Mixing device and suitable mixing blade

Abstract

Mixer blade (10; 70; 80; 100) for a mixing device (20), with a blade base body (2; 82) which is at least partially covered by a wear-resistant layer (4; 5; 6), and which has a front side (2a), a rear side (2b), a front end side (2e), a rear end side (2f) and a scraping edge (2c) which is designed to scrape along a drum inner wall at a distance, wherein the scraping edge (2c) and the front end side (2e) form a blade tip (3), characterized in that the wear-resistant layer (4; 5; 6) comprises: (a) a base layer (4) which at least partially covers the front side (2a) and the back side (2b) as well as the front end side (2e) and the scraper edge (2c) completely, (b) an intermediate layer (5) which partially covers the base layer (4) and completely covers the blade tip (3) to form an outer protective layer step (5a), and (c) a blade tip protection layer (6) which partially covers the intermediate layer (5) to form an inner protective layer step (6a) and completely covers the blade tip (3).

Description

Technological background

[0001] The invention relates to a mixing device, comprising a mixing drum with an inner drum wall and a drum longitudinal axis and a mixer shaft rotatable about the latter, on which a plurality of mixer blades are mounted, each with a blade arm and a blade base body fastened thereto, and which has a front side, a rear side, a front end side, a rear end side and a scraping edge, which is designed to scrape along a drum inner wall at a distance, wherein the scraping edge has an angle of attack α (alpha) with respect to a drum inner wall mantle line running parallel to the drum longitudinal axis, and wherein the scraping edge and the front end side form a blade tip.

[0002] Furthermore, the invention relates to a mixer blade for such a mixing device, having a blade base body which is at least partially covered by a wear protection layer and which has a front side, a back side, a front end side, a rear end side and a scraping edge which is designed to scrape along a drum inner wall at a distance, wherein the scraping edge and the front end side form a common blade tip.

[0003] Such mixing devices are used, for example, as solids mixers or mixing granulators. They typically comprise a mixing container for holding the material to be mixed and / or granulated. A driven mixer shaft is arranged within the mixing container, from which several spaced-apart mixing arms with attached mixing blades extend approximately radially to the shaft's longitudinal axis or at a defined angle to it. The mixing blades, through the centrifugal or vortex process, force the mixing and transport of the material.

[0004] The mixing devices can process high mass flows, which lead to high wear on the paddle arms and the mixer blades, which are therefore usually covered with a wear protection layer. State of the art

[0005] A variety of methods and devices have been proposed to improve the wear protection of mixer blades.

[0006] For example, DE 196 40 770 A1 discloses a mixer blade with a base body coated with a wear-resistant layer of bonded granular corundum or SiC. Parallel ribs made of hardened base material extend into the wear-resistant layer, extending transversely to the flow direction of the mixed material.

[0007] DE 17 59 599 B describes a mixer blade in which a wear-resistant coating is provided only in a small, triangular area around the blade tip, which clears one corner of the mixing vessel and is particularly susceptible to wear. The wear-resistant coating consists of a sintered hard metal plate arranged in a recess in the blade tip, whose outer contour is flush with the remaining working surfaces of the mixer blade.

[0008] DE 10 2005 026 924 B3 discloses a mixer blade in which the wear-prone end face (blade edge) is covered by several identically constructed, angled wear protection elements. One leg of which extends beyond half the end face, and the other leg extends along the adjacent mixer blade side wall, thus protecting the edge area of ​​the end face. Adjacent to these, the side surfaces are also covered with wear protection plates. The end-face wear protection elements are thicker than the lateral wear protection elements.

[0009] DE 200 04 488 U1 discloses a mixer blade with a base body and a blade nose attached thereto and several types of armor, such as a tip armor on the blade nose, a back armor above it and armor stiffeners on the side surface.

