Study On Preparation Technology Of Hybrid Thermal Conductive Fiber Composite Shell

In investment casting,silica sol shell is one of the most widely used shell.However,the coating prepared by silica sol has long drying time and low strength at room temperature,which leads to long shell making cycle and low production efficiency.In order to improve the comprehensive properties of silica sol shell,the way of adding 0.4%of refractory powder and mixing ratio of steel fiber,steel fiber and carbon fiber is 7:1 and 5:1is adopted,The fiber with the length of 2mm,3mm,4mm and 5mm was added into the mechanically stirred coating.The effects of fiber parameters on the apparent viscosity,thixotropy and suspension of the coating were studied.The normal temperature strength,baking strength,high temperature strength,high temperature self weight deformation and thermal diffusion coefficient of the shell were measured.The results show that the addition of fiber will affect the rheological properties of the coating.With the increase of shear rate,the apparent viscosity of the coating increases rapidly at first and then decreases slowly;with more and more carbon fiber replacing steel fiber,the apparent viscosity of the coating increases correspondingly;When the mixing ratio is 5:1 and the fiber length is 4mm,the thixotropy of the coating is the best,and the thixotropy ring area reaches 411.64 Pa·s^-1;at this time,the suspension of the coating is the best,reaching 92%.After adding the fiber,the normal temperature strength of the shell can be effectively improved.For the shell with different fibers,the normal temperature strength of the shell first increases and then decreases.When the fiber length is 4mm,the strength of the shell at room temperature is the highest,and then the bending strength of the shell at room temperature decreases with the increase of fiber length.The bending strength and high temperature bending strength of the roasted shell are similar to that of the normal temperature bending strength,which first increases and then decreases.The results show that the bending strength of the shell with 4mm steel fiber is the highest,which is 5.82mpa;when the carbon fiber in the shell replaces the steel fiber,the bending strength of the shell increases slightly,but the increase is not significant,and the maximum bending strength is 6.01mpa.When the fiber length is 4mm at 1200?,the high temperature bending strength of the shell is the highest.With the increase of fiber length,the self weight deformation at high temperature first decreases and then increases.When the fiber content is 0.4%,the hybrid ratio is 7:1,and the minimum deformation of the sample with 4mm fiber is 0.28%.When the temperature is low,the thermal diffusion coefficient decreases with the increase of test temperature,and increases with the increase of test temperature?The thermal diffusivity of the shell decreases with the decrease of the steel fiber content,which indicates that the steel fiber can play a good role in heat conduction and improve the heat dissipation capacity of the shell.