Influence of friction-lubrication characteristics varying with rolling speed on instability of chatter and slip in cold tandem rolling process

In the high-speed cold tandem rolling process of thin plate,chatter or slip instability gives rise to the deterioration of equipment and product quality.Macroscopic instability behavior is closely related to interfacial friction-lubrication con-dition which is generally characterized by the friction coefficient.However,with higher and higher speed requirements,the commonly used model of friction coefficient is no longer applicable and accurate.A novel approach is suggested to calculate the speed-dependent friction coefficient,in which the viscosity-pressure-temperature effects of the lubricant,surface roughness states of work rolls and rolled piece are comprehensively involved and the mixed flm lubrication theory is applied.Subsequently,the influences of friction coefficient on the instability of slip and chatter are investigated for a five-stand cold tandem rolling mill.On one side,the critical friction coefficient for each stand is determined by calculating the corresponding slip factor;on the other hand,the friction coefficient varying with rolling speed is combined with the model of theoretical critical rolling speed presented under constant friction coefficient,so that the speed threshold is determined.Furthermore,the stable and unstable regions corresponding to the rear three stands are individually discussed,and the technical strategies are proposed to suppress both slip and chatter frequently occurring in the actual rolling process.

High Precision Prediction of Rolling Force Based on Fuzzy and Nerve Method for Cold Tandem Mill

The rolling force model for cold tandem mill was put forward by using the Elman dynamic recursive network method,based on the actual measured data.Furthermore,a good assumption is put forward,which brings a full universe of discourse self-adjusting factor fuzzy control,closed-loop adjusting,based on error feedback and expertise into a rolling force prediction model,to modify prediction outputs and improve prediction precision and robustness.The simulated results indicate that the method is highly effective and the prediction precision is better than that of the traditional method.Predicted relative error is less than ±4%,so the prediction is high precise for the cold tandem mill.

Dynamics-based optimization of rolling schedule aiming at dual goals of chatter suppression and speed increase for a 5-stand cold tandem rolling mill

In the process of cold tandem rolling,chatter instability leads to serious impacts on enhancing rolling speed,improving product quality,reducing production cost and realizing intellectualization.Chatter occurs with the rolling speed up to a certain threshold value,but the critical speed is determined by both product specifications and rolling schedules.A 5-stand cold tandem rolling mill whose first three stands and subsequent two stands,respectively,have four and six rolls was investigated by formulating its dynamic equations with the corresponding structure-process coupling.By applying the stability-based calculation model about the critical rolling speed in each stand,the system dynamic responses around the critical rolling speed were simulated,and the system eigenvalues which represent instability and characteristic frequencies were figured out.Thereafter,via combining the critical rolling speeds with the system dynamic behavior,a dynamics-based optimization model of rolling schedule for the 5-stand cold tandem system was proposed for the purposes of both the chatter suppression and rolling speed increase.In the optimization model,eight rolling technique parameters(four strip thicknesses and four tensions between the upstream and downstream stands)were taken as design variables,and the constraint conditions were set as no chatter instability in all five stands,and the optimization goal was to maximize the outlet speed of the final stand.The pattern search method was introduced to solve the optimization model.By applying such a dynamics-based optimization model for the 5-stand cold tandem rolling process,the chatter instability was suppressed effectively and the rolling efficiency was improved considerably;therefore,such an optimization model is expected to be valuable for intelligent manufacturing of rolling process.

Control of Surface Thermal Scratch of Strip in Tandem Cold Rolling

The thermal scratch seriously affects the surface quality of the cold rolled stainless steel strip. Some researchers have carried out qualitative and theoretical studies in this field. However, there is currently a lack of research on effective forecast and control of thermal scratch defects in practical production, especially in tandem cold rolling. In order to establish precise mathematical model of oil film thickness in deformation zone, the lubrication in cold rolling process of SUS410L stainless steel strip is studied, and major factors affecting oil film thickness are also analyzed. According to the principle of statistics, mathematical model of critical oil film thickness in deformation zone for thermal scratch is built, with fitting and regression analytical method, and then based on temperature comparison method, the criterion for deciding thermal scratch defects is put forward. Storing and calling data through SQL Server 2010, a software on thermal scratch defects control is developed through Microsoft Visual Studio 2008 by MFC technique for stainless steel in tandem cold rolling, and then it is put into practical production. Statistics indicate that the hit rate of thermal scratch is as high as 92.38%, and the occurrence rate of thermal scratch is decreased by 89.13%. Owing to the application of the software, the rolling speed is increased by approximately 9.3%. The software developed provides an effective solution to the problem of thermal scratch defects in tandem cold rolling, and helps to promote products surface quality of stainless steel strips in practical production.

