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PDMS heat curing

Posted: Sun Oct 26, 2014 3:50 am
by tim.yoshi
Guys nobody want to share experience on how you are making your PDMS flat and cured?
I mean where do you heat curing it? In cocking oven? I heard someone made special unit with light bulb and thermal relay which controls temperature? Any more info?
Thanks.

PDMS heat curing

Posted: Sun Oct 26, 2014 4:49 am
by Metalcaster
Hi Tim,
You can use any type of oven except a gas oven. I suspect gas may have too much turbulence and possibility of getting dirt from the oven into the PDMS. So, best solution is any kind of electric oven with a temperature control. I have a small electric oven that I use for drying epoxy resins . I made sure the inside of the small oven is perfectly flat so the PDMS will be flat. I also check the aluminum tray for flatness and the platform. I found that running large prints on the platform can cause some bending of the platform. Small prints at 30 x 30 do not cause any distortion. Just the large prints that stick hard to the PDMS and the table. An electric cooking oven can also work... just need to make sure the inside is flat.

PDMS heat curing

Posted: Sun Oct 26, 2014 6:45 am
by behold3d
I use a cabinet and a blow dryer. I leave the cabinet cracked open and heat the inside for a half hr and place the vat in their, level it, and leave it in there for an hr. The cabinet is large enough so I can place the blow dryer on the bottom shelf and it heats the top shelf really well without worrying about debris settling in the PDms . I then turn off the dryer. Close the door and let it cool off naturally for an additional hr. I have two vats and I always have one sitting and ready.

PDMS heat curing

Posted: Sun Oct 26, 2014 7:32 am
by perpetual_dreamer
I use a cheap toaster oven and the PDMS saver method with the delrin I-beam that Mike sells. I feel I get a flat PDMS surface when I use the PDMS saver method compared to the old way of covering entire vat with pdms, as I don't have to worry about pdms flow and maintaining a slight slope around the waterfall. The vats I use are metal so any cheap toaster works now.. Don't have to worry about melting acrylic.. I just can't push the temp too high so as not to melt the delrin ibeam

PDMS heat curing

Posted: Sun Oct 26, 2014 11:43 am
by Robert Howle
Tim this video show the older saver method with Kirkrhino vat. Also shows the oven he an I use (and others use similar) with temps and times.

http://www.b9c.com/support/?mingleforumaction=viewtopic&t=958.8

PDMS heat curing

Posted: Sun Oct 26, 2014 1:14 pm
by akgold
Oddly I was using my over yesterday. Actually was using it for the first time to cook some food here at work, otherwise I have only used it maybe 5 or 6 times in the last 3 months since I bought it.
It quit working about 10 minutes into baking mode at 375 deg for 1 hr.
still won't work I can't believe this thing just quit anyone else have this problem?
also one of my nail UV lights all of a sudden quit the other is fine.
guess I am having electric appliance issues.
Bummer

PDMS heat curing

Posted: Sun Oct 26, 2014 1:40 pm
by Robert Howle
Replacement bulbs are very inexpensive on Amazon. No, had my oven (Oster brand) for about 1 yr. now. The other shoe will drop... always in threes.

My Best, Tim
Robert

PDMS heat curing

Posted: Mon Oct 27, 2014 12:46 am
by tim.yoshi
Ok, thanks for all, but I'm kind of conservator here - using old good acrylic vat. Made it thinner to decrease cost even further so now it's kind of supply material :)
But I thought about something like heated bed for FDM 3D printers. Or maybe a box with light bulbs controlled by thermal relay...

PDMS heat curing

Posted: Mon Oct 27, 2014 3:01 am
by Guest
After reading many of the (excellent and informative) forum posts and having read the article on the 'smoking gun' in relationship to the fogging of the PDMS, I started experimenting with 'cooking/baking' the PDMS at relatively high temperatures (176C/350F). So far it seems I am on the right track, as the first vat's (I have 3 of the latest aluminum vat's for testing and production) that are backed at 175C/350F are showing remarkably resistance against fogging. So back to this thread. Here is what I have put in place for PDMS heat curing:

a) I bought an affordable small oven, with top and bottom heating elements (NO hot air). It has a remarkable accurate temperature control (not expected for this price)
b) I modified the tray by adding some aluminum bars, in order to provide two parallel rails for the vats to sit/slide on (I can place two vats at a time). Also added two aluminum side-tracks to make sure the tray is 'tight' when placed in the oven. BTW no need to remove the tray once placed in the oven. Just place / remove vats.
d) I use a cover (backing tray that came with the oven) and a bottom cover to 'insulate' the vats from direct (radiation) heat. This allows for a 'slow' and even heating.

My temperature profile after adding the PDMS (50 grams) is as follows:

1) for 30 minutes just let it sit at room temperature in the oven to make sure the PDMS gets 'level'
2) increase temperature to 75C and let it soak for two hours (PDMS will totally cured by end of 2 hours)
3) increase temperature to 125/135C and let it soak for one hour
4) increase temperature to 180C/350F and let it soak for one hour
5) Oven switched off and let it cool down till environment temperature (don't know how long this takes as I typically go to bed by then)

IMPORTANT: you CAN NOT use the standard Delron bridge as supplied by B9C when going to 180C/350C. You will need to remove it after the 2 hours at 70C. If you want to know what happens if you ever forget, see last picture below :)
Now I use an aluminum bridge, so forgetting is no longer a 'problem'.

