WO1996033019A1

WO1996033019A1 - Method and device for wet-grinding and dispersing solid particles in liquids

Info

Publication number: WO1996033019A1
Application number: PCT/EP1996/001567
Authority: WO
Inventors: Friedrich Vock
Original assignee: Friedrich Vock
Priority date: 1995-04-21
Filing date: 1996-04-13
Publication date: 1996-10-24
Also published as: JPH11503666A; EP0824374A1

Abstract

The invention concerns a method and a device for wet-grinding and dispersing solid particles in liquids, using a stirrer-type grinder consisting of at least one chamber (1) containing grinding elements (3) and at least one rotor (2), the chamber (1) and rotor (2) being designed to be rotated independently of each other by at least one drive (8, 8') and the material to be ground (4) being fed into the grinding chamber (1) through a hollow shaft (5). The grinding elements (3) in the grinding chamber are strongly compressed by the rotation of the chamber. The rotor (2) is set in motion, the rotational speeds of the chamber (1) and the rotor (2) keeping in step with each other, the rotor (2) turning at a constant faster speed or constant slower speed than the chamber (1), or at alternating faster and slower speeds, or at the same speed. The material is fed into the chamber (1) containing the rotor (2) through a hollow shaft (5) and, after grinding, is thrown by centrifugal force through outlet openings (11) into a collector container (14).

Description

Method and device for wet grinding and dispersing solid particles in liquids

The invention relates to a method and a device for wet grinding of solid particles in liquids by means of an agitator mill consisting of at least one grinding chamber containing grinding media, at least one rotor, wherein the grinding chamber and the rotor can be set in rotation independently of one another by means of at least one drive are and the regrind can be introduced into the grinding chamber via a hollow shaft.

Wet grinding means the comminution of solid particles of high strength in a liquid phase; dispersing the crushing of agglomerates which consist of strongly adhering primary particles and whose primary particles are to be dispersed in a liquid phase. These wet processes are used in particular when the resulting products are to be further processed or used as a suspension, such as pigments and fillers in lacquer paints and printing inks, or magnetic solid particles for the coating of audio and video tapes.

Such a method or such a device is known from DE-44 19 919 C1. This is an agitator ball mill with a vessel which can be at least partially filled with the product to be treated, a grinding container which can be rotated about a central axis in the vessel and has at least one wall area with an outer separating device which is separate from the product can be flowed through, but retains grinding aid contained in the grinding container, and an agitator which is arranged within the grinding container and can be rotated independently of the latter about the central axis.

A further method and a further device of the gate according to the invention is described in DE 41 28 074 A1. This agitator mill consists of a preferably cylindrical, rotatable, with an inlet at its one end and an outlet at its other end, in which a stirrer shaft provided with stirring elements can be rotated. Agitators in the form of concentric rings are provided on the inner circumference of the grinding container, which engage radially inward between the agitators of the agitator shaft and whose inside diameter is smaller than the outside diameter of the agitators of the agitator shaft, which are also formed by annular disks.

DD 290 317 A7 describes a device which consists of an outer cylinder, which represents the grinding vessel, and a concentrically arranged inner cylinder, an annular grinding gap being formed between the outer cylinder and the inner cylinder, which is composed of particles, grinding media and Existing suspension is flowed through. Here, the inner cylinder is stationary and the outer cylinder is arranged to rotate, an annular effective grinding gap between the outer cylinder and the inner cylinder being formed by the deposition of grinding media and particles of the material to be ground on the rotating outer cylinder.

The object of the present invention is in particular to reduce the disadvantages of the prior art, i. H. Shortening the dwell times of the ground material in the device according to the invention, simplifying the process control, avoiding expensive cooling devices in the actual grinding device and the applicability to the broadest possible spectrum of the ground material to be processed.

This object is achieved according to the invention in that the grinding media located in the grinding chamber are strongly compressed by rotating the grinding chamber, in that the rotor is set in rotation, the rotational speeds of the grinding chamber and the rotor running in the same direction, and in that the rotor is constantly faster, constantly slower, alternating slower or faster or equally fast turns as the grinding chamber, that the ground material to be ground is passed through a hollow shaft into the grinding chamber containing the rotor and then the ground material is thrown into a collecting container via outlet openings as a result of the centrifugal force.

