Construction of a force method for estimating the longitudinal stability of the process of thin sheet rolling

Roman Romaniuk,Kateryna Levchuk,Yurii Hasylo,Olha Kriukovska,Dmitry Chasov

doi:10.15587/1729-4061.2019.160487

Roman Romaniuk, Kateryna Levchuk + Show 3 more

Open Access

https://doi.org/10.15587/1729-4061.2019.160487

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Abstract

We have analyzed theoretical features of rolls gripping capacity at simple rolling process under a steady mode. It is shown that depending on the conditions for deformation the ratio of the maximum gripping angle to a friction coefficient can be equal to, be less or more than 2. An experimental study has been performed involving the rolling of lead stepped samples measuring the forward creep at each step. Results of the experiment demonstrate that in the extreme case of deformation the forward creep is greater than zero, that is, there is a sufficient reserve of frictional forces so that reduction can be further increased, however, it is impossible. We have analyzed the balance of all horizontal forces at deformation site. It is shown that at each cross section the stretching horizontal contact forces are used not only to overcome the ejecting ones, but also to compensate for the longitudinal internal forces that occur as a result of plastic deformation of a metal. A force method for estimating the longitudinal stability of the sheet rolling process has been developed. An indicator of stability is a criterion that is determined from the diagrams of distribution of a normal contact stress and the stress of friction. It is shown that at a positive value of the criterion the rolling process proceeds under a steady mode; at a negative value, the stable process is impossible; and in the case it equals zero, the limit deformation occurs. A theoretical study has been conducted into determining the maximum gripping angle under different conditions of sheet rolling. It is shown that the ratio of the maximum gripping angle to a friction coefficient almost does not depend on a strip thickness, the diameter of rolls, as well as friction coefficient, and equals 1.43‒1.44. A decrease in the gripping capacity of rolls is explained by the effect, at a deformation site, not only of contact forces, but the internal forces as well.

Highlights

One of the important technological parameters that defines the stability of the rolling process is the gripping capacity of rolls
Disruption in the longitudinal stability of the rolling process leads to strip skidding in the rolls, and in some cases it is the cause of major accidents at rolling mills
The existence of internal forces at a deformation site has been proven in practice, for example, in experiments when bending the vertical lines drawn at the surface of a strip (Fig. 5)

Summary

Introduction

One of the important technological parameters that defines the stability of the rolling process is the gripping capacity of rolls. Where αy is the gripping angle under a steady mode; fy is the friction coefficient at a deformation site This inequality was derived from the condition that the sum of contact stretching forces is sufficient to overcome the sum of contact ejecting forces. Formula (1) was derived under important assumptions, and practical significance of the boundary gripping angles in practice is very high, for example, when developing modes of deformation at rolling mills. As it is known, the process of sheet rolling proceeds with tensions (front and rear). The improved method would make it possible to reliably determine the longitudinal stability of the process when developing and advancing deformation modes at industrial sheet mills

Literature review and problem statement

R σx 2k dhx

Assess the stability of the rolling process

Conclusions