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چكيده انگليسي :

98 Study on Roll Separation with Forced Vibration of Two Tandem Cold Rolling Mills Rasoul Shahsamandi Esfahani r shahsamandi@me iut ac ir Date of Submission 2012 29 2 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Mohammadreza Frouzan forouzan@cc iut ac irAbstract One of the problems in metal rolling products is forced vibrations in mill stands These vibrations candegrade the quality of the strip surface and can trigger self excited vibration chatter These vibrations canbe due to different components of equipment Some of these defects are eccentricity and ovality of rollers misalignment of coupling wear in gears and defects in bearing Rolling equipment of mill stands producessounds which will be increased when chatter happens It is supposed that the sounds are due to separation ofthe roller from strip or between the rollers themselves To analyze the vibrations a dynamic model of rolling stand has been developed in SIMULINK spaceof MATLAB software Rolling mills vibrations are produced as a result of interaction between the structureand the process therefore this model consists of two parts the model of process and the model ofstructure The model of structure is considered to possess two degrees of freedom which are vertical Themodel of the process is also considered to be dynamic Possible defects are considered as external forces Considering the fact that each defect produces a force with the specified frequency the defects of the systemcan be identified using frequency analysis of forced vibrations of the system For model verification data from two stand reversing cold mill of Foolad Mobarake Steel Company MSC have been used This unit consist of two four high F H rolling mills Thickness of the strip isreduced in three reversing passes The direction of rolling in second pass is reverse All the condition ofrolling are measured using tens sensors and saved as digital and analogue signals Comparing FFT of thedata with simulation result the defects of the equipment can be identified After investigation into data of two stand cold rolling unit it has been understand that the usual defectin this unit is eccentricity of the back up rollers In addition wear in one side of the tooth gear in the gearbox of the first stand has been observed To investigate the separation this phenomena has been modeledwith kinematical model Due to the fact that the effects of the inertial forces and spring back notconsidered a more complete model has been proposed using FE analysis Considering the fact that the amplitude of vibrations reaches its maximum amount during chatter thepossibility of separation has been investigated in chatter Experiments have been done to observe thevibrations of rollers Considering simulation and experiment results it has been proved that there is noseparation between strip and work roll also between rolls themselves when close to threshold speed of thechatter Keywords Rolling mills Forced vibration Separation Frequency analysis

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بررسي احتمال جدايش غلتك از ورق در ارتعاشات اجباري در نورد سرد دوقفسه

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