Patent Application
20190308199
The present invention relates to a milling device that can implement a milling operation allowing the milling parameters to be adjusted and that allows a high throughput of the milled material.
In conventional oscillating mills, the material to be milled is milled between a rotating rotor and a screen. The desired properties of the comminuted material, such as particle size and particle flow velocity, can be obtained by appropriately selecting the appropriate milling parameters, such as the rotational speed of the rotor and/or the amplitude of oscillation and frequency in the case where the rotor is oscillating. Proper selection of the appropriate milling parameters is also critical to avoid a significant increase in temperature which could be detrimental to the quality of the crushed material. During most milling operations, however, it can be difficult to choose the parameters that are appropriate during the entire milling operation. Indeed, during milling, the material can modify its properties, for example due to the high temperature and/or humidity, which makes the milling parameters insufficient. In order to obtain an acceptable and uniform particle size of the crushed material, it is necessary to modify the milling parameters during the milling operation. Another problem is to obtain a high throughput of the crushed material.
The present invention relates to a milling device for carrying out a milling operation, comprising:
a milling unit including a body comprising a milling chamber, which can be filled with a material to be milled, a rotor rotatably mounted around a shaft in the body, a screen, and a drive unit controlling the movements the rotor with respect to the screen during the milling operation;
wherein the drive unit is designed to impart an oscillation movement to the rotor around the shaft, the oscillation angle being variable during the milling operation; and
wherein the milling chamber is configured to direct the product to be milled in a direction substantially parallel to the rotation shaft of the rotor.
The milling device of the invention makes it possible to implement a milling operation in which it is possible to adjust the milling parameters, while allowing a high throughput rate of the crushed material.
Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which:
The material to be ground can be introduced into the upper milling chamber 20 via an inlet 32. During the milling operation, the material is crushed by the combined action of the rotor 4 and the screen 21, and the crushed material which has passed through the screen 21 leaves the milling unit 2 through an outlet 33 (from below).
The milling device 1 comprises a transmission element 61 comprising a milling shaft 6 on which the rotor 4 is mounted. The transmission element 61 is configured to transmit the drive of the drive unit 60 to the milling shaft 6.
According to a preferred form, the transmission element 61 comprises a transmission joint 62 for driving the milling shaft 6 via a transmission shaft 63, substantially orthogonal to the milling shaft 6. The milling shaft 6 is mounted in a milling shaft bearing 64 and the transmission shaft 63 is mounted in a transmission bearing 65.
The transmission element 61 can also be configured to drive the rotor 4 directly from the top or the bottom, i.e. to provide a functional connection according to the orientation of the rotation shaft 5 of the rotor 4 (direct transmission).
Advantageously, the transmission element 61 also comprises a connection unit 30 for functionally connecting the milling unit 2 to the drive unit 60, via the transmission element 61. The connection unit 30 is configured to enable the transmission element 61 to be removably connected to the drive unit 60. The connection of the transmission element 61 to the drive unit 60 may include a “tri-clamp” type collar or other suitable quick connect system.
When the milling unit 2 is connected to the drive unit 60, via the transmission element 61 and the connection unit 30, the drive unit 60 drives the milling shaft 6 in rotation around the shaft 5. The movements of the rotor 4 with respect to the screen 21 can be controlled so as to carry out the milling operation, i.e. to allow the splitting of the material to be crushed by the combined action of the rotor 4 and the screen 21, according to desired milling specifications.
The milling chamber 2, configured so that the material flows from top to bottom (between the inlet 32 and the outlet 33) in a direction substantially parallel to the rotation shaft 5 of the rotor 4 makes it possible to take advantage of gravity and increase the flow rate of the ground material as compared to a device in which the rotor and the screen are oriented horizontally. The flow rate of the milled material is also increased by the larger area of the concentric screen 21 as compared to to a screen placed under a rotor rotating along a horizontally oriented axis.
In one embodiment, the connection unit 30 includes an adapter module 31 configured to match the characteristics of the drive unit 60 to the needs of the milling unit 2 operably connected to the drive unit 60. It is thus possible to functionally connect different milling units 2 depending on the milling process that one wishes to carry out. One advantage of the connection unit 30 is that a single drive unit 60 can be used for a plurality of milling chambers 2, reducing the costs of the equipment.
The throughput rate of the material to be crushed entering the milling chamber 2 can be regulated by the addition of a metering system (not shown). The flow rate can also be changed by driving the material through an air flow (not shown).
A protective air flow 50 may be injected along the rotor shaft 5, directed towards the rotor 4 so as to prevent infiltration of the material to be crushed into the transmission element 61 and to avoid a risk of overheating of the transmission element 61 and of the rotor 4.
The drive unit 60 and/or the transmission element 61 may incorporate a cooling system to enable heat sensitive materials to be processed.
The milling device 1 can be adapted for cryogenic milling or vacuum milling. The milling device 1 can be used under an inert atmosphere to make it possible to treat explosive products.
