Injection molding device with microwave preheating and downstream sprue distribution and injection molding process with microwave preheating

Abstract

Proposed is an efficient injection molding device (1) for an injection molding process and for crosslinking, comprising: a mold (2) with an upper (3) and lower mold plate (4) for cavity formation (5), a injection unit (19), a microwave heater (10) for preheating with a microwave generator (17) and a waveguide (9) for the microwaves, wherein a flow bushing (12) is arranged in the waveguide (9) and the material from the injection unit (19) can flow through the flow bushing (12) and thus through the waveguide (9). It is characterized by a sprue manifold (7) which is connected to the flow bushing (12) so that the sprue manifold (7) is supplied with the material from the flow bushing (12), and a control device (18) to heat the material to a temperature below the mold temperature before injection.

Description

[0001] The invention relates to an injection molding device for carrying out an injection molding process with a rubber as a material and for causing cross-linking or vulcanization to produce an elastomeric plastic by heating according to the preamble of claim 1, and to an injection molding method according to the preamble of claim 12.

[0002] A method for producing rubber workpieces that are vulcanized in a mold is known from FR 2 617 754 A1, where the rubber has been previously heated with microwaves. A corresponding injection molding device is also known from US 7 604 473 B2, with which the material is initially heated to the temperature required for vulcanization. The mold into which the material is subsequently injected should, in principle, also be able to function without further heating. Furthermore, according to the prior art, rubber for an injection molding process is conventionally heated at constrictions in the piping system by contact between a heating mandrel and the flowing rubber.

[0003] From DE 24 40 987 A1 and DE 10 2014 008 603 A1, methods and devices for shortening the vulcanization cycle time in injection molding of rubber compounds or mixing heads with wave emitters are generally known.

[0004] The object of the invention is to provide a particularly efficient and time-saving injection molding device.

[0005] The problem is solved, starting from an injection molding machine or an injection molding process of the type mentioned above, by the characterizing features of claim 1 or claim 12.

[0006] The measures mentioned in the dependent claims make advantageous embodiments and further developments of the invention possible.

[0007] The injection molding device and the injection molding process according to the invention are primarily used for the production of an injection-molded part from an elastomeric plastic; for example, rubber profiles made of elastomers are produced. The starting material is a rubber, which undergoes cross-linking of its internal structure only through heating, thus becoming an elastomer or elastomeric plastic. This cross-linking process is, in particular, a vulcanization process. The starting material is often referred to as a mixture rather than a single material.

[0008] In injection molding, the material is injected into a mold, more precisely into a cavity inside a closed mold. The mold typically consists of an upper and a lower mold plate, which, when assembled, form or tightly enclose one or more cavities. The cavity thus forms a recess between the two mold plates. Its shape corresponds exactly to that of the molded part being produced.

[0009] A injection unit is provided for feeding the material, with which the material can be injected under pressure into the mold or cavity.

[0010] The invention offers a number of advantages over the previous state of the art: According to the invention, a microwave heater for preheating the material is provided with a microwave generator for generating microwaves and a waveguide for guiding the microwaves. A flow sleeve is arranged in the waveguide as a channel for the material. According to the invention, the injection unit is connected to the flow sleeve and forces the material through it. The material can flow through the flow sleeve and thus through the waveguide, but, since the flow sleeve is located in the waveguide, it is exposed to the microwaves and thereby to a heating process by the microwaves. This arrangement thus essentially performs the function of a flow heater.Microwave heating is adjustable and controllable; moreover, microwave heating requires significantly less time than heating via the surface of a flow pipe, allowing for operation similar to that of an instantaneous water heater and enabling rapid response to temperature changes. Furthermore, only the material or mixture is heated, while the surrounding environment does not need to be heated, depending on the material. In addition, the waveguide design is inherently chosen so that, as far as possible, only the flow pipe bushing and the material flowing through it are exposed to the microwaves.

[0011] If the material is only heated in contact with a surface, a disadvantage can also be that the surface cools down itself through heat emission and then heats the subsequent material less effectively.

[0012] One advantage of the flow sleeve can be that it has, for example, a narrow diameter, so that little material is exposed to the microwaves and can therefore heat up faster.

