Machine and method for forming boxes of paper or cardboard

A quadrangular machine for forming boxes from paper or cardboard blanks having a base and a plurality of segments connected to the base, comprising:

• a die operating on the base of the blank and movable along a direction of vertical movement;
• folding elements configured to interact with the segments of the blank to fold them and set them upright with their lateral sides juxtaposed to define vertical edges of the box;
• a plurality of feeders configured to unroll heat seal stay tapes and position pieces of predetermined length of the stay tapes vertically to face the vertical edges;
• a plurality of sealing heads equipped with corresponding pressers, which are heatable and movable towards and away from the box perpendicularly to the direction of movement to press the pieces of heat seal stay tape against the respective edges, and with corresponding blades which are movable as one with the pressers to cut the heat seal stay tapes,
• wherein each of the pressers comprises at least one portion which is movable independently of the corresponding blade towards and away from the box to press a corresponding portion of the heat seal stay tape against the respective vertical edge whilst the corresponding blade is at a position of non-interference relative to the heat seal stay tape.