49MnVS3非调质钢的两种轧制力模型对比

对49MnVS3非调质钢在变形温度750~1 000℃、应变速率0.1~50s~(-1)下进行单道次热压缩试验,根据真应力-真应变曲线得到周纪华-管克智变形抗力模型;分别采用艾克隆德模型和周纪华-管克智变形抗力模型计算49MnVS3非调质钢的平均单位轧制压力,并对计算结果进行了比较。结果表明:随着应变的增加,基于艾克隆德模型和周纪华-管克智变形抗力模型计算得到的平均单位轧制压力均增大;基于艾克隆德模型得到的平均单位轧制压力曲线波动较小,而基于周纪华-管克智变形抗力模型的波动则较大;在低应变速率下,基于艾克隆德模型计算得到的平均单位轧制压力较大,而在高应变速率下,基于周纪华-管克智变形抗力模型计算得到的平均单位轧制压力较大;基于周纪华-管克智变形抗力模型计算轧制力时,需要借助热模拟试验数据,该模型适用于控制模型;艾克隆德模型只需使用化学成分和轧制工艺参数即可计算平均单位轧制压力,应用更广泛,该模型适用于轧制工艺设计。     

带钢平整机轧制压力的计算模型

平整较厚带材时，变形区水平应力沿板厚不均匀分布对平整轧制压力的计算有着重要影响。在考虑带材入口和出口弹性变形区影响的冷轧轧制压力计算模型的基础上，通过修改弹性变形区入口和出口应力边界条件，提出平整轧制压力计算模型，并对弹性区入口和出口表面水平应力进行了计算。用该模型计算的平整轧制压力与原有计算模型和实测值进行对比，证明模型提高了精度。     

冷连轧机轧制力的影响因素

通过将轧制变形区划分为微单元,对变形区内轧制力影响因素的变化规律进行研究。根据微单元塑性变形方程式,建立单位轧制压力的计算模型。针对变形抗力、摩擦因数等非线性因素,建立基于神经网络校正系数和工作参考点方法的数学模型,分析其在变形区内的变化规律。针对轧辊压扁和轧制力计算的耦合现象,采用计算机迭代计算的模型完成轧制力的解耦计算。工业轧机实际数据验证了采用微单元方式计算轧制力预报精度高,可用于生产实践。     

基于影响函数法的轧制压力横向分布规律分析

轧制压力横向分布直接影响轧辊的弹性变形和轧件的出口厚度分布。文中基于影响函数矩阵法,对轧机辊系受力和弹性变形进行计算分析,研究轧制过程中弯辊力和压下率对轧制力横向分布的影响,揭示轧制压力横向分布系数与弯辊力呈近似线性增长、与压下率呈近似线性减小的规律。分析表明,通过调节弯辊力或在轧制规程中改变压下率设定,可改变轧制压力的分布。为轧制压力横向分布函数的在线快速计算和板凸度控制模型的建立提供基础。     

薄带平整轧制时轧制压力模型的研究

考虑到轧辊的弹性变形以及轧件的弹性变形,建立了一套新的薄带平整轧制时的轧制压力模型。在模型中,对于一般薄带,考虑到停滞区的不对称性,采用混合摩擦理论分析了变形停滞区的摩擦力分布;而对于极薄带材,根据平整时塑性区相对弹性区缩小,摩擦力模型中的停滞区的范围并不止于塑性区,有可能扩大到弹性变形区这一特性,对相应的单位轧制压力分布情况进行了详细推导。同时,为了验证相关模型的准确性,采用该模型对宝钢1550CAL平整机相关典型规格产品轧制压力进行了理论计算,并在线实测出相应的轧制压力,其计算结果与实测值很好吻合,完全达到了工程上所需要的预报精度要求。因而该模型具有重要的理论意义和实用价值,可作进一步的推广与应用。     

