极薄带轧制变形区接触轮廓及接触压力分析

轧制力模型的准确性对轧制过程中轧件厚度的控制起着决定性的作用。传统的轧制力模型假设轧辊为圆弧形,但是随着极薄带厚度的减小,变形区接触弧长远远大于轧件厚度,此时轧件已被压扁为非圆弧形轮廓。针对上述问题,Fleck基于赫兹接触理论准确求解了变形区轧辊轮廓,从而建立了新的轧制力模型,但是,Fleck解析方法比较复杂,针对不同的轧制工况建立了不同的计算方法。为了建立简化的解析方法,不仅统一了整个变形区轧制压力与摩擦力的表达式形式,而且忽略了中性区弹性卸载现象。通过对比简化模型计算结果与Fleck模型计算结果、实测的变形区轮廓,验证了简化解析模型的准确性。利用该简化模型分析了不同因素对变形区接触弧轮廓及接触压力分布的影响。结果表明,随着来料厚度减小、工作辊弹性模量减小、压下量增大,变形区轧辊弹性压扁越来越严重。     

一个精确计算压扁接触弧长模型及其在冷连轧机上的应用

以弹性接触理论为基础,利用Hertz基本公式,同时考虑轧辊的弱性压扁变形和轧件的弹性回复变形,推导出一个精确计算压扁接触弧长的模型。与多个有代表性的模型之间进行了对比分析,模型与实际情况更加相符。利用本模型建立的轧制压力模型计算精度优于原轧制力模型。     

弹性辊轧制过程的有限元仿真分析

为了得到轧制过程中轧辊及轧件的应力及变形情况分布,采用有限元软件Ls-dyna,通过三维弹塑性有限元方法,在工作辊与支撵辊均为弹性辊的情况下,对轧件精轧道次平辊轧制过程进行了仿真分析.详细介绍了有限元模型的建立,材料参数、边界条件及载荷的定义.仿真分析结果表明,轧制过程中接触弧内轧辊表面受到三向压应力作用;得出了工作辊的挠度曲线;支撑辊XY面剪应力呈现交变现象;同时分析了轧件的变形情况以及宽展曲线等.     

热轧带钢传热模拟及变形区换热系数的确定

采用数值模拟方法研究了带钢热轧区轧件传热和温度场分布规律.结合现场生产中测温数据,建立了轧制变形区内轧件与轧辊接触传热界面换热系数(HTC)统计模型.分析了辊缝变形区中轧件断面上温度演变和分布特点.研究结果表明,热轧带钢热轧区传热数值模拟计算结果与实际吻合良好;变形区内轧件与轧辊接触传热界面换热系数不仅与平均单位压力相关,而且与轧制速度相关;轧件在轧制变形区存在很大的温度梯度.     

轧辊弹性压扁对中厚板轧制压力预报精度影响的研究

建立中厚板轧制压力计算模型,分别采用简单轧制情况和考虑轧辊弹性压扁情况下轧件与轧辊接触面积计算模型来预报轧制压力,分析轧辊弹性压扁对中厚板轧制力预报精度的影响。结果表明,在中厚板轧制过程中考虑轧辊弹性压扁的情况下,当预报轧制压力小于实测值时,轧制压力的预报精度提高;当预报轧制压力大于实测值时,轧制压力的预报精度降低。     

大型筒节轧制力预报模型

 根据筒节和轧辊的几何关系,得到了筒节上下表面接触弧长的几何方程;根据现场数据和有限元方法,得到了筒节上下表面接触弧长的变形方程;结合几何方程和变形方程,并基于赫希柯克公式计算了考虑弹性压扁的筒节接触弧长。由于筒节外端对轧制力的影响远远大于接触摩擦的影响,结合接触弧长模型和材料变形抗力模型,基于现场数据和优化算法,优化得到了外端应力状态影响系数,从而建立了大型筒节轧制力预报模型。结果表明：上下辊的接触弧长不等,上辊接触弧长稍大于下辊接触弧长,上辊压下量大于下辊压下量,上辊和下辊的接触弧长之比约为1.3左右;将模型应用到筒节轧制中,计算轧制力与实测轧制力平均误差为9.2%,模型计算精度较高,能够满足工业应用要求。     

