JP2016037429A - Monolithic refractory for molten aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a monolithic refractory for molten Al alloy excellent in flowability, flexure strength, thermal spalling resistance and infiltration resistance to the molten Al alloy and having higher durability than that of conventional refractory.SOLUTION: A monolithic refractory contains a main raw material and a CaFraw material added to the main raw material. The main raw material consists of SiC raw material of 60 to 98 mass%, a hardening agent of 1 to 15 mass%, an amorphous SiOsuperfine powder of 1 to 8 mass% one or more kinds selected from AlO, CaO, ZrOand MgO which are added to a status with total sum of 100 mass% in the case where the total sum of each component is less than 100 mass%. The CaFraw material is added to the main raw material within a range satisfying ratio between an outer mass% value A of the CaFraw material and a mass% value B of the amorphous SiOsuperfine powder of 0.2≤(A/B)≤2.SELECTED DRAWING: None

Description

  The present invention relates to an amorphous refractory used in melting furnaces, holding furnaces, grooved induction furnaces and the like for molten aluminum alloys, and in particular, melting excellent in various properties such as corrosion resistance, penetration resistance, and spalling resistance. The present invention relates to an amorphous refractory for an aluminum alloy.

In melting furnaces and holding furnaces for aluminum alloys (hereinafter referred to as Al alloys), it is very important to select a refractory that comes into contact with the molten metal (in this case, molten Al alloy). For example, when an alumina / silica refractory is employed as the refractory, it is known that the molten Al alloy undergoes a reduction reaction represented by the formula (1) with the SiO ₂ component in the refractory.

2Al (l) + 3 / 2SiO ₂ (s) = Al ₂ O ₃ (s) + 3 / 2Si (l) (1)

Due to this reaction, there is a problem that Al ₂ O ₃ is generated and a deteriorated layer is formed at the interface between the molten metal and the refractory, thereby closing the inside of the furnace.

From the viewpoint of suppressing such a reduction reaction, Patent Document 1 discloses a refractory material for melting Al-Li alloy and a lining obtained by adding 5 to 20% calcium aluminate as a sintering agent to a high-purity refractory containing no silicic acid. A material (crucible) is disclosed. Patent Document 2 discloses a refractory material for melting an Al-Li alloy composed of carbon 30 to 50% by weight, SiC raw material 10 to 35% by weight, Al ₂ O ₃ 5 to 30% by weight, a binder and inevitable impurities. (Crucible) is disclosed.

  On the other hand, burner heating, heating with an electric heating element, grooved induction heating, and the like have been developed as heating methods for melting furnaces and holding furnaces in non-ferrous metal production facilities. Among these, the refractory used for the groove type induction heating is installed on the side wall and the lower part of the melting furnace and the holding furnace, and its shape becomes complicated. Therefore, construction is difficult with the crucibles and bricks disclosed in Patent Documents 1 and 2 and the like. Therefore, amorphous refractories such as ramming materials and dense castables are widely used as materials to replace bricks (see, for example, Patent Documents 3-5).

For example, Patent Document 3 discloses an amorphous refractory for an Al-Li alloy melting and refining furnace in which silicon nitride is blended with an alumina refractory material containing 85% by weight or more of Al ₂ O ₃ minutes. Patent Document 4 discloses that one or more kinds selected from among a poorly soluble phosphate, frit, and boron carbide are added to 100 parts by weight of a high-alumina low cement castable containing 80% by weight or more of Al ₂ O _3. Disclosed is a refractory for an Al alloy melting furnace containing a total of 0.5 to 3 parts by weight of the product. Furthermore, Patent Document 5 adds 0.5 to 5 wt% of a fluorinated compound together with ultrafine powder and a dispersant to a low cement castable made of conventional bauxite or high-purity alumina as an aggregate, thereby improving the fluidity and curability of the kneaded product. An improved amorphous refractory is disclosed.

  Further, in the refractory for molten Al alloy, the infiltration of the Al alloy into the refractory is another problem. When the Al alloy infiltrates into the refractory, structural spalling occurs and damage proceeds. Therefore, it becomes important to suppress the infiltration of the Al alloy into the refractory. Among Al alloys, it is known that, in particular, Al—Li alloys and Al—Zn alloys easily infiltrate into refractories.

