| 摘要 |
A method of manufacturing hollow rods of very thick wall, in which wall thickness to outside diameter ratio is 25% or more, such as those used as work stock for manufacturing oil-well drilling collars. A cross-type or rotary mill having three or four cone-type rolls is employed without using internal sizing tools such as plug or the like, whereby a hollow work piece is worked and reduced in both outside diameter and wall thickness to the target values. In order to obtain higher dimensional accuracy and to prevent deterioration of the work material in mechanical properties, the cross angle should be positive and the feed angle should be set within the range of 3 DEG </= beta </=20 DEG . |
