Immersion Nozzle Research Articles

Mathematical Modeling of Iron and Steel Making Processes. Swirling Flow Effect in Bottomless Immersion Nozzle on Bulk Flow in High Throughput Slab Continuous Casting Mold.

Swirling flow effectiveness on controlling the bulk mold flow has been acknowledged recently, concerning the productivity and its quality of continuous casting process. In this study, simple immersion nozzle without opposite face on the end of the nozzle is proposed. From the practical viewpoint, relationship between the throughput and bulk mold flow is investigated. Following results are obtained: 1) Numerical analysis fairly coincide with the experimental results for the cases: nozzle outlet, surface flow and velocity distributions along the narrow face. 2) Surface velocity decreases with increasing the axial length of the nozzle outlet, particularly in length from 20 to 60 mm. 3) For the high throughput case, considerably stable bulk mold flow can be obtained. 4) Bulk mold flows under different throughputs are similar with each other if (tangential velocity W in nozzle/axial velocity Vz in nozzle) of those have same magnitude with each other.

Mathematical Modeling of Iron and Steel Making Processes. Swirling Flow Effect in Off-center Immersion Nozzle on Bulk Flow in Billet Continuous Casting Mold.

It often occurs that setting up an immersion nozzle on the mold, nozzle axis does not coincide with the mold-axis. In this study, under the off-center nozzle with the mold-axis, bulk mold flow was investigated, and following issues were obtained: 1) For the case without swirl, the peak of the flow moves near the mold-wall with flowing down from the outlet of the nozzle due to the Coanda effect (shown in Appendix). 1) On the other hand, peak of the flow moves near the mold-axis with flowing down from the nozzle-outlet within considerable short distance, namely axisymmetric velocity distribution can be obtained within very short distance from the nozzle-outlet. 2) The surface flow patterns between coaxial and off-center nozzles are quite different. The flow pattern with coaxial nozzle is axisymmetric and simple, while the flow from one side to other side can be observed, with off-center nozzle.

連続鋳造モールド内浸漬ノズル近傍でのモールドパウダー巻き込みに及ぼす浸漬ノズルの濡れ性の影響

連続鋳造モールド内浸漬ノズル近傍でのモールドパウダー巻き込みに及ぼす浸漬ノズルの濡れ性の影響

連続鋳造モールド内浸漬ノズル吐出口近傍におけるモールドパウダー巻き込みに関する水モデル実験

連続鋳造モールド内浸漬ノズル吐出口近傍におけるモールドパウダー巻き込みに関する水モデル実験

Swirling Flow Effect in Immersion Nozzle on Flow in Slab Continuous Casting Mold.

With increasing requirement of steel productivity and quality in continuous casting in the conventional casting system using an immersion nozzle with side pouring holes, it is very difficult to establish a reasonable molten flow pattern. In order to overcome this difficulty, we propose a new method imparting a swirling motion to the flow in the immersion nozzle and to control the flow pattern in the mold. Obtained results are as follows: 1) High amplitudes of oscillation with a period of 10 to 15 sec are observed in the outlet flow of the immersion nozzle and meniscus flow in the conventional casting system, while these phenomena are remarkably suppressed using swirling motion in the immersion nozzle, which leads to very calm and uniform flow pattern at the outlets of the immersion nozzle, in the mold and on the meniscus in the mold. 2) The steady outlet flow softly impinges on the side wide face, and then turns around as a reverse flow along the other wide face describing a S-shaped curve in the cross section and clock-wise rotational flow in the vertical section. This outlet flow exerts a shearing-effect on the inner wall of the mold, leads to the considerable energy consumption and exerts a braking effect in the flow which results in suppression of self-excitation-vibration in the bulk mold flow and biased flow on the meniscus. In other words, imparting a swirling motion to the flow in the immersion nozzle, remarkably reasonable bulk mold flow can be obtained.

連鋳鋳型内メニスカスにおけるArガス気泡の挙動

The behavior of argon gas bubbles at meniscus in the continuous casting mold was studied using a Wood's metal model. Argon gas was injected into Wood's metal flow through a porous plate or an orifice set in the immersion nozzle. Both the diameter and the number of argon gas bubbles generated at meniscus regions were measured with a color high-speed video camera. Generation rate of argon gas at each region of meniscus was measured with a mass flow meter. The distribution of argon gas bubbles at meniscus was dependent on the flow rate of argon gas injected into the immersion nozzle, but was independent on the flow velocity of Wood's metal in the nozzle. The number of argon gas bubbles at meniscus was dependent on the diameter of bubble. The ratio of the number of argon gas bubbles at meniscus in a unit time was estimated as the following function of bubble diameter.n=Ωd-5.5where n is the ratio of the number of argon gas bubbles at meniscus in a unit time, Ω is the constant and d is the diameter of argon gas bubble.The flow velocity of Wood's metal at meniscus in mold was influenced by the injection rate of argon gas into the immersion nozzle.

