JPS59209455A - Heat insulating material for molten metal - Google Patents

Abstract

PURPOSE:To obtain high perfomance as a heat insulating material for a molten metal by using a hollow granular body having a bulk specific gravity and grain size in a specific range for said material. CONSTITUTION:A heat insulating material is constructed of a hollow granular body of which the shell is constituted of a heat-resistant inorg. material and which is calcined to <=0.5 bulk specific gravity and <=30mm. and >=3mm. max. size. Such heat insulating material is used as a heat insulating material for the molten metal in a ladle lined with bricks consisting essentially of magnesium oxide, by which the erosion of the ladle bricks is prevented and the working efficiency of the ladle is improved without damage on the bricks for long time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a hollow granule made of a fired product with a shell made of a heat-resistant inorganic substance, which covers the surface of molten metal such as molten steel, molten aluminum, and minilum to keep the molten metal warm and prevent oxidation. The present invention also relates to a heat insulating agent for molten metal that has characteristic performance, such as preventing melting damage to the fire-resistant inner wall bricks of ladle, etc. that house molten metal.

Conventionally, organic materials such as rice husks, wood flour, valve sludge, and their improvers, as well as inorganic materials such as vermiculite, shale, alumina, and silica sand, have been used as heat insulators for molten metal, especially molten steel in ladle for steelmaking. It is used in solid or powder form.

Among these, the organic matter containing the carbon source is easily carbonized and burned by the heat of the molten metal, and most of it disappears, and it also has the disadvantage of having a large specific gravity after combustion and poor heat retention ability. In addition, carbon reacts with the molten metal and causes a so-called carburization phenomenon, making the produced metal abnormal and inevitably reducing the yield. Further, although the various inorganic heat retaining agents mentioned above have little thermal change, they have a large bulk specific gravity and require a large amount to be used in order to obtain a constant heat retaining power, which is not economical. In general, the properties that a heat insulating agent for molten metal should have include: high heat retention, no oxidation of the surface of the molten metal, prevention of carburization, no generation of dust when handling the heat insulating agent, and handling. One example of this is to prevent erosion of the refractory bricks on the inside of the pot.

As a result of continuing research into a new moisturizer that maintains a high level of performance as described above and also solves the drawbacks of the conventional heat retaining agents mentioned above, the present inventor has developed a highly functional, economical, and easy-to-use moisturizer. They succeeded in developing a heat insulating agent for molten metal that can be manufactured using this method.

This heat insulating agent has a shell made of heat-resistant material and has a bulk specific gravity of 0.
5 or less, maximum dimension 30mm or less 3! It is characterized by the structure of hollow grains fired to a temperature of 11 or more, but especially in the case of molten steel, the shell structure contains more than 50% magnesium oxide as a heat-resistant inorganic and the shell has a porous structure. Material, bulk specific gravity 0.5 or less, maximum dimension 30 n+ m or less 3III+! Those having the structure of hollow particles fired as described above are suitable.

The heat-resistant inorganic substances used here include silicic acid, alumina, clay, magnesia, etc., which are raw materials for ceramics, and molten metals are materials that give a temperature above the melting point and are used in the steelmaking industry from around 250℃ of point alloys. J, which is used in practical applications, is around 600℃.

The composition of the inorganic material is determined depending on the temperature of the molten metal. As a result of research on the structure of a heat insulating agent adapted to various temperatures using this inorganic material, the present inventor found that hollow particles with specific gravity and particle size within a limited range have high performance as a heat insulating agent for molten metal. I learned that I can get it. Hollow granules have air inside them that does not move, so they can maintain an excellent heat insulating effect due to the pores. Also, the amount of inorganic material is relatively large (in both cases, the thermal conductivity is increased and the surface needs to be coated with a large amount of heat insulating agent to obtain the necessary heat retention power, which is not economical. Furthermore, when particles with a high bulk specific gravity are handled in large quantities, their fluidity deteriorates, and when they are placed on molten metal in a uniform layer thickness, diffusion and movement on the molten metal surface becomes difficult.

The dimensions of the hollow granules are significantly related to the heat retention effect, oxidation of the molten gold layer, and dust generation. When a molten metal surface is covered with a heat insulating agent, convection occurs intensely through the heat insulating material due to the temperature difference between the metal and the upper air, and heat conduction through the heat insulating material is also rapid. The physical properties of the insulation itself, such as reducing convection and heat transfer, are important. The effect of convection is related to the flow rate of moving air when the temperature gradient is constant, and heat insulating agents are affected by the size and shape of the gaps between objects, the density of the object's surface, etc. For hollow granules with a bulk specific gravity of 0.5 or less, the maximum size is 30r@2 or more, the voids between the granules become huge, the convection becomes strong, and the heat retention capacity decreases. Requires heat insulation. In addition, hollow particles with a particle size of 3 m or less have a large contact area between particles, which increases heat conduction and reduces heat retention, and the fluidity of the sphere increases, making it difficult to handle. It will exceed the limit.

