Pair of opposed co-operating refining elements

Apparatus for refining lignocellulosic material comprising a first refining element adapted for mounting on a first refiner disk, and a second refining element adapted for mounting on a second refiner disk juxtaposed with said first refiner disk, said first and second refiner disks adapted for relative rotation with respect to each other whereby a refining gap is created between said first and second refining elements mounted on said first and second refiner disks, said first refining element including a first radially projecting refining surface including a first inner refining zone including a plurality of raised bars separated by a plurality of grooves therebetween, a second restricted radial refining zone disposed radially outward of said first inner refining zone and including a plurality of raised bars, a third restricted radial refining zone disposed radially outward of said second restricted refining zone and being devoid of any raised bars, and a fourth restricted radial refining zone disposed radially outward of said third restricted radial refining zone and including a plurality of raised bars separated by a plurality of grooves therebetween, and said second refining element including a second radial refining surface having a fifth inner radial refining zone including a plurality of raised bars separated by a plurality of grooves therebetween, a sixth restricted radial refining zone disposed radially outward of said fifth inner radial refining zone and being devoid of any raised bars, and a seventh radial refining zone disposed radially outward of said sixth restricted radialy refining zone and including a plurality of raised bars separated by a plurality of grooves therebetween, said sixth restricted radial refining zone being located in direct juxtaposition with said second restricted radial refining zone.