EP1335794B1 - Centrifugal mill comprising two chambers - Google Patents

Abstract

The invention relates to a centrifugal mill (10) comprising a rotor (14) which is rotatably positioned in an operational rotating direction (R) about a rotational axis (X) in a housing, and a plurality of chambers (22). A centrifugal blade (24) is associated with each of the centrifugal chambers (22), along which blade the grinding stock (18) is displaced from a radial inner grinding stock supply (18) to a radial outer cutting edge, during operation of the centrifugal mill (10) and following centrifugal forces, the grinding stock emerging at the cutting edge from the rotor (14) of the centrifugal mill. Each centrifugal blade (24) comprises a wall (28) having a radial inner end edge (28a) and a radial outer end edge (28b) as well as a wearing unit (42/44) which is adjacently fixed to the radial outer end edge (28b) of the wall (28) of the blade, and on which the cutting edge (30) is arranged. Said blade wall (28) is embodied in an arched manner and exposes its concave surface (28c) to the grinding product (16) which moves along the same. According to the invention, precisely two centrifugal chambers (22) are provided. When the two cutting edges (30) of the centrifugal blades are connected to each other and form the mean perpendicular (M) on the line of connection, the radial inner end edge (28b) of the walls (24) of the two centrifugal blades (24) are arranged near said mean perpendicular (M).

Description

The invention relates to a centrifugal mill with a centrifugal mill rotor, in a centrifugal mill housing about an axis of rotation in a working direction of rotation is rotatably mounted and a plurality of centrifugal chambers wherein each of the spin chambers is a spinner blade is assigned, along which the regrind during operation of the spin mill due to centrifugal forces from a radially inner Mahlgutzufuhr to a radially outer spoiler edge moves from where it comes from the Schleudermühlenrotor emerges, each skimmer blade with a blade wall a radially inner end edge and a radially outer end edge and one adjacent to the radially outer end edge of the blade wall attached wear unit, on which the tear-off edge is arranged, wherein the blade wall is curved and formed on it assigns its concave surface along moving regrind. It was already noted at this point that in connection with the present invention under a curved course not necessarily a curved, for example circularly curved course meant must be, but that also meant a polygonal course can. This means that it is possible, for example, the curved Blade wall made up of a plurality of flat blade wall panels reassemble.

Such a centrifugal mill is for example from the prospectus of Anheter "BHS rotor mills" known.

A spin mill according to the preamble of Claim 1 is known from US-A-4,738,403.

A fundamental problem arising in the construction of centrifugal mills the expert always is, is a given Grist with the lowest possible energy consumption and the lowest possible To reduce wear on the spin mill as well as possible. With just This issue addresses a whole series of pamphlets. to The solution to this problem is always tried, on the one hand the ejection the grinding stock from the Schleudermühlenrotor and on the other hand, the crushing process to optimize the impact of the ground material against a baffle. Representative here, for example, on the very detailed and referenced a plurality of further citations EP 0 835 690 A1.

With the design of the grinding material feed area, through which the material to be ground in the spin mill rotor is introduced in the region of its axis of rotation, So far, the state of the art has been concerned only insofar as it concerns went, if possible, business interruptions due to blockages to prevent this feed area.

In contrast, the applicant has for the first time set the task, the Mahlgutzufuhrbereich in terms of energy consumption and the To improve wear of the spin mill and their grinding result.

This object is achieved by a centrifugal mill of solved at the beginning, which exactly two centrifugal chambers and in which the radially inner end edges of the blade walls of the two centrifugal blades then, if you have their two tear-off edges connects together and on this connecting line the perpendicular bisector is arranged in the vicinity of these mid-perpendicular, preferably the radially inner end edge of each blade wall in each case starting from whose radially outer end edge in an angular range of about 20 ° in front of Centered perpendicular to about 20 ° after the mid-perpendicular.

With this embodiment, the applicant has a in the art prevailing prejudice, according to which the centrifugal mill rotor at least three, better still at least four sling chambers should, as in a distribution of the ground material to a possible large number of spin chambers from each one of the spinner blades only a correspondingly small amount of ground material to the trailing edge needs to be accelerated. This affects the one on the one Wear of the centrifugal mill rotor favorable, and worry about the other making sure that each regrind particle is essentially the same Conditions along the centrifugal blade towards the trailing edge is accelerated, according to the opinion prevailing in the professional world.

