Tray assemblies and methods for manufacturing ceramic articles

Tray assemblies and methods for manufacturing ceramic articles are provided. In one embodiment, a tray assembly includes a tray body having a supporting surface operable to support a ceramic article for passage through a microwave drying apparatus during a microwave drying process and a microwave coupling cover associated with the tray body. The microwave coupling cover envelopes at least a portion of the ceramic article during the microwave drying process. The microwave coupling cover has a dielectric property such that a greater percentage of microwave energy is coupled into the ceramic article with the microwave coupling cover present during the microwave drying process than with the microwave coupling cover not present. Methods may include rotating the ceramic article when the ceramic article is about 40%-60 dry.

FIELD

The present specification generally relates to drying and manufacturing ceramic articles and, more specifically, to tray assemblies and methods for drying and manufacturing ceramic-forming, or ceramic, articles using microwave radiation.

BACKGROUND

Microwave heating may be utilized to remove moisture from moisture-laden ceramic forming, or ceramic, articles by providing microwave energy directly to the ceramic material being dried. However, fundamental non-uniformity in the exposed electromagnetic fields, resulting from the various modes existing inside of a microwave drying apparatus and inside the ceramic article, may lead to various drying challenges. For example, drying processes utilizing microwave heating may produce unevenly dried ceramic articles placed on microwave drying trays or tray assemblies such that some interior portions of the ceramic article may not be completely dried (i.e., cold regions) and other portions may be over heated (i.e., hot regions).

Accordingly, a need exists for alternative tray assemblies and methods for manufacturing ceramic articles.

SUMMARY

Embodiments described herein are generally related to alternative tray assemblies and methods for drying ceramic articles that reduce cold regions in the axial center skin of the ceramic articles. The cold regions may form due to inefficient or non-uniform microwave coupling of the microwave energy during the microwave drying process. Embodiments described herein provide for enhanced microwave energy coupling into the ceramic article to enable more uniform drying within the ceramic article. The term, “ceramic article” is used herein to denote a ceramic-forming article, or a ceramic article, before, during, or after being dried.

In one embodiment, a tray assembly includes a tray body having a supporting surface operable to support a ceramic article for passage through a microwave drying apparatus during a microwave drying process and a microwave coupling cover associated with the tray body. The microwave coupling cover envelopes at least a portion of the ceramic article during the microwave drying process. The microwave coupling cover has a dielectric property such that a greater percentage of microwave energy is coupled into the ceramic article with the microwave coupling cover present during the microwave drying process than with the microwave coupling cover not present.

In another embodiment, a tray assembly includes a tray body and a microwave coupling insert. The tray body has a supporting surface that is operable to support a ceramic article. The microwave coupling insert is located below the supporting surface of the tray body and surrounds at least a portion of the ceramic article. The microwave coupling insert has a dielectric property such that a greater percentage of microwave energy is coupled into the ceramic article with the microwave coupling cover present during a microwave drying process than with the microwave coupling cover not present.

In yet another embodiment, a method of manufacturing a ceramic article includes extruding a wet ceramic material with an extruder apparatus, cutting the extruded wet ceramic material to form a ceramic article, and placing the ceramic article onto a tray body, the tray body associated with a microwave coupling cover configured to cover at least a portion of the ceramic article. The method further includes subjecting the ceramic article to microwave radiation through at least the microwave coupling cover. The microwave coupling cover has a dielectric property such that a greater percentage of microwave energy is coupled into the ceramic article with the microwave coupling cover present than with the microwave coupling cover not present. After the ceramic article is subjected to microwave radiation, the ceramic article may be removed from the tray body when the ceramic article is at a target dryness and the tray body and microwave coupling cover may then be returned to the extruder apparatus.

