Method for metering foamed or foamable plastics, preferably in a discontinuous manner, in a direct gas injection process

Abstract

The present invention relates to a method for metering, preferably in a discontinuous manner, a foamed or foamable plastic (5). At least one first component (2) for forming the plastic (5) is introduced into a mixing chamber (11) of a mixing device (10) in which a rotatable stirring mechanism (30) is arranged around a rotation axis (31). The first component (2) is dosed with a gas (4) to affect the formation of a foam. The plastic (4) is metered out of the mixing chamber (11) through an outlet nozzle (18). According to the invention, the pressure in the mixing chamber (11) ranges from 0.2 bar to 15 bar. The gas (4) is injected into the first component (2), preferably directly into the mixing chamber (11), by means of a valve device (50). The stirring mechanism (30) distributes the gas (5) in the first component (2).

Description

[Technical field]

[0001] The present invention relates to a method for metering foamed or foamable plastics, preferably in a discontinuous manner. [Background technology]

[0002] WO 2017 / 004637 A1 discloses a method for metering foamed or foamable plastics in a discontinuous manner. A mixture of polyol and water as a first component and an isocyanate as a second component are conveyed into a mixing chamber of a mixing device. A stirring mechanism is rotatably arranged in the mixing chamber. Mixing and chemical reaction of the two components produces polyurethane, which is discontinuously metered out of the mixing chamber through an outlet nozzle. Due to the water, the chemical reaction forming the polyurethane produces carbon dioxide (CO2), which serves as a propellant gas for foaming the polyurethane.

[0003] Furthermore, WO 2017 / 004637 A1 discloses the introduction of air into the polyol before its introduction into the mixing chamber. This conditioning with air (introduction, dissolution, homogenization) is carried out in a pressure tank and usually takes from a few hours to a few days. The air forms the desired foam structure of the polyurethane. The air is usually dissolved in the polyol and becomes aerated when the pressure drop of the polyol-air mixture as it enters the mixing chamber drops below the saturation pressure of the dissolved air. Small microbubbles are generated, which become the nuclei of the foam cells formed by the propellant gas. The quality of the foam structure depends on many parameters, such as the pressure and temperature in the mixing chamber. Discontinuous metering leads to undesirable pressure fluctuations in the mixing chamber, making it difficult to provide a uniform foam structure. The setup of the entire process is very delicate and complex, since both the pressure in the mixing chamber and the amount of gas dissolved in the polyol must be precisely matched. Even a small change in pressure can lead to a large change in the foam structure of the final product produced by metering. The method known from WO 2017 / 004637 A1 therefore usually only performs stably within a narrow process window.

[0004] The present invention aims thereat to provide a method for metering foamed or foamable plastics, preferably in a discontinuous manner, which is carried out stably and which results in a consistently good foaming quality of the foamed or foamable plastics. Summary of the Invention

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

[0006] According to the invention, the pressure in the mixing chamber ranges from 0.2 bar to 15 bar, preferably from 0.5 bar to 5 bar, and the gas is injected by a valve device into the first component, preferably directly into the mixing chamber. The injection pressure of the gas must be selected to be correspondingly higher than the pressure in the mixing chamber in order to allow injection. The injection pressure is the pressure in the valve device at which the gas is released from an outlet. Preferably, the gas is injected into the first component with an injection pressure in the range from 0.5 bar to 60 bar, particularly preferably in the range from 0.5 bar to 30 bar, very particularly preferably in the range from 2 bar to 20 bar, preferably directly into the mixing chamber, and a stirring mechanism in the mixing chamber disperses the gas in the first component. Preferably, the valve device is open during a metering process and closed between two metering processes. Preferably, the gas is injected directly into the mixing chamber. However, a solution is also conceivable in which the gas is injected into the first component in the mixing chamber, preferably just before it reaches the first component, and then enters the mixing chamber together with the first component.

[0007] In the method according to the invention, the gas (preferably air, or nitrogen, or carbon dioxide) is preferably injected directly into the mixing chamber. Due to the direct gas injection, it is possible to dispense with the upstream gas injection in a separate pressure tank, or to reduce the extent of the upstream gas injection. Since the direct gas injection can increase the pressure in the mixing chamber compared to the pure upstream gas injection, other outlet nozzles (longer nozzles or nozzles with a smaller inner diameter) can be used for metering. Furthermore, it is possible to react much more quickly to any changes in the production parameters (emission rate, viscosity, temperature, etc.) compared to known methods in which the gas injection is completely upstream and separated in time from the actual metering.

[0008] With the method according to the invention, at least a significant proportion of the gas required for foaming is injected only when the foamed or foamable plastic is metered out. The amount of gas injected during a metering process corresponds to the amount of gas and / or fills up the amount of gas to the level required for the amount of plastic to be discharged in this metering process. However, the method according to the invention does not exclude the possibility that part of the required gas has already been supplied to the first component in an upstream gas conditioning process.

[0009] In one embodiment, a second component is delivered into the mixing chamber where a chemical reaction takes place between the first and second components, an example of this is the production of polyurethane (PU) produced by the chemical reaction of polyols with isocyanates.

[0010] During the chemical reaction, propellant gases may be released that may be necessary for the formation of foam cells, as already mentioned using the example of polyol, water and isocyanate.

[0011] In one embodiment, the first component is mixed with the second component after dispersion of the gas in the first component has been performed. This two-step method has the advantage that different process parameters can be set to, on the one hand, disperse or break down the gas in the first component and, on the other hand, achieve optimal mixing between the first component (with the small microbubbles it contains) and the second component.

