JPH11278939A - Alumina-silicon carbide refractory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optimum constituent condition of an alumina-silicon carbide refractory free from chromium, and excellent in corrosion resistance and spalling resistance as the lining refractory of a melting furnace for dust and an industrial waste. SOLUTION: This alumina-silicon carbide refractory is obtained by kneading a blend comprising a silicon carbide powder of 10-60 wt.%, a mixed powder of Si and Al, and/or an alloy powder of the Si and the Al, of 0.5-8 wt.% expressed in terms of Si and 1-10 wt.% expressed in terms of Al, and mainly an alumina powder of the remainder, by using a resin, and compacting the kneaded blend. The refractory can be heat-treated at 90-400 deg.C after compacting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alumina-silicon carbide refractory which exhibits excellent corrosion resistance to a molten material in a furnace and is suitably used for lining a melting furnace such as dust and industrial waste.

[0002]

2. Description of the Related Art Incinerators for dust and industrial waste from general households are made of high alumina refractories for corrosion resistance, and silicon carbide refractories for low adhesion and high corrosion resistance. Is used.

[0003] In recent years, due to the lack of landfill for incinerated ash after incineration, a method of melting dust, waste, and incineration ash at once has been realized. However, the conditions for using the refractory lining of the melting furnace are stricter because the temperature in the furnace is higher than that of the incinerator, and the refractory comes into contact with the melt. For this reason, general high alumina refractories have a remarkable lack of corrosion resistance. As a remedy, chromium-containing alumina refractories containing a chromium component to increase the corrosion resistance have been adopted.

[0004] However, although this chromium-containing alumina refractory exhibits sufficient corrosion resistance under the operating conditions of the melting furnace, it generates hexavalent chromium when an alkali component is present in the furnace interior of the melting furnace. It is unavoidable and poses a problem of environmental hygiene, and chromium-free is required.

On the other hand, as a silicon carbide refractory, an oxide type such as a clay bond using a clay is used,
A β-SiC bond fired in a reducing atmosphere using Si, a silicon nitride bond obtained by firing in a nitrogen atmosphere, and the like are known. However, these silicon carbide refractories are generally excellent in corrosion resistance, but when used in a melting furnace for dust and industrial waste, the molten material often contains alkali components, iron oxide components, and molten iron. Since it is contained, there is a problem that its corrosion resistance is impaired.

This alumina-silicon carbide refractory is also used as a lining for a blast furnace for iron making. In this method, Al is added to a silicon carbide refractory and a bond such as AlN or SIALON is formed by using nitrogen existing in an atmosphere under use conditions, and shows sufficient corrosion resistance. However, the atmosphere inside the melting furnace that melts dust and industrial waste is hotter than that of the blast furnace for ironmaking, the molten material contains alkali components, and moderate spalling resistance due to intermittent operation. Therefore, it is impossible to apply the refractory used in the blast furnace for ironmaking to a melting furnace for dust and industrial waste as it is.

[0007]

The problem to be solved by the present invention is as follows.
Maintains high corrosion resistance not only under relatively low temperature processing conditions, but also at high temperature and in contact with the furnace melt, and shows sufficient spalling resistance even during intermittent operation such as furnace repair. It is to obtain a chromium-free refractory suitable for lining for dust and industrial waste melting furnaces.

[0008]

According to the present invention, a predetermined amount of SiC powder is added to an alumina-silicon carbide refractory which is used in a blast furnace for iron making and has high corrosion resistance even under conditions of contact with hot metal. To ensure corrosion resistance and spalling resistance, and
The addition of a predetermined amount of Al significantly improves the corrosion resistance while ensuring the spalling resistance, and furthermore, the addition of the predetermined amount of Si prevents the digestion problem associated with the addition of Al from being reduced in the corrosion resistance and the spalling resistance. While resolved.

