中厚板辊式矫直过程弯辊作用分析

 为了进一步提高中厚板产品矫直质量,采用弹塑性差分的曲率积分方法,分析了弯辊对矫直效果的影响,研究了弯辊量与压下量的关系,为建立中厚板辊式矫直过程的弯辊设定模型奠定了基础。计算结果表明,为了使板材矫直后的残余曲率和残余应力最小化,施加弯辊时要考虑入口压下量的影响。单从降低残余曲率的角度考虑,小压下量和大压下量下都可以施加负弯辊,但正弯辊只适用于小压下量。从控制宽度方向残余应力的角度考虑,正弯辊施加于小入口压下量时弯辊作用明显,为了消除正弯辊对厚度方向残余应力的不利作用,采用正弯辊时入口压下量不宜过大。施加弯辊会增加矫直力,因此设定弯辊量时要考虑矫直机能力的限制。研究发现了弯辊对塑性变形率的影响规律：负弯辊出现了使塑性变形率随着入口压下量的增加而减少的阶段,正弯辊可消除塑性变形率为零的阶段。     

棒材二辊矫直过程曲率的全流程定量解析

为了摸清棒材斜辊矫直过程中各曲率的变化规律,应用小曲率平面弯曲弹复理论以及棒材弯曲弹复的曲率方程式,实现棒材一次反弯弹复的计算模型,基于棒材每旋转半周反弯一次的规律以及上一次弹复后的残余曲率认为是下一次弯曲的原始曲率,建立棒材全流程二辊矫直过程弯曲弹复模型,获得整个矫直过程中原始曲率、弯曲曲率、弹复曲率以及残余曲率的演变过程,得到棒材最终的残余曲率.应用该理论模型对现场生产过程进行了计算,与现场结果一致,验证了理论模型的正确性.应用所建立的理论模型对不同直径、不同材料屈服强度、不同原始挠度的棒材矫直过程分别进行分析,获得了不同来料参数情况下矫直过程的变形规律.该模型可以为二辊矫直机辊型优化设计与工艺参数计算提供理论依据.      

辊式矫直过程弹塑性弯曲数学模型

 为了完整和精确地计算辊式矫直过程,根据钢板和矫直机相应的初始条件和边界条件,采用曲率变化量积分的方法,建立了基于Prandtle Reuss增量理论的三维弹塑性弯曲解析数学模型。并分析了厚度08 mm的钢板矫直过程的变形行为,比较了计算曲率和实验曲率,误差在1 mm-1左右。该模型可以精确地计算辊式矫直过程的曲率,预测残余应力和板形,为全面分析辊式矫直过程提供技术支撑,对实际生产具有一定的指导意义。     

头部翘曲板材矫直策略分析

随着厚规格、高强度品种钢的大量开发,头部翘曲成为板材生产过程的一种常见缺陷,同时部分矫直机矫直能力不足,使头部翘曲板材矫直过程困难。本文以开发厚规格、高强度品种钢过程中频繁出现的头部翘曲呈蛇形板材矫不平问题为依托,采用弹塑性差分的曲率积分方法,研究头部翘曲对传统矫直过程残余曲率和矫直力的影响,提出利用静压矫直方法解决头部翘曲板材矫不平问题。通过理论分析和现场实践证明：静压矫直可以有效解决头部翘曲板材矫不平问题,改善板形,减小切损量。     

中厚板热矫直过程中曲率的解析

建立了中厚板热矫直过程中曲率解析的数学模型,采用数值算法快速、稳定地解析了该模型。研究结果表明：前几辊与轧件之间的接触角受原始曲率影响较大,随着轧件的前进,这种差别逐渐减小最后趋于一致,而矫直轨迹受原始曲率的影响较小;具有不同原始曲率的轧件在相同辊系压下量作用下的残余曲率都趋近于0;矫直过程中厚度方向的反弯和残余应力分...     

