Analysis of Mold Friction in a Continuous Casting Using Wavelet Entropy
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INTRODUCTION
IT is evident that the mold friction (MDF) between the strand and the mold is a directly measurable parameter for describing the stand/mold mechanical interaction and powder lubrication. In recent years, there has been an increasing awareness of MDF. Yao[1] has monitored the MDF to investigate the lubrication in mold. Meanwhile the root mean square (RMS) of MDF has also been discussed. The results show that the RMS of MDF can reflect the abnormality in advance and has obvious potential applications in the prediction of continuous casting. At present, MoldEXPERT developed by VAI[2,3] is the typical one, which can monitor the MDF online and continuously. Carlos et al.[4] have calculated the friction index through the driving force of the hydraulic vibration system with casting to characterize the lubrication state between the mold and the strand. Also, analysis of the different lubrication states is carried out under different conditions, but the definite principles and the processing methods used by Carlos are not published. In many practical castings, there are a lot of influence factors of friction such as protection slag performance, steel grade, mold oscillation mode, and vibration parameters. So it is still difficult to conduct in-depth analysis of the characteristics of a friction curve in MA YONG, Associate Professor, and WANG FANGYIN, PENG CHENG, GUI WEI, and FANG BOHAN, Graduate Students, are with the School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, Anhui, P.R. China. Contact e-mail: [email protected] Manuscript submitted October 20, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
different conditions in the time domain. As a result, the research of MDF has not always been smooth sailing. OZGU[5] has proposed that the application of a fast Fourier transform (FFT) will be a high-efficient technology in MDF analysis. And using the FFT method, the remarkable achievements of abnormal signal detection in continuous casting have been made by Alvarez.[6] The frequency domain characteristics of MDF are studied in Reference 7 in a continuous casting production process, and the results show that the frequency domain characteristics of the MDF are sensitive to the change of the process parameters, which can reflect the lubrication condition of the mold. FFT is an effective analytical method in the field of signal analysis. But FFT, which focuses on global transformation, cannot distinguish among changes in the local signal precisely. Since too many factors affect MDF and the characteristics of their effects on the MDF shows up in both the time domain and the frequency domain, how to carry out monitoring and analysis of the MDF in the time domain and the frequency domain simultaneously becomes a new focus. Wavelet analysis realizes local analysis of the time domain and the frequency domain synchronously, and the multiscale analysis method makes it suitable for time-varying signal analysis.[8] In addition, the wavelet entropy analysis, a combination of wavelet and entropy, cou
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