EP4371668A1 - Agitator mill with basket having slits - 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 (6) on the outlet side, which is preferably equipped with grinding elements (18) on its outer circumference and which engages over the outlet carrying the split tube, whereby a separation chamber is formed between the inner surface of the basket and the outlet carrying the split tube, wherein the basket has slots (10) for returning grinding bodies from the separation chamber to the grinding chamber, which slots open into the free end face (11) of the basket facing away from the grinding chamber.

Description

The invention relates to an agitator mill with a basket with slots according to the preamble of claim 1 and the corresponding basket according to the preamble of claim 6.

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 a back mill 1 can also be used for dry grinding. It can then be designed as a back 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.

By means of a rotational movement of the 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. 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, for example, via a belt drive 102 from a Electric motor 101. 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.

To ensure that grinding media are not discharged from the grinding chamber, a sieve or preferably a sieve in the form of a gap tube 8, hereinafter referred to as "gap tube", is usually installed in front of the outlet 7 and/or carried by the outlet 7. 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 9, since here the material to be ground or the grinding 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 9 have the opportunity to get out of the separation chamber and back into the grinding chamber 2. Otherwise, the separation chamber 9 is soon filled with grinding media and the grinding media then block the gap tube and possibly even cause it to wear out prematurely.

To prevent this, various openings 104 are provided in the basket 6. Through these openings 104, the grinding bodies can more easily pass from the separation chamber 9 into the grinding chamber 2. Fig.2 shows a basket 6 of a stirrer mill designed in this way, which served as a test or 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 5 on its outer surface, which cause a movement or circling of the grinding media 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 9 to escape back into the grinding chamber 2 through the openings 104.

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 9 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 9 through the openings 104; however, the tendency of the grinding media is to move towards the gap tube 8.

The DE 44 12 408 C2 describes an agitator mill with - a grinding container which encloses a grinding chamber which can be partially filled with grinding auxiliary bodies and through which grinding material can flow mainly axially, an agitator shaft which carries agitator elements arranged axially one behind the other, an outlet body which is connected to a grinding material outlet (48) of the grinding container, and a pre-classifying device which has a pre-classifying disk with an axial passage arranged immediately in front of the outlet body and which conveys auxiliary grinding bodies which have reached its area of action preferably radially outwards, characterized in that the pre-classifying disk is at the same time part of a rotating cage which encloses the outlet body to such an extent that it can be reached for a substantial part of the material to be ground through the pre-classifying disk.

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 at most one third, particularly preferably even a maximum of a 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.

During normal operation, this basket at least partially overlaps the outlet, 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 "slotted tube" is preferably a tube with various slots and/or differently shaped openings in the narrower sense, but in the broader sense the term "slotted 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 slots for returning grinding media from the separation chamber into the grinding chamber. These slots are designed in such a way that they open into the free front surface of the basket facing away from the grinding chamber.

This is based on the following insight of the inventors: The Fig.2 The entry area shown directly behind the free front face of the basket, in which the flow flows in a predominantly horizontal direction to enter the separation space, forms a too pronounced constriction. The latter 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 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.

The slots formed according to the invention thus result in the radial gap between the inner surface of the basket and the outer surface of the outlet or gap tube, which has to be passed through as the flow enters the separation chamber, being significantly enlarged at least in some areas. 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/or the grinding media being guided to the sieve is prevented and the grinding media can, at least in part, enter the separation chamber much more easily and with greater dynamics. A desirable Flow, whereby the grinding media are kept away from the gap tube and are carried through the slots more quickly and/or more easily from the separation chamber into the grinding chamber.

This means that 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 where the grinding media are introduced directly 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 means that the agitator mill can achieve an increased grinding effect, the gap tube experiences less wear during operation and fewer grinding media become stuck in or on the gap tube. This means that the agitator mill can be operated at a higher throughput, with an increased service life of the basket and less maintenance.

