EP0077530A1 - Method and arrangement for the selective grinding of a composite material, and application to the barking of wooden plaquettes - Google Patents

Abstract

The invention relates to a method for the selective grinding of a composite material, and to an arrangement for implementing the method. The method for grinding a material present in the form of an aggregate having at least two constituents of a different hardness, permitting the selective grinding of at least one of the constituents, saving at least one other constituent, is characterised in that it comprises an operation of hammering the material between at least one first member (1) acting in the manner of an anvil, and at least one second member (15) acting in the manner of a hammer, at least one of the said first and second members being deformable. The hammer is, for example, a resilient sphere (15), and the anvil a rotary drum (1) into which are introduced the spheres (15) and the material (4) to be ground. The invention applies to the grinding of wood in the form of small slabs, with a view to their barking. <IMAGE>

Description

The present invention relates to a method and to a device for the selective grinding of a composite material and to their application to debarking of wood chips.

This application to debarking of wood chips is only given by way of example and is not limiting, the method and the device being able to be applied with the arrangements which will be described below to all types of composite material. requiring grinding accompanied by a selection of the constituents of the material.

The wood factories of the cellulose factories are currently supplied from medium-sized logs (hardwood and softwood), and from previously debarked sawmill waste (around 20% of the raw material).

• - de la concurrence des "bois d'oeuvre", dont la demande croit,
• - de la concurrence du "bois de feu" dont le coût tend à s'ajuster sur celui de l'énergie.

In France, as in other EEC countries, the price of "pulpwood" increases faster than the average material index as a result:

• - competition from "lumber", the demand for which is growing,
• - competition from "fuelwood", the cost of which tends to adjust to that of energy.

Many forest plots are still very little or badly exploited, in particular hardwood and coppice of oak, beech or chestnut, ...) which would be used for the production of cellulose.

Mechanization of cultivation and harvesting resources is likely to lower operating costs.

It seems likely that the most rational and economical solution would be to reduce the branches and other small wood in the form of chips or "chips" on the site of slaughter.

The mechanized exploitation of fast-changing coppices (around five years), and certain dormant forests, could ensure, in France, an additional annual tonnage of around 8 million tonnes, enough to increase by around 60fl the French cellulose resources.

The main difficulty, for the use of small woods as source of cellulose, due to the presence of bark which should be separated effectively.

The bark and other debris could be used as fuel, either directly or as a source of methane or methanol.

An efficient method of dry debarking of wafers (in particular the "green wafers" produced in the forest, and the "gray wafers" of unpeeled edging) would therefore meet a market need, and a pressing expectation of the profession.

To this end, various methods have been proposed which consist in grinding the wafers using conventional means: hammer mills, ball mills ..., taking advantage of the fact that the bark is generally less resistant than wood, and, to remove the bark which is found in the finest part, by means of a dimensional classification.

Experience has shown that these processes, which largely rely on known techniques of wood crushing for the manufacture of particle boards, known techniques of bark grinding for the supply of furnaces to boilers, and techniques crushing and sorting of ores, have the main drawback of crushing a large part of the wood at the same time as the bark, which results in a significant loss of wood and in an often excessive reduction of the average size of the debarked chips as soon as we want to obtain a high debarking rate.

The best suited dry grinding methods, in this case, are those which involve shock phenomena such that the chip is placed, as well as its bark, as between "hammer" and "anvil", with constraints successive compression and decompression such that the bark peels off the wood, at the same time as it breaks.

It is also necessary that the grinding is sufficiently selective so that, under the effect of the shocks, the bark is broken into small particles, easily separable by sorting on a sieve, without however breaking the wood. The main difficulty for the application of these processes is that: if the bark generally has a higher breaking strength weak than that of wood, and this because it is less rich in cellulose, it is also generally more flexible and more compressible; so that the energy required to break the bark is often very similar, and sometimes even greater, than that which causes the wood to break. Under these conditions we can imagine that if the energy received by the wood, in the impact impact zone, is, per unit of area, the same size as that received by the bark, the wood can break almost as quickly , or sometimes even faster than the bark.

The object of the present invention, which is applicable to debarking of wood chips, is to provide a solution to the selective grinding of composite materials.

It has been envisaged in particular in American patent 1,807,383 to selectively grind the wooden plates by means of a horizontal rotating drum in which are placed metal balls or spheres covered with rubber.

