What does the term of investment casting refer to

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What does the term of investment casting refer to

Postby megan2008 » Mon Oct 28, 2013 10:30 am

Casting is obtained by casting metal objects, that is a good liquid metal smelting, with the casting, injection, inhalation, or other means of injecting the prepared mold, after cooling off the sand, cleaned (see casting cleaning) and post-processing (see post-casting process), obtained a certain shape, size and properties of objects.According to different methods for molding, casting can be divided into ordinary sand castings, metal castings, die casting, centrifugal casting, continuous casting parts, investment castings, ceramic mold casting, remelting castings, bi-metal castings.

The term 'investment' refers to the ceramic materials that are used to build a hollow shell into which molten metal is poured to make the castings. This term is derived from the solid mold process where a plaster-type material is poured, or invested, into a container that holds a clustered tree of small plastic patterns that are identical to the casting being produced. After the plaster has set, the disposable patterns are burned out leaving a hollow cavity into which the metal is poured.

The same method is used in the investment casting process (also known as the lost wax process). Wax is injected into an aluminum die to produce a pattern that is an exact replica of the part to be produced. The method is similar to diecasting, but with wax used instead of molten metal.

For every investment casting to be produced, a wax pattern must be created. These patterns then are assembled in clusters around a coated sprue to create the casting tree, which is repeatedly dipped into an agitated vat of ceramic, and allowed to dry. After a shell thickness of approximately 0.375 in. (9.525 mm) has been formed, the molds are dewaxed by either flash firing at high heat [1,400F (760C)] or autoclaving (pressure and steam), and the wax is drained and recycled back into the process. The hollow ceramic shells then are preheated to 800-2,000F (427-1,093C) depending on the alloy to be poured, and the molten metal is cast immediately into the hot shell. The casting process either is performed by gravity-pour or vacuum methods (gravity or counter-gravity).

After cooling, the ceramic is vibrated and blasted off the metal parts and discarded. The cast components are broken off the tree and run through cleaning/finishing processes, which are similar to those of other casting processes, such as cut off, grinding, heat treatment, straightening and blasting.

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