JPH11263674A - Ramming material for lining induction furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ramming material which has as a lining material for an induction furnace, such excellent permeation-inhibitory properties that the permeation of volatile components contained in a molten metal as impurities, such as Zn and fat and oil, from the working surface of the ramming material can be inhibited, and also, excellent heat resistance, excellent corrosion resistance, excellent thermal shock resistance and excellent proper sinterability of the working surface side. SOLUTION: This material is obtained by blending 100 pts.wt. of a composition consisting of boric acid used as a sintering additive, natural silica that has a >=98 wt.% SiO2 component content and <=5 mm grain size, and fused silica that has a >=98 wt.% Sin, component content and has <=5 mm grain size, with 0.1 to 1.0 pts.wt. of hydrous amorphous silicon dioxide having a 100 to 500 m<2> /g specific surface area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ramming material used as a lining material for an induction furnace for melting metals such as cast iron, and more particularly, to a ramming material used as a lining material for an induction furnace and contained as an impurity in molten metal. Furnace that excels in permeation suppression that can prevent infiltration of vaporized components such as Zn and oils and fats from the working surface, and has excellent heat resistance, corrosion resistance, thermal shock resistance, and excellent sinterability on the working surface side Ramming material for lining.

[0002]

2. Description of the Related Art As a lining material of an induction furnace for melting cast iron or the like, a natural siliceous ramming material containing boric acid as a sintering binder or a mixture of natural silica containing boric acid as a sintering binder and fused silica are conventionally used. Ramming materials and the like have been commonly used. It is desirable that the metal material such as pig iron to be melted and processed in the induction furnace contains as little impurities and as little deposits as possible. In recent years, however, materials containing a large amount of zinc (Zn) or fats and oils as impurities or deposits must be dissolved. The number of cases that must be increased. When a material containing a large amount of these Zn components and fats and oils is melted, Zn and fats and oils vaporized during the melting of the materials penetrate into the inside from the working surface of the ramming material, which is the lining material of the induction furnace, and the back side A part of the vaporized Zn reaches the coil side of the non-working surface and is cooled on the coil side of the non-working surface and solidifies as metallic zinc.

[0003] Further, a part of the vaporized oils and fats is carbonized by decomposition in a ramming material as a lining material and precipitates,
These solidified or precipitated metal Zn and carbonized are:
The insulating property of the ramming material as the lining material is reduced.
This decrease in insulation of the lining material causes a malfunction of a leak detection circuit provided as a safety measure to prevent a leak of the induction furnace from occurring, and significantly shortens its life. In some cases, a short circuit may occur between the coils due to metal Zn adhering to the vicinity of the coils, which may lead to coil damage or water leakage due to sparks.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned technical problems, and is excellent in heat resistance, corrosion resistance, thermal shock resistance, and proper sinterability on the working surface side. Not only Z
It is an object of the present invention to provide a ramming material capable of suppressing and preventing infiltration of n and fats and oils into a vaporized component.

[0005]

According to the present invention, SiO 2 is used.
_A composition comprising 98% by weight or more of ₂ components, natural silica having a particle size of 5mm or less, fused silica having a particle size of 5mm or less containing 98% by weight or more of SiO ₂ component, and boric acid as a sintering material A ramming material for lining an induction furnace, characterized in that 0.1 to 1.0 part by weight of hydrous amorphous silicon dioxide having a specific surface area of 100 to 500 m ² / g is added to 100 parts by weight. The ramming material of the present invention is composed of fused silica and natural silica mixed with boric acid as a sintering aid in two types of silica base powders, and in a small specific mixing range,
It is a remarkable feature that it is formed by combining hydrous amorphous silicon dioxide having a specific specific surface area.

