JPH07247174A - Thermal insulation antioxidant for graphite-containing refractory - Google Patents

Abstract

PURPOSE:To obtain a thermal insulation antioxidant with no problem in terms of environmental health, having function to prevent oxidation of the graphite under heating in a graphite-contg. refractory composition, also having such thermal insulation as to prevent the heat release after heating or during casting the refractory composition, and useful for coating the surface of graphite-contg. refractory with thermal insulation ranging from normal to elevated temperatures. CONSTITUTION:A mixture composed of 3-30wt.% of vermiculite heat treated at 300-1200 deg.C, l-30wt.%, in an unheated state, of an expandable material giving hollow texture on heating at >=800 deg.C such as obsidian, perlite, pitchstone or expanded shale, and 40-96wt.% of glass powder softening and melting at 400-1500 deg.C or refractory powder such as of pyrophyllite, sil=ica rock, chamotte, mullite, alumina, fused silica, zirconia or magnesia, is incorporated with 20-250wt.%, on an outer basis, of a liquid binder to obtain the aimed antioxidant. Because of containing the above-mentioned expandable material generating a gas at >=800 deg.C, this antioxidant, in the form of a coating film, produces closed pores advantageous for thermal insulation therein at 800 deg.C, also enabling its thermal insulation effect to be maintained even at >1100 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antioxidant for a graphite-containing refractory material having an antioxidant function for suppressing the oxidation of graphite during heating of the graphite-containing refractory material and a heat insulating property for suppressing heat dissipation.

[0002]

2. Description of the Related Art For example, a refractory composition for casting, which is used for manufacturing steel, is filled with molten steel at a temperature close to 1500 ° C. Therefore, a refractory composition containing graphite having excellent thermal shock resistance is used.
This graphite-containing refractory composition is preheated and used in order to prevent the occurrence of cracks due to a rapid thermal change immediately after pouring molten steel, but in this case, oxidation of graphite becomes a problem. Further, since this refractory composition contains graphite, the thermal conductivity is high,
Since the heat dissipation from the outer surface is large, the occurrence of cracks due to the sudden temperature drop from the end of heating to the start of casting and the occurrence of solidification of the metal in the inner hole due to heat dissipation during casting are also problems. .

[0003] As measures against these, the surface of the graphite-containing refractory composition is coated with an antioxidant on the surface of the graphite-containing refractory composition for the purpose of preventing the oxidation of the graphite during heating, and the surface of the graphite-containing refractory composition for the purpose of preventing heat dissipation after heating or during casting. Al ₂ O ₃ -SiO ₂ system and Al ₂ O
_{The 3-} SiO ₂ -CaO-based ceramic heat insulating fiber is attached.

When the above-mentioned antioxidant is used in combination with the ceramic heat insulating fiber, it can be expected to prevent the oxidation of graphite during heating and the heat dissipation after heating or during casting. The problem that the graphite-containing refractory composition is sucked into the pores of the ceramic insulating fiber and the surface of the graphite-containing refractory composition is exposed to oxidation of the graphite, or the binder of the ceramic insulating fiber disappears due to heating There is a problem that the fibers of the above float in the atmosphere.

Further, a graphite-containing refractory composition surface was constructed by applying an amorphous refractory containing leeks or expanded shale that had been hollow-structured by heat treatment or an amorphous refractory containing organic fibers disappearing by heating. A method for preventing heat dissipation can be mentioned, but since these amorphous refractories have high air permeability under high temperature conditions, oxidation of graphite becomes a problem unless an antioxidant is used together.

[0006]

The object of the present invention is to prevent the oxidation of graphite during heating of the graphite-containing refractory composition without causing environmental hygiene problems, and after heating or during casting. It is an object of the present invention to provide an antioxidant for coating the surface of a graphite-containing refractory material having a heat insulating property from room temperature to a high temperature, which has a heat insulating property for preventing heat dissipation of the above.

