Spin pack

Good pack design ensures that the melt inside the pack flows in a symmetrical manner with respect to the spinneret. If the spinneret is round, the melt flow in areas above the spinneret should be symmetrical with respect to the spinneret axis. If the spinneret is rectangular, the flow should be symmetrical with respect to the planes passing through the center lines in both the length and width directions. Care should also be taken to eliminate stagnant areas. 

The spinneret orifices or capillaries are contained in the lower part of the spinneret and are round for producing round fibers or in almost any shape desired. Triangular, trilobal, and octalobal fiber cross sections are common and are designed for luster and fiber feel eharaeteristics. The face of a spinneret is generally coated with a silicone spray to prevent resin from adhering to the spinneret. 

Die swell is always present in polypropylene spinning because its melt is viscoelastic. The viscoelasticity also gives rise to melt fracture if temperatures are too low or if orifice shear rates are too high. Melt fracture must be avoided. 

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Spinning pack Chimney air chamber Filaments Chimney door Convergence guide Insert tube Threading air valve... 

The melt-spinning process used to convert mesophase pitch into fiber form is similar to that employed for many thermoplastic polymers. Normally, an extruder melts the pitch and pumps it into the spin pack. Typically, the molten pitch is filtered before being extruded through a multi-holed spinnerette. The pitch is subjected to high extensional and shear stresses as it approaches and flows through the spinnerette capillaries. The associated torques tend to orient the liquid crystalline pitch in a regular transverse pattern. Upon emerging from the... 

Finally, the importance of using optimum processing conditions is illustrated in Table VI. Here similar formulations were examined but the spin pack temperature used in the preparation of the yarns was incresed. Both the oligomeric HALS 4 and 6 gave yarns with improved light stability when processed at the higher temperature. 

Undesirable adhesion to metal surfaces may cause a problem in injection molding, melt spinning, and thermoforming. In the melt spinning of PAS a variety of adhesion-related problems have been observed. These problems include the build up of polymer on spinneret surfaces resulting from both initial filament extrusion and lick-back from filament breaks. These adhesion-related problems lead to prematme spin pack failure and equipment down-time to replace spent spinneret packs, and can limit the use of PAS in certain melt spinning operations. 

A. James, Principles of spin pack design a guide to selecting components, Int. Fiber J., 1997,12, 2. 

The spin pump (metering pump) delivers the molten polymer to a spin pack, which consists of a top cap and a breaker plate to distribute polymer evenly, then into a filtration media and out of the spinneret. The filtration media contains either different layers of special sand, layers of different size of stainless steel screens, or sintered metals. In addition to removing the foreign particles, gel particles and undesirable conglomerate additives, filtration may also improve the polymer melt homogeneity due to its torturous path and high shear of the filtration media. 

Dwell time n. The time during a process in which a particular substance remains in one location (e.g., the time during which molten polymer remains in a spinning pack). 

Sand sand n. Used as a filter medium in fiber manufacture, particularly used in spinning packs for nylon or polyester production. 

A basic design of a melt spinning process is illustrated in Figure 1. Polymer, in the form of pellets or granules, is fed into an extmder, where it is melted and pumped via a positive displacement pump to the melt spin pack. The spin pack consists of filters and channels that supply... 

Typical equipment used to make PET fibers is shown in Figure 6. Prior to melting, the polymer chips must be thoroughly dried, t5q)ically under vacuum at elevated temperature for several hours. The equilibrium moisture content of PET imder ambient conditions is about 0.5% (11) and this much moisture would cause imacceptable levels of depolymerization. The dried polymer chips are fed to an extruder which melts the chips and forwards them to a metering pump, which delivers a volumetrically controlled flow of polymer into a heated spinning pack. 

FIGURE 20.1 Schematic representation of melt spinning setup (1) extruder drive, (2) extruder, (3) hopper, (4) screw, (5) manifold, (6) static mixer, (7) metering pump, (8) metering pump drive, (9) spin pack, (10) mesh filters, (11) distributor, (12) spinneret, (13) cross-flow quench chamber, (14) freshly spun yam, (15) godet, (16) idler roller, (17) friction-driven winder, (18) yarn bobbin. 

The dried polyester polymer is transported to extruders where it is melted, and piunped to spinning packs held in a spin manifold. The spin packs contain spiimeiets with a large number of fine holes through which the melted polymer flows to form filaments. Any contaminants in the polymer are removed by filtration prior to the spinneret. Different spinneret designs enable a wide range of fibre cross-sections to be produced including solid round, hollow and trilobal. 

A conventional spinning plant essentially consists of melting and filtration systems, melt distribution pipes for static mixtures, melt dosing pumps, a side color melt extruder, spinning packs, a quenching system, a takeup system, spin-finish baths, and a draw and heat system [29, 30]. 

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