基于接触摩擦量化作用的镁合金轧制力预报研究

本研究针对镁合金热轧制工艺,通过协调有限元分析结果及物理试验数据,提出一种关于热轧制接触摩擦因子的确定方法,耦合多轧制工艺参数进一步拟合出其求解关系式,工艺参数包括：轧制温度,轧制速度以及压下率。在之前对AZ31B镁合金板材轧制过程轧制力预报模型及温度场数学模型建立研究的基础上,综合考虑接触单位压力及摩擦应力两方面因素的作用,对前期轧制力预报模型进行了优化重构,经确定接触摩擦作用到轧辊的压力约占整体轧制力的4.36%。     

Measurements of friction in cold flat rolling

The effect of reduction, rolling speed and material properties on the variation of interfacial frictional and normal stresses in the roll gap during cold flat rolling is studied. The results confirm the conclusions of earlier research, emphasizing the dependence of the coefficient of friction, and hence the interfacial shear stress, on the process parameters. Preliminary experiments, using mineral oil with 1% oleic acid as lubricant, show the possible existence of hydrodynamic lubrication, at least over part of the contact area. The validity of the data is substantiated by comparing the roll separating forces, measured by transducers located under the bottom workroll, to those obtained by integrating the measured roll pressure distribution over the arc of contact. The comparison is found to be favorable, indicating that in spite of its shortcomings, the embedded pin technique gives reliable measurements.     

Stress analysis of asymmetrical cold rolling of clad sheet using the slab method

An analytical model for general asymmetrical cold rolling of clad sheet bonded before rolling was proposed to explore the plastic deformation behavior of the clad sheet using the slab method. The model allowed easy calculation of the neutral points between the upper and lower rolls and the clad sheet; rolling pressure distribution along the contact interface of the roll, horizontal stresses in the component layers of the clad sheet, shear stresses at the interface of the clad sheet, and rolling force. These characteristics as affected by various rolling conditions (e.g., thickness ratio and shear yield stress ratio of the raw clad sheet, roll speed ratio, reduction, frictional coefficient, roll radius ratio, etc.) were analyzed systematically. This approach yielded complete forms for the rolling pressure distribution, rolling force, and rolling torque. Moreover, the computational time required by this analytical model is about 1/20 to 1/25 of that required by the RUNGE KUTTA numerical method under the same rolling conditions.     

冷轧机轧制过程中的轧辊振动研究

以冷轧机轧辊垂直振动为研究对象,在分析冷轧机振动机理的前提下,建立轧机垂直振动简化模型,运用数值仿真方法,分析了轧制压下量、摩擦系数及辊缝阻尼的轧制工艺参数对轧机垂直振动的影响。分析结果表明:减小轧机压下量有利于提高轧机振动临界速度;增加辊缝摩擦系数有利于减小轧辊的振动位移;增加辊缝阻尼能够有效降低振动幅值。在此基础上提出了抑制冷轧机垂直振动方法为:优化各道次压下量,以使轧制临界速度由1340 m·min-1提升到1520 m·min-1;适当降低乳化液浓度,以使辊缝摩擦系数增大,此调节过程应考虑窜流现象;增设液压衬板减震器或多孔阻尼减震器,以增加辊缝阻尼。     

Friction evaluation in hot strip rolling by direct measurement in the roll gap of a model duo mill

Using a model duo mill, and model material and lubricants, the hot strip rolling process has been simulated. The normal roll pressure, the shear stress and the shear-stress angle in the roll gap of the mill was measured by load tranducers, the purpose being to evaluate assumed frictional influencing factors, such as: strip reduction, rolling velocity, lubrication and different materials rolled. In order to improve the present simple-friction model for force calculation in hot strip rolling that uses just an average friction value, three friction models were evaluated: the friction laws by Coulomb, Tresca and Wanheim-Bay. The best model was then chosen on the basis of the measurements made in this study. Finally, suggestions for the improvement of the model of strip rolling is made.     

