热轧板边裂缺陷成因及控制

针对河钢唐钢1 700线生产的热轧板边裂缺陷多的问题,利用扫描电镜对其产生原因进行了分析。结果表明,板卷边裂的产生与结晶器锥度不合理、弯月面处铜板变形、钢水过热度和拉速不匹配、结晶器液位波动等因素有关。通过解决结晶器跑锥问题、选择合适的结晶器锥度、控制钢水过热度以及拉速、杜绝结晶器液面波动等措施,板卷边裂率由6.32%降至0.87%,产品质量大幅提高,控制效果良好。     

轧制140方坯出现横裂的原因

本文分析了铸坯和轧制过程，检查了设备材料和工艺，从铜管的锥度亮变化上弄清轧制１４０方坯时出现横裂的原因。     

双锥度辊辊形参数对带钢瓢曲变形的影响

根据连续退火生产实际情况,运用MARC有限元软件,定量计算了连退炉内双锥度辊辊形参数对带钢瓢曲的影响.模拟发现在双锥度辊锥肩处,带钢张应力和横向应力发生突变,并且带钢横向压应力和等效应力都具有最大值,此处最先发生瓢曲变形,这与现场观测到的带钢瓢曲出现的位置完全吻合.随着总锥度和锥度比的增大,以及平直段长度和直径的减少,带钢发生瓢曲变形的概率都会增加.其中平直段长度对带钢发生瓢曲变形的影响最大,总锥度和锥度比其次,平直段直径的影响最小.     

65Mn小方坯角部龟裂成因分析及控制

65Mn钢小方坯角部龟裂对后续轧制影响极大.在分析裂纹成因的基础上,建立了钢水在结晶器中凝固的数学模型.计算结果表明,角部龟裂产生的根本原因是结晶器锥度过大,为方便生产现场管理,应使用旧结晶器铜管浇铸65Mn钢.生产实践表明,该方案解决铸坯角部龟裂的同时,还能有效降低结晶器使用成本.     

φ180结晶器铜管锥度设计

圆坯连铸机是从德马克公司引进的弧形连铸机,年产量52万t,为解决生产φ180mm规格的连铸坯,经常出现质量问题和漏钢事故的状况,通过研究,决定对φ180mm结晶器铜管锥度进行重新设计,采用等差数列的计算方法简化设计过程,从而实现连铸机正常生产.     

罗克普的高效连铸技术

罗克普公司的高效连铸技术代表了最新的高速连铸技术 ,其可以以更高的速度生产方坯和圆坯 ,而不需要凸形的或其他昂贵形的结晶器。与传统的连铸技术相比 ,其生产的铸坯内部和外部质量更好 ,且尺寸公差更小。罗克普的高效连铸技术的核心是结晶器。其长度比传统的结晶器长 2 5 % ,为 1m,且为抛物线形 ,由于其锥度合适 ,使得铸坯能很好地与铜管接触 ,并使气隙降到最小。抛物线的锥度和二次冷却的设计 ,都是通过计算机软件包—浇注过程模型确定的。精密成形的水套是由不锈钢制成的 ,其提供了均匀的水槽且环绕结晶器铜管的周围。罗克普的高效连铸…     

小方坯连铸机的高效改造

济钢第二炼钢厂对小方坯连铸机进行高效技术改造，将振动系统由原短臂四连杆式改造为半板簧连杆式；结晶器铜管长度由780mm加长到850mm，并对结晶器倒锥度、铜管壁厚进行优化，减小冷却水缝；建立二冷配水数学模型，确定二冷各段的配水比例，重新设计喷嘴数目和型号，实现了均匀强化冷却。改造后最高拉速由2．8m／min提高到3．5m／min，铸坯质量及铸机产量均有明显提高。     

方坯连铸结晶器三维热力耦合分析

采用ANSYS软件建立方坯连铸结晶器三维热力耦合模型,利用节点温度传递法模拟拉坯过程,对模型进行分析。通过瞬态分析得出结晶器铜壁和铸坯的三维稳态温度场,以铜壁温度场为热载荷,通过间接耦合方法分析结晶器铜壁受力状态。结果表明:铜壁最高温度点出现在结晶器热面中心距顶端约150 mm处(距弯月面约50 mm),最高温度142℃低于铜壁再结晶温度;铜壁热面最大位移出现在距铜壁顶端200 mm区域(弯月面下100 mm区域)角部位移为0. 112 mm;在弯月面附近等效应力达到最大值,从等效应力来看,整体应力值都在结晶器应力屈服强度之内,因此结晶器不会永久变形。     

