I used my 3D printer and downloaded the extrusion screw that Siemen Cuypers designed and posted to Thingiverse. I then edited the file so it had a hollow center (better for metal casting) and a different base where I could machine in a keyed shaft into the base. I then printed it out at 5% infill in PLA with 2 layer walls. I made the screw 80 mm in diameter and almost 2 feet long to account for shrinkage and machining. Then glued the 3 parts of the screw together for the final size.
I coated the print in ceramic shell and via the lost wax method I poured and cast a bronze copy of the screw which is what you can see in the photos. For some reason I can only add 3 pictures in a post?
Anyway, the next step is to machine the sides of the screw so it will fit inside a 3 inch bored hydraulic cylinder (like the ones that power back hoe digger machine arms). Then I’ll connect it up to a 1/3 hp motor with a 20:1 gear reducer. I will have a variable speed controller on the machine and I have two PID temperature controllers to vary the temperature of the tube in two different regions. I bought band heaters to warm up the wax as it passes through the cylinder. I will cut different shapes into steel end caps. These will become dies for the wax to come out of. One thing I wonder if I will need is a breaker plate? Do you think a breaker plate is necessary or helpful in extruders? I see them on commercial units but I am not really sure what their purpose is or how necessary they really are at the hobby level.
hi, impressive work. a few thoughts :
– you can’t use 1/3 Hp motor, even 800 W won’t be enough. it’s rather 3Kw in your case. You have to take into account the volume of the plastic but also the frictions caused by the screw along the barrel. apart from that, over time the extrusion screws build up stress in some areas, pushing even more against the barrel.
– leaving 0.3 mm play between screw and barrel was our best fit over time
– you may encounter some trouble turning this on size on the lathe. even with the high diameter the bronze screw will easily bend on your lathe. best option is a custom ‘follow rest’
– btw. I think there is a reason why traditional extrusions are done with chromoly based metals. such screws also receive various hardening and finishing treatments
– be very careful with making the barrel. welds will easily bend it and you are easily out of spec.
– there are few technical and scientifically documents about ‘extrusion screws’ here in the forum
keep us posted, btw. turning such a large screw on the lathe is around 12 hours and requires just a bit extra tooling (follow rest, limit switches)
@zapins
Wow, I am still super impressed with the amount of work you put into this.
It is absolutely great to see the dedication
is it a tapered bearing?
The screw has been machined fully. I made a bearing plate with a thrust bearing in it to take the force of the screw. I’ll be making the frame next week. Stay tuned for more pics.
Thanks for the link. That pdf has a ton of very useful info in it.
Machining is done on the screw. I need to machine a slot for a thrust bearing. Then I can weld up a frame for it and start testing it out to figure how much heat I need to get the wax soft but not liquid. I’m hoping the wax doesn’t squirt out the back.
@zapins,
Hi,
nice to see you back and sorry for late reply. Regarding breaker plate; I don’t know about wax but if it’s about recycled plastic, it works perfectly without and it also reduces energy consumption / required motor power a lot.
About the vents, I can only point to this thread here. There is a PDF which explains a lot. I know if you leave some clearance between the screw of 0.2 mm and the barrel the air problem is gone for most plastic; as I heard from our users. Possibly it goes also hand in hand with the final speed of the screw …
keep us posted
Little update. I found a local machinist. They are cutting the screw to size. There are 5 thousanths clearance between the screw and the hydraulic cylinder wall so the fit is pretty tight. Still waiting the back end of the screw it to be keyed so the motor shaft will fit but it shouldn’t be too much longer. Then I’ll weld up the frame and start testing. I wonder, do you think I’ll need a breaker plate? How necessary are breaker plates? Do they just even out the flow so it’s more consistent? Also do you think I’ll need to add vents to release trapped air?
I’m out of the country until April 11th. Hopefully in the week or two after I get back I’ll be able to make some progress on it and post updates with pics.
No premelt. I am hoping the wax will get gummy inside the extruder and not liquid at all.
I have found (using a rather large steel horse medicine syringe) that molten wax is very difficult to squirt out consistently into strings unless it is a specific temperature when the wax is gummy and slightly thicker than honey consistency.
I wonder if I’ll need to cool the wax as it comes out the nozzle? Once the machine is all welded together and functional playing with temperature and fine tuning the feed rate with a variable controller is going to take a while to figure out the right conditions to extrude properly.
Well isn’t that interesting! So the vent allows air out so it isn’t pushed into the extrudate?
I’m guessing it will probably need to be tiny for wax.
I notice that the vent is right above the midsection where the tines of the screw get wide again. That should make this area lower pressure and the wax less likely to be forced up the vent. Unfortunately I don’t have this on my screw. I wonder where the best location would be to place the vent?
Hmm interesting. I was wondering about backflow. I think I’ll try go for the closest tolerance I can get initially, test it out, and if it doesn’t work then I can always cut it down more.
I think I’ll do the tubing haha. The entire setup is going to be barely movable due to weight. The bronze screw is 30-40 lbs, the gear box and motor another 30-40 lbs, the cylinder is easily 70+ lbs and then all the framing I’ll need to make is going to weigh another 10 lbs or so. All in all we are talking close to 200 lbs! Not easily movable.
What is a vent? I have not read or heard about that? What does it do and where should I put it?
looks right to me, also have no idea how to get the breaker as insert like component but you’re getting there.
clearance, as it is wax, I can’t tell. i saw some materials even need a backflow, above 0.5 mm… i could imagine that the tolerances can be quite tight. there’s a table for sure for dealing with near liquids. hell you can even enjoy this certain blob sound, forever
you still may require a vent, for plastic its about a few micrometers.
you are sure about those tubing ? such a nice system deserves some solid plates one underneath the hopper works well for me, at least 15cm x 8 mm and you should be fine
i am sure @andyn can help you better with that things
g
Yes wax not plastic. The extruder will be for making wax sprues & basic building material for my sculptures and castings. The wax should help lubricate the screw as well once heated. It is pretty slippery stuff.
So basically the tighter the distance between the wall and the screw the better? I’m pretty sure I can get 0.1 mm tolerances without too much difficulty. The cylinder I am starting with has been bored and honed inside so it should be almost perfectly cylindrical to start with (hydraulic cylinders need to be close to perfect to work!).
If the 1/3 HP motor doesn’t put out enough power I’ll upgrade to a larger one. The gear reducer I have takes motors up to 1.13 hp, so I have quite a lot of wiggle room if it comes to that.
I’ll have to have a think about the breaker plate then. I wonder what the best way of including it in my setup is. Maybe I’ll weld two end caps together, the first one can act as a breaker plate with many holes drilled into it and the outer end cap will be the one with the final shape.
I could tig weld it, but from what I’ve noticed tig welding seems to put more heat into the piece because it is a slower process. At least the way I tig weld it does! Ha ha ha. Definitely not a pro welder.
Here is the general plan I have for mounting all the parts and installing the thrust bearing.
