WO2010024497A1

WO2010024497A1 - Refractory repairing material for equipment of iron/steel making, method for preparing thereof and composition comprising the same

Info

Publication number: WO2010024497A1
Application number: PCT/KR2008/006274
Authority: WO
Inventors: Dal Ho Son
Original assignee: Wonjin Worldwide Co., Ltd.
Priority date: 2008-08-29
Filing date: 2008-10-23
Publication date: 2010-03-04
Also published as: JP2010053012A; KR20080099216A; KR100890626B1; CN101434491A

Abstract

Provided is a method for synthesizing a refractory repairing material for equipment of iron/steel making with an excellent sinterability and corrosion resistance, and a monolithic repairing composition to protect equipment of iron/steel including the synthesized material. Specifically, a material including a magnesia (MgO) and silica (SiO2) is powdered and blended so that the content of MgO is present in an amount ranging from 50 to 80wt% based on the repairing material. The resulting mixture is sintered or melted at a high temperature, and synthesized with the material. The monolithic repairing composition to protect equipment of iron/steel making using the synthesized material has an excellent adhesive strength, corrosion resistance and sinterability.

Description

REFRACTORY REPAIRING MATERIAL FOR EQUIPMENT OF IRON/STEEL MAKING, METHOD FOR PREPARING THEREOF AND

COMPOSITION COMPRISING THE SAME [Technical Field] The present invention generally relates to a refractory repairing material for equipment of iron/steel making, a method for preparing thereof, and a composition comprising the same. More specifically, the present invention relates to a method to prepare a refractory repairing material that repairs the interior of various equipment such as a furnace, a ladle and a tundish used in iron/steel making, a repairing material prepared by the method, and repairing composition comprising the material. [Background Art]

For furnaces such as an electric furnace and a convert furnace, refractories are constructed in a container-shaped metal casing or a frame. The inner wall of the furnace requires a cyclic repair process in order to protect the refractories or repair damaged areas after treatment of a predetermined amount of molten steel, except for blast furnaces in which the fire is not extinguished before the refractories of the furnaces are newly constructed once the furnaces starts to operate.

In the furnace, molten steel is filled at a temperature higher than 1500°C, and various chemical reactions such as decarbonization and deoxidation occur. As a result, the furnace wall that contacts the molten steel is damaged by a corrosion effect of the molten steel, which may cause further damage if the partial damage is not properly repaired.

The furnace wall that contacts the molten steel is obtained by constructing refractory bricks, which can maintain their strength without being softened at a high temperature of more than 1500°C as well as endure a chemical reaction.

In other words, the refractory bricks require conditions such as a high refractoriness and strength, and an excellent thermal impact resistance or chemical corrosion resistance. The repair of the furnace wall consisting of the refractory bricks that satisfy the above conditions is divided into reconstruction and partial repair depending on the degree of corrosion and damage. Reconstruction is performed when a portion of the furnace wall is severely damaged and cannot be normalized by surface repair. After this damaged portion is completely removed, the portion is reconstructed with refractory bricks. Reconstruction is also performed when refractory bricks require overall repair at the end of its lifespan. Partial repair is performed when a damaged portion of the surface of the furnace wall is repaired to normalize the furnace wall.

Partial repair is performed while the furnace is maintained in a hot state. The hot repair operation is required because if the furnace is cooled, it would require a considerable amount of energy and time for heating after the repair.

Of the above two furnace wall repair scenarios, partial or overall reconstruction is performed with new refractory bricks to reconstruct the furnace wall, therefore the furnace wall is not easily damaged after reconstruction. However, partial repair is performed by spraying the furnace wall at a hot state, so that when the binding force of the damaged furnace wall with a covered repair layer is incomplete, the repair layer easily comes off by the molten steel. As a result, the damaged portion before the partial repair is additionally damaged, which results in the breaking of the furnace wall.

The repair of the furnace wall by spraying method fills up the damaged furnace wall by spraying repair material onto the wall. In addition to filling up, the repair operation is periodically performed to prevent damage or corrosion of the normal furnace wall due to molten steel of high temperature, thereby forming a coated layer to protect the furnace wall over the surface of the furnace wall to prolong the lifespan of the furnace wall.