[0012] As a setpoint for the volumetric flow rate of the gas injected at ambient pressure, a function can be used that depends on the product of the pressure in the mixing chamber and the output of the plastic per unit time. This may be a linear dependency. For example, the setpoint for the volumetric flow rate of the gas can be the function F ind = (m × (P MK × M AUS )) - F old can be determined using: Where: - F indis cm 3 the setpoint of the volumetric flow rate of the injected gas in units of s / s; - m is cm 3 is the slope in / s, - P MK is the dimensionless value of the pressure in the mixing chamber in bar, - M AUS is the dimensionless value of the discharge rate in g / s, - F old is cm 3 is the volumetric flow rate of the gas already dissolved in the first component in .mu.s / s.

[0013] Preferably, the volumetric flow rate of gas injected into the mixing chamber at ambient pressure is a value determined by a function F ind is equal to or greater than the value F ind The function for determining may preferably be used in a control loop as a lower limit for the volumetric flow rate to be injected.

[0014] This function returns the value F ind This takes into account the fact that when F is determined, in addition to the direct gas input, it must be taken into account that the first component (or at least one of the components, if multiple components are used) may already partially contain gas. This value is old and can be determined using various methods. In particular, it is conceivable to measure the density of the first component in the mixing chamber without injected gas and compare the density with the corresponding data sheet for this component. This allows the gas input and thus the already supplied volume flow rate F to be calculated in case of discrepancies. old Another possibility is to compare the density of the first component in the mixing chamber without injected gas with the same first component in the mixing chamber without injected gas after the application of a vacuum. This also makes it possible to determine the gas input and, therefore, the volumetric flow rate F already delivered. old This makes it easy to determine the already delivered volume flow rate Fold is determined, for example using the options described above, and then the required volume flow rate F for the finished product to be discharged from the mixing chamber. total must be subtracted from the value of F total can be calculated using the following function: F total = (m × (P MK × M AUS ))

[0015] The volume flow rate F already contained in the first component old After subtracting, the volumetric flow rate to be injected F ind can be determined.

[0016] The gradient may preferably be determined by a series of tests of the weighed plastic. For example, multiple tests with different gradients may be used to determine the point at which the weighed plastic no longer meets the requirements. This may be done in particular by visual inspection of the weighed product and comparison with the weighed product of the test, or by other suitable evaluation methods.

[0017] Preferably, for example, for polyurethane (PU), the gradient is 0.010 cm. 3 / s to 0.09cm 3 / s, particularly preferably 0.014 cm 3 / s to 0.022cm 3 / s, and said discharge rate is preferably in the range from 0.2 g / s to 120 g / s, very particularly preferably in the range from 0.2 g / s to 70 g / s.

[0018] Preferably, for example, for silicone, the gradient is 0.060 cm. 3 / s to 0.269cm 3 / s, and particularly preferably 0.075 cm 3 / s to 0.105cm 3 / s, and said discharge rate is preferably in the range from 0.2 g / s to 120 g / s, very particularly preferably in the range from 0.2 g / s to 10 g / s.

[0019] Preferably, the mixing chamber can be opened during one metering process and closed between two metering processes, in particular to allow discontinuous metering of foamed or foamable plastics by a direct gas injection process. It is particularly conceivable to close the mixing chamber by means of a stirring mechanism arranged in the mixing chamber so as to be axially displaceable. For closing, the stirring mechanism can take, for example, an axially closed position in which the outlet opening of the mixing chamber is closed. Of course, other possibilities are also conceivable which allow the mixing chamber to be closed.

[0020] Ideally, both the mixing chamber and the valve arrangement are open during one metering process and closed between two metering processes.

[0021] In a preferred embodiment, the valve device is opened during a metering process and closed between two metering processes. This can be done, for example, by a pressure regulating valve as part of the valve device, which sets the target flow rate to zero. The fact that the valve device can be closed between the two metering processes prevents too much gas from entering the mixing chamber during the pause between the two metering processes, which would be detrimental to the desired homogeneous foam structure. On the other hand, it can also prevent substances from the mixing chamber from accidentally entering the valve device and causing contamination or damage.

[0022] The valve arrangement may comprise a pressure regulating valve and a flow regulator, the output of the flow regulator being connected to the inlet of the pressure regulating valve and the outlet of the pressure regulating valve being connected to the mixing chamber.

[0023] The pressure regulating valve is preferably designed as a needle valve having a valve chamber, a needle displaceable in the valve chamber and a piston unit connected to the needle. A needle valve is, for example, a control valve in which a control gap is changed by the axial movement of a needle-like actuator. The piston unit allows the axial position of the needle to be determined as a function of the pressure in the valve chamber.

[0024] The pressure regulating valve makes it possible to maintain a constant pressure at the outlet of the flow regulator, which is connected to the valve chamber via the inlet of the pressure regulating valve, and which pressure is almost independent of the pressure in the mixing chamber. Even if one of the inlets of the flow regulator is provided with a means for keeping the pressure there constant, the flow regulator has a constant pressure state at the inlet and outlet, so that it is possible to provide a very precise flow rate. Overall, the valve device is able to deliver a very precise amount of air per unit of time. This precisely regulated amount of air allows plastics to be produced in the mixing chamber with a good and consistent foam structure.

[0025] The flow regulator is preferably designed as a mass flow controller (MFC), which determines the mass flow rate in such a way that pressure and temperature fluctuations do not affect the result of the regulating action.

