Take-up speed

Wow Strike ought to consider taking up speed as a second habit. Those reductions looked freaking easy ... 

The blends were prepared with two take-up speeds to achieve morphologies with different LCP fiber dimensions. The lower speed (L), leading to a draw ratio of 1 1, represents the normal blending procedure, which was what we used in our previous work [44]. The higher speed (H) resulting in a draw ratio of 6 1 was applied to form long highly oriented LCP fibers. The draw ratio for each strand was determined as the ratio between the die and strand cross-sections (Sq/Ss). 

The tensile properties of the extruded blends and composites are presented in Table 2. Compared to the neat PP, a clear reinforcement was achieved after twin-screw blending. The reinforcing effect was even more pronounced with the higher take-up speed (H), evidently due to the extremely fibrillar morphology, as seen in Fig. 3. 

Blends of polypropylene (PP) and liquid crystalline polymer (LCP) processed without melting the LCP were compared with conventional melt processed blends. In a first stage, PP was blended with 20 wt% of LCP in a twin-screw extruder with the take-up speed varied to achieve blends with different LCP fiber dimensions. In the second stage, these blends were processed both below and above the Tm of the LCP by extrusion and injection molding. 

We control fiber properties by changing the relative speeds of different stages of the process. Orientation is increased and fiber thickness decreased by increasing the final take-up speed relative to the rate at which the molten polymer strands leave the spinneret. To produce high modulus fibers we generally adopt conditions that maximize orientation. Fiber diameters... 

Brown and Chuah [84] and Oppermann el ol. [36] studied the spinning of partially oriented yam (POY) as a function of take-up speed from 500 to 5000m/min. Figures 11.18 and 11.19 show, respectively, development of the tenacity and elongation as a function of spinning speed. Tenacity increases with increasing... 

Figure 11.18 Tenacity of PTT fibers as a function of winder take-up speed, showing the effect of dpf and spinnerette diameter. Fibers indicated with filled symbols were spun with 0.35 mm diameter spinnerettes, while those indicated with open symbols were spun with 0.3 mm diameter spinnerettes...

The melt spinning process for PET fibers can be divided into three regions of take-up speed, as follows ... 

Ziabicki and Jericki reported the crystallization characteristics of PET as well as a theory of molecular orientation and oriented crystallization [5a], Besides these theoretical considerations, the rate of recrystallization understandably seems to play an important role, particularly in high-speed spinning. Little is known about the crystallinity gradient caused during melt spinning at high take-up speeds. 

The different recrystallization behavior as revealed by differential scanning calorimetry (DSC) complicates the understanding of structure formation as a dependence of take-up speed and seems to particularly correspond to the... 

Figure 13.3 Crystalline (fc) and amorphous (fa) orientation factors as a function of take-up speed for the three PET samples described in Table 13.1 , branched , linear (IV, 0.66) A, linear (IV, 0.61) [13]. From Some effects of the rheological properties of PET on spinning line profile and structure developed in high-speed spinning, Perez, G., in High-Speed Fiber Spinning, Ziabicki, A. and Kawai, H. (Eds), 1985, pp. 333-362, copyright (1985 John Wiley Sons, Inc.). Reprinted by permission of John Wiley Sons, Inc.

Figure 13.3 also shows the orientation factors of the crystalline and amorphous regions as a function of take-up speed, which is pronounced in the case of a branched PET polymer. The shift towards increased freezing temperatures in branched polymer samples seems to be an indicator of higher elasticity (Figure 13.4). 

George, H. H., Model of steady state melt spinning at intermediate take-up speeds, presentation given at the Joint Meeting of the US and Japanese Rheological Societies, Kona, HI, 6-9 April, 1979. 

A rapid method for determining the melt strength has been developed by Busse (1967). He extruded a polymer melt through a standard orifice at a given temperature and a standard rate. The thread obtained was taken up on a pulley with variable speed. During a test the take-up speed was gradually increased until the thread broke, while the tension was recorded as a function of time. 

Pennings and his collaborators have examined the hot drawing behaviour of the range of spun fibres. The fibres were stretched between moving rollers, and the draw ratio determined as the ratio of the take-up speed on the second roller to the... 

Fig. 3. Tensile strength at break, a, after hot-drawing against take-up speed during gel-spinning of UHMWPE at different concentrations of aluminium stearate (wt.- %) in the spinning solution (Die e = 14.5 cm, a = 6" and D = 1.8 mm). With permission of the publishers Chapman Hall Ltd, (C)...

Profile extrusions are the most difficult to make because changes in take-up speed or screw rotational speed alone are not enough to compensate for deficient product dimensions. In the case of sheet and film, if the edges of the sheet are not at the target thickness, they can be trimmed off and sent back to the extruder... 

Process conditions inlet melt temperature, mass flow rate into the die passage (or pressure at the inlet), die wall temperature, and take-up speed of the extrudate downstream from the die. 

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