EP3439774A1

EP3439774A1 - Mixing shaft

Info

Publication number: EP3439774A1
Application number: EP17715454.9A
Authority: EP
Inventors: Andreas Seiler; Matthias Bechtold; Martin Dörr; Christian LUKSCHE
Original assignee: Maschinenfabrik Gustav Eirich GmbH and Co KG
Current assignee: Maschinenfabrik Gustav Eirich GmbH and Co KG
Priority date: 2016-04-08
Filing date: 2017-04-03
Publication date: 2019-02-13
Anticipated expiration: 2037-04-03
Also published as: US10456758B2; CN109070027B; PL3439774T3; WO2017174521A1; US20190076802A1; DK3439774T3; JP2019513544A; CA3018023C; RU2683090C1; DE102016106536A1; DE202016106597U1; BR112018070393A2; AR108187A1; EP3439774B1; CN206897205U; ZA201806331B; PT3439774T; CN109070027A; KR102023350B1; TWI735554B

Abstract

The present invention relates to a mixing shaft (1) having a tool holder (2) and having a mixing vane (3), wherein the tool holder (2) has a recess in which a section of the mixing vane (3) is fastened. In order to provide a corresponding simple mixing shaft (1) with tool holders (2) which reliably permits individual exchange of individual mixing vanes in a simple manner, it is proposed according to the invention that a clamping part (11) inserted into the recess is provided for fixing the mixing vane section in the recess, wherein clamping part (11), recess and mixing vane section are designed such that a non-positively locking connection of the mixing vane in the recess is realized by means of the clamping part (11).

Description

mixing shaft

The present invention relates to a mixing shaft with a tool holder and a mixing blade, wherein a portion of the mixing blade is mounted in a recess of the tool holder.

There are known mixers with one or more mixing shafts arranged perpendicular to the mixing vessel bottom. The mixing shafts frequently have a plurality of mixing vanes which are arranged in several planes and extend radially outward from the longitudinal axis of the mixing shaft.

The mixing blades used as working tools are subject to wear and must therefore be renewed at certain intervals. It has been shown that the wear on the various mixing blades does not proceed at the same speed. Blades that are covered by a higher layer height of the mix, wear much faster than mixing blades, which are installed close to the Mischgutoberfläche.

It is known to screw the mixing blades directly to the mixing shaft. Although this has the advantage that each mixing blade can be mounted separately, it is disadvantageous that the fastening screws are exposed to wear and contamination by the mix, so that the mixing blades are often no longer easily removed from the tool holder after a long period of operation. There are therefore already advanced systems for mounting mixing blades on a tool holder, in which the clamping of the mixing blades is done centrally with mechanical or even hydraulic clamping devices. A disadvantage of these devices, however, is that due to the mechanical or hydraulic tensioning device an increased construction costs arises. Moreover, in these systems, only all mixing blades can be solved simultaneously, i. even those mixing blades, which should not be exchanged at all, must be solved.

The present invention is therefore based on the object to provide a simple mixing shaft with tool holder, which reliably allows the individual exchange of individual mixing blades in a simple manner. This object is achieved in that a clamping part inserted into the recess in the tool holder is used for fixing the mixing blade section in the recess, clamping part, recess and mixing blade section being designed such that a non-positive connection of the mixing blade in the recess is realized with the aid of the clamping part ,

In other words, each mixing blade is assigned its own clamping part which, in the event that the mixing blade is to be exchanged, is released in order to detach the mixing blade section from the tool holder. Thus, for example, it is possible that the recess has a first and a second recess section, wherein the mixing blade section is arranged in the first recess section and the clamping section is arranged at least partially in the second recess section.

For example, the clamping part can be completely accommodated in the second recess section, so that the first recess section is provided for receiving the mixing-blade section and the second recess section is for receiving the clamping section. However, it is also possible that the mixing blade section again has a mixing blade section recess into which a part of the clamping part is inserted, so that the clamping part can also be arranged partially in the first recess section.

