Title of Invention	AN IMPROVED METHOD FOR MAKING HONEYCOMB WXTRUSION DIE AND A PROCESS FOR PRODUCING CERAMIC HONEYCOMB STRUCTURES USING THE SAID DIE
Abstract	Abstract The invention disclosed relates to a process for forming oxide based dense ceramic composite coatings on reactive metal and alloy bodies. The process involves suspension of at least two reactive metal or alloy bodies in a special chamber through which the electrolyte is continuously circulated. Thyristor controlled, modified shaped wave multiphase alternating current power supply is applied across the said bodies and applied electric current is slowly increased to till the required current density is achieved and then maintained constant throughout the process. Electric potential is further increased gradually to compensate increased resistance of the coating. Thickness of the coating formed on the said bodies is monitored by the time for which above process is continued. The invention also relates to an apparatus for carrying out the above-defined process. The coatings obtained according to the present invention are found to exhibit higher density and excellent wear resistance.

Title of Invention

AN IMPROVED METHOD FOR MAKING HONEYCOMB WXTRUSION DIE AND A PROCESS FOR PRODUCING CERAMIC HONEYCOMB STRUCTURES USING THE SAID DIE

Abstract

Abstract The invention disclosed relates to a process for forming oxide based dense ceramic composite coatings on reactive metal and alloy bodies. The process involves suspension of at least two reactive metal or alloy bodies in a special chamber through which the electrolyte is continuously circulated. Thyristor controlled, modified shaped wave multiphase alternating current power supply is applied across the said bodies and applied electric current is slowly increased to till the required current density is achieved and then maintained constant throughout the process. Electric potential is further increased gradually to compensate increased resistance of the coating. Thickness of the coating formed on the said bodies is monitored by the time for which above process is continued. The invention also relates to an apparatus for carrying out the above-defined process. The coatings obtained according to the present invention are found to exhibit higher density and excellent wear resistance.

