Spin Welding
Spin Welding is a process in which two
parts are pressed together and while one part is held fixed
the other rotates at high speed. The friction between the
two parts then generates heat which causes the polymer to
melt at the ends. The molten polymer flows out of the weld-zone
giving rise to flash. When rotation stops, the weld cools
down and solidifies. The duration of the cycle is short which
makes it efficient, simple and a fast process.
The benefit of Spin Welding is that the molten
polymer is not exposed to air. This is important for materials
that are vulnerable to degradation or oxidation. Such a precautious
measure makes for a strong connection or weld.
Spin Welding Process:
According to DSM,
the Spin Welding process consists of four different phases;
the solid friction phase, the transient phase, the steady-state
phase and the cooling phase.
In the solid friction phase, heat is generated as a result
of the friction between the two surfaces. This causes the
polymer material to heat up until the melting point is reached.
The heat generated is dependent on the applied tangential
velocity and the pressure.
In the second phase, a thin molten polymer layer is formed
which grows as a result of the ongoing heat generation. In
this stage heat is generated by viscous dissipation. At first
only a thin molten layer exists and consequently the shear-rate
and viscous heating contributions are large. As the thickness
of the molten layer increases the degree of viscous heating
decreases.
Thereafter, (start of third phase) the melting rate equals
the outward flow rate (steady state). As soon as this phase
has been reached, the thickness of the molten layer is constant.
The steady-state is maintained until a certain "melt
down depth" has been reached at which point the rotation
is stopped.
At this point (phase 4) the polymer melt
cools and solidification starts, while film drainage still occurs
since the welding pressure remains. After all the material has
solidified, drainage stops and the joint is formed.
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