Doctor of Philosophy
Department of Mechanical Engineering
Jafari, Ali Asghar, Asymmetrical rolling and self-excited vibration in a hot roughing mill, Doctor of Philosophy thesis, Department of Mechanical Engineering, University of Wollongong, 1994. http://ro.uow.edu.au/theses/1572
Torsional vibration of drive shafts, rolls, and vertical vibration of rolling mill housings due to impact rolling loads should be considered because they can shorten the lives of rolling mill components. Moreover these dynamic loads can affect the quality and physical properties of the strip.
This thesis contains the simulation of different vibration modes in a hot Roughing mill which consists of a Horizontal mill with an attached Edger (Fig. 5.1). Four vibrations of the Roughing Mill system have been studied:
(i) torsional vibration of Horizontal mill
(ii) vertical vibration of Horizontal mill
(iii) torsional vibration of Vertical Edger
(iv) horizontal vibration of slab between the two mills.
There are many published works on torsional and vertical vibration of rolling mills especially for cold rolling. In their simulations, the vibrations were calculated with the excitation of a step or ramp-step function, but they did not consider the oscillation of rolling force and torques caused by the rolls having different velocities due to torsional vibration under asymmetrical rolling conditions. However, the following parameters have been taken into account when calculating the vibration in this thesis:
(i) asymmetry in horizontal mill (different roll speed)
(ii) variation of rolling force and torques (top and bottom rolls) in horizontal mill
(iii) backlash on the drives couplings
(iv) non-linear stiffness and damping of hot slab
(v) push-pull between the two mills during interaction conditions
The study showed that the asymmetry and slab vertical damping introduced the greatest damping on the torsional and vertical vibration of horizontal mill respectively. Moreover, higher vibrations amplitudes achieved in both mills as a result of backlash on shafts or push-pull between the two mills.
Stability and torsional vibration of horizontal mill for different slippage conditions also been investigated. The self-excited vibration (continual slippage when the torque is replaced by a friction torque) introduced the highest amplitude compared with normal slippage (no torque for a short time).