Cross-linking device with monomode applicator

Description

[0001] The present invention relates to a device for crosslinking one or more materials, in particular polar materials, contained in a workpiece, in particular rubber, by means of microwaves, with at least one microwave source.

[0002] Such devices are known and are used, for example, for vulcanizing rubber profiles. Typically, an elongated cavity is provided through which the rubber profile passes, during which the rubber profile is heated using various methods and subsequently vulcanized. In addition to heating using hot air and infrared radiation, microwaves are also fed into the cavity. These microwaves have the advantage that they penetrate the profile and heat it from the inside, rather than just heating the surface, where the heat is transported into the interior of the workpiece by thermal conduction. To couple the microwaves into the cavity, coupling slots are typically provided in a wall of the cavity, with a waveguide fed by a microwave source being arranged on the outside of the wall to feed the microwaves to the coupling slots.Within the waveguide, the microwaves propagate in a defined manner dependent on the waveguide's geometry. They can be adjusted using tuning devices to achieve an energy density maximum at a coupling slot, thus coupling the largest possible portion of the microwave energy into the cavity. At the same time, the portion of the microwave energy reflected back to the microwave source is kept to a minimum to prevent damage.

[0003] US 4,275,283 discloses a vulcanization device for heating rubber profiles with UHF energy. This vulcanization device has a cavity through which the rubber profile passes and has several coupling slots at opposite ends of the cavity. A hollow waveguide is arranged on the outside of the cavity, which conducts microwaves from a microwave source to the coupling slots. A tuning device is provided on an upper leg of the hollow waveguide.

[0004] A different approach to supplying microwaves to the workpiece is pursued in the subject matter known from JP 08108434 A. This discloses a vulcanization device for continuous workpieces, particularly made of foam rubber, with an interior space containing hot air and microwave areas. The microwaves are generated by microwave sources and fed into flexible waveguides that are guided through the interior space directly to the workpiece. They have output openings at their workpiece-side ends, so that the microwaves are output from the waveguides directly at the workpiece.

[0005] FR 2 548 507 A1 discloses a microwave applicator comprising a resonant tunnel and a microwave source for generating microwaves that can be coupled into the resonant tunnel via coupling slots. Rectangular mode filters are provided above the coupling slots, through which workpieces can be passed. Outside the mode filters, the microwaves can propagate uncontrollably in the resonant tunnel.

[0006] EP 1 205 724 A2 discloses a device for drying and / or sintering compacts made of composite materials. The device comprises a vacuum chamber in which a cavity resonator is arranged, into which microwaves generated by a microwave source can be coupled. The compacts can be fed into and removed from the cavity resonator by means of a conveyor device.

[0007] A disadvantage of all the objects known from the aforementioned prior art is that the microwaves can propagate in the cavity or interior in a manner that is almost impossible to control, meaning that a large proportion of the microwave energy does not reach the material to be crosslinked. Furthermore, the field distribution, in particular the energy density distribution of the microwave field, and thus also the position of the profile in the microwave field, cannot be determined or can only be determined to a very limited extent, so that it is left to chance whether the profile passes through an area with a sufficiently high energy density. The portion of the microwave energy actually absorbed by the profile in the previously known devices is therefore only approximately 20%. Furthermore, due to the uncontrolled propagation, the microwaves can have an undesirable influence on other components in or on the device.For example, when several microwave sources are located in close proximity to each other, a detrimental crosstalk effect can be observed. Furthermore, the microwaves must be extensively absorbed before they exit the device to prevent damage to the surrounding area.

[0008] The object of the present invention is to provide a device of the type mentioned above in which at least one of these disadvantages does not exist or exists to a lesser extent.

[0009] This object is achieved by an object having the features of claim 1. Advantageous developments of the invention are specified in the subclaims.

[0010] According to the invention, the device comprises a monomode applicator into which microwaves from the microwave source can be coupled, wherein the at least one monomode applicator has a first opening for inserting and removing the workpiece. A monomode applicator is a component in which at least one microwave can propagate as a monomodal wave, such as a waveguide, stripline, strip conductor, or a cavity resonator. A waveguide, stripline, or strip conductor has an input opening and another opening as an output opening for the microwave, wherein the microwave propagates from the input opening to the output opening.

[0011] A cavity resonator, on the other hand, has only one such opening through which the microwaves are coupled in and out. The microwaves are reflected off a wall, usually opposite the opening, and the length of the resonator is tuned to the wavelength of the monomodal microwaves in such a way that a standing wave is created.

