Wear resistant rotor

Abstract

A rotor for a stirred mill has a generally cylindrical rotor body, the outer wall of which defines an inner surface of a grinding chamber through which a material to be ground flows during operation of the stirred mill. A ceramic ring is arranged at the rotor end of the rotor body, with the rotor end facing the product inlet of the stirred mill. The invention further relates to a stirred mill with the rotor according to the invention, the use of the rotor according to the invention in a stirred mill for the production of dispersions, and a method for manufacturing the rotor.

Description

[0001] The invention relates to a rotor for a stirred mill, and in particular to a wear-resistant, dimensionally stable plastic rotor.

[0002] Stirred mills have a wide range of applications for grinding and dispersing solids in liquids. They are used, for example, in the production of adhesives, printing inks, cosmetics, pharmaceuticals, and also for the production of raw materials (especially silicon) for battery pastes. In a typical vertical stirred mill, a grinding chamber is formed by a rotor and a stator rotating around a vertically oriented central longitudinal axis. Dispersions are produced in this chamber, optionally with the use of grinding aids such as ceramic spheres. For this purpose, grinding tools, for example in the form of round pins, can be attached to the rotor and / or the stator. The material to be ground is fed into the grinding chamber via a product inlet, ground there, and discharged via a product outlet. Such a stirred mill is known, for example, from EP 1 992 412 A1.

[0003] Especially in the production of raw materials for battery pastes, finenesses of x50 = 100 to 200 nm must be achieved, which necessitates long grinding times. Due to the abrasiveness of the solid being processed, significant wear of the process zone in the grinding chamber is to be expected. Furthermore, metallic contamination in the final product should be avoided, so the use of a metal-free rotor for the stirred mill is preferred over the otherwise conventional steel rotor.

[0004] The use of ceramic and plastic rotors is known in the art. However, the production of ceramic rotors is very expensive and structurally complex. Due to their hardness, materials such as SSiC or SiSiC are very wear-resistant, but also prone to breakage. These two ceramics also have very good thermal conductivity, significantly higher than steel. However, the production of large components is very problematic.

[0005] Metallic contamination can also be avoided by using plastic rotors. However, depending on the material being ground, this type of rotor can wear out quickly. The plastic material suffers particularly in areas of compressed grinding media (areas of high energy density). It is also essential to check beforehand whether the plastic used for the rotor is compatible with the material being ground, i.e., whether its chemical resistance is guaranteed. The generally poor thermal conductivity of plastics is a significant disadvantage.

[0006] DE 10 2014 101 827 B3 describes a wear protection arrangement for a stirred mill. An object of the present invention is to provide a cost-effective rotor for a stirred mill that is dimensionally stable and, in particular, resistant to common solvents and can be used especially for the production of battery pastes. The wet milling of abrasive solids should be possible without disruptive wear in the final product.

[0007] The basic idea of ​​the invention is to use a rotor body for a stirred mill that incorporates a ceramic wear element in the high-energy-density region, particularly in the lower part of the process zone, i.e., at the lower end of the rotor. In vertically arranged stirred mills, in particular, high wear occurs at the bottom of the process zone, i.e., in the lower part of the rotor, due to gravity and the deflection of the grinding media by the product solids and the grinding media, combined with the high rotor speed. Generally, the highest wear in stirred mills occurs at the rotor end, i.e., at the point opposite the product inlet.

[0008] According to the invention, a rotor as defined in claim 1 is provided. The rotor has a generally cylindrical rotor body, the outer wall of which defines an inner surface of a grinding chamber through which a material to be ground flows during operation of the stirred mill. A ceramic ring is arranged in a region of the rotor with high energy input. This region is the side of the rotor opposite the product inlet to the stirred mill. In a vertical stirred mill, this is the lower section of the rotor body. In particular, a surface of the ceramic ring forms a section of the outer wall of the rotor that forms the inner surface of the grinding chamber. This section preferably extends to grinding tools arranged on the outer wall of the rotor. In this way, the ceramic ring can be secured against rotation and / or falling off by the grinding tools.

[0009] The ceramic ring is preferably connected to the rotor body, in particular by screws, adhesive bonding, or a form-fit connection. The rotor body is made of plastic, so the ceramic ring can also be cast into the rotor body.

[0010] The ceramic ring can have a substantially L-shaped cross-section, with the longer side of the L-shaped ceramic ring, i.e., its leg, located on the outer surface of the rotor. Alternatively, the ceramic ring can have a substantially U-shaped cross-section, with its legs located on the outer and inner surfaces of the rotor.

[0011] Preferably, the ratio L / D of the length L of the section of the rotor's outer wall formed by the ceramic ring to the rotor's outer diameter D is between 0.05 and 0.5. The ratio S1 / S2 of the thickness S1 of the section of the ceramic ring forming the rotor's outer wall to the total rotor wall thickness S2 is preferably between 0.1 and 0.9.

[0012] The plastic rotor can be made of at least one of the following materials: PA, PET, PEEK, PVDF, and POM. The ceramic ring, in turn, can be made of at least one of the following materials: ZrO₂, SSiC, SiSiC, and Si₃N₄.

[0013] The present invention further provides a stirred mill with a rotor according to the invention. Similar to a known mill, the stirred mill according to the invention also has a stator with an inner stator wall, wherein the rotor is arranged inside the stator. Furthermore, a product inlet and a product outlet are provided, and the grinding chamber is formed between the inner stator wall and the outer wall of the rotor. The material to be ground can be fed into the grinding chamber via the product inlet and out of the grinding chamber via the product outlet.

[0014] For a ratio of the rotor's outer diameter D to the stator's inner diameter D2, 0.6 ≤ D / D2 ≤ 0.95 is preferred. Furthermore, the stirred mill can have an inner stator arranged within a section of the rotor, with a product outlet formed between the rotor and an outer wall of the inner stator. For a ratio of the inner stator's outer diameter d22 to the rotor's inner diameter d1, 0.8 ≤ d22 / d1 ≤ 0.98 is preferred.

[0015] The invention further relates to the use of the rotor according to the invention in a stirred mill for the production of dispersions, in particular a battery paste, and to a method for manufacturing the rotor. The method comprises the step of joining, in particular by gluing, screwing or positive locking, a ceramic ring to the rotor body.

[0016] The invention is described in more detail below with reference to the figures, wherein Figure 1 a cross-sectional view of a state-of-the-art vertical stirred mill, Figure 2 a cross-sectional view of a rotor for a vertical stirred mill according to an embodiment of the present invention and Figure 3 Figure 1 shows a cross-sectional view of a rotor for a vertical stirred mill according to a further embodiment of the present invention.

[0017] Fig. 1 This shows an example of a section of a vertically arranged stirred mill according to the state of the art. The in Fig. 1The illustrated stirred mill has, in the usual manner, a grinding container or stator 2 with an internal grinding chamber 8. The grinding chamber 8 is at least partially filled with grinding media 43. The stirred mill also has an inner stator 22 and a rotor 35 rotatable about a central longitudinal axis 19. First tools 38 are attached to the rotor 35 and project into the grinding chamber 8. Second tools 74 are attached to the inner wall 9 of the container or stator and also project into the grinding chamber 8. The processed material is guided through a gap between the rotor 35 and the inner stator 22 to a protective screen 30, which retains the grinding media 43, and flows out via a discharge line 31.

[0018] The Figure 2 shows a cross-sectional view of a rotor for a system as described in Figure 1The vertical stirred mill shown. The rotor according to the illustrated embodiment of the invention has a general cylindrical rotor body 351 with an outer wall 32. The rotor body 351, with an outer diameter D, is made of plastic. The rotor, together with the in Figure 1 The stator shown, in operation of the stirred mill, is a grinding chamber through which the material to be ground flows.

[0019] The greatest wear on the rotor of a vertical stirred mill typically occurs in the lower region of the rotor, specifically in the area where high energy densities arise due to gravity and the deflection of the material being ground by the grinding media, combined with the high rotor speed. Generally, in stirred mills, both vertical and horizontal, the area experiencing the greatest wear is the area opposite the product inlet during operation. According to the present invention, a ring-shaped wear ring made of a hard and therefore highly wear-resistant ceramic material is provided precisely in this area. Examples of such materials include ZrO₂, SSiC, SiSiC, and Si₃N₄.Thus, the rotor 35 can be largely manufactured from a cost-effective rotor body, while the wear-prone sections are replaced by the wear-resistant ceramic material.

[0020] As shown in the section labeled Y and additionally enlarged, the Figure 2 In detail, the ceramic ring 352 can essentially have an L-shaped profile, with the short side of the L forming the underside and the long side, i.e., the leg of the L, forming the lower section of the outer surface 32, where the greatest wear occurs. The ceramic ring 352 thus forms the lower section of length L of the outer surface 32 and the underside of the rotor with a total wall thickness S2.

[0021] The ceramic ring 352 is connected to the rotor body, for example by screws, adhesive, or by being cast into the plastic. On the outer surface 32 of the rotor, the ceramic ring 352 preferably extends to the lowest row of grinding tools 38, as shown in the section marked X in the Figure 2 shown. Thus, the ceramic ring 352 can be additionally secured against twisting or falling off by the tools 38.

[0022] The wall thickness S1 of the ceramic ring relative to the total wall thickness S2 of the rotor should preferably be 0.1 < S1 / S2 < 0.9.

[0023] Figure 3 Figure 1 shows a cross-sectional view of a rotor according to a further embodiment of the present invention. As in Figure 2, the following applies: Figure 2 A ceramic wear element is attached to the lower section of the rotor body 351. According to the Figure 3 In the embodiment shown, this is again realized in the form of a ceramic ring 352, which, however - unlike in Figure 2- has an essentially U-shaped profile, such that - in addition to the underside and a section of the outer surface 32 - a section of the surface of the inner side of the rotor is also reinforced by the wear element through the second leg of the U, i.e., a section of the product discharge. This is shown in more detail in the section labeled Y in Figure 3 shown. On the outer side 32, the ceramic ring 352 can again extend at least as far as the lowest row of the grinding tools 38, as shown in the section marked X of the Figure 3 shown.

[0024] The invention further provides a stirred mill that uses the rotor according to the invention. For this purpose, only the rotor 35, as exemplified in the Figure 1 as shown, by means of a rotor according to the invention, such as that shown for example in the Figure 2 or 3The figure shows, replaced. Typical dimensions of such a stirred mill result in values ​​between 0.6 and 0.95 for the ratio of the outer diameter of the rotor 35 to the inner diameter of the stator 2. The ratio of the outer diameter of the inner stator 22 to the inner diameter of the rotor 35 is, for example, 0.8 to 0.98.

[0025] The rotor according to the invention can be produced, in particular, by connecting a ceramic ring 352 to the rotor body 351. This can be done, in particular, by gluing, screwing, or positive locking. If the rotor body 352 is made of plastic, the ceramic ring 352 can also be cast into the plastic body 351.

[0026] The rotor and the stirred mill using this rotor according to the present invention are particularly suitable for the production of dispersions requiring high fineness, for example finenesses of x50 = 100 to 200 nm, which necessitate long milling times, and these dispersions must be kept as free as possible from metallic contamination. This is the case, for example, for the raw material production of battery pastes.

Claims

1. A rotor (35) for an agitator mill, comprising a generally cylindrical rotor body (351), the outer wall (32) of which defines an inner surface of a grinding chamber through which the grinding material to be treated flows during operation of the agitator mill, characterized in that a ceramic ring (352) is arranged at the rotor end of the rotor body (351), wherein the rotor end is opposite the product inlet of the agitator mill, wherein the rotor body (351) is made of plastic.

2. The rotor (35) according to claim 1, wherein the rotor (35) is configured for use in a vertical agitator mill.

3. The rotor (35) according to claim 1 or 2, wherein the ceramic ring (352) is connected to the rotor body (351), in particular by screwing or form-fitting connection.

4. The rotor (35) according to any one of the preceding claims, wherein a surface of the ceramic ring (352) forms a portion of the outer wall (32) of the rotor forming the inner surface of the grinding chamber.

5. The rotor (35) according to claim 4, wherein the portion extends to grinding tools (38) arranged on the outer wall (32) of the rotor, and the ceramic ring (352) is secured by the grinding tools (38) against twisting and / or falling off.

6. The rotor (35) according to any one of the preceding claims, wherein the ceramic ring (352) has a substantially L-shaped cross-section and wherein the leg of the L-shaped ceramic ring (352) is arranged on the outer surface (32) of the rotor (35).

7. The rotor (35) according to any one of claims 1 to 5, wherein the ceramic ring (352) has a substantially U-shaped cross-section and wherein the legs of the U-shaped ceramic ring (352) are arranged on the outer surface (32) and the inner surface of the rotor (35).

8. The rotor (35) according to any one of the preceding claims, wherein the ratio L / D of the length L of the portion of the outer wall (32) of the rotor (35) formed by the ceramic ring (352) to the outer diameter D of the rotor (35) is between 0.05 and 0.5.

9. The rotor (35) according to any one of the preceding claims, wherein the ratio S1 / S2 of the rotor wall thickness S2 to the thickness S1 of the portion of the ceramic ring (352) forming the outer wall (32) of the rotor (35) is between 0.1 and 0.9.

10. The rotor (35) according to any one of the preceding claims, wherein the rotor body (351) comprises at least one of the following materials: PA, PET, PEEK, PVDF, and POM.

11. The rotor (35) according to any one of the preceding claims, wherein the ceramic ring (352) comprises at least one of the following materials: ZrO2, SSiC, SiSiC, and Si3N4.

12. An agitator mill comprising: a rotor (35) according to any one of the preceding claims; a stator (2) with a stator inner wall (9), wherein the rotor (35) is arranged inside the stator (2), a product inlet, and a product outlet, wherein a grinding chamber (8) is formed between the stator inner wall (9) and the outer wall (32) of the rotor (35), wherein the material to be ground can be fed into the grinding chamber (8) via the product inlet and can be discharged from the grinding chamber (8) via the product outlet.

13. Use of the rotor (35) according to any one of claims 1 to 11 in an agitator mill for producing dispersions, in particular a battery paste.

14. A method for manufacturing the rotor (35) according to any one of claims 1 to 11, characterized by the step of: - connecting, in particular bonding, screwing or form-fitting connecting, the ceramic ring (352) to the rotor body (351).

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