Coated sand is generally composed of refractory materials, binders, curing agents, lubricants and special additives.
(1) The refractory material is the main body constituting the coated sand. The requirements for refractory materials are: high refractoriness, less volatiles, round and solid particles. Naturally scrubbed silica sand is generally used. The requirements for silica sand are: high SiO2 content (more than 90% for cast iron and non-ferrous alloy castings, greater than 97% for cast steel parts); mud content not greater than 0.3% (for scrubbing sand)--[Specification of mud content in washing sand Less than; particle size 1 is distributed on adjacent 3 to 5 sieve numbers; the grain shape is rounded, the angular factor should be no more than 1.3; the acid consumption value is not less than 5 ml.
(2) Phenolic resins are commonly used as binders.
(3) The curing agent is usually urotropine; the lubricant is generally calcium stearate, which is used to prevent the agglomeration of the coating sand and increase the fluidity. The main role of the additive is to improve the properties of the coated sand.
(4) Basic proportion of coated sand into mass ratio (mass fraction, %) Description: Raw sand 100 scrub sand, phenolic resin 1.0 ~ 3.0 accounted for the original sand weight, urotropine (aqueous solution 2) 10 ~ 15 accounted for resin Heavy, calcium stearate 5 ~ 7 accounted for the weight of the resin, the additive 0.1 ~ 0.5 accounted for the original sand weight. 1:2) 10~15 accounts for the weight of the resin, calcium stearate 5~7 accounts for the weight of the resin, and the additive 0.1~0.5 accounts for the weight of the original sand.