Arrangement for the production of molded parts using microwave heating

Abstract

Arrangement (1) for the production of molded parts comprising an injection molding device (2), an injection molding tool (3) having a cavity (3.3, 3.31, 3.32, 3.33) and a microwave device, wherein the injection molding device (2) is configured to inject molding compound (6) under pressure into the cavity (3.3, 3.31, 3.32, 3.33) of the injection molding tool (3) via at least one outlet (2.1), wherein the microwave device (4) comprises a microwave conductor, at least one microwave-permeable guide channel (4.2) arranged in the microwave conductor for guiding the molding compound (6) from the outlet (2.1) into the cavity (3.3, 3.31, 3.32, 3.33) and a microwave generator, wherein the microwave conductor has an inlet opening (4.4) through which microwaves generated by the microwave generator are coupled into the microwave conductor. are capable of being coupled in for heating the molding compound (6) in the guide channel (4.2), characterized in that the microwave conductor is a single-mode applicator (4.1).

Description

[0001] An arrangement for producing molded parts comprising an injection molding device, an injection mold having a cavity, and a microwave device, wherein the injection molding device is configured to inject molding compound under pressure into the cavity of the injection mold via at least one outlet, the microwave device comprising a microwave conductor, at least one microwave-permeable guide channel arranged in the microwave conductor for guiding the molding compound from the outlet into the cavity, and a microwave generator, the microwave conductor having an inlet opening through which microwaves generated by the microwave generator can be coupled into the microwave conductor to heat the molding compound in the guide channel. The invention also relates to a microwave device for such an arrangement.

[0002] Various arrangements for manufacturing molded parts using an injection molding device are known in the prior art. JPS58220715A discloses a device with a cylinder made of a ceramic material and an injection mold, wherein molding compound, for example rubber or plastic, is injected into the injection mold under pressure by means of a piston. The molding compound is first melted in the cylinder using a microwave device located outside the cylinder. The use of microwaves is intended to significantly reduce the heating time required for melting the molding compound compared to conventional methods.

[0003] From JPS63156719U, another device is known that comprises an injection molding device with a cylinder and a piston, an injection mold, and a preheating chamber. First, the molding compound, for example, rubber, is placed in the preheating chamber and heated there by microwaves. Once the molding compound has been sufficiently heated and softened, it is pressed into a cavity of the mold by the piston. The molding compound may already be sufficiently heated in the preheating chamber so that it cross-links into a uniform component in the injection mold by being held there for a certain period of time. The microwave irradiation in the preheating chamber is intended to advantageously heat the molding compound uniformly from the inside out, while reducing the time required for heating.

[0004] Furthermore, US Patent 7,604,473 B2 discloses an injection molding machine for producing components with a specific shape from rubber or plastic material. The device has a feeding unit with which a pasty, vulcanizable molding compound is supplied to an injection chamber. From the injection chamber, the molding compound is forced through a nozzle by means of a piston, whereby the molding compound heats up due to the friction generated. A microwave-permeable section of the nozzle, preferably made of quartz, extends through a resonance chamber into which microwaves generated by a microwave generator are coupled. In this section of the nozzle, the molding compound is heated to a vulcanization temperature by microwaves. From the nozzle, the heated molding compound is injected into an injection mold, which is heated by heating elements, thereby ensuring stable cross-linking of the molding compound.

[0005] There is still a need for an improved arrangement for the production of molded parts compared to these solutions, with which high-quality molded parts can be produced, especially from crosslinking molding compounds.

[0006] The present invention is therefore based on the objective of providing an improved arrangement for the production of molded parts, with which high-quality molded parts can be produced from a molding compound, in particular from a cross-linking molding compound.

[0007] In an arrangement of the type mentioned above, this problem is solved on the one hand according to claim 1 by the fact that the microwave conductor is a single-mode applicator.

[0008] The fact that the guide channel is designed to be microwave-transparent in accordance with claim 1 means here and in the following that the guide channel transmits a large proportion of the microwave radiation and absorbs and / or reflects only a minor proportion of it.

