EP0665059A1 - Agitator ball mill - Google Patents

Abstract

An agitator ball mill for processing free-flowing products features a horizontally split housing (2a, 2b) as a grinding bin in which a disc-shaped agitator (1) is arranged to rotate. The product enters the grinding product inlet (17) and flows through an upper disc-shaped grinding chamber (8a), an outside deflection zone (10), and a lower disc-shaped grinding chamber (8b). At the lower grinding chamber (8b), a deflection zone (11) arranged radially to the inside is connected in which the product containing the grinding pearls is deflected to the upper grinding chamber (8a). In the area between the deflection zone (11) and the upper grinding chamber (8a), a branch channel (13) branches off radially to the inside to the separation zone (14), along which a partial stream of product flows to this separation zone (14) whereas a second partial product stream together with the grinding pearls enters the upper grinding chamber (8a).

Description

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

With the continuous flow through an agitator ball mill, depending on the flow rate and the viscosity of the millbase suspension, a drag force occurs which acts on the grinding media. As a result, the grinding media with the regrind are carried along from the entry into the grinding zone to the separating element at the exit. This can lead to pressing of the grinding media in front of the separating element, which is associated with increased wear and risk of clogging. This is particularly critical for very fine grinding with very small grinding media and at high throughput rates.

Several agitator ball mills are known which offer solutions to this problem in such a way that the entrained grinding media can be circulated in the mill and returned to the grinding zone (DE PS 37 16 587, DE PS 33 45 680, DE PS 28 11 899). The separation zone is located in the vicinity of the axis of rotation, usually within the agitator, so that grinding media are kept away from the separation element by centrifugal force.

In order to protect the separating element from rebounding grinding heads, the greatest possible spatial distance between the grinding zone and separation zone should be sought. With a greater distance of the flow path of the grinding media from the separation zone in the radial direction, the protection of the separation member against wear and clogging improves, ie the larger the diameter of the agitator, the better the design options for the separation zone and the grinding media guidance. The position of the separation zone within the agitator requires a pot-like shape. This makes it possible to arrange additional grinding active zones within the agitator. However, such internal rotating surfaces are very susceptible to deposits if they are arranged approximately perpendicular to the centrifugal force.

In addition, access to the grinding tools on the inside of the agitator for maintenance purposes with slim agitator shapes is made more difficult.

When the flow passes through the grinding zones in continuous operation, the grinding media is carried along by the grinding stock suspension. The level of drag force depends on the size and density of the grinding media, the flow rate and the viscosity of the suspension. This condition becomes particularly critical if the throughput and the solids concentration are high and if very small grinding media are used. The grinding media are then transported to the separation zone with the regrind and pressed there, which leads to blockages and wear. The grinding media should therefore be separated from the exiting material flow before reaching the separation zone and returned to the grinding zone via a recirculation opening.

The goal is, of course, a complete recirculation of the grinding media, so that a separation device is no longer required. In order to approximate this state, the design of the grinding zone and the grinding body return zone is of crucial importance. Ideally, one should ensure that the grinding media already have the direction of movement in which they flow through the grinding zone after the recirculation before branching off the emerging material flow. In this case, the grinding media should not be branched off from the millbase stream, but rather the millbase suspension from the millbase stream, since milling media are much more difficult to deflect than the suspension. Since the recirculation of the grinding media should take place using the centrifugal force, it follows that the flow through the grinding zone should also take place radially in this direction. The invention is based on the knowledge that the best separation effect is achieved when the separated millbase suspension flows in the opposite direction to the grinding media, ie radially inward against the centrifugal force to the separation zone.

The even circulation of the grinding media in the mill is hampered by the influence of gravity, since the bed is in the areas below the mill accumulates. This effect is particularly pronounced in mills with a cylindrical agitator and a vertical axis of rotation. This also leads to the fact that the grinding media is heavily compacted when the mill is at a standstill and the mill requires a considerably higher motor output to restart than for grinding operation. The aim should therefore be a grinding chamber geometry that has the shortest possible paths parallel to gravity.

The task therefore consists in the development of a generic agitator ball mill with a grinding zone and an agitator, which allow the unhindered circulation of the mill filling with the greatest possible exclusion of gravity, offer enough space for the design of a grinding media return system for complete grinding media separation and enable cleaning and maintenance-friendly construction.

According to the invention the object is achieved by the characterizing features of claim 1. Advantageous refinements can be found in the subclaims.

The ring-shaped agitator, which can be seen in the figures, is attached to the bottom of the vertically arranged drive shaft and is fitted with grinding pins. The walls of the housing opposite the agitator are also equipped with pins and, together with the agitator, form two flat, cylindrical cylindrical grinding chambers. The grinding rooms are located above and below the agitator and are connected to each other on their outer circumference by a toroidal transition. This transition can be designed as a further grinding chamber or as a deflection chamber. The separating member is preferably a slotted screen with a large cross-sectional area and is arranged coaxially within the hollow drive shaft. An inner deflection zone connects the two grinding rooms below the separator. A grinding media conveying device can be arranged between the drive shaft and the agitator, with which the grinding media circulation can be influenced.

The millbase suspension is on the upper housing part in the area of the drive shaft fed and evenly distributed when flowing through the annular gap between the shaft and the housing wall. The regrind then reaches the interior of the upper grinding chamber, where it is homogenized and dispersed at still low peripheral speeds. The upper grinding chamber is then flowed outwards in the radial direction, the peripheral speed and the dwell time increasing. After passing through the toroidal transition, the regrind enters the lower grinding chamber and flows radially from the outside to the inside. The crushing takes place in the outer areas of the two grinding rooms. A calming zone adjoins the interior of the lower grinding chamber, into which the entrained grinding media also reach. In the inner deflection zone, the ground material / grinding media mixture is deflected into a radially outward flow. After the inner deflection zone and in front of the upper grinding chamber, a first partial stream of regrind is branched off radially inwards and then directed upwards to the separation zone. Because the deflection of the first millbase partial stream takes place in an almost opposite direction to the millbase stream, the millbeads maintaining their flow direction, the first millbase partial stream can reach the separation zone completely free of millbeads. The separating element thus only serves as a protective device against loss of grinding media in the event of unsteady operating conditions, for example when starting up and stopping the mill. In normal operation, the separation zone is then free of grinding media, which reduces the risk of wear and clogging to a minimum.

The grinding media, together with another partial flow of the grinding stock, reach the upper grinding zone without being deflected. If, after the branching off of the first partial flow and in front of the inner region of the upper grinding chamber, a grinding material conveying device is provided in the connection there, the additional partial flow with the grinding media is accelerated by this device.

Because of the very short axial flow paths of the mill filling inside and outside between the two grinding rooms, the distribution of the grinding media in the Grinding rooms determined almost exclusively by flow and centrifugal forces, but not by gravity. The rotation of the agitator causes a radially outward force on the grinding media, which leads to a concentration of the grinding media in the outer area of the grinding chambers, where the majority of the grinding energy is also converted due to the high peripheral speeds. However, the compression of the grinding media bed is only slight there, since the radial forces due to the braking of the grinding media on the grinding pins of the housing are only small. The distribution of the grinding media in the grinding chambers and the grinding media circulation are thus largely determined by the drag force of the millbase suspension. A grinding media conveyor supports this mechanism and also reduces the risk of a short-circuit flow of the incoming millbase suspension to the separation zone.

The short axial grinding zone areas also have the effect that the grinding media are distributed very evenly when the mill is switched off and hardly any compaction takes place under the influence of gravity. This means that the mill can be started again without increased torque, which significantly reduces the necessary installed drive power. The shape of the agitator and the grinding chambers also has the advantage that internal surfaces perpendicular to the centrifugal force are minimized, thereby largely eliminating the risk of dead spaces for deposits.

