Coated microspheres and their uses
View Patent ↗The invention relates to microspheres coated with a phenolic novolak resin, a process for preparing them, and their use in making foundry shapes, e.g. molds, cores, sleeves, pouring cups, etc., which are used in casting metal parts.
1. A process for preparing microspheres coated with a phenolic novolak resin comprising:
(a) mixing a phenolic novolak resin with a refractory comprising heated microspheres;
(b) adding a catalytically effective amount of hexamethylene tetramine to said mixture; and
(c) allowing the mixture of (b) to cure.
2. The process of claim 1 wherein the phenolic resin is mixed with salicylic acid before mixing the phenolic novolak resin with microspheres.
3. The process of claim 2 wherein the amount of hexamethylene tetramine is from 10 to 25 percent based on the weight of the resin.
4. The process of claim 3 wherein the amount of microspheres is from 10 to 100 percent by volume based upon the volume of the refractory.
5. The process of claim 4 wherein the microspheres are hollow aluminosilicate microspheres.
6. The process of claim 5 wherein the temperature of the heated microspheres is from 200° C. to 300° C.
7. The process of claim 6 wherein the mixer is preheated to a temperature of from 105° C. to 205° C.
8. The process of claim 7 wherein other refractories, selected from the group consisting of silica sand, chromite sand, zircon sand, and mixtures thereof, are used in addition to the microspheres.
9. Microspheres coated with a phenolic novolak resin prepared in accordance with claim 1 , 2 , 3 , 4 , 5 , 6 , 7 , or 8 .