EQUIPMENT FOR MANUFACTURING PARTS MADE FROM FOAM BEADS

Abstract

The description refers to equipment for manufacturing parts made from foam, which includes a molding unit with a limited molding space, in which, adjacent to the molding space, at least two capacitor plates are arranged in connection with a radiation source for electromagnetic radiation, where the radiation source for electromagnetic radiation is designed to emit electromagnetic radiation; and in which the molding unit is formed from at least two half-molds, in which at least one of the two half-molds is made of conductive material and forms one of the two capacitor plates.

Description

[0001] Device for manufacturing a particle foam part

[0002] The present invention relates to a device for producing a particle foam part. WO 2013 / 05081 AI discloses a method for producing particle foam parts in which a mixture of foam particles and dielectric transfer fluid is heated by means of electromagnetic waves to fuse the foam particles into a particle foam part. Radio waves or microwaves are used as electromagnetic waves. The material of the foam particles is polypropylene (PP).

[0003] US Patent 3,060,513 describes a process for sintering moist thermoplastic foam particles. The particles are dielectrically heated and simultaneously compressed in the mold. Electromagnetic waves at a frequency of approximately 2 to 1000 MHz are applied.

[0004] A similar process is described in US 3,242,238, in which foam particles are moistened with an aqueous solution and exposed to an electromagnetic field with a frequency of about 5 to 100 MHz.

[0005] In GB 1,403,326 a method for welding expandable polystyrene foam particles is described in which the particles are moistened with an aqueous solution and exposed to an electromagnetic field of 5 to 2000 MHz.

[0006] WO 01 / 64414 AI describes another process in which polymer particles made of polyolefins, wetted with a liquid medium, are heated with electromagnetic waves, in particular microwaves. The temperature in the mold is controlled by adjusting the pressure within it.

[0007] In the processes described above, moist foam particles are heated with electromagnetic waves, whereby the electromagnetic energy is absorbed by the liquid and transferred to the particles.

[0008] US patent 5,128,073 describes thermoplastic particles coated with a high-frequency energy-absorbing material. These particles can be heated with electromagnetic waves, whereby the coating releases the electromagnetic energy and transfers it to the foam particles. Electromagnetic waves in the range of 40 MHz to 2450 MHz are used to weld the foam particles together.

[0009] These processes have been known for decades. Nevertheless, they have not caught on in practice. There are various reasons for this. These processes work very well with laboratory samples. However, the transition to industrial production has not yet been successful. A key reason for this is that the heat cannot be introduced uniformly into the foam particles. This results in an uneven welding process within the particle foam component.

[0010] In practice, foam particles are therefore almost exclusively welded using saturated dry steam, as described, for example, in WO 2014 / 128214 AI. Welding using electromagnetic waves has never gained widespread acceptance in practice compared to steam welding, even though electromagnetic wave welding offers significant advantages in principle. With electromagnetic waves, energy could be transferred much more precisely, eliminating the need to heat auxiliary components. When using steam, it must first be generated in a steam generator. The steam then has to be supplied to the tool via pipes. All these components must be heated to a sufficiently high temperature to prevent condensation, resulting in considerable heat loss.Furthermore, the steam generation and piping systems occupy most of the installation space in the device for manufacturing the particle foam part. If steam were not required to weld the foam particles, the entire device could be designed to be significantly more compact.

[0011] The invention is based on the objective of providing a device for manufacturing a particle foam part with which expandable thermoplastic foam particles can be efficiently and reliably welded. This objective is achieved by the subject matter of the independent claims. Advantageous embodiments are specified in the respective dependent claims.

[0012] A device for producing a particle foam part according to a first aspect of the present invention comprises

[0013] - a molding tool that delimits a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, and - the molding tool is configured to consist of at least two mold halves, wherein

[0014] at least one of the two mold halves is made of an electrically conductive material and forms one of the capacitor plates.

[0015] Because one half of the mold is made of an electrically conductive material and forms one of the capacitor plates, this capacitor plate is located in close proximity to the mold cavity. This minimizes losses and limits the electrical power required for welding foam particles. The electrically conductive material is preferably a metal, in particular aluminum, copper, or a suitable alloy. The mold half is contoured to match the mold cavity. Such an electrically conductive mold half can differ from conventional capacitor plates in its contouring. Conventional capacitor plates are flat.

[0016] Alternatively, both mold halves can be made of an electrically conductive material and each form one of the capacitor plates, with an insulating layer being arranged at least in the area where the two mold halves touch to electrically insulate the two mold halves.

[0017] Preferably, at least one electrically conductive mold half is provided with a plastic layer on its side that defines the mold cavity. Preferably, the plastic layer has a maximum thickness of 1 cm. The plastic layer is preferably made of a material that is not transparent to electromagnetic radiation. The material is preferably selected such that it has a similar electrical loss factor to that of the foam particles to be welded to the mold. This ensures uniform heating throughout the entire mold cavity, as the foam particles and the plastic layer that defines the foam particles heat up uniformly due to the electromagnetic radiation. A filling injector can be coupled to the at least one electrically conductive mold half. Such a filling injector is generally made of an electrically conductive metal.The electrically conductive mold half connected to the filling injector is then preferably electrically connected to ground together with the filling injector. A device for producing a particle foam part according to a further aspect of the present invention is also included.

[0018] - a molding tool that delimits a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, and

[0019] - the molding tool is formed from at least two mold halves, one of which has a through-opening for the supply of foam particles and / or a through-opening for the escape of air, the through-opening being covered by the other mold half when the molding tool is closed.

[0020] By covering the through-opening with the other mold half, it is unnecessary to provide a closing mechanism at the through-opening, as this opening is covered and thus sealed by the other mold half when the mold is closed. A filling injector can be connected to this through-opening, which differs from conventional filling injectors in that it does not have a closing mechanism to seal the opening leading into the mold cavity. This allows the filling injector to be designed much more simply than in conventional devices for producing particle foam parts. The through-opening, or...The through-holes are preferably arranged on a section of the mold half that is covered by the other mold half when the mold is closed and exposed when the mold is partially open. In this partially open state, the two mold halves still interlock, forming an enlarged mold cavity without any openings to the outside—except for the through-hole(s). In this partially open state, the mold cavity can be filled with foam particles that cannot escape due to the closed geometry of the mold cavity. This partially open state of the mold forms a so-called crack gap, which is why this state can also be referred to as the crack gap position of the mold.

[0021] The device for producing a particle foam part according to a further aspect of the present invention comprises

[0022] - a molding tool that delimits a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, and - the molding tool is configured to consist of at least two mold halves, wherein

[0023] - at least one of the mold halves is made of an electrically non-conductive material and has a degassing opening for air to escape, wherein the degassing opening is closed flush with the mold space by means of a degassing insert, wherein the degassing insert is made of an electrically non-conductive material or is arranged parallel to the capacitor plates.

[0024] The degassing insert can be a plate-shaped element with small holes that are permeable to air but not to the foam particles. The foam particles typically have a diameter of 3 to 5 mm when fed into the mold. Therefore, the holes in the degassing insert have a diameter of no more than 2 mm, and preferably no more than 1 mm. The degassing insert can be made of plastic. Such degassing inserts can be positioned at any point on the mold or on the mold half. However, the degassing insert can also be made of metal. For metallic degassing inserts, it is advantageous to position them approximately parallel to the condenser plates.Such a plate-shaped degassing insert, which is arranged approximately parallel to the capacitor plates, has little or no influence on the electric field generated by the capacitor plates, since the degassing insert extends approximately perpendicular to the field lines.

[0025] The degassing insert can also be made of sintered, porous material. It can be a sintered plastic, ceramic, or metal body. However, a sintered metal body has limited applicability due to its influence on the electric field lines.

[0026] The mold half can have several such degassing openings. A device for producing a particle foam part according to a further aspect of the present invention comprises

[0027] - a molding tool that defines a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which are connected to a source of electromagnetic radiation, wherein the source of electromagnetic radiation is configured to emit electromagnetic radiation, and

[0028] - that at least one of the mold halves is attached to one of the capacitor plates and that this capacitor plate is attached to a housing by means of several insulating bodies capable of withstanding pressure, wherein at least one of the insulating bodies is arranged on a rear side and another insulating body on a front side of the capacitor plate such that, both when opening and when closing the mold tool, the insulating bodies are subjected exclusively to pressure and not to tension.

