Method of controlling tandem rolling mills

A method of controlling a tandem rolling mill including n stands, where n is an integer, and utilized to roll a metal strip, said method comprising the steps of, at the time of changing the pass schedule during the operation of the mill, and before the size changing point of the strip reaches the first stand;

• changing the roll speed of the last stand to that of after size changing;
• changing the roll speeds of the other mill stands while maintaining the speed ratio of before size changing;
• when the size changing point reaches any intermediate stand (ith stand) between the first and (n-1)th stands, changing the roll speed of the ith stand so as to maintain the exit strip speed thereof at the speed of before size changing;
• at the same time changing the roll opening of the ith stand so as to maintain the intermediate strip tension between the ith and (i+1)th stands at the value of before size changing but to change the exiting strip gauge of the ith stand to a predetermined target value of after size changing;
• changing the roll opening of the (i-1)th stand to a predetermined set value of after size changing;
• changing the roll speeds of the roll stands on the upstream side of the ith stand while maintaining the volume speed of after size changing;
• and when the size changing point reaches the last stand;
• changing the roll openings of the last and the (n-1)th stands to predetermined set values of after size changing while at the same time changing the roll speeds of the first to the (n-1)th stands to predetermined preset values of after size changing.