Title of Invention

A PROCESS FOR THE PRODUCTION OF LOW DENSE REFRACTORY CASTABLE

Abstract

In the present invention, a process has been developed for the production of low dense and highly porous refractory castable using higher quantity of light weight aggregates such as hollow ceramic spheres of alumina & mullite along with calcined clay, calcined alumina and a chemical binder as raw materials. Incorporation of higher quantity of hollow-spheres and the distribution of various size fractions in the product mix resulted a low dense (1.15-1.25 gm/cc BD) and highly porous (50 - 56% porosity ) refractory castable compared to 1.45 - 2.10 gm/cc B.D. and 37 - 43% porosity obtained by existing known process. The low dense refractory castable mix produced by the present invention can be used in high temperature kilns & furnaces as heat insulating lining material which saves significant amount of fuel energy by preventing heat losses. 11

Full Text

The present invention relates to a process for the production of low dense refractory castable. The present invention is useful for producing low dense refractory castable for application as heat insulating material in industrial kilns and furnaces which prevent heat losses thereby saving energy. In the present day method for the production of light weight refractory castable, porous clay, pearlite, vermiculite, mullite hollow- spheres are used along with alumina or clay powder, alumina cement binder and other admixtures. All these coarse and fine raw materials are intimately mixed with required amount of water. The mixed mass in the plastic form is poured into the application places followed by drying at 110°C. References may be made to the work of Z. Benggen & Liu Xiuyun, paper presented at UNITECR'95 in Kyoto, Japan, Nov. 19-22, 1995, wherein it is shown that light weight castable produced from various combination of porous mullite aggregate, powder and alumina cement binder possesses bulk density in the range of 1.45-1.75 gm/cc even with the use of porous aggregate upto 70%. It is also cited in this literature that addition of floating particles could further lower the bulk density, however cavity collapse results in a larger bulk concentration which ultimately restrict the application temperature of the castable. In another reference, paper presented at UNITECR '99 in Berlin, Germany, Sept. 6-9, 1999 by H. Feldborg and B. Myhre, it is reported that light weight castable produced from various combination of mullite hollow-sphere, alumina aggregate & powder with alumina cement binder possesses bulk density in the range of 1.80-2.10 gm/cc and porosity in the range of 37-43% only. For superior heat insulating performances, further lowering of bulk density (less than 1.30 gm/cc) & increase in porosity (more than 50%) are necessary in a wide range of temperatures. Further, it is reported in the above literature that when the quantity of the hollow-sphere aggregate exceeded a certain limit (> 45%), the castable mix gets separated due to more water addition need by cement binder. Presence of CaO in alumina cement binder commonly used in present day method of production is also harmful for high temperature applications due to liquid formation with other alumino-silicate materials. The main disadvantages of the present day methods are : (a) Higher bulk density (1.45-2.10 gm/cc) & lower apparent porosity ( Less than 45 %) (b) Cement binder restricts the use of higher quantity of lightweight aggregates. (c) Forms liquid at higher temperatures due to the presence of CaO in alumina cement binder which is detrimental for high temp, applications. (d) Tailored made properties are not achievable (e) Restriction of application areas. The main object of the present invention is to provide a process for the production of low dense refractory castable which obviates the drawbacks as detailed above. Another object of the present invention is to provide a low dense refractory castable material which gives bulk density lower than 1.30 gm/cc and porosity more than 50 %. Yet another object of the present invention is to provide a process for the production of cement (CaO) free low dense refractory castable. In the present invention, a process has been developed for the