Title of Invention

AN IMPROVED PROCESS FOR PRODUCING ALUMINA CHROME REFRACTORY WITH EXCELLENT SLAG RESISTANCE AND HIGH HOT STRENGTH

Abstract An improved process for producing alumina-chrome refractozy with excellent slag resistance and high hot strength characterised in that the process comprises following steps : (i) alumina is blended with equivalent amount of chromite ore for 15 to 20 weight % Cr2O3; (ii) the blend is coground; (iii) the coground blend is treated with 2% by weight daxtrin solution and briquetted into briquettes/pellets by pressing the same uniaxially in a hydraulic press at a pressure of 1000 kg/cm2; (iv) the briquettes/pellets are sintered at 1550-l600°C followed by soaking azid cooling of the same to the ambient temperature in natural air; (v) the briquettes/pellets are crushed and ground into grogs; (vi) the grogs or white fused alumina are mixed with plastic clay and reactive Bayer's alupina, and pressed and fired into bricks to produce the refractory of chemical conrposition (by weight %)i Al2O,-50 to 65, Fe2O3-6,0 to 7.5 and Cr2O3-15 to 20.
Full Text The present invention relates to an improved process for producing alumina-chrome refractory with excellent slag resistance and high hot strength. The invention relates more particularly to a process for producing refractory bricks of increased slag resistance and hot strength from relatively low cost raw ingredients, for lining ladles, electric arc furnace (EAF) launders and blast furnace (BF) runners used in steel manufacturing plants. For manufacturing steel of improved quality at an increased efficiency the continuous casting method has been introduced in the steel industry, in which the chemical composition of the steel produced is adjusted in the ladles, causing an excessive stress on the refractory bricks used for lining the ladles. The refractory bricks produced in the existing process do not meet this extra stress imparted on them satisfactorily, particularly in respect of their slag resistance and hot strength. Moreover, in the existing process synthetic alumina and Cr2O3 are used, which are relatively exoensive and require to be fired at a relatively high temperature i.e. above 1600°C. For both these counts the cost of refractory bricks produced in the existing process is relatively high.
The object of the present invention is to provide a process for producing refractory bricks of relatively high slag resistance and hot strength at a relatively low cost.
In the invented process the alumina-chrome refractorie have been synthesised from relatively low cost chromite ores and Bayer's alumina (BA) or white fused alumina (WFA), which are available in plenty in India. The process comprises the following basic steps ;
(a) mixing chromite ore (Cr) with Bayer's alumina (BA), cogrinding,pressing and sintering the mixed;
(b) crushing and grinding the sintered mix to produce grog;
(c) mixing plastic clay and reactive AI2O, with the
grog (developed alumina-chrome grog)or white fused alumina (WFA) along with additional chromite ore.
(d) pressing, drying and firing the mix to produce
bricks.
The invention is described fully and particularly in an unrestricted manner with reference to the accompanying drawings in which Figure 1 is a flow chart showing the various steps followed in the invented process.
Referring to Fig. 1, the invented process comprises the following steps :-
(i) a batch of Bayer's alumina (BA) and chromite ore (Cr) is blended;
(ii) the blend is coground for about 5 hours keeping the grinding medium constant;
(iii) the coground blend is treated with 2% by weight of dextrin solution as binder and briquetted by pressing the same uniaxially at a pressure of 1000 kg/cm ;
(iv) the briquettes are sintered at a temperature of 1550-1600 C and soaked for a peiiod of about 6 hours and cooled to the ambient temperature in natural air;
(v) the sintered pellets are crushed, ground into grogs and stored ;
or WFA
(vi) the grogs/,are mixed with plastic clay and reactive Al2O3 along with additional chromite ore, pressed, dried and fired to produce bricks for lining ladles, EAF launders and BF runners.
The invented process is further described in the following examples :-
Example 1 : A 10 kg batch of Bayer's alumina (BA) and chromite ore (Cr) is coground in a ball mill for 5 hours. The coground mass is pressed into 60 mm briquettes/pellets in a hydraulic press at a pressure of 1000 kg/cm . The briquettes are fired at 1600°C for 6 hours and cooled to ambient temperature in natural air. The briquettes are crushed, ground and screened into different fractions.
Example 2 : The grogs, each of Al-Cr and WFA are blended with plastic clay, reactive alumina and chromite ore,and pressed into cylind^rical briquettes/pellets of diameter 50 mm and height 50 mm in a hydraulic press at a pressure of 1000 kg/cm , fired at 1500°C for 6 hours and cooled to ambient temperature in natural air. The cylinders are tested for chemical and thermo-physical properties.
The chemical composition and physical properties of the bricks produced in the existing process and of those produced in the invented process are presented in Table 1 from which it is noted that the physical properties of the bricks produced in the invented process ufing relatively low cost and readily available raw ingredients i.e. Bayer's alumina (BA), white fused alumina (WFA) and chromite ore (Cr) are similar and in certain respects superior to those of the bricks produced in the existing processes using relatively high cost raw ingredients i.e. synthetic alumina and Cr2O3.
Thus the present invention provides an improved process for producing alumina-chrome refractory with excellent slag resistance and high hot strength .characterised in that the process comprises following steps: (1) alunina is blended with equivalent amount of chromite ore for 15 to 20 weight % Cr2O3 ; (ii) blend is coground; (iii) the coground blead is treated with 2% by weight daxtrln solution and bxlquetted into briquettes/pellets by pressing the same uniaxially in a hydraulic press at a pressure of 1000 kg/cm ; (iv) the briquettes/pellets are sintered at 1550-1600°C followed by soaking and cooling of the same to the ambient temperature in natural air; (v) the briquettes/pellets are crushed and ground into grogs; (vi) the grogs or white fused alumina are mixed with plastic clay and reactive Bayer' s alumina, and pressed and fired into bricks to produce the refractory of chemical composition (by weight %): Al2O3,-50 to 65, Fe2O3-6.0 to 7.5 and Cr2O3-15 to 20.

