Title of Invention

A HIGH ALUMINA SELF FLOW CASTABLE REFRACTORY COMPOSITION AND ITS PROCESS FOR MANUFACTURE

Abstract

High alumina self flow castable refractory composition and a process for manufacture of such high alumina self flow castables The high alumina self flow castable refractory composition is obtained of selective mix of Fused alumina 65% to 70% by wt Reactive alumina 15% to 18% by wt Calcined alumina 2% to 5% by wt Micro fused silica 4% to 5% by wt and High alumina cement 1 to 4% by wt. wherein the distribution coefficient of grains is less than 0.24 and grain size is selected such that finer fractions below 325 BSS are less than 25% by wt The self flow character of the castables is achieved by use of selective good quality easily dispersible superfines together with selective additives Also, in the castables the volume of liquid is selected to exceed the pore volume of the basic structure to thereby form a liquid film around the particles to thereby minimise the friction between the particles It is thus possible to achieve self flow high alumina castables at a lower production and application costs having improved thermo mechanical properties and adapted to take its own shape without use of any vibrator and the like. The castable can be applied to produce complicated shapes and for thinner parts which are difficult to penetrate as well as for the repair of the original lining. Self flow castable wheel can be installed in walking beam reheat furnace, ladle and tundish back-up lining, ladle covers, sealing and repairing of reheat furnace roof and various intricate shapes The castable have easier installation capability without compaction by means of vibrator thereby also avoiding extensive human involvement.

