Title of Invention	"A PROCESS FOR MANUFACTURE OF CORDIERITE HONEYCOMB SUBSTRATES BY EXTRUSION WITH A PREDETERMINED RHELOGICAL PARAMETERS"
Abstract	A process for the manufacture of Cordierite honeycomb »ubst?Aates by extrusion with a predetermined Rheological parameters as yield stress (  ), Die entry velocity sensitivity factor < α ) die entry exponent <m>, shear stress ( TO > , die land velocity sensitivity factor < (2 ) and die land exponent <  > comprising the following stepss- B ) Raw material of Cordierite forming batch formula of 39% Indian talc, a total of different types of Indian c 1 ayts of 46% and 15% of alumina (1) are; intensely mixed in a batch mixer (2) for 5 to 10 minutes; b) and mixed with 2% methyl cellulose, 0.5H of glycerin, 5% wheat powder and 21% of water in a closed gap «igma blade mixer for 45 mintues <3>; c) the mixed paste is then de-aired by known means and extruded as herein defined in the form of .1 inch dia bar for subsequent rehological testing (4), the result of the test being analyzed by a fitting mathematical equation of 6-figure modelj and d) the accepted kneaded batch is then processed in a pug mill to obtain the de-aired blanks <7> and e) fed to the hydraulic extruder for honeycomb extrusion (8)5 f) the honeycomb extrusion is then dried <9> by known drying equipment; o g) and fired <10> in a furnace between 1350 C to o 1420 C to maintain optimized porosity and mechanical strength; followed by obtaining finished cordierite honeycomb product by cutting and grinding parallel the fired honeycomb extrusion.

Title of Invention

"A PROCESS FOR MANUFACTURE OF CORDIERITE HONEYCOMB SUBSTRATES BY EXTRUSION WITH A PREDETERMINED RHELOGICAL PARAMETERS"

Abstract

A process for the manufacture of Cordierite honeycomb »ubst?Aates by extrusion with a predetermined Rheological parameters as yield stress (  ), Die entry velocity sensitivity factor < α ) die entry exponent <m>, shear stress ( TO > , die land velocity sensitivity factor < (2 ) and die land exponent <  > comprising the following stepss- B ) Raw material of Cordierite forming batch formula of 39% Indian talc, a total of different types of Indian c 1 ayts of 46% and 15% of alumina (1) are; intensely mixed in a batch mixer (2) for 5 to 10 minutes; b) and mixed with 2% methyl cellulose, 0.5H of glycerin, 5% wheat powder and 21% of water in a closed gap «igma blade mixer for 45 mintues <3>; c) the mixed paste is then de-aired by known means and extruded as herein defined in the form of .1 inch dia bar for subsequent rehological testing (4), the result of the test being analyzed by a fitting mathematical equation of 6-figure modelj and d) the accepted kneaded batch is then processed in a pug mill to obtain the de-aired blanks <7> and e) fed to the hydraulic extruder for honeycomb extrusion (8)5 f) the honeycomb extrusion is then dried <9> by known drying equipment; o g) and fired <10> in a furnace between 1350 C to o 1420 C to maintain optimized porosity and mechanical strength; followed by obtaining finished cordierite honeycomb product by cutting and grinding parallel the fired honeycomb extrusion.

