EP3495036A1 - Mixer insert for static mixer, static mixer and method of manufacturing - Google Patents

Abstract

One-piece mixer insert (1) for a static mixer, comprising a first mixing element (2) with a plurality of intersecting first webs (6) and at least one along a longitudinal axis (L) to the first mixing element (2) adjacent and by a twist angle, in particular of 90 °, relative to the first mixing element (2) about the longitudinal axis (L) twisted, second mixing element (3) with a plurality of intersecting second webs (12), wherein the first webs (6) facing the second mixing element (3) first web ends (9) and the second webs (12) to the first mixing element (2) facing first web ends (9) and wherein a portion of the first and second web ends (10, 17) are arranged distributed over the outer periphery of the mixer insert (1) , wherein each of the over the outer circumference of the mixer insert (1) arranged distributed first web ends (9) material fit via a connecting portion (4), in particular a connecting web, with one of the outside the periphery of the mixer insert (1) arranged distributed second web ends (16) is connected.

Description

The invention relates to a one-piece (static) mixer insert according to the preamble of claim 1 for a static mixer, comprising a first mixing element with a plurality of intersecting (extending along the longitudinal central axis and angularly arranged to this) first webs and at least one along a longitudinal axis adjacent to the first mixing element and by a twist angle, in particular of 90 °, relative to the first mixing element about the longitudinal axis twisted, in particular identical, second mixing element with a plurality of intersecting (along the longitudinal central axis extending and angled to this arranged) second webs, wherein the first webs have first web ends facing the second mixing element and the second webs have first web ends facing the first mixing element, and wherein a part of the first and second web ends are distributed over the outer circumference of the mixer insert. The feature of the distributed arrangement of the first and second web ends over the outer circumference of the mixer insert means that these first and second webs or their web ends would end without the later to be explained, inventively provided connecting portions on the outer circumference, ie not inside the mixer insert. The first web ends facing the second mixing element are arranged between a first intersection plane, in which the first webs intersect and the second mixing element. Analogously, the second web ends are arranged between a second crossing plane, in which the second webs intersect and the first mixing element. Preferably, the webs are rectilinear, at an angle to and extending along the longitudinal central axis supporting portions of the mixing elements. Each mixing element has two groups of, preferably parallel, webs, where the two groups or the webs of the two groups intersect. Preferably, the two web groups are arranged so that perpendicular to the longitudinal axis between two webs of a group a web of the other group is added. At least one of the two groups has at least two webs, which are spaced perpendicular to the longitudinal axis, wherein a web of the other group is arranged between the webs. Preferably, each mixing element comprises between three and twenty, preferably between four and twelve distributed on the two groups arranged, perpendicular to the longitudinal axis juxtaposed webs. More preferably, the first and at least the second mixing element on the same number of webs and / or arrangement.

Furthermore, the invention relates to a static mixer according to claim 10, comprising at least one, preferably exclusively, a mixer insert according to the invention. The mixer insert is arranged in a preferably tubular or line-shaped surrounding housing, which is preferably formed by the inner circumference of a fluid line of a device, in particular an industrial manufacturing device, very particularly preferably a spray device.

Furthermore, the invention relates to a method for producing such a mixer insert according to the preamble of claim 11.

In the CH 642564 A1 is a basic technology for static mixer with a so-called. X-Grid structure described. The known mixer insert is arranged within a tubular container and comprises a plurality of individual mixing elements arranged one behind the other along a longitudinal axis of the mixer element and each comprising a plurality of intersecting webs. In the known mixer insert, the mixing elements are alternately relative to 90 ° about the longitudinal axis arranged twisted to each other. The known mixer insert or its individual mixing elements are expensive to produce in the metal casting process to destroy the mold. In addition, the filling of the tubular housing with individual mixing elements to form the mixer insert is time consuming. It has also become known, the individual mixing elements selectively welded together to form a one-piece mixer insert.

Various methods have become known to produce the aforementioned X-grid geometry more cost-effectively from plastic. Only exemplary is on the EP 2 001 580 B1 directed.

The applicant himself has described a production-optimized mixer insert, which consists of two plastic injection molded parts, which are perpendicular to one another for the formation of the mixer insert pushed. Such a mixer insert is in the WO 2017/097860 A1 disclosed. However, the known mixer insert is only conditionally or not at all suitable for high pressures, such as those which are suitable for example in feed lines for molten thermoplastic material in plastic injection molding devices, and also not for high temperatures which likewise occur in the aforementioned application.