An object of the present invention is to improve the previous device by an appropriate choice of the characteristics of the balls and their instructions for use, so as to obtain maximum efficiency.

The subject of the invention is therefore a process for grinding a material in the form of an agglomerate having at least two constituents of different hardness, making it possible to selectively grind at least one of the constituents while providing at least one another constituent by hammering the material by means of grinding tools of spherical shape arranged in a grinder, said tools being deformable and consisting of a core coated with an elastomer, characterized in that for a shock of the same total energy, l energy involved in the deformation of the tool is greater than that absorbed by the material to be cleaned, during an impact on the material to be cleaned, and less than that absorbed by the material to be ground, during an impact on the material to be ground.

dans laquelle, et dans un système d'unités homogènes :

• L = limite de résistance élastique du produit à ménager
• W = Energie individuelle des outils à l'instant du choc
• R = Rayon de courbure de l'outil
• E = Module d'élasticité de l'élastomère
• e = Epaisseur de la couche d'élastomère
• r = résistance à la rupture du produit à broyer.

Preferably, the energy involved, in shock phenomena, and therefore the mass and the height of fall of the tools, the radius of curvature of the spherical caps constituting the periphery of the tools, the thickness of the elastomer coating, and the modulus of elasticity of this elastomer, are chosen as a function of the breaking strength of the product to be ground and the limit of the elastic resistance of the product to be cleaned, so as to verify the double inequality:

in which, and in a system of homogeneous units:

• L = elastic resistance limit of the household product
• W = Individual energy of the tools at the moment of impact
• R = radius of curvature of the tool
• E = modulus of elasticity of the elastomer
• e = Thickness of the elastomer layer
• r = breaking strength of the product to be ground.

The invention also relates to a device for grinding a material in the form of an agglomerate having at least two constituents of different hardness, said grinding grinding at least one of the constituents and providing at least one other constituent, comprising a rotary cylinder (1), rotating about a substantially horizontal axis, means (6) for introducing the material (4) into the cylinder, means (28A, 28B, 29A, 29B, 30, 23, 24) for introducing hammer tools (15) acting as hammer into the cylinder, the internal wall of the cylinder acting as an anvil, the selective grinding being effected by the action of repeated shocks generated by the fall of the tools rotation of the cylinder, means for separating (21) and evacuating (26, 29) the grinding products, the hammering tools (15) comprising a ballasting core (16A, 16B) and an elastomer coating (17A, 17B), in the form of concentric spheres, characterized in that the weight P of s tools, the diameter D of the cylinder, the radius of curvature R of the tools, the thickness e of the elastomer, the modulus of elasticity E of the elastomer, the limit L of resistance of the product to be cleaned and the resistance r to the rupture of the product to be ground, are linked by the double inequality:

• - la figure 1 est une vue schématique en coupe longitudinale d'une installation d'écorçage de plaquettes de bois,
• - la figure 2 est une vue schématique en bout de la même installation,
• - les figures 3A à 3D représentent, en coupe, des organes déformables utilisés pour le broyage sélectif.

The invention will be better understood from the following description of an example of application of the invention to the debarking of wooden boards, given without any limitation being given, with reference to the appended drawing in which :

• FIG. 1 is a schematic view in longitudinal section of an installation for debarking wood chips,
• FIG. 2 is a schematic end view of the same installation,
• - Figures 3A to 3D show, in section, deformable members used for selective grinding.

In FIG. 1, the reference 1 designates a hollow metal cylinder, open at both ends, of substantially horizontal axis, driven in rotation about its axis.

As shown, the means for rotating the first cylinder advantageously consists, in a known manner, of bridges of the construction machine type comprising wheels 2 associated with drive motors such as 3.

The wheels are in contact with treads 5 with which the outer periphery of cylinder 1 is provided.

The strips of wood to be debarked are brought to a first end of the cylinder (on the left in FIG. 1) by means of a movable belt 6.

The cylinder 1 is provided with orifices such as slots for sifting the wood during debarking. (But these holes are optional, in their absence, sorting is done independently of the device).

The fines passing through the sieve are evacuated by a mat 9 placed under the cylinder 1.

The entire cylinder 1 is surrounded by a casing 10 visible in FIG. 2 which makes it possible to collect and collect the sieving products.

The dimensions of the cylinder are, for example, 3.50 m inside diameter and 8 to 9 meters in length.

