BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a method and a mill for crushing rubble according to the preambles of the claim 1 and 7, respectively. For purposes of this application and the invention disclosed, the term "rubble" is used to refer to building demolition materials and similar materials which during the crushing thereof create a dust formation.

2. Related Art

A method and a mill of the considered type are employed, for example, in plants for treating building demolition rubble for obtaining re-usable aggregate. A plant of this type is disclosed, for example, in IT-A-1 ,228,705 assigned to the applicant.

The crushing and discharging method of the known mills is illustrated below with reference to the schematic representation of Fig. 1. The first stage of the plant of the type disclosed in IT-A-1 ,228,705 is formed by a crushing and discharging station, whereby said crushing and discharging station is illustrated in Fig. 1 and designated as a whole by A. Said crushing and discharging station A is formed by a mill 1 , generally a hammer mill provided with hammers driven by a motor, and an underlying discharging device or box 2 for discharging the crushed material, for

example on a conveyor belt 3. The discharging device 2 is a separated, that is distinct device which is amovably associated to the mill 1. In more detail, the mill 1 has at the top thereof a charging opening 4 into which the rubble to be crushed is introduced by means of a reciprocating feeder 5 or other suitable feeder. Inside the mill body 7 is supported a rotor provided with the not shown crushing hammers, whereby said rotor is designed by 8 and can be driven by a not shown electric or diesei motor, in the direction indicated by the arrow f. The lower portion of the mill body 7 forms a hopper 9 which is closed below by a bottom 10 and is open at one of the lateral sides thereof, in the shown example at the front side 12. The mill hopper 9 is housed in said discharging device or box 2. The latter is formed by a vibrating box which is made up of two sidewalls 13 and 14 and a back wall 15 fixed to the mill body 7 and a bottom 10 which is connected to a not shown vibrating means supported by springs on a basement in a not shown manner. The front side 12 of said discharging box 2 is open to allow the crushed material to be discharged in the direction of the arrow F. The known crushing and discharging method comprises the following steps: a) crushing the rubble charged into the mill, b) failing/hurling the crushed rubble into the underlying discharging hopper to form a material layer having a lower height (h) than the height (H) of the hopper discharging opening, and c) discharging the crushed material.

Sheet steel deflectors indicated at 18 guide the introduced material towards the central crushing chamber and towards the middle portion of the mill hopper.

With the term "crushed material" is here intended the whole material passing through the mill, that is the effectively crushed material, the fine

gravel and sand-like throughgoing fractions as well as the not crushable fractions like reinforcement iron rods, pieces of wooden and aluminium door and window frames, large paper pieces of paper cement sacks, pieces of plastic sheets and so on.

After this preliminary introduction of the known mills it is pointed out that in all the prior art mills the wanted space between the level 19 of the crushed material level in the mill hopper 9 and the top side of said discharging opening 11 is always provided in order to ensure the free transit of said bulky pieces, particularly of the large wood and metal frame pieces as well as the iron rods, which latter present indeed the most different dimensions and entanglement shapes. Formation of dust.

As to the pneumatic aspect of the known hammer mills it is pointed out that in operation the rotating hammers act similarly to real fan wheels and create a strong depression inside the mill crushing chamber. Said depression sucks a large air quantity from outside through the charging opening 4 and discharges said air quantity, jet-like, into the mill hopper, and then the formed air/dust mixture is exhausted through the discharging opening 11 above the material layer 6, as illustrated by the chain arrows in Fig. 1.

Into the mill crushing chamber take place severe crushing phenomena as well as severe abrasion phenomena between the individual rubble parts with a consequent crumbling/chalking of the ciayish and cementish components. Thus, the air jet stream leaving the mill trails a large quantity of dust. Furthermore is to be considered the fact that upon impinging the crushed material layer in the mill hopper 9 and the discharging box 2 said air flow raises another great deal of dust. Said dust formations must be somehow separated or filtered away from the exhausted air/dust mixture

in order to fulfil the anti-pollution specifications which become, as known, always more severe in Italy and abroad. Dust separation.

