JPH06198404A - Hollow ceramic particle for heat insulation of molten steel and its production - Google Patents

Abstract

PURPOSE:To provide the hollow ceramic particles for heat insulation meeting requirements for absence of dust generatability, low oxygen potential of carbon harmful for steel in order to prohibit traces and reduction of SiO2, formation of a liquid phase at the boundary between the molten steel and a heat insulating material to prevent the erosion of the coating materials of a long nozzle and tundish, etc. CONSTITUTION:These ceramic particles are the calcined ceramic particles consisting of 10 to 60 parts magnesia and 90 to 40 parts wollastonite as main materials and outer and outer 5 to 15% binder material. The thickness of the skins of the ceramics is 0.1 to 0.5mm, the spherical diameter is 1 to 5mm and the compressive strength is 50gr to 1500gr. The generation of the traces of the carbon incorporated therein and the dust at the time of use after transportation is nearly entirely obviated. As a result, the generation of the dust is entirely obviated at the time of charging the particles into the tundish. The surfaces are efficiently coated after charging of the carbon and the desired heat insulating effect is obtd. The raw material of balls and foamed polystyrene balls are industrially easily obtd. and the mass production with a rotary kiln is possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-insulating material for tundish molten steel in a continuous casting method.

[0002]

2. Description of the Related Art Generally, in continuous casting of molten steel, when a small amount of inclusions in the molten steel discharged from a ladle are floated and removed, the molten steel is stably poured at a predetermined temperature while being poured into a mold. There is a tundish for hot water.

As described above, the function of the tundish is important in addition to the floating removal of a small amount of inclusions in the molten steel, and it is particularly important that the temperature drop of the molten steel due to the tundish is suppressed to a very small level so that the tundish can be kept in a predetermined temperature range. It is to secure pouring water.

This means that when pouring molten steel into a mold, it ensures proper fluidity of the molten steel and prevents pouring accidents due to adhesion of metal to nozzles for pouring or clogging. . Conventionally, in the tundish, a powdery or plate-like heat insulating material is added for the temperature effect of molten steel, the adsorption of molten steel inclusions in the tundish, and the prevention of air oxidation on the surface. Examples of the heat insulating material include carbon-based additives such as burnt rice husks or processed products thereof, or JP-A-54-54 from the viewpoint of heat insulating effect and economical efficiency.
As described in 5040, a plate-shaped heat insulating material in which CaO—SiO ₂ —Al ₂ O ₃ is used as a base material, and an alkali metal or alkaline earth metal carbonate and a small amount of carbon are added to the base material is used.

However, as described above, a plate-shaped heat insulating material containing burned fir or carbon has an adiabatic heat insulating property because it burns off early or reacts with a slight amount of high-temperature slag to dissipate heat of fusion from molten steel. In addition, the carbon in the molten steel is about 10 to 100 p. p.
It often happens that the components in the molten steel picked up by m are not suitable. Furthermore, when these heat insulating materials were added to the tundish, the dust generation was severe, and the work of the continuous casting plant,
Hygiene and environment are extremely bad.

Japanese Unexamined Patent Publication (Kokai) No. 64-150 is preheated to 100 ° C. to remove moisture from inorganic substances such as hirucite and obsidian, and an organic binder or an inorganic binder is used on the surface of minerals having many pores to form MgO powder. It was added and fixed, and then heated at 450 ° C. The MgO-based powder was not sintered, and the dust generation property is considerably improved over the plate-shaped heat insulating material, but it is still satisfactory. Absent. Furthermore, although the residual carbon content is far less than that of the plate-shaped heat insulating material, it cannot be said to be satisfactory for ultra-low carbon steel.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention has the following problems. (1) No dust generation, traces of carbon harmful to steel, SiO ₂
Material with low oxygen potential to prevent reduction of oxygen.

(2) A liquid phase is formed at the boundary between the molten steel and the heat insulating material.

(3) The long nozzle and tundish coating materials are not corroded.

The object of the present invention is to provide a heat retaining hollow ceramic particle having the above conditions and a method for producing the same.

[0011]

The present invention has solved the above-mentioned problems, and its gist is as follows.

(1) The following components and shapes are used in order to sufficiently satisfy the effect after the addition to the tundish.

