Conveyor tray apparatus with air bearing and air curtain and methods of use

Conveyor tray apparatus with air bearing and air curtain and methods of use are disclosed herein for use in manufacturing technical ceramics. The apparatus includes a tray body comprising a cradle having an outer surface disposed between opposing first and second sides, the cradle configured to receive a cylindrical object and having a plurality of air bearing holes. The tray body includes first and second support portions disposed at the respective first and second sides of the cradle. First and second air curtain housings are disposed on the respective first and second support portions. The air curtain housings each define an air plenum and an air exit opening that faces generally toward the outer surface of the cradle.

FIELD

This disclosure relates to apparatus comprised of conveyor trays with air bearing and air curtain features, and methods of using the trays in the manufacture of technical ceramics, and in particular conveyor trays used in handling ceramic green ware or ceramic fired ware, such as honeycomb shaped articles formed via extrusion, that can be used for the treatment of combustion engine exhaust gases, for example, as a catalyst support substrate or filter.

BACKGROUND

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 fragile, and can be difficult to handle or transport, particularly until the wet extrudate has been dried. Handling can cause shape distortion in wet honeycomb shapes, particularly those comprising thin web and/or 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 be susceptible to 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.

SUMMARY

Conveyor tray apparatus with air bearing and air curtain and methods of use are disclosed herein for use in manufacturing technical ceramics. As used herein, “air bearing” or “air curtain” are to be understood to function with gases other than air, such as nitrogen, and therefore “air bearing” and/or “air curtain” are interchangeable with “gas bearing” and “gas curtain”, respectively. The methods and apparatus disclosed herein help to reduce structural distortion, such as channel collapse, that may be encountered during the handling of ceramic-forming or ceramic structures, such as wet green honeycomb extrudate.

DETAILED DESCRIPTION

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 sections of wet honeycomb extrudate, termed “logs”, are to be cut from the extruder, transported, and dried. Hence the following descriptions and illustrations may 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.

The ceramic structures can be processed by any of the known methods for fabricating ceramic monoliths, such as for example, by extrusion. The process may be either a batch process (as with a ram extruder), or a continuous process (as with a screw-type extruder). Regardless of the process, the batch material to be extruded is forced through the die of the extruder to form an extrudate, which in the case of a honeycomb die, is extruded in the form of a log. After leaving the extruder, the log is dried and fired using the apparatus and method of the invention.

FIG. 1shows a conveyor system10. The conveyor system10comprises an air supply system30and a conveyor apparatus40. A cylindrical object such as an extruded log11is directed over a guide path A (arrow) of the conveyor apparatus40, after having left the extruder13. The conveyor apparatus40comprises one or more tray bodies12and first and second air curtain housings41,42. The conveyor apparatus40facilitates transport of extrudate such as an extruded log11, or pieces cut from such extrudate log such as the ceramic-forming, or ceramic, cylindrical objects17. As seen inFIG. 2, cylindrical object17has opposing first and second end faces,50,51a circumferential outer surface52extending between the first and second end faces50,51, and a longitudinal axis54extending through the first and second end faces50,51. After leaving the extruder13, the ceramic log11is supported and conveyed upon an air bearing surface to a dryer carrier20into a dryer where the object17is exposed to a heated drying environment which can be a microwave energy environment created by for example, a microwave applicator. Before entering the dryer, the logs11can be cut into smaller ceramic structures or ware17which are then dried in the drying apparatus and eventually sintered or fired for subsequent processing or use.

Cradle22has a plurality of apertures23disposed therein, through which air is allowed to circulate or move freely through the tray body12.

As seen inFIG. 2, each tray body12comprises a cradle22having opposing first and second sides45,46, and an outer surface47disposed between the first and second sides45,46, the outer surface47being configured to receive the extruded log11or cylindrical object17. The embodiment shown inFIG. 2has an upwardly concave cradle22which is preferably contoured to fit the surface of the ceramic ware or structure17. Cradle22has a plurality of air bearing holes23disposed through the outer surface47of the cradle22. Tray12also comprises first and second support portions48and49each of which are provided with a plurality of air curtain holes60. As seen inFIG. 1, one or more air conduits14supply the air bearing holes23and air curtain holes60with air, or other gas. The one or more conduits14can be connected to a common air supply pipe15. A mechanical saw16, whose velocity matches that of the extrudate exiting the extruder13, e.g. log11, is used to cut the log into pieces17of a desired (e.g. uniform) length. In some embodiments, air blower19and a humidifier18, such as Model No. CES-012AS010-483 Chromalox electric boiler manufactured by Emerson Electric Co. (Pittsburgh, Pa.) and Model No. LB-10 manufactured by Electro-Steam Generator Corp. (Alexandria, Va.), are disposed in a common air supply pipe15upstream of the individual conduits14, for maintaining the proper velocity and range of relative humidity for the air being supplied to the conveyor system10.

Thus, conveyor apparatus40is provided for a cylindrical object17having opposing first and second end faces50,51, a circumferential outer surface52extending between the first and second end faces50,51, and a longitudinal axis54extending through the first and second end faces50,51. Conveyor apparatus40comprises a tray body12comprising a cradle22(the embodiment shown inFIG. 2as being upwardly concave) having opposing first and second sides, and an outer surface47disposed between first and second sides45,46, outer surface47being configured to receive cylindrical object17, cradle22having a plurality of air bearing holes23disposed through cradle22, first support portion48being disposed at first side45of cradle22, and second support portion49disposed at second side46of concave cradle22.

As seen inFIGS. 1 and 3, first air curtain housing41is disposed on first support portion48, first air curtain housing defining a first air plenum70and a first air exit opening71, the first air exit opening71facing generally toward the outer surface47of the concave cradle22from the first side45. Similarly, and preferably symmetrically, second air curtain housing (not shown) is disposed on the second support portion49, the second air curtain housing defining a second air plenum and a second air exit opening, the second air exit opening facing generally toward the outer surface47of the concave cradle22from the second side46.

As seen inFIG. 3, tray body12comprises a first rounded external surface80at an intersection of the outer surface47of the cradle22and the first support portion48. Tray body12also comprises a second rounded external surface (not shown) at an intersection of the outer surface47of the cradle22and the second support portion49. In some embodiments, the rounded external surface comprises a radius of less than 0.5 inch. In other embodiments, the rounded external surface comprises a radius r3of between 0.05 inch and 0.5 inch. In other embodiments, the rounded external surface comprises a radius of between 0.15 inch and 0.35 inch.

As seen inFIG. 3, first air curtain housing41comprises a bottom portion90, a top portion91, and a proximal portion92extending between the top and bottom portions91,90, wherein the air exit opening71comprises an air curtain gap93between the proximal portion92and the bottom portion90of the first air curtain housing41. The bottom portion90of the first air curtain housing41comprises a terminal surface94facing toward the proximal portion92, and the proximal portion90of the first air curtain housing41comprises an inner surface95at least partially defining the first air plenum70, wherein the terminal surface94of the bottom portion90and the inner surface95of the proximal portion92of the first air curtain housing41define the first air curtain gap93. In some embodiments, the terminal surface94of the bottom portion92of the first air curtain housing41is disposed at an angle of 10 to 30 degrees with respect to an upper surface96of the bottom portion90of the first air curtain housing41.

As shown in the embodiment ofFIG. 3, the upper surface96of the bottom portion90of the first air curtain housing41can be generally horizontal, and the inner surface95of the proximal portion92of the housing41at the gas curtain gap93can then be disposed at an angle100of 10 to 30 degrees with respect to an upper surface96of the bottom portion90of the first air curtain housing.

As seen inFIG. 3, the proximal portion92of the first air curtain housing41can comprise an external surface97, and at least part98of the external surface97of the proximal portion92is substantially tangential to a part99of the outer surface47of the cradle22, i.e. the region closest to the interface portion80.

As shown in the embodiment ofFIG. 3, the proximal portion92of the first air curtain housing41comprises an external surface97, and at least part98of the external surface97of the proximal portion92is substantially vertical.

The proximal portion92(and in some embodiments, a substantially vertical part98) of the housing41is configured to be spaced away from the cylindrical object17by a cylindrical object-air curtain gap102.

In some embodiments, the tray body12comprises an axial length, and in a transverse cross-section perpendicular to the direction of the axial length, the concave portion defines a circular arc (as shown inFIG. 3), or an oval or elliptical arc. In some embodiments, the tray body12is fabricated of at least one material exhibiting low dielectric loss. In some embodiments, the tray body12is fabricated of bonded alumina or aluminosilicate fiber.

