FR2660579A1 - Method for grinding solid raw materials, such as minerals - Google Patents

Abstract

Method for grinding solid raw materials, such as minerals, in which the processed material is subjected to the compressive action of a movable member capable of compressing this material against a supporting surface and in which two parallel compression cylinders (1 and 2), of known type, and rotating in opposite directions from one another, and between which the material is entrained are implemented, one cylinder (1) being mounted on a fixed axle, the other cylinder (2) being mounted on a movable axle (5) while remaining parallel to the first one, and this movable axle is subject to the thrust of at least one pressing member (8, 8') and the method is furthermore characterised in that the thrust developed by this pressing member is controlled in order constantly to vary the pressure of the movable cylinder being exerted on the material bearing on the cylinder of fixed axle.

Description

The present invention relates to the field of grinding of raw materials such as ores with a view to reducing these materials to an appropriate particle size level in particular with a view to obtaining fines which can be used in subsequent processes.

The invention applies more particularly to a method and a grinding device using grinders of known type and consisting of two twin cylinders rotating in opposite directions.

The material, already brought beforehand to an appropriate level of fragmentation, is continuously discharged between the two cylinders and it undergoes a crushing passage resulting in -interrupting the internal bonding forces of the material to result in a new fragmentation with the obtaining of particles corresponding to a particle size level lower than the previous one.

A grinding machine of this type, consisting of two cylinders rotating in opposite directions, has been used since ancient times since in particular devices of this kind were used to crush and press the olives for the extraction of the oil .

More recently in the last century, this type of machine has experienced significant growth since it was used to crush, grind, press-, granulate (briquette) all kinds of mineral materials (coal, ores, clay etc ...) and organic (wheat, barley, rye, etc ...).

For the granulation operation (briquetting) the pressures used were the most important (for example 80 M Pa for briquetting (agglomerating) the coal without binder).

The study of the granulation process (agglomeration, briquetting) has shown that the relatively high pressure necessary for the process breaks up the grains of material inside the agglomerate, creating new surfaces. The newly created surfaces have a great reactivity which establishes new connections thus increasing the mechanical cohesion of the agglomerate.

This phenomenon of breakage of the grains as they pass through the high pressure zone of the rollers has also been exploited for grinding.

Numerous grinding installations and devices are thus currently known using, for the treatment of various materials, twin cylinders working in opposite directions and causing by crushing the fragmentation of the particles of material delivered between the cylinders.

French patent 78-05240 thus discloses a device using in particular two rollers for working with mineral materials with a view to their reduction into fine particles.

However, this technique, as clearly explained in the cited French patent, has limits to the extent that it is necessary to apply high pressure to obtain a break in the mechanical forces within the aggregates delivered to the machine, while this pressure in return causes a parasitic phenomenon of adhesion leading to a restructuring of the material from the finer particles obtained following the fragmentation.

This parasitic phenomenon, useful in the case of the use of compression rollers for the briquetting of the material, is a drawback when, on the contrary, it is desired to obtain particles in the form of fines.

The balance between the two phenomena of fragmentation and briquetting respectively depends on the peripheral speed of the cylinders.

In fact, to fill the maximum pressure zone well and thus break the grains inside this zone, the speed must be relatively low.

But at low speed, the agglomeration phenomenon is very important and therefore the outgoing granules have a high mechanical cohesion and an efficient grinding apparatus is required for post-grinding (deagglomeration).

If the speed is increased, the granules which exit are less resistant but the zone of maximum pressure is not well filled and the duration of the crushing is too short and consequently the grinding is less effective.

An important factor for the cohesion of the granules formed is the air trapped during the high compression of the material necessary for grinding. The expansion of this trapped air after the material has left the compression zone reduces the cohesion of the granules and can destroy them if the expansion is fast enough so that the air does not have time to escape gently. However, as mentioned above, the peripheral speed cannot be increased, otherwise the pressures necessary for grinding are not produced in the mass of the material.

Indeed, this type of roller mill rotates much slower than the usual roller mills (around 1.5m / s compared to 3-5m / s).