MENDED GENETIC BP NETWORK AND APPLICATION TO ROLLING FORCE PREDICTION OF 4-STAND TANDEM COLD STRIP MILL

In order to make good use of the ability to approach any function of BP (backpropagation) network and overcome its local astringency, and also make good use of the overallsearch ability of GA (genetic algorithms), a proposal to regulate the network's weights using bothGA and BP algorithms is suggested. An integrated network system of MGA (mended genetic algorithms)and BP algorithms has been established. The MGA-BP network's functions consist of optimizing GAperformance parameters, the network's structural parameters, performance parameters, and regulatingthe network's weights using both GA and BP algorithms. Rolling forces of 4-stand tandem cold stripmill are predicted by the MGA-BP network, and good results are obtained.

Multi-objective optimization of rolling schedule based on cost function for tandem cold mill

In terms of tandem cold mill productivity and product quality, a multi-objective optimization model of rolling schedule based on cost fimction was proposed to determine the stand reductions, inter-stand tensions and rolling speeds for a specified product. The proposed schedule optimization model consists of several single cost fi.mctions, which take rolling force, motor power, inter-stand tension and stand reduction into consideration. The cost function, which can evaluate how far the rolling parameters are from the ideal values, was minimized using the Nelder-Mead simplex method. The proposed rolling schedule optimization method has been applied successfully to the 5-stand tandem cold mill in Tangsteel, and the results from a case study show that the proposed method is superior to those based on empirical formulae.

Backup roll contour of a SmartCrown tandem cold rolling mill

SmartCrown was a new system developed by VAI for improving the strip profile and flatness control first applied in 1700 mm tandem cold rolling mills at Wuhan Iron ＆ Steel （Group） Corporation （WISCO）. After tracing and testing, the application of the conventional crown backup roll matching the SmartCrown work roll of the production mill led to heavy and nonuniform wear, and the edge spalling of the backup roll often occurred. A 3-dimension finite element model of roll stacks was established, which was used to analyze the above-mentioned problems, and it was found that the main reason was the highly nonuniform contact pressure distribution between the work roll and the backup roll. A new FSR （flexible shape backup roll） was developed and applied in 1700 mm tandem cold rolling mills. A lot of good actual effects of FSR, such as evident improvement in profile and flatness of strips, non-occurring edge spalling, wear uniform, and remarkable decrease in roll consumption were validated by long-term industrial applications.

1180 MPa级超高强钢冷连轧过程的厚度综合控制技术

针对超高强钢在冷轧过程中厚度波动大以及带头带尾厚度超差的问题,首先根据金属秒流量模型建立了厚度超差预测模型与辊缝调节量预估模型;随后开发了轧制过程中的厚度控制系统,并进行了辊缝调节量优化;最后建立了带钢头尾轧制过程中的轧制速度与张力优化模型。以国内某冷连轧机组的第1机架为技术应用对象,选择两种典型的超高强钢进行生产测试,测试结果表明:超高强钢AR4146E1与DU6220A1的厚度超差长度分别从70.3 m、36.89 m下降到了16.85 m、16.33 m。

基于随机森林特征选取和遗传算法优化的带钢厚度预测

在冷连轧生产过程中,带钢厚度精度是衡量产品质量和下游企业最为关心的重要指标之一。现有冷连轧带钢厚度精度预测方法主要关注带钢头部厚度命中率,不能反映整卷带钢的厚度精度和波动情况,为此,提出了一种基于深度学习算法的冷连轧带钢全长厚度连续预测模型,实现了从冷连轧工业生产数据到带钢全长厚度的映射。以某厂五机架冷连轧生产线的实际数据为数据集,首先使用随机森林法进行特征选取,以精简输入特征,然后采用遗传算法对DNN模型的初始权重和阈值进行优化,进一步提升模型性能。结果表明:此模型可较为准确和直观地反映整卷带钢厚度精度和波动随轧制时间变化的情况。在加减速和稳定轧制阶段,预测结果的相对误差均控制在±0.5%和±0.1%以内,精度满足实际生产要求。应用此模型,控制系统可以提升预设定精度,并在相应时刻进行预调节,从而达到提高带钢厚度精度的目的。

1220冷连轧机板形控制性能综合改善

针对1220冷连轧机生产中存在的板形问题,将理论分析、计算机仿真与现场实验相结合,全面研究其原料特点和板形控制的装备、工艺、数模技术现状后,提出合适的板形控制策略,并重新设计辊系初始辊形、建立板形控制目标曲线、调整弯辊力模型,提高了连轧机组板形控制性能和板形控制系统精度,使产品板形质量、轧制稳定性和轧辊表面磨损状态明显改善。

冷连轧机组弯辊力自动设定的实现

针对大型宽带钢冷连轧机组广泛采用的液压弯辊技术，深入分析了弯辊力对于板形的调控机理．在分析轧辊辊形、带钢宽度和轧制力等因素对弯辊力设定值影响的基础上，建立弯辊力自动设定模型，并得到了现场实测结果的验证．该模型成功地投入运行，实现了冷连轧机弯辊力的计算机自动设定．

模糊小脑模型神经网络在多辊冷连轧机轧制力预报模型中的应用

针对宽带钢多辊冷连轧机组特点,为提高轧制力的预报精度,在结合传统轧制压力模型的基础上把模糊算法和神经网络有机结合,设计出基于模糊小脑模型神经网络的多辊冷连轧机轧制力预报模型.通过对传统轧制力模型计算值、小脑模型预报计算值与实测值进行对比分析可知,基于模糊小脑模型神经网络的多辊冷连轧机轧制力预报模型具有较高的计算精度,更适合于多辊轧机在线计算机过程控制的应用,满足现场在线生产的要求,取得良好的板形板厚控制效果.

