An electric machine comprising a cylindrical stator, a cylindrical, rotating rotor frame within the stator, said rotor frame having an outer surface and an axial direction (A-A), and a pole arrangement on the outer surface of the rotor frame, wherein the pole arrangement comprises a plurality of segment pieces disposed circumferentially around the outer surface of the rotor frame, a plurality of pole pieces disposed circumferentially around the outer surface of the rotor frame and disposed alternatingly with said segment pieces, and permanent magnet pieces (41, 42) positioned between the segment pieces and the pole pieces, the segment pieces, the permanent magnet pieces (41, 42) and the pole pieces forming a continuous ring around the outer surface of the rotor frame, the electric machine comprising a plurality of such rings after each other in the axial direction (A-A), characterized in that: - each segment piece comprises a first inner edge seated against the outer surface of the rotor frame, a second opposite outer edge facing towards the stator, and side edges (23, 24) between the first inner edge and the second outer edge, said side edges (23, 24) comprising at the second outer edge inclined portions (23a, 24a) receiving the permanent magnet pieces (41, 42), each segment piece being fastened with a first bolt to the rotor frame, the first bolt extending between the segment piece and the rotor frame, - each pole piece comprises a first inner edge facing towards the outer surface of the rotor frame, a second outer edge facing towards the stator, and inclined side edges (53, 54) between the first inner edge and the second outer edge, each pole piece being fastened with a second bolt to the rotor frame, the second bolt extending between the pole piece and the rotor frame, whereby the permanent magnet pieces (41, 42) are pressed between the inclined side edges (53, 54) of the pole pieces and the inclined portions (23a, 24a) of the side edges (23, 24) of the segment pieces when the second bolt is tightened, - at least one axial air channel (A1, A2) passes through the rings and at least one radial air duct (R1, R2) passes between the rings. - each segment piece comprises a first inner edge seated against the outer surface of the rotor frame, a second opposite outer edge facing towards the stator, and side edges (23, 24) between the first inner edge and the second outer edge, said side edges (23, 24) comprising at the second outer edge inclined portions (23a, 24a) receiving the permanent magnet pieces (41, 42), each segment piece being fastened with a first bolt to the rotor frame, the first bolt extending between the segment piece and the rotor frame, - each pole piece comprises a first inner edge facing towards the outer surface of the rotor frame, a second outer edge facing towards the stator, and inclined side edges (53, 54) between the first inner edge and the second outer edge, each pole piece being fastened with a second bolt to the rotor frame, the second bolt extending between the pole piece and the rotor frame, whereby the permanent magnet pieces (41, 42) are pressed between the inclined side edges (53, 54) of the pole pieces and the inclined portions (23a, 24a) of the side edges (23, 24) of the segment pieces when the second bolt is tightened, - at least one axial air channel (A1, A2) passes through the rings and at least one radial air duct (R1, R2) passes between the rings.