Surprisingly, however, the investigations of the applicant have shown that by passing to a centrifugal mill rotor with only two centrifugal chambers (two-chamber rotor) with unchanged Mahlergebnis both a lower energy consumption and a lower wear on the spin mill can achieve. Like in Below are explained in more detail with reference to the accompanying figures 2 and 3 Applicant mainly attributes this to the improved grinding material feed behavior the two-chamber centrifugal mill according to the invention back:

In Figures 2 and 3, a centrifugal mill according to the invention is quite generally designated 10, wherein the spin mill housing 12 and the Schleudermühlen rotor 14 are shown only roughly schematically. In these figures, the movement of a Mahlgutpartikels 16 of a Grist distribution plate 18 of the rotor 14, the below one (not is arranged mill feed tube, to the baffle 20 of the Mill housing 12 in two different coordinate systems [x, y] and [x ', y'] shown. The baffle 20 can, as for example in the prospectus "BHS rotor mills" is shown, either of a plurality be formed of made of wear-resistant material baffles can (see page 6 of the prospectus) or alternatively from a material bed from already comminuted material (see page 8 of the prospectus).

The coordinate system [x, y] according to FIG. 2 is a with respect to the mill housing 12 and thus with respect to an external observer fixed coordinate system. Fig. 2 therefore shows the absolute movement the regrind particle 16 in the mill housing 12.

The coordinate system [x ', y'] according to FIG Rotor 14 fixed coordinate system, with the rotor 14 around the Turning axle X also rotates. The representation of the movement of the regrind particle 16 in this co-rotating coordinate system [x ', y'] is therefore suitable in particular relative to movements of the regrind particle 16 with respect to of the rotor 14 show. It is precisely these relative movements, however, for the collection of the millbase, i. the transition of the regrind particles 16 from the task plate 18 in the of the centrifugal blade or the Centrifugal 24 limited centrifugal chamber 22 of decisive Meaning are.

Namely, this movement phase ends when the particle 16 on the Ground material bed 26 hits, which occurs when the spinning blade is rotated 24 forms in front of this and the blade wall 28 protects against wear. at This collision, the particle 16 is braked in the case of catchment and his Relative speed with respect to the centrifugal blade 24 is zero reduced. In this case, ideally, a pre-crushing of the particle 16 instead of. After this impact, the particle 16 or its fragments is longitudinal the surface 26 a of the material bed 26 accelerated radially outward until he at the trailing edge 30 of the centrifugal blade 24 at point C the rotor 14 leaves and is accelerated to the baffle 20. On impact against the Baffle 20 is the main crushing of the particle 16th

This case described above is always present when the Particles 16 in the region of the surface 26 a of the material bed 26 on the Scooter blade 24 hits. On the other hand, it hits the radially inner boundary surface 26b of the material bed 26, it is from this radially inside, as indicated in Fig. 3 by the arrow D. As a result this reflection, the particle 16 thus moves not only against the desired conveying direction and is thus not fed, but he hinders also the supply of fresh regrind. In the worst case can the caused by the reflected particles backflow effect to a Blockage of Mahlgutzufuhr and thus to a business interruption lead the centrifugal mill 10.

According to the invention, it has now been recognized that the collection probability compared with the reflection probability in a simple manner thereby It can be increased that the length of the peripheral section between two consecutive spinner blades 24 relative to the circumferential length the reflection surface 26b increases. In a particularly effective way You do this by going from a three-chamber mill, as in the brochure "BHS rotor mills", to the invention Two-chamber mill passes.

By increasing the circumferential distance between two consecutive following centrifugal blades 24 but at the same time also the area possible impact points of the particles 16 on the material bed surface 26a of the centrifugal blade 24 increases. But that would have after the conventional idea about the physical processes in the rotor 14 of the Schleudermühle 10 due to the different distance over which the Particles 16 along the remaining length of the material bed surface 26a can be accelerated towards the tear-off edge 30, also the exit velocity the particle 16 from the rotor 14 and thus their kinetic Energy must vary greatly, which inevitably also had a negative effect on the crushing result.

Surprisingly, however, has in experimental runs a inventive Two-chamber mill no deterioration of the crushing result, but an improvement of the crushing result result. These test results are also confirmed by the result of Supported computer simulations, which is shown in Fig. 4.

In the diagram according to FIG. 4, the velocity of the particles 16 during their movement from their point of application to the spoiler edge 30 (radius r ₀ ) for three different rotor speeds and two different feed positions (r = 0 and r = 0.5 r ₀ ) shown. It can be seen immediately that the exit velocity of the particles 16 at the spoiler edge 30 (r = r ₀ ) at a given rotor speed practically does not depend on whether the particle 16 in question directly at the rotational axis X or at a radially outward location (r = 0 , 5 r ₀ ) begins its centrifugal force-induced movement along the material bed surface 26 a of the centrifugal blade 24.

Additional investigations also showed that the succession the particle along the material bed surface 26a by the distribution of Grindings on only two sling chambers not increased in one measure had, that thereby an ordered movement of these particles 16 along the surface 26a could have been questioned. Also this result contradicts the conventional ideas about the physical processes in centrifugal mills.

In contrast to those known from the brochure "BHS rotor mills" Three-chamber centrifugal mills, however, prove in the inventive Two-chamber centrifugal mills the position of the radially inner end edges the blade walls of the two centrifugal blades as one for the Quality of the crushing result essential feature. Is located this radially inner end edge too close to the associated radially outer End edge of the blade wall, so it can happen that on the distribution plate 18 abandoned ground material exits the spin rotor 14, without ever been in contact with a skimmer blade 24 in contact. These Understandably, moving regrind particles 16 that move in an uncontrolled manner degrade understandably the quality of the crushing result in a considerable Dimensions. Is the radially inner end edge of the blade wall, however, of the associated radially outer end edge too far, so the point B, at which the particles 16 accelerating material bed surface 26a in the particle 16 reflective surface 28b of the material bed 26th goes over too far radially inward on the distribution plate 18. In this way narrow the material beds 26 of the two centrifugal blades 24 the Regrind feed and thus complicate the supply of regrind in the Schleudermühle, which in extreme cases, in turn, to a blockage of Grist feed can lead.

These two effects are inventively prevented by the radially inner end edges of the blade walls near the mid-perpendiculars on the line connecting the demolition edges of the two centrifugal blades is arranged, preferably in an angular range of about 20 ° before to about 20 ° after this mid-perpendicular.

Blockage of the grinding material supply can further be prevented thereby be that the radially inner end edge of each blade wall in one Radial distance from the axis of rotation is arranged, the at least about 30%, preferably at least about 40%, of the radial distance of the Tear edge of the blade wall from the axis of rotation is.

If in further development of the invention, the convex surfaces of the Vane walls form the outer surface of the centrifugal mill rotor, so can thereby occurring on the outer surface of the centrifugal mill rotor Wear by itself from the baffle back to radially inward zurückbewegendes Grist be reduced as the distance of the outer surface of the Schleudermühlen rotor by this design measure on a considerable portion of the rotor circumference is greater than the distance of the Demolition edges of the baffle wall. This can be a significant amount of moving from the baffle back to radially inward Mahlguts fall by gravity down before it on the Outside surface of Schleudermühlen rotorstrifft and there leads to wear.

To improve the grinding result, the trailing edge can be adjacent above and / or below the associated regrind exit opening of Schleudermühlenrotors striking elements with preferably substantially be provided orthogonal to the circumferential direction facing striking surfaces, which are preferably made of low-wear material. These Impact elements can with their impact surfaces regrind, different from the The baffle again moved back radially inward, capture and again mince.

As can be seen from the above discussion of the physical processes in the Indentation of the ground material results in the spinning chambers of the rotor, and how this is also evident in Figs. 2 and 3, in addition to the Abrisskanten 30 and the radially inner end edges 32 of the centrifugal blades wear due to collisions with regrind particles 16 exposed. Therefore, it is proposed in development of the invention that also at the radially inner end edges 32 of the blade walls 28 wear elements are provided.

