Method of and apparatus for controlling the diameter of a clear extruded tube

摘要

The diameter of a molten clear extruded tube of a non derivatized cellulose solution is controlled by maintaining volume of clear liquid within the tube. The level of the liquid rises in response to a decrease in the diameter of the tube. A light beam passing through the tube is refracted in a straight line path when the liquid level rises above the level of the beam. The diameter of a molten clear extruded tube of a non derivatized cellulose solution extruding downwardly from an extrusion die is controlled by maintaining volume of the clear liquid within the tube. The level of the liquid rises in response to a decrease in the diameter of the tube. A light beam passing through the tube is refracted in a straight line path when the liquid level rises above the level of the beam. The refracting of the beam in turn triggers the introduction of air into the extruded tube to increase the diameter of the extruded molten tube. Independent claims are also included for the following: (a) extruding a transparent molten tube of non derivatized cellulose downwardly through an air gap and a mandrel having a stem terminating into a tube containing an internal bath of a clear liquid. The method comprises passing a refractable beam through the tube at a selected level above the enlarged lower portion of the mandrel. The beam is in a plane offset from the mandrel stem to prevent blockage of the beam's passage. The beam passes in a straight line path through the tube when the internal path of the clear liquid is below the level of the beam. The beam is refracted from its path when the liquid level rises above the selected level of the beam. This indicates a decrease in diameter of the tube. Air is introduced under pressure into the interior of the extruded tube. The refracted beam increases the diameter of the tube in the region of the air gap and lowers the internal bath level to a level below the selected level of the beam. The introduction of air into the tube is terminated in response to the straight line passage of the beam through the tube; and (b) an apparatus for controlling the diameter of the extruded tube which comprises: (i) an extrusion die for downwardly extruding a clear tube composed of a molten non derivatized cellulose solution; (ii) a volume controller for maintaining the volume of the clear liquid within the tube; (iii) a refractable beam of light emitter which emits light in a straight line path at a selected level above the liquid level in the tube; (iv) the tube and the liquid forming a lens for refracting the beam; and (v) sensor to sense the refraction of the beam.