WO2021188373A1 - Systems and methods for rapid firing of ceramic honeycomb bodies - Google Patents

Abstract

A firing system and methods for manufacturing ceramic honeycomb bodies. The firing system includes a first kiln asset comprising a heater that heats honeycomb bodies in the first kiln asset to a first top temperature and a flow generator that generates a flow of gas through channels of the honeycomb bodies during heating. A second kiln asset is configured to heat the honeycomb bodies to a second top temperature that is greater than the first top temperature. A hand-off zone is connected between the first kiln asset and the second kiln asset. A conveyor is configured to move honeycomb bodies from the first kiln asset through the hand-off zone to the second kiln asset. The first top temperature can be at least 600°C, at least 800°C, or for talc-containing mixtures, greater than a talc dehydroxylation temperature.

Description

SYSTEMS AND METHODS FOR RAPID FIRING OF CERAMIC

HONEYCOMB BODIES

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority under 35 EI.S.C. §119 of U.S. Provisional Application Serial No. 62/990692 filed on March 17, 2020, the content of which is relied upon and incorporated herein by reference in its entirety.

Background

1. Field

[0002] This disclosure relates to the manufacture of ceramic honeycomb bodies and more particularly to systems and methods for the rapid firing of ceramic honeycomb bodies.

2. Technical Background

[0003] Ceramic honeycomb bodies are used in a variety of applications, such in catalytic converters and particulate filters, which may be useful in treating pollutants or other undesired substances in vehicle engine exhaust or other fluid streams. Ceramic honeycomb bodies may be formed by firing green honeycomb bodies in kilns at elevated temperatures.

SUMMARY

[0004] Disclosed herein is a firing system for manufacturing ceramic honeycomb bodies. The firing system comprises a first kiln asset comprising a heater that heats honeycomb bodies in the first kiln asset to a first top temperature and a flow generator that generates a flow of gas through channels of the honeycomb bodies during heating; a second kiln asset configured to heat the honeycomb bodies to a second top temperature that is greater than the first top temperature; a hand- off zone connecting between the first kiln asset and the second kiln asset; and a conveyor configured to move honeycomb bodies from the first kiln asset through the hand-off zone to the second kiln asset. [0005] In some embodiments, the hand-off zone is configured to maintain honeycomb bodies within the hand-off zone at a temperature that is within 50°C of the first top temperature.

[0006] In some embodiments, the hand-off zone is configured to maintain honeycomb bodies within the hand-off zone at a temperature that is within 20°C of the first top temperature.

[0007] In some embodiments, the hand-off zone is configured to maintain honeycomb bodies within the hand-off zone at a temperature this is at least as high as the first top temperature.

[0008] In some embodiments, the conveyor comprises a first section extending through the first kiln asset and a second section extending through the second kiln asset, and wherein the first section is of a different type than the second section.

[0009] In some embodiments, the first section of the conveyor comprises a continuous belt comprising openings therethrough, and the second section of the conveyor comprises rollers. [0010] In some embodiments, the first top temperature is from 600°C to 1100°C.

[0011] In some embodiments, the first top temperature is from 600°C to 800°C.

[0012] In some embodiments, the ceramic-forming mixture comprises talc and quartz, and the first top temperature falls within a temperature range that is greater than a first temperature at which quartz transition completes, but less than a second temperature at which talc dehydroxylation initiates.

[0013] In some embodiments, the first top temperature is at least 900°C.

[0014] In some embodiments, the first top temperature is from 800°C to 1100°C.

[0015] In some embodiments, the first top temperature is falls within an inflection zone of a plot of shrinkage of the honeycomb bodies with respect to temperature.

[0016] In some embodiments, the second top temperature is greater than 1250°C.

[0017] In some embodiments, the second top temperature is from 1300°C to 1600°C.

[0018] In some embodiments, the firing system further comprises a third kiln asset connected to the second kiln asset via the conveyor, the third kiln asset being configured to generate gas flow through channels of honeycomb bodies received from the second kiln asset while cooling the honeycomb bodies.

[0019] In some embodiments, the conveyor is configured to index honeycomb bodies from the second kiln asset back into the first kiln asset after firing in the second kiln asset. [0020] In some embodiments, the first kiln asset is configured to generate the flow of gas through channels of honeycomb bodies received from the second kiln asset while cooling the honeycomb bodies to temperatures below the first top temperature.

[0021] In some embodiments, the first kiln asset comprises a plurality of ovens.

[0022] In some embodiments, the plurality of ovens are arranged in series along the conveyor.

[0023] In some embodiments, the plurality of ovens are arranged in parallel, wherein the conveyor comprises a first section that comprises plurality of branch lines connected to a common input trunk line and a common output trunk line, wherein one branch line extends through each oven, and wherein the common output trunk line is connected to a second section of the conveyor that extends through the second kiln asset.

[0024] In some embodiments, the second kiln asset comprises a tunnel kiln or roller hearth.

[0025] In some embodiments, the first kiln asset, the second kiln asset, or both, are configured to heat a plurality of separate zones to different temperatures.

[0026] Disclosed herein is a production line for manufacturing ceramic honeycomb bodies comprising the firing system of any of the preceding paragraphs.

[0027] Disclosed herein is a method of manufacturing a ceramic honeycomb body. The method comprises heating a honeycomb body comprising a ceramic-forming mixture to a first top temperature in a first kiln asset, the honeycomb body comprising a plurality of intersecting walls forming channels that extend longitudinally through the honeycomb body; flowing a gas through the channels of the honeycomb body during the heating of the honeycomb body up to the first top temperature in the first kiln asset; conveying the honeycomb bodies from the first kiln asset to a second kiln asset through a hand-off zone connected between the first kiln asset and the second kiln asset; and heating the honeycomb body in the second kiln asset to a second top temperature, greater than the first top temperature, that is sufficient to sinter ceramic materials in the honeycomb body.

[0028] In some embodiments, moving the honeycomb body through the hand-off zone comprises maintaining the honeycomb body at a temperature within 50°C of the first top temperature. [0029] In some embodiments, moving the honeycomb body through the hand-off zone comprises maintaining the honeycomb body at a temperature within 20°C of the first top temperature.

[0030] In some embodiments, moving the honeycomb body through the hand-off zone comprises maintaining the honeycomb body at a temperature at least as high as the first top temperature.

[0031] In some embodiments, conveying xxx the honeycomb body from the first kiln asset to the second kiln asset after heating the honeycomb body to the first top temperature.

[0032] In some embodiments, the first kiln asset comprises a plurality of ovens arranged in series along a conveyor.

[0033] In some embodiments, the first kiln asset comprises a plurality of subsections arranged in parallel with respect to each other, each subsection comprises one or more ovens.

[0034] In some embodiments, operation of the subsections is staggered such that a first subsection is unloading one or more honeycombs while a second subsection is firing or loading one or more honeycomb bodies.

[0035] In some embodiments, heating to the first top temperature, heating to the second top temperature, or both, comprises incrementally heating in plurality of adjacent zones of increasing temperature.

[0036] In some embodiments, the first top temperature is from 600°C to 1100°C.

[0037] In some embodiments, the first top temperature is from 600°C to 800°C.

[0038] In some embodiments, the ceramic-forming mixture comprises talc and quartz, and the first top temperature falls within a temperature range that is greater than a first temperature at which quartz transition completes, but less than a second temperature at which talc dehydroxylation initiates.

[0039] In some embodiments, the first top temperature is at least 900°C.

[0040] In some embodiments, the first top temperature is from 800°C to 1100°C.

[0041] In some embodiments, the first top temperature is falls within an inflection zone of a plot of shrinkage of the honeycomb bodies with respect to temperature.

[0042] In some embodiments, the second top temperature is greater than 1250°C. [0043] In some embodiments, the second top temperature is from 1300°C to 1600°C.

[0044] In some embodiments, the ceramic-forming mixture comprises talc and the first top temperature is greater than a talc dehydroxylation temperature of the ceramic-forming mixture. [0045] In some embodiments, the first top temperature lies within an inflection zone on a plot of shrinkage of the honeycomb body with respect to temperature.

