Abstract:
Systems and methods for drying skinned ceramic wares ( 10 ) using recycled microwave radiation are disclosed. The method includes irradiating wet skinned ceramic wares ( 10 W) in a first applicator section ( 124 W) with microwave radiation ( 212 ), wherein said irradiating ( 212 ) gives rise to reflected microwave radiation ( 212 R). The method also includes capturing a portion of the reflected microwave radiation ( 212 R) and irradiating a plurality of semi-dry skinned ceramic wares ( 105 ) in a second applicator section ( 124 S) with the reflected microwave radiation ( 212 R). Systems for carrying out the method are also disclosed.

Description:
[0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/068,845, filed on Oct. 27, 2014, the content of which is relied upon and incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates to microwave drying of ceramic wares, and in particular relates to systems and methods for drying skinned ceramic wares using recycled microwave radiation. 
         [0003]    The entire disclosure of any publication or patent document mentioned herein is incorporated by reference, including U.S. patent application Ser. No. 14/295,536, filed on Jun. 4, 2014. 
       BACKGROUND 
       [0004]    Ceramic greenwares having an array of microchannels are formed by extrusion and then processed (i.e., dried and fired) to form dry ceramic articles or “ceramic wares,” such as filters and catalytic converters having a honeycomb porous structure for use in exhaust-producing engines and related applications. Ceramic greenwares can be formed by extruding a plasticized batch comprising ceramic-forming components, or ceramic precursors, through a die, such as a die that produces a honeycomb structure, to form an extrudate of the ceramic-forming material. The extrudate that exits the extruder is cut transversely to the direction of extrusion to form a greenware piece. The piece may itself be transversely cut into shorter pieces after drying. 
         [0005]    The ceramic ware dimensions can vary due to drying and firing shrinkage during manufacturing. Ceramic wares can also be difficult to manufacture to the stringent external dimensional requirements set by original equipment manufacturers (OEMs) and the supply chain. To help ensure compliance with dimensional requirements, ceramic wares can be machined or “contoured” to a desired dimension. A thin layer of ceramic cement is then used to form an exterior skin that provides a smooth protective outer surface for the ceramic ware. 
         [0006]    The ceramic skin (also called “skin cement” or just “skin”) is applied wet, containing for example 10%-35% by weight of water. The skin needs to be dried to form the final ware or article. In some cases, the skin needs to be dried to greater than 98% dry (i.e., to having less than 2% of the original moisture content). The act or process of applying ceramic cement to the exterior of the ceramic ware is referred to herein as “skinning.” A ceramic ware having skin disposed thereon is referred to herein as a “skinned” ceramic ware. 
         [0007]    Ceramic wares are currently skinned after firing, and the skin is dried using hot air. However, this drying process often leads to the formation of cracks in the skin, which need to be repaired manually. The added labor and time for inspecting skinned honeycomb bodies and fixing of skin drying cracks leads to inefficiencies in product manufacturing. To avoid skin drying cracks, a slow drying process can be employed, but this results in additional product manufacturing inefficiencies. 
       SUMMARY 
       [0008]    An aspect of the disclosure is a method of drying wet skinned ceramic wares. The method includes: a) irradiating a plurality of the wet skinned ceramic wares in a first applicator section with microwave radiation have a wavelength λ and a first amount of microwave power P 1 , wherein said irradiating gives rise to reflected microwave radiation from the first applicator section; and b) capturing a portion of the reflected microwave radiation and irradiating a plurality of semi-dry skinned ceramic wares in a second applicator section with the reflected microwave radiation having a second amount of microwave power P 2 &lt;P 1  to form dried skinned ceramic wares. 
         [0009]    Another aspect of the disclosure is a method of performing microwave drying of multiple skinned ceramic wares formed from fired ceramic wares. The method includes: a) applying a layer of skin to each of the fired ceramic wares to form the multiple skinned ceramic wares; b) irradiating the multiple skinned ceramic wares in a first applicator section with microwave radiation; c) conveying the irradiated multiple skinned ceramic wares to a second applicator section while conveying additional multiple skinned ceramic wares into the first application section; and d) irradiating the multiple skinned ceramic wares in the second applicator section using a portion of the microwave radiation that is reflected from the first applicator section and then directed to the second applicator section. 
