EP0233812B1 - Impeller for a vacuum impact crusher - Google Patents

Abstract

A distributor wheel 20 comprises, downstream of each outlet aperture (24, 25) of its channels (22, 23), in relation to the direction of the projection of particles, a member (30, 33, 34) fixed for rotation with the wheel (20) and making it possible to form, at the end of the guide face of each channel (22, 23), a stable protective cushion composed of the particles themselves and extending the stable self-protection layer (28), and to eliminate the contact force between the particles and the wheel (20) before ejection and projection of the particles onto the target.

Description

The present invention relates to a vacuum projection mill wheel in which the particles to be ground are projected by centrifugal force onto an impact surface disposed inside a vacuum enclosure, as referred to in the preamble of the claim 1 (EP-A 101277)

It is known that this type of mill uses centrifugal force to project materials to be ground on targets at very high speeds, the entire device being placed under vacuum in order to avoid braking of the particles projected by the resistance of the air.

A vacuum crusher comprises a closed enclosure that is resistant to pressure and evacuated and at the top of which is placed a distributing wheel driven in rotation at high speed. The wheel is provided in its axis with a central feed chamber provided at its upper part with an axial orifice formed at the bottom of a hopper supplied with material to be ground by means of a metering device, for example screw, placed at the outlet of a supply chamber forming an airlock and which makes it possible to introduce the material into the vacuum enclosure.

The distributing wheel is also provided with a plurality of projection channels, the axes of which are centered in a median plane perpendicular to the axis and which open inwards into the supply chamber and outwards on the periphery of the wheel.

The material introduced by the metering device into the central feeding chamber is therefore driven by centrifugal effect in the channels and projected at the outlet of these on a set of plates forming targets and which are placed all around the wheel. , along the side wall of the enclosure. The lower part of the latter is in the form of a hopper and collects the fine powder formed by the bursting of the grains of material thus projected onto the targets by the channels of the wheel.

If the distributing wheel rotates at a sufficient speed, a radial and tangential acceleration is created inside the channels, making it possible to obtain the desired speed at the outlet. Inside these channels, there is a contact effect between the particles and the wheel which depends on the speed of rotation, which leads to a significant wear phenomenon. This abrasion phenomenon depends on the physical properties of the particles, but is always very important as soon as the ejection speed also becomes high, having regard to the high value of the particle-wheel contact effect and the relative speed of displacement of particles in the channels.

To achieve the protection of these channels, we know in French patent application 85-02234 in the name of the applicant, a distributor wheel in which the guide face of the particles in each channel has a positive curve, that is to say to say a curve winding in the same direction of rotation of the distributing wheel, and whose tracing, judiciously calculated, according to the coefficients of friction of the materials in contact, achieves the attachment on this curve of a stable layer of self-protection constituted by the particles themselves, with automatic regeneration of said layer at the same time as its wear.

In this device, thanks to the formation of the channels, the bearing faces of the particles formed by the bottom of said channels are therefore protected by a layer of particles, but the extreme point of the bottom of these channels located at the ejection orifice is a vulnerable point that should also be protected.

Furthermore, the movement of the particles to be ground, from the center to the periphery of the distributor wheel, takes place with a certain speed which cannot be canceled, otherwise the flow rate of the device would be zero.

The protection of this extreme point can be achieved by the formation of an embankment, thanks to the appropriate shapes of the distributor wheel. However, it is known that a cone-shaped slope has, at its intersection with the laying plane, a zero thickness which also constitutes a vulnerable point which can undergo wear. This solution cannot therefore be adopted.

To obtain no wear of the distributor wheel and effective protection at the level of the ejection orifice of the distribution channels, it is therefore necessary either to ensure that the particles move on slopes of non-zero thickness, or that the contact force between particles and slope is zero, especially when the thickness of the latter is almost zero.

The subject of the invention is therefore a new embodiment of a grinder wheel enabling these drawbacks to be remedied and having the characteristics of the characterizing part of claim 1.

According to the invention, the distributing wheel comprises, downstream of each outlet orifice of the channels with respect to the direction of projection of the particles, an element formed by a pallet integral in rotation with the wheel and making it possible on the one hand to create, at the end of the guide face of each channel, a protective mattress formed by the particles themselves and extending the stable layer of self-protection, and on the other hand to cancel the effort of contact between the particles and the wheel before the ejection and the projection of said particles on the target.