TABLE I
Comparative properties of bricks produced in the existing
and invented processes.

(Table Removed)

Note : V.G. – Very
Good Exc. - Excellent





We Claims :-
1. An improved process for produciqg alumina-chrome reflectory with excellent slag resistance and high hot strength characterised in that the process comprises following steps t (i) alumina is blended with equivalent amount of chromite ore for 15 to 20 weight % CT2O3; (ii) the blend is coground; (iii) the coground blend is treated with 2% by weight dextrin solution and briquetted into briquettes/pellets by pressix^ the same uniaxially in a hydraulic press at a pressure of 1000 kg/cm ; (iv) the briquettes/pellets are sintered at 1550-l600 C followed by soaking and coolix^ of the same to the ambient temperature in natural air; (v) the briquettes/pellets are crushed and ground into grogs; (vl) the grogs or white fused alumina are mixed with plastic clay and reactive Bayer's alumina, and pressed and fired into bricks to produce the refractory of chemical composition (by weight %): Al2O3- 50 to 65, PB2O3-6.0 to 7.5 and Cr2O3-15 to 20.
2. The process as claimed in claim 1, wherein the blend is coground for 5 hours in a ball mill keeping the grinding mediiam constant.
3. The process as claimed in any preceding claim, wherein the briquettes/pellets are of size 60 mm3.
4. The process as claimed in any preceding claim, wherein the briquettes/pellets are of diameter 50 mm and height 30 mm.

Documents:

3419-del-1997-abstract.pdf

3419-del-1997-claims.pdf

3419-del-1997-complete specification (granted).pdf

3419-del-1997-correspondence-others.pdf

3419-del-1997-correspondence-po.pdf

3419-del-1997-description (complete).pdf

3419-del-1997-drawings.pdf

3419-DEL-1997-Form-1.pdf

3419-del-1997-form-19.pdf

3419-del-1997-form-2.pdf

3419-del-1997-form-3.pdf

3419-del-1997-gpa.pdf


Patent Number 244075
Indian Patent Application Number 3419/DEL/1997
PG Journal Number 47/2010
Publication Date 19-Nov-2010
Grant Date 16-Nov-2010
Date of Filing 27-Nov-1997
Name of Patentee STEEL AUTHORITY OF INDIA LTD.
Applicant Address IRON & STEEL ENTERPRISE, ISPAT BHAWAN, LODI ROAD,NEW DELHI-110003, INDIA
Inventors:
# Inventor's Name Inventor's Address
1 MANI SHANKAR MUKHOPADHYAY RDCIS/SAIL,INDIA.
2 JAGDISH PRASAD RDCIS/SAIL,INDIA.
3 TAPAS KUMAR DE RDCIS/SAIL,INDIA.
4 KRISHNA CHARAN CHATTERJEE RDCIS/SAIL,INDIA.
PCT International Classification Number C04B 35/12
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA