BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a ceramic honeycomb structure the drying of which embodies the present invention;
FIG. 2 is a perspective view of the ceramic honeycomb structure with alternatively plugged channels;
FIG. 3 is an end elevational view of the ceramic honeycomb structure of FIG. 2;
FIG. 4 is a top perspective view of a microwave dryer with a plurality of ceramic honeycomb structures located within an interior thereof;
FIG. 5 is a cross-sectional top plan view of the microwave dryer of FIG. 4, with a plurality of ceramic structures located within the interior thereof;
FIG. 6 is a cross-sectional end elevational view of the microwave dryer of FIG. 4, with a plurality of ceramic structures located within the interior thereof;
FIG. 7 is a graph of integrated dissipation vs. length for a ceramic structure dried via conventional means;
FIG. 8 is a graph of integrated dissipation vs. width for a ceramic structure dried via conventional means;
FIG. 9 is a graph of integrated dissipation vs. length for a ceramic structure dried via conventional means, and a ceramic structure dried via the present inventive process;
FIG. 10 is a graph of integrated dissipation vs. width for a ceramic structure dried via conventional means, and a ceramic structure dried via the present inventive process; via conventional means;
FIG. 11 is a graph of integrated dissipation vs. length for three modeled sample of ceramic structures dried via the present inventive process;
FIG. 12 is a graph of integrated dissipation vs. width for three modeled sample of ceramic structures dried via the present inventive process;
FIG. 13 is a side perspective view of a first alternative embodiment of the present inventive method, including a pair of shield members shielding end faces of the ceramic structure;
FIG. 14 is a side perspective view of a second alternative embodiment of the present inventive method, including a pair of ceramic structures positioned end-to-end;
FIG. 15 is a top perspective view of a third alternative embodiment of the present inventive method, wherein the ceramic structure is spaced from the sidewalls of a microwave applicator on a support tray; and
FIG. 16 is a top perspective view of a fourth alternative embodiment of the present inventive method, including multiple spaced trays.
DETAILED DESCRIPTION
Several methods and procedures are known in the art for forming green ceramic honeycomb structures featuring a plurality of hollow passages or channels extending therethrough. The present inventive process is directed to drying such structures regardless of the specific method used to form the honeycomb shape. The present inventive method for drying ceramic honeycomb structures 10 includes providing microwave radiation from a microwave generating source 30 (FIGS. 4-6) located within a microwave housing 32, exposing the ceramic honeycomb structure 10 to the microwave radiation, and shielding at least one of the ends 13, 16 from directly receiving the microwave radiation, such that the radiation absorbed by the middle portion 17 of the ceramic structure 10 is equal to or greater than the radiation absorbed by the at least one end 13, 16, as described herein. It is noted that the present inventive process may be used to process either plugged or non-plugged ceramic structures.
In the illustrated example, the microwave housing 32 includes a bottom wall 34, a top wall 36, and a pair of side walls 38. The microwave generating source 30 extends downwardly from the top wall 36 and is centrally located within the microwave housing 32. In the illustrated example, a plurality of ceramic structures 10 are positioned within an interior 40 of the microwave housing 32, each supported by an associated support tray 42. It is noted that the present inventive method can be accomplished either via batch style or continuous-type flow processing, and that the housing 32 may be configured to house a single structure 10, or multiple structures. Further, the structure(s) may be horizontally or vertically oriented as the drying process is completed. A pair of planar shield members 44 are positioned within the interior 40 of the microwave housing 32 and vertically above the structure 10 between the microwave generating source 30 and the ends 13, 16 of the structure 10, thereby shielding the ends 13, 16 of the ceramic structure 10 from directly receiving the microwave radiation such that the radiation absorbed by a middle portion 17 of the ceramic structure 10 is equal to or greater than the radiation absorbed at the ends 13, 16. Preferably, the amount of radiation absorbed by the middle portion is within the range of from 0% to 60% greater than the radiation absorbed by the ends 13, 16 of the structure 10, and more preferably within the range of from 10% to 40%.
As best illustrated in FIG. 6, the shield members 44 are adjustable in several directions with respect to the ceramic structure 10 being processed, including a vertical direction 48 and a horizontal direction 50. Adjustment in the vertical direction 48 allows an operator to adjust the vertical distance of separation X between the uppermost portion of the ceramic structure 10 and the shield member 44. Preferably, the distance X is less than or equal to 1.5 times the wavelength of the microwave radiation, more preferably within the range of 1.5 to 1.0 times the wavelength of the microwave radiation, and most preferably is about 0.5 times the wavelength of the microwave radiation. Adjustment in the horizontal direction 50 allows the operator to adjust the amount of overlap Y each shield member 44 has with the associated ceramic structure 10. Preferably, the amount of overlap Y is within the range of from 0% to 30% of the overall length of the structure 10, and more preferably is within the range of from 0% to 10% of the overall length of the structure 10. Further, the relative angle θ between each shield member 44 and a longitudinal axis 53 of the ceramic structure 10 is also adjustable in a direction 51. Preferably, the angle θ is within the range of from 0° to 5°, and more preferably is about 0°. The adjustability of the shield members 44 allow fine tuning of the positions of the shield members 44 with respect to the ceramic structure 10 to optimize the drying thereof.
