Spinning processing method and apparatus therefor

A spinning processing apparatus for forming a section of reduced diameter in a metal tube, comprising:

• means for supporting and rotating the metal tube round a longitudinal axis thereof;
• a plurality of forming rollers arranged around the metal tube;
• means for rotating said forming rollers round the longitudinal axis of the metal tube in a direction opposite to a direction of rotation for the metal tube;
• a driving mechanism for radially driving the forming rollers toward the metal tube longitudinal axis to forcibly push the forming rollers on the metal tube;
• and
• means for moving the forming rollers relatively to the metal tube in an axial direction thereof.

A spinning processing method, comprising:

• rotating a metal tube around a longitudinal axis thereof;
• rotating a plurality of forming rollers, arranged around the metal tube, round the longitudinal axis of the metal tube in a direction opposite to a direction of rotation of the metal tube;
• radially moving the forming rollers toward the metal tube longitudinal axis into pressure contact with the metal tube, while moving the forming rollers relatively to the metal tube in an axial direction thereof, to draw the metal tube to form a section of reduced diameter;
• and
• during moving the forming rollers radially and relatively to the metal tube, setting a relative rotation speed between the forming rollers and the metal tube higher than a relative moving speed between the forming rollers and the metal tube in the axial direction so that a deviation between a spiral locus and a roller angle of the forming rollers is reduced to a negligible level.