EP4371669A1 - Agitator mill with basket with thickening - Google Patents

Abstract

Agitator mill with a grinding chamber containing grinding bodies and an agitator shaft rotating therein about a horizontal agitator shaft axis, which carries a plurality of grinding elements, preferably in the form of grinding disks, which are connected to it in a rotationally fixed manner and are spaced apart from one another in the direction of the horizontal axis and which move the grinding bodies, wherein the agitator shaft has a basket on the outlet side which is preferably equipped with grinding elements on its outer circumference and which overlaps the outlet carrying the gap tube, characterized in that the basket has a section with an enlarged outer diameter in the region of its free end.

Description

The invention relates to an agitator mill with a basket with a thickening according to the preamble of claim 1 and the corresponding basket according to the preamble of claim 9.

TECHNICAL BACKGROUND

The basic principle of a stirred mill will first be explained using the Fig.1 be explained.

In Fig.1 1 schematically shows an agitator mill 1 with a horizontal agitator shaft 3. The grinding bodies in the grinding container 16, which are usually designed as steel or ceramic balls, have been omitted.

When the agitator mill 1 is in operation, the material to be ground is pumped into or through the grinding chamber 2 enclosed by the grinding container 16 via the inlet 17 of the agitator mill 1. In the case of wet grinding, the material to be ground is a suspension or dispersion of a liquid, usually in the form of water, and solids. In other cases, such an agitator mill 1 can also be used for dry grinding. It can then be designed as an agitator mill with a vertical shaft, for example, through which the material to be ground is carried by a gaseous fluid, usually in a falling stream.

The present invention relates in its broadest aspect to both types of agitator mills. It is particularly preferred for use in agitator mills with a horizontal agitator shaft 3.

The grinding elements 5, which are connected to the agitator shaft 3 in a rotationally fixed manner and are often also designed and referred to as grinding disks, are set in rotation by a rotational movement of the agitator shaft 3. It is also possible, also within the scope of the invention to be described immediately, to design the grinding elements 5 in the form of individual pins. To generate the rotational movement The agitator shaft 3 can be driven by an electric motor 101, for example, via a belt drive 102. The drive of the agitator mill 1 is usually located in a housing 103 adjacent to the grinding container 16.

Due to the rotation of the grinding elements 5, the grinding bodies located in the grinding chamber 2, which are located near the grinding elements 5, are carried along in the circumferential direction of the grinding container 16. In the middle area between two grinding elements 5, the moving grinding bodies flow back in the direction of the agitator shaft 3 as soon as they have reached the apex area. This creates a circulating movement of the grinding bodies between two grinding elements 5.

The movement of the grinding media causes collisions and rolling over between the solids of the grinding material suspension pumped through the grinding chamber 2 and the grinding media. These collisions and rolling over lead to the splintering of fine particles from the solids in the grinding material suspension, so that the solids arriving at the outlet 7 of the agitator mill 1 are ultimately significantly smaller than the solids fed in at the inlet 17.

In order to ensure that grinding media are not discharged from the grinding chamber 2, a sieve or preferably a sieve in the form of a gap tube 8 is usually installed in front of the outlet 7 and/or carried by the outlet 7, hereinafter referred to as the "gap tube". A basket 6 is installed around this gap tube 8 and encompasses this gap tube 8. The basket serves to prevent the grinding media, which tend to be pushed towards the gap tube by the pressure of the feed pump, exerting undesirable grinding media pressure on the gap tube.

The basket 6 is usually attached in a rotationally fixed manner to the free end of the agitator shaft 3 facing the outlet 7. It then rotates with the agitator shaft 3.

The area between the rotating basket 6 and the gap tube 8 forms the separation chamber 15, since here the material to be ground or the ground material suspension is separated from the grinding bodies and finally exits the agitator mill 1 via the gap tube 8 and the outlet 7.

As a rule, however, the basket 6 can only fulfil its function if grinding media that have entered the separation chamber 15 have the opportunity to get out of the separation chamber and back into the grinding chamber 2. Otherwise, the separation chamber 15 will soon be filled with grinding media and the grinding media will then block the gap tube 8 and possibly even cause it to wear out prematurely.

