Simplified calculation of the bending torques of steel sheet and the roller reaction in a straightening machine

In the straightening of steel sheet, it is necessary to calculate the optimal reduction of the steel blank by the working rollers of the straightening machine so that the sheet produced has the minimum residual stress and curvature. In the simulation of sheet straightening in multiroller machines, the curvature and bending torques of the steel sheet at contact points with the working rollers are first calculated and then the straightening forces are determined. In straightening steel sheet, it is important to calculate the forces in the multiroller straightening machine. Such calculations are based on determination of the reaction of the roller bearings and the forces at the upper and lower working-roller cassettes in straightening. With insufficient bending torque, it is impossible to eliminate harmful residual stress and surface defects in the sheet. Extreme roller torques and forces at the roller cassettes often lead to defects of the sheet, fracture of the working and supporting rollers, and failure of the straightening machine. In the present work, an approximate method is proposed for calculation of the optimal cold-straightening parameters of the steel sheet in a multiroller machine. The calculations permit determination of the curvature of the neutral plane in the sheet on straightening, the residual curvature of the sheet after straightening, the bending torque and the reaction of the working-roller bearings, the residual stress in the sheet, the penetration of the plastic deformation into the depth of the steel sheet, and the relative deformation of the longitudinal surface fibers of the sheet on straightening as a function of the radius of the working rollers, the distance between the rollers of the straightening machine, the reduction of the sheet by the upper rollers, the sheet thickness, and its properties (Young’s modulus, yield point, and strengthening modulus). The results may be widely used at manufacturing and metallurgical plants.     

Preliminary straightening of thick steel sheet in a seven-roller machine

A mathematical model is proposed for determining the forces and torques in the preliminary cold straightening of thick steel sheet in a seven-roller machine. On that basis, the bearing reaction of the working rollers, the residual stress in the wall of the steel sheet, the proportion of plastic strain over the sheet thickness, and the relative strain of longitudinal surface fibers of the sheet in straightening may be determined as a function of the working-roller radius, the spacing between rollers of the straightening machine, the reduction of the sheet by the upper rollers, and the sheet thickness, as well as the Young’s modulus, yield point, and strengthening modulus of the sheet. The results may be used at manufacturing and metallurgical plants.     

Geometry of steel sheet in a seven-roller straightening machine

A method of determining the parameters of preliminary cold straightening of steel sheet on a seven-roller machine is proposed. The calculations permit the determination of the shape and curvature of the sheet’s central plane during and after straightening, as a function of the radius and spacing of the rollers, the reduction of the sheet by the upper rollers, the sheet thickness, and also the Young’s modulus, yield point, and hardening modulus of the steel. The results may be used at steel plants in the production of broad sheet and thick-walled pipe for pipelines.     

ARefined Model of Three-roller Elastoplastic Asym-metrical Pre-bending of Plate

The geometry of plate after edge pre-bending mode is compared with that after roll-bending mode and the relationship among edge pre-bending angle, pre-bending edge length, and cylindrical desired radius is presented for a three-roller plate bender with bottom rollers adjustable horizontally. The analytical moment-curvature model and springhaek model for pure bending are established, assuming that the stress-strain relationship of material is linear, and the material is in plain strain and yields according to Mises yield criterion. The mathematical model for three- roller edge pre-bending of plate is developed considering the effect of pre-bending edge length, bottom roller radius, friction between plate and roller, etc. The plate tensile test and plate bending test are done and the numerical results agree well with the test data. The results are shown graphically and analyzed in the following aspects： （1） the error between numerical results and test data of top roiler force; （2） the influence of bottom roller radius, relative curva- ture, and bending arc length on springback angle; （3） the relationship between springhack ratio and edge pre-ben- ding angle.     

