Take-up systems

The two main pathways for the uptake of toxic substances by plants are through their root systems and across their leaf cuticles. Stomata, the specialized openings in plant leaves that allow carbon dioxide required for photosynthesis to enter the leaves and oxygen and water vapor to exit, are also routes by which toxic substances may enter plants. The mechanisms by which plants take up systemic pesticides and herbicides, which become distributed within the plant, have been studied very intensvively. 

The blown film take-up system for LCP film must be capable of handling stiff film so that creases and folds do not form in the film as the bubble is flattened and pulled through the pinch rollers in the blown film process, shown schematically in Figure 11.19. A desiccant dryer is used to remove moisture from the LCP resin. As with any polyester, even small amounts of moisture can cause reduction in molecular weight, decreased melt strength, and other conditions that will adversely affect the quality of the film. Most LCP manufacturers recommend drying to less than 50 ppm, or dew point of -40°C [18]. 

In slit-film production, wide web extruded film, which is oriented in the machine direction by virtue of the take-up system, is slit into narrow tapes. These tapes are woven into fabrics for various end uses. 

If the product is being stripped from the carrier, the take-up system is a bit more complex. The speed control to provide constant speed during the cast is actually on the take-up roll for the carrier, and this speed is maintained by the tachometer feedback loop described previously The product, on the other hand, must be handled with a tensionless take-up system, since there is no carrier to provide the mechanical strength needed in a system under tension. This is accomplished by using a proximity sensor with a loop of tape where a servo-motor accelerates and decelerates the take-up roller, depending on where the loop is with respect to the sensor. This system provides a tensionless take-up system for the tape-cast product. Many different types of proximity sensors have been used in these systems. The main requirement is that the sensor detects the tape that is being speed controlled. At times, especially when the tape-cast product "blocks —that is, sticks to itself—a paper or other material must be interwoven between the layers on the roll. Machines have been built with all of these features added as options. 

The melt flows from the extruder into the die where it flows aroimd the bend and around the core tube. On the far side of the core tube, it forms a weld. Melt sticks to and is pulled by the moving wire. Details of the sizes and shapes of the die parts in contact with the melt are important in obtaining a smooth coating at high rates. The die exit usually is the same diameter as that of the coated wire and there is little drawdown. Die openings are small and pressures inside the die are high at ca 35 MPa (5000 psi). Wire take-up systems operate as high as 2000 m/min. 

The most common of these methods is fiber spinning. Figure 7.5.2 shows the basic features of this method. To avoid the problem of grabbing and pulling, the sample is continuously extruded from a tube and stretched by a rotating wheel or vacuum suction. The force on the tube or on the take-up system is measured. The fiber diameter is measured as a function of distance along the fiber, either photographically or by a video camera. 

Reactions represent the dynamic aspect of chemistry, the interconversion of chemical compounds. Chemical reactions produce the compounds that are sold by industry and that play a big role in maintaining the standard of living of our society they transform the food that we take up in our body into energy and into other compounds and they provide the energy for surviving in a hostile environment and the energy for a large part of our transportation systems. 

There is current interest in hydrogen sponge alloys containing lanthanum. These alloys take up to 400 times their own volume of hydrogen gas, and the process is reversible. Every time they take up the gas, heat energy is released therefore these alloys have possibilities in an energy conservation system. 

CHEOPS (we tested Version 3.0.1) is a program for predicting polymer properties. It consists of two programs The analysis program allows the user to draw the repeat unit structure and will then compute a whole list of properties the synthesis program allows the user to specify a class of polymers and desired properties and will then try the various permutations of the functional groups to find ones that fit the requirements. On a Pentium Pro 200 system, the analysis computations were essentially instantaneous and the synthesis computations could take up to a few minutes. There was no automated way to transfer information between the two programs. 

Quench. Attempts have been made to model this nonisotherma1 process (32—35), but the complexity of the actual system makes quench design an art. Arrangements include straight-through, and outside-in and inside-out radial patterns (36). The optimum configuration depends on spinneret size, hole pattern, filament size, quench-chamber dimensions, take-up rate, and desired physical properties. Process continuity and final fiber properties are governed by the temperature profile and extension rate. 

The wettabihty of a fabric is measured by the Gravimetric Absorbency Testing System (GATS). This test is a measure of the abiUty of the fabric to take up hquid spontaneously in the direction perpendicular to its plane (lateral absorbency). The amount of water driven from a reservoir beneath the sample is deterrnined. 

SpiHs should be confined and prevented from entering water sources. Smother with foam and take up residue with an absorbent and put into dmms for disposal. The suggested method of disposal is incineration at an approved waste handling facHity in a system equipped with a combustion gas scmbber system (23). 

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