[0010] DE 10 2007 015 423 A1 discloses a mixing blade for a mixing device comprising a base body having a front side, a rear side, a front end, a rear end, and a scraper edge. During operation, the scraper edge scrapes adhering mix from the drum wall and, together with the front end, forms a blade tip. The mixing blade also has guide ribs projecting from the front surface as steps that extend from the scraper edge through the front surface. The guide ribs continuously and precisely guide the mix away from the scraper edge, thus reducing its wear.

[0011] DE 203 07 420 U1 describes a device for mixing granular, abrasive materials. It has mixing blades whose base and blade tips are each provided with a wear-resistant coating. Wear can vary along the length of the mixing blade and is most severe at the outer ends. Accordingly, the thickness of the wear-resistant coating varies and is thickest at the blade tip.

[0012] From CN 1 08 004 544 A, a mixing blade with a wear protection layer applied over the entire surface is known, which consists of three layers, namely a metallic base layer, an intermediate layer and a nanoceramic layer. Technical task

[0013] The leading blade tip, which dips into the mix flow, and the scraper edge or face of the mixer blade, which scrapes along the inner drum wall, are particularly subject to wear. These components of the mixer blade are referred to individually or collectively as the "inflow area" below. Wear is caused, for example, by mix particles entering the gap between the mixer blade and the inner drum wall, destroying the contact surfaces of the mixer blade and the inner drum wall.

[0014] Due to wear in the inflow area, the gap becomes larger, and the scraping effect and effective mixing deteriorate. Depending on the radial angle of attack of the mixer blade, which typically ranges from 35° to 50°, the leading tip of the mixer blade becomes rounded, which further accelerates wear on the mixer tip and the adjacent scraper edge. When the mixer blade's adjustment capability is exhausted, it must be replaced, resulting in extensive downtime and high costs.

[0015] A particular wear effect is observed when, due to the angle of attack, a linear sliding movement of the mix occurs in the longitudinal direction of the scraper edge. This can initially lead to wear of the wear-resistant layer on the scraper edge in the longitudinal direction of the edge and subsequently to pronounced scouring within the volume of the scraper edge. In this scouring, which ultimately extends over the entire length of the scraper edge, mix particles can become trapped. These particles are continuously transported along the inner wall of the drum by the mixer blade. This leads to further damage to the scraper edge and thus to premature wear of the mixer blade and reduced service life.

[0016] The invention is based on the object of providing a mixer blade which has low wear and which, in particular when used in a solids mixer or in a mixing granulator, has a comparatively long service life even at high mass flows.

[0017] Furthermore, the invention is based on the object of providing a mixing device in the form of a solid mixer or a mixing granulator which has a comparatively long service life and which can be operated with low operating costs. Summary of the invention

[0018] With regard to the mixer blade, this object is achieved according to the invention, starting from the mixer blade of the type mentioned at the outset, in that the wear protection layer comprises: (a) a base layer which covers at least partially the front and back sides and completely the front end and the scraper edge, (b) an intermediate layer which partially covers the base layer and completely covers the blade tip, forming an outer protective layer step, and (c) a blade tip protection layer partially covering the intermediate layer to form an inner protection layer step and completely covering the blade tip.

[0019] The base body has a rectangular or essentially rectangular geometry, whereby the blade tip, in particular, can be rounded and / or the scraper edge can be chamfered. The blade tip is covered by a layered structure consisting of at least three wear protection layers. The layered structure comprises at least the base layer, the intermediate layer, and the blade tip protection layer.

[0020] The base layer covers the base body completely or partially. If the base body is only partially covered, the front and rear sides, as well as the front end and the scraper edge, and thus also the blade tip, are completely covered by the base layer.

[0021] The intermediate layer is applied directly or indirectly – that is, via at least one further intermediate layer – to the base layer. It completely covers the blade tip, but only partially covers the main body and the base layer. It forms a step relative to the base layer (or to the at least one intermediate layer), which is referred to here as the “outer protective layer step.” The height of the outer protective layer step is largely determined by the thickness of the intermediate layer, including any intermediate layers. This step height is preferably at least 1 mm or more, particularly preferably in the range from 1.5 to 8 mm, and in particular in the range from 3 to 6 mm. The transition from the lower level to the upper level of the protective layer step occurs gradually or continuously.

