2022.12.17
1. Commonly used refractory materials are corundum, zircon sand, silica sand, bauxite, kaolin clinker, magnesium oxide, diatomaceous earth, etc. When producing lost foam castings of different alloys, different refractory materials should be used to make coatings. Different alloy lost foam machines have different requirements for coating refractoriness, chemical stability and thermal insulation. Usually, diatomite, talcum powder and other refractory materials are used for the lost foam coating of aluminum castings; powdered refractory materials such as silica sand, bauxite, kaolin clinker, and brown corundum are commonly used for iron castings; corundum and zircon sand are commonly used for steel castings , magnesium oxide and other powdered refractory materials.
In addition to the correct selection of the type of refractory material to prepare the lost foam coating, the particle size, distribution and particle shape of the refractory material should also be correctly selected. Because the particle size and distribution and particle shape will affect the air permeability of the coating. According to reports, the refractory particles used in lost foam coatings should be round, and the particle size should be coarse and concentrated.
2. Commonly used binders can be roughly divided into two types: inorganic and organic, and can be used in one coating at the same time. Inorganic binder (high temperature binder): hydrophilic type: clay, bentonite, water glass, silica sol, phosphate, sulfate, polyaluminum chloride. Hydrophobic type: organic bentonite Organic binder (low temperature binder): Hydrophilic type: syrup, pulp waste liquid, dextrin, starch, polyvinyl alcohol (PVA), polyvinyl acetate emulsion, water-soluble phenolic resin, natural gum. Hydrophobic type: asphalt, coal tar, rosin, phenolic resin, dry vegetable oil, tallow oil, ethyl silicate, polyvinyl butyral (PVB)
3. Carrier: Lost foam coatings can be divided into water-based coatings and alcohol-based coatings, but water-based coatings are mostly used in production.
4. Suspending agent: The substance added to prevent the solid refractory material in the coating from settling is called suspending agent. Commonly used suspending agents for water-based coatings are: bentonite, attapulgite, sodium carboxymethyl cellulose, polyacrylamide, sodium alginate, etc. Commonly used suspending agents for organic solvent coatings are: organic bentonite, lithium bentonite, attapulgite, polyvinyl butyral, etc.
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