Papers by Author: Mei Jie Zhang

Abstract: The property of refractory matrix was dominated by both the maineral composition and particle packing behaviors. In this study, the theoretical packing density of refractory castables was calculated to design the particle size distribution (PSD) of its matrix. Four lightweight Al₂O₃-MgO castables with different matrix PSD (represented by q-value) were prepared and examined. Results show that a suitable q-value was needed to ensure acceptable properties including sintering characteristics, strength and slag resistance, which deteriorated distinctly at high q ( > 0.31). For the sample with q = 0.28, the matrix showed dense and uniform mirostructure, and the properties of castable reached a favorable compromise among sintering characteristics (apparent porosity = 14.8%, bulk density = 3.02g∙cm^-3, permanent linear change < 0.6%), strength (cold modulus of rapture = 12.4MPa, cold crashing strength=155.5MPa), and resistance against both slag corrosion (I_c = 22.4%) and penetration (I_p = 11.5%). The sample with q = 0.25 showed the highest strength and resistance against slag corrosion, but its slag penetration resistance was lower due to the existence of cracks between aggregates and matrix.

Abstract: Electromagnetic field (EMF) can promote the reaction between the Fe/Mn ion in slag and MgO-C refractories to form Mn-doped MgFe₂O₄ spinel. In order to further study the morphology and characteristics of Mn-doped MgFe₂O₄ spinel, the experiments were respectively carried out in medium-frequency induction furnace and resistance furnace. MgO-C refractories containing 6 wt.% carbon and iron-rich slag containing 53.62 wt.% Fe₂O₃ were used. The results show that the penetration layer in the slag line under EMF is obvious and the reduced Fe from FexO is distributed homogeneously in this layer. However in the resistance furnace having no EMF, there is not MgFe₂O₄ spinel but MgAl₂O₄ spinel formed. The iron content in Mn-doped MgFe₂O₄ spinels decrease dramatically from the erosion layer to penetration layer, while the manganese content in the spinel remains unchangeable.

Abstract: With molten salt method, a series of the hercynite powders were prepared using FeCl₂·4H₂O, active alumina and iron powder as raw material and KCl molten salt as reaction medium. The phase composition and micro-morphology were studied by techniques of XRD and SEM. The results showed that a high purity hercynite-alumina powder can be synthesized by molten salt synthesis method after heat treatment at 1000 °C in reducing atmosphere, the main phases were hercynite and α-Al₂O₃, and the increasing iron powder content can raise hercynite production quantity with developed crystal grain, the grain size was increased from 6μm to 10μm.

Abstract: The heating furnace in CSP plant of WISCO has a lightweight lining which is built by all fiber templates. In light of its good thermal insulation performance and short service life, the lining material for heating furnace was optimized in this article by using heat transfer calculation while the thickness stays light and the insulation performance stays good. The castable was applied to substitute for lightweight fiber materials to prolong the service life of heating furnace lining. Also, this article shows a contrast analysis of heat insulation layer while using different insulation material: the fiber felt, nanoinsulation board and super hydrophobic insulation board. The effect on the temperature of external shell and heat loss was analyzed and discussed. The results generate a new design of material composition, which not only prolongs the service life of heating furnace lining, but also reduces the cost.

Abstract: The fracture growth is one of primary causes which the refractory of ladle destroys. We have carried on the computation and the analysis to the ladle temperature field and the stress field coupling by he finite-element method. Attributes the crack state-of-art stress strain field using the J-integral, has established in the ladle refractory in the thermal load and under the molten steel load function its crack secure relations, and obtained the crack security change rule. These results have provided the support rationale to the equipment safe operation.

Abstract: The field synergy principle has been successfully used for optimization design of heat transfer exchanger. In this subject, the field synergy between the molten steel flow field and the inclusion concentration distribution is analyzed based on the mass transfer equations and removal mechanisms of inclusions. Then, inclusions removals of different particle sizes are numerically calculated for a two-strand tundish. The results show the large particle size inclusions are removed mainly by Stokes floatation and the removal efficiency has no obvious relationship on flow field. The small size inclusions removal efficiency is influenced by the synergy between the velocity vectors and the inclusion concentration gradients. So, changing the flow field mainly promotes the removal efficiency of small size inclusions. For the selected two-strand tundish, flow controls should be set for removing those inclusions which particle sizes are less than 100μm,. When the inclusion particle size is less than 10μm, the overall maximum removal efficiency is no more than 25%. So some new metallurgy techniques should be developed to improve the removal efficiency of small size inclusions. Keywords: Continuous tundish; Inclusion removal; Field synergy

Abstract: Flow control devices made of refractories are established in the tundish to modify the flow characteristics. In practical producing, the metallurgical function of flow control devices is weakened because of refractories corrosion. In this subject, an index named refractory wear factor which is used to evaluate the refractory wear was defined at first. And then, the characteristics of molten steel flow and the distribution of temperature and the refractory wear factor in a one-strand tundish equipped with flow control devices of a turbulence inhibitor, a weir and a dam were numerically simulated using the commercial CFD software. At last, the influence on refractory wear factor was analyzed. The following results were obtained. The high-speed molten steel is mainly confined to the injecting zone, especially to the turbulence inhibitor. The walls around the entering zone tundish and the weir wall faced to the flow direction have higher temperature than other walls. The highest value of refractory wear factor is focused on the inhibitor and bottom wall near the outlet. In order to keep the synchronization for the tundish, the refractories used in those zones should have higher anti-wear properties.

Abstract: The resistance coefficients through which gas flow permeable refractory are important properties and have great effect on the gas blowing parameters and gas-liquid two phase flowing characteristics in the metallurgy furnace such as ladles, tundish. In this paper, the resistance coefficients were measured according to the Forchheimer’s law. The results show when the gas flow rate is fixed, the viscosity resistance coefficient and inertia resistance coefficient decrease as the apparent porosity and average pore diameter increase. The viscous resistance coefficient is more lager than the inertial resistance coefficient. The resistance coefficients were analyzed by dimensional analysis and the statistical correlations between the resistance coefficients and parameters of porous permeable refractory were got based on the experimental data. In order to get high strength at low resistance coefficients, the raw materials particle degree were adjusted.

Abstract: The temperature distribution of the permeable brick was modeled using CFX software. The influence of magnesia and corundum on thermal shock resistance of non-cement bonded alumina-based permeable brick was investigated. The results indicated that, in the gas blow process, the high temperature regions near the working face of the brick gradually expanded with the increase of the gas flow rate. Therefore the inner part of the brick had the complex and large change of thermal stress. Further experiments demonstrated that thermal shock resistance of alumina-magnesia based castable refractory was better than that of alumina-chrome based castable refractory. With the increase of magnesia amount, the alumina-magnesia based castable refractory had more cycles of heating and water-cooling. When different kinds of corundum were added in the raw materials, the sample with tabular corundum showed the best thermal shock resistance, the one with white fused corundum performed worse and the one with fused dense corundum performed worst.

Abstract: The Al2O3-mullite system porous refractories were fabricated, and then pretreated by sol-gel. The samples were sintered at 1200°C for 3 hours. The microstructures and phases of the samples were analyzed by SEM and XRD respectively. The physical properties of the samples were measured according to National Standard of Refractory. Mullite-whiskers were formed in the pores of the samples. The pretreated samples were more permeable, and were greatly strengthened.