To prolong the lifespan of either normal furnace wall or damaged one, a spray material used in the partial repair using the spraying method performed at a hot state is sprayed on the furnace wall with a spray gun so as to adhere to the surface of the furnace wall while the spray material is mixed with water under high pressure. The spray material as a refractory material requires excellent adhesiveness with refractory bricks constituting the furnace wall and corrosion resistance as well as a short curing time. Moreover, the spray material must not spall or peel after spraying.

For silica-based inorganic binders which have been widely used as the spray material, its effect has been degraded as operation conditions of the furnace become severe gradually for improvement of the quality of steel. As a result, spray material which includes magnesia (MgO) or dolomite and a binder with a high melting point, has been developed. However, the spray material thus obtained has a low resistance to corrosion and adhesiveness. That is, the spray material that includes magnesia or dolomite is short of sinterability, so that moisture is evaporated rapidly when the spray material adheres to the furnace wall by spraying at a high temperature, thereby degrading the adhesiveness to the furnace wall.

The adhesiveness of the spray material depends on the temperature of the furnace wall. Since the spray operation is performed at a temperature of over 800°C, the spray material does not adhere to the furnace wall but may rebound from the surface of the furnace wall by repulsion of high vapor pressure generated while water sprayed with the spray material is rapidly evaporated. Moreover, since the state of the spray material adhered to the furnace wall is unstable by repulsion due to the vapor pressure, it easily falls off by a molten steel vortex or injection impact of scrap iron after the repair operation.

That is, the hot-sprayed material that has a weak adhesive strength may easily be damaged before the spray material forms a strong ceramic binding with the surface of the furnace wall while sintering by heat of the furnace wall. Therefore, although the sintering operation should be rapidly performed, the spray material that includes magnesia or dolomite as a main element requires a long sintering time, the initial rate the spray falls off is high, thereby decreasing the efficiency of protecting furnace wall.

In order to solve the shortcoming of the spray material that includes magnesia or dolomite as a main element, carbon-based spray materials have been developed. For carbon-based spray materials, the binder is carbonized by the heat of the furnace after spraying, thereby generating a carbon bond, this improves corrosion resistance and adhesive strength. However, it is difficult to mix moisture during the repair operation with a resin or pitch used to generate a carbon bond. Furthermore, there exist the problems that the carbon material requires a long duration for adhering to the furnace wall by carbonization, that is, curing takes time, and the carbon materials may be oxidized by water and air.

Meanwhile, monolithic forsterite-based repairing material, which has been conventionally used for equipment of iron/steel making, include MgO-SiO₂-based materials such as natural olivine, olivine, serpentine and talc with or without sintering. However, conventional monolithic forsterite materials have a large amount of impurities such as Fθ₂θ₃, form crystalline phase of forsterite partially and have low compactness, therefore the conventional monolithic forsterite materials have a weaker resistance to corrosion compared to that of monolithic magnesia repairing materials. As a result, it is difficult to commercialize monolithic forsterite materials. [Disclosure] [Technical Object] Various embodiments of the present invention are directed at providing a method for preparing a repairing material that includes forsterite as the main mineral fades, and a repairing composition for equipment of iron/steel making using the material obtained by the method. [Technical Solution]

There is provided a method for preparing the repairing material for equipment of iron/steel making not by using a natural forsterite mineral but by synthesizing the material so that it can have forsterite mineral facies with a combination of necessary materials. According to an embodiment of the present invention, a method to prepare a refractory repairing material for equipment of iron/steel making comprises sintering or melting (A) one or more minerals selected from the group consisting of magnesite, light burned magnesia and sintered magnesia; and at least one or more minerals selected from the following (B) and (C).

The sintered magnesia may include dead burned magnesia (DBM) and the like. (B) includes one or more minerals selected from the group consisting of olivine, serpentine, talc and pyroxene, and (C) includes one or more minerals selected from the group consisting of silica stone and silica sand.

The method to prepare a refractory repairing material for equipment of iron/steel making by using sintering process comprises: milling and mixing (A) one or more minerals selected from the group consisting of magnesite, light burned magnesia and sintered magnesia; and at least one or more minerals selected from the above (B) and (C); molding and drying the milled and mixed minerals; and sintering the dried mold minerals.

