TABLE OF CONTENTS There are four basic methods that can be used for the production of moulded threads:
Split tooling
Thread jumping
Collapsible coring
Rotary unscrewing
A very large number of screw-threaded components are injection moulded by this method. It involves machining half the thread form in each half of a split die as shown in Figure 13.5. The details of split tool construction were discussed in Chapter 12 for a variety of undercut components. The use of splits for moulding threads forms follows exactly the same method.
This is the cheapest method of all for the production of screw thread and is very widely used for the manufacture of closure threads. Figure 13.6 illustrates a typical jump undercut.
To jump eject a screw thread, it must have the appropriate form. Ordinary screw thread forms cannot be ejected by this method as the flanks and top and bottom of the thread present too great an undercut.
The form for jump ejecting a thread must be a well-rounded one such as a bottle thread. Before ejection takes place the undercut must have the freedom to expand and distort into a clear space. Thus, any restraining cavity walls must be moved away to permit this.
This is another very widely used method for producing screw threads and a very convenient one as the basic...
