EP1776191A1

EP1776191A1 - Centrifugal mill for grinding loose material

Info

Publication number: EP1776191A1
Application number: EP05743047A
Authority: EP
Inventors: Giorgio Berselli; Emer Sghedoni
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-05-28
Filing date: 2005-05-04
Publication date: 2007-04-25
Also published as: CN100515572C; WO2005118146A1; CN1956788A; RU2006146940A; ITMO20040138A1

Abstract

A centrifugal mill (1) for grinding loose material, comprising a frame (2) for supporting a grinding chamber (3) provided with a longitudinal axis (A) and with at least one opening (4, 5) for introducing and/or discharging respectively the material to be ground and the ground material, first means (6) for the articulation of the grinding chamber to the frame, which are formed proximate to one of the two opposite ends of the longitudinal axis (A) and are adapted to allow the grinding chamber (3) to perform a motion in which the longitudinal axis (A) rotates about a fixed axis (B) with which it shares a point of incidence (P), the angle of incidence between the axes (A, B) remaining substantially constant during the motion, means (8) for actuating the grinding chamber in the motion, which are provided proximate to the other end of the longitudinal axis, second means (7) for the articulation of the grinding chamber to the actuation means, and a solid body (9) that is formed inside the grinding chamber (3), a compartment delimited by internal walls (3a) of the grinding chamber (3) and by an external surface (9a) of the solid body (9) defining a portion of the chamber that is active for the milling.

