CN1268017A - High-uniformity multimode microwave cavity for ceramic processing - Google Patents

Abstract

The present invention belongs to the field of material processing technology and equipment, and the microwave cavity includes an enclosed microwave heating cavity and a 3 dB phase-shifting bridge waveguide installed below the underplate of the cavity. In the common wall between the waveguide and the heating cavity, there is channel hole as coupling element, and inside the cavity there is heat insulating structure. The present invention can raise the uniformity of microwave heating greatly to sinter dense ceramic product without using mechanical rotating mechanism, and has the advantages of high uniformity, no microwave leakage and no noise.

Description

The high-uniformity multimode microwave cavity that is used for pottery processing

The invention belongs to material processing technique and equipment technical field.

Engineering ceramics is more and more used at present, as the supercharger rotor of automobile engine, spark plug etc.The sintering method energy consumption of conventional oven formula thermal source is big, and sintering velocity is slow, and produces a large amount of pollutions, and microwave heat is to rely on the coupling of microwave field and material that material is heated, be a kind of mode of interior heat, do not have above-mentioned shortcoming, thereby promise to be desirable ceramic post sintering thermal source.But because pottery is the low-dielectric loss material, be used for the microwave electric field of its processing and microwave power, thereby need the microwave heating chamber of particular design far above common domestic microwave heating furnace.High electric field like this and high power add that the positive feedback effect (place that temperature more high more easy absorption microwave) of microwave in ceramic heat makes the heating uniformity problem very outstanding, and inhomogeneous heating can make and be prone to heat spot very much on the object to be processed and make course of processing failure.

The method that existing microwave heating equipment adopts in order to improve heating uniformity utilizes the mode stirrer method to change chamber internal electric field pattern; The periodically-varied cavity size; Modes such as translation or rotation material.These methods all have certain effect to the uniformity of improving microwave heating.Their something in common is that material to be machined is moved, or use the mechanical agitation parts that the chamber internal electric field is changed, thereby its shortcoming is all to need to adopt in microwave cavity the parts of motion to cause microwave leakage or sparking, also just limit the raising of microwave power, and can only improve the inhomogeneous inhomogeneous heating that causes of field distribution on the direction of transfer.Use the microwave source of higher frequency also can improve heating uniformity (as 28GHz, 60GHz then is 2450MHz at present), but when frequency increases, add that thermal penetration depth is corresponding to be reduced, and equipment cost can greatly increase.The mode that strengthens cavity size also can increase heating uniformity, but the microwave field density in the chamber can be reduced to the heating that is not enough to carry out ceramic material.Therefore wish to search out to improve the inhomogeneity new way of microwave heating.

The objective of the invention is for overcoming the weak point of prior art, a kind of high-uniformity multimode microwave cavity that is used for pottery processing is proposed, adopt the microwave coupling aperture of 3db phase shift bridge and particular design to make the microwave of feed-in in microwave cavity, produce rotary electromagnetic field, improved the uniformity of microwave heating greatly, make the ceramic product that microwave can the sintering even compact, exempted simultaneously to increasing the mechanical type rotating mechanism that uniformity adopts, it is good to have heating uniformity, no microwave leakage, advantages such as noiselessness.

A kind of high-uniformity multimode microwave cavity that is used for pottery processing that the present invention proposes, it is characterized in that, the microwave heating cavity that comprises sealing, be installed in the 3db phase shift bridge waveguide under this well floor, have slotted eye on the common wall of said waveguide and heating cavity, and be arranged on the insulation construction in this cavity as coupling element.

Said slotted eye as coupling element can be two orthogonal coupling slits.

The waveguide of said 3db phase shift bridge can be made up of two standard BJ-22 waveguides arranged side by side, and its common side-wall has the slit that length is Δ,

λ wherein _g' and λ _g" be respectively TE in the wide waveguide ₁₀, TE ₂₀The guide wavelength of ripple; In this slit, be provided with the capacitive compensation screw.

Said insulation construction can comprise two layer box bodies made from porous crack alumina material, layer box body the inside is provided with an alumina crucible that holds pottery to be processed in this, be filled with alumina fibre between said two layer box bodies, be filled with the carborundum fragment between layer box body and the alumina crucible in being somebody's turn to do, the upper wall of two layer box bodies has the thermometer hole that runs through.