[0012] The cross-sectional profile of the monomode applicator can, in principle, be chosen arbitrarily, but is typically rectangular or round. The propagation capability of an individual wave mode is determined primarily by the geometry and, in particular, by the geometry of the hollow cross-section of the monomode applicator. A wave mode is propagable if the wavelength to be transmitted is smaller than the cutoff wavelength (λ c ) mn belonging to the mode for the respective cross-section. The cutoff wavelength (λ c ) mn is calculated, for example, for a rectangular hollow profile with the height a and the width b as λ c mn = 2 m a 2 + n b 2 .

[0013] For the frequency f = 2.45 GHz preferred in microwave technology, a cutoff wavelength of 122.5 mm is obtained from (λ c ) mn = c ÷ (fc ) mn , where c is the speed of light of 3•10 11 < mm / s. For an H 10 wave, for example, where the cutoff wavelength is calculated with m = 1 and n = 0 as (λ c ) 10 = 2a, this results in a minimum height for the rectangular profile of 61.25 mm. The width of the profile is irrelevant for an H 10 wave. A cutoff frequency (fc ) mn can also be calculated for each cross-sectional profile for each wave mode with a given geometry, whereby the operating frequency must then be higher than this cutoff frequency. The calculation is usually carried out using mathematical simulation programs.

[0014] If a microwave with known properties is fed into the monomode applicator, the resulting monomode wave field can be precisely calculated or determined. This allows the position of the workpiece relative to the microwave field to be determined such that the workpiece lies in the area of a wave maximum or passes through the monomode applicator in the area of a wave maximum and can thus absorb the greatest possible amount of energy from the microwave and use it for heating. In addition, the known microwave field can be used to preferentially expose individual areas of a workpiece with complex geometries by aligning the workpiece to the microwave field. This allows the material properties to be selectively adjusted for specific applications, for example during the vulcanization of a rubber sealing profile. On the other hand, for workpieces with uneven material distribution, it is also possible to heat all areas equally.

[0015] With such monomode applicators, the proportion of microwave energy absorbed by the workpiece can be greatly increased compared to known devices by the targeted placement of the workpiece in the microwave field.

[0016] In addition, the volume power density P of the wave field can also be greatly increased, since the entire energy of the microwave source is concentrated in the single-mode wave, so that its electric field strength E increases. The volume power density P in W / m 3 is calculated from the electric field strength using the following formula: P = 2 π • f • ε 0 • ε r ′ • tanδ • E 2

[0017] Where f is the frequency in Hz, ε 0 is the electric field constant in As / Vm, ε r ' is the real part of the complex relative dielectric constant, tanδ is the material-specific loss factor of the polar material, and E is the electric field strength in V / m. The volume power density increases significantly with the field strength, since the field strength is quadratically included in the calculation formula.

[0018] By using the monomode applicator according to the invention, the overall energy efficiency of the device can be increased, thereby saving production resources. On the other hand, the proportion of wave energy radiated from the monomode applicator through any coupling opening is also low, so that smaller absorbers are sufficient to capture this wave component. Finally, a very significant advantage of using a monomode applicator is that, due to the very efficient use of the input energy, even weakly and very weakly polar materials can be heated with microwaves, including materials that would normally no longer be considered polar.

[0019] The monomode applicator is designed so that no microwaves can escape uncontrollably, and the resulting microwave field only spreads within the easily controlled interior space. This eliminates any negative impact on other components of the device. The monomode applicator is preferably closed except for the at least one opening for inserting and removing the workpiece and the input and output openings for the microwaves. The at least one opening for inserting and removing the workpiece can also be provided with a seal to prevent microwaves from escaping from the monomode applicator.

[0020] The monomode applicator is designed for continuous operation and, in addition to a first opening for inserting the workpiece, has a second opening for removing it. This second opening is then opposite the first opening, so that, for example, a profile-shaped continuous workpiece can be fed through the monomode applicator from the first to the second opening, as is also the case with cavities known from the prior art. This method is used, for example, to produce rubber seals for car doors.

[0021] In a continuously operated device with a single-mode applicator, the workpiece's transport direction can be transverse or parallel to the propagation direction of the microwaves in the single-mode applicator. In the first case, the path the workpiece travels through the microwave is comparatively short, but the position of the workpiece in the microwave field can be precisely selected, and the workpiece can be selectively cross-linked if it is a standing wave, such as in a cavity resonator. If the workpiece's transport direction is parallel to the propagation direction, longer distances can be covered with a single-mode applicator, but each area of the workpiece absorbs the same amount of microwave energy, since the profile passes through the wave maxima and minima one after the other.