[0013] The crosslinking and vulcanization temperatures are generally not the same. The vulcanization temperature corresponds to the set mold temperature. The crosslinking temperature begins at the temperature at which the chemical reaction is initiated (usually resulting in a very long vulcanization time). A relatively large difference can exist between these two temperatures because the higher temperature at which the vulcanization occurs significantly reduces the necessary vulcanization time. This is crucial for achieving the required crosslinking of a large portion of the material, thus enabling the part to be demolded. The remaining, considerably smaller portion of the vulcanization typically occurs outside the mold during cooling of the part through post-vulcanization, utilizing the residual heat stored during the injection molding process.

[0014] Another advantage of using the flow-through bushing is that the material is not heated by shearing at constrictions, as is otherwise common in the prior art; shearing also carries the risk of longer-chain polymers within the material breaking. This undesirable side effect of polymer chain breakage fundamentally alters the mechanical properties of the resulting elastomer, because shorter polymer chains form the basis after crosslinking.

[0015] It is particularly advantageous to expose the material to the microwaves immediately as it passes through the flow sleeve, provided, for example, that the material of the flow sleeve is microwave-permeable. This allows the material to be heated significantly more homogeneously and quickly than is possible with contact heating of previously heated surfaces. At the same time, such direct microwave heating offers the advantage that the heating surface is not cooled down again by contact, thus preventing a reduction in the heating of the subsequent material. In both respects, the invention is therefore superior to the conventional heating method using a heating mandrel.

[0016] However, it is also possible to provide an embodiment of the invention in which at least part of the material from which the flow sleeve is made is heated by the microwaves. In this case, the heating of the material can occur at least partially through contact with the heated surface of the flow sleeve.

[0017] According to the invention, a sprue distributor is provided to distribute the plastic material and introduce it into the at least one cavity at at least one or at least two different locations in the mold. This sprue distributor is connected to the flow sleeve, so that the sprue distributor is supplied with the material from the flow sleeve. The sprue distributor ensures that the material can enter the cavity(ies) quickly, as uniformly and homogeneously as possible, and completely fill them.

[0018] According to the invention, a control device is also provided, which first enables the temperature of the material to be controlled by regulating the microwave heater. The control device regulates the material temperature via the microwave heater to a temperature that is advantageously below the vulcanization temperature. Even if the crosslinking process has already begun due to heating by the microwave heater (e.g., to the crosslinking temperature), the vulcanization temperature has not yet been reached. Furthermore, a heating device for heating the mold is advantageously provided. The temperature of the heating device is also set or regulated by the control device. The mold is set to a temperature that is higher than the temperature of the material being injected into the mold.Advantageously, it is set to a temperature significantly higher than the material's curing temperature. Because the microwave heater does not yet bring the material to the temperature required for complete vulcanization, it is possible to avoid, or at least reduce, the vulcanization process occurring before the cavity is reached and filled. According to the invention, this measure also overcomes a technical prejudice, as prior art has generally considered it advantageous to bring the material directly to the vulcanization temperature, since this minimizes the need to heat the mold. However, the invention recognizes that the mold should be heated to a specific temperature anyway, one that is at least similar to the material's temperature.The temperature of the mold is similar to, but preferably significantly higher than, the curing temperature, because otherwise the material would be cooled down again immediately upon contact with the mold, which could even interrupt vulcanization. Therefore, it is advantageous if the mixture or material has not yet been brought to the vulcanization temperature before being injected into the mold, so that the final step to increase the degree of curing until vulcanization can only take place once the material is in the cavity. However, if the mold temperature is higher, especially significantly higher, than the material temperature, and particularly preferably higher than the curing or vulcanization temperature, the material still receives the amount of heat necessary for curing or vulcanization via the mold and can fully form an elastomer.

[0019] Since the workpieces are made of an elastomer or rubber, i.e., a thermal insulator, they conduct heat relatively poorly. Therefore, especially with cavities containing large volumes for the production of relatively thick or thick-walled injection-molded parts, achieving a homogeneous cross-linking is more difficult and time-consuming when a relatively cold material is heated only via one surface of the mold, because the heat penetrates the interior of the cavity less effectively. It is therefore advantageous if the material has already been heated to a temperature below its vulcanization temperature by the microwave heater before it is injected into the mold. This is particularly true for the areas of the material furthest from the heat source (cavity surface).