金属薄板滚压冲裁过程数值模拟及模具参数

研究了在没有压下辊的情况下滚压冲裁过程的运动学特性,据此提出了通孔滚压冲裁模具的设计方案.在此基础上,利用ABAQUS有限元软件进行了基于Shear Failure韧性断裂准则和任意拉格朗日一欧拉自适应网格技术的45号钢薄板滚压冲裁过程有限元仿真,分析了主要参数对断面质量的影响.仿真结果表明:方形孔滚压冲裁时,前后刃口依次经历板带弯曲、凸模压入、裂纹产生和发展、断裂和凸模拔出五个阶段;滚压冲裁断面的主要质量缺陷包括断面垂直度、毛刺、塌角、压痕等;影响滚压冲裁断面质量的主要因素包括侧隙、凸模高度、辊子半径等.减小标称侧隙和凸模高度、增大辊子半径均会使断面质量提高,其中又以对断面垂直度和毛刺高度的影响更为明显.对于45号钢一类的碳钢,后刃口标称侧隙以板厚的5%-10%为宜,前刃口标称侧隙可以更小:辊子半径应以大于板厚的100-150倍为宜;在保证板材完全断裂的前提下,应使凸模高度尽量减小.      

Elastoplastic Flexure of Round Steel Beams. 1. Springback Coefficient

Round steel beams are widely used in metallurgy, manufacturing, and construction. It is often irreplaceable in the production of machines and mechanical equipment on account of its excellent corrosion resistance and remarkable strength. Cylindrical springs for road and railroad vehicles are manufactured from round beams by means of special bending machines. Round beams also serve as blanks in the production of seamless pipe for the oil and gas industry. Stepped round beams are used as rollers in rolling and straightening mills. Steel rebar is manufactured from round beams of similar size. Outside Russia, the main producers of continuous-casting machines for the production of round billet are SMS Demag (Germany), Danieli (Italy), SMS Concast (Switzerland), and Siemens VAI (Austria). Russian producers include AO Chusovskii Metallurgicheskii Zavod, PAO Chelyabinskii Metallurgicheskii Kombinat, AO Volzhskii Trunbnyi Zavod, OAO Nizhneserginskii Metizno-Metallurgicheskii Zavod, AO Chepetskii Mekhanicheskii Zavod, PAO Severskii Trubnyi Zavod, and PAO Taganrogskii Metallurgicheskii Zavod. In the manufacture of parts from round beams and their use, they often experience elastic or elastoplastic flexure or complex torsion and flexure. In the present work, we propose an analytical method of calculating the residual curvature of round steel beams in elastoplastic flexure. In the calculations, the residual curvature of the round beam after flexure and the bending moments of the beam cross section in flexure are determined as a function of the beam radius, the Young’s modulus, the yield point, and the hardening modulus of the steel. The results may be widely used at manufacturing and metallurgical plants.     

二十辊轧机支撑辊组变形及板形调控分析

 板带材的产能和质量是一个国家工业水平发展的重要标志,铜板带材的生产能力和地位更加显著。森德威二十辊轧机是冷轧铜板带材轧制生产的关键设备,其最外层A、D支撑辊组的弯曲变形是最重要的板形调整手段之一。支撑辊组鞍座位移变化可以使支撑辊芯轴发生弯曲变形,变形会反映到背衬轴承上并且向下依次传递给中间辊和工作辊,最终影响板厚和板形。传统的假设折线法和超静定梁法将芯轴和背衬轴承考虑为一个整体,而忽略了两者之间的变形对整体支撑辊组变形的影响。因此,基于有限元方法进行仿真拟合各段背衬轴承弯曲变形得到简化后的一次函数表达式,将各段背衬轴承拟合结果汇总进而得到整体的支撑辊组弯曲变形的线性表达式,再结合辊系弹性变形模型和金属塑性变形模型构成的板形预报模型评估支撑辊组变形程度对板形和板厚的影响。研究结果表明,对上辊系中的4个鞍座施加不同的位移组合之后,板厚和板形分布在整个板宽方向上并非局部变化,而是呈现整体的变化趋势,且4个鞍座对板形和板厚的调整效果并不相同;在施加同样的鞍座位移条件下,中部鞍座比边部鞍座对板形和板厚的影响效果更加显著,并且即使在支撑辊组中心两侧施加对称的鞍座位移,其对板厚和板形的影响也是非对称的。     

Asymmetric deformation of metal and front flexure of thick sheet in rolling. Part 1

In thick-sheet rolling, formulas are obtained for the kinematic parameters of the deformation source, the torques, and the front flexure of the sheet leaving the rollers. A criterion for front linearity of the sheet is developed. The basic parameters affecting sheet flexure are the temperature gradient over the slab cross section and the insertion angle of the sheet in the rollers.     

