EP2785461B1 - Bed roller mill - Google Patents

Description

The invention relates to a compression mill bed materials, usually called horizontal roller mill, and a grinding process using such a mill.

Such a mill has a particular application for the grinding of mineral materials, particularly in the dry process, without limitation, for the manufacture of cement clinker.

The documents EP-0486371 and EP-0934120 describe such a type of mill which comprises a cylinder rotating along a horizontal axis, and whose inner wall constitutes a rolling track for a grinding roller, with axis of rotation parallel to the axis of the cylinder, applied under strong pressure on the running track. The material is fed at one end of the cylinder and spring at the other end.

Under the effect of the rotation of the cylinder, the material passes several times between the raceway and the grinding roller, and it is known to control the number of passes through material feeders, such as those described in the documents mentioned above.

In such a mill, the material advances from one end to the other of the cylinder undergoing successive grinding actions. Thus the particle size of the material is coarser in the part of the mill near the end of the inlet, than in the part of the mill near the end of the outlet.

Classically the material fed into the mill has a coarse grain size, with a maximum grain size of up to 120 mm. Due to the operation of the handling systems, the material flow is subject to fluctuations, and the particle size distribution is heterogeneous. This induces variations in the constitution and thickness of the material bed and, thereby, variations in the reaction of the forces exerted by the grinding roll which result in vibrations of the mill.

These vibrations create mechanical stresses that contribute to the reduction of the service life of the components of the machine, or even neighboring elements in the grinding machine.

We also know of the document WO97 / 39829 a wet milling method implemented in a mill having a circular track and a grinding roll, adapted to roll on the track and elastically pressed thereon.

In this prior art, the surface of the bed of material is standardized by the addition of water or other liquid sprayed under pressure by nozzles, which improves the distribution of materials in a layer of uniform thickness on Track.

According to a variant of this anteriority, the mill comprises a pre-compression roll, placed upstream of the grinding roll. This pre-compression roll is, like the grinding roll, pressed elastically on the circular track. The purpose of the pre-compression roll is to ensure that the layer of material is wrung out, and that the water that is squeezed out above the layer of material does not reach the grinding roll. The crusher of the document WO97 / 39829 would not be suitable for grinding dry materials. Without liquid spraying in order to standardize the surface of the bed of material, the pre-compression roller of this anteriority, which is not maintained at a distance from the track, would not make it possible to standardize the bed of material in the manner of the equalizing roller of the mill according to the invention. The object of the present invention is to provide a horizontal roll mill which overcomes the aforementioned drawbacks, the life of which is increased compared to horizontal roll mills known from the state of the art.

Another object of the present invention is to provide a grinding method implemented by a grinder according to the invention.

Other aims and advantages of the invention will become apparent from the following description which is given for information only and which is not intended to limit it.

• un cylindre à axe horizontal dont la paroi intérieure comporte une piste de roulement pour un rouleau de broyage, disposé intérieur audit cylindre,
• des moyens pour entraîner en rotation le cylindre autour de son axe,
• ledit rouleau de broyage, d'axe parallèle à celui de l'axe du cylindre,
• des moyens pour appliquer ledit rouleau de broyage contre la piste de roulement dudit cylindre,
• une entrée pour l'alimentation de matière à broyer située à l'une des extrémités dudit cylindre et une sortie pour la matière broyée à l'autre extrémité dudit cylindre.

Also the invention relates to a compression mill of material bed, comprising:

• a cylinder with a horizontal axis whose inner wall comprises a rolling track for a grinding roller, arranged inside said cylinder,
• means for rotating the cylinder about its axis,
• said grinding roller having an axis parallel to that of the axis of the cylinder,
• means for applying said grinding roller against the rolling track of said cylinder,
• an inlet for feeding material to be ground at one end of said cylinder and an outlet for the ground material at the other end of said cylinder.

• un rouleau égalisateur, disposé en amont dudit rouleau de broyage suivant le sens de rotation dudit cylindre, destiné à égaliser la surface du lit de matières,
• des moyens de maintien du rouleau égalisateur, à proximité et à distance de la piste de roulement dudit cylindre, interdisant tout contact entre ledit rouleau égalisateur et la piste de roulement.

