Patent EA-004152-B1 (EA)
Title: Method for extruding a continuous moulded body
Inventor: ZIKELI STEFAN
IPC: B29C48/08
Filed: 2001-04-18
Abstract: 1. A method of extruding a continuous moulding making use of an extrusion solution, in particular an extrusion solution containing cellulose, water and a tertiary amine oxide, said method comprising the following steps: - conducting the extrusion solution through an extrusion channel having a predetermined length and a predetermined diameter up to an extrusion-channel opening; - extruding the extrusion solution through the extrusion-channel opening so as to form an extruded continuous moulding; - conducting the extruded continuous moulding through an air gap having a predetermined air-gap height; accelerating the continuous moulding in the air gap; characterized by the following method steps: - controlling the density of heat flow Q which is averaged essentially over the air-gap height (H), to a value of wherein beta is the ratio of the length (L) to the diameter (D) of the extrusion channel (8) and wherein the value of the control parameter alpha is at least 0.1. 2. A method according to claim 1, characterized in that the value of the control parameter alpha is at least 0.2. 3. A method according to claim 2, characterized in that the value of the control parameter alpha is at least 0.5. 4. A method according to claim 3, characterized in that the value of the control parameter alpha is at least 1.0. 5. A method according to one of the above-mentioned claims, characterized by the following method step: - controlling temperature (TE) of extrusion solution in dependence upon the density of the heat flow Q. 6. A method according to one of the above-mentioned claims, characterized by the following method step: - controlling the temperature (TL) of the air surrounding the continuous moulding (11) in the air gap (12) in dependence upon the heat flow density Q. 7. A method according to claim 5 and/or 6, characterized by the following method step: - controlling a temperature difference Delta=TE-TL between the temperature TE of the extrusion solution and the temperature TL of the air surrounding the continuous moulding (11) in the air gap (12) to a value of: wherein m is the mass flow of the extrusion solution through the extrusion channel opening in g/s, CE is the specific heat capacity of the extrusion solution in W/mm<3>, d is the hole density of the holes provided on the nozzle disk in hole/mm<2> and H is the length of the air gap in mm. 8. A method according to claim 7, characterized in that the value beta is at least 2. 9. A method according to claim 21, characterized in that the value beta is at most 150. 10. A method according to claim 22, characterized in that the value beta is at most 100. 11. A method according to one of the claims 5 to 10, characterized in that the temperature TL is controlled while the temperature TE is kept substantially constant. 12. A method according to one of the claims 5 to 10, characterized in that the temperature TE is controlled while the temperature TL is kept substantially constant. 13. A method according to one of the above-mentioned claims, characterized in that the specific heat capacity CE of the extrusion solution is at least 2.1 J/(g K). 14. A method according to one of the above-mentioned claims, characterized in that the specific heat capacity CE of the extrusion solution is at least 2.9 J/(g K). 15. A method according to one of the above-mentioned claims, characterized by the following method step: - controlling the acceleration of the continuous moulding (11), which is averaged essentially over the air-gap height (H), to a value of wherein beta is the ratio of the length (L) to the diameter (D) of the extrusion channel and wherein the value of the control parameter delta is at least 0.3. 16. A method according to claim 15, characterized in that the value of the control parameter delta is at least 0.6. 17. A method according to claim 16, characterized in that the value of the control parameter delta is at least 1.5. 18. A method according to claim 17, characterized in that the value of the control parameter delta is at least 2.2. 19. A method according to one of the claims 15 to 18, characterized by the following method step: - controlling extrusion velocity VE of the continuous moulding (11) through the extrusion-channel opening (10) in dependence upon the mean acceleration a. 20. A method according to one of the claims 15 to 19, characterized by the following method step: - conveying the extruded continuous moulding (11) in a substantially tensile stress free manner on a conveying means (20) to a draw-off unit (15), said conveying means (20) being arranged after the air gap (12) or a coagulation bath zone (14). 21. A method according to claim 20, characterized by the following method step: - controlling the conveying speed of the conveying means (20) in dependence upon said mean acceleration a. 22. A method according to one of the claims 15 to 21, characterized by the following method step: - drawing off the extruded continuous moulding (11), when it has passed the air gap (12), by means of a draw-off unit (15) at a drawing-off velocity VA. 23. A method according to claim 22, characterized by the following method step: - controlling the drawing-off velocity VA of the draw-off unit (15) in dependence upon the mean acceleration a. 24. A method according to one of the claims 15 to 23, characterized by the following method step: - controlling the extrusion velocity VE of the continuous moulding (11) through the extrusion-channel opening (10) and/or the drawing-off velocity VA of the continuous moulding (11) by the draw-off unit (15) according to the following formula: wherein H is the air-gap height and gamma is a correction factor having a value between 7 and 7.4. 25. A method according to claim 24, characterized in that the value of the correction factor gamma is approx. 7.2. 26. A method according to one of the claims 15 to 25, characterized by the following method step: - drawing the extruded continuous moulding when it has left the extrusion channel opening in the air gap (12) by means of an airflow flowing around the continuous moulding in the direction of extrusion, the flow velocity of the air (13) exceeding the extrusion velocity of the continuous moulding (11). 27. A method according to claim 24, characterized by the following method step: - controlling the velocity of the air (13) in dependence upon the mean acceleration a and/or mean density of heat flow Q in the air gap.