Title of Invention

A PROCESS FOR THE PRODUCTION OF HIGH ALUMINA SELF FLOW CASTABLES

Abstract

A process for the production of high alumina self flow castables by mixing intimately 49.5- 72.5 wt% alumina aggregates of mixed particle grading, 0 - 28 wt % calcined clay aggregates of mixed particle grading, 18-30 wt% fine calcined alumina of blew 325 BS sieve particle size distribution, 2 wt% microfine silica with 11-12 wt% colloidal silica binder to obtain a castable mix, casting the product, air drying at room temperature of 22 - 24 hrs followed by drying at around 110°C for 2 hours, to obtain self flow castables.

Full Text

The present invention relates to a process for the production of high alumina containing self flow castable. The present invention is useful for producing high alumina (AI2O3) self flow castable with superior hot strength properties which can be used as high temperature refractory materials for application in iron & steel, cement & other high temperature processing industries. The self flow castable developed in the present invention is very useful for those application areas where vibrating is difficult and support anchors are set too closely due to small & narrow places. 70- 90% AI2O3 containing self flow castable of the present invention can be easily poured without segregation of particles due to its self flow characteristics. In the present day method for the production of 70-90% AI2O3 containing self flow castable, different kinds of synthetic high alumina aggregates are used such as calcined bauxite, tabular alumina, brown & white fused alumina, mullite, calcined clay etc with particular particle grading; finer materials such as calcined alumina, reactive alumina, sillimanite fines, binders such as colloidal silica, hydrated alumina without or with minor quantity of calcium alumina cement. All these coarse & fine raw materials are intimately mixed with binder. The mixed mass in the plastic form is poured into the application places followed by drying at 110°C . The product made out of this present day method does not give desired hot strength properties such as hot modulus of rupture (Hot MOR) value after prefiring at 1400°C for 2 hours as demanded by iron & steel industries. Reference may be made to the work of B. Myhre, paper presented at the Am. Ceram. Soc. 98th Annual Meeting held in Indianapolis, April 14- 17 , 1996 wherein it is shown that samples of several self flow castable compositions prefiredat1400°Cfor24 hours give hot MOR values to the extent of around 50 Kg/cm2, In another reference, Paper presented at UNTECR '97 in New Orlean, USA, Nov. 4-8, 1997, it is cited that few self flow castable compositions resulted hot MOR value more than 50 Kg/cm2 but again with 24 hrs firing at 1400°C. It is also reported in Part-3 of the paper presented by B. Myhre at the 98th annual meeting of Am. Cer. Soc. in 1996 that the castable samples prefired at 1400°C for 2 hrs give the Hot MOR value in the order of 25-30 Kg/cm2 only. However, from the applications point of view, it became necessary to achieve the hot MOR value more than 50 Kg/cm2 for the samples prefired at 1400°C for 2 hrs particularly for the iron & steel industries. The main disadvantages of the above processes are (a) Lower hot strength properties (Hot MOR) after prefiring at 1400°C for 2hrs. (b) Energy intensive. (c) Tailored made properties not achievable. (d) Restriction of application areas. The main object of the present invention is to provide a process for the production of high alumina containing self flow castable and cast product thereof which obviates the drawbacks as detailed above. Another object of the present invention is to provide a 70 - 90% alumina containing self flow castable material which gives hot MOR value more than 50 Kg/cm2 for the samples fired at 1400°C for 2 hrs. In the present invention, a process has been developed for the production of high alumina (A12O3) self flow castable and cast product with superior hot strength properties, hi this Process, the partite size distribution of product mix fill up the available void volume in a bed and is fully occuupied by the finer fractions and results in a dense body. The product produced by the present process has shown Hot MOR value in the range of 76-93 Kg/cm2 at 1400°C ( 2 hrs compared to only 25 - 50 Kg/ cm2 obtained by existing known process. The castable product produced by the present invention can be used in iron & steel, cement & other high temperature processing