| 摘要 |
PURPOSE: A method capable of replacing back up roll before fatigue breakage is not generated by calculating cumulative fatigue based on realtime variable roll force and number of revolutions at the roll force and actually approximately calculating fatigue received on the roll considering partial stress concentration due to wear of the roll. CONSTITUTION: The method for judging replacement time point of back up roll of rolling mill through controlling of degree of cumulative fatigue comprises the steps of obtaining contact stress of the back up roll by the following mathematical expression 1:£Mathematical Expression 1| where σc is contact stress, P is roll force, I is widthwise contact length of the back up roll and work roll, b is contact field generated by deflection of rolls; obtaining actual contact stress by substituting the obtained contact stress (σc) for the following mathematical expression 3:£Mathematical Expression 3| where σact is an actual contact stress, Rc is stress concentration rate, k is constant, and Wd is wear depth; measuring an actual number of revolutions (ni) after obtaining the number of revolutions (Ni) until destruction is occurred by substituting the obtained actual contact stress for the following mathematical expression 4:£Mathematical Expression 4| where a1 and a2 are constant, and σcritical is critical stress value; obtaining degree of fatigue (Fi) by substituting the obtained Ni and ni for the following mathematical expression 5:£Mathematical Expression 5| calculating a degree of cumulative fatigue by substituting the calculated degree of fatigue for the following mathematical expression 6 after calculating degree of fatigue of the back up roll at certain intervals:£Mathematical Expression 6| and judging that it is the right time for replacing the back up roll if the obtained degree of cumulative fatigue (F) is greater than degree of critical fatigue.
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