中间包等离子加热工业试验

控制中间包内钢水温度变化是提高生产率和产品质量的有效方法之一。中间包等离子加热能够弥补浇注过程中钢水温降,稳定钢水温度,提高铸坯质量。对某厂中间包等离子加热进行工业试验研究。采用三中空石墨电极等离子加热装置对中间包内钢水进行加热。通过两组中间包等离子加热试验,探究等离子加热对中间包内钢液温度变化和钢液成分及夹杂物特征的影响。结果表明,等离子加热中间包内钢水升温效果明显,升温速率可实现0.8 ℃/min,同时也能够使钢水温度保持稳定;等离子加热后中间包内钢水全氧含量下降,氮含量基本不变,碳含量略有升高;加热后钢液中夹杂物的数密度明显降低,分别下降了7.43%和19.68%。中间包等离子加热可稳定中间包内钢液过热度,促进了氧化物夹杂的上浮去除,提高了铸坯质量。     

薄板坯连铸单流中间包流场的数学模拟

采用数值计算的方法模拟单流中间包内钢液流动行为。计算模拟了无控流装置,应用挡渣墙坝,以及导流隔墙时中间包内钢液流动分布、温度场。结果表明：中间包无控流装置易在中间包中下部形成贯穿流,不利于新旧钢液混合以及夹杂物去除;导流隔墙可使钢液充分上扬,夹杂物易为覆盖渣俘获,有利于夹杂物去除;加装控流装置后,湍动能在到达控流装置前加强,有利于小粒径夹杂聚合上浮;而湍动能在经过控流装置后减弱,有利于钢液平稳流入结晶器;导流隔墙与堰坝组合均可使中间包内钢液充分混合,温度均匀,进出口温差减小。     

中间包内流体流动及夹杂物去除的研究

采用湍流流动的数学模型方法,对板坯中间包内的钢液流动及夹杂物去除率进行了模拟研究。系统分析了在中间包内设置控流设备对钢液流动状态、平均停留时间以及夹杂物颗粒排除率的影响。结果表明,设置挡墙和坝后,中间包内有效防止了短路流,延长了平均停留时间,夹杂物整体排除率明显提高,大大改善了中间包的冶金效果。     

板坯中间包结构优化实验研究

中间包内基本的物理现象是钢液的流动,其它冶金过程还包括钢液中夹杂物的去除、卷渣、温度和成分的均匀化等,都是在流动的钢液中进行的,因此研究中间包内钢液的流动是中间包冶金的基础。本研究通过中间包水模实验,结合现场生产实际,优化设计中间包内部结构,达到中间包内死区比例小,促进大型夹杂物的去除,延长钢液停留时间,促进温度和成分的均匀,提高铸坯质量的效果。     

双通道式电磁感应加热中间包冶金效果研究

双通道式电磁感应加热中间包不仅能够补偿浇铸过程中出现的热量损失，而且具有改善中间包内钢液流动、促进钢液中非金属夹杂物去除的作用。本研究在对双通道式电磁感应加热中间包内的电磁力和流场进行了数值模拟研究的基础上，通过工业试验研究，分析了电磁感应加热中间包通道内钢液流动和夹杂物的去除情况。结果表明，在电磁场作用下，连铸中间包通道内钢液在该电磁力作用下会呈螺旋式前进。随着感应加热时间的延长，夹杂物含量不断降低，夹杂物去除率不断提高，与无感应加热条件相比，在感应加热5、10、15 min时，夹杂物去除率分别达到6.9%、12.1%和22.4%。     

达钢五流小方坯中间包钢液流动数值模拟

针对达钢五流小方坯中间包,建立了描述钢液流动、传热以及夹杂物轨迹的数学模型。研究了钢液在中间包内的温度分布,比较了不同粒径夹杂物的上浮率。根据数值模拟的结果选择了最优的2#挡墙方案。     