Q235B钢矩形坯在结晶器中传热凝固行为的研究

将连铸过程连铸坯凝固收缩、鼓肚变形、气隙、保护渣及结晶器传热进行耦合求解,开发出了适用于165 mm×225 mm的Q235B钢矩形坯连铸过程中钢水传热凝固的计算模型,并利用该模型对拉速1.5 m/min工况下结晶器内连铸坯的传热凝固行为进行了详细计算。计算结果表明连铸坯宽面温度在气隙分布的影响下呈不均匀分布,且与现场坯壳比对研究可以发现振痕的形成分成了4个阶段,第1阶段发生在距弯月面0～0.17 m,高温区分布法向与拉坯方向垂直,法向垂直于拉坯方向的振痕形成;第2阶段发生在距弯月面0.17～0.26 m,温度分布呈现W形,法向与拉坯方向平行的振痕形成;第3阶段发生在距弯月面0.26～0.36 m,宽度方向温度进一步均匀化,法向与拉坯方向平行的振痕进一步向均匀化发展;第4阶段发生在距弯月面0.36～0.80 m,连铸坯宽面宽度方向的温度分布趋于稳定,振痕也趋于稳定。现场漏钢坯壳的振痕形貌图与计算的温度分布图相似,计算模型可以用来解释该工况下连铸坯的传热凝固行为。现场加大结晶器锥度和调整结晶器铜管刚度,漏钢率和铸坯鼓肚及脱方超标比例显著下降。     

150mm×150mm连铸坯形状缺陷的成因分析及解决措施

莱钢炼钢厂１５０ｍｍ×１５０ｍｍ连铸坯产生菱变、鼓肚和纵向凹陷等形状缺陷的主要原因是结晶器及二冷区的不均匀冷却。通过采取定期测量结晶器铜管倒锥度、限定铜管的通钢量为１５００ｔ、加强足辊对弧精度的调整等措施，使１５０ｍｍ×１５０ｍｍ连铸坯形状缺陷的发生率由８．１８％降至３．００％。     

薄板坯连铸结晶器锥度设计技术研究及应用

以提高结晶器使用寿命和铸坯表面质量为目标,通过建立漏斗区自有锥度、结晶器总锥度和结晶器局部锥度的计算模型,研究了漏斗区的宽度和深度、窄边铜板偏移量以及磨损对结晶器锥度沿高度方向分布的影响,提出了漏斗区自有锥度和局部锥度沿高度方向分布应与铸坯的凝固收缩相匹配的设计理念,对薄板坯连铸结晶器宽面铜板内腔形状及窄边锥度调控工艺进行了优化设计,为结晶器操作工艺及管理制度的优化提供了理论依据。基于上述研究工作,研发了适合于FTSC工艺的新型结晶器,进行了大量的工业生产试验。结果表明:在浇注宽度为1 520mm的铸坯时,窄边附加偏移量可由12mm降低到7mm,窄边铜板的使用寿命得到了大幅度的提高,过钢量为2.25万t后,窄边铜板最大磨损量由5mm降低到2mm以下;新型结晶器有效控制了铸坯窄面凹陷和表面纵裂纹的发生。     

双流板坯结晶器锥度动态保持技术的开发与应用

 详细介绍了山东富伦钢铁厂新建的国内首台2机2流不同断面板坯连铸机结晶器锥度动态保持技术的功能、设备构成和液压、电气控制原理,并推导得出浇注过程中结晶器宽边减轻力、碟簧预紧力与钢水静压力之间的定量关系。从2013年10月9日该技术正式投入使用至2013年11月12日,累计浇钢41 860 t,每个浇次平均连浇14炉,最大拉速可达1.4 m/min,彻底避免了跑锥问题,可使左、右锥度始终保持在±0.5 mm以内,铸坯内外部质量优良,实际使用效果令人满意。     