[0009] That the guide channel in the sense of claim 1 is set up to guide molding compound from the outlet of the injection device into the cavity means that the guide channel is arranged between the injection device and the injection molding tool, so that the molding compound is heated by the microwave field in the microwave conductor before it enters the cavity.

[0010] The arrangement according to the invention can in particular be a component of an injection molding machine or an injection molding machine.

[0011] According to the invention, the microwave conductor of the arrangement is a single-mode applicator. The single-mode applicator is designed such that at least one microwave is capable of propagating within it as a single-mode wave. The cross-sectional profile of the single-mode applicator can, in principle, be chosen arbitrarily. However, it should be noted that the propagation capability of a single wave mode is primarily determined by the geometry of the single-mode applicator and, in particular, by the geometry of its cross-sectional area. A wave mode is capable of propagation if the wavelength to be transmitted is smaller than the cutoff wavelength for the respective cross-sectional area corresponding to that mode. In particular, the cross-sectional profile of the single-mode applicator of the arrangement according to the invention is rectangular or round.

[0012] The arrangement according to the invention, which includes a single-mode applicator, offers several advantages in addition to the benefit that the injection molding device only injects precisely the amount of molding compound required for the production of the next component through the guide channel and heats it by microwave irradiation. This avoids heating larger quantities of material in the injection molding device and makes the process parameters of the molded part manufacturing process more stable and easier to control. For example, the molding compound can be heated by microwave irradiation to a temperature close to or at the curing temperature before injection into the cavity, thereby reducing the production time of the components manufactured with the arrangement according to the invention.This is possible if the molding compound is heated in such a way that complete cross-linking occurs later, allowing it to be injected into the cavity without any problems. The use of a single-mode applicator also has the advantage that, when a single-mode microwave with known properties is applied, the resulting single-mode wave field can be precisely determined. In this way, the single-mode applicator and the position of the guide channel within it can be precisely coordinated so that the molding compound is guided through a specific region of the microwave field. This allows the amount of energy introduced into the molding compound by the microwave irradiation to be determined exactly in advance, ensuring that the molding compound can be reliably heated to a specific temperature.For example, with the single-mode applicator, it is possible to guide the molding compound through the guide channel in a region of wave maximum, thus exposing the molding compound to the highest possible energy density. Likewise, the molding compound can be guided through a region below the highest possible energy density.

[0013] The use of a single-mode applicator can significantly increase the overall energy efficiency of the arrangement according to the invention.

[0014] Furthermore, the proportion of wave energy radiated from the single-mode applicator through any output coupling aperture is small, so that small absorbers are sufficient to absorb the radiated wave component. In addition, the use of the single-mode applicator has the advantage that, due to the very efficient use of the input energy, even weakly and very weakly polar materials can be heated with microwaves.

[0015] Preferably, the single-mode applicator is a cavity resonator. In a cavity resonator, the microwaves coupled in through the coupling aperture are reflected at a wall, particularly one opposite the coupling aperture, with the reflected wave being coupled back out through the coupling aperture. The length of the resonator is tuned to the wavelength of the single-mode microwave such that a standing wave is formed.

[0016] The aforementioned problem is further solved by an arrangement according to the preamble of claim 1 as per claim 3 in that the microwave conductor has a displaceable, microwave-reflecting reflection element by means of which a propagation length between the coupling aperture and the reflection element, along which the microwaves can propagate in the microwave conductor, can be adjusted. In particular, the reflection element is arranged within the microwave conductor and can be displaced within it.

[0017] The wave coupled into the microwave guide is reflected by the reflecting element, so that a standing wave forms within the microwave guide due to the superposition of the incident and reflected waves. Because the reflecting element is movable, the point within the microwave guide at which the wave is reflected is also movable. Therefore, the propagation length along which the microwaves can travel within the microwave guide can be adjusted by moving the reflecting element. Moving the reflecting element also shifts the position of the standing wave, with its antinodes and nodes, within the microwave guide, thus changing the energy density at a fixed location within the microwave guide and consequently also at the guide channel.By shifting the reflection element, the amount of energy introduced into the molding compound by means of microwaves can be specifically changed, so that the amount of energy can be adapted to, among other things, the type of molding compound, the amount of molding compound injected and / or the speed or pressure at which the molding compound is injected from the injection device into the guide channel.