[0029] Such insulating elements can generally withstand high pressure. However, they are very sensitive to tensile stress and can break easily. Particularly with large-volume molds, high compressive forces occur during closing and during the formation of the particle foam part, where the two mold halves are pressed together under high pressure, as well as considerable tensile forces when the mold is opened. This arrangement of the insulating elements ensures that they are not subjected to undue stress and reliably hold the capacitor plate in place over the long term.

[0030] Preferably, several insulating bodies are arranged between the capacitor plate and the housing to absorb the pressure forces that occur during closing and operation.

[0031] Preferably, at least one further insulating body is provided for holding one of the capacitor plates, this further insulating body extending in a direction transverse to the opening or closing direction of the forming tool. This insulating body transfers forces acting laterally on the capacitor plate to the housing.

[0032] At least one capacitor plate is electrically connected to the radiation source, and the radiation source is configured such that electromagnetic waves with an amplitude of at least 1 kV are present at the capacitor plate. Electromagnetic waves with an amplitude of at least 5 kV, at least 10 kV, or at least 20 kV can be present at the capacitor plate.

[0033] A device for producing a particle foam part according to a further aspect of the present invention comprises a molding tool that defines a molding chamber, wherein at least two capacitor plates are arranged adjacent to the molding chamber, which form a tool capacitor and are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, wherein

[0034] - a voltage measuring device is provided for measuring the electrical voltage applied to the tool capacitor, and the voltage measuring device is connected to a control device for regulating the electrical power based on the measured voltage.

[0035] The actual voltage drop across the capacitor allows for a very precise estimation of the heat input into the plastic, since electrical energy, and thus electrical power, is proportional to the square of the voltage. This enables simple and very precise control of the power supplied to the particle foam. Preferably, a voltage divider consisting of an isolation capacitor and a measuring capacitor is provided, forming a series circuit, with the series circuit connected in parallel to the tool capacitor. The voltage measuring device taps the voltage applied to the measuring capacitor. The capacitance of the isolation capacitor is preferably smaller than the capacitance of the measuring capacitor. In particular, the capacitance of the isolation capacitor is no greater than 1 / 100, preferably no greater than 1 / 1,000, and especially no greater than 1 / 10,000 of the capacitance of the measuring capacitor.This results in a voltage being applied to the measuring capacitor that is a predetermined fraction of the voltage applied to the tool capacitor. This fraction is determined by the ratio of the capacitances of the isolation capacitor and the measuring capacitor.

[0036] A diode is preferably connected in parallel to the measuring capacitor, which rectifies the voltage signal at the measuring capacitor.

[0037] The isolation capacitor preferably has a high dielectric strength and a low electrical capacitance. The isolation capacitor can be designed with insulating bodies for attaching one of the capacitor plates to a housing of the device, the insulating body being arranged between two capacitor plates of the isolation capacitor.

[0038] A device for producing a particle foam part according to a further aspect of the present invention comprises

[0039] - a forming tool that delimits a forming chamber, wherein at least two capacitor plates are arranged adjacent to the forming chamber, which are connected to a source of electromagnetic radiation, wherein the source of electromagnetic radiation is configured to emit electromagnetic radiation, and - the electromagnetic radiation source forms a generator resonant circuit and lines for guiding the electromagnetic waves together with the capacitor enclosing the forming chamber form a tool resonant circuit, wherein at least one of the two resonant circuits is tunable by changing an inductance or a capacitance, wherein a control device is provided which is configured such that the power supply from the generator resonant circuit to the tool resonant circuit is controlled by tuning the tunable resonant circuit.

[0040] If both resonant circuits have the same resonant frequency, then the maximum power is transferred from the generator resonant circuit to the tool resonant circuit. The greater the difference in resonant frequency, the lower the power transfer. Therefore, by changing the resonant frequency of one of the resonant circuits, the power transfer can be altered accordingly. The inductances of the two resonant circuits are primarily influenced by the lengths of the transmission lines used to carry the electromagnetic waves. These lines are typically coaxial cables or waveguides. By adding line segments of varying lengths, the inductance, and thus the resonant frequency, of a resonant circuit can be changed. A capacitor can also be included in the generator resonant circuit, and the distance between the capacitor plates can be varied to change the capacitance of the generator resonant circuit.Preferably, a motor is provided for adjusting the distance between the capacitor plates.

[0041] The maximum transmissible power ranges from 25 kW to 60 kW. This depends on the sizing of the generator and the cables connecting the generator resonant circuit to the tool resonant circuit.

[0042] A device for producing a particle foam part according to a further aspect of the present invention comprises a molding tool that defines a molding chamber, wherein at least two capacitor plates are arranged adjacent to the molding chamber, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, and

[0043] The mold has at least two mold halves, wherein at least one of the two mold halves of the mold is at least partially formed from a composite material comprising a plastic matrix material and bodies embedded in the matrix material, the embedded bodies being formed from a material that conducts heat better than the plastic matrix material. The embedded bodies are preferably particles or fibers that are completely embedded in the matrix material. The particles preferably have a maximum size of 3 mm, in particular a maximum size of 2 mm, or preferably a maximum size of 1 mm. The fibers preferably have a maximum length of 20 mm, in particular a maximum length of 10 mm, and preferably a maximum length of 5 mm.

[0044] The matrix material is preferably made of a non-electrically conductive plastic, such as an epoxy resin, in which the embedded bodies are completely encapsulated. If the embedded bodies and matrix material are separated from each other, the embedded bodies can be made of an electrically conductive material. If the embedded bodies are made of an electrically conductive material, it is advantageous, if they are fibers, to arrange them parallel to the adjacent capacitor plate. If, on the other hand, the embedded bodies are electrically non-conductive, their arrangement within the matrix material can be chosen arbitrarily.

[0045] The embedded materials are composed primarily of mineral substances, such as quartz sand, a ceramic material, aluminum oxide, aluminum nitride, glass granules, frits, silicon carbide, and / or magnesium oxide. The embedded materials can also be glass fibers or carbon fibers. Carbon fibers are generally electrically conductive, which is why they are preferably arranged parallel to the adjacent capacitor plate within the matrix material.

[0046] Magnesium oxide has a high heat capacity, which allows the mold to quickly absorb the heat introduced into the particle foam part during welding and to rapidly cool the particle foam part.

[0047] The composite material, consisting of the matrix material and the embedded bodies, is preferably made of materials that do not absorb RF radiation or absorb it only minimally. This composite material therefore does not affect RF radiation or only does so to a negligible extent. However, due to the highly thermally conductive embedded bodies, the composite material can quickly dissipate heat present in the mold cavity.

[0048] A mold half comprising such a composite material is preferably provided on its side bordering the mold cavity with a layer that absorbs RF radiation more strongly than the composite material. This heats the mold half in the area adjacent to the mold cavity when electromagnetic radiation is applied, thus ensuring that the foam particles within the mold cavity are heated uniformly. In particular, this layer exhibits a similar electrical loss factor to that of the foam particles to be welded to the molding tool.

[0049] The layer arranged on the side of the mold that defines the mold cavity is preferably a plastic layer. The plastic layer can be made, for example, of PET (polyethylene terephthalate), PEEK (polyetherketone), POM (polyoxymethylene), polyimide, and PMMA (polymethyl methacrylate).

[0050] The device for producing a particle foam part according to a further aspect of the present invention comprises

[0051] a molding tool that defines a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, and

[0052] The mold is formed from at least two mold halves, with at least one of the mold halves having areas on its side bordering the mold chamber that absorb electromagnetic radiation to varying degrees. When electromagnetic radiation is applied, the area with the higher absorption heats up to such an extent that the surface of the particle foam part being produced melts more in this area than in the rest of the mold. This area with the higher absorption can be shaped like a specific symbol, logo, or the like, so that this shape is imprinted on the finished particle foam part by melting its surface. This allows for marking of the particle foam part without the need for a separate process step.

[0053] The area of ​​the mold that absorbs electromagnetic radiation more strongly can, for example, be made of a material with a higher density than the rest of the area. Alternatively, or in combination, this area can also be made of a material with a greater thickness or of a different material that generally absorbs electromagnetic radiation better.

