The present Invention concerns a procedure for producing classi¬ fied -fines product from material constituted by coarser particles, in said procedure the material being first processed with a rotor crusher, from which the crushed material is transported, carried by an air flow, to a centrifugal classifier, which effects separation of the final fines product.

The rotor crusher is typically a means comprising a vertical shaft and thereto attached a rotor constituted by a horizontal disperser disk, a shell encircling this laterally, and feeding and output apertures or passages for the crushed material, located above and below the disperser disk. The material to be crushed is fed onto the disperser disk, which by centrifugal action flings the material against the encircling shell. In one existing rotor crusher type the shell consists of vertical plates on hitting which the material particles are crushed. In another rotor crusher type, again, the shell has been designed to be a housing in which is formed a mater¬ ial bed consisting of particles to be crushed and from which the particles flung out by the disperser disk rebound so that crushing mainly takes place as particles collide in the air.

In the crushing process effected by a rotor crusher, the material which pers ⁱ sts i _n coarser con iguration settles downward under gravity effect and escapes to the exit aperture below the disperser disk. The more finely divided material, on the other hand, ascends along with the air flow created by the rotating rotor and can be removed to an aperture or passage above the disperser disk. In some of the crushing apparatus designs of prior art a classifying space has been provided on top of the rotor crusher, which separates the most finely divided material carried by the air flow, to become a fines product. The residual coarse fraction may then be returned to the crusher for repeated crusher processing.

The object of the present invention is to devise a new kind of design solution, based on crushing effected with a rotor crusher

and on centrifugal classi ication, for producing a classified fines product, and which is particularly applicable in those cases in which the material consisting of coarser particles and constituting the initial material is moist. The Invention is characterized in that the material which is separated in the centrifugal classifier to constitute the coarse fraction is processed with a jet grinder, operating on compressed air, connected in conjunction with the classifier and from which the material is returned to the classi¬ fier in more finely ground condition.

The jet grinder is a means in which the material to be ground is mixed with hot compressed air, which is divided into flows which, after being accelerated, are made to collide with each other. Grinding will then take place in the collisions between material particles carried by said flows. The advantages of using a jet grinder as a component part in a process comprising crushing and classification is based on the fact that the grinder produces warm exhaust air which can be employed towards drying the moist material that is being processed in the crusher. If such moist material were processed in apparatus of prior art, comprising a rotor crusher and a classifying space provided in its conjunction, it would be neces¬ sary to arrange for separate drying of the material.

As an example of the conceivable applications of the procedure of the invention may be mentioned the manufacturing of a finely divid¬ ed product meant tα be used like cement or another equivalent bonding agent, from water-granulated, calciferous blast furnace slag. In that case the slag constitutes the moist material being supplied to the rotor crusher, this material being dried with the warm exhaust air conducted from the jet grinder to the crusher.

The invention further concerns an apparatus for producing classi¬ fied fines product from material constituted by coarser particles, by the procedure above described. The apparatus comprises, as ele¬ ments known in themselves in the art, a rotor crusher and a centrifugal classifier connected thereto through a passage and into which the crushed material has been arranged to go along with the air flow, and which performs the final fines product separation

with the aid of centrifugal force. The apparatus of the invention is characterized in that it comprises, in addition, a jet grinder operating on compressed air and connected in conjunction with the centrifugal classifier and arranged to comminute the material that is being separated as coarse fraction in the classifier, for re¬ peated classifying treatment.

The invention is described in greater detail in the following with the aid αf an example, referring to the attached drawings, wherein: -

Fig. 1 presents an apparatus according to the invention for produc¬ ing classified fines product, comprising a rotor crusher, a pneu¬ matic centrifugal classifier and a jet grinder, and

Fig. 2 presents, as indicated by arrows II-II in Fig. 1, part of the jet grinder.

The rotor crusher 1 belonging as a part to the apparatus depicted in Fig. 1 comprises a vertical shaft 3 rotated by an electric motor 2 and a rotor thereto attached and consisting of a horizontal dis¬ perser disk 4, and a shell 5, shaped as an annular housing, encirc¬ ling said disperser disk 4. Supply αf the material to be processed in the apparatus is through the passage 6 onto the rotating dis¬ perser disk 4 of the crusher 1, the disperser disk flinging the material particles against the encircling shell 3. As the apparatus operates, a material bed 7 consisting of particles to be crushed builds up on the shell 5 and from which the particles flung out by the disperser disk 4 rebound, to begin with obliquely upward, and thereafter downward conforming to the surface of said bed and shell in such manner that crushing of the material takes place einly as the particles collide in air. The material which remains coarser in the crusher 1 descends under gravity effect to the recycling pas¬ sage 8, starting at the lower end of the crusher, this passage recycling it to the crusher for another crushing treatment. In contrast, the more finely divided material produced by the crusher ascends with the air flow, upward to the passage 9 starting above the disperser disk 4 of the rotor, this passage leading to the

centrifugal classifier 10.

