Lesson Notes By Weeks and Term v4 - SHS 2

Lesson Video

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Performance objectives

• Describe the principles of sand casting.
• Identify the major components of the sand casting process.
• Demonstrate the steps involved in preparing a sand mold.
• Analyze the advantages of sand casting.

Lesson summary

This lesson introduces the fundamental manufacturing process of sand casting, a method used for centuries to create metal objects. In Ghana, this process is the backbone of many local industries, from the artisans in Suame Magazine in Kumasi and Kokompe in Accra who create spare parts for vehicles and grinding mills, to the craftsmen who produce our everyday aluminium cooking pots (*dadesen*) and coal pots. Understanding sand casting is not just an academic exercise; it is a gateway to appreciating local innovation, entrepreneurship, and the creation of essential products that power our communities.

Lesson notes

A. What is Casting? Casting is a manufacturing process where a liquid material (like molten metal) is poured into a mould, which contains a hollow cavity of the desired shape. The liquid material is then allowed to solidify. The solidified part is known as a casting. Once removed from the mould, this casting may undergo further finishing processes. B. What is Sand Casting? Sand casting is a specific type of casting that uses sand as the mould material. It is one of the oldest and most widely used casting methods due to its low cost and versatility. Advantages: Relatively inexpensive materials (sand, clay). Can be used to cast very large parts. Suitable for producing complex shapes. Can be used for a wide variety of metals (iron, steel, aluminium, brass). Disadvantages: Produces a rough surface finish. Less accurate in dimensions compared to other methods like die casting. Not suitable for very thin sections. C. Key Terminology in Sand Casting To understand the process, we must first learn the language. Pattern: A replica of the object to be cast. It is used to create the impression (the cavity) in the sand mould. Patterns are often made from wood, plastic, or metal. They are made slightly larger than the final product to account for metal shrinkage during cooling. Mould: The entire assembly of sand and containers that holds the hollow cavity into which molten metal is poured. Flask: A rigid box, typically made of wood or metal, that holds the moulding sand. A flask is made of two parts: Cope: The top half of the flask. Drag: The bottom half of the flask. Parting Line: The surface where the cope and drag separate. Moulding Sand: A special type of sand with three main components: Silica Sand (SiO₂): Provides the structure and can withstand high temperatures. Binder (e.g., Bentonite Clay): Holds the sand grains together when mixed with water, giving the mould its strength. Water: Activates the clay binder. Core: A separate insert made of sand, placed inside the mould cavity to create hollow sections or internal features in the final casting (e.g., the hole in a pipe fitting). Gating System: A network of channels that delivers the molten metal from the outside of the mould into the mould cavity. It consists of: Pouring Basin: A small funnel-shaped cavity at the top of the mould where the metal is poured. Sprue: A vertical channel through which the molten metal flows downwards from the pouring basin. Runner: A horizontal channel that connects the sprue to the gates. Gate: The point of entry where the molten metal enters the mould cavity itself. Riser (or Feeder): A reservoir of molten metal connected to the casting. As the casting cools and shrinks, the riser feeds extra molten metal into the mould to compensate for this shrinkage, preventing defects like voids or porosity. D. The Step-by-Step Sand Casting Process Let's imagine we are casting a simple, solid aluminium block.

Step 1: Pattern and Flask Preparation Place the drag (bottom half of the flask) upside down on a flat moulding board. Place the pattern for the block in the centre of the drag. Sprinkle a fine powder called parting sand over the pattern and the board surface. This prevents the sand in the cope from sticking to the sand in the drag.

Step 2: Ramming the Drag Place moulding sand into the drag, covering the pattern. Use a rammer to compact the sand firmly and evenly around the pattern. Add more sand and ram until the drag is full and level. Use a straight edge (strike-off bar) to scrape off the excess sand.

Step 3: Creating the Cope Flip the entire drag over so the moulding board can be removed. The pattern is now visible, embedded in the sand. Place the cope (top half of the flask) directly on top of the drag, aligning them with locating pins. Place the sprue pin (a tapered rod to form the sprue) a short distance from the pattern and a riser pin over the thickest part of the pattern. Sprinkle parting sand over the surface. Ram the cope with moulding sand, just like the drag.

Evaluation guide

• Apply the principles of sand casting to produce articles
• G
• roup work:
• Group students to describe accurately and honestly the processes used in sand