DE3130358A1 - DEVICE FOR HEATING AND / OR DRYING CONTINUOUS AREA MATERIALS WITH MICROWAVES - Google Patents

Description

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AGFA-GEVAERT

AKTIENGESELLSCHAFT 5090 Leverkusen, Bayerwerk

Patent department HRS-by-c

3 Q. 07, 81

Run through device for heating and / or drying of flat materials with microwaves

The present invention relates to a device for uniform heating and / or drying wider, using thin sheet-like webs of paper, plastic, textiles and photographic materials an energy transmitter fed by microwaves, which is used to carry out the material symmetrically two-part pipelines that are connected to each other.

Methods for dielectric heating and drying of moist materials by means of high-frequency fields are known - you use frequencies in the range of 13 and 27 Hz on the one hand, and frequencies in the microwave range on the other preferably 2450 MHz used. With this process, for example, paper, textiles and Coatings dried on different supports. Compared to high-frequency processes, microwaves offer higher specific heating outputs, because the heat generated by the dielectric loss in the Material increases proportionally with frequency.

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Conventional microwave dryers for flat materials use meandering pipe conductors running across the web, the material being passed through slots in the pipe conductor, e.g. US Pat. No. 3,672,066, US Pat. No. 3,449,836, US Pat. No. 3,475,827 Materials the local inhomogeneity of the heating, in particular the exponential decrease in the intensity of the wave advancing in the pipe due to the absorption in the material, and the heating due to standing waves, which are caused by reflection on the track edges and the pipe bends in the course of the meandering guidance of the rectangular pipe. Characteristic here are relatively sharply delimited temperature maxima in the material at a distance of half the pipe wavelength. In addition to the special dielectric behavior of the material (e.g. increase in dielectric loss (tg S) with temperature), the squared field strength dependence of the dielectric losses in particular contributes to the development of local overheating. In the arrangement according to GB 2 042 703 A, an attempt is made to reduce the effect of standing waves in pipes oriented transversely to the direction of the web by using two pipe conductors with different positions of the electric field maxima in relation to the point of action of the material passing through. In particular, a coincidence of the maximum field strength in the first pipe conductor with the minimum field strength in the second pipe conductor is sought. By such an arrangement, the effect of standing waves with respect to uneven heating across the web can be reduced, with more absorbent

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Material and larger web widths, on the other hand, remain the heating profile caused by the exponential absorption of the wave exist.

The invention is based on the object of a device of the type mentioned in the introduction, with which it is possible in a simple manner to have both a Heating and drying of the material as evenly as possible over the width of the material, in particular of the coatings of carrier materials, as well as, if certain maximum temperatures are observed, one as possible to achieve quick drying.

Based on a device of the type mentioned at the outset, this object is achieved according to the invention by that

a) the individual pipe elements parallel to each other and in their longitudinal direction parallel or in a small angle (3?) to the direction of travel of the Web are arranged,

b) the number of pipe elements proportional to the Width of the web is selected,

c) the width of the individual pipe elements are dimensioned _{according to the design of the H 10 field type,}

d) the length of the individual pipe elements is matched to a whole number of half-waves.

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e) to adjust the effective in each pipe element Microwave power magnetically acting adjustable iris couplers are provided, the one uniform or any course of the supplied microwave power transversely to the direction of web travel enable,

f) for feeding the individual pipe elements separate microwave generators are used in connection with circulators and

g) that to avoid unwanted electromagnetic Couplings between the pipe elements alternating an offset of the pipe elements ura one Quarter tube wavelength is provided.

It has now been found that, surprisingly, a completely uniform heating across the web results when parallel to the direction of travel of the web oriented pipeline systems are used, the number of parallel pipelines being proportional to the Web width is selected ..

In contrast to conventional microwave dryers, in which the sheet-like material passes through slots in a pipe is guided, which is arranged perpendicular to the web running direction, is in the "claimed method an arrangement of several parallel, two-part pipelines short-circuited on both sides used, which is oriented in the direction of travel of the web

