Abstract
Tubes of high density polyethylene were drawn with a conical mandrel. The changes of the draw ratios on the mandrel in the longitudinal direction of the tubes (the machine direction, MD) and in the hoop direction (the transverse direction, TD) were measured. The change of the draw ratio in the TD, λ2, is almost completely determined by the diameter and shape of the mandrel. At the early stage of mandrel drawing, the draw ratio in the MD, λ1, decreased with increasing λ2 and then suddenly began to increase. Namely, dλ1/dλ2 was negative at first, and then it became positive. In almost all regions of dλ1/dλ2>0, d2λ1/dλ22 was negative.
