Method and system for crack-free drying of high strength skin on a porous ceramic body
A method and system to dry crack-free and high strength skin including an inorganic binder of an average particle size (D 50 ) in a range between 10 nm and 700 nm on a porous ceramic body. The method includes supporting the honeycomb body on an end face such that axial channels and outer periphery are substantially vertical. A gas is flowed past the honeycomb body substantially parallel to the axial channel direction, substantially equally around the outer periphery of the skin, to uniformly dry the skin to form a partially dried skin under mild conditions. Then the partially dried skin may be dried more severely resulting in rapidly dried crack-free and high strength skin.
1. A method of drying a skin disposed on an outer periphery of a porous ceramic honeycomb body comprising a first end face, a second end face, and axial channels and the outer periphery extending from the first end face to the second end face, the method comprising:
supporting the honeycomb body on the first end face such that the axial channels and the outer periphery are substantially vertical;
drying the skin under a first set of conditions comprising flowing a first gas vertically to the honeycomb body at a first velocity, wherein at least a portion of the first flowing gas passes substantially equally around the outer periphery of the skin disposed on the outer periphery of the honeycomb body to uniformly dry the skin to a first dryness forming a partially dry skin that is less than 50% dry;
drying the partially dry skin to a second dryness under a second set of conditions different from the first set of conditions,
wherein the skin comprises an inorganic binder comprising an average particle size (D 50 ) in a range between 10 nm and 700 nm.
2. The method of claim 1 , wherein the second set of conditions comprises flowing a second gas vertically to the honeycomb body at a second velocity greater than the first velocity to dry the skin to the second dryness.
3. The method of claim 2 , wherein the first and second gases are air.
4. The method of claim 1 , further comprising:
controlling the relative humidity of the atmosphere in which the skin is in contact under the first set of conditions to between about 10% and about 40% relative humidity; and
controlling the temperature of the atmosphere in which the skin is in contact under the first set of conditions to between about 40° C. and about 60° C.,
wherein the first gas is flowed at greater than about 2.0 m/s past the outer periphery of the skin.
5. The method of claim 1 , wherein the second set of conditions comprises controlling the temperature of the atmosphere in which the skin is in contact to between about 60° C. and 150° C.
6. The method of claim 1 , wherein the second set of conditions comprises subjecting the skin to at least one of flowing a second gas vertically to the honeycomb body at a second velocity greater than the first velocity, microwave radiation, and infrared radiation to dry the skin to the second dryness.
7. The method of claim 1 , wherein the first set of conditions further comprises subjecting the skin to at least one of microwave radiation, radio frequency, and infrared radiation to dry the skin to the first dryness.
8. The method of claim 1 , wherein the first dryness is between 20% dry and 50% dry and the second dryness is between about 80% dry and 100% dry.
9. The method of claim 8 , further comprising drying the skin under the first set of conditions for less than about 120 minutes and drying the skin under the second set of conditions for less than about 120 minutes.
10. The method of claim 8 , further comprising drying the skin under the first set of conditions for less than about 30 minutes and drying the skin under the second set of conditions for less than about 30 minutes.
11. The method of claim 1 , further comprising controlling the temperature of the atmosphere in which the skin is in contact under the first set of conditions to between about 40° C. and about 60° C.
12. The method of claim 1 , wherein the first conditions are relatively gentle drying conditions and the second conditions are relatively harsh drying conditions.
13. The method of claim 1 , wherein air flow during the first conditions consists essentially of vertical air flow.
14. The method of claim 1 , wherein the first dryness is less than 40% dry.
15. The method of claim 1 , wherein the method prevents migration of the binder to an outer surface of the skin.