[0046] In some embodiments, a mixture of the glow of gas comprises 02 in a concentration of less than 10% by volume.

[0047] In some embodiments, the gas is flowed through the channels at a velocity of at least 4 m/s.

[0048] In some embodiments, heating the honeycomb body to the first top temperature comprises increasing temperature linearly.

[0049] In some embodiments, heating the honeycomb body to the first top temperature comprises heating the honeycomb body in a step-wise manner by moving the honeycomb body through a plurality of adjacent zones of increasing temperature.

[0050] In some embodiments, heating the honeycomb body to the first top temperature comprises heating the honeycomb body in a sawtooth manner by moving the honeycomb body through a plurality of adjacent zones, wherein each zone has a minimum temperature and a maximum temperature, and each zone is at the minimum temperature when receiving the honeycomb body and increased to the maximum temperature when the honeycomb body is in the zone.

[0051] In some embodiments, the maximum temperature of any given zone is approximately equal to a minimum temperature of a next zone adjacent to each given zone.

[0052] Disclosed herein is a method of manufacturing ceramic honeycomb bodies that comprises heating a honeycomb body comprising a ceramic-forming mixture to a first top temperature of at least 600°C , the honeycomb body comprising a plurality of intersecting walls forming channels that extend longitudinally through the honeycomb body; flowing a gas through the channels of the honeycomb body during the heating of the honeycomb body up to the first top temperature; and then heating the honeycomb body to a second top temperature, greater than the first top temperature, that is sufficient to sinter ceramic materials in the honeycomb body, without flowing the gas.

[0053] Disclosed herein is a method of manufacturing a ceramic honeycomb body from a green honeycomb body comprising a talc-containing ceramic-forming mixture. The method comprises heating the honeycomb body to a first top temperature that is greater than a talc dehydroxylation temperature of the ceramic-forming mixture while flowing a gas through longitudinal channels extending through the honeycomb body, wherein the longitudinal channels are formed by a plurality of intersecting walls of the honeycomb body; and then heating the honeycomb body to a second top temperature, greater than the first top temperature, that is sufficient to sintering together ceramic materials in the honeycomb body.

[0054] 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 understanding the nature and character of the claimed subject matter. 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 embodiment(s), and together with the description, serve to explain principles and operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] FIG. 1 shows a honeycomb body according to one embodiment disclosed herein.

[0056] FIG. 2 schematically illustrates a production line for manufacturing ceramic honeycomb bodies according to one embodiment disclosed herein.

[0057] FIG. 3 illustrates a firing cycle comprising at least a flow-through stage and a high temperature sintering stage according to one embodiment disclosed herein.

[0058] FIG. 4 schematically illustrates a firing system for carrying out the firing cycle of FIG. 3 according to one embodiment disclosed herein.

[0059] FIG. 5 illustrates flow-through heating or cooling of honeycomb bodies on a permeable conveyor according to one embodiment disclosed herein. [0060] FIG. 6 illustrates a hand-off zone between two kiln assets of the firing system of FIG. 4 according to one embodiment disclosed herein.

[0061] FIG. 7 is a perspective cross-sectional view of a firing system according to one embodiment disclosed herein.

[0062] FIG. 8 is a schematic top view of a firing system according to one embodiment disclosed herein.

[0063] FIGS. 9-11 show example heating and cooling cycles according to various flow-through heating and cooling methodologies disclosed herein.

[0064] FIG. 12 is a plot showing the shrinkage (or growth) with respect to temperature for a honeycomb body comprising a talc-containing, cordierite-forming batch mixture during firing according to one example disclosed herein.

[0065] FIG. 13 is an enlarged view of the encircled area in FIG. 12.

[0066] FIG. 14 is a plot showing the shrinkage (or growth) with respect to temperature for a honeycomb body comprising a talc-containing, aluminum titanate and cordierite-forming batch mixture during firing according to one example disclosed herein.

[0067] FIG. 15 is a plot of temperature data collected with respect to time at various locations within a honeycomb body comprising a talc-containing, cordierite-forming batch mixture that was fired utilizing flow-through heating to a first top temperature of 1000°C, high temperature sintering at a second top temperature of 1440°C, and flow-through cooling after firing according to one example disclosed herein.

DETAILED DESCRIPTION

[0068] Reference will now be made in detail to exemplary embodiments which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. The components in the drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the exemplary embodiments.

[0069] Numerical values, including endpoints of ranges, can be expressed herein as approximations preceded by the term “about,” “approximately,” or the like. When a numerical value is expressed as an approximation, two embodiments are included in this disclosure: one expressed as an approximation, and another not expressed as an approximation.

[0070] Ceramic honeycomb bodies can be formed by a variety of methods, including via extrusion of a ceramic-forming batch mixture that is cut into a green honeycomb body and subsequently fired. The batch mixture may have pore-formers such as organic starches and graphite, which are removed during the firing process (e.g., to increase the porosity of the ceramic material of the honeycomb bodies after firing). Oxidation of a pore former may be an exothermic reaction, which can lead to thermal gradients within the honeycomb bodies due to differential pore former removal rates. The differential pore former removal rates within the honeycomb bodies may be a result the spatially local temperatures and oxygen concentrations encountered within the honeycomb bodies during the firing process (e.g., different temperatures at centers of the honeycomb bodies in comparison to at the outer skins of the honeycomb bodies).

[0071] Thermal gradients may result in thermal stresses that correspondingly cause cracks in the honeycomb bodies during the firing cycle. The thermal gradients may be particularly pronounced as the size of the ceramic honeycomb body increases, for example honeycomb bodies having diameters larger than 8 inches and/or lengths longer than 8 inches. Long firing cycles involving slow ramp rates and long temperature holds may be helpful to reduce thermal stresses induced during the firing process, but these long cycles may negatively impact manufacturing efficiency.

[0072] The systems and methods disclosed herein result in faster firing cycles, increased manufacturing efficiency, defect free ceramic honeycomb bodies, lower capital cost kiln equipment, reduced need for process nitrogen (e.g., due to shorter firing cycles), simplified firing cycle complexity, and increased handling of organic component burn out.

[0073] According to embodiments disclosed herein, continuous firing processes are implemented that utilize convective flow-through heating in a first kiln asset up to a first top temperature in the range from 600°C to 1100°C. As described herein, it may be particularly advantageous to carry out the flow-through firing to temperatures above the talc dehydroxylation (~900-950°C) in talc-containing batch mixtures, such as used in cordierite-forming batches. Advantageously, convective flow-through heating up to this temperature range provides uniform heating (small or no thermal gradients) throughout the honeycomb bodies during a wide variety of growth and shrinkage events of the honeycomb body (e.g., organic component burn out, raw ingredient water loss, such as talc dehydroxylation, etc.).

[0074] Once the first top temperature is reached, the honeycomb bodies (partially-fired) can be transferred to a high temperature second kiln asset (without flow-through) to finish firing. The first and second kiln assets can be integrated and connected by a conveyor that enables hand-off between the two kiln assets at an elevated temperature (e.g., at the first top temperature of the first kiln asset) to avoid the need to reheat the honeycomb bodies and reduce the need to handle the honeycomb bodies when the honeycomb bodies are comparatively fragile (after debinding, but before significant sintering has occurred). Convective flow-through cooling can also be utilized at temperatures below about 1100°C to provide uniform cooling (thereby reducing thermal gradients during cooling), which further shortens the overall firing cycle while reducing defect formation. [0075] Advantageously, firing cycles utilizing the systems and methods disclosed herein can enable fast temperature ramp rates, efficient removal of organic components and/or dehydroxylation of raw materials, small spatial thermal gradients during firing, and/or reduced thermal stresses, while producing defect free honeycomb bodies, even in honeycomb bodies made from batch mixtures comprising large amounts of organic components.