Full Text	The present invention relates to a method for fabricatin'g honeycomb extrusion die useful for making ceramic honeycomb structures. This invention particularly relates to a novel method in which a fixture useful to make honeycomb extrusion die has been designed and fabricated. This invention also relates to the die so fabricated. This invention also relates to a simple and cost effective process of making honeycomb dies using the said fixture. The die made by the process of the present invention is useful for producing honeycomb structure of different materials such as quite, cordierite-mullite zirconia, spinel, zirconia- spinel, fly-ash, fly-ash-cement, silicon carbide and silicon nitride suitable for diverse applications. In addition, the extrusion die made according to the method of the present invention is useful for extruding honeycomb structures of different configurations, shapes, cell densities, open frontal areas, especially suitable for shock attenuation described in our co-pending Indian patent application no. 976/MAS/98 dated 6"' June 1998 and Energy efficient air heaters described in our co-pending application no. 30/MAS/99, dated 8"^ July 1999. BACK GROUND OF THE INVENTION Ceramic honeycombs can be engineered to achieve a unique combination of thermal, mechanical, electrical and acoustic properties depending on the three variables such as: a) relative density (p/p') where p is the density of the honeycomb divided by the density of solid, p^ by which it is made of, b) cell wall material and, c) the geometry of the cells (i.e., the cell size, prismatic or polyhedral etc.,). Because of this flexibility in design and hence in properties, these honeycombs offer great potential for a variety of applications such as molten metal filters, shock mitigation, energy conservation, light weight structures, biotechnology, thermal protection system tiles, etc. They play a crucial role as a catalyst support for automotive emission control of CO, NOx and hydrocarbons. It is also used as diesel exhaust filter where in addition to removing gaseous pollutants, the honeycomb is also critical in removing particulate from gas stream. It also serves to control gaseous and particulate emissions in stationary applications such as coal burning power plants, primarily for the removal of NOx. Hence, considering the importance of honeycomb structures for various application areas and also extrusion dies being the key component in producing the honeycomb structures a need was felt to undertake the research towards the development of extrusion dies Honeycomb dies are mainly composed of a monolithic structure with a large number of openings on one side, which coincides, with the cross section of a grid on the other side. The perfection of honeycomb structure extruded using the die as a function of how the opening on one side coincides with the cross section of the grid on the other side. This in turn allows uniform distribution of plastisized material to form the honeycomb structure. The fabrication of dies to form honeycomb structures is disclosed in several patents using Electrode Discharge Machining (EDM) techniques. The EDM process is a metal removal technique, which uses electricity to erode the material from a work specimen. U.S. Patent no. 3, 905,743 describes a method to fabricate the honeycomb extrusion honeycomb die which involves wire cutting of grids using wire electrode discharge machining on one side of the base plate followed by the fabrication of electrodes as per dimensions and spark erosion by electrode discharge machining to form the feed holes on the other side to communicate with the grids. US Patent no. 5, 630, 951 discloses an improved process of Electrode Discharge Machining for the fabrication of extrusion dies. This process involves the flushing of dielectric fluid through the feed holes to flush the machined material from the die body and the slot being formed by the travelling wire which in turn reduces the wire breakage and also improved performance of the die during use. us patent 5,702,659 describes a method for fabricating the honeycomb extrusion dies using abrasive grinding wheel to form slots and drilling of feed holes by gun drilling and electrochemical machining methods. These disclosed processes of making dies employing capital-intensive highly sophisticated machines based on Electrode Discharge Technique will contribute to a large extent towards the cost of fabrication of extrusion die. Accordingly, it would be beneficial if the use of highly sophisticated and capital intensive equipments are eliminated with a specially designed fixture which will help in locating and drilling the feed holes perfectly at the cross section of the grid using a conventional ordinary drilling machine. Since, the extrusion dies are the component in producing honeycomb structures and looking at the vast potential for the vide range of applications for these honeycomb structures. It is very important and advantages if a simple and cost effective process can be developed for the fabrication of these dies. OBJECTIVES OF THE INVENTION Therefore, the primary objective of the present invention is to develop a cost-effective method to fabricate an extrusion die for making ceramic honeycomb structures. Another objective of the present invention is to design and fabricate a fixture for feed holes location on one side of the die matching with the cross section of the grid on the other side. Another objective of the present invention is to develop a method to fabricate a fixture for drilling the feed holes on the die using a conventional drilling machine. Still another objective of the present invention is to provide a method of producing ceramic honeycomb structures from mullite, cordierite-mullite, zirconia, spinel, zirconia-spinel, fly-ash, cement, fly-ash and cement mixture, silicon carbide and silicon nitride using the extrusion dies fabricated following the method of the present invention. DESCRIPTION OF THE INVENTION The present invention has been developed based on the finding that if a fixture is designed and is properly used for locating and drilling of the feed holes on one side with respect to the cross section of the grid on the other side and thus, it is possible to fabricate the extrusion die employing the simple and conventional machining processes. Accordingly, the present invention provides an improved process for making honeycomb structures particularly from ceramic materials which comprises: (a) making a base plate of aluminum alloy, steel, brass, etc., of the desired shape and dimensions (b) milling the said plate in to slots by knowing methods along the step A of Fig. 1 in perpendicular directions to form a uniform grid pattern as depicted in Fig. 2. (c) Making a fixture by press fitting two metal strips into the perpendicular slits of a metallic block so as to obtain a ® shaped configuration as shown in Fig. 3 which in turn align the slit width on the preform of the die. (d) Fixing of the fixture on the moving table of a drilling machine in such a way so as to align the tip of the drill bit with centre of the © shaped elevation. (e) Placing of the slitted preform obtained in step (b) over the fixture obtained in step (c) and inserting the elevated © shaped stripes into the intersection of the grid of the said base plate. (f) Drilling feed holes on the other side of the said plate to a depth till © sign is visible through the centre of the hole, and (g) Drilling an array of equivalent through and through feed holes along the diameter of the junction of two steps which determines the formation of the peripheral wall of the honeycomb while extrusion. The desired process of making the die starts with conventional machining of stainless steel, aluminum alloy, gun metal or brass, which is machined into a base plate with steps A and B of desired shape depending on the shape of the honeycombs to be produced. Schematic diagram of a typical base body is shown in Fig. 1 of the drawing accompanying this specification. In the Fig. 1, Fig 1 (a) represents the front view and Fig. 1 (b) represents the sectional view. Further, the base plate has to be slitted into square grids along surface of step A by using a slitting saw to form a uniform grid pattern as depicted in Fig. 2. The dimensions of the grids and slots can be based on the configuration of the honeycombs to be produced. In order to drill the slitted base plate, the first step involves the fabrication of a fixture plate with a ® shaped elevation at the centre by press fitting two strips in to the perpendicular slits of the metallic block, which in turn aligns with the thickness of the slot on the preform of the die so as to hold the slitted preform firmly while drilling the holes this is illustrated in Fig. 3. In the Fig. 3, Fig. 3 (a) represents the front view and Fig. 3 (b) represents the side view. The above fixture is fitted to the moving table of a drilling machine in such a way that the drill bit tip is aligned with the intersection point of ® shaped elevation. Now the slitted base plate is placed over the above fixture in such a way that the ® shaped elevation exactly inserted into the intersection of the slits. Hence, it is possible to locate perfectly the intersection of the slit while drilling the hole on the other side. Now drilling is carried out using the conventional high-speed drilling machine using steel drill bits depending on the diameter of the slit width of the die. The drilling is carried out till the ® sign is visible through the centre of the hole as depicted in Fig.4. After the completion of the first feed hole, further holes are drilled by locating the remaining slit intersections into the fixture till all the slit intersections are connected with the feed holes. Finally, an array of equidistant through and through feed holes are drilled along the diameter of the junction of two steps which forms the peripheral wall of the honeycomb. Thus, completed die is press fitted in such a way that the external periphery of the step A match s with the internal diameter which in turn guide the extrudate under pressure. Further, the peripheral wall of the honeycomb can be controlled to the desired thickness by adjusting the gap between the external diameter of step A and the internal diameter of the extrusion ring. The die along with the extrusion ring can be fitted to the extrusion collar, which in turn fix at the mouth of the extrusion barrel of a conventional extruder. Hence, die-body, ring and collar form the complete die assembly for the extrusion of honeycomb structures as depicted in Figure 5. In the Fig. 5, Fig. 5 (a) represents the extrusion barrel, Fig. 5 (b) represents