For carrying out the dust separation it is known to employ a large separation or filtering chamber which extends from the mill lower part towards the ground. According to a first solution is provided the use of so called sleeve filters. Said sleeve filters are very expensive both in purchasing and servicing thereof and require a great energy consumption. Another solution provides a strong water spraying above the dust formation area, and sometimes also on the rubble before the crushing thereof. This sulution firstly requires a water availability and secondly needs a great quantity of water. Further it is noted that the treatment water can form contaminating percolations, which require an expensive treatment or disposal thereof.

A strong reduction of the needed water can be achieved by means of a dust separation chamber 21 (Fig. 1) which is defined by jute walls, is steadily wetted and is disclosed in the aforementioned IT-A-1 ,228,705. In said dust separation chamber are provided inner and outer water spraying nozzles 22. However, also said solution requires a water availability and involves, even if in a smaller and easily contrallable measure, the danger of said percolations. Operation irregularities.

The presence of water or moisture in the rubble, said crumbling/chalking of the clayish and cementish components tending to set, the weight of the crushed material in the mill discharging hopper as well as in the discharging box and the discharging vibrations causing a material compaction action create a phenomenon of strong progressive agglomeration of the crushed material in the discharging box, starting from the sidewalls and the bottom toward the discharging box interior.

Said agglomeration phenomenon leads to a progressive reduction of the real discharging box capacity so that the quantity of the discharged material is reduced and the level of the crushed material in the mill hopper increases and causes in a short time the filling of the mill hopper as far as the mill interior. If the operator does not stop the mill, said mill filling will cause demages of the mill internal components, the driving parts of the mill and lastly the mill stop.

The following operations for emptying the mill hopper and the underlying discharging box are carried out uncomfortably manually by a number of operators provided with picks, chisels, shovels and so on, whereby said emptying operations are very time consuming and involve long and therefore expensive stop periods of the whole plant.

Furthermore, it is pointed out that said kind of emptying operations are not occasionally but they occur several times a day.

SUMMARY OF THE INVENTION

The main object of the present invention is to provide a method and a mill for crushing rubble of the kind pointed out in the introductory part and capable of avoiding the prior art drawbacks as well as allowing a continuous crushing and discharging of the crushed material without any dust formation.

It is another object of the present invention to avoid that in the discharging device occur agglomerations reducing the original or useful cross-section and volume provided for discharging the crushed material.

These objects are solved by the present invention by the method set forth in claim 1 and the mill set forth in claim 7, respectively.

Further advantageous embodiments of the present invention are evident from the dependent claims concerning the crushing method and mill.

Claim 2 suggests an improvement providing a variable height of the discharging opening, that is of the discharged material flow or plug.

According to claims 3 and 4 it is possible to achieve a uniform and progressive dischargement of the crushed material, and the reinforcement iron rods or other bulky pieces do not impair at all the stability of the continuously self-reforming plug.

Claims 5 and 6 propose adjustment solutions able to automate the material crushing/discharging cycles.

Claim 8 discloses a mill embodiment providing a variable height of the discharging opening, that is of the discharged material flow or plug.

Claim 9 suggests a configuration of the hopper discharging opening capable of avoiding a dust formation also during the short starting phase of the crushing step.

An advantageuos improvement of the mill allowing the mill to autonomously carry out also the material discharging step is disclosed in claim 10.

Claim 11 suggests a mill provided with a discharging device associated to the mill hopp er, whereby said improved and combined mill forms a crushing and discharging station operating without dust formation.

Claims 12 and 13 disclose each a simple and reliable embodiment of a discharging device integrated into the mill or forming a discharging device associated with the mill, as well as preferred stroke values of the reciprocating discharging strokes.

Claim 14 suggests an alternate solution of the discharging means which is employable in the improved mill itself or in a discharging device which can be associated to said mill.

In claim 15 is disclosed a configuration of a discharging belt capable of reliably cope with the rough rubble crushing operation.

Claim 16 proposes to employ known detecting and adjustment means which under the control of a computer unit, allow an automatic carrying out of the crushing and discharging cycles.

In claim 17 is disclosed an arrangement of the means for detecting the height of the material flow being discharged, that is of the plug, outside the mill or crushing station, that is in a calm environment.

Claim 18 suggests a simple and operatively reliable coupling between the means for indirectly detecting the plug height and the adjustable means controlling the rate of the discharged material flow.

A mill stiffening measure, which can also be employable for functional and adjusting purposes, is disclosed in claim 19.

In claim 20 is proposed an advantageous embodiment of discharging means wich can be either provided in or associated to the mill and cause compulsory advance of the crushed material to be discharged as well as a simultaneous self-cleaning action.

Claim 21 suggests the configuration of the proposed discharging means in the form of discharging means which are distinct and can be associated both to the improved mill according to the present invention and to already extant mills in order to accomplish crushing and discharging stations operating according to the present invention, that is without dust formation.

Claims 22 is directed to an advantageous use of the improved mill or crushing station in rubble cruhing plants.

The present invention is based on the knowledge:

- that by varying the pneumatic mill behaviour and abolishing the space comprised between the crushed material level inside the mill hopper and the upper side of the discharging opening in the mill hopper - whereby, as pointed out above, heretofore said space was deemed essential by those skilled in the art - it is possible to wholly avoid any dust formation and all the disadvantages connected with said dust formation, and

- that, as corroborated by numerous repeated experiments, the wanted whole filling of the mill hopper with the crushed material in the form of a

"continuous plug" does not hinder at all the bulky pieces discharge both from the mill and the mill hopper or discharging box during the progressive discharging of said continuous plug.

The substantial advantages achieved with the present invention consist in the fact that is obtained a crushing operation without dust formation. And this is achieved without additional ancillary means, but only utilizing the crushed material itself as a "continuous plug". Furthermore, the proposed method and mill or crushing station make the known dust separation means superflous and allow a use of the improved crushing mill and station also in sites without water availability as well as in the neighbourhood of built-up areas.

Another important advantage is to be seen in the fact that by means of extremly simple means, which have a reliable operation and are advantageously self-cleaning, is ensured a reliable crushed material discharging and are wholly avoided the known agglomerations and the consequent mill stops.

Still another advantage consists in the easy possibility to transform extant crushing mills in mills or crushing stations according to the present invention.

Another advantage is that with the method and crushing mill according to the present invention it is possible to carry out a simple and reliable adjustment of the rubber quantity charged into the mill and the quantity of the crushed discharged material in order to continuously maintain the formation of the "continuous plug" consisting of crushed material.

It is pointed out that with the method und a crushing mill according to the present invention it is possible to avoid whatever pollution and to substantially improve the working conditions for the sole operator who is now necessary.

Still another advantage is that by providing a variable height of the discharging opening by means of a self-positioning flap valve it is possible to place the detecting means in a calm environment outside the discharging devices, in which latter the crushed material hurled out from the hammer chamber could damage detecting means placed therein. The present invention is further directed to a distinct discharging device per se as well as to the use of the improved mills and crushing stations in a plant for treating building demolition rubber and the like. The present invention as well as further advantages and features thereof will now be described below in connection with several preferred embodiments illustrated in the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, the following are shown diagrammatically or in principle: Fig. 1 shows a side elevational view of a known crushing mill with associated discharging device for the crushed material, partly in cross- section;

Fig. 2 shows a side elevational view of an improved mill according to the present invention with a discharging opening which can be closed by a guillotine-like sluice gate, in the closed position;

Fig. 2A shows a view similar to that of Fig. 2, however with the sluice gate in the open position;

Fig. 3 shows a view similar to that of Fig. 2, however with discharging means integrated into the mill and formed by a hopper bottom configured as a vibrating or reciprocating movable bottom;

Fig. 4 shows a view similar to that of Fig. 2, however with a distinct box¬ like discharging device provided with a vibrating or reciprocating movable bottom;

Fig. 5 shows a view similar to that of Fig. 2, however with a discharging means integrated into the mill and formed by the hopper bottom configured as an endless belt;

Fig. 6 shows a view similar to that of Fig. 2, however with a distinct box¬ like discharging device provided with an endless belt-like movable bottom; Fig. 7 shows an enlarged longitudinal cross-section taken along the discharging part of a mill according to the present invention, further provided with compulsory advancing means for the crushed material to be discharged, whereby said compulsory advancing means is provided on the movable bottom and the sidewatls of the hopper or the discharging device associated with the mill, and

Fig. 8 shows a preferred embodiment provided with a means allowing variations of the height of the discharging opening during operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic configurations of a known crushing mill 1 and a therewith associated discharging device 2 forming a rubble crushing station A for carrying out the known crushing and discharging method - operating with dust formation - are described in the introductory part with reference to Fig. 1.

The drawbacks and shortcomings of these known solutions have been likewise set forth in the introductory part.

Even if the mills or the crushing stations according to the present invention start from per se known units, the proposed improvements are such to lead - as it will be depicted hereinafter - to a rubble crushing and discharging method wich is, like the obtained results, conceptually wholly different.

In the Figures 1 to 7 common equal or equivalent parts are generically designated by the same reference numerals as well as by specific

reference numerals according to the different contemplated embodiments.

Particularly, as crushing unit 1 it is convenient to use a known hammer mill - due to its good efficiency, reliability and adjustment simplicity -.

However, this suggestion does not have a limitativ character with regard to the type of the used mill. Among the different embodiments of employable discharging devices 2 it is certainly possible to further use the known vibrating discharging box because the latter, used according to the present invention, is not pratically effected by the shortcomings of the known vibrating boxes as set forth in the introductory part.

According to the present invention the discharging device 2 associated to the mill 1 or the discharging means integrated, that is incorporated into the mill and illustrated hereinafter, should allow a so called "peeling-like" drawing or discharging of the crushed material from the bottom of the crushed material layer which now forms, in the hopper, a continuous column or "plug" 6. At the outlet of the hopper, that is before the hopper discharging opening 11, the plug 6 has a height H1, Fig. 7, which is a little higher than the height H of said discharging opening 11.

In an advantageous embodiment, Fig. 2, 2A, 7, above said discharging opening 11 the mill body 7 is provided with an horizontal frame 24 having for example a rectangular shape and consisting of beams 25, in the shown embodiment of "I" beams.

The mill 1 is supported by a known and not illustrated supporting structure.

In an advantageous embodiment according to the present invention the open side or discharging opening 11 of the hopper 9 is provided with a sluice gate 27, in the shown embodiment a guillotine-like one, which is illustrated in its closed position in Fig. 2 and in its wholly opened position in Fig. 2A. Said sluice gate 27 is for example movably mounted on guide

elements 28 and associated with driving means, for example in the form of a not illustrated rack-and-pinion drive or a likewise not illustrated cylinder-piston unit. The Fig. 2 and 2A show a sluice gate 27 which is movable in a vertical plane. In practice, it is also obviously possible to place said sluice gate in an oblique position, as per se already known, Fig. 1 , or in other positions as desired. Important is the fact that said sluice gate allows to close and open the provided discharging opening 11. As to the discharging devices or means it is pointed out that they can be configured in accordance with the present invention either as distinct devices or means 2 which can be associated to the mill 1 , for example to an extant mill, Fig. 4, 6, 7, or as discharging devices or means 17 which are integrated into the mill, Fig. 3, 5, 7. Therefore, the assembly formed by a mill with the relative discharging means integrated into the latter or associated to said mill, forms an improved mill or an improved crushing and discharging station A according to the present invention, respectively. The discharging and self-cleaning means 29 shown in Fig. 7 and described hereinafter can be provided both in the improved mills 1 and the crushing and discharging stations A according to the present invention.

Reference is now made to Fig. 3. The shown mill 1, which may have either a common discharging opening 11 , that is an opening 11 which is always open, or an opening provided with a sluice gate 27, is provided with a discharging means 17 which is integrated into the structure of the mill hopper 9. In more detail, the bottom 10, Fig. 1, of said mill hopper 9 is constructed as a movable bottom, for example as a carriage-like bottom 30 which is connected to a driving means 31. Said driving means can be formed either by known reciprocating drives or vibrating drives, as per se known in feeding boxes for incoherent materials. Advantageously, said driving means is preferably configured as an adjustable one.

The mehanical coupling between the movable bottom 30 and said mill discharging hopper 9 can be accomplished in whatever suitable manner, for example by means of not shown sliding guides. In the case of reciprocating drives have been obtained good results using eccentric crank gears associated with a geared motor with adjustable speed as well as with drives formed by hydraulic piston-cylinder units, whereby the piston rods are fixed to said carriage-like bottom 30. Preferably, between the hopper 9 and the fixed cylinders of said piston- cylinder units are interposed cushioning springs. Said known drives are not illustrated in detail. They can also be substituted by other operatively equivalent drives. With the usual sizes of the known hammer mills and discharging hoppers thereof have been achieved good results with reciprocating strokes of the movable bottom in the range of 3 to 15 cm, preferably in the range of 5 to 10 cm, and most preferably with strokes amounting to 8 cm. Of course, are also employable strokes having other stroke values, and this as a function of the material to be trated. In the case of said vibrating drives the preferred adjustments can concern the revolving speed of the eccentric and/or the degree of eccentricity. The carriage-like bottom 30 can be horizontal or, preferably, it can be slanting downwards and towards the discharging direction, as illustrated in Fig. 3. The carriage-like bottom 30 is advantageously supported on supporting rollers 32. Between the carriage-like bottom 30 and the fixed walls of said mill hopper 9 are advantageously provided not shown gasket elements, for example bellows-like gaskets or longitudinal lip seals forming chambers.

In order to obtain a more stable formation of the continuous plug 6 the sidewalls of said mill hopper can longitudinally project outside the mill body 7, as shown in Fig. 3 with chain-dotted lines.

In the embodiment of Fig. 4 to the mill hopper 9 is associated a discharging box 2 having a movable carriage-like bottom 34 provided with a respective driving means 31 , for example as described with regard to Fig. 3. Like the known vibrating box 2, Fig. 1, also the carriage-like box shown in Fig. 4 houses the discharging hopper 9 of a mill 1 , thereby forming a crushing and discharging station A.

Reference is now made to Fig. 7. For achieving a reliable material advance as well as a self-cleaning action of the hopper (Fig. 3) or of the discharging box 2 (Fig. 4) having both a carriage-like bottom 30 or 34, on said bottom 30 or 34 transversally to the discharging direction, arrow F, is fixed, for example welded, at least one push beam 35. Both for construction stiffening purposes as well as for achieving a back stroke of the movable bottom exluding whatever material compacting action, the push beam 35 is provided with a back roof-like covering 36. The beam 35 and the covering 36 define a wedge-like structure forming said self- cleaning means 29. Upstream to the push beam 35 and parallel to the latter is provided a wedge-like structure 38 which is fixed, for example welded, to the sidewalls of the hopper 9 (Fig. 3) or of the discharging box 2 having said carriage-like bottom 34 (Fig. 4 and 7), whereby the slanting or bent back side 39 of the wedge structure 38 faces the push beam 35. Lastly, in Fig. 7 the reference numeral 50 denotes an observation window by means of which during experimental operations it was possible to observe the behavior of the material inside the mill hopper 9 or the discharging box 2.

In the embodiment shown in Fig. 5 is provided again a discharging means 17 which is integrated into the mill hopper 9 and which is constructed as an endless belt 41 forming the movable bottom 42 of the discharging hopper 9. The belt 41 is mounted on two wheels 43 and 44, whereby the wheel 44 is a driving wheel and it is connected to a driving geared motor

45 with associated not shown speed variator. The upper belt section 46 of said belt 41 slides on a substantially continuous supporting plane or platform 47 which is formed for example as a supporting metal plate or as a number of boards which are disposed parallel to each other in the longitudinal direction, or as transversally disposed not shown rollers and so on. The purpose of these measures is to prevent the belt from damages due to the strong impingment on the belt of the crushed material as well as the reinforcement iron rods and so on during the starting phase, that is when the belt is not yet covered by the crushed material. During the normal operation said belt is covered by the crushed material plug, which avoids said danger.

Like the carriage-like bottoms 30 and 34 also the structure of said bottom configured as an endless belt 41 is supported on a not shown basement which can be realized in any suitable manner.

In a preferred embodiment, the discharging belt 41 is configured as a belt track which is produced in metal or plastics, for example in plastics incorporating a metal core and/or reinforcement fibers. In the embodiment illustrated in Fig. 6 with the mill 1 is associated a box¬ like discharging device 2 having a movable bottom 42 in the form of an endless belt 41 , as illustrated in Fig. 5, so that a crushing and discharging station A according to the present invention is formed. Reference is now made to Fig. 8. It can be seen that the upper part of the discharging opening 11 is provided with a flap valve 51 the axle 52 of which is pivotally supported in a dust tight manner at the top of the discharging opening 11 , transversally to the discharging direction F. Due to its own weight, and/or by means of not shown spring preloading means, said flap valve tends to take a vertical position, shown with dashed lines, so that when the mill hopper 9 or discharging means 2; 17 are emty the height of the discharging opening 11 becomes Hmin.

In use, the flow of the crushed material being discharged pushes the flap valve 51 , in the sense of opening the latter, so that the actual height value Ha of the discharging opening 11 increases, and more specifically it could increase up to the maximal height value H max., shown with dotted lines. The reference numeral 53 denotes an arm which is fixed to the flap valve axle 52 or, not shown, to the outer surface of the flap valve 51 itself, and is operatively connected to a per se known electric, pneumatic, hydraulic or mechanic detecting means generally denoted by 54. A mechanical coupling could be realized, in a not shown manner, for example by means of an arc-like rack the pinion of which is engaged with the detecting means 54, the output of which is connected to the means for adjusting the rubble quantity to be fed to the mill and/or the adjusting means 31 controlling the rate of the discharging material flow. Said detecting and adjusting/controlling means per se as well as the connection circuits thereof with each other and, preferably, with the mill superior control computer or processor are known by those skilled in the control technique and, therefore, not shown.

The operation of the improved mill or crushing and discharging station according to the present invention is as follows.

Reference is made to Fig. 2 to 7. During the short starting phase the crushed material as well as the components which cannot be crushed are hurled out from the mill into the underlying hopper. In a short time the material coming from the mill will wholly fill the mill hopper and when the material level 19 surpasses the height H and, reaching a height H1, begins to enter into the frame 24, in the hopper there will be a material column or "plug" 6, which closes the discharging opening 11 and so prevents an air and consequently a dust exhaust or emission from said discharging opening 11. This behavior is obtained in all the illustrated

embodiments of improved mills, discharging means 17 integrated into the mill 1 , and crushing and discharging stations A.

Under such conditions it will be sufficient to adjust the balance state between the quantity of rubble charged into the mill and the rate of material flow discharged by the mill hopper 9 incorporating the discharging means 17 (Fig. 3, 5 and 7), by the carriage-like discharging box 2 (Fig. 4, 7) or by the discharging box 2 having an endless belt bottom (Fig. 6). Said balance state can be controlled and maintained manually or adjusted in an automatic manner by controlling, singularly or in combination, the rubble feeder, the rotation speed of the mill hammers, the frequency and the length of the reciprocating strokes of the carriage- like bottoms, or the speed and the degree of eccentricity of the vibrating bottoms, or the speed of the discharging belt-like bottom. At any rate, the necessary circuits and the components thereof are well known to those skilled in the control and regulation technique, so that said circuits and components are not described and shown in detail. According to the present invention during operation the formation of the material plug 6 is kept up continuously, whereby the plug height H1 can vary for example within the range of the height of the frame 24, that is slightly above the discharging opening 11. Under such conditions the discharging opening 11 is always mantained "plugged up" in a so to say "fluidic" manner so that during the mill operation the formation of dust is always prevented, and this both from the mill and from the hopper 9 thereof as well as from the distinct discharging device 2. In fact, the mixture consisting of crushed parts having different sizes and the fine gravel and sand-like fractions forming the plug 6 renders said plug at the same time very packed and notwithstanding supple so that the plug has a "sealing behavior" with regard to the discharging opening 11.

During operation the material plug is formed continuously again, whereby the plug part which is peeled up from the plug bottom is continuously replaced by a corresponding plug top feed from the mill charging opening 4 such that the height H1 of the plug 6, for example inside the frame 24, is mantained continuously.

The push beam 35 during its pushing movement towards said fixed wedge 38 causes a compulsory snowplow-like advance of the material inside the discharging hopper or box so that the pushed material slides upon the wedge 38 and can be reliably discharged. The beam 35 during its back stroke creates between itself and the wedge 38 a void, in which falls the abovelying plug material.