[0076] Referring to FIG. 1, a honeycomb body 100 is illustrated comprising intersecting walls 102 that form a plurality of channels 104. As described herein, the walls 102 comprise a shaped ceramic-forming mixture before firing and a porous ceramic material after firing. For ease of discussion herein, the reference numeral ‘ 100g’ may be used to specifically refer to the honeycomb bodies 100 in the green (unfired) state, the reference numeral ‘100c’ may be used to refer specifically to the honeycomb bodies 100 in the ceramic (fired) state, and the reference numeral ‘100’ without suffix may be used to generally refer to the honeycomb bodies in any state or condition (e.g., fired, unfired, partially fired, green, ceramic).

[0077] The walls 102 and channels 104 form a honeycomb structure that is encased by a skin or outer peripheral surface 105. The channels 104 extend axially (longitudinally) through the honeycomb body 100, e.g., parallel to one another, from a first end 106 to a second end 108. As described herein, the honeycomb body 100 can be utilized in a variety of applications, such as for use in a catalytic converter (e.g., the walls 102 acting as a substrate to be loaded with a catalytic material) and/or as a particulate filter (e.g., in which some of the channels 104 are plugged to trap particulate within the channels 104). Such honeycomb bodies 100 can thus assist in the treatment or abatement of pollutants from a fluid stream, such as the removal of undesired components from the exhaust stream of a combustion engine of a vehicle. For example, the porous material of the walls 102 can be loaded with a catalytic material such as a three-way catalyst to treat one more compounds in a fluid flow (e.g., engine exhaust) through the channels 104 of the honeycomb body 100.

[0078] Some of the channels 104 of the honeycomb body 100 can be plugged to arrange the honeycomb body 100 as a particulate filter. Plugging can be performed using any suitable plugging process (e.g., patty plugging, slurry plugging, etc.) and plugging material (e.g., a cold set plugging cement). In some embodiments, some of the channels 104 are plugged at the first end 106, while some of the channels 104 not plugged at the first end 106 are plugged at the second end 108. Any suitable plugging pattern can be used. For example, alternating ones of the channels 104 can be plugged at the opposite ends 106, 108.

[0079] The honeycomb body 100 can be formed in any suitable manner. For example, a production line 10 capable of forming the honeycomb bodies 100 is illustrated in FIG. 2. According to various embodiments, organic and inorganic components are mixed together to form a ceramic-forming mixture 12. The ceramic-forming mixture may be considered and/or referred to herein as a batch or batch mixture. Organic components can include pore formers (e.g., starch particles, polymer beads, resins) that provide porosity to the resulting ceramic material of the ceramic honeycomb bodies 100c, binders (e.g., methylcellulose) that assist in maintaining the shape of the green honeycomb bodies lOOg before firing, a liquid vehicle to facilitate mixing and shaping of the ingredients, lubricants (e.g., oils) that assist in extrusion, and/or other additives to assist in shaping, handling, formation, or properties of the honeycomb body 100. The inorganic components can include one or ceramic and/or ceramic precursor materials (e.g., alumina, silica, titania, talc, clay, etc.) that results in one or more ceramic phases in the material of the ceramic honeycomb body 100c as a result of manufacturing via the production line 10. By way of example, the inorganic components can be combined as powdered materials and intimately mixed with the organic components and a liquid vehicle (e.g., water) to form a substantially homogeneous batch. [0080] The ceramic-forming mixture 12 can be shaped or formed into a honeycomb structure using any suitable forming means, such as molding, pressing, casting, extrusion, and the like. According to the embodiment depicted in FIG. 2, the ceramic-forming mixture 12 is extruded using an extruder 14. For example, the extruder can comprises a honeycomb extrusion die to form the honeycomb structure (the walls 102 and channels 104) of the extrudate extruded by the extruder 14. The extrudate can be extruded with a skin (i.e., forming the skin 105) or the skin can be added in a subsequent manufacturing step. The extruder 14 can be a hydraulic ram extrusion press, a two stage de-airing single auger extruder, or a twin screw mixer with a die assembly attached to the discharge.

[0081] The production line 10 can further comprise a cutting apparatus 16. For example, the cutting apparatus 16 is configured to cut green honeycomb bodies lOOg from the extrudate produced by the extruder 14. For example, the cutting apparatus can comprise a wire, laser, saw, blade, or other cutting implement used to separate lengths of the honeycomb extrudate from each other. The cutting apparatus 16 can be used to set a desired length for green honeycomb bodies lOOg, and therefore the ceramic honeycomb bodies 100c made by firing such green bodies.

[0082] After cutting, the green honeycomb bodies can be transported to a drier 18 that removed moisture from the green bodies lOOg. The dryer can utilize any suitable form of drying, such as microwave energy, convection, heat, or combination including these or other types of drying. After drying, the dry green honeycomb bodies lOOg can be fired in a firing system 20. As descried in more detail herein, firing system 20 comprises one or more kilns, ovens, furnaces, or other vessel capable of heating the honeycomb bodies 100 herein to the indicated temperatures (the terms “kiln”, “oven”, and “furnace” used interchangeably herein). As a result of firing, the ceramic honeycomb bodies 100c are produced.

[0083] FIG. 3 shows temperature with respect to time for a representative process for continuous firing of honeycomb bodies 100, e.g., with the firing system 20. In accordance with FIG. 3, the continuous firing operation is separated into multiple sections or stages. Three such stages designated as first stage 22, second stage 24, and third stage 26 are shown in FIG. 3. [0084] Corresponding equipment can be used for the firing system 20 that has separate kiln assets (e.g., separate oven or furnace assemblies) for each section or stage. In particular, as shown with reference to FIGS. 3-4, the systems and methods described herein comprise at least a first kiln asset 28 for heating the honeycomb bodies 100 in the first stage 22 and a second kiln asset 30 for heating the honeycomb bodies 100 in the second stage 24. As described in more detail herein, each of the kiln assets 28, 30 can comprises multiple independently heatable zones.

[0085] The first stage 22 provides convective flow-through heating of the honeycomb bodies 100 (that is, heating the honeycomb bodies 100 while simultaneously flowing a gas through the channels 104 of the honeycomb bodies 100) up to a first top temperature T1 at the beginning of the firing process. The second stage 24 provides high temperature firing of the honeycomb bodies 100, e.g., without flow-through by the flow 34, to a second top temperature T2 sufficient to form the ceramic honeycomb bodies 100c by reacting any remaining ceramic precursors and sintering together the ceramic material in the honeycomb bodies 100.

[0086] In some embodiments, the first top temperature T1 is at least 600°C, at least 700°C, at least 800°C, at least 850°C, at least 900°C, at least 950°C, or even at least 1000°C. In some embodiments, the first top temperature T1 is at most 1000°C, at most 1050°C, or even at most 1100°C. In some embodiments, the first top temperature is in a range between any of the preceding temperatures in this paragraph as endpoints, for example, from 600°C to 1100°C, from 600°C to 1050°C, from 600°C to 1000°C, from 600°C to 950°C, from 600°C to 900°C, from 600°C to 850°C, from 600°C to 800°C, from 700°C to 1100°C, from 700°C to 1050°C, from 700°C to 1000°C, from 700°C to 950°C, from 700°C to 900°C, from 700°C to 850°C, from 700°C to 800°C, from 800°C to 1100°C, from 800°C to 1050°C, from 800°C to 1000°C, from 850°C to 1100°C, from 850°C to 1050°C, from 850°C to 1000°C, from 900°C to 1100°C, from 900°C to 1050°C, from 900°C to 1000°C, from 950°C to 1100°C, from 950°C to 1050°C, or from 950°C to 1000°C. [0087] In some embodiments, the second top temperature T2 is at least 1250°C, at least 1300°C, or at least 1350°C. In some embodiments, the second top temperature T2 is at most 1600°C, at most 1550°C, at most 1500°C, or at most 1450°C. In some embodiments, the second top temperature T2 is in a range between any of the preceding temperatures in this paragraph as endpoints, for example, from 1250°C to 1600°C, from 1250°C to 1550°C, from 1250°C to 1500°C, from 1250°C to 1450°C, from 1300°C to 1600°C, from 1300°C to 1550°C, from 1300°C to 1500°C, or from 1300°C to 1450°C. In some embodiments, the second top temperature T2 is selected with respect to a reaction or sintering temperature range associated with the ingredients of the batch mixture 12 and/or with one or more selected ceramic phases desired to result from firing at the second top temperature T2, such as from about 1350°C - 1440°C for cordierite- forming batch mixtures or from about 1330°C - 1500°C for aluminum titanate-forming batch mixtures.

