Patent Application
20240316825
The invention relates to an apparatus for providing a liquid polymer component having a predefined air content, in particular for producing a plastics foam, according to the preamble of claim 1.
In the production of permanently elastic plastics foams, which are provided by mixing two individual components, such as polyol and isocyanate, in a mixing apparatus and are applied directly to the components to be sealed, such as covers or frame parts, to create a seal before they are fully reacted, it is necessary to charge one of the two liquid polymer components—generally polyol—with a well-defined amount of air in order to obtain a desired foam consistency in the end product.
This results in the problem that the liquid polymer components are generally provided in large vessels during the mixing operation, this having the effect that the air concentration in the liquid polymer component drops when the reservoir is refilled therewith. Since a certain length of time, for example 30 minutes, is generally required to mix the introduced air with the liquid through to complete saturation, the foam quality continually changes during this time. Accordingly, it is desirable to ascertain the current air content in the liquid polymer component in order to correspondingly be able to increase or decrease it as required, in order to set the desired air content to a value which as constant as possible within as short a time as possible.
In this context, to determine the air content in the liquid polymer component of a foam system, EP 098 04 280 A1 and EP 0 451 752 A2 disclose the use of measuring cylinders with standard flasks, into which a defined amount of the polymer component, which is charged with air and removed from the reservoir, is introduced at predefined chronological intervals.
In the closed space of the measuring cylinder, the gas content in the sample taken is ascertained after removal from the reservoir by means of compression and/or decompression. The method described in EP 98 04 280 and the associated apparatus have the deficiency that the air content in the liquid polymer component cannot be determined continuously, but only batchwise. In addition, the compression and decompression of the sample taken requires a comparatively long period of time, as a result of which the inaccuracy between the ascertained air content in the sample and the actual air content in the liquid polymer component in the reservoir owing to the time offset and the non-linear saturation behavior of the air in the liquid polymer component is additionally increased.
Accordingly, an object of the present invention is to provide an apparatus for providing a liquid polymer component to which air has been added and the air proportion of which is continuously measured and can be set to a desired default value in a short period of time.
This object is achieved by an apparatus having the features of claim 1.
Further features of the invention are described in the dependent claims.
According to the invention, an apparatus for providing a liquid polymer component having a predefined air content, as is used in particular for producing a plastics foam, comprises a pressure vessel, to which the liquid polymer component is fed through an opening. The feeding is performed depending on the fill level or batchwise at predefined chronological intervals, for example every 30 minutes or once per day.
The apparatus also comprises a pipeline, preferably in the form of a tubular screw conveyor, which is arranged on the bottom of the pressure vessel and has a multiplicity of air outlet nozzles, to which air from a compressed-air source arranged outside the pressure vessel 4 can be fed with a predefined excess pressure, and the air exits from the air outlet nozzles into the interior space of the pressure vessel and is physically dissolved in the liquid polymer component.
The apparatus also comprises a motor-operated stirring device, which in particular also can be operated with a variable rotational speed and which mixes the liquid polymer component with the air exiting the air outlet nozzles, with the result that this air physically dissolves in the liquid polymer component. This constantly increases the proportion of air in the liquid polymer component according to the feed of uncharged liquid polymer component, wherein the maximally achievable saturation, or its increase per unit time, varies and depends on the air pressure in the pressure vessel, the chemical properties of the polymer component, and the temperature. During or after the mixing of the polymer component with the further liquid polymer component, the air dissolved in the liquid first polymer component forms cores for air bubbles, which form intrinsically closed cavities in the cured 2-component plastics foam that influence the permanently elastic properties and also the pore size and compressibility of the plastics foam.
The apparatus according to the invention is distinguished in that an oxygen sensor is arranged in the circulation line and measures an actual value for the oxygen saturation of the air-charged polymer component. The apparatus also comprises an electronic open-loop and closed-loop control device, which is configured to modify the pressure and/or the amount of compressed air fed to the air outlet nozzles on the basis of the actual value for the oxygen saturation in the circulation line measured by the oxygen sensor, in such a way that the oxygen saturation of the liquid polymer component circulating in the circulation line assumes a predefined setpoint value, or approaches such a predefined setpoint value. If desired, the oxygen partial pressure in the liquid polymer component can be determined mathematically from the oxygen saturation, if it is required for further applications.