the extrusion die. Fig. 5 (c) represents the guided ring and Fig. 5 (d) represents the extrusion collar. The second aspect of the present invention lies in extruding honeycomb structures using ceramic formulations such as mullite, cordierite-muUite, zirconia, spinel, zirconia-spinel, fly-ash, fly-ash-cement, silicon carbide and silicon nitride suitable for diverse applications. The ceramic materials or precursors in corresponding stoichiometries are kneaded together with the organic binders such as methylcellulose, carboxy methyl cellulose, hydroxy methyl cellulose, etc., and plasticizer such as polyethylene glycol, glycerol, ethylene glycol, etc., to form an extrudable plasticized dough. The plastisized ceramic dough can further transferred to the extrusion assembly which on extrusion through the said die of present invention results in the formation of honeycomb structure which can be microwave dried and is subjected to sintering at the temperatures depending on the material of construction as illustrated vide examples detailed below. The Examples given below are provided only to illustrate the present invention and therefore should not be construed as limiting the scope of the invention. FABRICATION OF EXTRUSION DIES Example 1 A base plate of 139.5 mm dia and thickness of 10.0 mm was machined out of 7075 aluminum alloy block having approximate chemical composition of Al-90% (min), Si-0.40% (max), Fe-0.50% (max), Cu-1.20-2.00, Mn-0.3% (max), Mg-2.10-2.90%, Cr-0.10-0.11%, Zn-5.10-6.40%, Ti+Zr-0.20% (max). The base plate was machined to obtain a configuration where the step A shown in Fig. 1 (b) having oval shape having major axis of 123.7 mm & minor axis of 83.5 mm and thickness of 3.85 mm and a circular step B shown in Fig. 1 (b) having diameter of 120 mm and thickness of 6.15 mm. Using the slitting saw of thickness 0.70 mm, 28 numbers of slits having depths of 4.0 mm each were made along the major axis on the surface of the step A maintaining a gap of 3.0 mm between each of two adjacent slits with a universal milling machine. Now the base plate was rotated by 90° and 19 numbers of slits with above dimensions were made again so as to achieve a uniform grid pattern with 36 spikes per square inch. A fixture with a ® configuration with an elevation of 3.0 mm, made by press fitting of two stainless steel strips of 0.65 mm thickness into two perpendicular slots made at the centre on the fixture, was bolted on a moving table of the conventional high speed drilling machine in such a way that the intersection of ® shaped configuration of the fixture exactly aligns with the tip of the drill bit of dia. 2.5 mm. Now the slitted base plate is placed on the fixture in such a way that ® shape configuration inserts into the slits, made at the surface of step A. Using a conventional high speed-drilling machine, a hole of dia 2.5 mm and was drilled up to depth till a ® shaped sign is visible through the feed hole. Now further drilling was carried out as described above till all the slit intersections with © sign are connected with the feed holes. Now an array of feed holes of diameter 2.4 mm each were drilled maintaining a spacing of 1.4 mm between each holes along the diameter of the junction of two steps which allows the extra flow of the dough to form the peripheral wall of the honeycomb while extrusion. To fabricate the extrudate guide ring, a circular disc of outer diameter (O.D) 140.2 mm and thickness of 6.0 mm was machined out of a circular stainless steel (SS304) block of O.D. 156 mm using a conventional lathe machine. A configuration of oval shape with dimension having major axis of 125.0 mm and the minor axis of 85.0 mm was milled out using a conventional milling machine with rotary table attachment in such a fashion so as to fix the die body into the extrudate guide ring. During extrusion the die along with the extrudate guide ring can be fitted to the mouth of the conventional cylinder with a collar for producing the honeycomb structures as shown in figure 5. Example 2 A base plate of 120 mm dia and thickness of 9.75 mm was machined out of 7075 aluminum alloy with the chemical composition of Al-90% (max), Si-0.41% (max), Fe-0.5% (max), Cu-1.20% (max), Mn-0.3% (max), Mg-2.10% (max), Cr-0.10% (max), Zn-5,10% (max) and Ti+Zr-0.2% (max). The base plate was machined to obtain a configuration similar to the one shown in Fig. 1 (b) where the step A having diameter of 110 mm and thickness of 4.0 mm and step B having diameter of 120 mm and thickness of 5.75 mm. Using the slitting saw of thickness 0.20 mm, 80 numbers of slits having depth of 4.0 mm each were made on the surface of the step A while maintaining a gap of 0.91 mm between each of two adjacent slits with a universal milling machine. Now the base plate was rotated by 90° and 80 numbers of slits with above dimensions were made again so as to achieve a uniform grid work with 361 spikes per square inch. A fixture with a ® configuration with an elevation of 3.0 mm, made by press fitting of two stainless steel strips having 0.18 mm thicknesses each into two perpendicular slots made at the centre on the fixture, was bolted on moving table of the conventional high speed drilling machine in such a way that the intersection of ® shaped configuration of the fixture exactly align with tip of the drill bit of dia. 0.9 mm. Now the slitted base plate is placed on the fixture in such a way that ® shape configuration inserts into the slits, made at the surface of step A. Using conventional high speed drilling machine, a hole of dia 1.0 mm was drilled up to the depth till a ® shaped sign is visible through the feed hole. Now, further drilling was carried out as described above till all the slit intersections with © sign are connected with the feed holes. Now, an array of feed holes of diameter 0.8 mm each was drilled maintaining a spacing of 0.9mm diameter of the junction of two steps which allows the extra flow of the dough to form the peripheral wall of the honeycomb while extrusion. To fabricate the extrudate guide ring a circular ring of outer diameter 128 mm. Inner diameter of 111 mm, width of 13.3 mm and thickness of 9.3 mm was fabricated by machining of a stainless steel (SS304) tube. A step of outer diameter 119.0 mm and depth of 6.8 mm was cut along the inner diameter of the ring to fix the die body into the step. During extrusion, the die along with the extrudate guide ring can be fitted to the mouth of the conventional cylinder with a collar for producing the honeycomb structures as shown in figure 5. EXTRUSION OF HONEYCOMB STRUCTURES USING THE DIE OF THE PRESENT INVENTION Example 3. Preparation of silicon carbide (SiC) Honeycombs SiC powder having a particle size ranging from 2 to 10 \|j,m along with 1 - 6 wt. % of phenolic binder, 2- 5 wt. % of methyl cellulose (MC) binder, 1- 3 wt. % of polyethylene glycol (PEG) and 20- 30 wt. % of water as a plasticizing medium were kneaded in a sigma kneader to obtain the extrudable dough. The dough was placed in an extrusion cylinder and was extruded through the die fabricated according to the method described in the Example 1 at a pressure of 10 kg/cm^ and with an ejection rate of 50mm/min. The green honeycombs were then dried in a microwave oven, which were debindered initially at 550 °C under nitrogen flow and finally sintered at temperatures between 1800-2100 °C in vacuum. The resulting silicon carbide honeycombs are found to have an oval shape with dimensions of 93.6 mm major axis and minor axis of 62 mm with the wall thickness of 0.62 mm and having square channels of configuration of 2.3 mm x 2.3 mm after sintering. The cell density of the honeycomb structure prepared was found to be 54-channels/ square inch. The bulk density, apparent porosity and water absorption of the sintered silicon carbide honeycomb produced are found to be 1.529 g/cc, 51.45 %, 33,641 %, respectively. Example 4: Preparation of mullite (SAbOa.ZSiOi) honeycombs Mullite composition was formulated from clay and alumina along with 1- 5 wt. % of MC, 2 - 3 wt. % of PEG and 20 - 25 wt. % of water as a plasticizing medium were kneaded in a sigma kneader to achieve the extrudable dough. The dough was placed in an extrusion cylinder and was extruded through the die fabricated by the method described in the Example! with a pressure of about 10 kg/cm^ and at an ejection rate of 50mm/min. The green honeycombs were then dried in a microwave oven, which were debindered initially at 550 °C and finally sintered at temperatures between 1550 °C for four hours. The resultant mullite honeycombs are found to have an oval shape with dimensions of 111 mm major axis and minor axis of 74 mm and the wall thickness of 0.74 mm with the configuration of channels of 2.7 mm x 2.7 mm after sintering. The cell density of the honeycomb structure prepared was found to be 41channes/ square inch. The bulk density, apparent porosity and water absorption of the sintered mullite honeycomb are found to be 1.554 g/cc, 44.716 %, 28.770 %, respectively. Example 5: Preparation of zirconia (ZrOi) honeycombs Commercially available fine zirconia powder was mixed along with 1.5 - 3 wt. % of MC, 1.5 - 3 wt. % of PEG and 20 - 30 wt. % of water as a plasticizing medium was kneaded in a sigma kneader to achieve the extrudable dough. The dough was placed in an extrusion cylinder and was extruded through the die fabricated according to the method described in the Example lat a pressure of about 10 kg/cm^ and at an ejection rate of 40mm/min. The green honeycombs were then dried in a microwave oven, which were debindered initially 550 °C and finally sintered at temperatures between 1600 °C for three hours. The zirconia honeycombs structure so prepared are found to have an oval shape with dimensions of 87.6 mm major axis and minor axis of 58.4mm and the wall thickness of 0.65 mm with a square channel configuration of 2.1 mm x 2.1 mm after sintering. The cell density of the sample was found to be 58-channels/ square inch. The bulk density, apparent porosity and water absorption of the sintered zirconia honeycomb are found to be 4.785 g/cc, 17.823 %, 3.724 %, respectively. Example 6: Preparation of MgAl204 spinel honeycombs Initially a stoichiometric mixture of caustic magnesia and aluminum hydroxide was calcined at temperatures between 1000 and 1300 °C for 1 to 5 hours to get required spinel formation. Thus obtained spinel fine powder was dry milled in a ball mill to bring down the particle size to required range (5-15 \|j,m). Ground spinel powder was mixed along with 1-4 wt. % of MC, 1-3 wt. % of PEG and 20 - 30 wt. % of water and the mixture was kneaded in a sigma kneader to achieve the extrudable dough. The dough was placed in the