The microwave heating cavity of said sealing can be the circular cylindrical cavity of the closed at both ends that is made of copper material, and cavity diameter D is 240mm, and housing depth H is 312.9mm, and the loam cake of this sealing is equipped with the infrared temperature probe seat that is used for thermometric.

Principle of the present invention is to utilize waveguide 3db bridge to produce the exciting current of phase difference for pi/2, microwave coupling aperture by particular design makes the microwave of importing produce the electromagnetic field of rotary polarization in the microwave cavity of certain size, thereby improves the uniformity of Electric Field Distribution in the microwave cavity greatly.Because microwave heating is a kind of mode of heating of body heat source formula, the surface emissivity heat radiation can make surface temperature be lower than the material internal temperature, and suitable heat preserving mode is another essential condition that processes the uniform ceramic product of quality.Because the dielectric loss of ceramic material is very little, must there be certain trigger means to make machined material be suitable for the microwave system of pottery processing in formation.

Effect of the present invention:

The present invention has adopted a kind of brand-new technical scheme of improving the microwave cavity field uniformity, still make machined material and electric field generation relative motion, but be to make electric field motion rather than machined material motion, avoid the drawback of aforementioned various raising heating uniformity methods.Simultaneously the ceramic material of low dielectric loss is heated apace, improve the utilization ratio of microwave energy, make it to be applied to the various processing technologys of ceramic material.

The heating experiment shows, 99% purity alumina material of low-dielectric loss can be heated to more than 2000 ℃ from room temperature in 2 minutes with 1000 watts microwave power, and can make and be heated pottery and stably remain on predetermined different temperatures by regulating the microwave source power output.

The contrast and experiment that heating chamber heating uniformity of the present invention is done on the cavity cross section and along cylindrical side as can be seen, the heating chamber internal electric field distributing homogeneity with rotary polarization ripple has had obvious improvement.

Brief Description Of Drawings

Fig. 1 can produce the structural representation of waveguide 3db bridge that phase difference is the exciting current of pi/2 for of the present invention.

Fig. 2 is coupling aperture of the present invention and cavity body structure schematic diagram; Wherein,

Fig. 2 a is the schematic diagram that has on the common wall of waveguide and heating cavity as the slotted eye of coupling element;

Fig. 2 b is the schematic diagram that waveguide is connected with heating cavity.

Fig. 3 is that insulation of the present invention and heat trigger structural representation.

The comparison picture of Fig. 4 the present invention and common heating chamber effect; Wherein,

Fig. 4 a is the comparison picture of Temperature Distribution on the cavity cross section;

Fig. 4 b is along the Temperature Distribution of cavity cylindrical side (expanded view) picture.

Fig. 5 is the curve chart of the adjusting microwave source power output of present embodiment application.

Fig. 6 is the temperature indicator diagram of the infrared radiation thermometer of present embodiment application.

A kind of embodiment that is used for the high-uniformity multimode microwave cavity of pottery processing of the present invention's design comprises: the microwave heating cavity of sealing, be installed in the 3db phase shift bridge waveguide under this well floor, have slotted eye on the common wall of said waveguide and heating cavity, and be arranged on the insulation construction in this cavity as coupling element.Each several part is described in detail as follows in conjunction with each accompanying drawing:

What the present invention designed can produce the waveguide 3db bridge construction embodiment that phase difference is the exciting current of pi/2, as shown in Figure 1.This assembly is made up of two standard BJ-22 waveguides arranged side by side: 11 are common side-wall, and 12 is the capacitive compensation screw, in order to regulate the reactance at two ends, slit.13 is the microwave introducing port, and 14,15 is export mouth, and 16 is pale pinkish purple hole.Open one section slit crack with Narrow Wall of Waveguide wall equal height on common side-wall, forming one section wide is 1 wide waveguide for 2a+ δ, length.Wherein a is the wide wall length of BJ-22 waveguide, and δ is the thickness of common side-wall.The length of l does not have strict restriction, is advisable with appropriateness.But common side-wall gap length Δ is a key parameter, and it must satisfy

λ wherein _g' and λ _g" be respectively TE in the wide waveguide ₁₀, TE ₂₀The guide wavelength of ripple.In the present embodiment, the exportable equal and opposite in direction of 14,15 ports, phase difference are the microwave electric field of pi/2.

