Title of Invention	METHOD FOR SELECTIVE PLUGGING OF HONEYCOMB STRUCTURES .
Abstract	A method for selective sealing of channels in ceramic honeycomb structure comprising forming dried green plugs of ceramic material, followed by preparing a ceramic slurry containing a binder, selectively applying said slurry into the cells of a honeycomb structure, and sealing the same by inserting the plugs.

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FIELD OF THE INVENTION: This invention rotates to a method for selective plugging of channels in ceramic honeycomb structure. This invention further relates to a method of preparing solid plugs from green ceramic material, for selective sealing of open ends of channels In ceramic honeycomb structure. BACKGROUND OF THE INVENTION: Ceramic Honeycomb wall-flow fitters are used for solid partteutete nitration from gases in which the particulates are mixed or suspended. The ceramic wall-now filters are fabricated from a ceffuter or honeycomb structure in which mutually adjoining cells or hollow passages extend through the structure between a pair of its opposing end faces where the open, transverse cross-sections of the eels are exposed. Fabrication of waH-now filters involves plugging selectively the end faces of the ceU In checkered board pattern such that the cells open at one end face are plugged at other end face. The walls of the cells in such a honeycomb structure are thin and porous with high permeability, which allows the fluid to flow through while preventing soft) particles from flowing. The ceramic wall-flow filters used for exhaust emission ffltratton in diesel engines are subjected to variable flow rates in which the pressure applied to the plugs are variable and sometimes It Is higher at higher emission rates. Oue to continuous Impingement of gases on the plugs In ceramic filters over a period of time, the erosion of the plugs are fast and can get punctured r the strength of the plug sintered along with ceramic honeycomb is not adequate. -2- DPF is fabricated using various materials such as cordlerlte, slcort carbide etc. The process of manufacturing Honeycomb involves extrusion molding, folowed by drying and then alternately plugging the end faces, folowed by firing. DiTerent methods are available for plugging the end faces of Honeycomb. U.S. Patent No. 4,329,162 also discloses ceramic honeycomb filers in which selective seals are provided to the Inlet and outlet channels by injecting a slnterable material or other sealng cement into the appropriate ends of the channels to form a "checkerboard" array of open/closed channels at each end face. Thermal expansion mismatch is one of the major disadvantages of using ceramic cement for sealing of honeycomb eels and 1 increases the stress levels at the end face of the honeycomb cells at higher temperatures, which may lead to cracking of fiers in use. Also the honeycombs sealed with ceramic cement can only be used at tow temperatures compared to that fabricated completely from cordtertte. US. Patent No. 4,410,591 describe alernate methods of fabricating a multiple flow path body such as a stationary heat exchanger. A honeycomb structure Is provided having Is eels arranged in columns across Is open end faces, an open end face of a honeycomb structure is dipped into a flowable resist material and the resist material removed from selected columns by cutting I away together wih the common wals of the adjoining cells In the totocted column or, alternatively, the waJs between the adjoining eels of the selected columns are cut away at the open end face of the structure before dipping the end face into -3- the ftowable resist material and the resist material It blown from the selected columns using compressed air directed down the selected columns where the adjoining cell walls had been removed. The end face was thereafter dipped Into slurry of cement to form a sealed channel across each of the selected columns. The remaining flowable resist material was subsequently removed by heating. As the cross-sectional density of cells in the honeycomb structure is increased, for example to Improve the efficiency of a filter body, the tolerances needed for the removal of adjoining ceN walls required by the Nod, et al method requires the partial destruction of adjoining cells are sealed in a checkered or other possible alternating cell patterns at the end faces. European patent No. 42,301 discloses a method In which a ceramic honeycomb is selectively sealed by bonding a sealing member to each end face of the honeycomb. The sealing member has same outer shape as that of the honeycomb and has network of alternate open channels separated