Understanding Investment Casting - Process Basics
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Wax replicas of the desired castings are produced by injection molding. these replicas are called patterns.
At Hitchiner, molten wax is injected under high pressure into liquid-cooled, automated collapsable dies. Depending on part complexity, these tools may be single or multi-cavity.
The patterns are attached to a central wax stick, called a sprue, to form a casting cluster or assembly.
Hitchiner ring segment wax sub-assemblies are simply stacked to form the complete assembly. The ring is notched so that the optimum spacing is automatically achieved.
The shell is built by immersing the assembly in a liquid ceramic slurry and then into a bed of extremely fine sand. up to eight layers may be applied in this manner.
At Hitchiner, specialized shell building robots are used to build the shell. This automation provides for a consistent build and allows for larger molds than could be built by manual methods.
Once the ceramic is dry, the wax is melted out, creating a negative impression of the assembly within the shell.
Steam autoclaves or MCT-developed rotary dewax machines are used for this purpose. At Hitchiner, the wax is reclaimed, purified and recycled.
In the conventional process, used by most foundries, the shell is filled with molten metal by gravity pouring. as the metal cools, the parts and gates, sprue and pouring cup become one solid casting.
Hitchiner uses its exclusive Countergravity Casting Services to cast the mold. In these processes, molten metal is drawn into the mold cavity in a controlled fashion, resulting in superior castings. The vacuum is released when the parts and a portion of the gates have solidified, allowing the molten metal in the central sprue to return to the melt.
When the metal has cooled and solidified, the ceramic shell is broken off by vibration or water blasting.
After countergravity casting, the molds are discharged from the casting machine into a special hopper that separates the castings from the support materials. The individual castings may then be tumbled or vibrated, stripping them of all shell remnants.
Traditionally, the parts are cut away from the central sprue using a high speed friction saw.
Hitchiner's countergravity-cast parts do not have a solidified central sprue and therefore do not require this operation. Only a small gate stub remains after casting which is easily removed by a mass production grinding operation
After minor finishing operations, the metal castings—identical to the original wax patterns—are complete.
Hitchiner Manufacturing Co., Inc. has the capacity and experience to offer complete-to-print machining and subassembly operations, delivering a finished component ready for installation in the finished product.
Countergravity Casting Animation
Hitchiner first developed its exclusive countergravity processes for reasons of economics. However, a solid body of evidence has been generated to show that countergravity casting yields parts that are substantially better in quality than corresponding parts using the best ladle pouring procedures.