Method and unit for forming tubular lengths of web material, particularly in a labelling machine

A unit for forming tubular lengths of web material, comprising:

• a winding body to receive and wrap a portion of said web material into a tubular configuration with opposite ends overlapping, the winding body defining an axis;
• a sealing element comprising a rectilinear strip-like active working surface adapted to cooperate with said portion of said web material wrapped around said winding body to weld said ends so as to obtain a sleeve label, wherein said working surface comprises:
• at least a first region and a second region, each region defined by a longitudinal strip region parallel to the axis of the winding body, having a height corresponding to a height of said working surface, and positioned substantially adjacent laterally to one another, independently and controllably heatable to respective first operative temperature and second operative temperature, said second temperature being lower than said first temperature,
• wherein said first region of said working surface is configured to cooperate with said portion of said web material wrapped around said winding body at a first corresponding sleeve label region, over the whole of which said ends overlap and said second region is adapted to cooperate with said portion of said web material wrapped around said winding body at a second corresponding sleeve label region, over a part of which said ends overlap,
• wherein said sealing element comprises a rectilinear bar which defines said working surface;
• and
• an actuator assembly for moving said sealing element into and out of engagement with the overlapped edges of the web material wrapped around said winding body.