攀钢1 220 mm冷连轧机轧制力模型参数自学习分析

在冷连轧过程控制中,影响轧制力模型预报精度的主要因素是材料的屈服应力和摩擦系数。攀钢1 220 mm冷连轧机屈服应力模型通过机架屈服应力自学习、材料等级屈服应力自学习以及材料类别屈服应力补偿来确保屈服应力模型的计算精度。为提高摩擦系数模型的计算精度,除了在模型中充分考虑轧制速度、轧辊粗糙度及轧辊磨损等影响因素外,还引进了低速摩擦系数的自学习形式。另外,攀钢1 220 mm冷连轧机轧制力模型针对特定的轧制条件分别采用调整屈服应力和摩擦系数的自适应学习方法,在实际应用中能够迅速提高轧制力模型的预报精度。     

主应力法计算蛇形轧制的轧制力

使用主应力法建立蛇形轧制过程中轧制力与轧制力矩的解析预测模型。将解析模型的计算结果与实验结果进行比较,验证了解析模型的准确性。运用该模型对蛇形轧制过程中不同的异速比、轧辊偏移距离、压下量和摩擦系数对轧制力和轧制力矩的影响规律进行研究。同时研究"搓轧区"对轧制力和轧制力矩的影响。结果表明,异速比的增大将导致"搓轧区"的增大,从而使轧制力和上轧辊轧制力矩减小,下轧辊轧制力矩增加。当异速比增大到速度较大的轧辊带动速度较小的轧辊时,慢速轧辊的轧制力矩将变为负值。轧辊错位距离的增大导致"搓轧区"减小,从而导致轧制力增加,上、下轧辊轧制力矩减小。压下量的增加导致"搓轧区"的减小,从而导致轧制力和上、下轧辊轧制力矩的增加。轧辊与轧板之间摩擦系数的增加使"搓轧区"减小,同时导致轧制力和上、下轧辊轧制力矩同时减小。研究为蛇形轧制在超大厚度板材制造中的应用,提供了理论基础。     

辊缝油膜承载力对冷轧机振动的影响

针对某冷轧厂在线轧制过程中轧机的振动问题,从辊缝油膜承载力的角度分析其对轧机振动的影响,得出轧制过程中辊缝间距的减小导致辊缝油膜需提供更大的承载力来维持轧机稳定。从乳化液浓度、轧辊转速、乳化液金属微粒含量方面探讨了增强辊缝油膜承载力的方法,得出乳化液浓度与轧辊转速在增强油膜承载力的同时减小了辊缝的摩擦系数,也易导致轧机振动。通过试验得出,调节乳化液金属微粒含量能够在原有摩擦系数的基础上增强辊缝油膜承载力,从而保证轧机的稳定运行。     

An Analytical Modified Model of Clad Sheet Bonding by Cold Rolling Using Upper Bond Theorem

In this paper, clad sheet bonding by cold rolling was investigated using the upper bond theorem. Plastic deformation behavior of the strip at the roll gap was investigated, unlike previous methods; distinctive angular velocities are used for different zones in roll gap in present model and absolute minimum of rolling power function is achieved. Rolling power, rolling force, and thickness ratio of the rolled product affected by various rolling condition such as flow stress of sheets, initial thickness ratio, roller radius, total thickness reduction, coefficient of friction between rollers and metals and between components layer, roll speed, etc., are discussed. It was found that the theoretical prediction of the thickness ratio of the rolled product, rolling force, and rolling power are in good agreement with the experimental measurement.     

An experimental investigation on the deformation behavior during wire flat rolling process

In the present study a laboratory flat rolling machine is utilized to assess the deformation behavior of low and high carbon steel wires in wire flat rolling process. The effects of friction coefficient, rolling reduction and roll speed on rolling force and deformation behavior of the wires are experimentally investigated. It is found that the roll speed affects considerably the rolling force but a negligible effect on deformation behavior. It is noted that by increasing the roll speed, the rolling force may decrease or increase depending on the magnitude of the roll speed. Also, the deformation behavior of the wires in flat rolling is formulated. A relationship is developed for calculating the width of contact area between the wire and rolls as a function of rolling reduction. This relationship depicts that the width of contact area is proportional to square root of rolling reduction. Furthermore, two relationships are derived to predict the spreading of the wires after flat rolling. It is found that the relationships are applicable for both the low and high carbon steel wires.     

