Title of Invention

AN IMPROVED SYSTEM / PROCESS FOR COMPARATIVE EVALUATION OF DYNAMIC SLAG CORROSION RESISTANCE OF REFRACTORIES

Abstract

An improved system for comparative evaluation of slag corrosion resistance of different quality of refractories with desired metal and slag chemistry and the system comprises induction furnace (6) having inner volume such that 18 to 20 kg of metal can be melted, plurality of sample specimens (1) of different qualities, definite proportions of slag (5) and metal (4) inside the plurality of sample specimens (1), insulations of definite thickness and means (3) adapted for resisting metal-slag attack. The process for comparative evaluation of slag corrosion resistance of different quality refractories with desired metal and slag chemistry comprises lining of the induction furnace with sample specimens, addition of metal/steel to the induction furnace and heating and melting to attain desired temperature, addition of definite amount of slag of definite composition in the furnace, maintaining desired temperature ranging, draining out of metal and slag after completion of desired duration of evaluation, determining thickness of corroded sample specimens and evaluation of corrosion index.

Full Text

FIELD OF INVENTION The present invention relates to an improved system and process for comparative evaluation of dynamic slag corrosion resistance of refractories. More particularly, it relates to an improved system and a process for comparative evaluation of slag corrosion resistance of different quality refractories with desired slag chemistry and quantity at a high, specified temperature and duration in presence of specified grade and amount of liquid steel or metal. BACKGROUND ART In many applications, refractories are used in contact with liquid metal and slag. As for example, MgO-C bricks, used as refractory lining material in Basic Oxygen Furnace (BOF) come is contact with liquid steel and slag at a temperature of 1600 to 1700°C during operation. In steel ladles, MgO-C, high Al2O3, Al2O3-MgO-C bricks are generally used. Now-a-days different secondary metallurgical operations are carried out in these ladles and refractories are subjected to different kind of slag. It is, therefore, necessary to evaluate slag corrosion resistance of different varieties of refractories with different slags. Two types of slag corrosion resistance tests are generally carried out. One is static test and other is dynamic test. In the static test, measured quantity of powdered slag is put in a refractory crucible prepared from the test refractory brick/material and fired at a specified temperature for a specified duration. Remaining thickness and degree of slag penetration is measured after cooling. The main disadvantage of static test is that the slag become saturated with reaction product and becomes inactive. Another disadvantage of the static test is that the total refractory becomes hot but in actual application, there is a temperature gradient from the hot face to cold face. In ASTM method, a cylindrical drum lined with different test specimen is used. The drum is kept slightly inclined to the horizontal and there is an arrangement for rotation of the drum. The inside refractory lining of the drum heated by a burner from lower end and slag powder is added from the upper end of the rotating drum. The slag is melted due to high temperature, 2 reacts with the refractory and then falls from the lower end. After the test, remaining thickness is measured to evaluate comparative slag corrosion resistance. However, in this method temperature control is difficult and liquid steel is not present during the test. Thus, there is a need to provide a system and a process for evaluating slag corrosion resistance of different quality refractories with slag of desired chemistry and quality at high, specified temperature and duration in presence of specified grade and amount of liquid steel/metal and giving a clear indication about the performance of refractory in actual application like Basic Oxygen Furnace (BOF), ladles, blast furnace (BF) etc.. OBJECTS OF INVENTION The basic object of the present invention is to provide comparative evaluation of slag corrosion resistance of different quality of refractories with a desired slag chemistry and quantity in presence of liquid metal/steel. Another object of the present invention is to provide fast slag corrosion. The other object is to reduce evaluation time and cost of operation. SUMMARY OF INVENTION Thus, according to the basic aspect of