Page "learned" Paragraph 1307

The closed molding of flexible urethane foams has been a problem ever since the introduction of the material ( molding in open molds was more feasible ).

Satisfactory methods for polyester foams and even prepolymer polyether foams were never fully achieved.

Closed molding generally resulted in parts weighing more ( because of higher density ) than parts fabricated from free-blown foams.

This counteracted the gain from having no scrap loss.

In addition, there were difficulties with the flow and spreading of the foam mixture over the mold surface, trouble with lack of gel strength in the rising foam, and problems of splits.

The introduction of one-shot polyether foam systems, aided by the development of new catalysts, helped to alleviate some of the problems of closed molding.

While there are still many bugs to be ironed out, the technique is fast developing.

Other techniques

Simple systems are available that make it possible for urethane foam components to be poured, pumped, etc., into a void where they foam up to fill the void.

In a typical application -- the making of rigid urethane foam sandwich panels -- an amount of foam mixture calculated to expand 10 to 20% more than the volume of the panel is poured into the panel void and the top of the panel is locked in place by a jig.