Re: hdpe printing
- The basic path that we follow begins with cleaning out the milk jugs. Then we take the jugs to a recycler, who shreds the jugs into flakes. This flake is siphoned into our extruder, which is basically a heated pipe with an augur in it. The augur is run backwards so it pushes materials instead of pulling, and the plastic gets spit out of the nozzle.
That's the part where the melt flow index is going to get you; it takes a lot of torque to push that plastic around the barrel.
Once it's been extruded into filament, there aren't any special considerations that are needed for use in smaller machines.
Some pictures of the process can be found on our group's blog:
If you go back to the beginning, we recorded a lot of the work we did to print. It's not very organized, as it's mainly for our own members' purposes.
You can also google "WOOF 3D printed boat" to find a lot of articles that talk about what we did, though they don't really go into the technical portions.
--- In email@example.com, chuckm@... wrote:
> WOW - thanks for the info!
> That looks interesting.
> I see your jug mangler, but can you give me some specs on the filament
> making process? Maybe a picture of jugs parts to filament, please. What
> size filament do you try to print with? We have access to a MAkerbot with
> 0.35" extruder hole...it uses 1.75 mm PLA or ABS. And we have an extra
> printhead, again designed for 1.75 mm stock. It doesn't look too hard to
> make a bigger hotend, but the melt flow index is something we hadn't
> thought of before your post. Hmmm.
> We have access to HDPE surfactant jugs and would like to make prototype
> parts out of them...mainly agriculture/farm/farm shop related stuff - like
> a screw on funnel for quart oil bottles etc. Definitely NON FOOD CHAIN
> Any more stats or pix that you would be willing to share would be GREAT
> thanks!! If you want them semiprivate, I've included my email...
> > I'm working with a group that recycles milk jugs and extrudes them on a
> > large scale. The main problems that we run into:
> > 1) Bed Adhesion: HDPE doesn't like to stick to a lot of things. If it does
> > stick to it (For example, heated steel), it will be VERY difficult to
> > remove. Our solution to this is printing on top on a layer of HDPE, then
> > just cutting away the very bottom layer.
> > 2) Shrinkage: Like you said, HDPE has a huge coefficient of shrinkage. 2%
> > for milk bottle HDPE. ABS has something around 1.1%, and PLA is something
> > like .6%. This becomes more and more of a problem when you scale up. Our
> > prints often distort the wood base that they are attached to. We've had
> > plywood that is an inch thick have a noticeable curve to it after the part
> > cooled. On smaller parts (RepRap size) it may not be that extreme, but you
> > will definitely by fighting delam.
> > 3)Viscosity : Milk jug HDPE is made with the intent that it is blow
> > molded. It's melt flow index (related to viscosity) is around .55 - .7.
> > The melt flow index of HDPE used in injection molding (which is much more
> > similar to extruders on 3D Printers) is something like 6 or 7. The higher
> > number means it flows much easier. You need a pretty torque-y motor to be
> > able to push it and overcome the back pressure.
> > To answer your final question... Yes, all these problems can be overcome,
> > with some effort. If you make any progress with this, I'd love to hear
> > about it!
> > --- In firstname.lastname@example.org, "ebiz_59"
> > <chuckm@> wrote:
> >> I know most of you are beyond the filament printing stage, but Im still
> >> back there. I c people generally moving to pla although there is still
> >> some ABS work being done with heated beds. My understandind is that ABS
> >> thermal expansion coefficient is the main problem here. Which brings me
> >> to my questiion...id really like to recycle milk jugs and other hdpe
> >> into filament useable in 3 d printers, but I see that its thermal
> >> expansion coefficient is like twice that of ABS. Is this the reason to
> >> not use hdpe, and/or are there others? And can they overcome or am I
> >> working on a thought for which there is no good solution?
> >> Thanks, chuck