四流T型连铸中间包流场优化研究

以国内某厂所用中间包为研究对象,为了提高夹杂物在中间包内的上浮去除效果,改善原型中间包的流场特性,采用物理模拟和数值模拟的手段对中间包内不同挡墙结构下包内流场和温度场进行模拟研究。结果表明:原型中间包采用的坝对钢液上扬作用不理想,造成包内各流之间差异性大,包内平均死区比例达46. 15%,包内温度分布不均匀,对产品质量影响较大。改进后的挡墙可以明显提高各流之间的一致性,死区比例降低为20. 05%,对包内温度分布也有明显改善。     

连铸中间包控流装置优化数值模拟研究

针对板坯连铸机的中间包采用商业软件建立三维数学模型,计算不同中间包控流装置条件下中间包内的流场,分析不同方案对钢液流动状态和平均停留时间的影响,分析采用优化方案时钢中夹杂物的情况。结果表明,中间包控流装置的优化方案与原方案相比中间包的死区体积减少10.61%,中间包内开始出现示踪剂时间延长4.31%,均有利于中间包内钢液的混合和夹杂物上浮去除,同时采用优化方案钢中夹杂物水平能够满足生产工艺的要求。     

宝钢板坯连铸机中间包三维流场数模研究

本文开发了一个求解三维湍流Ｎ－Ｓ方程的计算机软件，根据宝钢板坯连铸机中间包的形状和操作参数建立了钢液流动的数学模型，并利用该软件进行数值计算分析中间包内钢液流动的合理性。宝钢现在使用的上，下挡墙结构的中间包，仍需改进，采用下，上，，下挡墙结构，更利于夹杂物上浮，均匀钢液温度。     

气幕挡墙中间包数理模拟及实践

根据武汉钢铁股份有限公司炼钢总厂三分厂二流板坯连铸中间包的操作工艺参数,采用数学与物理相结合的模拟方法,对比研究了气幕挡墙技术对中间包内钢液流动特性及夹杂物去除的影响,并根据研究结果进行了工业试验.研究结果表明:采用气幕挡墙技术,可有效地改善钢液的流动状态,延长钢液的平均停留时间,降低死区体积,提高夹杂物去除率,适应超纯净钢中间包冶金的需求.     

六流小方坯中间包流场优化水模研究

为改善某钢厂六流小方坯中间包钢液流场,净化中间包钢水以及改善钢水的温度分布,通过合理设计正交水模试验,考察各方案中间包死区体积、多流一致性等参数,以及两者的综合指标,表明影响该中间包流场综合特性的主次因素顺序为:孔径大小→导流孔倾角→挡墙位置→挡墙高度,其中导流孔径55mm,向上倾角30°,挡坝距中端400 mm,高度250 mm,此方案流场较为合理。     

Hydrodynamic performance of steelmaking tundish systems: a comparative study of three different tundish designs

Extensive water modelling was carried out to ascertain the influence of various types of baffle designs on the hydrodynamic performance of three different designs of steelmaking tundish systems. These included, a two-strand slab casting tundish, a six-strand billet casting tundish and a five-strand, skewed, delta shaped tundish. Plant scale operating conditions were scaled down respecting both geometric and Froude similarity and on the basis of the latter, the inflow rate of water into the model tundish systems was estimated via: Q_m = Λ^5/2Q_f.s. To quantify the hydrodynamic performance, residence time distribution (RTD) characteristics were measured using the conductivity measurement technique for a wide range of baffle designs. From such measurements as well as from flow visualisation studies, the following general observations have been made. The optimum design of baffles together with its number and position within the tundish appear to be a strong function of the basic tundish design (viz., the geometry, the number of operating strands etc.). Of the various types of baffles investigated in this work (dam, dam + weir, baffles with holes etc.), appropriately designed slotted baffles appear to modify the RTD characteristics most favourably towards superior metallurgical performances. Increase in the number of strands, asymmetricity in the tundish design and flawed operating conditions, (viz., large width to length ratio) were all found to influence the tundish performance adversely. A comparison of experimental results for the three tundish systems indicated that changing the characteristics of the baffle design can lead to significant performance improvement in the case of the two symmetric tundish systems (e.g., the two and the six strand tundishes), the five strand skewed, delta shaped tundish was, however, found to be somewhat insensitive to such changes. For such a tundish geometry, no design of the flow-modification devices tried, could bring the hydrodynamic performance any closer to the best results obtained for the two other tundish systems. Possible reasons for such observations are discussed in the text.     