It is to be understood that both the foregoing general description and the following detailed description present embodiments of the present disclosure, and are intended to provide an overview or framework for understanding the nature and character of the embodiments claimed herein. The accompanying drawings are included to provide a further understanding of the embodiments disclosed herein, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the present disclosure and together with the description serve to explain the principles and operations of the embodiments described herein.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments for tray assemblies for manufacturing and drying ceramic articles, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

As described herein, tray assemblies may generally comprise a tray body and a microwave coupling cover. The microwave coupling cover is operable to increase the coupling of microwave energy provided by a microwave drying apparatus into a ceramic article (e.g., a ceramic honeycomb structure) to efficiently heat and dry the ceramic article. By increasing the level of coupled microwave energy, more uniform drying and shorter drying times may be achieved. Additionally, embodiments described herein provide for the ability to achieve uniform drying with only one drying step rather than two or more (e.g., one microwave drying step and one conventional drying step), as well as the ability to dry multiple-piece ceramic articles.

Referring now toFIG. 1, an exemplary ceramic article manufacturing system100is illustrated. The system100may generally comprise an extruder apparatus102, a sawing apparatus108, a conveyor system130, and a microwaving drying apparatus132. It should be understood that embodiments described herein are not limited to the system100illustrated inFIG. 1, and that other systems having more or fewer components may be utilized. Extrudate in the form of wet ceramic material104may be processed by the extruder apparatus102at a desired extrusion rate in a direction indicated by arrow A. The wet ceramic material104may be transported toward the sawing apparatus108by a first bearing system106.

The sawing apparatus108is operable to cut the wet ceramic material104into ceramic articles112having a desired length. The sawing apparatus108may comprise a controller109that receives the velocity of the extrudate as an input and controls a blade110at the proper rate to cut the ceramic material104into ceramic articles112of the desired length. The ceramic articles112may be transported toward the conveyor system130(e.g., a belt or chain-link conveyor system) on a second bearing system114. The first and second bearing systems106,114may be air bearing systems to minimize deformation of the wet ceramic material104and ceramic articles112, respectively. Although the system100illustrates the use of two bearing systems, embodiments may utilize more or fewer bearing systems. Further, it should be understood that the conveyor system130may comprise any suitable system for conveying ceramic articles through the microwave drying apparatus132. Accordingly, no particular limitation is intended as to the type of conveyor or bearing system used to convey the ceramic material through the ceramic article manufacturing system100.

Positioned on the conveyor system130are one or more tray assemblies120operable to receive one or more ceramic articles112from the second bearing system114. As described in more detail below, the tray assembly120may comprise a tray body122and a microwave coupling cover124. Depending on the particular embodiment of the tray assembly120, the microwave coupling cover124may be positioned on the tray body122after the ceramic article is placed on the tray body122.

After the ceramic article112is maintained on or within the tray assembly120, the conveyor system130then transports the tray assembly120toward the microwave drying apparatus132in a direction as indicated by arrow B. The microwave drying apparatus132may comprise a microwave source (not shown), a microwave chamber133, and a waveguide assembly (not shown). The microwave chamber133generally comprises sidewalls134, a top135and a bottom136. In one embodiment, the sidewalls134, top135, and bottom136may be formed from a microwave-impermeable, non-magnetic material that exhibits a high electrical conductivity and resistance to oxidation. Each of the top135, bottom136and sidewalls134of the microwave chamber133may comprise an inner shell and an outer shell with a layer of insulation (e.g., fiberglass or a comparable insulating material) disposed therebetween. The microwave chamber133may be configured such that ceramic articles112and tray assemblies120pass through the inside of the microwave chamber133. Although not illustrated, the microwave drying apparatus132may further include entrance and exit walls having an opening to allow the tray assemblies120, ceramic articles112and conveyor system130to travel into and out of the microwave drying apparatus132. The openings should be sized such that microwave energy cannot escape the microwave chamber133. Entry and exit gates (not shown) operable to open and close may also be utilized to prevent microwave energy from escaping. Although the microwave drying apparatus132is illustrated as having a single microwave chamber, embodiments may utilize multiple microwave chamber having multiple corresponding microwave sources.