[0006] Hydrous amorphous silicon dioxide is generally obtained by melting a silica raw material such as silica sand with an alkali, making the resulting aqueous solution of alkali silicate acidic, and drying the resulting precipitate as a dried porous substance. So-called silica gel is a typical example, but in the present invention, among hydrous amorphous silicon dioxide, powdery particles having a relatively large specific surface area of 100 to 500 m ² / g are used. The hydrous amorphous silicon dioxide powder is composed of secondary particles in which spherical fine single particles (primary particles) of about 20 to 30 nm are aggregated in a grape shape,
The surface area is large, and because it is amorphous, it is much more reactive than crystalline silica particles such as the base material, and easily reacts with other substances such as boric acid from a relatively low temperature to be fusible. To produce a glass phase. In the present invention, by blending a specific amount of the hydrous amorphous silicon dioxide powder in combination with boric acid as a sintering material, the two interact to exert a synergistic effect, and both fused and natural silica base powder particles To close the gaps between the particles and effectively achieve the effect of suppressing the permeability of the lining material from the initial stage of the temperature increase after the furnace construction.

Although the mechanism by which this specific action and effect is achieved is not necessarily completely elucidated, it is present in the structure of the ramming material due to heat generation of a metal such as cast iron induced by a high-frequency current. This specific hydrous amorphous silicon dioxide and boric acid as a sintering aid are
Reacts relatively early in the temperature rise to form a glass phase,
It is presumed that this acts to fuse the gaps between the base silica particles, thereby closing the air-permeable pores inside the lining material. The induction furnace lining material is generally formed and constructed by ramming the above-described ramming material with an air rammer or the like,
At the time of furnace construction, there are countless fine pores in the base material particle gap.

In the early stage of operation of the induction furnace, before a sufficiently dense sintered layer is formed on the operation surface of the lining material, vapors of Zn, fats and the like vaporized in the molten metal are formed. When passing through these pore paths and reaching the back side (the coil side of the non-operating surface), the once formed steam path is not easily closed, and remains as a vapor passing pore path to the end. Therefore, in order to suppress and prevent the infiltration of vaporized components such as generated Zn and oils and fats into the inside, at the stage before the vaporized component vapor passage is formed at the initial stage of the operation of the induction furnace, air permeable pores are formed in the lining material. It is important that the particle gap fusing action to be closed is initiated. The present invention achieves, for the first time, pore blocking at the initial stage of operation of an induction furnace for a ramming material by the above configuration.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The ramming material for an induction furnace according to the present invention comprises:
As described above, the mixture is composed of a mixture of two kinds of silica base powder, boric acid as a sintering aid, and a specific hydrated amorphous silicon dioxide used in combination therewith. The boric acid powder as a sintering aid used in the induction furnace lining ramming material of the present invention is for forming an appropriate sintered layer on the operating surface of the induction furnace lining material. Is an important effect of promoting synergistic action with water-containing amorphous silicon dioxide having a specific surface area of 100 to 500 m ² / g to suppress the permeability of the lining material from the early stage of operating temperature rise after the construction of the furnace. Has both. The amount of boric acid added as the sintering aid is 0.02 to 1.2% by weight based on hydrated boric acid.
Particularly preferably, it is in the range of 0.05 to 1% by weight.
If the added amount of boric acid is less than 0.02% by weight based on hydrated boric acid, not only is it difficult to form a dense sintered layer having an appropriate thickness on the working surface side of the lining material, but also it is difficult to form the hydrated material. The synergistic effect with crystalline silicon dioxide is also reduced. On the other hand, when the added amount of boric acid exceeds 1.2% by weight, a sufficient sintered layer is formed on the working surface side, but the heat resistance of the lining material itself is greatly reduced and the corrosion resistance is also reduced.

Next, in the present invention, the fused silica powder as a silica base material constituting the ramming material includes S
Fused silica powder having an iO ₂ purity of 98% or more, preferably 98.5% or more and a particle size of 5 mm or less, preferably 4.8 mm or less is used. Fused silica has a small coefficient of thermal expansion, a purity of 98% by weight or more, and a particle size of 5 mm.
By blending the following fused silica powder, imparts excellent thermal shock resistance to the ramming material of the present invention, suppresses the occurrence of cracks, and even if cracks occur on the operating surface, the expansion of the cracks, It has the effect of inhibiting progress.