不同结构粒化器表面高炉渣液膜的流动特性

在高炉渣离心粒化热回收工艺中,粒化得到的颗粒尺寸对余热回收效果至关重要,而颗粒尺寸又与粒化器表面液膜的流动特性息息相关,因此增进对粒化器表面液膜流动特性的认识可为离心粒化技术提供指导。采用数值模拟方法研究了离心粒化过程中粒化器结构对液膜流动的影响;讨论了半径、倾角、深度等参数对粒化器表面液膜厚度的影响及其作用机理,并获取了流体在粒化器表面运动轨迹与液膜厚度的关系。结果表明:转杯粒化器的内倾角介于40°~60°之间或深度介于10~12mm之间时粒化效果最佳,其相应液膜厚度约为0.300mm。与等径的转盘粒化器相比,其液膜厚度减小约32%。粒化器结构对液膜厚度的影响可归因于粒化器表面流体运动轨迹长度的变化,当流体运动轨迹长度增大时,其对应的液膜厚度就越小,二者呈非线性负相关关系。     

二辊矫直机凹辊辊形设计

 针对某钢厂新引进的棒材二辊矫直机的辊子需要国外进口,成本昂贵的问题,在对矫直过程中残余曲率的变化规律及辊形计算方法研究的基础上,结合有限元计算,通过分析塑性变形以及矫直后的棒材平直度,对弯曲曲率进行修正,得出相应辊形并进行有限元模拟,直到矫直后的棒材平直度达到要求,进而得出合理的凹辊辊形。该辊形与实测的辊形进行对比,基本一致。     

双金属复合板矫直过程的弯曲及弹复解析

基于工程弹塑性力学建立了不同组坯方式下双金属复合板弯曲矫直过程截面弹塑性状态演变路径的解析模型.基于该模型分析不锈钢复合板矫直过程中的弯曲回弹特性,解释复合板弯曲回弹过程中截面的反向屈服现象,并将不锈钢复合板与单一材料板材弯曲过程进行对比.研究结果表明:双金属复合板在弯曲过程中截面会经历五种弹塑性状态,并伴随着不同的中性层偏移规律,弯曲回弹后的残余应力分布与单一材料板相比更加不均匀且可能进入反向屈服状态;复合板与单一材料板材的弯矩相对差值随着屈服强度比的增大而增大,其绝对值随着弯曲曲率先增大后减小.      

钢液湍流漩涡中夹杂物运动行为

为研究钢液中湍流漩涡对钢中夹杂物行为的影响,采用Matlab软件对不同尺寸夹杂物所受斯托克斯阻力、重力、向心力进行分析,并构建钢液湍流漩涡中夹杂物运动行为模型。计算结果表明:漩涡中尺寸0~23μm的夹杂物以0~1m/s的初始切向速度做向心运动,逐渐聚集至涡心,其跃迁轨迹呈螺旋锥形,跃迁角、跃迁起点和终点与粒径、涡速相关。粒径、涡速越大,跃迁角越大,跃迁终点离涡心越远;而大于此尺寸范围的夹杂物惯性作用较强,离心运动趋势较大,重力将超过斯托克斯阻力成为主要作用力。通过水模拟实验得出漩涡中夹杂物的运动轨迹为螺旋锥形,与理论模型结果一致。     

End-point accuracy of kinesthetically and visually based corrections to a mechanically perturbed aiming movement.

12 right-handed females performed a multi-degrees of freedom manual aiming movement which could be unexpectedly perturbed. Ss performed the task in either a full vision (FV) situation or while only the target to be reached was visible (TO). Neither the absolute constant error (ICEI) nor the variable error (VE) of aiming could differentiate the perturbed and unperturbed trials for the Ss submitted to the FV condition. However, significantly larger ICEI and VE were observed for the perturbed trials in the TO condition. This is taken to indicate that the sensorimotor representation of the movement developed through learning is more precise when learning occurs in the presence of more afferent sources. Further, the larger spatial error found in the TO condition for the perturbed trials suggests that, when a learned movement is forced out of its usual trajectory, the kinesthetic feedback available, and/or the corrective motor commands, are less accurate than those available when the movement follows its usual trajectory. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