• la figure 1 est une vue schématique en coupe dans un plan vertical de l'ensemble d'un broyeur utilisant une roue distributrice selon l'invention ;
• la figure 2 est une vue en coupe dans un plan vertical à plus grande échelle de la roue distributrice conforme à l'invention ;
• la figure 3 est une vue en coupe selon III-III de la figure 2 ;
• la figure 4 est une vue en perspective d'une palette prévue au niveau de chaque orifice d'éjection de la roue distributrice ;
• la figure 5 est une vue identique à la figure 3 montrant la formation des couches auto-protectrices dans la roue distributrice pendant le fonctionnement du broyeur ;
• la figure 6 est une vue de face de la palette d'éjection selon la flèche F de la figure 5 ;
• la figure 7 est une vue en coupe selon la ligne VII-VII de la figure 6.

According to another characteristic of the invention, the pallet is perpendicular to the plane of the wheel and provided with means ensuring, beyond the end of the guide face of each channel, the formation of self-protection slopes constituted by the particles themselves and of geometry and slope determined as a function of the coefficient of friction of the materials in contact and of the particle size of the material to be treated. The characteristics and advantages of the invention will be better understood on reading the description which follows of an exemplary embodiment and with reference to the appended drawings, in which:

• Figure 1 is a schematic sectional view in a vertical plane of the assembly of a crusher using a distributor wheel according to the invention;
• Figure 2 is a sectional view in a vertical plane on a larger scale of the distributor wheel according to the invention;
• Figure 3 is a sectional view along III-III of Figure 2;
• Figure 4 is a perspective view of a pallet provided at each ejection orifice of the distributor wheel;
• FIG. 5 is a view identical to FIG. 3 showing the formation of the self-protecting layers in the distributor wheel during the operation of the crusher;
• Figure 6 is a front view of the ejection pallet according to arrow F of Figure 5;
• FIG. 7 is a sectional view along the line VII-VII of FIG. 6.

In Figure 1, we see a cylindrical enclosure 1 with a vertical axis at the upper part of which is disposed a vertical duct of large section 2 having a branch on which is fixed a duct 3 connected to a vacuum pump not shown. Inside the duct 2 are arranged hoppers 4 and 5. The hopper 5 is connected to a vibrator 6.

Below the vibrating hopper 5 is disposed a hopper 7 supplied with material to be ground and whose axial outlet orifice opens into a central supply chamber 21 of a distributing wheel 20 constituting the upper part of the rotor of the mill. This wheel is pierced with several radial direction channels such as 22 and 23 regularly distributed.

In the extension of these channels and all around the enclosure, a target 8 is arranged, the impact surface of which is covered with a material resistant to wear and impact.

It is possible to determine between the external peripheral surface of the wheel 20 and the target 8 a zone of space into which the particles to be ground will be projected. Below this area of space is arranged a vibrating hopper 10 whose role is to collect the crushed pulverulent material to direct it towards the outlet 11 connected to a set of vacuum locks allowing the product to flow without breaking the vacuum in the enclosure.

The wheel 20 constituting the upper part of the rotor of the mill is secured to an elongated cylindrical tubular shaft 12. This shaft 12, driven by a motor 13, is guided and supported by a set of bearings and stops 14.

The motor 13 makes it possible to drive the wheel 20 in rotation at very high speeds.

In Figure 2, there is shown on a larger scale the dispensing wheel 20 inside which are formed a supply chamber 21 and two channels 22 and 23 opening at their ends inwardly into the supply chamber 21 and outwards on the periphery of the wheel through discharge orifices 24 and 25.

The hopper 7 is arranged in the axis of the dispensing wheel 20 and opens into the supply chamber 21 of said wheel. This distributing wheel 20 is constituted by a cover 26 and by a bottom 27 in the form of a circular plate, these two elements being integral with one another and driven in rotation at very high speeds by the shaft 12.

The granular material penetrates into the feed chamber 21 and is projected outward, by centrifugal effect passing through the channels 22 and 23. The particles thus projected by the channels strike the target 8 and are reduced to a fine powder. .

