Mixing device for providing foamed or expandable plastics

Abstract

Disclosed is a mixing apparatus (1) for mixing a first component (2) with a second component (3) to provide a foamed or expandable plastic (5), the mixing apparatus (1) comprising a mixing chamber (11), an agitator (30) disposed in the mixing chamber (11) and rotatable about an axis of rotation (31), a first inlet opening (13) for feeding the first component (2) into the mixing chamber (11), a second inlet opening (14) for feeding the second component (3) into the mixing chamber (11), the first inlet opening (13) being axially spaced from the second inlet opening (14), and an outlet opening (16) for feeding the plastic (5) out of the mixing chamber (11).

Description

[Technical field]

[0001] The present invention relates to a mixing device for mixing a first component with a second component to provide a foamed or foamable plastic. [Background technology]

[0002] WO2017 / 004637A1 discloses a mixing device having a mixing chamber and an agitator arranged therein for rotation around a rotation axis, the mixing chamber being provided with a first inlet opening for feeding a first liquid component and a second inlet opening for feeding a second liquid component. The first and second inlet openings are located at different axial heights in the mixing chamber and have a corresponding axial spacing. When viewed from the axial direction, the second inlet opening is located between the first inlet opening and an outlet opening through which the mixture of the first and second components can leave the mixing chamber. According to WO2017 / 004637A1, the mixing of the first and second components takes place only at the axial height of the second inlet opening, so that there is no or only minimal contamination at the axial height of the first inlet opening.

[0003] Furthermore, WO2017 / 004637A1 discloses the use of a polyol as a first component and an isocyanate and water as a second component to produce polyurethane foam. The polyol is filled with air before entering the mixing chamber. This air conditioning (introduction, dissolution, homogenization) is carried out in a pressure tank and usually requires a time consumption of several hours to several days. The air in the polyol promotes the desired foam structure of the polyurethane. However, the quality of the foam structure depends on many parameters such as pressure, temperature, etc. in the mixing chamber. If the outlet opening of the mixing chamber is used as a nozzle for feeding polyurethane foam and the outlet opening is opened at the beginning of the feeding process and closed again at the end of the feeding process, undesirable pressure fluctuations may occur in the mixing chamber, making it difficult to provide a uniform foam structure. Summary of the Invention

[0004] The invention is therefore based on the object of providing a mixing device with which a consistently good foaming quality of foamed or foamable plastics can be achieved even under changing conditions.

[0005] The object of the present invention is solved by the feature combination according to claim 1. Exemplary embodiments of the invention can be found in the claims dependent thereon.

[0006] According to the invention, a fluid brake is provided between the first and second inlet openings in the axial view, by which the mixing chamber is divided into a first and a second mixing chamber, the fluid brake serving to prevent the flow of the second component into the first mixing chamber. In a first shaft section located in the first mixing chamber, the agitator has first means for feeding a premix of gas and the first component. In a second shaft section located in the second mixing chamber, the agitator has second means for mixing the premix, which enters the second mixing chamber through the fluid brake, with the second component.

[0007] The gas inlet opening may be arranged axially adjacent to the first inlet opening for the first component, through which at least a portion of the gas may be introduced directly into the first mixing chamber. Providing a premix of gas and the first component may include breaking the gas into small microbubbles. Preferably, these microbubbles are evenly distributed in the first component so as to result in a homogeneous premix of the first component and the distributed microbubbles.

[0008] In principle, it is also conceivable that the first component is filled with air before entering the mixing chamber. However, even in this case, the first means of the agitator serve to convert the first component, for example with gas contained therein in dissolved form, into a premix. The gas present in dissolved form may fall below saturation pressure when entering the mixing chamber, causing the bubbling of gas bubbles. These gas bubbles are broken down by the first means into small microbubbles. However, it is preferred that a larger proportion of the gas is injected directly into the mixing chamber through said gas inlet opening. This directly injected portion of gas can be 80% or more. Preferably, the directly injected portion is 100%, if the portion of air in the first component that naturally or unintentionally entered the first component by the manufacturing process is ignored. The invention thus makes it possible to dispense with the usual gas or air conditioning upstream of the first component.

