Lead shot may be manufactured by dropping molten-lead droplets into water. Assum- ing that the droplets have the properties of solid lead at 300°C, calculate the time for the center temperature to reach 120°C when the water is at 100°C with h= 5000 W/m2 .°C, d=1.5 mm.

. Indicate if the viscosity of a polymer decreases with increases in (a) shear strain rate, (b) molecular weight, (c)temperature (d) pressure.   How are weld-lines caused in injection mouldings and how do they affect the quality of the components?   On a standard extruder screw, there are three sections – what are they called?

Given the table below and your judgement for extreme operational conditions, select polymers for the following applications respectively: a dry ice bucket (operating temperature of -78C), a teeth aligner, a hair dryer (operating temperature range of 60-80C) and a phone case. Table 15.2 Melting and Glass Transition Temperatures for Some of the More Common Polymeric Materials Material Polyethylene (low density) Polytetrafluoroethylene Polyethylene (high density) Polypropylene Nylon 6,6 Polyester (PET) Poly(vinyl chloride) Polystyrene Polycarbonate Glass Transition Temperature [°C (°F)] -110 (-165) -97 (-140) -90 (-130) -18 (0) 57 (135) 69 (155) 87 (190) 100 (212) 150 (300) a. Polypropylene, PET, PTFE, Polypropylene O b. PTFE, HDPE, HDPE, polypropylene c. LDPE, PTFE, Nylon, polypropylene O d. Nylon, PET, HDPE, PVC Oe. HDPE, LDPE, LDPE, PTFE Melting Temperature [°C (°F)] 115 (240) 327 (620) 137 (279) 175 (347) 265 (510) 265 (510) 212 (415) 240 (465) 265 (510)

List out various tests for the measurement of workability and explain any 2 in detail.