Tool insert, mould tool or core tool and method for producing moulds or cores

Abstract

The present invention relates to the selection of materials for methods for producing moulds ( 2 ) or cores ( 2 ′) for foundry purposes. When selecting the core box material, a special ceramic, such as for example silicon carbide or silicon nitride, is used instead of metals such as steel or aluminium. It is essential for the invention—that a material ( 7 ) for receiving the mixture ( 9 ) is introduced into a housing ( 3 ), the material consisting of silicon carbide or silicon nitride, —that electrical energy is supplied to the material ( 7 ) by way of electrodes ( 10 ) arranged in/on the housing ( 3 ) and in this way heat is supplied, leading to curing of the mixture ( 9 ). This allows longer service lives to be achieved for the core boxes as a result of low abrasive wear.

1 . A tool insert comprised of a material for mold or core tools for producing foundry cores with at least one cavity for holding a molding material mixture, wherein, in application, heat is supplied to the material by means of current, which causes a curing of the moulding-material mixture:
 characterized in that   the specific electrical resistance of the material is between 0.5 ohmmeters and 200 ohmmeters at an operating temperature of 150° C. to 180° C.,   the heat conductivity of the material is at least 0.56 W/(m*K),   the tool insert is comprised of at least two parts having at least one direct electrically conductive contact surface without an electrically insulating intermediate layer in the assembled state and   wherein the material comprises a contact surface for the electrically conductive connection to the respective electrode of a mold or core tool.   
     
     
         2 . The tool insert according to  claim 1 , characterized in that it comprises a sintered insert. 
     
     
         3 . The tool insert according to  claim 1 ,
 characterized in that, for the escape of water vapour or gases, the tool insert is porous and contains ventilation slits for the escape of water vapor or gases.   
     
     
         4 . The tool insert according to  claim 1 , characterized in that,
 the material is a special ceramic and thereby, the insert is also suitable for operation in mold or core tools having an external heater.   
     
     
         5 . A mold or core tool for producing molds moulds or cores for foundry purposes, wherein
 at least one tool insert according to  claim 1  is inserted into a housing,   the housing comprises at least two parts, which are movable together or apart respectively at the beginning and upon completion of a cycle process.   
     
     
         6 . A method for producing molds or cores for foundry purposes by means of adapting the specific electrical resistance of a tool insert to the specific electrical resistance of a mixture comprising of at least one molding material, in particular, foundry sand, and at least one water-containing inorganic binder curable by means of heat, and which has an electrical conductivity of at least 5·10−3 S/m. wherein:
 (1) at least one tool insert according to  claim 1  made of an electrically conductive material for holding the molding-material mixture is introduced into an electrically non-conductive housing, wherein the electrical conductivity of the material at an operating temperature between 150 and 180° C. is between 0.5 ohmmeters and 200 ohmmeters, 
 (2) electrical energy and thus heat is supplied to the tool insert via electrodes that are arranged in parallel in/on the housing, which cures the mixture, 
 (3) wherein the housing and the tool insert are respectively comprised of at least two separable parts, which are moved together or apart from each other respectively at the beginning and upon completion of the cycle process, and wherein the moved-together parts of the tool insert form a direct electrically conductive contact surface without an intermediate insulating layer, 
 (4) holes for ejection pins are provided within the tool, belonging to at least one electrode as well as to at least one part of the housing for removing the cores, 
 (5) both the tool as well as the electrodes and at least one part of the housing are one or more of: porous or ventilation slits are present for the escape of water vapor or gases, and 
 (6) the mold(s) or the core(s) are pressed out of the tool and removed by means of ejection pins after curing of the mixture and moving apart the housing parts.