[0054] The device for producing a particle foam part according to a further aspect of the present invention comprises

[0055] a molding tool that defines a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which are connected to a source of electromagnetic radiation, wherein the source of electromagnetic radiation is designed to emit electromagnetic radiation, and the molding tool is provided with cooling fins.

[0056] By providing cooling fins, such a mold can be cooled more quickly, especially if a fan is used to direct a cooling airflow onto the mold.

[0057] Such a mold preferably has two mold halves which can be pressed together by means of a press to form the mold cavity, each mold half having a pressing surface against which the press can act. The cooling fins are formed on areas outside the respective pressing surface of the mold halves.

[0058] The aspects explained above can be implemented individually or in any combination.

[0059] For all the aspects explained above, it is true that the electromagnetic radiation can be RF radiation.

[0060] Furthermore, in all configurations, one of the two capacitor plates can be electrically connected to ground. The other capacitor plate is directly connected to the radiation source, with the radiation being supplied as electromagnetic waves relative to the ground of this capacitor plate.

[0061] Preferably, the voltage measurement described above is used in conjunction with the control of the power transmission by means of matching the generator resonant circuit and the tool resonant circuit, since the voltage is proportional to the matching of the two resonant circuits, i.e., when the resonant frequencies of the two resonant circuits are the same, the voltage is highest and decreases more as the resonant frequencies of the two resonant circuits differ.

[0062] A device for producing a particle foam part according to a further aspect of the invention comprises

[0063] - a molding tool that defines a molding chamber, wherein at least two capacitor plates are arranged adjacent to the molding chamber, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is designed to emit electromagnetic radiation, and - the device comprises several workstations between which several molding tools are transported in a circuit, wherein at least the following workstations are provided:

[0064] - a filling station where the mold is filled with foam particles, - a welding station where the foam particles in the mold are welded together using electromagnetic radiation,

[0065] - at least one or more cooling or stabilizing stations for cooling the welded particle foam part, and

[0066] - a demolding station.

[0067] Preferably, the transport device is designed in such a way that several mold tools are transported in a cycle.

[0068] The device can have a cooling area along the transport device, wherein the cooling area is designed to accommodate several mold tools simultaneously.

[0069] Since the mold is often made of plastic, which conducts heat poorly, it is advisable to allow the particle foam part to cool for an extended period after welding before demolding. With such a device, which recirculates the mold, the individual workstations, especially the welding station, can be optimally utilized. A welding process takes approximately 30 seconds to 2 minutes. The duration of the welding process depends on the size of the particle foam part being produced, the material of the particle foam part, and the power input. Compared to conventional devices for producing particle foam parts, in which the foam particles are welded exclusively with steam, the welding process is very short. Therefore, such a machine can be operated at a significantly higher cycle rate compared to conventional devices.The cooling process typically takes longer than with conventional molds made exclusively of highly thermally conductive metal. When using multiple molds simultaneously, they can be cooled at the stabilizing stations. Cooling can be achieved solely through ambient air or actively by supplying a gaseous or liquid coolant. Different cooling systems can be provided at the individual stabilizing stations.

[0070] Using the devices described above, a particle foam part can be produced by filling the mold cavity with foam particles and welding the foam particles together by applying electromagnetic radiation. The resulting particle foam part is then demolded.

[0071] The foam particles used here preferably consist of an expandable, thermoplastic material.

[0072] A method for producing a particle foam part according to a further aspect of the present invention comprises the steps

[0073] Filling a mold cavity with foam particles,

[0074] - Welding of the foam particles, especially by applying electromagnetic radiation,

[0075] Demolding

[0076] The mold has two mold halves, which are arranged in a crack gap position for filling the mold. In this position, the mold halves are slightly spaced apart from each other relative to a closed position and are pressed together with the foam particles contained within them before welding. This method is characterized by the fact that, during filling, the mold halves are spaced apart from each other to varying degrees relative to the closed position in certain areas, so that when pressed together, the mold halves are drawn together to different degrees in different areas.

[0077] This results in the foam particles in the mold cavity being compressed to varying degrees in different areas of the mold. This allows for different densities to be achieved when the mold is closed, or for density differences caused by varying thicknesses of the mold cavity to be equalized or compensated for. For example, if wedge-shaped foam particle bodies are produced with the mold, the resulting foam particle part is typically significantly thinner at the front than at the rear. If one mold half is pivoted around a pivot axis located transversely to the longitudinal extent of the mold at the thinner end to form the crack gap, then a roughly constant density of the foam particles can be achieved when the mold is pivoted back into the closed position.This applies to all products with an approximately wedge-shaped cross-section.

[0078] However, there are other products whose thickness varies in a different way. Here, it is advantageous to provide at least one mold half consisting of two or more separate parts that can be moved independently of each other to create a crack gap. This allows the individual areas of the different parts of the mold half to be compressed to varying degrees when pressed together, thus compressing the foam particles within to different degrees. This design can also be used to ensure that areas of varying thickness within the mold cavity are compressed as uniformly as possible, thereby achieving the most consistent heating and welding quality throughout the entire particle foam part.However, it can also be advantageous, if certain areas need to be heated more intensely, to compress these areas more strongly so that the foam particles within them absorb electromagnetic radiation more effectively due to their higher density. This allows for a predetermined, non-constant temperature profile to be set during the production of the foam particle parts.

[0079] The invention is explained in more detail below by way of example with reference to the drawing. The drawing schematically shows:

[0080] Figure 1 shows an embodiment of a device for producing a particle foam part, Figures 2a and 2b each show a mold in a partially open position (Figure 2a) and a closed position (Figure 2b) in a sectional view,

[0081] Figure 3 shows a mold suitable for the production of large-volume particle foam parts, such as insulation panels, in a sectional view.

[0082] Figure 4 shows an electromagnetic radiation generator forming a tunable resonant circuit, and the forming tool in an electrical circuit diagram.

[0083] Figure 5 shows a control device for regulating the power supply in a circuit diagram, and

[0084] Figure 6 shows an embodiment of a device for manufacturing a particle foam part in a perspective view. The basic structure of a device 1 for manufacturing a particle foam part is shown in Figure 1. This device 1 comprises a material container 2, a mold 3, and a line 4 leading from the material container 2 to the mold 3. The material container 2 serves to hold loose foam particles. The material container 2 has a base 5, which is connected in the base region to a compressed air source 7 via a compressed air line 6. The compressed air line 6 is connected to several nozzles (not shown) arranged in the base 5, so that several air streams (= fluidizing air) can be introduced into the material container 2, which swirl the foam particles contained therein and thereby separate them.

[0085] An opening is formed in the area of ​​the bottom 5 of the material container 2, to which the conveying line 4 is connected. The opening can be closed by means of a slide valve (not shown).

[0086] Adjacent to the material container, a drive nozzle 8 is located in the conveying line 4. The drive nozzle 8 is connected to the compressed air source 7 via another compressed air line 9. The compressed air supplied to this drive nozzle 8 serves as the driving air, as it enters the conveying line 4 through the drive nozzle 8 and flows towards the mold 3. This creates a vacuum at the drive nozzle 8 on the side facing the material container 2, which draws foam particles from the material container.

[0087] The conveying line 4 leads into a filling injector 10, which is coupled to the mold 3. The filling injector 10 is connected to the compressed air source 7 via a further compressed air line 11. The compressed air supplied to the filling injector 10 is used, on the one hand, to fill the mold 3 by imparting a flow of foam particles towards the mold 3. On the other hand, the compressed air supplied to the filling injector 10 can also be used to blow the foam particles back from the conveying line 4 into the material container 2 once the filling process at the mold 3 is complete.

[0088] The mold 3 consists of two mold halves 12 and 13. At least one mold chamber 14 is defined between the two mold halves, into which the filling injector 10 opens for introducing the foam particles. The volume of the mold chamber 14 can be reduced by moving the two mold halves 12 and 13 together. When the mold halves 12 and 13 are moved apart, a gap is formed between them, which is referred to as a crack gap. Therefore, such a mold 3 is also called a crack-gap mold. The device 1 does not have a steam generator or a steam supply to the mold chamber 14, as is common in conventional devices for manufacturing particle foam parts. Moisture can enter the mold chamber 14 due to residual moisture contained in the foam particle material and moisture contained in the compressed air.However, the device 1 can also be equipped with a steam generator and a steam supply to the molding chamber 14 and / or to the conveying line 4 in order to supply saturated dry steam to the molding chamber 14 for heating the foam particles and / or to wet the foam particles on their transport from the material container 2 to the molding chamber 14. The foam particles located in the material container 2 can also be wetted with liquid water, for which purpose corresponding nozzles are arranged in the material container 2 to atomize the water.

