Sand molding apparatus with means for recirculating catalyst

An apparatus for hardening sand articles for foundry purposes such as sand molds and sand cores consisting of sand and a binder hardenable by a catalyst gas, comprising a molding box with means for passing air and a catalyst gas therethrough and connected to the atmosphere by a vent line provided with a first shut-off valve, a catalyst gas source connected to said molding box by a feed line provided with a second shut-off valve, a vacuum pumping means having a suction side and a pressure side, said suction side being connected to said molding box by a suction line, and said pressure side being connected to a reversible valve assembly which, in one position, connects said pressure side of the pumping means to the atmosphere and, in the other position, connects said pressure side of the pumping means to a return line leading to said catalyst gas source, means for closing said first and second shut-off valves, means to dispose, and said valve assembly in said one position to evacuate the molding box to the atmosphere and bring it to a predetermined pressure, less than atmospheric pressure, means for briefly opening said second shut-off valve in the feed line upon reaching substantially said predetermined pressure to feed catalyst gas from said catalyst gas source to said molding box causing an increase of the absolute pressure, means to switch said reversible valve assembly to the other position sortly after the beginning of delivery of catalyst gas to evacuate said molding box to said catalyst gas source to re-establish substantially the said predetermined pressure and to recycle the catalyst gas having passed through said sand article in said molding box to said catalyst gas source, means to reverse said reversible valve assembly to said one position and means to open said first shut-off valve in said vent line upon re-establishment of substantially said predetermined pressure to pass fresh air through said molding box and fill it with fresh air.

An apparatus for hardening sand articles for foundry purposes such as sand molds and sand cores consisting of sand and a binder hardenable by a catalyst gas, comprising a molding box with means for passing air and a catalyst gas therethrough and connected to the atmosphere by a vent line provided with a first shut-off valve, a catalyst gas source connected to said molding box by a feed line provided with a second shut-off valve, a vacuum pumping means having a suction side and a pressure side, said suction side being connected to said molding box by a suction line and said pressure side being connected to a reversible first valve assembly which, in one position, connects said pressure side of the pumping means to the atmosphere and, in the other position, connects said pressure side of the pumping means to a return line leading to said catalyst gas source, a reduced pressure vessel arranged in a bypass line connected to said suction through a second reversible valve assembly which, in one position, blocks said bypass line and, in the other position, switches the flowpath over to said bypass line, means to dispose said first and second shut-off valves and said first and second reversible valve assemblies in said one position to evacuate said molding box to the atmosphere to reduce it to a predetermined pressure less than atmospheric pressure, means to briefly open said second shut-off valve in the feed line upon reaching substantially said predetermined pressure to feed catalyst gas from said catalyst gas source to said molding box causing an increase of the absolute pressure, means to switch said first and second reversible valve assemblies to the other position shortly after beginning delivery of said catalyst gas to evacuate said molding via said reduced pressure vessel into said catalyst gas source to re-establish substantially the predetermined pressure in said molding box and to recycle said catalyst gas having passed through said sand article in the molding box to said catalyst gas source, means to reverse said first and means to open second valve assemblies to said one position and the first shut-off valve in the vent line upon re-establishment substantially of said predetermined pressure to pass fresh air through said molding box and fill it with fresh air.

An apparatus for hardening sand articles for foundry purposes such as sand molds and sand cores consisting of sand and a binder hardenable by a catalyst gas, comprising in combination, a molding box with means for passing dry air and a catalyst gas therethrough and connected to a pressurized dry air source by a vent line provided with a first shut-off valve, a catalyst gas source connected to said molding box by a feed line provided with a second shut-off valve, a vacuum pumping means having a suction side and a pressure side, said suction side being connected to said molding box by a suction line provided with a third vent valve to connect said molding box to the atmosphere and said pressure side being connected to a freezing dryer means for separating a substantial amount of said catalyst gas from a mixture consisting of catalyst gas and dry air coming from said molding box and passing through said freezing dryer means, a reversible valve assembly which is connected to said freezing means and which, in one position, connects said pressure side of the pumping means via said freezing dryer means to the atmosphere and, in the other position, connects said pressure side of the pumping means via said freezing dryer means to a return line leading to said catalyst gas source, control means to close said first and second shut-off valves and to establish said valve assembly in said one position to evacuate the molding box to the atmosphere and bring it to a predetermined pressure less than atmospheric pressure, said control means adapted for breifly opening said second shut-off valve in the feed line upon reaching substantially said predetermined pressure in said molding box to feed catalyst gas from said catalyst gas source to said molding box, said control means adapted for opening said first shut-off valve in said vent line for pressurized dry air for a predetermined period of time upon closing said second shut-off valve in the feed line for the catalyst gas to feed dry air to said molding box, said feeding of catalyst gas and dry air causing an increase of the absolute pressure in said molding box, said control means adapted for switching said reversible valve assembly to the other position shortly after the beginning of delivery of catalyst gas to evacuate said molding box to said catalyst gas source to re-establish substantially the said predetermined pressure and to recycle the residual catalyst gas leaving said freezing dryer means to said catalyst gas source, said control means adapted for switching said reversible valve assembly to said one position and opening said third vent valve in said suction line upon re-establishment of substantially said predetermined pressure to build up atmospheric pressure in said molding box.