The invention discloses precoated sand and a preparation method thereof, and belongs to the technical field of the
foundry industry. The precoated sand comprises, by weight, 100-110 parts of roughing sand, 2-4 parts of modified phenolic resin, 1-3 parts of a
coupling agent, 0.3-0.5 part of urotropine, 0.6-0.8 part of modified
lignin, 1-3 parts of a dry material, and 1-3 parts of
ethyl acetate. The precoated sand is formed by combining the specific components, especially, 1-Hydroxyethylidene-1,1-diphosphonic acid can be catalyzed by ceric
oxide to perform
dehydration reaction with the modified phenolic resin during heating, resin
carbonization is promoted, thus, the
binding force between the resin and the sand is reduced, and the collapsibility of the precoated sand is improved; and in addition, the ceric
oxide can also stop the modified phenolic resin from performing
free radical reaction caused by oxidation, so that the
heat resistance of the precoated sand is improved. Meanwhile, the invention further discloses the preparation method of the precoated sand. The method adopts the specific steps and the specific material adding sequence, and thus, the precoated sand which is good in
heat resistance and prone to collapsing can be obtained quickly.