JPH0147432B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a porous nozzle, which is a casting nozzle mounted on a ladle or tundish, which prevents deposits in base metal or steel, particularly alumina, from adhering to the inner circumferential surface of the nozzle through a gas seal. It is something. Currently, high alumina and alumina/carbon materials are often used as nozzle refractories for casting, but with these materials, precipitates in the steel, especially alumina particles, adhere to the inner circumferential surface of the hole in the nozzle refractory. As the usage time progressed, the thickness gradually increased, and in some cases, the nozzle hole was eventually blocked, resulting in the stoppage of operation.
In order to prevent this, argon gas is mainly blown into the nozzle refractory to form a gas film on the interface between the inner peripheral surface of the nozzle hole and the molten steel, or the molten steel flow is stirred by the blown gas and the temperature of the molten steel is increased. By making it uniform, the adhesion of alumina is prevented. Porous nozzles for gas blowing used for such purposes must have corrosion resistance,
In addition to having high thermal shock resistance, the most important condition is that the nozzle should be able to eject gas uniformly from each required area of the refractory. By the way, as a means of imparting such characteristics to porous refractories, for example,
No. 157570, Utility Model Publication No. 57-3642 or JP-A-57-
No. 17462 reports the use of spherical particles, but these are used for purposes such as stirring molten steel in a ladle, preventing oxidation or nitridation of the molten steel flow, or protecting or shielding the molten metal flow from harmful atmospheric gases. This is essentially different from the method aimed at preventing the adhesion of precipitates in steel, particularly alumina, which is the object of the present invention. In addition, the chemical properties and embodiments of the spherical particles used in the above-mentioned prior art have extremely high SiO ₂ content, and therefore have a disadvantage of poor corrosion resistance against oxygen gas during molten steel and oxygen cleaning. ing. The present invention was created in consideration of the current situation,
By using high-alumina spherical particles with excellent corrosion resistance, it achieves the required air permeability and uniform structure, and also has excellent corrosion resistance and thermal shock resistance, and is intended to prevent inclusions, especially alumina, from adhering to steel. The purpose of this project is to provide a porous nozzle for casting. The porous nozzle of the present invention will be explained in detail below. The physical properties that each of the embodiments of the present invention should have and their formulation are as follows.From the viewpoint of air permeability, corrosion resistance, and thermal shock resistance, air permeability is the essential basic physical property for porous nozzles. ,
It is necessary to consider pore size, distribution, and porosity.
The following is a list of considerations regarding these matters. (a) Regarding air permeability Air permeability indicates whether or not the required air permeability can be obtained, and is the most important physical property in preventing the adhesion of inclusions in steel. Regarding the air permeability of refractories, if the gas flow rate per unit time is Q, the pressure loss is ΔP, the nozzle surface area is A, and the thickness is L, then air permeability Kr=L/A・Q/ΔP......( 1). Therefore, if Q and ΔP can be set from the usage conditions or operating conditions when the nozzle is used, then since L and A are known, the air permeability can be calculated using equation (1). However, Q needs to be corrected for temperature and pressure, and ΔP needs to take into account gauge pressure and molten steel head pressure. From the general operating conditions based on the above (1)
The air permeability calculated using the formula is 0.01 to 0.5 (cc・
cm/ ^cm2・sec・_cmH2O ). (b) Regarding pore size and distribution Generally, as the pore size increases, the penetration of molten steel into the nozzle refractory or the erosion of the nozzle increases significantly. Therefore, by considering the balance between the molten steel head pressure and the surface tension acting between the molten steel and the refractory, it is possible to set a pore diameter that will prevent molten steel from penetrating. Now, if the height of molten steel is H (cm), the diameter of the pore that can prevent molten steel from entering ^cm2 is de (cm).
must satisfy the following inequality (2). de＜4T cosθ／ρ・g・H……(2) Here, T is the surface tension between molten steel and refractory, θ
Similarly, ρ is the contact angle, ρ is the molten steel density, and g is the acceleration of gravity. In the present invention, since alumina is the main material of the refractory, the T between alumina and molten steel is
and θ, H and ρ are determined by the operating conditions.
When calculated by substituting the value of into equation (2), the maximum value of the pore diameter is approximately 50μ under general operating conditions. On the other hand, the gas ejected into the molten steel through the pores must exist at the interface between the nozzle and the molten steel, and if the ejected gas reaches the turbulence of the molten steel flow, The purpose of gas seal cannot be achieved. Taking these things into consideration, the pore diameter is preferably about 7μ as a result of experiments. Further, from the viewpoint of uniform distribution of pores, it is desirable that the gaps between pores be small. (c) Regarding porosity Porosity is closely related to thermal shock resistance.
If cracks occur during use, air permeability will fluctuate, making it difficult to continue stable operations. When examining the relationship between thermal shock resistance and porosity in alumina refractories, thermal shock resistance becomes high when the porosity is approximately 20 to 25%. In view of the above points, the basic physical properties that a porous nozzle should have are: Air permeability 0.01-0.5 (cc・cm/cm ²・sec・cmH ₂ O) Pore diameter 7-50μ Porosity 20-25% It is a requirement that it be set within the range. Next, examples of specific implementations of the present invention based on these findings will be given. Example 1 Alumina spherical particles, commercially available fine powder sintered alumina, clay, and chromium oxide were adjusted to the content ratios shown in Table 1, phenolic resin was added, and the mixture was thoroughly kneaded with a fret mill. Afterwards, it was formed into a nozzle shape using a friction press and fired at 1700°C. In addition, in parallel with this, commercially available sintered alumina with non-spherical particles was used as an aggregate, and kneaded, molded and fired in the same manner. The basic physical properties, corrosion resistance, and thermal shock resistance of each example are shown in Table 1. Note that the composition or blending ratio is expressed in wt%, and various test methods were performed as described below throughout each of the following Examples. The erosion rate was determined by contacting each fired body for 45 minutes at 1650℃ using the rotary erosion method using 100% molten steel.
Repeatedly measure the amount of erosion loss, No. 2 to 18, No. 19 and No. 2 to 18, No. 19 and
20 and Nos. 21 to 28, the ratio of each amount of erosion is expressed as a 100% ratio. To determine the degree of cracking, a test specimen of 50 x 50 x 50 mm was made from each compound, placed in an electric furnace at 1500°C, rapidly heated, held for 20 minutes, then taken out and cooled in the air. Depending on the number of operations and the condition of the cracks, after 2 times, no cracks...◎ After 1 time, no cracks...○ After 1 time, small cracks occur...△ After 1 time, large cracks occur...× Impact resistance was evaluated. When considering Table 1, first of all, it is shown in Table 1.
Nos. 1 and 2 are conventional types that use non-spherical particles as aggregate, and Nos. 3 to 18 are those of the present invention. The product of the present invention has a higher air permeability as seen in No. 6 and No. 1 or No. 7 and No. 2, for example, compared to the conventional type with the same composition, and therefore has excellent air permeability. I understand. In addition, among the blends having approximately the same apparent porosity, average pore diameter, and air permeability, when comparing the present invention with spherical particles and the conventional type with non-spherical particles, for example, No. 4 As seen in No. 1, No. 6, and No. 2, it is recognized that No. 4 and No. 6 of the present invention using spherical particles are superior in corrosion resistance and thermal shock resistance, respectively. Nos. 7 and 8 have extremely good air permeability, but are poor in corrosion resistance and thermal shock resistance. This is because the particle size distribution tends to become coarser, so the matrix-equivalent portion decreases, making it porous and not providing sufficient strength. Nos. 9 to 11 were studied regarding clay content, but No. 11, which has a high clay content, had poor corrosion resistance and thermal shock resistance, and the influence on corrosion resistance and thermal shock resistance was investigated. Judging from this, it is desirable that the content be around 5wt% or less. Nos. 12 to 16 were examined regarding the content of chromium oxide, but while No. 16, which has a high chromium oxide content, has excellent corrosion resistance, it tends to have poor thermal shock resistance. Approximately 2 wt% or less is desirable. The chemical composition of the aggregate particles in Nos. 17 and 18 was investigated, and as a matter of course, No. 18 with a large amount of SiO ₂ has poor corrosion resistance. From the results of No. 17 and 18, the chemical composition of the aggregate particles is 89wt Al ₂ O ₃ .
% or more and SiO ₂ is desirably 11wt% or less. From the above results, in the case of firing at 1700℃, there are some problems with the corrosion resistance and thermal shock resistance of Nos. 7 and 8, which show high air permeability, but other than that, in these examples, the aggregate By adjusting the chemical composition and content of clay and chromium oxide of the particles, a porous nozzle with excellent air permeability, corrosion resistance, and thermal shock resistance can be obtained. In addition, in cases such as No. 7 or No. 8, where the corrosion resistance or thermal shock resistance is slightly inferior even though the air permeability is good, the firing temperature may be increased (as shown in Example 2) or additives may be added. It is an advantage of the present invention that corrosion resistance, thermal shock resistance can be improved by reinforcement (as shown in Example 3) or additive reinforcement (as shown in Example 3). Example 2 The tendency of the physical properties and characteristics of porous refractories obtained by adjusting the firing temperature was investigated. Among the formulations shown in Table 1, the firing temperature was increased for Nos. 7 and 8 and the results were shown as Nos. 19 and 20 in Table 2 when they were fired at 1760°C. These results show that the porosity is reduced and the thermal shock resistance is improved by increasing the strength, and the corrosion resistance is also slightly improved. However, it is still not considered sufficient to improve corrosion resistance, so we focused on zirconia, which has high corrosion resistance against molten steel.
