Shell Moulding Process Of Thin-wall Titanium Castings

On the basis of physical and chemical process of interface of Titanium/Zirconia ceramics, mechanics of curdle of Zirconia collosol and desiccation of silica sol binder, Zirconia-containing surface coating materials were optimized through experiment, Zirconia shell manufacturing process was developed to produce high quality thin-wall Titanium castings. The results showed that:1. Stripping layer with the depth of about 200um formed in the inner surface of Zirconia surface coating shell due to the thermal impact of Titanium melt. Surface contamination layer with the thickness of 20-200um generated because of thermal diffusion of zirconium and oxygen;The thickness of reacted layer in castings was 200um,100μm, 50μm when ZrO₂ ZrO₂(CaO), ZrO₂(Y₂O₃) were employed. Decomposition speed of ZrO₂ and the activity of zirconium were reduced due to the addition of Y₂O₃, as a result, the stability of corresponding surface coating material was the best and the contamination layer was the thinnest(50um), which is suited for our company to produce thin-wall castings.2. According to the experimental results of mechanics of curdle of ziconium sol and surface coatings, under the conditions of the diameters of zirconium collidal particles being 1-3um, pH of liquid being 3.8-4.2, the ratio of powder and liquid 3.2-3.4, the environmental temperature 22-24 °C and humidity 50-70%, due to the formation of three dimensional net-like Zr/O bonds of zirconium silica sol, the surface of shell is smoothed, the dimensional accuracy is high, the high temperature strength is high, the casting quality of Titanium is good.3. According to the mechanics of dry dynamics of silica sol, the coating process conditions were determined: the environmental temperature 24-26°C, the humidity 35-45% and air speed is 2-4m/s. Under these conditions, the wet strength of shell is high, air permeability is good, the coatings is not inclined to strip, the hardenability effect of coatings is the best.