Centrifugal molding

Centrifugal molding of composite materials is a processing technique limited to the production of axisymmetric hollow bodies.

The need to rotate molds at high speed, in order to generate sufficient centrifugal force for correct material processing, imposes a physical limitation on the combination of part diameter/rotation speed parameters. It is therefore common to distinguish two types of molding: those in which the material is produced solely under the influence of centrifugal force, and those, known as "rotation-projection" molding, in which compaction and roughing are assisted by mechanical means.

Since the centrifugal process can only be applied to a relatively small category of parts with simple profiles, it has not been the subject of very significant development since its introduction in the 1950s (the technology evolves when it is adapted to a new family of parts).

The main advantage of this process lies in its ability to process large quantities of raw materials in a short space of time (1,000 kg / h is not uncommon on rotation-projection type installations), which makes it competitive with the filament-winding technique on certain types of tubular parts. For sewage pipe manufacture, the diameter at which the centrifugal process becomes economically more attractive than filament winding would appear to be around 2.5 m, but once again, technical advances could shift this limit.

In most cases, the reinforcements are chopped glass fibers, which gives the average mechanical performance characteristic of composite materials produced by this method. For small-diameter parts, it is possible to incorporate continuous-fiber reinforcements (fabric), thereby improving the material's mechanical properties.

Reinforcements are incorporated into the composite material, either by pre-inserting mats (chopped glass fiber felts bonded with an organic binder) or fabrics into the mold, or by cutting rovings directly during centrifuging. In the latter case, the type of reinforcement is limited to glass fibers only, due to their brittle fracture mode and therefore ease of cutting.

The surface of the composite in contact with the medium is molded in the open air. The resin is generally wax-coated (top-coat) to ensure complete cross-linking. As a result, it consists of a more or less thick layer of pure resin, which sometimes limits its potential applications in process chemistry.