The object of the invention is a mill for styropor and similar light materials. The mill is primarily intended for milling waste styropor of any dimension and density, e.g. packaging material.

Due to ecological demands there has arisen the need for using styropor waste for some useful purpose instead of burning it and thereby freeing injurious gases. A good use of waste styropor is adding it as supplementary granulate to concrete in order to reach a better thermal isolation. For that purpose it is necesary to mill styropor pieces into granules of a certain size depending on the intended purpose of applying the concrete.

The technical problem solved by the present invention is how to make such a mill which will make possible the milling of styropor and similar light materials of dif¬ ferent shapes and dimensions in a continuous milling process to a defined and adjus¬ table particle size without any danger of stoppage or backward throwing out of un- milled or partly milled styropor pieces as well as a complete milling without any remains of unmilled pieces at a great capacity of the mill.

Known mills of such kind are realized with vertical shafts, whereunder a horizontally rotating milling plate with blades is arranged. Crumbled styropor is thrown out in radial direction near the plate through the circumference or the bottom of the mill. In the inlet of the shaft a security anti-return flap is placed which partly prevents the backward throwing out the unmilled styropor pieces.

A disadvantage of these mills is that the light styropor pieces move in the shaft in an uncontrolled manner and when due to gravity they fall to the bottom i.e. on the blade, they are partly crushed until they are again pushed up by different accidental forces caused by the rotating plate with blades. Thus the milling efficiency is rela¬ tively small since most of the time the stypopor pieces float in the shaft and the plate with blades rotates unexploited. It may even happen that at pushing new pieces into the shaft through the upper inlet, partly milled small pieces are thrown out. When the milling is finished, quite often some pieces accidentally move in the shaft in such a manner that they are not milled completely. Therefore they are considered as un¬ milled remains.

The technical problem is solved by the mill according to the invention in such a man¬ ner that under a vertical shaft a rotating plate is arranged, which comprises two blade levels and is surrounded by an exchangeable perforated cylinder, whose perforation size defines the particle size of the milled styropor.

The two blade levels on the rotating plate have a double purpose. Each styropor piece first meets the upper blades, which roughly cut it into smaller pieces, which through a central opening between the blades fall onto the lower level of blades that cut the styropor pieces near the cylindrical net to the size enabling them to pass through the net and through the funnel out of the mill, which ensures the above- mentioned defined particle size of the milled styropor.

The second equally important function of the lower blade level is to produce air suc¬ tion and thereby also the sucking of styropor pieces out of the shaft, between both blade levels and through the net into the funnel and out of the mill. This stream of air ensures the attraction of the styropor pieces to the upper and subsequently also to the lower blades and prevents the free movement of the styropor pieces in the shaft.

This makes possible a continuous input of styropor pieces into the shaft without the danger of their being thrown out backwards and at the end of the milling all styropor pieces are milled completely.

As it has already been mentioned, nets with different perforation sizes can be ex¬ changed, whereby the definition of the particle size is made possible.

For an easier filling of styropor into the shaft, preferably an arched part is arranged at its inlet, which makes possible the input of styropor pieces into the mill from the side i.e. in horizontal direction since such input is better suitable for manual filling.

The substance of the invention will be explained in more detail in following descrip¬ tion of the example of embodiment and of the drawing, in which show

Fig. 1 a cross section of the mill in the axial direction, Fig. 2 a top view of the plate with blades.

The mill for styropor and similar light materials basically consists of a shaft 1, which is arranged on a base 2 with legs 3 equipped with wheels 4 for the transport of the

machine. Under its bottom 5, the base 2 contains a vertically arranged power electromotor 6, on whose axle in the inside of the base 2 a plate 7 with two horizon¬ tally placed levels of blades 8 and 9 is arranged. Close to the plate 7 in the area of the lower blades 8, a cylindrical net 10 is arranged, whose size of perforation 11 defines the particle size of milled styropor. Between the net 10 and the blades 8 a relatively narrow gap 12 is formed. Over the blades 9 on the base 2 there is removably ar¬ ranged the shaft 1 for receiving styropor pieces, which are not shown in the drawing. On the top the shaft 1 is concluded by an arched inlet part 13, into which the styropor pieces are thrown manually.

On the base 2 on its lower part near the edge a funnel 14 for the outlet of the milled styropor is provided.

The lower level 8 of the blades is arranged in such a manner that at rotating it creates a stream of air from the inlet part 13 towards the outlet funnel 14 past both levels of blades 8 and 9 and through the net 10.

The blades 8, which are directly fixed on the plate 7, are flat and inclined as turbine vanes in order to create a stream of air. The outer edge 15 of each blade 8 is serrated and runs at a relatively short distance to the net 10, which distance is defined by the gap 12. On the blades 8 a ring 16 is placed, which acts as their binding element and as the carrier of the upper blades 9, which are preferably shaped trapezoidally and spa¬ tially inclined with regard to the ring 16.

The mill is preferably realized in such a manner that the upper inlet part 13 can be manually removed so that it can operate without it if e.g. the mill is connected to a transporting device for styropor.

The shaft 1 is also manually removable from the base 2 so that the net 10 can be ex¬ changed for another one with a different perforation 11. All these operations are performed without any tools. The opening and removing of the said parts is done only by releasing lever locks. The net 10 is freely placed inside the base 2.

The mill operates in such a manner that a styropor piece thrown through the inlet part 13 falls into the shaft 1, where it is received by the stream of air caused by the rotating blades 8 on the rotating plate 7. The styropor piece is at first roughly milled by the upper blades 9, then the smaller pieces fall through the ring 16 onto the blades

8, where the stream of air and the centrifugal force press them against the net 10, where the teeth of the outer edges 15 of the blades 8 mill them to the size enabling them to pass through the perforation 11 of the net 10 and further through the funnel 14 out of the mill.

The mill is manufactured according to known tecnological principles and with parameters defined on the basis of market needs.

It is clear that other variants of the mill for styropor and other light materials are pos¬ sible within the scope of the described substance of the invention since they are evi¬ dent to someone skilled in the art. So it is possible to realize the blades 8 and 9 in a different manner in order to achieve the same purpose. Also the stream of air through the mill can be effected by a separate means only partly connected to the plate 7 with blades 8 and 9 or independent of it.

The described example of embodiment of the mill is foreseen for smaller capacities and manual filling, yet it is obvious from the description that according to the same principle also bigger mills with greater capacities can be manufactured, e.g. with an automatic supply and removal of styropor.