extrusion cylinder and was pressed through the die fabricated according to the method described in example 2 with a pressure of 8- 10 kg/cm^ at an ejection rate of 100 mm/min. The green honeycombs were dried in microwave oven and debindered at 550 °C and then sintered at 1600 °C for 2 hours. The resultant spinel honeycombs are found to have an oval shape with dimensions of 87.6 mm major axis and minor axis of 58.4mm and the wall thickness 0.65 mm with a square channel configuration of 2.1 mm x 2.1 mm after sintering. The cell density of the spinel honeycomb was found to be 58-channels/ square inch. The bulk density, apparent porosity and water absorption of the sintered spinel honeycomb are found to be 3.051 g/cc, 6.713 %, 2.200 %, respectively. Example 7: Preparation of zirconia- spinel (Zr02-MgAl204) honeycombs Initially a stoichiometric mixture of caustic magnesia and aluminum hydroxide was calcined at temperatures between 1000 and 1300 °C for 1 to 5 hours to get required spinel formation. Thus obtained spinel powder was dry milled in a ball mill to bring down the particle size to required range (5-15 \|im). The fine spinel powder so prepared along with commercially available zirconia powders or baddeleyite and 1-4 wt. % of MC, 1-3 wt. % of PEG and 20 - 30 wt. % of water and the mixture was kneaded in a sigma kneader to achieve the extrudable dough. The dough was placed in the extrusion cylinder and was extruded through the die fabricated according to the method described in Example 2 with a pressure of about 10 kg/cm^ with an ejection rate of 90 mm/min. The green honeycombs were debindered and then sintered at 1600 °C for 3 hours. The zirconia - spinel honeycombs so prepared were found to have an oval shape with dimensions of 78 mm major axis and minor axis of 50.4 mm and the wall thickness of 0.54 mm with a square channel configuration of 1.8 mm x 1.8 mm. The cell density of the zirconia-spinel honeycomb was found to be 67-channels/ square inch. The bulk density, apparent porosity and water absorption of the sintered zirconia-spinel (60:40 mole %) honeycomb are found to be 3.155 g/cc, 5.45 %, 3.641 %, respectively. Example 8: Preparation of cement honeycombs Commercially available portland white cement along with 1-4 wt. % of methyl cellulose, 1-3 wt. % of PEG and 20 - 30 wt. % of water were mixed together and the mixture was kneaded in a sigma kneader to achieve the extrudable dough and was placed in the extrusion cylinder and was extruded through the die fabricated according to the method described in example 2. Thus obtained cement honeycomb was allowed to dry and the resultant honeycombs were cured at atmospheric temperature and pressures for one week time while spraying water for setting. The resultant cement honeycombs were found to have an oval shape with dimensions of 120 mm major axis and minor axis of 80 mm and the wall thickness 0.8 mm with a square channel configuration of 3 mm x 3 mm. The cell density of the sample was found to be 36-channels/ square inch. The bulk density, apparent porosity and water absorption of the cement honeycomb after curing at room temperature for a week time by spaying water are found to be 1.658 g/cc, 32.029 %, 19.311 %, respectively. Example 9: Preparation of cement- fly-ash honeycombs Various amounts of commercially available portland white cement ranging from 30 - 50 % and fly-ash along with 1-4 wt. % of MC, 1-3 wt. % of PEG and 20 - 30 wt. % of water were mixed and the mixture was kneaded in a sigma kneader to achieve an extrudable dough placed in the extrusion cylinder and was extruded through the die fabricated according to the method described in Example 2. Thus obtained cement-fly ash honeycomb was allowed to dried and cured at atmospheric temperature and pressures for one-week time while spraying water. The extruded fly ash - cement honeycombs so prepared were found to have an oval shape with dimensions of 120 mm major axis and minor axis of 80 mm and the wall thickness of 0.8 mm with a square channel configuration of 3 mm x 3 mm. The cell density of the sample was found to be 36-channels/ square inch. The bulk density, apparent porosity and water absorption of the cement honeycomb after curing at room temperature for a week time by spaying water are found to be 1.274 g/cc, 44.181 %, 34.659 %, respectively. Example 10: Preparation of silicon nitride Si3N4 honeycombs Commercially available Si3N4 powder was used to make Si3N4 honeycomb. Silicon nitride powder along with 1-4 wt. % of MC, 1-3 wt. % of PEG and 20 - 30 wt. % of water were mixed and the mixture was kneaded in a sigma kneader to achieve the extrudable dough placed in the extrusion cylinder and was extruded through the die fabricated according to the method described in Example 2. The resultant green honeycombs were then dried in a microwave oven, which were debindered at 550 °C in nitrogen and finally sintered at temperatures between 1800 to 2100 °C in vacuum. The silicon nitride honeycombs so prepared were found to have an oval shape with dimensions of 98 mm major axis and minor axis of 94 mm and the wall thickness of 0.70 mm with a square channel configuration of 2.4 mm x 2.4 mm. The cell density of the sample was found to be 50-channels/ square inch. Example 11: Preparation of mullite-cordierite (3Al203.2Si02-2Mg0.2.Al203.5Si02) honeycombs Cordierite-Mullite honeycombs were formulated fi^om clay, talc and alumina along with 1-4 wt. % of MC, 1-3 wt. % of PEG and 20 - 30 wt. % of water and the mixture was kneaded in a sigma kneader to achieve the extrudable dough. The dough was i placed in cylinder and was pressed through the die fabricated according to the method described in Example 2 with a pressure of about 15 kg/cm^ at an ejection rate of 30 mm/min. The green honeycombs were dried using microwave oven and debindered at 550 °C and sintered at 1400 °C in air. The mullite - cordierite honeycombs so prepared were found to be circular in shape with diameter of 104 mm and the wall thickness of 0.22 mm with a square channel configuration of 0.9 mm x 0.9mm. The cell density of the sample was found to be 361-channels/ square inch. The bulk density, apparent porosity and water absorption of the sintered cordierite-mullite honeycomb are found to be 1.561 g/cc, 44.938 %, 28.775 %, respectively. The mullite - cordierite honeycombs so prepared were found to be circular in shape with diameter of 104 mm and the wall thickness of 0.22 mm with a square channel configuration of 0.9 mm x 0.9mm. The cell density of the sample was found to be 361-channels/ square inch. The bulk density, apparent porosity and water absorption of the sintered cordierite-mullite honeycomb are found to be 1.561 g/cc, 44.938 %, 28.775 %, respectively. Example 12: Preparation of fly-ash honeycombs F\|y-ash, a waste material obtained from a thermal power plat was mixed along with 1-4 wt. % of MC, 1-3 wt. % of PEG and 20 - 30 wt. % of water and the mixture was kneaded in a sigma kneader to achieve the extrudable dough. The dough was placed in the extrusion cylinder and was pressed through the die prepared by the method described in Example 2 with a pressure of 8- 10 kg/cm^ at an ejection rate of 100 mm/min. The green honeycombs were dried in microwave oven and debindered at 550 °C and then sintered at 1350 °C for 2 hours. The fly-ash honeycombs so prepared were found to have an oval shape with dimensions of 87.6 mm major axis and minor axis of 58.4mm and the wall thickness 0.65 mm with a square channel configuration of 2.1 mm x 2.1 mm. The cell density of the sample was found to be 58-channels/ square inch. The bulk density, apparent porosity and water absorption of the fly-ash honeycomb after sintered at 1200 °C for 2 hours are found to be 2.065 g/cc, 6.917 %, 3.348 %, respectively. We Claim 1. An improved process for making die useful for making honeycomb structures particularly from ceramic materials which comprise (a) making a base plat of aluminum alloy steel, brass, etc., of circular, hexagonal or oval shape and dimensions (b) Milling the said plate into slots by known methods along the step A of Fig. 1 in perpendicular direction to form a uniform grid pattern as depicted in Fig. 2. (c) making a fixture by press fitting two metal strips into the perpendicular slits of a metallic block so as to obtain a ® shaped configuration as shown in Fig. 3 which in turn align the slit width on the preform of the die. (d) Fixing the fixture on the moving table of a drilling machine in such a way so as to align the tip of the drill bit with the centre of the © elevation. (e) placing the slated preform obtained in step (b) over the fixture obtained in step (c) and inserting the elevated ® shaped strips into the intersection of the grid of the said base plate (f) drilling feed holes on the other side of the said base plate to a depth till © sign is visible through the centre of the hole and (g) drilling an array of equidistant through and through feed holes along the diameter of the junction of two steps which determines the formation the peripheral wall of the honeycomb while extrusion 2. An improved method for making honeycomb structures using the die fabricated as claimed in claim 1 which comprises, (a) making an extrudable dough of appropriate materials particularly ceramic materials with a binder and a plasticizer (b) extruding the dough through a die made as claimed in claim 1 of the desired shape and configuration (c) subjecting the resultant honeycomb to heat treatment and (d) cooling the resultant honeycomb structure 3. An improved process as claimed in claim 2 wherein the ceramic material used for making the dough is selected from muUite, cordierite-muUite, zirconia, spinel, zirconia-spinel, fly-ash, fly-ash cement, silicon carbide and silicon nitride. 4. An improved process as claimed in claims 2 &3 wherein the binder such as methyl cellulose, carboxy methyl cellulose and hydroxy methyl cellulose are used. 5. An improved process as claimed in claims 2 & 3 wherein the plasticizer employed is selected from ethylene glycol, polyethylene glycol and glycerol are used. 6. An improved process as claimed in claims 2 to 3 wherein the heat treatment of the extruded product is effected at the desired temperature ranges as specified wide examples 3 to 12 depending on the processing materials. 7. A process for the making a die useful for making honeycomb structures, particularly of ceramic materials substantially as herein described with reference to the Example 1 & 2, and in Figs. 1 to 5 of the drawing accompanying this specification. An improved method of making honeycomb structure particularly of ceramic materials substantially as herein described with reference to the Examples 3 to 12.

