| 摘要 |
PURPOSE:To improve collapsing property after a binder for molding sand is used for casting of sand molds by using org. polyisocyanate compds. and specific polyol compds, as said binder. CONSTITUTION:Alcohol such as methanol, ethanol or the like is added to a compd. having methylol groups obtd. by the reaction of bisphenols and formaldehyde such as an aq. formalin soln. and after the pH is controlled to 4-8, these are allowed to react at 60-80 deg.C. The soln. of the resultant polyol comd. and an arom. polyisocyanate compd. such as diphenyl methane diisocyanate as binders are added at 0.3-5pts.wt. basing on 100pts.wt. molding sand, and these are mixed. The mixture is molded to a sand mold. Such sand mold has good collapsing property after casting, and improve the workability in the removal of castings and the reutilization rate of the molding sand. |