Full Text	This invention relates to a process for manufacture of Cordierite honeycomb substrates by extrusion. The Cordierite ceramic honeycomb substrate is generally used but not limited in Catalytic Converter for vehicular pollution control throughout the world. The invention particularly relates to the scientific process of achieving the Rheological characteristics of the extrusion paste for continuous extrusion of honeycomb substrates. Till date/ the composition of the paste, which is generally known in the art/ do not disclose any method of arriving at the correct composition. It appears/ the present few manufacturers have developed this composition by trial and error or through their long experience to achieve the extrusion characteristic. It is known in the art that the honeycomb material is formed from an extrudable material by using a conventional honeycomb die/ where the material flows through a plurality of feed passageways delivering it directly to intersection portions of a gridwork of interconnected discharge slots. It is also known that pure Cordierite is having a chemical formulae of 2MgO.2Al2O3,5Si02 and thus having 13.8% of MgO, 51.3% of SiO2 and 34.9% of A12O3. Thus the single-Phase pure Cordierite can be obtained by selecting the raw materials like clay ( major source of A12O3 & SiO2), Talc (major source of MgO & SiO2)/ silica/ magnesium aluminate/ magnesium carbonate/ pyrophilite/alumina etc. with respective proportions calculated from the individual chemical consti¬tuents of each raw materials. It is also known in the prior art that the above inorganic batch constituents may be mixed with the following organic constituents for their respective contributions to obtain the extrudable paste. For example* among organic binders such as methyl cellulose/ carboxy methyl cellulose/ hydroxyprophyl methyl cellulose/ polyvinyl alcohol/ starch/ wheat powder etc. among plasticizers and surface agents/ glycerin/ wax/ sodium stearate/ graphite etc. And many other materials such as activated charcoal/ starch powder/ sawdust and others may be used for achieving other properties of the honeycomb like pore formation and pore - size control. Therefore the main object of the present invention is to provide an extrusion paste/ which is essential for honeycomb extrusion of reasonable quality and yield/ having favourable Rheological properties for consistent and repeatable honeycomb extrusion. Another object of the present invention is to propose a process for preparation of Cordierite ceramic paste with the required Rheological parameters for successful honeycomb extrusion Yet another object of the present invention is to manufacture of Cordierite honeycomb substrate of consistent quality and high yield by extrusion suitable for use in Catalytic Converter for automobiles using fossil fuel. A further object of the present invention is to achieve the required Rheological parameters by various composition* derived from the local source of minerals, plasticizers, binders, lubricants and synthetic materials. A still further object of the present invention invention is to improve the manufacturing process of ceramic honeycomb for more consistent and repeatable yield through utilizing sci ent 1 f it: i al ly formulated Rheological considerations. According to the present invention there is provided a process for the manufacture of Cordierite honeycomb substrates by extrusion with s predetermined Rheological parameters as yield stress «3^ ), Die entry velocity sensitivity factor ( Of ), die entry exponent (m), shear stress a) raw material of Cordierite forming batch formula of 39% Indian talc, a total of different types of Indian clayis of 46% and 15% of alumina are} intensely mixed in a batch mixer for 5 to 10 minutes; b) and mixed with 2% methyl cellulose, 0.3% of glycerin, 5% wheat powder and 21% of water in a closed gap sigma blade mixer for 45 minutes; c) the mixed paste is then de-aired by known means and extruded as herein defined in the form of 1 inch dia bar for subsequent rehological testing, the result of the test being analyzed by a fitting mathematical lequation of 6-figure model 5 and d> the accepted kneaded batch is then processed in a plug mill to obtain the de-aired blanks, and e) fed to the hydraulic extruder for honeycomb extrusion; f> the honeycomb extrusion is then dried by known drying equipment; o o g) and fired in a furnace between 1350 C to 1420 C to maintain optimized porosity and mechanical strength? followed by obtaining finished cordierite honeycomb product by cutting and grinding parallel the fired honeycomb extrusion. The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non limiting exemplary embodiments of the invention represented in the accompanying figures and tables. Fig.1 - shows the flow diagram of the process for the manufacture of ceramic honeycomb. Figs, 2,3 - shows in tabular form (Tables 1,2) the si>: extrusion parameters against various experimental batches. Fig.4 - table shows the properties of honeycomb manufactured by the new process. In accordance with the present invention, there i* a process of deciding the composition of the extrudable Cordierite paste scientifically to obtain the desired Rheological parameters for achieving successful and much improved honeycomb extrusion with higher yield. The flow chart for modified process for ceramic honeycomb manufacture according to the present invention is shown in Fig.l. Thus the invention gives due importance to the Rheological parameter as given below which are ssystematic al ly achieved by various compositions which can be derived from the local sources of minerals, plasticizers/ binders/ lubricants and synthetic materials. Rheological parameters of ceramic cordierite paste. Symbols Ob Parameters 1. Yield Stress 2. Die entry velocity sensitivity factor 3. Die Entry Exponent ffl 4. Shear stress To 5. Die land velocity sensitivity factor p n 6. Die Land ExponentDesired values 0.15 to 0.35 MPa 0.001 to 0.07 MPa (mm/min)" 0.4 max. 0.001 to 0.002 MPa 0.001 to 0.02 MPa (mm/min) 0.45 max.n D r awba ck s_of_the_kn own_art; The characteristics of the extrusion paste suitable for ceramic honeycomb extrusion is never disclosed or revealed in the known art. The characteristics of an extrudable paste are those parameters which decides the paste flow through the honey¬comb extrusion dies under practical achievable force or pressure/ retain the thin walled intricate shapes immediately after extrusion/ flow laterally to join with each other to form monolithic structure. The characteristics of the extrudable paste may be similar to an SHEAR - THINNING liquid type as discussed in the rheological literature. However there is no disclosure or invention of the precise quantitative values of those characteristic para¬meters which are responsible for any successful ceramic honeycomb extrusion. In all of the known art so far patented or disclosed/ the paste for honeycomb extrusion is termed as "extrudable": and formulated using the binders and additives mentioned earlier for obtaining the suitable binding/ plasticising/ lubricating and other propoerties by trial-and-error method/. Thus there is a lack of definition of the required characteristics of the extrudable paste suitable of ceramic honeycomb extrusion. To achieve the identification of the Rheological parameters of the extrusion paste for the manufacture of the Cordierite ceramic honeycomb substrates by extrusion/ detailed studies of the honeycomb substrate extrusion behaviour with scientific and technological view points were undertaken. Numerous honeycomb extrusions are undertaken using the conventional plunger type extruder known in the art. During each extrusion cycle the Rheological parameters are measured by fitting the 6 - figure mathematical model and recorded with the corresponding honeycomb extrusion results. Thus the paste behaviour is quantified by fitting the model and the extent of fitting the curve is designated by Rl -square value. Through a series of experimentation the range of values for each of the Rheological parameters constituting the 6-figure mathematical model were obtained which are required for the good honeycomb extrusion. The following embodiment gives an examples those values. Further/ , it known to the people skilled in the art that the processing of the ceramic paste for extrusion is to be very precisely controlled to obtain good honeycomb extrusion. Sometimes/ even after very precise and careful control of processing/ the derived results,that is the defect free extrusion of honeycomb,is not achieved unless process conditions are changed or altered due to seasonal or other variations. For example/ if the temperature or humidity of the processing room is different then the fine powdered material while processing may absorb little more or less water which may change the total water content of the paste significantly altering the plasticity of the paste. Similarly there are many other factors like leftover waste in a cleaned machine/ frictional temperature rise of slightly over-worked mixing or extruding apparatus etc. may affect the workability of the extrudable paste considerably which are not normally be identified during mass production as an assignable cause. To overcome the above difficulty leading to fluctuations in the honeycomb extrudability of the extrusion paste/ a manufacturing process is further invented for effectively implementing the required control/ which is the key of any successful honeycomb extrusion and is outlined in the Figure - 1. This process of operation when applied not only improves the yields of the extrusion but also gives more repeatable and assignable extrusion results removing the uncertainty of good or bad extrusion due to less direct control of the ultimate'extrudability of the paste. The invented manufacturing process is capable of exercising the fine control essential for consistent and repeatable honeycomb extrusion. The above mentioned process steps yield the successful honeycomb extrusion by maintaining the Rheological parameter values within the required level as found out by this invention and as stated earlier. The good honeycomb extrudate after the above extrusion is dried uniformly using the available drying equipment. After being dried the honeycombs are fired in a furnace between 1350 C to 1420 C depending on the porosity and mechanical strength requirements. A single phase Cordierite is achieved by mixing the Cordierite forming batch formula of 39% Indian talc/ a total of 46% of different types of Indian clays and 15% alumina. After intensely mixing ( 2 of Fig. 1) these constituents/ the same batch is mixed ( 3 of Fig. 1) with 2% methyl cellulose/ 0.5% of glycerin/ 5% wheat powder and 21% of water in a closed gap Sigma blade mixer for 45 minutes. The mixed paste is then de-aired and extruded in the form of 1 inch dia bar for subsequent Rheological testing ( 4 of Fig.l). The bar is inserted in the barrel of the test fixture and the complete assembly is loaded in the Universal testing machine. A set of 4 mm dia cylindirical dies with different length-to-diameter ratios is assembled one die at a time at one end of the barrel. Through the other end of the barrel a piston type ram is introduced after inserting the 1 Inch dia test blank of extrudable Cordierite paste. The ram is programmed to descend at different fixed velocities and during each velocity step the load experienced by the extrusion is recorded. The results of test is then analyzed by fitting a 6-figure model of the pressure prediction assuming there is a plug flow in the die. The mathematical equation of the 6-figure model used is described later. The same paste is then parallely extruded through various conventional honeycomb dies available commercially. The results of the honeycomb extrusion is noted indicating good or bad extrusion with respect to the required quality with reasonable yield. The results of a series of experiments shows that any successful honeycomb extrusion primarily depends on the specific values of the Rheological parameters of the paste and such characteristics of the paste are defined, range of values are found out and claimed within the scope of this invention. The desirable values of the Rheological parameters are described in this patent application and also described how to obtain the desired Rheological parameters for achieving Sucessfull and much improved honeycomb extrusion. The desired Rheological parameters are obtained by formulating a range of extrusion paste batch compositions by incorporating Indian clays, talc, alumina, quartz, pyrophillite with various grades of wheat powder, tapioca starch, methyl cellulose, glycerin, polyvinyl, alcohol, polyethylene glycol, stearic acid, stearic salts, graphite, charcoal and other binders, plasticizer, lubricants available for the above purpose of controlling the Rheological parameters. The 6-figure model utilized for the analysis is p- Where P is the total extrusion pressure (MPa), V is the extrusion velocity in mm,min and other 6 parameters are already explained earlier ( in page 2). For good extrusion of honeycomb preferably upto 400 cells and wall thickness from 0.17 to 0.35 mm the Sigma (Ob) values are obtained between 0.15 to 0.35 MPa more precisely between 0.16 to 0.23 MPa and Alfa (d ) values between 0.001 - 0.07 MPa ( mm,min) and ' m value not above 0.40, Tow (To ) values between 0.001 - 0.002, Beta ( ft ) values between 0.001 - 0.02 and ' n' values not greater than 0.45. The upper value of the Sigma (CTO) is not limited by the value 0. 