 It follows from the above that it appears desirable, in order to obtain a grinding effect with an optimal useful yield and by reducing the briquetting phenomenon as much as possible, to cause a very rapid expansion of the air at the outlet of the zone. high pressure between the two cylinders, without increasing the speed of rotation.

It has indeed been clearly indicated above that an increase in the speed of rotation, if it reduces the speed of expansion of the air within the material, has the disadvantage of also reducing the time during which the aggregates of the material are subjected to high pressure, so that the grinding efficiency is thereby reduced as well.

And the grinders rotating at low speed produce (as clearly stated in the cited French patent) an undesirable compacting and concretion effect when the aim is to obtain particles, in particular fines.

An object of the invention is therefore to allow, while using the simple devices that constitute the twin compression cylinders, without increasing the rotation speed of the cylinders, to obtain rapid or even instantaneous relaxation of the air trapped in the particles subjected to high pressure, this expansion causing the breaking of the mechanical connections and consequently the grinding and obtaining of fragmented particles and leading to the desired degree of particle size.

Thus, the invention makes it possible, from a device of known general type, to obtain grinding of considerably improved efficiency without encountering the undesirable phenomenon of compacting and briquetting of the treated material.

It is thus possible, within the framework of the implementation of the invention, to treat the material by passing, possibly successively, through sets of grinding rollers, with a high yield in obtaining fines of suitable particle size, and by considerably reducing the phenomenon of briquetting.

To this end, the invention relates to a process for grinding solid raw materials, such as ores, in which the treated material is subjected to the compression action of a mobile member capable of compressing this material against a bearing surface. and in which two parallel compression cylinders, of known type, and rotating in opposite directions are used, and between which the material is entrained, one cylinder being mounted on a fixed axis, the other cylinder being mounted on a movable axis while remaining parallel to the first, and this movable axis undergoes the thrust of at least one pressure member and the method is further characterized in that the thrust developed by this pressure member is controlled so constantly varying the pressure of the mobile cylinder acting on the material bearing on the cylinder with a fixed axis.

According to a more particular embodiment of the invention, the pressure member consists of at least one jack and the pressure developed in the chamber of the jack is controlled so as to constantly vary the pressure of the movable cylinder exerted on the material resting on the cylinder of fixed axis.

According to another characteristic of the invention, two parallel jacks are used, each exerting a push on one of the two free ends of the axis of rotation of the cylinder, and the internal pressure within the chamber of each of the jacks is checked. so as to balance the thrusts developed by the two cylinders, and in addition, the thrusts developed by the two cylinders on the movable axis of the cylinder are varied constantly and in a synchronous and identical manner and thus reflected by this cylinder on the material treated in support on the fixed axis cylinder.

According to an alternative embodiment, the thrust exerted on the movable axis of the second cylinder follows a regular cycle by producing a pulsation of the pressure according to a substantially sinusoidal cycle.

According to yet another variant, the thrust follows a complex regular cycle consisting of a succession of repetitive modular bursts, each burst comprising itself pulses varying in amplitude and in frequency.

According to an alternative embodiment of the above method, the cycle of the pressure variation pulses is adapted to the nature and the physical characteristics of the material treated.

According to another variant embodiment, two twin jacks are used, each exerting a push on one of the two ends of the axis of rotation of the movable cylinder, and the pressure developed within each jack and checked on the corresponding end is checked. of said axis, the pressures exerted in each cylinder being as synchronous
And in particular the cycles of the pressure variation pulses exerted on each of the ends of the axis of the movable cylinder follow a regular cycle, the cycle of the variations exerted on one end of the axis being out of phase with respect to the cycle of the other end of the same axis, thus causing an instantaneous pressure gradient along the linear zone of contact between the movable cylinder and the material, gradient constantly moving along this zone.

The invention also relates to a grinding device in which the compression member consists of a first cylinder with a fixed axis and a second cylinder with a movable axis, parallel and coupled to the first, the second cylinder undergoing thrust. two cylinders twinned via the two ends of the axis of rotation of said second cylinder and each cylinder is controlled by means of programming the pressure.

And more particularly, the means for controlling the pressure within each of the jacks consist of a multi-way valve or register enabling the chamber of each of the jacks to be placed in communication successively with a first pressure source and with a second pressure source of value different from the first.

Other characteristics and advantages of the invention will emerge from the description which follows and which is given in connection with some embodiments presented by way of nonlimiting examples.

Figure 1 shows a schematic perspective view of a device with two pulsed pressure cylinders according to the invention.

FIG. 2 represents two positions of a register for adjusting the pressure variation within the cylinders controlling the compression of the movable cylinder according to the
Figure 1.

Figure 3 shows an embodiment of a grinding installation using the device of the invention.

We see by considering all of the Figures that to increase the speed of expansion of the air at the exit from the high pressure zone without increasing the speed of rotation, the pressure is oscillated by pulsating the force which brings the cylinders. Thus the decompression speed increases since to the material exit speed from the high pressure zone is added the pressure pulsation speed which abruptly decompresses it.

Likewise, this pressure pulse has a beneficial effect on the grinding since it allows a rearrangement of the grains released and fluidized by the air which is released.

The fluidization of the grains by the air which is released is a well-known phenomenon in roller presses for agglomeration where it plays a negative role preventing the material from compacting in the high pressure zone.

In the case of pulsed pressure grinding, the air is released after compression with the two beneficial consequences mentioned above (reduction of the mechanical cohesion of the agglomerate and rearrangement of the material in the grinding zone).

Pulsed pressure also has a crushing-grinding effect analogous to that produced in reciprocating crushing crushing machines, for example jaw crushers.

In particular by considering more particularly FIG. 1, it can be seen that, in the context of the invention, a first cylinder of fixed axis 1 has been produced, cooperating with a cylinder of mobile axis 2; the two cylinders being arranged in parallel and rotating in opposite directions.

These two cylinders can be supplied in a known manner from an upper hopper 3 which is itself supplied from a conveyor 4 discharging regularly and continuously between the two cylinders 1 and 2 a stream of aggregates corresponding to the product to be treated.

The axis 5 of the second cylinder 2 is mounted on two end bearings respectively 6 and 6 ', which are themselves integral with the rod 7, 7' of the piston displaceable in a jack 8, 8 '
Each of the cylinders 8, 8 'is supplied by the common pipe 9 from a first pressure source P 1 and a second pressure source P 2.

It is assumed in the context of the embodiment shown in
Figures 1 and 2 that the pressure source P 1 is at a level considerably higher than the pressure source P 2.

For example, the pressure source P 1 corresponds to a pressure exerted at the level of the cylinder 2, of the order of 500 kg per cm 2, while the pressure source P 2 can be considerably lower or even simply correspond to atmospheric pressure.

A sliding register valve for example as shown in Figure 2 is adapted to put the common pipe 9 supplying the two cylinders 8 and 8 'successively in communication with the high pressure source P 1 and the low pressure source P 2.

It is seen in these conditions that, according to the movement of the damper 10, the pressure developed in each of the cylinders 8 and 8 'and therefore transferred to the second cylinder will vary.

It is thus possible by moving the damper according to a regular cycle or not to cause a pulsation of variation of the pressures consequently a pulsation in the compressive force exerted by the cylinder 2 on the material that is to say on the particles and granules treated and supported on the first cylinder 1.

It can be seen that the whole of cylinder 2 is thus subjected to a thrust and a compression force which varies over time.

In a first embodiment, this thrust can be equal on the two bearings respectively 6 and 6 ′ so that it is the whole of the cylinder 2 which exerts a linear thrust in the zone of contact with the granules and particles treated, themselves resting on the cylinder of fixed axis 1.

In this case, the pressure variations developed from the cylinders 8 and 8 ′ may or may not follow a regular cycle depending on the characteristics of the material.

One can in particular envisage a pulsation of amplitude comprised between a maximum value of pressure at the level of cylinder 2 comprised between 500 and 1,000 kg. per cm2 and a minimum value which can go up to simple atmospheric pressure.

The frequency of the pulsations can be adjusted as a function of a control device which itself acts on the register 10.

It is thus seen that in the position of the damper according to Figure 2a the high pressure is in communication with the two cylinders, while in the position shown in Figure 2b, the cylinders are in communication with the lower pressure source causing by Consequently, instantaneous expansion in the area of the generators of the two twin cylinders located opposite.

This phenomenon makes it possible to achieve a relaxation of the compressed gases within the particles of material with a bursting effect consequently causing the fragmentation of the particles into finer elements.

While thanks to the rapid expansion thus obtained, it is possible optionally to adopt a peripheral speed of rotation of the cylinders greater than that usually practiced, which makes it possible to reduce or even eliminate the phenomenon of compaction and briquetting by concretion of the particles immediately after their fragmentation .

The definition of the pulsation cycle is not determined within the framework of the invention and could possibly be adopted by empirical tests or groping, depending on the materials treated.

To this end, the operating member of the register 10, which could be a simple pneumatic jack, can itself be controlled by a mechanical, electrical or electronic programming member which could consequently, depending on the desired objectives, cause the pulsations of desired intensities in amplitude and frequency.

According to an alternative embodiment of the method, the pulses imparted to the bearings respectively 6 and 6 'of the roller 2 and caused by the action of the piston 7 and 7' could be as synchronous.

It is thus possible to obtain, by an appropriate phase shift between the pulsation cycles printed on each of the pistons 7 and 7 ′, an effect of displacement of the point of maximum pressure along the generatrices of the facing cylinders.

It is in fact understood that if a bearing, consequently one end of the cylinder, undergoes maximum thrust, while the opposite bearing is at its minimum thrust level, the maximum pressure will be exerted between the two cylinders on the side of the bearing subjected to the maximum pressure.

The cycle continuing, the bearing subjected to a maximum pressure will see decreasing its pressure, while the opposite bearing will see increasing the thrust which it undergoes; thus in an extremely short instant (depending on the cycle and frequency of the pulses) the point (or zone) of maximum pressure will move along the cylinders from one level to the other to return to the first.

This causes an instantaneous pressure gradient along the two cylinders and this gradient changes over time in a cyclical manner (itself a function of the pulsation cycle), so that the high pressure zone follows a traveling wave. along the two cylinders.

In these conditions, a maximum relaxation effect of the air trapped at the level of each particle or granule being treated is caused, thereby causing, on the one hand, due to a relatively slow movement of the rollers, an accumulation of sufficient pressure, followed by an extremely rapid expansion with the desired effect of bursting and explosion of the particles leading to their fragmentation without parasitic phenomenon of concretion and subsequent re-agglomeration.

Figure 4 illustrates an embodiment of the invention inserted in a grinding circuit. We thus see according to this
Figure that the pulsed pressure roller mill can be integrated into a complete grinding circuit.

The crusher of the invention can thus be associated with crushing means, screening with recycling, pre-grinding, selection with recycling, grinding with the roller mill, selection with recycling on the roller mill and on the finishing mill, finishing mill with recycling and, in general, any unit for processing materials taken out of the cylinder mill, at pulsed pressure with recycling.

A schematic diagram of a grinding circuit with a roller mill for the manufacture of cement can be presented according to FIG. 3 in which after grinding by pulsed pressure roller mill 11 according to the invention, a final grinding is carried out in a ball mill 12, at the outlet of which the material is separated, for example in the separator 13. The desired fines are discharged at 14.

The passers with a higher particle size are recycled upstream of the supply to the cylinder mill at pulsed pressures; the intermediate particles are recycled according to 16 to the ball mill.

It should be noted that in general, and in particular for grinding, products approaching monogranularity (for example clinker) recycling improves the operation of the crusher since the grain size curve widens, compaction increases.

The assembly may advantageously include a device for disengaging the hydraulic circuit.

To protect the shredder from damage caused by the introduction of a metallic foreign body which can damage it, mechanical separators (screen for example), magnetic separators and metal detectors are currently used.

Following the detection of a metal body, the cylinder crusher is bypassed while the feed hopper is emptied. This avoids the passage of the metal body in the crusher.

This process has two major drawbacks - the handling circuit is complicated by this bypass.

- the quantity of product in the hopper is either
lost, either must be recycled after removal from the body
metallic.

To overcome these drawbacks, this new crusher, subject of the patent, is equipped with a device for discharging the hydraulic circuit for maintaining the pressure of the jacks which pushes the mobile cylinder. Thus, when a metal body has been detected, the pressure in the cylinders drops and the movable cylinder can move freely from the fixed cylinder and thus allow the detected metal body to pass without inconvenience to the crusher.

Claims (11)

1 - Process for grinding solid raw materials, such as ores, in which the treated material is subjected to the compression action of a movable member capable of compressing this material against a bearing surface and in which the works two parallel compression cylinders (1 and 2), of known type, and rotating in opposite directions to each other, and between which the material is entrained, a cylinder (1) being mounted on a fixed axis, l 'other cylinder (2) being mounted on a movable axis (5) remaining parallel to the first, and this movable axis undergoes the thrust of at least one pressure member (8, 8') and the method is further characterized in what we control the thrust developed by this pressure member so as to constantly vary the pressure of the movable cylinder acting on the material resting on the cylinder of fixed axis. 2 - Method according to claim 1, characterized in that the pressure member consists of at least one cylinder (8, 8 ') and the pressure developed in the cylinder chamber is controlled so as to constantly vary the pressure of the movable cylinder (2) acting on the material bearing on the cylinder of fixed axis (1). 3 - Method according to one of claims 1 or 2, and characterized in that one implements two parallel cylinders (8, 8 ') each exerting a push on one of the two free ends of the axis (5) of rotation of the cylinder, and the internal pressure within the chamber of each of the jacks is controlled so as to balance the thrusts developed by the two jacks (8, 8 ′), and moreover it is varied constantly and synchronously and identical the thrusts developed by the two cylinders on the movable axis (5) of the cylinder and thus reflected by this cylinder on the treated material resting on the cylinder of fixed axis. 4 - Method according to one of claims 1 to 3, and characterized in that the thrust exerted on the movable axis of the second cylinder (2) follows a regular cycle by achieving a pressure pulse following a substantially sinusoidal cycle. 5 - Method according to one of claims 1 to 4, and characterized in that the thrust follows a complex regular cycle and consisting of a succession of repetitive modular bursts, each burst itself comprising variable pulses in amplitude and frequency . 6 - Method according to one of claims 1 to 5, and characterized in that one adapts the cycle of pulses of pressure variations to the nature and physical characteristics of the treated material. 7 - Method according to one of claims 1 to 6, and characterized in that one uses two twin jacks (8 and 8 '), each exerting a push on one of the two ends of the axis (5) of rotation of the movable cylinder (2), and the pressure developed within each cylinder and transferred to the corresponding end of said axis is controlled, the pressures exerted in each cylinder being asynchronous. 8 - Method according to one of claims 1 to 7, and characterized in that the cycles of the pressure variation pulses exerted on each of the ends of the axis (5) of the movable cylinder (2) follow a regular cycle, the cycle of variations exerted on one end of the axis being out of phase with respect to the cycle of the other end of the same axis, thus causing an instantaneous pressure gradient along the linear zone of contact between the movable cylinder and the material, gradient constantly moving along this area. 9 - Grinding device for the implementation of the method according to one of claims 1 to 8 above, and wherein the compression member consists of a first cylinder with fixed axis (1) and a second cylinder (2) of movable axis (5), parallel and coupled to the first, the second cylinder undergoing the thrust of two twin cylinders (8, 8 ') via the two ends of the axis of rotation of said second cylinder and the method is characterized in that each cylinder is slaved to means for programming the pressure. 10 - Device according to claim 9 above, and characterized in that the pressure control means within each of the cylinders (8, 8 ') consist of a valve or register (10) with several channels allowing the communication of the chamber of each of the jacks (8, 8 ') successively with a first pressure source (P 1) and with a second pressure source (P 2) of value different from the first. 11 - Device according to one of claims 1 to 10, and characterized in that it comprises a metal body detector upstream of the cylinders, this detector being connected to control members capable of causing the pressure drop in the cylinders thereby allowing the movable cylinder to move away from the fixed cylinder for the passage of the metal body without damage to the surface of the cylinders.