PURPOSE: To improve the production efficiency by the rolling of a tapered rod having a high degressive rate by specifying the roll diameter ratio of the ratio of the diameter of a 1st pass rolling roll to the bar stock diameter prior to rolling.
CONSTITUTION: A bar rod 1 is rolled in a flat sectional shape by a pair of rolling rolls 2 of a 1st pass and this bar rod 1 is formed by its rolling in the tapered rod 10 having the reduced diameter taper 4 that the diameter becomes smaller according to heading for the rear part from the front part in rolling direction by a pair of rolling rolls 3 of a 2nd pass. In this case the rolling of R≥0.5 is executed with the bar rod diameter prior to rolling being taken as d0, the tapered rod min. diameter after rolling as d1, the degressive rate as R=1-(d1/d0)2, the diameter of 1st pass rolling roll 2 and DR, the ratio roll diameter as δ=DR/d0. In this case the ratio roll diameter is set as δ≤2,540/lIOR (l: bottom of natural logarithm).
MATSUSHITA TOMIHARU
ISHIKAWA SEIICHI