the present invention there is provided an improved system for comparative evaluation of slag corrosion resistance of different quality of refractories with desired metal and slag chemistry, the said system comprising: (i) induction furnace having inner volume such that 18 to 20 kg of metal can be melted; (ii) plurality of sample specimens of different quality lined in a definite manner in the induction furnace, the said sample specimens having dimensions such that the inner volume of the induction furnace is appropriate for melting the metal; (iii) definite proportions of slag and metal inside the plurality of sample specimens; 3 (iv) insulations of definite thickness between said refractory lining formed of sample specimens and furnace wall; (v) means adapted for resisting metal-slag attack. According to another aspect of the present invention there is provided a process for comparative evaluation of slag corrosion resistance of different quality refractories with desired metal and slag chemistry, the said process comprising: (i) lining the induction furnace with sample specimens of different quality refractories having almost same original thickness; (ii) adding metal/steel to the induction furnace; heating and melting to attain desired temperature, (iii) adding definite amount of slag of definite composition in the furnace at definite interval during the evaluation for 3 to 4 hrs. (iv) maintaining desired temperature ranging from 1500°C to 1650°C by measuring temperature at regular interval of 30 minutes. (v) draining out of metal and slag after completion of desired duration of evaluation, (vi) determining thickness of corroded sample specimens of different quality refractories after the furnace is cooled and samples are removed from the furnace, (vii) evaluation of corrosion index DETAILED DESCRIPTION OF THE INVENTION The system of the present invention for comparative evaluation of slag corrosion of refractories with metal and slag at high temperature comprises Medium Frequency Induction Furnace having capacity of melting 100 Kg. of steel. The induction furnace adapted for comparative evaluation is a vertical type crucible furnace of out side cross-section of 730 x 600 mm and 700 mm height. The refractory lining of the furnace comprises 50 mm thickness of ramming mass and 5 mm thick asbestos sheet inside the induction coil of the medium frequency induction furnace. The dimensions of the test specimens of the present invention are 228 to 232 mm (length) x 35 to 40 mm (width) x 25 to 30 mm (thickness). The combination of the samples and dimensions are such that ultimately leads to an appropriate inner volume of the furnace adapted to melt 4 18 to 20 kg of steel. 10 number of test specimens and an additional (dummy) refractory specimen are adapted for lining inside the induction furnace. The induction furnace of the present invention comprises safety backup lining prepared by ramming mass. The lining also comprises of 50 mm thick ramming mass and 5 mm thick asbestos sheet as insulation. Hollow steel pipe of 140 mm outside diameter and 250 mm height is adapted to format the said lining with test specimens inside the induction furnace. The annular gap between the rammed lining and the said format comprises ten test specimens and one dummy sample. Moist ramming mass inside the gap in the spaces between the test specimens is adapted for resisting the metal/slag attack. The said moist ramming mass comprises solution of MgSO4 with magnesia adapted to form highly refractory material at temperature higher than 1000°C. The process for formation of the system of the present invention involves the following process steps: 1. Modification of original lining of the induction furnace for evaluation of slag corrosion of the refractories. 2. Sample preparation by cutting from the sample bricks and drying at 110°C for 24 hrs. 3. Lining of induction furnace. 4. Drying of lining. 5. Melting of steel and temperature measurement at an interval of 30 minutes. 6. Addition of 1st lot of slag after reaching desired temperature (e.g.l650°C). 7. Removal of reacted slag and addition of fresh slag at an interval of 15 minutes. 8. Removal of steel and slag after the evaluation for 3 to 4hrs. 9. Cooling of furnace and dismantling of reacted test specimens. 10. Casting of test specimens after slag corrosion in Plaster of Paris for strengthening. 11. Cutting of test specimens vertically through the middle and wear measurement for comparison. 