METHOD FOR OPERATING A MIXED BALL MILL AND MIXED BALL MILL FOR THIS PUTTING

Description

[0001] The present invention relates to a method for operating a stirred ball mill according to the preamble of claim 1 and to a stirred ball mill for carrying out the method.

[0002] Stirred ball mills, also known as attritors, are known with a vertically or horizontally arranged stirring shaft.

[0003] In wet operation of corresponding stirred ball mills known from practice, a free-flowing grinding material suspension is conveyed, in particular continuously, by means of a pump from a product inlet on the feed side of a grinding chamber in a housing of the stirred ball mill to a product outlet on the discharge side of the grinding chamber.

[0004] The rotating agitator shaft of a grinding or stirring device, which may contain stirring elements such as rods or discs or simply be a smooth-walled agitator, transfers energy to a grinding media filling (not shown) within the grinding chamber. The stress and thus comminution of the material being ground occurs at the contact points of the grinding media moved by the rotation of the agitator shaft, primarily due to impact and shear forces. A solids content of 30% to 60% in the suspension is typical. This corresponds to a loading of 300 kg to 600 kg of material being ground per m³ of liquid, such as water.

[0005] A separation system, consisting in particular of a rotating outer basket and a static cylindrical sieve inside it, is arranged before the product outlet. In this separation system, the grinding media remaining in the mill are separated from the suspension containing the ground material, which then exits the stirred ball mill.

[0006] In principle, such a mill can also be operated dry, as is known from practical experience. However, to ensure similar conditions in the grinding chamber, especially with regard to particle concentration, only a very small gas flow (instead of a liquid in wet operation) can be supplied with the material being ground. This flow is insufficient on its own for product transport from the product inlet to the product outlet. This is due to the fact that gases are approximately 1000 times denser than liquids.

[0007] Within the grinding chamber itself, this typically causes no problems, as the movement of the agitator shaft and grinding media also carries the material being ground. However, the product discharge in the separation system becomes problematic. Here, material builds up and accumulates. These build-ups and accumulations grow "from the back" into the grinding chamber. This causes the material discharge to collapse, thus reducing the throughput of the dry-operated stirred ball mill. Ultimately, this leads to the disadvantage that continuous operation is no longer possible.

[0008] As a general background technology, a stirred mill according to DE 44 32 200 C1 comprises a grinding container enclosing a grinding chamber, an agitator rotatably arranged concentrically to the central longitudinal axis of the grinding container, a drive motor coupled to the agitator, a discharge line for the material being ground and the grinding aids leading out of the grinding chamber, a material being ground and grinding aid separation device separate from the agitated mill and connected to a discharge line (23), a material being ground and grinding aid return line connected to the separation device and a material being ground feed line on one side and to the grinding chamber on the other, and a material being ground pump into the material being ground feed line. The separation device has a housing in which a rotor, which can be rotated independently of the rotary drive of the agitator, is arranged to centrifuge the grinding aids from the material being ground and to convey them into the material being ground feed line and grinding aid return line.The grinding container, the material / grinding aid discharge line, the separating device, and the material / grinding aid feed and return lines form a closed system. Only the material pump located in the material feed line serves as a conveying device for the material and grinding aids in the material / grinding aid return lines.

[0009] Similarly, WO 2012 / 055388 A2 discloses as prior art a stirred ball mill for grinding dry or non-dry substances, comprising a grinding chamber at least partially filled with grinding media, an inlet and an outlet for the material to be ground, a screen located in an outlet area, a stirring shaft extending through the center of the grinding chamber, and several grinding elements arranged on the stirring shaft. A first cage is assigned to an inlet area and a second cage to an outlet area. A fluid inlet is assigned to the inlet area. A cleaning device is arranged in the center of the screen.

[0010] DE 10 2007 054 885 A1 relates to a process for fractionating a dispersion of oxide nanoparticles. It describes a wet milling process using membrane cross-flow filtration, in which the dispersion is forced across the membrane by driven rotating parts.

