EP2908954B1

EP2908954B1 - Impact mill for grinding loose material

Info

Publication number: EP2908954B1
Application number: EP13801771.0A
Authority: EP
Inventors: Gabriele Marchetti
Original assignee: Individual
Current assignee: MARCHETTI, STEFANO; PISANI, GIUSEPPE
Priority date: 2012-09-24
Filing date: 2013-09-23
Publication date: 2019-11-13
Anticipated expiration: 2033-09-23
Also published as: EP2908954A1; WO2014045255A1; ITMO20120230A1; EP2908954B8

Description

Technical Field

The present invention relates to an impact mill for grinding loose material.

Background Art

Impact mills for grinding loose material generally comprise a main rotor moving in rotation around a relative axis and having one or more hammers suitable for crushing the incoming material. The impact mills of known type also have a secondary rotor fitted with a plurality of blades suitable for sending the material to be ground towards the main rotor. The main rotor and the secondary rotor are arranged inside a grinding chamber and an inlet chamber respectively, communicating with one another.
The main rotor has a cylinder-shaped central core extending around the rotation axis and to which the crushing hammers are associated integral. More in particular, the crushing hammers have a portion exiting from the central core and which is suitable for impacting the material to be ground and a portion which is instead contained inside the base core to permit its being fastened to same.
The mills of known type can be classified as horizontal-axis mills or vertical-axis mills, depending on the spatial arrangement of the rotation axis of the main rotor. Examples of vertical-axis mills are disclosed in WO-2011/033345-A1 The present invention relates in particular to horizontal-axis mills. Two examples of horizontal-axis impact mills are described in WO2002022269 and in WO2008105019 , in both of which the secondary rotor is arranged above the main rotor and turns around a relevant axis arranged substantially parallel to the rotation axis of the main rotor itself.
In both these impact mills, the material to be ground is introduced inside the inlet chamber in correspondence to the upper extremity of same.
A drawback of this type of mill is tied to the fact that the blades of the secondary rotor tend to seize up in correspondence to the inlet area of the material to be ground. The material arriving from the introduction pipe builds up in fact by gravity in this area and interposes, during blade rotation, between the blades themselves and the side wall of the inlet chamber.
This drawback causes fast blade wear, due to the rubbing action of the blades on the material so interposed. The direct consequence of such blade wear is an inefficient distribution of the material to be crushed inside the grinding chamber, inasmuch as a part of such material manages to bypass the blades and ends up directly in the grinding chamber thus losing the synchronism with the hammers.
In the event of the material to be ground being in large pieces, the interposition of the same between the blades of the secondary rotor and the side wall of the inlet chamber can even cause the breakage of the blades themselves or of the transmission parts that drive them due to the resistance produced by the material so interposed.
Yet another drawback of this type of known mills consists in the difficult performance of the maintenance operations of the secondary rotor, which consequently implies high costs and long machine down times.
Furthermore, the conformation of the secondary rotor and of the relative inlet chamber of the mills of known type allows only small quantities of material to be worked at a time, thus preventing the complete exploitation of the volumetric capacity of the inlet chamber itself.
Yet another drawback of the known mills consists in the considerable waste of material related to the wear of the crushing hammers. In fact, once their portion protruding towards the outside of the base core becomes worn, the hammer must be replaced in its entirety, and consequently the portion contained inside the base core cannot be exploited for the grinding process.
JP-S57-9340U discloses a mill according to the preamble of claim 1.

Description of the Invention

The main aim of the present invention is to provide an impact mill which allows to overcome the drawbacks of the prior art.
In particular, the present invention intends increasing the grinding efficiency while at the same time reducing energy consumption compared to mills of known type.
Within this aim, one object of the present invention is to reduce the wear of the moving parts, and in particular of the blades of the secondary rotor.
Another object is to increase, with respect to mills of known type, the exploitation of the internal volume of the inlet chamber so as to allow working a larger quantity of material in the unit of time.
Yet another object of the present invention is to reduce the overall dimensions of the mill, grinding capacity being equal.
Not the last object of the present invention is to reduce material waste with respect to mills of known type, in particular by increasing the portion of the crushing hammers exploitable during the grinding process.
Another object of the present invention is to provide an impact mill for grinding loose material which allows overcoming the mentioned drawbacks of the state of the art within the ambit of a simple, rational, easy, effective to use and low cost solution.
The above mentioned objects are achieved by the present breaking impact mill for grinding loose material according to claim 1.

