JP5943032B2 - Manufacturing method of lightweight heat-insulating alumina / magnesia refractory - Google Patents

Description

  The present invention relates to alumina / magnesia refractories that are lightweight and have high heat insulation properties and a method for producing the same for various kilns, and more specifically, imparts high heat insulation properties while maintaining corrosion resistance and slag infiltration resistance. The present invention relates to a lightweight heat-insulating alumina-magnesia refractory that can be produced and a method for producing the same.

  Light-weight heat-insulating refractories are often used to provide heat insulation at sites that do not come into contact with melts such as molten steel. This is because lightweight heat-insulating refractories generally have poor corrosion resistance. By increasing the corrosion resistance of lightweight heat-insulating refractories, it can be used even in contact with melts, making it possible to insulate kilns that could not be insulated so far, and improving the energy efficiency due to the heat insulation effect. I can expect.

  Conventionally, it has been considered effective to use hollow particles having many closed pores in order to maintain the corrosion resistance while reducing the thermal conductivity of the lightweight heat-insulating refractory. Several lightweight heat-resistant refractories to which hollow alumina or the like is added as hollow particles have been proposed. For example, in Patent Document 1, a binder is added to a blended composition composed of 5 to 50% by weight of hollow alumina, and the remainder does not contain pore-forming substances, and is kneaded and molded, and then dried or fired or heated. A method for producing a refractory containing a hollow alumina for a molten metal container lining and a casting nozzle characterized by drying is disclosed. And in patent document 1, it says that low thermal conductivity can be implement | achieved, maintaining corrosion resistance by adding hollow alumina to a refractory.

  In Patent Document 2, basic bricks containing 20% by weight or more of MgO are obtained by adding hollow particles so that the content thereof is 3% by weight or more and 15% by weight or less at the time of brick production. Basic bricks with improved spall resistance are disclosed, and it is also described that alumina hollow particles or zirconia hollow particles having an outer diameter of 0.5 mm or more and 7 mm or less are used as hollow particles.

  A material excellent in corrosion resistance and slag infiltration resistance is alumina / magnesia refractory. Alumina-magnesia refractories improve the slag infiltration resistance by melting out the added magnesia into the slag, and when subjected to heat during use, a spinel formation reaction with expansion occurs and the structure becomes dense. Corrosion resistance is improved. For example, Patent Document 3 discloses a raw material mainly composed of 2 to 15% by mass of magnesia having a particle diameter of 0.3 mm or less, 2 to 15% by mass of hollow alumina particles having a particle diameter of 5 mm or less, and the balance being alumina. There is disclosed a lining casting material characterized in that 0.1 to 2% by mass of amorphous ultrafine silica powder is blended with 100% by mass of a composition comprising: In Patent Document 3, as a result of blending hollow alumina into the alumina / magnesia casting material, the thermal conductivity is lowered, and by making the temperature gradient steep in the casting material, slag infiltration can be significantly suppressed. .

Further, in Patent Document 4, one kind of refractory powder selected from alumina, quartzite, magnesia, gypsum, mullite, kaolin, titanium dioxide, and kibushi clay is blended with a combustible organic substance in zircon, if necessary. Two or more kinds added are foamed in the presence of carbonate, monometallic salt of phosphoric acid and water to form porous condensed particles, and then hollow sphere alumina is added to and mixed with the porous condensed particles, followed by molding. A method for producing a refractory heat-insulating brick, characterized by drying and firing, is disclosed. Patent Document 5 is characterized in that a pore-forming substance, a refractory material, and a quaternary ammonium silicate solution containing 15 to 60% by weight as SiO ₂ are mixed, molded, dried, and further fired. A method for manufacturing a lightweight refractory is disclosed.