The frequency of the microwave energy generated by the microwave source may vary depending on the particular microwave drying application. In one embodiment, the microwave source is operable to generate microwave energy having frequencies between about 10 MHz to about 100 GHz, and, in some embodiments, frequencies between about 20 MHz to about 6 GHz, or about 900 MHz to about 2.49 GHz. Further, the microwave source (or sources in embodiments having multiple microwave chambers) may be configured to vary the frequency of the microwave energy at different points during the microwave drying process.

FIGS. 2A-2Cdepict a perspective view components of an exemplary tray assembly120. Referring first toFIG. 2A, the tray assembly120includes a tray body122having a semi-cylindrical channel129having a longitudinal axis running parallel to a tray body longitudinal axis along a lengthwise direction as indicated by arrow C. The tray body122may be made of a material that increases in temperature when subjected to microwave radiation. Although the channel129is illustrated as having a semi-cylindrical configuration, embodiments are not limited thereto. The channel may be any shape that matches the contour of the ceramic article to be dried. For example, the channel may be rectangular to accept a ceramic article having a rectangular shape. In other embodiments, the shape channel may not match the contour of the ceramic article to be dried.

The channel129may also include a plurality of drainage holes127that enable liquid within the wet ceramic article to drain out of the tray body122, as well as enable vapor to escape. The drainage holes may provide for a faster ceramic article drying time. The channel129is not limited to the plurality of drainage holes127depicted inFIG. 2Aas channels may have other configurations that allow liquid and vapor to escape from the tray body. For example, a channel of one embodiment may be configured as a screen having openings through which liquid and vapor may travel. Other configurations are also possible.

In the illustrated embodiment, the tray assembly120further comprises an insulator125coupled to a bottom portion of the tray body122. The insulator125may be made of a material that is transparent to the applied microwave radiation and also is operable to thermally insulate the tray assembly120from the conveyor system during the drying process. The insulator125may be made of Lexan or Teflon, for example. It should be understood that other insulating materials may also be utilized.

FIG. 2Billustrates a tray body122having a ceramic article112placed thereon. The ceramic article112depicted inFIG. 2Bis configured as a cylindrical ceramic filter. It should be understood that ceramic articles may have other geometric configurations (e.g., rectangular). The ceramic article112may be placed on the tray body122such that it is positioned within the channel129and a ceramic article axis as indicated by arrow D is substantially parallel with the tray body longitudinal axis C. The direction of travel of the tray body122(and tray assembly120) along the conveyor may be along a conveyor travel axis indicated by arrow B, which is normal to the tray body longitudinal axis C (seeFIG. 1).

FIG. 2Cillustrates a tray assembly120having a ceramic article112disposed therein. A microwave coupling cover124is positioned on the tray body122so that the ceramic article112is enveloped by the microwave coupling cover124from above. A coupler longitudinal axis as indicated by arrow E may be substantially aligned (i.e., common) with the ceramic article longitudinal axis D. The microwave coupling cover124illustrated inFIG. 2Chas a length that is shorter than the length of the ceramic article112. As described in more detail below, the length of the microwave coupling cover124may vary depending on the particular drying application, and may envelope the ceramic article from the top, bottom and/or sides. Various embodiments of tray assemblies and associated methods will now be described below.