[0088] Optionally, the firing system 20 comprises a third kiln asset 32 for assisting with cooling in the third stage 26. In some embodiments, no designated equipment is used to provide cooling in the third stage 26. In some embodiments, the equipment of the first kiln asset 28 or the second kiln asset 30 is utilized to assist with cooling for the third stage 26. For example, in some embodiments, the ceramic honeycomb bodies 100c are moved back into the first kiln asset 28 to undergo convection (gas flow through the channels 104) during cooling (e.g., without heating or with increasingly low temperatures). If the third asset 32 is included, it can be arranged similarly to the first kiln asset 28, as described herein.

[0089] FIG. 5 schematically illustrates convective flow-through heating or cooling of the honeycomb bodies 100. In particular, a flow of gas 34 is directed axially through the honeycomb bodies 100 (via the channels 104). The flow 34 can be generated by a fan (e.g., high speed recirculating fan), blower, pump, compressor, vacuum, or other mechanism, and/or by otherwise creating a pressure differential across the opposite faces 106, 108 of the honeycomb bodies 100. The flow 34 through the honeycomb bodies 100 can be in either direction (e.g., top to bottom or bottom to top with respect to the orientation of the honeycomb bodies 100 in the system 20). The gas in the flow 34 can be any suitable mixture, such as ambient air, an inert gas such as nitrogen, or a low-oxygen mixture, e.g., of air and nitrogen. Relatively low oxygen mixtures (e.g., less than 10% or even less than 5% by volume) may be particularly advantageous for suppressing exothermic reactions during burn out of organic components in the ceramic-forming mixture 12 during initial firing of the green honeycomb bodies 1 OOg in the first stage 22.

[0090] As shown in FIG. 5, during convective flow-through heating or cooling, the honeycomb bodies can be positioned on a conveyor assembly 36 having openings 38 therethrough that promote flow-through of the flow 34. For example, the conveyor assembly 36 can be utilized to move the honeycomb bodies 100 to, from, or between any of the stages of the firing system 20. In some embodiments, the conveyor assembly 36 comprises a conveyor belt, rollers, carriage, trolley, rail, or other suitable conveyance or transport mechanism. The openings 38 can comprise gaps between discrete elements (e.g., gaps between separate rollers), or slots, slits, perforations, interstices, holes, or other openings. In some embodiments, the conveyor assembly 36 comprises a mesh, screen, chain-linked belt, or slotted plate upon which the honeycomb bodies 100 are carried. The openings can be relatively large, e.g., to minimize impedance to the flow 34, and/or sized to set a target flow impedance.

[0091] FIG. 6 illustrates a hand-off zone 40 between the first kiln asset 28 and the second kiln asset 30 according to one embodiment. In this embodiment, the hand-off zone 40 is implemented as an interface between a first section 42 of the conveyor assembly 36 associated with the first kiln asset 28 and a second section 44 of the conveyor assembly 36 associated with the second kiln asset 30. For example, the hand-off zone 40 may advantageously enable the first section 42 of the conveyor assembly 36 to be suitable for convective flow-through heating or cooling (e.g., comprising openings such as openings 38 in FIG. 5 that permit the flow 34 of gas through the honeycomb bodies 100 and the conveyor assembly 36), while the second section 44 of the conveyor assembly 36 is arranged to suitably handle the relatively higher temperatures of the second kiln asset 30 (ceramic sintering temperatures). To facilitate the use of different conveyance types and/or the transition between different conveyance types the honeycomb bodies 100 can be arranged on a refractory tray or setter 46, which is carried by the conveyor assembly 36. Similar to the first section 42 of the conveyor assembly 36, the setters 46 can be comprise openings and/or otherwise be permeable to facilitate flow-through in the first kiln asset 28.

[0092] In the illustrated embodiment, the first section 42 comprises a continuous belt-type conveyor, while the second section comprises a roller-type conveyor (e.g., chain- driven). In other embodiments, both the first and second sections 42 can be of the same type (e.g., rollers suited for both convective flow-through and high temperature firing). In some embodiments, the hand-off zone 40 is heated to an elevated temperature, e.g., the first top temperature Tl, to maintain the temperature of the honeycomb bodies 100 during transition between the kiln assets 28, 30. In some embodiments, the temperature in the hand-off zone 40 is within 50°C of the first top temperature T1 (i.e., first top temperature T1 ± 50°C), within 40°C, within 30°C, within 20°C, within 10°C, or even within 5°C of the first top temperature. In some embodiments, the temperature in the hand-off zone 40 is at least as high as the first top temperature T1.

[0093] For example, the hand-off zone 40 can be part of, or receive heat from, the first kiln asset 28 or the second kiln asset 30. Alternatively, the hand-off zone 40 can have a designated heater. In some embodiments, the honeycomb bodies 100 are held in the hand-off zone 40 for a period of time, e.g., while the ceramic honeycomb bodies 100c finish being fired or are unloaded from the second kiln asset 30 after firing. In this way, maintaining the hand-off zone 40 at or near the first top temperature T1 assists in efficient energy usage and more favorable firing conditions as the honeycomb bodies 100 do not need to be reheated and thereby are not subjected to multiple heating/cooling cycles.

[0094] FIG. 7 illustrates the firing system 20 comprising the first kiln asset 28 and the second kiln asset 30 according to one embodiment. In this embodiment, the first kiln asset 28 comprises two zones 48a and 48b, and the second kiln asset 30 comprises two zones, one of which is arranged in accordance with the hand-off zone 40 of FIG. 6, and the other is designated as zone 50. The honeycomb bodies 100 are carried by the conveyor assembly 36 through each of the zones (e.g., zones 48a, 48b, 40 and 50). As described with respect to FIG. 6, the conveyor assembly 36 of the firing system 20 in FIG. 7 comprises the first section 42 arranged as a continuous belt and the second section 44 arranged as a plurality of rollers (e.g., chain driven). If desired, one or more pairs of adjacent zones can be separated by a door that enables the honeycomb bodies 100 to be moved between adjacent zones when opened and/or provides temperature isolation from adjacent zones when closed.

[0095] The first kiln asset 28 comprises an oven 52 for each of the zones 48a, 48b. While each oven 52 is illustrated as associated with a single zone, the ovens 52 can be equipped with appropriate heaters and baffles or other structures to divide each of the ovens 52 into multiple adjacent zones of different temperatures. Each of the ovens 52 comprises a flow generator 54 for providing convective flow-through heating (and/or cooling) and one or more heaters 56 for controlling the temperature in the respective zone(s) for that oven 52. The ovens 52 can be configured to heat each zone (e.g., the zones 48a, 48b) to the same or different temperatures. For example, in some embodiments the first zone 48a is heated to a temperature that is less than the first top temperature T1 and the second zone 48b is heated to the first top temperature Tl, such that the honeycomb bodies 100 are more gradually or incrementally heated as the honeycomb bodies 100 are moved along the conveyor assembly 36. Such incremental heating may advantageously control burn out of organics from the green honeycomb bodies lOOg and/or reduce temperature gradients within the part, which assists in reducing cracking of the resulting ceramic honeycomb bodies 100c.

[0096] In the illustrated embodiment, the flow generator 54 comprises a fan assembly, although blowers, pumps, compressors, or other assemblies can also be used for providing a pressure differential across the honeycomb bodies 100, thereby creating the flow 34 of gas through the channels 104 of the honeycomb bodies 100. The heater 56 can comprise any suitable heat source capable of achieving and maintaining the desired temperature for each zone (e.g., the first top temperature Tl), such as a burner or electrically powered heating element.