[0022] The blade tip protection layer is applied directly or indirectly—via one or more intermediate layers—to the intermediate layer. It completely covers the blade tip, but only partially covers the base body and the intermediate layer. It forms a step relative to the intermediate layer (or to the at least one intermediate layer), which is referred to here as the "inner protection layer step."

[0023] The height of the inner protective layer step is largely determined by the thickness of the blade tip protective layer, including any intermediate layers. This step height is also preferably at least 1 mm or more, particularly preferably in the range of 1.5 to 8 mm, and especially in the range of 3 to 6 mm. The transition from the lower level to the upper level of the protective layer step occurs gradually or continuously.

[0024] The outer protective layer stage runs along the edge of the intermediate layer, and the inner protective layer stage runs along the edge of the blade tip protective layer. The two protective layer stages preferably run completely but at least partially spaced from each other, particularly in the area of ​​the front side of the base body. They form a stepped system on the base body of the mixer blade.

[0025] It has been shown that the at least triple layer structure, in combination with the stepped system, significantly improves the wear resistance and thus the service life of the mixer blade. The stepped system is designed so that – starting from the blade tip in the direction of transport of the mix – at least one sloping protective layer step, preferably at least two sloping protective layer steps, are created, which can lead to pressure relief for the mixer blade. Compared to a standard wear protection layer with a single base layer, the service life is extended by a factor of 3 to 5.

[0026] The wear protection layers can differ in their composition, but preferably the wear protection layers consist of the same material, such as a nickel-based hard metal alloy (NiCrBSi) containing spherical tungsten carbide particles.

[0027] The larger the total surface area of ​​the wear protection layers of the layer system on the base body surface, the more pronounced the wear protection can be, but also the more costly the production of the layer system. The total surface area of ​​the wear protection layers is therefore only as large as necessary to achieve the required wear protection. The wear-reducing effect of the stepped system contributes to the fact that the required total surface area with wear protection material can be smaller than would be the case without the stepped system.

[0028] In this regard, it has proven useful if the base body has a base body partial surface which is composed of the surfaces of the front side, back side, front end side, rear end side and scraper edge, wherein the base layer covers an area between 60% and 100%, preferably an area between 70% and 95% of the base body partial surface.

[0029] Furthermore, it has proven advantageous if the intermediate layer covers an area between 30% and 85%, preferably an area between 40% and 70% of the base layer.

[0030] The blade tip protection layer preferably covers an area between 20% and 60% of the intermediate layer, and more preferably an area between 30% and 50%.

[0031] In a further preferred embodiment of the mixer blade, the outer protective layer step has a longitudinal section running from the rear end face and / or from the scraper edge to a rear edge and / or to the front end face.

[0032] This length section of the outer protective layer step forms, for example, an angled, curved and, in particular, more or less straight line on the front side of the mixer blade, which extends, for example, diagonally from a lower corner to an upper corner; but which can also begin or end at the front end, at the rear end, at the scraper edge and / or at the trailing edge.

[0033] The inner protective layer step runs at a distance from the outer protective layer step and preferably has a length section that runs from the scraper edge to the front end face.

[0034] The wear-reducing effect of the stepped system depends on its design on the front side of the mixer blade and / or on the scraper edge. Therefore, a preferred embodiment is one in which the inner and outer protective layer steps on the front side and / or on the scraper edge have a minimum height of 1 mm or more, preferably in the range of 1.5 to 8 mm, particularly preferably in the range of 3 to 6 mm.

[0035] In a further preferred embodiment of the mixer blade, the base body has a plurality of elongated recesses which extend parallel to one another in the region of the scraper edge from the rear side to the front side and into which hard metal inserts are inserted.

[0036] The recesses are, for example, grooves cut into the scraper edge and preferably run perpendicular to the front and back. They are filled with hard metal in the form of strip-shaped inserts, which can optionally be covered with a layer of welding material. The groove filling is flush with the scraper edge. The inserts preferably have a width in the range of 12 to 15 mm and are preferably spaced apart from each other in the range of 2 to 4 cm.

