JP2012179628A - Hollow granular mold flux for continuously casting steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent alteration of melting characteristics of hollow granular mold flux caused by pulverization of the flux and scattering of powder dust while in use, by mitigating the pulverization even if the flux is conveyed by gas at high speed over a long distance.SOLUTION: The hollow granular mold flux includes 2.0-10.0 mass% organic binder made of one or more kinds among polysaccharides, a cellulose-based semisynthetic polymer, sodium alginate, a lignin compound, vinylic polymer compounds, polyethylene glycols, etc., and 1.0-10.0 mass% inorganic binder made of one or more kinds among sodium oxo acid salts, potassium oxo acid salts, etc., with respect to the entire amount.

Description

  The present invention relates to a mold flux for continuous casting that is used by being added to a mold in continuous casting of steel, and the flux is used when a long-distance gas conveyance is applied to convey the flux from a flux storage hopper to a continuous casting apparatus or the like. An object is to provide a material in which particles are difficult to powder.

  In continuous casting of molten steel, mold flux is sprayed on the molten metal surface in the mold. This flux melts on the surface of the molten steel to form a molten layer of slag, which keeps the molten steel warm, prevents oxidation and absorbs nonmetallic inclusions, and flows between the solidified shell of steel and the mold for lubrication. .

  Since the flux is likely to be scattered when it is a powder, the work environment may be deteriorated, so that a granular material having a particle size of 1 mm or less is often used. There is a method of extruding a clay-like material to form a granule, but there is a method of making a slurry of a flux component and spraying and drying it in a hot air drying tower. In this method, it is possible to produce almost spherical hollow granules by rapid evaporation of moisture.

  When such mold flux is used for continuous casting, for example, it is automatically supplied into the mold by a charging device as shown in Japanese Patent Application Laid-Open No. 11-239855 (Patent Document 1). In this charging device, a tube-shaped flexible screw conveyor is used to transfer the flux from the flux storage tank to the location of the flux charging chute to cope with changes in the relative position between the storage tank and the charging chute.

However, when the flux of granules is supplied by such a charging device, the granules may break and dust may be generated. Japanese Patent Application Laid-Open No. 10-156492 (Patent Document 2) discloses a method for producing a granular mold flux in which such measures are taken. According to that, using raw materials such as base material, SiO ₂ raw material, melting regulator and melting rate regulator as raw materials, any method such as extrusion granulation, stirring granulation, rolling granulation, fluidized granulation, spray granulation, etc. After granulating into granules, at least one of silicone oil, liquid paraffin, ethylene glycol and the like is added and mixed uniformly in a dry state. As a result, the frictional force of the flux with the screw conveyor and the charging device is remarkably relaxed, making it difficult for the granules to be broken, and the powdering is remarkably improved.

  On the other hand, what uses air is also employ | adopted as a means to convey a flux through a tube. Since transportation by gas does not increase the equipment cost so much even if the distance increases, it is particularly suitable for long distance transportation, and there are examples ranging from several tens of meters to about 100 m. However, it is known that the gas conveyance has a long distance, and friction between the flux particles and the pipe, collision between particles and friction increase, and the degree of pulverization becomes remarkable.

The applicant of the present invention has long been concerned with granulation of granules in gas transport of flux, and has devised a method for evaluating resistance to powdering and disclosed in Japanese Patent Laid-Open No. 2001-83071 (Patent Document 3). . According to this, it has been found that the degree of pulverization increases as the air transportation distance increases and the gas flow rate increases. When the product of the pipe length and the gas flow rate exceeds 1 m · m ³ / min, pulverization becomes significant. However, in Patent Document 3, there is only a method for evaluating the pulverization tendency of the flux, and there is no particular explanation regarding the method for producing the flux with less pulverization.

JP-A-11-239855 JP-A-10-156492 JP 2001-83071 A

  As described above, although cited document 3 has a problem of granulating powder in the gas conveyance of the flux, no countermeasure is provided for this, and a method for producing a flux with less powdering is described later. However, there is no literature. The method of preventing granulation of granules by mixing a lubricant such as silicone oil in Cited Reference 2 is intended to alleviate the frictional force of the flux especially in screw conveyors, etc. We cannot expect a big effect on the conversion. Then, this invention makes it a subject to provide the mold flux for continuous casting by which the powdering of the granule was reduced also in the gas conveyance of flux.