The granular materials, for example cement or pulverized coal, treated in centrifugal mills being fairly abrasive, we find in the mills a fairly rapid wear of the internal side wall of the projection channels, and also from the end of the channels to the level of the peripheral outlet orifice.

To avoid wear of the internal lateral wall of the channels 22 and 23, the guide face 22a and 23a of the particles in each of said channels has a positive curve A (FIG. 3), that is to say a curve s' winding in the same direction of rotation of the wheel distributor 20, and the layout of which, judiciously calculated, as a function of the coefficients of friction of the materials in contact, achieves the attachment on this curve A of a stable layer 28 (FIG. 5) of self-protection constituted by the particles themselves , with automatic regeneration of said layer at the same time as its wear.

Thus, thanks to the shape of the guide face 22a and 23a of the particles, there occurs in each of the channels 22 and 23 a accumulation 28 of particles until this accumulation draws a curve B in such a way that this layer fixes of particles therefore constitutes real protection for said guide faces.

However, this self-protection layer 28 has an almost zero thickness at the end 22b, 23b of each of the channels, so that this end constitutes a vulnerable zone undergoing significant wear.

The invention makes it possible to avoid this wear phenomenon in this area.

To this end, the distributor wheel 20 is provided at the end of each channel 22 and 23, at the outlet orifices 24 and 25, with an element designated as a whole by the reference 30.

This element 30 is constituted by a pallet integral with the wheel 20 or attached to it.

In the example shown, the pallet 30 is constituted by an extension of the external lateral face of the bottom 27 so as to form a vertical wall 31 oriented along a plane perpendicular to the plane of the distributing wheel 20. This vertical wall 31 is therefore arranged downstream of the orifice 24 and leave a cavity 32 behind the end 22b.

Inside this cavity 32 is mounted a first deflector 33 formed by a small independent plate applied against the vertical wall 31. The upper part of this first deflector 33 has the shape of a triangle whose apex 33a is directed towards the high and overflows above the vertical wall 31.

On the other hand, a second deflector 34 formed by a small independent plate is mounted inside the cavity 32, said second deflector 34 being attached to the first deflector 33. The upper part of this second deflector 34 also has the shape of 'a triangle whose apex 34a is directed upwards and whose height is less than the height of the tip 33a of the first deflector.

In the example shown, the lateral faces of the two deflectors 33 and 34 have a curvature determined so that the center of said curvatures coincides with the center O of the distributing wheel 20 on the axis of rotation. In addition, in horizontal projection in a horizontal plane of the wheel 20, the vertices 33a and 34a, respectively of the deflectors 33 and 34, are arranged on the same radius OX passing through the center O of the wheel 20, as seen on Figure 3.

The lateral faces of the two deflectors 33 and 34 can also be of planar shape and perpendicular to the radius OX.

The pallet 30 placed at the outlet of the channel 23 is identical to the pallet placed at the outlet of the channel 22.

In the case where the distributing wheel 20 has two opposite and symmetrical channels 22 and 23, the vertices 33a and 34a of the deflectors 33 and 34 of each pallet are located on the same diameter XOX ′ of said wheel 20.

Furthermore, the distributing wheel 20 includes means 40 (FIG. 2) for adjusting the starting point of the stable self-protection layer 28 formed by the particles in each channel 22 and 23. These means 40 consist of a disc 41 secured in rotation with the bottom 27 and placed in the axis of the wheel 20 below the supply chamber 21. This disc 41 has in relief on its upper face small studs (42, 43, ...) in shape of circular crown sectors.

The number of small studs corresponds to the number of channels formed in the distributing wheel 20. In the example shown, the distributing wheel 20 being provided with symmetrical channels, the disc 41 therefore comprises two small studs 42 and 43 diametrically opposite, the small stud 42 corresponding to channel 22 and the small pad 43 corresponding to channel 23.

The disc 41 is adjustable in rotation so as to modify the position of the small studs 42 and 43 relative to the inlet of the channels 22 and 23, which makes it possible to adjust the starting point of the self-protection layer in each channel in function of the particle size of the material to be treated and the coefficients of friction of the materials in contact.