Brief Description of the Drawings

Other characteristics and advantages of the present invention will become more evident from the description of a preferred, but not sole, embodiment of an impact mill for grinding loose material, illustrated purely as an example but not limited to the annexed drawings in which:

Figure 1 is an axonometric view of a mill according to the invention in a first embodiment;
Figure 2 is an axonometric section view of the mill of figure 1;
Figure 3 is a side elevation section view of a mill according to the invention in a second embodiment.

Embodiments of the Invention

With particular reference to such figures, globally indicated by 1 is an impact mill for grinding loose material.
The mill 1 comprises at least a main rotor 2 arranged mobile in rotation around a first axis 3 inside a grinding chamber 4.
More in detail, the grinding chamber 4 is delimited by two side walls 4a, arranged transversally with respect to the first axis 3 on opposite sides with respect to the main rotor 2, and by at least one connection wall 4b interposed between the side walls 4a and configured so as to surround at least in part the main rotor itself. The connection wall 4b therefore extends around the first axis 3.
The main rotor 2 comprises, as shown in the figures 2 and 3, at least two crushing elements 5 suitable for impacting the material to be ground. Alternative embodiments cannot however be ruled out wherein the main rotor comprises a larger number of crushing elements 5.
Each crushing element 5 is in practice made up of a relative plate made of antiwear material and associated integral, e.g., by means of threaded means, with a base core 6.
More in particular, each crushing element 5 has a front face turned towards the outside and intended to impact the material and a rear face associated with the base core 6.
The base core 6 is in turn associated integral with a movement transmission shaft, not visible in detail in the illustrations, which can be operated in rotation around the first axis 3 according to procedures known to the technician in the sector.
Preferably, the base core 6 has at least a linking surface 7, curvilinear and convex, placed between two consecutive crushing elements 5. In particular, the linking surface 7 corresponds to the portion of a cylindrical surface misaligned with respect to the first axis 3. More in detail, in the embodiment shown in the illustrations, wherein the main rotor comprises two crushing elements 5 arranged on opposite sides with respect to the first axis 3, the base core 6 has two linking surfaces 7. Each of such linking surfaces 7 has an extremity arranged in correspondence to the front face of a crushing element 5 and the opposite extremity arranged in correspondence to the rear face of the other crushing element 5. This conformation of the main rotor 2 is not however limitative, and consequently alternative embodiments cannot be ruled out which do not provide for the presence of the linking surfaces 7 or which provide for connection surfaces having only some of the aforementioned characteristics.
In the preferred embodiments shown in the illustrations, the connection wall 4b has, at least in correspondence to the upper portion of the grinding chamber 4, a plurality of impact surfaces 8 sloped the one to the other and turned towards the inside of the grinding chamber itself.
Such impact surfaces 8 are sloped in such a way as to define a plurality of protrusions and recesses consecutive and alternated to each other.
Preferably, at least one recess made up of two consecutive impact surfaces 8 defines an angle α between 80° and 110°, preferably between 90° and 110°. This occurs in particular for the impact surfaces 8 which are involved in the crushing process, i.e., those arranged in correspondence to the upper portion of the grinding chamber 4.
At least one protrusion made up of two consecutive impact surfaces 8 defines an angle β between 210° and 240°.
More in detail, the angle of inclination of the impact surfaces 8 and the speed of rotation of the main rotor 2 are such that the material struck by one of the crushing elements 5 is thrown against one of such impact surfaces 8 following the collision, whereby it is repelled and again struck by the other crushing element 5 which directs it towards another impact surface 8. This way, the material to be ground is in practice "rebounded" between the impact surfaces 8 and the crushing elements 5, and this results in particularly effective crushing. The grinding chamber 4 also has an unloading area 9 accessible from outside to pick up the ground material.
The mill 1 then also comprises a secondary rotor 10 arranged mobile in rotation around a second axis 11 inside an inlet chamber 12 communicating with the grinding chamber 4.
The inlet chamber 12 is also delimited by two side walls 12a arranged transversally to the second axis 11 on opposite sides with respect to the secondary rotor 10 and by at least a connection wall 12b placed between the side walls 12a to surround at least in part the secondary rotor itself. Preferably, the connection wall 12b that surrounds at least in part the secondary rotor 10 has a substantially circular extension.
The first and the second axis 3 and 11 are substantially horizontal and are arranged substantially parallel to one another.
Preferably, the inlet chamber 12 is arranged laterally with respect to the grinding chamber 4. More in detail, the inlet chamber 12 is arranged outside the vertical projection of the grinding chamber 4. This arrangement allows optimizing grinding efficiency because the working stroke of the main rotor 2, i.e., the stroke during which it is active in the material crushing process, is maximized. Alternative embodiments cannot however be ruled out wherein the inlet chamber 12 is arranged, in part or in whole, above the grinding chamber 4. According to the invention, the inlet chamber 12 has an inlet gap 13 of the material to be ground which is arranged on at least one of the side walls 12a.
The inlet gap 13 is arranged along the second axis 11.
In the preferred, but not exclusive, embodiments shown in the illustrations, the inlet chamber 12 has just one inlet gap 13 defined on one of the side walls 12a, the other side wall 12a being connected to the shaft transmitting movement to the secondary rotor 10. In the embodiment of figure 3, the inlet gap 13 has a substantially circular shape and misaligned with respect to the second axis 11. The secondary rotor 10 comprises a base plate 14 substantially facing the inlet gap 13 and which which are associated integral in rotation a plurality of throw elements 15 of the material to be ground.
The throw elements 15 extend starting from the perimeter edge of the base plate 14 towards the second axis 11.
More in detail, the throw elements 15 have an extremity arranged in correspondence to the perimeter edge of the base plate 14 and the opposite extremity spaced from the second axis 11 so as to define a receiving area 16 of the material to be ground, arriving from the inlet gap 13, free and without protrusions. The throw elements 15 are therefore arranged around such receiving area 16, the latter being arranged in correspondence to the central portion of the base plate 14.
In the embodiment shown in the illustrations, the base plate 14 has a substantially circular shape, the throw elements 15 have a substantially radial extension and are spaced radially from the second axis 11. More in detail, in the embodiments shown in the illustrations, the secondary rotor 10 has two throw elements 15 arranged on diametrically opposite sides of the base plate 14. Alternative embodiments cannot however be ruled out comprising a larger number of crushing elements 15.
The grinding chamber 4 and the inlet chamber 12 communicate with each other by means of a connection gap 17 defined on the respective connection walls 4a and 12a. The connection gap 17 is arranged in such a way that the material sent by the secondary rotor 10 is directed towards the lower portion of the grinding chamber 4.
The inlet chamber 12 also has a collection area 18 of the material to be ground entering from the inlet gap 13.
The collection area 18 is arranged at a lower height than the receiving area 16 and the connection gap 17. Suitably, the direction of rotation of the secondary rotor 10, the arrangement of the collection area 18 and of the connection gap 17 are such that the stroke completed by the throw elements 15 to send the material to be ground from the collection area 18 to the connection gap 17 is greater than the stroke completed by the secondary rotor itself to return from the latter gap to the collection area.
In the preferred but not exclusive embodiment shown in the illustrations, the inlet chamber 12 also comprises a sending channel 19 for the material. Such sending channel 19 comprises the connection gap 17 and is delimited by at least a sending wall 20 substantially tangential to the peripheral edge of the trajectory covered by the throw elements 15 and sloped with respect to a horizontal direction. The inclination of the sending wall 20 with respect to a horizontal direction substantially corresponds to the direction of sending of the material in the grinding chamber 4. Preferably, the sending wall 20 is sloped with respect to a horizontal direction by an angle between 1° and 90°, preferably between 20° and 40°.
More in detail, the throw elements 15 convey the material to be ground towards the connection gap 17 during their rotation around the second axis 11 and throw it inside the grinding chamber 4. The main rotor 2 and the secondary rotor 10 are synchronized together so that the material to be ground substantially impacts in a perpendicular way the front face of the crushing elements 5 upon their transit.
Advantageously, in an embodiment not shown in the illustrations, the mill 1 can comprise two main rotors 2 and two secondary rotors 10.
