EP3536406A1 - Agitator mill - Google Patents

Abstract

The invention provides an agitator mill for treating flowable millbase. The agitator mill comprises a grinding container (2), a grinding chamber (8) delimited by a container wall (9), and an agitator rotatable about the central longitudinal axis (19) with a rotor (35) having an internal diameter d351 on. On the rotor tools (38) are mounted, which extend in the direction of the container wall (9). The agitator mill further includes an inner stator (22) disposed within the rotor (35). Between the rotor (35) and an outer wall (23) of the inner stator (22) a Mahlgutabführkanal (47) is formed through which the material to be ground to the separator (30) and then to a drain line (31) is guided. The grinding chamber (8) is at least partially filled with grinding media of diameter c. Above the inner stator (22) is arranged a separator (30) with a diameter d30. For the distance s between rotor (35) and grinding element separating device (30), s = 0.5 * (d351 - d30) ≤ 5 * c.

Description

The invention relates to a stirred mill according to the preamble of claim 1.

The invention makes reference to the European patent specification EP 1 992 412 A1 , From this, such a stirred mill is known. Agitator mills are used to disperse suspensions, ie solids in liquids. This is used, for example, in the production of adhesives, printing inks, cosmetics or pharmaceuticals. For this purpose, the millbase 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, and comminuted together with Mahlhilfskörpern, such as ceramic balls, which are also referred to as a grinding media, and with the aid of tools which are arranged on the rotor and / or on the container wall. The stirring agglomerates are dispersed and crushed crystal structures. The original particle size of 100-500 microns can be reduced to less than 3 microns. The finished product is then directed via a Mahlgut-discharge channel through a Mahlkörpertrenneinrichtung, in particular in the form of a protective sieve, to a drain line. The rotor forms a kind of rotating cage around the separator.

In such Rührwerksmühlen the grinding media should be possible only in the grinding space between the rotor and the container wall. The grinding media are accelerated and concentrated outwardly by the tools mounted on the rotor and extending to the vicinity of the vessel wall and by the centrifugal forces created. If tools are arranged on the container wall, they extend in the direction of the rotor. The optionally arranged on the container wall tools are preferably arranged offset from the tools mounted on the rotor, so that they can pass through during the rotation of the rotor between the arranged on the container wall tools. The millbase flows through this dense grinding media packing in the direction of the rotor axis. By concentrating the grinding media in the grinding chamber can be largely avoided that they get into the grinding stock-discharge channel. In addition to the concentration of grinding media in the annular outer grinding chamber are in the grinding stock discharge channel Provided means to prevent flow through the grinding media to the separator.

In Mahlgut-discharge channel, which is usually located within the rotor and is limited by the rotor and the inner stator, are therefore possible no or very few grinding media. Nevertheless, the presence of grinding media on the separator can lead to increased pressure in the agitator mill, which can lead to a reduction in the product flow or even to automatic shutdown so as not to damage the agitator mill. In prior art agitator mills, wipers may be mounted on the separator to keep the media away from the separator. However, this may not be desirable in the dispersion of thermally sensitive materials, in particular explosives or other hazardous materials, since heat can be caused by the scrapers in the millbase.

The invention has for its object to avoid the flooding of grinding media on the Mahlkörpertrenneinrichtung due to drag forces and consequent blockage of the separator.

This object is achieved by the features of claim 1. The essence of the invention is to effectively prevent accumulation of grinding media on the separator by reducing the distance between rotor and separator. This can be achieved by increasing the diameter of the separating device, ie in particular the sieve diameter. In particular, the distance between the rotor and separator can be selected depending on the diameter of the grinding media, rather than exclusively depending on the size of the agitator mill. Furthermore, a maximum value, which is independent of the size of the grinding media, can be set for the distance. By this measure, the accumulation of trapped due to drag forces to the separator grinding media can be reduced. Thus, both a steady flow of product and a rapid reduction of the coarse grain is guaranteed in the product to be dispersed.

In particular, the object is achieved by an agitator mill having the following features. The agitator mill has a grinding container and a grinding chamber which is delimited by a container wall, and an agitator rotatable about the central longitudinal axis a rotor with an inner diameter d351. On the rotor tools are mounted, which extend in the direction of the container wall. Furthermore, second tools can be arranged on the container wall, which extend in the direction of the rotor. The agitator mill further includes an inner stator disposed within the rotor. Between the rotor and an outer wall of the inner stator, a Mahlgutabführkanal is formed, through which the ground material is passed to the separator and then to a drain line. The grinding chamber is at least partially filled with grinding media of diameter c. Above the inner stator, a separator is arranged with a diameter d30. From the difference between the inner diameter of the rotor and the diameter of the separator results in the size of the distance s between the rotor and separator. According to the invention, this distance s should be selected as a function of the diameter c of the grinding bodies, and s = 0.5 · (d351 - d30) ≦ 5 · c. In a further preferred embodiment, the distance s depending on the diameter c of the grinding media s ≦ 3 · c amount. Furthermore, according to an embodiment of the invention, the distance s, also irrespective of the size of the grinding bodies, should not exceed the value of 2 mm.

Preferably, the tools mounted on the rotor leave only a small gap to the container wall 9, wherein the gap has a gap width b, for which applies in relation to the diameter c of the grinding media: 4c ≤ b ≤ 6c, where the minimum gap width b is: 1 , 0 mm ≤ b ≤ 2.0 mm.

At the inner stator extending to the rotor stripping tools can be arranged. These stripping tools, if present, preferably overlap one another in the direction of the central longitudinal axis and are arranged on the inner stator such that they exert a pulse directed in the direction of flow on the grinding media when the rotor is driven.

Between the stripping tools and the rotor, a gap is preferably formed whose gap width e in relation to the diameter c of the grinding bodies is: 4c≤e≤6c, where the following applies for a minimum gap width e: 1.0 mm≤c≤2, 0 mm.

Furthermore, grinding element return channels for returning the grinding elements from the region of the separating device to the grinding chamber are formed in the agitator.

For the diameter c of the grinding media, preferably c ≦ 0.65 mm and preferably 0.02 mm ≦ c ≦ 0.3 mm.

Further features, advantages and details emerge from the following description of the invention with reference to the drawing. It shows
Fig. 1 FIG. 2: a detail of an agitator mill according to an embodiment of the invention as a vertical longitudinal section

beschrieben werden und kann insbesondere durch die Wahl den Durchmesser d30 des Schutz-Siebes 30 eingestellt werden.In the Fig. 1 shown agitator mill has in the usual way a grinding container 2 with an internal grinding chamber 8. The grinding chamber 8 is at least partially filled with grinding bodies 43 (not shown) with a diameter c. The agitator mill further comprises an inner stator 22 and a rotor 35 rotatable about a central longitudinal axis 19 with a diameter d351. In this case, a regrind discharge channel 47 is formed between an outer wall 23 of the stator 22 and the rotor 35. On the rotor 35 tools 38 are mounted, which protrude into the grinding chamber 8. Furthermore, 9 second tools 74, offset from the attached to the rotor 35 tools are arranged on the container wall. Above the stator 22 is located as a separating device, a protective sieve 30 which is rotationally symmetrical to the central longitudinal axis 19 is formed. The protective screen 30 prevents the flow of grinding media 43 in a downstream drain line 31, which is located within the inner stator 22. Between protective sieve 30 and rotor 35, a distance s is formed. The distance s can be as $$\mathrm{s}=\mathrm{0}.\mathrm{5}\cdot \left(\mathrm{d}\mathrm{351}-\mathrm{<figure-callout\; id="30"\; label="d"\; filenames="imgf0001.png"\; state="\{\{state\}\}">d</figure-callout>}\mathrm{30}\right)$$

can be described and can be adjusted in particular by the choice of the diameter d30 of the protective sieve 30.

With an increase in the dimensions of the agitator mill, the distance s between protective sieve 30 and rotor 35 has also been selected to be correspondingly greater. However, contrary to expectations, this does not lead to a proportional increase in the product flow. Rather, the product flow falls short of expectations.

This is due to the fact that it may happen in operation that due to the drag forces and despite a means for retaining the grinding media 43 they are washed ashore on the protective sieve 30. This can lead to flow reduction or complete blockage of the screen.

To effectively prevent this, the distance s between the protective screen 30 and rotor 35 is reduced. The distance s can be selected independently of the design of the agitator mill depending on the diameter c of the grinding media. This leads to a higher permeability of the agitator mill, since the risk of alluvium being flooded 43 drops to the protective screen 30 and thereby to a faster reduction of the coarse grain in the product to be dispersed.

bzw. $$\mathrm{0},\mathrm{5}\cdot \left(\mathrm{d}\mathrm{351}-\mathrm{d}\mathrm{30}\right)\le \mathrm{5}\cdot \mathrm{c}\mathrm{.}$$

According to the invention, the distance s between the protective sieve 30 and the rotor 35 is dependent on the grinding body diameter c $$\mathrm{s}\le \mathrm{5th}\mathrm{c}$$

or. $$\mathrm{0}.\mathrm{5}\cdot \left(\mathrm{d}\mathrm{351}-\mathrm{<figure-callout\; id="30"\; label="d"\; filenames="imgf0001.png"\; state="\{\{state\}\}">d</figure-callout>}\mathrm{30}\right)\le \mathrm{5}\cdot \mathrm{c}\mathrm{,}$$

In a further preferred embodiment, the distance s depends on the grinding body diameter c $$\mathrm{s}\le \mathrm{3}\cdot \mathrm{c}\mathrm{,}$$

In a further preferred embodiment, the distance s, regardless of the size of the grinding media, is no greater than 2 mm.

Although the above-described embodiment shows an agitator mill with a vertical central longitudinal axis 19, the described embodiments are also readily usable in a horizontal position or in an intermediate position.

Claims (11)

Agitator mill for treating flowable regrind, - With a grinding container (2) and a grinding chamber (8) which is bounded by a container wall (9), and - With a about a central longitudinal axis (19) rotatable agitator with a rotor (35) having a diameter d351, and - Wherein on the rotor (35) tools (38) are mounted, which extend in the direction of the container wall (9), and - With an inner stator (22) which is disposed within the rotor (35), and - Wherein a Mahlgutabführkanal is formed between the rotor (35) and an outer wall (23) of the inner stator (22), and - Wherein the grinding chamber (8) is at least partially filled with grinding media of diameter c, and - wherein above the inner stator (22) a Mahlkörpertrenneinrichtung (30) is arranged with diameter d30, and
characterized,
that for the distance s between the rotor (35) and the grinding element separating device (30): $$\mathrm{s}=\mathrm{0}.\mathrm{5}\cdot \left(\mathrm{d}\mathrm{351}-\mathrm{d}\mathrm{30}\right)\le \mathrm{5}\cdot \mathrm{c}\mathrm{,}$$

Agitator mill according to claim 1, wherein the following applies for the distance s between the rotor (35) and the grinding element separating device (30): $$\mathrm{s}=\mathrm{0}.\mathrm{5}\cdot \left(\mathrm{d}\mathrm{351}-\mathrm{d}\mathrm{30}\right)\le \mathrm{3}\cdot \mathrm{c}\mathrm{,}$$

Agitator mill according to claim 1 or 2, wherein s ≤ 2 mm. Agitator mill according to claim 1 to 3, wherein the Mahlkörpertrenneinrichtung (30) comprises a cylindrical protective sieve. Agitator mill according to claim 1 to 4, wherein the tools (38) attached to the rotor (35) leave only a small gap (39) to the container wall (9), wherein the gap between the tools (38) and the container wall (9) has a gap width b has, for the relative to the diameter c of the grinding media: 4c ≤ b ≤ 6c, where the minimum gap width b is: 1.0 mm ≤ b ≤ 2.0 mm. Agitator mill according to one of claims 1 to 5, wherein the inner stator (22) extending to the rotor (35) extending stripping tools are arranged. Agitator mill according to claim 6, wherein the scraper tools arranged on the inner stator (22) overlap one another in the direction of the central longitudinal axis (19) and are arranged on the inner stator (22) in such a way that they are driven when the rotor ( 35) exert a pulse directed in the direction of flow on the grinding media. An agitator mill according to claim 7, wherein a gap is formed between the stripping tools and the rotor (35), whose gap width e in relation to the diameter c of the grinding media is: 4c≤e≤6c, wherein for a minimum gap width e: 1.0 mm ≤ c ≤ 2.0 mm. Agitator mill according to one of claims 1 to 8, wherein second tools (74) are arranged on the container wall (22), which extend in the direction of the rotor (35). Agitator mill according to one of claims 1 to 9, wherein in the agitator (20) Mahlkörper-return channels (55) for returning the grinding media (43) from the region of Mahlkörpertrenneinrichtung (30) are formed in the grinding chamber (8). Agitator mill according to one of claims 1 to 10, wherein for the diameter c of the grinding media: $$\mathrm{c}\le \mathrm{0}.\mathrm{65}\mathrm{mm\; and\; preferred}\mathrm{0}.\mathrm{02}\mathrm{mm}\le \mathrm{c}\le \mathrm{0}.\mathrm{3}\mathrm{mm}\mathrm{,}$$

Images