KR930008544B1 - Mold slag - Google Patents

Abstract

The low fluorine flux being useful in continuous casting mold is composed of (in wt.%) 15-25 % CaO, 5-10 % F, 5-15 % BaO, 5-15 % B2O5, below 25 % BaO+B2O3, below 5 % Na2O, below 5 % Li2O, below 10 % MgO, below 10 % Al2O3, below 5 % C, 0.9-1.1 of (CaO+BaO) /SiO2, and balance inevitable impurities. The flux decreases the dissolved fluorine in water-soluble substance to react upon the cooling water of high pressure and high temperature in the continuous casting process.

Description

Low Fluorine Elution Molding Solvent

1 is a graph showing the fluorine elution amount of the casting solvent according to the conventional solution stirring time.

2 is a graph showing the melting characteristics of the solvent according to the conventional addition amount of F.

The present invention relates to a solvent which is used for continuous casting and consumed together with the drawing of cast steel while being applied to the molten steel surface in the mold and covering the molten steel surface, and more specifically, it is designed to suppress the fluorine dissolution to prevent environmental pollution. It relates to a fluorine elution template solvent.

In general, the casting solution is molten by slag and molten by the heat of molten steel, thereby preventing the molten steel from being oxidized by air, absorbing non-metallic inclusions floating in the molten steel, and infiltrating between the mold and the slab to lubricate. In addition, fluorine (F), which is essential in the solution, has a serious impact on environmental pollution.

In particular, in recent years, environmental pollution due to air pollution and water pollution has attracted attention around the world. In particular, water pollution caused by wastewater discharged into the sea or rivers has various adverse effects on the human body that uses these animals and plants as well as the death of animals and plants that consumed them.

On the other hand, fluorine contained in the water quality is very effective in the protection of children's teeth in the growth phase when the concentration of about 1 ppm is deliberately added to the water supply in Western countries.

However, when drinking more than 8ppm of fluoride content, cartilage, ligaments, muscles are known to be in a state in which calcification proceeds to the vertebrae and pelvis, which makes it impossible to move back and forth. In addition, if a child consumes more than 2ppm, white spots appear on the anterior teeth, and the entire surface of the sublarvae becomes white, causing holes or defects.

Therefore, in Korea, the water content of factory wastewater is strictly limited to 15 ppm or less.

On the other hand, even in steel mills, wastewater containing fluorine comes out through various paths due to the nature of the operation, and a large amount of money is put into the water purification treatment facility to treat it. In particular, in the regeneration process, a large amount of water is used to cool the cast steel, but since the fluorine content in the cooling water is much higher than the legal limit and the corrosion of the respirator is very severe, the removal of this fluorine during operation is very urgent.

On the other hand, the fluorine ions contained in the cooling water of the continuous casting process are mostly fluorides such as NaF and CaF ₂ contained in the solvent of the mold eluted in the cooling water. It contains a large amount of fluoride.

The most important role of the mold solvent used in the continuous casting process is lubrication between the mold and the slabs. The properties of the mold solvent which have the greatest influence on the lubrication are the high temperature melting point and viscosity.

For the control of such a viscosity and melting temperature of the mold powders, the alkali oxides and fluorides there is added to the _{CaO-SiO2-Al 2 O 3} 3 alloy, a double fluoride is known to be most effective in lowering the viscosity.

The fluoride contained in the casting solvent is eluted with cooling water as follows. The mold solvent melts into slag of liquid when it comes into contact with hot molten steel, and the slag penetrates between the mold and the cast together with the vibration of the mold and the drawing of the cast and exits the mold together with the cast.

The slag that penetrates between the mold and the slab is called a slag film. The slag film immediately hits the high pressure cooling water when it exits the mold and is then ground into powder.

The powder slag membrane reacts with high temperature and high pressure cooling water, elutes into water-soluble substances, and circulates and accumulates in the performance cooling water system. The degree to which fluorine in the accumulated cooling water is eluted depends on the type of fluorine compound in the slag film. On the other hand, as a method for reducing the fluorine contained in the above-mentioned performance cooling water, there are the following methods.

(1) A method for removing fluorine in cooling water through a wastewater purification process.

(2) A method of using a solvent of a mold that does not contain fluorine.

(3) A method of using a mold solvent capable of suppressing fluorine elution.

The most commonly used method of removing fluorine in wastewater is using CaO-based powders (CaO, CaCl ₂ , Ca (OH) _2, etc.) to convert fluorine ions into CaF ₂ which is poorly soluble in water. And a method for separating and removing fluorine ions using an ion exchange resin.

However, the method of using the CaO system has a problem of treatment of the residue due to the use of excess treatment agent and a problem that the treatment efficiency is lowered in the presence of the interference element in the cooling water.

In addition, the method using the ion exchange resin has a disadvantage in that the treatment cost is high and the concentration of fluorine ions in the treatable cooling water is limited.

In addition, the method (2) may be the best method of removing the fluorine source in principle, but there is a disadvantage that the material that can replace the fluoride contained in the solvent is very limited and expensive.

