JPH0753608B2 - Method for producing highly durable refractory material containing boron nitride - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a refractory material suitable for use in a place where a molten metal comes into contact, particularly in a molten steel continuous casting apparatus.

[Conventional technology]

In JP-A-55-34663, JP-A-56-139260, JP-A-59-169982, etc., a boron nitride-containing refractory is extremely stable against molten metal and slag and has excellent resistance. It is disclosed that it has a spalling property.

[Problems to be solved by the invention]

However, the conventional boron nitride-containing refractory has a compressive strength of 450 kg / cm ² or less and a hot bending strength of 190 kg / cm ² or less at 1400 ° C. Is not durable enough. Further, when the boron nitride-containing refractory is applied to the nozzle, there is a problem that pore blocking occurs due to alumina precipitation due to the thermal conductivity of the boron nitride itself.

Further, in the case where the boron nitride-containing refractory contains graphite, the contained graphite easily dissolves in the molten steel, and there is a problem in strength. A boron nitride-containing refractory containing no graphite is disclosed in JP-A-56-120575 and JP-A-56-139260, but only silicon metal is a component contributing to bonding. In the case of metallic silicon, bond strength is obtained by forming β-SiO, Si ₃ N ₄ , Si ₂ ON _2, etc., but these bonds cause problems in corrosion resistance and spalling resistance to molten steel.

On the other hand, metal aluminum is used to increase the bond strength of the dough by adding it to the refractory material similar to metallic silicon, but as a binder that fully exhibits the spalling resistance and corrosion resistance of the boron nitride-containing refractory material, The use of metallic aluminum instead of silicon is conceivable.

However, as described in JP-A-59-169982, the added metallic aluminum changes to Al ₄ C ₃ , AlN, Al ₂ O ₃ during the firing process or during use, but Al ₄ C ₃ , AlN The problem of digestion resistance comes out in the binding by.

The problem to be solved in the present invention is to eliminate the above-mentioned problems caused by adding metallic aluminum powder as a reinforcing binder to a refractory material containing boron nitride.

[Means for solving problems]

The present invention is effective for solving the problem of digestion resistance by the addition of metallic aluminum powder as a reinforcing binder in a boron nitride-containing refractory, so that it is effective to use Si in combination in the boron nitride-containing refractory, which is said to be harmful. It was completed based on the knowledge that

That is, the method for producing a boron nitride-containing highly durable refractory material of the present invention comprises 20% by weight of a boron nitride powder mainly composed of a hexagonal system.
In addition to the above, powder of Si ₃ N ₄ or SiC alone or mixed powder
~ 50% by weight, 10% to 50% by weight of Al / Si powder mixed or alloyed with Al / Si ratio within the range of 8/1 to 3/1,
Furthermore, after forming a mixture in which a resin which is a carbon product is added as a binder, the mixture is placed in a sheath filled with carbon powder and baked.

When this metal aluminum powder and metal silicon powder are used together, the ratio of Al / Si is important. If this ratio is larger than 8/1, there is no digestive protection effect due to the addition of Si, and if it is smaller than 3/1, the corrosion resistance, Spalling resistance is reduced.

When the content of boron nitride in the target refractory is 20% by weight or less, there is no effect of adding boron nitride, and no significant improvement effect on spalling resistance is observed.

In the present invention, various aggregates that can be used under the combination of boron nitride, metallic aluminum and metallic silicon can be applied, and can also be used in combination with various improving materials.

For example, SiC and Si ₃ N ₄ are aggregates that have a significant improvement effect due to the improvement of strength and hole blockability. In this case, if the addition amount of Si ₃ N ₄ or SiC alone or the mixed powder is less than 10% by weight, the effect of improving the strength and preventing the hole clogging cannot be obtained. When added in excess of 50% by weight, the corrosion resistance is excessively reduced, so that in the boron nitride-containing refractory material of the present invention, SiC, Si ₃ N
_The effect of addition by ₄ etc. appears when these addition amounts are in the range of 10% by weight to 50% by weight.

When MgO is used as the refractory aggregate of the present invention, Al
There is a problem due to calcination expansion of the secondary spinel formed as a result of the reaction with Al ₂ O ₃ generated from.

In aggregates containing a large amount of SiO ₂ , such as mullite and silica, the reduction action of Al ₂ on SiO ₂ makes the aggregate porous, resulting in reduced strength and reduced corrosion resistance.

