JPH0561992U - Electric heater - Google Patents

Abstract

(57) [Summary] [Structure] In a heating element made of silicon carbide, at least the heating portion is covered with an insulating spacer, or at least the heating portion is covered with a carbon or ceramic sheath material. It consists of filling the body with an inert gas. [Effect] When used in the space on the upstream side of the metal bath in a float glass plate, the effect of the atmosphere can be suppressed, the life of the silicon carbide heating element itself can be extended, and plate glass defects can be reduced. By appropriately disposing the silicon carbide type heating element from both sides of the metal bath, it is effective in soaking the glass ribbon and making the plate thickness uniform.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

INDUSTRIAL APPLICABILITY The present invention is used, for example, as a heating means for controlling temperature in a molten metal bath (referred to as a float bath) when a molten glass is supplied onto a molten metal bath to produce a glass sheet in a float glass plate. The present invention relates to an electric heater which has a high ambient temperature of about 1350 ° C. and can be suitably used as a heating means in a reducing atmosphere composed of a mixed gas of H ₂ gas and N ₂ gas.

[0002]

[Prior Art]

 Usually, the heater made of silicon carbide has high purity. Although it is made of recrystallized SiC and is used by directly exposing it to the atmosphere, it is necessary to extend the service life. It is known that the device has been devised such as to make an effort.

In addition, separately, for example, in the case of being used while being immersed in a molten metal in metal refining or the like, Al ₂ O ₃ powder is added to a mixture containing SiC particles and Si ₃ N ₄ as main constituent raw materials and molded. Which uses a heater coating tube (Japanese Patent Laid-Open No. 63-274085), or the heater is surrounded by a heat-resistant heater protective tube made of recrystallized SiC having a specific porosity, and a plasma is formed on the outer surface. Those in which an insulating coating such as a BN film is formed by thermal spraying (Japanese Patent Laid-Open No. 62-112983) are known.

[0004]

[Problems to be solved by the device]

As described above, for example, an ordinary silicon carbide heater is used as it is at the above-mentioned high temperature under a reducing atmosphere containing H ₂ gas and N ₂ gas in the presence of high-temperature molten glass. When exposed and used for electric heating, white powder, which is a reaction product with the atmosphere, adheres to the surface of the silicon carbide heater to reduce the calorific value, and this further grows and finally melts as described above. It often drops on glass and causes glass defects, and in some cases the heater itself breaks within a few days, resulting in an extremely short life.

Further, unlike the present invention, the above-mentioned known heater tube or one provided with a heat-resistant heater protection tube with an insulating coating does not have a complicated and easy structure, and prevents the above-mentioned influence and adverse effects. It is not appropriate above.

[0006]

[Means for solving problems]

 The present invention has been completed as a result of various investigations in view of the above-mentioned drawbacks of the prior art. By enclosing the part in a non-contact state, the adhesion of white powder etc. can be significantly reduced, the occurrence of defects in glass products can be significantly suppressed, and an electric heating heater that can extend the useful life of the heater is proposed. It is something to offer.

That is, the present invention relates to an electric heater, and in a heating element made of silicon carbide, at least the heating part thereof is covered with a carbon sheath material with an insulating spacer interposed, or an insulating spacer is provided in the heating element made of silicon carbide. The heat generating part is covered with a carbon or ceramic sheathing material and is filled with an inert gas between the heating element and the sheathing material, and the silicon carbide heating element has a rod-like or cylindrical shape. In addition, an insulating spacer was interposed between the both end areas to cover the heating element with a carbon sheath material. In addition, a spiral arranged on the metal bath of the float glass plate for controlling the heating of the glass substrate temperature. It is a cylindrical tubular heating element made of silicon carbide, and is appropriately arranged from both sides of the metal bath toward the center of the bath.

[0008]

【Example】

 Hereinafter, the present invention will be described with reference to the drawings based on specific embodiments. However, the present invention is not limited to this embodiment.

FIG. 1 is a side sectional view showing an example of the configuration of an electric heater of the present invention, in which the electric heat heater 1 generates heat from a rod-shaped silicon carbide heating element 2 having terminal connecting portions 6 at both ends. The part 3 is covered with a carbon sheath material 4 with insulating spacers 5 in the vicinity of both end regions.

FIG. 2 is a longitudinal cross-sectional view of the inside of a bath showing an example in which the electric heater of the present invention is used as a temperature adjusting heating means in the space on the upstream side of the float bath in a float glass plate. Molten glass 7 is supplied from the glass melting furnace side through the gap between twill 10 and lip tile 11 into the bath, flows over lip tile 11 and flows over molten metal 12 over float bath furnace bottom 16. Then, the dam member 14 forms the molten glass pool 8. The molten glass 7 supplied to the molten glass pool 8 passes between the dam member 14 and the molten metal bath 12 and is stretched by the traction force of a transport roll (not shown) provided on the downstream side of the molten metal bath 12, The ribbon 9 is formed.

In the upstream space 13 between the molten glass pool 8 and the flat arch 15 of the ceiling, the electric heater 1 has a temperature of about 1320 ° C. or 1360 ° C. in the presence of a mixed gas of H ₂ gas and N ₂ gas. It is preferably adopted in the atmosphere before and after, and is heated and adjusted to a specific temperature.

FIG. 3 is a sectional view of the inside of the bus of the upstream space 13 shown in FIG. 2 to which the electric heater 1 of the present invention is attached. The insulation is not shown in the sidewall 17 of the float bath. It is set so that it is supported by interposing materials.