Japanese Patent Publication No. 3-39031 JP-A-9-221353 JP 2011-241093 A Japanese Patent Publication No.42-24166 Japanese Patent Publication No.54-6561

However, the corrosion resistance of the refractory using the hollow particles as described above is not always satisfactory. For example, the hollow alumina-containing refractory manufactured in Patent Document 1 has a problem that the corrosion resistance against steelmaking slag is inferior, and there is a problem in using it as a lining refractory in contact with molten slag. This is probably because the bulk specific gravity of the refractory is reduced.
Further, in Patent Document 2, alumina bricks or zirconia hollow particles are blended with basic bricks mainly composed of MgO such as magcro bricks, and corrosion resistance can be imparted to some extent. However, since it is a basic brick, it easily infiltrates slag and has a problem of structural spalling. In addition, with regard to heat insulation, basic bricks originally have a large thermal conductivity, and there is a problem in terms of lowering the thermal conductivity.
Furthermore, although the lining cast material of Patent Document 3 can be expected to improve slag infiltration resistance and decrease thermal conductivity, it has the following problems. That is, the first problem is the dispersibility of the hollow alumina particles. The hollow alumina particles have a remarkably smaller density than the alumina particles used for the aggregate, and it is difficult to uniformly disperse them in the casting material. Since the casting material has fluidity, the hollow alumina particles cannot be sufficiently dispersed even by kneading. In addition, the hollow alumina particles float due to the density difference during curing until hardening, and when the vibration is applied by vibration molding or the like, the hollow alumina particles are more likely to float in the casting material, and the hollow alumina particles are made uniform. It cannot be dispersed and is unevenly distributed, and the corrosion resistance is extremely lowered at the unevenly distributed portion, and the decrease in thermal conductivity is not as specified. A second problem is that the risk of explosion increases. By blending hollow alumina particles and lowering the thermal conductivity, especially on the back side, the amount of heat is not sufficiently transferred during drying, moisture tends to remain and easily explode, and the temperature inside the material being heated Since the gradient becomes larger, it becomes easier to explode. Further, the construction of the casting material requires a lot of mechanical equipment such as a mixer, a metal frame, and a vibration device, and the installation cost thereof becomes enormous, which causes a problem that applicable kilns are limited.
From these problems, it can be said that the fixed refractory as disclosed in Patent Documents 4 and 5 is more desirable than the casting material disclosed in Patent Document 3. However, conventional fixed refractories have problems such as inferior corrosion resistance, and a solution to the problem has been demanded.

  Accordingly, it is an object of the present invention to provide a lightweight heat-insulating alumina / magnesia refractory that is excellent in slag infiltration resistance and has low thermal conductivity while ensuring corrosion resistance, and a method for producing the same.

In order to ensure the corrosion resistance of lightweight heat-resistant refractories, it is important to make the matrix denser, but since heat insulation is ensured with hollow particles, if the hollow particles break, heat insulation can not be obtained . Therefore, in Patent Document 1, molding pressures of about 1 ton / cm ² and 0.35 ton / cm ² are used as the molding pressure at which the hollow particles are not damaged. These molding pressures are the usual fixed refractories. The molding pressure is lower than the above, and a dense matrix structure cannot be obtained. In Patent Document 4, 40~100kg / cm ^2, Patent Document 5, a molding pressure of 500 kg / cm ² is used. Thus, as a prior art, in order to prevent the collapse | disintegration during shaping | molding of a hollow alumina, it has become desirable to shape | mold at a low forming pressure. Therefore, corrosion resistance will fall.
In order to obtain high corrosion resistance against molten metal and molten slag, it is necessary to use a dense refractory. In order to make it dense, the molding pressure at the time of refractory production may be increased. However, when the molding pressure is increased, there is a problem that the hollow particles are easily broken.
Accordingly, the present inventors have variously made it possible to secure a molding pressure that can provide sufficient corrosion resistance without destroying the hollow alumina during molding of the lightweight heat-insulating alumina / magnesia refractory containing hollow alumina. As a result of the study, the present invention has been completed.

That is, the present invention uses an alumina raw material and a magnesia raw material, 2-50% by mass of hollow alumina, 20-93.5% by mass of alumina material other than hollow alumina, 4-20% by mass of magnesia material, A raw material blend obtained by blending solid sodium silicate in an amount of 0.5 to 6% by mass is molded into a predetermined shape at a molding pressure of 1.2 to 3.0 ton / cm ² and then heated to 1150 ° C. or lower. An object of the present invention is to provide a method for producing a lightweight heat-insulating alumina / magnesia refractory.

