JP2573227B2 - Dry ramming material for crucible induction furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION << Industrial application field >> The present invention relates to a crucible-shaped induction material which has significantly improved the corrosion resistance, penetration resistance to molten metal and molten slag, and the resistance to cracking during rapid heating and quenching. The present invention relates to a dry ramming material for a furnace.

<< Conventional Technology >> Various metals such as iron, copper, and aluminum are melted and held by an induction furnace. There are two types of induction furnaces: crucible-type induction furnaces and groove-type induction furnaces.The crucible-type induction furnaces are mainly used for melting molten metal, and groove-type induction furnaces are mainly used for keeping and raising the temperature of molten metal. It is the purpose. These are properly used depending on the type of molten metal, the purpose of melting, operating conditions, and the like.

Various refractory materials such as silica, alumina, zirconia, magnesia, and spinel are used for the ramming material for induction furnaces depending on the molten metal, etc., but cast iron and alloy iron are melted in a crucible induction furnace. As the ramming material in this case, an acidic dry ramming material obtained by adding a binder to a crushed natural quartzite has been used. Since the crushed material of natural quartz has resistance to crack generation during rapid heating and quenching, it can be used for induction furnaces of various capacities and has the advantage of low price.

《Problems to be solved by the invention》 By the way, in accordance with the severer use conditions, recently, in order to improve corrosion resistance and thermal shock resistance, fused silica is used for a part of the crushed material of natural quartzite to oxidize. An acidic dry ramming material to which a binder such as silicon has been added, or an acid dry ramming material having no fused silica and only plain fused silica has been used. When using a furnace lined with an acid dry ramming material, the liner material has a sintered layer of glass bonding, which is a dense and impervious layer to the melt, on the high-temperature surface in contact with the molten metal. On the back side of the sintered layer, a hardened layer and an unsintered loose layer that are not as dense as the sintered layer are formed. The loose layer stops the cracks generated in the sintered layer from growing further in this layer.

However, with the recent changes in the economic environment, even in the workplace where induction furnaces are used, resource saving, energy saving,
We are promoting reduction of furnace unit consumption. For this reason, the lining materials of induction furnaces have been used under increasingly severe conditions. That is, as a lining material of an induction furnace for melting cast iron or ferromagnetic iron, a dry ramming material added to the above-mentioned crushed natural quartzite or an acid dry ramming material added to a binder of the crushed natural quartzite and fused silica. Or fusible silica, and an acid dry ramming material with a binder added is used, but its corrosion resistance, penetration resistance to molten metal and molten slag, and resistance to cracking during rapid thermal quenching, etc. The number of unsatisfied cases is increasing.

Particularly, in the case of a large crucible-type induction furnace in which cast iron or alloy iron is melted intermittently, and in the case of a crucible-type induction furnace in which scrap of galvanized steel sheet is melted. The intermittent operation is an operation method in which heating and keeping the temperature in the furnace even during the furnace shutdown in the past is stopped during the furnace shutdown and the heating is restarted when the operation is restarted. This intermittent operation intends to drastically reduce fuel costs and electric power costs consumed for heating and keeping the furnace closed.

In the case of melting by intermittent operation, the lining material is subjected to repeated stress due to rapid heating and quenching as the operation is stopped and restarted. For this reason, cracks due to expansion and contraction occur in the lining material, the cracks grow, and molten metal or molten slag penetrates into the cracks and leaks occur, which causes a decrease in the serviceability of the lining material . This phenomenon is different depending on the size of the furnace, and may not be a problem when the furnace volume is less than 10 tons, but there are many problems when the furnace volume is 10 tons or more.

On the other hand, when melting scrap of a galvanized steel sheet, there are the following problems. In recent years, as a measure against rust caused by salt damage of automobiles, there is a tendency to use more and more, and the thickness of zinc plating is also increasing. For this reason, the generation of scrap of galvanized steel sheet has recently increased, and the ratio of melting the scrap of galvanized steel sheet in a crucible-type induction furnace has been increasing in order to melt this scrap and use it as a raw material for cast iron. When galvanized steel sheet is melted in an induction furnace, the content of zinc in the molten metal is slightly about 0.5-0.7%
However, since zinc easily penetrates the lining material,
Zinc passes through fine cracks and the like to form a runner, and as a result, causes a problem of leakage of the hot water, thereby causing a problem that the durability of the lining material is greatly reduced. That is, in large furnaces, the cracks generated in the lining material are large, so it is often difficult to suppress crack growth even in the loose layer, and when the scrap of permeable zinc steel sheet is melted, In many cases, the reached molten metal penetrates even in minute gaps, which causes a decrease in the durability of the lining material.

On the other hand, the glass-bonded sintered layer is dense and impervious, so it has resistance to permeable molten metal such as galvanized steel sheet. Therefore, the occurrence of cracks on the lining surface increases. Further, since the binder reacts with the aggregate at a high temperature to generate a material having low melting point, there is a problem that the lining material containing a large amount of the binder is inferior in corrosion resistance. On the other hand, conventional acid dry ramming materials mainly composed of natural quartzite are not satisfactory in corrosion resistance, penetration resistance, resistance to crack propagation during rapid heating and quenching, and the like. This is because the properties such as corrosion resistance are significantly affected by the difference in the crystal form of the silica content of the natural quartzite and the purity of the SiO ₂ content, which causes a reduction in the durability and a variation in the durability.