[0037] Because these inserts are arranged transversely, particularly perpendicularly, to the longitudinal direction of the scraper edge, they counteract the aforementioned scouring of the scraper edge volume in the longitudinal direction. To protect the hard metal inserts, they are advantageously covered at least by the base layer, and in the area of ​​the blade tip, additionally by the intermediate layer and the blade tip protection layer.

[0038] With regard to the mixing device, the above-mentioned technical problem is solved according to the invention starting from a mixing device of the type mentioned at the outset in that at least some of the mixer blades are designed as mixer blades according to the invention.

[0039] This mixer blade features wear protection comprising at least a triple layer structure combined with at least a double protective layer step system. The blade tip is covered by at least three wear protection layers, comprising a base layer, an intermediate layer, and a blade tip protection layer, forming a step system with at least one outer protective layer step and one inner protective layer step at least on the front side of the mixer blade.

[0040] The mixer blade according to the invention is characterized by a long service life, which is increased by at least a factor of 3 compared to a mixer blade with a simple wear protection layer (base layer). This reduces downtime of the mixing device due to repair and replacement of mixer blades and thus lowers operating costs.

[0041] The advantages and properties of the mixer blade according to the invention explained above also apply to its use in the mixing device according to the invention and are hereby incorporated. Example

[0042] The invention is explained in more detail below using exemplary embodiments and a patent drawing. In detail, Fig. 1 different phases of the production of a wear protection layer on a base body of a first embodiment of the mixer blade according to the invention in a three-dimensional view, Fig. 2 shows a part of a mixing device according to the invention with mixer blades in different positions in a longitudinal section of the mixing drum, schematic representation, Fig. 3 a mixing device according to the invention with mixer blades in different positions in a cross section of the mixing drum in a schematic representation, Fig. 4 section “A” of Fig. 3 in an enlargement, Fig. 5 a photograph of a mixer blade according to the invention in a view of the front Fig. 6 the mixer blade of Fig. 4 in a section along the line L1-L2, Fig. 7 another embodiment of the mixer blade in one of the Fig. 4 corresponding view, Fig. 8 shows an embodiment of the mixer blade according to the invention equipped with reinforcing ribs in a three-dimensional schematic representation without the wear protection layers, and in a view of the rear side of the base body, Fig. 9 the mixer blade of Fig. 8 in a three-dimensional, schematic representation in a view of the front end with indicated wear protection layers, and Fig. 10 shows a further embodiment of a mixer blade in a three-dimensional, schematic representation.

[0043] The Fig. The mixer blade shown schematically in Figure 1 is assigned the reference number 10. Fig. 1(a) to (d) show process steps in their manufacture.

[0044] Fig. 1(a) shows a base body 2 made of a ductile, weldable steel, which is essentially cuboid-shaped with the approximate dimensions 36×11×3.5 cm 3and whose side surfaces are designated as follows: 2a Front 2b Back (not visible, opposite the front) 2c Scraper edge (front edge; scraper side facing the drum wall) 2d trailing edge (opposite the leading edge) 2e Front end 2f Rear end face (opposite the front end face)

[0045] The scraper edge 2c is bevelled (from the Fig. 4 and Fig. 6), also tapers slightly towards the front end face 2e and forms a blade tip 3 with it. This is the inflow area of ​​the mixer blade 1, which is immersed in the mixture flow and is particularly subject to wear.

[0046] A wear-resistant layer consisting of three protective layers 4, 5, and 6 is applied to the base body 2. The protective layers 4, 5, and 6, produced by autogenous deposition, consist of a nickel-based hard metal alloy (NiCrBSi) containing spherical tungsten carbide particles with a high hardness of approximately 3000-3500 HV. The protective layers 4, 5, and 6 have approximately the same and uniform thickness of around 5 mm.

[0047] In a first coating step, a base layer 4 is welded onto the base body 2 on all sides - with the exception of the rear edge 2d. Fig. Figure 1(b) shows the state after this coating step.

