Patent Application
20150273727
The methods and apparatus disclosed herein relate to the manufacture of technical ceramics, and more particularly to the production of ceramic honeycomb products useful, for example, the manufacture of catalytic converters and particulate filters for the treatment of combustion engine exhaust gases.
The fabrication of certain ceramic honeycomb structures from ceramic-forming powder mixtures is known. Plasticized mixtures are forced through extrusion dies to form lengths of wet extrudate which are then dried and fired to convert the extruded mixture to strong refractory ceramic materials.
Honeycomb structures can be square or closed cylindrical (circular, oval, elliptical, racetrack) cross-sections transverse to the axis of extrusion and direction of channel orientation in the bodies. The honeycomb channels, which may be of square, triangular, hexagonal, or other cross-sectional shape, are bounded by thin channel walls and can be present in channel densities of, for example, from 15 to 100 channels per cm2 of honeycomb cross-sectional area.
Geometries and materials provide ceramic honeycomb structures with relatively high strength and durability after firing. However, the wet honeycomb extrudate produced earlier in the process is relatively quite soft and subject to damage in the course of further handling, particularly until it has been dried.
Handling can cause shape distortion in wet honeycomb shapes comprising thin web and skin structures, or where especially large and heavy extrudate sections need to be transported. Further, extrudate sections of large diameter or frontal area transverse to the axis of extrusion can suffer from distortion and collapse of the honeycomb channel structure as that structure must bear the weight and withstand the lateral weight shifts of the upper structure in the course of transport.
The methods and apparatus disclosed herein help to prevent geometric distortion or channel collapse that may be encountered during the handling of wet honeycomb extrudate.
In one aspect the apparatus herein disclosed comprises a support tray for a cylindrical honeycomb extrudate, that extrudate being of a structure having a longitudinal axis and a circumferential surface. The support tray includes a tray body comprising an upper surface, with the upper surface having a concave portion configured to receive the circumferential surface of the cylindrical honeycomb extrudate. Further, the concave portion for receiving the wet extrudate is configured to be capable of contactingly supporting greater than one-third of the circumferential surface of the extrudate.
In another aspect of the present disclosure, a method for manufacturing a ceramic honeycomb is provided. That method includes steps of extruding a plasticized ceramic-forming batch material through a honeycomb extrusion die to form a length of wet honeycomb extrudate having a longitudinal axis and a circumferential surface, and then transferring the length of wet honeycomb extrudate to a support tray. The support tray comprises an upper surface that is capable of contactingly supporting greater than one-third of the circumferential surface of the extrudate. Thereafter the tray bearing the extrudate is transported to a dryer, and the extrudate is dried while supported on the dryer tray.
Computer dynamic simulations of the effects of handling stresses can predict and confirm the observed reductions in honeycomb damage derived from the use of the methods and apparatus disclosed herein. Those simulations show that the increased circumferential support offered to honeycomb extrudate supported by these trays significantly reduce both local contact pressures on wet log surfaces and stress levels inside the log structure to help reduce the possibility of honeycomb channel collapse or distortion during extrudate transport from the extruder to the dryer, and effectively address the hitherto unrecognized effects of lateral acceleration on gravitational cell distortion and collapse in larger honeycomb shapes. Accordingly, through the use of the disclosed methods and apparatus, reductions in wet extrudate handling damage, and therefore increases in the yields of ceramic honeycomb products may be achieved.
The methods and apparatus herein disclosed are further described below with reference to the appended drawings, wherein:
While the methods and apparatus herein disclosed are suitable for use in a number of different manufacturing environments and production line layouts, they offer particular advantages for those production approaches wherein relatively long sections of wet honeycomb extrudate, termed “logs”, are to be cut from the extruder, transported, and dried. Hence the following descriptions and illustrations frequently refer to the production and handling of such logs, particularly including logs of circular cylindrical cross-section, even though the use of the disclosed methods and apparatus are not limited thereto.
A feature of the support trays disclosed herein is the extent to which wet logs are capable of being contactingly supported about major portions of their circumferential surfaces by the concave support surface. Particular embodiments of the disclosed trays include those wherein the concave tray surfaces are configured to contactingly support greater than 40% of the circumferential surface of the extrudate, and in some embodiments even greater than 45% of the circumferential surface of the extrudate.
