Commercial waste, industrial waste, domestic waste, etc., e.g. (hard) plastics, textiles, composites, wheels, rubber or scrap wood (such as pallets and particle boards) must be comminuted in corresponding comminuting devices before they are definitively disposed of or in particular before they are returned to the cycle of valuable substances.
A central element of a conventional comminutor is a rotor unit which comprises a rotor equipped with knives which can be provided e.g. with concavely ground circular cutting crowns. The knives are fastened to knife holders, for example by screwing, which are welded into knife recesses or can be screwed, for example, the recesses being milled into the rotor. The comminution of the loaded material is accomplished between the knives rotating together with the rotor and stationary bed knives (stator knives, wiper elements).
After comminution between the rotating knives and the stator knives, the material is discharged through a screen device. This screen device determines the comminution factor according to the mesh size (e.g. 5 to 150 mm). The comminuted material passed through the screen is conveyed further by means of a conveying belt, a spiral conveyor, a chain conveyor or an exhaust system. Typically, the screen device contains screen plates which are screwed at their ends to a screen carrier (a screen cassette) or to a machine housing. To securely fasten the screen plates to the screen carrier or the housing, inter alia a plurality of screws is required.
While the comminutor is operated, the screwed joints are subjected to high stresses, and thus, the bearing surfaces of the screwed surfaces must be as parallel as possible with respect to each other to prevent, if possible, the screwed joints from getting released or being broken, resulting in severe damages of the complete comminuting device in operation. The parallelism of the bearing surfaces of the screwed surfaces can only be achieved if the screen cassette and the screen plates are manufactured with very small tolerances. Thereby, the manufacture of these components is very expensive. Moreover, the tightening torques when the screen plates are connected with screws must be exactly observed, so that the assembly can be exclusively carried out by correspondingly qualified personnel.
A further disadvantage of the screwed fastening of the screen plates in prior art is that the screwed joints are sometimes very difficult to access. For example, some screwed joints can be accessed only e.g. by a serviceman descending to a discharge means underneath the comminutor which conveys the comminuted material passed through the screen plates. As the screen plates are subject to wear and thus must be maintained regularly, the possibly hardly accessible screwed joints must be released and replaced by a serviceman at regular intervals, which is very time-consuming.
As the downtime of the comminutor should be minimized for economic reasons, it is desirable to provide a fastening possibility for screen plates to a screen carrier of a screen device for a comminutor which permits a facilitated and quicker maintenance, in particular a facilitated removal of worn out screen plates and assembly of new screen plates.