  As a countermeasure, Patent Document 6 discloses a cast refractory for aluminum and aluminum alloy in which a fluorine compound is contained in an amount of 0.01 to 30% by weight in the refractory. In this technology, the reason why the addition of fluoride prevents the penetration of Al alloy is obtained is that the fluorine compound present in the refractory reacts with the oxide, etc. suspended or suspended in the molten Al. As a result of the formation of coatings, grains, etc. on the surface of the refractory and increasing the surface tension of the molten Al, the wettability of the molten Al can be reduced.

JP-A-1-268826 JP-A-4-285065 JP-A-4-325457 JP 11-199334 A JP-A-3-177365 JP 2002-274959 A

  However, in the technology disclosed in Patent Documents 3-5, since the content of alumina is large, the coefficient of thermal expansion becomes large, and performance that can sufficiently satisfy the heat-resistant spalling property is not obtained. In addition, the technique disclosed in Patent Document 6 is not sufficient in terms of the effect of suppressing cracks, and the heat spalling property has not yet been sufficient.

Therefore, at present, when an alumina refractory is adopted as a refractory for a molten Al alloy, a high alumina refractory having an Al ₂ O ₃ content of 70 to 90% by weight is generally used. However, drastic improvement has not been achieved, and its durability has not been sufficient.

  In addition, in the groove type induction furnace, the refractory is used at a higher temperature than the melting furnace and the holding furnace body, and is also affected by the flow of the molten Al. Therefore, in the groove type induction furnace, measures against blockage and cracks in the groove portion are particularly required.

  The present invention has been proposed in view of such conventional circumstances, and has excellent spalling resistance even when applied to a melting furnace of an Al-Zn alloy that easily infiltrates refractories. An object of the present invention is to provide an amorphous refractory for a molten aluminum alloy, which can obtain reaction resistance (deterioration is hardly caused by reduction with an Al alloy).

  Non-oxides such as SiC (silicon carbide) and graphite are known as materials that do not easily react with molten Al. However, these materials have problems in workability and stability in an oxidizing atmosphere. In particular, amorphous refractories containing SiC as the main component are not well-suited with water, and the porosity of the construction body structure and the decrease in strength are conspicuous with an increase in the amount of construction water, and are hardly put into practical use. It was. Further, as described above, countermeasures against infiltration of molten Al are required for molten Al alloy refractories, but no countermeasure method for infiltration suppression is known for refractories mainly composed of SiC.

The inventors of the present application have made extensive studies on improvement of fluidity and suppression of infiltration in order to exhibit the excellent characteristics of SiC as an amorphous refractory composition for molten Al alloys. Amorphous SiO ₂ ultrafine powder and CaF _The present inventors have found that it is sufficient to utilize ₂ and have completed the present invention.

SiC is characterized by high thermal conductivity, high hardness, and excellent wear resistance, and is characterized by high heat spalling resistance due to a small coefficient of thermal expansion, and excellent corrosion resistance against non-ferrous molten metal. However, when used as the main raw material for the amorphous refractory as described above, the familiarity with water was poor, and the increase in the porosity and strength of the construction body structure accompanying the increase in the amount of construction water was remarkable. On the other hand, it has been found that by utilizing a specific amount of amorphous SiO ₂ ultrafine powder, the amount of water necessary for pouring construction is reduced, and a dense and high strength construction body is obtained. It has also been found that if alumina cement is used as a curing agent for the irregular refractory of the present invention, a construction body having excellent workability and high strength can be obtained.

On the other hand, amorphous SiO ₂ ultrafine powder has a drawback that it is reduced by molten Al alloy and becomes metal Si and dissolves into the Al alloy. In addition, this reaction also causes a problem that Al ₂ O ₃ precipitates in the molten Al alloy and becomes a plug.

As a countermeasure, the inventors of the present application added a CaF ₂ (calcium fluoride) combined with an amorphous SiO ₂ ultrafine powder in a specific ratio in an amorphous refractory mainly composed of SiC, thereby obtaining a molten Al alloy. It has been found that the reduction of the SiO ₂ ultrafine powder due to can be significantly suppressed. In the analysis by the inventors of the present application, a film made of Al ₂ O ₃ , SiO ₂ , and CaO was formed on the boundary surface between the molten Al and the refractory by adding CaF ₂ at a specific ratio. It is considered that the infiltration of the Al melt was suppressed by the film. Since the formation of the melt cannot be confirmed, SiO ₂ and CaO are transported to the Al melt interface via the gas phase, and a part of SiO ₂ is reduced by Al, whereby the above-described film is generated. it is conceivable that.

