Impact mill

Abstract

Impact knife mill with impact knives (1) rotating in a grinding chamber (2) and a sieve (5) enclosing the grinding chamber (2) and coaxial to the axis of rotation (3) of the impact knives (1), characterized in that the sieve (5) has a bent sheet of a wear-resistant steel alloy and sieve openings (9) that widen in the radial direction.

Description

[0001] The invention relates to a fly-blade mill with fly-blades rotating in a grinding chamber and with a sieve enclosing the grinding chamber and coaxial to the axis of rotation of the fly-blades.

[0002] The screens of such impact knife mills, which are used to grind material containing hard particles, such as nuts or cocoa beans, are subject to considerable wear. Conventionally, the screens used consist of arrays of spaced-apart bars with slotted openings between them. Replacing and replacing worn screens of this type requires considerable effort.

[0003] WO 97 / 43043 A1 discloses a mill for comminuting fibrous material. A grinding chamber, in which a grinding wheel with paddle-like blades rotates, has an inlet opening for material on its top side and an outlet designed as a screen on the bottom side. For comminution, the end edges of the blades, facing the boundary walls of the grinding chamber, interact with the grinding chamber wall. CN 2 618 667 Y discloses a hammer crusher with a curved bottom screen made of sheet metal.

[0004] DE 103 21 049 A1 describes a sieve for a stirred mill, which is used to separate the material to be ground and the auxiliary grinding media used in the stirred mill.

[0005] The invention is based on the object of creating a fly-blade mill of the type mentioned at the beginning with a new sieve which can be manufactured with less effort than conventional sieves and has a longer service life.

[0006] This task is solved by a sieve made of a bent sheet of a wear-resistant steel alloy and having sieve openings that widen in the radial direction.

[0007] Surprisingly, it has been found that such a screen according to the invention, which can be manufactured more easily from bent sheet metal than by assembling bars, shows hardly any signs of wear after a service life equivalent to that of conventional screens. The use of wear-resistant material in combination with the inventive geometric design of the screen openings leads to a significantly longer service life. The geometry of the screen openings is adapted to the trajectories of the high-kinetic-energy particles generated during comminution, resulting in fewer collisions in the opening area and thus less wear.

[0008] The Brinell hardness of the steel alloy used for the screen plate is preferably at least 300 HBW. Preferably, it is greater than 370 HBW.

[0009] The sieve openings are expediently widened to such an extent that the solid angle occupied by the sieve openings, relative to the axis of rotation of the impact blades, is larger on the outside of the sieve than on the inside.

[0010] In a particularly preferred embodiment of the invention, the solid angle and thus the width or diameter of the sieve opening on the outside of the sieve is 10 to 30% larger than on the inside, depending on the material thickness and the bending radius.

[0011] In a further embodiment of the invention, the sieve has openings in the form of slots that increase in width in the radial direction.

[0012] In particular, for a sheet thickness of 4 mm, the width can be 0.25 mm on the inside of the screen openings and 0.45 mm on the outside.

[0013] The slot openings can extend in the axial direction over a length of, for example, 50 mm. The tangential distance between the slots can be, for example, 1 mm.

[0014] In a particularly preferred embodiment of the invention, the sieve openings are produced by water jet cutting of the sheet metal forming the sieve.

[0015] The invention will be further explained below with reference to an embodiment and the accompanying drawings relating to this embodiment. They show: Fig. 1 a blade mill with a screen according to the invention in a vertical sectional view, Fig. 2 a partial side view of the impact knife mill of Fig. 1 sieve used, and Fig. 3 a partial view of the impact knife mill of Fig. 1 used sieve in a horizontal section.

[0016] One in Fig. The impact knife mill shown schematically in Figure 1 comprises a number of impact knives 1 that rotate in a grinding chamber 2 about a rotational axis 3. A shaft 4 carrying the impact knives 1 is connected to a drive unit (not shown) arranged outside the grinding chamber.

