Apparent clogging effect in vacuum-induced consolidation of dredged soil with prefabricated vertical drains

The improvement efficiency of a dredged slurry by vacuum preloading is greatly affected by the apparent clogging effect arising during the consolidation process, where the apparent clogging effect refers to the combined impacts of filter clogging and particle blinding around the drain due to particle migration and non-uniform consolidation. Three laboratory model tests with different types of soils were performed to investigate the apparent clogging effect. First, the filter clogging effect was investigated by scanning electron microscopy and cross-plane permeability tests. Second, changes in the particle size distribution due to particle migration were analysed at the micro- and macro-levels, and the particle migration induced blinding effect was assessed through the results of the compressibility and permeability tests. The test results indicated negligible particle migration in pure clay and relatively higher blinding effect in mixture soils. Finally, the effects of blinding due to particle migration and non-uniform consolidation on the overall consolidation rate were theoretically quantified. Both the analytical and tests results implied that the apparent clogging effect is predominantly by non-uniform consolidation rather than the particle migration-induced blinding effect, especially for cohesive marine clay.     

FeSiB非晶薄带中夹杂物的来源及形成机理

 为了制定合理的夹杂物控制工艺从而改善FeSiB非晶薄带的质量与性能,分析了FeSiB非晶薄带中夹杂物来源及其演变。结果表明,工业纯铁原料中存在组成为Al₂O₃、SiO₂的球形和椭球形夹杂。在冶炼过程中,尺寸为20～30 μm椭球形夹杂通过上浮去除,尺寸为1～3 μm的球形夹杂则会与母合金冶炼过程的脱氧产物结合,形成Al₂O₃质量分数更高的硅酸铝和硅酸铝钙夹杂物。这些夹杂物在喷带过程中一部分会聚集于喷嘴内壁形成结瘤物,而另一部分则会随合金熔体流出喷嘴进入非晶薄带中。     

Numerical simulation of Al2O3 deposition at a nozzle during continuous casting

The effects of various factors, such as argon flow rate and slide gate opening ratio, on the alumina deposition rate were researched by the numerical simulation method. The pressure in the nozzle is significantly affected by argon flow rate and slide gate opening ratio. To keep positive pressure in the nozzle, the argon flow rate should be increased with a decrease in slide gate opening ratio. The effect of argon flow rate on the alumina deposition rate depends on the condition of opening ratio or casting speed. The effect of increasing the argon flow rate on the deposition rate is not obvious when the opening ratio is small. The Al2O3 deposition rate decreases significantly with an increase in argon flow rate when the argon flow rate is low, but it decreases slowly when the argon flow rate reaches a certain value. The alumina deposition rate is linear with alumina content at different slide gate opening ratios and argon flow rates. The observed thickness of the deposition layer at the bottom and outlet of a real clogged nozzle is almost equal to the result of the numerical simulation.     

非钙处理对高等级齿轮钢夹杂物的影响

 为解决水口堵塞、B类夹杂物超标及控制Ds类夹杂物,通过热力学计算和工业试验研究了SCr420H齿轮钢钙处理与非钙处理对中间包夹杂物的影响。研究发现,非钙处理炉次中间包夹杂物数量低于钙处理炉次。非钙处理炉次中间包夹杂物主要为棱角状镁铝尖晶石;钙处理炉次夹杂物主要为Al₂O₃-CaO-MgO与CaS复合球状夹杂物。优化工艺后非钙处理炉次中间包高熔点尖晶石类夹杂物数量大幅降低,水口堵塞及B类夹杂物问题得到解决。非钙处理圆钢夹杂物评级结果为,A类不大于0.5,B类不大于0.5级,C类为0,D(细)类不大于1.0级,D(粗)类不大于0.5级,Ds类不大于1.0级。     

