11 of the disintegrator roll housing 1 the cross section of which is regulated by the necessary moveability of the charging trough 16 a contaminant separation opening 4 extends itself as seen circumferentially between the contamination separation wall 42 and the limiting wall 43 this extent is indicated by the lines 44 between the two separate lines 44 which represent the length of the contamination separation wall 42 as well as that of the limiting wall 43 the insert 5 possesses the lateral border 12 which limits the extent of the contamination separation opening 4 in the axial direction back to the side wall 18 between the side limitation 12 and the opposite limitation 13 see fig2 as well as between the lines 44 is to be found the contamination separation opening 4 thus the contamination separation opening 4 in the embodiment of fig1 is designed as an opening in the insert 5 since the insert 5 both in its circumferential direction as well as in its axial direction extends itself beyond the contamination separation opening 4 and to a certain extent also comprises part of the circumferential wall 11 of the disintegrator roll housing 1 in the direction of the arrow p and after the contamination separation opening 4 the insert 5 possesses a contact surface 53 which in the embodiment shown in fig1 is not interrupted in the axial direction this contact surface 53 strikes the abutment 41 of the disintegrator roll housing 1 upon an exchange of the insert 5 it is also possible that a determination can be made of both the size of the contamination separation opening 4 as well as its position in the.