by sealing portions in checkered pattern or any other desired pattern. The open channels in the sealing member are located corresponding to the eels of the honeycomb which are to be kept open. The extruded sealing members and green honeycomb are separately dried before the sealing members are fitted to the honeycomb body Itself, preferably by means or any organic adhesive, a glass material, or a ceramic material, foRowed by standard firing of the composite so formed. The ceramic honeycomb fHters produced by above method can not be sealed properly as the ceHs of the sealing member w* have different drying shrinkage than that In honeycomb resulting into mismatch of the cell openings In honeycomb to the sealing member. Otherwise, it requires exceptionally close absolute dimensional matching of both the structures, which can only be met with very high dimensional tolerances. It Is Impractical to fabricate the structures with such hfgft tolerances. -4- U.S. Patent No. 4,411,856 proposes the use of a mask completely covering one end face of the monolith, this mask being provided with passages and with pog- Kke extensions on the side facing the monolith. The pegs are placed into the ducts that are not to be sealed whereas the composition Is Introduced through the passages in the mask into the end regions of the ducts to be sealed. An attempt is made to take the aforementioned deviation of the monotth from a desired geometry Into account by making the mask utilized of an elastic material. This method may be applicable within limits. There is, though, the problem that the spacing of the above-mentioned pegs to the passages h fixed so that the compensation of the deviations of (he monoftfh from the desired geometry, obtained by the elasticity of the mask, remains restricted to very low values. US Paten No. 5,766,393 discloses a method where expansive material is used to temporarily seal the alternate holes of Honeycomb in checkerboard pattern. A ceramic material paste is used to plug the remaining holes. The green honeycomb thus fabricated is sintered to produce dfesel partfculate fitter. The expensive materials used for sealing are burnt during the process of Iking and forms oponing in checkerboard pattern. In another US patent 6,627,123, a powdered material Is charged Into selected cells of honeycomb and then It is compacted by vfcratton, centrifuge, manual compaction or some other method. After compaction of the powdered material into the cells of the honeycomb laser energy is applied to heat it sufficiently to become ftowable which is further solidifies after cooling to form plugs. -5- The fitters produced by such method does not ensure uniform plug length and it wi result to differential back pressure when the filter Is used for gas fHtration. Due to this, a mechanical stress wi be generated during application and It may result in detonation of mechanical strength of filter. Also, during the process of plugging of green honeycomb with a plastic material, usually the material Is either fMad Into the ceHs by applying high pressure or a material with high flowabiity is used to improve the workability. In case of highly plastic material, the pressure applied on the honeycomb end face Is high which may damage or deform the eels In the process while In case of highly ffowable material the dispersing medium diffuses into the cell waR which is adequate to soften the cell walls. Another problem with above method is the high shrinkage of plugging material compared to the honeycomb, whfch is being plugged. Due to (his the green honeycombs are subjected to high stress during drying. TNs may lead to crack generation In the Wars after firing. During the process of plugging honeycombs by above method, when laser energy Is applied the heating of powdered malarial Is only done white adjoining cells, which are open, are not subjected to any heating. As a result of this, temperature differential is attained at different locations on the end surface of the honeycomb. Also the center portion of the honeycomb Is at low temperature than the end faces. Due to this a high level of stress is generating which can cause cracking of honeycomb. -6- Apart from this, a close control on heating of powdered material Is also needed, as the plugging material, which Is being heated, can conduct enough heat to deform the ceB wafts. In another US Patent No. 5,062,911 the method of plugging green honeycomb structure is disclosed where dried green honeycomb is wetted, preferably with water, to re-plastlctze the ceramic material at the race and a sttt-wef end cap body Is then firmly fitted onto each face with sufficient force to Integrate the plasticized ceramic material of each into a substantially continuous phase. Any excess material from the end cap that extends beyond the sides of the honeycomb Itself as a result of this pressing operation can be trimmed off so that the edges of the end caps are flush with tfm sides of ttm honeycomb. The end caps are then selectively perforated by a hand-held punch or tool having a pin that Is sized and shaped appropriately to pierce the end cap fn a manner congruent wlh the size and shape of the channel openings to be exposed. In the methods explained for plugging of honeycombs, a ftowable material Is used. The ftowable material Is charged Into the honeycomb cells by capillary action In certain cases while sometimes a plastic paste is pushed into the ceUs by applying pressure. Charging of material wlh high flowablHty Into the honeycomb cells Is mostly preferred as It gives higher plug length compared to that achieved by using plastic mass. The desirable consistency for material with high flowabHKy for this purpose » achieved only at higher water content and the quantity of material charged Into the cells of honeycomb Is much higher than the material quantity of ceN walls with which it makes contact. Due to this, localized softening and deformation of cafe in the green honeycombs is seen as the binders in honeycomb readily absorb water from charged material. -7- Another drawback of these methods Include the generation of high street locations on the end face of the honeycomb cells due to high drying shrinkage of materials used for plugging. This can lead to crack generation at end face of the cetfs In honeycomb fitters. Non-uniformity in plug length is also commonly seen in the fitters produced by above methods, which further leads to lower mechanical durability when used for gas filtration application at higher temperatures. OBJECTS OF THE INVENTION: It is therefore, an object of this Invention to propose a method of preparing soHd plugs for selective sealing of channels in ceramic honeycomb structure which helps to avoid softening and deformation of eels during the method of plugging dried green ceramic honeycombs. It is further object of this invention to propose a method of preparing solid plugs for selective seating of channel in ceramic honeycomb structure which leads to uniform length of the plugs across the section of plugs between two end faces. Another object of this Invention to propose a method of preparing sold plugs for selective sealing of channels In ceramic honeycomb structure to reduce stress level in the honeycomb ceRs occurring due to higher drying shrinkage. Yet another object of this Invention to propose a method of preparing solid plugs for selective sealing of channels in ceramic honeycomb structure which haw better filtration efficiency and lower pressure drop. -8- Sti another object of this Invention to propose a method of preparing solid plugs for selective seating of channels fn ceramic honeycomb structure, which provides any desired length of plugs even with higher celt density. DESCRIPTION Of THE INVENTION: The various aspects of the invention are better understood with reference to the accompanying drawings, In which: Fig 1 depicts schematically the step of forming plugs by using plug-forming apparatus. Fig 2 depicts schematically the stainless steel wires for cutting plugs Into required length. Fig 3 depicts schematically a member used for removing plugs formed by using apparatus shown in Fig 1. Fig 4 depicts schematically the step of covering selective cells In a ceramic honeycomb wRh a mask. Fig 5 depicts schematically the step of applying ceramic slurry into eels of the honeycomb. Fig 6 depicts schematically the method of selectively applying ceramic slurry Into the cells of the honeycomb. Fig 7 depicts schematically the step of plugging honeycomb cedt selectively with solid ceramic plugs. DETAILED DESCRIPTION OF THE INVENTION: Thus according to this Invention Is provided a method for selective sealing of channels in ceramic honeycomb structure comprising, forming dried green plugs of ceramic material, followed by preparing a ceramic slurry containing a binder, selectively applying said slurry Into the cells of a honeycomb structure, and sealing the same by Inserting the plugs. -9- The step of forming the ceramic plug* comprises charging a plastic ceramic mix of plugging material Into the channels of fired honeycomb or plug forming apparatus. The ceramic material and slurry used are preferably of same composition as that used for fabricating honeycombs. However, it can also be made out of materials wUh therms) expansion nearer to that of honeycomb. The ceramk materials used