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The sand casting process is ancient and one of the mostcommon techniques for casting metal and, as its name indicates, sand is the keyfactor in its efficiency. In sand casting, for example, liquid metal is castinto a mold made of sand which serves to give shape to the material as it coolsand hardens. The sand that is incorporated in the process is not just sand butone that has been already carefully selected and treated in a manner thatensures casting accuracy, excellent quality, and strength.

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What Is Sand Casting?

Sand casting is the technique of making metal parts bypouring molten metal into a mold composed of sand. Molds are usually made intwo parts called, cope (the upper half) and drag (the lower half). A moldedpattern that depicts the part to be cast is used to build the sand mold, andthis cavity is filled with liquid metal. When the metal has cooled, the sand isremoved and the casting is complete.

Sands Appropriate for Sand Casting

In sand casting, not all sands are the same. Various kindsof sand can be utilized each possessing particular characteristics that willimpact the outcome of the casting.

1. Green Sand

Green sand is the most popular sand that is used for sand casting. It iscomposed of silica sand, bentonite clay (binder), water, and other additives.The term “green” does not mean the color of the sand but rather the fact thatthe sand is wet. Great versatility and cost efficiency makes green sand moldssuitable for casting metals such as brass, iron and aluminum.

Key Properties of Green Sand:

o Good moldability and plasticity corrosion

o High thermal resistance

o Easily reusable after conditioning

Dry Sand On the other hand, dry sand is already cured orbaked before the pouring of the metal as opposed to green sand. Theeffectiveness of durability of the mold is improved because drying the sandwill allow it to withstand higher temperatures. dry sand is mostly used whenlarge parts are to be casted or when better surface finishes are needed.

Key Properties of Dry Sand:

o Dry sandis associated with more strength and stability than green sand

o Moisturecontent is lowered leading to a lower probability of defects such as gasporosity

o Can beused to cast heavy and detailed metal parts

3. ResinSand

Molds made out of resin sand consist of silica sand and abinder such as furan or phenolic resin. The sand retains its shape well evenafter the pattern has been removed due to the presence of the binder in orderto remove the pattern. Because of its higher strength and the capability ofcasting intricate structures, this type of sand is frequently utilized forsophisticated casting processes.

Key Properties of Resin Sand:

o Greatrigidity and strength

o Accuratecastings with high definition surface finish

o Highmelting point

4. SodiumSilicate Sand

Sodium silicate is the binder of this sand. When bundledwith carbon dioxide (CO2), the paste cures and solidifies into a tough anddurable mold. Sodium silicate sand finds wider application in many specializedareas requiring higher strength and dimensional precision.

Key Properties of Sodium Silicate Sand:

o Relativelyquick setting when exposed to CO2

o Very highstrength hence low probability of cold shut

o Can beused for intricate castings with close tolerances

The Importance of Sand Properties

Sand used in sandcasting is of great consequence because itdetermines the success of the casting. Here are the critical characteristicsthat are essential in evaluating the proper sand for the application:

1. Permeability

Permeability is the ability of sand to permit the escape ofgas during the casting technique. Sand that is too dense can cause gases to betrapped which can subsequently lead to flaws in the final casting, forinstance, blowholes or gas porosities. Properly permeable sand promotes goodflow and defect-free sand castings.

2. Strength

The sand is expected to exhibit sufficient strength to standthe mold's shape in the course of metal pouring. Failed sand is likely to giveway under the weight of molten metal and defect the casting. To enhance thestrength and cohesiveness of the sand, different binders are added.

3. Refractoriness

This is ‘refractoriness’ and is the property of sand to holdwithout melting or degrading even when in contact with molten metal at hightemperature. Sands of high refractoriness never allow any distortion of themold at temperatures over 1000 degrees Celsius.

4. Collapsibility

Once the metal has cooled enough to turn solid, the sandmold should also be taken out without any damage to the casting itself. Sandswith good collapsibility are easy to break after cooling and so, minimize thedisfigurement caused in a casting when it is removed.

5. SurfaceFinish

The grain size and the uniformity of sand also alter thesurface quality of the finished casting. The finer the grain sand, the betterthe finish, whereas the coarser the grain, the worse the finish. It isessential to achieve a moderate degree of roughness to the surface of thecasting suitable for the purpose it is intended for.