The screen 21 may consist of a filtering portion 25 and of a support portion 26. The support portion 26 is provided with large openings 27 through which the milled material passes through the filter portion 25 during the milling operation. The support portion 26 may consist of a thick and solid element, ensuring a certain rigidity to the screen 21. The filtering portion 25 may be composed of thin apertures to facilitate a fluid flow rate of the materials. The screen 21 may be made of a metal alloy material. Preferably, the filter portion 25 and the support portion 26 are integrally formed so that the screen 21 is formed integrally. Such a screen 21 makes it possible, as opposed to screens consisting of several bonded or welded elements, to prevent the powdery materials from intruding into cavities, between the filtering part 25 and the support part 26. The cylindrical screen 21 allows a larger milling surface.
The screen 21 may be coupled to a vibration generator (not shown) so as to facilitate the flow of the crushed material through the screen 21. The effect of the vibration prevents the material from agglomerating in the openings of the screen 21 during the milling operation, thus allowing a continuous flow of the milled material, without human intervention. Indeed, the vibrations generated by the vibration generator is transmitted to the filter portion 25 of the screen 21 in a very efficient manner. This causes an acceleration of the circulation of the crushed material, in particular to avoid the risk of stagnation of powdery materials. In this case, the screen 21 formed in one piece is advantageous since the latter is devoid of bonding or welding areas and does not risk being weakened by the vibrations exerted by the vibration generator.
A detailed view of the rotor 4 is shown in
Preferably, the disc 42 occupies substantially the entire surface under the screen 21 so as to direct the material to be ground on the sides, i.e. passing through the screen 21.
Advantageously, the disc 42 has a frustoconical shape so that the material to be ground is guided towards the milling zone, i.e. towards the blades 41 and the screen 21. In this way, the frustoconical shape of the disc 42 prevents the material to be ground from lying too long (in other words, avoids a retention zone of the material to be ground) in the region between the rotor bearing 40 and the blades 41.
In one embodiment, the movement of the rotor 4 relative to the screen 21 comprises a rotation motion around the shaft 5. The rotational speed of the rotor 4 can be varied, for example, according to the milling method, the type of rotor 4 and/or of screen 21 and the material to be ground. The rotational speed of the rotor 4 can also be varied during the milling process.
The movement of the rotor 4 relative to the screen 21 also comprises an oscillation movement with an oscillation frequency that can be varied during the milling operation. In particular, the rotor 4 can be pivoted in one direction or the other with respect to the screen 21. The oscillation movement can occur with a predetermined oscillation angle (i.e. with a predetermined oscillation amplitude).
The predetermined oscillation angle can have a value between 0 and 360°. The predetermined oscillation angle may also correspond to several complete turns in the same direction.
The rotor can oscillate with an oscillation frequency between 0 and 4 Hz. The oscillation frequency can be varied during the milling operation. In a variant embodiment, a vibratory movement of the rotor 4 can be obtained when the latter is oscillated with an oscillation frequency of less than about 2°.
The movement of the rotor 4 relative to the screen 21 can also comprise an offset of the oscillation angle during the milling operation, for example at each oscillation of the oscillation movement of the rotor 4. Such an offset of the oscillation angle means that the angular position of the rotor 4 is shifted by the offset value of the oscillation angle after completion of one oscillation cycle (one oscillation motion). The offset of the oscillation angle can be between 0 and 90°. The offset of the oscillation angle can be varied during the milling operation.
According to one variant, not illustrated, the drive unit 60 may comprise a controller configured so as to determine milling parameters on the basis of signals supplied by a sensor. The parameters determined by the controller can then be used to control the drive unit 60 so as to drive the rotor 4 according to the determined parameters. In this way, the milling operation can be optimized depending on the material to be ground and the milling conditions, which are measured by the sensor. The movements of the rotor 4 can therefore be controlled in real time during the milling operation.
The movements of the rotor 4 relative to the screen 21 described above can be adjusted according to the milling parameters determined by the controller on the basis of the signals supplied by the sensor.
In the example of
According to a non-illustrated embodiment, a first longitudinal face 43 of the blade 41 has a profile which differs from a second longitudinal face 44 opposite to the first face 43. In this configuration, when the rotor 4 rotates in one direction, one of the first or second face 43, 44 corresponds to the leading edge, i.e. the side of the blade 41 which faces the material during the rotation of the rotor 4. When the rotor 4 rotates in the opposite direction, the other face 44, 43 corresponds to the leading edge. In this way, it is possible to carry out two different milling processes according to the direction of rotation of the rotor 4.
According to another embodiment, the blades 41 are configured to exert a thrust of the material towards the screen 21. This type of configuration of the blades 41 is particularly suitable when the rotor rotates at low speed, for example, when the rotor speed 4 is between 0 and 200 rpm. An example of such a configuration is shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 00820/16 | Jun 2016 | CH | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2017/053753 | 6/23/2017 | WO | 00 |