Full Text

The present invention relates to a method for fabricatin'g honeycomb extrusion die useful for making ceramic honeycomb structures. This invention particularly relates to a novel method in which a fixture useful to make honeycomb extrusion die has been designed and fabricated. This invention also relates to the die so fabricated. This invention also relates to a simple and cost effective process of making honeycomb dies using the said fixture. The die made by the process of the present invention is useful for producing honeycomb structure of different materials such as quite, cordierite-mullite zirconia, spinel, zirconia- spinel, fly-ash, fly-ash-cement, silicon carbide and silicon nitride suitable for diverse applications.
In addition, the extrusion die made according to the method of the present invention is useful for extruding honeycomb structures of different configurations, shapes, cell densities, open frontal areas, especially suitable for shock attenuation described in our co-pending Indian patent application no. 976/MAS/98 dated 6"' June 1998 and Energy efficient air heaters described in our co-pending application no. 30/MAS/99, dated 8"^ July 1999.
BACK GROUND OF THE INVENTION
Ceramic honeycombs can be engineered to achieve a unique combination of thermal, mechanical, electrical and acoustic properties depending on the three variables such as: a) relative density (p*/p') where p* is the density of the honeycomb divided by the density of solid, p^ by which it is made of, b) cell wall material and, c) the geometry of the cells (i.e., the cell size, prismatic or polyhedral etc.,). Because of this flexibility in design and hence in properties, these honeycombs offer great potential for a variety of applications such as molten metal filters, shock mitigation, energy conservation, light weight structures, biotechnology, thermal protection system tiles, etc. They play a crucial role as a catalyst support for automotive emission control of CO, NOx and hydrocarbons. It is also used as diesel exhaust filter where in addition to removing gaseous pollutants, the honeycomb is also critical in removing particulate from gas stream. It also serves to

control gaseous and particulate emissions in stationary applications such as coal burning power plants, primarily for the removal of NOx.
Hence, considering the importance of honeycomb structures for various application areas and also extrusion dies being the key component in producing the honeycomb structures a need was felt to undertake the research towards the development of extrusion dies
Honeycomb dies are mainly composed of a monolithic structure with a large number of openings on one side, which coincides, with the cross section of a grid on the other side. The perfection of honeycomb structure extruded using the die as a function of how the opening on one side coincides with the cross section of the grid on the other side. This in turn allows uniform distribution of plastisized material to form the honeycomb structure.
The fabrication of dies to form honeycomb structures is disclosed in several patents using Electrode Discharge Machining (EDM) techniques. The EDM process is a metal removal technique, which uses electricity to erode the material from a work specimen. U.S. Patent no. 3, 905,743 describes a method to fabricate the honeycomb extrusion honeycomb die which involves wire cutting of grids using wire electrode discharge machining on one side of the base plate followed by the fabrication of electrodes as per dimensions and spark erosion by electrode discharge machining to form the feed holes on the other side to communicate with the grids.
US Patent no. 5, 630, 951 discloses an improved process of Electrode Discharge Machining for the fabrication of extrusion dies. This process involves the flushing of dielectric fluid through the feed holes to flush the machined material from the die body and the slot being formed by the travelling wire which in turn reduces the wire breakage and also improved performance of the die during use.

us patent 5,702,659 describes a method for fabricating the honeycomb extrusion dies using abrasive grinding wheel to form slots and drilling of feed holes by gun drilling and electrochemical machining methods.
These disclosed processes of making dies employing capital-intensive highly sophisticated machines based on Electrode Discharge Technique will contribute to a large extent towards the cost of fabrication of extrusion die. Accordingly, it would be beneficial if the use of highly sophisticated and capital intensive equipments are eliminated with a specially designed fixture which will help in locating and drilling the feed holes perfectly at the cross section of the grid using a conventional ordinary drilling machine. Since, the extrusion dies are the component in producing honeycomb structures and looking at the vast potential for the vide range of applications for these honeycomb structures. It is very important and advantages if a simple and cost effective process can be developed for the fabrication of these dies.
OBJECTIVES OF THE INVENTION
Therefore, the primary objective of the present invention is to develop a cost-effective method to fabricate an extrusion die for making ceramic honeycomb structures.
Another objective of the present invention is to design and fabricate a fixture for feed holes location on one side of the die matching with the cross section of the grid on the other side.
Another objective of the present invention is to develop a method to fabricate a fixture for drilling the feed holes on the die using a conventional drilling machine.
Still another objective of the present invention is to provide a method of producing ceramic honeycomb structures from mullite, cordierite-mullite, zirconia, spinel, zirconia-spinel, fly-ash, cement, fly-ash and cement mixture, silicon carbide and

silicon nitride using the extrusion dies fabricated following the method of the present invention.
DESCRIPTION OF THE INVENTION
The present invention has been developed based on the finding that if a fixture is designed and is properly used for locating and drilling of the feed holes on one side with respect to the cross section of the grid on the other side and thus, it is possible to fabricate the extrusion die employing the simple and conventional machining processes. Accordingly, the present invention provides an improved process for making honeycomb structures particularly from ceramic materials which comprises:
(a) making a base plate of aluminum alloy, steel, brass, etc., of the desired shape and dimensions
(b) milling the said plate in to slots by knowing methods along the step A of Fig. 1 in perpendicular directions to form a uniform grid pattern as depicted in Fig. 2.
(c) Making a fixture by press fitting two metal strips into the perpendicular slits of a metallic block so as to obtain a ® shaped configuration as shown in Fig. 3 which in turn align the slit width on the preform of the die.
(d) Fixing of the fixture on the moving table of a drilling machine in such a way so as to align the tip of the drill bit with centre of the © shaped elevation.
(e) Placing of the slitted preform obtained in step (b) over the fixture obtained in step (c) and inserting the elevated © shaped stripes into the intersection of the grid of the said base plate.
(f) Drilling feed holes on the other side of the said plate to a depth till © sign is visible through the centre of the hole, and
(g) Drilling an array of equivalent through and through feed holes along the diameter of the junction of two steps which determines the formation of the peripheral wall of the honeycomb while extrusion.
The desired process of making the die starts with conventional machining of stainless steel, aluminum alloy, gun metal or brass, which is machined into a base plate

with steps A and B of desired shape depending on the shape of the honeycombs to be produced. Schematic diagram of a typical base body is shown in Fig. 1 of the drawing accompanying this specification. In the Fig. 1, Fig 1 (a) represents the front view and Fig. 1 (b) represents the sectional view.
Further, the base plate has to be slitted into square grids along surface of step A by using a slitting saw to form a uniform grid pattern as depicted in Fig. 2. The dimensions of the grids and slots can be based on the configuration of the honeycombs to be produced.
In order to drill the slitted base plate, the first step involves the fabrication of a fixture plate with a ® shaped elevation at the centre by press fitting two strips in to the perpendicular slits of the metallic block, which in turn aligns with the thickness of the slot on the preform of the die so as to hold the slitted preform firmly while drilling the holes this is illustrated in Fig. 3. In the Fig. 3, Fig. 3 (a) represents the front view and Fig. 3 (b) represents the side view.
The above fixture is fitted to the moving table of a drilling machine in such a way that the drill bit tip is aligned with the intersection point of ® shaped elevation. Now the slitted base plate is placed over the above fixture in such a way that the ® shaped elevation exactly inserted into the intersection of the slits. Hence, it is possible to locate perfectly the intersection of the slit while drilling the hole on the other side. Now drilling is carried out using the conventional high-speed drilling machine using steel drill bits depending on the diameter of the slit width of the die. The drilling is carried out till the ® sign is visible through the centre of the hole as depicted in Fig.4. After the completion of the first feed hole, further holes are drilled by locating the remaining slit intersections into the fixture till all the slit intersections are connected with the feed holes. Finally, an array of equidistant through and through feed holes are drilled along the diameter of the junction of two steps which forms the peripheral wall of the honeycomb. Thus, completed die is press fitted in such a way that the external periphery of the step A match s with the internal diameter which in turn guide the extrudate under pressure. Further, the