         [0010]    Another aspect of the disclosure is a system for performing microwave drying of skinned ceramic wares. The system includes: first and second applicator sections; a microwave source configured to generate microwave radiation having a wavelength λ; and a microwave waveguide system comprising a first microwave waveguide operably connected to the first applicator section and to the microwave source, and a second microwave waveguide operably connected to the second applicator section and to the first microwave waveguide at a circulator arranged between the microwave source and the first applicator section to define a reflected-microwave path from the first applicator section to the second applicator section. 
         [0011]    Additional features and advantages are set forth in the Detailed Description that follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings. It is to be understood that both the foregoing general description and the following Detailed Description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments, and together with the Detailed Description serve to explain principles and operation of the various embodiments. As such, the disclosure will become more fully understood from the following Detailed Description, taken in conjunction with the accompanying Figures, in which: 
           [0013]      FIG. 1  is an isometric side view of an example skinned ceramic ware; 
           [0014]      FIG. 2A  is a front-on, close-up view of a pre-skinned (i.e., unskinned) ceramic ware; 
           [0015]      FIG. 2B  is similar to  FIG. 2A , but for the skinned ceramic ware of  FIG. 1 ; 
           [0016]      FIG. 3  is a schematic side view of an example microwave drying system configured to perform microwave drying using recycled microwave radiation, wherein the system includes a single applicator divided into two sections; 
           [0017]      FIG. 4  is a top-down view of the microwave drying system of  FIG. 3 , but without the ceiling of the applicator to show the skinned ceramic wares within the applicator; 
           [0018]      FIG. 5  is a top-down view of the microwave drying system of  FIG. 4 , showing the applicator without the ceiling to illustrate an example of how the skinned ceramic wares are arranged within and conveyed through the two applicator sections; 
           [0019]      FIG. 6A  is a schematic view of wet skinned ceramic wares residing in the wet applicator section beneath a microwave waveguide segment and schematically illustrates the irradiation of the wet skinned ceramic wares with microwave radiation; 
           [0020]      FIG. 6B  is similar to  FIG. 6A  and illustrates how a portion of the microwave radiation gets reflected from the wet skinned ceramic wares, as well as from other items and surfaces (not shown), within the wet applicator section, and is captured by the microwave waveguide segment; 
           [0021]      FIG. 7  is similar to  FIG. 3 , and shows an example microwave drying system that utilizes spaced apart applicators to define the first and second applicator sections rather than using a single applicator divided into the two applicator sections; and 
           [0022]      FIG. 8  is a top-down view of wet skinned ceramic wares as arranged on the conveyor, illustrating an example configuration wherein adjacent wares are spaced apart from one another by a spacing S&lt;λ/2, where λ is the free-space wavelength of the microwave radiation. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Reference is now made in detail to various embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or like reference numbers and symbols are used throughout the drawings to refer to the same or like parts. The drawings are not necessarily to scale, and one skilled in the art will recognize where the drawings have been simplified to illustrate the key aspects of the disclosure. 
         [0024]    Cartesian coordinates are shown in some of the Figures for the sake of reference and are not intended to be limiting as to direction or orientation. 
         [0025]      FIG. 1  is an isometric side view of an example skinned ceramic ware  10 , while  FIG. 2A  is a front-on, close-up view of a pre-skinned (i.e., un-skinned) ceramic ware  10 P of  FIG. 1 .  FIG. 2B  is similar to  FIG. 2A  but for the skinned ceramic ware  10  of  FIG. 1 . The skinned ceramic ware  10  has a central axis A 1 , a front end  12 , a back end  14 , and a cylindrical outer wall  15  that includes cylindrical surface  16  on which is formed a layer of skin (“skin”)  18 . The ceramic ware  10  minus skin  18  constitutes the aforementioned pre-skinned or unskinned ceramic ware  10  of  FIG. 2A . The ceramic ware  10  can have any reasonable cross-sectional shape that can be obtained using an extrusion process, such as circular, elliptical, asymmetrical, etc. 
