The preform is heated in an induction unit outside the necking-in machine, clamped in the jaw chuck of the machine by an automatic feeding facility, and set in rotation. A necking-in roller installed on a 100° swivel support gradually moves material from the pipe to the centre of rotation. The number of swivel steps determines the wall thickness of the evolving bottom or neck of the vessel. A wall thickness bulge of up to 10x t0 is possible. To avoid slag inclusions in the centre of rotation, an optional cutting torch can be used to ensure a homogeneous material distribution and the vessel’s ultimate gas tightness.
Necking-in allows optimum determination of the wall thickness progression in the diameter reduction zone. Short tooling and cycle times, process reliability in production and constant material quality result in cost-effective manufacture.