  Moreover, the manufacturing method of the lightweight heat insulation alumina magnesia refractory of this invention is 4 mass% of 1 type, or 2 or more types selected from the group which consists of quartz sand powder, quartzite powder, rholite powder, silica flour, and refractory clay. It is blended in the following amount (excluding zero).

  Furthermore, the manufacturing method of the lightweight heat insulation alumina magnesia refractory of this invention mix | blends the organic binder and / or other inorganic binders except sodium silicate in the quantity of 4 mass% or less (excluding zero) by outer coating. It is characterized by.

Further, the present invention provides a lightweight insulation alumina magnesia refractories produced by the above production _method, Al ₂ O 3 from 65 to 94.7 wt%, MgO4～20 wt%, _SiO 2 1 to 5 wt% A lightweight heat-insulating alumina / magnesia refractory characterized by having a chemical composition of 0.3 to ₂ % by mass of Na ₂ O and K ₂ O and 8% by mass or less (including zero) of other components There is to do.

  According to the present invention, it is possible to obtain a lightweight heat-insulating alumina / magnesia refractory that is excellent in slag infiltration resistance and can have low thermal conductivity while ensuring corrosion resistance.

  In the lightweight heat-insulating alumina / magnesia refractory of the present invention, in order to obtain a dense refractory without destroying the hollow alumina, sodium silicate is blended to promote slipping of the particle surface of the hollow alumina to achieve higher molding. It enables molding under pressure. The lightweight heat-insulating alumina / magnesia refractory of the present invention will be described in detail below.

  The lightweight heat-insulating alumina / magnesia refractory of the present invention can be composed of raw materials such as hollow alumina, alumina raw materials other than hollow alumina, magnesia raw materials, sodium silicate and the like.

  Here, a hollow alumina is not specifically limited, For example, the commercial item obtained by the electromelting method etc. can be used. The amount of hollow alumina is 2 to 50% by mass, preferably 5 to 40% by mass. By blending hollow alumina in an amount within the above range, the thermal conductivity of the lightweight heat-insulating alumina / magnesia refractory can be reduced, and the heat insulation of the kiln constructed using the refractory is improved. Can contribute to energy saving. In addition, it is possible to increase the temperature gradient in the lightweight heat-insulating alumina / magnesia refractory in use, thereby further improving the slag infiltration resistance of the alumina / magnesia refractory having excellent slag infiltration resistance. . Here, if the amount of hollow alumina is less than 2% by mass, the effect of lowering the thermal conductivity is not sufficient, and if it exceeds 50% by mass, the corrosion resistance decreases, which is not preferable.

  Next, the alumina raw material other than hollow alumina is not particularly limited. For example, in addition to commercially available fused alumina and sintered alumina such as white fused alumina and brown fused alumina, calcined bauxite. Various alumina-based raw materials such as natural alumina such as calcined bang shale shale can be used. The amount of the alumina raw material other than hollow alumina is 20 to 93.5% by mass, preferably 36 to 88.2% by mass. Here, if the blending amount of the alumina raw material other than the hollow alumina is less than 20% by mass, it is not preferable because the corrosion resistance is poor, and if it exceeds 93.5% by mass, an appropriate expansion characteristic may not be obtained. This is not preferable because the expansion at the initial stage of the spinel formation reaction cannot be absorbed.

  In the lightweight heat-insulating alumina / magnesia refractory of the present invention, the total amount of the hollow alumina and the alumina raw material other than the hollow alumina is 70 to 95.5% by mass, preferably 76 to 93.2% by mass. Is within the range. Here, if the total amount is less than 70% by mass, the corrosion resistance is inferior, which is not preferable. If it exceeds 95.5% by mass, an appropriate expansion characteristic cannot be obtained, or expansion at the initial stage of the spinel formation reaction is not achieved. It is not preferable because it cannot be absorbed.