The grinding media with the suspension surrounding them and flowing through them must be transferred to a centrifugal field in order to establish a narrow grinding media packing structure and high normal forces between the grinding media. This succeeds in that the horizontal or vertical grinding chamber itself rotates about its axis like a centrifuge. The comminution process only starts when the compressed grinding media is additionally moved by rotating or vibrating tools, since only then the necessary shear stresses are generated on the solid particles. It is important that this relative movement and mixing movement is generated in the same direction as the chamber rotation, since only grinding media that move on a circular path build up the required centrifugal forces. Grinding media, the ex. are displaced from their circular path by moving tools, although they still have a speed, but do not generate any contact pressure on the next grinding media layer in the direction of the increasing radius. It is irrelevant whether the speed of the tool is greater or less than the grinding chamber speed if it is only in the same direction. The embodiments for initiating the relative movement in the same direction are carried out according to the subclaims by means of different variants:

The grinding chamber is set in rotation by means of a rotatable hollow shaft in such a way that the bed of grinding media contained therein is strongly compressed. This creates high normal stresses for the particle loading of the suspension. A rotor is also set in rotation via a hollow shaft, the rotor rotating in the same direction, but faster than the grinding chamber. An intensive slip movement is triggered both between the rotor surface and the bed of grinding media and between the inside of the grinding bed of the grinding chamber. Another preferred procedure for exciting a slip movement is that the grinding chamber and the rotor rotate in the same direction, but the rotor rotates more slowly than the grinding chamber.

Likewise, a combination of the two above-mentioned procedures is possible in that the grinding chamber and the rotor rotate in the same direction, but the speeds of the grinding chamber or of the rotor change with a constant, periodic, temporal change that the grinding chamber rotates faster once than the rotor and on the other hand the rotor rotates faster than the grinding chamber.

Another preferred procedure consists in that, for example, the grinding chamber is periodically braked from a maximum speed to a lower speed and then accelerated again to the maximum speed. In addition, it is conceivable to omit the rotor entirely in this driving style.

Another preferred procedure is to set the grinding media bed in motion with a shearing effect, the hollow shaft being set in vibration by means of a flexible coupling and by means of an unbalanced mass.

Furthermore, several grinding chambers with several rotors can be operated cascade one above the other or side by side in the container, each chamber being supplied with the associated rotor via the common hollow shaft.

A further advantageous method step consists in that the product stream is fed through the hollow shaft 5 via the rotor channels 41 into the grinding chamber 1 for a specific time interval ΔTi, and that the product supply is then stopped for a specific time interval ΔT ₂ , with Δ Ti during the time interval the speeds of rotor 2 and grinding chamber 1 are the same or almost the same and during the time interval ΔT ₂ the speeds of rotor 2 and grinding chamber 1 are different. In the time interval AT, the finest solid particles contained in the product stream are swept through the bulk material without shear for discharge (overflow), and the particles which are still too coarse will remain in the gap volume of the bulk material due to the classifying effect of the centrifuge function.

In the time interval ΔT ₂ , the product throughput is now interrupted and an intensive shear effect is initiated, as a result of which the coarser particles which remain in the gap volume of the grinding media bed and which are preferably coarser are stressed and crushed.

The periodic control of the described time interval "classifying" and "dispersing" results in a quasi-continuous process.

In addition, the above-mentioned object is achieved by a device for carrying out the method for wet grinding and dispersing solid particles in liquids in that the grinding chamber has a gaseous space arranged around the hollow shaft, that outlets on the circumference (10) of the grinding chamber are arranged for the regrind, and that the agitator mill is arranged directly on a collecting container for the regrind.

Further advantageous configurations result from the subclaims and their combinations.

To support the claims, a few exemplary embodiments are illustrated below with the aid of drawings.

Show it:

Fig. 1 is a sectional drawing of the agitator mill

Fig. 2 shows an example of a rotor

Fig. 3 shows an eccentrically mounted rotor

4 shows a rotor provided with a flexible coupling

Fig. 5 is a diagram for the brake acceleration method Fig. 6 shows another embodiment of an inventive

Rührwerksmühlθ Fig. 7 shows a cascade arrangement of the inventive

Contraption.

1 shows a sectional view of an agitator mill according to the invention. The agitator mill consists of a grinding chamber 1 with a rotor 2. The grinding chamber 1 is driven by a drive 8 'and a hollow shaft 5'. In the hollow shaft 5 'there is another hollow shaft 5 for the rotor 2 which is driven by the drive 8. The grinding chamber 1 is filled with grinding media 3. The ground material 4 reaches the grinding chamber 1 via the inflow 38 through the hollow shaft 5. The rotor 2 is shown in disk form in FIG. 1 and has agitating tools 28 at its peripheral end. The stirring tools 28 can have all possible conceivable known shapes, for example, as shown, rod-shaped pins. The hollow shaft 5 is closed at its end 37. Furthermore, the hollow shaft has lateral openings 39 at its lower end. Fig. 1 shows the state with the agitator mill rotating. The millbase passes through the hollow shaft 5 through the lateral openings 39 of the hollow shaft 5, through the rotor 2. The millbase 4 then reaches the circumference of the rotor 2 through the millbase 3 into the interior of the milling chamber 1. At the upper end of the Grinding chamber 1 has openings 11 which serve as outlet openings for the material to be treated 4. On the outside of the grinding chamber 1, shields 30, which are open to the container wall 14 and which extend to the periphery of the grinding chamber 1, are attached above the openings 11, so that the ground material can spray outwards as a result of the centrifugal forces. The various areas in the grinding chamber are indicated by the vertical dashed lines. In particular, during operation of the agitator mill, a gaseous space 9 is formed in its center. Furthermore, the grinding chamber (1) has a closable opening (40) in the lower region, which is opened, for example, for rinsing the grinding chamber (1). The entire agitator mill is fastened on a cover 36, which in turn closes a collecting container 14. An agitator 19 is provided in the collecting container 14 and is driven by the drive 33. A maximum regrind height 32 at a standstill and the regrind level 31 during operation of the agitator mill are shown in the collecting container (14). Furthermore, the collecting container 14 can be provided with a cooling 21. Reference numerals 22, 23, 34 and 35 are intended to indicate that a circular mode of operation is possible. By means of a pump 34, the regrind is fed through a line 23 into a circuit through the process. In order to ensure the possibility of sudden braking of the grinding chamber 1 or of the rotor 2, braking devices 43, 43 'are attached to the hollow shafts 5, 5'.

The basic principle of the agitator mill is that it is integrated into such a container at the same time. Since an enclosure is required for safety reasons anyway for machines with a rapidly rotating container, this requirement can be solved with the collecting container 14. The ground material emerging from the grinding chamber 1 is allowed to flow freely into the collecting container 14. In the grinding chamber 1 itself, a limited filling level is provided both for the ground material and for the grinding media, so that a radially limited gas space 9 is created in the center of the rotating chamber. The filling level of the grinding media and the grist level are different. The regrind 11 on the grinding chamber 1 can be realized by the correct arrangement of two to three bores with a guide to the outer casing. Here, the pipes rotating rapidly with the container act like pumps. After leaving these pipes, the regrind splashes through the container gas space against the container wall equipped with cooling. Irrespective of the degree of filling of the container, the entire wall surface can be used as a cooling device like a thin-film cooler.

The central gas space 9 of the grinding chamber 1 brings an additional effect for the release of the seal of the two rotating hollow shafts 5, 5 '. It only has to be sealed against a gas space 9 and not against the regrind 4 under conveying pressure and certainly not against the moving grinding media. A mechanical seal and a separating device can thus advantageously be dispensed with. It is also advantageous that the agitator mill arranged on the container can be moved up and down like a stationary agitator, so that the machine with the grinding media filling is easily accessible. A further advantage is that when the batch is changed, the overall cleaning of the system can also be carried out in a simple manner by simply adding detergent and pumping it in a circle in order to thus the agitator mill, including the grinding media filling, the circular container by spraying with a rotating grinding chamber, and the circuit with the pump, pipeline and fittings.

The filled-in granular bed usually consists of spherical granules, the density of which is greater than the density of the suspension (preferred ratio 1.5 to 4.0) with mono- or polydisperse spherical diameter distributions per different average diameters of <100 μm to 6 mm (preferred) <500μm).

The grinding media with the suspension surrounding them and flowing through them have to be transferred to a centrifugal field in order to establish a close packing structure and high normal forces between the grinding media. This is achieved by rotating the horizontal or vertical grinding chamber around its axis like a centrifuge.

The comminution mechanism, however, only starts when the compressed grinding media bed is additionally moved relatively by rotating or oscillating tools, since only then the necessary shear stresses are generated on the solid particles.