The coupling aperture of the present invention's design and cavity body structure embodiment are as shown in Figure 2.The present invention adopts the electric current coupled modes, promptly on the common wall 21 of waveguide and cavity grooved bore as coupling element.For satisfy exciting current in the space mutually vertical this condition, the coupling between 3db bridge and the heating chamber need adopt two orthogonal coupling slits 22, shown in Fig. 2 a.Open on the broadside of 3db bridge waveguide in the coupling slit, the direction in slit and waveguide limit angle at 45, and the center in each slit overlaps with waveguide broadside center line, as shown in Figure 1.This coupling slit is at r=57.7mm place, distance cylindrical cavity center.20 is cavity among Fig. 2 b, is the cylinder of a closed at both ends that is made of copper material.Directly through D=240mm, high H=312.9mm.Housing depth H can slightly adjust by the mode that adds connection pad between cavity stack shell and top cover.Plane, coupling aperture place and circular cylindrical cavity bottom surface 21 fit, and the 23rd, the waveguide-coupled section is the relative position of waveguide-coupled section and cavity, the 24th, be used for the infrared temperature probe seat of thermometric.

Heating chamber is the circular cylindrical cavity of a closed at both ends that is made of copper material.Calculate by electromagnetism, can get that the pass of electric field and magnetic field model and cavity size is in the heating chamber: electric field patterns ${\mathrm{TE}}_{\mathrm{nip}}:{\left(\frac{D}{\mathrm{\λ}}\right)}^2={\left(\frac{p}{2}\right)}^2\·{\left(\frac{D}{H}\right)}^2+{\left(\frac{{\mathrm{\μ}}_m}{\mathrm{\π}}\right)}^2$ Magnetic field model ${\mathrm{TM}}_{\mathrm{nip}}:{\left(\frac{D}{\mathrm{\λ}}\right)}^2={\left(\frac{p}{2}\right)}^2\·{\left(\frac{D}{H}\right)}^2+{\left(\frac{v_m}{\mathrm{\π}}\right)}^2$

Wherein D is a cavity diameter, and H is a housing depth, and λ is a microwave frequency, μ _Ni, ν _NiBeing respectively Bessel function or its derivative is zero separating, and p is an electromagnetic field half-wave number longitudinally.The pattern complementary relationship of utilizing hope to obtain, and with each constant substitution, the pass that obtains cavity diameter and height is: $\frac{p}{2}\·\frac{D}{H}=1.53$

Present embodiment is got one group of type solution D=240mm, then H=312.9mm.Can there be TE in the theory analysis chamber ₀₁₄, TE ₁₁₅, TM ₀₂₂, TM ₁₁₄, TM ₂₁₃Etc. multiple mode of resonance.But main mould will be TE ₀₁₄And TM ₁₁₄Housing depth can slightly adjust the error with corrected Calculation by the mode that adds connection pad between cavity stack shell and top cover.

The insulation construction embodiment of the present invention's design as shown in Figure 3.

The heating process of material in microwave field not only distributes relevant, and relevant with itself and the mode of insulation, the dielectric property of insulation material etc. with electromagnetic field.Microwave with the remarkable difference of conventional heating is, the heat energy that the external world provides during conventional heating is heated material by mode from outward appearance to inner essence, microwave heating then is to examine material itself to absorb microwave energy, heats by integral body and heats up.Therefore during microwave heating because the heat radiation on surface, general material internal temperature is higher than the surface.For most of ceramic materials, because its low-temperature dielectric loss is little, the strong heat radiation on surface makes its heating process elongated, even is difficult to reach the heating-up temperature of expection, even also seldom arrive the even temperature distribution in the electric field uniformly simultaneously.Therefore present embodiment is provided with the structure of an insulation and heat triggering in heating chamber.

Among Fig. 3, the 31st, sample, the 32nd, alumina crucible, the 33rd, the carborundum fragment, they be evenly distributed on crucible around.The 34th, porous crack alumina material, the 35th, alumina fibre, 36 is thermometer hole.Carbofrax material around being distributed in is a microwave absorbing material preferably, can the fast Absorption microwave energy, make material around reach uniform temperature after dielectric loss increase rapidly, thereby can be played the effect that heat triggers by Fast Heating.Such insulation construction, considered the following aspects: insulation material and microwave action a little less than, can be made microwave energy act on machined material itself by microwave penetration; Be coated on material surface, prevent heat loss through radiation, help to improve uniformity; Carbofrax material around being distributed in is a microwave absorbing material preferably, can the fast Absorption microwave energy make material around reach uniform temperature after dielectric loss increase rapidly, thereby can be by Fast Heating.

