Impurity separating device

An impurity separating device processing a fiber sample (102) containing a fiber (106) and impurity (104) and separating cylinders (112) rotating along a first direction and receiving the fiber sample (102) is provided. Each separating cylinder (112) is provided with a cylindrical surface (116); the length of each cylindrical surface (116) extends a longitudinal axis; a rigid pin (114) with a far end extends from the cylindrical surface (116); the pin can be selectively jointed with the fiber (106) of the fiber sample (102) and maintains the same; a collecting surface (126) receives the impurity (104) falling off each separating cylinder (112); a reverse air flow (122) moves in a separating area between the separating cylinder (112) and the collecting surface (126) and along a direction basically perpendicular to the separating cylinder (112) and facing the lower side of the separating cylinder (112); the reverse air flow (122) is provided with air flow speed in each position in the separating area; the air f