[0022] In a continuous process, several monomode applicators can be arranged one behind the other in the workpiece transport direction, with the workpiece passing through them. This allows specific heating sequences to be set, or different areas of a workpiece to be heated sequentially, depending on how the workpiece is aligned with the respective microwave field in the individual monomode applicators.

[0023] In a preferred embodiment, the at least one monomode applicator comprises a measuring device for measuring the energy density of microwaves reflected in the monomode applicator and a tuning device for adjusting properties of a microwave generated by a microwave source, wherein the measuring device and the tuning device are components of a control loop for adjusting a minimum energy density of the reflected microwaves. Thus, on the one hand, the microwave field can be finely adjusted to ensure maximum energy absorption by the workpiece. On the other hand, the amount of energy reflected back toward the microwave source in a cavity resonator can also be minimized, so that as little energy as possible needs to be absorbed by an absorber.

[0024] A monomode applicator can also have multiple areas with different geometries, with different monomodal microwaves capable of propagating in at least two of these areas. The monomode applicator can be designed so that the workpiece passes through these areas sequentially and is thus exposed to different microwave fields within a single monomode applicator. In this way, the heating process can be designed in a targeted manner, as with sequentially arranged monomode applicators, or different areas of the workpiece can be selectively heated sequentially, requiring only a single monomode applicator.

[0025] In addition to the at least one monomode applicator, the device can also have a cavity, such as those previously known from generic devices. In particular, this can be a hot gas cavity in which hot gas, in particular hot air, flows around the profile and is thus heated by convection. Means for generating infrared radiation, with which the workpiece is heated by radiant heat, can also be provided in such a cavity. Monomode applicators according to the invention can then be arranged in the cavity to design a compact overall device. Alternatively, for example, in order to avoid exposing the monomode applicators to the temperatures within the cavity, they can also be arranged in front of and / or behind the cavity in the transport direction of the workpiece.However, the at least one monomode applicator can also be used alone, without any additional means for heating the material, and can provide the entire crosslinking of the material contained in the workpiece.

[0026] In a preferred embodiment, the at least one monomode applicator is composed of multiple parts, and the parts can be separated from one another, particularly for inserting or placing a workpiece. Thus, the workpiece can be easily inserted into the monomode applicator at the beginning of a continuous process when the parting plane intersects the openings for inserting and removing the workpiece. The interior of the monomode applicator is also easily accessible for maintenance work.

[0027] If the at least one monomode applicator is arranged in a cavity that is accessible from one side through a flap or lid, one of the parts of the monomode applicator can be connected to this flap or lid. Particularly preferably, the connection is designed such that when the flap or lid is opened, the monomode applicator also opens, specifically in such a way that the workpiece can be inserted into it. Thus, when the cavity is opened, the workpiece can be inserted along the entire processing path, both inside and outside the applicator.

[0028] A microwave trap is preferably provided on the monomode applicator at the first and, if applicable, the second opening for inserting and removing the workpiece. This trap is intended to prevent microwaves from escaping or coupling from the monomode applicator into its surroundings, in particular into the surrounding cavity, and possibly causing damage there, exerting undesirable influences on other components, or interfering with other microwaves in the cavity. The microwave trap can, for example, be designed as a hollow body, in particular as a tube, whose cross-section and length are dimensioned such that the monomodal microwave cannot couple or escape from the monomode applicator into the cavity or its surroundings. The hollow body does not necessarily have to be made of a conductive material. It is also possible to form the hollow body from or provide it with a material such as Teflon or silicon carbide, which absorbs microwaves very well.In a preferred embodiment, such a microwave trap is constructed with a Teflon tube that extends through a hollow body made of a conductive material. Here, the hollow body can serve to reflect microwaves that have not yet been fully absorbed by the absorption material in the microwave trap toward the absorption material.

[0029] It has been found that with the monomode applicator according to the invention it is possible to crosslink a large number of elastomers and not only rubber, in particular those elastomers which require a comparatively high energy input for crosslinking because, for example, they absorb only little microwave energy and have not previously been considered suitable for crosslinking with microwaves. The device according to the invention is particularly suitable for crosslinking materials selected from the group of natural rubbers, polybutadiene rubbers, styrene-butadiene rubbers, acrylonitrile-butadiene rubbers, chloroprene rubbers, isoprene rubbers, butyl rubbers, ethylene-propylene rubbers, polysulfide rubbers, polyurethane rubbers, fluororubbers, chlorosulfonylpolyethylene rubbers and silicone rubbers, including cold- and hot-crosslinking silicone rubbers and liquid silicone rubber.The latter, in particular, has previously been considered unsuitable for microwave crosslinking. The material does not necessarily have to be polar.

[0030] In the following, the invention is explained in more detail with reference to figures in which preferred embodiments of the invention are shown.

[0031] They show: Fig. 1: a side view of an apparatus according to the invention, in which a workpiece is guided parallel to the propagation direction of the microwaves in a waveguide; Fig. 2: a profile view of a waveguide through which a profile-like workpiece passes, with the E and H fields drawn in; Fig. 3: a side view of an apparatus according to the invention, in which a workpiece is guided transversely to the propagation direction of the microwaves through several cavity resonators; Fig. 4: a side view of an apparatus according to Figure 3, wherein the cavity resonators have two different regions; Fig. 5: a side view of a device according to Figure 3 and 4 , where the cavity resonators have three different regions.

[0032] Figure 1shows a device 1 according to the invention with a cavity 2 through which a workpiece 3 in the form of an endless profile is passed. A monomode applicator 4 in the form of a hollow waveguide is arranged within the cavity 2. The hollow waveguide comprises a feed conductor 6 and an output conductor 7, as well as an application region 8 in which the microwaves propagate parallel to the transport direction T of the workpiece 3. The application region 8 is designed such that a monomode wave can propagate therein and act on the workpiece 3, causing it to be heated. Both the workpiece 3 and the monomode wave move in the transport direction T of the workpiece 3, with the wave usually moving through the applicator 8 considerably faster than the workpiece 3.On average, each part of the workpiece 3, both viewed longitudinally and in profile, absorbs the same amount of wave energy and the workpiece 3 is heated uniformly.

[0033] The workpiece 3 is in the embodiment according to Figure 1 guided in a working tube 10 for mechanical protection. The working tube 10 is made of a material transparent to microwaves, such as Teflon or quartz glass, and can therefore easily be guided through the single-mode applicator.

[0034] Figure 2shows a hollow waveguide 11 with a round profile, through which a workpiece 3 is guided centrally in the transport direction T, which here points out of the plane of the drawing. A monomode wave is also formed in the hollow waveguide 11, which propagates in the same transport direction T as the workpiece 3. The E-field component 12 of the microwave field is shown with the arrows pointing from bottom to top, with the distance between the arrows indicating the energy density of the field. In the same way, the H-field component 13 of the monomode wave is shown with arrows pointing from left to right. It can be seen that both the energy density of the E-field component and that of the H-field component are maximum in the region in which the workpiece 3 is guided through the microwave field. The microwave field or the E and H components 12, 13 of the microwave field are known or calculable in a monomode applicator according to the invention.Therefore, the workpiece 3 can be specifically arranged in the microwave field or guided through it in such a way that it absorbs a maximum possible amount of energy from the microwave or in such a way that, viewed in profile, individual areas of the workpiece 3 are preferentially heated by the microwave.

[0035] The Figures 3 to 5 also show devices 1 according to the invention with a cavity 2 and with several monomode applicators 4a to 4d arranged in the cavity 2, through which the workpiece 3 passes one after the other. Figures 3 , 4 and 5In the embodiments shown, the workpiece 3, which moves in the transport direction T, passes through the monomode applicators transversely to the propagation direction A of the microwaves. The monomode applicators 4a to 4d are cavity resonators that have only a single opening 14 for coupling in and out the microwaves. On the side opposite the opening 14, the monomode applicators 4a to 4d have walls 15 at which the microwaves are reflected, so that standing waves arise in the cavity resonators, as in the Figures 4 and 5 are indicated schematically.

[0036] In monomode applicators 4a to 4d, which are cavity resonators and in which the workpiece 3 passes through the microwave transversely to the propagation direction A, the energy distribution of the microwave field across the profile of the workpiece 3 is always the same. Depending on the relationship between the profile shape and dimensions of the workpiece 3 and the wavelength of the standing microwave, the profile can then be heated particularly uniformly or selectively. In order to ensure uniform or selective heating for more complex profile shapes of the workpiece 3, or to implement a specific heating sequence, Figures 4 and 5As shown, the cavity resonators can be divided into several regions in which different monomode waves are capable of propagating as cavity resonators due to the different geometries of the regions. Depending on the geometry of the respective regions, a different energy distribution of the microwave field can be provided in each region for the profile of the workpiece. If the geometry of the regions can be changed by moving walls (possibly by a motor) of a region of the monomode applicator or by changing its diameter, even the monomode wave can be changed during operation. Figure 4 Cavity resonators are shown, which are divided into a central region 16 and two identical side regions 17a, 17b, with different monomode waves being able to propagate in the central region 16 and the side regions 17a, 17b. The microwaves are coupled from the central region 16 into the side regions 17a, 17b.

[0037] In the embodiment according to Figure 5 the cavity resonators 3 have different regions 16, 17, 18, which are successively passed through by the workpiece 3. The side regions 17, 18 are formed as in the embodiment according to Figure 4 fed by the central area 16.

[0038] For all transverse cavity resonators of the Figures 3 , 4 and 5 , tube attachments 21a, 21b are provided at the workpiece openings 20a, 20b on the outside of the monomode applicator. These serve to shield the cavity resonator. They prevent microwaves from escaping from the cavity resonator into the cavity 2, where they could potentially cause damage or undesirable influences on other components or interfere with other microwaves in the cavity.

Claims

1. Device (1) for cross-linking one or more materials, in particular polar materials, in particular rubber, contained in a workpiece (3) by means of microwaves, having at least one microwave source and at least one single-mode applicator (4) into which microwaves from the microwave source can be coupled, wherein the at least one single-mode applicator (4) has a first opening (20a) for introducing the workpiece (3) and a second opening (20b) for guiding the workpiece (3) out, so that the workpiece (3) can be guided through the single-mode applicator (4), characterized in that a microwave trap is provided at the first opening (20a) and the second opening (20b).

2. Device (1) according to claim 1, characterized in that the at least one single-mode applicator (4) is a waveguide which is suitable for conducting single-mode microwaves.

3. Device (1) according to claim 1, characterized in that the at least one single-mode applicator (4) is a strip conductor suitable for conducting single-mode microwaves.

4. Device (1) according to claim 1, characterized in that the at least one single-mode applicator (4) is a cavity resonator in which a single-mode standing microwave can form.

5. Device (1) according to one of the preceding claims, characterized in that the first opening (20a) is closable.

6. Device (1) according to one of the preceding claims, characterized in that the transport direction (T) of the workpiece (3) runs transversely or parallel to the propagation direction (A) of the microwaves.

7. Device (1) according to one of the preceding claims, characterized in that a plurality of single-mode applicators (4a, 4b, 4c, 4d) are arranged one behind the other in the transport direction (T) of the workpiece (3) and are passed through by the workpiece (3).

8. Device (1) according to one of the preceding claims, characterized in that the at least one single-mode applicator (4) has, in particular in a coupling-in region of the microwave, a measuring device for measuring the energy density of reflected microwaves and a tuning device for adjusting properties of a microwave generated by a microwave source, the measuring device and the tuning device being components of a control loop for adjusting a minimum energy density of the reflected microwaves.

9. Device (1) according to one of the preceding claims, characterized in that the at least one single-mode applicator (4) has a plurality of regions (16, 17, 18) with different geometries, wherein different single-mode microwaves are capable of propagating in at least two of these regions (16, 17, 18).

10. Device (1) according to one of the preceding claims, characterized in that the device (1) has a cavity (2), in particular a hot gas cavity.

11. Device (1) according to one of the preceding claims, characterized in that the at least one single-mode applicator (4) is multi-part and the parts can be separated from one another, in particular for inserting or inserting a workpiece (3).

12. Device (1) according to claims 10 and 11, characterized in that the cavity (2) has a lid and a particularly upper part of the monomode applicator (4) is connected to the lid.

13. Device (1) according to one of the preceding claims, characterized in that the microwave trap is a tubular attachment and / or a hollow body which is preferably, but not necessarily, provided with or consists of a microwave-absorbing material.

14. Use of a device according to any one of claims 1 to 13 for cross-linking one or more materials comprised in a workpiece (3) by means of microwaves, wherein the material or materials are one or more elastomers selected in particular from the group of natural rubbers, polybutadiene rubbers, styrene-butadiene rubbers, acrylonitrile-butadiene rubbers, chloroprene rubbers, isoprene rubbers, butyl rubbers, ethylene-propylene rubbers, polysulfide rubbers, polyurethane rubbers, fluoro rubbers, chlorosulfonyl polyethylene rubbers and silicone rubbers including cold and hot-curing silicone rubbers and liquid silicone rubbers.