[0011] US 5,967,432 A explicitly concerns mills that do not use balls as grinding media, but rather grind the material through collision and friction between the grinding media and against the inner surface of the grinding chamber. Technical specifications related to the use of grinding media are generally not included in this document.

[0012] US Patent 2,595,117 A discloses a grinding process in a vertical mill with grinding media featuring a continuous discharge of grinding media and material being ground at the top, as well as an external separating device. In the separating device, "far oversized pieces of material" and grinding media are sorted out by an upward jet of air to be returned to the mill.

[0013] From DE 42 02 101 A1, a method for treating dry to moist material is known, wherein the material is conveyed through a moving pile of grinding media under the influence of gravity. During its passage through the grinding media pile, the material is subjected to comminution, for example. Shortly before exiting the pile or the comminution process, a fluid is added to this comminuted material and mixed with it. This publication discloses a tower grinding mill with a cylindrical, vertically oriented grinding chamber, inside which a screw agitator and grinding media are located. A material feed is arranged in the upper region and a material discharge is arranged in the bottom of the grinding chamber. Nozzles are radially arranged in the wall of the grinding chamber just above the material discharge and are inclined towards the material discharge. The axes of the nozzles intersect on the axis of the grinding chamber.The nozzles are intended to introduce a fluid shortly before and / or during product exit. This ensures that the fluid moves in the direction of material transport. In contrast, our method requires the fluid to move in a direction opposite to the direction of material transport.

[0014] EP 2 189 221 A2 discloses a stirred ball mill with a grinding chamber surrounding a stirring shaft, which is provided with a product inlet and a product outlet. The grinding media located within the grinding chamber (12) are activated by the rotation of the stirring shaft and retained in the grinding chamber by a separation and / or pre-classification device. For optimal energy and space utilization, a pre-crushing device is installed upstream of the grinding chamber. The pre-crushing device has either a static or dynamic gap guard.

[0015] The grinding vessel, known from DE 100 64 828 A1, which is radially spaced from the agitator, defines an annular-cylindrical grinding chamber with the agitator shaft. This chamber contains a separation device consisting of several tubular sieves that are part of a rotating cage. The sieves are inserted between the base plate and the ring disk of the cage.

[0016] DE 198 30 960 A1 discloses that, in an operating position of the separating device, an at least partially inelastic spacer holds the sieve elements at a first distance, resulting in a minimum sieve gap width corresponding to the operating width. In the cleaning position, the elements assume a position in which their relative distance is greater than the first. The elements are elongated, run approximately parallel to each other, and together form a plane-parallel sieve.

[0017] The present invention has and achieves the objective of improving the dry operation of stirred ball mills and, in particular, of preventing at least to a large extent the build-up and accumulation of ground material on the separation system, or in other words, a blockage of the separation system, before the product outlet.

[0018] This objective is achieved by a method for operating a stirred mill according to claim 1.

[0019] The inventive method for the dry operation of a stirred ball mill with a mill housing enclosing a grinding chamber in which a rotatable stirring shaft runs horizontally between an inlet side and an outlet side and in which grinding media are located, wherein On the feed side, material to be ground is fed into the grinding chamber via a product inlet. From the feed side, the material to be ground is transported along the agitator shaft in a transport direction parallel to the axial direction of the agitator shaft to the discharge side and is ground by the grinding media. On the discharge side, the ground material exits the grinding chamber by passing radially with respect to the transport direction through a separation system that retains the grinding media. The ground material then leaves the stirred ball mill through a product outlet downstream of the separation system. is characterized in that a discharge gas is directed at least partially against the direction of transport into the grinding chamber on the discharge side in the area of ​​the separation system, passes radially through the separation system together with ground material with respect to the direction of transport and thus leaves the grinding chamber together with ground material through the separation system and further through the product outlet.