[0009] For example, the first component can be a mixture of polyol and water, and the second component can be an isocyanate. When the polyol, water, and isocyanate are mixed together, polyurethane is formed with the gaseous CO2 released, which expands the polyurethane to produce polyurethane foam. The small microbubbles act as nuclei for the formation of foam cells. In addition to the amount of water added, the density and foam structure of the polyurethane foam can be influenced by clearly affecting the quality of the premix consisting of the polyol and the microbubbles contained therein.

[0010] A gas valve unit may be provided upstream of the gas inlet opening, by means of which the amount of supplied gas can be precisely regulated. Preferably, the gas valve unit comprises a mass flow controller and a pressure control valve, the outlet of which is connected to the inlet of the pressure control valve. The outlet of the pressure control valve is connected to the gas inlet opening of the mixing chamber. A constant pressure of the gas (preferably air) injected into the mixing chamber can be set by the pressure control valve. This allows the injection pressure to be kept constant even if the pressure of the mixing chamber changes, simplifying the supply of a precise amount of gas by the gas valve unit.

[0011] The fluid brake can have various designs, provided that it is suitable for dividing the mixing chamber into a first and a second mixing chamber and for preventing the flow of the second component into the first mixing chamber. The fluid brake can have a restriction, which allows the high pressure in the first mixing chamber to prevail, albeit to a small extent, over the second mixing chamber. This prevents the second component, such as an isocyanate, from entering the first mixing chamber and causing undesired chemical reactions or contamination there. The premix (of the first component and the gas) then passes through the restriction into the second mixing chamber and is mixed with the second component. The mixture of the premix and the second component then leaves the mixing chamber through the outlet opening. The fluid brake can also be provided by a suitable design of the mixing chamber itself, in that, for example, the walls of the mixing chamber are designed to be adapted, at least cross-sectionally, in particular to the components to be mixed, such that the technical effect of the fluid brake described above is achieved.

[0012] The fluid brake should also fulfil its inventive task without completely precluding small amounts of the second component from entering the first mixing chamber.

[0013] The restriction may be formed by a radial gap between the mixing chamber wall and the agitator. Preferably, the agitator is configured to be substantially rotationally symmetric. The agitator may have a shaft collar, and the radial gap may extend between the shaft collar and the mixing chamber wall. In the case of a rotationally symmetric agitator, the shaft collar may have a circular cross section with an outer diameter. The mixing chamber may be substantially cylindrical and have a cylindrical side surface with a circular cross section. The inner diameter of the cylindrical side surface is slightly larger than the outer diameter of the shaft collar. In the axial direction, the shaft collar may extend a few millimeters, for example 5 to 15 mm. Preferably, the agitator and the cylindrical mixing chamber are coaxially aligned with each other such that in the presence of a smooth shaft collar, a consistently large radial gap occurs in the circumferential direction. The radial gap may be smaller than 0.5 mm, even smaller than 0.1 mm.

[0014] The dimensions of the mixing chamber and the agitator depend on the required output (weight / unit time) of the plastics being fed. Typical output values ​​range from 0.05 g / s to 120 g / s. For example, the mixing chamber may have an axial length of 12 mm to 25 cm. The value of the inner diameter of the cylindrical mixing chamber may be from 6 mm to 30 mm.

[0015] In one exemplary embodiment, the agitator may move axially within the mixing chamber. Preferably, the agitator may assume an axially closed position, whereby the outlet opening of the mixing chamber is closed. When the agitator is displaced from this closed position, the outlet opening opens, whereby plastic may be dispensed from the mixing chamber. In an alternative embodiment, it is conceivable that the mixing chamber is displaced axially relative to the agitator, which in turn preferably assumes an axially closed position, whereby the outlet opening of the mixing chamber is closed. When the mixing chamber is moved from this closed position, the outlet opening opens, whereby plastic may be dispensed from the mixing chamber.

[0016] The outlet opening may be arranged substantially coaxially with the rotation axis of the agitator, and the axial closed position may represent the axial end position of the agitator. The mixing chamber may thus have a conically tapered end region with the outlet opening arranged in its center. In the closed position, the agitator may rest on this end region, thereby closing the outlet opening. If the agitator is then moved slightly from this closed position, an outlet gap between the agitator and the conically tapered end region opens. The plastic then reaches the outlet opening through this outlet gap.