Description

CENTRIFUGAL MILL FOR GRINDING LOOSE MATERIAL Technical Field The present invention relates to a centrifugal mill for grinding loose material. Background Art With particular but not exclusive reference to the ceramics sector, centrifugal mills for grinding loose material, for preparing for example ceramic mixes, enamels, screen-printing pastes or the like, are known. Known centrifugal mills substantially comprise a supporting frame for a grinding chamber provided with a longitudinal axis of symmetry, first means for the articulation of the grinding chamber to the frame, which are provided proximate to one of the two opposite ends of the axis of symmetry of said chamber and are suitable to allow a rotary motion thereof about a fixed axis with which it shares a point of incidence, and means for actuating the grinding chamber with said rotary motion about the fixed axis, which are formed proximate to the other end of the axis of symmetry, second articulation means being interposed between the grinding chamber and the actuation means. Grinding media, such as for example beads of various diameters, are provided inside the grinding chamber; the chamber is further provided with at least one opening for introducing and/or removing respectively the materials to be milled and the milled materials. The grinding chamber performs a motion that is similar to a precession motion. Despite not rotating about its own longitudinal axis, it in fact moves so that said axis rotates about a fixed axis that is incident thereto, the angle formed by the two axes remaining constant throughout the motion; accordingly, the longitudinal axis traces a cone about the fixed axis. As a consequence of this motion, the material to be milled is broken up between the grinding media and the internal walls of the grinding chamber. These known centrifugal mills are not free from drawbacks, including the fact that they require disadvantageously long times to perform the operations for loading the materials to be ground, for grinding, and for unloading the ground materials, which penalize production. Another drawback of known mills is that they do not allow to grind the materials uniformly, i.e., the milled materials have uneven dimensions scattered over a wide range of values. Another drawback of known centrifugal mills is that they have substantial dimensions and footprints. Disclosure of the Invention The aim of the present invention is to eliminate the above-mentioned drawbacks of known centrifugal mills by providing a centrifugal mill for grinding loose material that allows to reduce the time required to perform the operations for loading the materials to be ground, for milling, and for unloading the ground materials, thus increasing production. Another object of the present invention is to provide a centrifugal mill for grinding loose material that allows to grind the materials uniformly, i.e., allows to obtain ground materials with substantially uniform dimensions that are within a narrow range of values. Another object of the present invention is to provide a centrifugal mill for grinding loose material that provides reduced dimensions and footprints for an equal capacity. Within this aim, another object of the present invention is to provide a centrifugal mill that is simple, relatively easy to provide in practice, safe in use, effective in operation, and has a relatively low cost. This aim and these and other objects that will become better apparent hereinafter are achieved by the present centrifugal mill for grinding loose material, of the type that comprises a frame for supporting a grinding chamber provided with a longitudinal axis and with at least one opening for introducing and/or discharging respectively the material to be ground and the ground material, first means for the articulation of said grinding chamber to said frame, which are formed proximate to one of the two opposite ends of said longitudinal axis and are adapted to allow said grinding chamber to perform a motion in which said longitudinal axis rotates about a fixed axis with which it shares a point of incidence, the angle of incidence between said axes remaining substantially constant during said motion, means for actuating said grinding chamber in said motion, which are provided proximate to the other end of said longitudinal axis, and second means for the articulation of said grinding chamber to said actuation means, characterized in that it comprises a solid body that is formed inside said grinding chamber, the compartment delimited by the internal walls of said grinding chamber and by the external surface of said solid body defining the portion of said chamber that is active for said milling. Brief Description of the Drawings Further characteristics and advantages of the present invention will become better apparent from the following detailed description of a preferred but not exclusive embodiment of a centrifugal mill for grinding loose material, illustrated by way of non-limiting example in the accompanying drawings, wherein: Figure 1 is a schematic and partially sectional front view of a centrifugal mill according to the invention; Figure 2 is a partially sectional schematic side view of a centrifugal mill according to the invention; Figure 3 is a schematic enlarged-scale sectional view of the means for the actuation of the centrifugal mill according to the invention; Figure 4 is a schematic plan view of the plate of the actuation means of the centrifugal mill according to the invention; Figure 5 is a schematic front view of the plate of Figure 4; Figure 6 is a schematic front view of a detail of the actuation means of the centrifugal mill according to the invention; Figure 7 is a schematic front view of the discharge opening of the grinding chamber of the mill according to the invention. Ways of carrying out the Invention With reference to the figures, the reference numeral 1 generally designates a centrifugal mill for grinding loose material, particularly but not exclusively material used in the ceramics industry, such as for example raw materials for mixtures, enamels, screen printing pastes, et cetera. The mill 1 comprises a fixed supporting frame 2 for supporting a grinding chamber 3 provided with a longitudinal axis A, which is advantageously an axis of symmetry, and with at least one opening 4 for introducing the material to be ground and an opening 5 for discharging the ground material. First means 6 for the articulation of the chamber 3 to the frame 2 are formed proximate to one of the two opposite ends of the longitudinal axis A and are suitable to allow the chamber 3 to move so that the longitudinal axis A rotates about a fixed axis B, with which it shares a point of incidence P. The angle of incidence between the two axes A and B remains substantially constant during the motion of the chamber 3, which therefore, despite not rotating about its own longitudinal axis A, performs substantially a precession motion, tracing a cone about the fixed axis B. Second means 7 for the articulation of the chamber 3 to actuation means 8 that are suitable to move it are formed proximate to the other end of the longitudinal axis A. A solid body 9 is formed within the chamber 3; a compartment 10 delimited by internal walls 3a of the chamber 3 and by the external surface 9a of the body 9 forms the portion of the chamber 3 that is active for grinding. Conveniently, the body 9 has a base in common with the chamber 3 and lies at least partially in a direction that is substantially parallel to the longitudinal axis A, so that the compartment 10 assumes a substantially annular shape. Further, the body 9 is advantageously symmetrical with respect to the longitudinal axis A and substantially has the shape of a solid of rotation, such as a cylinder, a cone, a f ustum or the like. In the particular embodiment shown in the figures, the body 9 is substantially shaped like a frustum that converges toward the inside of the chamber 3; however, alternative embodiments are not excluded in which for example the body 9 can be shaped like a cylinder and can be even substantially as tall as the chamber 3. The fixed axis B is substantially vertical; however, it can also be arranged substantially horizontally or at an angle; consequently, therefore, the inclination of the chamber 3 varies. The intake opening 4 is conveniently formed proximate to the bottom of the compartment 10 and is connected to first means for feeding the material to be ground, such as a first pump 11, while the discharge opening 5 is formed proximate to the top of the compartment 10, i.e., proximate to the maximum filling level of said compartment; this arrangement of the two openings, the inlet opening 4 and the discharge opening 5, also allows continuous operation of the mill 1. Further, the mill 1 comprises means 12 for conditioning the chamber

