The present invention relates to a plant for crushing materials and recovering material fractions of a desired size. The invention specifically, but not exclusively, relates to the crushing of wooden materials, garbage and other refuse. It specially relates to crushing into fraction sizes suitable for stoking purposes (wood chips etc.), for the paper making industry, etc.

For the crushing of refuse, especially forest refuse, demolation wood waste and the like, a plurality of different constructions are available on the market. A common characteristic of these known constructions is that they are basically designed for giving a final fraction in one single working moment. The known constructions have several drawbacks, e.g. that they are relatively energy-demanding, that they do not make it possible to produce fractions of different dimensions without major modification of the construction, and that they are expensive to manufacture. Further, these known crushing plants have a poor degree of utilization of the capacity since material that has already been crushed hinders the feeding of new non-crushed material.

The present invention aims at eliminating or reducing these and other drawbacks of known crushing plants. More specifically the invention aims at providing a crushing plant which both saves energy and increases the capacity compared to the known constructions. Another purpose of the invention is to provide a crushing plant which has a simple and cost-saving design thereby simplifying the manufacture thereof. A further object of the invention is to provide a crushing plant which can be used for crushing different types of materials without any major adjustments. A still further object of the invention is to provide a crushing plant of the indicated type which permits crushing of a mixture of different materials, for example bark - twigs/knots - objects of iron.

These and other objects and advantages of the invention have been achieved by giving the crushing plant the characteristic features which are indicated in the enclosed claims and which are explained further in the following description of some special embodiments, to which the invention however is not restricted, reference being made to the enclosed drawings, wherein

Fig. 1 schematically shows a first embodiment of a crushing plant according to the invention together with a schematic material flow diagram for the plant,

Fig. 2 schematically shows an alternative embodiment of a crushing plant according to the invention with a corresponding material flow diagram, and

Fig. 3 schematically shows an example of mobile monting of a crushing plant according to the invention with a corresponding material flow diagram.

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The crushing plant shown in Figure 1 essentially consists of a coarse crusher 1, a feed hopper 10, a sieve 20, a fine crusher 30, a conveyor belt 40 under the sieve 20 and the fine crusher 30, and a discharge belt 50 for accepted material. 5 The material to be crushed is fed into the coarse crusher 1 having driving and crushing devices which are known per se and are schematically indicated by

2. The coarse crusher 1 is preferably of the screw type, and it can be fed with fine as well as coarse materials, e.g. logs and the like. After the coarse crushing in the coarse crusher 1 the material is fed into the feed hopper 10 via any

-10 suitable discharge opening from the coarse crusher, schematically designated by

3. In the feed hopper 10 there is a suitable conveyor device 11 which transports the coarsely crushed material to the sieve 20, preferably obliquely upwards. The conveyor 11 can be an endless conveyor belt - but it is preferably a chain feeder (marked by the projections 12) -running around two end rollers 13 and 14, of

1 which at least one is driven by a suitable motor (not shown). At the discharged end there is, above the roller 14, a feed roller 15 having projections 16 and which can be driven or idle. The amount of material to be fed to the sieve 20 from the conveyor 10 can be controlled by the driving of the conveyer 10 and the feed roller 15. In this manner one can prevent clogging of material and ensure optimal

20 utilization of the sieve 20, which is herein shown as a shaking sieve of the grid type which is known per se. At the sieve 20 a first accepted fraction is taken out, i.e. the material passing through the sieve. This accepted fraction of material falls down through a pocket 21 onto the conveyor belt 40 for being transported further thereon.

25 The material which is not accepted by (does not pass through) the sieve

20 at the discharge end of the sieve meets an obliquely upwardly directed air stream 22 created by a fan 23. The air stream 22 is adjusted such that the desired material, e.g. coarse wood chop, which is lighter than usual contaminants such as stones, metal pieces etc are blown to the fine crusher 30, whereas the

30 heavier contaminants fall down as reject material onto a conveyor belt 24 or any other suitable conveyor device for disposal. The material that can be crushed is then ground in the fine crusher 30 (which can be a mill of a type known per se) into a fine fraction of the desired size. The material discharged from the fine crusher 30 falls down onto the conveyor belt 40.

35 The conveyor belt 40 is preferably an endless belt, which runs around a front roller 41 and a rear roller 42, of which at least one is a drive roller. The conveyor belt 40 is preferably arranged for magnetic separation of magnetic

materials such as nails and the like from the material fractions which are carried along the belt 40. This magnetic separation can preferably be achieved in that the roller 40 is provided with one or more magnets, so that magnetic contaminants follow the conveyor belt 40 around the roller 42 to fall down into a collection pocket 43 when the magnetic force from the roller 42 ceases.

The accepted material which is discharged from the conveyor belt 40 is finally discharged to a suitable desired location, e.g. by falling down onto the discharge conveyor belt 50.

Figure 2 shows an alternative embodiment of the crushing plant according to the invention, wherein the fan 23 of Figure 1 has been replaced by a "throwing roller" 23'. Those elements of the embodiment according to Figure 2, which have a direct correspondence in Figure 1, have the same reference designations as in Figure 1. The embodiment according to Figure 2 is especially suitable when using a so-called disk sieve instead of a screen-type sieve. As is known a disk sieve consists of a plurality of rows of intermeshing rotating disks 20', the fraction size primarily being determined by the number of disks and the spacing between the same (lengthwise and widthwise). The disk sieve 20' is terminated by a "throwing roller" or a series of paralell disks 23', which are rotated at a speed sufficent for throwing the heavier contaminants over the fine crusher 30, the desired lighter material falling down into the fine crusher. The reject conveyor belt 24 of Figure 1 consequently has been moved to a location after the fine crusher 30, and it has the reference designation 24' in Figure 2. For the rest the function and the manner of operation of the plant is the same as has been described in connection with Figure 1. In Figure 3 there is schematically shown an example of mobile monting of the crushing device according to the invention. In the shown embodiment the plant is designed as trailer mounting, but other forms of mounting can, of course, also be envisaged such as switch-platform mounting, chassis mounting etc. In Figure 3 the same reference designations have been used for those elements which have a correspondence in Figure 1 and/or 2. It can be noted that the magnetic separation step has been deleted in this embodiment, but it is, of course, also possible to utilize magnetic separation also for mobile mounting of the plant.

Although the crushing plant according to the invention primarily is characterized in that the crushing takes place stepwise by a coarse crusher and a fine crusher, it also is advantageous in that a desired fraction can be taken out at the stage of the crushing in which the desired fraction has been obtained. The desired final fraction size can be adjusted as needed - on the one hand in the

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t sieve and on the other hand in the fine crusher or mill. The plant also offers advantages in that one is not bound to always make use of the entire plant. For example, when the starting material is relatively fine the fine crusher can be shut off. If, on the other hand, only coarse crushing is desired, e.g. for brittle materials such as glass, aluminum, etc., the sieve can be taken away and all of the coarsely crushed material be allowed to fall down onto the conveyor belt 40. The feed hopper 10 then also functions as a distributor to the conveyor belt 40 to provide for uniform feeding to the same since the coarse crusher does not always give a uniform flow. The crushing plant according to the invention thus permits the material to be fed at a suitable station, depending on the structure of the material, and the desired fraction to be taken out. As mentioned the plant is energy saving, i.a. because not all of the material has to pass through but "falls out" at a suitable fraction, especially before the energy-consuming fine crusher. The described plant can save energy in the order of 50%.

The invention is, of course, not restricted to the specific embodiments which have been described above and shown in the drawings, but many modifications and variations are possible within the scope of the subsequent claims.

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