35 MP a. It is also possible to extrude good honeycomb with Sigma ( ) more than 0.35 MP a provided the extruder and the die can be made extra strong to take the higher pressure requirement for higher Sigma (OL) value. If the value of Sigma (&o) is less than 0.15 MPa then the Cordierite honeycomb cannot be extruded and its monolithic honeycomb structure cannot be retained. EXAMPLES Example 1. A single phase Cordierite is achieved by mixing the Cordierite forming batch formula of 39% Indian talc, a total of 46% of different types of Indian clays and 15% of alumina. After intensely mixing ( 2 of Fig. 1) these constituents, the same batch is mixed ( 3 of Fig. 1) with 2% methyl cellulose, 0.5% of glycerin, 5% wheat powder and 21% of water in a closed gap Sigma blade mixer for 45 minutes. The mixed paste is then de - aired and extruded in the form of 1 Inch dia bar for subsequent Rheological testing ( 4 of fig. 1). The bar is inserted in the barrel of the test fixture and the complete assembly is loaded in the Universal testing machine. A set of 4 mm dia cylindirical die with different length-to-diameter ratios is assembled one die at a time in one end of the barrel. Through the other end of the barrel a piston type ram is introduced after inserting the I" dia test blank of extrudable Cordierite paste. The ram is programmed to descend at different fixed velocities and during each velocity step the load experienced by the extrusion is recorded. The results of test is then analyzed by fitting a 6-figure model of the pressure prediction assuming there is plug flow in the die. Six Extrusion Parameters obtained for this batch is as shown in Exp - 2 in Table - 1(Table Removed) This extrusion paste with the above mentioned values of rheological parameters yields successful honeycomb extrusion with very good quality and productivity. Whereas the other experiments with minor variations in binders and water quantity ( that is Exp. -I, Exp. -3 and Exp. -4) could not yield good honeycomb extrusion. The kneaded batch of Exp - 2 is pugmilled to obtain the de-aired blanks ( 7. of Fig-1), which are fed to the Hydraulic Extruder for honeycomb extrusion ( 8 of Fig. -1).The good honeycomb extrudates after the above extrusion of Exp - 2 are dried ( q of Fig - 1) uniformly using the drying equipment s available. After being dried the honey¬combs are fired ( 10 of Fig - 1) in a furnace between 1350°C to 1420°C depending on the porosity and mechanical strength requirements. After firing the ends of the honeycombs are cut and ground parallel to obtain the finished Cordierite honeycomb product ( 11 of Fig. 1). The physical, mechanical and thermal properties of various honeycomb manufactured using the claimed method is given in Table 3. example 2. Cordierite batch is prepared as explained in Example-1. But for varying water content between 19% & 22% and binder content between 2 & 3 %. In addition 2 % Binder PVA is added. The batches thus prepared is tested and analyzed. The results are shown in Table 2. These batches are extruded through various honeycomb dies. Batches having CT values between 0.15 to 0.35 shows good extrusion of honeycomb & retention of shape. Batches having (TQ value below 0.15 were not possible to extrude property due to die blockage. Body sticking to die and extruded honeycomb was slumpy and deforming. Therefore, batches with similar Rheological characteristics like Exp-5, Exp-9 and Exp - 7 yielded good honeycomb extrusion. With these batches the process described in Example-1 are followed which produced very good Cordieritie honeycomb finished products. The results of the various batches are tabulated in Figs. 2, 3 and 4 ( Tables I, 2 and 3). The invention described hereinabove is in relation to a non - limiting embodiment and as defined by the accompanying claims. WE CLAIM: 1. A process for the manufacture of Cordierite honeycomb substrates by extrusion with a predetermined Rheological parameters comprising the following steps; a) Raw material of Cordierite forming batch formula of 39% Indian talc, a total of different types of Indian clays and 15% of alumina(l) are; b) intensely mixed in a batch mixer (2); c) and mixed with 2% methyl cellulose, 0.5% of glycerin, 5% wheat powder and 21% of wheat in a closed gap sigma blade mixer for 45 minutes (3); d) the mixed paste is then de-aired and extruded (4) in the form of 1 inch dia bar for subsequent rheologicai testing (4) and, e) the accepted kneaded batch is then processed in a pug mill to obtain the de-aired blanks (7) and f) fed to the hydraulic extruder for honeycomb extrusion (8); g) the honeycomb extrusion is then dried (9);. h) and fried in a furnace between 1350°C to 1420° C depending on the porosity and mechanical strength requirements (10); i) the honeycomb are then cut and ground parallel to obtain the finished Cordierite honeycomb product (11). 2. A process for the manufacture of Cordierite honeycomb substrates by extrusion as claimed in claim 1 wherein for good extrusion of honeycomb upto 200 cells and wall thickness around 0.2mm the sigma (00) values are obtained between 0.15 to 0.35 MPa and alfa (1) values between 0.005-0.07 M Pa (mm/min)m and "nT value not above 0.40, Tow (T0) values between 0.001-0.002, Beta (B) values between 0.001-0.02 and V value not greater than 0.45. 3. A process for the manufacture of Cordierite honeycomb substrates by extrusion as herein described and illustrated.