In other words, borax (Borax, Na ₂ B ₄ O ₇ , nH ₂ O) is a substitute for fluoride. Since borax is a very unstable substance at room temperature, even if anhydrous borax is used, water in the air may be removed. Because of the absorption, there is a problem that foaming defects are generated on the surface of the cast steel, and the use of the high-speed casting that requires maximization of lubrication ability is not achieved because the effect of lowering the viscosity is less than fluoride.

Accordingly, the present inventors have continued to research and experiment with the solvent of the mold based on the method of (3) to improve the above problems, the effect of lowering the melting temperature and viscosity when containing B ₂ O ₃ is good, BaO-containing The present invention was proposed in view of the good suppression effect of fluorine elution. The object of the present invention is to use BaO and B ₂ O ₃ mixed instead of drastically reducing the amount of Na ₂ O in the solvent. By appropriately controlling the content of each component to form a solvent, it is possible to drastically reduce the elution of fluorine even when the solvent is introduced into the mold while the melting temperature, viscosity, gas generation amount and water absorption rate (hereinafter referred to as "the overall physical properties") are low. It is to provide a low fluorine dissolution mold solvent. EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In the present invention, in the low fluorine-dissolving mold solvent used for continuous casting, in weight%, CaO: 15-25%, F: 5-10%, BaO: 5-15%, B ₂ O ₃ : 5-15 %, Total amount of BaO and B ₂ O ₃ : 25% or less, Na ₂ O: 5% or less, Li ₂ O: 5% or less, MgO: 10% or less, Al ₂ O ₃ : 10% or less, C: 5% Hereinafter, the present invention relates to a low-fluorine elution template solvent composed of SiO ₂ and other unavoidable trace components above a range in which the ratio of (CaO + BaO) / SiO ₂ may be 0.9-1.1.

Hereinafter, the present invention will be described in detail through examples.

Example 1

In order to determine the fluorine elution mechanism of the conventional molding solvent, in the mold solvent prepared as shown in Table 1 below, the fluorine ratio was kept constant at 8% and the amount of Na ₂ O was changed as the first degree to prepare a sample. The sample was melted at 1300 ° C. to produce slag, coagulated and ground to a particle size of 68 μm or less.

5 g of the sample prepared in this way was added to 500 cc of distilled water maintained at 25 ° C. at a constant temperature, and the stirring time was changed to react the sample with distilled water. After a predetermined time, the solution was collected to measure the amount of fluorine. The results are shown in FIG.

TABLE 1

* Trace Component: FeO + Mno + TiO ₂ + P ₂ O ₅ + K ₂ O

** Vratio: (CaO + BaO) / SiO ₂

According to Figure 1 it can be seen that the amount of fluorine elution increases significantly as the amount of Na ₂ O increases.

In addition, while Na ₂ O is a bar with a fluorine elution for few samples it can be seen that a very small amount of 10ppm or so, recognizes that the Na ₂ O is a fluorine elution main reasons and addition of CaF ₂ with respect to the sample, excluding the Na ₂ O From the results The flow temperature and melting temperature were measured and the results are shown in FIG.

As shown in FIG. 2 showing the flow temperature and melting temperature characteristics of CaF ₂ addition, the melting property of the mold powder is required to be 1100 ° C. or less, but the melting property is 1300 ° C. or more. It can be seen that it cannot be used.

Accordingly, it can be seen that the flow temperature and the melting temperature should be controlled to be used as a utility mold powder by adding other compounds while excluding Na ₂ O.

Example 2

This embodiment is the first embodiment, each of the samples for the basis of the results, while significantly reducing the amount of Na ₂ O to compare the fluoride elution amount in the present invention material and the comparative material using a B ₂ O ₃ together instead of Na ₂ O of The amount of fluorine leached into the cooling water with respect to is measured by the following method.

That is, the samples blended with the chemical composition as shown in Tables 2 and 3 were melted at 1300 ° C. to produce slag, solidified, and ground to a particle size of 69 μm or less.

5 g of the sample thus prepared was weighed into 500 cc of distilled water maintained at 25 ° C. and stirred while reacting the sample with distilled water. The solution was collected to measure various properties. The results are shown in Tables 2 and 3 below.

TABLE 2

* Trace Component: FeO + MnO + TiO ₂ + P ₂ O ₅ + K ₂ O

TABLE 3

* Trace Component: FeO + MnO + TiO ₂ + P ₂ O ₅ + K ₂ O

Table 2 shows BaO and B ₂ O ₃ used alone, according to the prior art 1 is a kind of powder solvent used in continuous casting of low carbon steel (C: 0.04% or less), F is 8%, Na ₂ It contains 15% of O, has physical properties that hardly cause surface defects and process accidents of cast steel, and can be used at casting speeds of 1.0m / min to 1.5m / min. However, it can be seen that the fluorine elution amount in the slag film reaches 64 ppm.

In addition, the comparative materials (2, 3) is a change in the content of F and Na ₂ O in the case of the comparative material (2) lowered the F content, but slightly lowered the fluorine elution, but compared to the conventional material 1 with the best physical properties This is because of the high consumption, which is likely to lead to a lack of lubrication between molds and cast steels, and the generation of gas can cause foaming defects on the surrounding surface.

