JPH11228242A - Ramming material for induction furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ramming material used for an induction furnace as a material for lining the inner surface of the induction furnace, having excellent corrosion resistance and thermal shock resistance and not causing the advance of a crack to the coil side of a non-operated surface, even when the crack is generated on an operation surface due to the flow friction of a molten metal and thermal shock, because the ramming material forms a compact sintered layer on the operation surface in a proper thickness and leaves a powder layer without being hardened up to the coil side of the non-operated surface, and thereby capable of avoiding the generation of troubles such as the leak of the molten metal. SOLUTION: This ramming material for introduction furnaces comprises 1-7 wt.% of a powdery material having a particle diameter of >=0.5 mm, 30-80 wt.% of molten silica having a SiO2 purity of >=98% and a granule diameter of <=5 mm and the remainder of natural silica having a SiO2 purity of >=98% and a granule diameter of <=5 mm. The powdery particles having the particle diameter of <=0.5 mm are obtained by grinding a sintered product or a molten and solidified product having a porosity of <=2% and comprising 67-77 wt.% of SiO2 component, 18-28 wt.% of Al2 O3 component and totally 2-7 wt.% of at least one kind of component selected from TiO2 , Fe2 O3 , CaO, MgO, Na2 O and K2 O.

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 of an induction furnace for melting cast iron and the like, and more particularly, as a lining material of an induction furnace, a dense sintering layer on a working surface. Is formed with an appropriate thickness, and the non-operating surface is not cured up to the coil side, and the powder layer remains, so it has excellent corrosion resistance and thermal shock resistance, as well as the operating surface due to the flow friction and thermal shock of the molten metal. The present invention relates to a ramming material for an induction furnace that can prevent the occurrence of troubles such as hot metal leaks even when a crack is generated in the non-operating surface, even if the crack is generated.

[0002]

2. Description of the Related Art Conventionally, a lining material of an induction furnace for melting cast iron or the like includes a natural siliceous ramming material containing boric acid as a sintering binder and a natural siliceous material containing boric acid as a sintering binder. Silica-based ramming material,
Alternatively, a high-purity fused siliceous ramming material to which no sintering binder is added has been generally used. In the process of constructing the induction furnace, the lining of the furnace is usually set, for example, by setting a heat insulating sheet 3 on the inner surface side of the coil protection refractory 2 of the induction coil 1 as shown in FIG. Is first charged into the hearth, filled with an air rammer, and after finishing, the furnace-building cylinder 5 is set at the center on the furnace-bed, and the ramming material 4 is further placed between the furnace-building cylinder 5 and the heat insulating sheet 3. It is performed by charging and filling with an air rammer.

In the operation of the induction furnace, a metal to be melted is put into the inside of the lining material formed in the shape of a container, and the coil is energized for induction heating to melt the metal to form a molten metal. This lining material needs to be resistant to physical wear due to the flow friction of the molten metal, wear superimposed with chemical action such as erosion, or damage due to thermal shock, etc. It is preferable that the working surface side forms a dense and hard layer such as a sintered layer during the operation of the induction furnace, while the coil side of the lining material, that is, the non-working surface side is, for example, the working surface side. Even if damages such as cracks occur, a powder layer that is softer and less brittle than the working side layer may remain so that it does not propagate and reach the rear side (the coil side of the non-working side). preferable. However, among the above-mentioned conventional ramming materials, the ramming material to which boric acid is added forms a dense sintered layer near the surface on the working surface side by the addition of boric acid. As a result, the ramming material hardens to the coil side (back side), and the cracks generated on the working surface reach the coil side on the non-working surface. And in extreme cases,
In some cases, problems such as hot water leaks occurred.

On the other hand, a high-purity fused siliceous ramming material to which no sintering binder is added has a low coefficient of thermal expansion, so that cracks are less likely to occur. Although there is a sufficient powder layer and there are few troubles of molten metal leakage, it is difficult to form a dense sintered layer on the operating surface, so chemical erosion due to reaction with the molten metal component and physical melting due to electromagnetic induction stirring action of the molten metal Those which are susceptible to mechanical wear, have poor abrasion resistance, and do not have sufficient durability.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned technical problem, and a dense sintered layer having an appropriate thickness exists on an operating surface. A ramming material for induction furnaces with excellent corrosion resistance, thermal shock resistance, and extremely good durability is provided because a powder layer that is not cured remains on the back side, that is, on the non-operating surface coil side, and both layers are present in a well-balanced manner. It is intended to do so.