提高亚包晶钢板坯拉速对结晶器传热的影响

通过对提高亚包晶钢AQ钢种230 mm×1200 mm板坯拉速试验过程中结晶器冷却水参数、铜板测温等数据进行适时记录,并与数学模型及ANSYS商业软件相结合,研究了提高拉速对结晶器平均热流、局部热流、铜板温度场以及坯壳厚度的影响。结果表明,拉速由1.3m/min提高到1.5m/min时,平均热流增加0.1 MW/m²左右,宽边弯月面区域局部热流增加0.13 MW/m²,但均在合理范围内,这与采用高碱度高结晶温度的试验保护渣有关;结晶器窄/宽面平均热流比超过0.9,应适当减少结晶器锥度;宽面坯壳厚度平均减薄4 mm左右,应严格控制结晶器传热强度,以保证连铸工艺稳定和铸坯质量。     

Mold behavior and its influence on quality in the continuous casting of steel slabs: Part II. Mold heat transfer,mold flux behavior,formation of oscillation marks,longitudinal off-corner depressions,and subsurface cracks

Axial heat-flux profiles have been determined quantitatively from temperature measurements conducted on a slab mold under routine operating conditions. As in earlier studies, the heat flux was observed to have a maximum value at the meniscus and to decline with increasing distance down the mold. The mold heat flux increased with increasing casting speed and was greater with a mold powder having lower viscosity and melting point being applied as lubricant. The heat extraction was largest while casting 0.29 pet carbon steel and least for a 0.09 pet carbon grade; reducing the depth of the submerged entry nozzle increased the heat flux slightly in the upper region of the mold. Most significant was the higher heat flux observed at the meniscus of the outside-radius face, attributable to the locally greater copper plate thickness compared to that of the opposite broad face. All of the measurements can be explained straightforwardly by heat flow in the vicinity of the meniscus and the resulting behavior of the so-called slag rim adjacent to the mold wall. It is postulated that the difference in copper plate thickness between the two broad faces at the meniscus causes the slag rim to be smaller on the outside-radius face which gives rise to shallower oscillation marks, as observed, higher heat transfer, and a slightly thicker solid shell. The dissimilar behavior has implications for quality because the inside-radius shell, experiencing reduced heat extraction, cools and shrinks less than the outside-radius shell. Thus, for a given end-plate taper, the narrow face of the slab adjacent to the inside radius can push against the end plate, accelerating copper wear, and, owing to squeezing of the broad face, cause an off-corner depression and subsurface crack toward the mold exit. If this is correct, maintenance of the same copper plate thickness at the meniscus is fundamental to preventing such an occurrence. Moreover, adjustment of the heat extraction at the meniscus should be achievable by changing copper plate thickness, mold coating thickness/conductivity, cooling water velocity, cooling channel configuration, and mold flux composition for a given steel grade. Formerly Graduate Student, Centre for Metallurgical Process Engineering, The University of British Columbia,     

Hypnotic taper with or without self-help treatment of insomnia: A randomized clinical trial.

This study aimed to assess the efficacy of a minimal intervention focusing on hypnotic discontinuation and cognitive-behavioral treatment (CBT) for insomnia. Fifty-three adult chronic users of hypnotics were randomly assigned to an 8-week hypnotic taper program, used alone or combined with a self-help CBT. Weekly hypnotic use decreased in both conditions, from a nearly nightly use at baseline to less than once a week at posttreatment. Nightly dosage (in lorazepam equivalent) decreased from 1.67 mg to 0.12 mg. Participants who received CBT improved their sleep efficiency by 8%, whereas those who did not remained stable. Total wake time decreased by 52 min among CBT participants and increased by 13 min among those receiving the taper schedule alone. Total sleep time remained stable throughout withdrawal in both CBT and taper conditions. The present findings suggest that a systematic withdrawal schedule might be sufficient in helping chronic users stop their hypnotic medication. The addition of a self-help treatment focusing on insomnia, a readily available and cost-effective alternative to individual psychotherapy, produced greater sleep improvement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Calculation of Taper Rolling Time in Plan View Pattern Control Process

 The forward slip model with adhesion was used to derive the formula of calculating taper rolling time. The relation between the rolling time and the taper length and the relation between the rolling time and the taper thickness can be obtained. The numerical solution for this formula was used on site. According to the simulation result, the roll gap value should be changed linearly with rolling time.     

