Device for hardening foundry cores of a sand-containing molding material, wherein the device is adapted in order to subject the core, for its hardening, in a core molding tool, to a catalyst vapor/carrier gas mixture and subsequently to a pressurized air stream, each at a predetermined pressure and a predetermined temperature, wherein the device comprises: - a heating and mixing stage, which can be upstream of the core molding tool and which is in fluidic connection with a container containing an organic catalyst in liquid form by means a first line, wherein the liquid organic catalyst can be fed to the heating and mixing stage dosed via dosing means, - wherein the heating and mixing stage furthermore is in fluidic connection with a pressurized air source via at least one first pressure regulator by means of a second separate line, so that the pressurized air used as carrier gas can be fed in a dosed form to the heating and mixing stage, - wherein the liquid organic catalyst fed to the heating and mixing stage and the pressurized air fed to the heating and mixing stage are heated in the heating and mixing stage, so that the organic catalyst assumes its gaseous state, and together with the pressurized air a catalyst vapor/carrier gas mixture is produced, - wherein the heating and mixing stage is moreover connected via a third line, which can be closed by a valve, to the core molding tool, so that the catalyst vapor/carrier gas mixture can be passed through the sand-containing molding material in the core molding tool, - wherein, for a time-controlled flushing after the passage of the catalyst vapor/carrier gas mixture through the sand-containing molding material, the core molding tool, by a fourth line which can be closed with a valve, is in fluidic connection with the pressurized air source via a heating source which is adapted in order to heat the pressurized air streaming from the pressurized air source through the heat source to a predetermined temperature, characterized in that - the device has no preheater that heats the pressurized air before it is fed to the heating and mixing stage or to the heat source, so that the organic catalyst and the pressurized air are heated together in the heating and mixing stage, and - a first cutoff valve is arranged in the second line, which is closed at the beginning of the flushing, and - a second cutoff valve is arranged in the fourth line, which is open at the beginning of the flushing. - a heating and mixing stage, which can be upstream of the core molding tool and which is in fluidic connection with a container containing an organic catalyst in liquid form by means a first line, wherein the liquid organic catalyst can be fed to the heating and mixing stage dosed via dosing means, - wherein the heating and mixing stage furthermore is in fluidic connection with a pressurized air source via at least one first pressure regulator by means of a second separate line, so that the pressurized air used as carrier gas can be fed in a dosed form to the heating and mixing stage, - wherein the liquid organic catalyst fed to the heating and mixing stage and the pressurized air fed to the heating and mixing stage are heated in the heating and mixing stage, so that the organic catalyst assumes its gaseous state, and together with the pressurized air a catalyst vapor/carrier gas mixture is produced, - wherein the heating and mixing stage is moreover connected via a third line, which can be closed by a valve, to the core molding tool, so that the catalyst vapor/carrier gas mixture can be passed through the sand-containing molding material in the core molding tool, - wherein, for a time-controlled flushing after the passage of the catalyst vapor/carrier gas mixture through the sand-containing molding material, the core molding tool, by a fourth line which can be closed with a valve, is in fluidic connection with the pressurized air source via a heating source which is adapted in order to heat the pressurized air streaming from the pressurized air source through the heat source to a predetermined temperature, - the device has no preheater that heats the pressurized air before it is fed to the heating and mixing stage or to the heat source, so that the organic catalyst and the pressurized air are heated together in the heating and mixing stage, and - a first cutoff valve is arranged in the second line, which is closed at the beginning of the flushing, and - a second cutoff valve is arranged in the fourth line, which is open at the beginning of the flushing.