Twin fiber

The overlays thickness estimation is possible exploiting a twin fiber placed in the same deposition chamber and subject to the same coating procedure. The coated twin fiber can be cut by a precision cleaver and analyzed by scanning electron microscopy (SEM). One of the deposited thin overlay is clearly observable in the SEM image of the fiber section reported in Fig. 3.13. 

Good bulk and crimp stability can be obtained with bicomponent fibers (also known as conjugated fibers, twin fibers, or fibers of bilateral structure). The two components may lie side by side, and have a nucleus-mantle structure or a matrix-fibrillar (M/F) structure (Figure 12-10). The M/F fibers are known as matrix fibers in the United States and not as bicom-... 

Rebar appearance. A fiber optic sensor was designed to monitor the corrosion of rebar based on the change in color of the surface of rebar as a result of corrosion. A twin-fiber approach and a windowed approach have been reported so far. Both approaches are currently being tested in bridges in Vermont. ... 

In the twin-fiber design, the transmit fiber illuminates with broadband light a section of rebar, which modifies the spectrum through absorption and reflects light into the receive fiber. The gap between the fiber and the surface to be monitored is less than 10 mm. The signal travels back down the receive fiber, and the spectrum is measured. A spectrum shift indicates that corrosion is present. There is a clear difference in the spectrum between 0.5 and 0.8 pim of uncorroded rebar and corroded rebar. 

Fig. 19. Twin-orifice spinnerette design used in solution-spinning of hoUow-fiber membranes. Polymer solution is forced through the outer orifice, while...

A series of events can take place in response to the thermal stresses (/) plastic deformation of the ductile metal matrix (sHp, twinning, cavitation, grain boundary sliding, and/or migration) (2) cracking and failure of the brittle fiber (5) an adverse reaction at the interface and (4) failure of the fiber—matrix interface (17—20). 

Fig. 13. A hoUow-fibet reverse osmosis membrane element. Courtesy of DuPont Permasep. In this twin design, the feedwater is fed under pressure into a central distributor tube where half the water is forced out tadiaUy through the first, ie, left-hand, fiber bundle and thus desalted. The remaining portion of the feedwater flows through the interconnector to an annular feed tube of the second, ie, right-hand, fiber bundle. As in the first bundle, the pressurized feedwater is forced out tadiaUy and desalted. The product water flows through the hoUow fibers, coUects at each end of the element, and exits there. The concentrated brine from both bundles flows through the concentric tube in the center of the second bundle and exits the element on the right.

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. 

To calculate the WAXS fiber pattern of PTFE phase I, we assumed that the CF2 units are equally distributed around the chain axis due to the high mobility of twin reversals in the high-temperature phase. In other words, the electron density of the PTFE chains is cylindrically symmetric in space average. Thus we are able to calculate the mean molecular structure amplitude according to Eq. (26). 

A possible way to lower the costs of fibers and films of regenerated cellulose would be to run cellulose through a twin-screw ultrasonic extruder with a minimum of solvent and pass the extrudate through a stream of hot air to recover the solvent for reuse. This stronger cellophane could be used in place of many plastic films used today. A great number of derivates of cellulose have been made. Methyl, ethyl, carboxymethyl, hydroxyethyl, and hydroxypropyl ethers are made commercially today. These are used as water-soluble polymers, except for ethylcellulose, which is a tough plastic used in screwdriver handles and such. 

A third type of paper machine is also utilized to a lesser extent the twin wire machine. Instead of depositing a fiber slurry onto a moving wire, the fiber dispersions are delivered into the gap of two moving wires. Machines of this type remove water from both top and bottom surfaces by pressure. Twin wire machines are capable of very high speeds. 

Glass fiber reinforcements are added to plastics in order to improve mechanical and physical properties of the plastic. The traditional route to producing fiber reinforcement involves blending the fibers into plastic in a twin-screw extruder followed by pelletization (Chapter 5). The pellets are then molded using an injection molding machine (IMM) to form the fabricated products (Chapter 4). This action results in fiber attrition. 

The twin-screw injection molding extruder is an injection molding machine that is capable of both blending/compounding and extrusion in one step. Because it is a one step process, the fibers never go through the entire extrusion process as well as the pelletization that limits the fiber size, but are blended into the molten plastic before injection. The screw part of this machine is based on a non-intermeshing, counterrotating twin-screw extruder (Chapter 5). One of the screws in this machine is capable of axial movement and has a non-return valve on the end. This action enables the screw to inject and mold parts. 

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