[0006]

According to the present invention, SiO 2 is used.
_2-component 67 to 77 wt%, Al ₂ O ₃ component 18 to 2
8% by weight and TiO ₂ , Fe ₂ O ₃ CaO, MgO, N
a ₂ O and K ₂ O at least one component in a total amount of 2 to 7% by weight, and a particle size of 0 to 2% by crushing a sintered body or a molten and solidified body having a porosity of 2% or less. following a powder 1 to 7 wt% .5mm, SiO ₂ purity of 98% or more, less and fused silica 30 to 80 wt% particle diameter 5mm, balance, SiO ₂ purity of 98% or more, a particle diameter 5mm or less natural A ramming material for an induction furnace comprising silica is provided.

The ramming material for an induction furnace according to the present invention is obtained by combining two kinds of silica base powders of fused silica and natural silica with a small amount of a powder having a specific composition functioning as a sintering aid in a specific mixing range. This is a remarkable feature. That is, a small amount of TiO ₂ , Fe ₂ O
_{3. The} present invention comprising a powder obtained by pulverizing a sintered body or a melt-solidified body of a mixture in which at least one metal oxide selected from CaO, MgO, Na ₂ O and K ₂ O is combined and blended. This specific sintering aid, during operation of the induction furnace, in the ramming material as a lining material, to form a dense sintered layer with an appropriate thickness on the working surface, while the back side, that is, The effect is that an uncured powder layer remains on the non-operation surface coil side.

[0008] Although the mechanism by which the specific action and effect of the specific sintering aid of the present invention is achieved has not been clearly elucidated, it is not always clear, but it is induced by the high frequency current or low frequency current of the coil. The specific sintering aid present in the structure of the ramming material under the temperature range of the molten state caused by the heat of the cast metal such as cast iron gathers in the grain boundary phase of the structure particles to promote the fusion action of the structure particles. While the dense sintering layer is formed on the working side of the ramming material in contact with the molten metal, on the back side where the temperature is lower than the working side, the fusion promoting action by such a sintering aid does not occur, It is assumed that the powder layer remains as it is.

As will be apparent from the examples described later, in the induction furnace constructed by lining the ramming material of the present invention, the sintered layer and the powder layer are each formed with an appropriate thickness in a well-balanced manner. In addition, the occurrence of cracks and wear is suppressed as compared with a conventional induction furnace lined with a ramming material, and even when a crack occurs on the working surface due to the flow friction or thermal shock of the molten metal, the crack is formed on the non-working surface. Since it does not proceed to the coil side, it is possible to avoid the occurrence of troubles such as hot water leakage, and of course, it becomes an induction furnace lining material that is extremely excellent in heat resistance, corrosion resistance and thermal shock resistance.

[0010]

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 and a powder of a specific sintered body or a ground powder of a melt-solidified substance used as a sintering aid at a specific mixing ratio. The powder as the sintering aid used in the ramming material of the present invention contains 67 to 77% by weight, preferably 68 to 76% by weight of SiO ₂ component,
₂ O ₃ component is 18 to 28 wt%, preferably 19 to 27 wt%, and, TiO _2, Fe ₂ O _3, CaO,
At least one selected from MgO, Na ₂ O and K ₂ O
A sintered body having a porosity of 2% or less or a melt-solidified body containing 2 to 7% by weight, preferably 3 to 6% by weight in total of various kinds of metal oxide components is used as a raw material. It is a powder having a particle size of 0.5 mm or less by pulverizing a body or a melt-solidified body. This powder is used as a sintering aid to form a dense sintered layer on the working surface in an appropriate thickness in the ramming material as a lining material during operation of the induction furnace, while the back side That is, it has an important function of leaving a powder layer that is not cured on the non-operating surface side.

In the sintering aid powder of the present invention, the metal oxide component contained in the sintered body or the molten and solidified body is TiO.
_{2, Fe 2 O 3, CaO} , MgO, Na 2 O, is at least one selected from among K ₂ O, the combination also Fe ₂ O ₃ or MgO, and K and ₂ O among which such Those composed of components are more preferable from the viewpoint of sinterability. When a sintered body or a melt-solidified body having a composition outside the above range specified by the present invention, or a body having a porosity of 2% or more, the dense sintered layer and the residual powder layer are respectively provided. It is not possible to form a well-balanced induction furnace lining with an appropriate thickness.

It is also important that the powder as the sintering aid of the present invention has a particle size of 0.5 mm or less.
With a powder having a particle size exceeding 0.5 mm, the effect of forming an appropriate sintered layer on the operating surface side with a small amount of addition cannot be achieved sufficiently and effectively. The powder particle size is 0.4
mm is more preferable. In the present invention, the sintering aid powder is used in an amount of 1 to 7% by weight based on the total amount of the ramming material.
Preferably, 2 to 6% by weight is blended. 1% by weight
If it is less than 1, a sufficient powder layer remains on the non-operating surface side of the induction furnace lining material, but a dense sintered layer having an appropriate thickness cannot be formed on the operating surface side. On the other hand, if the amount exceeds 7% by weight, a sufficient sintered layer is formed on the working surface side, but the heat resistance is greatly reduced and the corrosion resistance is also reduced.