To prevent this, various openings 14 are provided in the basket 6. Through these openings 14, the grinding bodies can more easily pass from the separation chamber 15 into the grinding chamber 2. Fig.2 shows a basket 6 of a stirrer mill designed in this way, which served as a comparison object prior to the invention. Fig.2 the grinding media and/or grinding material flows, which have already been mentioned and which take place in the grinding container 16, are shown schematically. As can be seen, the basket 6 preferably also has grinding elements on its outer surface, which cause the grinding media to move or circle in the area between the basket and the inner wall of the grinding container 16. This circling of the grinding media makes it easier for the grinding media located in the separation chamber 15 to escape through the openings 14 back into the grinding chamber 2.

However, the inventors have found that even with the Fig.2 shown basket construction, there is still a certain tendency of the grinding media entering the separation chamber 15 to accumulate close to the gap tube 8 and block the gap tube 8 or even cause unnecessary wear. Both of these affect the separation performance of the gap tube 8. This tendency is indicated by the arrows in Fig.2 point in the direction of the gap tube 8, as indicated schematically. Grinding media can also be discharged from the separation chamber 15 through the openings 14; however, the tendency of the grinding media is to move towards the gap tube 8.

The DE 20 2009 011 656 U1 relates to a stirred mill for wet grinding, with a change of the product flow direction away from the drive, a grinding container which is Rotated by 180°, a central split tube that can be removed from the outside with a rotating centrifuge pot, and only one seal between the grinding chamber and the atmosphere.

The DE 100 64 828 A1 describes an agitator mill with an agitator and a grinding container arranged at a radial distance therefrom, wherein the grinding container and the agitator shaft delimit an annular cylindrical grinding chamber and a separating device arranged in the grinding container which retains auxiliary grinding bodies, wherein the separating device consists of several tubular sieves which are part of a rotating cage.

THE UNDERLYING TASK

In view of this, the object of the invention is to further improve the separation performance of the can.

THE INVENTIVE SOLUTION

According to the invention, this problem is solved with the features of the first main claim.

For this purpose, an agitator mill is assumed with a grinding chamber containing grinding elements and an agitator shaft rotating around a horizontal agitator shaft axis. The agitator shaft carries several grinding elements connected to it in a rotationally fixed manner and spaced apart from one another in the direction of the horizontal axis. These grinding elements are preferably designed in the form of grinding disks. When the agitator mill is in operation, they move the grinding elements described above.

The agitator shaft has a basket on the outlet side. This means that the basket preferably connects directly to the agitator shaft and is connected to it directly or indirectly. However, the agitator shaft and the basket are preferably not integrally formed with each other, which is why the agitator shaft and basket are two individual parts and the agitator shaft does not take on any direct tasks of the basket. In addition, the length of the basket is preferably no more than one third, particularly preferably no more than one quarter of the length of the agitator shaft.

The basket is preferably fitted with additional grinding elements on its outer circumference. As already mentioned, this not only allows an additional grinding effect to be achieved in the radial circumferential area between the outer circumference of the basket and the inner wall of the grinding container. Rather, this also creates the circular movement of the grinding elements that promotes the re-emergence of the grinding elements from the separation chamber. These grinding elements on the basket are preferably not designed like the grinding elements on the agitator shaft. While the grinding elements on the agitator shaft are preferably designed in the form of grinding disks, the grinding elements on the basket are preferably designed in the form of pins.

This basket overlaps the outlet at least partially during normal operation, with the outlet supporting the split tube. It is preferred that the basket overlaps the split tube along its entire length. In the context of these explanations, the "split tube" is preferably a tube with various slots and/or other-shaped openings in the narrower sense, but in the broader sense the term "split tube" includes any type of sieve body.

As explained in a previous section, this overlapping arrangement of the basket creates a free area between the inner surface of the basket and the outer surface of the outlet or the can supported by the outlet. This area is called the "separation space".

The agitator mill according to the invention is characterized in that the basket in question has a section with an enlarged outer diameter in the region of its free end facing away from the grinding chamber.

This "enlarged outer diameter" preferably represents an additional, A ring made integral with the basket, with which the outer diameter of the basket is enlarged in certain areas, while the outer diameter of the remaining area of the basket remains essentially constant. In a broader sense, however, the "enlarged outer diameter" also means an increasing outer diameter, i.e. an outer diameter of the basket that increases in sections or over the entire length of the basket. As a result, the entire basket or sections of the basket have an essentially truncated cone-shaped outer geometry, for example; with an outer diameter that increases - preferably continuously or even constantly - towards the free end of the basket.

