Analiza utrujanja delovnih valjev pri vročem valjanju pločevine : doktorska disertacija

slovenian

doktorska dela

2014

Univerza v Mariboru, Fakulteta za strojništvo

The fatigue analysis of working rolls in hot strip mills is presented in this doctoral thesis. Working rolls are thermo % mechanically loaded during the rolling process. Mechanical loads are presented on working rolls when plastic deformation of rolled metal occurs on two surfaces: (i) in the area between working roll and rolled metal; (ii) on the contact between working and back up roll. Thermal loadings on working rolls result in heat transfer between working roll and rolled strip. Contact loadings on the surface of the working roll was firstly determined by analytical equations and secondly with numerical simulation. Results of the numerical analysis serve as a basis for determination of service life of the working roll. Based on the experimental results of the fatigue material properties at rooms and at elevated temperatures, service life of the working roll was determined by using the Basquin equation in two different ways: (i) with use of the material properties at loading ratio R = -1 when mean stress effect was taken into the account by using the Goodman equation; (ii) directly with data at R = -oo. Besides the determination of the high cycle fatigue, a lot of other experimental work was performed. Chemical composition with microstructure before and after special heat treatment is given. Also hardness distribution in depth through the whole working layer is presented. Monotonic tensile and compressive tests were done at different temperatures of the specimens, which correspond to the real situation in the rolling gap. Besides tensile and compressive tests, also bending and Charpy impact toughness tests were done. Fracture mechanics parameters and fatigue crack growth analysis was experimentally determined and moreover, a complete fracture investigation was performed by using scanning electron microscope. At the end of the thesis a result of wear is shown, where special testing device was developed for this purpose.

08.08.2023