Mixing rotor and internal mixer

A mixing rotor for use in an internal mixer, the mixing rotor comprising:

• a rotor shaft portion that includes a cooling passageway formed therein;
• and
• a mixing blade portion that is formed in an outer circumferential portion of the rotor shaft portion,
• wherein the mixing blade portion includes a short blade at a predetermined length in an axis direction of the rotor shaft portion, and at least two long blades at lengths larger than the length of the short blade in the axis direction, each of the long blades including a land portion as an end surface of the long blade facing a radially outside of the mixing rotor,
• wherein the length of each of the long blades in the axis direction is set to be 0.6 times or more as large as a length of the mixing blade portion in the axis direction,
• wherein a biting angle of each of the long blades is set to an angle equal to or smaller than 31°, and
• wherein a center angle with respect to a land width as a width of the land portion in a cross-section of each of the long blades orthogonal to the axis direction is set to an angle equal to or larger than 7°.