JPH0696470B2 - Alumina cordierite refractory with melt penetration resistance and melt wear resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application) The present invention relates to a refractory for molten metal having a low melting point, which is composed of an alumina-cordierite molded product, characterized in that the matrix is predominantly a petalitic bond. Of alumina-cordierite refractory, which has melt penetration resistance, melt wear resistance, thermal shock resistance, and heat insulation, and is particularly suitable for the transport eve of aluminum melt.

(Prior art) Hot water is supplied from a melting furnace to a hand-held furnace by carrying a ladle with a truck on a forklift or rail, or by a gutter between the furnace and the molten metal into the atmosphere. There are problems such as heat loss due to contact, generation of oxides, pinholes due to gas absorption, and the like, increasing the defect rate. 2. Description of the Related Art Recently, an automatic hot water supply system has been in widespread use in which a molten metal transportation pipe is connected to a hot water supply path from a melting furnace to a manual furnace and from a manual furnace to a casting machine, and the molten metal is cast without being exposed to the atmosphere.

As a pipe for transporting molten aluminum, a pipe made of tubular ceramic fiber is used for the lining layer of steel pipe, or a castable refractory containing ceramic fiber is placed between the pipe and a formwork provided concentrically with it. It is used by pouring into and molding.

As the ceramics, silicon nitride, silicon carbide, alumina and calcium silicate are used. The structure of the pipe is such that a ceramic fiber is provided between a copper pipe and a silicon nitride pipe, or even if a crack occurs in the ceramic pipe and the molten metal exudes from the crack, the ceramic coated on the ceramic pipe A method of preventing the molten metal from leaking outside with a paper layer has been disclosed (Japanese Utility Model Publication No. 62-165056 and Japanese Utility Model Publication No. 64-54964).

(Problems to be Solved by the Invention) However, although the ceramic fiber or calcium silicate layer, which is the lining layer, works effectively as a heat insulating layer for preventing a decrease in hot water temperature, the ceramic fiber layer or calcium silicate layer has a large number of pores. There are cracks due to heat shrinkage due to the reaction between these layers and the molten aluminum at the contact part, etc., and the molten metal penetrates or adheres, resulting in blockage, and wear due to the flow of molten metal. Life is short. Silicon nitride and silicon carbide are excellent in thermal shock resistance, molten metal penetration resistance, and molten metal wear resistance, but they have high thermal conductivity and poor heat insulation, so the heat radiated from the pipe increases, Insulate the outside of the pipe with ceramic fiber (Japanese Utility Model No. 62-165056), heat from the outside of the pipe with a heater, or incorporate a heater (Japanese Patent Laid-Open No. 62-34658) to heat the pipe. It has the drawback of having to do it. Alumina has properties such as heat insulation, thermal shock resistance, molten metal penetration resistance, and molten metal wear resistance.
It is in the middle of calcium silicate and is not satisfactory. The applicant of the present application, as a result of research on a refractory material having excellent thermal shock resistance and molten metal permeation resistance of alumina, mixed refractory clay and aluminum phosphate into alumina raw materials such as sintered alumina, calcined alumina and calcined bauxite. Molding
A heat-treated refractory material has been disclosed (JP-A-59-213667). In the conventional alumina refractory, in order to improve the corrosion resistance, the amount of the refractory clay used was reduced as much as possible, high-pressure molding was performed, and the high-temperature firing was used to manufacture the disclosed invention. As a result of heat treatment at a relatively low temperature in combination with a large amount of aluminum phosphate, a dense refractory structure with a small porosity was obtained and the molten metal penetration resistance was improved. When the alumina refractory material according to the disclosed invention was applied to a pipe for transporting molten aluminum, the molten metal penetration resistance was sufficiently satisfied, but the thermal shock resistance and heat insulation were insufficient. A crack is generated while the molten metal at about 680 ° C intermittently passes through the pipe, and the molten metal enters the crack, so that the crack expands. Therefore, it is necessary for the pipe to have a higher thermal shock resistance in a usage state in which it is subjected to repeated stress of heating and cooling. Then, there remains a problem that heating from the outside of the pipe or the outside of the pipe has to be a heat insulating structure. Cordierite and petalite are known as materials for improving thermal shock resistance. Therefore, it is expected that the thermal shock resistance of the alumina refractory will be improved by adding cordierite or petalite to the alumina raw material. However, a refractory obtained by adding cordierite or petalite to an alumina-based raw material, using refractory clay as a binder, and press-molding and firing has a large penetration of the molten aluminum and cannot be used for a pipe for molten aluminum. Further, a refractory obtained by adding cordierite or petalite to an alumina-based raw material and using alumina cement as a binder, cast-molding and firing cannot be used for the same reason.

