Cooling roll

Green tea processing is designed to achieve a dry product exhibiting the desirable twisted leaf appearance, but without flavanol oxidation. This is accomplished by carrying out rapid enzyme inactivation either with steam in a rotating cylinder as practiced in Japan or with dry heat as practiced in the People s Republic of China. The inactivated tea is cooled, rolled partially dried, rerolled, and then completely dried. 

To produce amorphous anhydrous borax, the molten borax is run between two large water-cooled rolls, forming sheets about 1.6 mm thick, which are then crushed and screened to the desired particle size. Because the borax is cooled rapidly by the rolls, it remains largely amorphous, though it may contain some crystalline anhydrous borax. 

Calender - A machine equipped with two or more heavy, internally heated or cooled rolls, used for the continuous sheeting or plying up of rubber compounds. 

Sheet extrusion requires a broad die, in which an even distribution of the flowing polymer along its width, and an equal flow resistance at each point, has to be taken care of. Sheets are being extruded up to a width of 3 or 4 m, in thickness up to 3 cm. If desired, sheets can be produced with a wave-shape, by passing the, still plastic, extrudate between two profiled rolls. Film extrusion can be done in a similar way, as a matter of fact with a narrower die gap. After extrusion, sheets and films are cooled in a water bath or on polished cooling rolls. 

Downstream of the die, the extrudate (melt) is calibrated, cooled and packaged by an array of ancillary auxiliary devices including vacuum calibrators, water tanks, cooling rolls, haul-offs, cutters, and winders (Chapter 18). Upstream of the die, a melt pump may be interposed between the extruder and the die to produce a more uniform extrudate. The exact selection and arrangement of these component parts of an extrusion system will depend on the end product and tolerance requirements that have to be met.25 27> 33> 143 196>476... 

Cooling Roll These systems range from very inexpensive with rather poor surface non-uniform temperature control to the usually more desirable fand exoensive) rolls suitably cored to Dermit controlled circulation of... 

Figure 4. Anco cooling roll sketch. (Courtesy of Cherry-Burrell, Louisville, Kentucky.)...

Film extrusion can be done in a similar way, with a narrower die gap. After extrusion, sheets and films are cooled in a water bath or on polished cooling rolls. 

Metallization is done in a special chamber under a very high vacuum, usually as a batch process. As shown in Fig. 8.8, aluminum particles from a wire that is vaporized in a crucible or boat, at about 1700°C (3100°F), condense on the film being metallized as it runs past a cool roll. The layer of aluminum is typically 400 to 500 A in thickness, and is commonly specified in terms of light transmission, optical density, or electrical resistance. Thickness is controlled by the speed of the film, number of plating stations, and metal temperature, with a higher temperature... 

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