3, which are suitable to keep the material being ground at a preset temperature, so as to preserve its chemical and physical characteristics. The conditioning means 12 comprise an interspace 13, which is formed at least at the walls of the chamber 3 that delimit the compartment 10 and is associated with a conditioning fluid circuit of the type that comprises for example a duct 14 for introducing the fluid in the interspace 13, a duct 15 for the discharge of the fluid from the interspace 13, a heat exchanger 16 that is interposed between the discharge duct 15 and the intake duct 14, and second means for feeding the fluid from the heat exchanger 16 to the intake duct 14, such as for example a second pump 17. The internal walls 3 a of the chamber 3 and the external surface 9a of the body 9 are covered with a lining 18 that is made of a wear-resistant material, such as for example alumina. The first articulation means 6 and the second articulation means 7 comprise a respective articulation shaft, designated by the reference numerals 19 and 20, in which one end is rigidly associated with the chamber 3 at the respective end of the longitudinal axis A and the opposite end is articulated, by means of a spherical joint 21 and 22, respectively to the frame 2 and to the actuation means 8. The actuation means 8 comprise a shaft 23, which is a driving shaft and forms the fixed axis B; a plate 24, which is rigidly coupled to the shaft 23; and means 25 for guiding the articulation shaft 20, which are formed within the plate 24, are eccentric with respect to the shaft 23, and are suitable to make the corresponding end of the longitudinal axis A trace a substantially circular orbit about the fixed axis B, means 26 for adjusting the radius of said orbit being provided. The guiding means 25 comprise a substantially straight guide 27, which is formed in the plate 24 and with which a sliding block 28 is slidingly associated, such block being rigidly coupled to the second articulation means 7; rotary coupling means are interposed between the second articulation means 7 and the sliding block 28 and are for example of the type of a radial bearing 29, in which the external ring 29a is rigidly coupled to the spherical joint 22 and the internal ring is rigidly coupled to the sliding block 28. The adjustment means 26 comprise a linear actuator, such as for example a fluid-operated cylinder 30, which is substantially parallel to the guide 27 and has an end, constituted by a sleeve 31, that is rigidly coupled to the plate 24 and an opposite end, constituted by a stem 32, that is rigidly coupled to the sliding block 28. However, alternative embodiments in which the linear actuator is of a mechanical, electrical or electromechanical type are not excluded. Further, the actuation means 8 are provided with mass balancing means, such as for example a counterweight 33 for the chamber 3, which is rigidly coupled to the plate 24 and arranged opposite the guiding means 25 with respect to the fixed axis B. The balancing means, i.e., the counterweight 33, can be fixed or adjustable in terms of weight and/or position, according to the total masses to be balanced and in particular according to the total mass of the chamber 3 and of the materials being ground and of the grinding media introduced therein. Further, the mill 1 comprises means for stabilizing the motion of the chamber 3, such as for example an articulated system 34, which is associated with the frame 2 and the chamber 3 and is suitable to keep the chamber in orbit, preventing it from rotating about the longitudinal axis A. Conveniently, the mill 1 comprises means for adjusting the elevation of the discharge opening 5, which in the embodiment shown in the figures comprise a flange 35, which is arranged so as to close an opening 36 that is formed in the walls of the chamber 3 and in which there is a slot 37 that forms the discharge opening 5, the flange 35 being arrangeable with various orientations by way of a plurality of screw means, designated schematically by their respective axes 38, so as to change the elevation of the slot 37 as shown by the dashed lines. The possibility to change the elevation of the discharge opening 5, i.e., the overflow of the milled material that leaves the chamber 3, allows to change the useful volume of the compartment 10. However, alternative embodiments of the means for adjusting the elevation of the discharge opening 5 are not excluded; for example, the flange 35 might be fixed and the slot 37 might have an adjustable elevation, or one could associate with the opening 36 a closure system with an upward-moving gate, or said means might comprise a plurality of holes formed in the walls of the chamber 3 at various elevations, forming respective discharge openings, each associated with a respective cock that can be selectively opened and closed. In practice it has been found that the described invention achieves the intended aim and objects. In particular, it is noted that the presence of the solid body inside the grinding chamber increases the active grinding surface, and the grinding therefore occurs in a shorter time, increasing production. Further, the solid body, by increasing the active grinding surface, improves the results of the grinding, allowing to obtain materials that are milled with a substantially uniform particle size. The means for conditioning the grinding chamber allow to keep the material being ground at a temperature that can be preset, so as to preserve its physical and chemical characteristics; the counterweight instead allows to dampen the vibrations of the mill, stabilizing it. Finally, the arrangement of the intake and discharge openings also allows continuous operation of the mill. Finally, it is noted that the mill according to the invention simplifies washing operations with respect to cylindrical gravity mills (Alsing), since it requires partial filling of the volume of the grinding chamber with the washing water instead of total filling thereof, with consequent financial savings, reduced waste of water and better environmental protection. The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. All the details may further be replaced with other technically equivalent ones. In practice, the materials used, as well as the shapes and the dimensions, may be any according to requirements without thereby abandoning the protective scope of the appended claims. The disclosures in Italian Patent Application No. MO2004A000138 from which this application claims priority are incorporated herein by reference.