As noted above, shielding the ends 13, 16 of the ceramic structure 10 results in a more even power distribution within the ceramic structure 10, and as a result, a more uniform drying thereof. As best illustrated in FIG. 7, the integrated dissipation of the power absorbed by a structure subjected to microwave radiation within a conventional microwave drying, i.e., a drying that does not provide shielding, results in a power absorption that is significantly greater at the ends of the structure than an the middle portion thereof. Similarly, FIG. 8 illustrates that the power absorbed near the side wall 15 of the structure is also significantly greater than that absorbed near the center thereof.
Modeled examples were completed on given ceramic structures both with and without shielding. FIGS. 9 and 10 illustrate integrated dissipation vs. length of the structure, and integrated dissipation vs. width of the structure, respectively, for an unshielded sample 52 and a shielded sample 54. Further, modeled examples were completed on three variations of system configurations utilized for processing a given ceramic structure. FIGS. 11 and 12 illustrate integrated dissipation vs. length of the structure, and integrated dissipation vs. width of the structure, respectively, of the three examples A-C. Example A included the modeling of a 36 inch in length structure with the distance X of the shield members 44 above the structure 10 being 10 inches, the overlap Y of the shield members 44 with the structure 10 being 10 inches, the angle θ between the shield members 44 and the structure 10 being 0°, and the number of structures 10 within the interior 40 of the housing 32 being 5. Example B included the modeling of a 20 inch in length structure with a distance X of 10 inches, an overlap distance Y of 18 inches, an angle θ of 0°, and 5 structures 10 simultaneously located within the interior 40 of the housing 32. Example C included the modeling of a 36 inch in length structure 10 with a distance X of 20 inches, an overlap distance Y of 10 inches, an angle θ of 0°, and 5 structures 10 simultaneously located within the interior 40 of the housing 32. It is clear from the integrated power dissipation along the length and width of the structures that the shielded process reduces the edge heating effect. Moreover, the integrated dissipation along the major axis (FIG. 10) shows a more uniform heating as compared to the end heating occurring without shielding.
Alternative methods for shielding the ends 13, 16 and end faces 18, 20 of the ceramic structure 10 are also contemplated. It is noted that these alternative methods may be practice simultaneously with the other methods described herein. A first alternative embodiment includes the use of shield members 60 (FIG. 13) spaced from the end faces 18, 20 of the structure 10. In the illustrated example, the shield members 60 are placed within the tray 42 that supports and carries the structure 10 through the housing 32. Preferably, the shield members 60 are spaced a distance A from the associated end face 18, 20 of less than or equal to one quarter of the wavelength of the microwave radiation.
A second alternative embodiment includes spacing multiple simultaneously processed ceramic structures 10 (FIG. 14) a distance B from one another. In the illustrated example, two structures 10 are placed within the same tray 42 such that the distance A between the corresponding end faces 18, 20 reduces or eliminates access thereto by the drying microwave radiation. Preferably, the distance B is less than or equal to about one quarter of a wavelength of the microwave radiation.
Other alternative embodiments include placing the trays 42 (FIG. 15) relative to the sidewalls of a microwave applicator housing 32 (FIG. 5) such that the distance between the ends 18, 20 of honeycomb structures 10 and the associated sidewalls 38 (FIG. 5) is preferably less than about one half the wavelength of the microwave radiation. It is also useful to space multiple trays 42 (FIG. 16) within the interior 40 of a microwave applicator housing 32 such that the distance D between the trays 42 will provide a spacing of about one half of the wavelength of the microwave radiation between the honeycomb structures 10.
The present 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 relatively greater structural integrity with reduced deformation and degradation. The method further reduces the relative cracking and stress fractures within the desired structure produced during the drying process, reduces manufacturing costs associated with cycle times, is efficient to use, and is particularly well-adapted for the proposed use.
It will be understood from the foregoing that the specific devices and processes illustrated in the attached drawings and described in the foregoing specification are exemplary only, and that the specific dimensions and other physical characteristics relating to those embodiments are intended to be illustrative rather than limiting.
Patent Application
20080023886
