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.

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.

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.

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.

Strip flatness prediction of cold rolling based on ensemble methods

Aiming at the problem of insufficient prediction accuracy of strip flatness at the outlet of cold tandem rolling,the prediction performance of strip flatness based on different ensemble methods was studied and a high-precision prediction ensemble model of strip flatness at the outlet was established.Firstly,based on linear regression(LR),K nearest neighbors(KNN),support vector regression,regression trees(RT),and backpropagation neural network(BPN),bagging,boosting,and stacking ensemble methods were used for ensemble experiments.Secondly,three existing ensemble models,i.e.,random forest,extreme random tree(ET)and extreme gradient boosting,were used to conduct experiments and compare the results.The research shows that bagging,boosting,and stacking three ensemble methods have the most significant improvement in the prediction accuracy of the regression trees model,which is increased by 5.28%,6.51%,and 5.32%,respectively.At the same time,the stacking ensemble method improves both the simple model and the complex model,and the improvement effect on the simple base model is the greatest,which is 4.69%higher than that of the base model KNN.Comparing all of the ensemble models,the stacking ensemble model of level-1(ET,AdaBoost-RT,LR,BPN)paired with level-2(LR)was discovered to be the best model(EALB-LR)and can be further studied for industrial applications.

SENSITIVITY ANALYSIS FOR ROLLING PROCESS BASED ON SUPPORT VECTOR MACHINE

A method for the calculation of the sensitivity factors of the rollingprocess has been obtained by differentiating the roll force model based on support vector machine.It can eliminate the algebraic loop of the analytical model of the rolling process. The simulationsin the first stand of five stand cold tandem rolling mill indicate that the calculation forsensitivities by this proposed method can obtain a good accuracy, and an appropriate adjustment onthe control variables determined directly by the sensitivity has an excellent compensation accuracy.Moreover, the roll gap has larger effect on the exit thickness than both front tension and backtension, and it is more efficient to select the roll gap as the control variable of the thicknesscontrol system in the first stand.

Vibrations of tandem cold rolling mill: coupled excitation of rolling force and variable stiffness of fault-free back-up roll bearing

Vibration issues of a five-stand tandem cold rolling mill were found in the steel production practice,and the experimental observation and numerical analysis indicated that the vibrations were related to the back-up roll bearing.The results were validated by replacing the back-up roll bearing with the new bearing resulting in 30%decline in vibration amplitude.Models describing the four-row cylindrical roller bearing and the vertical system of the cold rolling mill including the bearing were established.Moreover,the mechanisms of periodic excitation and amplified vibrations of fault-free bearing were explained theoretically,along with the analysis of bifurcation behaviors of the motion states of the roller bearing and rolling mill system.It is found that the energy transmitted between vibrations with different frequencies if multiple excitation frequencies in the rolling mill system were close.

Deformation resistance prediction of tandem cold rolling based on grey wolf optimization and support vector regression

In the traditional rolling force model of tandem cold rolling mills,the calculation of the deformation resistance of the strip head does not consider the actual size and mechanical properties of the incoming material,which results in a mismatch between the deformation resistance setting and the actual state of the incoming material and thus affects the accuracy of the rolling force during the low-speed rolling process of the strip head.The inverse calculation of deformation resistance was derived to obtain the actual deformation resistance of the strip head in the tandem cold rolling process,and the actual process parameters of the strip in the hot and cold rolling processes were integrated to create the cross-process dataset as the basis to establish the support vector regression(SVR)model.The grey wolf optimization(GWO)algorithm was used to optimize the hyperparameters in the SVR model,and a deformation resistance prediction model based on GWO–SVR was established.Compared with the traditional model,the GWO–SVR model shows different degrees of improvement in each stand,with significant improvement in stands S3–S5.The prediction results of the GWO–SVR model were applied to calculate the head rolling setting of a 1420 mm tandem rolling mill.The head rolling force had a similar degree of improvement in accuracy to the deformation resistance,and the phenomenon of low head rolling force setting from stands S3 to S5 was obviously improved.Meanwhile,the thickness quality and shape quality of the strip head were improved accordingly,and the application results were consistent with expectations.

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。

Multi-Objective Optimization for Tandem Cold Rolling Schedule

Considering the multivariable, strong-coupled, and nonlinear features of tandem cold rolling mill, a mathematical model of multi-objective optimization was built to facilitate the design of new systems aiming at equating the relative load, preventing slip, and obtaining best shape. BP （back propagation） neural network based on Levenberg- Marquardt algorithm was used for predicting the rolling force. The multi-objective fuzzy theory and method were introduced during the optimization. With an example of 1 370 mm tandem cold rolling mill, the rolling schedule of the common rolling, the single-objective optimization design, and the multi-objective fuzzy optimization design were compared with each other. The results generated from the case study showed that the proposed approach could significantly decreased the values of three objective functions simultaneously and the performance of the optimal rolling schedule was satisfactory and promising. Moreover, the capability and usefulness of fuzzy application in tandem cold rolling schedule were clearly demonstrated.