         [0026]    In an example, skinned ceramic ware  10  has an array of longitudinally running cells  20  that are open at front and back ends  12  and  14  of the ware (see first close-up inset  11  of  FIG. 1 ). The cells  20  are defined by cell walls  22  (see second dose-up inset  12 ). In an example, cells  20  form a porous honeycomb structure. 
         [0027]    As noted above, skin  18  is usually applied to the cylindrical surface  16  of the unskinned ceramic ware  10 P after it has been dried and fired, and after the fired ceramic ware has been processed to have desired dimensions. This processing includes shaping or contouring, and can also include grinding of the front and/or back ends  12  and  14 . Typically, skin  18  does not cover the front and back ends  12  and  14  of the ceramic ware. 
         [0028]    The material making up skin  18  can be applied to cylindrical surface  16  of cylindrical wall  15  using any of the known methods, e.g., by a doctor blade operation, by an axial skinning operation, by a spray casting operation, by a tape casting operation, or the like. The material of skin  18  that contacts the underlying cylindrical surface  16  of cylindrical wall  15  bonds thereto when the skin is cured. 
         [0029]    In exemplary embodiments, skin  18  has a thickness TH on the order of millimeters, e.g., 0.5 mm to 4 mm. In one example, the skin thickness TH can be from about 0.5 mm to about 2.1 mm. For example, the skin thickness TH can be from about 0.5 to about 1.1 mm, or about 1.0 mm to about 1.5 mm, or even from about 1.4 mm to about 2.1 mm. When skin  18  is applied over an existing skin or the skin is a multi-layer skin, the total skin thickness TH can be about twice that of a single-layer skin. 
         [0030]    The composition of skin  18  can be any one of the compositions used in the art of ceramic ware formation. Example compositions for skin  18  are described in U.S. patent application Ser. No. 13/770,104, filed on Feb. 19, 2013. According to exemplary embodiments, the skin composition may comprise an inorganic filler material and a crystalline inorganic fibrous material. In exemplary embodiments, the inorganic filler material comprises at least 10% of the total weight of the inorganic solid components of the cement mixture and the crystalline inorganic fibrous material comprises less than 25% of the total weight of the inorganic solid components of the cement mixture. In an example, skin  18  is made of substantially the same material that constitutes pre-skinned ceramic ware  10 P. 
         [0031]    As discussed above, the process of forming skinned ceramic ware  10  includes drying the wet skin  18  after it is applied to the cylindrical surface  16  of cylindrical wall  15  of the unskinned ceramic ware  10 P. In the discussion below, a skinned ceramic ware whose skin is wet (i.e., undried) has an original moisture content (e.g., 10% to 35% by weight of water) is referred to herein as a “wet skinned ceramic ware”  10 W. A skinned ceramic ware whose skin is partially dried or “semi-dry” is referred herein as a “semi-dry skinned ceramic ware”  10 S. For convenience and for consistency of terminology, in the discussion below, a dried skinned ceramic ware is denoted  10 D. A reference to a “skinned ceramic ware”  10  can include a wet, a semi-dry or a dried skinned ceramic ware. 
         [0032]    In an example, the skin  18  of semi-dry skinned ceramic ware  10 S has a skin moisture content of between 30% and 60% of the original skin moisture content of the wet skinned ceramic ware  10 W. In an example, the skin  18  of a dried skinned ceramic ware  10 D has a moisture content of 10% or less of the original moisture content of the wet skinned ceramic ware  10 W. 
