Among the most common reasons for rolling-mill downtime are breakage of the roll fittings and their jamming by stray pieces of metal. These problems often occur due to inaccurate evaluation of the longitudinal force created by the rolls under emergency conditions. The longitudinal force is created due to the existence of reserve frictional forces in the deformation zone, and the magnitude of these frictional forces depends on the shape of the pass, the deformation regime, and the friction conditions on the contact surface. This problem has yet to receive adequate attention in the technical literature, there is no method for determining the magnitude of the frictional forces, and the method presently used in design work to calculate the strength of roll fittings is highly approximate. Here, we propose a method of determining the longitudinal forces created by rolls under emergency conditions. Breakdown passes will be used as an example to illustrate the method. To solve the given problem, we will see how changes take place in the deformation zone when the strip sticks in the roll fittings. Such external loading of the fittings shortens the forward-slip region, causes the strip to stick to the rolls, and lengthens the backward-slip region. Despite these changes, the rolling operation continues as a result of the reserve frictional forces in the deformation zone.
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