Patent Application
20210069940
The invention relates to a manufacturing method of thermoset polymers implemented by a low-pressure metering and mixing machine and preferably, a manufacturing method comprising a step of automatic calibration.
In general, low pressure dispensing machines for processing polyurethane or other thermoset polymers based on formulations with multiple reactive components, are conventionally also called dispensing machines, meter-mix or casting machines and are widely known.
Said dispensing machines comprise component circuits, each circuit corresponding to one component of the polymer formulation. Each component circuit is often heated to liquefy the component and to maintain the component liquid or at a desired viscosity and comprises a storage tank containing the component in a liquid form. Each component circuit can comprise a mixing head, a pump, a first hose or duct going to a three-way valve arranged at the mixing head and a second hose or duct back to the storage tank. It is advantageous to have each of the component flow permanently recirculating, going to the mixing head and back to the storage tank to get homogeneous temperature and constant flow rate.
In general, when processing chemistry includes small amount of reactive chemicals like compact polyurethane formulations (CPU), and when the machine can process a wide range of formulations at different outputs and back pressures, it is extremely important to adjust the flow rate of each component with precision in order to obtain the exact ratio in weight and therefore the targeted stoichiometry.
When the three-way valves open, the components are flowing into a mixing chamber and are mixed via a dynamic mixing turbine rotating at high speed and able to mix the components without introducing air. The liquid reactive mixture is then dispensed freely into the mold open-cavity or could be injected through a hose connected to the bottom of a closed mold generating then a backpressure in general below 10 bars.
In addition, pumps have internal leakages, which could be more or less severe depending upon their quality, the viscosity of pumped product and their working pressure and rotation speed. For a given viscosity, the flow rate is not linear and depends on the pressure and speed. In order to obtain an accurate and consistent flow of each of the components, a classical technique is widely used and based on manually weighing each of the components at determined time(s) to determine the mass flow rate and adjust the pumps speed. This technique is known as “calibration method” or “external calibration”, as the amount of each of the components is withdrawn out of the machine. The limitation is when the machine is supposed to dispense various sets of ratios at various outputs of the mixture obtained in a mold or in a container, with the creation of various backpressure level depending upon the geometry and molding method used. It would be much too long to perform a calibration point for each set of parameters.
The calibration method is often manual. A theoretical working pressure for each component is set and the operator is weighing in general at two different times the dispensed product for each component at an average speed or at the speed of one of the formulation and then is keying the resulting weights onto the machine via a man-machine interface. When the machine is dispensing multiple ratios, outputs with different working pressures, it is considered as an approximation that the deviation of the pumps is constant. The appropriate setting of the machine is entirely depending upon the operator, its care about the weighing operation and the scale precision. Improved apparatus using a scale linked to the machine have been proposed but the weighting operations remain done by an operator, component per component.
An alternative technology can be used, in particular when no efficient pressure control is available, said technology consists to equip each of the component circuits with a flow meter, either volumetric flowmeter or mass flowmeter in order to avoid frequent calibration and to automatically adjust the machine output during casting. Mass flow meters are often preferred as they are more robust but this technology is expensive.
Based on the above, the aim of the invention is to provide a manufacturing method implemented automatically with an accurate precision particularly in metering step without manual operations, without being expensive.
For this purpose, the object of the invention is a manufacturing method of a thermoset polymer comprising at least two components, said manufacturing method comprising at least the following steps:
Thanks to this manufacturing method and the dispensing machine of the invention, the metering step and particularly the calibration of mass flow is completely implemented automatically. Moreover, said dispensing machine of the invention guarantees a reliable calibration, free of operational or input error and is saving operator time.
According to a feature of the invention, the initial parameters can be pump speed and/or pump working pressure.
According to a feature of the invention, the calibration step can be implemented for several measuring points, preferentially for three to eight measuring points, distributed regularly or irregularly relative to the pump speed range and/or the pump working pressure. Advantageously, for each measuring point, a correction factor linked to the chosen pump speed is determined by step d) and recorded in the control unit by recording means such as a memory integrated in the control unit.
According to a feature of the invention, each measuring point is configured to cover in an optimized manner the full pump speed range and pressure range.
According to a feature of the invention, the steps a) to e) are implemented consecutively.
According to a feature of the invention, the measuring points are only different pump speeds as the pressure is no longer an initial parameter thanks to the use of a dynamic pressure regulator on each inlet. So, the measuring points are only implemented for various pump speeds as the pump working pressure is preferably controlled via a dynamic pressure regulator, which is able to maintain a constant pressure level independently of the pressure generated downstream the mixing head by the process.
According to a feature of the invention, the control unit comprises a memory configured to record history of calibration steps. This feature allows quality assurance, production trouble shooting and maintenance analysis. Advantageously, the manufacturing method comprises a step g) wherein the memory of the control unit records history of final relation data for each measuring points of each component.
According to a feature of the invention, the manufacturing method comprises a step h) wherein the control unit uses the records of history of final relation data and a step i) wherein the control unit suggests indications for calibration adjustments and/or pressure adjustments depending upon records used in step h). This feature allows helping the operator to follow a rigorous process and providing an accurate and reliable process.
According to a feature of the invention, the calibration adjustments can be an evaluation of the implementing frequency of the calibration step. For example, for a determined period if the calibration step is not implemented, the control unit suggests implementing said calibration step, in order to work with accurate parameters. Advantageously, the operator can set a frequency of implementation of the calibration step.
According to a feature of the invention, the dispensing machine and the control unit are destined to dispense multiple formulations, multiple outputs with different back pressures generated by the molds.
