In general, roll failure is determined by the combined effects of various stresses (including bending stress, torsion stress, contact stress, temperature stress caused by uneven or alternating temperature distribution and residual stress formed during roll manufacturing). Specifically, the failure of roller may be caused by the following three reasons: 1) unreasonable shape design of roller or insufficient design strength. For example, under the rated load, the roll break due to insufficient strength or contact fatigue over the allowable value, so that the roll surface fatigue spalling and so on; 2) the material, heat treatment or processing technology of the roller is not required. For example, the hot crack, adhesion and abrasion resistance of the roll is poor, and the material contains inclusions or excessive residual stress. 3) the roll is practical and unreasonable in the production process. When the hot rolling roll is not cool enough or not uniform, it will cause hot cracking of roll surface due to fatigue. The accident adhesion during cold rolling can lead to hot cracking and even surface peeling. In winter, the newly replaced cold rolling is suddenly stopped by high-load hot rolling or cold rolling machine. The hot rolling rolls are cooled suddenly, and the temperature stress is so high that the surface of the roll is peeled or even broken. Too much pressure or unreasonable process arrangement will result in the failure of roller.

 

 

It can be seen that in order to prevent the roll damage, efforts should be made from the aspects of design, manufacture and use.

 

 

When the rolling mill is designed, the strength of the roll is usually checked according to the given rolling load and roll parameters. As it is difficult to calculate accurately various factors affecting roll strength (such as temperature stress, residual stress, impact load value, etc.), the bending and torsion of rolls are generally not checked by fatigue during design, but the influence of these factors is included in the safety coefficient of rolls. The contact stress between working roll and supporting roll should be tested for fatigue in order to prevent spalling of roll surface.