You can follow the above process as i still do today by hand/manually, however I have just purchased on eBay a 'PID Temp controller' that will let me program the above sequence, so next time I won't have to manually adjust and wait for each step. (link to PID Temp controller http://www.ebay.com/itm/PID-TEMPERATURE-CONTROLLER-W-30-RAMP-SOAK-SSR-OUTPUT-/110627498979) (FYI: you need to add a SSR to this device power the oven)

Pictures of oven and the tray made for the vip's + cover:

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And this is what happens if you forget to remove the Delrin bridge before going to 180C/350F :

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and this is the solution I had to make after my Delrin bridge 'evaporated' :

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BTW: when placing the bridge, I always wrap the bridge with some paint-tape. This gives a 'perfect' sealing, preventing the PDMS from leaking under/aside the bridge.

One more picture of my vacuum pump for clearing the PDMS and the scale I use.

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PDMS heat curing

Posted: Mon Oct 27, 2014 3:19 am
by Guest
Before I forget, I needed to 're-build' all of the vat's as they unfortunately all had leaking problems. Even the ones that where brand new and still had the original PDMS in place.

Procedure for re-building the Aluminum vat's as i did:

I removed the glass carefully. Removed with a razor-blade all remaining silicon from the glass and the aluminum.
Used acetone to remove any remaining contamination.
Pre-coated the aluminum with a 'silicon primer. Let the primer dry for 15 minutes (!) before placing the glass with the Silicon glue.
Moderately coated the glass with Loctite Blue Silicon (5926). This is the same Blue Silicon as used for gaskets in car engines and can stand heat up to 200C ( http://www.loctite.co.uk/loctite-4087.htm?nodeid=8802627452929). Sometimes also know as VersaChem Super Blue - Silicone Gasket Maker (this one can even stand higher temperatures, up to 315C/600F).

Let it dry at 70C for a night and then finished it with a backing at 180C/350F for one hour and let it cool down naturally.

Now my vats are 100% leak-proof and ready for high temperature exposure when 'curing/baking' my PDMS

PDMS heat curing

Posted: Mon Oct 27, 2014 4:41 am
by Arno-Millenaar
It reads 'Guest' above as I had to ask Mike to change my login name (accidentally used my email as my login name). Mike kindly changed this in order to prevent spam email, etc. So just for reference its me: 'Arno' who posted the above two messages.

PDMS heat curing

Posted: Mon Oct 27, 2014 6:26 am
by Metalcaster
Hi Arno,
I had to do the same thing. When I got my new trays 1 was warped, 1 was perfect and 1 leaked. I did the same thing, took all the glass out and I used a black gasket silicone good for 800 oF Have not had any problems with leaks since then. The Black or the blue gasket sealant silicones are really good.

PDMS heat curing

Posted: Tue Oct 28, 2014 2:37 am
by jschoenly
I've only re-done my PDMS a few times but use a food dehydrator that I cut the center of the racks out. It's adjustable in temperature to about 165 or 180 max. I did the Acrylic VAT's a time or 2 with no worries of overheating.
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PDMS heat curing

Posted: Tue Oct 28, 2014 3:51 am
by Robert Howle
How long in the food hehydrator?

PDMS heat curing

Posted: Tue Oct 28, 2014 6:26 am
by Centaur
I just use our domestic oven (when my wife is out ;) ) I cook it for about an hour at 100, although I'm not using Sylgard, but an alternative. I'm still using the original, waterfall, coating method - the cliff method doesn't seem to bring any advantages, and is a lot more fiddly.

I'm going to try cooking at a higher temperature on the next recoat to see what happens (using a Kat Vat BTW).

PDMS heat curing

Posted: Tue Oct 28, 2014 11:59 am
by Arno-Millenaar
@Centaur

Can you share what 'alternative' you are using for the Sylgard and what the results are so far. Especially the resistance against 'fogging' is interesting to know. (I know this subject should be in a different thread)

PDMS heat curing

Posted: Thu Oct 30, 2014 5:02 am
by tim.yoshi
I heard about Polastosil, QSil and most interesting - ML Solar Cell Guard. But still no reliable confirmation that all that works as original.

PDMS heat curing

Posted: Thu Oct 30, 2014 6:21 am
by Arno-Millenaar
Just ordered (today) 1kg Polastosil M-2000 and the Catalyst OL-1 from Zakład Chemiczny "Silikony Polskie" in Poland. As soon as I have the first test results I will post the results on this forum.

PDMS heat curing

Posted: Thu Oct 30, 2014 6:29 am
by jschoenly
I think I usually let it in the dehydrator for about 2 hours, maybe less. It's been a little while since I did it so I forget the timing, Whatever the video used to recommend for the "hot box" curing.

PDMS heat curing

Posted: Thu Oct 30, 2014 6:53 am
by Robert Howle
Thanks, Jared

Robert