[0017] In an exemplary embodiment, the axial position of the stirrer is utilized to adjust the flow cross-section of an outlet gap of any shape upstream of the outlet opening between the axially displaceable stirrer and the mixing chamber, thereby influencing or adjusting the pressure in the mixing chamber. This exemplary embodiment can therefore also be designed without a conically tapering end region. Furthermore, it is not essential that the closed position is an axial end position.

[0018] The first agitator section and the second agitator shaft section are preferably connected to each other in a rotationally fixed manner. This results in a relatively simple construction of the agitator, which preferably consists of only two or three parts that are constructed integrally or rigidly connected to each other. The agitator shaft sections therefore rotate at the same rotational speed in the mixing chamber.

[0019] In an exemplary embodiment, the first means of the first axial section of the agitator is different from the second means of the second section of the agitator. This takes into account the fact that the requirements and objectives in the first mixing chamber are different from those in the second mixing chamber. In the first mixing chamber, the gas should be finely dispersed, stirred or finely distributed in the first component, whereas in the second mixing chamber, the first component (including the gas therein) and the second component should be mixed together. However, it is also conceivable that the first means of the first axial section of the agitator corresponds to the second means of the second section of the agitator.

[0020] The first means of the first shaft section of the agitator and / or the further means of the second section of the agitator may have a plurality of rows of radially extending projections or radial teeth, the rows may extend substantially in the axial direction. In an exemplary embodiment, the rows extend linearly and parallel to the axis of rotation of the agitator. However, the rows may also be inclined at an oblique angle with respect to the axis of rotation so that an axial flow is promoted when the agitator rotates. The inclination angle in the first shaft section may be different from the inclination angle in the second shaft section. For example, in order to prevent the second component from overflowing into the first shaft area, it is conceivable to have an inclination angle of 0° in the first shaft section and an inclination angle different from 0° (for example 5° to 15°) in the second shaft section in addition to a fluid brake.

[0021] The radial projections / teeth of one row may be axially offset from the radial projections of adjacent rows, thereby achieving good mixing and distribution of the gas.

[0022] If rows of radial projections are provided on both the first and second shaft sections of the agitator, the radial projections on the second section may be spaced further apart than the radial projections on the first section. The radial projections on the second shaft section may also be larger than the radial projections on the first shaft section. By this measure, finer mixing or dispersion in the first mixing chamber may be achieved.

[0023] Generally, the first means of the first shaft section will have a higher pitch number than the second means of the second shaft section, a higher pitch number meaning more projections or teeth provided per unit area.

[0024] The radial projections may each have a cross-sectional area that varies radially: when viewed radially, the projections may taper or widen as they extend outward.

[0025] The first means of the first axial section of the agitator and / or the second means of the second axial section of the agitator each have a number of blades, which guide the raw material, pushed outward by centrifugal force, radially inward, thereby promoting good and homogeneous mixing or dispersion of the gas.

[0026] To achieve a further mixing effect, the blades can have small openings so that as the agitator rotates, some of the ingredients caught by the blades are pushed through the small openings. [Brief description of the drawings]

[0027] The invention will now be explained in more detail with reference to the exemplary embodiments shown in the drawings.

[0028] [Figure 1] 1 shows a mixing device according to the present invention.

[0029] [Diagram 2] 2 shows an agitator of the mixing device of FIG. 1.

[0030] [Diagram 3] Another stirrer is shown.

[0031] [Figure 4] Three variations of the first shaft section of the agitator are shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Figure 1 shows a mixing device according to the invention, generally designated 1. The mixing device 1 has a housing 10 which defines a mixing chamber 11. In the mixing chamber 11, an agitator 30 is arranged which is rotatably mounted about an axis of rotation 31. The agitator 30 is substantially rotationally symmetrical with respect to the axis of rotation 31. The agitator 30 is driven by a drive shaft 12 which is only partially shown. For connection to the drive shaft 12, the agitator 30 has a pin-shaped shaft connection 32. Preferably, the connection between the drive shaft 12 and the shaft connection 32 is a force-fit connection.

