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ACME Screw Injection ! Injection – v6

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This topic contains 7 replies, has 3 voices, and was last updated by  NowProject 6 days ago.

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NowProject cgoflyn

ACME Screw Injection ! Injection – v6

09/02/2019 at 22:02

Hey,
after toying with an arbor, desktop and lever injection, I think the more cheap, powerful, light and easy to build injection is using a ACME rod of at least M20. Plunging plastic through a 25 mm tube seems near effortless with a larger wheel.

The materials are below 100 Euro and a day of work.

@s2019, any thoughts before I weld this together 🙂 ?

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starter
09/02/2019 at 23:17
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That is elegantly simple. Great job!

Does the piston retract enough to make feeding material easy? If not, welding in a spacer might help.

Are you going to configure this as a horizontal machine?

The other thought is that welded together it will all run hot (though some isolation could be configured in). It is also a single purpose configuration. The other option would be to still use your vertical frame to carry the load. In that case you could potentially be able to remove the injection tube and use the acme drive to compress a compression mold that is heated with simple cartridge heaters plugged into the existing controls.
The simplicity and effectiveness of the drive opens up a lot of options.
You made huge progress in a very short time.

dedicated
10/02/2019 at 12:15
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Very interesting! I can imagine this makes it way easier to put a lot of pressure. But I guess this also means you reduce the speed of injection a lot? Would be interesting to have a “normal” injection machine next to your concept and compare the advantages & disadvantages in relation to each other.
I would think this acts more as a combo of an extruder and an injection machine. Good for putting lots of pressure and being able to properly fill up the mold. But less good in terms of production speed. That’s just my theory though.

helper
10/02/2019 at 12:29
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@siemenc, yes, that’s what i thought too at the beginning but putting a heavy handwheel (8 kg ) on the screw made it really fast, you just need to kick off the wheel and it keeps spinning as it acts like a flywheel 🙂 I am still working on a better lead-screw with a larger pitch so things should get even faster – if that is really needed 🙂 Also, I had no recycled plastic during the tests so I used 3D printer PLA which made no noticeable resistance during the plunge. I will also have to check more complicated molds but I honestly, I am not worried. For now I try combining the standard v3 injection by removing the lever (and frame) and replace the screw over the barrel. It needs then also to be mounted on a bench for turning the wheel more easy. will let you know how it goes 🙂

helper
10/02/2019 at 13:25
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@s2019, as always thanks a lot for your input, I am honestly just a beginner in most of the stuff 😉

plunge retract: yes, this needs definitely some more attention and work. It should be more open and also allow to put different plunger geometries, such as a cone, seen in industrial screws attachments.

About the final layout I am not sure yet. I think for a light and low-budget variant a horizontal bench mount would do nicely since the main forces acting around the mounts and also it’s so much more pleasant to turn the wheel that way. the problem comes then with the feeding, so I am looking at a solution which enables to use the screw as feed plunger, no idea yet since this requires quite some machining. For now I am focusing on a max. 200 Euro machine.

The vertical layout (with the frame as seen in the arbor press) needs some testing next week but I am confident that it doesn’t need much floor mounting which is my biggest concern.

I also agree with your last thoughts, about the cartridge and opened possibilities. That’s going to be a heck of fun next week 🙂

starter
10/02/2019 at 22:52
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@cgoflyn , I’m glad the trial run worked well. I could not tell if the plunger rotates with the screw. I was concerned that once the clearance gap filled with molten plastic the torque needed would go up if the plunger rotates.

As far as the feed port is concerned, for those people that don’t have a shredder, having enough room to feed in strips of say 1.5-2 cm wide and 7-8 cm long makes life easier if you are cutting up recyclables by hand. I can cut up a laundry or shampoo bottle into strips with a utility knife very quickly but generating small chips takes longer. Maybe the whole assembly ends up mounted at an angle to make feeding chips or pellets easier as well. One advantage of the vertical configuration is that it is easy to add a heat shield that can also double as a fume hood. The fumes can then be ducted elsewhere. That may be more important for a compact desktop unit where the temptation is to use it indoors. Hopefully the V4 team can get some university involvement to get some measurements of what is released at different temperatures.

Maybe weld or thread a nut at the hub of the wheel so that you can drive it with a socket and a cordless. I found with my small unit that I end up doing several compactions to get a good fill. Perhaps with the long stroke of the screw that’s less important but low cost motor drive may be a good option to maintain.

As far as injection speed affecting throughput. I find most of the time is spent allowing the fresh charge of plastic enough time to melt.

Great progress! I’m very impressed with how quickly you can turn ideas into professional hardware.

helper
11/02/2019 at 00:13
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hey,
no, the plunger sits free there. I’d feel more happy to see it attached but that may require some more welds, … another cool homework to do 🙂 However, even with plastic it’s surprisingly easy, at least with a 8 kg steel wheel 🙂

shredding is indeed a bit annoying, having one may be even more. Currently I pull PLA from the spool, to fill the barrel right on size, a hand full, then push it straight into barrel, takes 15 secs 🙂 Doing stripes from a shampoo bottle with a scissor isn’t a too bad meditation exercise after all. Wouldn’t be a little machine cool for that task ? ‘This old Tony’ had this thing called ‘ultra sonic cutter’. Looks alright to me 🙂

Having it vertical isn’t a problem, and indeed of favour. You can mount it basically any way you like, along the foot edges of table for instance, or at a wall corner over your door, up side down whilst having fun sitting on the wheel, hell kids gonna like this, extruding plastic.

currently horizontal looks more promising, i am still exploring your cartridge idea. filling a larger container with less cut plastic. pre-heat it, and then push it out through a cone into the main chamber. that way you could possibly also pre-heat it in mass in the oven 🙂

what a ride and thanks again,
g

helper
11/02/2019 at 00:15
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@s2019, btw. having many of these cartridges, plugable on a main barrel would give you quite good control over colors, no ?

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