To prepare the sintering aid powder of the present invention, for example, high-purity silica powder, alumina powder, and TiO
₂ , one or more of metal oxide powders such as Fe ₂ O ₃ , CaO, MgO, Na ₂ O, and K ₂ O are mixed, water is added to the mixed powder, and the mixture is kneaded into a kneaded soil. The molded body after densification is formed by extrusion molding or press molding, and the dried molded body is sintered in a furnace at a temperature of 1350 to 1450 ° C. in an atmosphere gas atmosphere at a temperature of 1350 to 1450 ° C. or melted and solidified at a temperature of 1700 to 1800 ° C. The obtained sintered body or melt-solidified body is crushed and sieved to prepare a powder having a particle size of 0.5 mm or less.

Next, in the present invention, the fused silica powder as a silica base material constituting the ramming material is S powder.
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 4.5 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. Fused silica powder having a SiO ₂ purity of 98% or less is not preferred because of poor heat resistance, possibility of molten metal contamination, and difficulty in forming a dense sintered layer. 5m
Those with m or more are apt to cause segregation of particle size at the time of vibration filling molding, and it is difficult to mold a molded article having a uniform and sufficient strength as an induction furnace lining material, which is not preferable.

In the ramming material of the present invention, the fused silica powder is blended in an amount of 30 to 80% by weight, preferably 35 to 75% by weight. When the amount of the fused silica powder is less than 30% by weight, the thermal shock resistance of the ramming material is hardly improved, and when it exceeds 80% by weight, the residual swelling property is reduced. The effect is reduced.

The natural silica powder used in combination with the above-mentioned fused silica base powder may be a crushed or powdered natural silica stone produced in Japan or around the world. Among these natural silicas, the purity of SiO _{2 is} 98% or more, preferably 98.5%
As described above, those having a particle size of 5 mm or less, preferably 4.5 mm or less are used. 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. Natural silica powder with SiO ₂ purity of 98
% Or less is not preferred because heat resistance is inferior, there is a possibility of molten metal contamination, and it is difficult to form a dense sintered layer. It is difficult to mold into a molded body with uniform and sufficient strength as an induction furnace lining material,
Not preferred.

In the present invention, the amount of the natural silica powder is the balance of the amount of the fused silica and the amount of the sintering aid relative 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. Also,
If the amount exceeds 70% by weight, the corrosion resistance is improved,
The coefficient of thermal expansion increases and the thermal shock resistance decreases. The addition amount of the natural silica powder is particularly preferably in the range of 25 to 65% by weight.

To build an induction furnace using the ramming material of the present invention as a lining material, a method similar to the conventional method may be used.
For example, in the case of a 300 kg high frequency induction furnace, after setting the ramming material composition of the present invention on the inner surface of the refractory for coil protection inside the coil as shown in FIG. Then, a predetermined amount of the ramming compound is charged into the hearth, and filled with an air rammer. Next, after finishing the hearth construction surface smoothly, set the furnace cylinder at the center of the hearth, insert a predetermined amount of ramming material into the furnace wall between the furnace cylinder and the insulation sheet, and fill it with an air rammer Execute. 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 6 Fused silica powder (SiO 2)
₂ purity 98.5%, particle size 5mm or less) and natural silica rock powder (SiO ₂ purity 98.5%, particle size 5mm or less) and a sintering aid (chemical composition: SiO ₂ 72 wt.%, Al ₂ O ₃ 23
Wt%, Fe ₂ O ₃ 1.0 wt%, K ₂ O3.5 wt%, other 0.5% by weight, a porosity of 1.8% particle size 0.4mm or less powder sintered body) and Were prepared in the amounts as shown in Table 1 to prepare test materials for induction furnace ramming materials (Examples 1 to 6). These test materials were bonded to the 300 kg high frequency induction furnace shown in FIG. 1 by the following method. The laminating method was as follows. After setting the heat insulating sheet 3 on the inner surface of the refractory 2 for protecting the coil, a predetermined amount of the test material of Example 1 was charged into the hearth, and filled with an air rammer. After the completion of the construction, the hearth construction surface is finished smoothly, the furnace hearth cylinder 5 is set at the center of the hearth, and the partition plate 6 is placed between the furnace hearth cylinder 5 and the heat insulating sheet 3 as shown in FIGS. By setting at equal intervals, three types of test materials (Examples 1 to 3 and Example 4
To 6 were separately prepared) were charged in a predetermined amount into the furnace wall section. After charging the test materials, the surfaces of the test materials were made flat, the partition plate 6 was pulled out to the upper part of the furnace, and filled with an air rammer (construction height per operation: 60 to 70 mm). After construction, roughening of the construction surface is performed to prevent lamination on the joint surface, and the partition plate 6
Was set, and the furnace was filled up to the upper part in the same manner. After the furnace was completed, a melting test was performed using pig iron. That is, a test in which 200 kg of pig iron was held at 1600 to 1620 ° C. for 5 hours, and thereafter, tapping and cooling was repeated twice. Table 1 shows the results of evaluating the state of the lining material after the completion of the dissolution test.