It is another object of this invention to provide a dispensing machine for example a low-pressure metering and mixing machine, the dispensing machine being configured to manufacture thermoset polymers based on at least two different components, the dispensing machine comprising at least:
Thanks to this dispensing machine with integrated weighting device, it is possible to collect accurate and reliable weighting value since the weighting device is connected directly to the control unit which collects weighting value relative to the mass of a weighted volume of component without call on the operator.
According to a feature of the invention, the dispensing machine of the invention is allowing implementing the manufacturing method of the invention.
According to a feature of the invention, the dispensing machine comprises a dynamic pressure regulator. The calibration processing combined with the dynamic pressure control is allowing eliminating the influence of pressure created by molding, on the pump, therefore it is possible to calibrate pump depending upon the speed in order to dispense multi-formulation, various outputs and castings methods with an outstanding precision. Thanks to the dynamic pressure regulator, only the pump speed remains in the set of parameters.
According to a feature of the invention, the dynamic pressure regulator of the dispensing machine is able to maintain a constant pressure level independently of the pressure generated downstream the mixing head by the process.
According to a feature of the invention, the dynamic pressure regulator is configured to restrict the material flow with a mobile piston having an adjustable force or biasing member such that any increase of pressure downstream will increase the restricted area such that the total pressure upstream will stay approximately constant. The dynamic pressure regulator allows the operator to add an extra working pressure larger than what he may need during various casting operations and such that any additional backpressure downstream will make the regulator to self-adjust, keeping a constant upstream working pressure for the pump. Then it is therefore possible to set the pressure to a defined sufficient level for each component, and then make a careful external calibration and corresponding output adjustment. The machine will then accurately deliver a consistent output of each component during the working period, keeping on ratio, whatever the casting method and the backpressure are.
According to a feature of the invention, the weighting device comprises an arm supporting at one extremity a weighting sensor.
According to a feature of the invention, when a container is positioned on the weighting sensor, the presence of said container is detected and the control unit receives such information to start the calibration step.
The invention will be better-understood thanks to the detailed specification hereinafter, which describes an embodiment of the invention as example and based on the following figures.
The dispensing machine 100 of the invention illustrated in
According to the invention and as illustrated in
According to the invention, the dispensing machine 100 comprises a slidably integrated weighting device 106. The weighting device 106 comprises an arm 106a at one extremity of which, a weighting sensor 106b is arranged. The weighting device 106 is configured to be movable from at least an inactive position (illustrated in dotted line in
The control unit 101 is configured to control all the elements of the dispensing machine 100 such as the mixing head 103 and his inlets preferably equipped with dynamic pressure regulator 103a, the pump 104, the weighting device 106, the mixing chamber 105, the man-machine interface 102.
In order to manufacture a thermoset polymer, the dispensing machine 100 implements a manufacturing method, which will be described above. First, the operator needs to select or enter the components to be calibrated. This selection or this entry can be implemented in the control unit 100 via the man-machine interface 102. Then, if the inlet 103a are preferably equipped with dynamic pressure regulator the operator can adjust a working pressure above the back pressure needed for the casting process.
Then, the control unit 101, engages a calibration step calibration for each component. In order to do this, the control unit orders to the weighting device 106 to move into an active position or the operator move the weighting device 106 in an active position. Once the weighting device 106 in an active position, the control unit 101 orders to the mixing head 103 to pour a test-quantity of component determined by initial parameters in a container 1 arranged on a weighting device 106 of the dispensing machine 100, in order to obtain an actual volume of component, as seen in
The test-quantity of component is poured and the weighting device 106 weights the actual volume of said test-quantity of component. The weighting device 106 sends the weight information to the control unit 101.
The control unit 101 compares the actual mass of the actual volume with a theoretical mass determined from the initial parameters by using initial relation data between output flow rate and pump speed. The initial relation data is illustrated in
Then, the control unit 101 determines a correction factor at a determined pump speed for the calibration, in the graph it is at 30% of full pump speed, corresponding to the deviation, on the graph 2%.
As the deviation is not constant and may change with pump speed, for better results, the calibration step is implemented for several measuring points defined by a set of different pump speeds. In a preferred embodiment, if the pressure of each component is stable thanks to the dynamic pressure regulator, it is not necessary to perform calibration points at different pressures. Only the pump speed parameter is enough to get all necessary correction factors. For each zone of the pump speed range, the control unit will be able to meter the component taking into account the appropriate correction factor to deliver the mass flow rate and the amount of product according to the formulation of the component.
When all measuring points of a component is calibrated, depending upon the operator's choice the control unit may engages the same calibration procedure for the other(s) component(s).
Then, the control unit orders to at least one conveying member to convey each component in a mixing chamber 105 of the dispensing machine 100 and to a mixing element of the mixing chamber 105 to mix the components metered. Finally, the mixture obtained is dispensed or injected in a mold or in a container.
The invention is applicable to any low pressure metering and mixing machine, in the example of a three or four component machine which can process a wide range of formulations at different outputs and with different back pressures generated by the molds, if the machine is equipped with the dynamic pressure regulators, the invention is giving a novel, simple (only 3 to 8 measuring points) and automatic way of the calibration with a superior accuracy versus traditional methods.
Obviously, the invention is not limited to the embodiments described and represented with the annexed drawings. Modifications remain possible, in particular from the point of view of the constitution of the each element or by substitution of technical equivalents, without leaving for all that the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18305631.6 | May 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/062960 | 5/20/2019 | WO | 00 |
