Product,Engineering Plastics

Many thermoplastics are now accepted as engineering materials and some are distinguished by the loose description engineering plastics.The term probably originated as a classification distinguishing those that could be substituted satisfactorily for metals such as aluminium in small devices and structures from those with inadequate mechanical properties.This demarcation is clearly artificial because the properties on which it is based are very sensitive to the ambient temperature,so that a thermoplastic might be a satisfactory substitute for a metal at a particular temperature and an unsatisfactory substitute at a different one.

A useful definition of an engineering material is that it is able to support loads more or less indefinitely. By such a criterion thermoplastics are at a disadvantage compared with metals because they have low time-dependent
moduli and inferior strengths except in rather special circumstances. However, these rather important disadvantages are off-set by advantages such as low density, resistance to many of the liquids that corrode metals and above all, easy processability . Thus, where plastics compete successfully with other materials
in engineering applications it is usually because of a favourable balance of properties rather than because of an outstanding superiority in some particular respect, although the relative ease with which they can be formed into complex shapes tends to be a particularly dominant factor. In addition to conferring the
possibility of low production costs, this ease of processing permits imaginative designs that often enable plastics to be used as a superior alternative to metals rather than merely as a tolerated substitute.