t ≧ T, the thick portion 6c cannot be heated to a temperature higher than that of the other heating element surface (heating plate) 6a. If T> 3t, the thick portion 6c has an abnormally higher temperature than the other heating element surface (heating plate) 6a, and the heating plate 6a may break. Further, if a / 100 ≧ A, a sufficient amount of heat cannot be obtained, and the glass substrate existing near the thick portion 6c of the heat generating plate 6a cannot be sufficiently heated. Further, when A> a / 10, the high temperature region is widened, and the upward flow generated near the gap between the plate resistance heating element and the furnace side wall is weakened, and the plate resistance heating element of the present invention should be realized. It becomes impossible to realize heating with uniform temperature distribution and small heat convection.

[0009]

An embodiment of the present invention will be described with reference to the drawings.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The vertical glass melting furnace of one embodiment of the present invention has substantially the same structure as that shown in FIG. 6 except for the shape of the plate resistance heating element 6. As the material of the plate-shaped resistance heating element 6 of the present embodiment, platinum, platinum-rhodium alloy, molybdenum, molybdenum coated with platinum on the surface is used, and platinum or platinum-rhodium alloy is particularly preferable. . 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 of the plate resistance heating element 6 is a square plate having a side of 100 cm, and the plate resistance heating element 6 made of 90% Pt-10% Rh. Was installed. The opening 7 has a circular shape with a diameter of 10 mm,
The distance between adjacent openings was set to 20 mm. Also, FIG.
And a cross-sectional view of the plate resistance heating element 6 of FIG. 2 (A in FIG. 1).
As shown in (A line cross section), the plate-shaped resistance heating element 6 of the glass melting furnace according to the present embodiment is made of a punching plate having a thickness of 0.5 mm, and the side of the plate-shaped resistance heating element 6 at the terminal portion 6b. Except for the width of about 20 mm near the side (length of about 100 cm, thickness of about 0.5 mm) facing the furnace wall of the furnace main body 10 is a thick portion 6c having a thickness of about 1.0 mm. Then, the glass is heated by energizing the plate-shaped resistance heating element 6. At this time, the resistance value of the plate-shaped resistance heating element 6 is uniquely determined according to the temperature, and a predetermined amount of heat can be accurately generated by supplying a predetermined power. Further, the plate-shaped resistance heating element 6 is
Since a is evenly provided over the entire area of the horizontal cross section of the furnace body 10, the glass base material 4 is heated evenly over the entire area of the horizontal cross section, and the temperature distribution of the glass base material 4 in the horizontal cross section is Remarkably uniform.

As a result, convection of the glass substrate 4 due to temperature unevenness in the horizontal plane is prevented. Further, the glass base material 4 in the glass melting furnace has a maximum temperature at a portion in contact with the heat generating plate 6a, and the temperature becomes lower as the depth becomes lower than the heat generating plate 6a. Therefore, thermal convection hardly occurs in the glass substrate 4 below the heat generating plate 6a. When a voltage of 8.5 V is applied to the terminal portion 6b, when the surface of the plate resistance heating element 6 having a thickness of about 0.5 mm is heated to 1600 ° C., the thick portion 6c having a thickness of 1. The 0 mm side part generates heat up to 1650 ° C. Thus, as shown in FIG. 3A, the glass base material 4 near the gap between the heating element 6 and the furnace side wall of the furnace body 10 is heated to a higher temperature by increasing the temperature of the thick portion 6c of the plate-shaped resistance heating element 6. As a result, an ascending flow A is generated in the glass substrate 4 as shown by the arrow, and a descending flow in the gap is reduced. In addition, the glass substrate 4 that has passed through the gap is also the thick portion 6c of the heating element 6.
Since it has been heated in the high temperature region, melting or heating is sufficiently performed. As described above, it is possible to prevent the insufficiently melted or insufficiently heated glass substrate 4 from passing through the gap between the plate resistance heating element 6 and the furnace side wall of the furnace body 10.

Further, the plate-shaped resistance heating element 6 of the embodiment of the present invention
, The diameter of the opening 7 (the longest diagonal length when the opening shape is a polygon) D, the adjacent openings 7,
It is desirable to have the following relationship between the center-to-center distance P of 7'and the length (diameter in the case of a circle) L of the longest diagonal of the heat generating plate 6a (note that the diameter D and the two adjacent diameters are the same). (See FIG. 7 for the center-to-center distance P between the two openings and the length L of the longest diagonal of the heating plate 6a). By setting D> 1 mm and D / L <0.5 D / P> 0.1 D> 1 mm, the workability of the opening of the opening 7 is improved and the clogging of the opening due to undissolved material is prevented. Further, by setting D / L <0.5, the uniformity of the in-plane temperature distribution of the glass substrate is not impaired, and D / P>
By setting the value to 0.1, the nonuniformity of the heat history of the glass base material 4 is prevented. The plate-shaped resistance heating element 6 may have a sectional shape as shown in FIG. 4 (a sectional view taken along the line AA in FIG. 1). That is, it is not limited to a flat plate shape, but a corrugated plate shape (FIG. 4 (a)), a round plate shape (FIG. 4 (b)), a combined shape of a flat plate and a corrugated plate (FIG. 4 (c)), and a flat plate. A combination shape with a round plate (FIG. 4D) and the like.

[0013]

EFFECTS OF THE INVENTION By making the side of the plate resistance heating element facing the side wall of the furnace thicker than the other heating element surface, the thick portion can have a higher temperature than the other heating element surface. As a result, it is possible to prevent passage through the gap between the heating element of the glass base material that is melted or insufficiently heated and the furnace side wall.

[Brief description of drawings]

FIG. 1 is a perspective view showing a plate-shaped resistance heating element of a glass melting furnace according to an embodiment of the present invention and a side wall of a furnace body in the vicinity thereof.

2 is a sectional view of the plate-shaped resistance heating element of FIG. 1 (A- in FIG.
(A line cross section).

FIG. 3 is a diagram for explaining the flow of the glass base material in the vicinity of the gap between the thick portion and the furnace side wall of the plate resistance heating element of the present invention and the prior art.

FIG. 4 is a modification of the cross-sectional view (cross section taken along the line AA of FIG. 1) of the plate resistance heating element of the glass melting furnace of the example of the present invention.

FIG. 5 is a cross-sectional view of a conventional glass melting furnace.

FIG. 6 is a cross-sectional view of a conventional glass melting furnace using a plate-shaped resistance heating element.

FIG. 7 is a plan view of FIG.

[Explanation of symbols]

1 ... Raw material inlet, 2 ... Glass base outlet, 3 ... Glass raw material, 4 ... Glass base, 6 ... Plate resistance heating element, 6a ... Heating plate, 6b ... Terminal part, 6c ... Thick part, 7 ... Opening

Claims (2)

[Claims] 1. A vertical glass melting furnace comprising a glass raw material charging section, a heating section for melting the glass raw material, and a glass base outlet section, wherein the glass raw material heating section has a plate-like shape over substantially the entire horizontal section of the melting furnace. 1. A vertical glass melting furnace, comprising a resistance heating element, wherein a side portion of the resistance heating element facing a side wall of the resistance heating element has a thickness thicker than that of another heating element surface. 2. The thickness of the thick portion of the plate resistance heating element is T, the width of the thick portion is A, the length of one side of the plate resistance heating element is a, and the thickness of the heating element surface portion is The vertical glass melting furnace according to claim 1, wherein a relation of t <T ≦ 3t a / 100 <A ≦ a / 10 is satisfied when t is set.