[0026] As the measurement sensor of the mass flow controller, a calorimeter flow meter is preferably used.

[0027] The piston unit may comprise a pressure guide piston and a closing piston. The pressure guide piston is used to regulate the pressure. On the one hand, a first force, which depends on the pressure in the valve chamber, can act on the pressure guide piston. Preferably, the first force is proportional to the pressure prevailing in the valve chamber. On the other hand, a second force, which can be precisely regulated by means of a regulating device, acts on the pressure guide piston. When the pressure guide piston is in equilibrium, the needle in the valve chamber is not moved and remains stationary. If the valve chamber pressure is too low, the pressure guide piston and the needle coupled thereto move in one direction and the flow conditions in the pressure regulating valve change such that the valve chamber pressure rises again. The pressure guide piston then moves again in the other direction until an equilibrium is established between the first and second forces. This makes it possible to regulate the valve chamber pressure, the level or set value of which depends on the set second force. The needle valve can be closed by the closing piston. Preferably, the needle valve can be closed independently of the valve chamber pressure.

[0028] A spring element may be arranged between the pressure guide piston and the adjustable stiffener. For example, the spring element may be a coil spring. The distance between the pressure guide piston and the stiffener is varied by adjusting the stiffener, whereby the coil spring is compressed more or less. The force exerted by the spring element and / or the coil spring on the pressure guide piston varies accordingly. As an alternative to the spring element or the coil spring, the adjustable second force may also be provided by other means, such as air pressure.

[0029] In one embodiment, in the closed position of the needle, the closure piston presses against the pressure guide piston, which presses against the needle and holds it in the closed position. The force with which the closure piston presses against the pressure guide piston is preferably significantly greater (2x or more) than the force exerted on the pressure guide piston by the spring element. This allows the needle valve to be closed quickly and reliably by the closure piston.

[0030] A spring can urge the closure piston into a rest position in which the closure piston and the pressure guide piston are decoupled from each other, in which no force due to the closure piston acts on the pressure guide piston.

[0031] The needle, the pressure guide piston and the closure piston may be arranged coaxially with one another. Furthermore, the adjustable stiffener may also be arranged coaxially with the pressure guide piston. The adjustable stiffener is preferably a threaded sleeve having an axial position that is adjustable by a rotational movement via a screw thread. This allows the axial position of the stiffener, and thus the pressure in the valve chamber, to be adjusted very precisely.

[0032] In one embodiment, the valve chamber is separated by a membrane arranged between the needle and the piston unit. This membrane allows a good seal between the valve chamber and the piston unit. The membrane can have a specific wave structure that ensures a good fit and seal. In another embodiment, a clamp is provided on the membrane, which makes the membrane corrugated to ensure a good fit and seal.

[0033] The needle is preferably coupled to the piston unit by magnetic force. Magnets can be arranged on two opposite sides of the membrane, in which case the magnetic force acts through the membrane. Thus, it is not necessary to pierce the membrane between the needle and the piston unit in order to attach them. This reduces the risk of the membrane leaking. Of course, it is also possible to use a magnet on one side and a ferromagnetic material on the other side.

[0034] In one embodiment, the needle is made of plastic, preferably PEEK, which allows a good seal between the needle and the valve housing defining the valve chamber when the needle is in the closed position, in particular, material in the mixing chamber cannot penetrate into the pressure regulating valve.

[0035] The volume between the outlet of the flow regulator and the outlet of the pressure regulating valve is 5 cm 3 Less than 1cm, preferably 3 This minimizes deleterious compression effects of the (gas) volume, which makes it difficult to precisely control the amount of air injected.

[0036] A check valve may be provided between the outlet of the flow regulator and the inlet of the pressure regulator to prevent material from the mixing chamber from entering the typically very sensitive flow regulator in the event of a defect in the pressure regulator.

[0037] A booster unit may be provided before the inlet of the flow regulator, compressing the air pressure of a conventional compressed air supply network from about 5-7 bar to about 7-30 bar. To compensate for pressure fluctuations that may occur during operation of the booster unit, a large buffer volume may be provided between the booster unit and the inlet of the flow regulator. The large buffer volume may be created, for example, by using a piece of hose with an extra-large diameter and a long length.

[0038] The mixing device may include a flow brake that divides the mixing chamber into a first mixing region and a second mixing region.

[0039] The flow brake may include a restriction, which causes the pressure in the first mixing region to be slightly higher than the pressure in the second mixing region. This prevents the second component, such as an isocyanate, from entering the first mixing region and causing undesirable chemical reactions or contamination. A pre-mixture (of the first component and the gas) then passes through the restriction into the second mixing region to be mixed with the second component. The mixture of the pre-mixture and the second component then exits the mixing chamber through the exit opening.

[0040] The restriction may be formed by a radial gap between the mixing chamber wall and the stirring mechanism. Preferably, the stirring mechanism is configured to be substantially rotationally symmetric. The stirring mechanism may have a shaft collar, in which case the radial gap may extend between the shaft collar and the mixing chamber wall. In the case of a rotationally symmetric stirring mechanism, the shaft collar may have a circular cross section with an outer diameter. The mixing chamber may be substantially cylindrical and have a cylindrical outer surface with a circular cross section. The inner diameter of the cylindrical outer 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 2 mm to 15 mm. Preferably, the stirring mechanism and the cylindrical mixing chamber are coaxially aligned with each other, whereby a radial gap of a certain size is formed in the circumferential direction with a smooth shaft collar. The radial gap may be smaller than 0.5 mm, even smaller than 0.1 mm.