This is based on the following insight of the inventors: The Fig.2 The entry area shown directly behind the free front surface of the basket, in which the flow flows in a predominantly horizontal direction to enter the separation space, forms a too pronounced bottleneck. The latter is because the Fig. 2 The basket shown forms a circumferentially closed ring structure in this area.

When flowing through the narrow section, the grinding media flow theoretically has a higher flow velocity, which is actually desirable. However, the grinding media are mainly carried along in the axial direction and also have only limited opportunities to leave the basket. As a result, the grinding media often collide with the basket and/or the gap tube, which slows them down considerably. In addition, the narrow section is often so narrow that some grinding media collide with themselves, the basket and/or the gap tube at the entrance to the separation chamber and thus initially lose kinetic energy.

When the grinding media finally reach the outer peripheral surface of the gap tube under the openings, they often have too little kinetic energy to escape the suction of the gap tube and use the openings to exit back into the grinding chamber. As a result, some of the grinding media come to a standstill and settle on the outer peripheral surface of the gap tube. This further reduces the grinding media dynamics. Under unfavorable circumstances, the gap tube is at risk of becoming blocked after a certain period of operation.

The "grinding chamber" referred to here is the space inside the grinding container that is located between the inlet and outlet and is filled with grinding media and/or grinding material or grinding material suspension and is not enclosed by the basket. The grinding chamber is thus essentially the interior of the grinding container minus the internals that penetrate it and minus the separation space.

This increased outer diameter according to the invention has the effect that the gap between the outer contour of the basket and the inner contour of the grinding container becomes narrower. This gap is usually flowed through turbulently, but ultimately axially, and the narrowing of this gap leads to an increased flow speed and/or to increasing turbulence. The grinding media and the material to be ground are thus carried along at this point at a higher speed and/or with higher turbulence and thus receive a higher kinetic energy. As a result, grinding media flow more dynamically or at a higher speed into the separation space between the basket and the gap tube, which means that the grinding media, despite the suction that the gap tube also exerts on them, are not sucked in or are only sucked in to a reduced extent so that they remain on the surface of the gap tube. Rather, more grinding media can resist the suction and are carried out of the separation space into the grinding space, preferably through the breakouts in the basket mentioned above.

A "jamming" of the grinding media and/or the material to be ground or the grinding material suspension at the entrance to the basket is reduced and the grinding media can, at least in part, enter the separation chamber much more easily and with greater dynamics. A desirable flow is then created there, whereby the grinding media are kept away from the gap tube and are led back through the slots from the separation chamber into the grinding chamber more quickly and/or more easily. As a result, the gap tube is blocked less and experiences less stress and/or less wear, because the grinding media are returned to the grinding chamber more quickly and/or in a way that is gentler on the gap tube. Essentially in the area in which the grinding media are directly introduced through the slots (especially in the area between the outer circumference of the basket and the inner wall of the grinding container), additional turbulence is created and the surrounding grinding media bed is activated.

In general, this allows an increased grinding effect of the agitator mill to be achieved, the gap tube experiences less wear during operation and fewer grinding media become stuck in or on the gap tube.

This allows the agitator mill to be operated at a higher throughput with an increased service life of the basket and less maintenance effort.

PREFERRED TRAINING

There are a number of ways to design the invention in such a way that its effectiveness or usefulness is further improved.

A preferred embodiment of the invention consists in that the region with the increased outer diameter extends directly to the free front end of the basket. This means that the increased flow velocity does not drop off too soon, since the grinding bodies preferably retain this increased kinetic energy up to the area of the separation chamber.

Furthermore, it is particularly preferred if the section with the enlarged outer diameter has a substantially or preferably completely smooth outer surface outside of the ramp possibly formed by it, wherein this smooth outer surface can be cut by webs and/or openings.

It is particularly advantageous if the agitator mill is characterized by the fact that the section with the enlarged external diameter, including the ramp it may form, only accounts for between 45% and 20%, or better still, between 30% and 25%, of the length of the basket in the direction of the agitator shaft axis. This prevents the enlarged external diameter from exerting too strong a throttling effect overall, i.e. increasing the flow resistance to such an extent that the aim of forming a flow that allows the grinding media to enter the separation chamber more dynamically than before is counteracted.