As described above, the heat insulating agent of the present invention is a hollow granule, and it has been shown that the bulk specific gravity and dimensions are within the range of effectiveness and practical use. The present invention is not limited to circular spheres, and the object of the present invention can be achieved as long as the size of the particles is within the above range.

Magnesia bricks, which have a high content of magnesium oxide, are used as the material for the inner walls of ladles, which are containers for molten metal.
When magnesia chromium bricks, magnesia scratched carbon bricks, etc. are used, the slap that appears on the surface of the molten metal due to repeated use reacts with magnesium oxide, causing melting and damage at the contact point, causing wear and tear on the surface of the brick. This is problematic because the volume is partially reduced and the refractory bricks eventually need to be replaced or repaired, which is not economical and reduces the operating rate of the ladle. One way to counter this is to mix calcined magnesia into the stag to reduce corrosion loss, but it is said that increasing the amount of magnesia to increase the effect will make it difficult to manufacture clean steel (Tokuko Showa). 54-3064
7).

In constructing the shell made of heat-resistant inorganic material, which is the structure of the present invention, the shell containing 50% by weight or more of magnesium oxide as the heat-resistant inorganic material has a specific gravity of 0.5 or less and a maximum dimension of 30 m or less and 3 ni or more. By using the hollow granules made of the fired product as a heat insulator for molten metal in a ladle that is equipped with bricks, which are the main component of magnesium oxide, the melting damage of the ladle force balls can be prevented and the product can be used for a long period of time. It is possible to extremely improve the operating rate of the ladle without damaging the bricks or the ladle. The amount of magnesium oxide included in the heat insulator needs to be at least 50% by weight in order to have a long-term effect, and if it is less than this, the durability is insufficient. Granular molten metal heat insulating agents can also be easily produced. By creating voids in the shell or a rough structure with uneven surfaces, the apparent specific gravity of the grains is lowered,
In addition to lowering the bulk specific gravity and increasing the air content, it also resists the flow of moving air due to convection and improves the heat retaining effect as a heat retaining agent, and the degree of improvement is remarkable.

Common characteristics of the products of the present invention include the following effects. In other words, since there is no carbon source in the fired product, the carburization phenomenon does not occur at all), and because the hollow granules have been fired beforehand and become a fired product, they cannot be pulverized by contact and the structure This means that there is no generation of dust or the like, and it is extremely easy to handle in terms of movement, transportation, and dispersion.

As described above, structures with excellent properties can be easily and economically produced. How?

A flammable organic material, such as natural cellulose, is made into spherical, water-containing particles, and a heat-resistant inorganic powder is sprinkled on the surface to an even thickness to form a shell.

This inorganic material adsorbs moisture in the central sphere through capillary action, forming a dense layer, which makes it easy to move and handle. Then for water removal.

After drying, it is fired at the temperature necessary for firing the heat-resistant inorganic material to create hollow granules. During firing, the spheres, which have maintained their inner shell shape in advance, are burned and carbonized to form hollow bodies. In order to give the hollow body after firing the optimum bulk specific gravity and maximum and minimum dimensions, it is possible to adjust the dimensions of the inner sphere and the amount of coating, i.e., the thickness, to adjust the conditions regarding the thickness of the shell and the weight of the hollow granules. can be carried out quantitatively by an easy method. Regarding the components of the shell material to be coated, by adjusting the blending amount of magnesium oxide, hollow granules containing 50% by weight or more of magnesium oxide as a heat-resistant inorganic substance can be easily produced. In addition, in order to make the shell porous, if the shell composition is mixed with an appropriate amount of a combustible organic material or a foaming agent that vaporizes at the firing temperature, and a firing process is performed, the pores and surface will be created according to the amount and nature of the material. It is easily possible to create unevenness. Although the heat insulating agent of the present invention can be easily produced by the above method, organic matter such as nokulp is not completely burned out and remains inside the hollow body, even if it is not hollow. Any lightweight object within this range can function as the structure of the present invention. This is because even unfired or incompletely fired granules can become completely hollow granules when sprinkled onto the surface of high-temperature molten metal, and exhibit the same performance as fired products. It is.

The heat insulating agent of the present invention will be explained in more detail with reference to Examples below.

