Modeling of unsteadiness of fluid flows and level fluctuations in thin slab continuous casting moulds

Unsteady fluid flows and level fluctuations in a thin slab continuous casting mould have significant influence on product quality. In this study, the phenomena concerning transient flow features and free surface motions were analyzed by means of the large eddy simulation （LES） software with the smagorinsky SGS model--VisualCast （VCast） II, where the Simpler algorithm on a body-fitted mesh was used to resolve governing equations. A series of water analog experiments on the fluid flow and the surface wave in the moulds of thin slab continuous casting were also performed. The results of fluid regions, middle of vortex and level fluctuation from digital simulations were identical with the results of the water analog experiments.

Evaluation of the performance of mold powder for continuous casting of plate slabs

The No. 3 slab caster,which mainly provides slabs to the 5000 mm plate mill at Baosteel, was put into production in December,2004. The size of the biggest slab produced by this caster is 2300 mm in width and 300 mm in thickness. The designed output of the caster is 2.3 Mt/a. Slab surface longitudinal crack defects,which were related to the heat flux of the mold, frequently occurred in the early stage of the startup of the caster. As mild cooling powder is beneficial to the uniformity of the shell of initial slabs ,the concentration of stress is reduced, and the longitudinal cracking on the surface is avoided. This study evaluates the performance of several kinds of powder, and the results show that mold powder of high basicity, high crystallization proportion and low heat flux is to the benefit of the reduction of the longitudinal cracks on the surface and the defects of slabs.

Water modeling of mold powder entrapment in slab continuous casting mold

The optimal parameters were determined by the water modeling of slab casting. It was found that there are mainly three types of mold powder entrapment in slab continuous casting, i.e., the entrapment caused by the shearing flow near the narrow face of mold, the entrapment caused by vortexes around the submerged entry nozzle （SEN）, and the entrapment caused by the Ar bubbling. Both the velocity of the surface flow and the level fluctuation of the liquids are enlarged with increasing the casting speed, reducing the submersion depth of SEN, decreasing the downward angles of the nozzle outlets, and increasing the Ar flowrate, all of which increase the tendency of mold powder entrapment. Among the four above-mentioned factors, casting speed has the largest effect.

Recycling of Cristobalite Powder in Casting Mould

Cristobalite SiO2 can be obtained from the fused silica ceramic waste of ploysilicon plant, due to the phase conversion of fused silica to cristobalite during the process of polysilicon ingot. Cristobalite powder materials with high purity are manufactured by milling the discarded waste above. Thermal expansion rate of the cristobalite and gypsum bonding moulds were studied, which show that the thermal expansion of the cristobalite phase transition could effectively compensate for the shrinkage of the gypsum at the temperature between 200 ℃ and 400 ℃. Casting experiments with copper alloy show that the cristobalite can improve the thermal performance of moulds for precise casting of jewelry.

Experimental Study of Fluid Flow in Thin Slab Continuous Caster Mould with Water-Model

Model study is an efficient method for optimizing the siructure of the mould and the submerged entry nozzle (SEN). Based on the similarity criteria, a full-scale water model has been established in accordance with the mould of thin-slab caster of the CSP (Compact Strip Production) operation. The effects of SEN structure including outlet area, outflow angle, nozzle width, thick-ness and immersion depth have been studied under high speed casting by measuring the amplitude and the impetus of top waves. By the orthogonal experiment design, not only the influence of the faCtors was estimated, but also the optimum work condition was judged. The rules of the fluid flow phenomena were summarized. The principle for choosing a reasonable structure of SEN was discussed.

Optimization of Oscillation Model for Slab Continuous Casting Mould Based on Mould Friction Measurements in Plant Trial

Lubrication and friction between the mould and strand are strongly influenced by mould oscillation, and play an important role in slab quality and operating safety during continuous casting processes. Investigation of mould oscillation is therefore essential for getting a better online control of the mould processes. A feasible approach for the development and optimization of mould oscillation was put forward, which combined online measurement of mould friction, design of negative oscillating parameters and evaluation for powder consumption. Three different control models including sinusoidal and non-sinusoidal oscillation for mould oscillations were developed to investigate and evaluate the effects of oscillation on mould friction and powder lubrication. For the purpose of investigating mould friction between mould and strand, online measurement was carried out on a slab continuous caster equipped with a hydraulic oscillator. Also the comparison of the mould friction in sinusoidal and non-sinusoidal mould oscillation was made for subsequent analysis. The industrial experiment result shows that the combination of inverse control model and non-sinusoidal oscillation mode will contribute to the proper powder consumption, leading to a suitable effect of friction force on strand surface, especially for high speed continuous casting. The proposed method provides reliable basis for guiding and optimizing mould oscillation among control models, sinusoidal oscillation and non-sinusoidal oscillation.

