Mold for fabricating a monocrystalline blade by casting, a fabrication installation and method using the mold

A ceramic material mold for use in molding a turbine engine blade from a molten metal, the blade comprising a root, an inner platform, an airfoil, and an outer platform, and the mold comprising:

• a cavity having the shape of the blade;
• and
• an auxiliary grain duct comprising a first segment and a second segment extending the first segment, said first segment opening out at one end into a first portion of the cavity forming the root of the blade, and at another end into a second portion of the cavity forming a lip of the inner platform of the blade, said second segment opening out at one end into said second portion of the cavity, and at another end into a third portion of the cavity forming a lip of the outer platform of the blade;
• wherein the first segment of the auxiliary grain duct extends from a wall of the first portion of the cavity in a direction that forms an angle lying in the range 54° to 62° with said wall;
• wherein the second segment of the auxiliary grain duct extends from the second portion of the cavity in a direction forming an angle lying in the range 110° to 115° with said second portion;
• and
• wherein the second segment of the auxiliary grain duct extends from the third portion of the cavity in a direction forming an angle lying in the range 110° to 115° with said third portion.