[0089] Each of the mold halves 12 and 13 has a capacitor plate 15, 16. These capacitor plates are each made of a highly electrically conductive material, such as copper or aluminum. The filling injector 10 is located on mold half 13. The filling injector 10 extends through a recess in the capacitor plate 16, which is mounted on mold half 13.

[0090] The capacitor plates 15, 16 are connected to a generator 18 via electrical lines 17 for the transmission of high-frequency voltages.

[0091] The mold halves 12, 13 each have a base body that can be made of an electrically non-conductive material, particularly one that is essentially transparent to electromagnetic RF radiation, such as polytetrafluoroethylene (PTFE), polyethylene, especially UHMWPE, or polyetherketone (PEEK). Only the capacitor plates 15, 16 are electrically conductive. The "essentially transparent material" is a material that can be penetrated by electromagnetic radiation, especially RF radiation. However, this material can be specifically designed with a certain absorption property for electromagnetic RF radiation in order to convert some of the RF radiation into heat and to heat the mold halves 12, 13. This will be explained in more detail below.

[0092] The mold can optionally be connected to a vacuum pump 19, so that a vacuum can be applied to the mold chamber 14. This vacuum causes any moisture contained in the mold chamber 14 to be drawn off.

[0093] The condenser plates 15, 16 are preferably equipped with a cooling device. In the present embodiment, the cooling device is formed by fans 20, which direct cooling air onto the side of the condenser plates 15, 16 facing away from the mold chamber 14. To increase the cooling effect, cooling fins 21 can be provided on the condenser plates 15, 16. Alternatively or additionally, cooling lines can also be arranged on the condenser plates 15, 16, through which a cooling medium is guided. A liquid, such as water or oil, is preferably used as the cooling medium.

[0094] The following describes a method for manufacturing particle foam parts using the device described above:

[0095] The process comprises the following basic steps:

[0096] Filling the mold space 14

[0097] - Welding of the foam particles

[0098] Stabilize (optional)

[0099] demolding

[0100] Cleaning the tool (optional): To fill the mold chamber 14, air is blown into the bottom 5 of the material container via the compressed air line 6 to swirl and separate the foam particles contained therein. Simultaneously, motive air is also supplied to the drive nozzle, so that foam particles are drawn from the material container 2 into the conveying line 4 and transported by the motive air towards the mold 3. The mold chamber 14 is closed, with the mold halves 12 and 13 either fully closed or separated from each other by a crack gap.

[0101] The slide gate of material container 2 can be opened and closed sequentially. The opening and closing times are typically in the range of 500 ms to 1 s. This cyclical opening and closing of the slide gate intermittently feeds the foam particles from material container 2 to the conveying line 4. This breaks up any bridging of the foam particles within material container 2 and separates the foam particles. This is particularly advantageous for foam particles with an adhesive surface, such as eTPU foam particles.

[0102] Alternatively, intermittent suction can be achieved by intermittently supplying the motive air from the compressed air line 9 to the motive nozzle 8, which is located directly adjacent to the material container 2. The mold 12, 13 is equipped with at least one valve (not shown) which is open when foam particles are fed in, allowing the compressed air flowing into the mold chamber 14 to escape. This valve can be adjusted during filling of the mold chamber 14 such that a back pressure is created in the mold chamber 14. This allows the pressure in the conveying line and in the mold chamber 14 to be maintained, thus keeping the foam particles at a small volume. This enables more foam particles to be fed into the mold chamber 14 than would be possible without the application of the back pressure. After the back pressure is released, the foam particles expand in the mold chamber 14.

[0103] Another parameter for adjusting the fill quantity is the crack gap, i.e., the gap by which the two mold halves 12, 13 are spaced apart during filling. Using a crack gap during filling primarily increases the density in a thin area of ​​the particle foam part being produced.

[0104] As soon as it is determined that the mold chamber 14 is filled with foam particles, the filling injector 10 is closed. The foam particles in the line are blown back into the material container 2 by the compressed air supplied to the filling injector 10. The filling of the mold chamber 14 with foam particles is described in detail in German patent application DE 10 2014 117 332, and reference is made to this patent application in this regard.

[0105] After filling the mold cavity 14 with foam particles, these are heated by applying electromagnetic RF radiation. This RF radiation is generated by applying a high-frequency voltage of approximately 10 to the capacitor plates 15, 16. 4 V is applied at a frequency of 27.12 MHz.

[0106] The foam particles can be made from polyurethane (eTPU). Polyurethane has a dielectric loss factor D of 0.2 for electromagnetic radiation at a frequency of 1 MHz. In contrast, the dielectric loss factor of polypropylene (PP) for electromagnetic radiation at a frequency of 1 MHz is only 0.00035. The absorption capacity of polyurethane is therefore significantly higher than that of polypropylene. This makes it possible to introduce the heat required for welding the foam particles into the mold cavity 14 without additional heat-transferring materials, especially without aqueous solutions, since the foam particles themselves absorb the electromagnetic waves.Instead of polyurethane-based foam particles, expandable thermoplastic foam particles based on polyether block amide (ePEBA), polylactate (PLA), polyamide (ePA), polybutylene terephthalate (ePBT), polyester ether elastomer (eTPEE) or polyethylene terephthalate (ePET) can also be used.

[0107] These materials each possess functional groups (amide group, urethane group, or ester group) that induce a dipole moment. These functional groups are responsible for the molecules absorbing RF radiation. Therefore, other thermoplastic polymers that exhibit such dipole-moment-inducing functional groups are also suitable for RF welding.

[0108] Foam particles based on ePP (expandable polypropylene) or ePS (expandable polystyrene) can also be welded together to form particle foam parts. Since these materials absorb electromagnetic radiation only to a very limited extent, it is necessary to add a dielectric heat transfer medium, such as water. The foam particles can be wetted with the heat transfer medium in the material container 2 or during their transport from the material container 2 to the mold 3. Wetting in the line 4 has the advantage that the foam particles are wetted very uniformly and the heat transfer medium is evenly distributed in the mold chamber 14. This results in correspondingly uniform heating of the foam particles in the mold chamber 14.

[0109] The mold 3 can also be connected to a steam source (not shown) which supplies saturated dry steam to the mold chamber 14. This is advantageous when welding materials whose dielectric loss factor is temperature-dependent. Such materials include, for example, ePES (expandable polyethersulfone) or expandable polyamide. At low temperatures, the absorption of electromagnetic waves is low. Therefore, these foam particles are first heated by the steam and then, above a certain temperature, heated to even higher temperatures, either alone or additionally, by electromagnetic radiation. Alternatively, the foam particles can be wetted with a dielectric heat transfer medium, so that the dielectric heat transfer medium is heated by electromagnetic radiation to warm the foam particles to a predetermined temperature.Subsequently, the foam particles can be directly heated by electromagnetic radiation, as the absorption properties of electromagnetic radiation increase with rising temperature. The duration for which the electromagnetic RF radiation is applied depends on the volume of the mold cavity 14, the density of the foam particles, and the applied electrical power or voltage. Experiments have shown that, depending on the volume and the material from which the foam particles are formed, approximately 30 seconds to 2 minutes are required to reliably and completely weld the foam particles. An electrical voltage of 5 kV to 20 kV was applied during these tests.

[0110] Preferably, the temperature of the foam particles is measured during welding and the electrical power is regulated accordingly. The electrical power is preferably regulated such that the foam particles have a temperature slightly above their softening temperature. Instead of the temperature of the foam particles, another physical quantity related to the electrical power introduced into the mold cavity can also be measured. This could, for example, be the electrical voltage applied to the capacitor plates 15, 16.

[0111] The surface bounding the mold chamber 14 can be additionally heated. For this purpose, heating wires 34 can be arranged in the mold tool adjacent to the surface bounding the mold chamber 14. The heating wires 34 are connected to a power source 35, which supplies a heating current to the heating wires.