[0018] In one embodiment, the arrangement according to the invention comprises both the single-mode applicator and the movable, microwave-reflecting reflection element as described above, wherein the single-mode applicator in this embodiment can in particular also be a cavity resonator.

[0019] While the molding compound can preferably be heated to the curing temperature by microwave irradiation in the guide channel, thus making the introduction of further energy into the molding compound for its curing not strictly necessary, the arrangement according to the invention can, in one embodiment, include at least one heating device configured to supply energy to the molding compound within the cavity. In particular, the heating device can include heating elements arranged on the injection mold that heat the mold. The heating device has the advantage that the curing process is stable and controlled, and complete curing is reliably achieved even in larger injection-molded parts.Furthermore, it can be used when the molding compound is heated to a temperature close to the crosslinking temperature by microwave irradiation, so that additional heat is introduced with the heating device to start the crosslinking process.

[0020] Since the production of a molded part may require injecting the molding compound into the injection mold at very high pressure, for example, 50 to at least 200 MPa, the guide channel, and in particular its material, is preferably designed according to the maximum injection pressure such that the guide channel remains undamaged even after a large number of molded parts have been produced. In one embodiment, the guide channel can be formed at least partially from a microwave-transparent material such as polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), glass, and / or ceramic, preferably ceramic. All of the aforementioned materials have the advantage of being microwave-transparent in the sense of the arrangement according to the invention. The use of ceramic is particularly preferred, as this material is suitable, among other things, for very high pressures.

[0021] It is preferred that the injection molding device be configured to preheat the molding compound to a preheating temperature and introduce it into the guide channel at a temperature of at least 55 °C and at most 90 °C, particularly at least 60 °C and at most 85 °C, or especially at least 65 °C and at most 80 °C. A corresponding minimum temperature is advantageous to ensure that the molding compound has a sufficiently low viscosity to allow it to be easily introduced into and guided through the guide channel. At the same time, the temperature should not be too high to prevent unwanted chemical reactions and, for example, premature initiation of the crosslinking process.

[0022] In a further embodiment, the arrangement includes a feeder configured to supply the heated molding compound to at least one cavity of the injection mold. In particular, the feeder for the molding compound has at least one feed channel, and more specifically, several feed channels.

[0023] In one embodiment, the injection mold has multiple cavities. In particular, the injection mold has two, three, four, or more cavities. This has the advantage that the number of components produced per injection process can be increased according to the number of cavities by simultaneously filling all cavities with material within a single injection process using the injection device. This increases the material throughput of the arrangement according to the invention. In this embodiment, the arrangement can, in particular, have a feed in the form of a distributor with which the molding compound can be divided among each of the multiple cavities, for example, a hot runner distributor or a cold runner distributor. The distributor can, in particular, be arranged between the guide channel and the injection mold such that the molding compound is introduced from the guide channel into the distributor and from there into the cavity.The distributor can be configured as a hot runner distributor, meaning it is designed to distribute the molding compound to the cavities after it has been heated by the microwave device. Depending on the distributor's design, additional heat can be supplied to the molding compound within the hot runner distributor. Alternatively, in this embodiment, the arrangement can also be configured as a cold runner distributor, meaning it is designed to distribute the molding compound to the cavities before it has been heated by the microwave device. It can have multiple guide channels, with, for example, one guide channel being provided for each cavity. In this case, the distributor can be positioned between the injection molding device and the guide channels, so that the molding compound is fed from the outlet into the distributor and from there into the guide channels.Furthermore, the molding compound can be heated separately for each cavity in each guide channel using the microwave device, whereby all guide channels can be arranged in the same microwave conductor, but also several microwave conductors can be provided for one or more guide channels each.