六斜辊管材矫直过程精度解析

摘要：以管材六斜辊矫直过程为研究对象,推导了管材经一次反弯后,弹复曲率及残余曲率的演变过程。根据管材旋转一圈弯曲2次,计算了管材全流程矫直微元段的反弯次数;借助三次样条函数,以管材与矫直辊接触点为特征点,拟合出了管材在辊系中的弯曲形态。基于所获得的函数,可以获得任意位置处的弯曲曲率;对某一微梁段的反弯弹复过程进行循环迭代,计算出管材微梁段的最终残余曲率,进而得到最终的管材矫后的直线度精度。通过与现场矫直数据对比,证明该模型能够可靠地预测六斜辊矫直精度,为科学合理的设定矫直参数奠定了理论基础。     

辊式矫直过程的接触倾角与曲率耦合分析

研究了在辊式矫直过程中接触倾角与曲率的变化规律,采用曲率积分的方法主要研究了接触倾角、特殊位置与曲率相互耦合关系。结果表明：接触倾角具有累积效应,辊距越大累积效应越突出,减小倾角的措施可以采用增大曲率差商的积分值和减小压下量。大的接触倾角导致大的曲率,曲率的累积效应对残余曲率有负影响,累积效应越大,需采用倾斜量越大。交叉点与接触点对曲率影响很大,交叉点位置比较固定,呈递增趋势,接触点位置和接触倾角成正比。     

Residual Curvature of Longitudinal Profile Plate Roller in Leveling Process

Roller leveling process of longitudinal profile (LP) plate is hardly studied because plate thickness changes. Deformation characteristics and residual curvature during LP plate leveling process were investigated based on curvature integral by elastic-plastic differences. It was found that entry intermesh section is reduced with increasing thickness and entry intermesh should be from 0.7 to 1.1 mm for LP plate with 42/54 mm in thickness. In order to get satisfactory flatness along longitudinal direction, small entry intermesh should be selected and exit intermesh should be 0 mm. In addition, thickness section for LP plate which can be leveled by 11 roller leveler is from 24 to 60 mm. Finally, there is an intermesh schedule that could level LP plate with initial curvature less than elastic limit curvature.     

New Formulas of Shear Strain during Equal-channel Angular Pressing Process with Consideration of Influences of Velocity and Motion Traj ectory

The influences of die parameters on shear strain were investigated by using two-dimensional finite element simula-tion.New formulas of shear strain were proposed.According to the results of formulas,the shear strain showed a linear de-pendence on the difference between internal and external fillet radius and the slope was determined by the intersection angle. The simulation results indicated that the velocities of the points from different zones were different in the specimen and the motion trajectories of different points did not follow geometrical laws.The influences of the average velocity and the mo-tion traj ectory on shear strain were incorporated in the formula to calculate the shear strain produced during equal-channel angular pressing process.The reliability of simulation results has been partially validated by experiments.     

Improved Formulation of One-Step approach suitable for initially non-flat configurations and forward simulation

 In the traditional one-step formulations using shell elements, the computations of the curvature variation and bending stiffness matrix are simplified by omitting the rotational DOFs on the basis of initial flat blank and fully known final configuration. They are highly efficient but not suitable either for the forming processes with non-flat initial configurations, or for one-step forward and multi-step analyses. Thus a one-step formulation based on the rotation-free BST (Basic Shell Triangular) element is presented here. In this formulation, the following improvements are made: 1) the curvature variation can be calculated exactly and efficiently resorting to a patch of four elements without rotational DOFs, which makes the formulation suitable for non-flat initial configurations, one-step and multi-step forward or inverse analyses, 2) The penalty method, instead of traditional sliding constraint, is employed to treat contacts in the forming processes, which makes it possible to inspect some deformation defects such as wrinkling et al directly. To verify the improved formulation, a program has been developed, and the bending process of a rectangular tube is simulated, with particular attentions paid on cross-sectional distortion. The numerical results of the one-step simulation agree with those of incremental analysis and experimental values.     

