JP3197781B2 - Refractory material for aluminum-lithium alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractory for an aluminum-lithium alloy, and more particularly, to a melting furnace for contacting a molten aluminum-lithium alloy containing several percent of lithium.
The present invention relates to a refractory material suitably used as a lining material for a holding furnace, a ladle and the like.

[0002]

2. Description of the Related Art Molten aluminum-lithium alloys are highly reactive, and refractory materials that come into contact with the molten metal are susceptible to erosion.
For example, as a refractory material for aluminum alloys, a thermally and chemically stable alumina material is generally used, but when an alumina refractory material is applied to an aluminum-lithium alloy melting furnace, Alumina reacts with lithium to produce LiAlO _{2 and} is eroded. Also,
Graphite crucibles commonly used in the melting of aluminum, when used to melt aluminum-lithium alloys, are severely eroded and are prone to cracks due to thermal and structural spalling, with the melt reaching deep along the cracks There is a possibility that it cannot be used stably.

In order to obtain a refractory having corrosion resistance and thermal shock resistance to a molten aluminum-lithium alloy, various researches have been conducted so far, and the inventors of the present invention have previously reported that a specific amount of magnesia is contained. Alumina-magnesia refractory with excellent corrosion resistance to molten aluminum-lithium alloy has been developed. (JP-A-5-148014)

[0004] Alumina-magnesia refractory material has excellent corrosion resistance, and when used in a small induction melting furnace of aluminum-lithium alloy having a melting amount of about 200 kg, crack generation is slight and stable long life can be obtained. When used in a large induction furnace of 4 ton scale, the inner diameter of the furnace is about four times as large as that of the 200 kg melting furnace, so cracks during use are inevitable. , It cannot be used stably for a long period of time.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems in the alumina-magnesia refractory material previously developed for aluminum-lithium alloys, the present invention is based on an alumina-magnesia refractory material. It was made as a result of conducting various experimental investigations on the erosion properties of the composition and aluminum-lithium alloy molten metal, and the purpose was further without impairing the excellent corrosion resistance of the conventional alumina-magnesia refractory material. It is an object of the present invention to provide a refractory material for an aluminum-lithium alloy, which has improved thermal shock resistance and can prevent troubles caused by intrusion of molten metal (penetration) from cracks even when used in a large melting furnace.

[0006]

According to the present invention, there is provided a refractory material for an aluminum-lithium alloy according to the present invention, comprising 5 to 20% by weight of spinel and 0.5 to 5% of boric anhydride.
The composition of the invention is characterized in that the composition of the refractory material is composed of a spinel and boric anhydride of 0.3 mm or less.
The feature of.

[0007] To explain the significance and their reasons for limiting the content of each component in the refractory material of the present invention that an alumina substrate, spinel, for example, Al ₂ O ₃ 62~8
A composite refractory containing 2% by weight of MgO and 18 to 38% by weight of MgO. Similar to magnesia, it is a refractory chemically extremely stable against lithium and does not form a compound with lithium. Reaction with the molten alloy is suppressed.

Further, since spinel has a very low coefficient of thermal expansion as compared with magnesia, the inclusion of spinel further improves the resistance to thermal spalling compared to the case where magnesia is added, and suppresses the occurrence of cracks during cooling. Having. The preferred range of the content of spinel is 5 to 20% by weight. When the content is less than 5% by weight, the effect is only partially recognized. When the content exceeds 20% by weight, the expansion rate of the refractory material during use is reduced. The thermal shock resistance may decrease and cracks may increase.

Boric anhydride (B ₂ O ₃ ) mainly functions as a binder for hardening the refractory material, but boric anhydride reacts with lithium to form 2Li ₂ O.B _2.
Reaction products such as O ₃ and Li ₂ O.B ₂ O ₃ are generated, and these compounds are eluted to form a viscous thin film on the surface of the refractory material and protect the refractory material to protect the aluminum-lithium alloy. It acts to suppress erosion by molten metal. The content of boric anhydride is preferably in the range of 0.5 to 5% by weight. 0.
If the content is less than 5% by weight, the effect is small, and if 5% by weight is added, the effect is saturated, and if the content exceeds 5% by weight, no further effect can be expected, and the corrosion resistance of the refractory material tends to deteriorate. is there.

In the present invention, more excellent effects can be exhibited by limiting the particle size of both spinel and boric anhydride, which are components of the refractory, to 0.3 mm or less. The reaction between the aluminum-lithium alloy and the refractory material and the infiltration of the molten metal into the refractory material structure are performed mainly in the fine powder portion that binds the alumina that is the skeleton portion of the refractory material, so the grain size of the spinel is 0.3 mm or less. By setting the particle size of boric anhydride to 0.3 mm or less, the bonding of the refractory material is further strengthened and the protective effect of the coating on the refractory material is further enhanced.

