Instabilities in the Spinning Zone Draw Resonance

Draw resonance occurs in the extensional flow region of the spinning line after the extrusion of the filament. Draw resonance is the periodic fluctuation of the filament diameter at the take-up of the spinning line. Draw resonance manifests itself at a critical draw ratio as sustained periodic oscillations in spinline variables such as filament cross section and tension despite maintaining constant extrusion rate and take-up velocity. It can be recorded as a systematic deviation from unity in the ratio of maximum to minimum diameter of the drawn filament with increasing draw ratio. 

Draw resonance is an undesirable behavior of polymer fluids, which affects the stability of polymer processing. Avoiding draw resonance or draw resonance-induced spin breaks is essential in producing continuous fibers having uniform thickness and properties. 

This phenomenon has been observed in both Newtonian and power law fluids (non-Newtonian) and is experimentally found to be closely related to polymer properties (molecular stmcrnre, molecular weight distribution, shear viscosity, relaxation time, power law index) as well as to the spinning variables, such as draw ratio, cooling rate, melt temperature, and die geometry, and so on. 

Draw resonance is a hydrodynamic instability and not a viscoelastic one, albeit the former can be affected by fluid viscoelasticity. Thus, even Newtonian fluids can exhibit this phenomenon [8]. It has been reported both theoretically and experimentally that a Newtonian liquid sustains in-phase oscillations in force and area at draw ratios of 20 [9, 10]. Hence, the critical draw ratio for Newtonian fluids is taken as 20. This is true for an isothermal spinning system. 

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