Injection machine huge material loss

Hi, we built an injection machine using the precious plastic blueprints but with a few adaptations. We needed a barrel that could withold around 3 kg of PET, so many of the dimensions were adapted to be able to fulfill this requirement. For example, we have a 18cm diameter barrel. Such modifications have brought several challenges, among them the huge material loss. When pressing on the handle to inject the molten plastic, most of it flows up over the piston and is lost completely. This may be due to an expansion on the barrel by being exposed to the over 250 degrees celcius. If anyone has had a similar problem, how did you solve it? Thanks!!

This is a picture of our injection machine for u guys to have an idea of how much bigger it is compared to the regular one.

If you want to increase the volume it’s better to make the barrel longer rather than larger diameter. This will keep the cross sectional area down so requiring less force on the piston and you can have a greater temperature differential between the nozzle end and the retracted piston, so the plastic at the nozzle can be much less viscous and the plastic behind the piston can still be almost solid so less likely to bypass the piston.

3Kg is ambitious though, you might want to mount the barrel horizontally and you will need to come up with a better lever system for greater travel. Perhaps a rack and pinion or even a winch.

Thanks! Very helpfull! 🙂

I don’t think you’re going to get it to work well with an 18cm barrel. Compared with Dave’s design, you’ll need to apply 48x more force on the handle to generate the same injection pressure. Industrial machines do not have barrels this big and need high pressure hydraulics to work. The only way you’ll get it to work is by heating the mould, using a very wide nozzle and making the piston a very tight fit in the barrel. Then it might just work, very slowly.