Full Text

The present invention relates to high alumina self flow castable refractory composition and a process for manufacture of such high alumina self flow castables In particular, the invention provides for castable compositions which would not require any vibrator or the like for application in any desired shape and is self flowing with long life and good castable properties Various types of refractory castable compositions are known in the art Main problem for using those castable composition are that these castables are thixotropic in nature and application of a vibrator is a must for achieving the desired shape and properties of the product Introduction of a vibrator in the process often poses problem particularly in casting of complicated shapes Thixotropy is the property of increase of viscosity with reduction of shear rate of the suspension In order to solve the problem of thixotropy of castable composition, inventors after prolong research in this field were able to develop a self-flowing castable composition which will maintain dilatant flow behaviour i e, reduction of viscosity of castable with reduction of shear rate and thus was able to stop the use of vibrator during its application for producing different shapes as required in industry High alumina refractory castables have been extensively investigated for producing the desired castables because of their significant advantage over other refractory materials The characteristics that have made such castables so attractive are lower production and application costs, versatility and performance at high temperature High alumina self-flow castable composition is characterised by its flow on 'its own without any energy input like vibration etc , dunng its application interaction between particles present in the composition obstruct the flow of the castables and therefore interparticle forces should be kept as minimum as possible Further that to maintain self flowing nature of the composition the system has to be well dispersed and friction between the particles has to be minimised First one is accomplished by using good quality easily dispersible superfines together with proper additive while the second one is achieved by maintaining the volume of 2 liquid exceeding the pore volume of the basic substances which helps to form a liquid film around the particles. The shape of the particle is another factor that affects free flow Normally, particles approaching spheres will result in higher free flow values than angular or flaky particles. Size distribution of particles below 50 micron play a decisive role For self-flow castables a lower distribution co-efficient particles is required and that is kept below 0 26 The basic object of the invention is therefore to provide a self-flow high alumina castables at a lower production and application costs having improved thermo mechanical properties and adapted to take its own shape without use of any vibrator and the like. Further object is to produce a castable having easier installation capability without compaction by means of vibrator. Another object is to produce a high alumina castable which can be applied to produce complicated shapes and for thinner parts which are difficult to penetrate as well as for the repair of the original lining Yet another object is to reduce the installation time and lowered human involvement Yet further object is to provide self-flow castable which can be installed in walking beam reheat furnace, ladle and tundish back-up lining, ladle covers, sealing and repairing of reheat furnace roof and various intricate shapes. Thus according to one aspect of the present invention there is provided high alumina self flow castable refractory composition comprising Fused alumina 65% to 70% by wt. Reactive alumina 15% to 18% by wt Calcined alumina 2% to 5% by wt Micro fused silica 4% to 5% by wt and High alumina cement 1 to 4% by wt 3 wherein the distribution coefficient of grains is less than 0.24 and grain size is selected such that finer fractions below 325 BSS are less than 25% by wt of the total composition. In accordance with a preferred aspect the self flow castable composition is obtained of said fused alumina, reactive alumina, calcined alumina, micro fused silica and high alumina cement wherein the finer fractions below 325 BSS are maintained below 25% by wt of the total composition. In accordance with yet further preferred aspect the high alumina self flow castable refractory composition comprises . said fused alumina of particulate size 5 to 90 BSS in an amount of 65 to 70% by wt, said reactive alumina of particulate size of 300 to 350 BSS in an amount of 15% to 18% by wt , said calcined alumina of particulate size 300 to 350 BSS in amounts of 2 to 5% by wt., said micro fused silica of particulate size 300 to 350 BSS in amount of 4 to 5% by wt and said high alumina cement of particulate size 150 to 200 BSS in an amount of 1 to 4% by wt, and wherein the distribution coefficient of grains is less than 0.24 and the grain size is selected such that finer fraction below 325 BSS are less than 25% by wt. In accordance with further aspect of the present invention there is provided a process for production of high alumina self flow castable refractory composition comprising providing a selective mix of fused alumina 65% to 70% by wt, reactive alumina 15 to 18% by wt, calcined alumina 2% to 5% by wt., micro fused silica 4% to 5% by wt and high alumina cement 1 to 4% by wt, with dispersant in an amount upto 0.1% by wt and subjecting the mix to dry mixing for a period of five minutes , 4 adding