Abstract: An apparatus for hardening cores and/or molds made of sand with the addition of hardenable binding agents, which are used for casting molded bodies from flowable substances, is described, whereby an amount, predetermined by metering devices controlled via control valves, of the substance which causes the binding agent to harden is introduced into the core or mold by aid of compressed air the rate of flow of which is regulatable by a regulating valve, whereby this substance is mixed with this compressed air, and the regulating valve is automatically controlled according to a predetermined schedule. The apparatus can be carried out with considerably fewer components and the necessary control means can in particular be designed much more simply if, according to one embodiment, the regulating valve is controlled by means of a proportional pressure regulating valve which is operated by an external control means which also controls the other control valves.