Roll cooling stack

From the die, the sheet passes immediately to a cooling and finishing device in the form of a roll cooling stack. The usual configuration is a three-roll vertical stack with the sheet entering at the nip between the upper two rolls. Variations include up-stack working where the sheet enters between the lower two rolls, a... 

Figure 5.12 Schematicof a three-roll sheet cooling stack...

Stack rolls are usually of double shell design, giving internal high velocity liquid circulation at a controlled and uniform temperature. Each roll is equipped with its own individual temperature control system which is built into the take-off unit. The sheet gradually continues to cool as it travels around the rolls becoming sufficiently solidified so that it can continue down the line. 

In the case of slice production, the hot molten cheese is pumped through a manifold with 8-12 nozzles which extrude ribbons of cheese onto the first two or three counter-rotating chill rolls over which the cheese ribbons pass and are thereby cooled from 70-80 to 30°C. The ribbons are automatically cut into slices, which are stacked and packed. 

Sometimes, especially In sheet applications, the plastic is extruded, either horizontally or vertically, onto one roll in a three-roll stack of polishing rolls, rather than onto a chill roll. The roll stack is designed to exert pressure, and to impart desired surface characteristics to the sheet-either smooth or textured. The gap between the rolls helps in controlling the sheet thickness. The rolls are temperature-controlled, often with circulating hot oil, and the plastic next travels through a cooling section consisting of a number of smaller rolls in a frame. 

Sheet is an extruded product that is greater than 10 mils in thickness (below this the product is identified as film), 40 mils being typical. Resin is extruded through a die and passes through a cooling roll stack and conveyed to nip rolls, after which sheet is wound on rolls or cut and stacked or conveyed directly to a thermoforming machine. Sheet width is usually between 2 and 7 ft. 

This viscous carpet is then usually polished and cooled in a cooling and polishing roll stack by three or more cooled rolls (Figs. 2.8 and 2.9). Instead of smooth rolls with polished surfaces, engraved rolls can be used to... 

Fig. 2.9. Cooling and polishing roll stack and flat die of a production unit for 9 m wide geomembranes. The size of the railing and the 1201 waste container give an impression of the giant dimensions of the equipment. Two rolls are horizontally arranged and the third roll is offset downwards in the roll stack. The carpet of molten material is being drawn diagonally at 45° from the die into the roller nip...

Film and Sheet Lines Using the Roll Stack Process. There are no significant differences between the extrusion of fiat film and sheet. The main components of a sheet line are the extruder, the roll stack, the cooling section, the nip roll section, and the winder (see Fig. 23). The roll stack contains three rolls that are often referred to as polishing rolls. They are used to exert pressure on the sheet and to impart the surface conditions of the rolls to the plastic sheet. If a smooth surface is required, smooth rolls are used. If a textured surface is needed. 

The rolls are normally cored so that the temperature of the rolls can be controlled. This is usually done with circulating hot oil. It should be possible to adjust the temperature of each roll separately. The cooling section consists of a number of rolls positioned in a frame the sheet runs over and under the rolls to keep the sheet flat. At the end of the cooling section are the pull rolls or nip rolls these are rubber rolls that pull the sheet from the roll stack to maintain a certain tension in the sheet. After the nip rolls, the sheet is led to the winder that rolls the sheet on a core. Many different winders are available some winders automatically transfer the sheet to a new core when one package is full. 

Slot-die or extrusion coating involves the application of molten polymer resin through a slot die directly onto the surface of a nonwoven. Upon extrusion, the resin is smoothed and quenched by a cooling roll. Coating weight is controlled by slot size and extrusion rate. In a variant of this method, nonwoven fabrics are combined with an extruded film just after the die and before the roll-stack. The fabrics can be subsequently chemically bonded to give a sandwich structure. Such products are used as waterproof insales in shoes. 

This covers a number of possibilities. For example, motor-powered machinery operating underground fork-lifts carrying containers in a RORO (roll on roll off) vessel and fork-lifts operating in cool or freezer storage. It could also include ozone emissions from electric motors, cars in a multilevel car park, and stack emissions from coal, gas, or oil fired electricity generation. 

The takeoff unit for sheeting usually consists of a vertical stack of three driven, highly polished, chrome-plated rolls and a pair of driven, rubber-covered pull-off rolls. The chrome-plated rolls serve three purposes — cooling, gage control, and imparting a desired finish to the sheet. The cooling rolls are generally of twin-shell construction... 

Sheet should be cut to the desired length and stacked flat. Usually, a traveling power shear cuts the sheet automatically to the desired lengths. Roll temperatures have a decisive influence on the quality of the finished sheet. If the rolls are too hot, the sheet will not be cooled sufficiently for easy handling and will tend to curl in the transverse direction. If the rolls are too cold, the sheet will curl in the machine direction, resulting in a pitted surface. ... 

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