PRE-COATED SANDS
A fast curing shell moulding composition having the tensile strength of a conventional novolac resin when cured contains a fast curing novolac resin comprising a methylene chained polyphenylol wherein a major portion of the methylene linkages are coupled to adjacent phenylol groups at the o-o' and p-p' position, wherein at least about 19% of the methylene linkages are coupled to adjacent phenylol groups at the o-o' portions, and wherein at least about 3% of the total number of methylene linkages are coupled to adjacent phenylol groups at the p-p' positions.
The shell molding composition is produced from the fast curing novolac resin by uniformly coating refractory granules with the fast curing resin. The fast curing novolac resin can be prepared by blending a conventional novolac resin with a novolac resin having a large proportion of methylene linkages coupled to adjacent phenylol groups at the o-o' position. The fast curing novolac resin can also be prepared by a novel two step condensation reaction of phenol and formaldehyde. |
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