The internal angles tend to have less thickness as the time in contact with the material is less: it is for this reason that radius on internal corners have to be greater in relation to those
of external corners. Large radiuses improve the flow of the material inside the mould and help to distribute the stress over a wider area, increasing the strength of the part.
In the external corners there is a greater material thickness. This can be useful in zones where stress and wear are greater.
A recommended standard radius for polyethylene is:
• 5 mm for external angles (in any case always R>2 times the wall thickness)
• 10 mm for internal angles (R>4 times the wall thickness).
More rigid materials, like polyamide, require wider radiuses. They are recommended with values over:
• 10 mm for external angles
• 20 mm for internal angles