EP1474223A1

EP1474223A1 - Dynamic mixer

Info

Publication number: EP1474223A1
Application number: EP03731670A
Authority: EP
Inventors: Heinrich Schuchardt; Klemens KOHLGRÜBER
Original assignee: Bayer Technology Services GmbH
Current assignee: Bayer AG
Priority date: 2002-01-25
Filing date: 2003-01-13
Publication date: 2004-11-10
Anticipated expiration: 2023-01-13
Also published as: CA2474062C; DE50310861D1; CN1622851A; CN1309462C; ATE416026T1; JP4738737B2; EP1474223B1; CA2474062A1; WO2003061815A8; US6863432B2; US20030147304A1; WO2003061815A1; ES2316762T3; JP2005515062A; HK1078815A1; DE10248333A1

Abstract

Mixer comprising a housing having filling and emptying openings, two corotating stirrers and drivers for the stirrers, one of the stirrers being arranged centrally in the housing and having at least a drive shaft and at least one transverse beam fitted to the drive shaft and at least one stirring arm fitted at their ends to the transverse beam.

Description

Dynamic mixer

The invention relates to a mixer at least comprising a housing with a filling and emptying opening, two co-rotating stirrers and drive means for moving the stirrer, characterized in that a stirrer is arranged centrally in the housing, the stirrer being at least composed of a drive shaft attached to it a crossbar and at least one, preferably at least two, stirring arms attached to this crossbar.

To mix liquids and solids, mixers are often required to avoid deposits on walls and agitators, in which the surfaces are cleaned kinematically by the mixing elements. Examples of such devices are twin-screw extruders in the same direction.

A mixer with a large free volume is also required for processes with longer holding times. An example of an apparatus that meets this requirement is described in European patent application EP 0 917 941 AI.

Two degrees of freedom of movement are required for the most complete cleaning of surfaces. This is achieved in the apparatus according to EP 0 917 941 AI by two drive shafts.

In a mixer type known as a Buss-Ko-Kneader (cf.Mixing in the manufacture and processing of plastics, published by Verein Dt. Ingenieure, VDI-Ges. Kunststofftechnik, Düsseldorf, 1986, p. 200), a rotational movement becomes an axially oscillating movement of the Kneader shafts superimposed.

Apparatus with an eight-shaped housing (see, for example, EP 0 917 941 AI) are unsuitable for high-pressure processes. Furthermore, apparatus with good axial mixing is required for batch processes.

We are looking for a mixer with a cylindrical housing that has good, in particular axial, mixing in the product area and, in particular, is as completely self-cleaning as possible.

The invention relates to a mixer comprising at least one housing with a filling and emptying opening, two stirrers rotating in the same direction and

Drive means for moving the stirrer, characterized in that a stirrer is arranged centrally in the housing, the stirrer consisting of at least one drive shaft, attached to it at least one, preferably at least two, crossbars and at least one, preferably at least two, stirrer arm each terminally attached to this crossbar. that the other

Stirrer consists of at least one drive shaft and one or more stirring blades and is arranged eccentrically in the housing.

A mixer is preferred which is characterized in that, in the course of the rotation of the stirrers caused by the drive means, the stirring blades and the stirring arms pass over one another with the exception of their end faces, provided that they are not covered by the inner wall of the housing.

The agitator arms are extended in particular in the longitudinal direction of the agitator shaft.

A mixer is preferred in which the stirring blades and the stirring arms are of helical design. This ensures good axial mixing.

In a preferred embodiment, the stirrers are rotationally symmetrical as follows. An almost complete mutual cleaning is achieved if the symmetry of the stirrer in relation to the speed of their shafts has the following mathematical relationship (I):

ω, n_J

(I), ω, n _x ι

obey,

in the n-, the rotational symmetry of the centric stirrer, n ₂ the rotational symmetry of an engaging eccentric stirrer, ω- _. is the rotational speed of the central shaft, ω _{2 is} the rotational speed of the eccentric shaft and i, j are natural numbers.

A mixer is particularly preferred, characterized in that in formula (I) the numbers j = 1, i = 1.

For i = 1, j = 1 in formula (I) one obtains an ordinary internal toothing. Various other types of toothing are also possible, e.g. an involute toothing.

Also particularly preferred is a form of the mixer in which the number j = 1 and i> 1 in formula (I), where i is prime to n ₂ .

A variant of the mixer is very particularly preferred, characterized in that in formula (I) the number j> 1, the number i> 1, i being prime to n ₂ and j prime to n-.