Also, the method to prepare a refractory repairing material for equipment of iron/steel making by using melting process comprises: milling and mixing (A) one or more minerals selected from the group consisting of magnesite, light burned magnesia and sintered magnesia; and at least one or more minerals selected from the above (B) and (C); and melting the milled and mixed minerals.

In the method, the milling and mixing is performed such that the final content of magnesia is present in an amount ranging from 50 to 80 wt%, preferably from 60 to 70wt%, based on a prepared material. The minerals may be milled then mixed, or mixed then milled.

The prepared refractory repairing material includes forsterite as the main mineral facies and periclase as subsidiary mineral facies.

Specifically, in order to prepare a refractory repairing material of the present invention, the above start materials are milled. In the case of using the sintering process, it is preferable to pulverize the materials into fine powders. In case of using the melting process, it is preferable to mill the materials into coarse particles (less than 10mm in particle diameter).

After the start materials are weighed so that the final content of magnesia is present in an amount ranging from 50 to 80 wt%, preferably from 60 to 70wt%, based on a prepared material, moisture is added in a blender, and mixed without localization for more than 20 minutes.

In the case of using the sintering process, the well-mixed material is molded with a molding machine to have a ball or brick shape, and dried. The drying temperature is greater than 110⁰C, which is applied for over 10 hours to remove the moisture.

The dried ball or brick shaped molded material is charged in a sintering furnace, and the sintering is performed at a temperature of over 1500⁰C, preferably ranging from 1500 to 1800⁰C, for over 3 hours so as to form a compact sintered material and forsterite mineral facies.

In the case of using the melting process, the well-mixed material is injected into a melting furnace, and melted. Then, the molten materials are cooled by a natural drying method, and a melted ingot is milled or cut into a desired size to be used as a repairing material.

The melting is performed at a temperature ranging from 1850 to 2200⁰C, although this can vary depending on composition of the mixed material.

There is also provided a refractory repairing material for equipment of iron/steel making prepared by the above-described method.

Additionally, there is provided a refractory repairing composition for equipment of iron/steel making that comprises the above-described refractory repairing material, and optionally comprising magnesia.

The refractory repairing composition may further include a silica-based binder or a phosphoric acid-based binder.

In order to prepare the repairing composition the repairing material prepared through sintering is milled, and mixed with either magnesia or a binder.

The equipment of iron/steel making may include one selected from the group consisting of an electric furnace, a convert furnace, a ladle, a Rheinstahl Heraeus (RH) snorkel and a tundish, which cannot be limited herein but can be applied in any equipment that requires repair by molten steel at a high temperature.

The refractory repairing composition may be applied by spraying or coating so as to adhere easily to the inner wall of the equipment. [Advantageous Effects] A monolithic repairing composition made of the material prepared by the present method for synthesizing a forsterite material can improve the lifespan of refractory materials of iron and steel making with excellent sintering property and corrosion resistance. [Best Modes] As described above, a method for combining magnesite (MgCU3), light burned magnesia, sintered magnesia, olivine, serpentine, pyroxene, silica stone and silica sand as magnesia (MgO) sources and silica (Siθ₂) sources so that the content of magnesia (MgO) of forsterite mineral fades theoretically may be present in an amount ranging from 50 to 80wt%, preferably from 60 to 70wt%, and milling, sintering at a high temperature or melting the resulting combination to synthesize a repairing material for equipment of iron/steel making.

A monolithic repairing composition applied with the synthesized material made by the above preparing method is more resistant to corrosion rather than that of a monolithic repairing composition applied with a conventional

based material, and also has a better sintering property and corrosion resistance rather than a general monolithic magnesia repairing composition, thereby prolonging the lifespan of refractory materials.

As shown in Table 1, since a conventional olivine-based material has a low melting point, corrosion may increase when the olivine material is applied at a temperature ranging from 1550 to 1700⁰C for iron/steel making. As a result, forsterite material is synthesized to improve corrosion resistance.

[Table 1]

The present invention will be described in further detail with reference to the following examples. The following examples are illustrative, and thus are not limitative of the present invention.

Table 2 shows chemical ingredients of start materials to prepare a repairing material of the present invention. [Table 2]

* LO. I: Loss of Ignition

Table 3 shows the mixing ratio of start materials in conventional examples, present examples and comparative examples. The conventional examples include a conventional repairing material. In the comparative examples, the final content of magnesia is out of the range of the present invention.

