Development of a Rolling Chatter Model Considering Unsteady Lubrication

Abstract

Chatter, limiting the rolling speed for thin steel strips, has been identified as a serious limitation in increasing the efficiency of the cold rolling process. Many experimental investigations have led to the point that lubrication is one of the effective factors causing chatter. In this article, a new chatter model of the cold strip rolling with consideration of unsteady lubrication is proposed. The limiting shear stress concept and the variation of the lubricant viscosity with pressure are considered in this model. The results of the simulation are verified by comparing to experimental data. Also, a parametric study on the effect of some of the major parameters of rolling lubricant on the chatter critical speed is conducted. The results show that under the operating conditions of this paper, the limiting shear stress is an effective parameter.

Effect of Friction on Tandem Cold Rolling Mills Chattering

“…This can be expressed by the fact that during vibrations, the pressure distribution within the roll bite is changed and the Coulomb model can better reflect this issue. Also the friction stress in practice usually exceeds the lubricant limiting shear stress 20) and in the other hand, the amount of lubricant limiting shear stress is a function of the lubricant pressure. 28) In the following, as one of the most effective and controllable process parameters, the effect of friction on chatter in tandem mills is examined.…”

“…(6) and (8) The force balance equation in the x-axis can be expressed by the slab element. 20) ................ (10) In the above equation, if position x is larger than the neutral point position, xn, the minus sign is used, otherwise the plus sign should be used. Assuming that the rolling pressure, p, and the strip tensile stress, σx, are the principal stresses, it is concluded that σy = -p and with the yield criterion under the plane strain conditions (σx -σy = σk), Eq.…”

“…The displacements of the work roll center (yw) and the backup roll center (yb) caused by the rolling force variation (dfy) can be written as: 20) ... (15) The subscripts 'w' and 'b' signify the work and backup roll, respectively. M is the roll mass, C is the damping coefficient, K is the spring constant, and w is the strip width.…”

“…Specifications of the tandem rolling mill are reported in Table 1. 20) All rolling conditions in this unit are recorded in a data collection system (IBA) through several analog and digital signals. Characteristics of five coils under consideration in the third pass are presented in Table 2.…”

“…Particularly, they studied the effects of friction on chatter and gave an explanation for the existence of an optimal friction conditions. Heidari et al 20) developed a new chatter model of the cold strip rolling with consideration of unsteady lubrication. As a result, they showed that the lubricant's limiting shear stress is directly proportional to the chatter critical speed.…”