[0097] The first kiln asset 28 (of first stage 22) and the second kiln asset 30 (of second stage 24) are integrated together (e.g., connected by the hand-off zone 40) such that the transfer of the honeycomb bodies 100 between the first and second stages can occur at elevated temperature (e.g., at the first top temperature Tl in the first kiln asset 28 of the first stage 22). After high temperature firing of the honeycomb bodies 100 (e.g., at the second top temperature T2 in the second kiln asset 30 of the second stage 24), the honeycomb bodies 100 can be cooled in the second kiln asset 30, in an environment outside of the second kiln asset 30, and/or indexed back into the first kiln asset 28 (e.g., by reversing direction of the conveyor assembly 36) for convective flow-through assisted cooling. Thus, the first stage 22 and the third stage 26 can both be performed by the first kiln asset 28 in some embodiments.

[0098] If the first kiln asset 28 is utilized to provide convective flow-through cooling, the hand- off zone 40 can be utilized to assist in cooling the honeycomb bodies 100 to a selected temperature, e.g., at or around the first top temperature Tl, before convective flow-through cooling in the first kiln asset 28. Such an embodiment may be particularly advantageous where the zone 50 of the second kiln asset 30 is comprised by a batch kiln or oven that only has a single entrance/exit. In some embodiments, a back wall 58 of the second kiln asset 30 is not present, arranged as a door, or is otherwise opened or openable to enable the honeycomb bodies 100 to be moved out of the second kiln asset 30 without indexing back into the first kiln asset 28. If desired, the third kiln asset 32 (e.g., arranged akin to the first kiln asset 28, but either with or without the heater 56) can be located on the side of the second kiln asset 30 opposite to the first kiln asset 28, e.g., as illustrated in FIG. 4. For example, the second kiln asset 30 can in this way be arranged as a continuous-type type firing unit such as a roller hearth or tunnel kiln, in which the parts are traveling through the kiln and the thermal and atmospheric profile is a function of zone or distance into the kiln. Advantageously, such an arrangement enables the honeycomb bodies 100 to be moved by the conveyor assembly 36 continuously in one direction through the firing system 20. [0099] FIG. 8 illustrates another embodiment for the firing system 20 in which the first kiln asset 28 comprises multiple subassemblies arranged in parallel with respect to each other. More particularly, three such subsections of the first kiln asset 28 are illustrated in FIG. 8, and designated respectively in FIG. 8 with the reference numerals 28a, 28b, and 28c (considered together as the first kiln asset 28). Any number of such subsections of the first kiln asset 28 can be utilized and arranged in parallel.

[0100] Each of the subsections 28a-28c comprises one or more ovens. In the embodiment of FIG. 8, each of the subsections 28a-28c comprises three of the ovens 52 arranged in series (e.g., as also described with respect to the ovens 52 in FIG. 7), which ovens are designated for convenience of discussion as ovens 52a, 52b, and 52c. Any other number of the ovens can be utilized and arranged in series. As described with respect to FIG. 7, each of the ovens 52a- 52c defines a corresponding zone, which can heat to the same or different temperature as the other zones. For example, the ovens 52a-52c in each subsection 28a-28c can be arranged to increase in temperature, with the last oven 52c heating the honeycomb bodies 100 to the first top temperature Tl.

[0101] In this embodiment of FIG. 8, the first section 42 of the conveyor assembly 36 comprises a common input trunk line 60 connected to individual branch lines 62a, 62b, and 62c for directing the honeycomb bodies 100 respectively through the subsections 28a-28c. The opposite ends of the branch lines 62a-62c are connected to a common output trunk line 64 in the hand-off zone 40, which directs the honeycomb bodies 100 from each of the subsections 28a-28c, via the branch lines 62a-62c, to the second section 44, which directs the honeycomb bodies 100 through the second kiln asset 30 as described above. Each of the first section 42, input trunk line 60, branches 62a-62c, output trunk line 64, and the second section 44 of the conveyor assembly 36 can be the same or different conveyor types, as described above.

[0102] The embodiment of FIG. 8 is particularly advantageous for providing a constant throughput to the second kiln asset 30 when the second kiln asset 30 is arranged as equipment capable of high capacity and continuous firing of the honeycomb bodies 100, such as a roller hearth or tunnel kiln. For example, in some embodiments, the timing of the loading, firing, and unloading of the subsections 28a-28c is staggered such that at any given time a first of the subsections 28a- 28c is firing while a second of the subsections 28a-28c is loading unfired honeycomb bodies 100 and a third of the subsections 28a-28c is unloading partially fired honeycomb bodies 100 (the honeycomb bodies 100 are considered “partially fired” at this stage because firing will be completed in kiln asset 30).

[0103] For example, during a first time interval the subsection 28a can be loading while the subsection 28b is firing, and the subsection 28c is unloading. During a second time interval, the unfired honeycomb bodies in the now-loaded subsection 28a can be fired, while the partially fired honeycomb bodies 100 can be unloaded from the subsection 28b, and the now-emptied subsection 28c can be loaded with unfired honeycomb bodies. During a third time interval, the now-fired honeycomb bodies 100 can be unloaded from the subsection 28a, the now-emptied subsection 28b can be loaded with unfired honeycomb bodies, and the unfired honeycomb bodies in the now- loaded subsection 28c can be fired. After this third time interval, the process can be repeated from the first time interval. In this way, the second section 44 of the conveyor assembly 36, and therefore the second kiln asset 30, can be constantly supplied with partially-fired honeycomb bodies 100 from the subsections 28a-28c of the first kiln asset 28 (again, the honeycomb bodies 100 are considered “partially fired” at this stage because firing will be completed in the kiln asset 30). [0104] Regardless of the number of subsections used for the first kiln asset 28, or even if only a single section is used (comprising one or more ovens), by arranging the first kiln asset 28 and the second kiln asset 30 as separate assets, but connecting the separate assets together by the hand-off zone 40 (e.g., which is maintained at approximately the same temperature as the first top temperature Tl), the overall throughput of the system 20 can be maximized in an efficient manner. That is, any number of the subsections in the first kiln asset 28 can be arranged in parallel and/or any number of the ovens 52 arranged in series, to accommodate the potential throughput of the second kiln asset 30 and thus efficiently maximize the manufacturing output of ceramic honeycomb bodies 100c from the firing system 20.

[0105] In some embodiments, the flow-through heating (and/or cooling) in stage 22 (and/or stage 26) occurs in a single temperature zone (e.g., the first kiln asset 28 and/or each parallel subsection of the first kiln asset 28 comprises only a single one of the ovens 52). For example, use of a single zone is in contrast to the embodiments of FIGS. 7 and 8, in which the flow-through heating (and/or cooling) occurs in multiple zones (e.g., the zones 48a and 48b in FIG. 7 and/or the zones corresponding to each of the ovens 52a-52c in FIG. 8). Examples of profiles for managing temperature with respect to time for single zone heating and cooling are shown in FIG. 9. The solid line in FIG. 9 represents the temperature set point of the oven, while the dashed line provides one representative example of various temperature slowdowns, ramps, and holds (i.e., variations in the temperature and/or temperature ramp rate) over time. .

[0106] In the examples of FIG. 9, the honeycomb bodies 100 can be loaded into the kiln asset 28 at an initial temperature, such as room temperature or the ambient temperature. The first kiln asset 28 is then heated in a controlled manner up to the first top temperature Tl . The heating profile can be linear or incorporate slowdowns (durations of reduced heating rate) or holds (durations of no temperature increase) during time periods in which reactions are expected to take place (e.g., during burn out or other removal of organic components such as organic binders or pore formers). The flow rate (e.g., velocity) and oxygen level of the flow 34 during organic removal can also be controlled, e.g., increasing in velocity and/or decreasing in oxygen level during time periods of increased organic burn out or other reactions.