[0024] In one embodiment, the guide channel has a hollow cross-section through which the molding compound can be guided, and wherein the diameter of the hollow cross-section is at most 25 mm, preferably at least 4 mm and at most 20 mm, or particularly preferably at least 6 mm and at most 10 mm. This has the advantage that the maximum energy density of a stationary microwave generated by a wave maximum in the guide channel does not decrease too much across the diameter of the guide channel. As a result, the energy input into the molding compound is essentially constant throughout the entire hollow cross-section, so that the molding compound can be heated uniformly. In a further embodiment, the hollow cross-section of all molding compound-guiding means, in particular the guide channel and / or, if present, the feed channel of a feeder, is constant between the outlet of the injection device and an inlet opening of the cavity of the injection mold.In this way, the friction between the molding compound and the means guiding it, and thus the influence of friction on the temperature of the molding compound, is minimized.

[0025] The arrangement according to the invention can further comprise a control unit. The control unit is configured to control the energy input of the microwaves into the molding compound as a function of the process parameters of the injection molding device, in particular the start and end times of the injection process, the quantity of molding compound to be injected, the type of molding compound, the injection pressure, and / or the injection speed. The control unit can be used, in particular, to set, among other things, the start and end times of the microwave irradiation, the microwave frequency, and / or the microwave power. If the arrangement comprises a previously described movable, microwave-reflecting element, its displacement can also be controlled by the control unit, for example, by controlling a drive that causes the reflection element to be displaced.

[0026] The arrangement according to the invention can be used in particular for the production of components made from elastomeric molding compounds such as synthetic or natural rubbers as well as silicone materials and other crosslinking materials such as thermosets, as well as other thermoplastic polymers that can be heated by microwaves.

[0027] The problem is further solved by a microwave device comprising a microwave conductor, at least one microwave-permeable guide channel arranged in the microwave conductor for guiding molding compound, and a microwave generator, wherein the microwave conductor has an inlet opening through which microwaves generated by the microwave generator can be coupled into the microwave conductor for heating molding compound in the guide channel, wherein the microwave conductor is preferably a single-mode applicator designed as a cavity resonator and / or has a movable, microwave-reflecting reflection element by means of which a propagation length between the inlet opening and the reflection element along which the microwaves can propagate in the microwave conductor can be adjusted, characterized in that an inlet-side end of the guide channel is formed.to interact with an outlet of an injection molding machine and / or a compression molding machine, and which has an outlet-side end of the guide channel designed to be connected to the inlet of an injection mold, wherein adapters are provided in particular to enable connection to various injection molding machines and / or injection molds. Such a microwave device can be used to retrofit existing injection molding machines and / or compression molding machines to improve their performance or to adapt them for the production of molded parts from crosslinkable materials.

[0028] The invention will now be explained in more detail with reference to figures illustrating preferred embodiments of the invention.

[0029] They show Fig. 1 a schematic sectional view of the arrangement according to the invention in a first embodiment; Fig. 2 a schematic sectional view of the arrangement according to the invention in a second embodiment; and Fig. 3 a schematic sectional view of the arrangement according to the invention in a third embodiment.

[0030] In Fig. Figure 1 is a schematic sectional view of the arrangement 1 according to the invention in a first embodiment, wherein the arrangement is, in this case, part of an injection molding device that is not fully shown. The arrangement comprises an injection device 2, which is only partially shown, with an outlet 2.1, an injection mold 3, and a microwave device 4, which is also only partially shown. The injection mold 3 is multi-part and, in this case, designed as an injection mold. It has an upper mold half 3.1 and a lower mold half 3.2, which together define a cavity 3.3.

[0031] The microwave device 4 comprises a microwave generator (not shown), a single-mode applicator 4.1, which is configured as a cavity resonator, a guide channel 4.2, and a movable microwave-reflecting element 4.3. The single-mode applicator 4.1 has a coupling opening 4.4 (not shown) through which microwaves generated by the microwave generator can be coupled into the single-mode applicator 4.1, propagating in direction A within the applicator. The reflecting element 4.3 is connected to an electric drive 4.5 such that it can be moved along the single-mode applicator 4.1 by the drive, allowing the propagation length L, along which microwaves can propagate within the single-mode applicator 4.1, to be adjusted by moving the reflecting element 4.3.

[0032] The guide channel 4.2 is, firstly, at least partially located within the single-mode applicator 4.1 and consists of a microwave-permeable material, allowing it to be penetrated by the microwaves coupled into the single-mode applicator 4.1. Secondly, the guide channel 4.2 is located between the injection device 2 and the injection mold 3, or is connected to them, and furthermore includes a feed 5 by means of which the molding compound 6 can be supplied to the cavity 3.3.

[0033] The following is a rough description of the operation of the arrangement 1. In this case, rubber is used as the molding compound 6. This compound is heated in the injection device 2, for example by means of an extruder, to a preheating temperature between 65 °C and 80 °C, so that it is soft enough to be injected under pressure from the injection device 2 and through the outlet 2.1 into the guide channel 4.2 and guided through it. This can be done, for example, with a punch or piston provided in the injection device (not shown here). At the same time, the temperature is sufficiently low that the molding compound 6 does not yet crosslink. As it passes through the guide channel 4.2, the molding compound is exposed to the energy field of a monomodal microwave in the monomode applicator 4.1 is exposed to pressure, which heats the molding compound 6 to a temperature between the preheating temperature and the required curing temperature, and which may also be the curing temperature itself. Once the molding compound 6 is heated to the required curing temperature, it should be ensured that the molding compound 6 is injected into the cavity before the curing reaction starts. From the guide channel 4.2, the molding compound 6, still under the pressure applied by the injection device 2, is guided into the feed channel 5.1 of the feeder 5 and from there into the cavity 3.3 of the injection mold 3, where it subsequently cures completely.

[0034] In Fig. 2 shows a schematic sectional view of the arrangement 1 according to the invention in a second embodiment. In contrast to the one in Fig. In the first embodiment shown in Figure 1, the injection mold 3 has three cavities 3.31, 3.32, 3.33, with the feed 5 designed as a distributor 7 with several distribution channels 7.1. The distributor 7 is arranged between the guide channel 4.2 and the injection mold 3, so that the molding compound 6 is heated by the microwave device 4 before being distributed by the distributor 7 to the individual cavities 3.31, 3.32, 3.33. The distributor 7 is thus designed as a hot runner distributor. With the arrangement 1 of the second embodiment shown, three components can be produced in one process run. Of course, the number of cavities can be significantly larger than in the illustrated embodiment.

[0035] In Fig. Figure 3 shows a schematic sectional view of the arrangement 1 according to the invention in a third embodiment. In contrast to the one in Fig.In the second embodiment shown in Figure 2, a guide channel 4.21, 4.22, 4.23 is provided for each cavity 3.31, 3.32, 3.33, wherein the molding compound 6 is heated separately in each guide channel 4.21, 4.22, 4.23 by microwave irradiation. Furthermore, the distributor 7 is arranged between the outlet 2.1 and the guide channels 4.21, 4.22, 4.23, so that the molding compound 6 is heated by the microwave device 4 only after it has been distributed to the individual cavities 3.31, 3.32, 3.33. The distributor 7 is thus designed as a cold runner distributor. Reference symbol list 1. Arrangement 2 Spray device 2.1 Outlet 3 Injection mold tool 3.1 upper half of the mold 3.2 lower half of the mold 3.3 Cavity 3.31 Cavity 3.32 Cavity 3.33 Cavity 4 microwave oven 4.1 Single-mode applicator 4.2 Guide channel 4.21 Guide channel 4.22 Guide channel 4.23 Guide channel 4.3 Reflection element 4.4 Coupling opening 4.5 electric drive 5 Feed 5.1 Feed channel 6 Molding compound 7 distributors 7.1 Distribution channel A. Direction of propagation L Propagation length QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JPS58220715

[0002] JPS63156719U

[0003] US 7,604,473 B2

[0004]

Claims

[1] Arrangement (1) for the production of molded parts comprising an injection device (2), an injection mold (3) having a cavity (3.3, 3.31, 3.32, 3.33) and a microwave device, wherein the injection device (2) is configured to inject molding compound (6) under pressure into the cavity (3.3, 3.31, 3.32, 3.33) of the injection mold (3) via at least one outlet (2.1), wherein the microwave device (4) comprises a microwave conductor, at least one microwave-permeable guide channel (4.2) arranged in the microwave conductor for guiding the molding compound (6) from the outlet (2.1) into the cavity (3.3, 3.31, 3.32, 3.33) and a microwave generator, wherein the microwave conductor has an inlet opening (4.4) through which microwaves generated by the microwave generator are transmitted into the Microwave conductors can be coupled in to heat the molding compound (6) in the guide channel (4.2), characterized by , that the microwave conductor is a single-mode applicator (4.1). [2] Arrangement (1) according to claim 1, characterized by , that the single-mode applicator (4.1) is a cavity resonator. [3] Arrangement (1) according to the preamble of claim 1 or according to claim 1 or 2, characterized by , that the microwave conductor has a movable, microwave-reflecting reflection element (4.3) by means of which a propagation length (L) between coupling aperture (4.4) and reflection element (4.3), along which the microwaves can propagate in the microwave conductor, can be adjusted. [4] Arrangement (1) according to any of the preceding claims, characterized by at least one heating device which is set up to supply energy to the molding compound (6) within the cavity (3.3, 3.31, 3.32, 3.33). [5] Arrangement (1) according to any one of the preceding claims, characterized by, that the guide channel (4.2) is at least partially formed from a microwave-transparent material, in particular from polytetrafluoroethylene, polyetheretherketone, polyetherketoneketone, glass and / or ceramic, preferably from ceramic. [6] Arrangement (1) according to any one of the preceding claims, characterized by , that the injection device (2) is configured to introduce molding compound at a temperature of at least 55 °C and at most 90 °C, in particular at least 60 °C and at most 85 °C or in particular at least 65 °C and at most 80 °C into the guide channel. [7] Arrangement (1) according to one of the preceding claims, wherein the injection mold (3) has several cavities (3.3, 3.31, 3.32, 3.33), in particular at least two cavities (3.3, 3.31, 3.32, 3.33), wherein in particular a guide channel (4.2) is provided for each cavity (3.3, 3.31, 3.32, 3.33). [8] Arrangement (1) according to claim 7, characterized bya distribution device (7) having distribution channels (7.1) which is configured to distribute molding compound to the individual cavities (3.3, 3.31, 3.32, 3.33) of the injection molding tool (3), and wherein the distribution device (7) is in particular arranged and configured such that it distributes the molding compound to the cavities (3.3, 3.31, 3.32, 3.33) either before the guide through the guide channel (4.2) or after the guide through the guide channel (4.2). [9] Arrangement (1) according to any one of the preceding claims, characterized by a feeder (5) arranged between guide channel (4.2) and injection molding tool (3), which is designed to supply the heated molding compound (6) to the at least one cavity (3.3, 3.31, 3.32, 3.33) of the injection molding tool (3). [10] Arrangement (1) according to any one of the preceding claims, characterized by, that the guide channel (4.2) has a hollow cross-section whose diameter is at most 25 mm, preferably at least 4 mm and at most 20 mm or particularly preferably at least 6 mm and at most 10 mm. [11] Arrangement (1) according to any of the preceding claims, characterized by a control unit which is set up to control the energy input of microwaves into the molding compound (6) depending on process parameters of the injection device (2), in particular the start and end time of the injection process, the amount of molding compound to be injected, the molding compound type, the injection pressure and / or the injection speed. [12] Arrangement according to any of the foregoing claims, characterized by that it is part of an injection molding machine or an injection press. [13] Microwave device comprising a microwave conductor, at least one microwave-permeable guide channel (4.2) arranged in the microwave conductor for guiding raw material (6), and a microwave generator, wherein the microwave conductor has an inlet opening (4.4) through which microwaves generated by the microwave generator can be coupled into the microwave conductor for heating molding compound (6) in the guide channel (4.2), wherein the microwave conductor is preferably a single-mode applicator designed as a cavity resonator and / or has a movable, microwave-reflecting reflection element (4.3) by means of which a propagation length (L) between inlet opening (4.4) and reflection element (4.3), along which the microwaves can propagate in the microwave conductor, can be adjusted. characterized by, that an inlet-side end of the guide channel is designed to interact with an outlet of an injection device of an injection molding machine and / or an injection press and an outlet-side end of the guide channel is designed to be able to be connected to the inlet of an injection molding tool, wherein in particular adapters are provided with which a connection to various injection devices and / or injection molding tools is possible.

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