Green Sand Molds

A typical green sand mixture contains 89 percent sand, 4 percent water, and 7 percent clay. Green sand is an industry favorite because of its low cost and solid overall performance. The “green” in green sand refers to the moisture content present in the mixture during pouring.

Green sand molds have sufficient strength for most sand casting applications. They also provide good collapsibility, permeability, and reusability. The main difficulties arise to the moisture content. Too much moisture can cause defects in the casting, with the moisture tolerance dependent on the metal being cast.

Cold Setting Processes

Sometimes non-traditional binders are used in industrial sand casting. Conventional casting binders require heat to cure, while these alternative binders bond chemically at room temperature when mixed with sand – hence the term cold setting processes. Technically advanced, these relatively recent sand casting processes are growing in popularity. Cold setting processes are more expensive than green sand molds, but they produce castings with exceptional dimensional accuracy.

Shell Molding

Shell mold casting is a relatively recent invention in molding techniques for mass production and smooth finish; it was first used by Germany during the Second World War. The molding material is a mixture of dry, fine silica sand with minimal clay content and 3-8 percent thermosetting resin (phenol formaldehyde or silicon grease). When the molding mixture drops on to the heated pattern plate, a hard shell of around 6 mm thickness is formed. In order to cure the shell completely, it must be heated to 440 to 650°F (230 to 350t) for several minutes.