The effect of present embodiment:

Because electromagnetic field complex distribution in the heating chamber is difficult to accurate Calculation and measurement.The method that has for this reason adopted following qualitative demonstration electromagnetic field to distribute.Test paper is soaked in the CoCl2 aqueous solution, and its color is pink, places appropriate location in the chamber then.Through the heating of short time, the test paper color will be by the pink blueness that becomes under certain power, and the high more color of temperature is dark more, but the distribution of qualitative evaluation chamber internal electric field (temperature field) in view of the above.The contrast and experiment that Fig. 4 is to use this evaluation method that common cylinder heating chamber and heating chamber heating uniformity of the present invention are done on the cavity cross section and along cylindrical side.On Fig. 4 a cavity cross section (distance at the bottom of the chamber: left Figure 180 mm, middle Figure 110 mm, right Figure 40 mm)

The comparison of Temperature Distribution

On: common resonant cavity

Down: heating chamber of the present invention

(heating condition: incident power 0.6kW, heating time 3min.)

Fig. 4 b is along the Temperature Distribution (expanded view) of cavity cylindrical side

On: common resonant cavity

Down: heating chamber of the present invention

(heating condition: incident power 0.6kW, heating time 3min.) as can be seen, the heating chamber internal electric field distributing homogeneity with rotary polarization ripple has had obvious improvement.

The applicating example of present embodiment:

To be of a size of 4 * 6 * 40mm ³, purity is that 95% aluminium oxide (all the other are sintering aid) ceramic powder pressed compact is vertically put into insulation construction shown in Figure 3, total is put into heating cavity central authorities shown in Figure 2 again.By curve adjustment shown in Figure 5, the temperature indication that obtains infrared radiation thermometer is as Fig. 6 with the microwave source power output.Sintering temperature is 1550 ℃, the 40 minutes time (sintering time and temperature all are lower than the usual manner sintering).The ceramic body shrinkage 13% that sintering obtains, density are 99% of solid density.Sintered body size difference in the longitudinal direction is about 2%, and the size difference is no more than 1% between sample.Illustrate in the sintering cavity all to have obtained very even temperature distribution with short transverse on the inherent cross section, sample space of living in, thereby obtained the very consistent ceramic sintered bodies of size.

Claims (5)

1. one kind is used for the high-uniformity multimode microwave cavity that pottery is processed, it is characterized in that, the microwave heating cavity that comprises sealing, be installed in the 3db phase shift bridge waveguide under this well floor, have slotted eye on the common wall of said waveguide and heating cavity, and be arranged on the insulation construction in this cavity as coupling element.

2. microwave multimode application cavity as claimed in claim 1 is characterized in that, said slotted eye as coupling element is two orthogonal coupling slits.

3. microwave multimode application cavity as claimed in claim 1 is characterized in that, the waveguide of said 3db phase shift bridge is made up of two standard BJ-22 waveguides arranged side by side, and its common side-wall has the slit that length is Δ, λ wherein _g' and λ _g" be respectively TE in the wide waveguide ₁₀, TE ₂₀The guide wavelength of ripple; In this slit, be provided with the capacitive compensation screw.

4. microwave multimode application cavity as claimed in claim 1, it is characterized in that, said insulation construction comprises two layer box bodies made from porous crack alumina material, layer box body the inside is provided with an alumina crucible that holds pottery to be processed in this, be filled with alumina fibre between said two layer box bodies, be filled with the carborundum fragment between layer box body and the alumina crucible in being somebody's turn to do, the upper wall of two layer box bodies has the thermometer hole that runs through.

5. microwave multimode application cavity as claimed in claim 1, it is characterized in that, the microwave heating cavity of said sealing is the circular cylindrical cavity of the closed at both ends that is made of copper material, cavity diameter D is 240mm, housing depth H is 312.9mm, and the loam cake of this sealing is equipped with the infrared temperature probe seat that is used for thermometric.

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