热轧不锈钢板带粗轧机架高速钢轧辊的研制

由于不锈钢热轧板带产线粗轧温度高、压下量大、轧辊咬入角大、辊面受挤压力和摩擦力更大等工况特点,原轧辊材质的应用受到了限制。介绍了热轧不锈钢板带粗轧新型高速钢轧辊的研制情况,主要介绍了其化学成分、热处理工艺、内层材质的设计及其组织性能。该新型高速钢轧辊在国内某1 780 mm不锈钢热轧产线粗轧机组的应用取得了较好效果,毫米轧制量为7 000 t/mm,下机辊表面光洁,表面粗糙度为1.3～1.6 μm。     

Slab Analysis of Ring Rolling Assuming Constant Shear Friction

In this article, an analytic solution for ring rolling process based on the slab method theory is presented, in which the non-uniformity of the normal and shear stresses across the section of the deforming material throughout the plastic region is considered. The friction factor multiplied by the shear yield strength (τ = mk) is used to present friction between the main roll and the ring. The influence of the process parameters such as friction factor, feed speed, main roll rotational speed, and radii of the main roll and mandrel on process outputs is investigated. Complete expressions for the ring rolling pressure, force, and torque are obtained, and the position of neutral point is predicted. Comparison of the analytic results of this model with the experimental results of other investigators and FEM analysis show that they are in good agreement.     

Prediction of effect of rolling speed on coefficient of friction in hot sheet rolling of steel using sliding rolling tribo-simulator

In order to reduce the rolling force and the roll wear, the lubricants have been used in hot rolling of steel. In order to evaluate the tribological behavior at the interface between roll and workpiece in hot steel rolling, it is important to measure the coefficient of friction and examine the effect of the tribological factors on the coefficient of friction. In this paper, the effect of the rolling speed on the coefficient of friction is investigated using the tribo-simulator testing machine for hot rolling developed by the authors. The workpiece used is SPHC. The roll material is SKD11 and the surface roughnesses are 0.05 μm, 0.2 μm and 0.8 μm. The rolling tests are carried out at a temperature of 800 °C during a rolling distance of 400 mm, changing the rolling speed from 15 to 70 m/min. The colza oil is used as a base oil and the emulsion concentrations are 0.1% and 3.0%. The coefficient of friction at an emulsion concentration of 3.0% is independent on the rolling speed. On the other hand, the coefficient of friction at an emulsion concentration of 0.1% decreases with increasing rolling speed in the lower range of rolling speed, but it increases in increasing rolling speed in the higher range of rolling speed.     

Through-thickness shear strain control in cold rolled silicon steel by the coupling effect of roll gap geometry and friction

Through-thickness shear strain distribution in cold rolled non-oriented silicon steel under different roll gap geometries and friction coefficients was analyzed by finite element method (FEM). Cold rolling textures were also investigated quantitatively to validate the calculated shear strain distribution. The results showed that both direction and magnitude of shear strain through thickness depend sensitively on the two rolling parameters. The coupling effect of roll gap geometry and friction was satisfactorily explained based on their contributions to shear strain and the involved mechanisms. A shear strain distribution diagram (SSDD), which can clearly characterize the shear strain state with roll gap geometry, friction and through-thickness position as variables, was proposed to serve as a convenient tool for through-thickness shear strain control.     

Lubricity of volatile lubricants in sheet metal rolling

A series of experiments is carried out by using a rolling type tribometer to investigate the lubricity of the volatile lubricants at high speed forming. The roll material is the die steel alloy SKD11, and the workpiece material is the mild steel SPCE with a rough surface and the aluminum alloy A3004 with a smooth surface. Experimental results show that the friction coefficient decreases with increasing working velocity for both SPCE and A3004, in any lubricant. With an increase of reduction in thickness, the friction coefficient decreases for SPCE, but increases for A3004. Some volatile lubricants have the same lubricity as the generally used mineral oil with low-viscosity by judging from the value of friction coefficient, the surface appearance of rolled workpiece and the roll surface damage.     