双辊连续铸轧过程中轧制界面接触压力切块法建模与数值模拟

铸轧区可分为冷却区，铸造区和轧制区3个物理区。利用切块法分别推导出了铸造获轧制区变形过程静力平衡微分方程。在温度分布线性假设的基础上建立了轧制区变形抗力的简化模型，并在铸造区变形抗力的模型中引入了固相百分数来表征固态金属对变形抗力的影响。对铸造区利用龙格－库塔法对微分方程进行数值求解，而对轧制区则根据混合摩擦条件求出微分方程的解析解，从而建立了铸轧区轧制压力模型，利用该模型对轧制压力进行数值计算，计算结果与实测数据相吻合。     

基于非定值变形抗力板带温轧轧制力数学模型研究

对板带钢温轧过程的轧制力计算方法进行研究,建立了基于非定值变形抗力的轧制力计算模型。将变形区接触弧离散成微段单元,建立了各分段微单元关于变形量和变形速率的计算模型,确定了微段变形抗力。在卡尔曼平衡微分方程基础上,以弦代弧计算,建立了各微段的单位轧制压力。采用ANSYS/LS-DYNA有限元对温轧变形过程进行了仿真模拟,结果表明,所建立的温轧轧制力模型精度较高,计算结果比现有模型的计算结果更为准确。     

冷轧薄钢板"湿法"平整的轧制压力计算

平整是使冷轧薄钢板获得合理表面形貌的关键工艺。平整轧制压力的预测与控制直接影响钢板平整后的表面质量。本文作者采用刚性、弹塑性、全滑动和边界润滑等不同模型，进行了平整轧制压力预测模型的理论分析与模拟实验研究。结果表明：当矿井下量小于5%后，轧辊的弹性变形和钢板的弹性恢复对轧制压力的影响很大，不能忽略；采用边界润滑弹塑性模型计算得到的平整轧制压力较边界润滑刚性模型更接近实验值（相对误差减小约20%）。     

螺旋槽机械密封摩擦副界面流固耦合分析

基于建立的三维螺旋槽机械密封摩擦副界面的流、固有限元模型,数值模拟了动静环端面间的流体膜,得到液膜的压力分布规律,结果显示压力呈非线性分布;然后将得到的压力值作为边界条件之一导入到动环端面的静力学分析中,利用两者接触面间的自动迭代计算实现单向弱流固耦合分析,结果表明:最大变形发生在动环端面螺旋槽处,而最大应力发生在螺旋槽顶端;并进一步研究了动环的转速以及介质压力和粘度对最大变形和最大应力的影响规律,为密封性能的优化提供了有益的参考。     

冷轧铜板带斯通轧制力模型研究

对冷轧铜板带轧制力模型进行研究,通过算例比较得到斯通公式更适合铜板带冷轧情况。分析了布兰德-福特公式和斯通公式两种轧制力计算公式。采用不同的摩擦系数模型计算摩擦系数,使用实测数据对变形抗力模型通过最小二乘法进行拟合,将拟合所得数据代入斯通轧制力公式中计算,并将计算值与实际测量值进行比较,结果表明:采用多项式的变形抗力模型,利用斯通公式和前滑值获得摩擦系数,代入斯通轧制力公式中计算出的轧制力与实际轧制力吻合较好。     

Lubrication of Strip Rolling in the Low-Speed Mixed Regime

An analytical model for strip rolling in the low-speed mixed lubrication regime is developed. An average Reynolds equation for longitudinal saw-tooth surfaces under conditions of high fractional contact area, is combined with an analysis for asperity flattening under conditions of bulk plastic flow, to treat lubrication in the mixed regime. Analyses for the inlet zone and work zone and the influence of pressure on viscosity are included in the model. The model indicates that hydrodynamic lubrication effects are important at much lower speeds than previously considered possible. The film thickness predicted by the model is somewhat smaller than that measured using the oil drop method in rolling aluminum alloy with a mineral oil.     

