Roll-quenching

It is also evident that draw resonance hardly occurs if at all during chill-roll quenching or film blowing. Chill-roll quenching prevents spontaneous lengthening of the melt mechanically, while film blowing results in a two-directional orientation, which prevents a preferential lengthening in one direction. 

Polystyrene films and polyester (polyethylene terephthalate) films are only used in the biaxially stretched form, because unstretched films are very weak and brittle. To a lesser extent this is also true for polypropylene films. Roll-quenched flat film is used for many packaging applications, but below 0°C these films become brittle. Biaxially oriented polypropylene film, on the other hand, is not brittle at a temperature as low as — 50°C and is suitable for packaging frozen foods. 

Fig. 2. (a) Air knife quenching, (b) vacuum box quench, (c) electrostatic pinning, (d) nip roll quench, and (e) water bath. 

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. 

Because of the low glass transition temperature it is not possible to make clear film, stable at room temperature, by quenching. Some improvement in clarity may be obtained by cold rolling as this tends to dispose the crystal structure into layers (see Chapter 6). 

The Nippon Steel Corporation in 1972 pioneered the use of continuous annealing lines , in which rolled steel sheet is heat-treated and quenched under close computerised control while moving. For this advanced process to give its best results, especially when the objective is to make readily shapable sheet for automobile bodies, steel compositions have to be tailored specifically for the process composition and processing are seamlessly tied to each other. Today, dozens of these huge processing lines are in use worldwide (Ohashi 1988). 

Samples were deformed by rolling at room temperature after disordering and quenching (40% and 80% reduction in thickness) and after ordering by a 19h annealing at 300°C (30% reduction). Completely recrystallized samples were prepared by annealing 48h at 600°C. Resistivity measurement was done by the potentiometric method in liquid N2 relative to a dummy specimen (accuracy 3x10" ). 

Blends of EMA copolymer and EPDM containing vinyl norborene as a third monomer were also investigated. Blending was carried out at 180°C at a rotor speed of 100 rpm. After the reaction, the blends were quenched on the cold rolls and were sheeted out. They were examined by IR spectra. The reduction of peak area related to unsaturation indicated a progressive loss of EPDM due to reaction with EMA. The extent of reaction depended on the utilization of unsaturation which is estimated to be 14% for EMA/EPDM at a 70 30 ratio and 53% at a 50 50 blend ratio. The tensile properties exhibit synergism as the EMA proportions change from 0% to 50%. 

Summary of Pollutant Data for the Rolling Heat Treatment Quench Subcategory Verification Data... 

Figure 1. The quenched potential V() = rn — ml tanh( )] time direction is from the upper left to the lower right and the (/(-direction from the lower left to upper right. Classically, the field rolls down from the false vacuum at the bottom of the upper left to the true vacua in the lower left or upper right. The field fluctuates around such configurations. 

Monofilament is produced at a lower spinning speed, in comparison with chopped filament, because of the problem of heat buildup within the monofilament. The monofilament is generally cooled by passing it through cold water or by winding it on to a cold quench roll. 

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