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Quenta

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klcjr89

What I'm saying is that I would've been your first customer, if you supported PayPal on your site.

Issue resolved for 0.4mm. @klcjr89 Thanks anyways for pointing out the shortcoming in the payment system, I didn't realize it's so crappy from a customer view. I'll soon be back with paypal & some stocks.

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klcjr89

What I'm saying is that I would've been your first customer, if you supported PayPal on your site.

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Quenta
I have no intention of promoting the nozzle here. This thing is yet experimental. By the way I haven't sold any yet.

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Quenta
1. I wish not to write this because it is key in manufacturing
2. You are right about your concerns. To keep it all metal there is no seal. A certain level of precision in the machining of the pin / barrel is necessary to block molten plastic to enter the air chamber.
3. Your intuitions are somewhat right, but given the acorn-nut shape nozzle with a thin orifice, the plastic is rather likely to flow down than up.

Nevertheless in very long extrusion(like over 10 minutes, depending on the tolerance of the seal) sometimes a jam occurs. The fix for this is
a. more precision(smaller tolerance) between pin / barrel
b. retraction. Best if retraction forced between layers.
I can't directly observe the phenomenon, but the motion of the valve opening & closing seems to purge the plastic in the chamber like a pump. So it means you'll be fine if you have certain precision in its manufacturing & retract once in a while. The former is a little difficult, that is where your manufacturing competence is required.

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Quenta
Hello, this is just a note so that you won't need to reinvent wheels.
I've successfully machined out an all-metal, anti-ooze nozzle with a passive mechanical valve.
Its working perfectly fine with the E3D ecosystem(namely chimera or kraken).
It's currently in small lots production, available from here.

documentation can be found here.

I haven't decided on going for commercial production with this or not.

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newbob
I have no idea what amount of pressure would be needed - that would not be my biggest concern. More troublesome would be assuring that exactly the same amount of pressure over time would move the needle. If amount of pressure or time varied from retraction to retraction, system would never 'know' if plastic have been extruded through the nozzle or used to move the plunger.

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LoboCNC

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MKSA
And what pressure do you think it will have to act upon ? If there is no leak, a 1 bar in the "air chamber" at room T° will become how much at let say 200° ?

If the temp (in Kelvin) is increased by 2/3rd (300K to 500k), then the pressure in the air chamber should also increase from 1 bar to 1.66 bar..

An alternative to this that I'm pondering is replacing the silicone o-ring and air chamber with a pad of closed-cell silicone foam and have the piston press on that. That eliminates the problem of leaking seals. The amount of motion required is less than 1mm, so it should be doable with, say, a 3mm thick piece of foam.

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MKSA
And what pressure do you think it will have to act upon ? If there is no leak, a 1 bar in the "air chamber" at room T° will become how much at let say 200° ?

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newbob

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LoboCNC
OK, here's another version of the anti-ooze valve that eliminates the complex extruder motor driven actuation and instead uses the differential extrude/retract pressure to operate the valve, as leadinglights suggested. It uses compressed air in a small chamber in the heater block to push the valve pin against the inside of the orifice during retraction, when the inner pressure filament pressure is zero. During extrusion, the high extrusion pressure will push the valve pin upward against the air-spring. A sealed compression screw can be used to compress the air in the air chamber to the proper level. It still has an o-ring seal, which could be problematic, but at least this something I have a hope being able to fabricate.

Assem3.jpg

To push the pin up using pressure you'll need melted plastic press on part of the plunger, larger the surface area means bigger gasket and mechanism would be harder to clean/keep aligned once contaminated. I like the original cam idea better. Another negative is changing melt chamber volume when using pressure to produce mechanical energy.

What I find intriguing is the idea of offset chamber where filament is pressing on the wall as it's being fed which may speedup melting due to better heat transfer.

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newbob
What I find intriguing is the idea of offset chamber where filament is pressing on the wall as it's being fed which may speedup melting due to better heat transfer.