5 In the present invention, the process for comparative evaluation of dynamic slag corrosion resistance of refractories comprises major steps for comparative evaluation of 10 refractory specimens in induction furnace. At first refractory test specimens of sizes 228 to 232 mm long, 35 to 40 mm width and 25 to 30 mm thickness are cut from different quality of refractory bricks or prepared by casting/ramming from different monolithic refractories, which are to be comparatively evaluated. In the process step of lining ten test specimens and one additional refractory dummy specimen are lined inside a previously lined medium frequency induction furnace having capacity of melting about 100 kg of steel. The previously lined furnace works as safety backup lining and is prepared by ramming 90% MgO based ramming mass. Behind 50 mm thickness of ramming mass and 5 mm thick asbestos sheet are provided for lining over the induction coil. The said backup safety lining is prepared adapting a form to keep a cylindrical cavity of 220 mm diameter and 300 mm height. Then the backup lining is air dried for 48 hours and slowly preheated to 110°C for 24 hours. The backup safety lining is further strengthened by heating and melting 100 kg steel bars inside the induction furnace. The liquid metal thus formed is kept at 1650°C for 30minutes and then drained out from the furrnace 10 test specimens and 1 dummy specimen are placed vertically inside the annular gap between the rammed lining and format placed centrally inside the induction furnace. The gap between the test specimens and rammed lining is filled with moist ramming mass and rammed slowly. Ramming is also done upto 25 mm above the test specimens for proper positioning and fixing of the test specimens. The format is then removed and the bottom of the furnace is rammed with moist ramming mass for embedding the test specimens by 25 mm from the lower side. The working height of the specimens range between 170mm and 175 mm adapted for melting about 20 kg of steel. The gap between the test specimens are filled with special filling such that it should not become hard after the melting operation in the induction furnace and is adapted to resist metal/ slag attack. The said gap is filled with solution of MgSO4 with magnesia. At room temperature it gives strength but at higher temperature (>1000°C) MgSO4 dissociates to form MgO, which is highly refractory material. 6 The furnace, lined with test specimens is air dried for 16 hours and then electric bulb is adapted for slow drying of the furnace. Specified quantity of steel bar is charged inside the furnace and gradually heated by induction power for melting the steel. After melting, the temperature of the furnace is maintained by measuring temperature at regular intervals and measured quantity of desired slag powder is added. Then a part of reacted slag is taken out from the induction furnace and 25 to 50 gm of fresh slag powder is added at regular interval of 15minutes during the specified duration of 3 to 4 hrs. This helps in acceleration of corrosion reducing the evaluation time and cost. After completion of the process, metal and slag are drained out from the furnace and allowed to cool. Then the test specimens are taken out by sacrificing the additional sample (i.e. the dummy sample). The dummy sample is used along with the test specimens to facilitate dismantling by breaking. This helps in the easy removal of test specimens after the evaluation run is completed. The weak samples are strengthened by embedding the specimens in Plaster of Paris. The samples thus formed are dried before cutting. The test specimens are cut longitudinally and the wear is measured from the difference of original and final thickness. From the wear measurement, comparative evaluation is done. The comparative evaluation of refractory test specimens of different qualities is performed with liquid slag of any desired chemistry or metallurgical furnace [e.g. BOF, Ladle Furnace (LF), Vacuum Arc Degassing (VAD), etc.] in presence of liquid metal or steel in medium frequency induction furnace. Two standard test specimens in each evaluation are used so mat one set of comparative evaluation can be further compared with another set. The comparative evaluation is carried on at desired temperature of 1550 to 1650 °C and holding time in induction furnace of capacity 100 kg with variation of slag as well as metal. Results of slag corrosion evaluation are given in Table-1. In the process of evaluation five different qualities of bricks are evaluated by taking 2 test specimens from each quality. One of the quality (5GS-2) is taken as standard. Average wear (mm) is calculated from wear of 2 samples of same quality. Corrosion index is calculated by considering average wear of standard sample as 100. Corresponding index of other samples are determined by using the following relationship: 7 Average wear of sample A Corrosion index of sample A = x 100 Average wear of standard sample Test temperature and slag chemistry, slag amount and test duration are also indicated. For further comparison of one set of results with other sets, standard sample from same refractory is used in all sets of tests. Then corrosion index is used for comparative evaluation. The comparative numerical values are given in Table 1. Test temperature, slag chemistry, slag amount and test duration are also indicated in the Table. For further comparison of one set of results with other sets, standard sample from same refractory is used in all sets of tests. Then corrosion index of one set can be compared with other sets of evaluation. Table-2 indicates details of different experiments and other possibilities for getting an idea of the process of evaluation in induction furnace. Table-1 : Results of slag corrosion evaluation Date of evaluation: 16.9.2004 SI. Sample description Wear Avg.wear Corrosion No. (Different MgO-C Bricks) (mm) (mm) Index Chemical analysis of BOF 1 5GS-2 4.46 4.33 100 slag used for evaluation 2 Spl-I (80Fused3Al) 4.49 3.805 88 Constituents % 3 Spl-II (50Fused) 4.62 3.76 87 A12O3 1.01 4 Spl-III (50Fused3Al) 3.53 3.505 81 SiO2 15.19 5 DSP(N)(5Gr) 4.33 4.135 95 CaO 43.35 6 5GS-2 4.2 MgO 4.98 7 Spl-I (80Fused3Al) 3.12 MnO 0.94 8 Spl-II (50Fused) 2.9 FeO 32.56 9 Spl-III (50Fused3Al) 3.48 P2O5 1.01 10 DSP(N)(5Gr) 3.94 Test conditions: Rail Steel-17kg, Slag 375gm, Duration -3hr Temp: 1652°C(11.53hr),16330C (12.35 hr),1598°C (13.00 hr),1611 °C (13.30 hr),1575°C (14.00 hr),1620°C (14.10 hr),1661 °C (14.47hr) Slag : 50gm at 11.55AM ,50gm,25 gm,25 gm, 25 gm,25 gm, 25 gm,25 gm, 25 gm,25 gm, 25 gm, 25 gm and 25gm (last) at 2.50PM 8 Table 2 Details of different experiments and other possibilities Parameters Experimented Experimented Possible Different qualities of refractories Magnesia carbon having: i) 7% residual carbon ii) 9% residual carbon iii) 9% residual carbon and 3% aluminium. iv) 99% magnesium oxide v) 98%MgO Fused magnesia, etc. Magnesia carbon of different suppliers : i) Indigenous ii) Import i) High alumina ii)Castable refractories iii)Alumina magnesia carbon iv) Other refractories Slag chemistry BOF slag (wt%) LF slag (wt%) Slag of any other composition CaO 43.4 CaO 35.2 SiO2 15.2 SiO2 26.7 A12O3 1.0 AI2O3 22.4 MnO 0.9 MnO 4.4 FeO 32.6 FeO 1.7 MgO 5.0 MgO 8.8 P2O5 1.0 Metal Rail Steel Rail Steel Mild Steel, Pig Iron, Cast Iron, etc. Metal (kg) 17 18 Preferably Slag (gm) 375 500 Preferably Duration (hrs) 3 3.5 Preferably Temperature (°C) 1650-1700 1600-1650 1400-1700 BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES Figure 1 illustrates the refractory lining pattern of induction furnace for evaluation of slag corrosion in the present invention. Figure 2 illustrates the A-A sectional view of the refractory lining pattern of the present invention. 9 DETAILED DESCRIPTION OF THE ACCOMPANYING FIGURES In figure 1 the refractory lining pattern of induction furnace for evaluation of slag corrosion is illustrated. The sample specimens (1) are placed vertically inside the medium frequency induction furnace (6). The gap between the test specimens (1) and rammed lining (7) (shown in figure 2) is filled with moist special filling mass (3) and rammed slowly. The comparative evaluation of refractory test specimens (1) of different qualities is performed with liquid slag (5) in presence of liquid metal or steel (4) (also shown in figure 2) in medium frequency induction furnace (6). 10 We claim: 1. An improved system for comparative evaluation of slag corrosion resistance of different quality of refractories with desired metal and slag chemistry, the said system comprising: (i) induction furnace having inner volume such that 18 to 20 kg of metal can be melted; (ii) plurality of sample specimens of different quality lined in a definite manner in the induction furnace, the said sample specimens having dimensions such that the inner volume of the induction furnace is appropriate for melting the metal; (iii) definite proportions of slag and metal inside the plurality of sample specimens; (iv) insulations of definite thickness between said refractory lining formed of sample specimens and furnace wall; (v) means adapted for resisting metal-slag attack. 