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are. The length of the individual pipe conductors is matched to a whole multiple of half the pipe wavelength, the number of halves is like this chosen large that, taking into account the microwave absorption by the web material, an approx. 50% absorption the first time through the microwave by the pipe system fed at the end. The excitation in the pipe is thereby through a predominant proportion of continuous waves and a smaller proportion of standing waves. Due to the high attenuation of the standing wave (resonance), a critical coordination of the individual pipe conductors is required on the frequency of the generator is not required, in particular, minor detunings can be caused by materials different humidity can be tolerated. Another essential feature of the device is the parallel feed of the individual pipe conductors through separate microwave generators and circulators, the individual control and regulation of the power supplied by iris couplers and the practically completely uniform heating of the material in the transverse direction through slight twisting the direction of the pipe compared to the direction of travel of the Materials. Standing waves in the individual pipe conductors do not cause uneven heating of the material at right angles to the direction of travel, because the pipe conductors are arranged in the direction of travel and only a few degrees with it differ. All pipe halves are in two mirror-symmetrical shapes integrated metallic half-shells, one of which is used to introduce the material and

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supply purposes is designed to be hinged. Compliance maximum material temperature is ensured by the constant Control of the microwave excitation acting in each pipe conductor and through the process of direct current heating / i.e. the same direction of movement of the material and the fed-in microwave.

The pipe conductors arranged in parallel are to the * pressure of the radiation and coupling with each other with larger gap widths by means of conductive webs. bound. These webs reduce the unwanted electromagnetic Coupling between the individual pipelines that run parallel at a short distance. The width the web is in the range of 20 to 200% of the gap width and is corresponding to the microwave absorption chosen by the material. The individual pipe conductors represent strongly damped microwave resonators, which are operated at the frequency of the generator. The resonators are damped by the sorption of the material. Given a given microwave absorption of the material, there is one with the length of the pipe supplier increasing damping of the resonance. The wave is almost completely in the Material absorbed. For a given pipe length the attenuation increases with the absorption of the material, e.g. with increasing water content.

In general, if there is high attenuation, there is only a small amount of undesired electromagnetic coupling between adjacent ones Pipelines takes place: the web width can therefore

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be chosen relatively low. Conversely, the web width must be selected larger in the case of low absorption of the material (low moisture). A typical embodiment uses a gap width of 20 mm when feeding the pipe conductors with a frequency of 2450 MHz, a web width of 20 mm and a length of the pipe conductor of η = 10 half waves. With this dimensioning you can

2 materials can be effectively heated and dried with approx. 20 to 200 g H ₂ O / m (free water), whereby several dryers can be connected in series to limit the maximum temperatures. Such water-containing materials show absorptions of more than 3 db / m. If, for example, the length of such a pipe is set at 1 m, then there is an absorption of more than 75% when the microwave flows back and forth. This results in a relatively low waviness of the field profile along the pipe and the maximum electric field strength that occurs is severely limited so that electrical discharges emanating from metallic edges are avoided, which is of great importance when drying photographic material or thermally sensitive layers.

The material has a high level of microwave absorption especially in the initial stages of drying (wet area) before, in advanced drying and in the so-called Residual moisture range (e.g. equilibrium moisture compared to the relative moisture of the surrounding or towing puff) the microwave absorption can be down to less than

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1 db / m drop. The efficiency of a dryer of the same length but falls only slightly with decreasing absorption of the Material, because the field strengths in the pipe acting as a resonator due to the lower attenuation increase, whereby an equalization occurs: the dielectric heat loss P generated in the material is:

P = -1 £ ₀ . co. E ² . £ "

with Qq, a dimensionless constant for the dielectric properties in a vacuum, Cu = frequency, E = electric field strength, <5 "dielectric loss. In the case of very low absorption by the material, the length of the pipe can be up to 20 half-waves and can be enlarged more.

The undesired "electromagnetic, mainly electrical" coupling increases with lower material absorption. To avoid the excitation of other field types and radiation at the edge of the dryer, the web width is increased to up to 200% of the gap width between the half-shells. A special possibility of suppressing the coupling between adjacent tubular conductors resulted in a surprisingly simple manner by the alternating arrangement of the tubular conductor, that is, by. alternately displacement of adjacent tube conductor is / \ / 4 in the longitudinal direction. the coupling via the electrical component is characterized so strongly suppressed that in adjacent tube conductors, the electrical and magnetic maxima of the standing wave component are opposite to one another

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especially with a high proportion of standing waves, i.e. at short pipe length and / or low material absorption (residual moisture range) is an advantage.

