in order to avoid wear of the part 2 39 of the vibratory conveyor this unit 18 is secured by means of a rod 20 to a support 21 so that when the vibratory conveyor is moving the rod 20 with the unit 18 and associated rods 19 remains stationary the stroke length of the vibratory conveyor is substantially equal to the distance between two consecutive rods 19 whereby the entire perforated part 2 39 of the bottom of the vibratory conveyor can be kept free from incrustations since there is a risk that the transport of material with such a stationary unit 18 having rods 19 is hindered or even becomes completely impossible the device is also provided with a second unit 22 of rods 23 which can move along with the vibratory conveyor while the spacing of the rods 23 with respect to each other may correspond to the stroke length of the vibratory conveyor due to the cooperation of the rods 22 and the rods 19 agglomerations of pulverized material are pulverized again owing to suitable selection of the size of the openings of the sieve bottom e g 6 mm material with a particular size can fall through a steam medium coming.