  In addition, in Patent Document 6, the effect of preventing the penetration of molten Al alloy by adding fluoride is oxidized by reacting a fluorine compound present in the refractory with an oxide or the like suspended or suspended in the molten Al. It is said that the wettability of the Al molten metal can be weakened as a result of the fact that the coating film, grains, etc. of the object are generated on the surface of the refractory and the surface tension of the Al molten metal is increased. There wasn't. That is, it is considered that the effect of the present invention is obtained by at least a mechanism different from the technique disclosed in Patent Document 6.

The inventors of the present application have arrived at the present invention based on the new findings obtained as described above. First, the present invention is premised on an amorphous refractory for a molten aluminum alloy containing a refractory raw material and a curing agent. Then, molten aluminum alloy for monolithic refractories according to the present invention comprises a CaF ₂ material added to the main raw material and the main raw material. The main raw material is 60 to 98% by mass of SiC raw material, 1 to 15% by mass of curing agent, 1 to 8% by mass of amorphous SiO ₂ ultrafine powder, and the total is 100 when the total of the above components is less than 100% by mass. It is added to a state at which the _{mass%, Al 2 O 3, CaO} , consisting of one or more refractory materials selected from ZrO 2, MgO. The CaF ₂ raw material has a ratio (A / B) between the outer mass% value A of the CaF ₂ raw material and the mass% value B of the amorphous SiO ₂ ultrafine powder of 0.2 ≦ (A / B) ≦ 2. Is added to the main raw material within a range satisfying the above. Alumina cement can be used as the curing agent.

  According to the amorphous refractory of the present invention, not only the spalling resistance and the reaction resistance to the molten Al alloy are greatly improved, but also the heat resistant spalling resistance is improved. Moreover, since the fluidity | liquidity at the time of construction is fully securable, since the intensity | strength after 800 degreeC baking is also enough, there is no problem on construction. Therefore, if the amorphous refractory according to the present invention is applied to, for example, a grooved induction furnace for a molten Al alloy, the occurrence of cracks is reduced, and there is no Al blockage in the groove, thereby increasing the total life of the refractory. It can be greatly improved.

The amorphous refractory for molten aluminum alloy (hereinafter referred to as molten aluminum alloy) in the present invention includes a main raw material and a CaF ₂ raw material (calcium fluoride raw material) added to the main raw material.

The main raw material is added to a SiC raw material (silicon carbide raw material), a curing agent, amorphous SiO ₂ ultrafine powder, and a state where the total is 100% by mass when the total of these components is less than 100% by mass. And one or more refractory raw materials selected from Al ₂ O ₃ , CaO, ZrO ₂ , and MgO.

The addition amount of the SiC raw material is 60 to 98 mass% (60 mass% or more and 98 mass% or less). More preferably, it is 75-96 mass% (75 mass% or more and 96 mass% or less). When the addition amount of the SiC raw material is less than 60% by mass, the high thermal conductivity, the low thermal expansion coefficient and the low elastic modulus of the SiC raw material are not exhibited, and the heat resistance spalling property is lowered, which is not preferable. Further, if the added amount of SiC raw material exceeds 98 mass%, it reduces the amount of amorphous SiO ₂ ultrafine and curing agent which is an essential raw material, the function of amorphous SiO ₂ ultrafine and curing agent Since it is not exhibited, it is not preferable. In this invention, a SiC raw material has a role which improves heat-resistant spalling property as a main aggregate.

As the SiC raw material, SiC produced by a so-called Atchison method in which a mixture of SiO ₂ and carbon is reacted at an ultrahigh temperature to form SiC can be used. It is also possible to use SiC synthesized by reacting metal Si and C (carbon) at a high temperature.

  The purity of the SiC raw material is preferably 85% by mass or more, more preferably 90% by mass or more. When the purity of the SiC raw material is less than 85% by mass, the workability is lowered due to the influence of impurities such as carbon and metal Si, and the strength of the construction body is lowered.