Based on the aforementioned prior art, the present invention seeks to provide a one-piece and inexpensive mixer insert for static mixer, which can be easily and inexpensively manufactured from pressure and temperature stable materials, especially metal or ceramic. Furthermore, the object is to provide a static mixer with such a mixer insert and an optimized manufacturing method for producing such a mixer insert.

This object is achieved with respect to the one-piece mixer insert with the features of claim 1, ie in a generic mixer insert characterized in that each of the distributed over the outer circumference of the mixer insert first web ends of the first mixing element material fit via a connecting portion with a, in particular spatially closest, over the outer periphery of the mixer insert distributed second web ends of the axially adjacent second mixing element is connected. In other words, each of the second mixer insert facing and arranged on the outer circumference of the mixer insert first web ends in one piece or monolithically via a respective, formed in particular as a connecting web, connecting portion via in one of the first mixing element facing, arranged on the outer circumference second web ends of the second mixing element. As a result, the first web ends of the first mixing element, which are distributed over the outer circumference, support an associated second web end over the respective monolithically formed connecting section with a respective first web end, thus producing a layered, monolithic production of the mixer insert, in particular in a 3D printing process or in a generative process , most preferably in a powder bed process, even more preferably in a laser sintering process is possible. On a complex, previously used casting technique and the destruction of the mold for Entformungszwecken is therefore no longer necessary. At the same time, the mixing element according to the invention of pressure and temperature stable materials, in particular metal or ceramic manufacture, which is preferred, so that a pressure and temperature stable, monolithic mixer insert with at least two, preferably only two or three axially adjacent, each intersecting webs having Mixing elements results. Prefers it is, when the respective distributed over the outer circumference arranged first and second web ends interconnecting connecting portions, in particular in the form of connecting webs, extend both at an angle to the longitudinal extension of the respectively associated first web and at an angle to the longitudinal extent of the respectively associated second web. In other words, it is preferred if the connecting sections each span an angle (not equal to 180 °) with both webs connected via the respective connecting section.

With regard to the static mixer, the object is achieved with the features of claim 10, i. in a generic static mixer by the use of at least one, preferably exclusively designed according to the concept of the invention mixer insert, which is included to complete its mixer functionality in a tubular, formed for example by a fluid conduit surrounding housing with an inlet and an axially spaced outlet, wherein the inner diameter of the outer housing corresponds to the outer circumference of the mixer insert, possibly plus one (in particular low) clearance.

With regard to the method, the object is achieved with the features of claim 11, ie in a generic method, characterized in that the mixer insert monolithic, layer by layer along the longitudinal axis adjacent and perpendicular to the longitudinal axis extending layers constructed in a generative process or in a 3D printing process is first layered the first mixing element is constructed with its distributed over the outer circumference of the mixer insert first web ends and then to the distributed over the outer circumference arranged first web ends of the first mixing element in each case a preferred as Connecting web trained connecting portion is visibly connected (ie layered) and that each connecting portion in layers a second web or its second web end of the second mixing element is connected, wherein the second mixing element is also constructed in layers following the first mixing element, so that a one-piece , Monolithic mixer insert with at least two mixing elements twisted about the longitudinal axis results and the mixing elements are monolithically formed or connected to each other at their distributed over the outer circumference, mutually facing web ends via a connecting web.

Advantageous developments of the invention are specified in the subclaims.

All combinations of at least two of the features disclosed in the description, the claims and / or the figures fall within the scope of the invention.

In order to avoid repetition, features disclosed according to the device should also be regarded as being in accordance with the method and be able to be claimed. Likewise, according to the method disclosed features should also be considered as disclosed device and claimable.

