JPH0412064A - Surface treated graphite for monolithic refractory and monolithic refractory for pretreating hot metal - Google Patents

Abstract

PURPOSE:To provide surface treated graphite providing monolithic refractory suppressing occurrence of crack, having excellent durability, etc., by further coating graphite having the surface covered with a resin with a hydrophilic surfactant having low foaming properties. CONSTITUTION:Graphite having the surface coated with a resin is produced by a method of blending graphite (e.g. scaly graphite) with a resin (e.g. pitch) and granulating. Then the surface of the graphite coated with the resin is further covered with a hydrophilic surfactant having low foaming properties to produce surface treated graphite providing monolithic refractory. 1-10wt.% of the prepared surface treated graphite is blended with 5-30wt.% silicon carbide, 1-20wt.% agalmatolite, 1-10wt.% binder and the rest of alumina and (or) alumina silica material, cast into a square frame, dried and burnt to give monolithic refractory for pretreating hot metal having excellent durability.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a monolithic refractory used as a lining in molten iron preliminary treatment such as desiliconization, dephosphorization, and desulfurization of hot metal.

(Prior Art) In recent years, the trend towards high quality steel has progressed significantly, and efficient dephosphorization and desulfurization methods for hot metal have been developed. (Iron and steel 87″-4V
For example, immersion freeboard is suitable for large-volume, high-speed processing using the pot method.

As is clear from the description of FIG. 1, the lower part of the immersed freeboard is immersed in the molten metal 11, and the molten metal 11 is stirred by blowing 02, flux, etc. through the lance 12.

Freeboard 1 immersed in molten metal 11 in this way
3 consists of a cylindrical structure, and as shown in the partially enlarged view of FIG. 2, a core bar 1 is provided approximately at the center of the structure.

The core metal 1 is provided with studs 2, and the core metal 1 is sandwiched between the inner circumferential portion 4 and the outer circumferential portion 5 which are integrally lined with a monolithic refractory 3.

(Problem to be Solved by the Invention) However, since this freeboard 13 is used repeatedly, the entire inner peripheral portion 4 receives a high heat load, increasing the tendency of the lower part of the core bar 1 to open in a trumpet shape. Cracks are very likely to occur due to the action. - Once a crack occurs, the above-mentioned tendency is promoted and it gradually expands, and finally the base metal invades and melts the stud 2 and the core metal 1, causing the monolithic refractory 3 to fall off at an early stage.

In addition, in the outer circumferential portion 5, the slag 14' adheres to the outer circumferential surface and the outer circumferential surface becomes large, so that not only is it necessary to periodically remove the slag 14', but also the slag 14' and the outer circumferential portion 5 are removed. The monolithic refractories 3 were firmly adhered to each other and fell off together, which significantly shortened the durability of the freeboard 13.

Ordinary refractories with excellent spalling resistance have low strength, and if such refractories are used for the outer circumferential portion 5, they will quickly fall off due to the mechanical impact generated when the slag 14 is removed.

On the other hand, refractories with a high level of strength are inferior in durable poling properties, cause cracks and peeling, and are unable to increase the durability of the freeboard 13, so there has been a strong demand for early improvements in these issues.

(Means for Solving the Problems) In view of the above, the present inventors have conducted research and found that cracks in monolithic refractories, especially in freeboards with cored metals, are caused by heat caused by simple thermal cycles. The present invention was completed based on the discovery that the deformation of the core metal due to thermal expansion of the core metal, vibrations and mechanical shock during use, and the buoyancy of hot metal and molten steel has a large effect, in addition to spalling. It is. That is, the present invention is surface-treated graphite for monolithic refractories, which is made of graphite coated with a surface resin and coated with a low-foaming, hydrophilic surfactant. This is a monolithic refractory for hot metal pretreatment consisting of 5 to 30% by weight of waxite, 1 to 20% by weight of waxite, 1 to 10% by weight of binder, and the balance being alumina and/or alumina-siliceous material.

(Function) The monolithic refractory of the present invention is intended to effectively absorb thermal stress generated internally by the refractory and alleviate the stress. Carbon materials include natural graphite, artificial graphite, etc. etc. are used. Particularly, in consideration of high thermal conductivity, low thermal expansion, and cushioning properties due to the layered structure, flaky graphite is most desirable, and graphite 6 whose surface is coated with resin 7 as shown in FIG. 3 is used. As a coating resin.

One or more of tar, pitch, phenol, furan, and resin 7 with high fixed carbon content can be used, and among them, pitch that is compatible with graphite 6 is preferable.

One example of the resin coating is obtained by mixing commercially available scaly graphite and pitch at a ratio of 8=2 at 100 to 250°C and granulating the mixture to about 1 mm or less.

Furthermore, the surface of the resin-coated scale graphite is coated with a hydrophilic and low-foaming surfactant, such as sodium naphthalene sulfonate or sodium gluconate, either alone or in combination, to improve compatibility with added moisture. At the same time, by reducing the foaming caused by the surfactant, it becomes possible to reduce moisture content, thereby making the material more densified and suppressing a decrease in strength compared to untreated materials.

The method of coating with a hydrophilic surfactant is obtained by immersing resin-coated graphite scales in a 10-30% aqueous solution of the surfactant, or by uniformly applying the resin-coated graphite with a sprayer.

In this way, when the graphite 6 coated with the resin 7 is used, the resin softens and penetrates into the matrix, and between the graphite 6 and the matrix, the resin 7 diffuses around the graphite 6 as shown in FIG. A void 8 is formed around the wafer, and this void 8 contributes to the relaxation of thermal stress.

1 to 10% by weight of the surface-treated graphite thus obtained.
Preferably it is added in an amount of 2 to 5% by weight. If it is less than 1% by weight, the above effects cannot be expected, and if it exceeds 10% by weight, fluidity deteriorates and casting becomes difficult.

The silicon carbide material is 5 to 30% by weight, preferably 10 to 20% by weight.
It suppresses oxidation of the carbon material and exhibits high corrosion resistance and durable polling property when added in weight%.If the amount added is less than 5% by weight, the spalling resistance decreases significantly; If it exceeds 5in2, oxidation of silicon carbide itself occurs, resulting in a decrease in corrosion resistance and spalling resistance.

Rouseki has a large residual linear expansion and has a softening property, so even if a crack occurs, it is effective because it closes the crack by its expansion action, but if the amount added is less than 1% by weight, the above effect cannot be obtained, If it exceeds 20% by weight, stress becomes too large due to expansion, loosening the structure and reducing physical properties.

As a binder, alumina cement, sodium silicate,
One or more types such as aluminum phosphate are added in an amount of 1 to 10% by weight, preferably 2 to 5% by weight. If the amount exceeds 10% by weight, the strength development will be excessive, the stress generated per unit will also be large, and the spalling resistance will be reduced.

Conversely, if it is less than 1% by weight, the required strength cannot be obtained.

In particular, in order to increase the hot strength, ultrafine powder such as silica flour, activated alumina, clay, etc. is added as part of the binder.

As the aggregate, any alumina-based raw material such as chamotte, mullite, fused alumina, sintered alumina, andalusite can be used.

(Example) The present invention will be explained below using examples.

The formulations shown in Table 1 were kneaded with a mixer, poured into a freeboard frame, dried at 200'T for 12 hours, and then baked at 1400°C for 3 hours. Created a freeboard.

When the obtained freeboard was actually used in a 300T ladle, the results shown in Table 1 were obtained.

(Effects of the Invention) In the present invention, by limiting the material of the monolithic refractory lining the freeboard and using surface-treated graphite, the internal stress due to expansion deformation of the core metal etc. inherent in the refractory is reduced by the graphite. By absorbing it in the voids formed in the pores, it was possible to suppress the occurrence of cracks, prevent melting and damage of the studs and core metal for a long time, and improve the durability of the freeboard by about 20 to 30%.

Furthermore, the slag removal work can be carried out smoothly in a short time, and its industrial value is great.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an immersed freeboard, FIG. 2 is a partially enlarged sectional view of FIG. 1, and FIGS. 3 and 4 are enlarged schematic diagrams of a carbon material added to a monolithic refractory, FIG. 3 is a state diagram in which the surface of the carbon material is coated with resin, and FIG. 4 is a state diagram in which the resin is heated and diffused to form voids around the carbon material. 1... Core metal 2... Stud 3...
Monolithic refractory 4... Inner circumferential part 5... Outer circumferential part 6... Scaly graphite 7... Resin 11... Molten metal 13... Free board 14, 14''... Slag 8. ...Gap 12...Lance 15...Molten metal container Fig. 1 Fig.

Claims (2)

[Claims] (1) Surface-treated graphite for monolithic refractories, which is characterized by graphite coated with a surface resin and coated with a low-foaming and hydrophilic surfactant. (2) Surface-treated graphite coated with a surface resin and coated with a low-foaming and hydrophilic surfactant, 1 to 10% by weight, 5 to 30% by weight of silicon carbide, 1 to 20% by weight of Rouseki, and binder 1 ~10% by weight and the balance is alumina and/or
Or a monolithic refractory for hot metal pretreatment, characterized by being made of an alumina-siliceous material.