Stirring mill

Description

[0001] The invention relates to an agitator mill according to the preamble of claim 1.

[0002] The invention relates to European patent EP 1 992 412 A1, from which such a stirred mill is known. Stirred mills are used to disperse suspensions, i.e., solids in liquids. This is applied, for example, in the production of adhesives, printing inks, cosmetics, or pharmaceuticals. For this purpose, the material to be ground is fed via a feed channel into a grinding chamber of the stirred mill, which is formed between the outer wall of a rotor and a container wall. It is then comminuted together with auxiliary grinding media, such as ceramic balls (hereinafter also referred to as grinding media), and with the aid of tools arranged on the rotor and, if appropriate, also on the container wall. The stirring motion disperses agglomerates and comminutes crystal structures. The original particle size of 100–500 µm can be reduced to less than 3 µm.The finished product is then directed via a grinding media discharge channel through a grinding media separator, particularly in the form of a protective screen, into a grinding media discharge chamber located behind the separator, and then to a discharge line. The rotor forms a kind of rotating cage around the separator.

[0003] The problem with such vertical agitator mills is that air remains in the area of ​​the separation device after start-up. During operation, it is also desirable to maintain a narrow residence time distribution and enable plug flow within the device. Furthermore, deposits from the previous product can occur in conventional agitator mills, which can negatively impact the quality of the subsequent product. This requires complex cleaning after each product change. Cleaning devices used in conventional agitator mills have a displacement body that must be relatively small due to the required mobility.

[0004] The invention aims to provide an improved agitator mill that solves these problems. Furthermore, the invention aims to make it possible to implement these improvements in existing agitator mills through a simple modification.

[0005] According to the invention, an agitator mill according to claim 1 and a method according to claim 11 are provided.

[0006] The essence of the invention is to reduce the dead space behind or inside the separating device. Furthermore, it is possible to increase the flow rate of the product. By using a device for reducing the volume of the ground material discharge chamber and in particular by inserting a cylindrical body, a so-called packing body, with a central opening, in particular generally in the form of a hollow cylinder, the dead space behind or inside the separating device can be reduced. Furthermore, the packing body can be designed in such a way that it ensures a minimum product level. Furthermore, a device for setting a minimum level can ensure that product discharge is only possible above a certain minimum level. Both devices can also be used together. By means of the present invention, the dead space behind the separating device orThe protective screen of the agitator mill can be reduced and the position of the product discharge can be shifted upwards. By reducing the volume of the grinding material discharge chamber, the flow rate is also increased, thus reducing or largely preventing contamination of the channel walls by the flowing material itself.

[0007] In particular, the agitator mill according to the present invention comprises a grinding container and a grinding chamber defined by a container wall and at least partially filled with grinding media, and an agitator having a rotor rotatable about a central longitudinal axis arranged substantially vertically during operation. An internal stator is arranged within the rotor. Between the rotor and an outer wall of the internal stator, a grinding material discharge channel is formed, through which the grinding material is guided through a grinding media separation device toward a discharge pipe. The grinding media separation device is preferably designed in the form of a substantially vertically arranged cylinder, in particular a cylindrical sieve, with a height H. A grinding material discharge chamber is formed downstream of the grinding media separation device in the flow direction of the grinding material. A device for setting a minimum level of the product within the grinding material discharge chamber is arranged in the grinding material discharge chamber.Preferably, the interior of the separating device forms the grinding material discharge chamber and the minimum level in the grinding material discharge chamber is greater than or equal to 0.85 H.

[0008] The invention comprises an agitator mill for treating flowable ground material, comprising a grinding container and a grinding chamber defined by a container wall of the grinding container and at least partially filled with grinding media. Furthermore, the agitator mill comprises an agitator rotatable about a central longitudinal axis arranged substantially vertically during operation, with a rotor. An internal stator is arranged within the rotor. A ground material discharge channel is formed between the rotor and an outer wall of the internal stator, through which channel the ground material is guided through a grinding media separating device toward a discharge pipe. A ground material discharge chamber is formed downstream of the grinding media separating device in the flow direction of the ground material. A device for reducing the volume of the ground material discharge chamber is arranged within the ground material discharge chamber.

[0009] The grinding media separation device is preferably designed in the form of a substantially vertically arranged cylinder with a height H, the interior of which forms the grinding material discharge chamber. The device for reducing the volume of the grinding material discharge chamber can be formed by a packing element. The packing element preferably forms a product-tight seal with a discharge base of the agitator mill and has an overflow height h of the product in the vertical direction, wherein the height H of the grinding media separation device is greater than the overflow height h. According to the invention, h is greater than or equal to 0.85 H, particularly preferably greater than or equal to 0.95 H.

[0010] The filler body is preferably a substantially cylindrical hollow body. The device for reducing the volume of the grinding material discharge chamber can be made of plastic, metal, or ceramic. The device for reducing the volume of the grinding material discharge chamber can be designed to be temperature-controlled.

[0011] The separating device is preferably a cylindrical screen. The device for reducing the volume of the ground material discharge chamber can also be removable.

[0012] Preferably, the device for reducing the volume of the grinding material discharge chamber reduces the volume of the grinding material discharge chamber by at least 70%.

[0013] Tools that protrude into the grinding chamber are preferably attached to the rotor and, if applicable, to the container wall.

[0014] The agitator mill with the volume reduction device can also incorporate the minimum level setting device as described above. Both devices can be used separately or together to achieve the object of the present invention.

[0015] The invention further comprises a method for operating and cleaning an agitator mill according to claim 11.

[0016] As a result, when the agitator mill is operating, the flow rate of the material to be ground through the material discharge chamber is high enough to reduce product deposits, particularly in the material discharge chamber of the agitator mill.

[0017] The aforementioned devices for setting a minimum level in the ground material discharge chamber and / or for reducing the volume of the ground material discharge chamber, which can be installed particularly in an existing agitator mill, can reduce the dead volume behind the separating device. This allows the mill to be almost completely filled before the ground material can flow out. By increasing the discharge velocity, carryover of the ground material is prevented, thus reducing product loss and cleaning effort. This is utilized by the cleaning method according to the invention.

[0018] Further features, advantages and details will become apparent from the following description of the invention with reference to the drawings. Fig. 1 a section of a stirred mill according to an embodiment of the invention as a vertical longitudinal section, Fig. 2 a schematic sectional view of a filler body according to an embodiment of the invention and Fig. 3 a perspective view of a filler body according to an embodiment of the invention.

[0019] Figur 1 shows a longitudinal section through an agitator mill according to the invention. The agitator mill conventionally has a grinding container 2 with an internal grinding chamber 8. The grinding chamber 8 is at least partially filled with grinding media (not shown). The agitator mill further comprises an internal stator 22 and a rotor 35 rotatable about a central longitudinal axis 19. A grinding material discharge channel, which is also part of the grinding chamber 8, is formed between an outer wall 23 of the inner stator 22 and an inner wall of the rotor 35. Tools 38 can be attached to the rotor 35 and extend into the space between the rotor 35 and a container wall 9 of the grinding container 2. The tools 38 can alternatively or additionally be arranged on the container wall 9. The grinding material is generally introduced into the agitator mill from above and ground in the grinding chamber 8 by means of the grinding media.At the lower end of the grinding chamber 8, the material to be ground is guided to the inside of the rotor 35, i.e. into the part of the grinding chamber 8 between the inner stator 22 and the inside of the rotor 35. There it flows upwards, where any grinding media that have migrated with it are separated outwards into the grinding chamber 8. Above the inner stator 22 there is a separating device 30, for example a cylindrical protective sieve that is rotationally symmetrical to the central longitudinal axis 19. The separating device 30 prevents the flow of grinding media into a downstream drain line 4, which is located inside the inner stator 22. The completely ground material to be ground flows through the separating device 30 inwards into the drain line 4. Arrows in the . Fig. 1 illustrate the flow direction of the material to be ground through the agitator mill. The agitator mill has an outlet plate 42 below the grinding media separator 30. This outlet plate 42 is arranged inwardly with respect to the grinding media separator 30. The outlet line 4 is preferably arranged in the center of the outlet plate 42. Furthermore, the outlet plate 42 can be designed to taper conically in the direction of the outlet line 4. In other words, a radially outer side of the outlet plate 42 can be arranged higher in a vertical direction than the outlet line 4 during operation in order to simplify the product flow into the center and thus towards the outlet line 4.

[0020] Within the separating device 30, a device for reducing the volume of the ground material discharge chamber, in particular a filler body 1, is mounted, which reduces the volume of the ground material discharge chamber behind the separating device 30. Furthermore, this reduces air pockets in the product, which can increase the efficiency of the machine. Preferably, the separating device 30 is not closed, so that product flow through the entire surface of the separating device 30 is ensured. This can be seen in the figure by a reduction in the sectional area in the region of the ground material discharge chamber behind the separating device 30. In the following, the device for reducing the volume of the ground material discharge chamber is referred to as filler body 1. The filler body 1 is preferably designed to be product-tight with the drain base 4, so that the end product can only flow out above the filler body 1.The packing body 1 can, for example, be a cylinder with a central opening or a cylindrical hollow body. The packing body 1 can also be designed as an essentially cylindrical, rotationally symmetrical body. For example, the top and / or bottom of the packing body 1 can be fully or partially beveled. In the case of a hollow cylindrical shape, the top and bottom sides can each have a different inclination and / or inclination direction in the direction of the central longitudinal axis 19 than in the direction of the outer side. Depending on the design of the separating device 30, different shapes of the packing body 1 can thus be expedient. In the case of a product-tight design with the discharge base 42, a minimum level or a level that the product has in the grinding material discharge chamber is thus also ensured during operation in a vertical agitator mill.For this purpose, the fill body 1 has drainage channels 41, which define the overflow height h. However, the fill body 1 can also be designed with a smooth upper surface, i.e., without channels. The height H of the separating device 30 is greater than the overflow height h of the fill body.

[0021] A minimum product level of at least 85% of the height of the grinding media separating device should be ensured by the packing, so the overflow height h of the packing is h ≥ 0.85 H. Preferably, h is about 0.95 H. By means of the packing 1 shown, the volume of the grinding material discharge chamber is also reduced, for example, by at least about 70% and the height of a channel 41, which is formed immediately behind the separating device 30 by the packing 1 used, is reduced to, for example, about 10 mm, which leads to a flow rate of up to 2 m / s, at which excellent cleaning of the grinding material discharge channel 4 can be achieved.

[0022] The packing element 1 can be designed to be removable. However, the packing element 1 can also be designed or manufactured as a single piece with the discharge base 42 or the cover of the grinding material discharge chamber.

[0023] In another embodiment not forming part of the invention, the filler body 1 is designed such that it is not sealed against the discharge base 42 in a product-tight manner. This ensures only a reduction in volume within the separating device 30, i.e., the ground material discharge chamber, but not the aforementioned minimum product level. For example, spacers can ensure a defined distance from the discharge base 42, between which the product can drain.

[0024] The packing element 1 can also be designed so that it can be temperature-controlled. This ensures that the desired temperature of the product does not change or can be maintained during the dispersing process by inserting the packing element 1. Furthermore, the packing element 1 can be connected to an existing temperature system of the agitator mill, which is used in particular for cooling the components of the agitator mill. The separating device 30 is generally static, i.e., the packing element 1 also does not rotate. Therefore, connection to the temperature system of the agitator mill is easy to accomplish. If the packing element 1 is designed as a single piece with the machine, temperature control can be provided during the manufacturing process.

[0025] According to a further preferred embodiment, a device for setting a minimum level can also be provided, which, during operation, sets a minimum level of the product in the grinding material discharge chamber in a vertical agitator mill. In other words, a minimum level or a minimum product level is ensured or guaranteed in the grinding material discharge chamber. This reduces the dead space volume in the grinding material discharge chamber. This reduces air pockets in the product and ensures faster and more efficient processing and flow of the product. This device for setting a minimum level can be provided separately from or in addition to the packing 1. For example, the drain line 4 can be extended such that it reaches a certain height in the grinding material discharge chamber, i.e., within the separating device 30. This height is preferably at least 0.85 H.In other words, the product level within the ground material discharge chamber is at least 0.85 H. Particularly preferably, the height of the device for setting a minimum product level is 0.95 H. The device for setting a minimum product level can be removable or integral with the drain line 4. The device is sealed to the drain floor 42 in a product-tight manner. The device for setting a minimum product level can also be adjustable or controllable.

[0026] The packing according to the Fig. 1 The embodiment shown is shown separately in a sectional view in Fig. 2 The packing body 1 is designed to be rotationally symmetrical and is adapted to the grinding material discharge chamber behind the separating device 30 of an existing agitator mill. Due to the special design of the packing body, the grinding material discharge chamber is particularly in the upper area behind the separating device. Fig. 1 The channel 41 shown, which defines the overflow height h, is formed with a reduced cross-section, whereby the flow velocity is increased accordingly.

[0027] Fig. 3 shows a perspective view of the filler body 1 according to a preferred embodiment. This also shows a preferred arrangement of the channels 41. Other arrangements or dimensions may also be appropriate.

[0028] When starting up the agitator mill, it is desirable to displace any air in the outlet area with product as quickly as possible to prevent the formation of air pockets in the mill. Until now, the product has flowed out of the agitator mill at the lowest point of the separation device, with the air remaining above in the agitator mill. Using the packing element according to the invention and / or the device for setting a minimum level, the liquid or product outflow can be relocated upwards or to the highest point of the separation device. The dead space volume behind or inside the separation device is thus reduced, since product outflow is only possible above the packing element or the device for setting or ensuring a minimum level. This allows the mill to be completely filled before the material to be ground flows through the separation device.

[0029] After the product to be dispersed has passed through the separator, it should leave the agitator mill as quickly as possible. Therefore, the residence time distribution should be kept narrow, and plug flow is preferred.