[0020] This means that the discharge gas is introduced immediately upstream of the separation system. In this area, the discharge gas accelerates the ground material towards the separation system, preventing or at least reducing the settling of ground material on the surface of the separation system. Simultaneously, it blows away any small amounts of remaining ground material from the surface of the separation system. This effectively prevents clogging of the separation system.

[0021] A further preferred embodiment consists in the fact that, in addition to the material to be ground, a gas flow is introduced into the grinding chamber on the feed side of the stirred mill, and that the gas flow contributes to the transport of the material to be ground, that the gas flow constitutes only 5% to 20%, preferably 5% to 10% of the total amount of gas leaving the stirred mill through the separation system and the product outlet, and that the supply of discharge gas is selected such that the loading of the entire gas leaving the stirred mill through the separation system and the product outlet with discharged material is approximately 0.3 kg / m³ to 0.7 kg / m³.

[0022] Furthermore, it may be preferable to provide that the total gas load leaving the agitator mill through the separation system and the product outlet with discharged ground material is approximately 0.4 kg / m 3< to 0.6 kg / m 3<.

[0023] It is further preferred that an air classifier is supplied in-line with the gas-ground material mixture leaving the agitator mill through the separation system and the product outlet.

[0024] The invention further provides a stirred ball mill for carrying out the aforementioned method, wherein the separation system has a static sieve with a free perforation area selected such that the velocity of the gas exiting the stirred ball mill through the separation system and the product outlet is approximately 10 m / s to 30 m / s, preferably 15 m / s to 25 m / s.

[0025] Furthermore, a mill floor is present on the discharge side, which has discharge gas inlet bores for the discharge gas to enter the grinding chamber, and these discharge gas inlet bores are covered with a sieve.

[0026] It is further provided that the discharge gas inlet bores for the entry of the discharge gas into the grinding chamber are arranged and / or aligned in such a way that discharge gas is introduced into the grinding chamber at least partially, preferably substantially against the direction of transport.

[0027] Another preferred embodiment consists in the fact that the discharge gas inlet bores are supplied via a spiral discharge gas distribution housing with a common discharge gas intake line.

[0028] Further preferred and / or advantageous embodiments of the invention and its individual aspects result from combinations of the dependent claims as well as from the entire application documents presented.

[0029] The invention is explained in more detail below by way of example embodiments with reference to the drawing, in which Fig. 1 illustrates an embodiment of a stirred ball mill in a schematic sectional view, and Fig. 2 shows a schematic enlarged partial sectional view of the stirred ball mill from the Fig. 1 further details clarified.

[0030] The invention is explained in more detail by way of example using the embodiments and applications described below and illustrated in the drawings; that is, it is not limited to these embodiments and applications. Method and device features can also be derived analogously from the device and method descriptions, respectively.

[0031] Identical reference numerals in the individual figures and illustrations of the drawing denote identical or similar components, or components with the same or similar effect. The representations in the drawing also clearly indicate features that are not marked with reference numerals, regardless of whether such features are described subsequently or not. Conversely, features included in this description but not visible or depicted in the drawing are readily understandable to a person skilled in the art.

[0032] In the Fig. 1 and 2An exemplary longitudinal section or enlarged section thereof of a stirred ball mill 1 designed for dry operation is shown. The stirred ball mill 1 contains a mill housing 2, which encloses a grinding chamber 3, which is primarily cylindrical. A stirring shaft 4 is rotatably arranged horizontally between an inlet side 5 and an outlet side 6 of the mill housing 2 within the grinding chamber 3. Furthermore, grinding elements M, which are mostly made of steel, glass, or wear-resistant ceramic materials (though the present invention is not limited to these), are located in the grinding chamber 3. For the sake of clarity, only a few of these are shown as examples. Fig. 1 shown.