Full Text

This invention relates to a process for manufacture of Cordierite honeycomb substrates by extrusion.
The Cordierite ceramic honeycomb substrate is generally used but not limited in Catalytic Converter for vehicular pollution control throughout the world.
The invention particularly relates to the scientific process of achieving the Rheological characteristics of the extrusion paste for continuous extrusion of honeycomb substrates.
Till date/ the composition of the paste, which is generally known in the art/ do not disclose any method of arriving at the correct composition. It appears/ the present few manufacturers have developed this composition by trial and error or through their long experience to achieve the extrusion characteristic.
It is known in the art that the honeycomb material is formed from an extrudable material by using a conventional honeycomb die/ where the material flows through a plurality of feed passageways delivering it directly to intersection portions of a gridwork of interconnected discharge slots.
It is also known that pure Cordierite is having a chemical formulae of 2MgO.2Al2O3,5Si02 and thus having 13.8% of MgO, 51.3% of SiO2 and 34.9% of A12O3. Thus the single-Phase pure Cordierite can be obtained by selecting the raw materials like clay ( major source of A12O3 & SiO2), Talc (major source
of MgO & SiO2)/ silica/ magnesium aluminate/ magnesium carbonate/ pyrophilite/alumina etc. with respective proportions calculated from the individual chemical consti¬tuents of each raw materials.
It is also known in the prior art that the above inorganic batch constituents may be mixed with the following organic constituents for their respective contributions to obtain the extrudable paste.
For example* among organic binders such as methyl cellulose/ carboxy methyl cellulose/ hydroxyprophyl methyl cellulose/ polyvinyl alcohol/ starch/ wheat powder etc. among plasticizers and surface agents/ glycerin/ wax/ sodium stearate/ graphite etc. And many other materials such as activated charcoal/ starch powder/ sawdust and others may be used for achieving other properties of the honeycomb like pore formation and pore - size control.
Therefore the main object of the present invention is to provide an extrusion paste/ which is essential for honeycomb extrusion of reasonable quality and yield/ having favourable Rheological properties for consistent and repeatable honeycomb extrusion.
Another object of the present invention is to propose a process for preparation of Cordierite ceramic paste with the required Rheological parameters for successful honeycomb extrusion
Yet another object of the present invention is to manufacture of Cordierite honeycomb substrate of consistent
quality and high yield by extrusion suitable for use in Catalytic Converter for automobiles using fossil fuel.
A further object of the present invention is to achieve the required Rheological parameters by various composition* derived from the local source of minerals, plasticizers, binders, lubricants and synthetic materials.
A still further object of the present invention invention is to improve the manufacturing process of ceramic honeycomb for more consistent and repeatable yield through utilizing sci ent 1 f it: i al ly formulated Rheological considerations.
According to the present invention there is provided a process for the manufacture of Cordierite honeycomb substrates by extrusion with s predetermined Rheological parameters as yield stress «3^ ), Die entry velocity sensitivity factor ( Of ), die entry exponent (m), shear stress a) raw material of Cordierite forming batch formula
of 39% Indian talc, a total of different types of Indian clayis of
46% and 15% of alumina are}
intensely mixed in a batch mixer for 5 to 10 minutes;
b) and mixed with 2% methyl cellulose, 0.3% of
glycerin, 5% wheat powder and 21% of water in a closed gap sigma
blade mixer for 45 minutes;
c) the mixed paste is then de-aired by known means and extruded as herein defined in the form of 1 inch dia bar for subsequent rehological testing, the result of the test being analyzed by a fitting mathematical lequation of 6-figure model 5 and
d> the accepted kneaded batch is then processed in a plug mill to obtain the de-aired blanks, and
e) fed to the hydraulic extruder for honeycomb extrusion;
f> the honeycomb extrusion is then dried by known
drying equipment;
o o g) and fired in a furnace between 1350 C to 1420 C to
maintain optimized porosity and mechanical strength?
followed by obtaining finished cordierite honeycomb
product by cutting and grinding parallel the fired honeycomb
extrusion.
The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non limiting exemplary embodiments of the invention represented in the accompanying figures and tables.
Fig.1 - shows the flow diagram of the process for the manufacture of ceramic honeycomb.
Figs, 2,3 - shows in tabular form (Tables 1,2) the si>: extrusion parameters against various experimental batches.
Fig.4 - table shows the properties of honeycomb manufactured by the new process.
In accordance with the present invention, there i* a process of deciding the composition of the extrudable Cordierite paste scientifically to obtain the desired Rheological parameters for achieving successful and much improved honeycomb extrusion with higher yield. The flow chart for modified process for ceramic honeycomb manufacture according to the present invention is shown in Fig.l. Thus the invention gives due importance to the Rheological parameter as given below which are ssystematic al ly achieved by various compositions which can be derived from the local sources of minerals,
plasticizers/ binders/ lubricants and synthetic materials. Rheological parameters of ceramic cordierite paste.