[0033] The housing 10 is provided with three inlet openings, firstly a first inlet opening 13 through which the first component can be fed into the mixing chamber 11. The second inlet opening 14 is provided axially spaced apart from the first inlet opening 13. The axial distance between the first inlet opening and the second inlet opening 14 can be a few mm, for example 3-20 mm.

[0034] At the same axial height as the first inlet opening 13 in the housing 10 there is provided a gas inlet opening 15, through which gas 4 can be injected into the mixing chamber 11. The gas 4 is preferably air (it may also be nitrogen or CO2).

[0035] The mixing chamber 10 may be used to produce foamed or expandable plastics. For example, polyurethane foam may be produced by means of the mixing chamber 10. For this purpose, a liquid mixture of polyol and water as the first component 2 is introduced into the mixing chamber 11 through the first inlet opening 13. An isocyanate, which reacts with the polyol to form polyurethane, is selected as the second component 3. The polyurethane foam leaves the mixing chamber 11 through an outlet opening 16 located at the axial end 17 of the mixing chamber 11, which is arranged coaxially with the rotation axis 31. The outlet opening 16 is formed by a nozzle 18. The inner diameter of the nozzle 18 may be, for example, 1-8 mm or 2-5 mm. The length of the nozzle 18 may be 2-50 mm or 30 mm. The flow of the produced plastic, or the expanded or expandable polyurethane foam, is indicated at 5 in FIG. 1. The produced plastic leaves the mixing chamber 11 in the axial direction.

[0036] The agitator 30 has a cylindrical shaft collar 33, the outside diameter of which is slightly smaller than the inside diameter of the cylindrical mixing chamber 11. A small radial gap 34 is therefore formed between the shaft collar 33 and the mixing chamber wall 19. The radial gap 34 can be considered as part of a restriction or fluid brake that divides the mixing chamber 11 into a first mixing chamber 11a and a second mixing chamber 11b.

[0037] The agitator 30 can be moved axially (in the direction of the axis of rotation 31). Figure 1 shows the agitator 30 in an axial position in which there is an outlet gap 36 between the conical agitator tip 35 of the agitator 30 and the funnel-shaped insert 20 arranged at the axial end 17 of the mixing chamber 11. It is therefore possible for the plastic produced in the mixing chamber 11 to leave the mixing device 1 through the nozzle 18. In the closed position, the conical agitator tip 35 rests on the insert 20, thereby closing the outlet gap 36. In the closed position of the agitator 30, the outlet opening 16 is therefore closed. The axial extent of the gap between the agitator tip 35 and the insert 20 can take values ​​between 0 mm (closed position) and 2.5 mm. The axial position of the agitator 30 or the axial extent of the outlet gap 36 can be utilized to set a specific pressure in the mixing chamber 11. Means for precisely adjusting the axial position of the agitator 30 are not shown in Figure 1.

[0038] The axial stroke (difference between the closed position and the upper end position) is dimensioned such that, when viewed axially, the shaft collar 33 or fluid brake is always located between the first inlet opening 13 and the second inlet opening 14. The first inlet opening 13 and the gas inlet opening, which in this exemplary embodiment of the present specification are offset by 180°, therefore always open into the first mixing chamber 11a of the mixing chamber 11. The second inlet opening 14, however, always opens into the second mixing chamber 11b, regardless of the axial position of the agitator 30.

[0039] A gas valve unit, not shown in Fig. 1, can be connected to the gas inlet opening 4. The gas valve unit serves to inject a correct gas flow into the mixing chamber 11. It has been found that during the production of plastics, the amount of gas injected into the mixing chamber has a significant influence on the foam structure of the plastic.

[0040] For dispersing the gas 4 and / or for mixing the gas 4 with the first component 2, the agitator 30 has first means 38 in a first shaft section 37, which will be described in detail below with reference to Figs. 2-4. The first shaft section 37 of the agitator 30 is located in a first mixing chamber 11a of the mixing chamber 11. The first mixing chamber 11a is defined by a shaft collar 33 and a seal 21 inserted between the drive shaft 12 and the mixing chamber wall. A second shaft section 39, which extends from the shaft collar 33 to the agitator tip 35, is provided with second means 40 for mixing the premix comprising the first component 2 and the gas 4 with the second component 3. The second shaft section 39 is located in a second mixing chamber 11b of the mixing chamber 11.