[0009] Further, by heat-treating the resin in an appropriate temperature range and curing the resin, a resin bond is sufficiently formed, and a carbon bond is formed by heating during use. It has been optimized as

That is, in the present invention, the use amount of silicon carbide powder is 10 to 60% by weight, and a mixed powder of Si and Al is used.
And / or the alloy powder of Si and Ai is 0.5
About 8% by weight, and about 1 to 10% by weight as Al, with the balance being mainly composed of alumina powder kneaded and molded using a resin, or 90% after molding.
It is an alumina-silicon carbide refractory heat-treated at ~ 400 ° C.

When the amount of the silicon carbide powder is less than 10% by weight, the corrosion resistance and the spalling resistance are insufficient due to the influence of the alkali component contained in the furnace melt. If the amount of the silicon carbide powder exceeds 60% by weight, the corrosion resistance is reduced due to the influence of the iron oxide component and the molten iron contained in the melt in large amounts.

If the amount of Al in the mixed powder of Si and Al and / or the alloy powder of Si and Al to be blended is less than 1% by weight as Al, the AlN formed during use is reduced.
Insufficient amount of bond formation such as SALON and SIALON results in poor corrosion resistance. On the other hand, if it exceeds 10% by weight, the bond is excessively formed and the spalling resistance is poor.

Similarly, if the amount of Si in the mixed powder of Si and Al and / or the alloy powder of Si and Al is less than 0.5% by weight as Si, the bond formed during use is Is mainly composed of AlN, which causes a problem of digestion of the refractory while the temperature is lowered during a furnace shutdown time such as when repairing the furnace. On the other hand, if the amount of Si exceeds 8% by weight, the amount of Si-based bonds generated increases, and the corrosion resistance decreases, and at the same time, the spalling resistance decreases.

Al and Si may be added not only as a mixture in a predetermined amount but also as an alloy.
Even if they are added in combination, there is no difference in the effect as long as the Si component and the Al component are contained in predetermined amounts.

The alumina-silicon carbide refractory of the present invention comprises:
In addition to using the molded article as it is, it can also be used by heat treatment after molding. When the heat treatment temperature is 90 ° C. or higher, it is possible to prevent the structure of the refractory from deteriorating during use due to the volatile components remaining in the binder resin, thereby preventing the corrosion resistance from lowering. Also, 400
By performing the heat treatment at a temperature lower than 0 ° C., the decomposition of the binder resin is suppressed, and the shortage of the strength of the refractory and the decrease in the corrosion resistance can be prevented.

The reason for using a resin as a binder is as follows.
Since l and Si are used, it is to prevent problems during heat treatment and use. For example, when a phosphoric acid-based or water glass-based binder is used, hydrogen gas is generated during kneading by reaction with a metal. In addition, in the clay-water system, used water and Al react during the heat treatment to generate hydrogen gas. As the binder resin, a phenol resin, a furan resin, a pitch-modified phenol resin, etc. are desirable in view of conditions such as cost and workability, but of course, the present invention is not limited to these, and resins having properties and functions equivalent to these can be used. is there.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to examples.

The compounds in the proportions shown in Tables 1 to 3 were kneaded, the molding pressure was 2 tons / cm ² and the shape was 230 × 100.
It was molded by an oil press to a size of × 65 mm, and heat-treated at 200 ° C. to produce a prototype, unless otherwise specified, with its apparent porosity, compressive strength, and erosion state as a result of an erosion test. Examined the number of spalling spalls.

In the erosion test, L is used unless otherwise specified.
The CaO / SiO ₂ ratio (C / S ratio) was set to 0.
4. Slag assuming a dust incineration ash melt containing 8.5% by weight of Fe ₂ O _{3 and} 8.5% by weight of an alkali was added, and 160
Change the slag every 30 minutes at 0 ° C.
Repeated 0 times. This erosion test cycle is:
Considering the effects of non-continuous operation in the actual operation and the convenience of the laboratory instead of the continuous 20 times, once the test was repeated 10 times, it was completely cooled down, and then completely dismantled 10 times again the next day without dismantling. After the erosion test of the above cycle was continued, the degree of erosion was evaluated.

