Extruder roll stack

Fig. 9 Chill roll stack for sheet extrusion (1) sheet die with flow restrictor (2) molten sheet extrudate (3) lower chill roll (all chill rolls temperature controlled) (4) middle chill roll (imparts gloss/surface texture to sheet) (5) upper chill roll and (6) solidified sheet.

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. 

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. 

Film Lines Using Chill Roll Casting. Thin films are often cast on a chill roll rather than extruded into a roll stack. The main components of a cast film line are the extruder, the film die, the chill roll imit, the thickness gauging system, the surface treatment imit, and the winder. 

The plastic is introduced to the first feed port of the compoimding extruder, the filler is introduced to the second feed port, and the volatiles and air entrapment are removed from the vent port. A gear pump is placed between the compoimding extruder and the sheet die. The sheet is fed to a roll stack and from there it is handled as in a normal sheet line, as discussed earlier. 

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. 

The most popular method to produce sheets is using an extruder with polished stacked rolls that could include the use of an air knife (Figures 5.10 and 5.11). There is the extrusion process where an annular pipe-like cross section die is used (Chapter 17). The extrudate is slit in one or more places and then flattened via rolls into a sheet. In addition to using... 

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. 

The process used to make rubber separators involves mixing precipitated silica, water, and natural rubber to create a thin film. The natural rubber is received in smoked sheets or slabs, and it is normally worked in various pieces of equipment so that the silica, laden with water, can be incorporated. This rubber, silica, and water mixture is then fed to an extruder to create a thin, uniform layer that is sufficiently malleable to be fed into a calendar stack, which has grooved voids in the roll that will create the rib structure. 

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