Casting Sand, Green Sand, and Metal Casting Information

Green Sand: Green sand is also called as foundry sand or molding sand. This is utilized for sand casting. When this sand is oiled or moistened, it has a tendency to pack well and retain the shape. Green sand is a mix of pulverized coal, water, bentonite clay and sand. Out of these four components, the biggest part is that of the sand.  There are several proportions of these four components. The different ratios are used to adjust the surface finish, moldability and capacity of the hot molten metal to degas. The prime use of this sand is in the metal casting. The coal is usually called as sea coal in foundries. The amount of sea coal is less than 5 percent. It undergoes partial combustion when there is molten metal present and this causes offgassing of organic vapors.

Green sand is stored in flasks (as the casters call the container). These are boxes that do not have a bottom or lid. This box is divided into two half parts and these are connected together. These halves are called as the top or cope and bottom or drag flask.

As per its name, green sand is not green in color. The word “green” is used as it is used in the wet state.

Casting Sand: Some casting sands are oil bonded and foundry mix sand. This is a mixing of oil, resin and sharp fine silica sand. Such a mix can be utilized in sand casting of all varieties of metals. Some casting sands consist of 20 percent more oil and resin as compared to other brands. The objective is to ascertain the best mix for maximum green power and the best finish for the surface, that is possible.

The oil bonded sand is a substitute for water bonded green sands to be used for casting sand. The advantage over traditional, older sands is that as water is absent, the sand does not steam like the traditional sands. This sand is more secure to use than green sand. The reason is that potentially explosive quantities of steam are not generated. Due to this dearth of steam generation and the smooth texture of the sand, the oil bonded sand results in a smoother surface finish. The novice can use these sands and get professional results.

Use of casting sand: The same techniques, patterns and tools that are used for water bonded sands can be used for oil bonded casting sands. As the sand has better adhesive properties, there are fewer hassles with loose sand in the impression. The difference is that water cannot be used to manage loose sections. However, as the self adhesion is better, there are fewer problems of crumbling.

When the oil comes in contact with molten metal, it does not burn. When the castings are being shaken out, it is advisable to take off the sand that is burned. This sand that is burned can then be mixed again in the pile of fresh sand. It reabsorbs oil and works very well. After repeated use of this sand, the oil gets depleted. In this case, around 30W of non-detergent motor oil can be used to reload the sand with oil.