[0017] The grinding chamber 2 is enclosed on its vertical sides by a sieve 5 in the form of a cylindrical shell coaxial with the rotation axis 3. Adjoining the sieve 5 on the outside is an annular collecting chamber 6 for the crushed material to be ground, with an outlet 7.

[0018] The grinding chamber 2 can be continuously filled with grinding material via a screw conveyor 8. The impact knife mill shown is designed for a grinding material throughput of 3,000 kg / h and is used for grinding grinding material containing hard particles, such as nuts or cocoa beans.

[0019] As from Fig. 2 and Fig. As can be seen in Figure 3, the sieve 5 has sieve openings 9 in the form of vertical, parallel slots. The sieve is made of bent sheet metal, the thickness d of which is 4 mm in the illustrated embodiment. The slot length L is 50 mm in the illustrated embodiment, and the vertical spacing A between the arrangements of parallel slots is 20 mm. The respective spacing α between the parallel slots is 7 mm.

[0020] On the inside of the sieve, the width Bi of the slot-shaped sieve openings 9 is 0.25 mm in the illustrated embodiment, while the width Ba on the outside of the sieve is 0.35 mm. With a diameter of the cylindrical sieve of approximately 1,500 mm, the solid angle formed by the slot-shaped sieve openings 9 on the outside, relative to the radius up to the rotation axis 3, is significantly larger than the solid angle on the inside of the sieve.

[0021] The sieve openings 9 were produced by water jet cutting before bending the sheet.

[0022] The sheet metal from which screen 5 is made is made of an exceptionally wear-resistant steel alloy, whose Brinell hardness in the example shown is 400 HBW (according to standard EN ISO 6506-1). Such a material is offered, for example, under the name HARDOX by the Swedish company SSAB OXELÖSUND AB, S-613 80 Oxelösund, and under the name DILLIDUR by the German company Dillinger Hütte GTS, D-66763 Dillingen.

[0023] When using the impact knife mill described above to crush cocoa beans, the service life of sieve 5 was several times longer than that of conventional sieves.

Claims

[1] Impact knife mill with impact knives (1) rotating in a grinding chamber (2) and a sieve (5) surrounding the grinding chamber (2) and coaxial to the axis of rotation (3) of the impact knives (1), characterized by that the sieve (5) comprises a bent sheet of a wear-resistant steel alloy and sieve openings (9) widening in the radial direction. [2] Impact knife mill according to claim 1, characterized by that the Brinell hardness of the steel alloy is at least 300 HBW and preferably greater than 370 HBW. [3] Impact knife mill according to claim 1 or 2, characterized by that the solid angle taken up by the sieve openings (9) and related to the axis of rotation (3) is larger on the outside of the sieve (5) than on the inside. [4] Impact knife mill according to one of claims 1 to 3, characterized bythat the solid angle, in particular the width or diameter, of the sieve openings (9) on the outside of the sieve is up to 30% larger than on the inside of the sieve. [5] Impact knife mill according to one of claims 1 to 4, characterized by that the sieve (5) has sieve openings (9) in the form of slots with a width (B) increasing in the radial direction. [6] Impact knife mill according to claim 5, characterized by that with a sheet thickness of 4 mm, the width of the sieve opening (9) on the inside is 0.2 to 0.3 mm, in particular 0.25 mm, and on the outside 0.4 to 0.5 mm, in particular 0.45 mm. [7] Impact knife mill according to one of claims 1 to 6, characterized by that the slot-shaped sieve openings (9) extend in the vertical direction over a length of 50 mm. [8] Impact knife mill according to one of claims 1 to 7, characterized bythat the tangential distance between the slot-shaped sieve openings (9) is 4 mm tangentially. [9] Impact knife mill according to one of claims 1 to 8, characterized by that the sieve openings (9) are produced by water jet cutting of the sheet metal. [10] Screen for a blade mill, wherein the screen (5) encloses a grinding chamber (2) in which blades (1) rotate about a rotational axis (3), coaxially to the rotational axis (3), characterized by that the sieve (5) comprises a bent sheet of a wear-resistant steel alloy and sieve openings (9) widening in the radial direction.

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