Static characteristics of a new hydrodynamic–rolling hybrid bearing

An analytic model is developed to predict static characteristics of a new hydrodynamic–rolling hybrid bearing (HRHB). Experiments are carried out to measure the equilibrium positions, the load sharing, and the rotational speeds of the rolling bearing cage. The results show that the working states of HRHB are divided into two distinct phases by a transition speed at which the hydrodynamics and contact models are decoupled. The cage speeds can be used to determine transition speed. The theoretical results agree with the experimental results, and it can be employed to design the bearing parameters according to the expected performance.     

The Influence of Partially Textured Slider with Oriented Parabolic Grooves on the Behavior of Hydrodynamic Lubrication

An analytical model is developed to investigate a partially textured slider of infinite width with orientation parabolic grooves. The generating mechanism for hydrodynamic lubrication of the partial surface texturing in the sliding surface is similar to that of a step slider. By using the multigrid method, the hydrodynamic pressure generated by the partial surface texturing is obtained. The surface texturing parameters are numerically optimized to obtain maximum hydrodynamic effect in terms of the dimensionless average pressure for a given set of operating parameters. The results indicate that parameters such as groove orientation angle, depth, area density, and textured fraction have an obvious influence on the hydrodynamic pressure for partial surface texturing. However, the groove width has little or no effect on the dimensionless average pressure. The results of the study show that the hydrodynamic lubrication performance can be ameliorated by optimizing the surface texturing according to the operating parameters of the mechanical components.     

A Two-Wavelength Model of Surface Flattening in Cold Metal Rolling with Mixed Lubrication

A new model of surface flattening is developed for cold metal rolling in the mixed regime. Longitudinal surface roughness is modeled by two separate wavelengths. The new model follows the asperity crushing analysis of Sutcliffe (1999) for unlubricated rolling but additionally includes a hydrodynamic model to account for the effect of the lubricant. The effect of various parameters including speed, reduction in strip thickness, roughness wavelength and lubricant properties is examined. The results show similar behavior to previous models of mixed lubrication, with a speed parameter A_s having the most influence, and confirm the results for unlubricated rolling that the short wavelength components of the surface roughness persist more than the long wavelength components. The predicted changes in roughness are in good agreement with experiments.     

Analyses of thermal hydrodynamic lubrication in high-speed rolling. Part I: the effect of the roller's elastic deformation

A study of thermal hydrodynamic lubrication for high-speed strip rolling, which includes the roller's elastic deformation, was developed for a lubricant whose rheological behaviour satisfies the Barus' model. The difference in lubricating performances between an elastic roller and a rigid roller was assessed using parameters such as film thickness and pressure; temperature distributions in the fluid film, roller, and workpiece; separating force and shear torque. The elastic roller was made either of a unique material or its substrate was coated with one layer of a harder material to improve the wear resistance. The elastic deformation of the roller was obtained with the aid of Hitchcock's elastic-deformation theory and the biharmonic equation of Airy's stress function. It was found that the elastic deformation produces a substantial effect on some rolling characteristics.     

Effects of groove textures on fully lubricated sliding with cavitation

A two-dimensional computational fluid dynamics (CFD) model was developed to investigate the effects of groove textures on fully lubricated sliding with cavitation. The effects of cavitation pressure, sliding speed, sliding pitch angle and texture scale were discussed. It was found that the hydrodynamic pressure effect becomes more pronounced with higher cavitation pressure, and the hydrodynamic pressure decreases with the reduction of the sliding speed. Also with a sliding pitch angle, the hydrodynamic pressure is dependent on both pocket and wedge effects. Increasing groove number and reducing the groove size enhances the overall load capacity, but has a little effect on friction coefficient.     

Effects of groove textures on fully lubricated sliding with cavitation

A two-dimensional computational fluid dynamics (CFD) model was developed to investigate the effects of groove textures on fully lubricated sliding with cavitation. The effects of cavitation pressure, sliding speed, sliding pitch angle and texture scale were discussed. It was found that the hydrodynamic pressure effect becomes more pronounced with higher cavitation pressure, and the hydrodynamic pressure decreases with the reduction of the sliding speed. Also with a sliding pitch angle, the hydrodynamic pressure is dependent on both pocket and wedge effects. Increasing groove number and reducing the groove size enhances the overall load capacity, but has a little effect on friction coefficient.     

