means for making a pre-formed carton to proceed in a progress direction, the said carton having a plurality of side flaps or panels folded along folds which are essentially parallel to the said progress direction, on a central portion of the carton;

a movable element designed to move between a first position away from the route of the carton and a second position in which the said element is designed to be inserted underneath at an edge of at least one of said side flaps or panels, so that the latter is raised with respect to the said central portion in cooperation with the carton progress; and

folding means designed to fold a plurality of flaps or panels hinged by means of suitable longitudinal creases onto the said central portion, before one of the said flaps or panels are raised with respect to the central portion by the movable element, wherein the said folding means are section bars arranged longitudinally along the route of the carton and may be moved in a direction perpendicular to the said route, having a first end facing the direction of origin of the carton, with a rounded corner and arranged vertically to fit under the said flaps or panels, and a second end arranged parallel to the surface onto which the carton can be placed and above the said surface, the said section bars featuring, between the two ends, a twisting cross section.