极薄带轧制变形区轧辊压扁试验与有限元模拟

 极薄带在轧制及平整过程中,工作辊的弹性压扁对轧制压力的分布有很大影响,传统的轧制力模型已经不再适用。为了在极薄带板形板厚控制过程中得到准确的轧制力,Fleck提出了新的轧辊压扁模型。针对Fleck模型进行试验研究,同时进行有限元模拟分析。试验过程中使用合金工具钢轧辊,轧制不同厚度的轧件,通过显微镜测量变形区各部位的厚度,得到变形区轧辊的近似轮廓形状。试验与有限元模拟结果表明,随着轧件厚度的减小,变形区出现了明显的中性区,但是很难出现Fleck模型中提到的弹性卸载区,因此计算极薄带轧制力时可以忽略中性区内的弹性卸载区以简化轧制力模型。     

超高强钢冷轧过程轧制力计算的改进模型

 为了解决采用圆弧模型计算超高强钢冷轧过程轧制变形区轧辊压扁曲线误差较大的问题,充分考虑到超高强钢的轧制特点,通过分析不同压扁半径下轧辊压扁曲线的变化规律,构造出新型轧辊压扁曲线函数模型,给出了该函数中轧制变形区接触弧长特性参数与轧辊压扁曲线特性参数的求解方法。基于此,根据弹塑性理论中的变形与应力关系,推导了入口弹性变形区、塑性压下变形区以及出口弹性变形区单位轧制压力分布计算过程,建立了超高强钢冷轧过程总轧制力计算模型。并将其推广应用到某钢厂2030冷连轧机组,验证了该模型的计算准确度。结果表明,超高强钢冷轧过程轧辊压扁曲线用二次函数表示,更能准确反映轧辊压扁状态,其计算结果与实际值具有较高的吻合度。同时,为冷连轧机组生产超高强钢产品极限轧制能力的评估与轧制规程的制定提供了理论依据。     

冷轧板材接触弧长度的确定及轧制力计算

本文从轧辊和轧件的弹性变形出发,提出一个简便而精确的接触弧长度计算公式。在此基础上又提出了轧制压力计算方法——图表法和解析法(简化公式)。上述公式不仅为一般工程计算提供了方便的条件和较为符合实际的结果,并为电子计算机控制提供简便而又较为精确的轧制压力数学模型,对提高轧制力预报精度、减少计算机的内存占用量、提高在线的运算速度,都有着重要的实际意义。     

考虑轧件弹性变形的Hill轧制力显式公式

带钢的轧制力计算和轧辊的压扁计算互为条件 ,针对考虑轧件弹性变形的Hill轧制力公式和Hitchcock轧辊压扁公式 ,推导了它们的显式计算公式 ,从而避免了传统的迭代计算。     

转炉炉壳热应力分析

根据实际转炉建立实体模型。以有限元为手段,考虑了炉衬和炉壳材料的物性参数随温度变化的特点和炉衬与炉壳之间膨胀间隙,计算了转炉炉壳在温度载荷和炉衬膨胀压力同时作用下的热应力。所得结果可为转炉炉壳设计提供依据。     

焦炭热性能指标意义浅析

通过对焦炭在高炉内的历程及其变化规律的剖析,阐述焦炭热性能指标的意义,形象地把焦炭在高炉内的损耗分为三部分(M1,M2,M3)。指出M2对焦比及焦炭价格有一定的指导作用。     