peripheral wall of the honeycomb can be controlled to the desired thickness by adjusting the gap between the external diameter of step A and the internal diameter of the extrusion ring.
The die along with the extrusion ring can be fitted to the extrusion collar, which in turn fix at the mouth of the extrusion barrel of a conventional extruder. Hence, die-body, ring and collar form the complete die assembly for the extrusion of honeycomb structures as depicted in Figure 5. In the Fig. 5, Fig. 5 (a) represents the extrusion barrel, Fig. 5 (b) represents the extrusion die. Fig. 5 (c) represents the guided ring and Fig. 5 (d) represents the extrusion collar.
The second aspect of the present invention lies in extruding honeycomb structures using ceramic formulations such as mullite, cordierite-muUite, zirconia, spinel, zirconia-spinel, fly-ash, fly-ash-cement, silicon carbide and silicon nitride suitable for diverse applications.
The ceramic materials or precursors in corresponding stoichiometries are kneaded together with the organic binders such as methylcellulose, carboxy methyl cellulose, hydroxy methyl cellulose, etc., and plasticizer such as polyethylene glycol, glycerol, ethylene glycol, etc., to form an extrudable plasticized dough.
The plastisized ceramic dough can further transferred to the extrusion assembly which on extrusion through the said die of present invention results in the formation of honeycomb structure which can be microwave dried and is subjected to sintering at the temperatures depending on the material of construction as illustrated vide examples detailed below.
The Examples given below are provided only to illustrate the present invention and therefore should not be construed as limiting the scope of the invention.

FABRICATION OF EXTRUSION DIES Example 1
A base plate of 139.5 mm dia and thickness of 10.0 mm was machined out of 7075 aluminum alloy block having approximate chemical composition of Al-90% (min), Si-0.40% (max), Fe-0.50% (max), Cu-1.20-2.00, Mn-0.3% (max), Mg-2.10-2.90%, Cr-0.10-0.11%, Zn-5.10-6.40%, Ti+Zr-0.20% (max). The base plate was machined to obtain a configuration where the step A shown in Fig. 1 (b) having oval shape having major axis of 123.7 mm & minor axis of 83.5 mm and thickness of 3.85 mm and a circular step B shown in Fig. 1 (b) having diameter of 120 mm and thickness of 6.15 mm. Using the slitting saw of thickness 0.70 mm, 28 numbers of slits having depths of 4.0 mm each were made along the major axis on the surface of the step A maintaining a gap of 3.0 mm between each of two adjacent slits with a universal milling machine. Now the base plate was rotated by 90° and 19 numbers of slits with above dimensions were made again so as to achieve a uniform grid pattern with 36 spikes per square inch.
A fixture with a ® configuration with an elevation of 3.0 mm, made by press fitting of two stainless steel strips of 0.65 mm thickness into two perpendicular slots made at the centre on the fixture, was bolted on a moving table of the conventional high speed drilling machine in such a way that the intersection of ® shaped configuration of the fixture exactly aligns with the tip of the drill bit of dia. 2.5 mm. Now the slitted base plate is placed on the fixture in such a way that ® shape configuration inserts into the slits, made at the surface of step A.
Using a conventional high speed-drilling machine, a hole of dia 2.5 mm and was drilled up to depth till a ® shaped sign is visible through the feed hole. Now further drilling was carried out as described above till all the slit intersections with © sign are connected with the feed holes. Now an array of feed holes of diameter 2.4 mm each were drilled maintaining a spacing of 1.4 mm between each holes along the diameter of the junction of two steps which allows the extra flow of the dough to form the peripheral wall of the honeycomb while extrusion.

To fabricate the extrudate guide ring, a circular disc of outer diameter (O.D) 140.2 mm and thickness of 6.0 mm was machined out of a circular stainless steel (SS304) block of O.D. 156 mm using a conventional lathe machine. A configuration of oval shape with dimension having major axis of 125.0 mm and the minor axis of 85.0 mm was milled out using a conventional milling machine with rotary table attachment in such a fashion so as to fix the die body into the extrudate guide ring. During extrusion the die along with the extrudate guide ring can be fitted to the mouth of the conventional cylinder with a collar for producing the honeycomb structures as shown in figure 5.
Example 2
A base plate of 120 mm dia and thickness of 9.75 mm was machined out of 7075 aluminum alloy with the chemical composition of Al-90% (max), Si-0.41% (max), Fe-0.5% (max), Cu-1.20% (max), Mn-0.3% (max), Mg-2.10% (max), Cr-0.10% (max), Zn-5,10% (max) and Ti+Zr-0.2% (max). The base plate was machined to obtain a configuration similar to the one shown in Fig. 1 (b) where the step A having diameter of 110 mm and thickness of 4.0 mm and step B having diameter of 120 mm and thickness of 5.75 mm. Using the slitting saw of thickness 0.20 mm, 80 numbers of slits having depth of 4.0 mm each were made on the surface of the step A while maintaining a gap of 0.91 mm between each of two adjacent slits with a universal milling machine. Now the base plate was rotated by 90° and 80 numbers of slits with above dimensions were made again so as to achieve a uniform grid work with 361 spikes per square inch.
A fixture with a ® configuration with an elevation of 3.0 mm, made by press fitting of two stainless steel strips having 0.18 mm thicknesses each into two perpendicular slots made at the centre on the fixture, was bolted on moving table of the conventional high speed drilling machine in such a way that the intersection of ® shaped configuration of the fixture exactly align with tip of the drill bit of dia. 0.9 mm. Now the slitted base plate is placed on the fixture in such a way that ® shape configuration inserts into the slits, made at the surface of step A.

Using conventional high speed drilling machine, a hole of dia 1.0 mm was drilled up to the depth till a ® shaped sign is visible through the feed hole. Now, further drilling was carried out as described above till all the slit intersections with © sign are connected with the feed holes. Now, an array of feed holes of diameter 0.8 mm each was drilled maintaining a spacing of 0.9mm diameter of the junction of two steps which allows the extra flow of the dough to form the peripheral wall of the honeycomb while extrusion.
To fabricate the extrudate guide ring a circular ring of outer diameter 128 mm. Inner diameter of 111 mm, width of 13.3 mm and thickness of 9.3 mm was fabricated by machining of a stainless steel (SS304) tube. A step of outer diameter 119.0 mm and depth of 6.8 mm was cut along the inner diameter of the ring to fix the die body into the step. During extrusion, the die along with the extrudate guide ring can be fitted to the mouth of the conventional cylinder with a collar for producing the honeycomb structures as shown in figure 5.
EXTRUSION OF HONEYCOMB STRUCTURES USING THE DIE OF THE
PRESENT INVENTION
Example 3. Preparation of silicon carbide (SiC) Honeycombs
SiC powder having a particle size ranging from 2 to 10 |j,m along with 1 - 6 wt. % of phenolic binder, 2- 5 wt. % of methyl cellulose (MC) binder, 1- 3 wt. % of polyethylene glycol (PEG) and 20- 30 wt. % of water as a plasticizing medium were kneaded in a sigma kneader to obtain the extrudable dough. The dough was placed in an extrusion cylinder and was extruded through the die fabricated according to the method described in the Example 1 at a pressure of 10 kg/cm^ and with an ejection rate of 50mm/min. The green honeycombs were then dried in a microwave oven, which were debindered initially at 550 °C under nitrogen flow and finally sintered at temperatures between 1800-2100 °C in vacuum.

