CA2320796A1 - Wet process grinder equipped with baffle and outlet baffle for said grinder - Google Patents
Wet process grinder equipped with baffle and outlet baffle for said grinder Download PDFInfo
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- CA2320796A1 CA2320796A1 CA002320796A CA2320796A CA2320796A1 CA 2320796 A1 CA2320796 A1 CA 2320796A1 CA 002320796 A CA002320796 A CA 002320796A CA 2320796 A CA2320796 A CA 2320796A CA 2320796 A1 CA2320796 A1 CA 2320796A1
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- Prior art keywords
- partition
- matter
- mill
- outlet
- discharge chamber
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
- B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
- B02C17/00—Disintegrating by tumbling mills, i.e. mills having a container charged with the material to be disintegrated with or without special disintegrating members such as pebbles or balls
- B02C17/18—Details
- B02C17/183—Feeding or discharging devices
- B02C17/1835—Discharging devices combined with sorting or separating of material
- B02C17/1855—Discharging devices combined with sorting or separating of material with separator defining termination of crushing zone, e.g. screen denying egress of oversize material
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- Engineering & Computer Science (AREA)
- Food Science & Technology (AREA)
- Crushing And Grinding (AREA)
Abstract
The invention concerns a wet process autogenous or semi-autogenous or discharge grate-type grinder, comprising an outlet baffle between the grinding chamber and the outlet trunnion, said baffle consisting of an upstream wall and a downstream wall forming a section internal to the baffle called discharge chamber. The invention is characterised in that the baffle central part is provided with means integral with said baffle enabling part of the ground material to pass in the section central zone, the remainder of the material being evacuated towards the outlet trunnion (2). The invention also concerns the baffle for said grinder.
Description
MILL WORKING BY WET PROCESSING AND EQUIPPED WITH A
PARTITION, AND OUTLET PARTITION INTENDED FOR THE MILL
Subject of the invention The present invention relates to grinding mills working by wet processing, either of the autogenous type, also known as FAG (Full Autogenous Grinding) mills, or of the semi-autogenous type, also known as SAG (Semi Autogenous Grinding) mills, but also relates to ball mills using grid discharge.
The present invention relates more specifically to an outlet partition arranged in such mills.
Technological background There are two main families of mills that exist side by side; on the one hand, there are mills which work by wet processing and, on the other hand, there are mills which work by dry processing. In general terms, the solutions put forward for mills that work by dry processing cannot be read across directly to mills which work by wet processing.
The various types of mill are fitted with an outlet partition which allows the ground matter to be discharged towards an outlet trunnion. In some instances, the mills may be equipped with intermediate partitions separating two successive grinding chambers.
Mills which discharge through a grid comprise a partition generally made up of a frame, the upstream face of which is covered with grids pierced with a number of openings and which thus allow the sufficiently-ground matter to pass through while at the same time holding back the matter that is insufficiently ground, and the grinding bodies. The upstream face of which is some distance from the downstream face, which is preferably solid with the exception of a central discharge opening.
There is thus defined within the partition a small compartment which the matter which passes through the openings enters. This matter is able to circulate diametrically within the compartment. Lifting elements or lifters are provided in this partition so that as the mill rotates, the matter is lifted above the axis of the mill, from where it falls back down, possibly onto a deflector member, to be directed towards the central discharge opening.
In the case of mills which use overflow discharge (100% overflow), the mills have rather a tendency to keep the matter inside the grinding chambers for too long, which produces undesirable overly ground matters, the retention time being too long and the mill too full, which causes a certain slipping of the charge and reduces the throughput of the mill.
There is no deflector member in this type of mill, and the ground matters are removed directly by overflow via the central discharge opening towards the outlet trunnion.
In the case of mills using 1000 grid discharge, there is a deflector member present which forces the matter to follow a favoured path towards the outlet trunnion.
In this type of mill, it can be seen that these mills are often underfilled because they discharge the matter more and sometimes too quickly and therefore have a higher throughput. However, given that too little matter is held within the grinding chamber, the mill does not operate optimally. Furthermore, in the specific instance of ball mills, substantial wear of the grinding bodies is observed, and this is due to an increase in the direct (without matter in between) metal/metal impact either between the grinding bodies or between the grinding bodies and the lining. The loss of energy without any grinding effect, which is caused by these impacts and especially by the lack of matter to grind, should also be taken into account.
Several methods of regulating the passage of matter through the number of openings in the upstream wall of the partition have been proposed in order to control the level of matter within the grinding chamber, and therefore the retention time.
Document US-A-1787897 describes a partition intended to be placed between two successive grinding compartments and the frame of which consists of several segments joined together, each segment comprising two arms and a part corresponding to a portion of the circumference which is intended to hug the lining of the shell, the two arms being connected at the opposite end of the portion of the circumference by an essentially conical portion so that when the various frame segments are joined together, they create a conical deflector element. The upstream face of the wall covering the frame of the partition has openings (or apertures) in the conventional way, so as to allow sufficiently ground matter to enter the partition, whereas the rear face has no openings except for an annular discharge passage placed at the periphery of the conical element so as to remove the ground matters from the partition.
Publication FR-A-2126051 describes a method and a device which allow the amount of matter mixed with the grinding bodies in a grinding compartment of a tube mill of the ball type for example to be regulated, and in which grinding can take place either working by dry processing or working by wet processing. There is described in this document a partition intended to separate two successive grinding chambers or to be used as an outlet partition, which comprises means of regulating the level of matter within the grinding chamber, this partition consisting of vanes pivoting about a longitudinal axis so as to allow the useful volume to be adjusted or comprising a telescopic part also allowing this useful volume to be adjusted.
