TRANSFER FUNCTION ANALYSIS OF FILAMENT UNEVENNESS IN MELT SPINNING PROCESS

Abstract

Transients in melt spinning was analyzed by means of linearized perturbation equations, a valid analysis tool for small thickness variations in melt-spun filaments.Transfer function between each disturbance input and resultant filament unevenness was derived through invariant analysis on linearized perturbation equation. Theoretical transfer functions thus obtained were compared with experimental results for two different input disturbances: cooling air temperature and cooling air velocity.Results obtained are as follows;(1) Transfer functions computed and expressed in Bode diagram form show that variations in cooling air velocity and cooling air temperature are comparable to variations in extrusion rate and take up speed with respect to their effects on short term filament unevenness.(2) From result of melt spinning experiment it was found that, immediately below the spinneret, both cooling-air temperature and velocity were found to fluctuate considerably. Cooling air near the leeward filament was found to be considerably affected by the windward filament: air tempera-ture variation around the leeward filament was several times greater than the velocity variation and the leeward filament was more uneven than the windward filament.(3) Sensitivity of filament thickness variation to disturbances in cooling air velocity and cooling air temperature depends on the position where the disturbances are exerted. Under the present spinning conditions the spinline was most sensitive to cooling air disturbance approximately 7cm below the spinneret. In conclusion, variation in cooling air temperature was found to be an important cause of filament irregularity.