  Also, the magnesia material is not particularly limited, and for example, materials mainly composed of magnesia such as natural magnesia, sintered magnesia, and electrofused magnesia can be used. The particle size of the magnesia raw material is also not particularly limited, and can be used in any form of coarse particles, medium particles and fine powders. However, if the particle size of the magnesia raw material is coarse particles or medium particles, the refractory Is excessively expanded due to the spinel formation reaction when heated to 1200 ° C. or higher. However, if it is a fine powder, the expansibility and its control are easy, the magnesia raw material is preferably a fine powder, and it is particularly preferred to use 90% by mass or more of a fine powder having a particle size of 0.5 mm or less.

  Solid sodium silicate is used for the lightweight heat-insulating alumina / magnesia refractory of the present invention. Sodium silicate is relatively weak in strength. By adding sodium silicate, sodium silicate is destroyed prior to hollow alumina, alumina material, magnesia material, etc. during compression molding, and fine particles of sodium silicate are being molded. In order to disperse and equalize the pressure applied to the hollow alumina, it is considered that the sliding of the surface of the hollow alumina particles is promoted to enable molding at a relatively high molding pressure. As a result, the lightweight heat-insulating alumina / magnesia refractory can be densified and can have high corrosion resistance against molten metal and molten slag. The compounding quantity of sodium silicate is 0.5-6 mass%, Preferably it exists in the range of 0.8-5 mass%. Here, when the amount of sodium silicate is less than 0.5% by mass, it is not preferable because the destruction of the hollow alumina during molding cannot be prevented, and when it exceeds 6% by mass, the corrosion resistance decreases. Therefore, it is not preferable.

The lightweight heat-insulating alumina / magnesia refractory of the present invention can be blended with an organic binder or other inorganic binder other than sodium silicate. As the organic binder, for example, various binders such as pitch, phenol resin, molasses, pulp waste liquid, dextrin, methylcelluloses, and polyvinyl alcohol can be used. There is no problem as long as C (carbon) remaining after these organic binders are heated is within the range of the other components of the chemical components constituting the lightweight heat-insulating alumina / magnesia refractory described later.
Various inorganic binders other than sodium silicate can be used. For example, potassium silicate, bitter juice (MgCl ₂ ), sodium aluminate and the like can be used. As other inorganic binders, those composed of the same chemical components as those constituting the lightweight heat-insulating alumina / magnesia refractory described later are desirable because they do not increase other components described later.
When the organic binder or other inorganic binders other than sodium silicate are blended, the blending amount is 4% by mass or less (excluding zero), preferably 3% by mass or less (not including zero) by outer coating. It is. If the blending amount exceeds 4% by mass, the corrosion resistance is lowered, which is not preferable.

  The lightweight heat-insulating alumina / magnesia refractory of the present invention may contain silica sand, quartzite and rhostone powder, silica flour, refractory clay and the like. The amount of these raw materials is 4% by mass or less (excluding zero), preferably 3% by mass or less (excluding zero). Here, if the blending amount of these raw materials exceeds 4% by mass, the corrosion resistance is lowered, which is not preferable.

  Furthermore, metal powders such as metal silicon, metal aluminum, metal magnesium, aluminum-magnesium alloy, and iron powder can be used as lightweight heat-insulating alumina / magnesia refractories as long as the effects of the present invention are not impaired.

  When manufacturing the lightweight heat-insulating alumina / magnesia refractory according to the present invention, the raw material compounded so as to have the above-mentioned raw material compounding amount is batched or divided, and water is added and mixed as necessary. Mix and knead with a machine or kneader. For kneading, roller-type SWP, Simpson mixer, blade-type high-speed mixer, pressurized high-speed mixer, Henschel mixer, pressure kneader kneading machine as container fixed type; roller-type MKP as container-driven type Alternatively, a kneader such as a wet pan, a Conner mixer, a blade-type Eirich mixer, or a vortex mixer can be used. Moreover, pressurization or pressure reduction, a temperature control device, etc. (heating, cooling, or heat retention) can also be installed in these kneaders and mixers. Needless to say, the mixing or kneading time can be appropriately selected depending on the type of raw material, the blending amount, the type of binder, the temperature (room temperature, raw material or binder), the type or size of the mixer or kneader.

  The kneaded material obtained as described above can be formed by a hydraulic press, a toggle press, or the like, such as a friction press, a screw press or a hydro screw press, which is an impact pressure press. In addition, it can be molded by a molding machine called CIP. These molding machines can be provided with a vacuum deaeration device, a temperature control device (heating, cooling or heat retention) and the like.