water in desired proportion to the mix slowly and continuing mixing to thereby provide said free flowing castable refractory composition having distribution coefficient of grains less than 0.24 and the grain size such that finer fraction below 325 BSS constitute less than 25% by wt. In accordance with the preferred aspect in the process of manufacture of the high alumina self flow castable refractory composition disclosed above fused alumina of particular size 5-90 BSS, reactive alumina of particulate size 300 - 350 BSS preferably 325 BSS, calcined alumina of particulate size 300 to 350 BSS preferably 325 BSS, micro fine silica of particulate size 300 to 350 BSS preferably 325 BSS and high alumina cement of particulate size 150 to 200 BSS preferably 170 BSS are used Preferably, in the above disclosed process of the invention the coarser fraction is first taken in a mixer, the finer fraction was then added to it along with a dispersant and the whole ingredients were dry mixed for at least 5 minutes, then measured amount of water (in the range of 5 to 6%) by volume was added to it and mixed with constant stirring for at least 5 minutes to produce the composition. Dispersant used in the process may be selected from usual dispersants Dispersant is used in the range of 05 to 0 1% of the total substances and is added along with the finer fraction before addition of water in the composition Granulometry and grain size are the most important factors and are required to be closely controlled Granulometry is controlled by keeping the distribution coefficient of grains less than 0 24 and in the grain size form fraction below 325 BSS should be kept below 25% to obtain sufficient self flow The developed castable is high alumina based and CaO in small amount is used in the form of high alumina cement The castable contain silica to favour the formation of mullite and cement is added to impart green strength An inter-granular liquid is formed in this system that significantly reduced the 5 thermomechanical performance of the castable In order to diminish the amount of liquid phase at high temperature and simultaneously improve the refractoriness of the castable, a reduction of cement content was necessary. Fine and superfine particles improving particle packing, reducing water consumption and leading to low porosity castable. The incorporation of fine and superfine particles require the use of specific defloculants for dispersion, so optimum particle packing at high solid content could be attained. Cement content may be reduced to 1 - 3% to improve the refractonness of the composition at high temperature. The details of the invention its objects and advantages are explained hereunder in greater detail in relation to non-limiting exemplary embodiment as discussed hereunder. EXAMPLE-I RAW MATERIAL: Fused alumina Process The coarser particulates comprising 5-90 BSS are first taken in the mixer and thereafter the finer fractions comprising 150 - 350 BSS are added alongwith the dispergant.and the ingredients are allowed to dry mix for a period of five minutes Thereafter, 5-6% by volume of water was added and mixed with stirring for two to three minutes to provide the castable composition 6 Following are the physico-chemical properties of the castable obtained above Chemical wt % Al2O3 - CaO - 0.3-0 8% The physical properties of the castables of the invention (EXAMPLE - I) were tested and compared with the said properties of conventional castable in TABLE-I hereunder TABLE-I PHYSICAL PROPERTIES EXAMPLE -1 CONVENTIONAL CASTABLES B D gm/cc at 110°C/24 hrs 3.10 - 3 12 2 95 - 3 1 AP(%), after firing the sample at 12-14 12-15 1500°C/3hrs CCS,kg/cm2 at 110°C/24 hrs 450 - 500 400 - 500 At 800°C/3 hrs 500 -550 700 - 800 HMOR at 1400°C/30 mm, kg/cm2 45 - 55 45 - 50 Repeat PLC(%) at 1600°C/2 hrs -1 5 -1 to -1 8 Spalling resistance(cycles) water 7-8 5-6 quenching At 1200°C It would be evident from the above physical properties that the castables of the invention have significantly improved thermo-mechanical characteristics and being self-flow castables can take its own desired shape without need for the vibrator or the like used under the known art In particular, the self-flow castables of the invention have the following advantages : - Easier installation without compaction by means of vibrator, - It can be applied in complicated shapes and for thinner parts which are difficult to penetrate as well as for the repair of the original lining It can greatly decrease the installation time and lower human involvement This new mass can be installed in walking beam reheat furnace, ladle and tundish back-up lining, ladle covers, sealing and repairing of reheat furnace roof and various intricate shapes 7 WE CLAIM 1 High alumina self flow castable refractory composition comprising Fused alumina 65% to 70% by wt Reactive alumina 15% to 18% by wt Calcined alumina 2% to 5% by wt Micro fused silica 4% to 5% by wt. and High alumina cement 1 to 4% by wt. wherein the distribution coefficient of grains is less than 0 24 and grain size is selected such that finer fractions below 325 BSS are less than 25% by wt. of the total composition 2 High alumina self flow castable refractory composition as claimed in claim 1 comprising said fused alumina, reactive alumina, calcined alumina, micro fused silica and high alumina cement wherein the finer fractions below 325 BSS are maintained below 25% by wt of the total composition 3. High alumina self flow castable refractory composition as claimed in anyone of claims 1 or 2 comprising : said fused alumina of particulate size 5 to 90 BSS in an amount of 65 to 70% by wt; said reactive alumina of particulate size of 300 to 350 BSS in an amount of 15% to 18% by wt ; said calcined alumina of particulate size 300 to 350 BSS in amounts of 2 to 5% by wt, said micro fused silica of particulate size 300 to 350 BSS in amount of 4 to 5% by wt and said high alumina cement of particulate size 150 to 200 BSS in an amount of 1 to 4% by wt, and wherein the distribution coefficient of grains is less than 8 0 24 and the grain size is selected such that finer fraction below 325 BSS are less than 25% by wt. 4 High alumina self flow castable refractory composition as claimed in anyone of claims 1 to 3 preferably comprising . Fused alumina 65-70% of wt size Reactive alumina 15-18% of wt. size 300-350 BSS Calcined alumina 2-5% of wt size 300-350 BSS Microfine Silica 4-5% of wt. size 300-350 BSS High alumina cement 1-4%of wt size 150-200 BSS 5 High alumina self flow castable refractory composition as claimed in anyone of claims 1 to 4 wherein the dispersant used are selected from usual dispersants 6. High alumina self flow castable refractory composition as claimed as claimed in anyone of claims 1 to 5 wherein the dispersant is used in the range of .05 to 0 1% 7. A process for production of high alumina self flow castable refractory composition as claimed in anyone of claims 1 to 6 comprising providing a selective mix of fused alumina 65% to 70% by wt, reactive alumina 15 to 18% by wt, calcined alumina 2% to 5% by wt, micro fused silica 4% to 5% by wt and high alumina cement 1 to 4% by wt, with dispersant in an amount upto 0 1% by wt and subjecting the mix to dry mixing for a period of five minutes , adding water in desired proportion to the mix slowly and continuing mixing to thereby provide said free flowing castable refractory composition having distribution coefficient of grains less than 0 24 and the grain size such that finer fraction below 325 BSS constitute less than 25% by wt 9 8. A process of manufacture of the high alumina self flow castable refractory composition as claimed in claim 7 wherein fused alumina of particulate size 5-90 BSS, reactive alumina of particulate size 300 - 350 BSS preferably 325 BSS, calcined alumina of particulate size 300 to 350 BSS preferably 325 BSS, micro fine silica of particulate size 300 to 350 BSS preferably 325 BSS and high alumina cement of particulate size 150 to 200 BSS preferably 170 BSS are used 9 A process as claimed in anyone of claims 7 or 8 wherein the coarser fractions are first taken in a mixer, the finer fractions are then added to it along with a dispersant .and the whole ingredients dry mixed, then measured amount of water by volume is added to it and mixed with constant stirring for at least 5 minutes to produce the composition. 10 A process as claimed in anyone of claims 7 to 9 wherein the dispersant used in the process is selected from usual dispersants 11 A process as claimed in claim 10 wherein the dispersant is used in the range of .05 to 1% of the total substances 12 High alumina self flow castable refractory composition and a process for production of high alumina self flow castable refractory composition substantially as herein described. High alumina self flow castable refractory composition and a process for manufacture of such high alumina self flow castables The high alumina self flow castable refractory composition is obtained of selective mix of Fused alumina 65% to 70% by wt Reactive alumina 15% to 18% by wt Calcined alumina 2% to 5% by wt Micro fused silica 4% to 5% by wt and High alumina cement 1 to 4% by wt. wherein the distribution coefficient of grains is less than 0.24 and grain size is selected such that finer fractions below 325 BSS are less than 25% by wt The self flow character of the castables is achieved by use of selective good quality easily dispersible superfines together with selective additives Also, in the castables the volume of liquid is selected to exceed the pore volume of the basic structure to thereby form a liquid film around the particles to thereby minimise the friction between the particles It is thus possible to achieve self flow high alumina castables at a lower production and application costs having improved thermo mechanical properties and adapted to take its own shape without use of any vibrator and the like. The castable can be applied to produce complicated shapes and for thinner parts which are difficult to penetrate as well as for the repair of the original lining. Self flow castable wheel can be installed in walking beam reheat furnace, ladle and tundish back-up lining, ladle covers, sealing and repairing of reheat furnace roof and various intricate shapes The castable have easier installation capability without compaction by means of vibrator thereby also avoiding extensive human involvement.

Documents:

00538-cal-2000-abstract.pdf

00538-cal-2000-claims.pdf

00538-cal-2000-correspondence.pdf

00538-cal-2000-description(complete).pdf

00538-cal-2000-form-1.pdf

00538-cal-2000-form-18.pdf

00538-cal-2000-form-2.pdf

00538-cal-2000-form-3.pdf

00538-cal-2000-pa.pdf

538-cal-2000-granted-abstract.pdf

538-cal-2000-granted-claims.pdf

538-cal-2000-granted-correspondence.pdf

538-cal-2000-granted-description (complete).pdf

538-cal-2000-granted-examination report.pdf

538-cal-2000-granted-form 1.pdf

538-cal-2000-granted-form 18.pdf

538-cal-2000-granted-form 2.pdf

538-cal-2000-granted-form 3.pdf

538-cal-2000-granted-letter patent.pdf

538-cal-2000-granted-pa.pdf

538-cal-2000-granted-reply to examination report.pdf

538-cal-2000-granted-specification.pdf