Sand casting molds are created using a pattern of the desired object, which is then used to form a cavity in compacted sand. Here's a breakdown of the process:
Sand Mold Creation Process
The process of making a sand mold involves several key steps:
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Pattern Preparation: A pattern, typically made of wood, metal, or plastic, is created. It's a replica of the final casting, with allowances for shrinkage and machining.
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Mold Framing: A casting flask, usually composed of two parts called the cope (top) and drag (bottom), is used to contain the mold. This framework holds the sand and provides structure.
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Sand Mixing: A special sand mixture is prepared by combining silica sand with a binder. This binder helps the sand particles stick together to hold the shape of the mold.
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Sand Packing: The sand mixture is placed around the pattern inside the flask. It's carefully tamped down and compacted to ensure a dense, uniform mold. According to the provided reference, the sand mixture is tamped down as it is added around the pattern.
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Compaction: The mold assembly is sometimes vibrated to further compact the sand, ensuring the mold is dense and has no unwanted voids, according to the provided reference.
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Pattern Removal: Once the sand is compacted, the pattern is carefully removed, leaving a cavity in the shape of the desired casting.
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Gate and Runner System Creation: Passages, called gates and runners, are created within the mold to allow the molten metal to flow into the cavity.
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Venting: Small vent holes are created to allow gases to escape from the mold during casting.
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Core Placement (If needed): If the casting requires internal features or voids, sand cores are placed inside the mold before closing it.
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Mold Closing: The cope (top) and drag (bottom) sections of the flask are closed and clamped securely before pouring molten metal.
Types of Sand Molds
There are different methods used to create sand molds:
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Green Sand Molding: This is the most common method where the sand is moist and held together by clay.
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Air-Set Molding: The sand is mixed with a chemical binder that hardens at room temperature. As stated in the reference, air-set molds are often formed using a cope and drag flask.
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Dry Sand Molding: The mold is baked to increase its strength and rigidity.
Summary Table
| Step | Description |
|---|---|
| Pattern Creation | A replica of the casting is made with dimensional allowances. |
| Flask Preparation | A flask, often with cope and drag, is prepared to hold the mold. |
| Sand Mixing | Sand is mixed with a binding agent. |
| Sand Packing | The sand mix is packed around the pattern and tamped down as it's added. |
| Compaction | The mold assembly is sometimes vibrated to compact the sand. |
| Pattern Removal | The pattern is removed leaving a cavity. |
| Gate/Runner Creation | Passages for molten metal are created. |
| Venting | Holes are created for gas escape. |
| Core Placement | (If needed) Sand cores are placed for internal features. |
| Mold Closing | The cope and drag are closed, ready for casting. |
The result is a sand mold ready to receive molten metal to create the final cast part.