[0112] Instead of heating wires, fluid channels can also be provided in the mold halves 12, 13, through which a suitably tempered fluid flows. Preferably, the fluid is water or steam.

[0113] After the application of electromagnetic RF radiation, the mold chamber 14 is kept closed for a predetermined period, allowing the introduced heat to distribute evenly throughout the particle foam part and forming a very uniform weld between all foam particles. This process step is called stabilization. During stabilization, the particle foam part also cools slightly. Since the mold halves 12, 13 are made of a material that is essentially transparent to electromagnetic RF radiation, typically a plastic material with poor thermal conductivity, very little heat is dissipated to the outside when the mold chamber 14 is closed.

[0114] Mold halves 12, 13 made of plastic have the advantage over mold halves made of metal in that they provide significantly better thermal insulation and have a lower heat capacity. This allows the desired temperature cycles to be carried out much faster and with less energy, with the supplied heat being almost completely transferred to the foam particles.

[0115] During the stabilization process or part of the stabilization process, the condenser plates 15, 16 can be actively cooled by the cooling device 32, 33, thereby removing heat from the base bodies of the mold halves 12, 13 and thus also from the particle foam part.

[0116] After stabilization, the particle foam part is demolded by moving the two mold halves 12, 13 apart. The mold tool may be equipped with demolding plungers, which push the particle foam part out of one of the two mold halves 12, 13.

[0117] Stabilization is an optional process step. For certain materials and shapes, it can also be omitted. The larger the volume of the particle foam part to be produced, the more advantageous it is to stabilize the particle foam part in the mold after welding.

[0118] To increase throughput, electromagnetic RF radiation can be applied during filling and / or during the closing of a crack gap.

[0119] The electromagnetic radiation, in particular the RF radiation, can be applied during or even after filling the mold cavity 14 with foam particles, initially with low electrical power or low electrical voltage, in order to preheat the material to a certain temperature, and then the electrical power or electrical voltage can be gradually or suddenly increased.

[0120] It can also be advantageous to gradually increase the power or voltage of the electromagnetic RF radiation, so that a ramp is achieved over a period of, for example, 30 seconds to 3 minutes by gradually increasing the electrical power or voltage of the electromagnetic RF radiation. This results in very uniform heating of the foam particles.

[0121] Optionally, a negative pressure and / or vacuum can also be applied to the mold chamber 14. This is advantageous if the foam particles and / or the supplied compressed air contain a certain amount of moisture. The process described above is a dry process compared to welding with steam alone. As a result, the manufactured particle foam parts are dry or drier after the production process and can be processed more quickly in subsequent steps. It can also be advantageous to demold the warm particle foam parts and immediately process them further. This can lead to significant efficiency gains in production, as the intervals between individual process steps can be shortened, and the heat used to weld the foam particles can be at least partially utilized for subsequent process steps.

[0122] A forming tool 3 (Figure 2a, Figure 2b) is described below, which has a first mold half 12 and a second mold half 13 and can be used in the device 1 described above. For the sake of simplicity, moving devices, retaining elements, thermometers for measuring the temperature in the mold chamber, and other mechanical parts for opening and closing the tool have been omitted from Figures 2a and 2b.

[0123] The forming tool 3 is formed from two mold halves 12, 13, each of which has a base body 24, 25 made of an electrically conductive material. These base bodies consist, for example, of aluminum, copper, or a highly conductive alloy.

[0124] The two mold halves 12, 13 define a mold space 14 by means of an inner boundary surface 26, 27. The inner boundary surfaces 26, 27 of the two mold halves 12, 13 are provided with an electrically insulating coating 28, 29.

[0125] The electrically insulating coatings can be made of a material that is essentially transparent to electromagnetic radiation, especially RF radiation, such as PTFE, PE, or PEEK. However, they can also be made of a plastic material that exhibits a similar dielectric loss factor under the applied electromagnetic radiation as the plastic material to be processed in the mold cavity 14, in order to achieve uniform heating across the entire mold cavity 14 and at its edges when the electromagnetic radiation is applied. For this purpose, the coating 28, 29 is preferably made of a material with a moderate loss factor, such as PET (polyethylene terephthalate), PEEK (polyetherketone), POM (polyoxymethylene), polyimide, and PMMA (polymethyl methacrylate).These coatings 28, 29 are therefore essentially transparent to RF radiation, since they absorb only a small fraction of the electromagnetic radiation and, due to the relatively low loss factor, can be formed with a certain thickness of, for example, at least 2 mm, in particular at least 2.5 mm or at least 5 mm. The coating is preferably not thicker than 20 mm, in particular not thicker than 15 mm, and preferably not thicker than 10 mm, so that the fraction of the energy of the electromagnetic waves absorbed by the coating is small.

[0126] The electrically conductive base bodies 24, 25 form the capacitor plates of the mold 3. They therefore have an electrical connection to allow connection to the generator 18 or to ground 30. The generator 18 is a radiation source for generating electromagnetic radiation. Preferably, the generator is designed to generate RF radiation. The generator can also be designed to generate microwave radiation, whereby, in larger mold cavities 14, RF radiation allows for significantly more uniform heating than microwave radiation. Furthermore, most plastic materials absorb RF radiation much better than microwave radiation. Therefore, the use of RF radiation is preferred.

[0127] Because the mold halves 12, 13 both define the mold cavity 14 and simultaneously form the capacitor plates, the distance between the "capacitor plates" and the mold cavity 14 is very small and is determined solely by the electrically insulating coatings 28, 29. This results in very low losses of electromagnetic radiation, which in turn allows a very high proportion of the power to be transferred as heat into the foam particles being welded. Such a tool thus enables very efficient welding of the foam particles into a single foam particle.

[0128] In the present embodiment of the mold 3, the first mold half 12 has a bottom wall 31 and a circumferential side wall 32. In this embodiment, both the bottom wall 31 and the side wall 32 are formed from the electrically conductive base body 24 and the internally arranged coating 28. It is also possible for the side wall 32 to be formed solely from a non-electrically conductive material, in particular plastic, or only partially formed by means of the electrically conductive base body 24. The second mold half 13 forms a punch that can move into the cavity formed by the first mold half 12 and thus tightly seals the mold chamber 14. The tight seal between the two mold halves 12, 13 is at least tight enough to prevent foam particles contained therein from escaping. The mold chamber 14 is not necessarily gas-tight.

[0129] The two mold halves 12, 13 can be moved relative to each other by means of a press (not shown) and subjected to a predetermined force. A through-opening for feeding foam particles is arranged on the first mold half 12; this is referred to below as the filling opening 33. The filling injector 10 is connected to the filling opening 33. This filling injector 10 differs from conventional filling injectors in that it does not have a closing mechanism for closing the filling opening 33, as will be explained in more detail below.

[0130] The first mold half 12 has one or more passage openings for air to escape, which are hereinafter referred to as vent openings 34. The filling opening 33 and the vent openings 34 are arranged on a section or area, in particular an edge area, of the first mold half 12 that is concealed or covered by the second mold half 13 when the mold tool 3 (Figure 2b) is closed. This means that the filling opening 33 and the vent opening 34 are automatically closed when the mold tool 3 is closed by inserting the second mold tool 13 into the cavity formed by the first mold tool 12. Therefore, it is not necessary for the filling injector 10 to have a closing mechanism to close the filling opening 33.

[0131] This section or area is the area of ​​the first mold half 12 that is not covered by the second mold half 13; it is the area around which the mold halves are opened when moving apart into the crack gap position.

[0132] Preferably, the first mold half 12 is connected to ground 30. The filling injector 10 is coupled to the electrically conductive base body 24 of the first mold half 12, so that the filling injector 10 is also electrically connected to ground 30. The generator 18 generates electromagnetic waves or an alternating voltage relative to ground 30, which is applied to the base body 25 of the second mold half 13. This creates an alternating electromagnetic field, in particular RF radiation, in the mold chamber 14. With this design of the mold 3, it is important that the electrically conductive base bodies 24, 25 of the two mold halves 12, 13 are electrically insulated from each other. In the present embodiment, this is achieved by means of the coatings 28, 29. Preferably, the inner boundary surface 26, 27 of one of the two mold halves 12, 13 is contoured.In the context of the present invention, "contoured" means any shape that deviates from a flat boundary surface. In the present embodiment, the inner boundary surface 27 of the second mold half 13 is contoured. The inner boundary surface 26 of the first mold half 12 is not contoured in the area of ​​the bottom wall 31.