These operation cycles ensure both a reliable discharging and transfer of the plug material, for example on a conveyor belt 3 or the like, as well as an efficient self-cleaning action of the hopper 9 or the carriage-like box 2. In this manner it is possible to reliably avoid the known clogging agglomeration of the known vibrating discharging boxes. In the case of a belt-like movable bottom 42 the latter may also be provided on its upper surface with not shown transversally arranged section bars in order to facilitate said peeling drawing or discharging of the plug material. These section bars act with the ends thereof as scrapers with regard to the sidewalls of the hopper or the discharging box with a belt-like movable bottom so that also said section bar ends exert a self-cleaning or anticlogging action.

Due to the fact that the material drawing or discharging action from the plug bottom occurs in an efficient manner and the continuous plug 6 has a rather friable and "fluidic" consistency, it is stressed that in practice the non crushable pieces like reinforcement rods, joists, paper pieces of cement paper sacks, window and door frame pieces and the like, contrary to all expectations, gradually sink into the continuous plug, uniformly

advance and are discharged without any problems - regardless the shapes or entanglements thereof - from the discharging opening 11. Furthermore, it is pointed out that in mills having traditional discharging hoppers or boxes during the first starting phase the formation of the crushed material layer into the empty hopper 9 or discharging box 2 is accompanied - up to the completion of the material plug 6 - by a dust formation. In practice said drawback can be avoided by preliminarly filling - through the stopped mill - the underlying hopper 9 or discharging box 2 with gravel and/or sand, in case screened sand. Moreover, said shortcoming can also be simply avoided by providing a discharging opening 11 provided with a sluice gate 27. In this case the discharging opening 11 will be kept closed during the starting phase till the completion of the material plug 6 and then said opening 11 will be opened to allow the crushed material discharging step as depicted above. The alternate embodiments and operation of the mill 1 or crushing station A shown in Fig. 8 correspond in principle to those depicted in Fig. 7 and set forth in the description directed to the Fig. 2 to 7. The only difference relates the height H of the discharging opening 11 , whereby in the embodiments of Fig. 2 to 7 the actual height value H is a predetermined fixed height H, whereas in the embodiment of Fig. 8 the height of the discharging opening 11 is a variable height, the actual value Ha of which can range between a minimum height Hmin. and a maximum height Mmax.. Said range can be freely chosen. In operation the height Ha is always determined by the pushing action of the plug material inside the hopper 9 or discharging devices 2; 17, whereby said plug material continuously engages the flap valve 51 so that the plug level 19 inside the hopper is always higher than the actual discharging height Ha. Under such circumstances the plug 6 can always develop its "clogging" action with regard to the discharging opening 11 avoiding the dust formation and

exhaust according to the teaching of the present invention.lt is pointed out that employing a discharging opening having a variable discharging height Ha, the plug level 19 can of course drop below the beam frame 24. The solution illustrated in Fig. 8 facilitates, on one hand, the adjustment of the means 31 regulating the rate of the material or plug being discharged, because of the great possible variation range Hmim. - Hmax. and the correspondent longer adjusting or controlling time at disposal, and allows, on the other hand, an arrangement of the means 54, detecting the plug level 19 inside the mill, in a position outside the mill. In fact, the detecting means 54 detects the actual height Ha of the discharging opening 11 and consequently, indirectly and roughly, the plug level 19, which is always higher than the measured actual height Ha.

The different steps of the crushing and discharging method according to the present invention are inferable from the above structural and functional description of the improved mill 1 (Fig. 2, 2A), the mill 1, A into which is integrated the incorporated discharging device 17 (Fig. 3, 5, 7 and 8) as well as the crushing and discharging stations A (Fig. 4 and 6). In practice both the above decribed mill 1 and distinct discharging means 17 could be replaced by any other suitable device which is capable of carrying out the proposed method.

It resides expressly within the scope of the present invention to manufacture said distinct discharging means 2 to be associated to a mill 1 as well as said discharging means 17 to be integrated into the mill 1, as separately, that is individually per se manufactured and marketable devices, which can then be mounted on an extant mill for transforming the latter in an improved mill or a crushing station operating according to the teaching of the present invention, that is without dust formation or blowing off.