Method and device for the production of molds or cores for foundry purposes

Abstract

The invention relates to the production of molds or cores ( 2 ) for foundry purposes, wherein a mixture ( 3 ) of foundry sand and binder are produced and introduced into a mold or core tool ( 8 ), e.g. shot in a core shooter. A known binder or magnesium sulfate with and/or without at least one or additionally several crystallization waters is dispersed or dissolved in water and used as binder, which is then mixed with the foundry sand and introduced or shot into the mold tool or the core box ( 8 ). For hardening purposes, the water and a fraction of the crystallization water are vaporized by heating and driven out by a gaseous medium, all of which can be carried out very rapidly. After pouring, said core or mold consisting of foundry sand can be very rapidly removed from the tool with water and flushed due to the fact that the magnesium sulfate preserves its capability of dissolving.

1 . A process for producing molds or cores ( 2 ) for foundry purposes from a mixture ( 3 ) of foundry sand and binder, in which the foundry sand and binder are mixed and are introduced into a mold or core die ( 8 ) and the binder is then set, imparting the required strength to the mold or core ( 2 ), characterized in that magnesium sulfate is dissolved and/or dispersed in water and mixed as binder with the foundry sand and is then shot or introduced into the mold or core die ( 8 ), and in that the water is then heated inside the mold or core die and is at least partially evaporated and expelled from the mold or core die ( 8 ).  
     
     
         2 . The process as claimed in  claim 1 , characterized in that the mixture ( 3 ) of foundry sand and a dispersion and/or solution of magnesium sulfate in water is heated inside the mold or core die ( 8 ) by means of microwave and/or infrared radiators.  
     
     
         3 . The process as claimed in  claim 1 , characterized in that the mixture of foundry sand and a dispersion and/or solution of magnesium sulfate in water is heated inside the mold or core die ( 8 ) by the application of an electric voltage to the at least partially electrically conductive parts, which are insulated from one another, of the separable mold or core dies ( 8 ).  
     
     
         4 . The process as claimed in  claim 1 , characterized in that the electrically conductive core/mold, which consists of a mixture of foundry sand and a dispersion and/or solution of magnesium sulfate in water, is used as an electrical resistance of a resistance heating means and is heated by means of an applied electric voltage and the current which flows as a result.  
     
     
         5 . The process as claimed in  claim 3 , characterized in that the electric voltage is applied to electrodes which make contact with the core/mold, and in that the at least partially electrically conductive parts ( 8   a ,  8   b ), which are insulated from one another, of the separable mold or core dies ( 8 ) are preferably used for this purpose.  
     
     
         6 . The process as claimed in  claim 3 , characterized in that the electric voltage applied is an AC voltage.  
     
     
         7 . The process as claimed in  claim 3 , characterized in that the electric voltage applied is a pulsed, in particular square-wave, voltage.  
     
     
         8 . The process as claimed in  claim 6 , characterized in that an AC voltage with a high frequency of over 1000 Hz, for example 3000 Hz or more, is selected.  
     
     
         9 . The process as claimed in  claim 3 , characterized in that the voltage is controllable and in particular is selected to be greater than 1000 V or greater than 1500 V.  
     
     
         10 . The process as claimed in  claim 3 , characterized in that the introduction of power is controlled or regulated by variation in the pulse width of the electric voltage.  
     
     
         11 . The process as claimed in  claim 1 , characterized in that the water which has been evaporated by heating is expelled from the die ( 8 ) by means of a gaseous medium, such as nitrogen and/or carbon dioxide and/or air, this gaseous medium which is used to expel the evaporated water being passed through the die and therefore through the foundry mold which has been formed or through the core, by means of pressure or by means of suction and pressure reduction.  
     
     
         12 . The process as claimed in  claim 1 , characterized in that the water vapor which is produced by the heating in the die ( 8 ) is expelled using hot gas.  
     
     
         13 . The process as claimed in  claim 1 , characterized in that magnesium sulfate without water of crystallization or with at least one mole of water of crystallization mixed with magnesium sulfate with more than one mole of water of crystallization, if appropriate with up to seven mol of water of crystallization, is dissolved and/or dispersed in water and mixed as binder with the foundry sand, and in that the water and some of the water of crystallization are evaporated by heating and then expelled.  
     
     
         14 . The process as claimed in  claim 1 , characterized in that a highly or more highly concentrated dispersion or solution of magnesium sulfate with or without at least one mole of water of crystallization is mixed with hydrocolloid and this mixture ( 3 ) is used as binder.  
     
     
         15 . The process as claimed in  claim 1 , characterized in that more magnesium sulfate containing water of crystallization is mixed with the quantity of dissolution water which is predetermined for a defined quantity of foundry sand than is required to produce a saturated solution, and in that some of the magnesium sulfate is dispersed in the solution and mixed with the foundry sand as a dispersion.  
     