The erosion index was determined by indexing the erosion amount of each refractory with the erosion amount (thickness reduction dimension) of the calcined alumina brick having an Al ₂ O ₃ content of 95% by weight as 100. The smaller the erosion index, the better the corrosion resistance.

The spalling test was performed at 50 × 50 × 23.
A sample of 0 mm was cut out and embedded in carbon powder.
After heat-treating again at 500 ° C., the sample was immersed in molten pig iron at 1500 ° C. for 90 seconds, immediately cooled with water for 5 seconds, and then air-cooled. The cycle was repeated 15 times, and the number of cycles at the time of spalling was evaluated. The larger the number of cycles at the time of occurrence, the better the spalling resistance. The reason why the heat treatment is performed again at a high temperature before immersion in the molten pig iron is to remove the volatile components remaining after the initial heat treatment by performing the heat treatment again, thereby preventing explosion. A situation in which the volatile metal remains surrounded by the molten metal cannot occur under actual use conditions.

The calcined alumina brick made of 95% by weight of Al ₂ O ₃ having a porosity of 14.6%, a compressive strength of 150 MPa, an erosion index of 100, and the number of cycles at the time of spallation was made as a standard. 5 times.

[0023]

[Table 1] Table 1 shows the relationship between the amount of silicon carbide powder added and the properties. When the case of Example 1 in which the addition amount of the silicon carbide powder exceeds 10% by weight is compared with the case of Comparative Example 1 in which the addition amount of the silicon carbide powder is less than 10% by weight, the corrosion resistance of Example 1 is sufficient. On the other hand, in Comparative Example 1, the corrosion resistance was reduced. This is due to the influence of the alkaline component in the slag when the addition amount of the silicon carbide powder is less than 10% by weight. Further, comparing Example 5 in which the addition amount of silicon carbide powder is 60% by weight or less and Comparative Example 2 in which the addition amount exceeds 60% by weight, the corrosion resistance in Example 5 is sufficient, Sample No. 2 has reduced corrosion resistance. This means that the amount of silicon carbide powder added was 6
If it exceeds 0% by weight, it means that the corrosion resistance is reduced due to the influence of iron oxide in the slag. Also, comparing Example 1 and Example 2, and further Example 3 and Example 4, it can be seen that the particle size configuration of the silicon carbide powder can be selected relatively freely with the maximum particle size being 3 mm. In addition, as shown in the table, it can be seen that by setting the addition amount of the silicon carbide powder within an appropriate range, a refractory excellent in both corrosion resistance and spalling resistance can be obtained.

[0024]

[Table 2] Table 2 shows the relationship between the respective addition amounts of the Al powder and the Si powder and the characteristics of the refractory. In the same table, comparing Example 6 in which the addition amount of Si is 0.5% by weight or more and Comparative Example 3 in which the addition amount of Si is less than 0.5% by weight, Example 6 shows sufficient corrosion resistance in the erosion test, In addition, no crack was generated in the spalling test, but in the case of Comparative Example 3, the erosion thickness after the erosion test could not be measured. In the spalling test, the heat treatment was repeated before the test. The test could not be performed because of the cracks that sometimes occurred. This is because if the amount of Si added is less than 0.5% by weight, the effect of Si to prevent digestion of AlN generated during heating is insufficient. Further, comparing Example 7 which is close to the upper limit of 8% by weight of the added amount of Si with Comparative Example 4 which exceeds 8% by weight, in Example 7, neither the corrosion resistance nor the spalling resistance is reduced. . On the other hand, in the case of Comparative Example 4, both the corrosion resistance and the spalling resistance decreased. This is because excessive Si-based bonds such as β-SiC were formed when the amount of Si added exceeded 8% by weight. Furthermore, A
When comparing Example 8 in which the addition amount of l exceeds 1% by weight and Comparative Example 5 in which the addition amount is less than 1% by weight, the corrosion resistance in Example 8 is sufficient, whereas the corrosion resistance in Comparative Example 5 is low. Is declining. This is because the generation of Al-based bonds such as AlN is insufficient. In addition, as shown in Table 2, by setting the addition amounts of Al and Si within an appropriate range, it is possible to obtain a refractory excellent in both corrosion resistance and spalling resistance without causing digestion of the refractory. I understand.