[0007]

According to the present invention, a part of a raw material (hereinafter referred to as a foaming raw material) for forming a hollow structure by dehydration of water of crystallization during heat treatment is in a heat-treated state and the rest is in an unheated state. It is applied to the surface of a graphite-containing refractory composition in a form that is used in combination with glass powder or refractory powder, and has heat insulation from the foamed raw material that has been heat-treated from room temperature to the intermediate temperature range, and has not By forming sealed pores in the coating film that has been melted and vitrified by foaming of the foaming raw material in the heated state, excellent heat insulation is maintained from room temperature to high temperature, and the heat insulation is obtained by forming sealed pores. It was completed based on the basic idea that it can also have the effect of blocking air.

That is, the present invention is 300 to 1200 ° C.
3 to 30% by weight of vermiculite heat-treated at 1 to 30% by weight in the unheated state of foaming raw materials such as obsidian, pearlite, pine rock and expanded shale that hollow-structure by heat of 800 ° C or higher. And 4
Glass powder that softens and melts in the range of 0 to 1500 ° C, or a mixture of 40 to 96% by weight of refractory powder such as wax, silica stone, chamotte, mullite, alumina, fused silica, zirconia, and magnesia, and liquid It is an antioxidant having a heat insulating property in which 20 to 250% by weight of a binder is blended on the outside.

[0009] 3-10% by weight of vermiculite heat-treated at 300-1200 ° C, and obsidian, pearlite, pine shale, expanded shale, etc. which are hollow-structured by heat of 800 ° C or higher are From 30% by weight and 40 to 96% by weight of glass powder that softens and melts in the range of 400 to 1500 ° C., or refractory powder such as wax, silica, chamotte, mullite, alumina, fused silica, zirconia, and magnesia. 20 to 250% by weight of a liquid binder is externally added to the mixture to have heat insulating properties.

Since vermiculite contains a large amount of water of crystallization and causes large volume expansion at 300 ° C. or higher, when added in an unheated state, the unmelted coating film is destroyed during heating. Therefore, it is necessary to perform heat treatment at 300 to 1200 ° C. from the viewpoint of not destroying the coating film and from the fire resistance of vermiculite, and the addition amount is 3 to 30 wt%. If the amount of vermiculite is less than 3% by weight, the heat insulating property is poor, and if it exceeds 30% by weight, the volume ratio of the vermiculite in the heat insulating antioxidant is excessive, and the brush coating, spraying, and pouring are performed. Slip with workability cannot be obtained.

As a foaming raw material which is hollow-structured by heat of 800 ° C. or higher, obsidian, pearlite, pine rock, expanded shale, etc. can be used, but from the viewpoint of adding many small pores. , Obsidian and pearlite are preferred. Also,
The addition amount of the unheated foaming raw material needs to be 1 to 30% by weight, and if the addition amount is less than 1% by weight, the amount of foaming is small,
Poor heat insulation under high temperature conditions, and if it exceeds 30% by weight, it is impossible to maintain pores in the state of being hermetically sealed in the coating film melted and vitrified due to excessive foaming, and air entering from open pores. Oxidation occurs in the graphite-containing refractory.

Glass powder that softens and melts in the range of 400 to 1500 ° C. or refractory powder such as wax, silica, chamotte, mullite, alumina, fused silica, zirconia, and magnesia forms a molten glass film when heated. In addition to blocking the invasion of air from the outside, it is added to hold the gas generated when the unheated foaming raw material is heated in the coating film, and is heat-treated at a temperature of 300 to 1200 ° C. From the added amount of vermiculite of 3 to 30% by weight and the added amount of unheated foaming raw material of 1 to 30% by weight, inevitably 40 to
The amount added is 96% by weight. The glass powder or the refractory powder is used alone or in combination depending on the heating temperature of the graphite-containing refractory, and prevents the coating from being cut off due to the flow-down phenomenon due to the decrease in the viscosity of the molten glass during heating.

