Refiner element pattern achieving successive compression before impact

Abstract

A refiner for producing mechanical pulp has greater spacing between bars of the refiner grinding elements than is conventional. The grooves between the bars have a sloping bottom, making an angle of about 1.degree.-30.degree. (preferably 5.degree.-20.degree.) with respect to a straight line between the bars. The width of the grooves is about 10-50 mm. The relative rotation of the refiner elements (whether disks, cylindrical, or conical) with respect to each other results in sequential refining: a moving tension field, with successive compressions before impacts, and expansions, achieving increased fiber flexibility, more fiber rolling motion, and less fiber cutting. Pulp produced has increased fiber flexibility yet maintains a high content of long fibers, and higher refiner capacity also ensues. Also, the refiner of the invention can be used to mix treatment chemicals--such as bleaching chemicals in liquid form--into kraft pulp at high consistency (e.g. about 30-55%).

Dependencies are inferred from the claim text.