[0133] Such a forming tool 3 further differs from known forming tools for welding foam particles using electromagnetic waves in that the second forming tool 13 is designed like a punch and its electrical base body 25 is located at least partially within the cavity bounded by the first mold half 12, and thus the electrically conductive base body 25, which functions as a capacitor plate, is located very close to the mold space 14 or to the foam particles to be welded.

[0134] Another embodiment of the mold 3 is shown schematically in Figure 3. This mold 3 has two substantially flat capacitor plates 15, 16. One of the mold halves 12, 13 is attached to each of the capacitor plates 15, 16. As in the embodiment shown in Figure 1, the mold halves are made of a non-electrically conductive material. For details regarding the design of the mold halves 12, 13 and the materials from which they are made, reference is made to the explanations of the mold halves shown in Figure 1 to avoid repetition. This mold 3 has a housing 35 made of an electrically conductive material. The housing is preferably a metal housing.

[0135] The first capacitor plate 15 and the first mold half 12 are fixedly arranged in the housing. The second capacitor plate 16 and the second mold half 13 are coupled to a movement device, which in this embodiment is a hydraulic piston / cylinder unit 36. The movement unit can also be a pneumatic piston / cylinder unit or another actuator capable of providing the necessary force to hold the two mold halves 12, 13 together. The first mold half 12 is essentially plate-shaped, and the second mold half 13 has a bottom wall 37 and a circumferential side wall 38, thus defining a mold cavity open on one side. The second mold half 13 is provided with plungers 39, which can be inserted into the mold cavity to demold the molded part.Demolding occurs when, as the second mold half 13 is retracted by means of the piston / cylinder unit 36, the plungers 39 strike stop plates 40 and thus penetrate the mold cavity defined by the second mold half 13. The housing 35 has an opening 41a on its bottom, which can be closed by a horizontally movable door 41b. As the second mold half 13 is retracted, the door 41b opens, so that the demolded particle foam part falls out of the mold 3 through the open opening 41a and can be transported away by means of suitable conveying devices (not shown).

[0136] The second, movable capacitor plate 16 is electrically connected to ground 30 via the movement device and via the housing 35.

[0137] The first capacitor plate 15 is electrically connected to the generator 18 by means of suitable wave or coaxial conductors. The first capacitor plate 15 is fixedly connected to a rear wall of the housing 35 by means of several mechanical connections. Each mechanical connection has an insulating element 42. The mechanical connections and the insulating elements 42 extend approximately parallel to the direction of movement of the second mold half 13. In the present embodiment, the insulating element is made of ceramic. However, other good electrical insulating materials, such as glass, can also be used as the material for the insulating elements. The insulating elements 42 can withstand compressive loads. However, they are sensitive to lateral forces and tensile loads.On the rear side of the first capacitor plate 16, which is the side facing away from the mold half 12, there are a plurality of mechanical connections, each with one of the insulating bodies 42, between the capacitor plate 15 and the rear wall of the housing 35. These mechanical connections are preferably arranged in a regular grid so that they can absorb a high compressive force, distributed across the individual mechanical connections or across the individual insulating bodies 42, and transmit it to the housing 35.

[0138] Furthermore, on the front side of the capacitor plate 15, i.e., on the side where the mold half 12 is located, several mechanical connections with additional insulating elements 43 are arranged at the edge. The insulating elements 43 are designed in the same way as the insulating elements 42. These mechanical connections extend between the edge of the capacitor plate 15 and supports 44 projecting inwards from the walls of the housing 35, so that these mechanical connections or insulating elements 43 also extend approximately parallel to the direction of movement of the second mold half 13. This allows the forces acting on the first mold half 12 or on the first capacitor plate 15 when the mold is opened to be transferred to the housing 35.

[0139] Furthermore, additional mechanical connections may be provided, which are formed transversely to the direction of movement of the second mold half 13 or the second capacitor plate 16, which in turn have insulating bodies 45 in order to be able to transfer forces acting on the first capacitor plate 15 during maintenance or assembly, which are not aligned parallel to the direction of movement of the second capacitor plate 16 or the second mold half 13, to the housing 35.

[0140] Because all mechanical connections between the first capacitor plate 15 and the housing 35 have an insulating element 42, 43, 45, the first capacitor plate 15 is completely electrically insulated from the housing 35. The insulating elements 42, 43, 45 preferably have a length of at least 5 cm, more preferably at least 8 cm, and most preferably at least 10 cm, so that a sufficiently large distance is maintained between the housing 35 and the first capacitor plate 15 to prevent voltage flashovers between the capacitor plate 15 and the housing 35.

[0141] Electrical voltages from 1 kV to several kV, or up to 10 kV or several tens of kV, can be applied to a capacitor plate arranged in this way. A mold 3 designed in this manner is suitable for transmitting power in the range of 10 kW to 60 kW to the foam particles located in the mold chamber. This allows large-volume particle foam parts to be reliably produced with very short cycle times of 30 seconds to 2 minutes.

[0142] Figure 4 schematically shows, in an electrical circuit diagram, the generator 18, the tool capacitor formed by the capacitor plates 15, 16, which encloses the mold halves 12, 13, and a transmission line (hollow waveguide or coaxial line) 46 suitable for transmitting electromagnetic waves, by which the electromagnetic waves are transmitted from the generator 18 to the tool capacitor 15, 16. Preferably, the hollow waveguide forming the transmission line 46 is designed as a coaxial air line with an electrically conductive inner tube and an electrically conductive outer tube. The coaxial air line is dimensioned such that high-voltage signals can be reliably transmitted. The characteristic impedance is preferably set to approximately 50 Ω.

[0143] In this line 46, a generator-side inductance 47 and a tool-side inductance 48 are symbolically shown. These inductances are caused by the line itself, with the length of the respective line segments determining the magnitude of the respective inductance. A tool-side capacitor 49 is connected in parallel to the tool capacitor 15, 16. This capacitor 49 represents the electrical capacitance between the capacitor plate 15 and the housing 35 of the forming tool 3. The tool capacitor 15, 16, the capacitor 49, and the tool-side inductance 48 form a tool resonant circuit 50. A generator-side capacitor 51 is connected in series with the generator 18 and the generator-side inductance. The generator-side capacitor 51 and the generator-side inductance 47 form a generator resonant circuit 52.At least the generator-side capacitor 51 or the generator-side inductor 47 is designed to be variable, for example, by using a capacitor with variable-distance capacitor plates or by providing conductor sections of varying lengths. It is also possible that both the generator-side capacitor 51 and the generator-side inductor 47 are designed to be variable. The generator-side capacitor 51 can be equipped with a servo motor, the actuation of which changes the distance between the two capacitor plates, for example, by moving one of the two capacitor plates in a straight line, with both capacitor plates always remaining parallel to each other, or by pivoting one of the two capacitor plates.

[0144] By changing the capacitance of capacitor 51 or the inductance 47, the resonant frequency of the generator resonant circuit 52 can be changed or tuned. If the resonant frequencies of the generator resonant circuit and the tool resonant circuit coincide, then the maximum electrical power is transferred from the generator 18 to the tool resonant circuit 50 and thus to the tool capacitor 15, 16. By changing the resonant frequency of the generator resonant circuit 52, the transfer of electrical power can be controlled in a targeted manner, whereby the greater the difference between the resonant frequencies of the two resonant circuits 50, 52, the lower the transferred power. Tuning the generator resonant circuit 52 can therefore be used to selectively adjust the electrical power introduced into the mold chamber 14. In the present embodiment, the resonant frequency of the generator resonant circuit 52 is changed.It is equally possible to change the resonant frequency of the tool's resonant circuit 50. This has the same effect on the transmission of electrical power. However, it is more difficult to provide a variable capacitor or variable inductor on the tool side than on the generator side.

[0145] Figure 5 shows a device for regulating the electrical power supplied to the tool capacitor 15, 16 in a schematically simplified circuit diagram. The generator 18 is connected to the tool capacitor 15, 16. A measuring capacitor 53 is connected in parallel to the tool capacitor 15, 16, the electrical capacitance of which is a fraction of the electrical capacitance of the tool capacitor 15, 16. The measuring capacitor 53 is connected via a coaxial cable 54 to a voltage measuring device (voltmeter) 55. Preferably, a diode 56 is connected in parallel with the measuring capacitor 53. The coaxial cable 54 is connected in series with an inductor 58, which serves to filter high-frequency signals.

