A model of melt spinning has been developed for speeds above which the effects of gravity, inertia, and aerodynamic drag become significant. The model has as an upper bound the speed at which stress crystallization begins to occur on the spin line. For poly(ethylene terephthalate), these velocities are approximately 750 and 3500 meters/minute. The calculated temperature and velocity profiles are shown to agree with measured values. The stress at the freeze point is calculated and found to correlate well with the spun yarn birefringence which, in turn, is shown to predict uniquely the spun yarn physical properties on a “simple” spin line. The stress‐optical coefficient derived from the calculated stress at the freeze point and measured birefringence agrees well with the literature.
In recent years the spinning speeds of poly(ethylene terephthalate) (PET) fiber have increased to the point that significant structural development is being observed in the spun yarn. At even higher speeds significant crystallization has been obtained. Data characterizing these yarns will be presented and discussed showing the development of crystals and that the onset of this phenomena is related to the stress at the “freeze point.” The “freeze point” rises from around Tg at low speeds to the order of 200°C at high speeds. The spinline itself has been characterized by velocity and orientation profiles which show the crystallization process is extremely rapid, occurring over a few centimenters of the spinline.
A visualization study of the flow of fiber‐filled resin through cylindrically convergent channels has been conducted. Epoxy resins filled with glass fibers were tested to simulate the flows experienced during the processing of fiber reinforced thermoplastics. Specific phenomena which have been investigated include the kinematics, orientation of the suspended fibers, formation of possible unwanted stagnant eddies at the entrance of the channel, and the fiber length degradation. It was found that the extensional flow in the convergent channel plays an important role in orienting the fibers.
An investigation has been made of transient heat transfer and water removal on an unfelted cylinder dryer. This investigation has included the development of a theory for describing conduction of heat in the drying material and an experimental testing of the adequacy of the theory.The theory describes the heat transfer and evaporation of water in terms of a second-order partial-differential equation and appropriate boundary conditions. Numerical solutions obtained on a digital computer are presented.The experimental work, performed on a specially constructed laboratory dryer, included measurements of temperatures a t internal points in a drying sheet and also measurements of water removed during drying.Good agreement was found between theory and experiment, and the usefulness of the theory is demonstrated in the analysis of water removal in some drying experiments.Although the work was primarily concerned with a description of the paper drying process, the methods should apply equally well to the drying of other materials on heated cylinders.
The flexibility and stress-intensification factors presently applied in piping-flexibility analysis to account for the behavior of curved pipe in bending have been derived from theories and tests with no internal pressure. Pressure tends to reduce the effect of these factors but in smaller and relatively thick-wall piping commonly used in the past the effect is of a low order and may be neglected; in larger diameter relatively thin-wall piping the effect is pronounced and significant. Using strain-energy methods the present paper develops a theory establishing the flexibility and stresses due to in-plane and out-of-plane bending including the effect of internal pressure, and proves its adequacy by means of carefully conducted tests. In a final step, the complex theoretical formulas are reduced to a simple and readily usable approximation.
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