The previous blog was a primer on Green Sand Moulds. A green sand mould is made by pouring green sand into a mould maker and then a pattern is pressed into the sand. The pressure that is formed when the mould is pressed into the sand creates a form close to when a kid presses a pattern into Play-Doh to fabricate a shape.
The disadvantage of green sand moulds for castings is that their tolerance is not as tight as some other mould types such as ‘no bake castings’. By this if you have castings that need accurate dimensions or tight tolerance, you may go for green sand castings as they require a tad more machining compared to other types of moulds to achieve the intended result. Also, you will get an improved surface finish or a smoother surface through other casting processes.
The green sand required for the casting mould mostly comprises a mixture of Sand 75-85%, Water 2-4%, Bentonite Clay 5-11% and other materials 3-5%. Silica in the sand can turn out to be airborne in the casting process; therefore, foundries install air control systems that attract the silica particles and all other things out of the air for the safety of the foundry workers.
After you are done with the casting, the green sand cannot be reused for casting without it undergoing a rather expensive process of weeding out the materials to reuse what is still left usable in the sand mixture. An alternative method is to make use of new sand every time and retrieve the spent sand for other applications.
When sand is reused it comes out of landfills, the very place where usually spent green sand is spilled. Sand reuse enables the new user of the sand to purchase sand at reduced price compared to virgin sand. There aren’t any toxic substances present in the sand, so it is good on everybody’s part to reclaim and reuse the sand.