As we have indicated previously, during the operation of the mill, there occurs in each of the channels 22 and 23 a accumulation 28 of particles until this accumulation draws a curve B in such a way that this fixed curve of particles therefore constitutes real protection for the guide faces.

The particles introduced into the feed chamber 21 also form, during the operation of the mill, an embankment of particles 50 on the second deflector 34 of each pallet 30 which extends the curve B of the layer 28. The length of this slope 50 depends on the length of the second deflector 34 which is determined so that the thickness of the particle self-protection layer at the end 22b, 23b of each channel 22, 23 is sufficient to avoid wear of this end.

Given the triangular shape of the second deflector, the slope 50 has the shape of a dihedral tilted upwards determining two half-planes 50a and 50b of QT intersection (FIG. 6).

On the first deflector 33, a second slope 51 of particles is also formed, above the slope 50. Thanks to the triangular shape of the deflector 33, the slope 51 has the shape of a dihedral upwardly inclined determining two half-planes 51a and 51b of intersection TS. The half-plane TSV of the dihedral 51 determines a boundary layer in such a way that the component of its normal protection in the plane of the wheel 20 is in a direction substantially opposite to the direction of rotation ω of said wheel.

After the formation of the protective layer 28 in each channel 22, 23, and the formation of the slopes 50 and 51 on the deflectors 33 and 34 of each pallet 30, the particles of material to be treated introduced by the supply chamber 21 of the distributing wheel 20 will start to move and first slide on the mattress of trapped particles between curves A and B.

When the particles arrive in the half-plane 50a of the slope 50, thanks to the shape of this slope, said particles are blocked and change level and take the direction OX, which makes it possible to avoid direct ejection of these particles.

Then, the particles arrive at the point T on the half-plane TSV of the slope 51. Since the component of the normal of the half-plane TSV in projection in the plane of the wheel 20 is in a direction substantially opposite to the direction of rotation of said wheel, the contact force between the particles and the wheel in the TSV half-plane is canceled, the particles leave said wheel which does not cause wear of these parts.

In addition, the particle entrainment speed obtained by the rotation of the distributing wheel 20 being clearly greater than the relative speed of said particles in the TSV plane, said relative speed is therefore negligible compared to said entrainment speed, so that at the exit of the TSV plane the particles resume a horizontal trajectory and are projected on the target 8.

Depending on the nature of the product to be sprayed and on the grain size of the product which it is desired to obtain, the distributing wheel 20 must rotate at a greater or lesser speed. But in all cases, the creation of a protective mattress will be obtained, because the plating of the particles is independent of the speed of rotation of the wheel.

One thus carries out a self-protection by the product itself of the channels, of the end of these channels at the level of the outlet orifice and the pallet, which avoids any phenomenon of abrasion, while maintaining a speed of rotation sufficient of the distributor wheel to obtain the desired particle size.

On the other hand, depending on the coefficient of friction of the materials in contact as well as the particle size of the material to be treated, it is possible to modify the position of the small studs 42 and 43 by turning the disc 41 in one direction or the other to modify the starting point of the layer 28 in the channels 22 and 23 so as to obtain a determined position from the point Q and create at level of the ends 22b, 23b of the channels a protective mattress sufficient to avoid any wear.

Finally, the deflectors 33 and 34 of the pallets 30 can be mounted adjustable transversely and / or vertically to modify, as a function of the coefficients of friction of the materials in contact and the particle size of the material to be treated, the geometry of the slopes 50 and 51 and the position of the radius OX and / or OX ′ with respect to the ends 22b, 23b of the channels 22 and 23.

The deflectors 33 and 34 are easily replaceable and can, for example, be made of very hard and abrasion-resistant material.

The invention is not limited to the embodiment which has just been described; other improvements and variants can be imagined while remaining within the framework of the protection claimed.

Indeed, instead of using pallets comprising two independent deflectors, these two deflectors can be produced in a single piece. It is also possible to provide pallets integral with the cover 26 of the wheel, instead of the bottom 27, and to orient the vertices 33a and 34a of the deflectors 33 and 34 downwards, the ejection of the particles taking place in this case below the distributor wheel 20. This arrangement has advantages. Indeed, the crushed particles are not likely to fall on the cover and, consequently, to cause rapid and abnormal wear of said cover and the periphery of the wheel.

Claims (12)

1. A wheel for a vacuum projection grinder adapted to be driven rotationally for the high-speed projection of a granular material onto a target (8), and comprising a cover (26) and a base (27) between which are provided a feed chamber (21) and a plurality of channels (22,23) oriented in a direction perpendicular to the axis of said wheel (20) and leading outwards via outlet apertures (24,25), the guide faces (22a,23a) of said channels each having a curve A whose contour is calculated, in accordance with the coefficients of friction of the materials in contact, to cause a stable self-protective layer (28) consisting of the particles themselves to adhere to the curve A, and each outlet aperture (24,25) of the channels (22,23) relative to the direction of projection of the particles comprising an element consisting of a blade (30) which is rotationally integral with the wheel (20) and perpendicular to the plane of said wheel (20), characterised in that the blade (30) is provided with means (33,34) which ensure, beyond the end (22b,23b) of the guide face (22a,23a) of each channel (22,23) that self-protecting slopes (50,51) are formed, the geometry and inclination of which are determined in accordance with the coefficient of friction of the materials in contact and the particle size of the material being treated, these slopes making it possible, on the one hand, to create a protective cushion consisting of the particles themselves, level with the end (22b,23b) of the guide face (22a,23a) of each channel (22,23), and extending the stable self protective layer (28), and on the other hand to eliminate the contact force between the particles and the wheel (20) before the ejection and projection of said particles onto the target (8).

2. A wheel according to claim 1, characterised in that the means on the blade (30) for forming slopes (50,51) consist of two juxtaposed deflectors (33,34) of triangular shape and of different heights.

3. A wheel according to claim 2, characterised in that in projection in the plane of the distributor wheel (20), the apexes (33a,34a) of the respective triangular deflectors (33,34) are on the same radius OX passing through the centre O of said wheel and situated downstream of the end (22b,23b) of the guide face (22a,23a) of each channel (22,23) in relation to the direction followed by the particles inside the distributor wheel (20).

4. A wheel according to claims 2 and 3, characterised in that the side faces of the triangular deflectors (33,34) have a determined curvature the centre of which coincides with the centre O of the distributor wheel (20) on the axis of rotation.

5. A wheel according to claims 2 and 3, characterised in that the side faces of the triangular deflectors (33,34) are planar in shape and are at right angles to the radius of the distributor wheel passing through the apexes (33a,34a) of said deflectors.

6. A wheel according to one of the preceding claims, characterised in that the slopes of particles (50,51) formed by the two deflectors (33,34) are situated one above the other and are both in the form of a dihedron respectively defining two half-planes (50a,50b; 51a,51b) whose respective intersections QT and TS are situated in a plane perpendicular to the plane of the distributor wheel (20) and passing through the apexes (33a,34a) of the two triangular deflectors (33,34).

7. A wheel according to claim 6, characterised in that the half-plane (51a) of the slope (51) defines a stable boundary layer of particles whose component of its normal in projection in the plane of the distributor wheel (20) is in a direction substantially opposite to the direction of rotation of said wheel.

8. A wheel according to one of the preceding claims, characterised in that the blade (30) is integral with or fastened to the base (27) of the distributor wheel (20) and the apexes (33a,34a) of the deflectors (33,34) are directed upwards in relation to the plane of said wheel.

9. A wheel according to one of the preceding claims, characterised in that the blade (30) is integral with or fastened to the cover (26) of the distributor wheel (20) and the apexes (33a,34a) of the deflectors (33,34) are directed downwards in relation to the plane of said wheel.

10. A wheel according to one of the preceding claims, characterised in that the transverse and/or vertical position of the deflectors (33,34) is adjustable in accordance with the particle size of the material to be treated.

11. A wheel according to claim 1, characterised in that the distributor wheel (20) is provided with means (40) for adjusting the starting point of the stable selfprotective layer (28) formed by the particles in each channel (22,23) depending on the coefficients of friction of the materials in contact and on the particle size of the material to be treated.

12. A wheel according to claim 11, characterised in that the means (40) consist of a disc (41) fixed for rotation with the distributor wheel (20) and located on the axis of said wheel below the feed chamber (21), said disc (42) being provided on its upper face with small raised studs (42,43,...) in the shape of sectors of a circular crown.

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