[0048] A further protective layer in the form of an intermediate layer 5 is applied to the base layer 4. The state after this coating step is shown in Fig. 1(c). The intermediate layer 5 covers part of the surface of the base layer 4 (more precisely: approximately 30%), namely completely in the area of ​​the scraper edge 2c and the front end face 2e, and approximately 45% in the area of ​​the front face 2a. This forms an outer protective layer step 5a, which extends across the front face 2a as a line with a slightly progressive gradient, approximately diagonally from the lower corner 5b to the upper corner 5c. A further protective layer in the form of a blade tip protective layer 6 is applied to the intermediate layer 5. The state after this coating step is shown in FIG. Fig. 1(d). The blade tip protection layer 6 covers part of the surface of the intermediate layer 5 (more precisely: approximately 44% relative to the intermediate layer 5 and approximately 13% relative to the base layer 4), namely approximately 2 / 3 in the region of the scraping edge 2c, 1 / 2 of the front end face 2e, and approximately 30% in the region of the front side 2a. This forms a further, inner protective layer step 6a, which runs transversely across the scraping edge 2c and the front end face 2e and extends across the front side 2a as a line with a slight line bend from the scraping edge 2c to the front end face 2e.

[0049] A stepped system consisting of protective layer steps 5a, 6a is thus formed on the scraper edge 2c, the front end face 2e, and on the front side 2a of the mixer blade 10. The stepped system comprises a double step on the front side 2a, which is formed from the outer protective layer step 5a and, spaced therefrom, the inner protective layer step 6a, each with a step height of approximately 5 mm. The stepped system further comprises a single step on the scraper edge 2c and on the front end face 2e, which is formed from the inner protective layer step 6a, also with a step height of approximately 5 mm.

[0050] The above-described step system (5a; 6a) transforms three of the essentially flat surfaces of the base body 2 into surfaces which have a gradient starting from the blade tip 3, and it effects a pressure relief for the mixer blade 10 during the mixing or granulation process and, together with the triple layer structure (4; 5; 6), leads to approximately 1.52 times the material used compared to a single-coated embodiment as in Fig. 1b shows an average quadrupling of the service life.

[0051] The longitudinal section through a mixer 20 in Fig. Figure 2 shows the wall of a mixing drum 21 with a drive shaft 22, to which approximately 20 to 30 mixer blades 10 are attached to mixing arms 23 via support plates 23a, approximately perpendicular to the rotation axis 22a. The mixing arms 23 are spaced approximately 50 cm apart in the axial direction. The mixer blades 10 rotate, as indicated by the directional arrow 24, at a distance of approximately 5 cm in front of the inner wall of the mixing drum 21. The mixer blades 10 are arranged such that their scraper edge 2c forms an angle of attack α of 40 degrees with a surface line of the mixing drum's inner wall.

[0052] At the middle mixer blade 10' of the Fig. The angle of attack α is shown in Figure 2. The corresponding surface line lies at the same height as the rotation axis 22a and in front of it in the viewing direction. Due to the angle of attack, the mixed material slides along the scraper edge 2c.

[0053] For the lower mixer blade 10" of the Fig. 2 also shows a tilt angle β (beta), which indicates the forward tilt of the mixer blade flat sides (front side 2a; rear side 2b) relative to the longitudinal axis 23b of the support arm 23. The tilt angle β is 40 degrees in the exemplary embodiment. The directional arrows 25 symbolize the mixing material flowing against the mixer blade 10".

[0054] From the cross-sectional view of the mixer 20 of the Fig. Figure 3 schematically shows the mixing drum 21 with the drive shaft 22, from which several holding arms 23 extend radially outward, each with a mixer blade 10 attached to its free end. In the viewing direction, the mixer blades 10 are arranged one behind the other along the drive shaft. The inner wall of the mixing drum 21 is formed by a wear-resistant lining 21a, along which the mixer blades 10 sweep, leaving a narrow gap 26. Reference numeral 21b denotes a vertical center line of the mixing drum 21.

