An Approximate Model for Local Strain Variation over Material Thickness and Its Applications to Thick Plate Rolling Process

Abstract

This paper presents a three-parameter approximate model which computes the local strain variation over thickness direction of thick material in the roll gap. The three parameters were determined through finite element analysis. With the proposed model, we then carried out a series of plate rolling simulation to examine the effect of the arithmetic average aspect ratio (ratio of contact length between work roll and material to mean material thickness in the roll gap) and reduction ratio on the local strain variation over material thickness as material goes through rolling at many passes.Results reveal that a certain amount of relative difference between local strain at center and that at surface always exists as arithmetic average aspect ratio increases for whole plate rolling process. It also shows that the magnitude of local strain at material center is only 69 % of that at surface during rolling no matter how we regulate incoming material thickness, radius of work roll, reduction ratio, roll speed and friction condition when arithmetic average aspect ratio is greater than 1.0. It has been found that the heavy reduction with arithmetic average aspect ratio, 0.9 might be an optimum condition for refining grain size over material thickness in an approximately uniform manner.KEY WORDS: local strain variation; material thickness; arithmetic average aspect ratio; peening effect; plate rolling.ables such as roll diameter, material dimension, frictional condition and roll speed are changed. Hence, practical use of the kinematic strain model was quite limited.Kim and Hwang 13) developed a data regression-based model to calculate the local strain variation over thickness of strip. Their model took into account the effect of the process variables mentioned above. Five parameters in their model were determined from FE simulation of strip rolling. Since their model has many parameters it gives high prediction accuracy as far as it is applied to the finishing stands in strip rolling mill. However, their model becomes problematic to be applied to the rough rolling sequence of plate mill where the thickness of material is about 7-8 times larger than that strip thickness.In this paper, we propose a three-parameter approximate model which computes the local strain behavior over thickness direction of thick material during rolling. Each parameter in the proposed model is expressed in terms of process variables such as roll speed, incoming thickness of material, its outgoing thickness, radius of work roll and contact length. The three parameters are determined through finite element simulation of plate rolling. The model proposed in this study is especially useful when the contact length-roll gap ratio, l d /H m is low, say, less than 1.0. The rough rolling sequence of an actual plate mill usually has low value of contact length-roll gap ratio.We then carried out a series of numerical analysis to investigate the effect of the process variables on the amount of local strain variation over material thickness. We also studied how th...

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“…The total equivalent strain profiles after von Mises (black solid line) shown in Fig. 18 are already observed by several authors like Lachmann and Zouhar [102], Moon and Lee [134], Seuren et al [84] and Serajzadeh [135]. The first rolling case with the small roll gap ratio l c / h m shows a maximum total equivalent strain after von Mises below the surface.…”

“…This explains the maximum equivalent strain below the surface shown in Fig. 18 and observed by Lachmann and Zouhar [102] and others [84,134].…”