production of low dense and highly porous refractory castable using higher quantity of light weight aggregates such as hollow ceramic spheres of alumina & mullite along with calcined clay, calcined alumina as superfine raw materials. Since, use of cement binder with higher quantity of light weight aggregate cause the castable mix to segregate due to the presence of larger quantity of water, colloidal silica has been used as binder in the present process instead of cement. Incorporation of higher quantity of hollow-spheres and the distribution of various size fractions in the product mix resulted a low dense ( 1.15 - 1.25 gm/cc BD) & highly porous (50 - 56% porosity ) refractory castable compared to 1.45-2.10 gm/cc .B.D. & 37 - 43% porosity obtained by existing known process. The low dense refractory castable mix produced by the present invention can be used in high temperature kilns & furnaces as heat insulating lining material which saves significant amount of fuel energy by preventing heat losses. Accordingly, the present invention provides a process for the production of low dense refractory castable which comprises: i) intimate mixing of 65 - 75 wt% hollow-sphere aggregate of various size fractions, ii) addition of 7-25 wt% pulverized calcined alumina and 0-28 wt% calcined clay powder and their uniform mixing. iii) intimate mixing of 18-25 wt% colloidal silica binder of total batch to obtain a castable mix. In an embodiment of the present invention the hollow-sphere aggregates used may be made from aluminous material such as high alumina and mullite. In another embodiment of the present invention, the hollow sphere aggregates such as high alumina & mullite may be used singly or in the proportion of 6 : 7. In still another embodiment of the present invention, the different sizes of alumina hollow-spheres used may be selected from 50-70 wt% below 5 above 8,15-30 wt% below 8 above 16, 15-20 wt% below 16 above 30 BS sieve and the different sizes of mullite hollow-spheres used may be selected from 70-80 wt% below 4 above 6 and 20-30 wt% below 6 above 8 BS sieve. In yet another embodiment of the present invention, the chemical constituents of fine calcined clay powder used may be in the range of A12O3 38-40 wt%, Fe2O3 1.1-1.5 wt% and pass through 150 BS sieve. In yet another embodiment of the present invention, the silica content of colloidal silica used as binder may be in the range of 30 - 40 wt% and its particle size may be in the range of 10-15 nanometer. The detail process steps of the present invention are: (1) Intimate mixing of 65 - 75 wt% hollow- sphere aggregate of various size fractions. (2) Addition of 7-25 wt% pulverized calcined alumina and 0-28 wt% calcined clay powder and their uniform mixing. (3) Intimate mixing of 18-25 wt% colloidal silica of total batch to obtain a castable mix. The novelty of the present invention resides in obtaining a low dense refractory castable material which gives lower bulk density in the range of 1.15-1.25 gm/cc. which is much lower than the currently available similar materials ( 1.45 - 2.0 gm/cc). Further the porosity of the presently developed novel castable material is in the range of 50 - 56 % which is much above than the currently available similar materials ( 37-43%). The inventive step lie in using higher quantity of hollow-sphere aggregates along with colloidal silica as a synergistic mixture to produce the castable which reduces the unit weight of the castable mix as well as increases the porosity. The following examples are given by way of illustration and should not be construed to limit the scope of the present invention. Example-1 470 gms of below 4 above 6, 180 gms of below 6 above 8 BS sieve of mullite hollow-spheres, 280 gms of calcined clay powder, 70 gms of calcined alumina powder are intimately mixed with 250 cc of colloidal silica for a period of 15 minutes in a Hobert type of mixing equipment. To evaluate the properties of the castable mix, the mass was poured in a mould of 50 x 50 x 50 mm cube and allowed them for setting. Then the shaped cubes were released from the mould & allowed for 24 hrs air drying followed by 24 hrs drying at 110°C. The dried samples were heated at 1400°C for a period of 2 hrs soaking. The resultant product