Ejection of Helical plastic gear

[Rakesh Murali]

Hi all !

I am doing an academic study on injection moulding of plastic gears.

However, I am having a hard time imagining the ejection of a helical gear from the mold.

I have read in several places that the gear has to rotate slightly while ejection and that the ejection speed has to be low.
I am looking for a clearer explanation than this, please.

As far as I can imagine, the helical gear will have a fit with the mold after cooling.
Then, how does the gear rotate? What kind of provision is provided for this?
In my view, the mold and gear form somewhat of an internal helical gear drive. By this logic too, the gear will have axial motion if it is rotated but how is it rotated?:eek:

Any videos or rudimentary animations or pictures or diagrams will be very, very useful for me to understand this...

[JayDub]

Building rotation into mold ejection is very common, typically for threaded components, but a helical gear works on the same principle. The usual solution is to build a rack and pinion system into the mold. The rack moves as the mold opens and the pinion converts the linear motion to rotation. You can see some examples here:
https://na.dmecompany.com/Catalog/CatalogListing.aspx?CatalogId=DME&CatalogDetailId=1122

[moldingppm]

Rack and pinion, unscrewing unit, collapsible core, we even have a mold that we physically put a core in the mold, it molds and then we press it out using a hydraulic press.

This could be a few ways that you could do this.