Results of treatment of cancer of the cardia

Cancer of the cardia is traditionally discussed with cardiac cancer of the lower portion of the esophagus and upper gastric cancer invading the esophagus, and the specific characteristics of cancer of the cardia have never been clearly defined. We reviewed the outcome of 172 patients with adenocarcinoma of the cardia who had undergone radical surgery between 1949 and 1994 in the Division of Gastrointestinal Surgery of the Cancer Institute Hospital. The centers of the tumors were located within 2 cm above and below the boundary between the esophagus and the stomach, and their longitudinal diameter was less than 8 cm. We divided the patients into an early period (1949-1979; n = 79) and a late period (1980-1994; n = 93), and focused on the historical transition. There were no differences in patient gender or histology between the two periods. However, the late period was associated with fewer cases of esophageal invasion and shorter longitudinal diameter, as the age of the population advanced. The number of advanced cancers such as the localized and infiltrative type had decreased, and early cancer and early clinical stage had become more common, but despite the fact that the number of early cancers had increased, extended dissection, such as thoracic and paraaortic lymph node dissection, was performed more frequently. By clinical stage, the long-term outcome markedly improved in Stage I patient in the late period, and tended to improve in Stage II and III patients. This appears to have been attributable to the prevention of micrometastasis by extended dissection, although the number of early cancers is another major potential cause. There were no differences in the outcome of Stage IV patients between the two periods, and further advances in multimodality therapy must be awaited. The range of resection is basically proximal gastrectomy, and if there are adequate indications, the prognosis is favorable. In view of the status of lymphatic flow and lymph node metastasis, and long-term results, lateroaortic lymph node dissection is important. Since the number of early cancer patients has been increasing, if intraabdominal recurrence is prevented, intrathoracic lymph node dissection will contribute greatly to the outcome of such patients.     

The effect of amount of possession of the trait of hostility on accuracy of perception of hostility in others.

Some theories of personality hold that an individual's perception of others is influenced by his own personality characteristics; more specifically, that a trait of low social value will be projected more into others, and that insight into the possession of these characteristics reduces this distortion. These 2 hypotheses were tested by having a group of college students rate each other (including themselves) on degree of friendliness or hostility. Agreement with group rating about self yielded the insight score. In general, the hypotheses were supported; the "friendly" Ss were most accurate in their perception of others, and insight was positively associated with accurate perception. From Psyc Abstracts 36:04:4HL16M. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of rates of infection of two methods of emergency ventricular drainage

The rates of infection of two methods of external ventricular drainage in use at Atkinson Morley's Hospital--namely, (a) percutaneous drainage with Rickham reservoirs and (b) tunnelled ventriculostomies--were compared in this retrospective review. Percutaneous drainage of CSF with Rickham reservoirs was associated with a 27% rate of infection as identified by positive microbiological cultures; tunnelled ventriculostomy catheters had a 10% infection rate. The difference in the infection rate between the two methods was statistically significant (P < 0.015). Other variables examined, including the age and sex of the patients and the reasons for ventricular drainage, were not associated with an increased rate of infection. Most infections from either method were caused by a coagulase negative staphylococcus. The average duration of ventricular drainage before identification of positive cultures was 5.7 days for Rickham reservoirs and 6.0 days for ventriculostomies.     

浅析《野草》的版画特征

鲁迅先生一生热爱美术作品,对版画中木刻兴趣尤甚.<野草>作为其"写心之作",亦呈现出一些与木刻版画一致的审美特征:一是具有木刻版画的色彩特征,多对比、多冷色,有阴郁的美感;二是具有木刻版画的力度特征,环境描写、人物刻画处处刀锋毕现,遒劲有力,有一种"力之美".     

四辊破碎机车刀架的改造

针对四辊破碎机车刀架车削中存在的几个问题,详细介绍了电动车刀架的结构和工作原理,建立主要设计参数的数学表达式,并进行适当的分析。改造后,这种电动车刀架运行平稳、可靠、方便、省力,取得了预期的效果。     

Effect of antibiotics of chemotaxis of human leukocytes

The effect of 20 different antibiotics on chemotaxis by human neutrophils was studied. Human leukocytes incubated with chloramphenicol, rifampin, sodium fusidate, and tetracyclines in vitro showed markedly depressed migration. The mechanisms by which these antibiotics affect leukotaxis are discussed.