Rotor for eddy current retarder

A rotor for an eddy current retarder having a plurality of cooling fins provided around an outer surface of a drum, wherein the rotor comprises 0.05 to 0.15 weight % of C, 0.1 to 0.4 weight % of Si, 0.5 to 1 weight % of Mn, 0.2 to 1 weight % of Mo, 0.5 weight % or less of Ni, 0.01 to 0.03 weight % of Nb, 0.03 to 0.07 weight % of V, 0.0005 to 0.003 weight % of B, 0.02 to 0.09 weight % of Sol.Al, and 0.01 weight % or less of N, 0.05 weight % or less of P, and the balance substantially Fe, and a transverse cross section of each of the cooling fins is rectangular or trapezoidal, and heights of the cooling fins are equal, and the following expressions (1) to (3) are satisfied:

• 6 mm≦d≦11 mm (1)
• 25°≦θ≦55° (2)
• 20 mm≦H<200 mm (3)
• wherein
• d:
• distance between bottoms of the cooling fins
• θ:
• a fin angle in a longitudinal direction of the cooling fin with respect to a rotational direction of the rotor
• H=2h2/(t1+t2), however t1≧t2
• t1:
• thickness of the bottom of the cooling fin (unit:
• mm)
• t2:
• thickness of top of the cooling fin (unit:
• mm)
• h:
• height of the cooling fin (unit:
• mm).