for plug, slurry and honeycomb can be of cordferie, silicon, carbide, sicon nitride, mullite, alumina, zfrconia, aluminium tNanate etc. depending upon application. For low thermal expansion application cordlerRe or sWcon carbide Is predominantly used whHe for hfgh heat resistant application mufIKe, alumina zfrconia or aluminium titanata are used. Further, the method explained can also be used for plugging fired honeycombs where fired plugs can be inserted into the cells by using ceramic cement with thermal expansion nearer to that of honeycomb. This method of plugging can also be used for honeycombs having circular, rectangular or trigonal cells. The shrinkage of the material plugged into the cefls of honeycomb is significantly less and hence generates very small stress on the cell wads, thereby reducing the chances of crack generation in ceramic men. Fig 1 depicts an exemplary apparatus for forming dry green ceramic plugs. The apparatus can be made out of any corrosion resistant material, particularly from stainless steel. The apparatus has channels 1 extending in longitudinal direction and, which is open at end faces and with another opening along the surface 2 as shown In Fig 1. The channels extend parallel to each other separated by partition 3. -10- The width of the partition are equal and can be varied for which a typical value here is 2.1mm. The channels are having square cross section for which the width is 2.1mm. Further, the apparatus has fine SMS 4 of width 0.2mm and at equal distance of typically 7 mm from each other. These sIMs have depth of 2.1mm and the bottom 5 has circular hole of diameter 0.25 mm extending along the bottom in transverse direction of the apparatus. For making dried green ceramic plugs, ceramic raw materials with same composition as used in honeycomb extrusion are mixed for 4 hrs in a cone blender and then mixed with 20% water In a high shear mixer for 15 to 30 minutes. The mixed body prepared is kept for aging upto 12 hrs In a sealed container to avoid any moisture loss. Aging of body is done to get uniform distribution of moisture within the body. The aged body is mixed again in high shear mixer to get homogenous plastic body. The wet plastic ceramic mix Is flfted into the channels 1 of apparatus. After tVHng up of wet plastic ceramic mix Into the channel* 1 of apparatus In Fig 1, a stainless steel sheet of typically 1 mm thickness and having a sharp edge at one end is used to wipe the excess material oozed out on the surface of the apparatus. Further, stainless steel wires of typicaly 0.4 mm with metal beads at the ends as shown in Fig 2 are used to cut the plugs into required length. For cutting the plugs fWed Into the channels to required lengths the wire Is kept in stretched condition and run manually across the sifts 4 from the surface to the end of the slits in Fig 1. -11- The apparatus In Fig 1 fWed with wet ceramic mix in Us channels is Kept into an oven at 110*0 for 4 Hrs to dry and then removed for cooling it to ambient temperature. The ceramic material in the apparatus shrinks after drying and can be easily removed by pushing It from the end face of the channels using a member shown in Fig 3 with square cross section of 0.25 mm width and 50 mm length. By this method solid dried green plugs having square cross-section and of 6 mm length an 0.25 mm width are prepared. The plugs 3 shown In Fig 5 are formed by such method are having equal length measured across any section between two-ends of the plug. Dried green ceramic plugs can also be prepared by fUng up plastic mix Into a nred ceramic honeycomb and then drying it into oven at 11Q°C for 4 Hrs. To get suitable length and cross section of plug, fired honeycomb slices of required length are cut from the same lot of honeycombs, which are dried and kept for plugging. The cross section of plugs formed by this method exactly matches the ceRs of the dried green honeycombs, which are to be plugged. This method is adopted preferably If the deformation In ceHs of honeycomb Is more. A ceramic slurry used in the process of plugging honeycombs. It is preferably prepared out of same material as that used for extrusion of honeycombs. For preparing ceramic slurry 46% kaolin, 41% Talc and 13% Alumina by weight Is mixed and again blended with 5% methyl cellulose by weight for 2 hrs in a cone blender. Further, 36% water is added to the mix of ceramic materials and organic binder and then mixed for 30 minutes by using a stlrrer. To apply a thin coating of ceramic slurry on the cell walls at the end face 1 of the -12- honeycomb in Fig 4, a mask 2 with openings 2a In checkered pattern as shown in Fig 4 is used. The mask 2 can be