The oxygen sensor used is preferably a sensor which operates according to the luminescence process. Such sensors are known, for example from EP 2 461 154. The oxygen sensor 100 is preferably mounted in the circulation line using an adapter and can as a result measure the amount of bonded oxygen in the polymer during operation “inline”, as it were, and permanently. The oxygen sensor has a photosensitive membrane as contact surface with the polymer. A phosphor located in the sensor or the membrane is excited and thereupon emits light (fluorescence). If then oxygen flows past the sensor, the emission of the phosphor is reduced in proportion to the amount of oxygen in front of the sensor, this also being referred to as the quenching effect. Software in the electronic open-loop and closed-loop control device then calculates the oxygen content in the liquid polymer component in the region behind the photosensitive membrane, preferably on the basis of the change in the phosphor emission. The oxygen content is preferably converted into a value for the amount of air bound in the polymer. Using this value for the amount of air bound in the polymer, following that the further air charge in the liquid polymer component in the pressure vessel, which at the same time is the reservoir for the liquid polymer component, is then controlled in closed-loop fashion by modifying the feed duration and/or the magnitude of the pressure of the air fed into the pipeline arranged in the pressure vessel from the outside.
As recognized by the applicant, expressed in simplified terms the basic concept of the invention is based on measuring the oxygen content physically bound in the liquid polymer continuously, or at predefined chronological intervals, and using this to ascertain the content of the air bound in the polymer. Using the amount of air bound in the polymer that was measured by the oxygen sensor, following that the air charge in the polymer is controlled in closed-loop fashion by increasing the pressure in the pressure vessel and/or modifying the amount of air fed into the vessel per unit time, in order to thereby obtain a preferably constant polymer-to-air ratio, which in turn is critical for a constant quality of the polymer foam mixture after the two polymer components have been mixed.
The invention will be described below with reference to the drawings on the basis of a preferred embodiment. In the drawings:
As shown in
As shown in
The apparatus 1 also has a stirring device 14, which is operated by a motor 13, is indicated by a schematic rotor in
As can also be deduced from the illustration of
Arranged between the pump 26 and the outflow 24 is a known outlet valve 30, through which the air-charged liquid polymer component 2A can be fed to a known mixing device 40, in order to mix the first liquid polymer component 2A with the further liquid polymer component 2B in a mixing device 40, which is symbolically indicated by a Y-shaped line, in the known way. The intermixed polymer components 2A, 2B, which exit the mixing device 40 in the form of a liquid, uncured plastics foam 2A+2B, are preferably continuously deposited directly in the form of a bead onto a component, such as a cover or a door, on which the plastics foam mixture forms, for example, a correspondingly permanently elastic seal after curing. The first liquid polymer component 2A, which is charged with a predefined amount of air for core formation in the apparatus 1 according to the invention, May for example be polyol, and the second polymer component 2B is isocyanate in this case.
An oxygen sensor 100 is arranged in the circulation line 20 and preferably continuously measures an actual value for the oxygen saturation of the air-charged polymer component 2A. The apparatus 1 also comprises an electronic open-loop and closed-loop control device 50, which is connected to the oxygen sensor 100 and also the pump 26, which is preferably a metering pump, and an open-close valve 42 via lines, not designated in more detail, which open-close valve makes it possible to modify the pressure and/or the amount of compressed air fed to the air outlet nozzles 10 from the compressed-air source 12 on the basis of the actual value for the oxygen saturation in the circulation line 20 measured by the oxygen sensor 100. To this end, the pressure and/or the amount of the compressed air fed to the air outlet nozzles is increased, or decreased, in such a way that the oxygen saturation in the liquid polymer component 2A circulating in the circulation line 20 assumes a predefined setpoint value, or approaches such a predefined setpoint value.
In one embodiment of the invention, the aforementioned open-close valve 42 is opened and closed again by the electronic open-loop and closed-loop control device 50 for a predefined period of time, for example for 5 minutes, and the length of this period of time is increased for example by 10% or a fixed time value, for example 10 seconds, if the actual value for the oxygen saturation measured by the oxygen sensor 100 is less than the preferably empirically ascertained setpoint value. Opening the open-close valve 42 causes compressed air to flow from the compressed-air source 12 into the pipeline 8, preferably via a flow meter 16, and, through the air outlet nozzles 10, enter the liquid polymer component 2A, in which some of the air is physically dissolved depending on the pressure inside the pressure vessel 4, the current degree of saturation and the temperature in the liquid polymer component. The undissolved portion of the fed air rises and exits at the top side of the pressure container 4 through an air outlet channel 60, which can be closed by a pressure regulating valve.