[0146] The measuring unit, consisting of the measuring capacitor 53 and the diode 56, is separated from the tool capacitor 15, 16 by means of an isolating capacitor 59. The isolating capacitor has a high voltage rating. The capacitance of the isolating capacitor 59 is smaller than the capacitance of the measuring capacitor 53. As a result, a higher voltage drop occurs across the isolating capacitor than across the measuring capacitor 53. The ratio of the capacitance of the isolating capacitor 59 to the capacitance of the measuring capacitor 53 is preferably 1:100, 1:1,000, or 1:10,000. This reduces the voltage applied to the tool capacitor 15, 16 in the measuring unit 53, 56 to such an extent that it lies within a measuring range of the voltage measuring device 55 and can be reliably detected by it.

[0147] In this circuit, a voltage drop occurs across the measuring capacitor 53, which corresponds to the voltage applied to the tool capacitors 15, 16 and is reduced according to the ratio of the capacitance of the measuring capacitor 53 to the capacitance of the isolating capacitor 59. Due to the inclusion of the diode 56, only the half-waves of a specific polarity are present. The diode 56 thus rectifies the voltage across the measuring capacitor 53. This measuring voltage is measured by the voltage measuring device 55 and converted into a measurement signal. The measurement signal is forwarded to a control unit 57, which automatically controls the generator 18 to deliver a predetermined electrical power in order to generate a specific voltage across the tool capacitor or a specific measurement voltage across the measuring capacitor, which is a fraction of the voltage across the tool capacitor.

[0148] An embodiment of a device for manufacturing particle foam parts is described below with reference to Figure 6. This device 1 has several spatially separated workstations, which are connected to each other by a transport device 60. The transport device 60 can move several molds, each defining a molding chamber, between the individual workstations.

[0149] The transport device 60 has an upper transport section 61 and a lower transport section 62, along which the mold tools 3 are transported in different directions. The two transport sections 61, 62 are arranged parallel to each other, and at the ends of each transport section 61, 62 there is a lift device 63, 64, with which the mold tools can be moved between the transport levels downwards (lift device 63) or upwards (lift device 64). The two transport sections 61, 62 each have two narrow conveyor belts arranged parallel to each other, on which the mold tools 3 can be placed.

[0150] Along the upper transport section 61, in the conveying direction 65, a demolding station 66, an insertion station 67, a filling station 68, and a welding station 69 are arranged. The welding station comprises a press with a lower stationary plate at the level of the upper transport section 61 and an upper movable plate. A forming tool 3 can be positioned between each of the two plates (not shown) and pressed together by a press that actuates the two plates. The two plates are made of an electrically conductive material. The lower, stationary plate is connected to ground. The upper, movable plate is connected to an RF generator 18. The two plates thus form the capacitor plates 15, 16 described above, which accommodate the forming tool 3 between them.A cooling section 70 is provided on the lower transport section 62, where the molds heated at the welding station 69 and the particle foam parts contained therein can cool down. The cooling section 70 can cool the molds 3 solely with ambient air, can be equipped with a fan to supply the molds 3 with a cooling airflow, and / or can include a cold chamber cooled below room temperature by means of a chilled cooling medium to accelerate heat transfer from the mold 3. The cooling section 70 can accommodate several molds 3 simultaneously, since cooling or stabilizing the foam part within the mold is the longest step in the process.A mold storage system 71 is located on the lower transport section 62. This system is coupled to an automated storage unit for multiple molds, allowing different molds to be automatically coupled and uncoupled from the transport unit 60. The production of a particle foam part is completed in the demolding station 66, where the two-part mold is opened and the particle foam part produced within it is removed and dispensed.

[0151] The molds 3 have a locking mechanism 72 which securely closes the two mold halves of each mold when they are conveyed along the transport device 60. This locking mechanism 72 is automatically opened in the demolding station 66 to demold the particle foam parts, after which the two mold halves are reassembled and connected to each other by means of the locking mechanism 72. The locking mechanism connects the two mold halves so tightly that they do not separate during transport. The locking mechanism may have some play so that the two mold halves can be pulled apart slightly during filling to form a crack gap. The locking mechanism does not need to absorb the pressure generated in the mold cavity during welding. This pressure is dissipated via the press in the welding station 69.

[0152] The advantage of this device is that a very high throughput is possible with a single welding station, since welding a particle foam part typically takes no longer than 30 seconds to 2 minutes. The longest step is stabilizing and cooling the mold and the particle foam part within it. Because the cooling section can accommodate several molds simultaneously, multiple molds can be stabilized and cooled at the same time. This ensures that the processing of the molds in welding station 69 is not interrupted.

[0153] A further advantage of this device is that different tools, particularly those with different forming chambers, can be processed simultaneously in a circulating system. Preferably, each forming tool is equipped with its own machine-readable identification device. Such an identification device can be, for example, a barcode or an RFID chip. One or more corresponding readers for reading the identification device are arranged on the device along the transport unit 60, so that a control device (not shown) knows which tool is located at which workstation. This allows the individual tools to be handled independently. In particular, they can be subjected to electromagnetic waves of different voltage and / or duration at the welding station.The residence time in the cooling section and the cooling effect in the case of active cooling, for example by means of a fan, can also be individually controlled.

[0154] Compared to a conventional device for manufacturing particle foam parts, in which the foam particles are welded together using only hot steam, the present device is significantly more compact and much more flexible, as it can process several different molds simultaneously. Furthermore, energy can be introduced much more efficiently into the mold chamber using electromagnetic radiation.

[0155] It can also be advantageous to provide a water or steam supply line at the welding station, through which water and / or steam is supplied to the mold. This is particularly beneficial when welding foam particles that exhibit a low dielectric loss factor at low temperatures or generally. In such cases, a small amount of water or steam is supplied. The electromagnetic radiation heats the water to steam or further heats the steam. This heats the foam particles to a higher temperature, at which the dielectric loss factor is greater, causing them to absorb the electromagnetic radiation and heat up even further. It has been shown that a few hundred grams of water are sufficient for a mold chamber with a volume of 50 liters.If the foam particle material is, for example, ePS (expandable polystyrene), then 300 g or less of water is sufficient to heat and weld the foam particles in a mold chamber with a volume of 50 liters. With conventional welding, where the foam particles are heated solely with hot steam, quantities of steam equivalent to several kilograms of water are required for a mold chamber with a volume of 50 liters. Therefore, as a general rule, if foam particles that absorb electromagnetic radiation only minimally are to be welded, then a single addition of 300 g of water is sufficient for a mold chamber with a volume of 50 liters. For many materials that absorb electromagnetic radiation only minimally, even smaller quantities of water may suffice.For mold spaces with different volumes, the maximum required amount of water can be adjusted to the volume in the same proportion.

[0156] If water is heated in the mold chamber by means of electromagnetic radiation, it is advantageous to use a mold tool that has a pressure sensor with which the pressure in the mold chamber can be measured. This pressure is proportional to the temperature. The application of the electromagnetic radiation is then preferably regulated according to the measured pressure value, i.e., preferably set to a specific pressure value. With this device and the transport unit 60, the various aspects of the invention explained above, and in particular the different mold tools, can be used individually or in combination. List of reference numerals