Example 1 A finely powdered mixture of 100 parts of magnesia, 5 parts of kaolin, and 5 parts of bentonite was prepared as the material constituting the shell, and pulp obtained from waste newspaper was used as the hydrated natural fiber, which was then granulated. The powder was uniformly sprinkled on the granules with a maximum dimension of 22 m or less and 5 cm or more, to obtain 5.7 parts of granules with a maximum dimension of 22.7 + m or less and w11 or more. Next, this was dried at 95°C and fired at a maximum temperature of 1450°C to obtain a fired hollow granule. This item has a firing plate maximum size of 19.5 legs or less 4.7nu
As a result, the bulk specific gravity was 0.32.

195 kg of this hollow granule was uniformly spread into a ladle containing 300 tons of molten steel. The thickness was 45 mm. We investigated the heat retention effect, oxidation prevention effect, and dust prevention effect after bathing, and for comparison, we also conducted an experiment in which the product was coated with Yakikiri, a commercially available molten metal heat insulator, to the same thickness.

The temperature of the molten steel during tapping was 1630°C.

The results are shown in Table 1.

As shown in Table 1, the heat insulating agent using hollow particles according to the present invention had excellent properties in terms of heat retention effect, antioxidant effect, and dustproof effect. Further, no carburization phenomenon was observed.

In Table 1, the temperature drop after 30 minutes was measured using a thermocouple for measuring hot water temperature, and the antioxidant effect was observed by observing the surface condition.
The ◎ mark indicates no change, and the Δ mark indicates a slight change. Also,
The dust-proofing effect is determined by observing the degree of airborne dispersion such as falling dust. A mark ◎ indicates a state in which there is almost no disembarkation, and a mark X indicates a state in which both dust generation and disembarkation are severe (hereinafter, observations are made using the same criteria). did).

Table 1 Example 2 A fine powder containing 75% magnesium oxide, 100 parts of Magnesia, 10 parts of Honshu clay, and 10 parts of bentonite was mixed and mixed in the same manner as in Example 1. The granules were coated using a sprinkle method.

After drying the granules, they were fired at a maximum temperature of 1,480°C to obtain hollow spheres with strong shells. It was bulky. The thickness of the shell is approximately 0.
It was 5-llIn.

This hollow body weighing 50 kg was placed in 90 tons of molten steel in a ladle with a thickness of approximately 50 mm whose walls were made of magnesia bricks for insulation.
The performance of the molten metal as a heat insulator was investigated. For comparison, a test was conducted while comparing with a commercially available sintered metal heat insulating powder having a thickness of about 50++ uns. In order to confirm the results of magnesia brick erosion, it was used repeatedly 15 times. The results obtained using baked powder are those obtained during normal repeated operations under the same conditions.

The average humidity of the molten steel was 1560°C.

The results are shown in Table 2.

As shown in Table 2, in addition to the heat retention effect, oxidation prevention effect, and dust prevention effect, the magnesia brick exhibited the characteristic that no melting damage was observed. Erosion damage of magnesia bricks was determined based on appearance and volume reduction, as well as the concave phenomenon on the brick surface.

All white table 2 below Example 3 100 parts of magnesha, 5 parts of kaolin, 15 parts of bentonite
A material used for coating was prepared by adding 10% by weight of 48 mesh wood powder to the total mixed fine powder.

A sphere of hydrated natural fibers is coated, dried and fired.
Bulk specific gravity after firing 0.25, maximum dimension 9.51 or less 6.7
Hollow particles of mm or more were obtained. The surface was rough and the presence of pores was well recognized. For comparison, the above-mentioned mixed fine powder without wood flour was used as a material for coating, and coating, drying, and firing were performed. The bulk specific gravity of the fired product is 0.2
9. Maximum dimensions9. ．． A hollow body of 6 ml or less and 5 mm or more was obtained.

The porous material weighed 185 kg for 300 tons of molten steel, and 200 kg of granules prepared for comparison were used to coat the molten steel with an average layer thickness of 40 nwn.

The results are shown in Table 3.

Table 3 It was found that this product has a higher heat retaining ability than other conventional heat retaining agents.

that's all

Claims (1)

[Scope of Claims] (1) A heat insulating agent for molten metal, the shell of which is made of a heat-resistant inorganic material and which is made of hollow granules with a bulk specific gravity of 0.5 or less. 2. The heat insulating agent for molten metal according to claim 1, wherein the heat-resistant material contains at least 50% magnesium oxide. 3. The heat insulating agent for molten metal according to claim 1, wherein the hollow particles have a particle diameter of 3 to 30 mm. The heat insulating agent for molten metal according to claim 1, wherein the four-shell structure is porous. 5. The heat-resistant material contains at least 50% magnesium oxide, and the diameter of the hollow particles is 3 to 30 mm.
The heat insulating agent for molten metal according to claim 1, wherein the shell structure of the hollow particles is porous.