Symbols Ob

Parameters
1. Yield Stress
2. Die entry velocity
sensitivity factor
3. Die Entry Exponent ffl
4. Shear stress To
5. Die land velocity
sensitivity factor p
n
6. Die Land ExponentDesired values 0.15 to 0.35 MPa
0.001 to 0.07 MPa (mm/min)" 0.4 max. 0.001 to 0.002 MPa
0.001 to 0.02 MPa (mm/min) 0.45 max.n
D r awba ck s_of_the_kn own_art;
The characteristics of the extrusion paste suitable for ceramic honeycomb extrusion is never disclosed or revealed in the known art. The characteristics of an extrudable paste are those parameters which decides the paste flow through the honey¬comb extrusion dies under practical achievable force or pressure/ retain the thin walled intricate shapes immediately after extrusion/ flow laterally to join with each other to form monolithic structure. The characteristics of the extrudable paste may be similar to an SHEAR - THINNING liquid type as discussed in the rheological literature. However there is no disclosure or invention of the precise quantitative values of those characteristic para¬meters which are responsible for any successful ceramic honeycomb extrusion. In all of the known art so far patented or disclosed/ the paste for honeycomb extrusion is termed as "extrudable": and formulated using the binders and additives mentioned earlier for obtaining the suitable binding/ plasticising/ lubricating and other propoerties by trial-and-error method/. Thus there is a
lack of definition of the required characteristics of the extrudable paste suitable of ceramic honeycomb extrusion.
To achieve the identification of the Rheological parameters of the extrusion paste for the manufacture of the Cordierite ceramic honeycomb substrates by extrusion/ detailed studies of the honeycomb substrate extrusion behaviour with scientific and technological view points were undertaken. Numerous honeycomb extrusions are undertaken using the conventional plunger type extruder known in the art. During each extrusion cycle the Rheological parameters are measured by fitting the 6 - figure mathematical model and recorded with the corresponding honeycomb extrusion results. Thus the paste behaviour is quantified by fitting the model and the extent of fitting the curve is designated by Rl -square value. Through a series of experimentation the range of values for each of the Rheological parameters constituting the 6-figure mathematical model were obtained which are required for the good honeycomb extrusion. The following embodiment gives an examples those values.
Further/ , it known to the people skilled in the art that the processing of the ceramic paste for extrusion is to be very precisely controlled to obtain good honeycomb extrusion. Sometimes/ even after very precise and careful control of processing/ the derived results,that is the defect free extrusion of honeycomb,is not achieved unless process conditions are changed or altered due to seasonal or other variations.
For example/ if the temperature or humidity of the processing room is different then the fine powdered material while processing may absorb little more or less water which
may change the total water content of the paste significantly altering the plasticity of the paste. Similarly there are
many other factors like leftover waste in a cleaned machine/ frictional temperature rise of slightly over-worked mixing or extruding apparatus etc. may affect the workability of the extrudable paste considerably which are not normally be identified during mass production as an assignable cause.
To overcome the above difficulty leading to fluctuations in the honeycomb extrudability of the extrusion paste/ a manufacturing process is further invented for effectively implementing the required control/ which is the key of any successful honeycomb extrusion and is outlined in the Figure - 1. This process of operation when applied not only improves the yields of the extrusion but also gives more repeatable and assignable extrusion results removing the uncertainty of good or bad extrusion due to less direct control of the ultimate'extrudability of the paste. The
invented manufacturing process is capable of exercising the fine control essential for consistent and repeatable honeycomb extrusion.
The above mentioned process steps yield the successful honeycomb extrusion by maintaining the Rheological parameter values within the required level as found out by this invention and as stated earlier.
The good honeycomb extrudate after the above extrusion is dried uniformly using the available drying equipment. After being dried the honeycombs are fired in a furnace between 1350 C to 1420 C depending on the porosity and mechanical strength requirements.
A single phase Cordierite is achieved by mixing the Cordierite forming batch formula of 39% Indian talc/ a total of 46% of different types of Indian clays and 15% alumina. After intensely mixing ( 2 of Fig. 1) these constituents/ the same batch is mixed ( 3 of Fig. 1) with 2% methyl cellulose/ 0.5% of glycerin/ 5% wheat powder and 21% of water in a closed gap Sigma blade mixer for 45 minutes. The
mixed paste is then de-aired and extruded in the form of 1 inch dia bar for subsequent Rheological testing ( 4 of Fig.l). The bar is inserted in the barrel of the test fixture and the complete assembly is loaded in the Universal testing machine.
A set of 4 mm dia cylindirical dies with different length-to-diameter ratios is assembled one die at a time at one end of the barrel. Through the other end of the barrel a piston type ram is introduced after inserting the 1 Inch dia test blank of extrudable Cordierite paste. The ram is programmed to descend at different fixed velocities and during each velocity step the load experienced by the extrusion is recorded.
The results of test is then analyzed by fitting a 6-figure model of the pressure prediction assuming there is a plug

