| 摘要 |
PURPOSE:To prevent the inner surface of a pipe from becoming angular and to improve the quality and yield of a product by twisting the pipe in a titled method where plural sets of rolling mills consisting each of plural rolls are arranged in series. CONSTITUTION:Each stand of a drawing mill constituted of 28 sets of stands, for instance, has three rolls, and the calibers of adjoining two (n)th, (n+1)th stands are in the positional relation as shown by the figure, and the (n)th stand has a characteristic value (ovality) of b/a. Thereupon, all the stands are separated into two blocks of the 1st-14th and the 17th-28th stands to set a twisting device of material at the position of the 16th stand by removing the rolls of the 15th stand. That is, the rolls having the same shapes as those of the 14th stand are cut into the rolls having each a 15 deg. inclination, to use them as a twisting device. The material after being subjected to rolling reduction by the 14th stand is twisted while passing through the 16th stand, and is subjected to rolling reduction by the 17th stand while being twisted by 30 deg.. Thus the material is rolled by the succeeding stands in a state of being deviated by 30 deg. in phase from the state in the first half stands into a dodecagonal inner face thereby making the angular one uniform. |
