Necking-in consists of gradually reducing the diameter of the preform. The procedure is particularly suitable for neck forming and closing off pipes for pressurised vessels, gas cylinders or other metal bottles. Necking-in is suitable for both vessel bottoms and necks, resulting in a permanently gas-tight seal.
Necking-in in detail
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 line of part 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 4x 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.
Advantages of necking-in
Necking-in allows to use a tube or a preform, an increasement of the wall thickness in the diameter reduction zone. Cost-effective preforms, short cycle times and high process reliability in production result in cost-effective manufacture.