The size of the permissible gap width between the "half-shells containing the pipe conductor halves" is ultimately limited by the radiation to the outside. Even with a very large web width (more than 200% of the gap width), the gap width must be below half the free space wavelength stay. At 2450 MHz, values of in the extreme case 40 mm can be achieved. However, they are preferred Gap widths from 10 to 25 mm. In the case of gap widths over about 20% of the free space wavelength, the result is the distortion of the electric field curve of the H. wave an increasing decoupling of material passed through, so that at 2450 MHz gap widths over 25 mm are of little importance (for thin, dense materials up to approx. 1 mm). By using low frequencies, e.g. 915 MHz, correspondingly larger gap widths can be realized.

With gap widths about the size of half the pipe dimension results in a direction to the surface normal Particularly flat course of the electric field strength in the middle of the gap, even if the material guidance is not exact in the middle a relatively even microwave distribution.

sorption (heating) delivers.

The pipe elements are preferably of the same length and

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have a length of a multiple of half the wavelength of the feeding microwave, i.e. η .Α. / 2, where η can be a factor between 2 and 20 (n = 2.3, 4 .... 20).

The coordination of the pipe elements to resonate with the feeding microwave takes place through short-circuit slide and / or dielectric rods in the pipe elements both half-shells, which by means of adjustment devices more or less in the pipe elements can be brought in ·.

The setting of the range of services across the board primarily serve the coupling elements for <3ie microwave energy, the so-called iris couplers the strength of the magnetic coupling between the rectangular pipe feed line coming from the generator and the Determine pipe elements. Preferably with the variable iris coupler made an anechoic setting, with the control of the reflected Power at the output of the circulator takes place.

If the pipe conductors are tuned to resonance with the short-circuit slides, the iris couplers any heating profiles can be realized, for example also the increased heating of the edge areas. Preference is given to setting the same heating output per cm of web width, with compensation different output of the generators can. The iris coupler can be adjusted manually or automatically such as the control of the local rail time

W perature.

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The iris couplers are preferably arranged in a distance of a quarter tube wavelength away from the end of the Rohrleiterelemen'te.

To measure the strength present in each pipe the microwave intensity are square detectors opposite the coupling point in the foldable Half-shell arranged. These are not only used to monitor microwave excitation during operation, but they are also used to adjust the resonance tuning of the pipe conductors with the variably adjustable Short-circuit slide used.

The microwave energy is fed into a preferred embodiment on the entry side of the web. For effective use of the dryer or heating device includes rapid heating of the material on the inlet side to the maximum permissible material temperature and maintaining this value as evenly as possible during the passage through the area of action of the dryer. This requirement is met by the use of the so-called direct current principle. The direction of travel of material and microwave radiation in the pipes are in the same direction. Feeding the Microwave takes place on the inlet side of the material. The highest microwave power density on the inlet side causes a rapid rise in temperature in the material, while that in the direction of travel in the Pipeline exponentially decreasing microwave intensity is mainly used to cover the heat of vaporization.

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This principle becomes the common tendency that the temperature of the material on the exit side of the dryer is considerably higher than in large areas of the dryer, counteracted. Details of the temperature profile of the material in transit due to the dryer, of course, depend heavily on the material properties and the dwell time in the dryer away.

A particularly important feature of the arrangement according to the invention is the slight entanglement of the longitudinal direction of the pipe with respect to the direction of travel of the material. The setting of the angle j £ between the direction of movement of the material (web edge) and the longitudinal direction of the pipe serves to achieve uniform heating across the web. In the case of an exactly parallel alignment cG = O, only slight heating would result in the area of the webs. These strips of low heating become increasingly smaller as the angle ° 6 increases from zero until, depending on the web width, a value is assigned at which the lowest waviness of the local heating profile results across the web. This optimum angle Qf 'is reached when there is an approximately 10 to 20% overlap of the strips of material grasped by the pipe conductors. The value oC 'depends on the ratio of the gap width to the pipe dimension (narrow side) and, to a lesser extent, on the dielectric properties of the material. The feature of the arrangement is therefore a possibility of adjusting the angle during operation of the dryer.

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The microwave generators are preferred in a Execution foria on frequencies of 915 MHz: or 2450 MHz set.

The entirety of the pipe halves of each half-shell is through a gas-tight cover with a thin, low-loss film to prevent contamination of the Ducts or condensation covered. In connection with the hinged construction results such an easy way of cleaning the dryer. This cover lies directly on the Surface of the half-shells and is periodic in the area of the webs and at the edge of the half-shells Nozzle heads recessed at intervals fixed throughout. The nozzle heads located in the web area are used to supply entrained air, nitrogen and protective gases in the removal of flammable vapors to reduce their Ensure removal without condensation. The gases are fed in from the rear of the half-shells and can be tempered.