characteristics were : (Table Removed) Example - 2 400 gms of below 5 above 8, 200 gms of below 8 above 16, 150 gm of below 16 above 30 of alumina holospheres, 250 gms of calcined alumina powder are intimately mixed with 180 c.c. of colloidal silica for a period of 15 minutes in a Robert type of mixing equipment. To evaluate the properties of the castable mix, the mass was poured in a mould of 50 x 50 x 50 mm cube and allowed them for setting. Then the shaped cubes were released from the mould & allowed for 24 hrs air drying followed by 24 hrs drying at 110°C. The dried samples were heated at 1400°C for a period of 2 hrs soaking. The resultant product characteristics were : (Table Removed) Example - 3 270 gms of below 4 above 6, 80 gms of below 6 above 8 BS sieve of mullite hollow-sphere, 200 gms of below 5 above 8, 50 gms of below 8 above 16, 50 gms of below 16 above 30 of alumina holosphere, 150 gms of calcined clay powder, 200 gms of calcined alumina powder are intimately mixed with 200 c.c. of colloidal silica for a period of 15 minutes in a Robert type of mixing equipment. To evaluate the properties of the castable mix, the mass was poured in a mould of 50 x 50 x 50 mm cube and allowed them for setting. Then the shaped cubes were released from the mould & allowed for 24 hrs air drying followed by 24 hrs drying at 110°C. The dried samples were heated at 1400°C for a period of 2 hrs soaking. The resultant product characteristics were : (Table Removed) The main advantages of the present invention are : (1) The present process utilizes higher quantity of hollow-sphere aggregate thereby reducing the density of the castable mix and increasing the porosity. (2) The present process utilizes no cement (CaO) as a binder thereby permiting use of higher quantity of hollow-sphere aggregate and eliminates the chances of liquid phase formation at higher temperatures. (3) The present process achieved tailor made properties. (4) The present process removed the restriction of application areas. (5) The present process gives a low dense & highly porous castable mix with improved insulating properties thereby saving fuel energy. We claim : 1) A process for the production of low dense refractory castables which comprises: i) intimate mixing of 65 - 75 wt% hollow-sphere aggregate of various size fractions, ii) addition of 7-25 wt% pulverized calcined alumina and 0-28 wt% calcined clay powder and their uniform mixing, iii) intimate mixing of 18-25 wt% colloidal silica binder of total batch to obtain a castable mix. 2) A process as claimed in claim 1, wherein the hollow-sphere aggregates used are made from aluminous materials such as high alumina and mullite. 3) A process as claimed in claims 1-2, wherein the hollow sphere aggregates such as high alumina and mullite is used singly or in the proportion of 6 : 7. 4) A process as claimed in claims 1-3, wherein the different sizes of alumina hollow- spheres used are selected from 50-70 wt% below 5 above 8, 15-30 wt% below 8 above 16, 15-20 wt% below 16 above 30 BS sieve and the different sizes of mullite hollow-spheres used are selected from 70-80 wt% below 4 above 6 and 20-30 wt% below 6 above 8 BS sieve. 5) A process as claimed in claims 1-4 wherein the chemical constituents of fine calcined clay powder used is in the range of A12O3: 38 - 40 wt%, Fe2O3: 1.1 - 1.5 wt% and pass through 150 BS sieve. 6) A process as claimed in claim 1-5 wherein the silica content of colloidal silica binder used ranges from 30-40 wt% and its particle size is in the range of 10 - 15 nanometers. 7. A process for the production of low dense refractory castable substantially as herein described with reference to the examples.

Documents:

284-DEL-2002-Abstract-(12-01-2009).pdf

284-del-2002-abstract.pdf

284-DEL-2002-Claims-(12-01-2009).pdf

284-del-2002-claims.pdf

284-DEL-2002-Correspondence-Others-(12-01-2009).pdf

284-del-2002-correspondence-others.pdf

284-DEL-2002-Description (Complete)-(12-01-2009).pdf

284-del-2002-description (complete).pdf

284-del-2002-form-1.pdf

284-del-2002-form-18.pdf

284-DEL-2002-Form-2-(12-01-2009).pdf

284-del-2002-form-2.pdf

284-DEL-2002-Form-3-(12-01-2009).pdf

284-del-2002-form-3.pdf

284-del-2002-petition-137.pdf

284-del-2002-petition-138.pdf