HK1078815B - Dynamic mixer - Google Patents

Description

Power mixer

Technical Field

The invention relates to a mixing machine comprising at least one housing with a filling opening and a discharge opening, two co-rotating mixing elements and a drive device for driving the mixing elements, wherein a mixing element is arranged centrally in the housing, the mixing element comprising at least one drive shaft, at least one transverse beam mounted on the drive shaft and at least one, preferably at least two mixing arms mounted on the ends of the transverse beam.

Background

In order to mix liquids and solids, mixers in which the surface is cleaned by means of a mixing element in a moving manner are generally used to avoid deposits on the walls and on the mixing machine. An example of such an apparatus is a twin screw synchronous extruder.

In addition, for long residence time operations, a blender with a large free volume is required. An example of a device which meets this requirement is described in EP 0917941a 1.

Two degrees of freedom of movement are required in order to clean the surface as completely as possible. In the case of the device according to EP 0917941a1, this is achieved by two drive shafts.

In a mixer known as a Buss-Ko mixer (see Mischen Beimi Herstellen und Verarbeiten von Kunststoffen, published on page 200 by VDI-Ges. Kunststofftechnik, Dusseldoff in 1986), the axial vibration movement of the mixer shaft is superimposed on the rotational movement.

For high pressure operation, devices with an octagonal envelope (see e.g. EP 0917941a1) are not suitable.

Furthermore, for batch processing, good axial mixing is required.

Disclosure of Invention

In other words, a mixer is sought with a cylindrical housing which has a particularly good axial mixing effect in the production zone and which is especially as completely self-cleaning as possible.

The invention relates to a mixing machine comprising at least a housing with a filling opening and a discharge opening, two co-rotating mixing elements and a drive device for driving the mixing elements, characterized in that a mixing element is arranged centrally in the housing, the mixing element comprises at least one drive shaft, at least one cross member mounted on the drive shaft and at least one mixing arm each mounted on the end of the cross member, the further mixing element comprises at least one drive shaft and one or more mixing blades and the further mixing element is arranged eccentrically in the housing, the mixing blades and the mixing arms, except for their end faces, are wiped against one another during the rotation of the mixing element caused by the drive device, as long as they are not wiped by the inner wall surface of the housing.

These stirring arms extend in particular in the longitudinal direction of the stirrer shaft.

Preferably, the stirring blade and the stirring arm are helical. In this way, good axial mixing is obtained. Here, the helical shapes of the stirring blades and the stirring arms are either both right-handed or both left-handed.

In a preferred embodiment, the stirrer is shaped rotationally symmetrically as follows.

Practically complete cleaning of one another is achieved if the symmetry of the stirrer with respect to the rotational speed of the stirrer shaft complies with the following mathematical relationship (I):

ω₁/ω₂＝n₂j/n₁i (I)

wherein n is₁Number of arms, n, of the center agitator₂Denotes the number of blades, omega, of the centrifugal stirrer engaged₁Representing the speed of rotation of the central shaft, ω₂The rotation speed of the centrifugal shaft is shown, and i and j are natural numbers.

Particularly preferred is a mixer characterized in that in formula (I), j is 1 and I is 1.

For formula (I), I is 1 and j is 1, a common inner mesh is obtained. Other different forms of engagement, such as involute engagement, are also possible.

Likewise particularly preferred are those in which j is 1 and I is n in formula (I)₂And i > 1.

Particular preference is given to variants of such mixers in which I in formula (I) is n₂And j is n₁And j > 1, i > 1.

For inexpensive production, an engagement in which the thickness of the stirring blade is constant over a radius is preferable. The stirring blade may then be formed from a metal plate.

Further, if the number of the agitating arms is small, inexpensive production becomes easy. When I > 1 and j ═ 1 in formula (I), inexpensive production is achieved because of the preferred design of the type described above.

If i is selected to be n₂The prime number of (a), then maintains complete cleaning of the sides of the miniature centrifugal rotor.

If j > 1, the number of stirring blades is reduced. Since j is n₁So that the stirring arms of the central rotor are kept clean. However, the stirring shaft of the small rotor is no longer completely cleaned.

In a further variant of the mixer, the drive for the centrifugal mixer is arranged on the end side of the housing opposite the drive of the central mixer. The blender shape can be somewhat simplified if the best possible automatic cleaning of the blender is not important, but rather is to take advantage of the particularly short mixing time. For example, the concave or convex surface may be accessed by a straight surface.

A preferred mixer is characterized in that the additional mixing arm is arranged on the underside of the cross member and that at least one additional centrifugal mixer is arranged in the housing in the region below the cross member, whereby a stable construction is also obtained. At the same height of the vessel, the length of the stirring arm is halved.

If all product-contacting parts are to be cleaned by movement when the agitator is partly full, the cross-member of the central agitator should be arranged in the gas space. Subsequently, the driving of the centrifugal shaft preferably takes place correspondingly from below.

In a first experiment using the stirrer configuration of the present invention, it was found that the mixing time of the stirrer was much shorter than that of a conventional similar stirring machine (helical stirrer).

Furthermore, in a preferred embodiment of the invention, the cross-beam has a helical shape and causes a radial transport when the stirrer rotates. In a preferred embodiment of the invention, the mixing action in the region of the cross beam can be further increased and the housing wall opposite the cross beam can be kept free from contamination if the cross beam has additional grooves or ridges on the side facing the housing, which grooves or ridges have a conveying action in the radial direction, i.e. in the direction towards and away from the stirrer shaft.

Preference is given to a variant of the stirrer in which the outer surface of the stirring arm is 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 °, with respect to the radial direction of the central stirrer, so that it points towards the inner wall surface of the housing. In this way, when the stirrer is driven, an outward transport, i.e. towards the housing wall, is achieved.

In a further preferred variant of the stirring machine, the heating or cooling element can be mounted on the inner wall surface of the housing.

In addition, the housing can in fact also be equipped with known, conventional cooling or heating elements, such as double shells, electric coils, etc., through which a heat transfer medium can flow.

The stirrer of the invention is suitable for any mixing task in a chemical processing plant and can also be used as a reactor for stirring reactions, if necessary.

The outer shell need not be equipped at all with the inner member according to the invention. For example, for certain operations (degassing), a gas space can be left above the stirrer internals.

Particularly preferred are mixers in which the mixing arms of the central mixer are connected at one end to the drive shaft via a cross-member and at the other end to one another via a reinforcing ring.

The connection to such a ring forms a rigid frame structure, so that a more viscous (than without the reinforcement ring) product can be processed.

Drawings

The invention is described in detail below, by way of example, with reference to the accompanying drawings, in which:

FIG. 1a shows a mixer according to the invention in a front view, with a housing 1 shown in section;

FIG. 1b shows the mixer of FIG. 1a in a side view, again with the housing 1 sectioned;

FIG. 1c shows the mixer of FIG. 1a in a plan view, again with the housing 1 sectioned;

FIG. 2 shows a schematic perspective view of the stirrer of FIG. 1 a;

FIG. 3 shows the blender of FIG. 1a at various times during one half rotation of the large rotor in a cross-sectional view taken along line A-A of FIG. 1 a;

FIG. 4 shows a perspective view of a rotor of a variant of the agitator, which is similar to the rotor shown in FIG. 1a, but has only two agitator blades in the case of a smaller centrifugal rotor;

FIG. 5 is a cross-sectional view of the blender shown in FIG. 4 taken along line A-A of FIG. 1a, showing the relative positions of the mini-rotor and the central rotor (indicating relative movement) at various times during multiple turns;

FIG. 6 shows a schematic perspective view of a mixer rotor driving a centrifugal mixer from below;

FIG. 7 shows an embodiment of the blender having an additional stiffening ring;

FIG. 8 shows a variant embodiment of the mixer according to FIG. 1a, but with a mixing arm and a mixing blade;

FIG. 9 shows another embodiment of a blender having a centrally disposed cross beam and blending arms disposed above or below the cross beam;

FIG. 10 shows a variant of the mixer with two centrifugal mixers;

FIG. 11 shows a stirrer similar to that of FIG. 4 in a radial cross-sectional view, but with a paddle-like stirring arm having a rectangular cross-section.

