Foundry Sand Types

According to the different binders, foundry sand used for moulding can be divided into green sand, water glass sand and resin sand.

Green Sand (Clay Sand)

Clay sand is the mixture of natural silica sand, clay, additives and water. The clay used to make wet clay sand is bentonite clay. The compressive strength is generally 0.05 to 0.1 Mpa. The water content is 3.5 to 5%, and air permeability is more than 80. It is commonly used in machine molding and hand molding.

The sand made can be used to pour liquid metal without drying, which has the advantages of low production cost and short production cycle. Wet clay sand used in sand casting production accounts for about 60%. As the wet sand has a high moisture content, low strength and air permeability, the castings can easily have the porosity, coarse, sticky sand and sand expansion defects. In hand molding, the dimensional accuracy is low, so it is generally used only for the production of small and medium sized iron castings and non-ferrous alloy castings; while in mechanical modeling, the castings have high dimensional accuracy, so it is widely used for high-volume production of castings.

The clay used to make dry sand clay is ordinary clay, and its moisture content is high. The sand made should be dried in the temperature of about 250 ~ 400 ℃ and then be combined cast, and it is generally used for steel castings. Because of the high energy consumption, long production cycle, low dimensional accuracy, dry sand is gradually phased out.

Water Glass Sand (Sodium Silicate Sand)

Sodium silicate sand is a kind of foundry sand made by sodium silicate (aqueous solution of sodium silicate) as the binder. The sodium silicate added accounts for 6% to 8% of the sand quality.

Water glass hardening is necessary before pouring to improve strength. The hardening methods are: chemical hardening with CO2 gas and drying the heating surface. You can also put the hardening agent in the sand, and then it will harden by itself. By eliminating or greatly reducing the drying process, the emergence of sodium silicate sand simplified greatly the sand molding process.

However, because its collapsibility is poor and falling sand, sand cleaning and the sand recycling are very difficult, in iron casting, the sand sticks seriously, so it is not suitable for iron casting, but mainly used in steel casting production.

Resin Sand (Phenolic, Furan)

Resin sand is a kind of foundry sand with synthetic resin (phenolic resin and furan resin, etc.) as the binder. The resin added is about 3% to 6% of the sand quality. Resin sand can harden fast when heated 1 to 2 minutes, and its dry strength is high, so the castings made are accurate in size, the surface is smooth, and the collapsibility is excellent.

Since it has quick-drying and self-hardening characteristics, the modeling process is easier to become mechanization and automation. Resin sand is a promising new type of modeling material, and at present, it is mainly used in the manufacture of complex sand cores.

Since different sands have different advantages, in metal casting, we should adopt the right one to meet different needs.

Clay Sand, Green Sand

Furan Resin Sand

Dry Sand, Water Glass Sand

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