The "slots" are breakthroughs and/or openings and/or incisions with an elongated shape as a whole, which are provided in or on the basket.

A slot according to the invention provides a breakthrough in the outer surface of the basket to the grinding chamber at least in one area, but preferably not over the entire length of the slot. In this way, material can border on the slot in some areas, whereby the slot is virtually "covered", "lined" and/or surrounded by the material of the basket.

Furthermore, a slot according to the invention preferably does not have the same cross-section over its entire length and can change its extent and/or its shape in certain regions.

In the course of the mentioned "roofing" of a slot of the basket, it should also be mentioned here that it is preferred that a basket according to the invention is designed in such a way that each slot on its side facing away from the grinding chamber has material radially outwards and thus above the slot in areas directly adjacent to the slot. The slot is thus designed to be "roofed", whereby an "end ring" is formed in this area, which forms a preferably continuous circumferential surface.

This is necessary to stabilize the basket and prevent vibrations. Each slot thus tunnels under the end ring.

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 is that the slots also pass through the wheel disk that connects the basket to the agitator shaft, so that the slot in question is also connected to the grinding chamber via the wheel disk itself. This gives the grinding media the opportunity to also pass from the separation chamber into the grinding chamber via this wheel disk, promoted by the grinding media dynamics taking place in the grinding chamber on the other side of the wheel disk. This makes it even easier to remove the grinding media from the separation chamber.

In addition, it is particularly preferred that the slots tunnel under a stabilization ring formed on the side or in the area of the free end of the basket facing away from the grinding chamber. This stabilization ring is preferably designed in such a way that it extends radially outward further into the grinding chamber than the remaining diameter of the basket, which on the one hand increases the stability of the basket and on the other hand further improves the flow guidance or dynamics.

Another preferred embodiment consists in the fact that the main axes of the slots extend completely or at least essentially parallel to the agitator shaft axis. This is achieved when these main axes deviate from the agitator shaft axis by a maximum of 10°, preferably a maximum of 5°. The main axes run along the entire length of the slot, i.e. its entire extension length, preferably also parallel to the longitudinal axis of the basket and are located in the middle of the slot and thus at half the width of the slot.

In addition, it is particularly preferred if the flanks of the slots leading in the working direction of rotation have an angle of attack of 0° to 45° compared to the imaginary radial through their main axis. In this way, "shoveling surfaces" are formed on the basket, which lead to the grinding media being deflected and thus discharged even better.

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 the embodiment of the basket according to the invention from Fig.3 in front view.
• The Fig.6 shows a second embodiment of the basket according to the invention with stabilization ring in three-dimensional view.
• The Fig.7 shows the embodiment of the basket according to the invention with stabilization ring made of Fig.6 in side view.
• The Fig.8 shows the embodiment of the basket according to the invention with stabilization ring made of Fig.6 in sectioned side view, with the basket enclosing a split tube-supporting outlet.
• The Fig.9 shows the grinding container of an agitator mill from a sectional side view with a third embodiment of the basket according to the invention with a different stabilization ring shape.
• The Fig.10 shows a fourth embodiment of the basket according to the invention in side view.
• The Fig. 11 shows the embodiment of the basket according to the invention from Fig.10 in three-dimensional view.
• The Fig. 12 shows a fifth embodiment of the basket according to the invention in front view.
• The Fig. 13 shows the embodiment of the basket according to the invention from Fig. 12 in three-dimensional view.
• The Fig. 14 shows a sixth embodiment of the basket according to the invention in front view.
• The Fig. 15 shows the embodiment of the basket according to the invention from Fig. 14 in three-dimensional view.