[0107] In some embodiments, the velocity of the flow 34 is at least 2 m/s, at least 3 m/s, at least 4 m/s, or even at least 5 m/s. In some embodiments, the velocity of the flow 34 is in a range from 1 m/s to 10 m/s, from 2 m/s to 10 m/s, from 3 m/s to 10 m/s, from 4 m/s to 10 m/s, from 4 m/s to 10 m/s, from 5 m/s to 10 m/s, from 3 m/s to 9 m/s, from 3 m/s to 8 m/s, from 3 m/s to 7 m/s, from 3 m/s to 6 m/s, from 4 m/s to 8 m/s, from 4 m/s to 7 m/s, or from 4 m/s to 6 m/s. The oxygen (O2) level can be less than 20 vol%, less than 15 vol%, less than 10 vol%, or even less than 5 vol%, particularly during time periods of high organic removal (e.g., binder or pore former burn out). [0108] As described previously, upon reaching the first top temperature T1 of the flow-through firing in the first kiln asset 28, the honeycomb bodies 100 are transitioned into the second kiln asset 30 via the conveyor 36 (e.g., belts, rollers, etc.) at a temperature substantially equal to, or even slightly higher than, that of the first top temperature T1 (e.g., via the hand-off zone 40). The honeycomb bodies 100 are then heated to the second top temperature T2 at which the desired ceramic phase(s) (e.g., cordierite, aluminum titanate, mullite, silicon carbide, etc.) form and/or sinter. Upon cooling the resulting ceramic honeycomb bodies 100c can remain in the second kiln asset 30, or be transferred to a flow-through enabled cooling asset, such as the first kiln asset 28 or the third kiln asset 32. If the flow-through enabled asset comprises a heater (e.g., as with the first kiln asset 28), the temperature can be controlled during cooling. Similar to heating, the cooling rate can be linear or incorporate slowdowns or holds in regions of the cycle sensitive to strain (i.e. inflections in the thermal expansion curve), which may assist in reducing cracking. [0109] FIG. 10 illustrates example temperature profiles with respect to time for heating and cooling using multiple zones in the flow-through enabled assets. For example, in the embodiments of FIGS. 7 and 8 the flow-through heating (and/or cooling) occurs in multiple zones (e.g., the zones 48a and 48b in FIG. 7 and/or the zones corresponding to each of the ovens 52a-52c in FIG. 8. Each subsequent zone can be held at a different temperature, resulting in a step-wise increase (for heating) or decrease (for cooling) in temperature, as shown in FIG. 10. As shown, the temperature increase for each zone does not have to be constant (e.g., to accommodate burn out of organics or other reactions within the honeycomb bodies 100). Also, consecutive zones can be held at the same temperature to accommodate slow reactions.

[0110] The honeycomb bodies can be transitioned from zone to zone, e.g., via the conveyor 36, either continuously (e.g., a constant velocity) or by indexing the honeycomb bodies 100 forward to the next zone after pausing for a duration in each zone. As with single-zone heating, the flow rates and oxygen levels during organic removal can be controlled. Also as with the single-zone methodology described above, upon completion of flow-through firing in the first kiln asset 28, the honeycomb bodies can be transitioned into the second kiln asset 30 to complete firing. After firing, the resulting ceramic honeycomb bodies 100c can be cooled in the second kiln asset 30 or via flow-through in the first kiln asset 28 and/or the third asset 32.

[0111] In contrast to single-zone heating/cooling, the step-wise heating/cooling of FIG. 10 may drive a temperature differential, and at some points, a reaction gradient, from the leading to the trailing edge of the parts as the honeycomb bodies 100 are moved from zone to zone. Accordingly, different processes can be employed to limit the formation of such gradients. For example, rapid indexing or transfer at the interfaces between adjacent zones can be utilized to minimize such gradients. As another alternative, the velocity of the flow 34 can be reduced or even turned off as the honeycomb bodies 100 transition between zones and reestablished once the entirety of the honeycomb bodies 100 are fully positioned within the next zone. As another example, the zone temperature setpoints (i.e., increases in temperature between adjacent zones) can be set with temperature rate slowdowns or temperature rate holds corresponding to the onset of relevant reactions (e.g., pore former or organic binder burn out). One possible example showing such slowdowns and temperature rate holds is shown as a dashed line in FIG. 9. Such temperature rate slowdowns or holds can also be employed at time periods (and thus zones) corresponding to high shrinkage or high growth events, to minimize the dimensional variance across the honeycomb bodies 100, with larger temperature increases during relatively lower growth/shrinkage regions of the firing cycle. Similarly, instead of controller flow rate, the gas mixture of the flow 34 can be adjusted, e.g., with higher or lower oxygen levels, to promote or hinder various reactions (e.g., lower oxygen levels during regions of high amounts of organic component burn out). Gases such as nitrogen or carbon dioxide can be added to reduce the oxygen (O2) level. As another example, “intermediate zones” can be formed, e.g., through the mixing of temperatures from both adjacent zones to set the temperature of each intermediate zone as the average of the zone on either side. As another example, water vapor can be introduced at transitions between zones where the honeycomb bodies 100 are undergoing a dehydroxylation event, then water vapor levels reduced to promote dehydroxylation in the next zone once the entirety of the honeycomb bodies 100 are in the next zone. [0112] FIG. 11 illustrates examples of temperature profiles with respect to time during for “saw tooth” temperature control during multi-zone flow-through heating and cooling, which may also assist in reducing thermal gradients in the honeycomb bodies 100 during flow-through firing in the kiln asset 28 and/or cooling in the kiln asset 28 and/or 32. In the embodiment of FIG. 11, one or more zones (e.g., each zone) is cycled in temperature between a minimum temperature and a maximum temperature (e.g., instead of maintaining each zone at a constant temperature as shown in the examples of FIG. 10). More particularly, the dashed line in FIG. 11 illustrates a maximum temperature of each zone, the up and down arrows indicate a range for temperature cycling possible within each zone, and the solid line indicates the actual temperature experienced by the honeycomb bodies 100 in each zone.

[0113] For example, the maximum temperature of each zone can be approximately equal to the minimum temperature of the subsequent zone. For example, the minimum temperature of a subsequent zone can be within 10°C, 5°C, or even equal to the maximum temperature of the preceding zone. In this way, after the honeycomb bodies 100 are moved into a zone, the temperature of that zone is increased to its maximum while the honeycomb bodies 100 are in that zone. After a designated time period at the maximum temperature and/or upon reaching the maximum temperature, the temperature of the next zone is reduced to its minimum (which is approximately equal to the current temperature of the current zone), and the honeycomb bodies 100 are moved to the next zone.

[0114] For example, the minimum temperature of “Zone 2” in FIG. 11 is approximately equal to the maximum temperature of preceding “Zone 1”, thereby reducing thermal gradients experienced by the honeycomb bodies 100 when the honeycomb bodies 100 are transitioned from Zone 1 at its maximum temperature to Zone 2 at its minimum temperature. Once positioned in Zone 2, the temperature of Zone 2 can be increased to its maximum temperature (which is approximately equal to the minimum temperature of Zone 3), and the process repeated for each subsequent zone. In this way, the honeycomb bodies 100 are more gradually heated (indicated by the solid line in FIG. 11), thereby eliminating the step-wise transitions discussed with respect to FIG. 10, and corresponding reducing thermal and reaction gradients as the honeycomb bodies 100 transition between zones. [0115] As described with respect to FIG. 10, the temperature steps (difference between maximum and minimum temperature in each zone) do not need to be constant. Consecutive zones can be held at the same temperature or slowdowns implemented to accommodate slow reactions within the honeycomb bodies 100. As with the methodologies of FIGS. 9 and 10, upon completion of the flow-through heating in the first kiln asset 28, the honeycomb bodies 100 can be transitioned into the second kiln asset 30 for formation and/or sintering of the selected ceramic phase(s) and then cooling. As shown in FIG. 11 , the cooling can also have “saw-tooth” control, where the temperature is progressively decreased by dropping the temperature of each zone to its minimum while the honeycomb bodies 100 are in that zone and then transitioning the honeycomb bodies 100 into the next zone after increasing the temperature of the next zone to its maximum.

[0116] In some embodiments, flow-through heating is performed in accordance with the methodology described with respect to any one of FIGS. 9-11, while cooling is described with respect to a different methodology (e.g., heating is performed with respect to a first methodology, such as with respect to FIG. 11 , but cooling is performed with respect to a second methodology, such as with respect to FIG. 9). Furthermore, in some embodiments a combination of the methodologies can be incorporated in a flow-through heating and/or cooling temperature control cycle. For example, the “sawtooth” methodology of FIG. 11 can be employed during time periods (zones) in which thermal or reaction gradients are of more concern (e.g., during high growth or shrinkage events) and the step-wise methodology of FIG. 10 used during time periods (zones) in which relatively little thermal or material strain is expected to occur.