The resulting silicon carbide honeycombs are found to have an oval shape with dimensions of 93.6 mm major axis and minor axis of 62 mm with the wall thickness of 0.62 mm and having square channels of configuration of 2.3 mm x 2.3 mm after sintering. The cell density of the honeycomb structure prepared was found to be 54-channels/ square inch. The bulk density, apparent porosity and water absorption of the sintered silicon carbide honeycomb produced are found to be 1.529 g/cc, 51.45 %, 33,641 %, respectively.
Example 4: Preparation of mullite (SAbOa.ZSiOi) honeycombs
Mullite composition was formulated from clay and alumina along with 1- 5 wt. % of MC, 2 - 3 wt. % of PEG and 20 - 25 wt. % of water as a plasticizing medium were kneaded in a sigma kneader to achieve the extrudable dough. The dough was placed in an extrusion cylinder and was extruded through the die fabricated by the method described in the Example! with a pressure of about 10 kg/cm^ and at an ejection rate of 50mm/min. The green honeycombs were then dried in a microwave oven, which were debindered initially at 550 °C and finally sintered at temperatures between 1550 °C for four hours.
The resultant mullite honeycombs are found to have an oval shape with dimensions of 111 mm major axis and minor axis of 74 mm and the wall thickness of 0.74 mm with the configuration of channels of 2.7 mm x 2.7 mm after sintering. The cell density of the honeycomb structure prepared was found to be 41channes/ square inch. The bulk density, apparent porosity and water absorption of the sintered mullite honeycomb are found to be 1.554 g/cc, 44.716 %, 28.770 %, respectively.
Example 5: Preparation of zirconia (ZrOi) honeycombs
Commercially available fine zirconia powder was mixed along with 1.5 - 3 wt. % of MC, 1.5 - 3 wt. % of PEG and 20 - 30 wt. % of water as a plasticizing medium was kneaded in a sigma kneader to achieve the extrudable dough. The dough was placed in an

extrusion cylinder and was extruded through the die fabricated according to the method described in the Example lat a pressure of about 10 kg/cm^ and at an ejection rate of 40mm/min. The green honeycombs were then dried in a microwave oven, which were debindered initially 550 °C and finally sintered at temperatures between 1600 °C for three hours.
The zirconia honeycombs structure so prepared are found to have an oval shape with dimensions of 87.6 mm major axis and minor axis of 58.4mm and the wall thickness of 0.65 mm with a square channel configuration of 2.1 mm x 2.1 mm after sintering. The cell density of the sample was found to be 58-channels/ square inch. The bulk density, apparent porosity and water absorption of the sintered zirconia honeycomb are found to be 4.785 g/cc, 17.823 %, 3.724 %, respectively.
Example 6: Preparation of MgAl204 spinel honeycombs
Initially a stoichiometric mixture of caustic magnesia and aluminum hydroxide was calcined at temperatures between 1000 and 1300 °C for 1 to 5 hours to get required spinel formation. Thus obtained spinel fine powder was dry milled in a ball mill to bring down the particle size to required range (5-15 |j,m). Ground spinel powder was mixed along with 1-4 wt. % of MC, 1-3 wt. % of PEG and 20 - 30 wt. % of water and the mixture was kneaded in a sigma kneader to achieve the extrudable dough. The dough was placed in the extrusion cylinder and was pressed through the die fabricated according to the method described in example 2 with a pressure of 8- 10 kg/cm^ at an ejection rate of 100 mm/min. The green honeycombs were dried in microwave oven and debindered at 550 °C and then sintered at 1600 °C for 2 hours.
The resultant spinel honeycombs are found to have an oval shape with dimensions of 87.6 mm major axis and minor axis of 58.4mm and the wall thickness 0.65 mm with a square channel configuration of 2.1 mm x 2.1 mm after sintering. The cell density of the spinel honeycomb was found to be 58-channels/ square inch. The bulk density, apparent

porosity and water absorption of the sintered spinel honeycomb are found to be 3.051 g/cc, 6.713 %, 2.200 %, respectively.
Example 7: Preparation of zirconia- spinel (Zr02-MgAl204) honeycombs
Initially a stoichiometric mixture of caustic magnesia and aluminum hydroxide was calcined at temperatures between 1000 and 1300 °C for 1 to 5 hours to get required spinel formation. Thus obtained spinel powder was dry milled in a ball mill to bring down the particle size to required range (5-15 |im). The fine spinel powder so prepared along with commercially available zirconia powders or baddeleyite and 1-4 wt. % of MC, 1-3 wt. % of PEG and 20 - 30 wt. % of water and the mixture was kneaded in a sigma kneader to achieve the extrudable dough. The dough was placed in the extrusion cylinder and was extruded through the die fabricated according to the method described in Example 2 with a pressure of about 10 kg/cm^ with an ejection rate of 90 mm/min. The green honeycombs were debindered and then sintered at 1600 °C for 3 hours.
The zirconia - spinel honeycombs so prepared were found to have an oval shape with dimensions of 78 mm major axis and minor axis of 50.4 mm and the wall thickness of 0.54 mm with a square channel configuration of 1.8 mm x 1.8 mm. The cell density of the zirconia-spinel honeycomb was found to be 67-channels/ square inch. The bulk density, apparent porosity and water absorption of the sintered zirconia-spinel (60:40 mole %) honeycomb are found to be 3.155 g/cc, 5.45 %, 3.641 %, respectively.
Example 8: Preparation of cement honeycombs
Commercially available portland white cement along with 1-4 wt. % of methyl cellulose, 1-3 wt. % of PEG and 20 - 30 wt. % of water were mixed together and the mixture was kneaded in a sigma kneader to achieve the extrudable dough and was placed in the extrusion cylinder and was extruded through the die fabricated according to the method described in example 2. Thus obtained cement honeycomb was allowed to dry

and the resultant honeycombs were cured at atmospheric temperature and pressures for one week time while spraying water for setting.
The resultant cement honeycombs were found to have an oval shape with dimensions of 120 mm major axis and minor axis of 80 mm and the wall thickness 0.8 mm with a square channel configuration of 3 mm x 3 mm. The cell density of the sample was found to be 36-channels/ square inch. The bulk density, apparent porosity and water absorption of the cement honeycomb after curing at room temperature for a week time by spaying water are found to be 1.658 g/cc, 32.029 %, 19.311 %, respectively.
Example 9: Preparation of cement- fly-ash honeycombs
Various amounts of commercially available portland white cement ranging from 30 - 50 % and fly-ash along with 1-4 wt. % of MC, 1-3 wt. % of PEG and 20 - 30 wt. % of water were mixed and the mixture was kneaded in a sigma kneader to achieve an extrudable dough placed in the extrusion cylinder and was extruded through the die fabricated according to the method described in Example 2. Thus obtained cement-fly ash honeycomb was allowed to dried and cured at atmospheric temperature and pressures for one-week time while spraying water.
The extruded fly ash - cement honeycombs so prepared were found to have an oval shape with dimensions of 120 mm major axis and minor axis of 80 mm and the wall thickness of 0.8 mm with a square channel configuration of 3 mm x 3 mm. The cell density of the sample was found to be 36-channels/ square inch. The bulk density, apparent porosity and water absorption of the cement honeycomb after curing at room temperature for a week time by spaying water are found to be 1.274 g/cc, 44.181 %, 34.659 %, respectively.
Example 10: Preparation of silicon nitride Si3N4 honeycombs