PREFERRED EMBODIMENTS

First show Fig. 3 to Fig. 5 a first preferred embodiment of the basket 6 according to the invention in various views. The basket 6 is fitted on its outer circumference with additional grinding elements 18, which are arranged in the form of pins in horizontal rows running parallel to the agitator shaft axis 4, regularly around the circumference of the basket 6. The slots 10 are also distributed evenly over the circumference of the basket 6 and, as mentioned, cut both the wheel disk 12 facing the grinding chamber 2 and the front face 11 facing away from the grinding chamber 2. It can be advantageous if not every individual slot 10 is assigned one of the said rows, but instead there are immediately adjacent slots whose connecting area does not have any of the said rows. The slot 10 also tunnels under the end ring 19 on the side facing the front face 11, the end ring 19 being designed to be closed all the way around.

For the sake of simplicity and clarity, here and in the other figures, not every slot and not every grinding element is provided with a reference symbol, but only one slot and only one or two grinding elements as an example.

The front view of basket 6 is in Fig.5 shown, looking at the front face 11 facing away from the grinding chamber. Here, the angle of attack A of the slots can be seen, which means that the flanks 15 of the slots 10 leading in the working direction of rotation or their imaginary extensions are not radially perpendicular to the outer contour of the basket 6. This angle of attack A is preferably between 0° and 45°. For better illustration, an imaginary slot can also be seen in dashed lines, which is exactly radially perpendicular to the outer contour of the basket 6. The angle from the main axis of such a slot to the main axis 14 of a slot 10 according to the invention is plotted, which corresponds to the angle of attack A.

The Fig. 6 to Fig. 8 show a second preferred embodiment of the basket 6, wherein the basket 6 carries a stabilization ring 13 with an increased outer diameter. The slots 10 also tunnel under an end ring 19 on the side facing the end face 11, wherein the end ring 19 is part of the stabilization ring 13. The slots 10 preferably also run through the wheel disk 12 and the end face 11 facing the grinding chamber. The basket 6 is also equipped with additional grinding elements 18, whereby the above also applies here. The stabilization ring itself can also be provided with additional grinding elements 18, in particular with protruding pins or other agitators, which carry the grinding bodies in the circumferential direction. The pins of the stabilization ring are preferably arranged in alignment with the other pins of the basket described above, usually parallel to the agitator shaft axis 4, cf. Fig. 6 and 7 .

For a better overview, such a basket 6 is in Fig.8 shown in its preferred installation position, in which it encompasses an outlet 7 which carries a gap tube 8. It can be advantageous if the outlet 7 has a constriction (as in this case, designed like a "spool of thread" and possibly equipped with inlet and outlet slopes) which is arranged in such a way that the gap through which the flow into the separation chamber 9 takes place is enlarged by it. Even if such a constriction, unlike the slots or openings according to the invention, does not have any "shoveling" effect in the circumferential direction and therefore causes a different dynamic, it can still help to intensify the effect to be achieved according to the invention, especially in synergistic interaction with the slots or openings according to the invention.

Fig.9 finally shows a further preferred embodiment of the basket 6, wherein the basket 6 also carries a stabilization ring 13, which however has a pure cylinder section shape. The slots 10 here tunnel under the entire stabilization ring 13, which thus functions as an end ring at the same time. Fig.9 also shows schematically the flow behavior in the grinding container 16 of a stirred mill 1. At this point, the general functioning of a stirred mill should be mentioned, which is explained in the section "Technical Background" with the help of the Fig.1 and Fig.2 The basic function and flow behavior is the same or similar up to the area of basket 6 and should therefore not be repeated here. The Fig.9 However, the basket 6 shown has slots 10 which cut both the wheel disc 12 and the front surface 11 facing away from the grinding chamber. This allows grinding media and/or the grinding material suspension to enter the separation chamber 9 more easily, and above all the grinding media are discharged from the separation chamber 9 into the grinding chamber 2 by the flow thus formed through the slots, which is also facilitated by the additional connection to the grinding chamber via the partially slotted wheel disc 12. The grinding media are thus kept away from the gap tube 8 or the gap tube-carrying outlet 7 and, after being discharged from the separation chamber 9, lead to an increased grinding effect in the grinding chamber 2.