The comparative material (3) has a low F elution and a good viscosity, but has a melting temperature of 1100 ° C. or higher, resulting in a slow melting rate in the mold, and thus a thin slag layer, which is likely to cause surface defects due to the introduction of slag into the slab. .

In addition, the comparative material 3 greatly increases the amount of fluorine leached when Na ₂ O or Li ₂ O is further added to lower the melting temperature.

In addition, the comparative materials 4 and 5 used only B ₂ O ₃ instead of Na ₂ O, and the comparative material 4 added with 10% of B ₂ O ₃ had a high melting temperature and thus had the same disadvantages as those of the comparative material 3. In addition, the comparative material 5 has a drawback of absorbing moisture in the air by using a low F content and an optimum range or excessive amount of B ₂ O ₃ .

The comparative materials (6, 7) is a case of using BaO instead of Na ₂ O, both compared to the conventional material 1 F significantly reduced elution, but because the melting temperature or viscosity tends to be high, the casting speed does not require high consumption is low Only in limited cases can be used.

In addition, the comparative material (8) does not use fluoride at all, and there is no F elution and the melting temperature is moderate, but since the viscosity is high, the lubrication between the mold and the slabs is insufficient, and the gas generation amount and the water absorption rate are high. It can be seen that this occurs.

Table 3 shows the mixed use of BaO and B ₂ O ₃ , according to the comparative material (9) is added to BaO and B ₂ O ₃ 5% at the same time, respectively, Na ₂ O to adjust the melting temperature and viscosity Although 6% and 1% of Li ₂ O were added, the physical properties were very suitable compared to the conventional materials, but the F elution amount was 30 ppm, which is somewhat inferior to the objective of the present invention.

This is because the amount of BaO and B ₂ O ₃ used is small and the amount of Na ₂ O used to promote fluorine elution is relatively high.

Therefore, in order to reduce the amount of F elution, it is necessary to make the content of Na ₂ O 5% or less and BaO and B ₂ O ₃ 5% or more, respectively.

The comparative material 10 added BaO 20% and B ₂ O ₃ 10% and significantly lowered the amount of CaO similar in chemical properties to BaO, thereby lowering the V ratio to 0.83, but meeting the object of the present invention in terms of viscosity and F elution amount. It can be seen that you cannot.

Comparative material (11) reduced the content of BaO by 10%, increased the content of B ₂ O ₃ by 20%, and increased the CaO content to prevent excessively decreasing the melting temperature with increasing B ₂ O ₃ content. However, it can be seen that the water absorption rate and F elution amount increase with increasing B ₂ O ₃ content is not suitable for use of the present invention.

Therefore, the content of B ₂ O ₃ should also be limited to 15% or less in this respect, the content of BaO + B ₂ O ₃ should be within 25% and accordingly the V ratio is also within the range of 0.9-1.1.

Comparative materials (12, 13) is a case of changing the F content while satisfying the above-mentioned range, in the case of the comparative material 12, the F content is 4% and the content of Li ₂ O in order to match the viscosity and melting temperature 6 In spite of the low F content, the addition of excess Li ₂ O causes the melting temperature to be too low and the F elution also fails to meet expectations, and the comparative material with an F content of 12% excluding Li ₂ O (13) Has a high F content due to its high F content. Therefore, in order to satisfy the effects of the present invention, it can be seen that the Li ₂ O content of the F content is 5-10% or less.

Comparative material (14) is MgO content of 15%, the physical properties excluding the viscosity and F elution is satisfactory level, but also the viscosity value due to the decrease of CaO is high, so the use is limited when the casting speed is high. It can be seen that the MgO content should be within 10%.

On the other hand, the present invention material (15-17) is based on the above results, while maintaining the F content in the range similar to the conventional material 1, it is easy to adjust the viscosity of the casting solvent, Na ₂ which is the main cause of eluting F By suppressing the O addition as much as possible within 5% and controlling the content of each component to form a solvent, it is possible to drastically reduce the dissolution of fluorine even when the solvent is added to the mold while the melting temperature, viscosity, gas generation amount and water absorption rate are low. Able to know.

As described above, according to the present invention, instead of drastically reducing the amount of Na ₂ O in the solvent, a mixture of BaO and B ₂ O ₃ is used and the content of each component is appropriately controlled to form a solvent, so that the melting temperature, viscosity, It is possible to obtain a solvent of a low fluorine elution mold which can significantly reduce the elution of fluorine while having a low gas generation amount and a water absorption rate.

Claims (1)

Low fluorine elution template solvent used for continuous casting, in weight%, CaO: 15-25%, F: 5-10%, BaO: 5-15%, B ₂ O ₃ : 5-15%, BaO And the total amount of B ₂ O ₃ : 25% or less, Na ₂ O: 5% or less, Li ₂ O: 5% or less, MgO: 10% or less, Al ₂ O ₃ : 10% or less, C: 5% or less, ( A low fluorine injection mold solvent, characterized in that the composition is composed of SiO ₂ , and other unavoidable trace components in the range CaO + BaO) / SiO ₂ ratio can be 0.9-1.1.