Therefore, in the acidic dry ramming material, since there are restrictions on the mixing of components other than SiO _2, strong high-purity silica materials oriented, still, SiO ₂ single mainly composed of silica natural quartzite or fused silica At present, component-type dry ramming materials are used. Therefore, in the case of a large crucible-type induction furnace that operates intermittently or when galvanized steel sheet is melted, the current situation is that the service life is greatly reduced due to the above-mentioned situation.

The present invention has been made in view of such circumstances. The purpose is to improve the penetration resistance by increasing the thickness of the glass-bonded sintered layer by increasing the amount of binder used, and in conjunction with this, various factors such as corrosion resistance and resistance to crack initiation during rapid thermal quenching are considered. An object of the present invention is to obtain a lining material that does not cause deterioration in properties. This provides a liner that can achieve good results in large crucible-type induction furnaces that operate intermittently to melt cast iron and alloyed iron, and crucible-type induction furnaces that melt scrap galvanized steel sheets. What you want to do.

<< Means for Solving the Problems >> In order to achieve the above object, the dry ramming material for a crucible-type induction furnace of the present invention contains 10 to 98% by weight of fused silica,
It is characterized in that it contains 1 to 20% of silicon carbide of 1 mm or less, and the remainder is made of a refractory material. The dry ramming material for a crucible-type induction furnace according to another invention further has an average particle size of 0.1 to 2 mm.
It is characterized in that it contains 1 to 6% by weight of a μm siliceous ultrafine powder.

Silicon carbide is hard to leak to molten metal and slag,
Since the thermal conductivity is high and the coefficient of thermal expansion is small, it is known that silicon carbide is used as a refractory to improve the corrosion resistance and thermal shock resistance of the refractory. JP-A-48-67307 and JP-A-55-7
JP 7692 and the like also describe a refractory for an induction furnace utilizing these characteristics of silicon carbide. However, these are refractory materials for repair and are not dry ramming materials, or they do not add silicon carbide as a starting material, but generate silicon carbide during use, and have poor practicality. It relates to an alumina-based dry ramming material.

The invention of the present application is a dry ramming material based on fused silica-silicon carbide. However, although a dry ramming material based on alumina-silicon carbide is known, it is actually a dry ramming material based on silica-silicon carbide. Is not in practical use. The possible reason is that, for many years, the importance of the purity of SiO ₂ has been considered, and there is a concern that impurities when silicon carbide is oxidized may deteriorate properties such as corrosion resistance. Since silicon carbide is difficult to react and has poor sinterability, the addition of silicon carbide requires an extra binder for the formation of a sintered layer, which may deteriorate properties such as corrosion resistance, and silicon carbide has a high thermal conductivity. Therefore, there is a concern that the ratio of the sintered layer in the lining layer is increased and the properties such as corrosion resistance are reduced.

The inventors have conducted intensive studies and found that fused silica has a better sintering property than natural quartzite, and in particular, the sinterability is significantly improved even with a small amount of ultrafine silica powder. It has been found that, when a specific amount of silicon carbide is added to a mixture of quartzite and fused silica, various properties such as corrosion resistance are improved even when the binder is increased. In other words, if fused silica is used as the siliceous raw material and the particle size and usage ratio of silicon carbide are limited, the knowledge is obtained that the conventional acidic dry ramming material is significantly improved and the above-mentioned negative factors do not become apparent, The present invention has been completed.

Next, the use purpose and the use ratio of the raw material constituting the present invention will be described in detail.

As for the fused silica, those having a particle size of about 5 mm or less are adjusted in particle size, and 10 to 98% by weight is used. The fused silica has a high SiO ₂ content, a low coefficient of thermal expansion, and is easy to form a sintered layer, and therefore has excellent corrosion resistance and thermal shock resistance. Therefore, the dry-type ramming material using fused silica can minimize the amount of the binder used, so that it has excellent corrosion resistance and thermal shock resistance, and has good resistance to cracking during rapid thermal quenching. . If the amount used is 10% or less, the effect of addition is not obtained.

Silicon carbide has a particle size of 1 mm or less, and a weight of 1 to 20
%use. If it exceeds 1 mm, the dispersion is insufficient and the corrosion resistance and penetration resistance do not improve. If the used amount is 1% or less, the effect of adding silicon carbide does not appear, and if it exceeds 20%, the mixed amount of the Si component in the molten metal increases. Preferably, the particles having a particle size of 1 mm or less have a weight of 5 to 15%.

