(57) An apparatus comprises:
- weakening promoting means (14) suitable for generating weakening line means (15,
16) on a sheet material (4), said weakening promoting means (14) (14) comprising a
serrated profile,
- gripping means (3) arranged for advancing said sheet material (4) to a forming station
(7),
- folding means (25) downstream of said forming station (7) arranged for facing an
edge portion (33) of said sheet material (4) on a further edge portion (34) of said
sheet material (4), opposite said edge portion (33),
wherein said folding means comprises comb means (25) that acts on localised zones
of said sheet material (4).
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