page 261

45.3.5 Single Crystal Casting

•The process is effectively,

1.Prepare a mold so that one end is a heated oven, and the other end chilled. The part should be oriented so that the cooling happens over the longest distance.

2.Cast metal into the mold

3.Solidification will begin at the chill plate. These dendrites will grow towards the heated end of the part as long dendritic crystals. The part is slowly pulled out of the oven, past the chill plate.

4.Remove the solidified part.

•Parts made of a single crystal can have creep and thermal shock resistance properties.

•There are two variants to this technique,

directionally solidified - in this case the dendrites grow from the chill plate towards the other end.

single crystal - a helical constriction is used so that instead of parallel dendrites, only a single crystal is formed in the blade.

45.4 OTHER TOPICS

45.4.1 Furnaces

•Some of the types include,

-coreless induction - magnetic fields induce eddy currents throughout the entire furnace, resulting in melting

-core induction - magnetic fields induce eddy currents in a small section of the furnace, resulting in melting

-gas fired crucible - uses ignited gas and air to heat crucible in enclosed oven

-electric arc - arcs are used to heat metals

-cupolas - layers of metal and ore are placed in this refractory lined vessel, and ignited to produce large volumes of metal.

45.4.2 Inspection of Casting

•General problems with castings are,

-cavities