Foundry core with complex shape prodn. - involving filling core box with liquid sand mixt. under pressure

摘要

In the prodn. of complex foundry core from a self-hardening liquid sand mixt., filling of the core box is facilitated by applying a pressure of 0.2-1 bar for a few secs. on the kneaded sand mixt. Pressure may be applied e.g. using compressed air or mechanically. The mixt. contains a surfactant which forms a foam whose duration time is shorter than the time involved prior to the onset of setting. The mixt. contains a urea-formaldehyde-furfuryl alcohol resin (I) as binder and an alkylbenzenesulphonic acid as surfactant, the alkyl having 10-13C. Process is applicable to mass or batch prodn. Tool wear and prodn. time are reduced and trimming and parts assembly are eliminated. The cores have high surface density (1.4-1.7) and low internal density (1.2-1.3). Their Dietert permeability increases after setting and reaches 130-170 AFS units after 24 hrs., thus allowing evacuation of gas when casting the metal.