We're gonna need a bigger syringe....

Yesterday a post by Zach on another thread got me thinking.
He was talking about where to buy sets of syringes, but that the biggest that he had found was a 60ml one, which isn't big enough if you want to build big pieces out of a relatively stable monomer, that can be kept liquid for long periods of time.

So I thought to make this new thread dedicated to exactly that, syringes and dispensers! Wellcome all

The first device i thought about was air-pumps, like for bicycles. they exist in many sizes and are cheap. But they can't be replicated by RepRap and they have different issues, like the piston sealing, which will probably fail with denser fluids than air.

I also remember having used bigger syringes (maybe better called fluid pumps) in the lab. Maybe veterinary syringes is what we need? You know, the kind used for elephants and such

And then i had an inspiration: I am spanish and here we have a food specialty called churros. It's like a deep fried dough chip. To make it you need what's called a churrera and looks like this:
[www.gourmetsleuth.com]
[fficial%26sa%3DN" target="_blank" rel="nofollow">images.google.es]
[www.mareni.com]
[www.mareni.com]

yeah, that is definitely one of the reasons syringes were abandoned in favor of a thread driven filament extruder. you just cant store too much in a syringe.

however, there are bigger ones out there... i found a 150cc syringe last night that looked pretty good.

another idea i had, which is a post v1.0 idea is to try and reprap our own syringes... then we could do a large, gallon syringe with the type of tip required to mount a needle on it (they're pretty standard.)

also, someone else mentioned this on the blog... but if we have a vessel with constant pressure + constant size nozzle it will always extrude at the same rate. so we could just have a pressurized chamber that is filled with the stuff to extrude. that chamber could then be connected to the extruder nozzle (needle). realistically, all we really need with a syringe is the nice, precision needles. if we can make our own fluid containers, theres no limit to it.

of course this only works with stuff that can be extruded at room temp.

Yup, i also started thinking about devices that could be reprapped and my conclusion is that a syringe doesn't need to be cylindrical. it could be made out of slabs of polymer screwed together, to make a long box that would accept a square piston.
The difficulties here being to make everything tight enough to not get any leakage, as square pistons have weakpoints on that front at each corner. Do you think this is doable?

Also, the pressurised dispenser is definitely the best way to go if we can make very dense fluids travel along the tube and through a fine needle or nozzle, fighting viscosity. I think i read somthing along those lines in your blog, a pressurised bottle i mean, right?
This setup would add two devices to the whole rig: a pressure-tight bottle and a compressor or compressed air bottle. The setup would only be necessary for large reprapping operations, that need big amounts of polymer.
For smaller ops, you may use 60cc or 150cc syringes and refill if needed.

As by Mike's post in the polymer forum, i pasted a great idea that he had and that would make things a lot easier. The part of his post pertaining to the matter is pasted below. I follow up with some more ideas at the end:

ohiomike Wrote:
-------------------------------------------------------
> When I was working in the paint industry we would
> use pressure pots, some large enough to hold a 5
> gallon bucket. I think that is the way that I am
> looking at since the pot can sit off to the side
> and therefore be any size necessary to hold the
> pressure. That means I could cast it in concrete
> in insure safety, prevent tipping and save on
> costs. Embed bolts into the rim of the pot and you
> could gasket the top and thread down a heavy cover
> that will hold any amount of pressure you could
> desire. The large volume would mean very low
> pressures (like from a bicycle pump) would last
> forever. Also the pressure pot was nice because
> we could place plastic cups with very small
> amounts of a test sample inside without any
> problems. Buy tubing by the 100' roll and it costs
> maybe $0.10 to replace it if your resin cures in
> the tube (something I expect to happen a lot to
> me).
>
> I am working on a small scale pressure pot using
> disposable plastic bottles from fisher scientific
> (see the attached picture). I am hoping that this
> will work as a mixing vessel for binary polymers
> so that I can get some of pastes mixed

............


Hey, for the pressure pot, why not use a pressure cooker?
Any old one with a new joint would do, as we really don't need to build up that much pressure i guess.
We would need a pressure valve to let us pump air in, even stabilise the inner pressure.

