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Étude expérimentale et modélisation thermomécanique de l'étape de calibration dans le procédé d'extrusion de tubes en polyamide 12

Abstract : In polyamide 12 tube extrusion, calibration - or sizing - is the key step that affects subsequent mechanical properties. In external calibration, the extruded tube is pulled through a cylindrical calibrator located in a water tank under vacuum. The level of vacuum (DP) is adjustable. A water flow rate (DSU) is applied at the calibrator inner side creating a lubricant water layer at the polymer outer surface. Influence of calibration is twofold. Since it combines a quenching and a mechanical drawing of the tube external surface, high molecular orientation is generated in this zone. Simultaneously, the surface state of the tube can be affected by local catching to the calibrator surface. On-line video recording and lubricating water layer thickness measurements have been carried out to monitor the lubrication dependence of the polymer drawing kinematics. We have shown quantitatively that increasing the water layer thickness leads to a diminution of the draw ratio in calibrator, DrCAL (ratio between line velocity and velocity at the calibrator entrance). Lubrication and surface state have been correlated through microtopography. Tube molecular orientation was characterized by X-ray diffraction, light microscopy and birefringence measurements. Excellent correlation has been found between tube superficial crystalline orientation (DnSKIN) and DrCAL: a reduced elongation of the polymer in the calibrator leads to less superficial orientation. A thermomechanical model was also used to predict temperatures in the tube thickness and to show how drawing forces, concentrated at the external skin during the crystallization, lead to orientation. Besides, elongation at break has been found to strongly depend on DnSKIN and on the surface defects resulting from calibration. By showing the relationships between process parameters, tube structure, and mechanical properties, this study enables us now to fit the calibration parameters to improve lubrication and reduce the draw ratio in calibrator, in order to obtain strongly better properties.
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Submitted on : Monday, June 26, 2006 - 8:00:00 AM
Last modification on : Wednesday, November 17, 2021 - 12:27:20 PM
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  • HAL Id : pastel-00001816, version 1


Aurélien Carin. Étude expérimentale et modélisation thermomécanique de l'étape de calibration dans le procédé d'extrusion de tubes en polyamide 12. Sciences de l'ingénieur [physics]. École Nationale Supérieure des Mines de Paris, 2005. Français. ⟨NNT : 2005ENMP1313⟩. ⟨pastel-00001816⟩



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