[0013] Conventionally, the generation of white powder in a heating element made of silicon carbide is caused by the reaction of SiC constituting the heating element with N ₂ in the atmosphere and a slight amount of O ₂ in the presence of H ₂ having a high reducing power at high temperature. It is inferred that it was changed to SiON type or SiN type and precipitated. However, by taking the means shown in the embodiments of FIGS. 1 to 3 described above, the carbon C from the carbon sheath material reacts with a trace amount of O ₂ to form CO and further CO ₂ , and the carbon oxide The presence of the system gas prevents the formation of SiON and SiN 2 white powder, and the service life of the silicon carbide heating element can be remarkably extended without breaking in a short period of time. The carbon sheathing material may have a wall thickness of, for example, about 5 to 6 mm, but it is preferable to reduce the thickness within a range that allows strength.

FIG. 4 is another embodiment of the present invention, which is a sectional view of the inside of the bus in which the hanging electric heater 1 is arranged in the ceiling portion composed of ceiling bricks 19 and 20, and is a U-shape. In the silicon carbide heating element 2 formed in a mold, a wire netting wire 21 for electricity is fixed to the connecting portion 6 on the outside of the ceiling brick 20 with a fixture 22, and the carbonization is performed. The heating element 2 made of silicon is set in the ceiling brick 20 so as to be supported with an insulating material (not shown) interposed therebetween, while the sheath material 4 made of carbon is supported by the ceiling brick 19, and A carbon partition plate 18 having a notch at the bottom so as not to come into contact with the heating element 2 is arranged in the center between the two, and an insulating spacer 5 is covered on the top so as to intervene in a lid shape. As is clear from these examples, the silicon carbide heating element covered with the sheath material can have various shapes and can be arranged at appropriate places.

FIG. 5 shows still another embodiment. In place of the rod-shaped silicon carbide heating element in the embodiment shown in FIG. 3, a spiral type tubular silicon carbide heating element 2 is adopted. FIG. 6 is a cross-sectional view of the inside of the bus showing an example of the above. Also in the present embodiment, the periphery of the spiral cylindrical silicon carbide heating element 2 is covered with the carbon sheathing material 4, and the same operational effects as described above are exhibited. Alternatively, as the sheath material, use alumina, silica-alumina-based or other heat-resistant ceramic material including carbon material, and fill it with an inert gas, for example, N ₂ gas, as shown by arrow A. Then, since the silicon carbide heating element 2 is in an inert atmosphere completely shielded from the reducing atmosphere, it can be maintained in a stable state in which it is less likely to deteriorate. Of course, the inert gas can be filled from one side of the sheath material also in the above-mentioned embodiments 1 to 4.

The spiral cylindrical heating element is inserted in a pair from both sides of the bath as shown in the figure, and can be arranged in place of the rod-shaped heating element to heat the central portion of the glass ribbon. Can be suppressed. That is, when a conventional rod-shaped heating element is used, the temperature at the center of the glass ribbon is high and the temperatures at both ends are low, and therefore the viscosities are slightly different from each other. However, in the present embodiment, the adverse effect is eliminated. In addition to the above, the spiral cylindrical silicon carbide heating element can also be used as a means for appropriately supplementing both ends of the glass ribbon.

[0017]

[Effect of the device]

 As described above, according to the present invention, in the heating element made of silicon carbide, at least the heating portion is covered with the carbon sheath material with the insulating spacer interposed, or the carbon or ceramic sheath. By covering with a material and filling the space between the heating element and the sheath material with an inert gas, defects such as defects in sheet glass products can be significantly reduced even in the space on the upstream side of the so-called float bath. In addition, the silicon carbide heating element itself is significantly less damaged in a short period of time and the service life can be extended. In addition, in the case where the spiral cylindrical tubular silicon carbide heating element is adopted, It has the effect that the ribbon can be soaked and the plate thickness can be made uniform, which is extremely useful industrially.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an example of the configuration of an electric heater of the present invention.

FIG. 2 is a vertical sectional view showing an example in which the electric heater of the present invention is used in a so-called float bath.

FIG. 3 is a side sectional view corresponding to FIG. 2, showing a portion where an electric heater of the present invention is set in a float bath.

FIG. 4 is a partial side sectional view showing another embodiment of the float bath.

FIG. 5 is a partial side sectional view showing still another embodiment of the float bath.

[Explanation of Codes] 1 Electric Heater 2 Silicon Carbide Heating Element 3 Heating Part 4 Carbon Sheath Material 5 Insulating Spacer 8 Molten Glass Pool 12 Molten Metal Bath 13 Upstream Space

Claims (4)

[Scope of utility model registration request] 1. An electric heater comprising a silicon carbide heating element in which at least a heating portion is covered with a carbon sheath material with an insulating spacer interposed. 2. A heating element made of silicon carbide, at least the heating portion of which is covered with an insulating spacer, is covered with a sheath material made of carbon or ceramic, and an inert gas is filled between the heating element and the sheath material. An electric heater characterized by. 3. A silicon carbide heating element having a rod shape or a cylindrical shape, and an insulating spacer is interposed in both end regions of the heating element to cover the circumference of the heating element with a sheath material. Electric heater. 4. A spiral type cylindrical silicon carbide heating element arranged on a metal bath in a float glass plate for controlling heating of a glass base material, the heating element being formed from both sides of the metal bath toward a central portion of the bath. The electric heater according to any one of claims 1 to 3, which is arranged appropriately.