At the same time as the plates, the cylinder also receives a constant supply of organs or grinding tools 15 proportional to the flow rate of the plates, and constituted by deformable elastic spheres, formed by a dense 16 A ballast core, coated with a layer of elastomer 17 A (FIG. 3A).

The platelets to be treated most often have an average size of around 30 x 20 x 5mm, but they can occasionally be larger. larger or smaller, and spread around this average dimension.

A number of these chips still have their bark attached to the wood, but in many cases the bark has been detached from the wood when the chips are placed and is found in the form of pieces which have not yet been fractionated.

The tools 15, preferably spherical in shape, have a diameter close to 60mm, that is to say greater than the largest mean dimension of the inserts. It will therefore be easy, to recover them, to separate them from the plates by dimensional sorting.

The drum has a relatively high speed of rotation, of the order of 20 revolutions / minute, so that the centrifugal force presses the tools and the inserts against the interior wall, and helps them to go up, in the form of 'an embankment, in the direction of rotation, under the effect of friction forces. Elements fixed against the interior wall of the drum can possibly facilitate lifting.

The filling rate of the drum, in the case of the example cited, is of the order of 25%.

Arrived at the upper part of the embankment, the materials are tilted into a vacuum and fall back towards the lower generator of the drum. The tools, which have been said to be presented in the cited case, in the form of elastic spheres, also fall, and, a certain number of them strike individual plates or barks, already reached against the wall of the drum. . The struck plates are therefore taken as between "hammer" and "anvil", the hammer being constituted by the deformable elastic sphere and the anvil by the wall of the drum, itself deformable or not.

The mass of tools, of substantially spherical shape, and the quality and thickness of the elastomer which coats the ballasting core are chosen according to the nature of the wood to be treated: hardwood or softwood, hard or soft wood, wood green or dry wood, etc,

To achieve the aim pursued, which is the selective crushing of the bark, the energy involved in the shock phenomena must be sufficient to exceed the limit of elastic deformations of bark and cause it to break.

From this point of view, and taking into account the diameter of the drum, the mass of the tools must be sufficiently large.

On the other hand, to avoid breaking the wood, which is generally more resistant but less flexible than the bark, the tool should deform sufficiently, upon impact on the wood, so that the stress exerted 'does not exceed the elastic limit of wood.

In order to combine these two conditions, the elastomer that the tool covers will ultimately appear to be more flexible than wood and less flexible than bark, the coefficient of elasticity chosen obviously being a function of the thickness of the elastomer layer.

In addition, and, for reasons of energy saving, we will avoid choosing an elastomer that is too flexible, which would require an increase in the mass of the tools.

dans laquelle, et dans un système d'unités homogènes :

• L = Limite de résistance élastique du produit à ménager
• W = Energie individuelle des outils à l'instant du choc
• R = Rayon de courbure de l'outil
• E = Module d'élasticité de l'élastomère
• e = Epaisseur de la couche d'élastomère
• r = Résistance à la rupture du produit à broyer.

Preferably, the parameters of the tool are chosen as a function of the energy involved in the shock phenomena, and therefore of the mass and the height of fall of the tools, of the radius of curvature of the spherical caps constituting the periphery of the tools, the thickness of the elastomer coating, and the elastic modulus of this elastometer, the breaking strength of the product to be ground and the limit of the elastic resistance of the product to be cleaned, so as to check the double inequality

in which, and in a system of homogeneous units:

• L = Limit of elastic resistance of the household product
• W = Individual energy of the tools at the moment of impact
• R = radius of curvature of the tool
• E = modulus of elasticity of the elastomer
• e = Thickness of the elastomer layer
• r = Resistance to rupture of the product to be ground.

The above inequality, translated in terms of diameter D of the cylinder and mass weight P of the tool, is written:

For example, if we consider a lot of hardwood chips (oak or similar), for which we measured an average value of L close to 4 X 10 ⁷ NEEWTON / M ² and a value of r close to 3 X 10 ⁷ NEWTON / M ² , and, if we take tools weighing 500 grams, falling on average 3 meters in height, ie W - 15 joules, these balls having a spherical steel core of 45 millimeters in diameter and a coating in an elastometer of 7.5 millimeters thick, that is R - 3 X 10-and e = + 7.5 10 ^-3 , it is necessary to take an elastometer quality such that e is between 55 x 10 ⁶ and 85 X 10 ⁶ NEWTON / M ² . We would choose, for example: E = 7 X 10 ⁷ NEWTON / M ² .