industries where high hot strength properties are the prime requirement. Accordingly, the present invention provides a process for the production of high alumina self flow castables characterized in that the process comprises mixing intimately 49.5- 72.5 wt% alumina aggregates of mixed particle grading as herein described , 0 - 28 wt % calcined clay aggregates of mixed particle grading as herein described , 18-30 wt% fine calcined alumina below 325 BS sieve particle size distribution, 2 wt% microfine silica with 11-12 wt% colloidal silica to obtain a castable mix, casting the product, air drying at room temperature for 22 - 24 hrs followed by drying at 110°C for 2 hours to obtain self flow castables. In an embodiment of the present invention, high alumina aggregates used may be selected from synthetic raw materials such as calcined bauxite, tabular alumina, brown or white fused A12O3, mullite or mixture thereof. In another embodiment of the present invention, the mixed particle grading of high alumina aggregates used may be selected from 30-34 wt%, 14-20 wt% 16, 1.5-6 wt%, 1-3.5 wt%, 1-3 wt%, 2-6 wt% BS Sieve. In yet another embodiment of the present invention, the physico-chemical properties of the calcined clay aggregates used may be in the range of A1203 38-40 wt%, Ft2O3 1.1-1.5 wt%, bulk density : 230 - 2.40 gm/cc, apparent porosity 11 - 13%, mixed particle grading of 0 - 5 wt% below 16 above 30, 0 - 6.5wt % below 30 above 72, 0-16.5wt% below 100 above 325 mesh BS Sieve. In still another embodiment of the present invention, the alumina content of the fine calcined alumina used may be min 99% and pass through 325 BS Sieve ( 45 (j.m ) having particle size distribution in the range of 2-3 wt% below 45 above 20 urn, 5 -10wt% below 20 above 10 jam, 55 - 60 wt% below 10 above 5 (im, 20 - 25 wt% below 5 above 2 µm ,5-10 wt% below 2 µm. In yet another embodiment of the present invention silica (SiO2) and carbon content of microfine silica used may be Min 98 wt%, and max 0.5 wt% respectively and coarse particle (45(0. m) content may not exceed 0.2%. In another embodiment of the present invention, the solid content (SiO2) and particle size of colloidal silica used as binder may be in the range of 30 - 40 wt% & 10 -15 nanometer respectively. In another embodiment of the present invention the particle size distribution of the product mix may be in the range of 30 - 34 wt% below 3 above 6, 14-20 wt% below 6 above 16, 5.5 - 7 wt% below 16 above 30, 3 - 7.5 wt% below 30 above 72, 1 - 3 wt% below 72 above 100, 6 - 18 wt% below 100 above 325, 20 - 32 wt% below 325 BS Sieve. In still another embodiment of the present invention, mixing time of aggregates, fines & binder may be in the range of 12 - 15 minutes. The detail process steps of the present invention are : (1) mixing intimately for 12 - 15 minutes 49.5 - 72.5wt% high alumina aggregates of different particle grading, 0 - 28 wt % calcined clay aggregates of different particle grading, 18-30 wt% fine calcined alumina of particular particle size distribution, 2 wt% microfme silica with 11-12 wt% colloidal silica binder for specified time period to obtain a castable mix. (2) Casting the product. (3) Room temperature air drying for 22- 24 hrs followed by drying at 110°C for 22- 24hrs. (4) Firing the dried cast product at 14 00 °C for 2 hours soaking time. The process of the present invention provides for the production of high AhOs self flow castable and cast product with superior hot strength properties. In this process, the particle size distribution of product mix results in a dense body. The product produced by the present process shows Hot MOR value which varies from 76-93 Kg/cm2 at 1400°C ( 2 hrs) compared to only 25-30 Kg/cm2 obtained by existing known process. The novelty of the present invention resides in obtaining a self flow castable material which gives hot strength properties such as HMOR value in the range of 76 -93 Kg/cm2 which is much above the currently available similar materials (25 - 30 Kg/cm2) The inventive steps lie in selecting the compositions in such a way that the particle size distribution of the product mix falls within the range as specified below :. (Table Removed) The following examples are given by way of illustration and should not be construed to limit the scope of the present invention. Example - 1 340 gms of below 3 above 6/ 150 gms of below 6 above 16, 20 gms of below 16 above 30, 10 gms of below 30 above 72, 10 gms of below 72 above 100, 20 gms of below 