Increasing barrel size on injector

I would like to make injection molded bocce balls, with a volume of just under 600 cubic cm. Has anyone played around with increasing the injector barrel size?

Preliminary calculations: The current tube can hold around 280 cubic cm. I would need to approximately double the barrel’s length or boost the barrel ID up from a 26 to almost a 40mm, if I was to keep the barrel length.

I’m nervous about increasing width due to increased heating time, but increasing length will require a rework of the system for the lever arm. Right now, I’m leaning towards an increase in width. Logistically it seems the easiest.

Any thoughts? Has anyone had success in a barrel volume increase?

Cheers, Ders

In the PP injector design, when you increase the diameter of the barrel, the pressure you can generate decreases and given the linkage geometry it can be challenging to get it back up. Pressure may not be that important for a large volume mold like a bocce ball, but making smaller parts may be harder. For large volume, I would consider the rack and gear type machine. This design separates the stroke length from the injection force, so you can increase the stroke length.

My machine has a 40 mm ID barrel but I use an arbor press to provide the rack and gear function.

I think you will need margin on the 600CC volume. I find it hard to get a part that is more than 75% of the stroke volume.

When you succeed, I think you will have the largest injected part reported on the forum.
Good luck

As I mentioned, with a big open cavity mold may not need as much pressure to fill but pressure also helps reduce voids.

……………You can always work your way up by making the pallina ball first

Thank you for your thoughtful reply.
Hadn’t thought about the pressure decrease. Rack and gear sounds like the way to go. And thanks for the heads up on the 75%… Looks like the barrel widening is not the easy modification I had hoped. I have my work cut out for me, haha. To the drawing board!