Process for the uninterrupted manufacture of plastic film tubing

A process for the uninterrupted manufacture of plastic film tubing by the blowing up of a continuous film tubing formed by means of an extruder-injector having a nozzle tip and blowing head, including an inner cooling of the film tubing upon extrusion by the use of a gaseous cooling medium which is introduced in a substantially liquid form into an inner space of the film tubing where it is converted to its vaporous or gaseous state through heat absorption, before being discharged through a coolant outlet, characterized by introducing a cooling medium, selected from the group consisting of carbon dioxide, nitrogen, air and fluorized hydrocarbon halides, in its substantially liquid form inside the inner space of the film tubing in such a manner that it creates a coolant stream in a center of the inner space in one direction away from the nozzle tip and blowing head of the extruder until the stream reaches a reversing point, coolant particles in one of liquid or solid form being carried and held in suspension by said stream and the coolant stream fanning out substantially radially at the reversing point before changing into a sinking coolant stream in a falling direction opposite the one direction along the wall of the film tubing up to the coolant outlet of the blowing head;

• and causing the cooling medium while introducing it inside the inner space to reach the reversing point at such a distance from the nozzle tip and blowing head that the coolant particles in one of liquid or solid form can evaporate before the cooling medium reaches a section of the film tubing which lies below a frost line located within the tubing, whereby the section of the tubing only comes in contact with a sinking or falling vaporous and/or gaseous coolant stream.