ES2356855T3 - MILL AGITATOR. - Google Patents

Abstract

A stirrer mill comprises a grinding vessel (2) and a stirring shaft (5) arranged such that it can be driven to rotate therein. Mounted at the end of the stirring shaft (2) is a last stirring disc (17) on which is mounted a substantially cylindrically shaped cage (19) having perforations (20). Inside the cage (19) is arranged a screening device (23). The distance between a second-last stirring disc (14) and the last stirring disc (17) is such as to form a braided flow (32) while avoiding a preclassification of grinding material on the one hand and grinding aids (31) and coarse grinding material particles on the other hand. In the last stirring disc (17) are formed openings (22) through which the grinding material together with the grinding aids (31) enters an annular gap (28) which is formed by the last stirring disc (17) and an intermediate wall (27) coupled fixedly in rotation therewith. The grinding aids (31) and the coarse grinding material particles are separated inside the separating chamber (21) formed by the last stirring disc (17) and the cage (19).

Description

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

 An agitator mill of this type is known from EP0751830B1. In this last agitator mill, the distance between the last agitator disc that carries the cage and the adjacent agitator disc is substantially smaller than the distance between the other agitator discs. This is because between the stirring discs, with the exception of the last stirrer disk 5, the distance is respectively so large that so-called braided currents occur, that is, next to the stirring discs, the material to be ground circulates with Auxiliary bodies grind out because of the tangential impulses exerted by the stirring discs. In the central area between the adjacent stirring discs, the material to be ground and the auxiliary grinding bodies return to flow back towards the agitator shaft. In order for the mentioned braided currents to occur, the distance between the adjacent stirring discs must be sufficiently large. This distance is also defined by a so-called separation angle enclosed by two lines. A line extends between a radially inner end of a stirring disc in the agitator shaft. The other line extends parallel to the axis of the agitator shaft. For such braided currents to occur, the separation angle must be between 30º and 60º. For a particularly good separation of the grinding auxiliary bodies of the ground material, including the particles of the material to be ground, not yet crushed sufficiently, the distance between the last stirrer disk and the adjacent stirrer disk is clearly reduced , so that there takes place a prior classification before the separation device, avoiding the formation of a braided current. In this way, it is intended that at least an essential part of the auxiliary grinding bodies and the coarse particles of material to be ground, not yet sufficiently crushed, do not even reach the separation device, in which it is carried out then a secondary separation of the auxiliary grinding bodies and the coarse particles of material to be ground. The disadvantage of this is that by these measures the active grinding space is reduced and the separation chamber increases in total.

 From EP0700723A a stirrer mill is known with a grinding vessel that surrounds a milling chamber, an inlet of material to be ground and an outlet of ground material being provided at the same end of the milling chamber. An agitator shaft is provided in the grinding chamber that can be rotatably operated and in which stirring discs are arranged at equal distances between them. In the agitator disc adjacent to the ground material outlet there is a cylinder with passage slits. Within said cylinder there is a grill screen arranged in front of the ground material outlet. Between the last agitator disc, with respect to the material stream to be ground, and a contiguous lid of the grinding vessel is provided a relatively large clearance, from which inlet channels flow into a return channel made within the shaker tree On the agitator disc 30 adjacent to the grill screen, a deflection disk is formed which forms a groove with respect to the adjacent agitator disc. The return channel flows into said groove. The material to be ground circulates from the entrance of the material to be ground, dragging the auxiliary grinding bodies, through the milling chamber where it is ground and dispersed in a known manner. In the relatively large free space between the last agitator disc and the adjacent lid of the grinding vessel, it circulates to the return channel and, through it, to the slit between the deflection disk and the adjacent agitator disc 35, where the bodies Grinding aids are thrown out and are again dragged by the material to be ground that enters the milling chamber, returning to the milling process.

 The object of the invention is to configure a generic type agitator mill so that, without increasing the construction length, a more intense grinding and dispersion process is produced together with a better separation of the auxiliary grinding bodies and the coarse particles of material to be ground, not sufficiently ground. 40

 According to the invention, this objective is achieved by means of the characteristics indicated in the characterizing part of claim 1. By means of the measures according to the invention it is achieved that even between the last stirring disc and the adjacent stirring disc an intense grinding process and dispersion, also producing in this area the braided currents necessary for the process. The separation of the auxiliary grinding bodies and coarse particles of material to be ground, not sufficiently ground, takes place within the separation device. The intermediate part 45 which rotates together with the agitator shaft avoids the axial impact of the auxiliary grinding bodies and the coarse particles of material to be ground on the end plate that closes the screening device, causing the material to be It must be ground and the auxiliary grinding bodies are transported at high radial speed in the direction of the cage. Auxiliary grinding bodies and coarse particles not yet sufficiently ground, substantially, are released radially through the cage openings, while the finely ground and dispersed material is diverted into the cage around the outer edge of the intermediate wall and is evacuated through the sieve. The variants according to claims 2 to 5 lead to an increase in these effects.

 By means of the variant according to claim 6, it is achieved even more pronounced that even between the last stirring disc and the adjacent stirring disc the described twisted currents are produced, so that a grinding process takes place with the same intensity as between stirring discs arranged ahead. The variants according to claims 7 and 8 serve the same purpose.

 The variant according to claim 9 causes the material to be ground, with the normal concentration of

Auxiliary grinding bodies, the entire gap between the last agitator disc and the intermediate wall is passed through the steps.

 More advantages, features and details of the invention result from the following description of embodiments with the help of the drawing. They show:

Figure 1 a shaker mill in schematic representation, in a side elevation, in a partially open view,

Figure 2 a first embodiment for the agitator mill outlet area,

Figure 3 a second embodiment for the agitator mill outlet area,

Figure 4 a stirrer disk in a perspective representation,

Figure 5 a last agitator disk with cage in a perspective representation,

Fig. 6 another embodiment of a stirrer disk, 10

Figure 7 another embodiment of a last agitator disc with cage in a perspective representation and

Figure 8 shows a partial section through the last stirrer disk according to section line VIII-VIII in Figure 7.

 The agitator mill shown in the drawing has a machine upright 1 to which a grinding vessel 2 is detachably attached. In the machine upright 1 there is a drive motor 3 which drives a drive through a belt drive 4. stirring shaft 5 of a stirring mill 6. The stirring shaft 5 is rotatably housed 15 in bearings 7 in the machine stud 1. In the grinding vessel 2 itself, namely, at its opposite end to the machine stud 1, Shaker shaft 5 is not housed, that is, it is housed in cantilever in machine stile 1.

 The grinding vessel 2 is closed with respect to the machine upright 1 by means of a cover 8 crossed by the stirring shaft 5, a sealing being carried out by means of a shaft seal 9. In the area of the lid 8, in the grinding chamber 20 enclosed by the grinding vessel 2 enters an inlet of material to be ground 11. From the end of the milling vessel 2, opposite the inlet of material to be ground 11, from its bottom 12 which closes the milling chamber 10 an outlet of ground material 13 comes out.

 In the stirring shaft 5, stirring tools are arranged as stirring discs 14, as part of the stirring mechanism, the stirring discs 14 having holes 15 in their outer circumferential zone. The distances 25 a of the adjacent stirring discs 14 in the direction of the shaft 16 of the stirring shaft 5 are respectively equal. Only the distance between the stirring disc 14 directly adjacent to the cover 8, and the cover 8, is less than the distance a.

 As can be seen in Figure 2, the last stirrer disk 17, adjacent to the bottom 12, of the stirrer mechanism 6, is fixed by means of a fixing screw 18 to the stirrer shaft 5. The axial distance a 'of this stirrer disk 17 with respect to The next to last agitator disc 14 of the agitator mechanism 6 is identical to the corresponding axial distances a before mentioned 30 between the adjacent agitator discs 14. The diameters b of all stirring discs 14 and the diameter b 'of stirring disc 17 are also identical.

 In the outer circumference of the last stirrer disk 17 a cylindrical cage 19 is made, which can be configured in one piece with the last stirrer disk 17. It has numerous openings 20 distributed along its circumference. In the separation chamber 21 surrounded by the stirrer disk 17 and the cage 19, passages 22 of the last stirrer disk 17, carried out adjacent to the stirrer shaft 5.

 In the separation chamber 21, at the bottom 12 a screen device 23 is arranged concentrically to the axis 16. It is arranged at the bottom 12, namely in such a way that the screen device 23 can be pulled out after being released from the bottom 12. Therefore, it is non-rotatably connected with the grinding vessel 2. From the inner space 24 of the screening device 23 the exit of ground material 13 comes out. The screening device 23 can be formed by annular discs 40 arranged in a known way in its cylindrical circumference at a small distance between them. The inner side of the stirring disc 17, the cage 19 and the screening device 23 thus form a separation device 25. The screening device 23 may have a closed end plate 26, adjacent to the stirring disk 17. Therefore, the interior space 24 of the screen device 23 is connected to the separation chamber 21 only through the screen device 23.

 In the agitator mechanism 6, between the agitator disk 17 and the end plate 26 there is a closed intermediate wall 27 45 which rotates together with the agitator mechanism 6 and limits an interstitial space 28. While in the embodiment according to the figure 2, said intermediate wall 27 is fixed to the agitator shaft 5 with the fixing screw 18, in the exemplary embodiment according to figure 3, the intermediate wall 27 'is arranged directly on the agitator disk 17 by means of spacer parts 29 in the form of wings distributed by the circumference. The intermediate walls 27 and 27 'respectively extend radially at least along the end plate 26; therefore, it is applicable: c> d, where c is 50

diameter of the intermediate wall 27 and 27 'and d being the diameter of the end plate 26. Preferably, it is applicable: c> d, the corresponding intermediate wall 27' extending to near cage 19.