  The particle size of the SiC raw material is not particularly limited. A particle size blend generally used as an amorphous refractory (a casting material) can be used. For example, the maximum particle size is 6 mm, the particle size is 1 mm or more is 40 to 55 mass% (40 mass% or more and 55 mass% or less), and the particle size is 0.1 to 1 mm (0.1 mm or more and less than 1 mm) is 10 to 30. If mass% (10 mass% or more and 30 mass% or less), particle size less than 0.1 mm is 15-50 mass% (15 mass% or more and 50 mass% or less), etc., and the total amount is 100 mass% Good.

The addition amount of the curing agent is 1 to 15% by mass (1 to 15% by mass). More preferably, it is 2-10 mass% (2 mass% or more and 10 mass% or less). When the addition amount of the curing agent is less than 1% by mass, the strength of the construction body is not sufficiently obtained, and a film made of Al ₂ O ₃ , SiO ₂ , CaO at the Al molten metal interface is not stably formed. Absent. Moreover, when the addition amount of a hardening | curing agent exceeds 15 mass%, since an intensity | strength will not improve according to an addition amount and fluidity | liquidity will fall, it is unpreferable.

  As the curing agent, known cement, hydraulic alumina, phosphate, silicate, silica sol, resin and the like can be used. It is particularly preferable to use an alumina cement that can easily control the hardening behavior in casting. As the alumina cement, a high-purity high-alumina cement having a calcia content of less than 30% by mass and mainly composed of calcium aluminate and corundum is particularly preferable.

The addition amount of the amorphous SiO ₂ ultrafine powder is 1 to 8% by mass (1 to 8% by mass). More preferably, it is 2-6 mass% (2 mass% or more and 6 mass% or less). When the amount of amorphous SiO ₂ ultrafine powder added is less than 1% by mass, the amount of amorphous SiO ₂ ultrafine powder is insufficient with respect to the voids in the material, and as a result, a dense and high-strength construction body cannot be obtained. Therefore, it is not preferable. Furthermore, a stable film made of Al ₂ O ₃ , SiO ₂ , and CaO at the Al molten metal interface is not formed, which is not preferable. Also, if the amount of the amorphous SiO ₂ ultrafine powder exceeds 8 wt%, amorphous SiO ₂ ultrafine amount is excessive, undesirable because fluidity during construction is reduced (viscosity increase). In the present invention, the amorphous SiO ₂ ultrafine powder has a role of reducing the kneading moisture of the casting material to form a dense and high-strength construction body.

As the amorphous SiO ₂ ultrafine powder, what is generally called silica flour or silica fume can be used. Both are SiO ₂ fumes generated via the gas phase, and are generated as by-products when the metal Si is dissolved or when zirconia is produced by reducing zircon. The primary particle size is submicron particles. Further, the purity of the amorphous SiO ₂ ultrafine powder is preferably 90% or more of SiO _{2 and} may contain some zircon or zirconia.

In the CaF ₂ raw material, the ratio (A / B) between the outer mass% value A of the CaF ₂ raw material and the mass% value B of the amorphous SiO ₂ ultrafine powder satisfies 0.2 ≦ (A / B) ≦ 2. It is added to the main raw material within the range of More preferably, 0.3 ≦ (A / B) ≦ 1.5. When (A / B) is less than 0.2, a film composed of Al ₂ O ₃ , SiO ₂ , and CaO at the Al molten metal interface is not sufficiently formed, which is not preferable. Also, when (A / B) exceeds ₂ , a film made of Al ₂ O ₃ , SiO ₂ , and CaO at the Al molten metal interface is not sufficiently formed and the fluidity is lowered, which is not preferable.

As the CaF ₂ raw material, fluorite produced as a mineral product may be used, or a chemical reagent may be used. The purity of CaF ₂ is preferably 95% by mass or more. Further, the particle size of CaF ₂ is not particularly defined, but a particle size of 0.5 mm or less is preferable and a particle size of 0.3 mm or less is more preferable from the viewpoint of dispersibility in the material.