Comparative Examples 1 to 3 The same fused silica as in the Examples except that no sintering aid was used (Comparative Example 1) or hydrated boric acid was used as the sintering aid (Comparative Examples 2 and 3) A sample material for ramming material (Comparative Examples 1 to 3) was prepared by using natural silica stone and blending them in the amounts shown in Table 2, and bonded to an induction furnace in the same manner as in the Example, and similarly after completion of the furnace construction. After the dissolution test, the state of the lining material after the dissolution test was evaluated. Table 2 shows the results.

From the results shown in Tables 1 and 2, the corrosion resistance,
Regarding the infiltration resistance to the molten metal, the examples and comparative examples show almost the same performance. However, in Examples 1 to 6, all formed a good sintered layer, but did not contain a sintering aid. In Comparative Example 1, it was found that the sinterability was poor and a sufficient sintered layer was not formed. In each of the examples, a sufficient powder layer remained on the non-operating surface coil side, whereas the powder layers were not used in the lining materials of Comparative Examples 2 and 3 in which hydrous boric acid was blended as a sintering aid. It can be seen that the residual was not sufficient, and that the non-operating surface coil side was also hardened.

[0022]

[Table 1]

The sintering layer and powder layer in Table 1 were evaluated according to the following criteria. That is, the thickness of the sintered layer is 10 mm
Excellent (○) when the thickness is up to 20mm, the thickness of the sintered layer is 9mm or less and
When the thickness was 21 mm or more, it was poor (x), when the thickness of the powder layer was 25 mm or more, it was excellent (o), and when the thickness of the powder layer was 24 mm or less, it was poor (x).

[0024]

[Table 2]

Incidentally, the evaluation of the sintered layer and the powder layer in Table 2 was carried out according to the following criteria as in the case of Table 1. That is,
Excellent (○) when the thickness of the sintered layer is 10 mm to 20 mm, poor (×) when the thickness of the sintered layer is 9 mm or less and 21 mm or more, and excellent (○) when the thickness of the powder layer is 25 mm or more. ), Powder layer thickness is 24
When it was less than mm, it was evaluated as poor (x).

[0026]

The ramming material for an induction furnace according to the present invention has excellent corrosion resistance and thermal shock resistance when it is lined with the induction furnace wall, and a dense sintered layer is formed on an operating surface with an appropriate thickness. As a result, the powder layer remains without being cured on the non-operation surface coil side. For this reason, even if the molten metal enters through a fine crack generated on the working surface, the intrusion of the molten metal is prevented by this unhardened powder layer and does not reach the non-working surface, and the safety during furnace operation Is more reliably secured. In addition, the presence of the unhardened powder layer makes it easier to disassemble the furnace as compared with the conventional product using boric acid as a sintering binder, and can greatly reduce the labor required for disassembly. Further, since the powder layer remains on the coil side, the heat insulating effect of the furnace wall is improved, and the heat consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram (plan view) for explaining a process of lining a ramming material in an induction furnace.

FIG. 2 is a partial sectional view of FIG. 1;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 induction coil 2 refractory for coil protection 3 heat insulating sheet 4 lining material 5 furnace cylinder 6 partition plate

Claims (3)

[Claims] 1. An SiO ₂ component of 67 to 77% by weight, Al
18-28% by weight of ₂ O ₃ component and TiO ₂ , Fe ₂ O
₃ , pulverizing a sintered or molten solid containing at least one component selected from CaO, MgO, Na ₂ O and K ₂ O in a total amount of 2 to 7% by weight and having a porosity of 2% or less. 1 to 7% by weight of a powder having a particle size of 0.5 mm or less,
fused silica 3 with iO ₂ purity of 98% or more and particle size of 5 mm or less
0 to 80% by weight, with the balance being 98% or more of SiO ₂ purity,
A ramming material for an induction furnace, comprising a natural silica having a particle size of 5 mm or less. 2. The particle size of the pulverized powder of the sintered body or the melt-solidified body is 0.4 mm or less.
A ramming material for an induction furnace described in (1). 3. The method according to claim 1, comprising 2 to 6% by weight of the powder of the sintered body or the fused solid, 35 to 75% by weight of the fused silica and 19 to 63% by weight of the natural silica. A ramming material for an induction furnace according to claim 2.