The present invention is directed to the welding of a trailing sheet tail on a roll of sheet material to an underlying layer of the sheet material on the roll to form a finished roll product ready for packaging. A device for effecting the welding comprises a thermally conductive, heat sealing disk mounted for rotation about an axis, and a heating element for heating an inner portion of the disk so as to cause thermal conduction through an outer portion of the disk towards an outer peripheral surface thereof. The heat sealing disk is mounted for engagement with the outer surface of the trailing sheet tail to weld this tail to the underlying layer of sheet material on the roll.