Aggregates containing ZrO ₂ , such as zirconia and zircon, are difficult to manufacture due to firing problems due to the reduction of ZrO ₂ by Al.

Al ₂ O ₃ and spinel are effective in improving strength but not in preventing pore blockage.

The kneading of the blend in the production of the present invention is a blend of only fine powder and requires a granulation step. For example, a granulating mixer such as a Spartan mixer or a Henschel mixer can be used.

For molding, a rubber press is mainly used in terms of uniformity of quality, but a dynamic press, an oil press or the like can be adopted depending on the shape and the like.

Speaking of firing, BN, Al, and Si are used, and naturally firing in an oxidizing atmosphere is not possible. Firing in a nitriding atmosphere is also possible, but the strength decreases by about 20%, a large amount of nitrogen is required to maintain the atmosphere, and the cost increases, so firing in carbon powder is desirable. The filler in the sheath at the time of firing may be any that can be kept in a non-oxidizing atmosphere, and coke powder, scaly graphite, graphite electrode cutting waste, etc. can be used.

The boron nitride used is preferably a hexagonal crystal, but cubic and amorphous ones are also not plate-like and can be used if attention is paid to spalling resistance.

Of course, the refractory material produced by the present invention can be sufficiently applied to a place where it comes into contact with molten metal such as aluminum or copper.

〔Example〕

The compound as shown in Table 1 was granulated, rubber press molded and then fired in coke powder at 1450 ° C.

When the amount of Si ₃ N ₄ added is less than 10% by weight, the effect of improving the strength is not obtained as can be seen from Comparative Examples 1 and 2 and Example 1, and
Inferior wear resistance. It can be seen from Example 3 and Comparative Example 3 that the corrosion resistance is lowered when the Si ₃ N ₄ addition amount exceeds 50% by weight.

It can be seen from Examples 4 and Comparative Example 4 that the spalling resistance is lowered when the amount of BN added is less than 20% by weight.

It can be seen from Comparative Example 6 and Example 7 that the strength is low when the added amounts of Al and Si are less than 10% by weight. It also has low corrosion resistance and wear resistance. When it is more than 50% by weight, it can be seen from Example 8 and Comparative Example 7 that the spalling resistance is low.

Then, it was prepared from the formulations shown in Table 2 by the same method as in Table 1.

It can be seen that when the Al / Si ratio is higher than 8/1, digestion becomes easy, and when it is lower than 3/1, both corrosion resistance and spalling resistance are reduced.

Table 3 shows the TD nozzle made from the above refractories (caliber = 20
mm, wall thickness = 17 mm, length = 1 m).

Although the TD nozzle of Comparative Example 1 contains a large amount of BN, Si ₃ N
_{Since 4} was not added, hole clogging occurred, and due to insufficient wear resistance, the diameter increased slightly. Furthermore, the protective tube suffered breakage due to insufficient strength.

In Comparative Example 4, the spalling resistance was insufficient due to the insufficient amount of BN, and cracks were observed.

With the addition of alumina of Comparative Example 5, strength, corrosion resistance, and spalling resistance are not a problem from Table 1, but with the TD nozzle example, hole clogging occurs three times. Brought about a decline.

Comparative Example 6 lacks corrosion resistance due to lack of Al and Si,
The nozzle suffered melting problems.

[Effects of the Invention] The following effects can be achieved by the present invention.

(B) It is possible to solve the problems of insufficient strength and wear resistance, which are the drawbacks of BN-Al-Si reduction products.

(B) The hole blocking resistance was further improved. Corrosion resistance and spalling resistance can be considered satisfactory.

(C) By setting the added Al / Si ratio within the range of 8/1 to 3/1, it is possible to balance the digestion resistance, corrosion resistance, and spalling resistance with each other.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location C04B 35/58 103 U 102 E 102 F 102 T 35/56 101 D D 101 J 101 S

Claims (1)

[Claims] 1. A boron nitride powder mainly composed of a hexagonal system of 20% by weight or more, Si ₃ N ₄ or SiC alone or a mixed powder of 10 to 50% by weight, and an Al / Si ratio of 8/1 to. A mixture of Al and Si powders mixed or alloyed within the range of 3/1 in an amount of 10 to 50% by weight, and a resin which is a carbon product as a binder is further added to form a mixture, and then a sheath filled with carbon powder is formed. A method for producing a highly durable refractory material containing boron nitride, which is characterized in that it is housed inside and fired.