[0011]

In the present invention, the alumina serving as the skeleton portion is
Bonded at the boundary mainly composed of spinel, which is stable against lithium.The inclusion of spinel keeps the thermal expansion coefficient of the refractory low, and improves cracking resistance by improving thermal spalling resistance. Further, since the high-melting-point reaction product of boric anhydride and Li forms a viscous film on the surface of the refractory material, the erosion of the aluminum-lithium alloy melt on the refractory material is effectively suppressed, resulting from the jug. Work troubles can be avoided.

[0012]

Hereinafter, examples of the present invention will be described in comparison with comparative examples. Example 1 A refractory material having the composition shown in Table 1 was prepared by using an inner diameter of 200 m.
m, an outer diameter of 300 mm, a height of 200 mm, and a die having a void portion, stamped by hand polishing, molded into a sleeve having the above dimensions, and heated to a temperature of 300 ° C. for 6 hours to obtain a refractory material. A sample was obtained.

As shown in FIG. 1, the obtained sleeve-shaped refractory material sample was subjected to induction coil 5 and coil protection refractory 6.
, A graphite electrode 2 is set in a refractory material sample 1, the graphite electrode 2 is covered with a heat insulating material 3, and the temperature is raised to 900 ° C. in 1 hour for 30 minutes. After the holding, a spalling test was performed under the condition that the electricity was cut off, the temperature was lowered to 700 ° C., and the sample was taken out of the furnace and rapidly cooled, and the state of occurrence of cracks in the refractory material sample was observed. Table 1 shows the results. As shown in Table 1, in each of the refractory material samples according to the present invention, only a slight crack was found in the longitudinal direction on the inner surface of the sleeve-shaped sample, and the width was 0.1 mm or less, which was a practically no problem. And has excellent thermal shock resistance.

[0014]

[Table 1] << Table Note >> Evaluation: A sample which can be used without any practical problem was evaluated as ○.

Comparative Example 1 A refractory material having the composition shown in Table 2 was charged into a mold having the same shape and dimensions as in Example 1, and subjected to the same stamping and heating steps as in Example 1 to obtain a refractory material. Material samples were prepared. A spalling test was performed on the obtained refractory material sample under the same conditions as in Example 1, and the occurrence of cracks in the refractory material sample was observed. Table 2 shows the results. In addition, in Table 2, the values out of the conditions of the present invention are underlined.

[0016]

[Table 2] << Table Note >> Evaluation ○: Practical use possible △: Practical problem x: Practical use impossible

As can be seen from Table 2, the sample no. Sample No. 4 has many cracks on the outer surface and the bottom, and its maximum width is large enough to cause a practical problem, and the content of spinel exceeds the range of the present invention. 6 has a maximum crack width of 0.3 mm
And it was determined that there was a problem in practice. Sample No. having a spinel content less than the range of the present invention. In No. 5, the maximum width of the crack was small and the evaluation result was good.

Example 2, Comparative Example 2 Refractory materials (Sample Nos.
3) 2.5% of a 3% solution of gum arabic was added as a molding binder, and the surface pressure was 40 MPa by a hydraulic press.
At a pressure of 30 mm, an outer diameter of 70 mm, and a depth of 35 mm.

An Al-2.3% Li alloy is charged into the formed crucible, and after vacuum degassing for 15 minutes in an electric furnace whose atmosphere can be adjusted, argon gas is blown into the furnace to control the oxygen concentration to 20 ppm or less. The mixture was heated and melted while maintaining the temperature at 850 ° C. for 24 hours. Subsequently, the molten metal was removed by cooling to room temperature, and the erosion state of the crucible was observed. In any case, no erosion by the molten metal was observed.

On the other hand, refractory materials (samples Nos. 4 to 6) blended in the composition shown in Table 2 were similarly molded into a crucible shape and subjected to the same test. 4 and no.
No erosion was observed for No. 6; In No. 5, erosion reaching a depth of 2 mm was observed.

[0021]

As described above, according to the present invention, in addition to the corrosion resistance equivalent to that of the conventional alumina-magnesia refractory,
Further, a refractory material for an aluminum-lithium alloy having improved thermal shock resistance is provided. The refractory material can be used stably for a long period of time even when applied to a large melting furnace of 4 ton scale of an aluminum-lithium alloy, with a small generation of cracks and no risk of hot water. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part of an outline of a spalling test according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 sleeve-shaped sample 2 graphite electrode 3 heat insulating material 4 high-frequency induction furnace 5 induction coil 6 refractory for coil protection

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Kuroki 1 Minami Fuji, Ogakie-cho, Kariya-shi, Aichi Prefecture Toshiba Ceramics Co., Ltd. (56) References JP-A-5-148014 (JP, A) JP-A-64-21018 (JP, A) JP-A-62-12653 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/00-35/22 B22D 41/02

Claims (2)

(57) [Claims] 1. A refractory material for an aluminum-lithium alloy, comprising 5 to 20% by weight of spinel and 0.5 to 5% by weight of boric anhydride, the balance being alumina. 2. The refractory material for an aluminum-lithium alloy according to claim 1, wherein both the spinel and boric anhydride have a particle size of 0.3 mm or less.