Clamping part and mixing blade portion are thus introduced side by side in the recess to realize a jamming of the mixing blade section in the recess.

In a preferred embodiment, the clamping part is supported both on the mixing blade section and on a wall of the second recess section, wherein both clamping part and either the mixing blade section or the wall of the second recess section have mutually corresponding wedge surfaces.

As a result of the mutually corresponding wedge surfaces, which act like a ramp, this is pressed against the mixing blade section by inserting the clamping part. For example, the clamping part by means of one, two or more screws are attached to the tool holder. By tightening the screws then the clamping member is pulled along the corresponding wedge surfaces in the recess, whereby the mixing blade section is clamped within the recess.

In a particularly preferred embodiment, the clamping part has a Abdrückgewinde over which by means of a jacking screw, the clamping part can be pushed out of the recess again. For example, the Abdrückgewinde be arranged such that a Screw can be screwed into the Abdrückgewinde that the screw head facing away from the end of the screw on a surface of the mixing shaft, for example, on a surface of the tool holder, supported, so that by pressing the screw, the clamping member is pushed out of the recess.

The wedge angle, i. the angle which the wedge surfaces enclose to a plane perpendicular to the longitudinal axis of the mixing shaft can in principle be chosen freely. In practice, a value greater than 7 ° has proven itself. At this angle, a slight self-locking is to be expected. If this is not desired, the wedge angle must be greater, e.g. to about 15 °, to be selected.

In a further preferred embodiment, the second recess section is arranged in the axial direction next to the first recess section. This has the advantage that no additional force is exerted by the mixing blade on the clamping part by the expected rotational forces during use of the mixing shaft. In principle, the second recess section can be arranged in the axial direction both above and below the first recess section. In practice, it has proven useful if the second recess section is arranged in the axial direction above the first recess section, since then the assembly of the mixing blade section in the tool holder is easier to accomplish. The terms "above" and "below" refer to the intended working position of the mixing shaft. The end of the mixing shaft, which is located higher than the other end, is understood as the upper end. Therefore, when the second recessed portion is located above the first recessed portion, it means that the second recessed portion is located closer to the upper end of the mixing shaft than the first recessed portion. In a preferred embodiment, means for fixing the mixing shaft to a motor shaft or a drive shaft are provided at the upper end of the mixing shaft.

In a further preferred embodiment, the tool holder consists of a plurality of tool holder discs, which are connected to the tool shaft, and a clamping device for clamping the tool holder discs in the axial direction. The mixing shaft thus consists of the tool shaft, the tool holder discs, the clamping device for the tool holder discs, the clamping device for the mixing blades and the mixing blades.

The recess is then arranged in at least one tool holder disc. Such an embodiment has the advantage that the mixing shaft is modular and depending on the desired length of the mixing shaft simply more tool holder discs can be mounted on the shaft. For example, the shaft may have a hexagonal cross-section, while the tool holder discs have a hexagonal passage opening with which these over the shaft can be pushed. Such a configuration has the advantage that the tool holder discs are positively connected to the shaft, so that by rotating the shaft, the tool holder discs are rotated about its axis. It is possible that the recess, ie, the first recess portion and the second recess portion are arranged in the same tool holder disc.

In a preferred embodiment, a first part of the recess in a first tool holder disc and a second part of the recess in a second tool holder disc is arranged, in which case the tool holder discs are positioned side by side so that the first and the second part of the recess form the recess. It is particularly preferred if each tool holder disc has both a first and a second recess part which are each provided to form a recess together with a second recess part or a first recess part of a neighboring positioned further tool holder disc.

Thus, although in this embodiment each toolholder disc has at least a first and a second recess portion, they do not together form a recess in the same toolholder disc. Instead, the recess is first formed together with a corresponding recess part of an adjacent tool holder disc.

