Folding unit and method for forming an empty cardboard box by folding a blank around a mandrel

A folding method for forming an empty cardboard box (2), the folding method comprising the steps of:

• folding a blank (9) around a mandrel (37) supported by a folding head (36) so as to form the empty cardboard box (2);
• and
• moving at least two parts (49, 50) of the mandrel (37) relative to one another between an expanded configuration, in which the at least two parts (49, 50) are further from one another so as to confer a maximum size to the mandrel (37), and a contracted configuration, in which the at least two parts (49, 50) are closer to one another so as to confer a minimum size to the mandrel (37);
• wherein the folding head (36) supports the mandrel (37) so as to slide the mandrel (37) between a work position in which the mandrel (37) completely protrudes in a cantilever fashion from the folding head (36), and a transfer position in which the mandrel (37) moves backwards from the work position with a stroke that is greater than an axial extension of the empty cardboard box (2);
• wherein by moving from the expanded configuration to the contracted configuration and by moving from the work position to the transfer position, the mandrel (37) is axially and completely unraveled from the empty cardboard box (2) that has just been formed;
• and
• wherein the folding head (36) supports at least one locking element (47) which is arranged on a side of the mandrel (37) and is movable between a locking position, in which the at least one locking element (47) is pressed against a corresponding side wall of the mandrel (37), and a release position, in which the at least one locking element (47) is far from the corresponding side wall of the mandrel (37).

A folding unit (20) for forming an empty cardboard box (2), the folding unit (20) comprising:

• a mandrel (37) around which a blank (9) is folded to form the empty cardboard box (2);
• a folding head (36) which supports the mandrel (37);
• a storage unit (38) containing a pile of blanks (9);
• a folding drum (34) that rotates with a continuous motion around a first rotation axis (35) and supports the folding head (36) provided with the mandrel (37) so as to move the folding head (36) between a feeding station (S2) in which the blank (9) is coupled to the mandrel (37) and a transfer station (S3) in which the empty cardboard box (2) is released from the mandrel (37);
• and
• folding means, which are arranged between the feeding station (S2) and the transfer station (S3) and which fold the blank (9) into a tubular shape around the mandrel (37) so as to form the empty cardboard box (2);
• wherein the mandrel (37) comprises at least two parts (49, 50) which are mobile with respect to one another between an expanded configuration in which the at least two parts (49, 50) are further from one another so as to confer a maximum size to the mandrel (37), and a contracted configuration in which the at least two parts (49, 50) are closer to one another so as to confer a minimum size to the mandrel (37);
• wherein the folding head (36) supports the mandrel (37) so as to slide the mandrel (37) between a work position in which the mandrel (37) completely protrudes in a cantilever fashion from the folding head (36) and a transfer position in which the mandrel (37) moves backwards from the work position with a stroke that is greater than an axial extension of the empty cardboard box (2);
• and
• wherein by moving from the expanded configuration to the contracted configuration and and by moving from the work position to the transfer position, the mandrel (37) is axially and completely unravelled from the empty cardboard box (2) that has just been formed.