Take-up roll

Figure 3.9 Schematic of Loeb-Sourirajan membrane casting machine used to prepare reverse osmosis or ultrafiltration membranes. A knife and trough are used to coat the casting solution onto a nonwoven paper web. The coated web then enters the water-filled gel tank, where the casting solution precipitates. After the membrane has formed, it is washed thoroughly to remove residual solvent before being wound up on the take-up roll...

Fig. 14.2 A single strand emerging from the spinneret which undergoes die swell, then cooling to a point of solidification, drawn by the take-up roll.

Isothermal draw resonance is found to be independent of the flow rate. It occurs at a critical value of draw ratio (i.e., the ratio of the strand speed at the take-up rolls to that at the spinneret exit). For fluids that are almost Newtonian, such as polyethylene terephthalate (PET) and polysiloxane, the critical draw ratio is about 20. For polymer melts such as HDPE, polyethylene low density (LDPE), polystyrene (PS), and PP, which are all both shear thinning and viscoelastic, the critical draw ratio value can be as low as 3 (27). The maximum-to-minimum diameter ratio decreases with decreasing draw ratio and decreasing draw-down length. 

Fig. 1, Couette apparatus (A) for continuous growth of polyethylene macrofibres from dilute p-xylene solutions. The macrofibre grows on the surface of the Teflon rotor, leaves the vessel through a Teflon pipe, and is wound up on a take-up roll.

Flat sheet membranes are generally manufactured on a casting machine, which is shown schematically in Figure 1.35. A polymer solution is cast by a casting knife on a polyester or polyethylene support paper, which is continuously supplied from a roll. The cast polymer film is fed to the precipitation bath, where the actual membrane is formed. After a certain residence time in a rinse bath, where residue solvent is removed, the membrane is collected as a flat sheet on the take up roll. The membranes, which are obtained as up to 2 m wide continuous sheets, are then further processed into the desired module configuration. 

The current version ( ) of the fiber treatment process employs a drawing rig equipped with a solvent treatment tube where an as-spun PET monofilament briefly contacts a swelling agent, causing rapid crystallization of surface layers. Solvent exchange and drying steps quench the crystallization before the fiber is drawn between feed and take-up rolls. A skln/core morphology results... 

Figure 7.3.1. An example of industrial coating and drying apparatus. A coated liquid is deposited onto a substrate which is unwound from a supply roll at the coating station and passes through the three separate ovens(dryer) where the temperature and velocity of air is controlled independently. Finally dried coated substrate is taken up by a take-up roll.

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. 

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