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. 

casting

         

          Casting is a manufacturing process by which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various cold setting materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster and clay. Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods.

          Casting is a 6000 year old process.  The oldest surviving casting is a copper frog from 3200 BC.

          Principle of casting consists of introducing the molten metal into a cavity and mould of the desired shape and allowing it to solidify. When it is removed from the mould, the casting is of same shape but slightly smaller, due to contraction of metal. The molten metal passes through the four stages till the solidification takes place.

Aims In Making a Casting:

There are basically two reasons for making a casting .

1.                 liquid metal must be solidified before further processing is possible, as in smelters and refineries, etc.

2.                 To produce finished or semi-finished articles . the various reasons under this second category, which are of more importance,  can be

a.     Casting is often the cheapest and most direct way of producing a shape with certain desired mechanical properties.  Desired mechanical properties can be attained by operations like suitable control of alloy composition, grain structure and heat treatment.

b.     Casting is often the cheapest and most direct way of producing a shape with certain desired mechanical properties.  Desired mechanical properties can be attained by operations lie suitable control of alloy composition, grain structure and heat treatment.

c.      Certain metals and alloys such as highly creep resistant metal-based alloys for gas turbines can't be worked mechanical  and can be cast only.

d.     Heavy equipment like machine beds, ship's propellers, etc.  Can be cast easily in the required size rather than fabricating them by joining several smaller pieces.

Types of Casting Process:

• ·        Sand Casting
• ·        Shell  Casting
• ·        Plaster  Casting
• ·        Ceramic  Casting
• ·        Investment  Casting
• ·        Lost foam  Casting
• ·        Pressure Casting
• ·        Vacuum Casting
• ·        Die Casting
• ·        Centrifugal Casting
• ·        Squeeze Casting
• ·        Semi-solid Casting
• ·        Single crystal Casting
• ·        Directional solidification Casting
• ·        Slush Casting
• ·        Continuous Casting