For completeness, it should be noted that the US 4,690,341 in addition to a three-chamber centrifugal mill and a four-chamber centrifugal mill also a two-chamber centrifugal mill as a possible Embodiment disclosed. The well-known two-chamber centrifugal mill differs from the two-chamber centrifugal mill according to the invention however, in a number of essential features, the following to be explained in more detail with reference to FIG. This figure 6 is through slight addition of Figure 4 of US 4,690,341 emerged. In the Explanation of Figure 6 will therefore be the reference numerals according to the US 4,690,341 can be used:

To prevent excessive dust formation, the outer surface of the Rotor of the known two-chamber centrifugal mill essentially circular cylindrical educated. To this circular cylinder shape in the smallest possible To disturb the extent are also adjacent to the Abrisskanten 86 Grindings outlet openings very small. For this purpose, the Blade walls 56 and 58, at which the demolition edges 86 carrying Wear units 80 are attached, along chords of the circular cylinder, i. straight from a first point on the outer circumference of the rotor to a second point on the outer circumference of the rotor. To provide the circular cylinder shape are also the outer circumference of the rotor following walls 34 is provided on which wear plates 44 are mounted, which the Protect the rotor against regrind from the baffle wall. These Embodiment of the rotor as a closed rotor has compared to the invention Design of the rotor as an open rotor different Disadvantage.

As a result of the extension of the blade walls between two points on the Outer circumference of the rotor occurs in the known two-chamber centrifugal mill the effect already explained above that the transition point between which the regrind particles accelerate towards the tear-off edge Surface of the depositing on the blade wall material bed and the the material material particles radially inwardly reflecting surface of the Material bed extends relatively far radially inward and thus the Supply of regrind into the centrifugal mill rotor difficult, if not even leads to the blockage of this regrind supply.

In addition, due to the small width of the spoiler adjacent regrind exit opening also the risk of clogging in the area of the outer circumference of the rotor.

Finally, the straight course of the blade wall prevents the flexible one Use of the known two-chamber centrifugal mill for crushing Ground material of different material properties:

r -

gesuchter Konstruktionsradius

r₀ -

Ausgangsradius

β -

Öffnungswinkel der Spirale

ϕ -

Teilungswinkel

konstruiert werden, wobei das Vorzeichen " + " bei Konstruktion der Spirale von radial innen nach radial außen und das Vorzeichen "-" bei Konstruktion von radial außen nach radial innen verwendet wird.It is a known fact that the surface 26 a of the material bed 26 accumulating on the spinner blade 24, following the grinding stock particles 16, accelerates toward the trailing edge 30, essentially in the form of a logarithmic spiral. Such a logarithmic spiral can according to the regulation r = r 0 · Exp {± (π / 180) · tg β · φ} = r 0 · Exp {± 0.0175 · tg β · φ} With

r -

desired design radius

r ₀ -

exit radius

β -

Opening angle of the spiral

φ -

pitch angle

can be constructed using the sign "+" in construction of the coil from radially inward to radially outward and the sign "-" in construction from radially outward to radially inward.

An example of the construction of such a logarithmic spiral with an opening angle of β = 30 ° is shown in Fig. 5.

The opening angle β of the surface 26 a of the material bed 26 forming logarithmic spiral now depends in practice on the properties of the ground material. If the spin mill for example Sand treatment with wet sand with a water content of about 15% fed, so sets an opening angle of the logarithmic spiral of about 25 °. In the crushing of relatively round gravel is the Opening angle, however, between about 35 ° and about 45 °, while he in the crushing of pre-broken splittigem material between about 45 ° and about 55 °.

If we now examine the known from US 4,690,341 two-chamber centrifugal mill, so you notice that in this only processed material which is a logarithmic spiral with an opening angle of forms more than 35 °, otherwise at wear of the demolition edge element 86, the blade walls 56 and 58 no longer by a regrind material bed would be protected (see Fig. 6, upper centrifugal chamber).

As will be explained in more detail below with reference to FIG. 1, however, with the two-chamber mill according to the invention due to concave configuration of the material bed 26 bearing surface of Shovel wall easily also be processed material, the one Opening angle of the logarithmic spiral of a minimum of about 25 ° pulls.

In the just-mentioned Fig. 1, the structure of the spinning rotor 14th the two-chamber centrifugal mill 10 according to the invention, with reference to Figs. 2 and 3 has already been explained schematically, again in Detailed view of the plan:

In the illustration of FIG. 1 can be seen with removed cover plate a bottom plate 40 with a roughly schematic "mirrored S" -shaped shape. On this bottom plate 40 are the blade walls 28 of two centrifugal blades 24 arranged, for example, welded. The radially outer End 28a of these blade walls 28 is designed to be particularly wear-resistant and also carries a wear unit 42, on which the tear-off edge 30 carrying wear element 44 is arranged. At the in Fig. 1 right spinner blade 24 is the wear element in its worn State 44 'with the corresponding layer 30' of the trailing edge shown.