flow in the die. The mathematical equation of the 6-figure model used is described later.
The same paste is then parallely extruded through various conventional honeycomb dies available commercially. The results of the honeycomb extrusion is noted indicating good or bad extrusion with respect to the required quality with reasonable yield. The results of a series of experiments shows that any successful honeycomb extrusion primarily depends on the specific values of the Rheological parameters of the paste and such characteristics of the paste are defined, range of values are found out and claimed within the scope of this invention. The desirable values of the Rheological parameters are described in this patent application and also described how to obtain the desired Rheological parameters for achieving Sucessfull and much improved honeycomb extrusion. The desired Rheological parameters are obtained by formulating a range of extrusion paste batch compositions by incorporating Indian clays, talc, alumina, quartz, pyrophillite with various grades of wheat powder, tapioca starch, methyl cellulose, glycerin, polyvinyl, alcohol, polyethylene glycol, stearic acid, stearic salts, graphite, charcoal and other binders, plasticizer, lubricants available for the above purpose of controlling the Rheological parameters.
The 6-figure model utilized for the analysis is
p-
Where P is the total extrusion pressure (MPa), V is the extrusion velocity in mm,min and other 6 parameters are already

explained earlier ( in page 2).
For good extrusion of honeycomb preferably upto 400 cells and wall thickness from 0.17 to 0.35 mm the Sigma (Ob) values are obtained between 0.15 to 0.35 MPa more precisely
between 0.16 to 0.23 MPa and Alfa (d ) values between 0.001 - 0.07 MPa ( mm,min) and ' m value not above 0.40,
Tow (To ) values between 0.001 - 0.002, Beta ( ft ) values between 0.001 - 0.02 and ' n' values not greater than 0.45.
The upper value of the Sigma (CTO) is not limited by the value 0. 35 MP a. It is also possible to extrude good honeycomb with Sigma ( ) more than 0.35 MP a provided the extruder and the die can be made extra strong to take the higher pressure requirement for higher Sigma (OL) value. If the value of Sigma (&o) is less than 0.15 MPa then the Cordierite honeycomb cannot be extruded and its monolithic honeycomb structure cannot be retained.
EXAMPLES
Example 1.
A single phase Cordierite is achieved by mixing the Cordierite forming batch formula of 39% Indian talc, a total of 46% of different types of Indian clays and 15% of alumina. After intensely mixing ( 2 of Fig. 1) these constituents, the same batch is mixed ( 3 of Fig. 1) with 2% methyl cellulose,
0.5% of glycerin, 5% wheat powder and 21% of water in a closed gap Sigma blade mixer for 45 minutes. The mixed paste is then de - aired and extruded in the form of 1 Inch dia bar for
subsequent Rheological testing ( 4 of fig. 1). The bar is inserted in the barrel of the test fixture and the complete assembly is loaded in the Universal testing machine.
A set of 4 mm dia cylindirical die with different length-to-diameter ratios is assembled one die at a time in one end of the barrel. Through the other end of the barrel a piston type ram is introduced after inserting the I" dia test blank of extrudable Cordierite paste. The ram is programmed to descend at different fixed velocities and during each velocity step the load experienced by the extrusion is recorded.
The results of test is then analyzed by fitting a 6-figure model of the pressure prediction assuming there is plug flow in the die.
Six Extrusion Parameters obtained for this batch is as shown in Exp - 2 in Table - 1(Table Removed)