         [0033]      FIG. 3  is a schematic side view of an example microwave drying system (“system”)  100  for drying skinned ceramic wares  10  according to the methods disclosed herein. The system  100  includes a microwave dryer or applicator  110  that has an input end  112 , an output end  114 , walls  115  (see  FIG. 4 ), a ceiling  116 , and an interior divided into first and second interior sections (“sections”)  124 W and  124 S by a shielding member  130 , where the first section  124 W is the upstream section and the second section  124 S is the downstream section. 
         [0034]    In an example, shielding member  130  is a perforated metallic sheet configured to reduce an amount of coupling of microwave radiation between the first and second sections  124 W and  124 S while also allowing for skinned ceramic wares  10  to pass from the upstream section  124 W to the downstream section  124 S. As illustrated in  FIG. 3 , in an example, shielding member  130  is attached to ceiling  116  and downwardly depends therefrom (i.e., extends in the −z direction) towards conveyor  140  far enough to provide the reduced microwave radiation coupling while also allowing for the skinned ceramic wares  10  to be conveyed beneath the shielding member. 
         [0035]    The first section  124 W is referred to hereinafter as the “wet applicator section” because it receives wet skinned ceramic wares  10 W at the input end  112  of applicator  110 . The second section  124 S is referred to hereinafter as the “semi-dry applicator section” because it receives semi-dry skinned ceramic wares  10 S from the upstream wet applicator section  124 W, as explained below. 
         [0036]      FIG. 4  is a top-down view of system  100  but without ceiling  116  of applicator  110  so that that the wet and semi-dry skinned ceramic wares  10 W and  10 S can be seen within their respective wet and semi-dry applicator sections  124 W and  124 S. 
         [0037]    With reference to both  FIG. 3  and  FIG. 4 , system  100  includes a conveyor  140  that runs in the x-direction through the wet and semi-dry sections  124 W and  124 S of applicator  110 . The conveyor  140  extends into the input end  112  of the applicator  110  and extends out of the output end  114  of the applicator. The conveyor  140  has an input location  142  just upstream of input end  112  where wet skinned ceramic wares  10 W can be arranged for transport through applicator  110 . In an example, wet skinned ceramic wares  10 W are arranged on conveyor  140  at the input location  142  with their central axes A 1  oriented in the vertical direction, shown as the z-direction. 
         [0038]    The conveyor  140  also has an output or removal location  144  just downstream of output end  114  where dried skinned ceramic wares  10 D can be outputted or removed from system  100 . In an example, conveyor  140  has a conveyor speed in the range from 0.5 feet/minute to 2 feet/minute. In an example, the movement of conveyor  140  is continuous so that the skinned ceramic wares  10  are continually moved through the wet applicator section and then the semi-dry applicator section  124 S during the drying process. In an example, the conveyor  140  moves at a substantially constant conveyor speed. In another example, conveyor  140  moves and stops as needed during the drying process, for example, to accommodate a shield door to open and dose at shielding member  130 . 
         [0039]    System  100  includes a microwave system  200  operably arranged relative to applicator  110 . Microwave system  200  includes a microwave source system  206 , which in an example includes a microwave source  210 , such as a magnetron, that emits microwave radiation  212  (also referred to below as simply “microwaves”), and an antireflection device  214 , such as a stub tuner, operably arranged downstream of the microwave source to prevent reflected microwaves from reaching the microwave source. A source circulator (not shown) can be disposed between the microwave source  210  and the antireflection device  214  to direct reflected power back from the applicator(s) to a water load to minimize reflected power going back to the source magnetron  210 . An example magnetron  210  has a frequency f of 915 MHz and provides 100 kW of microwave power P 1 . 
         [0040]    In an example, the microwave frequency f can be in the range from 20 MHz to 20000 MHz. Microwaves  212  have a wavelength λ that is related to the microwave frequency f by the relationship λ=c/f, where c is the speed of light and is about 3×10 8  m/s. A frequency f=1000 MHz has a wavelength of about 0.3 m. 
