Effect of Ultrasonic Agitation Time on Properties of Steel Fiber-Reinforced Investment Casting Shells

In this work, steel fibers were used to strengthen the shells for investment casting while improving the shell's thermal conduction. The fibers were dispersed by ultrasound, and the influence of ultrasonic time on the dispersion of fibers in silica sol and effect of fibers dispersion in shell on the resulting green strength, fired strength, high-temperature self-load deformation and thermal conductivity of matrix were investigated. The results suggest that increasing the ultrasonic agitation time can effectively improve the dispersion of fibers in silica sol. When the ultrasonic power was 1000 W and the ultrasonic agitation time was 3 min, the fibers had been dispersed. When power became 1200 W, the fibers can be dispersed in only 2 min. And the green bending strength reached 3.26 MPa. The fired bending strength was 6.39 MPa. The high-temperature self-load deformation of the shell was 0.49%. The dispersion of fibers in the shell is an important factor affecting the performance of the shell. When the fibers are in the state of agglomeration, it cannot bond well with the shell and not play the role of bracing the shell. Meanwhile, when heat passes through the agglomerative fibers, it cannot be transferred out quickly, and even accumulate heat in the shell. When the fibers are in monofilaments state, the fibers in the shell can effectively resist the fracture load of the shell and enhance the bending strength of the shell through its debonding and pulling out with the matrix, as well as its own deformation and fracture. And, the mesh structure formed between the monofilaments can brace the shell and resist the deformation of the shell. Moreover, when the direction of heat transfer is parallel to the axial direction of the monofilaments, the heat can be quickly transferred to the outer wall of the shell through the monofilaments.