[0030] In conventional agitator mills, product deposits can occur, particularly in the product discharge area, i.e., in particular in the grinding material discharge chamber and the discharge line. Therefore, the agitator mill must be thoroughly cleaned by the user before each product change, as product deposits from the previous product may otherwise be present in the current production run. Such product carryover can negatively impact the quality of the subsequent product. By increasing the flow rate and avoiding air pockets in the product by reducing the volume of the grinding material discharge chamber and / or raising the product level within the grinding material discharge chamber according to the present invention, such deposits and the resulting product loss can be reduced or even avoided.

[0031] As described above, the object of the present invention can be achieved by setting a minimum product level in the grinding material discharge chamber and / or by reducing the volume in the grinding material discharge chamber. In particular, the embodiments can be used individually as alternative solutions or in combination to achieve the objective of the invention.

[0032] The invention further comprises a method for operating and cleaning an agitator mill using the above-described device for reducing the volume of the grinding material discharge chamber. This achieves the advantages set forth in the present description. Accordingly, by using the device according to the invention for reducing the volume of the grinding material discharge chamber according to the method according to the invention, the flow rate of the grinding material through the grinding material discharge chamber during operation of the agitator mill can be achieved to be sufficiently high to reduce product deposits, particularly in the grinding material discharge chamber of the agitator mill.

[0033] By inserting a packing or cylindrical hollow body and / or a device for setting a minimum level according to the invention, the cleaning effort of the agitator mill and the use of cleaning agents can be reduced. Furthermore, there is less product loss during production and a narrower and thus more favorable residence time distribution. Any air present in the agitator mill can be displaced during start-up.

[0034] The packing according to the invention can be installed in existing vertical agitator mills. This does not require complex and expensive modifications; it can be easily retrofitted or converted.

[0035] Depending on the separating device, shapes other than a cylindrical shape may also be useful.

[0036] This solution can be used in particular for all vertical agitator mills with a sieve-like separation device. List of reference symbols

[0037] 1 Packing body 2 Grinding vessel 4 Drain pipe 8 Grinding chamber 9 Vessel wall 19 Central longitudinal axis 22 Internal stator 23 Outer wall 30 Grinding body separator 35 Rotor 38 Tools 41 Channel 42 Outflow base h Overflow height HHeight of the grinding body separator

Claims

1. An agitator mill for treating flowable material to be ground, comprising - a grinding container (2) and a grinding chamber (8) which is bounded by a container wall (9) of the grinding container (2) and is at least partially filled with grinding bodies, and - an agitator with a rotor (35) rotatable about a central longitudinal axis (19) arranged substantially vertically during operation, and - an inner stator (22) arranged inside the rotor (35), and - wherein a ground material discharge channel is formed between the rotor (35) and an outer wall (23) of the inner stator (22), through which the material to be ground is passed through a grinding body separating device (30) in the direction of a discharge pipe (4), wherein a ground material discharge chamber is formed downstream of the grinding body separating device (30) in the direction of flow of the material to be ground, - characterized in that a device for reducing the volume of the ground material discharge chamber is arranged in the ground material discharge chamber, wherein the device for reducing the volume closes in a product-tight manner with a discharge bottom (42) of the agitator mill and has an overflow height h of the product in the vertical direction, wherein the height H of the grinding body separating device (30) is greater than the overflow height h, wherein h is greater than or equal to 0.85 H.

2. The agitator mill according to claim 1, wherein the grinding body separating device (30) is configured in the form of a substantially vertically arranged cylinder having a height H, the inner space of which forming the ground material discharge chamber, and the device for reducing the volume of the ground material discharge chamber is formed by a filling body (1).

3. The agitator mill according to any one of claim 1 or 2, wherein the device for reducing the volume of the ground material discharge chamber is a substantially cylindrical hollow body.

4. The agitator mill according to any one of the preceding claims, wherein the device for reducing the volume of the ground material discharge chamber is made of plastic or metal or ceramic.

5. The agitator mill according to any one of the preceding claims, wherein the device for reducing the volume of the ground material discharge chamber is configured to be temperature-controllable.

6. The agitator mill according to any one of the preceding claims, wherein the separating device (30) is a cylindrical screen.

7. The agitator mill according to any one of the preceding claims, wherein the device for reducing the volume of the ground material discharge chamber is removable.

8. The agitator mill according to any one of the preceding claims, wherein the device for reducing the volume of the ground material discharge chamber reduces the volume of the ground material discharge chamber by at least 70%.

9. The agitator mill according to any one of the preceding claims, wherein tools (38) projecting into the grinding chamber (8) are attached to the rotor (35) and optionally to the container wall (9).

10. The agitator mill according to any one of the preceding claims, comprising a device for setting a minimum level.

11. A method of operating and cleaning the agitator mill according to any one of the preceding claims, wherein by inserting the device for reducing the volume, the flow rate is increased and air entrapment is avoided.