JP2002060278A - Ramming material for induction furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ramming material for an induction furnace, which is excellent in heat resistance, resistance to thermal impact and corrosion resistance and has durability sufficiently durable to the long term operation under high temperature melting conditions and which can be suitably used as a lining material for not only a small size induction furnace but also a medium size high frequency induction furnace having a cast steel melting capacity of about 3 t. SOLUTION: The ramming material for the induction furnace is composed of 65 to 80 wt.% high purity magnesia particles having particle diameters of <=8 mm, containing a fine powder having particle sizes of <=63 μm and having a purity of >=98%, 1 to 6 wt.% alumina fine powder having particle diameters of <=63 μm and a purity of >=98% and the balance being alumina particles having particle diameters of 0.063 to 8 mm and a purity of >=98%.

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 for an induction furnace for melting cast steel at a high temperature, and more particularly, to a ramming material having a moderate residual expansion property, and having excellent heat resistance, thermal shock resistance and corrosion resistance. The present invention relates to a ramming material for an induction furnace, which can be suitably used as a lining material for a medium-sized high-frequency induction furnace having excellent cast steel melting ability of about 3 t.

[0002]

2. Description of the Related Art Heretofore, as a lining material for an induction furnace for melting a cast steel or the like at a high temperature, a basic ramming material mainly composed of magnesia such as magnesia or magnesia / spinel and alumina / magnesia have been mainly used. A neutral ramming material containing alumina as a main component is used.

[0003] Magnesia, which is a main component of the basic ramming material, has a high melting point of 2800 ° C and has characteristics chemically stable to molten metal and basic slag. But,
Magnesia has a high coefficient of thermal expansion and poor resistance to thermal shock. Therefore, when it is used for the furnace wall of an induction furnace where melting and tapping are repeated in a relatively short time, cracks are likely to occur on the inner surface of the furnace wall due to rapid temperature changes, and troubles such as hot water are caused by the cracks that have occurred. More likely to happen.
For this reason, a basic ramming material containing magnesia as a main component is mainly used for a small furnace of 1t class or less in consideration of operational safety.

On the other hand, the alumina / magnesia neutral ramming material is also called an alumina / spinel ramming material, and its main component is alumina, to which magnesia is added. This alumina-spinel material has a smaller thermal expansion coefficient of alumina, which is a main component of magnesia, which is a main component of the basic ramming material, and has excellent thermal shock resistance due to volume stability during hot. . However, heat resistance and corrosion resistance are inferior to magnesia, so that there is a disadvantage that the high-temperature melting operation has a high erosion rate and greatly reduces the durability.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been proposed in view of the state of the prior art, and has excellent heat resistance, thermal shock resistance and corrosion resistance. It does not cause any inconvenience such as cracking even when it changes, is stable against molten metal and basic slag, has a small amount of erosion, and has sufficient durability to withstand long-term operation under high-temperature melting conditions. It is an object to obtain a ramming material for an induction furnace provided.

In particular, not only for small induction furnaces, but also for lining of medium-sized high-frequency induction furnaces with a casting steel melting capacity of about 3 tons,
It is an object of the present invention to obtain a ramming material for an induction furnace that can be used sufficiently safely and stably.

[0007]

In order to achieve the above object, the ramming material for an induction furnace according to the present invention has a particle diameter of 63 μm.
65-80% by weight of high-purity magnesia particles having a particle size of 8 mm or less and a purity of 98% or more containing the following fine powder;
1 to 6% by weight of alumina fine powder with a purity of 98% or less and a purity of 98% or more
And a balance of alumina particles having a particle size of 0.063 to 8 mm and a purity of 98% or more.

In particular, the amount of the magnesia particles containing the fine powder is preferably 68 to 77% by weight.

The amount of the alumina fine powder is 2
It is preferably about 5% by weight.

Further, the content of the fine magnesia powder in the magnesia particles containing the fine powder is 16 to 34% by weight.
Is particularly preferred.

Further, the ramming material for an induction furnace according to the present invention has a residual expansion rate of 0.3 to 0.7% when heated at 1250 ° C. and a residual expansion rate when heated at 1500 ° C. It is particularly preferred that the expansion coefficient is 0.6 to 1.0%.

As described above, the ramming material for an induction furnace according to the present invention uses high-purity magnesia particles and high-purity alumina particles each having a particle size of 8 mm or less and a high-purity alumina particle each containing a very fine powder at a predetermined ratio. ~ 80% by weight,
The constitutional feature is that it has a composition of 20 to 35% by weight of alumina. Thereby, it is excellent in heat resistance, corrosion resistance, and thermal shock resistance, and has a feature in the effect of being excellent in durability.