Symmetric and Asymmetric Rolling Pure Copper Foil: Crystal Plasticity Finite Element Simulation and Experiments

A systematic study has been conducted aiming to attain an insight into the influence of coefficient of roll speed asymmetry, crystal orientation and structure on the deformation behavior, and crystallographic orientation development during foil rolling. Simulations were successfully carried out by using crystal plasticity finite element method(CPFEM),and a novel computational framework is presented for the representation of virtual polycrystalline grain structures. It has been found that asymmetric rolling(ASR) is more efficient in producing plastic deformation since it develops additional shear strain and activity of slip system compared with symmetric rolling(SR). For ASR, increase in the length of the shear zone, and decrease in the amount of the pressure and roll force would lead to further reduction. The shear strain path in SR and ASR is strictly influenced by the misorientation of neighbor grains, and corresponding {1 1 1} pole figures offer direct evidence of the spread of crystallographic orientation around the normal direction. The activity of slip systems was examined in detail and found that the predicted results are consistent with the surface layer model. The accuracy of the developed CPFEM model is verified by the fact that the simulated results of roll force coincide well with the experimental results.     

Research on the behavior of transversal crack in slab V–H rolling process by FEM

Cracks appear on slab corner which is an important quality problem in some steel works. The closure and growth of transversal crack on slab corner during multi-pass vertical–horizontal (V–H) rolling was simulated with the explicit dynamic finite element method (FEM) and the updating geometric method. The influences of the friction coefficient, the crack size, the edger roll shape, and the fillet radius of grooved edger roll on the closure and growth of cracks were analyzed with the crack width and the contact pressure on crack surfaces. For vertical rolling, the contact pressure on crack surfaces when the grooved edger roll is used is larger than that when the flat edger roll is used. However, after horizontal rolling, the cracks open again when using the grooved edger roll, which may close well when using the flat edger roll. With increase of the fillet radii of the grooved edger roll, the contact pressure on crack surfaces increases during V₁ pass and decreases during V₂, V₃ pass. Reduction of the friction coefficient between the slab and the rolls is helpful for the crack closure for both the flat edger roll and the grooved edger roll during vertical rolling. The experiments were performed for the behavior of transversal crack on the pure lead slab corner, and the calculated results have the same tendency of the crack behavior as the experimental ones.     

Analysis of cold rolling of ultra thin strip

In this paper, the cold rolling experiments of ultra thin steel strip were carried out on an experimental rolling mill. The cold rolling of ultra thin strip with roll edge kiss was analysed theoretically, and the rolling force, intermediate force between the work roll and backup roll, the roll edge kiss force, the strip shape after rolling are obtained for this special rolling, and they are compared for various reduction and friction coefficients. Simulation results show that the reduction has a significant influence on the shape of rolled strip, and the calculated rolling forces and strip profile are consistent with the measured values. The effect of friction in the roll bite on cold rolling of ultra thin strip with roll edge kiss is also discussed. Surface characteristic was measured and it is shown that the steel surface roughness value reduces with an increase of reduction.     

冷连轧打滑机理分析与控制研究

针对冷连轧机组生产过程中产生的打滑现象，从轧制原理的角度，由轧制力矩模型、前滑模型以及摩擦因数模型分析了打滑产生的机理，得到轧制负荷、前滑、轧辊原始粗糙度、轧制速度和轧辊周期状态是影响轧制过程中轧辊打滑的重要因素。针对某厂1 720 mm冷连轧机组的实际工况，结合打滑机理，通过采用降低打滑机架的轧制负荷，提高轧辊粗糙度，调整前后张力等措施，对打滑机架的相关参数进行了优化，有效地解决了打滑问题，在提高轧机的轧制稳定性的同时也缓解了备辊压力。     

冷连轧打滑机理分析与控制研究

针对冷连轧机组生产过程中产生的打滑现象，从轧制原理的角度，由轧制力矩模型、前滑模型以及摩擦因数模型分析了打滑产生的机理，得到轧制负荷、前滑、轧辊原始粗糙度、轧制速度和轧辊周期状态是影响轧制过程中轧辊打滑的重要因素。针对某厂1 720 mm冷连轧机组的实际工况，结合打滑机理，通过采用降低打滑机架的轧制负荷，提高轧辊粗糙度，调整前后张力等措施，对打滑机架的相关参数进行了优化，有效地解决了打滑问题，在提高轧机的轧制稳定性的同时也缓解了备辊压力。