The Fig. 10 and Fig. 11 show a further preferred embodiment of the basket 6 with slots 10 and additional grinding elements 18, whereby the outer contour of the basket 6 is designed in the form of a truncated cone. This design ensures that the air flows over the conical structure (unlike Fig.9 ) a flow obstacle is avoided and a continuously increasing flow dynamic is achieved as the flow over the basket. At the same time, the conical structure forms a kind of integral stabilization ring in the area of its free front end, in which no sudden narrowing takes place. The slots 10 in turn tunnel under a circumferentially closed end ring 19.

Good based on the Fig. 11 It can be seen that the basket forms a cylindrical inner circumferential surface on the inside, so that the separation chamber 9 does not taper conically (coming from the free front surface of the basket). This would be unproductive, as with a conical separation chamber there would be a risk that grinding media would jam after entering the separation chamber due to the conical inner profile.

The Fig. 12 and Fig. 13 show a further preferred embodiment of the basket 6. This also has a stabilization ring 13 and the slots 10 tunnel under an end ring 19. However, the slots 10 here run or are designed in such a way that they only penetrate the end face 11 by means of a circular bore.

The Fig. 14 and Fig. 15 show a further preferred embodiment of the basket 6. This also has a stabilization ring 13 and the slots 10 tunnel under an end ring 19. However, the slots 10 here run or are designed in such a way that they have an area in the area of the front surface 11 or on the side facing the front surface 11 where material is provided directly below the slots 10, whereby the slots 10 are virtually "lined" in some areas.

LIST OF REFERENCE SYMBOLS

1

Agitator mill

2

Grinding room

3

Stirring shaft

4

Stirrer shaft axis

5

Grinding element on stirring shaft (grinding disc)

6

Basket

7

Outlet

8th

split tube

9

Separation room

10

slot

11

Front surface (facing away from the grinding chamber)

12

Wheel disc

13

Stabilization ring

14

Main axis of a slot

15

Flank of a slot

16

Grinding container

17

inlet

18

Grinding organ on basket

19

End ring

101

Electric motor

102

Belt drive

103

Housing

104

breakthrough

A

Angle of attack

Claims (6)

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 several 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, wherein the agitator shaft (3) has a basket (6) on the outlet side, which is preferably equipped with grinding elements (18) on its outer circumference and which overlaps the outlet (7) carrying the split tube, whereby a separation chamber (9) is formed between the inner surface of the basket (6) and the outlet (7) carrying the split tube, characterized in that the basket (6) has slots (10) for returning grinding bodies from the separation chamber (9) into the grinding chamber (2), which slots open into the free end face (11) of the basket (6) facing away from the grinding chamber (2), wherein the slots (10) at least partially extend and/or change shape. Agitator mill (1) according to claim 1, characterized in that the slots (10) also pass through the wheel disc (12) which connects the basket (6) to the agitator shaft (3), so that the slot (10) in question is also connected to the grinding chamber (2) via the wheel disc (12) itself. Agitator mill (1) according to claim 1 or 2, characterized in that the slots (10) tunnel under a stabilization ring (13) formed on the side or in the region of the free end of the basket (6). Agitator mill (1) according to one of the preceding claims, characterized in that the main axes (14) of the slots (10) extend parallel to the agitator shaft axis (4). Agitator mill (1) according to claim 4, characterized in that the flanks (15) of the slots (10) leading in the working direction of rotation have an angle of attack (A) of 0° with respect to the imaginary radial through their main axis (14). up to 45°. Basket (6) which is preferably equipped with grinding elements (18) on its outer circumference and which overlaps the gap-tube-carrying outlet (7), characterized in that the basket (6) has slots (10) which open into the free end face (11) of the basket (6) facing away from the grinding chamber (2), the slots (10) changing their extent and/or shape at least in some regions.

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