Similarity considerations in the physical modelling of steel making tundish systems

To assess and quantify the relative importance of Reynolds and Froude numbers in reduced scale model studies (these cannot be simultaneously respected when the scale factor is less than unity), aqueous model investigations were carried out on three different laboratory scale tundish models. The experimental tundish systems included two strand, five strand skewed delta shaped and six strand rectangular shaped vessels. Experimental observations show that the depth of liquid in the model would only correspond to that in the full scale system, provided the model flow rate is scaled in accordance with the relationship: Q_m = λ^5/2 Q_f.S, in which, A is the geometrical scaling factor. Furthermore, on the basis of residence time distribution measurements in two different configurations of the five strand tundish, it was demonstrated explicitly that flow phenomena in tundish systems are largely dominated by inertial forces and are therefore, essentially Froude dominated.     

Investigation of Flow Characteristics in a Six‐Strand CC Tundish Combining Plant Measurements,Physical and Mathematical Modeling

The tundish plays a major role in the continuous casting process. The flow in a tundish has a very substantial effect on the quality of the final product and on efficient casting conditions. Efforts are being made worldwide to obtain the most favourable shape of tundish interior by using dams, weirs and gas curtains. The aim of these flow control devices is to reduce the dead zone areas and improve the conditions for the separation of non‐metallic inclusions. Numerous model studies are being carried out to explain the effect of the tundish working space shape and steel flow conditions on the inclusions floating processes. The presented article shows the results of investigations performed to obtain the mass exchange characteristics in the investigated tundish. The measurements were done directly at the steel plant during normal working conditions. By controlling the changing content of manganese in steel, the residence time distribution (RTD) characteristics were acquired. The RTD characteristics are also obtained with a water model of the tundish with dimensional scale of 1:3. Parallel to the water model, numerical simulation based on mathematical modelling of fluid flow, relying on the system of differential equations, is employed in the research work. Numerical simulations were carried out with the finite‐volume commercial code FLUENT using the standard k‐ε turbulence model. The primary purpose of the investigations carried out is to present the characteristics describing the transitory zone in a six‐strand tundish. It is shown that the F‐curve, describing the transitory zone, can be obtained by using different measurement techniques. Tracer concentration characteristics for the model of tundish obtained from both modelling techniques ‐ physical as well as numerical ‐ are very similar.     

Physical and mathematical modelling of flow and residence time distributions in different tundish designs

A steady state, three‐dimensional, turbulent flow model has been developed in‐house for analysis of melt flow and residence time distribution phenomena in steelmaking tundish system. The governing equations of flow, turbulence and tracer dispersion were derived in terms of the Cartesian co‐ordinate systems and solved numerically with their associated boundary conditions adapting a control volume based finite difference procedure. In the numerical solution scheme, the pressure‐velocity coupling was treated via the popular Simple (semi implicit method for pressure linked equations) algorithm. Prior to carrying out elaborate numerical predictions for tundish geometry, the model was applied to several standard test problems and evaluated against corresponding bench mark results. Thus, several typical test problems such as, flows in a cubic cavity, flows in ducts of rectangular cross‐section, flow over flat plate and so on were simulated numerically to assess the adequacy and appropriateness of the computational procedure developed. Results thus obtained together with the bench mark solutions indicated that the mathematical model is internally consistent and sufficiently robust. Accordingly, the turbulent flow model was applied to simulate flow and Residence Time Distributions (RTD) in four different tundish designs . These included, a single strand and a two strand slab casting tundish systems, a six strand rectangular shaped tundish and a six strand delta shaped billet casting tundish. Various RTD parameters (e.g., minimum break through time, t_min, time at which peak concentration occurs, t_peak and average residence time, t_av) were computed numerically in the four tundish systems and these were subsequently compared with corresponding experimental measurements derived from equivalent water model tundish systems. Except for the single strand tundish system, large differences between measurements and prediction (particularly on t_min and t_peak) were noted for the other three tundish geometries. Furthermore, the extent of such discrepancy was found to be relatively more pronounced for the multi‐strand tundish system. The possible reasons for such discrepancy is discussed in the text and it was shown computationally that relatively better agreement between theory and measurement can be achieved if, instead of the high Reynolds number k‐ε turbulence model, a low Reynolds number turbulence model is applied in the computational procedure.     