PARTITION, AND OUTLET PARTITION INTENDED FOR THE MILL
Subject of the invention The present invention relates to grinding mills working by wet processing, either of the autogenous type, also known as FAG (Full Autogenous Grinding) mills, or of the semi-autogenous type, also known as SAG (Semi Autogenous Grinding) mills, but also relates to ball mills using grid discharge.
The present invention relates more specifically to an outlet partition arranged in such mills.
Technological background There are two main families of mills that exist side by side; on the one hand, there are mills which work by wet processing and, on the other hand, there are mills which work by dry processing. In general terms, the solutions put forward for mills that work by dry processing cannot be read across directly to mills which work by wet processing.
The various types of mill are fitted with an outlet partition which allows the ground matter to be discharged towards an outlet trunnion. In some instances, the mills may be equipped with intermediate partitions separating two successive grinding chambers.
Mills which discharge through a grid comprise a partition generally made up of a frame, the upstream face of which is covered with grids pierced with a number of openings and which thus allow the sufficiently-ground matter to pass through while at the same time holding back the matter that is insufficiently ground, and the grinding bodies. The upstream face of which is some distance from the downstream face, which is preferably solid with the exception of a central discharge opening.
There is thus defined within the partition a small compartment which the matter which passes through the openings enters. This matter is able to circulate diametrically within the compartment. Lifting elements or lifters are provided in this partition so that as the mill rotates, the matter is lifted above the axis of the mill, from where it falls back down, possibly onto a deflector member, to be directed towards the central discharge opening.
In the case of mills which use overflow discharge (100% overflow), the mills have rather a tendency to keep the matter inside the grinding chambers for too long, which produces undesirable overly ground matters, the retention time being too long and the mill too full, which causes a certain slipping of the charge and reduces the throughput of the mill.
There is no deflector member in this type of mill, and the ground matters are removed directly by overflow via the central discharge opening towards the outlet trunnion.
In the case of mills using 1000 grid discharge, there is a deflector member present which forces the matter to follow a favoured path towards the outlet trunnion.
In this type of mill, it can be seen that these mills are often underfilled because they discharge the matter more and sometimes too quickly and therefore have a higher throughput. However, given that too little matter is held within the grinding chamber, the mill does not operate optimally. Furthermore, in the specific instance of ball mills, substantial wear of the grinding bodies is observed, and this is due to an increase in the direct (without matter in between) metal/metal impact either between the grinding bodies or between the grinding bodies and the lining. The loss of energy without any grinding effect, which is caused by these impacts and especially by the lack of matter to grind, should also be taken into account.
Several methods of regulating the passage of matter through the number of openings in the upstream wall of the partition have been proposed in order to control the level of matter within the grinding chamber, and therefore the retention time.
Document US-A-1787897 describes a partition intended to be placed between two successive grinding compartments and the frame of which consists of several segments joined together, each segment comprising two arms and a part corresponding to a portion of the circumference which is intended to hug the lining of the shell, the two arms being connected at the opposite end of the portion of the circumference by an essentially conical portion so that when the various frame segments are joined together, they create a conical deflector element. The upstream face of the wall covering the frame of the partition has openings (or apertures) in the conventional way, so as to allow sufficiently ground matter to enter the partition, whereas the rear face has no openings except for an annular discharge passage placed at the periphery of the conical element so as to remove the ground matters from the partition.
Publication FR-A-2126051 describes a method and a device which allow the amount of matter mixed with the grinding bodies in a grinding compartment of a tube mill of the ball type for example to be regulated, and in which grinding can take place either working by dry processing or working by wet processing. There is described in this document a partition intended to separate two successive grinding chambers or to be used as an outlet partition, which comprises means of regulating the level of matter within the grinding chamber, this partition consisting of vanes pivoting about a longitudinal axis so as to allow the useful volume to be adjusted or comprising a telescopic part also allowing this useful volume to be adjusted.
Document DE-477135 describes a deflector member in the form of a mobile cone secured to the mill, which allows the matter from the lifting elements (or lifters), in this case paddles, to be returned partially or in full towards the compartment upstream of the partition so that insufficiently ground particles which have entered the partition can be reground. Using this system, the matter passes once more through a grid, which in theory could allow to control the time matter is retained within the mill.
However, since this cone is an integral part of the mill, a substantial proportion of the regulating mechanism operates inside the mill. In actual fact, this device is particularly vulnerable because of wear and seizure through the jamming of grains and steel waste.
Various devices allowing some of the ground matter to be sent back to the grinding chamber have also been proposed.
Document FR-2261812 describes a very simple system for sending back to the grinding chamber the matters which are insufficiently ground (also known as "pebbles") associated with already worn grinding bodies, and which essentially comprises, in the central region of the end wall, a discharge tube which is associated with a two-way valve, so that the insufficiently ground matters can be led back to the grinding chamber while the sufficiently ground matter leaves this grinding chamber.
Document GB-A-2064364 describes a drum mill intended for a wet treatment of the autogenous or semi-autogenous type, and which has a partition adj acent to the outlet partition itself equipped with a trunnion for discharging the matter which is separated from the outlet partition by a space, the said upstream wall comprising, on the one hand, a first group of relatively small openings through which the finely ground matter leaving the mill can pass and travel towards the outlet trunnion and, on the other hand, a second group of relatively larger openings through which matter containing both fine particles and coarse particles can leave the mill. This second group of openings communicates with a matter outlet via deflection means which prevent this mixture from leaving the mill. In this case, the deflector elements act only on some of the matter, that is to say the proportion which has come from the relatively large openings, and not on all the matter from all the openings. This means that it will be impossible to correctly control the time for which the matter is retained inside the mill.
Document US-3078050 describes a mill of the autogenous type in which the matter is taken from the grinding chamber by a "fall" that enters the grinding chamber, the said fall having appropriate positioning means for removing the matter from the mill in a controllable way. This means that the mill described in this document has neither grid nor discharge chamber.
Furthermore, sustaining the falling conditions in a grinding chamber in a mill of the autogenous type is relatively problematical. This becomes impossible in the case of mill of the semi-autogenous type, or in the case of a ball mill.
Document WO 86/04526 describes a device for regulating the time that a matter is retained in the mill, which may be an autogenous mill, a semi-autogenous mill or a ball mill, and which comprises a reservoir chamber upstream of the outlet end. This mill is characterized in that it comprises a discharge duct more commonly called a "spoon" more or less coaxial with the mill, detached from the latter and longitudinally movable. This spoon enters the reservoir chamber through the outlet end of the mill and at its upstream end has a first opening made in its upper part. This spoon can be advanced as far as close to the upstream face of the reservoir chamber. It should be noted that this device known as a "spoon" is stationary relative to the rotation of the mill, and will not be able to withstand the moving mass if used in large mills. Furthermore, given that it is a stationary element, a particularly large clearance needs to be provided between the said spoon and the mill.
It should be noted that most of the regulating methods aim to propose either means allowing the insufficiently ground matter to be reinjected into the grinding chamber if necessary, or propose devices for partially blocking off the discharge region in order to increase the retention time and/or the amount of matter retained within the grinding chamber.
Nonetheless, last devices proposed are adjustable and mobile devices that can only be envisaged for small-sized mills. The present invention particularly aims at large and very large mills, the diameter of which may be as much as 12 metres or more.
Document US-A-2344162 describes a device for deflecting the ground matter towards the outlet trunnion and to send back to the grinding chamber the unground matter and the worn balls, whereas the aim of the device according to the present invention is also to deflect the ground matter towards the outlet trunnion but to eliminate the unground matter and the worn balls towards the outside of the mill so that they do not enter the grinding chamber because they would alter its effectiveness.
Document DE-A-549694 describes a mill working by dry processing in which an intermediate partition between two successive grinding chambers is present.
Nowhere can it be seen that there is regulation of the level. Only a stream of air is used to separate the fine particles from the matter that is to be ground.
Furthermore, the intermediate partition described has no grid.
Document US-A-2815176 again describes a mill working only by dry processing and intended for applications in which there is a desire to mix fine and coarse matters in a given percentage for producing graphite electrodes. Once again, use is made of a stream of air to eliminate the fine particles. Finally, this device has no grid and will not be able to separate the pebbles and there is no envisaged adjustment of the grinding level in the said mill.
Document DE-A-2848343 describes a device comprising an intermediate partition between two successive grinding chambers. It will be seen that a spindle or linkage passes through the various grinding chambers . The fact that such a spindle is present will not allow this to be used in large mills, given that this spindle is incapable of withstanding the significant masses in movement in this case. Finally, it can be seen that all the matter without distinction can pass from one chamber to the other.
Objects of the invention The present invention relates to a mill working by wet processing, either of the autogenous type or the semi-autogenous type, or also operating essentially by a grid discharge but which at the same time combines the advantages of a mill with grid discharge and a mill with overflow discharge.
More specifically, the present invention aims to propose novel means present in the partition which make it possible to influence the amount of matter in the grinding chamber by preventing this matter from leaving the mill too fast or in excessive quantity.
The present invention aims to propose a solution which is particularly simple from a mechanical point of view and which does not require the fitting of moving parts, as this would be unacceptable in certain applications, particularly in the case of large or very large mills.
Furthermore, the present invention aims to propose a solution which also makes it possible to avoid the discharge chamber becoming blocked with the insufficiently ground matter ("pebbles") and with the already worn grinding bodies.
_ g _ Main characteristic features of the present invention The present invention relates to a mill working by wet processing, of the autogenous type, semi-autogenous type or a ball mill, using grid discharge and comprising an outlet partition between the grinding chamber and the outlet trunnion. The said partition has two walls, the volume between the upstream wall and the downstream wall forming a compartment which the matter enters. This matter can circulate diametrically across the said compartment, which is called "discharge chamber".
The upstream wall is a wall essentially covered with pierced grids comprising a number of openings which allow the sufficiently ground matter to pass into the said compartment inside the partition.
The downstream wall, which is separated from the upstream wall, is preferably solid with the exception of the central part which remains open and faces towards the discharge trunnion.
The present invention is characterized by the fact that the said partition comprises means secured to this partition allowing some of the matter to pass (partially) into the central region of the compartment made between the upstream wall and the downstream wall of the partition and therefore towards the grinding chamber upstream of the said partition, the remainder of the matter being removed towards the outlet trunnion. This then makes it possible for the mill to run as a hybrid partly by discharge and partly by overflow.
The fact that the means are secured to the partition has the effect that these means will be subject to the rotation of the mill and can thus be used even in very large mills.
According to a first preferred embodiment of the present invention, the means allowing partial passage through the central region of the partition consist of deflectors in the form of metal sheets connecting the upstream wall to the downstream wall in the central region of the compartment. If all the deflectors are fitted, a discharge cone or pyramid and 100% discharge operation are obtained.
To make it possible to obtain a modulate operation of the removal of the matter from the partition between 0 and 1000 overflow, only some of these deflectors will be fitted, the others being removed.
The fact of fitting deflectors without openings in a certain number of sectors of the partition allows some of the ground matter to be deflected towards the outlet trunnion, the remainder dropping into the discharge chamber in such a way as to keep a practically constant level in the mill.
According to a second embodiment of the present invention, the means allowing a partial passage through the central region of the partition to be achieved consist in fitting a truncated cone in this region. To allow the removal of matter from the partition to be altered between 0 and 100% overflow, use is again made of a truncated cone which does not cover all the way across the discharge chamber. In this case, there will be an annular passage on the upstream side of the cone, which will allow a partial drop of the matter into the discharge chamber.
The fact of placing a more or less complete truncated cone in the internal compartment of the partition makes it possible to determine the amount of matter directed towards the outlet trunnion and the amount of matter dropping into the discharge chamber, so as to keep a practically constant level in the mill.
Particularly advantageously, deflector grids have also been placed in the compartment inside the partition in the most diametrical part thereof, that is to say towards the periphery. These grids allow matter or worn or broken grinding elements to be removed directly to the outlet trunnion without allowing them to be sent back to the discharge chamber.
Openings which allow the finer matter to pass through, possibly with return to the grinding chamber, may optionally be provided in these deflector grids.
To allow matter to be removed from the partition, provision is also made for the downstream wall to have an annular opening arranged around the region of attachment of the deflectors or of the cone.
Brief description of the figures Figure 1 depicts a view in longitudinal section of a ball mill with just one grinding chamber and fitted with a customarily-used outlet partition.
Figure 2 depicts a view in longitudinal section taken from Figure 1 and corresponding to a first embodiment of a partition fitted with means of regulating the level of matter within the grinding chamber.
Figures 3 depict several views in cross section on the axis X-X' of the partition depicted in Figure 2 seen from the trunnion end, for various mill charge conditions.
Figures depict several views in longitudinal section on section A-A according to a second embodiment of a partition equipped with means for regulating the level of matter within the grinding chamber for various mill charge conditions.
Figure 5 depicts a view in cross section on the axis X-X' of the partition of Figure 4D seen from the trunnion end in various mill charge conditions.
Figure 6 depicts a detail view of a grid used in a partition like the one described in Figure 5.
Figures 7 depict the options for the regulating means used in the second embodiment.
Description of several preferred embodiments of the i n « o n t i n n In the figures, identical references relate to identical or similar elements.
The mill in Figure 1 is a mill which works by wet processing and which is formed of a shell 1 borne by two conical ends 2 and 3. The outlet conical end 3 is secured to an outlet partition 15 of which an outlet trunnion 4 forms an integral part. On the inlet side, there is a trunnion 5 which also forms an integral part of the end 2. The trunnions are borne in bearings (not depicted) in Figure 1. The mill is driven by an annular gear and a pinion (not depicted). To protect the mill from wear, the shell 1 and the inlet and outlet ends 2 and 3 are covered with lining 8 and 9. Furthermore, the shell 1 has a manhole 7, the cover of which is formed of a part of the lining attached with clamps 10 and bolts 11.
The mill depicted in Figure 1 has just one grinding chamber 6 which is partially filled with grinding bodies 17 which in this instance are metal balls, and with matter to be ground.
Specific examples of the partition are depicted in greater detail in Figures 2, 3, 4, 5 and 7.
Customarily, the partitions essentially consist of a frame, itself comprising a certain number of sectors. In the various embodiments depicted in the figures, twelve steel sectors are joined together to create a partition. In the case of an outlet partition, these sectors directly hug the end 3 of the mill and are bolted to it by bolts (not depicted in the figures).
The partitions depicted in the various embodiments have an upstream face and a downstream face which define a volume 12 called the discharge chamber.
Customarily, the upstream face of the various sectors to separate coarse or insufficiently ground parts and worn balls from the fine particles. These deflector grids 18 also allow the insufficiently ground matters (pebbles) to be directed directly and selectively towards the outlet trunnion so that they can be removed.
The present invention aims to provide means which will allow the regulating of the level of matter in the compartment 12 of the partition and hence in the grinding chamber 6 which communicates with the compartment 12 via the grids 9, by deflecting a greater or lesser amount of matter towards the outlet trunnion while the undeflected matter falls into the compartment 12.
According to the embodiment depicted in Figures 2 and 3, all that is required is for deflectors 19 not to be fitted to a certain number of sectors of the partition, thus not forcing some of the matter contained in this sector to move towards the outlet trunnion.
This embodiment is depicted in detail in Figures 3a, 3b, 3c and 3d. In the case of Figure 3a, all the deflectors 19 are fitted, which forces all of the matter to move towards the outlet trunnion and thus prevents the mill from operating in overflow mode.
Figure 3d, in the other hand, depicts an arrangement in which none of the deflectors 19 is fitted, which allows the mill to operate in 100% overflow mode. Figures 3b .and 3c depict situations which are part way between the 100% grid (0% overflow) and 100% overflow situations, namely 50% and 75% overflow.
According to the embodiment depicted in Figures 4, the frustoconical part is produced using a cone.
According to the present invention, the cone is a cone which is truncated at the base, that is to say that it makes it possible to open a passage at the base of the cone on the upstream side of the partition. This allows some of the matter to pass towards the outlet joined together is covered with grids 14, also made of steel, which rest on the corresponding sectors.
These various grids, an example of which is depicted in greater detail in Figure 6, are pierced with a number of openings or apertures 20 which allow sufficiently ground matter to pass through. Wider openings 21, known as "pebbles ports" and located at several places on these grids make it possible to avoid the build-up of matter very difficult to grind and worn grinding elements in the grinding chamber, as this would reduce the efficiency of the latter.
The openings 20 in the grid widen from their inlet at the upstream face of the grid towards their outlet at the downstream face of the grid so that the particles which enter them can easily get out. The grids 9 may possibly be fitted with ribs (not depicted in the figures) on the upstream face side.
The centre of the upstream wall of the partition is in the form of an opening closed by a metal sheet covered with rubber on both sides and fixed to the frame so as to force the ground matter to pass through the grids.
The downstream wall of the frame has a central opening in the embodiment depicted in the various figures, which communicates directly with the outlet trunnion.
Customarily, the central part of the partition is fitted with a discharge cone or deflector, the vertex of which faces towards the outlet from the mill.
This discharge cone is generally in the form of a frustoconical central part so that the matter present in the compartment of the partition can be directed towards the outlet trunnion. To achieve this, the base of this frustoconical part faces in the upstream direction, while its vertex faces towards the downstream wall so as to cause the matter to slide directly towards the outlet trunnion.
Furthermore, .this partition is fitted with elements known as "deflector grids" 18 whose purpose is trunnion, the other part falling into the compartment 12.
More specifically, Figure 4a depicts a cone which does not allow operation in overflow mode (0% overflow) and occupies the whole of the central region of the compartment 12. Figure 4d depicts the conditions in which there is no cone fitted, allowing operation in overflow mode (100% overflow). Figures 4b and 4c depict intermediate situations.
Figure 7 depicts a partition in which the second embodiment has been used. As already mentioned, it can be seen that the upstream face is covered at the periphery with grids which have openings, whereas the central part is covered with a metal disc 16. The downstream face consists at the periphery of the lining or of a solid wall in the case of an intermediate chamber, whereas the central part is free.
The two walls define a compartment, the central part of which is fitted with radial elements which are arranged in such a way as to hold either the cones or the deflectors in place.
Figures 7b and 7c depict an exploded view of the various elements that make up the central region of the wall, wherein the various possibilities for the height of cones are proposed. The partial attachment of the cones is anticipated to be achieved by means known per se, of the bolts, nuts, etc. type.
The choice of cone type is governed by the type of matter to be ground and the desired fineness of the matter, with a view to obtaining a correct level of matter to be ground in the grinding chamber upstream.
However, since this cone is an integral part of the mill, a substantial proportion of the regulating mechanism operates inside the mill. In actual fact, this device is particularly vulnerable because of wear and seizure through the jamming of grains and steel waste.
Various devices allowing some of the ground matter to be sent back to the grinding chamber have also been proposed.
Document FR-2261812 describes a very simple system for sending back to the grinding chamber the matters which are insufficiently ground (also known as "pebbles") associated with already worn grinding bodies, and which essentially comprises, in the central region of the end wall, a discharge tube which is associated with a two-way valve, so that the insufficiently ground matters can be led back to the grinding chamber while the sufficiently ground matter leaves this grinding chamber.
Document GB-A-2064364 describes a drum mill intended for a wet treatment of the autogenous or semi-autogenous type, and which has a partition adj acent to the outlet partition itself equipped with a trunnion for discharging the matter which is separated from the outlet partition by a space, the said upstream wall comprising, on the one hand, a first group of relatively small openings through which the finely ground matter leaving the mill can pass and travel towards the outlet trunnion and, on the other hand, a second group of relatively larger openings through which matter containing both fine particles and coarse particles can leave the mill. This second group of openings communicates with a matter outlet via deflection means which prevent this mixture from leaving the mill. In this case, the deflector elements act only on some of the matter, that is to say the proportion which has come from the relatively large openings, and not on all the matter from all the openings. This means that it will be impossible to correctly control the time for which the matter is retained inside the mill.
Document US-3078050 describes a mill of the autogenous type in which the matter is taken from the grinding chamber by a "fall" that enters the grinding chamber, the said fall having appropriate positioning means for removing the matter from the mill in a controllable way. This means that the mill described in this document has neither grid nor discharge chamber.
Furthermore, sustaining the falling conditions in a grinding chamber in a mill of the autogenous type is relatively problematical. This becomes impossible in the case of mill of the semi-autogenous type, or in the case of a ball mill.
Document WO 86/04526 describes a device for regulating the time that a matter is retained in the mill, which may be an autogenous mill, a semi-autogenous mill or a ball mill, and which comprises a reservoir chamber upstream of the outlet end. This mill is characterized in that it comprises a discharge duct more commonly called a "spoon" more or less coaxial with the mill, detached from the latter and longitudinally movable. This spoon enters the reservoir chamber through the outlet end of the mill and at its upstream end has a first opening made in its upper part. This spoon can be advanced as far as close to the upstream face of the reservoir chamber. It should be noted that this device known as a "spoon" is stationary relative to the rotation of the mill, and will not be able to withstand the moving mass if used in large mills. Furthermore, given that it is a stationary element, a particularly large clearance needs to be provided between the said spoon and the mill.
It should be noted that most of the regulating methods aim to propose either means allowing the insufficiently ground matter to be reinjected into the grinding chamber if necessary, or propose devices for partially blocking off the discharge region in order to increase the retention time and/or the amount of matter retained within the grinding chamber.
Nonetheless, last devices proposed are adjustable and mobile devices that can only be envisaged for small-sized mills. The present invention particularly aims at large and very large mills, the diameter of which may be as much as 12 metres or more.
Document US-A-2344162 describes a device for deflecting the ground matter towards the outlet trunnion and to send back to the grinding chamber the unground matter and the worn balls, whereas the aim of the device according to the present invention is also to deflect the ground matter towards the outlet trunnion but to eliminate the unground matter and the worn balls towards the outside of the mill so that they do not enter the grinding chamber because they would alter its effectiveness.
Document DE-A-549694 describes a mill working by dry processing in which an intermediate partition between two successive grinding chambers is present.
Nowhere can it be seen that there is regulation of the level. Only a stream of air is used to separate the fine particles from the matter that is to be ground.
Furthermore, the intermediate partition described has no grid.
Document US-A-2815176 again describes a mill working only by dry processing and intended for applications in which there is a desire to mix fine and coarse matters in a given percentage for producing graphite electrodes. Once again, use is made of a stream of air to eliminate the fine particles. Finally, this device has no grid and will not be able to separate the pebbles and there is no envisaged adjustment of the grinding level in the said mill.
Document DE-A-2848343 describes a device comprising an intermediate partition between two successive grinding chambers. It will be seen that a spindle or linkage passes through the various grinding chambers . The fact that such a spindle is present will not allow this to be used in large mills, given that this spindle is incapable of withstanding the significant masses in movement in this case. Finally, it can be seen that all the matter without distinction can pass from one chamber to the other.
Objects of the invention The present invention relates to a mill working by wet processing, either of the autogenous type or the semi-autogenous type, or also operating essentially by a grid discharge but which at the same time combines the advantages of a mill with grid discharge and a mill with overflow discharge.
More specifically, the present invention aims to propose novel means present in the partition which make it possible to influence the amount of matter in the grinding chamber by preventing this matter from leaving the mill too fast or in excessive quantity.
The present invention aims to propose a solution which is particularly simple from a mechanical point of view and which does not require the fitting of moving parts, as this would be unacceptable in certain applications, particularly in the case of large or very large mills.
Furthermore, the present invention aims to propose a solution which also makes it possible to avoid the discharge chamber becoming blocked with the insufficiently ground matter ("pebbles") and with the already worn grinding bodies.
_ g _ Main characteristic features of the present invention The present invention relates to a mill working by wet processing, of the autogenous type, semi-autogenous type or a ball mill, using grid discharge and comprising an outlet partition between the grinding chamber and the outlet trunnion. The said partition has two walls, the volume between the upstream wall and the downstream wall forming a compartment which the matter enters. This matter can circulate diametrically across the said compartment, which is called "discharge chamber".
The upstream wall is a wall essentially covered with pierced grids comprising a number of openings which allow the sufficiently ground matter to pass into the said compartment inside the partition.
The downstream wall, which is separated from the upstream wall, is preferably solid with the exception of the central part which remains open and faces towards the discharge trunnion.
The present invention is characterized by the fact that the said partition comprises means secured to this partition allowing some of the matter to pass (partially) into the central region of the compartment made between the upstream wall and the downstream wall of the partition and therefore towards the grinding chamber upstream of the said partition, the remainder of the matter being removed towards the outlet trunnion. This then makes it possible for the mill to run as a hybrid partly by discharge and partly by overflow.
The fact that the means are secured to the partition has the effect that these means will be subject to the rotation of the mill and can thus be used even in very large mills.
According to a first preferred embodiment of the present invention, the means allowing partial passage through the central region of the partition consist of deflectors in the form of metal sheets connecting the upstream wall to the downstream wall in the central region of the compartment. If all the deflectors are fitted, a discharge cone or pyramid and 100% discharge operation are obtained.
To make it possible to obtain a modulate operation of the removal of the matter from the partition between 0 and 1000 overflow, only some of these deflectors will be fitted, the others being removed.
The fact of fitting deflectors without openings in a certain number of sectors of the partition allows some of the ground matter to be deflected towards the outlet trunnion, the remainder dropping into the discharge chamber in such a way as to keep a practically constant level in the mill.
According to a second embodiment of the present invention, the means allowing a partial passage through the central region of the partition to be achieved consist in fitting a truncated cone in this region. To allow the removal of matter from the partition to be altered between 0 and 100% overflow, use is again made of a truncated cone which does not cover all the way across the discharge chamber. In this case, there will be an annular passage on the upstream side of the cone, which will allow a partial drop of the matter into the discharge chamber.
The fact of placing a more or less complete truncated cone in the internal compartment of the partition makes it possible to determine the amount of matter directed towards the outlet trunnion and the amount of matter dropping into the discharge chamber, so as to keep a practically constant level in the mill.
Particularly advantageously, deflector grids have also been placed in the compartment inside the partition in the most diametrical part thereof, that is to say towards the periphery. These grids allow matter or worn or broken grinding elements to be removed directly to the outlet trunnion without allowing them to be sent back to the discharge chamber.
Openings which allow the finer matter to pass through, possibly with return to the grinding chamber, may optionally be provided in these deflector grids.
To allow matter to be removed from the partition, provision is also made for the downstream wall to have an annular opening arranged around the region of attachment of the deflectors or of the cone.
Brief description of the figures Figure 1 depicts a view in longitudinal section of a ball mill with just one grinding chamber and fitted with a customarily-used outlet partition.
Figure 2 depicts a view in longitudinal section taken from Figure 1 and corresponding to a first embodiment of a partition fitted with means of regulating the level of matter within the grinding chamber.
Figures 3 depict several views in cross section on the axis X-X' of the partition depicted in Figure 2 seen from the trunnion end, for various mill charge conditions.
Figures depict several views in longitudinal section on section A-A according to a second embodiment of a partition equipped with means for regulating the level of matter within the grinding chamber for various mill charge conditions.
Figure 5 depicts a view in cross section on the axis X-X' of the partition of Figure 4D seen from the trunnion end in various mill charge conditions.
Figure 6 depicts a detail view of a grid used in a partition like the one described in Figure 5.
Figures 7 depict the options for the regulating means used in the second embodiment.
Description of several preferred embodiments of the i n « o n t i n n In the figures, identical references relate to identical or similar elements.
The mill in Figure 1 is a mill which works by wet processing and which is formed of a shell 1 borne by two conical ends 2 and 3. The outlet conical end 3 is secured to an outlet partition 15 of which an outlet trunnion 4 forms an integral part. On the inlet side, there is a trunnion 5 which also forms an integral part of the end 2. The trunnions are borne in bearings (not depicted) in Figure 1. The mill is driven by an annular gear and a pinion (not depicted). To protect the mill from wear, the shell 1 and the inlet and outlet ends 2 and 3 are covered with lining 8 and 9. Furthermore, the shell 1 has a manhole 7, the cover of which is formed of a part of the lining attached with clamps 10 and bolts 11.
The mill depicted in Figure 1 has just one grinding chamber 6 which is partially filled with grinding bodies 17 which in this instance are metal balls, and with matter to be ground.
Specific examples of the partition are depicted in greater detail in Figures 2, 3, 4, 5 and 7.
Customarily, the partitions essentially consist of a frame, itself comprising a certain number of sectors. In the various embodiments depicted in the figures, twelve steel sectors are joined together to create a partition. In the case of an outlet partition, these sectors directly hug the end 3 of the mill and are bolted to it by bolts (not depicted in the figures).
The partitions depicted in the various embodiments have an upstream face and a downstream face which define a volume 12 called the discharge chamber.
Customarily, the upstream face of the various sectors to separate coarse or insufficiently ground parts and worn balls from the fine particles. These deflector grids 18 also allow the insufficiently ground matters (pebbles) to be directed directly and selectively towards the outlet trunnion so that they can be removed.
The present invention aims to provide means which will allow the regulating of the level of matter in the compartment 12 of the partition and hence in the grinding chamber 6 which communicates with the compartment 12 via the grids 9, by deflecting a greater or lesser amount of matter towards the outlet trunnion while the undeflected matter falls into the compartment 12.
According to the embodiment depicted in Figures 2 and 3, all that is required is for deflectors 19 not to be fitted to a certain number of sectors of the partition, thus not forcing some of the matter contained in this sector to move towards the outlet trunnion.
This embodiment is depicted in detail in Figures 3a, 3b, 3c and 3d. In the case of Figure 3a, all the deflectors 19 are fitted, which forces all of the matter to move towards the outlet trunnion and thus prevents the mill from operating in overflow mode.
Figure 3d, in the other hand, depicts an arrangement in which none of the deflectors 19 is fitted, which allows the mill to operate in 100% overflow mode. Figures 3b .and 3c depict situations which are part way between the 100% grid (0% overflow) and 100% overflow situations, namely 50% and 75% overflow.
According to the embodiment depicted in Figures 4, the frustoconical part is produced using a cone.
According to the present invention, the cone is a cone which is truncated at the base, that is to say that it makes it possible to open a passage at the base of the cone on the upstream side of the partition. This allows some of the matter to pass towards the outlet joined together is covered with grids 14, also made of steel, which rest on the corresponding sectors.
These various grids, an example of which is depicted in greater detail in Figure 6, are pierced with a number of openings or apertures 20 which allow sufficiently ground matter to pass through. Wider openings 21, known as "pebbles ports" and located at several places on these grids make it possible to avoid the build-up of matter very difficult to grind and worn grinding elements in the grinding chamber, as this would reduce the efficiency of the latter.
The openings 20 in the grid widen from their inlet at the upstream face of the grid towards their outlet at the downstream face of the grid so that the particles which enter them can easily get out. The grids 9 may possibly be fitted with ribs (not depicted in the figures) on the upstream face side.
The centre of the upstream wall of the partition is in the form of an opening closed by a metal sheet covered with rubber on both sides and fixed to the frame so as to force the ground matter to pass through the grids.
The downstream wall of the frame has a central opening in the embodiment depicted in the various figures, which communicates directly with the outlet trunnion.
Customarily, the central part of the partition is fitted with a discharge cone or deflector, the vertex of which faces towards the outlet from the mill.
This discharge cone is generally in the form of a frustoconical central part so that the matter present in the compartment of the partition can be directed towards the outlet trunnion. To achieve this, the base of this frustoconical part faces in the upstream direction, while its vertex faces towards the downstream wall so as to cause the matter to slide directly towards the outlet trunnion.
Furthermore, .this partition is fitted with elements known as "deflector grids" 18 whose purpose is trunnion, the other part falling into the compartment 12.
More specifically, Figure 4a depicts a cone which does not allow operation in overflow mode (0% overflow) and occupies the whole of the central region of the compartment 12. Figure 4d depicts the conditions in which there is no cone fitted, allowing operation in overflow mode (100% overflow). Figures 4b and 4c depict intermediate situations.
Figure 7 depicts a partition in which the second embodiment has been used. As already mentioned, it can be seen that the upstream face is covered at the periphery with grids which have openings, whereas the central part is covered with a metal disc 16. The downstream face consists at the periphery of the lining or of a solid wall in the case of an intermediate chamber, whereas the central part is free.
The two walls define a compartment, the central part of which is fitted with radial elements which are arranged in such a way as to hold either the cones or the deflectors in place.
Figures 7b and 7c depict an exploded view of the various elements that make up the central region of the wall, wherein the various possibilities for the height of cones are proposed. The partial attachment of the cones is anticipated to be achieved by means known per se, of the bolts, nuts, etc. type.
The choice of cone type is governed by the type of matter to be ground and the desired fineness of the matter, with a view to obtaining a correct level of matter to be ground in the grinding chamber upstream.
Claims (6)
1. Mill working by wet processing, of the autogenous type, semi-autogenous type or ball mill using grid discharge, comprising an outlet partition (15) between the grinding chamber (6) and the outlet trunnion (4), the said partition comprising an upstream wall (14) and a downstream wall (13) in order to form a compartment (12) inside the partition called discharge chamber, characterized in that the central part of the partition (15) is fitted with deflector members secured to this partition allowing some of the matter that is to be ground to be maintained into the central region of the compartment (12) and therefore in the discharge chamber of the said partition, the remainder of the matter being removed towards the outlet trunnion (4) of said mill.
2. Mill according to Claim 1, characterized in that the deflector members secured to the partition (15) and allowing some of the ground matter to be maintained in the discharge chamber (12) consist of deflectors (19) in the form of metal sheets connecting the upstream wall (14) to the downstream wall (13) of the discharge chamber, and which do not cover the whole of the central space of the partition.
3. Mill according to Claim 1, characterized in that the deflector members allowing some of the ground matter to be maintained in the discharge chamber (12) consist of a truncated cone leaving a passage on the upstream wall (14) side of the central region of the discharge chamber (12).
4. Mill according to any one of the preceding claims, characterized in that the said partition (15) consists of a frame comprising a certain number of sectors, said frame comprising, on the upstream face at the periphery, grids (9) which have openings (20 21), and, on the downstream face a solid wall which has an annular opening arranged, around the region of attachment of the deflector members.
5. Mill according to Claim 4, characterized in that the solid wall on the downstream face of said frame consists of the lining of the mill.
6. Mill according to any one of the preceding claims, characterized in that it comprises deflector grids (18) arranged in each sector of the partition (15), said grids allowing matter or worn or broken grindings elements to be removed directly to the outlet trunnion without allowing them to be sent back to the discharge chamber.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP98870034A EP0937503A1 (en) | 1998-02-20 | 1998-02-20 | Discharging device for a wet grinding mill |
| EP98870034.0 | 1998-02-20 | ||
| PCT/BE1999/000024 WO1999042217A1 (en) | 1998-02-20 | 1999-02-18 | Wet process grinder equipped with baffle and outlet baffle for said grinder |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2320796A1 true CA2320796A1 (en) | 1999-08-26 |
Family
ID=8236998
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002320796A Abandoned CA2320796A1 (en) | 1998-02-20 | 1999-02-18 | Wet process grinder equipped with baffle and outlet baffle for said grinder |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0937503A1 (en) |
| AU (1) | AU2504999A (en) |
| CA (1) | CA2320796A1 (en) |
| WO (1) | WO1999042217A1 (en) |
| ZA (1) | ZA991316B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101690905B (en) * | 2009-09-27 | 2011-08-03 | 东南大学 | Conical surface sieve flash device |
| IT201800003874A1 (en) * | 2018-03-22 | 2019-09-22 | Certech Spa Con Socio Unico | Mill for ceramic materials |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE549694C (en) * | 1932-05-03 | Miag Muehlenbau Und Ind Akt Ge | A viewing chamber for pipe, ball, compound mills or the like, traversed by a suction air stream. | |
| DE477135C (en) | 1927-06-28 | 1929-06-01 | Fried Krupp Grusonwerk Akt Ges | Drum mill for wet grinding |
| US1787897A (en) | 1929-08-13 | 1931-01-06 | Joseph V Durnin | Compartment tube grinding mill |
| US2344162A (en) * | 1940-11-26 | 1944-03-14 | Richard W Marland | Grinding mill discharge |
| US2815176A (en) * | 1955-04-06 | 1957-12-03 | Kennedy Van Saun Mfg & Eng | Apparatus for producing carbonaceous materials for electrodes |
| US3078050A (en) | 1960-01-08 | 1963-02-19 | Hardinge Harlowe | Autogenous grinding process and mill systems to perform the same |
| BE763140A (en) | 1971-02-18 | 1971-07-16 | Slegten Sa | METHOD FOR ADJUSTING THE QUANTITY OF MATERIAL IN A CRUSHING COMPARTMENT OF A BALL CRUSHER TUBE. |
| SE7402593L (en) | 1974-02-27 | 1975-08-28 | Ab Boliden | |
| DE2613062B2 (en) * | 1976-03-26 | 1979-03-01 | Polysius Ag, 4720 Beckum | Lifting wall |
| DE2848343A1 (en) | 1978-11-08 | 1980-05-22 | Bergheimer Emaillierwerk Herke | Transfer pattern application machine - has guide delivering adhesive sheet leading edge onto moving item |
| DE2848438A1 (en) * | 1978-11-08 | 1980-05-22 | Kloeckner Humboldt Deutz Ag | Tube mill for grinding material - has double plate material transfer with transfer orifice in baffle plate adjustable during operation |
| SE426916B (en) * | 1979-11-30 | 1983-02-21 | Boliden Ab | DEVICE FOR DRUM MILL FOR AUTOGEN OR SEMIAUTOGEN WATER MILLING |
| LU85767A1 (en) * | 1985-02-08 | 1986-09-02 | Communition Tech Comminutec | DEVICE FOR ADJUSTING THE TIME OF RETENTION OF MATERIAL IN A CRUSHER |
-
1998
- 1998-02-20 EP EP98870034A patent/EP0937503A1/en not_active Withdrawn
-
1999
- 1999-02-18 WO PCT/BE1999/000024 patent/WO1999042217A1/en active Application Filing
- 1999-02-18 ZA ZA9901316A patent/ZA991316B/en unknown
- 1999-02-18 CA CA002320796A patent/CA2320796A1/en not_active Abandoned
- 1999-02-18 AU AU25049/99A patent/AU2504999A/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| AU2504999A (en) | 1999-09-06 |
| EP0937503A1 (en) | 1999-08-25 |
| ZA991316B (en) | 1999-12-29 |
| WO1999042217A1 (en) | 1999-08-26 |
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