Structural foam moulding of any thermo-plastic material involves the use of foaming agents. This process reduces the density of bulky items, and thus allows important savings of material in terms of weight and cost. However thick parts require a long cooling time, ranging from 2 to 6 minutes, so a multistation rotary closing system is the appropriate solution.
Nowadays 8,10 or 18 station availability is combined with clamping forces from 30 up to 80 tons. As far as the moulding process is concerned, it is still to all intents and purposes Structural Foam Moulding, where low pressures are exerted in the mould. Consequently, low-cost alloy moulds can still be used when suitable, and very little clamping tonnage is required, thus allowing comparatively large surface areas to be produced with minimal tonnage.
One of the advantages of a rotary closing system is that it provides the best efficiency of the injection group, which constantly and regularly fills the moulds one after the other. The residence time into the barrel is reduced to a minimum, which assures a better quantity control and greater repeatability from shot to shot. On the carousel, one can use dissimilar moulds of items varying in shape and weight since each station can be set up with differing parameters. One or more stations can be skipped automatically whenever a mould is not available or when a given production quantity has been reached.
Due to added environmental pressures from state regulations, structural foam as well as coinjection, when associated with a multistation system, is an interesting solution to the recycling problems whether industrial scraps or the more difficult mixed plastic or post-consumer wastes are involved.