[0025]

[Table 3] Table 3 shows the effect when the amount of Al added exceeds the upper limit of 10% by weight in Example 9 and Comparative Example 6, and the other effects on the characteristics of the form of the addition of Al and Si. The results of the survey are shown.

First, in comparison with Example 9 and Comparative Example 6, Example 9 shows that Example 9 in which the addition amount of Al was 10% by weight or less was 9%.
%, And the spalling resistance is excellent, but Comparative Example 6 is 11% by weight of the example in which the addition amount of Al exceeds 10% by weight. In this case, the spalling resistance is reduced. ing. This is because the generation of Al-based bonds becomes excessive.

Example 10 shows an example in which Al and Si are added in the form of an alloy, and Example 11 shows an example in which Al alone and an alloy of Al and Si are mixed and added. In both cases, it can be seen that the function is produced without any difficulty in forming the bond. Further, according to Table 3, the amount of added A
There is a difference in the effect of addition when the particle size composition of the l powder and the Si powder is changed within an appropriate range, and when added in the form of a mixture of Al and Si, in the form of an alloy, or in the form of a combination thereof. Absent.

[0028]

[Table 4] Table 4 shows the results of examining the effect of the heat treatment temperature of the refractory on the properties.

The substrate of Example 3 in Table 1 was heat-treated at the temperatures shown in Table 4 for the purpose of comparing the cured state of the refractory.

First, as shown in Comparative Example 7, when the heat treatment temperature is 80 ° C., which is lower than 90 ° C., the strength during handling tends to be insufficient. This is due to insufficient curing of the resin. Also, if the resin bond is exposed to high temperatures during use without development, the corrosion resistance is reduced because the carbon bond cannot be sufficiently formed. When the heat treatment temperature is 90 ° C. or higher, 4
In the case of Examples 14 to 16 in the range up to 00 ° C., the strength and the corrosion resistance during handling are excellent. Further, as shown in Comparative Example 8, when heat treatment was performed at 450 ° C., decomposition of the cured resin progressed, and the porosity increased,
Strength decreases. As a result, the strength at the time of handling is insufficient, and the corrosion resistance is also reduced.

The molding method is not limited to an oil press, but may be a friction press, a rammer press, a C.I. I. It may be appropriately selected from P and the like in consideration of the number, shape and efficiency of the brick.

The molding pressure may be appropriately selected in consideration of the molding efficiency and the quality of the molded product.

[0033]

According to the present invention, high corrosion resistance is maintained not only under relatively low temperature conditions, but also at high temperature and under conditions of contact with the molten material in the furnace. A chromium-free refractory with sufficient spalling resistance and suitable for lining dust and industrial waste melting furnaces is obtained.

Claims (3)

[Claims] 1. The method according to claim 1, wherein the silicon carbide powder contains 10 to 60% by weight of
0.5 to 8% by weight of Si and 1 to 10% of Al
Alumina-silicon carbide refractories obtained by kneading and molding a mixture consisting of weight percent and the remainder mainly composed of alumina powder using a resin. 2. The alumina-silicon carbide refractory according to claim 1, wherein after kneading and molding, heat treatment is performed at 90 to 400 ° C. 3. The method according to claim 1, wherein the use is for lining of a melting furnace for dust and industrial waste.
2. The alumina-silicon carbide refractory described in 1. above.