The foaming raw material, glass powder or refractory powder is preferably adjusted in particle size so that the total particle size is 3 mm or less and kneaded with a liquid binder. Here, the liquid binder means a liquid material such as water, an organic solvent, an organic paste, silica sol, alumina sol, zirconia sol, and a powdery binder dissolved in water, an organic solvent or the like. In order to adjust the viscosity of the foaming raw material, glass powder or refractory powder to the graphite-containing refractory surface by brush coating, spraying or pouring using this liquid binder, the compounding amount is 20-25.
It is 0% by weight. In the present invention, any of these liquid binders can be used, but silica sol / alumina sol / zirconia sol is particularly preferable from the viewpoint of maintaining coating strength from room temperature to high temperature.

The kneading is carried out by a usual method using a mixer, and a coating film having heat insulating property and air blocking effect is formed on the entire surface of the refractory by brushing, spraying and pouring the kneaded product. To do.

[0015]

[Function] 300 contained in the heat insulating antioxidant of the present invention
The vermiculite that has been heat-treated to ~ 1200 ° C is
Adiabatic effect is exhibited up to 00 ° C, but when it exceeds 1100 ° C, it melts due to reaction with an alkali component in the antioxidant and loses its effect. However, the adiabatic antioxidant of the present invention also contains an unheated foaming raw material that generates gas in a temperature range of 800 ° C. or higher, and therefore, in the temperature range of 800 ° C. or higher, a sealed pore that is advantageous for heat insulation in the coating film Thus, it becomes possible to maintain the heat insulating effect even in a temperature range exceeding 1100 ° C.

[0016]

EXAMPLES Heat-treated vermiculite having a particle size of 1 to 0 mm, pearlite having a particle size of 1 to 0 mm as an unheated foaming raw material, borosilicate glass having a softening point of 800 ° C. as glass powder, and 200 to as refractory powder. 0 μm of pyrophyllite, and silica sol was used as a liquid binder. These vermiculite, pearlite,
Predetermined amounts of borosilicate glass and pyrophyllite were weighed and mixed, and further silica sol was externally added to the mixture to a degree of softness in consideration of brush application, and kneaded to form a slurry.
The slurry was brush-coated on the surface of a small piece of alumina-graphite refractory material to form a coating film of about 5 mm. This was heated in a gas furnace at a temperature rising rate of 600 ° C./hr to 700 ° C. × 2
After maintaining for 1 hour and after maintaining at 1200 ° C. for 2 hours, it was naturally cooled, and the state of coating film structure and oxide layer formation was observed with a reflection microscope.

Further, this slurry is used as a real-shaped alumina-
Brush the outer surface of the graphite nozzle to a thickness of 5 mm and 700 ° C.
Also, the temperature drop on the nozzle surface was measured when it was left in the air after heating at 1200 ° C. For comparison, a nozzle having a conventional ceramic fiber of 3 mm thickness and a nozzle not using a heat insulating material were similarly investigated.

FIG. 1 shows a test condition therefor, in which 1 is a heating box, 2 is an alumina-graphite nozzle, 3 is a thermocouple, 4 is a burner, and 5 is a heat insulating layer.

The results are shown in Tables 1 and 2.

[0020]

[Table 1]

[Table 2] As shown in Table 1 and Table 2, in the sample 3 in which the heat treatment temperature of the vermiculite was lower than that of the present invention, the coating film was destroyed due to the volume expansion of the vermiculite during heating, and the heat insulating effect and the antioxidant effect were obtained. Absent. On the other hand, in the case where the heat treatment temperature of the vermiculite was 300 ° C., and in the case where the heat treatment temperature of the sample was 1200 ° C., the coating film was not destroyed during heating.
200 ° C is desirable. In the case of Sample 4 in which the addition amount of the calculus preheated within the heat treatment temperature range of the present invention was smaller than that of the present invention, the temperature of the alumina-graphite nozzle surface after heating at 700 ° C. in the region where the heat insulation of the calculus was exhibited. The decrease is similar to that of Sample 1 without the heat insulating layer, and the desired heat insulating property cannot be obtained.
Further, in the case of the sample 6 in which the addition amount of the vermiculite was larger than that of the present invention, the volume ratio of the vermiculite in the compounding was too large, and even if it exceeded the outer limit of 250% by weight, which is the upper limit of addition of the liquid binder of the present invention, Slip with good workability cannot be obtained. From this, the addition amount of heat-treated vermiculite is 3 to 30% by weight.
Is desirable.

