JPS61108463A - Casting use spherical granular flux having good heat retaining property - Google Patents

Abstract

PURPOSE:To obtain a casting use spherical granular flux having a good heat retaining property by specifying a composition, a CaO/SiO2 ratio and a particle size distribution. CONSTITUTION:This composition contains 2-20wt% Al2O3, 3-30wt% fluoride of alkali and alkali earth metal, 2-30wt% oxide of alkali and alkali earth metal without including CaO, and 0.2-7wt% carbon powder, and contains as a balance CaO and SiO2 which become a ratio of 0.65-1.5 by a value of a CaO/SiO2 ratio. Also, as for the particle size distribution, in case of the particle granulated to <=3.0 particle diameter, the particle size distribution is >=90wt% particle diameter 0.1-2.0mm, <=5wt% particle diameter <0.1mm, and <=5wt% particle diameter 2.0-3.0mm.

Description

[Detailed Description of the Invention] (Industrial Application Field) The technical content described in this specification and book regarding the improvement of casting fluff used during steel casting, particularly during continuous casting, is to improve the heat retention properties of granular flux. It proposes development results for improvement.

(Prior Art) When casting steel, an additive called casting fluffx is added to the molten steel poured into a mold. Conventionally, since the additive was in powder form, dust was generated when it was added, which worsened the working environment.

The research group to which the inventors belong succeeded in developing a granular flux that can improve the working environment and obtain better surface quality of slabs, and has previously published Japanese Patent Application Laid-Open No. 50-141528. , was disclosed in Japanese Patent Application Laid-Open No. 53-70040. However, with recent dramatic advances in casting technology, a need has arisen for new granular flanks that specifically address high speed casting operations. This is because in continuous casting operations, as the casting speed increases, the flow of slag between the mold and the slab tends to be inhibited, and therefore the slag's lubricating function becomes poor, which affects the solidified shell of the slab. This is because the frictional force increases, making breakout more likely to occur.

(Problems to be Solved by the Invention) During high-speed casting operations, it is an important management point for stable operation to ensure a sufficient amount of slag flow and perform casting while maintaining slag lubricity.

Since this inflow slag is supplied from the molten slag layer where the casting flux is molten steel, the first priority is to ensure a sufficient molten slag layer on the molten steel.

The thickness of the molten slag layer is determined by the balance between the speed at which the casting flux turns into molten slag due to the heat of the molten steel, and the speed at which the molten slag flows between the mold and the slab, forms a slag film, and is consumed while fulfilling its lubricating function. In particular, in situations where higher slag consumption per hour is required due to high-speed casting, it is especially important to ensure a sufficient amount of molten slag, which is responsible for replenishing the consumption of slag lubrication, or in other words, a sufficient thickness of the molten slag layer. considered important.

However, in general, conventional granular fluxes, including doffed ones, tend to have a thinner melted slag layer than powdered fluxes, and this point has been empirically recognized, so granular fluxes are suitable for high-speed casting. It was decided to use Franks and it was a victory.

Now, regarding the melting process of casting flux, at the bottom of the casting flux coating layer added to the molten steel surface, molten slag progresses due to heat transfer from the molten steel surface, and therefore, two points in the vertical direction of this flux coating layer It is thought that the temperature difference can represent the heat retention and insulation properties.

Therefore, by simulating this melting into slag, the temperature difference between two measuring points vertically separated on the flux coating layer after a certain period of time from the start of heating was used as a heat retention evaluation index, and powdered flux and it were granulated using the conventional method. A comparison of the granular fluxes revealed that powders generally have a higher heat retention evaluation index and are superior in heat retention than granules.

Good heat retention means a large amount of heat storage within the coating layer, and it is assumed that the difference in the thickness of the molten slag layer between powder and granules is due to the difference in the amount of heat storage within the coating layer, that is, the difference in heat retention. Ru.

Heat transfer in a packed layer such as a flux coating layer for casting depends on the heat transfer constant between particles, but in cases where the voids are not sealed, such as in powder or granules, ventilation in the voids also accounts for a large proportion of the heat transfer. it is conceivable that.

When the heat source is located below and the heat is transferred upwards, as in the case of heat transfer problems in continuous casting molds, upward air currents are also generated, so the ventilation heat transfer through the gaps becomes even larger. Since the granules are much larger than the powder, the gap between the spaces and the air permeability of the spaces tend to be large, and this causes the granules to have inferior heat retention properties compared to the powder.

Based on the above findings, the inventors reduced the void space between particles in the granules, that is, increased the packing density.
This invention was developed as a result of research into whether it would be possible to obtain granules with heat retaining properties comparable to powders by reducing the air permeability of the voids, without the disadvantage of hot water dust generation that occurs with powders. This was the successful development of spherical granular flux.