2. A system as claimed in claim 1, wherein the plurality of sample specimens comprises 10 test specimens and 1 refractory dummy specimen. 3. A system as claimed in claims 1 and 2, wherein the test specimens having dimensions of 228 to 232 mm length, 35 to 40 mm width and 25 to 30 mm thickness adapted for proper combination of the test specimens and appropriate dimension of the induction furnace. 4. A system as claimed in claims 1 to 3, wherein the refractory lining comprises safety backup lining prepared by 50 mm ramming mass with 25 to 30 mm of the bottoms of the test specimens embedded in it 5. A system as claimed in claim 1, wherein the insulation in the refractory lining comprises asbestos sheet of thickness 5 mm. 6. A system as claimed in claim 1, wherein the means adapted for resisting metal and slag attack comprises solution of MgSO4 with magnesia to produce highly refractory materials at temperatures higher than 1000°C. 11 7. A process for comparative evaluation of slag corrosion resistance of different quality refractories with desired metal and slag chemistry, the said process comprising: (i) lining the induction furnace with sample specimens of different quality refractories having almost same original thickness; (ii) adding metal/steel to the induction furnace; heating and melting to attain desired temperature, (iii) adding definite amount of slag of definite composition in the furnace at definite interval during the evaluation for 3 to 4 hrs. (iv) maintaining desired temperature ranging from 1500°C to 1650°C by measuring temperature at regular interval of 30 minutes. (v) draining out of metal and slag after completion of desired duration of evaluation, (vi) determining thickness of corroded sample specimens of different quality refractories after the furnace is cooled and samples are removed from the furnace, (vii) evaluation of corrosion index 8. A process as claimed in claim 7, wherein addition of slag and molten metal comprises proportions of slag and metal in the sample specimens ranging from 375 to 500 gms, preferably less than 1000 gms and 17 to 18 kg, preferably less than 30 kg respectively. 9. A process as claimed in claims 7 and 8, wherein determination of thickness of corroded sample specimens ranges between 5 mm and 10 mm. 10. A process as claimed in claim 7, wherein the evaluation of corrosion index is done by relative comparison of wear of each test specimen against wear of a standard specimen which is considered as 100. Dated this the 15th day of March 2005. An improved system for comparative evaluation of slag corrosion resistance of different quality of refractories with desired metal and slag chemistry and the system comprises induction furnace (6) having inner volume such that 18 to 20 kg of metal can be melted, plurality of sample specimens (1) of different qualities, definite proportions of slag (5) and metal (4) inside the plurality of sample specimens (1), insulations of definite thickness and means (3) adapted for resisting metal-slag attack. The process for comparative evaluation of slag corrosion resistance of different quality refractories with desired metal and slag chemistry comprises lining of the induction furnace with sample specimens, addition of metal/steel to the induction furnace and heating and melting to attain desired temperature, addition of definite amount of slag of definite composition in the furnace, maintaining desired temperature ranging, draining out of metal and slag after completion of desired duration of evaluation, determining thickness of corroded sample specimens and evaluation of corrosion index.

Documents:

00167-kol-2005-abstract.pdf

00167-kol-2005-claims.pdf

00167-kol-2005-correspondence-1.1.pdf

00167-kol-2005-correspondence-1.2.pdf

00167-kol-2005-correspondence.pdf

00167-kol-2005-description(complete).pdf

00167-kol-2005-drawings.pdf

00167-kol-2005-form-1.pdf

00167-kol-2005-form-18.pdf

00167-kol-2005-form-2.pdf

00167-kol-2005-form-3.pdf

00167-kol-2005-p.a.pdf

167-KOL-2005-(01-02-2012)-FORM-27.pdf

167-KOL-2005-FORM 27.pdf

167-kol-2005-granted-abstract.pdf

167-kol-2005-granted-claims.pdf

167-kol-2005-granted-correspondence.pdf

167-kol-2005-granted-description (complete).pdf

167-kol-2005-granted-examination report.pdf

167-kol-2005-granted-form 1.pdf

167-kol-2005-granted-form 18.pdf

167-kol-2005-granted-form 2.pdf

167-kol-2005-granted-form 3.pdf

167-kol-2005-granted-pa.pdf

167-kol-2005-granted-reply to examination report.pdf

167-kol-2005-granted-specification.pdf