Abstract
The four-roll rolling process (4RP) enables the further evolution of sizing processes in rolling mills for round sections. The well-known advantages of the three-roll process over the two-roll process can be further improved using the 4RP. The participation of four rolls in the deformation zone instead of three or two leads to a significant increase in deformation efficiency. The present work shows a pass design method for pass sequences in the four-roll rolling process. Here, three basic types of roll groove geometries are discussed: the flat groove, the non-opened single-radius groove, and a tangentially opened type of a single radius groove. Based on a predefined cross-sectional evolution, grooves are found numerically to satisfy two conditions, i.e., the cross section of the rolled section and the groove filling criterion. The equations of the equivalent pass method, together with a suitable model for lateral spread and the geometric equations of the groove are solved by nonlinear optimization to minimize the sectional and filling errors of a specific pass. Combined for several rolling passes, a complete pass design can be carried out for the reduction of a specified initial section to a final section. The presented results show, how a pass design method for the four-roll rolling process can be constructed. The newly developed model is implemented in a software solution for pass design and analysis of full section rolling mills. An exemplified pass design is discussed to show the possibilities and limitations of the new model.
Highlights
Introduced to the market a few years ago, the four-roll rolling process (4RP) is a new method for sizing of round sections to minimize cross-sectional variations which occur during hot rolling due to the elastic mill behavior and interstand tensions in continuous rolling mills [1]
The present paper outlines the process of pass design for a four-roll rolling block which can be used for the sizing of round sections
The groove geometries are found by numerical optimization of an error function, minimizing deviations of groove filling and cross sections from their desired values
Summary
Introduced to the market a few years ago, the four-roll rolling process (4RP) is a new method for sizing of round sections to minimize cross-sectional variations which occur during hot rolling due to the elastic mill behavior and interstand tensions in continuous rolling mills [1]. Avellino et al [4] showed a control system for the 4RP rolling block, where the working roll diameter was calculated according to the rolling theory of the 3RP [5] These practical developments call for a theoretical treatment of the pass design problem for this new type of rolling mill. Each groove must fulfill two criteria: first an overor underfilling must be prevented, second the cross sections should satisfy a predefined degressive pass schedule From these two criteria, we can define an error function to be minimized by nonlinear optimization. We can define an error function to be minimized by nonlinear optimization With this procedure, the new model can automatically calculate a pass design for a given rolling task where the initial and final round sections, the desired number of passes and the nominal roll diameters are given as input values
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