Coated microspheres and their use
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 a foundry shape comprising:
(a) filling a tool, which is heated before and/or after filling the tooling, with microspheres coated with a phenolic novolak resin prepared by a process comprising:
(i) mixing a phenolic novolak resin with a refractory comprising heated microspheres;
(ii) adding a catalytically effective amount of hexamethylene tetramine to said mixture; and
(iii) allowing the mixture of (ii) to cure,
(b) curing the coated microspheres to form a cured foundry shape;
(c) removing the cured foundry shape from the tooling.
2. The process of claim 1 wherein the tool is heated to a temperature of 205° C. to 250° C.
3. The process of claim 1 where the uncured portion of the coated microspheres is removed before removing the foundry shape from the tooling.
4. The process of claim 1 wherein the phenolic novolak resin is mixed with salicylic acid before mixing the phenolic novolak resin with the micro spheres.
5. The process of claim 4 wherein the amount of hexamethylene tetramine is from 10 to 25 weight percent based upon the weight of the resin.
6. The process of claim 5 wherein the amount of microspheres is from 10 to 100 percent by volume based upon the volume of the refractory.
7. The process of claim 6 wherein the microspheres are hollow aluminosilicate microspheres.
8. The process of claim 7 wherein in the temperature of the heated microspheres is from 200° C. to 300° C.
9. The process of claim 8 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.