EP0180976B1 - Agitator mill, in particular an agitator ball mill - Google Patents

Abstract

An agitating mill, particularly an agitating ball mill, comprising a housing having an inlet for material to be ground and for air, an outlet for fines and air, and at least one horizontal agitator shaft which is provided with agitating members. The outlet for fines and air has a large area and is provided in the top wall of the housing and extends throughout the length and width of the top wall of the housing. A plurality of agitator shafts are preferably provided which are juxtaposed and superposed.

Description

The invention relates to an agitator mill, in particular an agitator ball mill according to the preamble of claim 1. Such a mill is already known from DE-A-1 757 942.

In the mills of this type known hitherto, the inlet is located in or near one end of the essentially cylindrical housing or grinding container and the outlet is in or near the opposite end wall. Pipe sockets are provided as the inlet and outlet.

In general, a high throughput capacity with good particle size distribution is desired, i.e. There should be as little coarse grain in the outlet as possible.

With increasing throughput, the energy to be introduced into the process increases, which is largely converted into heat. The throughput is limited by the corresponding temperature increase. If the ground material is fed into the mill together with air and the fine material is accordingly discharged with air, a cooling effect is associated with this air flow. This cooling effect - and with it the throughput, remains limited. The main disadvantage was that the outlet is relatively small - despite the limited throughput, this results in a relatively high flow velocity in the outlet, so that relatively large coarse particles are entrained by the flow. The coarse grain can be excreted through a downstream sifter - however, a correspondingly high effort is required. Cooled air has therefore already been used as a carrier medium. Chunks of frozen carbon dioxide have also been added to the mill at other mills. Each is to be used accordingly without costs.

In contrast, the invention has for its object to provide a device of the type mentioned, which has a relatively large throughput with a small, compact design with good grain distribution in the outlet. The solution to this problem is specified in the characterizing part of claim 1. The outlet is therefore provided in the upper housing wall. A relatively large space is available here. The outlet expediently extends over essentially the entire length and width of the upper housing wall. A large air flow can be passed through the large outlet at a relatively low speed, so that a correspondingly large cooling of the mill and the ground material is achieved. Thanks to the relatively small, even flow in the large-area outlet, you get a relatively even fine material with a uniform grain distribution. This classifying effect in the outlet can be increased by means of a deflecting grille made of inclined slats in the outlet, which adhere very coarse coarse particles (so-called "spray particles") and above all the grinding media.

A further improvement is achieved in that the inlet extends parallel to the (at least one) stirring shaft, essentially over the entire length of the stirring shaft (claim 5). A large throughput corresponds to the large inlet, since the inlet extends over the entire length of the mill, the entire volume is used evenly. The ground material is expediently introduced (blown in) into the mill with air, that is to say the inlet is designed as a ground material air inlet. At the same time as the regrind, the air is distributed evenly over the entire length of the mill, which is thus cooled evenly; local overheating is avoided.

In a further embodiment, the agitator shaft can be hollow (claim 8), so that air is sucked in from the outside through the plane shaft and let into the mill for the purpose of uniform cooling. For this purpose, in particular the stirring elements seated on the stirring shaft can be hollow and can be provided with at least one outlet for air (claim 9). As a result, the air is distributed particularly evenly over the entire grinding bed - the cooling is correspondingly uniform and, in particular, the finer particles of the ground material are automatically discharged to the outlet. This reduces the average residence time; the energy expenditure, the stress caused by an increase in temperature are reduced, the throughput is increased.

Thus, since the problem of heating, i.e. cooling is solved, a further embodiment of the invention provides a plurality of agitator shafts next to one another, preferably two rows of three agitator shafts each (claims 6 and 7). Accordingly, the throughput is increased - with a very compact design or small space requirement. The air introduced into the mill can also be cooled or conditioned; a different gas can be used instead of air.

An exemplary embodiment is described below with reference to the drawing:

• Fig. 1 einen vertikalen Schnitt gemäss Linie I - I in Fig. 2, quer zu den Rührwerkswellen, wobei auf der Mühle ein Sichter aufgesetzt ist;
• Fig. 2 einen axialen Schnitt nach Linie 11 - 11 in Fig. 1;
• Fig. 3 zeigt die Mühle nach Fig. 1 und 2 in Perspektive;
• Fig. 4 zeigt eine Einzelheit gemäss Linie IV in Fig. 2, nämlich einen Rührarm.
• Fig. 5 zeigt eine Abwandlung, ebenfalls im vertikalen Querschnitt.

Show it:

• 1 shows a vertical section along line I - I in FIG. 2, transverse to the agitator shafts, a classifier being placed on the mill;
• Fig. 2 is an axial section along line 11-11 in Fig. 1;
• Fig. 3 shows the mill of Figures 1 and 2 in perspective;
• Fig. 4 shows a detail along line IV in Fig. 2, namely an agitator.
• Fig. 5 shows a modification, also in vertical cross section.

