Method of controlling a hot strip finishing mill

A method of controlling a hot strip finishing mill for effecting continuous rolling by locating loopers between a plurality of consecutive stands and connecting a rear end of a preceding bar to a top end of a next bar, comprising the steps of:

• calculating a thickness on the delivery side of said each stand by use of actual values of a rolling force and a roll gap;
• controlling said roll gap of said each stand so that said delivery-side thickness coincides with a reference thickness;
• calculating an interstand mass flow variation by use of a mass flow variation on the delivery side of an upstream stand and a mass flow variation on the entry side of a downstream stand of two adjacent stands;
• controlling a roll peripheral speed of said upstream stand to make said interstand mass flow variation zero;
• controlling a speed of a looper driving motor so that a detected angle of said looper coincides with a predetermined reference angle until a connecting point between said preceding bar and said next bar reaches a position just before said upstream stand with respect to said looper and after passing through said downstream stand;
• simultaneously detecting a tension of a rolled material by use of a load undergone by said looper;
• controlling said roll peripheral speed of said upstream stand with respect to said looper so that said tension coincides with a reference tension during steady-state rolling;
• controlling a speed of a looper driving motor so that a looper roll coincides with a reference angle prescribed so as not to contact said rolled material until said connecting point passes through said downstream stand since after connecting point has reached the position just before said upstream stand with respect to said looper;
• detecting a tension of said rolled material on the basis of an actual value of rolling torque and the actual value of said rolling force of said upstream stand of said two adjacent stands;
• and
• controlling said roll peripheral speed of said upstream stand so that a detected tension coincides with a reference tension prescribed so as to decrease from a magnitude during steady-state rolling down to zero or a trace magnitude until said connecting point reaches said upstream stand after said connecting point has reached the position just before said upstream stand and so that said detected tension coincides with zero or a trace reference tension until said connecting point passes through said downstream stand after said connecting point has reached said upstream stand.