What is the step by step procedure in green sand molding?

Green sand molding is a fundamental and widely used method in metal casting to create a mold cavity for molten metal. The process involves using a pattern to form an impression in a prepared mixture of sand, clay, and water.

Here are the basic steps involved in making green sand molds:

The Green Sand Molding Procedure

The procedure is relatively straightforward, relying on the properties of "green sand" (moist sand mixture) to hold the shape of the pattern after it's removed.

Here is a breakdown of the essential steps:

1. Pattern is positioned in the flask.

   • A pattern (a model of the final part) is placed within a molding box called a flask. For parts with intricate shapes, the mold is often created in two halves (cope and drag), and the pattern is also split.

2. The flask is filled with conditioned sand.

   • Conditioned sand (green sand) is poured into the flask around the pattern. This sand is a mixture of silica sand, clay (like bentonite) as a binder, water for moisture, and sometimes other additives for performance.

3. Sand is compacted.

   • The sand is packed tightly around the pattern. This is crucial to ensure the mold cavity holds its shape and can withstand the pressure of the molten metal. Compaction can be done manually by ramming or using mechanical methods like jolting or squeezing.

4. Pattern is removed from the mold.

   • Once the sand is compacted, the pattern is carefully withdrawn from the sand mold. This action leaves behind a cavity that is an exact negative impression of the pattern.

5. Gating and risering system are completed.

   • Channels are cut or formed in the sand to create the gating system. This system allows molten metal to flow from the pouring basin into the mold cavity.
   • Risers are also added. These are reservoirs that feed molten metal into the cooling casting to compensate for shrinkage and prevent defects.

6. Cores are placed in the mold, if required.

   • If the final casting needs internal cavities, holes, or complex undercuts that cannot be formed by the pattern alone, pre-formed sand shapes called cores are inserted into the mold cavity.

7. Mold is assembled/closed.

   • If the mold was made in multiple parts (e.g., cope and drag), the parts are carefully assembled and securely fastened or weighted to prevent them from separating when the molten metal is poured.

Step-by-Step Overview

For clarity, here is a table summarizing the key actions:

Once these steps are complete, the mold is ready to receive molten metal to produce a casting.