Use of closed-pore microspheres of expanded pearlite as a filler for the production of mouldings for the foundry industry

Abstract

The present invention relates to the use of closed-pore microspheres of expanded perlite as a filler for producing moldings for the foundry industry, to a composition for producing moldings for the foundry industry, comprising closed-pore microspheres of expanded perlite as a filler, and a binder, the binder being selected from the group consisting of water glass, phenol-formaldehyde resins, two-component systems comprising as reactants a polyisocyanate and a polyol component containing free hydroxyl groups (OH groups), and starch, and also to moldings for the foundry industry and to a process for producing a molding for the foundry industry.

1 . A method of producing moldings for the foundry industry comprising using closed-pore microspheres of expanded perlite as a filler for moldings for the foundry industry, wherein the closed-pore microspheres have a closed foam structure with pores separated from one another, and a virtually smooth surface. 
     
     
         2 . The molding as claimed in  claim 15 , wherein the microspheres are obtainable by a process in which a perlite sand is expanded in a trickle channel having multistage temperature zones. 
     
     
         3 . The molding as claimed in  claim 15 , wherein the microspheres have a particle size d50 of 100 to 400 μm. 
     
     
         4 . The molding as claimed in  claim 15 , wherein the microspheres are closed on their surface. 
     
     
         5 . The molding as claimed in  claim 15 , wherein the microspheres have a ratio of pure density to apparent density of greater than 1.8, the apparent density and the pure density being determined with the helium pyknometer. 
     
     
         6 . The molding as claimed in  claim 15 , wherein the microspheres have a particle strength of above 1.3 N/mm 2 . 
     
     
         7 . The molding as claimed in  claim 15 , wherein the microspheres have a bulk density of below 500 kg/m 3 . 
     
     
         8 . The molding as claimed in  claim 15 , wherein the molding further comprises additional constituents selected from the group consisting of spheres of flyash, foamed glass, quartz sand, calcined kieselguhr, schamotte, cordierite, mullite, and mixtures thereof. 
     
     
         9 . The molding as claimed in  claim 15 , wherein the molding further comprises an organic or inorganic binder or a mixture of organic and inorganic binder and the binder is selected from the group consisting of water glass, phenol-formaldehyde resins, two-component systems comprising as reactants a polyisocyanate and a polyol component containing free hydroxyl groups (OH groups), and starch. 
     
     
         10 . The molding as claimed in  claim 15 , wherein the moldings for the foundry industry are selected from the group consisting of insulating or exothermic feeders, feeder surrounds, feeder sleeves, feeder caps, filling funnels, supply elements, and heating pads. 
     
     
         11 . The molding as claimed in  claim 15 , for producing insulating or exothermic feeders for nonferrous casting. 
     
     
         12 . A composition for producing moldings for the foundry industry, comprising closed-pore microspheres of expanded perlite as a filler, and a binder;
 wherein the closed-pore microspheres have a closed foam structure with pores separated from one another;   wherein the binder is selected from the group consisting of water glass, phenol-formaldehyde resins, two-component systems comprising as reactants a polyisocyanate and a polyol component containing free hydroxyl groups (OH groups), and starch.   
     
     
         13 . The composition as claimed in  claim 12 , wherein the microspheres are obtainable by a process in which perlite sand is expanded in a trickle channel having multistage temperature zones. 
     
     
         14 . The composition as claimed in  claim 12 , further comprising constituents selected from the group consisting of spheres of flyash, foamed glass, quartz sand, calcined kieselguhr, schamotte, cordierite, mullite, and mixtures thereof. 
     
     
         15 . A molding for the foundry industry, produced using
 closed-pore microspheres of expanded perlite, having a closed foam structure with pores separated from one another, and a virtually smooth surface;   and a binder, the binder optionally being selected from the group consisting of water glass, phenol-formaldehyde resins, two-component systems comprising as reactants a polyisocyanate and a polyol component containing free hydroxyl groups (OH groups), and starch.   
     
     
         16 . A process for producing a molding for the foundry industry, having the following steps:
 (a) producing or providing closed-pore microspheres of expanded perlite as defined in  claim 1 ,   (b) mixing the closed-pore microspheres of expanded perlite, produced or provided in step (a), with a binder and also optionally further constituents to give a composition, and   (c) molding and curing the composition from step (b) to give a molding   or   (i) producing or providing a composition comprising closed-pore microspheres of expanded perlite as a filler, and a binder, the binder being selected from the group consisting of water glass, phenol-formaldehyde resins, two-component systems comprising as reactants a polyisocyanate and a polyol component containing free hydroxyl groups (OH groups), and starch, and   (ii) molding and curing the composition from step (i) to give a molding.   
     
     
         17 . The method according to  claim 1 , wherein the closed-pore microspheres have a virtually smooth surface. 
     
     
         18 . The composition according to  claim 12 , wherein the closed-pore microspheres have a virtually smooth surface.