In the case of Sample 5 in which the amount of the unheated foaming raw material which becomes hollow by heating at 800 ° C. or more is smaller than that of the present invention, sealed pores advantageous for heat insulation should be formed in the coating film even after heating at 1200 ° C. On the contrary, in the case of the sample 7 in which the amount of the foaming raw material added is larger than that of the present invention, the amount of gas generated during heating of the foaming raw material becomes excessive, and after heating at 1200 ° C., the formation of open pores lowers the heat insulating property and oxidizes the nozzle. . From this, it is desirable that the addition amount of the unheated foaming raw material is 1 to 30% by weight.

On the other hand, Samples 8, 9, which are the examples of the present invention,
10, 11, 12, 13, 14 are all 700 ° C
After heating at 1200 ° C., heat insulation properties similar to those of Sample 2 with ceramic fiber attached are recognized, and nozzle oxidation does not occur. Further, as shown in Samples 13 and 14, the glass powder and the refractory powder have good heat insulating effects and antioxidation effects even if either one is used alone.

In addition to the above-described pearlite, obsidian, sessile rock, and expanded shale are used as the foaming raw material which is not heated to form a hollow structure by heat of 800 ° C. or higher.・ Chamotte, mullite, alumina, fused silica, zirconia, magnesia, etc. are used, but these are combined to make samples 15, 16, 17, 18, 19, 2
As a result of making 0 and performing the same confirmation as the evaluations shown in Table 1 and Table 2, it was confirmed that the sample 12 had the same heat insulating effect and antioxidant effect.

The heat insulating antioxidant of the present invention was applied to the outer surface of a continuous casting dipping nozzle in a thickness of 5 mm, and molten steel casting was carried out for 7 hours. As a result, there was no solidification of the metal in the nozzle or oxidation of the outer surface. Good results were obtained.

[0025]

EFFECTS OF THE INVENTION According to the present invention, there is no problem in environmental hygiene, a function of preventing oxidation of graphite during heating of a graphite-containing refractory composition, and heat insulation for preventing heat dissipation after heating or during casting. It is possible to obtain an antioxidant having properties.

As a matter of course, the heat-insulating antioxidant of the present invention can exert its effect even when applied over a graphite-containing refractory composition whose surface is previously coated with an antioxidant. Is.

[Brief description of drawings]

FIG. 1 is a diagram showing a test state of an antioxidant of the present invention.

[Explanation of symbols]

 1 heating box 2 alumina-graphite nozzle 3 thermocouple 4 burner 5 heat insulating layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Yakichi 1-1, Higashihama-cho, Hachimansai-ku, Kitakyushu, Fukuoka Prefecture Kurosaki Ceramics Co., Ltd.

Claims (1)

[Claims] 1. One or more kinds of obsidian, pearlite, pinelite, and expanded shale that hollow-structure by heat of 800 ° C. or higher at 3 to 30% by weight of vermiculite heat-treated at 300 to 1200 ° C. 1 to 30% by weight in the unheated state, 400 to 1
Glass powder that softens and melts in the range of 500 ° C, or a mixture of 40 to 96% by weight of one or more refractory powders of wax, silica, chamotte, mullite, alumina, fused silica, zirconia, and magnesia. An adiabatic antioxidant of a graphite-containing refractory material having a heat insulation property, which is obtained by blending 20 to 250% by weight of a liquid binder on the outside.