We decided to consider additives for aggregate particles. Example 3 The quality and quantity of additives added to aggregate particles were investigated. After adjusting the blending ratio as shown in Table 3, kneading and molding using a fret mill in the same manner as in Example 1. , Nos. 21 to 24 were fired at 1700° C. in the same manner as in Example 2, and Nos. 25 to 28 were fired at 1700° C. in the same manner as in Example 1. As expected, Table 3 clearly shows that the addition of zircon or zirconia improves corrosion resistance and thermal shock resistance. In particular, the improvement in thermal shock resistance is remarkable, because in the case of zirconia, fine cracks are generated due to the difference in thermal expansion between alumina and zirconia during firing, and the thermal stress generated by these cracks is alleviated. On the other hand, in the case of zircon, it is thought that the increase in strength due to firing is predominant. However, if the amount of zirconia added is larger than necessary, the proportion of fine cracks becomes too large, resulting in a decrease in strength. Regarding corrosion resistance, when the amount of zirconia or zircon added is relatively small, high corrosion resistance is shown due to the raw material characteristics, but when the amount added is large, cracks due to zirconia increase and the amount of SiO ₂ as a composition due to zircon decreases. This leads to an increase in corrosion resistance, and on the contrary, corrosion resistance deteriorates. Therefore, from Table 3, the desirable addition amount is 1 to 13 wt% for zirconia and 2 to 10 wt% for zircon.
It is estimated to be. The results of each of the examples detailed above are shown in FIG. 1 along with a line segment that increases the Kozeny-Carman equation, which is often used in powder beds and the like. As mentioned above, the air permeability Kr is expressed by equation (1), and the pore diameter de (cm) is expressed by equation (2), and at the same time,
The Kozeny-Carman equation is expressed by the following equation, where u is the cylinder velocity and ε is the porosity. u=(φc dp) ² gc/36KμL・ε ² /(1−ε) ²・ΔP…
...(3) If the equivalent diameters of the pores are de and rh, respectively, then de = 4rh = 4ε/(1-ε)Sv ......(4) Here, Sv is the surface area per unit volume of the particle,
Using the shape factor φc, Sv = 6/φc dp ......(5) From equations (3) and (1), the air permeability Kr for the particle diameter dp and porosity ε is: Kr = (φc dp) ² gc/36μK・ε ³ /(1−ε) ² ………(6
) Also, from (4)(5)(6), Kr=gc/16μK・ε・de ² ………(7) Since the behavior of the ventilation hole Kr is supported in this way, it is assumed that the vent hole Kr has a spherical shape that contributes to the present invention. Particles (particles recognized as spherical or substantially spherical) exhibit properties as shown in FIG. 1, and have two major characteristics. The first is that it agrees extremely well with the Kozeny-Carman equation. This makes everything related to manufacturing very easy to manage, and it is possible to theorize and think about various phenomena. Second, the air permeability corresponding to the same [(porosity)×(pore diameter) ² ] value is greater than that of a non-spherical material. In other words, the use of spherical particles provides better air permeability. This suggests that the pores are circular in shape, and there are relatively many through-holes, so the flow resistance is low. In other words, if you think about it the other way around, for the same air permeability, [(porosity) x (pore diameter) ² ] becomes smaller, and at the same time, since both porosity and pore diameter are factors involved in corrosion resistance, they become smaller. Naturally, this will improve corrosion resistance. As described above, the porous nozzle of the present invention exhibits excellent effects when attached to a molten metal container, and as long as the gist of the present invention is followed, the technical idea is limited to the examples of implementation described above. Needless to say, the invention is not limited to the above, and any applications or modifications derived therefrom are also included within the technical scope of the present invention.

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【table】 [Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between porosity, pore diameter, and air permeability in the present invention.

Claims (1)

[Scope of Claims] 1. The chemical composition of the spherical particles is 89 wt% or more containing Al ₂ O ₃ and 11 wt % or less containing SiO ₂ , and spherical or nearly spherical alumina particles are used as aggregate,
1. A porous nozzle characterized in that it has a structure that maintains an air permeability suitable for gas injection by kneading a blended material mixed with appropriate additives, molding, and then firing. 2 The blend according to claim 1 contains 70 to 100 wt% of alumina spherical particles with a particle diameter of 2.0 to 0.3 mm,
It is characterized by being formed with a particle size distribution and component composition consisting of 0 to 25 wt% of fine powder alumina with a particle size of 50 μ or less, 0 to 5 wt% of clay with a particle size of 15 μ, and 0 to 2.0 wt% of chromium oxide with a particle size of 20 μ or less. porous nozzle. 3. A porous material having a particle size distribution and a component composition according to claim 2, in which 1 to 13 wt% of zirconia powder with a particle size of 50 μm or less is added by replacing or partially replacing fine powder alumina or clay. quality nozzle. 4. A porous material characterized in that, in the particle size distribution and component composition described in claim 2, 2 to 10 wt% of zircon powder with a particle size of 70 μ or less is added as a substitute or partial substitute for fine powder alumina or clay. nozzle.