When using furan self-hardening sand process, attention should be paid to control the acid consumption value of ceramic sand.

Acid demand is the characterization of the amount of alkaline substances in the raw sand that can react with acid, and it can also characterize the amount of acid consumed by the raw sand itself that cannot participate in resin curing using an acid curing agent. It is different from the pH value of the raw sand. When the raw sand contains alkaline substances that are insoluble in water or carbonates that can react with acid, they do not affect the pH value, but can react with acid and affect the curing performance.

Acid consumption value is one of the important indexes of casting raw sand, especially for the furan resin self-hardening sand process using acid curing agents such as phosphoric acid, hydrochloric acid, benzene sulfonic acid and sulfonate. 

As we know, ceramic sand is a kind of artificial special sand produced by melting, crushing, screening and mixing bauxite minerals. The different producing areas of bauxite, the raw material of ceramic sand, result in different amounts of alkali metal oxides contained in bauxite itself. At the same time, higher alkali metal oxides are difficult to be effectively removed in subsequent production. Therefore, when using furan self-hardening sand process, more attention should be paid to controlling the chemical composition and acid consumption value of ceramic sand.

We found that some users use gem sand with high alkali metal oxide content as raw sand for the sake of cheap price. Because it contains a large amount of alkaline oxides such as potassium oxide, iron oxide, calcium oxide and magnesium oxide, the acid consumption value sometimes reaches more than 10ml / 50g, which has a negative impact on the curing process and the quality of castings. This is because this kind of ceramic sand contains a large amount of alkaline substances, which not only consumes a large amount of curing agent, but also interferes with the curing speed, strength and hard permeability, making the surface stability of sand mold worse, resulting in defects such as sand sticking and sand holes in castings. 

In daily production practice, the acid consumption of raw sand is generally controlled to be less than 5ml / 50g when using furan self-hardening sand process. The ceramic sand produced by bauxite is usually less than 1.5ml / 50g, which is the most ideal casting sand used at present.