Claims

CLAIMS 1. A centrifugal mill for grinding loose material, of the type that comprises: a frame for supporting a grinding chamber, which is provided with a longitudinal axis and with at least one opening for introducing and or discharging respectively the material to be ground and the ground material; first means for the articulation of said grinding chamber to said frame, which are formed proximate to one of the two opposite ends of said longitudinal axis and are adapted to allow said grinding chamber to perform a motion in which said longitudinal axis rotates about a fixed axis with which it shares a point of incidence, the angle of incidence between said axes remaining substantially constant during said motion; means for actuating said grinding chamber in said motion, which are provided proximate to the other end of said longitudinal axis; and second means for the articulation of said grinding chamber to said actuation means; characterized in that it comprises a solid body that is formed inside said grinding chamber, a compartment delimited by internal walls of said grinding chamber and by an external surface of said solid body defining a portion of said chamber that is active for said milling.

2. The mill according to claim 1, characterized in that said longitudinal axis is an axis of symmetry of said grinding chamber.

3. The mill according to one or more of the preceding claims, characterized in that said solid body lies at least partially in a direction that is substantially parallel to said longitudinal axis, said compartment being substantially annular.

4. The mill according to one or more of the preceding claims, characterized in that said solid body is substantially symmetrical with respect to said longitudinal axis.

5. The mill according to one or more of the preceding claims, characterized in that said grinding chamber and said solid body have a common base.

6. The mill according to one or more of the preceding claims, characterized in that said solid body is substantially shaped like a solid of rotation, such as a cylinder, a cone, a frustum or the like.

7. The mill according to one or more of the preceding claims, characterized in that said solid body is substantially shaped like a frustum that converges toward the inside of said grinding chamber.

8. The mill according to one or more of the preceding claims, characterized in that said solid body is substantially shaped like a cylinder.

9. The mill according to one or more of the preceding claims, characterized in that said solid body is substantially as tall as said grinding chamber.

10. The mill according to one or more of the preceding claims, characterized in that said fixed axis is substantially vertical.

11. The mill according to one or more of the preceding claims, characterized in that said fixed axis is substantially horizontal.

12. The mill according to one or more of the preceding claims, characterized in that said grinding chamber comprises an opening for introducing the material to be ground, which is formed proximate to the bottom of said compartment, and an opening for discharging the ground material, which is formed proximate to the top of said compartment.