The following is an embodiment of the invention described in more detail with reference to drawings. It shows:

Fig. 1 is a plan view of the device shown in simplified form,

Fig. 2 shows a partial section through the device along the line ÄÄ in Fig. 1,

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3 shows a partially cut-open device showing all the elements.

In Fig. 1, a microwave heating and / or drying device 1 is shown in the opened state in a simplified form. The web to be dried is moved through the device 1 from the left (arrow). The microwave device 1 consists of two half-shells 1a, 1b, which are hingedly connected to one another, for example. In the shells, pipe conductors 3 are incorporated parallel to one another, which are arranged crossed at an angle cC with respect to the direction of travel of the web. The entanglement 5 by the angle cC serves to achieve uniform heating of the web 2 transversely to its running direction. In a preferred embodiment, the angle can be adjusted either by changing the direction of travel of the web or by rotating the device 1 relative to the direction of travel of the web so that the slightest waviness of the local heating profile transversely to the web 2 arises.

The set 5 causes about a 10 to 20% overlap the strip of material grasped by the pipe conductors 3. The energy is used by the microwave device from a microwave generator 6 via a circulator and a rectangular pipe 9 and supplied via iris couplers 4 transferred to the pipe ladder 3. On the opposite side of the pipe to the energy supply side 3 are to tune the pipe conductors 3 to resonance short-circuit gate valves 8 in all pipe conductors 3 arranged.

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Fig. 2 shows a partial section through the mirror-symmetrically constructed half-shells la, 1b of the microwave device 1. The pipe conductors 3 are rectangular and are interrupted by a gap S through which the web 2 is passed. Ib and the conductive webs 15 are formed. The width b of the individual pipe elements 3 is _{dimensioned according to the design of the H 1Q} field type. (The field type in the right pipe is of the H ₁₀ (TE-10) mode). The width f of the conductive webs 15 between the adjacent pipe conductor halves 3 is between 20 and 200% of the gap width S.

In Fig. 3, a microwave device 1 is shown with all devices according to the invention. For representation of all parts, the web 2 was cut and the upper half-shell 1b partially cut and unfolded shown. The path 2 is in the direction of the arrow passed through the device 1 via rollers. The energy for heating and drying the web 2 is generated by microwave generators 6 via circulators 7, Rectangular feed lines 9 are fed to the device 1 and fed into the pipe 3 with iris couplers 4. The iris couplers 4 determine the strength of the magnetic coupling between the rectangular tube feed lines coming from the generator 6 9 and the pipe elements 3 are adjustable by adjusting devices 16 and protrude into the Border area between the pipe elements 3 and

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The Rohrleitereleraente 3 are in the lower half of the shell 1a drawn in dashed lines and the associated upper parts shown in the upper shell half 1b. By arranging the tubular conductor elements 3 in such a way that every second element by a quarter tube wavelength A / 4 is shifted in the longitudinal direction against the adjacent element, there is a special one Possibility of suppressing the coupling between adjacent pipes 3. The length of the two ■ side short-circuited pipe 3 is n times half the tube wavelength Δ, where η can be between 2 and 20.

The resonance of the microwave energy in the device is set with short-circuit slide 8, which with a Adjusting device 17 are designed to be adjustable. Dielectric tuning elements can also be used for tuning 14 can be used. To measure the strength of the microwave intensity present in each pipe conductor 3 square detectors 12 are arranged opposite the coupling point, these detectors 12 are used both to monitor the microwave energy during operation and to tune the pipe conductors by resonance 3 with the short-circuit sliders 8 or the dielectric tuning elements 14.

The entirety of the pipe conductor halves of each half-shell '1a, 1b is by a gas-tight cover with a thin low-loss film 10, preferably made of approx. 0.2 mm thick PTEE (Teflon), glass fabric reinforced,

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Covered to prevent contamination of the pipe ducts or the formation of condensation. In connection with the hinged construction (arrow), this results in a simple way of cleaning the device. This cover 10 rests directly on the surface of the half-shells 1a, 1b and is continuously fixed in the area of the webs and at the edge of the half-shells 1a, 1b by nozzle heads 11 sunk at periodic intervals. The nozzle heads 11 located in the web area serve to supply air or gases in the removal of flammable vapors / to ensure their removal without the formation of condensation. The drag air is supplied from the rear of the half-shells Ia ₇ 1b and can be tempered beforehand.

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Claims (16)

Patent claims : 1. / 'device for uniform heating and / or - '' Drying wide, thin, two-dimensional strips Paper, plastic, textiles and photographic materials using one with microwaves powered energy transmitter, which is used to carry out the material from symmetrically split pipes consists, which are interconnected, characterized in that a) the individual pipe elements (3) parallel to each other and in their longitudinal direction parallel or at a small angle (oC) to the running "■ direction of the web (2) are arranged, b) the number of pipe elements (3) proportzonal selected the width of the web (2) is, c) the width (b) of the individual pipe elements (3) are _{dimensioned according to the design of the H 10} field type, d) the length of the individual pipe elements (3) matched to a whole number of half-waves (A / 2) is, e) to adjust the microwave power effective in each pipe element (3) magnetically AG 1798 O I OUO OO adjustable iris couplers (4) • are seen that have an even or smooth allow any course of the supplied microwave power transversely to the direction of travel of the web, f) separate microwave generators for feeding the individual pipe elements (3) (6) can be used in conjunction with circulators (7) and g) that in order to avoid undesired electromagnetic coupling between the pipe elements (3) alternating an offset of the pipe elements (3) by a quarter tube wavelength (/ i / 4) is provided. 2. Device according to claim 1, characterized in that that several pipe halves (3) arranged in parallel and are connected to one another by parallel conductive webs (15) to form a continuous half-shell (1a, 1b). 3. Device according to claim 1, characterized in that that the energy transmitter consists of two mirror-symmetrical constructed half-shells (1a, 1b), each containing all pipe halves (3), consists. 4. Apparatus according to claim 3, characterized in that the half-shells (1a, 1b) on one longitudinal side of the Energy carriers are hingedly connected to each other AG 1798 - 20 / - are and a stationary half-shell (1a) and one hinged half-shell (1b) are present. 5. Apparatus according to claim 1, characterized in that that the width (f) of the conductive webs (15) between the adjacent pipe conductor halves (3) between 20% and 200% of the gap width (S) between the pipe conductor halves (3) assigned to one another. 6. Apparatus according to claim 1, characterized in that that the gap width (S) between the pipe halves (3) or the half-shells (1a, 1b) between 2% and 40% of the free space wavelength of the feeding microwave lies. 7. Apparatus according to claim 1, characterized in that the length of the individual pipe elements (3) is the same and η. A / 2 is with η = 2,3,4 to 20. 8. Apparatus according to claim 1, characterized in that for the coordination of each pipe element (3) In response to the feeding microwave, the pipe elements (3) in both half-shells (1a, 1b) each with a KurζSchlußschieber (8) and / or dielectric Rods (14) are equipped. 9. Apparatus according to claim 1, characterized in that that for the variable coupling of the microwave energy in the pipe parent elements (3) acting magnetically Iris coupler (4) in the narrow sides of the rectangular profiles of each of the pipe elements (3) in the stationary Half-shell (1a) are provided. AG 1798 O I O U O J - t 10. The device according to claim 9, characterized in that the iris coupler (4) at a distance of one Quarter tube wavelength (* »/ 4) from the end of the tube elements (3) are located remotely. 11. The device according to claim 1, characterized in that that for continuous control and adjustment of the microwave excitation in each pipe element (3) a detector (12) is provided at a point opposite the coupling point. 12. The device according to claim 1, characterized in that that the feeding (6,7,9) of the microwave energy is carried out on the inlet side of the web (2). 13. The device according to claim 1, characterized in that the angle (oC) between the longitudinal direction of the Tubular elements (3) and the running direction of the web (2) adjustable for even heating in the transverse profile is. 14. The device according to claim 1, characterized in that the frequency of the microwave generators (6) 915 or 2450 MHz is set. 15. The device according to claim 1, characterized in that the web (2) facing surfaces of the two half-shells (1a, 1b) with a 0.1 to 0.5 mm thick protective film (10) with a low dielectric constant are covered gas-tight. AG 1798 16. The device according to claim 15, characterized in that that the protective film (10) is fixed in the area of the webs (15) by sunk nozzle heads (11) is, which serve at the same time for the supply of gases to remove vapors from the web (2). AG .1798