The magnesia (M
The gO) component imparts properties such as heat resistance and corrosion resistance during the high-temperature melting operation to the ramming material for an induction furnace according to the present invention. In addition, the alumina (A
The l ₂ O ₃ ) component provides thermal shock resistance.

In the present invention, in particular, the magnesia particles contain a fine powder having a particle size of 63 μm or less,
It is important that alumina fine powder having a particle size of 63 μm or less be added in a range of 1 to 6% by weight based on the total compounding amount. This alumina fine powder mainly reacts with the magnesia fine powder in the above magnesia raw material during firing, and spinel (Mg)
A crystal having an Al ₂ O ₄ ) structure is generated. Thereby, the ramming material for an induction furnace according to the present invention, as a lining material for an induction furnace, remains in the sintered layer on the working surface side directly in contact with the molten metal or the slag or the hardened layer on the back side after heating and cooling. The expansion coefficient is maintained at an appropriate value, and the generation of cracks on the working surface side of the lining material can be suppressed. Further, it is possible to avoid the occurrence of cracks parallel to the furnace wall operating surface at the boundary between the sintered layer on the operating surface side and the hardened layer on the back side, which are often seen in conventional ramming materials. Therefore, there is little wear due to the projection or peeling of the lining material.

The ramming material for an induction furnace according to the present invention thus configured has a residual expansion rate of 0.3 to 0.7% when heated at 1250 ° C. and a residual expansion rate of 0.1% at 1500 ° C. 6 to 1.0%, each having a suitable range from the above viewpoint.

[0016]

DETAILED DESCRIPTION OF THE INVENTION As described above, the ramming material for an induction furnace according to the present invention has a high purity magnesia particle having a particle size of 8 mm or less and a purity of 98% or more containing fine powder having a particle size of 63 μm or less 65 to 80% by weight. % Of alumina fine powder having a particle size of 63 μm or less and a purity of 98% or more;
Alumina particles 14 to 34 having a purity of 98% or more with a size of 8 mm or less.
% By weight.

In the ramming material for an induction furnace according to the present invention, the raw materials of the magnesia and alumina components, which are constituents, have a purity of 98% or more. When the raw material purity is lower than the above specified value, when the ramming material is used as a lining material of an induction furnace, in a sintering melting step, etc., there are many miscellaneous crystals and compounds other than spinel crystals. Generate. As a result, not only the heat resistance, the chemical stability and the like are reduced, but also the desired residual expandability cannot be obtained. Further, impurities are eluted in the molten metal when the induction furnace is used, which causes a problem of contaminating the molten metal.

The raw material particles of magnesia, which is a main constituent, have an MgO purity of 98% or more, more preferably 9%.
It is not particularly limited as long as it is 8.5% or more and the particle size is 8 mm or less, more preferably 5.66 mm or less. For example, a commercially available high-purity magnesia clinker, electrofused magnesia, or the like may be used by pulverizing, sieving, or the like so as to conform to the above particle size standard. However, in the present invention, it is necessary that the magnesia raw material particles contain fine powder having a particle size of 63 μm or less. This is important from the viewpoint of generating an appropriate amount of spinel crystals by a reaction during firing with the compounded high-purity alumina fine powder.

Spinel crystals (MgAl_Two O_Four ) Is a mug
Nesia (MgO) and alumina (Al _Two O_Three ) 1: 1 anti
The amount of alumina fine powder is 1 to 6% by weight.
is there. Therefore, the above magnesia fine powder
It is sufficient to have a corresponding amount, but in general,
16-34% by weight in gnesia particles
Is preferred. The magnesia component according to the present invention
The heat resistance during high-temperature melting operation and the ramming material for induction furnaces
Provides corrosion resistance.

In the present invention, the magnesia particles are blended in an amount of 65 to 80% by weight. If the amount is less than 65% by weight, sufficient heat resistance and corrosion resistance during high-temperature melting operation cannot be obtained. On the other hand, if it exceeds 80% by weight, heat resistance and corrosion resistance during high-temperature melting operation can be obtained, but thermal shock resistance decreases. A more preferable range of the compounding amount is 68 to 7
7% by weight.

Next, in the ramming material for an induction furnace according to the present invention, the alumina component, which is another component, has a particle size of 63 μm or less and a purity of 98% or more, preferably 98.5% or more. Alumina fine powder 1-6% by weight
And 14 to 34% by weight of alumina particles having a particle size of 0.063 to 8 mm and a purity of 98% or more, preferably 98.5% or more.
Consists of Since alumina has a small coefficient of thermal expansion, in the present invention, the alumina component contributes to the volume stability of the working surface side in contact with the high-temperature molten metal. Alumina is also excellent in thermal shock resistance, forms a strong sintered layer together with other components, and prevents the propagation of cracks.

In the present invention, the alumina fine powder having a particle size of 63 μm or less is used as a magnesia raw material,
Reacts with magnesia fine powder of μm or less to produce spinel crystals. As a result, as the lining material for the induction furnace, the residual expansion coefficient after heating and cooling can be set to an appropriate value in the sintered layer on the operating surface side and the hardened layer on the back side thereof, and the cracks on the operating surface side This has the effect of suppressing the occurrence of blemishes. Conventionally, cracks parallel to the operating surface of the furnace wall at the boundary between the sintered layer on the operating surface side and the solidified layer on the back side, which often appear in this type of refractory material (ramming material), are considered. It is possible to reduce abrasion due to intrusion of metal into the lining material, and protrusion and peeling of the lining material.

The amount of the alumina fine powder is 1% by weight.
If it is less than 50%, the residual expansion rate after heating and cooling is small, and the effect of suppressing the generation of cracks on the working surface side of the lining material is small. On the other hand, if the compounding amount exceeds 6% by weight, the residual expansion rate after heating and cooling becomes too large, and the lining material protrudes and peels on the working surface side, and the coil cement on the non-working surface side of the lining material breaks. And deformation of the coil. Also,
An increase in the residual expansion rate after heating and cooling also increases the expansion in the furnace top direction, which may lead to wear of the upper part of the furnace wall and damage to equipment near the upper part of the furnace. More preferably, the compounding amount of the alumina fine powder is 2 to 5% by weight.

Next, as the raw material alumina particles,
If the purity is 98% or more, high-purity fused alumina or sintered alumina which has been conventionally used as a refractory lining the furnace wall of the induction furnace can be used. Also,
The particle size is usually 8 mm or less (provided that the particle size is 63 μm).
Excluding m or less. ), Preferably 5.66 mm or less. The compounding amount of the alumina particles is 65 to 80% by weight, which is the compounding amount of the magnesia particles including the fine powder, and 1 to 6% by weight, which is the compounding amount of the alumina fine powder, that is, 14 to 34% by weight. It is.

In order to build the induction furnace by using the ramming material for an induction furnace according to the present invention as a lining material, a method similar to the conventional method can be used. For example, in the case of the construction of a high-frequency induction furnace, as shown in FIG. 1, the ramming material for an induction furnace according to the present invention is bonded in the furnace as follows.
That is, after the heat insulating sheet 3 is set on the inner surface of the coil protection refractory 2 inside the induction coil 1, a predetermined amount of the ramming material 4 is charged into the hearth, and filled with an air rammer or the like. After the construction is completed, the hearth construction surface is finished smoothly, the furnace cylinder 5 is set at the center of the furnace hearth, and a predetermined amount of the ramming material 4 is mounted on the furnace wall between the furnace cylinder 5 and the heat insulating sheet 3. Insert and fill with an air rammer. The furnace wall is extended to the upper part while repeating the above-mentioned operation, and is filled up to the furnace upper part to complete the furnace construction. The new furnace thus constructed is first inserted with metal such as pig iron or cast steel into a vessel of the furnace cylinder 5 inside the lining material 4 and then heated according to a predetermined sintering schedule. Then, the molten metal is increased while gradually melting, and the ramming material 4 is subjected to sintering and melting. As a result, the working surface side of the ramming material 4 is firmly sintered, and a dense and stable sintered layer is formed.

[0026]

EXAMPLES Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to the following examples. [Examples] The ramming materials having the respective compositions shown in Examples 1 to 3 in Table 1 were used with a molding rammer for a workability index test of a plastic refractory of JIS R2574-77, and a weight of 100 was used. By dropping the sample twice, a sample having a diameter of 50 mm and a height of 50 mm was produced. This sample was heated at 1250 ° C. and 1500 ° C., respectively, kept for 3 hours, cooled, and the residual expansion rate was measured at any four positions in the diameter direction, and the average value was obtained. Further, the ramming material of each composition shown in Examples 1 to 3 of Table 1 was lined in a 300 kg high frequency induction furnace as shown in FIG. 1, and the molten metal was kept at 1700 to 1730 ° C. for 3 hours. Erosion tests were performed by contact with slag of the indicated composition. After the test, the amount of erosion of the ramming material was determined by measuring the cross-sectional area of the eroded part of the furnace wall. Further, the number of cracks on the working surface of the furnace wall after the test was 0.1 mm or more in width and 50 mm or more in length, and the presence or absence of cracks parallel to the working surface inside the ramming material was also determined. Table 3 shows the test results.

The evaluation of each test result shown in Table 3 is as follows.
The evaluation was performed according to the following evaluation criteria. The residual expansion rate is 1
In the case of heating at 250 ° C., the case of 0.3 to 0.7% was evaluated as ○, and the case outside the above range was evaluated as ×. Moreover, when it heated at 1500 degreeC, the case of 0.6-1.0% was set to (circle), and the outside of the said range was set to x. The amount of erosion in the erosion test results is an index of 11
When it was less than 0, it was evaluated as ○, and when it was 110 or more, it was evaluated as x. Regarding the number of cracks on the working surface, 9 or less were evaluated as ○, and 10 or more as X. Regarding the cracks parallel to the working surface, the case where there was no crack was evaluated as ○, and the case where there was crack was evaluated as ×.

[Comparative Examples] With respect to the ramming materials having the respective compositions shown in Comparative Examples 1 to 4 in Table 1, test samples were prepared in the same manner as in the examples, and each test was performed. Table 3 shows the test results.

[0029]

[Table 1] 1) The purity is 98% or more and the particle size is 8 mm or less. However, it contains 30% by weight of fine powder having a particle size of 63 μm or less. 2) The purity is 98% or more and the particle size is 63 μm or less. 3) The purity is 98% or more and the particle size is 8 mm or less.

[0030]

[Table 2]

[0031]

[Table 3]

From the above results, in Comparative Example 1 in which the blending amount of the alumina fine powder having a particle size of 63 μm or less is less than 1% by weight and in Comparative Example 2 in which the blending amount is more than 6% by weight, the residual expansion coefficient is too small. Or, it turns out to be too large and not suitable. On the other hand, in Examples in which the blending amount of the alumina fine powder is 1 to 6% by weight, the residual expansion rate when heated at 1250 ° C. is 0.3 to 0.7%, and
The residual expansion rate when heated at 1500 ° C. is 0.6 to
1.0%, all of which were within the appropriate range.

The amount of erosion after the erosion test was as follows.
In Comparative Example 3 in which the amount of the following magnesia particles (including fine powder having a particle size of 63 μm or less) is less than 65% by weight, the erosion index is as large as 110 or more. On the other hand, in Examples in which the blending amount was 65 to 80% by weight, the erosion index was 102 at the maximum.

Further, the number of cracks in the operating surface of the furnace wall after the erosion test was determined in Comparative Example 1 in which the amount of the alumina fine powder was less than 1% by weight and in the case where the amount of the magnesia particles was more than 80% by weight. In Comparative Example 4, the number was 10 or more. On the other hand, there were no seven or more in the examples.

In Comparative Example 1, after the erosion test,
Cracks parallel to the working surface were generated inside the ramming material, but no such cracks were observed in any of the examples.

[0036]

By using the ramming material for an induction furnace according to the present invention, the melting loss of the furnace wall can be reduced during the high-temperature melting operation of cast steel. At the same time, cracks generated in the furnace wall and cracks generated inside the furnace wall parallel to the operating surface can be suppressed, so that the durability of the induction furnace lining can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view for explaining a process of lining a ramming material in an induction furnace.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Induction coil 2 Refractory for coil protection 3 Insulation sheet 4 Lining material 5 Furnace cylinder

Claims (5)

[Claims] 1. A particle size of 8 including fine powder having a particle size of 63 μm or less.
mm and magnesia particles 65 to 80 having a purity of 98% or more.
% By weight, 1 to 6% by weight of alumina fine powder having a particle size of 63 μm or less and a purity of 98% or more, and the remainder having a particle size of 0.063 to 8 m
A ramming material for an induction furnace, comprising alumina particles having a purity of 98% or more in m. 2. The ramming material for an induction furnace according to claim 1, wherein the amount of the magnesia particles containing the fine powder is 68 to 77% by weight. 3. The compounding amount of the alumina fine powder is 2-5.
3. The ramming material for an induction furnace according to claim 1, wherein the ramming material is in weight%. 4. The ramming material for an induction furnace according to claim 1, wherein the content of the magnesia fine powder in the magnesia particles containing the fine powder is 16 to 34% by weight. 5. The residual expansion coefficient when heated at 1250 ° C. is 0.3 to 0.7%, and the residual expansion coefficient when heated at 1500 ° C. is 0.6 to 1.0%. The ramming material for an induction furnace according to any one of claims 1 to 4, characterized in that: