IE60186B1 - A rotary crusher having self-protecting projection vanes - Google Patents

Abstract

The rotor of the crusher receives the stones at its centre. It comprises three blades (20, 21) which, except on the ejecting edges (22), are protected against internal wear by their hollow shape which retains a protective layer of stones. These edges are protected from impacts by protecting plates (24) arranged radially in front of them. <IMAGE>

Description

The present Invention relates to crushing rocks, in order to obtain fragments therefrom. The essential problem in making crushers has long been the problem of resistance to wear by the rocks and fragments thereof, and by the dust due to crushing.

In order to solve this problem, prior art crushers include the following items which are themselves common to prior art crushers and to a crusher in accordance with the present invention: a rigid projection rotor having a vertical axis and provided with means for guiding it and driving it at high speed about said axis, with its direction of rotation and with the apposite direction respectively constituting a forwards direction and a backwards circumferential direction, said rotor itself comprising: -a floor delimited by an outer edge; -a ceiling delimited by an outer edge, disposed above said floor, and pierced by a central feed opening for continuously feeding said rocks down into said rotor; and - walls connecting said floor to said ceiling.

Same of these walls constitute projection vanes. Each of these vanes extends horizontally from a reception zone formed over a portion of its length in the vicinity of said axis in order to receive the rocks which arrive via said central feed opening in the ceiling. It continues up to a projection edge which is relatively far from said axis and which may be considered as constituting the longitudinally forward end of said vane. A rock received in said reception zone is entrained by the rotation of said vane and is thus subjected to centrifugal force. It moves under the action of this force along said vane while receiving thrust that progressively increases its circumferential speed. When it reaches said projection edge, it is projected tangentially outwards. In order to avoid the rocks wearing the vane, the shape of -the vane in plan is a hollow self-protecting shape: the vane extends rearwards from said projection edge, circumferentially behind the line of natural slope which is defined by said edge, with lines of natural slope being the equilibrium lines of the accumulation slopes which the rocks form spontaneously under the action of the centrifugal force upstream from an obstacle which begins by opposing the flow of rocks. The position of such a line is defined by the position of the flow threshold constituted by said obstacle. This threshold is constituted by the projection edge. The first rocks to arrive over the vane are retained in the hollow of the vane until they have formed a protective layer whose surface follows said line of natural slope.

Said line is approximately a logarithmic spiral about the axis of rotation, i.e. it follows a curve whose tangent is at all points at the same angle with a radial plane passing through said axis and the point under consideration. Thie angle depends an the nature, the size, and the roughness of the rocks to be broken, and also on the magnitude of the centrifugal farce which maintains the protective layer and which in turn depends on the speed of rotation of the rotor.

The angle in question included between the radial direction and the tangent to the natural line of talus slope may for example be close to 110 or else to 120 degrees, and may slightly vary in operation, when the interstices between the rocks of the protective layer fill up progressively with dust resulting from friction of the new rocks along said layer.

The protective layer formed in this way by the first rock protects the vane against any wear by the rocks which arrive thereafter, except at the projection edge which constitutes the flow threshold.

The projection edge is formed by a very hard part which may be replaceable in order to delay its wear and/or A. Ί allows for its easy replacement after having been worn. This part is in the form of a vertical blade which may be referred to as the projection blade. It is conventionally constituted by two superposed vertical bars of tungsten carbide which are set in steel supports that are bolted on the leading length of the projection vane.

Circumferentially in front of each projection edge, the peripheral wall of the rotor leaves an outlet opening for the rocks.

The projection rotor is surrounded by an external reception structure with an annular gap being left therebetween. The reception structure has hard shock surfaces for receiving direct shocks from the rocks projected by said rotor and for breaking said rocks to form rock fragments and dust. Some of the fragments return towards the rotor and subject it to rebound shocks on its peripheral surface constituted by its peripheral walls and/or by the outer edges of said floor and ceiling. The dust is entrained by the flow of air caused by rotation of the rotor.

The external reception structure is conventionally a fixed stator whose shock surfaces may be constituted by hard plates referred to as anvils**, or by fragments of rock retained in the stator in order to reduce wear thereof.

Known crushers of this type are described, for example, in the following patent documents: US-A-3,174,697 (Bridgewater), US-A-3,970,257 (MacDonald), which corresponds to French patent document FR-A-2,201,928 (in the same name), DE-U-8,630,185 (SBM Wageneder), and EP-A-0 „101,277 (Barmac).

The rotors of prior art crushers described in the abovementioned documents, or at least the floors thereof, are circular in shape. The rotors in the MacDonald, Barmac, and SBM Wageneder documents also include a ceiling which is likewise circular, which is superposed over the floor, and which has a cylindrical peripheral wall connecting the edge of the ceiling to the edge of the floor.

In the SBM Wageneder document, the projection blades axe disposed projecting a moderate distance radially from the circular peripheral surface of the rotor which thus forms, circumferentially behind each of said blades, a sector which is set back radially relative to said blade. A degree of protection is thus provided in said sector by said blade against said rebound shocks.

Such a disposition suffers from several severe drawbacks. One of them is that the projection blades are dangerously exposed to rebound shocks which frequently break them by virtue of the low ductility of the hard material from which they are generally made. Another drawback , is that the peripheral wall of the edges of the floor end the ceiling of the rotor are protected against rebound shocks over only a small circumferential sector behind each projection blade, i.e. over a small fraction of said setback sectors. A third drawback is that even ln the sector immediately following the projection blade, the peripheral wall of the rotor is worn by dust.

Zn the embodiment of the MacDonald document and in accordance with the Bazmac document the projection blade is, in contrast, radially set back relative to the circular peripheral wall of the rotor. The blade is then protected by the portion of the circular peripheral wall which is situated immediately ahead of said outlet opening. There is nothing to protect the peripheral wall. ln operation, such rotors are rapidly subjected to considerable external wear. This wear is particularly great on the circular external edge of the floor and also on the corresponding edge of the ceiling, if there is one. The wear also appears on the peripheral cylindrical wall, if present. The crusher therefore needs to be stopped and the worn parts need to be reconstituted by rebuilding using an electric arc or else they need to be replaced. The operating cost of the crusher is considerably increased by these operations.

The aim of the present invention is to reduce the V operating coat of a rotary crusher having self-protecting ♦ projection vanes, without reducing the effectiveness of the crusher*.

The invention also aims to enable the rotor of the crusher to be manufactured simply and cheaply while still conferring the great strength required by the rotor in view of the forces to which it is subjected.

More particularly, the invention aims to reduce the cost of rebuilding and/or replacing the outer zones of the rotor after they have been worn.

Simultaneously, the invention aims at reducing the rate at which such wear takes place in order to increase the period of operation of the crusher between two interruptions.

According to the invention there is provided a rotary crusher having self-protecting projecting vanes, said crusher being intended to break rocks and comprising: a rigid projection rotor having a vertical axis and provided with means for guiding and driving it in high speed rotation about said axis, with its direction of rotation and with the opposite direction respectively constituting a forwards circumferential direction and a backwards circumferential direction, said rotor itself comprising: a floor delimited by an outer edge, a ceiling delimited by an outer edge, disposed above said floor and pierced by a central feed opening * for continuously feeding said rocks down into said rotor, and •β·· fi walls connecting said floor to said ceiling, some of said walls constituting angularly successive projection vanes, each of said vanes receiving a fraction of said rocks in the vicinity of said axis and guiding said rocks up to a projection edge which constitutes a longitudinally front end of said vane at the periphery of said rotor, in such a manner that said rocks are projected tangentially out from said rotor by said edge, said vane having a hollow shape in plan with the concave side of the hollow directed circumferentially forwardly so that the rocks are retained behind said projection edge and constitute a protective layer protecting the remainder of said vane from wear, said projection edge being constituted by at least one projection blade of great hardness and/or replaceable for slowing down its wear and/or allowing for its easy replacement after wear, said walls also forming a circumferential succession of peripheral walls which separate said rotor from the outside space while leaving an outlet opening therebetween for said rocks circumferentially ahead of each of said projection edge, said peripheral walls constituting, together with said outer edges of the floor and the ceiling a peripheral surface of the rotor, said rotor having a set-back sector which, in beginning at a maximum radius point of a projection blade, and in which sector said peripheral surface diverges progressively and radially to the outside up to the interior of a circle centered around said axis and passing through said maximum radius point, in such a manner that the entirety of said set-back sector constitutes a protected sector in which said surface is protected against outer wear due to return shocks and to dust, said crusher further including an external reception structure which surrounds said projection rotor while leaving an annular gap thereabout and which has hard shock surfaces for receiving direct shocks from the rocks projected by said rotor and for breaking said rocks to form rock fragments and dust, some of said fragments returning towards said rotor and subjecting it to return shocks, certain parts of said dust being entrained by air currents generated by the rotation of said rotor, and delivery means for said rock fragments, characterized in that said peripheral walls of the rotor are constituted at least as to their major part by said projecting vanes, said external edges of said floor and of said ceiling being disposed to follow said vanes to the outside of said outlet openings of the rotor.

Preferably, the peripheral wall and the edges of the floor and the ceiling constitute along each protected sector with respect to the circumferential directions a mean progressive set-back angle in the range 2 to 10 degrees.

Said mean progressive set-back angle is the characteristic angle of a logarithmic spiral turning about said axis and starting from a maximum radius point to arrive at the rear end of said protected sector at the periphery of the rotor, said characteristic angle being the constant angle included between the tangents to said spiral and the tangents to the circles centered about said axis. Naturally, as the protected sector area extends, the peripheral surface of the rotor may space away from the spiral, inside and/or outside. Such is the case, if the peripheral walls of the rotor are constituted of flat sheet and if the edges of the floor and of the ceiling ΐ/ follow said walls.

Preferably, the total angular extension of the lengths of said peripheral walls located outside said protected sectors constitute a minor fraction of one turn of said rotor, so as to concentrate said external wear within limited sectors, in which replacements and/or weld resurfacing can be carried out economically on said walls.

Preferably, said progressive set-back extends to a point where 10¾ of said radius is at least reached, and still substantially more, by preference.

By preference, the rear fraction mentioned in claim 3 is a minor fraction, and experience demonstrates that it may then constitute a complementary protected sector.

Naturally, the top and bottom edges of said outlet opening from the following vane need not be exactly in alignment with said main length of the preceding vane.

It is apparent that the number of vanes may amount to two, four or five instead of three, which would correspond to a general shape of an elontaged parallelogram, a square or else a pentagon having cut away corners.

In addition and also by preference, in accordance with a disposition known perse by the MacDonald document, the rotor comprises circumferentially and upstream from each of said outlet openings a protective element which extends far enough so as to intercept early dangerous rock fragments which could break a part of highgrade hardness that constitutes said projection edge.

In this case, preferentially, said protective element upstream from each of said outlet openings is a protective plate forming a projection which extends substantially radially from the periphery of said projecting rotor, in such a manner that said dangerous fragments of rock are intercepted substantially at right angles by said protective plate, thereby subjecting it to frontal shocks, said protective plate being constituted, at least at the front face, by a material which is less hard than said very hard part.

Preferably, said protective plate extends up and down far enough also to protect the top and bottom edges of said outlet opening.

Preferably, said protective plate, in plan view, constitutes an obtuse angle with said portion of the peripheral wall situated circumferentially immediately in front thereof, thereby deflecting the streamlines of external air which flow relative to said' projection rotor in contact with said wall so as to deflect rode dust suspended in said air streamlines away from said outlet opening.

Finally, it is preferable for said protective plate to join the rear end of said main length of said projection vane, with said rear length of said vane being constituted by an extension of said protective plate extending into said projection rotor between said floor and ceiling in such a manner as to hold said protective plate by means of said rear length.

Various embodiments of tbe present invention are described in greater detail by way of non-limiting exanple with reference to the accompanying diagrammatic figures. Unless specified otherwise, these embodiments also implement the dispositions that are mentioned above as being preferred. When the same item is shown in several figures it is given the same reference symbol.

Figure 1 is a side view in axial section of a first crusher assembly in accordance with the invention; Figure 2 is a side view in axial section of a second crusher assembly in accordance with the invention; Figure 3 is a horizontal section view through a three-vane rotor for either of the two crushers, for example for the first crusher; Figure 4 is a plan view of the front length of a projection vane of said rotor, with the ceiling being assumed to be removed therefrom; Figure 5 Is a side view of the same front length; Figure 6 ls a view similar to Figure 4 showing a plan view of the front length of a rotor projection vane In the other of said two crushers, far example In the second crusher; Figure 7 Is a view of the Figure 4 rotor In section an an axial plane; and Figure 8 ls a horizontal section view through a five-vane rotoor · As shown in Figure 1, a first crusher having selfprotecting projection vanes In accordance with the invention has a vertical axis A and Includes a projection rotor 1. This rotor is mounted on a vertical shaft provided with protective hearings that are not visible in the figure. The shaft is rotated at high speed, e.g. at 1110 revolutions per minute, by a motor 5 via pulleys 3A and 3B and belts 4.

The rotor 1 includes a floor 8 and a ceiling 9. The celling has a central circular opening passing therethrough into which a vertical duct 6 is engaged to convey rocks from a hopper 7. The duct is provided with a device 15 for adjusting its level inside the rotor to compensate for the rate at which it is worn by the rocks which constitute the material to be crushed.

The floor and the ceiling are interconnected by vertical walls which are described in greater detail below with reference to Figure 3.

The stator of the first crusher is constituted by a horizontal circular ring 11 which constitutes the bottom of a rock box. A vertical cylinder 12 constitutes the outer wall of the stator and of the crusher as a whole. The top of it is armored above the level of crushed material 13. The crushed material is constituted by fragments of the rocks inserted from the hopper 7. A certain volume thereof is retained in the rock box. The stator is dosed around the duct 6 by an armored horizontal cover 14.

Vertical radial stiffeners 16 improve the performance of the stator and retain the substance 13 which accumulates in the rock box.

The crushed material exits towards the bottom portion of the stator through an annular gap 10 existing between the rotor and the rock box. This material ie removed via a conical bottom 17 and is then conveyed by transportation means such as a conveyor belt to a hopper or to some other storage means.

Figure 2 is a corresponding side view in axial section through a second crusher which may differ from the first crusher solely in the design of its stator. The rock box 13 of the first crusher has been replaced in the second crusher by anvils 19. The cylindrical wall 12 is then fitted with an * anvil-carrier ring 18 enabling each anvil 19 to be received and moved vertically by means of three slopes 18A disposed at 120* intervals.

Figure 3 is a horizontal section through a polygonal rotor in which said number N is equal to three.. This rotor is substantially in the form of an equilateral triangle having cutoff corners. Its direction of rotation is represented by an arrow F. This rotor of unitary construction comprises a horizontal ceiling 9 (not visible in this figure), a floor 8 which is likewise horizontal, with both the floor and the ceiling being made of thick metal sheet, and vertical plates 20, 21, 24, and 25 which constitute the three projection vanes. Each vane constitutes both a portion of the peripheral wall of the rotor and a wall for guiding and accelerating the material to be crushed. Each of these vertical plates constitute a length of one of said vanes.

Each vane is constituted, for the most part, by a main length 20 comprising a major front portion 20A and a minor rear portion 2QB on opposite sides of a point situated at a minimum distance from the axis A. The front end of said length is welded to a front length 21. Said front length forms one of the snail sides of said polygon and its front end is constituted by the projection edge 22 which may be at a distance 47 cm from the axis A, for example. As shown in Figures 4 end 5, the projection edge comprises a projection blade 22A constituted by two superposed removable steel plates 22B and 22C each of which carries two vertical bars of tungsten carbide. One of these bars 22D or 22E constitutes a portion of the projection edge 22, and the other such as 23 constitutes a portion of a protective bar which increases the lifetime of the part. The part is subjected to abrasion not only by the rocks which leave the projection vane by passing over its edge 22, but also to some extent by fragments of rock rebounding from the stator The bars such ae 23 provide the blade 22A and the front plate 21 with a degree of protection frcm abrasion by said fragments. They are situated at the may liman radius points of the rotor.

The parts 22B and 22C are fixed to the fixed portion of the front plate 21 by pairs of bolts 31.

Figure 5 is a side view of the same front plate seen from inside the rotor and shows these two interchangeable superposed parts 22B and 22C which carry respective tungsten carbide bars such as 22D and 22E having .identical characteristics. Hear takes place essentially in the middle of the front plate, thereby enabling the portions 22B and 22C to be Interchanged in order to extend lifetime.

As shown in Figure 6, the protective bars such as 23 may be replaced by a hard protective coating such as 23A formed on the exposed surface of each of the two parts such as 22F which are analogous to the parts 22B and 22C. This coating is advantageously constituted by email round particles or beads of tungsten carbide embedded in a binder such as a nickel cobalt alloy.

Although such protective bars or coatings have been used by the present inventors, it appears that it is often preferable to make the maximum radius points out pf hard steel.

Returning to Figure 3, it appears that the rear end of the front length 21 is closer to the axis of the rotor than ia its XTORC OnQ· The main length 20 of the vane has its rear end 11mi ting the outlet opening 21A of the following projection vane.

A protective plate 24 projects forwardly from said delivery opening, its circumferentially forward face is fitted with a removable wear plate 24B having a screw 24C for flying it by means of a nut 24E on the circumferentially rear face of the plate 24. This wear plate is made of a hard steel alloy or of chromium cast iron that withstands abrasion well, whereas the remainder of the rotor assembly is made of steel which is less hard and which is easier to machine and to weld. Said hard steel alloy is selected to be sufficiently ductile to withstand the hardest frontal shocks and sufficiently hard to withstand scraping erosion for a long time. Equipped in this way, -the plate 24 deflects the fragments that ricochet from the stator and also deflects streamlines of air charged with dust and sand as created by high speed rotation of the rotor. By doing this it contributes to protecting the projection blade 22A and it protects the edges of the floor 8 and the ceiling 9 around the outlet opening.

The radially outer end of the protective plate may be ' placed at a radius (i.e. at a distance from the axis A) which is slightly greater than the radius of the projection blade 22A as shown in Figure 3. However, it may also be placed at the same radius or at a slightly smaller radius (see Figure 8) and still provide useful protection to the blade, perhaps with the help of the rocks and the air flow leaving the delivery opening 21A.

Each protective plate 24 is placed in a substantially radial position. It joins the rear minor fraction of the main length 20 of the preceding projection vane with which it makes an obtuse angle facilitating deflection of external air streamlines. Each protective plate also extends inside the rotor.

Its inside portion 24A constitutes both a rear length of the projection vane serving to retain the rear end of the protective layer, and a rear stiffener far the main length 20 of said vane.

Each projection vane is fitted with at least one intermediate stiffener 25 projecting inwardly for reinforcing holding. Said reception zone lies between the stiffeners 24Ά and 25.

Wear plates 26 protect those zones of the floor 8 which are not naturally protected by the layer of material retained in the rotor. These wear plates are naturally held in place by centrifugal force without requiring bolts, by virtue of cleats 27, 28, and 29 fixed to the floor for this purpose.

In the center of the rotor, a hole 38 through the floor 8 receives a solid disk 30 called the distributor. The diameter of the distributor is about l/3rd the diameter of the rotor, 1. e. of the circle circumscribing the rotor. The distributor projects from the floor 8 and serves two purposes: firstly it distributes the material received towards the projection vanes, and secondly it fixes the rotor 1 oh the rotary shaft 2 and explained below with reference to Figure 7.

The rotor 1 is carried and driven via its floor 8. The floor is itself carried and driven, not directly by the shaft 2, but indirectly via a carrier plate 34 which is mounted by conventional mechanical means on the top end of the shaft 220 which is much smaller in diameter. This carrier plate is * separable from the rotor. Its diameter is slightly greater than one half of the diameter of the floor 8, and it is sufficiently thick to have all of the rigidity that may be desired.

Horizontal translation displacement of the rotor is prevented by the fact that the floor 8 has a central annular projection 40 projecting from its bottom face around its central hole 38 which projection is Inserted, at rest, with very little clearance in a central housing 44 in the carrier 3Q plate 34, and in operation, is pressed against the retaining shoulder 42 which constitutes the edge of the housing.

Vertical separating displacement is prevented by means of the distributor 30. The distributor is fixed to the shaft by a single axial screw 33 disposed in an axial well in the distri35 butor. In operation, the well is filled with rocks which i? protect the head of the screw from wear. A small gap is left between the peripheral surface of the distributor and the edge of the hole through the floor 8. This gap is maintained by an intermediate washer 36 which is fixed beneath the distributor . In order to make this possible, the peripheral surface of the washer is slightly conical, constituting a downwardly directed male cone which thrusts accurately against the inside surface of the annular projection 40 which is machined to constitute the corresponding female cone. Under these conditions, the risk of the Intermediate washer 36 being worn is very low because its position ensures that it is protected by the distributor 30 and the floor 8.

As for rotary displacement of the floor relative to the carrier plate 34, this is prevented by a horizontal radial key which is fixed to the carrier plate by two vertical pins 37.

Recesses are formed in the bottom faces of the washer 36 and the distributor 30 in order to receive said key and hold it in position.

The floor 8 and the ceiling 9 are respectively protected by removable wear plates 26 and 26A.

Figure 8 is a horizontal section view through, a five-vane rotor. It includes components analogous to all of the essential components of the above three-vane rotor. These analogous components have the same reference numerals plus 100.

Claims (9)

1. A rotary crusher having self-protecting projecting vanes, said crusher being intended to break rocks and comprising: a rigid projection rotor having a vertical axis and provided with means for guiding and driving it in high speed rotation about said axis, with its direction of rotation and with the opposite direction respectively constituting a forwards circumferential direction and a backwards circumferential direction, said rotor itself comprising: a floor delimited by an outer edge, a ceiling delimited by an outer edge, disposed above said floor and pierced by a central feed opening for continuously feeding said rocks down into said rotor, and walls connecting said floor to said ceiling, some of said walls constituting angularly successive projection vanes, each of said vanes receiving a fraction of said rocks in the vicinity of said axis and guiding said rocks up to a projection edge which constitutes a longitudinally front end of said vane at the periphery of said rotor, in such a manner that said rocks are projected tangentially out from said rotor by said edge, said vane having a hollow shape in plan with the concave side of the hollow directed circumferentially forwardly so that the rocks are retained behind said projection edge and constitute a protective layer protecting the remainder of said vane from wear, said projection edge being constituted by at least one projection blade of great hardness and/or replaceable for slowing down its wear and/or allowing for its easy replacement after wear, iC said walls also forming a circumferential succession of peripheral walls which separate said rotor from the outside space while leaving an outlet opening therebetween for said rocks circumferentially ahead of each of said projection edge, said peripheral walls constituting, together with said outer edges of the floor and the ceiling a peripheral surface of the rotor, said rotor having a set-back sector which, in beginning at a maximum radius point of a projection blade, and in which sector said peripheral surface diverges progressively and radially to the outside up to the interior of a circle centered around said axis and passing through said maximum radius point, in such a manner that the entirety of said set-back sector constitutes a protected sector in which said surface is protected against outer wear due to return shocks and to dust, said crusher further including an external reception structure which surrounds said projection rotor while leaving an annular gap thereabout and which has hard shock surfaces for receiving direct shocks from the rocks projected by said rotor and for breaking said rocks to form rock fragments and dust, some of said fragments returning towards said rotor and subjecting it to return shocks, certain parts of said dust being entrained by air currents generated by the rotation of said rotor, and delivery means for said rock fragments, characterized in that said peripheral walls of the rotor are constituted at least as to their major part by said projecting vanes, said external edges of said floor and of said ceiling being disposed to follow said vanes to the outside of said outlet openings of the rotor. < i U

2. A crusher according to claim 1, characterized in that the general shape of the rotor in plan is a convex polygon having symmetry of order N about said axis, where N is the number of said projection vanes, said polygon comprising, for each of said vanes, a short side consisting of a front length of said vane having a front end constituted by said projection edge, with the rear end of said short side being closer to said axis than said front end and joining a large side which constitutes a main rectilinear length of the same vane, with at least a front fraction of said main length approaching closer still said axis.

3. A crusher according to claim 2, characterized in that a rear fraction of said main rectilinear length extends said front fraction of said length rearwardly in diverging it progressively away from said axis to the vicinity of a front edge of said outlet opening of the following projection vane.

4. A crusher according to claim 3, characterized in that the general shape of said rotor in plan is an equilateral triangle having cut-off corners, said projection vanes being three in number, with the three cut-off corners of said triangle being constituted by said front lengths of said projection vanes, and with the three sides of said triangle being constituted by said main lengths of said vanes.

5. A crusher according to claim 4, in which said projecting rotor comprises flat steel plates which are cut and welded to constitute in a simple manner said floor, said ceiling and said projecting vanes outside of said projection edges. i> 2 a

6. A crusher according to claim 5, characterized in that said projecting vane comprises in addition to said front and said main length a rear length returning substantially radially towards the interior of said projecting rotor in order to stiffen said main length while retaining rocks at the rear end of said length.

7. A crusher according to claim 6, characterized in that said main length of each projecting vane is provided with at least one intermediate stiffener which projects towards the interior of said projecting rotor in order to reinforce the maintenance of said length about its mid part, said maintenance being ensured at the ends of said length by means of its connection to said front and said rear length.

8. A crusher according to claim 1, characterized in that across the extension of said set-back sector, said peripheral surface forms a mean progressive set-back angle ranging between 1 and 30 degrees relative to the circumferential directions, in order to protect said surface against external wear due to said return shocks and said dusts entrained by said air currents.

9. A crusher substantially as herein described with reference to and as illustrated in the accompanying drawings.