[0055] Fig. 4 shows a section around the mixer blade 10 of Fig. 3 in an enlargement. A portion of the mixed material flow 25 flowing towards the blade tip 3 enters the gap 26 between the mixer blade 10 and the inner lining 21a of the mixing drum 21 and is pressed, crushed and / or mixed by the action of the mixer blade 10. Another portion of the mixed material flow 25 reaches the front side 2a of the mixer blade 10 and is thrown upwards due to its inclination and the centrifugal force, as indicated by the directional arrows 27. During this process, the stage system with the double stage consisting of the inner protective layer stage 5a and the outer protective layer stage 6a contributes to reducing the contact pressure on the front side 2a, which leads to reduced wear. This can be attributed to the gradient that the double stage creates starting from the blade tip 3 on the front side 2a.

[0056] The photo of Fig. 5 shows a holding arm 23 with a mixer blade 10 mounted thereon. On the front side 2a, the step system consisting of the outer protective layer step 5a and the inner protective layer step 6a can be seen.

[0057] Fig. 6 shows a section through the mixer blade 10 along the line L1-L2 of Fig. 4 in a plan view of the front end face 2e. Here, the stepped system with the double step consisting of the outer protective layer step 5a and the inner protective layer step 6a on the front face 2a and, in addition, the single step consisting of the outer protective layer step 6a on the scraper edge 2c can be seen. In this respect, the gradient created by the stepped system on the scraper edge 2c due to the protective layer step 6a acts similarly to an increase in the angle δ, but without requiring a change in the tilt angle β or the angle of attack α.

[0058] The portion 27a of the mixed material flow 25 that reaches the front side 2a of the mixer blade 10 due to the mixer blade inclination is thrown upwards. The inner protective layer 6a and the outer protective layer 5a also contribute to reduced wear.

[0059] The Fig. 7 shows the view of Fig. 6. Identical reference numerals represent identical or equivalent components or parts of the mixer. The mixer blade 70 differs only in the stepped system of wear protection layers 4, 75, 76, which is formed here not only on the front side 2a, but also on the scraper edge 2c as a double step with an outer protective layer step 75a and an inner protective layer step 76a. The additional double step (75a; 76a) on the scraper edge 2c is created by the intermediate layer 75 not covering the base layer 4 over the entire length of the scraper edge 2c, but only over a length section thereof, and by the blade tip protection layer 76 not covering the entire intermediate layer 75 in the region of the scraper edge 2c, but only a length section thereof.

[0060] The mixer blade 70 thus has a stepped system with a double step of protective layers 75, 76 on the front side 2a and on the scraper edge 2c, as well as a single step on the front face 2e. This reinforces the wear-reducing effect of the stepped system of wear protection layers 4, 75, 76 explained above.

[0061] At the Fig. In the embodiment schematically illustrated in Figure 10, the mixer blade 100 is provided with three wear-protection layers 104, 105, 106, which form a stepped system configured as a double step on the front side 2a, on the scraper edge 2c, and on the front end face 2e. The double step comprises an outer protective layer step 105a and an inner protective layer step 106a.

[0062] The mixer blade 100 thus has a step system with a total of three double steps of wear protection layers 104, 105, 106, which further enhances the wear-reducing effect of the step system explained above. Fig. In the embodiment of the mixer blade 80 schematically shown in Figure 8, a plurality of reinforcing ribs 87 made of sintered hard metal are introduced into the region of the scraper edge 2c of the base body 82.

[0063] The reinforcing ribs 87 are created by inserting strip-shaped inserts made of sintered hard metal into grooves that extend from the front to the back of the base body 82. For fixation, the inserts are covered with a layer of welding material that ends flush with the stripping edge 2c. The reinforcing ribs 87 run parallel to one another and essentially extend from the stripping edge 2c perpendicular to the longitudinal direction of the base body 82. They have a uniform width of 14 mm and a distance of 30 mm from one another. They counteract the erosion of the stripping edge 2c in the longitudinal direction of the base body 82.