The present invention exhibits an effect by including a SiC raw material, a curing agent, amorphous SiO ₂ ultrafine powder, and a specific ratio of CaF ₂ raw material with respect to the amorphous SiO ₂ ultrafine powder. However, it is not essential that the main raw material is composed of only the SiC raw material, the curing agent, and the amorphous SiO ₂ ultrafine powder, and other refractory raw materials can be added as long as the effects of the present invention can be achieved. That, SiC raw material, when the curing agent, the sum of the components of the amorphous SiO ₂ ultrafine is less than 100 wt%, the sum can be added to other refractory material in condition to be 100 mass%. As the other refractory raw material, one or more selected from Al ₂ O ₃ , CaO, ZrO ₂ , and MgO can be used. For example, when the SiC raw material is 60% by mass, the curing agent is 1% by mass, and the amorphous SiO ₂ ultrafine powder is 1% by mass, the refractory raw material is added by 38% by mass.

As is well known, the melting point of Al is about 660 ° C., and the operating temperature of the Al melting furnace is about 1000 ° C. In addition, since the oxide formed during operation is mainly Al ₂ O ₃ , the amorphous refractory for molten Al alloy does not melt due to the reaction with molten slag like the refractory for iron making. Absent. However, it is necessary to suppress the reduction reaction by Al shown in the above formula (1). Therefore, the above-described Al ₂ O ₃ , CaO, ZrO ₂ , and MgO that are stable as oxides and hardly reduced by Al do not impair the effects of the present invention.

In view of corrosion resistance and volume stability, the other refractory raw material is preferably an alumina raw material. , For example, _Al 2 _{O 3} content of 80 mass% or more alum shale and bauxite, _Al 2 _{O 3} content of 95 mass% or more of the sintered alumina article and fused alumina, _Al 2 _{O 3} content of 98 weight % Or more of calcined alumina or the like can be used.

By using the above composition, a film made of Al ₂ O ₃ , SiO ₂ , and CaO at the Al molten metal interface can be stably formed.

Here, the formation mechanism of the film made of Al ₂ O ₃ , SiO ₂ , and CaO at the Al molten metal interface will be considered.

Although the reduction reaction of SiO ₂ by the molten Al is represented by the above formula (1), it is considered that a slightly more complicated reaction occurs in the pores of the refractory that is in contact with the molten Al. That is, for example, the thickness of the workpiece refractory in contact with the molten Al alloy in the melting furnace for Al alloy is about 150 to 200 mm, and the working surface is in contact with the molten Al alloy, but the opposite surface is in an atmosphere that can circulate with the atmosphere. ing. Therefore, on the working surface side, the molten Al alloy and oxygen react with each other, so the oxygen partial pressure is low, and on the opposite surface side, the oxygen partial pressure is higher than that on the working surface side. Therefore, there is an oxygen concentration gradient in the refractory.

As described above, since the oxygen partial pressure is low in the vicinity of the working surface, the decomposition of SiO ₂ by the formula (2) occurs, and it is possible to move in the pores as SiO (g).

SiO ₂ = SiO (g) + 1 / 2O ₂ (2)

  Furthermore, the CaO contained in the alumina cement is also likely to evaporate under a low oxygen partial pressure, and the state shown in the formula (3) occurs.

CaO = Ca (g) + 1 / 2O ₂ (3)

Since the equations (2) and (3) are equilibrium reactions, it is possible to return to SiO ₂ or CaO at the destination.

On the other hand, the oxygen partial pressure increases when a little distance from the working surface. Since the amorphous refractory of the present invention contains SiC as a main component, CaF ₂ reacts with SiC as shown in the formula (4) together with a small amount of oxygen. However, this reaction does not occur in the vicinity of an operating surface with an extremely low oxygen partial pressure.

SiC + 2CaF ₂ + 3 / 2O ₂ → SiF ₄ (g) + 2CaO + CO (4)

On the other hand, SiF ₄ is unstable when coexisting with CaO, and decomposes into SiO ₂ and CaF ₂ as shown in the equation (5).

2CaO + SiF ₄ (g) → SiO ₂ + 2CaF ₂ (5)

  In addition, the sum of Formula (4) and Formula (5) becomes Formula (6), and is an oxidation reaction of SiC.