For an inexpensive production, a toothing is preferred in which the stirring blades have a thickness that is constant over the radius. Then the stirring blades can be formed from sheet metal, for example. In addition, inexpensive production is facilitated if the number of stirring arms is small. This is achieved for a preferred design of the type mentioned above if i> 1 and j = 1 in formula (I).

If i is chosen to be non-prime to n ₂ , the complete cleaning of the lateral surfaces of the eccentric smaller rotor is retained.

The number of stirring blades is reduced for j> 1. With j, prime to n- _. the cleaning of the agitator arms of the centric rotor is retained. However, the agitator shaft of the smaller rotor is no longer completely cleaned.

In a further variant of the mixer, the drive means for the eccentric stirrer is arranged on the opposite face of the housing to the drive means of the central stirrer.

A mixer is particularly preferred in which the stirring blades and the stirring arms, when they are rotated by the drive means, completely sweep each other, with the exception of their end faces, provided that they are not covered by the inner wall of the housing. If it is not important for the mixer to be as completely self-cleaning as possible, but only the particularly short mixing time is to be used, the geometry of the mixer can be simplified somewhat. For example, concave or convex surfaces can be approximated by straight surfaces.

A preferred mixer also has a stable design, characterized in that additional stirring arms are arranged on the underside of the crossbars and that at least one additional eccentric stirrer is arranged in the area below the crossbars in the housing. With the same container height, the length of the mixing arms is halved. If all parts in contact with the product are to be cleaned kinematically when the mixer is partially filled, the crossbars of the central stirrer should be installed in the gas space. Accordingly, a drive of the eccentric shaft from below is preferably provided.

In initial tests with mixers of the stirrer geometry according to the invention, it was found that the mixing times of these mixers are considerably reduced compared to conventional, comparable agitators (spiral stirrers).

The mixing effect in the area of the crossbeams has to be further improved and the

Transverse bars opposite the housing wall can be kept free of any contamination if, in a preferred embodiment of the invention, the transverse bars have additional grooves or ridges on their side facing the housing wall, which have a conveying effect in the radial direction, i.e. towards or away from the stirrer shaft.

The same causes a corresponding spiral geometry of the crossbeams, which is used in a preferred embodiment of the invention.

A variant of the mixer is preferred, characterized in that the

The outer surface of the agitator arms is set at an angle α of at least 10 °, preferably at least 20 °, and less than 80 °, particularly preferably at least 30 ° and less than 60 °, relative to the radial to the central stirrer, so that it faces the inner wall of the housing.

As a result, when the stirrer is driven, an outward conveying direction, i.e. reached towards the housing wall.

In a further preferred variant of the mixer, heating or cooling elements can be attached to the inner wall of the housing. Otherwise, the housing can also be provided with the known conventional cooling or heating devices per se, for example with a double jacket through which heat carriers can flow, electrical heating coils etc.

The mixer according to the invention is suitable for any mixing tasks in chemical process technology, optionally also as a reactor for stirred reactions.

The housing does not have to be completely provided with the internals according to the invention. For example, for certain processes (degassing) a gas space over the

Be sure to keep the stirrer internals free.

A mixer is particularly preferred in which the stirrer arms of the central stirrer are connected at one end to the drive shaft via crossbars, while the other ends are connected to one another via a reinforcing ring.

This connection with a ring creates a rigid frame structure so that higher-viscosity products can be processed (than without a reinforcement ring).

The invention is explained in more detail below with reference to the figures.

Show it

Figure la shows the front view of a mixer according to the invention; the housing 1 is shown in section FIG. 1b shows the side view of the mixer from FIG. 1 a, the housing is again shown in section FIG. 1 c shows a top view of the mixer from FIG. 1 a, the housing is again shown in section

Figure 2 shows the isometric view of the stirrer of the mixer from Figure la 3 shows sectional views of the mixer from FIG. 1 a along the line AA in FIG. 1 a at different times during half a revolution of the larger rotor

4 shows the isometric representation of the rotors of a mixer variant, similar to that shown in FIG. 1a, but in the case of the smaller eccentric one

Rotor only two blades are present.