[0064] Out of Fig. 9 it can be seen that the hard metal inserts 87 are covered by the base layer 84 and in the area of ​​the blade tip 83 additionally by an intermediate layer 85 and by a blade tip protective layer 86.

Claims

[1] Mixer blade (10; 70; 80; 100) for a mixing device (20), with a blade base body (2; 82) which is at least partially covered by a wear-resistant layer (4; 5; 6) and which has a front side (2a), a rear side (2b), a front end face (2e), a rear end face (2f) and a scraping edge (2c) which is designed to scrape along a drum inner wall at a distance, wherein the scraping edge (2c) and the front end face (2e) form a blade tip (3), characterized by that the wear protection layer (4; 5; 6) comprises: (a) a base layer (4) which at least partially covers the front side (2a) and the back side (2b) as well as the front end side (2e) and the scraper edge (2c) completely, (b) an intermediate layer (5) which partially covers the base layer (4) and completely covers the blade tip (3) to form an outer protective layer step (5a), and (c) a blade tip protection layer (6) which partially covers the intermediate layer (5) to form an inner protective layer step (6a) and completely covers the blade tip (3). [2] Mixer blade according to claim 1, characterized by that the base body (2; 82) has a base body partial surface which is composed of the surfaces of the front side (2a), back side (2b), front end side (2e), rear end side (2f) and scraping edge (2c), wherein the base layer (4) covers an area between 60% and 100%, preferably an area between 70% and 95% of the base body partial surface. [3] Mixer blade according to claim 1 or 2, characterized by that the intermediate layer (5) covers an area between 30% and 85%, preferably an area between 40% and 70% of the base layer (4). [4] Mixer blade according to one or more of the preceding claims, characterized bythat the blade tip protection layer (6) covers an area between 20% and 60%, preferably an area between 30% and 50% of the intermediate layer (5). [5] Mixer blade according to one or more of the preceding claims, characterized by that the outer protective layer step (5a) has a longitudinal section running from the rear end face (2f) and / or from the scraping edge (2c) to a rear edge (2d) and / or to the front end face (2e). [6] Mixer blade according to claim 5, characterized by that the inner protective layer step (6a) runs at a distance from the outer protective layer step (5a) and preferably has a longitudinal section which runs from the scraping edge (2c) to the front end face (2e). [7] Mixer blade according to one or more of the preceding claims, characterized bythat the outer protective layer step (5a) and the inner protective layer step (6a) on the front side (2a) and / or on the scraping edge (2c) have a minimum height which is 1 mm or more and which is preferably in the range from 1.5 to 8 mm, particularly preferably in the range from 3 to 6 mm. [8] Mixer blade according to one or more of the preceding claims, characterized by that the base body (82) has a plurality of elongated recesses which extend parallel to one another in the region of the scraping edge (2c) from the rear side (2b) to the front side (2a) and are inserted into the insert parts (87) made of hard metal. [9] Mixer blade according to claim 8, characterized by that the hard metal inserts (87) are covered at least by the base layer (4), and in the region of the blade tip (3) additionally by the intermediate layer (5) and by the blade tip protective layer (6). [10] Mixing device (20), comprising a mixing drum (21) with a drum inner wall (21a) and a drum longitudinal axis (22a) and a mixer shaft (22) rotatable about the latter, on which a plurality of mixer blades (10; 70; 80; 100) are mounted, each with a blade arm (23) and a blade base body (2; 82) attached thereto, and which has a front side (2a), a rear side (2b), a front end face (2e), a rear end face (2f) and a scraping edge (2c) designed to scrape along the drum inner wall (21a) at a distance, wherein the scraping edge (2c) has an angle of attack (α) with respect to a drum inner wall mantle line running parallel to the drum longitudinal axis (22a), and wherein the scraping edge (2c) and the front end face (2e) form a blade tip (3), characterized by that at least a part of the mixer blades (10; 70; 80; 100) is designed according to one of claims 1 to 9.

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