| 摘要 |
PURPOSE:To improve the quick curability and bending strength of a shell mold formed of molding sand for producing a shell mold by coating the surface of said sand of specific two kinds of novolak type phenolic resins. CONSTITUTION:The resin prepd. by mixing a novolak type phenolic resin having 2.0-7.0 ratio O/P of the methylene group of an ortho bond (O) and para bond (P) indicating the bonding position of the methylene group to the -OH group of a phenol and contg. <=5% lubricant such as ethylene-bis-stearamide and a novolak type phenolic resin having 0.3-1.2 O/P ratio and both having 300-600 number average mol.wt. at a weight ratio of 1:9-9:1 is coated on the surface of molding sand in the stage of manufacturing coated sand which is a raw material for producing a shell mold for casting light alloys, etc. The shell mold using such coated sand cures quickly and has excellent bending strength. |
