Patent Application
20070252310
This invention relates to charging flowable materials into selected cells of a honeycomb structure and drying the flowable materials and honeycomb structure, and more particularly, to a method for drying the flowable materials and a green honeycomb structure.
Honeycomb structures having traverse cross-sectional cellular densities of approximately one tenth to one hundred cells or more per square centimeter have several uses, including solid particulate filter bodies and stationary heat exchangers. Such uses require selected cells of the structure to be sealed or plugged by manifolding and the like at one or both of the respective ends thereof. The term “sealed” and other corresponding grammatical forms, i.e., sealant, sealing, etc., are used herein to refer to both porous and non-porous methods of closing the open transverse cross-sectional areas of cells.
The reference numeral 10 (
In operation, contaminated fluid is brought under pressure to an inlet face and enters the filter 10 via those cells which have an open end at the inlet face. Because these cells are sealed at the opposite end face, i.e., the outlet face of the body, the contaminated fluid is forced through the thin porous walls 14 into adjoining cells which are sealed at the inlet face and open at the outlet face. The solid particulate contaminant in the fluid, which is too large to pass through the porous openings in the walls, is left behind and a cleansed fluid exits the filter 10 through the outlet cells and is ready for use.
For the mass production of such filters and heat exchangers, it is highly desirable to be able to seal selected cell channels ends as rapidly and as inexpensively as possible. Sealing these selected cells comprises inserting a plugging material into the open ends of selected cell channels and subsequently drying the plugged filter. Previous methods for drying have included firing a high porosity ware, such as a green honeycomb structure, within a drying oven, plugging the open ends of selected cell channels, and re-firing the plugged honeycomb structure. These previous techniques have resulted in cracks and stress fractures within the walls of the channels, and filter bodies with a decreased structural integrity. Moreover, these previous techniques are relatively expensive as well as time intensive.
A method for plugging and drying extruded honeycomb structures, such as ceramic particulate traps for diesel engines, is desired that is highly repeatable and accurate, while simultaneously having a short cycle time and resulting in a filter with a relatively greater structural integrity.
One aspect of the present invention is to provide a method for manufacturing a honeycomb structure, the method comprising providing a green honeycomb structure having a plurality of cell channels extending therethrough, inserting a plug material into at least a subset of the cell channels of the green honeycomb structure to form a plurality of plugs therein, and drying the plugs by exposing the plugs to electromagnetic energy. Preferably, the step of drying the plugs includes exposing the plugs to microwave energy. Preferably, the green honeycomb structure is manufactured from a cordierite forming precursor material.
The present inventive method is highly accurate and repeatable, may be completed in a relatively short cycle time, is relatively easy to perform, and results in a filter with a relatively greater structural integrity. The method further reduces the relative cracking and stress fractures within the desired structure produced during the drying process, reduces manufacturing costs as associated with the cycle times, is efficient to use, and is particularly well-adapted for the proposed use.
These and other advantages of the invention will be further understood and appreciated by those skilled in the art by reference to the following written specification, claims and appended drawings.
For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in
Several methods and procedures are known in the art for forming the honeycomb structure 12 of
In one aspect, the inorganic batch components can be selected from a magnesium oxide source; an alumina-forming source; and a silica source. The batch components are further selected so as to yield a ceramic article comprising predominantly cordierite, or a mixture of cordierite, mullite and/or spinel upon firing. For example, and without limitation, in one aspect, the inorganic batch components can be selected to provide a ceramic article which comprises at least about 90% by weight cordierite; or more preferably 93% by weight the cordierite. The cordierite-containing honeycomb article consists essentially of, as characterized in an oxide weight percent basis, from about 49 to about 53 percent by weight. SiO2, from about 33 to about 38 percent by weight. Al2O3, and from about 12 to about 16 percent by weight MgO.
To this end, an exemplary inorganic cordierite precursor powder batch composition preferably comprises about 33 to about 41 weight percent of an aluminum oxide source, about 46 to about 53 weight percent of a silica source, and about 11 to about 17 weight percent of a magnesium oxide source. Exemplary non-limiting inorganic batch component mixtures suitable for forming cordierite are disclosed in U.S. Pat. Nos. 3,885,977; 5,258,150; US Pub. No. 2004/0261384 and 2004/0029707; and RE 38,888.
The inorganic ceramic batch components can be synthetically produced materials such as oxides, hydroxides, and the like. Alternatively, they can be naturally occurring minerals such as clays, talcs, or any combination thereof. Thus, it should be understood that the present invention is not limited to any particular types of powders or raw materials, as such can be selected depending on the properties desired in the final ceramic body.
