The object of the invention is a mill, the purpose of which is to crush steel slag so that metal and slags and can be separated from each other, and which mill compris es a casing, cover and bottom, and there is a crushing element inside of the mill by means of which steel slag can be crushed.

All the mills known per se are single rotor mills, or they are provided with other crushing elements. With the aforementioned mills, however, a required impact ve locity, i.e. crushing velocity, is not reached, and they are not adequately suited for the materials mentioned above. The purpose of the invention is to eliminate the disadvantages mentioned above. The mill in accordance with the invention is characterized in that the crushing ele ment comprises two rotors rotating opposite to each other; inner rotor and outer ro tor, and that the material can be fed into the center of the inner rotor, from which it is thrown to the outer rotor in consequence of the centrifugal force, and further be- low, outside through outlet apertures on the bottom.

Various embodiments of the invention are disclosed in the dependent claims of the set of claims. The impact velocity even doubles with the invention, and additionally, the solution allows more powerful rotation speeds without material being stuck, be cause the counter circle is rotating. The invention is explained below with reference to the accompanying drawing, which presents a sectional view of the mill in accordance of the invention.

The aim of the mill is to crush steel slag so that metal and slags can be separated from each other. The mill comprises a casing 1, cover 2 and bottom 3. There is a crushing element inside of the mill by means of which steel slag can be crushed. The crushing element comprises two rotors rotating opposite to each other; inner ro tor 4 and outer rotor 5. Material 6 can be fed into the center of the inner rotor 4, from which it is thrown to the outer rotor 5 in consequence of the centrifugal force, and further below, outside through outlet apertures 7 on the bottom 3. The inner ro tor 4 comprises a frame plate 9, which rotates by means of a motor 8, on the top sur- face of which frame plate 9 there are radial crushing wings 10. The outer rotor 5 comprises a top frame plate 11, which rotates by means of a motor, on the circle of which top frame plate 11 there are crushing elements 12 pointing downwards. The outer rotor is connected to a further motor (not shown in the figure) by means of a tubular rotating axis 13 through which the material 6 to be crushed is to be fed in- side of the mill. The elements of the mill are produced from suitable steel material, which is strong and high-tensile.

The invention is not limited to the example described above, but it may be varied within the scope of the claims presented below. Besides crushing steel slag, the mill is thus suited for crushing also other slags, such as combustion ash. The separation of metals from the crushed mass can be carried out with methods known per se. Iron particles, for example, can be separated with magnetic separator, for example, and other non-magnetic metals with prior known chemical methods, for example. On the circle, there can be two or more wings 10 and crushing elements 12, e.g. six, eight or even more.