Referring now toFIGS. 3A-3C, an exemplary tray assembly220and a ceramic article112positioned therein are illustrated in a front view, side view and perspective view, respectively. The tray assembly220comprises a semi-cylindrical microwave coupling cover224and a tray body222. Rather than utilizing a microwave coupling cover that is positioned on the tray body such that it encloses the ceramic article from above as illustrated inFIG. 2C, the microwave coupling cover illustrated inFIGS. 3A-Cis configured as a microwave coupling insert224that is positioned below a supporting surface226of a tray body222. The ceramic article112may be supported directly on a semi-cylindrical supporting surface226or indirectly by use of optional spacers227illustrated inFIG. 4C. In one embodiment, the microwave coupling insert224is integral with the tray body222, while in another embodiment the microwave coupling insert224is removable from the tray body222such that tray inserts of varying material may be swapped into and out of the tray body222as necessary. Embodiments of this configuration may provide the benefit of eliminating the step of removing the microwave coupling cover prior to rotating the ceramic article 180° when the ceramic article is about 40%-60% dry, as described in detail below. Because the microwave coupling insert224provides enhanced coupling to at least a portion of a bottom half of the ceramic article112rather than the top (e.g., as illustrated inFIG. 2C), easy access to the to the ceramic article is provided. In one embodiment, the ceramic article112may be rotated manually or robotically. In another embodiment, rather than rotating the ceramic article112, the microwave coupling insert324may be enabled to automatically and mechanically rotate such that it envelopes at least a portion of a top half of the ceramic article112for continued exposure to microwave radiation.

In the illustrated embodiment ofFIGS. 3A-3C, the microwave coupling insert224envelopes the entire length (longitudinally) of the ceramic article112(i.e., an entire portion of a bottom half). However, the length of the microwave coupling cover may be shorter than the length of the ceramic article (seeFIGS. 4A-4C,5A-5C). To provide effective coupling of microwave energy into the ceramic article112, the length of the microwave coupling cover224in some embodiments is greater than or equal to λg, where λgis the wavelength of the microwave radiation generated by the microwave drying apparatus as it propagates within the ceramic article112. The thickness of the ceramic article112in some embodiments is between about λg/8 and about λg/2 to provide for optimal microwave coupling, as described in more detail below—with reference toFIG. 12.

To enable vapor and air to freely flow from the wet ceramic article112during the drying process, the microwave coupling cover224may be positioned and configured such that there is a gap123between the microwave coupling cover224(as well as the tray body material) and the ceramic article112. This may be achieved by the use of optional spacers227, for example. To ensure that impedance matching provided by the microwave coupling cover224is not compromised, the distance between the ceramic article112and the microwave coupling cover224should be less than about λo/10, where λois the wavelength of the microwave radiation utilized by the microwave drying apparatus as it propagates in air. At this distance, the gap123is transparent to the microwave radiation.

The material of the microwave coupling cover should enable the cover to act as a microwave coupler that increases the amount of microwave energy that is coupled into the ceramic article. In other words, the material of the microwave coupling cover provides enhanced impedance matching between air and the ceramic article. In selecting a material for the microwave coupling cover, the dielectric property of the material chosen should be halfway between the dielectric property of air (∈O), which surrounds the ceramic article, and that of a dried ceramic article (∈R2D). Considering the dielectric property of a dried ceramic article rather than the dielectric property of a wet ceramic article may aid in reducing overheating of a region of the ceramic article near the surface after it is dry. Dielectric property, as used herein, means a dielectric property having a real component and an imaginary component.

As an example and not a limitation, a material having a real component of a dielectric property of about 8 would be selected for a ceramic article having a dry dielectric property of 15, wherein the dielectric property of air is 1. The imaginary component of the dielectric property of the microwave coupling cover should be virtually zero, as a non-zero value would lead to a heating of the cover (e.g., as a susceptor material would) rather than providing enhanced coupling to the ceramic article. Additionally, a fairly conductive cover would shield the ceramic article from the electromagnetic energy. Therefore, the imaginary component of the dielectric property should be less than about 0.01. As an example and not a limitation, a material having a real component of the dielectric property of about 8 and an imaginary component near zero may be alumina with a porosity of less than about 2% (e.g., an alumina material having a dielectric property of 8.09-j0.008). Because the dielectric property requirements of the microwave coupling cover may be different for different types of ceramic articles, different materials having varying dielectric properties and porosities may be utilized depending on the type of ceramic material being processed. As an example and not a limitation, exemplary materials for the microwave coupling cover may include, but are not limited to, alumina, magnesia, spinel, silicon nitride, and aluminum nitride. Generally, the real component of the dielectric property should be within the range of five to ten for particular ceramic articles.

As described in more detail below, the microwave coupling covers described herein increase the level of microwave energy that is coupled into the ceramic article, which may provide improved-quality ceramic articles (e.g., ceramic articles having wet regions after drying), thereby increasing yield. Additionally, the amount of time necessary to effectively dry the ceramic articles is reduced because less microwave energy is reflected or dissipated, thereby saving energy costs.

Referring now toFIG. 12, a schematic illustration of the mediums of a tray body1122, a ceramic article1112, a microwave coupling cover1124, and microwaves1140propagating in air is provided. As an example and not a limitation, provided below are electromagnetic properties for the various mediums illustrated inFIG. 12, wherein the microwave coupling cover1124is made of alumina with a length (horizontal as shown inFIG. 12) of about four inches, thickness (vertical as shown inFIG. 12) of about one inch, and a gap1123of about 0.4 inches. η represents the impedance of the medium, which is the square root of the ratio between the magnetic permeability, μ=μ0μR, (μ0is the magnetic permeability of free space) and the dielectric permittivity, ∈=∈0∈R, (∈0is the dielectric permittivity of free space):

η=μɛ,Ω,.Eq.⁢(1)
The subscripts0,1,2, and3represent mediums of air, the microwave coupling cover, ceramic article, and tray body, respectively. In addition, subscripts “D” and “W” represent the dry and wet state of the ceramic article. The reflection coefficient Γ uses subscripts to indicate the interface between two mediums. For example, Γ01means the interface between air and the microwave coupling cover. The above electromagnetic properties may be further defined by:

The following electromagnetic properties are provided below as an example for illustrative purposes only. Embodiments described herein are not limited to the following electromagnetic properties in any way. In this example, the microwave coupling cover comprises an alumina material. The exemplary properties are as follows:Air: ∈0, μ0, η0=377Ω, Γ01=−0.5, Γ02D=−0.59, and Γ02W=−0.75;Microwave coupling cover: ∈R1=9, μR1=1, η1=126Ω, Γ12D=−0.13, Γ12W=−0.41;Dry ceramic article: ∈R2D=15, μR2D=1, η2D=97Ω, Γ2D3=0.52;Wet ceramic article: ∈R2W=50, μR2W=1, η2DW=53Ω, Γ2W3=0.52; andTray body: ∈R3=1.5, μR3=1, η3=307Ω, Γ30=0.19.

The reflection coefficients provided above show that the alumina microwave coupling cover provides enhanced impedance matching for oncoming electromagnetic waves, which in turn, results in enhanced efficiency and heating of the middle skin region of the ceramic article (i.e. the middle portion at the outermost periphery of the ceramic article). The following two examples further illustrate the enhanced coupling effect provided by a microwave coupling cover having the above properties.

Dry Ceramic Article—Nearing End of Drying Process

Assuming an input power of 100 W for the oncoming electromagnetic waves directed toward the ceramic article and tray assembly, an alumina microwave coupling cover having a reflectivity coefficient Γ01=−0.5 will reflect 40% of the power such that 50 W will be coupled into the alumina microwave coupling cover. Out of this 50 W, 87% gets coupled directly into the ceramic article (50 W*(1−Γ12)=43.5 W). By following a similar analysis, one may see that only 41% of the input power gets directly coupled into the ceramic article in the absence of the microwave coupling cover124(100 W*(1−Γ02)=41 W). Therefore, the power coupled into the ceramic article is lower when the microwave coupling cover is not present. The accumulated effect of this advantage over the drying time of approximately 20 minutes, which may include passage through a microwave drying apparatus having plurality of 100 W microwave applicators, is significant.

