Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Producing article having plural hollow channels
Reexamination Certificate
2000-07-10
2001-12-04
Fiorilla, Christopher A. (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Producing article having plural hollow channels
C264S630000, C264S656000
Reexamination Certificate
active
06325963
ABSTRACT:
The present invention relates to a method of firing cellular ceramic bodies, and more particularly, it relates to a method of firing the cellular ceramic bodies exhibiting problematic high-organic containing batches and to a tunnel kiln adapted for such a firing process.
BACKGROUND OF THE INVENTION
Ceramic products of a honeycomb shape, or ceramic honeycomb structures, i.e., cellular ceramic bodies, have been made by preparing a ceramic green body through mixing of ceramic materials with water and various carbonaceous materials, including extrusion and forming aids to form a plasticized batch, forming the body into a honcycomb-shaped ceramic green body through extrusion of the plasticized batch, and finally firing the honeycomb-shaped ceramic green body in a firing furnace at a predetermined temperature.
Extrusion and forming aids used in the above firing of the honeycomb structure include, specifically, organic binders and plasticizers and lubricants, such as methylcelloluse, carboxymethlcellulose, polyvinyl alcohol, alkali stearates and the like. Furthermore, other carbonaceous materials such as graphite have been included in the batch as a pore-forming agent.
It is known that the carbonaceous material release or the decomposition of the carbonaceous material, is an oxidation or exothermic reaction which releases large amounts of heat. Initially the exothermic reaction occurs at the skin or outer portion of the part, resulting in an initial thermal differential whereby the outer portion of the ceramic body is hotter than the core. Subsequently, the skin or outer portion exothermic reaction dies down, and the exothermic reaction region moves into the interior of the ware. Because typical substrates are comprised of ceramic materials, for example cordierite, which are good insulators, and exhibit a cellular structure comprising numerous channels, difficulties are encountered in effectively removing, either by conduction or convection, the heat from the ceramic body. Additionally, due to the cellular structure there is considerable surface area to promote binder reaction with the O
2
in the firing atmosphere, thus exacerbating this interior exothermic effect. As such, during the carbonaceous material release, the ceramic body exhibits either a positive or negative thermal differential; i.e., the core of the ceramic body exhibiting either a higher or lower temperature than that of the ceramic at
ear the surface. This exothermic reaction, which occurs in the 100 to 600° C. temperature range for carbonaceous materials such as an organic binder or the like, or in the 500-1000° C. temperature range if the body contains, for example, graphite, causes a significant temperature differential between the inside and outside of the part. This temperature differential in the part creates stresses in the ceramic body which may result in cracking of the part. This phenomenon is particularly true for large cellular ceramic parts or parts containing large amounts of organic materials.
Techniques for controlling and inhibiting the thermal differential and resultant crack development are well known. One technique involves reducing burner flame temperature by using excess air for burner combustion, resulting in a reduced flame to product temperature gradient and corresponding slower ware heating rates. However, the high excess air yields an undesirably high percentage oxygen-containing atmosphere that reacts with the organics thereby accelerating release and increasing the internal exothermic reaction. As such, minimization of the thermal differential which develops during organic release, must be accomplished through very slow firing schedules or, alternatively, firing schedules which are carefully matched to the particular ware in the kiln.
Use of atmosphere control in periodic-type kilns to affect carbonaceous material release is generally known. See, for example, U.S. Pat. Nos., 4,404,166 (Wiech, Jr.), 4,474, 731 (Brownlow et al.), 4,661,315 (Wiech Jr. et al.) and 4,927,577 (Ohtaka et al.). Although these methods have been shown to be effective enough for use in periodictype kilns, they are not generally considered to be effective in tunnel kilns due to the considerable influx of ambient air (20.9% oxygen) into the firing atmosphere.
The use of pulse firing technology as a substitute for proportional firing has also been disclosed as a method for controlling and inhibiting thermal gradients in periodic kilns. Pulse firing involves the use of either high fire or low fire burner output conditions only, and produces low heating rates without the use of considerable amounts of excess air (oxygen); see, for example Eur. Pat. Appl. No. 0 709 638 which discloses a method of firing ceramic formed bodies using a furnace having burners which alternate from a high to a low output firing state. Although the use of this firing technology has been somewhat effective in periodic kilns, resulting in a reduction in the incidences of cracking, this pulse firing technique poses difficulties when used in tunnel kilns. Due to the open nature of tunnel kilns it is necessary to control the ambient air ingress into the organic release zones of the kiln by other means.
Therefore, an object of the invention is to solve the above-mentioned problems of the prior art by providing an improved method and a tunnel kiln for firing ceramic honeycomb structural bodies which ensures stable production of high-quality crack-free product.
SUMMARY OF THE INVENTION
It is an object of the present invention to eliminate the above-mentioned problems, and to provide a process and a kiln for firing ceramic honeycomb structural bodies, which permits the production of ceramic honeycomb structural bodies exhibiting less cracks, a more uniform firing of the inner and outer portions of the green honeycomb structural bodies while employing short duration cycles.
The method of firing a green ceramic honeycomb structural body containing an organic or carbonaceous material is characterized by collecting and trapping, via the use of a collection trap, at least a portion of the carbonaceous material released from the body. The method next involves, subsequently, and prior to the material reacting within the firing atmosphere of the kiln, removing this collected/trapped released carbonaceous material.
The kiln according to the present invention is a tunnel kiln which comprises the following: a vestibule region; a carbonaceous material release region having a plurality of removal zones and associated carbonaceous material collection trap regions which are located downstream of the vestibule region; and a sintering region located downstream of the carbonaceous material release region. The tunnel kiln further includes an exhaust removal system which operatively communicates with the release region for removing released carbonaceous material. The exhaust removal system comprises at least one offtake opening in communication with a corresponding carbonaceous material collection trap, preferably located in the rooftop of each removal zone and operatively communicating with an exhaust fan, for removing and evacuating released and trapped carbonaceous material from the kiln release region.
REFERENCES:
patent: 3706289 (1972-12-01), Brewer
patent: 3744965 (1973-07-01), Remmey et al.
patent: 3865540 (1975-02-01), Loeffler
patent: 4005981 (1977-02-01), Turnbull
patent: 4051231 (1977-09-01), Bond et al.
patent: 4128394 (1978-12-01), Naito et al.
patent: 4133636 (1979-01-01), Flynn
patent: 4176162 (1979-11-01), Stern
patent: 4235830 (1980-11-01), Bennett et al.
patent: 4269592 (1981-05-01), Benton et al.
patent: 4291471 (1981-09-01), Bloom
patent: 4340555 (1982-07-01), Procter
patent: 4404166 (1983-09-01), wiech, Jr.
patent: 4474731 (1984-10-01), Brownlow et al.
patent: 4508669 (1985-04-01), Iwai et al.
patent: 4784603 (1988-11-01), Robak, Jr. et al.
patent: 4789332 (1988-12-01), Ramsey et al.
patent: 4795598 (1989-01-01), Billiet
patent: 4884969 (1989-12-01), Kolln et al.
patent: 4927577 (1990-05-01), Ohtaka et al.
patent: 4990086 (1991-02-01), Eustacchio
pa
Dull Alan T.
Hinkle Thomas S.
Witte Christopher S.
Zunic Edward F.
Corning Incorporated
Fiorilla Christopher A.
Gheorghiu Anca C.
Schaeberle Timothy M.
LandOfFree
Method for firing ceramic honeycomb bodies does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for firing ceramic honeycomb bodies, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for firing ceramic honeycomb bodies will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2572802