Effect of nozzle spray distance on the secondary cooling uniformity of continuous casting billet
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摘要: 研究了不同噴淋距離下連鑄小方坯二冷噴嘴的水量分布，建立了凝固傳熱模型分析了82B鋼連鑄坯的熱行為。該模型特別考慮了二冷區鑄坯表面寬度方向的水流密度分布，并根據鑄坯表面測溫結果進行了模型校正。采用凝固傳熱模型研究了噴嘴噴淋距離對連鑄二冷均勻性的影響。結果表明：噴嘴噴淋距離的增加有助于提高二冷水橫向分布的均勻性，導致鑄坯表面溫度橫向均勻性降低、縱向均勻性提高。這些效果有助于改善鑄坯內部裂紋，但是會對角部裂紋產生不利影響。在二冷區前段噴嘴采用低噴淋距離，二冷區末段采用高噴淋距離，既可以提高鑄坯角部溫度，又能降低表面最大回溫速率，有助于同時改善連鑄坯角部和內部裂紋。在此基礎上，提出了一種連鑄小方坯二冷噴嘴布置方式，即二冷區每段噴嘴噴淋距離沿拉坯方向逐漸增加，該方法有助于提高連鑄坯“縱?橫”冷卻均勻性。Abstract: In the secondary cooling zone of continuous casting, the cooling uniformity of the billet largely depends on water flux distribution and is closely related to crack formation. Nozzle spray distance is the main influencing factor of water flux distribution in continuous casting billet. Therefore, the investigation of the effect of nozzle spray distance on secondary cooling uniformity is of considerable importance in the design and optimization of the secondary cooling system of the billet. In the present study, the water flux distributions of the nozzles used in the secondary cooling zone of continuous casting of the billet were measured under different spray distances. A heat transfer and solidification model was established to analyze the thermal behavior of 82B steel billet. The model specifically considered the distribution of secondary cooling water along the transverse direction and was calibrated via comparing the measured and simulated surface temperatures. The effect of nozzle spray distance on the secondary cooling uniformity of the billet was investigated using the model. Results show that the increase in nozzle spray distance helps to improve the uniformity of secondary cooling water along the transverse direction, resulting in the decreased transverse uniformity and increased longitudinal uniformity of surface temperature. These effects are beneficial for the internal cracks but harmful for the corner cracks of the billet. Increasing the nozzle spray distance in the first segment of the secondary cooling zone and decreasing the nozzle spray distance in the second segment of the secondary cooling zone can decrease the maximum reheating rate and increase the corner temperature, thereby achieving the purpose of simultaneously improving the internal and corner cracks of the billet. On this basis, a nozzle arrangement method, i.e., gradually increasing the nozzle spray distance along the casting direction of each segment in the secondary cooling zone was proposed. This method contributes to the improvement of “longitudinal–transverse” cooling uniformity of the continuous casting billet.
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圖 6 足輥區水量橫向分布。（a）單個噴嘴；（b）兩個噴嘴
Figure 6. Water flux distribution in the foot-roller zone: (a) one nozzle; (b) two nozzles
圖 7 不同噴淋距離下噴嘴水量分布。（a）噴嘴B，100 mm；（b）噴嘴B，125 mm；（c）噴嘴B，150 mm；（d）噴嘴C，100 mm；（e）噴嘴C，125 mm；（f）噴嘴C，150 mm
Figure 7. Water flux distributions of the nozzles under different spray distances: (a) nozzle B, 100 mm; (b) nozzle B, 125 mm; (c) nozzle B, 150 mm; (d) nozzle C, 100 mm; (e) nozzle C, 125 mm; (f) nozzle C, 150 mm
圖 8 表面中心測量溫度和模擬溫度對比
Figure 8. Comparisons of the measured and simulated temperatures of the surface center
圖 9 噴嘴在不同噴淋距離下連鑄坯角部和表面中心溫度變化。（a）100 mm;（b）125 mm;（c）150 mm
Figure 9. Temperature variations of the billet corner and surface center under different nozzle spray distances: (a) 100 mm; (b) 125 mm; (c) 150 mm
圖 10 不同噴嘴噴淋距離下鑄坯中心固相率變化
Figure 10. Variation of the central solid fraction of the billet under different nozzle spray distances
圖 11 鑄坯表面溫度和中心固相率變化
Figure 11. Variations of the surface temperature and central solid fraction of the billet
表 1 82B鋼的主要化學成分(質量分數)
Table 1. Main chemical composition of 82B steel
% C Si Mn P S 0.82 0.20 0.73 0.017 0.004 
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表 2 現行工藝下噴嘴的噴淋距離和水壓值
Table 2. Spray distance and water pressure of the nozzles under the current process
Nozzle type Spray distance/mm Water pressure/MPa A 125 0.40 B 125 0.80 C 125 0.60
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中文字幕在线观看表 3 82B鋼主要連鑄工藝參數
Table 3. Main casting parameters of 82B steel
Item Value Sectional dimension/(mm×mm) 150×150 Casting speed/(m·min?1) 1.8 Pouring temperature/℃ 1503 Water flux of mold cooling/(m3·h?1) 112 Temperature difference between inlet and
outlet of mold water/℃6.02 Water flux of secondary cooling/ (m3·h?1) 35.8 Water temperature/℃ 35 Ambient temperature/℃ 25
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