GB2085319A

GB2085319A - Agitator ball mill

Info

Publication number: GB2085319A
Application number: GB8129266A
Authority: GB
Original assignee: Nagema VEB
Current assignee: Nagema VEB
Priority date: 1980-10-02
Filing date: 1981-09-28
Publication date: 1982-04-28
Also published as: BE890580A; DE3131370A1; DE3131370C2; DD153331A1; DK417081A; ES8205578A1; ES505912A0; GB2085319B; CH655450B

Abstract

An agitator ball mill has a separator device such that a build-up of grinding bodies before the separator sieve is avoided and the entire sieve area is affected by the movement of grinding bodies and ground material. Replacement of the separator sieve is made possible without emptying of the grinding container. The separator device consists of a flat sieve 11 arranged parallel with the axis of the agitator shaft 9 at the highest point at the end of the grinding chamber 6 in a lid 3 serving as a sieve housing and covered by a collecting hood 18 for ground material. This hood has an obliquely upwardly directed outlet pipe 5. <IMAGE>

Description

SPECIFICATION Agitator ball mill The invention relates to an agitator ball mill forthe continuous comminution and dispersion of liquidsolid mixtures, especially suspensions and for the fields of the paint industry, chemistry and the foodstuffs industry, having a horizontally arranged, cylindrical, double-walled grinding container closed at the ends by lids, which has an inlet for material for grinding at the top at one end and oppositely thereto at the other end an outlet for ground material, before which there is inserted a separator device formed as sieve, while an agitator mechanism formed from an agitator shaft mounted at one end with agitator elements secured thereon rotates at high speed in the grinding chamber.

Known agitator ball mills for the fine grinding and dispersion of paints, varnishes and other suspensions work with a mixture of grinding bodies and material for grinding, the material for grinding being metered continuously to the mill and discharged again in corresponding quantity. The decisive prerequisite for the correct operation of the mill is the continuous separation of the grinding bodies from the ground material. For this purpose various separator devices are known. Stationarily arranged separator devices formed as sieves are in widespread use in agitator ball mills with horizontal grinding containers.

An agitator ball mill of this kind provides as separating member a sieve body arranged concentrically of the agitator shaft axis and formed as a sieve box which is laterally withdrawable through the container wall, or as a double-walled insert. This sieve body however possesses operating disadvantages in that rapid blockage occurs from the interior outwards by reason of the axially acting build-u p- pressure of the fluid flow of the mixture of material for grinding and grinding bodies. Thus there is also the danger that the sieve may be pressed in. The tendency to blockage of the sieve is increased especially by the fact that the movement of the mixture of material for grinding and grinding bodies in relation to the sieve surface decreases from the circumference of the sieve to zero towards its centre (GDR-WP 69,998).The stationary sieve embodiments arranged concentrically of the agitator shaft axis at the ground material outlet and also the separator devices formed as annular gap separators have the common disadvantage that cleaning or replacement of this assembly is possible only with difficulty if at all when the agitator mill is in the closed condition. In order that the separator device may be removed the grinding container must always be at least partially emptied (Ger. Pat. Sp. 2,112,605).

Moreover a closed agitator mill is known in which one or more tubular sieve cartridges serve as sieve bodies, being arranged before the outlet at any point in the space between the shaft axis and the container wall and extending into the grinding chamber.

Although the sieve cartridges are easy to replace and clean and form a sufficiently large sieve area if several cartridges are used, these sieve bodies by their arrangement in the grinding chamber however constitute a resistance to flow and are subject to increased wear. Moreover within certain limits idle spaces are formed and thus the dispersion effect is disadvantageously influenced (Ger. Pub. Sp.

2,037,258).

An improved development provides placing the sieve cartridges outside the grinding chamber, in the material outlet pipe of the agitator mill. However this measure has the consequence that no more movement of the grinding bodies takes place in the region of the sieve area and thus the tendency to blockage of the sieve body is increased and the sieve effect is reduced (Ger. Pub. Sp. 2,154,713).

Furthermore an agitator mill with horizontally arranged container is known which has a filler pipe at one end and a further pipe at the other end in which the separator device is vertically insertable, the pipe also being connectable through tubes with the container. To hold back the grinding bodies there here serves a separator device equipped with one or more vibrators, being formed from a stack of separator members of disc or plate form arranged concentrically with one another and defined by radial gaps. Between each two stationary separator members there is provided a separator member which can be set into vibrating movement, or where several vibrators are used all separator members of the stack can be set in vibration.With this relatively expensive solution the requisite movement even of thickly flowing suspensions directly in the separator gaps is rendered possible thus the tendency to blockage of the separator device is reduced. However a dead space occurs in the pipe between container and separator device, in which no adequate movement of the suspension can take place. This drawback is increased by the fact that an increase of concentration of the grinding bodies takes place in the grinding container from the inlet for material for grinding to the separator device, leading to a build-up of grinding bodies in the pipe or in the tubes (Ger. Pub. Sp. 2,446,341).

The invention has the aim of most extensively eliminating the drawbacks of the known agitator mills in the separation of the ground material from the grinding bodies, increasing the dispersion and sieve effects and avoiding the loss of suspension, grinding bodies and solvent in exchanging the sieves, and carrying out this latter operation with less time expenditure.

The object of the invention consists in designing an agitator ball mill of the initially described kind and equipping it with a separator device in such a way that a build-up of grinding bodies before the separator sieve is avoided and the entire sieve area is affected by the movement of grinding bodies and ground material, while replacement of the separator sieve is made possible without emptying of the grinding container.

In accordance with the invention this is achieved in that the separator device consists of a flat sieve, is arranged lying parallel with the axis of the agitator shaft at the highest point at the end of the grinding chamber in the lid of the grinding container, formed as sieve housing, and is covered by a ground material collecting hood equipped with an obliquely upwardly directed outlet pipe. A further main feature in this connection is that the lid of the grinding container is formed from a lateral wall extending in U-form from beneath upwards and from a flat, outwardly obliquely inclined end wall, and possesses at the top a rectangular opening on which there is fitted a frame equipped with an aperture, for the accommodation of the flat sieve.

In development of the invention it is provided that the flat sieve is formed from gapped sieve wires arranged in rows and two tie bolts and angle support pieces arranged externally on both sides parallel with the sieve gaps, and is arranged with sieve gaps extending parallel to the longitudinal axis of the grinding container in the aperture of the frame.

Further features of the invention are that the lid is made double-walled on all sides and secured detachably to the grinding container and that the collecting hood for the ground material is detachably connected with the frame of the lid.

It further pertains to the invention that the agitator shaft extends with its free end into the lid and the outer agitator element arranged thereon is situated beneath the flat sieve.

Due to the measures in accordance with the invention oftheformation and horizontal arrangement of the separator device in the grinding container lid formed as sieve housing, the grinding chamber is closed off in such a way that no build-up of grinding bodies can occur even in the region of the separation zone and the entire sieve area is affected by the movement of the grinding bodies. Furthermore the mixture of ground material and grinding bodies rotating in the prolonged grinding chamber is subjected radially to a compression and decompression. These special advantages take their effect on the one hand positively upon the dispersion of the ground material and on the other upon the increase of the sieve effect.

The invention is to be explained in greater detail below by reference to an example of embodiment.

In the accompanying drawing:- Figure 1 shows diagrammatically a longitudinal section through the horizontal agitator mill with separator device and direction of throughflow of material for grinding indicated by arrows, Figure 2 shows the flat sieve in plan view as a detail, Figure 3 shows a cross-section along the line A-A in Figure 1 through the cap-like lid with flat sieve and collector hood for ground material.

As Figure 1 shows, the continuously operating agitator ball mill possesses a horizontally arranged cylindrical grinding container 1, the congruently formed ends of which are closed off by lids 2, 3 detachably secured thereto. The lid 2 is connected with the inlet pipe 4 and oppositely the lid 3 is connected with the outlet pipe 5 for the ground material. For the purpose of cooling, the grinding container is equipped with a double jacket 6. The feed of the material intended for grinding and dispersion takes place from above through the inlet pipe 4, which is arranged on the lid 2, formed as a flange, through the bore 7 into the grinding chamber 8, which is largely filled with freely movable grinding bodies.The suspension is ground and finely dispersed by the agitator mechanism rotating at high speed in the grinding container 1, the agitator shaft 9 of which is mounted at one end in the region of the grinding material inlet and sealed off from the grinding chamber 8. On the agitator shaft 9 there are secured several agitator elements 10 of disc form, or equally other known elements, arranged at equal intervals from one another. The material for grinding is distributed, kept in motion, supported in its passage through the grinding chamber and conveyed to the ground material outlet by the agitator elements. For the separation of the ground material from the grinding bodies there serves the flat sieve 11 arranged parallel with the axis of the agitator shaft 9 at the highest point at the end of the grinding chamber 8 in the lid 3 of the grinding container 1, formed as sieve housing.To accommodate the flat sieve the lid 3, formed with double walls like the grinding container, possesses an upwardly open cap-like form and consists of a lateral wall 12 extending in U-forn from below upwards and of a flat outwardly obliquely inclined end wall 13. On the rectangular opening 14 thus formed there is fitted a frame 15 which has an aperture 16 into which the flat sieve 11, preferably formed from gapped sieve wires 17 is inserted. For the intensive distribution of different concentrations of grinding bodies in the region of the separation zone of the grinding bodies from the ground material, the outer agitator element 10' of disc form fitted on the free end of the agitator shaft 9 extending into the cap-like lid 3 is situated almost centrally beneath the flat sieve.Above the flat sieve on the frame 15 a collecting hood 18 for ground material for the dispersed material issuing from the flat sieve is arranged detachably by means of a quick-action catch. The ground material separated from the grinding bodies is conducted away through the obliquely upwardly directed outlet pipe 5 connected with the ground material collecting hood 18.

Figure 2 shows the flat sieve which advantageously consists of a plurality of gapped sieve wires 17, the angle support pieces 19, 19' arranged on both sides parallel with the sieve gaps on the outsides and the tie bolts 20, 20' serving for clamping.

It can be seen in greater detail from Figure 3 that the flat sieve 11 with its angle support pieces 19, 19' and the gapped sieve wires 17 with sieve gaps extending parallel with the longitudinal axis of the grinding container lies in the aperture 16 of the frame 15 and is held in the frame of the lid 3 by the ground material collecting hood 18 arranged thereabove.

The horizontal arrangement of the flat sieve in the lid of the grinding container renders possible rapid removal and replacement thereof, in that after removal of the ground material collecting hood 18 the flat sieve 11 can be taken out of the aperture of the frame 15 and reinserted, without this involving emptying of the grinding container. Moreover siezing of splinters of grinding bodies in the flat sieve is made more difficult by the sieve gaps extending transversely of the flow direction of the grinding bodies.

When cleaning of the removed flat sieve is necessary the nuts of the tie bolts 20, 20' are slackened so that the gapped sieve wires 17 are only loosely held by the tie bolts between the angle support pieces 19, 19'. With sieve gaps widened thus it is possible to carry out the cleaning of the flat sieve of ground material and grinding body particles rapidly and thoroughly.

Claims

1. Agitator ball mill for the continuous comminution and dispersion of liquid-solid mixtures, having a horizontally arranged, cylindrical and double-walled grinding container closed at the ends by lids, which comprises an inlet for material for grinding at the top at one end and opposite thereto at the other end an outlet for ground material, before which a separator device formed as sieve is inserted, while in the grinding chamber an agitator mechanism formed from an agitator shaft, mounted at one end, with agitator element secured thereon, rotates at high speed, characterised in that the separator device consists of a flat sieve (11) and is arranged horizontally parallel with the axis of the agitator shaft (9) at the highest point at the end of the grinding chamber (8) in the lid (3) of the grinding container (1), formed as sieve housing, and is covered by a collecting hood (18) for ground material equipped with an obliquely upwardly directed outlet pipe (5).

2. Agitator ball mill according to Claim 1,char- acterised in that the lid (3) of the grinding container (1) is formed from a lateral wall (12) extending from below upwards in U-form and a flat, outwardly obliquely inclined end wall (13), and possesses at the top a rectangular opening (14) on which there is fitted a frame (15) provided with an aperture (16) for the reception of the flat sieve (11).

3. Agitator ball mill according to Claims 1 and 2, characterised in that the flat sieve (11) is formed from gapped sieve wires (17) arranged in rows on two tie bolts (20, 20') and angle support pieces (19, 19') arranged externally on both sides parallel with the sieve gaps, and is arranged with sieve gaps extending parallel with the longitudinal axis of the grinding container in the aperture (16) of the frame (15).

4. Agitator ball mill according to Claims 1 to 3, characterised in that the lid (3) is made doublewalled on all sides and detachably secured to the grinding container (1).

5. Agitator ball mill according to Claims 1 to 4, characterised in that the collecting hood (18) for the ground material is detachably connected with the frame of the lid (3).

6. Agitator ball mill according to the preceding Claims, characterised in that the agitator shaft (9) extends with its free end into the lid (3) and the external agitator element (10') arranged thereon is situated beneath the flat sieve (11).

7. Agitator ball mill substantially as described herein with reference to the accompanying drawings.