Also, the recess may be composed of more than two recess parts in different tool holder discs, so that the geometry of the recess can also be formed from more than two tool holder discs.

It is possible to form the parts of the recess such that the first part of the recess forms the first recess section and the second part of the recess forms the second recess section. However, this does not have to be the case. In a further preferred embodiment, the clamping part is screwed to the tool shaft or preferably to the tool holder. If the clamping part is designed in several parts, according to this embodiment, at least a part of the clamping part should be screwed to the tool shaft or preferably to the tool holder. In a further preferred embodiment, a protective element is provided, which is arranged in the second recess section and covers the clamping part. The protective element closes the second recess portion best completely and gap-free, and preferably also with respect to the mixing blade. The protective element can, for example, a protective cap may be, for example, made of a plastic or other easily removable material. The recess should be as flush as possible with the outer contour of the tool holder, so that prevents the cap inadvertently dissolves in operation from the recess portion.

Alternatively, the recess may also be filled with a hardening spray or casting compound, such as e.g. Silicone, to be closed.

In a further particularly preferred embodiment, the mixing blade section and the tool holder are connected to one another via a pin connection or another form-fitting connection. For example, the mixing blade section may have a passage opening, preferably of circular cross-section, and a pin may be arranged in the first recess section, which pin is connected to the tool holder. Then it can be pushed with its passage opening over the pin for attaching the mixing blade section.

The positive connection prevents at high peripheral speeds of the mixing shaft that the mixing blades emerge from the recess with reduced adhesion at the clamping connection by the centrifugal forces occurring. In a further preferred embodiment it is provided that the tool holder disc in a cross-section perpendicular to the axis of rotation is substantially annular, wherein the positive connection, for. B. the pin of a pin connection, closer to the inner radius of the circular ring shape than the outer radius is arranged. In a further preferred embodiment, in the event that the mixing blade section has an opening as part of the positive connection, it is provided that the clamping part at least partially covers this opening, wherein preferably the clamping part completely covers the opening. As a result, on the one hand the opening is additionally protected against dust and on the other hand reduces the static friction between the clamping part and mixing blade section, whereby the assembly and disassembly of the mixing shaft is easier.

In addition, a better clamping effect is achieved by this arrangement. Therefore, the clamping part is preferably arranged in the inserted state such that it partially or best completely overlaps in a projection on a plane perpendicular to the axis of rotation with the positive connection. In other words, the clamping part is arranged in the axial direction above or below the positive connection. In a further preferred embodiment it is provided that the clamping part has a maximum extent in the circumferential direction, which is greater than the maximum extent of the mixing blade section. Particularly in applications requiring a plurality of mixing blades which are only slightly spaced apart in the axial direction, the smallest distance between mixing blade section and tool holder in the axial direction is smaller than the necessary displacement path of the mixing blade section in the axial direction, in order to release the mixing blade from the positive connection , For insertion or removal of the mixing blade from the tool holders, the mixing blade can then be tilted relative to a plane perpendicular to the axis of rotation. This tilting is possible due to the corresponding wedge surfaces. The mixing blades can not be solved without tilting, ie only by axial relative movement relative to the tool holder. Further advantages, features and possible applications will become apparent from the following description of a preferred embodiment and the accompanying figures. Show it

FIG. 1 shows a perspective view of a mixing shaft according to the invention,

FIG. 1 a shows a perspective partial view of the embodiment of FIG. 1,

FIG. 2 shows a longitudinal section through an embodiment according to the invention of a mixing shaft,

FIG. 3 shows a plan view of a toolholder disk of the embodiment of FIG. 1,

FIG. 4 shows an isometric detailed view of a mixing shaft according to the invention,

5 shows a further isometric detailed view of a mixing shaft according to the invention, FIG. 6 shows a partial cross-sectional view of the embodiment of FIG. 1,

FIG. 7 shows a perspective front view of a clamping part,

FIG. 8 shows a perspective rear view of the clamping part of FIG. 7,

9 shows a longitudinal section through the shaft when using semi-circular cams,

10 is a perspective view of a mixing blade of the embodiment of FIG. 9; FIG. 11 is a partial sectional view of a second embodiment;

FIG. 12 shows a perspective view of a closure cap,

Figure 13 is an exploded view of a third embodiment and

Figure 14 is a perspective sectional view of the third embodiment.