(Means for solving the problem) This invention contains Alto3 at 2 to 20 wt%, alkali and alkaline earth metal fluorides at 3 to 30 wt%, and alkali and alkaline earth metal oxides not included in CaO. In particular, it contains 2 to 30 wt%, and 0.2 to 7 wt% of carbon powder, and the balance is 0.65 in terms of Cab/5tot ratio.
Particles consisting of a composition containing CaO and 5ift at a ratio of ~1.5, granulated to a particle size of 3.0 or less, with a particle size of 0.1 to 2.0 mm: 90 wt% or more and a particle size of 0. Less than 1mm: 5wt% or less particle size 2
．． 0-3. Omn+: A spherical, fine-grained flux for casting with good heat retention, characterized by a particle size distribution of 5 wt% or less, and the combination of the flux structure and particle size distribution is a key issue.

(for production).

First, the reason for limiting the flux composition as described above will be explained, and wt% is simply expressed as %.

Alzos: 2 to 20% The content of AlzO is too small and when it falls below 2%, the softening and dissolving rate increases and the flux dissolving rate becomes slow. In addition, if the 1203 content is too high, exceeding 20%, 130
At a low temperature of 0° C. or lower, the viscosity increases rapidly, crystals are very likely to crystallize during solidification, and surface defects such as slag are likely to occur.

Therefore AIZO in flux! The content is 2 to 20%.

Alkali metal and alkaline earth metal fluorides: 3-3
0% Alkali metal and alkaline earth metal fluorides mainly have the function of adjusting softening and melting temperatures, viscosity, etc., but if the amount exceeds 30%, the glass tendency is inhibited, while 3%
If it is too small, the softening and melting temperature will become too high, making it easy to cause unevenness on the surface of the molten steel, so it is limited to 3 to 30%.

Oxides of alkali metals and alkaline earth metals are converted into CaO
2 to 30% oxides of alkali metals and alkaline earth metals also have the function of adjusting the softening melting temperature, viscosity, etc., but if the amount exceeds 30%, the vitrification tendency is inhibited. It is not preferable, and if it is less than 2%, almost no effect can be expected, so 2 to 30
%, and the reason why -CaO is not included here is because its influence on the flux properties depending on basicity, which will be described later, is more important.

Carbon powder 0.2-7% Carbon powder can be blended with flaky graphite, coke powder, artificial graphite, globular graphite, uncharred powder, carbon black, etc., singly or in combination, to adjust the rate of dissolution and slagging. However, if it exceeds 7%, the rate of dissolving slag will slow down, inhibiting the generation of a sufficient dissolved slag layer, while 0.2%
If the amount is less, the ability to adjust the rate of dissolution and slagging cannot be expected, so it is limited to a range of 0.2 to 7%.

The flux composition of the present invention contains each of the above components, and the remainder consists of CaO and 5iOa, but the value of Cab/Sing in terms of weight percent ratio must be in the range of 0.65 to 1.5, and within this range. When it is lower than 1.0.65, the melting rate of Alto is poor and the viscosity value becomes too high, so it is preferable. There is a disadvantage that there is no flux, and if it exceeds 1.5, the melting temperature of the flux increases, which is also unsatisfactory.

In the above-mentioned proper composition of the flux, the particle size distribution of the flux in the form of spherical particles is particularly important.

Here, the general method for producing granular flux for casting is as follows.

Conventional methods for producing granules generally involve extrusion granulation, which allows for efficient mass production. Extrusion granulation is a well-known method of granulating a kneaded material by forcibly extruding it from a punching plate, and the shape of the resulting granules is columnar. Because such columnar objects have edges, the packing density is low and the air permeability of the voids is high.

Therefore, we tried making the powder finer by reducing the extrusion diameter, but the heat retention was inferior to that of powder, probably due to the high air permeability.

That is, in the case of extruded granules having a columnar shape with corners, even if the particle size is reduced to form fine granules, the desired improvement in heat retention cannot be expected.

Of course, there is a possibility if the particle size is made as small as possible, but it is clear that it is meaningless unless the particle size is one that can be generally mass-produced by extrusion granulation.

The inventors conducted research on the idea that in order to obtain granules with good heat retention properties, it would be best to increase the packing density and reduce the air permeability of the voids. It has been found that if the On+m range is 90% by weight or more and the granules have a particle size distribution close to normal distribution in this particle size range, it is possible to obtain the casting flux that is the object of this invention and ensure the heat retention properties. .

Now, Figure 1 shows the heat retention evaluation index and bulk specific gravity of the powdered flux (A), columnar granules (B), fine columnar granules (C), and spherical granules of the present invention (D) obtained by granulating the flux. The results are shown below.