[0041] Before describing the exemplary embodiment shown in Fig. 2-4 for the first means 38 and the second means 40 in more detail, the operation of the mixing chamber 1 is briefly described on the basis of the supply of polyurethane or polyurethane foam 5. A polyol as the first component 2 with water is supplied to the first mixing chamber 11a through the first inlet opening 13. At the same time, air is injected into the first mixing chamber 11a through the gas inlet opening 15. By rotating the agitator 30 and thus the first means 38, the injected gas 4 is dispersed in the first component 2. This generates small microbubbles of gas, which are finely distributed in the first component 2. The rotation speed of the agitator can be 1000-6000 rpm or 1500-4000 rpm.

[0042] Due to the predefined pressure in the first mixing chamber 11a, the premix from the first mixing chamber 11a enters the second mixing chamber 11b through the radial gap 34. There, the premix (polyol, water, microbubbles) is mixed with the isocyanate (second component 3) by the second means 40. During the reaction of the polyol, water and isocyanate, CO2 is produced in addition to the polyurethane. The microbubbles act as nuclei for the formation of CO2 bubbles that form the foam cells of the polyurethane. The polyurethane can be fed from the mixing chamber 11 through the outlet opening 16. Due to the restrictive effect of the fluid brake or radial gap 34, a (small) pressure gradient is created between the first mixing chamber 11a and the second mixing chamber 11b. The pressure gradient ensures that there is no substantial flow from the second mixing chamber 11b to the first mixing chamber 11a.

[0043] This prevents the isocyanate, or a mixture of isocyanate, polyol and water, from entering the first mixing chamber 11a and causing undesired contamination therein.

[0044] Once the feeding step is over, the agitator 30 moves from the position shown in FIG. 1 to the closed position in order to close the outlet opening 16. In so doing, the drive shaft 12 is braked so that the agitator 30 does not rotate any further in the mixing chamber 11. The axial lowering of the agitator tip 35 until it rests on the insert 20 and the gradual stopping of the agitator 30 can be adjusted in such a way that the agitator tip 35 sweeps and cleans the insert 20 by residual rotation. At the same time, the gas valve unit (not shown) is closed in order to prevent polyol from entering the valve unit or to prevent gas from accumulating too much in the first mixing chamber 11a. Due to the closing of the valve unit and the closing of the outlet opening 16, the mixing chamber is sealed off from the surroundings after the end of the feeding step. At the start of another feeding step, the two components 2, 3 and the gas 4 are again fed into the mixing chamber with the agitator 30 again rotating and displacing axially.

[0045] Figure 2 shows the agitator 30 of Figure 1 in isolation. Additionally, Figure 2 shows two flattened views of portions of the periphery of the agitator 30. Components or features of Figures 2-4 that are similar or identical to components and features of Figure 1 are given the same reference numerals.

[0046] The first means 38 for distributing gas and generating microbubbles comprises projections or teeth 41 which may have a rectangular cross section. The projections 41 extend radially outwards from a cylindrical core 42. The projections 41 having a rectangular cross section are arranged in axially extending rows with the longer edges of the rectangular cross section extending in the axial or circumferential direction. The course of the axial rows is highlighted by the arrows 43 in the flattened partial cross-sectional view of the periphery in FIG. 2. It can also be seen that the projections 41 of adjacent rows are arranged axially offset. When the agitator 30 rotates and thus the projections 41 move through the first component, this results in an avoiding or displacing movement of the first component together with the gas contained therein. The avoiding or displacing movement is represented diagrammatically by the arrows 44.

[0047] Like the first means 38, the second means 40 have projections or teeth 45 that are rectangular in cross section and arranged in axial rows (see arrows 43). Here too, an axial offset of the projections 45 of adjacent rows 43 is provided. From FIG. 2 it is clear that the pitch (number of projections per unit area on the circumference of the agitator 30) of the first shaft section 37 is greater than that of the second shaft section 39. The pitch of the first shaft section 37 relative to the pitch of the second shaft section can be in the range between 2 and 5, regardless of the specific arrangement and design of the projections 41, 45 in FIG. 2. A larger pitch results in a particularly fine and good distribution of the gas in the first mixing chamber. The avoidance and displacement movements 44 of the raw material in the first mixing chamber 11a are therefore more acute and delicate.