  This invention solves the said subject, Comprising: In the hollow granular mold flux for continuous casting of steel, 2.0-10.0 mass% of organic binders, and inorganic binder 1 are 1 with respect to mold flux whole quantity. It is a hollow granular mold flux for continuous casting of steel, characterized by containing 0.0 to 10.0% by mass. Here, the organic binder is at least one of polysaccharides, cellulose-based semi-synthetic polymers, sodium alginate, lignin compounds, vinyl-based polymer compounds, and polyethylene glycol, and the inorganic binder is sodium oxoacid salt, potassium oxo It is also characterized by being one or more of acid salts.

The hollow granular mold flux for continuous casting of steel of the present invention is also characterized in that it is for carrying a gas that is sent in a state where the flux is floated in a gas when the mold flux is supplied. At this time, the product of the conveyance distance in gas conveyance and the flow rate of gas is also characterized by being 10 m · m ³ / min or more. In addition, when the product of the transport distance and the gas flow rate in the gas transport is 10 m · m ³ / min, the increase in the ratio of the particle diameter with respect to the total flux of particles less than 150 μm is 20% by mass or less. To do.

  The hollow granular mold flux for continuous casting of steel according to the present invention contains a proper amount of an organic binder and an inorganic binder, so that the strength of the granules increases, and even when gas is conveyed at high speed over long distances, there is little powdering. Therefore, it is possible to prevent the occurrence of defects such as slag bears due to alteration of the melting characteristics of the flux due to powdering of the flux. Further, the working environment can be prevented from deteriorating by preventing dust from being scattered during use.

It is a graph which shows the relationship between the quantity of an organic binder, the powdered quantity of a flux, and bulk specific gravity. It is a graph which shows the relationship between the quantity of an inorganic binder, the powdered quantity of a flux, and bulk specific gravity.

The hollow granular mold flux for continuous casting of steel targeted by the present invention is a method for producing a slurry by suspending raw material powder in water and spraying it in a hot air drying tower. Is done. Examples of the raw material powder to be suspended in water include synthetic calcium silicate, wollastonite, portland cement, limestone, diatomaceous earth, and the like, and these are mixed so as to have a target CaO / SiO ₂ ratio. Further, a melting temperature and melt viscosity adjusting agent such as fluorite and Na compound, and carbon powder for adjusting the melting rate are added as necessary. These raw materials may be a mixture of the respective powders, or may be a premelt raw material obtained by melting and pulverizing a part or the whole other than the carbon powder.

Although not particularly limited for the components range of the flux in the present invention, as a result of mixing the raw materials as described above, as an analytical value, for example, SiO _2: 20 to 45 mass% (hereinafter,% as), CaO: _{25~45%, Al 2 O 3:} 1~15%, Na 2 O: 0.5~20%, F: 0.5~20%, C: a 0.5% to 10%, such as components.

  Here, in the present invention, an organic binder and an inorganic binder are added to the liquid in which the raw material powder is suspended. As the organic binder, a water-soluble polymer compound is used, which solidifies upon drying to produce an adhesive force. Thereby, the particles of the raw material powder are firmly fixed to increase the strength of the granule. Water-soluble polymer compounds used as raw materials for organic binders can be classified into natural polymers, semi-synthetic polymers, and synthetic polymers.

  Natural polymers mostly belong to polysaccharides and include starch, dextrin, guar gum, xanthan gum, gum arabic, carrageenan, pectin and the like. Semi-synthetic polymers include lignin compounds such as sodium alginate and calcium lignin sulfonate obtained by treating pulp waste liquor in addition to celluloses such as methylcellulose, carboxymethylcellulose, ethylcellulose, and hydroxyethylcellulose. As the synthetic polymer, vinyl polymer compounds such as polyvinyl alcohol, polyvinyl methyl ether, and polyvinyl pyrrolidone, polyethylene glycol, and the like can be used. These organic binders may be used alone or in combination of two or more.