Computer simulations were conducted for pressures and flows for a conveyor apparatus for a 5.66 inch diameter green ceramic honeycomb body having an outer skin (at radius 3.0594 inch) with a constant pressure in air bearing gap104(air bearing supply pressure) of 5 inches of water (0.1806 psig), wherein the ambient pressure is 0 psig, a 40 mil (0.040 inch) constant air bearing gap104, a housing41with proximal portion92of thickness t1of 0.125 inch, rounded tip of 0.01 inch radius r1, rounded edge of 0.5 inch radius r2at the intersection of the part98and the remainder of portion92, a bottom portion90of thickness t20.1875 inch with a gap93and a gap102each of 40 mils (0.040 inch), unless otherwise noted, the proximal portion92being at an angle100of 20 degrees, the bottom portion90being horizontal, and the tray body having a rounded edge99of 0.25 inch radius r3. Gap102was varied between 40 and 80 mils, and gap93was varied between 20 and 40 mils, while the air pressure in the chamber70was varied between 0 to 7.5 inches of water.

FIG. 4shows a graphical representation of the modeled normalized pressure and weight (P, W) of the supported cylindrical object plotted against the lateral distance in inches (L) i.e. the distance from vertical center line passing through the object in a transverse plane as shown inFIG. 3, wherein the air bearing gap104was 40 mils, the gap102between the air curtain and the object was 40 mil, and the gap93of the air curtain housing was 40 mil, and wherein the normalized weight of the object is shown in solid line, the pressure on the object with the air curtain housing in place, but with no flow coming out of the air curtain housing, shown by the small dashed line, and the pressure on the object with air curtain pressure in the chamber70was 2.5, 5.0, and 7.5 inches of water shown by the large dash line, the dash double dot line, and the dash single dot line, respectively.FIG. 4illustrates that the air curtain can provide an enhanced shroud of air around the cylindrical object to help reduce the lateral motion of the cylindrical object with respect to the tray body, thereby helping to reduce damage of the cylindrical object by, for example, hitting the tray body during transport of the object. Also, the conditions represented by the small dashed line (air curtain housing in place, but with no flow coming out of the air curtain housing) indicates a weakening of the air bearing effect, and appears to indicate a propensity to lateral instability.

FIG. 5shows a graphical representation of the modeled normalized pressure and weight (P, W) of the supported cylindrical object plotted against the lateral distance in inches (L) i.e. the distance from vertical center line passing through the object in a transverse plane as shown inFIG. 3, wherein the air curtain pressure inside chamber70was 5.0 inches of water, the air bearing gap104was 40 mils, and the gap102between the air curtain and the object was 40 mils, and wherein the normalized weight of the object is shown in solid line, the pressure on the object with the air curtain housing in place, but with no flow coming out of the air curtain housing, shown by the small dashed line, and the pressure on the object with the gap93of the air curtain housing being 20 mils or 40 mils, shown by the large dash line, and the dash double dot line, respectively.FIG. 5illustrates that for a given air curtain chamber pressure, a wider air curtain gap93results in more air curtain flow which can provide an even more enhanced shroud of air around the cylindrical object to help reduce the lateral motion of the cylindrical object with respect to the tray body, thereby helping to reduce damage of the cylindrical object by, for example, hitting the tray body during transport of the object.

FIG. 6shows a graphical representation of the modeled normalized pressure and weight (P, W) of the supported cylindrical object plotted against the lateral distance in inches (L) i.e. the distance from vertical center line passing through the object in a transverse plane as shown inFIG. 3, wherein the air curtain pressure inside chamber70was 5.0 inches of water, the air bearing gap104was 40 mils, and the gap102between the air curtain and the object was 40 mils, and wherein the normalized weight of the object is shown in solid line, and the pressure on the object with gap102between the air curtain housing and the cylindrical object being 40, 60 or 80 mils, shown by the small dash line, the large dash line, and the dash double dot line, respectively (the large dash line and the dash double dot line being essentially coincident with each other).FIG. 6illustrates that for fixed air curtain geometry and chamber pressure, and with some variation in the gap102between the air curtain and the cylindrical object, the air curtain can still provide an enhanced shroud of air around the cylindrical object to help reduce the lateral motion of the cylindrical object with respect to the tray body, thereby helping to reduce damage of the cylindrical object by, for example, hitting the tray body during transport of the object.

