Abstract:
A grinder for use in wet grinding having a roller or wheel rolling on a circular track and elastically pressed thereon. The materials to be ground are subjected to several layer on bed grinding operations to enable the rational utilization of this type of grinder. During the time between two successive grinding operations in the grinder, water or another liquid is introduced by nozzles to the materials. The materials are drained and/or dried by a screen so as to reduce water content to below 20% in volume.

Description:
TECHNICAL FIELD 
     The present invention relates to wet crushing and to crushers comprising at least one roller travelling over a circular track and elastically pressed against the latter. 
     BACKGROUND ART 
     Known crushers of the type defined above, a vertical crusher or ring crusher, in which a multi-granular layer of materials for crushing is compressed between the roller and the track with sufficient pressure to crush the grains and cause their fragmentation to smaller grains, are not suited to wet crushing as an excessive water content in the materials for crushing reduces their efficiency. In wet crushing, the materials for crushing generally have a water content of 10% to 60% by weight, with an average of 30%, which is incompatible with good crushing efficiency. 
     The object of the present invention is to permit the rational use of crushers of this type for wet crushing. 
     SUMMARY OF THE INVENTION 
     The process according to the present invention includes in subjecting the materials for crushing to several crushing operations by crushing in a layer or bed of materials and, during their dwell time in the crushing apparatus, and between two successive crushing operations, in adding water or another liquid to the materials to re-expand the layer of materials and to enable the progress of the materials through the crushing apparatus to be controlled and, possibly, to enable their grain size grading to be ensured, and then in draining the materials and/or removing moisture therefrom so as to reduce their water content to less than 20% by volume. The draining and moisture removal operations are carried out inside the crushing apparatus, which is arranged for this purpose, which makes it possible to achieve a considerable reduction in the cost of the plant by avoiding the use of auxiliary apparatus and means of transport between the different apparatus. 
     For the purpose of implementing the invention, use will be made of a crusher comprising a circular track, fictitiously divided into several track elements, or circular tracks, spaced apart from one another, where the successive crushing operations will be carried out, means for transferring the materials from one track or track element to the next, means for projecting water or another liquid onto the materials during their transfer from one track or track element to the next, and means suitable for ensuring the draining of the materials and/or removal of moisture therefrom prior to their next passage beneath the roller. In a ring crusher having a horizontal axis, the tracks will be disposed side by side. 
     The addition of water or of another liquid to the materials after each crushing operation makes it possible, on one hand, to improve the flow of the materials and their distribution in a layer of uniform thickness over the track, and, on the other hand, to remove the fine particles immediately after their production, which makes the subsequent crushing operations more efficient. 
     The water or any other liquid can be projected onto the materials when they are still on the track, for example by means of nozzles supplied under pressure which then constitute one of the means for transferring the materials from one track or track element to the next. In particular, when the crusher is of the rotary ring type and is driven in rotation at a speed greater than the critical speed so that the centrifugal force is sufficient to maintain a layer of materials over the entire periphery of the track provided on the ring, use can be made of nozzles placed inside the ring, in its upper portion and on the rising side, and the jets of which will be directed towards the track to detach the materials; the action of the jets can be supplemented by that of a scraper. Moisture removal can be effected through the action of the centrifugal force in the portion of the track located upstream of the crushing roller. A pre-compression roller can be provided on the track, immediately ahead of the crushing roller, to ensure complementary moisture removal by pressure. 
     According to a preferred form of embodiment of the invention, the crusher is of the rotary ring type and the material feed device comprises one or more baffle or deflecting plates arranged so as to intercept the materials detached from the track provided inside the ring and orientated so as to deflect them in a direction having a component parallel to the axis of the ring; additional water spraying means can be provided above the deflecting plate or plates to facilitate the flow of the materials. Alternatively, the deflecting plate or plates can be porous, and water or another liquid can be injected through the plate(s) to create a liquid film facilitating the flow of the materials. The deflecting plate or plates can comprise an upper screening surface and means for collecting and discharging the water and the fine crushed products that pass through this surface; they then constitute a means for draining the coarse materials. They can be flat or curved, and each plate will be orientatable about a horizontal axis, and possibly inclinable about a vertical axis, so as to be able to adjust the feeding speed of the materials for crushing and choose the point at which the materials deflected by the plate(s) fall back onto the track. The removal of moisture from the materials is carried out, through the action of the centrifugal force, in the area of the track located between the point at which the materials deflected by the deflecting plate or plates fall back onto the track and the roller. Preferably, this area will have an angular extent of at least 30°. 
     In the event of the track being formed inside a drum with a horizontal axis and of supply and discharge areas being arranged on either side of the track, drainage means can be provided in these areas to facilitate discharge of the water. For the same purpose, when the track is constituted by protection plates resting on the shell of the drum, which is generally the case, drainage means can be provided under the plates, in the crushing area. A grooved roller can also be used. At its ends, the drum will be provided with annular barrier-forming rims the inside diameter of which will be chosen to retain the material within the supply and discharge areas, respectively, while, at the same time, possibly enabling the water to be discharged by overflowing. These rims can be designed in such a way that is possible to change their inside diameter in order to adjust their height (radial dimension). The materials retained by these rims form, at least at the crushing area, a bank that prevents the materials compressed between the roller and the track from being expelled laterally by the pressure while, at the same time, enabling the water to be discharged partially through the said bank, if the supply area, or discharge area, respectively, is provided with drainage means, and partially by overflowing the bank. 
     A rotary screen, having a horizontal axis, can be placed at the crusher output to sort the crushed products. The rejects of the rotary screen can be returned to the track or to the crusher input by an internal recycling device comprising a conduit disposed inside the crusher, transversely to the track, means for supplying the said conduit with the screen rejects and, possibly, means for facilitating the flow of the rejects through the conduit. The screen can be integral with the body of the crusher or supported and driven by individual means. Water injection means can be provided in the rotary screen to facilitate discharge of the crushed products and possibly reconstitute with them a pulp of a composition suitable for subsequent processing. 
     According to a first alternative form of embodiment, the crusher comprises two tracks spaced axially from one another inside a drum with a horizontal axis, two rollers, each suitable for travelling over a track, means for bringing the materials for crushing into the drum, between the two tracks, and means for discharging the crushed materials at the two ends of the drum. 
     According to another alternative form of embodiment, the crusher comprises several tracks spaced axially from one another inside a drum with a horizontal axis, several rollers, each suitable for travelling over a track, means for introducing the materials for crushing into the drum at one of its ends, means for transferring the materials from one track to the next and means for discharging the crushed materials at the other end of the drum, drainage means for discharging the water being provided between the tracks. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description that follows makes reference to the accompanying drawings which show, by way of non-limitative examples, a preferred form of embodiment of the invention and two alternative forms of embodiment. In these drawings 
     FIG. 1 is a diagrammatic representation, in transverse cross-section, of a crusher designed according to the invention; 
     FIG. 2 is a cross-section along line A—A′ of FIG. 1, the roller and the internal equipment of the crusher being shown in elevation; 
     FIG. 3 is a view, analogous to that of FIG. 1, of an alternative form of embodiment; and 
     FIG. 4 is a view, analogous to that of FIG. 2, of another alternative form of embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The crusher shown in FIGS. 1 and 2 is a ring type crusher constituted by a drum  2  having a horizontal axis supported by one or more pairs of pads or skids  6  permitting its rotation about its axis. The drum is driven in rotation in the direction of arrow R by conventional means, not shown. It is constituted by a shell the median part of which is internally clad with wear plates and forms a ring bearing the crushing track. 
     A roller  4  is placed inside the shell so as to travel over track  18  when the drum is driven in rotation. The roller is integral with a shaft parallel to the axis of the drum and the ends of which, which are located outside the drum, are mounted in bearings capable of moving in slide ways or supported by pivoting arms; springs or jacks act on the bearings so as to press the roller against the track with a predetermined, adjustable force. This arrangement is conventional, and the shaft and the bearings have been omitted from the drawings to avoid impairing their legibility. The roller can be idle or driven in rotation by a geared motor. 
     In the form of embodiment shown in FIGS. 1 and 2, the surface of the track and the peripheral surface of the roller are cylindrical, but they could be frustoconical or cylindroconical, or formed of several portions having different diameters, as described, for example, in U.S. Pat. No. 9,109,788 in the name of the applicant. 
     The materials for crushing are introduced into the drum via a chute  20  disposed at one end of the drum; at the other end, where the crushed materials are discharged, the shell is prolonged by a cylindrical screen  14  which is surrounded by a collector means  15 . Nozzles  24 , placed inside the screen  14 , enable the crushed materials to be sprayed to improve screening and possibly produce a pulp of suitable composition for subsequent processing. 
     A chute  16 , disposed in the drum, transversely to the track, with an appropriate slope, enables the screen rejects to be returned to the supply area of the crusher. This chute is supplied at one of its ends, for example by a device for scraping the inner surface of the screen: water injection means can be provided to facilitate the flow of the rejects along the chute. 
     The crusher is equipped with a device for the stepwise feeding of the materials, constituted by water injection nozzles  12  and a screen  8 . 
     Nozzles  12 , mounted on a supply pipe, not shown, are disposed in such a way that their jets are directed towards the surface of the track to detach the layer of materials therefrom. The action of the nozzles could possibly be assisted by a scraper, parallel to the axis of the drum and disposed close to the surface of the track, as described in U.S. Pat. No. 9,109,788 in the name of the applicant; preferably, the edge of the scraper will not be in contact with the surface of the track, but at a short distance therefrom, to reduce wear. 
     Screen  8  is constituted by a flat or curved grid and a collecting recipient. It is mounted on a support  26  so as to be able to pivot about a vertical or inclined axis  28  thanks to a connecting rod and jack system, not shown. It can possibly be mounted to as to be able to pivot about a horizontal axis in order for it to be possible to change its angle of inclination. A chute  17  serves to supply to screen  14  the water and the fine crushed materials collected in the collector means of screen  8 . Means can be provided for transmitting oscillations or vibrations to screen  8 . 
     As seen in transverse cross-section, the inside of the crusher can be divided into five clearly defined areas: a crushing area BC, a raising area CD, a scraping area DE, a feed and drainage area EF and a moisture removal area FB. 
     In longitudinal cross-section, the inside of the crusher can be divided into three areas: a supply area  30 , a crushing area  31  and a discharge area  32 . The inner cladding of the supply and/or discharge areas can be designed to enable the water to be discharged by drainage. 
     In operation, the materials for crushing are introduced via chute  20  into the supply area  30  of the drum and there forms in this area a layer of materials the progress of which, parallel to the axis, is controlled by the feed device. A rim  21  of drum  2 , the inside diameter of which is substantially equal to that of the layer of materials present on the track forms a barrier permitting the formation of the layer. The speed of rotation of the drum is greater than critical speed, so that the layer of materials is retained on the wall of the drum by centrifugal force, over its entire periphery. A part of the water contained in the materials is possibly discharged in this area by drainage. 
     To take an elementary volume of the layer of materials present on the track, for example at the upstream end of crushing area BC, this volume is first subjected to crushing by compression between roller  4  and track  18  and then, remaining pressed against the track by centrifugal force, it is raised to the scraping area, where it is detached from the track and broken up by the jets of water from nozzles  12 . The grains of material forming this elementary volume then drop onto screen  8 , where the water and the grains that are sufficiently fine pass through the screening surface, are collected by the collector means and conveyed to rotary screen  14  via chute  17 , while the coarser grains slide along the screen. 
     The orientation and angle of inclination of the screen are such that the downward movement of the materials over the screen is accompanied by a movement that is parallel to the axis of the drum and the length of which is equal to a fraction of the width of the track. By adjusting the orientation of the screen, it is possible to control the progress of the materials to compel them to undergo several cycles of crushing before being discharged from the crusher. The action of the screen as an element of the stepwise feed device is comparable with that of the deflecting plates in the crusher that is the object of above-mentioned U.S. Pat. No. 9,109,788. 
     The drained materials drop from the screen onto the track, where they reconstitute a layer from which moisture is removed, through the action of centrifugal force, in area FB, between the point at which they drop and crushing area BC. To permit satisfactory moisture removal, the angular extent of area FB must be at least 30°; the relative positions of roller  4  and screen  8  will be chosen to meet this requirement. 
     The centrifugal force also produces, in the moisture removal area, a grain size grading of the solid particles, which improves the work of the crusher. 
     Upon leaving the moisture removal area, the materials enter the crushing area to begin a new cycle. The materials thus pass several times between the roller and the track before reaching the edge of the track adjacent to discharge area  32 , the number of crushing cycles being equal to the ratio of the progress per turn, or step, to the width of the track. It can be considered that each fraction of the track having a width equal to one step forms a fictitious track element. 
     When the materials arrive in the discharge area, they are deflected by screen  8  towards rotary screen  14 . The grains of crushed materials the dimensions of which are greater than those of the apertures in screen  14  are returned to the input of the crusher by internal recycling device  16 . The fine grains and the water are discharged at  22 . 
     On the output side, the drum is provided with a rim  23 , the inside diameter is approximately equal to that of the layer of materials. This rim permits the formation, in discharge area  32 , of a bank of materials which prevents an excessive quantity of materials from being entrained by the water when the fluidity of the layer of the materials present on the track is excessive, and which opposes expulsion of the materials through the effect of the pressure of the roller in the crushing area. Rims  21  and  23  can be designed in such a way that their inside diameter can be changed to adapt it to the nature and/or the behaviour of the crushed materials; they can, for example, be formed of exchangeable segments or rings. 
     As shown in FIG. 3, a pre-compression roller  5  can be placed on the track just before the crushing area to supplement removal of moisture from the layer of materials and prevent the water discharged by moisture removal above the layer of materials from reaching the crushing roller. Known means will be used to adjust the pressure exerted by roller  5  on the layer of materials. 
     Steps can be taken to facilitate the discharge of water in the crushing area: grooving the roller, providing drainage means under the protection plates of the track, etc. 
     Instead of being integral with drum  2 , screen  14  could be supported and driven independently. It could, for example, rotate at a speed below critical speed and be equipped with raising means or scoops enabling the recycling chute  16  to be supplied with the rejects. 
     Instead of comprising a single track fictitiously divided into track elements, the crusher could comprise several tracks axially spaced apart from one another along the drum, drainage andlor moisture removal means being provided between the tracks. 
     The crusher shown in FIG. 4 comprises two tracks,  18 ′ and  18 ″, disposed on either side of the median plane of the drum and axially spaced apart from one another, and two rollers  4 ′ and  4 ″ each travelling over a track. 
     The materials for crushing are brought via a chute, or any other supply means, not shown, into the space between the two tracks, where they form, through the effect of centrifugal force, a layer that is brought onto the two tracks by feed devices. 
     Each track is equipped with a step wise feed device, for example of the same type as that of the crusher of FIGS. 1 and 2, which ensures the displacement of the materials from the middle towards each end of the drum. These devices are not shown in FIG.  4 . 
     The shell of the drum is prolonged at each of its ends by a cylindrical screen  14 ′,  14 ″ equipped with water injection nozzles  24 ′,  24 ″. Collector means  15 ′,  15 ″ collect the water and the fine grains that have passed through the screens, and two recycling devices,  16 ′,  16 ″ enable the screen rejects to be sent back to the median area of the drum. 
     Each half of the crusher in FIG. 4 operates like the crusher in FIGS. 1 and 2. For the same production capacity, this construction enables the width of the track to be divided by two, which facilitates discharge of the water in the moisture removal area. 
     Many changes may be made to the forms of embodiment described through the use of equivalent technical means and it is clearly understood that such changes fall within the scope of the invention.