Injection-spin welding

In friction or spin-welding of thermoplastics, one of the two pieces to be jointed is fixed in the chuck of a modified lathe and rotated at high speed while the other piece is held against it until frictional heat causes the polymer to flow. The chuck is stopped, and the two pieces are allowed to cool under pressure. The process is limited to objects having a circular configuration. Typical examples are dual-colored knobs, molded hemispheres, and injection-molded bottle halves. 

In general, hollow components with apertures smaller in diameter than the body are made by blow moulding (either extrusion or injection blow moulding) although it is possible, in the case of objects having a circular cross-section at some point, for them to be injection moulded in two halves and then joined by spin welding (see Fig. 2). Such a method is sometimes used if particularly good control of wall thickness is necessary. 

Fig. 2, A component such as that shown could be injection moulded in two halves and then Joined by spin welding, as opposed to producing the com plete component by blow moulding.

This high-temperature-resistant polymer can be easily processed by conventional methods, including extrusion and injection molding. It can be joined by screw assemblies, snap-fit, press-fit, cold or hot heading, spin-welding, and heat-bonding. See Chapter 6 for more information about the adhesion treatment of ETFE. 

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