Further, these alumina-cordierite refractories were still insufficient in terms of thermal shock resistance as a pipe for transporting molten metal. JP-A-60-186461 discloses that in order to improve the thermal shock resistance of a cordierite refractory, fine particles of cordierite are dispersed with coarser particles of silicon carbide. Is not suitable for the purpose of the present invention because it lowers the heat insulating property. Therefore, the present inventor conducted a study to suppress the molten metal penetration resistance of the alumina-cordierite refractory, and in the combined use of cordierite and petalite and the combination with aluminum phosphate, it was possible to complete the present invention suitable for a pipe for transporting molten aluminum. did it.

(Means for Solving the Problems) This invention was made in order to solve the problems of the conventional refractory materials described above, particularly ceramic pipes. Cordierite powder 35 to 60% by weight, petalite powder Ten
-50%, alumina powder 10-40%, powdered aluminum was added as a binder, kneaded, molded, and fired. Alumina with melt penetration resistance and melt wear resistance. It relates to cordierite refractories.

(Function) Table 1 shows properties of raw materials for white cordierite and petalite. Both are raw materials with low expansion and excellent thermal shock resistance. Cordierite is highly porous and has a heat insulating property.

There are red and white cordierite, but red cordierite contains 2% iron, while white cordierite has a very low iron content of 0.15%, so it is a refractory material that comes into contact with molten aluminum that dislikes iron. When used for white cordierite, white cordierite is more suitable. Cordierite is used for thermal shock resistance and heat insulation. Use medium particles of 2 mm or less. Although cordierite has thermal shock resistance, the thermal shock resistance is still insufficient in a pipe through which molten aluminum at about 680 ° C passes. As a result of various studies, it was found that the addition of petalite powder having a low expansion property is effective for improving the thermal shock resistance. In order to improve the thermal shock resistance, it is necessary to strengthen the matrix portion, so it was preferable to use petalite, which has a lower expansion coefficient than cordierite, for the fine powder matrix portion. The petalite used was 125 μm or less. Alumina improves the corrosion resistance of the melt to wear. As the alumina, fine powder of 44 μm or less was used. As the aluminous raw material, corundum, calcined alumina, mullite, bauxite and the like can be used. Next, the use ratio of each raw material and its reason will be described.

Cordierite powder should be used 35 to 60% by weight. If it is less than 35%, the thermal shock resistance is insufficient. When it is 60% or more, the use amount of petalite and alumina is insufficient, so that the thermal shock resistance and the melt wear resistance are insufficient. Petalite powder is used at 10 to 50% by weight. If it is less than 10%, the thermal shock resistance is insufficient. When it is 50% or more, the amount of cordierite or alumina used is insufficient, so that the heat insulating property, heat resistance and melt wear resistance are insufficient. When the amount of petalite used is high, the thermal conductivity is high and the heat insulating property is lost. Alumina powder is by weight,
Use 10-40%. If it is less than 10%, the wear resistance of the melt is insufficient, and if it is more than 40%, the thermal shock resistance and heat insulation are insufficient. Aluminum phosphate is added as a binder to these powders and kneaded to form. Aluminum phosphate has excellent penetration resistance and corrosion resistance to molten aluminum. Various aluminum phosphates can be used as the binder. When molding is performed under high pressure, the structure of the molded body becomes dense and the thermal shock resistance is improved. A rubber press is suitable for forming pipes.
The molded body is dried and then baked at about 1000 ° C.

(Example) Table 2 shows an example of the product of the present invention. In all the examples, cordierite powder is white cordierite 2000 μm or less, petalite powder is 125 μm or less, and alumina powder is calcined alumina 4
4 μm or less and as a binder, manufactured by Taki Chemical Co., Ltd./
Aluminum phosphate 95% solution (commercial name: acidphos 75 was added to make 95% concentration) against 100 parts by weight of powder
8.6 to 9.6 parts by weight were used. 800k mixture with rubber press
It was molded into a pipe with a pressing force of g / cm ² . After drying, 1050 ℃
It was baked for 3 hours. The physical properties listed in Table 2 were measured for the test pieces after firing. The examples are all highly porous.

In aluminum penetration test, 50φ for 80 × 80 × 65mm material
The aluminum ADC-12 was placed in a crucible-shaped sample with a hole of 50 mm and 160g of aluminum ADC-12 was placed in the sample and kept at 900 ° C for 48 hours in the air. The size of the large depth is the penetration depth (m
m).