Magnesia (10% to 60%) and silica stone (90% to 40%) are the main materials, and outside% (10% to 5%).
%), A calcined hollow ceramic particle composed of a binder, bentonite, clay, etc., with a ceramic particle skin thickness of 0.1.
mm-0.5 mm, spherical diameter 1 mm-5 mm, hollow ceramic particles for heat insulation of molten steel.

(2) After being transported, it is fired as follows in order to have almost no dust generation when it is put into a tundish and to make the contained carbon a trace.

A spherical foamed synthetic resin having a diameter of 1 mm to 5 mm was placed in a plate-type rotary granulator, and the adhesive solution was sprayed while operating the granulator, and 200 mesh or less and 90% or more of magnesia and 200 Pre-mixed wollastonite with mesh or more, magnesia: wollastonite = (10-60): (90-
The powder in the ratio of 40) is sprayed alternately with the adhesive solution to granulate, and the granulated product is dried at 200 ° C. or lower, and then about 1300 ° C.
And the thickness of the ceramic particle skin is 0.1 mm to 0.
A method for producing a hollow ceramic for heat insulation of molten steel, which comprises producing 90% or more of hollow particles having a diameter of 5 mm and a diameter of 0.5 mm to 3 mm.

The present invention will be described in detail below.

Claim 1. Description of the main component of the heat insulating hollow ceramic particles of the present invention, the mixing ratio of magnesia and silica stone is (10-60): (90-4
The reason for setting 0) is that in the case of continuous casting, which has a long running time once in continuous casting, magnesia: silica stone: 60:40 is the flow of balls in the tundish, and sintering on the liquid phase in contact with molten steel. The thickness of the strip is suitable for tundish maintenance, and in the case of continuous casting of a single ladle, magnesia: silica stone = 10:90 can be used and is inexpensive. That is, the ratio of magnesia and silica stone is determined by how many ladles are continuously cast.

However, when the magnesia is more than 60%, the fire resistance is high, the liquid phase is thin, and the flow of the hollow balls into every corner of the tundish becomes poor. If the magnesia is less than 10%, the sintered layer in contact with the liquid phase is thick and it takes time to maintain the tundish, which is not desirable. Further, bentonite and clay which are added in an amount of 10% to 5% in the outer% are claimed in Claim 2. The purpose is to secure the strength of the hollow ball, to suppress dusting, and to quickly produce a thin liquid phase, but the upper limit of SiO ₂ from oxygen Pontecil is less than 10%.

The thickness of the ball skin is 0.1 mm to 0.5.
The reason for limiting the thickness to 0.1 mm is that if 0.1 mm or less, sufficient strength cannot be maintained, and if it is 0.5 mm or more, the bulk specific gravity of the hollow ball becomes large, and the effect of heat retention is reduced. By the way, claim 2. At a heating temperature of 1300 ℃, the average skin thickness is 0.3m
The compressive strength of the hollow balls is about 1 kg / 1 piece at m, does not crack during transportation, and does not generate dust when the tundish is charged.

Further, the reason for limiting the diameter of the balls to 1 mm to 5 mm is that the tundish has a refractory cover because it is heat insulating, and the charging port is narrow. In addition, hollow ceramic balls were made by attaching spherical particles of inorganic material to inorganic powder with an adhesive solution, and then
Since it is fired at a high temperature of 300 ° C., it is fundamental that spherical organic materials can be easily obtained at low cost.

The commercially available spherical foamed resin is
Basic materials such as fillers, plates, and heat insulating materials for transportation have a diameter of 1 mm to 20 mm, and those produced in large quantities have a size of 1 mm to 5 mm. However, the bulk specific gravity is 0.5 or less, that is, 3 mm to 5 mm is preferable in order to enhance the heat insulating effect.

Claim 2. Description The rotary granulator used in the production of the hollow ceramic balls of the present invention includes, for example, a plate granulator, a conical granulator, a drum granulator, etc. use.

As the spherical expanded synthetic resin to be put into this granulator, there are general-purpose resin expanded polystyrene, expanded polypropylene, etc., but due to the reasons described above, expanded polystyrene is easily available and inexpensive. 1mm for Styrofoam particles
Although there is a diameter of ˜20 mm, for example, a diameter of 1 mm to 5 mm was used as a preferable particle diameter. Although there are vinyl chloride type foam synthetic resins, harmful chlorine gas is emitted when baked at 1300 ° C, which is not preferable.

