Development Of A Coated Sand For Cast Steel

Since the beginning of the 21st century,with the rapid development of China’s foundryindustry,China has become a casting power,the annual output of castings is gradually higher than the total output of castings in the United States,Japan,Britain,France,Germany and other developed countries,it accounts for 1/3 of the world’s casting production.However,most foundries in China use modeling materials as disposable materials,which is consumed every year over 10 million tons,at the same time,it also causes a large amount of waste sand emissions,which seriously threaten the ecological environment;In addition,China’s casting scrap rate is as high as 10%to 15%,far higher than 5%of developed countries;In addition,1/4 of the production cost is spent on later casting cleaning,especially for steel castings with higher casting temperatures.Among the problems that currently appear in China’s foundry industry,molding materials bear important responsibilities,therefore,this paper develops a high-performance coated sand for cast steel.The research on the selection of the original sand of the coated sand,the influence on the steel casting and the preparation process found that:(1)No.1 aeolian sand has a lower mud content than No.2 sea sand,under the same conditions,it has the advantages of high bulk density,smooth rounded surface topography,small specific surface area and low gas generation,these are beneficial to improve the high strength properties of the coated sand and the surface quality of the cast steel.The No.2 raw sand has the advantages of higher SiO2 content and less melting point impurities than No.1 raw sand.Comprehensive investigation,the melting temperature of No.2 raw sand is higher than that of No.1 raw sand,that is,No.2 raw sand is beneficial to improve the high refractoriness of the coated sand,since this property plays a vital role in the yield of castings,we chose No.2 raw sand.(2)The cohesive fracture can significantly improve the high strength properties of the coated sand compared with the attachment fracture;The curing rate of the coated sand needs to be determined according to the complexity of the sand type and the sand core.When the sand moulds and cores are complex,the solidification rate of the coated sand can be reduced to ensure the complete filling of the casting moulds;Under the premise of ensuring the high-strength performance of the coated sand,reducing the amount of resin added can reduce the burning loss and avoid the defects of the pores caused by the gas;In order to meet the high pouring temperature of the steel castings,it is not enough to use only the No.2 raw sand with a high SiO2 content,it is necessary to add an addendum to the No.2 raw sand to further improve the high refractoriness of the cast steel coated sand and minimize the possibility of occurrence of chemical sticking sand;In order to solve the problem that the linear expansion coefficient of the mold is large due to the selection of the high SiO2 content,on the one hand,by using a three-screen sand of 70/140 mesh,the contact area between the sand grains is increased,On the other hand,a certain amount of chilled sand is added to increase the thermal conductivity of the entire mold.(3)In the optimization of process parameters of coated sand,the four-factor and three-level orthogonal experiments were carried out on the heating temperature A of the raw sand,the stirring time B after the resin was added,the amount C of the curing agent urotropine,and the stirring time D after the addition of the lubricant calcium stearate.Choosing the right combination of process parameters helps to increase the normal temperature tensile strength and hot tensile strength of the coated sand.