Wax Injection & Assembly
The first step in manufacturing an investment casting is the production of an exact wax replica of the casting. For this, a die having a cavity resembling the negative of the part is prepared. Wax is injected into the die under controlled pressure and temperature using a wax press. When the wax solidifies in the die, shape resembling the final product is obtained in wax.
At Zircast high quality of known fresh wax is used to make the patterns, as the repeatability of the dimension is and the casting finish is completely dependent on the quality of patterns injected.
Next stage in the production of the casting is the assembly of the wax replicas in the form of trees. This is a manual process wherein the wax replicas (patterns) are attached to wax runner bars by soldering or by application of a gas flame.
Shell Production & De-Waxing
Wax trees are dipped in a slurry of colloidal silica and Fused Quartz / Zircon powder of –200 mesh size. The tree is then coated with Fused Quartz / Zircon refractory of coarser sizes. This tree is allowed to dry for a few hours in an air conditioned room with controlled temperature and humidity. This process is repeated several times so that a sufficiently strong refractory coating is built around the wax trees.
Parameters such as the viscosity, density, pH of the slurry is monitored and controlled closely along with the shell room parameters like temperature and humidity to achieve high quality and finish on the casting.
The wax tree which is coated with refractories in the shell room is placed in an autoclave and heated by steam under pressure. The wax melts and drains out completely leaving behind a hollow shell. Utmost care is taken during De-waxing so that the shells do not develop any hairline cracks.
Melting & Pouring
The shells after de-waxing are heated in an gas fired / electrically heated shell firing furnace. The shells now become ready to receive the molten metal.
Solid charge materials like stainless steel, Carbon steel, ferroalloys and pure metals like nickel in calculated proportions are melted in an induction furnace.As soon as the metal has attained the necessary temperature, which is determined by a thermocouple, the metal is discharged into small hand ladles. Simultaneously , shells are removed from the firing furnace and the molten metal is poured into the hot shells. The metal fills the cavities in the shells and solidifies, resulting in castings having the desired shape.
Prior to pouring the metal into the shells, separate test piece is also cast which is tested in a spectrometer to ensure conformity to the desired composition.
Fettling & Finishing
This is essentially a cleaning operation which transforms the poured metal into a usable product. The refractory mass surrounding the metal is removed by knock out / vibration.
The cast parts are removed from the runner bars by cutting. Any residual refractory adhering to the castings are removed by leaching.
The in gate is removed by grinding or machining. The casting is then shot blast in order to give the required finish to the product.
Any additional operations such as heat treatment, machining, passivation etc are carried out depending on the customers requirement.