Experimental research on the characteristics of softening and melting of iron ores as significant factor of influence on gas permeability of blast furnace charge

It is widely accepted as a cohesive zone is directly influenced by softening and melting properties of iron ores, preparations (crowded, pellets, which represents about 90%, of the loads with metal furnace intake), or uncooked (raw ores ranked). Important results can be obtained through the study of behavior of ferrous materials at temperatures above 1000 ° C. Starting from research methods presented in the literature, this paper presents itself in carrying out their own laboratory experiments, conducted with the aim of analysing the softening and melting properties of sinter iron cores.


Introduction
Cohesive zone of blast furnace interior is by definition located in thebely of furnace is the area composed of pastos iron oresof softening and melting solid, coke, acid slag drops that run upward in the gaseous phase reducing valves with countercurrent.
Gas permeability of this area is very low, only one running windows gas coke solidly placed between layers of ore in the process of softening and melting. The temperature at which softening begins ferrous raw materials is called the start temperature of the cohesive zone and write with Tzc, the temperature at which melting the ends of ferrous raw materials is called melting temperature and note with Ttop. DT = difference between them Ttop-Tzc actually determine the thickness of cohesive zone.
The cohesive zone is thicker the upward flow of gaseous phase is more difficult. Softening, melting temperatures as well as the spread between them is in close correlation with the physical and chemical properties of ferrous materials with consideration of load capacity, i.e. to sinter ferrous which represents 90% of the loads of minerals. Study on the influence of chemical composition of sinter of Ib=Cao/SiO 2 and GR (reductibility degree) its effects on the cohesive zone is of great importance because of the shape and its position depends on the development of processes in the furnace.

Methodology
Crowded samples which have been subject to reduction under load have been specially trained in industrial agglomeration of machine at the ICEM Bucharest. Crowded samples were taken from the mixtures listed in Table 1. The tests we made shown that the higher is the reduction degree the higher is the crushing degree. Because pre-reduced materials obtained by reducing the iron ores (crude or prepared) are used in the blast furnace or the electric arc furnace, replacing the iron scrap, it is very important to know the behaviour of these materials during the heating -the correlation between the reducing degree and their melting and softening temperatures. The experiment plant 1-graphite crucible; 2-gas distributor; 3-intermediary plate; 4 -piston; 5 -rod; 6 -graphite support; 7 -seal device; 8 -piston support; 9 -fixed support; 10 -H 2 cylinder; 11 -reducing gas cylinder; 12 -measuring device; 13 -gas mixer; 14 -gas pipe; 15 -induction electric furnace That is why we tested the softening of these materials. The plant we used to run these tests is presented in Figure 1. The way of the experiments was the following: 2 -crushed and punctured in the material has been chosen fraction of 3-5 mm of which for experimentation have used amounts ranging between 240-310g, selected quantity must fill the graphite crucible in which reduction reaction occurs; -heating of the sample was made with the speed of 50-60 degrees/min; -starting at 750° C is inserted into the sample It with the flow of 6.5-7.5 l/min; -from 900° C is introduced with H 2 flow rate of 5 l/min up to 8 l/min so that the samples have a degree of reduction between 50-78%; -the temperature is measured at 3 minute and interval from the time the piston movement at a distance of approximative 2 minutes; -total of the piston stroke corresponding to a reduction of height equal to half of that of the sample and represents the beginning of melting characteristic (T top ) and travel of the piston is at the beginning of the characteristic started softening (T zc ); -after cooling and evacuation from the Crucible, the sample weighs in again and analyzes its layout.

Results
Experimental results are presented in Table 2.
Tabel 2-Experimental data on the characteristics of the softening and melting of sinters samples. The experimental data were processed mathematically statistical, obtaining based on their charts in

Conclusions
Conclusions on softening and melting characteristics of the studied agglomerates can be summarized as follows: -the increase in waste rock MgO to increase sinter characteristic T zc , T top , and ΔT= T top -T zc (samples No. 5, 6); -further provided with tools as random parameter studied Al 2 O 3 have not submitted acceptable correlation coefficients, however the growth of ΔT, which means a premature softening layers, a compactizare their faster, causing a decrease in permeability cohesive zone; -further provided with tools drawn with Cao/SiO 2 report variables confirmed the trends of growth and melting point of softening point with increasing basicity; -characteristic points are not influenced by the iron content variations; -agglomerates with higher MgO contents melted harder and longer intervals, with approx 1080ºC T zc and T top 1280-1410ºC; -it was noted that the growth of FeO in crowded place a sharp Tzc and Ttop, what can be explained by the formation of compounds of the type fayalit, which leads to less permeable cohesive areas; -the most powerful influence on the behavior of ferrous materials in the softening and melting, it is the degree of reduction of iron oxides, forming metallic iron support structures, which leads to ensure permeability layer plastic crowded condition. This very important conclusion has led in the direction of a research study of reducibility and mechanical strength of components of cargo around the country, furnaces especially crowded samples.