System for vacuum-refeeding sheets, in particular corrugated board sheets, to be used in printing and die cutting machines

A sheet-refeeding system for vacuum refeeding sheets, provided in a printing and die cutting machine also having a sheet-printing unit and a die cutting unit including a die cutter-holding cylinder, the system comprising:

• a support closure structure shaped as a hood having an interior, said support closure structure having an upper side and a bottom side;
• a central box located on said upper side of said support closure structure, said central box being open towards said support closure structure, whereby the interior of said box communicating at a lower side thereof with the interior of said support structure;
• a suction device positioned inside said central box;
• and
• a sheet-conveying unit fixed to said support closure structure at said lower side of said support closure structure,
• said sheet-conveying unit including:
• a first sheet-dragging motored knurled roller, located at an inlet of the refeeding system immediately downstream of an outlet roller of said sheet-printing unit;
• at least one second sheet-dragging motored knurled roller, placed at the inlet of the refeeding system immediately downstream of said first sheet-dragging motored knurled roller;
• a covering plate at which said first sheet-dragging motored knurled roller and said at least one second sheet-dragging motored knurled roller are positioned, said covering plate having at least two side slits through which said first sheet-dragging motored knurled roller and at least one second sheet-dragging motored knurled roller project to contact sheets being conveyed, said covering plate also having a plurality of rows of small holes, said rows of small holes being positioned upstream, downstream and between said side slits;
• at least one sheet-conveying line composed of a plurality of idle drive rollers, said sheet-conveying line being located below said central box and being immediately downstream of said at least one second sheet-dragging motored knurled roller;
• a driving pulley;
• an idle pulley;
• and
• at least a pair of toothed belts each located at a side of said sheet-conveying line, each of said toothed belts including on an external surface thereof a plurality of small dragging blocks acting on the sheets being conveyed from above to drag the sheets being conveyed, each of said toothed belts being driven by said driving pulley and said idle pulley to adjust an outlet speed of the sheets to the speed of inlet rollers of said die cutting unit downstream of the sheet refeeding system.