Commercially available Si3N4 powder was used to make Si3N4 honeycomb. Silicon nitride powder along with 1-4 wt. % of MC, 1-3 wt. % of PEG and 20 - 30 wt. % of water were mixed and the mixture was kneaded in a sigma kneader to achieve the extrudable dough placed in the extrusion cylinder and was extruded through the die fabricated according to the method described in Example 2. The resultant green honeycombs were then dried in a microwave oven, which were debindered at 550 °C in nitrogen and finally sintered at temperatures between 1800 to 2100 °C in vacuum.
The silicon nitride honeycombs so prepared were found to have an oval shape with dimensions of 98 mm major axis and minor axis of 94 mm and the wall thickness of 0.70 mm with a square channel configuration of 2.4 mm x 2.4 mm. The cell density of the sample was found to be 50-channels/ square inch.
Example 11: Preparation of mullite-cordierite (3Al203.2Si02-2Mg0.2.Al203.5Si02) honeycombs
Cordierite-Mullite honeycombs were formulated fi^om clay, talc and alumina along with 1-4 wt. % of MC, 1-3 wt. % of PEG and 20 - 30 wt. % of water and the mixture was kneaded in a sigma kneader to achieve the extrudable dough. The dough was i placed in cylinder and was pressed through the die fabricated according to the method described in Example 2 with a pressure of about 15 kg/cm^ at an ejection rate of 30 mm/min. The green honeycombs were dried using microwave oven and debindered at 550 °C and sintered at 1400 °C in air.
The mullite - cordierite honeycombs so prepared were found to be circular in shape with diameter of 104 mm and the wall thickness of 0.22 mm with a square channel configuration of 0.9 mm x 0.9mm. The cell density of the sample was found to be 361-channels/ square inch. The bulk density, apparent porosity and water absorption of the sintered cordierite-mullite honeycomb are found to be 1.561 g/cc, 44.938 %, 28.775 %, respectively.

The mullite - cordierite honeycombs so prepared were found to be circular in shape with diameter of 104 mm and the wall thickness of 0.22 mm with a square channel configuration of 0.9 mm x 0.9mm. The cell density of the sample was found to be 361-channels/ square inch. The bulk density, apparent porosity and water absorption of the sintered cordierite-mullite honeycomb are found to be 1.561 g/cc, 44.938 %, 28.775 %, respectively.
Example 12: Preparation of fly-ash honeycombs
F|y-ash, a waste material obtained from a thermal power plat was mixed along with 1-4 wt. % of MC, 1-3 wt. % of PEG and 20 - 30 wt. % of water and the mixture was kneaded in a sigma kneader to achieve the extrudable dough. The dough was placed in the extrusion cylinder and was pressed through the die prepared by the method described in Example 2 with a pressure of 8- 10 kg/cm^ at an ejection rate of 100 mm/min. The green honeycombs were dried in microwave oven and debindered at 550 °C and then sintered at 1350 °C for 2 hours.
The fly-ash honeycombs so prepared were found to have an oval shape with dimensions of 87.6 mm major axis and minor axis of 58.4mm and the wall thickness 0.65 mm with a square channel configuration of 2.1 mm x 2.1 mm. The cell density of the sample was found to be 58-channels/ square inch. The bulk density, apparent porosity and water absorption of the fly-ash honeycomb after sintered at 1200 °C for 2 hours are found to be 2.065 g/cc, 6.917 %, 3.348 %, respectively.

We Claim
1. An improved process for making die useful for making honeycomb structures
particularly from ceramic materials which comprise
(a) making a base plat of aluminum alloy steel, brass, etc., of circular, hexagonal or oval shape and dimensions
(b) Milling the said plate into slots by known methods along the step A of Fig. 1 in perpendicular direction to form a uniform grid pattern as depicted in Fig. 2.
(c) making a fixture by press fitting two metal strips into the perpendicular slits of a metallic block so as to obtain a ® shaped configuration as shown in Fig. 3 which in turn align the slit width on the preform of the die.
(d) Fixing the fixture on the moving table of a drilling machine in such a way so as to align the tip of the drill bit with the centre of the © elevation.
(e) placing the slated preform obtained in step (b) over the fixture obtained in step (c) and inserting the elevated ® shaped strips into the intersection of the grid of the said base plate
(f) drilling feed holes on the other side of the said base plate to a depth till © sign is visible through the centre of the hole and
(g) drilling an array of equidistant through and through feed holes along the diameter of the junction of two steps which determines the formation the peripheral wall of the honeycomb while extrusion
2. An improved method for making honeycomb structures using the die fabricated as
claimed in claim 1 which comprises,
(a) making an extrudable dough of appropriate materials particularly ceramic materials with a binder and a plasticizer
(b) extruding the dough through a die made as claimed in claim 1 of the desired shape and configuration
(c) subjecting the resultant honeycomb to heat treatment and
(d) cooling the resultant honeycomb structure

3. An improved process as claimed in claim 2 wherein the ceramic material used for
making the dough is selected from muUite, cordierite-muUite, zirconia, spinel,
zirconia-spinel, fly-ash, fly-ash cement, silicon carbide and silicon nitride.
4. An improved process as claimed in claims 2 &3 wherein the binder such as methyl
cellulose, carboxy methyl cellulose and hydroxy methyl cellulose are used.
5. An improved process as claimed in claims 2 & 3 wherein the plasticizer employed is
selected from ethylene glycol, polyethylene glycol and glycerol are used.
6. An improved process as claimed in claims 2 to 3 wherein the heat treatment of the
extruded product is effected at the desired temperature ranges as specified wide
examples 3 to 12 depending on the processing materials.
7. A process for the making a die useful for making honeycomb structures, particularly
of ceramic materials substantially as herein described with reference to the Example 1
& 2, and in Figs. 1 to 5 of the drawing accompanying this specification.
An improved method of making honeycomb structure particularly of ceramic materials substantially as herein described with reference to the Examples 3 to 12.

Documents:

0538-mas-2001 abstract duplicate.pdf

0538-mas-2001 abstract.pdf

0538-mas-2001 claims duplicate.pdf

0538-mas-2001 claims.pdf

0538-mas-2001 correspondence others.pdf

0538-mas-2001 correspondence po.pdf

0538-mas-2001 description (complete) duplicate.pdf

0538-mas-2001 description (complete).pdf

0538-mas-2001 drawings.pdf

0538-mas-2001 form-1.pdf

0538-mas-2001 form-19.pdf

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Patent Number

198045

Indian Patent Application Number

538/MAS/2001

PG Journal Number

08/2007

Publication Date

23-Feb-2007

Grant Date

13-Jan-2006

Date of Filing

03-Jul-2001

Name of Patentee

INTERNATIONAL ADVANCED RESEARCH CENTER FOR POWDER METALLURGY AND NEW MATERIALS(ARCI)

Applicant Address

OPP:BALAPUR VILLAGE, RANGA REDDY DISTRICT, HYDERABAD 500 005

Inventors:

#	Inventor's Name	Inventor's Address
1	IBRAM GANESH	C/O.INTERNATIONAL ADVANCED RESEARCH CENTER FOR POWDER METALLURGY AND NEW MATERIALS(ARCI), OPP:BALAPUR VILLAGE, RANGA REDDY DISTRICT, HYDERABAD 500 005

PCT International Classification Number

B32B18/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA