DEVICE FOR PRODUCING A PARTICULATED FOAM PART

Description

[0001] The present invention relates to a device for producing a particle foam part.

[0002] WO 2013 / 05081 A1, which discloses a device according to the preamble of claim 1, discloses a method for producing particle foam parts. A mixture of foam particles and dielectric transfer fluid is heated using electromagnetic waves to fuse the foam particles into a particle foam part. Radio waves or microwaves are used as the electromagnetic waves. The material of the foam particles is polypropylene (PP).

[0003] US Pat. No. 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 are applied at a frequency of approximately 2 to 1000 MHz.

[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 approximately 5 to 100 MHz.

[0005] GB 1,403,326 describes a process for welding expandable polystyrene foam particles, 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 A1 discloses another process in which polymer particles made of polyolefins, wetted with a liquid medium, are heated with electromagnetic waves, particularly microwaves. The temperature in the mold is regulated by controlling the pressure within it.

[0007] In the processes explained 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 Pat. No. 5,128,073 discloses thermoplastic particles coated with a material that absorbs high-frequency energy. These particles can be heated with electromagnetic waves, with the coating absorbing the electromagnetic energy and transferring it to the foam particles. Electromagnetic waves in the range of 40 MHz to 2450 MHz are used to weld the foam particles.

[0009] These processes have been known for decades. However, they have not been able to gain widespread acceptance in practice. There are various reasons for this. These processes work very well in laboratory samples. However, the transition to industrial production has not yet been successful. A key reason for this is that the heat cannot be distributed evenly into the foam particles. This prevents uniform welding within the particle foam part.

[0010] In practice, therefore, foam particles are almost exclusively welded using saturated dry steam, as known, for example, from WO 2014 / 128214 A1. Welding using electromagnetic waves has never been able to prevail in practice over welding with steam, even though welding with electromagnetic waves would have significant advantages in principle. With electromagnetic waves, the energy can be transferred much more precisely, making it unnecessary to heat auxiliary bodies. When using steam, it must first be generated in a steam generator. The steam must then be fed to the tool via pipes. All of these parts must be heated to a sufficiently high temperature so that the steam does not condense within them. This causes considerable heat loss.In addition, the steam generation and steam piping devices take up the most space in the device for producing the particle foam part. If steam weren't required to weld the foam particles, the entire device could be designed much more compactly.

[0011] The invention is based on the object of creating a device for producing a particle foam part with which expandable thermoplastic foam particles can be welded efficiently and reliably.

[0012] The problem is solved by the subject matter of the independent patent claim. Advantageous embodiments are specified in the respective subclaims.

[0013] An apparatus for producing a particle foam part according to a first aspect of the present invention comprises a mold which delimits a mold space, wherein at least two capacitor plates are arranged adjacent to the mold space and are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is designed to emit electromagnetic radiation, and the mold is formed from at least two mold halves, wherein at least one of the two mold halves is formed from an electrically conductive material and forms one of the capacitor plates.

[0014] Because one of the mold halves 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 to weld foam particles.

[0015] The electrically conductive material is preferably a metal, particularly aluminum, copper, or a corresponding alloy. The mold half is contoured to fit the mold cavity. Such an electrically conductive mold half can differ from conventional capacitor plates in its contouring. Conventional capacitor plates are flat.

[0016] Both mold halves can also be made of an electrically conductive material and each form one of the capacitor plates, wherein an insulating layer for electrically insulating the two mold halves is arranged at least in the area in which the two mold halves touch.

[0017] Preferably, the at least one electrically conductive mold half is provided with a plastic layer on its side bordering the mold cavity. The plastic layer preferably has a maximum thickness of 1 cm.

[0018] The plastic layer is preferably made of a material that is opaque to electromagnetic radiation. The material is preferably selected to have 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 surrounding the foam particles heat up evenly due to the electromagnetic radiation.

[0019] A filling injector can be coupled to the at least one electrically conductive mold half. Such a filling injector is typically 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.

[0020] An apparatus for producing a particle foam part according to a further aspect of the present invention comprises a mold which delimits a mold space, wherein at least two capacitor plates are arranged adjacent to the mold space and are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is designed to emit electromagnetic radiation, and the mold is designed from at least two mold halves, wherein one of the mold halves has a through opening for supplying 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 is in the closed state.

[0021] By covering the through-hole with the other mold half, it is not necessary to provide a closing mechanism at the through-hole, since this through-hole is covered and thus closed by the other mold half when the mold is closed. A filling injector can be connected to this through-hole. It differs from conventional filling injectors in that it does not have a closing mechanism for closing the opening leading into the mold cavity. This allows the filling injector to be designed much more simply than conventional devices for producing particle foam parts.

[0022] The through-opening(s) are preferably arranged on the mold half in a section which, when the mold is closed, is covered by the other mold half and is exposed when the mold is partially open. In this partially open state, the two mold halves of the mold still engage with each other and form an enlarged mold cavity with no openings to the outside, with the exception of the through-opening(s). In this partially open state of the mold, the mold cavity can be filled with foam particles which 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.

[0023] The device for producing a particle foam part according to a further aspect of the present invention comprises a mold which delimits a mold space, wherein at least two capacitor plates are arranged adjacent to the mold space and are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is designed to emit electromagnetic radiation, and the mold is formed from at least two mold halves, wherein at least one of the mold halves is formed from an electrically non-conductive material and has a venting opening for the escape of air, wherein the venting opening is closed off flush with the mold space by means of a venting insert, wherein the venting insert is formed from 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. The holes in the degassing insert are therefore designed with 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 arranged at any location on the mold or on the mold half. However, the degassing insert can also be made of metal. With metallic degassing inserts, it is advisable to use them at locations where they are arranged approximately parallel to the capacitor 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 transversely to the field lines.

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

[0026] The mold half can have several such venting openings.

[0027] An apparatus for producing a particle foam part according to a further aspect of the present invention comprises a mold which delimits a mold space, wherein at least two capacitor plates are arranged adjacent to the mold space and are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is designed to emit electromagnetic radiation, and in that one of the mold halves is fastened to at least one of the capacitor plates and this capacitor plate is fastened to a housing by means of a plurality of insulating bodies which can be subjected to pressure, wherein at least one of the insulating bodies is arranged on a rear side and a further insulating body is arranged on a front side of the capacitor plate in such a way that the insulating bodies are subjected exclusively to pressure and not to tensile stress both when the mold tool is opened and when it is closed.