The mill according to the invention according to the exemplary embodiment has an essentially box-shaped, rhombohedron-shaped housing 1 with two vertical end walls 2, 3, the lower wall 4, the upper wall 5 and two inclined ones Side walls 6, 7 on. The edges between the inclined side walls and the bottom or top wall are rounded. In this cross-sectionally rhombic housing (FIG. 1), six agitator shafts 8 with agitating elements 9 are arranged, in two rows with three shafts each next to one another. The orbits of the agitator arms overlap; the stirring arms are axially offset accordingly (cf. FIGS. 1 and 2). The upper row of agitator shafts is offset by half the axial distance from the lower. The inclination of the side walls 6, 7 corresponds to this axial offset. The rounding of the longitudinal edges of the housing corresponds to the orbits of the stirring arms. The regrind inlet 10 is provided on the inclined longitudinal wall 7 of the mill. This inlet 10 is designed as a shaft which extends essentially over the entire axial length of the mill (cf. FIGS. 1 and 2). This inlet is provided on the obliquely inclined side wall 7, which forms an angle greater than 90 degrees with the bottom wall 4 inside the mill. The outer wall 11 of the shaft is provided parallel to the inclined inner side wall 7 and merges into the bottom wall 4 with a curve 12. The inner side wall 7 ends at a distance above the bottom wall 4.

The outlet 13 is provided in the upper wall 5 of the housing 1 and extends essentially over the entire length and width of the upper housing wall, up to the curved areas; the width of the outlet 13 thus corresponds approximately to the center distance of the outer agitator shafts 8. A grid of inclined rods or lamellae 14 is inserted into this large-area outlet opening. A classifier housing 15, in which the impeller 15a of a centrifugal classifier rotates, is placed over this grid of oblique deflector blades. An intermediate piece 15b leads from the rectangular outlet opening 13 to the cylindrical classifier housing 15. The fine material reaches the inside of the classifier impeller 15a in the direction of the flow arrows and is separated from the classifying air as usual by means of a subsequent filter. The coarse material falls back inside the mill and is further crushed there.

In contrast, in the embodiment according to FIG. 5, the coarse material gets back into the grinding material inlet 10 via a funnel 32 attached to the sifter housing at the bottom and an inclined pipe 33 or a slide. The sifter is arranged correspondingly high above the mill and by means of a pipe piece 34 connected to the outlet 13 or the intermediate piece 15b.

The shafts 8 are designed as hollow shafts (tubes) and are provided with radial bores 16 in the interior of the mill. The agitator arms 9 are also hollow or tubular and are connected to the interior of the agitator shaft 8 via a radial bore. The stirring arms 9 have lateral openings 17 and / or an opening 18 at their outer end. Thus the inside of the mill is connected to the outside atmosphere.

Due to the vacuum or suction applied to the sifter 15, 15a and / or a downstream sifter, air is thus sucked in from outside through the hollow shafts 8 and stirring arms 9 through the mill. Due to the large number of stirring shafts 8 and stirring arms 9, the air is distributed finely and evenly over the entire grinding bed. In this way, the relatively very large inlet 10 and in particular very large outlet 13 are possible. The grinding bed is loosened up by the stirring arms 9 and the air flowing into the grinding bed at the same time. This improves the mobility of the grinding media 20. The fine material that forms is immediately blown out of the grinding bed, as it were in status nascendi. Above all, however, the grinding bed and the mill as a whole are cooled so that there is no overheating. This cooling effect makes it possible to arrange a plurality of agitator shafts 8 one above the other in rows. The dimensions of the mill in terms of length, width and height are practically unlimited, since the previous limitation no longer applies due to the heating. The grinding media and coarse material are retained by the deflector blades 14.

The bearings 21 are simultaneously cooled by the sucked-in air. Each agitator shaft 8 can be driven individually by a separate gear motor 22. The single drive is cheaper than a drive by a correspondingly larger motor via a transfer case, as indicated schematically in FIG. 3.

All mills should prevent fine material or dust from escaping from the inside of the mill. The sealing of the shaft openings through the housing walls is difficult here. The vacuum inside the mill reduces the leakage of fines. In addition, compressed air can be applied to the shaft end passages. For this purpose, in the exemplary embodiment, the end walls 2, 3 are double-walled from an inner wall and an outer wall 2a, 3a together with corresponding peripheral wall parts. Compressed air is introduced into the air chambers 23, 24 thus formed by means of one compressed air connection 25 each. The compressed air constantly flows through the shaft penetrations of the inner end walls 2, 3, which additionally prevents fine material from escaping (FIG. 2).

The regrind can be fed into the grinding room or agitation room with the exclusion of air or with additional conveying air.

In addition, air can be input finely distributed over the entire housing. For this purpose, the peripheral walls - the inclined side walls 6, 7 and the lower wall 4 and upper wall 5 - are constructed with double walls from an inner wall and an outer wall 4a, 5a, 6a, 7a arranged at a distance from this. The cavity 27 formed in this way is pressurized with compressed air by a pipe socket attached to the outer wall 6a beatable. The inner walls have openings 26 for the passage of air. These air inlet openings 26 are primarily provided in the lower wall 4, but not or less in the upper area of the mill. The various possibilities for introducing air into the grinding bed can be used individually or cumulatively. The introduction of air via hollow stirrer shafts and stirrers is most effective. In a further embodiment, valves are used in the mixing arms, which block the air outlet during the upper circulation phase of each mixing arm. The air streams emerging from the stirring elements are thus directed essentially downwards and not upwards. This benefits the uniformity of the grinding effect over the entire volume of the mill. 4, check valves 28 are installed in the stirring arms 9.

A seat 29 for a valve ball 30 or similar valve body is provided in each stirring arm. The valve seat is arranged radially inside and the valve ball radially outside. In the upper region of the orbit of the agitator arms 9, gravity thus presses the valve ball 30 - against the centrifugal force plus the pressure force of the higher air pressure in the agitator arm 9 - onto the valve seat and thus blocks the air outlet. In the lower area of the orbit, on the other hand, the weight of the valve ball 30 acts in the same direction as the centrifugal force and pressure force, the valve ball is therefore removed from the valve seat and the air flow is released downwards or into the lower area of the mill. In order to keep the weight and size of the valve ball 30 low and to ensure that the valve 28 closes securely, a compression spring 31 is provided according to FIG. 4, which also limits the valve lift.

Reference symbol list

• 1 housing
• 2-7 walls
• 2a - 7a outer walls, at a distance from the inner walls 2 - 7
• 8 agitator shafts
• 9 stirring elements / arms
• 10 regrind inlet
• 11 wall of 10
• 12 curvature of 11
• 13 outlet, in upper wall 5
• 14 slats in 13
• 15 classifier housing, over 13
• 15a classifier wheel
• 15b intermediate piece
• 16 radial bores of the hollow shafts 8
• 17 side openings or holes in 9
• 18 openings at the ends of 9
• 20 grinding media
• 21 bearings of 8
• 22 geared motor, each for 8
• 23, 24 purge air chambers
• 25 compressed air connection for 23, 24
• 25a air intake for 27
• 26 openings in the housing wall, especially the bottom wall 4
• 27 cavity
• 28 check valve
• 29 valve seat
• 30 valve ball
• 31 valve spring
• 32 funnels
• 33 tube / slide
• 34 pipe section

Claims (10)

1. Agitator mill, particularly a ball mill, with a housing having inlets for material to be ground and for air or a material-and-air inlet and a fine material-and-air outlet and with at least one horizontal shaft (agitator shaft) fitted with agitating and/or grinding means, characterised in that the fine material-and-air outlet (13) extends substantially over the total length and width of the upper wall (5) of the housing.

2. An apparatus according to Claim 1, characterised in that obliquely inclined and mutually parallel spaced apart deflector blades (14) (deflecting grid) are provided in the outlet (13).

3. An apparatus according to Claim 1 or 2, characterised in that a separating device, particularly a centrifugal force sieve (15, 15a) is disposed above the outlet (13).

4. An apparatus according to one of Claims 1 to 3, characterised in that the inlet (10) (or the inlets) extend or extends parallel with the at least one agitator shaft (8) and substantially over the total length of the agitator shaft (8).

5. An apparatus according to at least one of Claims 1 to 4, characterised in that a plurality of agitator shafts (8) are disposed alongside and/or above one another, the rotation paths of the correspondingly axially staggered agitator means (9) partially overlapping.

6. An apparatus according to Claim 5, characterised in that two rows of in each case three agitator shafts (8) are provided.

7. An apparatus according to one of Claims 1 to 6, characterised in that the agitator shaft(s) (8) is (are) hollow and have at least one air intake aperture outside the housing and at least one air outlet orifice (16) inside the housing.

8. An apparatus according to Claim 7, characterised in that the agitator means (9) are hollow and comprise at least one outlet orifice (17, 18) for air.

9. An apparatus according to Claim 8, characterised in that in front of the outlet orifices (17, 18) of the agitator means (9) there is a valve (28) with a valve seat (29) and valve ball (30) (or valve body), the valve ball (30) being provided between the valve seat (29) and the outlet (17, 18).

10. An apparatus according to one of Claims 1 to 9, characterised in that the housing is at least partially of double-walled construction, there being on the outer wall (2a to 7a) at least one inlet (25, 25a) for air, while on the inner wall there are a plurality of inlets (26) leading into the interior of the mill, or alternatively in that the inner wall is porous.

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