4) In a tempering process, glass plate, which is initially at a uniform temperature Ti, is cooled by suddenly reducing the temperature of both surfaces to Ts The plate is 20 mm thick, and the glass has a thermal diffusivity of 6x 10-7 m2 /s. (a) How long will it take for the midplane temperature to achieve 50% of its maximum possible temperature reduction? Ans t= 63 s (b) If (Ti -T5) = 300°C, what is the maximum temperature gradient in the glass at the above time? Ans. -2.36 104 °C/m.

"You did calculations using the simplified HAZ time-temperature formulas, assuming 3D heat flow, and are presenting your final internship conclusions to management. You realize with horror, in the middle of your presentation, that you forgot to label your calculated curves (below). Which curve is which? Pick the best answer A: "Plot 1 is HYPERFILL® and Plot 2 is p-GMAW. Since HYPERFILL® has the higher heat input, it cools more slowly."     B: "Plot 2 is HYPERFILL® and Plot 1 is p-GMAW. Since HYPERFILL® has the faster travel speed of the two processes, it cools faster."     C: "Plot 1 is p-GMAW and Plot 2 is HYPERFILL®. Since p-GMAW has the slower travel speed, it cools more slowly."     D: "Plot 2 is p-GMAW and Plot 1 is HYPERFILL®. Since p-GMAW has the lower heat input, it cools faster"     Both (A) and (D)

A 50-mm thick plate of carbon steel (AISI 1010) is annealed with a reheat stage taking the steel from its initial uniform temperature of 200 C to a minimum final temperature of 550 C. HEating is effected in a gas-fired furnace where products of combustion at Tamb = 800 C maintain a convection coefficient of h = 100 W/m^2K on both sides of the plate. How long should the plate be left in the furnace? Substantiate with relevant analysis and calculations.