Sheet cooling in a roller quenching machine

The temperature over the thickness and width of the quenched sheet is studied experimentally in the roller quenching machine at OAO Severstal’. The result permits industrial assessment of the efficiency of the first header with slotted nozzle and subsequent sections with flat spray nozzles. In addition, the length of the active water layer at the lower sheet surface may be estimated, and the optimal ratio of the flow rates in upper and lower cooling may be analyzed. The conclusions may be employed in developing the design, technology and software for automated control systems used in the heat treatment of steel sheet.     

铸坯导向辊温度分布及变形分析

对整体和辊套结构型式连铸机导辊的温度和受力变形进行数值模拟计算,结果表明:整体辊比辊套结构导辊的抗变形能力高且传热效果好;对需要采用辊套结构导辊的情况下,可以采用将辊套壁厚适当加大等方法优化辊套尺寸设计,并采用高强耐热材质的辊套来加强其抗变形能力;选择适当的二冷方式则可以避免由于其传热方面的弱点而影响导辊使用寿命或铸坯质量的问题;从而从铸机设备设计方面保证铸坯生产顺利,提高连铸机的综合经济技术指标.     

Production of sheet with regulated surface microtopography

The production of sheet (including auto-industry sheet) with regulated surface microtopography is considered, beginning with the surface preparation of the working rollers and ending with the formation of roughness beyond the deformation region. The dependence of the impressionability (K _Ra in terms of the amplitude and K _Pc in terms of the frequency) on the individual and combined effect of various factors—such as the surface properties of the sheet, the reduction in the deformation region, the sheet thickness, the rough-ness of the blank, the presence of tempering or washing fluid, the roller diameter, and the tensile stress in the deformation region—is analyzed. The results are consistent with the model of supporting stress in the deformation region. This information is of practical interest to technologists producing sheet with regulated surface microtopography.     

Effects of Material Properties and Punch Tip Radius on Spring-Forward in 90° V Bending Processes

Bending process is one of the most significant fields of application of sheet metal die. Sheet metals are exposed to some spring-back or spring-forward depending on elastic deformation following bending process. S235JR (1.0038) materials having a thickness of 4 mm were bent with 90° punches having 5 different tip radiuses. The bending process was carried out by making the punch waited on the material for 30 s (30 s wait bending) and by removing the punch without waiting (direct bending). Specimens were prepared in three forms as non-heat-treated, normalized and tempered. At the same time, all experiments were performed at a deformation speed of 25 mm/min. As a result, it was determined that as punch tip radius increased, the amount of spring-forward decreased. Although normalizing process applied to specimens increased the amount of spring-forward, tempering process decreased it. The amount of spring-forward was decreased in 30 s wait bending process.     

Asymmetric deformation of metal and front flexure of thick sheet in rolling. Part 2

Laboratory experiments are followed by the rolling of sheet in industrial conditions on 3600, 2300, and 5000 thick-sheet mills. The parameters that affect the front curvature of the sheet leaving the rollers are identified. The sheet-reduction conditions on the 3600 and 2300 mills are assessed, so as to determine the rolling parameters responsible for asymmetry of the process in the vertical plane. Means of compensating the sheet flexure at the roller exit are proposed.     

Longitudinal rolling in helicoid rollers

A new method of sheet rolling in helicoid rollers is considered. In this approach, the roller barrel is formed by a helicoid with rounded projecting tips. The effectiveness of the rollers is demonstrated, and their geometric parameters are determined. Depending on the mutual orientation of the rollers’ helical barrel surfaces, rolling will produce linear hardened zones on the strip, at some angle to its longitudinal symmetry axis. Such nonuniform deformation increases the strength of the sheet, thanks to the formation of local hardened zones, without overall loss of strip plasticity.     