[0041] The dimensions of the mixing chamber and the stirring mechanism depend on the required throughput (weight per unit time) of the plastic to be dispensed. Typical values ​​of the throughput range from 0.05 g / s to 120 g / s. For example, the mixing chamber can have an axial length of 12 mm to 25 cm. The inner diameter of the cylindrical mixing chamber can range from 6 mm to 30 mm.

[0042] In one embodiment, the stirring mechanism can be moved axially within the mixing chamber, preferably to an axially closed position closing the outlet opening of the mixing chamber, from which, when the stirring mechanism is moved again, the outlet opening opens so that the plastic can be metered out of the mixing chamber.

[0043] The outlet opening may be arranged substantially coaxially with the rotation axis of the stirring mechanism, in which case the axial closed position may constitute the axial end position of the stirring mechanism. The mixing chamber may have a conical end region, with the outlet opening arranged centrally relative thereto. In the closed position, the stirring mechanism may rest on this end region and thus close the outlet opening. If the stirring mechanism is then moved slightly from the closed position, an outlet gap opens between the stirring mechanism and the tapered end region. The plastic reaches the outlet opening through this outlet gap.

[0044] In one embodiment, the axial position of the stirring mechanism is used to adjust the flow cross-section of an outlet gap of any shape upstream of the outlet opening between the axially displaceable stirring mechanism and the mixing chamber, thus influencing and / or adjusting the pressure in the mixing chamber. This embodiment can also be designed without a conical tapered end. Moreover, it is not essential that the closed position is an axial end position.

[0045] The first part of the stirring mechanism and the second axial part of the stirring mechanism are preferably connected to each other in a rotationally fixed manner. This results in a relatively simple structure of the stirring mechanism, which preferably consists of only two or three parts constructed integrally or rigidly connected to each other. As a result, the axial parts of the stirring mechanism rotate at the same speed within the mixing chamber.

[0046] In one embodiment, a first mixing means located in the first portion of the stirring mechanism is different from a second mixing means located in the second portion of the stirring mechanism, taking into account the fact that the requirements and objectives in the first mixing zone are different from the requirements and objectives in the second mixing zone: in the first mixing zone, the gas should be finely dispersed, beaten or dispersed in the first component, whereas in the second mixing zone, the first component (within which the gas is contained) and the second component should be mixed together.

[0047] The first means of the first axial section of the stirring mechanism and / or the further means of the second section of the stirring mechanism may comprise a plurality of rows of radially extending projections or radial protrusions, the rows may extend substantially in the axial direction. In one embodiment, the rows run linearly parallel to the axis of rotation of the stirring mechanism. However, the rows may be inclined obliquely with respect to the axis of rotation so as to promote axial flow as the stirring mechanism rotates. The angle of inclination of the first axial section may be different from the angle of inclination of the second axial section. For example, it is conceivable that the angle of inclination of the first axial section is 0°, while the angle of inclination of the second axial section is different from 0° (e.g. 5°-15°) in order to prevent the second component from spilling into the first axial region in addition to the flow brake.

[0048] The radial protrusions / projections of one row may be axially offset from the radial protrusions of an adjacent row, allowing for better mixing and better distribution of the gas.

[0049] When rows of radial projections are provided on both the first axial portion and the second axial portion of the stirring mechanism, the radial projections on the second portion may be spaced apart from each other relative to the radial projections on the first portion. The radial projections on the second axial portion may be larger than the radial projections on the first axial portion. This measure allows for finer mixing or dispersion in the first mixing region.

[0050] Generally, the first means in the first axial portion has a larger pitch than the second means in the second axial portion, meaning that there are more projections or protrusions per unit area.

[0051] The radial projections may each have a cross-sectional area that varies in the radial direction, such that the projections taper or diverge outwards in the radial direction.

[0052] The first means of the first axial portion of the stirring mechanism and / or the second means of the second portion of the stirring mechanism may each comprise a number of blades for conveying radially inwardly material pushed outward by centrifugal force, which promotes good and homogeneous mixing and / or dispersion of the gas.

[0053] For additional mixing effect, the blades may have small openings through which some of the material trapped by the blades is forced as the agitator mechanism rotates.

[0054] The metering, preferably in a discontinuous manner, is intended to cover the case where the plastic is metered with a constant output (weight per unit time) for a limited time interval, for example a few seconds. Such a metering may be followed by pauses during which no plastic is metered. Discontinuous metering may therefore be the result of metering processes of different lengths and metering pauses of different lengths arranged in between. The output may also vary during a metering process or from metering process to metering process. [Brief description of the drawings]

[0055] The invention will now be explained in more detail with reference to the illustrated embodiments, in which: [Figure 1] FIG. 1 shows a plastic metering device in which the method according to the invention can be implemented. [Diagram 2] FIG. 2 shows a mixing device of the plastic metering device. [Diagram 3] FIG. 2 shows a pressure regulating valve as part of a valve arrangement according to the present invention. [Figure 4] FIG. 3 is a diagram showing a stirring mechanism of the mixer of FIG. 2. [Diagram 5] FIG. 13 is a diagram showing another stirring mechanism. [Figure 6] 10A to 10C are diagrams showing three modified examples of the first axial direction portion of the stirring mechanism. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0056] Figure 1 shows a plastic metering device, generally designated 1. This plastic metering device 1 serves to meter plastic, preferably in a discontinuous manner, which plastic is either already (partially) foamed when it leaves the plastic metering device 1 or (continues to) foam after it is discharged.