[0028] Such insulating bodies can generally withstand high pressure. However, they are very sensitive to tension and can break easily. Especially with large-volume molds, high compressive forces occur during closing and during the production of the particle foam part, where the two mold halves are pressed together with high pressure, as well as considerable tensile forces when opening the mold. This arrangement of the insulating bodies ensures that they are not subjected to excessive stress and reliably hold the capacitor plate over time.

[0029] Preferably, several insulating bodies are arranged between the capacitor plate and the housing in order to absorb the compressive forces occurring during closing and operation.

[0030] Preferably, at least one further insulating body is provided for holding the one capacitor plate, wherein this further insulating body extends in a direction transverse to the opening or closing direction of the mold. This insulating body dissipates forces acting laterally on the capacitor plate to the housing.

[0031] The 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 applied to the capacitor plate. Electromagnetic waves with an amplitude of at least 5 kV, at least 10 kV, or at least 20 kV can be applied to the capacitor plate.

[0032] An apparatus for producing a particle foam part according to a further aspect of the present invention comprises a molding tool which delimits a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which capacitor plates form a tool capacitor and are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is designed to emit electromagnetic radiation, wherein 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 on the basis of the measured voltage.

[0033] The actual electrical voltage drop across the capacitor allows a very precise estimation of the heat input into the plastic, since the electrical energy and thus the electrical power is proportional to the square of the voltage. This allows the power supplied to the particle foam to be controlled very precisely in a simple manner. Preferably, a voltage divider consisting of an isolating capacitor and a measuring capacitor is provided, which form 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 isolating capacitor is preferably smaller than the capacitance of the measuring capacitor. In particular, the capacitance of the isolating capacitor is not greater than 1 / 100, preferably not greater than 1 / 1,000 and in particular not greater than 1 / 10,000 of the capacitance of the measuring capacitor.This creates a voltage across the measuring capacitor that is a predetermined fraction of the voltage across the tool capacitor. This fraction is determined by the ratio of the capacitances of the isolation capacitor and the measuring capacitor.

[0034] A diode is preferably connected in parallel to the measuring capacitor to rectify the voltage signal at the measuring capacitor.

[0035] The isolating capacitor preferably has a high dielectric strength and a low electrical capacitance. The isolating capacitor can be formed on insulating bodies for attaching one of the capacitor plates to a housing of the device, wherein the insulating body is arranged between two capacitor plates of the isolating capacitor.

[0036] An apparatus for producing a particle foam part according to a further aspect of the present invention comprises a molding tool which delimits a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space and are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is designed 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 molding space forms 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 designed such that the power supply from the generator resonant circuit to the tool resonant circuit is controlled by tuning the tunable resonant circuit.

[0037] If the two resonant circuits have the same resonant frequency, the maximum power is transferred from the generator resonant circuit to the tool resonant circuit. The greater the difference in resonant frequencies, the lower the power transfer. Thus, by changing the resonant frequency of one of the resonant circuits, the power transfer can be altered accordingly.

[0038] The inductances of the two resonant circuits are primarily influenced by the lengths of the cables used to transmit the electromagnetic waves. These cables are usually coaxial cables or waveguides. By connecting cable sections of different 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, where the distance between the capacitor plates can be varied to change the capacitance of the generator resonant circuit. A motor is preferably provided to adjust the distance between the capacitor plates.

[0039] The maximum transferable power ranges from 25 kW to 60 kW. This depends on the dimensioning of the generator and the cables connecting the generator resonant circuit to the tool resonant circuit.

[0040] A device for producing a particle foam part according to a further aspect of the present invention has a molding tool which delimits a molding space, wherein at least two capacitor plates which are connected to a radiation source for electromagnetic radiation are arranged adjacent to the molding space, wherein the radiation source for electromagnetic radiation is designed to emit electromagnetic radiation, and the molding tool has at least two mold halves, wherein at least one of the two mold halves of the molding tool is formed at least partially from a composite material which has a matrix material formed from plastic and bodies embedded in the matrix material, wherein the embedded bodies are formed from a material which conducts heat better than the matrix material made of plastic.

[0041] 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.

[0042] The matrix material is preferably made of a non-electrically conductive plastic, such as an epoxy resin, in which the embedded bodies are completely enclosed. If the embedded bodies plus the 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 expedient for the embedded bodies to be fibers and to arrange them parallel to the adjacent capacitor plate. If, however, the embedded bodies are electrically non-conductive, their arrangement in the matrix material can be chosen arbitrarily.

[0043] The embedded bodies are preferably made of mineral materials, such as quartz sand, a ceramic material, aluminum oxide, aluminum nitride, glass granules, frits, silicon carbide, and / or magnesium oxide. The embedded bodies 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 in the matrix material.

[0044] 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 quickly cool the particle foam part.

[0045] The composite material consisting of the matrix material and the embedded bodies is preferably made of materials that do not or only minimally absorb RF radiation. This composite material therefore has little or no influence on RF radiation. However, due to the highly thermally conductive embedded bodies, the composite material can quickly dissipate heat in the mold cavity.

[0046] A mold half comprising such a composite material is preferably provided with a layer on its side bordering the mold cavity 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, allowing the foam particles located therein to be heated evenly. In particular, this layer has a similar electrical loss factor to that of the foam particles to be welded to the molding tool.

[0047] The layer arranged on the side of the mold defining the mold cavity is preferably a plastic layer. The plastic layer can be made of, for example, PET (polyethylene terephthalate), PEEK (polyether ketone), POM (polyoxymethylene), polyimide, and PMMA (polymethyl methacrylate).

[0048] The device for producing a particle foam part according to a further aspect of the present invention comprises a molding tool which delimits a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space and are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is designed to emit electromagnetic radiation, and the molding tool is designed from at least two mold halves, wherein at least one of the mold halves of the molding tool is designed, on its side delimiting the molding space, with regions which absorb electromagnetic radiation to different degrees, so that when electromagnetic radiation is applied, the region which absorbs the more electromagnetic radiation is heated in such a way that in this region a surface of a particle foam part to be produced is melted more strongly than in the remaining region.This area, which absorbs more electromagnetic radiation, can be shaped like a specific symbol, logo, or the like, so that this shape is embossed into the finished particle foam part by melting the surface of the particle foam part. This allows a marking to be applied to the particle foam part without requiring a separate process step.

[0049] The area of ​​the mold that absorbs electromagnetic radiation more strongly can, for example, be formed from a material with a higher density than the rest of the area. Alternatively, or in combination, this area can also be formed from a material with a greater thickness or from another material that generally absorbs electromagnetic radiation better.

[0050] The device for producing a particle foam part according to a further aspect of the present invention comprises a molding tool which delimits a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space, which capacitor plates are connected to a radiation source for electromagnetic radiation, wherein the radiation source for electromagnetic radiation is designed to emit electromagnetic radiation, and the molding tool is provided with cooling fins.

[0051] By providing the cooling fins, such a mold can be cooled more quickly, especially if a fan is used to direct a cooling air stream onto the mold.

[0052] Such a mold preferably comprises two mold halves that can be pressed together by a press to form the mold cavity. Each mold half has a pressing surface against which the press can engage. The cooling fins are formed on the mold halves in areas outside the respective pressing surface.

[0053] The aspects explained above can be implemented individually or in any combination.

[0054] For all aspects explained above, the electromagnetic radiation can be RF radiation.

[0055] Furthermore, in all designs, 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 fed to this capacitor plate as electromagnetic waves relative to ground.

[0056] Preferably, the voltage measurement explained above is used in conjunction with the control of the power transmission by means of the adaptation of the generator resonant circuit and the tool resonant circuit, since the voltage is proportional to the adaptation of the two resonant circuits, i.e. when the resonant frequency of the two resonant circuits matches, the voltage is at its highest and decreases the more the resonant frequencies of the two resonant circuits differ.

[0057] An apparatus for producing a particle foam part according to a further aspect of the invention comprises a molding tool which delimits a molding space, wherein at least two capacitor plates are arranged adjacent to the molding space and 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 a plurality of work stations between which a plurality of molding tools are conveyed in a circuit, wherein at least the following work stations are provided: a filling station at which the molding tool is filled with foam particles, a welding station at which the foam particles located in the molding tool are welded by means of electromagnetic radiation, at least one or more cooling or stabilizing stations for cooling the welded particle foam part, and a demolding station.

[0058] Preferably, the transport device is designed such that several molding tools are transported in a circuit.

[0059] The device may have a cooling area along the transport device, wherein the cooling area is designed to accommodate a plurality of molding tools simultaneously.

[0060] Since the mold is often made of plastic, which is a poor heat conductor, it is advisable to allow the particle foam part to cool for a longer period after it has been welded before it can be demolded. With such a device, which circulates the mold, the individual work stations, 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 to be produced, the material of the particle foam part, and the power supplied. Compared to conventional devices for producing a particle foam part, in which the foam particles are welded exclusively with steam, the welding process is very short. Therefore, such a machine can operate at a significantly higher cycle rate than conventional devices.Only the cooling process generally takes longer than with conventional molds, which are made exclusively of heat-conducting metal. When multiple molds are used simultaneously, they can be cooled simultaneously at the stabilizing stations. Cooling can be achieved solely through the available ambient air or actively by adding a gaseous or liquid coolant. Different cooling devices can be provided at each stabilizing station.

[0061] Using the devices described above, a particle foam part can be produced. The mold cavity is filled with foam particles, and the foam particles therein are welded together by applying electromagnetic radiation. The resulting particle foam part is then demolded.

[0062] The foam particles used here are preferably made of an expandable, thermoplastic material.

[0063] A method for producing a particle foam part according to a further aspect of the present invention comprises the steps Filling a mold cavity with foam particles, welding the foam particles, in particular by applying electromagnetic radiation, demolding, The mold comprises 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 compared to a closed position, and are pressed together before welding with the foam particles contained therein. This process is characterized by the fact that, when filling the mold, the mold halves are spaced apart from each other by different distances in some areas compared to the closed position, so that when pressed together, the mold halves are moved closer together by different distances in some areas.

[0064] As a result, the foam particles in the mold cavity are compressed to different degrees in different areas of the mold. This makes it possible to achieve different densities when the mold is closed, or to equalize or compensate for density differences caused by different thicknesses of the mold cavity. If, for example, wedge-shaped foam particle bodies are produced using the mold, the resulting particle foam part is generally considerably thinner in a front area than in a rear area. If one mold half is pivoted about a pivot axis arranged transversely to the longitudinal extent of the mold at the thinner end of the mold to form the crack gap position, then an approximately constant density of the foam particles contained therein can be achieved when the mold is pivoted back into the closed position.This applies to all products with a roughly wedge-shaped cross-section.

[0065] However, there are also other products whose thickness varies in other ways. In these cases, it is advisable to provide at least one mold half consisting of two or more separate parts that can be moved independently of each other to form a crack gap position. This allows the individual sections of the different parts of the mold half to be moved together to different degrees when pressed together, thereby compressing the foam particles contained therein to different degrees.

[0066] This embodiment can also be used to compress areas of the mold cavity with different thicknesses as evenly as possible, in order to achieve the most uniform heating and weld quality possible throughout the entire particle foam part. However, if certain areas are to be heated more intensely, it may also be advantageous to apply greater compression in these areas, so that the foam particles located there absorb electromagnetic radiation more strongly due to their higher density. This allows a predetermined, non-constant temperature profile to be set during the production of the foam particle parts.

[0067] The invention is explained in more detail below using the drawing as an example. The drawing shows schematically: Figure 1 shows an embodiment of a device for producing a particle foam part, Figures 2a, 2b each show a mold in a partially open position ( Figure 2a ) and a closed position ( Figure 2b ) in a sectional view, Figure 3 shows a molding tool which is suitable for producing large-volume particle foam parts, such as insulation panels, in a sectional view, Figure 4 shows a generator for electromagnetic radiation which forms a tunable oscillating circuit, and the molding tool in an electrical circuit diagram, Figure 5 shows a control device for controlling the power supply in a circuit diagram, and Figure 6 shows an embodiment of an apparatus for producing a particle foam part in a perspective view.

[0068] The basic structure of a device 1 for producing a particle foam part is shown in Figure 1This device 1 comprises a material container 2, a mold 3, and a line 4 leading from the material container 2 to the mold 3.

[0069] The material container 2 serves to hold loose foam particles. The material container 2 has a base 5, and is connected to a compressed air source 7 in the base area 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 and thereby separate the foam particles contained therein.

