INFLUENCES OF PIERCING RATIO, EXPANSION-RATIO, FEED, CROSS AND SKEW ANGLES ON AVAILABLE PIERCING SIZE RANGE IN ROTARY PIERCING PROCESS

A cone-type piercing mill was developed by the authors for materials w ith poor hot workability. This piercing mill is called ''the super pie rcer'' in Europe and America. This mill has a pair of cone-type main r olls supported at both ends with their roll axes inclined and crossed so as to enable piercing at high feed and cross angles. In order to en sure the best performance of the rotary piercing, disc rolls are adopt ed instead of plate guide shoes. The super piercer was put into practi ce at the small-diameter seamless tube plant operated in 1983. The rec ent progress in our research and development on the super piercer has resulted in the concept of ''the new super piercer'', which allows exp ansion piercing. Namely, the development of the skewing technology for disc roll axes and its application to the cone-type piercing technolo gy has realized remarkable increase in the expansion ratio. The new su per piercer was adopted as the core technology of the new medium-diame ter seamless tube plant operated in 1997. In this paper, studied in de tail were the influences of the piercing ratio, expansion ratio, feed and cross angles for main roll axes and skew angle for disc roll axes on the available piercing size range.