100 above 325 BS Sieve of calcined bauxite ; 50 gms of below 16 above 30, 50 gms of below 30 above 72, 150 gms of below 100 above 325 mesh BS Sieve of calcined clay ; 180 gms of fine calcined alumina, 20 gms of microfine silica are intimately mixed with 110 cc of colloidal silica for a period of 12 minutes in a Hobert type of mixing equipment. The mixed plastic mass was then poured in a mould of 50 x 50 x 50 mm cube and 150 x 25 x 25 mm rectangular shapes & allowed them for setting. Then the shaped samples 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 900°C & 1400°C with 2 hrs soaking time for evaluation of properties. The resultant product characteristics were : (Table Removed) Example - 2 300 gms of below 3 above 6, 200 gms of below 6 above 16, 60 gms of below 16 above 30, 30 gms of below 30 above 72, 30 gms of below 72 above 100, 60 gms of below 100 above 325 mesh (BS Sieve) calcined bauxite ; 300 gms of finer calcined alumina ; 20 gms of micro fine silica are intimately mixed with 120 cc of colloidal silica for a period of 15 minutes in a Hobert type of mixing equipment. The mixed mass was then powered in a mould of 50 x 50 x 50 mm cubes and 150 x 25 x 25 mm rectangular shapes & allowed them for setting. Then the shaped samples were released from mould & allowed for 24 hrs air drying followed by 24 hrs drying at 110°C. The dried samples were heated at 900°C & 1400°C with 2 hrs. soaking time for evaluation of properties. The resultant products characteristics were : (Table Removed) Example - 3 340 gms of below 3 above 6, 140 gms of below 6 above 16, 15 gms of below 16 above 30, 10 gms of below 30 above 72, 10 gms of below 72 above 100, 15 gms of below 100 above 325 mesh (BS sieve) calcined bauxite ; 40 gms of below 16 above 30, 40 gms below 30 above 72 & 140 gms of below 100 above 325 mesh (BS Sieve) Calcined clay; 25 gms of below 30 above 72 and 25 gms of below 100 above 325 mesh (BS Sieve) synthetic mullite ; 180 gms of finer calcined alumina, 20 gms of microfine silica were mixed intimately with 120 cc of colloidal silica in a Robert type of mixing equipment for a period of 15 minutes. The mixed mass was then poured into a mould of 50 x 50 x 50 mm cubes & 150 x 25 x 25 mm rectangular shapes & allowed them for setting. Then the shaped samples were released from the mould and allowed for 22 hrs air drying followed by 24 hrs drying at 110°C. The dried samples were heated at 900°C & 1400°C with 2 hrs soaking time for evaluation of properties. The resultant product characteristics were: (Table Removed) The main advantages of the present invention are : 1. The present process utilizes an unique combination of panicle grading thereby a cast product with superior hot properties (Hot MOR) is obtained. 2. The present process requires less time of heating ( 2 hrs only) to achieve desired Hot MOR value at 1400°C. 3. The present process saves energy for application in industries. 4. The present process achieved tailor made properties. We Claim: 1. A process for the production of high alumina self flow castables characterized in that the process comprises mixing intimately 49.5- 72.5 wt% alumina aggregates of mixed particle grading as herein described , 0 - 28 wt % calcined clay aggregates of mixed particle grading as herein described , 18-30 wt% fine calcined alumina below 325 BS sieve particle size distribution, 2 wt% microfine silica with 11-12 wt% colloidal silica to obtain a castable mix, casting the product, air drying at room temperature for 22 - 24 hrs followed by drying at 110°C for 2 hours to obtain self flow castables. 2. A process as claimed in claim 1 wherein high alumina aggregates used are selected from synthetic raw materials calcined bauxite, tabular alumina, white or brown fused A12O3, mullite or mixture thereof. 3. A process as claimed in claims 1-6 wherein the solid content of SiO2 in colloidal silica ranges from 30 - 40 wt% and the particle size ranges from 10-15 nanometer respectively. 4. A process as claimed in claims 1-8 wherein the mixing time ranges form 12-15 minutes. 5. A process for the production of high alumina containing self flow castable substantially as herein described with reference to given examples.

Documents:

121-del-2002-abstract.pdf

121-del-2002-claims.pdf

121-del-2002-correspondence-others.pdf

121-del-2002-correspondence-po.pdf

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

121-del-2002-form-1.pdf

121-del-2002-form-18.pdf

121-del-2002-form-2.pdf

121-del-2002-form-3.pdf