More in particular, the two main rotors 2 are mobile to each other in rotation around the first axis 3 in the same direction and with the same angular speed. The two main rotors 2 can be associated with the same movement transmission shaft or with two distinct shafts. Furthermore, each of the two main rotors 2 comprises two crushing elements 5 arranged diametrically opposite one another, where the crushing elements 5 of one of such main rotors 2 are angularly staggered with respect to the crushing elements 5 of the other main rotor 2.
In the same way, the two secondary rotors 10 are both mobile in rotation around the second axis 11 in the same direction and with the same angular speed. The two secondary rotors 10 can also be associated with the same movement transmission shaft or with two distinct shafts. Furthermore, each of the two secondary rotors 10 comprises two throw elements 15 arranged diametrically opposite one another, where the throw elements 15 of one of such secondary rotors 10 are angularly staggered with respect to the throw elements 15 of the other secondary rotor 10. Again, in this embodiment, each secondary rotor 10 is arranged inside a relative inlet chamber 12 having, in turn, a relative inlet gap 13 of the material to be ground.
Each secondary rotor 10 is therefore suitable for sending the material to be ground towards a respective main rotor 2. The staggering of the main rotors 2 and of the secondary rotors 10 allows considerably increasing the productivity of the mill 1 with respect to the presence of a single main rotor-secondary rotor pair.
More in particular, the stagger angle of the main rotors 2 and of the secondary rotors 10 depends on the number of crushing elements 5 and of throw elements 15 with which they are respectively equipped. For example, in the case of the main rotors 2 and of the secondary rotors 10 being equipped with two crushing elements 5 and with two throw elements 15 respectively, these will be respectively staggered by 90°.
The operation of the mill according to the invention is the following.
The material to be ground which is introduced through the inlet gap 13 reaches the receiving area 16 and, falling by gravity, arranges itself in the collection area 18 arranged in the lower part of the inlet chamber 12.
The material to be ground therefore arranges itself resting against the connection wall 12b of the inlet chamber 12.
During its rotation movement around the second axis 11, by means of the throw elements 15, the secondary rotor 10 drags the material to be ground from the collection area 18 towards the sending channel 19.
The material to be ground is then pushed by the throw elements 15 along a direction substantially parallel to the sending wall 20 and enters the grinding chamber 4 passing through the connection gap 17.
Once it has reached the grinding chamber 4, the material to be ground is struck by one of the crushing elements 5 of the main rotor 2 which turns in the same direction as the secondary rotor 10.
Following the collision with the crushing element 5, the material to be ground strikes one of the impact surfaces 8 of the connection wall 4b, becoming further broken up. The inclination of the impact surfaces 8 results in the material thus broken up being pushed away towards the main rotor 2 so as to strike the other crushing element 5 which has meanwhile completed half a revolution. This way the material to be ground impacts the crushing elements 5 several times before reaching the unloading area 9.
It has in practice been ascertained how the described invention achieves the proposed objects and in particular the fact is underlined that the claimed arrangement of the inlet gap permits preventing the material introduced into the inlet chamber from positioning itself between the throw elements and the connection wall of the inlet chamber. The result is therefore considerably less wear of the throw elements compared to mills of known type and a more efficient launching of the material to be crushed inside the grinding chamber. This particular conformation in fact allows reducing the vertical overall dimensions of the mill with respect to those of known type and, at the same time, maintaining the parallelism between the rotation axes of rotors, so the direction of launch of the material to be ground is substantially perpendicular to the impact surface of the crushing elements.
Furthermore, the structure of the secondary rotor allows optimizing the volumetric capacity of the inlet chamber and, therefore, conveying a larger quantity of material per unit of time into the grinding chamber compared to mills of known type.
Again, the inclination of the surfaces of the connection wall of the grinding chamber allows obtaining a very efficient reduction of the grain size of the material, inasmuch as the latter is repeatedly struck by the crushing elements before reaching the unloading area of the mill itself.
Finally, the particular conformation of the main rotor permits fully exploiting the thickness of the crushing elements, thus reducing material wastes and machine down times.