ER70S-6焊丝钢连铸全保护浇注工艺优化实践

唐钢公司长材事业部在拉拔生产ER70S-6焊丝钢时因氮质量分数高出现脆断情况,对此从焊丝钢连铸全过程保护浇注工艺改进以及连铸长水口、中间包密封、覆盖剂、浸入式水口和保护渣设计优化等方面采取措施,提高焊丝钢连铸保护浇注效果,降低焊丝钢氮质量分数(氮质量分数整体下降0.0012%),增强塑性和变形能力,避免焊丝钢因氮质量分数高导致其在拉拔和加工过程中金属流动性差造成的脆断现象。

1000~2200 mm宽板坯连铸机结晶器流场优化与应用

为改善某厂超低碳钢连铸过程中出现偏流、跳棒及水口堵现象,通过对中间包透气上水口、塞棒和浸入式水口等连铸功能耐材进行改进,将透气上水口改用特殊的弥散式透气材质,吹入的氩气气泡沿水口内壁形成均匀的气幕,表面气孔率较改进前提高5.2%,防止了夹杂物在水口内壁蓄积,缓解水口堵;将塞棒棒头由中心部位的吹氩孔由1个改为6个,实现360°均匀吹入氩气,减少棒头夹杂物蓄积;将浸入式水口改用无碳,低铝,高硅内衬,改变水口内壁材质,防止浸入式水口堵塞。改进后耐材在超低碳钢上推广应用,使得每浇次跳棒次数减少0.83次、降幅31.8%,水口堵造成的在线更换浸入水口频次减少了0.38支、降幅41.3%,稳定结晶器液面控制精度,提升冷轧卷夹杂合格率0.238%,并提高了单中间包连浇炉数0.53炉、增幅8%,使1000~2200 mm宽板坯连铸机结晶器流场得以优化。

薄板坯结晶器内卷渣现象的研究

基于相似原理，采用１∶１的水模型，模拟了薄板坯连铸结晶器内钢液─保护渣界面的流场，通过采用ＳＧ２００水工数据采集系统对液而波动进行了定量测量．结合流场显示研究了薄板坯连铸结晶器内钢液的卷渣机理，得出了薄板坯连铸结晶器内钢液的主要卷渣方式为旋涡卷渣和剪切卷渣．研究了各工艺参数，即水日类型、浸入深度、水口出口倾角、拉速等，对保护渣卷人量、卷入方式、卷人深度的影响．

连铸板坯结晶器浸入式水口试验研究

结合某厂两种断面的结晶器内腔尺寸 ,采用 1∶ 0 .6水模型研究方法 ,系统地研究了浸入式水口结构参数、吹气量、拉速等工艺操作参数同结晶器液面波动、流股对结晶器窄面的冲击力及涡心高度之间的关系 ,得出了适用于两种断面的合理的凹型浸入式水口。并利用水模拟实验和工厂试验进行了对比研究 ,结果表明 ,应用凹型浸入式水口取得了良好的效果。

F数计算及其与板坯连铸结晶器内钢水卷渣的关系

为了控制板坯连铸结晶器内钢水的卷渣,提出一种用结晶器流场数值模拟计算结果对前人研究出的液面波动指数F数进行计算的方法,研究了F数与液面波动及板坯浇注工艺参数的关系.研究表明：从结晶器流场的数值模拟计算结果中调用相应的计算F数所需的参数,可以方便地计算出F数.调整浇注工艺参数将F数控制在3～5就可以将液面波动控制在±（3～5） mm的合理范围内,从而减小或避免结晶器内的卷渣.

