Ceramic shell process

The technique applies for the fabrication of castings which need a high surface finish, in low-carbon alloys such as ultra low carbon stainless steel and nickel-based alloys with a finished weight of up to 550 kg. The ceramic shell process is a patented process and may only be used in accordance with the terms and conditions of the licence granted to the licensee. 

The pattern is made by pouring or injecting wax into a metal mould. In some cases a simple pattern may be prodnced in one step with an integral gating system, while in other cases complex patterns may be assembled from a nnmber of separate components prepared individually. In the ceramic shell process, after the wax pattern is formed it is dip-coated with a primary slurry coat of very fine particles to give a smooth surface it is then stuccoed with coarser refractory and dried. These steps are repeated until the required mould thickness is achieved. The primary and secondary dip-coats contain binders such as ethyl silicate, and the refractories are principally zircon, sillimanite... 

The ceramic shell process is widely employed for producing large castings in steel, nickel and other high melting point materials. The, block mould process is mainly used for light alloys and in the production of small and medium-size castings. 

This process is used to produce intricate, thin-section parts with great dimensional accuracy, fine detail, and very smooth surfaces. All ferrous and nonferrous alloys can be cast in investment molds. Investment casting begins with expendable wax patterns that are assembled into clusters, then coated with a series of successively coarser ceramic slurries. The assembly is then fired in a furnace to dry and harden the ceramic shell and to melt out the wax, leaving a cavity into which molten metal is poured to form the casting. 

The process as it is practiced now actually produces a ceramic shell of modest thickness (about 0.2-0.5 in. thick) around the wax pattern. The relatively thin shell when compared to solid mold casting not only saves material but also allows for more uniform and rapid cooling of the metal parts. This is an important factor in maintaining fine grain size that results in stronger parts. 

Colloidal silica serves two functions in the process. Since it is a low viscosity water-based liquid it is used as the vehicle to slurry the ceramic powders which make up the ceramic shell. The viscosities of slurries used in the process are usually similar to a thin crepe or pancake batter. They must be thin enough to flow into the surface details of the wax patterns such as the narrow grooves in a golf club head, but thick enough to leave a continuous... 

Ceramic shell moulding is a patented process (Replicast ) in which a polystyrene model is covered with a ceramic shell (2-3 mm thickness), based on ethyl silicate and refractory sand. The shell is hardened using ammonia and sintered at 1000 °C. The sintering cures the shell and bums away the polystyrene model. The metal is then poured into the shell. 

A very dangerous fire hazard in the form of a solid or dust when exposed to heat or flame. It can react violently with air, CI2, F2, HNO3, NO, Se, S, water, NH3, BrFs, trichloroethylene, nitryl fluoride. During storage it may form a pyrophoric surface due to effects of air and moisture. Depleted uranium (the by-product of the uranium enrichment process, with relatively low radioactivity) is used in armor-piercing shells, ship or aircraft ballast, and counterbalances. Uranium is also used in making colored ceramic glazes. 

Phillips J.N. and Dries H.W.A., Filtration of flyslag from the Shell coal gasification process using porous ceramic candles, in Gas Cleaning at High Temperatures, Clift R. and Seville J.RK., eds.. Chapman Hall, London, (1993), p. 127,... 

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