One good procedure would be finding the right pressure so that all the polymer is pushed out with one single pressurising phase, at the beginning.

This is how the process would work:
1) introduce an open pot containing the mixed up polymer you will use inside the pressure cooker.
2) dip a tube or pipe inside this pot so that it remains just above the bottom of the pot.
3) connect this tube to an outlet welded or epoxy-glued through the pressure cooker lid. This outlet should have a motor-controlled valve. Set valve to close now.
4) Close the pressure cooker and connect the polymer outlet to the dispenser-tube mounted on the RepRap.
5) Pressurise the pressure cooker with a footpump or an electric compressor. Use a manometer to achieve right pressure.
6) Open the outlet valve and start printing as soon as the polymer reaches the nozzle

The trick would be to pressurise enough so that the polymer-flow is constant over time. I think it's doable as the volume of polymer that will exit the device over time is small compared to the volume of the entire pressure cooker.
If nevertheless this is not possible with one pressurising phase, we would have to have a controlled compressor (or attentive foot ) that would keep the pressure constant.

does this make any sense?

yup, it makes great sense. one nice alternative would be to get a cheap regulator that would regulate air flow / pressure to whatever you need. then you can simply hook it up to an air compressor and it would just work.

man... once 1.0 comes out its going to be so sweet to be able to test all these ideas!!

Well, today I officially started my experimenting mischiefs for Reprap!
I went to buy a foot pump with a manometer that goes up to 7 bars (that's a 100 psi).
Also i went and bought the old fashioned type of pressure cooker, which has 1 outlet and a security release valve drilled through the lid. Its volume is 6 liters and is maThe de out of stainless steel.
Here is an image of a similar device i'm talking about:
[www.pans.com]

The first thing i did is connect the foot pump to the outlet and start pumping merrily! I achieved 2 bars of pressure and the security valve started venting.
That's more or less what the specs where saying.
I'm sure i can get this baby to work at 3 bars (40 psi for the inchy folks) without a hiccup. The outlet and the releasevalve are bolted in to the lid and can be unscrewed and replaced by other parts with absolutely no hassle.
The beam that goes across the lid is built in a wat that if the inside pressure gets too high, it will bend slightly so that the lid will slightly lift of from the seal and release the excess pressure (just in case somebody wants to start exercising steps-ups with the pump)

The second thing i did with the thing is... cook my dinner! Man i was hungry!

lol!

I was thinking about some sort of heated hydraulic pump. In college we had to draw up plans for one. This could keep the molten plastic under pressure as it was extruded through the machine.

I though about this too:

What if we inserted a heat resistant pot with CAPA or PP or PE inside the cooker, filled it up with enough water to reach half the height of the pot, closed and started heating.
This would provide us with a heating source to melt the polymer and a pressure source to press it out through the tube.
The question here is how do these polymers react with pressurized water vapor?

If they do react, we can change the water with a heating oil used in labs (mostly a mix of temperature resistant mineral oils). You first pressurize the cooker with the foot pump, then heat up.

But would the molten polymer remain liquid through it's travel through the tube?

Run the tubing though a larger copper tube and wrap it with a cheap heating coil. They are sold to prevent plumbing from freezing during the winter. wrap the copper tube in fiberglass to slow the heat transfer.

If you did that you would want as small a run of tubing as possible between the pot and the work table.

Most of the thermoplastics we are looking at are crosslinked dehydration polymers. I would be very surpised if they reacted much at the tempatures we are discussing.

The polymers I am looking at are isocyantes and would not like the presence of water at all, so this idea wouldnt work there.

Furfural blends could be used without the water at all since they would vaporize and pressurize the pot themselves. It would take a lot of experimentation but I would bet that level of heat would seriously reduce the cure time and the level of sulfuric acid necessary to cure a furfural. I would definatly use filler at those temps even with furfural to prevent a runaway reaction. Of course if you overcooked the pot you would end up needing to sandblast it to get it clean once the furfural cured. Although you could just line it with aluminum foil and prevent the worry. I would likely use the water anyway since furfural uses dehydration as the curing mechanism so that much water around is going to help prevent it from curing in the pot or running away.

This is definitely worth adding to the list of considerations since the pot could be cast concrete and heat is a lot easier to produce than compressed air.

Did you ever take a look at Adrian's post? Sorry I don't know how to add links but here is the address in text. [blog.reprap.org]

Yup i've seen that design. It's really quite ingenious!
And basically it's the same thing on a smaller scale.
The difference of what i'm trying to build here lies in the size and ease of refill of the apparatus. I am thinking that the device shouldn't be carried around by the Reprap tray. Once you grant this, the containers can be of any size. If the size and weight don't matter, some new possibilities open up.

Actually i think that the version with the plastic bottle might be easier to build for some, specially if your requirements don't call for large volumes of polymer to be printed out in one session. The one with the pressure cooker is just more practical if you are working with many different blends and big cuantities, like for polymer casts, and if you need to vary pressure and temperature parameters and in general terms, have controlled and reproductible parameters. Also, big pressurised vessels are easy to Reprap: cast them in concrete or use thick Polypropylene parts bolted together. The parts need to be extremely tough, but that's just a matter of proper design (casting not depositing).

One comment on what i've seen in the in the blog: people talk about pressurising the soda bottles up to 150 or 200 PSI (10 to 14 bars, 1000 to 1400 kilopascals). I just want to remind everybody that playing around with those kinds of pressures is inherently dangerous.
Test the vessels to it's maximum pressure and always incorporate a security release valve at half the pressure tested.
I remind you that materials like plastic (except some HDPE anf PP) and aluminum are fatigue-prone, so that the maximum pressure achievable will vary in time and the whole thing might start failing, maybe even bursting.

To avoid this, always work in the lowest pressures possible. This is an advantage of big vessels as well.

This week i will start building the pipes that will carry the polymer thourgh the cooker lid and by a tube towards a nozzle. I'll try to post some pictures and measures of the workings.

High pressures are scary, I know some of the people in here are engineers and are as comfortable handling them as I am handling sulfuric acid. Anything I build however will be designed for low pressure only.

It occured to me that multifunctionality is also a good consideration, a concrete pressure pot with a firebox cast underneath it would funtion as a pressure pot, a pressure cooker, or a still. Copper jacket the line and use a heating coil for the pressure cooker, use a cold water line instead for a still, and dont use anything for the pressure pot.

You could generate the furfural with the still (from garden clippings), neutalize the sludge (use it to fertilize your garden), make a polymer blend and then use the pot to deliver it to the printer, either with heat or compressed air depending on whats easiest for you.

Mike

Ah, another advantage about stainless steel pressure pots:
Furfural blends containing sulfuric acid are OK to use with stainless steel. That's really a big advantage. I believe that the Furfural based blends plus the ceramic blends proposed by Mike will be the two power horses of the non-thermoplastic Reprap polymers. They are just that cheap/versatile/easy to use/filler accepting... (by the way Mike, what's the polymer family behind the ceramic blends? if it's a trade secret, you can avoid answering . I know that Dupont has a product containing sand grains named Corian which i think is based on acrylic)

The product is Ashland's Pep-set Quantum line. Its listed under nobakes. Take a look around the site and check out the cold-box and furan stuff we also have. The refractory is sold under the name Exactherm, and the sand was standard silica sand.

[www.ashland.com]

I picked that resin system because I was one of the inventors of the Quantum line. I figure I understand it a little better than most, so I am not too worried about giving away my connection

The advantage of using a company like Ashland is that they have access to a massive number of resins of every possible type. They are a global company with a large EU presence (not so much in Oz unfortunatly) so might act as a great way to improve material consistancy. At the same time they are used to small job shops and are usually able to ship these materials in 5gal quanities without major issue or an unreasonable cost hike.

One potential advantage of picking a single company as the supplier for thermoset reprap efforts is we will have greater reproducibility of results.
Also if the volume gets large enough any company is going to start putting in development money to optimize a line of resins specifically for reprap.

I have a conflict of interest of course, I am hoping to be in a place to take advantage of a new technology on the supply side. I figure there are worst places to be than the most informed reprapper on the chemistry of these materials, and the only employee of Ashland with reprapping experience.

Mike

Okay, just made the test yesterday with the modified pressure cooker and although it did work flawlessly, i have a concern with adjusting the flow.
This is a big problem because we want to be able to have control on the volumes of deposited material, which will vary with the viscosity or each resin, the ambient temperature, small pressure differences inside the vessel and barometric pressures outside...
It still is possible to do this with the pressure cooker rig, but we would have to add some control hardware that would make everything more complex than we want at this moment in time. Maybe in a later phase of reprap this could be developed as a useful dispensing method, but not right now.

going back to the syringe idea... maybe try to build a rectangular box with a square piston and a threaded push rod. I'm thinking also about a very simple automatic refill mechanism.

They way that we used to control that problem with paint was to have an adjustable screw that controled how far the delivery orifice was allowed to open. We would then calibrate that for the different materials to standarize the delivery rate.

Stick a graduated cylinder under it for 30sec and check the volume, then adjust and repeat. So long as you do this each time for each machine, the variation between machines, locations, and materials becomes controlable. That means that you have to deliver more pressure to the tool than you intend to use, but only 1psi over is really required.

Mike

Look what i found:
[www.cammda.com]
They have exactly what we need as dispensers go: syringes, nozzels, pipes, airguns, pushers.... Actually, I'm sure we could easily recycle any silicon cartridge and plunger for our needs. But the prices for their cartridges are cheaper than to buy a silicone cartidge and empty and clean it.. all that hassle.
Below, from their online shop, the prices of cartridges in

Good spot, Fernando! :-)

from their site:

"Cartridges are made from High Density Polyethylene"

it would definitely be interesting to see if it would be possible to fabricate these syringes. i bet our biggest challenge would be uneven wall smoothness. hrm.

Yes, i thought bout that too, but here is what i imagined as a solution:

1) we could print out a square cartridge, made out of flat panels.
here the difficult part would be to make all the parts work together tightly. the panes could be bolted together with a bit of gasket silicone, that would solve that problem. The pusher on the other hand is more difficult, as it would be have a square section. sealing this may be done if you can wind a rubber gasket in a drilled canula around it's perimeter (i think i will have to make a small sketch of what i'm thinking, my description may not make sense).

2) why not print cylindrical cartridges in two halves, split along the length?
If we do it that way, we can use a half cylinder as a "shaper" on top of which we print panes of polymer, leaving a nicely regular hemi-cylindrical interior void.
Print two of those, bolt them together with gasket silicone and voila!

This is of course for the good of repraping as many parts as we can, the cartridges are quite cheap and buying a big stock online is not a problem. But i agree that having a 100% reprapable solution for this dispenser would make this a winner!

The current software approach is to slice and dice objects, but to make a hollow tube a continous spiral would produce a better result.

these might be SUPER easy to print out once someone makes Darwin 1.1, by slapping a turntable onto the build area thusly allowing us to print circular things really easily (position head, rotate table... boom, a circle.)

argh! darwin is so close... its almost agonizing =)

As you can see with the work that Vik and I have been doing, it's very much one thing to have a "working" 3D printer. It's quite another thing to have it print things nicely or even at all.

Yup, i can definitely see that. It dawns down on me how printing rounded shapes with sufficient resolution is a real hard thing to do with a cartesian positioning system. You probably need a rig that can position the nozzle within 1/4th of the width of the thread, and fast enough.

Maybe, in the new forum sections that i proposed to be created in one of my first posts, we need to add one section called "printing methods".
Here we would describe and discuss some printing mechanisms that would reach different goals: cartesian deposition, cylindrical coordinates deposition, casting in molds, using filling shapes to deposit uppon, etc.

I really think that we have to asses how the end shape has to perform and then select what printing method to use. Does the shape need to resist compression, shear, internal pressure, tension...

agreed. i think for now if we just make sure to start new threads, it will be easy to categorize things later. i'm gonna lock this thread... okies?