Molding and making surface sand in sodium silicate sand process
Because the metal static head of large steel castings is high and the pouring time is relatively long, the thermal, mechanical and chemical reactions between the metal and the mold are very strong; It is easy to produce metal penetration and sand sticking on the surface of the casting, especially at the hot spot concentration such as the hollow of the sand core or mold, which will deteriorate the surface quality of the casting, and even cause the sand cleaning workers to suffer from silicosis after working for several years.
In the process of CO hardened sodium silicate silica sand, the amount of sodium silicate is about 0.7% (accounting for the mass fraction of sand), while in the process of CO hardened sodium silicate ceramic sand, the amount of sodium silicate is less than 4% (accounting for the mass fraction of sand). The mixed sodium silicate pearl sand is first filled in the parts that are easy to stick to the sand (slender holes, corners and other hot spots) as the surface sand, and the rest parts are then filled with sodium silicate silica sand, Co, and coated after hardening. After pouring, the casting is easy to clean and has a high surface finish, which can play a role in preventing sand sticking.
Filling sand in lost foam casting process
At present, the development of lost foam casting technology shows the advantages of this process from different aspects, and has been applied to cast iron and cast steel products.
In order to ensure that the LFC sand has enough fluidity to fill the complex deep cavity of the foam shape, and the thicker coating layer has a certain mechanical strength to prevent box collapse, LFC requires that the roundness of the sand should be good enough. Using some characteristics of Fused Ceramic sand in lost foam casting can increase the yield of castings, reduce the cost and improve the labor environment.
A large cross on the oil field, made of ZG310-570, weighs 195kg. If ordinary silcia sand is used for the slender hole of this part, it is easy to have (vibration) filling not solid, which is easy to cause iron clad sand sintering and other phenomena, and cannot be cleaned. The Fused Ceramic sand is spherical, which is easy to flow when filling the model, compact and breathable. In addition, the Fused Ceramic sand has high strength, is not easy to be damaged, and there is less dust in the workshop, which can greatly improve the working environment of workers.
Matters needing attention in application of Fused Ceramic sand
Influence of A2l03 content on casting quality
The content of Al2O3 directly determines its refractoriness and sintering point. The higher the content, the higher the refractoriness and sintering point. The content of Al and 03 in Fused Ceramic sand used in the production of castings with different materials is also different. For example, for steel castings, the pouring temperature is generally above 1550 ℃, and Fused Ceramic sand with Al203 mass fraction greater than 72% is generally selected; On the contrary, due to low refractoriness and sand melting, the casting will stick to sand. When the pouring temperature of iron castings is about 1400 ℃, Fused Ceramic sand with Al2O3 content of 67% ~ 70% can be selected. The indexes of Fused Ceramic sand for steel castings can be referred to for large iron castings.
In addition, the content of Al2O3 also affects the crushing rate and durability of Fused Ceramic sand. Fused Ceramic sand with higher content of Al203 should be selected for occasions requiring multiple strong regeneration.