[0033] The stirring shaft 4, which rotates in the grinding chamber 3 during operation of the stirred ball mill 1, is generally a component of a grinding or stirring mechanism that is generally known and which may also contain stirring elements 4', such as rods or discs, or may simply be a smooth-walled stirring body. Details of grinding or stirring mechanisms are not discussed further here, as the present invention is independent of any such designs. The rotation of the stirring shaft 4 introduces energy into the grinding media filling in the grinding chamber 3. Typically, but not exclusively, the free volume of the grinding chamber 3 adjacent to the grinding or stirring mechanism is used. z.B. filled to 70% to 90% with grinding media M.

[0034] On the entry side 5 there is a product inlet 5' through which the material to be ground 7 is fed into the grinding chamber 3. The material to be ground 7 is in the Fig. 1 symbolized by small squares, which are only shown as examples in some places to maintain the clarity of the graphic representation.

[0035] In addition to the material to be ground 7, a small gas flow 10 is introduced into the grinding chamber 3 on the inlet side 5 of the agitator mill 1 (into the Fig. 1 and 2 The material to be ground 7 is introduced by a conveyor belt 4 (shown with arrows with long dashed lines), which contributes to the transport of the material to be ground 7 in a transport direction T parallel to the axial direction A of the agitator shaft 4, but is not sufficient on its own. The material to be ground 7 is transported from the input side 5 along the agitator shaft 4 in the transport direction T parallel to the axial direction A of the agitator shaft 4 to the discharge side 6, and is thereby ground by the grinding media M, primarily by the rotating agitator shaft 4 during operation of the stirred ball mill 1.

[0036] The ground material 7' then exits the grinding chamber 3 on the discharge side 6, passing radially with respect to the transport direction T through a separation system 8 that retains the grinding media M, i.e., holds them back in the grinding chamber 3. The ground material 7' then leaves the stirred ball mill 1 through a product outlet 6' located downstream of the separation system 8. The material to be ground 7' is in the Fig. 1 and 2 symbolized by small triangles, which are only shown as examples in some places to maintain the clarity of the graphic representation.

[0037] The separation system 8 typically includes a basket 18 rotating with the agitator shaft, which essentially retains the grinding media M in the grinding chamber 3, and a cylindrical static screen 12 arranged inside the basket 18 as a further barrier. The material being ground tends to cake or adhere to this static screen, a problem known from the prior art of dry-running stirred ball mills. This clogging of the static screen disrupts or even prevents the operation of such a stirred ball mill. If such build-up and adhesion also grows "from behind" into the grinding chamber, the gap between the rotating basket and the static screen becomes blocked, leading to further operational problems in such stirred ball mills. These disadvantages then render continuous operation impossible.

[0038] To counteract these disadvantages, the stirred ball mill 1 also has a mill base 13 on the discharge side 6, which closes off the mill housing 2 and has discharge gas inlet bores 14 for the inlet of discharge gas 9 (into the Fig. 1 and 2 (shown with arrows and short dashed lines) into the grinding chamber 3, details of which can be found in the enlarged illustration of the Fig. 2 They are easily recognizable.

[0039] These discharge gas inlet bores 14 are covered with a screen 15, such as a slotted screen. Furthermore, the discharge gas inlet bores 14 are arranged and / or oriented for the discharge gas 9 to enter the grinding chamber 3 such that the discharge gas 9 flows at least partially, preferably substantially, into the grinding chamber 3 in the opposite direction to the transport direction T. A spiral discharge gas distribution housing 16 is provided to supply the discharge gas inlet bores 14 with the discharge gas 9, which is arranged around the product outlet. 6' The discharge gas distribution housing 16 is connected to a discharge gas suction line 17, so that all discharge gas inlet bores 14 are supplied jointly from a discharge gas source (not shown).

[0040] During operation of the stirred ball mill 1, the discharge gas 9 is directed into the grinding chamber 3 on the discharge side 6 in the area of ​​the separation system 8. This causes the discharge gas 9, together with the gas volume flow 10 and the ground material 7', to pass radially or perpendicularly to the transport direction T through the separation system 8, and thus the discharge gas 9, the gas volume flow 10 and the ground material 7' leave the grinding chamber 3 through the separation system 8 and further through the product outlet 6'.