Instead of a slotted screen as a separating element, a rotating deflector wheel can also be installed, with which the emerging millbase suspension is classified according to the particle size. The deflector wheel is inserted into the mill as a complete unit with storage and drive from below. The deflector wheel either runs freely in the cavity of the drive shaft of the agitator or is additionally surrounded by a tight-fitting housing. The millbase suspension reaches the deflector wheel from the junction to the inner deflection zone. Sufficiently fine particles pass the wheel with the liquid and are removed by the hollow drilled drive shaft of the classifier and a fines collector. The rejected coarse material mixes with the grinding material / grinding media flow and is returned to the grinding zone.

Fig. 1

einen Vertikalschnitt bei einer ersten Ausführungsform und

Fig. 2

einen der Figur 1 entsprechenden Schnitt bei einer zweiten Ausführungsform.

Exemplary embodiments are explained in more detail below with reference to the drawings. Show it:

Fig. 1

a vertical section in a first embodiment and

Fig. 2

a section corresponding to Figure 1 in a second embodiment.

Figure 1 shows a first embodiment of the agitator ball mill for flowable regrind. The agitator 1 is designed in the form of an annular disk and arranged in a horizontally divisible housing 2a, 2b. The axis of rotation is vertical; the drive 3, the bearing 4 of the drive shaft 5 and the shaft seal 6 lie above the actual mill. The agitator 1 is fastened to the drive shaft 5 by means of bolts 12 by means of a connecting flange 7. The upper grinding chamber 8a and the lower grinding chamber 8b are located between the housing walls and the agitator surface. Both the agitator 1 and the housing walls are equipped with grinding pins 9a, 9b. A toroidal deflection zone 10 connects the two grinding spaces 8a, 8b on their outer circumference. The agitator 1 and the housing walls are also equipped with grinding pins in the deflection zone 10, so that this deflection zone forms a further grinding chamber. An inner deflection zone 11, in which the mixture of grinding media and grinding stock is deflected radially outward, is located on the inside of the grinding chambers 8a, 8b. The deflection zone 11 runs from the level of the lower grinding chamber 8b to the level of the upper grinding chamber 8a. A first partial flow of the millbase suspension is directed to a branch duct 13 and passed into the separating space 14, which is arranged in the interior of the connecting flange 7. This branch duct 13 extends radially inwards at an angle of less than 90 ° to the horizontal, preferably, as shown, at an acute angle to the connection between the deflection zone 11 and the upper grinding chamber 8a.

The separating member 15 in the circular cylindrical separating chamber 14 is preferably a slotted screen and is arranged symmetrically to the axis of rotation of the agitator 1 above the inner deflection zone 11 in the separating chamber 14 and at a level higher than the upper grinding zone 8a. Another partial flow of the ground material, together with the grinding media, reaches the upper grinding chamber 8a radially outward.

The grinding media are filled into the mill through the nozzle 16. The ground material is conveyed through the inlet 17 with a pump into the gap 18 between the upper housing part 19 and the connecting flange 7. After flowing through the upper grinding chamber 8a, the toroidal deflection zone 10, the lower grinding chamber 8b and the inner deflection zone 11, the first partial flow of the millbase suspension emerges from the mill after passing through the branch duct 13, the separating chamber 14 and the separating member 15 through the sieve tube 20 . The filter holder 21 forms the stator wall of the inner deflection zone 11 and the branch duct 13. In the lower part 2b of the housing there is a cover 22 which serves to empty the mill.

Figure 2 shows an embodiment as a wet grinder. Instead of a sieve as separating element 15, a deflector wheel classifier is used here, which enables the mill contents to be classified according to the grain size. The classifier is installed in the mill as a complete unit in exchange for the sieve insert. The deflector wheel classifier consists of the drive 24, the bearing 25 with shaft seal 26, a hollow shaft 27 and the deflector wheel 23. The deflector wheel 23 runs in a separate classifying housing 28, which is arranged in the separating space 14 'within the connecting flange 7. After passing through the inner deflection zone 11, the branch duct 13 'and the separating space 14', the regrind to be classified enters the stationary classifying housing 28 through the upper central opening 29. Coarse particles are rejected by the wheel 23, leave the classifying housing 28 through the coarse material channels 30a and 30b and return to the upper grinding zone 8a via a grinding media conveyor device 33. Two variants for the arrangement of the coarse material channels are shown; the coarse material channel 30a is in the inner stator 21 'arranged and leads the coarse material back into the end of the inner deflection zone 11. The coarse material duct 30b is located in the outer wall of the classifying housing 28 and guides the coarse material back into the branch duct 13 '. Fine particles flow radially inward through the deflector wheel 23 and leave the machine through the hollow shaft 27, the fine material collector 31 and the discharge pipe 32.

In the exemplary embodiment according to FIG. 2, the toroidal deflection zone 10 has no grinding pins and thus does not act as a further grinding chamber. In addition, between the branch duct 13 'and the upper grinding chamber 8a for the grinding media contained in the further partial flow of the grinding stock, a grinding media conveying device 33 is provided, which serves to accelerate radially outward in the direction of the upper grinding zone 8a, thereby supporting the circulation of the mill contents. This device can consist of radial, tangential or curved blades, which are mounted as a separate component between the connecting flange 7 and the agitator 1.

Claims (10)

Agitator ball mill for treating flowable regrind, consisting of a grinding container, an agitator rotatably arranged in the grinding container, the surface of which forms at least one grinding zone with the adjacent housing walls, through which the grinding material and grinding media flow, a grinding material inlet on the grinding container, fed via the grinding material to the grinding zone a central separating chamber which has a separating element and which adjoins the end of the grinding zone and a connection between the end and the beginning of the grinding zone, a first partial flow of grinding material entering the separating space and a further partial flow of grinding material together with the grinding media reaching the beginning of the grinding zone, characterized in that the agitator (1) is in the form of an annular disc and the grinding container is in the form of a horizontally divided housing (2a, 2b), the agitator is designed to be flat, the agitator (1) with the adjacent housing walls has an upper and a lower annular disc-shaped grinding chamber m (8a, 8b), these grinding chambers are connected to each other on the outer circumference of the agitator (1), a deflection zone (11) adjoins the inner region of the lower grinding chamber (8b) radially inwards, in which the ground material with the grinding media from the Level of the lower grinding chamber (8b) is deflected into the level of the upper grinding chamber (8a) and a branch duct (13, 13 ') for the first partial flow of regrind to the separation chamber () from the connection between the deflection zone (11) and the upper grinding chamber (8a) 14, 14 ') which extends radially inwards at an angle of less than 90 °. Agitator ball mill according to claim 1, characterized in that the branch duct (13, 13 ') extends radially inwards at an acute angle. Agitator ball mill according to claim 1 or 2, characterized in that, according to the Mouth of the branch duct (13, 13 ') and in front of the inner region of the upper grinding chamber (8a) a grinding media conveyor (33) is arranged. Agitator ball mill according to one of claims 1 to 3, characterized in that the connection between the upper and lower grinding chamber (8a, 8b) on the outer circumference of the agitator (1) is designed as a further grinding chamber. Agitator ball mill according to one of claims 1 to 3, characterized in that the connection between the upper and lower grinding chamber (8a, 8b) on the outer circumference of the agitator (1) is designed as a further deflection zone (10). Agitator ball mill according to one of claims 1 to 5, characterized in that the agitator (1) is carried by a connecting flange (7) which has a frustoconical inside, to which a circular-cylindrical separation space (14, 14 ') adjoins, adjacent to the frustoconical The inside of the truncated cone-shaped outside of a stator (21) runs, between the inside and outside the branch duct (13, 13 ') is formed and the separating member located in the separating space (14, 14') is carried by the stator (21). Agitator ball mill according to one of claims 1 to 6, characterized in that the agitator (1) is carried by a connecting flange (7) which is frustoconical on the outside, an upper part (19) of the housing (2a, 2b) runs at a distance therefrom and in the gap (18) thus formed, a regrind inlet (17) opens. Agitator ball mill according to claim 7, characterized in that the gap (18) opens at the bottom into the inner region of the upper grinding chamber (8a). Agitator ball mill according to one of claims 1 to 8, characterized in that the separating member is a slotted screen (15). Agitator ball mill according to one of claims 1 to 8, characterized in that the separating member is a rotary driven deflector wheel (23).

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