It is particularly advantageous if the section with the enlarged outer diameter has a smooth outer surface outside of the ramp it may form and outside of the grinding pins it supports. This also helps to avoid excessively increasing the flow resistance.

Ideally, the section with the enlarged outer diameter has grinding elements on its circumferential surface, preferably in the form of grinding rods, ideally in the form of at least one ring of grinding rods arranged one behind the other in the circumferential direction. Such grinding rods help to increase the grinding media dynamics in the sense that grinding media can escape from the grinding chamber more easily. In this respect, grinding rods have the great advantage over grinding disks in that they do not increase the flow resistance excessively.

FIGURE LIST

• The Fig.1 shows a state-of-the-art agitator mill from a sectional side view.
• The Fig.2 shows the grinding container of an agitator mill from a sectioned side view, whereby the basket has openings according to in-house considerations.
• The Fig.3 shows a first embodiment of the basket according to the invention in side view.
• The Fig.4 shows the embodiment of the basket according to the invention from Fig.3 in three-dimensional view.
• The Fig.5 shows a second embodiment of the basket according to the invention in side view.
• The Fig.6 shows the embodiment of the basket according to the invention from Fig.5 in three-dimensional view.
• The Fig.7 shows the grinding container of an agitator mill from a sectional side view with a third embodiment of the basket according to the invention.

PREFERRED EMBODIMENTS

First show Fig. 3 and Fig. 4 a first preferred embodiment of the basket 6 according to the invention in different views.

The basket 6 is provided on its outer circumference with additional grinding elements 11 which are arranged in the form of pins in horizontal rows running parallel to the agitator shaft axis 4 and regularly around the circumference of the basket 6.

The basket 6 also comprises several openings 14, already mentioned at the beginning, through which grinding bodies can be discharged from the separation chamber into the grinding chamber. This embodiment of the basket 6 has a preferred section 10 with an enlarged outer diameter, whereby this section 10 is formed integrally with the basket 6 at its free end 9 and extends up to the front side of the free end 9 of the basket 6. The section 10 with an enlarged outer diameter preferably has a ramp 12 which leads from the outer diameter of the basket 6, which is essentially constant in some areas, to the outer diameter of the section 10, which is essentially constant in some areas. This section 10 also preferably has additional grinding elements 11, preferably in the form of pins or rods. The free ends of the additional grinding elements 11 on the basket 6 preferably all end at essentially the same diameter and are preferably arranged in alignment with the other pins of the basket already described above, usually parallel to the agitator shaft axis 4.

The Fig. 5 and Fig. 6 show a second preferred embodiment of the basket 6 in different views, wherein the section 10 with enlarged outer diameter is an outer diameter that increases in sections, preferably continuously, towards its free end 9.

In the embodiment shown here, the basket 6 thus has a truncated cone-shaped outer geometry in sections - without the fastening sleeve for the agitator shaft 3. The basket 6 is in turn equipped on its outer circumference with additional grinding elements 11, which are in the form of pins in horizontal, rows running parallel to the agitator shaft axis 4 are arranged regularly around the circumference of the basket 6.

The basket 6 also comprises several of the openings 14 already mentioned at the beginning, through which grinding bodies can be discharged from the separation chamber into the grinding chamber. The free ends of the additional grinding elements 11 on the basket 6 preferably all end at essentially the same diameter and are preferably arranged in line with the other pins of the basket already described above, usually parallel to the agitator shaft axis 4. In addition, these additional pins or rods 11 are preferably arranged such that the longitudinal axis of the rods 11 intersects the agitator shaft axis 4 essentially orthogonally.

Fig.7 finally shows a further preferred embodiment of the basket 6, wherein the basket 6 again carries a section 10 with an enlarged outer diameter, but here without an additional ramp 12.

Fig.7 also shows schematically the flow behavior in the grinding container 16 of an agitator mill 1, in principle representative of all embodiments described so far.

At this point, we would like to first point out the general functioning of a stirred mill, which is explained in the "Technical Background" section with the help of the Fig.1 and Fig.2 The basic function and flow behavior are the same or similar up to the area of basket 6 and will therefore not be repeated here.