FIG. 1 shows a perspective view of a mixing shaft 1. The mixing shaft 1 has a tool holder, which in this embodiment consists of a multiplicity of tool holder disks 2. The tool holder disks 2 together form a cylindrical body which is rotated about its cylinder axis during operation. Over the outer surface of this cylinder stand a Plurality of mixing blades 3 ago. These mixing blades 3 may have chamfered edges 4, but need not. Therefore, in the figure, some mixing blades 3 are shown with corresponding bevelled edges, while other mixing blades do not have these edges. The mixing shaft 1 has at its upper end to a mounting flange 5, with which it can be attached to a corresponding drive shaft.

Immediately above or below the mixing blades 3 are protective caps 6 can be seen. The protective caps 6 are inserted into corresponding recess portions of the tool holder discs 2 and close with these flush. The protective caps 6 may, for example, be made of plastic.

In Figure 1 a is a partial perspective view of the embodiment of Figure 1 is shown. Both in Figure 1 and in Figure 1 a different mixing blade geometries are shown. In general, however, only a single geometry is used in a mixing shaft. However, the figures are intended to make it clear that basically different geometries can be used.

In addition, the protective caps 6 are partially shown above and partially below the mixing blades 3. As a rule, embodiments are preferred in which the protective caps are arranged either all above the mixing vanes or all below the mixing vanes.

The individual tool holder disks 2 are arranged on a tool shaft 10 (not shown in FIGS. 1 and 1a). In order to press the individual tool holder disks 2 toward one another, an upper annular end disk 7, a clamping ring 8 and a plurality of clamping screws 9 are provided. Under the cover plate 7 and the upper edge of the uppermost tool holder disc 2 an annular disc spring is installed (not shown). The clamping screws 9 can be secured in corresponding threaded holes of the clamping ring 8 so that it presses the lens 7 on the package of the tool holder writing 2 and this tensioned. In the clamped state, the plate spring generates a counterforce on the end plate in order to reliably prevent loosening of the clamping screws during operation. The tool holder discs are supported at the lower end of the tool shaft on a screwed with the shaft circular or annular end plate 7 ^' from.

Figure 2 shows a longitudinal section through the shaft 10 with a section through the clamping part 1 1. It can be seen here, the tool holder disc 2, which has a threaded bore 13. A clamping part 1 1 is screwed by means of the fastening screw 12 in the threaded bore 13 of the threaded holder plate 2. With the help of the clamping part 1 1, the mixing blade 3 is clamped within the tool holder. To a contamination of the fastening screw 12, in particular their Screw head, to avoid during operation, the recess in the tool holder disc is designed such that the protective cap 6 can be introduced into the recess so that it is substantially flush, to prevent dirt from entering the recess.

FIG. 3 shows a plan view of a tool holder disk 2. The hexagonal recess 14, which serves to receive a correspondingly shaped tool shaft 10, can be clearly seen. The tool holder disc 2, in the illustrated embodiment, has two recesses, in each of which a portion of a mixing blade 3 is inserted. In the illustrated embodiment, a mixing blade 3 has a circular opening through which a pin 15, which is connected to the tool holder disc 2, is guided. The portion of the other mixing blade 3, however, has two lobes on the left and right edges, in the two pins 16, which are both mounted on the tool holder disc, engage. The figure in the figure two different fastening systems, i. Attachment with a pin 15 or attachment with two pins 16, shown is only illustrative that different fastening systems can be used to make a positive connection. In general, an embodiment in which only one of the two fastening systems is used is preferable in order to reduce the storage of the corresponding mixing vanes. Only in the case that mixing blades of different geometries are used within the mixing shaft, different fastening systems can be used to identify the mixing blade geometry to ensure that the correct mixing blade geometry is always positioned in the correct recess. The pins, protrusions or recesses may also be formed with part-circular, e.g. be formed semicircular cross section or another cross section.

