1.Introduction
Due to the continuous development of machinery manufacturing, transportation and other industries, the demand for large-size bars is constantly increasing. Since 2008, more than 30 large-size square and round billet continuous casters have been installed in the country to produce high-quality, high-performance continuous casters. Cast products. The continuous casting machine is designed by both domestic OEM and foreign OEM, each with its own characteristics. For large-size square and round billet continuous casters, the nozzle arrangement of the secondary cooling and the working water pressure and air pressure are particularly important, which directly affect the internal and external quality of the continuous casting billet.
2. Nozzle selection of foot roller section
For the foot roll section of large-size square and round billet continuous casters, most continuous casters use solid cone, elliptical, and fan-shaped water nozzles, and very few continuous casters use fan-shaped aerosol nozzles.
The nozzle installation space of the foot roller section is limited by the distance between the foot rollers and the electromagnetic stirrer of the crystallizer, resulting in the nozzle being closer to the casting billet. The spray angle of the fan-shaped water nozzle can reach up to 120°, and the spray angle of the solid cone nozzle is 60-90°, the elliptical spray angle is 90x60°.
The spray distribution of the solid cone water nozzle is affected by the swirl fins installed inside the water flow channel. It is not recommended to use the cross swirling blade water nozzle. It is recommended to use the multi-cut and porous water nozzle to maintain the water flow distribution as much as possible. The symmetry of the solid cone water nozzle is shown in Figure 1.
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Figure 1 Swirl fins inside the water flow channel of a solid cone water nozzle
Fan-shaped nozzles are recommended to use thick fan-shaped nozzles. The spray coverage is approximately narrow and rectangular, and the spray distribution is trapezoidal, which can better transfer heat.
The oval water nozzle is commonly used in the continuous casting machine designed by Danieli Metallurgical Equipment Co., Ltd. The advantage is that it takes into account the roll spacing and the width of the billet to increase the spray coverage as much as possible, reduce the cooling intensity of a single point, and reduce The temperature fluctuation range of the billet in the direction of the casting machine reduces the thermal stress.
The fan-shaped aerosol nozzle is used in the bloom caster designed by Deutsche Mark. The nozzle has a relatively compact structure, small volume, and easy installation and maintenance, as shown in Figure 2.
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Figure 2 Compact aerosol spray
3.Selection of sector nozzles
The fan-shaped section of the large-size square and round billet continuous casting machine uses fan-shaped, solid-cone, elliptical, and rectangular aerosol nozzles, as shown in Figure 3.
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Figure 3 Aerosol nozzle
The sector space of the continuous caster is relatively open, and the nozzle installation is no longer restricted by the roller spacing, and a large spray angle can be used, up to 120°.
The bloom casters designed by Comcast generally use fan-shaped aerosol nozzles with a spray angle of 100°; the generous continuous casters designed by Danieli Metallurgical Equipment Co., Ltd. generally use elliptical aerosol nozzles with a long axis of spray angle. It is 90°, and the minor axis is 60° or 45°. The large round billet continuous casters designed by Danieli Metallurgical Equipment Co., Ltd. and voestalpine generally use solid cone-shaped aerosol nozzles with an injection angle of 60°. Domestic OEM-designed bloom casters generally use solid cone and rectangular aerosol nozzles; designed round billet continuous casters use 90° solid cone aerosol nozzles.
4.Nozzle spray characteristics
4.1Spray characteristics of water nozzles
The water nozzle flow rate has a certain relationship with the water pressure. The following formula can be used to calculate the water flow rate of the fan-shaped water nozzle:
Water flow of solid cone and oval water nozzles:
In the formula: P1, P2 are water pressure, Pa; Q1, Q2 are water flow, l/min.
The spray angle of the water nozzle also has a certain relationship with the water pressure. For the fan-shaped water nozzle, the spray angle increases with the increase of the water pressure, which can be approximately calculated as:
In the formula: P is the water pressure, Pa; α is the spray angle, º; a is the spray angle coefficient. For solid cone and oval water nozzles, the spray angle starts to increase and then decreases.
4.2Spray characteristics of aerosol nozzles
The water flow and air flow of the aerosol nozzle have a certain relationship with the water pressure and air pressure. Normally, under a given air pressure, the water flow and air flow can be calculated by the following formula:
Where: Pw is water pressure, Pa; Qw is water flow, l/min; aw, bw, cw, dw are water flow coefficients respectively.
Where: Pw is water pressure, Pa; Qa is water flow, l/min; aa, ba, ca, da are water flow coefficients respectively.
The spray angle of the aerosol nozzle is affected by the atomizing air pressure and the water pressure. When the air pressure is constant, the spray angle increases with the increase of the water pressure. The change is more obvious when the water pressure is low, and the change is more when the water pressure is high. Weak, fan-shaped aerosol nozzle D40197-2 at 2bar pressure and spray height 250mm, the spray coverage width is shown in Figure 4.
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Figure 4 The spray coverage of fan-shaped aerosol nozzle D40197-2 at different water pressures
In continuous casting production, when the air pressure is 2～2.5bar and the nozzle spraying distance is about 100mm, the lower limit of water pressure is recommended to be greater than 1.2bar. As the spray height increases, the lower limit of water pressure is increased to reduce the influence of air resistance on the spray angle. , The spray coverage meets the design requirements.
5.Conclusion
Each engineering technology company has a unique design feature of continuous casting machine. After the number of continuous casting nozzles and spray height are determined, they choose water nozzles and aerosol nozzles that suit their own continuous casting process. The nozzle specifications need to be considered due to the spray The difference in height leads to the difference in the lower limit of the spray water pressure of the nozzle to ensure that the appropriate working water pressure is selected, the nozzle sprays a good spray distribution, and the surface of the cast slab is uniformly cooled. When conditions permit, increase the spray coverage area as much as possible, reduce the cooling intensity of a single point, reduce the thermal stress of the slab, and optimize the internal and external quality of the slab.
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