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type:Journal Article, In hot rolling mills, bimetallic rolls are used because of the excellent hardness and wear resistance by applying high-speed steel (HSS) and ductile casting iron (DCI). Because most of the previous studies focused on surface spalling, almost no study is available for internal fatigue failure based on the stress during the rolling. In this study, therefore, a three-dimensional finite element method is applied to investigate the rolling stress of the work roll in the four-high rolling mill. A suitable chamfer geometry in the backup roll is discussed as well as the standard wear profile by considering those effects on the fatigue. Then, to evaluate the fatigue risk under compressive mean stress, the fatigue limit lines in the stress amplitude versus mean stress diagram are newly discussed. With the aid of previous experience in industries, the fatigue fracture risk is discussed by focusing on three critical points inside the work roll.

In hot rolling of steels, bimetallic rolls consisting of high-speed steel and ductile casting iron are extensively used because of their excellent hardness and wear resistance although the fatigue failure study is not available. To extend the roll life service, herein, a 3D finite element method is applied to investigate the residual stress and the rolling stress of the bimetallic work roll in the four-high rolling mill. The residual stress is analyzed by considering preheating, quenching, and tempering. Using the results as an initial condition, the rolling stress analysis is carried out consecutively. Then, the fatigue failure risk is discussed focusing on several critical points subjected to the largest stress amplitude inside of the work roll. The accuracy of the simple superposition method is also discussed to evaluate the risk conveniently.

A nanobubble generator with honeycomb structures producing a large amount of water including large nanobubble density in a short time is described. The nanobubble‐generating performance is investigated for large and small apparatus having different honeycomb cell dimensions by applying computational fluid dynamics (CFD) coupled with a population balance model (PBM). The CFD simulation shows that a significant pressure drop and shear stress occur in the bubbly flow in the honeycomb cell. The numerical model is based on the Eulerian multiphase model and the PBM is used to calculate the bubble size distribution. The obtained CFD‐PBM results are compared with the experimental results for large and small apparatus. Bubble size distributions in the honeycomb structure under different inlet absolute pressure can be predicted by the PBM. The maximum shear stress is determined as the main controlling factor for nanobubble generation.