Abstract: A cyclone separator for separating heavy particles and dust particles from fibre material. The separator includes a cyclone housing (2), an inlet tube (9) that opens substantially tangentially into the housing (2), an overflow pipe (6) for the removal of cleaned light-weight fibre material, and an underflow outlet (4) for discharging heavy particles and dust particles. To improve dust removal, a sieve member 7, 8 is arranged inside housing (2) substantially co-axial with the housing axis and into which inlet tube (9) opens tangentially. Additionally, pin-studded or spike-studded strips are mounted on an inside face of the cyclone housing or of the sieve member to preliminarily open up the fibre material. A coaxial sieve member having flat bars with vertical upper portions and inwardly-curved lower portions that bound a co-axial lower sieve opening is also provided.