         [0041]    In an example, the amount of microwave power P 1  employed in the drying process is based on the number of wet skinned ceramic wares  10 W present in the wet applicator section  124 W at a given time, wherein each wet skinned ceramic ware represents a certain amount of susceptible material. An example microwave power P 1  is in the range from 10 kW to 100 kW or is in the range from 10 kW to 90 kW. 
         [0042]    The microwave source system  206  is operably coupled to a microwave waveguide system  220  configured to guide microwaves  212 . In particular, microwave waveguide system  220  includes a number of microwave feed channels or microwave waveguides (hereinafter, “waveguides”), and in particular includes a first waveguide  222  that leads to wet applicator section  124 W and a second waveguide  242  that leads to semi-dry applicator section  124 S. The first and second waveguides  222  and  242  are operably connected at a circulator  234 , which is operably connected to antireflection device  214  via a waveguide  236 . 
         [0043]    The first waveguide  222  includes a first waveguide section  224  arranged within the wet applicator section  124 W adjacent ceiling  116 , while the second waveguide  242  includes a second waveguide section  244  arranged within the semi-dry applicator section  124 S adjacent the ceiling. The first and second waveguides  222  and  242  are respectively configured to deliver microwave radiation to the wet applicator section  124 W and the semi-dry applicator section  124 S in the manner described below. 
         [0044]      FIG. 5  is similar to  FIG. 4  and shows system  100  without the applicator ceiling  116  or microwave system  200  so that the wet and semi-dry skinned ceramic wares  10 W and  10 S can be seen in an example drying configuration within their respective wet and semi-dry applicator sections  124 W and  124 S. With reference to  FIG. 5 , applicator  110  has dimension LX and LY, which in one example are LX=15 feet and LY=6 feet. 
         [0045]    As best seen in  FIG. 4 , in an example embodiment, the first waveguide section  224  includes a U-shaped waveguide segment  226  that serves to define two spaced apart linear waveguide segments  228  that run perpendicular to conveyor  140  (i.e., they extend in the y-direction) to provide a good distribution of microwaves  212  within wet applicator section  124 W. The waveguide segments  228  each includes spaced-apart slots  230  through which microwaves  112  traveling in the linear waveguide segments  228  exit (leak) into wet applicator section  124 W. 
         [0046]    The second waveguide section  244  is configured similar to the first waveguide section  224  and includes a U-shaped waveguide segment  246  that serves to define two spaced apart linear waveguide segments  248  that run perpendicular to conveyor  140  (i.e., they extend in the y-direction) to provide a good distribution of microwaves within semi-dry applicator section  124 S. The waveguide segments  248  each includes spaced-apart slots  250  through which a portion of microwaves traveling in the linear waveguide sections exit (leak) into semi-dry applicator section  124 S. 
         [0047]    In the operation of system  100 , microwave source system  206  generates microwaves  212  (black arrows) having the aforementioned frequency f and power P 1 . Of the aforementioned example frequencies f, the frequency f=915 MHz corresponds to a (free-space) wavelength λ of about 33 cm, while the frequency f=2450 MHz corresponds to a wavelength λ of about 12 cm. Generally speaking, to obtain the most uniform drying of skin  18 , the skin thickness TH should be substantially smaller than the microwave wavelength λ, e.g., TH&lt;λ/10. For a skin thickness TH of 4 mm, the microwave frequency f=2450 MHz with the corresponding wavelength λ of about 12 cm easily satisfies this criterion. In general, any microwave frequency f consistent with this criterion and that is generally effective for microwave drying can be used. 
         [0048]    Microwaves  212  travel within waveguide  236  and through circulator  234  to first waveguide  222  and to first waveguide section  224 . The microwaves  212  traveling within first waveguide section  224  exit from slots  230  in the linear waveguide segments  228  and enter the wet applicator section  124 W. 
