Design Of Gradient Refractory And Thermal Stress Analysis Under Gradual Temperature Field

During the service process of lining refractory,the gradual temperature field and internal chemical reactions cause the material to expand or shrink,and mutual constraints to produce thermal stress.When the thermal stress is greater than the strength of the material,it will produce different forms of damage.But the temperature field has a positive effect on the unfired refractories.Therefore,based on the relationship between thermal stress and thermal expansion,the ideal thermal expansion curve is obtained.The thermal expansion performance of different refractory materials is studied.According to the ideal curve,the main material is determined,and the heating furnace of steel rolling clay brick is determined as the research object.The effect of different material composition and structure on the thermal expansion is studied.The ANSYS finite element method is used to compound the materials of different components and structures.Composition gradient and structural gradient refractories are formed respectively.Temperature fields and stress fields are simulated and analyzed before and after the composite.The main results are as follows:(1)The ideal thermal expansion coefficient decreases with the increase of temperature,and the slope of the curve keeps decreasing.The ideal thermal expansion rate curve approximates a straight line.After treatment at 600 ~oC,the thermal expansion coefficient of quartzite and bauxite refractory material decreases with the increase of temperature,that is consistent with the trend of ideal curve.Corundum spinel,high alumina,mullite,magnesia refractory material increase and then decrease with the temperature rising.Reference to the trend of ideal curve,the bauxite refractory material was determined as the main material.(2)Formed by the molding pressure,the porosity gradient is smaller.The stress of structural gradient DT1(more and more compact from high temperature surface to low temperature surface)is less than DT2(more and more loose from high temperature surface to low temperature surface).The thermal stress of DT1 is similar with the homogeneous structure,which molding pressure is 20 MPa.Formed by adding pore forming agent,the porosity gradient is larger.The stress of structural gradient CT1(more and more loose from high temperature surface to low temperature surface)is less than CT2(more and more compact from high temperature surface to low temperature surface).Compared with the homogeneous structures,the maximum stress value of CT1 is the smallest.(3)The thermal stress of the specimen decreases and then increases with the increase of the porosity leading to the phenomenon of(2).The main reasons are as follows:when the apparent porosity of the sample is at 17.5~22.8%,the porosity and crack show good absorption performance to thermal expansion with increase of the apparent porosity,thus reducing internal stress.When the apparent porosity of the sample is at 23.5~31.8%,with the increase of apparent porosity,the sample thermal conductivity decreases,and the sample internal temperature gradient increases,and the greater the thermal stress produced by temperature gradient is greater.Moreover,high temperature thermal expansion coefficient curve slope increase,the inconsistency and mutual constraints of expansion or contraction is aggravated,and thus the stress is greater.(4)Compared with the ideal thermal expansion curve,the addition of mullite is not conducive to the improvement of the thermal expansion curve of the sample.The thermal stress of the sample increases with the addition of mullite.Compared with uniform composition samples F0,F5,F10,mullite composition gradient FT1(mullite content increasing from high temperature surface to low temperature surface)and FT2(mullite content decreasing from high temperature surface to low temperature surface)are not conducive to reduce thermal stress.The mullitization of andalusite produces tiny cracks,which is beneficial to decrease the thermal stress,but the relationship between additions of andalusite and the maximum stress value is not obvious.The maximum stress value of the composition gradient HT2(andalusite content decreasing from high temperature surface to low temperature surface)is similar with the homogeneous structures added to the andalusite.(5)Guangxi white clay is beneficial to decrease of thermal stress of the sample.With the addition of Guangxi white clay,the thermal expansion performance curve of the sample is keeping close to the ideal thermal expansion performance curve,and the thermal stress of the sample decreases continuously.Compared with the homogeneous composition sample,the thermal stress of the component gradient NT2(Guangxi white clay content decreasing from high temperature surface to low temperature surface)decreases significantly,and NT2 is obviously superior to the NT1(Guangxi white clay content increasing from high temperature surface to low temperature surface).(6)This test combines basic theoretical research,performance testing and material design studying the relation between thermal expansion performance and temperature.Through the design of material structure and composition,the gradient performance is optimized.Different structural gradient and component gradient models are designed.Compared with the stress field of homogeneous structure and homogeneous component model,the structural gradient and composition gradient which are beneficial to reduce the thermal stress of samples are obtained.It is of great significance for the preparation of low cost and high performance gradient refractories,and has a guiding significance for the further design and development gradient refractories(phase gradient,structure gradient and composition gradient)and field applications.