 The configuration according to figure 3 also differs from that of figure 2 in that in the stirrer disk 17 ', on the side facing the adjacent stirrer disk 14, cavities 30 are made which have the same shape as the holes 15 in the stirring discs 14 and having the same cross section as the holes 15, but not leading into the separation chamber 21.

 As can be seen in Figure 4, the holes 15 of the stirring discs 14 may have a circular cross-section. Correspondingly, the cavities 30 in the stirrer disk 17 'according to Figure 5 are circularly configured.

 According to Fig. 6, the holes 15 'in the stirring discs 14 may have approximately the cross section 10 of outwardly extended trapezoids. The same applies to the cavities 30 'in the corresponding stirrer disk 17', as can be seen in Figure 7.

 The drive mode is as follows:

 During operation, the grinding chamber 10 is largely filled with auxiliary grinding bodies 31. By the entry of material to be ground 11, by means of a pump not shown a material to be ground, 15 capable of flowing , is continuously pumped through the grinding chamber 10. During operation, the agitator mechanism 6 is rotatably driven by the drive motor 3. The material to be ground circulates through the grinding chamber 10 in the direction of evacuation. of ground material formed by the exit of ground material 13. During this circulation it is subjected to strong shear stresses by the auxiliary grinding bodies 31 and, therefore, the particles of material to be ground are crushed and, in addition, the material to be ground is homogenized. This process is carried out in such a way that braided currents 32 shown in Figures 1 and 2 are produced between adjacent stirring discs 14 or 14 and 17. These are due to the material to be ground and the auxiliary grinding bodies. 31 receive stronger tangential pulses next to the corresponding stirring discs 14 or 14 and 17 than in the central zone between two adjacent stirring discs 14, 17. This means that, respectively, next to the stirring discs 14 or 14 and 17, the auxiliary grinding bodies 31 and 25

 the material to be milled circulates more strongly outward, while in the central area between two adjacent stirring discs 14 or 14 and 17 again circulate inward in the direction of the agitator shaft 5. This grinding and homogenization process it is identical between all stirring discs 14 and 14, 17 due to the identical distance a or a 'and its identical diameter b or b' and its identical speed. By means of the cavities 30 it is ensured that, also between the last stirring disc 17 'and the adjacent stirring disc 14, the braided current 32 described is identical to the braided current 30 mentioned above.

 According to the amount of material to be ground, that for each unit of time circulates through the milling chamber 10, an axial current is superimposed on the twisted streams 32 through the milling chamber 10. From the last twisted stream 32 between the penultimate agitator disc 14 and the agitator disc 17, adjacent to the agitator shaft 5, partial currents formed by material to be ground and auxiliary grinding bodies 13 pass, through the 35 steps 22 in the agitator disc 17, to the separation chamber 21 inside the cage 19. The sum of being partial currents corresponds substantially to the volume stream of material to be ground, fed through the inlet of material to be ground 11 and evacuated through the outlet of ground material 13. In the gap 28 formed by the stirring disc 17 and the rotating intermediate wall 27, the partial currents divert radially outwardly relative to each other. or to axis 16 and accelerate tangentially. Due to the rotational movement of the stirrer disk 17 and the intermediate wall 27, the material to be ground and the auxiliary grinding bodies 31 in the gap 28 in turn experience a particularly large, outwardly oriented acceleration, being this applies especially to the auxiliary grinding bodies 31 and to the particles of material to be ground, which are especially thick. Said particles of material to be ground and the auxiliary grinding bodies 31 are thrown out through the openings 20 of the cage 19. Therefore, the auxiliary grinding bodies 31 and the coarse particles of material that has been not grind sufficiently, they are fed back into the braided stream 32. The ground material - which has not been thrown through the cage 19 - is deflected in the annular groove 27a between the outer circumference 27b of the intermediate wall 27 and the cage 19, in a direction of axial circulation and evacuated through the screening device 23. Therefore, the separation of the auxiliary grinding bodies 31 and, if necessary, large particles of material that has been grinding occurs only within the separation device 25. 50

 To explain the relationships between the diameter b of the stirring discs 14, 17, 17 'and their axial distance a, á, which are relevant for the production of the twisted currents 32, the following should be noted: For the definition, a called separation angle  or . The angle  or  is formed between two lines 33 or 34. Line 33 extends from the inner end 35 of a stirring disc 14 in the stirring shaft 5 to the outer edge 36 of an adjacent stirring disc 14. In the other line 34 it is a line parallel to the axis 16. The separation angle  is that between the last stirring disc 55 or 17 'and the next adjacent stirring disc 14. For the mentioned twisted currents 32 to occur,

the separation angle is applicable: 30º < <60º or 30º < <60º. In other words, this means that also the separation angle  between the last stirring disc 17 or 17 'and the next adjacent stirring disc 14 is such that the mentioned twisted currents 32 occur even though the distances a and a' are not identical.

 Although in the described embodiments described, agitator mills with a horizontal axis 16 have been described, the invention can obviously also be applied in agitator mills with a vertical axis. 5

  Finally, the steps 22 in the stirring discs 17, 17 'can be actively carried out in terms of transport, as shown only in Figure 8. In this case, its walls 37 do not extend parallel to the axis 16 , but are inclined with a delay angle  with respect to a parallel to the axis 16, in the opposite direction to the direction of rotation 38 and in the direction of movement 39, that is, in the direction of the intermediate wall 27. Because of this , the material to be ground and the auxiliary grinding bodies 31 are attracted especially intensely to the interior of the passages 22 passing through them into the gap 28. Therefore, the sum of the partial currents before mentioned really corresponds approximately to the total volumetric current of the volumetric current of material to be milled introduced through the input of material to be ground 11 and evacuated through through the outlet of ground material 13, existing in this area, due to the existing braided current 32, the normal concentration of auxiliary grinding bodies 31 in the material to be ground, which are also passed 15 through steps 22 In the embodiments described above, for the angle  it was applicable  = 0 °. For practical realizations of 22 active steps regarding transport it is applicable: 0º < <45º.

Claims (9)

1. Agitator mill - with a grinding bowl (2)  - comprising a grinding chamber (10),  - in which, at one end, a feed of material to be ground (11) enters, 5  - from which, at the other end, there is a discharge of ground material (13), and that  - receives auxiliary grinding bodies (31), - with a stirring mechanism (6) arranged in the grinding chamber (10), which has  - a stirring shaft (5) that can be rotatably driven, with an axis (16),  - one last stirrer disc (17, 17 ') adjacent to the ground material outlet (13) and arranged in the stirrer shaft (5), 10 with a diameter b' and - stirring discs (14) arranged axially in front of the last stirring disc (17, 17 ') in the stirring shaft (5) at an axial separation between them, - defining the stirring discs (14) superimposed, adjacent to each other, a separation angle , and defining the last stirring disc (17, 17 ') and the stirring disc (14) adjoining a separation angle , 15 - each separation angle ,  being formed by a line (33) between a radially inner end (35) of a stirring disc (14, 17, 17 ') in the agitator shaft (5) and the outer edge (36) of a stirring disc (14) contiguous and along a parallel line (34) with respect to the axis (16), - applicable: 30º < <60º, - with a device for separating auxiliary grinding bodies (25) arranged in front of the ground material outlet 20 (13), which has  - a screening device (23) arranged directly in front of the ground material outlet (13) and - a cage (19) with radial drafts (20), which is fixedly connected with the last stirrer disk (17, 17 ') and that surrounds the sieve device (23) in the direction of the shaft (16), and  - with steps (22) made on the last stirrer disc (17, 17 '), adjacent to the stirrer shaft (5), into which the separation device (25) ends, characterized because also for the separation angle  between the last stirrer disk (17, 17 ') and the adjacent stirrer disk (14) is applicable: 30 ° < <60 ° and because in the separation device (25) between the last stirrer disk ( 17, 17 ') and the screening device (23) is arranged an intermediate wall (27, 27') that is non-rotatably connected with the stirring mechanism (6) and that extends at least along the diameter d of the screening device (23). 2. Agitator mill according to claim 1, characterized in that for the diameter c of the intermediate wall (27, 27 '), as for the diameter d of the screening device (23) it is applicable: c> d. 3. Agitator mill according to claim 2, characterized in that the intermediate wall (27, 27 ') extends to near the cage (19). 35 4. Agitator mill according to claim 1, characterized in that distance pieces (29) are provided between the intermediate wall (27 ') and the last agitator disc (17). 5. Agitator mill according to claim 1, characterized in that the distance a 'of the last agitator disc (17, 17') with respect to the directly adjacent agitator disc (14) is identical to the distance between all the above agitating discs (14) . 40 6. The agitator mill according to claim 1, characterized in that the above-mentioned agitator discs (14) are provided with holes (15) and that the last agitator disc (17 ') is provided with cavities (30) on its side facing the agitator disc (14) contiguous. 7. Agitator mill according to claim 6, characterized in that the cavities (30) have the same cross section as the holes (15). 8. Agitator mill according to claim 1, characterized in that the diameters b, b 'of all agitator discs (14,17) are identical. 9. Agitator mill according to claim 1, characterized in that the walls (37) of the passages (22) are configured with a delay angle in the opposite direction to the direction of rotation (38) of the agitator shaft (5), in the direction towards the intermediate wall (27, 27 ').