Wet Ceramic Article—at Beginning of Drying Process

As in the above example, the microwave drying apparatus is configured to propagate 100 W of electromagnetic radiation toward the ceramic article. With an alumina microwave coupling cover having the above properties present in the tray assembly, approximately 40% (50 W) of the 100 W will be coupled into the alumina microwave coupling cover. Out of this 50 W, 59% couples directly into the ceramic article (50 W*(1−Γ12)=29.5 W). By following a similar analysis, it is shown that only 25% of the 100 W of input power is directly coupled into the ceramic article in the absence of the alumina microwave coupling cover. Therefore, there is an approximate advantage of about 4.5% with the microwave coupling cover present than not present. Again, the accumulated effect of this advantage over the drying time of approximately 20 minutes through several 100 W microwave applicators is significant.

As described above with reference to the two examples, the microwave coupling cover increases the percentage of microwave energy that is coupled into a ceramic article. This increased coupling enables shorter drying times and a more enhanced drying of cold region without the need for additional drying furnaces, such as a convection drying furnace, for example.

Referring to the flowchartFIG. 13as well asFIG. 1, a method of manufacturing a ceramic article112using the exemplary ceramic article manufacturing system illustrated inFIG. 1will now be described in greater detail. After the ceramic article112is cut from the extrudate104(Block1310), the ceramic article112passes from the second bearing system114onto a tray body122such that the ceramic article112is at least partially enclosed by the microwave coupling cover124(Block1320). The microwave coupling cover124may be positioned on the tray body122by any appropriate method, such as manually or robotically. In embodiments wherein the microwave coupling cover is configured as a microwave coupling cover insert positioned within a tray body, such as the insert224and tray body222illustrated inFIGS. 3A-3B, for example, there may be no need to position the microwave cover onto the tray body.

After the ceramic article112is enclosed within the tray assembly120, the conveyor system130transports the tray assembly120toward the microwave drying apparatus132, which may have a plurality of microwave applicators and chambers (Block1330). In one embodiment, the tray assemblies120are transported through the microwave drying apparatus132at a continuous rate. The ceramic article112then receives microwave energy in the microwave drying apparatus at Block1340.

If the ceramic article is less than about 40% dry at Block1350, the process follows the N path to return to Block1340so that the ceramic article may continue to receive microwave energy. Because the microwave cover124may only cover approximately a top or bottom half of the ceramic article112, only the top or bottom portion of the ceramic article may receive the enhanced coupling benefits provided by the microwave cover124. Therefore, when the ceramic article is between about 40% and about 60% dry at Block1350, the process follows the Y path to Block1360where the ceramic article112may be rotated 180° around the axis of the ceramic article112such that the previously unexposed portion of the ceramic article112is now exposed to the enhanced coupling benefits provided by the microwave coupling cover124. The ceramic article112may be rotated after a particular time within the microwave drying apparatus132based on historical data that indicates how long a particular type of ceramic article should be in the microwave drying apparatus132until it is approximately 40%-60% dry. In another embodiment, the dryness of the ceramic article132may be monitored by a sensor (not shown).

In embodiments wherein the microwave coupling cover124envelopes a top portion of the ceramic article112, the ceramic article may be rotated by first disengaging the microwave coupling cover124from the tray body122to provide access to the ceramic article112. The ceramic article112may then be rotated and the microwave coupling cover124placed once again on the tray body122. The rotation of the ceramic article may112may be performed manually or robotically. In embodiments wherein the microwave coupling cover is configured as a microwave coupling insert (e.g., insert224ofFIGS. 3A-3C) and envelopes the ceramic article from below a supporting surface, the ceramic article112may be rotated directly without requiring a removal of the microwave coupling insert. After the rotation, the ceramic material may be subjected to additional microwave radiation until a target dryness is achieved at Block1360.

After the tray assembly120and the ceramic article112enclosed therein exits the microwave drying apparatus132, the microwave coupling cover124may be removed from the tray assembly120(or not) and the ceramic article112may be removed from the tray body122at Block1370. This process may be performed manually or robotically. The tray body122and microwave coupling cover124may be transported back to the beginning of the drying process (e.g., by one or more conveyor systems) to receive additional wet ceramic articles112(Block1395) if the end of the extrudate104is not reached at Block1380(N path), or returned to an offline location (Block1390) if the end of the extrudate is reached at Block1380(Y path).

Additional embodiments of tray assemblies having various configurations and methods for manufacturing ceramic articles associated therewith will now be described. Embodiments are not limited to the tray assembly configurations illustrated and described herein as variations and modifications may be utilized.

FIGS. 4A-4Cillustrate an embodiment wherein the microwave coupling cover is configured as a microwave coupling insert324that is positioned within a tray body322and operable to cover at least a portion of a bottom half of the ceramic article112. As described above with reference toFIGS. 3A-3C, the microwave coupling insert324may be integral with the tray body322or removable therefrom. The length of the microwave coupling324insert is shorter than the length of the microwave coupling insert illustrated inFIGS. 3A-3C.

To achieve optimal enhanced microwave energy coupling, the length of the microwave coupling insert324(or a top cover of embodiments described and illustrated herein) should be greater than or equal to λg, which is the wavelength of the microwave radiation propagating within the ceramic article112. For example, if the wavelength of the microwave radiation in the ceramic article is four inches, the length of the microwave coupling insert324should be greater than or equal to four inches. As described above, the thickness of the illustrated microwave coupling insert324is in some embodiments between about λg/8 and about λg/2, and the gap123about λo/10 to provide for optimal microwave coupling. Reducing the length of the microwave coupling insert or cover from a length that is the entire length of the ceramic article may provide the benefits of reducing the amount of material needed to manufacture the microwave coupling insert or cover as well as reducing the overall weight of the insert or cover.

Referring now toFIGS. 5A-5C, a tray assembly420having two microwave coupling inserts is illustrated. A microwave coupling insert424(i.e., a first microwave coupling insert) may cover a first portion of the ceramic article112and an additional microwave coupling insert428(i.e., a second microwave coupling insert) may envelope a second portion of the ceramic article. The first and second portions are illustrated as proximate the first and second ends of the ceramic article112. However, the microwave coupling covers424,428may cover other portions of the ceramic article112. The length of the first and second microwave coupling inserts424,428, which may be the same or different from one another, should be equal to or greater than λg as described above.

FIGS. 6A-6Cillustrate an embodiment in which a tray assembly520having a microwave coupling cover524envelopes a ceramic article112from above. The microwave coupling cover524comprises a semi-cylindrical shape and is operable to cover an entire top half of the ceramic article112. Although the illustrated microwave coupling cover524has a semi-cylindrical shape that substantially matches the contour of the ceramic article112, embodiments are not limited thereto. The microwave coupling cover524may be supported by directly engaging the tray body122or indirectly supported by the use of optional microwave-transparent spacers (not shown) made of Lexan, Teflon, for example. As described above, the microwave coupling cover524illustrated inFIGS. 6A-6Cmay be removed from the tray body122when the ceramic article112is rotated and removed from the tray body122at the end of the drying process.

Referring now toFIGS. 7A-3C, a tray assembly120having a microwave coupling cover124that covers a portion of the length of the ceramic article112located on a tray body122.FIGS. 7A-7Cdepict the embodiment illustrated inFIG. 2C. The length of the microwave coupling cover124illustrated inFIGS. 7A-7Cis shorter than the length of the microwave coupling cover524illustrated inFIGS. 6A-6C. The microwave coupling cover124is operable to envelope at least a portion of a top half of the ceramic article112. As described above with reference toFIGS. 4A-4C, the length of the microwave coupling cover124should be greater than or equal to λgto provide optimal enhanced microwave energy coupling.