[0048] A further difference between the protrusions 41 of the first axial section 37 and the protrusions 45 of the second axial section 39 is the radial height of the individual protrusions. The taller protrusions 41 (which extend radially further) promote finer and more thorough mixing / dispersion compared to the flatter protrusions 45.

[0049] Figure 3 shows another exemplary embodiment of the agitator 30. In contrast to the shaft collar 33 of figures 1 and 2, which has a smooth cylindrical side surface, here a shaft collar 46 is provided which is interrupted by an axial groove 46a. The areas of the shaft collar 46 between two adjacent grooves 46a, which can also be called projections 46b, are circumferentially wider than the projections 41 of the first shaft section 37 and the projections 45 of the second shaft section 39, and also represent fluid brakes which, in interaction with the adjacent mixing chamber wall 19 (see figure 1), prevent the second component from entering the first mixing chamber 11a. The preventing effect of the interrupted shaft collar 46 is smaller than that of the shaft collar 33 of the exemplary embodiment of figures 1 and 2. However, this also reduces the pressure gradient between the first mixing chamber 11a and the second mixing chamber 11b.

[0050] Preferably, the first means 38 of the stirrer 30 from Figure 2 is designed as a separate ring element which can be pressed into the pin-like shaft connection 32. This simplifies the manufacture of the stirrer 30.

[0051] 3 also shows that the projection 41 of the first shaft section can be formed by a separate ring element 47 which can be pressed onto the pin-like shaft connection 32. This simplifies the manufacture of the stirrer 30.

[0052] Figure 4 shows various variants of the ring element 47. Figure 4B shows the variant used in Figure 3. The projections 41 taper radially outwards so that the end faces of the projections directly facing the mixing chamber wall 19 are relatively small. As a result, the first component 2 and the gas 4, which are respectively supplied radially inwards, can be supplied relatively easily when the agitator 30 is rotating. During the rotation of the agitator 30, the time interval during which the end faces are directly facing the respective inlet openings 13, 15 is very short.

[0053] In contrast, in the variant of FIG. 4A, the projections 41 have an increased cross section, resulting in a relatively large front or circumferential area per projection 41. The time during which the end faces of the projections 41 face the inlet opening during rotation of the agitator 30 is correspondingly longer. This tends to make it more difficult to introduce the first component 2 and the gas 4. However, this causes the projections 41 to have radial undercuts, which cause the ingredients to be mixed and pushed inwards during rotation of the agitator. This reduces the adverse effects on good mixing that may be caused by centrifugal forces acting on the ingredients to be mixed.

[0054] In the variant of Figures 4A and 4B, the rows 43 of projections 41 extend parallel to the axis of rotation 31. However, they can also extend at an angle so that the ingredients located in the first mixing chamber 11a are pushed in the direction of the seal 21 (see Figure 1, i.e. away from the shaft collar 33). This results in stronger mixing / dispersion in the first mixing chamber 11a.

[0055] FIG. 4C shows a variant of a ring element 47 with several blades 48 arranged on its circumference. The blades 48 push the ingredients in the first mixing chamber 11a towards the interior of the mixing chamber, countering the centrifugal force. For good mixing / dispersion, the blades have small openings 49. Part of the ingredients captured by the blades is pushed through these openings 49, facilitating good mixing / dispersion. The axial height of the openings is offset from the axial height of the openings of the neighboring blades. This makes it possible to avoid possible dead spaces in the first mixing chamber 11a, where ingredients that are not optimally mixed can settle. [Explanation of symbols]

[0056] 1: Mixing chamber 2: First component 3: Second component 4: Gas 5: Plastic (polyurethane foam) 10: Housing 11: Mixing chamber (11a first mixing chamber, 11b second mixing chamber) 12: Drive shaft 13: First entrance opening 14: Second entrance opening 15: Gas inlet opening 16:Exit opening 17: Shaft end 18: Nozzle 19: Mixing chamber wall 20: Insert 21: Seal 30: Mixer 31: Rotation axis 32: Pin-shaped shaft connection 33: Shaft color 34: Radial clearance 35: Mixer tip 36: Exit gap 37: First axis section 38: First means 39: Second axis section 40:Second method 41: Protrusion / Teeth 42: Core 43: Column 44: Avoidance and Displacement Movements 45: Protrusion / Teeth 46: Shaft collar (46a: groove, 46b: protrusion) 47: Ring element 48: Blade 49: Opening