Sleeve deformation in a three-roller screw-rolling mill

The screw rolling of steel pipe in a three-roller mill is considered. Given the differences in the unitforce distribution within the deformation region, a method is developed for calculating the deformation parameters in sleeve rolling on a long mandrel. A method is presented for calculating the reduction and contact surface area of the metal and the roller, in the region where the diameter of the sleeve is reduced and in the region where the wall thickness is reduced. Account is taken of the tangential flow of metal into the gaps between the rollers, which is characteristic of the rolling of thin-walled pipe when the ratio of the diameter and the wall thickness is D_pi/S_pi > 8. The results are intended for industrial use in the production of pipe with D_pi/S_pi = 8–15, when the tolerances are ±6% on the wall thickness and ±0.5% on the diameter. The results provide a better understanding of the production of thin-walled pipe on screw-rolling mills.     

Effect of Thin Polymer Coatings on the Mechanical Properties of Steel Plates

The influence of powder coatings based on an epoxide polyester mixture on the mechanical properties of the plates made of rolled sheet steel is studied. The influence of 100-μm-thick coatings on the mechanical properties of specimens 0.7–1.5 mm thick is considered. The bending and tensile tests performed at room and elevated temperatures show that the thin coatings weakly affect the mechanical properties of the plates. In particular, the stiffness of the coated plates during tension and bending remains almost the same despite the fact that the elastic modulus of the coated plates is always slightly lower than Young’s modulus of steel because of an increased specimen thickness determined with allowance for the presence of a coating. The influence of the coatings is substantial in compressive stability tests. Under supercritical deformation conditions, the bearing capacity of the coated plates decreases substantially, and their critical stability load on the loss of stability falls by 20–30% (depending on the substrate thickness). This effect can be explained by the influence of the residual thermal stresses that appear in the specimens during coating deposition.     

Damage to thick steel sheet in cyclic plastic flexure

The laminar development of damage in thick 10Г2С1 steel sheet during cold plastic deformation by cyclic flexure is investigated. The steel is subjected to pure flexure in a symmetric cycle, with strain of amplitude 5.5%. The variation in steel strength indicates the damage kinetics in the plastic deformation. In the region of reversible damage, the rate of change in the strength increases to a maximum and then declines. In the region of irreversible damage there is no further change in strength of steel before failure occurs. An upper limit is proposed for the damage of the steel: 20–30% of N_f, where N_f is the number of cycles to failure in cyclic extension–compression. In structural terms, the upper limit of reversible damage is assumed to correspond to the transformation of cellular dislocation structure to band structure.     

粗轧带钢头部翘曲原因分析及控制措施

造成带钢头部翘曲的主要因素包括：板坯上下表面温度差、上下轧辊摩擦系数不等、上下轧辊辊速不等、上下辊辊径不同等。采用Marc有限元软件热力耦合分析法分析了各个影响因素对热轧带钢头部翘曲的影响规律,结果表明,翘曲量随上下表面温度差、摩擦系数比、辊速比及辊径比的增大而增大,但增大趋势各有不同。同时,提出了优化轧制规程、改善加热条件、采用适当的配辊方案、合理选择速度参数等解决带钢翘曲的措施。     

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。     

厚壁冷成型钢构件残余应力分析

从理论上将厚壁冷弯残余应力形成过程模拟成大变形加载(弯曲)和弹性卸载(回弹)过程,对不同厚度、不同相对弯曲半径下的冷成型厚钢板进行了大变形弯曲和回弹分析,得到了弯曲应力场和回弹应力场,将这两种应力场相叠加,得到了残余应力场,并分析了其分布规律,最后以国外的实测结果为基础进行了比较分析,证实了该理论分析方法的正确性,从而为进一步研究残余应力对厚壁冷成型钢构件性能的影响奠定了理论基础。