Velocity fiber spinning

Figure 6.20 Comparison between experimental and computed velocity profiles during fiber spinning using Denn and Fisher s viscoelastic model [4].

The polystyrene simulation followed the experiments of Bell and Edie (12) with good agreement. Figure 14.8 shows the simulation results for fiber spinning nylon-6.6 with a draw ratio of 40. The figure demonstrates the wealth of information provided by the model. It shows the velocity, temperature, axial normal stress, and crystallinity fields along the threadline. We see the characteristic exponential-like drop in diameter with locally (radially) constant but accelerating velocity. However, results map out the temperature, stress, and crystallinity fields, which show marked variation radially and axially. 

Isothermal Fiber Spinning of a Power Law Melt Derive the following expression for the axial velocity vz(z) resulting from the steady isothermal fiber spinning of a Power Law melt... 

FIGURE 3.22 Effect of take-up velocity on spin-line stress for polypropylene fibers at extrusion temperature of 230°C. (From Nadella, H.P., Henson, H.M., Spruiell, J.E. White, J.L. J. Appl. Polym. Sci., 1977, 21, 3003. With permission.)... 

Figures 12-13 and 12-14 show the behavior of orientation with increasing take-up velocity and spin line stress (/e, the function along the fiber axis, is the important characteristic). As expected, orientation increases with increasing take-up velocity and spin-line stress.

Fiber spinning of a Newtonian liquid (Chapter 7), including the spinneret flow and the region of velocity rearrangement, is studied using finite elements in... 

Figure 11.5. Transfer function between final area and inlet velocity for isothermal, low-speed spinning of a Newtonian liqnid. (a) Amplitude ratio (b) phase angle. Reprinted from Devereux, Computer Simulation of the Melt Fiber Spinning Process, Ph.D. dissertation, U. California, Berkeley, 1994.

The analysis of electrospinning process is based on the slender-body theory. It is widely used in fiber spinning of viscoelastic liquid. To simplify the mathematical description, a few idealizing assumptions are made. The jet radius R decreases slowly along the axial direction dR Z) dZ fluid velocity x> is uniform in the cross section of the jet. 

For unsupported polymeric membranes (i.e. hollow fibers), spinning parameters are cracial factors that must be controlled during hollow fiber preparation. These parameters include the amount and types of polymer, solvents, and additives mixed irrto the spimung dope, the dope and bore fluid flow rates, the fibre take-up velocity, the air gap distance (unless wet spinning is used), and the coagulant bath temperature [31,71]. The main challenges in hollow fiber spinning, as proposed by Puri [72], are ... 

For spinning of the textile PP mono- and multifilaments, the best solution is a laminar crossflow air quench duct with a minimum ratio of air quantity to air velocity. For spinning of fiber staple tows, the crossflowing quench air can be applied for rectangular spinnerets, i.e., inside-to-outside radial quenching, or double-direction turbulence quenching [141]. 

For polymer melts, fiber spinning results can be compared to true uniaxial extensional viscosity data measured by rod pulling. Figure 7.5.7 shows such a comparison for a low density polyethylene. We see qualitative agreement between the methods but, a very strong effect of upstream history is evident in the fiber data. Both die extrusion velocity and residence time in the die exert a big influence. 

The fiber-spinning process is used throughout the plastics industry to manufacture synthetic fibers. The process is schematically shown in Figure 4.37. The fibers are produced by the extrusion of the polymer through a die, usually of circular cross section, and taken up downstream at a higher velocity by the chill roll. The ratio of take-up velocity to extrusion velocity is known as the draw ratio (Dr). 

The fiber-spinning process is a prime example of uniaxial extension. The process consists of two regions (i) the first is the extrudate swell region, where normal forces accumulated during extrusion suddenly relax to cause swelling (ii) the second is the draw-down region, where the fiber diameter decreases according to the velocity... 

The die swell effect is neglected here as was done in the fiber-spinning analysis. In film casting no significant cooling is obtained between the face of the die and the chill-roll (see Section 5.2), whereas in the melt spinning of fibers cooling was very important. If the z component of the film velocity at the die lips is v o and at the freeze line is v, then the draw ratio, T)r, is defined as (see Eq. 9.27)... 

B.1 Isothermal Spinning of a Power-Law Fluid. Show that the axial velocity profile of a power-law fluid in the fiber-spinning process is given by the following equation ... 

In the spunbond process (Fig. 10), an aspiratory is used to draw the fibers in spinning and directiy deposit them as a web of continuous, randomly oriented filaments onto a moving conveyor belt. In the meltblown process (Fig. 11), high velocity air is used to draw the extmded melt into fine-denier fibers that are laid down in a continuous web on a collector dmm. 

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