[0057] The plastic metering device 1 comprises a mixing device 10 and a valve device 50. In the mixing device 10, a first component 2 and a second component 3 can be fed into a mixing chamber 11 in which a rotatably mounted stirring mechanism 30 is disposed. In the mixing chamber 11, the two components 2, 3 are mixed to form a plastic 5. For example, the first component 2 can be a mixture of polyol and water, which reacts with an isocyanate as the second component 3 in the mixing chamber 11 to form a polyurethane. This generates CO2, which causes the polyurethane to foam and / or (continues to foam) after it is metered out of the mixing chamber 11.

[0058] Furthermore, the mixing chamber 11 is supplied with gas 4, the amount of which is precisely regulated by a valve arrangement 50. For this purpose, the valve arrangement 50 comprises a pressure regulating valve 51 and a flow regulator in the form of a mass flow controller 52, which are connected to each other by a connection unit 53. Pressurized expanding gas 6 is supplied to the inlet 54 of the mass flow controller 52.

[0059] The gas 4 is injected directly into the first mixing area 11a of the mixing chamber 11 and mixed or finely dispersed in the first component 2 by the stirring mechanism 30. This forms small microbubbles in the first component 2. The pre-mixture then flows through the gap 34 into the second mixing area 11b of the mixing chamber 11. The microbubbles form a particularly homogeneous and fine foam structure, as will be described in more detail below.

[0060] An outlet 55 of the mass flow controller 52 is connected to an inlet 56 of the pressure regulating valve 51 via a connection unit 53 .

[0061] 2 shows the mixing device 10 in isolation. The stirring mechanism 30 is in this case substantially rotationally symmetrical about the axis of rotation 31. The stirring mechanism 30 is driven by a drive shaft 12, which is only partially shown. The stirring mechanism 30 has a pin-shaped shaft connection 32 for connection to the drive shaft 12. Preferably, the connection between the drive shaft 12 and the shaft connection 32 is a non-positive connection.

[0062] The housing of the mixing device 1 is provided with three inlet openings. Firstly, there is a first inlet opening 13, through which the first component 2 can be fed into the mixing chamber 11. A second inlet opening 14 for the second component 3 is provided at an axial distance from the first inlet opening 13. The axial distance between the first and second inlet openings 14 can be a few millimeters, for example 3 to 20 millimeters.

[0063] At the same axial height as the first inlet opening 13 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).

[0064] The plastic or polyurethane foam leaves the mixing chamber 11 through an outlet opening 16. This outlet opening 16 is arranged coaxially with the axis of rotation 31 and is located at the axial end 17 of the mixing chamber 11. 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 produced plastic leaves the mixing chamber 11 in the axial direction.

[0065] The stirring mechanism 30 has a cylindrical shaft collar 33 whose outer diameter is slightly smaller than the inner diameter of the cylindrical mixing chamber 11. A radial gap 34 between the shaft collar 33 and the mixing chamber wall 19 can be considered as part of a restriction or flow brake, which divides the mixing chamber 11 into a first mixing region 11a and a second mixing region 11b.

[0066] The stirring mechanism 30 is movable axially (in the direction of the axis of rotation 31). Figure 2 shows the stirring mechanism 30 in one axial position, with an outlet gap 36 between the conical stirring tip 35 of the stirring mechanism 30 and the funnel-shaped insert 20 located at the axial end 17 of the mixing chamber 11. As a result, the plastic produced in the mixing chamber 11 can exit the mixing device 1 through the nozzle 18.

[0067] In the closed position, the conical stirring tip 35 rests on the insert 20, thereby closing the outlet gap 36. In the closed position of the stirring mechanism 30, the outlet opening 16 is thus closed. The axial extent of the gap between the stirring tip 35 and the insert 20 can take values ​​between 0 mm (closed position) and 2.5 mm. The axial position of the stirring mechanism 30 and / or the axial extent of the outlet gap 36 can be used to set a specific pressure in the mixing chamber 11. Means for precisely adjusting the axial position of the stirring mechanism 30 are not shown in FIG. 2.

[0068] The axial stroke (difference between the closed position and the upper end position) is dimensioned such that, when viewed axially, the shaft collar 33 and / or the flow brake is always located between the first inlet opening 13 and the second inlet opening 14. As a result, the first inlet opening 13 and the gas inlet opening, which in this embodiment is offset by 180°, always open into the first mixing region 11a of the mixing chamber 11. However, the second inlet opening 14 always opens into the second mixing region 11b, regardless of the axial position of the stirring mechanism 30.

[0069] The stirring mechanism 30 has first means 38 on a first axial section 37 for dispersing the gas 4 and / or mixing the gas 4 with the first component 2. The first axial section 37 of the stirring mechanism 30 is located in a first mixing area 11a of the mixing chamber 11. The first mixing area 11a is defined by a shaft collar 33 and a seal 21 inserted between the drive shaft 12 and the mixing chamber wall 19. A second axial section 39 extending from the shaft collar 33 to the stirring tip 35 is provided with second means 40 for mixing a premix of the first component 2 and the gas 4 with the second component 3. The second axial section 39 is located in a second mixing area 11b of the mixing chamber 11. The first means 38 and the second means 40 will be described in more detail with reference to Figs. 4 to 6.

[0070] Before describing the pressure regulating valve 51 of the valve device 50 in more detail, the operation of the mixing chamber 1 will be briefly described, focusing on the metering of polyurethane and / or foamed polyurethane 5. Polyol together with water as the first component 2 is fed through the first inlet opening 13 to the first mixing area 11a. At the same time, air is injected into the first mixing area 11a through the gas inlet opening 15. By rotating the stirring mechanism 30, and thus the first means 38, the injected gas 4 is dispersed in the first component 2. This causes the formation of small microbubbles of gas, which are finely dispersed in the first component 2. The rotation speed of the stirrer can be 1000-6000 rpm or 1500 to 4000 rpm.

[0071] Due to the pressure present in the first mixing zone 11a, the premix from the first mixing zone 11a enters the second mixing zone 11b through the radial gap 34. In this second mixing zone 11b, the premix (polyol, water, microbubbles) is mixed with isocyanate (second component 3) by the second means 40. During the reaction of polyol, water and isocyanate, CO2 is produced in addition to polyurethane. Said microbubbles nucleate the formation of CO2 bubbles, which form foam cells in the polyurethane. The polyurethane is metered out of the mixing chamber 11 through the outlet opening 16. Due to the flow brake and / or the throttling effect of the radial gap 34, a (small) pressure gradient is created between the first mixing zone 11a and the second mixing zone 11b. This pressure gradient ensures that there is practically no flow from the second mixing zone 11b to the first mixing zone 11a. This prevents the isocyanate or the mixture of isocyanate, polyol and water from entering the first mixing region 11a and causing undesirable contamination therein.

[0072] When the metering process is to be ended, the stirring mechanism 30 is moved from the position shown in FIG. 2 to the above-mentioned closed position in order to close the outlet opening 16. The drive shaft 12 is braked so that the stirring mechanism 30 no longer rotates in the mixing chamber 11. The axial lowering of the stirring tip 35 until it rests on the insert 20 and the stopping of the stirring mechanism 30 can be coordinated so that the stirring tip 35 cleans and clears the insert 20 by the remaining rotation. At the same time, the valve device 50 is closed to prevent polyol from entering the valve device 50 or gas from accumulating too much in the first mixing area 11. Due to the closed valve device 51 and the closed outlet opening 16, the mixing chamber is sealed off from the environment after the metering process is ended. At the start of another metering process, the two components 2, 3 and the gas 4 are again fed into the mixing chamber with the stirring mechanism 30 rotated and axially displaced.

[0073] 3 shows an enlarged view of the pressure regulating valve 51. The pressure regulating valve 51 is designed as a needle valve with a valve chamber 57, a needle 58 movable in the valve chamber 57 and a piston unit 59 connected to the needle 58. The piston unit 59 comprises a pressure guide piston 60 and a closing piston 61. A membrane 62 is arranged between the piston unit 59 and the needle 58, which defines and seals the valve chamber 57.

[0074] The coupling between the needle 58 and the piston unit 59 is achieved by two magnets 63, 64, which are designed as disk magnets made of neodymium. The magnetic force between these two magnets acts through the membrane 62. The needle 58 is firmly connected to the magnet 63 via a needle holder 65. The magnet 64 is inserted into an intermediate piece 66, to which a spherical cap 75 of the pressure guide piston 60 is applied. The membrane 62 is fixed to the valve housing 68 by means of a threaded sleeve 67.

[0075] A coil spring 70 is arranged between the pressure guide piston 60 and an axially adjustable stiffener 69 in the form of a threaded sleeve, which stiffener 69 biases the pressure guide piston 60, and thus also the needle 58, to the left in the illustration of Figure 3. The force with which the coil spring 70 biases the pressure guide piston 60 depends on the axial position of the threaded sleeve 69. This axial position can be precisely adjusted by rotating the threaded sleeve 69.

[0076] When the needle 58 is fully moved to the left, it is in the closed position with the outlet 71 of the pressure regulating valve 51 closed. Via the membrane 62 and the intermediate piece 66, a biasing force opposite to that of the coil spring 70 acts on the pressure guide piston 60, which biasing force depends on the pressure in the valve chamber 57 and / or on the pressure at the inlet 56 of the pressure regulating valve 51. If the pressure guide piston 60 is in a state of force equilibrium, the needle 58 is not moved in the valve chamber 57. If the pressure in the valve chamber 57 decreases, the force pushing the pressure guide piston 60 to the right in the illustration of FIG. 3 also decreases. The needle 58 is therefore displaced to the right by the biasing force of the coil spring, which is no longer fully compensated, and the outlet 71 is closed and / or the flow cross-sectional area at the outlet 71 is reduced. This causes the pressure in the valve chamber 57 to rise again, as a result of which force equilibrium at the pressure guide piston 60 is restored.

[0077] The closing piston 61 serves to close the outlet 71 of the pressure regulating valve 51 when the metering process in the plastic metering device 1 and thus the supply of gas 4 should be terminated. In this case, the closing piston 61 is pressurized with compressed air by the air supply port 72, which presses the closing piston against the biasing force of a further coil spring 73 against the pressure guide piston 60. This counteracts the balance of forces (which would otherwise prevail) between the pressure in the valve chamber 57 and the force of the coil spring 70. As a result, the needle 58 moves to the closed position and is held there, independent of the pressure in the valve chamber 57. If the gas 4 flows out of the pressure regulating valve 51 again, the supply of compressed air to the closing piston 61 is stopped. The coil spring 73 then presses the closing piston back to its rest position, in which the closing piston 61 exerts no force on the pressure guide piston 60.

[0078] The connection unit 53, located between the outlet 55 of the mass flow controller 52 and the inlet 56 of the pressure regulating valve 51, includes a check valve 74 (see FIG. 1) that protects the mass flow controller 52 from the ingress of the first component 2 in the event that the pressure regulating valve 51 is damaged and no longer able to block the flow of the first component 2 through the valve chamber 57.

[0079] Figure 4 shows an isolated view of the stirring mechanism 30 of Figure 2. Additionally, Figure 4 shows a portion of the circumference of the stirring mechanism 30 in two developed views.

[0080] The first means 38 for dispersing gas and generating microbubbles comprises projections or protrusions 41, which may have a rectangular cross section. The projections 41 extend radially outward from a cylindrical core 42. The projections 41 with rectangular cross section are arranged in axially extending rows, with the longer edges of the rectangular cross section extending in the axial direction and therefore perpendicular to the circumferential direction. The contour of one axial row is highlighted by the arrow 43 in the partial section of the development of the circumference in FIG. 4. It can also be seen that the projections 41 of adjacent rows are arranged axially offset from one another. When the stirring mechanism 30 rotates and thus the projections 41 move through the first component, this leads to a yielding or displacement movement of the first component together with the gas contained therein. The yielding or displacement movement is indicated diagrammatically by the arrow 44. The first means 38 is designed as a separate ring element which can be pressed onto the pin-shaped shaft connection 32. This simplifies the manufacture of the stirring mechanism 30.

[0081] Like the first means 38, the second means 40 have projections or protrusions 45 of rectangular cross section arranged in axial rows (see arrows 43). Here too there is an axial offset of the projections 45 of adjacent rows 43. From FIG. 4 it is clear that the pitch (number of projections per unit area on the circumference of the stirring mechanism 30) of the first axial portion 37 is greater than the pitch of the second axial portion 39. The pitch of the first axial portion 37 relative to the pitch of the second axial portion can range between 2 and 5, regardless of the specific arrangement and design of the projections 41, 45 of FIG. 4. The greater the pitch, the finer and better the distribution of the gas in the first mixing zone. The yielding and displacement movements 44 of the material in the first mixing zone 11a are therefore finer and more delicate.

[0082] A further difference between the protrusions 41 in the first axial portion 37 and the protrusions 45 in the second axial portion 39 is the radial height of the individual protrusions. The greater height (greater radial extension) of the protrusions 41 promotes finer and more focused mixing / dispersion compared to the somewhat flatter protrusions 45.

[0083] FIG. 5 shows a further embodiment of the stirring mechanism 30. In contrast to the shaft collar 33 of FIG. 4, which has a smooth cylindrical outer surface, here a shaft collar 46 is provided which is interrupted by axial grooves 46a. The area of ​​the shaft collar 46 between two adjacent grooves 46a can also be called a protrusion 46b. The protrusion is circumferentially wider than the protrusions 41 of the first axial portion 37 and the protrusions 45 of the second axial portion 39, which creates an interaction with the adjacent mixing chamber wall 19 (see FIG. 1) and also constitutes a flow brake which prevents the second component from entering the first mixing area 11a. The inhibition effect of the interrupted shaft collar 46 is smaller than that of the shaft collar 33 of the embodiment of FIGS. 2 and 4. However, this also reduces the pressure gradient between the first mixing area 11a and the second mixing area 11b.

[0084] 5 also shows that the projection 41 of the first axial portion 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 stirring mechanism 30.

[0085] Figure 6 shows a different variant for the ring element 47. Figure 6B shows the variant used in figure 5. The projections 41 taper radially outwards in such a way 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 stirring mechanism 30 is rotating. Also, the time interval during which said end faces are directly facing the respective inlet openings 13, 15 when the stirring mechanism 30 is rotating is very short.

[0086] In contrast, in the variant of FIG. 6A, the protrusions 41 have a larger cross section, which results in a relatively large end or circumferential area per protrusion 41. When the stirring mechanism 30 rotates, the time period during which the end faces of the protrusions 41 face the inlet opening is correspondingly large. This tends to make the introduction of the first component 2 and the gas 4 more difficult. However, the protrusions 41 have a radial undercut, so that the materials to be mixed are pushed inwards when the stirring mechanism rotates. This reduces the adverse effects on good mixing that may be caused by centrifugal forces acting on the materials to be mixed.

[0087] In the variant of Figures 6A and 6B, the rows 43 of projections 41 run parallel to the axis of rotation 31. However, the rows may be inclined so that the material in the first mixing region 11a is pressed towards the seal 21 (see Figure 2, i.e. away from the shaft collar 33). This results in stronger mixing / dispersion in the first mixing region 11a.