Also at the radially inner end 28b of the centrifugal wall 28 is to protect them a wear element 46 is shown, whose worn state again indicated by 46 '.

In addition, in Fig. 1 for both the unworn state as also for the worn state of the centrifugal blades 24 the courses the logarithmic spirals of the surfaces 26a of the material bed 26 shown, on the one hand for a material with opening angle 25 ° (wet sand) and on the other hand for a material with opening angle 45 ° (pre-broken split material). One recognizes immediately that also at Processing of the material with opening angle 25 °, the blade wall 28th always reliably protected by the material bed 26 from wear because it assigns to it its concave surface 28c, and that only the for this particular Verschleiteile 44 and 46 exposed to wear are. But these wear parts 44 and 46 can in easier if needed Be replaced, the transition from the three-chamber design for the two-chamber construction the accessibility of this Consumables further improved.

In addition, it was found in experiments by the applicant that the specific wear, i. the removal of material on all wear elements the centrifugal mill during the crushing of the same Grind amount occurs, otherwise the same crushing conditions decreased by about 25%. This is accompanied by a lower idle power of the two-chamber rotor (always compared to an otherwise identical three-chamber rotor) and improved throughput through the Mill both when using a ring armor and a material bed as a baffle wall.

In Fig. 1 it can be seen further that the radially inner end 28 b of the Blade wall 28 near the mid-perpendicular M on the connecting line V the demolition edges 30 of the two centrifugal blades 24 are arranged is. The radial distance of the inner edge 32 of the wear element 46th from the axis of rotation X is indicated in Fig. 1 with d.

In addition, it can be seen that arranged in the region of the tear-off edge 30 Impact elements 50 with their impact surface 50a.

Finally, one recognizes in Fig. 1 and in comparison with that of the US 4,690,341 enormous width of the outlet openings 52, in recognizable there is no risk of clogging of these outlet openings 52.

Claims (5)

1. Centrifugal mill (10) with a centrifugal mill rotor (14) which is mounted in a centrifugal mill housing (12) so as to be rotatable about a rotational axis (X) in a working direction of rotation (R) and has precisely two centrifugal chambers (22),
   wherein a centrifugal blade (24) is associated with each of the centrifugal chambers (22), along which blade the grinding stock (18) moves during operation of the centrifugal mill (10) on account of centrifugal forces from a radially inner grinding stock inlet (18) to a radially outer trailing edge (30), at which it leaves the centrifugal mill rotor (14), wherein each centrifugal blade (24) comprises a blade wall (28) with a radially inner end edge (28b) and a radially outer end edge (28a) as well as a wearing unit (42/44) which is fastened to the radially outer end edge (28a) of the blade wall (28) adjacent thereto and at which the trailing edge (30) is disposed,
   wherein the blade wall (28) is curved and its concave surface (28c) is associated with the grinding stock (16) moving along it, and
   characterised in that, if the two trailing edges (30) of the centrifugal blades (24) are connected together and the mid-perpendicular (M) is formed on this connecting line (V), the radially inner end edge (28b) of each blade wall (28) of the two centrifugal blades (24) is disposed in an angular range from approximately 20° before the mid-perpendicular (M) to approximately 20° after the mid-perpendicular (M), in each case starting from the radially outer end edge (28a) of the blade wall (28).
2. Centrifugal mill according to Claim 1,
   characterised in that the radially inner end edge (28b) of each blade wall (28) is disposed at a radial distance (d) from the rotational axis (X) which is at least approximately 30%, preferably at least approximately 40%, of the radial distance of the trailing edge (30) of the centrifugal blade (24) from the rotational axis (X).
3. Centrifugal mill according to either of Claims 1 and 2,
   characterised in that the convex surfaces (28d) of the blade walls (28) form the outer face of the centrifugal mill rotor (14).
4. Centrifugal mill according to any one of Claims 1 to 3,
   characterised in that beater elements (50) are provided adjacent to the trailing edge (30) above or/and below the associated grinding stock exit opening (52) of the centrifugal mill rotor (14), which elements have beater faces (50a) which preferably point substantially orthogonally to the circumferential direction and are preferably made of wear-resistant material.
5. Centrifugal mill according to any one of Claims 1 to 4,
   characterised in that wearing elements (46) are provided at the radially inner end edges (28b) of the blade walls (28).

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