         [0049]      FIG. 6A  is a schematic view of wet skinned ceramic wares  10 W residing in wet applicator section  124 W beneath one of the waveguide segments  228 . The microwave radiation  212  that leaks from the waveguide segment  228  through slots  230  irradiates the wet skinned ceramic wares  10 W that reside within and are being conveyed through wet applicator section  124 W. A portion of this microwave radiation  212  is absorbed by wet skin  18  and initiates drying of the skin. Another portion of microwave radiation  212  is reflected by the wet skinned ceramic wares  10 W, as well as by the walls  15 , ceiling  16 , conveyor  140  (see  FIG. 3 ), and any other items (e.g., trays) or surfaces within the wet applicator section  124 W, as reflected microwave radiation  212 R, as illustrated in  FIG. 6B . 
         [0050]    The original water content in skin  18  of wet skinned ceramic wares  10 W represents a relatively small percentage of the total mass of ceramic material residing in wet applicator section  124 W because the other ceramic material in each wet skinned ceramic ware (i.e., the cylindrical wall  15  and cells  20 ) are dry. Consequently, there is a relatively high amount of reflected microwaves  212 R (white arrows) from the wet skinned ceramic wares  10 W as well as from the aforementioned walls  15 , ceiling  16 , conveyor  140 , and any other items (e.g., trays) or surfaces within the wet applicator section  124 W. 
         [0051]    A portion of the reflected microwave radiation  212 R enters the waveguide segments  228  through their spaced-apart slots  230 . In this manner, a portion of the reflected microwave radiation  212 R is captured by the waveguide segments  228  and travels back through the first waveguide  222  toward circulator  234 . The captured reflected microwave radiation  212 R is redirected by circulator  234  to travel within second waveguide  242  to second waveguide section  244  and to second waveguide segments  248 . 
         [0052]    In an example, the captured reflected microwave radiation  212 R has a power P 2  that is less than the inputted microwave power P 1  and represents between 5% and 50% of the inputted microwave power P 1 , or in another example represents between 20% and 50% of the inputted microwave power P 1 . 
         [0053]    The reflected microwave radiation  212 R exits (leaks from) the second linear waveguide segments  248  through their respective slots  250  and irradiate the semi-dry skinned ceramic wares  10 S that reside within and that are being conveyed through semi-dry applicator section  124 S, thereby further drying the semi-dry skin  18  of the semi-dry skinned ceramic wares  10 S. By the time the semi-dry skinned ceramic wares  10 S exit the semi-dry applicator section  124 S at the output end  114  of applicator  110 , they are dried skinned ceramic wares  10 D. 
         [0054]    Thus, the first and second waveguides  222  and  242  and the circulator  234  of microwave waveguide system  220  define a reflected-microwave path  215  from wet applicator section  124 W to semi-dry applicator section  124 S over which reflected microwave radiation  212 R can travel. 
         [0055]    It is noted that a portion of the reflected microwaves  212 R will also reflect from the semi-dry ceramic wares  10 S and be captured by the second microwave segments  248  and travel in the second waveguide  242  back toward circulator  234  as doubly reflected microwave radiation  212 RR (see  FIG. 3 ). This doubly reflected microwave radiation  212 RR is redirected by circulator  234  to anti-reflection device  214 , which prevents this doubly reflected microwave radiation from reaching microwave source  210 . 
         [0056]    It is also pointed out that the reflected microwave radiation  212 R used to irradiate semi-dry skinned ceramic wares  10 S in second applicator section  124 S originates in part from upstream wet skinned ceramic wares  10 W in the first application section  124 W. Thus, the reflected microwave radiation  212 R is not used to dry the same wet skinned ceramic wares  10 W from which a portion of the incident microwave radiation  212  is reflected but instead is used to dry downstream semi-dry ceramic wares in semi-dry applicator section  124 S that have already passed through wet applicator section  124 W. 