[0020] The mold is not directly exposed to the microwaves. Instead, it can be heated separately by a heating device. The material, however, which is injected into the mold or cavity, is already preheated. The material has been heated to a temperature similar to, but slightly lower than, the vulcanization temperature before it is injected into the cavity or mold. Thin or narrow sections of the cavity generally represent a particularly critical area, as the workpiece often has more delicate structures in these areas that must be manufactured with high precision. At the same time, precisely because these areas are so narrow, they can cool down rapidly in contact with a colder surface, potentially disrupting the curing process. This inherent difficulty can be overcome by the invention.

[0021] This also allows the entire injection molding process to be accelerated because the microwave heater preheats the material; that is, the heating occurs in stages and not entirely within the mold, which would be very time-consuming. By utilizing a principle similar to a continuous flow heater, little to no additional time is required for preheating. Furthermore, the material can be heated much more evenly than with contact heating in the cavity. A reduction in the overall cycle time is therefore possible. This can also lead to a reduction in unit costs and an increase in the potential output per unit of time.

[0022] The invention thus advantageously provides a self-contained, modular system that is directly controllable.

[0023] In one embodiment of the invention, the sprue distributor can be connected directly between the flow sleeve or waveguide on the one hand and the cavity on the other, so that, among other things, the material has to travel short distances after heating before reaching the cavity. This ensures that the material arrives in the cavity at a similar or, ideally, the same temperature as when it was heated in the flow sleeve. This also simplifies the control of the system.

[0024] In one embodiment of the waveguide, a reflector, in particular an adjustable reflector, can be arranged on the side opposite the microwave generator. This allows the energy maximum to be precisely adjusted to the material in the flow sleeve.

[0025] Depending on the embodiment of the invention, the mold can be designed differently. For example, the upper mold plate can be movable and / or the lower mold plate fixed. The mold basically consists of at least two parts so that it can be opened and the workpiece, the injection-molded part, removed. One mold plate can therefore be movable, and the other fixed.

[0026] As previously explained, it is advantageous for the flow bushing to be made of a microwave-permeable material so that the material is directly exposed to and heated by the microwaves. It is also conceivable that the flow bushing is partially permeable and is also partially heated by the microwaves. The flow bushing can, in principle, be made of glass, plastic, or ceramic, for example. Composite materials are also conceivable in order to tailor the properties of the flow bushing as precisely as possible. Such a composite material can also contain glass, plastic, or ceramic. The flow bushing can also be advantageously manufactured from two materials by joining them with a soldered joint.

[0027] In a further development of the invention, the control device can be connected to temperature sensors to obtain data for control purposes. The sprue can also be equipped with a temperature sensor, because the material flows through it immediately before reaching the cavity, allowing conclusions to be drawn about the material temperature. Alternatively, the temperature sensors can be arranged in the respective mold plates to measure the material temperature in the channels or in the cavity.

[0028] In one embodiment, the control device can be connected to the microwave heater to adjust the degree of heating of the material, because the material is heated directly by the microwaves and this can be directly influenced and adjusted by regulating the intensity.

[0029] In advantageous embodiments of the invention, the sprue distributor and / or the waveguide can be integrated into the mold, in particular into the upper mold plate. In this way, a compact mold with short flow paths can be achieved.

[0030] The sprue distributor can form the interface between the waveguide and / or flow bushing on the one hand and the mold on the other, in order to advantageously distribute the heated mixture evenly after heating and introduce it into the cavity(s) in this embodiment.

[0031] Furthermore, in one embodiment, the sprue distributor can be designed as a cold distributor whose operating temperature remains below that of the mold and / or which may be temperature-controlled. However, the cold distributor is generally only cooler relative to the material, whose temperature is typically above 100°C, e.g., around 120°C, while the mold temperature can easily reach 180°C. The cold distributor can, for example, have a temperature of approximately 60°C to 80°C. The lower temperature of the cold distributor may not be particularly significant, especially if the cold distributor is small and actually forms the interface between the flow sleeve and the cavity(s). Temperature control by the control device can thus be simplified because the control only needs to be performed at two points: the microwave heater and the mold. If necessary, the sprue distributor or...The cold distributor is only temperature-controlled via the monitoring device. In particular, the material should not lose its flowability on its way to the mold.

[0032] Accordingly, the above-mentioned advantages can be achieved by an injection molding process according to the invention, which serves to manufacture an injection-molded part from an elastomeric plastic and comprises the following process steps: - Providing rubber as a material, - Providing a mold with an upper mold plate and a lower mold plate which, when assembled, form at least one cavity into which the material can be placed, - Providing a injection unit for feeding the material, - Providing a microwave heater for preheating the material with a microwave generator for generating microwaves and a waveguide for guiding the microwaves, - wherein a flow bushing is provided or arranged in the waveguide, which is connected to the injection unit and forms a channel for the material.

[0033] This method is characterized by the fact that a sprue distributor for distributing the plastic material and introducing it into the at least one cavity is provided at at least two different locations on the mold. This distributor is connected to the flow sleeve, so that the sprue distributor is supplied with material from the flow sleeve. Furthermore, the material is preheated by the microwave heater as it flows through the flow sleeve to a temperature below the mold temperature, i.e., below the vulcanization temperature. The material is then distributed by the sprue distributor for introduction into the at least one cavity. Finally, the mold is heated to a temperature equal to or above the curing or vulcanization temperature.

[0034] A method according to the invention thus makes it possible to preheat the mixture directly, reliably, and in a controlled manner, without initiating a crosslinking / vulcanization process. Mechanical damage to the material, such as the breaking of polymer chains, can be avoided because shearing at constrictions in the heating channels is not necessary. This also reduces the energy consumption of the injection molding machine, as the mixture does not need to be subjected to such high pressures. Crosslinking or vulcanization can, however, occur very rapidly, with the heating of the mold ultimately supplying the remaining heat required to initiate the crosslinking or vulcanization process.

[0035] In embodiments of the method according to the invention, injection molding devices according to one of the embodiments of the invention can therefore be advantageously used. Example implementation:

[0036] An embodiment of the invention is illustrated in the drawings and is explained in more detail below, including further details and advantages. Specifically, the drawings show: Fig. 1: a schematic representation of an injection molding device or an injection molding process according to the invention, Fig. 2, Fig. 3: the installation of temperature sensors on the sprue manifold and in the cavity area, as well as Fig. 4: a further section of the injection molding device according to the invention.

[0037] Fig. Figure 1 shows a schematic section through a part of the injection molding device 1 according to the invention. It initially comprises a mold 2 with an upper mold plate 3 and a lower mold plate 4, wherein the upper mold plate 3 is movable and the lower mold plate 4 is fixed. To open the mold 2, the upper mold plate 3 is moved. Both mold plates 3 and 4 enclose a cavity 5, which spatially assumes the shape of the molded part. The two mold plates 3 and 4, which rest against each other in the closed state, are separated from each other by the cavity parting line 6. Above the movable mold plate 3, the sprue distributor 7 is arranged, which sits on the upper mold plate 3 and is separated from the upper mold plate 3 by a parting line 8. The waveguide 9 of the microwave heater 10 is integrated into the sprue distributor 7.The upper mold plate 3, the waveguide 9, and the sprue distributor 7 can therefore form a compact unit and be moved together. In . Fig. On the right side, a reflector 11 is arranged as the termination of the waveguide 9. In contrast, on the left side... Fig. A microwave generator (not shown) is arranged on the waveguide 9. The reflector 11 thus reflects the incident waves.

[0038] The waveguide 9 is traversed by a flow sleeve 12, which runs perpendicular to the longitudinal axis of the waveguide 9. The waves in the waveguide 12 thus impinge perpendicularly on the flow sleeve 12. The flow sleeve 12 is designed as a tube through which the material / mixture flows, since the flow sleeve 12 is directly connected via the connection 14 to an injection unit 19 (in Fig. 1 (shown only schematically) is connected.

[0039] The material is thus guided from the injection unit 19 through the flow sleeve 12, which is located in the waveguide 9. As it passes through the flow sleeve 12, the material is continuously irradiated and heated by microwaves within the waveguide 9. The maximum energy density is shifted onto the material in the flow sleeve 12 by the reflector 11. The microwave radiation is set so that the material remains fluid but below its vulcanization temperature, e.g., in the range of approximately 120°C.

[0040] Following the flow sleeve 12, the material enters the sprue distributor 7 and is injected into the cavity 5 at several points. The material also comes into contact with the surfaces of the mold plates 3, 4 in the area of ​​the cavity 5 inside the mold 2. Since the mold 2 has previously been heated by a heating device 20 to a temperature significantly higher than that of the material, the material does not cool down through this contact, but continues to heat up. On the contrary, the mold 2 is also heated to a significantly higher temperature, so that the material, which has already been heated to a temperature close to the curing temperature, now reaches the curing temperature, allowing the material (rubber) to vulcanize and ultimately form an elastomer, without the already preheated material or the...The preheated mixture requires a longer heating process, and a large amount of heat must first penetrate the material and reach the central areas of the cavity. This significantly speeds up the injection molding process.

[0041] Such an injection molding process therefore includes, among other things, the following process steps: - Preheating A of the material using a microwave heater 10 - Distributing B of the material through the sprue distributor 7 into the cavity 5 - Heating C of mold 2 or maintaining (C) the mold temperature at a temperature significantly above that of the injected material and thus also above the vulcanization temperature (e.g. 180°C).

[0042] The Fig. 2 and Fig. Figure 3 shows the installation of temperature sensors 15, 16: Both temperature sensors 15, 16 are installed here via the mold plates 3, 4. The temperature sensor 15, which measures the material temperature in the area of ​​the sprue distributor 7, is brought to the channel via the upper mold plate 3 (see Figure 3). Fig. 2).

[0043] To measure the temperature of the material in cavity 5, the temperature sensor 16 is guided to cavity 5 via the lower, fixed mold plate 4 (see figure). Fig. 3).

[0044] The structure of the injection molding device 1 is shown in Fig.Figure 4 shows that the mold 2 also consists of an upper mold plate 3 and a lower mold plate 4. The temperature sensor 15 for measuring the material temperature in the channels of the sprue 7 is integrated into the upper mold plate 3, while the temperature sensor 16, which measures the temperature of the material in the cavity, is integrated into the lower mold plate 4. The mold plates 3 and 4 are separated from each other by the cavity parting line 6. Another visible parting line 8 separates the upper mold plate 3 from the sprue 7, which is penetrated by the waveguide 9. The reflector 11 is located at the end of the waveguide 9 and is visible. Opposite it, at the other end of the waveguide 9, is the microwave generator 17.

[0045] Also shown is the control device 18, which receives the temperature measurement data from the two sensors 15, 16 and which is connected to the microwave generator 17 and thus regulates the intensity of the microwave radiation.

[0046] The injection molding device and injection molding process according to the invention thus not only enable an efficient and time-saving manufacturing process, but also allow for the precise production of the molded parts, even if these have particularly delicate structures. Furthermore, the crosslinking process for the formation of the elastomer is improved, enabling high quality with defined properties of the rubber material. Reference symbol list: 1 injection molding device 2 Form 3 upper form plate 4 lower form plate 5-cavity 6 Cavity separation plane 7 sprue distributors 8 Parting line upper mold plate - sprue distributor 9 waveguides 10 microwave heaters 11 Reflector 12 Flow socket 14 Connection to injection unit. 15 Temperature sensor for sprue distributor 16 Temperature sensor for cavity 17 Microwave generator 18 Control device 19 Injection unit 20 Heating device A. Preheating the material using the microwave heater B Distributing the material through the sprue distributor into the cavity C Heating the mold to vulcanization temperature

Claims

[1] Injection molding device (1) for carrying out an injection molding process with a rubber as a material and for causing cross-linking to produce an elastomeric plastic by heating, in particular for vulcanization, and for manufacturing an injection molded part from the obtained elastomeric plastic, comprising: a. a mold (2) with an upper mold plate (3) and a lower mold plate (4) which, in the assembled state, form at least one cavity (5) into which the material can be inserted, b. a injection unit (19) for supplying the material, c. a microwave heater (10) for preheating the material with a microwave generator (17) for generating microwaves and a waveguide (9) for guiding the microwaves , d. wherein a flow bushing (12) is arranged in the waveguide (9), which is connected to the injection unit (19) and forms a channel for the material, so that the material from the injection unit (19) can flow through the flow bushing (12) and thus through the waveguide (9) to be preheated by the microwaves, characterized by , that a sprue distributor (7) for distributing the plastic material and introducing it into the at least one cavity (5) is present at at least one, in particular at least two, different locations of the mold (2), which is connected to the flow sleeve (12) so that the sprue distributor (7) is supplied with material from the flow sleeve (12), wherein a heating device (20) is provided for heating the mold (2), and wherein a control device (18) is provided for controlling the microwave heater (10) and / or the heating device (20) of the mold (2) and / or the temperature of the material, which is configured to heat the material by the microwave heater (10) to a temperature below the temperature of the mold (2), in particular below the crosslinking and / or vulcanization temperature. [2] Injection molding device (1) according to claim 1, characterized by , that the sprue distributor (7) is connected directly between the flow bushing (12) and / or the waveguide (9) on the one hand and the at least one cavity (5) on the other. [3] Injection molding device (1) according to one of the preceding claims, characterized by, that a reflector (11), in particular an adjustable reflector (11), is arranged in the waveguide (9) on the side opposite the microwave generator (17). [4] Injection molding device (1) according to any of the preceding claims, characterized by , that a. the upper mold plate (3) is movable and the lower mold plate (4) is rigid or b. the upper mold plate is rigid and the lower mold plate is movable. [5] Injection molding device (1) according to any one of the preceding claims, characterized by , that the flow sleeve (12) is made of a material that is at least partially, and in particular completely, permeable to microwaves. [6] Injection molding device (1) according to any of the preceding claims, characterized by , that the flow bushing (12): a. made of glass, plastic or ceramic or b. made from a composite material consisting of at least two of the materials glass, plastic and ceramic c. is made of two different materials joined by a solder joint. [7] Injection molding device (1) according to one of the preceding claims, characterized by , that at least one temperature sensor (15, 16) is / are provided for measuring the material temperature and / or the temperature of the mold (2) and / or the temperature of the sprue distributor (7), which is / are connected to the control device (18). [8] Injection molding device (1) according to any one of the preceding claims, characterized by , that the control device (18) is connected to the microwave heater (10) to adjust the degree of heating of the material. [9] Injection molding device (1) according to any of the preceding claims, characterized by , that the sprue distributor (7) and / or the waveguide (9) is / are integrated into the mold (2), in particular into the upper mold plate (3). [10] Injection molding device (1) according to any one of the preceding claims, characterized by , that the sprue distributor (7) forms the interface between waveguide (9) and / or flow bushing (12) on the one hand and mold (2) on the other. [11] Injection molding device (1) according to any one of the preceding claims, characterized by , that the control device (18) is designed to control the temperature of the sprue distributor (7) and / or that the sprue distributor (7) is designed as a cold distributor whose temperature remains below the temperature of the mold (2) during operation and / or which is tempered, in particular by the control device (18), to keep the rubber flowing. [12] Injection molding process for manufacturing an injection molded part from an elastomeric plastic, comprising the following process steps: a. Providing rubber as a material, b. Providing a mold (2) with an upper mold plate (3) and a lower mold plate (4) which, in the assembled state, form at least one cavity (5) into which the material can be placed, c. Providing a injection unit (19) for feeding the material, d. Providing a microwave heater (10) for preheating the material with a microwave generator (17) for generating microwaves and a waveguide (9) for guiding the microwaves, e. wherein a flow bushing (12) is provided and / or arranged in the waveguide (9) which is connected to the injection unit (19) and forms a channel for the material, characterized by : f. Providing a sprue distributor (7) for distributing the plastic material and introducing it into the at least one cavity (5) at at least two different locations in the mold (2), which is connected to the flow sleeve (12) so that the sprue distributor (7) is supplied with the material from the flow sleeve (12), g. Preheating (A) of the material by the microwave heater (10) as it flows through the flow sleeve (12) to a temperature below the temperature of the mold (2), in particular below the crosslinking and / or vulcanization temperature, h. Distributing (B) the material through the sprue distributor (7) for introduction into the at least one cavity (5), i. Heating (C) the mold to a temperature and / or maintaining (C) the temperature of the mold equal to or above the temperature of the material, in particular equal to or above the crosslinking and / or vulcanization temperature. [13] Injection molding process according to claim 12, characterized by , that an injection molding device (1) according to one of claims 1-11 is used to carry out the process steps.

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