[0117] In order to monitor the temperature of the honeycomb bodies 100 during any heating or cooling process, infrared temperature measurement devices can be mounted with line of sight to the honeycomb bodies 100. For example, reading the temperature at the top faces of the honeycomb bodies 100 may assist in the capture of internal artifacts of temperature. In order to minimize condensation of organic components in the exhaust streams of the ovens 52, the exhaust gases can be flowed from hottest zone through to the coldest zone in the multi-zone flow-through systems.

EXAMPLES [0118] FIG. 12 illustrates a growth and shrinkage curve (which may be referred to simply as a shrinkage curve) for a honeycomb body comprising a cordierite-forming mixture that comprises methylcellulose (binder) and starch (pore former) as organic components, and clay, alumina, quartz/silica, and talc as cordierite-forming inorganic components. The plot of FIG. 12 correlates various weight loss, exothermic/endothermic, and shrinkage events that occur at different temperatures during firing of a honeycomb body to a corresponding amount of shrinkage detected in the honeycomb body. Positive values in FIG. 12 correspond to growth and negative values correspond to shrinkage. The shrinkage was detected as a change in axial length of the honeycomb body with respect to an initial axial length that the honeycomb body had when in the green state before firing.

[0119] Of particular note from FIG. 12, it can be seen that the dehydroxylation of talc (talc water loss), occurring primarily between about 800°C and 1000°C, corresponds to a significant amount of shrinkage of the honeycomb body. Accordingly, in some embodiments, the first top temperature is set or selected so that it avoids the temperature range at which an event, such as talc water loss, is contributing to a significant amount of shrinkage of the honeycomb bodies 100 (e.g., at a temperature that falls outside of the range of 800°C to 1000°C with respect to the example of FIG. 12). In some embodiments, the first top temperature T1 is set or selected so that it falls in a temperature range that is less than the initial talc dehydroxylation temperature (e.g., less than about 800°C with respect to the example of FIG. 12), but greater than the temperature at which one or more other significant events complete, such as clay water loss and/or quartz transition, which occur in the range of about 400°C - 550°C. As shown in FIG. 12, between the temperature at which quartz transition completes and at which talc water loss initiates, the shrinkage curve is particularly flat. Accordingly, in some embodiments the first top temperature T1 is selected so that it falls between the temperature at which quartz transition substantially completes and at which talc water loss (dehydroxylation) initiates. In some embodiments, the first top temperature T1 is set or selected so that it falls within a temperature range of at least 600°C, such as from 600°C to 800°C.

[0120] It can be particularly advantageous in some embodiments to select the first top temperature T1 as a temperature that is greater than the temperature at which the talc of a talc- containing ceramic-forming batch mixture has substantially finished dehydroxylation (“talc dehydroxylation temperature”) in order to provide the benefits of flow-through firing during essentially all events, before sintering-based densification, that contribute to growth or shrinkage (e.g., organic removal, alumina water loss, clay water loss, quartz transition, and/or talc dehydroxylation), while avoiding the honeycomb bodies 100 being transitioned between different kiln assets in the middle of a significant growth or shrinkage event.

[0121] At temperatures above the talc dehydroxylation temperature (e.g., starting at about 1100°C), the honeycomb body experiences another significant shrinkage event primarily associated with densification of the honeycomb body as the porous ceramic material undergoes initial sintering. As shown in FIG. 12 and enlarged in FIG. 13, the shrinkage curve exhibits an inflection point (point at which the shrinkage curve transitions from being concave to being convex) at a temperature that falls between the talc dehydroxylation event and the initial sintering event. The slope of the shrinkage curve in a region proximate to the inflection point, designated in FIG. 13 as an inflection region 66, is substantially constant and relatively flatter than the slope of the shrinkage curve at temperatures outside of the inflection region 66. Thus, the inflection region 66 corresponds to a temperature range at which comparatively less shrinkage is occurring, with respect to events on either side of that temperature range (e.g., talc dehydroxylation at lower temperatures and sintering-based densification at higher temperatures).

[0122] FIG. 14 illustrates a shrinkage curve for a talc-containing batch mixture designed to form a primary ceramic phase of aluminum titanate, with secondary phases of cordierite and mullite. Due to the different raw ingredients utilized in the batch mixture to collect the results of FIG. 14, the talc dehydroxylation temperature is less than that of FIG. 12 (i.e., at about 875°C - 900°C in FIG. 14 and at about 950°C - 975°C in FIG. 12). Accordingly, the inflection region 66 in the example of FIG. 14 is from about 900°C - 950°C and the inflection region 66 in the example of FIG. 12 is from about 975°C - 1025°C. Accordingly, the inflection point, and corresponding inflection region 66, that falls between talc dehydroxylation and sintering-based densification of honeycomb bodies comprising talc-containing batch mixtures is expected to be between about 800°C and 1100°C. [0123] In some embodiments, the first top temperature T1 of the first kiln asset 28 is set or selected so that it falls within the inflection region 66 of the shrinkage curve of the corresponding honeycomb bodies being fired. The inflection region 66 can be defined as the portion of the curve that spans a temperature range at which the instantaneous slopes of the shrinkage curve over that temperature range differ by an angle of less than 20°, less than 15°, or even less than 10° or 5° from an instantaneous slope (dashed line in FIG. 13) of the curve at an inflection point in the curve that falls between 800°C and 1100°C. Alternatively, the inflection region 66 can be defined as the portion of the curve over a range of temperatures that differ by at most about 25°C, at most about 20°C, at most 15°C, or even at most 10°C from an inflection point in the shrinkage curve that falls between 800°C and 1100°C.

[0124] FIG. 15 illustrates a firing cycle (temperature with respect to time) for honeycomb bodies comprising a cordierite-forming batch mixture corresponding to the shrinkage curve of FIG. 12 that was fired by the firing system 20 utilizing both flow-through heating and flow-through cooling, with a hand-off between the first stage 22 and the second stage 24 at the first top temperature T1 at 1000°C and the second top temperature T2 at 1440°C. More particularly, FIG. 15 shows multiple curves corresponding to data collected by temperature sensors arranged at various locations within one of the honeycomb bodies during firing, including at the bottom face center (BC), bottom outer skin (BS), axially middle center (MC), axially middle outer skin (MS), top face center (TC), and top face outer skin (TS). Firing of honeycomb bodies comprising a similar cordierite-forming batch mixture in a single kiln asset without flow-through heating or flow-through cooling may require a firing cycle having a duration of several days or even a week or more to fire, with organic removal and talc dehydroxylation events requiring temperature slowdowns and holds that span multiple days. In comparison, the honeycomb bodies were successfully fired in about twenty-five hours, with the first top temperature T1 being reached within about six hours, the second top temperature held for about ten hours, and cooling performed in about six hours.

[0125] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the claimed subject matter. Accordingly, the claimed subject matter is not to be restricted except in light of the attached claims and their equivalents.

Claims

What is claimed is:

1. A firing system for manufacturing ceramic honeycomb bodies, comprising: a first kiln asset comprising a heater that heats honeycomb bodies in the first kiln asset to a first top temperature and a flow generator that generates a flow of gas through channels of the honeycomb bodies during heating; a second kiln asset configured to heat the honeycomb bodies to a second top temperature that is greater than the first top temperature; a hand-off zone connecting between the first kiln asset and the second kiln asset; and a conveyor configured to move honeycomb bodies from the first kiln asset through the hand-off zone to the second kiln asset.

2. The firing system of claim 1 , wherein the hand-off zone is configured to maintain honeycomb bodies within the hand-off zone at a temperature that is within 50°C of the first top temperature.

3. The firing system of either one of claims 1 or 2, wherein the hand-off zone is configured to maintain honeycomb bodies within the hand-off zone at a temperature that is within 20°C of the first top temperature.