It is important here that this relative movement and mixing movement is generated in the same direction as the chamber rotation, since only grinding media that move on a circular path build up the required centripetal forces. Grinding bodies, which are displaced from their circular path by moving tools, for example, still have a speed, but do not generate any contact pressure on the next grinding body layer in the direction of increasing radius. It is irrelevant whether the speed of the tool is greater or less than the grinding chamber speed if it is only in the same direction,

The technical solution of introducing a relative movement into the grinding body structure compressed by centrifuging can be achieved with the different variants described above. 2 shows a possible embodiment of a rotor 2. The rotor 2 is connected to the hollow shaft 5, which is closed at the bottom. The hollow shaft 5 has lateral openings 39, to which two or more tubes 41 are connected. A hollow annular disc 42 is provided at the outer ends of the tubes 41. Rods 43 serving as stirring tools are attached to the hollow disk 42. The ground material can thus be conveyed outwards from the hollow shaft 5 through the tubes 41 via the disc 42 having cavities 26.

According to a further variant, an eccentrically mounted rotor is shown in FIG. 3. The hollow shaft 5 has an eccentricity e. The rotor 2 is rotatably supported in front of the lower part of the hollow shaft 5. The rotor 5 is dragged along by the grinding element immersion. The speed of the hollow shaft is from 0 (standstill) to the speed of the grinding chamber, not shown. The millbase is fed in via the lower end of the hollow shaft 5 through the rotor to the outside into the grinding chamber.

Another preferred embodiment is shown in FIG. 4. Here, a coupling 45 provided with a bellows is inserted in the hollow shaft 5. An unbalanced mass 46 is arranged below the flexible coupling, which is followed by the rotor 2, which actually rotates independently (as in FIG. 3). Here, too, the rotor can be dragged along with the grinding media. The essential point is that the relative movement of the grinding media is achieved with a rotor 2 excited to circular vibrations m.

5 shows a further variant for the driving style. A brake acceleration cycle is shown there in the form of a diagram.

The grinding chamber 1 is first accelerated to a maximum speed n _Tr -maχ and then decelerated to the speed n _T r- in by means of the brakes 43, 43 '. Then a new acceleration phase of the grinding chamber 1 to nτr-ma begins. The dashed curve shows the course over time of the bed of grinding media n _M κs. The difference between the curves n _Tr - ΠM _K S represents the slip ± Δn required for the shear.

For example, the following values of the different sizes can be considered:

ΠTR-OW ≡ 1800 revolutions min ^"1 nτR- in = 500 revolutions min ^Λ

ΔT = 20 s.

The terms Δtβr, Δt_β, and ΔT are to be understood here as the different times of the braking duration, the acceleration duration and the total duration of a cycle.

Another embodiment of an agitator mill is shown in FIG. 6. The hollow shaft 5 is open at its lower end and closed on the side. At the lower end there is a disk-shaped rotor with stirring tools. The rotor divides the grinding chamber into two partial chambers 6 and 7. The course of the product takes place in such a way that the ground material is guided through the hollow shaft 5 via the lower partial chamber 7 into the grinding bodies 3. The millbase 4 then reaches the upper subchamber 6 and then through the opening 16 into the collecting container 14. The diagram indicates that the lower subchamber 7 is filled with liquid, while the upper subchamber 6 has a gas cushion in the center as a result of the millbase overflow. This avoids the use of a mechanical seal.

Fig. 7 shows the use of several grinding chambers as a cascade. Here, three chambers 1, 1 'and 1 "are connected in parallel one above the other, each chamber 1, V and 1" being supplied with regrind by itself via the common hollow shaft 5. All the reference numerals in both the deleted and uncoated form correspond to the reference numerals in FIG. 1.

Claims

Expectations

1. Method for wet grinding and dispersing solid particles in liquids by means of an agitator mill consisting of at least one grinding chamber (1) containing grinding media (3), at least one rotor (2), the grinding chamber (1) and the rotor ( 2) can be set in rotation independently of one another by means of at least one drive (8, 8 ') and the regrind (4) can be introduced into the milling chamber (1) via a hollow shaft (5), characterized in that the chamber (1) located grinding body (3) by rotation of the grinding chamber (1) are strongly compressed so that the rotor (2) is set in rotation, the rotational speed (1) of the grinding chamber (1) and the rotor (2) runs in the same direction, and that the rotor (2) rotates constantly faster, constantly slower, alternately slower or faster or rotates at the same speed as the grinding chamber (1), that the regrind to be ground (4) through a hollow shaft (5) into the rotor (2) containing Passed grinding chamber (1) and then the ground material (4) is thrown as a result of the centrifugal force via outlet openings (11) into a collecting container (14).

2. The method according to claim 1, characterized in that the rotational speed of the grinding chamber (1) and / or the rotor (2) periodically initially increases steadily and, after a certain period of time, is suddenly braked by means of separate braking devices (43, 43 ') the grinding chamber (1) can be at rest when the rotor (2) is rotatable or the rotor (2) when the grinding chamber (1) is rotating.

3. The method according to claims 1 or 2, characterized in that the rotor (2) relative to the grinding chamber (1) performs eccentric movements.

4. The method according to claims 1, 2 or 3, characterized in that the rotor (2) is oscillating, the vibrations of the rotor (2) being generated by an unbalanced mass (25).

5. The method according to at least one of the preceding claims, characterized ge indicates that the grinding chamber (1) is arranged vertically and is conical in the lower part for receiving the grinding bodies (3).

6. The method according to any one of the preceding claims, characterized in that the regrind (4) runs through the grinding process in a circle, the regrind (4) being removed from the collecting container (14) and via the hollow shaft (5) into the grinding chamber (1 ) is returned by means of a pump (34).

7. The method according to any one of the preceding claims, characterized in that the regrind (4) via the downwardly closed hollow shaft (5) in the radial direction through the rotor (2) in the grinding chamber (1) is passed.

8. The method according to any one of the preceding claims, characterized in that the method is operated in a cascade manner in such a way that a plurality of grinding chambers (1, V, 1 ") with a plurality of rotors (2, 2 ', 2") one above the other or are arranged side by side.

9. The method according to at least one of the preceding claims, characterized ge indicates that the product stream for a certain time interval .DELTA.Ti through the hollow shaft (5) via the rotor channels (41) into the grinding chamber (1), and that the product supply for a certain time interval ΔT _{2 is} stopped.

10. The method according to claim 9, characterized in that during the time interval ΔTi the speeds of the rotor (2) and grinding chamber (1) are the same or nearly the same and during the time interval ΔT ₂ the speeds of the rotor (2) and grinding chamber (1) are different.

11. An apparatus for performing the method according to at least one of the preceding claims for wet grinding and dispersing solid particles in liquids consisting of an agitator mill with grinding media (3) containing Grinding chamber (1), a rotor (2), the grinding chamber (1) and the rotor (2) can be set in rotation independently of one another by means of at least one drive (8), and the ground material (4) via a hollow shaft (5) can be introduced into the grinding chamber (1), characterized in that the grinding chamber (1) has a gaseous space (9) arranged around the hollow shaft (5), that outlet openings (11) on the circumference (10) of the grinding chamber (1) are arranged for the regrind (4), and that the agitator mill is arranged directly on a collecting container (14) for the regrind (4).

12. The apparatus according to claim 11, characterized in that the rotor (2) relative to the grinding chamber (1) is mounted eccentrically.

13. The apparatus of claim 11 or 12, characterized in that the rotor (2) via a bellows (24) is arranged oscillating on the hollow shaft (5), wherein an additional unbalanced mass (25) to generate the vibration on the hollow shaft (5) ) is provided.

14. Device according to claims 11, 12 or 13, characterized gekennzeich¬ net that the rotor (2) is disc-shaped, has cavities (26) for discharge of the ground material (4) and is arranged on the hollow shaft (5) , wherein the downwardly closed hollow shaft (5) has lateral openings (27) which lead into the cavities (26).

15. Device according to one of the preceding claims, characterized gekenn¬ characterized in that the device several superimposed or side by side on the hollow shaft (5) cascaded grinding chambers (1, 1 ', 1 ") with rotors (2, 2', 2" ) having.

16. The device according to at least one of the preceding claims, characterized in that the grinding chamber (1) is cylindrical, conical or double-conical.

17. The device according to at least one of the preceding claims, characterized in that the collecting container (14) has an agitator (19).

18. The device according to at least one of the preceding claims, characterized in that the outer wall (20) of the collecting container (14) has a cooling (21).

19. The device according to at least one of the preceding claims, characterized in that the collecting container (14) has an outlet (22) for the regrind (4), the regrind (4) via a line (23) via the hollow shaft (5) is returned to the grinding chamber (1) by means of a pump (34).

20. The device according to at least one of the preceding claims, characterized in that the device can be operated vertically or horizontally, the hollow shaft (5) and the grinding chambers (1, V, 1 ") with the rotors (2, 2 ', 2" ) are stored horizontally or vertically.