According to the invention, said mill comprises:

• an equalizing roller, disposed upstream of said grinding roller in the direction of rotation of said cylinder, for equalizing the surface of the material bed,
• means for maintaining the equalizing roller, close to and away from the raceway of said cylinder, preventing any contact between said equalizing roller and the raceway.

According to the invention, said means for holding the equalizing roller near and at a distance from the raceway of said cylinder, on the one hand, and said means for applying said grinding roller against the rolling track of said cylinder, on the other hand on the other hand, are such that said equalizing roller is able to exert on the bed of materials a pressure which equalizes its surface, lower than the pressure exerted by said grinding roller on said bed of materials.

Such a crusher allows the implementation of a compression milling process of material bed in which, during each cylinder revolution, the material passes successively under the equalizing roller and then under the roller grinding, said equalizing roller exerting on the material bed a pressure which equalizes its surface, less than the pressure exerted by said grinding roll on said bed of materials.

According to one embodiment of the grinding method, said means for maintaining the equalizing roller guarantee a minimum distance between the tread and the surface of said equalizing roller, and in which the grinder is fed with a maximum grain size determined between 1 mm and 120 mm and said minimum distance greater than or equal to 0.5 times the determined maximum grain size is determined.

• le rouleau égalisateur est libre de rotation, apte à être entrainé en rotation autour de son axe grâce aux frottements avec le lit de matières ;
• le broyeur présente des moyens moteur pour entraîner en rotation le rouleau égalisateur de telle sorte que sa vitesse périphérique soit égale à la vitesse moyenne du lit de matières sur lequel ledit rouleau égalisateur est destiné à s'appliquer ;
• le broyeur est destiné à traiter des grains de taille maximale comprise entre 1 mm et 120 mm et dans lequel le diamètre du rouleau égalisateur est compris entre 100 mm et 660 mm ;
• lesdits moyens de maintien du rouleau égalisateur comprennent des moyens d'articulation, aptes à autoriser le déplacement dudit rouleau égalisateur selon une direction sensiblement radiale vers l'axe dudit cylindre et des moyens élastiques contraignant ledit rouleau égalisateur dans le sens opposé, vers la piste de roulement ;
• lesdits moyens de maintien dudit rouleau égalisateur assurent le maintien dudit rouleau égalisateur par ses deux extrémités, lesdits moyens de maintien comportant deux bras, chacun articulé, d'une part, à l'une des extrémités dudit bras audit rouleau égalisateur, suivant l'axe dudit rouleau égalisateur et, d'autre part, à l'autre extrémité dudit bras à un bâti dudit broyeur, suivant un axe de rotation parallèle à l'axe dudit cylindre ;
• la longueur dudit rouleau égalisateur est supérieure ou égale à la longueur dudit rouleau de broyage, ledit rouleau égalisateur étant disposé en correspondance dudit rouleau de broyage suivant la longueur du cylindre ;
• le broyeur présente des moyens pour contrôler le déplacement de la matière sur la longueur dudit cylindre de sorte que ladite matière ne parcourt qu'une fraction de longueur du cylindre à chaque tour de cylindre et passe plusieurs fois entre le cylindre et le rouleau de broyage, depuis ladite entrée d'alimentation de matières à broyer jusqu'à ladite sortie de matières broyées et dans lequel la distance entre la surface dudit rouleau égalisateur et la piste de roulement est variable suivant la longueur dudit cylindre, décroissante de ladite entrée vers ladite sortie ;
• lesdits moyens pour appliquer ledit rouleau de broyage contre la piste de roulement dudit cylindre sont tels que le rouleau de broyage exerce sur le lit de matières une pression moyenne entre 10 MPa et 40 MPa et lesdits moyens de maintien du rouleau égalisateur sont tels que le rouleau égalisateur exerce sur le lit de matières une pression inférieure à 10 MPa, de préférence inférieure à 1 MPa ;
• l'axe de rotation du rouleau égalisateur est parallèle à l'axe dudit cylindre.

According to optional features of the invention, taken alone or in combination:

• the equalizing roller is free to rotate, able to be rotated about its axis by friction with the bed of materials;
• the mill has motor means for rotating the taper roller such that its peripheral speed is equal to the average speed of the material bed on which said tilting roller is intended to apply;
• the mill is intended to treat grains with a maximum size of between 1 mm and 120 mm and in which the diameter of the equalizing roller is between 100 mm and 660 mm;
• said means for maintaining the equalizing roller comprise articulation means, able to allow the said equalizing roller to move in a direction substantially radial towards the axis of the said cylinder and elastic means constraining the said equalizing roller in the opposite direction towards the rolling ;
• said holding means of said equalizing roller maintain said equalizing roller by its two ends, said holding means having two arms, each articulated, on the one hand, at one end of said arm to said equalizing roller, along the axis said equalizing roller and, on the other hand, at the other end of said arm to a frame of said mill, along an axis of rotation parallel to the axis of said cylinder;
• the length of said equalizing roll is greater than or equal to the length of said grinding roll, said equalizing roll being disposed in correspondence of said grinding roll along the length of the roll;
• the mill has means for controlling the movement of the material along the length of said roll so that said material travels only a fraction of the length of the roll at each turn of the roll and passes several times between the roll and the milling roll, from said material feed inlet to be milled to said crushed material outlet and wherein the distance between the surface of said equalizing roller and the raceway is variable along the length of said cylinder, decreasing from said inlet to said outlet;
• said means for applying said grinding roll against the rolling track of said roll are such that the grinding roll exerts on the material bed an average pressure of between 10 MPa and 40 MPa and said means for holding the equalizing roll are such that the roll equalizer exerts on the bed of materials a pressure of less than 10 MPa, preferably less than 1 MPa;
• the axis of rotation of the equalizing roller is parallel to the axis of said cylinder.

• compris entre 2 fois et 6 fois ladite taille maximale des grains à broyer si, sous cette condition, le diamètre de rouleau égalisateur est supérieur ou égale à 0,15 fois le diamètre du rouleau de broyage et, autrement,
• au moins égale à 0,15 fois le diamètre du rouleau de broyage.

According to one embodiment of the grinding process, said grinding mill is fed with a material of a given maximum grain size and the diameter of said equalizing roller is selected as follows:

• between 2 and 6 times the maximum grain size to be milled if, under this condition, the equalizing roll diameter is greater than or equal to 0.15 times the diameter of the milling roll and, otherwise,
• at least equal to 0.15 times the diameter of the grinding roll.

The invention also relates to a method of grinding by material bed compression implemented by means of a grinder according to the invention, the holding means comprise said hinge means and wherein said grinder is fed into a material of a maximum grain size determined and the displacement stroke of said equalizing roller is adjusted so as to maintain the surface of the equalizing roller at a distance from the tread of between 0.5 times and 3 times the maximum size of the grains to be ground.

The grinding process and the mill according to the invention find a particular application for the grinding of materials in the dry process.

• la figure 1 est une vue schématique d'un broyeur conforme à l'invention, selon une coupe verticale, illustrant le cylindre et le rouleau de broyage (rouleau égalisateur non visible).
• la figure 2 est une vue schématique de côté du broyeur selon la figure 1.
• la figure 3 est une vue schématique du broyeur selon la figure 2, illustrant plus particulièrement lesdits moyens de maintien dudit rouleau égalisateur, selon un mode de réalisation non limitatif.
• la figure 4 est une vue de coupe d'un broyeur conforme à l'invention selon un second mode de réalisation, illustrant le cylindre et le rouleau égalisateur (rouleau de broyage non visible).

The invention will be better understood on reading the following description accompanied by the appended drawings among which:

• the figure 1 is a schematic view of a mill according to the invention, in a vertical section, illustrating the cylinder and the grinding roller (non-visible equalizing roller).
• the figure 2 is a schematic side view of the mill according to the figure 1 .
• the figure 3 is a schematic view of the mill according to the figure 2 , more particularly illustrating said holding means of said equalizing roller, according to a non-limiting embodiment.
• the figure 4 is a sectional view of a mill according to the invention according to a second embodiment, illustrating the cylinder and the equalizing roller (non-visible grinding roll).

• un cylindre 2 à axe A horizontal dont la paroi intérieure comporte une piste de roulement 20 pour un rouleau de broyage 3, disposé intérieur audit cylindre 2,
• des moyens pour entraîner en rotation le cylindre autour de son axe A,
• ledit rouleau de broyage 3, d'axe parallèle à celui de l'axe A du cylindre 2,

• des moyens pour appliquer ledit rouleau de broyage 3 contre la piste de roulement 20 dudit cylindre 2,
• une entrée 7 pour l'alimentation de matière à broyer située à l'une des extrémités dudit cylindre 2 et une sortie 8 pour la matière broyée à l'autre extrémité dudit cylindre 2.

Also the invention relates to a crusher 1 by compression of material bed 5, comprising:

• a cylinder 2 having a horizontal axis A, the inner wall of which comprises a rolling track 20 for a grinding roll 3, arranged inside said cylinder 2,
• means for rotating the cylinder about its axis A,
• said grinding roll 3 having an axis parallel to that of the axis A of cylinder 2,

• means for applying said grinding roll 3 against the rolling track 20 of said cylinder 2,
• an inlet 7 for feeding material to be ground at one end of said cylinder 2 and an outlet 8 for the ground material at the other end of said cylinder 2.

Said means for rotating the cylinder 2 may comprise a geared motor whose output axis has a pinion coupled to a ring gear, integral with the outer wall of the cylinder 2.

Said means for applying said grinding roll 3 against the tread 20 may comprise slides guiding the ends of the grinding roll 3, as well as jacks or springs able to exert on the ends of the grinding roll 3 the forces which are transmitted to the grinding roller 3.

According to one embodiment, said means for applying said grinding roller 3 against the rolling track 20 of said cylinder 2 are such that the grinding roller 3 exerts on the material bed 5 a mean pressure between 10 MPa and 40 MPa.

The supply of materials to the inlet 7 and / or the discharge of the materials to the outlet 8 can be obtained by means of pneumatic handling system.

Preferably, the mill has means (not shown) for controlling the movement of the material along the length of said cylinder 2 so that said material travels only a fraction of the length of the cylinder 2 at each cylinder turn 2 and passes several times. between the cylinder 2 and the grinding roll 3 from said material feed inlet 7 to be milled to said milled material outlet 8.

These means may comprise a device intended to ensure the advance of the material, from one end to the other of the cylinder 2 such as in particular described in the document EP-0486371 or EP-0934120 . Such a device comprises a scraper (or knife) placed at the interior of the cylinder, in the upper descending part, so as to detach the material from the raceway and one or, preferably, several deflector plates arranged under the scraper so as to intercept the material detached by the latter and the deviate towards the exit of the mill.

• un rouleau égalisateur 4 disposé en amont dudit rouleau de broyage 3 suivant le sens de rotation R dudit cylindre 2,
• des moyens de maintien 6 du rouleau égalisateur 4 à proximité et à distance de la piste de roulement dudit cylindre 2.

According to the invention, the mill comprises:

• an equalizing roller 4 arranged upstream of said grinding roller 3 in the direction of rotation R of said cylinder 2,
• means 6 for maintaining the equalizing roller 4 near and away from the raceway of said cylinder 2.

The means 4, 6 are such that, during each cylinder revolution 2, the material passes successively under the equalizing roll 4 and then under the grinding roll 3, said equalizing roll 4 exerting on the material bed 5 a pressure which equalizes its surface, lower than the pressure P exerted by said grinding roll 3 on said bed of materials 5.

Preferably, in operation the pressure of the equalizing roller on the material bed 5 is less than the pressure required to grind the material particles. For this purpose, said holding means 60 of the equalizing roll 4 are such that the equalizing roll 4 exerts on the material bed 5 a pressure of less than 10 MPa, preferably less than 1 MPa.

Preferably, the length of said equalizing roll 4 may be greater than or equal to the length of said grinding roll 3, said equalizing roll 4 being arranged in correspondence of said grinding roll 3 along the length of the roll 2.

According to the invention, said holding means 6 of the equalizing roller 4 guarantee a minimum distance between the tread 20 and the surface of said equalizing roller 4, preventing any contact between said equalizing roller 4 and the tread 20.

This minimum distance makes it possible to ensure that the granular materials of the bed of materials can be driven laterally, along the axis of the roll, under the action of the said equalizing roller 4, and thus to obtain a bed of materials of constant thickness over the length of the equalizing roller 4. This minimum distance can be determined according to the maximum grain size feeding the mill which can be between 1 mm and 120 mm. According to one embodiment, the minimum distance is greater than or equal to 0.5 times the maximum grain size determined.

According to one embodiment, the equalizing roller 4 is free to rotate, able to be rotated about its axis by friction with the material bed 5.

Alternatively, the mill may have drive means for rotating the equalizing roller 4 so that its peripheral speed is equal to the average speed of the material bed 5 on which said equalizing roller 4 is intended to apply.

According to one embodiment, the mill 1 is intended to grind grain with a maximum size of between 1 mm and 120 mm, the diameter of the equalizing roller 4 then being between 100 mm and 660 mm.

• compris entre 2 fois et 6 fois ladite taille maximale des grains à broyer si, sous cette dernière condition, le diamètre de rouleau égalisateur est supérieur ou égal à 0,15 fois le diamètre du rouleau de broyage 3 et, autrement,
• au moins égal à 0,15 fois le diamètre du rouleau de broyage 3, notamment inférieur à 0,5 fois le diamètre du rouleau de broyage 3.

Preferably, said mill 1 is fed into a material of a given maximum grain size and the diameter of said equalizing roll 4 is selected as follows:

• between 2 and 6 times the maximum grain size to be milled if, in the latter condition, the equalizing roll diameter is greater than or equal to 0.15 times the diameter of the milling roll 3 and, otherwise,
• at least equal to 0.15 times the diameter of the grinding roll 3, in particular less than 0.5 times the diameter of the grinding roll 3.

Said holding means 6 of the equalizing roller 4 may comprise articulation means capable of allowing said equalizing roller 4 to move in a substantially radial direction towards the axis A of said cylinder 2 and elastic means (not shown) forcing said roller equalizer 4 in the opposite direction, towards the raceway (20).

According to one embodiment, said holding means 6 of said equalizing roller 4 ensure the maintenance of said equalizing roller 4 by its two ends, said articulation means of said holding means 6 having two arms 60, each articulated on the one hand, at one end of said arm 60 to said roller equalizer 4, along the axis of said equalizing roller 4 and, on the other hand, at the other end of said arm 60 to a frame of said mill 1, along an axis of rotation B, in particular parallel to the axis A of said cylinder 2 .

Preferably, the displacement stroke of the equalizing roller 4 is limited by said holding means 6.

Advantageously, said grinder 1 is fed with a material of a maximum grain size determined and the displacement stroke of said equalizing roller 4 is adjusted so as to maintain the surface of the equalizing roller 4 at a distance from the raceway 20 included between 0.5 and 3 times the maximum size of the kernels to be grinded. The moving stroke of the equalizing roller 4 may be such that the equalizing roller 4 scans the entire range of value.

According to one embodiment, the mill 1 has said means for controlling the movement of the material along the length of said cylinder 2 so that said material travels only a fraction of the length of the cylinder 2 at each cylinder turn 2 and passes several times. between the cylinder 2 and the grinding roll 3 from said material feed inlet 7 to be milled to said milled material outlet 8.

Advantageously, according to this last embodiment, the distance "d" between the surface of said equalizing roller 4 and the rolling track 20 may be variable along the length of said cylinder 2, decreasing from said inlet 7 to said outlet 8. and according to the example shown in the figure 4 the axis of the equalizing roller 4 can be inclined with respect to the axis of the cylinder 2.

This arrangement makes it possible to take into account the fact that the grain size of the material is coarser in the part of the mill located near the end of the inlet 7 than in the part of the mill located near the end of the exit 8.

Thus the distance between the surface of the equalizing roller 4 and the running track 20 at the end of the roller on the input side 7 is greater than the distance between the surface of the equalizing roller 4 and the running track 20 at the end of the roll on the outlet side 8. The ratio between the two distances can be between 1 and 2.

Alternatively, the axis of rotation of the equalizing roller 4 is parallel to the axis A of the cylinder 2.

The mill and grinding processes according to the invention will find a particular application for the grinding of mineral materials and / or the grinding of materials in the manufacture of cement clinker, particularly in the dry process.

Naturally, other embodiments could have been envisaged by those skilled in the art without departing from the scope of the invention as defined by the claims below.

NOMENCLATURE

1.

Shredders

2.

Cylinder,

3.

Grinding roll,

4.

Tightening roller,

5.

Bed of materials,

6.

Holding means (equalizing roller),

7.

Entrance,

8.

Exit,

20.

Runway,

60.

Arms (means of articulation),

AT.

Horizontal axis,

B.

Rotation axis,

P.

Pressure,

R.

Sense of rotation.

Claims (16)

1. Method of grinding by compressing a bed of materials implemented by means of a compressive grinder (1) for a bed of materials (5), comprising:

   - a cylinder (2) with a horizontal axis (A) of which the inner wall comprises a raceway (20) for a grinding roller (3), arranged inside said cylinder (2),

   - means for rotating the cylinder about its axis (A),

   - said grinding roller (3), with an axis parallel to that of the axis (A) of the cylinder (2),

   - means for urging said grinding roller (3) against the raceway (20) of said cylinder (2),

   - an inlet (7) for supplying material to be ground located at one of the ends of said cylinder (2) and an outlet (8) for the ground material at the other end of said cylinder (2),

   - a smoothing roller (4) arranged upstream of said grinding roller (3) in the direction of rotation (R) of said cylinder (2),

   - means for keeping (6) the smoothing roller (4) adjacent to and separated from the raceway of said cylinder (2), prohibiting any contact between said smoothing roller (4) and the raceway (20), method wherein, at each turn of the cylinder (2), the material consecutively passes under the smoothing roller (4) then under the grinding roller (3), said smoothing roller (4) exerting on the bed of materials (5) a pressure that smoothes its surface, said pressure being lower than the pressure (P) exerted by said grinding roller (3) on said bed of materials (5).
2. Method for grinding according to claim 1, wherein said means of keeping (6) the smoothing roller (4) guarantee a minimum distance between the raceway (20) and the surface of said smoothing roller (4), and wherein the grinder is supplied with a determined maximum grain size between 1 mm and 120 mm and said minimum distance greater than or equal to 0.5 times the determined maximum grain size is determined.
3. Method for grinding according to claim 2, wherein the smoothing roller (4) can freely rotate, driven in rotation about its axis thanks to the friction with the bed of materials (5).
4. Method for grinding according to claim 2, having motor means for driving in rotation the smoothing roller (4) in such a way that its peripheral speed is equal to the average speed of the bed of materials (5) whereon said smoothing roller (4) is applied.
5. Method for grinding according to one of claims 1 to 4 wherein grains of a maximum size between 1 mm and 120 mm are processed and wherein the diameter of the smoothing roller (4) is chosen between 100 mm and 660 mm.
6. Method for grinding according to one of claims 1 to 5, wherein said means for keeping (6) the smoothing roller (4) comprises means of articulation, able to authorise the displacement of said smoothing roller (4) according to a substantially radial direction towards the axis (A) of said cylinder (2) and elastic means forcing said smoothing roller (4) in the opposite direction, towards the raceway (20).
7. Method for grinding according to claim 6, wherein said means for keeping (6) said smoothing roller (4) provide for the maintaining of said smoothing roller (4) by its two ends, said means of articulation of said means of keeping (6) comprising two arms (60), each one articulated, on the one hand, at one of the ends of said arm (60) to said smoothing roller (4), according to the axis of said smoothing roller (4) and, on the other hand, at the other end of said arm (60) to a frame of said grinder (1), according to an axis of rotation (B) parallel to the axis (A) of said cylinder (2).
8. Method for grinding according to one of claims 1 to 7, wherein the length of said smoothing roller (4) is greater than or equal to the length of said grinding roller (3), said smoothing roller (4) being arranged in correspondence with said grinding roller (3) according to the length of the cylinder (2).
9. Method for grinding according to one of claims 1 to 8, having means for controlling the displacement of the material over the length of said cylinder (2) in such a way that said material travels only a fraction of the length of the cylinder (2) at each turn of the cylinder (2) and passes several times between the cylinder (2) and the grinding roller (3) from said inlet (7) for supplying material to be ground to said outlet (8) of ground material and wherein the distance (d) between the surface of said smoothing roller (4) and the raceway (20) varies according to the length of said cylinder (2), decreasing from said inlet (7) to said outlet (8).
10. Method for grinding according to one of claims 1 to 8, wherein the axis of rotation of the smoothing roller (4) is parallel to the axis (A) of the cylinder (2).
11. Method for grinding according to one of claims 1 to 10, wherein said means for urging said grinding roller against the raceway of said cylinder are such that the grinding roller (3) exerts on the bed of materials an average pressure between 10 MPa and 40 MPa and said means for keeping (6) the smoothing roller are such that the smoothing roller (4) exerts on the bed of materials (5) a pressure lower than 10 MPa, more preferably lower than 1 MPa.
12. Method for grinding according to one of claims 1 to 11, wherein said grinder (1) is supplied with a material of a determined maximum grain size and the diameter of said smoothing roller (4) is chosen in the following way:

    - between 2 times and 6 times said maximum size of the grains to be ground if, in this condition, the diameter of the smoothing roller is greater than or equal to 0.15 times the diameter of the grinding roller (3) and, otherwise,

    - at least equal to 0.15 times the diameter of the grinding roller (3).
13. Method for grinding according to claim 6, wherein said grinder (1) is supplied with a material of a determined maximum grain size and the course of displacement of said smoothing roller (4) is adjusted in such a way as to keep the surface of the smoothing roller (4) separated from the raceway (20) between 0.5 times and 3 times the maximum size of the grains to be ground.
14. Method for grinding according to one of claims 1 to 13 wherein the materials are ground in said grinder (1) in a dry process.
15. Compressive grinder (1) for a bed of materials (5), comprising:

    - a cylinder (2) with a horizontal axis (A) of which the inner wall comprises a raceway (20) for a grinding roller (3), arranged inside said cylinder (2),

    - means for rotating the cylinder about its axis (A),

    - said grinding roller (3), with an axis parallel to that of the axis (A) of the cylinder (2),

    - means for urging said grinding roller (3) against the raceway (20) of said cylinder (2),

    - an inlet (7) for supplying material to be ground located at one of the ends of said cylinder (2) and an outlet (8) for the ground material at the other end of said cylinder (2),

    characterised in that it comprises:

    - a smoothing roller (4) arranged upstream of said grinding roller (3) in the direction of rotation (R) of said cylinder (2), intended to smooth the surface of the bed of materials,

    - means for keeping (6) the smoothing roller (4) adjacent to and separated from the raceway of said cylinder (2), prohibiting any contact between said smoothing roller (4) and the raceway (20),

    and wherein said means for keeping (6) the smoothing roller (4) adjacent to and separated from the raceway of said cylinder (2), on the one hand, and said means for urging said grinding roller (3) against the raceway (20) of the cylinder (2), on the other hand, are such that said smoothing roller (4) is able to exert on the bed of materials (5) a pressure that smoothes its surface, said pressure being lower than the pressure (P) exerted by said grinding roller (3) on said bed of materials (5).
16. Use of the method for grinding according to one of claims 1 to 14 or of the grinder (1), according to claim 15 for the grinding of mineral materials and/or the grinding of materials in the manufacture of cement clinker.

Images