[0088] FIG. 6C shows a variant of a ring element 47 with a number of blades 48 arranged circumferentially. The blades 48 push the material in the first mixing area 11a towards the interior of the mixing chamber, countering the centrifugal forces. For better mixing / dispersion, the blades have small openings 49. Some of the material captured by the blades is pushed through these openings 49, promoting good mixing / dispersion. The axial height of said openings is offset from the axial height of the openings of the adjacent blades. This makes it possible to avoid dead spaces in the first mixing area 11a, where non-optimally mixed material may stagnate. [Explanation of symbols]

[0089] 1 Mixing chamber 2 First component 3. Second Component 4. Gas 5 Plastic (Polyurethane Foam) 6 Expanding Gas 10 Mixing device 11 Mixing chamber (11a first mixing region; 11b second mixing region) 12 Drive shaft 13 First entrance opening 14 Second entrance opening 15 Gas inlet opening 16 Exit opening 17 Axial end 18 Nozzles 19 Mixing chamber wall 20 Insert 21 Seal 30 Stirring mechanism 31 Rotation axis 32 Pin-shaped shaft connection 33 Shaft color 34 Radial clearance 35 Stirring tip 36 Exit Gap 37 1st axis direction part 38 First means 39 2nd axis direction part 40 Second means 41 Protrusion / protrusion 42 cores 43 columns 44 Yield and Displacement Movements 45 Protrusion / protrusion 50 Valve gear 51 Pressure Regulating Valve 52 Flow Regulator / Mass Flow Controller 53 Connection unit 54 Mass flow controller inlet 55 Mass flow controller outlet 56 Pressure Regulating Valve Inlet 57 Valve chamber 58 Needle 59 Piston unit 60 Pressure Guide Piston 61 Closed piston 62 membrane 63 Magnet 64 Magnet 65 Needle holder 66 Intermediate Piece 67 Threaded Sleeve 68 Valve Housing 69 Stiffeners / Threaded Sleeves 70 Coil spring 71 Pressure Regulating Valve Outlet 72 Air supply port 73 Coil Spring 74 Check valve 75 Spherical Cap

Claims

1. A method for metering a foamed or foamable plastic (5), preferably in a discontinuous manner, comprising: At least one first component (2) for forming a plastic (5) is conveyed into a mixing chamber (11) of a mixing device (10) having a rotatable stirring mechanism (30) arranged around a rotation axis (31), The first component (2) is doped with a gas (4) to affect the formation of foam, The plastic (4) is metered out of the mixing chamber (11) through an outlet nozzle (18), The pressure in the mixing chamber (11) ranges from 0.2 bar to 15 bar, The gas (4) is injected by a valve device (50) into the first component (2), preferably directly into the mixing chamber (11); The stirring mechanism (30) disperses the gas (5) within the first component (2) in the mixing chamber (11). A method comprising:

2. 10. The method of claim 1 , The volumetric flow rate of the gas injected into the mixing chamber (11) at ambient pressure is a function F ｉｎｄ = (m × (P ＭＫ × M ＡＵＳ )) - F ｏｌｄ and Where: -F ｉｎｄ is cm ３ is the setpoint of the volumetric flow rate of the injected gas in s; - m is cm ３ / s, where - P ＭＫ is the dimensionless value of the pressure in the mixing chamber (11) in bar, - M ＡＵＳ is the dimensionless value of the discharged amount in g / s, and F ｏｌｄ is cm ３ is the volumetric flow rate of the gas already dissolved in the first component (2) in / s. A method comprising:

3. The method according to claim 1 or 2, The mixing chamber (11) and / or the valve device (50) are open during one metering process and closed between two metering processes. A method comprising:

4. The method according to any one of claims 1 to 3, A second component (3) is delivered into the mixing chamber (11) where a chemical reaction takes place between said first component (2) and said second component (3). A method comprising:

5. 5. The method of claim 4, During the above chemical reaction, propellant gas is released. A method comprising:

6. The method according to claim 4 or 5, After the gas is dispersed in the first component (2), the first component (2) is mixed with the second component (3). A method comprising:

7. The method according to any one of claims 1 to 6, As a set value for the volumetric flow rate of the gas injected at ambient pressure, a function is used, which depends on the product of the pressure in the mixing chamber (11) and the output of the plastic (5) per unit time. A method comprising:

8. The method according to any one of claims 1 to 7, The valve arrangement (50) comprises a pressure regulating valve (51) and a flow regulator (52), preferably in the form of a mass flow controller (52); The outlet (55) of the mass flow controller (52) is connected to the inlet (56) of the pressure regulating valve (51); The outlet (71) of the pressure regulating valve (51) is connected to the mixing chamber (11). A method comprising:

9. 11. The method of claim 10, The inlet (54) of said mass flow controller (52) is subjected to a pressure of between 4 bar and 300 bar, preferably between 7 bar and 30 bar. A method comprising:

10. 12. The method according to claim 10 or 11, The pressure at the outlet (55) of the mass flow controller (52) is between 5 bar and 30 bar. A method comprising:

11. 13. The method according to any one of claims 10 to 12, The pressure regulating valve (51) has a needle (58) and a piston unit (59) connected to the needle, The piston unit (59) comprises a pressure guide piston (60) and a closing piston (61); In pressure control operation, the pressure guide piston (60) is separated from the closing piston (61), and when the pressure regulating valve (51) is to be closed, the closing piston (61) is pressed against the pressure guide piston. A method comprising:

12. The method according to any one of claims 8 to 11, The mass flow controller (52) has a calorimeter as a measurement sensor. A method comprising:

13. 13. The method according to any one of claims 1 to 12, The valve device (50) comprises a pressure regulating valve (51) designed as a closable needle valve A method comprising:

14. The method according to any one of claims 1 to 13, The mixing device (10) has a flow brake, which separates the mixing chamber (11) into a first mixing region (11a) and a second mixing region (11b). A method comprising:

15. 15. The method of claim 14, The stirring mechanism (30) has a first axial portion (37) having a first means (38) for dispersing a gas in a liquid, and a second axial portion (39) having a second means (40) for mixing two liquids. A method comprising:

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