Method and apparatus for helical cutting of a tubular film

An apparatus for helically cutting a flexible tubular film of substantially predetermined diameter into a flat strip comprising a reel of lay flat tubular film, a rotating unwind device for discharging the lay flat tube from the reel, the unwind device being arranged to rotate either

• a) by installing the reel in an unwind stand which makes the axis of the reel rotate around its middle point, while the lay flat film is discharged from the reel in a discharge zone extending parallel with its rotating axis;
• or
• b) by keeping the axis of the reel fixed and unwinding the lay flat film by means of spinning devices rotating around the reel, whereby the discharge zone parallel with the axis of the reel is brought to spin around the reel together with the spinning devices, and the lay flat film is hauled off over one end of the reel, such that it will rotate around its middle axis with the same rotational velocity as that of the spinning devices;
• supply means for supplying the flattened tubular films to a first position, means at the first position for advancing the flattened film at a substantially predetermined velocity from the first position to an expansion zone where it is expanded from the flattened form into a circular cylindrical form, the axis of the cylinder being aligned with the axis of rotation of the rotating unwind device, a generally circular cylindrical mandrel over which the expanded cylindrical tubular film is passed axially thereof, cutting means for helically cutting the cylindrical tubular film passing along the mandrel into a flat strip, and means for removing the helically cut strip from the mandrel at an angle to the mandrel axis, wherein the mandrel is hollow with an external diameter slightly less than the diameter of the expanded tubular film, and comprising means in the expansion zone for supplying air continuously through the hollow mandrel in the direction of the first position under a pressure sufficient to inflate the flattened tubular film into a stiff generally circular cylindrical tube that makes a sliding fit with the mandrel and resists deformation during the helical cutting thereof, characterized by comprising moveable support means placed around the outside of the tubular film in a generally circular arrangement close upstream of or at the upstream end of the mandrel arranged to drive the cylindrical surface of the tube with an axial and circumferential component of movement aligned with the axial movement of the film and the rotation of the rotating unwind device.