Cooling strength

Laser cooling strength f), coolant heating /jlc and the sympathetic heating exerted by the SC ions on the LC ions determine the LC ion temperature. 

EOY speeds are the most recent development in PET spinning (78). Properties are similar to HOY and appear to be limited by the differential cooling rate from filament surface to filament core. This leads to radial distribution of viscosity, stress, and, consequentiy, molecular orientation (75). Eiber tensde strength is limited. Nevertheless, speeds up to 7000 m /min are commercial and forecasts are for speeds up to 9000 m /min by the year 2000 (79). Speeds to 9000 m/min have been studied (68,80,81). 

Modified ETEE is less dense, tougher, and stiffer and exhibits a higher tensile strength and creep resistance than PTEE, PEA, or EEP resins. It is ductile, and displays in various compositions the characteristic of a nonlinear stress—strain relationship. Typical physical properties of Tef2el products are shown in Table 1 (24,25). Properties such as elongation and flex life depend on crystallinity, which is affected by the rate of crysta11i2ation values depend on fabrication conditions and melt cooling rates. 

Ethylene—tetrafluoroethylene copolymers respond weU to melt bonding to untreated aluminum, steel, and copper with peel strengths above 3.5 kN/m (20 Ibf/in.). Eor melt bonding to itself, hot-plate welding is used. The material is heated to 271—276°C, and the parts are pressed together during cooling. 

Hot tack strength is the abiUty of a heat-seal layer to hold together while molten, before the seal cools and sets up. This is a technically important property which is difficult to measure reproducibly in the laboratory. Owing to the reinforcing effect of ionic bonding on melt strength, ionomer sealing layers provide superior performance in a wide spectmm of appHcations. 

Steam treatment imparts increased corrosion resistance for ferrous P/M parts. The parts are heated to 400—600°C and then exposed to superheated steam. After cooling, the parts are usually oil dipped to further increase corrosion and wear resistance, and to enhance appearance (see Corrosion and CORROSION control). Heat treated parts are seldom steam treated because annealing reduces hardness and tensile strength. 

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