冷连轧机成品板面粗糙度控制技术的研究

以宝钢2 030 5机架冷连轧机为研究对象,经过现场试验与理论研究,在分析了影响冷连轧机成品带钢表面粗糙度的主要因素的基础上,提出了一套冷连轧机成品板面粗糙度预报模型,给出了针对冷连轧机的成品板面粗糙度控制方案,并将其应用到现场成品板面粗糙度控制,命中率达到80%以上。

1420冷连轧机的动态特性及颤振分析

冷连轧的颤振现象是世界各国普遍关心的课题。针对我国某钢厂1420冷连轧出现的颤振现象,从实测入手分析了它的振源和颤振频率,又用有限元分析方法验证了机座发生颤振的实验结论。作为颤振振因的深化研究,对颤振出现前的“拍振”现象进行了分析,推证了轧制过程中有一个自激频率f存在,而且当它与轧机系统的某个固有频率无限接近时会立即引起轧机工作的不稳定。最后,通过建立该系统的非线性扭振微分方程和它的摄动解,进一步证明这种不稳定现象出现是由于轧制速度提高到一定值时系统内产生了负阻尼,其结论是负阻尼是引起轧机颤振的振因。

热滑伤判断条件及其影响因素

为了研究冷连轧高速生产过程中的热滑伤问题,在首次引入滑伤指数新概念的基础上,给出了判断冷连轧过程中是否发生热滑伤的不等式,并定量分析了热轧来料温度、总压下率、轧制速度、压下规程以及乳化液流量密度等因素对热滑伤的影响。同时提出了防止热滑伤的措施,把此措施用于实际生产中,并取得了较大的经济效益。

乳化液性能对摩擦系数影响机理及工程实用模型的研究

以往现场对冷连轧过程中摩擦系数的研究主要偏重于带钢特性、轧制工艺以及工艺润滑制度,乳化液的pH值、铁粉含量、皂化值等性能参数对摩擦系数的影响以定性研究为主且不能定量分析,本文以某冷轧薄板厂1220五机架冷连轧机组为研究对象,在大量的现场实验与理论研究的基础上,充分结合冷连轧机组的设备与工艺特点,定量研究了乳化液性能对摩擦系数的影响,建立了相应的工程实用模型,并将其应用到生产实践,使得轧制压力的预报精度控制在15%以内。

冷连轧机乳化液冷却润滑系统设计优化

我国冷连轧机及乳化液冷却润滑系统逐步由成套引进向国内自主集成转变,本文提出了一系列乳化液系统的优化设计方案,包括供液主箱容积的优化、乳化液温度控制技术优化及回液泵组变频控制等。通过设计优化,提高了乳化液的品质,降低了运行成本,为我国冷连轧机乳化液冷却润滑系统设计提供借鉴和参考。

1220五机架冷连轧机板形曲线的改进

为了改善宝钢1220冷连轧机组原有目标曲线的边部缺陷,同时考虑到整体板形中浪较多的实际问题,在对1220机组板形控制基本模型与板形曲线补偿模型的机理进行分析的基础上,结合该冷连轧机的生产工艺特点,建立了一套板形曲线补偿模型,编制出相应的模拟软件。将新的板形目标曲线应用到生产实际中,取得了良好的使用效果,具有进一步推广应用的价值。

基于遗传算法的冷连轧轧制规程优化设计

合理的轧制规程是使轧制过程达到最佳状态的重要保证。轧制规程涉及的有关数学模型和需要考虑的约束条件较多,因此其优化设计也较为复杂。应用遗传算法进行轧制规程优化设计,即以负荷均衡和板形良好为目标,在一定的约束条件下,对压下率分配比进行编码。通过遗传算子操作并保留每代优势个体,从而得到冷连轧轧制规程。对某1370冷连轧机进行设计比较,表明该方法优化速度快,适合在实际中应用。

SmartCrown冷连轧机板形控制新技术改进研究与应用

SmartCrown板形控制新技术在宽带钢冷连轧机首次工业应用中存在SmartCrown工作辊窜辊行程利用不充分、工作辊磨损严重且不均匀等问题。采用ANSYS有限元建立辊系三维有限元模型,分析了辊间压力对磨损辊形的影响。在解析掌握1 700冷连轧机引进的SmartCrown辊形基础上,研究开发出了改进的SmartCrown plus新辊形,经过现场工业试验研究,SmartCrown plus工作辊取得磨削量小,且磨损更均匀化,其辊形自保持性良好的明显效果,现已成功投入1 700大型工业轧机实际应用。