(V) GAS COOLING- IS PRESSURE OR VELOCITY MOST IMPORTANT?

This paper will debunk the age-old theory that the smaller the vacuum furnace, the faster it will quench supposition. Our study compared the cooling rates of three vacuum high pressure gas quenching furnaces- a large 10 bar vacuum furnace equipped with a 600 HP blower motor to smaller 10 bar and 20 bar vacuum furnaces both equipped with a 300 HP motors. The experiment consisted of four identical loads of 75 steel bars standing vertically. The total weight of the entire set up was 3,060 pounds. Five (5) TC’s in total were imbedded 3” deep into the bars (4 at the corners and one in the middle). The location of every thermocouple was maintained on all four runs.

In comparing the critical cooling temperatures for H13 in the 1850F to 1300 F range, the furnace that is almost 3 times larger in volume (110 cubic feet versus 40 cubic feet of hot zone) and half the operating pressure cooled 2 times faster than its smaller counterparts. These tests prove a very important fact- that the gas velocity is more meaningful than pressure (bar) when it relates to cooling rates.