This extrusion paste with the above mentioned values of rheological parameters yields successful honeycomb extrusion with very good quality and productivity. Whereas the other experiments with minor variations in binders and water quantity ( that is Exp. -I, Exp. -3 and Exp. -4) could not yield good honeycomb extrusion.
The kneaded batch of Exp - 2 is pugmilled to obtain the de-aired blanks ( 7. of Fig-1), which are fed to the Hydraulic
Extruder for honeycomb extrusion ( 8 of Fig. -1).The good honeycomb extrudates after the above extrusion of Exp - 2 are dried ( q of Fig - 1) uniformly using the drying equipment s available. After being dried the honey¬combs are fired ( 10 of Fig - 1) in a furnace between 1350°C to 1420°C depending on the porosity and mechanical strength requirements. After firing the ends of the honeycombs are cut and ground parallel to obtain the finished Cordierite honeycomb product ( 11 of Fig. 1). The physical, mechanical and thermal properties of various honeycomb manufactured using the claimed method is given in Table 3.
example 2.
Cordierite batch is prepared as explained in Example-1. But for varying water content between 19% & 22% and binder content between 2 & 3 %. In addition 2 % Binder PVA is added. The batches thus prepared is tested and analyzed. The results are shown in Table 2. These batches are extruded through various honeycomb dies. Batches having CT values between 0.15 to 0.35 shows good extrusion of honeycomb & retention of shape. Batches having (TQ value below 0.15 were not possible to extrude property due to die blockage. Body sticking to die and extruded honeycomb was slumpy and deforming. Therefore, batches with similar Rheological characteristics like Exp-5, Exp-9 and Exp - 7 yielded good honeycomb extrusion. With these batches the process described in Example-1 are followed which produced very good Cordieritie honeycomb finished products.
The results of the various batches are tabulated in Figs. 2, 3 and 4 ( Tables I, 2 and 3).
The invention described hereinabove is in relation to a non - limiting embodiment and as defined by the accompanying claims.

WE CLAIM:
1. A process for the manufacture of Cordierite honeycomb substrates by extrusion with a predetermined Rheological parameters comprising the following steps;
a) Raw material of Cordierite forming batch formula of 39%
Indian talc, a total of different types of Indian clays and 15% of
alumina(l) are;
b) intensely mixed in a batch mixer (2);
c) and mixed with 2% methyl cellulose, 0.5% of glycerin, 5%
wheat powder and 21% of wheat in a closed gap sigma blade
mixer for 45 minutes (3);
d) the mixed paste is then de-aired and extruded (4) in the form of
1 inch dia bar for subsequent rheologicai testing (4) and,
e) the accepted kneaded batch is then processed in a pug mill to
obtain the de-aired blanks (7) and
f) fed to the hydraulic extruder for honeycomb extrusion (8);
g) the honeycomb extrusion is then dried (9);.
h) and fried in a furnace between 1350°C to 1420° C depending on the porosity and mechanical strength requirements (10);
i) the honeycomb are then cut and ground parallel to obtain the finished Cordierite honeycomb product (11).
2. A process for the manufacture of Cordierite honeycomb substrates by
extrusion as claimed in claim 1 wherein for good extrusion of
honeycomb upto 200 cells and wall thickness around 0.2mm the
sigma (00) values are obtained between 0.15 to 0.35 MPa and alfa (1)
values between 0.005-0.07 M Pa (mm/min)m and "nT value not above
0.40, Tow (T0) values between 0.001-0.002, Beta (B) values between
0.001-0.02 and V value not greater than 0.45.
3. A process for the manufacture of Cordierite honeycomb substrates by
extrusion as herein described and illustrated.

Documents:

2752-del-1996-abstract.pdf

2752-del-1996-claims.pdf

2752-del-1996-correspondence-others.pdf

2752-del-1996-correspondence-po.pdf

2752-del-1996-description (complete).pdf

2752-del-1996-drawings.pdf

2752-del-1996-form-1.pdf

2752-del-1996-form-19.pdf

2752-del-1996-form-2.pdf

2752-del-1996-form-3.pdf

2752-del-1996-form-6.pdf

2752-del-1996-gpa.pdf

2752-del-1996-petition -138.pdf

abstract.jpg

« Previous Patent

Next Patent »

Patent Number

214392

Indian Patent Application Number

2752/DEL/1996

PG Journal Number

08/2008

Publication Date

22-Feb-2008

Grant Date

11-Feb-2008

Date of Filing

11-Dec-1996

Name of Patentee

BHARAT HEAVY ELECTRICALS LTD.

Applicant Address

BHEL HOUSE, SIRI FORT, NEW DELHI-110049, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	RATHINDRA NATH DAS	MANAGER/CTI/BHEL/BANGALORE-560012, INDIA.
2	MADHUSOODANA CHENGALA DAMODARA	SCIENTIFIC OFFICER/CTI/BHEL/EPD/BANGALORE-560012, INDIA.

PCT International Classification Number

C04B 35/16

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA