GB1577984A

GB1577984A - Mill

Info

Publication number: GB1577984A
Application number: GB12049/78A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-03-25
Filing date: 1978-03-28
Publication date: 1980-10-29
Also published as: ES468203A1; FR2384545A1; IT1093918B; FR2384545B1; IT7821612A0

Description

(54) MILL (71) I, JEAN MORITZ, of 13, avenue du Languedoc 83430 SAINT MANDRIER SUR MER, France, of French nationality, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a grinding mill which can be run at higher speeds than usual. The invention also relates to such a mill coupled with a sorting or pre-selector device.

The possibility of constructing mills having drinding rollers bearing on a grinding surface has been known for a long time. In such a mill material is crushed between the grinding rollers and the grinding surface as the grinding surface rotates. The rate of grinding can be increased by increasing the speed of rotation of the grinding surface but this has the disadvantage that, at high speds, material to be ground is flung from the grinding surface by centrifugal force and thus does not pass under grinding rollers.

We have now discovered a mill which can allow a fast speed of rotation of its grinding surface while maintaining a high grinding efficiency.

Thus, the present invention consists in a grinding mill comprising a rotatable conical or frusto-conical grinding surface and at least one grinding roller bearing on said grinding surface; wherein the grinding surface is surrounded by an annular chamber such that fluid passed into the chamber is directed past the grinding surface thereby causing finer particles to be removed from the grinding surface. Such a fluid (generally air) can be used, therefore. to separate sufficiently ground particles from coarser particles. Nonetheless it is quite acceptable for coarser particles to be removed by this fluid since they can be returned to the grinding surface by, for example, baffles.

The present invention therefore also consists in the grinding mill of the invention together with a pre-selector adapted to allow passage away from the grinding surface of material which has become sufficiently well ground and to direct towards the grinding surface for further grinding material which is still too coarse.

The pre-selector conveniently comprises one or more, preferably about 3, frustoconical baffles.

The inclination of the grinding surface helps prevent particles being ground from being flung outwards by centrifugal force; particles are, therefore, retained in the grinding area for longer allowing the speed of rotation of the grinding surface to be increased. As a result, the production rate of the mill is increased.

The grinding rollers are preferably cylindrical, in which case their axes extend parallel to the generatrix of the grinding surface. Conveniently, each grinding roller is mounted for rotation on a support which is articulated to the body of the mill. In general, each roller may be fixed to a panel which is removably fixed to the body of the mill. Although it is usual for each grinding roller to be free to rotate on its support and in use to be driven by frictional contact with the grinding surface it is possible for the power train to run in the opposite direction: one or more of the rollers would then drive a freely rotatable grinding surface.

An annular chamer communicatable with a pressure source may be provided around the grinding surfaces. The purposes of this is to direct by means of a fluid (preferably a gas, and conveniently air) ground particles from the grinding surface to a pre-selector.

In practice, the particles will be directed upwards to impinge on frusto-conical baffles which will cause the less well ground particles to fall back by gravity onto the grinding surface. Feeders may be attached to the grinding surface such that they sweep round the annular chamber to return any material to the grinding chamber which has spilled over into the annular chamber.

The grinding surface, which may be fixed on a table, may be provided with a guide surface at its centre. This guide surface is conveniently a cone and it directs material supplied from above (for example by pouring) towards the periphery of the grinding surface or, when the grinding surface is an annular ring, actually onto the grinding surface.

A preferred embodiment of the present invention is illustrated by the accompanying drawing which shows, partly in section, a complete mill plus pre-selector. A frame 1 supports a drum 2 which has a number of lateral openings 3 each of which is closed by a removable panel 4. Cylindrical grinding rollers 5 are rotatably mounted on supports 6 whih are pivotally fixed to pins 7 extending horizontally with respect to panels 4. Since the rollers 5 are cylindrical, the axes of supports 6 must lie parallel to the localinclination of the grinding surface. To each support 6 is fixed a hemi-sperical cup-like member 8 which contacts the edge of a sperical opening 9 formed in panel 4. The purpose of this is to prevent dust produced during operation of the mill from escaping.

Grinding rollers 5 rest on a frusto-conical grinding surface 10 which forms an annular ring fixed to a rotatable table 11. The inclination of the grinding surface is, of course, downwards towards the centre. The drum 2 extends below the panels 4 as a widened annular air box 2a which communicates via a tangential duct 12 to the outlet of a fan or blower. Grinding surface 10 carries at its periphery helical feeders 13 which move in air box 2a and return spillage to the grinding surface.

The rotatable table 11 is fixed to a central sleeve 14 which is attached to a pivot 15 via a suitably lubricated guide bush. The rotatable table 11 also carries near ites periphery a ring 16 which is mounted, with the interposition of rollers, for rotation relative to drum 2. The ring 16 is attached to a toothed crown wheel 18 which rests on rollers 19. The rollers 19 are rotatable about a horizontal axles and mesh with a pinion gear wheel 20 which is keyed to the output shaft 21 of a speed reduction gear driven by motor 23.

Drum 2 is surmounted by a pre-separator 25. This pre-separator comprises a frustoconical skirt 26 which has, over part of its height, a series of openings 27 extending over practically the whole periphery of the pre-separator. Frusto-conical baffles 28 are arranged inside the skirt 26. Cone 29 is provided over the centre of the rotatable table 11. This cone distributes material arriving from the base of the pre-separator to the various grinding rollers.

The material to be ground is supplied by means of a feed screw 31 which receives material to be ground from a hopper and deposits it onto a stationary distributor tray 32. Scraper or rake members 33, which may be driven by central sleeve 14 via a shaft 34, are fixed to a hub and their purpose is to send material on the distributor tray falling towards the grinding surface.

Under certain circumstances, when it is desired to accelerate drying, pivot member 15 may be hollow and cone 29 may have holes or perforations 30 near its base to provide a passage for pressurized air, preferably warm or hot air as indicated by arrow 24.

To operate the mill, motor 23 is started.

This rotates the rotatable table 11 and the scraper or rake members 33. The material to be ground is then fed into feeder screw 31 which directs it to the upper part of preseparator 25. The material is guided by the cone 29 to the grinding surface 10 where it is crushed under rollers 5 as they rotate by frictional contact with the rotating grinding surface. Finely ground material is forced upwards into the pre-separator 25 by a current of air arising from the air box 2a and, optionally, from the hollow pivot 15 via holes 30. The material thus projected strikes the frusto-conical baffles 28 after it has passed through openings 27. The larger particles fall back onto the brinding surface and the finer particles continue upwards. As this process continues, the particles become perfectly dry.The fine particles ultimately pass into a selector 35 where they are graded according to size - coarser particles being returned to the mill.

WHAT I CLAIM IS 1. A grinding mill comprising a rotatable conical or frusto-conical grinding surface and at least one grinding roller bearing on said grinding surface; wherein the grinding surface is surrounded by an annular chamber such that fluid passed into the chamber is directed past the grinding surface thereby causing finer particles to be removed from the grinding surface.

2. A mill according to claim 1, in which the or each said grinding roller is cylindrical.

3. A mill according to claim 1 or claim 2, in which the or each said grinding roller is mounted on a support which is articulated to the body of the mill.

4. A mill according to any one of the previous claims, in which the annular chamber has means for connection to a high pressure fluid.

5. A mill according to claim 4, which additionally comprises one or more feeders attached to said grinding surface and which sweep round said annular chamber.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. grinding surface such that they sweep round the annular chamber to return any material to the grinding chamber which has spilled over into the annular chamber. The grinding surface, which may be fixed on a table, may be provided with a guide surface at its centre. This guide surface is conveniently a cone and it directs material supplied from above (for example by pouring) towards the periphery of the grinding surface or, when the grinding surface is an annular ring, actually onto the grinding surface. A preferred embodiment of the present invention is illustrated by the accompanying drawing which shows, partly in section, a complete mill plus pre-selector. A frame 1 supports a drum 2 which has a number of lateral openings 3 each of which is closed by a removable panel 4. Cylindrical grinding rollers 5 are rotatably mounted on supports 6 whih are pivotally fixed to pins 7 extending horizontally with respect to panels 4. Since the rollers 5 are cylindrical, the axes of supports 6 must lie parallel to the localinclination of the grinding surface. To each support 6 is fixed a hemi-sperical cup-like member 8 which contacts the edge of a sperical opening 9 formed in panel 4. The purpose of this is to prevent dust produced during operation of the mill from escaping. Grinding rollers 5 rest on a frusto-conical grinding surface 10 which forms an annular ring fixed to a rotatable table 11. The inclination of the grinding surface is, of course, downwards towards the centre. The drum 2 extends below the panels 4 as a widened annular air box 2a which communicates via a tangential duct 12 to the outlet of a fan or blower. Grinding surface 10 carries at its periphery helical feeders 13 which move in air box 2a and return spillage to the grinding surface. The rotatable table 11 is fixed to a central sleeve 14 which is attached to a pivot 15 via a suitably lubricated guide bush. The rotatable table 11 also carries near ites periphery a ring 16 which is mounted, with the interposition of rollers, for rotation relative to drum 2. The ring 16 is attached to a toothed crown wheel 18 which rests on rollers 19. The rollers 19 are rotatable about a horizontal axles and mesh with a pinion gear wheel 20 which is keyed to the output shaft 21 of a speed reduction gear driven by motor 23. Drum 2 is surmounted by a pre-separator 25. This pre-separator comprises a frustoconical skirt 26 which has, over part of its height, a series of openings 27 extending over practically the whole periphery of the pre-separator. Frusto-conical baffles 28 are arranged inside the skirt 26. Cone 29 is provided over the centre of the rotatable table 11. This cone distributes material arriving from the base of the pre-separator to the various grinding rollers. The material to be ground is supplied by means of a feed screw 31 which receives material to be ground from a hopper and deposits it onto a stationary distributor tray 32. Scraper or rake members 33, which may be driven by central sleeve 14 via a shaft 34, are fixed to a hub and their purpose is to send material on the distributor tray falling towards the grinding surface. Under certain circumstances, when it is desired to accelerate drying, pivot member 15 may be hollow and cone 29 may have holes or perforations 30 near its base to provide a passage for pressurized air, preferably warm or hot air as indicated by arrow 24. To operate the mill, motor 23 is started. This rotates the rotatable table 11 and the scraper or rake members 33. The material to be ground is then fed into feeder screw 31 which directs it to the upper part of preseparator 25. The material is guided by the cone 29 to the grinding surface 10 where it is crushed under rollers 5 as they rotate by frictional contact with the rotating grinding surface. Finely ground material is forced upwards into the pre-separator 25 by a current of air arising from the air box 2a and, optionally, from the hollow pivot 15 via holes 30. The material thus projected strikes the frusto-conical baffles 28 after it has passed through openings 27. The larger particles fall back onto the brinding surface and the finer particles continue upwards. As this process continues, the particles become perfectly dry.The fine particles ultimately pass into a selector 35 where they are graded according to size - coarser particles being returned to the mill. WHAT I CLAIM IS

1. A grinding mill comprising a rotatable conical or frusto-conical grinding surface and at least one grinding roller bearing on said grinding surface; wherein the grinding surface is surrounded by an annular chamber such that fluid passed into the chamber is directed past the grinding surface thereby causing finer particles to be removed from the grinding surface.

6. A mill according to any one of the

preceding claims, which additionally comprises a guide surface centrally positioned with respect to said grinding surface.

7. A mill according to any one of the preceding claims which additionally comprises a pre-selector capable of allowing passage away from said grinding surface of finer particles and directing towards said grinding surface coarser particles.

8. A mill according to claim 7, in which said pre-selector comprises one or more frusto-conical baffles.

9. A mill according to claim 7 or claim 8, in which said grinding surface is provided with a duct at its centre for the passage of a fluid across said grinding surface.

10. A mill according to claim 1, substantially as herein described with reference to the accompanying drawing.