Influencing factor of sinter body strength and its effects on iron ore sintering indexes

Sinter body strength, which reflects the strength of sinter, plays an important role in the improvement of sinter. In this study, the sinter body strengths of iron ores were measured using a microsintering method. The relationship between the chemical composition and sinter body strength was discussed. Moreover, sinter-pot tests were performed. The effects of sinter body strength on the sintering indexes were then elucidated, and the bottom limit of sinter body strength of blending ores was confirmed. In the results, the compressive strengths（CSs） of iron ores are observed to decrease with the increasing of the contents of loss on ignition（LOI）, SiO 2, and Al2O3; however, LOI of less than 3wt% does not substantially influence the CSs of fine ores. In the case of similar mineral composition, the porosity, in particular, the ratio between the number of large pores and the total number of pores, strongly influences the sinter body strength. With an increase of the blending-ore CSs used in sinter-pot tests, the yield, productivity, and tumbler strength increase, and the solid fuel consumption decreases. The CSs of the blending ores only slightly affect the sintering time. The CS bottom limit of the blending ores is 310 N. When the CSs of the blending ores increase by 10%, the yield, productivity, and tumbler index increase by 1.9%, 2.8%, and 2.0%, respectively, and the solid fuel consumption decreases by 1.9%.

Fundamental mechanism of effects of MgO on sinter strength

MgO-containing flux may have a series of effects on the quality of sinter and performances of the blast furnace.Thus,the fundamental mechanism of the effects of MgO on the sinter strength was investigated.Both the chemical reagent and industrial flux were used for preparing the specimens.The experimental results show that the sinter strength decreases with MgO addition.There are three reasons for it.The first reason is diffusion rate.Almost all of the CaO may react with Fe2O3 and generate CaO Fe2O3,but most of MgO cannot react with Fe2O3,and it still remains in the state of original minerals.The diffusion rate of MgO in iron oxide is only 17.51μm/min in 30 min.The second reason is the fluidity and ability to generate liquid phase.In the case of Fe2O3 mixed with CaO,there is some liquid phase formed above 1200℃,while in the case of Fe2O3 mixed with MgO,even at 1200 and 1220℃,there is still no liquid phase.The third reason is self-strength.In the case of industrial flux,the compression strength of the specimens made of Fe2O3 and limestone is 0.52 and 0.71 kN at 1150 and 1180℃,respectively,while that of the specimens made of Fe2O3 and magnesite is 0.48 and 0.56 kN,respectively.Therefore,the fundamental mechanism of the effects of MgO additive on sinter strength can be better understood based on the diffusion rate of MgO in iron oxides,the fluidity of liquid phase,and the self-strength of bonding phase.

Compression curve analysis and compressive strength measurement of brittle granule beds in lieu of individual granule measurements

Powders in granulated form are used in various processes to facilitate convenient usage. The durability of the formed granules is a crucial parameter, typically evaluated by the compressive strength of the gran- ules. However, especially for granules with a diameter in the order of tens of microns, statistically relevant testing of individual granules is not a feasible alternative, and in such cases uniaxial bed compression is required. There has not been consensus on whether uniaxial compression of a granule bed can be used to study the fracture of micron size or brittle granules. In our case study of a bed of sintered kaolinite granules with diameters under 100 μm, we show how the compressive strength of individual granules can be obtained from the compressive measurement of the entire bed by plotting the relative density versus the logarithmic pressure scale. We compressed the kaolinite powder with different loads; microscopy confirmed that below the ana- lyzed strength the granules are intact, though the granules start to fracture in the curved region on the compression curve. We found that angle-fitting can be used to locate the average compressive strength on the compression curve and to follow the evolution of strength with sintering temperature. The experi- ments in unison demonstrate that compression curve analysis is applicable for strength analysis of brittle granules.

Vital role of hydroxyapatite particle shape in regulating the porosity and mechanical properties of the sintered scaffolds

The effect of particle shape on the porosity and compressive strength of porous hydroxyapatite （HA） scaffolds was investigated by sintering the mixture of rod-shaped HA （r-HA） and spherical HA （s-HA） with polyacrylamide used as the sacrificial template. It was found, for the first time, that addition of r-HA into s-HA could exponentially decrease the porosity of sintered HA scaffolds and enhance their compressive strength with the increase of r-HA content. The mechanism, according to the results from scanning electron microscopy and X-ray diffraction, lies in the restriction of s-HA to the grain formation and growth of r-HA during sintering and results in the fusion of r-HA with s-HA. These findings suggest that mixture of r-HA and s-HA might provide a new and facile way to improve the compressive strength of oorous HA scaffolds.