Development of Swirling Flow Generator in Immersion Nozzle.

It is very critical to develop a cheap, simple and safe swirling generator because an introduction of swirl motion is very effective to control the flow in the continuous casting mold and refining process. Here, a twist-tape-swirling-blade is proposed and its characteristics are investigated. Obtained results are as follows; (1) Numerical results obtained by the k-e turbulence model and experimental results coincide with each other for the tangential velocity distributions at the outlet of the swirl blade. (2) A slightly strained tangential velocity can be seen just below the swirling blade, but the tangential velocity becomes axi-symmetric at a downstream position, which is within the distance of 100 mm from the outlet of the swirling blade. (3) Knowing the axial velocity and twist ratio of the swirl blade, the corresponding tangential velocity and pressure drop can be deduced through the relationship between dimensionless radial position and tangential velocity.

スラブCC鋳型内流動に及ぼす底無し浸漬ノズル内での旋回流動効果に関する水モデル実験

スラブCC鋳型内流動に及ぼす底無し浸漬ノズル内での旋回流動効果に関する水モデル実験

製鋼 ＣＣタンディッシュ熱間リサイクル技術の改善

In recent years, the diversification in steel grades and smaller lot in weight is strongly desired among customers. Those results in the decrease of sequential casting ratio, and the refractory cost of tundish raises. To solve this problem, tundish recycle operation in hot condition was developed in Chita Plant, Daido Steel Co. Moreover several improvements are applied to TDR operation to extend TD life. They are summarized as follows: (1) The immersion nozzle quick exchange operation and the slide valve quick exchange operation have been developed in order to avoid the problem of refractory life such as immersion nozzle and slide valve. (2) The improvement of stopper tip refractory makes it possible to decrease the failure in not only stopping molten steel at the end of cast but also the break of stopper tip at the beginning of cast. As the result, we succeeded in the extension of the TDR operation and the TD refractory cost is decreased to 40% of that without TDR operation.

連続鋳造浸漬ノズルの介在物付着機構

連続鋳造浸漬ノズルの介在物付着機構

連続鋳造浸漬ノズルの介在物付着に及ぼす耐火物材質の影響と介在物付着モデルに基づく考察

連続鋳造浸漬ノズルの介在物付着に及ぼす耐火物材質の影響と介在物付着モデルに基づく考察

Prevention of Air Suction from the Contact-part between Sliding Gate and Immersion Nozzle.

With increasing requirement of steel quality in continuous casting, it is extremely important to regulate reasonably flow rate of molten steel without either biased flow or reoxidation by the suction of air from around the contact-part between sliding gate (SG) and immersion nozzle (SEN). In this study, a novel/method to prevent the suction of air from all around the contact-part between the SG and SEN during controlling the flow rate of molten steel, has been developed by giving a step to the SEN. The effects of the step in the SEN on the prevention of air suction from all around the contact-part can be summarized as follows: (1) The flow squeezed passing through the SG is turned abruptly just before the step in the SEN and, as a reverse flow, passes towards the contact-part between the SG and SEN, where its kinetic energy is converted into the pressure energy as a kind of impinging-flow-action, resulting in a positive pressure on the contact-part. (2) With increasing amount of sliding-gate-opening, the distance downstream from the gate to the step, that is necessary for the contact-pressure to be positive on the contact-part, becomes wider. Over some opening amount, the contact pressure is always positive under the condition that a dimensionless step width (ratio of step-width to inner-diameter of nozzle) is over 0.15. From the above-mentioned issues, it is found possible to prevent the air suction from all around the contact-part between the SG and SEN using the SEN with the step beneath the sliding gate.

Swirling Effect in Immersion Nozzle on Flow and Heat Transport in Billet Continuous Casting Mold.

A numerical analysis and water model study of the mold region of a continuous casting apparatus are performed with a novel injection concept using swirling flow in the pouring tube, to control the heat and mass transfer in the continuous casting mold. As a result, the following results were found: (1) By changing swirl strength, it is easy to control the flow pattern as well as the direction of the flow. (2) Uniform velocity distribution can be obtained within a very short distance from the outlet of the nozzle. (3) Heat and mass transfer near the meniscus can be remarkably activated compared with a conventional straight type immersion nozzle without swirl. (4) Swirl helps the superheat in the melt dissipate. (5) Penetration depth of nozzle outlet flow is decreased remarkably by the application of swirling. Those findings mentioned above are very useful to control the flow pattern in the billet and bloom continuous casters.

