Anti-Veining Additive for Silica Sand Mold

Abstract

This invention relates generally to a composition for silica sand cores and molds suitable for in the casting of metals. The sand core composition contains a hinder and a uniformly dispersed anti-veining additive. The mixed metal oxides collapse into a visco-plastic state when the foundry mold / core is heated by the molten metal during casting. A change in state of the MMOx from solid to a visco-plastic at the casting high temperatures provides space and lubricity within the foundry shape sufficient to compensate for the thermally-induced physical expansion of the silica grains. Thereby avoiding the mechanical forces which cause cracks and fissures in the mold or core that produce veins and other surface imperfections associated with the high coefficient of thermal expansion of silica sand.

Description

FIELD OF THE INVENTION[0001]The present invention relates to metal founding, and more particularly to a method of making a silica sand-based mold which improves the quality of metal castings by reducing veining defects. This invention relates to silica sand mold / core additives for controlling thermal expansion of sand mold / cores during metal casting operations.BACKGROUND OF THE INVENTION[0002]In a metal casting process, a cavity is first shaped in a mold. The mold inner cavity surface is the active surface and has a configuration corresponding to the exterior surface of the product desired to be manufactured. Molten metal is poured into the mold cavity and takes the shape of the cavity. As the metal cools it solidifies into a metal casting product having a shape corresponding to the mold cavity imprint.[0003]Silica sand is commonly used for molds and cores because it is readily available and inexpensive in most of the world. A drawback of using silica sand is that it has a high coef...

AI Technical Summary

Benefits of technology

This patent describes a way to improve the surface finish of silica sand molds and cores used in casting metal parts. The improvement is achieved by adding mixed metal oxides to the sand to create spaces and lubricity within the mold or core when it is heated by the molten metal during casting. This prevents cracks, veins, and other surface flaws that can occur when the mold or core expands and contracts during the casting process. The resulting products have a better surface finish and are less expensive to manufacture.

Problems solved by technology

A drawback of using silica sand is that it has a high coefficient of thermal expansion, including a high coefficient of thermal expansion at temperatures below the solidification temperatures of iron and steel.

When this happens, the surface layer (in the absence of suitable additions to the mold) cracks, these cracks open up, and metal runs into the cracks to produce veins on castings which are highly undesirable.

Of course, such surface grinding or machining increases the casting cost.

The expansion may cause pieces of the core to flake off, which leaves a rough surface finish, and thermal expansion produces cracks in the core.

These particulate materials, and other organic material used in the prior art provide some strain accommodation but most the prior art organic additives are brittle and do not plastically deform as the mold is heated.

These organic materials often decompose and generate undesirable gas at metal pouring temperatures.

While VEINSEAL® does reduce veining, this material is considered to be relatively expensive in the casting industry.

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