Roll stack

Sheet can be produced by melt extmsion, but in this case a three-roll stack of quenching roUs is generally used (Fig. 2). More than three roUs may be used where necessary. The roUs may be mounted vertically or horizontally. The web is extmded through a slot die in a thickness close to the desired final thickness. The die is in very close proximity to the first chill roU or chill-roll nip. The web may be cast horizontally directly onto the upper chill roU of the stack as shown (Fig. 2), or it may be extmded into the first nip directly. The roUs quench the sheet and provide the surface polish desired. In some applications, matte or embossed roUs maybe used to impart special surface characteristics for certain functions. Where the utmost in optical (glazing) quality is desired the trend has been to mount the roU stack horizontally. The hot melt is then extmded vertically down into the first nip. This avoids problems associated with sag of a horizontal hot melt no matter how short the distance between die and quench. 

Forest products industries know that temperature increases in piles of sawdust and bark. In pulp and paper mills, self-heating develops in amassed tree chips. Paper rolls stacked hot tend to self-heat, as occasionally do stored bales of waste paper. The wood-base panel products particleboard, hardboard, and fiberboard self-heat after being stacked too hot in the factory. Where in structures the framing lumber, wood-base panels, and lignocellulosic insulation is heated by items such as steam pipes, temperatures tend to rise above that of the heat source. 

Memphis, Tcnn X, XTC, adam, beans, clarity, lover s special, rolls, stacks, double slacks, labs None... 

Fig. 183b. y-Monoclinic sulphur showing sheared-penny rolls stacking of 8-membered rings. 

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.

Table 6.4. Influence of Die and Roll Stack Variables on Sheet Characteristics...

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. 

Figure 2, Cross-section of sheet extrusion die and three-roll stack.

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. 

The MPS cell is based on a COTS cell design with a capacity of 5.8 Ah (20 Wh) in a format 176065 (thickness, width and height in mm). Space-dedicated batches are manufactured and selected based on LAT procedures. The MPS cell design qualified in 2003 has a prismatic shape with elliptical rolled stack as shown in Figure 14.17. This cell has a lithium cobalt oxide (LCO) positive electrode that can sustain 7-10 year LEO missions despite the larger energy degradation over the life compared to NCA cells. At variance with NCA, LCO cells do not have lithium reserve. However, LCO is the most used material for consumer cells and batteries and is the base of COTS cells. 

Fig. 2.7. Flat die of equipment for 5 m wide HDPE geomembranes. The die is fed by two extmders, connections far right The arrangement of the countersink screws on the top indicates the line of the coathanger-shaped duct. The choker bar can be adjusted by tlie nuts of the protruding bolts, and the die lips can be adjusted by the hexagon socket screws on the far left. The carpet of molten material leaves the die lip horizontally and is pulled into the gap between the two bottom rollers of the polishing roll stack. This and the following two figures courtesy Naue GmbH Co. KG...

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. 

Figure 23 shows the plastic sheet going up along the center roll and making an S-wrap around the center roll and top roll this is called upstack operation. Sheet lines can also run in the downstack mode, where the material makes an S-wrap around the center roll and bottom roll. The rolls do not have to be in the vertical position they can be in a horizontal position or any angle between vertical and horizontal. In fact, in some roll stacks, the angle is adjustable. 

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. 

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. 

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