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LoboCNC
OK, here's another version of the anti-ooze valve that eliminates the complex extruder motor driven actuation and instead uses the differential extrude/retract pressure to operate the valve, as leadinglights suggested. It uses compressed air in a small chamber in the heater block to push the valve pin against the inside of the orifice during retraction, when the inner pressure filament pressure is zero. During extrusion, the high extrusion pressure will push the valve pin upward against the air-spring. A sealed compression screw can be used to compress the air in the air chamber to the proper level. It still has an o-ring seal, which could be problematic, but at least this something I have a hope being able to fabricate.

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aimdy
this is the machine i was referring to. you can see here a basic cartoon of what happens in the heater block

[www.cel-robox.com]

this shows the needle valves (pin) as well from outside the heater block in the dual material head

[cel-uk.com]

they offer a single material head, with 2 nozzles for .3mm and .8mm and a dual material head with .4mm nozzles.

The main issue is as I mentioned in my initial post. The machine's proprietary software and slicer provides calibration tools so the machine knows how to precisely calibrate the pin movements. Additional issues may result from the user not properly calibrating their machines. Also as the machine is closed source the manufacturer provide firmware updates, which is one way fine tuning of the pin behavior can be implemented. On a well calibrated machine the user should have no problem other than the longevity of the o-rings.

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newbob
There's (was?) printer made in Australia with valve in the nozzle. From what I recall it was causing all sorts of issues.

Found it: https://www.wiltronics.com.au/Robox-3Dprinting/nozzle-valve-system/

From their description though, it looks like needle valve is not used during retractions:

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When they want to pause printing, or switch nozzles, the current nozzle is plugged completely with a small needle, stopping the flow of filament and producing a perfect ‘end’ to the line or layer of print. This also facilitates the ability of the printer to manage the pause and resume function, another CEL-Robox innovation.

Printing head costs $2500 which could mean that users see some value in such design....LAST EDIT: used, like new CEL-Robox on Amazon goes for $300 so maybe not :)

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aimdy
hello LoboCNC, i am not sure how far along you are but please check the following patents before investing a lot of money in this project. the design you mention is already in use in a fairly popular machine, the only difference is that the filament in yours feeds parallel to the valve pin. as you guessed the o-ring seal is the weakest point as it generally last only about 500hrs in this harsh environment, sometimes more sometimes less. The issue in the particular head i am referring to is that it fails due to pressure then the filament is allowed to escape through the orifice or at the thread area in that location. I have two of these machine and it is a common issue acknowledged by the manufacturer. Maybe a particularly strong o-ring with high temp resistance will do the trick. Not sure how well ptfe will perform but it could limit what materials you can print with as already observed. You may not be working on this for any financial gain so this message may not be applicable to you, i was not sure. In either case i am sure you can complete the project and your head will print well if implemented correctly, but for retail purposes you may face a road-block unless you are able to design it as such that you do not infringe on any of the patent claims and that would require a pretty good lawyer. I hope this is useful, i design 3D printers and innovative parts too so I would hate for you to get in trouble over patent infringement law.

[www.google.com]
[www.google.com]

Best,
Moh

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Lykle
afaik, the retraction does not suck the molten filament up into the heat block.
It simply relieves some of the pressure, but there is no negative movement of the molten plastic.
So yeah, closing the needle will have a pulse effect of pushing some filament out.
That can be used, by retracting early and closing the valve slowly, using the pushed out material to finish the track.
That would take a lot of control and precision in the needle valve.

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leadinglights
Whether the pin pushes any filament through the nozzle or not would depend on if the filament retract was effective before the pin closed off the nozzle.

In the case of the floating nozzle, since the lifting of the nozzle to meet the pin is done by retracting the filament, I think there would be nothing in the nozzle to be pushed out. Incidentally, the nozzle being lifted would help it to clear the print in the case of multi filament printers.

Regarding obelisk79's concern that the nozzle would wobble, I think it is easy to engineer around that problem - LoboCVC's thought about the diaphragm spring sounds like a very good way of de-wobbling as well as helping with the sealing.

Mike