高速重轨钢中尖晶石夹杂物的形成及控制

 高速重轨钢采用无铝脱氧工艺,但是钢中常发现大颗粒纯的MgO-Al₂O₃夹杂物,严重影响产品质量。为了明确高速重轨钢中尖晶石夹杂物的来源,进一步控制重轨钢中夹杂物,通过对重轨钢拉伸断口进行分析,结合水口结瘤物分析、热力学计算及典型夹杂物分析,系统研究了高速重轨钢中尖晶石夹杂物的形成机理。结果表明,重轨钢中的尖晶石夹杂物分为单独存在的尖晶石和钙铝酸盐包裹的尖晶石两类。其中钙铝酸盐包裹的尖晶石为CaO-SiO₂-Al₂O₃-MgO复合夹杂物在降温冷却过程中析出,析出温度与夹杂物中Al₂O₃和MgO质量分数有关;单独存在的小尺寸尖晶石夹杂物为钢液凝固冷却过程中析出,与钢液成分有关。此外,研究还表明,水口结瘤也是重轨钢中出现大颗粒镁铝尖晶石夹杂物的重要原因之一。因此,严格控制合金辅料中Mg、Al_s等杂质元素质量分数,防止钢液发生二次氧化、降低耐火材料侵蚀等,尽可能降低夹杂物中的Al₂O₃和MgO质量分数,对控制重轨钢中尖晶石夹杂物,提高产品质量至关重要。     

中薄板坯流程生产IF钢中包水口结瘤控制

采用扫描电镜、能谱分析等方法,对BOF-RH-CC中薄板坯流程生产含钛IF钢浸入式水口结瘤的原因进行了分析。结果表明,含钛IF钢水口结瘤的原因为水口本体内部的C与SiO2发生反应产生氧化性气体,氧化性气体和钢水中的[Al]、[Ti]反应在水口内壁上形成反应层,反应层促进了钢水中原有的Al2O3和Al-Ti-O复合夹杂物快速向水口内壁沉积。Ti的存在加重了水口结瘤的发生。以全流程氧位控制为目标,通过转炉终点控制、RH精炼、顶渣改质、中薄板坯连铸等工艺优化,使RH出站钢水T[O]质量分数控制在35×10^-6以下,中包钢水T[O]质量分数控制在30×10^-6以下,水口结瘤现象得到明显改善,单支水口平均连浇炉数由1.2炉提高至3炉,单支水口连浇时间提高到177 min。     

注水井回灌过程中堵塞问题实验研究

采用砂柱在实验室内模拟井灌过程中注水井周围砂层的堵塞过程。通过测定渗透系数的变化来分析堵塞的程度，同时，通过测定水样悬浮物浓度、细菌数目、溶解氧、TOC等水质参数的变化来分析井灌过程中可能发生的物理、生物堵塞。试验分别采用平均粒径为0.59 mm和0.34 mm的两种砂样。试验结果分析表明：悬浮物颗粒填充砂粒介质空隙引起的机械堵塞和微生物积聚、繁殖堵塞介质空隙引起的生物堵塞是砂柱堵塞的主要原因；砂柱上部对悬浮物和微生物的过滤、吸附作用强，堵塞也更严重；介质粒径差异对堵塞过程和堵塞程度的影响明显，平均粒径较小的砂柱更容易发生堵塞，而平均粒径为0.59 mm的砂柱渗透系数减小持续时间长，渗透系数减小的幅度大。     

Study on clogging of submerged-entry nozzles during CSP casting high-Al steel in WISCO

对武汉钢铁股份有限公司CSP产线＂BOF—LF—RH—CC＂工艺流程生产高铝钢（w（A1s）=0．20％～O．45％）水口结瘤的现象进行了研究，研究表明造成 水口结瘤的重要原因在于钙处理工艺不当，使钢中生成大量CaS和xCaO·yAl2O3类的高熔点复合夹杂物。通过钙处理工艺优化后，使得高铝钢的平均连浇炉数由原来的3．25炉迅速提高到10．86炉的水平，基本解决了CSP产线高铝钢钢水可浇性差的技术难题。