FIG. 7shows a graphical representation of the modeled mass flow rate (M), in lbm per second per inch, of the flow out of the air curtain through gap93(“AC flow” or “ACF”), the flow out of the gap102(“gap flow” or “GF”), and the total flow supplied to the air bearing plus air curtain and flowing out of the object-air curtain gap102(“total flow” or “TF”), each plotted against air curtain supply pressure, wherein the air curtain pressure inside chamber70(or “ACP”) in inches of water, the air bearing gap104was 40 mils, and the object-air curtain gap102between the air curtain and the object was 40 mils, and the air bearing supply pressure was 5.0 inches of water, and wherein the flows corresponding to an air curtain exit gap93of 20 mils are shown by large dash lines, and wherein the flows corresponding to an air curtain exit gap93of 40 mils are shown by solid lines, the AC flow (ACF) being the lowest pair of solid & dashed lines, the gap flow (GF) being the middle pair of solid & dashed lines, and the total flow (TF) being the top pair of solid & dashed lines.

In use, air (or some other gas or combination of gases) is supplied to the air bearing holes with sufficient pressure to levitate the cylindrical object above the surface of the tray body12, and air (or some other gas or combination of gases) is supplied to the air curtain holes with sufficient pressure to help reduce contact between the cylindrical object and the tray body12in a stable manner.

In other embodiments disclosed herein, a method is provided of conveying a cylindrical object17having opposing first and second end faces50,51, a circumferential outer surface52extending between the first and second end faces50,51, and a longitudinal axis54extending through the first and second end faces50,51, the method comprising: moving the object17into proximity with a tray body12such that the object17is disposed over the tray body12; flowing a first gas up through the tray body12to suspend the object17above the tray body12such that the object17and the tray body12are spaced apart by a tray body-object gap104; and flowing a second gas downward into the tray body-object gap104. In some embodiments, the first and second gases are air. The second gas is directed into the tray body-object gap104along the circumferential outer surface52of the object17. In some embodiments, the second gas is directed into the tray body-object gap104along the circumferential outer surface of the object simultaneously from locations on opposite sides45,46of the tray body12. In some embodiments, the tray body-object gap104is between 30 and 50 mils, and in some embodiments about 40 mils. In some embodiments, the gas is directed into the tray body-object gap104at a location about 90 degrees from vertical (seeFIG. 3). In some embodiments, the gas is directed into the tray body-object gap104at an angle100of about 20 degrees with respect to horizontal. In some embodiments, the gas is directed into the tray body-object gap104from a gas curtain housing41disposed on the tray body12.

The method can further comprise transporting the cylindrical object17into a dryer, and then a kiln.

In some embodiments, the air curtain gap93, is 10 to 50 mils, and in some of these embodiments, 20 to 40 mils; in some of these embodiments, the air curtain gap93is a longitudinal slit in the tray body12.

In some embodiments, the air curtain supply pressure in chamber70is 1 to 8 inches of water; in other embodiments, 2 to 7.5 inches of water; in other embodiments, 2.5 to 7.5 inches of water; and in some embodiments, about 5 inches of water.

In some embodiments, the air bearing supply pressure is 3 to 7 inches of water; in other embodiments, 4 to 6 inches of water; in other embodiments, about 5 inches of water.

In some embodiments, the mass flow rate through the air bearing holes is greater than 0.0005 lbm per second per inch; in some of these embodiments, the mass flow rate is 0.0005 to 0.0015 lbm per second per inch.

In some embodiments, the mass flow rate through the air curtain gap93is greater than 0.0005 lbm per second per inch; in some of these embodiments, the mass flow rate is greater than 0.001 lbm per second per inch; in some of these embodiments, the mass flow rate is 0.001 to 0.0025 lbm per second per inch.

In some embodiments, the mass flow rate of the total air flow passing through the object-air curtain gap102is greater than 0.0015 lbm per second per inch; in some of these embodiments, the mass flow rate is greater than 0.002 lbm per second per inch; in some of these embodiments, the mass flow rate is 0.002 to 0.003 lbm per second per inch.

In some embodiments, the object-air curtain gap102is 30 to 90 mils; in other embodiments, 40 to 80 mils; and in some embodiments, about 40 mils.

In some embodiments, the air curtain gap93is 10 to 50 mils; in other embodiments, 20 to 40 mils.

In some embodiments, the air bearing gap104is 10 to 70 mils; in other embodiments, 20 to 60 mils; in other embodiments, 30 to 50 mils; and in some embodiments, about 40 mils.

The cylindrical object can be comprised of ceramic-forming ingredients, and the cylindrical object can then be dried and fired to form a ceramic selected from the group consisting of cordierite, aluminum titanate, silicon carbide, mullite, spinel, alumina, silicon nitride, and combinations thereof.