Patent ID: 8226023

Claim:
A refiner ( 1 ) comprising a stator ( 2 ) and a rotor ( 4 ), the stator ( 2 ) and the rotor ( 4 ) comprising a flat portion ( 7 , 9 ) and a conical portion ( 8 , 10 ), the conical portion ( 8 ) having a first end ( 17 ) of smaller diameter (D 1 ) and a second end ( 18 ) of greater diameter (D 2 ) such that the first end ( 17 ) of the conical portion ( 8 , 10 ) having smaller diameter (D 1 ) is directed towards the flat portion ( 7 , 9 ) and the second end ( 18 ) of the conical portion ( 8 , 10 ) having greater diameter (D 2 ) is directed away from the flat portion ( 7 , 9 ), and which flat portion ( 7 , 9 ) and the conical portion ( 8 , 10 ) comprise refining surfaces ( 11 , 12 , 13 , 14 ) provided with blade bars ( 20 ) and blade grooves ( 21 ) therebetween, and that the refining surface ( 12 ) of the conical portion ( 8 ) of the stator ( 2 ) comprises at least an outer zone ( 23 ) arranged at the second end ( 18 ) of the conical portion ( 8 ) having greater diameter (D 2 ) and an inner zone ( 22 ) arranged relative to the outer zone ( 23 ) on the side of the first end ( 17 ) of the conical portion ( 8 ) having smaller diameter (D 1 ), the length of the outer zone ( 23 ) being half of the total length (D) between the first end ( 17 ) and the second end ( 18 ) of the conical portion ( 8 ) of the stator ( 2 ) and that a portion of the length of the blade bars ( 20 ) in the outer zone ( 23 ) of the conical portion ( 8 ) of the stator ( 2 ) create a negative blade bar angle (α) having a value of minus 1 degree to minus 30 degrees relative to the rotation direction (RD) of the rotor ( 4 ) such that they have a retentive effect on the material to be refined and that this portion of the length of the blade bars ( 20 ) in the outer zone ( 23 ) of the conical portion ( 8 ) of the stator ( 2 ) corresponds to at least 10% of the total length (D) between the first end ( 17 ) and the second end ( 18 ) of the conical portion ( 8 ) of the stator ( 2 ).