Cage Speed of Hydrodynamic Rolling Hybrid Bearings

Hydrodynamic bearings are subjected to wear during starts and stops due to the absence of sufficient film pressure to effect complete separation of the sliding surfaces. In an earlier publication, our group reported the development of a new hydrodynamic rolling hybrid bearing (HRHB) to overcome the wear problem in hydrodynamic bearings. In the configuration, the transition of operation modes between the rolling bearing supporting state and the hydrodynamic bearing supporting state was realized by the clearance of the rolling bearing. Here we report on the development of a method to identify the operation modes for HRHBs based on monitoring the cage speed of the rolling bearing. The variation of cage speed with the shaft speed is measured. The effects of external load and starting time on the cage speed are also investigated experimentally. The results show that variation in the cage speed reflects changes in the load on the rolling bearing, as well as the operation modes of the HRHBs. With increases in the shaft speed, the variation in the cage speed presents three stages: the increasing stage, the decreasing stage, and the stationary stage. In the first two stages, the HRHB works at the rolling bearing supporting state while in stationary stage, the HRHB works at the hydrodynamic bearing supporting state. In additions to its property of no wear sufferance during starts and stops, compared to hydrodynamic bearings there is little risk of catastrophic failure with HRHBs during any interruption to the lubricant supply and compared to rolling bearings there is no fatigue failure. Therefore this hybrid design is useful at very high speeds.     

Wear mechanisms of statically loaded hydrodynamic bearings by contaminant abrasive particles

Wear mechanisms in hydrodynamic bearings by contaminant abrasive particles in the oil were investigated. This type of wear is one of the main factors responsible for failure of hydrodynamic bearings especially when operating in dusty environments. A test bearing system was developed to study this type of wear under carefully controlled conditions. Experiments were conducted with two shaft materials and three liner materials, giving a total of six material combinations. The circumferential liner wear distribution and the relative magnitude of shaft and liner wear were found to depend mainly on the shaft-to-liner hardness ratio. A smaller hardness ratio resulted in relatively more liner wear and less shaft wear. A model is proposed to account for this behaviour whereby the action of the abrasive particle is considered to consist of both cutting and rolling motions.     

Effect of Micro-Dimples on Hydrodynamic Lubrication of Textured Sinusoidal Roughness Surfaces

Surface texturing has been applied to improving the tribological performance of mechanical components for many years. Currently, the researches simulate the film pressure distribution of textured rough surfaces on the basis of the average flow model, and however the influence of roughness on the film pressure distribution could not be precisely expressed. Therefore, in order to study the hydrodynamic lubrication of the rough textured surfaces, sinusoidal waves are employed to characterize untextured surfaces. A deterministic model for hydrodynamic lubrication of microdimple textured rough surfaces is developed to predict the distribution of hydrodynamic pressure. By supplementing with the JFO cavitation boundary, the load carrying capacity of the film produced by micro-dimples and roughness is obtained. And the geometric parameters of textured rough surface are optimized to obtain the maximum hydrodynamic lubrication by specifying an optimization goal of the load carrying capacity. The effect of roughness on the hydrodynamic pressure of surface texture is significant and the load carrying capacity decreases with the increase of the roughness ratio because the roughness greatly suppresses the hydrodynamic effect of dimples. It shows that the roughness ratio of surface may be as small as possible to suppress the effect of hydrodynamic lubrication. Additionally,there are the optimum values of the micro-dimple depth and area density to maximize the load carrying capacity for any given value of the roughness ratio. The proposed approach is capable of accurately reflects the influence of roughness on the hydrodynamic pressure, and developed a deterministic model to investigate the hydrodynamic lubrication of textured surfaces.