FIG. 4 shows a further isometric detailed view of a mixing shaft according to the invention.

It can be seen here that the recess in the tool holder extends over two tool holder disks 2. The part of the recess disposed in the lower tool holder disc 2 includes the first recess portion. In this recess portion, a portion of the mixing blade 3 is positioned. The second recess portion is partially disposed in the part of the recess provided by the upper tool holder disk 2. The clamping part 1 1 is thus partially in the provided by the lower tool holder disc Ausspa- and partially arranged in the provided by the upper tool holder disc 2 recess part. The protective cap 6 has in the embodiment shown a U-shape, wherein on the outer side of a U-leg, a rib is arranged, which engages in a corresponding groove 18 which is arranged in the inner wall of the second recess portion. The protective cap 6, preferably made of plastic, can then be clipped into the corresponding recess so that it engages in the groove 18. For protection, the protective cap can be pierced with a tool, for example, and levered out of the recess.

The recess is formed in stages in the axial direction, d. H. The recess has a section with a smaller width in the circumferential direction and a section with a greater width in the circumferential direction. The width of the mixing blade section corresponds approximately to the smaller width, so that the mixing blade section can be inserted into the section with the smaller width. However, the height of the mixing blade section in the axial direction is slightly larger than the height of the section with the smaller width, so that the mixing blade section protrudes slightly into the section with the greater width.

This ensures that the clamping part 1 1 is supported on the mixing blade section and not on the upper side of the lower tool holder disc, thus enabling a secure frictional connection.

FIG. 5 shows a further isometric detailed view of a mixing shaft according to the invention. In this embodiment, the mixing blade 3 has a passage opening 15, in which a pin engages. In the embodiment shown here, the pin is formed integrally with the tool holder disc 2.

Furthermore, here the section through the clamping part 1 1 is selected such that a further bore 17 with subsequent Abdrückgewinde 17 ^' can be seen. This hole 17 with Abdrückgewinde 17 ^' is only required for disassembly of the clamping part 1 1. First, the screws 12 are released. To press the clamping part 1 1 out of its position, a screw is screwed into the bore 17, the screw is then, for example. On the tool shaft 10 pushes to press the clamping part 1 1 radially outward.

This becomes even clearer by means of the cross-sectional view shown in FIG. 6 through the clamping part 11. It can be seen here that the clamping part 1 1 is held by means of the two fastening screws 12 on the tool holder disc 2. The further bore 17/17 ^' can be used to press the clamping part 1 1 of the tool holder disc 2. Figures 7 and 8 show two perspective views of the clamping part 1 1. The clamping part 1 1 has an inclined wedge surface 19. By mounting the clamping part 1 1 on a tool holder disc 2, the clamping part 1 1 can be pressed radially inward by means of the fastening screws 12 which engage in the corresponding holes 20, so that the wedge surface 19, which rests against a corresponding wedge surface of the tool holder disc 2 , clamped the section of the mixing blade in the tool holder.

FIG. 9 shows a longitudinal section through the shaft when using half-round cams for fastening the mixing blade in the tool holder. A perspective view of the mixing blade 3 of this embodiment is shown in FIG. In this embodiment, the mixing blade 3 has two semicircular cams 21, which engage in corresponding bores 16 of the toolholder disk 2. In the embodiment shown, the cams are integrally connected to the mixing blade. In principle, the cams could instead be attached to the tool holder disk 2, in which case the portion of the mixing blade 3 would have to have corresponding bores or recesses for receiving the cams.

