PDMS Application

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Eddie J
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PDMS Application

Post#1 » Tue Mar 19, 2013 9:10 pm

Ive been reading through the forums, very excited about trying out a B9Creator and looking to learn as much as i can until that time.
One problem that seems to crop up in a number of topics is the PDMS coating on the vat being uneven or having bubbles and causing troubles with how the part is built.

Im not able to try this myself, no printer yet. But perhaps we can throw some ideas around? Part of my work involves casting parts with resins, so i have a few ideas on ways to get a better coating of PDMS

Does the PDMS have to be thickly applied? Or would a thin layer work just as well for the duration of one print? In order to get a more even application, could you apply it with a spraygun or airbrush?
How viscous is it? And how long does it take to cure?
I was thinking to quickly apply a new thin layer of PDMS for each print (or two?) with a spraygun.

To remove any air in the mix, perhaps degassing the PDMS with a vacuum would work? Unless the oxygen in the PDMS is liable to be removed too from degassing? (not sure in what way PDMS "contains oxygen")

Or lastly, to get a denser PDMS (nearly typoed "PMS" there!) - perhaps letting it cure in a pressure chamber of 50psi would get better results and a stronger layer?

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mikej
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PDMS Application

Post#2 » Tue Mar 19, 2013 9:16 pm

Needs to be thick enough not to tear and to "contain" enough oxygen. Typically about 1/8" (3mm) thick seems to work best, might get away with half that amount.

Even thickness is not an issue, the resin is less viscous than honey and spreads out pretty fast. Bubbles always pop in the Sylgard 184 PDMS before it cures. Takes about 48 hours to cure at room temp. ~2 hours at 195`F.
Degassing is not needed, bubbles come out even when fast cured in a hot box.

I think a new layer after every print would be a big pain (need to empty and clean the vat, recoat, etc.). I often do several prints a day back to back.

I've only tested Sylgard 184, no experience with others, but my gut says that denser versions will not absorb oxygen as readily and that's a bad thing.
Measure Twice, Cut Once.

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Eddie J
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PDMS Application

Post#3 » Tue Mar 19, 2013 10:36 pm

Sounds like its a good method already then, just needs to be handeled with care to not rip off.
How would you remove the PDMS? Water or alcahol? Or just peel it off?

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mikej
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Post#4 » Wed Mar 20, 2013 12:53 am

It peels off easily (too easily sometimes?)
Measure Twice, Cut Once.

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Eddie J
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PDMS Application

Post#5 » Wed Mar 20, 2013 5:00 am

Ok thats good to know its easy to remove. Ill probably get testing some alternatives, Sylgard is quite expensive and seems tricky to get in europe. This SF45 version sounds good, but shame about the slight cloudyness.
For any B9ers interested, grabbed a datasheet:
http://ncnc.engineering.ucdavis.edu/pages/equipment/Sylgard_184_data_sheet.pdf

EDIT: Uk B9ers can get a nice 250ml pack (coats about 6 vats?) from here
http://www.ellsworthadhesives.co.uk/index.php/catalogsearch/result/?q=sylgard+184
Will have a price out of them tomorrow.
Seems alternatives are stupidly viscous...

armstrom
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PDMS Application

Post#6 » Wed Mar 20, 2013 7:16 am

Mike, I haven't re-read your entire prototype build log so please forgive me if this has been asked and answered... Did you ever experiment with PTFE coatings? I have seen some optically clear PTFE in spray (rattle can) form. Also, it's possible to buy optically clear sheets of PTFE. Obviously this would be an entirely different method of release (hydrophobic layer rather than oxygen inhibited cure). Just curious.
-Matt

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mikej
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Post#7 » Wed Mar 20, 2013 12:01 pm

Eddie - Good find, hope the price is similar to the US. Look forward to your alternative tests and results.

armstrom - I've not tried spray on PTFE but my experience is, if the entire layer cures (no oxygen inhibited lubricating layer left against the surface) then you can not slide off, you can only peel off.
Measure Twice, Cut Once.

armstrom
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PDMS Application

Post#8 » Thu Mar 21, 2013 2:24 am

And peeling is when you run into patent issues with the deep pocketed manufacturers, right? Thanks for the info!
-Matt

thebigconsultant
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Post#9 » Wed Jun 12, 2013 10:32 pm

Mike,

Just out of interest? What is the price of Sylgrad 184 in the US?

In the UK, it is £44 from the above mentioned supplier (in Scotland), for a 500g kit. ... The 1.1Kg kit is £78

darthviper107
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PDMS Application

Post#10 » Thu Jun 13, 2013 3:39 am

You can get the kit for $50 on ebay in the U.S.

thebigconsultant
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Post#11 » Thu Jun 13, 2013 4:09 am

I have ordered some samples of a possible alternative, and I will experiment further when I have time and budget.

I have ordered some Sylgard for now. But I am going to make 35 VAT's, and try out some alternatives. I have also been compiling some information on the specifications of possible alternatives, and I hope to try them out. ... By the way, Sylgard is actually subject to US Embargo on export in the event of war etc. So can / could be withdrawn at anytime ... lol, especially, as the USA is very warlike! ;)

Just in case, I would like alternatives!

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mikej
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Post#12 » Thu Jun 13, 2013 3:13 pm

I added an instructional video to the wiki describing the re-coating process.
http://b9creator.pbworks.com/w/page/64025207/Replacing%20the%20PDMS
Measure Twice, Cut Once.

form
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PDMS Application

Post#13 » Thu Jun 13, 2013 4:01 pm

Fantastic video Mike.
If I might make a small suggestion, would you consider making a video of the calibration of the build table onto the vat as your next step, as that was the only part that stressed me out during the entire building of this brilliant B9 machine that you have created.

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mikej
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Post#14 » Thu Jun 13, 2013 4:08 pm

Thanks.
Calibration, First Print & Software Overview are next up on the slate.
Measure Twice, Cut Once.

vchmiele
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PDMS Application

Post#15 » Sun Jun 16, 2013 5:11 pm

Would it be helpful to degas the PDMS in a vacuum chamber?

form
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PDMS Application

Post#16 » Sun Jun 16, 2013 5:29 pm

Mike has previously stated its unnecessary as the bubbles pop when drying and after watching the drying process (1st recoat after 4 x50 micron prints)I personally wouldn't bother either

vchmiele
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PDMS Application

Post#17 » Mon Jun 17, 2013 7:40 am

Any suggestions on where to get a low temp oven for curing the PDMS?

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perpetual_dreamer
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PDMS Application

Post#18 » Mon Jun 17, 2013 7:50 am

^ I'd think a $20 toaster oven would do just fine
Image

squonk
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Post#19 » Mon Jun 17, 2013 8:34 am

My conventional oven goes as low as 170, so I just use that. Ovens with a "keep warm" function probably can go that low, as well.

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mikej
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Post#20 » Mon Jun 17, 2013 8:53 am

Might want to check it with a good thermometer first, just to be safe. The temperature of deformation for acrylic is around 90C, 194F. Get that hot and the VAT will start to warp.
Measure Twice, Cut Once.

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