Ultrafine silica powder having an average particle size of 0.1 to 2 μm is used in an amount of 1 to 6% by weight. Silica ultrafine powder is silica flour or amorphous silica ultrafine powder, etc. Ultrafine powder enters between particles and bonds easily with each other, so that it can be sintered at a low temperature. However, the change in volume is small. Therefore, the amount of the binder used can be reduced. The average particle size of the siliceous ultrafine powder is
If it is 0.1 μm or less, the dispersion of the ultrafine silica powder is poor,
The bulk increases and the lining workability deteriorates. The effect on sinterability is the same, and ultrafine silica powder of 0.1 μm or less is expensive and not economical. If it is 2 μm or more, the sinterability of ordinary silica fine powder is not changed, and the sintering strength of the lining material is insufficient. When the amount of the ultrafine siliceous powder is 1% or less, the effect of the addition is not exhibited, and when the amount is 6% or more, the bulk of the compounded powder becomes large, the workability deteriorates, and the packing density at the time of construction decreases. Preferably, the particle size is 0.1
It is better to set the thickness of 2 to 2 μm to 3 to 5%.

As the remaining refractory material, either natural quartzite or a binder can be used. For natural quartzite, crushed natural quartzite of about 5 mm or less is used with particle size adjustment.
Those having a high SiO ₂ content are preferred. As the binder, silicates such as boron oxide, boric acid and sodium silicate, and phosphates such as aluminum phosphate can be used. The binder reacts with the aggregate at elevated temperatures to produce a low-melting material, thus promoting sintering of the lining. On the other hand, when this binder is used in a large amount, there is a disadvantage that the thermal shock resistance is reduced. The primary use of the binder is to add a binder to the lining to provide the necessary strength to prevent wall collapse during sintering of the lining. Accordingly, in the case of a small furnace in which wall collapse is relatively unlikely to occur, such as a crucible-type induction furnace of 5 tons or less, the binder need not be particularly used. This is because the fine powder portion has the same sintering action as the binder.

<< Effect of the Invention >> Since the dry ramming material of the present invention has the above-described configuration, it has the following features.

(1) Since the glass-bonded sintered layer has a dense structure, silicon carbide remains in the structure without being oxidized. Therefore, the glass-bonded sintered layer is excellent in corrosion resistance, thermal shock resistance, resistance to crack generation during rapid thermal quenching, and penetration resistance, so that the durability of the lining material is improved.

(2) Since the glass-bonded sintered layer is dense and thick, the penetration of high vapor pressure components such as zinc and Mg in the molten zinc-plated steel sheet can be suppressed, and the durability of the lining material can be reduced. Is improved.

<< Examples >> Table 1 Nos. 1 to 7 are examples of the present invention, and Nos. 8 to N
o.10 is a conventional acidic dry ramming material as a comparative example.
After sufficiently mixing the blends using the raw materials shown in Table 1, they were filled while applying vibration to prepare test specimens. The filling rate of the test specimen was as shown in Table 1.

Next, the specimen was sintered at 1000 ° C. and 1500 ° C. for 3 hours each, and after cooling, the compressive strength was measured. No. 6 does not use any binder, while No. 2 has a lower compressive strength than other materials due to the combined use of ultrafine silica powder, despite the small amount of binder added. However, the hot bending strength showed a higher value than the comparative product. No.6, No.2 and
No. 3 uses silica fine powder. No. 6 uses no binder, while No. 2 uses 0.6
No. 3 was added by 1.2 parts by weight.
From these properties, it was shown that the one using silica ultrafine powder has sinterability without using a binder, and the corrosion resistance, thermal shock resistance and penetration resistance are improved even if the binder is increased. Have been. With respect to thermal shock resistance, a corrugated brick-shaped specimen was sintered and tested by an acoustic emission method (AE method). The AE method reads the elastic waves generated when the refractory structure is destroyed when a large thermal stress is suddenly applied to the refractory, using a sensor to read the AE count number, and evaluates the thermal shock resistance based on the magnitude of the value. It is. The smaller the AE count, the better the thermal shock resistance. All of the products of the present invention exhibited better thermal shock resistance than the comparative products.

For corrosion resistance and penetration resistance, trapezoidal columnar specimens were sintered at 1000 ° C, glued to the inside of a crucible in a high frequency induction electric furnace to form a tube, and cast iron and slag were inserted inside the tube. The specimen was kept at 5 ° C. for 5 hours to react with the molten metal. After the molten metal was discharged and cooled, the specimen was taken out, the amount of erosion and permeation by the slag and the amount of erosion and permeation by the metal were measured, and the values were compared using an index with No. 9 being 100. The product of the present invention is
Both the corrosion resistance and the penetration resistance showed excellent values.

As described above, the dry-type ramming material of the present invention is excellent in corrosion resistance, penetration resistance and thermal shock resistance to molten metal and molten slag. It is suitable as a lining material in the case of a large crucible-type induction furnace that melts during operation or in the case of a crucible-type induction furnace that melts scrap of galvanized steel sheet.

Claims (2)

(57) [Claims] 1. A dry-type ramming material for a crucible-type induction furnace, comprising 10 to 98% by weight of fused silica, 1 to 20% of silicon carbide having a particle size of 1 mm or less, and the remainder made of a refractory material. 2. The dry ramming material for a crucible-type induction furnace according to claim 1, wherein the material contains 1 to 6% by weight of a siliceous ultrafine powder having an average particle size of 0.1 to 2 μm.