Detailed Description

Example 1

Fig. 1a, 1b, 1c show a blender according to the invention in a front view, in a side view and in a plan view, where the housing 1 is shown in a sectional view.

A cylindrical housing 1 is shown, with an axis 6 of a central stirrer 2 mounted on two cross beams 7 supporting helical stirring arms 8, 9, and six helical stirring blades 12 arranged on an axis 11 of the centrifugal stirrer 3. There is an inlet 4 and an outlet 5 on 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 a substantially constant thickness over the radius (constant thickness in radial section, which increases in response perpendicular to the metal sheet towards the center of the rotor).

n₁The number of the stirring arms 8, 9, n₂Number of stirring blades 12, omega₁As the central axis rotation speed, omega₂Is the centrifugal shaft rotation speed, I and j are natural numbers, and applies to the following formula (I):

ω₁/ω₂＝n₂j/n₁i (I)

in this example, the stirrer shape is now chosen with the following numbers: n is₁＝2，n₂6, 7, and 1. i is n₂The prime number of (c).

Fig. 2 shows the stirrers 2, 3 in isometric projection.

FIG. 3 is a radial cross-sectional view of the blender along line A-A of FIG. 1 in 15 different snapshots of two shaft rotation. The respective rotation angles of the central stirrer 2 are shown.

Example 2

Fig. 4 shows a variant of the mixing machine according to fig. 1 and 2, but with four of the mixing blades 12 on the centrifugal shaft 3' removed. Again, this applies to:

ω₁/ω₂＝n₂j/n₁i (I)

wherein n is₁＝2，n₂2, 7 and 3. i is n₂The prime number of (c); j is n₁The prime number of (c).

FIG. 5 illustrates radial cross-sections of the blender shown in FIG. 4 in overlapping snapshots.

Fig. 10 shows a variant of the mixing machine according to fig. 4, in which two centrifugal mixers 3 ″ and 3 * are combined in cross section with a central mixer 2.

Example 3

Fig. 6 shows an embodiment of the mixer with three cross beams 7 and three mixing arms 8, 9'.

With respect to the rotor in fig. 6, the following relationship applies:

ω₁/ω₂＝n₂j/n₁i (I)

wherein n is₁＝3，n₂2, 5 and 4. i is n₂J is n₁The prime number of (c).

The centrifugal rotor is driven from below.

Example 4

Fig. 7 shows a stirrer of a stirrer according to the invention, in which the stirring arms of the central stirrer are connected to the drive shaft 6 on one end by a cross beam 7 and on the other end by a reinforcing ring 13.

By the connection with a ring 13, a rigid frame structure is formed, so that a product with a higher viscosity than without the reinforcement ring can be processed with the mixer.

Here, the rotational speed ratio is 2: 5. The central stirrer supports three stirring arms and the centrifugal stirrer 3' supports three stirring blades.

With respect to the rotor in fig. 7, the following relationship applies as well:

ω₁/ω₂＝n₂j/n₁i (I)

wherein n is₁＝3，n₂3, 5, and 2. i is n₂J is n₁The prime number of (c).

Example 5

Fig. 8 shows a stirrer combination of a stirrer, which has only one stirring arm 8 'and one stirring blade 12' on the centrifugal stirrer 3.

Fig. 9 shows a variant of the mixer according to fig. 6, in which the cross member 7 also supports further mixing arms 18, 19, 20 on its underside. On the lower part of the device, another centrifugal stirrer 3 "is mounted, which is engaged with the stirring arms 18, 19, 20 and driven from below.

Example 6

Fig. 11 shows a radial section through a stirrer 2, 3 according to a variant of the stirrer according to the invention. The construction of the stirrer corresponds in principle to that shown in fig. 1, but the stirring arms 28, 29 are designed in the shape of paddles and have a rectangular cross section. The speed ratio of the shafts 6, 11 is 1: 2. The central stirrer 2 has two stirring arms 28, 29 in the form of paddles, and the centrifugal stirrer 3 supports the two stirring paddles 2. The outer surfaces of the stirring arms 28, 29 each make an angle α of 45 ° with the radial direction.

This shape of the stirrers 2, 3 is particularly suitable for being placed in a vessel having heating or cooling coils 23 on the inner wall. If the direction of rotation is adjusted such that the central stirrer 2 is conveyed outwards, a strong incident flow of the heating/cooling coil 23 is achieved. As a result, the heat transfer to the hybrid material is improved.

Claims (18)

1. A mixer comprising at least a housing (1) with a filling opening (4) and a discharge opening (5), two co-rotating mixers (2, 3) and drive means for driving the mixers (2, 3), characterized in that one mixer (2) is arranged centrally in the housing (1), that the mixer (2) comprises at least one drive shaft (6), at least one cross-member (7) mounted on the drive shaft and at least one respective mixing arm (8, 9) mounted on the end of the cross-member, that the other mixer (3) comprises at least one drive shaft (11) and one or more mixing blades (12) and that the other mixer is arranged eccentrically in the housing (1), that during the rotation of the mixers (2, 3) caused by the drive means, the mixing blades (12) and the mixing arms (8, 9) other than the end faces thereof, as long as they are not wiped by the inner wall surface of the housing (1).

2. A mixer according to claim 1, wherein two of said cross-members are mounted on said drive shaft.

3. A mixer according to claim 1, wherein said mixing blade (12) and said mixing arms (8, 9) are helical.

4. A mixer according to claim 2, wherein the spirals of the mixing blade (12) and the mixing arm (8, 9) are either both right-handed or both left-handed.

5. A mixer according to any one of claims 1 to 4, wherein the symmetry of the mixer (2, 3) with respect to the rotational speed of its shaft (6, 11) complies with the following mathematical relationship (I):

ω₁/ω₂＝n₂j/n₁i (I)

wherein n is₁Denotes the number of mixing arms of the central mixer (2), n₂Indicates the number of the stirring blades of the engaged centrifugal stirrer (3) (. omega.)₁Representing the rotational speed, omega, of the central shaft (8)₂The rotating speed of the centrifugal shaft (9) is shown, and i and j are natural numbers.

6. A mixer according to claim 5, wherein j is 1 and i is 1.

7. A mixer according to claim 5, wherein j is 1, i > 1, i is n₂The prime number of (c).

8. A mixer according to claim 5, wherein j > 1, i > 1 and i is n₂J is n₁The prime number of (c).

9. A mixer according to any of claims 1 to 4, wherein the mixing blades (12) have a constant thickness over their radius.

10. A mixer according to any of claims 1 to 4, wherein the drive means for the centrifugal mixer (3) is arranged on the opposite side of the housing (1) to the drive means of the central mixer (2).

11. A mixer according to any of claims 1-4, wherein the mixing arms (8, 9) of the central mixer (2) are connected to each other at their ends by means of a reinforcement ring (12).

12. A mixer according to any of claims 1-4, wherein additional mixer arms (8 ', 9 ') are arranged on the bottom side of the cross-member (7) and at least one additional centrifugal mixer (3 ') is arranged in the housing (1) in the area below the cross-member (7).

13. A mixer according to any of claims 1-4, wherein the cross-member (7) has a spiral shape and causes radial transport when the mixers (2, 3) are rotated.

14. A mixer according to any of claims 1-4, wherein grooves or ridges which cause radial transport when the mixers (2, 3) are rotated are provided on the side of the cross member (7) facing the inner wall of the housing.

15. A mixer according to any of claims 1-4, wherein the outer surfaces of the arms (8, 9) are at an angle α of at least 10 ° and less than 80 ° with respect to the radial direction of the central mixer (2).

16. A mixer according to claim 15, wherein said angle α is at least 20 ° and less than 80 °.

17. A mixer according to claim 16, wherein said angle α is at least 30 ° and less than 60 °.

18. A mixer according to any of claims 1-4, wherein a heating or cooling element (23) is provided on an inner wall surface of the housing (1).