The process further comprises cutting or segmenting 36 the green honeycomb form into green honeycomb structures of a desired length, and thereafter removing dust 38 from the green honeycomb structures as formed during the cutting step 36, i.e., the green ceramic precursor cutting dust. The dust is removed to improve the adherence of the plug material to the wall and to improve the adherence of the mask to the end of the structure. The dust removal step is preferably accomplished by passing high velocity air through the cell passages 22 of the structure after the cutting step to dislodge and remove any cutting dust. Each end face 18, 20 of each honeycomb structure 12 is then masked 40 with a suitable mask, and selected cell passages 22 are charged with a plugging material to form plugs 42 in selected ones of the cell channels to form a plugged, green honeycomb structure, as described below.
The plugged, green honeycomb structure is then dried 44 by exposing the plugged, green honeycomb structure to an electromagnetic energy, in accordance with the present invention. The dried, plugged, green honeycomb structure may then be fired 46 for further sintering and to form the fired ceramic article. Several steps of this overall process are known to those skilled in the art, and as such the steps of extruding 30, the primary cutting step 32, the step of drying 34, the secondary cutting step 36, and the masking step 40 are not discussed in detail herein.
The step of plugging the green honeycomb structure 12 includes charging or otherwise introducing a flowable plugging cement material, such as a slurry preferably comprising a water diluted ceramic solution, into selected cell channels 22 as determined by the plugging mask. Formation of plugging masks may be by the method taught in U.S. Ser. No. 11/287,000 filed Nov. 20, 2005, for example, entitled “Apparatus, System and Method For Manufacturing A Plugging Mask For A Honeycomb Substrate” which is hereby incorporated by reference herein. An example of the plugging process 42 is best illustrated in
The electromagnetic drying step 44 comprises drying the plugs 56 as formed within the cell channels 22 of the green honeycomb structure 12 by exposing the plugs 56 to electromagnetic energy. Preferably, this electromagnetic energy is provided in the form of microwave, however, other suitable forms of electromagnetic energy may also be utilized for the drying of the plugs 56. The microwave drying of the plugs 56 results in a relatively quick and uniform heating of the green honeycomb structure and the plugs 56, thereby reducing shrinkage of the plugs 56 and decreasing the heat stress exerted on the porous walls 14 of the green honeycomb structure 12 during the drying step 44 as compared to conventional drying means. This reduction in stress as exerted on the porous walls 14 results in a greater structural integrity of the resultant particulate filter. The plugs 56 are preferably exposed to the microwave energy until the water content of the plugs 56 are less than 50% of a 100% wet plug weight, more preferably less than 10% of the 100% wet plug weight, and most preferably less than about 5% of the 100% plug weight, with the 100% wet plug weight being defined as the water content of the plug 56 prior to being exposed to the microwave energy. Preferably, the microwave energy is provided within the range of from about 3 MHz to about 3 GHz, more preferably within the range of from about 27 MHz to about 2.45 GHz, and most preferably within the range of from about 915 MHz to about 2.45 GHz. Further, the electromagnetic drying step 44 includes exposing the plugged green honeycomb structure to a power lever per unit volume of preferably between 0.0001 kW/in3 and 1.0 kW/in3, and more preferably within the range of between 0.001 kW/in3 and about 1.0 kW/in3. Moreover, the energies as noted above are preferably applied to the plugged green honeycomb structure for a time of less than or equal to 60 minutes, and more preferably for a time of less than or equal to 5 minutes. Electromagnetic drying, such as microwave drying, is discussed in U.S. Pat. No. 6,706,233 and US 2004/0079469.
As noted above, the firing or sintering step 46 may be conducted subsequent to electromagnetically drying 44 the green honeycomb structure. This step is preferably conducted via conventional sintering means at a temperature of above 1300° C. and for a sufficient time so as to form a predominant phase of cordierite. It is also noted that the drying step is preferably conducted with the honeycomb structure in a horizontal orientation.
One aspect of the present invention is to provide a method for manufacturing a honeycomb structure, the method comprising providing a green honeycomb structure having a plurality of cell channels extending therethrough, inserting a plug material into at least a subset of the cell channels of the green honeycomb structure to form a plurality of plugs therein, and drying the plugs by exposing the plugs to electromagnetic energy.
It will become apparent to those skilled in the art that various modifications to the preferred embodiment of the invention as described herein can be made without departing from the spirit or scope of the invention as defined in the appended claims. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and the equivalents thereto.