[0041] Due to the arrangement and orientation of the discharge gas inlet bores 14, the discharge gas 9 is directed into the grinding chamber 3 on the discharge side 6 in the area of ​​the separation system 8 in a direction deviating from the transport direction T. The processes in the grinding chamber 3, i.e., the transport of the material to be ground 7 along the agitator shaft 4 in the direction from the feed side 5 to the discharge side 6 and the grinding process itself, are not affected by the inflowing discharge gas 9, since the discharge gas 9 does not reach these areas of the grinding chamber 3, but rather flows into the separation system 8 in accordance with the general transport movement of the material to be ground 7, 7'.

[0042] It should be noted that the gas volume flow rate 10, as stated above, is small and constitutes only 5% to 20%, preferably only 5% to 10%, of the total gas volume leaving the agitated mill 1 through the separation system 8 and the product outlet 6'. In other words, the proportion of the discharge gas 9 to the total gas volume leaving the agitated mill 1 through the separation system 8 and the product outlet 6' is, in the present embodiment, at least 80%, preferably at least 90%, and at most 95%.

[0043] The supply of discharge gas 9 is selected such that the loading of the entire gas leaving the stirred mill 1 through the separation system 8 and the product outlet 6' with discharged ground material 7' is approximately 0.3 kg / m 3< to 0.7 kg / m 3< , preferably approximately 0.4 kg / m 3< to 0.6 kg / m 3< .

[0044] The static sieve 12 of the separation system 8 is further preferably designed such that it has a free perforation area selected such that the flow velocity (volume flow rate) of the gas leaving the agitator mill 1 through the separation system 8 and the product outlet 6' is approximately 10 m / s to 30 m / s, preferably 15 m / s to 25 m / s. This flow velocity is defined as follows: Durchtrittsgeschwindigkeit = Volumenstrom / freie Lochfläche

[0045] The discharge gas 9 accelerates the ground material 7' immediately before the separation system 8, allowing it to easily pass through the rotating basket 18 and, more importantly, the static screen 12, preventing it from adhering to the surfaces, as explained above. This flow rate can generally be selected to ensure reliable product transport from the grinding chamber 3 through the separation system 8 to the outside. The rotating basket 18 and, in particular, the static screen 12 remain unobstructed and do not impede the continuous operation of the stirred ball mill 1.

[0046] Although it was described above that the discharge gas 9 is supplied along the agitator shaft 4 in the opposite direction to the transport or conveying direction T of the material being ground 7, this is not intended to be a limiting factor. Preferably, the inflow direction of the discharge gas 9 through the discharge gas inlet bores 14 into the grinding chamber 3 is such that this inflow direction is at an angle of > 0° to the aforementioned transport direction T, in particular an angle between 90° and 180°. In other words, it is preferred that the discharge gas 9 is not supplied along the agitator shaft 4 in the transport or conveying direction T of the material being ground 7.

[0047] The stirred ball mill 1 can still be used according to the specifications in the Fig. 1 The embodiment shown includes an air classifier 11, which is supplied in-line with the gas-ground material mixture leaving the stirred ball mill 1 through the separation system 8 and the product outlet 6'. Reference symbol list

[0048] 1 Stirred ball mill 2 Mill housing 3 Grinding chamber 4 Agitator shaft 4' Agitators 5 Feed side 5' Product inlet 6 Discharge side 6' Product outlet 7 Material to be ground 7' Ground material 8 Separation system 9 Discharge gas 10 Gas flow rate 11 Air classifier 12 Static screen 13 Mill base 14 Discharge gas inlet bores 15 Screen 16 Spiral discharge gas distributor housing 17 Discharge gas suction line 18 Basket A Axial direction M Grinding body T Transport direction