[0070] In the area of ​​the bottom 5 of the material container 2, an opening is formed to which the conveying line 4 is connected. The opening can be closed by means of a slide (not shown).

[0071] Adjacent to the material container, a drive nozzle 8 is located in the feed 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 drive air, as it enters the feed line 4 through the drive nozzle 8 and flows toward the molding tool 3. This creates a negative pressure at the drive nozzle 8 on the side facing the material container 2, which draws foam particles from the material container.

[0072] The feed line 4 opens into a filling injector 10, which is coupled to the molding tool 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 molding tool 3 by forcing the flow of foam particles toward the molding tool 3 using the compressed air. 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 feed line 4 into the material container 2 once the filling process at the molding tool 3 is complete.

[0073] The mold 3 is formed from two mold halves 12, 13. At least one mold cavity 14 is defined between the two mold halves, into which the filling injector 10 for introducing the foam particles opens. The volume of the mold cavity 14 can be reduced by moving the two mold halves 12, 13 together. When the mold halves 12, 13 are moved apart, a gap is formed between the mold halves 12, 13, which is referred to as a crack gap. Therefore, such a mold 3 is also referred to as a crack-gap mold.

[0074] The device 1 can neither have a steam generator nor a steam supply to the molding chamber 14, as is usual with conventional devices for producing particle foam parts. Moisture can enter the molding chamber 14 through the residual moisture contained in the material of the foam particles and through the moisture contained in the compressed air. However, the device 1 can also be designed with a steam generator and a steam supply to the molding chamber 14 and / or to the conveyor line 4 in order to supply saturated dry steam to the molding chamber 14 for heating the foam particles and / or to wet foam particles during 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 water in liquid form, with corresponding nozzles being arranged in the material container 2 for this purpose, which atomize the water.

[0075] A capacitor plate 15, 16 is arranged on each of the mold halves 12, 13. These capacitor plates are each made of a highly electrically conductive material, such as copper or aluminum. The filling injector 10 is arranged on the mold half 13. The filling injector 10 extends through a recess in the capacitor plate 16, which is mounted on the mold half 13.

[0076] The capacitor plates 15, 16 are connected to a generator 18 via electrical lines 17 for transmitting high-frequency voltages.

[0077] The mold halves 12, 13 each have a base body, which can be made of an electrically non-conductive material that is essentially transparent to electromagnetic RF radiation, such as polytetrafluoroethylene (PTFE), polyethylene, especially UHMWPE, or polyether ketone (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 deliberately designed with a certain absorption property for electromagnetic RF radiation in order to convert a portion of the electrical RF radiation into heat and to heat the mold halves 12, 13. This will be explained in more detail below.

[0078] The mold can optionally be connected to a vacuum pump 19 so that a negative pressure or vacuum can be applied to the mold cavity 14. This negative pressure causes moisture contained in the mold cavity 14 to be removed.

[0079] The capacitor plates 15, 16 are preferably provided with a cooling device. In the present embodiment, the cooling device is formed by fans 20, which direct cooling air to the side of the capacitor plates 15, 16 facing away from the molding chamber 14. To increase the cooling effect, cooling fins 21 can be provided on the capacitor plates 15, 16.

[0080] Alternatively or additionally, cooling lines can be arranged on the capacitor plates 15, 16, through which a cooling medium is conducted. A liquid, such as water or oil, is preferably used as the cooling medium.

[0081] A process for producing particle foam parts using the device described above is explained below: The process comprises the following basic steps: Filling the mold cavity 14 Welding the foam particles Stabilizing (optional) Demolding Cleaning the tool (optional)

[0082] To fill the molding chamber 14, air is injected via the compressed air line 6 into the area of ​​the bottom 5 of the material container to swirl and separate the foam particles contained therein. At the same time, propellant air is also supplied to the propellant nozzle, so that foam particles are drawn from the material container 2 into the conveying line 4 and transported by the propellant air toward the molding tool 3. The molding chamber 14 is closed, whereby the mold halves 12, 13 can be fully closed or spaced apart by a crack gap.

[0083] The slide valve of the 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 valve intermittently feeds the foam particles from the material container 2 to the conveying line 4. This can break up any bridging of the foam particles in the material container 2 and separate the foam particles. This is particularly useful for foam particles with an adhesive surface, such as eTPU foam particles.

[0084] Intermittent suction can also alternatively be achieved by intermittently supplying the driving air from the compressed air line 9 to the driving nozzle 8 arranged directly adjacent to the material container 2.

[0085] The molding tool 12, 13 is provided with at least one valve (not shown) that is opened when foam particles are fed in, allowing the compressed air flowing into the molding chamber 14 to escape. This valve can be adjusted when filling the molding chamber 14 such that a counterpressure develops in the molding chamber 14. This maintains a high pressure in the feed line and in the molding chamber 14, thereby keeping the foam particles at a small volume. This allows more foam particles to be fed into the molding chamber 14 than would be possible without the counterpressure. After the counterpressure is released, the foam particles expand in the molding chamber 14.

[0086] 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. The use of a crack gap during filling primarily increases the density in a thin region of the particle foam part being produced.

[0087] As soon as it is determined that the mold cavity 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 with the compressed air supplied to the filling injector 10.

[0088] The filling of the mold cavity 14 with foam particles is described in detail in the German patent application DE 10 2014 117 332, which is why reference is made to this patent application in this regard.

[0089] After filling the mold cavity 14 with foam particles, they are heated by applying electromagnetic RF radiation. This RF radiation is generated by applying a high-frequency voltage of approximately 10 4 V at a frequency of 27.12 MHz to the capacitor plates 15, 16.

[0090] The foam particles can be based on polyurethane (eTPU). Polyurethane has a dielectric loss factor D of 0.2 for electromagnetic radiation with a frequency of 1 MHz. In contrast, the dielectric loss factor of polypropylene (PP) for electromagnetic radiation with 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 to weld the foam particles into the mold cavity 14 without additional heat-transfer materials, in particular without aqueous solutions, since the foam particles themselves absorb the electromagnetic waves.

[0091] Instead of polyurethane-based foam particles, foam particles made of expandable thermoplastics 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.

[0092] These materials each contain functional groups (amide group, urethane group, or ester group) that create a dipole moment. These functional groups are responsible for the molecules absorbing RF radiation. Therefore, other thermoplastics containing such functional groups that create a dipole moment are also suitable for welding with RF radiation.

[0093] Foam particles based on ePP (expandable polypropylene) or ePS (expandable polystyrene) can also be welded to form particle foam parts. Since these materials absorb electromagnetic radiation only to a very low degree, 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 evenly and the heat transfer medium is evenly distributed in the mold cavity 14. This leads to a correspondingly uniform heating of the foam particles in the mold cavity 14.

[0094] The mold 3 can also be connected to a steam source (not shown), with which saturated dry steam can be supplied to the mold cavity 14. This is useful when welding materials whose dielectric loss factor is temperature-dependent. Such materials include, for example, ePES (expandable polyether sulphone) or expandable polyamide. At low temperatures, the absorption properties of electromagnetic waves are low. Therefore, these foam particles are first heated using steam and then, from a certain temperature, heated to even higher temperatures, either alone or additionally, using electromagnetic radiation. Alternatively, the foam particles can be wetted with a dielectric heat transfer medium, so that the electrical heat transfer medium is heated using electromagnetic radiation to heat the foam particles to a predetermined temperature.Afterwards, the foam particles can be heated directly due to electromagnetic radiation, since the absorption properties of electromagnetic radiation increase with increasing temperature.

[0095] The duration of application of the electromagnetic RF radiation depends on the volume of the mold cavity 14, the density of the foam particles, and the applied electrical power or voltage. Tests have shown that, depending on the volume and the material from which the foam particles are formed, approximately 30 seconds to approximately 2 minutes are required to reliably and completely weld the foam particles. An electrical voltage of 5 kV to 20 kV was applied.

[0096] 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 can also be measured that is related to the electrical power introduced into the mold cavity. This could, for example, be the electrical voltage applied to the capacitor plates 15, 16.

[0097] The surface bordering the mold cavity 14 can also be temperature-controlled. For this purpose, heating wires 34 can be arranged in the mold adjacent to the surface bordering the mold cavity 14. The heating wires 34 are connected to a power source 35, which can be used to feed a heating current into the heating wires.

[0098] Instead of heating wires, fluid channels can also be provided in the mold halves 12, 13, through which a correspondingly temperature-controlled fluid flows. The fluid is preferably water or steam.

[0099] After applying the electromagnetic RF radiation, the mold cavity 14 is kept closed for a predetermined period of time, whereby the introduced heat is evenly distributed throughout the particle foam part and a very uniform bond is formed between all foam particles. This process step is referred to as 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, which is usually a plastic material that conducts heat poorly, little heat is dissipated to the outside when the mold cavity 14 is closed.

[0100] Mold halves 12, 13 made of plastic have the advantage over metal mold halves in that they offer significantly better thermal insulation and, at the same time, have a lower heat capacity. This allows the desired temperature cycles to be carried out much faster and with less energy, with the heat supplied being transferred almost entirely to the foam particles.

[0101] During the stabilization period or part of the stabilization period, the capacitor plates 15, 16 can be actively cooled by the cooling device 32, 33, whereby heat is removed from the base bodies of the mold halves 12, 13 and thus also from the particle foam part.

[0102] After stabilization, the particle foam part is demolded by moving the two mold halves 12, 13 apart. The mold can be provided with demolding rams for demolding, with which the particle foam part is pushed out of one of the two mold halves 12, 13.

[0103] Stabilization is an optional process step. It can be omitted for certain materials and shapes. The larger the volume of the particle foam part to be produced, the more expedient it is to stabilize the particle foam part in the mold after welding.

[0104] To increase throughput, electromagnetic RF radiation can be applied during filling and / or closing of a crack gap.

[0105] The electromagnetic radiation, in particular the RF radiation, can be applied during filling or 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 gradually or suddenly increase the electrical power or electrical voltage.

[0106] It may also be useful to gradually increase the power or voltage of the electromagnetic RF radiation, so that a ramp is carried out over a period of time, for example, 30 seconds to 3 minutes by gradually increasing the electrical power or voltage of the electromagnetic RF radiation. This achieves very uniform heating of the foam particles.

[0107] Optionally, a negative pressure and / or vacuum can also be applied to the molding chamber 14. This is useful if the foam particles and / or the supplied compressed air have a certain moisture content.

[0108] The process described above is a dry process compared to welding with steam alone. This means that the manufactured particle foam parts are dry, or drier, after the production process and can be transferred to further processing steps more quickly. It may also be expedient to demold the warm particle foam parts and transfer them directly to further processing. This can significantly increase efficiency in production, as the pauses between individual process steps can be shortened, and the heat applied to weld the foam particles can also be used, at least in part, for subsequent process steps.

[0109] Subsequently, a forming tool 3 ( Figure 2a, Figure 2b ) which has a first mold half 12 and a second mold half 13 and can be used in the device 1 described above. Movement devices, holding elements, thermometers for measuring the temperature in the mold space and other mechanical parts for opening and closing the tool are shown in Figure 2a, 2b omitted.

[0110] The mold 3 is formed from two mold halves 12, 13, each having a base body 24, 25 made of an electrically conductive material. These base bodies consist, for example, of aluminum, copper, or a highly electrically conductive alloy.

[0111] The two mold halves 12, 13 delimit 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.

[0112] The electrically insulating coatings can be made of a material that is essentially transparent to electromagnetic radiation, in particular RF radiation, such as PTFE, PE, or PEEK. However, they can also be made of a plastic material that has a similar dielectric loss factor when exposed to electromagnetic radiation as the plastic material to be processed in the mold cavity 14, in order to achieve uniform heating throughout the entire mold cavity 14 and at the edge region of the mold cavity 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 (polyether ketone), POM (polyoxymethylene), polyimide, and PMMA (polymethyl methacrylate).These coatings 28, 29 are thus essentially transparent to RF radiation, since they absorb only a small proportion of the electromagnetic radiation. Due to the relatively low loss factor, they 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 no thicker than 20 mm, in particular no thicker than 15 mm, and preferably no thicker than 10 mm, so that the proportion of the electromagnetic wave energy absorbed by the coating is small.

[0113] The electrically conductive base bodies 24, 25 form the capacitor plates of the molding tool 3. They therefore have an electrical connection for connection to the generator 18 or to ground 30. The generator 18 represents a radiation source for generating electromagnetic radiation. The generator is preferably designed to generate RF radiation. The generator can also be designed to generate microwave radiation; with larger mold cavities 14, significantly more uniform heating is possible with RF radiation than with microwave radiation. In addition, most plastic materials can absorb RF radiation significantly better than microwave radiation. Therefore, the use of RF radiation is preferred.

