A method to make an airtight wrapper having a structured assembly completely wrapped by a wrapping sheet made of a weldable material, said structured assembly having a group of smoking articles partly wrapped by a reinforcement insert, said method comprising:
- positioning the wrapping sheet, folded to a “U” shape, with respect to the structured assembly, so as to define a first larger panel and a second larger panel of said wrapping sheet in contact with respective larger walls, front and rear, of said structured assembly, and a first smaller panel of said wrapping sheet in contact with a smaller head wall of said structured assembly,
- wherein said wrapping sheet, once positioned with respect to the structured assembly, respectively has:
- an upper flap connected to said first larger panel and a lower flap connected to said second larger panel, said upper flap and said lower flap protruding beyond a smaller bottom wall of said structured assembly,
- upper transverse flaps , connected to said first smaller panel (135), and protruding laterally from said smaller head wall,
- rear, and front longitudinal flaps, respectively connected laterally to said first larger panel and to said second larger panel and which protrude beyond respective smaller lateral walls of said structured assembly;
- bringing said lower flap and said upper flap nearer to each other and welding them to each other, defining:
- a transverse edge formed by the welded lower flap and upper flap, disposed substantially aligned with said larger front wall,
- a second smaller panel disposed folded, adjacent to said smaller bottom wall, between said second larger panel and said lower flap to which it is connected by a transverse folding line,
- lower transverse flaps, connected to said second smaller panel, and protruding laterally from said smaller bottom wall and opposite said upper transverse flaps;
- folding said transverse edge on said first larger panel and on said front longitudinal flaps, rotating said transverse edge by 180° along said transverse folding line toward said larger front wall of said structured assembly;
- folding the upper and lower transverse flaps toward said smaller lateral walls;
- folding the rear and front longitudinal flaps toward said smaller lateral walls, overlapping one on top of the other, and also part of said transverse edge, above said transverse flaps, and welding said rear and front longitudinal flaps with respect to each other to seal said airtight wrapper,
- wherein said method further comprises:
- making at least two cuts in said wrapping sheet, defining two free lateral fins and a central portion of said lower flap, said at least two cuts being made in a position such as to separate, before folding the lower transverse flaps toward said smaller lateral walls, said lower flap from the respective lower transverse flaps, so as to be able to fold said lower transverse flaps freely with respect to said transverse edge,
- wherein, during the folding of said front longitudinal flaps, said lateral fins of said transverse edge overlap in a planar and extended shape, without substantial deformations, on said longitudinal flaps.