SiC + 3 / 2O ₂ → SiO ₂ + CO (6)

Therefore, it can be considered that CaF ₂ acts like a catalyst and enables transport of the SiO ₂ component via the gas phase from the inner surface of the refractory to the surface of the working surface. For this reason, the transport amount of the SiO ₂ component to the surface of the working surface can be increased by the reaction of the formulas (4) and (5) by containing a certain amount of CaF ₂ component. However, since it is basically an oxidation reaction, the maximum value of the transport amount is determined by the supply amount of oxygen, and even if the amount of CaF ₂ is increased, it is saturated to a constant value.

As a result of the above, the SiO ₂ component is transported to the Al molten metal surface by the reaction of the formulas (2), (4) and (5), and a part thereof becomes Al ₂ O ₃ by the reaction of the formula (1). Further, since the CaO component is transported by the reaction of the formula (3), it is considered that a film made of Al ₂ O ₃ , SiO ₂ , and CaO was formed at the Al molten metal interface.

Based on the above considerations, the inventors of the present application have found that the conditions under which this film is formed can be arranged by the ratio of the content of CaF ₂ and SiO ₂ . That is, when the amount of CaF ₂ is small and the amount of SiO ₂ is large, the reactions of equations (4) and (5) do not proceed and the supply of the SiO ₂ component becomes insufficient, so that the film formation is incomplete. Further, CaF ₂ content is often, if the amount of SiO ₂ is small, (2) a reaction for the amount of SiO ₂ is less supplied by the, the incomplete Again. Therefore, it is considered that a stable film made of Al ₂ O ₃ , SiO ₂ , and CaO was formed by setting the ratio of the SiO ₂ component and the CaF ₂ component within a specific range.

  In addition, the well-known various additives can be mix | blended with the above raw material in the range which does not inhibit the effect of this invention. For example, aluminum borate, aluminum fluoride, barium sulfate, which are known as non-ferrous molten metal hard-wetting substances, and, if necessary, clay, aluminum powder, metal fibers, organic fibers, ceramic fibers, condensed phosphates as dispersants , Polyacrylates, polycarboxylates, polymers or copolymers thereof, and the like can be added.

  Moreover, the amorphous refractory according to the present invention is not limited to the casting construction at the use site, but can be carried into the use site as a precast block formed in advance and installed in various furnaces for use.

Example 1
Examples and comparative examples are presented below to illustrate the amorphous refractory of the present invention. In addition, this invention is not limited to the following illustrations.

  In Tables 1 and 2, the properties of the amorphous refractories adjusted by blending and kneading the raw materials at the blending ratios shown in the tables are evaluated.

  The SiC raw material used in each formulation is manufactured by the Atchison method, and the purity is 97% by mass. The purity of the electrofused alumina is 98% by mass. In addition, the particle diameter of SiC raw material and the particle diameter of electrofused alumina are also shown in Tables 1 and 2. In Tables 1 and 2, “6-1 mm” means that the particle size is 1 mm or more and 6 mm or less. “−1 mm” means that the particle size is less than 1 mm.

The purity of the calcined alumina is 99.8% by mass, and the particle size is 20 μm or less. Silica fume is used for the amorphous SiO ₂ ultrafine powder. As the CaF ₂ raw material, pulverized powder of fluorite is used. The purity of the CaF ₂ raw material is 97% by mass, and the particle size is 0.1 mm or less. As the alumina cement, high alumina cement having an alumina component of 74% by mass was used. Furthermore, a polycarboxylate was added as a dispersant. In Tables 1 and 2, “-” means that the component is not included.

Further, Table 1 and Table 2 show chemical components of each formulation. The chemical components are representative three components of SiC, Al ₂ O ₃ and SiO ₂ . The balance when the total of the representative three components is less than 100% by mass is a component derived from impurities such as CaO.

  The irregular refractories obtained by the respective blends were evaluated for fluidity, bending strength, heat spalling resistance, and wet resistance and listed in Tables 1 and 2.

  The fluidity was evaluated by a kneaded material obtained by adding 5.0% by mass of water to each formulation and kneading according to a conventional method. In the evaluation, a flow cone having an upper side 70φ, a lower side 100φ, and a height of 60 mm defined in JIS R 2521 was used, and a vibration of 2.7 G was applied for 5 seconds. The diameter of the irregular refractory after spreading was measured in the direction where the maximum was recognized and the direction perpendicular thereto, and the average value of the diameters in these two directions was taken as the flow value. “+” Indicates that the flow value is less than 160 mm. “++” indicates that the flow value is 160 or more and less than 180 mm. “++++” indicates that the flow value is 180 mm or more. Here, a flow value of less than 160 mm was determined to be poor fluidity.