5 shows the section along line A-A in FIG. 1 a through a mixer according to FIG. 4. The relative position of the smaller rotor in relation to the central rotor was drawn in at various points in time in the course of several revolutions (representation of the relative movements)

Figure 6 shows the isometric view of the rotors of a mixer with drive of the eccentric stirrer from below

7 shows an embodiment of the mixer with an additional stiffening ring. FIG. 8 shows an embodiment variant of the mixer according to FIG

Stirring arm and a stirring blade

Figure 9 shows another embodiment of the mixer with centrally arranged crossbeams and stirrer arms arranged above and below

FIG. 10 shows a mixer variant with two eccentric stirrers. FIG. 11 shows a radial section through a mixer similar to FIG. 4 but with leaf-shaped stirring arms which have a rectangular cross section.

Examples

example 1

Figures la, b, c show a mixer according to the invention in front, side and top views, each with the housing 1 shown in section.

The cylindrical housing 1 is shown, the central stirrer 2 with a shaft 6 on which two crossbars 7 are attached, which support the helical stirring arms 8, 9, and the eccentric stirrer 3 with a shaft 11 on the six helical stirring blades 12 are arranged. An inlet 4 and an outlet 5 are attached to the top and bottom of the housing 1, respectively. The drive units for the stirrers 2, 3 are not shown.

The stirring blades 12 have an approximately constant over the radius

Thickness. (In the radial section, the thickness is constant, so it increases perpendicular to the plate towards the center of the rotor.)

With n-, the number of stirring arms 8, 9, n _2, the number of stirring blades 12, ω- _. the rotational speed of the central shaft, ω ₂ the rotational speed of the eccentric shaft and i and j natural numbers apply according to formula (I):

ω 1 _ ⁿ ιJ

(I) - ω n

In the present case, a stirrer geometry is chosen in which the numbers

nι = 2, n ₂ = 6, i = 7, j = 1 mean. The number i is prime to n ₂ .

Figure 2 shows the stirrers 2 and 3 in an isometric projection.

Figure 3 shows a radial section through the mixer according to line A-A in Figure 1 in 15 different snapshots of the rotation of the two shafts. The respective rotation angle of the central stirrer 2 is indicated.

Example 2

FIG. 4 shows a variant of the mixer according to FIGS. 1 and 2, but four of the stirring blades 12 have been removed on the eccentric stirrer 3 '. Again:

! =. ₍ i ₎ . ω ₂ n

Here is

n ₂ = 2, i = 7, j = 3.

The number i is prime to n ₂ ; j is prime to n- _. ,

FIG. 5 shows a radial section through a mixer according to FIG. 4 in snapshots drawn one above the other. The larger stirrer 2 was held. The relative position of the smaller stirrer 3 'was drawn in at different times in the course of several revolutions. FIG. 10 shows a modification of the mixer shape according to FIG. 4, in which two eccentric stirrers 3 "and 3 '" are combined with a central stirrer 2 in cross section.

Example 3

Figure 6 shows an embodiment of the mixer with three crossbars 7 and three stirring arms 8, 9, 9 '.

The following relationship applies to the rotors in FIG. 6:

ω n _x ι

It is

n ₂ = 2, i = = 5, j = ^■ 4.

The number i is prime to n ₂ ; j is prime to n- _. ,

The eccentric rotor is driven from below.

Example 4

FIG. 7 shows the stirrer of a mixer according to the invention, in which the stirrer arms of the central stirrer are connected at one end to the drive shaft 6 via crossbars 7, while the other ends are connected to one another via a reinforcing ring 13. This connection with a ring 13 creates a rigid frame structure, so that products with a higher viscosity can be processed with the mixer than without a reinforcement ring.

The speed ratio here is 2: 5. The central stirrer carries 3 stirring arms, the eccentric stirrer 3 'has three stirring blades.

The relationship also applies to the rotors in FIG. 7:

ω, n ₂ J ω n ι

It is

^ = 3, n ₂ = 3, i = 5, j = 2.

The number i is prime to n ₂ ; j is prime to n * _. ,

Example 5

Figure 8 shows the stirrer combination of a mixer with only one stirrer arm 8 'and a stirrer blade 12' on the eccentric stirrer 3.

^• In Figure 9, a variation is shown to the mixer according to Figure 6, in which the transverse beam 7 further additionally on its underside stirring arms 18, 19, carry 20th In the lower part of the arrangement a further eccentric stirrer 3 "is attached, which engages in the stirrer arms 18, 19, 20 and is driven from below. Example 6

FIG. 11 shows a radial line through the stirrers 2, 3 of a variant of the mixer according to the invention. The construction of this mixer basically corresponds to the embodiment shown in FIG. 4, but the stirring arms 28, 29 are designed in the form of a sheet and have a rectangular cross section. The speed ratio of shafts 6 and 11 is 1: 2. The central stirrer 2 carries two stirring arms 28, 29, which are designed in sheet form, the eccentric stirrer 3 carries two stirring blades 22. The outer surface of the stirring arms 28, 29 is in each case set at an angle α = 45 ° with respect to the radial.

