Method and mold tool or core tool for producing molds or cores

A method for producing molds or cores for foundry purposes by means of adapting the specific electrical resistance of the material of the tool insert to the specific electrical resistance of a mixture consisting of at least one molding material, in particular, foundry sand, and at least one inorganic water-containing binder that can be cured by means of heat, which has an electrical conductivity of at least 5·10-3 S/m, wherein:

• at least one tool insert made of an electrically conductive material for holding the 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. at least approximately corresponds to the specific electrical conductivity of the mixture at a temperature between approximately 100° C. to 130° C.,
• electrical energy and heat is supplied to the tool insert via electrodes that are arranged in parallel in/on the housing, leading to the curing of the mixture,
• wherein the housing is made of at least two housing parts, which are movable together or apart from each other at the beginning and upon completion of the cycle process of the mold or core production and form a direct contact surface when moved together,
• wherein 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 sand core,
• wherein both the tool as well as the electrodes as well as at least one part of the housing are porous and/or ventilation slits are present for the escape of water vapor or gases, and
• wherein 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,
• characterized in that a material is used for tool inserts which has the following characteristics:
• (1) it comprises a sintered solid body, which has a Mohs hardness of more than 4, wherein
• (2) 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., and,
• (3) the heat conductivity is at least 0.56 W/(m*K).