made out of any material preferably with stainless steel sheet. Openings made in the mask are of the same dimension as that In honeycomb. The green honeycomb to be plugged with dried green plugs is kept vertically on a Rat surface and the mask is placed on the end face of the honeycomb in such a way that it covers the cells of honeycomb in checkerboard pattern. A thin coat of ceramic slurry is applied on the surface of the cell waRs at the end face as depicted In Fig 5. An enlarged view of ceR waNs across the section taken along the (ing X-X In honeycomb coated with ceramic slurry is shown in Fig 7. For applying ceramic slurry into the cells a fine brush is used. The brush is dipped Into ceramic slurry to adhere sufficient quantity of material Into It and then the material adhering to the brush is discharged by mopping it on the surface of the eels of honeycomb which are kept open for plugging. The ceramic slurry when applied using a brush Is easily absorbed Into the cells due to gravitational force as well as capillary action. So, the quantity of material discharged Into cells depends on the consistency of slurry made and dimension of the cefts. For plugging of green honeycombs the ceramic slurry applied is very small In quantity In order to avoid any softening of ceR walls. Also, N Is required to get a thin coat of slurry on the surface of ceR waRs. To optimize the quantity of slurry being discharged Info the cells, a pick and place mechanism can also be used where material flow can be controlled. A small quantity of slurry is picked and released into the cells selected for plugging as -13- shown In Fig 6. During (hi* process aft- Is blown from the other end of the channel in which slurry Is released to achieve e required length of slurry coating from the end face of the cells. The air blown from the other end of the channels also Increases the evaporation of water present In slurry. Thus, a very small quantity of water remains in the slurry coated on the honeycomb cell walls and which is not adequate to diffuse into the cell waifs thereby preventing the softening of ceH watts. Plug also may be soaked with slurry by wing truth or other moans. The plugs formed are now inserted into the cells fully to match one of the end surfaces of the plugs to the end face of the honeycomb. The method of masking and then plugging of cefe is done on the other end face of the honeycomb as explained earlier in such a way that the celts which are plugged on opposite side are open at tWs end. -14- WE CLAIM: 1. A method for selective seating of channels In ceramic honeycomb structure comprising, forming dried green plugs of ceramic material, followed by preparing a ceramic slurry containing a binder, selectively applying said slurry into the cells of a honeycomb structure, and sealing the same by inserting the plugs. 2. The method wherein the ceramic material used for plugging has a thermal expansion similar to that of the honeycomb. 3. The method as claimed In claims 1 and 2, wherein the material used for plug, slurry and honeycomb is selected from cordiertite, sicon carbide, sWcon nitride, muNite, alumina and aluminium tianate and zirconia. 4. The method as claimed in claim 1, wherein the step of preparing ceramic plugs comprises charging a plastic ceramic mix of plugging material into the channels of a plug forming apparatus and drying ft. 5. The method as claimed in claim 4, wherein said plug forming apparatus is a tired honeycomb. 6. . The method as claimed In claim 5, wherein said fired honeycomb Is produced from honeycombs to be plugged, -15- 7. The process as claimed In claim 1, wherein said ceramic honeycomb has 10 to 600 cells par square inch, preferably 100 to 400 cells per square inch. 8. The method as claimed in claim 1, wherein the cross section of the celts in the honeycomb structure can be square, circular, rectangular or the Wee. Dated this 26th day of DECEMBER, 2005.

Documents:

01183-kol-2005-claims.pdf

01183-kol-2005-description complete.pdf

01183-kol-2005-drawings.pdf

01183-kol-2005-form 1.pdf

01183-kol-2005-form 2.pdf

01183-kol-2005-form 3.pdf

1183-KOL-2005-FORM-27-1.pdf

1183-KOL-2005-FORM-27.pdf

1183-kol-2005-granted-abstract.pdf

1183-kol-2005-granted-claims.pdf

1183-kol-2005-granted-correspondence.pdf

1183-kol-2005-granted-description (complete).pdf

1183-kol-2005-granted-drawings.pdf

1183-kol-2005-granted-examination report.pdf

1183-kol-2005-granted-form 1.pdf

1183-kol-2005-granted-form 18.pdf

1183-kol-2005-granted-form 2.pdf

1183-kol-2005-granted-form 3.pdf

1183-kol-2005-granted-gpa.pdf

1183-kol-2005-granted-reply to examination report.pdf

1183-kol-2005-granted-specification.pdf