The invention is based on the idea to design the mixer insert such that it can be manufactured by means of a 3D printing method or alternatively a generative method, such as a powder bed method, very particularly preferably a laser sintering method of metal or ceramic, preferably without the need to remove the support material or again to be removed support structures use or to build up. According to the invention this is achieved in that arranged over the outer periphery of the mixer insert and the second mixing element facing first web ends of the first intersecting ridges of the first mixing element and distributed over the outer circumference, the first mixing element facing second web ends of the second intersecting ridges of monolithically formed or connected to the second mixing element or are each connected via a connecting portion of the mixer insert material, in particular metal or ceramic. The connecting sections, in particular the connecting webs, preferably extend at an angle both to the longitudinal extent of the respective first and of the respective second web connected or formed monolithically via the respective connecting section. Very particular preference is given to an embodiment in which no free web ends exist in the transition region between the first mixing element and the second mixing element, but instead pass over corresponding connecting sections into the respectively adjacent mixing element. By monolithically connecting the distributed over the outer circumference, and the other mixing element facing web ends of the first and second mixing element is not only a revolutionary manufacturing of the mixer insert made of metal or ceramic in a 3D printing process or in a generative process allows, but the pressure stability the resulting mixer insert is significantly increased in comparison to known mixer inserts with the respective adjacent mixing element facing free web ends, as axial forces can be supported or accommodated via the intermediate elements.

Very particularly preferred is an embodiment of the static mixer insert, wherein the distributed not over the outer circumference arranged, first and second web ends, ie those web ends in the interior of the mixer insert are also not formed as free ends, but monolithically or materially formed with the respective axially adjacent mixing element or are connected. This is achieved in a further development of the invention preferably in that the first and second web ends, which are not distributed over the outer circumference, meet one another along a transverse axis extending perpendicular to the longitudinal axis and are connected to one another in a material-locking manner, in particular perpendicular to the longitudinal axis. Possibly. and preferably this transverse axis is completed or terminated at both ends by first and / or second webs arranged from the outer circumference and / or connecting sections connecting them (in particular connecting webs).

In classical X-Grid geometry, each mixing element has two intersection planes spaced along the longitudinal axis, in which webs of the mixing element intersect.

In a further development of the invention, this is not the case in a mixer insert according to the invention, but the mixing elements of the mixer insert according to the invention are suitably designed so that they each have only a single crossing plane extending perpendicularly to the longitudinal center axis in which webs of the respective mixing element intersect. The feature 'to intersect' means that the webs not only meet in a crossing plane, but also extend beyond the crossing plane. In this way, an embodiment of the mixing element can be realized, which has at the most in the area of the mixer insert ends, ie at the ends facing away from each other free web ends, which point away axially from all adjacent mixing elements. Particularly useful is an embodiment of the mixer insert, wherein the intersecting first webs and / or the intersecting second webs of an opening along the longitudinal axis angle between 89 ° and 1 °, preferably between 80 ° and 10 °, even more preferably between 70 ° and 20 °, very particularly preferably between 60 ° and 30 °, even more preferably between 59 ° and 53 °, very particularly preferably of 56 ° span, in particular, which is preferred if the ratio between height and longitudinal extent of a respective the mixer elements along the longitudinal central axis and the diameter of the respective mixer element should be one to one. The webs preferably clamp with the longitudinal central axis at an angle which corresponds to half the above-mentioned angle between each two intersecting webs.

In classical X-Grid geometry, each mixer element has intersecting lands extending from an outer peripheral side of the associated mixing element to a diametrically opposite outer peripheral side of the mixing element. In a further development of the invention, this is not the case here - this means that according to a preferred embodiment, none of the first and second webs extends from an outer peripheral side of the associated mixing element to a diametrically opposite outer peripheral side of the mixing element.

Particularly useful is an embodiment of the mixer insert, wherein the longitudinal extent of the mixer insert is an even multiple of the outer envelope outer diameter, ie the outer diameter of the mixer insert. In this case, it is preferable if the ratio of the length of each mixer insert to its diameter measured perpendicular to the longitudinal extent is one to one. As already mentioned, an embodiment of the Mixer insert particularly preferred in which all the second mixing element facing the first web ends of the first webs of the first mixing element materially connected to the second mixing element, in particular with the first mixing element facing the second web ends of the second webs of the second mixing element. In principle, it is particularly preferred if the (outer) envelope contour of the mixer insert is circular cylindrical.

According to a preferred embodiment, it is provided that at least on a part of the webs, in particular on or in the region of the first and / or second web ends and / or of the first mixing element wegweisenden web ends of the second mixing element monolithically formed with the respective webs fluid conductor elevations are provided which taper, in particular like an arrow, along the longitudinal axis (perpendicular to this) in the opposite direction to the direction of flow of fluid passing through a finished mixer insert so as to deflect the fluid laterally so as to prevent the fluid from directly against a surrounding the mixer insert in a finished static mixer surrounding wall is pressed. As a result, dead zones and thus deposition effects in the region of the boundary of the web ends are reduced to the peripheral wall, as well as pressure losses.

