Home made granulators.

[Scooby]

Has anyone any advice on making granulators?

I want to turn used plastic objects to a granule form again so i can injection mould with it.
Ive read what there is on here and had a question posted for a short while on a thread with no replies so thought i would ask what i want in my own thread and get a decent discussion going without the same old answer of hireing a chipper being posted.

I dont think a wood chipper either a) cuts it small enough, b) is clean and tidy enough (even if it was a brand new chipper that has had no wood in it previously the machine will still spray it everywhere), c) they are noisey and big,

So im after making perhaps a wooden box with spinning blades in it, a chute for the objects to be dropped in and a chute for the granules to fall out.
I considered having a blade spinning round on a flat sheet that has a few big holes in it so the plastic would drop through the hole and be sliced as it did so, any bigger bits get sliced up until they are small enough to fall down the chute.

Buying isnt an option, this is a hobby project and im not spending hundreds of pounds/dollars buying one, i also dont have 3 phase power and i dont agree with converters.

I am a very good engineer and can make anything so really am after some pointers, how do the commercial ones work for example?

[Scooby]

All the people on this site and no-one knows how a granulator works?

I am very supprised.

I dont need or want a set of drawings for making my own, i want to know how they work so i can make my own,

[TOTALLYRC]

Silly Rabbit, chippers are for wood.

All kidding aside I have seen inside on for cutting plastic tubing back into small pieces.
It basically uses a large milling cutter and feeds the tube in at a controlled rate. The cutting edges come close to a staionary anvil and it cut clean. If you could crush you stuff so it would go between rollers so the feed rate could be controlled. it would. I would just stack 3 or 4 cutters on a shaft to give you the width that you need.

Although you would get long thin pieces, it might work for you.

If you are going to use the box idea, try a set of contra rotating blades, I think it would help with chopping the stuff down to size. A bottom plate with holes sized to the finished size your are after would keep the granules in play untill they were small enough to fall thru. You will most likely have to take air flow into consideration. as the granules approach final size they will float or follow the air flow

[Scooby]

Thankyou for your reply,

I have considered tipped circular saw blades (contra rotating) but your milling cutter suggestion gives me a whole new area to think about or at least that sort of set up.

I mentioned wood chippers as everything else ive read on here regarding granulators suggest hireing a chipper and i didnt want to get more replies saying the same.

[TOTALLYRC]

Originally Posted by Scooby Thankyou for your reply, I have considered tipped circular saw blades (contra rotating) but your milling cutter suggestion gives me a whole new area to think about or at least that sort of set up. I mentioned wood chippers as everything else ive read on here regarding granulators suggest hireing a chipper and i didnt want to get more replies saying the same.

Having serviced wood chippers in the past I knew right away that the chips would be way too big to introduce into an extruder.
I work on extruders at work and see what size granules of virgin plastic come in at, I knew what size you were looking to get.

Keep me posted, as I am looking to do some injection molding in the future once a few of the cnc projects are finished.

Mike

[Fixittt]

the endmill thing is a good idea. ever see what a rouging endmill does to plastic if the speeds and feeds are correct? The chips are fairly large and plentiful. A fly cutter might do as well. Just like any type of plastic you will have to battle heat. heat will make the plastic melt and stick to the cutting devise.
Something like a blender with a type of hardware cloth on the bottom might also work (beefed up thought) the size of the holes in the hardware cloth will dictate how big the pieces have to be to fall thru into a catch pan.

[Scooby]

The fly cutter idea is quite good,

On a funny turn of events i was given a motor the other day which was mounted and driving two saw blades, not suitable for this purpose but the parts are.

I aim to post up a guide on making this project and the injection moulder once im finished, more of a complete guide if you like

[Scooby]

Here is a picture that took me a long time to aquire (im supprised i didnt get one posted through here but alas no, it was a decent and thoughtful ebayer who sent it to me in the end) but is the most important picture ive seen on this subject since i started so i will share it with everyone else. All i was after was a picture like this, now i have it everything is clear, i hope it will help others in future as well.

The granulators use a milling cutter style set up that basically cuts away at anything put into it, i am going to use some horizontal miller side cutters for this purpose and ill report back how i get on.

[TOTALLYRC]

Originally Posted by Scooby Here is a picture that took me a long time to aquire (im supprised i didnt get one posted through here but alas no, it was a decent and thoughtful ebayer who sent it to me in the end) but is the most important picture ive seen on this subject since i started so i will share it with everyone else. All i was after was a picture like this, now i have it everything is clear, i hope it will help others in future as well. The granulators use a milling cutter style set up that basically cuts away at anything put into it, i am going to use some horizontal miller side cutters for this purpose and ill report back how i get on.

That looks like stage 1 ,as you will probably get log strips, not granuals or little beads of plastic. I could see multiple passes thru the machine, with a screen with the proper sized hole to let finished product drop out.

Mike

[HuFlungDung]

I have not made a granulator, but I think it might be worth a shot to use the blades from a dado head, or several dado heads, depending on how wide the material that you need to shred would be. Wood working blades are so cheap compared to milling cutters.

You'd need to space the blades/chippers at regular intervals on a simple arbor, and provide a slotted stator blade to serve as the cutting anvil. The spacers on the arbor would be large diameter, allowing only about 1/8 inch of sawblade to protrude. This would prevent uncut material from sneaking through uncut, or wrapping round the mandrel.

The stator blade would look like a block of wood with saw kerfs for the chippers to pass through. Of course, you'd need a tiny bit of clearance so that the chippers could pass through unimpeded.

The mandrel would need a good method of retention to prevent the whole assembly from moving endwise and allowing the chippers to rub on or destroy the stator blade.

You might want to experiment with moderate blade speeds, as you don't want to melt the plastic and end up with a big stuck, gooey mess. Perhaps a positive infeed system would be worth a consideration, rather than hoping that gravity will do the job.

[Geof]

Hu's idea for an infeed system is wise I think, and you need to orient the feed to the blade so the teeth are pushing the the material out not trying to drag it in.

Also figure out guarding to make sure you don't get chips of fingers and hands in there; this will contaminate your plastic.

[TOTALLYRC]

Originally Posted by Geof Hu's idea for an infeed system is wise I think, and you need to orient the feed to the blade so the teeth are pushing the the material out not trying to drag it in. Also figure out guarding to make sure you don't get chips of fingers and hands in there; this will contaminate your plastic.

The water in your blood will flash into steam in the extruder and cause inperfections in you final products, not to mention how hard it is to do anything one handed.


Saftey first.

Mike