4. The firing system of any one of claims 1-3, wherein the hand-off zone is configured to maintain honeycomb bodies within the hand-off zone at a temperature this is at least as high as the first top temperature.

5. The firing system of any one of claims 1-4, wherein the conveyor comprises a first section extending through the first kiln asset and a second section extending through the second kiln asset, and wherein the first section is of a different type than the second section.

6. The firing system of claim 5, wherein the first section of the conveyor comprises a continuous belt comprising openings therethrough, and the second section of the conveyor comprises rollers.

7. The firing system of any one of claims 1-6, wherein the first top temperature is from 600°C to 1100°C.

8. The firing system of any one of claims 1-7, wherein the first top temperature is from 600°C to 800°C.

9. The firing system of any one of claims 1-8, wherein the ceramic-forming mixture comprises talc and quartz, and the first top temperature falls within a temperature range that is greater than a first temperature at which quartz transition completes, but less than a second temperature at which talc dehydroxylation initiates.

10. The firing system of any one of claims 1 -9, wherein the first top temperature is at least 900°C.

11. The firing system of any one of claims 1-10, wherein the first top temperature is from 800°C to 1100°C.

12. The firing system of claim 11, wherein the first top temperature is falls within an inflection zone of a plot of shrinkage of the honeycomb bodies with respect to temperature.

13. The firing system of any one of claims 1-12, wherein the second top temperature is greater than 1250°C.

14. The firing system of any one of claims 1-13, wherein the second top temperature is from 1300°C to 1600°C.

15. The firing system of any one of claims 1-14, further comprising a third kiln asset connected to the second kiln asset via the conveyor, the third kiln asset being configured to generate gas flow through channels of honeycomb bodies received from the second kiln asset while cooling the honeycomb bodies.

16. The firing system of any one of claims 1-15, wherein the conveyor is configured to index honeycomb bodies from the second kiln asset back into the first kiln asset after firing in the second kiln asset.

17. The firing system of claim 16, wherein the first kiln asset is configured to generate the flow of gas through channels of honeycomb bodies received from the second kiln asset while cooling the honeycomb bodies to temperatures below the first top temperature.

18. The firing system of any one of claims 1-17, wherein the first kiln asset comprises a plurality of ovens.

19. The firing system of claim 18, wherein the plurality of ovens are arranged in series along the conveyor.

20. The firing system of claim 18, wherein the plurality of ovens are arranged in parallel, wherein the conveyor comprises a first section that comprises plurality of branch lines connected to a common input trunk line and a common output trunk line, wherein one branch line extends through each oven, and wherein the common output trunk line is connected to a second section of the conveyor that extends through the second kiln asset.

21. The firing system of any one of claims 1-20, wherein the second kiln asset comprises a tunnel kiln or roller hearth.

22. The firing system of any one of claims 1-21, wherein the first kiln asset, the second kiln asset, or both, are configured to heat a plurality of separate zones to different temperatures.

23. A production line for manufacturing ceramic honeycomb bodies comprising the firing system of any one of claims 1 -22.

24. A method of manufacturing a ceramic honeycomb body comprising: heating a honeycomb body comprising a ceramic-forming mixture to a first top temperature in a first kiln asset, the honeycomb body comprising a plurality of intersecting walls forming channels that extend longitudinally through the honeycomb body; flowing a gas through the channels of the honeycomb body during the heating of the honeycomb body up to the first top temperature in the first kiln asset; conveying the honeycomb bodies from the first kiln asset to a second kiln asset through a hand-off zone connected between the first kiln asset and the second kiln asset; and heating the honeycomb body in the second kiln asset to a second top temperature, greater than the first top temperature, that is sufficient to sinter ceramic materials in the honeycomb body.

25. The method of claim 24, wherein moving the honeycomb body through the hand-off zone comprises maintaining the honeycomb body at a temperature within 50°C of the first top temperature.

26. The method of either one of claims 24 or 25, wherein moving the honeycomb body through the hand-off zone comprises maintaining the honeycomb body at a temperature within 20°C of the first top temperature.

27. The method of any one of claims 24-26, wherein moving the honeycomb body through the hand-off zone comprises maintaining the honeycomb body at a temperature at least as high as the first top temperature.

28. The method of any one of claims 24-27, wherein the first kiln asset comprises a plurality of ovens arranged in series along a conveyor.

29. The method of any one of claims 24-28, wherein the first kiln asset comprises a plurality of subsections arranged in parallel with respect to each other, each subsection comprises one or more ovens.

30. The method of claim 29, wherein operation of the subsections is staggered such that a first subsection is unloading one or more honeycombs while a second subsection is firing or loading one or more honeycomb bodies.

31. The method of any one of claims 24-30, wherein heating to the first top temperature, heating to the second top temperature, or both, comprises incrementally heating in plurality of adjacent zones of increasing temperature.

32. The method of any one of claims 24-31, wherein the first top temperature is from 600°C to 1100°C.

33. The method of any one of claims 24-32, wherein the first top temperature is from 600°C to 800°C.

34. The method of any one of claims 24-33, wherein the ceramic-forming mixture comprises talc and quartz, and the first top temperature falls within a temperature range that is greater than a first temperature at which quartz transition completes, but less than a second temperature at which talc dehydroxylation initiates.

35. The method of any one of claims 24-34, wherein the first top temperature is at least 900°C.

36. The method of any one of claims 24-35, wherein the first top temperature is from 800°C to 1100°C.

37. The method of claim 36, wherein the first top temperature is falls within an inflection zone of a plot of shrinkage of the honeycomb bodies with respect to temperature.

38. The method of any one of claims 24-37, wherein the second top temperature is greater than 1250°C.

39. The method of any one of claims 24-38, wherein the second top temperature is from 1300°C to 1600°C.

40. The method of any one of claims 24-39, wherein the ceramic-forming mixture comprises talc and the first top temperature is greater than a talc dehydroxylation temperature of the ceramic-forming mixture.

41. The method of claim 40, wherein the first top temperature lies within an inflection zone on a plot of shrinkage of the honeycomb body with respect to temperature.

42. The method of any one of claims 24-41, wherein a mixture of the glow of gas comprises C in a concentration of less than 10% by volume.

43. The method of any one of claim 24-42, wherein the gas is flowed through the channels at a velocity of at least 4 m/s.

44. The method of any one of claim 24-43, wherein heating the honeycomb body to the first top temperature comprises increasing temperature linearly.

45. The method of any one of claim 24-44, wherein heating the honeycomb body to the first top temperature comprises heating the honeycomb body in a step-wise manner by moving the honeycomb body through a plurality of adjacent zones of increasing temperature.

46. The method of any one of claim 24-45, wherein heating the honeycomb body to the first top temperature comprises heating the honeycomb body in a sawtooth manner by moving the honeycomb body through a plurality of adjacent zones, wherein each zone has a minimum temperature and a maximum temperature, and each zone is at the minimum temperature when receiving the honeycomb body and increased to the maximum temperature when the honeycomb body is in the zone.

47. The method of claim 46, wherein the maximum temperature of any given zone is approximately equal to a minimum temperature of a next zone adjacent to each given zone.

48. A method of manufacturing ceramic honeycomb bodies comprising: heating a honeycomb body comprising a ceramic-forming mixture to a first top temperature of at least 600°C, the honeycomb body comprising a plurality of intersecting walls forming channels that extend longitudinally through the honeycomb body; flowing a gas through the channels of the honeycomb body during the heating of the honeycomb body up to the first top temperature; and then heating the honeycomb body to a second top temperature, greater than the first top temperature, that is sufficient to sinter ceramic materials in the honeycomb body, without flowing the gas.

49. A method of manufacturing a ceramic honeycomb body from a green honeycomb body comprising a talc-containing ceramic-forming mixture, the method comprising: heating the honeycomb body to a first top temperature that is greater than a talc dehydroxylation temperature of the ceramic-forming mixture while flowing a gas through longitudinal channels extending through the honeycomb body, wherein the longitudinal channels are formed by a plurality of intersecting walls of the honeycomb body; and then heating the honeycomb body to a second top temperature, greater than the first top temperature, that is sufficient to sintering together ceramic materials in the honeycomb body.