Question for those with extruder experience

Precious Plastic Machine Development
#1

I am working on a project where I want to use the basic design of the extruder, but I’m not using it to extrude molten plastic like most folks here.

Ultimately I need to figure out a way to convey shredded plastic through a 3/4″ (19mm) fitting to end up into a tank/bin. Once the plastic is conveyed through this relatively small hole it will be used with another process. I want to use the “extruder” to force/convey shredded plastic into a tank where it will be used with another process. I am not intending on melting the plastic, I basically just want to force the shredded plastic from the hopper into the tank, so I wasn’t planning on using heaters on the barrel like the extruder.

My plan was to use the auger bit like the original design, although I see a lot of work has been done on a custom made extruder screw.

My question is do you think this will work without heating the plastic? Will the auger bit be able to “force” the material without melting it? Any thoughts greatly appreciated!

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#2

G’day Wess, from looking at your design I can see 2 problems straight off. 1. The “screw” is to small in diameter so any plastic coming in from the hopper will have to be screened to a very small size. 2. The reduction on your nozzle will automatically jam as the screw will pack plastic into it and the particles will not flow out. A better option would be to look at how grain augers are built and use that as a basis for you design. Merv

#3

Are you stuck with the 3/4″ inlet to your pressure vessel?
(I can’t be the only one curious about the pressure vessel!?)

My 1st thought is could your feed be redesigned to be gravity fed with no moving parts?
well I guess you’d need some sort of gate…

2nd thought is keeping the whole supply line at 1″, or expanding it to >1″
would be better than compressing to 3/4. If you had an airline just upstream of
your pressure valve, maybe a puff of compressed air could clear the valve?
Unless it’s huge, the pressure vessel would probably need another air outlet for this to work. Ideally the air inlet would angle towards the valve, and might want to cover
your upstream hopper to make sure you don’t end up with shreds everywhere 🙂

#4

I agree with what others have said about the restriction possibly causing problems. If it jams and the screw keeps turning it may melt the plastic, or it may just stop feeding and all the material will rotate with the screw.

But if you’re using a small (3/4″) ball valve with shredded plastic, you may have problems closing it unless the shreds are very small.

#5

I guess what I don’t have shown here is the 3/4″ diameter pipe is actually a valve (the tank will be pressurized at times), and the valve is actually a 1″ nominal but the bore of the valve is 3/4″ (ball valve). I am concerned that the screw may not be able to push/force the plastic through the reduced diameter, but maybe it’s not enough of a change that it could. After all if it can push molten plastic (which is not thin) through a tiny orifice to make string, maybe it would work for this.

Next week I will probably give it a try, I already have all the parts. This is the configuration I have to work with, I was just seeing if anyone had any specific suggestions that might lead to success sooner… 🙂

#6

It should work fine. It would function just like an auger on a CNC machine taking chips into a tank. The only concern I see in your design drawing is the auger pushes into a smaller diameter tube. For simplicity, I would just take the 1in barrel all the way to the tank.