Sand Casting

Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced in specialized factories called foundries. Over 70% of all metal castings are produced via a sand casting process

          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 cut-off and re-used also.

          Properly conditioned sand is an important  factor in obtaining good castings.  There are very few  natural sands which possess all the qualities of moulding  sand. Many sands, therefore have to be mixed up properly generally, natural sand d with adequate quantities of clay, lime, magnesia, potash soda, horse manure, saw dust, cow dung, coal dust, etc. Are used. New sand as well as used sand must be properly prepared before it can be used. Ratio of old sand to new sand can be high for light castings but it decreases for medium and large castings.

          Silica enables the moulding sand capable of withstanding high temperature but it has no bond. Clay is used to impart necessary bond to the moulding sand, but excessive quantity of clay causes cracking of the mould after drying. Addition of small quantities of lime, magnesia, iron oxide, soda, etc. Reduces melting point of silica.

Process cycle:

·        mold making

·        clamping

·        pouring

·        cooling

·        removal

·        trimming

Advantages of Sand Casting:

1) Casting can be used to create complex pad geometries, including Goth external arid internal shapes.

2) Some casting operations are capable of producing parts to net shape. No further manufacturing parts are needed.

3) Casting can be used to produce

4) Casting process can be performed on any metal that can be heated to the liquid state.

5) Some casting methods are highly suited far mass production.

6) Casting is the easiest and quickest way (technique) from drawing (design) to the production.

Disadvantages of Sand Casting:

1) Limitation on mechanical properties.

2) Porosity (empty spaces within the metal - reduces the strength of metal).

3) Poor dimensional accuracy and surface finish.

4) Safety hazards to humans and environmental problems.

5) Removal of pattern of the thin and small parts is very difficult.