[0011] Fused silica powder having a SiO ₂ purity of 98% or less is not preferred because heat resistance is inferior and corrosion resistance to molten metal and various slags is reduced.
When the material is not less than mm, particle size segregation is apt to occur at the time of material input or vibration filling, and it is difficult to form a molded body having a uniform structure and sufficient strength as an induction furnace lining material, which is not preferable. In the ramming material of the present invention, 30 to 80% by weight, particularly preferably 35 to 7% by weight of the fused silica powder is used.
It is preferable to mix in a range of 5% by weight. If the blended amount of the fused silica powder is less than 30% by weight, the effect of improving the thermal shock resistance of the ramming material does not appear remarkably, and if it exceeds 80% by weight, the residual swelling property is reduced. The effect of suppressing generation is reduced.

As the natural silica powder used in combination with the above-mentioned fused silica base powder, crushed products or powders of natural silica produced in Japan and around the world can be used. Further, even among these natural silicas, the purity of SiO _{2 is} 98% or more, preferably 98.5.
% Or more and a particle size of 5 mm or less, preferably 4.5 mm
Use the following. The natural silica has a characteristic of being excellent in corrosion resistance and imparts excellent corrosion resistance to the ramming material of the present invention. Further, it has such characteristics that the coefficient of thermal expansion is relatively large, and further, the residual expandability is recognized after heating and cooling. Natural silica powder having an SiO ₂ purity of 98% or less is not preferred because heat resistance is inferior and corrosion resistance to molten metal and various slags is unfavorable. Particle size segregation easily occurs at the time of filling, and it is difficult to form a molded body having sufficient strength with a uniform structure as an induction furnace lining material, which is not preferable.

In the present invention, the amount of the natural silica powder is the balance of the total amount of the fused silica and the sintering aid with respect to the total amount of the ramming material. If the added amount of the natural silica is less than 15% by weight, not only the corrosion resistance of the ramming material is deteriorated, but also a proper residual expansion property cannot be obtained.
If the amount exceeds 70% by weight, the corrosion resistance is improved, but the coefficient of thermal expansion is too large, and the thermal shock resistance tends to be reduced. The addition amount of the natural silica powder is particularly preferably from 25 to 65% by weight from the above viewpoint.

The hydrated amorphous silicon dioxide which is added to the composition comprising the above fused silica, natural silica base and boric acid sintering aid in the ramming material of the present invention has a specific surface area of 1%.
Powder of a porous amorphous hydrous silicon dioxide substance in the range of from 00 to 500 m ² / g, preferably in the range of from 150 to 450 m ² / g, for example, SiOH groups or coordinating or chemically adsorbed H _A particulate powder made of silica gel, porous glass or the like having ₂ O is used.

The water-containing amorphous silicon dioxide powder particles used in the present invention are generally composed of particles (secondary particles) in which fine spherical single particles (primary particles) of about 20 to 30 nm are aggregated in a grape-like manner. Although the particle size and the like of the powder are not necessarily limited to this, the average particle size is 1.8 to 2.8 μm.
It is preferable to use those having a diameter of about m. Such a powder is obtained by, for example, melting a silica raw material such as silica sand with an alkali, acidifying an aqueous solution of the obtained alkali silicate, and pulverizing a resulting porous material such as silica gel or the like into a powder by drying a dried precipitate. Although it can be prepared by a method such as obtaining it, it can also be procured by selecting from commercially available products, for example, carplex and the like can be mentioned as commercially available products. When an appropriate amount of the water-containing amorphous silicon dioxide powder particles is added to the ramming material, the particles enter the gaps between the particles of the ramming material and suppress the air permeability of the filled lining material.

The amount of the water-containing amorphous silicon dioxide powder added is
0.02 to 1.2% by weight of boric acid as a sintering aid, 30 to 80% by weight of fused silica, and 0.1 to 1.0 part by weight based on 100 parts by weight of a composition composed of natural silica.
Preferably it is 0.15 to 0.9 parts by weight. If the amount of the water-containing amorphous silicon dioxide powder is less than 0.1% by weight, the effect of suppressing the permeability of the ramming material is small, and if it exceeds 1.0% by weight, the filling property during furnace construction is reduced.

The ramming material of the present invention is prepared by adding a predetermined amount of hydrous amorphous silicon dioxide powder to a mixed powder composition comprising the above-mentioned boric acid, fused silica powder and natural silica powder in a predetermined ratio. The ramming material of the present invention obtained in this manner can be used as a lining material to build an induction furnace by using a method similar to a conventional method. For example, in the case of a high-frequency induction furnace, After setting a heat insulating sheet on the inner surface of the coil-protecting refractory inside the coil, a predetermined amount of the ramming material is charged into the hearth and filled with an air rammer.

Next, after finishing the hearth construction surface smoothly,
The furnace-building cylinder is set at the center of the hearth, and a predetermined amount of ramming material is charged into the furnace wall between the furnace-building cylinder and the heat insulating sheet and filled with an air rammer. The furnace wall is extended to the upper part while repeating the above operation, and the furnace is completed by filling up to the furnace upper part. A raw material such as pig iron is charged into a lining material container of the furnace thus constructed, and a coil is energized to melt the raw material metal.

[0019]

EXAMPLES Examples 1 to 8 Fused silica powder (SiO 2)
₂ 98.5% pure, and natural silica rock powder (SiO ₂ purity 98.5% particle diameter 5mm or less), particle size 5mm or less) and a sintering aid (Arimizu borate crystal powder) and respectively Table 1, Table 2 Was added to the powder mixture blended in the amount shown in the above, specific surface area 200 m ² / g,
Hydrous amorphous silicon dioxide powder having an average particle size of 2.3 μm was added in the amounts shown in Tables 1 and 2, respectively, and mixed to prepare test materials for each induction furnace ramming material (Examples 1 to 3). 8).
The test materials of Examples 1 to 8 were prepared according to JIS R 2574.
The ramming material of each ramming material was evaluated by hitting and filling 100 times with a molding rammer for -77. Also, the height 5 obtained by impact-filling and molding 100 times with the molding rammer is obtained.
In a state where the test piece of 0 mm was not removed from the molding cylinder, the test piece was set in the air permeability measuring device shown in FIG. 1 and the air permeability was measured to evaluate the air permeability of each test piece. Furthermore, instead of the molding cylinder of the molding rammer, the inner diameter is 5 mm.
Using a 0 mm paper tube, the test materials of Examples 1 to 8 shown in Table 1 and Table 2 were charged 100 times and each test material was charged in a predetermined amount so that a test piece having a height of 50 mm was obtained. 100
A round-filled test piece with a height of 50 mm was obtained, which was heated to 900 ° C. in a resistance heating electric furnace, cooled, and then set in a permeability measuring device shown in FIG. The air permeability was evaluated. 1 and 2, reference numeral 1 denotes a ramming material molded body sample, 2 denotes a molding cylinder, 3 denotes a manometer, 4 denotes a side seal material, 5 denotes a measuring instrument main body, and 6 denotes a cylinder with a scale. The water level and the pressure in the measuring instrument body indicated by reference numeral 5 before the measurement after the piece set are constant when the cock above the graduated cylinder indicated by reference numeral 6 is opened, and when the cock above the graduated cylinder is opened. Wait until the fall stops. Thereafter, the cock between the manometer and the measuring instrument body was opened for 30 seconds, and the amount of water dropped into the graduated cylinder was measured, and indicated by an index of the amount of ventilation. Further, the compression strength of the test piece was measured by a compression tester. Tables 1 and 2 show the results of these evaluations.

"Comparative Examples 1 to 5 and Reference Example 1" As shown in Table 3, test materials having the same formulation as in Examples 1 to 3 except that no water-containing amorphous silicon dioxide powder was added (Comparative Example 1) 1 to 3), and a test material to which a water-containing amorphous silicon dioxide powder was added in an amount equal to or less than a specified lower limit of the present invention (Comparative Example 4); Further, test materials (Reference Example 1) containing a large amount of hydrated boric acid as much as 1.5% by weight were prepared, treated in the same manner as in the above Examples, and evaluated in the same manner. Table 3 shows the results. From the results shown in Tables 1 to 3, the ramming materials of Examples 1 to 8 show good performance in all properties such as filling property, air-suppressing effect, strength and the like. In the case of the ramming material added with not less than 0.0% by weight (Comparative Example 5: the added amount is 1.1% by weight), the filling property is greatly reduced, and the ramming material not containing the hydrated amorphous silicon dioxide (Comparative Examples 1 to 3), To 0.
It can be seen that the ramming material of not more than 05% by weight (Comparative Example 4) has almost no ventilation suppression effect.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

In Tables 1 to 3, (○) indicates that the evaluation of the filling property is excellent, (良好) indicates that the evaluation is satisfactory, and (x) indicates that the evaluation is inferior. Regarding the evaluation of air permeability control, the air flow rate of Comparative Example 9 was set to 100 (index), and when the air flow rate (index) was 69 or less, (優) was displayed as excellent and the air flow rate (index) was 69. When the airflow rate (index) is 71 or more, (△) is displayed as poor when the air permeability (index) is 71 or more. Further, regarding the strength evaluation, when the compressive strength is 0.6 MPa or more and 4.9 MPa or less, (○) is displayed as excellent, and the strength exceeds 0.4 MPa and 0.6 MPa or more.
When the value is less than or more than 4.9 MPa and less than 5.1 MPa, (△) is displayed as good, and when it is 0.4 MPa or less or 5.1 MPa or more, poor (×) is displayed. .

[0025]

The ramming material for an induction furnace according to the present invention has a corrosion resistance and a thermal shock resistance when it is lined with an induction furnace wall by the above-described structure, and a dense sintered layer having an appropriate thickness on a working surface. In addition to the characteristics of the conventional ramming material such as being formed, the ventilation of the lining material can be significantly reduced. In the case of a 10-ton medium-frequency induction furnace in which a material containing a large amount of Zn components and fats and oils is melted, when the conventional ramming material is repeatedly melted about 250 times, even if the remaining thickness of the lining material is sufficient. ,
Under the influence of infiltrated Zn components and carbon from oils and fats, the insulation of the lining material decreases, and the hot water leak detector frequently malfunctions,
The furnace had to be dismantled and rebuilt, but by lining the ramming material of the present invention, Zn
When a material containing a large amount of components and fats and oils is not dissolved, the material can be repeatedly melted for about 300 to 330 times in a normal material life, and the durability can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a schematic view of an air flow measurement device in a state of air flow measurement of a molded ramming material immediately after molding.

FIG. 2 is a schematic diagram of an air flow measuring device in a state where air flow of a molded ramming material after heating and cooling at 900 ° C. is measured.

[Explanation of symbols]

 Reference Signs List 1 Ramming material molded sample 2 Molding cylinder 3 Manometer 4 Side seal material 5 Measuring instrument body 6 Cylinder with scale

Claims (4)

[Claims] 1. A composition containing 98% by weight or more of a SiO ₂ component,
With respect to 100 parts by weight of a composition comprising 98% by weight or more of natural silica having a particle size of 5 mm or less and a SiO ₂ component and having a particle size of 5 mm or less and boric acid as a sintering material,
A ramming material for lining an induction furnace, comprising 0.1 to 1.0 parts by weight of hydrous amorphous silicon dioxide having a specific surface area of 100 to 500 m ² / g. 2. The ramming material for lining an induction furnace according to claim 1, wherein the boric acid as the sintering material is contained in an amount of 0.02 to 1.2% by weight based on hydrated boric acid. 3. The ramming material for lining an induction furnace according to claim 2, wherein the water-containing amorphous silicon dioxide has a SiO ₂ purity of 90% by weight or more. 4. The composition according to claim 1, wherein said composition is a fused silica of 30 to 80.
The induction furnace lining according to any one of claims 1 to 3, wherein the composition is a composition composed of 0.02 to 1.2% by weight of a boric acid sintered material and the balance being natural silica. Ramming material.