  The bending strength was evaluated by a test method according to JIS R 2553 using a test piece having a shape of 40 mm × 40 mm × 160 mm. Here, the bending strength after baking at 800 ° C. for 3 hours is evaluated. The test piece was prepared by adding 5.0% by mass of water to each composition, casting the kneaded material kneaded according to a conventional method into a mold having the above shape, curing at room temperature for 24 hours, and then removing the frame, followed by 110 ° C. for 24 hours. After drying, it was produced by baking at 800 ° C. for 3 hours. Here, a bending strength of less than 10 MPa was determined to be poor.

  The heat spalling resistance was evaluated based on the number of cycles in which cracks were generated by repeating heating and quenching cycles on a test piece having a shape of 40 mm × 40 mm × 160 mm. The test piece was prepared by adding 5.0% by mass of water to each formulation, casting the kneaded material kneaded according to a conventional method into a mold of the above shape, curing at room temperature for 24 hours, and then removing the frame and drying at 110 ° C. for 24 hours. Was generated. In the heating and quenching cycle, a test piece was put into an electric furnace heated to 1000 ° C. and heated for 15 minutes, and then removed from the electric furnace and rapidly cooled with running water for 2 minutes. This heating and quenching cycle was repeated 10 times to observe how many times cracks occurred in the test piece. “+” Indicates that a crack occurred in less than 3 cycles. “++” indicates that a crack occurred in 3 to 6 cycles. “++++” indicates that a crack occurred after the seventh cycle. The one with a smaller number of cycles in which cracks occurred (less than 3 cycles) was determined to have poor heat spalling resistance.

  The infiltration resistance was evaluated by immersing a test piece having a shape of 5 mm × 114 mm × 230 mm in a 55% Al—Zn compound liquid melting furnace for 6 months, and evaluating the thickness of the deteriorated layer formed on the contact surface with the Al alloy. The test piece was prepared by adding 5.0% by mass of water to each formulation, casting the kneaded material kneaded according to a conventional method into a mold of the above shape, curing at room temperature for 24 hours, and then removing the frame and drying at 110 ° C. for 24 hours. Was generated. The generated thickness of the deteriorated layer was obtained by collecting and cutting the test piece and observing the contact surface with the Al alloy. “+” Indicates that the thickness of the deteriorated layer is 10 mm or more. “++” indicates that the thickness of the deteriorated layer is 5 to 10 mm (5 mm or more and less than 10 mm). “++++” indicates that the thickness of the deteriorated layer is less than 5 mm. The one where the deteriorated layer was formed thick (10 mm or more) was determined to be poor infiltration resistance.

  Moreover, the symbol described in the comprehensive evaluation column in the table is a comprehensive evaluation of the above characteristics. “A” is attached to a composition which is excellent in all characteristics. “◯” is inferior to “◎” but has a practically no problem. “Δ” is attached to the formulation in which one item is determined to be defective for each property excluding the heat-resistant spalling property. "X" is attached to the formulation in which two or more items are determined to be defective or the heat-resistant spalling characteristics are determined to be poor for each characteristic.

  As can be understood from Tables 1 and 2, in Examples 1 to 18, excellent characteristics were obtained for each of the characteristics of fluidity, bending strength, heat spalling resistance, and infiltration resistance.

  Here, the composition shown in Table 1 will be briefly described.

In Table 1, Examples 1-5 have changed the mixture ratio of the SiC raw material. In Examples 6 to 10, the blending ratio of the amorphous SiO ₂ ultrafine powder is changed. In Examples 11 to 14, the above-described ratio (A / B) is changed. In Examples 15 to 18, the mixing ratio of the alumina cement is changed.

  Hereinafter, each comparative example in Table 2 will be briefly described.

