Patent Application
20170334091
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.
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.
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.
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.
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.
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.
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 P1, 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 P2<P1 to form dried skinned ceramic wares.
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.
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.
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.
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:
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.
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.
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
As noted above, skin 18 is usually applied to the cylindrical surface 16 of the unskinned ceramic ware 10P 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.
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.
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.
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 10P.
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 10P. 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” 10W. A skinned ceramic ware whose skin is partially dried or “semi-dry” is referred herein as a “semi-dry skinned ceramic ware” 10S. For convenience and for consistency of terminology, in the discussion below, a dried skinned ceramic ware is denoted 10D. A reference to a “skinned ceramic ware” 10 can include a wet, a semi-dry or a dried skinned ceramic ware.
In an example, the skin 18 of semi-dry skinned ceramic ware 10S has a skin moisture content of between 30% and 60% of the original skin moisture content of the wet skinned ceramic ware 10W. In an example, the skin 18 of a dried skinned ceramic ware 10D has a moisture content of 10% or less of the original moisture content of the wet skinned ceramic ware 10W.
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 124W and 124S while also allowing for skinned ceramic wares 10 to pass from the upstream section 124W to the downstream section 124S. As illustrated in
The first section 124W is referred to hereinafter as the “wet applicator section” because it receives wet skinned ceramic wares 10W at the input end 112 of applicator 110. The second section 124S is referred to hereinafter as the “semi-dry applicator section” because it receives semi-dry skinned ceramic wares 10S from the upstream wet applicator section 124W, as explained below.
With reference to both
The conveyor 140 also has an output or removal location 144 just downstream of output end 114 where dried skinned ceramic wares 10D 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 124S 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.
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 P1.
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 3×108 m/s. A frequency f=1000 MHz has a wavelength of about 0.3 m.
In an example, the amount of microwave power P1 employed in the drying process is based on the number of wet skinned ceramic wares 10W present in the wet applicator section 124W at a given time, wherein each wet skinned ceramic ware represents a certain amount of susceptible material. An example microwave power P1 is in the range from 10 kW to 100 kW or is in the range from 10 kW to 90 kW.
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 124W and a second waveguide 242 that leads to semi-dry applicator section 124S. 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.
The first waveguide 222 includes a first waveguide section 224 arranged within the wet applicator section 124W adjacent ceiling 116, while the second waveguide 242 includes a second waveguide section 244 arranged within the semi-dry applicator section 124S adjacent the ceiling. The first and second waveguides 222 and 242 are respectively configured to deliver microwave radiation to the wet applicator section 124W and the semi-dry applicator section 124S in the manner described below.
As best seen in
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 124S. 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 124S.
In the operation of system 100, microwave source system 206 generates microwaves 212 (black arrows) having the aforementioned frequency f and power P1. 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<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.
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 124W.
The original water content in skin 18 of wet skinned ceramic wares 10W represents a relatively small percentage of the total mass of ceramic material residing in wet applicator section 124W 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 212R (white arrows) from the wet skinned ceramic wares 10W 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 124W.
A portion of the reflected microwave radiation 212R enters the waveguide segments 228 through their spaced-apart slots 230. In this manner, a portion of the reflected microwave radiation 212R is captured by the waveguide segments 228 and travels back through the first waveguide 222 toward circulator 234. The captured reflected microwave radiation 212R is redirected by circulator 234 to travel within second waveguide 242 to second waveguide section 244 and to second waveguide segments 248.
In an example, the captured reflected microwave radiation 212R has a power P2 that is less than the inputted microwave power P1 and represents between 5% and 50% of the inputted microwave power P1, or in another example represents between 20% and 50% of the inputted microwave power P1.
The reflected microwave radiation 212R exits (leaks from) the second linear waveguide segments 248 through their respective slots 250 and irradiate the semi-dry skinned ceramic wares 10S that reside within and that are being conveyed through semi-dry applicator section 124S, thereby further drying the semi-dry skin 18 of the semi-dry skinned ceramic wares 10S. By the time the semi-dry skinned ceramic wares 10S exit the semi-dry applicator section 124S at the output end 114 of applicator 110, they are dried skinned ceramic wares 10D.
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 124W to semi-dry applicator section 124S over which reflected microwave radiation 212R can travel.
It is noted that a portion of the reflected microwaves 212R will also reflect from the semi-dry ceramic wares 10S 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 212RR (see
It is also pointed out that the reflected microwave radiation 212R used to irradiate semi-dry skinned ceramic wares 10S in second applicator section 124S originates in part from upstream wet skinned ceramic wares 10W in the first application section 124W. Thus, the reflected microwave radiation 212R is not used to dry the same wet skinned ceramic wares 10W 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 124S that have already passed through wet applicator section 124W.
An aspect of the method of drying wet skinned ceramic wares according to the disclosure includes maintaining the first applicator section 124W with either a sufficient number of wet skinned ceramic wares 10W 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 212R. Thus, in an example, as wet skinned ceramic wares 10W move through the first applicator section 124W by the action of conveyor 140, the other wet skinned ceramic wares 10W are added to the conveyor at the input location 142 (see
The semi-dry skinned ceramic wares 10S passing through semi-dry applicator section 124S do not require as much microwave power to dry as the wet skinned ceramic wares 10W of wet applicator section 124W. Thus, system 100 is configured to recycle the reflected microwave radiation 212R from wet applicator section 124W and direct it to the semi-dry applicator section 124S for drying the semi-dry skinned ceramic wares 10S. In an example, P2<P1 and the ratio of an amount of recycled microwave power P2 provided to semi-dry applicator section 124S using reflected microwaves 212R as compared to the microwave power P1 directed to the wet applicator section 124W is in the range 0.05≦P2/P1≦0.5, or in another example is in the range 0.05≦P2/P1≦0.4.
Because system 100 makes use of a single applicator 110 divided into two immediately adjacent sections 124W and 124S rather than two spaced apart applicators, the skinned ceramic wares 10 can be processed quickly.
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 10W at a conveyor speed of about 1 foot/minute, a microwave frequency of 915 MHz and a microwave power P1 of 60 kW. In another example, system 100 is capable of processing about 333 wet skinned ceramic wares 10W at a conveyor speed of 1 foot/minute, a microwave frequency of 915 MHz and a microwave power P1 of 100 kW.
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.
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.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2015/057536 | 10/27/2015 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62068845 | Oct 2014 | US |