The molding pressure by the molding machine as described above can be molded within a range of 1.2 to 3.0 ton / cm ² , more preferably 1.5 to 3.0 ton / cm ² . If the molding pressure is 1.2 ton / cm ² or more, a denser refractory than castable can be obtained. A molding pressure of less than 1.2 ton / cm ² is preferable because a sufficiently dense molded body cannot be obtained. When the molding pressure is higher than 3.0 ton / cm ² , hollow alumina particles are formed. Since it may be destroyed, it is not preferable.

  Note that the number of times of tightening by the molding machine is appropriately selected in consideration of the size of the refractory to be molded, the type of raw material, the blending amount, the type of binder, the temperature (room temperature, raw material and binder), the type and scale of the molding machine, etc. It goes without saying that you can do it.

  In producing the lightweight heat-insulating alumina / magnesia refractory of the present invention, a spinel formation reaction takes place, so that it should not be heated to a temperature exceeding 1150 ° C. In the case of heating at about 500 ° C or less, a hot air circulation type drying heating furnace can be used, and when heating at a temperature higher than that is required, batches such as electric heating type, gas heating type, oil heating type, etc. If it is a continuous type, such as a single kiln, such as a shuttle kiln or a carbell kiln, a tunnel kiln is optimal. Of course, any type of heating furnace can be used as long as the temperature is sufficiently adjustable and uniform heating is possible.

The lightweight heat-insulating alumina / magnesia refractory of the present invention produced as described above is made of Al ₂ O ₃ 65-94.7 mass%, MgO 4-20 mass%, SiO ₂ 1-5 mass%, Na ₂ O + K. ₂ O has a chemical composition of 0.3 to ₂ % by mass and other components of 8% by mass or less (including zero).

Al ₂ O ₃ is in the range of 65 to 94.7% by mass, preferably 73.5 to 93.2% by mass. If Al ₂ O ₃ is less than 65% by mass, the corrosion resistance is poor, which is not preferable. On the other hand, if Al ₂ O ₃ exceeds 94.7% by mass, an appropriate expansion characteristic cannot be obtained, and expansion at the initial stage of the spinel formation reaction cannot be absorbed.

  MgO is in the range of 4 to 20% by mass, preferably 5 to 16% by mass. In the lightweight heat-insulating alumina / magnesia refractory, the presence of MgO can impart expansion behavior to the refractory. If MgO is less than 4% by mass, the expansion characteristics cannot be sufficiently obtained, and the effect of improving the corrosion resistance accompanying densification is insufficient, which is not preferable. Moreover, when MgO exceeds 20 mass%, expansion | swelling will become large too much and a spalling resistance will fall, or the particle | grains of a hollow alumina may be crushed depending on the case, and the suppression effect of thermal conductivity cannot be acquired. This is not preferable.

SiO ₂ is in the range of 1 to 5 mass%. In addition to inorganic binders such as sodium silicate and potassium silicate, SiO ₂ is derived from silica sand, quartzite, rholite powder, silica flour, refractory clay, and the like. Some are derived from alumina materials and magnesia materials. In order to densify the structure having the effect of improving the corrosion resistance of the lightweight heat-insulating alumina / magnesia refractory, it is important to develop stress relaxation properties at high temperatures together with the above-mentioned expansion characteristics. Therefore, by forming a liquid phase in the lightweight heat-insulating alumina / magnesia refractory at a high temperature, the light-weight heat-insulating alumina / magnesia refractory has a deformable function. By combining SiO ₂ with Na ₂ O and K ₂ O, which will be described later, it is possible to impart stress relaxation properties that match the expansion behavior. Here, it is not preferable that SiO ₂ is less than 1% by mass because sufficient stress relaxation cannot be obtained. On the other hand, if SiO ₂ exceeds 5% by mass, the corrosion resistance is lowered, which is not preferable. Due to the balance between creep characteristics and corrosion resistance, SiO ₂ is preferably in the range of 1.5 to 4% by mass.