Comparative Example 1 is a blend of conventional alumina amorphous refractory mainly composed of fused alumina. Further, the CaF ₂ raw material is added so that the above (A / B) is 0.75. This comparative example 1 is inferior in heat-resistant spalling properties. This is inferior in spalling resistance due to the high thermal expansion coefficient of alumina. Further, by containing CaF ₂ raw material 3 mass%, also even though the (A / B) is within the scope of the present invention and 0.75, was inferior erosion Jun resistance. This is presumably because a film composed of stable Al ₂ O ₃ , SiO ₂ , and CaO could not be formed at the Al molten metal interface because it was not composed mainly of SiC.

Comparative Example 2 is a blend containing 99% by mass of SiC raw material, 1% by mass of amorphous SiO ₂ ultrafine powder, and not containing alumina cement as a curing agent. This Comparative Example 2 has poor fluidity and bending strength.

  Comparative Example 3 is a blend in which the addition amount of the SiC raw material is 50% by mass, which is further smaller than that of Example 5. This Comparative Example 3 is extremely inferior in spalling resistance.

Comparative Example 4 is a blend not containing amorphous SiO ₂ ultrafine powder in comparison with Examples 6 to 10. This Comparative Example 4 has poor fluidity, bending strength and infiltration resistance. In Comparative Example 5, in comparison with Examples 6 to 10, a formulation with an amorphous SiO ₂ ultrafine a lot 10 mass%. This Comparative Example 5 is very sticky and has poor fluidity.

  Comparative Example 6 is a blend in which the ratio (A / B) is as low as 0.1 in comparison with Examples 11-14. This Comparative Example 6 has poor infiltration resistance. Moreover, the comparative example 7 is the mixing | blending which made the said ratio (A / B) high with 2.5 in contrast with Examples 11-14. This Comparative Example 7 has poor infiltration resistance and fluidity.

  Comparative Example 8 is a blend containing no alumina cement in comparison with Examples 15-18. This Comparative Example 8 has poor fluidity, bending strength, and infiltration resistance. Moreover, the comparative example 9 is the mixing | blending which increased alumina cement as 20 mass% in contrast with Examples 15-18. This Comparative Example 9 has poor fluidity.

  As described above, according to each embodiment of the present invention, it is possible to obtain an amorphous refractory that is excellent in fluidity, bending strength, and heat spalling resistance and excellent in infiltration resistance against a molten Al alloy.

(Example 2)
About Example 3 with high comprehensive evaluation in Table 1, it applied to the inductor block of the Al alloy melting furnace for 55% Al-Zn alloy melting | dissolving amount of 50t, and was used by the actual machine. For comparison, Comparative Example 3 in Table 2 (conventional alumina amorphous refractory) was applied to the inductor block and used in the same equipment. In the formulation of Comparative Example 3, the average life was 8.9 months (sample number n = 13), whereas in the formulation of Example 3, the average life was 30 months (sample number n = 3). . Also from this result, it can be understood that the amorphous refractory according to the present invention is excellent in durability.

  As described above, according to the present invention, it is excellent in heat spalling resistance and infiltration resistance against molten Al alloy, and realizes an amorphous refractory for a molten Al alloy that has higher durability compared to conventional refractories. Can do.

  The present invention is excellent in fluidity, bending strength, heat spalling resistance and infiltration resistance against molten Al alloy, and can realize an amorphous refractory for a molten Al alloy that has higher durability than conventional refractories. It is useful as an amorphous refractory for molten Al alloys.

Claims (2)

An amorphous refractory for a molten aluminum alloy containing a refractory raw material and a curing agent,
SiC raw material 60-98 mass%,
1 to 15% by mass of a curing agent,
1 to 8% by mass of amorphous SiO ₂ ultrafine powder,
One or more refractory raw materials selected from Al ₂ O ₃ , CaO, ZrO ₂ , and MgO, which are added in a state where the total is 100% by mass when the total of the above components is less than 100% by mass,
A main raw material consisting of
CaF ₂ raw material added to the main raw material,
Including
The CaF ₂ raw material has a ratio (A / B) between the outer mass% value A of the CaF ₂ raw material and the mass% value B of the amorphous SiO ₂ ultrafine powder of 0.2 ≦ (A / B) ≦ 2. An amorphous refractory for a molten aluminum alloy, which is added to the main raw material within a satisfactory range.   The amorphous refractory for a molten aluminum alloy according to claim 1, wherein the hardener is alumina cement.