Melt spinning heat transfer

The manufacture of large monofilaments, certainly larger than 100 denier, must be carried out in a water-quench process because of the inherent limitation of forced convective heat-transfer with gases. Conventional screw extruders are used for melting and conveying the polypropylene resin, just as in the case of the melt-spinning processes described above. Often, however, there are no metering pumps used in the process. 

The three processes have many features in common. The conversion of the spun polymer melt or solution to a solid fibre involves cooking, solvent evaporation or coagulation depending on the spinning type used. Cooling of a fine filament is generally very rapid solvent evaporation involves simultaneous outward mass transfer and inward heat transfer while coagulation involves both of the two-way mass transfers. 

The distinction between them is made by the technique used for solidification. Melt spinning consists of extruding a molten polymer and into an appropriate medium (gas or liquid), where it is solidified by the transfer of heat. Dry spinning involves the extrusion of a polymer solution into a heated gas, where the solvent is removed and the fiber solidified. Wet spinning represents the extrusion of a polymer solution into a liquid chemical bath. The subsequent solidification takes place by mass transfer. In reaction spinning, a prepolymer (partially reacted material) is extruded into a heated fluid medium, where solidification takes place by chemical reaction. 

Wet spinning represents a somewhat different case from melt or dry spinning. For example, temperature effects and heat transfer play a much smaller role than in the other two principal spinning types. On the other hand, pre-extrusion effects may be more important for wet spinning than for dry spinning. Unfortunately, data related to such effects are even sparser for wet spinning than for melt spinning. 

J. L. White, Dynamics, heat transfer and rheological aspects of melt spinning a critical review, Polym. Eng. Rev. 1, 297-362 (1981). 

The processes we have considered thus far - extrusion, wire coating, and injection and compression molding - are dominated by shear between confined surfaces. By contrast, in fiber and film formation the melt is stretched without confining surfaces. It is still possible to gain considerable insight from very elementary flow and heat transfer models, but we must first parallel Section 2.2 and develop some basic concepts of extensional flow. The remainder of the chapter is then devoted to an analysis of fiber formation by melt spinning. 

The fundamental analysis of dry spinning is much less advanced than that of melt spinning. In the formulation of the spinline equations, it is necessary to take into consideration both heat and mass transfer as well as the force balance and the variation of the elongational viscosity with both temperature and solvent concentration. ... 

Heat Transfer Coefficient and the Melt-Spinning Process... 

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