Bentonite for casting is mainly composed of montmorillonite minerals. Bentonite is generally used as a wet binder for clay sand. Natural montmorillonite is classified according to the main types and relative contents of exchangable cations, mainly: sodium montmorillonite, calcium montmorillonite, magnesium montmorillonite, lithium montmorillonite, oxymontmorillonite and so on. Calcium bentonite, sodium bentonite and some mixed bentonite are commonly used in casting production. According to the provisions of the machinery industry standard "Bentonite and Clay for Casting" JB/T 9227-1999, the classification, classification and technical indicators of bentonite for casting are as follows:
1) Bentonite for casting is classified according to its main exchangeable cation. It is represented by the symbol "P" and the chemical element symbol of the main exchangable cation. If the amount of an exchangeable cation accounts for 50% or more of the cation exchange capacity, it is called the main exchangeable cation: if the amount of any exchangeable cation accounts for less than 50% of the cation exchange capacity, it is represented by two exchangeable cations with relatively more content (the symbol of the cation with more content is in the front). For example, bentonite with sodium ion as the main exchangeable cation is represented by PNa, which is called sodium bentonite; The bentonite with calcium ion and sodium ion as the main exchange cation is represented by PCaNa, which is called calcium sodium bentonite.
2) Casting shadow hole soil can be divided into acidic and alkaline two categories according to the different pH value, respectively expressed by S and J.
3) Bentonite for casting is divided into four grades according to the wet compressive strength value of process samples.
4) Bentonite for casting is divided into four grades according to the value of hot and wet tensile strength of process samples.
5) The brand of bentonite for casting is expressed in the order of classification and grading code. For example, the acid calcium bentonite with a wet compressive strength of 30-50kPa and a hot wet tensile strength of 0.5-1.5kPa is labeled PCaS-3-5.
6) Technical indicators. Various grades of casting with shadow clay, the amount of methylene blue adsorption per 100 g of soil should be at least 20g above: the mass fraction of water should not be greater than 12.0%, winter allowed not more than 15%; More than 95% of its quality should be cast by No. 200 for screening.
