Bimetallic rolls are widely used in hot rolling mills because of excellent hardness, wear resistance, and high temperature properties. Considerable residual stresses are produced for the bimetallic roll during quenching. Moreover, severe thermal stresses are caused by heating-cooling thermal cycles during subsequent hot rolling process. Fracture from the roll center may occur due to the residual stress adding to the thermal stress, and therefore, it is desirable to investigate the residual stress to improve roll service life. Therefore, FEM simulation of the bimetallic roll is performed for the quenching process. It should be noted that a large number of experimental data of the core and shell material are utilized for the wide range of temperature considering the quenching. The generation mechanism for the residual stress is discussed focusing on the effect of temperature gradient and phase transformation. Furthermore, the effects of shell-core ratio and diameter on residual stress are considered. Results show that the residual stress only slightly increases with increasing shell-core ratio, while significantly increases with increasing diameter.
Bimetallic rolls are widely used in steel rolling industries because of the excellent hardness, wear resistance, and high temperature properties. Controlling the residual stress distribution is important to improve the roll fatigue life due to the compressive residual stress at the roll surface. Recently, to reduce the tensile residual stress appearing at the roll center, quenching heat treatment is performed just after heating the roll non-uniformly instead of heating the roll uniformly with enough time. In this paper, therefore, the residual stresses are compared after between the uniform heating quenching and the non-uniform heating quenching on the basis of the FEM simulation. The results show that tensile stresses at the roll center for non-uniform heating are smaller than that for uniform heating by 400 MPa, although the same compressive stresses appear at the surface. The effect of creep on stress relaxation is also considered in this study. By considering creep, the maximum tensile residual stress decreases by 8% for uniform heating and by 15% for non-uniform heating.
In this paper, the effect of a slight pitch difference between a bolt and nut is studied. Firstly, by varying the pitch difference, the prevailing torque required for the nut rotation, before the nut touches the clamped body, is measured experimentally. Secondly, the tightening torque is determined as a function of the axial force of the bolt after the nut touches the clamped body.The results show that a large value of pitch difference may provide large prevailing torque that causes an anti-loosening effect although a very large pitch difference may deteriorate the bolt axial force under a certain tightening torque. Thirdly, a suitable pitch difference is determined taking into account the anti-loosening and clamping abilities. Fourthly, fatigue experiments are conducted using three different values of pitch difference for various stress amplitudes. It is found that the fatigue life could be extended when a suitable pitch difference is considered Furthermore, the chamfered corners at nut ends are considered, and it is found that the finite element analysis with considering the chamfered nut threads has a good agreement with the experimental observation. Finally, the most desirable pitch difference required for improving both anti-loosening and fatigue life is proposed.
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