JPH024649B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a molded article for blowing gas into molten metal.

In recent years, in order to improve the quality of steel, for example, gas is blown into molten metal through a porous plug,
Desulfurization or degassing and separation of nonmetallic inclusions are performed.

The porous plug is subject to erosion and abrasion by the stirring molten metal flow, and when the ladle is empty, the wear and tear is significant due to spalling due to cooling.

Therefore, various attempts have been made to improve the material and structure of molded bodies for gas injection, such as porous plugs.

The molded body must have a uniform pore size,
It is desired that the material not form a sintered layer during use and that it has high hot strength, but currently corundum, mullite, and basic materials are often used. but,
These materials tend to form a sintered layer, and because molten steel penetrates from the surface of use, uniform bubbling is not possible. The degree of progress is not constant due to the progress of oxidation and contraction, resulting in pore blockage, pore formation, uneven distribution (and decrease in porosity), and changes in operating surfaces (when used multiple times). Therefore, gas injection cannot be performed uniformly throughout the entire operation and cannot be performed at a fixed location. Moreover, it could not be said to be satisfactory as it was easy to cause structural spalling.

The gas-blown molded article of the present invention improves this drawback, and contains 4 to 50% by weight of carbon powder and a binder.
It is characterized by being a fireproof material containing 20% by weight or less, with the remainder consisting of magnesia, spinel, or a combination thereof.

By adding 4 to 50% by weight of carbon powder, fine pores can be created by removing volatile matter from the binder and turning it into coke. It also helps prevent sintering during use and maintains uniform micropores. Furthermore, it reduces wetting with molten steel, prevents metal insertion, and increases corrosion resistance and cooling resistance. This was confirmed by measuring the pore size distribution, and was also determined from the fact that the spalling resistance and corrosion resistance did not deteriorate significantly even as the service life increased.

When the amount of carbon powder is less than 4% by weight, a sintered layer is likely to be formed, and the wetting to molten steel becomes large, corrosion resistance is poor, and fine pore formation and uniform maintenance of fine pores during use cannot be achieved.

When the amount of carbon powder exceeds 50% by weight, oxidation resistance and strength are extremely reduced. In addition, since it is difficult to sinter, the joints can be separated easily when replacing the plug, and the plug can be easily removed and is less likely to be damaged. In addition, since there is no bare metal and it contains carbonaceous material, oxygen cleaning of the plug after multiple uses can be done effectively in a short time.

Also, if it is necessary to impart oxidation resistance,
It is preferable to impart oxidation resistance by adding silicon carbide powder, silica powder, etc., but the strength is slightly inferior to that of the above-mentioned Si.

Further, the content of these silicon carbide powders and silica powders is 10% by weight or less, preferably 5% by weight or less.

The magnesia refractory material preferably has a content of 70 to 95% by weight, and if it is less than 70% by weight, the characteristics of the refractory aggregate cannot be fully utilized, resulting in loss of corrosion resistance and wear resistance. If it exceeds 95% by weight, the characteristics will be too biased only to the refractory aggregate, the spalling resistance will decrease, it will be easy to sinter during use, and uniform fine pores will not be maintained. The binder promotes fine pore formation by using a binder that remains in the form of carbon when heated, such as pitch, phenolic resin, or other resin. That is, by removing volatile matter from the binder and turning it into coke, it creates fine pores and carbon bonding, thereby imparting strength.The appropriate amount is 20% by weight or less, and if it exceeds 20% by weight, the strength will be insufficient.

Further, the refractory aggregate is appropriately selected from known magnesia materials, but from the viewpoint of corrosion resistance and abrasion resistance, it is preferable to use one with as high a purity as possible, and MgO of 95% by weight or more is preferable.

The spinel may be of theoretical value, magnesia rich, or alumina rich.

Sintered alumina, fused alumina, mullite, bauxite, etc. are used as the alumina to be mixed in these, and the sintered alumina preferably contains 95% by weight or more of Al ₂ O ₃ .

Further, the molded article for gas blowing of the present invention contains silicon,
The oxidation resistance and strength of the molded article can be increased by adding aluminum, magnesium, calcium, etc. alone, a mixture thereof, or an alloy thereof.

The molded body for gas blowing is used in the form of a plug, but it can also be molded into a suitable shape such as a sliding plate brick for gas blowing, a nozzle brick, etc. In addition, in the case of a sliding plate brick, the sliding properties are also improved, making it preferable.

Examples will be described below.

First Example: Particle size distribution of 2 to 1 mm diameter and 1 to 0.2 mm diameter
Using magnesia clinker with 98% MgO by weight,
This was mixed with 4% by weight of Coal Pitch as a binder. First, magnesia clinker is placed in a heating mixer and heated and mixed at 190°C for 30 minutes, then pitch is added and heat kneaded for 15 minutes.

Next, add 5% by weight of carbon black and
After heating and kneading for a minute, the clay obtained by allowing it to cool and sizing the crushed pieces was molded into a molded product of 700 kg/cm ² using an oil press.
A truncated conical porous plug base brick with a diameter of 58 mm, a lower surface of 104 mm, and a height of 220 mm was obtained. Then the bare brick
By reducing and firing at 1500℃, magnesia
A carbonaceous porous plug was obtained.

In addition, in the case of firing, it is fired at a temperature of 1200 to 1500°C, and in the case of unfired, it is heat treated at a temperature of 150 to 200°C. The molding pressure is selected between 400 and 700 Kg/ ^cm2 . As a result, the apparent specific gravity is 3.54, the bulk specific gravity is 2.59,
A material with an apparent porosity of 27.1% and a compressive strength of 175 Kg/cm ² was obtained.

Second Example Magnesia clinker with 98% MgO by weight
A raw material for clay was prepared using a spinel clinker containing 67% by weight of Al ₂ O ₃ and 27% by weight of MgO.

First, put both magnesia clinker and spinel clinker in a heated mixer and mix for 30 minutes.
Heat and mix at 190°C, add pitch, and heat and knead for 15 minutes. Next, metal silicon and carbon black were added, heated and kneaded for 10 minutes, allowed to cool, and the resulting clay was crushed and sized, and the resulting clay was molded using an oil press at a pressure of 700 kg/cm ²
A truncated conical porous plug base brick was obtained.
Thereafter, magnesia spinel carbon porous plugs were obtained by reduction firing at 1500°C.

Claims (1)

[Claims] 1. 4 to 50% by weight of carbon powder, 20% by weight of binder
A molded article for gas injection, which is made of a refractory material including the following, the remainder being made of magnesia, spinel, or a combination thereof. 2. The molded article for gas blowing according to claim 1, wherein the binder remains in the form of carbon when heated.