Styrofoam can be easily dissolved in an organic solvent, especially when a 5% PVA solution is sprayed, the surface of the styrene is slightly melted, and when a mixture of magnesia, silica stone, a small amount of bentonite, and clay is sprayed, it will be fast. The powder is collected and solidified. PVA itself also collects and solidifies the powder. Before it is put into a firing kill, it is heated and dried at about 80 ° C. for about 5 minutes in order to obtain sufficient strength so that it is not pulverized before being put into the kiln through a hopper, a conveyor, etc. Then, the dried hollow ceramic balls are heated to about 130 in a firing kiln.
Heat at 0 ° C., hold time 15-30 minutes.

Incidentally, the rotation speed of the plate granulator is 80 times / minute, the granulation time is 50 minutes, the adhesive solution is 9 l, and the granulation amount is 50 kg / 1 time.

[0026]

[Action]

Dust generation property and carbon content As described above, the hollow ceramic ball of the present invention is heated at about 1300 ° C. for 15 to 30 minutes as shown in the manufacturing method,
This causes the powder of magnesia and silica stone to sinter, eliminating dust generation and leaving carbon traces.

FIG. 1 shows a mixture of magnesia and wollastonite, the mixture of which has a different mixing ratio, and a high-temperature microscope of Lights and a heated sample thereof.
The results of line diffraction are shown. At 1200 [deg.] C., magnesia and apatite are mixed with each other in the mixing ratio MgO, 10% to 90%, and akermanite is confirmed by X-ray. Also, as a result of observation with a high temperature microscope, the melting start temperature changes depending on the mixing ratio of magnesia and silica stone, but it can be said that the sintering state is 1350 ° C. or lower in each mixing.

Further, the thin-skin hollow ceramic balls should not be pulverized during transportation or in the process of packing, and the load test of the ceramic hollow balls was conducted.

Three kinds of bentonite balls of 10%, 5% and 0% were externally compounded with 60% of magnesia and 40% of silica stone, dried at 60 ° C. for 3 hours, and then the inner diameter was 15 cm and the depth was 3 c.
After heating the plate-shaped refractory of m to 800 ° C., 50 g of balls are put on it, heated and baked at 1000 ° C. to 1300 ° C. for 10 minutes, and 10 balls each arbitrarily taken out are placed on the scallops. FIG. 2 shows the relationship between the heating temperature, the amount of bentonite added, and the compressive strength, which is called the compressive strength based on the weight when crushed. As is clear from this, at the above-mentioned firing temperature of 1300 ° C., 500 gr / 1 without addition of bentonite.
When the amount of bentonite added is increased, the compressive strength is increased and it becomes difficult to break.

Further, the carbon content is decreased by heating and calcination as the heating temperature rises. The state is shown in Table 1. The C analysis method is based on the elemental analysis method. 13 from this table
The heating temperature of 1300 ° C. to 1350 ° C. is extremely important in order to prevent dust and the contained carbon from becoming traces at 00 ° C.

[0031]

[Table 1]

The influence on dust generation and molten steel quality will be described.

In the present invention, a powder of MgO and a powder of apatite are mixed, and a polymer organic adhesive solution is sprinkled on the surface of a spherical expanded synthetic resin at the center, and when a suitable ceramic layer is formed, this is mixed with 200 It is dried at 1300 ° C or below after drying at ℃ or less to make a sintered ball, which is generally used in commonly used burned grain (A), steamed grain (B), the product of the present invention, and iron mills as shown in Fig. 3. The results and method are shown.

The air velocity was changed on the filter paper, and the weight of the dust collected in 1 minute was observed. The results are shown in Table 2. The measurement results are shown in FIG. 4. The conventional product is dusted at a wind speed of 4.8 m / sec, and on the contrary, the hollow ball is not dusted at 4.8 m / sec. By the way, since it is thrown in through the hole in the tundish refractory lid, the hot air blown out through the hole is 3.0-4.
At 8 m / sec, no dusting of the hollow ceramic balls was observed, which is extremely good for environmental hygiene.

Table 3 shows the chemical analysis values of the ball raw materials.

From Tables 2 and 3, no carbon was found in the raw material MgO of the hollow ceramic balls, silica stone or hollow ceramic balls, and as a result of X-ray analysis, no free SiO ₂ was found in the raw materials. Contrary to this, Table 2 is free from Si
O ₂ is high and carbon is 3.58%, and steamed rice grain is high in SiO ₂ and carbon is 74.44%, which is very high and harmful to molten steel.

[0037]

[Table 2]

[0038]

[Table 3]

Oxygen Potential FIG. 5 shows the slag of SiO ₂ —CaO—MgO at 1600 ° C.
Activity of. As is clear from this figure, SiO ₂ is 40
% Or less, no oxidation of molten steel can occur. Also, SiO ₂ is 4
If it is 0% or less, the reaction with the main component SiC of the long nozzle does not occur. As will be described later in Examples, SiO _{2 of the} hollow ceramic balls is approximately 32% and the other is a basic component such as CaO or MgO. Oxidation of molten steel by SiO _{2 No} oxidation of SiC by SiO ₂ occurs.

Forming a liquid phase at the boundary between the molten steel and the heat insulating material The molten steel reacts with oxygen in the air and is oxidized. In order to prevent this, it is effective to create a liquid phase of the heat insulating material at the contact surface between the molten steel and air, that is, the surface of the molten steel.

When a hollow ceramic ball is put in through a narrow hole in a tundish, it comes into contact with molten steel at about 1550 ° C. It is desirable to contact the molten steel, immediately form a thin liquid phase, and carry a heat insulating material with good fluidity and lightness to every corner of the tundish. The liquid phase also prevents the dissipation of heat from the molten steel and sinters the hollow ceramic balls above it, the sintered layer also preventing the dissipation of part of the heat. A layer is formed on top of this without reacting to prevent heat dissipation. The generation of the liquid phase will be described with reference to FIGS. 1 and 6. Sintered materials of 60% to 10% magnesia and other silica stones melt above 1500 ° C. Also, trace amount of FeO in molten steel
If so, a low-melting substance is formed. It is believed that this liquid phase carries the hollow ceramic balls. In order to confirm this, 10 kg of molten steel was made in a vacuum melting furnace, gradually returned to normal pressure at 1580 ° C, and quickly magnesia: silica stone = 50: 5.
No. 0 hollow ceramic balls were charged, and after 8 minutes, the hollow ceramic balls were taken out, and the state is shown in FIG. There is a black thin liquid phase on top of the molten steel, the composition of which is CaO ・ SiO ₂・ FeO ・ MgO and the melting temperature is 12 according to X-ray analysis.
It is an extremely thin layer at 00 ℃ ~ 1250 ℃, which is a clear amber color and has a thickness of about 3 mm. According to X-ray analysis, the melting temperature of Monteiselite, CaO ・ SiO ₂・ MgO is 1500 ℃. ~ 1600 ℃ and clear liquid phase
There is a sintered layer and unreacted layer to prevent heat dissipation of molten steel.

Reaction with long nozzle and tundish wall material Magnesia: silica stone = 60:40 balls were crushed, and 8
A long nozzle of 5 mm × 15 mm × 12 mm was molded, the material of the long nozzle of the same type and the coating material were brought into contact with each other as shown in FIG. 8, and baked at 1600 ° C. for 10 hours in a reducing atmosphere. The resulting long nozzle material (a), coating material (b)
There was no change in both, the upper layer of the same quality as the heat insulating material melted, and neither the contact surface (a) nor the contact surface (b) was melted.

[0043]

【Example】

 Example 1.

[0044]

[Table 4]

Example 2. Example of manufacturing method Granulator used (for example, Marumerizer) Granulation condition Rotation 80 r. p. m Spherical foamed resin Styrofoam, particle size 1 to 5 mm Single dose 60 l Adhesive solution Single dose 9 l Polyvinyl alcohol (PVA). 5% solution Seawater magnesia clinker powder 200 mesh or less, one-time input 45kg Natural silica stone powder (made in Korea) 200 mesh or less, one-time input 5kg Drying condition 180 ° C 3 minutes Firing condition 1350 ° C ± 20 ° C 20 The obtained balls are the same as those in Example 1. It is I.

Example 3. Seawater magnesia clinker powder 200 mesh or less, one-time input amount 25 kg Natural silica stone (made in Korea) 200 mesh or less, one-time input amount 25 kg Other Example 2. Is the same as. The balls obtained are from Example 1. Is C.

Example 4. Seawater magnesia clinker powder 200 mesh or less, one-time input amount 30 kg Natural silica stone powder (Korea) 200 mesh or less, one-time input amount 20 kg Other Example 2 Is the same as. The balls obtained are from Example 1. It is D.

Example 5. Seawater magnesia clinker powder 200 mesh or less, once input Blast furnace slag-powder: Similar to natural silica stone and composition. 200 mesh or less, one-time charging amount, etc. Example 2 Is the same as. The ball obtained is E.

The following table shows various effects when the ball obtained according to the present invention and the conventional heat insulating material are applied to an actual machine.

[0050]

[Table 5]

Sample A. B. C. D is the heat insulating material of the present invention, and is used in Example 4. 18t mass production at a production plant and used in a tundish. B. C is a conventional heat insulating material. The effect of heat retention is the temperature drop rate in the tundish (℃
/ Hr), the reaction with molten steel is A1 in molten steel and Si in heat insulating material.
O ₂ reacts and contaminates the molten steel.

The reaction formula is 4Al + 3SiO ₂ → 2Al ₂ O ₃ + 3Si Therefore, as an evaluation of molten steel contamination, Si pickup in molten steel is used (⊚: no reaction, ○: almost no reaction, Δ: slight reaction, X: Large reaction in FIG. 9) FIG. 9 shows the Si pickup when the heat insulating material in the above table was used. The firing temperature, raw material particle size, and PVA solution concentration will be described below.

[0053]

[Table 6]

[0054]

[Table 7]

[0055]

[Table 8]

[0056]

EFFECTS OF THE INVENTION No dust was generated when the tundish was charged, the steel was not contaminated by carbon and silicon, the scene was well covered after the ball was charged, and the desired heat retaining effect was obtained. The ball raw material, Styrofoam balls, are industrially easily obtained and can be mass-produced in a continuous kiln.
It is industrially possible and satisfying.

[Brief description of drawings]

FIG. 1 is a diagram showing the results of observing the changes in the proportions, the firing start temperature, and the melting start temperature of a powder of MgO and apatite ground to 300 mesh or less and observing the changes in their proportions with a high-temperature microscope of Lights.

FIG. 2 is a diagram showing the heating strength of a hollow ceramic ball.

FIG. 3 is a diagram showing a dusting measurement method, and an explanatory diagram of a mode in which a heat insulating material is put in the wind tunnel to change the wind speed, and dust is collected by a filter paper to measure the weight.

FIG. 4 is a diagram showing a relationship between wind speed and amount of scattering.

FIG. 5 is a diagram showing an oxygen potential of SiO ₂ · CaO / MgO system.

FIG. 6 is a state diagram of three components of SiO ₂ , CaO, and MgO, and shows a change when CaO and SiO ₂ (silica stone) are mixed with MgO and heated.

FIG. 7 is a view showing a state where a ball is put into an actual furnace and pulled up.

8A and 8B are diagrams in which the material of the long nozzle and the tundish are brought into contact with the ball and the reactivity with the ball is examined.

FIG. 9 is a diagram showing the relationship between the type of heat insulating material and the amount of Si pickup in molten steel.

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[Procedure amendment]

[Submission date] February 5, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] Figure 8

[Correction method] Change

[Correction content]

[Figure 8]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuto Shibata 57 Mitsukecho, Seto City, Aichi Prefecture Tokai Mineral Co., Ltd.

Claims (2)

[Claims] 1. Magnesia 10-60, silica stone 90-4
A ceramic skin thickness of 0.1 mm
0.5mm, ball diameter 1mm-5mm, compressive strength 500gr
~ 1500 mmgr, carbon traces contained, hollow ceramic particles for heat insulation of molten steel characterized by almost no generation of dust after use after transportation. 2. A diameter of 1 mm to 5 mm in a plate type rotary granulator.
The spherical organic substance is added and the adhesive solution is sprayed while operating the granulator, and magnesia of 200 mesh or less and 90% or more and silica stone of 200 mesh or less and 90% or more (10 to 60%) (90-40%) of the mixture is sprayed alternately with the adhesive solution, the granulated product is dried at 200 ° C. or lower, and then fired at about 1300 ° C. to produce the hollow particle of claim 1. A method for producing a hollow ceramic for heat insulation of molten steel.