3
Nylon is a hygroscopic material.
Nylon is a hygroscopic material.
Over time it will abosorb in excess of 3% of its mass of
water from the atmosphere. The rate of moisture absorption
is time, relative humidity and temperature dependant.
In
the initial production trials for the 4 gang socket components
were produced within two days of injection moulding. Therefore
the mouldings can be considered to be in their "dry
as moulded" condition.
However,
in subsequent production, mouldings were produced in a
mass volume production and used over a period of months.
During this time they would have abosorbed a significant
amount of moisture.
Absorbed
moisture during ultrasonic welding has a number of effects:
- It
reduced the modulus of the material, hence increases
attenuation and damping of the ultrasonic waves.
- Due
to the weld temperatures it vapourises at the weld front
and produces a weak, foamed weld.
- Nylon
is highly susceptible to hydrolytic degradation. The
presence of moisture and the weld temperatures can induce
localised degradation of the weld leading to a brittle
weld structure.
For
these reasons it is important that Nylon is either moulded
soon (within approx. 1 day) of moulding, or that components
are stored in a sealed desiccated bags or dried prior
to welding.
Other
materials susceptible to such atmospheric moisture effects
include polycarbonate (PC), polyethylene terephthalate
(PET) and polybutylene terephthalate (PBT).
|