With maritime pine chips from the Landes forest, it was found that a softer treatment than for oak was necessary because L and R have values substantially half. In this case it was retained, after experimentation: W = 10 joules, R = 3 X 10 ^-2 , e = 10 ² and E = 4 X 1 ₀ ⁷ NEW _{TON / M} ² .

With the application of these conditions, it becomes possible to crush the bark while preserving the wood with the best yield.

It can also be provided, but this is not essential, that the inner wall of the drum is itself coated with a layer of elastomer. On the other hand, it is desirable that the material constituting the drum or its lining or internal shielding resist the attack of the organic acids secreted by the vegetable materials, and this in order to avoid both an attack of the drum and a possible coloring of the platelets with metallic salts. In addition, good abrasion resistance is sought, due to the frequent presence of silica in batches of platelets.

In order to allow a rapid evacuation of the fine materials originating from the crushing of the bark, the drum can be provided with lights of sufficiently small size so that the plates are retained inside the drum. In this case, a casing surrounds the drum to collect fines and dust, and, suitable devices such as conveyor belt, ventilation circuit and cyclone separator, make it possible to evacuate this waste which it may be advantageous to burn.

During the rotation of the drum, the materials progress naturally from one end to the other, and are subjected to a repeated treatment of successive shocks.

The average residence time required for treatment will depend on the nature of the wood. For example, for maritime pine edgings, and, with the tools defined above, this treatment time would be of the order of 30 minutes for a debarking rate close to 90%.

In order to improve the mixing of materials in the drum, and, to avoid segregation, it is recommended to regularly alternate the direction of rotation of the drum (5 to 10 times per treatment cycle for example).

At the exit of the drum, the treated materials are retained up to a certain level using a movable threshold 20 of adjustable height which makes it possible to adjust the filling rate.

• - Une fraction grossière, supérieure par exemple à 40mm, qui contient les outils et quelques plaquettes de grande taille lesquels sont recyclés vers l'entrée du cylindre par un convoyeur vertical 22, alimentant un tapis 23 et une trémie 24 ;
• - Une fraction moyenne, comprise par exemple entre 10 et 40 mm, composée principalement des plaquettes de bois écorcées, bonnes pour la fabrication de cellulose, et évacuées vers le lieu d'utilisation par la trémie 25 et le tapis 26 ;
• - Une fraction fine, inférieure à 10 mm, qui contient les écorces broyées qui n'auraient pas été évacuées directement au travers de la paroi du tambour, et un certain nombre de petites particules de bois, détachées ou cassées au cours du traitement. Cette perte en bois sera d'autant plus faible que le traitement, suivant le procédé, aura été le mieux ajusté. Ces fines sont envoyées sur le tapis 9 par une trémie.

The treated materials and the tools that cross the threshold are then directed to a sorting means such as a battery of sieves 21 with square-mesh shaking, which separates them into three fractions:

• - A coarse fraction, for example greater than 40mm, which contains the tools and some large pads which are recycled to the inlet of the cylinder by a vertical conveyor 22, feeding a belt 23 and a hopper 24;
• - An average fraction, for example between 10 and 40 mm, composed mainly of debarked wood chips, good for the manufacture of cellulose, and evacuated to the place of use by the hopper 25 and the carpet 26;
• - A fine fraction, less than 10 mm, which contains crushed bark which has not been discharged directly through the wall of the drum, and a certain number of small particles of wood, detached or broken during the treatment. This loss of wood will be all the lower as the treatment, according to the process, will have been the best adjusted. These fines are sent to the belt 9 by a hopper.

Depending on the nature of the batches of wafers that one may have to process, it is possible, with the application device given by way of example, to change the nature of the tools.

The tools are stored in storage hoppers 28A, 28B. A switch 30 located on the coarse material recycling circuit allows to direct the tools to the storage hopper assigned to them. The supply of tools to the installation is done by the base of the hoppers by conduits 29A, 298. By the set of these storage hoppers, the number of which can be greater than two, it is also possible to vary the proportion of tools put into action in the drum and thus increase or decrease the number of shocks caused for a known residence time of the inserts in the drum.

From a general point of view, it is understood that the treatment of softwoods will justify more flexible or relatively lighter tools, while certain very resistant barks may require less flexible or heavier tools.

• - soit utilisant, comme indiqué dans la figure 3A, des sphères composites constituées d'un noyau sphérique central 16A et d'une enveloppe en élastomètre 17A. On peut alors modifier la masse jusqu'à une certaine limite, en augmentant ou en diminuant la densité du noyau par la matière qui le constitue, ou en changeant son diamètre. S'il-le faut, et pour obtenir des outils plus légers, on peut également réaliser le noyau à l'aide d'une sphère creuse 16B (fig.3B), cette sphère 16B étant entourée d'une enveloppe en élastomère 17B.

In the case of tools of spherical shape, the variation in mass and flexibility can be obtained in different ways, some non-limiting examples of which are given below:

• - Either using, as shown in Figure 3A, composite spheres consisting of a central spherical core 16A and an elastometer shell 17A. We can then modify the mass up to a certain limit, by increasing or decreasing the density of the core by the material which constitutes it, or by changing its diameter. If necessary, and to obtain lighter tools, the core can also be produced using a hollow sphere 16B (fig.3B), this sphere 16B being surrounded by an elastomeric envelope 17B.

• - Soit en utilisant des outils hétérogènes constitués d'une masse sphérique 37 en élastomètre contenant des charges réparties, sous forme de petites billes non déformables 38 par exemple en métal (fig.3C).

The greater or lesser flexibility of the tool is then obtained by varying both the thickness and the quality of the elastometer which coats the core. In such a case of composite tools with core, the proper deformation of the core will most often be negligible compared to that of the elastometer.

• - Either by using heterogeneous tools made up of a spherical mass 37 in an elastometer containing distributed loads, in the form of small non-deformable balls 38, for example made of metal (fig.3C).

• - Soit en utilisant des sphères pleines homogènes pour lesquelles la masse n'est fonction que du diamètre et de la masse spécifique de l'élastomètre (non représentées).
• - Soit en utilisant une simple enveloppe sphérique creuse déformable, éventuellement gonflable ou que l'on pourrait lester à l'aide d'un fluide approprié (non représentée).

The flexibility will then depend on the quality of the elastometer and the relative volume occupied by the small non-deformable balls.

• - Or by using homogeneous solid spheres for which the mass is only a function of the diameter and the specific mass of the elastometer (not shown).
• - Or by using a simple hollow spherical deformable envelope, possibly inflatable or which could be ballasted using an appropriate fluid (not shown).

One can also conceive of other types of tools, applicable within the framework of the present invention, such as that represented in section in FIG. 3D, and comprising a dense core 47, surrounded by spherical caps 48 situated side by side and made of an elastomer.

Under these conditions, the face of the tool which presents itself upon impact retains a spherical shape, but it is possible to obtain a greater transfer of energy per unit of surface struck.

According to different modes of application, one can then choose to have the elastometer at the level of the spherical caps, or on the contrary to arrange it in place of the core and to surround it with metallic spherical caps, which could be more favorable for the dissipation of heat energy, the tool retaining sufficient ability to deform.

The invention, which has been described with reference to an installation for debarking wood chips, makes it possible to solve other problems of selective grinding.

The principles of the invention will be easily implemented by those skilled in the art according to the problem considered.

• Dans le cadre de la présente invention, la déformabilité du "marteau", et ou de "l'enclume", est choisie de façon telle que : lors d'un choc sur le matériau à ménager, l'énergie localisée dans la déformation du "marteau" et ou de "l'enclume" soit supérieure à celle absorbée par ce matériau, et, que lors d'un choc sur le matériau à broyer l'énergie absorbée par ce matériau en vue de sa rupture, soit supérieure à celle localisée dans la déformation du "marteau" et ou de "l'enclume".

The following considerations are important:

• In the context of the present invention, the deformability of the "hammer", and / or of the "anvil", is chosen so that: during an impact on the material to be housed, the energy localized in the deformation of the "hammer" and / or "anvil" is greater than that absorbed by this material, and, that during an impact on the material to be ground the energy absorbed by this material with a view to its rupture, is greater than that localized in the deformation of the "hammer" and or of the "anvil".

Under these conditions, for a shock involving the same total energy, and distributed over an equivalent surface, the energy absorbed per unit area of the material to be housed is less than that absorbed per unit area of the material to be ground.

In addition, in the context of the present invention, the total energy involved in the individual shocks and related to the impact surface of the shock, as well as the deformability of the "hammer" and or of the "anvil", are chosen so that the specific energy transmitted to the material to be housed in the impact zone remains below the specific energy of rupture of this material, and preferably maintain this material within the range of elastic deformations; while the specific energy transmitted to the material to be ground in the impact zone on this material is beyond the specific detachment or rupture energy of this material, i.e. beyond the range of elastic deformations relating to this material.

In the context of the present invention, a preferential condition for the application of the method is to choose the nature of the materials constituting the "hammer" and or "anvil" in such a way that their deformations, upon impact, do not exceed by the limit of the elastic deformations proper to these materials, and, that the "hammer" and / or "the anvil" therefore regains, after the impact, substantially its initial shape.

Another preferential condition is to choose the tools and the materials so that the thermal energy dissipated within the "hammer" and / or the "anvil", in the deformations which accompany the shocks can be evacuated properly without causing an excessive rise in temperature.

A third preferential condition for applying the method independent of the previous two, is that the shape and size of the "hammer" are such that the surface of the impact zone is at most of the same order of magnitude as the size of the most small parts to spare, so as not to exceed excessive forces on these small parts.

A fourth preferential, non-essential and non-limiting condition for the application of the method is that the "hammer" is of substantially spherical shape, or that it always appears, in front of the impact, in the form of a portion deformable sphere, in which case, its deformation being greater upon impact on the material to be housed than on the material to be ground, the surface area of distribution of forces is greater with respect to the material to be housed than with vis-à-vis the material to be ground which further reduces the stresses on the material to be housed.

Finally, the best performance is obtained by choosing tools and grinders so as to check the above-mentioned inequalities.

Claims (7)

1 / Method for grinding a material in the form of an agglomerate having at least two constituents of different hardness, making it possible to selectively grind at least one of the constituents while providing at least one other constituent by hammering the material by means of grinding tools of spherical shape arranged in a grinder, said tools being deformable and consisting of a core coated with an elastomer, characterized in that for a
impact of the same total energy, the energy involved in the deformation of the tool is greater than that absorbed by the material to be housed, during an impact on the material to be housed, and less than that absorbed by the material to be grind, upon impact on the material to be ground. 2 / A method according to claim 1, characterized in that the material constituting the deformable part of the tool is chosen so that its deformations remain within the elastic limits. 3 / A method according to claim 1, characterized in that the energy involved, in shock phenomena, and therefore the mass and the height of fall of the tools, the radius of curvature of the spherical caps constituting the periphery of the tools, the thickness of the elastomer coating, and the modulus of elasticity of this elastomer, are chosen according to the breaking strength of the product to be ground and the limit of the elastic resistance of the product to be cleaned, so as to verify double inequality:

in which, and in a system of homogeneous units: L = elastic resistance limit of the household product W = Individual energy of the tools at the moment of impact R = radius of curvature of the tool E = modulus of elasticity of the elastomer e = Thickness of the elastomer layer r = breaking strength of the product to be ground. 4 / Device for grinding a material (4) in the form of an agglomerate having at least two constituents of different hardness rent, said grinding grinding at least one of the constituents and providing at least one other constituent, comprising a rotary cylinder (1), rotating around a substantially horizontal axis, means (6) for introducing the material (4) into the cylinder, means (28A, 28B, 29A, 29B, 30, 23, 24) for introducing into the cylinder hammering tools (15) acting as hammer, the internal wall of the cylinder acting as an anvil, the selective grinding carried out under the action of repeated shocks generated by the fall of the tools from the rotation of the cylinder, means for separating (21) and evacuating (26, 29) the products of the grinding, the hammering tools (15) comprising a ballasting core (16A, 16B) and an elastomer coating (17A, 17B), in the form of concentric spheres, characterized in that the weight P of the tools, the diameter D of the cylinder, the radius of curvature R of the tools , the thickness e of the elastomer, the modulus of elasticity E of the elastomer, the limit L of resistance of the product to be cleaned and the breaking strength r of the product to be ground, are linked by the double inequality:

5 / Device according to claim 4, characterized in that the means for separating and discharging the ground products comprise a battery of sieves separating the ground material, the formed material and the hammering tools (15) entrained with the ground products . 6 / Device according to claim 5, characterized in that it comprises means (22, 23, 24) for bringing the hammering tools (15) to the inlet of the cylinder (1). 7 / Device according to claim 6, characterized in that it comprises members (28A, 28B) for storing hammering tools associated with supply means (29A, 29B) for bringing said tools to the inlet of the cylinder.

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