[0157] 1 Device 40 38 Side wall

[0158] 2 material containers, 39 pestles

[0159] 3 forming tool 40 stop plate

[0160] 4 Line 41a Opening

[0161] 5 Floor 41b Door

[0162] 6 Compressed air line 45 42 Insulation body

[0163] 7 Compressed air source 43 Insulation body

[0164] 8 Drive nozzle 44 Holder

[0165] 9 Compressed air line 45 Insulation body

[0166] 10 Filling injector 46 Line

[0167] 11 Compressed air line 50 47 Generator-side inductance

[0168] 12 Mold half 48 Tool-side inductance

[0169] 13 Mold half 49 Tool-side capacitor

[0170] 14 Form space 50 Tool oscillation circle

[0171] 15 Capacitor plate 51 Generator-side capacitor

[0172] 16 Capacitor plate 55 52 Generator resonant circuit

[0173] 17 electrical line 53 measuring capacitor

[0174] 18 AC voltage source 54 Coaxial cable

[0175] 19 Vacuum pump 55 Voltmeter

[0176] 20 fan 56 diode

[0177] 21 Cooling fin 60 57 Control unit

[0178] 22 Heating wire 58 Inductance

[0179] 23 Power source 59 Isolation capacitor

[0180] 24 Base body 60 Transport device

[0181] 25 Base body 61 upper transport section

[0182] 26 inner boundary surface 65 62 lower transport route

[0183] 27 inner boundary surface 63 lift equipment

[0184] 28 Coating 64 Lift equipment

[0185] 29 Coating 65 Conveyor direction

[0186] 30 Mass 66 Demolding station

[0187] 31 Floor wall 70 67 Insertion station

[0188] 32 Side wall 68 Filling station

[0189] 33 Filling opening 69 Welding station

[0190] 34 Vent opening 70 Cooling section

[0191] 35 Housing 71 Mold storage system

[0192] 36 Piston / cylinder unit 75 72 Locking mechanism

[0193] 37 Floor wall

Claims

Patent claims Device for manufacturing a particle foam part, comprising a molding tool that delimits a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, and the molding tool is formed from at least two mold halves, wherein at least one of the two mold halves is made of an electrically conductive material and forms one of the capacitor plates. Device according to claim 1, characterized by that both mold halves are made of an electrically conductive material and each form one of the capacitor plates, wherein at least in the area where the two mold halves lie against each other an insulating layer is arranged for electrical insulation of the two mold halves. Device according to claim 1 or 2, characterized by that at least one electrically conductive mold half is provided with a plastic layer on its side that borders the mold space. Device according to claim 3, characterized by that the plastic layer has a maximum thickness of 1 cm. Device according to claim 3 or 4, characterized by that the plastic layer is made of a material that is not transparent to electromagnetic radiation. Device according to any one of claims 1 to 5, characterized by that a filling injector is coupled to at least one electrically conductive mold half, wherein the electrically conductive mold half and the filling injector are electrically connected to ground. Device for producing a particle foam part, in particular according to one of claims 1 to 6, comprising a molding tool that delimits a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, and the molding tool is formed from at least two mold halves, wherein One of the mold halves has a through-opening for the supply of foam particles and / or a through-opening for the escape of air, wherein the through-opening is covered by the other mold half when the mold tool is closed. Device according to claim 7, characterized by that no additional closing mechanism is provided for closing the opening for feeding foam particles and that it can only be closed by the other half of the mold. Device for manufacturing a particle foam part, in particular according to one of claims 1 to 8, comprising a molding tool that delimits a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, and the molding tool is formed from at least two mold halves, wherein at least one of the mold halves is made of an electrically non-conductive material and has a degassing opening for air to escape, wherein the degassing opening is closed flush with the mold space by means of a degassing insert, wherein the degassing insert is made of an electrically non-conductive material or is arranged approximately parallel to the capacitor plates.

10. Device according to claim 9, characterized by that the mold half has several such degassing openings.

11. Device for producing a particle foam part, in particular according to one of claims 1 to 8, comprising a forming tool that delimits a forming space, wherein at least two capacitor plates are arranged adjacent to the forming space, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, and that at least one of the mold halves is attached to one of the capacitor plates and that this capacitor plate is attached to a housing by means of several insulating bodies capable of withstanding pressure, wherein at least one of the insulating bodies is arranged on a rear side and another insulating body on a front side of the capacitor plate such that, both when opening and when closing the mold tool, the insulating bodies are subjected exclusively to pressure and not to tension. Device according to claim 11, characterized by that at least one further insulating body is provided for holding one of the capacitor plates, wherein this further insulating body extends in a direction transverse to the opening or closing direction of the forming tool.

13. Device according to claim 11 or 12, characterized by that at least one capacitor plate is electrically connected to the source of electromagnetic radiation and that the source of radiation is designed such that electromagnetic waves with an amplitude of at least 1 kV are present at the capacitor plate.

14. Device for producing a particle foam part, in particular according to one of claims 1 to 13, comprising a forming tool that delimits a forming space, wherein at least two capacitor plates (15, 16) are arranged adjacent to the forming space, which form a tool capacitor and are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, wherein a voltage measuring device (55) is provided for measuring the electrical voltage applied to the tool capacitor (15, 16), and the voltage measuring device (55) is connected to a control device (57) for regulating the electrical power based on the measured voltage.

15. Device according to claim 14, characterized by that a voltage divider is formed from an isolating capacitor (59) and a measuring capacitor (53), which form a series circuit and the series circuit is connected in parallel to the tool capacitor, wherein the voltage measuring device (55) taps off the voltage applied to the measuring capacitor.

16. Device according to claim 15, characterized by that a diode (56) is connected in parallel to the measuring capacitor (53).

17. Device for producing a particle foam part, in particular according to one of claims 1 to 16, comprising a molding tool that delimits a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, and the electromagnetic radiation source forms a generator resonant circuit and lines for guiding the electromagnetic waves together with the capacitor enclosing the mold space form a tool resonant circuit, wherein at least one of the two resonant circuits can be tuned by changing an inductance or a capacitance, wherein a control device is provided which is designed such that the power supply from the generator resonant circuit to the tool resonant circuit is controlled by tuning the tunable resonant circuit.

18. Device according to any one of claims 1 to 17, characterized by that the electromagnetic radiation is RF radiation.

19. Device according to any one of claims 1 to 18, characterized by that one of the two capacitor plates is electrically connected to ground.

20. Device for producing a particle foam part, in particular according to one of claims 1 to 19, comprising a molding tool that defines a molding chamber, wherein at least two capacitor plates are arranged adjacent to the molding chamber, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, and the molding tool is formed from at least two mold halves, wherein at least one of the mold halves of the molding tool is formed at least partially from a composite material comprising a matrix material made of plastic and bodies embedded in the matrix material, wherein the embedded bodies conduct heat better than the plastic matrix material.

21. Device according to claim 22, characterized by that the embedded bodies are particles or fibers.

22. Device according to claim 20 or 21, characterized by that the embedded bodies are formed from mineral substances such as quartz sand, a ceramic material, aluminum oxide, aluminum nitride, glass granules, frits, silicon carbide and / or magnesium oxide.

23. Device according to one of claims 20 to 22, characterized by that the mold half is provided on its side bordering the mold space with a layer that absorbs RF radiation more strongly than the composite material.

24. Device for producing a particle foam part, in particular according to one of claims 1 to 23, comprising a molding tool that delimits a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, and The molding tool is formed from at least two mold halves, wherein at least one of the mold halves of the molding tool has areas on its side bordering the mold space which absorb electromagnetic radiation to varying degrees, so that when electromagnetic radiation is applied, the area that absorbs more electromagnetic radiation heats up in such a way that a surface of a particle foam part to be produced is melted more strongly in this area than in the rest of the area.

25. Device for producing a particle foam part, in particular according to one of claims 1 to 24, comprising a molding tool that defines a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which are connected to a source of electromagnetic radiation, wherein the source of electromagnetic radiation is designed to emit electromagnetic radiation, and the molding tool is provided with cooling fins.

26. Device according to claim 25, characterized by that the mold tool has two mold halves which can be pressed together by means of a press to form the mold cavity, each mold half having a pressing surface on which the press can act, and cooling fins being formed on areas outside the respective pressing surface of the mold halves.

27. Device for producing a particle foam part, in particular according to one of claims 1 to 26, comprising a forming tool that delimits a forming space, wherein at least two capacitor plates are arranged adjacent to the forming space, which are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is configured to emit electromagnetic radiation, and The device comprises several workstations between which several mold tools are transported in a circuit by means of a transport device, wherein at least the following workstations are provided: - a filling station where the mold is filled with foam particles, - a welding station where the foam particles in the mold are welded together using electromagnetic radiation, - at least one or more cooling stations for cooling the welded part- foam parts, and - a demolding station.

28. Device according to claim 27, characterized by that the transport device is a transport device that moves the mold tools around in a cycle. Device according to claim 27 or 28, characterized by that a cooling area is provided along the transport device, whereby the cooling area can accommodate several mold tools simultaneously.

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