The total amount of Na ₂ O and K ₂ O is 0.3-2% by mass, preferably 0.3-1.5% by mass. Na ₂ O and K ₂ O are derived from inorganic binders such as sodium silicate and potassium silicate. Na ₂ O and K ₂ O are for reducing the melting point of SiO ₂ and exhibiting the expansion and absorption ability from a lower temperature. If the total amount of Na ₂ O and K ₂ O is less than 0.3% by mass, the melting point of SiO ₂ cannot be lowered sufficiently and the expansion at the initial stage of the spinel formation reaction cannot be absorbed, which is not preferable. . Further, if the total amount of Na ₂ O and K ₂ O exceeds 2% by mass, it is not preferable because it causes a decrease in corrosion resistance like SiO ₂ .

  In addition, the lightweight heat-insulating alumina / magnesia refractory of the present invention can accept other components up to an amount of 8% by mass or less (including zero), preferably 5% by mass or less (including zero). Other components include inevitable impurities derived from the above raw materials, C derived from organic binders, and the like.

Hereinafter, the lightweight heat-insulating alumina / magnesia refractory of the present invention will be further described by way of examples.
Using the friction press, the kneaded material obtained by blending various raw materials at the blending ratios described in Table 1 (Product of the present invention) and Table 2 (Comparative product), and adding water as necessary, 2 to 230 mm × 150 mm × 80 mm.
In addition, the comparative product 12 in Table 2 is a casting material corresponding to Patent Document 3, and by adding 8.5% by mass of water as an outer shell to the raw material mixture and casting into a mold, it is 230 mm × A sample of 150 mm × 80 mm was used.
All the samples obtained as described above were dried at 200 ° C. for 24 hours.

In the table above,
Electrofused magnesia contains 95% by mass of fine powder having a particle size of 0.5 mm or less;
Seawater magnesia clinker is 100% by mass of fine powder having a particle size of 0.5 mm or less;
Sodium silicate is a powder composed of SiO ₂ : 53% by mass, Na ₂ O: 25% by mass and the balance is crystal water, and potassium silicate is SiO ₂ : 28% by mass, K ₂ O: 22% by mass, An aqueous solution whose balance is composed of water;
Alumina cement is composed of CaO: 17% by mass of CaO.Al ₂ O ₃ (CA) mineral and corundum;
The phenolic resin is a novolac type phenolic resin solution having a resin content of 60% by mass;
The chemical component is the result of measurement by fluorescent X-ray analysis according to JIS R 2216;
The porosity is a result measured by the method defined in JIS R 2205. The higher the porosity, the better the heat insulation, but the lower the corrosion resistance;
The thermal conductivity at 1000 ° C. is the result of measurement using a 114 mm × 114 mm × 65 mm sample by the hot wire method of JIS R 2251-1, and there is no problem if it is approximately 4.0 W / mK or less. More preferably, it is 0.0 W / mK or less;
The residual expansion rate after firing at 1500 ° C. was determined by heating the sample of 115 mm × 35 mm × 35 mm at 5 ° C./min in a box-type electric furnace and holding it for 3 hours after reaching 1500 ° C. The residual expansion coefficient was calculated from the dimensional change before and after firing in the direction. If the residual expansion rate is too small or too large, there is a problem, and the appropriate value is in the range of 1 to 3%;
The coefficient of expansion under a load of 1500 ° C. is 1500 ° C. when a sample for hot creep measurement (φ50 mm × 50 mm) is prepared and the temperature is increased (5 ° C./min) under a load of 0.2 MPa according to JIS R 2658. The amount of expansion was measured when the value reached. It is essential that the amount of expansion be negative, and it is more preferable that the amount of expansion exceeds -1% because the degree of freedom of expansion absorption increases.
As the corrosion resistance test, a rotary drum erosion test by oxygen-propane heating was performed. A synthetic slag containing 34% by mass of SiO ₂ , 15% by mass of Fe ₂ O ₃ , 12% by mass of Al ₂ O ₃ and 30% by mass of CaO as an erodant was used at 1600 ° C. for 5 hours. The erodant was replaced every hour. The sample after the test was cut in the center in the longitudinal direction, and the amount of erosion and the amount of infiltration were measured. When the amount of erosion increases, the remaining dimension becomes thin and the heat insulation effect is canceled. If the erosion index generally exceeds 120, the heat insulation effect is canceled, which is not preferable.