Claims

An impact mill (1) for grinding loose material, comprising:
- at least a main rotor (2) moving in rotation around a first axis (3) inside a grinding chamber (4);

- at least a secondary rotor (10) moving in rotation around a second axis (11) inside an inlet chamber (12) of the material to be ground communicating with said grinding chamber (4), said secondary rotor (10) being suitable for sending the material to be ground inside said grinding chamber (4);

- said inlet chamber (12) and said grinding chamber (4) being delimited by at least two respective side walls (4a, 12a) arranged substantially transversal to said first and second axes (3, 11), respectively and by at least a connection wall (4b, 12b) placed between the respective side walls (4a, 12a) to surround at least in part the relative rotor (2, 10), said first and second axes (3, 11) being arranged substantially horizontally and parallel to one another;
characterised by the fact that said inlet chamber (12) has an inlet gap (13) of the material to be ground defined on at least one of said side walls (12a),
by the fact that said inlet gap (13) is arranged along said second axis (11) of rotation,
by the fact that said secondary rotor (10) comprises a base plate (14) facing said inlet gap (13) and with which are associated integral a plurality of throw elements (15) for throwing the material to be ground, where said throw elements (15) extend starting from the perimeter edge of said base plate (14) towards said second axis (11) and are spaced from the latter so as to delimit a receiving area (16) of the material to be ground, arriving from the inlet gap (13), free and without protrusions, substantially facing said inlet gap (13), said receiving area (16) being arranged in correspondence to the central portion of the base plate (14),
by the fact that said inlet chamber (12) and said grinding chamber (4) communicate with each other by means of a connection gap (17) defined on the respective connection walls (4b, 12b), said connection gap (17) being arranged so that the material sent by said secondary rotor (10) is directed towards the lower portion of said grinding chamber (4), said main rotor (2) and said secondary rotor (10) being synchronized together so that the material to be ground substantially impacts in a perpendicular way the front face of said crushing elements (5) upon their transit,
and by the fact that said inlet chamber (12) has a collection area (18) of the material to be ground entering from said inlet gap (13), said collection area (18) being arranged at a lower height than said receiving area (16) and said connection gap (17).
Mill (1) according to claim 1, characterised by the fact that said inlet chamber (12) comprises at least a sending channel (19) of the material defining said connection gap (17), said sending channel (19) being delimited by at least one sending wall (20) substantially tangential to the edge of the trajectory covered by said throw elements (15) and sloped with respect to a horizontal direction.
Mill (1) according to claim 2, characterised by the fact that said sending wall (20) is sloped with respect to a horizontal direction by an angle between 20° and 40°.
Mill (1) according to one or more of the preceding claims, characterised by the fact that said throw elements (15) are suitable for conveying the material to be ground towards said connection gap (17) during their rotation around said second axis (11) and for throwing it inside said grinding chamber (4) and by the fact that said secondary rotor (10) and said main rotor (2) turn in a concurrent direction and are synchronised together so that the material to be ground impacts in a substantially perpendicular way on the surface of said crushing elements (5) upon their transit.
Mill (1) according to one or more of the preceding claims, characterised by the fact that the connection wall (4b) of said grinding chamber (4) has, at least in correspondence to the upper portion of the grinding chamber itself, a plurality of impact surfaces (8) sloped with respect to one another so as to define a plurality of protrusions and recesses which are consecutive and alternated to each other.
Mill (1) according to claim 5, characterized by the fact that said impact surfaces (8) are substantially flat and sloped with respect to one another so as to define at least a protrusion with an angle between 80° and 110° and at least a recess with an angle between 210° and 240°.
Mill (1) according to one or more of the preceding claims, characterised by the fact that said main rotor (2) comprises a plurality of crushing elements (5) intended to impact the material sent by said secondary rotor (10).
Mill (1) according to one or more of the preceding claims, characterised by the fact that said main rotor (2) comprises at least a linking surface (7) placed between two of said consecutive crushing elements (5), said linking surface (7) being convex and curvilinear.
Mill (1) according to claim 8, characterized by the fact that said linking surface (7) has a substantially circular extension and is misaligned with respect to said first axis (3).
Mill (1) according to one or more of the preceding claims, characterised by the fact that it comprises at least two of said main rotors (2) having substantially the same first axis (3) of rotation and the crushing elements (5) of which are staggered to each other and at least two of said secondary rotors (10) having substantially the same second axis (3) of rotation and the throw elements (15) of which are staggered to each other, each of said secondary rotors (10) being suitable for sending the material to be ground towards a respective main rotor (2).