| Sand casting is the main method of casting process,in which the green sand has the widest range of adaptability.The coal green sand is widely used in the world,which is a great waste of sand and serious pollution.The harmful gases are produced during the casting process can not only pollute the environment but also harm the health of workers.Therefore,the green production of sand casting has extremely important significance to the realization of "green casting".Environment-friendly yellow loam sand was developed by Donghua University and company,the sand is composed of inorganic material and has a yellow color.Environment-friendly sand is used in foundry production,the workshop is clean,no harmful gases and the waste sand does not pollute the environment.Environment-friendly sand can be used as molding(core)sand material because it has a higher wet-compressive strength.In this paper,casting recycling performance and thermal physical properties of the Environment-friendly sand were studied.Firstly,the effect of heat on the casting performance of environment-friendly yellow loam sand was studied.The changes of wet-compressiv strength and permeability of Environment-friendly sand and coal sand have been measured after repeated loss heating at different temperature.In addition,differential thermal analysis and thermal gravimetric analysis of environment-friendly sand were carried out by thermal-analyzer,and the morphological changes of the molding sand during the heating process were observed using a thermal platform microscope.Through analyzing the DSC-TG curve and high temperature form changes to explain the changes of the wet-compressive strength of molding sand at different burning temperature.The results show that the environment-friendly sand has more moderate downtrend of strength,wider temperature range of adaptation,stronger resistant to burning loss and better recycling performance than conventional coal sand with the increase of the burning temperature.Secondly,the environment-friendly sand was added a small amount of additives,and study the compressive strength,residual strength,high temperature thermal expansion property,high temperature hot pressing strength and storage stability to get the better performance of environment-friendly sand.The results show that the compressive strength and high-temperature hot pressing strength can be greatly improved when the environmentally friendly sand is added appropriate amount of additives.Although the residual strength has certain promotion,it still within a reasonable range and collapsibility is very good.The thermal expansion property is reduced,which can effectively prevent the deformation of casting,and the good storage stability can make the environment-friendly sand keep good performance before modeling.Thirdly,a series of experiments were carried out.The thermal physical properties,such as coefficient of thermal conductivity,specific heat capacity,thermal diffusivity and high temperature thermal expansion were studied,and compared with the coal sand to further understand the thermal properties of environment-friendly sand.The effect of additives content on the thermal properties of environment-friendly sand was studied.The results show that coefficient of thermal conductivity and specific heat capacity of environment-friendly sand are higher than that of coal sand,the thermal diffusivity is slightly lower and the coefficient of thermal expansion is basically the same.The coefficient of thermal expansion and the coefficient of thermal conductivity can be greatly reduced,the specific heat capacity and thermal diffusivity will increase when the environment-friendly sand was added to the appropriate amount of additives.These excellent thermal physical properties of environment-friendly sand can effectively ensure the quality of castings in the cooling and solidification process.Finally,the environment-friendly sand was tested for pouring and compared with coal sand in order to verify the effect of environment-friendly yellow loam on casting quality and casting defects.The applicability of environment-friendly yellow loam sand was mainly studied from two aspects: the degree of sticky sand and the surface roughness.The results show that the surface of environment-friendly sand casting can form a sintered shell,which can be peeled off by tapping.The casting surface is smooth and fine,casting quality is good.The study has the basic guiding function on the understanding of the recycling performance of environment-friendly sand,the control of the casting cost,and the promotion of the production process of green casting. |