Claims

1. A mixing device (1) for mixing a first component (2) with a second component (3) to provide a foamed or expandable plastic (5), said mixing device (1) comprising: a mixing chamber (11); an agitator (30) disposed in the mixing chamber (11) and rotatable about an axis of rotation (31); a first inlet opening (13) for feeding said first component (2) into said mixing chamber (11); a second inlet opening (14) for feeding the second component (3) into the mixing chamber (11), the first inlet opening (13) being axially spaced from the second inlet opening (14); an outlet opening (16) for the plastic (5) to exit the mixing chamber (11); a fluid brake is provided between the first inlet opening (13) and the second inlet opening (14) when viewed in the axial direction, dividing the mixing chamber (11) into a first mixing chamber (11a) and a second mixing chamber (11b) by the fluid brake, the fluid brake serving to prevent the flow of the second component (3) into the first mixing chamber (11a); the agitator (30) has first means (38) of a first shaft section (37) in the first mixing chamber (11a) for supplying a premix of gas and the first component (2), and second means (40) of a second shaft section (39) in the second mixing chamber (11b) for mixing the premix, which passes through the fluid brake into the second mixing chamber, with the second component (3).

2. a gas inlet opening (15) is provided axially adjacent to the first inlet opening (13), through which at least a portion of the gas (4) can be introduced directly into the first mixing chamber (11 a), A mixing device (1) according to claim 1.

3. A gas valve unit for adjusting the amount of gas supplied is provided upstream of the gas inlet opening (15). A mixing device (1) according to claim 2.

4. The fluid brake has a restriction. A mixing device (1) according to any one of claims 1 to 3.

5. the restriction is formed by a radial gap (34) between the mixing chamber wall (19) and the agitator (30), A mixing device (1) according to claim 4.

6. the agitator (30) is substantially rotationally symmetrical and has a shaft collar (33), the radial gap (34) extending between the shaft collar (33) and the mixing chamber wall (19), A mixing device (1) according to claim 5.

7. the agitator (30) is displaceable in the axial direction and, in an axially closed position, closes the outlet opening (16) of the mixing chamber (11), A mixing device (1) according to claim 1.

8. the outlet opening (16) is arranged substantially coaxially with respect to the rotation axis (31) of the agitator (30), and the axial closed position represents an axial end position of the agitator (30), A mixing device (1) according to claim 7.

9. the first shaft section (37) of the agitator (30) and the second shaft section (39) of the agitator (30) are connected to each other in a rotationally fixed manner, A mixing device (1) according to claim 1.

10. the first means (38) of the first shaft section (37) of the agitator (30) are different from the second means (40) of the second shaft section (39) of the agitator (30), A mixing device (1) according to claim 1.

11. the first means (38) of the first shaft section (37) of the agitator (30) and / or the second means (40) of the second shaft section (39) of the agitator (30) preferably have a plurality of radial projections (41, 45) arranged in a row (43) extending substantially in the axial direction, A mixing device (1) according to claim 1.

12. the radial projections (41, 45) of a row (43) are offset in the axial direction relative to the radial projections (41, 45) of adjacent rows, A mixing device (1) according to claim 11.

13. When rows (43) having radial protrusions (41, 45) are provided on both the first shaft section (37) and the second shaft section (39) of the agitator (30), the radial protrusions (45) on the second shaft section (39) are spaced apart from each other more than the radial protrusions (41) on the first shaft section (37). A mixing device (1) according to claim 11 or 12.

14. each of the radial protrusions (41, 45) having a cross-sectional area that varies in the radial direction; A mixing device (1) according to claim 1.

15. the first means (38) of the first shaft section (37) of the agitator (30) and / or the second means (40) of the second shaft section (39) of the agitator (30) each have a plurality of blades (48), and the raw material pushed outward by centrifugal force is guided radially inward by the blades (48). A mixing device (1) according to claim 1.

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