Principle of Multi-roller Straightening Process and Quantitative Resolutions of Straightening Strategies

The multi-roller straightening process of section steel is analyzed by the springback theory of small curva- ture plane bending. The theoretical analysis results prove the curvature unification in straightening process and clear- ly reveal the principle of the multi-roller straightening process. The principle can be described as~ the initial curva- tures are reduced by several times anti-bendingl meanwhile the initial curvature differences are diminished and the residual curvatures are unified~ finally, the member after curvature unification is straightened by the last anti-ben- ding. With the plastic region ratios becoming larger, the initial curvatures are more easily unified in straightening process. Based on the plastic region ratios and the required number of roller systems for unifying the initial curva- tures, the large deformation straightening strategy and the small deformation straightening strategy are redefined. The new definition provides an important theoretical basis for setting reliable reduction rules. Through the theoretical analysis results, a new straightener design philosophy is proposed to improve the straightening quality and further increase the adjustment precision as well as the flexibility of the last roller system. The adjustable end roller emerges as the times required, achieving a good effect in practical application.     

Manual Bar Bending—An Occupational Hazard for Construction Workers in Developing Nations

Bar bending is the process of bending reinforcement bars to required angles in civil and construction engineering. Manual bar bending involves strenuous physical activity, which is usually performed in a poor ergonomic environment at a construction worksite. This could lead to chronic musculoskeletal disorders such as low back pain among bar benders. The aim of this study is to assess the ergonomics of manual bar bending and thereby develop a customized optimal workplace for bar bending. Biomechanical analysis was done using a three-dimensional Schultz–Andersson model to determine the influence of the diameter of the bar on the compressive force (Fc) at L5/S1. The effect of table height, grip arm distance, and back bend angle on Fc were also evaluated. Fc decreased up to 53%, with an increase of table height by 400?mm, and up to 41%, with an increase of grip arm distance by 500?mm; however it increased with back bend angle. Fc was higher than the NIOSH safety limit of (3.4?kN) in all cases except when bending 8?mm bars. A quick field reference for optimal table height and grip arm distance was prepared based on subjects’ anthropometry and diameter, using Nash bargaining principles.     

Residual stresses in rails due to roll straightening

The knowledge of residual stresses in rails due to roll straightening has become increasingly important for the evaluation of the fatigue behaviour of rails. The residual stresses are induced both by the bending process and the roll contact leading to a very complicated distribution especially near those parts of the surface where the roll contact had taken place. So far, no clear picture has emerged with respect to the residual stress field, either from experiments or from simulations. This study intends to clarify the residual stress distribution by simulation with a fully three-dimensional model taking into account both the bending and contact process. This work shows that especially in those areas where the roll contact happens compressive residual longitudinal stresses appear on the surface. Furthermore, a very steep gradient of the residual longitudinal stress distribution near the surface is observed which is reported also in very recent X-ray and neutron diffraction experimental investigations.     

天铁焦化厂提高焦炉装煤量生产实践

针对天铁焦化厂装煤量偏低的现象,分析出其产生原因,通过调整配合煤细度、改造平煤杆与推焦杆、重新制定平煤时间、优化平煤方式等改进措施,降低了炼焦工序成本,提高了焦炉装煤量,取得了较高的经济效益。     

辊式矫直机矫直过程有限元仿真

建立了辊式矫直机的有限元模型,对其矫直过程进行动态有限元仿真。对不同规格的钢板分别进行仿真,将模型中的压下量按实际参数设定,并将其计算结果与实际情况进行比对,检验了模型的可靠性。对其残余应力分布进行分析,得出消除板坯翘曲必须控制长度方向上节点之间的纵向残余应力差值的结论。建立的辊式矫直机的参数化模型,能够方便地调整矫直工艺参数,并对其矫直效果进行分析,对辊式矫直机工艺参数的设定具有一定的指导意义。