Prediction and Control of Thermal Scratch Defect on Surface of Strip in Tandem Cold Rolling

The thermal scratch significantly influences the surface quality of the cold rolled stainless steel strip. In or der to establish a precise mathematical model of oil film thickness in deformation zone, the lubrication in cold rolling process of B443NT stainless steel strip was studied in the laboratory. According to the principle of statistics, a math- ematical model of critical oil film thickness in deformation zone for thermal scratch was built, with fitting and regres- sion analytical method, and then based on temperature comparison method, the criterion for deciding thermal scratch defect was put forward. Storing and calling data through SQI. Server 2005, a software on thermal scratch control was developed in the Microsoft Visual Studio 2008 environment by MFC technique for stainless steel in tandem cold roll- ing, and then it was used into the practical production. Statistical results demonstrated that the hit rate of thermal scratch arrives at 91.47%, the occurrence rate of thermal scratch is decreased by 87.81%, and rolling speed is in- creased by 7.3%. The developed software is of significance to the control of products quality of stainless steel strips, and the analysis and solution to the problem of thermal scratch defects in tandem cold rolling.

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.

Modeling and Analysis of Interstand Tension Control in 6-high Tandem Cold Rolling Mill

The interstand tension control is one of the most important ways to meet tight tolerances for strip product quality during tandem cold rolling process. Using coordinate analysis and parabolic approximation for the mass flow balance principle, the strip velocities eliminating the use of forward slips and backward slips were calculated. In order to reduce the effect of roll eccentricity on the tension measurement, a filter based on bilinear transformation was de- signed. Applying a first-order Taylor series approximation, the transfer function matrix model of interstand tension stress was derived. The actual measurements on-site and the final calculation results showed that the established model had high calculation accuracy and was beneficial for interstand tension control of random cold rolling process.

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.

5+1型冷连轧机组不同轧制模式下乳化液油箱优化方法

为了实现国内某厂新建5+1型冷连轧机组的新型3+1润滑液系统中乳化液油箱分配的最优化,建立了5+1型冷连轧机组带钢出口温度模型并编写出口温度模件,给出了各个机架在带钢轧制过程中产生的温度和乳化液吸收温度。分析了带钢出口温度对热滑伤的影响,明确了各道次乳化液的作用。得到了不同轧制模式下乳化液油箱排列组合。为了防治打滑和热滑伤,开发了乳化液油箱优化方法,并根据现场实际数据做了具体算例,轧制过程中带钢打滑因子和热滑伤指数得到了优化,有效提高了机组的轧制稳定性。

改进人工鱼群算法在冷连轧负荷分配优化中的应用

针对冷连轧机负荷分配寻优速度缓慢的问题,采用了基于改进人工鱼群算法的优化方法。由于基本人工鱼群算法后期收敛速度慢、精度不高,所以对其中觅食行为的视野和步长进行了优化。首先给定一个较大的视野和步长,随着算法的迭代,视野不断减小,到某一值后不再改变,同时步长随着视野的减小而同比例减小。结合某钢厂五机架冷连轧机,以轧制力成比例分配为目标函数,以压下率为约束条件,通过MATLAB对轧制负荷分配的寻优过程进行仿真,结果表明改进后的人工鱼群算法在轧制负荷分配方面,具有算法实现简便、收敛速度快等优点,而且与典型轧制规程相比,各机架出口厚度误差最大为4.26%,为实际生产中轧制规程的制定提供了有效的方法。

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。

基于神经网络的冷连轧机轧制力预报模型

为了提高冷连轧机轧制力预报精度,提出一种解析数学模型结合神经网络校正模型的计算方法,建立冷连轧机轧制力预报模型。采用径向基函数的局部映射和全局线性映射相结合的神经网络校正模型求解带钢变形抗力和轧制变形区的摩擦因数;并采用轧制变形区离散化方法分析轧制变形区内张力、摩擦力及金属变形抗力等在带钢轧制方向上的分布规律,从而建立轧制力在线计算数学模型。现场实测数据离线仿真结果表明,采用此基于神经网络的冷连轧机轧制力预报模型预测轧制力,其预测误差小于8.9%,此模型能用于指导生产实践。

冷连轧高速轧制过程中摩擦因数机理模型的研究

在现场试验与理论分析的基础上,针对现有摩擦模型对冷连轧高速轧制过程中摩擦因数的预报精度不高、通用性不强等问题,首先对润滑油膜厚度计算模型与摩擦因数返算方法进行了推导,然后定量研究了辊缝中润滑油膜厚度与摩擦因数之间的关系,最终建立起一套适合冷连轧高速轧制的摩擦因数机理模型,并将其应用于宝钢冷轧薄板厂1220五机架冷连轧机与宝钢冷轧厂2030五机架冷连轧机的生产实践。应用结果表明:提高了轧制的稳定性与带材的控制精度,减小了相关模型的自学习与自适应系数波动,取得了良好的使用效果。