非对称五流圆坯连铸中间包水模实验研究

采用水模实验研究了控流装置对非对称五流圆坯连铸中间包内流场的影响.通过测定模型中间包内各水口的RTD曲线,计算了中间包流场的平均停留时间及死区、活塞区和混合区的体积.提出了控流装置的开孔位置、大小、角度和布置方式对多流连铸中间包流动特性的影响规律.提出了能够合理分配钢水和有效减小死区的控流装置结构.     

Reduction of Tundish Skull and Yield Improvement in Steel Plants Through Physical Modeling of Steelmaking Tundish Systems

New types of furniture (also termed as flow modifiers or baffles) were incorporated in industrial scale, slab and bloom casting tundish systems with an aim to reduce residual metal loss (i.e., tundish skull) at the end of sequence casting. To this end, water model experiments were carried out in which, slag vortexing phenomena during emptying of tundish was studied embodying different types of furniture into existing tundish designs. These in general indicate that a wedge shaped bottom together with an embedded pouring box applied in conjunction have the potential to reduce tundish skull and improve yield losses significantly. In addition, limited residence time distribution measurement experiments were made to investigate metallurgical performance of modified design tundish systems. These indicate that deployment of new furniture with minor design modifications, despite contributing to a reduction in tundish capacity (10–12%), do not influence metallurgical performance of steelmaking tundish systems to any significant extent. Accordingly, designs of currently employed slab (32 and 37 tonnes capacity respectively) and bloom casting tundish (10 and a 17 tonnes capacity respectively) systems were modified in four different steel mills and plant trials conducted to assess the extent of yield improvement. Significant improvements in yield losses, to the extent of 50–60%, have been confirmed by the industry during sequence casting.     

Numerical Investigation of the Fluid Flow in Continuous Casting Tundish Using Analysis of RTD Curves

 A detailed mathematical procedure of the optimization of the fluid flow in a tundish water model with and without flow control devices (weir and dam) was carried out using the commercial CFD code FLUENT 60. The (k ε) two equation model was used to model turbulence. The residence time distribution (RTD) curves were used to analyze the behavior of the flow in tundish. The location of flow control devices in the tundish was studied. The results show that the flow modifiers play an important role in promoting the floatation of nonmetallic inclusions in steel. Comparing the three geometric configurations that are considered (bare tundish, weir, weir+dam), the tundish equipped with the arrangement (weir+dam) is a best and optimal geometric configuration of tundish.     

废弃镁碳砖在中间包干式料中的应用研究

将整形和未整形的两种废弃镁碳砖回收颗粒(3～1mm)部分取代中档烧结镁砂颗粒(3～1mm)用于中间包干式料,研究了两种颗粒加入量的不同对干式料性能的影响。结果表明:整形和未整形颗粒均可用于中间包干式料,整形后颗粒加入量不宜超过30%,未整形颗粒加入量不宜超过15%。将添加30%整形颗粒的中间包干式料用于转炉中间包,可满足现有连铸工艺要求,达到原有干式料的使用效果。     

异型中间包结构优化对帘线钢夹杂物的影响

为了解决帘线钢中因大颗粒夹杂物导致的拉拔断裂问题,通过水模型研究结果对异型中间包结构改进优化,并将优化异型中间包结构进行工业试验。结果表明,挡墙优化结构后,去除夹杂物的效果明显提高,采用优化的挡墙中间包生产的帘线钢铸坯中夹杂物尺寸不大于10 μm比例为87.95%,平均尺寸为6.7 μm;大颗粒的高MgO类和高SiO2类夹杂物已得到有效去除,盘条中B细不大于0.5级比例达到97.56%。