Dynamic viscosity of abs

I was wondering if anyone has done work on determining the dynamic viscosity of either abs or pla. I would like to calculate the Reynolds number for different nozzle configurations.

Wish it was easier than it is... everything is tucked away in a textbook or some paid CFD program somewhere.

As a general rule, IDK if this helps you, but the ideal melting temperature for extrusion of almost every single polymer will hit a dynamic viscosity of about 500-2000 cP.

What are different nozzle "configurations" ? Inner Diameters? Lengths?

Edited 1 time(s). Last edit at 03/22/2013 09:04PM by Simba.

I'm interested in creating turbulent flow in the transition between the original filament diameter to the nozzle diameter and at that point, inject dye, so that the color will mix fully. So, it would be a matter of varying the internal diameters.

Oh that is fantastic.

What do you think about using a nonturbulent "mixer" like the kinds put at the end of viscous 2-part epoxy cartridges?

[www.mcmaster.com]

Edited 1 time(s). Last edit at 03/22/2013 09:11PM by Simba.

I just thought it would be simpler to inject the dye 0.5 mm from the internal end of the nozzle, have the turbulence mix it fully. There could be miltiple colors extruded from the same nozzle, with perhaps a quick dump to the side of the object to purge what little ink would be present after each color change. Varying the diameters would make it easy to machine.

Can you tell me more about the "Dye" - is it particles of colorant (ferrite, aquamarine, etc) or actual dye like RIT brand dye.

I think realizing a multi-extruder into a single nozzle is the easiest part of this build. A good cnc company should be able to put 3-6 0.5mm diameter nozzles to a central feeding point...The "purge" pillar is a good starting idea.

I think it's going to be an uphill battle at that short a distance though. It would work with some serpentine microchannel flow paths, but that increases your resistances a great deal more than you want. I think if i were to pull our my theory/CFD simulations, it would say that basically no mixing would be going on. So, how do you propose we make the turbulance that is required without extruding a ton of material?

Machining it is not a problem, I have my own cnc machines. For the serpentine channels, I could see them perhaps machined into a flat block with a cover bolted over it, though the smallest endmill I have is 1/16'' which may be too large.I built a bowden style prototype a few days ago to test this idea out. This is the first bowden type hot end I've ever made, so am having problems with it back feeding molten plastic because of the pressure. Without any numbers to calculate with, I made a chamber about 0.2'' diameter and the exit 0.5 mm diameter. The color inlet is drilled in at an angle, entering just below the chamber exit, with the intention of using the transitional forces as a mixer.

I have not worked out what dye to use yet. Certainly not a water based dye, I was thinking of using some oil based paint such as Estes modeling paint thinned out with paint thinner.

Open to suggestions.

Edited 1 time(s). Last edit at 03/23/2013 01:18AM by Evil Monkey.

OK, just realized, you have a huge challenge to overcome before moving forward. The heat will smoke out any liquid at temps of 200C except except mineral oil. Does that even mix with plastic?

There are liquid pigments used to color plastic, either in the production of masterbatch or as an alternative to masterbatch or powder. Would those withstand the temps, or do they usually get mixed at lower temps and get burned off, leaving the color behind? It might be hard to find anything in quantities that aren't massive however.

IanJohnson Wrote:
-------------------------------------------------------
> There are liquid pigments used to color plastic,
> either in the production of masterbatch or as an
> alternative to masterbatch or powder. Would those
> withstand the temps, or do they usually get mixed
> at lower temps and get burned off, leaving the
> color behind? It might be hard to find anything
> in quantities that aren't massive however.

I can get you samples of anything. Let me try. just send me a link for liquid colorant. IF it is an additive, it must withstand temps upwards of 300C, then it will be fine.

Also nice engineering - how does the fluid pump region make the bend? Two holes aligned at 90 degrees and drilled into eachother? I am impressed, generally.

Thanks. In the heater block, there are two holes meeting at 90 degrees. The horizontal outside hole is plugged with a grub screw. Not shown is th 0.5 mm hole in the side of the extruder nozzle which is drilled at a 55 degree angle and comes out below the mixing chamber. The syringe is just for testing, my intention is to eventually use a servo motor running on the spar pins on a RAMPs 1.4. I will have to research colorant a bit.

I calculated the Reynolds numbers based on dynamic viscosity of between 0.5 and 2 Newton seconds per meter squared and unfortunately am getting very laminar flow.

Evil Monkey Wrote:
-------------------------------------------------------
> I calculated the Reynolds numbers based on dynamic
> viscosity of between 0.5 and 2 Newton seconds per
> meter squared and unfortunately am getting very
> laminar flow.


Called it! And I didn't even have to do the complex math
Yeah it sucks, but I realized mixing was out of the question when the stuff barely mixes with itself enough to make a stress free-extrusion. The molecular weight is high, the viscosity is high, the mixing distance is tiny, and so nothing really is working to the effect of turbulent flow here.

However, that doesn't mean you shouldn't try. There is the great possibility that high temperature + semi-similar materials (oil in ABS) could cause rapid diffusion of the dye in the molten polymer.

Also, how about other ideas - you could have a very hydrophobic metal mesh can carries and spreads the oily colorant through surface tension throughout the bulk of the extrusion area.

What I was thinking of doing next was trying to making almost like an ink well right before the end of the nozzle. Colorant could be injected into the well and would coat the outside of the filament as it goes by, right before it is extruded, no mixing needed. This is similar to that sharpie coating someone put up on Thingiverse for use at the cold end. Which makes me wonder what sharpie markers are composed of. Will have to cut one open and find out.

No need

BTW, a sharpie is dye. I know because if you hit it with flash light energy it splits into yellow and blue + some black, so mainly that means it is a rich blue dye.

You want something like a dry erase marker. Those are made with filler particle like iron oxide powder or carbon black, that can't be washed or create stains on anything non-porous.

I still think the secret will be as with an inkjet, or your computer screen, particles so small (<50 microns) that you cant see it is really only 3 colors. Then again, there is an issues of how to get good quality color with that method. I think it is just spot size controls the color "intensity" of that subpixel.

Quote
Simba
As a general rule, IDK if this helps you, but the ideal melting temperature for extrusion of almost every single polymer will hit a dynamic viscosity of about 500-2000 cP.

Hey mate just wondering where you found this information. It would be handy to have an article telling me why this is the optimal dynamic viscosity, cheers.

Edited 1 time(s). Last edit at 04/23/2014 11:38PM by MacLean17.