An alternative mounting option is shown in the isometric view of Figure 11 as a second embodiment of the invention. On the one hand, the wedge-shaped clamping part 1 1 is arranged below the mixing blade 3 here. On the other hand, here a separate pin 21 is provided, which engages both in a corresponding opening 15 in the mixing blade and in a corresponding opening 22 in the tool holder disc 2. In this case, the length of the pin portion of the pin 21, which engages in the mixing blade 3 is smaller than the height of the mixing blade 3 is selected to allow for easier removal or a more compact design of the tool holder discs. The clamping part 1 1 covers in this case the passage opening 22 in the mixing blade 3 completely. In this embodiment, the smallest distance a between the mixing blade section 3 and the tool holder 2 in the axial direction is greater than the height b of the mixing blade section 3 in the axial direction. Alternatively, it can also be smaller. It may even be the smallest distance a between the mixing blade section and the tool holder in the axial direction smaller than the necessary displacement c of the mixing blade section in the axial direction, in order to release the mixing blade from the positive connection.

FIG. 12 shows a perspective view of the inside of the protective cap 6. It can be seen that the cap 6 has a rib 18 which runs around on three sides and engages in corresponding grooves 19 of the toolholder disk 2. In addition, it has on the fourth edge a recess 23, so as to allow a possible gap-free completion of the mixing blade 3.

Figure 13 is an exploded perspective view of a third embodiment of the invention. As far as possible, the same elements have been given the same reference numbers. By way of example, two tool holder disks 2 are shown here, which together have a recess for receiving a mixing blade 3 and a clamping part 25, 26. The clamping part 25, 26 consists of a first part 25 and a second part 26. The two parts 25, 26 have mutually corresponding wedge surfaces 27. The two parts 25, 26 are superimposed so that the corresponding wedge surfaces 27 lie on each other. The second part 26 of the wedge element has a bore 29, which is designed here as a stepped bore. The first part of the clamping part 25 has a threaded bore 28. With the aid of a fastening screw 30, the second part 26 can be attached to the first part 25. By tightening the screw 30, the first part 25 is pulled in the direction of the second part 26, so that it is displaced on the wedge surfaces 27 and the two-part wedge element 25, 26 expands in the axial direction, whereby the clamping effect is achieved.

As can be seen in Figure 14 in a perspective sectional view, the second part 26 of the clamping part is attached to the tool holder disc 2 by means of the fastening screw 12. In this case, the second part 26 of the clamping part is designed such that it is substantially flush with the peripheral surface of the tool holder disks 2. If now the fastening screw 30 is tightened or loosened, this leads to a relative movement of the first part of the clamping part 25 in the radial direction due to the force applied by the fastening screw 30 force and in the axial direction due to the mutually corresponding wedge surfaces 27, whereby the wedge element in the axial direction " thicker "or" thinner "is to pinch the mixing blade 3 within the recess in the tool holder disc 2 or to solve. To prevent fouling of the heads of the screws 12, 30 during operation, plugs are introduced into the stepped bores.

reference numeral

1 mixing shaft

2 tool holder discs

3 mixing blades

4 bevelled edges

5 mounting flange

6 protective caps

7 lens

7 ^' screwed lens

8 clamping ring

9 clamping screws

10 tool shaft

11 clamping part

12,30 fixing screw

13.28 threaded hole

14 hexagonal recess

15 pen

16 two pins

17,29 bore

17 ^' push off thread

18 groove / rib

19 wedge surface / groove

20 holes

21 cams / separate pin

22 corresponding opening

23 recess

24 plugs

25 first part of a clamping part

26 second part of a clamping part

27 wedge surfaces

Claims

Patent claims

1. mixing shaft with a tool holder and a mixing blade, wherein the tool holder has a recess in which a portion of the mixing blade is fixed, characterized in that an inserted into the recess clamping part for fixing the mixing blade portion is provided in the recess, wherein clamping part, recess and mixing blade portion are formed such that with the aid of the clamping part a frictional connection of the mixing blade is realized in the recess.

2. Mixing shaft according to claim 1, characterized in that the recess has a first and a second recess portion, wherein the mixing blade portion is arranged in the first recess portion and the clamping part is at least partially disposed in the second recess portion.

3. mixing shaft according to claim 2, characterized in that the clamping part is supported both on the mixing blade portion and on a wall of the second recess portion, wherein both the clamping part and either the mixing blade portion or the wall of the second recess portion have mutually corresponding wedge surfaces.

4. mixing shaft according to claim 2, characterized in that the clamping part is supported both on the mixing blade portion and on a wall of the second recess portion, wherein the clamping part is formed in two parts and the two parts of the clamping part have mutually corresponding wedge surface.

5. Mixing shaft according to claim 4, characterized in that the first part of the clamping part has a threaded bore and the second part of the clamping part has a through hole, which are arranged such that the second part of the clamping part by means of a screw passing through the through hole of the second clamping part engages in the threaded bore of the first part of the clamping part, can be attached to the first part of the clamping part, so that the corresponding wedge surfaces lie on each other, and by turning the screw, the two parts of the clamping member can be moved relative to each other.

6. mixing shaft according to one of claims 1 to 5, characterized in that the tool holder has an axis of rotation and the mixing shaft is provided to be rotated about the axis of rotation.

Mixing shaft according to claim 6, characterized in that the second recess portion is arranged in the axial direction adjacent to the first recess portion.

Mixing shaft according to claim 6 or 7, characterized in that the tool holder consists of a tool shaft and a plurality of tool holder discs which are connected to the tool shaft, wherein the recess is arranged in at least one tool holder disc.

Mixing shaft according to claim 8, characterized in that the recess consists of two recess parts, wherein the first recess part in a first tool holder disc and the second recess part are arranged in a second tool holder disc, wherein the tool holder discs are positioned side by side such that the first and the second recess part form the recess.

Mixing shaft according to claim 9, characterized in that each tool holder disc both a first and a second recess part, which are each provided to form a recess together with a second recess part or a first recess part of a neighboring positioned another tool holder disc.

Mixing shaft according to one of claims 1 to 10, characterized in that the clamping part is screwed to the tool shaft or preferably with the tool holder.

Mixing shaft according to claim 1 1, characterized in that a protective element is provided, which is arranged in the second recess portion and covering the clamping part, wherein the protective element completely closes the second recess portion, wherein preferably the protective element is a protective cap.

Mixing shaft according to one of claims 1 to 12, characterized in that the mixing blade section and the tool holder are connected to one another via a positive connection, preferably via a pin connection.

Mixing shaft according to claim 13, characterized in that the mixing blade portion a passage opening, preferably of circular cross-section, and in the first recess portion a pin is arranged, which is connected to the tool holder, wherein pushed for attaching the mixing blade portion of this with its passage opening over the pin can be.

15. Mixing shaft according to claim 13 or 14, characterized in that the tool holder disc in a cross section perpendicular to the axis of rotation is substantially annular, wherein the positive connection is arranged closer to the inner radius of the circular ring shape than at the outer radius.

16. Mixing shaft according to claim 14 or 15, characterized in that the mixing blade section has an opening as part of the positive connection and the clamping part at least partially covers the opening, wherein preferably the clamping part completely covers the opening.

17. Mixing shaft according to one of claims 1 to 16, characterized in that the clamping part in the circumferential direction has a maximum extent which is greater than the maximum extent of the mixing blade section.

18. Mixing shaft according to one of claims 13 to 16, characterized in that the smallest distance (a) between the mixing blade section and tool holder in the axial direction is smaller than the necessary displacement path (c) of the mixing blade section in the axial direction to the mixing blade of the positive connection to solve.