Green sand casting

What is green sand casting?

Green sand casting is a common sand casting process using green sand as the molding material.Green sand does not mean sand in green cloor,but is a kind of wet quartz sand in  the sense that it is used in a wet environment.

The mold is made by ramming prepared sand around a pattern,held in a flask. The patterns are withdrawn,leaving the mold cavity into which metal will be poured.Molds are made in two halves,an upper portion, the cope, and a lower portion,the drag.The boundary between cope and drag is known as the parting line. 

Cores, made from sand bonded with resins and baked to give sufficient strength, may be supported within the mold cavity to form the internal structure of hollow castings. Chills of various designs may be embedded in the mold cavity wall to control the solidification process. 

Risers are reservoirs of molten metal used to ensure that all regions of the casting are adequately fed until solidification is complete. Risers also act as heat sources and thereby help promote directional solidification. Molten metal is introduced into the mold cavity through a sprue and distributed through a system of gates and runners.

What are the materials of green sand casting?

Green sand casting is suitable for manufacturing various cast iron castings,like ductile iron castings,gray iron castings.It is also suitable for producing some simple aluminum castings.As steel castings require larger air permeability,so it is not workable for making steel castings.

Advantages of green sand castings?

*Simple production process:Comparatively,the production proces of green sand casting is easier than other casting process.
*Low production cost:For its low material cost and simple casting process,the production cost of green sand casting is low.
*High production rate:For the floor molding with green sand,we could produce castings about 200 sand boxes each day.Now we are also developing automatic molding production line,it could produce green sand castings of 20t each day.

Disadvantages of green sand castings?

*Defects are easy produced:With green sand casting process,defects like sand residuals,sand holes,air holes and shrinkages are common.
*Rough surface:As the simple production process,the surface of green sand castings is rough.If iron foundry choose fine green sand,then the surface will be better,but the cost of fine green sand is higher.
*Bad casting dimensions:The size tolerance of green sand casting is CT11-CT12.So it is only suitable for castings with low size accuracy.