Claims

1. Method for the dry operation of a stirring ball mill (1) with a mill housing (2) enclosing a grinding chamber (3) in which a rotatable agitator shaft (4) runs horizontally between an inlet side (5) and a discharge side (6) and in which grinding media (M) are located, wherein: - material (7) to be ground is fed into the grinding chamber (3) on the inlet side (5) through a product inlet (5'), - the material (7) to be ground is transported from the inlet side (5) along the agitator shaft (4) in a transport direction (T) parallel to the axial direction (A) of the agitator shaft (4) to the discharge side (6) and is thereby ground by the grinding media (M), - ground material (7') exits the grinding chamber (3) on the discharge side (6) by passing radially with respect to the transport direction (T) through a separation system (8), which holds the grinding media (M), and - the ground material (7') then leaves the stirring ball mill (1) through a product outlet (6') downstream of the separation system (8), characterized in that a discharge gas (9) is directed at least partially against the transport direction (T) into the grinding chamber (3) on the discharge side (6) in the region of the separation system (8), passes radially with respect to the transport direction (T) together with ground material (7') through the separation system (8) and thus leaves the grinding chamber (3) together with ground material (7') through the separation system (8) and further through the product outlet (6').

2. Method according to claim 1, characterized in that the discharge gas (9) on the discharge side (6) in the area of the separation system (8) is directed substantially against the transport direction (T) into the grinding chamber (3).

3. Method according to claim 1 or 2, characterized in that in addition to the material to be ground (7) on the inlet side (5) of the agitator mill (1), a gas volume flow (10) is introduced into the grinding chamber (3), and that the gas volume flow (10) contributes to the transport of the material to be ground (7), the gas volume flow (10) constitutes only 5% to 20%, preferably 5% to 10%, of the total amount of gas leaving the agitator mill (1) through the separation system (8) and the product outlet (6'), and the supply of discharge gas (9) is selected such that the load of the total gas with discharged material (7') leaving the agitator mill (1) through the separation system (8) and the product outlet (6') is approximately 0.3 kg / m3 to 0.7 kg / m3.

4. Method according to claim 3, characterized in that the load of the total gas with discharged material (7') leaving the agitator mill (1) through the separation system (8) and the product outlet (6') is approximately 0.4 kg / m3 to 0.6 kg / m3.

5. Method according to one of the preceding claims, characterized in that an air classifier (11) is supplied in-line with the gasground material mixture leaving the agitator mill (1) through the separation system (8) and the product outlet (6').

6. Stirring ball mill (1) for carrying out the method according to one of claims 1 to 5, characterized in that a mill floor (13) is provided on the discharge side (6) which has discharge gas inlet bores (14) for the discharge gas (9) to enter into the grinding chamber (3), and that these discharge gas inlet bores (14) are covered with a screen (15), and the discharge gas inlet bores (14) for the discharge gas (9) to enter into the grinding chamber (3) are arranged and / or oriented such that discharge gas (9) is introduced at least partially into the grinding chamber (3) against the transport direction (T), and the separation system (8) has a static sieve (12) with a free perforation area selected such that the passing velocity of the gas leaving the agitator mill (1) through the separation system (8) and the product outlet (6') is approximately 10 m / s to 30 m / s.

7. Stirring ball mill (1) according to claim 6, characterized in that the discharge gas inlet bores (14) for the entry of the discharge gas (9) into the grinding chamber (3) are arranged and / or aligned such that discharge gas (9) is introduced into the grinding chamber (3) substantially against the transport direction (T).

8. Stirring ball mill (1) according to claim 6 or 7, characterized in that the separation system (8) has a static sieve (12) with a free perforation area which is selected such that the passing velocity of the gas leaving the agitator mill (1) through the separation system (8) and the product outlet (6') is approximately 15 m / s to 25 m / s.

9. Stirring ball mill (1) according to one of claims 6 to 8, characterized in that the discharge gas inlet bores (14) are supplied via a spiral discharge gas distribution housing (16) with a common discharge gas intake line (17).