The pattern that is not used in sand casting in a foundry is the casting itself.
Understanding Sand Casting Patterns
In the sand casting process, a pattern is a crucial tool. It is a model of the final object to be cast, slightly oversized to account for metal shrinkage during cooling. The pattern is used to create the mould cavity within the sand. Once the mould is ready, the pattern is removed, leaving a void that matches the shape of the desired part.
Types of Patterns Used in Sand Casting
Foundries utilize various types of patterns depending on the complexity, size, and production volume of the casting. Some common types include:
- Single Piece Pattern (Loose Pattern): The simplest type, representing the entire casting as one piece.
- Split Pattern: Divided into two or more parts, typically along the parting line, to facilitate easy removal from the mould.
- Match Plate Pattern: Patterns mounted on opposite sides of a single plate, ensuring accurate alignment of the cope and drag sections of the mould.
- Cope and Drag Pattern: Separate patterns for the cope (top) and drag (bottom) parts of the mould.
- Follow Board Pattern: Used for patterns that are fragile or have delicate projections, providing support during moulding.
- Skeleton Pattern: A framework used for very large castings, providing the basic shape which is then filled with sand.
These patterns can be made from materials like wood, metal, or plastic.
Why the Casting is Not a Pattern
The casting is the output of the sand casting process, not an input or tool used to create the mould.
As explained in the reference: "Molten material is poured into the mould cavity to make a casting, after solidification and hence, it does not constitute the pattern."
The process flow is:
- Pattern: Used to create the mould cavity.
- Mould Cavity: Created by the pattern.
- Molten Material: Poured into the mould cavity.
- Solidification: Molten material cools and hardens within the cavity.
- Casting: The solidified part, which is the final product.
Therefore, the casting is the result of pouring molten material into the mould that was shaped by the pattern. It does not serve the function of creating the mould cavity itself.
Practical Insight
Imagine baking a cake. The cake pan is like the pattern – you use it to shape the batter (molten material) into the desired form (the mould cavity). The finished cake itself (the casting) is the final product and is not used to create the pan or another cake.
Summary Table
| Component | Role in Sand Casting Process | Is it a Pattern? |
|---|---|---|
| Pattern | Creates the mould cavity shape | Yes |
| Mould Cavity | Void left by the pattern, receives molten metal | No |
| Molten Material | Poured into the mould cavity | No |
| Solidified Material | Hardened molten metal inside the cavity | No |
| Casting | The final product after solidification | No |
In conclusion, while various types of patterns are essential for creating the mould in sand casting, the casting itself—the solidified final product—is not a pattern.