板坯连铸结晶器铜板温度场的数值仿真

针对 14 0 0mm× 170mm板坯连铸机结晶器铜板的结构优化改造 ,基于控制容积的有限差分方法对改造前后两种铜板结构参数和深入式水口结构参数条件下结晶器铜板的三维稳态温度场进行了数值仿真研究。由仿真得出的结果表明 ,结晶器宽面铜板经优化改造后 (螺栓间距由 16 0mm改成 135mm、冷却水槽由 6 3条改为 5 5条 )传热效果明显增强 :在拉速为 1.4m min时弯月面附近区域改造后结晶器内弧和外弧宽面热面铜板最高温度值分别比改造前结晶器降低了 15℃和 16℃。

唐钢新型薄板坯连铸结晶器的设计和使用效果

针对唐钢超薄热带生产线中FTSC工艺的H2长漏斗型结晶器在使用过程出现的问题,开发设计了新的漏斗型结晶器。这种漏斗型结晶器将H2结晶器下部的漏斗区改为平面区,结晶器漏斗区高度由2 100 mm缩短为900 mm,并通过模拟计算和优化设计,使结晶器内腔曲面形状各部分平滑过渡,使其具有生产铸坯承受变形应力小的优点。工业应用试验获得了成功,结果表明,使用新型结晶器较好地消除了开浇初期铸坯纵裂现象,提高了铸坯质量,新型结晶器对于钢种和铸坯断面具有良好的适应性,使用寿命达到了进口铜板的水平。

板坯连铸结晶器内钢液流动数值模拟

利用商业软件 ＰＨＯＥＮＩＣＳ建立一个三维有限差分模型，对板坯连铸结晶器内钢液流动进行了数值模拟．重点研究了浸入式水口结构尺寸和工艺参数对连铸结晶器内液面系动能和窄面冲击压力分布的影响．计算结果与水模实验结果吻合较好．

连铸中心偏析控制研究进展

连铸坯中心偏析会对铸坯质量及其后续的轧制产生不利影响。在简要阐述连铸生产过程中铸坯中心偏析缺陷产生原因的基础上,介绍了国内外低过热度浇注技术、二次强冷技术、电磁搅拌技术、轻压下技术、结晶器喂带技术等铸坯中心偏析控制方法与机制,并特别对结晶器喂带技术在连铸中的应用进行了展望。

连铸板坯表面纵向裂纹的形成原因

对连铸板坯表面纵向裂纹的形成原因进行了分析研究,发现浸入式水口在浇注过程中损坏和结晶器保护渣性能不佳是主要因素。采取了相应的改进措施后,钢板表面线状缺陷的发生率大幅度降低。

连铸板坯表面星状裂纹的形成与控制

研究了连铸成品板坯表面的微裂纹缺陷——板坯表面星状裂纹的特征、形成机理、影响因素及解决措施。

板坯连铸机结晶器钢液卷渣的水模型研究

针对安钢超低头板坯连铸机结晶器液面卷渣现象 ,用 0 6∶1 0水模型 ,研究了水口浸入深度 30mm、6 0mm和 110mm时 ,铸坯拉速 1 0～ 0 7m min、水流量 2 6 2 4～ 18 4m3 min范围内水口浸入深度、拉速对结晶器内钢液卷渣程度的影响。提出卷渣指数J =V·h (t·H) ,式中V 拉速 ;h 1 10大波值 ;t 开始卷渣时间 ;H 水口浸入深度。结果得出 ,为防止安钢板坯结晶器液面卷渣 ,当水口浸入深度为 110mm时 ,拉速应≤0 90m min ;浸入深度 6 0mm时 ,拉速应≤ 0 85m min ;J应 <1 37× 10 - 2 mm s2 。

连铸板坯结晶器温度场数学模型

建立了结晶器铜板二维非稳态传热数学模型，研究了结晶器铜板温度场。利用工厂实例值对模型进行了验证。讨论了拉速、冷却水流速、铜板厚度、水垢和铜板镀层对结晶器温度分布的影响。

宽板坯连铸结晶器内卷渣现象试验研究

结合宽板坯连铸结晶器的4种断面尺寸,采用1∶1水模型进行试验,研究了浸入式水口吹气量、水口浸入深度、水口吐出孔数、水口底部形状、拉速和结晶器断面宽度等工艺参数对结晶器内流体流动行为的影响情况,观察到结晶器内水口周围有旋涡卷渣和液面扰动卷渣,断面1/4区域是液面扰动卷渣,窄面区域有"类旋涡"卷渣和剪切卷渣。结果表明,结晶器内的卷渣与各种工艺参数是相关的,对工艺参数进行优化,就可减少卷渣的发生。