Fluidized Bed: An Energy Efficient Heat Treating Technology For Cast Al Alloys
D. Apelian, S. K. Chaudhury, WPI, Worcester, MA; J. S. Keist, Arizotah, LLC, Plymouth, MN
Post solidification heat treatment of cast Al alloys is often required to improve mechanical properties and better microstructural control. The heat treat cycle consists of a solution treatment, followed by quenching and an aging step. These heat treating steps may require several hours using conventional air resistance furnaces and contribute a substantial increment to the overall manufacturing cost. The major constraint to production flow in manufacturing operations using conventional furnaces arises from its labor intensive batch processing method; the relatively slow heating rate gives rise to cycle times in the range of 10-15 hours. Fluidized bed heat treating offers a more efficient means of energy transfer compared to conventional electric resistance furnaces and thus provides an energy efficient heat treating method. High heating rate of castings in fluidized bed is due to forced convectional heating. The high thermal mass of the bed material in fluidized bed ensures rapid and uniform heating of castings. In this paper, we will review the fundamentals of fluidized bed, highlight their advantages and examine applications and limitations of fluidized bed to heat treat cast Al alloys. Mechanical properties data along with the resultant microstructure as a result of extensive trials with fluidized bed technology will be presented, reviewed and discussed.