According to the invention, the static mixer insert according to the invention can be produced monolithically, preferably from metal or ceramic, in a 3D printing process or in a generative process, very particularly preferably in a powder bed process, even more preferably in a laser sintering process or alternative generative process. It is essential that the mixer insert is built up in layers in the axial direction, ie in the direction of its longitudinal extension, wherein the layers are perpendicular to the longitudinal axis build up or extend. In this case, first the first mixing element is built up in layers and indeed with its first, later a second mixing element facing web ends, which then pass in layers or connected to respective connecting portions, in particular connecting webs, then connect directly to the second web ends of the second mixing element to be built up, which face the first mixing element. The connecting sections remain in the mixer insert, so no longer have to be removed, resulting in not only a surprisingly simple manufacturable mixer insert, but also a particularly pressure-stable and due to the choice of materials and temperature stable mixer insert.

Further advantageous embodiments of the mixer insert which can be produced by means of a method according to the invention are disclosed in connection with the explanation of the device-specific features.

With at least one, preferably exclusively a mixer insert according to the invention, which comprises several, in particular exclusively two or exclusively three mixing elements, of which adjacent mixing elements are arranged rotated by an angle of rotation, for example of 90 ° or less, about the longitudinal central axis to each other, can be easily Form a static mixer in which the mixer insert is received in a surrounding housing. The static mixer is characterized in that the mixer insert is accommodated in a, in particular tubular housing, which is preferably formed of metal or ceramic, and most preferably by an industrial device, such as an injection molding device, or a fluid line or a fluid conduit provided therein Fluid line section is formed.

The static mixer according to the invention and / or the one-piece mixer insert according to the invention is particularly, but not limited to, for use in plastic injection molding machines for mixing of thermoplastic, molten plastic to be sprayed for homogenizing the temperature profile.

Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawings.

Fig. 1, 4

 

sowie

Fig. 6 bis Fig. 9

unterschiedliche, teilweise perspektivische Ansichten eines nach dem Konzept der Erfindung ausgebildeten Mischereinsatzes, umfassend ausschließlich zwei axial benachbarte Mischelemente, deren Stege monolithisch über Verbindungsabschnitte miteinander verbunden sind,

Fig. 3

eine perspektivische Darstellung der die Mischelemente bzw. deren Stegenden monolithisch miteinander ausbildenden bzw. verbindenden Verbindungsabschnitte bzw. eine entsprechende Verbindungsabschnittsgeometrie, und

Fig. 2 und Fig. 5

zur besseren Nachvollziehbarkeit eine isolierte Darstellung der eigentlich monolithisch miteinander verbundenen Mischelemente ohne Verbindungsabschnitte.

These show in:

Fig. 1, 4th

such as

FIG. 6 to FIG. 9

different, partially perspective views of a trained according to the concept of the invention mixer insert comprising only two axially adjacent mixing elements whose webs are connected monolithically via connecting portions,

Fig. 3

a perspective view of the mixing elements or their web ends monolithically with each other forming or connecting connecting portions or a corresponding connection section geometry, and

FIGS. 2 and 5

for better traceability an isolated representation of the actually monolithically interconnected mixing elements without connecting sections.

In the figures, like elements and elements having the same function are denoted by the same reference numerals.

In the figures, a one-piece, monolithic (static) mixer insert 1, in this case made of metal for forming a static mixer by arranging the mixer insert 1 in a tube, not shown, or line-shaped surrounding housing is shown. The mixer insert 1 has a circular cylindrical (outer) envelope contour. The mixer insert 1 comprises a lower in the plane of the first mixing element 2 and an axially along a longitudinal axis L adjacent second mixing element 3. The two mixing elements 2, 3 are formed monolithically avoiding free web ends or go over each other via connecting portions 4, which only for reasons the better traceability or identifiability in the figures are shown graphically or in color contrast - in reality, they see from their outer surface or nature of the actual mixing elements 2, 3, ie go into this seamlessly.

The first mixing element 2 has a plurality of first webs 6 crossing each other in a single first intersection plane 5, which extend along the longitudinal central axis L and are arranged at an angle thereto or span an angle therewith. In the exemplary embodiment shown, two intersecting first webs each span an angle α of 56 ° in the present case.

The first webs 6 are divided into two groups 7, 8 of webs, wherein the first webs 6 of the groups 7, 8 are arranged alternately perpendicular to the longitudinal center axis L. The first webs 6 have the first mixing element 3 facing the first web end 9, which are arranged axially between the second mixing element 3 and the single first crossing plane 5. The first web ends 9 are divided into a part of distributed over the outer circumference arranged first web ends 10 and a part of inner first web ends 11th

The second mixing element 3 is constructed virtually identical to the first mixing element 2 with the essential difference that the second mixing element 3 is arranged rotated relative to the first mixing element 2 by 90 ° about the longitudinal central axis L. The second mixing element 3 comprises a plurality of intersecting second webs 12, which intersect in a single second crossing plane 13. Also, the second intersecting webs 12 span an angle α oriented in the longitudinal axis L or opening along the longitudinal axis L of 56 ° in the exemplary embodiment. The second webs 12 are also divided into two groups 14, 15 of perpendicular to the longitudinal center axis L alternating second webs. The second webs 12 have the second mixing element 2 facing second web ends 16, which in turn are divided into a part of distributed over the outer circumference second web elements 17 and a part of inner second web ends 18th

Out Fig. 1 It can be seen that each of the first web ends 10 arranged distributed over the outer circumference is connected via a respective web-shaped connecting section 4 to an axially opposite (closest) second web end of second web ends 17 arranged distributed over the outer circumference. The respective first and second web ends 10, 17 which are distributed over the outer circumference and connect connecting sections 4 with one another are each web-like and extend both at an angle to the longitudinal extent of the respectively associated first web 6 and the respectively associated second web 12. Also, the respective inner first and second web ends 11, 18 are interconnected via connecting portions, wherein the connecting portions for connecting the inner web ends 11 , 18, as turned out Fig. 3 results, along a perpendicular to the longitudinal axis L extending transverse axis Q extend.

It can thus be seen in the figures that in the transition region of the first and second mixing element 2, 3 no free web ends exist, but they continue over a respective connecting portion, in each axially opposite or nearest web end of the axially adjacent mixing element.

For clarity, is only in the Fig. 8 . 9 with the arrow F shown an axial, along the longitudinal axis L extending flow direction (flow direction) of at least one, by means of a finished static mixer, comprising a mixer insert 1 according to the invention to be mixed fluid or drawn. It can be seen that the first webs in the region of their distributed over the outer circumference arranged first web ends 10 have in the radial direction raised fluid guide elevations 19 or tapering, which tap against the fluid flow direction F and thus deflecting fluid flowing laterally, creating a direct impact of at least Preventing a fluid on or a flow against a surrounding the mixer insert 1 in a finished static mixer peripheral wall.

Such fluid conductor elevations 19 can also be found again at web ends 20 of the second webs 12 facing away from the first mixing element 2 or that part of these web ends 20 which terminate at the outer circumference.

Of course, the mixer insert 1 shown can also be produced without the fluid conductor elevations 19.

The mixer insert 1 shown in the figures, designed according to the concept of the invention, is constructed in layers in the axial direction, in particular by laser sintering, starting in the drawing plane below, so that the mixer insert 1 during production in layers along the longitudinal axis L, in the drawing plane from below grows upwards. At the first web ends 9 in each case connects to a connecting portion 4, which then merges into a next, associated second web end 16. It is essential that at least all distributed over the outer circumference arranged first web ends 10 via a respective connecting portion 4 with an associated, in particular spatially next distributed over the outer circumference arranged second web end 17 are connected or formed monolithic. As explained, in the present case all the free, first and second web ends 9, 16 are connected to one another, that is to say also the inner first web ends 11 and the inner second web ends 18.

reference numeral

1

mixer insert

2

first mixing element

3

second mixing element

4

connecting portion

5

first crossing level

6

first bridges

7

first group of first bridges

8th

second group of the first bridges

9

first bridge ends

10

Part of distributed over the outer circumference of the mixer insert arranged first webs

11

Part of the first webs arranged in the interior

12

second bridges

13

second crossing level

14

first group of second bridges

15

second group of second bridges

16

second bridge ends

17

Part of distributed over the outer circumference of the mixer insert arranged second webs

18

Part of the arranged inside the second webs

19

Fluid conductor uplifts

20

web ends of the second webs facing away from the first mixing element

L

longitudinal axis

Q

transverse axis

α

Angle between intersecting webs

F

Flow direction (flow direction) of fluid

Claims (11)

One-piece mixer insert (1) for a static mixer, comprising a first mixing element (2) with a plurality of intersecting first webs (6) and at least one along a longitudinal axis (L) to the first mixing element (2) adjacent and by a twist angle, in particular of 90 °, relative to the first mixing element (2) about the longitudinal axis (L) twisted, second mixing element (3) with a plurality of intersecting second webs (12), wherein the first webs (6) facing the second mixing element (3) first web ends (9) and the second webs (12) to the first mixing element (2) facing first web ends (9) and wherein a portion of the first and second web ends (10, 17) are arranged distributed over the outer periphery of the mixer insert (1) .
characterized,
in that each of the first web ends (10) distributed over the outer circumference of the mixer insert (1) is materially connected via a connecting section (4), in particular a connecting web, to one of the second web ends (17) distributed over the outer circumference of the mixer insert (1) , Mixer insert (1) according to claim 1,
characterized,
that the mixer insert (1) as a monolithic component, in particular of metal or ceramic, is made in a 3D printing process or in a generative method, particularly in a powder bed process, preferably in a laser sintering process, or in a 3D printing process. Mixer insert according to one of claims 1 or 2,
characterized,
in that the first and second web ends (11, 18) not distributed over the outer circumference, in particular together with a part of the first and second web ends (10, 17) distributed over the outer circumference, are preferred over a perpendicular to the longitudinal axis (L) are from an outer peripheral side to a diametrically opposite outer peripheral side of the mixer insert (1) extending, connecting portion (4) are materially interconnected. Mixer insert according to one of the preceding claims,
characterized,
in that the first webs (6) extend exclusively in a first intersection plane (5) extending perpendicular to the longitudinal axis (L) and the second webs (12) extend exclusively in a direction perpendicular to the longitudinal axis (L) to the first intersection plane (5). cross parallel second crossing plane (13). Mixer insert according to one of the preceding claims,
characterized,
in that the intersecting first webs (6) and / or the intersecting second webs (12) have an angle (a) which opens along the longitudinal axis (L) between 89 ° and 1 °, preferably between 80 ° and 10 °, still further preferably between 70 ° and 20 °, very particularly preferably between 60 ° and 30 °, even more preferably between 59 ° and 53 °, more preferably span of 56 °. Mixer insert according to one of the preceding claims,
characterized,
that none of the first and second webs (6, 12) extends from an outer peripheral side of the associated mixing element (2, 3) to a diametrically opposite outer peripheral side of the mixing element (2, 3). Mixer insert according to one of the preceding claims,
Characterized,
in that the longitudinal extent of the mixer insert (1) is an even multiple of the outer envelope diameter of the mixer insert (1). Mixer insert according to one of the preceding claims,
characterized,
in that all first web ends (9) of the first webs (6) of the first mixing element (2) facing the second mixing element (3) are connected in a material-locking manner to the second mixing element (3). Mixer insert according to one of the preceding claims,
characterized,
in that at least part of the first and / or second web ends (9, 16) and / or at least part of the web ends (20) of the second webs (12) pointing away from the first mixing element extend along the longitudinal axis (L) and are formed perpendicular to this, preferably arrow-like, tapered Fluidleiterhebungen for displacing fluid. A static mixer having a housing having an inlet and an outlet axially spaced therefrom arranged mixer insert (1) according to one of the preceding claims. Method for producing a mixer insert (1) according to one of Claims 1 to 9,
characterized,
in that the mixer insert (1) is monolithic, in layers, with layers adjacent to the longitudinal axis (L) and extending perpendicular to the longitudinal axis (L), in a 3D printing process or in a generative process, in particular in a powder bed process, preferably in a laser sintering process , is first constructed in layers, the first mixing element (2) with its over the outer periphery of the mixer insert (1) distributed first web ends (10) is constructed and then distributed to the distributed over the outer circumference arranged first web ends (10) of the first mixing element ( 2) in each case one connecting section (4), in particular a connecting web, is connected in layers and that a second web (17) of the second mixing element (3) is connected to each connecting section (4) in layers.

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