Option 2 is the unscrewing of the thread. Specialists call this de-spindling. Here the mould core, where the thread is incorporated on the front, unscrews from the plastic part before it is ejected. The difficulty when demoulding the internal thread is that there is no room to move the slide inwardly with a linear movement such as with external thread. The question is, how do you release the thread or undercut? The solution is to unscrew the core from the mould contour using the thread. Previously, all movements that were important for demoulding were linear movements in either the main demoulding direction of the machine or the secondary demoulding direction through a moving slide. But for unscrewing, a circular or screwing movement is required. The screwing movement for a core can be produced in different ways. The three common types of operating a mould core are: the unscrewing unit, the drive via a gear with gear rack or a gear with a high-helix lead screw.
In Figure 2.22 the plastic part is shown with the mould core which is injection moulded with the thread.
3.Drive Types for De-spindling
Hydraulic Unscrewing Unit
The hydraulic unscrewing unit is an additional device that either is screwed onto the injection mould or to the machine. It is connected to the injection moulding machine and driven and regulated from this. It can either be electrically or hydraulically operated. These unscrewing units are highly flexible in their handling. They can be used for demoulding threads which are on the fixed half or the moving half or on the split line face. The unscrewing unit produces the screwing movement and drives either a small gear or the mould core directly. Unscrewing units can be obtained in different types and options from the manufacturers of standard mould components or manufacturers of injection moulding machines.