Here, regarding the heat retention evaluation index, the sample was melted by heat transfer by unidirectional heating from the bottom only using the measuring device shown in Figure 2, which simulates the experimental melting and slagging behavior that approximates the melting state in the practice of casting flux. Then, while heating from the bottom, the heat transfer state in the sample layer was measured at two points A and A in the vertical direction.
Evaluation was made based on the temperature difference of B exhibiting a temperature profile as shown in FIG.

In FIG. 2, 1 is a graphite crucible, 2 is its bottom wall heating device, 3 is a refractory insulation brick, 4 is a temperature sensor, and 5 is a sample.

According to FIG. 1, it is clear that the spherical granules (D) have heat retaining properties comparable to powder.

This is because, as shown in Figure 1, spherical granules have a larger bulk specific gravity than columnar granules, and as shown in Figure 4, they have a higher packing density, so they have fewer voids, and their spherical shape makes the voids more breathable. It can be said that the reason for the improvement in heat retention is that there is less heat retention.

Here, the particle size is expressed by the JIS standard full-length sieve opening, while the bulk specific gravity is expressed by an inner diameter of 50 mmφ and a volume of 100 c.
The sample is placed in a cylindrical container c from a height within 50 mm from one end of the container until it slightly overflows, and the sample is expressed as the weight when cut into 100 cc pieces.

The above-mentioned spherical granules (D) are powders having a composition within the aforementioned range, with a particle size of 0.1 to 2.0 nua in 90% or more, a particle size of less than 0.1 mm in 5.0% by weight or less, and a particle size of 2. ．． Omm~
3. Onv is granulated to 5.0% by weight or less,
Ideally, there should be no particles with a particle size of 0.1 mm or less, but if the particle size is 5.0 mm or less, dust will not be a problem in practical use. Particles with a particle size of 3II11 or more may be drawn in from the molten steel menscus in an unmelted state, so ideally there should be no particles with a particle size of 2.0 to 3, and 0IIIm at all. If it is below, heat retention will not deteriorate.

Particle size 0.1mm+~2. Omm' needs to be at least 90% by weight in order to obtain sufficient heat retention, and within this particle size range it is desirable to have a particle size distribution close to the emmetropic distribution.

As described above, the granular flux with good heat retention according to the present invention has a particle size distribution close to the emmetropic distribution, which improves the packing density and helps improve heat retention, but it is desirable to have as fine particles as possible from the special purpose of casting flux.

When various granulation methods are considered from this point of view, it is possible to devise and apply granulation methods that can obtain spherical granules, such as transfer granulation, fluidized bed granulation, and agitation granulation.

The feature of this invention is the spherical granules that are extremely inexpensive and have excellent heat retention properties, and are cheaper than, for example, hollow granules produced by rapid heating and foaming, and can provide the same or better effects.

(Example) Next, examples of this invention will be shown.

Table 1 shows the working conditions when a casting flux having the following components was used for high-speed slab casting.

Flux composition A e zo: l: 6.4%, CaFt: 3.5%
, Na, O: 4.5% MgO: 1.5%, Ba
O: 5.4%, C: 3.5%, the rest is Cab/5i
(h: Composition consisting of CaO and SiO2 in a ratio of 1.05.

Here, as conventional examples, powder and columnar granules produced by a conventional method,
As a comparative example, the results of testing the same spherical granules as the present invention and granules having a different particle shape distribution are also shown, but the comparative example could not be evaluated for breakout due to the small number of tests.

(Effects of the Invention) It is clear from Examples that the spherical granules of the present invention ensure a sufficient thickness of the molten slab layer and are completely free from problems of slab surface defects and breakouts. is very effective in stably performing high-speed casting operations and obtaining slabs with few surface defects.

[Brief explanation of the drawing]

Figure 1 is a graph showing measurement examples of heat retention evaluation index and bulk specific gravity for four types of samples with different shapes, Figure 2 is a cross-sectional view of the heating test device for flux melting used to compare heat retention evaluation index, Figure 3 is a graph showing an example of temperature difference measurement, and FIG. 4 is a microscopic sketch diagram showing the filling status of spherical and columnar granules. Figure 1 Figure 2

Claims (1)

[Claims] 1. 2 to 20 wt% of Al_2O_3, 3 to 30 wt% of alkali and alkaline earth metal fluorides, 2 to 30 wt% of alkali and alkaline earth metal oxides, excluding CaO. % and contains carbon powder of 0.2 to 7 wt%, and the balance is 0.65 in terms of CaO/SiO_2 ratio.
Particles consisting of a composition containing CaO and SiO_2 with a ratio of ~1.5 and granulated to a particle size of 3.0 mm or less, particle size 0.1 to 20 mm: 90 wt% or more particle size 0.1 mm : 5 wt% or less Particle size: 2.0 to 3.0 mm A spherical fine-grained flux for casting with good heat retention properties, characterized by having a particle size distribution of 5 wt% or less.