Sand Casting | Metal Casting

Sand Casting:

Casting is a solidification process. Therefore, the microstructure can be finely tuned, such as grain structure, phase transformations and precipitation. However, defects such as shrinkage porosity, cracks and segregation are also intimately linked to solidification. These defects can lead to lower mechanical properties. A subsequent heat treatment is often required to reduce residual stresses and optimize mechanical properties.

Sand casting uses natural or synthetic sand (lake sand)  which is mostly a refractory material called silica (SiO2). The sand grains must be small enough so that it can be packed densely; however, the grains must be large enough to allow gasses formed during the metal pouring to escape through the pores. Larger sized molds use green sand (mixture of sand, clay and some water). Sand can be re-used, and excess metal poured is cutoff and re-used also.

The process is fairly straightforward: you make a pattern of what you want to cast, then use the pattern to make a sand mold, and then pour molten metal into the mold. After the metal freezes you end up with the piece that you want.

The sand used for green sand molding is critical and determines the favorable or unfavorable outcome of the casting.  It controls the tolerances, surface finish and the repeatability while in production.  Remembering that the tolerances on sand castings are usually wider than the other casting methods.

Ex: Gears, Pulleys, Crankshafts, Connecting Rods, Propellers, heavy Machine base etc.

The most common metals are Iron, Steel, Bronze, Brass and Aluminium. The process is to make medium to large parts like Valve bodies, Locomotive components and Construction Machinery. Likewise small parts of Buckles, Handles, knobs, and Hinges.

The sand casting process involves the use of a furnace, metal, pattern and Sand mould. The metal is melted in a furnace and then ladled and poured into the cavity of the sand mould, which is formed by the pattern. The sand mould separates along a parting line and the solidified casting can be removed.

Advantages:

1. Low cost of mould materials and equipment

2. Large casting dimensions may be obtained

3. Wide variety of metals and alloy (Ferrous and Non-Ferrous) may be cast

Disadvantages:

1. Rough surface

2. Poor dimensional accuracy

3. High machining tolerances

4. Coarse grain structure

5. Limited wall thickness (2.5 – 5 mm)