6 and 7 represents an imaginary extension of the internal surface extended through the outlet to provide a line of reference the innermost portions of the dividers preferably do not extend inwardly toward the inside of the apparatus beyond the dashed line 25 in order to maintain the same clearance which exists between the impact elements and the internal surface of the chamber the effectiveness of this arrangement for rejecting aggregates of fibers is illustrated by the dashed path of fiber aggregate 26 shown deflecting off of the leading surface 16 one can see that if the fiber aggregate strikes the ridges at a very shallow angle nearly parallel to the direction of travel of the impact elements the inward slant of the leading face of the divider need not be as great as if the fiber aggregate approaches at a steeper angle it may be necessary to do some experimentation to determine the optimum angle for a particular system but an inward slant of about 45 u00b0 has been found to work very well it is within the scope of this invention that the dividers be other than plates as shown but plates are very convenient for example by cutting a series of bevelled continuous or semi continuous slots out of a very thick solid surface the same effect can essentially be achieved fig5 is similar to fig4 simply illustrating a slightly different profile for the innermost portion of the dividers the leading surfaces of the innermost portion of the dividers of fig5 are identical to those of fig4 except the pathway taken by escaping fibers has been slightly altered by the orientation of the dividers extending downwardly further into the outlet the dashed lines 27 show the position of the plates in fig4.