Edge boil is all too common when you’re molding FRP manhole covers—particularly those striving for the H20/H25 and C250/EN124 standards. Due to the size, fiber density, and required resins, optimizing the injection process of FRP manhole covers often plague molders with expensive labor-intensive post-mold work. Edge boil occurs—in this case—when the center of the part reacts and cures at a faster rate than the outer edge. This reaction generates exothermic heat causing the styrene on the outer perimeter, which has not yet fully cross-linked, to boil.

Using the Infusatrol™ injection software controlling the Infuser PRG automated injection system, JHM Technologies, Inc. developed a solution by programming the catalyst ratio to progressively decrease as the resin filled the mold. Progressively decreasing the catalyst during injection insured a far more even cure, removing edge boil, pits, and ferning! Using this method provided additional ideal characteristics! The center mass is thicker, slowing the exothermic heat generation. Slowing of the exothermic generation allows the outer edge to progress further in cure before the full extent of the heat is generated – despite the fact that the perimeter resin has had as much as 6 minutes lead time over the last resin entering the mold.

FRP Manhole Covers