| Investment casting,also known as precision casting or lost wax casting,is a near-net forming technology with a high utilization rate of raw materials,and belongs to a liquid forming process.Silica sol is widely used shell for investment casting.However,there are disadvantages such as low wet strength and long shell-making cycle.And the thermal diffusion performance of the shell is particularly important for investment casting.A higher thermal diffusion ability will improve the thermal expansion,thermal shock stability,and thermal conductivity of the shell to a certain extent.In this work,the steel fiber was selected as the reinforcing phase in the shell matrix to study the rheological properties of the steel fiber slurry,and to explore the influence of the change of the steel fiber content on the slurry performance.and to conduct the thermal diffusion coefficient of the steel fiber shell sample.The steel fiber reinforced shell is compared with the no fiber shell,and the mechanism of steel fiber in the heat conduction of the shell is analyzed.The green strength,fired strength,high temperature strength and high temperature self load deformation of shell were investigated,which is the purposes to find out the best shell for investment casting.The results show that apparent viscosity curve of steel-containing pulp showed a trend of increasing rapidly at first and then decreasing slowly.The thixotropic ring with a 3mm length of 0.4%fiber slurry has the best performance.The area of the thixotropic ring is183.48Pa·s-1.Its suspension is 82%.4mm length,0.3%content and 0.4%content fiber slurry thixotropic properties are the closest.The area of the thixotropic ring is 166.2Pa·s-1,168.36Pa·s-1 and the suspension property is 81%.The change of steel fiber content will affect the flexural strength of the shell at room temperature,after firing,and high temperature,as the amount of fiber increases,its strength first rises and then declines.Contrast with blank shell,all have a certain degree of improvement.It shows that the steel fiber shares the load during the stress process of the shell.High fiber content will have a greater negative impact on the shell and reduce the strength of the shell.The high temperature self-weight deformation of the fiber shell is different from the bending strength of the shell.It is caused by its own mass changing with temperature,Increase with fiber addition.It shows a trend of decreasing first and then increasing.As the fibers clump,entangle,and agglomerate.Intensify the unevenness of the bearing capacity of the shell itself against deformation,creep occurs with increasing temperature,as a result,macroscopically,the amount of deformation increases with the increase of fiber content.The difference in fiber content in the shell will also have a greater impact on the thermal diffusion capacity of the shell.By comparing with the thermal diffusivity of the blank shell,it is found that the thermal diffusion coefficient change curve of the steel fiber shell is significantly improved compared with the blank shell.The increase of the steel fiber content will also increase the thermal diffusion coefficient of the shell,after observing and analyzing the morphological characteristics of fiber distribution in the coating.The needle-like distribution of the steel fibers in the shell is most beneficial to the heat conduction of the shell. |
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