Anti-ooze valve for extruder

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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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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.

Indeed. Pressure variation plus leakage condemn this air system.

Now, what about the molten plastic leaking at the cold end (and likely blocking it) due to the extra pressure needed to open the valve ?

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

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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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.

Not enough pressure, no extrusion. Of course, once there is enough to open the valve, a new cohort of issues will arise, unreliable extrusion flow one of them. Could simply end up spitting plastic blobs.
Fact is, I don't see how this could work at all.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

If the extrusion process was controlled by adjusting the pressure, then I'd be more worried about pressure fluctuations. However, the extrusion processes is controlled by the rate at which filament is fed into the hot end. Because the molten filament is largely incompressable, what gets shoved in one end has to come out the other, and the pressure will automatically adjust to whatever it takes to keep the valve open, Also, the pressure needed to open and close the valve only needs to be maybe 10psi, whereas pressures inside the hot end during normal extrusion are on the order of a few hundred psi. I don't think the fluctuation of 10 psi because of the valve is going to cause much of an issue at all. When I get some time, though, I'll try it out and let you know how it works out.

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.

Edited 4 time(s). Last edit at 04/03/2018 09:45AM by Quenta.

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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.

Very interesting - and pretty similar to what I've been playing with. A couple of questions:
1. What material is your valve pin made of?
2. How does the valve pin seal against the chamber with the spring? If it is an imperfect seal, do you have problems with the valve pin pushing shut during a long extrusion?
3. It also looks like there is a hole through the center of the valve pin that would actually let filament flow up in behind the pin? That seems counter-intuitive.

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.

Edited 2 time(s). Last edit at 04/04/2018 12:35AM by Quenta.

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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.

I would order two nozzles right now from you if you offered PayPal on your website.

Lastly, I do not see the E3D Volcano version for sale on your website.

Edited 1 time(s). Last edit at 04/04/2018 01:52AM by klcjr89.

I have no intention of promoting the nozzle here. This thing is yet experimental. By the way I haven't sold any yet.
The 0.8mm one was working perfect, but I just machined out one of 0.4mm, this didn't work; it jammed almost immediately. I guess the plastic isn't going down but going up, clogging itself shut.

I guess I need to work on even thinner hole on the pin, or make the orifice thinner.

the dimensions of the successfull 0.8mm nozzle are:
1.orifice thickness : 0.5mm
2.pin hole diameter : 0.4mm
3.nozzle bore : 0.8mm

in diagram I mean like this

I guess if the dimensions were proportional to the above then it would work, but drilling a 0.2mm is indeed quite difficult. Maybe I could go with 0.6mm bore & 0.3mm pin hole.

Edited 3 time(s). Last edit at 04/04/2018 11:48AM by Quenta.

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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.

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

Edited 1 time(s). Last edit at 04/04/2018 12:21PM by klcjr89.

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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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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.

Please post here as soon as stock is available. I hope I don't miss out