  The inventive products 1 to 18 are based on the composition of the comparative product 1 and examined the requirements of the present invention. The inventive products 1 to 18 are all low thermal conductivity, appropriate residual expansion coefficient, appropriate It had an expansion coefficient under a load of 1500 ° C., high corrosion resistance, and high slag resistance.

Since the comparative product 1 does not contain hollow alumina, the thermal conductivity exceeds 4.0 W / mK and there is no heat insulation.
Comparative product 2 was prepared by blending 1% by mass of hollow alumina, and a sufficient amount of heat insulation was not obtained (compounding, chemical composition: mass%) with a small amount of blending.
Comparative product 3 was obtained by blending 60% by mass of hollow alumina, and the amount of erosion increased rapidly, resulting in a problem in corrosion resistance.
In Comparative Example 4, the MgO content was 3.0% by mass, the residual expansion was not sufficiently obtained, and the effect of densifying the structure was not sufficiently obtained. Therefore, there was a problem with corrosion resistance due to the large amount of erosion.
Comparative product 5 had a MgO content of 23% by mass and improved corrosion resistance, but the residual expansion was large and the expansion under load was almost zero. Further, it was not preferable because the cracking easily occurred when the expansion coefficient under load was positive.
The comparative product 6 does not contain sodium silicate and potassium silicate, the Na ₂ O + K ₂ O content is 0.2% by mass derived from raw materials other than sodium silicate and potassium silicate, and SiO ₂ The content was small and the expansion coefficient under load was positive. In this case, too, cracking in the actual machine was likely to occur, which was not preferable. In the erosion test, cracks due to the inability to absorb expansion occurred in the specimen, and slag infiltrated there, leading to an increase in the amount of infiltration.
The comparative product 7 was a case where the SiO ₂ content was as high as 5.4% by mass, and the amount of erosion increased and a problem was observed in terms of corrosion resistance.
Comparative product 8 does not contain sodium silicate and potassium silicate, and the content of Na ₂ O + K ₂ O is 0.2% by mass derived from raw materials other than sodium silicate and potassium silicate. Particle breakage was observed. Therefore, there was a problem in heat insulation with high thermal conductivity. Further, since the Na ₂ O + K ₂ O content is small, the expansion coefficient under load is also positive, and it is not preferable because the actual machine tends to crack easily.
Comparative product 9 had a large Na ₂ O + K ₂ O content of 2.1% by mass, and a significant reduction in corrosion resistance was observed.
Comparative product 10 was a case where the molding pressure was 0.8 ton / cm ² , but the molding pressure was low, and a dense structure was not obtained. Therefore, although the thermal conductivity is low, the amount of erosion is large and there is a problem in the corrosion resistance.
Comparative product 11 was a case where the molding pressure was 3.5 ton / cm ² , but the molding pressure was too high, and the hollow alumina was broken during molding, resulting in high thermal conductivity.
Although the comparative product 12 is a cast construction product, there was a problem in corrosion resistance because a dense structure was not obtained.

Claims (3)

Using alumina raw material and magnesia raw material, 2-50 mass% of hollow alumina, 20-93.5 mass% of alumina raw material other than hollow alumina, 4-20 mass% of magnesia raw material, 0 of solid sodium silicate A raw material blend formed by blending in an amount of 5-6 mass% is molded into a predetermined shape at a molding pressure of 1.2-3.0 ton / cm ² and then heated to 1150 ° C. or lower. Manufacturing method for lightweight heat-insulating alumina / magnesia refractories.   2. One or more selected from the group consisting of silica sand powder, silica powder, rholite powder, silica flour and refractory clay are blended in an amount of 4% by mass or less (excluding zero). The manufacturing method of the lightweight heat insulation alumina magnesia refractory of description. The lightweight heat-insulating alumina / magnesia according to claim 1 or 2, comprising an organic binder and / or other inorganic binder excluding solid sodium silicate in an amount of 4% by mass or less (excluding zero). Refractory manufacturing method.