Effect of Composition of Immersion Nozzle on Occurrence of Blister in Steel Sheet.

The effect of the inner porous refractories-molten steel reaction on the incidence of blisters and the mechanism whereby the incidence of blisters is prevented by using an immersion nozzle with a silicaless inner porous refractories that does not react with the molten steel were studied. The following results were obtained:(1) Blisters are caused by 0.5 mm and larger argon gas bubbles, and particularly 1.0 mm and larger argon gas bubbles have a strong bearing on the incidence of blisters in the sheet product.(2) The mechanism whereby the incidence of blisters depends on the number of sequence cast heats can be explained by the increase in argon gas bubble diameter caused by the inner porous refractories-molten steel reaction in the later heats in the sequence cast.(3) Fine argon gas bubbles can be stably introduced into the molten steel by using an immersion nozzle with a silicaless inner porous refractories that does not react with the molten steel. This stable injection of fine argon gas bubbles helps prevent the occurrence of blisters in the sheet product.

Improvement of slab quality of ultra-low carbon steel in curved mold type continuous casting machines

The casting speed of ULC-Ti steel in a curved mold type continuous casting machine used to be restricted by the formation of pencil pipe defects. These defects being caused by Ar bubbles at the immersion nozzle, a casting method without addition of Ar gas has been developed. With this method, casting speed could be raised and, at the same time, the occurrence of pencil pipe defects and phosphorous slivers reduced. The increase in alumina slivers could partly be compensated for by the higher casting speed made possible by the new casting method.

Improvement of Life of Immersion Nozzle with Gas-injection.

The mechanism by which cracks occur in the immersion nozzle with silicaless inner porous refractory developed to stabilize the injection of argon gas into molten steel, and the prevention of nozzle cracking were investigated. The results obtained were as follows.(1) Models for estimating the crack formation pressure and hot argon gas inlet pressure for the immersion nozzle were proposed. Using those models, a theory for preventing nozzle cracking according to casting conditions was worked out.(2) With the immersion nozzle with silicaless inner porous refractory, the hot argon gas inlet pressure does not drop. Therefore, when the initial gas inlet pressure is substantially high, a longitudinal crack tends to occur easily in the powder line which deteriorates in strength due to in the latter half of casting operation.(3) By increasing the immersion nozzle wall thickness to improve its strength and controlling the hot argon gas inlet pressure below the crack formation pressure, it is possible to prevent cracks in the immersion nozzle with silicaless inner porous refractory.

ガス吹き込み型浸漬ノズルの割れ発生防止

ガス吹き込み型浸漬ノズルの割れ発生防止

ブローホール欠陥発生に及ぼす耐火物・溶鋼間反応の影響

ブローホール欠陥発生に及ぼす耐火物・溶鋼間反応の影響

Reaction Rate between Alumina Graphite Immersion Nozzle and Low Carbon Steel.

Reaction Rate between Alumina Graphite Immersion Nozzle and Low Carbon Steel.

Reaction Mechanism between Alumina Graphite Immersion Nozzle and Low Carbon Steel.

Reaction between refractory and molten steel causes clogging in the immersion nozzle in continuous casting process. Reaction mechanism between the silica-containing alumina graphite nozzle and the molten steel was studied on the observation of the used immersion nozzle and the basic experments. The results are summarized as follows, (1) The used immersion nozzle refractory reveals a reacted zone where the SiO2 and C contents are reduced and there are many pores. (2) The overall reaction in the refractory can be arranged as SiO2 (s)+C (s)=SiO (g)+CO (g) (3) The reactions of the refractory with the Al-killed molten steel and the Ti-killed molten steel are given by the following equations: (Al-killed steel) 3SiO2(s)+3C(s)+4Al=2Al2O3(s)+3Si+3C (Ti-killed steel) low C and high Ti region 5SiO2(s)+5C(s)+6Ti=2Ti3O5(s)+5Si+5C high C and low Ti region 5SiO2(s)+5C(s)+3Ti=Ti3O5(s)+5Si+5CO (g) (4) With the SiO2-C refractory containing no Al2O3, 50% of SiO2 is reduced by the C to the SiO gas, and the remaining 50% is reduced by the C to SiC. On the other hand, with the Al2O3-SiO2-C refractory, all of SiO2 is reduced to the SiO gas.