     
         16 . The process as claimed in  claim 1 , characterized in that the foundry sand is mixed with the dispersed or dissolved binder in a weight ratio of from 97:3 to approximately 80:20.  
     
     
         17 . The process as claimed in  claim 1 , characterized in that approximately 100 parts by weight of foundry sand are mixed with approximately 3 parts by weight to approximately 20 parts by weight of dispersed or dissolved binder.  
     
     
         18 . The process as claimed in  claim 17 , characterized in that approximately 5 to 10 parts by weight of binder in dispersed or dissolved form are mixed with approximately 100 parts by weight of sand.  
     
     
         19 . A device ( 1 ) for producing foundry molds or cores ( 2 ), having at least one heating device for setting purposes, wherein the device ( 1 ) for producing foundry molds is a molding machine and the device for producing cores is a core-shooting machine, characterized in that at least one microwave generator ( 9 ) is installed as heating device on the molding machine or on the core-shooting machine ( 1 ), and in that at least one microwave antenna ( 10 ), which is or can be coupled to the microwave generator ( 9 ) via a waveguide ( 11 ), is arranged in the region of the mold die ( 8 ) for the foundry mold or for the core.  
     
     
         20 . The device as claimed in  claim 19 , characterized in that, by setting the device ( 1 ) to a gas purge operation to expel gases or water vapor, the microwave generator ( 9 ) can be simultaneously coupled to the antenna ( 10 ) via the waveguide ( 11 ).  
     
     
         21 . The device as claimed in  claim 19 , characterized in that the setting movement to set the device to the gas purge operation automatically couples the microwave generator ( 9 ) to the microwave antenna ( 10 ).  
     
     
         22 . The device as claimed in  claim 19 , characterized in that the path of the waveguide ( 11 ) can be interrupted and has a coupling ( 12 ) at the location where it is interrupted, and in that the antenna-side part of the waveguide ( 11 ) is optionally arranged on or connected to the gas purge hood ( 13 ) or in the mold die ( 8 ).  
     
     
         23 . The device as claimed in  claim 19 , characterized in that the microwave generator ( 9 ) can be coupled or is connected, via a branched waveguide ( 11 ) or via two waveguides ( 11 ), to an antenna ( 10 ) arranged in the gas purge hood ( 3 ) and to an antenna ( 10 ) arranged in the mold die ( 8 ).  
     
     
         24 . A device for producing foundry molds or cores ( 2 ), having at least one heating device for setting purposes, wherein the device for producing foundry molds is a molding machine and the device for producing cores is a core-shooting machine, into which machine a mold or core die ( 8 ) can be or is inserted, characterized in that the heating device provided is an electrical resistance heating means, in which the electrically conductive core ( 2 ) or the mold forms the electrical resistance, and in that the mold or core die ( 8 ), which for removal of a mold or core ( 2 ) is composed of a plurality of parts ( 8   a ,  8   b ), is at least partially electrically conductive and is insulated at the locations of contact between its parts, and in that the parts ( 8   a ,  8   b ) of the die ( 8 ) in each case have at least one electrical terminal ( 17 ) for application of an electric voltage for the resistance heating device.  
     
     
         25 . The device as claimed in  claim 24 , characterized in that the resistance heating device has a voltage source ( 19 ) with a frequency converter for increasing the frequency, and/or a pulse former ( 21 ) for forming a pulsed voltage.  
     
     
         26 . The device as claimed in  claim 24 , characterized in that the resistance heating device has a voltage source and a transformer ( 22 ) for increasing the voltage, which are connected, via supply conductors, to the terminals ( 17 ) on the parts ( 8   a ,  8   b ) of the mold or core die ( 8 ).  
     
     
         27 . The device as claimed in  claim 24 , characterized in that at least one part ( 8   b ) of the mold or core die ( 8 ) has a plurality of electrical terminals ( 17 ), and in that switches ( 24 ) for alternately or optionally applying a voltage to these terminals ( 17 ) are provided between the terminals and the voltage source ( 19 ), so that alternately one switch ( 24 ) is closed and the others are open.  
     
     
         28 . The device as claimed in  claim 24 , characterized in that in the case of a mold or core die ( 8 ) composed of more than two parts ( 8   a ,  8   b ), each part has an electrical terminal ( 17 ) and electrical supply conductors, and in each case two parts, cyclically, of a die of this type are always connected to the voltage source ( 19 ).  
     
     
         29 . The device as claimed in  claim 24 , in which the foundry mold or the core can be produced from a mixture of foundry sand and a binder, which is a dispersed or dissolved magnesium sulfate, characterized in that the device ( 1 ) can be set to the gas purge operation for expulsion of the water vapor which is formed during the heating steps.