[0114] 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 minimizes electromagnetic radiation losses, resulting in a very high proportion of the power transferred as heat into the foam particles to be welded. Such a tool thus allows for very efficient welding of the foam particles into a particle foam part.

[0115] In the present embodiment of the molding tool 3, the first mold half 12 has a bottom wall 31 and a circumferential side wall 32. In the present 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 material, or to be formed only partially 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 cavity 14. The tight seal between the two mold halves 12, 13 is at least tight enough that foam particles located therein cannot escape. The mold cavity 14 is not necessarily sealed gas-tight.

[0116] 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.

[0117] A through-opening for supplying foam particles is arranged on the first mold half 12, which 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 explained in more detail below.

[0118] The first mold half 12 has one or more through openings for the escape of air, which are referred to below as vent opening 34.

[0119] The filling opening 33 and the venting openings 34 are arranged in a section or region, in particular an edge region, of the first mold half 12, which in the closed state of the mold 3 ( Figure 2b ) is concealed or covered by the second mold half 13. As a result, the filling opening 33 and the vent opening 34 are automatically closed when the mold 3 is closed by inserting the second mold 13 into the cavity formed by the first mold 12. As a result, it is not necessary for the filling injector 10 to have a closing mechanism with which the filling opening 33 is closed.

[0120] This section or area is the area of ​​the first mold half 12 which is not covered by the second mold half 13, is the area around which the mold halves are opened when moving apart into the crack gap position.

[0121] 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 electrical 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 cavity 14.

[0122] With such a design of the molding tool 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.

[0123] 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.

[0124] Such a molding tool 3 further differs from known molding tools for welding foam particles by means of electromagnetic waves in that the second molding tool 13 is stamp-like and with its electrical base body 25 is located at least partially within the cavity delimited 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 molding space 14 or to the foam particles to be welded.

[0125] A further embodiment of the molding tool 3 is shown in Figure 3 shown schematically. This mold 3 has two essentially flat capacitor plates 15, 16. One of the mold halves 12, 13 is attached to each of the capacitor plates 15, 16. The mold halves are as in the Figure 1shown embodiment is formed from a non-electrically conductive material. Regarding the design of the mold halves 12, 13 and the materials from which the mold halves are formed, in order to avoid repetition, reference is made to the explanations for the Figure 1 shown mold halves.

[0126] This mold 3 has a housing 35 made of an electrically conductive material. The housing is preferably a metal housing.

[0127] 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 the present embodiment is a hydraulic piston / cylinder unit 36. The movement unit can also be a pneumatic piston / cylinder unit or another actuator that can apply 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, so that it delimits a mold cavity that is open on one side. The second mold half 13 is provided with a ram 39, which can be moved into the mold cavity to demold it.Demolding occurs when the second mold half 13 is retracted by means of the piston / cylinder unit 36, causing the plungers 39 to strike stop plates 40 and thus penetrate into the mold cavity defined by the second mold half 13. The housing 35 has an opening 41a at its bottom, which can be closed with a horizontally movable door 41b. When the second mold half 13 is retracted, the door 41b is opened, so that the demolded particle foam part falls out of the mold 3 through the open opening 41a and can be transported away by suitable conveying means (not shown).

[0128] The second, movable capacitor plate 16 is electrically connected to the ground 30 via the movement device and via the housing 35.

[0129] The first capacitor plate 15 is electrically connected to the generator 18 by means of suitable waveguides or coaxial conductors.

[0130] 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 body 42. The mechanical connections or the insulating bodies 42 extend approximately parallel to the direction of movement of the second mold half 13. In the present exemplary embodiment, the insulating body is made of ceramic. However, other materials with good electrical insulation, such as glass, can also be provided as the material for the insulating bodies. The insulating bodies 42 can absorb 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 over the individual mechanical connections or over the individual insulating bodies 42, and can transmit it to the housing 35.

[0131] Furthermore, on the front side of the capacitor plate 15, i.e., on the side on which the mold half 12 is located, a number of mechanical connections with further insulating bodies 43 are arranged in the edge region. The insulating bodies 43 are designed in the same way as the insulating bodies 42. These mechanical connections extend between the edge region of the capacitor plate 15 and holders 44 projecting inward from the walls of the housing 35, so that these mechanical connections or insulating bodies 43 also extend approximately parallel to the direction of movement of the second mold half 13. As a result, the forces acting on the first mold half 12 or on the first capacitor plate 15 when the mold is opened can be transferred to the housing 35.

[0132] Furthermore, additional mechanical connections can 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 transmit 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.

[0133] Because all mechanical connections between the first capacitor plate 15 and the housing 35 comprise an insulating body 42, 43, 45, the first capacitor plate 15 is completely electrically insulated from the housing 35. The insulating bodies 42, 43, 45 preferably have a length of at least 5 cm, in particular at least 8 cm, and particularly preferably at least 10 cm, so that a correspondingly large distance is created between the housing 35 and the first capacitor plate 15 in order to prevent voltage flashovers between the capacitor plate 15 and the housing 35.

[0134] 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 way is suitable for transferring a power in the range of 10 kW to 60 kW to the foam particles located in the mold cavity. This allows for the reliable production of large-volume particle foam parts with very short cycle times of 30 seconds to 2 minutes.

[0135] Figure 4shows a schematic electrical circuit diagram of the generator 18, the mold capacitor formed by the capacitor plates 15, 16, which encloses the mold halves 12, 13, and a line (hollow waveguide or coaxial line) 46 suitable for transmitting the electromagnetic waves, with which the electromagnetic waves are transmitted from the generator 18 to the mold capacitor 15, 16. The hollow waveguide forming the line 46 is preferably 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.

[0136] A generator-side inductance 47 and a tool-side inductance 48 are symbolically shown in this line 46. These inductances are caused by the line itself, with the length of the respective line sections 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 molding tool 3. The tool capacitor 15, 16, the capacitor 49, and the tool-side inductance 48 form a tool resonant circuit 50.

[0137] 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 inductance 47 is designed to be variable, for example by providing a capacitor with capacitor plates whose distance is variable or by providing line sections of different lengths. It is also possible for both the generator-side capacitor 51 and the generator-side inductance 47 to be designed to be variable. The generator-side capacitor 51 can be provided with a servomotor, the actuation of which changes the distance between the two capacitor plates, for example byone of the two capacitor plates is moved in a straight line, whereby both capacitor plates are always parallel to each other, or one of the two capacitor plates is pivoted.

[0138] By varying the capacitance of capacitor 51 or inductance 47, the resonant frequency of generator resonant circuit 52 can be changed or tuned. If the resonant frequencies of the generator resonant circuit and the tool resonant circuit match, the maximum electrical power is transferred from generator 18 to tool resonant circuit 50 and thus to tool capacitor 15, 16. By varying the resonant frequency of generator resonant circuit 52, the transfer of electrical power can be specifically controlled, whereby the greater the difference between the resonant frequencies of the two resonant circuits 50, 52, the lower the transferred power. Tuning generator resonant circuit 52 can thus be used specifically to adjust the electrical power introduced into mold cavity 14.

[0139] In the present embodiment, the resonant frequency of the generator resonant circuit 52 is varied. It is equally possible to vary the resonant frequency of the tool 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 inductor on the tool side than on the generator side.

[0140] Figure 5shows a device for regulating the electrical power supplied to the tool capacitor 15, 16 in a simplified schematic 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 line 54 to a voltage measuring device (voltmeter) 55. A diode 56 is preferably connected in parallel to the measuring capacitor 53. The coaxial line 54 is connected in series with an inductor 58, which serves to filter high-frequency signals.

[0141] The measuring unit, formed from the measuring capacitor 53 and the diode 56, is separated from the tool capacitor 15, 16 by an isolating capacitor 59. The isolating capacitor has a high dielectric strength. 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 or 1:1,000 or 1:10,000. As a result, the voltage present across the tool capacitor 15, 16 is reduced in the measuring unit 53, 56 such that it lies within a measuring range of the voltage measuring device 55 and can be reliably detected by the latter.

[0142] In this circuit, a voltage drops across the measuring capacitor 53 that corresponds to the voltage present at the tool capacitor 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. By providing the diode 56, only the oscillation halves of a specific polarity are present. The diode 56 thus rectifies the voltage present at the measuring capacitor 53. This measuring voltage is measured by the voltage measuring device 55 and converted into a measuring signal. The measuring signal is forwarded to a control device 57, which automatically controls the generator 18 to output a predetermined electrical power in order to generate a specific voltage at the tool capacitor or a specific measuring voltage at the measuring capacitor, which is a fraction of the voltage at the tool capacitor.

[0143] The following is based on Figure 6An embodiment of an apparatus for producing particle foam parts is explained. This apparatus 1 has several spatially separated workstations, which are connected to one another by a transport device 60. With the transport device 60, several molding tools, each defining a molding space, can be moved between the individual workstations.

[0144] The transport device 60 has an upper transport path 61 and a lower transport path 62, along which the molds 3 are transported in different directions. The two transport paths 61, 62 are arranged parallel to one another, and at the ends of each of the two transport paths 61, 62 there is a lifting device 63, 64, with which the molds can be moved between the transport levels downwards (lifting device 63) or upwards (lifting device 64). The two transport paths 61, 62 each have two narrow conveyor belts arranged parallel to one another, onto which the molds 3 can be placed.

[0145] On 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 platen at the level of the upper transport section 61 and an upper movable platen. A molding tool 3 can be arranged between each of the two plates (not shown) and pressed together by means of a press that actuates the two plates. The two plates are made of an electrically conductive material. The lower, stationary platen is connected to ground. The upper, movable platen is connected to an RF generator 18. The two plates thus form the capacitor plates 15, 16 explained above, which hold the molding tool 3 between them.

[0146] 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 located therein can cool. The cooling section 70 can cool the molds 3 solely with ambient air, can be provided with a fan to subject the molds 3 to a cooling air stream, and / or can comprise a cold chamber cooled by a cooled cooling medium below room temperature to accelerate the heat transfer from the mold 3. The cooling section 70 can accommodate several molds 3 simultaneously, since cooling or stabilizing the foam part located in the mold is the longest-lasting process step.

[0147] On the lower transport path 62 there is a mold storage system 71 which is coupled to an automatic warehouse for storing several molds, so that different molds can be automatically coupled into or out of the transport device 60.

[0148] The production of a particle foam part is completed in the demoulding station 66, in which the mould consisting of two halves is opened and the particle foam part produced therein is removed and dispensed.

[0149] The molds 3 have a closing mechanism 72, with which the two mold halves of the respective mold are firmly closed together as they are conveyed along the transport device 60. This closing mechanism 72 is automatically opened in the demolding station 66 for demolding the particle foam parts, and then the two mold halves are reassembled and connected to each other by means of the closing mechanism 72. The closing mechanism connects the two mold halves so firmly that they do not come apart during transport. The closing mechanism can have some play so that the two mold halves can be pulled apart slightly during filling to form a cracking gap. The closing mechanism does not have to serve to absorb the pressure generated in the mold cavity during welding. This pressure is dissipated via the press in the welding station 69.

[0150] 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-lasting step is the stabilization or cooling of the mold and the particle foam part contained therein. Since the cooling section can accommodate several molds simultaneously, several molds can be stabilized or cooled simultaneously. This does not interrupt the processing of the molds in welding station 69.

[0151] A further advantage of this device is that different tools, in particular those with different mold cavities, can be processed simultaneously in circulation. Preferably, each mold is provided 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 device 60, so that a control device (not shown) knows which tool is located at which workstation. This allows the individual tools to be treated individually. In particular, they can be exposed to electromagnetic waves of different voltages and / or durations at the welding station.The residence time in the cooling section and the cooling effect can also be individually controlled with active cooling, for example by means of a fan.

[0152] Compared to a conventional device for producing particle foam parts, in which the foam particles are welded solely with hot steam, this device is significantly more compact and significantly more flexible, as it can process several different molds simultaneously. Furthermore, the energy can be introduced much more efficiently into the mold cavity using electromagnetic radiation.

[0153] It may also be useful to provide a water or steam supply line at the welding station, through which water and / or steam is fed to the mold. This is particularly advantageous when foam particles are to be welded that have a low dielectric loss factor or generally only a low dielectric loss factor. In such a case, a small amount of water or steam is added. The electromagnetic radiation heats the water to steam or the steam is heated further. 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 further. It has been shown that just a few hundred grams of water are sufficient for a mold cavity with a volume of 50 liters.For example, if the foam particle material is ePS (expandable polystyrene), 300 g or less of water is sufficient to heat and weld the foam particles in a mold cavity with a volume of 50 liters. With conventional welding, in which the foam particles are heated solely using superheated steam, steam quantities equivalent to several kilograms of water are required for a mold cavity with a volume of 50 liters.

[0154] Therefore, if foam particles that only slightly absorb electromagnetic radiation are to be welded, a single addition of 300 g of water is sufficient for a mold cavity with a volume of 50 liters. For many materials that only slightly absorb electromagnetic radiation, even smaller amounts of water may be sufficient. For mold cavities with other volumes, the maximum required amount of water can be adjusted to the volume in the same ratio.

[0155] If water is heated in the mold cavity using electromagnetic radiation, it is advisable to use a molding tool with a pressure sensor that can measure the pressure in the mold cavity. This pressure is proportional to the temperature. The irradiation of the electromagnetic radiation is then preferably regulated according to the measured pressure value, i.e., preferably set to a specific pressure value.

[0156] In this device with the transport device 60, the different aspects of the invention explained above and in particular the different molding tools can be used individually or in combination. Reference sign list

[0157] 1 Device 2 Material container 3 Mold 4 Line 5 Base 6 Compressed air line 7 Compressed air source 8 Drive nozzle 9 Compressed air line 10 Filling injector 11 Compressed air line 12 Mold half 13 Mold half 14 Mold cavity 15 Capacitor plate 16 Capacitor plate 17 Electrical line 18 Alternating voltage source 19 Vacuum pump 20 Fan 21 Cooling fin 22 Heating wire 23 Power source 24 Base body 25 Base body 26 Inner boundary surface 27 Inner boundary surface 28 Coating 29 Coating 30 Mass 31 Bottom wall 32 Side wall 33 Filling opening 34 Vent opening 35 Housing 36 Piston / cylinder unit 37 Bottom wall 38 Side wall 39 Tappet 40Stop plate 41aOpening 41bDoor 42Insulating body 43Insulating body 44Holder 45Insulating body 46Cable 47Generator-side inductance 48Tool-side inductance 49Tool-side capacitor 50Tool resonant circuit 51Generator-side capacitor 52Generator resonant circuit 53Measuring capacitor 54Coaxial cable 55Voltmeter 56Diode 57Control device 58Inductance59Separation condenser 60Transport device 61Upper transport section 62Lower transport section 63Lift device 64Lift device 65Conveyor direction 66Demolding station 67Insertion station 68Filling station 69Welding station 70Cooling section 71Mould storage system 72Closing mechanism

Claims

1. A device for producing a particle foam part, comprising a molding tool (3) which delimits a mold cavity (14), at least two capacitor plates being arranged adjacent to the mold cavity (14) and connected to a radiation source (18) for electromagnetic radiation, the radiation source (18) for electromagnetic radiation being designed to emit electromagnetic radiation, and the molding tool (3) being formed from at least two mold halves (12, 13), the two mold halves (12, 13) delimiting the mold cavity (14) by means of an inner boundary surface (26, 27) in each case and at least one of the two mold halves being formed from an electrically conductive material and forming one of the capacitor plates, characterized in that the inner boundary surface (26, 27) of the mold half formed from electrically conductive material is contoured and the mold cavity comprises regions of different thicknesses.

2. The device according to claim 1, characterized in that both mold halves (12, 13) are formed from an electrically conductive material and form one of the capacitor plates in each case, an insulating layer (28, 29) for electrically insulating the two mold halves (12, 13) being arranged at least in the region in which the two mold halves adjoin each other.

3. The device according to claim 1 or 2, characterized in that the at least one electrically conductive mold half (12, 13) is provided with a plastic layer (28, 29) on its side delimiting the mold cavity.

4. The device according to claim 3, characterized in that the plastic layer has a thickness of at most 1 cm.

5. The device according to claim 3 or 4, characterized in that the plastic layer is formed from a material which is not transparent to the electromagnetic radiation.

6. The device according to any one of claims 1 to 5, characterized in that a filling injector (10) is coupled to the at least one electrically conductive mold half, the electrically conductive mold half (12, 13) and the filling injector (10) being electrically connected to ground.

7. The device for producing a particle foam part according to any one of claims 1 to 6, characterized in that one of the mold halves (12, 13) comprises a through-opening for supplying foam particles and / or a through-opening for allowing air to escape, the through-opening being covered by the other mold half in the closed state of the molding tool.

8. The device according to claim 7, characterized in that no additional closing mechanism for closing the through-opening is provided at the through-opening for supplying foam particles and can be closed solely by the other mold half.

9. The device according to any one of claims 1 to 8, wherein the at least two capacitor plates (15, 16) are arranged so as to form a tool capacitor, characterized in that a voltage measuring device (55) is provided for measuring the electrical voltage present at the tool capacitor (15, 16), and the voltage measuring device (55) is connected to a control device (57) for regulating the electrical power on the basis of the measured voltage.

10. The device according to claim 9, characterized in 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 with the tool capacitor, the voltage measuring device (55) tapping off the voltage present at the measuring capacitor, a diode (56) being connected preferably in parallel with the measuring capacitor (53).

11. The device according to any one of claims 1 to 10, characterized in that the electromagnetic radiation source forms a generator resonant circuit and lines for guiding the electromagnetic waves together with the capacitor surrounding the mold cavity form a tool resonant circuit, at least one of the two resonant circuits being tunable by changing an inductance or a capacitance, a control device being 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.

12. The device according to any one of claims 1 to 11, characterized in that the electromagnetic radiation is RF radiation and / or one of the two capacitor plates is electrically connected to ground.

13. The device according to any one of claims 1 to 12, characterized in that the molding tool is provided with cooling fins.

14. The device for producing a particle foam part according to any one of claims 1 to 13, characterized in that the device comprises a plurality of work stations between which several molding tools are conveyed in circulation by means of a transport device, at least the following work stations being provided: - a filling station at which the molding tool is filled with foam particles, - a welding station at which the foam particles located in the molding tool are welded by means of electromagnetic radiation, - at least one or more cooling stations for cooling the welded particle foam part, and - a demolding station.

15. The device according to claim 14, characterized in that the transport device is a transport device that conveys the molding tools in circulation, and / or that a cooling zone is provided along the transport device, the cooling zone being capable of receiving several molding tools at the same time.