A well designed hinge will maximize molecular orientation — and orientation gives
strength. In the same context, sharp corners must be avoided because they will act as
stress risers (see Figures 1 and 2). Gates need to be positioned to ensure that the melt
will flow perpendicularly to the hinge. Gate positioning will be discussed further in
subsection 2.4. Hinges longer than 6 inches should be designed in 2 or more sections
with small gaps or breaks between sections, this improves hinge life and reduces tool
flexing.
For better hinge life, parts need to be flexed a few times immediately after molding (cold
drawing) while they are still warm. This will allow for the web to elongate well beyond its
yield point without breakage.