Due to the narrowing of the radial gap between the section 10 with the enlarged outer diameter and the inner wall of the grinding container 16, the local flow velocity increases (as mentioned) and/or increased turbulence occurs. This is in Fig.7 indicated schematically by the additional vortex on the outlet side of the grinding container 16, which forms a "9" so to speak.

This allows grinding media and/or the grinding material suspension to enter the separation chamber 15 more easily or more dynamically. This reduces the tendency of the grinding media to be unable to escape the suction of the sieve/slotted tube and thus to permanently or long-term adhere to the outer peripheral surface of the slotted tube and block it. Instead, the grinding media are discharged more quickly through the openings 14 from the separation chamber 15 into the grinding chamber 2 by the more lively flow according to the invention. This is in Fig.7 indicated by the additional arrows that point from the opening 14 shown into the grinding chamber 2. In addition, the higher flow speeds and/or turbulence in the radial area between the outer circumference of the basket 6 and the inner wall of the grinding container 16, preferably between the grinding elements 11, create an additionally increased flow, which further activates the surrounding grinding media bed. The grinding media are thus kept away from the split tube 8 or the split tube-carrying outlet 7 or are discharged from the separation chamber 15 and lead to an increased grinding effect in the grinding chamber 2 after discharge from the separation chamber 15.

LIST OF REFERENCE SYMBOLS

1

Agitator mill

2

Grinding room

3

Stirring shaft

4

Stirrer shaft axis

5

Grinding element carried by agitator shaft

6

Basket

7

Outlet

8th

split tube

9

Free end of the basket

10

Section with enlarged outer diameter

11

Grinding organ carried by basket

12

ramp

13

not awarded

14

breakthrough

15

Separation room

16

Grinding container

17

inlet

101

Electric motor

102

Belt drive

103

Housing

Claims (7)

Agitator mill (1) with a grinding chamber (2) containing grinding bodies and an agitator shaft (3) rotating therein about a horizontal agitator shaft axis (4), which carries a plurality of grinding elements (5), preferably in the form of grinding disks, which are connected to it in a rotationally fixed manner and are spaced apart from one another in the direction of the horizontal axis and which move the grinding bodies, the agitator shaft (3) having a basket (6) on the outlet side, which is preferably equipped with grinding elements (11) on its outer circumference and which overlaps the outlet (7) carrying the split tube, the basket (6) having a section (10) with an enlarged outer diameter in the region of its free end (9), characterized in that the section (10) with the enlarged outer diameter forms a ramp (12) running obliquely to the horizontal on the side facing away from the free end (9) of the basket (6), which has a smooth outer surface cut by webs and/or openings. Agitator mill (1) according to claim 1, characterized in that the section (10) with the enlarged outer diameter extends directly to the free end (9) of the basket (6). Agitator mill (1) according to one of the preceding claims, characterized in that the section (10) with the enlarged outer diameter, including the ramp (12) possibly formed by it, in the direction along the agitator shaft axis (4) makes up between 45% and 20%, better between 30% and 25%, of the length of the basket (6) in the direction of the agitator shaft axis (4). Agitator mill (1) according to one of the preceding claims, characterized in that the section (10) with the enlarged outer diameter has a smooth outer surface outside the ramp (12) possibly formed by it. Agitator mill (1) according to one of the preceding claims, characterized in that the section (10) with the enlarged outer diameter carries grinding elements (11) on its circumferential surface, preferably in the form of grinding rods, ideally in the form of at least one ring of grinding rods arranged one behind the other in the circumferential direction. Agitator mill (1) according to claim 5, characterized in that the free ends of the grinding elements (5) of the agitator shaft (3) end at the same diameter as the other grinding elements (11) carried by the basket (6). Basket (6), designed as a spare part to be subsequently attached, preferably by screwing it onto the agitator shaft (3), which is preferably equipped with grinding elements (11) on its outer circumference and, in the assembled position, overlaps the outlet (7) carrying the gap tube, the basket (6) having a section (10) with an enlarged outer diameter in the region of its free end (9), characterized in that the section (10) with the enlarged outer diameter forms a ramp (12) running obliquely to the horizontal on the side facing away from the free end (9) of the basket (6), which has a smooth outer surface cut by webs and/or openings.

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