In a correspondingly converse manner, the duration for which the compressed air flows through the open-close valve from the compressed-air source 12 into the pressure vessel 4, and thus the amount of fed air, is shortened by the electronic open-loop and closed-loop control device 50 if the current actual value measured by the oxygen sensor 100 exceeds the setpoint value. If the actual value is the same or substantially the same as the setpoint value for the oxygen saturation, the valve 42 is preferably closed until the feed of uncharged first liquid polymer component 2A starts again.
As indicated in
The pressure regulating valve 62 is preferably a pneumatically controllable 3/2-way valve, to the control input 62I of which a predefined variable control pressure from a further compressed-air source 64 can preferably be applied. The fluidic connection between the interior space of the pressure vessel 4 and the surrounding area is opened up by the pressure regulating valve 62 if the pressure in the interior space of the pressure vessel 4 exceeds the control pressure, which can be set sensitively and preferably mechanically to 4 bar, for example via a needle valve, which is not shown in more detail. As is indicated purely schematically in
This embodiment of the invention has the advantage that the pressure in the interior space of the pressure vessel 4 can be advantageously set very sensitively to a predefined value without a complex electronic pressure regulating device being required for this, although one can also be used as an alternative. At the same time, it is ensured that the compressed air which was introduced into the pressure vessel 4 from the compressed-air source 12 during the aforementioned 11 chronological interval and may have a pressure of 4.5 bar or more can exit from the interior space of the pressure vessel 4 at all when the control pressure of the further compressed-air source 64 is exceeded. This is the basic prerequisite for a substantially constant air stream in the liquid polymer component 2A, which considerably facilitates the closed-loop control to a predefined setpoint value for the oxygen saturation of the liquid polymer component 2A and advantageously increases the closed-loop control accuracy.
It can be seen as a further advantage of the embodiment of the invention described above that the pressure regulating valve 62 is automatically closed, as it were, if the pressure in the pressure vessel 4 undershoots the control pressure owing to the air flowing continuously from the air outlet channel 60 after the open-close valve 42 of the compressed-air source 12 has been closed, without any additional electronically actuated valves or other components being required for this.
According to a further concept on which the invention is based, at least one pressure sensor 28, shown in
In a preferred embodiment of the invention, the pressure sensor 28 and the oxygen sensor 100 are arranged upstream of the pump 26, that is between the outflow 24 of the pressure vessel 4 and the pump 26 in the circulation line 20. This results in the advantage that pressure fluctuations in the circulation line 20 that are caused by removing the liquid polymer component 2A in the mixing device 40 do not influence, or have a considerably reduced influence, on the pressure of the liquid polymer component 2A when the oxygen saturation is being determined in 9 the oxygen sensor 100. This makes it possible for the oxygen sensor to measure, with high accuracy, the actual value for the oxygen saturation of the liquid polymer component 2A even while the liquid polymer component 2A is being fed to the mixing device 40, as a result of which quality fluctuations in the finished foam 13 mixture that result from an excessively high or low oxygen proportion in the liquid polymer component 2A, can be counteracted already in good time. The pressure sensor 28 is particularly preferably arranged at the level of the oxygen sensor 100 on the opposite side of the circulation line 20. At the same time or alternatively, it may be arranged downstream of the pump/metering pump 26, as is likewise indicated schematically in
In the preferred embodiment of the invention, the oxygen sensor 100 has a photosensitive membrane 102 containing phosphor, which forms an inner wall portion 20a of the circulation line 20, as shown in
In order to determine the actual value for the amount of air present in the liquid polymer component 2A as an absolute value, the electronic open-loop and closed-loop control device 50 is advantageously configured to determine the amount of air present in the liquid polymer component 2A per unit volume or per unit mass of the liquid polymer component 2A as an absolute value from the actual value for the oxygen saturation ascertained by the oxygen sensor 100 and the sensor electronics 108 coupled thereto. This absolute value may then be fed in the known way as control parameter to an electronic controller, for example a PID controller, which is preferably implemented in the electronic open-loop and closed-loop control device 50 as software. To this end, the electronic open-loop and closed-loop control device 50 is configured to determine the amount of air present in the liquid polymer component 2A per unit volume and/or per unit mass on the basis of values for the oxygen saturation that were ascertained empirically by measurements beforehand and to determine the associated amount of air present in the liquid polymer component 2A, and these amounts of air can be stored in a memory 52 of the electronic open-loop and closed-loop control device 50. The values for the oxygen saturation and the amount of air per unit volume/unit mass are preferably determined beforehand on the basis of compression-decompression measurements, as are described for example in EP 098 04 280 A1 or EP 0 451 752 A2, and stored permanently in the memory 52 as pairs of values.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 117 879.7 | Jul 2021 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/067862 | 6/29/2022 | WO |