The task of the pneumatic centrifugal classifier 10 comprised in the apparatus is to divide the solids that have been conducted into it, into a classified fines product consisting of the most finely divided particles and a coarse fraction consisting of coarser par¬ ticles. The classifier 10 comprises a substantially cylindrical classifying space 11 with horizontal axis, with which said passage 9 connects tangential ly. Moreover, with the classifying space 11 connects tangentially a passage 13 provided with a blower 12, through this passage being blown into said space an air flow gener¬ ating and maintaining a centrifugal field. The air, and the solids conducted into the classifier, are thereby set in rotary motion within the classifying space 11, where the fines product becomes separated to reside in the centre of the classifying space and the coarse fraction, on its margin. The fines product is removed to an exit aperture 14 located roughly on the horizontal central axis of the classifying space 11, this aperture leading to the fines pro¬ duct cyclone 13, whence the air accompanying the fines product returns through the passage 16 and blower 12 to the classifying space 11, to be reused as classifying fluid. The coarse fraction departs to the exit aperture 17 in the lower part of the classify¬ ing space 11, which leads to the coarse product cyclone 18. The extra air is removed from the classifier 10 to the passage 19.

In the centrifugal classifier 10 the coarse fraction accumulating in the coarse product cyclone 18 is processed, as taught by the invention, with a et grinder 20 connected in conjunction with the classifier. The coarse fraction goes further from the coarse pro¬ duct cyclone 18 through the passage 21 to a feed chamber 23, pro¬ vided with screw conveyor 22, whence it goes, pushed by the screw conveyor, into a mixing space 24, into which is conducted hot com¬ pressed air through the passage 25. The pressure of the compressed air that is used may be, for instance, 16 bar and its temperature about 350 ^β C. The particles of the coarse fraction are mixed with the compressed air and go along therewith, with high velocity, into two curved passages 26, tapering down at their ends, (Fig. 2) the ends 27 of which are placed against each other so that the flows

conducted through the passages collide. The material particles carried by the flows break up on impact so that grinding of the material is the end result. The ground material, and the air, goes thereafter through the passage 28 to the filter 29, where they are separated. The ground material is fed from the filter 29 through the passage 30, tangential ly into the classifying space 11 of the centrifugal classifier 10, for repeated classifying treatment. The escaping air, which has a temperature still higher than 100 ^β C, goes from the filter 29 to the blower 31, which blows it through the passage 32 into the recycling passage of the rotor crusher 1, to serve as recycling fluid and as drying agent for the material sup¬ plied to the crusher through the passage 6.

The apparatus just described may be used e.g. tα comminute granu¬ lated blast furnace slag to become a finely divided, cement-like product. The granulated moist slag, which has particle size in the range fron 0 to 50 mm and moisture content about 10%, is fed into the rotor crusher 1, which dries.it with the aid of the exhaust air derived from the jet grinder 20 and comminutes it to particle size 0-2 mm. The slag that has been comminuted in this way goes along with the air flow to the centrifugal classifier 10, which separates particles smaller than the separation limit of 20 urn to form the fines product in the cyclone 15. Air, containing the moisture which was present in the slag, is removed from the apparatus, at a rate equivalent to the input of air into the apparatus, to the passage 19. The coarse fraction separating in the cyclone 18, which has particle size in the range from 20 Ji to 2 mm, is conducted to the jet grinder 20, and after comminution effected by the latter it returns to undergo another classifying treatment, in which the material which has been ground to particle size less than 20 *f± is separated to join the fines product, while the coarser material returns, as coarse fraction, once again to the jet grinding step. In this way, the apparatus produces, from slag, completely dry, finely divided end product which has particle size in the range from 0 to 20 urn.

It is obvious to a person skilled in the art that different embodi¬ ments αf the invention are not confined to the example presented

here and that they may rather vary within the scope of the claims stated below.