Roll transfer techniques

Another version of finish apphcation with transfer rolls is the loop transfer system, Fig. 2.5.A loop of fabric is immersed in finish liquid and then squeezed with the fabric to be treated between squeeze rollers. The finish is transferred to the fabric at a much lower wet pickup than possible by direct immersion. These roll transfer techniques are especially useful for the backside application of finishes, for example hand builders and flame retardants, to pile fabrics (without crushing the pile). 

One-dimensional nanostructures should be grown directly on the transducers, but, depending on the deposition conditions, this may not always be possible due to high temperatures, pressures or the aggressive ambient required for their preparation. In these cases, they have to be transferred afterwards. The easiest way to transfer is by drop coating, but other techniques such as dielectrophoresis or roll transfer may be used. In the case of single-nanowire devices, nanomanipulation can also be used. 

The general problem of resupplying a system with a solid lubricant is discussed elsewhere in this book, and various possible techniques are mentioned, but resupply by transfer from some form of reservoir is the most successful technique, and the only one which has been used commercially. It has been used in spacecraft, and in terrestrial applications for vacuum or for very high or very low temperatures, while rolling bearings lubricated by solid lubricant composite retainers or cages have been commercially available for over thirty years. 

According to the published reports the tests were generally satisfactory, but there appear to have been no operational uses of the technique, and little or no further testing in the intervening forty years. This may be partly due to the complication of arranging a suitable feed system, and partly to the satisfactory development of alternative techniques such as composite retainers and transfer films, and lead lubrication for rolling bearings in vacuum ... 

Two-Roll Coating - Any coating technique in which two rolls are involved can be generally called two-roll coating. One roll is in contact with the liquid coating and transfers the liquid to a web that is wrapped around the second roll. The first roll is called the applicator roll and the second roll is called the back-up roll. 

For the case of two-dimensional roll cells, Malkus and Veronis also performed calculations on the heat transfer rate by using an approximate technique that they considered as being within 2 percent of the exact value, for Rayleigh numbers up to three times the critical. In accordance with experiment, their results show a 5/4-power dependence of heat transfer rate on temperature difference (or a 1/4-power dependence of Nusselt number on the Rayleigh number). 

Various printing techniques like flexographic and gravure have been introduced into microtechnology as tools for roll-to-roll manufacturing. These techniques rely on masters that have HL/HB patterns to confine inks, with a soft contact to transfer the ink to paper or polymer substrate. 

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