Sand casting is the easiest way to form a mould for single use. Unlike productions moulds, sand casting moulds are destroyed when the casting is removed. A new mould must be made from the same model to create a duplicate part. This process would be inefficient for a large production shop but is often ideal for a small shop that occasionally needs to fabricate custom metal parts. The initial equipment investment for moulding sand can be quickly recovered since it can be reused many times.
- Skill level:
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Things you need
- 2 pieces of ¾-inch plywood slightly larger than your forms
- Part model
- Parting dust
- Wooden flask (form for moulds)
- Casting sand
- Flat packing block
- Utility knife
- Pipe or dowel rod
Place your part model on a piece of 3/4-inch plywood.
Sprinkle the model and the surface of the plywood with parting dust.
Separate the two halves of the wooden flask. The flask is like a four-sided box with no top or bottom. It is divided into two sections to make a two-piece mould form. Set the top half aside. Place the bottom half of your flask on top of the plywood (from Step 2). Keep the model as close to the centre of the form as possible.
Fill the portion of the flask containing the model with casting sand.
Compact the casting sand with a packing block. Any flat piece of wood or metal can be used for this purpose. It is imperative to remove any voids in the casting sand.
Level the top of the casting sand by drawing a pipe or dowel across the top of the form. The sand must completely fill the form for the mould to remain intact.
Place the second piece of plywood over the top of the form.
Turn the form over. The board you placed on top will now become the bottom of the form.
Remove the plywood from the top of the form to reveal the model.
Score a fine line around the edges of the model with a utility knife. Add a fine layer of parting dust around the edges of the model. With this step, the bottom half of the mould is complete.
Put the empty top half of the flask in position over the completed bottom half.
Create the bottom of the pouring channel by pressing a pipe or dowel 1/2-inch into the top of the sand near the model.
Hold the pipe or dowel upright while filling the top half of the form with casting sand.
Compact the sand in the top half of the form with a packing block.
Remove the pipe or dowel.
Place a piece of plywood over the top form. Lift the top half of the form off of the bottom. Turn it over and set it aside.
Remove the model from the bottom half of the mould. Use the blade of a utility knife to lift it clear of the casting sand without disturbing the impression.
Excavate a channel between the model impression and the pouring channel, in the bottom half of the mould, with your utility knife.
Put the top half of the mould back in place.
Melt your metal in the furnace. Pour the metal slowly into the pouring channel with a ladle. The mould is full when the molten metal reaches the top of the hole in the sand.
Allow the casting to cool. Separate the form halves to remove the casting.
Tips and warnings
- Do not start your furnace until you have completed the mould. Making a good mould takes time and patience. Don't get in a race with your furnace.
- Finer grades of casting sand cost more initially but can save polishing time.
- Wear appropriate safety gear. Gloves, boots and eye protection are highly recommended for pouring molten metal.
- Some metals, like lead, give off toxic fumes. Wear an approved respirator when working with any potentially toxic materials.
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