  The amount of the organic binder added is suitably 2.0 to 10.0% with respect to the total amount of mold flux sprayed and dried in the hot air drying tower. FIG. 1 is a graph showing the relationship between the amount of the organic binder, the amount of pulverization when the air is conveyed under certain conditions, and the bulk specific gravity of the flux. From this, the organic binder increases the strength of the granules when the amount increases to some extent, but the strength decreases on the contrary when the amount further increases. As shown in FIG. 1, it was found that the bulk specific gravity decreases in such a range where the strength decreases. Therefore, the decrease in strength when the amount of the organic binder is large is considered to be due to an increase in the hollow portion of the granule. The organic binder also has an action of dispersing the carbon powder, and it is necessary to add it in order to exhibit this effect. Therefore, the addition amount of the organic binder is 2.0 to 10.0%, preferably 2.5 to 7.0% with respect to the total amount of the mold flux.

  On the other hand, as the inorganic binder, an inorganic substance that dissolves in water and solidifies when dried is used, and sodium oxoacid salts such as sodium carbonate, sodium aluminate, sodium phosphate, and sodium silicate are suitable. In addition, potassium carbonate or other potassium oxoacid salts in which potassium is used in place of sodium of the above compounds can be used. Moreover, you may use these 1 type or in mixture of 2 or more types. The component of the inorganic binder is considered to adhere to the particle surface of the raw material powder and solidify by drying, and fix the powder particles to increase the strength of the granules.

  The amount of the inorganic binder added is suitably 1.0 to 10.0% with respect to the total amount of mold flux sprayed and dried in the hot air drying tower. FIG. 2 is a graph showing the relationship between the amount of the inorganic binder, the amount of pulverization when air-conveyed under a certain condition, and the bulk specific gravity of the flux. As can be seen from the graph, when the amount is increased to a certain extent as in the case of the organic binder, the strength of the granule is increased. However, when the amount is further increased, the strength is decreased. As in the case of the organic binder, the bulk specific gravity is reduced in such a range that the strength is reduced, and the decrease in the strength is considered to be due to an increase in the hollow portion of the granule. Inorganic binders are cheaper than organic binders, and organic binders are necessary for the dispersion of carbon powder, but it is advantageous in terms of cost to use inorganic binders by minimizing the use. Moreover, when there is much quantity of an organic binder, there exists a possibility of causing the increase in the carbon content of a slab, and also from this point, a large amount of use is not preferable. Therefore, the addition amount of the inorganic binder is 1.0 to 10.0%, preferably 1.5 to 9.0% with respect to the total amount of the mold flux.

  In addition, the component of an inorganic binder is used not only for binders, such as sodium carbonate, but also for component constitution such as addition of sodium. In this case, it acts as a component of the flux component as well as a binder, and is included in the added amount of the inorganic binder. However, for example, when sodium carbonate is melted together with other materials as a raw material for producing a premelt agent, it does not dissolve in water when the raw material powder is made into a slurry. not enter.

  The hollow granular mold flux for continuous casting of steel according to the present invention is particularly suitable for applying gas conveyance when supplying mold flux. That is, gas conveyance is often applied to long-distance conveyance. For example, there is an example in which a pipe length is 50 m to 90 m. By the way, two types of methods are generally known as a method for conveying powder particles, and there are a low concentration high speed transport method and a high concentration low speed transport method.

  In the low-concentration high-speed transportation method, the granular material is floated and transported at an air velocity of 10 to 30 m / s by applying a pressure of about 100 kPa or less at the transportation source. On the other hand, the high-concentration low-speed transportation system makes the section of the pipe intermittently closed by intermittently sending out the powder particles in a state where the gas is pressurized to, for example, several hundred kPa at the transportation source, It is conveyed at an air velocity of about several m / s by energy.

  The high-concentration low-speed transportation method has a problem that the air pressure must be increased as the piping becomes longer. On the other hand, since the hollow granular mold flux of the present invention is hollow, it has a small bulk specific gravity and can be easily floated in a gas. As a result, the pipe can be transported smoothly even over long distances, so a low concentration high speed transportation system is adopted.

The degree of collapse of the hollow granular mold flux during gas conveyance increases as the conveyance distance increases and also increases as the gas flow rate increases. If the product of the transport distance and the gas flow rate is 10 m · m ³ / min or more, the degree of collapse may be significant depending on the type of flux, but the hollow granular mold flux of the present invention has gas under such conditions. Even if it is applied to conveyance, the degree of collapse is small. The product of the transport distance and the gas flow rate corresponds to, for example, a case where a transport distance of 50 m is transported at a flow rate of 0.2 m ³ / min (pipe diameter is 19 mm), and the air velocity at that time is 12 m / s. It becomes.

As a test method for the degree of collapse when gas is conveyed, the gas is actually conveyed for a distance of 50 m at a gas flow rate of 0.2 m ³ / min. In other words, the product of the transport distance and the gas flow rate is 10 m · m ³ / min, but if the increase in the ratio of particles with a particle diameter of less than 150 μm to the total flux is 20% by mass or less, the product is good. It can be said. The hollow granular mold flux of this invention corresponds to such a thing.

Hereinafter, the present invention will be described in detail by way of examples.
In producing the hollow granular flux of the present invention, fluxes having the components shown in Table 1 were prepared as basic flux excluding the binder component. These fluxes were prepared as pre-melt raw materials obtained by mixing raw materials for making a predetermined flux component such as synthetic calcium silicate, Portland cement, fluorite, etc., and melting and pulverizing all but the carbon powder. This pre-melt raw material powder and the above carbon powder were mixed so as to become the components shown in Table 1.

  To the basic flux shown in Table 1, various organic binders and inorganic binders shown in Table 2 were blended and water was added to suspend them into a slurry. Furthermore, this was sprayed and dried in a hot air drying tower to obtain a hollow granular flux. In addition, the compounding quantity of the organic binder shown in Table 2 and an inorganic binder is a ratio with respect to the flux whole quantity which is the sum total with a basic flux.

The bulk density of the hollow granular flux produced as described above was measured, and the results are shown in Table 2. Moreover, it tested about the extent of the collapse | disintegration when carrying gas. The test method carried 2.0 kg of flux through a pipe having an inner diameter of 19 mm and a length of 50 m at a gas flow rate of 0.2 m ³ / min. Thereafter, the amount of increase in the ratio of the particles having a particle size of the flux of less than 150 μm to the total amount of the flux was determined. The results are also shown in Table 2.

  Flux numbers 1 to 14 are those according to the present invention, and the addition amount of the organic binder and the inorganic binder is appropriate. Therefore, the amount of increase of grains less than 150 μm was 20% or less as defined in the present invention. Therefore, it is a flux suitable for gas conveyance which sends a long distance at a high speed in a state of being suspended in the gas.

  On the other hand, the flux of No. 15 as a comparative example has a small amount of organic binder added, and the flux of No. 16 has a small amount of inorganic binder added.

  Moreover, since the flux of No. 17 which is a comparative example has too much addition amount of the organic binder, and the flux of No. 18 has too much addition amount of the inorganic binder, the bulk specific gravity becomes small in any case, and accordingly, the particle size of less than 150 μm There was a lot of increase.

  In addition, the fluxes of No. 19 and No. 20 which are comparative examples had too many total addition amounts of a plurality of types of organic binders and inorganic binders, respectively, so that the bulk specific gravity was small and the amount of increase of grains less than 150 μm was large.

Claims (5)

The hollow granular mold flux for continuous casting of steel contains 2.0 to 10.0% by mass of organic binder and 1.0 to 10.0% by mass of inorganic binder with respect to the total amount of mold flux. Hollow granular mold flux for continuous casting of steel. The organic binder is one or more of polysaccharides, cellulose-based semi-synthetic polymers, sodium alginate, lignin compounds, vinyl-based polymer compounds, and polyethylene glycol, and the inorganic binder is sodium oxoacid salt or potassium oxoacid salt. The hollow granular mold flux for continuous casting of steel according to claim 1, characterized in that it is at least one of them. The hollow granular mold for continuous casting of steel according to claim 1 or 2, characterized in that, when supplying the mold flux, it is for conveying the gas in a state where the flux is floated in the gas. flux. 4. The hollow granular mold flux for continuous casting of steel according to claim 3, wherein the product of the transport distance in the gas transport and the gas flow rate is 10 m · m ³ / min or more. When the product of the transport distance and the gas flow rate in gas transport is 10 m · m ³ / min, the amount of increase in the ratio of the particles having a particle diameter of less than 150 μm to the total flux is 20% by mass or less. Item 5. A hollow granular mold flux for continuous casting of steel according to Item 3 or 4.

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