         [0057]    An aspect of the method of drying wet skinned ceramic wares according to the disclosure includes maintaining the first applicator section  124 W with either a sufficient number of wet skinned ceramic wares  10 W to be processed or, at the end of the run, dummy ceramic wares or other material or objects or items that can be used in place of the last set of wet skinned ceramic wares to ensure a proper or desired amount of reflected microwave radiation  212 R. Thus, in an example, as wet skinned ceramic wares  10 W move through the first applicator section  124 W by the action of conveyor  140 , the other wet skinned ceramic wares  10 W are added to the conveyor at the input location  142  (see  FIG. 5 ). In an example, this backfilling process is carried out so that the wet applicator section  124 W has substantially the same configuration of wet skinned ceramic wares  10 W being conveyed therethrough at any given time. This in turn ensures that substantially the same amount of reflected microwaves  212 R is generated and recycled to the semi-dry applicator section  124 S. 
         [0058]    The semi-dry skinned ceramic wares  10 S passing through semi-dry applicator section  124 S do not require as much microwave power to dry as the wet skinned ceramic wares  10 W of wet applicator section  124 W. Thus, system  100  is configured to recycle the reflected microwave radiation  212 R from wet applicator section  124 W and direct it to the semi-dry applicator section  124 S for drying the semi-dry skinned ceramic wares  10 S. In an example, P 2 &lt;P 1  and the ratio of an amount of recycled microwave power P 2  provided to semi-dry applicator section  124 S using reflected microwaves  212 R as compared to the microwave power P 1  directed to the wet applicator section  124 W is in the range 0.05≦P 2 /P 1 ≦0.5, or in another example is in the range 0.05≦P 2 /P 1 ≦0.4. 
         [0059]    Because system  100  makes use of a single applicator  110  divided into two immediately adjacent sections  124 W and  124 S rather than two spaced apart applicators, the skinned ceramic wares  10  can be processed quickly. 
         [0060]    The use of a single microwave source system  110  reduces cost and increases drying efficiency. In an example, system  100  is capable of processing about 200 wet skinned ceramic wares  10 W at a conveyor speed of about 1 foot/minute, a microwave frequency of 915 MHz and a microwave power P 1  of 60 kW. In another example, system  100  is capable of processing about 333 wet skinned ceramic wares  10 W at a conveyor speed of 1 foot/minute, a microwave frequency of 915 MHz and a microwave power P 1  of 100 kW. 
         [0061]      FIG. 7  is similar to  FIG. 3  and illustrates an example embodiment of an alternate configuration for system  100  wherein two spaced apart applicators  110 W and  110 S are used to define wet applicator section  124 W and  124 S instead of the single applicator  110  with shielding member  130 . In the example configuration of system  100  of  FIG. 7 , the shielding member  130  is no longer required, but the overall distance that the skinned ceramic wares  10  need to travel may be greater so that the drying time may be longer. 
         [0062]      FIG. 8  is a top-down view of a plurality of wet skinned ceramic wares  10 W on conveyor  140  illustrating an example drying configuration wherein adjacent wet skinned ceramic wares  10 W (which become semi-dry skinned ceramic wares as they pass through to semi-dry applicator  124 S) are spaced apart by a spacing S. In an example, the spacing S&lt;λ/2, wherein A is the aforementioned (free-space) microwave wavelength of microwave radiation  212 , as noted above. In another example, the spacing S&lt;λ/10. The example drying configuration reduces the amount of reflected microwave radiation  212 R (i.e., reduces the amount of reflected microwave power or energy) during the drying process. This provides for increased loading in the wet and semi-dry applicator sections, which makes for more efficient drying and higher throughput of system  100 . In an example, the spacing S is adjusted to adjust the amount of reflected microwave radiation  212 R. For example, the spacing S can be adjusted to increase the amount of reflected microwave radiation  212 R rather than minimize the amount of reflected microwave radiation in order to increase the amount of microwave power P 2  delivered to the semi-dry applicator section  124 S. 
         [0063]    It will be apparent to those skilled in the art that various modifications to the preferred embodiments of the disclosure as described herein can be made without departing from the spirit or scope of the disclosure as defined in the appended claims. Thus, the disclosure covers the modifications and variations provided they come within the scope of the appended claims and the equivalents thereto.