In terms of thermal shock resistance, a pipe-shaped specimen having an inner diameter of 50 mm, an outer diameter of 80 mm and a length of 200 mm was heated at 850 ° C. for 20 minutes, and then cold water was applied to the outer surface of the pipe for cooling for 30 seconds. After cooling, it was air-cooled and dried, and the same method as described above was repeated. Then, the number of repetitions and the occurrence of cracks on the pipe surface were measured. A wear resistance test was conducted as a substitute for the wear resistance of the molten metal. In the wear resistance test, the volume of the concave surface generated on the falling surface of the test piece when 15 kg of iron shots having a diameter of 3 mm was dropped from the height of 7 m onto the surface of the test piece was measured as the wear amount. For air permeability measurement, 1kg / cm
² and 2 kg / cm ² of compressed air. The thermal conductivity was measured according to the hot wire method according to JIS R 2618-79. As the sample, a sample having a diameter of 100 mm and a length of 100 mm divided into two semi-cylindrical columns was used.

Table 3 shows comparative examples. Comparative Example No. 6 is a high-strength castable refractory made of alumina low-alumina cement, and No. 7
Is an alumina castable refractory, No. 8 is an alumina aluminum phosphate bond castable refractory, and No. 9 is a calcium silicate heat insulating castable refractory, all of which are commercial products. No.10, No.11 and No.12 are test compounds.No.10 is white cordierite 2mm or less / 47 parts by weight, white cordierite 0.2mm or less / 53 parts by weight and acidhod 75/12 parts by weight. Were mixed, rubber molded at 800 kg / cm ² , and fired at 1050 ° C. No. 11 is white cordierite 2 mm or less / 42 parts by weight, petalite 0.125 mm or less / 20 parts by weight electrified high alumina cement Super 38 parts by weight water 21.1
Parts by weight were mixed, subjected to vibration casting, and fired at 700 ° C. No. 12 is white cordierite 2 mm or less / 47 parts by weight, petalite 0.125 mm or less / 53 parts by weight with acidphos 75 /
9.1 parts by weight are mixed, rubber molded at 800 kg / cm ² , and 1050 ℃
It was baked in. Next, the example and the comparative example will be compared. In the aluminum penetration test, no penetration was observed in all of Examples No. 1 to No. 5, whereas Comparative Examples No. 10 and No.
At 11, they were 3.4 mm and 10.4 mm, respectively. This is because cordierite is porous, and when cordierite is used for the matrix together with the aggregate, the penetration of the molten metal increases due to the lack of compactness in the matrix part, and the aluminum phosphate bond has an impermeability resistance. It shows that it is good. In the thermal shock test, cracks were not seen even in all 10 times except 8 times of No. 4 in the example, while 3 in Comparative example commercial products No. 6 to No. 9.
A large crack has occurred after ~ 6 times. It is shown that the use of petalite, which is a low expansion raw material, in the matrix improved the thermal shock resistance of the examples. In the molten metal wear resistance test, the amount of wear is 0.62 to 1.17 cc in Example, but it does not reach No. 6 high-strength castable refractory,
It shows that it is superior to No. 9 heat-insulating castable refractories. In the measurement of air permeability, Examples No. 1 to No. 5 showed higher values than the commercial products No. 6, No. 7 and No. 9. The thermal conductivity is 0.93 to 1.20 in the example, and does not reach the heat-insulating castable refractory of No. 9, but is a lower value than the castable refractories of No. 6, No. 7, and No. 8. And shows that it has heat insulation.

(Effects of the Invention) When the refractory material of the present invention is used in a molten metal transport pipe, it has only thermal shock resistance, so unexpected troubles due to cracking of the pipe are eliminated and safe operation is possible. Moreover, the wear resistance is more than double that of the pipe made of calcium silicate, so that the life is extended. Although the present invention has high porosity and high air permeability, it does not permeate the molten aluminum and is excellent in molten metal abrasion resistance and thermal shock resistance. It can also be used for lining low-melting metal melt holding furnaces, lining molten metal gutters, and ladle for transportation.

Claims (1)

[Claims] 1. An aluminum phosphate is added as a binder to a raw material powder consisting of 35-60% cordierite powder, 10-50% petalite powder, and 10-40% alumina powder, and kneaded.
Alumina-cordierite refractory having melt penetration resistance and melt wear resistance, characterized by being molded and fired.