High Performance Sand Casting Technology
Treated sand is packed around a metal, plastic, or wooden pattern half. The mold halves are removed and assembled with or without cores and the metal is poured into the sand casting cavity. The molds are broken to remove the metal parts.
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Manufactured sand casting The most used metal casting process is sandcasting. Silica sand is mostly used in sand casting operations. Close to all casting metals can be sand cast. Sand casting process is behind the manufacture of several items in the modern industry such as valves, pump housings, cylinder heads, engine blocks and many others.Why use sand in sand casting?
The main reason sand is preferred in sand casting operations is because it is inexpensive as compared to other materials. Sand also has a high resistance to elevated temperatures and as such sand casting boasts of being one of the few processes that can be used for metals with high melting temperatures such as Titanium, Nickel and Steel.
In the creation of a sand mold to be used for the sand casting process, our company uses water and clay mixture to hold the mold together. All this is done in our laboratory to ensure proper control of all the aspects of sand that is very crucial in sand casting.Types of sand used in sand casting
In the manufacturing process of sand casting, we use two general types of sand namely:
Synthetic sand- It is mostly preferred in sand casting manufacture because of it gives the san casting mixture more permeability, higher green strength, and greater refractory strength. In a laboratory, synthetic sand is mixed starting with pure silicon oxide sand base.
Naturally bonded Sand- This sand is less expensive as compared to synthetic sand. It contains a lot of impurities of organic nature that reduces fusion temperature of mixture used in casting; it also lowers its binding strength and requires higher moisture content.Properties of a sand casting mixture
In the preparation of a sand casting mixture the following properties are taken into considerations.
Moisture content- The other properties of the mixture like strength and permeability can directly be affected by the moisture content. Bubbles can be entrapped in the metal castings if there is too much moisture content in the sand mixture.
Grain size- This is the size of each particle of sand to be used in the sand mixture in the sand casting process.
Permeability- This refers to the ability of the sand mold to allow air, gases and steam to escape during the sand casting process. A good mixture should have high levels of permeability. Strength- A good sand mixture should have highest level of strength. This is the ability of the mixture to maintain its geometric shape under mechanical stress conditions during the sand casting process.
Grain shapes- This is the shape of each individual sand grain based on the way they are visible. If the grains are less rounded they are considered to be more irregular whereas the ones that are round in shape are said to be regular. This is something that should be kept in mind.
Collapsibility- This the ability of the sand mixture to collapse when subjected to force. This property in a mold allows the metal casting to shrink freely during solidification in the casting process. Without adequate collapsibility hot tearing, cracking and or shrinkage will occur in the casting.
Reusability- A good sand mixture or mold should be able to be reused in other subsequent casting processes. Reusability refers to the ability of the mold to be reused to produce other castings in other manufacturing operations that will follow.
Flowability- Flowability of the mixture is vital during a detailed casting. Flowability refers to the ability of the mold sand mixture to flow over and fill the sand casting pattern in the impression making phase.
Refractory Strength- This is the ability of the sand mixture to withstand high temperature levels. As the molten metal is poured in the sand casting manufacture, the mold mixture should not crack, melt, burn or even sinter. During the manufacture of a sand casting it is important to note that some properties in sand casting mold mixture complement each other and as such tradeoffs of different properties is often needed to reach a compromise that provides a sand casting mold mixture with adequate properties for the specific cast application.
There are various types of molds that we use in making sand castings such as Green sand molds, dry sand molds and skin dried molds.