13. The mill according to one or more of the preceding claims, characterized in that it comprises means for adjusting the elevation of said discharge opening.

14. The mill according to one or more of the preceding claims, characterized in that said means for adjusting the elevation of said discharge port comprise a flange, which is arranged so as to close an opening formed in the walls of said grinding chamber and in which there is a slot that forms said discharge opening, the elevation of said slot being adjustable or said flange being arrangeable with various orientations.

15. The mill according to one or more of the preceding claims, characterized in that said means for adjusting the elevation of said discharge opening comprise an opening that is formed in the walls of said grinding chamber and with which a closure system with an upward-moving gate is associated.

16. The mill according to one or more of the preceding claims, characterized in that said means for adjusting the elevation of said discharge opening comprise a plurality of holes, which are formed in the walls of said grinding chamber at various elevations and form respective discharge openings, each one of said holes being associated with a respective cock that can be opened and closed selectively.

17. The mill according to one or more of the preceding claims, characterized in that it comprises mass balancing means associated with said actuation means.

18. The mill according to one or more of the preceding claims, characterized in that said balancing means are adjustable in terms of weight and/or position according to the masses to be balanced.

19. The mill according to one or more of the preceding claims, characterized in that said balancing means comprise a counterweight for said grinding chamber.

20. The mill according to one or more of the preceding claims, characterized in that it comprises means for conditioning said grinding chamber.

21. The mill according to one or more of the preceding claims, characterized in that said conditioning means comprise an interspace, which is formed at least at the walls of said grinding chamber that delimit said compartment and is associated with a circuit of a conditioning fluid.

22. The mill according to one or more of the preceding claims, characterized in that said circuit comprises at least one duct for introducing said fluid into said interspace, at least one duct for discharging said fluid from said interspace, a heat exchanger that is interposed between said discharge duct and said intake duct, and means for feeding said fluid from said heat exchanger to said intake duct.

23. The mill according to one or more of the preceding claims, characterized in that it comprises a lining of the internal walls of said grinding chamber and/or of said external surface of said solid body.

24. The mill according to one or more of the preceding claims, characterized in that each one of said first and second articulation means comprises a respective articulation shaft, in which one end is associated with the grinding chamber at the respective end of said longitudinal axis and the opposite end is articulated by means of a spherical joint respectively to said frame and to said actuation means.

25. The mill according to one or more of the preceding claims, characterized in that said actuation means comprise a driving shaft that forms said fixed axis, a plate that is rigidly coupled to said driving shaft, and means for guiding the articulation shaft of said second articulation means, which are formed in said plate, are eccentric with respect to said driving shaft and are suitable to make the corresponding end of said longitudinal axis trace a substantially circular orbit about said fixed axis.

26. The mill according to one or more of the preceding claims, characterized in that it comprises means for adjusting the radius of said orbit, which are associated with said guiding means.

27. The mill according to one or more of the preceding claims, characterized in that said guiding means comprise a substantially straight guide, which is formed in said plate and with which a sliding block is associated so that it can slide, said sliding block being rigidly coupled to said second articulation means.

28. The mill according to one or more of the preceding claims, characterized in that it comprises rotary coupling means interposed between said second articulation means and said sliding block.

29. The mill according to one or more of the preceding claims, characterized in that said adjustment means comprise a linear actuator, which is substantially parallel to said substantially straight guide and has an end that is rigidly coupled to said plate and an opposite end that is rigidly coupled to said sliding block.

30. The mill according to one or more of the preceding claims, characterized in that said counterweight is rigidly coupled to said plate and is arranged opposite said guiding means with respect to said fixed axis.

31. The mill according to one or more of the preceding claims, characterized in that it comprises means for stabilizing said motion of said grinding chamber, which are suitable to prevent its rotation about said longitudinal axis.

32. The mill according to one or more of the preceding claims, characterized in that said stabilizing means comprise an articulated system, which is associated with said frame and said grinding chamber.