Study On Vibration Mechanism For Chatter Marks And Characteristics Identification Method Of Twenty-high Roll Mill

Stainless steel products are widely used in our daily life such as aerospace, communication, automobile industry and so on. With the rapid development of manufacturing industry, the demand for steel products continues to increase. And at the same time the improvement of machining accuracy and quality leads to increasingly higher demands for performance and quality of steel products. While unfortunately dark and light chatter marks are prone to produce on the surface of steel strip which results in a bad surface quality and even a bad influence on the steel service, in which situation the steel company suffer a great deal of economic loss, consequently chatter marks have been recognized as a main restriction to the increased productivity and the quality of steel strip. So a further study on the vibration mechanism and available detect methods as well as the control strategies for chatter marks is meaningful to restrain or eliminate chatter marks on the steel surface theoretically and practically.Aiming to an accurate identification and monitoring for chatter marks, this paper firstly studies the vibrations mechanism for chatter marks of twenty-high roll mill. The features of the varying main driven roll torque in different work conditions are studied based on an established coupling model of torsional vibration and rolling skid, and then the relationship between the torisional vibration and chatter marks is explained. The relationship between the varying rolling forces in forward and backward skidding area with different exert stragies of rolling parameters and chatter marks vibrations is studied. A time-varying contact stiffness dynamic model with a local defect on work roll and FEA model with a local defect on support bearing are established respectively, the vibration mechanisim for chatter marks attributes to these two kind of local defects are explained. Several identification methods for chatter marks are proposed based on entropy, data-driven wavelet as well as wavelet packet et al., and combined with Lab VIEW an online monitoring system for twenty-high roll mill chatter marks vibration is established.The theoretical analyses are validated by the test data. The main contents are as follows:① The torsional dynamic model of the roll mill transmission system has been established considering the rolling skid between rolls, the relationship between the torsional stimulation and chatter marks vibration is analysed. Torsional vibration characteristics are obtained based on various rolling speeds and friction coefficients between rolls, based on which the control measures are proposed for torsional vibration. The established model is validated by the test data; furthermore it also provides a basis for the identification of chatter marks vibration attribute to torsional vibration.② Aiming to understand the relationship between rolling parameters and chatter marks vibration, the rolling force and its variation regular are analyzed in the rolling process according to the variation of the forward slid area and backward slid area; The coupling dynamic model in vertical direction and horizontal direction of Sendzimir twenty-high roll mill is established, and based on this model the chatter marks vibration is studied considering the varying rolling force and rolling speed, furthermore the relationship between rolling parameters and chatter marks vibration is better explained. The coupling dynamic model of the senzimir roll mill and the rolling force’s variation rule are validated by test datas, and which provides a theoretical and practical base for the analysis and identification of chatter marks.③ Aiming to figure out the vibration mechanism and characteristics for chatter marks, time-varying contact stiffness has been analyzed considering the edge contact effect resulting from local defect on the roll. Meanwhile the vibration characteristics are analyzed with a local defect in the support bearing based on an established twenty-high roll mill FEA model. Agreement between experimental results and simulated results verify the effectiveness of models and correctness of the analytical process, which provide a practical support for studying on vibration mechanism for chatter marks.④ Aiming to settle the problem of vibration features’ identification for chatter marks, the vibration characteristics of chatter marks and torsional signal are studied based on the envelop spectrum entropy and permutation entropy respectively. Based on the adaptive wavelet, the vibration signals are studied when there is an obvious defect on the roll surface. Meanwhile energy distribution of wavelet packet decomposition is used to analyze the vibration characteristics of chatter marks. Fine agreement between experimental results and simulated results verify the effectiveness of the listed methods.⑤ Based on the research of the relationship between vibration characteristics of chatter marks and vibration mechanism according to the rolling skid between rolls, variation of rolling parameters and local defects(roll surface and bearing et.al). In addition, combined the research of the decision for best sensors location, vibration characteristics of chatter marks are successfully extracted through the acquired vibration signals. Chatter marks on-line monitoring system is developed based on the software of Labview for Sendzimir twenty-high roll mill. The system has the functions of data emission with cable and wireless, data acquisition, data processing and data playback, etc. Good performance of the system is validated by a series of tests, which provides a practical tool for monitoring chatter marks.