The start materials in Table 3 are mixed, and milled into fine powders to mold the materials with a size of 230 x 114 x 65mm. The molded materials are dried in a drying furnace at 110°C for 24 hours, and sintered in a Shuttle Kiln at 1500°C for 3 hours. Also, Table 3 shows the property of the synthesized materials.

LfI

X -1

Q H) Q) (D

3

^■π

^. fD Q. S¹

S¹ Q) cn (D

Q⁾ cn TJ

3 cn

3^" O

(D o cn o (D (D

^■σ X n Q) Q)

—1

C cn Q) 3

.3

(D

3^' rp_ cn

(D cn π

ZT n (D

3 cn

Q) Q) n 3

(D Q.

(D Q⁾ CΛ

N-

Q. (D

T3 Q). Q. (D

—j U) O

Q) n Q) 0

(D

3 3 •α

Q⁾ cn

.3 3 fl> Q) Q)

(D

b^le es ^l pa^r change are tested and measured by KSL 3503 and KSL 3117, respectively. As for testing the adhesive strength, each of the above compositions are adhered to the surface of refractory bricks of the walls of a steel-making furnace by coating them at a thickness of 5mm over the surface and sintered at 1350º'. Then, a steel ball of IKg is dropped off ten times from the height of 50cm to the surface of the bricks, thereby generating a crack in the sintered composition layer.

V represents when a complete crack is generated,

represents when a crack occurs, and

represents when there is no crack or when a fine crack is generated only in the site where the steel ball is dropped.

As shown in Table 4, the refractory material used to spray an electric furnace applied with the synthesized material prepared by the method of the present invention shows the high adhesive strength and corrosion resistance.

Claims

[What is Claimed is]

1. A method to prepare a refractory repairing material for equipment of iron/steel making, the method comprising sintering or melting (A) one or more minerals selected from the group consisting of magnesite, light burned magnesia and sintered magnesia; and at least one or more minerals selected from the following (B) and (C):

(B) one or more minerals selected from the group consisting of olivine, serpentine, talc and pyroxene; and

(C) one or more minerals selected from the group consisting of silica stone and silica sand.

2. The method according to claim 1, wherein the method comprises: milling and mixing (A) one or more minerals selected from the group consisting of magnesite, light burned magnesia and sintered magnesia; and at least one or more minerals selected from the above (B) and (C); molding and drying the milled and mixed minerals; and sintering the dried mold minerals.

3. The method according to claim 1, wherein the method comprises: milling and mixing (A) one or more minerals selected from the group consisting of magnesite, light burned magnesia and sintered magnesia; and at least one or more minerals selected from the above (B) and (C); and melting the milled and mixed minerals.

4. The method according to claim 2 or 3, wherein the milling and mixing is performed such that the final content of magnesia is present in an amount ranging from 50 to 80 wt% based on a prepared material.

5. The method according to claim 4, wherein the milling and mixing is performed such that the final content of magnesia is present in an amount ranging from 60 to 70wt% based on a prepared material.

6. The method according to claim 1, wherein the prepared refractory repairing material includes forsterite as the main mineral facies and periclase as subsidiary mineral facies.

7. The method according to claim 1 or 2, wherein sintering is performed at a temperature ranging from 1500 to 1800⁰C.

8. The method according to claim 1 or 3, wherein melting is performed at a temperature ranging from 1850 to 2200⁰C.

9. A refractory repairing material for equipment of iron/steel making, the material prepared by the method described in one of claims 1 to 3.

10. A refractory repairing composition for equipment of iron/steel making, the material comprising the refractory repairing material described in one of claims 1 and 3, and optionally comprising magnesia.

11. The refractory repairing composition according to claim 10, further comprising a silica-based binder or a phosphoric acid-based binder.

12. The refractory repairing composition according to claim 10, wherein the equipment of iron/steel making includes one selected from the group consisting of an electric furnace, a convert furnace, a ladle, a Rheinstahl Heraeus (RH) snorkel and a tundish.

13. The refractory repairing composition according to claim 10, wherein the refractory repairing composition is applied by spraying or coating.