Section 7 - Optimizing Performance
Spin Welding Process
The formal definition of spin welding is “An assembly process in which thermoplastic parts with rotationally– symmetric mating surfaces are joined together under pressure using unidirectional circular motion. The heat generated during the rotational contact melts the plastic in the
The spin welding process is divided into five distinct phases. In Phase I, the rotational friction generates heat. Frictional heating is intensified with both axial (press vertical) and joint surface velocities. In Phase II, the friction results in abrasive forces which strip off surface roughness, generating wear particles causing the surfaces of the polymer to begin to melt. As the polymer reaches its crystalline melting point or glass transition temperature, it enters Phase III, where heat starts to be generated by internal friction within the molten region. This continues in Phase IV, where the temperature of the molten layer remains relatively constant. Because plastics are poor conductors of heat, the surface heat is transferred slowly to the interior and much of it remains localized. At this point, the rotation is stopped and we enter Phase V where the molten material
.is allowed to cool under pressure for a short period called the Hold Time.
Material Considerations
Materials that can be friction (i.e. vibration) welded can also be joined with by spin welding. The semicrystalline thermoplastics are more readily joined using spin welding than ultrasonics. Using compatible polymers, spin welding is capable of making reliable hermetic seals.
Joining of dissimilar polymers is possible using the spin weld process although it generally produces lower strength weld joints. By designing the weld joint with an undercut, the polymer with the lower melting temperature will flow into the undercut, creating a mechanical union.
Dukane Manual Part No. | Page 59 |