The thermal distortion of continuous-casting billet molds

Preliminary mathematical analyses involving plate bending theory and two-dimensional elastic calculations have revealed that the dominant component contributing to the distortion of continuous-casting billet molds is thermal expansion in the transverse directions. A three-dimensional, elasto-plastic, finite-element analysis of the mold wall has then shown that localized yielding initiates in a region close to the meniscus. The plastic flow is a result of the high thermal stresses induced by the geometric restraint to bending coupled with the locally high temperatures. The resultant distortion profile of the mold down the centerline of a face exhibits a maximum outward bulge of 0.1 to 0.3 mm, which is bounded above by a region of negative taper (1∼2 pct/m) and below by a region of positive taper (∼0.4 pct/m). Measurements of mold wall movement in an operating billet caster using linear displacement transducers compare favorably with model predictions, except in the meniscus region. Case studies of several industrial billet molds have shown that lowering the meniscus level with respect to the location of constraints, or modifying the method of support of the mold tube within its housing so as to reduce the restraint to thermal expansion in the meniscus region, may minimize the extent of permanent distortion. Also, wall thickness can have a significant effect on thermal distortion. Increasing wall thickness results in an increase in both peak wall temperatures and thermal gradients. The former increases the local distortion while the latter causes higher thermal stress levels and possibly permanent distortion. Of the casting variables that can be manipulated to major advantage, cooling water flow rate is the most important. Increasing the water velocity reduces mold wall temperatures, as well as both the total and permanent distortion of the wall.     

管材试样的长短对延伸率的影响

在GB／T228—2002（金属材料室温拉伸试验方法）（见附录D第D2．2章节）规定．管段压扁试样平行长度只要大于等于标距长度与二分之一直径的长度之合。即满足要求。在实际标准执行中发现，在满足这一要求的前提下。平行长度的长短对产品的延伸率有很大的影响。难以反映材料本身塑性的真实性、稳定性及同一性。本文通过试验对这一结论进行论证。并对国标（金属材料室温拉力试验方法）再修订时有关管材取样类型提出了建议。     

超音速雾化器的气体流场分布研究

利用Pitot管对超音速雾化器出口处的气体流场分布进行了研究。研究结果表明，在出口处的雾化气体呈轴线近似对称的双峰分布，峰值沿着远离导液管出口端面的方向而逐渐减小。通过对气体流场分布的分析，提出倒涡流锥概念，可以很好的解释导液管下端形成负压的原因，并认为理想的雾化过程是在倒涡流锥范围内完成的。     

MCCR产线低碳钢高拉速技术研究与应用

通过统计和分析现场数据,得出限制MCCR薄板坯连铸连轧低碳钢拉速提高的主要因素为结晶器热像图中的冷齿和结晶器液面波动,对冷齿和液面波动的成因进行研究,并提出有效控制措施。研究结果表明,结晶器热像图中的冷齿与结晶器弯月面凝固收缩特性相关,受冷却铜板厚度、碳当量、拉速及保护渣影响,反映到铸坯实物上为凹陷或者裂纹缺陷,需合理匹配形成最优参数组合,以降低因冷齿造成的漏钢风险。当结晶器铜板厚度减薄量在6.7%以内时,一冷水维持原设计流量;当结晶器铜板厚度减薄量在6.8%～11.1%时,拉速4.0 m/min以上时需降低10%的一冷水流量;当结晶器铜板厚度减薄量在11.2%～15.6%时,所有拉速下需降低18%的一冷水流量,同时使用高碱度B型保护渣。针对高拉速下结晶器液面波动问题,通过数值模拟研究浸入式水口插入深度、拉速、结晶器断面宽度及电磁制动等参数对结晶器内流场和温度场的影响规律,得到不同拉速和不同断面条件下电磁制动电流的合理配置,使得拉速达到5.5 m/min时钢液面最大流速仍小于0.3 m/s。上述研究结果应用后,结晶器冷齿问题得到有效缓解,110 mm厚的薄板坯最高拉速达到5.8 m/m...