Adequate support of extrudate sections in still other embodiments of the disclosed trays include those wherein the concave portion is directly adjacent the circumferential surface of the extrudate along a contact line subtended by an included angle of greater than 120 degrees as measured from a longitudinal axis of the extrudate. More generally, that line of contact will be subtended by an included angle of greater than 120 degrees but less than 180 degrees as measured from a longitudinal axis of the extrudate.
The extent to which the disclosed trays provide more circumferential support to extrudate in the course of transport is reflected in
For the case of extrudate of circular cross-section as illustrated in
Computer dynamic simulations to study acceleration effects on honeycomb structures of the size, density, and plastic yield characteristics of various plasticized extrudate compositions are helpful in understanding the effects of such acceleration on honeycomb shape distortion. Acceleration effects involving the distortion and collapse of honeycomb channel structure in extrudate regions proximate to tray support surfaces can also be evaluated.
Simulation results indicate that, even for extrudates of relatively low elastic modulus and yield strength such as used for ceramic honeycomb production, increasing the extent of circumferential support for the extrudates significantly reduces the incidence of shape defects in dried honeycombs. The modified support surfaces not only reduce circumferential shape deformation, but also reduce honeycomb channel deformation and collapse under combinations of gravitational and lateral accelerations such that honeycomb structures can sustain increased forces in automated extrudate handling systems.
In trays according to some embodiments of the present disclosure that are designed for the support of logs or other extrudate of circular cross-section transverse to its longitudinal axis, as shown for example in
In some embodiments, the tray is required to support the extrudate while the extrudate is subjected to a drying process and the tray is made of a material that withstands conditions in the dryer. Where dielectric or microwave heating of the extrudate is the drying method of choice, the tray in some embodiments is fabricated predominantly of one or more materials exhibiting low dielectric loss. Examples of suitable low-loss materials include bonded alumina and aluminosilicate fiber materials.
Various embodiments of the tray used for the practice of the honeycomb manufacturing methods disclosed herein are made by factoring the circumferential size of the extrudate being processed, and the particular manufacturing environment and log transport systems to be employed in the manufacture. In some embodiments of those methods, the step of transporting the tray to the dryer may involve subjecting the extrudate support tray to lateral accelerations not much greater than 0.1 g as measured transversely to the longitudinal axis of the extrudate. In those cases, trays providing extrudate support only modestly greater than that covering one-third of the circumferential surface of the extrudate may be useful. On the other hand, where the step of transporting the tray to the dryer involves subjecting the extrudate to a lateral acceleration of greater than 0.25 g, or even greater than 0.4 g, contacting support over 40% or more of the circumferential extrudate surface may be required.
Where extrudate of large diameter or cross-section transverse to the longitudinal axis of the extrudate is being processed, greater circumferential support may be required to withstand lateral acceleration loads. For example, where the extrudate has a minimum diameter greater than 25 cm and/or where lateral acceleration loads of 0.5 g or greater are anticipated, trays providing contacting support of 45% or more of the circumferential surface of the extrudate may be used.
In conclusion, as the foregoing examples and illustrations have shown, the disclosed tray designs and methods can effectively minimize part distortion due to weight-induced collapse under the lateral forces that may be encountered in material handling systems. Thus geometric defects generated during handling that might otherwise result in the rejection of parts, or require the removal of defective surface material from dried extrudates and corresponding reductions in the useable diameters of the machined parts, can be substantially avoided.
While the foregoing descriptions provide particular examples of methods and apparatus for more effective and economic honeycomb manufacture, it will be appreciated that those examples have been offered for purposes of illustration only, and that other embodiments of the disclosed methods and apparatus may be adapted for similar purposes within the scope of the appended claims.
This application is a divisional of and claims the benefit of U.S. patent application Ser. No. 12/394539, filed Feb. 27, 2009, which is hereby incorporated by reference for all purposes as if fully set forth herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12394539 | Feb 2009 | US |
| Child | 14738249 | US |