This form of stirrer 2, 3 is particularly suitable for arrangement within a container which has heating or cooling coils 23 on the inner wall. If the direction of rotation is set in such a way that the central stirrer 2 conveys to the outside, an intensive flow against the heating / cooling coils 23 is achieved. This improves the heat transfer to the mix.

Claims

Patent claim

1. Mixer at least comprising housing (1) with a filling (4) and emptying opening (5), two co-rotating stirrers (2) and (3) and drive means for moving the stirrers (2) and (3), characterized in that that a stirrer (2) is arranged centrally in the housing (1), the stirrer (2) comprising at least one drive shaft (6), attached to it at least one, preferably at least two crossbars (7) and at least one each, on this crossbar (7 ) stirring arm attached at each end

(8, 9) the other stirrer (3) consists of at least one drive shaft (11) and one or more stirring blades (12) and is arranged eccentrically in the housing (1),

2. Mixer according to claim 1, characterized in that in the course of the rotation of the stirrers (2) and (3) brought about by the drive means, the stirring blades (12) and the stirring arms (8, 9) brush each other with the exception of their end faces, as long as they are not covered by the inside wall of the housing (1).

3. Mixer according to claim 1 or 2, characterized in that the stirring blades (12) and the stirring arms (8, 9) are helical.

4. Mixer according to one of claims 1 to 3, characterized in that the

Spiral of the stirring blades (12) and stirring arms (8, 9) is either both right-handed or both left-handed.

5. Mixer according to one of claims 1 to 4, characterized in that the symmetry of the stirrer (2) and (3) in relation to the speed of their shafts (6) and (11) of the following mathematical relationship (I): ω 1 _ n ₂ J

(I), n _x ι

obey in the n- _. the rotational symmetry of the centric stirrer (2), n ₂ the rotary

, tion symmetry of an engaging eccentric stirrer (3), ω _{1 is} the speed of the central shaft (8), ω _{2 is} the speed of the eccentric shaft (9) and i, j are natural numbers.

6. Mixer according to claim 5, characterized gekennzeiclmet that the numbers j = 1, i =

1 mean.

7. Mixer according to claim 5, characterized in that the number j = 1 and i> 1, where i is prime to n ₂ .

8. Mixer according to claim 5, characterized gekennzeiclmet that the number j> 1, the number i> 1 where i are prime to n ₂ and j prime to n _\ .

9. Mixer according to one of claims 1 to 8, characterized in that the stirring blades (12) have a constant thickness over their radius.

10. Mixer according to one of claims 1 to 9, characterized in that the drive means for the eccentric stirrer (3) on the opposite side of the housing (1) to the drive means of the central stirrer (2) is arranged.

11. Mixer according to one of claims 1 to 10, characterized in that the stirring blades (12) and the stirring arms (8, 9), with the exception of their end faces, completely sweep over one another, provided that they are not covered by the inner wall of the housing (1) ,

12. Mixer according to one of claims 1 to 11, characterized in that the stirring arms (8, 9) of the central stirrer (2) are connected to one another at their ends via a reinforcing ring (13).

13. Mixer according to one of claims 1 to 12, characterized in that additional stirring arms (8 ', 9') are arranged on the underside of the crossbars (7), and that at least one additional eccentric stirrer (3 ') in the area below the Crossbar (7) is arranged in the housing (1).

14. Mixer according to one of claims 1 to 13, characterized in that the crossbeams (7) have a spiral geometry which cause radial conveyance during the rotation of the stirrer (2, 3).

15. Mixer according to one of claims 1 to 12, characterized in that grooves or combs are provided on the side of the crossbar (7) facing the housing inner wall, which bring about radial conveyance during the rotation of the stirrer (2, 3).

16. Mixer according to one of claims 1 to 15, characterized in that the outer surface of the stirring arms (8, 9) with respect to the radial to the central stirrer (2) at an angle α of at least 10 °, preferably at least 20 ° and less than 80 °, is particularly preferably set at least 30 ° and less than 60 °.

17. Mixer according to one of claims 1 to 16, characterized in that on the inner wall of the housing (1) heating or cooling elements (23) are attached.