Oven for drawing fibres at elevated temperature

1. Oven for drawing fibre at elevated temperature, comprising:

guide rolls on two sides of the oven opposite one another, the guide rolls dictating a zigzag up-and-down drawing trajectory for the fibre in the oven which is at least 20 meters long,

driving mechanisms associated operatively with each of the guide rolls for driving each of the guide rolls at a selected peripheral velocity,

a control system operatively connected to the driving mechanisms for separately setting and controlling the selected peripheral velocity of each of the guide rolls so as to draw the fibre as it traverses the drawing trajectory in the oven, and wherein

the control system includes devices for determining the power uptake of the driving mechanisms so that each of the guide rolls may be driven at a selected peripheral velocity so as to prevent slip between the fibre and the guide rolls.

2. Oven according to claim 1 , wherein the guide rolls are cylindrical and have a length of at least 20 cm, several fibres being able to be passed over the guide rolls simultaneously next to one another.

3. Oven according to claim 2 , wherein the bending of the roll during the drawing is less than 0.1%.

4. Oven according to claim 1 , wherein the drawing trajectory is at least 50 m and the oven contains at least 4 guide rolls.

5. Oven according to claim 1 , further comprising devices for creating a gas flow in a direction substantially perpendicular to the transport direction of the fibres between the guide rolls.

6. Oven according to claim 1 , further comprising devices for heating or cooling the gas stream to create a temperature gradient in a direction perpendicular to the transport direction.

7. Oven according to claim 1 , further comprising a gas purification installation.

8. Process for drawing a fibre containing solvent, which comprises:

passing the fiber at elevated temperature inside an oven via driven guide rollers on two opposite sides thereof, said driven guide rollers dictating a zigzag up-and-down trajectory which is at least 20 meters long,

driving each of the guide rollers at a selected peripheral velocity by driving mechanisms,

controlling the drive mechanisms by a controller so as to separately set and control the selected peripheral velocity of each of the driven guide rolls to draw the fibre as it traverses the drawing trajectory in the oven, wherein

the step of controlling the drive mechanisms comprises determining the power uptake of the driving mechanisms to allow each of the guide rolls to be separately controllably driven by the controller at the selected peripheral velocity which prevents slip between the guide roll and the fiber, and

recovering the solvent being removed from the fiber, in a gas purification installation operably connected to said oven.

9. Process according to claim 8 , further comprising creating a temperature gradient in the oven in the direction perpendicular to the transport direction of the fibre, wherein the temperature is higher at the end of the drawing trajectory.

10. Process for producing a highly oriented polyethylene fibre, comprising drawing, in a single step, a lowly oriented polyethylene precursor fibre in an oven as set forth in any one of claims 1 , 2 , 3 , 4 , 5 , 6 or 7 , at a drawing temperature of between 135 and 160° C. and a draw ratio of at least 2.5 to form a highly oriented polyethylene fibre having a tensile modulus of at least 1000 g/den and a strength of at least 30 g/den.

11. Process according to claim 10 , wherein the precursor fibre has a tensile modulus of between 150 and 500 g/den and a tensile strength of between 5 g/den and 20 g/den.

12. Process according claim 10 , wherein the drawing temperature is virtually the same in all parts of the oven.

13. Process according to claim 10 , wherein the precursor fibre has been made by drying and simultaneously drawing in an oven which on two sides opposite one another, is provided with guide rolls dictating a zigzag up- and- down drawing trajectory for the fibre in the oven, wherein the drawing trajectory is at least 20metres long and the guide rolls are driven by driving mechanisms, and wherein the fiber is a polyethylene gel fibre containing solvent, said oven further comprising a gas purification installation, removing the solvent and recovering the solvent in the gas purification installation.

14. Process according to claim 13 , wherein the temperature of the fibre is in all parts of the fibres trajectory through the oven more than 10°lower than the melting temperature of the lowly oriented precursor fibre to be formed.

15. Process according to claim 14 wherein the temperature of the gas is in all parts of the oven more than 10°lower than the melting temperature of the fibre to be formed.

16. Oven according to claim 1 , wherein the driving mechanisms include electromotors.