FIGS. 8A-8Cillustrate an exemplary microwave tray assembly620having a cylindrical microwave coupling cover624that completely envelopes the entire length of the ceramic article112. In another embodiment, the microwave coupling cover624may completely envelope only a portion of the ceramic article112. The ceramic material112may be supported directly on a supporting surface626(FIG. 8A) or indirectly with the use of optional spacers627(FIG. 8C). The illustrated microwave coupling cover624may have the same properties as those microwave coupling covers described above. Microwave coupling covers that completely envelope the ceramic article may remove the step of rotating the ceramic article when the ceramic article is about 40%-60% dry because both the top and bottom half of the ceramic article is covered by the microwave coupling cover.

To enable a reduction of material and weight, as well as to increase air flow around the ceramic article112of a microwave coupling cover, the tray assembly720illustrated inFIGS. 9A-9Ccomprises a microwave coupling cover724having a plurality of axially extending coupler strips728made of a coupling material as described above. The coupler strips728may be arranged so that microwave coupling cover724completely envelopes at least a portion of the ceramic article112. The ceramic article112may be supported directly on a supporting surface726(FIG. 9A) or indirectly with the use of optional spacers727(FIG. 9C). The coupler strips728may be maintained with connectors (not shown) that may be transparent of microwave radiation to achieve a microwave coupling cover having a desired shape. A ceramic article dried using the tray assembly720illustrated inFIGS. 9A-9Cmay need a slight rotation when the ceramic article is about 40%-60% dry. This may be achieved by gripping the ends of the ceramic article and providing the slight rotation, or by slightly rotating the microwave coupling cover724. The coupler strips may also be utilized in an embodiment that covers a top or a bottom of the ceramic article.

Now referring toFIGS. 10A-10C, a tray assembly820having a microwave coupling cover configured as an inner cover824and an additional coupling cover configured as an outer cover828is illustrated. The illustrated successive covers824,828are separated by a gap125of less than about λo/10 to allow air flow and prevent condensation on the respective covers824,828. However, the inner cover824and outer cover828may be positioned on the tray body122such that they contact one another. As described above regardingFIGS. 2A-2C, the successive covers824,828may be directly or indirectly supported by the tray body122. The inner and outer covers824,828may be made of different coupling materials, or similar materials having different porosities and dielectric properties, and may be selected to increase the coupling of microwave energy into the ceramic article112, as described above with reference toFIG. 2D.

FIGS. 11A-11Calso illustrates a tray assembly920having two microwave coupling covers. A microwave coupling cover924(i.e., a first microwave coupling cover) may envelope a first portion of the ceramic article112and an additional microwave coupling cover928(i.e., a second microwave coupling cover) may envelope a second portion of the ceramic article. The first and second portions are illustrated as proximate the first and second ends of the ceramic article112. However, as described above with reference to the microwave coupling inserts424,428illustrated inFIGS. 5A-5C, the microwave coupling covers924,928may cover other portions of the ceramic article112. The length of the first and second microwave coupling covers924,928, which may be the same or different from one another, should be equal to or greater than λg as described above. As described above, the first and second microwave coupling covers924,928may be directly or indirectly supported by the tray body122.

The tray assemblies and methods described herein are particularly suitable for drying ceramic articles such as ceramic honeycomb structures, for example. Drying, as used herein, refers to a reduction in the liquid content of the ceramic article to a target dryness value. Embodiments described herein may provide enhanced microwave coupling into the ceramic article by the use of one or more microwave coupling covers that aid in impedance matching between air and the ceramic article. Embodiments may improve the quality of dried ceramic materials by reducing or eliminating the formation of wet and/or hot spots within the ceramic article. Further, embodiments may reduce both the time the ceramic article needs to be in a microwave drying apparatus and the amount of microwave energy needed to completely dry the ceramic article or to attain the target dryness.